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Vol. 52, No. 8 (2003)

2003-04-20
GENERAL
Some new soliton wave solutions for (2+1)-dimensional Broer-Kaup equations
Tang Deng-Bin, Zhao Xi-Qiang, Wang Li-Min, Zhang Yiao-Ming
2003, 52 (8): 1827-1831. doi: 10.7498/aps.52.1827
Abstract +
By a simple transformation, (2+1)-dimensional Broer-Kaup equations are turned to a simple equation. Some new soliton solutions are obtained by combining the tra nsformation with the homogeneous balance method. The method given in this paper can be used to solve other nonlinear physical model.
A conservation theorem of Hojman for systems of generalized classical mechanics
Zhang Yi
2003, 52 (8): 1832-1836. doi: 10.7498/aps.52.1832
Abstract +
The conservation theorem and the symmetries for systems of generalized classical mechanics are studied. In terms of the invariance of the ordinary differential equations under the infinitesimal transformations, this paper established the Li e symmetrical transformations of the systems in the high-dimensional extended ph ase space, which only depend on the canonical variables, and a new type of conse rvation laws are directly obtained from the Lie symmetries of the systems. Actua lly, the conservation laws are the generalization of a conservation theorem of H ojman to generalized classical mechanics. Finally, an example is given to illust rate the application of the results.
LamDe' function and perturbation method to nonlinear evolution equations
Liu Shi-Kuo, Fu Zun-Tao, Liu Shi-Da, Wang Zhang-Gui
2003, 52 (8): 1837-1841. doi: 10.7498/aps.52.1837
Abstract +
The perturbation method is applied to the multi-order exact solutions of nonline ar evolution equations. The exact solutions to the zeroth-order equation can be derived by Jacobi elliptic function expansion method, and then the first-order a nd the second-order equations can be rewritten as the homogeneous Lam equa tion and inhomogeneous Lam equation, respectively. They can be solved by using Lam functions and the Jacobi elliptic function expansion method. Thus, the mu lti-order solutions are obtained to the nonlinear evolution equations.
LamDe' function and invariants of multi-order exact solutions among nonline ar evolution equations
Liu Shi-Kuo, Chen Hua, Fu Zun-Tao, Liu Shi-Da
2003, 52 (8): 1842-1847. doi: 10.7498/aps.52.1842
Abstract +
Applying the perturbation method, the nonlinear evolution equations are expanded as multi-order approximate equations. And based on Lam equation and Lam function, these multi-order approximate equations can be solved by Jacobi elliptic function expansion method, where multi-order exact solutions of nonlinear evol ution equations are derived. Then the invariants of the multi-order exact soluti ons are found among different nonlinear evolution equations.
Bidirectional solitary wave solutions and soliton solutions for two nonlinear ev olution equations
Li Zhi-Bin, Xu Gui-Qiong
2003, 52 (8): 1848-1857. doi: 10.7498/aps.52.1848
Abstract +
The homogeneous balance method for constructing solitary wave solutions and soliton solutions is further developed on obtaining quasi-solution by using step-by- step principle.The main advantage of the extended approach is to avoid the probl em of “intermediate expression swell”.The effectiveness of the method is demon strated by application to the generalized Boussinesq equation and the bidirectio nal Kaup-Kupershmidt equation.The one-soliton,two-soliton and three-soliton solutions with multipe collisions are derived for these two equations with the assistance of Maple.
Exact solution of a kind of n-dimensions non-spherical harmonic oscillator p otential
Long Chao-Yun, Cai Shao-Hong, Chen Ming-Lun
2003, 52 (8): 1858-1861. doi: 10.7498/aps.52.1858
Abstract +
In this paper,the Schrdinger equation with a non-spherical harmonic oscillator potential in n-dimensions is solved.The exact energy equation and the normalized wave function are obtained.The general formulas of matrix elements of op erator rs are presented.
Electron oscillation between coupled quantum wells with periodic driving
Liang Jiu-Qing, Yin Wen, Lai Yun-Zhong, Yan Qi-Wei
2003, 52 (8): 1862-1866. doi: 10.7498/aps.52.1862
Abstract +
The behaviour of an electron between two quantum wells, is studied by exact solution of a time-dependent Schrdinger equation. The time-dependent electron occupation-probability is obtained analytically as a function of the energy difference between the two wells, coupling constant and driving frequency. The condit ion that electron can be trapped in a single quantum well is obtained.
Study of the crystallization kinetics of Zr60Al15Ni2 5 bulk glassy alloy
Li Jin-Fu, Wang Hong-Hua, Zhou Yao-He, Yan Zhi-Jie
2003, 52 (8): 1867-1870. doi: 10.7498/aps.52.1867
Abstract +
This paper reports the investigation on the crystallization kinetics of Zr6 0 Al15Ni25 bulk glassy alloy under isothermal annealin g by differential scanning calorimetry. The results show that the incubation time is very smal l even at a low annealing temperature (743 K) and the exothermic peak width, ref lecting the time for the actual crystallization process, increases greatly when annealing temperature decreases. This suggests a growth-controlled crystallizati on process. The Avrami exponents indicate that the crystallization mechanism cha nges at different annealing temperatures. The change of the crystallization mech anism is attributed to the great change of the mobility of atoms at different te mperatures.
Analysis on the chaotic pseudo-random sequence complexity
Cai Jue-Ping, Song Wen-Tao, Li Zan
2003, 52 (8): 1871-1876. doi: 10.7498/aps.52.1871
Abstract +
In this paper, the conventional pseudo-random sequence linear complexity is disc ussed, and a new criterion is proposed, based on the approximate entropy. It is proved that the criterion is able to distinguish different complex chaos and cha otic pseudo-random sequences with short observed sequence. Simulations indicate that the method is effective, and the corresponding theories are proved right.
Experimental study of shock wave propagating character in targets driven by an i nclined-incident laser
Huang Xiu-Guang, Wu Jiang, Wang Rui-Rong, Ma Min-Xun, He Ju-Hua, Ye Jun-Jian, Gu Yuan, Fu Si-Zu
2003, 52 (8): 1877-1881. doi: 10.7498/aps.52.1877
Abstract +
With the folding target and double-step target,the propagating character of shock wave driven by an inclined-incident (with angle of ~45°) laser was studied on “Shenguang-Ⅱ” high-power laser facility.The result indicated that the shock wave in the target still propagates along the vertical direction to the target surface.Also the same result was verified indirectly by another experiment based on the measurement for spatial intensity distribution of x-ray radiated from jet plasmas.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
The propagator for an arbitrary integral spin
Zhang Peng-Fei, Ruan Tu-Nan, Huang Shi-Zhong, Wu Ning, Zheng Zhi-Peng
2003, 52 (8): 1882-1890. doi: 10.7498/aps.52.1882
Abstract +
Based on the solution to Bargmann-Wigner equation for an arbitrary integral spin , a further investigation on the projection operator and propagator for an arbit rary integral spins is carried out. The explicit form of the projection operator s for integral spins constructed by Behrends and Fronsdal is checked and confirm ed; the commutation rules and general expressions for the Feynman propagator for a free particle of an arbitrary integral spin are derived.
NUCLEAR PHYSICS
Signature inversion in odd-odd nuclei in the mass region A=100
Luo Xiang-Dong, Zheng Ren-Rong, Zhu Shun-Quan
2003, 52 (8): 1891-1894. doi: 10.7498/aps.52.1891
Abstract +
With the model of an axially symmetric rotor plus two quasi-particles, the signature inversion (SI) in two odd-odd nuclei 102Rh and 98Rh in the mass region A=100 is studied. The calculated result shows that the possible SI mechanism, which has been confirmed by the calculation of odd-od d nuclei in the A=160 and A=80 regions (i e, the competition between the n-p interaction and the coriolis force in low K space) is also appropriate for odd-odd nuclei in the A=100 region. This seems to indicate that there mi ght be a universal mechanism of SI in odd-odd nuclei for different mass regions.
ATOMIC AND MOLECULAR PHYSICS
Measurement of the backscattering yields for protons of H+2, H+3 cluster ions in channeling condition
V.A. Khodyrev, V.S. Kulikauskas, Yang Chao-Wen
2003, 52 (8): 1895-1900. doi: 10.7498/aps.52.1895
Abstract +
Rutherford backscattering spectrum of protons in H+2,H+3 cluster ions have been measured in channeling directions and of silicon crys tal. It has been found that, under the same velocity of 650 keV/p, the backscattering probability for protons of H+2 cluster ions is great er than that of H+ projectile, and the backscattering probability for protons of H+3 is gr eater than that of H+2. The ratio of backscattering yields of channeling di rection to that of random direction is defined and the depth dependence of ratio distribution is calculated.
H+5 cluster ion and its neutral products H3 and H4
Yang Bai-Fang, Miao Jing-Wei, Yang Chao-Wen, Shi Mian-Gong
2003, 52 (8): 1901-1905. doi: 10.7498/aps.52.1901
Abstract +
The experimental results for H+5 cluster ions are reported . The formation an d dissociation of H+5 cluster ions were discussed. Accord ing to theory, sta ble H+n cluster ions may be formed by H+3 core with one or more H 2 molecule. On the other hand, there exist conditions for the reactio n of H+3 and H2 in a rf ion source. In the experiments, the ion beam was accelera ted by van de Graff and selected by 90° analysis magnet in the condition of cur rent for mass number 5, and then diffracted by 20° analysis magnet, the energy spectrum of ion beam was obtained. From the spectrum, it is found that H+5 cluster ions may be formed from the ion-molecular interaction between H+3 ion and H2 neutral molecule in rf ion source and that there may exist H3 and H4 neutral clusters among the products of H+5 c luster ions.
Numerical simulation of the evolution of highly charged ions in an electron-bea m ion trap
Yuan Xing-Qiu, Chen Chong-Yang, Li Hui, Zhao Tai-Zhe, Guo Wen-Kang, Xu Ping
2003, 52 (8): 1906-1910. doi: 10.7498/aps.52.1906
Abstract +
The physical mechanism,which determines the evolution of highly charged ions in an electron-beam ion trap,is presented. The numerical simulation of the evolut ion of highly charged ions was performed, and the comparision of the result with experiments was carried out. Finally, parameter study was made.
Theoretical study of the infrared spectrum of clusters
He Chun-Long, Wang Feng, Li Jia-Ming
2003, 52 (8): 1911-1915. doi: 10.7498/aps.52.1911
Abstract +
According to the time correlation function theory, the infrared spectrum of clu sters can be calculated by using the molecular dynamics simulation. As an examp le, the infrared spectrum of C60 is calculated using orthogonal tight -bind ing molecular dynamics simulation. The calculated infrared spectrum is sufficien t to identify the experimental infrared spectrum. The above method is a powerful tool for the study of nano systems.
CLASSICAL AREA OF PHENOMENOLOGY
Squeezing effect of light caused by Bose-Einstein condensate composed of interac tive atoms
Zhou Ming, Fang Jia-Yuan, Huang Chun-Jia
2003, 52 (8): 1916-1919. doi: 10.7498/aps.52.1916
Abstract +
The Hamiltonian operator of a system of single-mode light field interacting with Bose-Einstein condensate(BEC) of two-level atoms is suggested within the rotati ng-wave approximation. The influence of the interaction between atoms in the BEC on the quadrature squeezing properties of single-mode squeezed light interactin g with atomic BEC is studied under Bogoliubov approximation. The results show th at the fluctuations of two quadrature components of light evolve periodically in a cosine law and their squeezing properties are determined mainly by the initia l squeeze factor and squeeze direction angle of light, and that the interaction between atoms in BEC changes the amplitude and period of fluctuation of light.
The production and elimination of the spatial singularity for ultrashort chirp ed pulse-beam propagation in free space
Yang Zhen-Jun, Hu Wei, Fu Xi-Quan, Lu Da-Quan, Zheng Yi-Zhou
2003, 52 (8): 1920-1924. doi: 10.7498/aps.52.1920
Abstract +
We study the propagation of ultrashort chirped pulsed beams in free space. We find that the slowly-varying envelope approximation and complex amplitude envelope are not suitable for ultrashort chirped pulsed beams anymore, because they lead to the spatial singularity that is inconsistent with the physical significanc e of the beam propagation. And the chirp influences the spatial singularity mor e seriously than the width of the pulsed beam does. The spatial singularity can be eliminated by using the complex analytical signal theory. In this paper, we g ive the simulations of spatial singularity about ultrashort chirped pulsed Gauss ian beams with a series of parameters, and the conditions that lead to the spati al singularity etc. We think that the broad spectrum of the ultrashort pulsed be am is the original reason for the spatial singularity.
Two-dimensional periodically poled LiNbO3 nonlinear photonic crystal
Ni Pei-Gen, Ma Bo-Qin, Cheng Bing-Ying, Zhang Dao-Zhong
2003, 52 (8): 1925-1928. doi: 10.7498/aps.52.1925
Abstract +
A two-dimensional periodically poled lithium niobate crystal with a 13.64 μm period was fabricated. The inverted duty cycle was about 23%. The second harmonic output for the second-order quasi-phase-matching (QPM) against the input was measured. The maximum second harmonic internal conversion efficiency was higher than 40%. All results implied that the second-order QPM could be used to obtain high-frequency conversion efficiency. Compared with the first-order QPM, the second-order QPM can reduce the requirement for the poling technique and the mask fabrication.
Broadband two-photon absorption and optical power limiting properties of a novel organic compound
He Guo-Hua, Zhang Jun-Xiang, Ye Li-Hua, Cui Yi-Ping, Li Zhen-Hua, Lai Jian-Cheng, He An-Zhi
2003, 52 (8): 1929-1933. doi: 10.7498/aps.52.1929
Abstract +
The two-photon absorption (TPA) property and optical power limiting behaviour of a novel double-conjugated segment organic molecule have been investigated, and its TPA spectrum and optical power limiting curve have been experimentally obtai ned. Strong TPA and broadband optical power limiting properties from 700 nm to 1 100 nm in the near infrared region have been demonstrated in the tetrahydrofuran (THF) solution with 1×10-2mol/L concentration. It has three peaks o f TPA cross section at 730,850 and 980 nm. The maximum TPA cross section is σ′ 2=25.9×10-47cm4·s·photon-1 at 850nm, which is about 1-2 orders of magnitude larger than usual organic molecules.
Effect of spinning single-mode fibres on second-order polarization mode dispersi on
Dong Hui, Fu Song-Nian, Wu Chong-Qing
2003, 52 (8): 1934-1937. doi: 10.7498/aps.52.1934
Abstract +
This paper describes the effect of spinning single-mode fibres on the second-order polarization mode dispersion(PMD). We find theoretically that spinning fibr es can reduce the first-order PMD, but it may be harmful to the second-order PMD , which is an important problem to the fibre communication system over 10 Gb/s.
Diagnostics and compression of sub-10 femtosecond laser pulses
Deng Li, Liao Rui, Liu Ye-Xin, Shou Qian, Wen Jin-Hui, Lin Wei-Zhu
2003, 52 (8): 1938-1942. doi: 10.7498/aps.52.1938
Abstract +
The amplitudes and phases of femtosecond pulses generated from a home-made KLM Ti: Sapphire laser are diagnosed by using the technique of second-harmonic generation frequency-resolved optical gating. The results indicate that the profiles of the pulses are sech2 shapes and the phases are approximately cub ic dependent of the time. The chirped pulses of 17 fs(FWHM) are compressed to near Fourier transform limited pulses of 8.5 fs with a double-prism system to compensate for the second-order dispersion.
Finite difference time domain method for the study of band gap in two-dimensiona l phononic crystals
Wang Gang, Wen Ji-Hong, Han Xiao-Yun, Zhao Hong-Gang
2003, 52 (8): 1943-1947. doi: 10.7498/aps.52.1943
Abstract +
In this paper, by transforming the isotropy elastodynamic equations into the first-order hyperbolic ones, we have improved the O(2,4) finite difference time domain method with the staggered grid. Using the approach in this paper, we calculated the band gap in two-dimensional phononic crystals. The calculated and measured results match well.
On the absence of some resonance modes in acoustic scattering by spherical scatt erers in isotropic elastic media
Wu Rui-Xin, Wang Yao-Jun
2003, 52 (8): 1948-1953. doi: 10.7498/aps.52.1948
Abstract +
Resonance scattering by iron spheres in plaxiglass matrix is investigated numer ically. Based on the analysis of the zero and singular points of the scattered l ongitudinal and transverse wave coefficients, the absence of some resonance mode s is found to appear only in the scattered longitudinal wave modes of the lowest order. The absence of some resonance modes results from the fact that the zero points of the numerator and denominator of scattered longitudinal wave coefficie nts are located at the same positions in the complex frequency plane.
Acoustic head wave on the borehole wall in a porous formation and the causes for its accompanying electromagnetic field
Hu Heng-Shan
2003, 52 (8): 1954-1959. doi: 10.7498/aps.52.1954
Abstract +
To understand the propagation mechanism of the acoustic head wave and its accompanying electromagnetic field during logging in a porous formation, we studied the displacement characteristics of the wave. Calculations by both the fast compre ssional branch-cut-integral and the real-wavenumber-integral methods show that the head wave travels along the borehole wall with the fast compressional wave velocity, but it differs from a plane compressional wave in two aspects. First, the head wave causes radial displacement as well as axial displacement. Second, it is composed of the gradients of the fast and slow compressional potentials and the rotation of the shear potential. The gradient of the slow compressional potential constitutes the dominating part of the fluid filtration. It is the slow compressional potential that induces electric field that accompanies the acousti c head wave during acousto-electric well logging. And it is the shear potential that induces magnetic field that accompanies the acoustic head wave.
Studies on the relationship between acoustic emission characteristics and fractu re toughness of materials
Zhu Bo, Wang Cheng-Guo, Cai Hua-Su, Cai Xun
2003, 52 (8): 1960-1964. doi: 10.7498/aps.52.1960
Abstract +
The corelation between acoustic emission characteristics and their fracture toughness has been investigated in this paper based on the study of high-strength al uminum alloy cracking process by using advanced acoustic emission experiment sys tem and smooth tensile specimens as well as DCB specimens with premade cracks. E xperimental results showed that the specimens emitted strong signals with an amp litude above 35 dB when a stable crack extension started at K1C. Stro nger and more complicated acoustic emission signals were found during unstable crack extension, and the cumulative energy of acoustic emission events were found to b e linearly related with the macroscopic fracture energy.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Field structure and electron density profile in circularly polarized femtosecond laser interaction with a linear plasma
He Feng, Yu Wei, Lu Pei-Xiang
2003, 52 (8): 1965-1969. doi: 10.7498/aps.52.1965
Abstract +
The electron density profile is solved self-consistently in circularly polarized femtosecond laser vertically interacting with a linear plasma. The result show s that a set of electron islands and cavities are produced in the relativistic p lasma. The laser energy is partially trapped in these cavities due to strong sta tic electric fields caused by the separation of electrons and ions. The dependen ce of the trapped static electric energy on the laser intensity is also discusse d.
The impurity transport in HT-6M tokamak
Xu Wei, Wan Bao-Nian, Xie Ji-Kang
2003, 52 (8): 1970-1978. doi: 10.7498/aps.52.1970
Abstract +
The space-time profile of impurities has been measured with a multichannel visible spectroscopic detect system and UV rotation-mirror system in the HT-6M tokamak. An ideal impurity transport code has been used to simulate impurities (carbon and oxygen) behaviour during the OH discharge. The profiles of impuritie s diffusion and convection coefficient, impurities ion densities in different io nized state, loss power density and effective charge number have been derived. T he impurity behaviour during low-hybrid current drive has also been analyzed, th e results show that the confinement of particles, impurities and energy has been improved, and emission power and effective charge number have been reduced.
Threshold analysis for the limit cycle and chaotic oscillation of the radiation field in a traveling wave tube amplifier
Ding Wu, Zhang Zhi-Chou, Hao Jian-Hong
2003, 52 (8): 1979-1983. doi: 10.7498/aps.52.1979
Abstract +
In terms of the coupled equations of the radiation field and motion of the electron in a traveling wave tube amplifier, the threshold current at which the limit cycle or chaotic oscillation of the radiation field starts occurring is obtained. The result of numerical calculation shows that the nonlinear unsteady states may appear in a certain range of the parameters for the radiation field. The eff ect of the detuning on the threshold is relatively strong when the interaction r egion is longer. The relations of the output power with the three parameters (de tuning, current and interaction length) become chaotic when the device operates in the highly nonlinear regime, and the higher output power can be obtained if t he parameters are controlled suitably.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Hamiltonian system approach for simulation of acoustic and elastic wave propagat ion
Cao Yu, Yang Kong-Qing
2003, 52 (8): 1984-1992. doi: 10.7498/aps.52.1984
Abstract +
This paper develops a system with quasi-particles on a discrete lattice, Hamiltonian description of this system is presented,which can simulate acoustic and elastic waves. The nine-point interaction models are used and interaction coefficients are determined in this system. The connection between Hamiltonian system approach and acoustic or elastic wave equations are proved, and the relations between their physical quantities are presented. The symplectic algorithms that are used in the given media models and simulation results are presented.
Calculation of surface energy of Cu crystal with modified embedded-atom method
Ma Fei, Zhang Jian-Min, Xu Ke-Wei
2003, 52 (8): 1993-1999. doi: 10.7498/aps.52.1993
Abstract +
The surface energies on 12 different planes of Cu crystal have been calculated with modified embedded-atom method. The results show that the lowest surface ener gy, as predicted, corresponds to the close-packed plane (111) of face-centered c ubic (FCC) structure. The surface energies on other planes show a tendency to in crease with increasing angle between the planes and (111) plane. So the relative values in surface energy for other planes could be estimated by their geometric relationship. The geometric structure factors and the methods applied to determ ine them could be used directly for surface energy and other property calculatio ns in the materials with FCC structure. The (111) texture observed extensively i n Cu, Ag and other FCC films results from the surface energy minimization.
Effect of nitrogen on oxygen precipitation in Czochralski silicon during high-te mperature annealing
Jiang Le, Yang De-Ren, Yu Xue-Gong, Ma Xiang-Yang, Xu Jin, Que Duan-Lin
2003, 52 (8): 2000-2004. doi: 10.7498/aps.52.2000
Abstract +
The effect of nitrogen on the oxygen precipitation during high-temperature annea ling in Czochralski silicon was investigated. After annealing under different co nditions, the variation of oxygen precipitation and the bulk microdefects(BMDs) density with annealing time at high temperatures was measured, and transmission electronic microscope was used to observe the microstructure of oxygen precipita tes. It was found that nitrogen doping strongly enhanced oxygen precipitation du ring high-temperature annealing; furthermore, the densities of BMDs in the annea led NCZ samples were higher than those in the corresponding CZ ones. Therefore, it is considered that the nitrogen can react with vacancy and oxygen to form N-V -O complexes to enhance the nucleation of oxygen precipitates, and the oxygen pr ecipitates are plates with strong inner stress.
Constitutive study for tungsten alloy under high pressure
Hua Jing-Song, Jing Fu-Qian, Dong Yu-Bin, Tan Hua, Zhou Xian-Ming, Hu Shao-Lou, Shen Zhong-Yi
2003, 52 (8): 2005-2009. doi: 10.7498/aps.52.2005
Abstract +
This article describes a method which combines the static pressure experiment,dynamic experiment and theoretical calculation to obtain the parameters in the SCG constitutive model for tungsten alloy under high pressures. By using the constitutive model we obtained in numerical simulation that the calculated profiles of particle velocity are in accordance with the experimental results. We also conducted some other simulations by using different constitutive models and compared them with experimental results. The results show that the constitutive model we obtained was the best.
Finite-element methods for viscoelastic and azimuthally anisotropic media
Yang Hui-Zhu, Du Qi-Zhen
2003, 52 (8): 2010-2014. doi: 10.7498/aps.52.2010
Abstract +
With the importance of the fractured strata in the oil exploration, researchers have paid more attention to the wave propagation in viscoelastic and anisotropic media. Provided the rocks are weakly viscoelastic, the viscoelastic problems can be solved as a series of elastic problems by using the time increment method. At each step we determine the viscoelastic deformations and the corresponding viscoelastic loads, which are added to the load vectors for the next step. On this basis, the finite-element recursive formulae of viscoelastic and azimuthally anisotropic media are established. The numerical simulations show the characteristics of wavefields in the viscoelastic and azimuthally anisotropic media.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Anomalous thermal conductivity enhancement in the mixed state of MgB2
Yang Dong-Sheng, Wu Bai-Mei, Li Bo, Zheng Wei-Hua, Li Shi-Yan, Chen Xian-Hui, Cao Lie-Zhao
2003, 52 (8): 2015-2019. doi: 10.7498/aps.52.2015
Abstract +
The thermal conductivity of MgB2 polycrystalline sample in the mixed state has been investigated as a function of magnetic field (0-7 T) and temperature (5-45 K). The thermal conductivity increased rapidly in low magnetic fields, and became saturation in higher fields. This behaviour correlates with the two-gap electronic structure of MgB2. Analysis indicates that the remarkable en hancement of thermal conductivity of MgB2 polycrystalline sample in the mixed state cannot be completely attributed to the electronic contribution.
Dynamic behaviours of an exciton confined in coupled quantum dots driven by an a lternating current electrical field
Liu Cheng-Shi, Ma Ben-Kun, Wang Li-Min
2003, 52 (8): 2020-2026. doi: 10.7498/aps.52.2020
Abstract +
With a two-site Hubbard model and Floquet theorem, we investigate the dynamic behaviour of an exciton confined in a coupled double-quantum-dot system driven by an alternating current(AC) electrical field. The calculation shows that the quasi-energy levels versus the amplitude of the external field undergo a series o f exact-crossing and avoid-crossing. Generally, the initially localized state can remain forever at the first exact-crossing point of two ground quasi-energy levels. Increasing the interaction of the electron and hole, the degree of dynamical localization is enhanced. At the second exact-crossing point of ground quasi-energy levels, this kind of dynamical localization is decayed. At the point of avoid-crossing and offset from the exact-crossing, the dynamical localiz ation ceases to maintain. This demonstrates the possibility to control the excit on states on extremely short time scales using the appropriate AC field with the adjustable amplitude and frequency, which may be useful for quantum information processing.
Dynamic behaviours of an exciton confined in coupled quantum dots driven by a hi gh alternating current electrical field
Liu Cheng-Shi, Ma Ben-Kun
2003, 52 (8): 2027-2032. doi: 10.7498/aps.52.2027
Abstract +
With the three-site Hubbard model and Floquet theorem, we investigate the dynamic behaviours of an exciton confined in three-quantum-dots molecules driven by an alternating current electrical field. The calculations show that the initia l localized state is hold up for a certain value of strength and frequency of th e alternating current field. In order to understand the dynamical property, we a pply the perturbation theory to solve the Floquet function and obtain the analyt ical solution of quasi-energy. We find that the dynamical localization can be bu ilt at the crossing point of quasi-energies for strong and moderate fields.
The quantum fluctuation of parallel mesoscopic RLC circuit
Long Chao-Yun
2003, 52 (8): 2033-2036. doi: 10.7498/aps.52.2033
Abstract +
In this paper,the quantization of parallel mesoscopic RLC circuit is given and the quantum wavefunction and the corresponding energy levels are obtained by using unitary transformation. The quantum fluctuation of the voltage and current are calculated.
Nanoelectromechanics in a quantum wire irradiated by a THz electromagnetic field
Yang Mou, Zhou Guang-Hui, Xiao Xian-Bo
2003, 52 (8): 2037-2040. doi: 10.7498/aps.52.2037
Abstract +
We study the nanoelectromechanics in a quantum wire connecting two reservoirs irradiated under an external terahertz (THz) electromagnetic field. Using the free-electron model at ballistic regime we calculated the two-level electron wavefunction and the Rabi oscillation of electron probability between the two levels. Using a statistical operator we calculated the nanoelectronic force in the wire. The result consists of two terms, which corresponds to the case with or without external field. The term without field parameter is consistent with the existing experimental observation and theoretical calculation, and the other term from the external field can be explained by the quantum coherent theory.
A novel single-electron analog-to-digital converter
Zhang Zhi-Yong, Wang Tai-Hong
2003, 52 (8): 2041-2045. doi: 10.7498/aps.52.2041
Abstract +
The ideal single-electron transistor has a folding I-V characteristic. Multi-threshold periodic transmitting function can be achieved by using a complementary single-electron transistor structure, which can be used to simplify the analog-to-digital(A/D) converter. A novel 3-bit A/D converter by using the complementary single-electron transistor structure has many advantages including a simple structure, high speed and low power.
A physical-based percolation model for gate oxide TDDB
Ma Zhong-Fa, Zhuang Yi-Qi, Du Lei, Bao Jun-Lin, Li Wei-Hua
2003, 52 (8): 2046-2051. doi: 10.7498/aps.52.2046
Abstract +
Based on the physical mechanism of gate oxide TDDB, a percolation model for gate oxide degradation was brought forward, in which the occurrence and build up of deep energy-level defects, such as E′ center and oxygen vacancy were considered to be the right cause of oxide breakdown. It was pointed out that, during TDDB the stressed defects were produced in the oxide, which form local states in oxide forbidden gap. And the volume of these local states is directly proportional to the external electric field, especially when the field strength is high enough. With the by-pass of stressing time, the concentration of defects in the oxide grew continually. As an effect, the distance between neighboring local states become shorter. So, hopping or tunneling probabilities of electrons between these local states increase swiftly. As a result, a conduction path will form when the distance between neighboring local states reaches a critical value. At the same time, in terms of energy band theory, an extended energy level will form in the oxide forbidden gap. Accompanied by a rapid increase of SILC, the gate oxide undergoes breakdown.
Abnormal coercivity behaviour in the magnetic percolation region of a magnetic g ranular composite
Zhang Xiao-Yu, Chen Ya-Jie
2003, 52 (8): 2052-2056. doi: 10.7498/aps.52.2052
Abstract +
MnZn-ferrite/SiO2 particle composites are prepared by mechanical ball ing. We study the relations of effective permeability μ, specific magnetization σ and coercivity Hc with the MnZn-ferrite concentration. The results indicate that an abrupt change emerges in effective permeability when the volume percentage of MnZn-ferrite particles is near V=98%, which means that a magnetic percolation phenomenon occurs in the system. Meanwhile, it is found that the coercivity Hc exhibits an anomalous behaviour that depends strongly on the microstructure of the composite. Above the percolation threshold, the variation of coercivity can be mostly explained in terms of dipolar interaction between magnetic particles, whereas below the percolation threshold, the decrement of Hc is ascribed dominantly to increasing specific magnetization σ. At the same time, we determine the measured percolation threshold Vc=97. 9%, which can be derived from the maximum of d2μ/dV2.
Structure and magnetic properties of Nd0.5Sr0.4Pb0.1MnO3 manganites
Lu Yi, Li Qing-An, Di Nai-Li, Cheng Zhao-Hua, Xue Yan-Jie, Zhang Li, Chen Na, Xiao Hong-Wen, Zhang Bai-Sheng, Chen Dong-Feng
2003, 52 (8): 2057-2060. doi: 10.7498/aps.52.2057
Abstract +
Structure,magnetic and transport properties of polycrystalline Nd0.5S r0.4Pb0.1MnO3 were experimentally studied by ne utron powder diffraction at room temperature and magnetic measurement.The neutron diffraction shows that the space group of this orthorhombic structure is Pnma,i.e.its structure exhibits crystal field distortion.Its Curie temperature TC equals 273K by the M-T curve.According to the R-T curve,it shows a ferromagnetic metal- paramagnetic semiconductor transition as temperature increases and Tp =225 K.Using the competing between manganites crystal field and double exchange inter action explains the metal property at room temperature.
Colossal magnetoresistance effect in the perovskite-type La0.9Sb 0.1MnO3 material
Duan Ping, Tan Guo-Tai, Dai Shou-Yu, Chen Zheng-Hao, Zhou Yue-Liang, Lü Hui-Bin
2003, 52 (8): 2061-2065. doi: 10.7498/aps.52.2061
Abstract +
The colossal magnetoresistance oxide compound La0.9Sb0.1Mn O3 has been prepared by solid-state reaction method.The electrical transport and magnetic properties have been measured by superconducting quantum interference device magnetometer.The valence state of Sb is confirmed to be +5 through x-ray photoelectron spectroscopy,so this compound is an electron-doped colossal magnetoresistance material.
Dipolar defect complexes in single-crystal PbWO4
Tong B.Tang, Feng Xi-Qi
2003, 52 (8): 2066-2074. doi: 10.7498/aps.52.2066
Abstract +
We have previously demonstrated the presence of the defects complex [2(La3 + Pb)·-V″Pb]in La-doped lead tungs tate (PWO). That earl ier experimental technique was supplemented with x-ray photoelectron, visible ab sorption and infrared absorption spectroscopies in the present investigation on PWO crystals doped with 3+, 4+ or 5+ cations, or co-doped with 3+ and 5+ impurit ies. Useful information has been deduced on dopant lattice sites, dipolar defect s complexes, their relation with materials properties, and their transformation during annealing. Some of the deductions have also been corroborated with comput er simulation. The present work argues against the conception that impedance spe ctroscopy cannot provide definite conclusions on defect structures in ionic soli ds.
Piezoelectric activity and its stability of polytetrafluoroethylene(PTFE)films
R. Gerhard-Multhaupt, W. Kuenstler, Xia Zhong-Fu, Ma Shan-Shan, Zhu Jia-Qian, Qiu Xun-Lin, Zhang Ye-Wen
2003, 52 (8): 2075-2080. doi: 10.7498/aps.52.2075
Abstract +
Piezoelectricity of non-polar space charge electret, porous PTFE film with unidi rectional mechanical stretch was studied. Piezoelectricity of double-layer stack s of porous PTFE and non-porous polymer films (such as PTFE, PI, FEP and PCTFE) with space charge layer were investigated. The results of preliminary investigat ion pointed out that under the optimal poling conditions, piezoelectric coeffici ent d33 of porous PTFE with external electrode was up to 186 pC/N whi c h is close to the value of ferroelectric ceramics PZT, and was about one order o f magnitude that of ferroelectric polymer PVDF. Outstanding thermal stability of piezoelectricity for soft PTFE porous film was reported. Influences of poling parameters such as poling time, corona electrical field and charging temperature etc, as well as charge density stored in the material on piezoelectricity were investigated. The influences of charging parameters on piezoelectricity were also explained by means of charge dynamic character and the material property.
Thermodynamic effect on transmitted intensity perturbance of air-gaped Glan-typ e polarizing prisms
Li Hong-Xia, Wu Fu-Quan, Fan Ji-Yang
2003, 52 (8): 2081-2086. doi: 10.7498/aps.52.2081
Abstract +
An analytical study on transmitted intensity perturbance of air-gaped Glan-type polarizing prisms with varying rotation angle is given. The perturbance strongly affects the quality of transmitted polarizing light. Our study shows that the t ransmitted intensity sensitively relies on the incident angle. The minute random variation of the incident angle around the structure angle of air-gaped Glan-ty pe polarizing prism gives rise to the perturbance found in the experiment. The i nfluence of the variation of temperature on the disturbance is discussed. Effect ive ways for reducing the disturbance are presented.
Optical properties of InGaAs self-assembled quantum dots with InAlAs wetting lay er
Zhu Tian-Wei, Zhang Yuan-Chang, Xu Bo, Liu Feng-Qi, Wang Zhan-Guo
2003, 52 (8): 2087-2091. doi: 10.7498/aps.52.2087
Abstract +
A new self-assembled quantum dots system where InGaAs dots are formed on InAlAs wetting layer and embedded in GaAs matrix has been fabricated. The photolumines cence linewidth increases with increasing temperature, which is very different from normal In(Ga)As/GaAs quantum dots. The results are attributed to a higher e nergy of the wetting layer which breaks the carrier transfer channel between dot s and keeps the dots more isolated from each other.
The relationship between fatigue life and grain size of polycrystalline metals
Li Mei-Juan, Hu Hai-Yun, Xing Xiu-San
2003, 52 (8): 2092-2095. doi: 10.7498/aps.52.2092
Abstract +
In order to explore the effect of grain size on fatigue life, a formula of fatig ue life for polycrystalline metals,which depends on the grain size and cyclic st rain amplitude, is derived based on the non-equilibrium statistical theory of fa tigue fracture and the model of interface energy. Subsequently, the fatigue life s of pure copper and 70-30 brass with different grain sizes are calculated accor ding to the formula which is achieved in this paper, and the results are in agre ement with the experimental results.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Hawking radiation of Dirac particles in a nonuniformly rectilinearly acceleratin g black hole with electric and magnetic charge
Zhao Zheng, Zhang Jing-Yi
2003, 52 (8): 2096-2101. doi: 10.7498/aps.52.2096
Abstract +
The Hawking radiation of Dirac particles on event horizon of nonuniformly rectilinearly accelerating black hole with electric and magnetic charge is studied in this paper. First, we construct the symmetrized null tetrad from which the spin coefficients and Dirac equation are derived. Next, by proposing a generalized tortoise coordinate transformation, the Dirac equation is decoupled successfully near the event horizon surface. Finally, following the method of Damour and Ruffini, the temperature on the horizon surface and the thermal spectrum formula of Dirac particles are obtained. The result is also discussed.
Stefan-Boltzmann's law of the Dirac field of static spherically symmetric black holes
Meng Qing-Miao
2003, 52 (8): 2102-2104. doi: 10.7498/aps.52.2102
Abstract +
Using the statistical entropy of the Dirac field of static spherically symmetric black hole, the Stefan-Boltzmann's law of static spherically symmetric black ho les is calculated, and we obtain a conclusion that the radiant emittance of a bl ack hole is proportionate to quartic power of temperature of the event horizon o f the black hole. It is found that the value of Stefan-Boltzmann constant in curved space-time is different from that in Euclidean space-time, and the constant has different value in different space-time.