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Volume 19 Issue 8
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Original Articles
Synchronization of Uncertain Time Delay Chaotic Systems using the Adaptive Fuzzy Method
GUAN Xin-Pin, HUA Chang-Chun
Chin. Phys. Lett. 2002, 19 (8): 1031-1034 .  
Abstract   PDF(pc) (462KB) ( 464 )
We consider the sychronization problem of a class of the first-order differential-delay chaotic systems. We utilize time-delay fuzzy logic systems to approximate continuous nonlinear time-delay functions, so that the precise mathematical model need not be known. Adopting the adaptive fuzzy control method, we construct a class of state feedback controllers which can render the closed-loop error systems to be asymptotically stable.We carry out simulations of synchronizing Mackey-Glass and logistic chaotic systems, and the results are reasonable.
Reversible Decoherence of a Mesoscopoic Superposition Driven by a Time-Dependent External Field
HOU Bang-Pin, WANG Shun-Jin, YU Wan-Lun
Chin. Phys. Lett. 2002, 19 (8): 1035-1037 .  
Abstract   PDF(pc) (279KB) ( 777 )
By using the normal-ordering technique in the coherent state
representation, we discuss the dynamical evolution of the coherence of a Schrödinger cat state in a high Q cavity coupled to another resonator in the presence of external fields. During the progression of the coherence, We pay particular attention to the effect of the external fields, as well as the initial phase of the Schrödinger cat state,
Permanent Electric Dipole Moment of an Rb Atom
HUANG Xiang-You, YOU Pei-Lin
Chin. Phys. Lett. 2002, 19 (8): 1038-1040 .  
Abstract   PDF(pc) (281KB) ( 429 )
We experimentally determine the conjecture that hydrogen-like atoms such as Rb and Cs may have large permanent electric dipole moments (EDMs). The saturated Rb vapour fills a cylindrical capacitor in the experiment. The influence of the vapour dielectric medium on capacitance is measured with a digital capacitance meter. Supposing that the measurement influence comes from the permanent EDMs of Rb atoms, from the experimental result we find that the EDM is large, i.e., dRb ≥ 8.6e x 10-9cm.
Preparation of Entangled States of Three Particles by Adiabatic Passage
GUO Jian-You
Chin. Phys. Lett. 2002, 19 (8): 1041-1043 .  
Abstract   PDF(pc) (262KB) ( 386 )
We propose a novel technique for the creation of entangled states of three particles, based upon an adiabatic passage induced by a suitably crafted time-dependent external field. We derive the corresponding adiabatic and bare conditions for the preparation of entangled states. We obtain the time evolutions of the energy of the system and the populations involving the initial state and target entangled state.
Entanglement of Two-Qubit Quantum Heisenberg XYZ Chain
XI Xiao-Qiang, HAO San-Ru, CHEN Wen-Xue, YUE Rui-Hong
Chin. Phys. Lett. 2002, 19 (8): 1044-1047 .  
Abstract   PDF(pc) (360KB) ( 468 )
We derive the analytic expression of the concurrence in the quantum Heisenberg XYZ model and discuss the influence of parameters J, Δ, and Γ on the concurrence. By choosing different values Γ and Δ, we obtain the XX, XY, XXX and XXZ chains. The concurrence decreases with increasing temperature. When T → 0, the concurrence reaches its maximum value 1, i.e., the entangled state, | > = √2/2 (|01> - |10>), is maximum entanglement. For the XXZ chain, when Γ → ∞, the concurrence will meet its maximum value Cmax = sinh(1/T)/cosh(1/T).
Realization of the Fredkin Gate by Three Transition Pulses in a Nuclear Magnetic Resonance Quantum Information Processor
XUE Fei, DU Jiang-Feng, SHI Ming-Jun, ZHOU Xian-Yi, HAN Rong-Dian, WU Ji-Hui
Chin. Phys. Lett. 2002, 19 (8): 1048-1050 .  
Abstract   PDF(pc) (358KB) ( 595 )
We have experimentally realized the Fredkin gate with only three transition pulses in a solution of alanine. It appears that no experimental realization of the Fredkin gate with fewer pulses has been reported yet. In addition, the simple structure of our scheme makes it easy to be implemented in experiments.
Entropy in the NUT-Kerr-Newman Black Holes in the Background of de Sitter Space-Time
GE Xian-Hui, SHEN You-Gen,
Chin. Phys. Lett. 2002, 19 (8): 1051-1053 .  
Abstract   PDF(pc) (210KB) ( 342 )
We calculate the entropy of the fermion field in the NUT-Kerr-Newman black holes in the background of the de Sitter space-time by using the improved brick-wall method and the membrane model. Here the Euler characteristic of the black holes is over two. The results show that, as the cut-off is properly chosen, the entropy in the black hole satisfies the Bekenstein-Hawking area law.
Chaos Control and Anti-control via a Fuzzy Neural Network Inverse System Method
REN Hai-Peng, LIU Ding
Chin. Phys. Lett. 2002, 19 (8): 1054-1057 .  
Abstract   PDF(pc) (496KB) ( 500 )
We propose a new method for chaos control and anti-control, which is referred to as the fuzzy-neural network inverse system method (FNNIS). The Sugeno-type fuzzy-neural network (FNN) is employed to learn the kinetics of the system to be controlled, then the FNN model is used with the inverse system method to make the system to be controlled to track the reference input. If the system to be controlled is chaotic and the reference input is non-chaotic, chaos control can be implemented via the FNNIS method. If the system to be controlled is non-chaotic and the reference input is chaotic, chaos anti-control can be implemented. Theorems about the effect of the FNN model error upon control are established. The simulation results show that this method is feasible and effective for chaos control and anti-control.
Nonperturbative Calculation of Shear Viscosity from the Basis of the Keldysh Field in Thermal Ф4 Theory
WANG En-Ke
Chin. Phys. Lett. 2002, 19 (8): 1058-1060 .  
Abstract   PDF(pc) (259KB) ( 390 )
The nonperturbative result of the shear viscosity in thermal
Ф4 theory is given by solving the Bethe-Salpeter (B-S) integral equation in the closed time formalism in real time. By introducing a two-legs-truncated Green function it is shown that the B-S equation is decoupled in the basis of Keldysh field.
Geometrical Method for the Generalized Moore Equations of a One-Dimensional Cavity with Two Moving Mirrors
LI Ling, , LI Bo-Zang
Chin. Phys. Lett. 2002, 19 (8): 1061-1064 .  
Abstract   PDF(pc) (461KB) ( 598 )
Extending the approach proposed by Cole and Schieve (1995 Phys. Rev. A 52 4405)for a one-dimensional cavity with one moving mirror, we develop a geometrical method to solve exactly the generalized Moore (GM) equations for a one-dimensional cavity with two moving mirrors. As examples of applying our method, the GM equations are solved in detail when the two mirrors oscillate resonantly, and the dependences of the solutions on the frequency and dephasing of the mirror motions are investigated.
Halo Structure of Isobaric Analog States in A = 21 and 17 Mirror Nuclei
ZHOU Shu-Hua, ZHOU Jing
Chin. Phys. Lett. 2002, 19 (8): 1065-1067 .  
Abstract   PDF(pc) (356KB) ( 428 )
The root-mean-square (rms) radius of the last nucleon in the 2s1/2 state of 21Ne, 21Na, 17O, and 17F are found to be 4.4±0.5, 5.2±0.6, 4.3±0.5, and 5.0±0.6 fm, respectively, from transfer reaction data. The results show that the 2s1/2 states of 21Na and 17F are proton halo states, while the analogous states in their mirror nuclei 21Ne and 17O can be considered as neutron skin states. Comparisons among the rms radii of these states lead us to expect that a neutron halo nucleus has a proton halo mirror partner, and the Coulomb barrier is a determinant factor limiting the extension of the rms radius of the loosely bound proton.
One-Proton Halo in 31Cl with Relativistic Mean-Field Theory
CAI Xiang-Zhou, SHEN Wen-Qing, , REN Zhong-Zhou, JIANG Wei-Zhou, FANG De-Qing, ZHANG Hu-Yong, ZHONG Chen, WEI Yi-Bin, GUO Wei, MA Yu-Gang, ZHU Zhi-Yuan
Chin. Phys. Lett. 2002, 19 (8): 1068-1070 .  
Abstract   PDF(pc) (326KB) ( 496 )
We investigate proton-rich isotopes 31,32Cl using the nonlinear relativistic mean-field model. It is shown that this model can reproduce the properties of these nuclei well. A long tail appears in the calculated proton density distribution of 31Cl. The results of relativistic density-dependent Hartree theory show a similar trend of tail density distribution. It is strongly suggested that there is a proton halo in 31Cl and it is indicated that there may exist proton skin in 31Cl. The relation between the proton halo in 1Cl and the new proton magic number is discussed.
Halo Nature of 14,15C
LIU Zu-Hua
Chin. Phys. Lett. 2002, 19 (8): 1071-1073 .  
Abstract   PDF(pc) (304KB) ( 368 )
We have used spectroscopic factors extracted from the (d,p) transfer reactions to calculate asymptotic normalization coefficients and root-mean-square (rms) radii for the valence neutron in 14,15C. The obtained rms radii are 4.57±0.30, 5.78±0.36 and 5.82±0.60 fm for the first 1-, 0- excited states of 14C and the ground state of 15C, which are 1.84, 2.33 and 2.32 times larger than the size of their cores, repectively. These large values imply that 15C as well as 14C in its first 1-, 0- states are halo nuclei.
Experimental Test of the Non-reproducibility of Cross Sections in Dissipative Reactions
DONG Yu-Chuan, WANG Qi, TIAN Wen-Dong, LI Song-Lin, LI Zhi-Chang, LU Xiu-Qin, ZHAO Kui, FU Chang-Bo, LIU Jian-Cheng, JIANG Hua, HU Gui-Qing
Chin. Phys. Lett. 2002, 19 (8): 1074-1077 .  
Abstract   PDF(pc) (415KB) ( 375 )
Two independent measurements of cross sections for the 19F+93Nb dissipative heavy ion collisions have been performed at incident energies from 100 to 108 MeV in a step of 250 keV. In the two measurements, two independently prepared targets were used. All other experimental conditions were identical in both experiments. The data indicate that non-reproducibility of the non-self-averaging oscillation is yielded in the two measurements. This supports the recent theoretical predictions of spontaneous coherence, slow phase randomization and extreme sensitivity in highly excited complex quantum systems.


Isospin Effects of the Mean Field and Two-Body Collision on the Fragmentation Process
LIU Jian-Ye, XING Yong-Zhong, GUO Wen-Jun, ZUO Wei, LI Xi-Guo,
Chin. Phys. Lett. 2002, 19 (8): 1078-1081 .  
Abstract   PDF(pc) (517KB) ( 451 )
Isospin effects of the mean field and two-body collision on the
fragmentation as well as their dependences on the momentum-dependent interaction at intermediate energy heavy ion collisions are studied by using an isospin-dependent quantum molecular dynamics model. We find the prominent isospin effects of the multiplicity of the intermediate mass fragments Nimf, where Nimf depends sensitively on the isospin effect of in-medium nucleon-nucleon cross section and weakly on the variation of symmetry potential in the intermediate energy region. The momentum dependence interaction enhances the sensitivety of Nimf on the isospin effect of two-body collision.
Centrality Dependence of Flow in High Energy Nucleus-Nucleus Collisions
YANG Hong-Yan, ZHOU Dai-Cui, YANG Chun-Bin, CAI Xu
Chin. Phys. Lett. 2002, 19 (8): 1082-1084 .  
Abstract   PDF(pc) (325KB) ( 364 )
Directed flow and elliptic flow of final state particles in high energy nucleus-nucleus collisions in the EMU01 experiment have been studied. The dependences of directed flow and elliptic flow on incident energy and impact centrality of outgoing particles are presented. The results exhibit strong dependence of flow on centrality and energy. We also suggest a more reliable way to determine the event plane resolution here.
Determination of the Geometric Structure of Core Excited Silane Based on Photoabsorption Spectra Near the Si 2p Edge
XU Ru-Qing, ZHANG Wei-Hua, LI Jia-Ming,
Chin. Phys. Lett. 2002, 19 (8): 1085-1087 .  
Abstract   PDF(pc) (282KB) ( 403 )
The photoabsorption spectra near the Si 2p edges of SiH4 have been studied based on the multiple-scattering self-consistent-field method. Our theoretical calculations provide clear assignments of the inner-shell photoabsorption spectra. In comparison with high-resolution experimental spectra, the geometric structure of the Si 2p excited SiH**4 is recommended as C2v symmetry.
Interference Dynamics of Hydrogen Atoms in High-Frequency Dichromatic Laser Fields
CHENG Tai-Wang, LI Xiao-Feng, FU Pan-Ming, CHEN Shi-Gang
Chin. Phys. Lett. 2002, 19 (8): 1088-1091 .  
Abstract   PDF(pc) (461KB) ( 410 )
We investigate the ionization and high-order harmonic generation of a hydrogen atom in high-frequency (several atomic unit) super strong (up to several tens of atomic unit dichromatic laser fields. An effective iterative method in the high frequency Floquet theory framework is used in the calculations. We have considered two kinds of dichromatic laser fields, i.e., 1ω - 2ω and 1ω - 3ω. We find that, in both the cases, the ionization and high-order harmonic generation show evident dependence on the relative phase and strength of the additional harmonic field. The dynamical origin of these interference effects is also discussed.
Dynamics and Cycle of Interstellar H2O and OH Masers
LIU Han-Ping, SUN Jin, FANG Wei-Hai, T. Thissen
Chin. Phys. Lett. 2002, 19 (8): 1092-1095 .  
Abstract   PDF(pc) (233KB) ( 397 )
We prepsent an improved radiative pumping model for interstellar H2O and OH masers. This overcomes the defects of former radiative models, and is compatible with astronomical conditions. For the regions of strong H2O and OH formation, it is shown that the rotational population is affected by collisions less than that by radiation. A reasonable scheme for both regeneration and destruction of interstellar H2O and OH molecules is investigated. It can close the dynamical cycle of interstellar H2O and OH species, and can give an appropriate interpretation for both interstellar H2O and OH masers. This model has been confirmed by experiments.
Vibrational Energy-Spectra and Infrared Absorption of α-Helical Protein Molecules
PANG Xiao-Feng, CHEN Xiang-Rong
Chin. Phys. Lett. 2002, 19 (8): 1096-1099 .  
Abstract   PDF(pc) (295KB) ( 424 )
The quantum energy-spectra, including high excited states, of
vibrational amide-I or of intramolecular excitations in α-helical protein molecules, are calculated by the discrete nonlinear Schrödinger equation together with the parameters appropriate to the systems. The distribution of energy levels obtained is basically consistent with the experimental values obtained by infrared absorption and Raman scattering. Utilizing the energy-spectra we explain the laser-Raman spectrum from metabolically active escherichia coli and we present some further features of the infrared absorption of the protein molecules.
A New Method of X-Ray Holographic Tomography
XIE Hong-Lan, CHEN Jian-Wen, GAO Hong-Yi, LU Pei-Xiang, XU Zhi-Zhan
Chin. Phys. Lett. 2002, 19 (8): 1100-1102 .  
Abstract   PDF(pc) (277KB) ( 504 )
A new method of x-ray holographic tomography, called the pre-amplified x-ray holographic tomography, is proposed to develop x-ray three-dimensional microscopic imaging technique. In this method, the key component is a micro zone plate taken as an imaging element like an optic lens in x-ray field. Some advantages of the method are shown by a numeric example. The method may make it possible to obtain x-ray microscopic imaging of biological specimens at high resolution in three dimensions.
Phase Dependence of the Inversionless Gain in a Λ System with Near-Degenerate Levels
WU Jin-Hui, ZHANG Hui-Fang, GAO Jin-Yue
Chin. Phys. Lett. 2002, 19 (8): 1103-1105 .  
Abstract   PDF(pc) (340KB) ( 553 )
Due to interaction with the vacuum of the radiation field, near-degenerate lower levels in a Λ system have an additional coherence term, the spontaneously generated coherence (SGC) term. For such a system, we investigate the effect of the relative phase between two coherent fields on the inversionless gain in the presence of SGC. We find that the inversionless gain, which stems from both spontaneously generated coherence and dynamically induced coherence, can be modulated by the relative phase.
High-Efficient Blue-Light Generation by Intracavity Frequency Doubling with LiB3O5
LIN Xue-Chun, LI Rui-Ning, CUI Da-Fu, YAO Ai-Yun, FENG Yan, BI Yong, XU Zu-Yan
Chin. Phys. Lett. 2002, 19 (8): 1106-1107 .  
Abstract   PDF(pc) (242KB) ( 552 )
We have investigated the generation of high-efficient blue light in critically type-I phase-matched LiB3O5 (LBO) with intracavity frequency doubling of diode-pumped Nd:YAG laser. A maximum output power of 502 mW at 473 nm blue light was obtained and the overall optical-to-optical efficiency is up to 11.2 %, to the best of our knowledge, this is the highest conversion efficiency for 473 nm output by using a diode pumped Nd:YAG laser through LBO.
Yb3+-Doped Non-π-Phase-Shifted Distributed Feedback Fibre Lasers
FAN Wei, CHEN Bai, LI Xue-Chun, CHEN Lan-Rong, CHEN Shao-He, LIN Zun-Qi
Chin. Phys. Lett. 2002, 19 (8): 1108-1111 .  
Abstract   PDF(pc) (546KB) ( 454 )
Distributed feedback (DFB) fibre lasers usually have two longitudinal modes symmetrically located at each side of the Bragg wavelength because they have the same lowest gain threshold. In order to obtain single longitudinal output, π-phase-shift, DFB fibre lasers were often adopted. However, we found that, even with no π-phase-shift, the single frequency output can be acquired from Yb3+-doped fibre DFB lasers. The polarization beat frequency was measured to be 366 MHz.
A Novel Method for Measuring the Absolute Phase of a Few-Cycle High Intensity Laser
ZENG Zhi-Nan, LI Ru-Xin, YU Wei, XU Zhi-Zhan
Chin. Phys. Lett. 2002, 19 (8): 1112-1114 .  
Abstract   PDF(pc) (433KB) ( 363 )
The effect of the absolute phase of the few-cycle driving laser field on the generation and measurement of high-order harmonic attosecond pulses is investigated theoretically. We find that the generated attosecond soft-x-ray pulse is locked to the oscillations of the driving laser field, but not to the envelope of the laser pulse, and the intensity ratio of two adjacent attosecond pulses is exponential as a function of the absolute phase. Based on these results, we propose a novel method to detect the absolute phase of the driving laser field by measuring the spatial distribution of the photoelectrons induced by the attosecond soft-x-ray pulse and the driving laser field.
Optical Transient Relaxation of an Ag-BaO Composite Thin Film with Supercontinuum Probe
WANG Dan-Ling, YANG Hong, JIANG Hong-Bing, GONG Qi-Huang, ZHANG Qi-Feng, WU Jin-Lei
Chin. Phys. Lett. 2002, 19 (8): 1115-1118 .  
Abstract   PDF(pc) (571KB) ( 487 )
The optical transient absorption spectra of an Ag-BaO thin film have been detected at a wavelength ranging from 400 nm to 1000 nm using the pump supercontinuum probe technique with resolution of 130 fs. We have observed the optical ultrafast relaxation, in which the electrons near the Fermi level of Ag nanoparticles were excited to a non-equilibrium state and then returned to an equilibrium state. The decay time was exponentially fitted and varied from 0.67 ps to 4 ps for different components of the supercontinuum probe. The peak of an unoccupied state for silver at level X'4 was estimated to be 1.47 eV above the Fermi level.
Monopole Charge Domain in High-Gain Gallium Arsenide Photoconductive Switches
SHI Wei, CHEN Er-Zhu, ZHANG Xian-Bin, LI Qi
Chin. Phys. Lett. 2002, 19 (8): 1119-1121 .  
Abstract   PDF(pc) (241KB) ( 500 )
Considering that the semi-insulating gallium arsenide photoconductive switches can be triggered into the high gain mode and no reliable theories can account for the observed transient characteristics, we propose the monopole charge domain model to explain the peculiar switching phenomena occurring in the high gain mode and discuss the requirements for the lock-on switching. During operation on this mode, the applied field across the switch and the lock-on field are all larger than the Guun threshold field. Our developed monopole charge domain is based on the transferred-electron effect, but the domain is only composed of large numbers of electrons piled up due to the negative differential mobility. Using the model and taking the physical mechanism of the avalanche impact ionization and recombination radiation into consideration, we interpret the typical phenomena of lock-on effect, such as, delay time between the beginning of optical illumination and turning-on of the switch, conduction mechanism of the sustaining phase. Under different conditions of bias field intensity and incident light energy, the delay time of the switching are calculated. The results show that the physical mechanism of impact ionization and recombination radiation occurring in the monopole charge domain is responsible for the lock-on switching.
                        
Fe-doped BaTiO3 Thin Films with Large Third-Order Nonlinear Optical Susceptibility
WANG Wei-Tian, YANG Guang, DUAN Ping, ZHOU Yue-Liang, CHEN Zheng-Hao
Chin. Phys. Lett. 2002, 19 (8): 1122-1124 .  
Abstract   PDF(pc) (322KB) ( 701 )
Iron doped BaTiO3 epitaxial thin films were fabricated using the pulsed laser deposition technique. The target was an Fe/BaTiO3 two-material physical assembly. The films were grown on MgO (100) substrates at 650°C. The crystalline property of the films was studied with x-ray diffraction. The result indicated that the Fe-doped BaTiO3 films did not degrade their crystallinity at the dopant concentration of 4 mol%. The nonlinear optical properties of the films were determined using Z-scan method at the wavelength of 532 nm with laser duration of 10 ns. The real and imaginary parts of the third-order nonlinear susceptibility X3 were determined to be 3.67 x 10-7 esu and 4.82 x 10-8 esu, respectively.
Thermally Stable Guest-Host Polyetherketone Poled Polymer for Electro-Optical Applications
PAN Qi-Wei, FANG Chang-Shui, QIN Zhi-Hui, GU Qing-Tian, WU Xiang-Wen, SHI Wei, YU Jin-Zhong
Chin. Phys. Lett. 2002, 19 (8): 1125-1127 .  
Abstract   PDF(pc) (317KB) ( 540 )
The high glass transition temperature polymer polyetherketone doped with disperse red 13 (DR13/PEK-c) has been prepared by the spin-coating method. Through in situ second-harmonic generation, the corona poling temperature was optimized by measuring the temperature dependence of the in-situ second-harmonic generation signal intensity under the poling electric field. The linear electro-optic coefficients of the poled polymer films have been determined at 632.8 nm by using a simple interferometric technique. The polymer system was measured after 13000 h, and found that it remained 80% of its initial value.
Bistatic Reverberation in Shallow Water: Modeling and Data Comparison
LI Feng-Hua, LIU Jian-Jun
Chin. Phys. Lett. 2002, 19 (8): 1128-1130 .  
Abstract   PDF(pc) (393KB) ( 713 )
Bistatic and monostatic reverberation data were recorded in the 2001 Asian Sea International Acoustic EXperiment (ASIAEX). A model based on the normal mode theory has been developed to calculate bistatic bottom reverberation in shallow water to explain the recorded data. The comparisons between the monostatic and bistatic reverberation data are discussed, and the comparisons between model predictions and measured bistatic reverberation data are also presented. The numerical and experimental results show that the numerical predictions from the bistatic reverberation model fit the experimental data well, and the long-range bistatic reverberation with a time delay can be approximately expressed by the monostatic reverberation data.
Free Field Reciprocity Calibration in a Convergent Spherical Acoustic Wave of a Focusing Transducer
SHOU Wen-De, YAN Jia-Yong, WANG Hong-Zhang, QIAN De-Chu
Chin. Phys. Lett. 2002, 19 (8): 1131-1134 .  
Abstract   PDF(pc) (568KB) ( 587 )
Basis on the reciprocity theorem of acoustic field, we derive the formula of reciprocity coefficient of a convergent spherical acoustic wave and calculate a series of the diffraction corrective factor curve of reciprocity coefficient of transducers. Using these formulas and corrective factors, we calibrate the free field transmitting current response and the free field voltage sensitivity of a focusing transducer by the self-reciprocity method. Experimental results of reciprocity calibration of the focusing transducer in the frequency range of 2 MHz to 5.4 MHz are presented.

Fractal Dimension of Randomly Branched Polymers in a Good Solvent
BA Xin-Wu, ZHANG Shu-Wen, WANG Hai-Jun, WANG Su-Juan, HAN Ying-Hui
Chin. Phys. Lett. 2002, 19 (8): 1135-1140 .  
Abstract   PDF(pc) (212KB) ( 623 )
We propose a concept of subchain for the randomly branched polymers. As a direct application of this concept, the asymptotic expression of the average mean square radius of gyration is determined to give the fractal dimensions, in which the excluded volume effect is taken into consideration. Furthermore, We investigate a scaling relation that is associates with the Flory exponent v, the fractal dimension df and polydispersity exponent τ.
Electron Temperature Control in Inductively Coupled Nitrogen Plasmas by Adding Argon/Helium
KANG Zheng-De, PU Yi-Kang
Chin. Phys. Lett. 2002, 19 (8): 1139-1140 .  
Abstract   PDF(pc) (250KB) ( 1280 )
A new technique, adding argon or helium into nitrogen plasma, has been used to regulate the electron temperature in an inductively coupled plasma. The electron temperature is determined by analysing the intensity ratio of two nitrogen spectrum lines. The results show that, when the total pressure is 0.7 Pa, the electron temperature increases with the increase of the He partial pressure in He/N2 plasma, but the electron temperature decreases with the increase of the Ar partial pressure in Ar/N2 plasma. The regulation effect of electron temperature is weaker in higher pressure N2/He plasma of 2.6 Pa.
Bootstrap Current Increment After Siliconization on the HT-7 Tokamak
ZHANG Xian-Mei, WAN Bao-Nian, LU Yuan-Cheng
Chin. Phys. Lett. 2002, 19 (8): 1141-1143 .  
Abstract   PDF(pc) (381KB) ( 428 )
We present some results for the estimatation of the bootstrap current after siliconization on the HT-7 tokamak. After siliconization, the plasma pressure gradient and the electron temperature near the boundary are larger than that before siliconization. These factors influence the ratio of the bootstrap current to the total plasma current to increases from several percent to above 10%. The results are expected to explain the previous experimental phenomena that, after siliconization, the plasma current profile is broadened and the higher current can be obtained easily on the HT-7 tokamak experiment.
Molecular Dynamics Simulation of Microstructure Transitions in a Large-Scale Liquid Metal Al System During Rapid Cooling Processes
LIU Rang-Su, DONG Ke-Jun, LI Ji-Yon, YU Ai-Bing, ZOU Rui-Ping
Chin. Phys. Lett. 2002, 19 (8): 1144-1147 .  
Abstract   PDF(pc) (576KB) ( 506 )
We perform a molecular dynamics (MD) simulation of microstructure transitions in a large-scale system consisting of 400000 atoms of liquid metal Al by the Clare supercomputer. A cluster-type index method is proposed to describe the structures of various short-range-order clusters in the liquid system. It is demonstrated that the icosahedron cluster (12 0 12 0) plays the most important role in the microstructure transition and that some larger clusters (containing more than 130 atoms) are formed in the system during the rapid cooling processes. It is obvious that the larger clusters are formed by means of combining some middle clusters, and that the middle clusters are formed with several smaller clusters. However, the larger clusters are not formed to be the multi-shell configuration as shown in the mass spectrum analysis of the cluster configurations of Al obtained by gaseous deposition, ionic spray methods and so on. This result can be used to explain the essential distinction between the cluster configurations of Al formed by two different ways.
Kinetics of Glass Transition of Zr41Ti14Cu12.5Ni10Be22.5 AlloySolidified in a Drop Tube
LI Gong, SUN Li-Ling, LIU Ri-Ping, JING Qin, ZHANG Jun, Li Qiang, WANG Wen-Kui,
Chin. Phys. Lett. 2002, 19 (8): 1148-1151 .  
Abstract   PDF(pc) (388KB) ( 691 )
Droplets of Zr41Ti14Cu12.5Ni10Be22.5 glass-forming alloy with different sizes are solidified in a drop tube containerless process. The glass transition temperature Tg of Zr41Ti14Cu12.5Ni10Be22.5 glassy spheres solidified with different cooling rates is investigated by using a differential scanning calorimeter. It was found that all the amorphous spheres show an increase of Tg with the heating rate. The glassy spheres have a unique value for glass transition activation energy Eg= 435.50kJ/mol, which is independent of cooling rate q. The insensitivity of Tg to q is interpreted by an extension of the free volume model for flow.
Optical Properties of ZnCdSe/ZnMgSe Multiple Quantum Wells Grown by Molecular Beam Epitaxy
LÜ, You-Ming, SHEN De-Zhen, LIU Yi-Chun, LI Bing-Hui, LIANG Hong-Wei, ZHANG Ji-Ying, FAN Xi-Wu
Chin. Phys. Lett. 2002, 19 (8): 1152-1154 .  
Abstract   PDF(pc) (334KB) ( 707 )
OWe study the optical properties of ZnCdSe/ZnMgSe multiple quantum wells using photoluminescence (PL) and Raman scattering spectra. In the PL spectra, an intense emission band coming from free exciton luminescence of the quantum wells can be observed from 80 K to 300 K. The exciton binding energy is evaluated by the dependence of PL intensity on the temperature, showing the behaviour of the better two-dimensional excitons. The result indicates that the enhancement of the confinement effect is due to containing Mg in the barrier layers. At room temperature, Raman scattering spectra are classified into the confined optical modes and folded optical modes. This confirms the formation of a multilayer system with a higher crystalline quality.
Influence of the Boundary Condition on the Short-Time Dynamic Behaviour of the Ising-Like Phase Transition in Square-Lattice Fully Frustrated XY Models
LUO Meng-Bo, CHEN Qing-Hu, JIAO Zheng-Kuan
Chin. Phys. Lett. 2002, 19 (8): 1155-1157 .  
Abstract   PDF(pc) (327KB) ( 407 )
We investigate the influence of the boundary condition on the short-time dynamic behaviour of the Ising-like phase transition in square-lattice fully frustrated (FF) XY models with periodic and fluctuating twist boundary condition. The transition temperature Tc and the dynamic and static critical exponents z, 2β/v, and v are estimated for both cases using the short-time dynamic scaling analysis. The results show that both models have the same critical exponents, indicating that the boundary condition has nearly no effect on the short-time dynamic behaviour of the FFXY model.
Influences of Thalliation on the Morphology and Critical Temperature of Tl2Ba2CaCu2O8 Thin Films
LEI Chong, ZHAO Xin-Jie, WANG Tian-Sheng, PENG Wei, YU Hong-Chun, CHEN Ying-Fei, TIAN Yong-Jun, LI Lin
Chin. Phys. Lett. 2002, 19 (8): 1158-1160 .  
Abstract   PDF(pc) (851KB) ( 477 )
Tl2Ba2CaCu2Ox (Tl-2212) thin films were prepared by the two-step technique. A precursor film was first prepared by the pulsed laser deposition method, and then experienced the incorporation of thalliation in a one-step or two-step annealing process. The experimental results show that the two-step annealing process produces dense and smooth films, and that the one-step annealing process produced a high critical temperature film of 101K, but the transition width is wide. Precursor films with homogeneous Ba2Ca1.3Cu2.1Ox composition are essential for producing high quality Tl-2212 films.
Surface Stability of Epitaxial Elastic Films by the Casimir Force
ZHAO Ya-Pu, Wen J. Li
Chin. Phys. Lett. 2002, 19 (8): 1161-1163 .  
Abstract   PDF(pc) (200KB) ( 428 )
We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical wavelength of the surface perturbation.
Surface Effects on Wannier Excitons in Superlattices: Monte Carlo Simulation
K. Afif, A. Benyoussef, J. Diouri
Chin. Phys. Lett. 2002, 19 (8): 1164-1167 .  
Abstract   PDF(pc) (388KB) ( 375 )
Using a Monte Carlo quadrature, we calculate by a variational method the binding energy Eb of wannier excitons in N-periods m-CdMnTe/n-CdTe superlattices, including or not including the step discontinuity in the potential barrier at the interface, and with varying N as well as well-width. The calculation is performed in the framework of the effective mass approximation for both heavy-hole and light-hole excitons. The degree of excitonique localisation dependence on those parameters is accurately illustrated.
Electrical Transport and Low-Field Magnetoresistance in La2/3Ca1/3MnO3/YSZ Composites
YUAN Song-Liu, XIA Zheng-Cai, LIU Sheng, LI Zhong-Yi, PENG Gang, TANG Jie, ZHANG Guo-Hong, ZHANG Li-Jiang, FENG Wen, XIONG Cao-Shui
Chin. Phys. Lett. 2002, 19 (8): 1168-1171 .  
Abstract   PDF(pc) (506KB) ( 501 )
Electrical transport and low-field magnetoresistance (MR) are
reported for (1-x)LCMO/xYSZ composites (0 < x < 80%)(LCMO = La2/3Ca1/3MnO2 and YSZ being yttria stabilized zirconia). Different transport and MR behaviour are observed for x < 2% and x > 2%. In particular, the composite with x ≤ 1% shows a wide temperature window with a large constant MR below the transition. Based on the microscopy analysis, a possible interpretation is presented for different observations for x < 2% and x > 2% with emphasis on the boundary effect arising from insulating YSZ layers.
Polarization-Induced Charges in Modulation-Doped AlxGa1-xN/GaN Heterostructures Through Capacitance-Voltage Profiling
ZHOU Yu-Gang, SHEN Bo, YU Hui-Qiang, LIU Jie, ZHOU Hui-Mei, ZHANG Rong, SHI Yi, ZHENG You-Dou, T. Someya, Y. Arakawa
Chin. Phys. Lett. 2002, 19 (8): 1172-1175 .  
Abstract   PDF(pc) (422KB) ( 456 )
Polarization-induced charges in modulation-doped Al0.22Ga0.78N/GaN heterostructures were investigated by the capacitance-voltage (C--V) method. The C--V profile of the Pt/Al0.22Ga0.78N/GaN Schottky diodes with various Al0.22Ga0.78N thickness shows significant differences due to change of the polarization field in the heterostructures. Numerical simulation based on the experimental results indicates that the sheet density of the polarization-induced charges at the heterointerface is 6.78 x 1012cm-2 in the samples with the Al0.22Ga0.78N thickness of 30 nm or 45 nm. The charge density reduces to 1.30 x 1012cm-2 in the sample with the Al0.22Ga0.78N thickness of 75 nm. It is thought that the reduction of the polarization-induced charges at the heterointerface is due to the partial relaxation of the Al0.22Ga0.78N layer on GaN. This work provides a technique for quantitative characterization of the polarization-induced charges in AlxGa1-xN/GaN heterostructures.

Electron-Phonon Coupling in Anion Metallic Solids and Superconducting MgB2
YIN Dao-Le, YANG Fan, QI Zhi, HAN Ru-Shan
Chin. Phys. Lett. 2002, 19 (8): 1176-1178 .  
Abstract   PDF(pc) (197KB) ( 344 )
We analyse the Hopfield factor of the newly found superconductor MgB2 using the linear muffin-tin orbital method. Based on a uniform transferred charge density model raised, it is shown from our calculation that the high difference of electronegativity between boron and magnesium favours the high l (l+1) angular momentum hybridization and then the Hopfield factor. Our analysis is consistent with experimental results. Comparison with the cuprate superconductors are also discussed.
A New Method for Preparing Superconducting MgB2 Films from Diborane
WANG Dian-Sheng, FU Xing-Hua, ZHANG Zheng-Ping, YANG Jian
Chin. Phys. Lett. 2002, 19 (8): 1179-1180 .  
Abstract   PDF(pc) (366KB) ( 425 )
We report on a new preparation method for magnesium diboride (MgB2) films by chemical vapor deposition (CVD) from diborane (B2H6). It is a two-step ex-situ approach, with the precursor boron films grown by CVD from B2H6 at 460°C, and followed by a post-annealing process in magnesium (Mg) vapor at 830°C. The prepared MgB2 thin films on Al2O3 polycrystalline substrates have an onset transition temperature of 35 K and zero-resistance temperature of about 24 K. Well-crystallized MgB2 grains were clearly observed in the SEM images and confirmed by x-ray diffraction analysis. The advantages of the proposed method are the feasibility to prepare large-area superconducting films and the compatibility with semiconductor technology.
Point Contact Andreev Reflection Measurement of the Spin Polarization of Ferromagnetic Alloy NiFeSb
LI Zhuang-Zhi, TAO Hong-Jie, WEN Hai-Hu, ZHANG Ming, LIU Zhu-Hong, CUI Yu-Ting, WU Guang-Heng
Chin. Phys. Lett. 2002, 19 (8): 1181-1183 .  
Abstract   PDF(pc) (479KB) ( 391 )
We have studied the temperature-dependent and barrier-strength-dependent Andreev reflection tunneling spectroscopy with point contacts consisted of newly synthesized half-metallic alloy NiFeSb and Nb tip. By fitting the data to the generalized Blonder-Tinkham-Klapwijk theory a spin polarization P = 0.52 was obtained.
Mean-Field Calculations for the Three-Dimensional Holstein Model
LUO Qiang, LIU Chuan
Chin. Phys. Lett. 2002, 19 (8): 1184-1186 .  
Abstract   PDF(pc) (265KB) ( 437 )
The electron-phonon Holstein model is studied in three spatial
dimensions. It is argued that this model can be used to account for major features of the high-Tc BaPb1-xBixO3 and BaxK1-xBiO3 systems. Mean-field calculations are performed via a path integral representation of the model. Charge-density-wave order parameters and transition temperatures are obtained.
Monte Carlo Simulations of Mixed Highly Frustrated Systems
K. Afif, A. Benyoussef, M. Hamedoun
Chin. Phys. Lett. 2002, 19 (8): 1187-1190 .  
Abstract   PDF(pc) (351KB) ( 807 )
We have performed Monte Carlo simulations on the mixed highly
frustrated K2CuxMn1-xF4 and FexMn1-xTiO3 systems. Transitions of random systems with well-established universality classes are obtained. This study allows us to investigate mainly the usual and reentrant spin glass and criticality associated to these states. The ratio x of substitution (or dilution) is found to be of great influence on the nature of this criticality.
Formation and Distribution of Space-Charge in Cross-Linked Polyethylene
ZHANG Ye-Wen, LI Ji-Xiao, ZHENG Fei-Hu, PENG Zong-Ren, WU Chang-Shun, XIA Zhong-Fu
Chin. Phys. Lett. 2002, 19 (8): 1191-1194 .  
Abstract   PDF(pc) (437KB) ( 546 )
The formation and distribution of space-charge in cross-linked
polyethylene (XLPE) sample are investigated by means of pressure wave propagation, infrared spectroscopy, and electrostatic force microscopy (EFM). The related mechanism of space-charge distribution and the structure of XLPE are discussed. The EFM images show that quite large quantitative space-charges locate at the surface of spherulites.
Coherence and Decoherence of a Localized Excitation on a Surface Adatom
GAO Shi-Wu, H. Petek, J. Aizpurua, P. Apell
Chin. Phys. Lett. 2002, 19 (8): 1195-1198 .  
Abstract   PDF(pc) (389KB) ( 375 )
A theory of coherent excitation of a localized state on an adatom by two-photon photoemission spectroscopy (TR-2PPE) is presented within a microscopic model and the time-dependent formalism. Coherent oscillation and incoherent population decay of the excitation are obtained, and are shown to attain well-defined lifetime constants only in the long-delay limit. In addition, we have found a competing excitation channel via electron transfer. The theory is applied to Cs/Cu (111), which reproduces a few qualitative features observed in recent experiments. The effect of atomic motion on the 2PPE spectra, which manifests dominantly as a redshift in the spectrum, has been analysed.
Effect of Substrates on CuInSe2 Nanoparticle Thin Films by Radio Frequency Reactive Sputtering
HUANG Shi-Yong, ZHANG Li-De, LI Guang-Hai, DAI Zhen-Hong, ZHU Xiao-Guang, QU Feng-Qi, FU Sheng-Qi, ZHONG Yu-Rong, MIAO Y
Chin. Phys. Lett. 2002, 19 (8): 1199-1202 .  
Abstract   PDF(pc) (563KB) ( 629 )
CuInSe2 (CIS) nanoparticle thin films have been prepared by rf reactive magnetron sputtering from compound ternary fan-shaped targets on low temperature substrates with pure argon gas as the atmosphere. The stoichiometry of the ternary compound semiconductor quantum dots can be easily controlled by the ratios of the ternary elements and sputtering parameters. CIS nanoparticle thin films regularly shaped and distributed reasonably uniform in size on substrates of 7059 glass etc can be grown in this way. The average particle diameter can be varied between 40 and 80 nm by appropriate choice of the substrate temperature, power density and total CIS coverage. The optical and electrical properties of the CIS films have also been studied.
Anomalous Temperature Dependence of Photoluminescence in GaInNAs/GaAs Multiple Quantum Wells
LIANG Xiao-Gan, JIANG De-Sheng, BIAN Li-Feng, PAN Zhong, LI Lian-He, WU Rong-Han
Chin. Phys. Lett. 2002, 19 (8): 1203-1206 .  
Abstract   PDF(pc) (503KB) ( 478 )
Photoluminescence (PL) spectra of GaInNAs/GaAs multiple quantum wells (MQWs) grown on a GaAs substrate by molecular beam epitaxy are measured in a range of temperature and excitation power densities. The energy position of dominant PL peak shows an anomalous S-shape temperature dependence instead of the Varshni relation. By the careful inspection, especially for the PL under lower excitation power density, two near band-edge peaks are well identified. They are assigned to carriers localized in nitrogen-induced bound states and interband excitonic recombinations respectively. It is suggested that the temperature-induced switch of such two luminescence peaks in relative intensity causes a significant mechanism responsible for the S-shape shift observed in GaInNAs. A quantitative model based on the thermal depopulation of carriers is used to explain the temperature dependence of the PL peak related to N-induced bound states.
Negative Dispersion of Lattice Waves in a Two-Dimensional Yukawa System
LIU Yan-Hong, LIU Bin, YANG Si-Ze, WANG Long
Chin. Phys. Lett. 2002, 19 (8): 1207-1210 .  
Abstract   PDF(pc) (545KB) ( 673 )
Collective motion modes existing in a two-dimensional Yukawa system are investigated by molecular dynamics simulation. The dispersion relations of transverse and longitudinal lattice waves obtained for hexagonal lattice are in agreement with the theoretical results. The negative dispersion of the parallel longitudinal wave is demonstrated by the simulation, and is explained by a physical model.
Electrical Conductivity of Synthetic Quartz Crystals at High Temperature and Pressure from Complex Impedance Measurements
WANG Duo-Jun, LI He-Ping, LIU Cong-Qiang, YI Li, DING Dong-Ye, SU Gen-Li, ZHANG Wei-Gang
Chin. Phys. Lett. 2002, 19 (8): 1211-1213 .  
Abstract   PDF(pc) (417KB) ( 664 )
An electrical conductivity measurement system under high-pressure conditions with a multi-anvil high-pressure apparatus by an ac complex impedance method was set up. With this system, we have successfully measured the electrical conductivity of synthetic quartz under pressure up to approximately 1.0 GPa in the temperature range 661-987 K. The values of electrical conductivity decrease with the increasing pressure and increase with the increasing temperature. The activation enthalpies for the α-quartz crystals are 1.10-1.28 eV. The electrical conductivity of α-quartz is ionic, with Na ions moving in channels parallel to the c-axis being the predominant current carrier.
Neutral Barium Cloud Evolution at Different Altitudes
LI Lei, XU Rong-Lan
Chin. Phys. Lett. 2002, 19 (8): 1214-1216 .  
Abstract   PDF(pc) (321KB) ( 413 )
Considering the joint effects of diffusion, collision, oxidation and photoionization, we study the evolution of barium cloud at different altitude in the space plasma active experiment. The results present the variation of the loss rate, number density distribution, and brightness of the barium cloud over the range from 120 to 260 km, this can be divided into oxidation, oxidation plus photoionization and photoionization regions.
A Quasi-One-Dimensional Model for a Solar Flux Tube
YANG Zhi-Liang, ZHANG Hong-Qi, ZHANG Mei, FENG Xue-Shang
Chin. Phys. Lett. 2002, 19 (8): 1217-1220 .  
Abstract   PDF(pc) (246KB) ( 360 )
We develop the quasi-one-dimensional flux tube model with magnetohydrodynamical equations. In order to know whether the magnetic field can maintain their similar structure from photosphere to chromosphere, we suppose that the flux tube is thin in radius relative to the length, the quantities in the cross section is averaged. The radii of the flux tube and the magnetic field are numerically simulated. One of the important results shows that the fluxtube does not expand quickly as existed model when it is out of the photosphere with high velocity. This is consistent with observations of the magnetic field in photosphere and chromosphere.
56 articles