Current Issue

Volume 8 Issue 5
Online Date:
Previous Issue    Next Issue
Original Articles
Fractal Nature of a Fracture Surface in Layered Solids
CAO Qunshen, PENG Gongwen, TIAN Decheng,
Chin. Phys. Lett. 1991, 8 (5): 218-221 .  
Abstract   PDF(pc) (133KB) ( 316 )
We study the crack propagation in layered solids and find that when there exists an easy-fractured layer, the fractal surface becomes more rough, which is characterized by larger fractal dimension.
Degenerate Parametric Down Conversion of Squeezed Light
Li Shiqun, WU Lingan*
Chin. Phys. Lett. 1991, 8 (5): 222-224 .  
Abstract   PDF(pc) (127KB) ( 507 )
The quantum fluctuations of the pump and signal waves are derived for degenerate parametric down conversion from a pump field initially in the squeezed state. It is found that, to the quadratic term, while the degree of squeezing of the pump wave decays gradually, that of the generated signal beam increases up to a maximum then decays.
Improved Activation of Mg+ and P+ Dual Implantation into GaAs
SHEN Honglie, ZHOU Zuyao, XIA Guanqun, ZOU Shichang
Chin. Phys. Lett. 1991, 8 (5): 225-228 .  
Abstract   PDF(pc) (223KB) ( 436 )
Co-implantation of phosphorus was used to enhance the activation of the implanted magnesium in GaAs. Improved activations were observed in dually implanted samples by either furnace annealing or rapid thermal annealing. For dose of 5x1014 cm-2 Mg+, an activation of 74% with a sheet resistance 216Ω/⊗ was obtained for dual implant compared to the activation of 33% and sheet resistance of 367Ω/⊗ for single implant after rapid thermal annealing. The results suggest that the high carrier concentration can be obtained by this technique.
Semi-empirical Formula of the Gas Gain in Limited Proportional Region
TANG Xiaowei
Chin. Phys. Lett. 1991, 8 (5): 229-231 .  
Abstract   PDF(pc) (135KB) ( 440 )
Considering the space charge effect on gas multiplication a semi- empirical formula of the gas gain in limited proportional region is proposed. Two parameters of gas multiplication, the, threshold of limited proportional region Vs and the coefficient of space charge suppression B, are introduced. Analyzed the experimental data the values of these parameters under different experimental conditions are obtained.
Heating Finite Beta Tokamak-Plasmas by Alfven Waves
HUANG Lin, QIN Xiaoming, DING Ning, LONG Yongxing
Chin. Phys. Lett. 1991, 8 (5): 232-235 .  
Abstract   PDF(pc) (175KB) ( 450 )
Heating finite betas (relative to low beta) tokamak plasmas by Alfven waves is studied by means of a linearized kinetic model which takes into account ion sound and transit time magnetic pumping as well as the effect considered by preceding authors. In cylindrical geometry, a set of three second-order differential equations in r for the perturbed fields Er, E, and E|| is solved numerically. The results lead to a significant conclusion that Alfven wave heating may be an advanced way of heating plasmas in future tokamaks.
Investigation of Density Fluctuations with Different Toroidal Magnetic Field in KT-5B Tokamak
ZENG Lei, CAO Jinxiang, ZHAN Furu, LIU Wandong, CHANG Liyan, YU Changxuan, ZU Qinxin*
Chin. Phys. Lett. 1991, 8 (5): 236-239 .  
Abstract   PDF(pc) (177KB) ( 488 )
Microturbulence density fluctuations with drift-wave characteristics in KT-5B tokamak were investigated. The density fluctuation power spectrum S(k) can be fitted into S(k) ∝ k, in which α is in inverse proportion to the toroidal magnetic field BT. Both averaged frequency and width (FWHM) of the frequency spectrum are increasing functions of BT. The phase velocity from the statistical dispersion is larger for k < 20cm-1 than that for k≥ 20cm-1.

Experimental Observations of Surface Electrostatic Wave on KT-5B Tokamak
ZHU Shiyao, HAN Shensheng
Chin. Phys. Lett. 1991, 8 (5): 240-243 .  
Abstract   PDF(pc) (153KB) ( 471 )
Shear Alfven waves have been successfully excited in KT-5B small tokamak by means of the one turn longitudinal loop antenna located in the shadow area. The measured antenna loadings show their rich structure, and the loadings are also found to be sensitive to the plasma current. Preliminary evidence of surface electrostatic wave was observed.
Tilted Angle Implantation of Xe Ions in potassium Titanyl Phosphate
WANG Keming, SHI Borong, WANG Zhonglie, ZHAO Qingtai, LIU Xiangdong, LIU Jitian, LIU Yaogang*
Chin. Phys. Lett. 1991, 8 (5): 244-247 .  
Abstract   PDF(pc) (206KB) ( 544 )
200keV Xe ions were implanted in potassium titanyl phosphate (KTP) at deferent angles: 0°, 45° and 60°. The lateral spread of Xe ions in KTP was studied by Rutherford backscattering of 2.1 MeV He ions. The result is compared with the theoretical prediction. The lateral spread is found in good agreement with calculated value within 17 %.
Influences of Some Impurities on the Optical Transparency of Doped Bismuth Germanate Crystals
HU Guanqin, FENG Xiqi, HUA Sukun, ZHAO Yuanlong
Chin. Phys. Lett. 1991, 8 (5): 248-250 .  
Abstract   PDF(pc) (160KB) ( 439 )
Optical microscopy, optical transmission spectra, sweep electron microscope, electron microprobe analysis etc. were used to study the appearance and machanism of formation of the defects caused by impurities which seriously affect the optical transparency of doped bismuth germanate. The methods of improving the optical transparency were also discussed.
Temperature Hysteresis in Shape Memory Alloys
XU Huibin
Chin. Phys. Lett. 1991, 8 (5): 251-254 .  
Abstract   PDF(pc) (229KB) ( 460 )
The martensitic phase transformation which produces shape memory is connected with a hysteresis. Some of the applications of shape memory alloys require small hysteresis loops, other require large ones. It is therefore important to be able to control the size of the hysteresis. For that purpose three different methods were introduced in the present paper. Mechanical vibration narrowed the hysteresis loops in both NiTi and CuZnAl alloys up to 17%, while the width of the hysteresis loops in a NiTi alloy decreased 3~4 times by addition of the third element Cu. With help of a special heat treatment a nearly hysteresis-free phase transformation occured in a Ti-51Ni(at.%) alloy. The size of the hysteresis is determined by the interfacial energies of the phase boundaries and these will be big, if the E-modulus and the lattice distortion are big.

Preparation and Properties of Evaporated CdTe and All Thin Film CdTe/CdS Solar Cells
Shahzad Naseem
Chin. Phys. Lett. 1991, 8 (5): 255-258 .  
Abstract   PDF(pc) (216KB) ( 759 )
Cadmium telluride thin films were prepared by vacuum evaporation of CdTe powder in an attempt to fabricate all thin film solar cells of the type CdTe/CdS. Characterization of CdTe has shown it to have a band gap of 1.522eV and a resistivity of 22Ω-cm. As prepared, solar cells exhibited low values of output parameters. Given quantity of copper was then deposited on top of the CdTe/CdS solar cells and the whole system was annealed at 350°C. This copper doping changed the output parameters favorably with a maximum efficiency of 1.9%.
Correlation between Carrier Concentration and Superconductivity in the 123-phase System
HE Zhenhui, XIA Jiansheng, WANG Shunxi, CAO Liezhao, CHEN Zuyao, ZHANG Han, FANG Minghu, XU Zhu’an, ZHANG Qirui
Chin. Phys. Lett. 1991, 8 (5): 259-262 .  
Abstract   PDF(pc) (205KB) ( 461 )
Besides the structure and oxygen content, the resistance-temperature relationship, Hall carrier concentration (nH) and midpoint temperature of superconducting transition (Tc) were measured for more than six 123-phase systems with elemental substitution. No correlation is found between the oxygen content and Tc, nor is between the orthorhombic structure and Tc. Instead, an unmonotonic relationship is jound between nH and Tc. The optimum nH for the highest Tc is about 3.8 x1021cm-3. All this draws a conclusion that nH is a parameter to describe the high Tc superconductivity.
Upper and Lower Bounds to the Free Energy Density of a One-dimensional Spin Glass Model
TIAN Guangshan
Chin. Phys. Lett. 1991, 8 (5): 263-266 .  
Abstract   PDF(pc) (160KB) ( 454 )
In this paper, a one-dimensional short-ranged spin-glass model in a random magnetic field is studied. Noticing convexity of the partition function, we use Jensen's inequality to obtain a lower bound to the averaged free energy density and the slope inequality for an upper bound. These bounds are derived under very general conditions and they can be used as tests for various approximate methods such as the replica method.
Crystallographic and Magnetic Properties of R2 Fe17Cx with R=Y, Pr, Nd, Sm, Gd, Dy, and Er
LIN Qin, SUN Yunxi, LAN Jian, LU Shizhong, JIANG Hongwei
Chin. Phys. Lett. 1991, 8 (5): 267-270 .  
Abstract   PDF(pc) (164KB) ( 342 )
A series of R2 Fe17Cx compounds (R=Y, Pr, Nd, Sm, Gd, Dy, and Er; x=0, 0.5 and 1.0) were synthesized. X-ray diffraction analyses showed that the crystal structure is rhombohedral Th2Zn17 type for R=Pr, Nd, Sm, and Gd. For R=Y, Dy and Er, a structure transformation from hexagonal Th2Ni17 type (x=0.5) to rhombohedral Th2Zn17 type (x=1.0) was observed. The introduction of C into R2Fe17 leads to an expansion of the lattice. It strongly enhances Curie temperature. C atoms occupy interstitially the nearest neighbour sites to the R atoms in the lattice. The anisotropy of R sublattice was strengthened. A uniaxial anisotropy was observed in Sm2Fe17C0.5 at room temperature.
A Potential Diode Laser Second Harmonic Generation Organic Crystal-MHBA
TAO Xutang, YUAN Duorong, ZHANG Nan, JIANG Minhua, SHAO Zhongshu
Chin. Phys. Lett. 1991, 8 (5): 271-273 .  
Abstract   PDF(pc) (126KB) ( 569 )
A prospective new organic material: 3-methoxy-4-hydroxy-benzaldehyde (MHBA) with powder second harmonic generation efficiency 30 times as large as that of urea and the cutoff wavelength of 370nm is reported. MHBA belongs to monoclinic system space group P21, and the unit cell parameters are: a=14.057Å, b=7.875Å , c=15.037Å and β=115.45°, the general physicalchemical properties are also presented.

15 articles