Vol. 53, No. 9 (2004)

Mei symmetry of variable mass systems with unilateral holonomic constraints
Li Hong, Fang Jian-Hui
2004, 53 (9): 2807-2810. doi: 10.7498/aps.53.2807
Abstract +
In this paper,the Mei symmetry of variable mass systems with unilatera l holonomic constraints is studied. The definition and criterion of the Mei symm etry of variable mass systems with unilateral holonomic constraints are given. T he structure equation and conserved quantity of the Mei symmetry are obtained. A n example is given to illustrate the application of the result.
The interaction of excitons with phonons and solution of breathers in one-dimensional molecular chain
Tian Qiang, Xu Quan
2004, 53 (9): 2811-2815. doi: 10.7498/aps.53.2811
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By virtue of the method of continuum limit,we obtained the solitons of the vibration of lattice in one-dimensional harmonic and anharmonic molecule chains,through which the equations of exciton and phonon are solved. On considering th e cubic anharmonic potential,the vibration of lattice in one\|dimensional mole cule chain has a solution of kink soliton and on considering the quartic anharm onic potential,the vibration of lattice in one-dimensional molecule chain has a so lution of breathers.
Poincaré-Cartan integral invariant of a nonholonomic constrained generalized mechanical system
Li Ai-Min, Zhang Ying, Li Zi-Ping
2004, 53 (9): 2816-2820. doi: 10.7498/aps.53.2816
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Based on generalized Apell-Четаев constrained conditions and taking into a ccount the inherent higher-order nonholonomic constraints,the generalized Poincaré-Cartan integral invariant for a generalized mechanical system with higher- order subsidiary nonholonomic constraints is formulated. We can show that the ex istence of Poincaré-Cartan integral invariant for such a system is equivalent to the generalized canonical equation of a nonholonomic constrained generalized mechanical system.
Compacton solutions and floating compacton solutions of one type of nonlinear equations
Yin Jiu-Li, Tian Li-Xin
2004, 53 (9): 2821-2827. doi: 10.7498/aps.53.2821
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Study one type of nonlinear equations,namely generalized Camassa-Holm equation C(n):u\-t+ku\-x+β\-1uxxt+β\-2(un+1)x+β\-3u\-x(u\+n)xx+β\- 4u(u\+n)xxx=0.Obtain abundant exact solutions by four ansasz,particularly when k≠0,we obt ain compacton solutions;while whenk=0,we obtain floating compacton solution s.At last,we also study other forms of fully nonlinear generalized Camassa-Holm equation,and their compacton solutions are governed by nonlinear equations.
A simple fast method in finding the analytical solutions to a class of nonlinear partial differential equations
Xie Yuan-Xi, Tang Jia-Shi
2004, 53 (9): 2828-2830. doi: 10.7498/aps.53.2828
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By introducing,a new transformation and selecting appropriate trial functions ,nonlinear partial diff erential equations can be converted to algebraic equations,and their related coe f ficients can be easily determined by making use of the method of undetermined coefficients. Finally,the analytical solutions to a class of nonlinear partial di fferential equations are successfully derived. One can easily see that this meth od used herein is particularly simple.
A novel solution to singly quantized vortex in big N Bose-Einstein condensate
Li Fa-Shen, Xu Yan, Li Xi-Guo, Zuo Wei, Jia Duo-Jie
2004, 53 (9): 2831-2834. doi: 10.7498/aps.53.2831
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An approximate analytical wave function is presented for an oblate ellipsoidal big N Bose-Einstein condensate(BEC) in a xi-symmetr ic harmonic traps. The relationship between the undetermined parameter C and the total particle number N,the aspect ratio λ of the BEC is obtained by varying t he energy functional. The parameter Cvaries extremely slowly versus N (orλ),and it becomes a fixed value 0.321646 when both Nand λare very large.
The groud-state wave function and evolution of the interference pattern for a Bose-condensed gas in 3D optical lattices
Yang Huan-Song, Xu Zhi-Jun, Cheng Cheng, Wu Qiang, Xiong Hong-Wei
2004, 53 (9): 2835-2842. doi: 10.7498/aps.53.2835
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Based on the Gross-Pitaevskii equation and by using the effective chemical poten tial,we study the distribution of the Bose-condensed gas in the combined potenti als (magnetic trap and three-dimensional optical lattices).The normalized ground-state wave function is given from the distribution of the Bose-condensed gas.The analytical expression of the density distribution of the Bose-condensed gas is given by using the propagator method when the combined potentials and only the optical lattices are switched off,respectively.When the combined potentials are switched off,the theoretical results of this work agree well with the experiment by Greiner et al.When only the optical lattices are switched off,it is show n that the interference pattern will oscillate in the magnetic trap.In addition,the evolution of the interference pattern is also investigated in the case of an isotropic magnetic trap.
A five-dimensional cosmic branes solution in Einstein-Maxwell-dilaton gravity model
Tao Bi-You, Yan Jun
2004, 53 (9): 2843-2845. doi: 10.7498/aps.53.2843
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A new five-dimensional cosmic branes solution in Einstein-Maxwell-dilaton gravit y model is obtained in this paper,the physical meanings of this solution are ana lyzed and discussed.
The double noncommutative spacetime and the double complex symmetric gravitational theory
Shao Ying, Wu Ya-Bo, Dong Peng
2004, 53 (9): 2846-2851. doi: 10.7498/aps.53.2846
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In this paper,the double complex symmetric gravitational theory is established and the concrete expression of the static spherically symmetric double complex metrics is derived by introducing the double complex symmetric metric tensors. In this theory the Moffat's results are extended,the hyperbolic complex symmetric gravitational theory is naturally obtained and the famous Schwarzchild solution is contained as the special case. Moreover,in the linearized weak field approximation the hyperbolic complex symmetric gravitational theory can automatically free from the potential problem of negative energy ghost states. Furthermore,the double complex symmetric gravitational action in the double noncommutative spacetime can be constructed by extending the double complex coordinates to the double noncommutative relation satisfied and doubling the Moyal star product.
Nonequilibrium statistical information theory
Xing Xiu-San
2004, 53 (9): 2852-2863. doi: 10.7498/aps.53.2852
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In t his paper, we propose a nonequilibrium statistical information theory, whose ke rnel is information(entropy) evolution equation describing information evolution law. A nonlinear evolution equation of Shannon information (entropy) is derived . The statistical physical information is introduced and its nonlinear evolution equation is derived. Both of these two information (entropy) evolution equatio ns show that the temporal change rate of statistical information (entropy) densi t y originates together from their drift, diffusion and dissipation (production) i n coodinate space (and state variable space). The expressions of drift informati on flow and diffusion information flow, the concise formulas of statistical entr opy production rate and statistical information dissipation are given. The stati stical information dissipation (or increase) rate being equal to its statistical entropy production (or decrease) rate of the dynamic system, the information di ffusion and information dissipation occuring at the same time are proved. The d ynamic mutual information and dynamic channel capacity reflecting the dynamic di ssipative character in transmission process is presented. The similarities and dissimilarities between Shannon information (entropy),its evolution equation an d physical information (entropy),its evolution equation are discussed.
Determining the controllable conditions for time-delayed feedback chaos control
Zhang Xiao-Ming, Peng Jian-Hua, Chen Guan-Rong
2004, 53 (9): 2864-2870. doi: 10.7498/aps.53.2864
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Based on Hopf bifurcation theory and methods in time-delayed systems, we ana lytically determine some general conditions of time-delayed feedback control of three-dimensional autonomous chaotic systems. With this method, a criterion for the stability of periodic solution under control and for the direction of Hopf b ifurcation is derived theoretically studied. Applying the method to the control of some three-dimensional autonomous chaotic systems, we can analytically find the cont rollable parameter in this region. Choosing parameters in it, we can successfull y stabilize chaotic orbits to periodic states.
Study of a discrete chaotic system based on tangent-delay for elliptic reflecting cavity and its properties
Sheng Li-Yuan, Sun Ke-Hui, Li Chuan-Bing
2004, 53 (9): 2871-2876. doi: 10.7498/aps.53.2871
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Based on the physical model of ellipse reflecting cavity, the tangent-delay operation is proposed to change the evolution route of the systems , and a new class of discrete chaotic map systems is deduced based on the tangen t-delay operation. Simulation experiments show that the discrete chaotic systems have many special properties such as the maximum Lyapunov exponent is over zero , unchangeable equiprobability distribution and zero correlation in total field, there exists a square chaotic attractor when tangent delays one unit, and becom e ergodic state when tangent delays more units than one. The discrete chaotic sy stems can generate 2 independent pseudo-random sequences together. All of the pr operties suggest that the class of chaos systems possesses the potential applica tion in encryption.
A symbolic dynamics approach for the complexity analysis of chaotic pseudo-random sequences
Xiao Fang-Hong, Yan Gui-Rong, Han Yu-Hang
2004, 53 (9): 2876-2881. doi: 10.7498/aps.53.2876
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By considering a chaotic pseudo-random sequence as a symb olic sequence, we present a symbolic dynamics approach for the complexity analys is of chaotic pseudo-random sequences. The method is applied to the cases of Logistic map and one-way coupl ed map lattice to demonstrate how it works, and a comparison is made between it and the approximate entropy method. The results show that this method is app licable to distinguish the complexities of different chaotic pseudo-random seque nces, and it is superior to the approximate entropy method.
Study on phase-space reconstruction of chaotic signal based on wavelet transform
You Rong-Yi, Chen Zhong, Xu Shen-Chu, Wu Bo-Xi
2004, 53 (9): 2882-2888. doi: 10.7498/aps.53.2882
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Using the methods of the wavelet transform and the nonlinear dynamics, the b ehavior of chaotic signals in phase space is studied. It is indicated that, in p hase space reconstruction, the wavelet transform of chaotic time series is essen tia lly a projection of strange attractor on the axis of the space that filter vect ors opened, which in correspondance with the method of phase space reconstructio n proposed by Packard et al. The experimental results show that, after d oing wavelet transform, the architecture of attractor trajectory is similar to t he original one, and the nonlinear invariants such as correlation dimension and Kolmogorov entropy are reserved. These results show that wavelet transform is ef fective for studying chaotic signal.
Superharmonic resonance bifurcation control of parametrically excited system based on state feedback strategy
Fu Wen-Bin, Tang Jia-Shi
2004, 53 (9): 2889-2893. doi: 10.7498/aps.53.2889
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A nonlinear parametric feedback control is propo sed to modify the steady-state resonance responses, thus to reduce the amplitude of the response and to eliminate the saddle-node bifurcations that take place i n the resonance responses. The nonlinear gain of the feedback control is determi ned by analyzing the bifurcation function associated with the corresponding freq uency-response equation and the Jacobian matrix. It is shown by illustrative exa mples that the proposed nonlinear feedback is effective for controlling superhar monic resonance responses.
The study of a cellular automaton traffic flow model with mixed different-maximum-speed vehicles on single lane
Kuang Hua, Kong Ling-Jiang, Liu Mu-Ren
2004, 53 (9): 2894-2898. doi: 10.7498/aps.53.2894
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Based on the NS models of traffic flow, a cellular automaton traffic mo del with different-maximum-speed vehicles mixed on single lane is proposed. We p resent the fundamental diagrams of traffic flow under different parameters by us ing computer numerical simulation. The model's traffic flow characters are prese nted and analyzed.
A study on multi-speed cellular automata model of traffic flow of main-road with two-lane under the traffic light control
Peng Lin, Tan Hui-Li, Wu Da-Yan, Liu Mu-Ren, Kong Ling-Jiang
2004, 53 (9): 2899-2904. doi: 10.7498/aps.53.2899
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A multi-speed and two-lane cellular automata model of traffic flow was proposed to simulate the main road traffic in city under the open boundary condi tions. By considering many real factors, the effects on traffic flow and velocit y of the main-road, produced by the bus stop and the time switched between the green light and the red light, have been analyzed. The result can reflect the re al traffic flow of the main-road in city under the control of the traffic lights .
Study on the corner effect in new grooved-gate nMOSFET
Tong Jian-Nong, Shen Xu-Bang, Zou Xue-Cheng
2004, 53 (9): 2905-2909. doi: 10.7498/aps.53.2905
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The function and influence of the corner effect in groovedgate MOSFET is simulated using classical twodimensional device simulator PISCESⅡ. The electric field of the channel in groovedgate metalorganic semiconductor field effect transistor(MOSFET) and impact on the threshold and hot carrier effect are studied. The corner effect is very favorable to suppressing short channel effects and hot carrier effects. The impact of corner effect on groovedgate MOSFET is changed with the change of the corner, and is the largest at about 45°. Therefore, the groovedgate MOSFET has a very great application prospect in deep submicro device architecture.
Optical absorption of nanoclusters by sequentially implanting into SiO2 glass and subsequently annealing in a selected atmosphere
Zhang Li, Ren Feng, Chen Hai-Bo, Shi Ying, Jiang Chang-Zhong, Fu Qiang
2004, 53 (9): 2910-2914. doi: 10.7498/aps.53.2910
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Ag and Cu ions were implanted sequentially into SiO2glass by using a metal vapor vacuum arc (MEVVA) source in the room temperature. Both of the doses were 5×1016 ions/cm2The accelerated voltage for Ag was 43kV and for Cu 30kV with the ion flux density~2mA/cm2The valence states of composite sa mples were observed in details by x-ray photoelectron spectroscopy (XPS). The results showed that there were metallic Ag and Cu and CuO in the sample. The formation of alloy nanoclusters have been evidenced by selected area electron diffraction (SAED), energy dispersive xray spectra (EDS) and optical absorption spectra which fit the result of theoretical simulation well. After annealed at different temperatures for 1h in either oxidizing (air) or reducing(70%N2+30%H2 gas mixture, gas pressure 20Pa) atmosphere, the absorption peaks shifted to blue and appeared a new peak during annealing in reducing atmosphere. Applying the free electron model of metal particles, we have calculated the average size of nanoclusters annealed at different temperatures, the results showed that the size of nanoclusters increased gradually with the enhancement of temperature. AgCu alloy nanoclusters were decomposed after annealing in oxidizing atmosphere. Cu atoms migrated to the surface of the sample and are oxidized; Ag nanoclusters were formed due to low oxygensilver interaction. For the sample annealed in reducing atmosphere, the alloy decomposed to Ag and Cu nanoclusters.
Magnetic Salisbury screen and its high-frequency response
Wu Rui-Xin, Chen Ping
2004, 53 (9): 2915-2918. doi: 10.7498/aps.53.2915
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We have studied the possibility of constructing magnetic Salisbury screen, and the frequency response of reflectivity of the screen in microwave frequency range. We have found that magnetic Salisbury screen has a lower reflectivity when magnetic susceptibility satisfies χ″χ′. If the frequency response of magnetic susceptibility is in the relax type of domain wall resonance, we could make filmtype Salisbury screen, in which the thickness of the screen may be in the order of micrometer or even submicrometer. The reflectivity of the screen depends on the characteristic impedance zr of the magnetic film that is determined by ferromagnetic resonant frequency and susceptibility under a static field. The frequency response of reflectivity shows that the magnetic film Salisburyscreen has a broadband frequency range for absorbing microwaves well.
Study of relational nuclear databases and online services
Fan Tie-Shuan, Guo Zhi-Yu, Liu Wen-Long, Ye Wei-Guo, Feng Yu-Qing, Song Xiang-Xiang, Huang Gang, Hong Ying-Jue, Chen Jin-Xiang, Tang Guo-You, Shi Zhao-Min, Liu Chi, Chen Jia-Er, Liu Ting-Jin, Huang Xiao-Long
2004, 53 (9): 2919-2924. doi: 10.7498/aps.53.2919
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A relational nuclear database management and webbased services software system has been developed. Its objective is to allow users to access numerical and graphical representation of nuclear data and to easily reconstruct nuclear data in original standardized formats from the relational databases. It presents 9 relational nuclear libraries: 5 ENDF format neutron reaction databases (BROND, CENDL, ENDF, JEF and JENDL), the ENSDF database, the EXFOR database, the IAEA Photonuclear Data Library and the charged particle reaction data from the FENDL database. The computer programs providing support for database management and data retrievals are based on the Linux implementation of PHP and the MySQL software,and are platformindependent. The first version of this software was officially released in September 2001.
Formation mechanism of interface charges in the metal-semiconductor superlattices
Li Shu-Ping, Wang Ren-Zhi
2004, 53 (9): 2925-2930. doi: 10.7498/aps.53.2925
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ASA energy band calculation method. The results show that the origin of interface charge Qss is the rearrangement of valence electrons in the metal and semiconductor atomic layers at the metalsemiconductor interface. The formation mechanism of the interface charge Qss in this paper is similar to that of Tung's model of the polarization of the chemical bonds at metalsemiconductor interfaces. Both of them can account for the origin of interface charge Qss even at the monocrystalline metalsemiconductor interfaces.
Electronic band structure of ferroelectric SrBi2Nb2O9
Cai Meng-Qiu, Yin Zhen, Zhang Ming-Sheng, Tang Chun-Hong
2004, 53 (9): 2931-2936. doi: 10.7498/aps.53.2931
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The electronic band structures of SrBi2Nb2O.9 (SBN) in both the ferroelectric and paraelectric phases were calculated using firstprinciples method. The paraelectric phase is of an indirect band gap of 1.57eV ; whereas the ferroelectric phase is of a direct band gap of 2.23eV. The valence band maxima of both the paraelectric and ferroelectric phases are mainly contributed from O2p states; while the conduction band minima are from Nb4dand Bi6p states. When transforming from the paraelectric to the ferroelectric phases, the strong hybridization between Nb4d and O2pand BiO(2) hybridization enhance the distortion of NbO6poctahedra and reduce the total energy of the system,in favor of stabilizing the ferroelectric phase. The calculation shows that the low leak current in SBN is related to Bi6p state.
Study on coherent phase modulation of coherent population trapping in V-type atomic system
Wang Li-Qiang, Li Yong-Fang, Bi Dong-Yan, Cheng Yan-Chun, Cao Dong-Mei, Zhang Chong-Jun
2004, 53 (9): 2937-2942. doi: 10.7498/aps.53.2937
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It is realized that coherent population trapping (CPT) and electromagnetically induced transparency (EIT) are modulated by coherent phase modulation in a Vtype atomic system excited by delaytime laser pulses; the modulation period can reach femtosecond order if the proper energy levels are selected. The relation between the delaytime laser pulse and the population of each energy level are investigated by the numerical and analytical solutions. The characteristic and regularity of population modulated by laser fields phase are obtained as well. Utilizing this mechanism, one can get the quantum switch,of which the modulation period can get to femtosecond order.
Study of the electron transfer in Xeq+-He collisions
Chen Xi-Meng, Cai Xiao-Hong, Yang Wei, Shao Cao-Jie, Cao Zhu-Rong, Yu De-Yang, Lu Rong-Chun
2004, 53 (9): 2943-2946. doi: 10.7498/aps.53.2943
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The cross section ratios of the double to single electron transfer of helium target induced by Xeq+(q=15,17,19,21,23) ions are measured by means of the position sensitive and timeofflight techniques. By considering an onestep transfer mechanism, we modify the extended classical overbarrier model. It is found that the calculated single and double electrontransfer cross sections using the modified model show excellent agreement with the experimental data of Andersson et al. and Selberg et al, and improves the agreement with the present measured double to single electrontransfer ratio considerably.
The vectorial properties of paraxial beams propagating in a uniaxial crystal
Luo Hai-Lu, Hu Wei, Yi Xu-Nong, Zhu Jing
2004, 53 (9): 2947-2952. doi: 10.7498/aps.53.2947
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The vectorial properties of paraxial beams propagating perpendicular to the optical axis of a uniaxially anisotropic crystal are investigated. By relying on a suitable planewave angular spectrum representation of the electromagnetic field, we obtain the analytical expressions of optical fields. The longitudinal component is expressible in terms of the first correction of the transverse field. Moreover, the extraordinary beams can induce ordinary beams in terms of the second correction of the transverse field.
Phase-contrast imaging with microfocus x-ray source
Chen Min, Xiao Ti-Qiao, Luo Yu-Yu, Liu Li-Xiang, Wei Xun, Du Guo-Hao, Xu Hong-Jie
2004, 53 (9): 2953-2957. doi: 10.7498/aps.53.2953
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We report the experimental results of the inline phasecontrast imaging with a microfocus xray source. The minimized focused spot size of the xray source is about 05μm. According to the optical transfer function of the microfocus xray source, the effects of the size of the xray source, the coherent length of xray on the imaging resolution are discussed. The phasecontrast images of the fresh biomaterials are obtained with 10μm resolution. Compared with the absorptioncontrast image of the sample, the finestructure of the fresh biomaterials can be observed distinctly in the phasecontrast image.
Light coupling in Y-cut doped lithium niobate crystals
Gao Yuan-Mei, Liu Si-Min, Guo Ru, Huang Chun-Fu, Wang Da-Yun
2004, 53 (9): 2958-2963. doi: 10.7498/aps.53.2958
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We experimentally study the light coupling behaviors between the transmittinglight and reflected light in ycut lithium niobate crystals. When the epolarized incident light is launched into the crystals along +y axis and -y axis, respectively, we find that the time behaviors of the reflectivity and transmissivity are almost identical for both cases, respectively. Whereas when the opolarized incident light is launched into the crystals along +y axis and -y axis, respectively, the time behaviors of the reflectivity and transmissivity for both cases are obviously different. We investigate the physics mechanism of these phenomena preliminarily.
Solution of radial equation of Kepler’s problem by pseudo-angular-momentum method and normalization of eigenstate and coherent state
Li Wen-Bo, Li Ke-Xuan
2004, 53 (9): 2964-2969. doi: 10.7498/aps.53.2964
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By using the pseudoangularmomentum method, the radial equation for bound state of Kepler's problem is solved and the analytic expression for eigenstate is derived. The result shows that the normalization of eigenfunction that should be done carefully is quite peculiar. The corresponding coherent state is also discussed.
Electromagnetically induced transparency in a four-level atomic system driven by three coupled fields
Liu Zheng-Dong, Wu Qiang
2004, 53 (9): 2970-2973. doi: 10.7498/aps.53.2970
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We study the spontaneous emission in a fourlevel atomic system driven by three coupled fields. We have demonstrated the existence of electromagnetically induced transparency (EIT) with a set of suitable parameters, and we find that the light levels of the drive fields are as weak as that of the spontaneous emission with the EIT.
Diffraction-induced spectral switches of spherically aberrated polychromatic Gaussian beams
Lü Bai-Da, Zhao Guang-Pu
2004, 53 (9): 2974-2979. doi: 10.7498/aps.53.2974
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Starting from the propagation law of the crossspectral density function, an analytical expression for the onaxis spectrum of spherically aberrated pol y chromatic Gaussian beams diffracted at an aperture is derived, the aberration f ree result is obtained as a special case treated in the paper. Detailed numerica l calculations and physical analysis are presented. It is shown that the onaxis spectrum in the near field may be redshifted and blueshifted in co mparison wi th the aberrationfree case, and the spectral switch may also take place. In pa r ticular, the influence of spherical aberration on the behavior of spectral swit ches is illustrated.
Incoherently coupled screening soliton pairs composed of spatially incoherent multimode beams
Chen Yuan-Yuan, Wang Qi, Shi Jie-Long
2004, 53 (9): 2980-2985. doi: 10.7498/aps.53.2980
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Incoherently coupled screening soliton pairs composed of spatially incoherent mu ltimode beams can be established in biased photorefractive media under steadys t ate conditions, every soliton constituent of which is not only spatially incoher ent with respect to each other, but also to itself. We study that the property o f th ese incoherently coupled soliton pairs in brightbright, darkdark configurati on s by the coherent density approach and get the intensity expression of these sol iton pairs. The propagation characteristics of coherent components that compose each soliton constituent of the coupled soliton pairs are discussed in detail.
Optimal designs for high-power vertical cavity surface emitting lasers
Ning Yong-Qiang, Yan Chang-Ling, Qin Li, Liu Yun, Wang Li-Jun, Cao Jian-Lin, Li Hui-Qing, Zhang Jie, Cui Da-Fu, Xu Zu-Yan
2004, 53 (9): 2986-2990. doi: 10.7498/aps.53.2986
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Vertical cavity surface emitting lasers (VCSEL's) lase in a single longitudin al mode, have a circularly symmetric output beam that can be very tightly focused, offer extremely high coupling efficiencies into optical fiber, and can be mas s produced in two-dimensional arrays relative to the conventional edge-emitting semi conductor laser. To obtain a high optical output power, besides enlarging of VCS EL's lasing area, the key points are proper number of quantum wells, homogeneous dist ribution of current density in the active layer and good thermal control. The dependenc e of VCSEL's performance on the number of quantum wells, the active diameter, th e thermal conductivity and the electric resistance of the material; and the dist ance between electri cal contacts are investigated. By optimizing the design parameters for a 980 nm In0.2Ga0.8As/GaAs VCSEL, a maximum continuous wave (cw) output power of 1.95 W at room temperature is obtained, which to our knowledge is the highest cw output power of any single VCSEL so far.
Interaction potential between spatial optical solitons based on holographic focusing mechanism
Jiang Jin-Huan, Li Zi-Ping
2004, 53 (9): 2991-2994. doi: 10.7498/aps.53.2991
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The interactions between spatial optical solitons based on holographic focusing mechanism propagating in opposite directions are studied by means of variational method. It is shown that the coherent interactions are insensitive to relative phase between two beams in some cases, and this is just the result of the recent paper.
Effect of the pump light on the beam quality of the diode pumped laser
Guo Zhen, Cai De-Fang, Wen Jian-Guo, Tang Ying-De, Fu Jun-Mei, Wang Shi-Yu
2004, 53 (9): 2995-3003. doi: 10.7498/aps.53.2995
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Effect of the pump light on the quality of diode pumped laser (DPL) has been di scussed. Based on the end pump system, the equation of the laser field has been studied, which shows that the distribution of the laser gain can affect the la ser mode and make the base mode of the laser to drift off from the Gauss distrib ution . A factor is proposed to estimate the scale of the affection, which is called a f fection factor of pump light. Calculations on the end pump laser prove that the factor is practical and convenient. Study on the Qswitched laser show that the field distribution of the pulse is also affected by the distribution of the pump beam. The rising edge of the pulse usually evolves from far to near gauss distribution. The phenomenon is called as the field evolution of the pulse risin g edge.
Measurement of spectral phase of femotosecond laser pulse using SPIDER technique
Wang Peng, Wang Zhao-Hua, Wei Zhi-Yi, Zheng Jia-An, Sun Jing-Hua, Zhang Jie
2004, 53 (9): 3004-3009. doi: 10.7498/aps.53.3004
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We present an experimental set up and the calculation approach for the measureme n t of the spectral phase of femtosecond laser pulse by using a spectral phase int erferometry for direct electric reconstruction (SPIDER) technique in this paper, the method for determining crucial parameters as Ωand τwas given. W ith the femtosecond laser pulse from the Ti:sapphire laser, we obtained the phase of the laser spectrum by using the SPIDER, the temporal profile of the original laser pulse was deduced based on the result. It reveals the FWHM width is 107fs, which is in good agreement with the result measured directly by using an autocorrelat or.
Response characteristic of femtosecond LT-GaAs photoconductive switches at different voltage bias
Deng Li, Liu Ye-Xin, Shou Qian, Wu Tian-Hong, Lai Tian-Shu, Wen Jin-Hui, Lin Wei-Zhu
2004, 53 (9): 3010-3013. doi: 10.7498/aps.53.3010
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The response characteristic of a LTGaAs photoconductive switch formed in a cop lanar waveguide at different voltage bias is studied with photocurrent autocorre lation measurement technique. The experimental results show that the switching t ime increases from ~200fs to ~750fs, when the bias voltage ascends from 0.5×104 to 9.5×104 V/cm. This phenomenon is attributed to the increase of carr ier capture time arising from the potential barrier lowering (FrenkelPoole eff ect) and the fieldenhanced thermal ionization.
Existence curves of asymmetric photorefractive holographic spatial optical solitons
Liu Jin-Song
2004, 53 (9): 3014-3019. doi: 10.7498/aps.53.3014
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It has been proved that there exist asymmetric holographic spatial optical solit on pairs in biased photorefractive crystals. The two solitons from such a pair h ave equal width and unequal amplitudes. The soliton existence curves of such sol iton pairs are given and three regions of different behaviors exist in these curves. That is, for a given value of bias field, the width of holographic solitons depends strongly on the ratio of the total peak input intensity of the two solitons from a pair to the intensity of the background light when the ratio is small or large enough, whereas it remains relatively constant in a middle r egion. The extent of the middle region for the asymmetric case is smaller than t hat for the symmetric case.
Interaction between optical spatial solitons in nonlocal Kerr media
Xie Yi-Qun, Guo Qi
2004, 53 (9): 3020-3024. doi: 10.7498/aps.53.3020
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In this paper, it is discussed that a pair of optical beams copropagates in no nlocal Kerr media, which is governed by the nonlocal nonlinear Schr?dinger equa tion (NNLSE). A new approximate linear model to the NNLSE is presented for the s trong nonlocal Kerr media with arbitrary response functions. An analytical solut ion in Gaussian form to the model is obtained. It is shown that the phase of eac h of the two beams is depended on the total input power. As a concrete example, th e interaction of two beams with the intensity of one of the beams much stronger than that of the other is discussed. It is found that the phase shift of the wea ker (probe) beam is very large within rather short propagating distance in the c ase of soliton, which can be controlled by modulating the input power of the str onger (pump) beam.
Influence of off-waist incidence on evolution of the Gaussian beam in the nonlocal nonlinear media
Guo Qi, Xu Chao-Bin
2004, 53 (9): 3025-3032. doi: 10.7498/aps.53.3025
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In this paper, we discuss the evolution of the offwaist incident Gaussian beam in the nonlocal nonlinear media by use of the (1+1)dimensional strongly nonlocal model. An exact analytical solution for the evolution is obtained. We find that no matter how high the power of the incident beam is, the beam width will oscillate periodically and no spatial soliton will exist, which is substantially different from the onwaist incident case. The influence of the input power and incident position on beam evolution is also discussed. The higher the input power, the narrower the beam width is. The incident position determines the initial evolution trend. The definition of a “spatial chirp” is given, to our knowledge, for the first time. The physical origin of the above phenomenon is that the different incident position corresponds to the different spatial chirp. The concept of the spatial chirp provides a new physical qualitative insight into the evolution of optical beams. The comparisons of beam evolutions in focusing media, in defocusing media and in linear homogeneous media are also given.
Stability of photovotaic spatial soliton with two-wavelength components
Ouyang Shi-Gen, Jiang De-Sheng, She Wei-Long
2004, 53 (9): 3033-3041. doi: 10.7498/aps.53.3033
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An approximate method is presented to calculate the full width at half maximum(F WHM) of photovoltaic(PV) spatial solitons(PVSSs) with twowavelengths component . An advanced numerical analysis i ndicates that two coaxial hyperbolic secant beams, provided that they satisfy th e functional relations of FWHM with amplitudes of this type of PVSS, will be ver y close to solitons when they propagate in PV crystals. Besides, this type of PV S S tends to be stable against small axial perturbations and small refractive inde x perturbations due to variations of temperature of the crystal. However, if the pro files of intensity of two coaxial signal beams with different wavelengths diff e r mildly from those of PVSS, the two beams will tend to experience cycles of co mpression and expansion; and if the profiles of intensity of the signal beams di ffer significantly from those of PVSS, these two signal beams will diffuse endle ssly.
Dark-bright photovoltaic soliton pair with two-wavelength components
Quyang Shi-Gen, She Wei-Long
2004, 53 (9): 3042-3048. doi: 10.7498/aps.53.3042
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We present a scheme to realize coupled dark-bright photovoltaic spatial-soliton pairs with two-wavelength components. With the propagating beam method we numeri cally study the spatial dynamic properties of these coupled solitons, finding th e possibility to use such coupled solitons in all-optical beam switching.
Propagation of optical pulses through one-dimensional photonic crystals with a dispersive and gain defect layer
Yu Tian-Bao, Liu Nian-Hua
2004, 53 (9): 3049-3053. doi: 10.7498/aps.53.3049
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The propagation of a pulse through onedimensional photonic crystals with a dispersive and gain defect layer is discussed. The dispersion and gain of the defect layer is described by Lorentz oscillator model. It is found that the pulse pea k exhibits subluminal and superluminal behaviors with varying strength of the os cillator. The Poynting vector and energy velocity can be negative, but the latte r is never faster than the vacuum light speed c. The advance or delay of the pulse peak is a result of the coherent superposition of all Fourier components which experienced different phase shift and different amplification in the medium.
Synthesis and optical properties of durable opal photonic crystals with high crystalline quality
Yuan Chun-Wei, Wang Jing, Huang Zhong-Bing, Tang Fang-Qiong
2004, 53 (9): 3054-3058. doi: 10.7498/aps.53.3054
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Polystyrene (PS) colloidal crystal multilayers with high crystalline quality are fabricated quickly from aqueous colloidal solutions by the vertical deposition method at certain temperature and humidity. Optical properties, which are determined by the photonic band structure, are discussed by means of light transmission and reflection measurements. By scanning electron microscopy (SEM), the morphology of the samples is characterized and the ordered close package of the spherical colloids in planes parallel to the substrate surface is illustrated. Furthermore, facecenteredcubic (fcc) phase is proved by transmission ele ctron microscope (TEM). To avoid friability and redispersal, the colloidal c rystals multilayers are dried slowed and sintered at 105℃ for 6 hours to enlarg ement of the contact section between nearestneighbor PS spheres. Experiments h ave proved the efficiency and practicability of the method.
Raman scattering of ethanol solvent in a photonic crystal with a variational lattice constant
Ni Pei-Gen, Cheng Bing-Ying, Zhang Dao-Zhong, Liu Xiao-Dong
2004, 53 (9): 3059-3064. doi: 10.7498/aps.53.3059
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A silica colloidal photonic crystal in ethanol solution, whose lattice constant varies with the height of the crystal, was prepared. The Raman intensities of th e ethanol solution induced by a picosecond intense laser were measured at differ ent heights, and two phenomena were found: (1) although the frequency of Raman s ignals generated within the photonic crystal is equal to that of the photonic ps eudogap of the photonic crystal, the Raman intensity attenuation measured is not reduced to the extent of that in the conventional transmission experiment; (2) although the transmission of an incident beam with the wavelength of the Raman s ignal is strongly dependent on the height of crystal, the intensity of th e Raman scattering generated within the silicaethanol colloidal photonic crystal does n ot change with the height, i.e. it is insensitive to the pseudogap. These anti i ntuitive phenomena may be directly interpreted using the fact that the propagati on mechanism of the monodirectional incidental laser is intrinsically different from that of the Raman signals from inner light sources inside a photonic crysta l, and the Raman signals scattered by defects deep inside the crystal and genera ted in the surface layer contribute largely to the measured intensities.
Study on dispersion characteristics of a tilted birefringent filter
Jia Ya-Qing, Zhu Xiao-Nong
2004, 53 (9): 3065-3070. doi: 10.7498/aps.53.3065
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We present theoretical investigations of the second and the thirdorder group d elay dispersion caused by a tilted birefringent filter (TBF). The expression for the group delay of TBF is deduced and the corresponding dispersions are calcula ted. The influence of the parameters such as the thickness, the tilting angle an d the rotation angle of the birefringent plate on dispersions are discussed. Com parison between the dispersion characteristics of a GiresTournois interferomet er (GTI) and those of TBF is also present.
Study of pulse transmission properties in nonlinear optical loop mirror
Tan Bin, Li Zhi-Yong, Li Shi-Chen
2004, 53 (9): 3071-3076. doi: 10.7498/aps.53.3071
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We have studied the pulse transmission properties in a nonlinear optical loop mi rror (NOLM) with abnormal despersion and obtained the firs t maximum of transmission, the compression ratio and related soliton order at th e first maximum as functions of nomarlized loop length. With the comparison of t ransmission and compression properties of both transmission limited and chirped pulses in long and short loop loop length NOLMs, we conclude that long NLOM is f it for pulse shaping, while short NOLM is fit for pulse compression.
A novel design methodology for superstructure fiber Bragg grating comb-filter
Sun Jun-Qiang, Zhang Xin-Liang, Huang De-Xiu, Cao Hui, Xiao Ling-Yan
2004, 53 (9): 3077-3082. doi: 10.7498/aps.53.3077
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A novel superstructure fiber Bragg grating (SFBG) combfilter for multiwavele ngth laser is proposed. This SFBG is characterized by its singlegrating struct ure, both refractive index modulation and local chirp abundant in variation, sym metri cal reflection peaks, narrow bandwidth and standard channel spacing. Based on layerpeeling inverse scattering technique, adopting independent channelbycha nnel apodizingwindowing method rather than integral apodizingwindowing proce dure, the desired SFBG is figured out successfully. The fa brication techniques for this SFBG are discussed as well. Reflection spectrum, group time delay and group time delay ripple are analyzed by the method of transf ormation matrix. The results show that this SFBG satisfied all requirements of designing target. In DWDM optical fiber telecommunication systems, this novel SFB G is a promising candidate for the perfect high performance combfilter used in multiwavelength laser.
Slow waves propagation in BISQ poroelastic model
Cui Zhi-Wen, Wang Ke-Xie, Cao Zheng-Liang, Hu Heng-Shan
2004, 53 (9): 3083-3089. doi: 10.7498/aps.53.3083
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The slow compressional wave (P2wave) in porous media based on BISQ model is investigated. The lowfrequency approximate expression for velocity and attenua t ion of P2wave is presented. Compared with Biot model, BISQ model predicts tha t the attenuation of P2 waves is very large at low frequency and decreases with increasing characteristic squirt flow length (R), the velocity lowfrequency limit is not zero and decreases with increasingR, variation of the ratio of pore fluiddisplacement to bulkdisplacement is similar to that of attenuation and its phase is diffe rent from that of Biot model. The seepage flow induced by P2 wave at the fluidporous media interface is larger than that of Biot model. For the sake of contrast, the p roperties of the fast compressional wave are also presented. Two conclusions are induced from the BISQ model: there is no squirt mechanism in inviscid fluid-satura ted porous media and there is no “dynamic compatibility” phenomenon in viscid fluid-saturated porous media.
Limitation for the energy spectrum analysis for the understanding of the turbulent cascade
Cai Qing-Dong, Li Cun-Biao, Meng Qing-Guo
2004, 53 (9): 3090-3093. doi: 10.7498/aps.53.3090
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Simple examples were applied to show that the “cascade" and “inverse cascade” presented in an energy spectrum even without real physical cascade processes. T he misleading comprehension should appear if energy spectrum was considered as a un ique evidence of the energy cascade in turbulence.
Dynamics of zonal flow based on resistive interchange mode turbulence
Peng Xiao-Dong, Yin Shao-Quan
2004, 53 (9): 3094-3098. doi: 10.7498/aps.53.3094
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Dynamics of zonal flow excitation in tokamak plasmas is investigated based on th e re sistive interchange mode turbulence. Employing lowfreedom approach, the resist i ve interchange mode turbulencezonal flow system is solved both analytically an d numerically. Our results show that the largescale zonal flow or oscillating z o nal flow can be excited in the case of sufficiently high pressure gradient (driv ing force).
Diamond-like carbon films deposited on optical glass substrate by using ECR microwave acetone plasma CVD method
Wang Jiu-Li, Zhang Gu-Ling, Fan Song-Hua, Liu Chi-Zi, Yang Si-Ze, Yang Wu-Bao
2004, 53 (9): 3099-3103. doi: 10.7498/aps.53.3099
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Smoothing, dense and uniform nano-crystalline diamondlike carbon films are pr epared by using electron cyclotron resonance (ECR) microwave acetone plasma chemical vapor deposition (CVD) method. Atomic force microscope shows that, the surface roughness of this film is less than 10nm, the average grain size is abou t 100nm, and there are no distinct Raman shift peaks. Middle infrared spectra sh ow the existence of sp1, sp2, and sp3 mixed C—C bond, sp3 mixed CH3,CO, COOH and other oxygenic hydrocarbons in the film. The micr ohardness is about 4GPa, bulk elastic modulus is about 11 GPa tested by nano-indentation. Without absorption in closed infrared area, the refractive index is 1.576 and the calculated deposition rate is 460 nm/h for the film.
Emission spectral tomography algorithm based on multi-objective optimization and its application in plasma diagnosis
Le Shu-Ping, Li Bing-Ying, He Xing-Dao, Wan Xiong, Yu Sheng-Lin, Wang Chang-Kun
2004, 53 (9): 3104-3113. doi: 10.7498/aps.53.3104
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A multiobjectiveoptimizationbased emission spectral tomography alg or ithm(EST) is proposed. Its reconstruction results for asymmetrical emission coefficient field are studied by numerical simulation with compute r. The results show that this algorithm has faster convergences and higher recon struction precision than that of traditional algorithms and is suitable for real time reconstruction of emission coefficient field with incomplete data. In the experiment of argonarc plasma diagnosis, the threedimensional reconstructio ns of temperature and atomic (ionic) density fields are accomplished with this a lgorithm and the spectrum relativeintensity method.
Analysis of the characteristics of low-frequency modes in a corrugated waveguide filled with plasma
Li Cheng-Yue, Yan Yang, Liu Sheng-Gang, Xie Hong-Quan, Liu Pu-Kun
2004, 53 (9): 3114-3118. doi: 10.7498/aps.53.3114
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A corrugated waveguide filled with an infinitely thin annular plasma is immersed in a strong longitudinal magnetic field. By means of fluid model and linear field theory,the dispersion relation of the electromagnetic wave propagation along the system is derived. The dispersion characteristics and beamwave interactions of lowfrequency plasma modes are analyzed in two cases of various densities of plasma by numerical computation. It is found that the dispersion relation with out electron beam satisfies exactly the Floquet theorem and the frequency of electromagnetic wave could not be confined by plasma oscillation frequency. The low-frequency plasma modes can even be coupled with TM modes as the plasma density i s increased.
Simulation study of microstructure transition of liquid metal in during solidification processes
Liu Rang-Su, Qin Shu-Ping, Hou Zhao-Yang, Chen Xiao-Ying, Liu Feng-Xiang
2004, 53 (9): 3119-3124. doi: 10.7498/aps.53.3119
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A computer simulation tracking study for the rapid solidification processes of liquid metal In system has been performed by means of molecular dynamics method.U sing the index method of HoneycuttAndersen(HA)and the cluster bondtype index method,the bondtypes,clusters and cluster configurations of In atoms are anal yzed.It has been found that,contrary to conventional metals(such as Al),the rela tive number of 1551,1541 bond types,related to the icosahedral configuration,is decreased remarkably with decreasing temperature;the total number of 1421,1422 a nd 1431 bond types,related to the fcc and hcp structures,only changes a little;t he total number of 1321,1311,1301 and 1201 bond types,related to the rhombohedra l structure,increases remarkably,and then gradually plays a dominant role.Finall y,the amorphous structure is formed mainly with rhombohedral structures and mixe d up with clusters of cubic(fcc,bcc)and hcp structures.However,the icosahe dral and various polyhedra structures,which occupied a dominant position in the previous amorphous structure of metal Al,vanish completely in the present amorph ous structure of metal In.This is just the physical origin in microstructure for the obvious difference between the g(r) curves of amorphous In having a spl itting second peak with a lower front subpeak and a higher behind one,and the g(r) curves of amorphous Al having a splitting second peak with a higher fro nt subpeak and a lower behind one.
Prediction of failure time for floating gate ROM devices at low dose rate in space radiation environment
He Bao-Ping, Guo Hong-Xia, Gong Jian-Cheng, Wang Gui-Zhen, Luo Yin-Hong, Li Yong-Hong
2004, 53 (9): 3125-3129. doi: 10.7498/aps.53.3125
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The experiments of ionizing radiation were performed on floating gate ROM device s by using 60Coγrays. The experimental aim was to examine the radi ation response at various dose rates. According to the extrapolation technique and the failu re criteria we defined,the parameter failure and function failure of devices vs. dose rate were studied. Finally, based on the function of failure timevs. doserate, the failure time of floating gate ROM device in space radiation environm ent was predicted.
Preparation and thermal transport properties of CoSb3 nano-compounds
Yu Bai-Lin, Tang Xin-Feng, Qi Qiong, Zhang Qing-Jie
2004, 53 (9): 3130-3135. doi: 10.7498/aps.53.3130
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CoSb3 micrometer powder was synthesized by solidstate reaction using high pu rity powder of Co,Sb as the starting materials.CoSb3 nano-powder was prepared by highenergy ballmilling.CoSb3 block material with the average grain size of 150nm was prepared by Spard Plasma Sintering(SPS).The influence of nanostru cture on thermal transport properties of CoSb3 was investigated systematicall y .When the grain size of CoSb3 decreases from micrometer to namometer,the lattice thermal conductivityκL of compounds falls remarkably,while the carries thermal conductivity κc decreased less drastically than did the lattice thermal conductivity κL.The decrease in thermal conductivity of CoSb3 compounds with decreasing grain size was mainly due to the reduction in lattice thermal conductivity.
Influence of Si concentration on the evolution of shape and size of self-assembled Ge islands
Deng Ning, Chen Pei-Yi, Li Zhi-Jian
2004, 53 (9): 3136-3140. doi: 10.7498/aps.53.3136
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The influence of Si concentration on the shape transition of self-assemble d SiGe islands was investigated. SiGe islands with different Si concentrations were grown by UHV/CVD. The topography and size distribution of islands were cha racterized by atomic force microscopy. The results show that the critical volum e increases with Si concentration, at which the islands change from pyramids to domes. A modified m odel was established and used to explain the influence of Si concentration on the sha pe transition by introducing the revised strain energy term depending on Si conc entration. Domeshaped as well as pyramidshaped unimodal SiGe islands were gr own under suitable conditions. This research indicates that the shape and size o f the selfassembled ialnds can be controlled more accurately by adjusting Si c oncentration.
First principle study on optical properties of KTa0.5Nb0.5O3
Wang Yuan-Xu, Wang Chun-Lei, Yuan Min, Zhao Ming-Lei, Zhong Wei-Lie
2004, 53 (9): 3141-3145. doi: 10.7498/aps.53.3141
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We have calculated the optical properties(the imaginary part of the dielectric f unction ε2(ω),the optical absorption coefficient I(ω),the reflectiv ity R(ω)) of tetragonal and cubic crystals of KTa0.5Nb0.5O3 by the full potential linearized augmented plane wave method (FLAPW).Our calcul ated tetragonal optical spectra show three big peaks around 3,7 and 23 eV along a and b separately.Along c,there are three mainly peaks at 4,8,23 eV respectively,among which the one at 4 eV is sharp and high.Comparing optical pr operties in the tetragonal and cubic phass,we concluded that the tetragonal phas e has more anisotropic optical responses.
Influence of constant-current corona charging on electret state of porous PTFE film electret
Wu Yue-Hua, Xia Zhong-Fu, An Zhen-Lian, Wang Fei-Peng, Qiu Xun-Lin
2004, 53 (9): 3146-3151. doi: 10.7498/aps.53.3146
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The influence of constantcurrent and constantvoltage corona charging technique on the electret state of porous polytetrafluoroethylene(PTFE) film electret has been studied by constant current and constantvoltage corona charging at room temperature, is othermal surface potential decay, thermally stimulated discharge(TSD) and SEM(sc anning electron microscope), etc. Compared to the constantvoltage corona charging, the current through films is constant during constantcurrent charging, the r efore, the trapping possibility along the thickness direction of porous structur e increases and the charge density goes up, which improves the charge storage ab ilit y of the electret. However, the charges trapped in the dielectric surfaces of the interfaces with different depths along the thickness of the sample are externally stimulated during storage or application, their transport paths to the back electrode from the trapping positions are relatively shorter according to the hopping model of the charges, therefore the charge decay is accelerated and the charge sta bility is decreased.
The chemisorption of CO on a disordered binary alloy (NixCu1-x) and the mutual influence of chemisorption and surface segregation
Zhang Hui, Zhang Guo-Ying, Li Xing, Liu Shi-Yang
2004, 53 (9): 3152-3156. doi: 10.7498/aps.53.3152
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The atomic structural model of the NixCu1-x disordered binary alloy was set up for the cases with or without consideration of surface segrega tion by computer program ming.Then the model of the chemisorption of CO on the surface of the material wa s set up with a coverageθ=05. The electronic structure of CO chemisorpti on on the top and hollo w sites of the NixCu1-xdisordered binary alloy was calculated (considering and not considering the segregation).The calculated results show that (1) the CO ad sorbd at top site on the surface is stable and, (2) the chemisorp tion makes the surface density of states of the disordered binary alloy lowered, the ener gy ba nd widened and the localization of d orbital weakened and, (3) the chemisorpti on of CO on the surface restricts the surface segregation of Cu, then the mutual influence of chemisorption and multiplayer surface segregation is discussed at an electronic level.
Stochastic resonance of an Ising spin system driven by stochastic external field
Shao Yuan-Zhi, Zhong Wei-Rong, Lin Guang-Ming, Li Jian-Can
2004, 53 (9): 3157-3164. doi: 10.7498/aps.53.3157
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The study on interesting stochastic resonance of the Ising spin system (ISS), subject to a joint external field of weak sinusoidal modulation and stochastic white noise, was carried out through solving the meanfield equation of motion ba sed on Glauber dynamics, and some new features in the dynamic response and stochasti c resonance of the above ISS were also revealed. The periodic ally driven stochastic ISS shows the occurrence of characteristic nonequilibrium d y namic phase transition when the frequency and amplitude of driving field, the te mperature of system and noise intensity attain a specific accordance in quantity . Somewhat similar to the situation in sole sinusoidal field, our primary result indicates that the dynamic transition of ISS in an applying stochastic fieldre tains probably the feature of both discontinuous transition at low temperatures and continuous transition at high temperatures. The analysis was made concerning the nonequilibrium dynamic transition induced in the Ising spin system by exter nal stochastic force in detail.
Nonequilibrium dynamic phase transition of an Ising spin system driven by various oscillating field
Shao Yuan-Zhi, Zhong Wei-Rong, Lin Guang-Ming
2004, 53 (9): 3165-3170. doi: 10.7498/aps.53.3165
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We have studied both the dynamic response and the relevant nonequilibrium dynami cal p hase transition of an Ising spin system subject to three sorts of oscillating fi eld i.e. sinusoidal, square and sawtooth waves. The above three sorts of externa l field drive dynamically the Ising spin system in either simply gradual ( abrupt) way or their combination respectively. In the case of both sinusoidal and squar e ways, it was observed that the Ising spin system displays a low_temperature sy mmetr y-breaking ordered phase and a high_temperature symmetric disordered phase as well as the dynamic transition between two dynamical phases above. We also detected the tri_critical point separating high_temperature continuous dynamic transition and low_temperature discontinuous one on the boundary of dynamic transition. The trend of dynamic transition boundary and the dependence of tri_critical point upon the system temperature, the frequency and amplitude of the driving field we re revea led as well. In contrast, nodynamic transition occurs any longer and the system always stays in symmetry-breaking ordered state if the external field takes the form of sawtooth wave. The preceding discrepancy in dynamic response and transi tion is attributed to the perturbative characteristic of different oscillating f ields.
Exchange-coupling interaction and effective anisotropy of NdFeB nanocomposite permanent magnetic materials
Zhu Ming-Gang, Li Wei, Gao Ru-Wei, Han Guang-Bing, Feng Wei-Cun
2004, 53 (9): 3171-3176. doi: 10.7498/aps.53.3171
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Taking Nd2Fe14B/αFe as a typical sample and adopting the cubic grain model,we investigated the exchange-coupling interaction between different magnetic grains and the effective anisotropy of nanocomposite permanent materials in this paper . The effective anisotropy of nanocomposite permanent materials, Keff, is equal to statistical mean values of the effective anisotropy of magnetically soft and hard grains. Every grain's anisotropy is determined by the anisotropy constants of the coupled part at grain boundaries and the internal uncoupled part. The ca lculated results reveal that the distributions of soft and hard grain sizes influence th e effective anisotropy. When the sizes of magnetically soft and hard grains are identical, the effective anisotropy decreases with the reduction of grain size a nd hard phase component, and decreases rapidly while the grain size is less than 20nm. When the soft-grain sizes are of some definite values, Keff shows a maximum value with the variation of the hard-grain size. The hard-grain s izes corre spo nding to the maximum of Keffdecrease with the increase of soft phase components and the reduction of softgrain sizes. The grain size dependence ofKeffis bas ically similar to that of coercivity. The decrement of coercivity for nanoco m posite permanent materials is mainly due to the reduction of effective anisotrop y.
Study on the coercivity and step effect of mixed magnetic films by micromagnetism and Monte Carlo simulation
Weng Zhen-Zhen, Feng Qian, Huang Zhi-Gao, Du You-Wei
2004, 53 (9): 3177-3185. doi: 10.7498/aps.53.3177
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The magnetic properties of ferromagnetically and antiferromagnetically mixed fi lms are simulated by micromagnetism method based on the principle of energy mini mum and Monte Carlo technology. The hysteresis loops, spin configurations, and the influences of exchange constant JAA, uniaxial anisotropy constant K, dipolar interaction constant Dand diluted ratio of ferromagnetic ato m X on the coercivity Hc at the ground states are studied systematical ly for the systems studied. A t the same time, the temperature dependence of the coercivity is calculated. The simulated results indicate that: (1) a steplike hysteresis is evidently observed in the mixed magnetic films, and the result calculated by a simple Ising model reveals that the steplike effect can be attributed to the different response of the clusters with different size and different diluted ratio of antiferromagn etic atom on the external field; (2) at the ground states, as 0.5≤X≤1.0,the value of Hc increases with increasing values ofK, JAA, but decreases with increasing value of D; (3) a peak exists in the HcX curves. These simulated resu lts explain the experimental facts about the granular films with antiferromagnetic coupling. The T dependence of the value ofHc for the films with diffe rent magnitude of X can be well described by the law of Tα. But the value of α has a complex variation with the change of X.
Structure phase transition and magnetic properties of nanocrystalline Zn0.6CoxFe2.4-xO4
Wang Jin-Zhi, Fang Qing-Qing
2004, 53 (9): 3186-3190. doi: 10.7498/aps.53.3186
Abstract +
A series of nanocrystalline powders Zn06CoxFe24-xO4 ( x=0—030) was synthesized by the solgel technique. The structure and mag netic properties was investiga ted and analyzed through the xray diffraction (XRD) patterns and the vibrating sample magnetometer (VSM). The experimental results show that αFe2O3 tra nsitio nal phase appears in the temperature range from 550℃ to 800℃. Single-phase zinc-cobalt ferrites with a spinel structure are obtained when the temperature is beyond 800℃. With relatively higher values of the cobalt content x=0075 — 015, the specific saturation magnetization climbs up at first and then falls d o wn with the increase of the cobalt content. The coercive force strength Hc of Zn06CoxFe24-xO4 reaches its highest value 47520A/m when x=0075 at 1300℃. Hc increas es slowly with temperature near 1200℃ when x≥015 and remains in a flat s tate at 1200—1300℃ and moderate increase is obtained by increasing the x value. High specific saturation magnetization and coercive force can be obtained simultaneo usly when the cobalt content is near 010
Giant magnetostriction of melt-spun Fe85Ga15ribbons
Li Yang-Xian, Qu Jing-Ping, Liu Guo-Dong, Hu Hai-Ning, Liu Zhu-Hong, Dai Xue-Fang, Zhang Ming, Cui Yu-Ting, Chen Jing-Lan, Wu Guang-Heng
2004, 53 (9): 3191-3195. doi: 10.7498/aps.53.3191
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Large magnetostrictions of -1300 and +1100 ppm have been obtained in our Fe85Ga15ribbon samples. This was attributed to the shape anisotropy of ri bbon and the existence of Ga atom clusters with preferential orientation in the melt-spun Fe85Ga15 alloys. A small increase of magnetostriction with increasing temperature w as observed between 163 and 321K. However, at higher temperatures, the magnetost riction increases sharply with increasing temperature.
Femtosecond spectral studies of electron spin injection and relaxation in AlGaAs / GaAs MQW
Sun Feng-Wei, Deng Li, Shou Qian, Liu Lu-Ning, Wen Jin-Hui, Lai Tian-Shu, Lin Wei-Zhu
2004, 53 (9): 3196-3199. doi: 10.7498/aps.53.3196
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The electron spin injection and relaxation in AlGaAs/GaAs multi quantum well(MQW) are studied with f emtosecond saturation absorption measurements. A electron spin relaxation time of 80±10ps is deduced. The relaxation mechanism is attributed to the randomizat ion of the local magnetic field arising from the spinorbit coupling.
Dielectric and ferroelectric properties of BaBi4Ti4O15 ceramics and their dependence on lattice structure
Zhong Wei-Lie, Zhang Pei-Lin, Wang Chun-Lei, Li Zheng-Fa, Qiu Zhong-Ping, Ge Hong-Liang
2004, 53 (9): 3200-3204. doi: 10.7498/aps.53.3200
Abstract +
Good quality barium bismuth titanate (BaBi4Ti4O15) ceramics is fabric ated successfully with BaBi4Ti4O15 nanopowders prepared by Sol-Gel p rocess. The ferroelectric to paraelectric phase transition of barium bismuth titanate ceram ics was studied by determining the dielectric and saturated ferroelectric proper ties of barium bismuth titanate. All measurements show barium bismuth titanate m ay be a kind of order_disordered relaxor ferroelectrics with a diffused phase transition which is a firstordered one, and its dielectric and saturated fe rroelectric properties depended strongly on its lattice structure.
Photonic band in quasi-fractal photonic crystal structure including idealized metal
Zheng Rui-Sheng, Feng Yu-Chun, Niu Han-Ben, Li Yan
2004, 53 (9): 3205-3210. doi: 10.7498/aps.53.3205
Abstract +
The photonic band of a set of quasi_fractal photonic crystals, which have similar structure and include idealized metal, is computed by finite-differ ence time_domain method. The result shows that there are photonic band gaps in t his kinds of quasi-fractal photonic crystals. It is found that, with increasing fractal series, the width of the photonic band gap is enlarged, the frequency of the photonic band totally trends to high frequency quickly, at the same time, the photonic band is quickly hauled to line and become a energy level.
Exciton tunnelling in ZnCdSe quantum well/CdSe quantum dots
Jin Hua, Zhang Li-Gong, Zheng Zhu-Hong, Kong Xiang-Gui, An Li-Nan, Shen De-Zhen
2004, 53 (9): 3211-3214. doi: 10.7498/aps.53.3211
Abstract +
Exciton tunneling through ZnSe barrier layer of various thicknesses is invest igated in a novel Zn072Cd028Se/CdSe coupled quantum well/quantum dots (QW/QDs) structure using photoluminescence spectra and nearresonant pumpprobe mea surements. Fast exciton tunneling from quantum well to quantum dots is observed by transient differential transmission. The tunneling time is 18ps, 44ps, 39 ps for barrier thickness of 10nm, 15nm, 20nm, respectively.
The design of visible light stealth material
Xu Wen-Lan, Zhang Shuan-Qin, Xu Yi
2004, 53 (9): 3215-3219. doi: 10.7498/aps.53.3215
Abstract +
The coarse particles theory, the fine particles theory and the bridge theory w ere used to calculate the absorption and scattering coefficients of the particle s separately according to their size compared with the light wavelength. The dif fuse reflectivity of the coating with the particles was obtained. The influences of the various parameters of the coating, such as the optical constants of the particles and the binder, the size and the volume fraction of the particles, on the diffuse reflectivity were discussed. Taking TiO2 as the example, the compu ter design method of visible light stealth coating is introduced.
XPS study of fluorinated diamond-like carbon films prepared by reactive magnetron sputtering
Jiang Mei-Fu, Ning Zhao-Yuan
2004, 53 (9): 3220-3224. doi: 10.7498/aps.53.3220
Abstract +
Fluorinated diamond_like carbon(F_DLC) films were prepared by radio frequency(RF) reactive magnetron sputtering with trifluoromethane (CHF3) and argon as source gases, and pure graphite as a targ et. The influence of source gas flow rate ratio on the film bonding configuration, sp2/sp3 hybrid ratios and optical band gap were investigated by Raman, Infrared transmission spectra, UV_visible spectra and XPS spectra. The results show that F-DLC films with high fluorine content, wide optical band gap and ultra-low diel ectric constant can be prepared by RF reactive magnetron sputtering technique in low input RF power (60W), high pressure (2.0Pa) and proper sour ce gas flow ratio (Ar/CHF3=2∶1).
3UCVD deposition SiO2 on SiC wafer and its C-V measurement
Tang Xiao-Yan, Zhang Yi-Men, Zhang He-Ming, Zhang Yu-Ming, Dai Xian-Ying, Hu Hui-Yong
2004, 53 (9): 3225-3228. doi: 10.7498/aps.53.3225
Abstract +
The SiO2layer as a gate dielectric is grown on p_type 4H-SiC wafer by means of 3UCVD. Positive oxide charge density only has 1.6×1011cm-2, its result is superior to conventional thermally oxidized process. A new front tofront device with advantages over conventional test structure is used for high_frequ ency C-V measurement.
The structural optical and electrical properties of films prepared by screen print
Xu Jin-Bao, Zheng Yu-Feng, Li Jin, Sun Yan-Fei, Wu Rong
2004, 53 (9): 3229-3233. doi: 10.7498/aps.53.3229
Abstract +
Thin films of iron pyrite(FeS2)have been prepared by screen print. X-ray diff raction (XRD) patterns were used to identify the nature of t he films. Special attention has been devoted to the structural parameters(cell and sulfur positional parameter), bond distances and angles, lattice constants. The procedure used in this study was the full profile refinement of x-ray powde r diffraction patterns using the Rietveld method. Here we report on the influnce of film thickness for resitivity, Hall mobility and optical energygap etc.
The synthesis and thermoelectric properties of double-atom-filled BamCenFeCo3Sb12 compounds
Luo Pai-Feng, Tang Xin-Feng, Li Han, Liu Tao-Xiang
2004, 53 (9): 3234-3238. doi: 10.7498/aps.53.3234
Abstract +
The single_phase double_atom_filled p_type BamCenFeCo3Sb12 c ompounds were synthesized using the solid_state reaction method and also the melt reac tion method. Thermoelectric properties of the p_type BamCenFeCo3Sb 12 compound were investigated, and the results indicated that the electri cal conductivity of the p_type BamCenFeCo3 Sb12 is intervenient between the electrical conductivities of single_atom _filled compounds BamFeCo3Sb12 and CenFeCo3Sb12.It d ecreased with increasing Ba and Ce fill ing fraction. With the same filling fraction, the lattice thermal conductivity o f BamCenFeCo3Sb12 is found to be smaller than that of Ba mFeCo3Sb12 and CenFeCo3Sb12.
Junction capacitance models of SiGe HBT
Lü Yi, Zhang He-Ming, Dai Xian-Ying, Hu Hui-Yong, Shu Bin
2004, 53 (9): 3239-3244. doi: 10.7498/aps.53.3239
Abstract +
When SiGe HBT is in the case of normal operation, depleted approximation is not suited, and the influence of movable charge should be taken into account when c onsideri ng of their junction capacitance. Based on the analysis and study of the carr ier tr ansport of SiGe HBT, emitter junction capacitance model is developed by consider ing the carrier distribution, and the collector junction capacitance model is al so established for different current densities including base extending eff ect. The junction capacitance models are used to simulate frequency characteristics. The results of simulation show good agreements with the experimental data.