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Volume 9 Issue 2
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Original Articles
Time Eigenvectors and Their Applications
FENG Kaiyin, HUANG Xiangyou
Chin. Phys. Lett. 1992, 9 (2): 57-60 .  
Abstract   PDF(pc) (137KB) ( 490 )
Time eigenvectors and time operator are constructed from energy eigenvectors of system. Some features of them are described. Their applications to harmonic oscillating system and to double wave description of system are discussed.
Soliton Chain Solutions to the Two-Dimensional Higher Order Korteweg de Vries Equations of Lax Hierarchy
WU Ying, YANG Xiaoxue
Chin. Phys. Lett. 1992, 9 (2): 61-64 .  
Abstract   PDF(pc) (168KB) ( 498 )
The two-dimensional higher order Korteweg de Vries equations of Lax hierarchy are constructed. Their soliton chain solutions are derived by Hirota'sbilinear transformation method, and the various variants of the soliton chainsolutions are investigated in some details.

A Method for Calculating Stable and Unstable Manifolds of High Periodic Hyperbolic Orbits
ZHAO Hong, GU Yan
Chin. Phys. Lett. 1992, 9 (2): 65-68 .  
Abstract   PDF(pc) (170KB) ( 433 )
A new method for calculating one-dimensional stable and unstable mariifolds of hyperbolic points with arbitraryhigh periods is proposed. By using this method we were able to pinpoint with high precision the homoclinic and heteroclinic tangencies for the periodic hyperbolic orbits which appeared in the Hénon map.


Receiving Information From Noising Signal Using Bistable Systems
HU Gang+, GONG Dechun, WEN Xiaodong, QIN Guangrong, LI Rong
Chin. Phys. Lett. 1992, 9 (2): 69-72 .  
Abstract   PDF(pc) (215KB) ( 473 )
An electric circuit is used to simulate a bistable system. The input signal is a word consisting of a sequence of pulses, which contains certain information, rather than a purely sinusoidal signal. It is found that the portion of information received from the output of the bistable system can be greatly enhanced under the stochastic resonance condition.


Preparation and Properties of Silver Colloids Produced by Laser-Induced Reduction of Silver Nitrate
LIANG Erjun, WANG Yuntao, WANG Yujin, HAO Qingxiu ZHANG Pengxiang*
Chin. Phys. Lett. 1992, 9 (2): 73-76 .  
Abstract   PDF(pc) (306KB) ( 484 )
Silver colloids have been prapared by laser-induced reduction of silver nitrate. The properties of the colloids were studied with transmission electron microscopy, visible-ultraviolet absorption and Raman spectroscopy. We find that the growth of the silver grains is dependent on the laser illumination time. Two characteristic absorption bands of the colloids are located near 390 and 560nm, respectively. Not only are the silver colloids much cleaner than those prepared by chemical reduction methods, but also surface enhanced Raman scattering active. The method may be of interests for ultrafine particle studies as well.

Nonlinear Optical Properties of Perfectly Polarized KIO3 Single Crystal
YIN Xin, LÜ, Mengkai, ZHANG Shaojun, LI Fuqi
Chin. Phys. Lett. 1992, 9 (2): 77-78 .  
Abstract   PDF(pc) (109KB) ( 356 )
The nonlinear optical properties of a perfectly polarized KIO3 single crystal were investigated. The principal refractive indices and nonlinear optical coeffi-cients have been measured. The results are as follows: n1=1.6967, n2 =1.8329, n3=1.8358 for 0.5893μm; d31=1.2 |d31 (LiIO3)|, d32=1.8|d31(LiIO3)|. The in-tensity of the frequency-doubled light of the KIO3 single crystal with 2.96rnm thickness is 1.2 times as large as that of the KTP single crystal with the same thickness.

Surface Modification of Medical Polyurethane by Plasma Treatment
LI Dejun, ZHAO Jie, GU Hanqing*, LU Mozhu*, DING Fuqing*, HU Jianfang**
Chin. Phys. Lett. 1992, 9 (2): 79-82 .  
Abstract   PDF(pc) (201KB) ( 921 )
The wettability and surface structure of plasma treatment on medical polyurethane were studied. Two kinds of gas, N2, Ar, were used to create the low-temperature plasma under low pressure. The wettability was investigated by means of the sessile drop method using water, the results show that the contact angle of water decreases from 78.8o to 61.9o as the treatment time increases. The results of electron spectroscopy for chemical analysis indicate that original chemical bonds were broken up after plasma treatment, which was the main reason for the surface modification. At same time, the results of electron spinning resonance show that the amounts of radicals did riot increase significantly after treatment, which is advantageous to clinical practice of polyurethane.

New Phenomenon of the Hysteresis of 4He in Vycor Glass
JIN Xin*, XU Xiaonong*, YAN Yong*, A. L. Thomson, D. F. Brewer, S. Haynes, N. Sharma
Chin. Phys. Lett. 1992, 9 (2): 83-85 .  
Abstract   PDF(pc) (164KB) ( 415 )
The low temperature part of hysteresis curves of the freezing and melting processes of 4He in vycor glass with the lowest temperature 0.4K were measured,as the pressure ranged from 36.45 to 55.18 (105 Pa). Some novel characteristics of these curves were observed in such high temperature and pressure range.They may result from the existence of superfluid 4He.

Main Features of Electronic States of Fullerene
WANG Huaiyu, HAN Rushan*, SHEN Dianhong**
Chin. Phys. Lett. 1992, 9 (2): 86-89 .  
Abstract   PDF(pc) (209KB) ( 447 )
Electronic densities of states of C60 are calculated under tight binding approxi-mation to reflect their covalent features. sp3 hybridization and its compositions are analysed. In C60 cluster, π orbitals play key roles owing to their constituting bridge bonds and behaving either like electron donors or acceptors dependent on possible dopants.


Investigation of the Insulator-Metal Transition Mechanism in trans-Polyacetylene
CUI Yunlong, LIN Senhao, ZHANG Jiahua
Chin. Phys. Lett. 1992, 9 (2): 90-92 .  
Abstract   PDF(pc) (147KB) ( 444 )
By using the Hamiltonian included in the static Su-Schrieffer-Heegermodel and the Coulomb potential of solitons and ions, we investigated the insulator-metal transition mechanism in Na-doped trans-polyacetylene and gave the dependence of the Pauli susceptibility for 8.33% Na doping on the various widths and arrangements of the solitons.

Exciton Binding Energy as a Function of Barrier Width in Coupled Quantum Well Structures
SHI Junjie+, PAN Shaohua
Chin. Phys. Lett. 1992, 9 (2): 93-96 .  
Abstract   PDF(pc) (219KB) ( 448 )
Excitons in a coupled quantum well structure (CQWS), consisting of two wells separated by a thick barrier, and in the two boundaries, the potential being infinite, are studied. The binding energy is calculated as a function of the barrier width. It is shown that there is a maximum in the binding energy as a function of the barrier width for an asymmetric CQWS, where as the binding energy is a monotonically decreasing function of the barrier width for a symmetric CQWS. Moreover, the binding energy in an asymmetric CQWS is larger than that in a symmetric CQWS.

Transport Through Fibonacci Coupled Quantum Dots
PING Wensheng*, FENG Weiguo**, WU Xiang**, ***
Chin. Phys. Lett. 1992, 9 (2): 97-100 .  
Abstract   PDF(pc) (195KB) ( 431 )
We have studied the transport properties of a quasi-periodical one-dimensional system. This system consists of a sequence of Fibonacci coupled quantum dots. Using the transfer-matrix method; and taking account of the experimental technique, we have proposed the formalism of the electron transmission rate for the chain of quantum dots. From the numerical results, we found that the transmission spectra of the system have a rich structure, which just depends on the coupling between quantum dots.

Adsorption of Au on β-SiC(111) Surfaces
LU Wenchang, YE Ling, ZHANG Kaiming
Chin. Phys. Lett. 1992, 9 (2): 101-104 .  
Abstract   PDF(pc) (217KB) ( 418 )
The adsorption properties of Au on β-SiC(111) surfaces are studied using the charge self-consistent extended Huckel theory. The intermixing between Auatom and, β-SiC could happen only on the Si-terminated (111) surface. In the case of Si-terminated, there is a intrinsic surface state in the energy gap, and the Fermi energy is pinned at this surface state. But in the case of C-terminated, the surface state exists near the top of the valence band.


Properties of DC SQUIDs Made from YBCO and TBCCO Films
CHEN Yingfei, CHEN Lie, TAO Hongjie, LI Jingdong, WU Peijun, YANG Qiansheng, SHAO Kai*
Chin. Phys. Lett. 1992, 9 (2): 105-108 .  
Abstract   PDF(pc) (305KB) ( 482 )
Double-microbridge dc superconducting quant um interference devices(SQUIDs) have been fabricated from the postannealed Y1Ba2Cu3Oy and T12Ba2Ca2Cu3Oy, thin films by chemical etching and ion milling patterning technique. The applied magnetic field dependences of the voltage of the YBCO and TBCCO SQUIDS have been studied at temperature ranging from 4.2 to 23K and at 77K. The largest output voltage of the devices were 3.4,μV/Ф0 (at 5 K ) for YBCO and 60μV/Ф0(at 77K) for TBCCO. The properties of the output of these devices have been discussed.


MOCVD Growth of GaAs/AlxGa1-xAs Superlattices and Their Smoothing Effects
XU Xiangang, HUANG Baibiao, REN Hongwen, LIOU Shiwen, JIANG Minhua
Chin. Phys. Lett. 1992, 9 (2): 109-112 .  
Abstract   PDF(pc) (347KB) ( 494 )
This paper presents metalorganic chemical vapor deposition (MOCVD) growth of GaAs/AlxGa1-xAs superlattices in our laboratory. Superlattice structures are characterized by using cross-sectional transmission electron microscopy, and the results show that they are in agreement with designed parameters. The superlattice used as bufferlayer can smooth out interface fluctuations. The high mobility of Ga-containing species and the anisotropic growth rate of GaAs on differentfacets lead to the planarization of the wavy interface, whereas the low mobility of Al-containing species tends to preserve the surface shape.

15 articles