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Chin. Phys. B  
  Chin. Phys. B--2011, Vol.20, No.2
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The influence of isotope substitution of neon atom on the integral cross sections of rotational excitation in Ne–Na2 collisions

Zang Hua-Ping, Li Wen-Feng, Linghu Rong-Feng, Cheng Xin-Lu, Yang Xiang-Dong
Chin. Phys. B 2011, 20 (2): 020301;  doi: 10.1088/1674-1056/20/2/020301
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This paper applies the multiple ellipsoid model to the 16Ne (20Ne, 28Ne, 34Ne)–Na2 collision systems, and calculates integral cross sections for rotational excitation at the incident energy of 190 meV. It can be seen that the accuracy of the integral cross sections can be improved by increasing the number of equipotential ellipsoid surfaces. Moreover, by analysing the differences of these integral cross sections, it obtains the change rules of the integral cross sections with the increase of rotational angular quantum number J', and with the change of the mass of isotope substitution neon atom. Finally, the contribution of different regions of the potential to inelastic cross sections for 20Ne–Na2 collision system is investigated at relative incident energy of 190 meV.

Reduced Dirac equation and Lamb shift as off-mass-shell effect in quantum electrodynamics

Ni Guang-Jiong, Xu Jian-Jun, Lou Sen-Yue
Chin. Phys. B 2011, 20 (2): 020302;  doi: 10.1088/1674-1056/20/2/020302
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Based on the accurate experimental data of energy-level differences in hydrogen-like atoms, especially the 1S–2S transitions of hydrogen and deuterium, the necessity of introducing a reduced Dirac equation with reduced mass as the substitution of original electron mass is stressed. Based on new cognition about the essence of special relativity, we provide a reasonable argument for the reduced Dirac equation to have two symmetries, the invariance under the (newly defined) space–time inversion and that under the pure space inversion, in a noninertial frame. By using the reduced Dirac equation and within the framework of quantum electrodynamics in covariant form, the Lamb shift can be evaluated (at one-loop level) as the radiative correction on a bound electron staying in an off-mass-shell state–a new approach eliminating the infrared divergence. Hence the whole calculation, though with limited accuracy, is simplified, getting rid of all divergences and free of ambiguity.

Dark states and Aharonov–Bohm oscillations in multi-quantum-dot systems

Wang Qiong, Liu Jun, Tang Ning, Zeng Hao-Sheng
Chin. Phys. B 2011, 20 (2): 020303;  doi: 10.1088/1674-1056/20/2/020303
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We study the formation of dark states and the Aharonov–Bohm effect in symmetrically/asymmetrically coupled three- and four-quantum-dot systems. It is found that without a transverse magnetic field, destructive interference can trap an electron in a dark state. However, the introduction of a transverse magnetic field can disrupt the dark state, giving rise to oscillation in current. For symmetrically structured quantum-dot systems, the oscillation has a period of one flux quanta. But for asymmetrically structured dot systems, the period of oscillation is halved. In addition, the dephasing due to charge noise also blocks the formation of dark states, while it does not change the period of oscillation.

Entanglement dynamics of two-qubit systems in different quantum noises

Pan Chang-Ning, Li-Fei, Fang Jian-Shu, Fang Mao-Fa
Chin. Phys. B 2011, 20 (2): 020304;  doi: 10.1088/1674-1056/20/2/020304
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The entanglement dynamics of two-qubit systems in different quantum noises are investigated by means of the operator-sum representation method. We find that, except for the amplitude damping and phase damping quantum noise, the sudden death of entanglement is always observed in different two-qubit systems with generalized amplitude damping and depolarizing quantum noise.

Distributed quantum computation with superconducting qubit via LC circuit using dressed states

Wu Chao, Fang Mao-Fa, Xiao Xing, Li Yan-Ling, Cao Shuai
Chin. Phys. B 2011, 20 (2): 020305;  doi: 10.1088/1674-1056/20/2/020305
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A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LC circuit through mutual inductance, are used for implementing quantum gates. By using dressed states, quantum state transfer and quantum entangling gate can be implemented. With the help of the time-dependent electromagnetic field, any two dressed qubits can be selectively coupled to the data bus (the last LC circuit), then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed. As a result, the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme.

Scaling of entanglement entropy for spin chain with Dzyaloshinskii–Moriya interaction

Du Long, Hou Jing-Min, Ding Jia-Yan, Zhang Wen-Xin, Tian Zhi, Chen Ting-Ting
Chin. Phys. B 2011, 20 (2): 020306;  doi: 10.1088/1674-1056/20/2/020306
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This paper investigates the entanglement in an XX-type spin chain with Dzyaloshinskii——Moriya interaction under an external magnetic field. The von Neumann entropy of entanglement between two blocks for the ground state of the system is evaluated. It analyses and discusses the scaling behaviour of the entanglement entropy.

Stability properties of vector solitons in two-component Bose–Einstein condensates with tunable interactions

Zhang Xiao-Fei, Zhang Pei, He Wan-Quan, Liu Xun-Xu
Chin. Phys. B 2011, 20 (2): 020307;  doi: 10.1088/1674-1056/20/2/020307
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By using a unified theory of the formation of various types of vector-solitons in two-component Bose–Einstein condensates with tunable interactions, we obtain a family of exact vector-soliton solutions for the coupled nonlinear Schrödinger equations. Moreover, the Bogoliubov equation shows that there exists stable dark soliton in specific situations. Our results open up new ways in considerable experimental interest for the quantum control of multi-component Bose–Einstein condensates.

The dynamics of nonstationary solutions in one-dimensional two-component Bose–Einstein condensates

Lü Bin-Bin, Hao Xue, Tian Qiang
Chin. Phys. B 2011, 20 (2): 020308;  doi: 10.1088/1674-1056/20/2/020308
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This paper investigates the dynamical properties of nonstationary solutions in one-dimensional two-component Bose–Einstein condensates. It gives three kinds of stationary solutions to this model and develops a general method of constructing nonstationary solutions. It obtains the unique features about general evolution and soliton evolution of nonstationary solutions in this model.

Comments on "Inverse scattering method and soliton solution family for the Einstein–Maxwell theory with multiple Abelian gauge fields"

Wei Yi-Huan
Chin. Phys. B 2011, 20 (2): 020401;  doi: 10.1088/1674-1056/20/2/020401
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This paper points out that equations (18a) and (18b) in Ref. [7] [Gao Y J 2008 Chin. Phys. B 17 3574] only possess the solutions Mργε. So, there does not exist the so-called soliton solution family for the Einstein–Maxwell theory with multiple Abelian gauge fields shown in Ref. [7].

Nonlinear electrodynamics coupled to teleparallel theory of gravity

Gamal G. L. Nashed
Chin. Phys. B 2011, 20 (2): 020402;  doi: 10.1088/1674-1056/20/2/020402
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Using nonlinear electrodynamics coupled to teleparallel theory of gravity, regular charged spherically symmetric solutions are obtained. The nonlinear theory is reduced to the Maxwell one in the weak limit and the solutions correspond to charged spacetimes. One of the obtained solutions contains an arbitrary function which we call general solution since we can generate from it the other solutions. The metric associated with these spacetimes is the same, i.e., regular charged static spherically symmetric black hole. In calculating the energy content of the general solution using the gravitational energy–momentum within the framework of the teleparallel geometry, we find that the resulting form depends on the arbitrary function. Using the regularized expression of the gravitational energy–momentum we obtain the value of energy.

Post-post-Newtonian deflection of light ray in multiple systems with PPN parameters

Gong Yan-Xiang, Wu Xiao-Mei
Chin. Phys. B 2011, 20 (2): 020403;  doi: 10.1088/1674-1056/20/2/020403
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The post-Newtonian scheme in multiple systems with post-Newtonian parameters presented by Klioner and Soffel is extended to the post-post-Newtonian (PPN) order for light propagation problem in the solar system. Under considering the solar system experiment requirement, a new parameter ε is introduced. This extension does not change the virtue of the scheme on the linear partial differential equations of the potential and vector potential mentioned in previous work. Furthermore, this extension is based on the former work done by Richter and Matzner in one global system theory. As an application, we also consider the deflection of light ray in the global coordinates. And the deflection angle of light ray is obtained with post-Newtonian parameters.

Temperature and thermodynamic geometry of the Kerr–Sen black hole

Lan Ming-Jian
Chin. Phys. B 2011, 20 (2): 020404;  doi: 10.1088/1674-1056/20/2/020404
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This paper studies the thermodynamic properties of the Kerr–Sen black hole from the viewpoint of geometry. It calculates the temperature and heat capacity of the black hole, Weinhold metric and Ruppeiner metric are also obtained respectively. It finds that they are both curved and the curvature scalar of Weinhold curvature implies no information about the phase transition while the Ruppeiner one does. But they both carry no information about the second-order phase transition point reproduced from the capacity. Besides, the Legendre invariant metric of the Kerr–Sen black hole has been discussed and its scalar curvature gives the information about the second-order phase transition point.

The universal sound velocity formula for the strongly interacting unitary Fermi gas

Liu Ke, Chen Ji-Sheng
Chin. Phys. B 2011, 20 (2): 020501;  doi: 10.1088/1674-1056/20/2/020501
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Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P=2E/3V is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.

Effect of a localized impurity on soliton dynamics in the Bose–Einstein condensates

Yang Ru-Shu, Yao Chun-Mei, Wu Zong-Fu
Chin. Phys. B 2011, 20 (2): 020502;  doi: 10.1088/1674-1056/20/2/020502
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By using a multiple-scale method, we analytically study the effect of a localized impurity on the soliton dynamics in the Bose–Einstein condensates. It is shown that a dark soliton can be transmitted through a repulsive (or attractive) impurity, while at the position of the localized impurity the soliton can be quasitrapped by the impurity. Additionally, we find that the strength of the localized impurity has an important effect on the dark soliton dynamics. With increasing strength of the localized impurity, the amplitude of the dark soliton becomes bigger, while its width is narrower, and the soliton propagates slower.

Performance characteristics and optimal analysis of a nonlinear diode refrigerator

Wang Xiu-Mei, He Ji-Zhou, Liang Hong-Ni
Chin. Phys. B 2011, 20 (2): 020503;  doi: 10.1088/1674-1056/20/2/020503
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This paper establishes a model of a nonlinear diode refrigerator consisting of two diodes switched in the opposite directions and located in two heat reservoirs with different temperatures. Based on the theory of thermal fluctuations, the expressions of the heat flux absorbed from the heat reservoirs are derived. After the heat leak between the two reservoirs is considered, the cooling rate and the coefficient of performance are obtained analytically. The influence of the heat leak and the temperature ratio on the performance characteristics of the refrigerator is analysed in detail.

Solution and transcritical bifurcation of Burgers equation

Tang Jia-Shi, Zhao Ming-Hua, Han Feng, Zhang Liang
Chin. Phys. B 2011, 20 (2): 020504;  doi: 10.1088/1674-1056/20/2/020504
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Burgers equation is reduced into a first-order ordinary differential equation by using travelling wave transformation and it has typical bifurcation characteristics. We can obtain many exact solutions of the Burgers equation, discuss its transcritical bifurcation and control dynamical behaviours by extending the stable region. The transcritical bifurcation exists in the (2+1)-dimensional Burgers equation.

Phase space reconstruction of chaotic dynamical system based on wavelet decomposition

You Rong-Yi, Huang Xiao-Jing
Chin. Phys. B 2011, 20 (2): 020505;  doi: 10.1088/1674-1056/20/2/020505
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In view of the disadvantages of the traditional phase space reconstruction method, this paper presents the method of phase space reconstruction based on the wavelet decomposition and indicates that the wavelet decomposition of chaotic dynamical system is essentially a projection of chaotic attractor on the axes of space opened by the wavelet filter vectors, which corresponds to the time-delayed embedding method of phase space reconstruction proposed by Packard and Takens. The experimental results show that, the structure of dynamical trajectory of chaotic system on the wavelet space is much similar to the original system, and the nonlinear invariants such as correlation dimension, Lyapunov exponent and Kolmogorov entropy are still reserved. It demonstrates that wavelet decomposition is effective for characterizing chaotic dynamical system.

Stochastic impulsive control for the stabilization of Lorenz system

Wang Liang, Zhao Rui, Xu Wei, Zhang Ying
Chin. Phys. B 2011, 20 (2): 020506;  doi: 10.1088/1674-1056/20/2/020506
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This paper derives some sufficient conditions for the stabilization of Lorenz system with stochastic impulsive control. The estimate of the upper bound of impulse interval for asymptotically stable control is obtained. Some differences between the system with stochastic impulsive control and with deterministic impulsive control are presented. Computer simulation is given to show the effectiveness of the proposed method.

Synchronization of spatiotemporal chaotic systems and application to secure communication of digital image

Wang Xing-Yuan, Zhang Na, Ren Xiao-Li, Zhang Yong-Lei
Chin. Phys. B 2011, 20 (2): 020507;  doi: 10.1088/1674-1056/20/2/020507
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Coupled map lattices (CMLs) are taken as examples to study the synchronization of spatiotemporal chaotic systems. In this paper, we use the nonlinear coupled method to implement the synchronization of two coupled map lattices. Through the appropriate separation of the linear term from the nonlinear term of the spatiotemporal chaotic system, we set the nonlinear term as the coupling function and then we can achieve the synchronization of two coupled map lattices. After that, we implement the secure communication of digital image using this synchronization method. Then, the discrete characteristics of the nonlinear coupling spatiotemporal chaos are applied to the discrete pixel of the digital image. After the synchronization of both the communication parties, the receiver can decrypt the original image. Numerical simulations show the effectiveness and the feasibility of the proposed program.

Noise-induced synchronous stochastic oscillations in small scale cultured heart-cell networks

Yuan Lan, Liu Zhi-Qiang, Zhang Hui-Min, Ding Xue-Li, Yang Ming-Hao, Gu Hua-Guang, Ren Wei
Chin. Phys. B 2011, 20 (2): 020508;  doi: 10.1088/1674-1056/20/2/020508
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This paper reports that the synchronous integer multiple oscillations of heart-cell networks or clusters are observed in the biology experiment. The behaviour of the integer multiple rhythm is a transition between super- and sub-threshold oscillations, the stochastic mechanism of the transition is identified. The similar synchronized oscillations are theoretically reproduced in the stochastic network composed of heterogeneous cells whose behaviours are chosen as excitable or oscillatory states near a Hopf bifurcation point. The parameter regions of coupling strength and noise density that the complex oscillatory rhythms can be simulated are identified. The results show that the rhythm results from a simple stochastic alternating process between super- and sub-threshold oscillations. Studies on single heart cells forming these clusters reveal excitable or oscillatory state nearby a Hopf bifurcation point underpinning the stochastic alternation. In discussion, the results are related to some abnormal heartbeat rhythms such as the sinus arrest.

Robust fault-sensitive synchronization of a class of nonlinear systems

Xu Shi-Yun, Yang Ying, Liu Xian, Tang Yong, Sun Hua-Dong
Chin. Phys. B 2011, 20 (2): 020509;  doi: 10.1088/1674-1056/20/2/020509
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Aiming at enhancing the quality as well as the reliability of synchronization, this paper is concerned with the fault detection issue within the synchronization process for a class of nonlinear systems in the existence of external disturbances. To handle such problems, the concept of robust fault-sensitive (RFS) synchronization is proposed, and a method of determining such a kind of synchronization is developed. Under the framework of RFS synchronization, the master and the slave systems are robustly synchronized, and at the same time, sensitive to possible faults based on a mixed H-/H performance. The design of desired output feedback controller is realized by solving a linear matrix inequality, and the fault sensitivity H- index can be optimized via a convex optimization algorithm. A master-slave configuration composed of identical Chua's circuits is adopted as a numerical example to demonstrate the effectiveness and applicability of the analytical results.

Lattice Boltzmann simulation for the energy and entropy of excitable systems

Deng Min-Yi, Tang Guo-Ning, Kong Ling-Jiang, Liu Mu-Ren
Chin. Phys. B 2011, 20 (2): 020510;  doi: 10.1088/1674-1056/20/2/020510
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The internal energy and the spatiotemporal entropy of excitable systems are investigated with the lattice Boltzmann method. The numerical results show that the breakup of spiral wave is attributed to the inadequate supply of energy, i.e., the internal energy of system is smaller than the energy of self-sustained spiral wave. It is observed that the average internal energy of a regular wave state reduces with its spatiotemporal entropy decreasing. Interestingly, although the energy difference between two regular wave states is very small, the different states can be distinguished obviously due to the large difference between their spatiotemporal entropies. In addition, when the unstable spiral wave converts into the spatiotemporal chaos, the internal energy of system decreases, while the spatiotemporal entropy increases, which behaves as the thermodynamic entropy in an isolated system.

Consensus of high-order continuous-time multi-agent systems with time-delays and switching topologies

Yang Tan, Jin Yue-Hui, Wang Wei, Shi Ying-Jing
Chin. Phys. B 2011, 20 (2): 020511;  doi: 10.1088/1674-1056/20/2/020511
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Consensus problems of high-order continuous-time multi-agent systems with time-delays and switching topologies are studied. The motivation of this work is to extend second-order continuous-time multi-agent systems from the literature. It is shown that consensus can be reached with arbitrarily bounded time-delays even though the communication topology might not have spanning trees. A numerical example is included to show the theoretical results.

Reference model based consensus control of second-order multi-agent systems

Li Jian-Zhen
Chin. Phys. B 2011, 20 (2): 020512;  doi: 10.1088/1674-1056/20/2/020512
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This paper deals with the consensus problem of multi-agent systems with second-order dynamics. The objective is to design algorithms such that all agents will have same positions and velocities. First, a reference model based consensus algorithm is proposed. It is proved that the consensus can be achieved if the communication graph has a spanning tree. Different from most of the consensus algorithms proposed in the literature, the parameters of the control laws are different among agents. Therefore, each agent can design its control law independently. Secondly, it gives a consensus algorithm for the case that the velocities of the agents are not available. Thirdly, the effectiveness of the input delay and the communication delay is considered. It shows that consensus can be achieved if the input delay of every agent is smaller than a bound related to parameters in its control law. Finally, some numerical examples are given to illustrate the proposed results.

Tuning of the periodicity of stable self-organized metallic templates

Wang Xiao-Chun, Zhao Han-Yue, Chen Nan-Xian, Zhang Yong
Chin. Phys. B 2011, 20 (2): 020513;  doi: 10.1088/1674-1056/20/2/020513
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The atomic and electronic structures of Pb bilayer/Pt(111) are investigated with two theoretical calculations. We find that the stable (2×2)/(3×3) Pb/Pt(111) structure is a promising candidate for being used as a template with self-organized ordered Pb semi-cluster array on the first Pb monolayer. This stable structure can realize the ordered Au single-atom array around the Pb semi-clusters that can cause selective adsorption of noble atoms. The size of Pb magic number semi-cluster plays a more important role in determining the periodicity of the template than the lattice constant misfit between the substrate and the overlayer. This leads to quite a different periodicity between the two stable templates, which are (2×2)/(3×3) Pb/Pt(111) and Pb/Cu(111). Therefore, by considering the size of the stable semi-clusters and carefully selecting different substrate materials, we can tune the density of Pb semi-clusters as the nucleation points and then tune the periodicity of the stable template.

Exact calculation of the minimal thickness of the large optical path difference wind imaging interferometer

Zhang Chun-Min, Ai Jing-Jing, Ren Wen-Yi
Chin. Phys. B 2011, 20 (2): 020701;  doi: 10.1088/1674-1056/20/2/020701
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This paper gives the relation between spatial ray and its projection on paper plane based on the vector form of reflective law. Using the method of prism expansion, it obtains the exact expression of the exit height. The exit height can ensure that the incident rays, at arbitrary direction and arbitrary angle, after several transmission and reflection in the two right-angle reflectors, finally pass through the exit surface. Furthermore, it analyses the effects of different parameters on the exit height through computer simulation, and some important conclusions are obtained. The physical meaning of the sign of exit height is described, and the exact expression of the minimal thickness of the large optical path difference wind imaging interferometer is gained. This work is of great scientific significance to the static, real-time simultaneous detection of atmospheric wind field, and it will provide a theoretical and practical guidance for the miniaturization design and engineering realization of wind imaging interferometer.

Lie symmetry and Mei conservation law of continuum system

Shi Shen-Yang, Fu Jing-Li
Chin. Phys. B 2011, 20 (2): 021101;  doi: 10.1088/1674-1056/20/2/021101
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Lie symmetry and Mei conservation law of continuum Lagrange system are studied in this paper. The equation of motion of continuum system is established by using variational principle of continuous coordinates. The invariance of the equation of motion under an infinitesimal transformation group is determined to be Lie-symmetric. The condition of obtaining Mei conservation theorem from Lie symmetry is also presented. An example is discussed for applications of the results.

Conformal invariance and conserved quantities of Birkhoff systems under second-class Mei symmetry

Luo Yi-Ping, Fu Jing-Li
Chin. Phys. B 2011, 20 (2): 021102;  doi: 10.1088/1674-1056/20/2/021102
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This paper proposes a new concept of the conformal invariance and the conserved quantities for Birkhoff systems under second-class Mei symmetry. The definition about conformal invariance of Birkhoff systems under second-class Mei symmetry is given. The conformal factor in the determining equations is found. The relationship between Birkhoff system's conformal invariance and second-class Mei symmetry are discussed. The necessary and sufficient conditions of conformal invariance, which are simultaneously of second-class symmetry, are given. And Birkhoff system's conformal invariance may lead to corresponding Mei conserved quantities, which is deduced directly from the second-class Mei symmetry when the conformal invariance satisfies some conditions. Lastly, an example is provided to illustrate the application of the result.

A density-functional theory for (BAs)n clusters (n=1–14): structures, stabilities and electronic properties

Liu Zhi-Feng, Lei Xue-Ling, Liu Li-Ren, Liu Huo-Yan, Zhu Heng-Jiang
Chin. Phys. B 2011, 20 (2): 023101;  doi: 10.1088/1674-1056/20/2/023101
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This paper investigates the lowest-energy structures, stabilities and electronic properties of (BAs)n clusters (n=1–14) by means of the density-functional theory. The results show that the lowest-energy structures undergo a structural change from two-dimensional to three-dimensional when n=4. With the increase of the cluster size (n≥6), the (BAs)n clusters tend to adopt cage-like structures, which can be considered as being built from B2As2 and six-membered rings with B–As bond alternative arrangement. The binding energy per atom, second-order energy differences, vertical electron affinity and vertical ionization potential are calculated and discussed. The caculated HOMO–LUMO gaps reveal that the clusters have typical semiconductor characteristics. The analysis of partial density of states suggests that there are strong covalence and molecular characteristics in the clusters.

Accurate studies on the full vibrational energy spectra and molecular dissociation energies for some electronic states of halogen molecule

Lü Jian-Liang, Ren Wei-Yi, Xu Ping-Chuan, Chen Tai-Hong
Chin. Phys. B 2011, 20 (2): 023102;  doi: 10.1088/1674-1056/20/2/023102
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This paper obtains accurate vibrational spectroscopic constants and full vibrational energy spectrum by the algebraic method (AM) for some electronic states of halogen diatomic molecules. Motivated by the recent success of obtaining the dissociation energies of Li2 molecule by using a new analytical formula, it further extends the formula to study the dissociation energies of halogen diatomic molecules. The results show that the AM spectrum and the theoretical dissociation energies agree well with RKR data and experimental data respectively.

Calculation of scattering parameters for ultracold 6Li–7Li elastic collisions

Zhang Ji-Cai, Sun Jin-Feng, Liu Yu-Fang
Chin. Phys. B 2011, 20 (2): 023401;  doi: 10.1088/1674-1056/20/2/023401
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This paper theoretically studies the elastic scattering properties in a mixture of 6Li and 7Li atoms at cold and ultracold temperatures. Based on the constructed accurate interatomic potential of the triplet state for 6Li7Li mixture by the mass scaling method, it calculates the interspecies s-wave scattering lengths and the p-wave scattering lengths by the variable phase method and the semiclassical method, respectively. The scattering length is in good agreement with the experiment. The partial-wave and total cross sections are also calculated and a rich resonance structure is found.

Cooling of rubidium atoms in pulsed diffuse laser light

Cheng Hua-Dong, Wang Xu-Cheng, Xiao Ling, Zhang Wen-Zhuo, Liu Liang, Wang Yu-Zhu
Chin. Phys. B 2011, 20 (2): 023701;  doi: 10.1088/1674-1056/20/2/023701
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This paper reports an experiment on laser cooling of 87Rb atoms in pulsed diffuse light, which is the key step towards a compact cold atom clock. It deduces an empirical formula to simulate the pulse cooling process based on the loading of cold atoms in cooling time and the loss in the dead time, which is in agreement with the experimental data. The formula gives a reference to select the parameters for the cold atom clock.

Invisible anti-cloak with elliptic cross section using phase complement

Yang Yu-Qi, Zhang Min, Yue Jian-Xiang
Chin. Phys. B 2011, 20 (2): 024101;  doi: 10.1088/1674-1056/20/2/024101
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Based on the theory of phase complement, an anti-cloak with circular cross section can be made invisible to an object outside its domain. As the cloak with elliptic cross section is more effective to make objects invisible than that with circular cross section, a scaled coordinate system is proposed to design equivalent materials of invisible anti-cloak with elliptic cross section using phase complement. The cloaks with conventional dielectric and double negative parameters are both simulated with the geometrical transformations. The results show that the cloak with elliptic cross section through phase complement can effectively hide the outside objects.

Signal-to-noise ratio of lensless ghost interference with thermal incoherent light

Zhang Er-Feng, Dai Hong-Yi, Chen Ping-Xing
Chin. Phys. B 2011, 20 (2): 024201;  doi: 10.1088/1674-1056/20/2/024201
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Factors influencing the signal-to-noise ratio (SNR) of lensless ghost interference with thermal incoherent light are investigated. Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object, the position of the object in the imaging system and the transverse size of the light source. Furthermore, the effects of these factors on the SNR are discussed in detail by numerical simulations.

Realization of double resonance for a bright frequency-tunable source of narrowband entangled photons Hot!

Yang Jian, Zhao Tian-Ming, Zhang Han, Yang Tao, Bao Xiao-Hui, Pan Jian-Wei
Chin. Phys. B 2011, 20 (2): 024202;  doi: 10.1088/1674-1056/20/2/024202
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In this paper, we report an interesting phenomenon when precisely adjust the tuning crystal for double-resonance of a type-II configured parametric amplifier cavity, which is later verified as a cavity-enhanced effect in optics alignment. The theoretical result indicates that an angle accuracy error within 0.09o is necessary to achieve a high contrast ratio of 100:1 for a cavity with a finesse of about 205, which is crucial but high-demanding to get a high-quality narrowband entanglement source. Meanwhile, we figure out a method to release such a high requirement and get high visibility in a moderate-accuracy alignment.

Decoherence of photon-subtracted squeezed vacuum state in dissipative channel

Xu Xue-Xiang, Yuan Hong-Chun, Fan Hong-Yi
Chin. Phys. B 2011, 20 (2): 024203;  doi: 10.1088/1674-1056/20/2/024203
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This paper investigates the decoherence of photo-subtracted squeezed vacuum state (PSSVS) in dissipative channel by describing its statistical properties with time evolution such as Wigner function, Husimi function, and tomogram. It first calculates the normalization factor of PSSVS related to Legendre polynomial. After deriving the normally ordered density operator of PSSVS in dissipative channel, one obtains the explicit analytical expressions of time evolution of PSSVS's statistical distribution function. It finds that these statistical distributions loss their non-Gaussian nature and become Gaussian at last in the dissipative environment as expected.

Graded index profiles and loss-induced single-mode characteristics in vertical-cavity surface-emitting lasers with petal-shape holey structure

Liu An-Jin, Qu Hong-Wei, Chen Wei, Jiang Bin, Zhou Wen-Jun, Xing Ming-Xin, Zheng Wan-Hua
Chin. Phys. B 2011, 20 (2): 024204;  doi: 10.1088/1674-1056/20/2/024204
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The 850-nm oxide-confined vertical-cavity surface-emitting lasers with petal-shape holey structures are presented. An area-weighted average refractive index model is given to analyse their effective index profiles, and the graded index distribution in the holey region is demonstrated. The index step between the optical aperture and the holey region is obtained which is related merely to the etching depth. Four types of holey vertical-cavity surface-emitting lasers with different parameters are fabricated as well as the conventional oxide-confined vertical-cavity surface-emitting laser. Compared with the conventional oxide-confined vertical-cavity surface-emitting laser without etched holes, the holey vertical-cavity surface-emitting laser possesses an improved beam quality due to its graded index distribution, but has a lower output power, higher threshold current and lower slope efficiency. With the hole number increased, the holey vertical-cavity surface-emitting laser can realize the single-mode operation throughout the entire current range, and reduces the beam divergence further. The loss mechanism is used to explain the single-mode characteristic, and the reduced beam divergence is attributed to the shallow etching. High coupling efficiency of 86% to a multi-mode fibre is achieved for the single-mode device in the experiment.

Mode decoupling in solid state ring laser based on stimulated Raman effect in polar crystals

Luo Zhang, Yuan Xiao-Dong, Ye Wei-Min, Zeng Chun, Ji Jia-Rong
Chin. Phys. B 2011, 20 (2): 024205;  doi: 10.1088/1674-1056/20/2/024205
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In this paper we study the gain saturation induced mode-coupling control in solid state ring laser devices based on the stimulated Raman effect of the polar crystals in order to realize solid state ring laser gyroscopes. We theoretically investigate the mode coupling induced by gain saturation between clockwise (CW) and counterclockwise (CCW) propagating laser modes. Because the CW and CCW running waves are pumped with counter-propagating lasers respectively, the independent coexistence can be ensured.

Investigation on the hydrodynamics of slab x-ray laser plasma by nonuiform line focused laser irradiation

Cheng Tao, Li Ying-Jun, Meng Li-Min, Li Xi-Bo
Chin. Phys. B 2011, 20 (2): 024206;  doi: 10.1088/1674-1056/20/2/024206
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Based on the two-dimensional model, this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations. It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma. Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity. Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm2 to 1.0 TW/cm2 are proved acceptable in slab x-ray lasers.

Passive harmonic mode locked all-normal-dispersion Yb-doped fibre lasers

Kong Ling-Jie, Xiao Xiao-Sheng, Yang Chang-Xi
Chin. Phys. B 2011, 20 (2): 024207;  doi: 10.1088/1674-1056/20/2/024207
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Passive harmonic mode-locking of dissipative solitons is demonstrated in all-normal dispersion Yb-doped fibre lasers. A difference equation model of the mode-locked fibre lasers is adopted to simulate the intra-cavity nonlinear dynamics. Hysteresis phenomena around the mode-locking threshold, and the effect of introducing linear phase bias are discussed. The passive harmonic mode-locking as one kind of multipulsing operations is revealed. Moreover, the simulation shows the bistability between multipulsing and single-pulse or period multiplication.

Spontaneous-emission control by local density of states of photonic crystal cavity

Jiang Bin, Zhang Ye-Jin, Zhou Wen-Jun, Chen Wei, Liu An-Jin, Zheng Wan-Hua
Chin. Phys. B 2011, 20 (2): 024208;  doi: 10.1088/1674-1056/20/2/024208
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The local density of states (LDOS) of two-dimensional square lattice photonic crystal (PhC) defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre (for example, at the point (0.3a, 0.4a), where a is the lattice constant) is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point (0.3a, 0.4a) is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials (quantum dots) in the lasers.

Improved high birefringence photonic crystal fibres with dispersion flattened and single mode operation

Fu Bo, Li Shu-Guang, Yao Yan-Yan, Zhang Lei, Zhang Mei-Yan
Chin. Phys. B 2011, 20 (2): 024209;  doi: 10.1088/1674-1056/20/2/024209
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A kind of improved high birefringence photonic crystal fibre (PCF) is proposed in this paper. The characteristics of birefringence, dispersion and leakage loss are studied by the multipole method. Numerical results show that the improved PCF possesses the properties of a flat dispersion and single mode operation. Moreover, with the operating wavelength λ = 1.55μm, the modal birefringence increases greatly in comparison with that of the original PCF, and the leakage loss is about 104 times smaller than that of the original PCF because the modification gives rise to the strong confinement of guided modes. It is expected that the improved PCF can be used as high birefringence and dispersion flattened fibres.

Thermal characteristics of double-layer thin film target ablated by femtosecond laser pulses

Gao Xun, Song Xiao-Wei, Lin Jing-Quan
Chin. Phys. B 2011, 20 (2): 024210;  doi: 10.1088/1674-1056/20/2/024210
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Thermal characteristics of tightly-contacted copper–gold double-layer thin film target under ablation of femtosecond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper–gold film with different maximal electron temperature of 1.15×103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold–copper interface is only about 0.04×103 K at the same time scale. It is also found that electron–lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.

Fast generation of controllable equal-intensity four beams based on isosceles triangle multilevel phase grating realized by liquid crystal spatial light modulator

Liu Xiang, Zhang Jian, Wu Li-Ying, Gan Yu
Chin. Phys. B 2011, 20 (2): 024211;  doi: 10.1088/1674-1056/20/2/024211
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Liquid crystal spatial light modulator (LCSLM) realizing equal-intensity multiple beams often has some features, i.e., phase valley between two adjacent pixels, flyback region when phase decreases immediately from 2π to 0, and inevitable backplane curvature, which are different from those of most conventional diffractive optical elements (DOEs), such as static DOEs. For optimal intensity uniformity, equal-intensity multi-beam generation must be considered for these artifacts. We present a tunable-grating method in which the intensity uniformity can be improved by considering the LCSLM artifacts. For instance, tuning phase modulation depth of the grating, called isosceles triangle multilevel phase grating (ITMPG), can be used not only to improve the intensity uniformity, but also to fast steer four beams with narrow beamwidths, determined by the same effective aperture of ITMPG. Improved intensity uniformity and high relative diffraction efficiency are demonstrated through experiments with phase-only LCSLM.

Electro-optical properties of polymer stabilized cholesteric liquid crystal film

Ma Ji, Zheng Zhi-Gang, Liu Yong-Gang, Xuan Li
Chin. Phys. B 2011, 20 (2): 024212;  doi: 10.1088/1674-1056/20/2/024212
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Liquid crystals (LCs) and polymers are extensively used in various electro-optical applications. In this paper, normal mode polymer stabilized cholesteric LC film is prepared and studied. The effects of chiral dopant and monomer concentrations on the electro-optical properties, such as contrast ratio, driving voltage, hysteresis width and response time, are investigated. The reasons of electro-optical properties influenced by the concentrations of the materials are discussed. Through the proper material recipe, the electro-optical properties of polymer stabilized cholesteric LC film can be optimized.

Theoretical investigation of band-gap and mode characteristics of anti-resonance guiding photonic crystal fibres

Yuan Jin-Hui, Sang Xin-Zhu, Yu Chong-Xiu, Xin Xiang-Jun, Zhang Jin-Long, Zhou Gui-Yao, Li Shu-Guang, Hou Lan-Tian
Chin. Phys. B 2011, 20 (2): 024213;  doi: 10.1088/1674-1056/20/2/024213
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With the full-vector plane-wave method (FVPWM) and the full-vector beam propagation method (FVBPM), the dependences of the band-gap and mode characteristics on material index and cladding structure parameter in anti-resonance guiding photonic crystal fibres (ARGPCFs) are sufficiently analysed. An ARGPCF operating in the near-infrared wavelength is shown. The influences of the high index cylinders, glass interstitial apexes and silica structure on the characteristics of band-gaps and modes are deeply investigated. The equivalent planar waveguide theory is used for analysing such an ARGPCF filled by the isotropic materials, and the resonance and the anti-resonance characteristics can be well predicted.

Semiconductor optical amplifier used as regenerator for degraded differential phase-shift keying signals

Xi Li-Xia, Li Jian-Ping, Du Shu-Cheng, Xu Xia, Zhang Xiao-Guang
Chin. Phys. B 2011, 20 (2): 024214;  doi: 10.1088/1674-1056/20/2/024214
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Phase and amplitude regeneration are necessary for degraded differential phase-shift keying communication systems. This paper proposes a regenerator based on semiconductor optical amplifier for differential phase-shift keying signals. The key regeneration mechanism is theoretically analysed. The effectiveness of semiconductor optical amplifier based regenerator is demonstrated by comparing the bit error rate and eye diagrams before and after regeneration for 40-Gbit/s differential phase-shift keying 1080-km transmission systems. The results show that regeneration effects are very well. Bit error rate is less than 10-12 with the regenerator.

Correlation between microbubble-induced acoustic cavitation and hemolysis in vitro

Zhang Chun-Bing, Liu Zheng, Guo Xia-Sheng, Zhang Dong
Chin. Phys. B 2011, 20 (2): 024301;  doi: 10.1088/1674-1056/20/2/024301
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Microbubbles promise to enhance the efficiency of ultrasound-mediated drug delivery and gene therapy by taking advantage of artificial cavitation nuclei. The purpose of this study is to examine the ultrasound-induced hemolysis in the application of drug delivery in the presence of microbubbles. To achieve this goal, human red blood cells mixed with microbubbles were exposed to 1-MHz pulsed ultrasound. The hemolysis level was measured by a flow cytometry, and the cavitation dose was detected by a passive cavitation detecting system. The results demonstrate that larger cavitation dose would be generated with the increase of acoustic pressure, which might give rise to the enhancement of hemolysis. Besides the experimental observations, the acoustic pressure dependence of the radial oscillation of microbubble was theoretically estimated. The comparison between the experimental and calculation results indicates that the hemolysis should be highly correlated to the acoustic cavitation.

Poisson theory and integration method for a dynamical system of relative motion

Zhang Yi, Shang Mei
Chin. Phys. B 2011, 20 (2): 024501;  doi: 10.1088/1674-1056/20/2/024501
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This paper focuses on studying the Poisson theory and the integration method of dynamics of relative motion. Equations of a dynamical system of relative motion in phase space are given. Poisson theory of the system is established. The Jacobi last multiplier of the system is defined, and the relation between the Jacobi last multiplier and the first integrals of the system is studied. Our research shows that for a dynamical system of relative motion, whose configuration is determined by n generalized coordinates, the solution of the system can be found by using the Jacobi last multiplier if (2n-1) first integrals of the system are known. At the end of the paper, an example is given to illustrate the application of the results.

Numerical simulation of two-dimensional granular shearing flows and the friction force of a moving slab on the granular media

Cai Qing-Dong, Chen Shi-Yi, Sheng Xiao-Wei
Chin. Phys. B 2011, 20 (2): 024502;  doi: 10.1088/1674-1056/20/2/024502
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This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system. The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part, but diverts from Gaussian distribution nearby the wall. The macroscopic stress along the vertical direction has large fluctuation around a constant value, the non-zero average velocity occurs mainly near the moving wall, which forms a shearing zone. In the shearing movement, the volume of the granular material behaves in a random manner. The equivalent friction coefficient between moving slab and granular material correlates with the moving speed at low velocity, and approaches constant as the velocity is large enough.

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

Yang Yan, Li Sheng-Tao, Ding Can, Cheng Peng-Fei
Chin. Phys. B 2011, 20 (2): 025201;  doi: 10.1088/1674-1056/20/2/025201
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This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady IV (current–voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.

Propagation and interaction of ion–acoustic solitary waves in a quantum electron–positron–ion plasma

Han Jiu-Ning, Luo Jun-Hua, Sun Gui-Hua, Liu Zhen-Lai, Li Shou-Yi
Chin. Phys. B 2011, 20 (2): 025202;  doi: 10.1088/1674-1056/20/2/025202
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This paper discusses the existence of ion–acoustic solitary waves and their interaction in a dense quantum electron–positron–ion plasma by using the quantum hydrodynamic equations. The extended Poincaré–Lighthill–Kuo perturbation method is used to derive the Korteweg-de Vries equations for quantum ion–acoustic solitary waves in this plasma. The effects of the ratio of positrons to ions unperturbation number density p and the quantum diffraction parameter He (Hp) on the newly formed wave during interaction, and the phase shift of the colliding solitary waves are studied. It is found that the interaction between two solitary waves fits linear superposition principle and these plasma parameters have significantly influence on the newly formed wave and phase shift of the colliding solitary waves. The investigations should be useful for understanding the propagation and interaction of ion–acoustic solitary waves in dense astrophysical plasmas (such as white dwarfs) as well as in intense laser-solid matter interaction experiments.

Effects of dust size distribution in ultracold quantum dusty plasmas

Qi Xue-Hong, Duan Wen-Shan, Chen Jian-Min, Wang Shan-Jin
Chin. Phys. B 2011, 20 (2): 025203;  doi: 10.1088/1674-1056/20/2/025203
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The effect of dust size distribution in ultracold quantum dusty plasmas are investigated in this paper. How the dispersion relation and the propagation velocity for the quantum dusty plasma vary with the system parameters and the different dust distribution are studied. It is found that as the Fermi temperature of the dust grains increases the frequency of the wave increases for large wave number dust acoustic wave. The quantum parameter of Hd also increases the frequency of the large wave number dust acoustic wave. It is also found that the frequency ω0 and the propagation velocity v0 of quantum dust acoustic waves all increase as the total number density increases. They are greater for unusual dusty plasmas than those of the usual dusty plasma.

Intermittency of the density fluctuations and its influence on the radial transport in the boundary of J-TEXT

Zhu Meng-Zhou, Zhuang Ge, Wang Zhi-Jiang, Pan Yuan
Chin. Phys. B 2011, 20 (2): 025204;  doi: 10.1088/1674-1056/20/2/025204
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To improve the understanding of the turbulence intermittency, a detailed investigation of the intermittency of the density fluctuations has been performed in the boundary of J-TEXT. The intermittency of the density fluctuations and its influence on the radial transport are reported. The probability distribution functions of the density fluctuations are not scale-invariant, being inconsistent with the self-organized criticality hypothesis. The underlying dynamics of the intermittency are detected using the quiet-time statistical method. The probability distribution function of the quiet times shows double-power-law regions, indicating the existence of correlations between the successive burst events.

Structural transition of FeSe under high pressure

Li Wei, Chen Jun-Fang, He Qin-Yu, Wang Teng, Pan Zhong-Liang
Chin. Phys. B 2011, 20 (2): 026101;  doi: 10.1088/1674-1056/20/2/026101
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The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase α-FeSe and hexagonal NiAs-type phase β-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the αβ phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the αβ phase transformation.

Relaxed energy and structure of edge dislocation in iron

Zhang Yan, Xie Li-Juan, Zhang Jian-Min, Xu Ke-Wei
Chin. Phys. B 2011, 20 (2): 026102;  doi: 10.1088/1674-1056/20/2/026102
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With modified analytical embedded-atom method and molecular dynamics simulation, this paper simulates the strain energy and the equilibrium core structure of a<100> edge dislocation in BCC metal iron on atomistic scale. In addition, the trapping effect of dislocation on vacancy is investigated as well. The results show that the equilibrium dislocation core is quite narrow and has a C2v symmetry structure. Calculated strain energy Es of the dislocation is a linear function of ln (R/2b) while R≥5.16 Å (1 Å=0.1 nm), in excellent agreement with the elasticity theory prediction. Determined core radius and energy are 5.16 Å and 0.62 eV/Å, respectively. The closer the vacancy to the dislocation line is, the lower the vacancy formation energy is, this fact implies that the dislocation has a trend to trap the vacancy, especially for a separation distance of the vacancy from dislocation line being less than two lattice constants.

Effects of the sputtering power on the crystalline structure and optical properties of the silver oxide films deposited using direct-current reactive magnetron sputtering

Gao Xiao-Yong, Zhang Zeng-Yuan, Ma Jiao-Min, Lu Jing-Xiao, Gu Jin-Hua, Yang Shi-E
Chin. Phys. B 2011, 20 (2): 026103;  doi: 10.1088/1674-1056/20/2/026103
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This paper reports that a series of silver oxide (AgxO) films are deposited on glass substrates by direct-current reactive magnetron sputtering at a substrate temperature of 250 oC and an oxygen flux ratio of 15:18 by modifying the sputtering power (SP). The AgxO films deposited apparently show a structural evolution from cubic biphased (AgO + Ag2O) to cubic single-phased (Ag2O), and to biphased (Ag2O + AgO) structure. Notably, the cubic single-phased Ag2O film is deposited at the SP = 105 W and an AgO phase with <220> orientation discerned in the AgxO films deposited using the SP > 105 W. The transmissivity and reflectivity of the AgxO films in transparent region decrease with the increase the SP, whereas the absorptivity inversely increases with the increase of the SP. These results may be due to the structural evolution and the increasing film thickness. A redshift of the films' absorption edges determined in terms of Tauc formula clearly occurs from 3.1 eV to 2.73 eV with the increase of the SP.

Ab initio studies on the mechanic and magnetic properties of PdHx

Cui Xin, Liang Xi-Xia, Wang Jian-Tao, Zhao Guo-Zhong
Chin. Phys. B 2011, 20 (2): 026201;  doi: 10.1088/1674-1056/20/2/026201
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Based on ab initio total energy calculations, the structural, electronic, mechanic, and magnetic properties of PdHx are investigated. It is found that bulk modulus of PdHx is larger than the metal Pd with the hydrogen storage except Pd4H2. The calculated results for the magnetic moments show that the hydrogen addition weakens the magnetic properties of the PdHx systems. A strong magneto-volume effect is found in PdHx structures as well as Pd. The transition from paramagnetism to ferromagnetism is discussed. The corresponding densities of states for both structures are also shown to understand the magnetic behaviour.

Solving the initial condition of the string relaxation equation of the string model for glass transition: part-II

Zhang Jin-Lu, Wang Li-Na, Zhao Xing-Yu, Zhang Li-Li, Zhou Heng-Wei, Wei Lai, Huang Yi-Neng
Chin. Phys. B 2011, 20 (2): 026401;  doi: 10.1088/1674-1056/20/2/026401
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The string model for the glass transition can quantitatively describe the universal α-relaxation in glassformers. The string relaxation equation (SRE) of the model simplifies the well-known Debye and Rouse–Zimm relaxation equations at high and low enough temperatures, respectively. However, its initial condition, necessary to the further model predictions of glassy dynamics, has not been solved. In this paper, the general initial condition of the SRE for stochastically spatially configurative strings is solved exactly based on the obtained special initial condition of the SRE for straight strings in a previous paper (J. L. Zhang et al. 2010 Chin. Phys. B 19, 056403).

Surface reconstruction on stishovite SiO2, HfO2 and rutile TiO2 (001)

Tang Fu-Ling, Yue Rui, Lu Wen-Jiang
Chin. Phys. B 2011, 20 (2): 026801;  doi: 10.1088/1674-1056/20/2/026801
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This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO2, HfO2 and rutile TiO2 (001) by using classical molecular dynamics. It is found that these three surfaces relax instead of reconstruction at 0 K, and have little possibility to reconstruct below 40 K. Above 40 K, surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain. Several reconstruction patterns with approximate surface energies are found, and electrostatic potentials on them are also provided in comparison with possible microscopic results.

Study on the defect-related emissions in the light self-ion-implanted Si films by a silicon-on-insulator structure

Wang Chong, Yang Yu, Yang Rui-Dong, Li Liang, Xiong Fei, Bao Ji-Ming
Chin. Phys. B 2011, 20 (2): 026802;  doi: 10.1088/1674-1056/20/2/026802
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This paper reports that the Si+ self-ion-implantation are conducted on the silicon-on-insulator wafers with the 28Si+ doses of 7×1012, 1×1013, 4×1013, and 3×1014 cm-2, respectively. After the suitable annealing, these samples are characterized by using the photoluminescence technique at different recorded temperatures. Plentiful emission peaks are observed in these implanted silicon-on-insulator samples, including the unwonted intense P' band which exhibits a great potential in the optoelectronic application. These results indicate that severe transformation of the interstitial clusters can be manipulated by the implanting dose at suitable annealing temperatures. The high critical temperatures for the photoluminescence intensity growth of the two signatures are well discussed based on the thermal ionization model of free exciton.

Aggregation of ferromagnetic and paramagnetic atoms at edges of graphenes and graphite Hot!

Zhou Hai-Qing, Yang Huai-Chao, Qiu Cai-Yu, Liu Zheng, Yu Fang, Hu Li-Jun, Xia Xiao-Xiang, Yang Hai-Fang, Gu Chang-Zhi, Sun Lian-Feng
Chin. Phys. B 2011, 20 (2): 026803;  doi: 10.1088/1674-1056/20/2/026803
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In this work we report that when ferromagnetic metals (Fe, Co and Ni) are thermally evaporated onto n-layer graphenes and graphite, a metal nanowire and adjacent nanogaps can be found along the edges regardless of its zigzag or armchair structure. Similar features can also be observed for paramagnetic metals, such as Mn, Al and Pd. Meanwhile, metal nanowires and adjacent nanogaps cannot be found for diamagnetic metals (Au and Ag). An external magnetic field during the evaporation of metals can make these unique features disappear for ferromagnetic and paramagnetic metal; and the morphologies of diamagnetic metal do not change after the application of an external magnetic field. We discuss the possible reasons for these novel and interesting results, which include possible one-dimensional ferromagnets along the edge and edge-related binding energy.

Novel high-voltage power device based on self-adaptive interface charge

Wu Li-Juan, Hu Sheng-Dong, Zhang Bo, Li Zhao-Ji
Chin. Phys. B 2011, 20 (2): 027101;  doi: 10.1088/1674-1056/20/2/027101
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This paper presents a novel high-voltage lateral double diffused metal–oxide semiconductor (LDMOS) with self-adaptive interface charge (SAC) layer and its physical model of the vertical interface electric field. The SAC can be self-adaptive to collect high concentration dynamic inversion holes, which effectively enhance the electric field of dielectric buried layer (EI) and increase breakdown voltage (BV). The BV and EI of SAC LDMOS increase to 612 V and 600 V/μm from 204 V and 90.7 V/μm of the conventional silicon-on-insulator, respectively. Moreover, enhancement factors of η which present the enhanced ability of interface charge on EI are defined and analysed.

Boron/nitrogen pairs Co-doping in metallic carbon nanotubes: a first-principle study

Ouyang Fang-Ping, Peng Sheng-Lin, Chen Ling-Na, Sun Shu-Yuan, Xu Hui
Chin. Phys. B 2011, 20 (2): 027102;  doi: 10.1088/1674-1056/20/2/027102
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By using the first-principles calculations, the electronic structure and quantum transport properties of metallic carbon nanotubes with B/N pairs co-doping have been investigated. It is shown that the total energies of metallic carbon nanotubes are sensitive to the doping sites of the B/N pairs. The energy gaps of the doped metallic carbon nanotubes decrease with decreasing the concentration of the B/N pair not only along the tube axis but also around the tube. Moreover, the IV characteristics and transmissions of the doped tubes are studied. Our results reveal that the conducting ability of the doped tube decreases with increasing the concentrations of the B/N pairs due to symmetry breaking of the system. This fact opens a new way to modulate band structures of metallic carbon nanotubes by doping B/N pair with suitable concentration and the novel characteristics are potentially useful in future applications.

Effect of oxygen vacancy defect on the magnetic properties of Co-doped ZnO

Weng Zhen-Zhen, Zhang Jian-Min, Huang Zhi-Gao, Lin Wen-Xiong
Chin. Phys. B 2011, 20 (2): 027103;  doi: 10.1088/1674-1056/20/2/027103
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The influence of oxygen vacancy on the magnetism of Co-doped ZnO has been investigated by the first-principles calculations. It is suggested that oxygen vacancy and its location play crucial roles on the magnetic properties of Co-doped ZnO. The exchange coupling mechanism should account for the magnetism in Co-doped ZnO with oxygen vacancy and the oxygen vacancy is likely to be close to the Co atom. The oxygen vacancy (doping electrons) might be available for carrier mediation but is localized with a certain length and can strengthen the ferromagnetic exchange interaction between Co atoms.

Electron tunneling in single layer graphene with an energy gap

Xu Xu-Guang, Zhang Chao, Xu Gong-Jie, Cao Jun-Cheng
Chin. Phys. B 2011, 20 (2): 027201;  doi: 10.1088/1674-1056/20/2/027201
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When a single layer graphene is epitaxially grown on silicon carbide, it will exhibit a finite energy gap like a conventional semiconductor, and its energy dispersion is no longer linear in momentum in the low energy regime. In this paper, we have investigated the tunneling characteristics through a two-dimensional barrier in a single layer graphene with an energy gap. It is found that when the electron is at a zero angle of incidence, the transmission probability as a function of incidence energy has a gap. Away from the gap the transmission coefficient oscillates with incidence energy which is analogous to that of a conventional semiconductor. The conductance under zero temperature has a gap. The properties of electron transmission may be useful for developing graphene-based nano-electronics.

Evaluation of thermal resistance constitution for packaged AlGaN/GaN high electron mobility transistors by structure function method

Zhang Guang-Chen, Feng Shi-Wei, Zhou Zhou, Li Jing-Wan, Guo Chun-Sheng
Chin. Phys. B 2011, 20 (2): 027202;  doi: 10.1088/1674-1056/20/2/027202
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The evaluation of thermal resistance constitution for packaged AlGaN/GaN high electron mobility transistor (HEMT) by structure function method is proposed in this paper. The evaluation is based on the transient heating measurement of the AlGaN/GaN HEMT by pulsed electrical temperature sensitive parameter method. The extracted chip-level and package-level thermal resistances of the packaged multi-finger AlGaN/GaN HEMT with 400-μ m SiC substrate are 22.5 K/W and 7.2 K/W respectively, which provides a non-invasive method to evaluate the chip-level thermal resistance of packaged AlGaN/GaN HEMTs. It is also experimentally proved that the extraction of the chip-level thermal resistance by this proposed method is not influenced by package form of the tested device and temperature boundary condition of measurement stage.

Thermopower in parallel double quantum dots with Rashba spin–orbit interaction

Xue Hui-Jie, Lü Tian-Quan, Zhang Hong-Chen, Yin Hai-Tao, Cui Lian, He Ze-Long
Chin. Phys. B 2011, 20 (2): 027301;  doi: 10.1088/1674-1056/20/2/027301
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Based on the Green's function technique and the equation of motion approach, this paper theoretically studies the thermoelectric effect in parallel coupled double quantum dots (DQDs), in which Rashba spin–orbit interaction is taken into account. Rashba spin–orbit interaction contributions, even in a magnetic field, are exhibited obviously in the double quantum dots system for the thermoelectric effect. The periodic oscillation of thermopower can be controlled by tunning the Rashba spin–orbit interaction induced phase. The interesting spin-dependent thermoelectric effects will arise which has important influence on thermoelectric properties of the studied system.

Electronic structures of stacked layers quantum dots: influence of the non-perfect alignment and the applied electric field

Jia Bo-Yong, Yu Zhong-Yuan, Liu Yu-Min, Han Li-Hong, Yao Wen-Jie, Feng Hao, Ye Han
Chin. Phys. B 2011, 20 (2): 027302;  doi: 10.1088/1674-1056/20/2/027302
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Electronic structures of the artificial molecule comprising two truncated pyramidal quantum dots vertically coupled and embedded in the matrix are theoretically analysed via the finite element method. When the quantum dots are completely aligned, the electron energy levels decrease with the horizontally applied electric field. However, energy levels may have the maxima at non-zero electric field if the dots are staggered by a distance of several nanometers in the same direction of the electric field. In addition to shifting the energy levels, the electric field can also manipulate the electron wavefunctions confined in the quantum dots, in company with the non-perfect alignment.

Enhancement-mode AlGaN/GaN high electronic mobility transistors with thin barrier

Ma Xiao-Hua, Yu Hui-You, Quan Si, Yang Li-Yuan, Pan Cai-Yuan, Yang Ling, Wang Hao, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2011, 20 (2): 027303;  doi: 10.1088/1674-1056/20/2/027303
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An enhancement-mode (E-mode) AlGaN/GaN high electron mobility transistor (HEMTs) was fabricated with 15-nm AlGaN barrier layer. E-mode operation was achieved by using fluorine plasma treatment and post-gate rapid thermal annealing. The thin barrier depletion-HEMTs with a threshold voltage typically around -1.7 V, which is higher than that of the 22-nm barrier depletion-mode HEMTs (-3.5 V). Therefore, the thin barrier is emerging as an excellent candidate to realize the enhancement-mode operation. With 0.6-μm gate length, the devices treated by fluorine plasma for 150-W RF power at 150 s exhibited a threshold voltage of 1.3 V. The maximum drain current and maximum transconductance are 300 mA/mm, and 177 mS/mm, respectively. Compared with the 22-nm barrier E-mode devices, VT of the thin barrier HEMTs is much more stable under the gate step-stress.

Characterization of Al2O3/GaN/AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors with different gate recess depths

Ma Xiao-Hua, Pan Cai-Yuan, Yang Li-Yuan, Yu Hui-You, Yang Ling, Quan Si, Wang Hao, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2011, 20 (2): 027304;  doi: 10.1088/1674-1056/20/2/027304
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In this paper, in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal--insulator--semiconductor (MIS) high electron mobility transistors (HEMTs), we demonstrate better performances of recessed-gate Al2O3 MIS-HEMTs which are fabricated by Fluorine-based Si3N4 etching and chlorine-based AlGaN etching with three etching times (15 s, 17 s and 19 s). The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT. Through the recessed-gate etching, the transconductance increases effectively. When the recessed-gate depth is 1.02 nm, the best interface performance with Τit=(0.20-1.59) μs and Dit=(0.55-1.08)×1012 cm-2·eV-1 can be obtained. After chlorine-based etching, the interface trap density reduces considerably without generating any new type of trap. The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices. By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times, it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively.

Erratum to "Quantum compact model for thin-body double-gate Schottky barrier MOSFETs"

Luan Su-Zhen, Liu Hong-Xia
Chin. Phys. B 2011, 20 (2): 027305;  doi: 10.1088/1674-1056/20/2/027305
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Negative capacitance in doped bi-layer organic light-emitting devices

Li Nuo, Gao Xin-Dong, Xie Zuo-Ti, Sun Zheng-Yi, Ding Xun-Min, Hou Xiao-Yuan
Chin. Phys. B 2011, 20 (2): 027306;  doi: 10.1088/1674-1056/20/2/027306
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This paper reports that the doped bi-layer organic light-emitting devices are fabricated by doping in different regions of the light-emitting layer, the admittance and luminance spectra to characterize the capacitance and luminance of the device are measured. Negative capacitance (NC) appeared at low frequencies when the doped devices are biased with high voltages. The measured phase difference between AC voltage applied across the device and AC current flowing through the device show that the device is inductive when NC appears.

A new model analysis of the third harmonic voltage in inductive measurement for critical current density of superconducting films

Zhang Xu, Wu Zhi-Zhen, Zhou Tie-Ge, He Ming, Zhao Xin-Jie, Yan Shao-Lin, Fang Lan
Chin. Phys. B 2011, 20 (2): 027401;  doi: 10.1088/1674-1056/20/2/027401
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The critical current density Jc is one of the most important parameters of high temperature superconducting films in superconducting applications, such as superconducting filter and superconducting Josephson devices. This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation. Using this model, it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for Jc. The theoretic curve is consistent with the experimental results about measuring superconducting film, especially when the third-harmonic voltage just exceeds zero. The Jc value of superconducting films determined by the inductive method is also compared with results measured by four-probe transport method. The agreements between inductive method and transport method are very good.

Influence of oxygen pressure on critical current density and magnetic flux pinning structures in YBa2Cu3O7-x fabricated by chemical solution deposition

Ding Fa-Zhu, Gu Hong-Wei, Zhang Teng, Dai Shao-Tao, Xiao Li-Ye
Chin. Phys. B 2011, 20 (2): 027402;  doi: 10.1088/1674-1056/20/2/027402
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This paper studies the effect of oxygen partial pressure on the fabrication of YBa2Cu3O7-x films on (00l) LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). As the oxygen partial pressure increases to 1500 Pa, a great increase in the superconducting properties is observed at high magnetic fields parallel to the YBCO c axis. The cross-sectional transmission electron microscope images show that a high density of stacking faults in the size range of 10-15 nm may act as flux pinning centres to enhance the critical current density of the YBCO films.

Magnetic entropy change and large refrigerant capacity of Ce6i2Si3-type GdCoSiGe compound

Shen Jun, Zhang Hu, Wu Jian-Feng
Chin. Phys. B 2011, 20 (2): 027501;  doi: 10.1088/1674-1056/20/2/027501
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Magnetic entropy change (Δ SM) and refrigerant capacity (RC) of Ce6Ni2Si3-type Gd6Co1.67Si2.5Ge0.5 compounds have been investigated. The Gd6Co1.67Si2.5Ge0.5 undergoes a reversible second-order phase transition at the Curie temperature TC = 296 K. The high saturation magnetization leads to a large Δ SM and the maximal value of Δ SM is found to be 5.9 J/kg,cdot,K around TC for a field change of 0-5 T. A broad distribution of the Δ SM peak is observed and the full width at half maximum of the Δ SM peak is about 101 K under a magnetic field of 5 T. The large RC is found around TC and its value is 424 J/kg.

Ferrimagnetism and abnormal spin–lattice coupling in dilute magnetic ferroelectric (Bi0.46Na0.46Ba0.08)TiO3:Co Hot!

Fan Jing, Dong Xin-Wei, Song You, Wang Ke-Feng, Liu Jun-Ming, Jiang Xiang-Ping
Chin. Phys. B 2011, 20 (2): 027502;  doi: 10.1088/1674-1056/20/2/027502
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We have investigated the low-temperature magnetism and spin–lattice coupling in (Bi0.46Na0.46Ba0.08)TiO3:Co in order to understand the magnetoelectric effect in such artificially synthesized dilute magnetic ferroelectrics. It is revealed that the as-prepared (Bi0.46Na0.46Ba0.08)TiO3:Co at Co content of 20% ~ 30% exhibits fascinating ferrimagnetism which is robust against magnetic field, the abnormal spin–lattice coupling characterized by a negative magnetostriction effect; and the suppressed magnetic moment within the temperature range of 30 K ~ 50 K is identified. These magnetic behaviours at low temperatures can be explained by the competition between the ferrimagnetic response and the magnetic moment suppression induced by the abnormal spin–lattice coupling effect. Finally, the ferroelectric and magnetodielectric properties are also discussed.

Study of NiCuZn ferrite powders and films prepared by sol–gel method

Gao Liang-Qiu, Yu Guo-Jian, Wang Ying, Wei Fu-Lin
Chin. Phys. B 2011, 20 (2): 027503;  doi: 10.1088/1674-1056/20/2/027503
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This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol–gel method. The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated. The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700℃ ~1000℃. The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 du. Powders obtained from Ni0.4Cu0.2Zn0.4Fe1.9O4 gel have better magnetic properties than those from gels with other composition. After heat-treating at 900℃ for 3 h, coercivity Hc and saturation magnetization Ms are 9.7 Oe (1 Oe = 80 A/m) and 72.4 emu/g, respectively. Different from the powders, NiCuZn films produced on Si (100) from the Ni0.4Cu0.2Zn0.4Fe2O4 gel formed at room temperature possess high properties. When heat-treating condition is around 600℃ for 6 min, samples with low Hc and high Ms will be obtained. The minimal Hc is 16.7 Oe and Ms is about 300 emu/cm3. In comparison with the films prepared through long-time heat treating, the films prepared through short heat-treating time exhibits better soft magnetic properties.

Release of charges under external fields of PbLa(Zr,Sn,Ti)O3 ceramic

Zhang Chong-Hui, Xu Zhuo, Gao Jun-Jie, Yao Xi
Chin. Phys. B 2011, 20 (2): 027701;  doi: 10.1088/1674-1056/20/2/027701
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This paper investigates the pyroelectric of poled antiferroelectric (AFE) ceramic Pb0.97La0.02(Zr0.69Sn0.196 Ti0.114)O3 and its remnant polarization dependence of hydrostatic pressure. The results show that the bound charges of poled sample can be released in short time by temperature field or pressure field. The released charge abruptly forms a large pulse current. The phenomena of released charge under external fields result in the ferroelectric-AFE phase transition induced by temperature or hydrostatic pressure.

Infrared quantum cutting conversion luminescence of Tb(0.7)Yb(3):FOV

Chen Xiao-Bo, Kang Dong-Guo, Li Song, Wen Lei, Yu Chun-Lei, Hu Li-Li, Zhou Jing
Chin. Phys. B 2011, 20 (2): 027801;  doi: 10.1088/1674-1056/20/2/027801
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The infrared quantum cutting of oxyfluoride nanophase vitroceramics Tb(0.7)Yb(3):FOV has been studied in the present paper. The actual quantum cutting efficiency formula calculated from integral fluorescence intensity is extended to the case of Tb(0.7)Yb(3):FOV. The visible and the infrared fluorescence spectra and their integral fluorescence intensities are measured from static fluorescence experiment. Lifetime curve is measured from dynamic fluorescence experiment. It is found that the total actual quantum cutting efficiency η of the excited 5D4 level is about 93.7%, and that of excited (5D3, 5G6) levels is 93.5%. It is also found that the total theoretical quantum cutting efficiency upper limit ηx%Yb of the 485.5 nm excited <5D4 level is about 121.7%, and that of 378.5 nm excited (5D3, 5G6) levels is 137.2%.

Fabrication and electrochemical properties of free-standing single-walled carbon nanotube film electrodes

Niu Zhi-Qiang, Ma Wen-Jun, Dong Hai-Bo, Li Jin-Zhu, Zhou Wei-Ya
Chin. Phys. B 2011, 20 (2): 028101;  doi: 10.1088/1674-1056/20/2/028101
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An easily manipulative approach was presented to fabricate electrodes using free-standing single-walled carbon nanotube (SWCNT) films grown directly by chemical vapor deposition. Electrochemical properties of the electrodes were investigated. In comparison with the post-deposited SWCNT papers, the directly grown SWCNT film electrodes manifested enhanced electrochemical properties and sensitivity of sensors as well as excellent electrocatalytic activities. A transition from macroelectrode to nanoelectrode behaviours was observed with the increase of scan rate. The heat treatment of the SWCNT film electrodes increased the current signals of electrochemical analyser and background current, because the heat-treatment of the SWCNTs in air could create more oxide defects on the walls of the SWCNTs and make the surfaces of SWCNTs more hydrophilic. The excellent electrochemical properties of the directly grown and heat-treated free-standing SWCNT film electrodes show the potentials in biological and electrocatalytic applications.

Optical and atomic force microscopic study on step bunching in BaB2O4 crystal growth

Pan Xiu-Hong, Jin Wei-Qing, Liu Yan, Ai Fei, Jin Fei, Xie Jun-Jie
Chin. Phys. B 2011, 20 (2): 028102;  doi: 10.1088/1674-1056/20/2/028102
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The formation of macrostep during high-temperature phase of barium meta-borate (α-BaB2O4) single crystal growth has been investigated by both optical in-situ observation system and atomic force microscopy (AFM). The in-situ observation results demonstrate that the critical linear size of growing facet exceeding the size that the macrostep generates is significantly anisotropic. The critical linear sizes are around 280 μm and 620 μm for {1010} and {1010} planes, respectively. AFM study illustrates that macrostep train with a height of 150 nm ~ 200 nm is one typical morphological feature of the as-grown crystal surface. The riser of each macrostep consists of several straight and parallel sub-steps, indicating the occurrence of step bunching. Additionally, triangular sub-steps with heights of several nanometers on the treads of the macrosteps are found to be another typical feature of surface morphology, which implies a microscopically competitive bunching of sub-steps between various crystallographic orientations.

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

Li Shang-Sheng, Ma Hong-An, Li Xiao-Lei, Su Tai-Chao, Huang Guo-Feng, Li Yong, Jia Xiao-Peng
Chin. Phys. B 2011, 20 (2): 028103;  doi: 10.1088/1674-1056/20/2/028103
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High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K. The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively. The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique. The electrical properties including resistivities, Hall coefficients, Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method. The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized. With the increase of quantity of additive boron, some high-index crystal faces such as 113 gradually disappear, and some stripes and triangle pits occur on the crystal surface. This work is helpful for the further research and application of boron-doped semiconductor diamond.

Martensitic transformation in Cu-doped NiMnGa magnetic shape memory alloys

Li Pan-Pan, Wang Jing-Min, Jiang Cheng-Bao
Chin. Phys. B 2011, 20 (2): 028104;  doi: 10.1088/1674-1056/20/2/028104
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This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L21 cubic austenite by Cu substituting for Ni in the Ni50-xCuxMn31Ga19 (x=2-10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (kF) is applied to evaluate the change of the martensitic transformation temperature. The increase of kF leads to the increase of the martensitic transformation temperature.

High power nano-LiMn2O4 cathode materials with high-rate pulse discharge capability for lithium-ion batteries

Chen Ying-Chao, Xie Kai, Pan Yi, Zheng Chun-Man, Wang Hua-Lin
Chin. Phys. B 2011, 20 (2): 028201;  doi: 10.1088/1674-1056/20/2/028201
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Nano-LiMn2O4 cathode materials with nano-sized particles are synthesized via a citric acid assisted sol–gel route. The structure, the morphology and the electrochemical properties of the nano-LiMn2O4 are investigated. Compared with the micro-sized LiMn2O4, the nano-LiMn2O4 possesses a high initial capacity (120 mAh/g) at a discharge rate of 0.2 C (29.6 mA/g). The nano-LiMn2O4 also has a good high-rate discharge capability, retaining 91% of its capacity at a discharge rate of 10 C and 73% at a discharge rate of 40 C. In particular, the nano-LiMn2O4 shows an excellent high-rate pulse discharge capability. The cut-off voltage at the end of 50-ms pulse discharge with a discharge rate of 80 C is above 3.40 V, and the voltage returns to over 4.10 V after the pulse discharge. These results show that the prepared nano-LiMn2O4 could be a potential cathode material for the power sources with the capability to deliver very high-rate pulse currents.

Lattice potential energy and standard molar enthalpy in the formation of 1–dodecylamine hydrobromide (1–C12H25NH3·Br)(s)

Liu Yu-Pu, Di You-Ying, Dan Wen-Yan, He Dong-Hua, Kong Yu-Xia, Yang Wei-Wei
Chin. Phys. B 2011, 20 (2): 028202;  doi: 10.1088/1674-1056/20/2/028202
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This paper reports that 1-dodecylamine hydrobromide (1–C12H25NH3·Br)(s) has been synthesized using the liquid phase reaction method. The lattice potential energy of the compound 1–C12H25NH3·Br and the ionic volume and radius of the 1–C12H25NH3+ cation are obtained from the crystallographic data and other auxiliary thermodynamic data. The constant-volume energy of combustion of 1–C12H25NH3·Br(s) is measured to be ΔcUmo(1–C12H25NH3·Br, s) =–(7369.03±3.28) kJ·mol-1 by means of an RBC-II precision rotating-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of combustion of the compound is derived to be ΔcHmo(1–C12H25NH3·Br, s)=–(7384.52±3.28) kJ·mol - 1 from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound is calculated to be ΔfHmo(1–C12H25NH3·Br, s)=–(1317.86±3.67) kJ·mol-1 from the standard molar enthalpy of combustion of the title compound and other auxiliary thermodynamic quantities through a thermochemical cycle.

A three-dimensional time-dependent theory for helix traveling wave tubes in beam-wave interaction

Peng Wei-Feng, Hu Yu-Lu, Yang Zhong-Hai, Li Jian-Qing, Lu Qi-Ru, Li Bin
Chin. Phys. B 2011, 20 (2): 028401;  doi: 10.1088/1674-1056/20/2/028401
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This paper presents a three-dimensional time-dependent nonlinear theory of helix traveling wave tubes for beam-wave interaction. The radio frequency electromagnetic fields are represented as the superposition of azimuthally symmetric waves in a vacuum sheath helix. Coupling impedance is introduced to the electromagnetic field equations' stimulating sources, which makes the theory easier and more flexible to realize. The space charge fields are calculated by electron beam space-charge waves expressed as the superposition solutions of Helmholtz equations. The focusing forces due to either a solenoidal field or a periodic permanent magnetic field is also included. The dynamical equations of electrons are Lorentz equations associating with electromagnetic fields, focusing fields and space-charge fields. The numerically simulated results of a tube are presented.

InGaN/GaN multiple quantum well solar cells with an enhanced open-circuit voltage

Zhang Xiao-Bin, Wang Xiao-Liang, Xiao Hong-Ling, Yang Cui-Bai, Hou Qi-Feng, Yin Hai-Bo, Chen Hong, Wang Zhan-Guo
Chin. Phys. B 2011, 20 (2): 028402;  doi: 10.1088/1674-1056/20/2/028402
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In this paper, InGaN/GaN multiple quantum well solar cells (MQWSCs) with an In content of 0.15 are fabricated and studied. The short-circuit density, fill factor and open-circuit voltage (Voc) of the device are 0.7 mA/cm2, 0.40 and 2.22 V, respectively. The results exhibit a significant enhancement of Voc compared with those of InGaN-based hetero and homojunction cells. This enhancement indicates that the InGaN/GaN MQWSC offers an effective way for increasing Voc of an In-rich InxGa1-xN solar cell. The device exhibits an external quantum efficiency (EQE) of 36% (7%) at 388 nm (430 nm). The photovoltaic performance of the device can be improved by optimizing the structure of the InGaN/GaN multiple quantum well.

Ultra-low on-resistance high voltage (>600 V) SOI MOSFET with a reduced cell pitch

Luo Xiao-Rong, Yao Guo-Liang, Chen Xi, Wang Qi, Ge Rui, Florin Udrea
Chin. Phys. B 2011, 20 (2): 028501;  doi: 10.1088/1674-1056/20/2/028501
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A low specific on-resistance (RS,on) silicon-on-insulator (SOI) trench MOSFET (metal–oxide–semiconductor–field–effect–transistor) with a reduced cell pitch is proposed. The lateral MOSFET features multiple trenches: two oxide trenches in the drift region and a trench gate extended to the buried oxide (BOX) (SOI MT MOSFET). Firstly, the oxide trenches increase the average electric field strength along the x direction due to lower permittivity of oxide compared with that of Si; secondly, the oxide trenches cause multiple-directional depletion, which improves the electric field distribution and enhances the reduced surface field (RESURF) effect in the SOI layer. Both of them result in a high breakdown voltage (BV). Thirdly, the oxide trenches cause the drift region to be folded in the vertical direction, leading to a shortened cell pitch and a reduced RS,on. Fourthly, the trench gate extended to the BOX further reduces RS,on, owing to the electron accumulation layer. The BV of the MT MOSFET increases from 309 V for a conventional SOI lateral double diffused metal–oxide semiconductor (LDMOS) to 632 V at the same half cell pitch of 21.5 μm, and RS,on decreases from 419 mΩ·cm2 to 36.6 mΩ·cm2. The proposed structure can also help to dramatically reduce the cell pitch at the same breakdown voltage.

Numerical analysis of In0.53Ga0.47As/InP single photon avalanche diodes

Zhou Peng, Li Chun-Fei, Liao Chang-Jun, Wei Zheng-Jun, Yuan Shu-Qiong
Chin. Phys. B 2011, 20 (2): 028502;  doi: 10.1088/1674-1056/20/2/028502
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A rigorous theoretical model for In0.53Ga0.47As/InP single photon avalanche diode is utilized to investigate the dependences of single photon quantum efficiency and dark count probability on structure and operation condition. In the model, low field impact ionizations in charge and absorption layers are allowed, while avalanche breakdown can occur only in the multiplication layer. The origin of dark counts is discussed and the results indicate that the dominant mechanism that gives rise to dark counts depends on both device structure and operating condition. When the multiplication layer is thicker than a critical thickness or the temperature is higher than a critical value, generation–recombination in the absorption layer is the dominative mechanism; otherwise band-to-band tunneling in the multiplication layer dominates the dark counts. The thicknesses of charge and multiplication layers greatly affect the dark count and the peak single photon quantum efficiency and increasing the multiplication layer width may reduce the dark count probability and increase the peak single photon quantum efficiency. However, when the multiplication layer width exceeds 1 μm, the peak single photon quantum efficiency increases slowly and it is finally saturated at the quantum efficiency of the single photon avalanche diodes.

A new level set model for cell image segmentation

Ma Jing-Feng, Hou Kai, Bao Shang-Lian, Chen Chun
Chin. Phys. B 2011, 20 (2): 028701;  doi: 10.1088/1674-1056/20/2/028701
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In this paper we first determine three phases of cell images: background, cytoplasm and nucleolus according to the general physical characteristics of cell images, and then develop a variational model, based on these characteristics, to segment nucleolus and cytoplasm from their relatively complicated backgrounds. In the meantime, the preprocessing obtained information of cell images using the OTSU algorithm is used to initialize the level set function in the model, which can speed up the segmentation and present satisfactory results in cell image processing.

A traffic flow cellular automaton model to considering drivers' learning and forgetting behaviour

Ding Jian-Xun, Huang Hai-Jun, Tian Qiong
Chin. Phys. B 2011, 20 (2): 028901;  doi: 10.1088/1674-1056/20/2/028901
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It is known that the commonly used NaSch cellular automaton (CA) model and its modifications can help explain the internal causes of the macro phenomena of traffic flow. However, the randomization probability of vehicle velocity used in these models is assumed to be an exogenous constant or a conditional constant, which cannot reflect the learning and forgetting behaviour of drivers with historical experiences. This paper further modifies the NaSch model by enabling the randomization probability to be adjusted on the bases of drivers' memory. The Markov properties of this modified model are discussed. Analytical and simulation results show that the traffic fundamental diagrams can be indeed improved when considering drivers' intelligent behaviour. Some new features of traffic are revealed by differently combining the model parameters representing learning and forgetting behaviour.

Refractivity estimations from an angle-of-arrival spectrum

Zhao Xiao-Feng, Huang Si-Xun
Chin. Phys. B 2011, 20 (2): 029201;  doi: 10.1088/1674-1056/20/2/029201
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This paper addresses the probability of atmospheric refractivity estimation by using field measurements at an array of radio receivers in terms of angle-of-arrival spectrum. Angle-of-arrival spectrum information is simulated by the ray optics model and refractivity is expressed in the presence of an ideal tri-linear profile. The estimation of the refractivity is organized as an optimization problem and a genetic algorithm is used to search for the optimal solution from various trial refractivity profiles. Theoretical analysis demonstrates the feasibility of this method to retrieve the refractivity parameters. Simulation results indicate that this approach has a fair anti-noise ability and its accuracy performance is mainly dependent on the antenna aperture size and its positions.

Properties of hyperon stars rotating at Keplerian frequency

Wen De-Hua, Chen Wei
Chin. Phys. B 2011, 20 (2): 029701;  doi: 10.1088/1674-1056/20/2/029701
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The structure and properties of a Keplerian rotating hyperon star with an equation of state (EOS) investigated using the relativistic σωρ model are examined by employing an accurate numerical scheme. It is shown that there is a clear rotating effect on the structure and properties, and that hyperon star matter cannot support a star with a mass larger than 1.9 MΘ, even a star rotating at the fastest allowed frequency. The constraints of the two known fastest rotating frequencies (716 Hz and 1122 Hz) on the mass and radius of a hyperon star are also explored. Furthermore, our results indicate that the imprint of the rapid rotation of a hyperon star on the moment of inertia is clear; the backward equatorial redshift, the forward equatorial redshift and the polar redshift can be distinguished clearly, the forward equatorial redshift is always negative; and its figuration is far from a spherical symmetric shape.
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