Chin. Phys. B
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CN 11-5639/O4
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Chin. Phys. B  
  Chin. Phys. B--2005, Vol.14, No.5
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GENERAL

A class of integrable expanding model for the coupled AKNS-Kaup-Newell soliton hierarchy  

Yang Hong-Xiang, Xu Xi-Xiang
Chin. Phys., 2005, 14 (5): 869-874 doi: 10.1088/1009-1963/14/5/001
Full Text: [PDF 215 KB] (Downloads:665)
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An isospectral problem is established by means of a sub-algebra of Loop Lie algebra ?1, from which the coupled AKNS-Kaup-Newell soliton hierarchy is derived. Subsequently, the integrable expending model i.e. integrable coupling is constructed through enlarging the corresponding Loop algebra into ?2.

Homotopy perturbation method of equatorial eastern Pacific for the El Ni?o-Southern Oscillation mechanism      

Mo Jia-Qi, Lin Wan-Tao
Chin. Phys., 2005, 14 (5): 875-878 doi: 10.1088/1009-1963/14/5/002
Full Text: [PDF 203 KB] (Downloads:484)
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The EI Ni?o/La Ni?a and the Southern Oscillation (ENSO) is an interannual phenomenon involved in the tropical Pacific Ocean- atmosphere interactions. In this paper, the aim is to create an asymptotic solving method of nonlinear equation for the ENSO models. And based on a class of oscillator of ENSO models, employing the method of homotopic mapping, the approximation solution of corresponding problem is studied. It is proved from the results that homotopic method can be used for analyzing the sea surface temperature anomaly in the equatorial eastern Pacific and the thermocline depth anomaly of the atmosphere-ocean oscillation for ENSO model.

The third-order Lagrange equation for mechanical systems of variable mass  

Ma Shan-Jun, Ge Wei-Guo, Huang Pei-Tian
Chin. Phys., 2005, 14 (5): 879-881 doi: 10.1088/1009-1963/14/5/003
Full Text: [PDF 173 KB] (Downloads:1283)
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In this paper, based on the third-order D’Alember-Lagrange principle for mechanical systems of variable mass, the third-order Lagrange’s equations of mechanical systems of variable mass have been obtained. From the equations the motion of mechanical systems of variable mass can be studied. In addition, the equations may enrich the theory of third-order differential equation.

Hojman's conservation theorems for generalized Raitzin canonical equations of motion    

Qiao Yong-Fen, Li Ren-Jie, Zhao Shu-Hong
Chin. Phys., 2005, 14 (5): 882-887 doi: 10.1088/1009-1963/14/5/004
Full Text: [PDF 220 KB] (Downloads:423)
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Using the Lie symmetry under infinitesimal transformations in which the time is not variable, Hojman’s conservation theorems for Raitzin’s canonical equations of motion in generalized classical mechanics are studied. The generalized Raitzin’s canonical equations of motion are established. The determining equations of Lie symmetry under infinitesimal transformations are given. The Hojman’s conservation theorems of the system are established. Finally, an example is also presented to illustrate the application of the result.

Discrete variational principle and the first integrals of the conservative holonomic systems in event space     

Zhang Hong-Bin, Chen Li-Qun, Liu Rong-Wan
Chin. Phys., 2005, 14 (5): 888-892 doi: 10.1088/1009-1963/14/5/005
Full Text: [PDF 217 KB] (Downloads:469)
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The intent of this paper is to show that first integrals of discrete equation of motion for the conservative holonomic systems can be determined explicitly by investigating the invariance properties of the discrete Lagrangian in event space. The result obtained is a discrete analogue of Noether’s theorem in the calculus variations. The two examples are given to illustrate the applications of the result.

Controlled quantum teleportation and secure direct communication

Gao Ting, Yan Feng-Li, Wang Zhi-Xi
Chin. Phys., 2005, 14 (5): 893-897 doi: 10.1088/1009-1963/14/5/006
Full Text: [PDF 209 KB] (Downloads:618)
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We present a controlled quantum teleportation protocol. In the protocol, quantum information of an unknown state of a 2-level particle is faithfully transmitted from a sender (Alice) to a remote receiver (Bob) via an initially shared triplet of entangled particles under the control of the supervisor Charlie. The distributed entangled particles shared by Alice, Bob and Charlie function as a quantum information channel for faithful transmission. We also propose a controlled and secure direct communication scheme by means of this teleportation. After ensuring the security of the quantum channel, Alice encodes the secret message directly on a sequence of particle states and transmits them to Bob supervised by Charlie using this controlled quantum teleportation. Bob can read out the encoded message directly by the measurement on his qubit. In this scheme, the controlled quantum teleportation transmits Alice’s message without revealing any information to a potential eavesdropper. Because there is not a transmission of the qubit carrying the secret message between Alice and Bob in the public channel, it is completely secure for controlled and direct secret communication if perfect quantum channel is used. The feature of this scheme is that the communication between two sides depends on the agreement of the third side.

Quantum logic networks for controlled teleportation of a single particle via W state   

Yuan Hong-Chun, Qi Kai-Guo
Chin. Phys., 2005, 14 (5): 898-901 doi: 10.1088/1009-1963/14/5/007
Full Text: [PDF 231 KB] (Downloads:445)
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We discuss the scheme for probabilistic and controlled teleportation of an unknown state of one particle using the general three-particle W state as the quantum channel. The feature of this scheme is that teleportation between two sides depends on the agreement of the third side (Charlie), who may participate the process of quantum teleportation as a supervisor. In addition, we also construct efficient quantum logic networks for implementing the new scheme by means of the primitive operations.

H tracking control of coupled spatiotemporal chaos with parametric uncertainties based on fuzzy observers      

Dou Chun-Xia, Zhang Shu-Qing
Chin. Phys., 2005, 14 (5): 902-907 doi: 10.1088/1009-1963/14/5/008
Full Text: [PDF 262 KB] (Downloads:402)
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Due to the interactions among coupled spatio-temporal subsystems and the parametric uncertainties, it is difficult to achieve the tracking control of the coupled spatio-temporal chaos with parametric uncertainties. However every subsystem of the coupled spatio-temporal chaos can be approximated by a set of fuzzy models. Considering that all states of the subsystem are not available, fuzzy observers are suggested to estimate these states. Based on these fuzzy models and observers, and the consideration of the parametric uncertainties, a newfuzzy tracking control scheme is proposed, where a linear matrix inequalities (LMI) is employed to represent the feedback controller. The parameters of the controller are obtained by using convex optimization techniques of LMI. The robust stability of the controlled system is guaranteed in this scheme. The tracking performances are tested by simulation as an example.

Chaos and chaotic control in a fractional-order electronic oscillator     

Gao Xin, Yu Jue-Bang
Chin. Phys., 2005, 14 (5): 908-913 doi: 10.1088/1009-1963/14/5/009
Full Text: [PDF 347 KB] (Downloads:722)
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In this paper, we study the chaotic behaviours in a fractional-order chaotic electronic oscillator . We find that chaos exists in the fractional-order electronic oscillator with an order being less than 3. In addition, we numerically simulate the continuances of the chaotic behaviours in the electronic oscillator with orders from 2.8 to 3.2. Finally, we further investigate the method of controlling a fractional-order electronic oscillator based on adaptive backstepping. Numerical simulations show the effectiveness and feasibility of this approach.

A novel sliding mode nonlinear proportional-integral control scheme for controlling chaos   

Yu Dong-Chuan, Wu Ai-Guo, Yang Chao-Ping
Chin. Phys., 2005, 14 (5): 914-921 doi: 10.1088/1009-1963/14/5/010
Full Text: [PDF 366 KB] (Downloads:620)
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A novel sliding mode nonlinear proportional-integral control (SMNPIC) scheme is proposed for driving a class of time-variant chaotic systems with uncertainty to arbitrarily desired trajectory with high accuracy. The SMNPIC differs from the previous sliding mode techniques in the sense that a nonlinear proportional-integral action of sliding function is involved in control law, so that both the steady-state error and the high-frequency chattering are reduced, and meanwhile, robustness and fastness are guaranteed. In addition, the proposed SMNPIC actually acts as a class of nonlinear proportional- integral-differential (PID) controller, in which the tracking error and its derivatives up to (n-1)th order as well as the integral of tracking error are considered, so that more useful information than traditional PID can be implemented and better dynamic and static characteristics can obtained. Its good performance for chaotic control is illustrated through a Duffing-Holmes system with uncertainty.

Chaotic time series prediction using mean-field theory for support vector machine    

Cui Wan-Zhao, Zhu Chang-Chun, Bao Wen-Xing, Liu Jun-Hua
Chin. Phys., 2005, 14 (5): 922-929 doi: 10.1088/1009-1963/14/5/011
Full Text: [PDF 478 KB] (Downloads:598)
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This paper presents a novel method for predicting chaotic time series which is based on the support vector machines approach and it uses the mean-field theory for developing an easy and efficient learning procedure for the support vector machine. The proposed method approximates the distribution of the support vector machine parameters to a Gaussian process and uses the mean-field theory to estimate these parameters easily, and select the weights of the mixture of kernels used in the support vector machine estimation more accurately and faster than traditional quadratic programming-based algorithms. Finally, relationships between the embedding dimension and the predicting performance of this method are discussed, and the Mackey-Glass equation is applied to test this method. The stimulations show that the mean-field theory for support vector machine can predict chaotic time series accurately, and even if the embedding dimension is unknown, the predicted results are still satisfactory. This result implies that the mean-field theory for support vector machine is a good tool for studying chaotic time series.

Improvement of driving safety in road traffic system    

Li Ke-Ping, Gao Zi-You
Chin. Phys., 2005, 14 (5): 930-934 doi: 10.1088/1009-1963/14/5/012
Full Text: [PDF 340 KB] (Downloads:519)
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Road traffic system is a complex system in which human participate directly. In this system, human factors play a very important role. In this paper, a kind of control signal has been designated at a given site (i.e., signal point) of the road. Under the effect of control signal, the drivers will decrease their velocities when their vehicles pass the signal point. Our aim is to transit the traffic flow states from disorder to order, and then improve the traffic safety. We have tested this technique for the two-lane traffic model that is based on the deterministic NaSch traffic model. The simulation results indicate that the traffic flow states can be transited from disorder to order. Different order states can be observed in the system, and these states are safer.

Imaging properties of coherent anti-Stokes Raman scattering microscope     

Yuan Jing-He, Xiao Fan-Rong, Wang Gui-Ying, Xu Zhi-Zhan
Chin. Phys., 2005, 14 (5): 935-941 doi: 10.1088/1009-1963/14/5/013
Full Text: [PDF 2407 KB] (Downloads:491)
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Coherent anti-Stokes Raman scattering (CARS) microscope with the combination of confocal and CARS techniques is a remarkable alternative for imaging chemical or biological specimens that neither fluoresce nor tolerate labeling. CARS is a nonlinear optical process, the imaging properties of CARS microscopy will be very different from the conventional confocal microscope. In this paper, the intensity distribution and the polarization property of the optical field near the focus was calculated. By using the Green function, the precise analytic solution to the wave equation of a Hertzian dipole source was obtained. We found that the intensity distributions vary considerably with the different experimental configurations and the different specimen shapes. So the conventional description of microscope (e.g. the point spread function) will fail to describe the imaging properties of CARS microscope.
NUCLEAR PHYSICS

Two-source emission of relativistic alpha particles in 16O-Em interactions at 3.7 A GeV    

Song Fu, Zhang Dong-Hai, Li Jun-Sheng
Chin. Phys., 2005, 14 (5): 942-948 doi: 10.1088/1009-1963/14/5/014
Full Text: [PDF 282 KB] (Downloads:432)
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The emission of alpha projectile fragments has been studied in 16O-emulsion interactions at 3.7 A GeV.The angular distributions of relativistic alphas cannot be explained by a clean-aut participant-spectator model.Therefore it is assumed that alphas originate from two distinct sources differing in their temperatures.

I-V characteristics of foilless diodes   

Liu Guo-Zhi, Huang Wen-Hua, Yang Zhan-Feng
Chin. Phys., 2005, 14 (5): 949-952 doi: 10.1088/1009-1963/14/5/015
Full Text: [PDF 258 KB] (Downloads:358)
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Some physical characteristics of foiless diodes are obtained and analyzed by numerical simulations. Relations between diode current and configuration parameters, diode voltage and external magnetic field are investigated. Employing these relations and assuming that the external magnetic field is intense enough, the diode current can be approximately written as Ib=(7.5/x)(x+(0.81-x)/(1+0.7Ld2/δr))(r2/3-1)3/2, in which is the A-K gap, the outer radius of cathode, and the radius of drifting tube;x=ln(Rp/Rc),δr =Rp-Rc , . This expression is comparatively accurate for with different configuration parameters and voltages, results obtained from this expression are consistent with that of numerical simulations within an error of 10%.
CLASSICAL AREAS OF PHENOMENOLOGY

Composite second-order performance improvement in optical fibre CATV transmission system using chirped fibre grating

Ye Qing, Liu Feng, Cai Hai-Wen, Qu Rong-Hui, Fang Zu-Jie
Chin. Phys., 2005, 14 (5): 969-973 doi: 10.1088/1009-1963/14/5/019
Full Text: [PDF 357 KB] (Downloads:596)
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Theoretically, we analyze the dispersion compensation characteristics of the chirped fiber grating (CFG) in an optical fiber cable television (CATV) system and obtain the analytic expression of the composite second-order (CSO) distortion using the time-domain form of the field envelope wave equation. The obtained result is in good agreement with the numerical simulation result. Experimentally, we verify the result by making use of the tunable characteristics of CFG to change the dispersion compensation amount and obtain an optimal CSO performance in a 125-km fiber transmission link. Both the theoretical and experimental results show that the CSO performance can be improved by properly choosing the dispersion compensation amount for a certain fiber transmission link.

Proposal of many-party controlled teleportation for multi-qubit entangled W state

Huang Zhi-Ping, Li Hong -Cai
Chin. Phys., 2005, 14 (5): 974-979 doi: 10.1088/1009-1963/14/5/020
Full Text: [PDF 220 KB] (Downloads:423)
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A scheme of M-party controlled teleportation for N-qubits entangled W state via (N-1) EPR pairs and one (M+2)-qubits GHZ state is proposed. We achieve the teleportation in such a way that M agents execute the Hadamard transformation, perform the measurement on their qubits and tell the outcome of measurement to receiver. Then we discuss that the receiver can not fully recover the state of the sender if one agent does not cooperate.

Evolution of field entropy and entanglement in the intensity-dependent two-mode Jaynes-Cummings model    

Gao Yun-Feng, Feng Jian, Wang Ji-Suo
Chin. Phys., 2005, 14 (5): 980-984 doi: 10.1088/1009-1963/14/5/021
Full Text: [PDF 251 KB] (Downloads:529)
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The evolution of the entanglement degree of two-mode fields and atom with the intensity-dependent coupling is investigated by using von Neumann entropy. The results for the initial fields in both coherent states and two-mode squeezed vacuum state are calculated. The influence of the field intensity on the entropy is discussed. It is found that the field and atom are in maximum entanglement but go with periodic pulse disentanglement completely under the condition of strong initial field.

Resonantly enhanced continuous-wave four-wave mixing with spontaneously generated coherence in a five-state cold atomic medium

Li Jia-Hua, Luo Jin-Ming, Yang Wen-Xing, Peng Ju-Cun
Chin. Phys., 2005, 14 (5): 985-990 doi: 10.1088/1009-1963/14/5/022
Full Text: [PDF 272 KB] (Downloads:446)
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Using Schr\"odinger-Maxwell formalism, we propose and analyze a continuous-wave four-wave mixing (FWM) scheme for the generation of coherent light in a five-state double-\Lambda atomic system with or without spontaneously generated coherence (SGC) based on electromagnetically induced transparency (EIT). We derive the corresponding explicit analytical expressions for the generated FWM field under the steady-state condition. The influence of hyperfine sublevel and SGC effect on the amplitude of the generated FWM field is predicted in details via the derived analytical expressions. We also give a brief discussion on the experimental realization of the proposed scheme.

Output-power controllable erbium-doped fibre laser via a high-birefringence fibre loop mirror with applied stress

Liu Yan-Ge, Feng Xin-Huan, Li Yao, Yuan Shu-Zhong, Zhang Wei-Gang, Kai Gui-Yun, Dong Xiao-Yi
Chin. Phys., 2005, 14 (5): 991-994 doi: 10.1088/1009-1963/14/5/023
Full Text: [PDF 242 KB] (Downloads:439)
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In this paper, a novel output-power controllable erbium-doped fibre laser, based on a strain-applied high-birefringence fibre loop mirror (HBFLM), was proposed and demonstrated. The reflectivity of HBFLM could be changed from about 0.8% to 100% because the fibre length and birefringence of the high-birefringence fibre (HBF) were altered via bonding a part of HBF to the centric surface of an uniform-strength cantilever beam and applying different stress at end of the beam. As a result, the laser output power could be adjusted and controlled in a dynamic range of more than 33 dB. The laser is not only a controllable and adjustable output-power laser with simple configuration and low cost, but also can be used for optimizing the output characteristics of a linear cavity laser via easily finding out the optimized reflectivity of the reflectors.

Dark decay behaviours of photorefractive grating induced by two deep-trap levels in Ce:BaTiO3

Zhang Ming, Xu Ying, Hong Zhi
Chin. Phys., 2005, 14 (5): 995-998 doi: 10.1088/1009-1963/14/5/024
Full Text: [PDF 232 KB] (Downloads:330)
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Dark decay behaviors of photorefractive grating in Ce:BaTiO3 crystal are studied experimentally. It is observed that two deep-trap levels, i.e. Fe-ion deep level and Ce-ion deep level, both participate in the photorefractive process. A simplified two-deep model is presented based on the one-deep trap model and the shallow-deep trap model, with which we analyze quantitatively the contribution of each deep level to the whole space-electric field and thus the photorefractive grating varying with the different grating wave vectors and different writing intensities.

Luminescence of transient single cavitation bubbles in non-aqueous liquids produced by the modified tube-arrest method

Wu Xian-Mei, Ying Chong-Fu, Li Chao
Chin. Phys., 2005, 14 (5): 999-1005 doi: 10.1088/1009-1963/14/5/025
Full Text: [PDF 8183 KB] (Downloads:372)
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Large transient single bubbles of effective diameters in cm’s were generated by the modified tube-arrest method in 7 nonaqueous liquids besides water and in glycerin-water mixtures. During collapse, nearly all these bubbles gave off light emissions of various intensities, which in 6 liquids were correlated with the saturation vapor pressure and viscosity of the respective liquid. Bubbles in ethylene glycol and propylene glycol did not follow this rule, but those in the former liquid showed some unusual regularity in luminescence variation and bubbles in both liquids were particularly bright. The luminous properties of the transient single bubble are compared with those of the usual stable single bubble.
ATOMIC AND MOLECULAR PHYSICS

Spectra of highly ionized nickel

Yang Zhi-Hu, Du Shu-Bin, Zeng Xian-Tang, Su Hong, Wang You-De, Zhang Yan-Ping
Chin. Phys., 2005, 14 (5): 953-958 doi: 10.1088/1009-1963/14/5/016
Full Text: [PDF 230 KB] (Downloads:269)
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The spectrum of highly ionized nickel in the region 120-400 ? was studied by means of the beam-foil method. Nickel ions of 45 and 70 MeV were provided by the HI-13 tandem accelerator at China Institute of Atomic Energy. Numerous lines attributed to Ni XIII to XX transitions have been identified, and eighteen lines of them were newly measured.

Relativistic calculation of dielectronic recombination for He-like krypton     

Shi Xi-Heng, Wang Yan-Sen, Chen Chong-Yang, Gu Ming-Feng
Chin. Phys., 2005, 14 (5): 959-963 doi: 10.1088/1009-1963/14/5/017
Full Text: [PDF 286 KB] (Downloads:557)
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Dielectronic recombination cross sections and rate coefficients of He-like Kr are calculated employing the relativistic Flexible Atomic Code (FAC) in which autoionization rates are calculated based on relativistic distorted-wave approximation and the configuration interaction is considered. The Auger and total radiative rates of some strong resonances are listed and compared with the results from MCDF and HULLAC methods. The n-3 scaling law is checked and used to extrapolate rate coefficients. We also show the variation of DR branching ratio with different DR resonances or atomic number Z. The effect of radiative cascades on DR cross sections are studied.

Positron total cross sections for collisions with O2, H2O and CH4 in energy range from 30 to 3000eV

Shi De-Heng, Liu Yu-Fang, Sun Jin-Feng, Zhu Zun-Lue, Yang Xiang-Dong
Chin. Phys., 2005, 14 (5): 964-968 doi: 10.1088/1009-1963/14/5/018
Full Text: [PDF 246 KB] (Downloads:404)
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Total (elastic plus inelastic) cross sections for the scattering of positrons by three molecules (O2, H2O and CH4) in the energy range from 30 to 3000eV are calculated using the additivity rule model at Hartree-Fock level. A complex optical model potential modified by incorporating the concept of bonded atom which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule is firstly employed for the TCS calculation of positron-molecule scattering. The quantitative total cross sections are compared with those obtained in experiments and other theories wherever available, and good agreement is obtained in the energy range from 30 to 3000eV. It is shown that the additivity rule model together with the modified complex optical model potential is completely suitable for the total cross section calculations of the positron-molecule scattering.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Internal stress and yield strength of copper films on substrates

Zhang Jian-Min, Zhang Yan, Xu Ke-Wei
Chin. Phys., 2005, 14 (5): 1006-1010 doi: 10.1088/1009-1963/14/5/026
Full Text: [PDF 238 KB] (Downloads:422)
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Internal stress and yield strength of pure copper films on substrates were characterized by X-ray diffraction and thermal-cycle substrate curvature methods. The internal stress was of tension, and decreased with increasing working-gas (argon) pressure and increased with increasing film thickness. Tensile yield strength of copper film on steel substrate was reciprocal to the film thickness. Similarly, the compressive yield strength depended strongly on the film thickness, the thinner the film thickness, the larger the compressive yield strength.

Conductance of three-terminal molecular bridge based on tight-binding theory

Wang Li-Guang, Li Yong, Yu Ding-Wen, Tagami Katsunori, Tsukada Masaru
Chin. Phys., 2005, 14 (5): 1011-1014 doi: 10.1088/1009-1963/14/5/027
Full Text: [PDF 257 KB] (Downloads:465)
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The quantum transmission characteristic of three-benzene ring nano-molecular bridge is investigated theoretically by using Green's function approach based on tight-binding theory with only a π orbital per carbon atom at the site. The transmission probabilities that electrons transport through the molecular bridge from one terminal to the other two terminals are obtained. The electronic current distributions inside the molecular bridge are calculated and shown in graphical analogy by the current density method based on Fisher-Lee formula at the energy points E=±0.42, ±1.06 and ±1.5, respectively, where the transmission spectra appear peaks. We find that the transmission spectra are related to the incident electronic energy and the molecular levels strongly, and the current distributions agree well with Kirchhoff quantum current momentum conservation law.

Atomic-scale calculation of energies of Cu (001) twist boundaries

Zhang Jian-Min, Wei Xiu-Mei, Xin Hong, Xu Ke-Wei
Chin. Phys., 2005, 14 (5): 1015-1020 doi: 10.1088/1009-1963/14/5/028
Full Text: [PDF 267 KB] (Downloads:600)
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Unrelaxed energies for Cu (001) twist grain boundaries (GBs) have been calculated using Modified Analytical Embedded Atom Method (MAEAM). The results show that, except zero energy at (perfect crystal), a small cusp exists at the twist angle of 36.87° corresponding to , which agrees with experimental results. For other misorientations, the GB energies keep almost constant even for a twist angle as small as 1.94°. Homogeneous expansion and that perpendicular to the GB plane result in obvious decrease of energy, especially the latter.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Effects of spin-orbit interaction and magnetic field on the electron transport in quasi-1D ferromagnetic/semiconductor/ferromagnetic system  

Li Yu-Xian, Li Bo-Zang
Chin. Phys., 2005, 14 (5): 1021-1024 doi: 10.1088/1009-1963/14/5/029
Full Text: [PDF 247 KB] (Downloads:465)
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Based on the transfer matrix method, we investigate the effects of Rashba spin-orbit interaction and magnetic field on the electron transport in a quasi one-dimensional FM/S/FM system, where FM and S represent the ferromagnetic metal and semiconductor, respectively. The results show that the oscillating scope of the transmission increases with the magnetic field increasing. In the antiferromagnetic alignment, the spin-up and spin-down electrons have the same contribution to the transmission even if a magnetic field is applied. In the ferromagnetic alignment, however, at certain strengths of Rashba spin-orbit interaction and of magnetic field, the transmission coefficient for spin-up electrons is bigger than that for spin-down electrons, and the sign of the spin polarization changes, which is opposite to that in the absence of the magnetic field.

Effects of temperature and electron effective mass on bias-dependent tunnelling magnetoresistance

Li Fei-Fei, Li Zheng-Zhong, Xiao Ming-Wen
Chin. Phys., 2005, 14 (5): 1025-1031 doi: 10.1088/1009-1963/14/5/030
Full Text: [PDF 301 KB] (Downloads:323)
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In this paper, we study effects of temperature and electron effective mass within the barrier on the bias dependence and sign-change behavior of the tunneling magnetoresistance (TMR) in ferromagnetic junctions. A significant decrease of the tunneling magnetoresistance with elevating temperature is obtained, in accordance with experiments. In addition to the height of barrier potential \left( \phi\right) discussed in our previous papers, the electron effective mass \left( m_{B}\right) within the barrier region is found to be another important factor that physically controls the sign-change behavior of the TMR. The critical voltage (V_{c}) at which TMR changes sign will increase with \phi and decrease with m_{B}, respectively.Furthermore, both the zero-bias TMR and V_{c} will decrease if temperature rises. These results are hoped to be of practical use for experimental investigations.

Efficient photovoltaic cells from low band-gap fluorene-based copolymer            

Tian Ren-Yu, Yang Ren-Qiang, Peng Jun-Biao, Cao Yong
Chin. Phys., 2005, 14 (5): 1032-1035 doi: 10.1088/1009-1963/14/5/031
Full Text: [PDF 245 KB] (Downloads:435)
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Polymer photovoltaic cells based on low band-gap copolymer, poly[2,7-(9,9-dioctyl)fluorene-co-5,5’-(4,7-diselenophenyl)-2,2’-yl-2,1,3-benzothiadiazole] (PFSeBT), were investigated, focusing on the effects of cathode and blend concentration on device performances. The best device, with active layer from PFSeBT: PCBM=1:2 blend and with LiF/Al as cathode, shows an open-circuit voltage of 1.00 V, a short short-circuit current density of 4.42 mA/cm2, and energy conversion efficiency of 1.67% under AM1.5 illumination (100 mW/cm2). The short-circuit current density shows the dependence of power law dependence to on the incident light intensity with the power index of 0.887. All devices show spectral response until up to 680 nm. The results indicate that PFSeBT is a potential polymer functioning as electron donor in polymer photovoltaic cells.

Influence of external voltage on electronic transport properties of molecular junctions: the nonlinear transport behaviour 

Li Zong-Liang, Wang Chuan-Kui, Luo Yi, Xue Qi-Kun
Chin. Phys., 2005, 14 (5): 1036-1040 doi: 10.1088/1009-1963/14/5/032
Full Text: [PDF 510 KB] (Downloads:419)
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The influence of external voltage on the charge transport properties of benzene-1,4-dithiolate molecular junction has been investigated. Variations of the geometric and electronic structures for the molecule caused by the applied voltage are calculated at ab initio level. Based on the numerical results, we find that the energy shift and expansion coefficients in the end-site of the molecule for the frontier molecular orbitals show nearly linear dependence on voltage in the interesting voltage interval. The charge transport properties of the molecular junction are then studied by employing the elastic scattering Green’s function method. It is shown that the voltage has an obvious effect on the I-V characteristic of the molecular junction, particularly the shape of the conductance curves. The I-V curves are consistent with the experimental measurement quite well.

Fabrication and characteristics of Ni-germanide Schottky contacts with Ge                

Han De-Dong, Liu Xiao-Yan, Kang Jin-Feng, Xia Zhi-Liang, Du Gang, Han Ru-Qi
Chin. Phys., 2005, 14 (5): 1041-1043 doi: 10.1088/1009-1963/14/5/033
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In this study, Ni germanide Schottky barrier diodes on n-Ge (100) substrate were fabricated by sputtering metal Ni on Ge, followed by annealing in N2 atmosphere from 300 to 500oC in a furnace. The results of x-ray diffraction (XRD) show that the Ni germanides were formed and the diffraction line of (111) were observed in all samples. The structure of Ni germanide is orthorhombic with lattice parameters a=5.811, b=5.381, c=3.428. However, the lines (121) and (002) were observed only in the samples annealed at a temperature higher than 400oC. The influence of annealing temperature on the electrical properties of Ni germanide Schottky barrier diodes on n-Ge (100) substrate was investigated. Experimental results indicate that Schottky barrier diodes on n-Ge (100) with current-voltage (I-V) rectifier characteristics were obtained. The Ion/Ioff ratio of the Schokky diode obtained by using a 300oC annealing process is the highest. The Schottky barrier heights were evaluated by the capacitance-voltage method.

Interaction of mesoscopic Josephson junction with the excited even and odd coherent states

Zhan You-Bang
Chin. Phys., 2005, 14 (5): 1044-1050 doi: 10.1088/1009-1963/14/5/034
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The interaction of a mesoscopic Josephson junction (MJJ) with the excited even and odd coherent states is investigated. Some properties of the supercurrent in the MJJ in the presence of nonclassical light fields, such as collapse and revival phenomenon, the current--voltage step, dc component fluctuation and quantum coherence of supercurrent, are studied. It is shown that the expectation values and the fluctuation of supercurrent can exhibit dc components. It is also shown that the static supercurrent flows, dc components of the supercurrent fluctuation and correlation function of the dc supercurrent components, are related to the phase of the light field.

Preisach analysis of (La0.2Nd0.8)0.67Pb0.33MnO3

Cao Xian-Sheng, Xiao Chun-Tao, Gywn Williams, Roy Roshko
Chin. Phys., 2005, 14 (5): 1051-1054 doi: 10.1088/1009-1963/14/5/035
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The perovskite (La0.2Nd0.8)0.67Pb0.33MnO3 (LNPMO) with a Curie temperature TC=220K has been characterized by measuring the zero field cooled (ZFC) and field cooled (FC) moments over wide range of temperature 2K

Effects of grain size distribution on remanence and coercivity of Pr2Fe14B nanocrystalline magnet

He Shu-Li, Zhang Hong-Wei, Rong Chuan-Bing, Chen Ren-Jie, Shen Bao-Gen
Chin. Phys., 2005, 14 (5): 1055-1059 doi: 10.1088/1009-1963/14/5/036
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The demagnetization curves of Pr2Fe14B nanocrystalline magnets are calculated using micromagnetic finite-element method. The samples with three different distributions of grain size are simulated. The remanence enhancement does not depend on grain size distribution but on the mean diameter of grains. The influence of grain size distribution on coercivity is affected by the strength of intergrain exchange coupling.
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