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Volume 21 Issue 11
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Original Articles
Construction of the Darboux Transformaiton and Solutions to the Modified Nizhnik--Novikov--Veselov Equation
HU Heng-Chun, LOU Sen-Yue,
Chin. Phys. Lett. 2004, 21 (11): 0-2076 .  
Abstract   PDF(pc) (471KB) ( 692 )
A kind of modified Nizhnik--Novikov--Veselov equation is investigated via the Darboux transformation and some soliton solutions are constructed. The property of excitation is also discussed.
Two-Component Wadati--Konno--Ichikawa Equation and Its Symmetry Reductions
QU Chang-Zheng, YAO Ruo-Xia, LI Zhi-Bin
Chin. Phys. Lett. 2004, 21 (11): 2077-2080 .  
Abstract   PDF(pc) (216KB) ( 627 )
It is shown that two-component Wadati--Konno--Ichikawa (WKI) equation, i.e.~a generalization of the well-known WKI equation, is obtained from the motion of space curves in Euclidean geometry, and it is exactly a system for the graph of the curves when the curve motion is governed by the two-component modified Korteweg--de Vries flow. Group-invariant solutions of the two-component WKI equation which corresponds to an optimal system of its Lie point symmetry groups are obtained, and its similarity reductions to systems of ordinary differential equations are also given.

Periodic and Chaotic Breathers in the Nonlinear Schrödinger Equation
LIU Xue-Shen, QI Yue-Ying, DING Pei-Zhu
Chin. Phys. Lett. 2004, 21 (11): 2081-2084 .  
Abstract   PDF(pc) (392KB) ( 483 )
The breathers in the cubic nonlinear Schr\"odinger equation are investigated numerically by using the symplectic method. We show that the solitonlike wave, the periodic, quasiperiodic and chaotic breathers can be observed with the increase of cubic nonlinear perturbation. Finally, we discuss the breathers in the cubic-quintic nonlinear Schrödinger equation with the increase of quintic nonlinear perturbation.
Analysis of High Accuracy Conservation-Element and Solution-Element Schemes
LIU Kai-Xin, WANG Jing-Tao
Chin. Phys. Lett. 2004, 21 (11): 2085-2088 .  
Abstract   PDF(pc) (505KB) ( 575 )
We propose a technique to construct higher accuracy conservation element and solution element (CE/SE) schemes. A second-order CE/SE scheme is established and its stability condition is examined on the basis of the von Neumann necessary condition. From the viewpoints of accuracy and efficiency, the applied range of the one-order CE/SE scheme and the high-order ones is discussed through some numerical examples.
Derivation of Exact Eigenvalues and Eigenfunctions Based on the Analytical Transfer Matrix Method
HE Ying, CAO Zhuang-Qi, SHEN Qi-Shun
Chin. Phys. Lett. 2004, 21 (11): 2089-2092 .  
Abstract   PDF(pc) (314KB) ( 624 )
We extend the analytical transfer matrix method (ATMM) to calculate both the energy eigenvalues and wavefunctions for the Morse potential and the regulated Coulomb potential. Derivations of the exact eigenenergies and eigenfunctions are presented in detail by the ATMM. We compare our results with that obtained by relaxational approach and the eigenvalue moment method, and it is shown that the ATMM can produce accurate eigenvalues. The eigenfunctions by the ATMM are also proven to be correct and meaningful.

Transport of Spin-Polarized Current Through a Mesoscopic Ring with Two Leads Induced by Aharonov--Bohm and Aharonov--Casher Phases
GAO Ying-Fang, ZHANG Yong-Ping, LIANG Jiu-Qing
Chin. Phys. Lett. 2004, 21 (11): 2093-2096 .  
Abstract   PDF(pc) (501KB) ( 843 )
Increasing the Efficiencies of Random-Choice-Based Quantum Communication Protocols with Delayed Measurement
DENG Fu-Guo, LONG Gui-Lu, , WANG Yan, XIAO Li,
Chin. Phys. Lett. 2004, 21 (11): 2097-2100 .  
Abstract   PDF(pc) (195KB) ( 727 )
The security of quantum communications lies in the capability of the legitimate parties to detect eavesdropping. Here we propose to use delayed measurement to increase the efficiency of protocols of quantum key distribution and quantum secret sharing that uses a random choice of measuring-basis. In addition to a higher efficiency, these measures also bring the benefit of much reduced amount of classical communications.
Linear Optical Implementation for Quantum Teleportation of Unknown Two-Qubit Entangled States
Chin. Phys. Lett. 2004, 21 (11): 2101-2104 .  
Abstract   PDF(pc) (360KB) ( 712 )
We present a linear optical implementation for quantum teleportation of an unknown two-qubit entangled state by using linear optical elements, such as beam splitters, phase shifters, and half wave plates. This method is based on the single photon representation of quantum bits. Four location qubits and one polarization qubit are used to realize quantum logical operations in the teleportation procedure of the unknown two-qubit entangled state.
Analysis of Runaway Evaporation and Bose--Einstein Condensation by Time-of-Flight Absorption Imaging
CHEN Shuai, ZHOU Xiao-Ji, YANG Fan, XIA Lin, SUN Ya-Ya, WANG Yi-Qiu, CHEN Xu-Zong,
Chin. Phys. Lett. 2004, 21 (11): 2105-2108 .  
Abstract   PDF(pc) (302KB) ( 676 )
The achievement of Bose--Einstein condensation (BEC) in our experiment is reported. The process of BEC formation is observed by detecting the image after free expansion, in which the effectiveness of runaway evaporative cooling is shown by measuring the optical density of the atom cloud. About 2×105 87Rb atoms in the |F=2,mF=2> state are condensed into the condensate. The ratio of axial-to-radial size of the condensate released from the magnetic trap is investigated in theory and experiment.
Asymptotic Quasinormal Modes of the Garfinkle--Horowitz--Strominger Dilaton Black Hole
CHEN Song-Bai, JING Ji-Liang
Chin. Phys. Lett. 2004, 21 (11): 2109-2112 .  
Abstract   PDF(pc) (271KB) ( 500 )
Using the monodromy technique proposed by Motl and Neitzke (Adv. Theor. Math. Phys. 7(2003)307), we investigate the analytic forms of the asymptotic quasinormal frequencies for the massless scalar perturbation in the Garfinkle--Horowitz--Strominger dilaton spacetime. We find that the real parts of the quasinormal frequencies are TH ln 3. This agrees with that of the quasinormal modes in the Schwarzschild spacetime. Our result implies that Hod’s conjecture about ln 3 is still valid for the black hole spacetime in the string theory.
Resonant Interaction Between a Weak Gravitational Wave and a Microwave Beam in the Double Polarized States Through a Static Magnetic Field
LI Fang-Yu, YANG Nan
Chin. Phys. Lett. 2004, 21 (11): 2113-2116 .  
Abstract   PDF(pc) (222KB) ( 360 )
We investigate the resonant interaction of a weak gravitational wave with a microwave beam in a coupling electromagnetic system, which consists of a Gaussian beam with double polarized transverse electric modes, a static magnetic field and fractal membranes. We find that under the synchroresonance condition, a high-frequency gravitational wave in amplitude 10-30 and frequency 3 GHz may produce the perturbative photon flux of 2.15 × 10s-1 in a surface of 10-2 m2. The perturbative photon flux can be pumped out from the background photon fluxes and one may obtain the amplified signal photon flux of 2.15 × 104 s-1 by cascade fractal membranes. It is worth studying this effect for the detection of high-frequency relic gravitational waves in quintessential inflationary models and the high-frequency gravitational waves expected by possible laboratory schemes.
Possible Origin of Magnetic Fields in Very Dense Stars
A. Perez Martinez, H. Perez Rojas, H. J. Mosquera Cuesta
Chin. Phys. Lett. 2004, 21 (11): 2117-2119 .  
Abstract   PDF(pc) (191KB) ( 343 )
We discuss the bosonization of a relativistic very dense Fermi gas in a magnetic field and the consequent Bose--Einstein condensation of the resulting relativistic vector gas of charged particles. The model may be applied to paired spin-up electrons. We show that such systems may maintain self-consistently magnetic fields of order 1010-1013 G. That pairing could be the origin of large magnetic fields in some white dwarfs and neutron stars. For fields large enough (~ 1013 for white dwarfs), the system becomes unstable and collapses.
Cellular Automation Model of Traffic Flow Based on the Car-Following Model
LI Ke-Ping, GAO Zi-You
Chin. Phys. Lett. 2004, 21 (11): 2120-2123 .  
Abstract   PDF(pc) (501KB) ( 502 )
We propose a new cellular automation (CA) traffic model that is based on the car-following model. A class of driving strategies is used in the car-following model instead of the acceleration in the NaSch traffic model. In our model, some realistic driver behaviour and detailed vehicle characteristics have been taken into account, such as distance-headway and safe distance, etc. The simulation results show that our model can exhibit some traffic flow states that have been observed in the real traffic, and both of the maximum flux and the critical density are very close to the real measurement. Moreover, it is easy to extend our method to multi-lane traffic.
Characteristics of Period-Adding Bursting Bifurcation Without Chaos in the Chay Neuron Model
YANG Zhuo-Qin, LU Qi-Shao
Chin. Phys. Lett. 2004, 21 (11): 2124-2127 .  
Abstract   PDF(pc) (276KB) ( 567 )
A period-adding bursting sequence without bursting-chaos in the Chay neuron model is studied by bifurcation analysis. The genesis of each periodic bursting is separately evoked by the corresponding periodic spiking patterns through two period-doubling bifurcations, except for the period-1 bursting occurring via Hopf bifurcation. Hence, it is concluded that this period-adding bursting bifurcation without chaos has a compound bifurcation structure closely related to period-doubling bifurcations of periodic spiking in essence.
Measure Synchronization of High-Cycle Islets in Coupled Hamiltonian Systems
CHEN Shao-Ying, WANG Guang-Rui, CHEN Shi-Gang
Chin. Phys. Lett. 2004, 21 (11): 2128-2131 .  
Abstract   PDF(pc) (595KB) ( 645 )
Measure synchronization is a new phenomenon found in coupled Hamiltonian systems recently and it is interesting to understand its properties comprehensively. We discuss the measure synchronization of a coupled pair of standard maps in high period quasi-period orbits, and the measure synchronization transition is associated with the transition of coupled systems from quasi-periodicity to chaos. This behaviour is very different from that found by Hampton and Zanette [Phys. Rev. Lett. {\bf 83} (1999) 2179].
Dependence of Structure and Haemocompatibility of Amorphous Carbon Films on Substrate Bias Voltage
GUO Yang-Ming, MO Dang, LI Zhe-Yi, LIU Yi, HE Zhen-Hui, CHEN Di-Hu
Chin. Phys. Lett. 2004, 21 (11): 2132-2135 .  
Abstract   PDF(pc) (441KB) ( 487 )
Tetrahedral amorphous hydrogenated carbon (ta-C:H) films on Si(100) substrates were prepared by using a magnetic-field-filter plasma stream deposition system. Samples with different ratios of sp3-bond to sp2-bond were obtained by changing the bias voltage applied to the substrates. The ellipsometric spectra of various carbon films in the photon energy range of 1.9--5.4eV were measured. The refractive index n and the relative sp3 C ratio of these films were obtained by simulating their ellipsometric spectra using the Forouhi--Bloomer model and by using the Bruggeman effective medium approximation, respectively. The haemocompatibility of these ta-C:H films was analysed by observation of platelet adhesion and measurement of kinetic clotting time. The results show that the sp3 C fraction is dependent on the substrate bias voltage, and the haemocompatibility is dependent on the ratio of sp3-bond to sp2-bond. A good haemocompatibility material of ta-C:H films with a suitable sp3 C fraction can be prepared by changing the substrate bias voltage.

Charmonium Spectrum from Quenched Lattice QCD with Tadpole\\ Improvement Action
LIU Da-Qing
Chin. Phys. Lett. 2004, 21 (11): 2136-2139 .  
Abstract   PDF(pc) (237KB) ( 429 )
We report our lattice simulation on the charmonium spectra in the quenched approximation. Because the complete adjustment on all the nonperturbative parameters needs much calculation time, we only adjust two of them, but with some rescaling for mass splitting. After the rescaling, the calculated masses of meson are 3.030GeV (ηc), 3.080GeV (J/ψ), 3.546GeV (hc) and 3.412 GeV (xc0) respectively, which is in agreement with the experimental results.
Investigation of Exotic Structure of the Largely Deformed Nucleus 23Al in the Relativistic-Mean-Field Model
CHEN Jin-Gen, , CAI Xiang-Zhou, WANG Ting-Tai, MA Yu-Gang, REN Zhong-Zhou, FANG De-Qing, ZHONG Chen, WEI Yi-Bin, GUO Wei, ZHOU Xing-Fei, , WANG Kun, MA Guo-Liang, TIAN Wen-Dong, ZUO Jia-Xu, MA Chun-Wang, CHEN Jin-Hui, YAN Ting-Zhi, SHEN Wen-Qing
Chin. Phys. Lett. 2004, 21 (11): 2140-2143 .  
Abstract   PDF(pc) (416KB) ( 638 )
A candidate for proton halo nucleus 23Al is investigated based on the constrained calculations in the framework of the deformed relativistic mean field (RMF) model with the NL075 parameter set. It is shown by the constrained calculations that the ground state of 23Al has a large deformation that corresponds to the prolate shape. With that large deformation, the non-constrained RMF calculation predicts that there appears an inversion between the 2s1/2 [211] and 1d5/2 [202] shells. The valence proton of 23Al is weakly bound and occupies 2s1/2 [211] and 1d5/2 [202] with the weights of 56% and 29%, respectively. The calculated RMS radius for matter is in agreement with the experimental one. It is also predicted that the difference between the proton RMS radius and the neutron one is very large. This suggests that there exists a proton halo in 23Al.

Band Structure in the Doubly Magic Nucleus 56Ni
DONG Bao-Guo, GUO Hong-Chao
Chin. Phys. Lett. 2004, 21 (11): 2144-2146 .  
Abstract   PDF(pc) (425KB) ( 464 )
Band structures near yrast lines of the Z=N doubly magic nucleus 56Ni are investigated with the configuration-dependent cranked Nilsson--Strutinsky approach. The observed deformed bands are confirmed as highly deformed and their properties are explained theoretically. The calculated transition quadrupole moments Qt, ~ 1.7 eb at low spin as well as the kinematic and dynamic moments of inertia J(1) and J(2) for configurations of interest are found to be generally in good agreement with the observed results. Two terminating states at 20+ and 29_ for the two observed bands and other terminations in 56Ni are also predicted. It is found that the configuration-dependent cranked Nilsson--Strutinsky approach is better in the description of nuclear properties and band structures at high spin than other models.

Two-Quasiparticle Bands and Isomers in 98Sr
LI Ming-Liang, ZHU Sheng-Jiang, J. H. Hamilton, A. V. Ramayya, J. K. Hwang, CHE Xing-Lai, ZHANG Zheng, YU Ying-Nan, ZHENG Ran-Cheng, I. Y. Lee, J. O. Rasmussen, Y. X. Luo, W. C. Ma
Chin. Phys. Lett. 2004, 21 (11): 2147-2150 .  
Abstract   PDF(pc) (668KB) ( 690 )
Rotational bands in neutron-rich 98Sr nucleus have been investigated by measuring high-fold prompt λ-ray coincidence events of the spontaneous fission of 252Cf with the Gammasphere detector array. A deformed K=3 band built on the 1838 keV level has been confirmed and extended. Another deformed K=6 band based on the 2535keV level has been established. Both the bands originate most probably from the v 2/9[404] v2/3[411] two-quasiparticle configuration with Ω=|Ω12|and Ω=|Ω1- Ω2|, respectively. Based on the delay-coincidence measurements, the half-lives for the K=3 and K=6 band head levels have been obtained to be 13±3 ns and 4.5± 1.0 ns, respectively.

Quasielastic Scattering of the Halo Nucleus 6He at 25 MeV/u from a 9Be Target
PANG Dan-Yang, YE Yan-Lin, JIANG Dong-Xing, ZHENG Tao, WANG Quan-Jin, LI Zhi-Huan, LI Xiang-Qing, GE Yu-Cheng, WU Cui-E, ZHANG Gao-Long, HU Qing-Yuan, WANG Jia, A. Ozawa, Y. Yamaguchi, R. Kanungo, D. Fang, I.Tanihata
Chin. Phys. Lett. 2004, 21 (11): 2151-2154 .  
Abstract   PDF(pc) (398KB) ( 425 )
The differential cross sections of quasielastic scattering of a 25MeV/u 6He from 9Be target have been measured. The double-folding model approach is applied to generate the real part of the optical potential. The imaginary potential parameters as well as some of the real potential parameters are studied in comparison with the experimental data. The effect of the unstable nucleus is discussed.
Domain Wall in the Linear Sigma Model
MAO Hong, LI Yun-De, HUANG Tao
Chin. Phys. Lett. 2004, 21 (11): 2155-2158 .  
Abstract   PDF(pc) (231KB) ( 412 )
We discuss the role of the axial U(1)A symmetry in the chiral phase transition using the U(Nf)R×U(Nf)L linear sigma model with two massless quark flavours. We expect that above a certain temperature, the axial U(1)A symmetry will be effectively restored as well as SU(Nf)R×SU(Nf)L. Then we can construct a string-like static solution of the η string and a kink-like classical solution of the domain wall during the chiral phase transition. We give out the possible signals for detecting the domain wall in ultrarelativistic heavy-ion collisions.

Medium Density and Parton Energy Loss in Gold--Gold Collisions from the Recombination Model
YANG Chun-Bin, TAN Zhi-Guang
Chin. Phys. Lett. 2004, 21 (11): 2159-2162 .  
Abstract   PDF(pc) (335KB) ( 345 )
The pion production at mid-rapidity in gold--gold collisions at √s=200GeV is investigated by the parton recombination model. The density of the hot medium produced in the collisions and the hard
parton energy loss effect are obtained by fitting the experimental data. Both of them are found to have power-law dependence on the number of binary collisions. The implication of such dependence on the nuclear modification factor is discussed.
Ab Initio Calculation of Vacancies and Interstitials in NiS2
WANG Tao, DAI Yong-Bing, OUYANG Si-Ke, WU Jian-Sheng, SHEN He-Sheng
Chin. Phys. Lett. 2004, 21 (11): 2163-2166 .  
Abstract   PDF(pc) (322KB) ( 608 )
An ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations has been utilized to investigate the electronic structure, atomic geometry, formation energy to provide a better understanding of properties of Ni disilicide. The vacancy and interstitial formation energies largely depend on the atomic chemical potentials. The formation energies of vacancies VSi and VNi are in the range of 0.04--0.56 eV and 1.25--2.3eV, respectively and the formation energies of Si and Ni interstitials are 3.89--4.42 eV and 0.67--1.71 eV, respectively. The smaller Ni interstitial formation energy is in agreement with the experimental result that Ni interstitial atom is dominant diffusion species in NiSi2
Relationship and Discrepancies Among Typical Interatomic Potential Functions
LIM Teik-Cheng
Chin. Phys. Lett. 2004, 21 (11): 2167-2170 .  
Abstract   PDF(pc) (363KB) ( 1311 )
We develop a simultaneous relationship among parameters of the generalized version of the Lennard-Jones, Morse, Rydberg and Buckingham pair potentials, and the two-body portion of the Kaxiras--Pandey potential function by introducing a set of scaling factors. These potential functions are selected according to their frequent adoption in condensed matter and molecular computation. In addition to verifying the parametric relations, theoretical plots of these potential curves show that each of these potential functions is unique in terms of their characteristic shape. However, gaps between these potential functions are narrowed for interatomic interactions possessing lower separation energy and longer interatomic equilibrium distance. Finally, comparison with the {\it ab initio} results shows that the extended-Rydberg potential energy curve gives the best agreement among the five empirical potential functions, for the specific case of hydrogen
Surface-Induced Melting of Metal Nanoclusters
YANG Quan-Wen, ZHU Ru-Zeng, WEI Jiu-An, WEN Yu-Hua
Chin. Phys. Lett. 2004, 21 (11): 2171-2174 .  
Abstract   PDF(pc) (521KB) ( 516 )
We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermodynamic theory based on Kofman’s melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature Tpre=T0-T0svlvsl)/(ρLξ) (T0 is the melting point of bulk metal, γsv the solid--vapour interfacial free energy, γlv the liquid--vapour interfacial free energy, γsl the solid--liquid interfacial free energy, ρ the density of metal, L the latent heat of bulk metal, and ξ the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length ξ of a metal can be obtained easily by Tpre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature Tpre of Cu is obtained by MD simulations, then ξ is obtained. The melting point Tcm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.
Self-Mixing Interference in Dual-Polarization Microchip Nd:YAG Lasers
WAN Xin-Jun, ZHANG Shu-Lian, LIU Gang, FEI Li-Gang
Chin. Phys. Lett. 2004, 21 (11): 2175-2178 .  
Abstract   PDF(pc) (530KB) ( 635 )
The self-mixing interference in dual-polarization microchip Nd:YAG lasers is demonstrated. Under optical feedback, the orthogonal polarization components of the laser would undergo antiphase intensity modulations; at high feedback level, the polarization switching appears. We also observe that the laser self-mixing sensitivity changes periodically with the frequency difference of orthogonal polarizations. An initial theoretical model is put out and agrees well with the experiments. The results are useful for self-mixing sensitivity enhancement and offer a new way of absolute distance measurement.
Lasing Characteristics of Tm3+:Ho3+ Codoped Silica Fibre Laser Pumped by 1.18-μm Raman Fibre Laser
DONG Shu-Fu, CHEN Guo-Fu, WANG Xian-Hua, ZHAO Shang-Hong
Chin. Phys. Lett. 2004, 21 (11): 2179-2181 .  
Abstract   PDF(pc) (359KB) ( 565 )
The fundamental characteristics of Fabry--Perot-cavity continuous-wave Tm--Ho codoped silica fibre lasers pumped by a 1.18 μm Raman fibre laser are presented. A maximum output power of 930 mW at 1880nm is generated for a fibre length of 1 m from the transition of Tm3+, with a slope efficiency of 32.4%. For a 3-m-long fibre, the maximum output power decreases to 650 mW at 1960 nm due to the laser emission from Ho3+ with a lower slope efficiency of 25%, which clearly shows the effective energy transfer from Tm3+ to Ho3+. The wavelength red-shifting of the laser emission originates from the transition competition and the emission cross section difference between Tm3+ and Ho3+.
High Efficiency Continuous-Wave Tm:Ho:GdVO4 Laser Pumped by a Diode
YAO Bao-Quan, HE Wan-Jun, WANG Yue-Zhu, ZHANG Xing-Bao, LI Yu-Feng
Chin. Phys. Lett. 2004, 21 (11): 2182-2183 .  
Abstract   PDF(pc) (303KB) ( 562 )
We report a high efficiency cw diode-pumped cryogenic Tm(5at.%), Ho(0.5at.%):GdVO4 laser. The pumping source is a fibre-coupled laser diode with fibre core diameter of 0.4mm and numerical aperture of 0.3, supplying power 14.8W at 793.6nm. For input pump power of 13.6W at 794.2nm, the maximum output power of 4.2W, optical-to-optical conversion efficiency of 31% and slope efficiency 38% have been attained at 2.0485μm. To our knowledge, the operating performance is the best among the previously reported Tm:Ho:GdVO4 lasers. We also analyse the influence of pump wavelengths (from 792 nm to 794.2 nm) on the output power, the optical-to-optical conversion efficiency increases with the longer pump wavelength which is closer to the absorption peak of 797 nm in Tm,Ho:GdVO4.
A Powerful Simple Shooting Method for Designing Multi-Pumped Fibre Raman Amplifiers
NING Ji-Ping, HAN Qun, CHEN Zhi-Qiang, LI Jia-Qiang, LI Xiao-Guang
Chin. Phys. Lett. 2004, 21 (11): 2184-2187 .  
Abstract   PDF(pc) (357KB) ( 496 )
A simple shooting method dedicated to the design of multipump discrete Raman fibre amplifiers (RFAs) is proposed and discussed in detail. A novel scheme to provide a good initial guess for backward lightwaves is also proposed to improve the efficiency and robustness of the method. Using the proposed method, a discrete RFA with four backward pumps and 93 signal channels is simulated for the maximum number of interaction waves considered simultaneously in the RFA design reported previously, to our best knowledge. The numerical simulation results show that the proposed method is fast and robust. It can be used in the design of RFAs with various configurations including co-, counter- and bi-directional-pump schemes to provide an actual modelling.
Generation of Stable Picosecond Chirp-Free Pulses at 10 GHz from a Nonpolarization Maintaining Regeneratively Mode-Locked Fibre Laser
TAN Bin, LI Zhi-Yong, WANG Zhao-Ying, GE Chun-Feng, JIA Dong-Fang, NI Wen-Jun, LI Shi-Chen
Chin. Phys. Lett. 2004, 21 (11): 2188-2190 .  
Abstract   PDF(pc) (467KB) ( 346 )
A 10 GHz regeneratively mode-locked fibre laser (RMLFL) at 1550 nm constructed with commercially available radio frequency components is presented. Chirp-free hyperbolic secant pulses with duration from 4.4 ps to 8 ps and output reaching 3.6 mW are acquired. Without any cavity length or polarization maintaining mechanism, the error-free operation of this RMLFL can be carried out in room temperature.
Characterization of Hermite--Gaussian Beams by Using Hartmann--Shack Wavefront Sensor
GAO Chun-Qing, GAO Ming-Wei, Weber Horst
Chin. Phys. Lett. 2004, 21 (11): 2191-2194 .  
Abstract   PDF(pc) (432KB) ( 579 )
A Hartmann--Shack wavefront sensor (HSWS) is used in characterization of Hermite--Gaussian beams that are generated from a laser-diode pumped mode generator. By measuring the intensity distribution and the phase gradient distribution of the Hermite--Gaussian beams, we determine the beam width, radius of curvature and M2-factor from the images recorded in the HSWS. The results obtained from the HSWS measurement are compared with the ones obtained from the caustic measurement.
A Method for Distinguishing Attosecond Single Pulse from Attosecond Pulse Train
HUO Yi-Ping, ZENG Zhi-Nan, LI Ru-Xin, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (11): 2195-2197 .  
Abstract   PDF(pc) (296KB) ( 573 )
The driving laser field assisted attosecond soft-extreme-ultraviolet (XUV) photo-ionization was used successfully to measure the duration of the attosecond pulse based on the cross-correlation method. However, this method in principle cannot distinguish a single attosecond pulse from the attosecond pulse train. We propose a technique for directly distinguishing attosecond single pulse from attosecond pulse train based on the photo-ionization of atoms by attosecond XUV pulse in the presence of a two-colour strong laser pulse.
Optical Stabilizer Based on Optical Bistable Devices with All-Fibre Construction
LI Cheng, YE Hong-An, ZHAO Xue-Zeng, YANG Jiu-Ru, ZHANG Xin-Ming, LU Guo-Hui,
Chin. Phys. Lett. 2004, 21 (11): 2198-2200 .  
Abstract   PDF(pc) (322KB) ( 416 )
We propose a fibre optical stabilizer constituted by a photoelectric-hybrid optical bistable device in which fibre Bragg grating is used as a light intensity modulator. The intensity noise-reducing ability is well improved through the method by employing two feed signals. As a result, the light intensity variation can be reduced to ~ 1/64.
Optical Bistability by Using a Tunable Fibre Laser with Fibre Fabry--Perot
Lü Guo-Hui, YE Hong-An, LI Jun-Qing, SUN Xiu-Dong, ZHANG Xin-Ming
Chin. Phys. Lett. 2004, 21 (11): 2201-2204 .  
Abstract   PDF(pc) (474KB) ( 534 )
We observe a novel hybrid optical bistability by using an electro-optically tuned cw fibre laser with a fibre Fabry--Perot filter. The principles of the optical bistable device in two operation manners are analysed. The applications in monitoring the wavelength shift of a tunable fibre laser and fibre sensor of digital type are also discussed.
A Novel All-Optical Switch in a Double-Loop Sagnac Ring Coupled with a Nonlinear Ring Resonator
LI Jun-Qing, LI Li, ZHAO Jia-Qun, LI Chun-Fei
Chin. Phys. Lett. 2004, 21 (11): 2205-2208 .  
Abstract   PDF(pc) (441KB) ( 484 )
We propose a novel configuration of all-optical switch based on a double-loop Sagnac ring coupled with a nonlinear ring resonator. In the case of self-phase modulation, the reducing switching threshold power down to mW is predicted, which is the improvement of earlier works on all-optical switches. The switch optimization is analysed. A way to increase the response speed of all-optical switches is suggested.
Diode-Pumped Self-Starting Mode-Locked Nd:YVO4 Laser with Semiconductor Saturable Absorber Output Coupler
JIA Yu-Lei, WEI Zhi-Yi, ZHENG Jia-An, LING Wei-Jun, WANG Yong-Gang, MA Xiao-Yu, ZHANG Zhi-Gang
Chin. Phys. Lett. 2004, 21 (11): 2209-2211 .  
Abstract   PDF(pc) (379KB) ( 523 )
By using a semiconductor saturable-absorber output coupler as a mode-locking device, we experimentally realized the operation of a diode-pumped passively mode-locked Nd:YVO4 laser. Stable laser pulses with duration of 2.3ps were generated at the output power of about 1W. With increasing the pump power to 9 W, the maximum mode-locked power of 1.7 W was obtained, which corresponds to a slope conversion efficiency of 44% and optical-to-optical conversion efficiency of 19%.
Compression of Soliton Pairs in Dispersion-Decreasing Fibres
CUI Hu, XU Wen-Cheng, LIU Song-Hao
Chin. Phys. Lett. 2004, 21 (11): 2212-2215 .  
Abstract   PDF(pc) (479KB) ( 408 )
The compression of soliton pairs in fibres with decreasing dispersion is studied. The results show that generation of high-quality stable pedestal-free pulses is strongly affected by the interaction between soliton pairs. The initial phase difference between two solitons can modify soliton interaction and can make the neighbouring solitons never collide periodically. The soliton pairs can be compressed selectively so that one of the two solitons can achieve enhanced compression by controlling the initial phase difference.
Spectroscopic Properties of Kiton Red in Hybrid TiO2/Ormosil Films
WANG Bao-Ling, HU Li-Li
Chin. Phys. Lett. 2004, 21 (11): 2216-2218 .  
Abstract   PDF(pc) (379KB) ( 570 )
TiO2/ormosil films doped with kiton red have been prepared by the sol-gel method. Spectroscopic properties of the entrapped dye are studied by absorption and emission techniques. The results indicate that the absorption and fluorescence spectra of kiton red depend strongly on the properties of the ormosil matrices. The heat-treatment of dye-doped film leads to the increasing fluorescence intensity and the largest intensity is obtained after heat-treatment of 150°C.
Heat Transport Behaviour in One-Dimensional Lattice Models with Damping
ZHU Heng-Jiang, ZHANG Yong, ZHAO Hong
Chin. Phys. Lett. 2004, 21 (11): 2219-2222 .  
Abstract   PDF(pc) (428KB) ( 783 )
We investigate the heat transport behaviours of two typical lattice models, the Fermi--Pasta--Ulam-β model and the Ф4 lattice model, in the presence of damping which imitates the effect of the thermal radiation and the thermal diffusion to the surroundings through the sample boundary. It is found that the damping does not affect the thermal conductivity, but can change the heat flux dumped into the lattice chain. We also discuss possible applications under the heuristic guidance of our numerical results. In particular, we suggest a way to measure the thermal conductivity experimentally in the presence of large energy loss arisen from the radiation and the diffusion.

Mechanism for Influence of Nose Bluntness on Asymmetric Vortices
WANG Gang, LIANG Xin-Gang
Chin. Phys. Lett. 2004, 21 (11): 2223-2226 .  
Abstract   PDF(pc) (757KB) ( 663 )
Pressure distributions on slender bodies are measured at various roll angles; it is found that the side loads on the blunted-nose slender body are as small as one-third of that on a pointed-nose one, or even zero at some roll angles. Numerical simulation shows that different flow structures are generated on the leeside of the bodies with different noses. The results confirm that a structure of U-shaped horseshoe vortex develops on the top of the blunted nose due to the closed type of surface flow separation. The shear layer separated from the nose is entrapped into the horseshoe vortex core and forms two main vortices on the two sides of the body. The function of this structure is to hold in the two main nose vortices and to restrict the emergence of asymmetry.
Optimization of the Loading Process of the QUIC Magnetic Trap for the Experiment of Bose--Einstein Condensation
CHEN Shuai, ZHOU Xiao-Ji, YANG Fan, XIA Lin, WANG Yi-Qiu, CHEN Xu-Zong,
Chin. Phys. Lett. 2004, 21 (11): 2227-2230 .  
Abstract   PDF(pc) (409KB) ( 1140 )
The magnetic quadrupole-Ioffe configuration (QUIC) trap in our Bose--Einstein condensation experiment is introduced. The magnetic trap loading process after laser cooling is analysed and the optimization of the loading process is studied experimentally. Calculation of the magnetic field explains the loss of the atoms during the loading process of the QUIC trap. The number of atoms loaded in the QUIC trap is increased by 40% after optimization in comparison with the normal loading process.
Dispersion Characteristics of a New Slow-Wave Structure
WU Jian-Qiang
Chin. Phys. Lett. 2004, 21 (11): 2231-2233 .  
Abstract   PDF(pc) (506KB) ( 1080 )
The microwave excitation in a new slow-wave structure, i.e.the plasma-filled coaxial cylindrical dielectric-loaded cylindrical waveguide, is investigated by using the self-consistent linear field theory in considering the collision effect between electrons and ions in the plasma via the collision frequency term. The determinant dispersion equation of the beam--wave interaction with a complex value of angular frequency is derived. The effects of plasma collision frequency on the output frequency and the wave growth rate of the beam-wave interaction are calculated and discussed.
Modes of Homogeneous Barrier Discharge at Atmospheric Pressure in Helium
WANG Yan-Hui, WANG De-Zhen
Chin. Phys. Lett. 2004, 21 (11): 2234-2237 .  
Abstract   PDF(pc) (554KB) ( 661 )
The discharge modes of a homogeneous barrier discharge at atmospheric pressure in helium are investigated with a one-dimensional fluid model. It is found that, either in single peak discharge or in multipeak discharge, there are two discharge modes: glow and Townsend modes. The structure and features of the two modes are compared. The conditions forming the two modes are discussed.
Characterization of a Dielectric Barrier Plasma Gun Discharging at Atmospheric Pressure
ZHANG Guang-Qiu, GE Yuan-Jing, ZHANG Yue-Fei, CHEN Guang-Liang
Chin. Phys. Lett. 2004, 21 (11): 2238-2241 .  
Abstract   PDF(pc) (489KB) ( 924 )
We develop a plasma gun based on dielectric barrier discharge and working at atmospheric pressure. A theoretical model to predict the gun discharge voltage is built, which is in agreement with the experimental results. After investigating the characterization of discharging gun and utilizing it for polymerization, we find that the gun can be used as a source to generate a stable uniform plasma for different plasma-processing technologies.
Photoluminescence of Dislocations in Nitrogen Doped Czochralski Silicon
LI Dong-Sheng, YANG De-Ren, E. Leoni, S. Binetti, S. Pizzini
Chin. Phys. Lett. 2004, 21 (11): 2242-2244 .  
Abstract   PDF(pc) (374KB) ( 582 )
We investigate optical properties of dislocations in nitrogen-doped and nitrogen-free Czochralski silicon. The dislocations are formed during crystal growth, but not formed during deformation. The results show that in nitrogen-doped samples, a broad band replaced the D1 band of dislocation, regardless of dislocation density. The replacement of D1 band is caused by the non-irradiation combination induced by oxygen precipitation. Moreover, a new emission at 0.975eV is observed in both the nitrogen-free and doped samples when the dislocation density is lower than 104 cm-2.
Adsorption of Si on Cu(100) and (111) Surfaces
HE Guo-Min
Chin. Phys. Lett. 2004, 21 (11): 2245-2248 .  
Abstract   PDF(pc) (542KB) ( 428 )
Employing the density-functional theory within the generalized gradient approximation, we investigate the interaction between atomic Si and the Cu(100) and (111) surfaces. Various structures of on-surface adsorption as well as surface-substitutional adsorption for a wide range of Si coverage are considered. Our results show that both Cu(100) and (111) surfaces are active for adsorption of Si. The c(2×2)-Si/Cu(100) surface alloy is energetically favourable for a large range of Si chemical potential while c(2×2)-Si/Cu(111) is energetically favourable only under Si rich conditions.
Properties of Diamond-Like Carbon Films Synthesized by Dual-Target Unbalanced Magnetron Sputtering
LIU Cui, LI Guo-Qing, GOU Wei, MU Zong-Xin, ZHANG Cheng-Wu
Chin. Phys. Lett. 2004, 21 (11): 2249-2251 .  
Abstract   PDF(pc) (354KB) ( 1272 )
Smooth, dense and uniform diamond-like carbon films (DLC films) for industrial applications have successfully been prepared by dual-target unbalanced magnetron sputtering and the DLC characteristics of the films are confirmed by Raman spectra. It is found that the sputtering current of target plays an important role in the DLC film deposition. Deposition rate of 3.5μm/h is obtained by using the sputtering current of 30 A. The friction coefficient of the films is 0.2--0.225 measured by using a pin-on-disc microtribometer. The structure of the films tends to have a growth of sp3 bonds content at high sputtering current. The compressive residual stress in the films increases with the increasing sputtering current of the target.
Analysis of Photosensitivity of Copolymer Optical Fibre Preform
MA Hui, LI Zeng-Chang, MING Hai, ZHANG Qi-Jin, TAM Hwa-Yaw, ZHANG Yong-Sheng, ZHANG Tao, WANG Pei, XIE Jian-Ping
Chin. Phys. Lett. 2004, 21 (11): 2252-2254 .  
Abstract   PDF(pc) (348KB) ( 750 )
The photosensitivity of copolymer optical fibre preform is analysed in comparison with the doped one. The effects of write conditions such as pump power and pump time have been studied. Then, the preform is drawn into single mode polymer optical fibre with core refractive index of 1.499, and core-cladding refractive-index difference of 0.008. Long-period birefringence gratings with period of 120um are fabricated in the fibre. The duty cycle is 50%, and the refractive index change in the exposed area is about 1×10-3.
Unified Understanding of Giant Magnetoresistance Effect and Magnetization in Granular Films with Two-Particle Size Distribution
Jian-Qing WANG$, Jordan Peck, Finnobarr O’Grady, Nam Kim
Chin. Phys. Lett. 2004, 21 (11): 2255-2258 .  
Abstract   PDF(pc) (346KB) ( 783 )
The giant magnetoresistance (GMR) effect and magnetization curves of Cu80Co20 granular thin films are studied and measured in a superparamagnetism temperature (180K). The correlation between the GMR effect and the magnetization is analysed in a unified framework. These two independent properties are fitted by assuming that there are two size distributions in the Co nano-particle population. Under an assumption, good fittings are achieved for both the GMR and the magnetization, using the minimal number of parameters. The obtained average particle sizes for the smaller and larger particles are 1.0 nm and 2.8 nm, respectively. In fitting the magneto-transport, a power scaling relationship with the particle size for each size population is proposed, and the fitted results reveal that a certain degree of magnetic bulk scattering is present in larger particles.
Binding Energy of Biexcitons in GaAs Quantum-Well Wires
LIU Jian-Jun, CHEN Xiao-Fang, LI Shu-Shen
Chin. Phys. Lett. 2004, 21 (11): 2259-2262 .  
Abstract   PDF(pc) (310KB) ( 740 )
The binding energy of a biexciton in GaAs quantum-well wires is calculated variationally by use of a two-parameter trial wavefunction and a one-dimensional equivalent potential model. There is no artificial parameter added in our calculation. Our results agree fairly well with the previous results. It is found that the binding energies are closely correlative to the size of wire. The binding energy of biexcitons is smaller than that of neutral bound excitons in GaAs quantum-well wires when the dopant is located at the centre of the wires.

Electron Transport of an Impurity Quantum Wire Under THz Electromagnetic Field Illumination
LI Yuan, ZHOU Guang-Hui, XIAO Xian-Bo, CHENG Fang, LIAO Wen-Hu
Chin. Phys. Lett. 2004, 21 (11): 2263-2266 .  
Abstract   PDF(pc) (306KB) ( 440 )
We theoretically investigate the effect of a single finite-size attractive impurity on the electron transport of a semiconductor quantum wire under the influence of a terahertz electromagnetic field illumination. In the free-particle framework, the time-dependent electronic states are obtained by introducing an unitary transformation, and the electronic transmission of the system is obtained by using the scattering matrix approach. In the case of the field frequency resonant with the lateral energy spacing of the two lowest levels, a step-like structure for the transmission probability versus the total electron energy is predicted. Furthermore, due to the interplay between the single impurity and the applied field, the transmission probability curve in the non-resonant case shows a structure of a resonance dip on the interference pattern background with certain parameters of the impurity.
Enhancement of Quantum Current in Mesoscopic Coupled Rings
JI Ying-Hua, LUO Hai-Mei, HU Ju-Ju, LIU Gang,
Chin. Phys. Lett. 2004, 21 (11): 2267-2270 .  
Abstract   PDF(pc) (381KB) ( 444 )
We discuss the relationship between external magnetic field and persistent currents of three mesoscopic-coupled rings with charge discreteness. Through numerical calculation and analysis, it is found that the properties of the persistent currents depend on both external magnetic flux and coupled factors. The positive coupling between the rings will decrease the persistent currents when 0 < m < 1 with m being the coupling coefficient. The quantum current magnification effect appearing in the rings is also investigated.
Effect of PbS on Properties of the Er3+-doped TeO2-based Glasses
WANG Guo-Nian, DAI Shi-Xun, ZHANG Jun-Jie, XU Shi-Qing, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (11): 2275-2277 .  
Abstract   PDF(pc) (319KB) ( 503 )
Novel Er3 doped TeO2-based glasses containing PbS have been prepared in argon atmosphere in carbon crucibles. The thermal analysis and spectroscopic properties of those glasses have been considered in terms of sulfide influence. Judd--Ofelt theory is introduced to calculate the bandwidth and the emission cross-section. The results demonstrate that addition of PbS into tellurite glasses results in increasing bandwidth from 71.8 to 78.4 nm, for improving emission cross-section from 6.6 to 8.1×10-21,cm2 and slightly decreasing emission lifetime from 3.4 to 3.1 ms compared to pure oxide glass.
Fabrication of Pentacene Thin-Film Transistors with Patterned Polyimide Photoresist as Gate Dielectrics and Research of Their Degradation
LIANG Yan, DONG Gui-Fang, HU Yuan-Chuan, HU Yan, WANG Li-Duo, QIU Yong
Chin. Phys. Lett. 2004, 21 (11): 2278-2280 .  
Abstract   PDF(pc) (407KB) ( 523 )
Pentacene organic thin-film transistors using commercial photoresist as gate dielectrics were fabricated. The photoresist was spin-coated and directly patterned by photolithography. As a result, the fabrication processes were greatly reduced. With the characteristics of the transistors measured, the degradation of the transistors was investigated. In the search for the factors causing degradation, a transistor using poly(methyl methacrylate) as the gate dielectric was also fabricated. It is regarded that the degradation is caused by the changes at the interface between photoresist and pentacene film.

Thermal Diffusivity of Ordered Double Perovskite A2FeMoO6 ( A = Ca, Sr and Ba)
LIU Xiao-Jun, HUANG Qiao-Jian, NIU Dong-Lin, XU Sheng, ZHANG Shu-Yi
Chin. Phys. Lett. 2004, 21 (11): 2281-2284 .  
Abstract   PDF(pc) (498KB) ( 945 )
Thermal diffusivity has been investigated in ordered double perovskite Sr2FeMoO6 by means of transient surface grating technique in the temperature range of 300--450K. The thermal diffusivity shows an appreciable decrease from 39 mm2/s at 300 K to 37 mm2/s at 360 K in the ferromagnetic phase, and then steeply drops to 10 mm2/s with further increasing temperature above the critical temperature Tc~380 K. Such an abrupt decrease of the thermal diffusivity has been ascribed to the structural phase transition at Tc. We further investigate the lattice effect on the thermal diffusivity in A2FeMoO6 (A= Ca, Sr and Ba) by substitution of Ca2+ or Ba2+ ions for Sr2+ ions at 300 K. We find that the thermal diffusivity increases from 35 mm2/s for A= Ca to 41 mm2/s for A= Ba. Considering the change of the Fe--O--Mo bond angle from 152.4°C for A= Ca to 180°C for A= Ba, the increased thermal diffusivity for Ba compound has been ascribed to the enhanced hybridization between transition-metal d and oxygen p states due to the larger Fe--O--Mo bond angle and hence the wider one-electron bandwidth
Evidence of the Griffiths Phase in Doped Manganites Studied by Electron Paramagnetic Resonance Measurements
YUAN Song-Liu, LIU Sheng, CAO Heng, SHANG Jing-Lin, DONG Bo, XIA Zheng-Cai, LI Jian-Qing
Chin. Phys. Lett. 2004, 21 (11): 2285-2288 .  
Abstract   PDF(pc) (479KB) ( 993 )
A systematic investigation of electron paramagnetic resonance above the Curie temperature Tc is performed on polycrystalline (La1-xYx)x2/3Ca1/3MnO3 (x=0, 0.15 and 0.2) samples. The results indicate anomalous paramagnetic behaviour below a temperature TG and, the anomalous extent
increases with cooling from TG. Especially, the resonance linewidth ΔHpp anomalously increases with cooling for the temperature range of TCG. The experimental observation is discussed within the framework of the Griffiths theory that predicts the existence of ferromagnetic clusters above TC. We explain the observed anomalous paramagnetic behaviour to be due to the magnetic heterogeneity caused by the ferromagnetic clusters which appear in the Griffiths phase.
Magnetic Properties of One-Dimensional Ferrimagnetic Mixed (1,3/2) Spin Chain with Single-Ion Anisotropy
Ekrem Aydiner
Chin. Phys. Lett. 2004, 21 (11): 2289-2291 .  
Abstract   PDF(pc) (322KB) ( 478 )
We have carried out Monte Carlo simulations to study the magnetic properties of a mixed S=1 and S=3/2 ferrimagnetic system interacting antiferromagnetically on a one-dimensional spin chain with single-ion anisotropy. It has been shown that at sufficiently low temperatures, the system has magnetization plateaus near the ground state under an external field. Other interesting physical quantities such as the specific heat and the Néel order at low temperatures are also discussed.
Frequency Upconversion Emission of Er3+-Doped Strontium--Lead--Bismuth Glasses
SUN Hong-Tao, DAI Shi-Xun, XU Shi-Qing, HU Li-Li, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (11): 2292-2294 .  
Abstract   PDF(pc) (372KB) ( 591 )
Er3+-doped strontium--lead--bismuth glasses for developing potential upconversion lasers have been fabricated and characterized. Under 975 nm excitation, intense green and red emissions centred at 525, 546, and 657 nm, corresponding to the transitions 2H11/24I15/2, 4S3/24I15/2, and 4F9/24I15/2, respectively, were observed at room temperature. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for 525 and 546nm emissions, and energy transfer upconversion for 657nm emission.

Time-Resolved Terahertz Spectroscopy with Free-Space Electro-Optic Sampling
ZHANG Liang-Liang, ZHAO Guo-Zhong, ZHONG Hua, HU Ying, ZHANG Cun-Lin
Chin. Phys. Lett. 2004, 21 (11): 2295-2297 .  
Abstract   PDF(pc) (466KB) ( 663 )
We present a time-resolved ultrafast measurement in terahertz (THz) frequency region by means of the free-space electro-optic sampling. The fast delay scan technique is used to suppress the noise with low frequency and to improve the signal-to-noise ratio of the system. The transmission spectra of different materials are obtained. The optical properties of these materials in a THz region are shown. The broadening of spectrum and chirping phenomena are illustrated. We find that polystyrene is an excellent material for the THz application.
Red Organic Light-Emitting Diodes Utilizing a Novel Metal Complex as the Host Material
WEI Peng, QIAO Juan, GAO Yu-Di, WANG Li-Duo, QIU Yong
Chin. Phys. Lett. 2004, 21 (11): 2298-2300 .  
Abstract   PDF(pc) (460KB) ( 493 )
Red organic light-emitting diodes (OLEDs) utilizing a novel metal complex with a tridentate ligand, salicylidene-o-aminophenolato (8-quinolinoato) aluminium (Al(Saph-q)) as the host material, have been fabricated. In the OLEDs, N,N’-bis-(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4-’diamine (NPB) and 4-(dicyanomethylene)-2-(t-butyl)6-methyl-4H-pyran (DCJTB) are used as the hole-transporting and dopant materials, respectively. Compared with the OLEDs using tris(8-quinolinolato) aluminium (Alq3) as the host material, improved device performance with higher efficiency (0.62lm/W) has been achieved, in the consideration that developing host materials is a promising way to achieve excellent red emission OLEDs.
Photoluminescence Characterization of Nanocrystalline ZnO Array
CHANG Yong-Qin, YU Da-Peng, LI Guo-Hua, FANG Zai-Li, ZHANG Ye, CHEN Yao-Feng, YANG FU-Hua
Chin. Phys. Lett. 2004, 21 (11): 2301-2304 .  
Abstract   PDF(pc) (478KB) ( 659 )
High-density and uniform well-aligned ZnO sub-micron rods are synthesized on the silicon substrate over a large area. The morphology and structure of the ZnO sub-micron rods are investigated by x-ray diffraction, transmission electron microscopy and Raman spectra. It is found that the ZnO sub-micron rods are of high crystal quality with the diameter in the range of 400--600 nm and the length of several micrometres long. The optical properties were studied by photoluminescence spectra. The results show that the intensity of the ultraviolet emission at 3.3 eV is rather high, meanwhile the deep level transition centred at about 2.38 eV is weak. The free exciton emission could also be observed at low temperature, which implies the high optical quality of the ZnO sub-micron rods. This growth technique provides one effective way to fabricate the high crystal quality ZnO nanowires array, which is very important for potential applications in the new-type optoelectronic nanodevices.

SiC-Based p+ nn+ Diode for Picosecond Semiconductor Closing Switch
ZHANG Fei, LI Cheng-Fang
Chin. Phys. Lett. 2004, 21 (11): 2305-2307 .  
Abstract   PDF(pc) (384KB) ( 584 )
We study a SiC-based diode with a p+ nn+ structure for picosecond semiconductor closing switch and discuss the physical process, which underlies the operation principle of high-power closing switch based on a delayed breakdown diode. By two-dimensional mixed device-circuit simulations, we demonstrate a single device reliably operated at 4 kV and at risetime 11 ps with high output dV/dt=276 kV/ns, which is in good agreement with the experimental results.
Ultrafast Photoelectric Effects in Heterojunctions of La0.7Sr0.3MnO3 and Si
Lü Hui-Bin, JIN Kui-Juan, HUANG Yan-Hong, HE Meng, ZHAO Kun, ZHOU Yue-Liang, CHENG Bo-Lin, CHEN Zheng-Hao, DAI Shou-Yu, YANG Guo-Zhen
Chin. Phys. Lett. 2004, 21 (11): 2308-2309 .  
Abstract   PDF(pc) (261KB) ( 1026 )
Ultrafast photoelectric effects have been observed in p--n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3-/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2 ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of ~25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV/mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser.

A Novel Magnetic Linear Encoder Designed by Using the Slant Multi-Phase Filtering Model
SHI Yu, XING Huai-Zhong, ZHANG Huai-Wu, LIU Ying-Li, JING Yu-Lan, ZHONG Zhi-Yong
Chin. Phys. Lett. 2004, 21 (11): 2310-2312 .  
Abstract   PDF(pc) (452KB) ( 714 )
A novel design model based on the slant multi-phase filtering model is presented. A magnetic linear encoder with sinusoidal output voltage waveform has been investigated, and the improved sinusoidal output waveform can be easily acquired. A minimum 6% of distortion factor, when the difference of slant phase is 2π/3, is observed. It is found that the Wheatstone bridge type sensor, made of NiFe(450A)/NiO(300A) bilayers deposited on Si (001) substrate, can enhance both output signal and thermal stability, and then can be widely used in the field of magneto-resistive sensor.
Pseudo-Spin Model for the Cytoskeletal Microtubule Surface
CHEN Ying, QIU Xi-Jun, LI Ru-Xin
Chin. Phys. Lett. 2004, 21 (11): 2313-2315 .  
Abstract   PDF(pc) (213KB) ( 402 )
Due to the inherent symmetry structures and the electric properties in the microtubule (MT), we treat the MT as a one-dimensional ferroelectric system and describe the nonlinear dynamics of dimer electric dipoles in one protofilament of the MT by virtue of the double-well potential. Consequently, the physical problem has been mapped onto the pseudo-spin system, and the mean-field approximation has been taken to obtain some physical results, including the expression for the phase transition temperature Tc and the estimated value of Tc (about 312 K).
Effects of Magnetic Coupling on Profile of Emission Lines and Images of an Accretion Disc Around a Black Hole
MA Ren-Yi, WANG Ding-Xiong, LEI Wei-Hua, YAO Guo-Zheng
Chin. Phys. Lett. 2004, 21 (11): 2316-2319 .  
Abstract   PDF(pc) (400KB) ( 442 )
The profiles of emission lines and images of an accretion disc around a black hole (BH) are simulated by considering the effects of the magnetic coupling (MC) of a central BH with the disc. The MC effects are discussed for both slow- and fast-spinning BHs, and the following results are obtained. Firstly, the width of the emission lines and the brightness of the disc are reduced and augmented for slow- and fast-spinning BHs, respectively. Secondly, the image of the disc becomes dimmer and brighter near the inner edge of the disc for slow- and fast-spinning BHs, respectively. It turns out that all these results arise from the MC effects on the position of the dominant emission region of the accretion disc.
Extra Dimensions and Vacuum Dark Energy Models
CHEN Chi-Yi, SHEN You-Gen,
Chin. Phys. Lett. 2004, 21 (11): 2320-2322 .  
Abstract   PDF(pc) (197KB) ( 494 )
The role of vacuum energy or cosmological constant in cosmology is discussed in a kind of nontrivial higher-dimensional model. Under the framework of Einstein's gravity, we obtain the corresponding equations of motion and find that the cosmological constant and vacuum energy in the full regime does not drive its acceleration, but decelerates the expansion of the universe. The dimension of space is required to be n=3 if we regard vacuum energy or cosmological constant as the candidate to drive the accelerated expansion of the universe.
68 articles