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Chin. Phys. B  
  Chin. Phys. B--2005, Vol.14, No.6
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The discrete variational principle in Hamiltonian formalism and first integrals

Zhang Hong-Bin, Chen Li-Qun, Liu Rong-Wan
Chin. Phys. B 2005, 14 (6): 01063;  doi: 10.1088/1009-1963/14/6/001
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The aim of this paper is to show that first integrals of discrete equation of motion for Hamiltonian systems can be determined explicitly by investigating the invariance properties of the discrete Lagrangian in phase space. The result obtained is a discrete analog of the theorem of Noether in the Calculus of variations.

Exact discrete soliton solutions of quintic discrete nonlinear Schr?dinger equation

Li Hua-Mei, Wu Feng-Min
Chin. Phys. B 2005, 14 (6): 01069;  doi: 10.1088/1009-1963/14/6/002
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By using the extended hyperbolic function approach, we consider a quintic discrete nonlinear Schr?dinger (QDNLS) equation and obtained new exact localized solutions ,including discrete bright soliton solution, dark soliton solution, alternating phase bright soliton solution and alternating phase dark soliton solution ,if a special constraint is imposed on coefficients of the equation.

Exact solutions of N-dimensional harmonic oscillator via Laplace transformation

Chen Gang
Chin. Phys. B 2005, 14 (6): 01075;  doi: 10.1088/1009-1963/14/6/003
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The N-dimensional Schr?dinger equation for the harmonic oscillator is reduced to a first-order differential equation in terms of the Laplace transformation and the exact bound state solutions are derived. It is shown that this method to solve the Schr?dinger equation may serve as a substitute for the standard functional, analytical approach also in lower dimensions.

Stochastic resonance in an asymmetric bistable system driven by multiplicative and additive noise

Xu Wei, Jin Yan-Fei, Li Wei, Ma Shao-Juan
Chin. Phys. B 2005, 14 (6): 01077;  doi: 10.1088/1009-1963/14/6/004
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The phenomenon of stochastic resonance (SR) in a bistable system driven by multiplicative and additive white noises and a periodic rectangular signal with a constant component is studied according to the theory of signal-to-noise ratio (SNR) in the adiabatic limit. The analytic expression of the SNR is obtained for arbitrary signal amplitude without being restricted to small amplitudes. We find that the effects of the multiplicative noise intensity D and additive noise intensity α on SNR are different: the SNR-αcurve shows SR for almost the whole range of static asymmetry r, but the SNR-D curve only displays SR for some values of static asymmetry r. It is more sensitive to control SR through adjusting the additive noise intensity α than adjusting the multiplicative noise intensity D, when the asymmetry of bistable potential r is not too large. Moreover, the static asymmetry r decreases the SNR.

Another anticontrol method of chaos in the sense of Devaney from a Takagi-Sugeno fuzzy system via the overflow nonlinearity

Lu Jun-Guo
Chin. Phys. B 2005, 14 (6): 01082;  doi: 10.1088/1009-1963/14/6/005
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Another simple and systematic decentralized feedback anticontrol algorithm of chaos in the sense of Devaney is proposed for arbitrarily given discrete-time Takagi-Sugeno (TS) Fuzzy systems. Based on a given discrete-time TS Fuzzy system, the new chaotification algorithm uses the decentralized state feedback control and the overflow nonlinear function of the 2’s complement arithmetic to construct a chaotic system. Based on Shi-Chen theorem, we mathematically prove that the constructed system is indeed chaotic in the sense of Devaney. In particular, an explicit formula for the computation of chaotification parameters is also obtained. A numerical example is used to visualize and illustrate the theoretic results.

Another anticontrol method of chaos in the sense of Devaney from a Takagi-Sugeno fuzzy system via the overflow nonlinearity

Shi Xia, Lu Qi-Shao
Chin. Phys. B 2005, 14 (6): 01088;  doi: 10.1088/1009-1963/14/6/006
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Noise effects on coherence resonance and synchronization of Hindmarsh-Rose (HR) neu model are studied. The coherence resonance of a single HR neuron with Gaussian white ndded to membrane potential is investigated in situations before, near and after the Hopf bifuion, separately, with the external direct current as a bifurcation parameter. It is shown that ehough there is no coupling between neurons, uncoupled identical HR neurons driven by a comm noise can achieve complete synchronization when the noise intensity is higher than a critical va Furthermore, noise also enhances complete synchronization of weakly coupled neurons. It is cluded that synchronization in bursting neurons is easier to be induced than in spiking ones,oupling enhances the sensitivity of synchronization of neurons to noise stimulus.

A complementary least-mean-square algorithm of adaptive filtering for SQUID based magnetocardiography

Li Zhuo, Chen Geng-Hua, Zhang Li-Hua, Yang Qian-Sheng, Feng Ji
Chin. Phys. B 2005, 14 (6): 01095;  doi: 10.1088/1009-1963/14/6/007
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We present a complementary least-mean-square algorithm of adaptive filtering for SQUID based magnetocardiography, in which both rapid convergence and fine tracking are realized by switching the weight parameters back and forth between two filters according to the least mean square principle.

Hybrid CIS-DFT method to study electric field effects on electronic excited states of ethylene

Ma Mei-Zhong, Zhu Zheng-He, Chen Xiao-Jun, Xu Guo-Liang, Zhang Yong-Bin, Mao Hua-Ping, Shen Xiao-Hong
Chin. Phys. B 2005, 14 (6): 01101;  doi: 10.1088/1009-1963/14/6/008
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The present work is devoted to the study of the effects of external dipole electric field on the molecular structure of ethylene using a hybrid method which combines the single-excitation configuration interactions (CIS) with density functional theory(DFT), i.e. CIS-DFT(B3LYP). It is found that the effects of electric dipole field on the molecular geometry (D2h, D2d and C2v), dipole moment, transition dipole moment, polarizability and, particularly, excitation energy of ethylene are rather remarkable. The advantages of hybrid CIS-DFT method are that it can determine the symmetry of molecule and the correct order of excitation as well as the Molecular Orbital(MO) electron configuration, thereby the electronic excitation states of ethylene are easily derived out, and most of them are in agreement with those obtained in experiments or references. It may be the first time the effects of external electric field on ethylene molecule have been considered. Compared with other ab initio methods, the CIS-DFT method is relatively accurate and low in computation cost. We expect that it can be used to study other closed-shell molecules.

Energy-crossings and their effects on the spectra of the neon-like ions

Dong Chen-Zhong, Xie Lu-You, Wan Jian-Jie, Jiang Jun
Chin. Phys. B 2005, 14 (6): 01108;  doi: 10.1088/1009-1963/14/6/009
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Excitation energies, transition wavelengths and probabilities of the 2p6, 2p5 3l,2s 2p6 3l (l = 0; 1; 2) states along the Ne-like isoelectronic sequence from Z =21?92 have been calculated by using the Multi-conˉguration Dirac-Fock package GRASP92 and a newly developing radiative transition program REOS99. In the calculations, the correlation and relaxation e?ects are included systematically.Based on the calculations, all possible energy crossings among the level groups with the same parity and total angle momentum have been presented. It is found that there are strong conˉguration interactions in some particular Z regions with energy-crossings, and which can cause a dramatic change of the related transition probabilities.

Asymmetry of the photoionization rate of H atoms by a sequence of one-cycle laser pulses

Bai Li-Hua, Zhang Jing-Tao, Xu Zhi-Zhan
Chin. Phys. B 2005, 14 (6): 01114;  doi: 10.1088/1009-1963/14/6/010
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Using an unperturbated scattering theory, the characteristics of H atom photoionization are studied respectively by a linearly and by a circularly polarized one-cycle laser pulse sequence. The asymmetries for photoelectrons in two directions opposite to each other are investigated. It is found that the asymmetry degree varies with the carrier-envelope (CE) phase, laser intensity, as well as the kinetic energy of photoelectrons. For the linear polarization, the maximal ionization rate varies with the CE phase, and the asymmetry degree varies with the CE phase in a sine-like pattern. For the circular polarizaion, the maximal ionization rate keeps constant for various CE phases, but the variation of asymmetry degree is still in a sine-like variation pattern.

Experimental observation of pump-probe spectra of caesium D2 line with a vapour cell

Wang Yan-Hua, Yang Hai-Jing, Zhang Tian-Cai, Wang Jun-Min
Chin. Phys. B 2005, 14 (6): 01120;  doi: 10.1088/1009-1963/14/6/011
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Pump-probe spectra of cesium (Cs) D2 line are experimentally investigated in a Cs atomic vapor cell with co-propagating orthogonal linearly-polarized pump and probe laser beams. Absorption-reduction dips duo to electromagnetically induced transparency (EIT) in multi-Λ-type Zeeman sublevels of 6 S1/2 F=3 – 6 P3/2 F’=2 hyperfine transition and absorption-enhanced peaks due to electromagnetically induced absorption (EIA) in 6 S1/2 F=4 – 6 P3/2 F’=5 hyperfine transition are demonstrated. With detuned pump beam abnormal sign-reversed signals inside the EIT dip and the EIA peak are clearly observed.

Total cross sections for electron scattering at 10-5000eV by polyatomic molecules CF4, CF3H, C2F4, C2F6, and C2H3F3

Sun Jin-Feng, Xu Bin, Liu Yu-Fang, Shi De-Heng
Chin. Phys. B 2005, 14 (6): 01125;  doi: 10.1088/1009-1963/14/6/012
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The additivity rule and complex optical potential approach have been employed to obtain the total (elastic and absorption) cross sections for electron scattering by molecules (CF4, CF3H, C2F4, C2F6, and C2H3F3) over an incident energy range from 10 to 5000eV. Compared with other calculations and experimental data wherever available, excellent agreement has been obtained. Above 1000eV, there are no experimental dates for CF3H, C2F4, C2F6 and C2H3F3, so the present results can provide comparison and foretell for experimental research

Fractional Fourier transform of flat-topped multi-Gaussian beams based on the Wigner distribution function

Wu Ping, Lü Bai-Da, Chen Tian-Lu
Chin. Phys. B 2005, 14 (6): 01130;  doi: 10.1088/1009-1963/14/6/013
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By using the Wigner distribution function (WDF), the fractional Fourier transform (FRFT) of flat-topped multi-Gaussian(FTMG) beams is studied. Analytical expressions for the intensity distribution, beam width, far-field divergence angle,M2 factor and K parameter of FTMG beams are derived. The influence of fractional order on transformation properties of FTMG beams in the FRFT plane is illustrated with numerical examples.

Application of an approximate vectorial diffraction model to analysing diffractive micro-optical elements

Niu Chun-Hui, Li Zhi-Yuan, Ye Jia-Sheng, Gu Bei-Yuan
Chin. Phys. B 2005, 14 (6): 01136;  doi: 10.1088/1009-1963/14/6/014
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Scalar diffraction theory, although simple and efficient, is too rough for analyzing diffractive micro-optical elements. Rigorous vectorial diffraction theory requires extensive numerical efforts,and is not a convenient design tool. In this paper we employ a simple approximate vectorial diffraction model which combines the principle of the scalar diffraction theory with an approximate local field model to analyze the diffraction of optical waves by some typical two-dimensional diffractive micro-optical elements. Both the TE and TM polarization modes are considered. We have found that the approximate vectorial diffraction model can agree much better with the rigorous electromagnetic simulation results than the scalar diffraction theory for these micro-optical elements.

Optical polarized properties related to the oxygen vacancy defect in the PbWO4 crystal

Liu Ting-Yu, Zhang Qi-Ren, Zhuang Song-Lin
Chin. Phys. B 2005, 14 (6): 01142;  doi: 10.1088/1009-1963/14/6/015
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The electronic structures, dielectric functions, complex refractive index and absorption spectra for the PbWO4(PWO) crystal with and without oxygen vacancy VO2+ have been calculated using the full-potential (linearized) augmented plane-wave (FP-LAPW) + local orbitals (LO) method with the lattice structure optimized. The calculated results indicate that the optical properties of the PWO crystal show anisotropy and its optical symmetry coincides with the lattice structure geometry of the PWO crystal. The calculated absorption spectra indicate that the stoichiometric PWO crystal does not display absorption band in the visible and near-ultraviolet range. However, in this range, the absorption spectra of the PWO crystal containing VO2+ exhibit two peaks at 3.35eV(370nm) and 2.95eV(420nm), respectively. It reveals that the 350nm and 420nm absorption bands are related to the existence of VO2+ in the PWO crystal.

Linear entropies in the Jaynes-Cummings model with intensity-dependent coupling in a phase-damped cavity

Zhou Qing-Chun, Zhu Shi-Ning
Chin. Phys. B 2005, 14 (6): 01147;  doi: 10.1088/1009-1963/14/6/016
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We investigate the evolution of a quantum system described by the Jaynes-Cummings model with an arbitrary form of intensity-dependent coupling by displaying the linear entropies of the atom, field and atom-field system in the large detuning approximation. The cavity field is assumed to be coupled to a reservoir with a phase-damping coupling. The effects of cavity phase damping on the entanglement and coherence loss of such a system are studied.

Influence of atomic motion on squeezing of double-mode field in interaction with a moving V-type three-level atom

Zhu Ai-Dong, Zhang Shou, Zhao Yong-Fang
Chin. Phys. B 2005, 14 (6): 01152;  doi: 10.1088/1009-1963/14/6/017
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The influences of atomic motion on squeezing of the double-mode field are investigated in the interaction with a moving V-type three level atom by means of the quantum theory and the method of numerical analysis. The results show, on the one hand, when the initial photon field is in non-correlative coherent state of double-mode, only the quadrature U1 is squeezed and the squeezed degree of U1 increases with the increasing of the parameter β which denotes the atomic motion and structure of the field mode. On the other hand, when the initial field is in the vacuum squeezed state of double-mode, the quadrature U2 is squeezed principally and we can obtain a steady squeezed light by choosing an appropriate parameter β.

Time evolution of the intensity correlation function in a single-mode laser driven by both the coloured pump noise with signal modulation and the quantum noise with cross-correlation between the real and imaginary parts

Cheng Qing-Hua, Cao Li, Xu Da-Hai, Wu Da-Jin
Chin. Phys. B 2005, 14 (6): 01159;  doi: 10.1088/1009-1963/14/6/018
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Using the linear approximation, we have studied the time evolution of intensity correlation function C(t) in a single-mode laser driven by both the colored pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts. In the case of the pump noise self-correlation time, we find that the time evolution of C(t) varies with modulation signal frequency Ω, amplitude B, and net gain ɑ0. (i) As the Ω increases, the time evolution of C(t) experiences a process changing from the monotonous descension to the descension with a flat appearing initially, and finally to the a form of damping oscillation; (ii) As the B increases, it experiences from monotonous descension to the appearance of a maximum; (iii) As the net gain ɑ0 increases, it experiences a process repeatedly changing from the monotonous descension to monotonous ascension, and to the appearance of a maximum, finally to monotonous descension again. However, in the case of, the time evolution of C(t) only exhibits a form of damping oscillation .

Thermal entanglement in 1D optical lattice chains with nonlinear coupling

Zhou Ling, Yi Xue-Xi, Song He-Shan, Guo Yan-Qing
Chin. Phys. B 2005, 14 (6): 01168;  doi: 10.1088/1009-1963/14/6/019
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The thermal entanglement of spin-1 atoms with nonlinear coupling in an optical lattice chain is investigated for two-particle and multi-particle systems.It is flund that the relation between linear coupling and nonlinear coupling is the key to determine thermal entanglement, which shows in what kinds of atomsthermal entanglement exists.Thisresult is true both for two-particle and multi-particle systems. For multi-particle systems,the thermal entanglement does not decrease greatly,and the critical temperature decreases only slightly.

Theory of passively mode-locked lasers with self-frequency shift and saturable absorber response

Song Li-Jun, Shi Xiao-Juan, Li Lu, Li Zhong-Hao, Zhou Guo-Sheng
Chin. Phys. B 2005, 14 (6): 01174;  doi: 10.1088/1009-1963/14/6/020
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A general theoretical model for passively mode-locked lasers is presented, in which both the self-frequency shift and either a fast or a slow saturable absorber response are taken into account. An exact soliton-like solution and conditions for its existence are obtained under a definite compatible condition. The stability of the solution is analyzed by using a variational method, and a parameter region, in which the solution is linearly stable, is acquired theoretically. To verify the theoretical predictions, a typical example is given for stable pulse propagation over a long distance. The numerical results show that the soliton-like solution is stable under some perturbations within the linearly stable region and quite an arbitrary Gaussian pulse converges to the exact soliton-like solution after evolution in a distance.

Formation of arrayed holes on metal foil and metal film by multibeam interfering femtosecond laser beams

Zhao Quan-Zhong, Qiu Jian-Rong, Zhao Chong-Jun, Jiang Xiong-Wei, Zhu Cong-Shan
Chin. Phys. B 2005, 14 (6): 01181;  doi: 10.1088/1009-1963/14/6/021
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We report on an optical interference method to fabricate arrayed holes on metal nickel foil and aluminum film deposited on glass substrate by means of five-beam interference of femtosecond laser pulses. Optical microscope and scanning electron microscope observations revealed that arrayed holes of micrometer-order are fabricated on both metal foil and metal film. The present technique allows one-step, large-area, micrometer processing of metal materials for potential industrial applications.

New equation of turbulent fibre suspensions and its solution and application to the pipe flow

Lin Jian-Zhong, Li Jun, Zhu Li, Olson James A.
Chin. Phys. B 2005, 14 (6): 01185;  doi: 10.1088/1009-1963/14/6/022
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The mean motion equation of turbulent fiber suspension and the equation of probability distribution function for mean fiber orientation are derived. The successive iteration for calculating the mean orientation distribution of fiber and the mean and fluctuation-correlated quantities of suspension is presented. The equations and their solutions are applied to a turbulent pipe flow of fiber suspension, and a corresponding experiment is performed. It is found that theoretical and experimental results are in good agreement. The obtained results for turbulent pipe flow of fiber suspension show that the flow rate of fiber suspension is large under the same pressure drop in comparison with the rate of Newtonian flow in the absence of fiber suspensions. Fibers play an important role in reducing the flow drag. The amount of reduction in drag augments with the increase in the concentration of the fiber mass. The relative turbulent intensity and Reynolds stress in the fiber suspensions are smaller than those in the Newtonian flow under the same condition, which illustrates that the fibers have an effect on suppressing the turbulence. The amount of suppression is directly proportional to the concentration of the fiber mass.

Fast electron dynamics in lower hybrid current drive experiment on HT-7 tokamak

Shi Yue-Jiang, Wan Bao-Nian, Chen Zhong-Yong, Hu Li-Qun, Lin Shi-Yao, Ruan Huai-Lin, Qian Jin-Ping, Zhen Xiang-Jun, Ding Bo-Jiang, Kuang Guang-Li, Li Jian-Gang, HT-7 Team
Chin. Phys. B 2005, 14 (6): 01193;  doi: 10.1088/1009-1963/14/6/023
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Dynamic behaviour of fast electron in lower hybrid current drive (LHCD) experiment is a crucial issue in the sense of enhancing plasma performance. A new hard x-ray diagnostic system on HT-7 allows the investigation of the lower hybrid wave dynamics. The behaviour of fast electron is studied in several kinds of LHCD experiments, including long pulse discharges, high performance discharges and counter-LHCD experiments.

First-principle study of Li ion diffusion in copper thin film

Xiong Zhi-Hua, Lei Min-Sheng
Chin. Phys. B 2005, 14 (6): 01199;  doi: 10.1088/1009-1963/14/6/024
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The diffusion mechanism of Li ion in a copper thin film is investigated from first-principle calculations. The energy barriers for possible spatial hopping pathways are calculated with the adiabatic trajectory method. Theoretically, we have identified that lithium can diffuse through a copper thin film by successive nearest neighbor vacancy-atom exchanges at room temperature. It is found by comparing the different mechanisms that the nearest neighbor vacancy assisted jumping is highly probable. It is also confirmed that more free diffusion may be observed by increasing the number of copper vacancies in the thin film.

Lasing action of high quality ZnO thin film deposited by radio-frequency magnetron sputtering

Yao Zhi-Gang, Zhang Xi-Qing, Shang Hong-Kai, Teng Xiao-Ying, Wang Yong-Sheng, Huang Shi-Hua
Chin. Phys. B 2005, 14 (6): 01205;  doi: 10.1088/1009-1963/14/6/025
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ZnO thin films are deposited on SiO2 substrates by radio-frequency magnetron sputtering. A and B excitons are observed from the absorption spectra at room temperature. A, B and C excitons are observed from the reflectance spectra at 19 K. These results indicate that the obtained ZnO films have a good wurtzite structure. We obtain the stimulated emission resulting from electron-hole plasma. The lasing spectrum is observed, which consist of a large number of narrow peaks with an around 0.5 nm spacing in between, corresponding to a self-formed cavity length of around 31.5 μm. The self-formation of laser cavity in the ZnO thin film is closed related to its the hexagon structure.

Zeeman effects on the coherent tunnelling conductance in normal-metal/superconductor/normal-metal double tunnel junctions

Dong Zheng-Chao
Chin. Phys. B 2005, 14 (6): 01209;  doi: 10.1088/1009-1963/14/6/026
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The coherent quantum transport is investigated in normal-metal/superconductor/normal-metal(N/S/N) double tunnel junctions under a Zeeman magnetic field on the S.Taking simultaneously into account the electron-injected current from one Nelectrode and the hole-injected current from the other Nelectrode,we derive a general formulafor the differential conductance in the N/S/N system.It is shown that the conductance spectrum exhibits oscillatory behaviour with the bias voltage, and the oscillation amplitude is reduced wiht increasing temperature and Zeeman magneti field, the Zeeman energy can lead to the Zeeman splitting of conductance peaks.In the tunnel limit, a series of bound states of quasiparticles will form in the S.

Effective nonlinear AC response to composite with spherical particles

Chen Xiao-Gang, Liang Fang-Chu, Wei En-Bo
Chin. Phys. B 2005, 14 (6): 01217;  doi: 10.1088/1009-1963/14/6/027
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An effective nonlinear alternative-current (AC) response to granular nonlinear-composite with spherical inclusions embedded in a host medium under the action of an external AC field is investigated by using a perturbation approach. The local potentials of composite at higher harmonics are derived both in a region of local inclusion particles and in a local host region under the action of a sinusoidal field E1sinωt +E3sin3ωt, with frequencies ω and 3ω. An effective nonlinear-response to composite and the relationship between the effective nonlinear-responses at the fundamental frequency and the third harmonics are also studied for the spherical inclusions in a dilute limit.

Electrical resistivity of a novel oxadiazole derivative as a function of pressure and temperature using a diamond anvil cell

Luo Ji-Feng, Han Yong-Hao, Tang Ben-Chen, Gao Chun-Xiao, Li Min, Zou Guang-Tian
Chin. Phys. B 2005, 14 (6): 01223;  doi: 10.1088/1009-1963/14/6/028
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The in-situ electrical resistance measurement on the microcrystal of 1,4-bis[(4-methyloxyphenyl)-1,3,4-oxadiazolyl]- 2,5-bisheptyloxyphenylene (OXD-2) has been carried out under conditions of high pressure and temperatures higher than room temperature by using the diamond anvil cell (DAC). Sample’s resistivity was calculated with a finite element analysis method. The temperature and pressure dependencies of the resistivity of OXD-2 microcrystal were measured up to 150 oC and 16 GPa. The resistivity of OXD-2 decreases with increasing temperature, indicating that OXD-2 exhibits organic-semiconductor conducting property in the region of experimental pressure. Between 90-100 ℃, the resistivity drops with the temperature, which reveals a temperature-induced phase transition. As the pressure increases, the resistivity of OXD-2 increases and reaches a maxium at about 6 GPa, and then begins to decrease at higher pressures. Combining the in-situ x-ray diffraction data with the resistivity measurement results under pressure, the anomaly resistivity drop after 6 GPa is confirmed to be from the pressure-induced amorphous phase transition of OXD-2.

Thermodynamics of squeezed states in mesoscopic circuits

Ji Ying-Hua, Luo Hai-Mei, Liu Qing, Lei Min-Sheng
Chin. Phys. B 2005, 14 (6): 01227;  doi: 10.1088/1009-1963/14/6/029
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Based on information theory, we present a density matrix to discuss coherent and squeezed states for a mesoscopic LC circuit with time-dependent frequency. With the relevant operators included in the density matrix, a connection between the appearance of coherent and squeezed states is established, i.e., the quantum state evolution of system is highly relevant to the initial state. Generally speaking, due to the effect of circumstance temperature, mesoscopic LC circuit will evolve to squeezed state when it initially lies in an excited state. In particular, at a low temperature, step changes of circuit parameters will result in the squeezed minimum uncertainty state if the resonance frequency remains consistent after the change.

Effect of electron-phonon interactions on dynamical localization of semiconductor superlattices

Wang Zhi-Gang, Duan Su-Qing, Zhao Xian-Geng
Chin. Phys. B 2005, 14 (6): 01232;  doi: 10.1088/1009-1963/14/6/030
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Effect of the electron-phonon interactions on the property of dynamical localization of semiconductor superlattices in a single-band model under the actions of the electric dc and acfield, respectively, are investigated. The results show that the electron-phonon interactions can destroy the dynamical localization of the electron. For the same phonon frequency, when the strength of the electron-phonon interactions becomes larger, the electron is more quickly scattered. When the phonon frequency equals to the Bloch frequency ΩB in dc field or Ωin ac field or one of them in dc-ac field, the electron initially localized at the 0th site can be rapidly scattered to the other sites, where Ω is the frequency of the ac field. The property of the dynamical localization of the electron is seriously destroyed by the photon-phonon resonant field.

Evolution of structure and magnetic properties of nanocrystalline FeXN thin films via Ta and Al addition

Wu Guo-Guang, Wu Dong-Ping, Zheng Kuo-Hai, Wei Fu-Lin, Yang Zheng, Kamzin A. S.
Chin. Phys. B 2005, 14 (6): 01238;  doi: 10.1088/1009-1963/14/6/031
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Nanocrystalline FeAlN and FeTaN films are prepared by direct growth and crystallization of their as-deposited amorphous films, respectively. Although both films show soft magnetism of nanocrys-talline, the uniaxial anisotropy is to be observed different. Measurements of microstructure reveal that Ta addition leads to higher N-solubility in these films, and results in larger lattice dilation and more compressive stress. The uniaxial anisotropy is the consequence of the anisotropic distribution of inter-stitial N atoms in anα-Fe lattice. Al is easy to react with nitrogen, therefore, the α-Fe is purer in an FeAlN films than in an FeTaN ˉlm and the stress is tensile in FeAlN film. The difference of anisotropy may be attributed to the difference between the microstructures in both films.

Physical properties of ferroelectric superlattice A3/B3 system in electric field

Jiang Wei, Lo Veng-Cheong, Bai Bao-Dong
Chin. Phys. B 2005, 14 (6): 01243;  doi: 10.1088/1009-1963/14/6/032
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The transverse Ising model (TIM) in the effective-field theory based on the differential operator technique is developed to study the physical properties of a ferroelectric superlattice A3/B3 system. The effects of an external electric field on the polarization, susceptibility and pyroelectric coefficient of the ferroelectric superlattice A3/B3 system are discussed in detail. The susceptibility of the ferroelectric superlattice A3/B3 system decreases with the increasing of the electric field, implying that the polarization is weak.

Dependence of interface motion on pressure in ferroelectrics

Ai Shu-Tao
Chin. Phys. B 2005, 14 (6): 01246;  doi: 10.1088/1009-1963/14/6/033
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The motion of the paraelectric-ferroelectric interface in KNbO3 under hydrostatic pressure is studied in the framework of the mean-field theory. The kink solution is applied to the calculations of the width and velocity of the interface at different pressures. The calculations are based on the experimental data for the Curie-Weiss constant and the parameter of the Ginzburg-Landau expression for the free energy. The response to hydrostatic pressure and tricritical point is investigated nonempirically.

Spectroscopic properties and thermal stability of Er3+/Yb3+-codoped fluorophosphate glasses

Li Tao, Zhang Qin-Yuan, Zhao Chun, Feng Zhou-Ming, Shi Dong-Mei, Deng Zai-De, Jiang Zhong-Hong
Chin. Phys. B 2005, 14 (6): 01250;  doi: 10.1088/1009-1963/14/6/034
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A comprehensive study on the thermal stability and spectroscopic properties of Er3+/Yb3+-codoped Al(PO3)3-based fluorophosphate glasses have been reported for 1.5-mm fiber amplifiers in this paper. From optical absorption spectra, the Judd-Ofelt parameters of Er3+ in the glasses and then several important optical properties, i.e., the radiative transition probability, the branching ratio and the spontaneous emission probability, have been calculated by Judd-Ofelt theory. The fluorophosphate glass exhibits broadband near-infrared emission at 1.53 mm with a full width at half-maximum over 63 nm, and a large calculated stimulated-emission cross-section of 6.85×10-21 cm2.

SiCGe/SiC heterojunction and its MEDICI simulation of optoelectronic characteristics

Lü Zheng, Chen Zhi-Ming, Pu Hong-Bin
Chin. Phys. B 2005, 14 (6): 01255;  doi: 10.1088/1009-1963/14/6/035
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Optoelectronic characteristics of the SiC1-xGex /SiC heterojunction photodiode are simulated using MEDICI after the theoretical investigation of key properties for SiC1-xGex. The calculations show that SiC1-xGex /SiC with x=0.3 may have a small lattice mismatch with 3C-SiC and a good response to the visible light and near infrared light. The response spectrum of the SiC1-xGex /SiC heterojunction photodiodes, which consists of a p-type SiC1-xGex absorption layer with a doping concentration of 1′1015cm-3, a thickness of 1.6μm and x=0.3, has a peak value of 250mA/W at 0.52μm and the peak value can even reach 102 mA/W at 0.7μm.

A microwave emissivity model of sea surface under wave breaking

Wei En-Bo, Ge Yong
Chin. Phys. B 2005, 14 (6): 01259;  doi: 10.1088/1009-1963/14/6/036
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With effective medium approximation theory of composites, a remedial model is proposed for estimating the microwave emissivity of sea surface under wave breaking driven by strong wind on the basis of an empirical model given by Pandey and Kakar. In our model, the effects of the shapes of seawater droplets and the thickness of whitecaps layer (i.e. a composite layer of air and sea water droplets) over the sea surface on the microwave emissivity are investigated by calculating the effective dielectric constant of whitecaps layer. The wind speed is included in our model, and the responses of water droplets shapes, such as sphere and ellipsoid, to the emissivity are also discussed at different microwave frequencies. The model is in good agreement with the experimental data of microwave emissivity of sea surface at microwave frequencies of 6.6, 10.7 and 37 GHz.

Evolution characteristics of the precipitation in the Yangtze River delta based on the probability density

Zeng Hong-Ling, Gao Xin-Quan, Zhang Wen
Chin. Phys. B 2005, 14 (6): 01265;  doi: 10.1088/1009-1963/14/6/037
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The dryness/wetness (DW) grade data of the Yangtze River delta are transformed in this paper into the temporal evolution of precipitation probability (PP), and its hierarchically distributive characters are revealed. Research results show that the precipitation of the Yangtze River delta displays the interannual, interdecadal, as well as more than a century quasi-periodic changes, and the periods are all significant at a confidence level of more than 0.05. In the DW grade series of 530 years, although the frequency of the small probability events (SPEs) of drought/flood in each area of the Yangtze River delta is different, the frequency of the SPEs triggered by the climatic background state is yet the same. This research result fully narrates the significant impact of the climatic evolution as a background state upon the occurrence of SPEs, which will play an instructional role in climatic prediction theory and in raising the accuracy of climatic prediction.

Electron capture in fp shell at presupernova stage

Luo Zhi-Quan, Liu Men-Quan, Lin Li-Bin, Peng Qiu-He
Chin. Phys. B 2005, 14 (6): 01272;  doi: 10.1088/1009-1963/14/6/038
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The electron capture of neutron-rich nuclei in fp shell in massive stars at presupernova stage is discussed based on the nuclear shell model. The Gamow-Teller resonance transition strength is modified by introducing a Gaussian function. As a result, the electron capture rate in high density is evidently larger than the previous results given by some authors.
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