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Volume 22 Issue 6
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Original Articles
Kepler Problem in Lagrangian Formulation Discussed from Topological Viewpoint
XU Gong-Ou, XU Ming-Jie
Chin. Phys. Lett. 2005, 22 (6): 1303-1304 .  
Abstract   PDF(pc) (166KB) ( 715 )
The Kepler problem in Lagrangian formulation is discussed from the topological viewpoint. Essential points are analysed. Along the same line of thoughts, it is possible to study the Kepler problem in Hamiltonian formulation as well as in quantum mechanics from the topological viewpoint for showing quantum--classical correspondence.
Monte Carlo Simulation of Kerr Effect and Giant Magnetoresistance in CoxAg1-x Granular Films
YANG Yan-Min, ZHONG Ke-Hua, FENG Qian, JIANG Li-Qin, HUANG Zhi-Gao
Chin. Phys. Lett. 2005, 22 (6): 1305-0308 .  
Abstract   PDF(pc) (262KB) ( 587 )
Based on the Monte Carlo simulation, we present the theoretical calculation of the Kerr loops and giant magnetoresistance (GMR) curves in CoxAg1-x granular films. The calculated results of both the Kerr loops and the GMR curves are in good agreement with the experimental ones. The anisotropy energy and the dipolar interaction evidently influence the Kerr loops and the GMR effect and it is found that with the increasing Co content X, the value of anisotropy constant K decreases and the value of dipolar interaction constant D increases. The values of Kt for the CoXAg1-X granular films are calculated, which plays an important role in explaining the GMR effect of the granular films. Here Kt is a parameter related to the resistivity at zero field and to the scattering parameter constant.
The Monte Carlo Generator for J/ψ Decays with Angular Distribution
PING Rong-Gang, DU Shu-Xian
Chin. Phys. Lett. 2005, 22 (6): 1309-1312 .  
Abstract   PDF(pc) (226KB) ( 543 )
We present a Monte Carlo scheme to generate events of J/ψ decays with angular distributions based
on the acceptance--rejection sampling method. We test this scheme with J/ψ → pp and J/ψ → ΛΛ → ppπ+π-, and the results show that the input angular distributions are well reproduced, and efficiency of the HOWL generator of this scheme is also discussed.
Analysis of Observable Quantities from Excited Rubidium Impacted by Electrons at Low Incident Energy
LIU Yi-Bao, PANG Wen-Ning, DING Hai-Bing, SHANG Ren-Cheng
Chin. Phys. Lett. 2005, 22 (6): 1312-1314 .  
Abstract   PDF(pc) (231KB) ( 510 )
The observable quantities (Stokes parameters, orientation parameter L+, alignment angle γ, linear-light-polarization degree Plin) of rubidium, excited from S to P and scattered by electrons at 20eV, are calculated with the two distorted wave methods, i.e. the ordinary distorted wave method distorted wave method (ODWM) and the indirect-relativistic distorted wave method (IRDWM). Compared to the measured results of superelastic electron scattering from laser excited rubidium at incident energy 20eV, the result shows that the two kinds of theoretical calculations are partially in agreement with the experimental results. When scattering angle is smaller than 45°, the Stokes parameters and both the calculations of orientation parameter and alignment are consistent with the measured data. Within the scattering angles 70°-120°, the IRDWM results are in agreement with the measurements, which shows that indirect relativistic effects exist during the process of rubidium scattering by low-energy electrons.
Properties and Application of Intermediate Entangled State Representation
PANG Qian-Jun
Chin. Phys. Lett. 2005, 22 (6): 1315-1317 .  
Abstract   PDF(pc) (191KB) ( 402 )
We introduce the intermediate entangled state \α> and discuss its properties of \α>λ,v. We obtain the expression of the two-mode Wigner operator in the \α>λ,v representation. We find that the projection operator \α>λ,v, λ,v< α\is just the Radon transformation of the two-mode Wigner operator. Using the \α λ,v ,representation, we successfully obtain the eigenvalues and eigenvectors of a bipartite system coupled in a quite complicated way.
Preparation of Two-Qutrit Entangled State in Cavity QED
LIN Xiu-Min, ZHOU Zheng-Wei, WU Yu-Chun, WANG Cheng-Zhi, GUO Guang-Can
Chin. Phys. Lett. 2005, 22 (6): 1318-1320 .  
Abstract   PDF(pc) (223KB) ( 740 )
We propose a scheme to generate a 3×3-dimensional maximally entangled state of two particles. Two three-level atoms interact with a strongly detuned cavity so that the cavity is only virtually excited and efficient decoherence time of the cavity is greatly prolonged. Compared to other protocols, this protocol is simpler and has a higher fidelity.
Effect of Spin on Thermodynamical Quantities around Reissner--Nordström Black Holes
LI Zhong-Heng
Chin. Phys. Lett. 2005, 22 (6): 1321-1324 .  
Abstract   PDF(pc) (245KB) ( 521 )
Using the quantization procedure involving in the Boulware vacuum state and Killing time t, we evaluate the entropy density, energy density, pressure and equation of state around the Reissner--Nordström black hole by the Wentzel--Kramers--Brillouin approximation on the Teukolsky-type master equation. We find that, near the event horizon, there exist subleading order terms with spin dependence beyond the expected Minkowskian high-temperature contribution. In particular, the terms are important and cannot be neglected for near-extremal black hole cases. At large r, the Boulware state approaches the Minkowski vacuum and the theory agrees with that performed in Minkowski spacetime.
Codimension-Two Bifurcation Analysis in Hindmarsh--Rose Model with Two Parameters
DUAN Li-Xia, LU Qi-Shao
Chin. Phys. Lett. 2005, 22 (6): 1325-1328 .  
Abstract   PDF(pc) (232KB) ( 823 )
Bifurcation phenomena in a Hindmarsh--Rose neuron model are investigated. Special attention is paid to the bifurcation structures of two parameters, where codimension-two generalized-Hopf bifurcation and fold-Hopf bifurcation occur. The classification of firing patterns as well as the transition mechanism in different regions on the parameter plane are obtained.
Phase Synchronization in Small World Chaotic Neural Networks
WANG Qing-Yun, LU Qi-Shao
Chin. Phys. Lett. 2005, 22 (6): 1329-1332 .  
Abstract   PDF(pc) (235KB) ( 629 )
To understand collective motion of real neural networks very well, we investigate collective phase synchronization of small world chaotic Hindmarsh--Rose (HR) neural networks. By numerical simulations, we conclude that small world chaotic HR neural networks can achieve collective phase synchronization. Furthermore, it is shown that phase synchronization of small world chaotic HR neural networks is dependent on the coupling strength, the connection topology (which is determined by the probability p), as well as the coupling number. These phenomena are important to guide us to understand the synchronization of real neural networks.
Dynamics of the Spiral Tip in a Closed Belousov--Zhabotinsky Reaction
ZHANG Hui-Jie, WANG Peng-Ye, ZHAO Ying-Ying
Chin. Phys. Lett. 2005, 22 (6): 1333-1335 .  
Abstract   PDF(pc) (906KB) ( 518 )
Dynamics of spiral tip rotating in a closed system of the light sensitive Belousov--Zhabotinsky reaction is studied under a homogeneous and steady illumination. The time dependence of the kinematical parameters of meandering spiral is presented and the experimental evidence is obtained for self-synchronization of the spiral tip in a closed B-Z system without external feedback.
Multiplexing Chaotic Signals Generated by Colpitts Oscillator and Chua Circuit Using Dual Synchronization
SHI Zhi-Guo, RAN Li-Xin, CHEN Kang-Sheng
Chin. Phys. Lett. 2005, 22 (6): 1336-1339 .  
Abstract   PDF(pc) (219KB) ( 780 )
We demonstrate multiplexing chaotic signals generated by two totally different dynamic systems (one is a Colpitts oscillator and the other is a Chua circuit) using dual synchronization and propose a method to select the proper coupling parameters. In the response systems, the cross coupling method is used, in which the voltage difference between the sum of two master oscillators and one slave oscillator is converted to current and then feed into the other slave oscillator. The result in this letter offers a potential multiuser coherent chaotic communication scheme where different chaotic oscillators can be used in one system.
Different Types of Solitary Wave Scattering in the Fermi--Pasta--Ulam Model
WEN Zhen-Ying, ZHAO Hong
Chin. Phys. Lett. 2005, 22 (6): 1339-1343 .  
Abstract   PDF(pc) (276KB) ( 688 )
We show that the scattering between two solitary waves in the Fermi--Pasta--Ulam model with interaction potential V(x)=αx2/2+x4/4 can be classified into four types according to the configurations of the solitary waves. For three of the four types, the large solitary wave can lose energy and the small one can gain in average by collision. For the other one type in a special parameter region we encounter an anomalous scattering, i.e. the large solitary wave gains energy and the small one loses energy. Numerical investigations are performed for the anharmonic limit case of α=0 and the general case of α≠0 and comparisons between them are made.
New Laser Doppler Velocimetry with Wide Dynamic Range and Clear Directional Discrimination
GUI Hua-Qiao, Lü Liang, HE De-Yong, XU Jun, XIE Jian-Ping, ZHAO Tian-Peng, WANG An-Ting, MING Hai
Chin. Phys. Lett. 2005, 22 (6): 1344-1346 .  
Abstract   PDF(pc) (233KB) ( 749 )
We present a new laser Doppler velocimetry based on self-mixing effect using a single longitudinal-mode vertical-cavity surface-emitting laser modulated by a dynamic triangular current. It can indicate the direction of velocity without ambiguity in a wide dynamic range of 5.2--479.9mm/s. The accuracy of velocity measurement is better than 3.1% in the whole velocity range when a diffusing target is used for measurements. More interestingly, it works very well on different diffusing surfaces, even on a black glossy photographic paper.
Phase Transition of Graphitic-C3N4 under High Pressure by In Situ Resistance Measurement in a Diamond Anvil Cell
HAN Yong-Hao, LUO Ji-Feng, GAO Chun-Xiao, MA Hong-An, HAO Ai-Min, LI Yan-Chun, LI Xiao-Dong, LIU Jing, LI Ming, LIU Hong-Wu, ZOU Guang-Tian
Chin. Phys. Lett. 2005, 22 (6): 1347-1349 .  
Abstract   PDF(pc) (316KB) ( 783 )
In situ} resistance measurement of Graphitic-C3N4 has been performed under high pressure in a diamond anvil cell. The result reveals that there are changes of electron transport behaviour. As the pressure increases from ambient to 30GPa, three abnormal resistance changes can be found at room temperature and two are found at 77K. The abnormal resistance dropped at 5GPa is close to the phase transition pressure from the P6m2 structure to the p structure predicted by Lowther et al. [Phys. Rev. B 59 (1999) 11683] Another abnormal change of resistance at 12GPa is related to the phase transition from g-C3N4 to cubic-C3N4 [Teter and Hemley, Science 271 (1996) 53].
Photons from a Chemically Equilibrating Quark--Gluon Plasma at Finite Baryon Density
HE Ze-Jun, , LONG Jia-Li, MA Yu-Gang, MA Guo-Liang,
Chin. Phys. Lett. 2005, 22 (6): 1350-1353 .  
Abstract   PDF(pc) (240KB) ( 379 )
We study hard photon production in a chemically equilibrating quark--gluon plasma at finite baryon density based on the Jüttner distribution of partons of the system. We find that the photon yield is a strongly increasing function of the initial quark chemical potential.

Rotation Driven Shape-Phase Transition of the Yrast Nuclear States with O(6) Symmetry in the Interacting Boson Model
MU Liang-Zhu, LIU Yu-Xin
Chin. Phys. Lett. 2005, 22 (6): 1354-1357 .  
Abstract   PDF(pc) (376KB) ( 464 )
In a framework of the interacting boson model (usually referred to as IBM-1) with angular momentum projection on the coherent state, we obtain the energy surface functional of nuclei in terms of angular momentum and shape parameters. Analysing the rotation driven effect on the equilibrium shape shows that the yrast states of the nuclei with O(6) symmetry will experience a shape-phase transition from γ-soft deformed to triaxially deformed and then to spherical shape along the yrast line as the angular momentum increases.
Theoretical Study on the Rotational Bands and Shape Coexistence of 179,181,183Au in the Particle--Triaxial-Rotor Model
CHEN Guo-Jie, LIU Yu-Xin, , SONG Hui-Chao
Chin. Phys. Lett. 2005, 22 (6): 1358-1361 .  
Abstract   PDF(pc) (252KB) ( 414 )
We perform a series of theoretical calculations and investigation for nuclei 179,181,183Au in the
particle--triaxial-rotor model with variable moment of inertia. The calculated energy spectra in 179,181,183Au agree well with the experimental data globally. The obtained results indicate that the nuclei 179,181,183Au have prolate deformation and involve shape coexistence with different deformation parameters in different bands. The main configuration of bands 1, 2, 3 and 5 in these nuclei are identified as [541]1/2- (π h9/2, α=1/2), [541]1/2- (π h9/2, α=-1/2), [530]1/2- (π f7/2) and [660]1/2+ (π i13/2), respectively.
Reflection-Asymmetric Shell Model Description of the Neutron-Rich 142,145Ba Nuclei
CHEN Yong-Jing, CHEN Yong-Shou, ZHU Sheng-Jiang, GAO Zao-Chun, TU Ya
Chin. Phys. Lett. 2005, 22 (6): 1362-1365 .  
Abstract   PDF(pc) (241KB) ( 442 )
The reflection asymmetric shell model has been applied to describe the octupole deformed bands in neutron-rich even-even 142Ba and odd-N 145Ba nuclei. The alternating parity bands of 142Ba and the simplex s=-i bands of 145Ba are calculated and compared with the available experimental data. The calculated results are in good agreement with the experimental data. The spin and parity assignments of ground-state of 145Ba are discussed. The results show that the present work is a useful attempt to further explore the nuclear reflection asymmetry in neutron rich region.

SD-Pair Shell Model for Identical Nuclear Systems
LUO Yan-An, PAN Feng, NING Ping-Zhi, Jerry P. Draayer
Chin. Phys. Lett. 2005, 22 (6): 1366-1369 .  
Abstract   PDF(pc) (224KB) ( 499 )
Typical spectra corresponding to vibrational, rotational and γ-soft cases were studied within the framework of nucleon-pair shell model truncated to SD-subspace. It is found that the three limiting cases all can be reproduced approximately. The analysis not only shows that the IBM indeed has a sound shell model foundation, but also confirms that the truncation scheme adopted in the SD-pair shell model seems to be reasonable.
Measurement of the Breakup Cross Sections in 6He+9Be Reaction at 25MeV/Nucleon
WANG Jia, YE Yan-Lin, JIANG Dong-Xing, ZHANG Gao-Long, PANG Dan-Yang, LI Zhi-Huan, ZHENG Tao, LI Xiang-Qing, WANG Quan-Jin, HU Qing-Yuan, WU Cui-E, A. Ozawa, Y. Yamaguchi, R. Kanungo, D. Fang, I. Tanihata
Chin. Phys. Lett. 2005, 22 (6): 1370-1373 .  
Abstract   PDF(pc) (390KB) ( 473 )
The breakup reaction cross sections were measured for the reaction of 6He at 25MeV/nucleon from 9Be target with intensity of 105pps. By fitting the energy spectra of breakup α particles with Gaussian functions, the angular distribution of differential cross sections in the laboratory system has been extracted and compared with the Serber model calculations. The good agreement between the calculation and the experimental data favours a dominant configuration of the 4He core plus valence neutrons for the structure of 6He.
Potential Energy of the Di-nuclear System
JIA Fei, XU Hu-Shan, HUANG Tian-Heng, LI Wen-Fei, XU Hua-Gen, CHEN Ruo-Fu, LI Jun-Qing
Chin. Phys. Lett. 2005, 22 (6): 1374-1377 .  
Abstract   PDF(pc) (266KB) ( 391 )
We perform the calculation of the nucleus--nucleus interaction potential of the dinuclear system with deformed nuclei. Based on the calculated results by properly treating the double-folding method, some results from the analytical expressions for calculating both the nuclear and the Coulomb interactions are investigated. It is concluded that the analytical formula to calculate the Coulomb interaction by Wong [Phys. Rev. Lett. 31(1973)766] can reproduce good double folding results. However the results by the parametrized Morse formula, which are used to calculate the nuclear interaction, greatly deviate from the double folding results, unless the distance of nuclei is adjusted to be shifted to a smaller relative distance determined by the same distance between the nuclear surfaces as one of them pertains to the deformed nuclei. Using the double folding method to calculate the nuclear interaction and employing Wong’s analytical formula to calculate the Coulomb interaction can keep good precision and can cost much less computation time.
Nucleation for Lennard-Jones Fluid by Density Functional Theory
FU Dong
Chin. Phys. Lett. 2005, 22 (6): 1378-1381 .  
Abstract   PDF(pc) (215KB) ( 417 )
A non-mean field density functional theory is employed to investigate the vapour--liquid nucleation. The excess Helmholtz free energy functional is formulated in terms of a local density approximation for short ranged repulsion and a density-gradient expansion for long-ranged attractions. An analytical expression for the direct correlation function of a Lennard-Jones fluid is utilized to take into account the effect of long-ranged attractions on intermolecular correlations. With the predicted bulk properties and surface tension as input, the nucleation properties including density profile, work of formation and number of particles at the reduced temperatures T*=0.694 and 0.741 are investigated. The obtained number of particles in the critical nucleus agrees well with the simulation data.
A High-Efficiency Electron Momentum Spectrometer for Direct Imaging of Orbital Electron Density
REN Xue-Guang, NING Chuan-Gang, DENG Jing-Kang, ZHANG Shu-Feng, SU Guo-Lin, LI Bin, CHEN Xue-Jun
Chin. Phys. Lett. 2005, 22 (6): 1382-1385 .  
Abstract   PDF(pc) (360KB) ( 730 )
Direct three-dimensional images for orbital electron density are obtained by using our newly developed electron momentum spectrometer with simultaneous detection in energy and momentum, and the instruments resolutions of Δθ = ±0.7°, ΔФ= ±1.9°, ΔE = 1.2eV, and ΔT = 2.0ns. The detection efficiency is about 100 times higher than conventional spectrometers. The design and performance of the apparatus are reported together with the experimental results on argon to show the extensive improvements in experimental resolutions, detection efficiency and versatility.
Average Dissipative and Dipole Forces on a Three-Level Atom in a Laguerre--Gaussian Beam
WANG Zheng-Ling, YIN Jian-Ping
Chin. Phys. Lett. 2005, 22 (6): 1386-1389 .  
Abstract   PDF(pc) (237KB) ( 480 )
By means of the optical Bloch equations based on the atomic density matrix elements, the general expressions of the average dissipative force, dipole force and the mechanical torque acting on a Λ-configuration three-level atom in a linearly-polarized Laguerre--Gaussian beam (LGB) with an angular momentum of lh are derived, and the general properties of the average dissipative and dipole force on the three-level atom in the linearly-polarized LGB are analysed. We find a resonant property (with two resonant peaks) of the dissipative force and a non-resonant property (with two pairs of non-resonant peaks) of the dipole force on the three-level atom, which are completely different from those on the two-level atom. Our study also shows that all of general expressions on the three-level atom will be simplified to those on the two-level atom in the approximation of large detuning.
Spectral Effects for an Ultrashort Pulse Train Propagating in a Two-Level Atom Medium
LIU Bing-Xin, GONG Shang-Qing, SONG Xiao-Hong, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2005, 22 (6): 1390-1393 .  
Abstract   PDF(pc) (283KB) ( 440 )
We investigate the spectra of a femtosecond pulse train propagating in a resonant two-level atom (TLA) medium. It is found that higher spectral components can be produced even for a 2π femtosecond pulse train. Furthermore, the spectral effects depend crucially on both the relative shift Ф and the delay time τ between the successive pulses of the femtosecond pulse train.
Enhanced Three-Photon Absorption by Symmetric Twisted Intramolecular Charge Transfer
GUO Fu-Quan, YANG Jun, ZHANG Qi-Jin, MING Hai
Chin. Phys. Lett. 2005, 22 (6): 1394-1397 .  
Abstract   PDF(pc) (227KB) ( 314 )
We report on a novel organic chromophore with symmetric twisted intramolecular charge transfer (TICT) state on excitation. The properties of nonlinear transmission induced by three-photon absorption (3PA) are demonstrated pumped with nanosecond laser pulse. Large 3PA cross sections as high as the order of 10-74cm6s2 have been obtained for nanosecond and picosecond laser pulses at 1064nm from intensity-dependent transmission measurements. Similar two emissive behaviours from one-photon and three-photon excited fluorescence spectra indicate that the linear and nonlinear fluorescences share the same TICT relaxation process from the excited states. The intensity dependence of upconversion fluorescence on the incident intensity obeys the cubic law that characterizes the three-photon absorption.
Double Electron Processes in Low Energy Isotope Bare Ions 13C6+ with Helium Collisions
YU De-Yang, CAI Xiao-Hong, LU Rong-Chun, SHAO Cao-Jie, LU Jun, RUAN Fang-Fang, ZHANG Hong-Qiang, CUI Ying, XU Xu, SHAO Jian-Xiong, DING Bao-Wei, YANG Zhi-Hu, CHEN Xi-Meng
Chin. Phys. Lett. 2005, 22 (6): 1398-1400 .  
Abstract   PDF(pc) (212KB) ( 537 )
The isotopic bare ion 13C6+ was employed to collide with helium at 4.15-11.08keV/u. The relative partial cross sections were measured by position-sensitive and time-of-flight coincident techniques. It is shown that the direct-ionization (DI) process can be completely ignored in this region, the transfer ionization (TI) process is the most important double-electron channel, and the probability of the pure double-electron capture (DC) process is quite small. The cross-section ratio of the total double-electron (DE) process (i.e. DC+TI) to the single-electron capture (SC) process is experimentally determined to be approximately a constant of 0.09 ± 0.03 in this region, and this value is obviously smaller than the predictions of the classical over-barrier models and the semi-empirical scaling laws. It is found that the cross-section ratio of pure DC to DE decreases obviously as the projectile velocity increases. Because the pure DC process only comes from the radiation de-excitation following the DC process and are competed by the TI process (comes from the auto-ionization following the DC process), this implies that the population of the two captured electrons depends distinctly on the collision velocity. Comparison with works on Ar16+-He by Wu et al. [Phys. Rev. A 48 (1993) 3617] reveals that the strong projectile-dependent character of the pure DC process exists.
Temporal and Spectral Properties of Subcycle THz Pulses in Near-Field Zone
YANG Yu-Ping, YAN Wei, XU Xin-Long, SHI Yu-Lei, WANG Li
Chin. Phys. Lett. 2005, 22 (6): 1401-1404 .  
Abstract   PDF(pc) (0KB) ( 411 )
In a novel generation and detection configuration of terahertz (THz) radiation, we investigate experimentally and numerically the properties of sub-cycle THz pulses in the near field. It is found that the sub-cycle THz pulses experience significant spectral and temporal deformation in the near-field zone. The variations of both the pulse waveform and spectral distribution of the THz electric field are clearly observed in our experiments when the spot size of source is changed. Numerical simulations based on Gaussian distribution are performed to explain the details of the data and lead to an excellent agreement with the experimental results.
Tuning of Detection Wavelength in a Resonant-Cavity-Enhanced Quantum-Dot-Embedded Photodiode by Changing Detection Angle
ZHANG Hao, ZHENG Hou-Zhi, XU Ping, PENG Hong-Ling, TAN Ping-Heng, YANG Fu-Hua, NI Hai-Qiao, ZENG Yu-Xin, GAN Hua-Dong, ZHU Hui
Chin. Phys. Lett. 2005, 22 (6): 1405-1408 .  
Abstract   PDF(pc) (238KB) ( 422 )
We have fabricated a resonant-cavity-enhanced photodiode (RCE-PD) with InGaAs quantum dots (QDs) as an active medium. This sort of QD-embedded RCE-PD is capable of a peak external quantum efficiency of 32% and responsivity of 0.27A/W at 1.058μm with a full width at half maximum (FWHM) of 5nm. Angle-resolved photocurrent response eventually proves that with the detection angle changing from 0°to 60°, the peak-current wavelength shifts towards the short wavelength side by 37nm, while the quantum efficiency remains larger than 15%.
Tm:Ho:YLF Amplifiers at 2.049μm with a Tm:Ho:GdVO4 Oscillator
HE Wan-Jun, YAO Bao-Quan, JU You-Lun, WANG Yue-Zhu, LI Yu-Feng, YANG Feng
Chin. Phys. Lett. 2005, 22 (6): 1409-1412 .  
Abstract   PDF(pc) (239KB) ( 638 )
We report cw diode-pumped cryogenic Tm:Ho:YLF amplifiers at 2.049μm with a Tm:Ho:GdVO4 oscillator. Not only the single- and double-pass, but also the single- and double-end pump amplifiers with a 10-mm-length medium are compared. A measured maximum small-gain coefficient of 1.3cm-1 is achieved for the double-pass and double-end pump amplifier. The maximum extracted power of 8.5W, the gain of 3.2 and extracted efficiency of 32% have been obtained with an input signal power of 3.9W. The difference of the hosts in the oscillator and amplifier has little influence on the characteristic of the amplifier output. Additionally, the extracted efficiency of the quasi-continuous-wave amplifier with a repetition rate of 10kHz is the same as the cw one.
High Power Diode-End-Pumped Nd:YAG 946-nm Laser and Its Efficient Frequency Doubling
ZHOU Rui, , ZHAO Shi-Yong, , CAI Zhi-Qiang, , ZHANG Qiang, , WEN Wu-Qi, , DING Xin, , WANG Peng, , DING Li-Li, YAO Jian-Quan,
Chin. Phys. Lett. 2005, 22 (6): 1413-1415 .  
Abstract   PDF(pc) (209KB) ( 637 )
We report a high power operation of the 44F3/24I9/2 transition in diode-end-pumped laser at 946nm. The maximum output of 5.1W is obtained with a short linear plano-concave cavity, and the slope efficiency is 24.5% at incident pump power of 23.3W. To our knowledge, this is the highest value of the LD-pumped Nd:YAG 946nm lasers that employ the conversional Nd:YAG rod as the gain medium. By intracavity frequency doubling with an LBO crystal, up to 982mW cw output power in the blue spectral range at 473nm is achieved at an incident pump power of 10.9W with a compact three-element cavity, leading to optical-to-optical conversion efficiency of 9%. The conversion efficiency should be increased to 15.1%, if the rather low absorption coefficient of this Nd:YAG is considered.
Antiphase State in Passively Q-Switched Yb:YAG Microchip Lasers with a Nd,Cr:YAG as Saturable Absorber
GU Xue-Wen, ZHANG Qiu-Lin, ZHANG Dong-Xiang, FENG Bao-Hua, ZHANG Xiao-Hua, ZHANG Guang-Yin
Chin. Phys. Lett. 2005, 22 (6): 1416-1419 .  
Abstract   PDF(pc) (251KB) ( 809 )
We experimentally investigate the antiphase dynamics phenomenon that occurs in a diode-pumped passively Q-switched Yb:YAG multimode laser with a Nd,Cr:YAG saturable absorber. Due to the effect of spatial hole burning, the multimode lasers with one, two, or three modes at different pump power are observed, and the pulses sequences display classic antiphase dynamics.

Diode-Pumped Passive Q-Switched 946-nm Nd:YAG Laser with 2.1-W Average Output Power
ZHANG Ling, LI Chun-Yong, FENG Bao-Hua, WEI Zhi-Yi, LI De-Hua, FU Pan-Ming, ZHANG Zhi-Guo
Chin. Phys. Lett. 2005, 22 (6): 1420-1422 .  
Abstract   PDF(pc) (206KB) ( 967 )
We demonstrate a diode-pumped passive Q-switched 946nm Nd:YAG laser with a diffusion-bonded composite laser rod and a co-doped Nd,Cr:YAG as saturable absorber. The average output power of 2.1W is generated at an incident pump power of 14.3W. The peak power of the Q-switched pulse is 643W with 80kHz repetition rate and 40.8ns pulse width. The slope efficiency and optical conversion efficiency are 17.6% and 14.7%, respectively.
Two-Dimensional Photovoltaic Dark Spatial Solitons of Partially Spatially Incoherent Light
LI Jin-Ping, LU Ke-Qing, ZHAO Wei, YANG Yan-Long, ZHU Xiang-Ping, GUO Xiao-Hui
Chin. Phys. Lett. 2005, 22 (6): 1423-1425 .  
Abstract   PDF(pc) (312KB) ( 820 )
We report a successful experimental observation of two-dimensional photovoltaic dark solitons in an anisotropic crystal with partially spatially incoherent light beams. This kind of solitons results from the bulk photovoltaic effect, which depends on the direction of propagation of the optical beam and on the orientation of the intensity gradient, with respect to the principal axes of the crystal.
High-Average-Power Third Harmonic Generation at 355nm with CsB3O5 Crystal
WU Yi-Cheng, CHANG Feng, FU Pei-Zhen, CHEN Chuang-Tian, WANG Gui-Ling, GENG Ai-Cong, BO Yong, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2005, 22 (6): 1426-1428 .  
Abstract   PDF(pc) (271KB) ( 760 )
A 17.7W average power output at 355nm by the third harmonic generation (THG) of 1064nm light has been obtained with the nonlinear optical crystal CsB3O5 (CBO). The fundamental light source is a diode-pumped Nd:YAG laser with a pulse duration of 70ns and a repetition rate of 7kHz. A CBO crystal cut for type-II PM angles is used in the experiment. The THG energy conversion efficiency with CBO is twice as large as that with LBO. As a THG crystal, CBO has better performance than that of LiB3O5 crystal (LBO).
Propagation Control of Soliton Trains in Dispersion-Shifted Fibres in the Presence of Third-Order Dispersion
CUI Hu, XU Wen-Cheng, LUO Ai-Ping, LIU Song-Hao
Chin. Phys. Lett. 2005, 22 (6): 1429-1432 .  
Abstract   PDF(pc) (261KB) ( 534 )
The evolution of soliton trains in dispersion-shifted fibres (DSFs) in the presence of third-order dispersion (TOD) is investigated. The results show that the collision of neighbouring solitons in the trains can be suppressed by means of a proper TOD, but the maximum transmission distance (or bandwidth) is limited by the increasing soliton separation that results from the TOD. It is also shown that the separation can be suppressed by adjusting the initial phase or amplitude difference between the solitons. These results are helpful to re-establish the potential application of the soliton-based optical-communication systems in DSFs.
Parity Checking and Generating Circuit with Nonlinear Material in All-Optical Domain
Kuladeep Roy Chowdhury, Debduti De, Sourangshu Mukhopadhyay
Chin. Phys. Lett. 2005, 22 (6): 1433-1435 .  
Abstract   PDF(pc) (101KB) ( 1089 )
An all-optical parity checker and parity bit generator circuit is proposed, in which optical non-linear materials are used as switching devices. High-speed (above GHz) logic operations can be achieved by this all-optical circuit that is tremendously fast than its equivalent electronic counterpart. Here these circuits are used to check the errors in optical data through a transmission line.

Identification of Ag37Sn33Te30 Phase-Change Films for Optical Data Storage
ZHANG Xue-Ru
Chin. Phys. Lett. 2005, 22 (6): 1436-1438 .  
Abstract   PDF(pc) (322KB) ( 423 )
The Ag37Sn33Te30 film has been investigated to determine its suitability as phase change optical recording alloy based on static tester and atomic force microscopy measurements. Switching properties and the recording bit topography of the film are studied. With a writing pulse of power 2.5mW, width 10μs, and an erasure pulse of power 0.25mW, width 10μs, optical contrast of 31.8% is obtained. Re-crystallization experiments identify the Ag37Sn33Te30 film as a suitable phase change material for optical data storage with a complete erasure time of 1.1μs at low erasure power.
A Photonic Bandgap Filter Using Metallic Hilbert Curves
LI Hong-Qiang, WEI Ze-Yong, CHEN Hong, ZHANG Ye-Wen
Chin. Phys. Lett. 2005, 22 (6): 1439-1442 .  
Abstract   PDF(pc) (283KB) ( 430 )
We theoretically suggest that a metallic plate with Hilbert curves can possesses multiple resonances in a linear scale, leading to multiple stop bands and pass bands for electromagnetic waves over a wide frequency range. The forward transmission from a line source nearby a small plate covered by four cells with Hilbert curves is checked by a probe at the far field, the results agree well with the multiple resonance frequencies calculated by the plane wave incidence under a periodic boundary condition, the return loss spectra show that radiations of a line antenna working at 4.5GHz can be greatly enhanced, which results from the interaction of the antenna and the subwavelength metallic plate. This kind of metallic pattern is very practical in multi-frequency functioned wave devices with sub-wavelength sizes.
Negative Dispersion Mirrors in Ta2O5SiO2 for Femtosecond Ti:Sapphire Lasers by Using Gires--Tournois Interferometers
LIAO Chun-Yan, WU Zu-Bin, FAN Zheng-Xiu, SHAO Jian-Da, WANG Zhuan, ZHANG Zhi-Gang
Chin. Phys. Lett. 2005, 22 (6): 1443-1445 .  
Abstract   PDF(pc) (274KB) ( 537 )
We design and experimentally demonstrate some negative dispersion mirrors with optimized Gires--Tournois interferometers. The mirror structure is composed of 38 alternating Ta2O5 and SiO2 layers and could be regarded as two sections: high-reflectivity section consisting of a series of quarter-wavelength optical thickness stacks and negative-dispersion section consisting of only 13 layers. The designed mirrors exhibit the expected performance. These mirrors were fabricated by using ion beam sputtering. By adopting such mirrors, dispersion of a mode-locked femtosecond Ti:sapphire laser has been compensated for mostly. With two series of the mirrors, 32fs and 15fs pulses have been obtained respectively.
A 4×4 Strictly Nonblocking Silicon-on-Insulator Thermo-Optic Switch Matrix
YANG Di, LI Yan-Ping, CHEN Shao-Wu, YU Jin-Zhong
Chin. Phys. Lett. 2005, 22 (6): 1446-1448 .  
Abstract   PDF(pc) (199KB) ( 398 )
A 4×4 strictly nonblocking thermo-optic switch matrix implemented with a 2×2 Mach--Zehnder switch unit was fabricated in silicon-on-insulator wafer. Insertion losses of the shortest and the longest path in the device are about 14.8dB and 19.2dB, respectively. The device presents a very low loss dependent on wavelength. For one switch unit, the power consumption needed for operation is measured to be 0.270W--0.288W and the switching time is about 13±1μs.
A Silicon-on-Insulator-Based Thermo-Optic Waveguide Switch with Low Insertion Loss and Fast Response
LI Yan-Ping, YU Jin-Zhong, CHEN Shao-Wu
Chin. Phys. Lett. 2005, 22 (6): 1449-1451 .  
Abstract   PDF(pc) (330KB) ( 427 )
A silicon-on-insulator-based thermo-optic waveguide switch integrated with spot size converters is designed and fabricated by inductively coupled plasma reactive ion etching. The device shows good characteristics, including low insertion loss of 8±1dB for wavelength 1530--1580nm and fast response times of 4.6μs for rising edge and 1.9μs for falling edge. The extinction ratios of the two channels are 19.1 and 18dB, respectively.

Low Power-Consumption and High Response Frequency Thermo-Optic Variable Optical Attenuators Based on Silicon-on-Insulator Materials
FANG Qing, CHEN Peng, XIN Hong-Li, WANG Chun-Xia, LI Fang, LIU Yu-Liang
Chin. Phys. Lett. 2005, 22 (6): 1452-1455 .  
Abstract   PDF(pc) (252KB) ( 443 )
A novel silicon-on-insulator thermo-optic variable optical attenuator with isolated grooves based on a multimode interference coupler principle is fabricated by the inductive coupled plasma etching technology. The maximum fibre-to-fibre insertion loss is lower than 2.2dB, the dynamic attenuation range is from 0 to 30dB in the wavelength range 1500--1600nm, and the maximum power consumption is only 140mW. The response frequency of the fabricated variable optical attenuator is about 30kHz. Compared to the variable optical attenuator without isolated grooves, the maximum power consumption decreases more than 220mW, and the response frequency rises are more than 20kHz.
Simulating High Reynolds Number Flow by Lattice Boltzmann Method
KANG Xiu-Ying, LIU Da-He, ZHOU Jing, JIN Yong-Juan
Chin. Phys. Lett. 2005, 22 (6): 1456-1459 .  
Abstract   PDF(pc) (272KB) ( 467 )
A two-dimensional channel flow with different Reynolds numbers is tested by using the lattice Boltzmann method under different pressure and velocity boundary conditions. The results show that the simulation error increases, and the pressure and the flow rate become unstable under a high Reynolds number. To improve the simulation precision under a high Reynolds number, the number of fluid nodes should be enlarged. For a higher Reynolds-number flow, the velocity boundary with an approximately parabolic velocity profile is found to be more adaptive. Blood flow in an artery with cosine shape symmetrical narrowing is then simulated under a velocity boundary condition. Its velocity, pressure and wall shear stress distributions are consistent with previous studies.
Linear Stability of Flows in a Squeeze Film
ZHU Ke-Qin, REN Ling, LIU Yi
Chin. Phys. Lett. 2005, 22 (6): 1460-1463 .  
Abstract   PDF(pc) (245KB) ( 319 )
We study linear stability of viscous flows in a squeeze lubrication film, in which the flow varies slowly in space and time, between two parallel plates moving normal to each other with a slow constant speed, generalizing the inviscid results of Aristov and Gitman [J. Fluid Mech. 464 (2002) 209]. The temporal evolution of two-dimensional disturbances for this physical situation, including the asymptotic behaviour of a long term or the transient behaviour of some time interval, is obtained by the construction of a low-dimensional Galerkin method. It is found that the wall boundaries typically play dual roles of stabilizer and destabilizer. They constrain the development of disturbances and have stabilizing influences. However, they give rise to velocity shear, which is diffused by viscosity and thereby tends to destabilize the flow.
A Geometry Model for Tortuosity of Streamtubes in Porous Media with Spherical Particles
YUN Mei-Juan, YU Bo-Ming, ZHANG Bin, HUANG Ming-Tao
Chin. Phys. Lett. 2005, 22 (6): 1464-1467 .  
Abstract   PDF(pc) (322KB) ( 950 )
A geometry model for tortuosity of tortuous streamtubes in porous media with spherical particles is proposed based on the assumption that some particles in a porous medium are unrestrictedly overlapped and hence of different configurations. The proposed model is a function of porosity with no empirical constant imposed on it. The model predictions are found to be in good agreement with the available experimental data.

High Bootstrap Current Fraction during the Synergy of LHCD and IBW on the HT-7 Tokamak
ZHANG Xian-Mei, WAN Bao-Nian, WU Zhen-Wei, HT- Team
Chin. Phys. Lett. 2005, 22 (6): 1468-1470 .  
Abstract   PDF(pc) (227KB) ( 412 )
More than 70% of the total plasma current is sustained by the bootstrap current and current drive during the synergy of lower hybrid current driving (LHCD) and ion Berstein wave (IBW) heating on the HT-7 tokamak. The lower hybrid non-inductive current source is off-axis and well localized, and more than 35% bootstrap current plasma has been obtained. The IBW in controlling electron pressure profile can be integrated into the LHCD target plasma. The largest steep gradient of the electron pressure profile in the region ρ~0.5-0.7 mostly comes from the electron temperature profile, which may induce the large fraction bootstrap current. The large off-axis bootstrap current can help to create negative magnetic shear, and the good plasma confinement is achieved.
Effects of Dual-Electrode Biasing on Er in a Toroidal Plasma
LU Rong-Hua, PAN Ge-Sheng, WANG Zhi-Jiang, WEN Yi-Zhi, LIU Wan-Dong, WAN Shu-De, YU Chang-Xuan, WANG Jun, XIAO De-Long, XU Min
Chin. Phys. Lett. 2005, 22 (6): 1471-1473 .  
Abstract   PDF(pc) (220KB) ( 561 )
Two externally biased electrodes were inserted into the plasma on the KT-5C tokamak to test the effects on modifying the radial electric field Er other than single biasing. Using various combinations of biasing voltage, the influences of double biasing are compared with the single biasing. It turns out that the effect of dual-biasing is also effective as a single one, but the outer electrode seems to be shielded by the inner one and show less influence. The results clearly show that the radial electric field Er changed by external biasing is intrinsically an effect localized at the edge of the plasma, which is caused by the electrode induced radial current; and dual-electrode biasing using the method similar to the single biasing seems not to be able to increase more distinctly the peaking effect on Er than the single biasing.

Non-Monotonicity of Excited State Populations Observed in a Cu--He Hollow Cathode Discharge
ZHENG Xu-Tao
Chin. Phys. Lett. 2005, 22 (6): 1474-1477 .  
Abstract   PDF(pc) (222KB) ( 701 )
An interesting non-monotonic structure in the distribution of excited state populations is observed in a Cu--He hollow cathode discharge, and this is explained by $l$-changing collisions of the excited states with background gas atoms. At helium pressure of 0.1 Torr and cathode current of 200-300mA, relative populations of He I 1snp 1P (n= 2-16) states are measured with the corresponding VUV radiation intensities, and are plotted against excitation energies. As energy levels increase, populations of high-n (n> 10) states are found to decrease much more quickly than low-n (n< 7) populations. For intermediate states (n= 7-10), the declining tendency is interfered by population transfers from 1sns 1S states due to l-changing collisions, and an obvious non-monotonic structure is formed at relatively low electric current. Measurements have also been carried out for He II np 2P (n= 2-14) series, in which the l-changing collisions are overwhelmed by Stark quenching of the n2S states and thus population interference does not occur.
Structural, Transport and Magnetic Properties of KxCoO2 (x=0.36)
FU Guang-Cai, DONG Cheng, LI Ming-Xing, GUO Juan, YANG Li-Hong
Chin. Phys. Lett. 2005, 22 (6): 1478-1480 .  
Abstract   PDF(pc) (307KB) ( 526 )
Layered potassium cobaltate KxCoO2 with x=0.36 has been successfully synthesized in KOH fluxes at 480°C , and its hydrated form K0.36CoO2`yH2O (y≤0.8) has been obtained by intercalation with water. The diffraction peaks of K0.36CoO2 can be indexed by an orthorhombic cell similar to Na0.5CoO2, and K0.36CoO2`0.8H2O is isostructural with its sodium analog, monolayer hydrate NaxCoO2`yH2O. While the samples KxCoO2 and K0.36CoO2 yH2O (y <0.8) show semiconductor behaviour, a metal-insulator transition around 30K was observed in the sample KxCoO2`0.8H2O. Both the samples show complicated magnetic behaviour, and they are primarily paramagnetic in the range from 5K to 300K with a spin-glass-like transition around 56K.
Pd--Si Binary Bulk Metallic Glass Prepared at Low Cooling Rate
YAO Ke-Fu, RUAN Fang
Chin. Phys. Lett. 2005, 22 (6): 1481-1483 .  
Abstract   PDF(pc) (243KB) ( 702 )
We report that binary bulk metallic glasses can be made up to 6mm in diameter in a Pd--Si alloy system by air cooling at slow cooling rate (about 8K/s). The high stability of the undercooled liquid and the large glass-forming ability (GFA) of the binary alloy are contributed to the removing of heterogeneous impurities in the alloy melt by employing the fluxing technique. It has been found that decreasing cooling rate can increase the supercooled liquid region and thermal stability of the glassy alloy. After fluxing, a wider supercooled liquid region (ΔT=58K) and higher glass-forming ability have been obtained in a Pd81Si19 binary glassy alloy prepared by slow cooling rate.
Analysis of Ni75-3x/4Al25-x/4Crx Grain Boundary Structures with a Double Species Model
ZHENG Li-Ping, MA Yu-Gang, XU Zi-Jian, ZHU Zhi-Yuan, LI Dou-Xing
Chin. Phys. Lett. 2005, 22 (6): 1484-1487 .  
Abstract   PDF(pc) (266KB) ( 510 )
Based on the Monte Carlo simulation conjoined with the embedded atom method (EAM) potentials, a double species model is employed to study the Ni75-3x/4Al25-x/4Crx structure, i.e. impure Ni3Al together with a grain boundary structure at the equilibrium. At the grain boundary, the model shows that Ll2-Ni3Al transforms into fcc-Ni when x increases from 0 to 0.40; then fcc-Ni transforms into Ll2-Ni3Cr when x increases from 0.40 to 2.40.
Nanoporous Structure in Low-Dielectric Films with Positronium Annihilation Lifetime Spectroscopy
HU Yi-Fan, SUN Jia-Ning, D. W. Gidley
Chin. Phys. Lett. 2005, 22 (6): 1488-1491 .  
Abstract   PDF(pc) (316KB) ( 506 )
We investigate nano-porous structures in thin low-dielectric films, i.e. the pore sizes, distributions, and interconnectivity, by using depth profiled positronium annihilation lifetime spectroscopy (PALS). It is found that PALS has good sensitivity to probe both interconnected and closed pores in the range from 0.3nm to 30nm, even in the film buried beneath a diffusion barrier. A series of low dielectric constant films of organosilicon-silsequioxane with different weight percentages of porogen have been comparatively investigated. The PALS technique can be used to distinguish the open porosity from the closed one, to determine the pore size, and to detect the percolation threshold with the increasing porosity that represents the transition from closed pores to interconnected pores. Furthermore, the pore percolation length can be derived.
Quantum Confinement of Si Nanosphere with Radius Smaller than 1.2nm
ZHAO Pu-Qin, HU Dong-Sheng, WU Xing-Long
Chin. Phys. Lett. 2005, 22 (6): 1492-1495 .  
Abstract   PDF(pc) (216KB) ( 565 )
We calculate the density of states, the squared optical matrix element along the x direction, and the band gap of Si nanosphere with radius r smaller than 1.2nm using the method of linear combination of atomic orbitals. It is shown that the quantum confinement effect of Si nanocrystals exists obviously, fulfilling E =1.92 + 0.23/r1.8, but the band gap exhibits fluctuation with nanocrystal size, which is caused by the dangling bonds of atoms in outer layers. The obtained result indicates that the surface chemical bonds have larger influence on the energy band structure of Si nanosphere when its radius is smaller than 1.2nm.

Ground State Properties of a Local Sine-Gordon Model with Two Scatters
CHEN Yu-Guang, CHEN Hong, ZHANG Yu-Mei
Chin. Phys. Lett. 2005, 22 (6): 1496-1499 .  
Abstract   PDF(pc) (693KB) ( 656 )
We investigate the local sine-Gordon model with two scatters by a variational method. The renormalization mass is calculated. It is found that there is an Ising-like phase transition, which is analogous in the global sine-Gordon model with two frequencies. The renormalization mass can be modulated by the distance between the two scatters.
Red Up-Conversion Luminescence Process in Oxyfluoride Glass Ceramics Doped with Er3+/Yb3+
YU Hua, ZHAO Li-Juan, LIANG Qin, MENG Jie, YU Xuan-Yi, TANG Bai-Quan, TANG Li-Qin, XU Jing-Jun
Chin. Phys. Lett. 2005, 22 (6): 1500-1503 .  
Abstract   PDF(pc) (247KB) ( 505 )
The phonon-assisted quantum cutting (PQC) model is presumed to clarify the red up-conversion luminescence process in Er3+/Yb3+ co-doped glass ceramics by the excitation and emission spectra. The red up conversion luminescence of Er3+ ions mainly comes from three-photon absorption by the PQC process when the rare earth ions are doped in the glass ceramics and excited by 980nm pumped-laser. Er3+ ions absorb three-photons and relax to the 4+G11/2 state and then emit red up-conversion luminescence by the PQC process. The factor coefficient for the relation of pump-laser power and up-conversion intensity (P-I) is found by the analysis of excitation spectra of the red luminescence, which plays a major role to understand the true red up-conversion luminescence process. The new P-I relation is explained by the model of PQC.
First-Principles Calculation for the Electron--Phonon Coupling Constant of Superconducting MgB2
CHEN Xiang-Rong, GUO Hua-Zhong, CAI Ling-Cang, GAO Jie
Chin. Phys. Lett. 2005, 22 (6): 1504-1506 .  
Abstract   PDF(pc) (216KB) ( 942 )
We use a first-principles plane wave method with the new relativistic analytic pseudopotential of the Hartwigsen, Goedecker and Hutter (HGH) scheme and the pseudopotential of the Troullier--Martins scheme to calculate the electron--phonon coupling constant λ of superconducting MgB2. The calculated results show that there is a peak at about 300-350cm-1 in the electron--phonon spectral functional α2F(ω), duo to the coupling of the electrons to the acoustic phonon, and the relativistic effect appears in the high frequencies zone. All the results agree well with the present and previous experimental data.

Spin-Polarized Tunnelling Magnetoresistance Effects in La0.833K0.167MnO3/SrTiO3 Polycrystalline Perovskite Manganites
WU Jian, ZHANG Shi-Yuan, HU Xiu-Kun
Chin. Phys. Lett. 2005, 22 (6): 1507-1510 .  
Abstract   PDF(pc) (258KB) ( 474 )
A sample of La0.833K0.167MnO3-SrTiO3(LKMO/STO) is fabricated by the sol-gel method. The microstructure, magnetic and transportation properties have been studied. X-ray diffraction patterns indicate that the structure of LKMO/STO is a homogeneous solid solution phase. The resistivity of LKMO/STO shows the insulator behaviour, which is different from La0.833K0.167MnO3 (LKMO) whose resistivity shows metal--insulator transition with decreasing temperature. The low-field (mLa0.833K0.167MnO3/SrTiO0 H=0.02T) magnetoresistance decreases from 11% to 0.2% with the increasing temperature from 4K to 220K for the LKMO/STO sample. The magnitude of magnetoresistance in a strong field (La0.833K0.167MnO3/SrTiO0H=5.5T) almost increases linearly with decreasing temperature and reaches the maximum of 65% at the low temperature of 4.2K, which is much higher than that of LKMO (40%). The enhanced low-field magnetoresistance effects are quantitatively explained by the spin-polarized tunnelling at grain boundaries.
Origin of the Downturn in Inverse Susceptibility Observed above the Curie Temperature in Perovskite Manganites
YUAN Song-Liu, CHEN Wei, ZHAO Li-Feng, DOYANANDA Debnath, MIAO Ju-Hong, WANG Yong-Qiang, YUAN Li, SHANG Jing-Lin, XIAO Li-Xia, CAO Heng, XIA Zheng-Cai
Chin. Phys. Lett. 2005, 22 (6): 1511-1514 .  
Abstract   PDF(pc) (228KB) ( 512 )
The measurement of low-field susceptibility X as a function of temperature T for La2/3Ca1/3MnO3 shows a significant downturn in 1/X (T) above the Curie temperature TC, a behaviour generally observed in perovskite manganites. Such a downturn is argued to be due to the segregation of ferromagnetic clusters with larger spins in the paramagnetic matrix. Based on this consideration, a phenomenological expression for X(T) is proposed, in which the total susceptibility is assumed to be a sum of two susceptibilities arising from magnetic entities in the PM background and the FM clusters with T-dependent effective spins, respectively. The result is in good agreement with the experimental data obtained in La2/3Ca1/3MnO3.
Oxygen Pressure Dependence of Properties of Epitaxial LaAlO3 Films Grown on Si (100)
XIANG Wen-Feng, LU Hui-Bin, CHEN Zheng-Hao, HE Meng, ZHOU Yue-Liang
Chin. Phys. Lett. 2005, 22 (6): 1515-1517 .  
Abstract   PDF(pc) (297KB) ( 748 )
Heteroepitaxial LaAlO3 films were grown on a SrTiO3/Si (100) substrate by laser molecular beam epitaxy under different oxygen pressures, and their properties such as crystallinity and electrical characteristics were experimentally investigated using the various measurement methods. The results show that most properties depend mainly on the deposition oxygen pressure. The crystallinity and the C-V and I-V characteristics can be greatly improved with the increasing oxygen deposition pressure. Moreover, after annealed at 1050°C in N2 ambient, the C-V and I-V characteristics of LAO films deposited at the lower oxygen pressure are also improved due to the decrease of oxygen vacancies in LAO films.

Temperature-Dependent Photoluminescence in Coupling Structures of CdSe Quantum Dots and a ZnCdSe Quantum Well
JIN Hua, ZHANG Li-Gong, ZHENG Zhu-Hong, AN Li-Nan, LU You-Ming, ZHANG Ji-Ying, FAN Xi-Wu, SHEN De-Zhen
Chin. Phys. Lett. 2005, 22 (6): 1518-1521 .  
Abstract   PDF(pc) (238KB) ( 609 )
A coupling structure of CdSe quantum dots (QDs) and a ZnCdSe quantum well (QW) is fabricated by using the molecular-beam epitaxy technique. The effect of temperature on the photoluminescence (PL) of the structure is studied. The results reveal that the activation energy of exciton dissociation in the coupling QDs/QW structure is much higher than that of simple CdSe QDs, which is attributed to the exciton tunnelling from the QW to QDs through a thin ZnSe barrier layer. The results also reveal that the position and width of the emission band of the QDs vary discontinuously at certain temperatures. This phenomenon is explained by the QD ionization and exciton tunnelling from the QW to the QDs. It is demonstrated that the coupling structure significantly improves the PL intensity of CdSe QDs.
A New Method with Sandwiched Composite Films for Encapsulating Flexible OLEDs
LI Yang, WANG Li-Duo, DUAN Lian, QIU Yong
Chin. Phys. Lett. 2005, 22 (6): 1522-1525 .  
Abstract   PDF(pc) (441KB) ( 655 )
We introduce a novel method for sandwiched-composite-film encapsulation that successfully extends the lifetime of flexible organic light-emitting diodes (FOLEDs). The encapsulation layers include two parts: one is a thin multilayer barrier coating, which is made up of two applications of alternating layers composed of a polymer layer (consisting of UV capable resins) and a ceramic layer (consisting of titanium nitride with excellent barrier performance), and the other is a thick polymer film of approximately 70μm in thickness fabricated by a doctor blade onto the thin encapsulation film described above. FOLEDs encapsulated by this novel method have a longer lifetime, and this lifetime is 74 times as much as the lifetime of unencapsulated ones.

Analysis of X-Ray Photoelectron Spectroscopy of Polymethyl Methacrylate Etched by a KrF Excimer Laser
ZHU Xiao-Li, LIU Shi-Bing, CHEN Tao, JIANG Yi-Jian, ZUO Tie-Chuan
Chin. Phys. Lett. 2005, 22 (6): 1526-1529 .  
Abstract   PDF(pc) (225KB) ( 541 )
The C 1s and O 1s electrons in polymethyl methacrylate etched by different incident laser intensities are analysed by x-ray photoelectron spectroscopy. The results show that when the incident laser fluence increases gradually, the percentage of carbon atoms in C-C bonds decreases while the one in carbonyl group (C=O) and alkoxy group (C-O) increases, and the percentage of oxygen atoms in C=O bonds increases while the one in C--O bonds decreases. Based on the analysis of the chemical structure, the energy level transition, energy diversion, and dissociation of bonds are theoretically examined, which is consistent with the experimental results.
Electronic Properties of Red P-Type Tl2S5 Single Crystals
G. A. Gamal, M. Abou Zied, A. A. Ebnalwaled
Chin. Phys. Lett. 2005, 22 (6): 1530-1532 .  
Abstract   PDF(pc) (220KB) ( 565 )
Single crystals of red Tl2S5 were prepared by a special modified vertical Bridgman and Stockbarger technique. This growth was performed in our laboratory. The influences of temperature on the electrical conductivity, Hall mobility, carrier concentration, and thermoelectric power (TEP) were carried out in the temperature range 277-413K. Throughout these measurements, various physical parameters such as effective mass of charge carriers, carrier mobility, diffusion coefficient, and the relaxation time for both majority and minority carriers were found.
Non-Thermal Effects on CO--NO Surface Catalytic Reaction on Square Surface: Monte Carlo Study
M. Khalid, A. U. Qaisrani, W. Ahmad
Chin. Phys. Lett. 2005, 22 (6): 1533-1535 .  
Abstract   PDF(pc) (210KB) ( 509 )
A Monte Carlo simulation of the CO--NO heterogeneous catalytic reaction over a square surface has already been studied with a model based on the Langmuir--Hinshelwood (LH) mechanism. The results of this study are well known. Here we study the effects of transient non-thermal mobility of monomer (CO) based on precursor mechanism, diffusion of adsorbed nitrogen and oxygen atoms, on the phase diagram. The interesting feature of this model is the yield of a steady reactive window, while simple LH mechanism is not capable of producing a steady reactive state.


Reduction of Concentration Quenching in a Nondoped DCM Organic Light-Emitting Diode
LIU Zhen-Gang, CHEN Zhi-Jian, GONG Qi-Huang
Chin. Phys. Lett. 2005, 22 (6): 1536-1539 .  
Abstract   PDF(pc) (375KB) ( 844 )
We obtain a nondoped red organic light-emitting diode (OLED) structure ITO/pc-PPV (~30nm)DCM (~30nm) /BCP (~30nm)Mg:Ag, where DCM refers to 4-(dicyanomethylene)-2-methyl-6-[(4-dimethylaninostyryl)-4-H-pyran]. The OLED shows pure and stable red luminescence depending on the driving voltages. The maximum luminance is 330Cd/m2 and the turn-on voltage is as low as ~2V. The reason why the concentration quenching of DCM could be reduced in this structure is investigated. In the preparation process, both the hole-transporting layer and the emitter layer are formed by the spin-coated method. It is believed that this method can lead to a new way to avoid the concentration quenching of red-emitting materials.
Dynamic Simulation of Single DNA Molecule at the Base Level
LEI Xiao-Ling, WANG Xiao-Feng, HU Jun, FANG Hai-Ping
Chin. Phys. Lett. 2005, 22 (6): 1540-1543 .  
Abstract   PDF(pc) (268KB) ( 524 )
A mesoscopic discrete dsDNA model at the base level is proposed based on the statistical model (Phys. Rev. Lett. 82 (1999) 4560). The numerical simulations reproduce the 65 pN plateau and those on the force vs extension for different supercoiling degrees are favourable with the experimental data. Our model has potential applications on the study of short DNA segments and provides a bridge between the statistical models and atomic modelling.

Quasi Scale-Free Parameter Networks of Ion Source Experiments
HAN Xiao-Pu, LIU Zhi-Min, HU Chun-Dong
Chin. Phys. Lett. 2005, 22 (6): 1544-1547 .  
Abstract   PDF(pc) (243KB) ( 483 )
We study some parameter networks of ion source adjustment experiments and find quasi-scale-free characters. Their nodes are parameter settings of every discharge and connected by each of adjacent discharge. Their cumulative degree distributions obey the expression of stretched exponential distribution’s rank-ordering form, and their degree distributions exhibit product-form by two functions, one is similar to an exponential form, and the other is close to a power law. An index is presented to measure how this distribution is close to the power law and how this distribution is used in the analysis of these parameter networks. The mode of parameter adjustment decides that the quasi-scale-free networks are formed naturally.
Evolution of Weighted Networks with Exponential Aging of Sites
XU Xin-Jian, WU Zhi-Xi, WANG Ying-Hai
Chin. Phys. Lett. 2005, 22 (6): 1548-1551 .  
Abstract   PDF(pc) (257KB) ( 616 )
We study the growth of weighted networks with exponential aging of sites. Each new vertex of the network is connected to some old vertices with proportional (i) to the strength of the old vertex and (ii) to e-ατ, where τ is the age of the old vertex and α is a positive constant. As soon as the preferential attachment is modified by such factors, the interesting quantities of the produced network (the vertex degree, vertex strength, clustering coefficient and average path length) will be significantly transformed.
Stochastic Acceleration of Electrons by the Right-Hand Extraordinary Mode in the High Density Plasma Region
XIAO Fu-Liang, ZHENG Hui-Nan, WANG Shui
Chin. Phys. Lett. 2005, 22 (6): 1552-1555 .  
Abstract   PDF(pc) (263KB) ( 450 )
The resonant acceleration of electrons by the superluminous R-X mode is evaluated in the high density plasma region of Earth, specifically around the geostationary orbit. The corresponding resonant frequency range together with the harmonic N required for producing a significant acceleration is studied in detail. It is found that the stochastic acceleration is basically controlled by the harmonic N and a dimensionless parameter α=|Ωe2|/ωpe2 (where |Ωe| and ωpe are the electron gyrofrequency and plasma frequency respectively). For α= 0.1 (around the geostationary orbit), there are not gyroresonances occurring between electrons and right-hand extraordinary-mode electromagnetic waves until higher harmonics N ≥ 4; while for α= 0.5, the gyroresonance begins at N=2. Substantial acceleration of electrons by the right-hand extraordinary mode is possible for those higher harmonic (N>1) resonances over a wide range of wave normal angles θ. This indicates that higher harmonic resonance can play an important role on the electron acceleration in the high density plasma region (α<1).
Matching Condition in γ-γ Annihilation Absorption
LIU Dang-Bo, CHEN Lei, LING Jia-Jie, YOU Jun-Han
Chin. Phys. Lett. 2005, 22 (6): 1556-1559 .  
Abstract   PDF(pc) (228KB) ( 457 )
Two-photon annihilation (γ-γ reaction) is an important absorption mechanism in γ-ray physics and γ-ray astronomy. Using the markedly simplified direction-averaged cross section of annihilation σ(ω, ω’) for a normal isotropic ambient radiation field around the γ-ray source, we obtain a matching condition for the energies of two interacting photons, which ensures the attainment of the maximum annihilation probability. This is a new result that is helpful to obtain a better understanding for the absorption behaviour in the γ-γ annihilation process, and this predicts some possible line-like absorption structures in the emergent γ-ray continuous spectra. Some inferences of the matching condition are also presented.
Search for the Multi-TeV Gamma Rays from the Shell-Like SNR G40.5-0.5 Using the Tibet Air Shower Array
ZHANG Ji-Long, TAN You-Hen, LU Hong, WANG Hui
Chin. Phys. Lett. 2005, 22 (6): 1560-1562 .  
Abstract   PDF(pc) (446KB) ( 655 )
Using observation data of the Tibet air shower array in different periods, a region with the highest excess of 4.4σ in the multi-TeV was detected from the SNR G40.5-0.5 direction, although statistically insignificant yet. The position of the highest excess is located around the EGRET unidentified source 3EG J1903+0550.
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