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Volume 12 Issue 5
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Original Articles
Summation over Steepest-Descent Contours in Path Integral Approach to Quantum Cosmology
LI Lixin
Chin. Phys. Lett. 1995, 12 (5): 257-260 .  
Abstract   PDF(pc) (5737KB) ( 721 )
In this paper a suggestion of summation over steepest-descent contours in path integral approach to quantum cosmology is given, with which the wave function describing the evolution of the universe can be uniquely specified.
Scalar Wormhole at Finite Temperature
PAN Rongshi, SU Rukeng, SU Chenggang
Chin. Phys. Lett. 1995, 12 (5): 261-264 .  
Abstract   PDF(pc) (183KB) ( 359 )
The wormhole solution of a finite temperature scalar ø4 field coupled to gravity is given. It is shown that Hubble constant and the size of the wormhole neck all increase with temperature. Temperature dependences for other physical properties of wormhole are also discussed.

Application of 14N(d, α )12C Nuclear Reaction to the Concentration Analysis of Nitrogen in Iron Meteorites
HU Beilai, A. L. Hanson, K. W. Jones
Chin. Phys. Lett. 1995, 12 (5): 265-268 .  
Abstract   PDF(pc) (202KB) ( 362 )
The 14N(d, α )12C nuclear reaction has been used to measure the nitrogen content in iron meteorites. The analysis was made with 2.0MeV2H+ beam from Brookhaven 3.5MV research electrostatic accelerator. The detection limits of about 1 ppm were achieved.
Velocity Selection of Atomic Beam by Laser
CAI Weiquan, CHEN Hongxin, LI Fusheng, SHU Wei, SUN Shundi, WANG Yuzhu
Chin. Phys. Lett. 1995, 12 (5): 269-272 .  
Abstract   PDF(pc) (198KB) ( 425 )
It is possible to deflect a group of atoms with a certain velocity from an effusive atomic beam if we use a properly detuned laser beam with a small angle off orthogonal to the atomic beam. Theoretical and initial experimental results of this simple method for velocity selection are given.
Gauge Problem in S-Matrix Theory of Above-Threshold Ionization
CHEN Shigang
Chin. Phys. Lett. 1995, 12 (5): 273-276 .  
Abstract   PDF(pc) (174KB) ( 441 )
The gauge problem of Keldysh-Faisal-Reiss theories is discussed. It is found that the E-gauge used by Keldysh is more reasonable than the A-gauge used by Reiss. The Keldysh theory is then developed further. Its differential ionization rate gives more hot electrons than Reiss's and therefore better agrees the experimental result. The another remarkable point is that the differential ionization rate as a function of energy is rapidly oscillatory.
Electron Cyclotron Maser Instability and the Relaxation of Runaway Instability in Tokamak Plasma
CHEN Xiaoping, SHI Bingren
Chin. Phys. Lett. 1995, 12 (5): 277-280 .  
Abstract   PDF(pc) (210KB) ( 486 )
We have introduced the electron cyclotron maser instability to tokamak plasma and proved that the maser instability can take place in runaway discharges. This instability amplifies the electron cyclotron emission in a rather lower frequency compared to gyrofrequency.
Parameter Estimation of a Spherical Top Inductively Coupled Plasma Source with Global Model
WU Hanming, LI Ming, CHEN Yunming, WU Chengkang
Chin. Phys. Lett. 1995, 12 (5): 281-284 .  
Abstract   PDF(pc) (205KB) ( 497 )
Using spatially averaged global model, we succeed in obtaining some plasma parameters for a low pressure inductively coupled plasma source of our laboratory. As far as the global balance is concerned, the models can give reasonable results of the parameters, such as the global electron temperature and the ion impacting energy, etc. It is found that the ion flow is hardly affected by the neutral gas pressure. Finally, the magnetic effects are calculated by means of the method. The magnetic field can play an important role to increase plasma density and ion current.
Range Distribution Parameters of Implanted 19F Ions in Ni0.8Fe0.2 Alloy
TAN Chunyu, XIA Yueyuan, LIU Xiangdong, LIU Jitian, WANG Fengxiang
Chin. Phys. Lett. 1995, 12 (5): 285-288 .  
Abstract   PDF(pc) (207KB) ( 433 )
Depth profiles of fluorine in 19F+ implanted Ni0.8Fe0.2a alloy have been accurately measured by using 19F(p,α γ)16O resonance nuclear reaction at ER = 872.lkeV. A proper convolution calculation method was used to extract the true distribution of fluorine from the experimental excitation yield curves. The range parameters, Rp and ΔRp, were thereby obtained and compared with those simulated wit TRIM90 code. It shows that the experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental Δ Rp values are systematically larger than the calculation values.
Influence of the Position of the Fermi Level on an Infrared Active Defect in Irradiated Silicon
SHI Yi, WU Fengmei, ZHENG Youdou, SUEZAWA Masashi*, SUMINO Koji*
Chin. Phys. Lett. 1995, 12 (5): 289-292 .  
Abstract   PDF(pc) (226KB) ( 377 )
Influence of the position of the Fermi level on the infrared active defect, so-called higher order bands (HOB), has been investigated in neutron irradiated silicon by using infrared absorption and Hall-effect measurements at low temperatures. The optical excitation and the introduction of thermal donors (TD) effectively alter the position of the Fermi level. Similar optically active behaviors between the HOB and TD+ have been observed. It is suggested strongly that the mechanism of the Fermi level influencing on the HOB is the same as that of the TD+.

A New Phase Transition in Dense Vortices
CHEN Zhijian, ZHANG Yumei*, XU Bowei
Chin. Phys. Lett. 1995, 12 (5): 293-296 .  
Abstract   PDF(pc) (194KB) ( 411 )
An improved XY model is adopted for the vortices in the superconductors. In the case of high density, the fugacity should be modified by the higher harmonics. By use of the variational effective potential, we analyze the discontinuous phase transition for the dense vortices below the Kosterlitz-Thouless transition temperature.
Possible Transition in D-Valine and L-Valine Single Crystal Samples
YANG Hongshun, LOU Fengming, WANG Wenqing, SHENG Xiangrong, ZHUANG Zhizhong, SHI Lei, CHEN Zhaojia
Chin. Phys. Lett. 1995, 12 (5): 297-300 .  
Abstract   PDF(pc) (235KB) ( 399 )
The specific heats and temperature dependence of the x-ray powder diffractions for the D-valine and the L-valine single crystal samples have been studied. It is found that there is a specific heat jump at 272.0K for the D-dine samples but no jump at the same temperature for the L-dine sample. The lambda like transition means that the co-operative effect is involved in this transition. There is no crystal structure transition in the temperature range of 123-293K for the D-dine sample. The transition of the D-valine sample might be the possible D-L transition which is proposed by Abdus Salam.
Synthesis of β-FeSi2 Film by Reactive Deposition-Solid Phase Epitaxy
WANG Lianwei, SHEN Qinwo, CHEN Xiangdong, LIN Xian, LIN Chenglu, ZOU Shichang
Chin. Phys. Lett. 1995, 12 (5): 301-304 .  
Abstract   PDF(pc) (233KB) ( 414 )
Reactive deposition-solid phase epitaxy has been developed for the epitaxial growth of thick β-FeSi2film. Compared with the solid phase epitaxy, the crystal quality was improved. The orientation relationship mainly depends on the depositing condition. Observation by transmission electron microscope revealed the polycrystalline nature and the mean crystallite size was about 200nm.
Light Emission Excited by Schottky Hot Electrons in A1-MgF2-Au( Cu) Thin-Film Devices
JIANG Mengshu, WEI Qinghua, SHU Qiqing*, ZHENG Keqin*
Chin. Phys. Lett. 1995, 12 (5): 305-308 .  
Abstract   PDF(pc) (188KB) ( 544 )
A new type of light-emitting device with Al-MgF2-Au(Cu) junction and the role of residual O2 in fabrication of Al-MgF2-Au(Cu) thin film devices were reported in our other papers. In this paper, we made a further careful investigation about its current-voltage (I - V), current-temperature (I - T) characteristics and the observed light emission spectra in detail. We find the presence of Schottky high field emission in an evaporated sandwich structure of Al-MgF2-Au(Cu) junctions, and argue that the radiation process is mainly due to Schottky hot electrons, which excite surface plasmon-polariton (SPP), then SPP couples to external radiation through surface roughness.
Mechanical Dissipation at Different Orientation of Magnetic Field in High-Tc Superconductor
LI Jie, ZHU Jinsong, WANG Yening
Chin. Phys. Lett. 1995, 12 (5): 309-312 .  
Abstract   PDF(pc) (200KB) ( 427 )
The mechanical dissipation of (Bi0.9Pb0.1)2 Sr2 Ca2Cu3O10+y and YBa2Cu3O7-x ceramics were measured as a function of the angle θ between the orientation of the transverse magnetic field and the vibrating direction at fixed temperature and magnetic field with the vibrating reed technique. A relation between Q-1 (or f) and The angle θ, i. e. Δ Q-1 (or Δ f) ~ (Ha cosθ)1.5 was found and this indicated that only the magnetic field component parallel to the vibrating direction Ha cosθ gives rise to the enhancement of internal friction and resonant frequency in ceramic sample. The anisotropic deformation of flux-line-lattice is used to explain the observed results.
Far Infrared Resonance Transition Study of the Chain-End S = 1/2 Modes in an S = 1 Antiferromagnetic Chain
LU Wei, SHEN Xuechu, LIU Pulin, M. von Ortenberg, J . Tuchendler, J . P. Renard, ZHENG Fen
Chin. Phys. Lett. 1995, 12 (5): 313-316 .  
Abstract   PDF(pc) (191KB) ( 469 )
The unpaired spin S = 1/2 states which occur at the ends of an S = 1 Heisenberg-like antiferromagnetic chain, have been observed recently in low-temperature electron spin-resonance measurements of Ni(C2H8N2)2 NO2 ClO4containing selected impurities. We present here a further study on this topic by far infrared transmission spectra under the magnetic field. The splitting of S = 1/2 modes was clearly observed and explained by the interaction of S = 1/2 modes at two nearby chains, which can be separated by vacancy-like defect.
Photoluminescence of C60 Single Crystals
LI Chaorong, WANG Gang, ZHANG Jiaming*, MAI Zhenhong, ZHAO Tienan, XU Lu, XIE Sishen
Chin. Phys. Lett. 1995, 12 (5): 317-320 .  
Abstract   PDF(pc) (229KB) ( 594 )
The photoluminescence (PL) spectra of C60 single crystals grown under double temperature gradient (DTG) and single temperature gradient (STG) techniques were investigated at room temperature. The results show that the PL emission intensity increases first and then decreases with increasing illuminated power density for the C60single crystals grown by both DTG and STG techniques. Furthermore, one main peak with a shoulder peak can be clearly distinguished at low illumination, while only one main peak without the shoulder peak can be seen at high illumination. The main peak undergoes a continuous blue shift and broadening with the increase of illuminated power density. The difference of PL emission energy at the same illumination density of DTG and STG samples may correlated with the degree of both the orientational disorder of C60 molecule and lattice perfectness. The Laue diffraction patterns show that the DTG sample has stronger strains and poorer crystalline quality than the STG sample.
16 articles