The explicit expression of the transverse photon wavefunction Ф_γ⊥(u,P²) at the leading twist with the on-shell and the off-shell momenta are calculated in the effective low-energy theory derived from the instanton vacuum of QCD, where both the space-like region as well as the time-like one of the momenta for the virtual photons are investigated. In addition, the problem about the consistency between the two different definitions of the transverse photon wavefunction with chiral-odd Dirac structure, σ_μv, has been considered, and proven to be true at the leading order by means of the sum rule method. A brief discussion of the dependence of the transverse light-cone photon wavefunction Ф_γ⊥(u,P²) nd its coupling, F_γ^⊥(u,P²) to the corresponding quark--antiquark current with respect to P², and that about the end-point behaviour of the transverse photon wavefunction is given.

It is well known that a computationally efficient model for calculation of radiation impedance of an arbitrarily shaped piston has been developed. We simplify the proposed algorithm by using geometric characteristics and intrinsic relationship between the analytic expressions. As an example, the method accuracy is illustrated and the radiation impedance of a right-angled triangular piston is calculated. The numerical results are in good agreement with that obtained directly by the quadruple integral method.

By decomposing the Bogomol’nyi self-dual equation in the Abelian Chern--Simons Higgs model, we find a self-dual topological term that was ignored all the time in the Bogomol’nyi self-duality equation due to the improper decomposition of the complex Higgs field. We also present a new self-dual equation that includes the topological term. It is shown that the self-dual vortex just arises from the symmetric phase of the Higgs field Ф=0. Using our Ф-mapping theory, the inner topological structure of the vortex and double vortex is given.

On the basis of analytical transfer matrix theory, we fine a generalized quantization condition. By introducing a new type of modified momentum, our quantization condition has the same form as the Bohr--Sommerfeld formula. Numerical and analytical comparisons show that the present method is exact.

We introduce a generalized intermediate entangled state representation |β>_λ to study the energy spectrum of an electron in a uniform magnetic field and a harmonic potential through algebraic calculation. We find that the degeneracy of the energy levels is disappeared due to the existence of the additional potential. We make it clear that the eigenfunction is just the expression of eigenvector, defined in n Fock space, in |β>_λ representation.

We propose a simultaneous quantum secure direct communication scheme between one party and other three parties via four-particle GHZ states and swapping quantum entanglement. In the scheme, three spatially separated senders, Alice, Bob and Charlie, transmit their secret messages to a remote receiver Diana by performing a series of local operations on their respective particles according to the quadripartite stipulation. From Alice, Bob, Charlie and Diana’s Bell measurement results, Diana can infer the secret messages. If a perfect quantum channel is used, the secret messages are faithfully transmitted from Alice, Bob and Charlie to Diana via initially shared pairs of four-particle GHZ states without revealing any information to a potential eavesdropper. As there is no transmission of the qubits carrying the secret message in the public channel, it is completely secure for the direct secret communication. This scheme can be considered as a network of communication parties where each party wants to communicate secretly with a central party or server.

Since the special relativity can be viewed as the physics in an inverse Wick rotation of four-dimensional (4D) Euclid space, which is at almost equal footing with the 4D Riemann/Lobachevski space, there should be important physics in the inverse Wick rotation of 4D Riemann/Lobachevski space. Thus, there are three kinds of special relativity in de Sitter(dS)/Minkowski/anti-de Sitter(AdS) space at almost equal footing, respectively. There is an instanton tunnelling scenario in the Riemann--de Sitter case that may explain why Λ be positive and link with the multiverse.

We study a two-level atom in interaction with a real massless scalar quantum field in a spacetime with a reflecting boundary. We calculate the rate of change of the atomic energy for the atom. The presence of the boundary modifies the quantum fluctuations of the scalar field, which in turn modifies the rate of change of the atomic energy. It is found that the modifications induced by the presence of a boundary make the spontaneous radiation rate of an excited atom to oscillate near the boundary and this oscillatory behaviour may offer a possible opportunity for experimental tests for geometrical (boundary) effects in flat spacetime.

We examine the random motion of a charged test particle with a nonzero classical velocity driven by quantum electromagnetic vacuum fluctuations in a cylindrical spacetime and calculate both the velocity and position dispersions of the test particle. It is found that the dispersions display different behaviour in different directions. These differences can be understood as a result of the topology of the configuration and initial physical conditions.

We extend Parikh’s recent work to the arbitrarily dimensional Schwarzschild black holes whose Arnowitt--Deser--Misner (ADM) mass is identical to its mass parameter. We view Hawking radiation as a tunnelling process across the event horizon. From the tunnelling probability we also find a leading correction to the semiclassical emission rate. The result consists with an underlying unitary theory.

The radiation of black hole contributes to the shrinking of the event horizon such that the background space-time should not be fixed. In this study we take into account the self-gravitation effect to study the radiation of Kerr--Newman--Kasuya black hole as tunnelling. Using the facts of energy conservation and angular momentum conservation we derive the tunnelling rate and show that the spectrum of the radiation as tunnelling is not purely thermal.

The quasinormal modes associated with the decay of Dirac field perturbation around a Schwarzschild-anti-de Sitter black hole with a global monopole (SAdSBHGM) are calculated using the Horowitz--Hubeny approach. For the large SAdSBHGM, we find that η has little effect on the quasinormal frequencies. However, for the intermediate and small SAdSBHGM, in the limit η→1/√8π, the real parts of the fundamental quasinormal frequencies approximate the linear functions of T, and the imaginary ones approximate the linear functions of r₊.

The intensity correlation time T is studied by employing a gain-noise model of a single-mode laser driven by coloured pump noise τ₁ and coloured quantum noise τ₂ with coloured cross-correlation τ₃ with a bias signal modulation. By using the linear approximation method, we detect that a maximum (i.e. resonance) exists in the curves of the intensity correlation time T versus the noise intensities D and Q when the noise correlation coefficient λ is positive; and a minimum (i.e. suppression) exists in the T-D and T-Q curves when λ is negative. When λ is zero, T increases monotonously with increase of D and decreases monotonically with increase of Q. Furthermore, the curve of T versus the pump noise self-correlation time τ₁ is also studied. Our study shows that, no matter what the value of λ is, there exist one maximum and one minimum in the T-τ₁ curve.

Performance characterization of chaotic masking encoding and decoding is studied in synchronization injected semiconductor lasers under condition of injected-feedback. The modulation response function of chaotic masking encoding and its response factor are theoretically deduced and analysed by small-signal analysis. It is numerically demonstrated that there are peak values between 1.52GHz and 3.18GHz when the injection coefficient is between 0.2 and 0.8. The chaotic synchronization error equation is theoretically deduced and its root is given by small-signal analysis under condition of chaotic masking encoding. The chaotic decoding formula is also theoretically demonstrated. There are the least dale values of synchronization errors between the modulation frequencies of 0.79GHz and 1.91GHz when the injection coefficient is between 0.1 and 0.8 in numerical simulation. The numerical result is well consistent with the theoretical demonstration.

We propose a Bang-Bang control scheme that can synchronize master--slave chaotic systems. The chaotic systems considered here are structurally different from each other. Different from some control strategies reported previously, the scheme proposed here can be taken as a general one that is independent of the chaotic system itself.

A broad angular response supermirror is designed by the simplex optimization method and fabricated by dc magnetron sputtering. The negative effect of the interfacial imperfection, mainly consulting from interface roughness and diffusion, is emerged in the calculation of the precise performance of the supermirror. The reflectivity of such a supermirror is measured by the x-ray diffraction instrument (XRD) at Cu K_α line (λ=0.154nm). The experimental reflectivity is about 30% in a fixed broad grazing incident angular range (0.55°--0.85°). The fitting data prove that the thickness of each layer, which is larger than the prospect 0.5nm, is different from the designed one and the roughness in the supermirror is about 0.85nm.

We study hard photon production from a two-loop level (bremsstrahlung and annihilation with scattering) in a chemically equilibrating quark--gluon plasma at finite baryon density based on Jüttner distribution of partons of the system. We find that the photon yield from the two-loop level increases obviously with the increasing initial quark chemical potential.

We study the effects of a laser beam from the laser diode operating at 980nm on the violet-excited ZnS:Cu and SrAl₂O₄:Eu phosphor powders. Two contrary phenomena, i.e., infrared-induced permanent quenching and short-lived enhancement of phosphorescence, are observed. The defect levels play a significant role in both the processes. It is demonstrated that the phosphorescence induced by the violet beam can be controlled by another infrared beam. The turn-off and turn-on behaviour means that doping luminescent centres into host materials is a considerable way to design a new all-optical switch and may control the output of laser beams in the fibre lasers and optical communications.

We report an experiment of trapping of neutral ⁸⁷Rb atoms on a self-made atomchip. The H-shaped atomchip is made by magnetron sputtering technology, which is different from the atomchip technology of other teams. We collect 3×10^{6 87}Rb atoms in the mirror magneto-optical trap (MOT) using the external MOT coils, and 1×10^{5 87}Rb atoms are transferred to U-MOT using U-shaped wire in chip and a pair of bias coils.

A method for effectively generating long-lived Mössbauer photons and methods for proving the associated Mössbauer effects are reported. For the first time, we observed resonant propagation and resonant absorption of 40-keV Mössbauer photons emitted from ¹⁰³Rh through (γ,γ’) process excited by bremsstrahlung. This is a new efficient way to generate long-lived isomer (>1ms) for Mössbauer spectroscopy with sufficient brilliance. An abnormally large ratio of resonant absorption between horizontal and vertical directions indicates horizontal trapping of Mössbauer photons and anisotropic Mössbauer emission, which can be attributed to gravitational effect on the ¹⁰³Rh Mössbauer isomer with extremely narrow 10^-19eV linewidth.

A scheme used for controlling the population transfer and the dissociation rate of Na₂ molecules is described by using the quantum wavepacket dynamical method. It is theoretically shown that the population transfer and the dissociation rate of Na₂ molecules can be controlled by pump and probe laser pulses with appropriate widths of pulses, sequence and intensities.

We present experimental measurements of L-shell production cross sections L_α, L_β and L_γ for tantalum and thulium by electron impact at incident electron energies from about one to three times the threshold energy. From the experimental data, the total production cross section and mean ionization cross section are deduced. The influence of electrons reflected from the substrate is corrected by the electron transport bipartition model. The measured cross sections are compared with the theoretical predictions.

A quasi-relativistic distorted-wave approximation is developed to investigate the direct electron-impact ionization processes, in which the configuration interactions are considered in the initial and final states of target. As an example, the direct detailed-level electron-impact ionization cross sections for the ground and low excited states of Ar⁶⁺(3s²⁺, 3p²⁺, 3s3d) are calculated in the energy range from 1.02 to 15I_th (I_th the ionization threshold). Comparison with the available data demonstrates that our results are reasonable. The effects of configuration interactions are discussed, and the validity of transformation principles by statistical weights between configuration-averaged and detailed-level electron-impact ionization cross sections is analysed.

The polarization of spin-polarized electrons, produced from a new GaAs spin-polarized electron source, is determined by an optical electron polarimeter. The He 3 ³P → 2³S₁ (388.9nm) transition is used for the optical electron polarimetry. The structure and performance of the experimental setup of spin-polarized electron source and optical electron polarimeter are described. The result of polarization of 30.8% averaged spin-up and spin-down polarized electrons is obtained and presented.

We investigate the translocation of single polymer chain through a nanopore located on a membrane with different solvents in the two sides of the membrane. For the case under study, the effect of solvents on the translocation dynamics is significant, and as a result, the mean first passage time shortens remarkably compared with that calculated in the case of good solvents on both the sides of the membrane. In addition, we also discuss the condition such that the present result holds true.

We propose an experimental approach for investigation of the polycrystalline deformation behaviour at a grain scale. The technique is characterized by the joint application of micro material testing systems and the intragranular deformation analysis methods. It is attempting to map the deformation evolution at grain scale during the elastic and plastic deformations of polycrystalline specimens.

An optimal feedback control of two-photon fluorescence in the ethanol olution of -dicyanomethylene-2-methyl-6-p-dimethyl-aminostryryl-4H-pyran (DCM) sing pulse-shaping technique based on genetic algorithm is emonstrated experimentally. The two-photon fluorescence of the DCM ethanol solution is enhanced in intensity of about 23%. The second armonic generation frequency-resolved optical gating (SHG-FROG) trace ndicates that the effective population transfer arises from the ositively chirped pulse. The experimental results appear the potential pplications of coherent control to the complicated molecular system.

Based on the transfer matrix method, we present a new one-dimensional steady-state model of vertical-cavity semiconductor optical amplifiers (VCSOAs), in which the longitudinal carrier concentration distribution in the active region and the discontinuity of the refractive index inside the cavity is taken into consideration. The model is theoretically proven to be a reliable one for describing the standing wave effect in a periodic gain structure. By using this model, some optical amplification characteristics of VCSOAs are investigated.

We demonstrate a 511W laser diode pumped composite Nd:YAG ceramic laser. The optical pumping system is consisted of five laser diode stacked arrays arranged in a pentagonal shape around the ceramic rod whose size is Ф6.35×144mm. When the pumping power is 1600W, the cw laser output up to 511W at 1064nm can be obtained with a linear plano--plano cavity, and the optical-to-optical efficiency is 31.9%. To our knowledge, this is the highest value of laser output by using a newly invented composite Nd:YAG ceramic rod as the gain medium.

A low-threshold random laser with one mirror and feedback is investigated in the PMMA film containing rhodamine 590 and TiO₂ nano-particles. Incoherent and coherent laser emission is observed. Effect of particle concentration on light emission is explored, and the optimum particle concentration is obtained. Optical microscopy and scanning probe microscopy are used to investigate the film structure, and the principle of incoherent and coherent laser is analysed.

The third-order optical nonlinearities and responses of poly(methyl methacrylate) (PMMA) coating films containing J-like aggregates of a thiadicarbocyanine dye, 3,3’-diethyl-2,2’-thiadicarbocyanine iodide (DTDCI), are measured by degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profiles of the DFWM signal of PMMA coating films containing J-like aggregates of DTDCI are found to consist of three components: i.e., the coherent instantaneous nonlinear response (electronic response) and the two slow responses with decay time constants of about 0.8ps and about 7.0ps. The electronic component of the effective third-order nonlinear susceptibility, x⁽³⁾_e, of one of the present films is as high as about 2.1 × 10^-8esu, and the figure of merit of third-order nonlinearity F (F =x⁽³⁾/α) is evaluated to be about 1.9 × 10^-13esu cm at 850nm.

We realize a stable self-starting passively mode-locking all-solid-state laser by using novel GaAs mirrors as the absorber and output coupler. The GaAs mirror is grown by the technology of metal organic chemical vapour deposition at low temperature. With such an absorber as the output coupler in the laser resonator, laser pulses with duration of 42ps were generated at a repetition rate of 400MHz, corresponding to the average power of 590mW.

The propagation of dark solitons in nonlinear media that include gain and loss described by a nonlinear Schrödinger equation is investigated. Based on the direct approach of perturbation theory, the width, height and other related quantities of dark solitons are obtained. It is shown that stationary propagation of dark solitons is found to be possible in the presence of both gain and absorption. The results obtained by means of our analytic method are in excellent agreement with numerical simulations. Our results are helpful for the research into the optical soliton transmission system.

Using the cascaded structure of a linear and a second-order nonlinear photonic crystals, we realize a high-efficiency optical parametric amplifier in the case of exact phase matching. This proposal is verified using the slow-envelope nonlinear finite difference time domain numerical method. Compared with the case of the individual nonlinear photonic crystal structure, the oscillation threshold is decreased obviously, and the peak power amplification factor of the transmitted signal is enhanced more than 20 times.

Linear transmission, reflection and absorption spectra for a new two-dimensional photonic crystal with periodically arranged resonant atoms are examined. Numerical results show that a twin-gap structure with forbidden bands displaced from a non-doped bandgap structure can be produced as a result of atomic polarization. The absorption spectrum is also significantly altered compared to the single atom entity.

Deformation of some air holes often occurs during the fabrication process of photonic crystal fibres (PCFs). Effects of the location and size of deformation holes on the properties of actual triangular lattice PCFs are investigated in detail. Numerical results demonstrate that the properties of PCFs, especially birefringence, are sensitive to the location and size of deformation holes. These would be very helpful to improve the fabrication technique of the PCF and also offers an efficient way to design high birefringence PCF.

We provide a novel hollow-core holey fibre that owns a random distribution of air holes in the cladding. Our experiments demonstrate that many of the features previously attributed to photonic crystal fibres with perfect arrangement of air holes, in particular, photonic bandgap guidance, can also be obtained in the fibre. Additionally, this fibre exhibits a second guided mode with both the two-lobe patterns, and each pattern is in different colour.

We describe a novel compact power splitter with tunable power splitting ratios based on multimode interference couplers employing area modulation in a polymer. The experiments show large tuning ranges with splitting ratio varies from 6:94 to 88:12 and low heating power of 5mW for π phase shift.

A noncontact ultrasonic motor based on a non-symmetrical electrode is proposed. This motor has the advantages of using a simple driving electrode and having a high revolution speed. The revolution speed of its three-blade rotor can reach 5100rpm under a driving voltage of 20V. A method operated easily is proposed to measure the output torque.

Absorption of acoustic wave propagation in a large variety of lossy media is characterized by an empirical power law function of frequency, α₀|ω|^y. It has long been noted that the exponent y ranges from 0 to 2 for diverse media. Recently, the present author [J. Acoust. Soc. Am. 115 (2004) 1424]
developed a fractional Laplacian wave equation to accurately model the power law dissipation, which can be further reduced to the fractional Laplacian diffusion equation. The latter is known underlying the Lévy stable distribution theory. Consequently, the parameters y is found to be the Lévy stability index, which is known to be bounded within 0

Some important concepts in the nonstandard analysis theory of turbulence are presented. The point structure, on which differential equations are defined, is analysed. The distinction between the uniform point and the non-uniform point, as well as between the standard point and the nonstandard point, is shown. A new kind of equations, which differ essentially from those in existent theory, is emphasized. These new equations can hold at non-uniform points. The applicability of the Navier--Stokes equations to turbulence is discussed. Some illustrations of the nonstandard analysis theory of turbulence are also presented.

Strong white light emission is observed from femtosecond laser propagation in air. The divergence angle of the white light emission is measured to be about 5mrad. Young’s double-slits and a Michelson interferometer are used to investigate the coherence. The wavelength components of the white light emission are identified to have a good spatial coherence and a coherence time of about 0.5ps.

The study of electrical resistivity of simple binary liquid alloy Na--K is presented as a function of concentration. Hard sphere diameters of sodium (Na) and potassium (K) are obtained through the inter ionic pair potentials evaluated using Troullier and Martins ab-initio pseudopotentials, which have been used to calculate partial structure factors S(q). The Ziman formula for calculating resistivity of binary liquid alloys has been used. Form factors are calculated using ab-initio pseudopotentials. The results suggest that the first principle approach for calculating pseudopotentials with in the frame work of Ziman formalism is quite successful in explaining the electrical resistivity data of compound forming binary liquid alloys.

The compression behaviour of Ni₇₇P₂₃ amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using in-situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state is determined by fitting the experimental data according to the Birch--Murnaghan equation. It is found that the structure of Ni₇₇P₂₃ amorphous alloy is stable under pressures up to 30.5GPa. Within the pressure range from zero to the experimental one, the pressure-induced structural relaxation is reversible.

Electronic structures of PbWO₄ crystals containing F-type colour centres with the lattice structure optimized are studied within the framework of the fully relativistic self-consistent Dirac--Slater theory, using a numerically discrete variational (DV-Xα) method. The calculated results show that F and F⁺ centres have donor energy levels in the forbidden bands. Their optical transition energies are 1.84eV and 2.21eV, respectively, which correspond to the 680nm and 550nm absorption bands. It is predicted that the 680nm and 550nm absorption bands originate from the F and F⁺ centres in PbWO₄ crystals.

LiAlO₂ single crystals doped with Ti at concentration 0.2 at.% are grown by the Czochralskl technique with dimensions Ф42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO₂ and Ti: LiAlO₂. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600--800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the V_Li and V₀ absorptions, respectively. The peaks at 716nm and 798nm may stem from the V_Li⁺ and F⁺ absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti⁴⁺-doping produces more lithium vacancies in the LiAlO₂ crystal. The intensities of [LiO₄] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO₂ crystals.

Thermal stress-induced birefringence in borate glass which has been irradiated by 800-nm femtosecond laser pulses is observed under cross-polarized light. Due to the high temperature and pressure formed in the focal volume, the material at the edge of the micro-modified region is compressed between the expanding region and the unheated one, then stress emerges. Raman spectroscopy is used to investigate the stress distribution in the micro-modified region and indicates the redistributions of density and refractive index by Raman peak shift. We suggest that this technique can develop waveguide polarizers and Fresnel zone plates in integrated optics.

The microstructure of Co₅₀Ni₂₂Ga₂₈ ribbon with the L₁₀ structure is examined. The band-like morphology is observed. These bands with the width in a range of 40--200nm appear along the transverse direction of the ribbon. The giant magnetoimpedance (GMI) effect in this alloy is measured. The results show that Co₅₀Ni₂₂Ga₂₈ exhibits a sharp peak of the GMI effect. The maximum GMI ratio up to 360% is detected. The GMI effect measured versus temperature shows large jumps of the magnetoimpedance amplitude at the reversal martensitic transformation temperature 240°C and Curie temperature 375°C respectively. The jump ratios of the magnetoimpedance amplitude examined at these temperatures are about 5 and 10, respectively.

We propose a pseudo-hydrodynamic (PHD) model that has hyperbolic principal part. It formally converges to the corresponding energy-transport model in the limit of zero momentum relaxation time. Numerical examples have demonstrated the regularization effects of the PHD model.

Elastic properties of platinum nitride (PtN) are studied by first-principles calculations with the fully relativistic full potential linearized augmented plane-wave (LAPW) method, the plane-wave ultrasoft pseudopotential (PW-PP) and the projector-augmented wave (PAW) methods. The results reveal that: (1) the scalar relativistic scheme is sufficient to treat the valence electronic structure, i.e. the spin-orbit effect has little effect on the bulk modulus value of platinum nitride; (2) the all-electron full potential method is no more accurate than the pseudopotential and PAW-based methods when calculating the lattice constant and bulk modulus properties of the platinum nitride; (3) platinum nitride in zinc-blende structure is unstable and its crystal structure is still an open problem.

We investigate the magnetic transitions in a (La_1-xB_x) _2/3Ca_1/3MnO₃ system, which consists of paramagnetic and ferromagnetic domains, based on a magnetic theoretical percolation model. In the mean-field approximation, the resistance as a function of temperature and magnetic field has been derived analytically and simulated numerically. It is found that the dependence of the critical temperature on magnetic field is linear when applied magnetic field is not too strong. Our theoretical predications are in good agreement with recent experimental observations.

The optical absorption of GaAs nanorings (NRs) under a dc electric field and a terahertz (THz) ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magnetic flux in the presence of a magnetic field perpendicular to the NRs plane. Numerical calculation shows that the excitonic effects are essential to correctly describe the optical absorption in NRs. The applied lateral THz electric field, as well as the dc field leads to reduction, broadening and splitting of the exciton peak. In contrast to the presence of a dc field, significant optical absorption peak arises below the zero-field bandgap in the presence of a THz electric field at a certain frequency. The optical absorption spectrum depends evidently on the frequency and amplitude of the applied THz field and on the magnetic flux threading the NRs. This promises potential applications of NRs for magneto-optical and THz electro-optical sensing.

Porous titanium is produced by the powder metallurgy method. Dependence of the electrical conductivity on the porosity and pore size is investigated and the experimental results are compared with a number of models. It is found that the minimum solid area model could be successfully applied to describe the relationship between the electrical conductivity and the porosity of porous titanium. This kind of conductivity increases with increasing pore sizes.

Energy bandstructures of [100] oriented Si and Ge quantum nanowires with various cross-sections are calculated by using the sp³d⁵s^* tight-binding model with a supercell approach. Results are compared with those obtained by the first principles method (i.e., density functional theory, or DFT). The differences in the bandstructure between silicon and germanium nanowires are analysed and it is shown that germanium keeps indirect-bandgap and the silicon nanowire along the [100] direction becomes direct-bandgap when the wire diameter shrinks. It is shown in comparison with the available experimental data that the tight-binding method is adequate in predicting the bandstructure parameters relevant to the carrier transport in mesoscopic nanowire devices and is far superior to the DFT method in terms of computational cost.

We investigate the origin of ultraviolet (UV) emission from Mg_0.12Zn_0.88O alloy thin films with a wurtzite structure fabricated on c-plane Al₂O₃ substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg_0.12Zn_0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region.

Thermal diffusivity has been investigated in a manganite thin film La_0.6Sr_0.4MnO₃ by means of transient grating (TG) technique at room temperature. A new method, which is generalized to two-layered samples of the thin film deposited on a semi-infinite substrate, is established to fit the TG signals. The thermal diffusivity of the La_0.6Sr_0.4MnO₃ thin film with a thickness of 200nm on an MgO (100) substrate is determined to be 0.92mm²/s, which is slightly smaller than that of the single crystal sample (1mm²/s).

We present theoretical study on quantum tunnelling in n-coupled single-molecule magnets (SMMs) by spin-coherent-state path integral. It is found that, due to weak coupling between SMMs, the tunnelling process involving more than one-spin-flip is effectively blocked and the main contribution to the relaxation of the magnetization comes from the tunnelling processes involving just one-spin-flip. Starting from the negative saturated magnetization, the effect of the antiferromagnetic on tunnelling coupling is found to be qualitatively different from the ferromagnetic coupling. A criterion is developed to determine both the nature and the strength of the exchange coupling from the position of the first resonance of a spherical sample with homogeneous magnetization.

We investigate the photoinduced resistance change (Δ R/R) in a La_0.6Sr_0.4MnO₃ film (T_c\sim 325K) at different applied dc currents I (0.1--2.0mA) at 295K. At I = 0.1mA, we have found a significant photoinduced ΔR/R～17% under photo-irradiation at excitation energy E_exc = 3.05eV and pump power P_pump = 2.5mJ/cm², which has been ascribed to the photo-excited down-spin e_g carriers and hence the spin-disorder in the ferromagnetic metallic state. With increasing applied electric current to 2.0mA, the magnitude of the photoinduced ΔR/R is reduced to 3%, which may be attributed to current-induced ordering of the localized spins.

We investigate the effect of CH-doped and F-doped on dielectric properties of SiCOH films deposited by decamethylcyclopentasiloxane (DMCPS) electron cyclotron resonance plasma. The dielectric constant k is closely related to the configurations of films. For the films deposited only using DMCPS, the minimum k is as low as 2.88. By adding CH₄ in the precursor, the k value can be reduced to 2.45 due to the film density decreasing by incorporating large size CH_x groups. By adding CHF₃ in the precursor, the k value can also be reduced to 2.48 due to the incorporation of the weak-polarization F atom. Thus the dielectric constant for SiCOH films depends on not only the film density but also the polarization of atoms. By increasing the film density or by reducing the polarization of atoms under the condition of a lower film density, the low dielectric constant SiCOH films can be obtained.

Point imaging by a photonic crystal slab due to the negative refraction is studied by the finite-difference time-domain method. With a layer metal coating on one termination of a photonic crystal (PC) slab which intensifies the light reflection, one image occurs in the same side with the point source by negative refraction and reflection at the two sides of the photonic crystal slab, which brings about a new kind of imaging for the PC slab.

Luminescence spectra of SrAl₁₂O₁₉:Pr³⁺,Mn²⁺ under VUV--UV excitation are investigated. The characteristic emissions between 4f levels and the excitation of 5d for Pr³⁺ are observed. The emission of Mn²⁺ peaks at 517nm and the excitations due to the ground to multiplets are observed at 276, 360, 386 and 426nm. However, the spectral overlap between the emission of Pr³⁺ and excitation of Mn²⁺ is absent, suggesting that the quantum splitting cannot be achieved via a Pr³⁺--Mn²⁺ ion pair in the host SrAl₁₂O₁₉.

A thin film encapsulation of organic light-emitting diodes (OLEDs) is investigated with a multi-layer stack of polyacrylate-Ag-polyacrylate-Ag-polyacrylate-Ag-polyacrylate (PAPAPAP). It is shown that the fabrication of polyacrylate films by a wet process does not affect the electroluminescent (EL) characteristics of the devices and polyacrylate films together with the silver layers can perform to minimize oxygen and water diffusion into the organic light-emitting device. The structure of polyacrylate(20μm)-Ag(200nm) polyacrylate(20μm)-Ag(200nm)-polyacrylate(20μm)-Ag(200nm)-polyacrylate(20μm) is demonstrated to enhance dramatically the lifetime of OLEDs.

We present an extension of the original simple model for f--d transition proposed by Duan and co-workers [Phys. Rev. B 66(2002)155108; J. Alloys Compound. 366(2004)34] to the case applicable to heavy lanthanide and actinide ions in crystals and apply it to the interpretation of the low-temperature f--d excitation spectra of Ho³⁺ doped in crystals LiYF₄ and CaF₂. A consistent assignment of all the transition bands is obtained.

Cubic phase Mg_xZn_1-xO/MgO multilayer heterostructures (c-Mg_xZn_1-xO/MgO MHs) are grown on Si(100) and quartz substrates by reactive electron beam evaporation at low temperature (250°C). Cross-sectional morphology observations by field-emission scanning electron microscopy show the legible interfaces of c-Mg_xZn_1-xO/MgO MHs. X-ray diffraction demonstrates that c-Mg_xZn_1-xO/MgO MHs are of highly (100)-oriented. Optical transmission investigations of c-Mg_xZn_1-xO/MgO MHs on quartz substrates reveal the coexistence of the two phases, c-Mg_xZn_1-xO and MgO. Photoluminescence examination indicates the emergence of deep-ultraviolet emission centred at about 290nm along with the blue shift of the ultraviolet emission from 405nm to 396nm when the nominal thickness of c-Mg_xZn_1-xO well layers of MHs is diminished to 3nm, which is probably originated from quantum confinement effect.

Thermal annealing effect on InAs quantum dots grown on vicinal (100) GaAs substrates is studied in comparison with dots on exact (100) GaAs substrates. We find that annealing acts stronger effect on dots with vicinal substrates by greatly accelerating the degradation of material quality, as well as slightly increasing the blueshift of the emission wavelength and the narrowing of PL linewidth. It is attributed to the higher strain in the dots formed on the vicinal substrates.

Considering the Coulomb many-body interactions, we investigate the intersubband optical processes of the quantum well by using the semiconductor Bloch equations. We calculate the evolution of intersubband absorption spectral line shape as a function of lattice temperature and electron density. It is found that the coupling of intersubband plasmons can reduce and red-shift the lower energy resonance, simultaneously enhance and blue-shift the higher energy resonance. The dependence of cascading resonances on temperature and electron density is also discussed.

The composition, elastic strain and structural defects of InGaN/GaN multiple quantum wells (MQWs) are comparatively investigated by using x-ray diffraction (XRD), transmission electron microscopy and Rutherford backscattering/channelling. The InGaN well layers are fully strained on GaN, i.e. the degree of relaxation is zero. The multilayered structure has a clear defined periodic thickness and abrupt interfaces. The In composition is deduced by XRD simulation. We show how the periodic structure, the In composition, the strain status and the crystalline quality of the InGaN/GaN MQWs can be determined and cross-checked by various techniques.

A new crystal of aluminophosphate, AlPO₄.H₂O, is synthesized from two-batch aqueous solution under hydrothermal conditions. Three types of the crystal habits, i.e. the tetragonal double pyramid, the tetragonal prism and the plate-type tetragonal prism, are found from batch-A solution. Two types of the crystal habits, i.e. the hexagonal pyramid and the strip-type tetragonal prism, are found from batch-B solution. The change of crystal morphology is originated from the fluctuation of the synthesis conditions, such as the supersaturation, the temperature and the impurity content. It causes change of the step energies, the defect density and the step roughness, and further, change of the growth rates. Since the crystal morphology is sensitive to the mass transport mechanism, the crystal habits could be changed under the microgravity.

A series of dye-sensitized solar cells based on ZnO-modified TiO₂ nano-porous films have been prepared. The current--voltage characteristics of the cells show that the ZnO-modification can improve the open-circuit voltage and the fill factor but can decrease the short-circuit current. Dark current and transient photovoltage measurements are used to study the back reaction. It is indicated that the recombination process is suppressed by blocking the hole transporting from the nano-porous TiO₂ since the surface of the semiconductor is almost fully covered with ZnO as a barrier layer.

We investigate the emergence of scale-free behaviour in a traffic system by using the NaSch model to simulate the evolution of traffic flow. A kind of evolution networks has been proposed, which is based on the evolution of the traffic flow. The network growth does not take into account preferential attachment, and the attachment of new node is independent of degree. The simulation results demonstrate that the output distribution of links is well described by a scale-free distribution.

We investigate the mixing structure of directed and evolutionary US flight network. It is shown that such a network is a hierarchical network, with average assortativity coefficient -0.37. Application of the information-based method that can give the same result provides a way to explore the structure of complex networks.

A new hybrid preferential model (HPM) is proposed for generating both scale-free and small world properties. The topological transition features in the HPM from random preferential attachment to deterministic preferential attachment are investigated. It is found that the exponents γ of the power law are very sensitive to the hybrid ratio (d/r) of determination to random attachment, and γ increases as the ratio d/r increases. It is also found that there exists a threshold at d/r = 1/1, beyond which γ increases rapidly and can tend to infinity if there is no random preferential attachment (r=0), which implies that the power law scaling disappears completely. Moreover, it is also found that when the ratio d/r increases, the average path length L is decreased, while the average clustering coefficient C is increased. Compared to the BA model and random graph, the new HPM has both the smallest L and the biggest C, which is consistent with most real-world growing networks.

A three-dimensional magnetohydrodynamics (MHD) code is designed specially for global simulations of the solar wind--magnetosphere--ionosphere system. The code possesses a high resolution in capturing MHD shocks and discontinuities and a low numerical dissipation in examining possible instabilities inherent in the system. The ionosphere is approximated by a spherical shell with uniform height-integrated conductance. The solar wind is steady, and the interplanetary magnetic field is either due northward or due southward. The code is then run to find solutions of the whole system. It is found that the system has never reached a steady state, but keeps oscillating with a period of about one hour in terms of density variation at the geosynchronous orbit. However, if a certain artificial resistivity is added either in the whole numerical box or in the reconnection sites only, the reconnections change from intermittent to steady regime and the oscillation disappears accordingly. We conclude that the Earth’s magnetosphere tends to be in a ceaseless oscillation status because of the low dissipation property inherent in the magnetospheric plasma, and the oscillation may be driven by intermittent magnetic reconnections that occur somewhere in the magnetopause and/or the magnetotail.

A new approach of detecting the black hole spin in x-ray binaries is proposed based on the model of the coexistence of the Blandford--Znajek (BZ) and magnetic coupling (MC) processes, in which the BZ process is used to power the jet emissions from x-ray binaries, and high frequency quasi-periodic oscillations (QPOs) are explained by a rotating hotspot in the inner region of the accretion disc surrounding a fast-spinning black hole. It is shown that the black hole spins of several x-ray binaries (XTE J1550-564, GRO J1665-40 and GRS 1915+105) can be constrained in a rather narrow range, provided that QPOs and jets coexist in these sources.