Table of contents

The physics of pizza tossing and the next generation of micromotors Is diamagnetism possible classically? Phase dynamics of two coupled oscillators under external periodic force Optical communications through dense matter

It is known that the heterogeneity of scale-free networks helps enhancing the efficiency of trapping processes performed on them. In this paper, we show that transport efficiency is much lower in a fractal scale-free network than in non-fractal networks. To this end, we examine a simple random walk with a fixed trap at a given position on a fractal scale-free network. We calculate analytically the mean first-passage time (MFPT) as a measure of the efficiency for the trapping process, and obtain a closed-form expression for MFPT, which agrees with direct numerical calculations. We find that, in the limit of a large network order V, the MFPT ⟨T⟩ behaves superlinearly as with an exponent much larger than 1, which is in sharp contrast to the scaling ⟨T⟩∼V^θ with θ⩽1, previously obtained for non-fractal scale-free networks. Our results indicate that the degree distribution of scale-free networks is not sufficient to characterize trapping processes taking place on them. Since various real-world networks are simultaneously scale-free and fractal, our results may shed light on the understanding of trapping processes running on real-life systems.

We construct a version of the discrete Wigner function (DWF) for any dimension. This DWF will be constructed from the continuous Wigner function (CWF). In addition, this DWF has many properties of the CWF.

We are discussing the long-time scaling limit for the anomalous diffusion composed of the subordinated Lévy-Wiener process. The limiting anomalous diffusion is in general non-Markov, even in the regime, where ensemble averages of a mean-square displacement or quantiles representing the group spread of the distribution follow the scaling characteristic for an ordinary stochastic diffusion. To discriminate between a truly memory-less process and the non-Markov one, we are analyzing the deviation of the survival probability from the (standard) Sparre Andersen scaling.

We consider the increase of the spatial variance of some inhomogeneous, non-equilibrium density (particles, energy, etc.) in a periodic quantum system of condensed-matter type. This is done for a certain class of initial quantum states which is supported by static linear response and typicality arguments. We directly relate the broadening to some current auto-correlation function at finite times. Our result is not limited to diffusive behavior, however, in that case it yields a generalized Einstein relation. These findings facilitate the approximation of diffusion constants/conductivities on the basis of current auto-correlation functions at finite times for finite systems. Pursuing this, we quantitatively confirm the magnetization diffusion constant in a spin chain which was recently found from non-equilibrium bath scenarios.

The idea of the preferred frame as a remedy for difficulties of the relativistic quantum mechanics in description of the non-local quantum phenomena was undertaken by physicists such as J. S. Bell and D. Bohm. The possibility of the existence of a preferred frame was also seriously treated by P. A. M. Dirac. In this paper, we propose an Einstein-Podolsky-Rosen–type experiment for testing the possible existence of quantum preferred frame. Our analysis suggests that to verify whether a preferred frame of reference in the quantum world exists, it is enough to perform an EPR-type experiment with a pair of observers staying in the same inertial frame and with use of the massive EPR pair of spin–one-half or spin-one particles.

We identify the correlation in a state of two identical particles as the residual information beyond what is already contained in the 1-particle reduced density matrix, and propose a correlation measure based on the maximum entropy principle. We obtain the analytical results of the correlation measure, which make it computable for arbitrary two-particle states. We also show that the degrees of correlation in the same two-particle states with different particle types will decrease in the following order: bosons, fermions, and distinguishable particles.

We introduce and discuss kinetic models for wealth distribution which include both taxation and uniform redistribution. The evolution of the continuous density of wealth obeys a linear Boltzmann equation where the background density represents the action of an external subject on the taxation mechanism. The case in which the mean wealth is conserved is analyzed in full details, by recovering the analytical form of the steady states. These states are probability distributions of convergent random series of a special structure, called perpetuities. Among others, Gibbs distribution appears as steady state in case of total taxation and uniform redistribution.

We calculate the W^±γj+X production cross-sections at next-to-leading-order QCD for Tevatron and LHC collisions. We include leptonic decays of the W to light leptons, with all off-shell effects taken into account. The corrections are sizable and have significant impact on the differential distributions.

We study the electroweak single production of fourth-family t' quarks via the process ep→t'ν at the Large Hadron electron Collider (LHeC). We calculate the background and signal cross-sections for the mass range 300–800 GeV. It is shown that the LHeC can discover a single t' quark up to the mass of 750 GeV for the optimized mixing parameters.

We confront a recent visco-plastic description of dense granular flows (Jop P. et al., Nature, 441 (2006) 727) with multi-directional inhomogeneous steady flows observed in non-smooth contact dynamics simulations of 2D half-filled rotating drums. Special attention is paid to check separately the two underlying fundamental statements into which the considered theory can be recast, namely i) a single relation between the invariants of stress and strain rate tensors and ii) the alignment between these tensors. Interestingly, the first prediction is fairly well verified over more than four decades of small strain rate, from the surface rapid flow to the quasi-static creep phase, where it is usually believed to fail because of jamming. On the other hand, the alignment between stress and strain rate tensors is shown to fail over the whole flow, what yields an apparent violation of the visco-plastic rheology when applied without care. In the quasi-static phase, the particularly large misalignment is conjectured to be related to transient dilatancy effects.

We present an analytical model and molecular-dynamics simulations of the phonon heat transport in nanowires and nanoribbons with anharmonic lattices and dynamically rough surfaces and edges. In agreement with recent experiments on heat transport in single-crystalline silicon nanowires with rough surfaces, our model and simulations predict finite and length-independent phonon thermal conductivity in such quasi–one-dimensional systems, in contrast to anomalous phonon thermal conductivity of corresponding momentum-conserving systems with atomically smooth surfaces, divergent with the system length. Within our model, the main cause of thermal conductivity reduction is the momentum-nonconserving scattering of longitudinal acoustic phonons by anharmonic side phonon leads in quasi–one-dimensional phonon waveguides with dynamically rough surface or edge layers. We also show that the superdiffusion of thermal energy in nanoribbons with atomically smooth edges is replaced by the normal diffusion or subdiffusion in nanoribbons with dynamically rough edges.

We incorporate a solvent model of interacting Langevin dipoles into the Poisson-Boltzmann formalism of mobile point-like ions close to a single charged surface. Our model aims at understanding the interplay between the diffuse double layer and the polarization of water due to a surface-induced dipolar ordering. We account for interactions between the Langevin dipoles, which leads to an intrinsic spatial decay length of the solvent polarization. An analytical solution of the free energy in the weak perturbation limit is presented and compared with the nonlinear regime. From our analytical results we derive conditions for the optimal polarization at the surface and for the sign inversion of the electrostatic potential.

We derive the Mode-Coupling Theory (MCT) of the glass transition as a Landau theory, formulated as an expansion of the exact dynamical equations in the difference between the correlation function and its plateau value. This sheds light on the universality of MCT predictions. While our expansion generates higher-order non-local corrections that modify the standard MCT equations, we find that the square-root singularity of the order parameter, the scaling function in the β regime and the functional relation between the exponents defining the α and β time scales are universal and left intact by these corrections.

We have studied the wetting properties of water droplets onto lattices of square micro-cavities. The contact angle has been measured along the triple line and the obtained values have been compared to both Cassie-Baxter and Wenzel models. Despite the large values of the apparent contact angle, the contact line appears to be well pinned on the lattice of square cavities. This leads to anisotropic droplet shapes, reflecting the lattice geometry. Imaging the cavities from below just after drop deposition reveals that the liquid is invading them. The drop is thus in an hybrid state where it presents a large contact angle value while it is sticking on the substrate.

By means of molecular-dynamics simulations we firmly establish the long-awaited existence of strong correlations between structure and dynamics for a glass-forming system: supercooled water. We find molecules with similar structural (and dynamical) properties to be clustered in space, thus reveling the existence of structured regions with low dynamic propensity and unstructured ones with a high-mobility tendency.

Strain-induced structural changes (SCs), which include chemical reactions (CRs) and phase transitions (PTs), are studied here numerically under compression and torsion of a sample in a rotational diamond anvil cell (RDAC). The results change the fundamental understanding of the interpretation of experimentally observed effects and measurements and the extraction of information on material behavior from system (sample) behavior. These effects include the nontrivial, nonlinear interaction between strongly heterogeneous stress and plastic strain tensor fields and SC kinetics, the effect of change of material strength during SC, the simultaneous occurrence of direct and reverse SCs in different regions, strong strain localization, and pressure self-multiplication.

A free-energy functional for a crystal that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function is developed. To test how accurately this free-energy functional describes the symmetry breaking first-order phase transition of freezing, we use it to investigate the crystallization of fluids interacting via the inverse power potential; u(r)=(σ/r)ⁿ. In agreement with simulation results we find that under the fluid-solid co-existence the f.c.c. structure is more stable for n=12, whereas for soft repulsions (n⩽6) the b.c.c. structure is more stable.

An anomalous reversal of the direction of exciton spin polarization is found in an optical-orientation study of Al_x Ga_1−x As alloys. A negative degree of circular polarization of excitonic photoluminescence is observed in direct-gap AlGaAs under excitation with circularly polarized light with the photon energy lying in a narrow range just above the free-exciton transition. The resonant switching of the polarization direction is attributed to the effect of the minor residual strain in the epitaxial film that results in lifting of the degeneracy of the light-and heavy-hole sub-bands. The electron g-factor is estimated from combined time-resolved and Hanle-effect data and amounts to 0.056–0.086 for x=15% alloy.

A Langevin equation for the quantum Brownian motion of a spin of arbitrary size in a uniform external dc magnetic field is derived from the phase space master equation in the weak coupling and narrowing limits, for the quasiprobability distribution (Wigner) function of spin orientations in the configuration space of polar and azimuthal angles following methods long familiar in quantum optics. The closed system of differential-recurrence equations for the statistical moments describing magnetic relaxation of the spin is obtained as an example of applications of this equation.

The effect of Rashba spin-orbit (SO) interaction on the hole states in a quantum dot is studied in the presence of an external magnetic field. We demonstrate here that the Rashba SO coupling has a profound effect on the energy spectrum of the holes revealing level repulsions between the states with the same total momentum. We also show that the resulting spin-orbit gap is much larger than the corresponding one for the electron energy levels in a quantum dot. Inter-hole interactions only marginally reduce the spin-orbit gap. This enhanced Rashba effect would manifest itself in the tuneling current which depends on the spin-orbit coupling strength.

We consider the two-pocket model of the iron pnictides with generic interactions, and show that the low-energy effective theory of this model belongs to a wide class of Hamiltonians with enhanced symmetry. We consider the effect of symmetry breaking perturbations around such systems and explore the physical consequences. Our analysis reveals that the presence of the spin density wave with ordering wave vector (π, 0) necessarily implies the existence of odd-sign s-wave superconductivity. We predict a spin-triplet resonance at the wave vector (π, 0) whose frequency depends linearly on applied field and is independent of temperature. We also discuss the possible presence of a novel orbital density wave state as a close competing order encompassed by the emergent SO(6) symmetry.

The spin-orbit (SO) coupling effect is investigated by self-consistently diagonalizing a model Hamiltonian with competing antiferromagnetic (AF) and d-wave superconductivity (DSC) orders for high-temperature superconductors. SO-coupling–induced spin-split and -flip competition with AF order can lead to a double-peak spectrum of the vortex-core state, and vortex charge sign change. Scanning tunneling microscopy spectra on differential conductance and nuclear magnetic resonance experiments on vortex charges for YBa₂Cu₃O_7−x are interpreted.

We study the dimensional dependence of the interplay between correlation and disorder in two dimensions at half-filling using the 2D t- t' disordered Hubbard model with deterministic disorder both at zero and finite temperatures. Inclusion of t' without disorder leads to a metallic phase at half-filling below a certain critical value of U. Above this critical value U_c correlation favours an antiferromagnetic phase. Since disorder leads to double occupancy over the lower-energy site, the competition between Hubbard U and disorder leads to the emergence of a metallic phase, which can be quantified by the calculation of Kubo conductivity, gap at half-filling, density of states, spin order parameter, inverse participation ratio (IPR) and bandwidth. We have studied the effect of disorder on the system in a very novel way through a deterministic disorder which follows a Fibonacci sequence. The behaviour of different quantities shows interesting features on going from a two- to quasi–one-dimensional system.

Experimental and theoretical investigations on the integer quantized Hall effect in gate-defined narrow Hall bars are presented. At low electron mobility the classical (high-temperature) Hall resistance line R_H(B) cuts through the center of all Hall plateaus. In contrast, for our high-mobility samples the intersection point, at even filling factors ν=2, 4, ..., is clearly shifted towards larger magnetic fields B. This asymmetry is in good agreement with predictions of the screening theory, i.e. taking Coulomb interaction into account. The observed effect is directly related to the formation of incompressible strips in the Hall bar. The spin-split plateau at ν=1 is found to be almost symmetric regardless of the mobility. We explain this within the so-called effective g-model.

We propose a time-dependent density functional theoretical (TDDFT) approach in momentum () space for the study of electron transport in molecular devices under arbitrary biases. The basic equation of motion, which is a time-dependent integrodifferential equation obtained by Fourier transform of the time-dependent Kohn-Sham equation in spatial coordinate () space, is formally exact and includes all the effects and information of the electron transport in the molecular devices. The electron wave function is calculated by solving this equation in a finite -space volume. This approach is free of self-energy function and memory term related to the electrodes in the space and beyond the wide-band limit (WBL). The feasibility and power of the approach are demonstrated by the calculation of current through one-dimensional systems.

We investigate the effects of magnetic impurities in a superconducting state with s_± pairing symmetry. Within a two-band model, we find that the intra-band magnetic scattering serves as a pair breaker while the inter-band magnetic scattering preserves pairing and hardly affects transition temperature in the Born limit. We also show that the same physics can persist beyond the weak-scattering region. Our results coincide with recent experimental measurements in iron-based superconductors and thus provides an indirect evidence of the possible s_± pairing symmetry in these materials.

In view of the recent experimental facts in the iron-pnictides, we make a proposal that the itinerant electrons and local moments are simultaneously present in such multiband materials. We study a minimal model composed of coupled itinerant electrons and local moments to illustrate how a consistent explanation of the experimental measurements can be obtained in the leading-order approximation. In this mean-field approach, the spin-density-wave (SDW) order and superconducting pairing of the itinerant electrons are not directly driven by the Fermi surface nesting, but are mainly induced by their coupling to the local moments with momentum match. The presence of the local moments as independent degrees of freedom naturally provides strong pairing strength for superconductivity and also explains the normal-state linear-temperature magnetic susceptibility above the SDW transition temperature. We show that this simple model is supported by various anomalous magnetic properties which are in quantitative agreement with experiments.

We propose to confine massless Dirac fermions in a graphene-based quantum annulus induced by an inhomogeneous magnetic field. It is found that influenced by an effective magnetic potential well the degeneracies of the relativistic Landau levels can be lifted, and the angular-momentum transitions in the ground state can occur by adjusting the geometry of the annulus and/or the magnitude of the magnetic field. Especially for high magnetic fields the system can form the strongly localized states in the annulus and around its boundaries, and some energy levels can reconverge to the Landau levels. Moreover, it is predicted that the dipole-allowed optical transitions between the low-lying energy levels can be measured by far-infrared spectroscopy, and the optical spectrum consists of a series of unequally spaced peaks.

We show how to induce pairing of Cooper pairs (and, thus, 4e superconductivity) as a result of local embedding of a quantum impurity in a Josephson network fabricable with conventional junctions. We find that a boundary double sine-Gordon model provides an accurate description of the dc Josephson current patterns, as well as of the stable phases accessible to the network. We point out that tunneling of pairs of Cooper pairs is robust against quantum fluctuations, as a consequence of the time reversal invariance, arising when the central region of the network is pierced by a dimensionless magnetic flux φ=π. We find that, for φ=π, a stable attractive finite coupling fixed point emerges and point out its relevance for engineering a two-level quantum system with enhanced coherence.

We present a mean-field dynamical theory for single semiflexible polymers which can precisely capture, without fitting parameters, recent fluorescence correlation spectroscopy results on single-monomer kinetics of DNA strands in solution. Our approach works globally, covering three decades of strand length and five decades of time: it includes the complex cross-overs occurring between stiffness-dominated and flexible bending modes, along with larger-scale rotational and center-of-mass motion. The accuracy of the theory stems in part from long-range hydrodynamic coupling between the monomers, which makes a mean-field description more realistic. Its validity extends even to short, stiff fragments, where we also test the theory through Brownian hydrodynamics simulations.

Djungarian hamsters (Phodopus sungorus) acclimated to short photoperiod display episodes of spontaneous daily torpor with metabolic rate depressed by ∼70%, body temperature (T_b) reduced by ∼20 °C, and heart rate (HR) changing from ∼70 bpm during torpor to ∼570 bpm during arousal from torpor associated with remarkable resistance to arrhythmogenesis. The cardiac dynamics of heartbeat interval fluctuations (RR_i) obtained from high-resolution telemetric ECG recordings during daily torpor were studied using nonlinear techniques of signal processing. The nature of cardiac dynamical properties assessed from pointwise Hölder exponents (h) is shifted from strong irregularity of sinus bradyarrhythmia during low-T_b torpor towards smooth regularity on spontaneous rewarming during arousal. The pattern of h fluctuations indicates that both fractality and multifractal properties of RR_i's were decreased during torpor. The cardiac rhythm exhibits both deterministic and stochastic components with intermittency of alterations of prevalence of one over the other on short time scales. During the low-T_b state, RR_i dynamics exhibt nonlinear properties that temporarily shift to linear characteristics during entry into and arousal from torpor. Sympatho-vagal antagonism of autonomic cardiac control is markedly relaxed but remains active and highly alert when animals are torpid and temporarily out of the mainstream of competition.

In this paper we analyze the behavior of the daily Sunspot Number (SN) from the Sunspot Index Data Center (SIDC), the mean Magnetic-Field (MF) strength from the National Solar Observatory/Kitt Peak (NSO/KP) and Total Solar Irradiance (TSI) means from Virgo/SoHO, in the context of the q-Triplet which emerges within nonextensive statistical mechanics. Distributions for the mean solar Magnetic Field show two different behaviors, with a q-Gaussian for scales of 1 to 16 days and a Gaussian for scales longer than 32 days. The latter corresponds to an equilibrium state. Distributions for Total Solar Irradiance also show two different behaviors (approximately Gaussian) for scales of 128 days and longer, consistent with statistical equilibrium and q-Gaussian for scales <128 days. Distributions for the Sunspot Number show a q-Gaussian independent of timescales, consistent with a nonequilibrium state. The values obtained ("q-Triplet"≡{q_stat, q_sen, q_rel}) demonstrate that the Gaussian or q-Gaussian behavior of the aforementioned data depends significantly on timescales. These results point to a strong multifractal behavior of the dataset analyzed, with the multifractal level decreasing from Sunspot Number to Total Solar Irradiance. In addition, we found a numerically satisfied dual relation between q_stat and q_sen.

In the millihertz range, a single magnetometer can detect magnetic waves in the near-field regime. For such long wavelengths, it can measure the world-wide magnetic-background noise due to any charge displacement on Earth and within its environment. In this frequency band, the normal modes of the Earth's free oscillations exist and when excited, they shake the air column above them, up to the ionosphere where the moving charges emit a magnetic fluctuation, via Ampère's law. We show the magnetic-background noise spectrum obtained by an FFT analysis of 72 consecutive hours of magnetic-seismic calm. It is mostly due to vertical charge oscillations. Even in the absence of a quake larger than M_w= 5.2, spherical and toroidal modes are deected. Instrumental and analytical perspectives are discussed.