Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2005, Vol.14, No.2
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GENERAL

Nonlocality and purity in atom—field coupling system

Cai Xin, Huang Guang-Ming, Li Gao-Xiang
Chin. Phys., 2005, 14 (2): 223-230 doi: 10.1088/1009-1963/14/2/001
Full Text: [PDF 277 KB] (Downloads:385)
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The effects of initial field state and thermal environment on quantum nonlocality and linear entropy in an atom—field coupling system are investigated. We found that if the cavity is lossless and the reservoir is in vacuum, the atom—field state can exhibit quantum nonlocality periodically and the linear entropies of the atom and the field also oscillate periodically with a period the same as that of quantum nonlocality. And if the cavity dissipation is very weak and the average photon number of the reservoir is very small, the quantum nonlocality will be lost and the linear entropies of the atom and the field oscillate with a decreasing amplitude. The rapidity of the loss of the quantum nonlocality depends on the amplitude of the initial squeezed coherent state, the cavity damping constant κ and the average photon number N of the thermal reservoir. The stronger the field and the larger the constant κ and the average photon number N could be, the more rapidly the nonlocality decreases.

Dynamic properties of the cubic nonlinear Schr?dinger equation by symplectic method

Liu Xue-Shen, Wei Jia-Yu, Ding Pei-Zhu
Chin. Phys., 2005, 14 (2): 231-237 doi: 10.1088/1009-1963/14/2/002
Full Text: [PDF 308 KB] (Downloads:342)
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The dynamic properties of a cubic nonlinear Schr?dinger equation are investigated numerically by using the symplectic method with different space approximations. The behaviours of the cubic nonlinear Schr?dinger equation are discussed with different cubic nonlinear parameters in the harmonically modulated initial condition. We show that the conserved quantities will be preserved for long-time computation but the system will exhibit different dynamic behaviours in space difference approximation for the strong cubic nonlinearity.

First integrals of the discrete nonconservative and nonholonomic systems

Zhang Hong-Bin, Chen Li-Qun, Liu Rong-Wan
Chin. Phys., 2005, 14 (2): 238-243 doi: 10.1088/1009-1963/14/2/003
Full Text: [PDF 234 KB] (Downloads:543)
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In this paper we show that the first integrals of the discrete equation of motion for nonconservative and nonholonomic mechanical systems can be determined explicitly by investigating the invariance properties of the discrete Lagrangian. The result obtained is a discrete analogue of the generalized theorem of Noether in the Calculus of variations.

The forms of three-order Lagrangian equation in relative motion

Ma Shan-Jun, Liu Ming-Ping, Huang Pei-Tian
Chin. Phys., 2005, 14 (2): 244-246 doi: 10.1088/1009-1963/14/2/004
Full Text: [PDF 178 KB] (Downloads:489)
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In this paper, the general expressions of three-order Lagrangian equations in a motional coordinate system are obtained. In coordinate systems with some specific forms of motion, the expressions corresponding to these equations are also presented.

The multi-component Tu hierarchy of soliton equations and its multi-component integrable couplings system

Xia Tie-Cheng, Wang Hong, Zhang Yu-Feng
Chin. Phys., 2005, 14 (2): 247-250 doi: 10.1088/1009-1963/14/2/005
Full Text: [PDF 211 KB] (Downloads:343)
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A new simple loop algebra \widetilde{G}M is constructed, which is devoted to the establishing of an isospectral problem. By making use of the Tu scheme, the multi-component Tu hierarchy is obtained. Furthermore, an expanding loop algebra \widetilde{F}M of the loop algebra \widetilde{G}M is presented. Based on the \widetilde{F}M, the multi-component integrable coupling system of the multi-component Tu hierarchy has been worked out. The method can be applied to other nonlinear evolution equation hierarchies.

New exact solutions of nonlinear Gross—Pitaevskii equation with weak bias magnetic and time-dependent laser fields

Li Hua-Mei
Chin. Phys., 2005, 14 (2): 251-256 doi: 10.1088/1009-1963/14/2/006
Full Text: [PDF 221 KB] (Downloads:681)
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By using the mapping method and an appropriate transformation, we find new exact solutions of nonlinear Gross—Pitaevskii equation with weak bias magnetic and time-dependent laser fields. The solutions obtained in this paper include Jacobian elliptic function solutions, combined Jacobian elliptic function solutions , triangular function solutions, bright and dark solitons, and soliton-like solutions.

Separability criteria for multipartite quantum mixed states

Zhao Hui
Chin. Phys., 2005, 14 (2): 257-262 doi: 10.1088/1009-1963/14/2/007
Full Text: [PDF 213 KB] (Downloads:324)
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The separability of mixed states in multipartite quantum systems is investigated. If a quantum state in a multipartite system with an arbitrary dimension is separable, some quantity in relation to Hermitian matrix is positive.

Nonthermal effect of dilatonic black holes

Lü Jun-Li
Chin. Phys., 2005, 14 (2): 263-267 doi: 10.1088/1009-1963/14/2/008
Full Text: [PDF 211 KB] (Downloads:299)
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The quantum nonthermal effect of the spherically symmetric and rotating dilatonic black holes is studied. A crossing of the positive and negative Dirac energy of particles occurs near dilatonic black holes. We find that the dilaton coupling parameter α affects the energy of spontaneous radiant particles. The energy of particles decreases when the coupling parameter α increases.

Late-time tails in a stationary axisymmetric EMDA black hole geometry

Pan Qi-Yuan, Jing Ji-Liang
Chin. Phys., 2005, 14 (2): 268-273 doi: 10.1088/1009-1963/14/2/009
Full Text: [PDF 238 KB] (Downloads:248)
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The late-time tails of massless and self-interacting (SI) (massive) scalar fields are investigated analytically in a stationary axisymmetric Einstein—Maxwell dilaton-axion (EMDA) black hole geometry. It is shown that the asymptotic behaviour of massless perturbations is dominated by an inverse power-law decaying tail and the intermediate asymptotic behaviour of SI (massive) perturbations is dominated by an oscillatory one.

Chaos communication based on synchronization of discrete-time chaotic systems

Lu Jun-Guo, Xi Yu-Geng
Chin. Phys., 2005, 14 (2): 274-278 doi: 10.1088/1009-1963/14/2/010
Full Text: [PDF 223 KB] (Downloads:827)
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A novel chaos communication method is proposed based on synchronization of discrete-time chaotic systems. This method uses a full-order state observer to achieve synchronization and secure communication between the transmitter and the receiver. Further, we present a multiple-access chaotic digital communication method by combining the observer with the on-line least square method. Simulation results are also given for illustration.

Adaptive synchronization with nonlinear input

Zhang Xin-Ying, Guan Xin-Ping, Li Hui-Guang
Chin. Phys., 2005, 14 (2): 279-284 doi: 10.1088/1009-1963/14/2/011
Full Text: [PDF 230 KB] (Downloads:519)
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This paper considers the adaptive synchronization problem of the drive—response type chaotic systems. Using a transmitted scalar signal with an unknown time-delay, a response system is constructed. By appropriately selecting the observer gain and designing the controller, synchronization can be achieved in the presence of the drive system's disturbances and unknown parameters. A well-known chaotic system, Chua's circuit, is considered as an illustrative example to demonstrate the effectiveness of the proposed approach.

New localized excitations in a (2+1)-dimensional Broer—Kaup system

Bai Cheng-Lin, Liu Xi-Qiang, Zhao Hong
Chin. Phys., 2005, 14 (2): 285-292 doi: 10.1088/1009-1963/14/2/012
Full Text: [PDF 460 KB] (Downloads:461)
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Starting with the extended homogeneous balance method and a variable separation approach, a general variable separation solution of the Broer—Kaup system is derived. In addition to the usual localized coherent soliton excitations like dromions, lumps, rings, breathers, instantons, oscillating soliton excitations, peakon and fractal localized solutions, some new types of localized excitations, such as compacton and folded excitations, are obtained by introducing appropriate lower-dimensional piecewise smooth functions and multiple-valued functions, and some interesting novel features of these structures are revealed.

Parametric optimum design of an irreversible spin quantum refrigeration cycle

Lin Bi-Hong, Chen Jin-Can
Chin. Phys., 2005, 14 (2): 293-300 doi: 10.1088/1009-1963/14/2/013
Full Text: [PDF 292 KB] (Downloads:343)
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The general performance characteristics of an irreversible quantum refrigeration cycle using many non-interacting spin-1/2 systems as the working substance and consisting of two adiabatic and two isomagnetic field processes are investigated, based on the quantum master equation and semi-group approach. Expressions for several important performance parameters such as the coefficient of performance, cooling rate and power input are derived. By using numerical solutions, the cooling rate of the refrigeration cycle subject to the finite cycle duration is optimized. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal region of the coefficient of performance and the optimal ranges of the temperatures of the working substance and the times spent on the two isomagnetic field processes are determined. Moreover, the optimal performance of the cycle in the high-temperature limit is also analysed in detail. The results obtained here are further generalized, so that they may be directly used to describe the performance of the quantum refrigeration cycle using spin-J systems as the working substance.

Intrinsic flux noise level of an rf SQUID involving two Josephson junctions connected in series

Mao Bo, Dai Yuan-Dong, Wang Fu-Ren
Chin. Phys., 2005, 14 (2): 301-305 doi: 10.1088/1009-1963/14/2/014
Full Text: [PDF 241 KB] (Downloads:404)
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The time-dependent characteristics of a radio frequency superconducting quantum interference device (rf SQUID) involving two Josephson junctions connected in series are studied. First the dynamics of the total flux is given. Then the intrinsic flux noises in both nonhysteretic and hysteretic modes are investigated. The result shows that it is necessary to properly reduce the critical current ratio of the two junctions for low intrinsic noise level. When the critical current ratio is properly reduced, the intrinsic flux noise level of a two-junction rf SQUID is generally close to or slightly larger than that of a single junction rf SQUID, but no more than one order-of-magnitude.

Photophysical characteristics of polyaniline with photochromic azobenzene side groups

Feng Wei, Huang Kun, Wan Mei-Xiang
Chin. Phys., 2005, 14 (2): 306-310 doi: 10.1088/1009-1963/14/2/015
Full Text: [PDF 261 KB] (Downloads:459)
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Photochromic characteristics and optical molecular reorientation in conducting polymer such as polyaniline derivatives containing photochromic azobenzene moieties (PAPNPAPOA) in side chain are studied. Changes in the UV—vis absorption, refractive index, thickness, contact angle and morphology of these films after irradiation of a linearly polarized light with a wavelength of 365nm are measured. The trans-cis isomerization of PAPNPAPOA is proved irreversible even after withdrawing the UV light for a long time. That the structure of main-chain attends by the trans-cis isomerization of side-chain is confirmed by the absorption and the solution colour during the UV irradiation. These effects are discussed by taking the trans-cis isomerization of azobenzene into consideration.

Local structural distortion and magnetotransport properties of Nd0.5Pb0.5-xSrx (Mn, Fe)O3

Kou Zhi-Qi, Di Nai-Li, Lu Yi, Ma Xiao, Li Qing-An, Cheng Zhao-Hua
Chin. Phys., 2005, 14 (2): 311-316 doi: 10.1088/1009-1963/14/2/016
Full Text: [PDF 273 KB] (Downloads:317)
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Structural and magnetotransport properties of Fe-doped Nd0.5Pb0.5-xSrx (Mn, Fe)O3 are investigated by means of x-ray diffraction (XRD), M?ssbauer spectroscopy and transport measurements. Both XRD patterns and M?ssbauer spectra indicate that structural distortion decreases with Sr doping. Furthermore, it is found that Sr doping results in decrease of the resistivity at room temperature and increase of magnetoresistance. In samples, the same ratio of Mn3+ to Mn4+ is kept. So we would rather attribute these changes to the local structural distortion than the double exchange (DE) interaction. The local structural distortion of the Mn(Fe)O6 octahedron which results from the Jahn—Teller effect, can localize the conduction electrons. In this regard, we provide another evidence to prove that this Jahn—Teller distortion is an important factor that affects the transport property above Tc besides the DE coupling.
CLASSICAL AREAS OF PHENOMENOLOGY

Entropy squeezing of the field interacting with a nearly degenerate V-type three-level atom

Zhou Qing-Chun, Zhu Shi-Ning
Chin. Phys., 2005, 14 (2): 336-342 doi: 10.1088/1009-1963/14/2/020
Full Text: [PDF 265 KB] (Downloads:631)
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The position- and momentum-entopic squeezing properties of the optical field in the system of a nearly degenerate three-level atom interacting with a single-mode field are investigated. Calculation results indicate that when the field is initially in the vacuum state, it may lead to squeezing of the position entropy or the momentum entropy of the field if the atom is prepared properly. The effects of initial atomic state and the splitting of the excited levels of the atom on field entropies are discussed in this case. When the initial field is in a coherent state, we find that position-entropy squeezing of the field is present even if the atom is prepared in the ground state. By comparing the variance squeezing and entropy squeezing of the field we confirm that entropy is more sensitive than variance in measuring quantum fluctuations.

High pulse-shape fidelity realized in stimulated Brillouin scattering generator with Stokes seed injection

Yang Jun, Lü Zhi-Wei, He Wei-Ming, Lü Yue-Lan
Chin. Phys., 2005, 14 (2): 343-348 doi: 10.1088/1009-1963/14/2/021
Full Text: [PDF 255 KB] (Downloads:463)
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In order to realize high pulse-shape fidelity of stimulated Brillouin scattering, a generator with Stokes seed injection is suggested and investigated. Theoretical and experimental researches show that the SBS duration becomes longer with the increase of the seed intensity, and the best pulse-shape fidelity of above 90% is experimentally obtained.

Bright—dark incoherently coupled photovoltaic soliton pair

Hou Chun-Feng, Pei Yan-Bo, Zhou Zhong-Xiang, Sun Xiu-Dong
Chin. Phys., 2005, 14 (2): 349-352 doi: 10.1088/1009-1963/14/2/022
Full Text: [PDF 207 KB] (Downloads:427)
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The coupling between two mutually incoherent optical beams that propagate collinearly in open-circuit photovoltaic photorefractive media is investigated. It is shown that an incoherently coupled bright—dark spatial soliton pair can be formed due to photovoltaic effect. The physical properties of such a soliton pair are also discussed.

High-efficiency single-pass cw quasi-phase-matched frequency doubling based on PP-MgO:SLT

Zhang Bai-Gang, Yao Jian-Quan, Lu Yang, Xu De-Gang, Ding Xin, Wang Peng, Zhang Tie-Li, Ji Feng
Chin. Phys., 2005, 14 (2): 353-358 doi: 10.1088/1009-1963/14/2/023
Full Text: [PDF 256 KB] (Downloads:600)
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We demonstrate a single-pass cw quasi-phase-matched (QPM) frequency doubling based on periodically poled MgO-doped stoichiometric lithium tantalate (PP-MgO:SLT) with crystal length of 20mm. For the maximum 1064nm fundamental power of 7.69W, the maximum conversion efficiency and the maximum output second-harmonic power are 11.8% and 905mW, respectively. In the experiment we found that the optimum temperature of the oven for PP-MgO:SLT should be adjusted with the change of the fundamental power and the focal length. In addition, angular acceptance bandwidth and temperature acceptance bandwidth are studied. Their experimental results are in good agreement with the theoretical calculations.

Pulse-front matched ultra-broadband optical parametric chirped pulse amplifier for sub-12 fs pulse generation

Zhao Wei, Liu Hong-Jun, Wang Yi-Shan, Wang Hong-Ying, Cheng Zhao, Chen Guo-Fu
Chin. Phys., 2005, 14 (2): 359-365 doi: 10.1088/1009-1963/14/2/024
Full Text: [PDF 287 KB] (Downloads:588)
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We propose a LBO-based ultra-broadband chirped pulse optical parametric amplifier employing pulse-front-matching to yield transform-limited sub-12-fs pulses. Measurement of the maximum possible gain bandwidth for the LBO-based OPCPA demonstrates more than 60nm gain bandwidth FWHM. For the generation of TL pulses by the use of this OPCPA, a suitable combination of OPCPA and PFM is first presented. The PFM pump geometry realizes tilt-free signal amplification, and permits this OPCPA to generate TL sub-12-fs pulses.

Subpicosecond pulse compression in nonlinear photonic crystal waveguides based on the formation of high-order optical solitons

Chen Xiong-Wen, Lin Xu-Sheng, Lan Sheng
Chin. Phys., 2005, 14 (2): 366-371 doi: 10.1088/1009-1963/14/2/025
Full Text: [PDF 275 KB] (Downloads:495)
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We investigate by numerical simulation the compression of subpicosecond pulses in two-dimensional nonlinear photonic crystal (PC) waveguides. The compression originates from the generation of high-order optical solitons through the interplay of the huge group-velocity dispersion and the enhanced self-phase modulation in nonlinear PC waveguides. Both the formation of Bragg grating solitons and gap solitons can lead to efficient pulse compression. The compression factors under different excitation power densities and the optimum length for subpicosecond pulse compression have been determined. As a compressor, the total length of the nonlinear PC waveguide is only ten micrometres and therefore can be easily incorporated into PC integrated circuits.

Behaviour of a wideband double-pass discrete Raman amplifier with simultaneous reflection of signals and multi-pump

Wang Zhu-Yuan, Cui Yi-Ping
Chin. Phys., 2005, 14 (2): 372-377 doi: 10.1088/1009-1963/14/2/026
Full Text: [PDF 251 KB] (Downloads:303)
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The behaviour of a high efficient double-pass discrete Raman amplifier with 80nm bandwidth was studied theoretically and experimentally. In this Raman amplifier, by using a one-end gilt fibre as the broadband reflector,signals and multi-pump are simultaneously reflected to propagate through the gain fibre for a second time in the opposite direction of the input. An increase in net gain of more than 150% has been achieved compared with that in the typical co-pumped Raman amplifier. The advantages of this new configuration have been studied by comparing with the currently existing Raman amplifier configurations. Also, the influencing factors for the gain increase have been analysed, including the pump-to-pump Raman interactions and the length of gain fibre.

Composite particle and field theory in atomic quantum Hall effect

Zhao Bo, Chen Zeng-Bing
Chin. Phys., 2005, 14 (2): 378-381 doi: 10.1088/1009-1963/14/2/027
Full Text: [PDF 207 KB] (Downloads:349)
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In this paper, we explore the composite particle description of the atomic quantum Hall (QH) effect. We further give the Chern—Simon—Gross—Pitaevskii (CSGP) effective theory for the atomic Hall liquid, which is the counterpart of Chern—Simon theory in electron Hall effect. What we obtained is equivalent to the Laughlin wavefunction approach. Our results show that in terms of composite particles, the atomic Hall effect is really the same as the electronic QH effect. The CSGP effective theory would shed new light on the atomic QH effect.
ATOMIC AND MOLECULAR PHYSICS

Spontaneous emission spectrum of a four-level atom in a double-band photonic crystal

Wang Jian, Yang Dong, Zhang Han-Zhuang
Chin. Phys., 2005, 14 (2): 323-330 doi: 10.1088/1009-1963/14/2/018
Full Text: [PDF 279 KB] (Downloads:345)
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The spontaneous emission spectrum from a four-level atom in a double-band photonic crystal has been investigated. We use the model which assumes three atomic transitions. One of the transitions interacts with the free vacuum modes, and the other two transitions couple to the modes of the isotropic photonic band gap (PBG), the anisotropic PBG and another free vacuum. The effects of the fine structure of the lower levels on the spontaneous emission spectrum of an atom are investigated in detail in the three cases. New features of four (two) transparencies with two (one) spontaneous emission peaks, resulting from the fine structure of the lower levels of an atom, are predicted in the case of isotropic PBG modes.

Differential, elastic integral and moment transfer cross sections for electron scattering from N2 at intermediate- and high-energies

Shi De-Heng, Liu Yu-Fang, Sun Jin-Feng, Zhu Zun-Lue, Yang Xiang-Dong
Chin. Phys., 2005, 14 (2): 331-335 doi: 10.1088/1009-1963/14/2/019
Full Text: [PDF 222 KB] (Downloads:526)
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A complex optical model potential modified by incorporating the concept of bonded atom, with the overlapping effect of electron clouds between two atoms in a molecule taken into consideration, is firstly employed to calculate the differential cross sections, elastic integral cross sections, and moment transfer cross sections for electron scattering from molecular nitrogen over the energy range 300—1000eV by using additivity rule model at Hartree—Fock level. The bonded-atom concept is used in the study of the complex optical model potential composed of static, exchange, correlation polarization and absorption contributions. The calculated quantitative molecular differential cross sections, elastic integral cross sections, and moment transfer cross sections are compared with the experimental and theoretical ones wherever available, and they are found to be in good agreement with each other. It is shown that the additivity rule model together with the complex optical model potential modified by incorporating the concept of bonded atom is completely suitable for the calculations of differential cross section, elastic integral cross section and moment transfer cross section over the intermediate- and high-energy ranges.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

New analytical potential energy function for doubly charged diatomic molecules

Wang Fan-Hou, Yang Chuan-Lu, Zhu Zheng-He, Jing Fu-Qian
Chin. Phys., 2005, 14 (2): 317-322 doi: 10.1088/1009-1963/14/2/017
Full Text: [PDF 247 KB] (Downloads:517)
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A new analytical potential function for doubly charged diatomic ions is proposed as V(R)=(sum\limitsn=0 to k an Rn-1) exp (-ak+1R)+C/R, where an, ak+1 and C are parameters, and R is the nuclear distance. This function can be used to describe the potential curves for doubly charged diatomic ions with both potential minimum and maximum, or without any stationary point. As examples, potential functions of this form for ground states of BH2+, He22+ and HF2+ have been derived. The calculations using the theoretical method QCISD with basis set 6-311++G* have shown that the potential minimum of BH2+ is at Rmin=0.147nm, the maximum at Rmax=0.185nm, and ΔE=Emax-Emin=0.062 eV; for He22+Rmin=0.0736nm, R max =0.105nm, and ΔE= E max-E min=0.71 eV. It is found that the potential curve for HF2+ is one with a singly repulsive branch. The force constants and spectroscopic data for BH2+ and He22+ have also been worked out.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Computer simulation of the collision frequency of two particles in optical tweezers

Xu Sheng-Hua, Li Yin-Mei, Lou Li-Ren, Sun Zhi-Wei
Chin. Phys., 2005, 14 (2): 382-385 doi: 10.1088/1009-1963/14/2/028
Full Text: [PDF 215 KB] (Downloads:406)
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Optical tweezers have been successfully used in the study of colloid science. In most applications people are concerned with the behaviour of a single particle held in the optical tweezers. Recently, the ability of the optical tweezers to simultaneously hold two particles has been used to determine the stability ratio of colloidal dispersion. This new development stimulates the efforts to explore the characteristics of a two-particle system in the optical tweezers. An infinite spherical potential well has been used to estimate the collision frequency for two particles in the optical trap based on a Monte Carlo simulation. In this article, a more reasonable harmonic potential, commonly accepted for the optical tweezers, is adopted in a Monte Carlo simulation of the collision frequency. The effect of hydrodynamic interaction of particles in the trap is also considered. The simulation results based on this improved model show quantitatively that the collision frequency drops down sharply at first and then decreases slowly as the distance between the two particles increases. The simulation also shows how the collision frequency is related to the stiffness of the optical tweezers.

Influences of the surface elastic energy term K13 on the critical fields of liquid crystal cells and experimental measurement of K13

Guan Rong-Hua, Wang Chui-Ru, Yu Hui, Kang Wen-Xiu, Huai Jun-Xia, Yang Guo-Chen
Chin. Phys., 2005, 14 (2): 386-392 doi: 10.1088/1009-1963/14/2/029
Full Text: [PDF 284 KB] (Downloads:332)
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Based on the modified formula of Rapini—Papoular, the equation and boundary condition of the director of weak anchoring nematic liquid crystal (NLC) cell have been obtained in the case of existence of the surface elastic energy term K13. The influences of K13 on the threshold field and the saturation field have been studied in detail with the methods of analytical derivation and numerical calculation. A new method of checking whether K13 exists or not is given in theory. Combining with the previous work, we also propose an experimental plan to measure the value of K13 with a wedge-shaped planar-aligned weak anchoring NLC cell. The numerical experiments are carried out to verify the feasibility of our method.

Molecular field theory for nematic liquid crystal film with finite layers

Zhang Zhi-Dong, Li Jing, Wei Huai-Peng
Chin. Phys., 2005, 14 (2): 393-397 doi: 10.1088/1009-1963/14/2/030
Full Text: [PDF 232 KB] (Downloads:382)
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The nematic liquid crystal film composed of n molecular layers is studied based upon a spatially anisotropic pair potential, which reproduces approximately the elastic free energy density. On condition that the system has perfect nematic order, as in the Lebwohl—Lasher model, the director in the film is isotropic. The effect of the temperature is investigated by means of molecular field theory. Some new results are obtained. Firstly, symmetry breaking takes place when taking account of the temperature, and the state with the director along the normal of the film has the lowest free energy. Secondly, the N—I phase transition temperature increases as an effect of finite sizes instead of decreasing as in the Lebwohl—Lasher model. Thirdly, the nematic order is induced in the layers near the surface in the isotropic phase.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Magnetotransport properties of La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3 sandwiches

Zhao Kun, Feng Jia-Feng, Huang Yan-Hong, Wong Hong-Kuen
Chin. Phys., 2005, 14 (2): 398-403 doi: 10.1088/1009-1963/14/2/031
Full Text: [PDF 265 KB] (Downloads:417)
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La2/3Ca1/3MnO3(LCMO)/YBa2Cu4O8(YBCO)/LCMO sandwiches are prepared by the facing-target sputtering technique. The superconducting transition temperature as a function of spacer layer thickness is described by the magnetic proximity effect in the superconductor/ferromagnet structure. The metal—semiconductor transition temperature exhibits a nonmonotonic behaviour which is strongly dependent upon the YBCO layer thickness, and is also shown from the measurement of resistance and magnetoresistance. These results imply that the magnetic spin interaction between the two LCMO layers may occur through the normal-conductive YBCO layer.

The influence of K4Fe(CN)6 on the photosensitivity of cubic AgCl microcrystal

Li Xiao-Wei, Liu Rong-Juan, Geng Ai-Cong, Yang Shao-Peng, Fu Guang-Sheng
Chin. Phys., 2005, 14 (2): 404-408 doi: 10.1088/1009-1963/14/2/032
Full Text: [PDF 236 KB] (Downloads:363)
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The influence of K4Fe(CN)6 at various doping concentrations on the photosensitivity of cubic AgCl microcrystals has been investigated by using the microwave absorption and phase-sensitive measurement technique. The time behaviour of free photoelectrons in AgCl microcrystals is analysed by using computer simulation as a function of three parameters of shallow electron trap (SET) including doping concentration, trap depth and capture cross-section (CCS). It is found that the three parameters of SET play different roles on the free photoelectron decay time (FDT). After considering the threshold effects of the three parameters and their collective effects, the trap depth value, the CCS value, and the optimal doping concentration of the SET introduced by the dopant K4Fe(CN)6 in cubic AgCl microcrystals can also be determined, and the best photosensitivity of cubic AgCl can be obtained.

Effects of bias on dynamics of an AC-driven two-electron quantum-dot molecule

Wang Li-Min, Duan Su-Qing, Zhao Xian-Geng, Liu Cheng-Shi
Chin. Phys., 2005, 14 (2): 409-419 doi: 10.1088/1009-1963/14/2/033
Full Text: [PDF 385 KB] (Downloads:368)
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The effects of bias on the dynamical localization of two interacting electrons in a pair of coupled quantum dots driven by external AC fields have been numerically investigated. With an effective two-site model and Floquet formalism, the time-dependent Schr?dinger equation is numerically solved and the Pmin, the minimum of the population evolution of the initial state within a certain time period, is used to quantify the degree of the dynamical localization. Results indicate that the bias can change the energy of the initial state and break the dynamical symmetry of the system with a pure AC field. And the amplitude of the AC field with dynamical localization phenomenon changes with bias. All the numerical results are explained by the perturbation theory and two-level approximation.

Pico-second photoelectric characteristic in manganite oxide La0.67Ca0.33MnO3 films

Zhao Kun, Huang Yan-Hong, Lü Hui-Bin, He Meng, Jin Kui-Juan, Chen Zheng-Hao, Zhou Yue-Liang, Cheng Bo-Lin, Dai Shou-Yu, Yang Guo-Zhen
Chin. Phys., 2005, 14 (2): 420-421 doi: 10.1088/1009-1963/14/2/034
Full Text: [PDF 182 KB] (Downloads:392)
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Ultrafast photoelectric characteristic has been observed in La0.67Ca0.33MnO3 films on tilted SrTiO3 substrates. A pico-second (ps) open-circuit photovoltage of the perovskite manganese oxide films has been obtained when the films were irradiated by a 1.064μm laser pulse of 25 ps duration. The rise time and full width at half-maximum of the photovoltage pulse are ~300 ps and ~700 ps, respectively. The photovoltaic sensitivity was as large as ~500 mV/mJ.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

A pseudo-spin model for the wall of cytoskeletal microtubule

Chen Ying, Qiu Xi-Jun, Li Ru-Xin
Chin. Phys., 2005, 14 (2): 427-432 doi: 10.1088/1009-1963/14/2/036
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A pseudo-spin model is intended to describe the physical dynamics of unbound electrons in the wall of cytoskeletal microtubule (MT). Due to the inherent symmetry of the structure and the electric properties in the MT, one may treat it as a one-dimensional ferroelectric system, and describe the nonlinear dynamics of dimer electric dipoles in one protofilament of the MT by virtue of the double-well potential. Consequently, the physical problem has been mapped onto the pseudo-spin system, and the mean-field approximation has been taken to get some physical results.

Population transfer and coherence in the adiabatic limit by counterintuitive and intuitive pulse sequences

Zhou Yan-Wei, Ye Cun-Yun
Chin. Phys., 2005, 14 (2): 433-438 doi: 10.1088/1009-1963/14/2/037
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Two approaches of achieving population transfer and coherence are investigated for the three-level Λ system in the adiabatic limit. The effects of the laser pulse sequence on the population transfer efficiency and coherence are studied. Coherent control of quantum state and population is studied by numerical simulation based on self-consistent set of density matrix equations. It can be seen that the counterintuitive pulse sequence is more efficient in population transfer and coherence than the intuitive one.

Magnetic extraction of energy from black hole accretion disc and its application to astrophysics

Ye Yong-Chun, Wang Ding-Xiong, Gong Xiao-Long
Chin. Phys., 2005, 14 (2): 439-447 doi: 10.1088/1009-1963/14/2/038
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A new configuration of magnetic field (NCMF) in black hole (BH) magnetosphere is proposed by considering the effects of the screw instability. Three mechanisms of extracting energy magnetically are involved in the NCMF: (1) the Blandford—Znajek (BZ) process; (2) the magnetic coupling (MC) process; (3) a new scenario (henceforth the DL process) for extracting rotational energy from the disc, which is related to the open field lines connecting the disc with the astrophysical load. The expressions for the powers and torques of the above energy mechanisms are derived by using two kinds of the equivalent circuits. It turns out that the power and efficiency of extracting energy magnetically from the BH accretion disc are all augmented in the NCMF. It is shown that a very steep emissivity can be produced in a NCMF, which is consistent with the recent XMM-Newton observation of the nearby bright Seyfert 1 galaxy MCG-6-30-15.
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