Table of Content

20 December 2008, Volume 17 Issue 12 Previous Issue    Next Issue

GENERAL

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Soliton solution and interaction property for a coupled modified Korteweg-de Vries (mKdV) system Yang Jian-Rong, Mao Jie-Jian 2008, 17 (12):  4337-4343.  doi: 10.1088/1674-1056/17/12/001 Abstract ( 0 )   PDF (299KB) ([an error occurred while processing this directive])   The Hirota's bilinear direct method is applied to constructing soliton solutions to a special coupled modified Korteweg-de Vries (mKdV) system. Some physical properties such as the spatiotemporal evolution, waveform structure, interactive phenomena of solitons are discussed, especially in the two-soliton case. It is found that different interactive behaviours of solitary waves take place under different parameter conditions of overtaking collision in this system. It is verified that the elastic interaction phenomena exist in this (1+1)-dimensional integrable coupled model.

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New periodic wave solutions, localized excitations and their interaction for 2+1-dimensional Burgers equation Ma Hong-Cai, Ge Dong-Jie, Yu Yao-Dong 2008, 17 (12):  4344-4353.  doi: 10.1088/1674-1056/17/12/002 Abstract ( 0 )   PDF (4215KB) ([an error occurred while processing this directive])   Based on the B?cklund method and the multilinear variable separation approach (MLVSA), this paper finds a general solution including two arbitrary functions for the (2+1)-dimensional Burgers equations. Then a class of new doubly periodic wave solutions for (2+1)-dimensional Burgers equations is obtained by introducing appropriate Jacobi elliptic functions, Weierstrass elliptic functions and their combination in the general solutions (which contains two arbitrary functions). Two types of limit cases are considered. Firstly, taking one of the moduli to be unity and the other zero, it obtains particular wave (called semi-localized) patterns, which is periodic in one direction, but localized in the other direction. Secondly, if both moduli are tending to 1 as a limit, it derives some novel localized excitations (two-dromion solution).

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Noether symmetries of discrete mechanico-electrical systems Fu Jing-Li, Chen Ben-Yong, Xie Feng-Ping 2008, 17 (12):  4354-4360.  doi: 10.1088/1674-1056/17/12/003 Abstract ( 0 )   PDF (201KB) ([an error occurred while processing this directive])   This paper focuses on studying Noether symmetries and conservation laws of the discrete mechanico-electrical systems with the nonconservative and the dissipative forces. Based on the invariance of discrete Hamilton action of the systems under the infinitesimal transformation with respect to the generalized coordinates, the generalized electrical quantities and time, it presents the discrete analogue of varitional principle, the discrete analogue of Lagrange-Maxwell equations, the discrete analogue of Noether theorems for Lagrange-Maxwell and Lagrange machanico-electrical systems. Also, the discrete Noether operator identity and the discrete Noether-type conservation laws are obtained for these systems. An actual example is given to illustrate these results.

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Lie symmetry and Hojman conserved quantity of Nambu system Lin Peng, Fang Jian-Hui, Pang Ting 2008, 17 (12):  4361-4364.  doi: 10.1088/1674-1056/17/12/004 Abstract ( 0 )   PDF (140KB) ([an error occurred while processing this directive])   This paper studies the Lie symmetry and Hojman conserved quantity of Nambu system. The determining equations of Lie symmetry for the system are given. The conditions for existence and the form of the Hojman conserved quantity led by the Lie symmetry for the system are obtained. Finally, an example is given to illustrate the application of the results.

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Routh method of reduction for Birkhoffian systems in the event space Zhang Yi 2008, 17 (12):  4365-4368.  doi: 10.1088/1674-1056/17/12/005 Abstract ( 0 )   PDF (123KB) ([an error occurred while processing this directive])   For a Birkhoffian system in the event space, this paper presents the Routh method of reduction. The parametric equations of the Birkhoffian system in the event space are established, and the definition of cyclic coordinates for the system is given and the corresponding cyclic integral is obtained. Through the cyclic integral, the order of the system can be reduced. The Routh functions for the Birkhoffian system in the event space are constructed, and the Routh method of reduction is successfully generalized to the Birkhoffian system in the event space. The results show that if the system has a cyclic integral, then the parametric equations of the system can be reduced at least by two degrees and the form of the equations holds. An example is given to illustrate the application of the results.

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N-particles intermediate coordinate-momentum representation and its application Xu Shi-Min, Xu Xing-Lei, Jiang Ji-Jian, Li Hong-Qi, Wang Ji-Suo 2008, 17 (12):  4369-4374.  doi: 10.1088/1674-1056/17/12/006 Abstract ( 0 )   PDF (180KB) ([an error occurred while processing this directive])   This paper constructs the new common eigenvectors of n intermediate coordinate-momentum operators which are complete and orthonormal. The intermediate coordinate-momentum representation of a multi-particles system is proposed and applied to a general n-mode quantum harmonic oscillators system with coordinate-momentum coupling.

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On entanglement invariant for a double Jaynes-Cummings model Man Zhong-Xiao, Xia Yun-Jie 2008, 17 (12):  4375-4377.  doi: 10.1088/1674-1056/17/12/007 Abstract ( 0 )   PDF (141KB) ([an error occurred while processing this directive])   In a recent paper [Phys. Rev. A 76 042313 (2007)], Sainz and Bjork introduced an entanglement invariant $\mathcal{E}$ under evolution for a system of four qubits interacting through two isolated Jaynes-Cummings Hamiltonians. This paper proves that this entanglement invariant $\mathcal{E}$ is closely connected with the linear entropy between two independent subsystems.

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Quantization rules for low dimensional quantum dots Xu Tian, Cao Zhuang-Qi, Fang Jing-Huai 2008, 17 (12):  4378-4381.  doi: 10.1088/1674-1056/17/12/008 Abstract ( 0 )   PDF (180KB) ([an error occurred while processing this directive])   This paper applies the analytical transfer matrix method (ATMM) to calculate energy eigenvalues of a particle in low dimensional sharp confining potential for the first time, and deduces the quantization rules of this system. It presents three cases in which the applied method works very well. In the first quantum dot, the energy eigenvalues and eigenfunction are obtained, and compared with those acquired from the exact numerical analysis and the WKB (Wentzel, Kramers and Brillouin) method; in the second or the third case, we get the energy eigenvalues by the ATMM, and compare them with the EBK (Einstein, Brillouin and Keller) results or the wave function outcomes. From the comparisons, it finds that the semiclassical method (WKB, EBK or wave function) is inexact in such systems.

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Generation of atomic Greenberger-Horne-Zeilinger states and cluster states through cavity-assisted interaction Huang Xiu-Hua, Lin Xiu-Min, Lin Gong-Wei, Chen Zhi-Hua, Tang Yao-Xiang 2008, 17 (12):  4382-4387.  doi: 10.1088/1674-1056/17/12/009 Abstract ( 0 )   PDF (372KB) ([an error occurred while processing this directive])   This paper proposes a scalable scheme to generate n-atom GHZ states and cluster states by using the basic building block, i.e., a weak coherent optical pulse |α> being reflected successively from a single-atom cavity. In the schemes, coherent state of light is used instead of single photon source, homodyne measurement on coherent light is done instead of single photon detection, and no need for individually addressing keeps the schemes easy to implement from the experimental point of view. The successful probabilities of our protocols approach unity in the ideal case.

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Direct implementation of a scalable non-local multi-qubit controlled phase gate via optical fibers and adiabatic passage Tang Yao-Xiang, Lin Xiu-Min, Lin Gong-Wei, Chen Li-Bo, Huang Xiu-Hua 2008, 17 (12):  4388-4395.  doi: 10.1088/1674-1056/17/12/010 Abstract ( 0 )   PDF (206KB) ([an error occurred while processing this directive])   This paper presents a direct implementation scheme of the non-local multi-qubit controlled phase gate by using optical fibers and adiabatic passage. The smaller operation number for implementing the multi-qubit controlled phase gate and needlessness for addressing individually save physical resource and lower the difficulties of experiment. Meanwhile, the scheme is immune from some decoherence effects such as the atomic spontaneous emission and the fibers loss. In principle, it is scalable.

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A combined statistical model for multiple motifs search Gao Li-Feng, Liu Xin, Guan Shan 2008, 17 (12):  4396-4400.  doi: 10.1088/1674-1056/17/12/011 Abstract ( 0 )   PDF (1064KB) ([an error occurred while processing this directive])   Transcription factor binding sites (TFBS) play key roles in gene's expression and regulation. They are short sequence segments with definite structure and can be recognized by the corresponding transcription factors correctly. From the viewpoint of statistics, the candidates of TFBS should be quite different from the segments that are randomly combined together by nucleotide. This paper proposes a combined statistical model for finding over-represented short sequence segments in different kinds of data set. While the over-represented short sequence segment is described by position weight matrix, the nucleotide distribution at most sites of the segment should be far from the background nucleotide distribution. The central idea of this approach is to search for such kind of signals. This algorithm is tested on 3 data sets, including binding sites data set of cyclic AMP receptor protein in E.coli, PlantProm DB which is a non-redundant collection of proximal promoter sequences from different species, collection of the intergenic sequences of the whole genome of E.Coli. Even though the complexity of these three data sets is quite different, the results show that this model is rather general and sensible.

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Dispersion relation of excitation mode in strongly interacting fermions matter Wang Yan-Ping, Chen Ji-Sheng 2008, 17 (12):  4401-4406.  doi: 10.1088/1674-1056/17/12/012 Abstract ( 0 )   PDF (201KB) ([an error occurred while processing this directive])   This paper analyzes the dispersion relation of the excitation mode in non-relativistic interacting fermion matter. The polarization tensor is calculated with the random phase approximation in terms of finite temperature field theory. With the polarization tensor, the influences of temperature,particle number density and interaction strength on the dispersion relation are discussed in detail. It finds that the collective effects are qualitatively more important in the unitary fermions than those in the finite contact interaction matter.

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Exponential synchronization of stochastic impulsive perturbed chaotic Lur'e systems with time-varying delay and parametric uncertainty Ma Tie-Dong, Zhang Hua-Guang, Fu Jie 2008, 17 (12):  4407-4417.  doi: 10.1088/1674-1056/17/12/013 Abstract ( 0 )   PDF (415KB) ([an error occurred while processing this directive])   This paper is devoted to investigating the scheme of exponential synchronization for uncertain stochastic impulsive perturbed chaotic Lur'e systems. The parametric uncertainty is assumed to be norm bounded. Based on the Lyapunov function method, time-varying delay feedback control technique and a modified Halanay inequality for stochastic differential equations, several sufficient conditions are presented to guarantee the exponential synchronization in mean square between two identical uncertain chaotic Lur'e systems with stochastic and impulsive perturbations. These conditions are expressed in terms of linear matrix inequalities (LMIs), which can easily be checked by utilizing the numerically efficient Matlab LMI toolbox. It is worth pointing out that the approach developed in this paper can provide a more general framework for the synchronization of multi--perturbation chaotic Lur'e systems, which reflects a more realistic dynamics. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.

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Discontinuous bifurcation and coexistence of attractors in a piecewise linear map with a gap Qu Shi-Xian, Lu Yong-Zhi, Zhang Lin, He Da-Ren 2008, 17 (12):  4418-4423.  doi: 10.1088/1674-1056/17/12/014 Abstract ( 0 )   PDF (930KB) ([an error occurred while processing this directive])   Coexistence of attractors with striking characteristics is observed in this work, where a stable period-5 attractor coexists successively with chaotic band-11, period-6, chaotic band-12 and band-6 attractors. They are induced by different mechanisms due to the interaction between the discontinuity and the non-invertibility. A characteristic boundary collision bifurcation, is observed. The critical conditions are obtained both analytically and numerically.

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Multiscale entropy based study of the pathological time series Wang Jun, Ma Qian-Li 2008, 17 (12):  4424-4427.  doi: 10.1088/1674-1056/17/12/015 Abstract ( 0 )   PDF (170KB) ([an error occurred while processing this directive])   This paper studies the multiscale entropy (MSE) of electrocardiogram's ST segment and compares the MSE results of ST segment with that of electrocardiogram in the first time. Electrocardiogram complexity changing characteristics has important clinical significance for early diagnosis. Study shows that the average MSE values and the varying scope fluctuation could be more effective to reveal the heart health status. Particularly the multiscale values varying scope fluctuation is a more sensitive parameter for early heart disease detection and has a clinical diagnostic significance.

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The chaotic property in the autoionization of Rydberg lithium atom Zhou Hui, Li Hong-Yun, Gao Song, Zhang Yan-Hui, Jia Zheng-Mao, Lin Sheng-Lu 2008, 17 (12):  4428-4433.  doi: 10.1088/1674-1056/17/12/016 Abstract ( 0 )   PDF (537KB) ([an error occurred while processing this directive])   This paper presents theoretical computations of the ionization rate of Rydberg lithium atom above the classical ionization threshold using semiclassical approximation. The yielded random pulse trains of the escape electrons are recorded as a function of emission time such that allow for relating themselves to the terms of the recurrence periods of the photoabsorption. This fact turns to illustrate that it is ionic core scattering processes which give rise to chaos in autoionization dynamics and are verified by comparison of our results with the hydrogen atom situation readily. In order to reveal the chaotic properties in detail, the sensitive dependence of the ionization rate upon the scaled energy is discussed for different scaled energies. This approach provides a simple explanation for the chaotic character in autoionization decay of Rydberg alkali-metal atoms.

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Integral sliding mode control for a class of nonlinear neutral systems with time-varying delays Lou Xu-Yang, Cui Bao-Tong 2008, 17 (12):  4434-4439.  doi: 10.1088/1674-1056/17/12/017 Abstract ( 0 )   PDF (200KB) ([an error occurred while processing this directive])   This paper focuses on sliding mode control problems for a class of nonlinear neutral systems with time-varying delays. An integral sliding surface is firstly constructed. Then it finds a useful criteria to guarantee the global stability for the nonlinear neutral systems with time-varying delays in the specified switching surface, whose condition is formulated as linear matrix inequality. The synthesized sliding mode controller guarantees the reachability of the specified sliding surface. Finally, a numerical simulation validates the effectiveness and feasibility of the proposed technique.

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The effect of ACC vehicles to mixed traffic flow consisting of manual and ACC vehicles Xie Dong-Fan, Gao Zi-You, Zhao Xiao-Mei 2008, 17 (12):  4440-4445.  doi: 10.1088/1674-1056/17/12/018 Abstract ( 0 )   PDF (3583KB) ([an error occurred while processing this directive])   This paper studies the effect of adaptive cruise control (ACC) system on traffic flow by using simulations. The multiple headway and velocity difference (MHVD) model is used to depict the motion of ACC vehicles, and the simulation results are compared with the optimal velocity (OV) model which is used to depict the motion of manual vehicles. Compared the cases between the manual and the ACC vehicle flow, the fundamental diagram can be classified into four regions: I, II, III, IV. In low and high density the flux of the two models is the same; in region II the free flow region of the MHVD model is enlarged, and the flux of the MHVD model is larger than that of the OV model; in region III serious jams occur in the OV model while the ACC system suppresses the jams in the MHVD model and the traffic flow is in order, but the flux of the OV model is larger than that of the MHVD model. Similar phenomena also appeared in mixed traffic flow which consists of manual and ACC vehicles. The results indicate that ACC vehicles have significant effect on traffic flow. The improvement induced by ACC vehicles decreases with the increasing proportion of ACC vehicles.

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Effect of multi-velocity-difference in traffic flow Mo Ye-Liu, He Hong-Di, Xue Yu, Shi Wei, Lu Wei-Zhen 2008, 17 (12):  4446-4450.  doi: 10.1088/1674-1056/17/12/019 Abstract ( 0 )   PDF (501KB) ([an error occurred while processing this directive])   Based on the optimal velocity models, an extended model is proposed, in which multi-velocity-difference ahead is taken into consideration. The damping effect of the multi-velocity-difference ahead has been investigated by means of analytical and numerical methods. Results indicate that the multi-velocity-difference leads to the enhancement of stability of traffic flow, suppression of the emergence of traffic jamming, and reduction of the energy consumption.

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Statistical-mechanical analysis of multiuser channel capacity with imperfect channel state information Wang Hui-Song, Zeng Gui-Hua 2008, 17 (12):  4451-4457.  doi: 10.1088/1674-1056/17/12/020 Abstract ( 0 )   PDF (687KB) ([an error occurred while processing this directive])   In this paper, the effect of imperfect channel state information at the receiver, which is caused by noise and other interference, on the multi-access channel capacity is analysed through a statistical-mechanical approach. Replica analyses focus on analytically studying how the minimum mean square error (MMSE) channel estimation error appears in a multiuser channel capacity formula. And the relevant mathematical expressions are derived. At the same time, numerical simulation results are demonstrated to validate the Replica analyses. The simulation results show how the system parameters, such as channel estimation error, system load and signal-to-noise ratio, affect the channel capacity.

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Agreement coordination for second-order multi-agent systems with disturbances Zhang Chun-Xi, Li Hui, Lin Peng 2008, 17 (12):  4458-4465.  doi: 10.1088/1674-1056/17/12/021 Abstract ( 0 )   PDF (442KB) ([an error occurred while processing this directive])   This paper is devoted to the study of consensus problems for the second-order multi-agent systems with external disturbances, switching topology and communication time-delay. Firstly, we perform a model transformation and separate the agreement states from the disagreement states. Secondly, according to this system, we derive a sufficient condition for consensus problem without disturbances by using the Lyapunov-based approach. Furthermore, we give a design criterion in terms of bilinear matrix inequality for the control protocol in the presence of disturbances. Finally, numerical simulations are provided to show the effectiveness of our strategies.

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A new method for detecting pulse gamma ray with scattered electrons Xia Liang-Bin, Ouyang Xiao-Ping, Wang Qun-Shu, Kang Ke-Jun, Tan Xin-Jian 2008, 17 (12):  4466-4471.  doi: 10.1088/1674-1056/17/12/022 Abstract ( 0 )   PDF (3061KB) ([an error occurred while processing this directive])   This paper describes a newly designed gamma pulse detector of current mode that uses the scattered electron method. Tungsten is used as the scattering target, an organic thin film scintillator ST401 is used to collect the scattered electrons. The spatial distribution of the electronic energy-flux density is studied by using the MCNP code. The optimization of the target and the thickness of the scintillator are also discussed. The results indicate that the energy response is relatively flat in the range of 0.4 to 5 MeV.

THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

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Towards the understanding of 11P1 meson mass spectrum Feng Xue-Chao, Jiang Feng-Chun, Chang Tong-Qin, Feng Jun-Lan 2008, 17 (12):  4472-4475.  doi: 10.1088/1674-1056/17/12/023 Abstract ( 0 )   PDF (170KB) ([an error occurred while processing this directive])   Based on the meson-meson mixing and Regge trajerory, this paper establishes the mass relations which can describe the mass spectrum of 11P1 meson state. Using these mass relations, it obtains the mass of K1B, h1(1380) and hc(1P) to be 1358.5MeV, 1468MeV and 3543.9MeV, respectively. The results are compared with other theoretical results and should be tested by experiments in the future.

ATOMIC AND MOLECULAR PHYSICS

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Numerical exploration of population transfer of Rydberg-atom by single frequency-chirped laser pulse Zhang Xian-Zhou, Ren Zhen-Zhong, Jia Guang-Rui, Guo Xiao-Tian, Gong Wei-Gui 2008, 17 (12):  4476-4480.  doi: 10.1088/1674-1056/17/12/024 Abstract ( 0 )   PDF (1049KB) ([an error occurred while processing this directive])   This paper has calculated that Rydberg atoms can be transferred to states of lower principal quantum number by exposing them to a frequency chirped microwave pulse. The atoms experience the consequence: 70p-69s-68p-67s-66p by a constant amplitude field in the adopted model. This study shows that the complete population transfer is related to the chirp rate and the carrier frequency.

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The theoretical study on the potential energy curves for X1∑+, A1∏ and C1∑- states of SiO molecule Xu Guo-Liang, Lü Wen-Jing, Liu Yu-Fang, Zhu Zun-Lue, Zhang Xian-Zhou, Sun Jin-Feng 2008, 17 (12):  4481-4484.  doi: 10.1088/1674-1056/17/12/025 Abstract ( 0 )   PDF (222KB) ([an error occurred while processing this directive])   This paper applies the symmetry-adapted-cluster/symmetry-adapted-cluster configuration-interaction (SAC/SAC-CI) method to optimize the structures for X1∑+, A1∏ and C1∑- states of SiO molecule with the basis sets D95++, 6-311++G and 6-311++G**. Comparing the obtained results with the experiments, it gets the conclusion that the basis set 6-311++G** is most suitable for the optimal structure calculations of X1∑+, A1∏ and C1∑- states of SiO molecule. The whole potential energy curves for these electronic states are further scanned by using SAC/6-311++G** method for the ground state and SAC-CI/6-311++G** method for the excited states, then use a least square method to fit Murrell--Sorbie functions, at last the spectroscopic constants and force constants are calculated, which are in good agreement with the experimental data.

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A new analysis of the ν2 fundamental band of H2O+ Zheng Rui, Li Song, Hou Shun-Yong, Huang Guang-Ming, Duan Chuan-Xi 2008, 17 (12):  4485-4491.  doi: 10.1088/1674-1056/17/12/026 Abstract ( 0 )   PDF (197KB) ([an error occurred while processing this directive])   This paper reports that the absorption spectra of H2O+ have been measured by tunable mid-infrared diode laser spectroscopy in the spectral range of 1100--1380cm-1. The H2O+ ions are generated in an AC glow discharge of the gaseous mixtures of H2O/He and detected with the velocity modulation technique. Forty new lines are assigned to the μ2 fundamental band of H2O+ (\tilde {X}2B1 )1. The observed lines together with other data published previously are fitted to the standard effective Hamiltonian of an asymmetric top, yielding a set of improved rotational constants, spin-rotation constants and their quartic and sextic centrifugal distortion constants for the μ2=1 vibrational state of H2O+.

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Quantum interference in laser-assisted photo-ionization excited by a femtosecond x-ray pulse Ge Yu-Cheng 2008, 17 (12):  4492-4497.  doi: 10.1088/1674-1056/17/12/027 Abstract ( 0 )   PDF (1150KB) ([an error occurred while processing this directive])   The photoelectron energy spectra (PESs) excited by monochromatic femtosecond x-ray pulses in the presence of a femtosecond laser are investigated. A PES is composed of a set of separate peaks, showing interesting comb-like structures. These structures result from the quantum interferences between photoelectron wave packets generated at different times. The width and the localization of each peak as well as the number of peaks are determined by all the laser and x-ray parameters. Most of peak heights of the PES are higher than the classical predictions.

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Spin polarization effect of Ni2 molecule Yan Shi-Ying, Zhu Zheng-He 2008, 17 (12):  4498-4503.  doi: 10.1088/1674-1056/17/12/028 Abstract ( 0 )   PDF (290KB) ([an error occurred while processing this directive])   The density functional theory (DFT) method (b3p86) of Gaussian 03 is used to optimize the structure of the Ni2 molecule. The result shows that the ground state for the Ni2 molecule is a 5-multiple state, symbolising a spin polarization effect existing in the Ni2 molecule, a transition metal molecule, but no spin pollution is found because the wave function of the ground state does not mingle with wave functions of higher-energy states. So the ground state for Ni2 molecule, which is a 5-multiple state, is indicative of spin polarization effect of the Ni2 molecule, that is, there exist 4 parallel spin electrons in Ni2 molecule. The number of non-conjugated electrons is greatest. These electrons occupy different spatial orbitals so that the energy of the Ni2 molecule is minimized. It can be concluded that the effect of parallel spin in the Ni2 molecule is larger than that of the conjugated molecule, which is obviously related to the effect of electron d delocalization. In addition, the Murrell-Sorbie potential functions with the parameters of the ground state and other states of the Ni2 molecule are derived. The dissociation energy De for the ground state of the Ni2 molecule is 1.835eV, equilibrium bond length Re is 0.2243\,nm, vibration frequency \omegae is 262.35cm-1. Its force constants f2, f3 and f4 are 1.1901aJ.nm2, --5.8723aJ.nm-3, and 21.2505\,aJ.nm-4 respectively. The other spectroscopic data for the ground state of the Ni2 molecule \omegae\chie, Be and \alphae are 1.6315cm-1, 0.1141\,cm-1, and 8.0145x10-4cm-1 respectively.

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Xe-Kr laser induced collisional ionization system and experimental preparation of its initial state: Four-photon resonant excitation Zhang Hong-Ying, Lu Zhen-Zhong, Fan Rong-Wei, Chen De-Ying 2008, 17 (12):  4504-4509.  doi: 10.1088/1674-1056/17/12/029 Abstract ( 0 )   PDF (581KB) ([an error occurred while processing this directive])   This paper proposes a novel one-color Xe-Kr laser induced collisional ionization system. Considering the level scheme of the system, it finds that the initial state of the reaction--the four 4f levels with even J of Xe--can be prepared through method of four-photon resonant excitation by dye laser with wavelength of ～440nm. Absorption of an additional photon (the transfer laser) of the same wavelength will complete the laser induced collisional ionization process. The resonance enhanced ionization spectrum of Xe by four laser photons at ～440nm is measured through time-of-flight mass spectrometry, this aims at the preparation of the initial state of the system proposed. The Stark broadening of the measured spectrum is observed and consistent with the previous study. Analysis of the measured resonance ionization spectrum implies the feasibility of ～440nm four-photon resonant excitation of the initial 4f state of the Xe-Kr system proposed in this paper, which prepares for a further experiment of laser induced collisional ionization.

CLASSICAL AREAS OF PHENOMENOLOGY

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Third-order ghost interference with thermal light Li Hong-Guo, Zhang Ying-Tao, Cao De-Zhong, Xiong Jun, Wang Kai-Ge 2008, 17 (12):  4510-4515.  doi: 10.1088/1674-1056/17/12/030 Abstract ( 0 )   PDF (566KB) ([an error occurred while processing this directive])   A scheme for third-order ghost interference with thermal light is proposed. The visibility and resolution of the interference fringe related to the bandwidth of the spatial frequency spectrum of the source are analyzed. The results show that the visibility of the third-order ghost interference fringe is much higher than that of the second-order one.

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Control of period-one oscillation for all-optical clock division and clock recovery by optical pulse injection driven semiconductor laser Li Jing-Xia, Zhang Ming-Jiang, Niu Sheng-Xiao, Wang Yun-Cai 2008, 17 (12):  4516-4522.  doi: 10.1088/1674-1056/17/12/031 Abstract ( 0 )   PDF (2601KB) ([an error occurred while processing this directive])   The period-one oscillation produced by an external optical pulse injection driven semiconductor laser is applied to clock recovery and frequency division. By adjusting the repetition rate or injection power of the external injection optical pulses to lock the different harmonic frequencies of the period-one state, the clock recovery and the frequency division (the second and third frequency divisions) are achieved experimentally. In addition, in frequency locking ranges of 2GHz and 1.9GHz, the second and third frequency divisions are obtained with the phase noise lower than --100dBc/Hz, respectively. Our experimental results are consistent well with the numerical simulations.

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Fine splits of photon emission spectrum of hydrogen atom caused by transitions between different dressed states in intense high frequency laser field Zhou Zhao-Yan, Yuan Jian-Min 2008, 17 (12):  4523-4528.  doi: 10.1088/1674-1056/17/12/032 Abstract ( 0 )   PDF (246KB) ([an error occurred while processing this directive])   The photon emission spectrum of the hydrogen atoms in an intense high-frequency laser pulse is simulated by using one-dimensional soft Coulomb potential. Regular fine structures appear on the two sides of both the odd and even multiples of photon energy of the laser field besides the ordinary odd harmonic peaks. It is proved that the splits of the fine structures are responsible for hyper-Raman lines and the energy spacing between the odd harmonic lines is equal to the difference in energy between the eigenstates with the same parity of the time averaged Krameters-Henneberger (KH) potential. By analysing the features of the fine structures, we also verify that the so-called even order harmonics under the stabilization condition are indeed hyper-Raman lines caused by the transitions between the dressed atomic states with different values of parity.

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Simulated human eye retina adaptive optics imaging system based on a liquid crystal on silicon device Jiang Bao-Guang, Cao Zhao-Liang, Mu Quan-Quan, Hu Li-Fa, Li Chao, Xuan Li 2008, 17 (12):  4529-4532.  doi: 10.1088/1674-1056/17/12/033 Abstract ( 0 )   PDF (2080KB) ([an error occurred while processing this directive])   In order to obtain a clear image of the retina of model eye, an adaptive optics system used to correct the wave-front error is introduced in this paper. The spatial light modulator that we use here is a liquid crystal on a silicon device instead of a conversional deformable mirror. A paper with carbon granule is used to simulate the retina of human eye. The pupil size of the model eye is adjustable (3--7mm). A Shack-Hartman wave-front sensor is used to detect the wave-front aberration. With this construction, a value of peak-to-valley is achieved to be 0.086Λ, where Λ is wavelength. The modulation transfer functions before and after corrections are compared. And the resolution of this system after correction (69lp/m) is very close to the diffraction limit resolution. The carbon granule on the white paper which has a size of 4.7μm is seen clearly. The size of the retina cell is between 4 and 10μm. So this system has an ability to image the human eye's retina.

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Fabrication of high-quality colloidal photonic crystals with sharp band edges for ultrafast all-optical switching Feng Tian-Hua, Dai Qiao-Feng, Wu Li-Jun, Guo Qi, Hu Wei, Lan Sheng 2008, 17 (12):  4533-4540.  doi: 10.1088/1674-1056/17/12/034 Abstract ( 0 )   PDF (7193KB) ([an error occurred while processing this directive])   Application of the pressure controlled isothermal heating vertical deposition method to the fabrication of colloidal photonic crystals is systematically investigated in this paper. The fabricated samples are characterized by scanning electron microscope and transmission spectrum. High-quality samples with large transmissions in the pass bands and the sharp band edges are obtained and the optimum growth condition is determined. For the best sample, the transmission in the pass bands approaches 0.9 while that in the band gap reaches 0.1. More importantly, the maximum differential transmission as high as 0.1/nm is achieved. In addition, it is found that the number of stacking layers does not increase linearly with concentration of PS spheres in a solution, and a gradual saturation occurs when the concentration of PS spheres exceeds 1.5 wt.%. The uniformity of the fabricated samples is examined by transmission measurements on areas with different sizes. Finally, the tolerance of the fabricated samples to baking was studied.

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Electrohydromechanical analysis based on conductivity gradient in microchannel Jiang Hong-Yuan, Ren Yu-Kun, Ao Hong-Rui, Antonio Ramos 2008, 17 (12):  4541-4546.  doi: 10.1088/1674-1056/17/12/035 Abstract ( 0 )   PDF (2229KB) ([an error occurred while processing this directive])   Fluid manipulation is very important in lab-on-a-chip system. This paper analyzes phenomena which use the alternating current (AC) electric field to deflect and manipulate coflowing streams of two different electrolytes (with conductivity gradient) within a microfluidic channel. The basic theory of the electrohydrodynamics and simulation of the analytical model are used to explain the phenomena. The velocity induced for different voltages and conductivity gradient are computed. The results show that when the AC electrical signal is applied on the electrodes, the fluid with higher conductivity occupies a larger region of the channel and the interface of the two fluids is deflexed. It will provide some basic references for the people who want to do more study in the control of diffrent fluids with conductivity gradient in microfluidic channel.

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The collision efficiency of spherical dioctyl phthalate aerosol particles in the Brownian coagulation Feng Yu, Lin Jian-Zhong 2008, 17 (12):  4547-4553.  doi: 10.1088/1674-1056/17/12/036 Abstract ( 0 )   PDF (466KB) ([an error occurred while processing this directive])   The collision efficiency in the Brownian coagulation is investigated. A new mechanical model of collision between two identical spherical particles is proposed, and a set of corresponding collision equations is established. The equations are solved numerically, thereby obtaining the collision efficiency for the monodisperse dioctyl phthalate spherical aerosols with diameters ranging from 100 to 760nm in the presence of van der Waals force and the elastic deformation force. The calculated collision efficiency, in agreement with the experimental data qualitatively, decreases with the increase of particle diameter except a small peak appearing in the particles with a diameter of 510nm. The results show that the interparticle elastic deformation force cannot be neglected in the computation of particle Brownian coagulation. Finally, a set of new expressions relating collision efficiency to particle diameter is established.

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The effect of surface roughness on rarefied gas flows by lattice Boltzmann method Liu Chao-Feng, Ni Yu-Shan 2008, 17 (12):  4554-4561.  doi: 10.1088/1674-1056/17/12/037 Abstract ( 0 )   PDF (803KB) ([an error occurred while processing this directive])   This paper studies the roughness effect combining with effects of rarefaction and compressibility by a lattice Boltzmann model for rarefied gas flows at high Knudsen numbers. By discussing the effect of the tangential momentum accommodation coefficient on the rough boundary condition, the lattice Boltzmann simulations of nitrogen and helium flows are performed in a two-dimensional microchannel with rough boundaries. The surface roughness effects in the microchannel on the velocity field, the mass flow rate and the friction coefficient are studied and analyzed. Numerical results for the two gases in micro scale show different characteristics from macroscopic flows and demonstrate the feasibility of the lattice Boltzmann model in rarefied gas dynamics.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Analysis of DαHα spectrum emitted in front of the limiter in HT--7 Huang Juan, Wan Bao-Nian, Daren Stotler, Xiao Bing-Jia, Wu Zhen-Wei, the HT--7 team 2008, 17 (12):  4562-4567.  doi: 10.1088/1674-1056/17/12/038 Abstract ( 0 )   PDF (1110KB) ([an error occurred while processing this directive])   In order to understand the recycling and emission processes of hydrogen atoms in HT--7, spectral profiles of the DαHα line emitted in front of the limiter have been observed with a high-resolution spectrometer and simulated by using the neutral particle transport code DEGAS 2. The results show that four processes are necessary to interpret the DαHα line shape: 1) atom desorption, 2) molecular dissociation, 3) particle reflection, and 4) charge-exchange. The products of the first two processes are cold atoms which emit photons near the peak of DαHα line shape, and those from the last two are warm atoms contributing to the blue side of the spectrum. For a typical ohmic discharge (shot 68520 ne (0)≈3x1019m-3, these components contribute 32%, 15%, 32% and 21%, respectively. DαHα line shapes under different plasma parameters are also discussed in this paper.

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A cold plasma plume with a highly conductive liquid electrode Chen Guang-Liang, Chen Shi-Hua, Chen Wen-Xing, Yang Si-Ze 2008, 17 (12):  4568-4573.  doi: 10.1088/1674-1056/17/12/039 Abstract ( 0 )   PDF (1338KB) ([an error occurred while processing this directive])   A cold dielectric barrier discharge (DBD) plasma plume with one highly conductive liquid electrode has been developed to treat thermally sensitive materials, and its preliminary discharging characteristics have been studied. The averaged electron temperature and density is estimated to be 0.6eV and 1011/cm3, respectively. The length of plasma plume can reach 5cm with helium gas (He), and the conductivity of the outer electrode affects the plume length obviously. This plasma plume could be touched by bare hand without causing any burning or painful sensation, which may provide potential application for safe aseptic skin care. Moreover, the oxidative particles (e.g., OH, O*, O3) in the downstream oxygen (O2) gas of the plume have been applied to treat the landfill leachate. The results show that the activated O2 gas can degrade the landfill leachate effectively, and the chemical oxygen demand (COD), conductivity, biochemical oxygen demand (BOD), and suspended solid (SS) can be decreased by 52%，57%，76% and 92%, respectively.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Investigation of the topological shape of bovine serum albumin in solution by small-angle x-ray scattering at Beijing synchrotron radiation facility Dong Shu-Qiang, Li Li-Qin, Liu Peng, Dong Yu-Hui, Chen Xi-Meng 2008, 17 (12):  4574-4579.  doi: 10.1088/1674-1056/17/12/040 Abstract ( 0 )   PDF (958KB) ([an error occurred while processing this directive])   This paper reports that at a newly constructed small-angle x-ray scattering station of Beijing Synchrotron Radiation Facility, the topological shape of ligand--free bovine serum albumin in solution has been investigated. An appropriate scattering curve is obtained and the calculated value of the gyration radius is 31.2?±0.25? (1?=0.1nm) which is coincident with other ones' results. It finds that the low-resolution structure models obtained by making use of ab initio reconstruction methods are fitting the crystal structure of human serum albumin very well. All of these results perform the potential of the beamline to apply to structural biology studies. The characteristics, the defects, and the improving measures of the station in future are also discussed.

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Structural transformation of Ge dimmers on Ge(001) surfaces induced by bias voltage Qin Zhi-Hui, Shi Dong-Xia, Gao Hong-Jun 2008, 17 (12):  4580-4584.  doi: 10.1088/1674-1056/17/12/041 Abstract ( 0 )   PDF (5759KB) ([an error occurred while processing this directive])   Scanning tunneling microscopy is utilized to investigate the local-bias- voltage-dependent transformation between (2x1) and c(4x2) structures on Ge(001) surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80V. Similar transformation is also found on an epitaxial Ge islands but at a slightly different critical bias voltage of -1.00V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the vacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.

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Synthesis and photoluminescence property of boron carbide nanowires Bao Li-Hong, Li Chen, Tian Yuan, Tian Ji-Fa, Hui Chao, Wang Xing-Jun, Shen Cheng-Min, Gao Hong-Jun 2008, 17 (12):  4585-4591.  doi: 10.1088/1674-1056/17/12/042 Abstract ( 0 )   PDF (9231KB) ([an error occurred while processing this directive])   Large scale, high density boron carbide nanowires have been synthesized by using an improved carbothermal reduction method with B/B2O3/C powder precursors under an argon flow at 1100℃. The boron carbide nanowires are 5--10μm in length and 80--100nm in diameter. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations show that the boron carbide nanowire has a B4C rhombohedral structure with good crystallization. The Raman spectrum of the as-grown boron carbide nanowires is consistent with that of a B4C structure consisting of B11C icosahedra and C-B-C chains. The room temperature photoluminescence spectrum of the boron carbide nanowires exhibits a visible range of emission centred at 638nm.

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The solution of a wedge disclination dipole interacting with an annular inclusion and the force acting on the disclination dipole Song Hao-Peng, Fang Qi-Hong, Liu You-Wen 2008, 17 (12):  4592-4598.  doi: 10.1088/1674-1056/17/12/043 Abstract ( 0 )   PDF (358KB) ([an error occurred while processing this directive])   The interaction between a wedge disclination dipole and an elastic annular inclusion is investigated. Utilizing the Muskhelishvili complex variable method, the explicit series form solutions of the complex potentials in the matrix and the inclusion region are derived. The image force acting on the disclination dipole center is also calculated. The influence of the location of the disclination dipole and the thickness of the annular inclusion as well as the elastic dissimilarity of materials upon the equilibrium position of the disclination dipole is discussed in detail. The results show that a stable equilibrium point of the disclination dipole near the inclusion is found for certain combinations of material constant. Moreover, the force on the disclination dipole is strongly affected by the position of the disclination dipole and the thickness of annular inclusion. The repulsion force incerases (or the attraction force reduces) with the increase of the thickness of the annular inclusion. An appropriate critical value of the thickness of the annular inclusion may be found to change the direction of the force on the disclination dipole. The present solutions include previous results as special cases.

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Study on the dose rate upset effect of partially depleted silicon-on-insulator static random access memory Zhao Fa-Zhan, Liu Meng-Xin, Guo Tian-Lei, Liu Gang, Hai Chao-He, Han Zheng-Sheng, Yang Shan-Chao, Li Rui-Bin, Lin Dong-Sheng, Chen Wei 2008, 17 (12):  4599-4605.  doi: 10.1088/1674-1056/17/12/044 Abstract ( 0 )   PDF (2343KB) ([an error occurred while processing this directive])   This paper implements the study on the Dose Rate Upset effect of PDSOI SRAM (Partially Depleted Silicon-On-Insulator Static Random Access Memory) with the Qiangguang-I accelerator in Northwest Institute of Nuclear Technology. The SRAM (Static Random Access Memory) chips are developed by the Institute of Microelectronics of Chinese Academy of Sciences. It uses the full address test mode to determine the upset mechanisms. Specified address test is taken in the same time. The test results indicate that the upset threshold of the PDSOI SRAM is about 1x108Gy(Si)/s. However, there are few bits upset when the dose rate reaches up to 1.58x109Gy(Si)/s. The SRAM circuit can still work after the high level γ ray pulse. Finally, the upset mechanism is determined to be the rail span collapse by comparing the critical charge with the collected charge after γ ray pulse. The physical locations of upset cells are plotted in the layout of the SRAM to investigate the layout defect. Then, some layout optimizations have been taken to improve the dose rate hardened performance of the PDSOI SRAM.

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Hydrostatic pressure effect on the electron mobility in a ZnSe/Zn1－xdx Se strained heterojunction Bai Xian-Ping, Ban Shi-Liang 2008, 17 (12):  4606-4613.  doi: 10.1088/1674-1056/17/12/045 Abstract ( 0 )   PDF (412KB) ([an error occurred while processing this directive])   With a memory function approach, this paper investigates the electronic mobility parallel to the interface in a ZnSe/Zn1－xdx Se strained heterojunction under hydrostatic pressure by considering the intersubband and intrasubband scattering from the optical phonon modes. A triangular potential approximation is adopted to simplify the potential of the conduction band bending in the channel side and the electronic penetrating into the barrier is considered by a finite interface potential in the adopted model. The numerical results with and without strain effect are compared and analyzed. Meanwhile, the properties of electronic mobility under pressure versus temperature, Cd concentration and electronic density are also given and discussed, respectively. It shows that the strain effect lowers the mobility of electrons while the hydrostatic pressure effect is more obvious to decrease the mobility. The contribution induced by the longitudinal optical phonons in the channel side is dominant to decide the mobility. Compared with the intrasubband scattering it finds that the effect of intersubband scattering is also important for the studied material.

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Compact-like discrete breather and its stability in a discrete monatomic Klein--Gordon chain Xu Quan, Tian Qiang 2008, 17 (12):  4614-4618.  doi: 10.1088/1674-1056/17/12/046 Abstract ( 0 )   PDF (356KB) ([an error occurred while processing this directive])   This paper studies a discrete one-dimensional monatomic Klein--Gordon chain with only quartic nearest-neighbor interactions, in which the compact-like discrete breathers can be explicitly constructed by an exact separation of their time and space dependence. Introducing the trying method, it proves that compact-like discrete breathers exist in this nonlinear system. It also discusses the linear stability of the compact-like discrete breathers, when the coefficient (β) of quartic on-site potential and the coupling constant (K4) of quartic interactive potential satisfy the given conditions, they are linearly stable.

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Relations between compositional modulation and atomic ordering degree in thin films of ternary III—V semiconductor alloys Zhang Li-Ping, Zheng Zhen, Liang Jia-Chang, Le Xiao-Yun, Zou Chao, Liu Huan-Li, Liu Ye 2008, 17 (12):  4619-4621.  doi: 10.1088/1674-1056/17/12/047 Abstract ( 0 )   PDF (444KB) ([an error occurred while processing this directive])   This paper derives the expressions for the ordering degree and the modulation factor of A and B atoms in AxB1-xC epilayers of ternary III--V semiconductor alloys. Using these expressions, it identifies quantitatively the alternating atom-enhanced planes, compositional modulations, atomic ordering degree on the group-III sublattices and the fine structure of NMR spectra.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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A new physics-based self-heating effect model for 4H-SiC MESFETs Cao Quan-Jun, Zhang Yi-Men, Zhang Yu-Ming 2008, 17 (12):  4622-4626.  doi: 10.1088/1674-1056/17/12/048 Abstract ( 0 )   PDF (620KB) ([an error occurred while processing this directive])   A new self-heating effect model for 4H-SiC MESFETs is proposed based on a combination of an analytical and a computer aided design (CAD) oriented drain current model. The circuit oriented expressions of 4H-SiC low-field electron mobility and in-complete ionization rate, which are related to temperature, are presented in this model, which are used to estimate the self-heating effect of 4H-SiC MESFETs. The verification of the present model is made, and the good agreement between simulated results and measured data of DC I-V curves with the self-heating effect is obtained.

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Phase coherence of the electron and hole in a ferromagnetic film in proximity with a superconductor Yu Hua-Ling, Wang Zhi-Guo, Peng Ju 2008, 17 (12):  4627-4634.  doi: 10.1088/1674-1056/17/12/049 Abstract ( 0 )   PDF (580KB) ([an error occurred while processing this directive])   The scattering matrix approach between the clean and dirty limits is developed for the study of tunneling spectra in a ferromagnetic film in proximity to a superconductor. The minigap and the damped oscillation from ``0" to ``π" state in tunneling conductance are attributed to the phase coherence of the electrons and the corresponding Andreev-reflected holes in the ferromagnetic film. The calculated results provide a reasonable explanation for the behavior observed in recent experiments.

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Research on reverse recovery characteristics of SiGeC p-i-n diodes Gao Yong, Liu Jing, Yang Yuan 2008, 17 (12):  4635-4639.  doi: 10.1088/1674-1056/17/12/050 Abstract ( 0 )   PDF (236KB) ([an error occurred while processing this directive])   This paper analyses the reverse recovery characteristics and mechanism of SiGeC p-i-n diodes. Based on the integrated systems engineering (ISE) data, the critical physical models of SiGeC diodes are proposed. Based on heterojunction band gap engineering, the softness factor increases over six times, reverse recovery time is over 30% short and there is a 20% decrease in peak reverse recovery current for SiGeC diodes with 20% of germanium and 0.5% of carbon, compared to Si diodes. Those advantages of SiGeC p-i-n diodes are more obvious at high temperature. Compared to lifetime control, SiGeC technique is more suitable for improving diode properties and the tradeoff between reverse recovery time and forward voltage drop can be easily achieved in SiGeC diodes. Furthermore, the high thermal-stability of SiGeC diodes reduces the costs of further process steps and offers more freedoms to device design.

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Dynamics of a pair of electron and hole in semiconductor superlattice under an intense electric field Yan Jie-Yun 2008, 17 (12):  4640-4644.  doi: 10.1088/1674-1056/17/12/051 Abstract ( 0 )   PDF (1146KB) ([an error occurred while processing this directive])   This paper investigates the behavior of a pair of electron and hole in semiconductor superlattice under an external electric field with the consideration of Coulomb interaction. By numerically calculating the corresponding probability in the nearest neighbor tight binding approximation, we find that the single electron (or the hole) can not be dynamically localized due to the Coulomb interaction, while the dynamic localization of exciton (the pair of the electron and hole) still exists. Moreover we find that with the increase of the intensity of electric field, the exciton can be dynamically localized more completely.

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Dependence of current-voltage characteristics of pseudomorphic AlAs/In0.53a0.47s/InAs resonant tunneling diodes on quantum well widths Zhang Yang, Zhang Yu, Zeng Yi-Ping 2008, 17 (12):  4645-4647.  doi: 10.1088/1674-1056/17/12/052 Abstract ( 0 )   PDF (1208KB) ([an error occurred while processing this directive])   This paper studies the dependence of I-V characteristics on quantum well widths in AlAs/In0.53Ga0.47As and AlAs/In0.53Ga0.47As/InAs resonant tunneling structures grown on InP substrates. It shows that the peak and the valley current density in the negative differential resistance region are closely related with quantum well width. The measured peak current density, valley current densities and peak-to-valley current ratio of resonant tunneling diodes are continually decreasing with increasing well width.

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Study of (Ga, Mn)N prepared by Mn-Ion implantation using optical techniques Xu Da-Qing, Zhang Yi-Men, Zhang Yu-Ming, Li Pei-Xian, Wang Chao, Lü Hong-Liang, Tang Xiao-Yan, Wang Yue-Hu 2008, 17 (12):  4648-4651.  doi: 10.1088/1674-1056/17/12/053 Abstract ( 0 )   PDF (521KB) ([an error occurred while processing this directive])   This paper reports that (Ga, Mn)N is prepared using implantation of 3at.% Mn Ions into undoped GaN. Structural characterization of the crystals was performed using x-ray diffraction(XRD). Detailed XRD measurements have revealed the characteristic of Mn-Ion implanted GaN with a small contribution of other compounds. With Raman spectroscopy measurements, the spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 747, 733 and 566\,cm-1 identified as E-1(LO), $A1(LO) and E2H, respectively. The Mn-doped GaN layers exhibit additional excitations at 182, 288, 650--725, 363, 506cm-1 and the vicinity of $E2H mode. The modes observed at 182, 288, 650--725\,cm-1 are assigned to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation. Other new phonon modes are assigned to Mnx-Ny, Gax-Mny modes and the local vibrational mode of Mn atoms in the (Ga, Mn)N, which are in fair agreement with the standard theoretical results.

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The magnetic and dielectric properties of multiferroic Sr- substituted Zn2-Y hexagonal ferrites Xu Fang, Bai Yang, Ai Fen, Qiao Li-Jie 2008, 17 (12):  4652-4655.  doi: 10.1088/1674-1056/17/12/054 Abstract ( 0 )   PDF (798KB) ([an error occurred while processing this directive])   The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites (Ba2-xSrxZn2Fe12O22, 1.0≤x≤1.5) are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due to the transformation from ferrimagnetic to antiferromagnetic phase. Moreover, permittivity rises with increasing Sr content. Under a certain external magnetic field, the phase transition of helical spin structure of Ba0.5Sr1.5Zn2Fe12O22 at about 295K seems to open a possibility for the room-temperature ferroelectricity induced by magnetic field. But its low resistivity prevents the observation of ferroelectric and magnetoelectric properties at room-temperature.

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Optical parameters and energy levels splitting of Ho3+ in Ho3+: GdVO4 Wang Ce, Chen Xiao-Bo, Zhang Chun-Lin, Zhang Yun-Zhi, Liu Jin-Ying, Wang Ya-Fei, Liu Da-He, Du Shuai, Xu Xiao-Ling, Wang Lei, Li Song 2008, 17 (12):  4656-4664.  doi: 10.1088/1674-1056/17/12/055 Abstract ( 0 )   PDF (597KB) ([an error occurred while processing this directive])   Ho3+: GdVO4 is a new laser material suitable for high-power laser systems. In this paper we measure the absorption spectra of Ho3+ in the sample Ho3+: GdVO4. The intensity parameters are calculated by using the Judd---Ofelt theory. Some predicted spectroscopic parameters, such as the spontaneous radiative transition rate, branching ratio and integrated emission cross section are dealt with. And we also compare the optical parameters with those of other materials. From these results, it is found that there are many transitions which have large oscillator strengths and large integrated emission cross sections. Especially the transitions such as 5F4 → 5I8, 5S2 → 5I8, 5F5 → 5I9 and 5I7 → 5I8 are useful in solid-state lasers and other fields. Finally, we discuss the splitting of the energy levels of Ho$3+ in the crystal GdVO4 based on the group theory.

CROSSDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Synthesis of industrial diamonds using FeNi alloy powder as catalyst Zhou Lin, Jia Xiao-Peng, Ma Hong-An, Zheng You-Jin, Li Yan-Tao 2008, 17 (12):  4665-4668.  doi: 10.1088/1674-1056/17/12/056 Abstract ( 0 )   PDF (2718KB) ([an error occurred while processing this directive])   Synthesis of diamond single crystals in Fe80Ni20-C system was carried out in a cubic anvil high-pressure and high-temperature apparatus. This paper reports that the surface morphology and inclusion distribution of the grown diamonds had been observed. It finds that the inclusions in cubic and octahedral diamonds radiated along certain crystal orientation, while the inclusion distribution in cubo-octahedral diamond seemed independent of crystal orientation. By using scanning electron microscope, the surface morphology of the three shapes of diamonds was observed. The results of Mossbauer spectrum indicated that there were iron-inclusions Fe3C and Fe-Ni alloy in the diamonds. According to the Fe-C phase diagram, FeFe3C should have formed during the quenching process. Nickel might have an inhibitory effect on the formation of Fe3C.

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Synthesis and photoluminescence properties of Nd2O3 nanoparticles modified by sodium bis 2-ethylhexyl sulfosuccinate Ren Jian-Hua, Zhao Tong-Gang, Liu Jian-Hua, Kong Juan, He Jia-Xin, Guo Lin 2008, 17 (12):  4669-4672.  doi: 10.1088/1674-1056/17/12/057 Abstract ( 0 )   PDF (323KB) ([an error occurred while processing this directive])   This paper reports that Nd2O3 nanoparticles modified by AOT(sodium bis(2-ethylhexyl) sulfosuccinate) were prepared using microemulsion method in the system of water and propanol/AOT/toluene. Transmission electron microscopy shows that the Nd2O3 nanoparticles take the shape of sphere with 18\,nm and 31nm with different preparation. The organic sol of Nd2O3 nanoparticles is very stable at room temperature. X-ray diffraction results show that the product has hexagonal phase structure. Two ultraviolet emission band at 344\,nm and 361\,nm corresponding to the transition of 4D3/2→4I9/2 and 2P3/2→4I112 or 4D3/2 →4I13/2 were observed.

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Off-axis dose distribution for rectangle proton beam Gou Cheng-Jun, Luo Zheng-Ming, Huang Chu-Ye, Feng Xiao-Ning, Wu Zhang-Wen 2008, 17 (12):  4673-4676.  doi: 10.1088/1674-1056/17/12/058 Abstract ( 0 )   PDF (475KB) ([an error occurred while processing this directive])   This paper modifies an analytical algorithm originally developed for electron dose calculations to evaluate the off-axis dose distribution of rectangle proton beam. This spatial distribution could be described by Fermi-Eyges theory since a proton undergoes small-angle scattering when it passes through medium. Predictions of the algorithm for relative off-axis dose distribution by a 6cm*6cm initial monoenergetic proton beam are compared with the results from the published Monte Carlo simulations. The excellent level of agreement between the results of these two methods of dose calculation (<2%) demonstrates that the off-axis dose distribution from rectangle proton beam may be computed with high accuracy using this algorithm. The results also prompts the necessity to consider the off-axis distribution when the proton is applied to clinical radiotherapy since the penumbra is significant at the distal of its range (about 0.6cm at the Bragg-peak depth).