中国物理B

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Soliton solution and interaction property for a coupled modified Korteweg-de Vries (mKdV) system

杨建荣, 毛杰健

2008 (12): 4337-4343. doi: 10.1088/1674-1056/17/12/001

摘要 ( 2358 )

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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

马红彩, 葛东杰, 于耀东

2008 (12): 4344-4353. doi: 10.1088/1674-1056/17/12/002

摘要 ( 1624 )

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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

傅景礼, 陈本永, 谢凤萍

2008 (12): 4354-4360. doi: 10.1088/1674-1056/17/12/003

摘要 ( 1749 )

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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

蔺鹏, 方建会, 庞婷

2008 (12): 4361-4364. doi: 10.1088/1674-1056/17/12/004

摘要 ( 1874 )

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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

张毅

2008 (12): 4365-4368. doi: 10.1088/1674-1056/17/12/005

摘要 ( 1670 )

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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

徐世民, 徐兴磊, 蒋继建, 李洪奇, 王继锁

2008 (12): 4369-4374. doi: 10.1088/1674-1056/17/12/006

摘要 ( 1560 )

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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

满忠晓, 夏云杰

2008 (12): 4375-4377. doi: 10.1088/1674-1056/17/12/007

摘要 ( 1911 )

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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

许田, 曹庄琪, 方靖淮

2008 (12): 4378-4381. doi: 10.1088/1674-1056/17/12/008

摘要 ( 1476 )

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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

黄秀花, 林秀敏, 林功伟, 陈志华, 汤耀祥

2008 (12): 4382-4387. doi: 10.1088/1674-1056/17/12/009

摘要 ( 1807 )

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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

汤耀祥, 林秀敏, 林功伟, 陈立波, 黄秀花

2008 (12): 4388-4395. doi: 10.1088/1674-1056/17/12/010

摘要 ( 1583 )

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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

高丽锋, 刘鑫, 官山

2008 (12): 4396-4400. doi: 10.1088/1674-1056/17/12/011

摘要 ( 1296 )

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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

王艳萍, 陈继胜

2008 (12): 4401-4406. doi: 10.1088/1674-1056/17/12/012

摘要 ( 1671 )

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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

马铁东, 张化光, 浮洁

2008 (12): 4407-4417. doi: 10.1088/1674-1056/17/12/013

摘要 ( 1827 )

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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

屈世显, 卢永智, 张林, 何大韧

2008 (12): 4418-4423. doi: 10.1088/1674-1056/17/12/014

摘要 ( 1697 )

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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

王俊, 马千里

2008 (12): 4424-4427. doi: 10.1088/1674-1056/17/12/015

摘要 ( 1652 )

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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

周慧, 李洪云, 高嵩, 张延惠, 贾正茂, 林圣路

2008 (12): 4428-4433. doi: 10.1088/1674-1056/17/12/016

摘要 ( 1619 )

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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

楼旭阳, 崔宝同

2008 (12): 4434-4439. doi: 10.1088/1674-1056/17/12/017

摘要 ( 1525 )

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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

谢东繁, 高自友, 赵小梅

2008 (12): 4440-4445. doi: 10.1088/1674-1056/17/12/018

摘要 ( 1739 )

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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

莫业柳, 何红弟, 薛郁, 时伟, 卢伟真

2008 (12): 4446-4450. doi: 10.1088/1674-1056/17/12/019

摘要 ( 1527 )

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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

汪辉松, 曾贵华

2008 (12): 4451-4457. doi: 10.1088/1674-1056/17/12/020

摘要 ( 1423 )

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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

张春熹, 李慧, 林鹏

2008 (12): 4458-4465. doi: 10.1088/1674-1056/17/12/021

摘要 ( 1752 )

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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

夏良斌, 欧阳晓平, 王群书, 康克军, 谭新建

2008 (12): 4466-4471. doi: 10.1088/1674-1056/17/12/022

摘要 ( 1517 )

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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.

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Towards the understanding of ¹1P₁ meson mass spectrum

冯学超, 蒋逢春, 常同钦, 冯军兰

2008 (12): 4472-4475. doi: 10.1088/1674-1056/17/12/023

摘要 ( 1854 )

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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 K_1B, h₁(1380) and h_c(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.

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Numerical exploration of population transfer of Rydberg-atom by single frequency-chirped laser pulse

张现周, 任振忠, 贾光瑞, 郭笑天, 公伟贵

2008 (12): 4476-4480. doi: 10.1088/1674-1056/17/12/024

摘要 ( 1921 )

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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

徐国亮, 吕文静, 刘玉芳, 朱遵略, 张现周, 孙金锋

2008 (12): 4481-4484. doi: 10.1088/1674-1056/17/12/025

摘要 ( 1713 )

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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⁺

郑锐, 李松, 侯顺永, 黄光明, 段传喜

2008 (12): 4485-4491. doi: 10.1088/1674-1056/17/12/026

摘要 ( 1951 )

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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

葛愉成

2008 (12): 4492-4497. doi: 10.1088/1674-1056/17/12/027

摘要 ( 1333 )

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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

阎世英, 朱正和

2008 (12): 4498-4503. doi: 10.1088/1674-1056/17/12/028

摘要 ( 1291 )

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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 D_e for the ground state of the Ni₂ molecule is 1.835eV, equilibrium bond length R_e is 0.2243\,nm, vibration frequency \omega_e 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 \omega_e\chi_e, B_e and \alpha_e 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

张洪英, 鲁振中, 樊荣伟, 陈德应

2008 (12): 4504-4509. doi: 10.1088/1674-1056/17/12/029

摘要 ( 1296 )

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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.

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Third-order ghost interference with thermal light

李洪国, 张颖涛, 曹德忠, 熊俊, 汪凯戈

2008 (12): 4510-4515. doi: 10.1088/1674-1056/17/12/030

摘要 ( 1626 )

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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

李静霞, 张明江, 牛生晓, 王云才

2008 (12): 4516-4522. doi: 10.1088/1674-1056/17/12/031

摘要 ( 1344 )

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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

周兆妍, 袁建民

2008 (12): 4523-4528. doi: 10.1088/1674-1056/17/12/032

摘要 ( 1273 )

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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

姜宝光, 曹召良, 穆全全, 胡立发, 李超, 宣丽

2008 (12): 4529-4532. doi: 10.1088/1674-1056/17/12/033

摘要 ( 1364 )

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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

冯天华, 戴峭峰, 吴立军, 郭旗, 胡巍, 兰胜

2008 (12): 4533-4540. doi: 10.1088/1674-1056/17/12/034

摘要 ( 1507 )

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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

姜洪源, 任玉坤, 敖宏瑞, AntonioRamos

2008 (12): 4541-4546. doi: 10.1088/1674-1056/17/12/035

摘要 ( 1642 )

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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

冯宇, 林建忠

2008 (12): 4547-4553. doi: 10.1088/1674-1056/17/12/036

摘要 ( 1365 )

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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

刘超峰, 倪玉山

2008 (12): 4554-4561. doi: 10.1088/1674-1056/17/12/037

摘要 ( 1483 )

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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.

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Analysis of D_αH_α spectrum emitted in front of the limiter in HT--7

黄娟, 万宝年, DarenStotler, 肖炳甲, 吴振伟, theHT--team

2008 (12): 4562-4567. doi: 10.1088/1674-1056/17/12/038

摘要 ( 1438 )

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In order to understand the recycling and emission processes of hydrogen atoms in HT--7, spectral profiles of the D_αH_α 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 D_αH_α 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 D_αH_α 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 n_e (0)≈3x10¹⁹m^-3, these components contribute 32%, 15%, 32% and 21%, respectively. D_αH_α 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

陈光良, 陈仕华, 陈文兴, 杨思泽

2008 (12): 4568-4573. doi: 10.1088/1674-1056/17/12/039

摘要 ( 1415 )

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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.

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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

董淑强, 李丽琴, 刘鹏, 董宇辉, 陈熙萌

2008 (12): 4574-4579. doi: 10.1088/1674-1056/17/12/040

摘要 ( 1221 )

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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

秦志辉, 时东霞, 高鸿钧

2008 (12): 4580-4584. doi: 10.1088/1674-1056/17/12/041

摘要 ( 1364 )

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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

鲍丽宏, 李晨, 田园, 田继发, 惠超, 王兴军, 申承民, 高鸿钧

2008 (12): 4585-4591. doi: 10.1088/1674-1056/17/12/042

摘要 ( 1333 )

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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

宋豪鹏, 方棋洪, 刘又文

2008 (12): 4592-4598. doi: 10.1088/1674-1056/17/12/043

摘要 ( 1315 )

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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

赵发展, 刘梦新, 郭天雷, 刘刚, 海潮和, 韩郑生, 杨善潮, 李瑞宾, 林东生, 陈伟

2008 (12): 4599-4605. doi: 10.1088/1674-1056/17/12/044

摘要 ( 1311 )

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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/Zn_1－xd_x Se strained heterojunction

白鲜萍, 班士良

2008 (12): 4606-4613. doi: 10.1088/1674-1056/17/12/045

摘要 ( 1620 )

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With a memory function approach, this paper investigates the electronic mobility parallel to the interface in a ZnSe/Zn_1－xd_x 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

徐权, 田强

2008 (12): 4614-4618. doi: 10.1088/1674-1056/17/12/046

摘要 ( 1504 )

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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

张丽平, 郑震, 梁家昌, 乐小云, 邹超, 刘焕礼, 刘冶

2008 (12): 4619-4621. doi: 10.1088/1674-1056/17/12/047

摘要 ( 1337 )

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This paper derives the expressions for the ordering degree and the modulation factor of A and B atoms in A_xB_1-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.

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A new physics-based self-heating effect model for 4H-SiC MESFETs

曹全君, 张义门, 张玉明

2008 (12): 4622-4626. doi: 10.1088/1674-1056/17/12/048

摘要 ( 1570 )

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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

郁华玲, 王之国, 彭菊

2008 (12): 4627-4634. doi: 10.1088/1674-1056/17/12/049

摘要 ( 1296 )

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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

高勇, 刘静, 杨媛

2008 (12): 4635-4639. doi: 10.1088/1674-1056/17/12/050

摘要 ( 1547 )

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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

阎结昀

2008 (12): 4640-4644. doi: 10.1088/1674-1056/17/12/051

摘要 ( 1638 )

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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/In_0.53a_0.47s/InAs resonant tunneling diodes on quantum well widths

张杨, 张予, 曾一平

2008 (12): 4645-4647. doi: 10.1088/1674-1056/17/12/052

摘要 ( 1544 )

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This paper studies the dependence of I-V characteristics on quantum well widths in AlAs/In_0.53Ga_0.47As and AlAs/In_0.53Ga_0.47As/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

徐大庆, 张义门, 张玉明, 李培咸, 王超, 吕红亮, 汤晓燕, 王悦湖

2008 (12): 4648-4651. doi: 10.1088/1674-1056/17/12/053

摘要 ( 1302 )

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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 E₂^H, respectively. The Mn-doped GaN layers exhibit additional excitations at 182, 288, 650--725, 363, 506cm^-1 and the vicinity of $E₂^H 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 Mn_x-N_y, Ga_x-Mn_y 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

徐芳, 白洋, 艾芬, 乔利杰

2008 (12): 4652-4655. doi: 10.1088/1674-1056/17/12/054

摘要 ( 1508 )

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The magnetic and dielectric properties of Sr-substituted Zn₂-Y hexagonal ferrites (Ba_2-xSr_xZn₂Fe₁₂O₂₂, 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 Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂ 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

王策, 陈晓波, 张春林, 张蕴芝, 刘金英, 王亚非, 刘大禾, 杜帅, 徐小灵, 王磊, 李崧

2008 (12): 4656-4664. doi: 10.1088/1674-1056/17/12/055

摘要 ( 1395 )

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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 Ho³⁺ in the crystal GdVO₄ based on the group theory.

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Synthesis of industrial diamonds using FeNi alloy powder as catalyst

周林, 贾晓鹏, 马红安, 郑友进, 李彦涛

2008 (12): 4665-4668. doi: 10.1088/1674-1056/17/12/056

摘要 ( 1105 )

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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

任建华, 赵同刚, 刘建华, 孔娟, 贺加欣, 郭林

2008 (12): 4669-4672. doi: 10.1088/1674-1056/17/12/057

摘要 ( 1448 )

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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 ⁴D_3/2→4I_9/2 and 2P_3/2→⁴I₁₁₂ or ⁴D_3/2 →⁴I_13/2 were observed.

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Off-axis dose distribution for rectangle proton beam

勾成俊, 罗正明, 黄初叶, 冯晓宁, 吴章文

2008 (12): 4673-4676. doi: 10.1088/1674-1056/17/12/058

摘要 ( 1057 )

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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).

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