We propose a model of weighted networks in which the structural evolution is coupled with weight dynamics. Based on a simple merging and regeneration process, the model gives power-law distributions of degree, strength and weight, as observed in many real networks. It should be emphasized that, in our model, the nontrivial degree--strength correlation can be reproduced and in agreement with empirical data. Moreover, the size-growing evolution model is also presented to meet the properties of real-world systems.

We propose a scheme of entanglement swapping and concentration in a system consisting of multi-pair entangled trapped Bose--Einstein condensates (BECs). In this scheme, entanglement swapping is accomplished by using interference-pattern joint measurements and detecting the total number of condensed atoms leaking out of relevant traps while entanglement concentration is realized by controlling inter-atomic nonlinear and tunnelling interactions. Three- and four-pair BEC schemes are investigated in detail. It is found that with the increasing number of the entangled pairs, the region of entanglement concentration is broadened and the amount of concentrated entanglement is enhanced.

We describe a protocol for telecloning a quantum state to M distant users via an (M+1)-particle W state. In the scheme, two atoms interact simultaneously with a highly detuned cavity mode with the assistance of a classical field. The scheme is insensitive to the cavity decay and the thermal field. Moreover, the Bell-state measurement can be achieved by detecting two atoms separately. Thus telecloning can be realized in a simple way.

Employing a polarization compensator, an optical fibre quantum key distribution (QKD) system based on polarization coding has been developed. To obtain the compensator setting parameters, the measurement of the laser pulse polarization is performed with one single photon detector. We obtain a sifted key bit rate of about 2kbits/s and a qubit error rate lower than 10% within 3.5h. It is shown that polarization coding can be used for QKD over optical fibres as well. At the same time, the system is simple, easy to operate, practical and user-friendly. It gains more advantages than other systems over optical fibres when used in local area quantum communications and where the functional agility is important.

A new theoretical scheme for quantum secure direct communication is proposed, where four-qubit symmetric W state functions as quantum channel. It is shown that two legitimate users can directly transmit the secret messages by using Bell-basis measurements and classical communication. The scheme is completely secure if the quantum channel is perfect. Even if the quantum channel is unsecured, it is still possible for two users to perform their secure communication. One bit secret message can be transmitted by sending a bit classical information.

We propose optical implementation for the quantum clock synchronization (QCS) algorithm by using only linear optical elements. Our method is based on the single photon representation of qubits. Two kinds of linear optical realization schemes, i.e., the location-plus-polarization-qubit scheme and the all-location-qubit scheme, are proposed, respectively. Linear optical realizations of three-qubit and four-qubit QCS algorithm are explicitly presented.

We analyse the chaotic dynamics of storage-ring free-electron lasers and report a bi-directional coupled scheme with the coupling strength varied periodically to synchronize two chaotic storage-ring free-electron lasers. The period is the same as the period of system's external modulation. The possibility of synchronization is proven according to the Lyapunov stability theory. The results of numerical simulation are obtained. Both the numerical simulation and theoretic analysis show that two storage-ring free-electron lasers can be controlled in the synchronization in a short time with this method.

We analyse the integrable boundary conditions for the one-dimensional N-component generalized Bariev model with a hard-core repulsion. The Bethe ansatz equations and the energy spectrum are obtained in the framework of the nested Bethe ansatz method.

The saddle point equation of Ginzburg--Landau Hamiltonian for the diluted Ising model is developed. The ground state is solved numerically in two dimensions. The result is partly explained by the coarse-grained approximation.

A new idea to design fibre-based digital autocorrelation technique for completely characterizing ultrashort pulses is presented. Feasibility of the design is demonstrated by theory. The technique is found to promise minimized optical alignment requirements, compact configuration, high time resolution, and short measurement time.

Zn_1-xMg_xO films are grown on A-sapphire substrates by molecular beam epitaxy, and Mg content in the Zn_1-xMg_xO films is measured by electron probe microanalysis (EPMA) when the acceleration voltage, the emission current, and the magnification are set to be 1kV, 30μA and 1000, respectively. The dead time is controlled within 17%--20% during the easurement with the receive angle of characteristic x-ray of 45°. The Mg content of the ZnMgO film is calculated by the low energy calibration and the ZAF calibration. By comparing the measurement result with the theoretical analysis and the EPMA result with the inductively coupled plasma (ICP), one can obtain that the measured value of Mg content of the samples is in good agreement with the theoretical analysis no matter whether the phase separation exists or not, and the correctness of ICP and EPMA is valid when Mg content in the samples is less than 0.5.

A new combination Monte Carlo (MC) technique of the classical Metropolis algorithm and the Swendsen--Wang cluster algorithm is proposed. Upon application of the MC technique, the thermodynamic properties of a generalized two-dimensional XY model with chiral Dzyaloshinski--Moriya (DM) interactions are simulated for various DM interactions. The specific heat, order parameter and the integrated correlation time are simulated. We find that there exists a high-temperature Kosterlitz--Thouless-type phase transition related to strong DM spin chiralities. As the DM strength increases the critical temperature of the Kosterlitz--Thouless phase transition increases. It is shown that the combination algorithm is faster than the Metropolis algorithms.

A multisymplectic variational framework for the nonlinear elastic wave equation is presented. The modified internal energy corresponding to the approximate nonlinear elastic wave equation is derived. we obtain the equation, its associated local energy and momentum conservation laws as well as the multisymplectic form simultaneously directly from the variational principle.

We obtain a solution of the DGLAP equation to extract the gluon distribution function from the deep inelastic structure function F₂ and its derivative with respect to ln Q² at low x in the next-to-leading order of perturbation theory. The values of the gluon distribution are found in the range 10^-4 ≤ x ≤ 10^-2 at Q²=20GeV². We test its validity by comparing it with that of Glück, Reya and Vogt. The detailed analysis is given for the HERA data.

Levels in the neutron-rich ¹¹²Ru nucleus have been investigated by observing prompt gamma-rays from the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The ground-state band and the one-phonon g-vibrational band have been confirmed and extended with spin up to 16ħ and 15ħ, respectively. The other two side bands, one proposed as two-phonon g-vibrational band and the other proposed as two-quasiparticle band, have been observed for the first time. The total-Routhian-surface calculations show that rotational ¹¹²Ru nucleus has triaxial deformation with parameters β₂～0.27 and γ=-29 °. The observed band crossing in the yrast band is due to the alignment of a pair of h_11/2 neutrons according to the cranked shell model calculations. The possible configuration for the quasiparticle band has also been discussed.

The evolution of shower parton distributions in a jet is investigated in the framework of a quark recombination model. The distributions are parameterized and the Q² dependence of the parameters is given by polynomials of ln Q² for a wide range of Q².

Electron cloud instability (ECI) may take place in a positron storage ring when the machine is operated with a multi-bunch positron beam. According to the actual shape of the vacuum chamber in the BEPCII, a programme which is different from the other simulation codes has been developed. Because of the distance between dipole magnet and sextupole, the quadrupole magnet of BEPCII is very short, much of the photoelectrons can be produced and can move in magnetic fields. The motion of electrons in various kinds of magnetic fields is studied in detail, especially for the solenoid field which will be wound in the vacuum pipe of BEPCII. Simulation shows that the solenoid field is very effective to confine the electrons to the vicinity of the vacuum chamber wall and to make an electron free region at the vacuum pipe centre.

We use the relative phase difference of two bichromatic fields of equal frequency differences for the coherent control of spontaneous emission of a three-level atom in the Λ configuration. Effects such as selective and total cancellation of fluorescence decay are obtained simply by varying the phase difference. The phase dependence of fluorescence spectra is attributed to the fact that the four different field components induce the transitions in a closed loop configuration.

We express a description of the state-selection role for a polar molecule in a hexapole electrostatic field. By a quantum mechanical treatment of the molecular Stark energy and a classical mechanical treatment for the molecular trajectory in the field, we present the calculated results of the different molecular rotational state selection and beam focus and discuss the influence of the high order Stark effect, the beam speed on the results for the symmetric top molecule CH₃CN, CH₃I, and the asymmetric top molecule CH₂F₂ in the hexapole field. The method established and results obtained can be taken as a guide for hexapole state selection and beam focus of polar top molecules.

Due to coupling effect, we show that it is difficult to realize the left-handed material by placing metallic wires directly into a ferrite matrix. However by introducing an insulating material round the metallic wires to decouple the direct interaction between the metallic wire and ferrite matrix, we have proposed two microstructures, which are shown by numerical simulation to have negative refractive indexes. The influence of microstructure on the transmission property is also examined.

Outline imaging by THz time domain spectroscopy is proposed. Spectroscopic splitting at interface is reported. The principle of outline imaging is put forward. Experimental results demonstrate the feasibility of outline imaging by spectroscopic splitting. It is shown that clear outline image of sample interface could be achieved easily by this technique. The spatial resolution is about 0.6mm. The THz-beam focus, the scanning step and the THz pulse width are the critical factors affecting the imaging resolution. The signal-to-noise ratio of this technique could be improved greatly compared to the conventional transmission imaging.

We propose a novel configuration for clock extraction by converting the NRZ data into the PRZ data and by employing a polarization-maintaining fibre loop mirror (PMFLM) which is usually used as an optical comb filter. It is found that the PMFLM can simply be constructed by a polarization controller and polarization-maintaining fibre (PMF). We theoretically analyse the principle of PMFLM for the NRZ-to-PRZ conversion. Experimentally we demonstrate 10Gbit/s all-optical clock recovery through our proposed setup. It is shown that recovered clock signal with an extinction ratio above 10dB can be achieved.

We study the generation of an entangled motional coherent state of two distant ions trapped in two cascaded cavities, in which the motional mode of the each ion is coupled to the respective cavity field via a linear-mixing interaction. The master equation is solved analytically by using the characteristic function method. It is found that the generated entangled coherent state resulted from the initial preparation of an even coherent state is more robust than that from an odd coherent state under the dissipation of the cavity.

An efficient and high-power diode-laser single-end-pumped Nd:YVO₄ laser with cw emission at 1342nm is presented. With a crystal single-end-pumped by a fibre-coupled diode laser, an output power of 7.36W is obtained from the laser cavity of concave-convex, corresponding to an optical-to-optical conversion efficiency of 32.8%. The laser is operated in TEM₀₀ mode with small rms noise amplitude of 0.3%. This represents, to the best of our knowledge, the highest power obtained from a diode-laser single-end-pumped Nd:YVO₄ cw laser at 1342nm so far.

An arbitrary three-phase shifting algorithm is introduced in order to achieve full range spectral optical coherence tomography imaging of biological tissue. Theoretical treatment behind this approach is given and experimentally verified. It is shown that this method is capable of eliminating the undesired auto correlation and complex conjugate images, leading to the un-obscured full range spectral OCT imaging. An intact porcine eye is used to demonstrate the potential of such a method for biological imaging.

Amorphous/crystalline n--n-isotype Si heterojunctions are made by a pulsed Q-switched second harmonic generation Nd:YAG laser. The process includes melting and subsequently fast resolidification of a thin front layer of monocrystalline Si by laser pulses to create an amorphous layer (phase transition). Different laser energy densities are used to form the amorphous layer on a monocrystalline Si substrate, the results of the electrical characteristics of the heterojunctions are dependent strongly on the laser energy density. Optoelectronic properties such as current--voltage, capacitance--voltage, and spectral sensitivity are measured in a-Si/c-Si heterojunctions (in the absence of anti-reflecting coating and frontal grid contact) prepared by different laser energy densities. The built-in-potential values extracted from current--voltage measurements are close to the published results of (n-p) amorphous/crystalline heterojunction made by glow discharge and plasma enhanced chemical vapour deposition. Furthermore, examination of the formation of amorphous pattern on Si surface is carried out with the help of optical microscopy. Best photovoltaic performance is recognized to be at 5.6J/cm². The photodetector shows a wide spectral response, and the peak response is at 780nm. On the other hand, this peak is independent of laser energy.

We demonstrate a pulse compression technique through filamentation in an argon-filled cell. By using a pair of chirped mirrors for dispersion compensation, we have successfully compressed the 53fs pulse to 15fs with good spatial qualities and good pulse stability. The total transmitted efficiency is more than 75%. The influence of the experiment parameters to the compressed pulses is also studied experimentally.

Single attosecond pulses can be generated when an intense laser pulse focused in a volume of a few cubic wavelengths (λ³) is reflected from a solid plasma surface. With relativistic two-dimensional particle-in-cell simulations, we investigate the effects of the incident laser intensity and the target surface profiles on attosecond pulse generation. Usually the width of the reflected attosecond pulse decreases and its electromagnetic energy density increases with increasing laser intensity, while the energy conversion efficiency to the attoseond pulse decreases. By changing the target surface profile, such as using a convex surface or adding proper preplasma, one can further shorten the attosecond pulse duration and meanwhile increase its energy density.

Characteristics of optical switching in a twin-core fibre coupler are numerically analysed under short pulse input by using supermode theory. The dynamic nonlinear coupled supermode equations are derived. The numerical results show that the input pulse width determines the power transfer and the pulse temporal profile in the output ports. The optimal switching characteristics can be obtained by selecting an appropriate initial pulse width. In addition, the switching characteristic curves are insensitive to the input pulse shape for either fundamental soliton pulse or Gaussian pulse input, but sensitive to pulse sharpness. A reduced switching power and a sharper switching transition can be obtained by using the sharp super-Gaussian pulse.

A multiwavelength and multiangle mathematical model (MWMA) is developed, and the corresponding influence factors of the model are analysed by the numerical calculation. Combined with measurement data of radiation flux and the curve in theoretical calculation, particle sizes of different materials can be obtained. It is found that smoke particle size gradually decreases from land plaster, cotton wick, beech wood, polyurethane, sandalwood, decahydronaphthalene, to N-heptane.

Triple-periodical photonic crystal heterostructures (ABC)^N for multichannel ultranarrow transmission filters are designed and demonstrated. Theoretical calculations and experimental results from TiO₂/SiO₂ constructed heterostructures show that each transmission channel can reach subnanometre scale, implying technical importance of such structures in the fields of integrated optics, optical communications for the design of high-performance multichannel filters, wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) systems, etc.

We demonstrate a 10.7Gb/s-line-rate L-band wavelength-division-multiplexer (WDM) loop transmission over a 1890-km standard single-mode fibre (SSMF) with a 100-km amplifier spacing as well as non-return-to-zero (NRZ) format. The dispersion compensating fibre (DCF) plus chirped fibre Bragg grating (CFBG) is employed for hybrid inline dispersion compensation. The power penalty of each channel is less than 3dB after three-loop transmission. The experimental results show that high-performance CFBGs can be successfully used in ultra-long haul (>1000km) WDM systems. We also point out that the all-CFBG compensation scheme is not suitable for re-circulating loop transmissions.

The characteristics of dust plasma sheath in an oblique magnetic field are investigated with a fluid model. Hot electrons, cold ions, neutral particles, and dust grains are taken into account in this system. We perform a numerical simulation of the sheath. The results reveal that the magnetic field has significant effects on the sheath structure, and it also makes the suspension position of dust shift away from the wall.

The characteristics of magnetohydrodynamic fast wave propagation in the solar stratified atmosphere are studied by the ray tracing method. The propagation behaviour of the wavefronts is described in detail. A magnetic field incorporating the characteristics field spreading expected in flux tubes is used, which represents the main feature of an active region. Partly ionization is considered beside the stratified solar atmosphere consisting chromosphere, transition region and corona. The study may explain the characteristics in observations of Moreton and extra-ultraviolet image telescope (EIT) waves. The wavefront incurred by the disturbance initialized at the base of the transition region propagates fast initially due to strong magnetic field, and it slows down when arriving beyond the region of flux-tube. Meanwhile, the wave propagates in the corona with a more consistent speed, as seen in the observation of EIT waves. The speeds and propagated characteristics in chromosphere and corona of the wavefronts are in agreement with those observed in H_α Moreton and EIT waves, respectively.

Effects of dipole moment on the horizontal dust lattice waves in one-dimensional dust chain are investigated. The general dispersion relations are derived. The waves are sensitive to the direction of the dipole moment, which has an angle θ (0≤θ≤π) with respect to the vertical direction.
When the waves are self-excited, it is shown that the real part of frequency for longitudinal wave is increased, while it is decreased for the horizontal transverse wave with increasing θ. When the waves are externally exited, both the real and imaginary parts of wave number are decreased for the longitudinal and transverse waves with increasing θ.

A new eigen-mode equation for the tokamak high-n (the toroidal mode number) ideal magnetohydrodynamic (MHD) ballooning mode in tokamak plasmas is derived to include the toroidal effects that are significant for stability of configurations with internal transport barriers (ITBs). For tokamak equilibria of shift circular flux surfaces, these toroidal effects basically are the finite inverse aspect ratio and the Shafranov shift. The former yields the averaged favorable curvature stabilization while the latter further strengthens this effect, leading to a low shear stable channel connecting the first and second stability regions, and to the shrinkage of unstable region in the (s,α) diagram. The dependence of the critical shear, below which the plasma is stable, on these effects is given. These results are important for understanding the ITB physics to some regards.

The propagation property of an electromagnetic wave in a thin plasma layer at high pressure is investigated with the finite-difference time-domain method. The effects of the non-uniformity of plasma distribution, and the frequency of incident wave on the propagation property of the electromagnetic wave are discussed. Numerical results indicate that the phase shift and the reflectivity of wave are sensitive to plasma density distribution, and reflectivity is lower at the middle band of frequency for different plasma distributions.

We develop the multi-slice method for calculating wavefunction of a crystal consisting of atomic columns. The new method reduces numerical calculation from two dimensions to one dimension and is much faster than that of the traditional multi-slice method. The calculated result by the one-dimensional method is in agreement with that of the traditional one.

We investigate the crystallization kinetics of Co₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂ bulk metallic glass. It is found that Co₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂ alloy shows extraordinary glass-forming ability, and a fully glassy rod with a diameter of 10,mm can be formed. Thermal analysis exhibits that this glassy alloy has a high thermal stability. Johnson--Mehl--Avrami analysis of isothermal differential scanning calorimetry demonstrates that the crystalline phases homogeneously nucleates at a constant rate and grows linearly at a constant rate in three dimensions in the supercooled liquid of the glassy alloy.

Deformation twinning is evidenced by transmission electron microscopy examinations in electrodeposited nanocrystalline (nc) Ni with mean grain size 25nm upon cryogenic rolling. Two twinning mechanisms are confirmed to operate in nc grains, i.e. heterogeneous formation via emission of partial dislocations from the grain boundary and homogeneous nucleation through dynamic overlapping of stacking faults, with the former being determined as the most proficient. Deformation twinning in nc Ni may be well interpreted in terms of molecular dynamics simulation based on generalized planar fault energy curves.

We design a pulsed power source based on the technique for explosive-driven demagnetization. The physical process and geometry structure of this power source are described in detail and several formulae are deduced to predict some important properties of the power source. With a Ф 40mm×20mm×10mm cylindrical magnet, the maximum output voltage and current reaches 125.5V and 862.9A, respectively. The rise time of the front edge of the output voltage is about 264ns. On the 0.05Ω simulative load, the net power is 37kW.

Using the four-probe method, we investigate the electrical conductivity of Cu₃N under high pressure with the diamond anvil cell. Cu₃N is a semiconductor at ambient pressure showing a band gap about 1eV. With the application of quasi-hydrostatic pressures, its resistance decreases dramatically over five orders of magnitude from ambient to 9GPa. The compound became a metal at pressure about 5.5GPa, which is in well agreement with the recent first principle calculation.

The lowest energy structures of (SiO₂)_nO₂ cluster skeletons with size from n=2 to 12 is investigated theoretically by genetic algorithm. The calculations based on the Tsuneyuki--Tsukada--Aoki--Matsui (TTAM) and Flikkema--Bromley (FB) potentials give the same result: n=4 and n=8 are the magic numbers in the virtual (SiO₂)_nO₂ cluster sequence. This conclusion is in agreement with the experimental observation on the [(SiO₂)_nO₂H₃]^- cluster sequence. The comparison of the present results with those from the density-functional-theory calculations on (SiO₂)_nO₂H₄ shows that addition of H atoms to the O terminals of (SiO₂)_nO₂ clusters to form the complex (SiO₂)_nO₂H₄ clusters has only minor influence on the relative energies and the structures of different isomers. This means that the magic behaviour of the clusters [(SiO₂)_nO₂H₃]^- (n=4, 8) observed in our previous experiment is originated from the stability of the cluster skeletons (SiO₂)_n0₂ (n=4, 8).

The comparative study of epitaxial 380-nm-thick p-Al_0.91Ga_0.909 N materials without and with special surface chemical treatment is systematically carried out. After the treatment process, the deep level luminous peak in the 10K photoluminescence spectrum is eliminated due to the decrease of surface nitrogen vacancy V_N related defective sites, while the surface root-mean-square roughness in atomic force microscopy measurement is decreased from 0.395nm to 0.229nm by such a surface preparation method. Furthermore, the performance of surface contact with Ni/Au bilayer metal films is obviously improved with the reduction of the Schottky barrier height of 55meV. The x-ray photoelectron spectroscopy (XPS) results show a notable surface element content change after the treatment which is considered to be the cause of the above-mentioned surface characteristics improvement.

A GaAs/AlGaAs two-dimensional electron gas (2DEG) structure with the high mobility of mu_2K=1.78×10⁶cm¹/Vs has been studied by low-temperature Hall and Shubnikov de Hass (SdH) measurements. Quantum lifetimes related to all-angle scattering events reduced from 0.64ps to 0.52ps after illuminating by Dingle plots, and transport lifetimes related to large-angle scattering events increasing from 42.3ps to 67.8ps. These results show that small-angle scattering events become stronger. It is clear that small-angle scattering events can cause the variation of the widths of the quantum Hall plateaus.

We theoretically investigate the Kondo effect of a three-terminal transport quantum dot (QD) embedded in an Aharonov--Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We find that in this system, the Kondo effect depends sensitively on the parity and size of the ring; the Kondo screening cloud can be tuned by tuning the coupling strength of the reservoir-dot. Thus this model might be a candidate for future device applications.

We detect the photo-induced carriers in near-stoichiometric iron doped LiNbO₃ crystal by the holographic technique. The results show that the dominant carriers are electrons in the sample with Li/Nb ratio of 0.9988. By analysis of the OH^- absorption spectra of the crystal, we contribute the electron domination in near-stoichiometric Fe-doped LiNbO₃ crystal to the existence of Nb_Li which provides the anti-site defect to Fe²⁺.

We prepare 2×(NiFe/CoZnO)/ZnO/(CoZnO/Co)×2 spin valve structures used for spin injection by sputtering and photolithography. In the junctions, the free magnetic layer 2×(NiFe/CoZnO) and the fixed magnetic layer (CoZnO/Co)×2 are used to realize the spin valve functions in the external switch magnetic field. Since the wide gap semiconductor ZnO layer is located between the two magnetic semiconductor layers CoZnO, the electrical spin injection from the magnetic semiconductor CoZnO into the non-magnetic semiconductor ZnO is realized. Based on the measured magnetoresistance and the Schmidt model, the spin polarization ratio in the ZnO semiconductor is deduced to be 11.7% at 90K and 7.0% at room temperature, respectively.

Dependences of anticrossing gaps between pairs of subbands in Al_xGa_1-xN/GaN double quantum wells (DQWs) on the width and the Al composition of the central barrier of the DQWs and on the well width of the DQWs have been investigated by solving the Schrödinger and Poisson equations self-consistently. It is found that the anticrossing gaps are not influenced by the polarization-induced electric field in the DQWs. The anticrossing gaps decrease with increasing the width and the Al composition of the central barrier of the DQWs, as well as with the increasing well width of the DQWs. According to the results of the calculation, the anticrossing gaps can reach 150meV in Al_xGa_1-xN/GaN DQWs. There is significant coupling between the two wells of the DQWs when the width of the central barrier of the DQWs is narrower than 2nm.

A block model is used to calculate the combinative energy in LnBa₂Cu₃O_7-x (Ln=Y, Er, Nd) systems, and the energy has no difference for orth-I and orth-II in the plateau range. Namely, no matter what phase it is, when the oxygen deficiency is in the range of δ～0.35--0.55, the plateau appears in the energy -δ curves, and the combinative energy has close correlation with the T_c value. The result in the present work gives some hints to reconsider the role of the order of oxygen defects or its effect on superconductivity in LnBa₂Cu₃O_7-x. The existence of the orth-II seems not to be the reason for the plateau in the T_c curve. This is an important problem for LnBa₂Cu₃O_7-x and some suggestion is given in the discussion.

Infrared absorption spectra of La_0.67-xPr_xCa_0.33MnO₃ (x=0, 0.18 and 0.36) are experimentally studied in the temperature range 20--300K. Absorption peak splitting corresponding to the stretching oscillation of the Mn--O bond, together with a shift of peak position, is observed below the Curie temperature. These features weaken and even disappear as the samples are warmed up to the Curie temperature, which indicates that this anomaly may be a result of phase separation in the compounds.

Thermal hysteresis in the resistivity of La_2/3Ca_1/3MnO₃ thin films grown on tilted SrTiO₃ substrates is simulated by using the random network model on the basis of mixed-phase percolation between metallic and insulating domains. The metallic-insulating transition temperatures during the warming process are lower than those during the cooling process due to the difference in fraction of metallic domains between warming and cooling process. With an external magnetic field, the metallic--insulating transition temperatures shift to a higher value and the resistivities are reduced. The excellent agreement between the simulation and the experimental data further verifies that phase separation plays a crucial role in the transport process of La_2/3Ca_1/3MnO₃ thin films.

The synthesis and magnetoelectric (ME) characterization of bilayers of Pb(Zr,Ti)O₃ (PZT) and hot pressed manganite perovskite La_0.7Sr_0.3MnO₃ (LSMO) are discussed. Very strong ME interactions are measured for the bilayers. The bilayers exhibit superior ME coupling compared to thick-film composites prepared by tape casting process. Data of the ME voltage coefficient have been obtained as functions of bias magnetic field H, temperature and frequency. The transverse coupling is stronger than the longitudinal interactions and a maximum in the ME voltage coefficient is measured at 225K. The frequency dependence of the ME voltage coefficient reveals a peak at the electromechanical resonance due to radial modes.

We have studied the interfacial reactions between amorphous LaAlO₃ thin films and Si substrates, using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interfacial layer between LaAlO₃ film and Si substrate is SiLa_xAl_yO_z. The depth distributions of La, Si and Al chemical states show that the ratio of La 4d_3/2 to Al 2p of the interfacial layer remains unchanged with the depth compared to that of the LaAlO₃ film. Moreover, the Si content in the interfacial layer gradually decreases with increasing thickness of the interfacial layer. These results strongly suggest that the Al element is not deficient in the interfacial layer, as previously believed, and the formation of a SiLa_xAl_yO_z interfacial layer is mainly due to the diffusion of Si from the substrate during the LaAlO₃ film deposition. With the understanding of the interfacial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics.

The imaging quality of a lossy left-handed material (LHM) slab is studied. The exact solution is obtained for the interaction of a monochromatic source with a lossy LHM slab by Fourier integrals in wave number domain. It is found that a small amount of loss may have a strong suppression of the super-resolution ability. However, the resolution of a lossy slab can still be better than a conventional lens because the evanescent wave can still be partly restored if the loss is small enough. The localized field with large amplitude (surface bright spots) near the interfaces of the slab is related to the resonance of the coupling between surface waves at the interfaces. The evanescent wave restoration and the surface bright spots are two relevant phenomena. The distance of the bright spots is close to the half of the resolution length.

The upconversion luminescence and dynamics in Er³⁺/Yb³⁺ codoped nanocrystalline yttria (7--65nm) are studied under 980-nm pulsed laser excitation. It is found that the red emission of ⁴F_9/2--⁴I_15/2 and the green emission of ²H_11/2/⁴S_3/2 in nanoparticles with lower concentration of Yb³⁺ result from a two-photon excitation. In nanocrystals with higher Yb³⁺ concentration, the red emissions from a two-photon excitation, while the green emissions from a three-photon excitation. The luminescence dynamics indicates that as the particle size decreases, both the rise and the decay time constants become shorter. As the size decreases to several nanometres, the rise process nearly disappears, suggesting that the upconversion luminescence originates mainly from self-excitation of Er³⁺, instead of the energy transfer of Yb³⁺ to Er³⁺.

We report the spectroscopic properties and thermal stability of Tm³⁺-doped Ga₂O₃-GeO₂-Bi₂O₃-PbO(PbF₂) glasses for 1.47-μm optical amplifications. Effects of PbF₂ doping on the optical properties and thermal stability of Tm³⁺-doped gallate--germanium--bismuth--lead glass are investigated. The measured peak wavelength and full width at half-maximum of the fluorescence are 1465nm and ～ 120nm, respectively. Significant enhancement of the 1.47-μm emission and the lifetime of a ³⁺H₄ level with increasing PbF₂ doping have been observed. The presence of GeO₂ provides two potentials of increasing the thermal stability and shortening the ultraviolet cutoff band of host glasses.

A Si-based novel Fabry--Perot microcavity device that can emit blue-green light at room temperature is proposed and fabricated. One of its Bragg reflectors consists of periodically stacked a-SiO₂/a-Si:H layers deposited on the glass by plasma enhanced chemical vapour deposition. The other reflector is a sputtered Al film. The active region between both the reflectors is constructed by a p-type a-SiC_x:H/intrinsic-type a-SiC_x:H junction from which the electroluminescence (EL) is originated. The EL spectra of this device are recorded by RENISHAW RM2000, a sharp and strong EL peak at 483nm with FWHM of 20nm is observed when the device is driven by dc voltages of 8V, 12V and 18V at room temperature. The intensity of EL increases with the applied voltage while the luminescence wavelength keeps unchanged. Compared with the EL spectra from the sample without the Bragg reflector, the luminescence intensity is about 10 times enhanced and the peak is narrowed greatly. The luminescence mechanism is analysed in detail.

Two kinds of subwavelength hole arrays in metallic films are designed to verify the important role of the periodicity in enhanced transmission of light. The measured optical spectra show that the quasiperiodic hole arrays exhibit an enhanced transmission peak centred at 707nm with a transmission intensity of about 20%, while no plasmon resonance peak is found for the amorphous hole arrays. When the hole diameter decreases in the quasiperiodic structure, the position of the transmission peak shifts slightly, and the transmittance drops. These phenomena indicate the important role of the long-range structural order (particularly the periodicity) in assisting the coupling of incident light wave with the surface plasmon modes of the metallic structures.

Defects in ZnO films grown by radio-frequency reactive magnetron sputtering under variable ratios between oxygen and argon gas have been investigated by using the monoenergetic positron beam technique. The dominate intrinsic defects in these ZnO samples are O vacancies (V₀) and Zn interstitials (Zn_i) when the oxygen fraction in the O₂/Ar feed gas does not exceed 70% in the processing chamber. On the other hand, zinc vacancies are preponderant in the ZnO films fabricated in richer oxygen environment. The concentration of zinc vacancies increases with the increasing O₂ fraction. For the oxygen fraction 85%, the number of zinc vacancies that could trap positrons will be smaller. It is speculated that some unknown defects could shield zinc vacancies. The concentration of zinc vacancies in the ZnO films varies with the oxygen fraction in the growth chamber, which is in agreement with the results of photoluminescence spectra.

Zincblende CrSb (zb-CrSb) layers with room-temperature ferromagnetism have been grown on relaxed and strained (In,Ga)As buffer layers epitaxially prepared on (001) GaAs substrates by molecular-beam epitaxy. The structural characterizations of CrSb layers fabricated under the two cases are studied by using synchrotron grazing incidence x-ray diffraction (GID). The results of GID experiments indicate that no sign of second phase exists in all the zb-CrSb layers. Superconducting quantum interference device measurements demonstrate that the thickness of zb-CrSb layers grown on both relaxed and strained (In,Ga)As buffer layers can be increased to ～12 monolayers (～3.6nm), compared to ～3 monolayers (～1nm) on GaAs directly.

Novel AlGaN/GaN high electron mobility transistors (HEMTs) with an insulated gate have been demonstrated by oxidizing the surface of an AlGaN layer using inductively coupled O₂ plasma. X-ray photoelectron spectroscopy measurement reveals that O₂ plasma treatment can produce a thin oxidized layer on the AlGaN surface. The insulated-gate devices are realized by plasma oxidization before gate metallization. The reverse gate leakage current of the fabricated HEMT has been reduced in two orders of magnitude, and the cut-off frequency increases from 5.4GHz to 6.5GHz.

Spiking neurons usually change their membrane properties, especially ion channel activity, during adaptation or synaptic modification to improve information processing and transmission. Using simple and biophysically realistic models, our analyses reveal that activity-dependent regulation of membrane properties contributes to sensitivity adaptation that improves the neuron ability of detecting sub-threshold signals in the presence of background noises. The improvement is achieved by regulating the conductance of ion channels on the membrane, dependent on the neuron firing activity.

We construct a system of magnetic tweezers and apply it to study the interaction between histones and DNA. The condensation of DNA by purified histones at low ionic strengths is directly monitored by recording the length of the DNA as a function of elapsed time. It is found that DNA condensates in a dynamic manner. The binding of histones to DNA is energetically favoured, but the tension applied on DNA tends to unravel the DNA-histone complex. The competition between the two processes determines the rate of the DNA condensation.

We have investigated the collective behaviour of an array of coupled minimal cytosolic Ca²⁺ oscillation models by numerical methods, taking into account the external noise resulting from the random extracellular stimulation. It is found that the system size, i.e. the number of minimal cytosolic Ca²⁺ oscillation models, has an optimal value, at which the system collective dynamics shows the best performance. The effect of the coupling strength has also been studied. Such a phenomenon of system-size resonance has been found for different coupling strengths, but the optimal system size increases when the coupling strength increases.

Photoacoustic tomography (PAT) is a powerful imaging technique for medical diagnosis because it combines the merits and most compelling features of light and sound. We describe a PAT experimental system constructed in our laboratory which consists of a Q-switched Nd:YAG pulse laser operating at 532nm with a 8-ns pulse width to generate the photoacoustic signals from a biological sample. Two-dimensional photoacoustic imaging of blood vessel networks 1cm below the tissue surface is achieved. We also successfully demonstrate that the system is capable of imaging the blood vessels over the ex vivo rat brain with skull and skin intact.

Nonlinear weak solution theory is applied to determine the parameters of a wide cluster in an ``anisotropic'' higher-order traffic flow model. These parameters are the maximal and minimal densities and the travelling wave speed in the solution structure. Numerical experiments show that the convergent simulation results are in good agreement with those obtained from the analytical expressions.

A new estimation based on the Shannon entropy for the power-law distribution parameter is presented. The maximum likelihood estimation (MLE) of the parameter is discussed and the relation between the MLE and the moment estimation of the parameter is given out. It is shown that the minimum Shannon entropy estimation is equivalent to the MLE giving the log expectation.

We construct a family of self-similar solutions to describe radiatively inefficient accretion flows with outflow. We show that outflow has important effects on the dynamical structure of accretion flows. In particular, we prove that outflow can be an effective mechanism of removing the released gravitational energy of accreted gas.