The exact homoclinic orbits and periodic soliton solution for the Boussinesq equation are shown. The equilibrium solution u₀=-1/6 is a unique bifurcation point. The homoclinic orbits and solitons will be interchanged with the solution varying from one side of -1/6 to the other side. The solution structure can be understood in general.

Linear thermal expansion coefficient (TEC) of Ti bulk is investigated by means of molecular dynamics simulation. The elastic minimum image convention of periodic boundary conditions is introduced to allow the bulk to adjust its size according to the new fixed temperature. The TEC and the specific heat of Ti are compared to the available theoretical and experimental data.

We propose the concept of the quantum generalized subspace projector measurement (QGSPM). The distinguished properties of QGSPM is revealed: no matter what the state of the system is prior to the measurement and what the measured result occurs, the state posterior to the measurement can be collapsed onto the specified subspace. Subsequently, the quantum generalized case-projector measurement (QGCPM), as a special case of QGSPM, is also discussed carefully. It is demonstrated that no matter what measured result occurs, the state of the system posterior to QGCPM can be collapsed into one of pure states. Consequently, QGCPM can be used to generate the maximally entangled pure states for multiple particles. As illustrative examples, several concrete methods of generating entanglement are proposed for two two-level particles. It is found that the maximally entangled pure states of two 2-level particles can be generated just by a single QGCPM and the corresponding QGCPM operators are physically realizable in principle if an ancillary four-dimensional quantum system can be introduced.

Unambiguous quantum state filtering is applied to evaluation of the decoherence sensing of entangled quantum channels consisting of N-mode entangled coherent states. It is found that quantum entanglement can enhance the performance of decoherence sensing while the increase of the mode numbers in the entangled probe field can slightly improve the sensing performance only in the weak field regime.

An efficient quantum secure direct communication network protocol with the two-step scheme is proposed by using the Einstein--Podolsky--Rosen (EPR) pair block as the quantum information carrier. The server, say Alice, prepares and measures the EPR pairs in the quantum communication and the users perform the four local unitary operations to encode their message. Anyone of the legitimate users can communicate another one on the network securely. Since almost all of the instances in this scheme are useful and each EPR pair can carry two bits of information, the efficiency for qubits and the source capacity both approach the maximal values.

An efficient multiparty quantum secret sharing scheme is proposed with Greenberger--Horne--Zeilinger (GHZ) states following some ideas in quantum dense coding. The agents take the single-photon measurements on the photons received for eavesdropping check and exploit the four local unitary operations I, σ_z, σ_x and iσ_y to code their message. This scheme has the advantage of high capacity as each GHZ state can carry two bits of information. The parties do not need to announce the measuring bases for almost all the photons, which will reduce the classical information exchanged largely. The intrinsic efficiency for qubits and the total efficiency both approach the maximal values.

Under the enlightenment of the scheme of Mancini and Bose [Phys. Rev. A 70(2004)022307), we discuss two-atom entanglement in a fibre-connected triple-distant-atom system. Under adiabatic approximation, we obtain an effective Hamiltonian in form of the triple-body Ising-model interaction. The existence of a third atom is found to damage the other two-atom entanglement. The nearest-neighbouring two atoms that share a larger Ising strength are more strongly entangled.

In accordance with the holographic principle, by counting the states of the scalar field just at the event horizon of the Vaidya--Bonner black hole, the holographic entropy bound of the black hole is calculated and the Bekenstein--Hawking formula is obtained. With the generalized uncertainty principle, the divergence of state density at event horizon in the ordinary quantum field theory is removed．With the residue theorem, the integral trouble in the calculation is overcome. The present result is quantitatively tenable and the holographic principle is realized by applying the quantum field theory to the black hole entropy problem. Compared with some previous works, it is suggested that the quantum states contributing to black hole entropy should be restricted on the event horizon.

We investigate the first law of thermodynamics in the case of the (2+1)-dimensional Banados--Teitelboim--Zanelli black holes and Kerr--de Sitter spacetimes. In particular, we focus on the integral mass formulas. It is found that by assuming the cosmological constant as a variable state parameter, both the differential and integral mass formulas of the first law of black hole thermodynamics in the asymptotic flat spacetimes can be directly extended to those of rotating black holes in anti-de Sitter and de Sitter backgrounds. It should be pointed that these formulae come into existence in any dimensions.

Drawbacks of the ingoing Eddington--Finkelstein coordinates in describing the quantum thermal properties of the evaporating Vaidya black hole are presented. A new coordinate system we proposed previously [Acta Phys. Sin. 46(1997)1273] is employed. In this new coordinate system, the thermal radiation temperature of the Vaidya black hole is discussed again with the back reaction method.

Quantum gravity can modify the usual energy--momentum dispersion relation. We provide evidence for the argument that the modified dispersion relation is constrained by the black hole thermodynamics, for consistency of quantum gravity.

The quantum well (QW) semiconductor lasers have become main optical sources for optical fibre communication systems because of their higher modulation speed, broader modulation bandwidth and better temperature characteristics. In order to improve the quality of direct-modulation by means of the stochastic resonance (SR) mechanism in QW semiconductor lasers, we investigate the behaviour of the SR in direct-modulated QW semiconductor laser systems. Considering the cross-correlated carrier noise and photon noise, we calculate the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated laser system by using the linear approximation method. The results indicate that the SR always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient of the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity.

Information transmission is studied in the cases of amplitude and frequency modulations where there is an impulsive jamming in the signal. By using the array approach of nonlinear elements, we find that for both the periodic and aperiodic modulations, the information transmission can be enhanced by adding independent external noise on every element of the array. The dependence of information transmission on the size of array and the impulsive interval of the jamming are also studied.

A bailout embedding method for controlling chaos can make the chaotic orbits targeting into Kolmogorov--Arnold--Moser orbits. We apply this method to a high-dimensional system with two coupled standard maps. The numerical simulation shows that this method could obtain target islands in order and hence could be used to control chaos. Moreover, it is robust in the presence of weak external noise.

We study the complete synchronization between different systems. Based on our new idea about structure adaptation, a new synchronized method, i.e. the structure adaptive method, is proposed. We believe that this self-adaptive mechanism correctly represents essential characteristics of self-adaptation in complex systems. We also show that this method is reasonable both from the coupling viewpoint in physics and from the controller design viewpoint in control theory.

We study the energy levels of the hydrogen atom in the noncommutative phase space with simultaneous space--space and momentum--momentum noncommutative relations. We find new terms compared to the case that only noncommutative space--space relations are assumed. We also present some comments on a previous paper [Alavi S A hep-th/0501215].

We consider that the observable cosmological constant is the sum of the vacuum (Λ_vac) and the induced term (Λ_ind-3m²/4) with m being the ultra-light masses ($\ap$ Hubble parameter) implemented in the theory from supergravities arguments and non-minimal coupling. In the absence of a scalar buildup of matter fields, we study its effects on spontaneous symmetry breaking with a Higgs potential and show how the presence of the ultra-light masses yields some important consequences for the early universe and new constraints on the Higgs and electroweak gauge bosons masses.

Within the framework of the low-energy effective theory arising from the instanton vacuum model of QCD, the longitudinal virtual photon light-cone wavefunction, Ф_γ||(u,P²), corresponding to the nonlocal quark--antiquark vector current is calculated at the low-energy scale. The coupling constant, F_γ(P²) or equivalently f_γ(P²), of the quark--antiquark vector current to the virtual photon state is also obtained by imposing the normalization condition to the photon wavefunction. The behaviour of the coupling constant as well as the obtained photon wavefunction is discussed.

To study chemical equilibrium of hadronic matter created in relativistic heavy ion collisions, phase shifts for the I=2ππ elastic scattering and cross sections for the I=2 and 0ππ←→ρρ and I=0 ππ←→ωω reactions are calculated with the prior and post forms. While the post--prior equivalence holds for the elastic scattering, the post--prior discrepancy of the inelastic scatterings relies on the spin-dependent terms of quark-antiquark potential.

We propose an inverse idea of controlling the evolution of the population inversion by a time-dependent coupling between the cavity field and a two-level system described through the Jaynes--Cummings model. We demonstrate the detailed procedure by obtaining the population evolution taking the non-sinusoidal form, which is different from the previous sinusoidal Rabi oscillation as the cavity field frequency and coupling parameters are constant during the interaction time.

Following a previous systematic theoretical study of the ground-state properties of over 7000 nuclei from the proton drip line to the neutron drip line in the relativistic mean field model [Prog. Theor. Phys. 113(2005)785], which is in fair agreement with existing experimental data, we observe a few spurious shell closures, i.e. proton shell closures at Z=58 and Z=92. These spurious shell closures are found to persist in all the effective forces of the relativistic mean field model, e.g. TMA, NL3, PKDD and DD-ME2.

The exotic structures of the ground state of the mirror nuclei ¹⁷Ne and ¹⁷N are investigated by means of the asymptotic normalization coefficient (ANC) method to explore the role of the Coulomb interaction. The probabilities of a valence nucleon outside the binding-potential are P=56.69±_7.46^2.98% for ¹⁷Ne and P=45.51±_5.81^2.32% for ¹⁷N. The rms radii are (r²)^1/2=5.06±_0.30^0.11fm and (r²) ^1/2=4.24±_0.16^0.06fm, respectively. The results obtained are nearly independent of the potential parameters. According to the halo occurrence conditions, it is suggested that ¹⁷Ne is a two-proton halo and ¹⁷N is a two-neutron skin. Moreover, two effects of the Coulomb interaction on the exotic structure are analysed. From the present results, the exotic structure of the nucleus in the proton-rich side is more obvious than that of its mirror nucleus because of the Coulomb interaction.

The angular distributions of elastic scattering for the ⁶Li +²⁰⁸Pb system have been measured at several energies around the Coulomb barrier. The parameters of optical potential are extracted by means of a phenomenological optical model analysis. It is found that the real and imaginal potentials show a pronounced energy dependence. The behaviour of the potential at the nearly especially sub-barrier energies in the ⁶Li+²⁰⁸Pb system is quite different from the results of some previous reports observed in other systems, such as ¹⁹F+²⁰⁸Pb and ¹⁶O+²⁰⁸Pb. This unusual threshold phenomenon indicates that breakup channel is strongly coupled with the elastic channel and has obvious effects on optical potential.

Recently, two papers presented by Ortigoso et al. [Phys. Rev. Lett. 93 (2004) 073001 and Phys. Rev. A 72 (2005) 053401] develop a novel strategy in which the best sustainable molecular alignment/orientation has been achieved. We intend to analyse the dynamic mechanisms, including those Ortigoso et al. have not clarified.

We present a four-state model for calculating the two-photon absorption of multi-branched molecules by using the time-depended function method. The numerical results indicate that the two-photon absorption cross section has a strong enhancement for three-branch molecules compared to two-branch structures. The maximal two-photon-absorption cross section is 2.358×10^-47cm⁴s/photon. At the same time, the charge-transfer process for the charge-transfer states is visualized in order to explain mechanism about the maximal TPA cross section.

The binding energy spectrum of all valence orbitals and the momentum distributions of highest occupied molecular orbital (HOMO: 8a_g, 7b_u+7a_g, 4b_u, 2b_g+4a_g and 2a_u in 1, 4-dioxane are investigated by electron momentum spectroscopy (EMS) with 600eV impact energy. The experimental results are consistent with theoretical calculations of C_2h chair conformation using the Hartree--Fock method and density functional theory with 6-311++G and AUG-CC-PVTZ basis sets.

The ionization process in the collisions of He²⁺ with C^q+ (q=0--5) is investigated by using the continuum-distorted-wave eikonal-initial-state approximation. Double-differential cross sections for 1s and 2s sub-shells are obtained at the electron-ejected angle θ= 0° with the projectile energy ranging from 30keV/u to 10MeV/u. Variation of ionization mechanisms with q in C^q+ is studied, and the dependences on the projectile energies and target sub-shells are also discussed. It is found that in the whole energy range, the absolute values of soft collision (SC) and binary encounter (BE) peaks decrease with increasing q. For the lower incident energies, the electron capture to the projectile continuum (ECC) peak decrease with increasing q as well as SC and BE peaks. For the higher incident energies ( >1 MeV/u), the absolute value of ECC peak increases with increasing q, so that the crossings of cross sections appear for C^q+ with different q. This can be explained by the matching of velocities between the projectile and the electron initially bound to the target.

The state selection and beam focus of linear triatomic molecules (OCS, HCN, ClCN, BrCN and ICN) with doubling states in a hexapole electric field have been numerically realized. The method is based on a quantum mechanical treatment of the molecular Stark energy and a classical mechanical treatment for the molecular trajectory in the field. In linear molecules with doubling states, the second-order Stark effect can be neglected and the doubling states have the same value of J and M. The influences of the molecular properties, state energies, and the apparatus parameters such as molecular beam temperature and length of the hexapole, on the role of state selection and focus have been discussed. The method established here can be taken as a guide for hexapole experiment of orientation of polar molecules.

Different cross sections for the elastic scattering of electrons by N₂ at impact energies of 10, 15, 20, 30, 40eV have been calculated and compared with the experimental data and other theoretical results. The present results are obtained by the momentum space coupled channels optical method. In this method, the e--molecule system has a single centre and the interaction of e--nuclei is expanded by a multipole expansion.

We experimentally study energy-pooling collision in the Rb--Cs vapour mixture at low densities in a cell. Atoms are excited to Rb(5P_1/2) and Cs(6P_3/2) states using two single-mode diode lasers. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique is adopted. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to Rb(5P_1/2 → 7S_1/2) and Cs(6P_3/2 → 8S_1/2) transitions, respectively, which could be translated parallel to the pump beams. The excited atom densities are combined with the measured fluorescence ratios to determine cross section for the energy-pooling process [i.e. Rb(5P_1/2) +Cs (6P_3/2) → Cs(8S_3/2)+Rb (5S_1/2)]. The cross section is 3.79×10^-14cm² ± 45%.

We study the dynamics of spin autocorrelation function and the non-equilibrium decay of magnetization in the Griffiths phase of randomly site diluted Ising magnetic systems by Monte Carlo simulation. The results show that the relaxations are non-exponential for both two- and three-dimensional diluted Ising magnetic systems. At a long timescale, the asymptotic dynamics of the spin autocorrelation function C(t) behaves in the form of C(t) ～ exp{-A(ln t)^d/d-1}, expected by the theoretical prediction based on clustering arguments. Furthermore we show that the evolution of the spin autocorrelation function satisfies rather well a stretched exponential form of C(t) ～ exp{-(t/t)^β} even at quite small timescales.

According to the vectorial structure of non-paraxial electromagnetic beams and the method of stationary phase, the analytical TE and TM terms of non-paraxial linearly polarized Gaussian beam are presented in the far field. The influence of linearly polarized angle on the relative energy flux distributions of the whole beam and its TE and TM terms is studied. The beam spot of the TE term is perpendicular to the direction of linearly polarized angle, while that of the TM term coincides with the direction of linearly polarized angle. The whole beam spot is elliptical, and the long axis is located at the direction of linearly polarized angle. The relative energy flux distribution of the TE term is relatively centralized in the direction perpendicular to the linearly polarized angle. While that of the TM term is relatively centralized in the direction of linearly polarized angle. To obtain the isolated TM and TE terms, a polarizer should be put at the long and the short axis of the whole beam spot, respectively.

We study the nonlinear effects in the quantum states transfer technique from photons to matter waves in the three-level case, which may provide the formation of a soliton atom laser with nonclassical atoms. The validity of quantum transfer mechanism is confirmed in the presence of the intrinsic nonlinear atomic interactions. The accompanied frequency chirp effect is shown to have no influence on the grey solitons formed by the output atom laser and the possible quantum depletion effect is also briefly discussed.

Optical feedback characteristics in He--Ne dual frequency lasers are studied systematically in different feedback power ratios with a variable attenuator. Feedback power ratios vary from 0.010 up to 0.998. Five distinct regimes of self-interference effects are found and defined as regimes I, II, III, IV and V. Accordingly, five optical feedback levels have been put forward in He--Ne dual frequency lasers. Strong mode competitions are observed in regimes III and IV. In regime V, multiple feedback effects are investigated. The basic theoretical analysis is also presented. Our results can advance the research of self-mixing interferometer and displacement sensor of He--Ne orthogonally polarized dual frequency lasers.

We report the compact diode-pumped continuous-wave (CW) Nd:LuVO₄ lasers operated at 916nm and 458nm for the first time. The maximum output power of 780mW at 916nm laser is obtained with a slope efficiency of 9.3%. We generate 50mW of 458nm blue laser employing a type-I critical phase-matched LBO crystal.

A laser-diode-pumped 1.54-μm passive Q-switched erbium doped glass laser was reported. We utilize a laser diode with wavelength of 973nm to pump a 1-mm Er/Yb co-doped phosphate glass with the erbium and ytterbium concentrations of 1wt.% and 21wt.%, respectively. A Co²⁺:MgAl₂O₄ slab crystal was used as a passive Q-switcher. Q-switched pulses with repetition frequency of 800Hz, width of 7.4ns, peak power of 2.2kW and average power of 13.3mW were obtained when absorbed pump power was 475mW. A sandwich structure of the Q-switched microchip Er/Yb glass laser was demonstrated, which shows shorter pulse width of 6.8ns. Dependences of pulse duration and repetition frequency on pump power were also investigated.

We have experimentally demonstrated pulses 0.4mJ in duration smaller than 12fs with an excellent spatial beam profile by self-guided propagation in argon. The original 52fs pulses from the chirped pulsed amplification laser system are first precompressed to 32fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12fs.

We report a microstructure-fibre-based parametric amplification experiment in telecom band with ultra-high gain slope. A peak on-off gain of 52.3dB is achieved using 25m high nonlinear microstructure fibre (MF) and only 5.3W pump power. The parametric gain slope is up to 580dBW^-1km^-1. From the experimental data, the linear coefficient of the MF is estimated to be about 66.7W^-1km^-1. The experiment shows the great potential of MFs in practical fibre parametric amplifiers.

We study a femtosecond Ti:sapphire laser pumped optical parametric amplifier (OPA) at 1053nm. The OPA generates stable signal pulses with duration smaller than 100fs, wavelength drift smaller than 0.5nm, and pulse-to-pulse fluctuation of about ±4%, by employing an external seeder. In a terawatt laser pumped large-aperture LiNbO₃ OPA, pulse energy at signal has been scaled up to 4mJ. This mJ-class femtosecond OPA at 1053nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.

The directional light emission from a single subwavelength slit surrounded by periodic grooves in layered films consisting of Ag and transparent dielectric is analysed numerically by the finite difference time domain method. The results show that the transmission through this structure is strongly confined by the modulation of the dielectric film with grooves on the output side. The role of evanescent waves in this phenomenon is discussed. It is the re-diffraction of the evanescent waves (that are generated by the diffraction of the subwavelength slit) caused by the grooves on the dielectric film that leads to the directional transmission. Some suggestions are given to obtain beaming light with high transmittance.

An optical microelectromechanical-system (MEMS) pressure sensor based on multi-layer circular diaphragm is described and analysed by using the proposed novel analytical approach and the traditional transfer matrix method. The analytical expressions of the deflection of multi-layer diaphragm and absolute optical reflectance are derived respectively. The influence of residual stress on the deflection of diaphragm is also analysed. Simulation results given by the finite element method are consistent with the ones which are analysed by using the analytical approach. The analytical approach will be helpful to design and fabricate the optical MEMS pressure sensors with multi-layer diaphragm based on Fabry--Perot interferometry.

We develop a fast microwave-induced thermoacoustic tomography system based on a 320-element phase-controlled focus linear transducer array. A 1.2-GHz microwave generator transmits microwave with a pulse width of 0.5μs and an incident energy density of 0.45mJ/cm², and the microwave energy is delivered by a rectangular waveguide with a cross section of (80.01±0.02)×10^-4m². Compared to single transducer collection, the system with the multi-element linear transducer array can eliminate the mechanical rotation of the transducer, hence can effectively reduce the image blurring and improve the image resolution. Using a phase-controlled focus technique to collect thermoacoustic signals, the data need not be averaged because of a high signal-to-noise ratio, resulting in a total data acquisition time of less than 5s. The system thus provides a rapid and reliable approach to thermoacoustic imaging, which can potentially be developed as a powerful diagnostic tool for early-stage breast caners.

The spectral, angular and polarization characteristics of thermal radiation from plane-parallel Si films are studied experimentally. Pronounced spectral and angular peaks demonstrate the presence of thermal radiation coherence. Two kinds of multilayer films are designed to obtain favourable radiant properties. The ZrO₂--Ge--ZnS film has a broad anti-reflection band in the wavelength range from 3.5μm to 8μm. The spectral and angular emissivities of the MgF₂--ZnS--Ge--Al film are tremendously enhanced compared with those of an uncoated aluminium film. This can be helpful to the design of elements that generate controlled thermal radiation.

We mainly focus on the study of precipitating cloud merging associated with vortex merging. The vortex and precipitating cloud merging are simulated by the cloud resolving model from 0000 21 to 1800 23 July 2003. The results show that the model well simulates vortex circulation associated with precipitating clouds. It is also proven that the vortex merging follows the precipitating cloud merging although vortices show the spatial and temporal differences. The convection vorticity vector is introduced to describe the merging processes. Two merging cases are identified during the 42-h simulation and are studied.

We propose a simple model for turbulent contribution to the frictional drag in a wall-bounded turbulent flow based on the characteristic parameters of turbulent bursting events. It is verified on water and drag-reducing surfactant solution flows investigated by particle image velocimetry in experiments. It is obtained that the turbulent contribution to the skin friction factor is linearly proportional to the product of the spatial frequency and strength of turbulent bursts originated from the wall.

The gas flow characteristics for various shapes of micro diffuser/nozzles have been experimentally investigated. The micro diffuser/nozzles with the lengths of 70μm, 90μm, 125μm and the taper angles of 7°, 10°, 14° are designed and fabricated based on silicon micromachining technology for optimizing and comparing. The flat-wall diffuser/nozzle is 40μm × 5μm in depth and width. An experimental setup is designed to measure the gas flow rates under controlled temperature and pressure condition. Optimized values for the taper angle and the length of the diffuser/nozzle are experimentally obtained.

The non-uniform argon dc glow discharge plasma system has been constructed in a very special design to investigate the effects of variable tube radius on plasma parameters. By using isolated computer controlled three couples of a double probe (TCDP) system, the electron temperature, electron density, the reduced electric field, and electron drift velocity are measured at low and intermediate pressures. It is shown that the electron temperature and reduced electric field (density) decreases (increases) as the radius decreases, at low discharge current and pressures. For large radius regions, at high discharge currents and pressures, the behaviour of the plasma parameters of specially reduced electric field change similarly to those in a uniform discharge system.

The finite-difference-time-domain method is applied to simulate the two-dimensional propagation of a p- polarization mode electromagnetic wave in atmospheric plasma and metal layer for strong electron--neutral collisions. It is indicated that for a giving electron density profile, the p-polarization attenuation is very different from the s-polarization attenuation and it depends even strongly on the incident angle. The mechanism of p-polarization attenuation is analysed by the interference of wave and the relationship between the attenuation property and the main parameters is given.

A new method named the magnetic glow-arc plasma source ion implantation (MGA-PSII) is proposed for inner surface modification of tubes. In MGA-PSII, under the control of an axial magnetic field, which is generated by an electric coil around the tube sample, glow arc plasma moves spirally into the tube from its two ends. A negative voltage applied on the tube realized its inner surface implantation. Titanium nitride (TiN) films are prepared on the inner surface of a stainless steel tube in diameter 90mm and length 600mm. Hardness tests show that the hardness at the tube centre is up to 20GPa. XRD, XPS and AES analyses demonstrate that good quality of TiN films can be achieved.

Crystal structure, electrical properties and Raman spectra of BaBi_1-xPb_xO₃ are reported. The result of x-ray diffraction shows that the specimen is pure, and the lattice parameters decrease continuously in the semiconducting range, whereas it vibrates similarly to a sine wave in the superconducting range, which is ascribed to the existence of oxygen vacancies and the function of breathing modes of Bi(Pb)O₆. The temperature dependence of resistivity indicates that the electrical property of the samples is connected sensitively with the crystal structures. Raman spectra show that the specimen becomes disorder when x increases, and the critical temperature T_C depends not only on the deformation potential of the soft A_lg mode derived from the Bi(Pb)O₆ rigid rotation, but also on the energy shift of the mode.

The crystal structure and electric properties of BaTiO₃ nanocrystals are studied by in situ high-pressure synchrotron radiation x-ray powder diffraction. The phase transition takes place not only in the samples of BaTiO₃ nanocrystals that are tetragonal phase with grain sizes more than 100nm, but also in the samples of BaTiO₃ nanocrystals that are cubic phase with grain sizes less than 100nm. The pressures of phase transition are found to increase with decrease of the grain size from about 4 to 10GPa for crystallites ranging from 200 to 10nm in radius. The bulk moduli are calculated according to Birch--Murnaghan state equation before and after the phase transition.

Similarity in the electron diffraction patterns of the Cd_5.7Yb icosahedral quasicrystal and its cubic approximant Cd₆Yb crystal is studied in detail by using transmission electron microscopy. The icosahedral twofold axes are parallel to the cubic <1ττ²> (τ=1.618...) or < 001> directions, the icosahedral pseudo-twofold axes are parallel to the cubic <15 21 25> directions, the icosahedral threefold axes are parallel to the cubic <111> and the icosahedral fivefold are parallel to the cubic <0.1τ> directions. Based on those observations a general stereographic projection is given to illustrate the exact orientation relationship.

We investigate mosaic structure evolution of GaN films annealed for a long time at 800°C grown on sapphire substrates by metalorganic chemical vapour deposition by high-resolution x-ray diffraction. The result show that residual stress in GaN films is relaxed by generating edge-type threading dislocations (TDs) instead of screw-type TDs. Compared to as-grown GaN films, the annealed ones have larger mean twist angles corresponding to higher density of edge-type TDs but smaller mean tilt angles corresponding to lower density of screw-type TDs films. Due to the increased edge-type TD density, the lateral coherence lengths of the annealed GaN films also decrease. The results obtained from chemical etching experiment and grazing-incidence x-ray diffraction (GIXRD) also support the proposed structure evolution.

Using the molecular dynamics method, the stability of small He-vacancy clusters is studied under the condition of the high He and low vacancy densities. The result shows that there is a competition between He atoms detrapped and self-interstitial atoms (SIAs) emitted during the clustering of He atoms. When the He number is above a critical value of 9, the SIA emission is predominant. The SIA emission can result in deep capture of He atoms since the binding energy of He to a He-vacancy cluster is increased with the number of SIAs created. The cluster thus grows up. In addition, more SIAs are created when the temperature is elevated. The average volume of a He atom is increased. The cluster expansion takes place at high temperature.

The sound velocities along the release path of annealed LY12-Al are measured by using a velocity interferometer system for any reflector (VISAR) technique. The shear modulus and yield strength are then obtained. Comparison of the experimental results with those of unannealed LY12-Al shows that anneal has little influence on sound velocities and shear modulus though it weakens the yield strength considerably, and changes the dependence of yield strength upon shock stress. The ratio of shear modulus to yield strength of unannealed LY12-Al increases with shock stress monotonically while that of annealed LY12-Al exhibits much more complicated behaviour.

Growth dynamics of epitaxial (Ba,Sr)TiO₃ thin films deposited at different temperatures on SrRuO₃/SrTiO₃ substrates by pulsed laser deposition is investigated by transmission electron microscopy. The films exhibit a layered structure comprising sublayers with distinctive features in regard to the remaining strain, density of misfit dislocations and/or lattice defects, and growth habit. We correlate these temperature-dependent features with the predominant misfit-strain relaxation mechanisms for each one of the detected growth regimes. The thickness dependence of the film structure is discussed within the framework of the predictions for a kinetically modified Stranski--Krastanov growth mode.

We present direct experimental evidence that ferromagnetic (FM) transition in doped manganites is introduced by exchanged polarons rather than `bare' e_g electrons and the FM transition depends on hopping energy of polarons regardless of variation of experimental methods. The observed universal relationships between polaron hopping energy and FM transition suggest a simply polaron exchange picture for understanding the origin of FM ordering in the complex strongly correlated electronic materials of manganites.

We present our measured photoluminescence of the quadrupolar transitions of the yellow series excitons of cuprous oxide at 2K. By tuning the excitation energy in the two-photon quadrupolar absorption scheme of Cu₂O, it is found that the band-gap value associated with this optical process can be characterized by a sharp resonance at 2.036eV at cryogenic temperature. This energy value is helpful to guide a proper excitation for creating cold excitonic gas in this crystal.

Based on the Heisenberg equations of motion for the electron orbital and spin degrees of freedom in two-dimensional electronic systems with both Rashba and Dresselhaus spin-orbit couplings, we show that an ac electric field can cause an ac spin Hall current in such a system. In contrast to some previous theoretical prediction, the spin Hall current will be suppressed completely in the dc limit. We argue that the suppression of dc spin Hall currents in such a system is actually a much natural result of the dynamic spin evolution due to the combined action of a dc external electric field and the intrinsic spin-orbit coupling.

The electronic structures of Co3 Cu3 superlattices with the orientations of (100), (110) and (111) are calculated by the first-principle method within the framework of the density functional theory. It has been found that the spin-dependent scattering and charge transfers are prominent at interfaces compared to the interior layers for the three orientation superlattices. We also evaluate the magnetoresistance ratio by using the two-current model. The results show that the giant magnetoresistance ratio decreases in the order of (110), (100), (111) orientations for Co3Cu3 models (49.4%, 37.7%, 29.3%, respectively). Further analysis shows that an expansion of average atomic volume would enhance the magnetic moment of Co, which is consistent with other calculation and experimental results. In addition, the giant magnetoresistance effect is analysed from the point of charge transfer.

Epitaxial films of Ga_1-xMn_xN have been grown on c-sapphire substrates by low-pressure metal-organic vapour phase epitaxy. The samples show ferromagnetic behaviour up to a temperature of T=380K with hysteresis curves showing a coercivity of 50--100Oe. No ferromagnetic second phases and no significant deterioration in crystal quality with the incorporation of Mn can be detected by high-resolution x-ray diffraction. The result of x-ray absorption near-edge structures indicates that Mn atoms substitute for Ga atoms. The Mn concentrations of the layers are determined to reach x=0.038 by proton-induced x-ray emission.

We present a magnetic force microscopy study of surface magnetic microstructure changes at high temperatures in 2:17-type Sm(Co,Fe,Cu,Zr)_z (z～7.4) magnets. Surface magnetic microstructures are found to change greatly in parallel and vertical specimens after heat-treatment at 400°C for one hour in vacuum of 10^-5Torr with Ar gas as protecting atmosphere. Changes of microstructures are attributed to the formation of a soft-magnetic surfaces layer in the specimens, resulting from Sm volatilization due to high temperature. This hypothesis is further confirmed by the heat-treatment experiments at 400°C for 0.5h and 2h. Finally, the existence of the soft-magnetic layers, which consist primarily of Fe--Co compounds, is verified by the results of both XRD and XPS of the vertical specimens before and after heat-treatment.

Giant magnetic field induced strain (MFIS) up to 6.2% is achieved in the Ni₅₀Mn_27.5Ga_22.5 single crystals with 5M martensitic structure at room temperature. The switching magnetic field was about 2.4kOe for the magnetostrain. A `magnetization jump’ effect in the switching field applied along the initially hard direction confirms the occurrence of the large magnetostrain. The temperature dependence of the magnetostrain is investigated in lower temperature range. A linear decrease of the magnetostrain is observed with increasing temperature, but a strong decrease is monitored near the reverse martensitic transformation temperature.

Wave reflection and refraction at the interface between a normal media and a one-dimensional left-handed material (1DLHM) with a hyperbolic dispersion relationship is studied. It is found that in a special case that the boundary is perpendicular to one asymptotic line of the hyperbola, phase matching cannot be achieved unless the 1DLHM is regarded to be intrinsically lossy. After introducing a small loss factor to the 1DLHM, a reasonable solution for the phase matching is obtained. According to the analytical result, a wave confined to a thin layer near the boundary is found, which can be excited at the interface as a reflected wave or a refracted wave attenuating drastically away from the boundary inside the 1DLHM in both cases.

We report that the composites of ZnO/porous Si (PS) can exhibit intensively white photoluminescence (PL) under proper excitation wavelength. The PS sample is formed by electrochemical anodization of n-type (111) silicon. ZnO films are then deposited on the PS surface by pulsed laser deposition (PLD). ZnO is transparent in the visible region, so the red PL from PS can be transmitted through the ZnO films. White PL from the ZnO layer on PS can be obtained, which consists of blue-green emission from ZnO and red emission from PS. The x-ray diffraction (XRD) pattern shows that the ZnO films deposited on PS surface are non-crystalline. Due to the roughness of the PS surface, some cracks appear in the ZnO films, which could be seen from the scanning electron microscopy (SEM) images.

We report the crystallization and photoluminescence (PL) properties of amorphous Si:H/SiN_x:H multilayer (ML) films treated by step-by-step laser annealing. The results of Raman measurements show that the nanocrystalline Si (nc-Si) grains are formed in the a-Si:H layers under the constrained growth mechanism. The blue shift of PL peak with grain size is observed and can be attributed to the quantum confinement effect. For comparison, we also report the crystallization and PL of a-Si:H/SiN_x:H ML samples by normal one-step treatment. This method of step-by-step laser treatment will be a candidate to make nc-Si quantum dots in amorphous Si:H/SiN_x:H ML as an active layer in microcavities.

Indium tin oxide/Si-rich SiO₂/p-Si structured devices are fabricated to study the electroluminescence (EL) of the Si-rich SiO₂ (SRO) material. The obvious peaks at ～1050nm and ～1260nm in the EL are ascribed to localized state transitions of amorphous Si (α-Si) clusters. The EL afterglow associated with α-Si clusters is observed from this structure at room temperature, while the afterglow is absent in the case of optical pumping. It is believed that carrier-induced defects act as trap centres in the α-Si clusters, resulting in the EL afterglow. The phenomenon of the EL afterglow indicates the limits of EL performance and electrical modulation of the SRO material with a larger fraction of α-Si clusters.

Atomic force microscopy (AFM) and power-dependent micro-photoluminescence (μ-PL) spectroscopy are used to study the structure and exciton energy states in InAs quantum dots (QDs) grown on an In_0.35Ga_0.65As template on GaAs (311)B. The In_0.35Ga_0.65As template, consisting of a two-dimensionally modulated layer of closely packed connected cells, has a remarkable effect on the optical properties of the InAs QDs. By comparing the emission spectra of the samples without and with InAs QDs and the work carried out by Gong et al. [J. Cryst. Growth 251 (2003) 150; Appl. Phys. Lett. 81 (2002) 3254] we conclude that the existence of the In_0.35Ga_0.65As template enhances the photo-absorption and therefore the exciton emission from the QDs due to efficient exciton transfer from the template into the QDs. Furthermore, the PL emission from the QDs clearly reveals four discrete energy levels, S, P, D, and F with increasing excitation power.

Amorphous carbon films are deposited on the Mo film/ceramic substrates, which are pretreated by a laser spattering chiselling technique (2 line/mm), by using the microwave chemical vapour deposition technique. The films are characterized by x-ray diffraction, Raman spectrum, optical microscopy, and scanning electron microscopy. The experimental result indicates that the laser spattering chiselling pretreated techniques can essentially improve the field emission uniformity and the emission site density of the amorphous carbon thin film devices so that its emission site density can reach the level of actual application (undistinguishable by naked eye) from a broad well-proportioned emission area of 50mm × 50mm. This kind of device can show various digits and words clearly. The lowest turn-on field below 1V/m, the emission current density over 5.0±0.mA/cm², and the highest luminance 1.0×10³cd/m² are obtained. Meanwhile, the role of the laser spattering chiselling techniques in improving the field emission properties of the amorphous carbon film are explained.

Single crystalline ZnSe nanowires with both zincblende and wurtzite structures have been synthesized via a chemical vapour deposition method under different growth conditions. The nanowires are usually 50--80nm in diameter, and several tens of microns in length. Room-temperature photoluminescence spectra from zincblende and wurtzite ZnSe nanowires show a broad luminescence band peaked at around 2.71eV and a deep level emission band peaked at around 2.00eV, respectively. Effects of post-growth annealing on the photoluminescence of these nanowires have been investigated. Strong room-temperature band-edge emission could be obtained from the annealed zincblende ZnSe nanowires.

For ZnO/diamond structured surface acoustic wave (SAW) filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition (MOCVD). The properties of the ZnO films are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.

Cubic boron nitride (c-BN) films were deposited on highly-oriented (111) bulk c-BN crystal by using the rf magnetron sputtering method. The growth films are characterized by micro-Raman spectroscopy (μ-RS) and scanning electron microscopy (SEM). The results show that the high crystallization electron transparent c-BN films in thickness of about 10μm are obtained. Island and step growth models are clearly shown.

Current--voltage characteristics of ballistic carbon-nanotube field-effect transistors are characterized with an iterative simulation program. The influence of carbon-nanotube chirality and diameter on the output current is considered. An analytical current--voltage expression under the quantum capacitance limit and low-voltage application is derived. Our simulation results are compared with actual measurement data.

A monolithic uncooled 8×8 microbolometer array with boron-doped a-Si (a-Si:B) thermistors as active elements is presented. The a-Si:B film was deposited by plasma enhanced chemical vapour deposition. To decrease the thermal conductance of the microbolometer, a-Si:B thermistor was formed on a four-leg suspended microbridge. The improved porous silicon micromachining techniques described here enable the integration of the sensor array with the metal--oxide--semiconductor readout circuitry. The sacrificial material of porous silicon is prepared in the first step. It is then well protected all the time during the fabrication of metal--oxide--semiconductor field effect transistors and microbolometers before being released. Measurements and calculations show that the uncorrected uniformity of the 8×8 microbolometer array is about 4.5%, and the detectivity of 2.17×10⁸cm Hz^1/2W^-1 is achieved at a chopping frequency of 30Hz and a bias voltage of 5V with a thermal response time of 12.4ms.

We demonstrate high efficiency red organic light-emitting diodes (OLEDs) based on a planar microcavity comprised of a dielectric mirror and a metal mirror. The microcavity devices emitted red light at a peak wavelength of 610nm with a full width at half maximum (FWHM) of 25nm in the forward direction, and an enhancement of about 1.3 factor in electroluminescent (EL) efficiency has been experimentally achieved with respect to the conventional noncavity devices. For microcavity devices with the structure of distributed Bragg reflectors (DBR)/indium-tin-oxide(ITO)/V₂O₅/N,N'-di(naphthalene-1-yl)-N,% N'-diphenyl benzidine(NPB)/4-(dicy-anome-\linebreak thylene)-2-t-butyl-6(1,1,7,7-tetrame-thyljulolidyl-9-enyl)-4H-pyran(DCJTB):% tris(8-hydroxyquinoline) aluminium\linebreak (Alq₃)/Alq₃/LiF/Al, the maximum brightness arrived at 37000cd/m² at a current density of 460.0mA/cm², and the current efficiency and power efficiency reach 13.7cd/A at a current density of 0.23mA/cm² and 13.3lm/W at a current density of 0.04mA/cm², respectively.

The unzipping process of double-stranded DNA is analysed using a discrete model at the base level [Chin. Phys. Lett. 22(2005)1540]. The numerical results are consistent with the experimental observations on the force-displacement behaviour including the sequence-dependence. We find that the hydrogen bond interaction in a base pair is crucially important to the force--displacement profile.

We introduce a feedback mechanism to study the spreading of an epidemic by analytical methods and large scale simulations in exponential networks. It is found that introducing the feedback mechanism can reduce the density of infected individuals. Furthermore, it does not change the epidemic threshold (critical point) λ_c. These results can help us to understand epidemic spreading phenomena on social networks more practically and design appropriate strategies to control social infections.

Most epidemic models for the spread of diseases in contact networks take the assumption of the infected probability of a susceptible agent dependent on its absolute number of infectious neighbours. We introduce a new epidemic model in which the infected probability of a susceptible agent in contact networks depends not on its degree but on its exposure level. We find that effective average infection rate ^-λ (i.e., the average number of infections produced by a single contact between infected individuals and susceptible individuals) has an epidemic threshold ^-λ_c=1, which is related to recovery rate, epidemic mechanisms and topology of contact network. Furthermore, we show the dominating importance of epidemic mechanisms in determining epidemic patterns and discussed the implications of our model for infection control policy.

The energy transfer between ions (protons) and low frequency waves (LFWs) in the frequency range f₁ from 0.3 to 10Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low frequency waves and ions has two means. One is that the energy is transferred from low frequency waves to ions and ions energy increases. The other is that the energy is transferred from ions to low frequency waves and the ion energy decreases. Ion gyratory motion plays an important role in the energy transfer processes. The electromagnetic field of f₁ LFWs can accelerate or decelerate protons along the direction of ambient magnetic field and warm or refrigerate protons in the parallel and perpendicular directions of ambient magnetic field. The peak values of proton number densities have the corresponding peak values of electromagnetic energy of low-frequency waves. This implies that the kinetic Alfven waves and solitary kinetic Alfven waves possibly exist in the high-altitude cusp region.

Numerical simulation is an important tool that is helpful for us to understand the process of structure formation in the universe. However, many simulation results of cold dark matter (CDM) halos on a small scale are inconsistent with observations: the central density profile is too cuspy and there are too many substructures. Here we point out that both the problems may be connected with a hitherto unrecognized bias in the simulated halos. Although CDM halos in nature and in simulation are both virialized systems of collisionless CDM particles, gravitational encounter cannot be neglected in the simulated halos because they contain many fewer particles. We demonstrate this by two numerical experiments, showing that there is a difference on the microcosmic scale between the natural and simulated halos. The simulated halo is more akin to globular clusters where gravitational encounter is known to lead to such drastic phenomena as core collapse. Such an artificial core collapse process appears to link the two problems together in the bottom-up scenario of structure formation in the ΛCDM universe. The discovery of this bias also has implications on the applicability of the Jeans theorem in galactic dynamics.