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Chin. Phys. B  
  Chin. Phys. B--2006, Vol.15, No.3
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Lie-form invariance of nonholonomic mechanical systems

Xia Li-Li, Wang Jing, Hou Qi-Bao, Li Yuan-Cheng
Chin. Phys. B 2006, 15 (3): 0467;  doi: 10.1088/1009-1963/15/3/001
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The Lie-form invariance of a nonholonomic mechanical system is studied. The definition and criterion of the Lie-form invariance of the nonholonomic mechanical system are given. The Hojman conserved quantity and a new type of conserved quantity are obtained from the Lie-form invariance. An example is given to illustrate the application of the results.

Lie symmetries, perturbation to symmetries and adiabatic invariants of Poincaré equations

Chen Xiang-Wei, Liu Cui-Mei, Li Yan-Min
Chin. Phys. B 2006, 15 (3): 0470;  doi: 10.1088/1009-1963/15/3/002
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Based on the invariance of differential equations under infinitesimal transformations, Lie symmetry, laws of conservations, perturbation to the symmetries and adiabatic invariants of Poincar\'{e} equations are presented.The concepts of Lie symmetry and higher order adiabatic invariants of Poincar\'{e} equations are proposed. The conditions for existence of the exact invariants and adiabatic invariants are proved, and their forms are also given. In addition, an example is presented to illustrate these results.

A hyperbolic function approach to constructing exact solitary wave solutions of the Hybrid lattice and discrete mKdV lattice

Zha Qi-Lao, Sirendaoreji
Chin. Phys. B 2006, 15 (3): 0475;  doi: 10.1088/1009-1963/15/3/003
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Some new exact solitary wave solutions of the Hybrid lattice and discrete mKdV lattice are obtained by using a hyperbolic function approach. This approach can also be applied to other nonlinear differential-difference equations.

Teleportation of a two-atom entangled state using a single EPR pair in cavity QED

Ji Xin, Li Ke, Zhang Shou
Chin. Phys. B 2006, 15 (3): 0478;  doi: 10.1088/1009-1963/15/3/004
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We propose a scheme for teleporting a two-atom entangled state in cavity quantum electrodynamics (QED). In the scheme, we choose a single Einstein--Podolsky--Rosen (EPR) pair as the quantum channel which is shared by the sender and the receiver. By using the atom--cavity-field interaction and introducing an additional atom, we can teleport the two-atom entangled state successfully with a probability of 1.0. Moreover, we show that the scheme is insensitive to cavity decay and thermal field.

Quantum circuits for realizing deterministic and exact teleportation via two partially entangled pairs of particles

Li Wen-Dong, Zhang Jian-Li, Gu Yong-Jian
Chin. Phys. B 2006, 15 (3): 0482;  doi: 10.1088/1009-1963/15/3/005
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Deterministic and exact teleportation can be achieved via two partially entangled pairs of particles [Gu Y J 2006 {\em Opt. Comm.} {\bf 259} 385]. The key point of the protocol is a generalized measurement described by a positive operator-valued measure, which can be realized by performing a unitary operation in the extended space and a conventional Von Neumann orthogonal measurement. By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the teleportation. Our method for constructing quantum circuits differs from the usual methods based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements.

Entanglement diversion and quantum teleportation of entangled coherent states

Cai Xin-Hua, Guo Jie-Rong, Nie Jian-Jun, Jia Jin-Ping
Chin. Phys. B 2006, 15 (3): 0488;  doi: 10.1088/1009-1963/15/3/006
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The proposals on entanglement diversion and quantum teleportation of entangled coherent states are presented.In these proposals, the entanglement between two coherent states,\alpha\rangle and $|-\alpha\rangle$, with the same amplitude but a phase difference of $\pi$ is utilized as a quantum channel. The processes of the entanglement diversion and the teleportation are achieved by using the 50/50 symmetric beam splitters, the phase shifters and the photodetectors with the help of classical information.

Quantum teleportation by entanglement swapping with trapped ions

Zheng Xiao-Juan, Fang Mao-Fa, Cai Jian-Wu, Liao Xiang-Ping
Chin. Phys. B 2006, 15 (3): 0492;  doi: 10.1088/1009-1963/15/3/007
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An effective teleportation scheme for an unknown ionic internal state via trapped ions is proposed without joint Bell-state measurement (BSM). In the constructed quantum channel process, we make use of entanglement swapping to avoid decrease in entanglement during the distributing of particles. Thus our scheme provides new prospects for quantum teleportation in a longer distance. The distinct advantage of our scheme is insensitive to the heating of vibrational mode. Furthermore, our scheme has no any individual optical access, and the successful probability also can reach 1.

Gaussian wave formalism model for propagation of charged-particle beam through a first-order optical systems

Chen Bao-Xin
Chin. Phys. B 2006, 15 (3): 0496;  doi: 10.1088/1009-1963/15/3/008
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An elliptical Gaussian wave formalism model of a charged-particle beam is proposed by analogy with an elliptical Gaussian light beam. In the paraxial approximation, the charged-particle beam can be described as a whole by a complex radius of curvature in the real space domains. Therefore, the propagation and transform of charged-particle beam passing through a first-order optical system is represented by the \textit{ABCD}-like law.As an example of the application of this model, the relation between the beam waist and the minimum beam spot at a fixed target is discussed. The result, well matches that from conventional phase space model, and proves that the Gaussian wave formalism model is highly effective and reasonable.

The quantum spectra analysis of the circular billiards in wells

Zhang Yan-Hui, Zhang Li-Qin, Xu Xue-You, Ge Mei-Hua, Lin Sheng-Lu, Du Meng-Li
Chin. Phys. B 2006, 15 (3): 0502;  doi: 10.1088/1009-1963/15/3/009
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We use a recently defined quantum spectral function and apply the method of closed-orbit theory to the 2D circular billiard system. The quantum spectra contain rich information of all classical orbits connecting two arbitrary points in the well. We study the correspondence between quantum spectra and classical orbits in the circular, 1/2 circular and 1/4 circular wells using the analytic and numerical methods. We find that the peak positions in the Fourier-transformed quantum spectra match accurately with the lengths of the classical orbits. These examples show evidently that semi-classical method provides a bridge between quantum and classical mechanics.

Robust synchronization of uncertain chaotic systems

Li Fang, Hu Ai-Hua, Xu Zhen-Yuan
Chin. Phys. B 2006, 15 (3): 0507;  doi: 10.1088/1009-1963/15/3/010
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This paper investigates robust unified (lag, anticipated, and complete) synchronization of two coupled chaotic systems. By introducing the concepts of positive definite symmetrical matrix and Riccati inequality and the theory of robust stability, several criteria on robust synchronization are established. Extensive numerical simulations are also used to confirm the results.

Relation between the complex Ginzburg--Landau equation and reaction--diffusion system

Shao Xin, Ren Yi, Ouyang Qi
Chin. Phys. B 2006, 15 (3): 0513;  doi: 10.1088/1009-1963/15/3/011
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The complex Ginzburg--Landau equation (CGLE) has been used to describe the travelling wave behaviour in reaction--diffusion (RD) systems. We argue that this description is valid only when the RD system is close to the Hopf bifurcation, and is not valid when a RD system is away from the onset. To test this, we study spirals and anti-spirals in the chlorite-iodide-malonic acid (CIMA) reaction and the corresponding CGLE. Numerical simulations confirm that the CGLE can only be applied to the CIMA reaction when it is very near the Hopf onset.

Bursting and spiking due to additional direct and stochastic currents in neuron models

Yang Zhuo-Qin, Lu Qi-Shao
Chin. Phys. B 2006, 15 (3): 0518;  doi: 10.1088/1009-1963/15/3/012
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Neurons at rest can exhibit diverse firing activities patterns in response to various external deterministic and random stimuli, especially additional currents. In this paper, neuronal firing patterns from bursting to spiking, induced by additional direct and stochastic currents, are explored in rest states corresponding to two values of the parameter $V_{\rm K}$ in the Chay neuron system. Three cases are considered by numerical simulation and fast/slow dynamic analysis, in which only the direct current or the stochastic current exists, or the direct and stochastic currents coexist. Meanwhile, several important bursting patterns in neuronal experiments, such as the period-1 ``circle/homoclinic" bursting and the integer multiple ``fold/homoclinic" bursting with one spike per burst, as well as the transition from integer multiple bursting to period-1 ``circle/homoclinic" bursting and that from stochastic ``Hopf/homoclinic" bursting to ``Hopf/homoclinic" bursting, are investigated in detail.

Estimation of luminescence lifetime in frequency domain

Zhang Fu-Jun, Xu Zheng, Zhao Su-Ling, Lou Zhi-Dong, Yang Sheng-Yi, Xu Xu-Rong
Chin. Phys. B 2006, 15 (3): 0526;  doi: 10.1088/1009-1963/15/3/013
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Absorption is the origin of luminescence. But it must be noticed that the lifetime of luminescence might reversely influence the rate of absorption. In this paper, it is reported that the luminescence intensity of copper and manganese changes with the driving frequency at constant voltage.The variation of luminescent intensity depends only on the lifetime of luminescence but not on the type of quenching or other factors. Generally the rate of absorption is dominantly determined by the material property and the lifetime of luminescence centres, the absorption of shorter lifetime centre will be larger than that of the longer lifetime centre at the same excited condition.

Accurate calculation of the elastic scattering properties of 7Li atoms at ultralow temperatures

Sun Jin-Feng, Zhang Ji-Cai, Wang Jie-Min
Chin. Phys. B 2006, 15 (3): 0531;  doi: 10.1088/1009-1963/15/3/014
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The elastic scattering properties for collisions between two ${}^7$Li atoms are investigated in the cold and ultracold regimes separately. Based on recent theoretical and experimental results, we present the improved hybrid potentials for the singlet X$^1\dsum\nolimits_{\rm g}^ + $ and triplet a$^3\dsum\nolimits_{\rm u}^ +$ ground states of the Li$_2$. Our calculated values for the scattering lengths $a$ and the effective ranges $r_\e $ are compared with previous ones, and found them to be in good agreement. The scattering lengths are $34.6a_0$ for the singlet state and $-27.6a_0$ for the triplet state. Shape resonances occur in the collisions at low energies. We also calculate the total cross sections and the energy positions of shape resonances for both X$^1\dsum\nolimits_{\rm g}^ + $ and a$^3\dsum\nolimits_{\rm u}^ +$ states.

A non-Markov ratchet model of molecular motors: processive movement of single-headed kinesin KIF1A

Xie Ping, Dou Shuo-Xing, Wang Peng-Ye
Chin. Phys. B 2006, 15 (3): 0536;  doi: 10.1088/1009-1963/15/3/015
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A fluctuating ratchet model of non-Markov process is presented to describe the processive movement of molecular motors of single-headed kinesin KIF1A,where the fluctuation perturbation to the local potential is introduced and the detailed ATPase pathway of the motor is included. The theoretical results show good quantitative agreement with the previous experimental ones.

Entropy evolvement properties in a system of Schr?dinger cat state light field interacting with two entangled atoms

Liu Tang-Kun
Chin. Phys. B 2006, 15 (3): 0542;  doi: 10.1088/1009-1963/15/3/016
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The field entropy can be regarded as a measurement of the degree of entanglement between the light field and the atoms of a system which is composed of two-level atoms initially in an entangled state interacting with the Schr\"{o}dinger cat state. The influences of the strength of light field and the phase angle between the two coherent states on the field entropy are discussed by using numerical calculations. The result shows that when the strength of light field is large enough the field entropy is not zero and the degrees of entanglement between the atoms and the three different states of the light fields are equal. When the strength of the light field is small, the degree of entanglement is maximum in a system of the two entangled atoms interacting with an odd coherent state; it is intermediate for a system of the two entangled atoms interacting with the Yurke--Stoler coherent state, and it is minimum in a system of the two entangled atoms interacting with an even coherent state.

Diode-pumped tunable laser with dual Cr:LiSAF rods

Xie Guo-Qiang, Wang Tao, Zhu He-Yuan, Qian Lie-Jia
Chin. Phys. B 2006, 15 (3): 0547;  doi: 10.1088/1009-1963/15/3/017
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We propose and demonstrate a simple approach to lower the thermal quenching effect and improve the output power of Cr:LiSAF lasers, which is accomplished by employing two laser rods. The resonator contains two laser rods and is designed by using two ``X'' folding cavities in cascade. A tunable laser output of $\sim $ 180\,mW has been achieved with the pump of single-striped laser diodes. Compared with lasers using single gain rod, the laser with dual rods shows less severe thermal effect and increases the output by more than two times.

Near-field imaging of a square-lattice metallic photonic-crystal slab at the second band

Feng Shuai, Feng Zhi-Fang, Ren Kun, Ren Cheng, Li Zhi-Yuan, Cheng Bing-Ying, Zhang Dao-Zhong
Chin. Phys. B 2006, 15 (3): 0552;  doi: 10.1088/1009-1963/15/3/018
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Imaging properties of a two-dimensional photonic crystal slab lens are investigated through the finite-difference time-domain method. In this paper, we consider the photonic crystal slab consisting of a square lattice of square metallic rods immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the photonic crystal slab, we find that a good-quality image can form at the frequencies in the second TM-polarized photonic band. Comparing the images formed at different frequencies, we can clearly see that an excellent-quality image is formed by the mechanisms of simultaneous action of the self-collimation effect and the negative-refraction effect.

Analyses of edge plasma characteristics in HL-2A

Hong Wen-Yu, Yan Long-Wen, Qian Jun, Pan Yu-Dong, Wang En-Yao, Luo Cui-Wen, Xu Zheng-Yu, Pan Li, Li Qiang, Yuan Bao-Shan, Liu Li, Ding Xuan-Tong
Chin. Phys. B 2006, 15 (3): 0556;  doi: 10.1088/1009-1963/15/3/019
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The edge plasma characteristics are studied by both a movable array of Mach/Reynolds stress/Langmuir 10-probes in the boundary region and the fixed flush probe arrays on the 4 divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The dependence of the Reynolds stress on poloidal flow in the edge plasma is analysed. The result indicates that the sheared poloidal flow in tokamak plasma can be induced by the radial gradient of Reynolds stress. In the divertor experiments of HL-2A, the profiles of the electron temperature, density and floating potential on divertor plates are measured by the flush probe arrays. The edge electron temperature in divertor configuration is higher than that in limiter configuration. The temperature asymmetry between outer and inner target plates is observed. The result of magnetic surface reconstructed from 18 Mirnov coils signals is presented. Both the particle recycling and the impurity flux in the bulk plasma during divertor discharges are discussed. Neutral gas pressure in divertor chamber, measured by fast ionization gauge during divertor discharge, is given.

Interaction of solitary waves in magnetized warm dusty plasmas with dust charging effects

Xue Ju-Kui
Chin. Phys. B 2006, 15 (3): 0562;  doi: 10.1088/1009-1963/15/3/020
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In consideration of adiabatic dust charge variation, the combined effect of the external magnetized field and the dust temperature on head-on collision of the three-dimensional dust acoustic solitary waves is investigated. By using the extended Poincar\'e--Lighthill--Kuo method, the phase shifts and the trajectories of two solitons after the collision are obtained. The effects of the magnitude and the obliqueness of the external magnetic field and the dust temperature on the solitary wave collisions are discussed in detail.

Successive particle acceleration by use of two tightly focused ultra-short intense laser pulses

Chen Min, Sheng Zheng-Ming, Zhang Jie
Chin. Phys. B 2006, 15 (3): 0568;  doi: 10.1088/1009-1963/15/3/021
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We suggest a scheme of electron acceleration by use of two tightly focused ultra-short intense laser pulses at a 100TW level. Electrons obtain a preliminary acceleration with a small angular spread by the longitudinal ponderomotive force of the first pulse. They are then injected and further accelerated to hundreds of MeV by the second laser pulse.

Surface properties of diamond-like carbon films prepared by CVD and PVD methods

Liu Dong-Ping, Liu Yan-Hong, Chen Bao-Xiang
Chin. Phys. B 2006, 15 (3): 0575;  doi: 10.1088/1009-1963/15/3/022
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Diamond-like carbon (DLC) films have been deposited using three different techniques: (a) electron cyclotron resonance---plasma source ion implantation, (b) low-pressure dielectric barrier discharge, (c) filtered---pulsed cathodic arc discharge. The surface and mechanical properties of these films are compared using atomic force microscope-based tests. The experimental results show that hydrogenated DLC films are covered with soft surface layers enriched with hydrogen and sp$^{3}$ hybridized carbon while the soft surface layers of tetrahedral amorphous carbon (ta-C) films have graphite-like structure. The formation of soft surface layers can be associated with the surface diffusion and growth induced by the low-energy deposition process. For typical CVD methods, the atomic hydrogen in the plasmas can contribute to the formation of hydrogen and sp$^{3}$ hybridized carbon enriched surface layers. The high-energy ion implantation causes the rearrangement of atoms beneath the surface layer and leads to an increase in film density. The ta-C films can be deposited using the medium energy carbon ions in the highly-ionized plasma.

The characteristics of confined ablation in laser propulsion

Zheng Zhi-Yuan, Zhang Jie, Hao Zuo-Qiang, Yuan Xiao-Hui, Zhang Zhe, Lu Xin, Wang Zhao-Hua, Wei Zhi-Yi
Chin. Phys. B 2006, 15 (3): 0580;  doi: 10.1088/1009-1963/15/3/023
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Compared with direct ablation, confined ablation provides an effective way to obtain a large target momentum and a high coupling coefficient. By using a transparent glass layer to cover the target surface, the coupling coefficient is enhanced by an order of magnitude. With the increase of the gap width between the target surface and the cover layer, the coupling coefficient exponentially decreases. It is found that the coupling coefficient is also related to the thickness of the cover layer.

Impurity behaviours of HL-2A divertor tokamak during the initial operation period

Cui Zheng-Ying, Sun Ping, Pan Yu-Dong, Li Wei, Wang Quan-Ming, Cao Zeng, Wang Ming-Xu
Chin. Phys. B 2006, 15 (3): 0585;  doi: 10.1088/1009-1963/15/3/024
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The divertor configuration was successfully formed and the siliconization as a wall conditioning was first achieved on HL-2A tokamak experimentally in 2004. The divertor configuration is reconstructed by the use of the CFC code. Impurity as an important issue is investigated in the experiments with divertor configuration and wall conditioning. Impurities dramatically decrease after both the divertor configuration is formed and silicon is coated on the surface of the vacuum vessel.

Tomographic analysis of the central magnetohydrodynamic oscillations on the HT-7 tokamak

Ma Tian-Peng, Ruan Huai-Lin, Hu Li-Qun, Wan Bao-Nian, Gao Xiang, Zhen Xiang-Jun, Zhou Li-Wu, Sun You-Wen, Gao Wei, Chen Zhong-Yong, Lin Shi-Yao, Kong Wei
Chin. Phys. B 2006, 15 (3): 0593;  doi: 10.1088/1009-1963/15/3/025
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Multi-channel soft x-ray (SX) detectors are applied to generate images of magnetohydrodynamic (MHD) oscillation on the HT-7 tokamak, and the data from SX cameras are analysed by using the Fourier--Bessel harmonic reconstruction method and the singular value decomposition. The image reconstruction of SX emissivity is obtained on the assumption of plasma rigid rotation. One of the important phenomena in the HT-7 discharge is the transition from the sawtooth oscillations to the MHD oscillations when the plasma density grows higher. The MHD structure observed in the SX tomography is featured as follows: the magnetic surface of MHD structure is made up of the crescent-shaped ``hot core'' and the circular ``cold bubble''. The structure of the magnetic surface is relatively stable. It rotates in the direction of the electron diamagnetic drift at a frequency being the oscillation frequency of the MHD oscillations.

Effect of longitudinal applied magnetic field on the self-pinched critical current in intense electron beam diode

Liu Guo-Zhi, Huang Wen-Hua, Shao Hao, Xiao Ren-Zhen
Chin. Phys. B 2006, 15 (3): 0600;  doi: 10.1088/1009-1963/15/3/026
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The effect of applied longitudinal magnetic field on the self-pinched critical current in the intense electron beam diode is discussed. The self-pinched critical current is derived and its validity is tested by numerical simulations. The results shows that an applied longitudinal magnetic field tends to increase the self-pinched critical current. Without the effect of anode plasma, the maximal diode current approximately equals the self-pinched critical current with the longitudinal magnetic field applied; when self-pinched occurs, the diode current approaches the self-pinched critical current.

Effect of element Re on the grain boundary cohesion of α-Fe

Chen Zheng-Zheng, Wang Chong-Yu
Chin. Phys. B 2006, 15 (3): 0604;  doi: 10.1088/1009-1963/15/3/027
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The effect of Re segregation on the $\alpha $-Fe $\Sigma $5 [001] (010) grain boundary (GB) is investigated by using a software called DMol and discrete variational method (DVM). Based on the Rice--Wang model, the calculated segregation energy and defect formation energy show that Re is a strong cohesive enhancer. We also calculated the interatomic energy (IE) and bond order (BO) of several atomic pairs to investigate the mechanism of the cohesive effect of Re microscopically and locally. The results show that IEs of atomic pairs formed by those atoms which cross the plane of GB are strengthened due to the segregation of Re, while the BOs of the corresponding pairs are slightly decreased. This discrepancy demonstrates that IE which contains the Hamiltonian of interaction between atoms is a good quantity to describe the bonding strength. The analysis suggests that the electronic effect between atomic pair which comes directly from Hamiltonian is the key factor. The charge density is also presented, and the result indicates that the bonding strength between the Fe atoms on the GB is enhanced due to the segregation of Re, which is consistent with the analysis of IE.

Investigation on quenching at a high-angle Cu grain boundary on an atomic scale

Zhang Lin, Wang Shao-Qing, Ye Heng-Qiang
Chin. Phys. B 2006, 15 (3): 0610;  doi: 10.1088/1009-1963/15/3/028
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We have performed molecular dynamics simulations of structural changes due to quenching the melting interface at a Cu $\Sigma $5(310)/[001] symmetrical tilt grain boundary. The simulation results suggest that the grain boundary structures due to quenching are different from those due to heating up to the same temperature. The calculated atom density profiles show that the grain boundary structures can be significantly changed as they are quenched to quite low temperatures.

Design of quantum VQ iteration and quantum VQ encoding algorithm taking $O(\sqrt N )$ steps for data compression

Pang Chao-Yang, Zhou Zheng-Wei, Chen Ping-Xing, Guo Guang-Can
Chin. Phys. B 2006, 15 (3): 0618;  doi: 10.1088/1009-1963/15/3/029
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Vector quantization (VQ) is an important data compression method. The key of the encoding of VQ is to find the closest vector among N vectors for a feature vector. Many classical linear search algorithms take $O(N)$ steps of distance computing between two vectors. The quantum VQ iteration and corresponding quantum VQ encoding algorithm that takes $O(\sqrt N )$ steps are presented in this paper. The unitary operation of distance computing can be performed on a number of vectors simultaneously because the quantum state exists in a superposition of states. The quantum VQ iteration comprises three oracles, by contrast many quantum algorithms have only one oracle, such as Shor's factorization algorithm and Grover's algorithm. Entanglement state is generated and used, by contrast the state in Grover's algorithm is not an entanglement state. The quantum VQ iteration is a rotation over subspace, by contrast the Grover iteration is a rotation over global space. The quantum VQ iteration extends the Grover iteration to the more complex search that requires more oracles. The method of the quantum VQ iteration is universal.

The influence of trapping centres on the photoelectron decay in silver halide

Li Xiao-Wei, Zhang Rong-Xiang, Liu Rong-Juan, Yang Shao-Peng, Han Li, Fu Guang-Sheng
Chin. Phys. B 2006, 15 (3): 0624;  doi: 10.1088/1009-1963/15/3/030
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Photoelectron is the foundation of latent image formation, the decay process of photoelectrons is influenced by all kinds of trapping centres in silver halide. By analysing the mechanism of latent image formation it is found that electron trap, hole trap, and one kind of recombination centre where free electron and trapped hole recombine are the main trapping centres in silver halide. Different trapping centres have different influences on the photoelectron behaviour. The effects of all kinds of typical trapping centres on the decay of photoelectrons are systematically investigated by solving the photoelectron decay kinetic equations. The results are in agreement with those obtained in the microwave absorption dielectric spectrum experiment.

Analytical analysis of surface potential for grooved-gate MOSFET

Zhang Xiao-Ju, Gong Xin, Wang Jun-Ping, Hao Yue
Chin. Phys. B 2006, 15 (3): 0631;  doi: 10.1088/1009-1963/15/3/031
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The improvement of the characteristics of grooved-gate MOSFETs compared to the planar devices is attributed to the corner effect of the surface potential along the channel. In this paper we propose an analytical model of the surface potential distribution based on the solution of two-dimensional Poisson equation in cylindrical coordinates utilizing the cylinder approximation and the structure parameters such as the concave corner $\theta _0 $. The relationship between the minimum surface potential and the structure parameters is theoretically analysed. Results confirm that the bigger the concave corner, the more obvious the corner effect. The corner effect increases the threshold voltage of the grooved-gate MOSFETs, so the better is the short channel effect (SCE) immunity.

Numerical simulation of transconductance of AlGaN/GaN heterojunction field effect transistors at high temperatures

Chang Yuan-Cheng, Zhang Yi-Men, Zhang Yu-Ming
Chin. Phys. B 2006, 15 (3): 0636;  doi: 10.1088/1009-1963/15/3/032
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Based on the investigation of the influence of temperatures on parameters, including polarization, electron mobility, thermal conductivity, and conduction band discontinuity at the interface between AlGaN and GaN, the temperature dependence of transconductance for AlGaN/GaN heterojunction field effect transistors (HFETs) has been obtained by using a quasi-two-dimensional approach, and the calculated results are in good agreement with the experimental data. The reduction in transconductance at high temperatures is primarily due to the decrease in electron mobility in the channel. Calculations also demonstrate that the self-heating effect becomes serious as environment temperature increases.

Research of the behaviour of O chemisorption on the (110) surface of Rhx--Pt1-x alloy

Zhang Hui, Zhang Guo-Ying, Wang Rui-Dan, Zhong Bo
Chin. Phys. B 2006, 15 (3): 0641;  doi: 10.1088/1009-1963/15/3/033
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An atomic group model of the disordered binary alloy Rh$_{x}$--Pt$_{1-x}$ has been constructed to investigate surface segregation. According to the model, we have calculated the electronic structure of the Rh$_{x}$--Pt$_{1 - x }$alloy surface by using the recursion method when O atoms are adsorbed on the Rh$_{x}$--Pt$_{1-x }$(110) surface under the condition of coverage 0.5. The calculation results indicate that the chemical adsorption of O changes greatly the density of states near the Fermi level, and the surface segregation exhibits a reversal behaviour. In addition, when $x<0.3$, the surface on which O is adsorbed displays the property of Pt; whereas when $x>0.3$ it displays the property of Rh.

Investigation of the characteristics of GIDL current in 90nm CMOS technology

Chen Hai-Feng, Hao Yue, Ma Xiao-Hua, Zhang Jin-Cheng, Li Kang, Cao Yan-Rong, Zhang Jin-Feng, Zhou Peng-Ju
Chin. Phys. B 2006, 15 (3): 0645;  doi: 10.1088/1009-1963/15/3/034
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A specially designed experiment is performed for investigating gate-induced drain leakage (GIDL) current in 90nm CMOS technology using lightly-doped drain (LDD) NMOSFET. This paper shows that the drain bias $V_{\rm D}$ has a strong effect on GIDL current as compared with the gate bias $V_{\rm G}$ at the same drain--gate voltage $V_{\rm DG}$. It is found that the difference between $I_{\rm D}$ in the off-state $I_{\rm D}-V_{\rm G}$ characteristics and the corresponding one in the off-state $I_{\rm D}-V_{\rm D}$ characteristics, which is defined as $I_{\rm DIFF}$, versus $V_{\rm DG}$ shows a peak. The difference between the influences of $V_{\rm D}$ and $V_{\rm G}$ on GIDL current is shown quantitatively by $I_{\rm DIFF}$, especially in 90nm scale. The difference is due to different hole tunnellings. Furthermore, the maximum $I_{\rm DIFF }$($I_{\rm DIFF,MAX})$ varies linearly with $V_{\rm DG}$ in logarithmic coordinates and also $V_{\rm DG}$ at $I_{\rm DIFF,MAX}$ with $V_{\rm F}$ which is the characteristic voltage of $I_{\rm DIFF}$. The relations are studied and some related expressions are given.

Terahertz field-induced modulations of intersubband absorptions in quantum wells

Zhang Yong-Hua, Wang Chang
Chin. Phys. B 2006, 15 (3): 0649;  doi: 10.1088/1009-1963/15/3/035
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Nonlinear optical properties of intersubband electrons in a 3-level quantum well under intense terahertz field are investigated by using a density matrix approach. The results show that the terahertz fields with different frequencies cause the distinct modulations of the intersubband absorptions. The terahertz-induced sideband and Autler--Towns splitting in the absorption spectrum are obtained, respectively for the terahertz-photon energy below and close to the transition energy between the ground and first excited state.

Monte Carlo simulation of in-plane spin-polarized transport in GaAs/GaAlAs quantum well in the three-subband approximation

Kong Ling-Gang, Liu Xiao-Yan, Du Gang, Wang Yi, Kang Jin-Feng, Han Ru-Qi
Chin. Phys. B 2006, 15 (3): 0654;  doi: 10.1088/1009-1963/15/3/036
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We develop a Monte Carlo (MC) tool incorporated with the three-subband approximation model to investigate the in-plane spin-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electron occupation of higher subbands and the intersubband scattering on the spin dephasing have been studied. Compared with the corresponding results of the simple one-subband approximation model, the spin dephasing length is reduced four times under 0.125\,kV/cm of driving electric field at 300K by the MC tool incorporated with the three-subband approximation model, indicating that the three-subband approximation model predicts significantly shorter spin dephasing length with temperature increasing. Our simulation results suggest that the effects of the electron occupation of higher subbands and the intersubband scattering on the spin-dependent transport of GaAs 2-dimensional electron gas need to be considered when the driving electric field exceeds the moderate value and the lattice temperature is above 100K. The simulation by using the MC tool incorporated with the three-subband approximation model also indicates that, under a certain driving electric field and lattice temperature, larger channel widths cause spins to be depolarized faster. Ranges of the three components of the spins are different for three different injected spin polarizations due to the anisotropy of spin--orbit interaction.
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