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Volume 13 Issue 12
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Original Articles
Traversable Lorentzian Wormholes in Brans-Dicke’s and Induced Gravity Theories
ZHAO Feng, LIU Liao
Chin. Phys. Lett. 1996, 13 (12): 881-884 .  
Abstract   PDF(pc) (191KB) ( 476 )
We generalize Visser ’s method to construct traversable Lorentzian wormholes from surgically modified Friedman-Robertson-Walker spacetimes in both Brans-Dicke’s theory and induced theory of Gravity. Our result shows, in both cases, the exotic matter is unavoidable to occur at the throats of the wormholes.
Targeting in the System Described by Nonlinear Differential Equations
QIN Tuan-fa, NI Wan-sun, DU Gong-huan, CHEN Guang-zhi
Chin. Phys. Lett. 1996, 13 (12): 885-888 .  
Abstract   PDF(pc) (220KB) ( 448 )
A method which directs trajectories to the predetermined continuous target orbits in the system described by nonlinear differential equations with perturbation of available system parameters and the conditions for achieving targeting is given. The target orbits may be the unstable solution or even may not be the solution of the system. Numerical experiments are given in the periodically forced Brusselator.
Tensor Charge of the Nucleon from QCD Sum Rules
HE Han-xin
Chin. Phys. Lett. 1996, 13 (12): 889-892 .  
Abstract   PDF(pc) (205KB) ( 507 )
The nucleon's tensor charges (isovector gvT = δu - δd and isoscalar gsT = δu + δd) are calculated using the QCD (quantum chromodynamics) sum rules in the presence of an external tensor field. By combining the mass sum rule of nucleon, we derive a simplified form for proton tensor charges, which gives gvT = 1.27 and gsT = 1.31, or δu = 1.29 and δd = 0.02 at the scale of nucleon mass, with an uncertainty about 20%.
In Superdeformed Bands ΔI = 2 Staggering
XING Zheng, WANG Xiao-chun, CHEN Xing-qu
Chin. Phys. Lett. 1996, 13 (12): 893-895 .  
Abstract   PDF(pc) (198KB) ( 501 )
By using triaxial-particle-rotor model with a perturbation term, ΔI = 2 staggering effects in the γ-transition energies of superdeformed bands built upon j15/2 orbitals are investigated. The general features of ΔI = 2 staggering which have been observed are obtained in the calculations. The model provides a possibility to fit the calculated values to the experimental data.
Observation of New Nuclide 239Pa
YUAN Shuang-gui, YANG Wei-fan, MOU Wan-tong, ZHANG Xue-qian, LI Zong-wei
Chin. Phys. Lett. 1996, 13 (12): 896-898 .  
Abstract   PDF(pc) (209KB) ( 452 )
A new nuclide 239Pa was produced by 50MeV/u l8O bombardment of natural uranium via multi-nucleon transfer reactions (238U-lp+2n). Protactinium was chemically separated from the uranium target and other produced elements. Then in that chemical fraction the growth and decay of 239U gamma rays were observed, identifying the 239U parent as 239Pa. Subsequent to 239Pa β- decay, with a half-life of 106±30min, gamma rays of 522.0, 562.0, 638.5 and 681.0keV were also observed.

Spin-Orbit Components of Resonant Satellite Photoionization of Atomic Cu
LIU Jin-chao
Chin. Phys. Lett. 1996, 13 (12): 899-901 .  
Abstract   PDF(pc) (169KB) ( 462 )
A new approach of the study on the spin-orbit components of resonant satellite photoionization has been carried out from many-body perturbation theory. The 3d8 4s2 (1G, 3F,1D) satellite lines of atomic Cu are resonantly enhanced and separated by the spin-orbit splitting at the energy of the 3p63d104s → 3p5 (2 P1/2, 2 P3/2) 3d10 4s2 transitions. The calculated results showing that the spin-orbit splitting leads to the separation of resonant peaks of satellite lines are in good agreement with experiment.
Eigenchannel Theory and R-Matrix Theory
LI Jia-ming, VO Ky-lan, YAN Jun, QU Yi-zhi
Chin. Phys. Lett. 1996, 13 (12): 902-905 .  
Abstract   PDF(pc) (235KB) ( 433 )
We here combine the eigenchannel theory and R-matrix theory to calculate the eigenchannel parameters of multichannel quantum defect theory directly. There are two advantages: (1) an analytical unified treatment of perturbed discrete Rydberg states, autoionizing states and their adjacent continuum to avoid numerical calculations, outside the R-matrix box; (2) clear assignment of overlapped resonances.

A Photon Switch Based on the Quantum Nonlocality
GUO Guang-can, ZHENG Shi-biao
Chin. Phys. Lett. 1996, 13 (12): 906-908 .  
Abstract   PDF(pc) (153KB) ( 400 )
We present a scheme to realize a photon switch for controlling the state of the field in a cavity between a coherent state and a Schrödinger cat state. In the scheme, an atom crosses two cavities continually. The atom is resonant with the first cavity mode, and off-resonant with the second cavity mode. The detection of the atomic state leaves the two cavity modes in an entangled state. We can determine whether the second cavity field is in a coherent state or in a Schrödinger cat state via the detection of the photon in the first cavity.
Ti X-Ray Laser Shadowgraphy Experiment
HUANG Wen-zhong, LIU Su-ping, PENG Han-sheng, GU Yu-qiu, ZHANG Qi-ren, CAI Yu-qin, YOU Yong-lu, HONG Wei, LI Yu-tong, CHUNYU Shu-tai, YANG Shang-jin, ZHANG Chuan-fei, ZHAO Yong-kuan, WEN Shu-huai, ZHANG Jie, ZHANG Guo-ping, ZHANG Tan-xin
Chin. Phys. Lett. 1996, 13 (12): 909-912 .  
Abstract   PDF(pc) (256KB) ( 606 )
An x-ray laser shadowgraphy experiment was conducted on Xingguang-II laser facility in 1996. A multi-layer spherical mirror was used as an imaging element and a high sensitivity CCD camera as a detector. We measured the near-field image of the Ti x-ray laser beam. With a Ti x-ray laser beam as a backlight source, we obtained a clear CU mesh image, demonstrating the potential as advanced diagnostic measurements to study high density plasmas in inertial confinement fusion research.
Optical Bistability in Incident-Dependent Two-Dimensional Nonlinear Optical Superlattices
CHEN Xiang-fei, LU Ya-lin, LU Yan-qing, MIN Nai-ben(N. B. Ming)
Chin. Phys. Lett. 1996, 13 (12): 913-915 .  
Abstract   PDF(pc) (190KB) ( 385 )
It is shown that, when two coherent waves are obliquely incident to a one-dimensional nonlinear optical superlattice containing Kerr-form dielectric nonlinearity, an incident-dependent two-dimensional nonlinear optical superlattice can be constructed. This structure can be bistable. There exist two types of optical bistable mechanism, i. e., the index-modulation mechanism and distributed feedback mechanism. Owing to the index-modulation mechanism, the threshold for the bistability is lower than that of a more traditional one-dimensional distributed feedback structure.
Experiment on the Nonlinear Phenomena in an Electron Cyclotron Resonance Plasma
YAO Xin-zi, JIANG De-yi
Chin. Phys. Lett. 1996, 13 (12): 916-918 .  
Abstract   PDF(pc) (184KB) ( 368 )
Two hysteresis loops and tristable states in an electron cyclotron resonance plasma system have been observed and oscillatory waveforms and their power spectra in different stable state are described in this paper. As the microwave power was increased, the oscillation with original fundamental frequency gradually transferred to harmonic frequencies and then sudden jumped to a regular oscillation with single fourth harmonic frequency.
Electron-Phonon Interaction in Small Systems
WANG Zhong-he, ZHANG Cun-zhou, ZHANG Guang-yin
Chin. Phys. Lett. 1996, 13 (12): 919-922 .  
Abstract   PDF(pc) (218KB) ( 505 )
The effects of electron-phonon interaction have to be taken into account for the physical process in a small system of condensed matters. The electron-phonon interaction in a I-D finite lattice system has been analyzed. The relation between the electron-phonon interaction and the symmetric properties of electronic states and phonons are considered, the transition probabilities are discussed.
Experimental Evidences of Nearly Single-Crystalline Diamond Film
WANG Qi-min, CHEN Qing-gui, SHI Ri-hua, DONG Rong-kang
Chin. Phys. Lett. 1996, 13 (12): 923-926 .  
Abstract   PDF(pc) (524KB) ( 524 )
The experimental evidences of a nearly single-crystalline diamond film, which was prepared by high temperature heteroepitaxial growth method, have been shown by scanning electron microscopy, transmission electron diffraction and x-ray double crystal diffraction methods.
Giant Magneto-impedance Effect in Nanocrystalline Fe73.5CuNb3Si13.5B9 Ribbons
CHEN Chen, GUO Hui-qun, ZHAO Tong-yun, LI Min, LUAN Kai-zheng, SHEN Bao-gen, LIU Yi-hua, ZHAO Jian-gao, ME Liang-mo
Chin. Phys. Lett. 1996, 13 (12): 927-930 .  
Abstract   PDF(pc) (244KB) ( 416 )
Magneto-impedance (MI) effects have been observed in amorphous and nanocrystalline Fe73.5CuNb3Si13.5B9 ribbons. Large MI values have been obtained in nanocrystalline samples (NCS), but not in as-quenched samples (AQS). The magnetic responses of impedance of nanocrystalline samples share some common features with that of Co-based amorphous wire and ribbon samples. The field dependencies of effective permeability for nanocrystalline samples have shown a sharp change at the anisotropy field. The effective permeability and the hysteresis loops for AQS and NCS have been shown to be responsible for their MI effects. The sensitivity of the magnetic responses in the nanocrystalline sample can reach 50%/Oe.
Magnetic Properties and Mössbauer Spectroscopy for Complex Fe(tpa)(NCS)2
YU Zhi, LI Chong, XIA Yuan-fu(HSIA Yuan-fu), YOU Xiao-zeng
Chin. Phys. Lett. 1996, 13 (12): 931-933 .  
Abstract   PDF(pc) (202KB) ( 445 )
The studies of Mössbauer spectroscopy and magnetic properties for complex Fe(tpa)(NCS)2 exhibit that low spin → high spin (HS) transition may be thermally induced. The impurities such as HS-Fe2+ residue and HS-Fe3+, that were caused by compound preparation, play a significant role in the investigation of spin transition curve. The Mössbauer spectroscopy is used to observe the impurities as separated forms from the spin transition phase directly, and the magnetic susceptibility measurement is used to determine the total paramagnetism from all HS phases. With these two useful tools, an exact spin transition curve was defined by removing the magnetic contribution of the impurities.

Influence of Annealing on Crystal Structure and Properties of SrBi2Ta2O9 Thin Films Prepared by Pulse Laser Deposition
YANG Ping-xiong, ZHENG Li-rong, WANG Lian-wei, LIN Cheng-lu
Chin. Phys. Lett. 1996, 13 (12): 934-936 .  
Abstract   PDF(pc) (279KB) ( 494 )
The perovskite-like SrBi2Ta2O9 (SBT) thin films have been fabricated on Si/SiO2/Ti/Pt substrate by pulse laser deposition. The crystallization and ferroelectric property were clearly dependent on the annealing time and temperature. The SBT thin film with fine grain size and well-saturated square hysteresis loop was obtained after annealing at 750°C for 90min. Good ferroelectric properties were obtained from the SBT film annealed under this condition; Pr and Ec were 8.4μC/cm2 and 57kV/cm, respectively.

Visible and Ultraviolet Reflectivity of Hg0.8Cd0.2Te
JIANG Run-qing, HU Xie-rong, FANG Jia-xiong
Chin. Phys. Lett. 1996, 13 (12): 937-939 .  
Abstract   PDF(pc) (127KB) ( 440 )
The fundamental reflectivity spectra of Hg0.8Cd0.2Te have been investigated. The feature of the spectra is the presence of El and E2 peaks within the fundamental absorption region. A three dimensional saddle point is used to fit the El and El+ Δl critical point and some simulated calculation is done for E2 at X point. The measured and calculated reflectivities are compared and prominent features of the reflectivity spectra are identified with critical point transition at the and X points in the Brillouin zone.

Photoluminescence and Electroluminescence of the Blue Emission of Devices Based on Poly (p-Phenylenevinylene) Copolymers
MA Dong-ge, HONG Zhi-yong, ZHAO Xiao-jiang, JING Xia-bin, WANG Fo-song, SHI Jia-wei, LIU Ming-da, JIN En-shun, LI Shu-wen
Chin. Phys. Lett. 1996, 13 (12): 940-943 .  
Abstract   PDF(pc) (241KB) ( 514 )
Bright blue polymer light-emitting diodes have been fabricated by using the poly(pphenylenevinylene)-based copolymers with 10 C long aliphatic chains as the electroluminescent layers, PBD in PMMA and Alq3 as the electron-transporting layers, and aluminum as the cathode. The multilayer structure devices show 190cd/m2 light-emitting brightness at 460nm, 15 V turn-on vol- tage. It is found that the intensities of photoluminescence and electroluminescence (EL) increase with increasing aliphatic chain length, the EL intensity and operation stability of these polymer light-emitting diodes can be improved by reasonable design of the structure.
Blue Electroluminescent Diodes Utilizing Blend of Poly (2, 5- Dibutoxyphenylene) in Poly (N-Vinylcarbazole)
HUANG Jing-song, ZHANG Hai-feng, AN Hai-yan, TIAN Wen-jing, HOU Jing-ying, CHEN Bai-jun, LIU Shi-yong, SHEN Jia-cong
Chin. Phys. Lett. 1996, 13 (12): 944-946 .  
Abstract   PDF(pc) (192KB) ( 506 )
Blue emission from polymer blends composed of poly (2,5-dibutoxyphenyiene) (PPP) in a matrix polymer poly (N-vinylcarbazole) (PVK) is reported. The light-emitting layer can be fabricated by spin-coating of PPP-PVK blend solution without subsequent processing or heat treatment. A cell structure of glass substrate /indium-tin-oxide /PPP-PVK blend/aluminum is employed. Blue light emission with a peak position at 448nm occurs at a bias of about 8V.

Blue Light Emission from Hydrogenated Amorphous Silicon Carbide Prepared by Xylene Source in Plasma-Enhanced Chemical Vapour Deposition System
MA Tian-fu, CHEN Kun-ji, DU Jia-fang, XU Jun, LI Wei, HUANG Xin-fan
Chin. Phys. Lett. 1996, 13 (12): 947-949 .  
Abstract   PDF(pc) (202KB) ( 434 )
We chose xylene C8H10 as carbon source instead of conventional methane CH4 to fabricate a-Sil-xCx: H films using plasma-enhanced chemial vapour deposition method. The optical band gap of this material could be widened to 3.1eV. And the infrared absorption spectra of our films manifest the existence of aromatic ring in them. Strong blue light emission with a peak wavelength of 490nm has been observed at room temperature.

Liquid Encapsulated Melt Zone Processing of GaAs
ZHOU Bo-jun, CHEN Wei-hua, E. Jensen, A. Amini, R. Abbaschian
Chin. Phys. Lett. 1996, 13 (12): 950-952 .  
Abstract   PDF(pc) (157KB) ( 469 )
A liquid encapsulated melt zone process has been developed for single crystal growth of GaAs. Single crystals of 40mm long have been grown with this technique. To avoid unwanted nucleation events and maintain a constant crystal diameter, from top to bottom growth using a short zone with a convex zone surface was found to give the best results. An arsenic overpressure way used to in conjunction with a B2O3 encapsulant in order to suppress arsenic dissociation from the melt and maintain the stoichiometry of the crystal.

Short-Term Memory and Its Biophysical Model
WANG Wei, ZHANG Kai, TANG Xiao-wei
Chin. Phys. Lett. 1996, 13 (12): 953-956 .  
Abstract   PDF(pc) (249KB) ( 475 )
The capacity of short-term memory has been studied using an integrate-and-fire neuronal network model. It is found that the storage of events depend on the manner of the correlation between the events, and the capacity is dominated by the value of after-depolarization potential. There is a monotonic increasing relationship between the value of after-depolarization potential and the memory, numbers. The biophysics relevance of the network model is discussed and different kinds of the information processes are studied too.
Two Different Burster Spatial Distributions of Gamma-Ray Bursts ?
CHE Hai-hong, LI Ti-pei, YANG Yu-xuan
Chin. Phys. Lett. 1996, 13 (12): 957-960 .  
Abstract   PDF(pc) (223KB) ( 1119 )
By using the first, second and third electronic burst and transcient source experiment catalogs, a joint analysis of spatial and temporal distributions and hardness ratios of gamma-ray bursts is performed. Turning point features at Cmax/Cmin ~ 6 are found. This probably indicates the existence of two components of burster population which have distinct spatial distributions.
23 articles