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Volume 20 Issue 8
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Original Articles
Equivalent Anti-symmetry Performance of Three-Dimensional Hetergeneous Anisotropic Composites
LI Yong, SONG Jian ZHANG Zhi-Min
Chin. Phys. Lett. 2003, 20 (8): 1189-1191 .  
Abstract   PDF(pc) (257KB) ( 314 )
Starting from the physical features of materials, heterogeneous anisotropic composites (HACs) are analysed on the basis of the understanding and applications of its equivalent anti-symmetry performance. Moreover, the design parameter is optimized to attain the goal of maximizing the use of materials, which is quite meaningful. The HAC structure is defined as a kind of equivalent structures according to the structure and properties of materials. We apply the mature plate theory and the composite materials laminate theory in analysis of the HAC structure, and in this way a new concept and a new idea are expected.
An Almost-Poisson Structure for Autoparallels on Riemann-Cartan Spacetime
GUO Yong-Xin, SONG Yan-Bin, ZHANG Xiao-Bin, CHI Dong-Pyo
Chin. Phys. Lett. 2003, 20 (8): 1192-1195 .  
Abstract   PDF(pc) (210KB) ( 424 )
An almost-Poisson bracket is constructed for the regular Hamiltonian formulation of autoparallels on Riemann-Cartan spacetime, which is considered to be the motion trajectory of spinless particles in the space. This bracket satisfies the usual properties of a Poisson bracket except for the Jacobi identity. There does not exist a usual Poisson structure for the system although a special Lagrangian can be found for the case that the contracted torsion tensor is a gradient of a scalar field and the traceless part is zero. The almost-Poisson bracket is decomposed into a sum of the usual Poisson bracket and a “Lie-Poisson”bracket, which is applied to obtain a formula for the Jacobiizer and to decompose a non-Hamiltonian dynamical vector field for the system. The almost-Poisson structure is also globally formulated by means of a pseudo-symplectic two-form on the cotangent bundle to the spacetime manifold.
Probabilistic Teleportation of the Three-Particle Entangled State by the Partial Three-Particle Entangled State and the Three-Particle Entangled W State
DAI Hong-Yi, LI Cheng-Zu, CHEN Ping-Xing
Chin. Phys. Lett. 2003, 20 (8): 1196-1198 .  
Abstract   PDF(pc) (193KB) ( 625 )
We present a scheme to teleport an unknown three-particle entangled state from a sender to either one of two receivers. The partial three-particle entangled state and the three-particle entangled W state are considered as the quantum channels. An unknown three-particle entangled state can be perfectly teleported probabilisticly by performing two generalized Bell measurements and the Hadamard operation at sender's side and introducing an appropriate unitary transformation in each receiver's laboratory conditioned on the simple measurement outcome of the other. All kinds of unitary transformations are given in details. This scheme can be directly generalized to teleport an unknown three-particle entangled state from a sender to any one of N receivers by the partial three-particle entangled state and the (N + 1)-particle entangled W state.
A Novel Controllable Beam Splitter for Guided Atoms
LIU Nan-Chun, GAO Wei-Jian, YIN Jian-Ping,
Chin. Phys. Lett. 2003, 20 (8): 1199-1201 .  
Abstract   PDF(pc) (299KB) ( 416 )
We propose a novel atomic beam splitter for guided atoms composed of a U-shaped current carrying conductor and an additional bias magnetic field, and study the dynamic process of atomic beam splitting in the beam splitter by Monte-Carlo simulations. Our study shows that the splitting ratio of the beam splitter can be continuously adjusted from 0 to 1 by changing the additional bias field. In addition, the transverse temperature of guided atoms at the outlets of the beam splitter are also estimated and explained qualitatively.
Evolution and Collision of Bose-Condensed Gas in One-Dimensional Optical Lattices and a Far-Off Resonant Laser Beam
LIU Shu-Juan, XU Zhi-Jun, SUI Cheng-Hua, HUANG Lin, XIONG Hong-Wei
Chin. Phys. Lett. 2003, 20 (8): 1202-1205 .  
Abstract   PDF(pc) (364KB) ( 401 )
Evolution of a Bose-condensed gas in one-dimensional optical lattices is investigated in the presence of a potential barrier created by a far-off resonant laser beam. After the magnetic trap and optical lattices are switched off, by using the propagator method, the analytical result of the evolution of the density distribution of the Bose-condensed gas is given. In particular, the collision between the condensate and the potential barrier is shown in this paper.
An Abnormal Vibrational Mode of Torsion Pendulum
ZHAO Liang, TU Ying, GU Bang-Ming, HU Zhong-Kun, LUO Jun,
Chin. Phys. Lett. 2003, 20 (8): 1206-1209 .  
Abstract   PDF(pc) (514KB) ( 563 )
In the experiment for the determination of the gravitational constant G, we found an abnormal vibrational mode of the torsion pendulum. The abnormal mode disappeared as a magnetic damper was introduced to the torsion pendulum system. Our experimental results also show that the magnetic damper can be used to suppress the high frequency vibrational noises to torsion pendulums effectively.
Measurement of the Floor Tilt in Experimental Determination of the Gravitational Constant
WU Shu-Chao, HUANG Yu, FAN Shu-Hua, LUO Jun
Chin. Phys. Lett. 2003, 20 (8): 1210-1213 .  
Abstract   PDF(pc) (460KB) ( 425 )
A prototype of a device with an impact structure for measuring the floor tilt has been built in our laboratory. The mechanical construction and the capacitive transducer of the device are introduced. Experimental results indicate that the floor tilt is about 16 μrad in our cavity laboratory, and the uncertainty ΔG/G caused by such tilt is less than 0.54 parts per million (ppm), so the floor tilt can be reasonably neglected in the experimental determination of the gravitational constant G with the total uncertainty of about 10 ppm.

Performance of an Accelerometer Suspended by a Pendulum
GAO Shang-Wei, LUAN En-Jie, ZHOU Ze-Bing, LUO Jun
Chin. Phys. Lett. 2003, 20 (8): 1214-1216 .  
Abstract   PDF(pc) (256KB) ( 352 )
Performances of an accelerometer suspended by a pendulum and set on ground directly are both discussed. Theoretical analysis shows that the isolation from seismic disturbances of such a suspending accelerometer is equal to that of a narrow band-pass electronic filter. This means that the effect of seismic noises to the accelerometer can be substantially suppressed by means of a pendulum suspension during its performance tests.

Stochastic Multiresonance for Periodically Modulated Noise in a Single-Mode Laser
WANG Jun, CAO Li, , WU Da-Jin,
Chin. Phys. Lett. 2003, 20 (8): 1217-1220 .  
Abstract   PDF(pc) (329KB) ( 449 )
Multiplicatively introducing the noise and the signal into the gain-noise model of a single-mode laser system, we detect the two forms of stochastic resonance (the single-peak form stochastic resonance and stochastic multiresonance) in the curve of the dependence of signal-to-noise ratio upon the noise correlation time. Moreover, when the correlation coefficient and the intensities of both noises are changed, the two forms of stochastic resonance alternate.
Experimental Measurement for Shock Velocity-Mass Velocity Relationship of Liquid Argon Up to 46 GPa
MENG Chuan-Min, SHI Shang-Chun, DONG Shi, YANG Xiang-Dong, TAN Hua, JING Fu-Qian,
Chin. Phys. Lett. 2003, 20 (8): 1221-1222 .  
Abstract   PDF(pc) (294KB) ( 518 )
Shock properties of liquid argon were measured in the shock pressure up to 46 GPa by employing the two-stage light gas gun. Liquid nitrogen was used as coolant liquid. The cryogenic target system has been improved to compare with the previous work. Shock velocities were measured with self-shorting electrical probes. Impactor velocities were measured with an electrical-magnetic induction system. Mass velocities were obtained by mean of shock impendence matching method. The experimental data shows that the slope of experimental Hugoniot curve of liquid argon begins to decrease above 30 GPa.
Breaking of Chiral Symmetry in 104Rh and Its Neighbouring Nuclei
PENG Jing, MENG Jie, , ZHANG Shuang-Quan
Chin. Phys. Lett. 2003, 20 (8): 1223-1226 .  
Abstract   PDF(pc) (836KB) ( 521 )
The possible chiral doublet structures in 104Rh with the asymmetric configuration πg-19/2 vh11/2 have been studied in the triaxial particle-rotor model. The spectra, the I - ω relations and the transition probabilitiessupport the existence of the chiral bands in this nucleus. The γ-deformation interval -35°≤ γ ≤ -25°for appearance of chiral doublets in 104Rh is given. With appropriate moment of inertia and the configuration πg-19/2 vh11/2, the experimental spectra in 104Rh, 106Rh, 108Rh, 110Ag have been well reproduced by the yrast bands of the triaxial particle-rotor-model calculation.
Description of Superdeformed Bands of the Nuclei in A ~ 60 Mass Region
LIU Yu-Xin, , MENG Xiang-Ming
Chin. Phys. Lett. 2003, 20 (8): 1227-1230 .  
Abstract   PDF(pc) (461KB) ( 342 )
Using the supersymmetry scheme including many-body interactions, we investigate the superdeformed (SD) bands of the nuclei in A ~ 60 mass region systematically. Quantitatively good results of the γ-ray energy spectra and the dynamical moments of inertia are obtained. It shows that the supersymmetry approach is powerful to describe the generic rotational property of SD states of light nuclei.
Description of 114Cd in the E(5) Symmetry
ZHANG Jin-Fu, LONG Gui-Lu, , SUN Yang, ZHU Sheng-Jiang, LIU Feng-Ying, JIA Ying
Chin. Phys. Lett. 2003, 20 (8): 1231-1233 .  
Abstract   PDF(pc) (294KB) ( 407 )
By analysing the known low-lying levels and the E2 transition rates, it is shown that the empirical scheme of 114Cd is in good overall agreement with the predictions of the transitional dynamical symmetry E(5) proposed by Iachello [Phys. Rev. Lett. 85 (2000) 3580]. This suggests that 114Cd may be better described by an E(5) nucleus than a U(5) nucleus as known before.

Nuclear Radii Extracted from Experimental Reaction Cross Sections
ZHANG Hu-Yong, SHEN Wen-Qing, REN Zhong-Zhou, MA Yu-Gang, JIANG Wei-Zhou, CAI Xiang-Zhou, ZHONG Chen, CHEN Jin-Gen, GUO Wei, WEI Yi-Bin, ZHOU Xing-Fei, MA Guo-Liang, WANG Kun
Chin. Phys. Lett. 2003, 20 (8): 1234-1237 .  
Abstract   PDF(pc) (265KB) ( 441 )
We illustrate typical experimental reaction cross sections σR which have obtained on RIBLL at Heavy Ion Research Facility of the Institute of Modern Physics (IMP) at Lanzhou. The corresponding nuclear radii are extracted from the measured experimental σR using the Glauber model. Meanwhile, theoretical nuclear radii are also calculated using Relativistic density-dependent Hartree and spherical relativistic mean-field theory with Pauli blocking. For comparison, the nuclear radii of these nuclei are also calculated using the empirical radius format in which the deformation has been taken into account. From the given experimental and theoretical nuclear radii, we suggest that there may exist proton halo structure in 23Al, 27P and may exist proton skin structure in 24Al. We also find that the deformation plays a great role to the nuclear radii.

Neutron Star Composition in Strong Magnetic Fields
MAO Guang-Jun, V. N. Kondratyev, A. Iwamoto, LI Zhu-Xia, WU Xi-Zhen, W. Greiner, I. N. Mikhailov
Chin. Phys. Lett. 2003, 20 (8): 1238-1241 .  
Abstract   PDF(pc) (396KB) ( 548 )
We study the neutron star composition in the presence of a strong magnetic field. The effects of the anomalous magnetic moments of both nucleons and electrons are investigated in relativistic mean field calculations for a β-equilibrium system. Since neutrons are fully spin polarized in a large field, generally speaking, the proton fraction can never exceed the field free case. An extremely strong magnetic field may lead to a pure neutron matter instead of a proton-rich matter.
Theoretical Analysis of Ionic Autoionization Spectra of Lanthanum in the Energy Region of 90650-91500 cm-1
ZHANG Xin-Feng, PENG Yong-Lun, ZHONG Zhi-Ping, QU Yi-Zhi, SUN Wei, XIA Dan, XUE Ping, XU Xiang-Yuan,
Chin. Phys. Lett. 2003, 20 (8): 1242-1243 .  
Abstract   PDF(pc) (358KB) ( 417 )
Eigenquantum defects μα and transformation matrix U of La+ are calculated from the first principles by relativistic multichannel theory, and dipole matrix elements Dα are obtained by fitting the experimental spectra. With these parameters, ionic autoionization spectra of lanthanum via an intermediate state (Xe)5d6d1P1 of La+ in the energy region of 90650-91500cm-1 are calculated within the framework of multichannel quantum defect theory. Our calculated spectra are in general agreement with the experimental data.

Optimal Truncation in Ionization of Hydrogen by Electron Impact
ZHANG Cheng-Hua, NIU Ying-Yu, WU Wei, QIU Wei, XIN Jun-Li, WANG Xiao-Wei, WANG Jing-Yang
Chin. Phys. Lett. 2003, 20 (8): 1244-1246 .  
Abstract   PDF(pc) (318KB) ( 326 )
An analytic expression for the ionization amplitude of hydrogen by electron impact is found to contain a polynomial by an optimal truncation in an asymptotic series and a convergent series. The ionization amplitude, i.e., transition matrix element on the energy shell, is decomposed into two parts: the structure-scattering factor and correlation factor, based on an approximation of projectile plane wave in coplanar asymmetric geometries. The contribution of these factors to the triple differential cross section is evaluated using the method of optional truncation of asymptotic and convergent series.
Generation of Very Energetic Ions from Intense Femtosecond Laser Interactions with Rare Gas Clusters in a Dense Jet
LI Shao-Hui, WANG Cheng, ZHU Pin-Pin, WANG Xiang-Xin, LI Ru-Xin, NI Guo-Quan, XU Zhi-Zhan
Chin. Phys. Lett. 2003, 20 (8): 1247-1250 .  
Abstract   PDF(pc) (373KB) ( 366 )
Very energetic ions, which are detected by time-of-flight spectrometry with the maximum energy up to 1.3 MeV and an average energy of 68 keV, are generated in the explosion of large Xe clusters in a dense jet irradiated with a high intensity (~1016W/cm2) 50 fs laser pulse from a Ti:sapphire TW laser at 790 nm wavelength. The interaction of intense laser pulses with a jet of argon clusters is also performed and high average ion energies are observed. The dependence of energy of the ions on gas backing pressure is examined, suggesting that the results are consistent with the absorption efficiency of the laser energy by the cluster plasmas.
Investigation of Electron Injection Parameters in Vacuum Laser Acceleration
SHAO Lei, HUO Yu-Kun, CAO Na, PANG Ju, CHEN Zhao, XIE Yong-Jie, ZHANG Shao-Yin
Chin. Phys. Lett. 2003, 20 (8): 1251-1253 .  
Abstract   PDF(pc) (575KB) ( 479 )
We investigate the parameters such as the energy gains, comparisons for linearly and circularly polarized laser fields, the electron incident polarization azimuth angle, the electron incident crossing angle, and the electron incident momentum, etc., which are crucial for experimental test of the vacuum laser acceleration scheme in capture and acceleration scenario (CAS) [see, e.g., Phys. Rev. E 66 (2002) 066501]. Physical explanation of these features has been presented based on the CAS scheme. The results show that all those parameters are in the reasonable ranges obtainable by presently experimental facilities.

ABCD-Type Law for Charged-Particle Beam Transport in Paraxial Approximation
CHEN Bao-Xin, SUN Bie-He
Chin. Phys. Lett. 2003, 20 (8): 1254-1256 .  
Abstract   PDF(pc) (171KB) ( 360 )
Based on the similarity between charged-particle beam transversal transport and transmission of ellipse Gaussian light beam in paraxial approximation, it is shown that charged-particle beam transversal transport in real space is governed by the ABCD-type law for a complex curvature radius of the charged-particle beam in which the beam transverse emittance plays the role of wavelength; from this, a novel technique for characterizing charged-particle beam is proposed. Finally, this analogy provides an insight observation that it is hopeful to attain possible coherent charged-particle beam in favorable accelerator environment.
Observation of Electromagnetically Induced Transparency in a Zeeman-Sublevel System in Rubidium Atomic Vapor
XIAO Feng, GUO Rui-Min, CHEN Shuai, ZHANG Yu, LI Lu-Ming, CHEN Xu-Zong
Chin. Phys. Lett. 2003, 20 (8): 1257-1260 .  
Abstract   PDF(pc) (621KB) ( 479 )
We observed electromagnetically induced transparency (EIT) in a Zeeman-sublevel system using rubidium atomic vapor at the temperature of 75°C, in which the width of the EIT signal is only 0.6 MHz. Two different methods were performed to observe the EIT signal in our experiment.
Theoretical Analysis of Characteristics of GaxIn1-xNyAs1-y/GaAs Quantum Well Lasers with Different Intermediate Layers
ZHANG Wei, XU Ying-Qiang, NIU Zhi-Chuan, WU Rong-Han
Chin. Phys. Lett. 2003, 20 (8): 1261-1263 .  
Abstract   PDF(pc) (311KB) ( 306 )
Based on the band anticrossing model, the effects of the strain-compensated layer and the strain-mediated layer on the band structure, gain and differential gain of GaInNAs|GaAs quantum well lasers have been investigated. The results show that the GaNAs barrier has a disadvantage in increasing the density of states in the conduction band. Meanwhile, the multilayer quantum wells need higher transparency carrier density than the GaInNAs|GaAs single quantum well with the same wavelength. However, they help to suppress the degradation of the differential gain. The calculation also shows that from the viewpoint of band structure, the strain-compensated structure and the strain-mediated structure have similar features.

Performance Improvement of Distributed and Discrete Raman Amplifiers with a Fibre Loop Mirror
CHI Rong-Hua, LU Ke-Cheng, YUN Peng, LI Yi-Gang, DONG Xiao-Yi, CHEN Wen-Zhao, YANG Guang-Ming, LIU Zhao-Bing
Chin. Phys. Lett. 2003, 20 (8): 1264-1268 .  
Abstract   PDF(pc) (349KB) ( 442 )
We use a fibre loop mirror to reflect the residual pump power (RPP) into the fibre for solving the problems of the RPP in Raman amplifiers. The experimental results show that the novel bi-directional pumping scheme without adding extra pump lasers is effective, and higher gain and lower noise are obtained for both the distributed and the discrete Raman amplifiers.
Limit of Spectral Resolution in Terahertz Time-Domain Spectroscopy
Jingzhou Xu, Tao Yuan, Samuel Mickan, X. -C. Zhang
Chin. Phys. Lett. 2003, 20 (8): 1266-1268 .  
Abstract   PDF(pc) (220KB) ( 509 )
The pulsed nature of terahertz time-domain spectroscopy (THz-TDS) sets a fundamental limit on its spectral resolution. The spectral resolution of THz-TDS can be improved by increasing the duration of the temporal measurement, but is limited by the dynamic range of the system in the time domain. This paper presents calculations and experimental results relating the temporal dynamic range of a THz-TDS system to its spectral resolution. We discuss three typical terahertz sources in terms of their dynamic range and hence achievable spectral resolution.
Rotational Symmetry and Absolute Sign of Second-Order Susceptibility of α-Quartz
LÜ, Rong, WANG Hong-Fei
Chin. Phys. Lett. 2003, 20 (8): 1269-1271 .  
Abstract   PDF(pc) (444KB) ( 498 )
We investigate the rotational symmetry and absolute sign of the effective second order susceptibility of the right-handed z-cut α-quartz crystal in different crystal orientations through the second-harmonic-generation phase interference between standard and reference of thin α-quartz plates. The D3 rotational symmetry of the z-cut α-quartz crystal shows 6 alternating sign sections of the second order susceptibility in the 360°rotation, which leads to two distinctive interference patterns between the reference and standard second harmonic field. From this information, the sign of the interference pattern in the second harmonic phase measurement could be readily derived.
Wavelength Converter Based on Linearly Chirped Gratings in Lithium Niobate Through Cascaded Second-Order Processes
GAO Shi-Ming, YANG Chang-Xi, JIN Guo-Fan
Chin. Phys. Lett. 2003, 20 (8): 1272-1274 .  
Abstract   PDF(pc) (441KB) ( 490 )
We report a wavelength converter based on linearly chirped gratings in a lithium niobate crystal through cascaded second-order nonlinear processes. The influence of the chirp coefficient on the conversion bandwidth and the efficiency is analysed. The exact phase matching point is optimized at the 0.33 times of the waveguide total length. When the waveguide length is 3cm, the bandwidth of the linearly chirped grating increases 42% with the efficiency penalty of 1.7 dB compared with the periodic grating. At the same mean conversion efficiency of -1.4 dB via adjusting the waveguide total lengths, the bandwidth of the linearly chirped grating is 36% broader than the periodic grating.
Second Harmonic Generation from Co Magnetic Thin Films
LU Yong-Xiong, YE Jun, JIN Qing-Yuan
Chin. Phys. Lett. 2003, 20 (8): 1275-1278 .  
Abstract   PDF(pc) (461KB) ( 411 )
The magnetization-induced second harmonic generation (MSHG) in the sputtered and epitaxial-grown Co thin films was studied. The magnetic contrast of the MSHG intensity could be clearly distinguished for the cobalt films prepared by both the methods, but the signal measured in air for sputtered films was not smoother than that for the in-situ measurement of epitaxial films. Compared with the magneto-optical Kerr effect, the MSHG shows some new behaviour indicating that more information could be obtained if these two methods are combined. The MSHG reveals a giant nonlinear Kerr rotation in orders of magnitude larger than its linear one.
Three-Wave Resonant Interactions in Self-Defoucsing Optical Media
CUI Wei-Na, HUANG Guo-Xiang, SUN Chun-Liu
Chin. Phys. Lett. 2003, 20 (8): 1279-1282 .  
Abstract   PDF(pc) (783KB) ( 361 )
A three-wave resonant interaction for nonlinear excitations created from a continuous-wave background is shown to be possible in a isotropic optical medium with a self-defocusing cubic nonlinearity. Under suitable phase-matching conditions the nonlinear envelope equations for the resonant interaction are derived by using a method of multiple-scales. Some explicit three-wave solitary wave and lump solutions are discussed.
Microstructure on Surface of LiNbO3:Fe Induced by a Single Ultra-Short Laser Pulse
CHENG Guang-Gua, J.D.White, LIU Qing, WANG Yi-Shan, ZHAO Wei, CHEN Guo-Fu
Chin. Phys. Lett. 2003, 20 (8): 1283-1285 .  
Abstract   PDF(pc) (201KB) ( 638 )
A tightly-focused femtosecond Ti:sapphire laser pulse is used to initiate micro-explosions on the surface and internal to an Fe:LiNbO3 crystal. The resulting structure is morphologically different from that induced in an isotropic sample such as fused silica. The regular pyramid and irregular pyramid craters on the surface of the sample are produced at different positions of focal points. The craters suggest vaporization of materials in the process of micro-explosion due to the expansion of high temperature plasma. The embossment pyramids on the surface present the dynamical process of large volume material displacements under high temperature and pressure, and re-crystallization of anisotropy crystal materials.
Enhanced Transmission Stability of Polarization Solitons in Birefringent Fibres with an Optical Phase Conjugator
CHEN Wei-Cheng, XIE Jia-Ning, LU Hong, XU Wen-Cheng
Chin. Phys. Lett. 2003, 20 (8): 1286-1289 .  
Abstract   PDF(pc) (373KB) ( 364 )
An optical phase conjugator is used to enhance transmission stability of polarization solitons in highly birefringent fibres. Two polarization solitons form a breather in fibres with low birefringence firstly and the optical phase conjugator is used to make the spectra of polarization solitons converse, which results in the fact that the polarization soliton along the fast axis is compressed due to the strengthened self-phase modulation effect. Two polarization solitons are compressed further due to the cross-phase modulation effect. The enhanced nonlinear effects make the central peak frequencies of two polarization solitons shift to the larger range in opposite directions so that they trap each other fully to suppress the effect of birefringence.
Tow-Dimensional Micro-grating Formed by Polystyrene Spheres
ZHANG Qi, NI Pei-Gen, MENG Qing-Bo, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2003, 20 (8): 1290-1292 .  
Abstract   PDF(pc) (239KB) ( 508 )
We report a simple method to make two-dimensional plane gratings that can be used as splitters. In the self-assembly process, the colloidal spheres can form single layer square or triangular lattice on a flat surface and in our experiments the triangular lattice is a more common structure. As an incident beam passes through the triangular lattice, it can be split into seven sub-beams, among which six beams have the same density and scattering angle. This grating is not sensitive to the polarization direction of the incident light.
Sinusoidally Chirped Fibre Bragg Gratings
ZHANG Lin, YANG Chang-Xi
Chin. Phys. Lett. 2003, 20 (8): 1293-1295 .  
Abstract   PDF(pc) (449KB) ( 397 )
A sinusoidal chirp structure is proposed to improve the performance of fibre gratings as dispersion compensators and multichannel filters. Nearly ideal reflection spectra from sinusoidally chirped fibre gratings are exhibited. The bandwidth utilization defined as the ratio of -1dB to -30dB bandwidths could be higher than 0.85, even up to 0.985. The sinusoidal chirp can be applied to the sampled fibre gratings to enhance channel uniformity. We demonstrate 141 uniform channels with a 25-GHz spacing for high dense wavelength multiplexing applications.
W0.95Ni0.55 Compressive Strain Thin Film Stripe Window Induced Photoelastic Waveguide Structure in InGaAsP/InP Double Heterostructure
GAO Wen-Sheng, XING Qi-Jiang, YUAN Zhi-Jun, HU Tao
Chin. Phys. Lett. 2003, 20 (8): 1296-1299 .  
Abstract   PDF(pc) (375KB) ( 372 )
We calculate profiles of strain field and dielectric constant variations in InGaAsP/InP double heterostructures beneath a 110-nm-thick W0.95Ni0.55 compressive strain thin-film stripe window. The theoretical results demonstrate the form of the photoelastic waveguide structure in the InGaAsP/InP double heterostructures. The strength of the photoelastic waveguide structure caused by a 20-μm-wide W0.95Ni0.55 compressive strain thin film stripe window is 2.9 x 10-2-0.7 x 10-2 in the depth range from 1μm to 2μm of the InGaAsP/InP double heterostructure. The turning point between waveguide and antiwaveguide is also determined. The theoretical results have demonstrated that the photoelastic waveguide structure may confine well the lateral light of the InGaAsP/InP double heterostructure when the width of the W0.95Ni0.55 compressive strain thin-film stripe window is 5 times greater or 0.93 times smaller than the depth of the photoelastic waveguide structure.
Supercontinuum Generation in Holey Microstructure Fibres with Random Cladding Distribution by Femtosecond Laser Pulses
LI Shu-Guang, HOU Lan-Tian, JI Yu-Ling, ZHOU Gui-Yao
Chin. Phys. Lett. 2003, 20 (8): 1300-1302 .  
Abstract   PDF(pc) (352KB) ( 490 )
It is reported that supercontinuum spectrum from 440 to 1050 nm can be generated in holey microstructure fibres (HMFs) with random cladding distribution by Ti:sapphire femtosecond laser pulses with central wavelength of 800 nm. Based on the method of the effective refractive index and the analogy of step-index fibre, we have calculated the effective mode area and the group velocity dispersion (GVD). It is found that the HMFs have specifically ability of localizing light and controlling GVD. The mechanism of supercontinuum generation in the HMFs with random cladding distribution is that the balance between the GVD and the self-phase modulation in the anomalous dispersion region leads to formation of solitons and fission of high order solitons.
Experimental and Theoretical Evidence for the Existence of Broad Forbidden Gaps in the Three-Component Composite
ZHANG Shu, HUA Jia, CHENG Jian-Chun
Chin. Phys. Lett. 2003, 20 (8): 1303-1305 .  
Abstract   PDF(pc) (347KB) ( 550 )
The influence of localized resonance on the properties of band-gaps of the two-dimensional periodic composite are analysed numerically and experimentally by comparing the two-component phononic crystal with the three-component one. The three-component composite which exhibits localized resonance in the elastically soft coating ring is composed of a square array of coated cylinders embedded in an epoxy resin. The coated cylinders consist of a steel inner core and rubber coating, which has much smaller wave velocity and mass density than the matrix and the inner material. The measured transmission power of the three-component composite drops to the noise level in a broad ultrasonic frequency interval by contrast to the binary composite, which is in good agreement with the calculation using the finite element method.
Collective Oscillation of Relativistic Electrons in Hot Plasma
MA Jin-Yi, QIU Xi-Jun, ZHU Zhi-Yuan
Chin. Phys. Lett. 2003, 20 (8): 1306-1308 .  
Abstract   PDF(pc) (188KB) ( 386 )
The interactions between relativistic electrons in a hot plasma are analysed theoretically. By splitting the electron density fluctuations into the individual part and the collective part, we are concerned with the collective oscillation of the relativistic electrons resulting from the Coulomb interactions. Consequently, we derive the frequency of the hot plasma and the “Debye length” with relativistic modification.
X-Ray and Extreme Ultraviolet Emission from Small-Sized Kr Clusters Irradiated by 150-fs Laser Pulses
WANG Qi, CHENG Yuan-Li, ZHAO Yong-Peng, XIA Yuan-Qin, CHEN Jian-Xin, XIAO Yi-Fan
Chin. Phys. Lett. 2003, 20 (8): 1309-1311 .  
Abstract   PDF(pc) (353KB) ( 437 )
X-ray and extreme ultraviolet (EUV) emission from Kr clusters irradiated by 150-fs laser pulses at the peak laser intensity of 5 x 1015W/cm2 was experimentally investigated. Strong transitions (10 nm-13 nm) from Kr X and Kr IX were observed and some spectral lines from Kr XIII and Kr XIV, which have been predicted to be not produced by optical-field-ionization at the laser intensity used, also appeared. The laser energy absorption and the intensity of x-ray emission started to grow remarkably above the backing pressure of 0.5 MPa and to decrease at the backing pressure of 3 MPa. It is suggested that an optimum backing pressure may exist for Kr clusters heated by 150 fs laser pulses at a certain laser intensity to produce x-ray emission.
Vertical and Smooth, etching of InP by Cl2/CH4/Ar Inductively Coupled Plasma at Room Temperature
SUN Chang-Zheng, ZHOU Jin-Bo, XIONG Bing, WANG Jian, LUO Yi
Chin. Phys. Lett. 2003, 20 (8): 1312-1314 .  
Abstract   PDF(pc) (314KB) ( 1585 )
We study the room-temperature dry etching of InP by inductively coupled plasma (ICP) using Cl2/CH4/Ar mixtures. Etches were characterized in terms of anisotropy and surface roughness by scanning electron microscopy and atomic force microscopy, respectively. It is found that the flow ratio between Cl2 and CH4, ICP power, rf chuck power, and table temperature can greatly influence the etching results. By adjusting etching parameters, vertical sidewall and smooth surface can be obtained simultaneously, together with a moderate etch rate and a good select ratio. The root-mean-square surface roughness is measured to be as low as 0.27 nm. To our knowledge, this is the best result for InP to date. The etch rate is 855 nm/min, and the selectivity ratio over SiO2 is estimated to be higher than 15:1. The stoichiometry of the etched surface has also been investigated by Auger electron spectroscopy. The etched surface is found to manifest a slight P deficiency, and the ratio between P and In reaches the stoichiometric value within about 0.75 nm depth into the surface.
A Reverse Monte Carlo Study on the Structure of Fluid Hg
HONG Xin-Guo, TAMURA Kozaburo
Chin. Phys. Lett. 2003, 20 (8): 1315-1318 .  
Abstract   PDF(pc) (458KB) ( 466 )
The structure of fluid Hg along the liquid-vapour coexistence curve has been modelled by applying the reverse Monte Carlo method to the structural factors recently obtained by x-ray diffraction using synchrotron radiation at SPring-8 [J. Non-Cryst. Solids 312-4 (2002) 284]. The modelling reveals that the distribution of coordination numbers of the first-neighbour shell, P(N), broadens and shifts to lower values at high temperature and high pressure. The main peak of bond angle distributions function P(cos), located at 60°, is rather sharp at room temperature, but it damps and broadens seriously as temperature increases. When approaching the metal-non-metal transition, P(N) of the atoms with shorter bonds broadens and shifts toward lower values noticeably, but little change occurs for that of longer bonds. The changes of the coordination number and the distribution of the atoms with the shorter bond are closely related to the metal-non-metal transition of fluid Hg.
Aligned ZnO Nanofibre Array Prepared by Vapor Transport in Air
XU Chun-Xiang, SUN Xiao-Wei, CHEN Bai-Jun, SUN Chang-Qing, TAY Beng-Kang, LI Sui-Xiang Sean
Chin. Phys. Lett. 2003, 20 (8): 1319-1322 .  
Abstract   PDF(pc) (336KB) ( 442 )
An aligned zinc oxide nanofibre array has been fabricated by heating the mixture of ZnO, Ga2O3, and graphite powders in atmosphere. The ZnO nanofibre showed a uniform size of about 150 nm in diameter and 50μm in length. The nanofibres grew predominantly along one direction. Both x-ray diffraction (XRD) and Raman shift spectra show that the product is composed of ZnO with the typical hexagonal structure. The good crystallinity of these ZnO nanofibres has been verified by photoluminescence spectra with strong UV emission at 287 nm and weak green band emission observed at room temperature. The component of the product was analysed by XRD, Raman shift spectrum, x-ray energy dispersion (EDX) and x-ray photoelectronic energy spectroscopy (XPS). The growth process and the characteristics can be interpreted by vapor-liquid-solid mechanism.
Characteristics of Shallow Electron Traps in Cubic AgCl Microcrystals Doped with K4Fe(CN)6
LI Xiao-Wei, GENG Ai-Cong, YANG Shao-Peng, HAN Li, FU Guang-Sheng
Chin. Phys. Lett. 2003, 20 (8): 1323-1325 .  
Abstract   PDF(pc) (247KB) ( 435 )
A model is proposed to describe the photoelectron decay process at room temperature in cubic AgCl microcrystals homogeneously doped with K4Fe(CN)6. By combining calculation of the kinetic equations resulted from the model with a microwave absorption dielectric-spectrum measuring technique, the capture cross-section and the trap depth of shallow electron traps induced by [Fe(CN)6]4- at room temperature are obtained, which are 3.560 x 10-17cm2 and 0.115 eV, respectively. Based on the two parameters, the optimal doping amount of K4Fe(CN)6 is easily gained to be 2 ppm by computer calculation.
Experimental Studies of Liquid Viscosity in Immiscible Al-In Alloys
LIU Guang-Rong, BIAN Xiu-Fang, SUN Min-Hua
Chin. Phys. Lett. 2003, 20 (8): 1326-1328 .  
Abstract   PDF(pc) (347KB) ( 647 )
The liquid viscosity of immiscible Al-In alloys was measured using an oscillating-cup viscometer. It has been found that the viscosity of Al-In melts changes abruptly at the critical temperature of liquid-liquid phase separation during the cooling process. The experimental data above the temperature of phase separation are fitted to the Arrhenius equation. The fitted results show that the temperature dependence of the viscosity obeys the Arrhenius relationship.
Low Resistivity C54 Phase TiSi2 Films Synthesized by a Novel Two-Step Method
LI Dan-Feng, GU Chang-Zhi, GUO Cai-Xin, YUE Shuang-Lin, HU Chang-Wen,
Chin. Phys. Lett. 2003, 20 (8): 1329-1332 .  
Abstract   PDF(pc) (351KB) ( 961 )
Synthesis and growth properties of the TiSi2 film on a Si (001) substrate are investigated. A novel two-step method is used for deposition of the C54 phase TiSi2 film with low resistivity. The first step is the formation of the C49 phase TiSi2 at a relative low substrate temperature of 400°C, followed by rapid thermal annealing process at 850°C in N2 for the formation of the C54 phase TiSi2 as the second step. Finally, selective wet etching is employed to remove the un-reaction Ti on the surface and the low resistivity C54 TiSi2 film can be obtained. The films deposited under various parameters are evaluated by scanning electron microscopy, x-ray diffraction and the resistivity measurement. Compared with other sputtering technologies used commonly for TiSi2 synthesis, this two-step method has apparent advantages such as the mild synthesis temperature and the high purity of the final product with low resistivity, uniform large area and improving surface roughness. In addition, the film also shows that the low coefficient of resistivity-temperature appears in the temperature range from 20°C to 800°C.
Improved Electric Transport Properties of a Multi-wall Carbon Nanotube
LI Qiu-Hong, WANG Tai-Hong
Chin. Phys. Lett. 2003, 20 (8): 1333-1335 .  
Abstract   PDF(pc) (334KB) ( 449 )
Up to now quantized conductance of the carbon nanotube has only been observed by replacing the tip of a scanning probe microscope with the tube and putting the other end of the tube in a liquid metal [Science 280 (1998) 1744]. Probably cleaning the tube by the liquid metal has improved its quality and gives rise to the quantized conductance. We report on a new method to improve the electric transport properties of a single multi-wall carbon nanotube by Joule heating. Our experiment indicates that the conductance of the tube can be greatly improved just by repeated scanning the bias voltage in vacuum.
Quantum-Confined Stark Effect of Vertically Stacked Self Assembled Quantum Disks
LIU Jin-Long, LI Shu-Shen, NIU Zhi-Chuan, YANG Fu-Hua, FENG Song-Lin
Chin. Phys. Lett. 2003, 20 (8): 1336-1339 .  
Abstract   PDF(pc) (494KB) ( 481 )
We study the electronic energy levels and probability distribution of vertically stacked self-assembled InAs quantum disks system in the presence of a vertically applied electric field. This field is found to increase the splitting between the symmetric and antisymmetric levels for the same angular momentum. The field along the direction from one disk to another affects the electronic energy levels similarly as that in the opposite direction because the two disks are identical. It is obvious from our calculation that the probability of finding an electron in one disk becomes larger when the field points from this disk to the other one.
Dynamical Localization in a Two-Electron Quantum Dot Molecule Biased by a dc Voltage
WANG Li-Min, DUAN Su-Qing, ZHAO Xian-Geng, LIU Cheng-Shi, MA Ben-Kun
Chin. Phys. Lett. 2003, 20 (8): 1340-1343 .  
Abstract   PDF(pc) (460KB) ( 476 )
We study the dynamics of two interacting electrons in a coupled-quantum-dot system with time-dependently external electric field. The numerical results of the two-particle states reveal that the dynamical localization still exists under appropriate dc and ac voltage amplitudes. Such localization is different from the stationary localization phenomenon. Our conclusion is instructive to the field of quantum function devices.
High Efficiency Infrared to Visible Upconversion in Er3+/Yb3+-Doped Lead Halide Tellurite Glass
ZHANG Li-Yan, YANG Jian-Hu, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2003, 20 (8): 1344-1346 .  
Abstract   PDF(pc) (359KB) ( 368 )
Strong upconversion luminescence of Er3+/Yb3+-doped lead halide tellurite glass under 976 nm excitation is demonstrated. Three emission bands centered at 525 nm, 545 nm, and 655 nm resulting from the transitions from the excited states 2H11/2, 4S3/2, and 4F9/2 to the ground state 4I15/2, respectively, are observed even at 60 mW pumping power. The power dependent intensity and the upconversion mechanisms responsible for the luminescences are evaluated and discussed. The obtained results might provide useful information for the developments of upconversion lasers.
Visible Upconversion Emission in Er3+-Doped GeO2-PbO-PbF2 Glass
YANG Zhong-Min, XU Shi-Qing, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2003, 20 (8): 1347-1349 .  
Abstract   PDF(pc) (357KB) ( 653 )
The upconversion fluorescence emission of Er3+-doped 60GeO2-20PbO-20PbF2 glass was experimentally investigated under the pump of 976-nm laser diode. The results reveal the existence of intense emission bands centered around 524, 545, and 657 nm at room temperature. The green emission at 524 and 545 nm is due to the 4S3/2 + 2H11/24I15/2 transition and the red emission of 657 nm originates from the 4F9/24I15/2 transition of Er3+. The quadratic dependence of the green and red emissions on excitation power indicates that a two-photon absorption process occurs under the 976-nm excitation. The excited- state absorption from 4I11/2 and the cross relaxation between two Er3+ ions in the 4I11/2 state contribute to the green emission. The red emission at 657 nm is attributed to the excited-state absorption and cross relaxation processes in the 4I13/2 level as well as the 4S3/2 level nonradiative transition of Er3+.
Optical and Electronic Properties of InGaN/GaN Multi-Quantum-Wells Near-Ultraviolet Lighting-Emitting-Diodes Grown by Low-Pressure Metalorganic Vapor Phase Epitaxy
LI Zhong-Hui, YANG Zhi-Jian, QIN Zhi-Xin, TONG Yu-Zhen, YU Tong-Jun, LU Shu, YANG Hua, ZHANG Guo-Yi
Chin. Phys. Lett. 2003, 20 (8): 1350-1352 .  
Abstract   PDF(pc) (360KB) ( 1333 )
The near-ultraviolet lighting-emitting-diodes (UV-LEDs) with the InGaN/GaN multi-quantum-well (MQW) structure were grown by low-pressure metalorganic vapor phase epitaxy. The double crystal x-ray diffraction revealed a distinct second-order satellite peak. The near-ultraviolet InGaN/GaN MQW LEDs have been successfully fabricated to emit at 401.2 nm with narrow FWHM of 14.3 nm and the forward voltage of 3.6 V at 20 mA injection current at room temperature. With increasing forward current from 10 mA to 50 mA, the red-shift of the peak wavelength was observed due to the band-gap narrowing caused by heat generation.

Fermion Bound States Around Skyrmions in Doped Antiferromagnets
KOU Su-Peng
Chin. Phys. Lett. 2003, 20 (8): 1353-1355 .  
Abstract   PDF(pc) (206KB) ( 456 )
We show the skyrmion effects in doped antiferromagnets for the uniform flux phase. The low energy effective theory of the t' - J model can be mapped onto the massive quantum electrodynamics. There exist Fermion bound states around skyrmions. For each sublattice, there exist induced fractional fermion numbers around the skyrmions. The total induced fermion number is zero due to the “canceling effect”between two sublattices with opposite charges.

Growth of MgB2 Thin Films by Chemical Vapor Deposition Using B2H6 as a Boron Source
WANG Shu-Fang, ZHU Ya-Bin, LIU Zhen, ZHOU Yue-Liang, ZHANG Qin, CHEN Zheng-Hao, LU Hui-Bin, YANG Guo-Zhen
Chin. Phys. Lett. 2003, 20 (8): 1356-1358 .  
Abstract   PDF(pc) (362KB) ( 546 )
Superconducting MgB2 thin films were grown on single crystal Al2O3 (0001) by chemical vapor deposition using B2H6 as a boron source. MgB2 film was then accomplished by annealing the boron precursor films in the presence of high purity magnesium bulk at 890°C in vacuum. The as-grown MgB2 films are smooth and c-axis-oriented. The films exhibit a zero-resistance transition of about 38 K with a narrow transition width of 0.2 K. Magnetic hysteresis measurements yield the critical current density of 1.9 x 107A/cm2 at 10 K in zero field.
Temperature-Induced Magnetization Reorientation in GdFeCo/TbFeCo Exchange-Coupled Double Layer Films
WANG Xian-Ying, ZHANG Yue-Pin, LI Zuo-Yi, SHEN De-Fang, GAN Fu-Xi
Chin. Phys. Lett. 2003, 20 (8): 1359-1361 .  
Abstract   PDF(pc) (369KB) ( 487 )
GdFeCo/TbFeCo exchange-coupled double-layer (ECDL) films used for center aperture type magnetically induced super resolution were investigated through experiments and theoretical calculation. The ECDL films were prepared by the magnetron sputtering method. Polar Kerr effect measurements showed that magnetization reorientation occurred in the GdFeCo layer with the temperature rising, which was subsequently analysed by the micromagnetic calculation based on the mean-field theory and a continuum model. Theoretical analysis is in agreement well with the experimental results.
Photon-Storage in Optical Memory Cells Based on a Semiconductor Quantum Dot-Quantum Well Hybrid Structure
BIAN Song-Bao, TANG Yan, LI Gui-Rong, LI Yue-Xia, YANG Fu-Hua, ZHENG Hou-Zhi, ZENG Yi-Ping
Chin. Phys. Lett. 2003, 20 (8): 1362-1365 .  
Abstract   PDF(pc) (436KB) ( 396 )
We report a new type of photonic memory cell based on a semiconductor quantum dot (QD)-quantum well (QW) hybrid structure, in which photo-generated excitons can be decomposed into separated electrons and holes, and stored in QW and QDs respectively. Storage and retrieval of photonic signals are verified by time-resolved photoluminescence experiments. A storage time in excess of 100 ms has been obtained at a temperature of 10 K while the switching speed reaches the order of ten megahertz.
Thermal Annealing of SiO2 Fabricated by Flame Hydrolysis Deposition
ZHANG Le-Tian, XIE Wen-Fa, WU Yuan-Da, XING Hua, LI Ai-Wu, ZHENG Wei, ZHANG Yu-Shu
Chin. Phys. Lett. 2003, 20 (8): 1366-1368 .  
Abstract   PDF(pc) (279KB) ( 1741 )
Amorphous SiO2 films were fabricated on Si substrates by flame hydrolysis deposition as buffer layers applied in the planar optical waveguides. Then the Si wafers with the porous particles were put into electric furnace annealing at different temperatures for consolidation in air. The products were characterized by x-ray diffraction, x-ray
photoelectron spectroscopy, atomic force microscopy, and variable angle spectroscopic ellipsometry. It was found that different structures at different annealing temperatures were obtained. When the annealing temperature arrives at 1400°C, SiO2 is continuous and dense and the refractive index at 1550 nm is 1.4564, which is highly desirable.
Preparation of Silver-Coated Polystyrene Composite Particles
CHEN Zhuo, ZHAN Peng, ZHANG Jian-Hui, WANG Zhen-Lin, ZHANG Wei-Yi, MIN Nai-Ben
Chin. Phys. Lett. 2003, 20 (8): 1369-1371 .  
Abstract   PDF(pc) (292KB) ( 865 )
We report a feasible approach to the preparation of monodispersed metal-shell composite microspheres based on a combination of surface reaction and surface seeding techniques. The method was implemented for coating polystyrene (PS) spheres with silver shell having a variable thickness by controlling the amount of reagents in the reaction procedure. These composite spherical particles in dimensions of the submicrometer range may become attractive building blocks for the creation of metallo-dielectric photonic band gap materials when they are organized into crystals.
Surface Plasmon-Assisted Excitation of Atomic Visible Light Spectral Lines in the Impact of Highly Charged Ions 126Xeq+ on Solid Surfaces
ZHANG Xiao-An, ZHAO Yong-Tao, LI Fu-Li, YANG Zhi-Hu, XIAO Guo-Qing, ZHAN Wen-Long
Chin. Phys. Lett. 2003, 20 (8): 1372-1375 .  
Abstract   PDF(pc) (511KB) ( 615 )
We measured the visible light spectral lines of sputtering atoms from solid surfaces of Al, Ti, Ni, Ta and Au which are impacted by 150 keV 126Xeq+ (6 ≤ q ≤ 30). It is found that intensities of the light spectral lines are greatly and suddenly enhanced when the charge state of the ion is raised up to a critical value. If assuming that potential energy released from the incident ion due to capturing one electron is enough to excite a surface plasmon, we can estimate the critical charge states and obtain the results very well consistent with the measurements for the above mentioned target materials. This means that a surface plasmon induced by one electron capture can enhance the excitation of atomic visible light spectral lines in the impact of a highly charged ion on a solid surface.
Room-Temperature AlGaAsSb/InGaAsSb Multi-Quantum-Well Lasers with High Characteristic Temperature
ZHANG Xiong, LI Ai-Zhen, ZHENG Yan-Lan, XU Gang-Yi, QI Ming
Chin. Phys. Lett. 2003, 20 (8): 1376-1378 .  
Abstract   PDF(pc) (307KB) ( 456 )
Planar structure AlGaAsSb/InGaAsSb lasers operated at 2.01μm with high characteristic temperature have been fabricated from a strained multiple quantum-well heterostructure. To decrease the free carrier induced absorption of optical mode in the mid-infrared, we design a broaden waveguide layer in the laser structures to decrease the optical mode distribution in the heavy doped cladding layer, therefore it can be absorbed easily. To enhance the characteristic temperature of laser diodes, Al constituent up to 80% was applied to the AlGaAsSb cladding layer. The laser diodes with a threshold current density of 1.8 kA/cm2 can be pulsed operating up to 340 K. The characteristic temperature T0 is 125 K and 90 K in the operating temperature ranges 170-220 K and 230-340 K, respectively. The emission spectrum shows a multiple longitudinal mode.
A Transition from Eutectic Growth to Dendritic Growth Induced by High Undercooling Conditions
LÜ, Yong-Jun, WEI Bing-Bo
Chin. Phys. Lett. 2003, 20 (8): 1379-1382 .  
Abstract   PDF(pc) (402KB) ( 901 )
Cu-8 wt.%Al eutectic alloy was undercooled by up to 187 K (0.14TE) using a drop tube technique. The crystal growth and phase selection mechanisms were investigated during containerless rapid solidification. It is found that the microstructural morphology is characterized by lamellar eutectic growth at small undercoolings. However, if the liquid alloy is undercooled by more than 25 K, eutectic growth will be suppressed completely and the dendritic growth of (Cu) solid solution dominates its solidification process. When the undercooling exceeds 153 K, a microstructural transition from coarse dendrite to equiaxed dendrite takes place.
Heterogeneous Nucleation Induced by Capillary Wave During Acoustic Levitation
LÜ, Yong-Jun, XIE Wen-Jun, WEI Bing-Bo
Chin. Phys. Lett. 2003, 20 (8): 1383-1386 .  
Abstract   PDF(pc) (360KB) ( 582 )
The rapid solidification of acoustically levitated drops of Pb-61.9 wt.%Sn eutectic alloy is accomplished. A surface morphology of spreading ripples is observed on a sample undercooled by 15 K. The ripples originate from the center of sample surface, which is also the heterogeneous nucleation site for eutectic growth. The Faraday instability excited by forced surface vibration has brought about these ripples. They are retained in the solidified sample if the sound pressure level exceeds the threshold pressure required for the appearance of capillary waves. Theoretical calculations indicate that both the pressure and displacement maxima exist in the central part of a levitated drop. The pressure near the sample center can promote heterogeneous nucleation, which is in agreement qualitatively with the experimental results.
Apparatus for Real-Time Measurement of Stress in Thin Films at Elevated Temperatures
AN Bing, ZHANG Tong-Jun, YUAN Chao, CUI Kun
Chin. Phys. Lett. 2003, 20 (8): 1387-1389 .  
Abstract   PDF(pc) (349KB) ( 554 )
As a prerequisite of biaxial zero creep experiments, a novel sensitive apparatus is developed for real-time film-stress measurement during thermal cycles. The optical sensor with a fixed multi-beam emitter and a CCD detector is investigated during an annealing process of Ag/Co multilayer thin film. The monitoring plots of stress as functions of temperature and time demonstrate the capability of this set-up. The typical sensitivity for measuring the wafer curvature radius is 2km.
Scaling in Aggregation Process with a Kernel Related to the Reaction Activities
KE Jian-Hong, LIN Juan-Juan, LIN Zhen-Quan
Chin. Phys. Lett. 2003, 20 (8): 1390-1392 .  
Abstract   PDF(pc) (194KB) ( 307 )
We study the kinetics of a reversible aggregation model in which an aggregation reaction occurs between any two clusters and the fragmentation of the larger clusters occurs simultaneously. By investigating the mean-field rate equation of the process with a kernel related to the reaction activities we obtain the asymptotic solution of the cluster-mass distribution. It is found that the kinetic evolution behaviour of the clusters depends crucially on the details of the rate kernel. The cluster-mass distribution in the irreversible aggregation system obeys a conventional scaling law; while for the reversible case, the conventional scaling description of the cluster-mass distribution breaks down and the system falls in a modified scaling region.
Structural Properties of US Flight Network
CHI Li-Ping, WANG Ru, SU Hang, XU Xin-Ping, ZHAO Jin-Song, LI Wei, CAI Xu
Chin. Phys. Lett. 2003, 20 (8): 1393-1396 .  
Abstract   PDF(pc) (452KB) ( 696 )
We analyse the directed, weighted and evolutionary US flight network, in which vertices are the airports and the flights connecting two airports represent the edges. It is shown that such a network displays two important features recently found in small-world networks. First, the average shortest-path length is 2.4 s, the clustering coefficient of the entire network, 0.618, is greatly larger than that of the random networks with the same N (system size) and (average degree), 0.065. We study the detailed flight information both in a week and on a whole. In both the cases, using the Pareto distributions, we find the degree distributions follow two-segment power laws. The weight distributions have power-law tails with the exponents of around 2, and the clustering coefficient distributions follow linear distributions.
Static Displacement due to Seismic Moment Tensor Sources in a Layered Half-Space
HE Yu-Mei, WANG Wei-Min, YAO Zhen-Xing
Chin. Phys. Lett. 2003, 20 (8): 1397-1400 .  
Abstract   PDF(pc) (545KB) ( 452 )
The expressions for static displacements on the surface of a layered half-space due to static point moment tensor source are given in terms of the generalized reflection and transmission coefficient matrix method. The validity and precision of the new method is illustrated by comparing the consistency of our results with the analytical solution given by Okada's code employing the same point source and homogenous half-space model. The computed vertical ground displacement using the moment tensor solution of the Lanchang-Gengma earthquake displays considerable difference with that of a double couple component. The effect of a soft layer at the top of the homogenous half-space on a shallow normal-faulting earthquake is also analysed. Our results show that more seismic information would be obtained utilizing seismic moment tensor source and layered half-space model.
Ionospheric Feedback Instability in the Coupling of Magnetosphere-Ionosphere
WANG Xu-Yu, CAO Jin-Bin
Chin. Phys. Lett. 2003, 20 (8): 1401-1404 .  
Abstract   PDF(pc) (200KB) ( 399 )
The ionospheric feedback instability is discussed by using the
conductivity argument. We give an exact quantitative description to show that the free energy for this instability comes from the reduction of the Joule dissipation produced by the pre-existing convection electric field through self-consistent changes in ionization and conductivity due to Alfvénic perturbations in the ionosphere. By the over-reflection of Alfvén waves, the energy in the active ionosphere is pumped into the magnetosphere, which is contrary to the usual case whereby energy carried by Alfvén waves is deposited in the ionosphere by Joule dissipation. The ionospheric feedback enhances the electron E x B drift. The electron conductivity is controlled by the ion Perdersen conductivity rather than by the electrons Pedersen conductivity. We also provide a qualitative theoretical explanation to the intense aurora favoured by a lower ambient ionospheric conductivity in the ionospheric feedback instability.
Refractive Interstellar Scintillation for Flux Density Variations of Two Pulsars
ZHOU Ai-Zhi, WU Xin-Ji, , A. Esamdin,
Chin. Phys. Lett. 2003, 20 (8): 1405-1408 .  
Abstract   PDF(pc) (485KB) ( 313 )
The flux density structure functions of PSRs B0525+21 and B2111+46 are calculated with the refractive interstellar scintillation (RISS) theory. The theoretical curves are in good agreement with observations [Astrophys. J. 539 (2000) 300] (hereafter S2000). The spectra of the electron density fluctuations both are of Kolmogorov spectra. We suggest that the flux density variations observed for these two pulsars are attributed to refractive interstellar scintillation, not to intrinsic variability.

A Search for Extremely Young Stellar Objects
WU Yue-Fang, WANG Jun-Zhi, WU Jing-Wen
Chin. Phys. Lett. 2003, 20 (8): 1409-1412 .  
Abstract   PDF(pc) (617KB) ( 499 )
We have observed 22 sources in 13CO and C18O J = 1 - 0 lines with a 13.7-m telescope at Qinghai station of PMO, NAOC. The samples were chosen with new criteria so that the sources are much redder and fainter than those chosen before. All the 22 sources were detected with the pair lines of 13CO and C18O and are suitable for analysing star formation except one multiple emission source IRAS 20300+3909. Physical parameters were derived from the local thermodynamic equilibrium assumption. The excitation temperature and column density of C18O are 13 K and 1.5 x 1015cm-2, respectively, on the average. Eleven sources in the samples have line widths larger than 3 km/s. The IRAS color indices are larger than those of class-0 objects. The intermediate and far infrared energy distributions show that the emission peaks of the samples fall in far infrared or longer wavelengths except IRAS 20149+3955, indicating that they may be very young stellar objects. Analyses of line widths and bolometric luminosity show that seven of those sources may be extremely young high or intermediate mass stellar objects.
66 articles