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Volume 14 Issue 3
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Original Articles
Transmitting Multiple Information Signals by a Single Chaotic Carrier
ZHOU Chang-song, CHEN Tian-lun
Chin. Phys. Lett. 1997, 14 (3): 161-164 .  
Abstract   PDF(pc) (190KB) ( 450 )
A method for transmitting multiple digital information signals by a single transmitted chaotic signal is presented. The information signals are encoded by modifying some tunable parameters of a chaotic system and decoded at the receiver by following the parameter modulation in the transmitter via synchronization. The Lorenz system is used to demonstrate the validity, robastness and security of the method.
Instability of the Random Fixed Point of Renormalization Group for the Spin Systems with Quenched Disorder
WU Xin-tian, GONG Chang-de
Chin. Phys. Lett. 1997, 14 (3): 165-168 .  
Abstract   PDF(pc) (213KB) ( 589 )
The replica trick used in the renormalization group (RG) for the disordered spin systems is discussed. The recursion relations of RG are derived in a more general situation in which the coupling constants can have arbitrary symmetry to the replica indices. It is shown that the random fixed point found by Luther, Grinstein and Lubensky is unstable. This instability implies that the replica symmetry should be broken in the RG for the disordered systems.
On Isotope Thermometers
WEI Zhi-yong, ZHU Yong-tai
Chin. Phys. Lett. 1997, 14 (3): 169-172 .  
Abstract   PDF(pc) (229KB) ( 392 )
The ratio of isotope yields integrated over a part of their energy spectrum is proposed to extract nuclear temperature of the excited emitter nucleus formed in heavy ion reactions. The nuclear temperature extracted from the isotope ratio is consistent with that extracted from the relative populations of the particle unstable states.
Accurate Analyses of the On-Axis Fields of a Circular Disk by Transient and Harmonic Excitation
ZHU Xian-yang, LI Jing, REN Lang, WANG Wen-bing
Chin. Phys. Lett. 1997, 14 (3): 173-175 .  
Abstract   PDF(pc) (174KB) ( 372 )
The computation of near zone fields is very important in many practical applications. Accurate analyses of the on-axis fields of a circular disk by transient and harmonic excitation show that there is an energy uprising zone on the axis rather than a non-decaying one, provided that the disk is excited by a rectangular pulse, the duration of which is less than the ratio of the radius to the light velocity. Similar results corresponding to the time-harmonic excitation are also given, which are quite different from the conclusions derived by Silver.

Ion Acoustic Wave Pumped Free Electron Laser
ZHU Xiong-wei
Chin. Phys. Lett. 1997, 14 (3): 176-178 .  
Abstract   PDF(pc) (116KB) ( 482 )
In this paper, the problem of free electron laser excitation by a relativistic electron beam passing through background plasma with ion acoustic wave as wiggler is studied. Under the case of Compton and Raman regime, both the linear dispersion relation and the growth are presented. The analysis makes no assumption on the relative relation of the beam density and the background plasma electron density, and the result is also fit to both ion ripple laser case and the large amplitude ion acoustic wave case.
Light Amplification in Non-photorefractive Doped Polymer Film at Red Light Wavelength
XU Jing-jun, FANG Qi-yin, MA Chao-li, ZHANG Guang-yin, SUN Qian, ZHANG Guo-quan, LIU Si-min, TIAN Guo-yun, WU Qiang, CHEN Xiao-bo
Chin. Phys. Lett. 1997, 14 (3): 179-182 .  
Abstract   PDF(pc) (206KB) ( 352 )
Experimental studies of light amplification with dynamic multiwave gratings recorded in an acceptor-donor-substituted azobenzene-doped poly(methyl methacrylate) thin film by multi-wave mixing are reported. The amplification gain was measured to be as high as 6.7, and the operation at red light wavelength decreases the absorption losses.
Double-Injection Bifurcation Optical Active Switch Integrated on Silicon-on-Insulator for 1.3 μm Operation
ZHAO Ce-zhou, CHEN Ai-hua, LIU En-ke, LI Guo-zheng
Chin. Phys. Lett. 1997, 14 (3): 183-186 .  
Abstract   PDF(pc) (264KB) ( 473 )
Based on the double-injection effect, the dual-mode interference principle and the free-carrier plasma dispersion effect, a double-injection bifurcation optical active switch integrated on silicon-on-insulator has been proposed and fabricated. Its insertion loss and crosstalk are measured to be less than 5.32 and -14.4dB, respectively, at wavelength 1.3μm and the total switching current 90mA. Response time is about 180ns.
Loss Increase Induced by H2 Loading in GeO2 Doped Optical Fiber
AN Hong-lin, CUI Xiao-ming, WEN Peng-yue, LIN Xiang-zhi, LIU Hong-du, E. Y. B. Pun, P. S. Chung
Chin. Phys. Lett. 1997, 14 (3): 187-189 .  
Abstract   PDF(pc) (152KB) ( 604 )
The increase of absorption loss in photosensitivity enhanced optical fiber via H2 loading induced in the making process of fiber grating was measured. From the results it can be seen that hydroxyl induced by exposing the H2 loaded GeO2-doped optical fiber to 248nm light causes large absorption loss at 1.4μm. A reaction model is postulated to describe the process that leads to the loss increase and photosensitivity enhancement in GeO2 -doped optical fiber.
X-Ray Nonspecular Scattering from Amorphous Mo Films
MA Hong-ji, JIANG Xiao-ming, CUI Ming-qi, XIAN Ding-chang
Chin. Phys. Lett. 1997, 14 (3): 190-193 .  
Abstract   PDF(pc) (208KB) ( 388 )
X-ray nonspecular scattering method is used to study the structures of Mo thin films fabricated with magnetron sputtering under different Ar pressures. The results show that with the increase of Ar pressure, the density of amorphous Mo film decreased; the surface roughness of the films increased, while the surface coherent length decreased. The abnormal glow discharging in the sputtering processes interprets the observed results well.
Synthesize of Metallic Glasses in Immiscible Mo-Cu System by Ion Mixing of Multilayers
CHEN Yi-gang, LIU Bai-xin
Chin. Phys. Lett. 1997, 14 (3): 194-197 .  
Abstract   PDF(pc) (302KB) ( 478 )
In the properly designed Mo-Cu multilayered films by free energy concern, several new metallic glasses, were obtained by ion mixing in an immiscible Mo-Cu system. To elucidate the unexpected glass formation, a Gibbs free energy diagram was constructed on the basis of Miedema’s model, with a special consideration to include the interfacial free energy into the initial state of the multilayered films. It turned out that the interfacial free energy raised the multilayered films to an energetic state higher than that of the amorphous phase in a specific range depending on the fraction of interfacial atoms and that the ion-induced glass transition observed in this system was generated by the interfaces.
Giant Magnetoresistance and Madnetic Precipitates in Melt Spun Cu88Co12 Alloy
WANG Wen-dong, ZHU Feng-wu, WENG Jun, XIAO Ji-mei, LAI Wu-yan
Chin. Phys. Lett. 1997, 14 (3): 198-201 .  
Abstract   PDF(pc) (212KB) ( 365 )
The melt spun Cu88Co12 has obvious giant magnetoresistance (GMR) after annealed at 450°C for 0.5h. By means of filed ion microscope with atom probe (FIM-AP), the spherical Co precipitates were clearly observed in this alloy for the first time. The average diameter of the particles is about 1.7nm in the specimen annealed at 450°C for 2h, which has the highest GMR of 30.7% at 1.5K. By using both persistence size method and direct measurement method on micrographs from FIM, the size distribution of the Co particles was determined. These results are very useful for testing the present theory on the relationship between GMR and microstructure.
Dynamical Evolution of Highway Traffic Flow: from Microscopic to Macroscopic
WANG Bing-hong, HUI Pak-ming, GU Guo-qing
Chin. Phys. Lett. 1997, 14 (3): 202-205 .  
Abstract   PDF(pc) (230KB) ( 501 )
In this paper, a derivation of the macroscopic mean field theory of the cellular automaton (CA) model of highway traffic flow starting from the microscopic dynamical point of view is presented. Starting from an equation describing the time evolution of the Boolean state variable at each site of the basic CA model, and using a two-site approximation for the multi-site correlation functions, a dynamical mapping between the macroscopic average speeds v(t + 1) and v ( t ) at different time can be derived. Mean field results consistent with the simulation data are obtained by considering the attractors of the mapping and their corresponding basins.
The “Cigar” Type of Solid-Liquid Phase Transition of the Two-Dimensional Ternary System
YAO Yu-cui
Chin. Phys. Lett. 1997, 14 (3): 206-208 .  
Abstract   PDF(pc) (116KB) ( 431 )
In this paper, the free energies of solid and liquid phase of two-dimensional Collins ternary system have been given, the equations of phase equilibrium between solid and liquid have been found. The “cigar” type of solid-liquid phase transition has been discussed. The phase diagrams obtained are similar to those of the three-dimensional true alloy system.
Damage Removal and Strain Relaxation in As+-Implanted Si0.57Ge0.43 Epilayers Grown by Gas Source Molecular Beam Epitaxy
ZOU Lü-fan, WANG Zhan-guo, SUN Dian-zhao, FAN Ti-wen, LIU Xue-feng, ZHANG Jing-wei
Chin. Phys. Lett. 1997, 14 (3): 209-212 .  
Abstract   PDF(pc) (380KB) ( 415 )
The damage removal and strain relaxation in the As+-implanted Si0.57Ge0.43 epilayers were studied by double-crystal x-ray diffractornetry and transmission electron microscopy. The results presented in this paper indicate that rapid thermal annealing at temperatures higher than 950°C results in complete removal of irradiation damage accompained by the formation of GeAs precipitates which enhance the removal process of dislocations.
Giant Magnetic Tunneling Effect in 81NiFe/A12O3/Fe Junction
CHEN Hui-yu, FENG Yong-jia, SU Chang
Chin. Phys. Lett. 1997, 14 (3): 213-216 .  
Abstract   PDF(pc) (259KB) ( 346 )
A new effect, spin-polarized magnetovoltage (MV) effect, is observed in an 81NiFe/A12O3/Fe junctions with cross-strip-electrode configuration. When one ferromagnetic electrode carries current, a voltage can be found between the ends of the other ferromagnetic electrode, and it varies with the magnetization process of the two ferromagnetic electrodes. The MV ratio, which is much larger than the magnetoresistance ratio for the same junction, has reached 53% at room temperature.
Nonlinear Magnetic Response of Superconducting Flux Arrays with Random Pinning
NI Jun, GU Bing-lin, Shuichi Iwata
Chin. Phys. Lett. 1997, 14 (3): 217-220 .  
Abstract   PDF(pc) (219KB) ( 440 )
The static nonlinear magnetic response of randomly pinned flux-line lattice in a type-II super-conductor has been investigated using variational replica-symmetry-broken method. A peak in the curve of susceptibility as a function of external magnetic field is found. When the magnetic field is low, there is a softening in the susceptibility as an effect of pinning potential with nonzero correlation length. At some critical magnetic field, the softening changes into hardening. After reaching the maximum in hardening, the susceptibility decreases to its value of piire states with the increase of magnetic field.
Oxidation State of Cu and Superconductivity in Bilayer T1-Based Cuprates
CHEN Xiao-jia, XU Zhu-an, JIAO Zheng-kuan, ZHANG Qi-rui
Chin. Phys. Lett. 1997, 14 (3): 221-224 .  
Abstract   PDF(pc) (219KB) ( 465 )
The oxidation state of Cu in the homologous Tl2Ba2Can-1CunO2n+4+δ(n = 1 - 4) series has been analyzed in terms of the bond valence sums. It is found that the totally mobile hole concentration nH,t of the type-I CuO2 planes at the optimal level increases with increasing number of CuO2 layers per unit cell from 1 to 3, and the largest nH,t is observed to be 0.474 when n = 3, which just corresponds to the highest Tc in the bilayer T1-based materials, and then it decreases with the increase of n. It is indicated that the correlation between the maximum value of Tc and n is similar to that between nH,t and n.
Microstructure and Magnetization Investigations of Cu-Doping Effect on La2CuO4+δ Crystal
DONG Xiao-li, ZHAO Bai-ru, ZHAO zhong-xian, LIU Wei, ZHOU Lei, XU Bo, CHEN Hong, CHE Guang-can, NI Yong-ming, YIN Bo, LI Jing-wei, ZHAO Li-hua, XU Zhong-yu
Chin. Phys. Lett. 1997, 14 (3): 225-228 .  
Abstract   PDF(pc) (611KB) ( 473 )
Measurement and characterization were carried out on Cu-doped and undoped La2CuO4+δ samples prepared under the same conditions. The magnetization measurement on the Cu-doped La2CuO4+δ sample shows coexistence of long-range antiferromagnetic order and superconductivity. A stripe-like structure was observed at room temperature on the ab-plane of Cu-doped La2CuO4+δ sample by transmission electron microscope. While for the undoped La2CuO4+δ sample no such behavior or structure feature was found. In this letter, these phenomena were discussed in terms of phase separation.

Giant Magnetoresistance in Granular Perovskite La0.8Sr0.2MnO3
ZHANG Ning, DING Wei-ping, GUO Zai-bin, ZHONG Wei, DU Kai-he, DU You-wei
Chin. Phys. Lett. 1997, 14 (3): 229-232 .  
Abstract   PDF(pc) (276KB) ( 375 )
The electric and magnetic properties in granular perovskite La0.8Sr0.2MnO3 have been investigated. A giant magnetoresistance (GMR) has been observed at temperatures well below TC, the Curie temperature, associated with crystal intrinsic magnetic properties. The granular GMR effect is also isotropic but shows some characteristics different from those in the films and crystals of similar perovskites. This suggests an effect of interfacial spin-dependent tunneling in the granular perovskite at temperatures much lower than TC. In addition, with the reduction of grain size, an evident superparamagnetic behavior has been observed.
Low-Noise YBa2Cu3O7 dc-SQUIDS and Magnetometers Using Step-Edge Junctions
NIE Jia-cai, CHEN Lie, YANG Tao, HUANG Ming-qiang, WU Pei-jun, LIU Gui-rong, LI Lin
Chin. Phys. Lett. 1997, 14 (3): 233-236 .  
Abstract   PDF(pc) (223KB) ( 451 )
Superconducting quantum interference devices (SQUlDs) using YBa2Cu3O7step-edge grain boundary junctions on LaAlO3 substrates were fabricated. The I-V and V-Ф characteristics of these step-junction dc-SQUIDS were studied. A modulation voltage exceeding 16μV was attained with Ls = 60pH at 77K. At 77K, a square washer configuration with inductance Ls = 150pH yields flux noise of about 5.08 x 10-5Ф0/√Hz at frequencies above 100Hz, increasing to 1.1 x10-4Ф0/√Hz below 1 Hz. The corresponding magnetic field and energy resolution were 270 fT/√Hz and 3.68x10-29J / Hz respectively, above 100 Hz, and increasing to 710 fT/√Hz and 1.8 x10-28 J/Hz over a signal frequency range to below 1 Hz.
Cosmic Perturbations in Yang-Mills Inflation
Chin. Phys. Lett. 1997, 14 (3): 237-240 .  
Abstract   PDF(pc) (231KB) ( 437 )
We elaborate the quantum Yang-Mills inflationary model. We find that a slow-rolling inflation occurs naturally in the presence of a thermal component produced by the decay of Yang-Mills condensate. The magnitude of cosmic perturbation is found to be closer to the observed value than that of scalar inflationary models.
21 articles