Search

Article

x

Vol. 52, No. 12 (2003)

2003-06-20
GENERAL
Mei symmetry, Noether symmetry and Lie symmetry of Hamiltonian system
Luo Shao-Kai
2003, 52 (12): 2941-2944. doi: 10.7498/aps.52.2941
Abstract +
The Mei symmetry, i.e. the form invariance, of a Hamiltonian system is studied. The definition and the determining equation of Mei symmetry in the Hamiltonian system are given. The relations among the Mei symmetry, the Noether symmetry and the Lie symmetry are studied, and the conserved quantities of Hamiltonian system are obtained. An example is given to illustrate the application of the result.
Form invariance and Lie symmetry of relativistic mechanical system
Fang Jian-Hui, Chen Pei-Sheng, Zhang Jun, Li Hong
2003, 52 (12): 2945-2948. doi: 10.7498/aps.52.2945
Abstract +
We study the form invariance and Lie symmetry of a relativistic mechanical syste m. Firstly, we give the definition and criterion and conserved quantity of the f orm invariance and Lie symmetry in the system. Next, the relation between the fo rm invariance and Lie symmetry of the system is obtained. Finally, we give an ex ample to illustrate the application of the result.
New multi-order exact solutions to a kind of nonlinear evolution equations
Fu Zun-Tao, Liu Shi-Kuo, Liu Shi-Da
2003, 52 (12): 2949-2953. doi: 10.7498/aps.52.2949
Abstract +
Based on the Lamé equation and new Lamé functions, the perturbation method and Jacobi elliptic function expansion method are applied to get the multi-order ex act solutions of a kind of nonlinear evolution equations (such as mKdV equation, nonlinear Klein-Gordon equation Ⅱ etc.), where some more new multi-order exact solutions are found among different nonlinear evolution equations. These multi- order exact solutions correspond to different periodic solutions, which can dege nerate into different solitary wave solutions, such as band-soliton, bell-shaped solitary wave, etc.
Bound states of Klein-Gordon equation for scalar and vector linear potentials
Zhao Ding-Feng, Chen Gang
2003, 52 (12): 2954-2956. doi: 10.7498/aps.52.2954
Abstract +
The s-wave bound state solutions of Klein-Gordon equation are obtained when a linear-type scalar potential is not less than its vector potential, and its solutions are expressed by the confluent hypergeometric function.
Exact solution for a harmonic oscillator with a time-dependent inverse square po tential by path-integral
Wang Ping, Yang Xin-E, Song Xiao-Hui
2003, 52 (12): 2957-2960. doi: 10.7498/aps.52.2957
Abstract +
Using coordinate-transformation we transformed a harmonic oscillator with time-d ependent mass and a time-dependent inverse potential into a harmonic oscillator with time-independent mass and a time-independent inverse potential accordingly. In terms of the relation between these two different harmonic oscillators' prop agators we derived the exact wavefunction of the former by Feynman path-integral . We also discussed the harmonic oscillator with more additional potentials.
The uncertainty relations and minimum uncertainty states
Liu Ping, Deng Wen-Ji, Xu Yun-Hua
2003, 52 (12): 2961-2964. doi: 10.7498/aps.52.2961
Abstract +
Based upon some basic properties of Hermitian operators and Hilbert state vector s, the Heisenberg's uncertainty relations are analyzed in details. The necessary and sufficient condition for the minimum uncertainty states is re-obtained dire ctly from our proof. We propose also the problem of squeezed states for any coup le of dynamical variables, and solve it by using the bosonic creation and annihi lation operators.
Thermodynamics stability for ground state CUO
Zhu Zheng-He, Xue Wei-Dong
2003, 52 (12): 2965-2969. doi: 10.7498/aps.52.2965
Abstract +
Based on the quantum mechanics, statistical thermodynamics and Debye solid theory,we have successfully calculated thermodynamic functions, energy, entropy and G ibbs functions of CUO(g),indicating that CUO(g) is stable, particularly more sta ble with rising temperature, and also providing the structural parameters of CUO (g) which are valuable for reference.
On the formula for entropy production rate
Xing Xiu-San
2003, 52 (12): 2970-2977. doi: 10.7498/aps.52.2970
Abstract +
In this paper we derive a statistical formula for entropy production rate,namely the law of entropy increase in 6N- and 6-dimensional phase spaces. The exp ression is P=kD(Δqθ)2,which means the entropy produc tion rate P eq ual to the product of diffusion coefficient D,the mean square value of the spac e gradient of the percentage departure from equilibrium θ and Boltzmann constan t k. It shows that the macroscopic entropy production in a nonequilibrium system is caused by spatially stochastic and inhomogeneous departure from equilibrium of the number density of micro-states. As its application, we use this formula t o investigate three nonequilibrium physical topics: free expansion of a gas, Bro wnian motion, and the deformation and fracture of solids. The expressions for th eir entropy production,and the first and second time rates are presented. A new physical inference that the change of micro-structure within the system during a n irreversible process is inhomogeneous has been drawn and confirmed. We also ca lculate the entropy production rate in the stationary state, derive a special fo rmula, present the actual expressions of two examples: directed atomic diffusion and molecular motor. All these theoretical results are either in agreement with experiment or reasonable in physics.
Using pulse voltage differential feedback method to control chaos in the buck co nverter
Zou Yan-Li, Luo Xiao-Shu, Wang Bing-Hong, Fang Jin-Qing
2003, 52 (12): 2978-2984. doi: 10.7498/aps.52.2978
Abstract +
We analyze the mechanism of generating chaos in the buck converter through three kinds of typical switching logical diagrams, point out that when the switch S i s on, the capacity charges too fast.This is the main reason why chaos is generat ed in the circuit. Then based on the above analysis, we present the method of us ing output voltage pulse differential feedback to control chaos in the buck conv erter. Theoretical analysis, numerical calculation and circuit simulation demons trate the validity of this chaos control method.
AlGaN/GaN heterojunction wavefunction half analytic model based on quantum distu rbance
Li Pei-Xian, Hao Yue, Fan Long, Zhang Jin-Cheng, Zhang Jin-Feng, Zhang Xiao-Ju
2003, 52 (12): 2985-2988. doi: 10.7498/aps.52.2985
Abstract +
Based on the quantum disturbance theory,a half-analytic model was achieved that can be used in the calculation of the eigen function and eigen energy of the two-dimensional clectron gas in a AlGaN/GaN heterojunction.The theoretical analysis and calculation result of the model were given.The calculation result was compared with that of the difference method.The method in this paper is superior to the difference method when solving a large-scale problem because of its convergence and efficiency and is well fitted for the calculation of the quantum well problem in the AlGaN/GaN heterostructure.
The characters of riddled basins in coupled chaotic synchronized maps with addit ive noises
Tan Ning, Xu Jian-Xue, Kang Yan-Mei, Chen Yong-Hong
2003, 52 (12): 2989-2994. doi: 10.7498/aps.52.2989
Abstract +
In real systems, because of the inevitable noise, a chaotic synchronized attractor A will turn into a metastable attractor A′ with an average lifetime . We analyze a two-dimensional coupled map with additive noises and find analytica lly that the riddled basin of A′ will disappear when >2T, where T is the duration of an experiment. Acc ording to the characters of the riddled basin without noises, it is found that t he riddled basin will turn into not only a temporal riddled basin but also a reg ular fractal basin. This result is universal in two-dimensional coupled chaotic synchronized maps, and the further numerical calculations can also confirm this point.
Nonlinear adaptive multi-step-prediction of chaotic time series based on points in the neighborhood
Xiao Xian-Ci, Gan Jian-Chao
2003, 52 (12): 2995-3001. doi: 10.7498/aps.52.2995
Abstract +
In this paper a class of nonlinear adaptive multi-step-prediction algorithm base d on the manifold theory was proposed. We have performed the multi-step-predicti on by exploiting images of P-step iterations of several nearest neighbors with t his method. The simulation indicated that this method was available and could im prove the prediction speed, and that the series of the standard deviation of err or after prediction has an exponential growth ratio that is the largest Lyapunov exponent.
Study of hyperchaotic behavior in quantum cellular neural networks
Wang Sen, Ma Xi-Kui, Cai Li
2003, 52 (12): 3002-3006. doi: 10.7498/aps.52.3002
Abstract +
The nonlinear dynamical behavior of a quantum cellular neural network (QCNN) by coupling quantum-dot cellular automata was investigated. The theoretical analysis and simulation for a three-cell coupled QCNN has been done by using the polarization of a quantum-dot cell and the quantum phase as state variables. The com plex and abundant chaotic behaviors can be observed. Chaotic oscillations occur very easily. Two positive maximum Lyapunov exponents have been calculated in ord er to verify the hyperchaotic behavior.
A study of coupling effect in cellular automata model of traffic flow for two-l ane with open boundary conditions
Peng Lin, Tan Hui-Li, Kong Ling-Jiang, Liu Mu-Ren
2003, 52 (12): 3007-3013. doi: 10.7498/aps.52.3007
Abstract +
An improved two-lane cellular automaton model for traffic flow was proposed to d escribe the highway traffic under the opening boundary conditions by considering the relative motion of vehicles and the relation of deceleration probability. N umerical simulation have been carried out. The results show the complicated evol ution process of traffic flow. The flow of vehicles can be controlled by the cou pling coefficient b. Different values of b have different effects on the critica l point from free to jam phase.
The influence of polarized light on fluorescence emission in total internal refl ection microscopy
Wang Chen, Yuan Jing-He, Wang Gui-Ying, Xu Zhi-Zhan
2003, 52 (12): 3014-3019. doi: 10.7498/aps.52.3014
Abstract +
Based on Maxwell equations, we have discussed the different evanescent fields made by excitation with different polarized incident fields, and their influence on fluorescence emission. Our analysis showed that the incident light of p-polar ization produces an ellipitically polarized evanescent field; at the same time, the incident light of s-polarization produces a pure s-polarization evanescent f ield. The probability of the excitation of fluorescent molecules by an evanescen t wave varies with the fluorescent molecules orientation, which will in turn res ult in the anisotropic fluorescence emission.
Synthesis and magnetism of the intercalation compound Fe0.95PS3(MV)0.11
He Yun, Huang Hong-Bo, Shao Ting, Xia Yuan-Fu, Dai Yao-Dong
2003, 52 (12): 3020-3026. doi: 10.7498/aps.52.3020
Abstract +
The intercalation compound Fe0.95PS3(MV)0.11 (MV is the methylviol ogen cation) has been prepared. Its crystal structure and magnetism have been in vestigated by x-ray diffraction (XRD), susceptibility measurements and Mssbaue r experiments. Its XRD pattern can be indexed in a monoclinic unit cell with a=0 .879nm, b=0.944?nm, c=1.070nm, β=114.76°. The distance between layers of this intercalation compound is increased by 0.33nm compared with that of FePS3. Th e data of susceptibility show that second-order magnetic phase transitions have occurred when the temperature changed from 300K down to 4.2K. A ferromagnetic ph ase transition occurred below TC=84K. An antiferromagnetic phase tran sition occurred below TN=26K. The results of Mssbauer spectra taken in the t emperatur e range of 12 to 300K indicate that there are three kinds of divalent ions with their high spin states, which imply a charge transfer from guest to the Fe—S e g antibonding orbitals of the FePS3 host lattice, and some ions have been re leased from the FePS3 host lattice and then some vacancies have been formed. T he ferromagnetism originates from a canting of the spins of Fe2+, whe reas the antiferromagnetism occurred when the canting of the spins of Fe2+ have been modified at the lowest temperatures.
ATOMIC AND MOLECULAR PHYSICS
Study on the photofragment excitation spectrum of SO+2 in the range of 281-332nm
Wang Zhong, Zhang Li-Min, Wang Feng, Li Jiang, Yu Shu-Qin
2003, 52 (12): 3027-3034. doi: 10.7498/aps.52.3027
Abstract +
With the preparing of SO+2(2A1( 000)) by [3+1] multiphoton ioniz ation of the neutral SO2 molecules at 380.85nm,the photofragment exci tation (P HOFEX) spectrum in ultraviolet (UV) (281-332nm) wavelength range has been obtain ed.The PHOFEX spectrum in the UV range was assigned essentially to the SO+2(,)←SO+2(2A1) transitions.The transitions fr om 2A1(000) to the bend vibration levels of SO+2() were suggested,new harmon ic bend vibrational frequency ν2=241.78±0.92cm-1 and the anharmonicity constant X22=-1.71±0.01cm-1 for SO+2() was deduced.By using th e SO+ PHOFEX spectra in UV and in visible range (562-664nm), the symm etry of ,, states of SO+2 and the predissociation mechanism of SO+2(,,) were determined,that is,(i)the symmetry of ,, states of SO+2 s hould be 2 B2,2B1,2A1,( ii) around ,, states there should be two r epulsive states of symmetry α2A2 and β2B2,converging to the dissociation limit of SO+(X2П)+O(3Pg),(iii)the couplings betw een 2B1 and α2A2 and betwee n 2 B2 and β2Β2,lead to the dissociation to S O+(X2П)+O(3Pg).
CLASSICAL AREA OF PHENOMENOLOGY
Globalized numerical modeling of electromagnetic scattering from conductive targ ets with open cavity and electrically large size
Nie Zai-Ping, Wang Hao-Gang
2003, 52 (12): 3035-3042. doi: 10.7498/aps.52.3035
Abstract +
In this paper, the electromagnetic scattering from conductive target with open cavity has been simplified as two (inner and outer) equivalent models by using the equivalence principle and introducing an equivalent magnetic current in the aperture of the cavity. For the inner part of the cavity, the equivalent conductance matrix has been obtained by use of connection scheme. Approximate boundary in tegral method has been used to describe the coupling between inner and outer pa rts of the cavity, and to obtain the aperture equivalent magnetic current. Final ly, the general combined field integral equation was presented to form the elec tromagnetic model of the scattering problem, and the multilevel fast multipole a lgorithm was used to solve this problem efficiently. Numerical examples show go od agreement between calculated results and measured data.
Temperature field and formation of crater on the surface induced by high curren t pulsed electron beam bombardment
Qin Ying, Wang Xiao-Gang, Dong Chuang, Hao Sheng-Zhi, Liu Yue, Zou Jian-Xin, Wu Ai-Min, Guan Qing-Feng
2003, 52 (12): 3043-3048. doi: 10.7498/aps.52.3043
Abstract +
The present paper aims at revealing the formation mechanism of craters on the surface of metals produced by the bombardment of a high-current pulsed electron beam. Based on experimental investigations and a physical model, the temperature field and melting process are simulated for Al and two kinds of steels. The star ting melting positions, largest crater depths, and melting layer thicknesses are obtained, which agree satisfactorily with experimentally observed values. It is confirmed that temperature rises faster at a sublayer instead of on the extreme surface due to the maximum energy deposition located at about 1/3 of the total penetration depth of the beam. Such a special sublayer heating and melting mode causes eruptions of the sublayer liquid through the outer surface and produces t he typical surface crater morphology.
Reflection and refraction on the surface of a biaxial crystal
Shen Wei-Min, Jin Yong-Xing, Shao Zhong-Xing
2003, 52 (12): 3049-3054. doi: 10.7498/aps.52.3049
Abstract +
A method to solve the problems about reflection and refraction on the surface of a biaxial crystal is introduced, which can be applied to calculating refractive index, polarization direction, wave vector, Poynting vector of refracted waves for any direction of incidence and any orientation of major axes. The formulae t o calculate electric amplitude and optical power of each light beam are derived. The results of numerical calculations for a KTP crystal are given.
Application of Haar-Gaussian wavelet transform to edge-detection
S. Jutamulia, Wang Dong, Zhao Wen-Jie, Song Fei-Jun, Song Jian-Li, Yao Si-Yi
2003, 52 (12): 3055-3060. doi: 10.7498/aps.52.3055
Abstract +
The Haar-Gaussian wavelet transform is applied to analyze the pattern edges in the frequency domain and to establish a physical model for the edge detection. The bandwidth-matching algorithm is proposed. A telecentric optics is used to achieve a high-precision edge detection results with large-depth of focus.
Propagation of flattened-Gaussian beams in uniaxial crystals
Luo Shi-Rong, Lü Bai-Da
2003, 52 (12): 3061-3067. doi: 10.7498/aps.52.3061
Abstract +
The propagation of flattened-Gaussian beams(FGBs) in uniaxial crystals is studied based on the paraxial vector theory of the propagation of beams in uniaxially anisotropic media. Analytical propagation equations are derived, which permit us to study the propagation properties of FGBs in unaixal crystals in a simple way. It is shown that the initial circular symmetry of FGBs cannot be kept up, and the state of polarization of FGBs varies during propagation due to the anisotropy of crystals. The spatial evolutions of ordinary and extraordinary components, as well as these in x and y directions in the crystals originating from input FG Bs are illustrated with detailed numerical examples.
Study on mechanisms for enhancement kinetics of lasing gases in an optimized sea led-off CO2 laser
Cheng Cheng
2003, 52 (12): 3068-3074. doi: 10.7498/aps.52.3068
Abstract +
The kinetics of gases (CO2, N2 and He) in an optimized se aled-off CO2 laser are discussed in details. A comparison of numerical results shows that the po pulation of the laser levels is increased by optimizing the lasing gases, with t he increase of an excited N2 impacting to the upper laser level. Also , decreas ing the electron momentum transition frequency and increasing discharge current result in the increase of the relaxation of the upper rotational laser levels an d the decrease of the level lifetime, thus the lasing saturation intensity in a resonator is increased finally.
One-dimensional photovoltaic dark spatial solitons with fully incoherent white l ight
Yang Li-Sen, Liu Si-Min, Guo Ru, Huang Chun-Fu, Wang Da-Yun, Lu Yi
2003, 52 (12): 3075-3081. doi: 10.7498/aps.52.3075
Abstract +
We have experimentally observed, one-dimensional photovoltaic dark spatial soli tons in LiNbO3∶Fe crystal using white light from an incandescent la mp. A blac k-like soliton and a pair of gray solitons are excited from odd and even initial conditions, respectively. The waveguides induced by them can guide both incoher ent white light and coherent light. Their multi-mode structures are clearly obse rved by a probe coherent beam. The experiments demonstrate the presence of one- dimensional white light photovoltaic dark spatial solitons and show that it is p ossible that the coherent beams are controlled and guided by fully incoherent wh ite light dark spatial solitons.
A low-pass filter of wide stopband with a novel dual-layer fractal photonic band gap structure
Li Zheng-Fan, Liu Hai-Wen, Sun Xiao-Wei, Qian Rong, Zhou Min
2003, 52 (12): 3082-3086. doi: 10.7498/aps.52.3082
Abstract +
The concept of the photonic bandgap(PBG) is extended to a novel architecture wh ich consists of two fractal PBG plates stacked up in the direction perpendicular to the plane of the substrate. This novel, dual-layer fractal PBG is presented here as the substrate for a microstrip line, and the resulting configuration builds a low-pass filter of wide stop-band. In the specific design, the dual-layer PBG includes two kinds of fractal PBGs with different periodicities in which one fractal PBG consists of a first-order Sierpinski carpet, and the other consists of third-order Sierpinski gasket. Simulated and measured transmission parameters in comparison with the corresponding two filters with monolayer PBG show that the filter with the proposed fractal PBG drastically enhances the width of the stop-band.
The relationship between the resonant wavelength of the long period fiber grati ng and its exposure
Zhang Dong-Sheng, Jiang Li, Zhang Wei-Gang, Li Li-Jun, Fan Wan-De, Yuan Shu-Zhong, Kai Gui-Yun, Dong Xiao-Yi
2003, 52 (12): 3087-3091. doi: 10.7498/aps.52.3087
Abstract +
In this paper we have derived the Bragg equation of long-period fiber gratings by using interference theory. According to the color centers model and Kramers-Kronig principle, we have studied, theoretically and experimentally, the relationship between the resonant wavelength of the grating and its exposure. The result shows that the resonant wavelength of the long-period fiber grating changes with the UV exposure in the form of the sum of two decaying exponential functions an d the rate of change is controlled by the duty ratio of the mask. The resonant w avelength of the long-period fiber grating is inversely proportional to the duty ratio of the mask.
Generalized Tschebyshev polynomial and its application in solving the strong cou pling waveguide equations
Meng Yi-Chao, Guo Qi-Zhi, Tan Wei-Han
2003, 52 (12): 3092-3097. doi: 10.7498/aps.52.3092
Abstract +
In this paper, by means of generalized Tschebyshev polynomial, the analytical so lution is derived for (N+1)×(N+1) waveguide couplers arranged in a ring with strong coupling. As a concrete example, the solution of 5×5 waveguide couplers is calculated, and the relationship between strong and weak couplings is analyze d. The property of generalized Tschebyshev polynomial is discussed in detail.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Study on the relationship of average ionization stage with the electron temperat ure for Au laser produced plasma
Xie Fang-Jun, Zhang Hong, Cheng Xin-Lu, Yang Xiang-Dong, Zhang Ji-Yan, Yang Guo-Hong
2003, 52 (12): 3098-3101. doi: 10.7498/aps.52.3098
Abstract +
A collisional radiative model based on the spin-orbit-split-arrays was developed and used to determine the charge state distributions. The atomic structure code of Cowan and the spin-orbit-split-arrays model is used to calculate all the emission spectra of the different gold species, and a non-local thermodynamic eguilibrium model is coupled to calculate the ion populations and the charge state distributions at a given density and temperature. The relationship between average charge state and the electron temperature is given.In general, the avera ge charge state increases with electron temperature, except between 3800 and 390 0 eV. The reason for this unusual region is that the ionization potential increa ses much sharply between Au51 and Au52.
Calculation and analysis on the wave reflected characteristics of plasma before the conductor plate
Su Wei-Yi, Yang Juan, Wei Kun, Mao Gen-Wang, He Hong-Qing
2003, 52 (12): 3102-3107. doi: 10.7498/aps.52.3102
Abstract +
Regarding the nonuniform plasma plate as uniform multilayer slabs, the total wave energy reflectance of the interface between the plasma before a conductor plate and the atmosphere or vacuum can be calculated by applying the equivalent input impedance method. The result obtained is that the reflection characteristics are affected by electron number density, plasma thickness, frequency and transmitting direction of the incident wave. Changing any factor of them, the total wave energy reflectance can be reduced greatly. In the low frequency band, the d istribution of electron number density almost does not affect the reflectance. B ut in the high frequency band, it will affect the reflectance. The effect of pla sma thickness, wave frequency, electron number density distribution on it is alm ost independent of the wave polarizing direction.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Formation of self-assembly and the mechanism of Si nanoquantum dots prepared by low pressure chemical vapor deposition
M. Ikeda, S. Miyazaki, Peng Ying-Cai
2003, 52 (12): 3108-3113. doi: 10.7498/aps.52.3108
Abstract +
Si nanoquantum dots have been formed by self-assembled growth on the both Si—O—Si and Si—OH bonds terminated SiO2 surfaces using the low-pressur e chemical vapor deposition (LPCVD) and surface thermal decomposition of pure SiH4 gas. We have experimentally studied the variation of Si dot density with Si—OH bonds density, deposition temperature and SiH4 pressure, and analyzed qu alitatively the formation mechanism of the Si nanoquantum dots based on LPCVD surface thermal dynamics principle. The results are very important for the control of the density and size of Si nanoquantum dots, and have potential applications in the new quantum devices.
Ordered arrays and magnetic properties of cobalt nanoparticles
Wang Yu-Ping, Wang Yan-Guo, Yang Hai-Tao, Shen Cheng-Min, Du Shi-Xuan, Su Yi-Kun, Gao Hong-Jun
2003, 52 (12): 3114-3119. doi: 10.7498/aps.52.3114
Abstract +
Monodisperse cobalt nanoparticles are produced by high-temperature thermal decomposition method. The influence of the size of nanoparticles, evaporation temperature, organic solvent, and concentration on the formation of the cobalt nanoparticles array is studied by transmission electron microscopy and ultraviolet absorption. Preliminary results of the cobalt nonoparticles magnetic properties are presented. These results lay a good foundation for the further study of the physical properties and the application in nanoscale devices of magnetic nanoparticles.
Buckling behavior of carbon nanotube under compression
Wang Yu, Wang Xiu-Xi, Ni Xiang-Gui, Wu Heng-An
2003, 52 (12): 3120-3124. doi: 10.7498/aps.52.3120
Abstract +
The buckling behavior of carbon nanotubes(CNTs) under compression is simulated, by using the Tersoff-Brenner potential to describe the interactions in CNTs. The results show that Young modulus of CNTs decreases as the radii of CNTs increase. The Young modulus of zigzag CNT is higher than that of armchair CNT. The micro characteristic of the nanotube buckling is explained from the viewpoints of energy and structure distortion.
Polaron and admittance spectroscopy of yttrium-doped lead tungstate single cryst al
Xu Hua, Shen Han, Chen Min, Li Jing-De
2003, 52 (12): 3125-3129. doi: 10.7498/aps.52.3125
Abstract +
Both DC and AC conductance of Y-doped PbWO4 single crystal have been studied over a temperature range from ambient temperature to 160 ℃. Results of DC conductivity indicate that the carriers in PbWO4 in such a temperature ra nge are polarons other than ions, for a transition of polarons from energy band conduction to hopping conduction which characterized by a minimum of conductivity has been observed. AC conductivity obtained from admittance analysis is almost 3-orders higher than that of DC analysis, it ought to be mainly ascribed to the effect of dielectric. If conductivity and dielectric constant of a given system change together with frequency, AC measurement can only yield a total admittance spectrum, but is unable to separate conductivity spectrum from dielectric spectrum.
Deposition of nanoporous silica thin films by sol-gel
He Zhi-Wei, Zhen Cong-Mian, Lan Wei, Wang Yin-Yue
2003, 52 (12): 3130-3134. doi: 10.7498/aps.52.3130
Abstract +
Low dielectric constant thin film of nanoporous silica synthesized by sol-gel was deposited on Si(100) substrate by spin coating. By detecting —CH3 substituted for —OH species, which can avoid the destruction of network, surface modification was identified by Fourier transform infrared spectroscope. The hole size was about 70-80 nm observed from scanning electron microscope. By adjusting the pH value of the sol, we found that the gel time increased with the decrease o f the pH value of the sol. When heating the modified film at different temperatu res (60-400 ℃), we can obtain the lowest dielectric constant 2.05 at 300 ℃ .
A molecular dynamics study of energetic particle bombardment on diamond
Li Rong-Bin, Dai Yong-Bing, Hu Xiao-Jun, Shen He-Sheng, He Xian-Chang
2003, 52 (12): 3135-3141. doi: 10.7498/aps.52.3135
Abstract +
Molecular dynamic simulations, utilizing the Tersoff many-body potential, are used to investigate the microscopic processes of a single boron atom with an energy of 500 eV implanted into the diamond (001) 2×1 reconstructed surface. By calculating the variation of the mean coordination number with time,the lifetime of a thermal spike created by B bombardment is about 0.18ps. Formation of the split-interstitial composed of projectile and lattice atom(B—C) is observed. The total potential energy of the system decreases about 0.56 eV with a stable B split-interstitial existing in diamond. Lattice relaxations in the diamond (001) 2×1 reconstructed surface or near surface of the simulated have been discussed, and the results show that the outermost layer atoms tend to move inward and other atoms move outward, while the interplanar distance between the outermost layer and the second layer has been shortened by 15%,compared with it s starting interplanar distance. Stress distribution in the calculated diamond c onfiguration is inhomogeneous. After boron implanted into diamond with an energy of 500 eV, there is an excess of compressively stressed atoms in the lattice, w hich induces the total stress being compressive.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Density functional theory study on the electronic structure of UAl3 a nd USn3
Tan Ming-Qiu, Tao Xiang-Ming, Xu Xiao-Jun, Cai Jian-Qiu
2003, 52 (12): 3142-3149. doi: 10.7498/aps.52.3142
Abstract +
We report an ab initio study on the electronic properties of 5f states in UX3( X=Al,Sn) by full-potential linear muffin tin orbitals L(S)DA calculations. The r elativistic effects which are quite remarkable for heavy atoms such as U, have b een treated by using scalar relativistic and spin-orbital coupling corrections. The calculations presented in this article have addressed following issues:first ly, the numerical results illustrates the different U 5f itineracy in UAl3 and USn3 qualitatively, and then the heavy fermion behavior of USn3 ;secondly, u sing Stuttgart-fatband analysis, we have confirmed the above conclusion quantita tively. In addition to the above results, the calculation involved in this resea rch has resolved the discrepancy between previous density functional theory stud ies on these compounds, especially the band structure dispersion in M-X directio n of simple cubic USn3. In conclusion, this study has approached a mo re precis e description for these uranium compounds on the basis of modern density functio nal theory calculation and described USn3 as a heavy fermion system d ue to its localized U 5f electronic states theoretically.
The thermal/electronic transport properties of new superconductor MgB2 and MgCNi3
Wu Bai-Mei, Li Bo, Yang Dong-Sheng, Zheng Wei-Hua, Li Shi-Yan, Cao Lie-Zhao, Chen Xian-Hui
2003, 52 (12): 3150-3154. doi: 10.7498/aps.52.3150
Abstract +
The temperature dependence of thermal conductivity and electronic conductivity in superconductor MgB2, MgCNi3 and Bi2Sr2Ca0.9Ce0.1Cu2O8+y are presented. The thermal conductivity of Bi2Sr2Ca0.9Ce 0.1Cu2O8+y shows a peak under Tc observ ed in cuprates, but those of MgB 2 and MgCNi3 decrease monotonously. We calculate the elec tron thermal condu ctivity and the phonon thermal conductivity by Wiedemann-Franz law. The electron s contribute a large fraction to the thermal conductivity in normal state of MgB 2 and MgCNi3 because of the non-localigation of mutual eff ect of electrons. The analysis on electronic thermal conductivity indicates that the scattering by impurities prevails in electronic thermal resistance of both samples.
First-principles calculations on the geometry and the electronic structure of Pb Te(001) surface
Ma Jian-Xin, Jia Yu, Liang Er-Jun, Wang Xiao-Chun, Wang Fei, Hu Xing
2003, 52 (12): 3155-3161. doi: 10.7498/aps.52.3155
Abstract +
The geometry and electronic structure of PbTe(001) surface are calculated using the density functional theory method. It is shown that the (001) surface has no reconstruction and exhibits a significant oscillatory geometric relaxation. The top-to-second layer distance contracts by 4.5% and the second-to-third layer dis tance expands by near 2.0%. In addition, the surface shows a strong rumpling. Th e electronic structure of PbTe(001) surface differs from that of the bulk. With respect to the bulk energy gap at the L point, the surface energy gap broadens a t the X point. The surface states or resonance states are localized mainly near the top of the valence band and the bottom of the conduction band, while there a re no new surface states appearing in the fundamental energy gap. The density of state at Fermi level of the relaxed structure of PbTe(001) surface is very low, thus it is very stable.
Order-disorder transitions and inverse melting in vortex lattices
Wang Jin, Zhao Zhi-Gang, Liu Mei, Xing Ding-Yu
2003, 52 (12): 3162-3167. doi: 10.7498/aps.52.3162
Abstract +
Using Monte Carlo molecular dynamics simulation for a two-dimensional vortex lattice with random pinning, thermal fluctuations and vortex-vortex interactions, we study the order-disorder transition from a Bragg glass to an amorphous vortex glass or a vortex liquid in the pinning strength-temperature phase diagram. In order to determine the order in the vortex lattice, we calculate the static structure factor and evaluate the finite size exponent from the configurations of the vortex lattice. It is found that the Bragg glass region is sandwiched in between the disordered vortex glass phase at lower temperatures and the vortex liquid phase at higher temperatures, exhibiting inverse melting behavior. We attribute the unusual inverse melting behavior to the temperature dependence of the v ortex-vortex interactions.
The influence of Gd doping at A site on the magnetic and electrical properties i n La0.7Sr0.3MnO3
Gao Gui-Zhen, Liu Ning, Tong Wei, Zhang Yu-Heng
2003, 52 (12): 3168-3175. doi: 10.7498/aps.52.3168
Abstract +
The M-T curves, M-H curves, infrared spectra, Raman spectra,ρ-T curves and MR -T curves of La0.7-xGdxSr0.3MnO3 (x= 0.00, 0.10, 0.15, 0.20, 0.30 , 0.40, 0.50, 0.60, and 0.70) are studied. The experimental results indicate tha t with increasing Gd doping, the system undergoes a transition from long-range f erromagnetic order to the cluster-spin glass state and further to an antiferroma gnetic order. With heavily doping content, the transport property exhibits an ab normal behavior under magnetic background. The variation in magnetic structure a nd extra magnetic coupling caused by Gd doping lead to colossal magnetoresista nce.
Spin polarized dependent Hall effect in metallic granular film Fe15.16Ag84.84
Chen Wei-Ping, Feng Shang-Shen, Jiao Zheng-Kuan
2003, 52 (12): 3176-3180. doi: 10.7498/aps.52.3176
Abstract +
We report the preparation of metallic granular film Fe15.16Ag84. 84, grown on glass substrate and single crystals silicon substrate respectively, u sing magnetron sputtering method. The applied field H dependences of Hall effect and Hall coefficient RH in this specimen have been investigated. We observed the spin-dependent scattering anomalous phenomenon in the applied field H depend ence of Hall voltage UH, which suggests a corresponding relationship with the magnetoresistance. A proper explanation has been given based on spin-dependent s cattering effect or tunneling effect.
Large magnetoresistance in Cox-C1-x granular films on Si(1 00) substrate prepared by pulsed laser deposition
Zhu Dan-Dan, Zhang Xiao-Zhong, Xue Qing-Zhong
2003, 52 (12): 3181-3185. doi: 10.7498/aps.52.3181
Abstract +
A large positive magnetoresistance (MR) has been observed in Cox-C1-x gr anular films prepared on Si(100) substrates by pulsed laser deposition (PLD). Co 0.02-C0.98 sample has the largest room-temperature MR of 2 2% at the magnetic field B=1T. It is noted that in the Cox-C1-x/Si s tructure, the MR at room-temperature is much larger than that at low temperatures. The room-te mperature positive MR of the Cox-C1-x films has a B2/ 3 dependence when B<1T and a B1/2 dependence when B>1T. Such magnetotransport pr opert ies have never been reported before. It appears that some new mechanisms play im portant roles in the magnetotransport of the Cox-C1-x film s. Further stu dy on the MR mechanism of the Cox-C1-x/Si structure will n ot only shed l ight on the study of spin electronics and magnetism, but also make possible the application of the Cox-C1-x/Si in information industry.
Influence of grid voltage on charge storage ability of porous PTFE film electret s
Wu Yue-Hua, Xia Zhong-Fu, Wang Fei-Peng, Qiu Xun-Lin
2003, 52 (12): 3186-3190. doi: 10.7498/aps.52.3186
Abstract +
The influence of grid voltage on charge storage ability of porous polytetrafluoroethylene (PTFE) film electrets has been systematically studied by means of constant voltage corona charging with a grid, thermal pulse technique, open-circu it thermally stimulated discharge current spectra and monitoring the charging cu rrent through samples during the charging. The origin of the influence has been discussed by using the charge dynamic characteristic and microcosmic structure analysis of the materials. It was found that too high a grid voltage may lead to the declination of charge density deposited in the porous sample and enhance th e charge decay, and thus, to the decrease of piezoelectricity and thermal stabil ity of the porous film. For negatively corona charged porous PTFE, excellent cha rge storage ability can be performed at an optimal grid voltage, which will impr ove its piezoelectric activity in the application to the electret piezoelectric sensor film with dipolar space charges.
Effect of atomic fluctuation on the localized modes in one-dimensional system
Zhang Da-Cheng, Wang Lu-Xia, Liu De-Sheng, Han Sheng-Hao, Xie Shi-Jie
2003, 52 (12): 3191-3196. doi: 10.7498/aps.52.3191
Abstract +
In the frame work of the tight-binding approximation, the effect of defects and disorder on the vibrational modes in one-dimensional systems was studied through a random distribution model. It was found that the Goldstone mode of a so liton or polaron is pinned and its frequency is shifted up to a finite value. Th e weak mode g4 of a soliton is enhanced. The staggered modes keep the ir localization even if there is a large lattice fluctuation. Some new modes appear when the perfect soliton or polaron configuration is disturbed.
The nonlinear characteristics study of the effect of salt on denaturation transi tion of DNA
Pang Xiao-Feng, Liu Sheng-Gang, Dong Rui-Xin, Yan Xun-Ling
2003, 52 (12): 3197-3202. doi: 10.7498/aps.52.3197
Abstract +
The nonlinear dynamics model of DNA was studied, which is related to the salt concentration. The nonlinear dynamics equation and kink solution were obtained, the influence of salt on phase boundary and phase transition force of DNA denaturation were discussed. These results obtained by numerical calculations are in agreement with experimental data in DNA.