The approximate generalized conditional symmetry (AGCS) approach we previously proposed [Chin. Phys. Lett.23(2006)527] is applied to study the perturbed general KdV--Burgers (KdVB) equation. Complete classification of those perturbed general KdVB equations which admit certain types of AGCSs is obtained. Approximate solutions to the perturbed equations can be derived from the corresponding unperturbed ones.

Two new (2+1)-dimensional modified Kadomtsev--Petviashvili (mKP) equations are presented, which are related to a hierarchy of (1+1)-dimensional soliton equations. Through the nonlinearization of Lax pair and the Riemann--Jacobi inversion technique, the algebro-geometric solutions of both the mKP equations are obtained.

The weak Darboux transformation of the (2+1) dimensional Euler equation is used to find its exact solutions. Starting from a constant velocity field solution, a set of quite general periodic wave solutions such as the Rossby waves can be simply obtained from the weak Darboux transformation with zero spectral parameters. The constant vorticity seed solution is utilized to generate Bessel waves.

We show that restricting the states of a charged particle to the lowest Landau level introduces noncommutativity between general curvilinear coordinate operators. The Cartesian, circular cylindrical and spherical polar coordinates are three special cases of our quite general method. The connection between U(1) gauge fields defined on a general noncommuting curvilinear coordinates and fluid mechanics is explained. We also recognize the Seiberg--Witten map from general noncommuting to commuting variables as the quantum correspondence of the Lagrange-to-Euler map in fluid mechanics.

The s-wave Klein--Gordon equation for the bound states is separated in two parts to see clearly the relativistic contributions to the solution in the non-relativistic limit. The reliability of the model is discussed with two examples chosen specifically.

Continuous--variable entanglement in the interacting system of a mesoscopic Josephson junction with a squeezed field is investigated. It is shown that when the cavity field is initially prepared in a squeezed vacuum state and the junction in its lowest energy state, the coupling system can evolve into a two-mode Gaussian state. The time-dependent characteristic function in the Wigner representation for the system is analytically obtained, and the squeezing degree of the initial cavity field turns out to have not only an apparent enhancing but also a weakening effect on the entanglement of the coupling system under suitable parameter conditions.

We study the decoherence process of an exact solvable model that consists of a central spin-1/2 coupling to the surrounding anisotropy spin-1/2 chain in transverse fields. The Loschmidt echo is calculated to study the character of decoherence with different degree of anisotropy. Our results show that the degree of anisotropy γ greatly affects the decoherence process of the central spin-system when the spin chain is in weak transverse fields, but it gives weak effect in the strong transverse field. The decoherence process of the central system changed dramatically along the line of the critical points, and this may be explained as the reflection of quantum phase transitions.

The quantum secure direct communication protocol recently proposed by Cao and Song [Chin. Phys. Lett. 23(2006)290] (i.e., the C-S QSDC protocol) is revisited. A security leak is pointed out. Taking advantage of this leak, an eavesdropper may adopt the intercept--measure--resend strategy to attack the quantum channel such that in the C-S QSDC protocol the secret message can be completely eavesdropped. To fix the leak, the original version of the C-S QSDC protocol is revised. As a consequence, the security is improved and assured at least in the case of an ideal quantum channel.

We analyse the capacity of a simultaneous quantum secure direct communication scheme between the central party and other M parties via M+1-particle GHZ states and swapping quantum entanglement. It is shown that the encoding scheme should be secret if other M parties wants to transmit M+1 bit classical messages to the centre party secretly. However, when the encoding scheme is announced publicly, we prove that the capacity of the scheme in transmitting the secret messages is 2 bits, no matter how large M is.

We propose a novel protocol for quantum secure direct communication with cluster states. In this protocol, the two legitimate users, Alice and Bob, can directly transmit the secret messages by using the Bell-basis measurement and Z-basis measurement, respectively, in classical communication. Since our quantum secure direct communication protocol is based on the cluster state, it is easily processed by a one-way quantum computer.

We investigate the collective modes of a quasi-two-dimensional (Q2D) superfluid Fermi gas in Bardeen--Cooper--Schrieffer Bose--Einstein condensation (BCS-BEC) crossover. For solving a generalized Gross--Pitaevskii equation by using a time-dependent variational method, we take a trial wavefunction with the form of hybrid Gaussian-parabolic type, which not only reflects the Q2D character of the system and also allows an essentially analytical approach of the problem. We present a Q2D criterion that is valid for various superfluid regimes and displays clearly the relation between the maximum condensed particle number and the parameters of trapping potential as well as atom--atom interaction. We show that due to the small particle number in the Q2D condensate, the contribution to oscillating frequencies by the quantum pressure in the strong confinement direction is significant and hence a Thomas--Fermi approximation can not be used.

The spatial synchronization and temporal coherence of FitzHugh--Nagumo (FHN) neurons on complex networks are numerically investigated. When an optimal number of random shortcuts are added to a regular neural chain, the system can reach a state which is nearly periodic in time and almost synchronized in space. More shortcuts do not increase the spatial synchronization too much, but will obviously destroy the temporal regularity.

We study the order parameter probability distribution at the critical point for the three-dimensional spin-1/2 and spin-1 Ising models on the simple cubic lattice under periodic boundary conditions. The finite size scaling relation for the order parameter probability distribution is tested and verified numerically by microcanonical Creutz cellular automata simulations. The state critical exponent δ, which characterizes the far tail regime of the scaling order parameter probability distribution, is estimated for three-dimensional Ising models using the cellular automaton simulations at the critical temperature. The results are in good agreement with the Monte Carlo calculations.

The conceptual design of a cryogenic system at temperature 2K for the Peking University Free Electron Laser (PKU-FEL) facility is carried out. In order to minimize the scale of the cryogenic system and the running cost, the superconducting accelerator and the superconducting injector will mainly run at a long-pulsed mode. Optimization of the 2-K cryogenic system is carried out based on the heat load estimation and running parameters. Total cooling power of 52.5W for the long-pulsed mode is necessary for the PKU cryogenic system. The PKU cryogenic system will be the first 2-K system for accelerators in China and will provide experience for similar facilities.

In the applications of neutron guides and focusing devices, by using the Ni/Ti multilayer supermirrors (SM), the neutron flux is significantly enhanced, because the critical reflective angle of supermirrors increases m times compared to the one of natural bulk Ni. We design and fabricate the Ni/Ti multilayer supermirrors by considering the effect of the interfacial imperfection, such as interface roughness and diffusion, and by using the direct current magnetron sputtering technology. The reflective performances of these supermirrors are measured on a V14 neutron beam line at the Berlin Neutron Scattering Centre (BENSC), Germany. The measurement data suggest that the critical angles of the supermirrors are 1.5 and 2.2 times that of bulk Ni, respectively.

In the minimum electromagnetism coupling model of interaction between photon and electron (positron), we accurately calculate photon chain renormalized propagator and obtain the accurate result of differential cross section of Bhabha scattering with a photon chain renormalized propagator in quantum electrodynamics. The related radiative corrections are briefly reviewed and discussed.

The pure annihilation type decays B⁰_d→phiγ and B_s→ργ receive only colour suppressed penguin contributions with a very small branching ratio in the standard model. When we include the previously neglected electromagnetic dipole operator, the branching ratios can be enhanced to R( B⁰_d→Фγ)\simeq 1×10^-11 and R(B_s→ργ) ～ (6-16)×10^-10, which are one order magnitude larger than previous study using the QCD factorization approach. The new effect can also give a large contribution, of order 10^-9, to transverse polarization of B→Фρ and B→ωФ, which is comparable to the longitudinal part. These effects can be detected in the LHCb experiment and the super-B factories.

The importance of imposing physical boundary conditions on the T-matrix to remove the nonperturbative renormalization prescription dependence is stressed and demonstrated in two diagonal channels ¹P₁ and ¹D₂, with the help of Padé expansion.

Current experiment results show that neutrinos have non-zero masses and that different neutrino flavours may mix and undergo a transformation to each other. Neglecting matter effects for simplicity and by solving the Friedmann--Robertson--Walker geodesic equations of the time-like particle, we preparatively investigate the vacuum oscillation or separation of neutrinos on the cosmic scale.

We investigate the cross sections of the elastic electron or positron scattering from ²⁰⁸Pb, ¹²C, ^12,16O and ^28,32S by the relativistic partial-wave expansion method using the static charge density distribution from the self-consistent relativistic mean field model and also calculate the charge form factor for ^12,16O and ^28,32S. The numerical results are compared with the available data. Calculations indicate that the extended charge density distributions of¹²O and ²⁸S have observable effects on the cross sections of the electron or positron scattering as well as the charge form factors.

Electroexcitations of the dominantly T=1 particle--hole states of ¹²C are studied in the framework of the harmonic oscillator shell model. All possible T=1 single-particle--hole states of all allowed angular momenta are considered in a basis including single-particle states up to the 1f-2p shell. The Hamiltonian is diagonalized in this space in the presence of the modified surface delta interaction. Correlation in the ground state wavefunctions by mixing more than one configuration is considered and shows a major contribution that leads to enhance the calculations of the form factors. A comparison with the experiment shows that this model is able to fit the location of states and a simple scaling of the results give a good fit to the experimental form factors.

The γ-rays and protons from E_d=20keV deuterons incident on a D--Ti target are measured. The branching ratio of the ²H (d,γ)⁴He reaction to the ²H (d,p)³H reaction is obtained to be Γ_γ/Γ_p=(1.06±0.42)×10^-7, and the astrophysical S factor of the ²He(d,γ)⁴He reaction is deduced to be (5.7±2.4)×10^-6.

Excitation functions are measured for different charge products of the ¹⁹F+²⁷Al reaction in the laboratory energy range 110.25--118.75MeV in steps of 250keV at θ_lab=57°, 31° and -29°. The coherence rotation angular velocities of the intermediate dinuclear systems formed in the reaction are extracted from the cross section energy autocorrelation functions. Compared the angular velocity extracted from the experimental data with the ones deduced from the sticking limit, it is indicated that a larger deformation of the intermediate dinuclear system exists.

We study the average property of the isospin effects of reaction mechanism induced by neutron-halo nuclei within the isospin-dependent quantum molecular dynamics model. We find that the extended neutron density distribution for the neutron-halo projectile brings an important isospin effect into the reaction mechanism, which induces the decrease of nuclear stopping R; however, it induces the obvious increases of the neutron-proton ratio of nucleon emissions (n/p)_nucl for all of the beam energies in this work, compared to the same mass stable colliding system.

Intermediate stage of the three and four-pronged events is investigated in the reaction ²⁰⁸Pb+¹⁹⁷Au at beam energy 11.67MeV/u. Multiprong events are analysed numerically using an empirical mass-dependent velocity-range relation. Using the measured three-dimensional coordinates of correlated tracks, it is ossible to determine the quantities such as mass transfer and total kinetic energy loss. These quantities are then used to study the intermediate stage of the reaction. It has been observed that mass transfer and total kinetic energy loss at the first step of the reaction decides the multiplicity of an event at the second stage of the sequential fission process.

A theoretical method of real-space wave-packet propagations with patch meshes is used to study the photoabsorption processes of hydrogen atoms. A complete spectrum of optical oscillator strength densities for transitions from the 1s state to the final states of p channel including infinite Rydberg series and adjacent continuum states is calculated. The calculation result agrees well with the analytical solution of hydrogen atoms. The present proposed method should be very useful in applications of various quantum dynamical processes.

Atomic simulations using embedded atom method (EAM) are performed for Cu <100> nanobelts to study the structural and mechanical behaviour. Cu <100> nanobelts are along [001] taken as the z-axis and have a rectangular cross section in the x-y plane, with [100] and [010] taken as x and y axes. The periodic boundary is used along the z-axis to simulate an infinitely long nanobelt, and other surfaces are free. The simulations are carried out under the mechanical loading with an elongation strain rate of 8.0×10⁸s^-1 along the z-axis. The results show that the nanobelt undergoes a transition from the initial structure with a <100> axis and {100} lateral surfaces to a new structure with the <112> as the z-axis and the lateral surfaces are {111} and {110} respectively, instead of the original {100} surfaces. The mechanism of the structural transition is ascribed to the dislocation propagation through the nanobelt under the external stresses.

The coherent effects including counter-rotating coupling on spontaneous emission are presented for a microwave driven V-type three-level atom. Novel coherent effects are realized: (i) There is an infinite series of spectral lines, which are separated by the microwave frequency, independent of the separation of the excited states, no matter whether the microwave transition is resonant or not. This is in sharp contrast to the case of the weak coupling, where the spectral interval is mainly determined by the separation of the excited states. (ii) Selective appearance and inhibition of the spectral lines are obtained simply by varying the microwave Rabi frequency. (iii) Spectral lines have a twofold structure. The physical mechanisms are analysed by employing the dressed states representation.

The Coulomb potential recapture effect in above-barrier ionization with ultrashort long-wavelength laser pulses is investigated theoretically by solving the one-dimensional time-dependent Schrödinger equation. We find that electrons can be recaptured with considerable possibility by the Coulomb potential near the end of the pulse though atoms are ionized almost completely within the first few half optical cycles. Therefore there is a high probability of the atom surviving after the pulse. We also check this process in the three-dimensional case and find that this kind of stabilization can still exist in three-dimensional atoms.

The effect of pulse temporal profiles on the Autler--Townes (AT) splitting in photoelectron spectra is theoretically studied by employing the time-dependent wave packet method for a rotational Na₂ molecule. The AT splitting which results from the sufficient Rabi oscillations is affected by the pulse profile and molecular alignment. The AT splitting may be observed only by utilizing proper pulse profiles with a certain intensity.

We propose a novel scheme to decelerate a cw precooled molecular beam by using an optical Stark decelerator, which is composed of a red-detuned cw semi-Gaussian beam. The dynamical process of the optical Stark deceleration for a cw methane molecular beam is studied by Monte Carlo simulations. It is realized that the proposed optical Stark decelerator can be used to continuously slow a cw methane molecular beam with a longitudinal temperature of 30mK, and a maximum reduction in the most probable speed of 0.388m/s (corresponding to a relative change of 9.93%) can be obtained by using a single semi-Gaussian beam with a power of 500W and a maximum central intensity of about 7.96×10⁷W/cm².

A theoretical model is established to simulate the penetration process of C₂₀ clusters in oxides (Al₂O₃, SiO₂) at different incident velocities. The induced spatial potential by the incident clusters is described by the dielectric response formalism, in which the Mermin-type dielectric function is adopted to provide a realistic evaluation of the electronic properties of the oxides. The charge distribution of individual ions is derived by using the Brandt--Kitagawa effective charge model, also under the consideration of the asymmetric influence from the wake potential. The stopping power of the clusters and the Coulomb explosion processes are derived by solving the motion equation of the individual ions, when taking into account the multiple scattering effect simulated by using the Monte Carlo method. It is found that the dynamical interaction potential between ions leads to a spatial asymmetry to the cluster structure and the charge distribution for high velocity clusters, and will not be in effect as the incident velocities decrease.

Using closed orbit theory, we study the influence of the two parallel metal surfaces on the recurrence spectra of a hydrogen atom placed in the region between the two surfaces. The results show that the metal surfaces have significant effect on the photoabsorption process. Each resonance peak in the recurrence spectra is associated with one electronic closed orbit. In our work, we put the first metal surface at the critical value d_c and vary the second metal surface. The results show that when the distances between the hydrogen atom and the two metal surfaces are close to the critical value d_c, the number of the closed orbits is the greatest and there are more peaks in the recurrence spectra. When the distance between the atom and the second metal surface is larger or smaller than d_c, the number of the closed orbits decreases and there are fewer peaks in the recurrence spectra. The agreement between the semiclassical alculation spectra and the quantum calculation spectra suggests that our analysis is correct.

The optical erasure dynamics in a batch-thermal fixing scheme of holographic storage in photorefractive crystals is investigated theoretically and experimentally. The inter-batch optical erasure time constant τ_F is introduced to specify the optical erasure to compensated gratings, and measured in a sophisticated experiment. The experimental result shows that τ_F is much longer than the intra-batch optical erasure time constant τ_E. The difference between τ_F and τ_E is fundamental for enhancing nonvolatile storage density.

A novel ridge-waveguide multisection (MS) distributed feedback (DFB) laser, which consists of two identical DFB sections but different ridge widths, is proposed to generate beating-type self-pulsations (SPs). The spatiotemporal dynamic response of such a multisection DFB laser is calculated based on a large-signal travelling-wave model. Self-pulsating output at about 150GHz is predicted, and evidences for the beating mechanism of the SPs are provided. To the best of our knowledge, this is the first report on SP generated by MS-DFB lasers with varied ridge width. Compared to other alternatives, such devices are much easier to implement and also enjoy the advantages of lower cost and higher design freedom.

Theoretical analysis and experimental measurement of pulse-width jitter of diode laser pulses are presented. The expression of pulse power spectra with all amplitude jitter, timing jitter and pulse-width jitter is deduced. The power spectra with and without pulse-width jitter are numerically simulated. The simulation results indicate that the pulse-width jitter will contribute considerably noise to the pulse power spectrum while the product of pulse width and angular frequency is larger than 1. The experimental measurement of pulse-width jitter of a gain-switched Fabry--Perot laser diode with 2.4GHz repetition rate is also reported. In comparison of the noise power spectra of the first, fourth and seventh harmonics of the pulse repetition rate, 2.3ps pulse-width jitter is obtained.

An edge emitting laser based on two-dimensional photonic crystal slabs is proposed. The device consists of a square lattice microcavity, which is composed of two structures with the same period but different radius of air-holes, and a waveguide. In the cavity, laser resonance in the inner structure benefits from not only the anomalous dispersion characteristic of the first band-edge at the M point in the first Brillouin-zone but also zero photon states in the outer structure. A line defect waveguide is introduced in the outer tructure for extracting photons from the inner cavity. Three-dimensional finite-difference time-domain simulations apparently show the in-plane laser output from the waveguide. The microcavity has an effective mode volume of about 3.2(λ/n_slab)³ for oscillation mode and the quality factor of the device including line defect waveguide is estimated to be as high as 1300.

A compact laser diode-pumped solid-state Nd:LuVO₄ acousto-optic Q-switched laser is demonstrated at 916nm of a quasi-three level for the first time. A pulse width of 130ns is observed when the pulse-repetition frequency is 10kHz. The laser experiment shows that the Nd:LuVO₄ crystal can be used for efficient diode-pumped Q-switched lasers.

Stimulated Raman scattering (SRS) of picosecond pulses is investigated in a new crystal SrWO₄. The second harmonic generation of a mode-locked Nd:YAG laser system is used as the pump source. In an external single-pass configuration, the SRS thresholds for the first to the fourth Stokes lines are measured. For the first Stokes line, the steady-state gain coefficient of the SrWO₄ crystal is calculated to be 15.96cm/GW. In our experiment, as many as five Stokes lines (559.23nm, 589.61nm, 623.49nm, 661.50nm, 704.44nm) and three anti-Stokes lines (506.97nm, 484.34nm, 463.65nm) are observed, and the total conversion efficiency is as high as 62%.

We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive--photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening-photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those
induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.

We solve the nonlinear Schrödinger equation with higher order terms, which describes the propagation of femtosecond pulses in optical fibres, by means of a direct perturbation method for dark solitons. An exact dark-soliton solution of the higher order nonlinear Schrödinger equation is found, provided that parameters satisfy certain conditions. The soliton’s velocity with the high order effects as well as the formula for calculation of the first-order correction representing the perturbation-induced radiative field is presented.

We report on transparent Ni²⁺-doped MgO-Al₂O₃-SiO₂ glass ceramics with broadband infrared luminescence. Ni²⁺-doped MgO-Al₂O₃-SiO₂ glass is prepared by using the conventional method. After heat treatment at high temperature, MgAl₂O₄ crystallites are precipitated, and their average size is about 4.3nm. No luminescence is detected in the as-prepared glass sample, while broadband infrared luminescence centred at around 1315nm with full width at half maximum (FWHM) of about 300nm is observed from the glass ceramics. The observed infrared emission could be attributed to the ³T_2g ( ³F) → ³A_2g ( ³F) transition of octahedral Ni²⁺ ions in the MgAl₂O₄ crystallites of the transparent glass ceramics. The product of the fluorescence lifetime and the stimulated emission cross section is about 1.6×10^-24s cm².

We perform a comprehensive experimental study on holographic and thermal-fixing characteristics of Zn:Fe:LiNbO₃. The measured hologram decay time constants, respectively caused by optical readout and under dark condition, with thermal fixing are 15 times and 75 times longer than that obtained without thermal fixing. This suggests that Zn:Fe:LiNbO₃ crystals are suitable for thermal fixing. Multiplexed recordings of 300 holograms using different thermal fixing schemes verify that a proper multiplexing scheme such as track-division thermal-fixing scheme for disc-type holographic storage can effectively compensate for the negative effect of zinc-doping on the dynamic range, thus the storage density is enhanced.

A cyanine dye, 2-[7-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3,5-heptatrienyl]-% 1,3,3-trimethyl-3H-indolium iodide (NK-125), is doped in 4-cyano-4’-pentylbiphenyl (5CB), and the mixture is sandwiched between two pieces of rubbed glass plates. The third-order nonlinear optical properties of the oriented NK-125-5CB layers are measured by the resonant femtosecond degenerate four-wave mixing (DFWM) technique at 760nm. The third-order nonlinear optical susceptibility of one of the present samples is 5.5×10^-8esu. The slow DFWM response of the NK-125-5CB layers due to a population grating is accelerated by the increasing laser power because of amplified spontaneous emission (ASE). On the other hand, we do not observe a similar phenomenon for NK-125-polyethylene glycol (PEG-400). Oriented NK-125 molecules in nematic liquid crystals must have very high ASE efficiency. Hence the population grating in a DFWM signal disappears within about 4ps. It is expected that NK-125-5CB can be used as a material for very fast all-optical switching.

A concrete two-dimensional photonic crystal slab with triangular lattice used as a mirror for the light at wavelength 1.3μm with a silicon-on-insulator (SOI) substrate is designed by the three-dimensional plane wave expansion method. For TE-like modes, the bandgap in the Γ-K direction is from 1087nm to 1559nm. The central wavelength in the bandgap is about 1.3μm, hence the incident light at wavelength 1.3μm will be strongly reflected. Experimentally, such a photonic crystal slab is fabricated on an SOI substrate by the combination of EBL and ICP etching. The measurement of its transmission characteristics shows the bandgap edge in a longer wavelength is about 1540nm. The little discrepancy between the experimental data and the theoretical values is mainly due to the size discrepancy of the fabricated air holes.

The mode-area scaling properties of helical-core optical fibres are numerically studied and the limit of core size for achievable single-mode operation is explored. By appropriate design, helical-core fibres can operate in a single mode with possible scaling up to 300μm in core diameter with numerical aperture 0.1.

A novel 1×2 multimode interference photonics switch structure based on thermal controlling effect is proposed. A ridge waveguide of photosensitive polymer, benzocyclobutene (BCB 4024-40) on silica clad is used as a design structure. A temperature changes as a result of electrode heating are analysed by employing a two-dimensional finite difference thermal model considering both conduction and convection mechanisms. The switching characteristics due to changes in effective index are analysed by the two-dimensional finite difference beam propagation method with transparent boundary condition. The proposed structure works well with low crosstalk level of -28dB and low switching power relatively to the structural upper cladding thickness.

Hybrid ZnO/ormosils films are prepared by the sol-gel method. A FT-IR spectrometer, 900UV/VIS/NIR spectrophotometer, atomic force microscope, and ellipsometer are employed to investigate microstructure and optical properties of the films fired at different temperatures. The results show that the films with high transmittance and low surface roughness could be obtained at the heat-treatment temperature of 150°C, the refractive index and thickness of the film are 1.413, 2.11μm, respectively. Higher temperatures (350°C, 550°C) change the film microstructure severely, and then decrease the transmittance of the films.

We investigate the elastic waves excited by an arbitrary plane piezoelectric source on the surface of a multilayered medium. Based on the previous studies, the 2D elastic wavefield in the multilayered medium is extended to 3D space. The propagator matrix for the 3D wavefield is investigated and the displacement-stress response for the boundary conditions is obtained. The excitation and propagation of the Rayleigh and Love waves are analysed further. It is found that the propagation velocity of the Rayleigh and Love waves does not depend on the propagation azimuth θ in the plane parallel to the free surface of the multilayered medium while the displacement is strongly dependent on the azimuth θ.

We present a theoretical model for acoustic nonlinearity measurement of dispersive specimens at high frequency. The nonlinear Khokhlov--Zabolotskaya--Kuznetsov (KZK) equation governs the nonlinear propagation in the SiO₂/specimen/SiO₂ multi-layer medium. The dispersion effect is considered in a special manner by introducing the frequency-dependant sound velocity in the KZK equation. Simple analytic solutions are derived by applying the superposition technique of Gaussian beams. The solutions are used to correct the diffraction and dispersion effects in the measurement of acoustic nonlinearity of cottonseed oil in the frequency range of 33--96MHz. Regarding two different ultrasonic devices, the accuracies of the easurements are improved to ±2.0% and ±1.3% in comparison with ±9.8% and ±2.9% obtained from the previous plane wave model.

We numerically investigate the quenched random directed sandpile models which are local, conservative and Abelian. A local flow balance between the outflow of grains during a single toppling at a site and the total number of grains flowing into the same site plays an important role when all the nearest-neighbouring sites of the above-mentioned site topple for once. The quenched model has the same critical exponents with the Abelian deterministic directed sandpile model when the local flow balance exists, otherwise the critical exponents of this quenched model and the annealed Abelian random directed sandpile model are the same. These results indicate that the presence or absence of this local flow balance determines the universality class of the Abelian directed sandpile model.

We investigate the characteristics of the transition from laminar to turbulent flow in the microtube with a diameter of 310μm. The microscopic particle image velocimetry is used to measure the water flow at Re=1600--2500 in the microtube. It is found that the flow transition occurs at Re=1600--1900, and the streamwise streaks and vortices appear in the transitional flow fields. These experimental observations provide a validation for the theoretical prediction of unstable travelling waves in pipe flow.

We propose a new model for the effective thermal conductivities of nanofluids, which is derived from the fact that nanoparticles and clusters coexist in the fluids. The effects of the compactness and the perfectness of the contact between nanoparticles in clusters on the effective thermal conductivity of nanofluids are analysed. The proposed model indicates that the effective thermal conductivity of nanofluids decreases with the increasing concentration of clusters. The model predictions are compared with and are in good agreement with the available experimental data.

A lattice Boltzmann model (LBM) has been developed for simulating magnetohydrodynamics (MHD) along the line of Dellar [J. Comput. Phys. 179(2002)95]. In this model the magnetic field is presented by a vector valued magnetic distribution function which obeys a vector Boltzmann equation. The truncated error of the equilibrium distribution in the present model is up to order O(u⁴) in velocity u rather than the usual O(u³). For verification, the model is applied to solve the shock tube problem and the main features of the flow predicted by the model are found to compare well with the corresponding results obtained with high-order semi-discrete schemes [J. Comput. Phys. 201(2004)261]. The numerical experiments have also shown that the present LBM model with the equilibrium distribution truncated at O(u⁴) performs much better in terms of numerical stability than those truncated at O(u³).

A novel atmospheric pressure plasma apparatus (APPA) is designed with a liquid electrode, and its discharging characteristics are studied. Relatively uniform and intense discharge can be realized in the APPA system. An experimental study on removal of NO molecules is carried out by using the APPA, and more than 95.5% of NO is decomposed when the NO initial concentration is lower than 400ppm. Removal of NO efficiency increases rapidly with the increasing discharge power. Compared with the absence of O₂, more NO₂ is generated with the increase of O₂ concentration. However, most of the NO molecules are decomposed to N₂ and O₂ directly, when O₂ concentration changes from 0 to 1.1vol%.

The glass transition process of argon is studied by molecular dynamics simulations with Lennard-Jones potential. The cage effect appears at about 24K. The Lindemann length of argon is found to be 0.55Å. Two relaxation processes are clearly observed near the glass transition temperature, which is in agreement with the mode-coupling theory.

We report on stacking fault (SF) detection in free-standing cubic-SiC epilayer by the Raman measurements. The epilayer with enhanced SFs is heteroepitaxially grown by low pressure chemical vapour deposition on a Si(100) substrate and is released in KOH solution by micromechanical manufacture, on which the Raman measurements are performed in a back scattering geometry. The TO line of the Raman spectra is considerably broadened and distorted. We discuss the influence of SFs on the intensity profiles of TO mode by comparing our experimental data with the simulated results based on the Raman bond polarizability (BP) model in the framework of linear-chain concept. Good agreement with respect to the linewidth and disorder-induced peak shift is found by assuming the mean distance of the SFs to be 11Å in the BP model.

ZrC/ZrB₂ multilayered coatings with bilayer periods of 3.5--40nm are synthesized by rf magnetron sputtering. Analyses of x-ray diffraction, scanning electron microscopy and nanoindentation indicate that multilayered coatings possess much higher hardness and greater fracture resistance than monolithic ZrC and ZrB₂ coatings. A maximum hardness (41.7GPa) and a critical fracture load (73.7mN) are observed in the multilayer with La=32nm deposited at the substrate bias -40V. Higher residual stress built in the ZrC layer can be released by periodic insertion of ZrB₂ into the ZrC layer. A clear multilayered structure with mixed ZrB₂ (001), ZrB₂ (002) and ZrC (111) orientations should be responsible for the enhanced mechanical properties.

The solid--liquid interface motion of NaBi(WO₄)₂ (NBWO) melt crystal growth is observed in an in situ system, in which the whole processes of interface transition from flat interface and cellular to dendrite are visualized. The spacing of the dendrite under smaller temperature gradient turns out to be larger than that under larger temperature gradient, which is found to be sensitive to the temperature distribution. The mechanism of dendrite growth of NBWO is studied based on the model of the growth units of anion coordination polyhedra. The {001} face has two apex links, so it shows higher stability and has high growth rate and forms the arm of dendrite, whereas the {010} face has only one apex link, and thus shows relative slower growth rate and firstly forms the branches.

The elastic constants of the B1 structure NaCl under pressure are obtained by using the ab initio plane-wave pseudopotential density functional theory method. The obtained zero pressure lattice constant and elastic constants are in good agreement with the available experimental data. It is found that the elastic constants C₁₁ and C₁₂ and the bulk modulus B increase monotonically with pressure P, however C₄₄ increases monotonically when P≤28GPa and decreases when P>28GPa. Moreover, we discuss the B1-B2 structure phase transition of NaCl and obtain the transition pressure of 28.3GPa.

Planar polymer multi-model waveguides doped with Ag nano-particles and rhodamine B are fabricated and investigated by the spectroscopy analysis method as well as the M-line method. Experimental results shown that fluorescence enhancement occurs when excited by a wide band wavelength with Ag nano-particle concentration at a certain level. The maximum enhancement factor in our experiment is obtained to be about 3.8 when excited by 350nm. Our study may have potential applications in polymers optical elements, such as polymer waveguide lasers and amplifiers.

The magnetic field dependent transport behaviour of Co contacted multi-wall nanotubes is investigated. A sample with three Co electrodes has been measured by two-channel method with an in-plane magnetic field. When the in-plane magnetic field is perpendicular to the tube, high positive magnetoresistance up to 30% is btained at low temperature from 3K to 25K and with field parallel to the tube, negative magnetoresistance up to 15% is observed only from the high resistance junction. The detailed positive and negative magnetoresistance behaviour also changes with temperature.

Heavily boron-doped thick diamond films with higher superconducting transition temperatures have been prepared by electron assisted chemical vapour deposition method. The results of scanning electron microscopy, Raman spectroscopy, x-ray diffraction, and Hall effect indicate that the films have nice crystalline facets, a notable decrease in the growth rate, and an increase in the tensile stress. Meanwhile, the film resistivity decreases with the increase of the carrier concentration. Our measurements show that the films with 4.88×10²⁰cm^-3 and 1.61×10²¹cm^-3 carrier concentration have superconductivity, with onset temperatures of 9.7K (8.9K for zero resistance) and 7.8K (6.1K for zero resistance), respectively.

One- and two-photon absorption and excited fluorescence of the CdSe and the core-shell structure CdSe/ZnS quantum dots (QDs) in n-hexane is investigated. The linear and nonlinear absorption coefficients are measured and the two-photon-absorption cross sections of the QDs are also obtained. For both one-photon fluorescence and two-photon fluorescence, the emission efficiency of CdSe/ZnS is much higher than that of CdSe, originating from the effective surface passivation of the core-shell structure.

The elastic properties and electronic structure of B2 phase binary TiM (M=Fe, Co, Ni, Pd, Pt and Au) and ternary Ti₅₀Ni_43.75Pd_6.25, Ti₅₀Ni_43.75Cu_6.25 shape memory alloys are studied by the plane-wave psedudopotential method within the local density approximation. The elastic constants and density of states are calculated. Our calculations show that the martensitic transformation behaviour of these alloys is closely related to their elastic properties. The Ti d DOS at the Fermi level is mainly
responsible for the B2 phase stability of these alloys.

We simulate the THz radiation’s time domain waveforms of both the near field and the far field of a GaAs large aperture photoconductive antenna based on the current surge model. Because the micro-kinetic factors, such as transient state changes of current carrier’s mobility and lifetime of current carriers, are taken into account in the calculation, we find out the influences of these factors on the THz radiation intensity by changing the above parameters. The results are of guiding significance to design of high-power photoconductive THz radiation antenna materials.

We propose a heterogeneous agent herding model, in which the agent clusters are in active or inactive states. When agent clusters are in active states, they tend to buy or sell. In active states, an exchange may occur when two heterogeneous agent clusters encounter each other, and they may merge into a bigger one when two homogeneous agent clusters meet. The ratio of successful exchange or merging depends on two parameters: i.e. the reliability k, reflecting the credible degree in the interacting agent clusters, being the space effect of the market, and the response degree q, reflecting the influence of the former trading to the current action, being the time effect of the market. Our numerical calculation shows that the dynamics of the model exhibits some behaviour very close to real markets when tuning the reliability and the degree of reaction to some specific values.

We investigate a spatial Prisoner’s Dilemma game with nonlinear attractive effect on regular small-world networks. The players located on the sites of networks can either cooperate with their neighbours or defect. In every generation, each player updates its strategy by firstly choosing one of the neighbours with a probability proportional to A^α denoting the attractiveness of the neighbour, where A¹ is the collected payoff and α (≥0) is a free parameter characterizing the extent of nonlinear effect. Then each player adopts its strategy with a probability dependent on their payoff difference. Using Monte Carlo simulations, we investigate the density ρ_C of cooperators in the stationary state for various values of α and the rewiring probability q of the network. It is shown that the introduction of such attractive effect remarkably promotes the emergence and persistence of cooperation over a wide range of the temptation to defect for the same network structures. We also point out that long-range connections either enhance or inhibit the cooperation, which depends on the value of α and the payoff parameter b.

Using a special solution of the Euler equation, the relation between the position of the typhoon centre and the induced flow (background wind) is found. The relation can be used to predict the typhoon track. The prediction of the track for No 1 tropical cyclone, CHANCHU, is concretely provided.

We re-study the one-dimensional electric field structure of an outer gap accelerator by considering the physical limit of trans-field height. Inside the outer gap, the charge depletion creates a large electric
field along the magnetic field lines. Electrons and/or positrons are accelerated to ultra-relativistic energies by this longitudinal electric field, and then radiate γ-ray photons by curvature radiation. The collision of these γ-rays and ambient x-ray photons further produce radiating particles, resulting in a stationary gap. We solve the structure of this longitudinal electric field together with the distributions of electrons and positrons and γ-ray photons for an aligned rotator. Our results indicate that the outer gap can extend to the light cylinder using reasonable parameters.