Table of contents

Antibubbles have been produced and studied with the help of a high-speed camera. An antibubble is defined as a fluid object constituted by a thin air shell surrounding a liquid and surrounded by the same liquid. Images reveal some key physical processes and fluid instabilities which take place when an antibubble forms and dies. The collapsing speed of the air film has been measured. Culik's theory does not apply. A new mechanism has been introduced.

It is known that the efficiency of scattering of light by a particle is related to its size, geometry and optical constants of the material, since the theory of scattering by small particles developed by Mie in the beginning of the 20th century. However, the Mie scattering theory is valid just for a few special cases like a homogeneous sphere embedded on a medium of homogenous refraction index. More recently, some theoretical simulations on planar nano- particles have shown that the optical resonances are dependent on the shape of the particle. Simultaneously, local field enhancements take place on the particles when excited by an incident wave.

A comprehensive knowledge of the optical behaviour of planar particles is of great importance for the development of optical devices at the nanoscale, as well as for the fast developing field of photonic crystals and the emerging field of diffractive optics.

In this paper, we present optical investigations on arrays of triangular nanoparticles with sizes comparable with the wavelength. Particles were produced using the method developed by Fischer and the optical measurements have been made using a scanning confocal microscope and a total-internal-reflection system.

The scattering of light by particles of some materials when excited by an evanescent field show a strong dependence on their relative orientation in the direction of incidence. The measured scattering patterns change with the polarization of light.

A range of experimental and theoretical techniques have been applied to the study of transient negative ions (resonances) formed in electron scattering from the Group II metals Mg, Zn, Cd, and Hg at incident electron energies below the first ionization potential. A wealth of resonance structures have been observed and from the experimental observations and theoretical information, classifications are proposed for some of these negative ion states.

Pristine arc-produced multi-walled carbon nanotubes are contacted to liquid mercury in situ in a transmission electron microscope. The conductance G(V) for all tubes increases with increasing bias voltage V. This is related to the electronic density of the nanotubes. Similar G(V) behaviour is observed for HOPG-graphite contacted in air with Hg, with dG(V)/dV∼0.3G₀. Variations observed in the conductance are related to nanotube–Hg contact effects. For tubes barely touching the Hg surface, the conductance is low (typically G(V=0)∼0.1–0.5G₀); G(V) may maximize around V=1.5–2 V or continue to increase linearly depending on the MWNT–Hg contact. For good contacts the maximum low-bias conductance is 1G₀. Non-conducting tubes are observed having a low-bias conductance smaller than 10⁻³G₀. High-voltage tube failure usually occurs at the contact with Hg for clean tubes, or at tube defects. An important phenomenon is the formation of a Hg bubble near the contact nanotube–Hg surface when the nanotube is negatively biased, under high bias current conditions, indicating the heating effect of hot electrons injected into the mercury.

A review of double resonance Raman spectroscopy is presented. Non-zone centre phonon modes in solids can be observed in the double resonance Raman spectra, in which weak Raman signals appear in a wide frequency region and their combination or overtone modes can be assigned. By changing the excitation laser energy, we can derive the phonon dispersion relations of a single nanotube.

This paper reviews recent investigations of the electronic structure and the optical properties of intercalated single-wall carbon nanotubes (SWCNTs) and C₆₀ filled SWCNTs (peapods) using electron energy-loss spectroscopy (EELS) in transmission as a probe. The results from these one-dimensional nanostructures are compared to C₆₀ fullerides and intercalated graphite, which are well understood prototypes of carbon-based intercalation compounds. In detail, the structural changes were analysed by electron diffraction and the doping level and the matrix element weighted unoccupied density of states (DOS) by an analysis of the C 1s core-level excitations. Regarding the optical properties, the intercalation gives rise to a charge transfer to the peapods (SWCNTs) which leads to the formation of a free charge carrier plasmon in the loss function which is analysed within the framework of an effective Drude–Lorentz model.

Fluorocarbons are the main species used in etching plasmas and their properties are driven by CF_x (x = 1–3) radicals. Previous calculations on CF and CF₂ show low-lying resonances which may lead to dissociative electron attachment under standard plasma conditions. Here the R-matrix method is used to treat electron collisions with the polyatomic radical CF₃ at its equilibrium geometry using a coupled states expansion. These calculations concentrate on obtaining low-energy, sub-10 eV, elastic and excitation cross-sections. A CF₃⁻ bound state of ¹A₁ symmetry is detected but no low-lying resonances. These findings suggest that CF₃ is unlikely to undergo dissociative electron attachment; the possible consequences of this for etching plasmas are discussed.

Using a spatial light modulator to modify the phase of a light beam we create a spatially coherent, white-light beam containing an optical vortex. All the spectral components are helically phased; hence the beam carries an orbital angular momentum that is an integer multiple of ℏ per photon. A low-dispersion prism, positioned after the modulator, ensures that the vortices associated with each spectral component are co-axial. In addition, deliberate introduction of slight spectral dispersion means that the vortices associated with each wavelength no longer overlap. Subsequent examination near the beam axis reveals the chromatic effects predicted by Berry (2002 New J. Phys.466; 74).

Vertically aligned carbon nanofibres were grown at temperatures as low as 120°C by plasma-enhanced chemical vapour deposition (PECVD). A systematic study of the temperature dependence of the growth rate found an activation energy of 0.23 eV, much less than that for thermal chemical vapour deposition (1.2–1.5 eV). This suggests that growth occurs by surface diffusion of carbon on nickel. Vertically aligned carbon nanofibres were grown by PECVD on to flexible plastic substrates. We show that individual lines and dots of free-standing 20–50 nm diameter nanotubes can be grown on to chromium-covered polyimide foil. The scalable deposition method allows large-area coverage without damaging or bending the sensitive substrate material. Field-emission cathodes were made for the purpose of demonstration.

In an attempt to improve the field emission (FE) characteristics of carbon nanotubes (CNTs), we have performed a first-principles study on MgO-coated CNTs. A MgO slab covering a CNT tip under a strong electric field shows dielectric screening behaviours with applied electric fields up to 0.3 V Å⁻¹ and the effective dielectric constant approaches the bulk value within a few MgO layers. It is also found that the surface conduction band state of the MgO slab shifts down to the Fermi level as the applied electric field increases, indicating a FE mechanism different to that for CNTs without insulator coating. Electron emission via the surface conduction band of the insulator at the Fermi level is expected to enhance the FE current significantly, in agreement with a recent experiment.

Surface plasmon polariton resonance in metallic clusters embedded in a matrix is broadened due to the interface decay channel of the plasmon lifetime. This non-classical broadening effect is caused by adsorbate-induced local density of states near the Fermi level of the cluster. We study theoretically the broadening effect for realistic small noble clusters extending Persson's theory for adsorbate-induced damping of the plasmon resonance by taking into account the interband transitions in the dielectric function of the cluster. The broadening of the surface plasmon resonance caused by the interface decay channel is significantly influenced by the interband transitions in the metallic cluster.

We investigate the production mechanisms of p, d, t, ³He, ⁴He, ⁶Li, , and in Pb+Pb collisions at 158 A GeV measured near zero transverse momentum with the NA52 experiment at the CERN SPS. We find evidence that nuclei and antinuclei in Pb+Pb collisions are mainly produced via the coalescence mechanism out of a thermalized source of hadrons, at a time close to the thermal freeze-out of hadrons corresponding to a temperature of ~120 MeV.

Single-walled carbon nanotubes (SWNTs), synthesized by a catalytic decomposition of alcohol (alcohol CVD method, ACCVD), are compared with high-pressure CO (HiPco) SWNT samples through optical spectroscopic measurements such as resonant Raman scattering, optical absorption and near infrared fluorescence. By the ACCVD method, SWNTs were synthesized either on zeolite catalyst-support particles or directly on the surface of a quartz substrate; in the latter case, a simple dip-coat technique was employed for mounting the metal catalyst. Specific morphological characteristics of as-grown SWNTs generated on zeolite support are presented using SEM and TEM, revealing that the SWNTs produced by the proposed method possess the significant quality of being almost free from amorphous carbons or metal particle impurities. The quality and diameter distribution of SWNTs were investigated and discussed through the results of Raman scattering and optical absorption. The average diameter was slightly smaller for SWNTs grown on zeolite particles than for HiPco SWNTs. Finally, fluorescent emission spectra from isolated SWNTs in an aqueous surfactant suspension were measured for various excitation wavelengths to determine the structural (n,m) distribution of the SWNTs. The narrower chirality distribution for ACCVD SWNTs grown on zeolite compared with HiPco SWNTs was demonstrated.

Stable configurations and full symmetry groups of double wall carbon nanotubes are determined. These are used to calculate phonon bands for commensurate tubes. In particular, the modes with rigid walls are analysed and weak interlayer interaction is confirmed. Taking infra-red measurements is found to be a suitable method for characterizing double wall tubes. The heat capacity in the low temperature region is predicted to be lower than for single wall layers.

The recently introduced surface plasmon (SP) toy black hole model has been extended in order to emulate a rotating black hole (Kerr metric). The physical realization of this model involves a droplet of an optically active liquid on the metal surface, which supports the propagation of SPs. Such droplets are shown to exhibit giant optical activity in the frequency range near the SP resonance of a metal–liquid interface.

We review our experimental and theoretical studies on the ultra-small single-walled carbon nanotubes (SWNTs) fabricated in the 1 nm channels of AlPO₄-5 (AFI) zeolite single crystals. The structure of the SWNT was characterized by transmission electron microscopy (TEM), diffuse x-ray diffraction, and micro-Raman measurements, all consistently indicating a diameter of 0.4 nm, at or close to the theoretical limit. The large curvature in the 0.4 nm SWNTs makes the nanotubes marginally stable. On the one hand, the free-standing 0.4 nm SWNTs can be thermally destroyed at a much lower temperature than larger sized SWNTs but, on the other hand, it introduces a variety of interesting material characteristics such as the large split of the G-like Raman modes, softening of the radial breathing modes, closing of the semiconducting gap so that the (5,0) nanotubes are metallic, and the enhancement of the electron–phonon coupling that makes these ultra-small nanotubes superconducting at a relatively high temperature (15 K). Band structure and dielectric function of the 0.4 nm SWNTs were calculated using the local-density-functional approach. The calculated dielectric functions yield predictions in very good agreement with the experimentally measured absorption spectra. The absorption bands can be identified as dipole transitions between states in the vicinity of the van Hove singularities. Further confirmation of these dipole-allowed transitions was obtained by the resonant Raman excitation spectrum. Electric transport measurements were conducted on the SWNT@AFI crystals. As the zeolite matrix is insulating, electric conduction can be ascribed to the nanotubes. It was shown that the conductivity of the 0.4 nm SWNTs is governed by a 1D electron hopping process at temperatures above 20 K. The measured magnetic and transport properties revealed that at temperatures below 20 K, these ultra-small SWNTs exhibit superconducting behaviour with a mean-field superconducting transition temperature of 15 K. The superconducting characteristics display smooth temperature variations owing to 1D fluctuation. The observed anisotropic Meissner effect, the superconducting gap and fluctuation supercurrent were consistently explained on the basis of the Ginzburg–Landau formalism. By means of lithium doping, the electronic structure of the ultra-small SWNTs can be modified. Results of a first-principles calculation as well as experimental observation show that the SWNT@AFI system can adsorb lithium atoms up to a density as high as 10 wt%.

We obtain exact travelling wave solutions for three families of stochastic one-dimensional non-equilibrium lattice models with open boundaries. These solutions describe the diffusive motion and microscopic structure of (i) shocks in the partially asymmetric exclusion process with open boundaries, (ii) a lattice Fisher wave in a reaction–diffusion system, and (iii) a domain wall in non-equilibrium Glauber–Kawasaki dynamics with magnetization current. For each of these systems we define a microscopic shock position and calculate the exact hopping rates of the travelling wave in terms of the transition rates of the microscopic model. In the steady state a reversal of the bias of the travelling wave marks a first-order non-equilibrium phase transition, analogous to the Zel'dovich theory of kinetics of first-order transitions. The stationary distributions of the exclusion process with n shocks can be described in terms of n-dimensional representations of matrix product states.

We investigate the phase space of parameters in the Pati–Salam model derived in the context of D-brane scenarios, requiring a low energy string scale. We find that a non-supersymmetric version complies with a string scale as low as ~10 TeV, while in the supersymmetric version the string scale rises to ~2 × 10⁷ TeV. The limited energy region for RGE running demands a large tan β in order to have experimentally acceptable masses for the top and bottom quarks.

Using in situ x-ray diffraction and Raman scattering techniques, we have investigated the behaviour of single-walled carbon nanotubes bundles under non-hydrostatic pressures. It is seen that the diffraction line corresponding to the two-dimensional triangular lattice in the bundles is not reversible for pressures beyond 5 GPa, in sharp contrast to earlier results under hydrostatic pressure conditions. Most interestingly, radial breathing and tangential Raman modes of the pressure-cycled samples from 21 and 30 GPa match very well with those of the starting sample. Raman and x-ray results put together clearly suggest that the ordering of tubes in the bundles is only marginally regained with a very short coherence length on decompression.

The effect of electron–dust collision on small-amplitude nonlinear dust acoustic (DA) waves in two-component thermal dusty plasma consisting of positively charged (due to thermionic emission) dust grains and electrons has been investigated incorporating the nonadiabaticity of dust-charge variation arising due to delays in the dust charging, i.e. due to small nonzero values of ω_pd/ν_ch, where ω_pd is the dust-plasma frequency and ν_ch is the dust-charging frequency. The propagation of small-amplitude DA waves is governed by a modified Korteweg–de Vries–Burger equation in which the Burger term arising due to the charge delay induced dissipation. Numerical investigations reveal that this equation has a shock-wave solution. Numerical investigations also reveal that in the absence of collision-induced dissipation the charge-delay-induced dissipation also causes the generation of a DA shock wave in two-component dusty plasma.

The name 'Haeckelite' has been proposed to designate a three-fold coordinated network generated by a periodic arrangement of pentagons, hexagons and heptagons (Terrones H et al 2000 Phys. Rev. Lett84 1716). Starting from a planar Haeckelite array, tubular structures are obtained by applying the same wrapping procedure as for the usual nanotubes, which are rolled up sheets of graphene. This paper is a short review of the structural properties of Haeckelite nanotubes, as investigated by computer molecular modelling. The Haeckelite nanotubes may adopt various shapes, among which coiled structures, double-screw molecules, corrugated cylinders, and pearl-necklace-like nanotubes are the most spectacular. It is shown that some of these structures may explain exotic forms of C nanostructures revealed by electron microscopy on samples produced experimentally. The identification of the possible Haeckelite structure of a nanotube by electron diffraction and scanning tunnelling microscopy is discussed.

We have applied the FTIR-luminescence/FT-Raman technique to map the near-infrared photoluminescence (PL) of water–surfactant dispersions of single-walled carbon nanotubes (SWNTs) in broad excitation (250–1500 nm) and emission (800–1700 nm) ranges. The excitation wavelength was scanned by using the monochromatized light of standard xenon and tungsten halogen lamps. The PL maps are presented for SWNTs with a mean diameter of ~1.3 nm prepared by the pulsed laser vaporization method. When dispersed by powerful ultrasonic agitation and separated by ultracentrifugation, these nanotubes show structured absorption bands and a PL quantum yield as high as ~10^-3. This indicates a large fraction of individual nanotubes in the dispersion. Electronic interband transition energies of nanotubes derived from the PL data correspond reasonably to the energies calculated in the modified tight-binding model of Ding et al.

The basic concepts and characteristics of Raman spectra from carbon nanotubes (both isolated and bundled) are presented. The general characteristics of the radial breathing mode, tangential mode (G band), disorder-induced mode (D-band) and other Raman features are presented, with the focus directed toward their use for carbon nanotube characterization. Polarization analysis, surface enhanced Raman spectroscopy and complementary optical techniques are also discussed in terms of their advantages and limitations.

We report on electrical resistance measurements of single multiwalled carbon nanotubes (MWNTs) in different environments (ambient air, H₂, O₂ and the electrolytes LiClO₄, KCl, KMnO₄ and H₃PO₃). The gate dependence is studied using back-gating, electrochemical gating and gates evaporated directly onto the nanotubes (NTs). MWNTs at room temperature are p-doped. Upon changing the environment a change of the doping state of the MWNTs is inferred from the linear resistance. The effect of the environment on the contacts is negligible in our experiments. The p-doping is proposed to originate from the specific adsorption of an oriented dipole layer of water on the nanotube, which is affected by the kind of ions.

Using the explicit numerical solution of the axially symmetric Gross–Pitaevskii equation we study the dynamics of interaction among vortex solitons in a rotating matter-wave bright soliton train in a radially trapped and axially free Bose–Einstein condensate to understand certain features of the experiment by Strecker et al (2002 Nature417 150). In a soliton train, solitons of opposite phase (phase δ = π) repel and stay apart without changing shape; solitons with δ = 0 attract, interact and coalesce, but eventually come out; solitons with a general δ usually repel but interact inelastically by exchanging matter. We study this and suggest future experiments with vortex solitons.

We investigate two schemes of quantum teleportation with a W state, which belongs to a different class from the Greenberger–Horne–Zeilinger class. In the first scheme, the W state is shared by three parties, one of whom, called a sender, performs a Bell measurement. It is shown that the quantum information of an unknown state is split between two parties and recovered with a certain probability. In the second scheme, a sender takes two particles of the W state and performs positive operator valued measurements. For the two schemes, we calculate the success probability and the average fidelity. We show that the average fidelity of the second scheme cannot exceed that of the first one.

We study hexagon patterns in non-Boussinesq convection of a thin rotating layer of water. For realistic parameters and boundary conditions we identify various linear instabilities of the pattern. We focus on the dynamics arising from an oscillatory side-band instability that leads to a spatially disordered chaotic state characterized by oscillating (whirling) hexagons. Using triangulation we obtain the distribution functions for the number of pentagonal and heptagonal convection cells. In contrast to the results found for defect chaos in the complex Ginzburg–Landau equation, in inclined-layer convection, and in spiral-defect chaos, the distribution functions can show deviations from a squared Poisson distribution that suggest non-trivial correlations between the defects.

Nodal lines (phase singularities, optical vortices) are the generic interference fringes of complex scalar waves. Here, an exact complex solution of the time-independent wave equation (Helmholtz equation) is considered, possessing nodal lines which are braided in the form of a borromean, or pigtail braid. The braid field is a superposition of counterpropagating, counterrotating, non-coaxial third-order Bessel beams and a plane wave whose propagation is perpendicular to that of the beams. The construction is structurally stable, and can be generalized to a limited class of other braids.

The interaction of CH₃ and H with amorphous hydrocarbon surfaces plays a central role during plasma deposition of such films. Recently, this interaction has been explored in particle beam experiments. A rate equation model has been proposed which explains the experimental observations on the basis of elementary surface reactions. This model includes several parameters which have the meaning of either a reaction cross section or a rate constant. The predictive power of the model and its applicability to more complex hydrocarbon deposition processes hinges on a reliable determination of the model parameters. In this paper, we develop a Bayesian analysis of the data. The result of this analysis are estimation distributions for each parameter rather than single numbers. We use this in-depth information to draw valuable conclusions about the ability of the model to describe the surface reactions. We find strong indications for a dependence of the reaction cross sections on the particles' angle of incidence.

In this paper we consider a model for intracellular Ca²⁺ waves where the ion channels (excitability) is distributed in spatially distinct clusters. We report that channel noise in conjunction with spatial clustering can result in the onset of spatially and temporally extremely coherent Ca²⁺ signals at levels of stimulant well below the threshold of Ca²⁺ oscillations for homogeneously distributed channels. The physiological significance of this phenomenon is strongly enhanced cellular Ca²⁺-signalling capability with few agonist molecules binding.

Double-wall carbon nanotubes are the molecular analogues to coaxial cables. Narrow diameter double-walled carbon nanotubes (DWNTs) have been obtained by catalytic chemical vapour deposition process with high yield and characterized by scanning and transmission electron microscopy. We examine the inelastic light scattering spectrum of mostly DWNTs with internal tubes of subnanometre diameter. We observe particularly narrow radial breathing modes corresponding to the internal tubes of diameter less than 0.7 nm of double-walled tubes. The D band is found to be strongly helicity dependent and the tangential modes in narrow diameter DWNTs are found to be often down-shifted.

Physicists routinely claim that the fundamental laws of physics are 'time symmetric' or 'time reversal invariant' or 'reversible'. In particular, it is claimed that the theory of quantum mechanics is time symmetric. But it is shown in this paper that the orthodox analysis suffers from a fatal conceptual error, because the logical criterion for judging the time symmetry of probabilistic theories has been incorrectly formulated. The correct criterion requires symmetry between future-directed laws and past-directed laws. This criterion is formulated and proved in detail. The orthodox claim that quantum mechanics is reversible is re-evaluated. The property demonstrated in the orthodox analysis is shown to be quite distinct from time reversal invariance. The view of Satosi Watanabe that quantum mechanics is time asymmetric is verified, as well as his view that this feature does not merely show a de facto or 'contingent' asymmetry, as commonly supposed, but implies a genuine failure of time reversal invariance of the laws of quantum mechanics. The laws of quantum mechanics would be incompatible with a time-reversed version of our universe.

Results are presented from Monte Carlo calculations of the electric charge on dust grains in a plasma produced during the slowing down of radioactive decay products of californium nuclei in neon. The dust grain charging is explained as being due to the drift of electrons and ions in an external electric field. It is shown that the charges of the grains depend on their coordinates and strongly fluctuate with time. The time-averaged grain charges agree with the experimental data obtained on ordered liquid-like dust structures in a nuclear-track plasma. The time-averaged dust grain charges are used to carry out computer modelling of the formation of dynamic vortex structures observed in experiments. Evidence is obtained for the fact that the electrostatic forces experienced by the dust grains are potential in character. The paper is supplemented by a video clip showing the typical dynamics of the simulated vortex dust structure.

We have developed a well controlled method for manipulating carbon nanotubes. The first crucial process involved is to prepare a nanotube array, named a nanotube cartridge. We have discovered ac electrophoresis of nanotubes by which nanotubes are aligned at the knife-edge. The nanotubes used were multiwalled and prepared by an arc discharge with a relatively high gas temperature. The second important process is to transfer a nanotube from the nanotube cartridge onto a substrate in a scanning electron microscope (SEM). Using this method, we have developed nanotube tips and nanotube tweezers that operate in a scanning probe microscope (SPM). The nanotube probes have been applied for the observation of biological samples and industrial samples to clarify their advantages. The nanotube tweezers have demonstrated their motion in an SEM and have operated to carry nanomaterials in a SPM.

We have also developed the electron ablation of a nanotube to adjust its length and the sharpening of a multiwall nanotube to have its inner layer with or without an end cap at the tip. For the sharpening process, the free end of a nanotube protruding from the cartridge was attached to a metal-coated Si tip and a voltage was applied to the nanotube. When a high voltage was used in the saturation current regime, the current decreased stepwise in the temporal variation, indicating the sequential destruction of individual nanotube layers. The nanotube was finally cut at the middle of the nanotube bridge, and its tip was sharpened to have an inner layer with an opened end. Moving up the cartridge before cutting enables us to extract the inner layer with an end cap.

It is evidenced that the maximum current in each layer during the stepwise decrease depends on its circumference, and the force for extracting the inner layer with ~5 nm diameter is ~4 nN.

A description using the Ising model is proposed for the C₇₀ molecular orientational ordering in C₇₀ one-dimensional crystals formed inside single-wall carbon nanotubes (SWNTs). It is shown that the observed standing and lying alignments can be deduced naturally from the present Ising model where the SWNT diameter effectively changes the 'effective field' acting on C₇₀ molecules. The thermal expansion of the C₇₀ intermolecular distance is well described by this model. The possibility of antiferro-orientational ordering is also suggested.

Graphite is a layered material that is very flexible, in which each layer is able to curve in order to form cages, nanotubes, nanocoils, nanocones, etc. In this paper, we demonstrate that various synthetic routes are capable of producing graphite-like nanomaterials with fascinating electronic and mechanical properties. There are other layered systems, which could curl and bend, thus generating novel nanostructures with positive and negative Gaussian curvature. In this context, we will also demonstrate that hexagonal boron nitride, tungsten disulfide (WS₂), molybdenum disulfide (MoS₂) and rhenium disulfide (ReS₂) are also able to create nanocages, nanotubes and nano-arrangements exhibiting novel physico-chemical properties that could revolutionize materials science in the 21st century.

First principles calculations using density functional theory were carried out to obtain the geometrical properties and the radial breathing mode (RBM) frequency of 40 different single-walled carbon nanotubes with small diameter. Fourteen chiral nanotubes with diameters less than 0.8 nm were considered, for which the number of atoms in the unit cell is not larger than 200. From the achiral (zigzag, armchair) nanotubes all those having a diameter less than 1.6 nm were considered. The geometrical parameters deviate from the values obtained from simple wrapping of a perfect hexagonal sheet. The deviation from the ideal behaviour increases with increasing curvature. The most prominent change is the increase of the diameter with respect to its ideal value. The lattice constant along the tube axis exhibits a slight shrinking. The RBM frequency does not follow the usually assumed 1/d behaviour; there is a general softening with increasing curvature. The softening of the RBM frequency cannot be described by a simple function of the diameter; it also depends on the chiral angle and the metallicity of the tube. In addition to this, the coupling of the totally symmetric radial motion with the totally symmetric tangential motion(s) has a non-negligible effect.

The study of carbon nanotubes, since their discovery by Iijima in 1991, has become a full research field with significant contributions from all areas of research in solid-state and molecular physics and also from chemistry. This Focus Issue in New Journal of Physics reflects this active research, and presents articles detailing significant advances in the production of carbon nanotubes, the study of their mechanical and vibrational properties, electronic properties and optical transitions, and electrical and transport properties. Fundamental research, both theoretical and experimental, represents part of this progress. The potential applications of nanotubes will rely on the progress made in understanding their fundamental physics and chemistry, as presented here. We believe this Focus Issue will be an excellent guide for both beginners and experts in the research field of carbon nanotubes.

It has been a great pleasure to edit the many excellent contributions from Europe, Japan, and the US, as well from a number of other countries, and to witness the remarkable effort put into the manuscripts by the contributors. We thank all the authors and referees involved in the process. In particular, we would like to express our gratitude to Alexander Bradshaw, who invited us put together this Focus Issue, and to Tim Smith and the New Journal of Physics staff for their extremely efficient handling of the manuscripts.

Focus on Carbon Nanotubes Contents

Transport theory of carbon nanotube Y junctionsR Egger, B Trauzettel, S Chen and F Siano

The tubular conical helix of graphitic boron nitrideF F Xu, Y Bando and D Golberg

Formation pathways for single-wall carbon nanotube multiterminal junctionsInna Ponomareva, Leonid A Chernozatonskii, Antonis N Andriotis and Madhu Menon

Synthesis and manipulation of carbon nanotubesJ W Seo, E Couteau, P Umek, K Hernadi, P Marcoux, B Lukic, Cs Mikó, M Milas, R Gaál and L Forró

Transitional behaviour in the transformation from active end planes to stable loops caused by annealingM Endo, B J Lee, Y A Kim, Y J Kim, H Muramatsu, T Yanagisawa, T Hayashi, M Terrones and M S Dresselhaus

Energetics and electronic structure of C₇₀-peapods and one-dimensional chains of C₇₀Susumu Okada, Minoru Otani and Atsushi Oshiyama

Theoretical characterization of several models of nanoporous carbonF Valencia, A H Romero, E Hernández, M Terrones and H Terrones

First-principles molecular dynamics study of the stretching frequencies of hydrogen molecules in carbon nanotubesGabriel Canto, Pablo Ordejón, Cheng Hansong, Alan C Cooper and Guido P Pez

The geometry and the radial breathing mode of carbon nanotubes: beyond the ideal behaviourJeno Kürti, Viktor Zólyomi, Miklos Kertesz and Guangyu Sun

Curved nanostructured materialsHumberto Terrones and Mauricio Terrones

A one-dimensional Ising model for C₇₀ molecular ordering in C₇₀-peapodsYutaka Maniwa, Hiromichi Kataura, Kazuyuki Matsuda and Yutaka Okabe

Nanoengineering of carbon nanotubes for nanotoolsYoshikazu Nakayama and Seiji Akita

Narrow diameter double-wall carbon nanotubes: synthesis, electron microscopy and inelastic light scatteringR R Bacsa, E Flahaut, Ch Laurent, A Peigney, S Aloni, P Puech and W S Bacsa

Sensitivity of single multiwalled carbon nanotubes to the environmentM Krüger, I Widmer, T Nussbaumer, M Buitelaar and C Schönenberger

Characterizing carbon nanotube samples with resonance Raman scatteringA Jorio, M A Pimenta, A G Souza Filho, R Saito, G Dresselhaus and M S Dresselhaus

FTIR-luminescence mapping of dispersed single-walled carbon nanotubesSergei Lebedkin, Katharina Arnold, Frank Hennrich, Ralph Krupke, Burkhard Renker and Manfred M Kappes

Structural properties of Haeckelite nanotubesPh Lambin and L P Biró

Structural changes in single-walled carbon nanotubes under non-hydrostatic pressures: x-ray and Raman studiesSukanta Karmakar, Surinder M Sharma, P V Teredesai, D V S Muthu, A Govindaraj, S K Sikka and A K Sood

Novel properties of 0.4 nm single-walled carbon nanotubes templated in the channels of AlPO₄-5 single crystalsZ K Tang, N Wang, X X Zhang, J N Wang, C T Chan and Ping Sheng

Lattice dynamics and symmetry of double wall carbon nanotubesM Damnjanović, E Dobardžić, I Milošević, T Vuković and B Nikolić

Optical characterization of single-walled carbon nanotubes synthesized by catalytic decomposition of alcoholShigeo Maruyama, Yuhei Miyauchi, Yoichi Murakami and Shohei Chiashi

Electronic structure and the field emission mechanism of MgO-coated carbon nanotubesYoung-Woo Son, Seungwu Han and Jisoon Ihm

Controlled low-temperature growth of carbon nanofibres by plasma depositionS Hofmann, B Kleinsorge, C Ducati and J Robertson

Electronic properties of intercalated single-wall carbon nanotubes and C₆₀ peapodsT Pichler, X Liu, M Knupfer and J Fink

Double resonance Raman spectroscopy of single-wall carbon nanotubesR Saito, A Grüneis, Ge G Samsonidze, V W Brar, G Dresselhaus, M S Dresselhaus, A Jorio, L G Cançado, C Fantini, M A Pimenta and A G Souza Filho

Contacts, non-linear transport effects and failure in multi-walled carbon nanotubesC Berger, Y Yi, J Gezo, P Poncharal and W A de Heer

Raman spectroscopy of small-diameter nanotubesM Hulman, R Pfeiffer and H Kuzmany

Multiple-layer conduction and scattering property in multi-walled carbon nanotubesK Tsukagoshi, E Watanabe, I Yagi, N Yoneya and Y Aoyagi

Trapping and aligning carbon nanotubes via substrate geometry engineeringY M Wang, Wei-Qiang Han and A Zettl

Curvature effects on the structural, electronic and optical properties of isolated single-walled carbon nanotubes within a symmetry-adapted non-orthogonal tight-binding modelValentin N Popov

Syntheses of single- and double-wall carbon nanotubes by the HTPAD and HFCVD methodsToshiki Sugai, Toshiya Okazaki, Hiromichi Yoshida and Hisanori Shinohara

Ensemble averaging of conductance fluctuations in multiwall carbon nanotubesB Stojetz, Ch Hagen, Ch Hendlmeier, E Ljubovic, L Forró and Ch Strunk

Electronic effects in scanning tunnelling microscopy of metal-filled multiwalled carbon nanotubesRichard Czerw, Jiwen Liu and David L Carroll

Christian Thomsen, Technische Universität Berlin, Germany Hiromichi Kataura, Tokyo Metropolitan University, Japan

We present a study of the vibrational frequencies of hydrogen molecules adsorbed in bundles of single wall carbon nanotubes. The frequencies are extracted from the analysis of first-principles molecular dynamics trajectories. We study the case of molecules inside the nanotubes (endohedral) and in the interstitial pores between the nanotubes (exohedral). We find that, in both configurations, the stretching frequencies are redshifted with respect to the free H₂ molecule. However, whereas all the exohedral molecules exhibit a redshift of around 45 cm⁻¹, the endohedral molecules show two frequencies, one close to that of the exohedral molecules and the other similar to that of free H₂.

Elastic, electronic and vibrational properties of seven models of nanoporous carbon are reported. The studied structures are periodic graphitic arrangements with heptagonal and octagonal rings of carbon, known as Schwarzites. The calculations were performed within a non-orthogonal tight binding framework which has been shown to be reliable for diamond, graphene layers, fullerenes and carbon nanotubes. In contrast with previous studies, each structure was properly relaxed, so that differences between each model must be assigned to intrinsic properties rather than to differences in their construction. Thermodynamic properties were calculated from the vibrational density of states.

We report total-energy electronic structure calculations that provide the energetics of encapsulation of C₇₀ fullerenes in carbon nanotubes. The encapsulation processes for C₇₀ in tubes thicker than (17,0) are all exothermic. We find that the lying arrangement is energetically favourable for the thin nanotubes, whereas the standing arrangement is favourable for thick nanotubes. To explore the stable molecular arrangements in the nanotubes, we further study the energetics and electronic structures of one-dimensional chains of C₇₀. It is found that the standing intermolecular arrangement is the most stable structure for the chain due to the large intermolecular interaction. The electronic structures of the chains strongly depend on the mutual orientation of adjacent molecules. We find flat dispersion bands around the Fermi level of the standing chains and a possibility of spin polarization on the one-dimensional chain of C₇₀.

Here we investigate the stabilization process on the active outer/inner surfaces (or the end plane of a graphene sheet) for shortened cup-stacked-type carbon nanotubes caused by annealing, utilizing both analytic and electrochemical techniques. The suggested schematic procedure for loop formation is as follows: (a) formation of single-type loops between neighbouring truncated conical graphene layers at 900–1200 °C through a zipping mechanism after the evolution of hydrogen gas; (b) the transition from single- to multi-type loops above 1500 °C accompanying a decrease in specific surface area.

This paper reviews recent results in the field of carbon nanotube (CNT) research obtained at our institute at EPFL. We show in particular that CNTs can be synthesized by the catalytic vapour deposition (CVD) technique with high efficiency and purity. Furthermore, we present recent examples of advances in the large-scale production of CNTs as well as in the chemical and mechanical manipulation of CNTs. The chemical manipulation involves covalent and non-covalent sidewall functionalization of single-wall CNTs and preparation of inorganic coatings on CVD-grown nanotubes for the realization of fibres and CNT-reinforced composites. Mechanical manipulation aims at the application of CNTs as tips for scanning probe microscopy.

Using tight-binding as well as classical molecular dynamics we simulate the formation of single-wall carbon nanotube T-, Y- and X-junctions via the fusing of two nanotubes. We propose energetically efficient pathways for this process in which all atoms maintain their sp² arrangements throughout. Recent experimental advances have greatly increased the plausibility of synthesizing multiterminal junctions as proposed in the simulations. We further report I–V characteristics of one of the junctions thus formed.

We employed a novel synthetic route for the generation of a boron nitride (BN) filamentary nanostructure. A pre-formed filamentary microstructure was used as a template instead of a conventional metal catalyst. BN nanotubes exhibiting the geometry of an Archimedes spiral were obtained via a post-heating process at temperatures above 1750 °C on the intermediate BN microstructures pre-formed under heating to 1700 °C. An enthalpy was found to primarily determine the structures of the resultant helical–conical nanotubes (HCNTs). Therefore, the structural parameters, particularly the apex angles of the cones, can be easily varied via simple annealing. This unique structural property is favourable to interlayer sliding in the HCNT structure, as was documented during electron beam induced deformation. HCNTs can be bent by an angle as high as 180° at room temperature and, then, fully recover the starting morphology after the release of an external stress, exhibiting a spring-like behaviour. The striking elasticity and flexibility of these nanotubes stem from both the high stiffness and the extraordinary flexibility of the BN filaments, and the ease of interlayer sliding in a graphitic structure. The novel BN tubular geometry broadens the range of known helical cone structures. Structural models were developed taking into account the disclination angles or apex angles, wrapping modes, coincidence site lattices and packing patterns of the BN HCNTs.

We describe a generalization of Landauer–Büttiker theory for networks of interacting metallic carbon nanotubes. We start with symmetric starlike junctions and then extend our approach to asymmetric systems. While the symmetric case is solved in closed form, the asymmetric situation is treated by a mixture of perturbative and non-perturbative methods. For N > 2 repulsively interacting nanotubes, the only stable fixed point of the symmetric system corresponds to an isolated node. Detailed results for both symmetric and asymmetric systems are shown for N = 3, corresponding to carbon nanotube Y junctions.

The properties of nonlinear dust kinetic Alfvén waves in a collisionless, low (but finite)-β, dust–ion plasma are investigated by employing the pseudo-potential approach, which is valid for arbitrary amplitude solitary waves. It is shown both analytically and numerically that a dusty plasma model can support solitary waves consisting of density humps or dips. Furthermore, the properties of these solitary waves are found to be significantly modified by the speed and obliqueness of the wave propagation. The findings of the present investigation should be useful in understanding the formation of coherent nonlinear soliton structures in space and astrophysical dusty plasmas, such as in planetary rings and cometary tails.

Well crystallized aligned zinc oxide nanoscale tubular structures have been fabricated via vapour phase growth on large area substrates. The ZnO nanotubes have regular polyhedral shapes, hollow cores with diameters of 30–100 nm, lengths over a few tens of micrometres and wall thicknesses of 4–10 nm. In morphology, the nanotubes were either straight or twisted with several straight parts. The microstructure of the tubular material was investigated in detail by using high-resolution transmission electron microscopy (HRTEM), Z-contrast imaging and compositional line profile analysis. The chemical composition of individual tubular structures was found to be stoichiometric ZnO using selected area energy dispersive x-ray spectroscopy and electron energy loss spectroscopy. X-ray diffraction (XRD) and selected area electron diffraction results indicated that the ZnO nanotubes had wurtzite crystal structure. XRD analysis and HRTEM investigations indicated the ZnO nanotubes were grown along the [001] direction. The growth of the tubular ZnO nanostructures was found to be closely related to the hexagonal nature of the ZnO crystal and the peculiar growth conditions used.

We report on our computation of electron-energy transfer rates for vibrational excitation of O₂. This work was necessitated by inadequacies in the electron-impact cross section databases employed in previous studies and, in one case, an inaccurate approximate formulation to the rate equation. Both these inadequacies led to incorrect energy transfer rates being published in the literature. We also demonstrate the importance of using cross sections that encompass an energy range that is extended enough to appropriately describe the environment under investigation.

We present a theoretical analysis of the phase diagram of two-component bosons on an optical lattice. A new formalism is developed which treats the effective spin interactions in the Mott and superfluid phases on the same footing. Using this new approach we chart the phase boundaries of the broken spin symmetry states up to the Mott to superfluid transition and beyond. Near the transition point, the magnitude of spin exchange can be very large, which facilitates the experimental realization of spin-ordered states. We find that spin and quantum fluctuations have a dramatic effect on the transition, making it first order in extended regions of the phase diagram. When each species is at integer filling, an additional phase transition may occur, from a spin-ordered insulator to a Mott insulator with no broken symmetries. We determine the phase boundaries in this regime and show that this is essentially a Mott transition in the spin sector.

We investigate the superfluid properties of a Bose–Einstein condensate (BEC) trapped in a one-dimensional periodic potential. We study, both analytically (in the tight binding limit) and numerically, the Bloch chemical potential, the Bloch energy and the Bogoliubov dispersion relation, and we introduce two different, density dependent, effective masses and group velocities. The Bogoliubov spectrum predicts the existence of sound waves, and the arising of energetic and dynamical instabilities at critical values of the BEC quasi-momentum which dramatically affect its coherence properties. We investigate the dependence of the dipole and Bloch oscillation frequencies in terms of an effective mass averaged over the density of the condensate. We illustrate our results with several animations obtained solving numerically the time-dependent Gross–Pitaevskii equation.

A simple two-atom model is shown to describe a Bose–Einstein condensate of alkali atoms subjected to external magnetic field ramps near a Feshbach resonance. The implications uncovered for two atoms in a trap can be applied at least approximately to a many-atom condensate. A connection to observations is accomplished by scaling the trap frequency to achieve a density comparable to that of the experiments, which yields the fraction of atom pairs in the gas that become molecules. A sudden approximation is used to model the external magnetic field ramps in the vicinity of a two-body Feshbach resonance. The results of this model are compared with recent experimental observations of Donley et al (2002 Nature417 529).

Although photoassociation and the Feshbach resonance are feasible means in principle for creating a molecular Bose–Einstein condensate (MBEC) from an already quantum-degenerate gas of atoms, collision-induced mean-field shifts and irreversible decay place practical constraints on the efficient Raman delivery of stable molecules. Focusing on stimulated Raman adiabatic passage, we propose that the efficiency of both mechanisms for producing a stable MBEC can be improved by treating the density of the initial atom condensate as an optimization parameter.

We discuss quantum fidelity decay of classically regular dynamics, in particular for an important special case of a vanishing time-averaged perturbation operator, i.e. vanishing expectation values of the perturbation in the eigenbasis of unperturbed dynamics. A complete semiclassical picture of this situation is derived in which we show that the quantum fidelity of individual coherent initial states exhibits three different regimes in time: (i) first it follows the corresponding classical fidelity up to time , (ii) then it freezes on a plateau of constant value, (iii) and after a timescale it exhibits fast ballistic decay as where is a strength of perturbation. All the constants are computed in terms of classical dynamics for sufficiently small effective value of the Planck constant. A similar picture is worked out also for general initial states, and specifically for random initial states, where , and . This prolonged stability of quantum dynamics in the case of a vanishing time-averaged perturbation could prove to be useful in designing quantum devices. Theoretical results are verified by numerical experiments on the quantized integrable kicked top.

The dynamics of large-sized (70–180 µm) spherical bronze particles in a direct current glow discharge plasma was studied experimentally under microgravitation conditions. The temperatures, velocities, pair correlation functions and self-diffusion coefficients of macroparticles were measured at various discharge currents. The charges of dust particles (on the order of 10⁶ e) corresponded to high surface potentials of about 30–40 V.

We investigate the low-temperature phase diagram of the exactly solved su(4) two-leg spin ladder as a function of the rung coupling and magnetic field H by means of the thermodynamic Bethe ansatz (TBA). In the absence of a magnetic field the model exhibits three quantum phases, while in the presence of a strong magnetic field there is no singlet ground state for ferromagnetic rung coupling. For antiferromagnetic rung coupling, there is a gapped phase in the regime H < H_c1, a fully polarized gapped phase for H > H_c2 and a Luttinger liquid magnetic phase in the regime H_c1 < H < H_c2. The critical behaviour derived using the TBA is consistent with the existing experimental, numerical and perturbative results for the strong coupling ladder compounds. This includes the spin excitation gap and the critical fields H_c1 and H_c2, which are in excellent agreement with the experimental values for the known strong coupling ladder compounds (5IAP)₂CuBr₄·2H₂O, Cu₂(C₅H₁₂N₂)₂Cl₄ and (C₅H₁₂N)₂CuBr₄. In addition we predict the spin gap for the weak coupling compounds with , such as (VO)₂P₂O₇, and also show that the gap opens for arbitrary .

We study the dynamics of a simplified model of atmospheric convection. The model represents a layer of dry air kept in statistically stationary radiative–convective equilibrium. We discuss the behaviour and the spatial organization of the pattern of convective plumes that emerge in the system, and analyse the intermittency properties of the heat flux field.

Causality imposes strong restrictions on the type of operators that may be observables in relativistic quantum theories. In fact, causal violations arise when computing conditional probabilities for certain partial causally connected measurements using the standard non-covariant procedure. Here we introduce another way of computing conditional probabilities, based on an intrinsic covariant relational order of the events, which differs from the standard one when this type of measurement is included. This alternative procedure is compatible with a wider and very natural class of operators without breaking causality. If some of these measurements can be implemented in practice, as predicted by our formalism, the non-covariant, conventional approach should be abandoned. Furthermore, the description we promote here would imply a new physical effect where interference terms are suppressed as a consequence of the covariant order in the measurement process.

Superflow of a Bose–Einstein condensate in an optical lattice is represented by a Bloch wave, a plane wave with periodic modulation of the amplitude. We review the theoretical results of the interaction effects in the energy dispersion of the Bloch waves and in the linear stability of such waves. For sufficiently strong repulsion between the atoms, the lowest Bloch band develops a loop at the edge of the Brillouin zone, with the dramatic consequence of a finite probability of Landau–Zener tunnelling even in the limit of a vanishing external force. Superfluidity can exist in the central region of the Brillouin zone in the presence of a repulsive interaction, beyond which Landau instability takes place where the system can lower its energy by making a transition into states with smaller Bloch wavenumbers. In the outer part of the region of Landau instability, the Bloch waves are also dynamically unstable in the sense that a small initial deviation grows exponentially in time. In the inner region of Landau instability, a Bloch wave is dynamically stable in the absence of persistent external perturbations. Experimental implications of our findings will be discussed.

I formulate a 'pseudo-paradox' in the theory of a dilute Bose gas with repulsive interactions: the standard expression for the ground state energy within the Gross–Pitaevskii (GP) approximation is lower than that in the Bogoliubov approximation, and hence, by the standard variational argument, the former should prima facie be a better approximation than the latter to the true ground state—a conclusion which is of course opposite to the established wisdom concerning this problem. It is shown that the pseudo-paradox is (unsurprisingly) resolved by a correct transcription of the two-body scattering theory to the many-body case; however, contrary to what appears to be a widespread belief, the resolution has nothing to do with any spurious ultraviolet divergences which result from the replacement of the true interatomic potential by a delta-function pseudopotential. Rather, it relates to an infrared divergence which has the consequence that (a) the most obvious form of the GP 'approximation' actually does not correspond to any well-defined ansatz for the many-body wavefunction, and (b) that the 'best shot' at such a wavefunction always produces an energy which exceeds, or at best equals, that calculated in the Bogoliubov approximation. In fact, the necessity of the latter may be seen as a consequence of the need to reduce the Fock term in the energy, which is absent in the two-particle problem but dominant in the many-body case; it does this by increasing the density correlations, at distances less than or approximately equal to the correlation length , above the value extrapolated from the two-body case. As a by-product I devise an alternative formulation of the Bogoliubov approximation which does not require the explicit replacement of the true interatomic potential by a delta-function pseudopotential.

In this paper the results of experimental investigation of the dynamic behaviour of macroparticles charged via photoemission are presented. The experimental data have been obtained for bronze particles subjected to solar radiation under conditions of microgravity (on board the Mir space station). The distribution of velocity, temperatures and charge, as well as the friction coefficient and diffusion constants, have been found. The analysis of the results obtained has shown that the polarization effects of opposite charges may appreciably influence the transport processes in a two-component electron–dust plasma, consisting of positively charged dust and emitted electrons.

Previous work has shown that dynamic heterogeneity and conduction block can occur in homogeneous heart fibres during prolonged pacing at rapid rates. Here we investigated the mechanism for conduction block following the delivery of one to four premature stimuli using a coupled maps computer model of a one-dimensional canine heart fibre. The coupled maps model allowed us to identify the roles that velocity (V) restitution, action potential duration (D) restitution and cardiac memory (M) played in the development of spatial heterogeneity and conduction block. We found that the likelihood of conduction block could be reduced by three methods. (1) By altering the V restitution function so that conduction slowed at very short rest intervals (I). (2) By altering the D restitution function to reduce the sensitivity of D to changes in I. (3) By increasing the contribution of cardiac memory (M). Although the results of this study need to be confirmed experimentally, they suggest several potential interventions that may reduce the probability of arrhythmia induction.

The rich variety of micron-scale features observed in the orientation-dependent surface morphology of crystalline silicon during anisotropic wet chemical etching is shown to have its origin at the atomistic scale. Realistic Monte Carlo simulations show that the pyramidal hillocks on Si(100) are the result of local stabilization of distributed apex atoms by (metal) impurities from solution. In the absence of this stabilization, shallow round pits are formed on Si(100) as a result of the anisotropy between (one layer deep) pit nucleation and (isotropic) step propagation. It is also concluded that nosed zigzag structures at vicinal (110) are the combined result of misaligment and the etching anisotropy, showing that the nucleating mechanisms of morphologically related structures such as pyramidal hillocks and nosed zigzags are not necessarily the same. The simulations confirm that the formation of (one layer deep) triangular and hexagonal pits on exact Si(111) and of polygonal (saw-shaped) and straight terraces in vicinal Si(111) depends on the relative rate of [11] and [2] step propagation and on the misorientation of the surface with respect to Si(111).

Meissner fraction in the superconducting state of lead archaeological artifacts is used to evaluate the mass of the uncorroded metal in the sample. Knowing the total mass of the sample, the mass of all corrosion products is established. It is shown that this mass correlates with the archaeological age of the lead artifacts over a time span of ∼2500 years. Well-dated untreated lead samples from Tel-Dor, the Persian period, Caesarea, the Byzantine and the Crusader periods as well as contemporary data were used to establish the dating correlation. This new chemical dating method is apparently applicable to lead artifacts buried in soils with pH > 6.5. In such soils the corrosion process is very slow and the corrosion products, mainly PbO and PbCO₃, accumulate over hundreds of years. The method presented is in principle non-destructive.

We derive exact closed-form expressions for the first few terms of the short-distance Taylor expansion of the one-body correlation function of the Lieb–Liniger gas.

Patterns of convection in internally heated, self-gravitating rotating spherical fluid shells are investigated through numerical simulations. While turbulent states are of primary interest in planetary and stellar applications the present paper emphasizes more regular dynamical features at Rayleigh numbers not far above threshold which are similar to those which might be observed in laboratory or space experiments. Amplitude vacillations and spatial modulations of convection columns are common features at moderate and large Prandtl numbers. In the low Prandtl number regime equatorially attached convection evolves differently with increasing Rayleigh number and exhibits an early transition into a chaotic state. Relationships of the dynamical features to coherent structures in fully turbulent convection states are emphasized.

Intracellular Ca²⁺ dynamics allows for the observation of wave formation from elemental release events to the global phenomenon. It shows propagating waves with deterministic features and at the same time probabilistic behaviour like variable periods. Formulation and analysis of deterministic wave models sheds new light on experimental observations and contributes to the theory of nonlinear propagating waves by exhibiting new instabilities. That is demonstrated with the example of Ca²⁺ waves with energized mitochondria. Stochastic models can describe spatio-temporal structures from localized puffs to propagating waves. They explain the origin of long timescales in Xenopus oocytes and wave generation. The implications of the results of both approaches for the theory of intracellular Ca²⁺ dynamics is discussed.

We have adapted the transfer matrix method to the confinement of a single polymer molecule in tube-like cavities. The method is exact and numerically efficient for realistic polymer models such as the freely rotating chain and the rotational isomeric chain models. It allows us to calculate the chain end distribution function from which the longitudinal end-to-end distance and the free energy are obtained. The confinement is modelled as a cylindrical potential with soft walls or as a harmonic potential. Known scaling laws are recovered for long chains and strong confinement and new scaling behaviour is found in the intermediate regime. The effect of anchoring one chain end to a base plate of a semi-infinite tube is also studied.

When subject to an external time-periodic perturbation of frequency f, a Josephson-coupled two-state Bose–Einstein condensate may respond with a constant chemical potential difference Δμ = khf, where h is Planck's constant and k is an integer. We propose an experimental procedure to produce ac-driven atomic Josephson devices that can be used to define a standard of chemical potential. We investigate how to circumvent some of the specific problems derived from the present lack of advanced atom circuit technology. We include the effect of dissipation due to quasiparticles, which is essential to help the system relax towards the exact Shapiro resonance, and set limits to the range of values which the various physical quantities must have in order to favour the achievement of a stable and accurate chemical potential difference between the macroscopic condensates.

Low-pressure plasmas offer a unique possibility of confinement, control and fine tailoring of particle properties. Hence, dusty plasmas have grown into a vast field and new applications of plasma-processed dust particles are emerging. There is demand for particles with special properties and for particle-seeded composite materials. For example, the stability of luminophore particles could be improved by coating with protective Al₂O₃ films which are deposited by a PECVD process using a metal-organic precursor gas.

Alternatively, the interaction between plasma and injected micro-disperse powder particles can also be used as a diagnostic tool for the study of plasma surface processes. Two examples will be provided: the interaction of micro-sized (SiO₂) grains confined in a radiofrequency plasma with an external ion beam as well as the effect of a dc-magnetron discharge on confined particles during deposition have been investigated.

The adaptive electrode consists of a two-dimensional array of single electrodes each individually voltage controllable to produce local modifications in the plasma edge. This paper presents an experimental study on the nature of the perturbation introduced by the DC biasing of the pixels, using suspended particles as tracers. The particles above a negative pixel show an expansion of the sheath but for high negative voltages the particle can no longer levitate. This is explained by the reduction of the RF enhancement of the charge on the particle. Under certain conditions the sheath above a positive pixel evolves into multiple double layers, setting up a negative pre-sheath far into the plasma.

We extend our exact reformulation of the bosonic many-body problem in terms of a stochastic Hartree ansatz to a stochastic Gutzwiller ansatz for the Bose–Hubbard model. The use of this ansatz makes the corresponding Monte Carlo scheme more efficient for strongly correlated bosonic phases like the Mott insulator phase or the Tonks phase. We present a first numerical application of this stochastic method to a system of impenetrable bosons on a 1D lattice showing the transition from the discrete Tonks gas to the Mott phase as the chemical potential is increased.

Physical concepts developed to describe instabilities in traffic flows can be generalized in a way that allows one to understand the well-known instability of supply chains (the so-called 'bull-whip effect'). That is, small variations in the consumption rate can cause large variations in the production rate of companies generating the requested product. Interestingly, the resulting oscillations have characteristic frequencies which are considerably lower than the variations in the consumption rate. This suggests that instabilities of supply chains may be the reason for the existence of business cycles. At the same time, we establish some links to queueing theory and between micro- and macroeconomics.

We report on the experimental detection of a drift bifurcation for dissipative solitons, which we observe in the form of current filaments in a planar semiconductor–gas-discharge system. By introducing a new stochastic data analysis technique we find that due to a change of system parameters the dissipative solitons undergo a transition from purely noise-driven objects with Brownian motion to particles with a dynamically stabilized finite velocity.

We study Landau damping in dilute Bose–Einstein condensed gases in both spherical and prolate ellipsoidal harmonic traps. We solve the Bogoliubov equations for the mode spectrum in both of these cases, and calculate the damping by summing over transitions between excited quasiparticle states. The results for the spherical case are compared to those obtained in the Hartree–Fock (HF) approximation, where the excitations take on a single-particle character, and excellent agreement between the two approaches is found. We have also taken the semiclassical limit of the HF approximation and obtain a novel expression for the Landau damping rate involving the time-dependent self-diffusion function of the thermal cloud. As a final approach, we study the decay of a condensate mode by making use of dynamical simulations in which both the condensate and thermal cloud are evolved explicitly as a function of time. A detailed comparison of all these methods over a wide range of sample sizes and trap geometries is presented.

We showed earlier how to predict the writhe of any rational knot or link in its ideal geometric configuration, or equivalently the average of the 3D writhe over statistical ensembles of random configurations of a given knot or link (Cerf and Stasiak 2000 Proc. Natl Acad. Sci. USA97 3795). There is no general relation between the minimal crossing number of a knot and the writhe of its ideal geometric configuration. However, within individual families of knots linear relations between minimal crossing number and writhe were observed (Katritch et al 1996 Nature384 142). Here we present a method that allows us to express the writhe as a linear function of the minimal crossing number within Conway families of knots and links in their ideal configuration. The slope of the lines and the shift between any two lines with the same slope can be computed.

We consider a dense ultracold Fermi gas in the presence of a Feshbach resonance. We investigate how the threshold for bound state formation, which is just at the Feshbach resonance for a dilute gas, is modified due to the presence of the Fermi sea. We make use of a preceding framework of handling this many-body problem. We restrict ourselves to the simple case where the chemical potential μ is negative, which allows us to cover in particular the classical limit where the effect is seen to disappear. We show that, within a simple approach where basically only the effect of Pauli exclusion is included, the Fermi sea produces a large shift of the threshold, which is of the order of the width of the Feshbach resonance. This is in agreement with very recent experimental findings.

A curvature self-interaction of the cosmic gas is shown to mimic a cosmological constant or other forms of dark energy, such as a rolling tachyon condensate or a Chaplygin gas. Any given Hubble rate and deceleration parameter can be traced back to the action of an effective curvature force on the gas particles. This force self-consistently reacts back on the cosmological dynamics. The links between an imperfect fluid description, a kinetic description with effective antifriction forces and curvature forces, which represent a non-minimal coupling of gravity to matter, are established.

A novel quaternary compound semiconductor material, Ga_{1 − x}In_xN_yAs_{1 − y}(0 < x, y < 1), was successfully used in demonstrating optically pumped continuous-wave vertical-cavity surface-emitting lasers emitting at 1280 nm. The epitaxial heterostructures of each laser wafer were grown in a single nucleation process by conventional molecular beam epitaxy using a nitrogen radio-frequency plasma source. The lasers consist of GaAs/AlAs distributed Bragg reflector mirrors and 6 or 15 Ga_0.65In_0.35N_0.014As_0.986/GaAs quantum wells with special strain-mediating layers. The laser characterization was carried out by using a fibre pigtailed 980 nm pump laser diode, 980/1300 nm wavelength division multiplexer and an optical spectrum analyser. A high optical output power of 3.5 mW was coupled lenslessly into a standard single-mode fibre.

In discrete time, coined quantum walks, the coin degrees of freedom offer the potential for a wider range of controls over the evolution of the walk than are available in the continuous time quantum walk. This paper explores some of the possibilities on regular graphs, and also reports periodic behaviour on small cyclic graphs.

Various self-excited motions in dusty plasmas involving spatial variations of macroparticle charge are considered. Two basic types of instabilities in these systems are examined numerically and analytically. The main attention is given to the vortex motions of macroparticles. Conditions suitable for creating the instabilities examined are discussed. Experimental observations of self-excited oscillations in dc-glow, and capacitive rf, discharges are presented. It is shown that spatial variation of dust charge can account for many phenomena observed in inhomogeneous laboratory dusty plasmas.

It is shown that shear waves in a strongly coupled dusty plasma with nonuniform plasma pressure and dust density can be destabilized. The dispersion relation as well as the instability condition have been found and investigated in detail.

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus c₄₄^∞ can be measured in addition to the longitudinal modulus c₁₁^∞ already well above the thermal glass transition. On slow cooling of the liquid through the thermal glass transition temperature T_g, both moduli show a kink-like behaviour and the function c₁₁^∞ = c₁₁^∞(c₄₄^∞) follows a generalized Cauchy relation (gCR) defined by the linear relation c₁₁^∞ = 3c₄₄^∞ + constant, which completely hides the glass transition. In this work we show experimentally that on fast cooling this linear transformation becomes violated within the glassy state, but that thermal ageing drives the elastic coefficients towards the gCR, i.e. towards a unique glassy state.

We develop an analytical method for calculating local correlations in strongly interacting one-dimensional (1D) Bose gases, based on the exactly solvable Lieb–Liniger model. The results are obtained at zero and finite temperatures. They describe the interaction-induced reduction of local many-body correlation functions and can be used for achieving and identifying the strong-coupling Tonks–Girardeau regime in experiments with cold Bose gases in the 1D regime.

We study the one-dimensional dynamical behaviour of an atomic wavepacket moving across an opaque and spatially oscillating optical barrier. The tunnelling probability shows a dramatic dependence on the frequency of the barrier oscillation. Transmission of the atomic wavepacket is, in fact, dominated by inelastic or elastic effects, depending on whether the oscillation period is comparable to or shorter than the atom–barrier interaction time. In the elastic regime, in particular, we find that full transparency becomes possible at energies where the stationary barrier would otherwise be essentially opaque. We predict that both inelastic and elastic resonant tunnelling regimes could be observed with atomic condensates impinging on a spatially oscillating optical barrier. A few applications will also be discussed.

We revisit the topic of the mean field ground state of a spin-1 atomic condensate inside a uniform magnetic field (B) under the constraints that both the total number of atoms (N) and the magnetization () are conserved. In the presence of an internal state (spin component) independent trap, we also investigate the dependence of the so-called single spatial mode approximation on the magnitude of the magnetic field and . Our results indicate that the quadratic Zeeman effect is an important factor in balancing the mean field energy from elastic atom–atom collisions that are known to conserve both N and .

We study the internal dynamics of bosonic atoms in an optical lattice. Within the regime in which the atomic crystal is a Mott insulator with one atom per well, the atoms behave as localized spins which interact according to some spin Hamiltonian. The type of Hamiltonian (Heisenberg, Ising), and the sign of interactions may be tuned by changing the properties of the optical lattice, or applying external magnetic fields. When, on the other hand, the number of atoms per lattice site is unknown, we can still use the bosons to perform general quantum computation.

Dust clusters containing from one up to 12 particles arranged in a horizontal plane were formed in an inductively coupled rf plasma. When an axial magnetic field was applied to the dust cluster, the cluster rotated as a rigid body in the left-handed direction with respect to the field. The cluster rotation occurred at a magnetic field of tens of gauss in our experiment, which was two to three orders less than that used in previous experiments and that predicted by the models in the literature. In particular, the angular velocity dependence on magnetic field strength varied with number of particles in the cluster and with the structural configuration of the cluster. Other rotational properties such as cluster radius, angular momentum and threshold magnetic field were measured. The dependence of the radial confinement electric field on the magnetic field was also obtained. Finally, comparisons were made between our experimental results and various existing theoretical models. Possible explanations for angular velocity saturation and periodic pauses for the planar-2 configuration, which were observed in our experiments, are given.

An analytical model, based on a simple physical analogy, and a non-linear analytic/numerical model of the large-scale structure (averaged over the size of a single cell) of a two-dimensional (2D) lattice have been developed. In the first model, a physical analogy between the lattice layer steady state and the stressed state of a rotating solid body was used to derive the model equations and the model is shown to be in good agreement with the results of a 2D simulation. The non-linear model is derived from the force balance between external and internal forces in the continuum limit and compares favourably with an experimental example.

We review recent experimental and theoretical work on the creation of bright matter wave solitons in Bose–Einstein condensates. In two recent experiments, solitons are formed from Bose–Einstein condensates of  ⁷Li by utilizing a Feshbach resonance to switch from repulsive to attractive interactions. The solitons are made to propagate in a one-dimensional potential formed by a focused laser beam. For repulsive interactions, the wavepacket undergoes dispersive wavepacket spreading, while for attractive interactions, localized solitons are formed. In our experiment, a multi-soliton train containing up to ten solitons is observed to propagate without spreading for a duration of 2 s. Adjacent solitons are found to interact repulsively, in agreement with a calculation based on the nonlinear Schrödinger equation assuming that the soliton train is formed with an alternating phase structure. The origin of this phase structure is not entirely clear.

A theoretical model is developed to account for the anomalies reported for the thermal conductivity (κ) of the high-T_cYBa₂Cu₃O_7−δ cuprate superconductors. We begin with the lattice thermal conductivity by incorporating the scattering of phonons with defects, grain boundaries, tunnelling states, charge carriers and phonons in the model Hamiltonian. The lattice thermal conductivity dominating in this cuprate is an artifact of strong phonon defects, tunnelling states and the impurity scattering mechanism below T_c. Later on, the scattering of electrons with impurities is investigated in order to assess their role in thermal conduction. We also look for the spin-wave (magnon) contribution for thermal conductivity. It is noticed that at very low temperatures (T < 10 K), κ increases and shows an almost T² dependence on the temperature, and is attributed to spin-wave thermal transport. Further, at 60 K, κ develops a broad peak and then decreases as the temperature is increased. The anomalies are well accounted for in terms of interaction between the phonon impurity and the carrier impurity. We conclude that the behaviour of the thermal conductivity is determined by competition among the several operating scattering mechanisms for the heat carriers and a balance between electron, magnon and phonon contributions. Numerical analysis of thermal conductivity from the present model shows results similar to those revealed from experiments.

We report the experimental observation of the disruption of the superfluid atomic current flowing through an array of weakly linked Bose–Einstein condensates. The condensates are trapped in an optical lattice superimposed on a harmonic magnetic potential. The dynamical response of the system to a change of the magnetic potential minimum along the optical lattice axis goes from a coherent oscillation (superfluid regime) to a localization of the condensates in the harmonic trap ('classical' insulator regime). The localization occurs when the initial displacement is larger than a critical value or, equivalently, when the velocity of the wavepacket's centre of mass is larger than a critical velocity dependent on the rate of tunnelling between adjacent sites.

Laboratory experiments have shown that single non-conductive dust grains can attain large electric potentials due to triboelectric charging. When grains within a dust cloud interact, they become charged. An electric field forms when upwinds within the cloud cause a separation of large and small particles. We have performed laboratory experiments to determine the necessary conditions for triboelectric charging in a cloud of Martian regolith simulant to break down a low-pressure CO₂ atmosphere and create electrical discharges. The range of pressures and the simulated wind speeds over which discharges are observed have been determined. The effects of particle-size distribution on the observed discharge rates are also discussed.

Motivated by recent experiments (Claussen et al 2003 Preprint cond-mat/0302195) we investigate the magnetic-field dependence of the Josephson frequency of coherent atom–molecule oscillations near a Feshbach resonance. Far off resonance this frequency is determined by two-atom physics. However, the Josephson frequency is relatively large in this case and a description purely in terms of scattering lengths turns out to be inadequate. In particular, we have to include the effective range parameter of the interatomic interaction in our calculations. Close to resonance, the frequency deviates from the two-body results due to various many-body shifts. Considering also the many-body effects, we find perfect agreement with the experimental results over the entire range of magnetic field.

The low-energy properties of two-dimensional ensembles of dipole-coupled magnetic nanoparticles are studied as a function of structural disorder and particle coverage. Already small deviations from a square particle arrangement lift the degeneracies of the microvortex (MV) magnetic configuration and result in a strongly inhomogeneous magnetic order of the particle ensemble. The energy distribution of metastable states is determined. For a low degree of disorder a strongly asymmetric shape with a pronounced peak of the ground-state energy results. In contrast, for a strong disorder a Gaussian-like distribution is obtained. The average dipole energy Ē_dip decreases with increasing structural disorder. Above a coverage-dependent degree of disorder Ē_dip resembles the average dipole energy of a random particle set-up, for which a simple scaling behaviour is derived. The role of vacancies has been studied for a square particle array by determining the angular distribution of the preferred MV angle as a function of the vacancy concentration. Preferred angles along the axial as well as along the diagonal directions of the square array are obtained. A corresponding investigation for disturbed square arrays yields preferred MV angles only along the axial directions. The effect of dipole-quadrupole corrections resulting from the finite size of the particles is quantified.

The renormalization group (RG) method is applied to the study of discrete dynamical systems. As a particular example, the Hénon map is considered as being applied to describe the transverse betatron oscillations in a cyclic accelerator or storage ring possessing a FODO-cell structure with a single thin sextupole. A powerful RG method is developed that is valid correct to fourth order in the perturbation amplitude, and a technique for resolving the resonance structure of the Hénon map is also presented. This calculation represents an application of the RG method to the study of discrete dynamical systems in a unified manner capable of reducing the dynamics of the system both far from and close to resonances, thus preserving the symplectic symmetry of the original map.

Numerical solutions of stationary force balance equations are used to investigate the possible dust configurations (dust structures) in complex plasmas between two floating potential plane electrodes. The distance between electrodes is assumed to be larger than the ion-neutral mean free path and the hydrodynamic description is used. It includes the known forces operating in this limit, the ionization source and the dust charge variations. The stationary balance equations are solved both in the case of the presence of one-size dust grains and for the case of a mixture of grains with two different sizes. Recent micro-gravity experiments with single-size dust grains and two-different-size dust grains show the formation of a system of dust sheaths and dust voids between the two plane electrodes. The observed configurations of dust structures depend strongly on the gas pressure and the degree of ionization used. The numerical investigations are able to show the necessary conditions for the types of structure to be created and give their size. The size of the structures observed is larger than the ion-neutral mean free path and is of the order of magnitude of that obtained numerically. The numerical investigations give details of the spatial distributions, the dust particles, the electron/ion densities, the ion drift velocity and dust charges inside and outside different dust structures. These details have not yet been investigated experimentally and can indicate directions for further experimental work to be performed. The single-dust-sheath structure with single-size dust particles surrounded by dust free regions (dust wall-voids) and floating potential electrodes is computed. Such a structure was observed recently and the computational results are in agreement with observations. It is shown that more often a dust void in the centre is observed. It is found that a dust void in the centre region between two electrodes is formed if the ionization rate is larger than the critical ionization rate and that in the presence of the floating potential walls the central void should be surrounded by two dust sheaths. The necessary condition for this dust structure to be formed is found to be that between the sheaths and the walls there are formed two other wall-void regions. The size of the central void and the distributions of the structure parameters in the two sheaths and in the three voids are computed. The qualitative features of the structure obtained in the numerical computations correspond to those observed. The distributions of the structure parameters in the case of the two dust sheaths are quite different from that for the case of a single central sheath. The possible structures between the electrodes for the case of the presence of dust particles of two different sizes are analysed numerically. It is shown that dust particles with different sizes cannot coexist in equilibrium at the same position and that the regions with different size dust particles must be separated in space. This conclusion is in agreement with most observations performed so far. It is illustrated numerically that for the case where the central void is present the dust particles of larger size form a separate dust sheath which should be located at larger distances from the centre than that for the smaller dust particles. This result also coincides qualitatively with the observations. Computations for the distributions of the parameters in the larger size dust sheath were performed both in the case where the central part is occupied by a dust sheath with smaller size dust particles and for the case where in the central part there exists a dust void surrounded by dust sheaths with smaller size dust particles. The size of the dust void between the sheaths with different size dust particles is calculated and shown to be small as compared to the sheath thickness. In the sheath with larger size dust particles the distribution of dust and plasma parameters differs qualitatively from that of the first dust sheath with smaller size dust particles. The stability of the stationary structures both with respect to excitation of dust convection cells and with respect to oscillations of dust void size is discussed.

Pattern formation is a subfield of nonlinear dynamics in spatially extended systems. Although the latter term is often used narrowly to describe nonlinear systems with not too many degrees of freedom, in general it may be applied to describe more or less everything that happens in the Universe. Thus this statement can hardly be used as a definition. More precisely, the field of pattern formation focuses on systems where the nonlinearities conspire to form spatial patterns that sometimes are stationary, travelling or disordered in space and time. The latter is often referred to as spatio-temporal chaos.

The past two decades have provided major progress in the field of pattern formation. We now have a well-developed theoretical framework for understanding weakly nonlinear patterns that can be described by Ginzburg-Landau-type theories. Close to the onset of instability, our understanding of time-independent or simple time-dependent patterns is quite advanced. Phase field models for the investigation of interfacial instabilities are leading to a breakthrough. Nonlinear phase diffusion equations that are derived from first principles allow the investigation of the `elastic' properties of pattern dynamics even in the fully nonlinear region.

Rapid progress continues to be made possible by a close collaboration of experiment and theory. Advances in computational power are enabling the study of complex spatio-temporal patterns in systems of large spatial extent. In experiment, the increase in computational power combined with novel imaging technology allows the analysis of millions of high-resolution digital images. For instance, novel visualization and data analysis techniques have yielded progress in identifying and studying the nonequilibrium dynamics of extended systems in terms of the spatial and temporal evolution of defect structures that are found in many spatio-temporal chaotic systems. Numerical simulations based on first principles or on general higher-order equations can now be conducted in large systems under realistic boundary conditions.

Pattern formation is a truly interdisciplinary science. The similarity in fundamental mechanisms and the accompanying mathematics brings together scientists from many disciplines, such as biology, chemistry, fluid dynamics, material science, mathematics, medicine, geophysics, ecology, physics and surface science. We believe that the articles collected here provide an overview of the widespread activities within this field.

We feel that New Journal of Physics, as a purely electronic journal, is particularly useful for our field of research: if a picture says a thousand words, a movie can say many more about the spatio-temporal dynamics of a pattern. We would like to thank all of the authors for their contributions and, in many cases, for bearing the additional burden of including moving pictures for the undoubted benefit of readers.

Focus on Pattern Formation Contents

Ferrofluid drops in rotating magnetic fieldsAlexander V Lebedev, Andreas Engel, Konstantin I Morozov and Heiko Bauke

Excitation waves in reaction-diffusion media with non-monotonic dispersion relationsChad T Hamik and Oliver Steinbock

Formation of a drop: viscosity dependence of three flow regimesAlexander Rothert, Reinhard Richter and Ingo Rehberg

Local periodic forcing of CO oxidation on a Pt(110) surfaceJ Wolff and H H Rotermund

Localized nonequilibrium nanostructures in surface chemical reactionsM Hildebrand, M Ipsen, A S Mikhailov and G Ertl

Fluctuations in catalytic surface reactionsR Imbihl

The corkscrew instability of a Fréedericksz domain wall in a nematic liquid crystalAlberto de Lózar Muñoz, Thomas Bock, Matthias Müller, Wolfgang Schöpf and Ingo Rehberg

Dark-in-bright solitons in Bose-Einstein condensates with attractive interactionsP G Kevrekidis, D J Frantzeskakis, Boris A Malomed, A R Bishop and I G Kevrekidis

Photo-induced travelling waves in condensed Langmuir monolayersY Tabe, T Yamamoto and H Yokoyama

Deterministic and stochastic models of intracellular Ca²⁺ wavesM Falcke

Patterns of convection in rotating spherical shellsR Simitev and F H Busse

Dynamic mechanism for conduction block in heart tissueJeffrey J Fox, Mark L Riccio, Paul Drury, Amanda Werthman and Robert F Gilmour Jr

Plume patterns in radiative–convective flowsA Parodi, K A Emanuel and A Provenzale

Sub-threshold Ca²⁺ wavesJ W Shuai and P Jung

Whirling hexagons and defect chaos in hexagonal non-Boussinesq convectionYuan-Nan Young, Hermann Riecke and Werner Pesch

Breakup of spiral waves caused by radial dynamics: Eckhaus and finite wavenumber instabilitiesMarkus Bär and Lutz Brusch

Eberhard Bodenschatz, Cornell University, USA Ronald Imbihl, Universität Hannover, Germany Ingo Rehberg, Universität Bayreuth, Germany

We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. The dynamics can be qualitatively explained by the modified reaction-diffusion model proposed by Reigada, Sagués and Mikhailov.

We demonstrate a possibility to generate localized states in effectively one-dimensional Bose-Einstein condensates with a negative scattering length in the form of a dark soliton in the presence of an optical lattice (OL) and/or a parabolic magnetic trap. We connect such structures with twisted localized modes (TLMs) that were previously found in the discrete nonlinear Schrödinger equation. Families of these structures are found as functions of the OL strength, tightness of the magnetic trap and chemical potential, and their stability regions are identified. Stable bound states of two TLMs are also found. In the case when the TLMs are unstable, their evolution is investigated by means of direct simulations, demonstrating that they transform into large-amplitude fundamental solitons. An analytical approach is also developed, showing that two or several fundamental solitons, with the phase shift π between adjacent ones, may form stable bound states, with parameters quite close to those of the TLMs revealed by simulations. TLM structures are also found numerically and explained analytically in the case when the OL is absent, the condensate being confined only by the magnetic trap.

A liquid crystal with slightly positive dielectric anisotropy is investigated in the planar configuration. This system allows for competition between electroconvection and the homogeneous Fréedericksz transition, leading to a rather complicated bifurcation scenario. We report measurements of a novel instability leading to the `corkscrew' pattern. This state is closely connected to the Fréedericksz state as it manifests itself as a regular modulation along a Fréedericksz domain wall, although its frequency dependence indicates that electroconvection must play a crucial role. It can be understood in terms of a pitchfork bifurcation from a straight domain wall. Quantitative characterization is performed in terms of amplitude, wavelength and relaxation time. Its wavelength is of the order of the probe thickness, while its ondulation amplitude is an order of magnitude smaller. The relaxation time is comparable to the one obtained for electroconvection.

The internal reaction-induced fluctuations which occur in catalytic CO oxidation on a Pt field emitter tip have been studied using field electron microscopy (FEM) as a spatially resolving method. The structurally heterogeneous Pt tip consists of facets of different orientations with nanoscale dimensions. The FEM resolution of roughly 2 nm corresponds to a few hundred reacting adsorbed particles whose variations in the density are imaged as brightness fluctuations. In the bistable range of the reaction one finds fluctuation-induced transitions between the two stable branches of the reaction kinetics. The fluctuations exhibit a behaviour similar to that of an equilibrium phase transition, i.e. the amplitude diverges upon approaching the bifurcation point terminating the bistable range of the reaction. Simulations with a hybrid Monte Carlo/mean-field model reproduce the experimental observations. Fluctuations on different facets are typically uncorrelated but within a single facet a high degree of spatial coherence is found.

Nonequilibrium localized stationary structures of submicrometre and nanometre sizes can spontaneously develop under reaction conditions on a catalytic surface. These self-organized structures emerge because of the coupling between the reaction and a structural phase transition in the substrate. Depending on the reaction conditions they can either correspond to densely covered spots (islands), inside which the reaction predominantly proceeds, or local depletions (holes) in a dense adsorbate layer with a very small reactive output in comparison to the surroundings. The stationary localized solutions are constructed using the singular perturbation approximation. These results are compared with numerical simulations, where special adaptive grid algorithms and numerical continuation of stationary profiles are used. Numerical investigations beyond the singular perturbation limit are also presented.

The effect of local periodic forcing on uniformly oscillating CO oxidation on a Pt(110) surface is investigated utilizing our recently developed addressable catalyst approach. The heating, provided by a focused laser beam, serves as the locally applied external force. The observations are ascribed to the interaction between local actuation and global coupling through the gas phase leading to the suppression of the locally developed patterns.

We observe the drop pinch-off at a nozzle for different viscosities and investigate three consecutive flow types. In its first stage the neck of the drop shrinks in an accelerated manner similar to the instability of a liquid cylinder. In the vicinity of the pinch point the motion becomes self-similar at a certain time. The self-similar domain consists of two flow regimes separated by a second transition point. The viscosity dependence of the transition points can be described by linear functions. Moreover, it is uncovered that both transitions occur when two different critical neck radii are reached. These radii are found to be independent of viscosity.

We report results on chemical wave propagation obtained from experiments with a modified Belousov-Zhabotinsky reaction. Under pseudo-one-dimensional reaction conditions, excitation pulses either form closely stacked, stable wavepackets or merge with a slow leading pulse in front-to-back collisions. Moreover, wave stacking can involve the cascading formation of metastable clusters. These phenomena are due to anomalous dispersion relations in which the derivative of the pulse speed with respect to wavelength can involve negative values. Wave stacking and merging are also observed in thin reaction layers where they affect the evolution of target patterns. Additional results on the concentration dependences of the overall dynamics and pulse speeds are presented.

Drops of a ferrofluid floating in a non-magnetic liquid of the same density and spun by a rotating magnetic field are investigated experimentally and theoretically. The parameters for the experiment are chosen such that different stationary drop shapes including non-axis-symmetric configurations could be observed. Within an approximate theoretical analysis the character of the occurring shape bifurcations, the different stationary drop forms, as well as the slow rotational motion of the drop is investigated. The results are in qualitative, and often quantitative agreement, with the experimental findings. It is also shown that a small eccentricity of the rotating field may have a substantial impact on the rotational motion of the drop.

From time to time in physics, single technical achievements have spawned an explosion of research activity and have led to the genesis of entirely new avenues of investigation. Precisely this occurred in the field of quantum gases - the topic of this Focus Issue - following the achievement of Bose-Einstein condensation in a dilute alkali gas in 1995. These experiments built on the foundational work on quantum fluids in dense systems, such as superfluid helium, and the technical achievements of laser cooling in atomic physics. Dilute quantum gases have already proved to be an incredibly fertile ground for exploring a wide range of macroscopic quantum phenomena. The rapid pace of experimental discovery and theoretical advance is evident and every year continues to bring significant achievements. A great advantage is that microscopic observations can be made directly and compared with the predictions of many-body theoretical formulations founded on interaction parameters which are completely determined - something which is not possible in their dense fluid counterparts.

This Focus Issue brings together papers which cover many of the topical aspects of quantum gases: optical lattices, quantum degenerate fermions, quantum atom optics, molecular Bose-Einstein condensation, vorticity, and quantum fluctuations in systems of reduced dimensionality. One pervasive theme is the flexibility which arises from the ability to control the interactions, even dynamically if necessary. In quantum gases, this can be effected in two ways, either by changing the internal nature of the pairwise potentials by a Feshbach resonance, or by changing the nature of external potentials in which the atoms are confined and supported against gravity. The external potential may be used to spin gases to high vorticity, imprint on the system a periodic optical lattice potential, or even change the effective dimensionality.

Optical lattices are particularly well represented in this Focus Issue. This is where there is the strongest connection with the physics of solids and strongly correlated fluids. Interest in optical lattices is partly due to the recent experimental demonstration that in these systems one can study the quantum phase transition from a Mott insulator, where the atoms are localized to individual sites of the optical potential, to a superfluid phase with long-range order. In contrast to a condensed matter system, the transition can be easily dynamically controlled since it is induced by simply varying the depth of the optical potential.

Another area of focused interest is in fermionic gases where there is an ongoing effort, both experimentally and theoretically, to observe and characterize the high-temperature superfluid transition that should occur with enhanced pairwise interactions. If realized, this quantum system would allow experimental investigation of the crossover from Bose-Einstein condensation of dilute weakly-interacting composite bosons to the superconducting-like transition that occurs in a system of weakly interacting fermions.

The topics of this Focus Issue represent well the building blocks of quantum gas studies which should allow the exploration of a wide range of macroscopic quantum phenomena in a highly controllable and clean system in which the effects of disorder may be completely absent. Given the recent progress, it will be intriguing to see where this field leads in the future.

Focus on Quantum Gases Contents

Anisotropic dissipation of superfluid flow in a periodically dressed Bose-Einstein condensateD M Stamper-Kurn

Rapidly rotating Bose-Einstein condensates in anharmonic potentialsG M Kavoulakis and Gordon Baym

Feshbach resonances and collapsing Bose-Einstein condensatesJ N Milstein, C Menotti and M J Holland

Three-body recombination of cold fermionic atomsH Suno, B D Esry and Chris H Greene

Bogoliubov spectrum and Bragg spectroscopy of elongated Bose-Einstein condensatesC Tozzo and F Dalfovo

Quantum atom optics with Bose-Einstein condensatesKlaus Mølmer

Creation of effective magnetic fields in optical lattices: the Hofstadter butterfly for cold neutral atomsD Jaksch and P Zoller

The Josephson frequency of resonantly coupled atomic and molecular condensatesR A Duine and H T C Stoof

Superfluid current disruption in a chain of weakly coupled Bose–Einstein condensatesF S Cataliotti, L Fallani, F Ferlaino, C Fort, P Maddaloni and M Inguscio

Bright matter wave solitons in Bose–Einstein condensatesK E Strecker, G B Partridge, A G Truscott and R G Hulet

Spin dynamics for bosons in an optical latticeJuan José García-Ripoll and Juan Ignacio Cirac

Mean field ground state of a spin-1 condensate in a magnetic fieldWenxian Zhang, Su Yi and Li You

Atom resonant tunnelling through a moving barrierM L Chiofalo, M Artoni and G C La Rocca

Local correlations in a strongly interacting one-dimensional Bose gasD M Gangardt and G V Shlyapnikov

Shift of the molecular bound state threshold in dense ultracold Fermi gases with Feshbach resonanceR Combescot

Landau damping in trapped Bose condensed gasesB Jackson and E Zaremba

An exact reformulation of the Bose–Hubbard model in terms of a stochastic Gutzwiller ansatzIacopo Carusotto and Yvan Castin

Chemical potential standard for atomic Bose–Einstein condensatesSigmund Kohler and Fernando Sols

The short-distance first-order correlation function of the interacting one-dimensional Bose gasMaxim Olshanii and Vanja Dunjko

The relation between the Gross–Pitaevskii and Bogoliubov descriptions of a dilute Bose gasA J Leggett

Superfluidity of Bose–Einstein condensate in an optical lattice: Landau–Zener tunnelling and dynamical instabilityB Wu and Q Niu

Density-optimized efficiency for magneto-optical production of a stable molecular Bose–Einstein condensateMatt Mackie, Anssi Collin, Kalle-Antti Suominen and Juha Javanainen

A two-atom picture of coherent atom–molecule quantum beatsBogdan Borca, D Blume and Chris H Greene

Superfluid dynamics of a Bose–Einstein condensate in a periodic potentialC Menotti, A Smerzi and A Trombettoni

Phase diagram of two-component bosons on an optical latticeEhud Altman, Walter Hofstetter, Eugene Demler and Mikhail D Lukin

Murray J Holland University of Colorado at Boulder, USA

We investigate the dynamics of neutral atoms in a 2D optical lattice which traps two distinct internal states of the atoms in different columns. Two Raman lasers are used to coherently transfer atoms from one internal state to the other, thereby causing hopping between the different columns. By adjusting the laser parameters appropriately we can induce a non-vanishing phase of particles moving along a closed path on the lattice. This phase is proportional to the enclosed area and we thus simulate a magnetic flux through the lattice. This set-up is described by a Hamiltonian identical to the one for electrons on a lattice subject to a magnetic field and thus allows us to study this equivalent situation under very well defined controllable conditions. We consider the limiting case of huge magnetic fields—which is not experimentally accessible for electrons in metals—where a fractal band structure, the Hofstadter butterfly, characterizes the system.

The formal equivalence between bosonic atoms and photons, and the rich possibilities for manipulation of atomic states, has led to numerous proposals for generation of atomic states with properties similar to the ones of the non-classical states of light, e.g. squeezed states and Schrödinger cat states. We present a number of research directions for quantum optics in which atoms seize or have already seized the role of the photons.

The behaviour of the momentum transferred to a trapped Bose-Einstein condensate by a two-photon Bragg pulse reflects the structure of the underlying Bogoliubov spectrum. In elongated condensates, axial phonons with different numbers of radial nodes give rise to a multibranch spectrum which can be resolved in Bragg spectroscopy, as shown by Steinhauer et al (2003 Phys. Rev. Lett.90 060404). Here we present a detailed theoretical analysis of this process. We calculate the momentum transferred by numerically solving the time-dependent Gross-Pitaevskii (GP) equation. In the case of a cylindrical condensate, we compare the results with those obtained by linearizing the GP equation and using a quasiparticle projection method. This analysis shows how the axial-phonon branches affect the momentum transfer, in agreement with our previous interpretation of the observed data. We also discuss the applicability of this type of spectroscopy to typical available condensates, as well as the role of nonlinear effects.

Recombination of identical, spin-polarized fermions in cold three-body collisions is investigated. We parametrize the mechanisms for recombination in terms of the `scattering volume' V_p and another length scale r₀. Model two-body interactions were used within the framework of the adiabatic hyperspherical representation. We examine the recombination rate K₃ as a function of the collision energy E for various values of V_p. Not only do we consider the dominant J^Π = 1⁺ case, but also the next-leading order contributions from J^Π = 1^- and 3^-. We discuss the behaviour near a two-body resonance and the expected universality of fermionic recombination. Comparisons with boson recombination are considered in detail.

We investigate the quantum state of burst atoms seen in the recent Rb-85 experiments at JILA. We show that the presence of a resonance scattering state can lead to a pairing instability generating an outflow of atoms with energy comparable to that observed. A resonance effective field theory is used to study this dynamical process in an inhomogeneous system with spherical symmetry.

Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can exhibit a rich variety of vortex phases, including a vortex lattice, a vortex lattice with a hole, and a giant vortex. Using an augmented Thomas-Fermi variational approach to determine the ground state of the condensate in the rotating frame - valid for sufficiently strongly interacting condensates - we determine the transitions between these three phases for a quadratic-plus-quartic confining potential. Combining the present results with previous numerical simulations of small rotating condensates in such anharmonic potentials, we delineate the general structure of the zero-temperature phase diagram.

The introduction of a steady-state spatially periodic Raman coupling between two components of an ultracold atomic gas produces a dressed-state gas with an anisotropic and tunable dispersion relation. A Bose-Einstein condensate (BEC) formed in such a gas is consequently characterized by an anisotropic superfluid critical velocity. The anisotropic dissipation of superfluid flow is quantified by considering the scattering of impurities flowing through this superfluid. A gradual transition from the isotropic nature of an uncoupled BEC to the anisotropic periodically-dressed condensate is obtained as the strength of the Raman coupling is varied. These results present a clear signature for future experimental realizations of this novel superfluid.

We calculate radiative corrections to the masses of the Higgs bosons in a minimal supersymmetrical model that contains an additional non-anomalous U(1)' gauge symmetry. With some fine-tuning of the U(1)' charges of the Higgs fields, it is possible to suppress the Z-Z' mixing. We use this fact, along with the lower bound on the lightest Higgs mass after LEP II era, as a criterion to restrict the set of parameters in our analysis. We calculate the mass of the lightest Higgs and its mixing with the other Higgs bosons in a large region of the parameter space.

We show that energy concepts can contribute to the understanding of human travel behaviour. First, the average journey times for different modes of transport are inversely proportional to the energy consumption rates measured for the respective human physical activities. Second, when daily travel-time distributions for different modes of transport such as walking, cycling, bus or car travel are appropriately scaled, they turn out to have a universal functional relationship. This corresponds to a canonical-like energy distribution with exceptions for short trips, which can be theoretically explained. Combined, this points to a law of constant average energy consumption for the physical activity of daily travel. Applying these natural laws could help to improve long-term urban and transport planning.

We have measured the temperature dependence of the magnetic hyperfine field in Ag-coated Fe(110) islands on W(110) between 4 and 300 K using nuclear resonant scattering of synchrotron radiation. The decay of the spontaneous magnetization of the islands with increasing temperature differs distinctly from the bulk characteristics and is not described by a simple Bloch's T^3/2 law. The deviation is attributed to quantization of spin-waves as a result of geometric confinement in the islands. The data can be explained assuming an effective energy gap in the spin-wave spectrum of ΔE = 6.7±1 meV.

The stability of cationic gold clusters doped with one transition metal atom was investigated by a mass spectrometric analysis of fragments resulting from high fluence irradiation of a cluster beam. Strongly enhanced abundances are found for Au₅X⁺, X = V, Mn, Cr, Fe, Co, Zn, which implies that these species are far more stable towards fragmentation than their neighbouring cluster sizes. Here we interpret the enhanced stability of these clusters within a shell model approach for two-dimensional (2D) systems: the number of delocalized electrons in Au₅X⁺ is six, which is a magic number for 2D systems. Quantum chemical calculations for Au_NZn⁺ (N = 2-6) predict planar structures that are stabilized by the influence of the dopant atom. Also, the main features of the calculated molecular orbitals are well reproduced by a simple electron-in-a-box model. The present report constitutes the first observation of 2D magic numbers in size dependent properties of metal clusters.

The control of the confinement of charged microparticles in a plasma is an important topic for the dusty plasma community. Earlier experiments have used control over individual microparticles or a single particle cloud to obtain information about the potential structure of the surrounding plasma. In this paper, experiments that make use of active control of two microparticle clouds suspended in a plasma are discussed. Here, an array of three electrodes is used to modify the potential between the two clouds. Through the application of an applied perturbation on one of the array elements, the two clouds are allowed to interact. Particle image velocimetry techniques are used to obtain spatial maps of the interaction process. The experimental measurements show that an apparent recoil occurs between the two particle clouds as a result of the interaction. A simple model is used to show that a recoil may be a possible outcome of the interaction process.

We study the de Haas-van Alphen oscillations in the magnetization of the Hofstadter model. Near a split band the magnetization is a rapidly oscillating function of the Fermi energy with lip-shaped envelopes. For generic magnetic fields this structure appears on all scales and provides a thermodynamic fingerprint of the fractal properties of the model. The analysis applies equally well to the two dual interpretations of the Hofstadter model and the nature of the duality transformation is elucidated.

Qualitative analysis of two new effects related to the influence of a strong magnetic field on the state of complex dusty plasmas is given. First, it is shown that the dust shape asymmetry, together with the presence of plasma charging flux, creates an angular momentum flux on a dust grain causing its rotation. The value of the estimated angular velocity is compared with that already observed. The magnetic moment related to the balance of the angular momenta transfer by plasma flux and the friction on neutrals is estimated. It is estimated that the interactions of these magnetic moments are usually much weaker than the Coulomb interactions. Apart from the magnetic moments induced by plasma flux the dust grain can have an intrinsic magnetic moment. Both of them create an average magnetization in complex plasmas. Second, it is shown that an increase in an external magnetic field first decreases the dust charges (when the electrons in the charging process start to be magnetized) and then, with a further increase of the magnetic field, the dust charges increase (when the ions in the charging process start to be magnetized). Only the limiting cases of strong electron and ion magnetization are discussed.

Two configurations that are designed for laboratory investigations of dusty-plasma equilibria are being prepared for operation. The first configuration has a vertical magnetic field that confines horizontally a vertically oriented, 6.4 cm diameter, low-temperature, alkali-metal-ion plasma column. The plasma is produced via the Q-machine method (Rynn and D'Angelo 1960 Rev. Sci. Instrum.31 1326) with contact-ionized alkali-metal ions and thermionically emitted electrons. The dust grains will be injected to form a small number of horizontal dusty-plasma layers levitated electrostatically above the plasma sheath. The advantage of using a Q-machine plasma source is the insensitivity of its plasma production to the background pressure of neutral particles. The plan is to study the competition between neutral-particle cooling and streaming-ion energization in dusty-plasma crystallization and decrystallization (i.e., freezing and melting) over a wide range of neutral-particle pressure. The second configuration has a large vacuum chamber (2 m diameter, 4 m length) and a large, solenoidal, magnetic field (0.1 T) that will magnetically confine small-diameter dust grains in a large-volume dusty plasma. The advantage of producing a large-volume, dusty plasma in a strong magnetic field is the ability to meet the criterion that the dust gyroradius is much smaller than the dusty-plasma-column diameter. The plan is to study third-component effects in microinstabilities and the influence of size distribution on magnetized dusty-plasma equilibrium and stability.

The germicidal effects of a non-equilibrium atmospheric pressure plasma generated by a novel resistive barrier discharge on representatives of the two classes of bacteria (Gram-negative and Gram-positive) are discussed. The plasma exposure, while being lethal to both bacterial classes, also produced gross structural damage in the Gram-negative E. coli while none was observed in the more structurally robust Gram-positive Bacillus subtilis. An electrophysical process involving the role of the electrostatic tension on a charged body in a plasma is invoked to explain both observations. Since the efficacy of this electrophysical process depends not only on the tensile strength of the bacterial cell wall but also on its shape and texture, the need for more experimental studies, using a wide range of bacteria belonging to various morphological groups, is suggested. Ways to further test the validity of this electrophysical lysis mechanism for Gram-negative bacteria on one hand, and also to extend its operation to the more robust Gram-positive bacteria on the other, are suggested.

The dispersion properties and excitation mechanisms of `dipole oscillons' in a dusty plasma containing charged elongated rod-like dust grains are investigated in the presence of streaming plasma particles for cases without and with an external static magnetic field. In a magnetized dusty plasma, a new `oscillon-ion lower-hybrid' mode is found, which can be excited by the equilibrium energy of cross-field drifting ions.

We present the results of time resolved spectroscopy measurements of the Hα line of atomic hydrogen in an Ar-C₂H₂ radiofrequency plasma. The presence of the fast (high-energy) and slow (low-energy) components of the hydrogen atoms can be deduced from the Doppler broadening of the Hα line. With the appearance of the dust particles, the Hα profile became narrower, indicating reduction of the fast component. We discuss several mechanisms for the formation of the fast hydrogen atoms in our plasma. The main cause for the reduction of the hydrogen atom fast component is the plasma change from electropositive to electronegative, decreasing the sheath's width and voltage. The change of plasma conditions coincides with the end of the dust coagulation/agglomeration when the dust particles become multiply negatively charged. We propose here a new experimental technique for detection of the dust coagulation/agglomeration phase.

We present and discuss the method of multiple-wavelength Rayleigh-Mie scattering ellipsometry for the in situ analysis of nanoparticles. It is applied to the problem of nanoparticles suspended in low-pressure plasmas. We discuss experimental results demonstrating that the size distribution and the complex refractive index can be determined with high accuracy and present a study on the in situ analysis of etching of melamine-formaldehyde nanoparticles suspended in an oxygen plasma. It is also shown that particles with a shell structure (core plus mantle) can be analysed by Rayleigh-Mie scattering ellipsometry. Rayleigh-Mie scattering ellipsometry is also applicable to in situ analysis of nanoparticles under high gas pressures and in liquids.

We use silane-hydrogen plasmas to synthesize silicon nano-crystals in the gas phase and thermophoresis to collect them onto a cooled substrate. To distinguish between nano-crystals formed in the plasma and those grown on the substrate, as a result of surface and subsurface reactions, we have simultaneously deposited films on a conventional substrate heated at 250 °C and on a second substrate cooled down to 90 °C. A series of samples deposited at various discharge pressures, in the range of 400 mTorr to 1.2 Torr, have been characterized by Raman spectroscopy and ellipsometry. At low pressure (400-500 mTorr), the films are amorphous on the cold substrate and micro-crystalline on the hot one. As pressure increases, gas phase reactions lead to the formation of nano-crystalline particles which are attracted by the cold substrate due to thermophoresis. Consequently, we obtain nano-crystalline silicon thin films on the cold substrate and amorphous thin films on the heated one in the pressure range of 600-900 mTorr. Moreover, the analysis of the Raman spectra of the samples obtained on the cold substrate shows broadening and a small spectral shift as pressure is increased, indicating a decrease in crystal size with pressure. Finally, for yet higher discharge pressures (above 900 mTorr), the high reaction rates favour the formation of amorphous clusters resulting in the deposition of amorphous silicon films on both substrates.

In a standard quantum key distribution (QKD) scheme such as BB84, two procedures, error correction and privacy amplification, are applied to extract a final secure key from a raw key generated from quantum transmission. To simplify the study of protocols, it is commonly assumed that the two procedures can be decoupled from each other. While such a decoupling assumption may be valid for individual attacks, it is actually unproven in the context of ultimate or unconditional security, which is the Holy Grail of quantum cryptography. In particular, this means that the application of standard efficient two-way error-correction protocols like Cascade is not proven to be unconditionally secure. Here, I provide the first proof of such a decoupling principle in the context of unconditional security. The method requires Alice and Bob to share some initial secret string and use it to encrypt their communications in the error correction stage using one-time-pad encryption. Consequently, I prove the unconditional security of the interactive Cascade protocol proposed by Brassard and Salvail for error correction and modified by one-time-pad encryption of the error syndrome, followed by the random matrix protocol for privacy amplification. This is an efficient protocol in terms of both computational power and key generation rate. My proof uses the entanglement purification approach to security proofs of QKD. The proof applies to all adaptive symmetric methods for error correction, which cover all existing methods proposed for BB84. In terms of the net key generation rate, the new method is as efficient as the standard Shor-Preskill proof.

The phase diagram for orientational ordering of hydrogen monolayers on graphite and boron nitride is revised in view of current theory and experimental observations from nuclear magnetic resonance (NMR) studies recently reported for ortho-H₂ concentrations 0.35 ⩽ c ⩽ 0.92 and temperatures 0.14 ⩽ T ⩽ 1.80 K. The characteristic interaction coupling Γ₀ = 0.50 ± 0.03 K and the crystalline field amplitude V₀ = 0.70 ± 0.10 K are derived from experimental data, and distinct types of the local orientationally ordered structures are analysed using a proposed model for site-diluted uniaxial quadrupoles on a triangular plane lattice of hexagonal symmetry. The long-range periodic pinwheel structure and the short-range quadrupolar glass (QG) phase are stable above the 2D site-percolation limit, c_p = 0.72, and for 0.48 < c < c_p, respectively, where quadrupolar-order effects dominate. At very low T, the QG phase shows instability with respect to local dipole-like polarization effects and the ground state changes to a hindered rotor state. Two para-rotational local ordered PRA and PRB structures driven, respectively, by positive and negative crystalline fields are well distinguished, experimentally and theoretically, and are rather different from the unique PR phase suggested earlier by Harris and Berlinsky.

We argue that dust immersed in a plasma sheath acts as a surfactant. By considering the momentum balance in a plasma sheath, we evaluate the dependence of the plasma surface pressure on the dust density. It is shown that the dust may reduce the surface pressure, giving rise to a sufficiently strong tangential force. The latter is capable of confining the dust layer inside the sheath in the direction perpendicular to the ion flow.

The plasma crystal experiment PKE-Nefedov, the first basic science experiment on the International Space Station (ISS), was installed in February 2001 by the first permanent crew. It is designed for long-term investigations of complex plasmas under microgravity conditions. `Complex plasmas' contain ions, electrons, neutrals and small solid particles - normally in the micrometre range. These microparticles obtain thousands of elementary charges and interact with each other via a `screened' Coulomb potential. Complex plasmas are of special interest, because they can form liquid and crystalline states (Thomas et al 1994 Phys. Rev. Lett. 73 652-5, Chu and I 1994 Phys. Rev. Lett. 72 4009-12) and are observable at the kinetic level. In experiments on Earth the microparticles are usually suspended against gravity in strong electric fields. This creates asymmetries, stresses and pseudo-equilibrium states with sufficient free energy to readily become unstable. Under microgravity conditions the microparticles move into the bulk of the plasma (Morfill et al 1999 Phys. Rev. Lett. 83 1598), experiencing much weaker volume forces than on Earth. This allows investigations of the thermodynamics of strongly coupled plasma states under substantially stress-free conditions. In this first paper we report our results on plasma crystals, in particular the first experimental observations of bcc lattice structures.

A numerical model is presented to simulate steady states of complex (`dusty') plasmas under microgravity conditions. The model uses a fluid description for the plasma as well as for the dust microparticles. This is achieved by using an appropriate equation of state for the crystalline phase of the dust. The only forces assumed to act on the dust particles are the electric force, ion drag and pressure gradients. The model is used to study the formation of the stable `void' present in recent microgravity experiments. The structure of the dust clouds when the void is present is examined and explained.

For the electronic properties of large clusters the interaction of the free electron gas with the ion core lattice may result in additional quantization phenomena which are well known in the area of surface and thin-film physics. We measured the geometric and electronic properties of silver and gold clusters grown in nanopits on graphite with low-temperature scanning tunnelling microscopy and spectroscopy in combination with high-resolution photoemission. With the emergence of a Shockley surface state on the top (111) facets of gold clusters with a size of about 10⁴ atoms, we observed one explicit example for the influence of the ion core lattice. The two-dimensional confinement of the surface state is set into the context of a possible one-dimensional confinement perpendicular to the surface, analogous to quantum well states in thin metal films. The basic mechanisms for the dependence of the electronic structure on the cluster size and the shape are tentatively discussed within a `bulk limit', introducing the bulk band structure into the description of the clusters.

Low-temperature ultrahigh-vacuum scanning tunnelling microscopy and spectroscopy was employed to analyse the electronic transport through the ligand-stabilized metal cluster Au₅₅[P(C₆H₅)₃]₁₂Cl₆, prepared as a monolayer on Au(111) substrates. The current-voltage behaviour is governed by charge-quantization phenomena expected for a nanometre-sized metallic particle. The related electric capacitances of the involved tunnelling junctions have been determined from accompanying current-distance measurements. Resonant tunnelling through states of the ligands can be ruled out as a relevant process in electronic transport through the clusters.

The instability of drift waves against zonal flows and streamers is discussed. Unlike in previous treatments, we do not make the assumption that their frequency is resonant with drift wave packets. In this more general treatment we find at least two unstable roots even in the simple case of a monochromatic pump drift wave, and potentially an infinite multitude of roots for a more complicated drift wave spectrum. One of them is the well known modulational instability in resonance with the drift wave packets; the other is a new instability corresponding to the inelastic refraction of drift waves at the streamer. It is nontrivial which of the many roots is the most unstable one.

The nonlinear ion acoustic wave propagating obliquely with respect to an external magnetic field is studied in a homogeneous magnetized electron-positron-ion plasma. It is found that the amplitude of the solitary structure increases with the percentage presence of positrons, which is opposite behaviour to the previous study of these waves in an unmagnetized plasma. The speed of the obliquely propagating soliton in a magnetized plasma turns out to be subsonic, while it is supersonic in the unmagnetized case already studied.

The kinetic theory of dusty plasmas, in which the absorption of electrons and ions by dust particles is the dominating interaction process, is derived from first principles. The charging process is shown to imply a considerable modification of properties in comparison with usual plasmas. Not only the electric charge, but also the mass, the angular momentum and the inner energy of the dust particles are new dynamic variables. Their influence on the kinetic behaviour of dusty plasmas is also considered.

A fluid dynamic approach is used in a unified fully nonlinear treatment of the properties of the dust-acoustic, ion-acoustic and Langmuir-acoustic solitons. The analysis, which is carried out in the wave frame of the soliton, is based on total momentum conservation and Bernoulli-like energy equations for each of the particle species in each wave type, and yields the structure equation for the `heavy' species flow speed in each case. The heavy (cold or supersonic) species is always compressed in the soliton, requiring concomitant contraints on the potential and on the flow speed of the electrons and protons in the wave. The treatment clearly elucidates the crucial role played by the heavy species sonic point in limiting the collective species Mach number, which determines the upper limit for the existence of the soliton and its amplitude, and also shows the essentially similar nature of each soliton type. An exact solution, which highlights these characteristic properties, shows that the three acoustic solitons are in fact the same mathematical entity in different physical disguises.

Starting from N = 1 scalar supermultiplets in (2+1) dimensions, we build explicitly the composite superpartners which define an N = 2 superalgebra induced by the initial N = 1 supersymmetry. The occurrence of this extension is linked to the topologically conserved current out of which the composite superpartners are constructed.

The research field of complex (dusty) plasmas has seen a sustained rapid growth in recent years. This can be attributed to the remarkable discovery of new states of (soft) matter - the liquid and crystalline plasmas - in 1994. Following this discovery, many researchers throughout the world decided to explore and investigate the new physics that was beckoning. Now the field produces about one scientific publication per day, many links to other disciplines are being forged (e.g. colloid physics, solid state, granular media, environmental research, etc) and application potentials are under investigation, too (e.g. nanostructured materials, plasma cleaning devices, adaptive electrodes, particle manipulation and modification, etc). The young field of complex (dusty) plasmas is beginning to come of age. This seemed like an excellent time to produce a Focus Issue on the topic. Through the diversity of the contributions the reader is able to get a synoptic view of the field which, of course, a review article cannot provide. The papers cover basic aspects of dust-plasma interactions in the laboratory, under microgravity conditions and in space, as well as the application of plasma-processed micro-particles. The contributions focus on the latest scientific advances in complex plasmas. Judging from the huge response to the announcement of the Focus Issue in New Journal of Physics, we, the editors, conclude that the field is still growing and that the timing for the Focus Issue is just right!

We would like to express our appreciation to Alexander Bradshaw who initiated this Focus Issue. Finally, we wish to thank the editorial team, especially Tim Smith, the many referees and the contributors for their excellent work.

Focus on Complex (Dusty) Plasmas Contents

Microscopic visco-elastic motions of narrow two-dimensional dust Coulomb liquids under modulated shear stressMing-Hua Chang and Lin I

Solitons, shocks and vortices in dusty plasmasP K Shukla and A A Mamun

Mutual interactions of magnetized particles in complex plasmasV V Yaroshenko, G E Morfill, D Samsonov and S V Vladimirov

Formation and behaviour of dust particle clouds in a radio-frequency discharge: results in the laboratory and under microgravity conditionsM Mikikian, L Boufendi, A Bouchoule, H M Thomas, G E Morfill, A P Nefedov, V E Fortov and the PKE-Nefedov team

Modelling of two differently sized dust species in plasmas under micro-gravityM R Akdim, W J Goedheer and R P Dahiya

Dust-acoustic modes in plasmas with dust distributions and charge fluctuationsFrank Verheest, Gerald Jacobs and Tom Cattaert

Zonal winds and dipolar vortices in a rotating dusty magnetoplasmaP K Shukla, P K Dwivedi and L Stenflo

Structural, dynamical and melting properties of two-dimensional clusters of complex plasmasMinghui Kong, B Partoens and F M Peeters

Levitation and agglomeration of magnetic grains in a complex (dusty) plasma with magnetic fieldD Samsonov, S Zhdanov, G Morfill and V Steinberg

A unified view of acoustic-electrostatic solitons in complex plasmasJ F McKenzie and T B Doyle

New microscopic and macroscopic variables in dusty plasmasP P J M Schram, S A Trigger and A G Zagorodny

A fluid model for colloidal plasmas under microgravity conditionsG Gozadinos, A V Ivlev and J P Boeuf

PKE-Nefedov: plasma crystal experiments on the International Space StationAnatoli P Nefedov, Gregor E Morfill, Vladimir E Fortov, Hubertus M Thomas, Hermann Rothermel, Tanja Hagl, Alexei V Ivlev, Milenko Zuzic, Boris A Klumov, Andrey M Lipaev, Vladimir I Molotkov, Oleg F Petrov, Yuri P Gidzenko, Sergey K Krikalev, William Shepherd, Alexandr I Ivanov, Maria Roth, Horst Binnenbruck, John A Goree and Yuri P Semenov

Dust as a surfactantA M Ignatov, P P J M Schram and S A Trigger

Optimization of plasma parameters for the production of silicon nano-crystalsNihed Chaâbane, Andriy V Kharchenko, Holger Vach and Pere Roca i Cabarrocas

In situ nanoparticle diagnostics by multi-wavelength Rayleigh-Mie scattering ellipsometryG Gebauer and J Winter

Hα emission in the presence of dust in an Ar-C₂H₂ radio-frequency dischargeI Stefanovic, E Kovacevic, J Berndt and J Winter

Excitation of dipole oscillons in a dusty plasma containing elongated dust rodsM Salimullah, P K Shukla, I Sandberg and G E Morfill

Plasma interaction with microbesM Laroussi, D A Mendis and M Rosenberg

Laboratory-device configurations for investigating new dusty-plasma equilibriaM E Koepke and N Sato

Note on the charging and spinning of dust particles in complex plasmas in a strong magnetic fieldV N Tsytovich, N Sato and G E Morfill

Controlled interactions of two microparticle clouds in a dc glow discharge dusty (complex) plasmaE Thomas Jr

Collision-dominated dust sheaths and voids - observations in micro-gravity experiments and numerical investigation of the force balance relationsV N Tsytovich, G Morfill, U Konopka and H Thomas

Experimental evidence for electrostatic discharging of dust near the surface of MarsC E Krauss, M Horányi and S Robertson

Large-scale steady-state structure of a 2D plasma crystalS Zhdanov, R A Quinn, D Samsonov and G E Morfill

The rotation of planar-2 to planar-12 dust clusters in an axial magnetic fieldFelix Cheung, Alex Samarian and Brian James

Instability of shear waves in a nonuniform dusty plasmaG Sorasio, P K Shukla and D P Resendes

Self-excited motions in dusty plasmas with gradient of charge of macroparticlesO S Vaulina, A A Samarian, O F Petrov, B W James and V E Fortov

The plasma-sheath boundary near the adaptive electrode as traced by particlesB M Annaratone, M Glier, T Stuffler, M Raif, H M Thomas and G E Morfill

Examples for application and diagnostics in plasma–powder interactionH Kersten, R Wiese, G Thieme, M Fröhlich, A Kopitov, D Bojic, F Scholze, H Neumann, M Quaas, H Wulff and R Hippler

Dynamics of dust grains in an electron–dust plasma induced by solar radiation under microgravity conditionsV E Fortov, A P Nefedov, O S Vaulina, O F Petrov, I E Dranzhevski, A M Lipaev and Yu P Semenov

The dynamics of macroparticles in a direct current glow discharge plasma under micro-gravity conditionsA P Nefedov, O S Vaulina, O F Petrov, V I Molotkov, V M Torchinskii, V E Fortov, A V Chernyshev, A M Lipaev, A I Ivanov, A Yu Kaleri, Yu P Semenov and S V Zaletin

Dynamic vortex dust structures in a nuclear-track plasmaV A Rykov, A V Khudyakov, V S Filinov, V I Vladimirov, L V Deputatova, D V Krutov and V E Fortov

Electrodynamic structure of charged dust clouds in the earth's middle atmosphereW A Scales and G Ganguli

Greg Morfill, Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany Holger Kersten, Institut für Niedertemperatur-Plasmaphysik e.V. Greifswald, Germany

Interaction of magnetic particles with each other and with a magnetic field was studied experimentally in a complex plasma. Monodisperse plastic microspheres with magnetic filler were suspended in an rf symmetrically driven discharge to form a multilayer dust cloud. The magnetic field induced a magnetic moment in the grains. The particles were pulled upward in the direction of the magnetic field gradient and their levitation height increased. This was used as a new diagnostic method to calculate the particle charge and the thickness of the plasma sheath. It was demonstrated that the particle weight can be compensated for. Some particles formed agglomerates due to magnetic attraction between the grains. Analysis of the particle interaction forces showed that at intermediate magnetic fields (used in the experiment) the particles can agglomerate only if their kinetic energy is high enough to overcome the barrier in the interaction potential. The possibility of magnetically induced formation of a plasma crystal was discussed.

The static and dynamical properties of two-dimensional mesoscopic clusters of equally charged classical particles are investigated through the Monte Carlo simulation technique. The particles are confined by an external harmonic potential. The ground-state configuration and the position of the geometry induced defects are investigated as a function of the inter-particle interaction (Coulomb, dipole, logarithmic and screened Coulomb). The eigenmodes are investigated and the corresponding divergence and rotor are calculated which describe the `shearlike' and `compression-like' modes, respectively. The melting behaviour is found to be strongly influenced by the inter-particle interaction potential: a small cluster with a short-range interaction melts earlier than one with long-range interaction. The melting temperature is related to the energy barriers between the ground state and the metastable states. For larger clusters, the melting scenario changes and is strongly influenced by the location of the topological defects.

It is shown that the Rossby and dust-Alfvén waves in a rotating dusty magnetoplasma are coupled due to the spatial nonuniformity of the angular rotation velocity of the dust fluid. The nonlinear wave interaction is governed by a pair of equations comprising the evolution of the dust fluid vorticity and the dust-Alfvén wave magnetic field. These nonlinear equations are then used to investigate the generation of zonal winds and the formation of a dipolar vortex. The results are relevant for understanding the origin of the strong turbulence and large scale structures, which are often observed in the planetary magnetospheres.

Charge fluctuations in dusty plasmas are discussed starting from charge, mass, momentum and current equations for the combined dusty plasma. This allows a generic description of low-frequency waves in plasmas with dust distributions, and leads to the damping and other modifications of the dust-acoustic and related modes, like generalized dust-Coulomb modes.

A self-consistent two-dimensional hydrodynamic model for a dusty argon plasma has been developed to model more than one dust species. Results are presented for situations where dust particles with two different diameters have been included. The final steady state solution is achieved after three injection steps of the dust particles. At every injection phase dust particles of only one size are let in and the simulation is continued until the steady state solution is achieved. Results show that the differently sized dust particles form crystals at different positions. These dust clouds have an influence on each other by means of positive space charge layers created due to the argon ions, which cannot match the steep dust crystal boundaries. The screened Coulomb interaction between the two differently sized dust species is neglected. The electric potential, ion density, electron density and electron energy show significant changes after each injection phase, even at an amount of dust that is small compared to that studied during the micro-gravity experiments.

In this paper we report the first observation on submicron dust particle clouds grown in a radio-frequency sputtering discharge under microgravity conditions. These results have been obtained in the PKE-Nefedov (Plasma Kristall Experiment) chamber in the framework of a French-German-Russian programme. A dust-free region, usually called the `void', is observed in the laboratory and under microgravity conditions even with submicron particles. In this region, successive generations of particles can be grown, leading to the coexistence of particles with various sizes. Each generation of particles constitutes a cloud separated from the others by a definite sheath. Dynamics of these clouds have been investigated showing vortex-like motions or independent behaviour of small heaps of particles, emphasizing both attractive and repulsive effects between dust clouds. As these particles drastically influence the plasma properties, the growth kinetics is followed through the evolution of the discharge current.

Various mutual dust-dust interactions in complex plasmas, including the forces due to induced magnetic and electric moments of the grains are discussed. It is shown that the dipole short-range forces can be responsible for the formation of field-aligned chains. Such chains may incorporate a few tens of individual particles, as frequently observed in experiments.

Three important classes of nonlinear phenomena, namely solitons, shocks and vortices in dusty plasmas, have been discussed. The static and mobile charged dust grains have been considered in order to study all of these nonlinear phenomena. The effects of nonplanar geometry, dust grain charge fluctuations, dust fluid temperature, vortex-like ion distribution, strong dust correlation etc on the properties of dust ion-acoustic/dust-acoustic solitons have also been analysed. The implications of these theoretical investigations in experimental observations of soliton and shock formation in dusty plasmas are briefly discussed.

The microscopic visco-elastic motion of a quasi-2D dusty plasma liquid confined to a width of about 15 interparticle distances under square stress pulses shorter than thermal relaxation time from a chopped laser beam is investigated experimentally. The stress-enhanced excitations of hopping vortices are responsible for particles in the laser driven zone reaching, after a higher initial velocity, a constant nonzero terminal forward velocity and partial plastic deformation through the loss of the structure memory. The driven particles around domains with caged shear motion still partially keep the structural memory and demonstrate partial elastic backwards motion with exponential relaxation after turning off the laser.

Since in-depth sensing indentation load-depth data of the entire loading-unloading cycle are available, more information than a single hardness value and an elastic modulus can be extracted from the experimental data. The conventional hardness H(h) = F(h)/A_C(h) and the differential hardness H_d(h) = dF/dA_C are calculated as continuous functions of depth h and compared to each other in this paper (F: load, A_C: contact area). It turns out that H_d describes the momentary material resistance to deformation, whereas H integrates over deformation states from first tip-sample contact to current penetration h. This difference is particularly important for materials not homogeneous in depth (e.g. layer systems), and for situations where time-dependent external factors influence the momentary deformation resistance. Photoplasticity is considered as an example for the latter.

The origin of anomalous electron thermal turbulence from spatial gradients in magnetized plasmas is described. Laboratory experiments demonstrating key features of drift waves are reviewed. The turbulent electromagnetic fields produce an anomalous transport that scales with both the gradient parameters and microscopic plasma scale length parameters. The change from the micro-scale dominated gyro-Bohm to the macro-scale dominated Bohm scaling laws is discussed. The close correlations between the electron turbulent transport theory and the confinement properties measured in the steady state hot electron plasmas produced in tokamak devices are presented.

Ultrafast energy exchanges of a non-Fermi electron gas with the lattice are investigated in silver clusters with sizes ranging from 4 to 26 nm using a femtosecond pump-probe technique. The results yield evidence for a cluster-size-dependent slowing down of the short-time energy losses of the electron gas when it is strongly athermal. A constant rate is eventually reached after a few hundred femtoseconds, consistent with the electron gas internal thermalization kinetics, this behaviour reflecting evolution from an individual to a collective electron-lattice type of coupling. The timescale of this transient regime is reduced in small nanoparticles, in agreement with speeding up of the electron-electron interactions with size reduction. The experimental results are in quantitative agreement with numerical simulations of the electron kinetics.

Bispectral analysis has been proposed as a diagnostic for Reynolds stress (RS) as a driving mechanism of zonal flows (ZF) in toroidally confined plasmas. A turbulence simulation code was used to test this technique on a well-defined system. It turned out that the geodesic acoustic mode dominates the poloidal flow spectrum and that it reduces radial transport in the same way as does a low-frequency ZF. Using the total cross-bicoherence, a correlation between RS and large-scale poloidal flows could be detected. The experimentally more accessible auto-bicoherences did not prove to be a useful quantity for studying this interaction. RS was not observed as a precursor of the flow; rather it appears simultaneously in the region of radial flow shear.

A flow invariant in quantum field theory is a quantity that does not depend on the flow connecting the UV and IR conformal fixed points. We study the flow invariance of the most general sum rule with correlators of the trace Θ of the stress tensor. In even (four and six) dimensions we recover the results known from the gravitational embedding. We derive the sum rules for the trace anomalies a and a' in six dimensions. In three dimensions, where the gravitational embedding is more difficult to use, we find a non-trivial vanishing relation for the flow integrals of the three- and four-point functions of Θ. Within a class of sum rules containing finitely many terms, we do not find a non-vanishing flow invariant of type a in odd dimensions. We comment on the implications of our results.

Silicon nanocrystals with diameters between 2.5 and 7 nm were prepared by CO₂ laser pyrolysis of silane in a gas flow reactor. A small portion of the particles created in the reaction zone was extracted as a molecular beam through a conical nozzle and deposited at low energy on substrates. Placing suitable masks in front of the substrate, micro- and nanostructured films were obtained. The patterned structures were characterized by atomic force microscopy and transmission electron microscopy while their optical properties were studied by laser scanning confocal microscopy. Nanostructures as small as 30 nm could be produced. The photoluminescence emanating from a regular array of 1.2 μm sized dots composed of Si nanocrystals was studied with spatial, spectral and temporal resolution.

Using a recently commissioned tandem mass spectrometer system, BESTOF, we have carried out systematic investigations (using also deuterated molecules) on the interaction of various molecular cluster ions (including stoichiometric acetone and acetonitrile cluster ions and protonated ethanol cluster ions) with a hydrocarbon-covered stainless steel surface. Besides observing competitive chemical reactions for the stoichiometric cluster ions driven by the energy transfer in the surface collision (intra-cluster reactions versus surface H-atom pick-up reactions), we were able to see clear evidence that unimolecular dissociation kinetics determines the production of the observed decay patterns in collision energy-resolved mass spectra (CERMS). From characteristic shifts in these CERMS we can deduce corresponding binding energies, i.e., {D}((CD₃CN)₂⁺ - CD₃CN) = 0.66 eV, {D}((C₂H₅OH)₂H⁺ - C₂H₅OH) = 0.95 eV, and for the protonated dimer {D}((C₂H₅OH)H⁺ - C₂H₅OH) = 1.6 eV. The first value is in good agreement with values currently calculated using the B3LYP (Becke-Lee-Yang-Parr) density functional and the 6-311G(d, p) basis set, the latter values are in good agreement with values derived earlier from thermochemical data.

Moreover, in the case of the protonated ethanol cluster ion, it is possible to arrive at a single (universal) breakdown graph for the trimer composed of data derived from monomer, dimer and trimer CERMS. This can be achieved by renormalizing the energy scale in the CERMS for the monomer, dimer and trimer ions (taking into account the conversion from translational to internal energy and assuming that the clusters behave like a statistical ensemble with the corresponding degrees of freedom).

Nanometre vibration measurement of an audio speaker and a highly sensitive sound reproduction experiment have been successfully demonstrated by a self-aligned optical feedback vibrometry technique using the self-mixing modulation effect in a laser-diode-pumped microchip solid-state laser. By applying nanometre vibrations to the speaker, which produced nearly inaudible music below 20 dB (200 µPa) sound pressure level, we could reproduce clear sound in real time by the use of a simple frequency modulated wave demodulation circuit with a -120 dB light-intensity feedback ratio.

In complete analogy with the Seiberg-Witten map defined in noncommutative geometry we introduce a new map between a q-deformed gauge theory and an ordinary gauge theory. The construction of this map is elaborated in order to fit the Hopf algebra structure.

In this paper we present an automatic image recognition technique used to identify clouds and aurorae in digital images, taken with a CCD all-sky imager. The image recognition algorithm uses image segmentation to generate a binary block object image. Object analysis is then performed on the binary block image, the results of which are used to assess whether clouds, aurorae and stars are present in the original image.

The need for such an algorithm arises because the optical study of particle precipitation into the Earth's atmosphere by the Ionosphere and Radio Propagation Group at Lancaster generates vast data-sets, over 25 000 images/year, making manual classification of all the images impractical.

Contractive states for a free quantum particle were introduced by Yuen (Yuen H P 1983 Phys. Rev. Lett. 51 719) in an attempt to evade the standard quantum limit for repeated position measurements. We show how appropriate families of two- and three-component `Schrödinger cat states' are able to support non-trivial correlations between the position and momentum observables leading to contractive behaviour. The existence of contractive Schrödinger cat states is suggestive of potential novel roles of non-classical states for precision measurement schemes.

We present two schemes to perform continuous variable (2, 3) threshold quantum secret sharing (QSS) on the quadrature amplitudes of bright light beams. Both schemes require a pair of entangled light beams. The first scheme utilizes two phase sensitive optical amplifiers, whilst the second uses an electro-optic feedforward loop for the reconstruction of the secret. We examine the efficacy of QSS in terms of fidelity, as well as the signal transfer coefficients and the conditional variances of the reconstructed output state. We show that both schemes in the ideal case yield perfect secret reconstruction.

The electron emission from size-selected sodium clusters excited by a 400 nm femtosecond laser-pulse of moderate intensity (<10¹⁰ W cm^-2) has been studied for cluster sizes Na_n⁺ with n = 16, 46, 70, 139 and 250. In all cases the kinetic energy distributions show a simple exponential behaviour. Comparison with statistical theory shows that even for the smallest cluster the emission process is purely statistical emission from a thermalized hot electron gas, which takes place on a picosecond timescale after the excitation.

We study in detail the ability of the reactor experiment KamLAND for discriminating existing solutions to the solar neutrino problem and giving accurate information on neutrino masses and mixing angles. We include in this analysis the information obtained from the latest SNO-NC (neutral current measurement) results and other solar data. Assuming that the expected signal corresponding to various `benchmark' points in the two-dimensional (Δm², tan ²θ) mixing plane, we develop a fully fledged χ² analysis which includes the KamLAND spectrum and other existing solar evidence. A complete model of statistical and known systematical errors for 1 and 3 years of observations is included and exclusion plots are presented.

We find a much higher sensitivity, in particular, for values of Δm² lying in the central part of the large mixing angle (LMA) region. The situation would be more complicated for values that are closer to the edge of the LMA region (the HLMA region, i.e. Δm²⩽2×10^-5 eV² and Δm²⩾8 - 9×10^-5 eV² or tan ²θ far from ~0.5). In this case KamLAND, with or without any solar data, will only be able to select multiple regions in the parameter space, in the sense that different possible values of the parameters would produce the same signal. Finally, in conclusion, we point out that there is not only a problem in the determination of Δm² in the HLMA region, but also in the discrimination of the values of the mixing angle if one considers values that are not close to the present best-fit points.

The NA52 experiment measured particle and antiparticle yields at 0° production angle over a wide range in rapidity in lead-lead (Pb-Pb) collisions at 158 A GeV/c with a minimum bias trigger. Besides (10⁶) antiprotons () and (10³) antideuterons () a total of five antihelium-3 () were found. The resulting invariant differential production cross sections at p_t≃0 GeV/c turn out to be E (d³σ)/(dp³) = (2.5 ± 1.8) × 10^-7 bc³ GeV^-2 at a rapidity of y = 3.4 in the laboratory system and (5.9 ± 3.4) × 10^-8 bc³ GeV^-2 at y = 4.0. The results are discussed in the framework of a simple coalescence model.