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Vol. 35, No. 9 (1986)

1986-05-05
CONTENT
DYNAMICAL BEHAVIOR OF A SYSTEM WITH DELAYED FEEDBACK
Huo Yu-ping, Zhao Yong
1986, 35 (9): 1115-1125. doi: 10.7498/aps.35.1115
Abstract +
In this paper, the necessary and sufficient conditions of a system with delayed feedback have been derived. In order to study the bifurcation and chaotic behavior, an asymptotic expansion of the solution in terms of the inverse delay time (TR-1) has been obtained. In long delay time limit, the first order effect in TR-1 is to prolong period of the motion. More interesting phenomena are about the higher order terms. The TR-2 terms lead to some hysteresis processes (some bistability) at each bifurcation point. And the third approximation in TR-1 influences the period-doubling bifurcation, i.e. the ratio of the periods below and at the transition point is not exact two. It is also shown that, some instable windows appear at merging points of the chaotic bands and lead to some mode-locked phenomena.
STABLE REGION OF TOKAMAK DEVICE FEEDBACK CONTROL (Ⅱ)——EXPBEIMENTAL
Shen Zhong-qing, Zheng Shao-bai, WANG LONG
1986, 35 (9): 1126-1133. doi: 10.7498/aps.35.1126
Abstract +
A stable region experiment of feedback control in CT-6B Tokamak has been can-ducted. Two feedback systems have been used simultaneously to control the heating field and the vertical magnetic field in the Tokamak. The experimental results were compared with the linear theory described in the part (I) of our paper. We found that the experimental stable regions is somewhat small than that predicted by the linear feedback theory.
THE TRIAL AND ERROR PROCEDURES IN THE DIRECT METHOD (Ⅱ)
Zheng Qi-tai
1986, 35 (9): 1134-1141. doi: 10.7498/aps.35.1134
Abstract +
Some trial and error procedures are often used in the proceeds of structure determination. The present paper provides some procedures to determine phase of structure factor and to build molecular model (selecting E value and starting set, determining atomic kind and occupancy). Many unknown structures have been solved succes-fully by means of these procedures.
ANALYSIS ON CRYSTAL FIELD PARAMETER OF RARE EARTH IONS IN RX COMPOUNDS
Yang Gui-ling, Xu You, Lu De-ling, Zhai Hong-ru
1986, 35 (9): 1142-1147. doi: 10.7498/aps.35.1142
Abstract +
The experimental data of CFP B40 of rare earth ions in RX compounds is analyzed. On this basis, we propose a new relation, through which the CPP B40 values in RX compounds can be calculated by the simple point charge model, namely, B40=k3(B40)p + c3 The CFP B40 values in a lot of RX compouuds were determinded by this relation. Results are in good agreement with experimental values. Finally, the meaning of the relation are discussed.
EXPERIMENTAL STUDIES OF F3+ COLOR CENTERS IN LiF CRYSTAL
Zheng Li-xing, Ruan Yong-feng, Guo Shao-zhang, Wan Liang-feng, Li Hao
1986, 35 (9): 1148-1157. doi: 10.7498/aps.35.1148
Abstract +
In this paper, we describe systematically some experimental results of the optical characters of the creaion of F3+ centers in LiF crystal by electron bombardment under different conditions. The relative density between F3+ and F2 centers are analysed from fluorescence spectra. The experimental results show that irradiation temperature plays an important role in the creation of F3+ and F2 centers and affects the relative density of F3+ and F2 centers. The main results are as follows: (1) Irradiation at liquid nitrogen temperature and then warming up to room temperature in the dark can create F3+ canters with high density, which can be seen from the fluoreseence spectra, as fluorescence of F3+ centers centered at 530 nm is much stronger than that of F2 center (670 nm) and fewer N centers and R centers are presented in absortion spectra. (2) From dynamic fluorescence spectra, it can be shown that in the samples irradiated at liquid nitrogen temperature, the density of F3+ centers increase rapidly when F2+ centers decays. But in the samples irradiated at room temperature the growth of F3+ and F2 centers are approximatly with the came rate. (3) We observd the band width and double pike structure of the fluorescence excitation spectra of F3+ and F2 centers.
MUTUAL EFFECT ON PHASE TRANSITION TEMPERATURES OF TWO PHASES IN AgI(α-Fe2O3) COMPOSITION ELECTROLYTES
Zhao Zong-yuan, Chen Li-quan
1986, 35 (9): 1158-1163. doi: 10.7498/aps.35.1158
Abstract +
DC and ac conductivities of AgI(α-Fe2O3) composite electrolytes have been measured. It is found that the Morin transition temperature of α-Fe2O3 is dereased by the addition of AgI. The results of M?ssbauer spectra and susceptibility are qualitatively coincide with electrical measurement. Phase transition temperature of AgI from α to βphase is also significantly lowered by the existance of α-Fe2O3. The experiments have been shown that phase transition temperature of the two phases in composite electrolyte were influenced each other.
STUDY ON THE SHORT RANGE STRUCTURES OF BINARY AMORPHOUS ARSENIC-SELENIUM SYSTEM BY EXAFS
Wang Wen-cai, Ge Sen-lin, Chen Yu
1986, 35 (9): 1164-1171. doi: 10.7498/aps.35.1164
Abstract +
The EXAFS of amorphous semiconductor a-As2Se3, a-AsSe, a-As0.05 Se0.95 and a-As2Se3) after annealing at different temperatures lower than Tg are measured by 12 kW rotating anode X-ray diffraction equipment. Analyses of the determined radial structural functions shows that although the short range structure of a-As2Se3 is very similar to that for crystalline As2Se3, some changes take place in its radial structural function after annealing. The structural relaxation in a-As2Se3, quenched from melt, has also been observed. The short range structures for different components of As in binary As-Se system seem to be different.
EFFECT OF HYDROGEN ON YOUNG'S MODULUS OF NICKEL
Zhang Tong-yi, Jiang Fang-xing, Chu Wu-yang, Xiao Ji-mei
1986, 35 (9): 1172-1181. doi: 10.7498/aps.35.1172
Abstract +
A Bordoni type apparatus was used to measure the relative changes of the apparent Young's modulus and elastic strain of a sustained displacement specimen during aging at room temperature after charging with hydrogen or artificial partial stress relaxation. The Young's modulus was gradully increasing and the elastic strain decreasing during aging after artificial partial stress relaxation. However, the situation was just opposite during aging after charging, i.e., the Young's modulus was gradually decreasing and the elastic strain increasing. It has been proved that the presence of nickel hydride brings about the increase of the Young's modulus of pure nickel due to the change of chemical bond. The decomposition of hydride and escaping of hydrogen atoms from the specimen during aging after charging cause the decrease of the Young's modulus of nickel.
MEASUREMENT OF SOME LEVEL-WIDTHS IN 40Ca BETWEEN 9.5 AND 10.5 MEV
Gu Mu, Gu Xi-liang, Guo Zhen-di, Hu Yu-de, Qian Jing-hua, Yang Fu-jia
1986, 35 (9): 1182-1191. doi: 10.7498/aps.35.1182
Abstract +
The total widths of two excited states at 9603.9 keV, 10321.0 keV and of a doublet at 9864.6, 9868.8 keV in 40Ca have been measured with resonance γ-ray absorption. The gamma radiations from 39K (p, γ) reaction at EP=1307.2 keV, 2042.8 keV and 1595.0 keV have been selected to excite the corresponding levels in 40Ca. The accurate results for the widths of the 9603.9 keV and 10321.0 keV states are obtained for the first time, they are 188±47eV and 91±15eV, respectively. For the 9864.6 and 9868.8 keV states, they are 100±24eV and 899±214 eV. Because the 9864.6 and 9868.8 keV states are close-lying doublet, the resonance γ-ray absorption techniqque was used in a special style: there will be two groups of gamma rays to be used to excite the same two levels, so the cross excitation occurs. We extended the corresponding exper mental analysis. In addition, (p,γ) yield measurenents have been made to extract the level widths of the 9603.9 keV, 10321.0 keV states. And the results are in agreement with the values deduced from resonance γ-ray absorption. The (p, γ) resonance strengths and isospins of the 9603.9 keV and 10321.0 keV states in 40Ca have also been discussed.
A STUDY ABOUT THE EXISTENCE OF DIHYDRIDE PHASE ON HYDROGEN CHEMISORBED Si(111) SURFACE
Hu Ji-huang, Liu Guo-hui, Wang Xun
1986, 35 (9): 1192-1198. doi: 10.7498/aps.35.1192
Abstract +
The chemisorption states of atomic hydrogen on Si (111) surface have been studied by means of thermal desorption spectra. Two desorption peaks β1 and β2 were observed. At low hydrogen exposure only peak β1 could be seen. The peak β2 appeared at higher hydrogen exposure and could not exist if the sample was exposed to hydrogen at a temperature higher than 400℃ or was annealed above 380℃ after hydrogen exposure. The saturated coverage of β2 was less than that of β1 by a factor of 2. The peak β1 is related to the top site adsorption of H on surface Si atoms as reported by previous works. The relatively high activation energy of desorption for β2 implies that its adsorption state is likely to be a chemical, bonding state instead of a non-bonding state as postulated by Schulze and Hender. All the above desorption behaviors of β1 and β2 are quite similar to those of monohydride phase and dihydride phase of H on Si (100) surface. Therefore, it is reasonable to deduce that the β1 and β2 states correspond to the monohydride and dihydride phase on Si (111) respectively. A triangle dimer stacking fault model of Si (111) (7×7) reconstruction proposed by McRae could be used to give an exp-laination of forming surface silicon dimer bond and thus the dihydride phase on clean Si (111) surface.
ON THE ABERRATION THEORY FOR WIDE AND NARROW ELECTRON BEAMS IN A COMBINED ELECTROMAGNETIC FOCUSING SPHERICAL CATHODE LENS SYSTEM
Ximen Ji-ye, Zhou Li-wei, Ai Ke-cong
1986, 35 (9): 1199-1209. doi: 10.7498/aps.35.1199
Abstract +
In the present study, an aberration theory for both wide and narrow electron beams in a combined electromagnetic focusing spherical cathode lens system is discussed. The general formulae of aberration coefficients for first and third order transversal geometrical and chromatic aberrations on any ideal image plane have been derived under following conditions, i.e., when the objective and image fields have finite curvatures and when the cathode is immersed in magnetic and transversal electric fields. Based on the variational analysis method and the trajectory calculation method, the relationship between the wide electron beam slstem and the narrow electron beam system has been considered in detail. It has been shown that these two different electron beam systems can be treated equally and their aberration equations and coefficients can be expressed in a universal form, if one considers the definite energy and angular initial distributions and utilizes the first order linear trajectory equation. In the present paper, electron frajectories are described in the vector form. The aberrations are expressed in the matrix form and are thus appropariate for computer calculations.
RELATIVISTIC ABERRATION THEORY FOR A COMBINED ELECTROMAGNETIC FOCUSING-DEFLECTION SYSTEM POSSESSING A SPHERICAL CATHODE LENS
Ximen Ji-ye, Zhou Li-wei, Ai Ke-cong
1986, 35 (9): 1210-1222. doi: 10.7498/aps.35.1210
Abstract +
In the present paper, by means of the variational principle, the relativistic aberration theory for a combined electromagnetic foeusing-deflection system possessing a spherical cathode lens is studied. We have discussed the following general cases: electrons emitted from the cathode possess definite energy and angular initial distributions; the objective and image fields have finite curvatures; the cathode is situated in both magnetic and transversal electric fields. For these general cases the general formulae of aberration coefficients for first and third order transversal geometrical and chromatic aberrations on any ideal image plane are given in explicit form. The above-mentioned aberration coefficient formulae can be applied to the following eases: either the wide electron beam system or the narrow electron beam.system; either the relativistic or the non-relativistic electron optical system; either the cathode or the screen having the spherical or the planar shapes. In the present work, the electron trajectories are described in the complex form. The aberrations are expressed in the matrix form, and are thus suitable for computer computations.
BRIEF REPORT
MECHANISM OF HIGHLY COERCIVITY ON EPITAXIAL Co-FERRITES
Du You-wei, Lu Huai-xian, Wang Ting-xiang, Xue Rong-hua, Cheng Liang, Hu Hong-quan
1986, 35 (9): 1223-1226. doi: 10.7498/aps.35.1223
Abstract +
The particles of Zn0.2Fe2.8O4, ferrite are prepared by chemical Co-precipitation. The shape of particles are nearly spherical and their mean diameter is about 300?. Epitaxial cobalt ferrite layer is coated on their surface. Coercivity Hc and ferromagnetic resonance line width △H are measured. According to, experimental results, the effective mangnetic anisotropy constant Ku is about 5×105 erg/cm2. That is induced by interface interaction between the inner core of Zn0.2Fe2.8O4 and Co-Fe epitaxial layer. The distance of interaction is about the total thickness of two oxygen ion layers.
THE EFFECT OF FLOWING PLASMA IN TOKAMAK ON TEARTING MODES
Wang Mao-quan
1986, 35 (9): 1227-1232. doi: 10.7498/aps.35.1227
Abstract +
In this article, the activities of tearing modes was analyzed when the plasma in Tokamak has a flowing velocity. The analysis and numerical calculation indicate, the total flowing of the plasma (equiylent to a. plasma with a rotational frequency) does not influence the activities of tearing modes, only causes the rotation of the magnetic island with a frequency equal to the rotational frequency, of the plasma, The applied helical magnetic field can suppress the rotation of the plasma effectively in the tearing layer. The role of stabilization of the helical magnetic field on the tearing modes is not affected by the plasma rotation.
SUPPRESSING THE TEARING MODES IN TOKAMAK BY ELECTRON CYCLOTRON RESONANCE HEATING
Wang Mao-quan, Zhan Ru-juan
1986, 35 (9): 1233-1237. doi: 10.7498/aps.35.1233
Abstract +
Using the localization of electron cyclotron resonance heating, the profile of plasma current is improved so that the conditions of stabilities of tearing modes are also improved. As long as the absorbed region of electron cyclotron resonance heating covers the resonance layer of tearing modes, the effect of stabilizinl is very good. It is not necessary to require that electron cyclotron resonance surface must coincide with that of tearing mode strictly. In the period of electron cyclotron heating, the tearing mode is suppressed effectively.
INTERFACE EFFECT PETWEEN DIFFERENT PHASES IN THE PROCESS OF PHASE SEPARATION AND CRYSTALLIZATION OF AN AMORPHOUS Li+ CONDUCTOR
Yu Wen-hai, Yang Yuan
1986, 35 (9): 1238-1242. doi: 10.7498/aps.35.1238
Abstract +
We found that, in the isothermal treatment process of the amorphous Li+ conductor B2O3-0.7 Li2O-0.7 LiCl-0.1 Al2O3, the plot of the conductivity vesus time rises at first, then, after passing a maxium falls monotonically, and followed by two flat sections. It has been established that these phenomena are due to the phase sparation and crystallization of this amorphous material. In this work, we develop a view point of interface effect between different phases, i.e. we consider that there is a high conductivity layer at the interface between different phases and its contribution compensates or exceeds the decrease of conductivity caused by the bulk effect, of the crystallization. On the basis of this interface effect, an explanation about the above-mentioned experimental plot is given.
THEORETICAL INVESTIGATION OF HEAVY FERMION SUPERCONDUCTIVITY IN ITINERANT FERROMAGNETS
Feng Shi-ping
1986, 35 (9): 1243-1247. doi: 10.7498/aps.35.1243
Abstract +
We have discussed the superconductivity in itinerant ferromagnets for P-wave superconductors. Result shows that the ferromagntic superconductor can be formed for some special parameter's at some temperature.
THE CALCULATION OF HEAVY QUARK FORCE AND POTENTIAL IN SU(2) LATTICE GAUGE THEORY
Dong Shao-jing
1986, 35 (9): 1248-1252. doi: 10.7498/aps.35.1248
Abstract +
The heavy quark-antiquark force and potential are calculated by means of Monte Carlo method in 4 dimensional symmetry lattice gauge theory for a single plaquette EXP action which has a good scaling behaviour. The renormalization group treatment and the icosahedral subgroup approximation to SU(2) are used. The resultes agreet with Coulomb plus linear form obtained from phenomenological string theories.
STUDY OF VALENCE-BAND PROPERTIES IN a-Si1-xCx:H BY UV PHOTO-ELECTRON SPECTROSOPY
Zhang Fang-qing, Xu Xi-xiang, Chen Guang-hua, Jiang Zhi-chen, Chen Zhen-shi, Qi Shang-kui
1986, 35 (9): 1253-1258. doi: 10.7498/aps.35.1253
Abstract +
We studied the valence-band (VB) spectra of hydfogenated amorphous silieon-earbon alloy film (a-Si C:H:) by means of UPS technique and analysed the influence of doping and surface oxidation on VB spectra. Accompanied with XPS and AES analysis, we preliminarily investigated the distribution and bonding property of valence electrons in the alloy films.