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Volume 16 Issue 7
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Original Articles
Berry Phases for Many-Spin Systems with Anisotropy Exchange Interaction in a Strong Magnetic Field
YANG Lin-guang, YAN Feng-li, LI Bo-zang
Chin. Phys. Lett. 1999, 16 (7): 469-471 .  
Abstract   PDF(pc) (175KB) ( 359 )
An approximate instantaneous eigenstate is presented for the many-spin system possessing the anisotropy exchange interaction in a strong magnetic field by the perturbation method. Based on the instantaneous eigenstate, the Berry phase of this state is worked out. Furthermore, the effect of the anisotropy exchange interaction on the Berry phase of the state for the many-spin system is studied.
Squeezing for n-Mode Quadratures Studied by Integration Within an Ordered Product Technique
FAN Hong-yi, LIU Nai-le
Chin. Phys. Lett. 1999, 16 (7): 472-474 .  
Abstract   PDF(pc) (207KB) ( 413 )
The squeezing operator S(n) and the corresponding squeezed state |0>s for n-mode quadrature operators are founded. The normally ordered form of S(n) is derived by means of the technique of integration within an ordered product of operators. Moreover, the existence of higher-order squeezing for n-mode quadratures in the State |0>s is demonstrated.
Current Reversal in a Flashing Correlation Ratchet
ZHAO Tong-jun, ZHAN Yong, ZHUO Yi-zhong, WU Xi-zhen
Chin. Phys. Lett. 1999, 16 (7): 475-477 .  
Abstract   PDF(pc) (226KB) ( 456 )
A flashing correlation ratchet model is proposed, in which the transport of Brownian particles driven by additive colored noise of Ornstein-Uhlenbeck type in a flashing ratchet is studied by Monte Carlo simulation. The stationary current vs the noise strength and the correlation time is obtained and analyzed. For a fixed rate of potential flashing, the novel phenomena of current reversal and reentry occur. The conditions for the occurrence of these phenomena are found. The influence of the flipping rate is also discussed. This finding might be relevant to the fact that the protein motors with similar structure can move in opposite directions on the same kind of microtubule.
Proposal of A New Space Atomic Frequency Standard
WANG Xin-qi, WANG Yu-zhu
Chin. Phys. Lett. 1999, 16 (7): 478-480 .  
Abstract   PDF(pc) (294KB) ( 418 )
A new prototype atomic fountain clock working in the micro-gravity environment is proposed. The successive Ramsey interactions of cold atoms and oscillatory field are realized by means of computer-controlled periodic motion of oscillatory field while the cold atoms stay still relatively in the prototype. Preliminary analyses in comparison with the atomic fountain clock working on the ground show that higher stability is obtainable in the prototype.
A New Derivation of Standard Quantum Chromodynamics Evolution Equation
Chin. Phys. Lett. 1999, 16 (7): 481-483 .  
Abstract   PDF(pc) (151KB) ( 399 )
Standard evolution equation including virtual graphs is derived in time ordered perturbative theory. We propose a new cutting rule in deep inelastic scattering processes, which provides a useful tool for discussing the connections among the real and virtual cut diagrams and better understanding of evolution equation.
Moment Analysis of Process J/ψ → ρηπ and 1-+ Exotic Hybrid
YU Hong, SHEN Qi-xing
Chin. Phys. Lett. 1999, 16 (7): 484-486 .  
Abstract   PDF(pc) (219KB) ( 353 )
Does an exotic 1-+ hybrid candidate ρ (1405) in the vicinity of a2 (1320) exist? It is worth to confirm this state in the process J/ψ → ρηπ at the BEPC (Beijing Electron-Positron Collider)/BES (Beijing Spectrameter). Considering ρ (1405), a2 (1320) and a0 (1450) overlap in this mass region, the three-state coupling structure mode is discussed by using the generalized moment analysis method. A series of moments for the mode and a criterion are given for confirming the exotic 1-+ hybrid.

High Spin States and Signature Inversion in 84Rb
HAN Guang-bing, WEN Shu-xian, WU Xiao-guang, LIU Xiang-an, LI Guang-sheng, YUAN Guan-jun, PENG Zhao-hua, WENG Pei-kun, YANG Chun-xiang, MA Ying-jun, LU Jing-bin
Chin. Phys. Lett. 1999, 16 (7): 487-489 .  
Abstract   PDF(pc) (189KB) ( 381 )
High-spin states in 84Rb have been studied by using the 70Zn (18O, p3n) 84Rb reaction at a beam energy of 75MeV. The γ- γ coincidence, excitation function and ratios for directional correlation of oriented states were performed. A new level scheme was established in which the positive and negative parity bands have been extended up to 17+ and 17- with excitation energy about 7MeV. The signature splitting and signature inversion of the positive parity yrast bands were observed and are discussed.

Monte Carlo Simulation of J/ψ and ψ Suppression
YAO Xiao-xia, , ZHAO Wei-gin, PANG Yang
Chin. Phys. Lett. 1999, 16 (7): 490-492 .  
Abstract   PDF(pc) (293KB) ( 335 )
A general cascade package is used to handle the J/ψ and ψ production and absorption for different ET bins in S-U and Pb-Pb collisions. We study the combined effect of nuclear absorption and final state interaction with co-movers on the J/ψ and ψ suppression. The experimental data of J/ψ production can be fitted for different ET-bins in S-U collisions and for lower ET-bins in Pb-Pb collisions. However, ψ data for high ET-bins in both S-U and Pb-Pb collisions can not be explained.

High Resolution Elastic Recoil Detection Analysis with Q3D Magnetic Spectrometer
LU Xiu-qin, FU Chang-bo, LIANG Gang, GUO Ji-Yu, ZHAO Kui, LI Shu-yuan, LIU Jian-cheng, JIANG Hua, YANG Bing-fan
Chin. Phys. Lett. 1999, 16 (7): 493-495 .  
Abstract   PDF(pc) (256KB) ( 471 )
Elastic recoil detection analysis technique with ΔE - E particle identification and Q3D momentum analysis has been developed to determine high resolution depth profiles in thin foils and multilayer systems. A depth resolution of 1.2nm was achieved at the surface of the samples using a high quality 100MeV 127I beam. The method was applied to depth profile analysis of C/LiF multilayers, superconductor and GaN foil samples.

Dimuon Production from Heavy Quark Decay in Heavy-Ion Collisions at √s = 5.5 TeV
ZHOU Dai-cui, Denis JOUAN, LIU Han, CAI Xu
Chin. Phys. Lett. 1999, 16 (7): 496-498 .  
Abstract   PDF(pc) (279KB) ( 320 )
The production of heavy-flavor quark c(c) and b(b) in pp collisions is described under perturbative quantum chromodynamics framework, the extrapolation from hadron-hadron up to nucleus-nucleus collisions is based on geometrical model by taking into account the nucleus shadowing effect. We simulate the heavy quark production, the decay to dilepton and effects of detection and analysis technique of the pairs, and predict the muon rate and the invariant mass spectrum of dimuons that could be detected in forward region in Pb-Pb collisions at large hadron collider energies.
Evidence for Different Fission Behavior of Hot Nuclei Formed in Central and Peripheral Collisions of 40Ar+209Bi Reaction at 25 MeV/u
WU En-jiu, ZHENG Ji-wen, XIAO Zhi-gang, ZHANG Chun, TAN Ji-lian, YIN Shu-zhi, WANG Su-fang, JIN Gen-ming, YIN Xu, SONG Ming-tao, JIN Wei-yang, PENG Xing-ping, LI Zu-yu, WU He-yu, HE Zhi-yong, JIANG Dong-xing , QIAN Xing
Chin. Phys. Lett. 1999, 16 (7): 499-501 .  
Abstract   PDF(pc) (251KB) ( 420 )
Correlated fission fragments from the reaction of 25 MeV/u 40Ar+209Bi and their further correlation with a particles have been studied for peripheral and central collisions simultaneously. The excitation energy at scission deduced from postscission multiplicity is about 172.5 MeV. The fission timescale deduced from prescission multiplicity is about 4 x10-21 s. Systematic analysis of the mass and energy distributions of fission fragments as a function of the initial temperature of hot fissioning nuclei reveals the existence of different fission behavior of hot nuclei formed in central and peripheral collisions. Experimental data demonstrate the change of fission behavior at T ~ 4MeV.

Formal Scattering Approach to High-Order Harmonic Generation
GAO Liang-hui, LI Xiao-feng, GUO Dong-sheng, FU Pan-ming
Chin. Phys. Lett. 1999, 16 (7): 502-504 .  
Abstract   PDF(pc) (247KB) ( 400 )
By using the time-independent formal scattering theoretical approach, we develop a nonperturbative quantum electrodynamics theory to describe high-order harmonic generation (HHG). This theory recovers the semi-classical interpretation of Corkum (Phys. Rev. Lett. 71 (1993) 1994) and gives the same phenomenological cutoff law. The HHG emission rate is expressed as an analytic closed form. We also discuss the connection between HHG and the above threshold ionization from the scattering viewpoint.
Measurement of Zinc K-Shell Ionization Cross Sections by Electron Impact
TANG Chang-huan, LUO Zheng-ming, AN Zhu, LI Tai-hua
Chin. Phys. Lett. 1999, 16 (7): 505-507 .  
Abstract   PDF(pc) (206KB) ( 579 )
Electron-induced Zn ionization cross sections, which are scarce, have been obtained from measurement of Kα x-ray emission at energies from near threshold to 25keV. The influence of substrate of thin target on ionization cross sections has been corrected by using the bipartition model of electron transport. The experimental results are satisfactory as compared with empirical formula of Green and Cosslett.

Diode-Laser-Array Single-End-Pumped 5W Nd:YVO4/KTP Continuous-Wave Solid-state Green Laser
LIU Jun-hai, WANG Chang-qing, LU Jun-hua, LI Guang-ming, SHAO Zong-shu, WANG Ji-yang, LIU Yao-gang, JIANG Min-hua
Chin. Phys. Lett. 1999, 16 (7): 508-509 .  
Abstract   PDF(pc) (181KB) ( 322 )
ontinuous-wave radiation of 5W at 532nm was produced with an Nd:YVO4/KTP intracavity frequency-doubled laser end-pumped by a diode-laser-array at pump power of 17.2 W, giving optical conversion efficiency of 29.1 %. The output power stability was measured to be better than 1.5% in short term operation. The pump-induced thermal lensing was also measured, showing good agreement with the performance of the laser.
General Frequency-Intensity Cooperation in Stable Multimode Lasers
WANG Kai-ge
Chin. Phys. Lett. 1999, 16 (7): 510-512 .  
Abstract   PDF(pc) (209KB) ( 373 )
In a homogeneously broadened laser model, we find a simple and general law for stable multimode operation, which shows a nonlinear cooperative relationship between the frequencies and intensities of laser modes.
Erbium Doped Fiber Amplifier Gain Flattening Using Long-Period Fiber Gratings
CHEN Gen-xiang, JIAN Shui-sheng, LI Tang-jun, LIU Chun-ning, XIE Zeng-hua
Chin. Phys. Lett. 1999, 16 (7): 513-515 .  
Abstract   PDF(pc) (206KB) ( 912 )
Based on theoretical and experimental studies on the optical properties of long-period gratings (LPGs), an erbium doped fiber amplifier (EDFA) gain equalizer was fabricated by writing three long period gratings with designed properties in hydrogen-loaded standard singlemode fibers. The LPGs were written by a KrF excimer laser at 248nm with amplitude masks. The gain variation of ±3dB in the EDFA is reduced to ±0.3dB with a bandwidth of 30nm and the total insertion loss of the device is less than 0.3dB.
Electrically Tunable Optical Fiber Mach-Zehnder Interferometer
XING Jie, FU Li-bin, XU Wan-jing, LIN Xiang-zhi, LIU Hong-du, LI Yi-jun, SHAO Yan-bin, HU Dan-ping, CHEN Yan-chuan
Chin. Phys. Lett. 1999, 16 (7): 516-517 .  
Abstract   PDF(pc) (161KB) ( 319 )
An electrically tunable optical fibre Mach-Zehnder interferometer is reported, based on the magnetostrictive effect. The period and peak wavelength of the interference spectrum can be electrically tuned to match the International Telecommunication Union's standard wavelength grid and so it is promising to be used in dense wavelength division multiplexing technology.
Anisotropic Behavior Analyzed by Laser-Generated Lamb Waves for Fiber Composite Plates
CHENG Jian-chun, HAN Jun-bo, ZHANG Shu-yi, Yves Berthelot
Chin. Phys. Lett. 1999, 16 (7): 518-519 .  
Abstract   PDF(pc) (185KB) ( 280 )
Analyses of the anisotropic behavior of a fiber composite plate from the laser-generated ultrasonic Lamb waveforms propagating in different directions are presented by employing wavelet transform techniques. The time-frequency representation plots of the waveforms clearly exhibit the anisotropic behavior of the composite plate. The plots also indicate that the waveform mainly consists of three or four lower-order Lamb wave modes, and other higher-order modes can be neglected in extracting elastic stiffness properties by comparison of theory with experimental waveforms. The group velocity of each mode is calculated according to the group delay and the source-receiver distance.
A Heat Transport Model Including the Effect of Non-Maxwellian Electron Distribution and Its Application in Laser Produced Plasma
ZHU Shao-ping, GU Pei-jun
Chin. Phys. Lett. 1999, 16 (7): 520-522 .  
Abstract   PDF(pc) (216KB) ( 482 )
An electron heat transport model is given for studying laser-to-x-ray conversion of inertial confinement fusion. The electron heat flux is derived based on a non-Maxwellian electron distribution, and the behavior of the heat flux is discussed. The effect of the non-Maxwellian electron distribution on inverse bremsstrahlung heating rate and electron-ion heat transfer rate are also included in the present model. The simulation results show that the effects of the non-Maxwellian electron distribution on laser absorption efficiency, laser-to-x-ray conversion efficiency and electron temperature in the coronal region are important.
Doping-Induced Structure Phase Transition of Layered Ferroelectrics Sr2+xBi4-xTi5-xNbxO18
HAN Jie, ZOU Guang-tian, GE Zhong-jiu
Chin. Phys. Lett. 1999, 16 (7): 523-525 .  
Abstract   PDF(pc) (231KB) ( 362 )
Raman spectra of layered ferroelectrics Sr2+xBi4-xTi5-xNbxO18 (0 ≤ x ≤ 2) and Sr2+xBi4-xTi5-xNbxO18 at room temperature in the range of 20-1000cm-1 were investigated. Vibration modes were assigned with the internal mode approach. Two doping-induced structure phase transitions were observed at about x = 0.5 and 1.25 for Sr2+xBi4-xTi5-xNbxO18, separately.
Binding Energy of Excitons Bound to Neutral Donors in Two-Dimensional Semiconductors
LIU Jian-jun, LI Yu-xian, KONG Xiao-jun, LI Shu-shen
Chin. Phys. Lett. 1999, 16 (7): 526-528 .  
Abstract   PDF(pc) (197KB) ( 392 )
The binding energies of excitons bound to neutral donors in two-dimensional (2D) semiconductors within the spherical-effective-mass approximation, which are nondegenerate energy bands, have been calculated by a varia-tional method for a relevant range of the effective electron-to-hole mass ratio σ. The ratio of the binding energy of a 2D exciton bound to a neutral donor to that of a 2D neutral donor is found to be from 0.58 to 0.10. In the limit of vanishing σ and large σ, the results agree fairly well with previous experimental results. The results of this approach are compared with those of earlier theories.
Temperature-Dependent ac Conductivity of the Fibonacci Lattice
DING Jian-wen, YAN Xiao-hong, FANG Xian-cheng
Chin. Phys. Lett. 1999, 16 (7): 529-531 .  
Abstract   PDF(pc) (197KB) ( 337 )
A new practical equation is derived from the Miller-Abrahams theory for different site-energies, and the temperature-dependent conductivity of Fibonacci lattice is calculated by a real-space renormalization-group approach. It is shown that there exist two types of temperature-dependent conductivity at low- and high-frequencies. Furthermore, it is found that the low-frequency conductivity oscillates dramatically with temperature.
Colossal Magnetoresistance Without Double Exchange Mechanism in Spinel FeCr2S4
SHI Lei, DONG Qiu-zhao, YANG Zhao-rong, CHEN Zhi-wen, ZHANG Yu-heng
Chin. Phys. Lett. 1999, 16 (7): 532-534 .  
Abstract   PDF(pc) (259KB) ( 536 )
The crystal structure of spinel FeCr2S4, which shows a semiconductor-metal transition and paramagnetic-ferrimagnetic transition at Tc = 170K , was determined by x-ray powder diffraction. It is found that the spinel FeCr2S4 belongs to a normal spinel structure [Fe2+]t[Cr3+2]oS4. The result clearly shows that the spinel FeCr2S4 has neither mixed valence of Fe3+ and Fe2+ ions or Cr3+ and Cr2+ ions for a double-exchange magnetic interaction, nor a Jahn-Teller cation such as Cr3+. The spinels represent a distinct class of colossal magnetoresistance materials, with magnetic ordering driven by superexchange rather than double exchange.
Quantum Well Controller
XUE Fang-shi
Chin. Phys. Lett. 1999, 16 (7): 535-537 .  
Abstract   PDF(pc) (259KB) ( 411 )
A quantum well controller (QWC) consisting of a direct-gap/indirect-gap quantum well and a doping interface is proposed to control the dynamic operation of the Gunn active layer. Through the Monte Carlo simulation a new relaxation mode for this new device is found. The oscillation and amplification behavior of the Gunn active layer under the control of the QWC is investigated theoretically and experimentally. All work demonstrates the great control capacity of the QWC and provides a new way to improve the performance of semiconductor devices. A new oscillation diode made of the QWC and a Gunn active layer has been designed and fabricated. In the 8mm band the highest pulse output power of these diodes is 2.55 Wand the highest conversion efficiency is 18%.
Interchain Order and Ferromagnetic State in Organic Ferromagnets
WANG Wei-zhong, YAO Kai-lun, LIN Hai-qing, LI Hong-tao
Chin. Phys. Lett. 1999, 16 (7): 538-540 .  
Abstract   PDF(pc) (223KB) ( 372 )
Two kinds of alignment of two neighboring organic ferromagnetic chains are studied with Su-Schrieffer-Heeger Hamiltonian added by Hubbard repulsion and antiferromagnetic correlation between side radicals and main chain. The results show that interchain coupling makes the energy gap decreasing. The out-of-phase alignment of two chains is energetically preferred to the in-phase alignment and it is a more possible ferromagnetic structure if the oscillatory part of interchain coupling of the in-phase is small. The spin density and dimerization along the main chain are also discussed.
Coherent Inverse Compton Scattering Responsible for Pulsar Polarized and Unpolarized Emission
LIU Ji-feng, QIAO Guo-jun, XU Ren-xin
Chin. Phys. Lett. 1999, 16 (7): 541-543 .  
Abstract   PDF(pc) (253KB) ( 313 )
A coherent inverse Compton scattering (ICS) mechanism is used to get polarization properties of radio emission of pulsars. It is found that particles moving along a ring with radius θ' = l/(√3γ)simultaneously contribute via coherent ICS. The circular polarization can be easily gotten as well as linear polarization at the same time. Our theory releases the upper limit of Lorentz factor γ≤20 put by curvature radiation, and γ may take several thousands in ICS. firtherrnore, subpulse position angles do take diverse values, while mean position angle is associated with the projection of magnetic field lines. So it is natural to get commonly-seen S-shaped swing of mean position angles. Finally we present a simulation for position angle rotation, linear polarization, circular polarization of PSR1508+55, which means that the coherent ICS may be responsible for radio emission.

Radiation and Vertical Structure of Slim Accretion Disk
WANG Jian-min, LU Fang-jun, ZHOU You-yuan
Chin. Phys. Lett. 1999, 16 (7): 544-546 .  
Abstract   PDF(pc) (224KB) ( 358 )
The vertical structure of the disk should be specified in order to compare the theoretical model with the observed spectrum of active galactic nuclei. All the existing calculations of vertical structure of the accretion disk were based on the standard model. In this paper the vertical structure of the slim disk is calculated, which may be suitable for wider ranges of parameters. The spectrum for higher accretion rate tends to the universal form Fv ∝ v-1 and the universal cutoff energy, which is consistent with the self-similar solution for the case with a super-Eddington accretion rate.

27 articles