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Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.5
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Application of a multiregion model to the EM scattering from a rough surface with or without a target above it

Wang An-Qi, Guo Li-Xin, Chai Cao
Chin. Phys. B 2011, 20 (5): 050201;  doi: 10.1088/1674-1056/20/5/050201
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An efficient multiregion model is introduced to calculate the electromagnetic scattering from a perfectly electrical conducting (PEC) rough surface with or without a PEC target above it. In the multiregion model, the rough surface is split into multiple regions depending on their position along the rough surface. Two intermediate regions are chosen as the dominant region. If a target is located above the rough surface, the target will also be included in the dominant region. The method of moments (MOM) is only adopted on the dominant region to ensure validity. Hence, the new model can greatly reduce the number of unknowns associated with full MOM analysis. The induced electric currents on the other regions are obtained by approximately considering the mutual coupling between different regions along the rough surface. Compared with the published hybrid method, this new model is not only suitable for EM scattering from a target above a rough surface but also applicable for just rough surfaces. Several numerical simulations are presented to show the validity and efficiency of the multiregion model.

Electromagnetic scattering from two-layered rough interfaces with a PEC object: vertical polarization

Wang An-Qi, Guo Li-Xin, Chai Cao
Chin. Phys. B 2011, 20 (5): 050202;  doi: 10.1088/1674-1056/20/5/050202
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Electromagnetic (EM) scattering from a stack of two rough interfaces separating a homogeneous medium with a perfectly electric conducting (PEC) object has been calculated through the method of moments for vertical polarization. Theoretical formulations of EM scattering from multi-layered rough interfaces with a PEC object have been derived in detail and the total fields and their normal derivatives on the rough interfaces are solved. The two-layered model is a special case. In this work, a Gaussian rough surface was applied to simulate the rough interface. A cylinder was located above, between or below the two-layered rough interfaces. Through numerical simulations, the validity of this work is demonstrated by comparing it with existing scattering models, which are special cases that include a PEC object located above/below a single-layered rough interface and two-layered rough interfaces without an object. Subsequently, the influences of characteristic parameters, such as the relative permittivity of the medium, as well as the average height between the two rough surfaces, on the bistatic scattering coefficient are discussed.

Ground eigenvalue and eigenfunction of a spin-weighted spheroidal wave equation in low frequencies

Tang Wen-Lin, Tian Gui-Hua
Chin. Phys. B 2011, 20 (5): 050301;  doi: 10.1088/1674-1056/20/5/050301
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Spin-weighted spheroidal wave functions play an important role in the study of the linear stability of rotating Kerr black holes and are studied by the perturbation method in supersymmetric quantum mechanics. Their analytic ground eigenvalues and eigenfunctions are obtained by means of a series in low frequency. The ground eigenvalue and eigenfunction for small complex frequencies are numerically determined.

Conservation issue of pairwise quantum discord and entanglement of two coupled qubits in a two-mode vacuum cavity

Chen Qiu-Ying, Fang Mao-Fa, Xiao Xing, Zhou Xiang-Feng
Chin. Phys. B 2011, 20 (5): 050302;  doi: 10.1088/1674-1056/20/5/050302
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The conservation issues of pairwise quantum discord and entanglement of two qubits coupled to a two-mode vacuum cavity are investigated by considering the dipole–dipole interaction between two qubits. It is found that the sum of the square of the pairwise quantum discords and the sum of the square of the pairwise concurrences are both conserved in the strong dipole–dipole interaction limit. However, in the middle dipole–dipole and weak dipole–dipole interaction limits, the sum of the square of the pairwise concurrences is still conserved while the sum of the square of the pairwise discords is not. The crucial reason for this is that the quantum discords are not equivalent if the measurements are performed on different subsystems in a general situation. So it is very important for quantum computation depending on the quantum discord to select the target performed by the measurements.

Some applications of a new coherent-entangled state in two-mode Fock space

Meng Xiang-Guo, Wang Ji-Suo, Liang Bao-Long
Chin. Phys. B 2011, 20 (5): 050303;  doi: 10.1088/1674-1056/20/5/050303
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Using the technique of integration within an ordered product of operators, we find a new kind of coherent-entangled state (CES), which exhibits both coherent and entangled state properties. The set of CESs makes up a complete and partly nonorthogonal representation. Using a beam splitter, we propose a simple experimental scheme to produce the CES. Finally, we present some applications of CESs in quantum optics.

Coherence generation and population transfer in a three-level ladder system

Zhang Bing, Jiang Yun, Wang Gang, Zhang Li-Da, Wu Jin-Hui, Gao Jin-Yue
Chin. Phys. B 2011, 20 (5): 050304;  doi: 10.1088/1674-1056/20/5/050304
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This work explores the effect of spontaneous emission on coherence generation and population transfer in a three-level ladder atomic system driven by two pulses in counterintuitive order. With adiabatic evolution and the weak-dephasing approximation, we find that a large coherence and population transfer can be achieved even with spontaneous decay rate. The maximum coherence and population transfer decrease with the increase of spontaneous decay rate from the highest state to intermediate state. But this effect can be compensated by shortening the pulse width and enlarging the delay time. Results show that the coherence generation and population transfer never depend on the spontaneous decay rate from the intermediate state to ground state. The validity of the analytic solution is examined by numerical calculation.

Dense coding with a two-qubit Heisenberg XYZ chain under the influence of phase decoherence

Sulayiman Simayi, Aihemaiti Abulizi, Mushajiang Yaermaimaiti, Cai Jiang-Tao, Qiao Pan-Pan
Chin. Phys. B 2011, 20 (5): 050305;  doi: 10.1088/1674-1056/20/5/050305
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We investigate the joint effects of phase decoherence, Dzyaloshinskii–Moriya (DM) interaction and inhomogeneity of the external magnetic field (b) on dense coding in a two-qubit anisotropic Heisenberg XYZ spin chain. Analytical expressions are obtained for the dense coding capacity. It is found that valid dense coding is always possible with this model when the system is initially prepared in the maximum entangled state. Moreover, optimal dense coding can be implemented for this initial state as long as the mean spin–spin coupling constant J+ of the XY plane is larger than b and the DM interaction despite the intrinsic decoherence. Non-maximal entangled initial states are found to be undesirable for dense coding with this model.

Discord under the influence of a quantum phase transition

Wang Lin-Cheng, Shen Jian, Yi Xue-Xi
Chin. Phys. B 2011, 20 (5): 050306;  doi: 10.1088/1674-1056/20/5/050306
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This paper studies the discord of a bipartite two-level system coupling to an XY spin-chain environment in a transverse field and investigates the relationship between the discord property and the environment's quantum phase transition. The results show that the quantum discord is also able to characterize the quantum phase transitions. We also discuss the difference between discord and entanglement, and show that quantum discord may reveal more general information than quantum entanglement for characterizing the environment's quantum phase transition.

A new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology for practical quantum key distribution system

Zhong Ping-Ping, Zhang Hua-Ni, Wang Jin-Dong, Qin Xiao-Juan, Wei Zheng-Jun, Chen Shuai, Liu Song-Hao
Chin. Phys. B 2011, 20 (5): 050307;  doi: 10.1088/1674-1056/20/5/050307
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Three clock synchronization schemes for a quantum key distribution system are compared experimentally through the outdoor fibre and the interaction physical model of the the clock signal and the the quantum signal in the quantum key distribution system is analysed to propose a new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology to reduce quantum bits error rates under some transmission rate conditions. The proposed synchronization scheme can not only completely eliminate noise photons from the bright background light of the the clock signal, but also suppress the fibre nonlinear crosstalk.

Deterministic generation of Greenberger–Horne–Zeilinger and W states for three distant atoms via adiabatic passage

Song Pei-Jun, Lü Xin-You, Si Liu-Gang, Yang Xiao-Xue
Chin. Phys. B 2011, 20 (5): 050308;  doi: 10.1088/1674-1056/20/5/050308
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We propose two schemes for generating Greenberger–Horne–Zeilinger and W states of three distant atoms. In the present schemes, the atoms are individually trapped in three spatially separated optical cavities coupled by two optical fibres. Performing an adiabatic passage along dark states, the population of cavities and fibres excited is negligible under certain conditions. In addition, the spontaneous decay of atoms is also efficiently suppressed based on our proposals. Furthermore, the discussion about the entanglement fidelity is given and we point out that our schemes work robustly with small fluctuations of experimental parameters.

Quantum secret sharing based on quantum error-correcting codes

Zhang Zu-Rong, Liu Wei-Tao, Li Cheng-Zu
Chin. Phys. B 2011, 20 (5): 050309;  doi: 10.1088/1674-1056/20/5/050309
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Quantum secret sharing(QSS) is a procedure of sharing classical information or quantum information by using quantum states. This paper presents how to use a [2k-1,1,k] quantum error-correcting code (QECC) to implement a quantum (k,2k-1) threshold scheme. It also takes advantage of classical enhancement of the [2k-1,1,k] QECC to establish a QSS scheme which can share classical information and quantum information simultaneously. Because information is encoded into QECC, these schemes can prevent intercept-resend attacks and be implemented on some noisy channels.

Probabilistic remote preparation of a high-dimensional equatorial multiqubit with four-party and classical communication cost

Dai Hong-Yi, Zhang Ming, Chen Ju-Mei, Li Cheng-Zu
Chin. Phys. B 2011, 20 (5): 050310;  doi: 10.1088/1674-1056/20/5/050310
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This paper presents a protocol for probabilistic remote preparation of a high-dimensional equatorial multiqubit with four-party, consisting of a sender and three receivers. The quantum channel is composed of a partial entangled high-dimensional four-particle state. We calculate the successful total probability and the total classical communication cost required for this scheme. It is shown that both the entangled resources and classical communication cost are greatly reduced.

The dependence of fidelity on the squeezing parameter in teleportation of the squeezed coherent states

Zhang Jing-Tao, He Guang-Qiang, Ren Li-Jie, Zeng Gui-Hua
Chin. Phys. B 2011, 20 (5): 050311;  doi: 10.1088/1674-1056/20/5/050311
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This paper investigates an analytical expression of teleportation fidelity in the teleportation scheme of a single mode of electromagnetic field. The fidelity between the original squeezed coherent state and the teleported one is expressed in terms of the squeezing parameter r and the quantum channel parameter (two-mode squeezed state) p. The results of analysis show that the fidelity increases with the increase of the quantum channel parameter p, while the fidelity decreases with the increase of the squeezing parameter r of the squeezed state. Thus the coherent state (r=0) is the best quantum signal for continuous variable quantum teleportation once the quantum channel is built.

Scheme for implementing perfect quantum teleportation with four-qubit entangled states in cavity quantum electrodynamics

Tang Jing-Wu, Zhao Guan-Xiang, He Xiong-Hui
Chin. Phys. B 2011, 20 (5): 050312;  doi: 10.1088/1674-1056/20/5/050312
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Recently, Peng et al. [2010 Eur. Phys. J. D 58 403] proposed to teleport an arbitrary two-qubit state with a family of four-qubit entangled states, which simultaneously include the tensor product of two Bell states, linear cluster state and Dicke-class state. This paper proposes to implement their scheme in cavity quantum electrodynamics and then presents a new family of four-qubit entangled state 4>1234. It simultaneously includes all the well-known four-qubit entangled states which can be used to teleport an arbitrary two-qubit state. The distinct advantage of the scheme is that it only needs a single setup to prepare the whole family of four-qubit entangled states, which will be very convenient for experimental realization. After discussing the experimental condition in detail, we show the scheme may be feasible based on present technology in cavity quantum electrodynamics.

Scheme to generate and discriminate a type of multipartite maximally entangled states in ion-trap

Xue Li, Huang Shou-Sheng, Wu Lie, Ji Yong-Yun, Jiang Nian-Quan
Chin. Phys. B 2011, 20 (5): 050313;  doi: 10.1088/1674-1056/20/5/050313
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This paper proposes a scheme to generate, in an ion-trap, a type of multipartite maximally entangled state which was first introduced by Chen et al. [Chen P X, Zhu S Y and Guo G C 2006 Phys. Rev. A 74 032324]. The maximum entanglement property of these states is examined. It also demonstrates how to discriminate among these states in the ion-trap.

Generation of Wn state with three atoms trapped in two remote cavities coupled by an optical fibre

Li Yan-Ling, Fang Mao-Fa
Chin. Phys. B 2011, 20 (5): 050314;  doi: 10.1088/1674-1056/20/5/050314
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We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre. One is implemented by controlling the interaction time, the other is implemented via the adiabatic passage. The influence of various decoherence processes, such as spontaneous emission of the atoms and photon leakages of the cavities and the optical fibre, on the fidelity is also investigated. It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present.

Exact analytical solutions of three-dimensional Gross–Pitaevskii equation with time–space modulation

Hu Xiao, Li Biao
Chin. Phys. B 2011, 20 (5): 050315;  doi: 10.1088/1674-1056/20/5/050315
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By the generalized sub-equation expansion method and symbolic computation, this paper investigates the (3+1)-dimensional Gross–Pitaevskii equation with time- and space-dependent potential, time-dependent nonlinearity, and gain or loss. As a result, rich exact analytical solutions are obtained, which include bright and dark solitons, Jacobi elliptic function solutions and Weierstrass elliptic function solutions. With computer simulation, the main evolution features of some of these solutions are shown by some figures. Nonlinear dynamics of a soliton pulse is also investigated under the different regimes of soliton management.

Macroscopic resonant tunneling in an rf-SQUID flux qubit Hot!

Cong Shan-Hua, Wang Yi-Wen, Sun Guo-Zhu, Chen Jian, Yu Yang, Wu Pei-Heng
Chin. Phys. B 2011, 20 (5): 050316;  doi: 10.1088/1674-1056/20/5/050316
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We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.

A new metric for rotating black holes in Gauss–Bonnet gravity

Yue Rui-Hong, Zou De-Cheng, Yu Tian-Yi, Yang Zhan-Ying
Chin. Phys. B 2011, 20 (5): 050401;  doi: 10.1088/1674-1056/20/5/050401
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This paper presents a new metric and studies slowly rotating Gauss–Bonnet black holes with a nonvanishing angular momentum in five dimensional anti-de Sitter spaces. Taking the angular momentum parameter a up to second order, the slowly rotating black hole solutions are obtained by working directly in the action. In addition, it also finds that this method is applicable in higher order Lovelock gravity.

Steady-state probability density function in wave turbulence under large volume limit

Yeontaek Choi, Sang Gyu Jo
Chin. Phys. B 2011, 20 (5): 050501;  doi: 10.1088/1674-1056/20/5/050501
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We investigate the possibility for two-mode probability density function (PDF) to have a non-zero flux steady state solution. We take the large volume limit so that the space of modes becomes continuous. It is shown that in this limit all the steady-state two- or higher-mode PDFs are the product of one-mode PDFs. The flux of this steady-state solution turns out to be zero for any finite mode PDF.

Entropic noise induced stability and double entropic stochastic resonance induced by correlated noises

Zeng Chun-Hua, Wang Hua, Wang Hui-Tao
Chin. Phys. B 2011, 20 (5): 050502;  doi: 10.1088/1674-1056/20/5/050502
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For the activated dynamics of a Brownian particle moving in a confined system with the presence of entropic barriers, this paper investigates a periodic driving and correlations between two noises. Within the two-state approximation, the explicit expressions of the mean first passage time (MFPT) and the spectral power amplification (SPA) are obtained, respectively. Based on the numerical computations, it is found that: (i) The MFPT as a function of the noise intensity exhibits a maximum with the positive correlations between two noises (λ>0), this maximum for MFPT shows the characteristic of the entropic noise induced stability (ENIS) effect. The intensity λ of correlations between two noises can enhance the ENIS effect. (ii) The SPA as a function of the noise intensity exhibits a double-peak by tuning the noise correlation intensity λ, i.e., the existence of a double-peak behaviour is the identifying characteristic of the double entropic stochastic resonance phenomenon.

Effects of quantization on detrended fluctuation analysis

Zhu Song-Sheng, Xu Ze-Xi, Yin Kui-Xi, Xu Yin-Lin
Chin. Phys. B 2011, 20 (5): 050503;  doi: 10.1088/1674-1056/20/5/050503
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Detrended fluctuation analysis (DFA) is a method foro estimating the long-range power-law correlation exponent in noisy signals. It has been used successfully in many different fields, especially in the research of physiological signals. As an inherent part of these studies, quantization of continuous signals is inevitable. In addition, coarse-graining, to transfer original signals into symbol series in symbolic dynamic analysis, can also be considered as a quantization-like operation. Therefore, it is worth considering whether the quantization of signal has any effect on the result of DFA and if so, how large the effect will be. In this paper we study how the quantized degrees for three types of noise series (anti-correlated, uncorrelated and long-range power-law correlated signals) affect the results of DFA and find that their effects are completely different. The conclusion has an essential value in choosing the resolution of data acquisition instrument and in the processing of coarse-graining of signals.

Denoising via truncated sparse decomposition

Xie Zong-Bo, Feng Jiu-Chao
Chin. Phys. B 2011, 20 (5): 050504;  doi: 10.1088/1674-1056/20/5/050504
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This paper proposes a denoising algorithm called truncated sparse decomposition (TSD) algorithm, which combines the advantage of the sparse decomposition with that of the minimum energy model truncation operation. Experimental results on two real chaotic signals show that the TSD algorithm outperforms the recently reported denoising algorithms–-non-negative sparse coding and singular value decomposition based method.

New results on stability criteria for neural networks with time-varying delays

O.M. Kwon, J.W. Kwon, S.H. Kim
Chin. Phys. B 2011, 20 (5): 050505;  doi: 10.1088/1674-1056/20/5/050505
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In this paper, the problem of stability analysis for neural networks with time-varying delays is considered. By constructing a new augmented Lyapunov–Krasovskii's functional and some novel analysis techniques, improved delay-dependent criteria for checking the stability of the neural networks are established. The proposed criteria are presented in terms of linear matrix inequalities (LMIs) which can be easily solved and checked by various convex optimization algorithms. Two numerical examples are included to show the superiority of our results.

Correlation dimension based nonlinear analysis of network traffics with different application protocols

Wang Jun-Song, Yuan Jing, Li Qiang, Yuan Rui-Xi
Chin. Phys. B 2011, 20 (5): 050506;  doi: 10.1088/1674-1056/20/5/050506
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This paper uses a correlation dimension based nonlinear analysis approach to analyse the dynamics of network traffics with three different application protocols--HTTP, FTP and SMTP. First, the phase space is reconstructed and the embedding parameters are obtained by the mutual information method. Secondly, the correlation dimensions of three different traffics are calculated and the results of analysis have demonstrated that the dynamics of the three different application protocol traffics is different from each other in nature, i.e. HTTP and FTP traffics are chaotic, furthermore, the former is more complex than the later; on the other hand, SMTP traffic is stochastic. It is shown that correlation dimension approach is an efficient method to understand and to characterize the nonlinear dynamics of HTTP, FTP and SMTP protocol network traffics. This analysis provided insight into and a more accurate understanding of nonlinear dynamics of internet traffics which have a complex mixture of chaotic and stochastic components.

Persistent excitation in adaptive parameter identification of uncertain chaotic system

Zhao Jun-Chan, Zhang Qun-Jiao, Lu Jun-An
Chin. Phys. B 2011, 20 (5): 050507;  doi: 10.1088/1674-1056/20/5/050507
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This paper studies the parameter identification problem of chaotic systems. Adaptive identification laws are proposed to estimate the parameters of uncertain chaotic systems. It proves that the asymptotical identification is ensured by a persistently exciting condition. Additionally, the method can be applied to identify the uncertain parameters with any number. Numerical simulations are given to validate the theoretical analysis.

Impulsive control of chaotic systems and its applications in synchronization

Wu Bo, Liu Yang, Lu Jian-Quan
Chin. Phys. B 2011, 20 (5): 050508;  doi: 10.1088/1674-1056/20/5/050508
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In this paper, some novel sufficient conditions for asymptotic stability of impulsive control systems are presented by comparison systems. The results are used to obtain the conditions under which the chaotic systems can be asymptotically controlled to the origin via impulsive control. Compared with some existing results, our results are more relaxed in the sense that the Lyapunov function is required to be nonincreasing only along a subsequence of switchings. Moreover, a larger upper bound of impulsive intervals for stabilization and synchronization is obtained.

A new perturbation method to the Tent map and its application

Wang Xing-Yuan, Wang Lin-Lin
Chin. Phys. B 2011, 20 (5): 050509;  doi: 10.1088/1674-1056/20/5/050509
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Disturbance imposed on the chaotic systems is an effective way to maintain its chaotic good encryption features. This paper proposes a new perturbation method to the Tent map. First it divides the Tent map domain into 2^N parts evenly and selects a particular part from them, then proliferates the Tent map mapping trajectory of this particular part, which can disturb the entire system disturbance. The mathematical analysis and simulated experimental results prove that the disturbed Tent map has uniform invariant distribution and can produce good cryptographic properties of pseudo-random sequence. These facts avoid the phenomenon of short-period caused by the computer's finite precision and reducing the sequence's dependence on the disturbance signal, such that effectively compensate for the digital chaotic system dynamics degradation.

Chaos and quantum Fisher information in the quantum kicked top

Wang Xiao-Qian, Ma Jian, Zhang Xi-He, Wang Xiao-Guang
Chin. Phys. B 2011, 20 (5): 050510;  doi: 10.1088/1674-1056/20/5/050510
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Quantum Fisher information is related to the problem of parameter estimation. Recently, a criterion has been proposed for entanglement in multipartite systems based on quantum Fisher information. This paper studies the behaviours of quantum Fisher information in the quantum kicked top model, whose classical correspondence can be chaotic. It finds that, first, detected by quantum Fisher information, the quantum kicked top is entangled whether the system is in chaotic or in regular case. Secondly, the quantum Fisher information is larger in chaotic case than that in regular case, which means, the system is more sensitive in the chaotic case.

Global exponential synchronization between Lü system and Chen system with unknown parameters and channel time-delay

Ma Tie-Dong, Fu Jie
Chin. Phys. B 2011, 20 (5): 050511;  doi: 10.1088/1674-1056/20/5/050511
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This paper proposes a nonlinear feedback control method to realize global exponential synchronization with channel time-delay between the Lü system and Chen system, which are regarded as the drive system and the response system respectively. Some effective observers are produced to identify the unknown parameters of the Lü system. Based on the Lyapunov stability theory and linear matrix inequality technique, some sufficient conditions of global exponential synchronization of the two chaotic systems are derived. Simulation results show the effectiveness and feasibility of the proposed controller.

Adsorption-controlled transition of the electrical properties realized in Hematite (alpha-Fe2O3) nanorods ethanol sensing

Wang Chong, Wang Fei-Fei, Fu Xing-Qiu, Zhang En-Di, Xu Zhi
Chin. Phys. B 2011, 20 (5): 050701;  doi: 10.1088/1674-1056/20/5/050701
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Alpha-Fe2O3 nanorods are synthesized through a hydrothermal method with no surfactant introduced and ethanol sensors are fabricated from these nanorods. The device can respond to ethanol vapour in a concentration range from 1 to 1500 parts per million and shows both p-type and n-type responding characteristics during the investigation of the ethanol sensing. The sensor displays a p-type characteristic when the ethanol concentration is low and converted into an n-type characteristic as the concentration exceeds a certain value. Such a phenomenon is attributed to the chemisorbed oxygen, which leads to different modifications of the energy band at the surface, namely, depletion layer or inversion layer.

Smith–Purcell free electron laser based on the semi-elliptical resonator

Meng Xian-Zhu, Wang Ming-Hong, Ren Zhong-Min
Chin. Phys. B 2011, 20 (5): 050702;  doi: 10.1088/1674-1056/20/5/050702
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A novel Smith–Purcell (S–P) free electron laser composed of an electron gun, a semi-elliptical resonator, a metallic reflecting grating and a collector, is presented for the first time. This paper studies the characteristics of this device by theoretical analysis and particle-in-cell simulation method. Results indicate that tunable coherent S–P radiation with a high output peak power at millimeter wavelengths can be generated by adjusting the length of the grating period, or adjusting the voltage of the electron beam. The present scheme has the following advantages: the semi-elliptical resonator can reflect all radiation with the emission angle θ and random azimuthal angles, back onto the electron beam with same-phase and causes the electrons to be modulated, so the output power and efficiency are improved.

High accuracy calculation of the hydrogen negative ion in strong magnetic fields

Zhao Ji-Jun, Wang Xiao-Feng, Qiao Hao-Xue
Chin. Phys. B 2011, 20 (5): 053101;  doi: 10.1088/1674-1056/20/5/053101
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Using a full configuration-interaction method with Hylleraas-Gaussian basis function, this paper investigates the 110+, 11(–1)+ and 11(–2)+ states of the hydrogen negative ion in strong magnetic fields. The total energies, electron detachment energies and derivatives of the total energy with respect to the magnetic field are presented as functions of magnetic field over a wide range of field strengths. Compared with the available theoretical data, the accuracy for the energies is enhanced significantly. The field regimes 3 < γ < 4 and 0.02 < γ < 0.05, in which the 11(–1)+ and 11(–2)+ states start to become bound, respectively, are also determined based on the calculated electron detachment energies.

The structure and the potential energy function of AlSO (CS,X2A'')

Yang Ze-Jin, Gao Qing-He, Li Jin, Linghu Rong-Feng, Guo Yun-Dong, Cheng Xin-Lu, Zhu Zheng-He, Yang Xiang-Dong
Chin. Phys. B 2011, 20 (5): 053102;  doi: 10.1088/1674-1056/20/5/053102
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By using the B3P86/aug-cc-pvtz method, the accurate equilibrium geometry of the AlSO (CS,X2A'') molecule has been calculated and compared with available theoretical values. The obtained results show that the AlSO molecule has a most stable structure with bond lengths of ROAl=0.1864 nm, ROS =0.1623 nm, RAlS =0.2450 nm, together with a dissociation energy of 13.88 eV. The possible electronic states and their reasonable dissociation limits for the ground state of the AlSO molecule were determined based on the principle of atomic and molecular reaction statics. The analytic potential energy function of the AlSO molecule was derived by the many-body expansion theory and the contour lines were constructed for the first time, which show the internal information of the AlSO molecule, including the equilibrium structure and stable point. The analysis demonstrates that the obtained potential energy function of AlSO is reasonable and successful and the present investigations provide important insights for further study on molecular reaction dynamics.

Parametric analysis of the planar metamaterials based on complementary double-ring resonators

Lu Wei-Bing, Ji Zhong-Fu
Chin. Phys. B 2011, 20 (5): 054101;  doi: 10.1088/1674-1056/20/5/054101
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The planar metamaterials comprising complementary double-ring resonators (CDRRs) show its left handed behaviour. As a consequent work, this paper presents a detailed parametric study on the magnetically resonant transmission characteristics of the complementary double-ring metamaterials based on its structural parameters. This will be useful for the design of compact planar metamaterials based on the transmission lines loaded with CDRRs.

Investigation of a wideband folded double-ridged waveguide slow-wave system

He Jun, Wei Yan-Yu, Gong Yu-Bin, Wang Wen-Xiang
Chin. Phys. B 2011, 20 (5): 054102;  doi: 10.1088/1674-1056/20/5/054102
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The folded double-ridged waveguide structure is presented and its properties used for wide-band traveling-wave tube are investigated. Expressions of dispersion characteristics, normalized phase velocity and interaction impedance of this structure are derived and numerically calculated. The calculated results using our theory agree well with those obtained by using the 3D electromagnetic simulation software HFSS. Influences of the ridge-loaded area and broad-wall dimensions on the high frequency characteristics of the novel slow-wave structure are discussed. It is shown that the folded double-ridged waveguide structure has a much wider relative passband than the folded waveguide slow-wave structure and a relative passband of 67% could be obtained, indicating that this structure can operate in broad-band frequency ranges of beam–wave interaction. The small signal gain property is investigated for ensuring the improvement of bandwidth. Meanwhile, with comparable dispersion characteristics, the transverse section dimension of this novel structure is much smaller than that of conventional one, which indicates an available way to reduce the weight of traveling-wave tube.

Photon tunneling and transmittance resonance through a multi-layer structure with a left-handed material

He Ying, Zhang Xia, Yang Yan-Fang, Li Chun-Fang
Chin. Phys. B 2011, 20 (5): 054103;  doi: 10.1088/1674-1056/20/5/054103
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This paper investigates the photon tunneling and transmittance resonance through a multi-layer structure including a left-handed material(LHM). An analytical expression for the transmittance in a five-layer structure is given by the analytical transfer matrix method. The transmittance is studied as a function of the refractive index and the width of the LHM layer. The perfect photon tunneling results from the multi-layer structure, especially from the relation between the magnitude of the refractive index and the width of the LHM layer and those of the adjoining layers. Photons may tunnel through a much greater distance in this structure. Transmittance resonance happens, the peaks and valleys appear periodically at the resonance thickness. For an LHM with inherent losses, the perfect transmittance is suppressed.

Quantum interferences in four-wave mixing processes inside a cavity driven by quantized fields

Li Peng-Bo
Chin. Phys. B 2011, 20 (5): 054202;  doi: 10.1088/1674-1056/20/5/054202
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Interferences in the quantum fluctuations of the output fields are demonstrated in four-wave mixing processes inside a cavity, which is driven by two quantized fields at the signal and the idler frequencies. These interferences depend on the phase fluctuations of the input fields and induce mode splitting in the transmission spectra.

Transition state to mode locking in a passively mode-locked erbium-doped fibre ring laser

Liu Jia-Rui, Xu Wen-Cheng, Luo Zhi-Chao, Luo Ai-Ping, Yin Hai-Sen
Chin. Phys. B 2011, 20 (5): 054203;  doi: 10.1088/1674-1056/20/5/054203
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The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simple model has been established to explain the experimental observation.

Angular spectrum characters of high gain non-critical phase match optical parametric oscillators Hot!

Liu Jian-Hui, Liu Qiang, Gong Ma-Li
Chin. Phys. B 2011, 20 (5): 054204;  doi: 10.1088/1674-1056/20/5/054204
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The angular spectrum gain characters and the power magnification characters of high gain non-walk-off colinear optical parametric oscillators have been studied using the non-colinear phase match method for the first time. The experimental results of the KTiOAsO4 and the KTiOPO4 crystals are discussed in detail. At the high energy single resonant condition, low reflective ratio of the output mirror for the signal and long non-linear crystal are beneficial for small divergence angles. This method can also be used for other high gain non-walk-off phase match optical parametric processes.

Surface second-harmonic generation based on periodically poled LiNbO3 nonlinear optical crystal

H. Nili-Ahmadabadi, A.R. Khorsandi
Chin. Phys. B 2011, 20 (5): 054205;  doi: 10.1088/1674-1056/20/5/054205
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We have generated a second-harmonic generation (SHG) of a Q-switched microchip Nd:YAG laser on the surface of a periodically poled LiNbO3 (PPLN) nonlinear crystal near the grazing incidence angle. Three individual SHG waves as transmitted homogeneous, inhomogeneous and reflected radiations have been generated and their intensities are measured and characterized within a desirable range of about 10 different incidence angles of the Nd:YAG laser as pump source on the PPLN surface. The basic of surface nonlinear radiation is also investigated and similar results are calculated and extracted from the theory. Comparison between calculated and measured data shows that they are in good agreement with each other.

Elliptical Gaussian solitons in synthetic nonlocal nonliear media

Cheng Shuang, Wang Qi, Ge Li-Juan, Shi Jie-Long, Ding Hai-Xia, Shen Ming
Chin. Phys. B 2011, 20 (5): 054206;  doi: 10.1088/1674-1056/20/5/054206
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This paper studies analytically and numerically the dynamics of two-dimensional elliptical Gaussian solitons in a "double-self-focusing" synthetic nonlocal media featuring elliptical and circular Gaussian response with different degrees of nonlocality. Based on the variational approach, it obtains the approximately analytical solution of such Gaussian elliptical solitons. It also computes the stability of the solitons by numerical simulations.

High-power terahertz radiation from surface-emitted THz-wave parametric oscillator

Li Zhong-Yang, Yao Jian-Quan, Xu De-Gang, Zhong Kai, Wang Jing-Li, Bing Pi-Bin
Chin. Phys. B 2011, 20 (5): 054207;  doi: 10.1088/1674-1056/20/5/054207
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We report a pulsed surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals pumped by a multi-longitudinal mode Q-switched Nd:YAG laser. Through varying the phase matching angle, the tunable THz-wave output from 0.79 THz to 2.84 THz is realized. The maximum THz-wave output was 193.2 nJ/pulse at 1.84 THz as the pump power density was 212.5 MW/cm2, corresponding to the energy conversion efficiency of 2.42×10-6 and the photon conversion efficiency of about 0.037%. When the pump power density changed from 123 MW/cm2 to 148 MW/cm2 and 164 MW/cm2, the maximum output of the THz-wave moved to the high frequency band. We give a reasonable explanation for this phenomenon.

Solvent-vapour treatment induced performance enhancement of amplified spontaneous emission based on poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1, 4-phenylene vinylene]

Zhang Bo, Hou Yan-Bing, Teng Feng, Lou Zhi-Dong, Liu Xiao-Jun, Hu Bing, Wu Wen-Bin
Chin. Phys. B 2011, 20 (5): 054208;  doi: 10.1088/1674-1056/20/5/054208
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In this work, performance enhancements of amplified spontaneous emission (ASE) from poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) have been achieved via solvent vapour treatment. Correlations between the morphology of the film and the optical performance of polymer-based ASE are investigated. The active layers are characterised by atomic force microscopy and optical absorption. The results show that the solvent-vapour treatment can induce the MEH-PPV self-organisation into an ordered structure with a smooth surface, leading to enhanced optical gain. Thus the solvent-vapour treatment is a good method for improving the optical properties of the MEH-PPV.

Engineering the light propagating features through the two-dimensional coupled-cavity photonic crystal waveguides

Feng Shuai, Wang Yi-Quan
Chin. Phys. B 2011, 20 (5): 054209;  doi: 10.1088/1674-1056/20/5/054209
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This paper studies the propagating characteristics of the electromagnetic waves through the coupled-resonator optical waveguides based on the two-dimensional square-lattice photonic crystals by the finite-difference time-domain method. When the traditional circular rods adjacent to the centre of the cavities are replaced by the oval rods, the simulated results show that the waveguide mode region can be adjusted only by the alteration of the oval rods' obliquity. When the obliquity of the oval rods around one cavity is different from the obliquity of that around the adjacent cavities, the group velocities of the waveguide modes can be greatly reduced and the information of different frequencies can be shared and chosen at the same time by the waveguide branches with different structures. If the obliquities of the oval rods around two adjacent cavities are equal and they alternate between two values, the group velocities can be further reduced and a maximum value of 0.0008c (c is the light velocity in vacuum) can be acquired.

Broad and ultra-flattened supercontinuum generation in the visible wavelengths based on the fundamental mode of photonic crystal fibre with central holes

Yuan Jin-Hui, Sang Xin-Zhu, Yu Chong-Xiu, Xin Xiang-Jun, Shen Xiang-Wei, Zhang Jin-Long, Zhou Gui-Yao, Li Shu-Guang, Hou Lan-Tian
Chin. Phys. B 2011, 20 (5): 054210;  doi: 10.1088/1674-1056/20/5/054210
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By coupling a train of femtosecond pulses with 100 fs pulse width at a repetition rate of 76 MHz generated by a mode-locked Ti: sapphire laser into the fundamental mode of photonic crystal fibre (PCF) with central holes fabricated through extracting air from the central hole, the broad and ultra-flattened supercontinuum (SC) in the visible wavelengths is generated. When the fundamental mode experiences an anomalous dispersion regime, three phases in the SC generation process are primarily presented. The SC generation (SCG) in the wavelength range from 470 nm to 805 nm does not emerge significant ripples due to a higher pump peak power and the corresponding mode fields at different wavelengths are observed using Bragg gratings. The relative intensity fluctuations of output spectrum in the wavelength ranges of 530 nm to 640 nm and 543 nm to 590 nm are only 0.028 and 0.0071, respectively.

Adaptive and optimal detection of elastic object scattering with single-channel monostatic iterative time reversal

Ying Ying-Zi, Ma Li, Guo Sheng-Ming
Chin. Phys. B 2011, 20 (5): 054301;  doi: 10.1088/1674-1056/20/5/054301
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In active sonar operation, the presence of background reverberation and the low signal-to-noise ratio hinder the detection of targets. This paper investigates the application of single-channel monostatic iterative time reversal to mitigate the difficulties by exploiting the resonances of the target. Theoretical analysis indicates that the iterative process will adaptively lead echoes to converge to a narrowband signal corresponding to a scattering object's dominant resonance mode, thus optimising the return level. The experiments in detection of targets in free field and near a planar interface have been performed. The results illustrate the feasibility of the method.

Perturbation to Mei symmetry and Mei adiabatic invariants for discrete generalized Birkhoffian system

Zhang Ke-Jun, Fang Jian-Hui, Li Yan
Chin. Phys. B 2011, 20 (5): 054501;  doi: 10.1088/1674-1056/20/5/054501
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Based on the concept of discrete adiabatic invariant, this paper studies the perturbation to Mei symmetry and Mei adiabatic invariants of the discrete generalized Birkhoffian system. The discrete Mei exact invariant induced from the Mei symmetry of the system without perturbation is given. The criterion of the perturbation to Mei symmetry is established and the discrete Mei adiabatic invariant induced from the perturbation to Mei symmetry is obtained. Meanwhile, an example is discussed to illustrate the application of the results.

Decoherence of elliptical states in phase space

Wang Yue-Yuan, Liu Zheng-Jun, Liao Qing-Hong, Wang Ji-Cheng, Liu Shu-Tian
Chin. Phys. B 2011, 20 (5): 054201;  doi: 10.1088/1674-1056/20/5/054201
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The effects of decoherence on elliptical states which concern the quantum superposition of N coherent states on an ellipse in the α plane are studied. The characteristic decoherence times are determined. The evolutions of the Wigner functions associated with these states are investigated theoretically and the losses of nonclassicality as a result of decoherence are discussed. The result shows that the decoherence of elliptical states is slower than circular states relying on the number of coherent states and the amplitude, and the constructed states have a higher resilience to losses.

Magnetic quantum oscillations in a monolayer graphene under a perpendicular magnetic field

Fu Zhen-Guo, Wang Zhi-Gang, Li Shu-Shen, Zhang Ping
Chin. Phys. B 2011, 20 (5): 058103;  doi: 10.1088/1674-1056/20/5/058103
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The de Haas–van Alphen (dHvA) oscillations of electronic magnetization in a monolayer graphene with structure-induced spin–orbit interaction (SOI) are studied. The results show that the dHvA oscillating centre in this system deviates from the well known (zero) value in a conventional two-dimensional electron gas. The inclusion of SOI will change the well-defined sawtooth pattern of magnetic quantum oscillations and result in a beating pattern. In addition, the SOI effects on Hall conductance and magnetic susceptibility are also discussed.

Observation of chaotic ELMs in HL-2A tokamak

Huang Yuan, Nie Lin, Yu De-Liang, Liu Chun-Hua, Feng Zhen, Duan Xu-Ru
Chin. Phys. B 2011, 20 (5): 055201;  doi: 10.1088/1674-1056/20/5/055201
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The high confinement mode (H-mode) operation is recently obtained in HL-2A divertor configuration, the corresponding edge localized mode (ELM) is recognized as being of type III. Time intervals in ELM time series are analysed to obtain the information about the ELM process. Signatures of unstable periodic orbits (UPOs) are detected, which are indicators of chaos and may be used to control the big ELM events.

Two dynamics modes in planar wire array Z pinch implosion

Sheng Liang, Wang Liang-Ping, Wu Jian, Li Yang, Peng Bo-Dong, Zhang Mei
Chin. Phys. B 2011, 20 (5): 055202;  doi: 10.1088/1674-1056/20/5/055202
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Two dynamics modes, named short ablation mode and long ablation mode, are observed in implosion experiments of planar wire array Z pinch on 'QiangGuang-I' facility utilizing an optical streak camera. The long ablation mode has a lagged trajectory compared with the short ablation mode. For shot 10035 in a short ablation mode, the initial time of K-shell radiation is consistent with the interaction time for ablation plasma arriving at the centre of wire array, while for shot 10038 in long ablation mode, the initial time of K-shell radiation is about 10 ns earlier. In the two modes, the partial ablation plasma could traverse the wire array plane and then collide in the centre to form a dense plasma column with a diameter of 2.2 mm for shot 10035 and 1.5 mm for shot 10038.

Unidirectional expansion of lattice parameters in GaN induced by ion implantation

Fa Tao, Li Lin, Yao Shu-De, Wu Ming-Fang, Zhou Sheng-Qiang
Chin. Phys. B 2011, 20 (5): 056101;  doi: 10.1088/1674-1056/20/5/056101
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This paper reports that the 150-keV Mn ions are implanted into GaN thin film grown on Al2O3 by metal–organic chemical vapour deposition. The X-ray diffraction reciprocal spacing mapping is applied to study the lattice parameter variation upon implantation and post-annealing. After implantation, a significant expansion is observed in the perpendicular direction. The lattice strain in perpendicular direction strongly depends on ion fluence and implantation geometry and can be partially relaxed by post-annealing. While in the parallel direction, the lattice parameter approximately keeps the same as the unimplanted GaN, which is independent of ion fluence, implantation geometry and post-annealing temperature.

Effect of substrate temperature on microstructure and optical properties of single-phased Ag2O film deposited by using radio-frequency reactive magnetron sputtering method

Ma Jiao-Min, Liang Yan, Gao Xiao-Yong, Zhang Zeng-Yuan, Chen Chao, Zhao Meng-Ke, Yang Shi-E, Gu Jin-Hua, Chen Yong-Sheng, Lu Jing-Xiao
Chin. Phys. B 2011, 20 (5): 056102;  doi: 10.1088/1674-1056/20/5/056102
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Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag2O films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2:3 by changing substrate temperature (Ts). Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag2O films deposited at values of Ts below 200 oC are (111) preferentially oriented, which may be due to the smallest free energy of the (111) crystalline face. The film crystallization becomes poor as the value of Ts increases from 100 oC to 225 oC. In particular, the Ag2O film deposited at Ts = 225 oC loses the (111) preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films.

Theoretical calculations of thermophysical properties of single-wall carbon nanotube bundles

Miao Ting-Ting, Song Meng-Xuan, Ma Wei-Gang, Zhang Xing
Chin. Phys. B 2011, 20 (5): 056501;  doi: 10.1088/1674-1056/20/5/056501
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Carbon nanotube bundles are promising thermal interfacial materials due to their excellent thermal and mechanical characteristics. In this study, the phonon dispersion relations and density of states of the single-wall carbon nanotube bundles are calculated by using the force constant model. The calculation results show that the inter-tube interaction leads to a significant frequency raise of the low frequency modes. To verify the applied calculation method, the specific heat of a single single-wall carbon nanotube is calculated first based on the obtained phonon dispersion relations and the results coincide well with the experimental data. Moreover, the specific heat of the bundles is calculated and exhibits a slight reduction at low temperatures in comparison with that of the single tube. The thermal conductivity of the bundles at low temperatures is calculated by using the ballistic transport model. The calculation results indicate that the inter-tube interaction, i.e. van der Waals interaction, hinders heat transfer and cannot be neglected at extremely low temperatures. For (5, 5) bundles, the relative difference of the thermal conductivity caused by ignoring inter-tube effect reaches the maximum value of 26% around 17 K, which indicates the significant inter-tube interaction effect on the thermal conductivity at low temperatures.

Structures of Pt clusters on graphene doped with nitrogen, boron, and silicon: a theoretical study

Dai Xian-Qi, Tang Ya-Nan, Dai Ya-Wei, Li Yan-Hui, Zhao Jian-Hua, Zhao Bao, Yang Zong-Xian
Chin. Phys. B 2011, 20 (5): 056801;  doi: 10.1088/1674-1056/20/5/056801
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The structures of Pt clusters on nitrogen-, boron-, silicon- doped graphenes are theoretically studied using density-functional theory. These dopants (nitrogen, boron and silicon) each do not induce a local curvature in the graphene and the doped graphenes all retain their planar form. The formation energy of the silicon-graphene system is lower than those of the nitrogen-, boron-doped graphenes, indicating that the silicon atom is easier to incorporate into the graphene. All the substitutional impurities enhance the interaction between the Pt atom and the graphene. The adsorption energy of a Pt adsorbed on the silicon-doped graphene is much higher than those on the nitrogen- and boron-doped graphenes. The doped silicon atom can provide more charges to enhance the Pt-graphene interaction and the formation of Pt clusters each with a large size. The stable structures of Pt clusters on the doped-graphenes are dimeric, triangle and tetrahedron with the increase of the Pt coverage. Of all the studied structures, the tetrahedron is the most stable cluster which has the least influence on the planar surface of doped-graphene.

Magnetic properties of Co-doped SnO: first-principles calculations

Tan Xing-Yi, Chen Chang-Le, Jin Ke-Xin, Cao Xian-Sheng, Xing Hui
Chin. Phys. B 2011, 20 (5): 057101;  doi: 10.1088/1674-1056/20/5/057101
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Based on density functional theory calculations, the electronic and magnetic properties of Co-doped SnO are investigated. It is found that the spin-polarized state, with a magnetic moment of about 1.0 μB per Co-dopant, is more favorable in energy than the non-spin-polarized state. Moreover, the origin of the ferromagnetism in Co-doped SnO is found to be the double exchange mechanism. Our results indicate that Co-doped SnO is a possible candidate of the p-type spintronics material.

Numerical study on the dependence of ZnO thin-film transistor characteristics on grain boundary position Hot!

Zhang An, Zhao Xiao-Ru, Duan Li-Bing, Liu Jin-Ming, Zhao Jian-Lin
Chin. Phys. B 2011, 20 (5): 057201;  doi: 10.1088/1674-1056/20/5/057201
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The dependence of transistor characteristics on grain boundary (GB) position in short-channel ZnO thin film transistors (TFTs) has been investigated using two-dimensional numerical simulations. To simulate the device accurately, both tail states and deep-level states are taken into consideration. It is shown that both the transfer and output characteristics of ZnO TFTs change dramatically with varying GB position, which is different from polycrystalline Si (poly-Si) TFTs. By analysing the mechanism of the carrier transportation in the device, it is revealed that the dependence is derived from the degrees of carrier concentration descent and mobility variation with GB position.

Investigation of current transport parameters of Ti/4H–SiC MPS diode with inhomogeneous barrier

Song Qing-Wen, Zhang Yu-Ming, Zhang Yi-Men, Chen Feng-Ping, Tang Xiao-Yan
Chin. Phys. B 2011, 20 (5): 057301;  doi: 10.1088/1674-1056/20/5/057301
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The current transport parameters of 4H–SiC merged PiN Schottky (MPS) diode are investigated in a temperature range of 300–520 K. Evaluation of the experimental current–voltage (IV) data reveals the decrease in Schottky barrier height Φb but an increase in ideality factor n, with temperature decreasing, which suggests the presence of an inhomogeneous Schottky barrier. The current transport behaviours are analysed in detail using the Tung's model and the effective area of the low barrier patches is extracted. It is found that small low barrier patches, making only 4.3% of the total contact, may significantly influence the device electrical characteristics due to the fact that a barrier height of 0.968 eV is much lower than the average barrier height 1.39 eV. This shows that ion implantation in the Schottky contact region of MPS structure may result in a poor Ti/4H–SiC interface quality. In addition, the temperature dependence of the specific on-resistance (Ron - sp), T2.14, is determined between 300 K and 520 K, which is similar to that predicted by a reduction in electron mobility.

Photovoltage analysis of a heterojunction solar cell

Xiong Chao, Yao Ruo-He, Geng Kui-Wei
Chin. Phys. B 2011, 20 (5): 057302;  doi: 10.1088/1674-1056/20/5/057302
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According to the p–n junction model of Shockley, the relationship between the equilibrium carrier concentrations of n-type and p-type semiconductors on the edges of the depletion region of a p–n junction solar cell is analysed. The calculation results show that the photovoltage can exceed the built-in voltage for a special kind of heterojunction solar cell. When the photovoltage exceeds the built-in voltage under illumination, the dark current and the photocurrent are impeded by the peak of voltage barrier at the interface and the expression of the total IV characteristic is given.

Negative tunnelling magnetoresistance in spin filtering magnetic junctions with spin–orbit coupling

Li Yun
Chin. Phys. B 2011, 20 (5): 057303;  doi: 10.1088/1674-1056/20/5/057303
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We present theoretical calculations of spin transport in spin filtering magnetic tunnelling junctions based on the Landauer–Büttiker formalism and taking into account the spin–orbit coupling (SOC). It is shown that spin-flip scattering induced by SOC is stronger in parallel alignment of magnetization of the ferromegnet barrier (FB) and the ferromagnetic electrode than that in antiparallel case. The increase of negative tunnelling magnetoresistance with bias is in agreement with recent experimental observation.

Optically controlled SiCGe/SiC heterojunction transistor with charge-compensation layer

Pu Hong-Bin, Cao Lin, Chen Zhi-Ming, Ren Jie
Chin. Phys. B 2011, 20 (5): 057304;  doi: 10.1088/1674-1056/20/5/057304
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A novel optically controlled SiCGe/SiC heterojunction transistor with charge-compensation technique has been simulated by using commercial simulator. This paper discusses the electric field distribution, spectral response and transient response of the device. Due to utilizing p-SiCGe charge-compensation layer, the responsivity increases nearly two times and breakdown voltage increases 33%. The switching characteristic illustrates that the device is latch-free and its fall time is much longer than the rise time. With an increase of the light power density and wavelength, the rise time and fall time will become shorter and longer, respectively. In terms of carrier lifetime, a compromise should be made between the responsivity and switching speed, the ratio of them reaches maximum value when the minority carrier lifetime equals 90 ns.

Different temperature dependence of carrier transport properties between AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures

Song Jie, Xu Fu-Jun, Huang Cheng-Cheng, Lin Fang, Wang Xin-Qiang, Yang Zhi-Jian, Shen Bo
Chin. Phys. B 2011, 20 (5): 057305;  doi: 10.1088/1674-1056/20/5/057305
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The temperature dependence of carrier transport properties of AlxGa1-xN/InyGa1-yN/GaN and AlxGa1-xN/GaN heterostructures has been investigated. It is shown that the Hall mobility in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures is higher than that in Al0.25Ga0.75N/GaN heterostructures at temperatures above 500 K, even the mobility in the former is much lower than that in the latter at 300 K. More importantly, the electron sheet density in Al0.25Ga0.75N/In0.03Ga0.97N/GaN heterostructures decreases slightly, whereas the electron sheet density in Al0.25Ga0.75N/GaN heterostructures gradually increases with increasing temperature above 500 K. It is believed that an electron depletion layer is formed due to the negative polarization charges at the InyGa1-yN/GaN heterointerface induced by the compressive strain in the InyGa1-yN channel, which effectively suppresses the parallel conductivity originating from the thermal excitation in the underlying GaN layer at high temperatures.

Magnetization of mixed ferri-ferrimagnets composed of Prussian blue analogs A1xA21-xB

Jiang Wei, Guan Hong-Yu, Lo Veng-Cheong
Chin. Phys. B 2011, 20 (5): 057501;  doi: 10.1088/1674-1056/20/5/057501
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The magnetization of ternary metal Prussian blue analogues A1xA21-xB, formed by three different sublattices A1, A2 and B, is studied by using the effective-field theory with self-spin correlations. Effects of the mole fraction x, the anisotropy and the transverse magnetic field on the magnetization are discussed.

Synthesis and magnetic properties of Fe100-xMox alloy nanowire arrays

Gao Hua, Gao Da-Qiang, Xue De-Sheng
Chin. Phys. B 2011, 20 (5): 057502;  doi: 10.1088/1674-1056/20/5/057502
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The Fe100-xMox (13 < x < 25) alloy nanowire arrays are synthesized by electrodeposition of Fe2 + and Mo2 + with different ionic ratios into the anodic aluminum oxide templates. The crystals of Fe100-xMox alloy nanowires gradually change from polycrystalline phase to amorphous phase with the increase of the Mo content and the nanowires are of amorphous structure when the Mo content reaches 25 at%, which are revealed by the X-ray diffraction and the selected area electron diffraction patterns. As the Mo content increases, the magnetic hysteresis loops of Fe100-xMox alloy nanowires in parallel to the nanowire axis are not rectangular and the slopes of magnetic hysteresis loops increase. Those results indicate that the magnetostatic interactions between nanowires and the magnetocrystalline anisotropy both have significant influences on the magnetization reversal process of the nanowire arrays.

Influence of Ga+ ion irradiation on thermal relaxation of exchange bias field in exchange-coupled CoFe/IrMn bilayers

Qi Xian-Jin, Wang Yin-Gang, Miao Xue-Fei, Li Zi-Quan, Huang Yi-Zhong
Chin. Phys. B 2011, 20 (5): 057503;  doi: 10.1088/1674-1056/20/5/057503
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This paper reports that the CoFe/IrMn bilayers are deposited by magnetron sputtering on the surfaces of thermally-oxidized Si substrates. It investigates the thermal relaxations of both non-irradiated and Ga+ ion irradiated CoFe/IrMn bilayers by means of holding the bilayers in a negative saturation field. The results show that exchange bias field decreases with the increase of holding time period for both non-irradiated and Ga+ ion irradiated CoFe/IrMn bilayers. Exchange bias field is also found to be smaller upon irradiation at higher ion dose. This reduction of exchange bias field is attributed to the change of energy barrier induced by ion-radiation.

Short range order transformation and magnetostriction of Fe83Ga17 ribbons

Zhu Jie, Peng Fu-Ling, Fang Mei-Ling, Li Ji-Heng, Gao Xue-Xu, Yu Rong-Hai
Chin. Phys. B 2011, 20 (5): 057504;  doi: 10.1088/1674-1056/20/5/057504
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The relationship between magnetostriction and structure of melt-spun Fe83Ga17 ribbons are investigated by XRD and Mõssbauer spectrum technique (MS). As the heat-treatment temperature increases from 650oC to 800oC, the magnetostriction coefficient of Fe83Ga17 ribbon first increases and then decreases. The largest magnetostriction coefficient (-578.4 ppm) is achieved in those specimens quenched at 750oC. According to the XRD and Mõssbauer spectrum analysis, a small quantity of DO3 phase is precipitated in Fe83Ga17 ribbons when quenched from 650oC and the DO3 phase is gradually transformed into B2-like phase if quenched at higher temperature. However, both DO3 and B2-like phases disappear when the temperature increases up to 800oC. From this point of view, B2-like phase might be beneficial to the enhancement of magnetostrictive properties of melt-spun ribbons.

Microwire formation based on dielectrophoresis of electroless gold plated polystyrene microspheres

Jiang Hong-Yuan, Ren Yu-Kun, Tao Ye
Chin. Phys. B 2011, 20 (5): 057701;  doi: 10.1088/1674-1056/20/5/057701
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Microspheres coated with a perfectly conductive surface have many advantages in the applications of biosensors and micro-electromechanical systems. Polystyrene microspheres with the diameter of 10 upmum were coated with a 50 nm-thick gold layer using an electroless gold plating approach. Dielectrophoresis (DEP) for bare microspheres and shelled microspheres was theoretically analysed and the real part of the Clausius–Mossotti factor was calculated for the two kinds of microspheres. The experiments on the dielectrophoretic characterisation of the uncoated polystyrene microspheres and gold coated polystyrene microspheres (GCPMs) were carried out. Experimental results showed that the gold coated polystyrene microspheres were only acted by a positive dielectrophoretic force when the frequency was below 40M Hz, while the uncoated polystyrene microspheres were governed by a negative dielectrophoretic force in this frequency range. The gold coated polystyrene microspheres were exploited to form the microwire automatically according to their stable dielectrophoretic and electric characterisations.

Optical and structural investigation of a-plane GaN layers on r-plane sapphire with nucleation layer optimization

Zhang Jin-Feng, Xu Sheng-Rui, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2011, 20 (5): 057801;  doi: 10.1088/1674-1056/20/5/057801
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Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers: (A) a GaN nucleation layer deposited at low temperature (LT); (B) an AlN nucleation layer deposited at high temperature; or (C) an LT thin AlN nucleation layer with an AlN layer and an AlN/AlGaN superlattice both subsequently deposited at high temperature. The samples have been characterized by X-ray diffraction (XRD), atomic force microscopy and photoluminescence. The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A, indicating a reduction in crystal defect density. Furthermore, the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely. The improved optical property, corresponding to the enhanced crystal quality, is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.

Theoretical study on the positron annihilation in Rocksalt structured magnesium oxide

Liu Jian-Dang, Zhang Jie, Zhang Li-Juan, Hao Ying-Ping, Guo Wei-Feng, Cheng Bin, Ye Bang-Jiao
Chin. Phys. B 2011, 20 (5): 057802;  doi: 10.1088/1674-1056/20/5/057802
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Based on the atomic superposition approximation (ATSUP) and first-principles pseudopotential plane-wave methods, the bulk and Mg mono-vacancy positron lifetime of magnesium oxide were calculated using Arponen–Pajamme and Boro'nski–Nieminen positron-annihilation-rate interpolation formula respectively. The calculated values are in good agreement with experimental values and the first-principles method gives more convincing results. The positron annihilation density spectra analysis reveals that positrons mainly annihilate with valence electrons of oxygen atoms when the magnesium-vacancy appears within magnesium oxide.

Synthesis, thermionic emission and magnetic properties of (NdxGd1-x)B6

Bao Li-Hong, Zhang Jiu-Xing, Zhou Shen-Lin, Tegus
Chin. Phys. B 2011, 20 (5): 058101;  doi: 10.1088/1674-1056/20/5/058101
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Polycrystalline rare-earth hexaborides (NdxGd1-x)B6 (x = 0, 0.2, 0.6, 0.8, 1) were prepared by the reactive spark plasma sintering (SPS) method using mixed powder of GdH2, NdH2 and B. The effects of Nd doping on the crystal structure, the grain orientation, the thermionic emission and the magnetic properties of the hexaboride were investigated by X-ray diffraction, electron backscattered diffraction and magnetic measurements. It is found that all the samples sintered by the SPS method exhibit high densities (> 95%) and high values of Vickers hardness (2319 kg/mm2). The values are much higher than those obtained in the traditional method. With the increase of Nd content, the thermionic emission current density increases from 11 to 16.30 A/cm2 and the magnetic phase transition temperature increases from 5.85 to 7.95 K. Thus, the SPS technique is a suitable method to synthesize the dense rare-earth hexaborides with excellent properties.

Investigation of ageing effects on the electrical properties of polyaniline/silver nanocomposites

Asma Binat Afzal, Muhammad Javed Akhtar
Chin. Phys. B 2011, 20 (5): 058102;  doi: 10.1088/1674-1056/20/5/058102
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Polyaniline(PANI)/Ag nanocomposites, synthesized by incorporation of separately prepared silver nanoparticles in 1-methyl-2-pyrrolidinone(NMP) solution of PANI, have been aged at the accelerated temperature of 120 oC to simulate a storage period of 2 years at 25 oC. The accelerated ageing of these materials is done by using the activation energy calculated from data collected using heat flow calorimetry (HFC). The impedance spectroscopic studies of NMP plasticized aged nanocomposite films suggest a microphase separation into reduced and oxidized repeat units. There is crosslinking of the PANI films during ageing thereby obstructing the charge transfer between PANI chains and silver nanoparticles. As a result, the resistivity is increased.

Impact of nitrogen doping on growth and hydrogen impurity incorporation of thick nanocrystalline diamond films

Gu Li-Ping, Tang Chun-Jiu, Jiang Xue-Fan
Chin. Phys. B 2011, 20 (5): 058104;  doi: 10.1088/1674-1056/20/5/058104
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A much larger amount of bonded hydrogen was found in thick nanocrystalline diamond (NCD) films produced by only adding 0.24% N2 into 4% CH4/H2 plasma, as compared to the high quality transparent microcrystalline diamond (MCD) films, grown using the same growth parameters except for nitrogen. These experimental results clearly evidence that defect formation and impurity incorporation (for example, N and H) impeding diamond grain growth is the main formation mechanism of NCD upon nitrogen doping and strongly support the model proposed in the literature that nitrogen competes with CHx (x=1,2,3) growth species for adsorption sites.

Influence of 60Co gamma radiation on fluorine plasma treated enhancement-mode high- electron-mobility transistor

Quan Si, Hao Yue, Ma Xiao-Hua, Yu Hui-You
Chin. Phys. B 2011, 20 (5): 058501;  doi: 10.1088/1674-1056/20/5/058501
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AlGaN/GaN depletion-mode high-electron-mobility transistor (D-HEMT) and fluorine (F) plasma treated enhancement-mode high-electron-mobility transistor (E-HEMT) are exposed to 60Co gamma radiation with a dose of 1.6 Mrad (Si). No degradation is observed in the performance of D-HEMT. However, the maximum transconductance of E-HEMT is increased after radiation. The 2DEG density and the mobility are calculated from the results of capacitance–voltage measurement. The electron mobility decreases after fluorine plasma treatment and recovers after radiation. Conductance measurements in a frequency range from 10 kHz to 1 MHz are used to characterize the trapping effects in the devices. A new type of trap is observed in the F plasma treated E-HEMT compared with the D-HEMT, but the density of the trap decreases by radiation. Fitting of Gp/ω data yields the trap densities DT= (1 - 3) × 1012 cm-2· eV-1 and DT= (0.2-0.8) × 1012 cm-2·eV-1 before and after radiation, respectively. The time constant is 0.5 ms-6 ms. With F plasma treatment, the trap is introduced by etch damage and degrades the electronic mobility. After 60Co gamma radiation, the etch damage decreases and the electron mobility is improved. The gamma radiation can recover the etch damage caused by F plasma treatment.

Early effect modeling of silicon-on-insulator SiGe heterojunction bipolar transistors

Xu Xiao-Bo, Zhang He-Ming, Hu Hui-Yong, Ma Jian-Li
Chin. Phys. B 2011, 20 (5): 058502;  doi: 10.1088/1674-1056/20/5/058502
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Silicon germanium (SiGe) heterojunction bipolar transistor (HBT) on thin silicon-on-insulator (SOI) has recently been demonstrated and integrated into the latest SOI BiCMOS technology. The Early effect of the SOI SiGe HBT is analysed considering vertical and horizontal collector depletion, which is different from that of a bulk counterpart. A new compact formula of the Early voltage is presented and validated by an ISE TCAD simulation. The Early voltage shows a kink with the increase of the reverse base–collector bias. Large differences are observed between SOI devices and their bulk counterparts. The presented Early effect model can be employed for a fast evaluation of the Early voltage and is useful to the design, the simulation and the fabrication of high performance SOI SiGe devices and circuits.

Substrate bias effects on collector resistance in SiGe heterojunction bipolar transistors on thin film silicon-on-insulator

Xu Xiao-Bo, Zhang He-Ming, Hu Hui-Yong, Qu Jiang-Tao
Chin. Phys. B 2011, 20 (5): 058503;  doi: 10.1088/1674-1056/20/5/058503
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An analytical expression for the collector resistance of a novel vertical SiGe heterojunction bipolar transistor (HBT) on thin film silicon-on-insulator (SOI) is obtained with the substrate bias effects being considered. The resistance is found to decrease slowly and then quickly and to have kinks with the increase of the substrate–collector bias, which is quite different from that of a conventional bulk HBT. The model is consistent with the simulation result and the reported data and is useful to the frequency characteristic design of 0.13 μm millimeter-wave SiGe SOI BiCMOS devices.

A biosensor based on graphene nanoribbon with nanopores: a first-principles devices-design

Ouyang Fang-Ping, Peng Sheng-Lin, Zhang Hua, Weng Li-Bo, Xu Hui
Chin. Phys. B 2011, 20 (5): 058504;  doi: 10.1088/1674-1056/20/5/058504
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A biosensor device, built from graphene nanoribbons (GNRs) with nanopores, was designed and studied by first-principles quantum transport simulation. We have demonstrated the intrinsic transport properties of the device and the effect of different nucleobases on device properties when they are located in the nanopores of GNRs. It was found that the device's current changes remarkably with the species of nucleobases, which originates from their different chemical compositions and coupling strengths with GNRs. In addition, our first-principles results clearly reveal that the distinguished ability of a device's current depends on the position of the pore to some extent. These results may present a new way to read off the nucleobases sequence of a single-stranded DNA (ssDNA) molecule by such GNRs-based device with designed nanopores

The balance of flexibility and rigidity in the active site residues of hen egg white lysozyme

Qi Jian-Xun, Jiang Fan
Chin. Phys. B 2011, 20 (5): 058701;  doi: 10.1088/1674-1056/20/5/058701
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The crystallographic temperature factors (B factor) of individual atoms contain important information about the thermal motion of the atoms in a macromolecule. Previously the theory of flexibility of active site has been established based on the observation that the enzyme activity is sensitive to low concentration denaturing agents. It has been found that the loss of enzyme activity occurs well before the disruption of the three-dimensional structural scaffold of the enzyme. To test the theory of conformational flexibility of enzyme active site, crystal structures were perturbed by soaking in low concentration guanidine hydrochloride solutions. It was found that many lysozyme crystals tested could still diffract until the concentration of guanidine hydrochloride reached 3 M. It was also found that the B factors averaged over individually collected data sets were more accurate. Thus it suggested that accurate measurement of crystal temperature factors could be achieved for medium-high or even medium resolution crystals by averaging over multiple data sets. Furthermore, we found that the correctly predicted active sites included not only the more flexible residues, but also some more rigid residues. Both the flexible and the rigid residues in the active site played an important role in forming the active site residue network, covering the majority of the substrate binding residues. Therefore, this experimental prediction method may be useful for characterizing the binding site and the function of a protein, such as drug targeting.
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