The integrability of quantum systems is charactized by the algebraic notion of dynamical symmetry, hence the nonintegrability of quantum systems should be discussed topologically in reference to corresponding integrable ones. A topological approach is proposed. The topological map in general is shown to be constituted of the piecewise diffeomorphic maps interrupted by sudden nondiffeomorphic maps and thus has the similar typical feature of stretching-folding stretching ...... as the Smale horse-shoe map.

We investigate the dynamics of pulses in a cigar-shaped Bose-Einstein condensate with repulsive atom-atom interactions without using Thomas-Fermi approximation. In the linear level our results give the Bogoliubov excitation spectrum for sound propagation with speed c = c₀/√2, where c₀ is the speed for the case without trap. We develop a Korteweg-de Vries (KdV) description for dark soliton propagation in the system and show that it is the quantum pressure that contributes the dispersion necessary for the formation of the dark solitons.

Using Ф-mapping method and kth-order topological tensor current theory, we present a unified theory of describing k-dimensional topological defects and obtain their topological quantization and motion equations. It is shown that the inner structure of the topological tensor current is just the dynamic form of the topological defects, which are generated from the zeros of the m-component order parameter vector field. In this dynamic form, the topological defects are topologically quantized naturally and the topological quantum numbers are determined by the Hopf indices and the Brouwer degrees. As the generalization of Nielsen's Lagrangian and Nambu's action for strings, the action and the motion equations of the topological defects are also derived.

Using the Hamiltonian lattice gauge theory, we perform some
variational calculations to obtain the ground-state energy of SU(3) gauge field and scalar (0⁺⁺) glueball mass. The agreement of our data with the strong and weak expansion results in the corresponding limits indicates that this method can provide us reliable information in the most interesting medium region. The trial wave function used in our variational method is also proved to be a good first approximation of the ground-state of the SU(3) gauge field. Upgrading this function according to correlations of adjacent plaquettes may mean better result.

Based on an analysis of the inherent nodal structures of wave functions of 4-boson systems, we found that the internal energy of the 4⁺₁ state should be lower because its structure can be optimized without suffering a strong constraint arising from symmetry (while other 1≤L≤3 states suffer from this kind of constraints). Furthermore, two superior structures favorable in binding are found to be allowed to be possessed by 4⁺ states. These findings would lead to the appearance of two adjacent 4⁺ states, as a common feature, in the low-lying spectra of 4 boson systems.

A short cavity Er/Yb-P/Al/Si codoped fiber grating laser is demonstrated, with a pair of fiber Bragg gratings whose central resonant wavelengths are around 1551 nm and the reflectivities are 10.5 and 15 dB. The threshold value is about 48 mW and the slope efficiency is 1.1%. The signal-to-noise ratio is 59 dB, and the output central wavelength is 1550.94 nm. The peak power of 1.112 mW at a pump power of 80 mW has been achieved.

A novel fibre-optic sensing system used for temperature-strain
discrimination is presented. This system consists of an extrinsic Fabry-Perot interferometric sensor (EFPI) and a chirped in-fibre Bragg grating (CFBG) in series. The EFPI and the CFBG are wavelength-division-multiplexed (WDM) to provide strain and temperature information, respectively. The wavelength-shift of the CFBG induced by temperature change in the 1.55μm region is interrogated with an intensity-based scheme, allowing fast measurement of temperature. The cavity length change of the EFPI is measured in the 1.3μm region,
allowing strain to be measured without cross-talk from the temperature sensor, i.e. the CFBG. Experimental results show that the achieved accuracies for strain and temperature measurement are ±20 x 10^-6 and ±2°C, respectively.

One-dimensional particle-in-cell simulation is presented for the interaction of ultrashort, linearly polarized intense laser pulses with thin foil targets. The results indicate that the strong competition between electromagnetic and electrostatic ponderomotive forces produced, respectively, by the laser and the electrostatic fields leads to novel behaviours of target-electrons. It shows that the interaction is dominated by the 2ω (ω is laser frequency) component of the electrostatic ponderomotive force as well as that of the electromagnetic ponderomotive force.

Drift mode linear growth rate and quasi-linear ion thermal transport in the reversed magnetic shear plasma are investigated by using the two-fluid theory, previously developed by Weiland and the Chalmers group [J. Nucl. Fusion, 29 (1989) 1810; ibid. 30 (1990) 983]. The theory is here extended to including both the radial electrical field shear
(d E_r/d_r) and the electron fluid velocity (V_e) in the sheared coordinate system. Here, V_e describes the coupling between the safety factor q and the E_r x B velocity V_E. Their influences on the growth rate and associated ion thermal transport are obtained numerically, In addition, the ion heat pinch in the reversed shear plasma is observed. Qualitatively, the present conclusions are in good agreement with the experimental results.

Carbon nanotubes with finite lengths should be natural components of future “nano devices”. Based on orthogonal tight-binding molecular dynamics simulations, we report our study of formation energies, optimal geometrical structures and active sites of carbon nanotubes with finite lengths. This should be useful to understand the properties of such natural components.

The nominal composition of Yb₃C₆₀ compound is characterised by means of x-ray photoelectron spectroscopy. Evidence of the divalent state for the Yb cation in the as-grown crystalline Yb₃C₆₀ is obtained. After exposure to air the Yb₃C₆₀ compound transforms to an amorphous phase and Yb₂O₃ compound, while the valence state of the Yb cations changes from divalent to trivalent.

GaInNAs/GaAs single-quantum-well (SQW) lasers have been grown by solid-source molecular beam epitaxy. N is introduced by a home-made dc-active plasma source. Incorporation of N into InGaAs decreases the bandgap significantly. The highest N concentration of 2.6% in GaInNAs/GaAs QW is obtained, corresponding to the photoluminescence (PL) peak wavelength of 1.57μm at 10 K. The PL peak intensity decreases rapidly and the PL full width at half maximum increases with the increasing N concentrations. Rapid thermal annealing at 850°C could significantly improve the crystal quality of the QWs. An optimum annealing time of 5s at 850°C was obtained. The GaInNAs/GaAs SQW laser emitting at 1.2μm exhibits a high characteristic temperature of 115 K in the temperature range of 20°C-75°C.

Epitaxial monocrystalline Si was grown on porous silicon by ultra-high vacuum electron beam evaporation. Results of reflection high energy electron diffraction, atomic force microscopy, cross-section transmission electron microscopy and Rutherford backscattering spectrometry and channeling (RBS/C) show a good quality of the epitaxial layer. Furthermore, silicon-on-insulator materials were successfully produced by bond and etch back of porous silicon. The quality of the silicon on insulator samples was investigated by RBS/C and spreading resistance profiling. Experimental results show that both the crystalline quality and electrical quality are good. In addition, the interface between the top Si layer and SiO₂ buried layer is very sharp.

We report the optical oscillations with monolayer periodicity observed by an oblique-incidence reflectance difference (OIRD) technique on the epitaxial growth of Nb-doped SrTiO₃ on SrTiO₃ substrate. The periodicity was verified by the simultaneously measured reflection high-energy electron diffraction intensity oscillations. The OIRD oscillation damps during deposition, but can recover after the growth is interrupted for some time. We interpret the optical oscillations as a result of the periodic changes of the surface morphologies due to the two-dimensional layer-by-layer growth of thin films.

The expression of the ground-state energy of the electron coupled simultaneously with a Coulomb potential and a longitudinal-optical phonon field in parabolic quantum dots and wires is derived within the framework of Feynman variational path integral theory. We obtain a general result with arbitrary electron-phonon coupling constant, Coulomb binding parameters, and confining potential strength, which could be used for further numerical calculation of polaron properties. Moreover, it is shown that all the previous path-integral formulae for free polarons, bound polarons, and polarons confined in parabolic quantum dots and wires can be recovered in the present formalism.

The (Co_0.34Fe_0.66)_0.42(SiO₂)_0.58 (volume fraction) granular films were fabricated by using magnetron sputtering technique, and a saturated Hall resistivity ρ_xys of about 29μΩ.cm was observed at room temperature, which was almost 3 orders of magnitude greater than that in the pure ferromagnetic sample. The measured linear dependence of resistivity ρ_xx vs log₁₀T and magnetoresistance effect indicated that the Co_0.34Fe_0.66 volume fraction in the films were near percolation threshold. The giant Hall effect in (Co_0.34Fe_0.66)_0.42(SiO₂)_0.58 granular film may originate from percolation phenomenon.

The nonlinear properties and the dielectric properties of a new TiO₂-based varistor system, TiO₂.Y₂O₃.Nb₂O₅, have been investigated. The (Nb, Y)-doped TiO₂ ceramics have nonlinear coefficients of α =5-8 and a lower breakdown electrical field of 6-12V.mm^-1, in which the varistor of (99.3mol%)TiO₂.(0.6mol%)Y₂O₃.(0.1mol%)Nb₂O₅ composite sintered at 1400°C has a nonlinear coefficient of α =7.8 and a maximum breakdown electrical field of 12 V.mm^-1 at 1 mA.cm^-2. Also, the relative dielectric constants of the composite reach more than 85000, which is almost unchanged within the temperature range from -20 to 280°C and the frequency range of 0.5 K-2 MHz. Due to these properties the (Nb, Y)-doped TiO₂ varistors has varistor capacitance bifunctional components, which are quite useful in the situation that the voltage protection and high frequency noise absorption are meanwhile required.

The critical current density J_c and n-value have been studied from 40 K to critical temperature for four types of Bi-system 2223 tapes with different sheaths. The experimental results demonstrate that the change of J_c can be divided into three parts and n-value has some decrease with a decrease in temperature. In engineering application, a proper working temperature can be selected to satisfy the practical requirement. Furthermore, the temperature effects on critical stress for Ag-sheath tape was also studied. The results demonstrate that the critical stress does not change monotonously with a decrease in temperature. It increases first, then decreases with the further decrease in temperature.

Structural features of MgB₂ superconductors prepared under different conditions have been analysed by means of transmission electron microscopy. The MgB₂ crystal is identified to have a hexagonal structure with the space group of P6/mmm. Superconducting materials synthesized under a high pressure of 6 Gpa are made of regularly stacked grains as large as a few microns in sizes. Stacking faults and microstructure properties of grain boundaries either with or without impurities, appearing in a sample with the critical current density greater than 10⁵A/cm², have been systematically investigated.

The nearly single phase (R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ compounds (R= La, Pr, Nd, Sm, Eu, Gd and Y) with T_c about 100 K were prepared under high pressure and high temperature using the cubic anvil apparatus. The T_c is much higher than that of the traditional R-123 superconductors without doping Ca on the rare-earth site. For various rare earths with different ionic radius, the (R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ compounds have almost the same critical temperature. This is different from the result of the ion-size effect of rare-earth ions in R_1-xPr_xBa₂Cu₃O_7-δ compounds. Our results show that Pr has the same properties as other rare earths in the 123-phase compounds due to the doping of Ca.

The oscillation of tunnel splitting in Fe₈ molecular clusters is obtained as a function of magnetic field applied along the hard axis by means of instanton method with both semiclassical treatment and the effective potential field description of quantum spin system. The theoretical splittings of the instanton method are compared with the numerical result by diagonalization of spin Hamilton operator and experimental observations. By taking the appropriate parameters, our theory formula yields the result as the same as the experimental observation.

The luminescent properties of Gd₃PO₇:Eu were investigated in UV and VUV regions. This phosphor has so strong emissions around 618.5 nm under UV excitation, especially around 209\,nm, so that it has a better colour saturation than that of Y₂O₃:Eu. It would be a new potential red phosphor for lamp and other applications with UV-excitation source or even for displaying device. In the VUV excitation spectrum of Eu³⁺ emissions, energy absorptions by Gd³⁺, Gd-O and PO^3-₄ were observed, on which it can be inferred that there are three kinds of energy transferring processes to Eu³⁺ ions. The energy absorptions of Gd³⁺, Gd-O and PO^3-₄ are induced by 4f → 4f transitions, band-gap transition of Gd₃PO₇ and intramolecular (2t₂ → 2a, 3t₂) transition, respectively. The energy transfer efficiency of the PO^3-₄ intramolecular transition is lower compared with that of the band-gap transition (Gd-O).

CoCrFeO₄ nanocrystals have been synthesized using a sol-gel method. The specimen has an average grain size of 8.1 nm. The zero-field-cooled and field-cooled curves show a superparamagnetic transition occurring at a blocking temperature of T_B ≈ 249 K. The increase in coercivity of CoCrFeO₄ nanocrystals with the decreasing temperature has been detected below the blocking temperature and could be explained by the Stoner-Wohlfarth theory. The temperature dependence of saturation magnetization shows that Bloch's law holds but with the Bloch exponent lower than the bulk value.

Based on SS-model [Somogyi R and Stucki J W J. Biol. Chem. 266 (1991) 11068] for the generation of intracellular Ca²⁺ concentration oscillations, we consider a time-delay for the binding kinetics of the Ca²⁺ channel and find a significant phenomenon that the oscillation takes two quite different modes when a parameter of the system across a threshold. One is a quick oscillation mode and the other is a slow oscillation mode. They are different from each other on oscillation frequencies for more than ten times. The change of oscillation form with parameters and its critical behaviour are illustrated by numerical simulation results.

A dynamical model is presented for a thin layer of granular materials similar to that for shallow viscous fluid. We have obtained analytically the expressions for the “thermal expansion”, dispersion relation, and dependence of instability onset on driving frequency and viscosity, which are in agreement with experiments. The numerical calculation for the nonlinear problem reproduces the experimental phenomena for a one-dimensional system.

In the frame of the γ-ray pulsar outer gap model, e^± pairs in the pulsar magnetosphere are produced by the cascade of e^± pairs through synchrotron radiation of the return current from the outer gap. These pairs are accelerated mono-energetically to relativistic energies in the pulsar wind driven by low-frequency electromagnetic waves. Using Monte Carlo simulations, we generate a sample of the mature γ-ray pulsars in our Galaxy and calculate the positron production rate from these pulsars. With a simple leaky box model, we calculate the ratio of cosmic-ray positron to total electrons. Our result indicates that the pulsar contribution to the cosmic ray positron peaks at about 40 GeV and the observed e⁺/(e^-+e⁺) ratio can be explained by this model.

Some interesting behaviour of accreting particles in the gap region between the horizon of the Kerr black hole and the inner edge of the surrounding disc is investigated. The following results are obtained: (i) Spacetime coincidence of the maximum of angular velocity of accreting particles and that of the black hole horizon is extended to the more general disc-accretion. (ii) The Possibilities is discussed of negative energy of accreting particles in prograde orbit inside the ergosphere of the Kerr black hole, which is surrounded by strong enough magnetic field.

With the idea of the beaming models, we derive a relation between the observed polarization and Doppler-corrected magnitude, that is, the observed polarization is in anti-correlation with the Doppler-corrected magnitude. Making use of the infrared data observed simultaneously by Impey et al. [Mon. Not. R. Astron. Soc. 200 (1982) 19; 209 (1984) 245] and Holmes et al. [ibid. 210 (1984) 961] we found that (1) there is a significant correlation between the observed maximum polarization and Doppler-corrected magnitude but the polarization is not in anti-correlation with the Doppler corrected magnitude; (2) the maximum infrared polarization is strongly correlated with the maximum optical polarization. Our conclusion is that the infrared polarization depends only on the degree of ordering of the magnetic field in the synchotron
emission regions and not on the beaming effect. Both infrared and optical emissions originate from the synchrotron radiation.

Using the mock galaxy catalogues created from the N-body
simulations, various biasing prescriptions for modeling the
relative distribution between the galaxies and the underlying dark matter are statistically tested by using scale-scale correlation. We found that the scale-scale correlation is capable of breaking the model degeneracy indicated by the low order clustering statistics, and could be taken as an effective discriminant among a variety of biasing models. Particularly, comparing with the APM bright galaxy catalogue, we infer that the two parameter Lagrangian biasing model gives the best fit to the observed clustering features.