Table of contents

Scroll waves exist ubiquitously in three-dimensional excitable media. The rotation centre can be regarded as a topological object called the vortex filament. In three-dimensional space, the vortex filaments usually form closed loops, and can be even linked and knotted. We give a rigorous topological description of knotted vortex filaments. By using the φ-mapping topological current theory, we rewrite the topological current form of the charge density of vortex filaments, and using this topological current we reveal that the Hopf invariant of vortex filaments is just the sum of the linking and self-linking numbers of the knotted vortex filaments. We think that the precise expression of the Hopf invariant may imply a new topological constraint on knotted vortex filaments.

Solutions in the Grammian form for a variable-coefficient Kadomtsev–Petviashvili (KP) equation which has the Wronskian solutions are derived by means of Pfaffian derivative formulae.

We present a noncommutative version of the Ablowitz–Kaup–Newell–Segur (AKNS) equation hierarchy which possesses the zero curvature representation. Furthermore, we derive the noncommutative AKNS equation from the noncommutative (anti-)self-dual Yang–Mills equation by reduction, which is an evidence for the noncommutative Ward conjecture. Finally, the integrable coupling system of the noncommutative AKNS equation hierarchy is constructed by using the Kronecker product.

Cooperation among individuals is considered to play an important role in the evolution of complex networked systems in physical, biological, economical and even epidemiological worlds, but its effects on the development of the systems is not so clear. We consider a specific kind of primal cooperation in a group of individuals, i.e., an individual never cooperates with others except when compelled to do so. The lowest level of compelled cooperation, in which cooperators share no message or resources, is investigated in the background of complex networks driven by the simple game rock-paper-scissors. Simulation results show that with the evolution of the systems, the cooperation will spread all over the networks, and finally results in systems with modular structures and a scale-free property.

The topological properties of the spatial coherence function are investigated rigorously. The phase singular structures (coherence vortices) of coherence function can be naturally deduced from the topological current, which is an abstract mathematical object studied previously. We find that coherence vortices are characterized by the Hopf index and Brouwer degree in topology. The coherence flux quantization and the linking of the closed coherence vortices are also studied from the topological properties of the spatial coherence function.

Decomposition of a composite system C into different subsystems, A + B or D + E, may help in avoiding decoherence. For example, the environment-induced decoherence for an A+B system need not destroy entanglement present in the D + E system (A + B = C = D + E). This new approach opens some questions also in the foundations of the quantum computation theory that might eventually lead to a new model of quantum computation.

We present an efficient one-step scheme for a single spin measurement based on nuclear magnetic resonance (NMR) techniques. This scheme considerably reduces the time of operation using a spin star network where a target spin and an ancillary spin are coupled to a ring of N spins. As opposed to the proposal in [Phys. Rev. Lett. 97(2006) 100501] using a cubic lattice crystal to achieve a cubic speedup, the distinct advantage of this scheme is that under ideal conditions it requires the application of only one step to create a system of N correlated spins. In the process of single spin measurement, the total macroscopic magnetization, the individual magnetization and the transfer fidelity are calculated analytically as simple cosine functions of time and the amplitude of irradiation.

An alternative protocol is proposed to implement three-qubit phase gate between photon and atoms in a high-Q bimodel optical cavity The idea can be extended to directly implement N-qubit phase gate, and the gating time that is required to implement the protocol does not rise with increasing number of qubits. The influence of cavity decay and atomic spontaneous emission on the gate fidelity is also discussed.

A scheme is proposed for implementing a controlled-NOT gate via superconducting quantum interference device (SQUID) in cavity-QED. The controlled-NOT gate can be achieved by coupling the SQUID to a single-mode microwave cavity field or classical microwave pluses. The scheme may be experimentally realizable.

We present the generation of six-particle Greenberger–Horne–Zeilinger (GHZ) states via deterministic entanglement concentration and generalize the scheme to the case of 2N particles. We show that arbitrary 2N-particle GHZ states can be obtained with certain probability via entanglement concentration. This may provide a new perspective for the preparation of multi-particle GHZ states. This study is also an exploration on the theory of deterministic entanglement concentration.

Using anomalous viewpoint, we study the Hawking radiation from a kind of topological Kerr Anti-de-Sitter (Kerr-AdS) black hole with one rotational parameter. We employ the covariant gauge and gravitational anomalies. The result supports the Robinson–Wilczek opinion and shows that the Hawking temperature can be correctly determined by cancelling covariant gauge and gravitational anomalies at the horizon.

We numerical simulate the propagation behaviour and people distribution trait of epidemic spreading in mobile individuals by using cellular automaton method. The simulation results show that there exists a critical value of infected rate fluctuating amplitude, above which the epidemic can spread in whole population. Moreover, with the value of infected rate fluctuating amplitude increasing, the spatial distribution of infected population exhibits the spontaneous formation of irregular spiral waves and convergence phenomena, at the same time, the density of different populations will oscillate automatically with time. What is more, the traits of dynamic grow clearly and stably when the time and the value of infected rate fluctuating amplitude increasing. It is also found that the maximal proportion of infected individuals is independent of the value of fluctuating amplitude rate, but increases linearly with the population density.

We investigate a kind of chaos generating technique on a type of n-dimensional linear differential systems by adding feedback control items under a discontinuous state. This method is checked with some examples of numeric simulation. A constructive theorem is proposed for generalized synchronization related to the above chaotic system.

The permanent magnet synchronous motors (PMSMs) may experience chaotic behaviours with systemic parameters falling into a certain area or under certain working conditions, which threaten the secure and stable operation of motor-driven. Hence, it is important to study the methods of controlling or suppressing chaos in PMSMs. In this work, the Takagi–Sugeno (T-S) fuzzy impulsive control model for PMSMs is established via the T-S modelling methodology and impulsive technology. Based on the new model, the control conditions of asymptotical stability and exponential stability for PMSMs have been derived by the Lyapunov method. Finally, an illustrated example is also given to show the effectiveness of the obtained results.

We report the results of using the fast independent component analysis (FastICA) algorithm to realize blind extraction of chaotic signals. Two cases are taken into consideration: namely, the mixture is noiseless or contaminated by noise. Pre-whitening is employed to reduce the effect of noise before using the FastICA algorithm. The correlation coefficient criterion is adopted to evaluate the performance, and the success rate is defined as a new criterion to indicate the performance with respect to noise or different mixing matrices. Simulation results show that the FastICA algorithm can extract the chaotic signals effectively. The impact of noise, the length of a signal frame, the number of sources and the number of observed mixtures on the performance is investigated in detail. It is also shown that regarding a noise as an independent source is not always correct.

We study the self-organization of phase synchronization in coupled map scale-free networks with chaotic logistic map at each node and find that a variety of ordered spatiotemporal patterns emerge spontaneously in a regime of coupling strength. These ordered behaviours will change with the increase of the average links and are robust to both the system size and parameter mismatch. A heuristic theory is given to explain the mechanism of self-organization and to figure out the regime of coupling for the ordered spatiotemporal patterns.

We investigate the motion of the globally coupled maps (logistic map) driven by uniform disorder. It is shown that this disorder can produce multi-synchronization for the globally coupled chaotic maps studied by us. The disorder determines the synchronized dynamics, leading to the emergence of a wide range of new collective behaviour in which the individual units in isolation are incapable of producing in the absence of the disorder. Our results imply that the disorder can tame the collective motion of the coupled chaotic maps.

Though applying master stability function method to analyse network complete synchronization has been well studied in chaotic dynamical systems, it does not work well for phase synchronization. Moreover, it is difficult to identify phase synchronization with the angle of rotation for non-phase-coherent attractors. We employ the recurrences plot method to detect phase synchronization for several regular networks with non-phase-coherent attractors. It is found that the coupling strength μ is different for different coupled networks. The coupling strength μ is reduced as completed coupled network scale enlarges, the coupling strength μ of star coupled network is irrelevant to network scale, and these two regular networks are easier to achieve phase synchronization. However, for ring and chain coupled networks, the larger the phase synchronization couple strength μ is, the larger the network scale is, and it is more difficult to achieve phase synchronization. For same scale network, once ring coupled structure becomes a chain coupled structure, phase synchronization becomes much more difficult.

Since the Jost solutions of the derivative nonlinear Schrödinger equation do not tend to the free Jost solutions, when the spectral parameter tends to infinity(|λ| → ∞), the usual inverse scattering transform (IST) must be revised. If we take the parameter κ = λ⁻¹ as the basic parameter, the Jost solutions in the limit of |κ| → ∞ do tend to the free Jost solutions, hence the usual procedure to construct the equations of IST in κ-plane remains effective. After we derive the equation of IST in terms of κ, we can obtain the equation of IST in λ-plane by the simple change of parameters λ = κ⁻¹. The procedure to derive the equation of IST is reasonable, and attention is never paid to the function W(x) introduced by the revisions of Kaup and Newell. Therefore, the revision of Kaup and Newell can be avoided.

A (2+1)-dimensional nonlinear partial differential evolution (NLPDE) equation is presented as a model equation for relaxing high-rate processes in active barothropic media. With the aid of symbolic computation and Hirota's method, some typical solitary wave solutions to this (2+1)-dimensional NLPDE equation are unearthed. As a result, depending on the dissipative parameter, single and multivalued solutions are depicted.

The quantum thermodynamic functions of a harmonic oscillator coupled to a heat bath through velocity-dependent coupling are obtained analytically. It is shown that both the free energy and the entropy decay fast with the temperature in relation to that of the usual coupling from. This implies that the velocity-dependent coupling helps to ensure the third law of thermodynamics.

We present a model of gauge theory based on the symmetry group G × SU(2) where G is the gravitational gauge group and SU(2) is the internal group of symmetry. We employ the spacetime of four-dimensional Minkowski, endowed with spherical coordinates, and describe the gauge fields by gauge potentials. The corresponding strength field tensors are calculated and the field equations are written. A solution of these equations is obtained for the case that the gauge potentials have a particular form with spherical symmetry. The solution for the gravitational potentials induces a metric of Schwarzschild type on the gravitational gauge group space.

We apply the k_T factorization approach to deal with the B → K transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain F_T^B→K(0) = 0.25 ± 0.01 ± 0.02, where the first error is caused by the uncertainties from the pionic wavefunctions and the second is from that of the B-meson wavefunctions. This result is consistent with the light-cone sum rule results obtained in the literature.

We give a direct method for calculating the quark-number susceptibility at finite chemical potential and zero temperature. In this approach the quark-number susceptibility is totally determined by G[μ](p) (the dressed quark propagator at finite chemical potential μ). By applying the general result in our previous study [Phys. Rev. C 71 (2005)015205, 034901, 73 (2006) 016004] G[μ](p) is calculated from the model quark propagator proposed by Pagels and Stokar [Phys. Rev. D 20 (1979) 2947]. The full analytic expression of the quark-number susceptibility at finite μ and zero T is obtained.

We analyse the vertex D^*D^*ρ with the light-cone QCD sum rules. The strong coupling constant D^*D^*ρ is an important parameter in evaluating the charmonium absorption cross sections in searching for the quark-gluon plasmas. Our numerical value for the D^*D^*ρ is consistent with the prediction of the effective SU(4) symmetry and vector meson dominance theory.

Aiming at using sphericity as a tool to study the isotropy-equilibrium property of a multi-particle system, in particular the hadronic final state IFS produced in instanton-induced DIS events, we discuss in detail the dependence of sphericity on multiplicity and the multiplicity distribution, as well as on the isotropy degree of the system. A rotational symmetric model with a fluctuating isotropy-degree is constructed, which can fit the mean and width of sphericity of the Monte Carlo IFS-results simultaneously The IFS from the Monte Carlo simulation is found to be not ideally isotropic but has a probability of 4.7% to be isotropic within error of 5%. The results provide us a description of how far the IFS departs from equilibrium. The method developed is applicable to any Monte Carlo generated multi-particle system, for which the isotropy-equilibrium property is significant.

The fragmentation cross sections of reactions ¹²C + ²H, ¹²C, ¹⁴N, ¹⁶O at beam energies from 50 to 100 MeV/nucleon are investigated using the isospin-dependent Boltzmann–Langevin equation model It is found that fragment species increase approximately with the increasing target mass. The fragment species and some fragments production cross sections in reactions of ¹²H, ¹²C, ¹⁴N, ¹⁶O show an obvious variation at the beam energies from 50 to 80 MeV/nucleon. However the calculated fragment production cross sections do not change much when the incident energy increases from 80 to 100 MeV/nucleon.

The ⁸Li(p, d)⁷Li reaction plays an important role in the inhomogeneous Big Bang nucleosynthesis and in the seed-nuclide production phase for the r-process. For the first time, its angular distribution at backward angles was measured in inverse kinematics at E_c.m. = 4.0 MeV by using an ⁸Li secondary beam. The result of measurement includes the contributions of ⁸Li(p, d₀)⁷Li and ⁸Li(p, d₁)⁷Li^*. The ⁸Li(p, d₀)⁷Li component is estimated to be 40%∼58% in the mixture angular distribution by analysing the measured result.

In the framework of the relativistic mean field theory, we investigate ⁰ condensation along with K⁻ condensation in neutron star matter including the baryon octet. The results show that both ⁰ and K⁻ condensations can occur well in the core of the maximum mass stars for relatively shallow optical potentials of in the range of −10MeV ∼ −160 MeV. With the increasing optical potential of , the critical densities of decrease and the species of baryons appearing in neutron stars become fewer. The main role of ⁰ condensation is to make the abundances of particles become identical leading to isospin saturated symmetric matter including antikaons, nucleons and hyperons. K⁻ condensation is chiefly responsible for the softening of the corresponding equation of state, which leads to a large reduction in the maximum masses of neutron stars. In the core of massive neutron stars, neutron star matter including rich particle species, such as antikaons, nucleons and hyperons, may exist.

Bunch lengthening phenomenon is resulted from one of the most severe single bunch instabilities in storage rings. We develop a new code to calculate the single bunch length and energy spread in storage rings using FORTRAN. In this code, wake field is calculated using an analytical formula, which is different from the previous ones. The bunch length and energy spread under different bunch currents are calculated for BEPCII by using this code, and the tracking results are in good agreement with those from other codes. The calculated energy spread clearly shows that the longitudinal microwave instability threshold is around 65mA for BEPCII storage ring.

On the platform of the 3DH₂⁺ system, we perform a numerical simulation of its photoionization rate under excitation of weak to intense laser intensities with varying pulse durations and wavelengths. A novel method is proposed for calculating the photoionization rate: a double exponential decay of ionization probability is best suited for fitting this rate. Confirmation of the well-documented charge-resonance-enhanced ionization (CREI) effect at medium laser intensity and finding of ionization saturation at high light intensity corroborate the robustness of the suggested double-exponential decay process. Surveying the spatial and temporal variations of electron wavefunctions uncovers a mechanism for the double-exponentially decayed photoionization probability as onset of electron ionization along extra degree of freedom. Henceforth, the new method makes clear the origins of peak features in photoionization rate versus internuclear separation. It is believed that this multi-exponentially decayed ionization mechanism is applicable to systems with more degrees of motion.

We obtain the isomer spectra of C₃₀ and C₃₁ clusters by time-going-backward quasi-dynamics method and perform molecular dynamics simulations of the cluster growth from isolated atoms in He buffer gas at 2500 K. The geometrical structures of the isomers of C₃₀ and C₃₁ can be classified into closed cages, open cages, bowls, sheets and other irregular shapes, where closed cages are found to have the lowest potential energies. However, dynamics simulations show that the sheet structures of C₃₀ and C₃₁ are the dominant outcome at the simulation temperature. Compared with relevant experimental results, we propose a different view in interpreting the experimental data and a research procedure to predict isomers that would be formed most probably under specific experimental conditions.

We propose and experimentally investigate a coherent population trapping state based magnetometer prototype with ⁸⁷Rb atoms. Through modulating Zeeman sublevels with an ac magnetic field, not only a phase sensitive detection scheme suitable for miniature magnetometer is realized, but also the detection resolution of magnetic field intensity could be improved by a factor of two. Our study result indicates that it is a promising low power consumption miniature sensitive low magnetic field sensor offering spatially resolved measurement at the sub-millimetre level.

Theoretical and interpretative study on the subject of photodetachment of H⁻ near a partially reflecting surface is presented, and the absorption effect of the surface is investigated on the total and differential cross sections using a theoretical imaging method. To understand the absorption effect, a reflection parameter K is introduced as a multiplicative factor to the outgoing detached-electron wave of H⁻ propagating towards the wall. The reflection parameter measures, how much electron wave would reflect from the surface; K = 0 corresponds to no reflection and K = 1 corresponds to the total reflection.

A simple model for the direct ionization and transfer ionization probabilities in A²⁺ +He collisions in a wide projectile energy range is proposed based on the Bohr–Lindhard model and the classical statistical model. The calculated cross sections are in satisfactory agreement with the experimental data available.

A symmetrical π-shaped metamaterial is investigated. Numerical simulations exhibit the negative-refractive property of this structure. The complex refractive index n, wave impedance z, effective permittivity ∊ and effective permeability μ have been retrieved from the simulated S parameters. The negative-refractive band lies between 11.2GHz and 13.05GHz. The frequency band with high transmission with low loss occurs between 11.95GHz and 12.5 GHz, which is helpful for practical applications. The mechanism of the electromagnetic resonance is also revealed.

An analytical expression for the average intensity of four-petal Gaussian beams in turbulent atmosphere is derived. Studies show that in turbulent atmosphere, the contour lines of four-petal Gaussian beams with lower order N evolve into a number of petals with the increase in propagation distance, the contour lines with higher order N can reserve four-petal distribution at longer propagation distance than that with lower order N. These properties are similar to those in free space. However, with further increases of the propagation distance, the contours lines in turbulent atmosphere are different from those in free space.

We investigate the reduction of the group velocity propagation resulting from the steep change of the refractive index by the coherent population oscillation in erbium-doped optical fibre. The largest delay is measured to be about 8.75ms corresponding to a group index of 1.312 × 10⁶. The time delay or advancement depends on the pump intensity. Influences of the ion density on the fractional delay and the group velocity reduction of light propagation are studied. Based on our discussion the optimization parameters should be selected in order to obtain more appropriate time delay and the slowdown of group velocity.

We present the phase control of photon correlations in a driven four-level system in the double lambda configuration. The strong correlation and the anticorrelation are obtained when the collective phase of four applied laser fields is varied. The coherent control is based on the phase-dependent coherent population trapping (CPT). The strong correlation occurs when the system operates near CPT, while the anticorrelation occurs when the system is far away from CPT.

The quadrature squeezing spectra in the resonance fluorescence of a V-type three-level atom driven by a coherent field and coupled to a single-mode cavity is investigated. For weak excitation, the fluorescence field exhibit squeezing in the out-of-phase quadrature. The coupling between the atom and the cavity mode can greatly enhance the squeezing centred at the laser frequency. More importantly, for strong excitation, under the effect of the cavity-atom coupling, the in-phase quadrature of fluorescence can exhibit two-mode squeezing at the two inner sideband frequencies. By working in the dressed-state representation and hiring secular approximation, we give an analytical explanation for the effect. The result shows, under appropriate conditions, the squeezing can be greatly enhanced by appropriately tuning the cavity resonant frequency.

Excitation power-dependent micro-photoluminescence spectra and photon-correlation measurement are used to study the optical properties and photon statistics of single InAs quantum dots. Exciton and biexciton emissions, whose photoluminescence intensities have linear and quadratic excitation power dependences, respectively, are identified. Under pulsed laser excitation, the zero time delay peak of second order correlation function corresponding to exciton emission is well suppressed, which is a clear evidence of single photon emission.

We present a realistic and efficient scheme for sub-half-wavelength atom localization. This scheme is based on the phase-dependent electromagnetically induced transparency in a four-level system in the double-Λ configuration. We use a strong bichromatic field (one component of which is standing-wave field) as the driving components, and a weak bichromatic field as the probe components. By choosing the collective phase of the four applied components, the atom is localized in either of the two half-wavelength regions with 50% detecting probability when the absorption to the probe fields is detected.

We study the competition between dispersion and absorption of doubly-dressed four-wave mixing (DDFWM) and dressed six-wave mixing. In the case of weak coupling fields limit, we find DDFWM signal is affected by destructive interference between four-wave mixing(FWM) and six-wave mixing as well as constructive interference between FWM and eight-wave mixing. By analysing the difference between two kinds of doubly dressing mechanisms (parallel cascade and nested cascade) in this opening five-level system, we can further understand the generated high-order nonlinear optical signal dressed by multi-fields.

Based on our previous study [Chin. Phys. Lett. 24 (2007) 2238] in which the Fresnel operator corresponding to classical Fresnel transform was introduced, we derive the fractional Fourier transformation operator, and the optical operator method is then enriched.

We introduce the concept of truncated states obtained via iterative processes (TSI) and study its statistical features, making an analogy with dynamical systems theory (DST). As a specific example, we have studied TSI for the doubling and the logistic functions, which are standard functions in studying chaos. TSI for both the doubling and logistic functions exhibit certain similar patterns when their statistical features are compared from the point of view of DST.

We investigate a high-energy good-beam-quality krypton-lamp-pumped pulsed Nd:YAG solid-state laser with one pump cavity The symmetrical resonator laser is developed and is rated at 80 J with beam parameter product 12mm mrad. The total system electro-optics efficiency of the lamp-pumped YAG laser is as high as 3.3% and the stability of output energy is ±2% with pulse width tunable between 0.1ms and 10 ms. The experimental results are consistent with the theoretical analysis and simulation.

We present the design and experimental results for a diode pumped Nd:YLF regenerative amplifier applied to amplify a nanosecond laser pulse. Numerical simulation shows that the maximum output energy and the best stability can be obtained when the regenerative amplifier operates in a saturated mode for all pulse duration and temporal profiles. Using extra post-pulse is a good method to decrease the square-pulse distortion caused by gain saturation effect. The amplifier shows output energy of 4.2mJ with a total energy gain of more than 10⁷ and output energy stability of better than 1% rms. When extra post-pulse is added, square-pulse distortion is decreased from 1.33 to 1.17 for the amplifier that is seeded with an optical pulse of 3 ns.

High resolution mode-selective excitation in the mixture of C₆H₆ (992cm⁻¹) and C₆D₆ (945 cm⁻¹) is experimentally achieved by adaptive femtosecond pulse shaping based on the genetic algorithm (GA), and second harmonic generation frequency-resolved optical gating (SHG-FROG) is adopted to characterize the original and optimal laser pulses, and its mechanism is experimentally validated by tailoring the frequency components of the pump pulses at the Fourier plane. It is indicated that two-pulse coherent mode-selective excitation of the Raman scattering mainly depends on the effective frequency components of the pump pulse related to specific molecular vibrational mode. The experimental results have attractive potential applications in the complicated molecular system.

Optical nonlinear refractive properties of a series of Mo(W)/S/Cu planar square clusters are investigated using the Z-scan technique with the ns laser pulses at the wavelength of532nm. The result shows that the planar metal clusters containing the halogen ligands demonstrate the self-focusing effect, and the other planar metal clusters demonstrate the self-defocusing effect. These facts indicate that the halogen ligands can act as crucial factors in determining the sign of the nonlinear refraction of the Mo(W)/S/Cu planar metal clusters. The analysis of the experimental data shows that the planar clusters with halogen ligands possess greater refraction volume of the excited state than that of the ground state, while the other planar clusters possess the smaller refraction volume of the excited state than that of the ground state.

Two soluble polymer grafted multi-walled carbon nanotubes (MWNTs), including poly(N-vinylcarbazole)-MWNTs and poly(methyl methacrylate)-MWNTs, are synthesized. Their nonlinear optical properties and optical limiting (OL) performances are investigated by z-scan method with 527nm nanosecond laser pulses. These grafted MWNTs dissolved in chloroform show much better optical limiting performance than those of MWNTs and C₆₀ in toluene solution. Nonlinear absorption and nonlinear scattering mechanism are taken into consideration for explaining the observed results. The comparison of the experimental results shows that nonlinear absorption is the dominant mechanism for OL performance of these new samples.

We investigate the Kerr nonlinearity of a V-type three-level atomic system where the upper two states decay outside to another state and hence spontaneous generated coherence may exist. It is shown that dark state and hence perfect transparency present under certain conditions. Meanwhile, the Kerr nonlinearity can be controlled by manipulation of the decay rates and the splitting of the two excited states. Therefore, enhanced Kerr nonlinearity without absorption can be obtained under proper parameters.

Incoherent white light from an incandescent source is employed to fabricate volume phase zone plates in LiNbO₃: Fe, for the first time to our knowledge, which can guide and modulate the input white light or laser light. The diffractive efficiency of the white light volume phase zone plates fabricated can reach as high as 12%. In addition, we test the volume phase zone plates by a probe beam and find that the volume phase zone plate is present in the direction perpendicular to the c-axis and absent in the direction parallel to the c-axis. This directly proves the existence of photovoltaic photorefractive anisotropy of white light.

We report an efficient Q-switched laser action based on a semiconductor saturable absorber mirrors (SESAMs) as passively Q-switched laser starter and a Yb:LYSO alloyed crystal as gain material pumped directly by 974 nm In GaAs laser diodes. The output pulse duration is measured to be about 7μs, while the average power and the repetition rate of the pulse chain are about 0.92 W and 6.2kHz, respectively, under 12.5 W absorbed pumping power. The Q-switched mode-locked pulse train is also observed in this setup. The laser performance shows that Yb:LYSO is a promising laser gain medium for laser-diode pumped compact solid-state lasers.

We calculate structural, electronic properties and chemical bonding of borate Li₄CaB₂O₆ under high pressure by means of the local density-functional pseudopotential approach. The equilibrium lattice constants, density of states, Mulliken population, bond lengths, bond angles as well as the pressure dependence of the band gap are presented. Analysis of the simulated high pressure band structure suggests that borate Li₄CaB₂O₆ can be used as the semi-conductor optical material. Based on the Mulliken population analysis, it is found that the electron transfer of the Li atom is very different from that of other atoms in the studied range of high pressures. The charge populations of the Li atom decrease with the pressure up to 60 GPa, then increase with the pressure.

A polarizing beam splitter (PBS) and a non-polarizing beam splitter (NPBS) based on a photonic crystal (PC) directional coupler are demonstrated. The photonic crystal directional coupler consists of a hexagonal lattice of dielectric pillars in air and has a complete photonic band gap. The photonic band structure and the band gap map are calculated using the plane wave expansion (PWE) method. The splitting properties of the splitter are investigated numerically using the finite difference time domain (FDTD) method.

The plasmon waveguide based on double chain of gold cylinders is studied using the finite-difference time-domain method (FDTD). The wavelength of the incident Gaussian beam ranges from 650 to 1200nm, and the corresponding attenuation factors are calculated. We also present a Y-splitter with 90° splitting angle, each branch in the form of double chains. The transmission efficiencies for different wavelengths are evaluated.

The effects of working pressure on properties of Al₂O₃ thin films are investigated. Transmittance of the Al₂O₃ thin film is measured by a Lambda 900 spectrometer. Laser-induced damage threshold (LIDT) is measured by a Nd:YAG laser at 355nm with a pulse width of 7ns. Microdefects were observed under a Nomarski microscope. The samples are characterized by optical properties and defect, as well as LIDT under the 355nm Nd:YAG laser radiation. It is found that the working pressure has fundamental effect on the LIDT. It is the absorption rather than the microdefect that plays an important role on the LIDT of Al₂O₃ thin film.

Optical amplified characteristics of inner cladding fibres with InP thin films are tested. The results indicate that this kind of fibres exhibit better optical amplification, which is advantageous for short lengths of fibres. The amplification coefficients of per unit length are 1.40–5.12 dB/m at the wave band from 906 to 1044 nm, 1.40–15.35dB/m from 1080 to 1491 nm, and 1.86–7.44dB/m from 1524 to 1596 nm. Based on the hydrogen atomic model, we calculate the comparative size of the InP particle a_B = 8.313nm. The result displays the quantum size effect. By calculating the change of the energy band of particles with different sizes, the experimental data are explained by quantum size effect.

The condition of the single fundamental mode (HE₁₁) transmission in hollow core Bragg fibres is investigated theoretically by the transfer matrix method. The influences of core size and cladding parameters on the single HE₁₁ mode bandwidth are analysed, showing that the maximal bandwidth is more sensitive to the core size than the cladding. The numerical results show that sufficiently broad bandwidth of single HE₁₁ mode transmission can be achieved by proper fibre design. A simple and fast method based on improved hollow metal waveguide model is proposed to optimize fibre structure parameters for the maximal single HE₁₁ mode bandwidth.

We propose the high speed signal wavelength conversion based on stimulated Raman effect on silicon waveguides. Simulation results of non-return-to-zero (NRZ) pseudorandom bit sequence (2⁷-1 code) at 500-Gb/s rate of conversion in an ultrasmall silicon-on-insulator (SOI) optical waveguide are presented by co-propagating pump optical field. The most attractive issue is that the inverted converted signal can be obtained at the same wavelength as that of primary signal. In addition, the conversion performances, including extinction ratio (ER) and average peak power of conversion signal, depend strongly on the launching pump intensity.

We obtain an asymptotic solution to the vertical branch-cut integral of shear waves excited by an impulsive pressure point source in a fluid-filled borehole, by taking the effect of the infinite singularity of the Hankel functions related to shear waves in the integrand at the shear branch point into account and using the method of steepest-descent to expand the vertical branch-cut integral of shear waves. It is theoretically proven that the saddle point of the integrand is located at k_s-i/z, where k_s and z are the shear branch point and the offset. The continuous and smooth amplitude spectra and the resonant peaks of shear waves are numerically calculated from the asymptotic solution. These asymptotic results are generally in agreement with the numerical integral results. It is also found by the comparison and analysis of two results that the resonant factor and the effect of the normal and leaking mode poles around the shear branch point lead to the two-peak characteristics of the amplitude spectra of shear waves in the resonant peak zones from the numerical integral calculations.

Ambient noise data measured in an experiment conducted near the sea route are analysed. It is found that at low frequency, the measured horizontal correlation coefficients at different separations oscillate much larger than that predicted by the classical ambient noise model. The theoretical analyses show that the observed phenomenon is mainly caused by windy noise together with the discrete shipping noise nearby. An ambient noise model is proposed to include the effects caused by both the noise sources and can be used to forecast the ambient noise field near a sea route.

We investigate the methods to optimize the directivity of point source array by using pseudostochastic sequences. Maximum-length sequence (MLS) array and Quadratic-residue sequence (QRS) array are theoretically analysed, and their simulated responses are shown. The results indicate that pseudostochastic sequences can be used to optimize the directivity of point source array.

We employ the homotopy analysis method (HAM) to obtain approximate analytical solutions to the heat-like and wave-like equations. The HAM contains the auxiliary parameter ħ, which provides a convenient way of controlling the convergence region of series solutions. The analysis is accompanied by several linear and nonlinear heat-like and wave-like equations with initial boundary value problems. The results obtained prove that HAM is very effective and simple with less error than the Adomian decomposition method and the variational iteration method.

Thermal conductivity of submicron-thick aluminium oxide thin films prepared by middle frequency magnetron sputtering is measured using a transient thermo-reflectance technique. A three-layer model based on transmission line theory and the genetic algorithm optimization method are employed to obtain the thermal conductivity of thin films and the interfacial thermal resistance. The results show that the average thermal conductivity of 330–1000 nm aluminium oxide thin films is 3.3 Wm⁻¹K⁻¹ at room temperature. No significant thickness dependence is found. The uncertainty of the measurement is less than 10%.

We present (1) the dynamical equations of deforming body and (2) an integrated method for deforming body dynamics and unsteady fluid dynamics, to investigate a modelled freely self-propelled fish. The theoretical model and practical method is applicable for studies on the general mechanics of animal locomotion such as flying in air and swimming in water, particularly of free self-propulsion. The present results behave more credibly than the previous numerical studies and are close to the experimental results, and the aligned vortices pattern is discovered in cruising swimming.

The linear stability of plane Poiseuille flow is extended to the cases of two wall boundaries maintaining different slip coefficients β₁ and β₂. We determine the slip coefficient pairs, β_1c and β_2c, which yield the same critical Reynolds number as the classical no-slip case. It is found that the wall slip may stabilize the flow for β₁ > β_1c and β₂ > β_2c, whereas slightly destabilize the flow for β₁ < β_1c and β₂ < β_2c.

Adopting Yoshizawa's two-scale expansion technique, the fluctuating field is expanded around the isotropic field. The renormalization group method is applied for calculating the covariance of the fluctuating field at the lower order expansion. A nonlinear Reynolds stress model is derived and the turbulent constants inside are evaluated analytically. Compared with the two-scale direct interaction approximation analysis for turbulent shear flows proposed by Yoshizawa, the calculation is much more simple. The analytical model presented here is close to the Speziale model, which is widely applied in the numerical simulations for the complex turbulent flows.

We propose and analyse a new model of thermocapillary convection with evaporation in a cavity subjected to horizontal temperature gradient, rather than the previously studied model without evaporation. The pure liquid layer with a top free surface in contact with its own vapour is considered in microgravity condition. The computing programme developed for simulating this model integrates the two-dimensional, time-dependent Navier–Stokes equations and energy equation by a second-order accurate projection method. We focus on the coupling of evaporation and thermocapillary convection by investigating the influence of evaporation Biot number and Marangoni number on the interfacial mass and heat transfer. Three different regimes of the coupling mechanisms are found and explained from our numerical results.

Interactions of adjacent synthetic jet actuators with varying relative amplitude and the relative phase of driving voltage are measured using a particle image velocimetry (PIV). Varying relative amplitude or relative phase of driving voltage of the adjacent actuators vectors the direction of the ensuing merged jet of the adjacent synthetic jets. The vectoring mechanism of the adjacent vortex pairs, attract-impact causing deflection (AICD), is provided to explain why the merged jet is generally vectored to the side of the phase-leading synthetic jet or the synthetic jet with higher driving voltage.

The fractal expressions for flow rate and hydraulic conductivity for power-law fluids in a single capillary are derived based on the fractal nature of tortuous capillaries. Every parameter in the proposed expressions has clear physical meaning. The flow rate and hydraulic conductivity for power-law fluids are found to be related to the tortuosity fractal dimension and the power-law index. The flow rate for power-law fluids increases with the increasing power-law index but decreases with the increasing tortuosity fractal dimension. Good agreement between the model predictions for flow in a fractal capillary and in a converging-diverging duct is obtained. The results suggest that the fractal capillary model can be used to model the power-law fluids with different rheological properties.

A new model consisting of an inhomogeneous porous medium saturated by incompressible fluid is investigated. We focus on the effects of inhomogeneity for the streamline patterns and instabilities of the system. Influences of the 'mean porosity' and gradient of distributions of porosity are also emphasized. The results cannot be obtained by studying the media with constant porosity as carried out by other researchers, and have not been discussed before.

The weakly nonlinear regime of single mode ablative Rayleigh–Taylor instability is studied, with consideration of preheat effect and the width of the ablation front. The Rayleigh–Taylor linear growth rate agrees well with the direct numerical simulation. For the density perturbation, the amplitude distribution of the fundamental mode has one peak value whereas those of the second and third harmonics have two and three peak values, respectively. Harmonics generation versus wave number is also given and it is close to the result of direct numerical simulation.

A sawtooth-free period is produced following the pellet injection in the pellet fuelled discharge of q_a = 3.4 (where q_a is the safety factor at the plasma boundary) in the HL-2A tokamak. Establishment of the current profile such as in the hybrid scenario is studied under the condition of pellet injection in HL-2A. It is shown that a q-profile of weak negative shear is produced immediately after the pellet injection, and it then evolves to a broad flat profile with q₀ > 1 (where q₀ is the safety factor at the centre). The measured MHD mode structures evidence consistencies of the evaluated q-profile with locations of the q = 1 surface in the sawtoothing period and of the q = 2 surface in the sawtooth-free period. TRANSP analysis indicates that the energy confinement is enhanced substantially during and after pellet injection, which is resulted from the q-profile optimization and the plasma density peaking.

We carry out a comparison between the characteristics of radio frequency- and pulse-sheath near insulating substrates driven by dual frequency (DF) sources making use of the fluid model in which the self-bias voltage on the electrode is obtained consistently under a current balance condition. The results show that the combination of the higher and lower frequency source modulate the characteristics of the radio-frequency- and pulse-sheath: the higher frequency makes the physical quantities oscillate fast while the slow oscillating contour of variation in physical quantities is modulated by the lower frequency source. However, there are some differences between the capacity of mitigating the charging effects on the surface of the insulator, i.e., the pulsed driven plasma gains an advantage over the radio-frequency driven one because the 'off' state of the pulse allow more electrons to reach the insulating surface to neutralize the positive charge due to the incident ion as the pulse being in the pulse's duty. In addition, the ion energy distribution (IED) bombarding the surface of the insulator has a range of energy for the radio-frequency bias while that for the pulse bias is discontinuous.

We investigate the fragmentation behaviour of decamethylcyclopentasiloxane (DMCPS) plasma using a quadrupole mass spectrometry, which is used as the precursor to deposit SiCOH film in an electron cyclotron resonance (ECR) plasma system. The structure of DMCPS molecules comprises a fivefold Si-O ring and ten -CH₃ groups bonded at five Si atoms. In ECR discharge plasma, the main fragmentation behaviour of DMCPS includes two stages. One is the breaking of fivefold Si-O rings and then the formation of threefold Si-O rings and Si-O chain species. The other is the decomposing of hydrocarbon groups from Si atoms and then the crosslink of hydrocarbon species. Combined with the bonding configuration of SiCOH films, the relation between species in ECR plasma and films structures is analysed.

ZnO nanoflowers are synthesized on AlN films by solution method. The synthesized nanoflowers are composed of nanorods, which are pyramidal and grow from a central point, thus forming structures that are flower-shaped as a whole. The nanoflowers have two typical morphologies: plate-like and bush-like. The XRD spectrum corresponds to the side planes of the ZnO nanorods made up of the nanoflowers. The micro-Raman spectrum of the ZnO nanoflowers exhibits the E₂ (high) mode and the second order multiple-phonon mode. The photoluminescence spectrum of the ZnO nanoflowers exhibits ultraviolet emission centred at 375 nm and a broad green emission centred at 526 nm.

Large quantities of metal indium single-crystalline wires with diameters ranging from tens of nanometres to a few micrometres were synthesized on Si substrates. Unlike traditional methods for the fabrication of nanowires or nanorods, liquid indium was squeezed out of the pores and cracks from porous an InAlN layer to form the wires. Continuous pushing out of liquid metal indium under strength, lowering of liquid—solid interfaces and the confinement of the cracks all contribute to the growth of indium wires. Our experiments have shed some light on the possibility of synthesizing large quantities quasi-1D nano/sub-micron structures with specified cross-sectional geometry using the similar method.

By means of low-temperature (10K) Fourier transform infrared absorption spectroscopy, the kinetics of nitrogen indiffusion in Czochralski (CZ) silicon annealed at 1150–1250°C in nitrogen ambient is investigated. Moreover, the nitrogen diffusivities in CZ silicon at elevated temperatures deduced herein are in good agreement with those previously obtained in float-zone silicon, thus leading to the conclusion that the nitrogen indiffusion in CZ silicon at elevated temperatures is via nitrogen pairs.

The minority carrier lifetime of as-grown germanium-doped Czochralski (GCZ) silicon wafers doped with germanium concentrations [Ge]=10¹⁶−10¹⁸ cm⁻³ is investigated in comparison with conventional CZ silicon samples. It is found that the lifetime distribution along the ingot changes with the variation of [Ge]. There is a critical value of [Ge] = 10¹⁶ cm⁻³ beyond which Ge can obviously influence the lifetime of as-grown ingots. This phenomenon is considered to be associated with the competition or combination between the oxygen related thermal donors (TDs) and electrically active Ge-related complexes. The related formation mechanisms and distributions are also discussed.

The computations of the phonon dispersion curves (PDC) of four equiatomic Li-based binary alloys, namely Li_0.5Na_0.5, Li_0.5K_0.5, Li_0.5Rb_0.5 and Li_0.5Cs_0.5, to second order in the local model potential is discussed in terms of the real-space sum of Born von Karman central force constants. Instead of the concentration average of the force constants of metallic Li, Na, K, Rb and Cs, the pseudo-alloy atom (PAA) is adopted to compute directly the force constants of four equiatomic Li-based binary alloys. The exchange and correlation functions due to Hartree (H) and Ichimaru–Utsumi (IU) are used to investigate the influence of screening effects. The phonon frequencies of four equiatomic Li-based binary alloys in the longitudinal branch are more sensitive to the exchange and correlation effects in comparison with the transverse branches. However, the frequencies in the longitudinal branch are suppressed due to IU-screening function than the frequencies due to static H-screening function.

Polymerization of C₆₀ is realized under high temperature and high pressure. X-ray diffraction reveals a rhombohedral lattice structure in the product, and solid-state ¹³C nuclear magnetic resonance spectroscopy confirms the formation of sp³ bonds between C₆₀ molecules. Specific heat is then measured over the temperature range of 300–2 K. It is found that its specific heat values are significantly less than those in fullerite within the region of 80–2K, and this huge reduction is attributed to the suppression of intermolecular librational modes in polymerized C₆₀. An excellent fit to the experimental data over the entire temperature range is provided by a model, which needs to include only three-dimensional and two-dimensional translational modes in various contributions at different temperatures.

We investigate the thermal expansion property of the Tb₂Fe₁₄Cr₃ compound by means of x-ray diffraction. The result shows that the Tb₂Fe₁₄Cr₃ compound has a hexagonal Th₂Ni₁₇-type structure. Negative thermal expansion is found in the Tb₂Fe₁₄Cr₃ compound from 296 to 493K by x-ray dilatometry The coefficient of the average thermal expansion is = -2.82 × 10⁻⁵K⁻¹. In the temperature range 493–692K, the coefficient of the average thermal expansion is = 1.59 × 10⁻⁵K⁻¹. The physical mechanism of thermal expansion anomaly of the Tb₂Fe₁₄Cr₃ compound is discussed according to the temperature dependence of magnetization measured by a superconducting quantum interference device.

We present a multi-level growth model that yields some of the key features of perovskite oxide film growth as observed in the reflection high energy electron diffraction (RHEED) and ellipsometry studies. The model describes the effect of deposition, temperature, intra-layer transport, interlayer transport and Ostwald ripening on the morphology of a growth surface in terms of the distribution of terraces and step edges during and after deposition. The numerical results of the model coincide well with the experimental observation.

The self-assembled InAs quantum dots (QDs) on GaAs substrates with low density (5 × 10⁸ cm⁻²) are achieved using relatively higher growth temperature and low InAs coverage by low-pressure metal-organic chemical vapour deposition. The macro-PL spectra exhibit three emission peaks at 1361, 1280 and 1204 nm, corresponding to the ground level (GS), the first excited state (ES1) and the second excited state (ES2) of the QDs, respectively, which are obtained when the GaAs capping layer is grown using triethylgallium and tertiallybutylarsine. As a result of micro-PL, only a few peaks from individual dots have been observed. The exciton-biexciton behaviour was clearly observed at low temperature.

The coupling between magnetism and structural distortions in BiFeO₃(BFO) is investigated using density functional theory by considering the spin-orbit effect. Computational results show that the resulting magnetization M is rotated by reversal of sense of rotation of the oxygen octahedra in the double cell. The resulting magnetization is determined by the antiferrodistortive (AFD) distortions and ferroelectric (FE) displacements. This work clarifies the previous view that magnetism is only coupled with, and determined by, FE displacements. The excellent ferroelectricity is attributed significantly to the anomaly of Born effective charge of Bi, which is caused by the stereochemically active long pair of Bi 6s.

The pressure induced phase transition of ZnS from the wurtzite (WZ) and the zincblende (ZB) structures to the rocksalt (RS) structure and the temperature induced phase transition from the ZB structure to the WZ structure are investigated by ab initio plane-wave pseudopotential density-functional theory (DFT), together with the quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from the WZ-ZnS and the ZB-ZnS to the RS-ZnS are 17.20 and 17.37 GPa, respectively. The zero-pressure transition temperature from the ZB-ZnS to the WZ-ZnS is 1199 K. All these results are consistent with the available experimental data. Moreover, the dependences of the normalized primitive cell volume V/V₀ on pressure and thermal expansion coefficient α on temperature are also obtained successfully.

The migration of a polaron at polymer/polymer interface is believed to be of fundamental importance for the transport and light-emitting properties of conjugated polymer-based light emitting diodes. Based on the one-dimensional tight-binding Su–Schrieffer–Heeger (SSH) model, we have investigated polaron dynamics in a one-dimensional polymer/polymer system by using a nonadiabatic evolution method. In particular, we focus on how a polaron migrates through the conjugated polymer/polymer interface in the presence of external electric field. The results show that the migration of polaron at the interface depends sensitively on the hopping integrals, the potential barrier induced by the energy mismatch, and the strength of applied electric field which increases the polaron kinetic energy.

We study the effect of electron-phonon interaction on current and zero-frequency shot noise in resonant tunnelling through a series triple-quantum-dot coupling to a local phonon mode by means of a nonperturbative mapping technique along with the Green function formulation. By fixing the energy difference between the first two quantum dots to be equal to phonon frequency and sweeping the level of the third quantum dot, we find a largely enhanced current spectrum due to phonon effect, and in particular we predict current peaks corresponding to phonon-absorption and phonon-emission assisted resonant tunnelling processes, which show that this system can be acted as a sensitive phonon-signal detector or as a cascade phonon generator.

We have performed low temperature resistivity ρ(T) and specific heat C(T) measurements on a superconducting polycrystalline Nb_0.75Mg_0.25B₂ sample. The results indicate that the superconducting transition temperature is ∼ 4.6 K. The zero temperature upper critical field determined from the resistivity and specific heat is 3123 Oe. The electronic coefficient of specific heat γ_n = 4.51 mJmol⁻¹K² and the Debye temperature Θ_D = 419K are obtained by fitting the zero-field specific heat data in the normal state. At low temperatures, the electronic specific heat in the superconducting state follows C_es/γ_nT_c = 2.84exp(-1.21T_c/T). This indicates that the superconducting pairing in Nb_0.75Mg_0.25B₂ has s-wave symmetry.

Four-component Bogoliubov-de Gennes equations are applied to study the tunnelling conductance spectra G(E) of half-metallic ferromagnet/ferromagnet/s-wave superconductor tunnel junctions. It is found that only for noncollinear magnetizations, there exists nonzero G(E) structure within the energy gap, which is a signature of appearance of the novel Andreev reflection and spin-triplet pairing correlations.

We propose a non-stationary method to measure the energy relaxation time of Josephson tunnel junctions from microwave enhanced escape phenomena. Compared with the previous methods, our method possesses simple and accurate features. Moreover, having determined the energy relaxation time, we can further obtain the coupling strength between the microwave source and the junction by changing the microwave power.

A model describing surface quenching of isolated ion centres in nanocrystals is proposed based on the energy transfer between the doped ions and the nanocrystalline surface quenching centres. The quenching rate depends on the position of the ions in the nanocrystal, hence the decay curve under non-selective excitation is generally nonexponential The decay curve calculated with this model is in good agreement with that of the ⁴T₁ → ⁶A₁ emission in ZnS:Mn²⁺ nanocrystals.

Polymers are a kind of attractive hosts for laser dyes because of their superior optical homogeneity, and high transparency in pumping and lasing range. Copolymers usually have higher damage threshold and better photostability than mono-polymers. Solid dye samples based on copolymer of methyl methacrylate (MMA) with 2-hydroxypropyl methacrylate (HPMA) doped with 1-, 3-, 5-, 7-, 8-pentamethyl-2, 6-diethylpyrromethene-BF₂ (PM567) are prepared. Spectra and lasing properties of the samples are studied. Compared to the samples based on monopolymer polymethyl methacrylate (PMMA), enhanced slope efficiency and photostability are obtained in the copolymers. The highest slope efficiency is 45.1%, and nearly one-fold increase of photostability is obtained. The longest useful lifetime of 4390 pumping pulses is presented with the pump energy as high as 183 mJ per pulse at repetition rate of 10 Hz. The results indicate that the laser performances of solid dye mediums can be greatly increased using copolymer of MMA with HPMA as host.

We investigate the luminescence properties of Bi³⁺ and RE³⁺ (RE = Tb or Eu) in a Y₃Ga₅O₁₂ (YGG) host system. The additional doping of Bi³⁺ can enhance the luminescence of Tb³⁺ or Eu³⁺ in this host. Energy transfer from Bi³⁺ to Tb³⁺ and Eu³⁺ is observed and the mechanism of energy transfer is investigated. Mechanism of energy transfer can be explained as electric multipole interaction since the Bi³⁺ emission band and Tb³⁺ or Eu³⁺ excitation band overlaps and the Bi³⁺ emission intensity decreases while the intensity of Tb³⁺ or Eu³⁺ increases with the increase of Tb³⁺ or Eu³⁺ concentration. Therefore, Bi³⁺ ion is a kind of efficient sensitizer to the Tb³⁺ and Eu³⁺ activators in the Y₃Ga₅O₁₂ host.

Low-frequency (2.72–3.70Hz) relaxation oscillations at 100 m Torr at higher absorbed power were observed from time-varying optical emission of the main discharge chamber and the periphery. We interpret the low frequency oscillations using an electromagnetic model of the slot impedance with parallel connection variational peripheral capacitance, coupled to a circuit analysis of the system including the matching network. The model results are in general agreement with the experimental observations, and indicate a variety of behaviours dependent on the matching conditions.

Electroluminescence performances from a tuning biscyclometlated iridium complex with benzyl group are demonstrated in double-layered polymer light-emitting devices (PLEDs) using a blend of poly(9,9-dioctylfluorene) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole as a host matrix. Blue-green electrophosphorescent emission with a peak at 521 nm and a shoulder at 492 nm was observed. The highest luminance efficiency of 4.8 cd/A at current density of 0.56mA/cm² and a maximum luminance of 1944cd/m² at 217.6 mA/cm² were achieved in the devices at the dopant concentration of 8%. The luminous performance of the devices becomes better with increasing dopant concentrations from 1% to 8%. This implies that the concentration quenching of this iridium complex with benzyl group can be efficiently inhibited in the devices.

We demonstrate near-infrared organic light-emitting devices with a periodically arranged tris(8-quinolinolato)aluminum (Alq₃):copper phthalocyanine (CuPc)/4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminost-yry)-4H-pyran (DCM) multilayer structure. DCM and Alq₃ doped with CuPc were periodically deposited. Room-temperature electrophosphorescence was observed at about 1.1 μm due to transitions from the first excited triplet state to the singlet ground state (T₁ – S₀) of CuPc. In this device, we utilize the overlap between the Q band π-π^* at about 625 nm of the absorption spectra of CuPc and the PL spectra of the DCM. The near-infrared emission intensity of the CuPc-doped Alq₃ device with DCM increases about 2.5 times larger than that of the device without DCM. We attribute the efficiency enhancement to the better overlap between the PL spectra of DCM and the absorption spectra of CuPc.

Bright organic electroluminescent devices are developed using a metal-doped organic layer intervening between the cathode and the emitting layer. The typical device structure is a glass substrate/indium-tin oxide (ITO)/copper phthalocyanine(CuPc)/N,N-bis-(1-naphthl)-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/Tris(8-quinolinolato) alu-minum(Alq₃)/Mg-doped CuPc/Ag. At a driving voltage of 11 V, the device with a layer of Mg-doped CuPc (1:2 in weight) shows a brightness of 4312 cd/m² and a current efficiency of 2.52 cd/A, while the reference device exhibits 514 cd/m² and 1.25 cd/A.

We theoretically investigate the electrical transport property of a quantum dot with longitudinal optical phonons. The conductance through the dot connected to two leads is calculated by the nonequilibrium Green function within the Landauer—Büttiker framework. The numerical examples of the conductance with different electron—phonon coupling strengths show that the presence of a phonon field typically results in the suppression of the main peak accompanied by some phonon side peaks. Both the main peak and the side peaks are sensitive to the electron—phonon coupling strength, which is related to temperature. Our results for this system are consistent with some related previous works but the calculation is comparatively simple.

We investigate the properties of symmetrical triangular quantum wells composed of InGaAs/InAs chirped superlattice, which is grown by gas source molecular beam epitaxy via digital alloy method. In the quantum well structure tensile AlInGaAs are used as barriers to partially compensate for the significant compressive strain in the wells, the strain compensation effects are confirmed by x-ray measurement. The photoluminescence spectra of the sample are dominated by the excitonic recombination peak in the whole temperature range. The thermal quenching, peak energy shift and line-width broadening of the PL spectra are analysed in detail, the mechanisms are discussed.

The sputtering process of Ar+Ni(100) collision systems is investigated by means of constant energy molecular dynamics simulations. The Ni(100) slab is mimicked by an embedded-atom potential, and the interaction between the projectile and the surface is modelled by using the reparametrized ZBL potential. Ni atom emission from the lattice is analysed over the range of 20–50 eV collision energy. Sputtering yield, angular and energy distributions of the scattered Ar and of the sputtered Ni atoms are calculated, and compared to the available theoretical and experimental data.

The electrical and structural properties of polycrystalline Cu(In,Ga)Se₂ films grown on polyimide (PI) substrates below 400° C via one-stage and three-stage co-evaporation process have been investigated by x-ray diffraction spectra (XRD), scanning electron microscopy (SEM) and Hall effect measurement. As shown by XRD spectra, the stoichiometric CIGS films obtained by one-stage process exhibit the characteristic diffraction peaks of the (In_0.68Ga_0.32)₂Se₃ and Cu(In_0.7Ga_0.3)₂Se. It is also found that the film structures indicate more columnar and compact than the three-stage process films from SEM images. The stoichiometric CIGS films obtained by three-stage process exhibit the coexistence of the secondary phase of (In_0.68Ga_0.32)₂Se₃, Cu_2-xSe and Cu(In_0.7Ga_0.3)₂Se. High net carrier concentration and sheet conductivity are also observed for this kind of film, related to the presence of Cu_2-xSe phase. As a result, when the CIGS film growth temperature is below 400° C, the three-stage process is inefficient for solar cells. By using the one-stage co-evaporation process, the flexible CIGS solar cell on a PI substrate with the best conversion efficiency of 6.38% is demonstrated (active area 0.16 cm²).

A large number of ZnS nanosaws are synthesized on Si substrates in the presence of Au catalyst by thermally evaporating ZnS powder. Morphologies and structures of thus-grown ZnS nanosaws are characterized by a field emission scanning electron microscopy (FE-SEM) and a transmission electron microscopy (TEM). The results show that temperature of the Si substrates used for collection of the products is a critical experimental parameter for the formation of ZnS nanostructures with different morphologies. The growth mechanism of the ZnS nanosaws is discussed on the basis of the experimental findings.

An all-thin-film (ATF) electrochromic device for modulating the optical transmittance is manufactured using magnetron sputtering. The devices consists of MoO₃ as the main electrochromic layer, LiBO₂+Li₂SO₄(LiBSO) as the ion conductor layer, and NiO_x as the complementary electrochromic layer. Glass covered with indium tin oxide (ITO) is used as the substrate and the ITO film is used as the bottom electrode. The ITO film deposited o the top of the devices is used as the other electrode. The structure and morphology of the films are characterize by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The devices exhibit good optical properties with low transmittance values in the coloured state, and the optical modulation is measured by spectrophotometer in the wavelength range from 400 to 800 nm. The average visible light transmittance reaches 50.2% and 3.7% i bleached and coloured state, respectively. The results indicate that such a monolithic system has great potential to be applied in smart windows.

ZnO thin films are prepared on glass substrates by filtered cathode vacuum arc (FCVA) deposition technique. A new method is demonstrated to extract the refractive index, thickness and optical band gap of ZnO thin films from the transmission spectrum alone. The refractive index is calculated from the extremes of the interference fingers. The transmission spectrum is divided into two terms, non-interference term and interference effect term. The thickness of thin films is calculated by simulating the interference term, and the non-interference term is used to calculate optical band gap with the gained thickness. The results are compared with measurements by using an ellipsometry and a scanning electron microscope.

As proposed by Herminghaus, a hierarchical structure could render any surface nonwettable as long as the roughness amplitude at small scales is sufficient to suspend a free liquid surface. Recently we reported that the wettability of La_0.7Sr_0.3MnO₃, an intrinsic hydrophilic oxide, can be tuned from superhydrophilicity to superhydrophobicity by hierarchical microstructures generated by annealing the coatings of La_0.7Sr_0.3MnO₃ powder in nanometric scale at different temperatures. Here we further demonstrate the similar phenomenon observed on LaMnO₃ coatings, which conforms THAT the surface geometrical structure is a key factor to determine the wettability.

The carbonyl iron flakes are fabricated by high-energy ball milling. The effective permeability is measured and calculated for the composite consisting of flakes embedded in a nonmagnetic matrix. The magnetic flakes with a shape anisotropy and random spatial distribution of normal direction are considered to calculate the complex permeability of magnetic flake materials. Its analytical model is derived from the Landau–Lifshitz–Gilbert equation and Bruggeman's effective medium theory. The calculated results agree well with the experiment.

An organic integrated pixel with organic light-emitting diodes (OLEDs) driven by organic thin film transistors (OTFTs) is fabricated by a greatly simplified processing. The OTFTs are based on copper phthalocyanine as the active medium and fabricated on indium-tin-oxide (ITO) glass with top-gate structure, thus an organic integrated pixel is easily made by integrating OLED with OTFT. The OTFTs show field-effect mobility of 0.4 cm²/Vs and on/off ratio of 10³ order. The OLED is driven well and emits the brightness as large as 2100 cd/m² at a current density of 14.6 μA/cm² at −19.7 V gate voltage. This simple device structure is promising in the future large-area flexible OLED displays.

Organic thin transistors (OTFTs) on indium tin oxide glass substrates are prepared with polymethyl-methacrylate-co-glyciclyl-methacrylate (PMMA-GMA) as the gate insulator layer and copper phthalocyanine as the organic semiconductor layer. By controlling the thickness, the average roughness of surface is reduced and the OTFT performance is improved with leak current decreasing to 10⁻¹¹ A and on/off ratio of 10⁴. Under the condition of drain-source voltage −20 V, a threshold voltage of −3.5 V is obtained. The experimental results show that PMMA-GMA is a promising insulator material with a dielectric constant in a range of 3.9–5.0.

In order to improve nano-scale phase change memory performance, a super-clean interface should be obtained after chemical mechanical polishing (CMP) of Ge₂Sb₂Te₅ phase change films. We use reactive ion etching (RIE) as the cleaning method. The cleaning effect is analysed by scanning electron microscopy and an energy dispersive spectrometer. The results show that particle residue on the surface has been removed. Meanwhile, Ge₂Sb₂Te₅ material stoichiometric content ratios are unchanged. After the top electrode is deposited, current-voltage characteristics test demonstrates that the set threshold voltage is reduced from 13 V to 2.7V and the threshold current from 0.1mA to 0.025mA. Furthermore, we analyse the RIE cleaning principle and compare it with the ultrasonic method.

The scaling behaviour of fluctuation for a download network we investigated a few years ago based upon Zhang's Econophysics web page is presented. A power law scaling, namely σ ∼ 〈f〉^α exists between the dispersion σ and average flux 〈f〉 of the download rates. The fluctuation exponent α is neither ½ nor 1, which were claimed as two universal fluctuation classes in previous publication, while it varies from ½ to 1 with the time window in which the download data are accumulated. The crossover behaviour of fluctuation exponents can be qualitatively understood by the external driving fluctuation model for a small-size system or a network traffic model which suggests congestion as the origin.

We numerically investigate the effect of four kinds of partial attacks of multiple targets on the Barabási-Albert (BA) scale-free network and the Erdös-Rényi (ER) random network. Comparing with the effect of single target complete knockout we find that partial attacks of multiple targets may produce an effect higher than the complete knockout of a single target on both BA scale-free network and ER random network. We also find that the BA scale-free network seems to be more susceptible to multi-target partial attacks than the ER random network.

A continuum opinion dynamic model is presented based on two rules. The first one considers the mobilities of the individuals, the second one supposes that the individuals update their opinions independently. The results of the model indicate that the bounded confidence ∊_c, separating consensus and incoherent states, of a scale-free network is much smaller than the one of a lattice. If the system can reach the consensus state, the sum of all individuals' opinion change O_c(t) quickly decreases in an exponential form, while if it reaches the incoherent state finally O_c(t) decreases slowly and has the punctuated equilibrium characteristic.

A number of researching works have shed light on the field of complex networks recently. We investigate a wide range of real-world networks and find several interesting phenomena. Firstly, almost all of these networks evolve by overlapping new small graphs on former networks. Secondly, not only the degree sequence of the mature network follows a power-law distribution, but also the distribution of the cumulative occurrence times during the growing process are revealed to have a heavy tail. Existing network evolving models do not provide interpretation to these phenomena. We suggest a model based on the team assembling mechanism, which is extracted from the growing processes of real-world networks and requires simple parameters, and produces networks exhibiting these properties observed in the present study and in previous works.

We investigate the stability and dissociation of methane, which is the most abundant organic molecule in the universe, using diamond anvil cell (DAC) with in situ Raman spectroscopy up to 903 K and 21 GPa. At the temperatures of 793 and 723K and the corresponding pressures of 16.15 and 20.30 GPa, methane dissociates to form carbon 'soot' and heavier hydrocarbons involving C=C and C=C bonds. However, if the pressure is not very high, methane remains stability up to the highest temperature of 903 K of the work. The four symmetric C-H bonds of methane split at high temperatures and at high pressures, and there is at least one phase transition of crystalline symmetry from face centred cubic (fcc) to hexagonal close packed (hcp) before dissociation.

Measurements of energetic particles obtained by the two geosynchronous satellites (1991-080 and LANL-97A) are performed to investigate the plasma injection boundary and source region during the magnetospheric substorms. The measurement method is developed to allow remote sensing of the plasma injection time and the radial distance of injection boundaries by using measured energy dispersion and modelling particle drifts within the Volland–Stern electric field and the dipole magnetic field model. The radial distance of the injection boundary deduced from a dispersion event observed by the LANL-97A satellite on 14 June 1998 is 7.1R_E, and the injection time agrees well with the substorm onset time identified by the Polar Ultraviolet Imager. The method has been applied to an event happened at 22.9 UT on 11 March 1998, when both the satellites (1991-080 and LANL-97A) observed the dispersionless character. The results indicate that the radial distance of injection source locates at 8.1R_E at magnetotail, and particles move earthward from magnetotail into inner magnetosphere at 22.5 UT.

The tsunami model of the origin of multi-ring basins is analysed with the theory of deep water waves generated by an initial surface deformation, which is set as a parabolic crater. We obtain an approximate formula for calculating the ring radius. The formula applied to some multi-ring basins on the Moon, Mercury and Mars gives almost equidistant spacing of the rings within the main ring (the IV ring); this agrees with the previous conclusion that the IV ring marks the end of the fluidized region. Besides this, the theory of deep water waves does not require similar crustal structure at each basin-impact site on all three planets which is required in the theory of shallow water waves.

Our newly developed CESE MHD model is used to simulate sun-earth connection event with the well-studied 12 May 1997 CME event as an example. The main features and approximations of our numerical model are as follows: (1) The modified conservation element and solution element (CESE) numerical scheme in spherical geometry is implemented in our code. (2) The background solar wind is derived from a 3D time-dependent numerical MHD model by input measured photospheric magnetic fields. (3) Transient disturbances are derived from solar surface by introducing a mass flow of hot plasma. The numerical simulation has enabled us to predict the arrival of the interplanetary shock and provided us with a relatively satisfactory comparison with the WIND spacecraft observations.

In the case of a low beta plasma β ≪ m_e/m_i, the electron acceleration by small amplitude solitary kinetic Alfvén wave is studied. It is found that the electron can be only accelerated along the ambient magnetic field. The maximum velocity of accelerated electron approaches to twice Alfvén velocity. In the perpendicular direction, the dc electric field acceleration term and surfing acceleration term almost cancel each other out.

Based our previous work [Mod. Phys. Lett. A 22 (2007) 783, Gen. Relat. Grav. 39 (2007) 653], some properties of modified Chaplygin gas (MCG) as a dark energy model continue to be studied mainly in two aspects: one is the change rates of the energy density and energy transfer, and the other is the evolution of the growth index. It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not, but the corresponding transformation points are different from each other. Furthermore, it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter, and the energy of transfer flows from dark energy to dark matter. The evolution of the interaction term with an ansatz 3Hc² ρ is discussed with the MCG model. Moreover, the evolution of the growth index f in the MCG model without interaction is illustrated, from which we find that the evolutionary trajectory of f overlaps with that of the ΣCDM model when a > 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.

We study the constraint on deceleration parameter q from the recent SNeIa Gold dataset and observational Hubble data by using a model-independent deceleration parameter q(z) = ½ – a/(1 + z)^b under the five-dimensional bounce cosmological model. For the cases of SNeIa Gold dataset, Hubble data, and their combination, the present results show that the constraints on transition redshift z_T are 0.35^+0.14_−0.07, 0.68^+1.47_0.58, and 0.55^+0.18_−0.09 with 1σ errors, respectively.