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Volume 10 Issue 11
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Original Articles
Quantum Particle Subject to Impulsive Collisions
CHEN Yongcong
Chin. Phys. Lett. 1993, 10 (11): 641-644 .  
Abstract   PDF(pc) (207KB) ( 387 )
The effects of strong impulsive collisions on the time evolution of a quantum particle are studied. A general formalism is proposed in which a given collision effectively randomizes the momentum of the particle while leaving the position of the particle unchanged. This is then applied to a damped harmonic oscillator. It is explicitly shown that a Gaussian wave packet approaches equilibrium at t →∞. Relations to macroscopic quantum coherence are discussed.
Backgrounds Constrain on the Torsion Detection
ZHANG Chengmin
Chin. Phys. Lett. 1993, 10 (11): 645-647 .  
Abstract   PDF(pc) (161KB) ( 633 )
The sources of torsion, macroscopic rotation and aligned spin are discussed. In the case of Dirac spin particle as a direct sensor for torsion, the detection of torsion-spin effect is constrained by the larger backgrounds strongly, which are magnetic-spin and rotation-spin. Increasing the source of the torsion is equivalent to increasing the background itself. So, the conclusion is that Dirac particle spectra experiments have no hope to give the evidence for torsion directly in some special torsion gravity theory.
Unified Description of the EMC Effect and Nuclear Shadowing Effect
LI Guanglie, SHEN Jianping, YU Mingjian
Chin. Phys. Lett. 1993, 10 (11): 648-651 .  
Abstract   PDF(pc) (152KB) ( 442 )
The parton evolution model is improved by using the modified Alteralli-Parisi equation which can describe the nuclear shadowing and antishadowing effects in the small x region. Within the theoretical framework of the improved parton evolution model, the unified description of the European Muon Collaboration (EMC) effect, and nuclear shadowing and antishadowing effects is given without introducing the nuclear shadowing factor.
Study on Anomalous Nuclear Fusion Reaction by Using HV Pulse Discharge
HE Jingtang, ZHANG Yingping, REN Guoxiao, ZHU Guoyi, QIAN Zhongmin, DONG Xiaoli, DAI Changjiang, HU Saixiong, WANG Long*, YI Sunsheng*
Chin. Phys. Lett. 1993, 10 (11): 652-655 .  
Abstract   PDF(pc) (179KB) ( 604 )
A study on anomalous nuclear fusion reaction by using 10kV pulsed high voltage discharge in deuterium was completed. During high voltage (HV) pulses no neutron signal was detected, but two peaks of gamma rays were detected. The energies of two gamma rays are at 425 and 870keV, respectively. It might be explained as 108Pd* and 56Fe* excited by high energy charged particles de-exciting radiations. Neither neutron signal nor gamma signal was detected in the intervals between the pulses.
Interaction Time Study of the Dissipative Process in the Reaction 19F+45Sc
WANG Qi, LI Songlin, LU Jun, XU Hushan, YIN Xu, FAN Enjie, GUO Zhongyan, ZHU Yongtai, XIE Yuanxiang, LI Zhichang, LU Xiuqin, HU Xiaoqing
Chin. Phys. Lett. 1993, 10 (11): 656-659 .  
Abstract   PDF(pc) (138KB) ( 506 )
Excitation functions have been measured for the dissipative products of 4 ≤ Z ≤ 12 in 19F8++45Sc reaction from 102 to 108MeV by a step of 300keV at θl = 42°. The energy coherence widths have been extracted and the dinuclear system lifetimes of the order of 10-21 s have been deduced by analysing the cross section fluctuations.
Energy and Target Dependence of Azimuthal Distributions at Mid-Rapidity in Mediate-Energy Nuclear Reactions
MA Yugang, SHEN Wenqing, FENG Jun
Chin. Phys. Lett. 1993, 10 (11): 660-663 .  
Abstract   PDF(pc) (207KB) ( 488 )
The azimuthal distributions at mid-rapidity for 40Ar-induced reactions are investigated by nuclear transport theory. The rotation-like behavior which is one of collective motions becomes stronger with the increasing of the impact parameter and weaker with the increasing of the projectile energy. At about 85 MeV/nucleon the rotation-like behavior almost vanishes for 40Ar + 27Al system. While the rotation-like behavior becomes weaker and the out-of-plane enhancement of particle emission is revealed with the increasing of target mass. Some quantitative agreements with the experiment data are also obtained.
Experimental Observation of Electric Field Induced C60 Redistribution in Benzene Solution
HAN Yanong, GAO Xiaoming, ZHANG Weijun, DING Hongyu, XIA Yuxing, ZANG Wencheng*, GU Gang*, YANG Ping*, DU Youwei*, FENG Duan*
Chin. Phys. Lett. 1993, 10 (11): 664-666 .  
Abstract   PDF(pc) (143KB) ( 844 )
We report the experimental observation of electric field induced C60 redistribution in benzene solution by thermal blooming change of transmitted light. The polarization of C60 molecules in external field is analyzed.
Growth and x-Ray Diffraction Study of a New Laser Crystal Nd3+ : NaY (WO4)2
HE Yizong, WANG Guofu, LUO Zundu
Chin. Phys. Lett. 1993, 10 (11): 667-668 .  
Abstract   PDF(pc) (133KB) ( 392 )
A new laser crystal Nd3+ :NaY (WO4)2 up to 10x10x20mm with low threshold can be obtained from the system of Y2(WO4)3- Na2 WO4 by top seeded solution growth method. The crystal rod of Ф2.5 x 5 mm was pumped by xenon flashlamp and 1.06μm laser output was gained. Using a D/max-rA type diffractometer, the x-ray powder diffraction data of NaY (WO4)2 were obtained.
Structural Change of SiO2 Glass Under High Pressure -- a Molecular Dynamics Study
Chin. Phys. Lett. 1993, 10 (11): 669-672 .  
Abstract   PDF(pc) (186KB) ( 604 )
Pressure-induced structural transition in SiO2 glass at 300K. has been investigated by molecular dynamics simulation., The compression of SiO2 glass appears to be accommodated by three processes occuring in our calculation. Below 10GPa, the Si-O, O-O and Si-Si bond distances decrease with compression. Also in this pressure region the O-Si-O angle is always peaked at about 109°. Above 10 GPa, the Si-0 bond distance increase quickly with compression and the O-Si-O angle deviates from 109°. At about 46 GPa, the structural information shows that the coordination number of Si becomes six. Then, the structural behavior of SiO2 glass becomes normal with further compression.

Differential Scanning Calorimetry of Ferroelectric Liquid Crystal MBOPDOB Near Phase Transitions
YIN Zhen*, ZHANG Ming-sheng
Chin. Phys. Lett. 1993, 10 (11): 673-675 .  
Abstract   PDF(pc) (173KB) ( 416 )
Differential scanning calorimetric results of ferroelectric liquid crystal D-4-(2-methylbutoxy)phenyl 4-decyloxybenzoate (MBOPDOB) were recorded. The overcooling of Sm C* phase in the sample promotes the ordering of the molecular orientation. Small heat of the Sm A-Sm C* transition manifests a continuous second-order nature of the transition which is attributed to a large temperature range of the Sm A phase and a small spontaneous polarization. A model structure concerning the small polarization is also discussed.

Anomalous Dielectric Behavior in Nanometer-Sized Amorphous Silicon Nitride
WANG Tao, ZHANG Lide, MOU Jimei*
Chin. Phys. Lett. 1993, 10 (11): 676-679 .  
Abstract   PDF(pc) (283KB) ( 436 )
An anomalous dielectric behavior in nanometer-sized amorphous silicon nitride is reported. The dielectric constant of nanometer-sized amorphous silicon nitride has strong dependence on frequency at room temperature (RT), which is completely different from the conventional coarse-grain silicon nitride. The maximum of the dielectric constant of nanometer-sized amorphous silicon nitride-at RT is about 40 times larger than that of the conventional silicon nitride. The anomalous dielectric behavior is explained by a kind of mechanism of polarization, that is, interfacial polarization.

Two-Photon Absorption in Polydiacetylene-Toluene Sulfonate
PENG Jingcui, PENG Jian
Chin. Phys. Lett. 1993, 10 (11): 680-683 .  
Abstract   PDF(pc) (174KB) ( 485 )
The two-photon absorption process has been investigated on polydiacetylene-toluene sulfonate. The two-photon absorption coefficient has been derived within tight-binding approximation and its numerical calculation bas been carried out. The results are discussed in terms of quasi-one-dimensional excitons on the polymer backbones.

Observation of Spin-Conversion of Positronium in Zeolite
CHEN Zhiquan, WANG Shaojie (S. J. Wang)
Chin. Phys. Lett. 1993, 10 (11): 684-687 .  
Abstract   PDF(pc) (229KB) ( 506 )
We have measured the positron lifetime spectra of zeolite 13X as a function of exposed air pressure. Four lifetime components have been obtained and properly assigned. The longer lifetimes τ3 and τ4, are attributed to ortho-positronium annihilating in the β-cage and supercage in zeolite respectively. More interesting observation is that the positron annihilation parameters vary significantly with the exposed air pressure. It is interpreted in terms of the spin-conversion of positronium with paramagnetic oxygen.

Pinning Potential and Critical Current Densities in Powder Melting Processed Y(Ho)BCO Samples
LIU Peng, LI Jingwei, YIN Bo, GUO Shuquan, ZHAO Zhongxian, FENG Yong, ZHOU Lian
Chin. Phys. Lett. 1993, 10 (11): 688-691 .  
Abstract   PDF(pc) (186KB) ( 430 )
Magnetic relaxation and magnetization of the powder melting Y1-xHoxBa2Cu3O7 (x =0.2, 0.4 and 0.6) samples have been measured at the temperature of 70K. The pinning potential U and magnetization critical current density Jc have been obtained according to the Anderson-Kim model and Bean model. It is found that both U and Jc were influenced by doping Ho. In the sample with x = 0.4 the pinning potential U has a Value of 3.2eV when the field is equal to 1 kG and parallel to c-axis, which is the highest one we have known in the high Tc superconductors.

The 450 nm Up-Conversion Fluorescence of Crystalline TmP5O14
CHEN Xiaobo, ZHANG Guangyin, CHEN Jinkai, SHANG Meiru, LI Jiangwei
Chin. Phys. Lett. 1993, 10 (11): 692-694 .  
Abstract   PDF(pc) (133KB) ( 571 )
This paper reports the 450nm up-conversion fluorescence of the crystalline TmP5O14 at room temperature induced by pulsed DCM dye laser. It is found that the up-conversion mechanism is the excited state absorption.
Infrared Reflection Spectroscopy on the Linear Chain Heisenberg Antiferromagnetic Crystal NENP
LU Wei, M. von Ortenberg, J. Tuchendler, J. P. Renard, O. Neumann, R. Geick
Chin. Phys. Lett. 1993, 10 (11): 695-697 .  
Abstract   PDF(pc) (134KB) ( 429 )
The vibration modes of crystal NENP [Ni(C2H8N2)2NO2 ClO4] in the wavenumber range of 50-5000cm-1 are studied by the infrared reflection spectra The dielectric function property of the sample is obtained by the Kramers-Kroning calculation on the reflection spectra. The dielectric function polarization property induced by the vibration mode polarization in far infrared region is investigated.

Growth of Nd : YAG Free from Core and Dislocation
XU Tianhua, WU Zihe, PENG Weiqing, ZHEN Qimeng, ZHOU Jianmin, ZHANG Shengxiu, XIE Sanwen, XU Guangyu, HANG Changmin
Chin. Phys. Lett. 1993, 10 (11): 698-701 .  
Abstract   PDF(pc) (368KB) ( 515 )
Nd : YAG crystals free from core and dislocation have been grown by using the “controlled reversion of solid -liquid interface” method. The basic idea of the method is to combine the respective advantages of both the convex and the flat interface growth and to overpass “safely” the interface reversion so that the whole crystal could be grown in stable fluid flow states.
Wormhole Wave Functions in the Superstring Theory
WANG Wenfu
Chin. Phys. Lett. 1993, 10 (11): 702-704 .  
Abstract   PDF(pc) (109KB) ( 454 )
We consider the dynamics of the Robertson- Walker geometry using the point-like field-theory effective action of superstrings. The exact solutions have been found for corresponding Wheeler-DeWitt equation. These solutions satisfy the needs of Hawking’s and Kim's boundary conditions for the wormhole wave function. Thus they can provide a quantum-mechanical description of wormholes in the superstring theory.
18 articles