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Volume 18 Issue 10
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Original Articles
A Coupled Computational Scheme on Thermal and Phase Structures of Subducting Slabs
JING Zhi-Cheng, NING Jie-Yuan
Chin. Phys. Lett. 2001, 18 (10): 1297-1300 .  
Abstract   PDF(pc) (369KB) ( 440 )
The thermodynamic processes underwent by olivine, the chief mineral of subducting slabs, are important in studying the mechanisms of deep-focus earthquakes and the interaction between slabs and the surrounding mantle. We proposed a modified coupling scheme to calculate slabs' thermal and phase structures, which presents a high computational accuracy at an accessible CPU expense. Using the new code of computation, we calculated the thermal and phase structures of the Kurile subduction zone.

Three-Particle Entangled States of Continuum Variables
FAN Hong-Yi
Chin. Phys. Lett. 2001, 18 (10): 1301-1304 .  
Abstract   PDF(pc) (199KB) ( 441 )
We introduce three-particle entangled state of continuum variables, which is a generalization of Greenberger-Horne-Zeilinger entangled states composed of discrete states. The completeness relation and partly non-orthonormal property of such states are proved. Their Schmidt decomposition is manifestly shown and their generation is briefly discussed.
A Two-Party Probabilistic Communication Complexity Scenario via Werner States
XUE Peng, LI Chuan-Feng, GUO Guang-Can
Chin. Phys. Lett. 2001, 18 (10): 1305-1307 .  
Abstract   PDF(pc) (200KB) ( 423 )
We propose a probabilistic two-party communication complexity scenario with a prior Werner state and analyse the communication abilities of quantum correlations (entanglements) and classical correlations. This process can be used as an entanglement monotone of Werner states.
Generation of Maximally Entangled Bell State in a Coupled Quantum Dot
ZHANG Ping, FAN Wen-Bin, DUAN Su-Qing, ZHAO Xian-Geng
Chin. Phys. Lett. 2001, 18 (10): 1308-1311 .  
Abstract   PDF(pc) (351KB) ( 299 )
We show how the two interacting electrons in a field-driven coupled quantun dot can be used to prepare maximally entangled Bell states. The time durations of oscillatory electric field for producing and maintaining such highly entangled states are identified by both analytic and exact numerical solution of the quantum dynamical equations.
Total Quantum Statistical Entropy of Reissner-Nordstrom Black Holes: Scalar Field Case
XU Dian-Yan
Chin. Phys. Lett. 2001, 18 (10): 1312-1315 .  
Abstract   PDF(pc) (208KB) ( 286 )
The total quantum statistical entropy of Reissner-Nordstrom (RN) black holes is evaluated. The spacetime of the black holes is divided into three regions-region 1,( r > ro), region 2, ( ro > r > ri), and region 3, (ri > r > 0 ), where ro is the radius of the outer event horizon, and ri is the radius of the inner event horizon. The total quantum statistical entropy of RN black holes is S = S1 + S2 + S3, where Si, ( i = 1,2,3) is the entropy, contributed by region Si (i = 1,2,3). The detailed calculation shows that S2 ≈ 0. S1 = (π2/45) [ kbAo2β3], S3 = -(π2/45) [kbAi2β3], where Ao and Ai are, respectively, the area of the outer and inner event horizons. Thus, as ri approaches ro, in the extreme case the total quantum statistical entropy of RN black holes approaches zero.
Coupled Solitons in Alternating Heisenberg Ferromagnetic Chains with a Small Magnon Band Gap
ZHU Shan-Hua, HUANG Guo-Xiang
Chin. Phys. Lett. 2001, 18 (10): 1316-131 .  
Abstract   PDF(pc) (213KB) ( 389 )
The coupled soliton excitations in an alternating Heisenberg ferromagnetic chain with a small magnon band gap are considered. Based on a quasi-discrete multiple scale approach, a set of coupled mode equations is derived which describe the dynamics of strongly coupled acoustic upper cut-off and optical lower cut-off modes. Coupled magnetic band gap soliton solutions are explicitly provided and their frequency properties are discussed.
Superdeformed Bands with ΔI = 4 Bifurcation of the Odd-A Nuclei in the A ~ 190 Region
LIU Yu-Xin, , ZHOU Jian-Hang, WANG Jia-Jun
Chin. Phys. Lett. 2001, 18 (10): 1319-1322 .  
Abstract   PDF(pc) (393KB) ( 327 )
The γ-ray energy (Eγ) spectra of the superdeformed(SD) bands of odd-A nuclei in the A ~ 190 mass region are investigated systematically. It is found that ΔI = 4 bifurcation exists in the SD bands. Within the supersymmetry scheme including many-body interactions and a perturbation possessing the SO(5) (or SU(5)) symmetry on the rotational symmetry, the Eγ spectra, dynamical moments of inertia and Eγ difference δ4Eγ(I) of these bands are evaluated. Quantitative good results are obtained. They show that the scheme is powerful to describe the ΔI = 4 bifurcation. The ΔI = 4 bifurcation may then come from the perturbation holding the SO(5) (or SU(5)) symmetry on the rotation. In a microscopic point of view, the ΔI = 4 bifurcation may be result from the combination among the β-phonon, γ-phonon and the rotation.
Search for Signature Inversion in πi13/2 vi13/2 Band in Odd-Odd 178Ir
ZHANG Yu-Hu, T. Hayakawa, M. Oshima, Y. Toh, J. Katakura, Y. Hatsukawa, M. Matsuda, N. Shinohara, T. Ishii, H. Kusakari, M. Sugawara, T. Komatsubara, K. Furuno
Chin. Phys. Lett. 2001, 18 (10): 1323-1326 .  
Abstract   PDF(pc) (761KB) ( 426 )
Search for the πi13/2 vi13/2 band in 178Ir have been conducted through the 152Sm(31P,5nγ)178Ir reaction and the excitation functions, x-γ and γ-γ-t coincidence measurements. Five rotational bands have been newly identified. The low-spin signature inversion in the πi13/2 vi13/2 band has been confirmed by the observations of linking transitions and signature crossing at I = 25.5ħ. The inversion phenomenon in πh11/2 vi13/2, πh9/2 vi13/2, and πh13/2 vi13/2 structures in 178Ir provides a unique testing ground for different theoretical interpretations.
Spectra Statistics for the Odd-Odd Nucleus 86Nb
ZHENG Ren-Rong, ZHU Shun-Quan, CHENG Nan-Pu,
Chin. Phys. Lett. 2001, 18 (10): 1327-1330 .  
Abstract   PDF(pc) (462KB) ( 377 )
The energy levels of the odd-odd nucleus 86Nb at low spins are calculated by using quasi-particles plus a rotor model. The distribution of the nearest-neighbor spacing and the spectral rigidity are studied. We find that the chaotic degree of the energy spectra increases with the increasing spin and reaches a maximum at I = 10; then it decreases gradually for the spins above I = 10. The recoil term in the model Hamiltonian makes the energy spectra slightly regular. The Coriolis force, however, makes the spectra chaotic and plays a major role in the spectral statistics of the odd-odd nucleus 86Nb.
Intermediate Mass Dilepton Production in a Chemically Equilibrating Quark-Gluon Matter
HE Ze-Jun, ZHOU Wen-Jie, ZHANG Jia-Ju, LIU Bo
Chin. Phys. Lett. 2001, 18 (10): 1331-1333 .  
Abstract   PDF(pc) (267KB) ( 317 )
Dilepton production during the chemical equilibration of the quark-gluon matter with the finite baryon density has been studied. We find that due to slowing down of the cooling rate and high initial temperature of the quark-gluon matter produced at RHIC energies, the quark phase contribution to dileptons with intermediate masses is significantly heightened and is much larger than that calculated by the evolution of thermodynamic equilibrium system. The latter has shown an enhancement of intermediate mass dileptons from the quark phase. Therefore, such an enhancement of dileptons should be a signature for the quark-gluon matter formation.
Relativistic Channel Theory: Abnormal Fine Structures of n2D Rydberg States for Alkali Atoms
XIA Dan, LI Jia-Ming,
Chin. Phys. Lett. 2001, 18 (10): 1334-1336 .  
Abstract   PDF(pc) (203KB) ( 407 )
Based on relativistic channel theory, we have studied the fine structures of n2D Rydberg states for alkali atoms, and explained the abnormal fine structures owing to the competition effect of the spin-orbit interaction and the relativistic effect of the exchange interactions between the excited electron and the core electrons.
Laser Amplification Mechanism in an Nd3+-Doped Polymer Optical Fiber
Chin. Phys. Lett. 2001, 18 (10): 1337-1340 .  
Abstract   PDF(pc) (334KB) ( 492 )
The Judd-Ofelt theory was applied to optical-absorption transitions in an Nd3+-doped polymer optical fiber to obtain intensity parameters (Ω2 = 0.83 x 10-20cm2, Ω4 = 1.64 x 10-20cm2, Ω6 = 4.04 x 10-20cm2) the radiative lifetime (371 μs) and quantum efficiency (0.73) of the 4G5/2level, from which we found that the transition probability from 4G5/2 to 4I9/2(Aij = 1995.7 s-1) is higher than others. Thus, in the polymer system, the traditional four-level laser system for the Nd3+ was substituted by a three-level system. Furthermore, we have calculate the emission cross section(σeij =2.45 x 10-21cm2), and solved the differential equations of the single-pass gain. In comparsion with the case of the inorganic optical fiber, an increased saturated intensity is observed.
Observation of Hyperfine Structure of the 23II1g State in Na2
WANG Wei-Sheng, SHANG Jian-Yuan, SUN Zhen-Rong, WANG Zu-Geng
Chin. Phys. Lett. 2001, 18 (10): 1341-1343 .  
Abstract   PDF(pc) (366KB) ( 264 )
We reported the results of the hyperfine structure (HFS) of the 23II1g state in Na2. The relative ultraviolet and visible fluorescence spectra of molecular sodium were measured by means of Doppler-free two-photon spectroscopy technique. The HFS of the 23II1g(v = 78, J = 37, Ω = 1) level was first observed and its HFS constant was measured to be C = -4.92±0.26MHz. The intermediate enchancing and upper energy levels were labled by the experimental and theoretical methods.

Experimental Study of Single-Electron Detachment Cross Sections of Cu- in Collision with He
LI Guang-Wu, ZHANG Xue-Mei, WU Shi-Min, LU Fu-Quan, PENG Xian-Jue, YANG Fu-Jia
Chin. Phys. Lett. 2001, 18 (10): 1344-1345 .  
Abstract   PDF(pc) (276KB) ( 453 )
The single-electron detachment cross-sections of Cu- in collision with He have been measured in the range of 10-30keV by a growth rate method. The typical value of the cross section is 7.63 x 10-16cm2 at an energy 20keV. The experimental uncertainty of the results is about ±8%.
A Vector Theory on Spatial Solitons in Kerr Media
SHE Wei-Long, ZHENG Xi-Guang, NI Xiao-Hui, GUO Hong
Chin. Phys. Lett. 2001, 18 (10): 1346-1349 .  
Abstract   PDF(pc) (350KB) ( 446 )
A new vector theory which concerns the necessary and sufficient conditions of the self-trapping of a linearly polarized light beam in Kerr media is presented after generalization of Fermat's principle. It is rigidly proven under these conditions that 1+1-dimensional spatial solitons can exist in Kerr media but 2+1-dimensional solitons cannot. A new form of the general equation for 1+1-dimensional solitons in Kerr media is put forward and some of its solutions have been obtained.
Photoluminescence Study of CdSexS1-x Quantum Dots in a Glass Spherical Microcavity
JIA Rui, JIANG De-Sheng, TAN Ping-Heng, SUN Bao-Quan, ZHANG Jing-Bo, LIN Yuan
Chin. Phys. Lett. 2001, 18 (10): 1350-1352 .  
Abstract   PDF(pc) (650KB) ( 448 )
The photoluminescence (PL) of CdSexS1-x semiconductor quantum dots (QDs) in a glass spherical microcavity is investigated. The CdSexS1-x semiconductor clusters embedded in glass matrix are fabricated by using the heat treatment method. Periodical structures consisted of sharp spectral lines are observed in the PL spectra of CdSexS1-xQDs, which can be well explained by the coupling with whispering gallery modes of the spherical microcavity based on the Mie scattering theory.
Optimization of Drive Pulse Configuration for a High-Gain Transient X-Ray Laser at 19.6nm
LU Xin, LI Ying-Jun, ZHANG Jie
Chin. Phys. Lett. 2001, 18 (10): 1353-1355 .  
Abstract   PDF(pc) (581KB) ( 480 )
An Ne-like transient collisional excitation x-ray laser at 19.6 nm ( J = 0 → 1, 3p → 3s) was investigated numerically using a sophistic hydrodynamic code for a 100 μm thick Ge planar target irradiated by a nano-second prepulse followed by a picosecond main optical laser pulse. The simulations indicate that for a given peak intensity, the main pulse has an optimal duration to generate the maximum effective gain. An effective gain as high as 200 cm-1 was obtained for the optimized drive pulse configuration.
Thermal Effect in KTP Crystals During High Power Laser Operation
YAO Jian-Quan, YU Yi-Zhong, CHEN Jin, ZHANG Fan, WANG Peng, WANG Tao, ZHANG Bai-Gang
Chin. Phys. Lett. 2001, 18 (10): 1356-1359 .  
Abstract   PDF(pc) (487KB) ( 993 )
We report the theoretical and experimental studies of the thermal effect of the KTP crystal during high power operation. From the dependence of the refractive index temperature coefficients on wavelength, the dependence of the optimum phase-matching angles on temperature is derived. In the experiment, the angle of the frequency-doubled KTP crystal is tilted to compensate for the thermal effect and to obtain ΔФ = 0.7°when the green laser output power is 30W and the KTP crystal temperature about 80°C. We obtained the highest stable output power greater than 40W with an L-shape flat-flat intracavity frequency-doubled Nd:YAG laser. The experimental results are very consistent with the theoretical analysis.
Adiabatic Enhanced Compression of Ultrashort Pulses in Fibers with Slowly Decreasing Dispersion
XU Wen-Cheng, ZHANG Shu-Min, LUO Ai-Ping, CHEN Wei-Cheng, LIAO Chang-Jun, LIU Song-Hao, WU Jian, LOU Cai-Yun, GAO Yi-Zhi
Chin. Phys. Lett. 2001, 18 (10): 1360-1362 .  
Abstract   PDF(pc) (348KB) ( 472 )
We investigate the adiabatic enhanced compression of ultrashort pulses from a distributed feedback laser operated at 1550nm in fibers with slowly decreasing dispersion (FSDD). High-quality pulse compressions from 4.4ps down to 1.1ps in a 100m FSDD and from 4.4ps down to 830fs in a 500m FSDD are obtained. The Raman self-frequency shift of femtosecond pulse in the compression is observed. Theoretical analyses are in good agreement with experimental results.
Guided Modes in a Two-Dimensional Photonic Crystal Waveguide Consisting of Nearly-Free-Electron Metals
XIAO San-Shui, HE Sai-Ling, ZHUANG Fei
Chin. Phys. Lett. 2001, 18 (10): 1363-1365 .  
Abstract   PDF(pc) (424KB) ( 431 )
Guided modes in a two-dimensional photonic crystal consisting of nearly-free-electron metals are considered. To avoid time-consuming convolution, modified time-stepping formulas are used in a finite-difference time-domain approach. The guided modes in the metallic photonic crystal waveguide are related to those in a conventional metallic waveguide. A cut-off frequency exists, and consequently a mode gap at low frequencies in the photonic crystal metallic waveguide.
Space and Time Coherence of Acoustic Field in Shallow-Water
GUO Liang-Hao, GONG Zai-Xiao, Wu Li-Xin
Chin. Phys. Lett. 2001, 18 (10): 1366-1368 .  
Abstract   PDF(pc) (385KB) ( 811 )
New experimental measurements of signal coherence in shallow water are presented. For signals with low frequencies of about 500 Hz in an iso-velocity shallow water with slit-sand bottom and a water depth of about 45 m, the vertical coherence has no distinct depth dependence at ranges of 18.5, 55.5, and 92.5 km, but it has obvious range dependence. The horizontal coherence lengths are all greater than 40 wavelengths, and the time coherence lengths are all greater than 510s at these ranges. These experimental results show that low-frequency acoustic field has strong spatial coherence and temporal stability in iso-velocity shallow water.
Ultrasonic Properties of the MgB2 Superconductor
LI Shao-Chun, WANG Ru-Ju, LI Feng-Ying, LIU Zhen-Xing, ZHU Jia-Lin, YU Ri-Cheng, JIN Chang-Qing
Chin. Phys. Lett. 2001, 18 (10): 1369-1370 .  
Abstract   PDF(pc) (279KB) ( 411 )
The sound velocities of longitudinal and shear waves are measured on polycrystalline MgB2 superconductor with Tc of 39K. The specimen used in the experiments is pressed and heated using the MgB2 powder. The elastic moduli, Debye temperature and specific heat at room temperature are obtained based on sound velocity data. The results indicate that the velocities are much higher than those in the usual materials, while elastic constants remain reasonably soft, which may be due to the high transition temperature of the MgB2 superconductor.
Viscous Fingering Patterns and Fractal Nature in Two-Dimension Porous Media
TIAN Ju-Ping, YAO Kai-Lun,
Chin. Phys. Lett. 2001, 18 (10): 1371-1373 .  
Abstract   PDF(pc) (660KB) ( 455 )
A new computer model of viscous fingering (VF) in a porous medium is presented. The simulation results show that the VF pattern is in agreement with the experimental results. The simulation on the sweep efficiency also agrees with experiment results. The surface fractal dimension as a function of viscous ratio is found.
Effects of Polarization on Super-hot Electron Generation in Femtosecond Laser-Plasma Interaction
ZHANG Ping, LIANG Tian-Jiao, CHEN Li-Ming, LI Yu-Tong, CHEN De-Bao, LI Zu-Hao, HE Jing-Tang, WEI Zhi-Yi, WANG Long, TAMG Xiao-Wei, ZHANG Jie
Chin. Phys. Lett. 2001, 18 (10): 1374-1376 .  
Abstract   PDF(pc) (618KB) ( 939 )
The effects of laser polarization on super-hot electron (>100 keV) generation have been studied in the interaction of femtosecond laser light (800nm, 150fs, 6 x with a pre-formed plasma from a slab Cu target. For p-polarized laser pulses, high-energy γ-rays of the energy ~ 400keV were detected, the electron temperatures deduced from the γ-ray spectra were 66 and 52keV, respectively, in normal and reflective directions of the solid target, and hot electrons were emitted out of the plasma mainly in the normal direction. In contrast, there were nearly no γ-rays >100keV found for s-polarized laser pulses, The hot electron temperature was 26keV and the emission of hot electrons was parallel to the laser field. The superposition of resonant field with electrostatic field excited by escaping electrons may contribute to the high-energy γ-ray or super-hot electron (> 100keV) generation.
Observation of Thomson Scattering off Entropy Waves in a Laser-Produced Plasma
ZHENG Jian, BAI Bo, LIU Wan-Dong, YU Chang-Xuan, JIANG Xiao-Hua, YUAN Xiao-Dong, LI Wen-Hong, ZHENG Zhi-Jian
Chin. Phys. Lett. 2001, 18 (10): 1377-1379 .  
Abstract   PDF(pc) (610KB) ( 454 )
A new feature in the Thomson scattering spectrum is observed from a laser-produced aluminum plasma, which may be the Thomson
scattering off entropy waves in the plasma. Such a feature is only observable when the energy of the heater beam is low enough.
Self-Organized Filaments in Dielectric Barrier Discharge in Air at Atmosphere Pressure
DONG Li-Fang, LI Xue-Chen, YIN Zeng-Qian, QIAN Sheng-Fa, OUYANG Ji-Ting, WANG Long
Chin. Phys. Lett. 2001, 18 (10): 1380-1382 .  
Abstract   PDF(pc) (822KB) ( 1015 )
The self-organized filament pattern created by dielectric barrier discharges in air at atmosphere pressure is investigated experimentally. The density and dimension of filament are analysed quantitatively. The experimental results show that the distance of neighbour filaments decreases with the increasing applied voltage or with the decreasing width of the gas gap, Also, the diameter of filament also decreases with the increasing applied voltages or with the decreasing width of gas gap.

Microstructure Transition of Liquid Metal Al During Heating and Cooling Processes
LIU Rang-Su, LIU Hai-Rong, ZHENG Cai-Xing, LU Xiao-Yong, PENG Ping, LI Ji-Yong
Chin. Phys. Lett. 2001, 18 (10): 1383-1385 .  
Abstract   PDF(pc) (347KB) ( 428 )
A simulation study of the transition properties of microstructures of liquid metal Al during heating and cooling processes has been performed by the molecular dynamics method. It is demonstrated that in the temperature range of 1800--350K, the 1551, 1541, 1431, 1311, 1321, and 1422 bond types represented by the Honeycutt-Andersen index play an important role. Especially, the 1551 bond type plays a leading role and is the decisive factor for the change of the second peak of the pair distribution function from a smooth sine peak into two split secondary peaks via a platform during all the processes of microstructure transitions. From the variation curve of the
1551 bond type, it can be clearly seen that there are five rapidly changing ranges corresponding qualitatively to the critical transition points of microstructures of the system detected experimentally.
Molecular Dynamics Study of the Microstructure of Near Grain Boundary Distortion Region in Small Grain Nano-NiAl Alloy
WANG Jing-Yang, WANG Xiao-Wei, J. Rifkin, LI Dou-Xing
Chin. Phys. Lett. 2001, 18 (10): 1386-1388 .  
Abstract   PDF(pc) (512KB) ( 670 )
Using the molecular dynamics simulation method, the microstructure of the distortion region near the curved amorphous-like grain boundary in nano-NiAl alloy is studied. The results show that due to the internal elastic force of high energy grain boundary, a distortion layer exists between grain and grain boundary. The lattice expansion and the decreasing structure factor are observed in this region. Stacking fault in samples with grain size 3.8 nm is clearly observed across the distortion region at the site very close to grain. The influences of different grain sizes on average distortion degree and volume fractions of the distortion region, grain and grain boundary are also discussed.
Structural and Electronic Properties of RuSi, RuGe and OsSi
HE Guo-Min, LI Shu-Ping, HUANG Mei-Chun
Chin. Phys. Lett. 2001, 18 (10): 1389-1391 .  
Abstract   PDF(pc) (511KB) ( 416 )
Structural and electronic properties of RuSi, RuGe and OsSi are investigated by first-principles density-functional calculations based on ultrasoft pseudopotential and generalized gradient approximations for the exchange-correlation functional. The bulk moduli for RuGe and OsSi which have not been available from experiments are predicted to be 2.08 and 2.65 Mbar. Though all these compounds with a B20 structure are semiconductors according to the calculation, their band gaps are overestimated compared to those from experiments by a factor of about two.
Monte Carlo Simulation of the Temperature-Dependent Resistance for (La1-xYx)2/3Ca1/3MnO3 (0 ≤ x ≤ 0.2)
LI Zhong-Yi, YUAN Song-Liu, PENG Gang, TANG Chao-Qun
Chin. Phys. Lett. 2001, 18 (10): 1392-1394 .  
Abstract   PDF(pc) (352KB) ( 420 )
Resistance as a function of temperature for optimally doped manganese perovskites is simulated based on a random resistor network model which is generated through the Monte Carlo method by identifying neighbours in each cubic lattice randomly occupied by ferromagnetic metallic particles. Only one parameter, i.e., the number density of ferromagnetic particles, is used as an adjustable parameter, and it is shown that the model yields excellent agreement with measured resistance data in (La1-xYx)2/3Ca1/3MnO3 (0 ≤ x ≤ 0.2) for temperatures covering the whole range from high-T insulating behaviour to low-T metallic state.
Binding Energy of an Exciton in the Quantum Dot Under a Magnetic Field
XIE Wen-Fang
Chin. Phys. Lett. 2001, 18 (10): 1395-1397 .  
Abstract   PDF(pc) (257KB) ( 485 )
The author reports a calculation of the binding energy of the ground and some excited states of excitons in parabolic quantum dots in the presence of an external magnetic field. Calculations are made by using the method of few-body physics within the effective-mass approximation. The results are obtained for several strength values of magnetic field as a function of the quantum dot radius.
Electron Spin Pairing and the Phase Diagram of High-Tc Superconductors
GUO Wei, HAN Ru-Shan
Chin. Phys. Lett. 2001, 18 (10): 1398-1400 .  
Abstract   PDF(pc) (208KB) ( 408 )
The origin of the instability of the normal state of electrons in the superconducting copper oxides is shown by the K-J model, in which the superexchange (K) between local moments and the Kondo exchange (J) between electron and local moment are considered. The suppression of superexchange via impurity doping may induce effective spin coupling between electrons and triplet pairing ( S = 1, Sz = 0 ). The spin pairing theory explains the phase diagram of the high-Tc superconductors, especially the superconducting transition temperature Tc, the pseudogap temperature T* and the magnetic crossover temperature Tn as a function of the doped hole concentration. The universal expression for the empirical law of the superconducting transition temperature is derived from the theory.
Isostructural Transition of MgB2 Under High Pressure
SUN Li-Ling, T. Kikegawa, WU Qi, ZHAN Zai-Ji, WANG Wen-Kui,
Chin. Phys. Lett. 2001, 18 (10): 1401-1403 .  
Abstract   PDF(pc) (339KB) ( 404 )
The high-pressure behaviour of superconductor MgB2 with hexagonal structure has been investigated by the in-situ synchrotron radiation x-ray diffraction method under pressures up to 42.2GPa in a diamond anvil cell. An abrupt decrease of about 7% in the unit cell volume of this material occurs in the pressure range of 26.3 to 30.2 GPa. A split of Raman spectrum was also observed. The jump of compression curve and Raman spectrum are ascribed to an isostructural transition in MgB2 at the pressure of 30.2GPa.
Dynamic Scaling and Universality of Two-Dimensional Random-Bond Potts Model
YING He-Ping, BIAN Bao-Jun, JI Da-Ren, Lothar Schülke
Chin. Phys. Lett. 2001, 18 (10): 1404-1407 .  
Abstract   PDF(pc) (359KB) ( 423 )
Short-time dynamics and universality are investigated for the random-bond Potts model with a trinary distribution of quenched randomness on a two-dimensional triangular lattice. The universal power-law scaling behaviour is applied to estimate the exponents z and β/v. Emphasis is placed on dynamic Monte Carlo evolutions for different multi-disorder amplitudes. Our results indicate that the quenched impurities cause a change of the critical universality.
Origin of (105) Reflection of X-Ray Diffraction and Quantitative Evaluation of Alignment Degree for Sintered Nd-Fe-B Magnets
HE Ye-Qing, ZHOU Shou-Zeng, ZHANG Zhen-Rong, HAN Bao-Shan
Chin. Phys. Lett. 2001, 18 (10): 1408-1410 .  
Abstract   PDF(pc) (398KB) ( 379 )
A new method for quantitatively evaluating the alignment degree of sintered Nd-Fe-B magnets by x-ray diffraction spectra has been proposed. It has been experimentally revealed that the strong (105) reflection existed in almost all x-ray diffraction spectra of sintered Nd-Fe-B magnets stems from the misalignment grains whose easy axes are at an angle of 15.5°with respect to the orientated direction of the magnet.
Structure and Photoluminescence of InGaAs Quantum Dots Formed on an InAlAs Wetting Layer
ZHANG Yuan-Chang, HUANG Chang-Jun, YE Xiao-Ling, XU Bo, DING Ding, WANG Ji-Zheng, LI Yue-Fa, LIU Feng-Qi, WANG Zhan-Guo
Chin. Phys. Lett. 2001, 18 (10): 1411-1414 .  
Abstract   PDF(pc) (396KB) ( 479 )
We have developed a new self-assembled quantum dot system where InGaAs dots are formed on an InAlAs wetting layer and embedded in the GaAs matrix. The structure is realized by special sample designation and demonstrated by low-temperature photoluminescence measurements. In contrast to the traditional InAs/GaAs quantum dots dominated by the ensemble effect, the temperature dependence of photoluminescence of such a quantum dot structure behaves as decoupled quantum dots. This can be attributed to the enhanced potential confinement for the dots provided by a higher-energy barrier in the wetting layer.
Multiplet-Splitting of the Quasi-Atomic-Like Core-Valence-Valence Auger Spectra of Zinc Metal
YUAN Jian-Min
Chin. Phys. Lett. 2001, 18 (10): 1415-1417 .  
Abstract   PDF(pc) (295KB) ( 404 )
Multiplet-splitting of the quasi-atomic-like core-valence-valence (CVV) Auger spectra of zinc metal is calculated by explicitly considering the so-called hole-hole interaction in the final valence states of the Auger transition. We assume that before the Auger transition occurs, the occupied valence states relax to screen the core-hole which results in a redistribution of the valence electrons, in particular within the atom that contains a hole in the core. The supercell method is used to calculate the electronic states concerned by the Auger transition, which is accomplished by the self-consistent full-potential linearized augmented plane wave method. In each supercell, one atom is considered to have a core-hole and many others without it. Due to the relaxation and screening, the valence states at the site of the Auger transition are more localized compared with those in the ground state metal. The multiplet peaks of the quasi-atomic-like CVV Auger spectra of zinc metal are obtained by calculating the Auger transition matrix elements between the referred states.

Surface Acoustic Wave Velocity and Electromechanical Coupling Coefficient of GaN Grown on (0001) Sapphire by Metal-Organic Vapor Phase Epitaxy
CHEN Zhen, LU Da-Cheng, WANG Xiao-Hui, LIU Xiang-Lin, HAN Pei-De, YUAN Hai-Rong, WANG Du, WANG Zhan-Guo, HE Shi-Tang, LI Hong-Lang, YAN Li, CHEN Xiao-Yang
Chin. Phys. Lett. 2001, 18 (10): 1418-1419 .  
Abstract   PDF(pc) (238KB) ( 550 )
High-quality and high-resistivity GaN films were grown on (0001) sapphire face by metal-organic vapor phase epitaxy. To measure the surface acoustic wave properties accurately, we deposited metallized interdigital trans-ducers on the GaN surface. The acoustic surface wave velocity and electromechanical coupling coefficient were measured, respectively, to be 5667m/s and 1.9% by the pulse method.
Structure and Inclination Angle of the Spiral Galaxy M31
MA Jun,
Chin. Phys. Lett. 2001, 18 (10): 1420-1422 .  
Abstract   PDF(pc) (530KB) ( 461 )
The mathematical form, the symmetry of the spiral structure, and the projection of the galactic disc on the image of the spiral galaxy M31 have been directly studied. It is found that M31 has two symmetric arms, i.e., the pitch angles of the two arms are nearly equal. They are 7.7°and 8.0°, respectively. Using the method proposed in this letter, the inclination angle of the galactic disc of M31 is also obtains , which is 77.5° and is in good agreement with previously published results.
Relativistic Beaming Effect of γ-Ray Emission from γ-Ray-Loud Blazars
MEI Dong-Cheng, , XIE Guang-Zhong, QIN Yi-Ping, JIANG Ze-Jun,
Chin. Phys. Lett. 2001, 18 (10): 1423-1426 .  
Abstract   PDF(pc) (248KB) ( 515 )
We have studied the luminosity-timescales relation of 29 γ-ray-loud blazars with observed minimum variation time scales. Following the acceleration model of Ghisellini and Maraschi,(1989 Astrophys. J. 340 189), a relation between the variation of the timescale in γ-rays and that in other wavebands has been derived. Both the observed and Doppler-corrected γ-ray luminosity-timescales relations have been calculated. The observed luminosity of the majority of sources is above the Eddington limit. The intrinsic luminosity of all sources is below the Eddington limit, suggesting that the γ-ray emission of the γ-ray-loud blazar originates from relativistic jets.
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