In this paper, we express the differential equations of a noncentral dynamical system in Ermakov formalism to obtain the Ermakov invariant. In term of Hamiltonian theories and using the Ermakov invariant as the Hamiltonian, the Poisson structure of a noncentral dynamical system in four-dimensional phase space are constructed. The result indicates that the Poisson structure is
degenerate and the noncentral dynamical system possesses four invariants: the Hamiltonian, the Ermakov invariant and two Casimir functions.

The Painlev\'e property, inverse recursion operator,infinite number of symmetries and Lie symmetry reductions of the coupled Burgers equation are given explicitly. Three sets of infinitely many
symmetries of the considered model are obtained by acting the recursion operator and the inverse recursion operator on the trivial symmetries such as the identity transformation, the space translation and the scaling transformation respectively. These symmetries constitute an infinite dimensional Lie algebra while its finite dimensional Lie point symmetry subalgebra is used to find possible symmetry reductions and then the group invariant solutions.

In this paper, the finite symmetry transformation groups and then symmetries of Lax integrable nonlinear physical systems, the Davey--Stewartson equation and the (2+1)-dimensional Camassa--Holm
equation are investigated by means of a simple direct method.

This paper studies flexural-torsional doubly coupled vibration through periodic thin-walled
open cross-section beams composed of two kinds of materials.Based on the doubly coupled vibration equation, plane wave expansion method for the thin-walled beams is provided. If the filling fraction keeps constant, the lattice is one of the factors that affect the normalized gap width. If the lattice and filling fraction keeps constant, the Young modulus contrast plays a fundamental role for the band gap width, but not density contrast. Finally, the frequency response of a finite periodic
binary beam is simulated by finite element method, which provides an attenuation of about 40dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.

The influence of noise on the remote preparation of a qubit by an entangled pair is investigated. In Bloch sphere representation, we use the trace distance to describe how close the final state is to the original state to be prepared. Our studies include two cases. Firstly, we consider the sender
and the receiver sharing a mixture of two Bell states as quantum channel in remote state preparation (RSP), and calculate the trace distance as a function of mixture ratio and angle of a state to be prepared. Secondly, the system--environment interaction is taken into account by including stochastic
fluctuating terms in the system Hamiltonian. Solving the Bloch equations, we obtain the evolution density matrix of the system. We then apply this stochastic model to study the effect of noise on the trace distance of RSP.

We consider the teleportation in the background of Kerr--Newman spacetime. Because of the Hawking effect,the fidelity of the teleportation is reduced. The results also show the fidelity is closely related to the mass, charge and rotating velocity of the black hole: high fidelity can be reached for massive, slowly rotating Kerr--Newman black holes.

In this paper, we investigate numerically the chaotic behaviours in the fractional-order Genesio--Tesi system. We find that chaos exists in the fractional-order Genesio--Tesi system with order less than 3. The lowest order we find to have chaos is 2.4 in this fractional-order Genesio--Tesi system. We propose a drive-response synchronization method for synchronizing the fractional-order chaotic Genesio--Tesi systems only using a scalar drive signal. This synchronization approach, based on stability theory of fractional-order systems, is simple and theoretically rigorous. It does not require the computation of the conditional Lyapunov exponents.Simulation results are used to visualize and illustrate the effectiveness of the proposed synchronization method.

The dynamics of fractional-order systems have attracted increasing attentions in recent years. In this paper, we study the synchronization technique based on the master--slave synchronization scheme and apply it to the synchronization of two coupled nonlinear fractional-order electronic chaotic oscillators. Simulations show that two coupled fractional-order chaotic oscillators can be brought to an exact synchronization with appropriate coupling strength. It is interesting that the synchronization rate of the fractional-order chaotic oscillators is slower than its integer-order counterpart; however, with the increase of system order, the curves of synchronization error can be smoothened, which indicates that the master--slave synchronization of two coupled fractional order oscillators can be smoothened and stabilized.

We have investigated chaotic synchronization in the generalized sense for the degenerate optical parametric oscillator (DOPO). The numerical results show that two unidirectional coupling DOPOs in chaos can be completely phase synchronization or anti-phase synchronization with a suitable coupling coefficient under which the maximum condition Lyapunov exponent (MCLE) is negative. Phase synchronization and anti-phase synchronization of chaos can be realized through positive and negative coupling. On the other hand, the different synchronization states depend on the coupling types used in the DOPO systems.

An experimental set-up for ac-measurement of thermopower between room temperature and 1200K by using modulated laser-heating has been developed. The method shows many advantages compared with the conventional dc-measurements: convenience, applicability to small samples, possibility to measure the anisotropy of single crystals, and capability to continuously trace the temperature dependence of thermopower. The thermopower of a very short piece of pure Pt was measured with the present set-up to test the reliability and accuracy of our new method.

We demonstrate a special four-probe scanning tunnelling microscope (STM) system in ultrahigh vacuum (UHV), which can provide coarse positioning for every probe independently with the help of scanning electron microscope (SEM) and fine positioning down to nanometre using the STM technology. The
system allows conductivity measurement by means of a four-point probe method, which can draw out more accurate electron transport characteristics in nanostructures, and provides easy manipulation of low dimension materials. All measurements can be performed in variable temperature (from 30K to 500K), magnetic field (from 0 to 0.1T), and different gas environments. Simultaneously, the cathodoluminescence (CL) spectrum can be achieved through an optical subsystem. Test measurements using some nanowire samples show that this system is a powerful tool in exploring electron
transport characteristics and spectra in nanoscale physics.

The capture cross sections at stellar energies are very difficult to measure directly. Hence, data are usually evaluated by using indirect methods or extrapolations from the experimental data
obtained at the lowest possible energies. The asymptotic normalization coefficient (ANC) approach of the transfer reactions provides a reliable way for the determination of the capture cross sections at stellar energies. By virtue of its reliability, we have calculated the capture cross sections of
the ^{10}Be（n，γ）^{11}Be reaction by using nuclear ANC method. ^{11}Be is a well-known neutron halo nucleus with two weakly bound states.As a typical example, we have shown that the radiative cross sections for a nucleon captured into a halo state are obviously enhanced. The enormous enhancement of the capture cross section is just due to the large overlap of the incident neutron wave with the extended tail of the halo. The ^{10}Be（n，γ）^{11}Be capture reaction is involved in the inhomogeneous big-bang nucleosynthesis. We have evaluated its reaction rates at stellar energies with the nuclear ANC method.

Using an isospin- and momentum-dependent hadronic transport model,effects of the symmetry energy on several observables in heavy-ion collisions induced by radioactive beams at intermediate energies
are studied. It is found that rapidity distribution of the isospin asymmetry of nucleon emissions, transverse momentum distribution of the ratio of free neutrons to protons at mid-rapidity, kinetic energy distribution of the ratio of \pi^{-}/\pi^{+} as well as evolution of the isospin fractionation are all sensitive to the symmetry energy.

Variational calculations are carried out with a multiconfiguration-interaction wavefunction on the 1s^{2}2p2p ^{1}D^{e} and 1s^{2}2p3p ^{3}P^{e} states to obtain the energies including the mass polarization and relativistic corrections for the beryllium isoelectronic sequence (Z=4--10). The oscillator strengths,transition rates and wavelengths are also calculated. Our results are compared with other theoretical and experimental data in the literatures. The fine structure and hyperfine structure of 1s^{2}2p3p^{3}P^{e} state are also explored.

The transition energies and the dipole oscillator strengths for the 1s^{2}2s--1s^{2}np (2≤n≤9) and 1s^{2}2p--1s^{2}nd (3≤n ≤9) of lithium-like Sc18+ ion are calculated by using the full core plus correlation method. The fine structure splittings of 1s^{2}np and 1s^{2}nd (n ≤9) states are determined from the expectation values of spin-orbit and spin-other-orbit interaction operators. The quantum defects of these series, as function of principal quantum number n, are obtained. The agreement between the f-values obtained from three alternative formulae is excellent. Comparisons of our results with experimental data available in the literature are carried out.Combining the single-channel quantum defect theory with the discrete oscillator strengths obtained in this work, this paper obtains the behaviour of discrete oscillator strengths and oscillator strength densities corresponding to the bound-free transitions adjacent to ionization threshold.

The energies, equilibrium geometries and harmonic frequencies of the triplet excited states (a^{3}Σ^{+}_{u}and b^{3}Π_{u} of spin-aligned trimer ^{7}Li_{2} are firstly calculated by using a symmetry adapted cluster-configuration interaction method. The potential curves for the two excited states have least squares fitted by the Murrell--Sorbie function.The spectroscopic data (B_{e}, α_{e}, ω_{e} , and ω_{e}χ_{e}) and the force constants (f_{2}, f_{3} and f_{4} are calculated. It is found that the spin-aligned triplet excited state b^{3}Π_{u} is more stable than the ground state X^{1}Σ^{+}_{g}, and that the Murrell--Sorbie function form is suitable not only for the ground state but also for the spin-aligned triplet excited states. Comparison between the theoretical determinations of dissociation energies, equilibrium interatomic distances and harmonic frequencies with the experimental data about a^{3}Σ^{+}_{u} and b^{3}Π_{u} clearly shows that the present work represents a significant improvement in agreement between theories and experiments.

The electromagnetic properties of the interface between a left-handed material and a conventional nonlinear material were investigated theoretically and numerically. We found a new phenomenon---optical bistability of the interface. It was shown that the incident intensity, incident angle and permeability ratio between the left-handed and the nonlinear materials could dramatically affect the optical bistable behaviour. We also compared the bistable behaviours of different electromagnetic modes. The results indicated that the TE mode was prior to the TM mode to obtain optical bistability for the same parameter.

Multiple order self-diffractions by femtosecond laser-induced transient grating in CeO_{2} doped 75TeO_{2}-25Nb_{2}O_{5}-5ZnO glass are investigated by pump-probe technique. The glass structure and component are investigated by Raman and visible--NIR absorption spectra. It is showed that there exists Ce^{3+} ion in tellurite glass, and the transient grating is created by the optical Kerr effects and improved by the excited particle grating from the resonant absorption of the ^{1}S_{0}to ^{1}F_{3} electronic energy transition of Ce^{3+} ion, and the conversion efficiency of the first order diffraction signal reaches about 11%. The results indicate that CeO_{2} doped 75TeO_{2}-25Nb_{2}O_{5}-5ZnO glass has potential applications in ultra-fast all-optical switching.

Vertical deposition technique to fabricate thin film solid artificial opals is becoming widely used. In the present work, we report our research on solvent modification and its effect on the quality of colloidal crystals. We used aqueous ethanol mixture solution to replace the ethanol solution, and used the vertical deposition technique to pack the spherical colloids into close-packed arrays. High quality samples can be prepared with thickness up to 20μm in one step. Furthermore, large spheres (diameters greater than 500nm) were successfully crystallized. Scanning electron microscopy (SEM) and optical methods were used to measure sample thickness and uniformity. The number of layers was calculated from the spectral separation of the Fabry--Perot fringes.

The focal field of a solid immersion lens (SIL) system with a high-pass angular spectrum filter is calculated by using a vector method. Numerical results show that for a radially (azimuthally) polarized input field, a high-pass angular spectrum filter can reduce the light-spot (dark-spot) size
of the SIL system. For a linearly polarized input field, however, the focal field cannot be optimized and the optical storage density of the SIL system cannot be improved by using a simple high-pass filter, either.

We propose a new conception of depolarization vector to describe the effect of depolarization induced by the second-order polarization mode dispersion (PMD). Deriving the formula of pulse broadening induced by the second-order PMD, we find that the polarization-dependent chromatic dispersion (PCD)
always enhances the pulse broadening. However the depolarization vector decreases the pulse broadening. The pulse broadening is correlated with the bit-rate of a transmission system. By adjusting the directions of the Stokes vector of initial state of polarization, initial first-order polarization dispersion vector and depolarization vector to be parallel to each other,one can obtain an optimum dispersion compensation. But when the PCD is not equal to zero, the optimum dispersion cannot achieve a complete compensation,and the minimum pulse broadening is equal to σ= (2^{1/2}/4)( DCF/T_{0}).

Nonlinear propagation of focused ultrasound in layered biological tissues is theoretically studied by using the angular spectrum approach (ASA), in which an acoustic wave is decomposed into its angular spectrum, and the distribution of nonlinear acoustic fields is calculated in arbitrary planes
normal to the acoustic axis. Several biological tissues are used as specimens inserted into the focusing region illuminated by a focused piston source. The second harmonic components within or beyond the biological specimens are numerically calculated. Validity of the theoretical model is examined by measurements. This approach employing the fast Fourier transformation gives a clear visualization of the focused ultrasound, which is helpful for nonlinear ultrasonic imaging.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

In this paper the density profile behaviour and the particle confinement operation regime on HL-1M have been studied under the pellet injection (PI),supersonic molecular beam injection (SMBI), gas puffing (GP) and lower hybrid current drive experimental situations. The relationships between density profile, particle confinement time and edge safe factor have been explored. The density profile, which is measured by six-channel far-infrared ray laser interferometer has been analysed by using the peaking coefficient calculation code. Changes of the outward and inward diffusion velocities before and after the peaking of the central density profile have been calculated using the global particle balance equations. The particle confinement operation regimes have been discussed. The peaking density profile can be easily obtained under the condition of efficient fuelling. In ohmic discharges, confinement time increases as the peaking density profile factor rises, and is saturated at a critical value related to the fuelling efficiency. The particle confinement time of SMBI lies between the values of GP and PI, and its value is about 3--5 times of the energy
confinement time.

In the fluid model, we derive a dispersion relation for the toroidal drift modes of tokamak plasmas, including the ion pressure gradient and the magnetic field gradient and curvature. It is shown that the magnetic field gradient and curvature (MFGC) can cause instabilities at the rational surface, which are of toroidicity-induced (TI) modes. On the other hand, it is discovered that the ion pressure gradient can stabilize the present MFGC instabilities. The critical threshold of ion pressure gradient, which makes the growth rate reduced to zero, is obtained both analytically and
numerically.

C_{4}F_{8} plasma with the addition of H_{2} is generated by the inductively coupled plasma (ICP) method. The relative densities of CF,CF_{2}, H and F radicals are determined by actinometric optical emission spectroscopy (AOES) as a function of the gas flow rate ratio R=H_{2}/(H_{2}+C_{4}F_{8} at a pressure of 0.8 Pa and an input r.f.power of 400W, while that of HF is measured by quadrupole mass spectrometry (QMS). The results show that plasma activity increases firstly and then decreases with increasing R. As the gas flow rate ratio R changes from 0 to 0.625, relative densities of both CF and CF_{2} decrease, and the relative [CF] has a similar tendency as the calculated [CF], indicating that CF radicals are generated mainly by the electron impact dissociation of CF_{2} radicals. Production of HF is also discussed.

Xu Rong-Kun, Li Zheng-Hong, Yang Jian-Lun, Xu Ze-Ping, Ding Ning, Guo Cun, Jiang Shi-Lun, Ning Jia-Min, Xia Guang-Xin, Li Lin-Bo, Song Feng-Jun, Chen Jin-Chuan

Chin. Phys. B 2005, 14 (8): 01613; doi: 10.1088/1009-1963/14/8/026
Full Text: PDF (997KB) (
644
)

The main results of investigation on the tungsten wire array Z-pinch implosion experiment performed on Qiang-Guang I facility in 2003 are reported in this paper. A set of diagnostic equipments including an x-ray power meter (XRPM), a 1D spatial-temporal x-ray meter and a pinhole camera was used to study implosion process and x-ray radiation characteristics of the tungsten wire array. In the experiment, the maximum x-ray yield of 36.6kJ was obtained for an optimizing load with a diameter of 8mm and a length of 20mm, which consists of 32 5-μm-diameter tungsten wires. The experimental results show that the region of x-ray emission decreased at a rate of 6.4×10^{6}cm/s by analysing the data of the 1D spatial-temporal x-ray meter. It also shows that the peak time of x-ray
radiation was prior to the time when plasmas were compressed into a near-axis region.

The plasma with high spatial uniformity at moderate pd values is achieved by using a dielectric barrier discharge reactor with two liquid electrodes. The electrical and optical characteristics of the discharge are investigated by spatiotemporally resolved measurement. Results show that the plasma with high spatial uniformity can be maintained in a wide range of applied voltages and corresponding input powers as well. The influence of wall charges on the discharge power and the spatial uniformity is discussed.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Using quantum chemistry ab initio method, geometry optimization of the singlet and triplet electronic states are performed for three isomers (ring,bowl and cage structures) of C_{20}. From the optimized geometries, MP2 calculation gives a result which does not agree with Hund's rule, i.e. the singlet state has a lower energy for all the three isomers. Further more,total charge densities and electrostatic potentials of three isomers are given by the UHF wavefunctions, the results indicate negative charges located in the central area of cage and bowl structures, and the bond character of ring structure is analysed.

Si(110) surface morphology evolution under normal-incident Ar^{+} ion sputtering has been studied as a function of Si temperature with the ion energy of 1.5keV and the ion flux 20μA/cm^{2}. During temperature rising from room temperature to 800℃, Si(110) surface morphology changes from a dim dot/hole pattern to a distinct dot one, meanwhile the surface
roughness increases steadily. The usually-accepted Bradley--Harper model fails to explain these data. By taking into account the Ehrlich--Schwoebel effect in the nanostructuring process, a simulation work was conducted based on a continuum dynamic model, which reproduces the experimental results.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Band structures, density of states, chemical bonding properties, and frequency-dependent linear and nonlinear optical properties have been investigated in terms of the density functional theory and an anharmonic oscillator model for HgGa_{2}S_{4} (HGS) and Hg_{0.5}Cd_{0.5}Ga_{2}S_{4} (HCGS) crystals. The results obtained show that the top valence bands (VBs) are contributions from Ga--S bonding states and the bottom conduction bands (CBs) are mostly due to Ga--S antibonding states for the HGS crystal, and the top VBs mostly originates from the S-3p states and the bottom CBs are mainly composed of the Ga--S antibonding states for the crystal HCGS. The population analysis shows that both crystals have mixed ionic-covalent bonds. The interactions between Ga and S atoms mostly appear as covalent character, and the Hg--S and Cd--S bonds have substantially ionic characters in HGS and HCGS crystals, respectively. The calculated refractive indices of HGS are compared with the experimental ones, and are found to be in agreement with the experiment data in the low-energy region. It is also found that the band gap of HGS is smaller than that of HCGS, and that the second-order susceptibilities of HGS are larger than those of HCGS.

The current--voltage (I--V) characteristics of Ni silicide/n-Si(100) contacts,which were formed from solid-state reaction of Ni--Si with a thin Ti capping layer at different annealing temperatures, were measured at temperatures ranging from 80K to room temperature. The low temperature I--V curves exhibit an excess current at the low bias region which is significantly larger than that predicted by the traditional thermionic emission (TE) model. A double-Schottky barrier height (SBH) model simplified from Tung's pinch-off model is used to analyse the measured I--V curves, from which the extent of the SBH inhomogeneity can be extracted. Higher annealing temperature results
in larger SBH inhomogeneity, implying the degradation of the silicide film uniformity. The thin Ti capping layer increases slightly both the NiSi phase transfer temperature and the thermal stability of the formed NiSi film.

The hot-carrier effect (HCE) of deep-submicron PMOSFETs has been investigated. It is found that the HCE includes both generation of interface states and formation of positive fixed charges in the gate oxide. We present experimental evidences showing that two degradation mechanisms are important in the case of deep-submicron PMOSFETs. Firstly, the generation of positive fixed oxide charges is significant in the case of deep-submicron PMOSFETs, which degrades the threshold voltage and even limits the transistor lifetime. For advanced analogy and mixed signal applications, process and device reliability limits need to be set up based also on threshold voltage shift, in addition to traditional methods of the transconductance degradation or gate oxide lifetime. Secondly, the
generation of interface states by holes influences the device characteristics. Some speculation on the HCE formation process is included.

The dependence of coercivity on the grain size in nanocomposite Nd_{2}Fe_{14}B/ɑ-Fe magnets with different distributions of magnetically soft and hard phases is investigated by means of statistical mean. The calculations show that when there exists no soft phase, the coercivity of magnets decreases monotonically with hard grain size reducing. For a given volume fraction of hard phase, the coercivity of nanocomposite Nd_{2}Fe_{14}B/ɑ-Fe magnets with a random distribution of soft and hard grains shows a peak value as a function of hard grain size. When the hard grain size is larger than an optimum value of soft grain size (15nm), the nanocomposite Nd_{2}Fe_{14}B/ɑ-Fe magnets with the multilayer structure of soft and hard grains can possess a higher coercivity than that with the random distribution of soft and hard grains.

In order to avoid the complicated influence of grain boundaries on the resistivity in the investigation of the ``intrinsic'' magnetoresistance (MR) effect, the magnetic and magnetotransport properties of La_{0.67}Ca_{0.33}MnO_{3} and La_{0.67}Ca_{0.33}Mn_{0.96}Fe0.04O_{3} single crystals were investigated. Owing to the absence of grain boundaries in the single crystals, MR ratio under 40×10^{5}A/m is about two orders of magnitude larger than that in polycrystalline counterparts. A further enhancement of MR ratio from 3400% to 17600% was achieved by a few percent of Fe doping. On the basis of the small polaron model, the activation energy derived from fitting the resistivity above T_{c} was found to increase upon introducing Fe. A connection between the strong localization of electrons arising from magnetic polarons and the enhancement of MR was observed in the single crystals.

The effective dielectric response of granular composites, in which spheroidal particles with graded shells are randomly distributed in a host matrix, is investigated. General expressions for the effective dielectric constant of the composites and partial resonant condition are obtained in
the dilute limit by use of a quasi-static approximation. In particular, spheroidal particles with a power-law gradation profile in the shells are studied in detail. We find that, by adjusting the dielectric gradient profile in the shells, the shape and structure of particles, it is possible
to enhance the effective dielectric constant of the composite and to realize partial resonance. Under the partial resonant conditions, the coated spheroidal particles with graded shells within the host matrix can be regarded as equivalent homogeneous spheroids embedded in the same host. The equivalent spheroids have the same dielectric constant as the original cores and semiaxes equal to those of the original shells: i.e., the partial resonant system behaves as if the cores of the particles were enlarged and the shells were absent.

The dependence of the spectral distribution of photoelectron emission from silver nano-particles embedded in BaO semiconductor thin film on external voltage and the size of silver nano-particles is predicted and investigated theoretically. The photoelectron emission response curves to light of wavelength between 0.2 and 0.8μm are given. The dependence of the wavelength threshold on the size of silver nano-particles and external field strength is also shown. Photoemission in the
visible spectrum is explained as due to the optical resonance absorption in the silver particles. This could be of importance in designing field-assisted photocathodes and finding their optimum
operation conditions.

The features of interaction of femtosecond laser pulses with photocathode are studied theoretically in this paper. The surface temperature of the metal cathode film while femtosecond laser pulses irradiation is studied with two-temperature model. With a simple photoelectric model we obtain the
optimum metal film thickness for the back-illuminated photocathode. The generated ultrashort photocurrent pulses are strongly dependent on the temperature of the electron gas and the lattice during the femtosecond laser pulse irradiation on the photocathode.

8000 CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

We propose that the emissions of an advection-dominated accretion flows (ADAF) disc are the seed
photons up-scattered to x-ray and TeV γ-rays in Mkn 501 and the instability of an ADAF disc may explain the 23-day quasi-periodic oscillation period observed in the x-rays and TeV lightcurves of Mkn 501.In this model, the ADAF emissions of optical and x-rays go into the jet and are up-scattered to high energies by relativistic electrons. In this process, the instability occurring in ADAF results in the quasi-periodic variation in the seed photons and therefore causes the variation in high energy x- and γ-rays.

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