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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.4
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Lie symmetries and conserved quantities of discrete nonholonomic Hamiltonian systems

Wang Xing-Zhong,Fu Hao,Fu Jing-Li
Chin. Phys. B 2012, 21 (4): 040201;  doi: 10.1088/1674-1056/21/4/040201
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This paper focuses on studying Lie symmetries and conserved quantities of discrete nonholonomic Hamiltonian systems. Firstly, the discrete generalized Hamiltonian canonical equations and discrete energy equation of nonholonomic Hamiltonian systems are derived from discrete Hamiltonian action. Secondly, the determining equations and structure equation of Lie symmetry of the system are obtained. Thirdly, the Lie theorems and the conservation quantities are given for the discrete nonholonomic Hamiltonian systems. Finally, an example is discussed to illustrate the application of the results.

The element-free Galerkin method of numerically solving a regularized long-wave equation

Cheng Rong-Jun,Ge Hong-Xia
Chin. Phys. B 2012, 21 (4): 040203;  doi: 10.1088/1674-1056/21/4/040203
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The element-free Galerkin (EFG) method is used in this paper to find the numerical solution to a regularized long-wave (RLW) equation. The Galerkin weak form is adopted to obtain the discrete equations, and the essential boundary conditions are imposed by the penalty method. The effectiveness of the EFG method of solving the RLW equation is investigated by two numerical examples in this paper.

Content-based image hashing using wave atoms

Liu Fang,Leung Hon-Yin,Cheng Lee-Ming,Ji Xiao-Yong
Chin. Phys. B 2012, 21 (4): 040204;  doi: 10.1088/1674-1056/21/4/040204
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It is well known that robustness, fragility, and security are three important criteria of image hashing; however how to build a system that can strongly meet these three criteria is still a challenge. In this paper, a content-based image hashing scheme using wave atoms is proposed, which satisfies the above criteria. Compared with traditional transforms like wavelet transform and discrete cosine transform (DCT), wave atom transform is adopted for the sparser expansion and better characteristics of texture feature extraction which shows better performance in both robustness and fragility. In addition, multi-frequency detection is presented to provide an application-defined trade-off. To ensure the security of the proposed approach and its resistance to a chosen-plaintext attack, a randomized pixel modulation based on the R閚yi chaotic map is employed, combining with the nonliner wave atom transform. The experimental results reveal that the proposed scheme is robust against content-preserving manipulations and has a good discriminative capability to malicious tampering.

Compact implicit integration factor methods for some complex-valued nonlinear equations

Zhang Rong-Pei
Chin. Phys. B 2012, 21 (4): 040205;  doi: 10.1088/1674-1056/21/4/040205
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The compact implicit integration factor (cIIF) method is an efficient time discretization scheme for stiff nonlinear diffusion equations in two and three spatial dimensions. In the current work, we apply the cIIF method to some complex-valued nonlinear evolutionary equations such as the nonlinear Schrödinger (NLS) equation and the complex Ginzburg-Landau (GL) equation. Detailed algorithm formulation and practical implementation of cIIF method are performed. The numerical results indicate that this method is very accurate and efficient.

New WKB method in supersymmetry quantum mechanics

Tian Gui-Hua
Chin. Phys. B 2012, 21 (4): 040301;  doi: 10.1088/1674-1056/21/4/040301
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In this paper, we combine the perturbation method in supersymmetric quantum mechanics with the WKB method to restudy an angular equation coming from the wave equations for a Schwarzschild black hole with a straight string passing through it. This angular equation serves as a naive model for our investigation of the combination of supersymmetric quantum mechanics and the WKB method, and will provide valuable insight for our further study of the WKB approximation in real problems, like the one in spheroidal equations, etc.

Robustness of quantum discord to sudden death in nuclear magnetic resonance

Xu Jian-Wei,Chen Qi-Hui
Chin. Phys. B 2012, 21 (4): 040302;  doi: 10.1088/1674-1056/21/4/040302
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We investigate the dynamics of the entanglement and quantum discord of two qubits in liquid state homonuclear nuclear magnetic resonance. Applying a phenomenological description for nuclear magnetic resonance under a relaxation process, and taking a group of typical parameters of nuclear magnetic resonance, we show that when a zero initial state experiences a relaxation process, its entanglement disappears completely after a sequence of so-called sudden deaths and revivals, while the quantum discord retains remarkable values after a sequence of oscillations. That is to say, the quantum discord is more robust than entanglement.

Rotational symmetry of classical orbits, arbitrary quantization of angular momentum and the role of the gauge field in two-dimensional space

Xin Jun-Li,Liang Jiu-Qing
Chin. Phys. B 2012, 21 (4): 040303;  doi: 10.1088/1674-1056/21/4/040303
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We study quantum-classical correspondence in terms of the coherent wave functions of a charged particle in two-dimensional central-scalar potentials as well as the gauge field of a magnetic flux in the sense that the probability clouds of wave functions are well localized on classical orbits. For both closed and open classical orbits, the non-integer angular-momentum quantization with the level space of angular momentum being greater or less than 2h is determined uniquely by the same rotational symmetry of classical orbits and probability clouds of coherent wave functions, which is not necessarily 2π-periodic. The gauge potential of a magnetic flux impenetrable to the particle cannot change the quantization rule but is able to shift the spectrum of canonical angular momentum by a flux-dependent value, which results in a common topological phase for all wave functions in the given model. The well-known quantum mechanical anyon model becomes a special case of the arbitrary quantization, where the classical orbits are 2π-periodic.

Irreversibility of a quantum walk induced by controllable decoherence employing random unitary operations

Xu You-Yang,Zhou Fei,Chen Liang,Xie Yi,Xue Peng,Feng Mang
Chin. Phys. B 2012, 21 (4): 040304;  doi: 10.1088/1674-1056/21/4/040304
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Quantum walk is different from random walk in reversibility and interference. Observation of the reduced reversibility in a realistic quantum walk is of scientific interest in understanding the unique quantum behavior. We propose an idea to experimentally investigate the decoherence-induced irreversibility of quantum walks with trapped ions in phase space via the average fidelity decay. By introducing two controllable decoherence sources, i.e., the phase damping channel (i.e., dephasing) and the high temperature amplitude reservoir (i.e., dissipation), in the intervals between the steps of quantum walk, we find that the high temperature amplitude reservoir shows more detrimental effects than the phase damping channel on quantum walks. Our study also shows that the average fidelity decay works better than the position variance for characterizing the transition from quantum walks to random walk. Experimental feasibility to monitor the irreversibility is justified using currently available techniques.

Quantum state swap for two trapped Rydberg atoms

Wu Huai-Zhi,Yang Zhen-Biao,Zheng Shi-Biao
Chin. Phys. B 2012, 21 (4): 040305;  doi: 10.1088/1674-1056/21/4/040305
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The quantum swap gate is one of the most useful gates for quantum computation. Two-qubit entanglement and a controlled-NOT quantum gate in a neutral Rydberg atom system have been achieved in recent experiments. It is therefore very interesting to propose a scheme here for swapping a quantum state between two trapped neutral atoms via the Rydberg blockade mechanism. The atoms interact with a sequence of laser pulses without individual addressing. The errors of the swap gate due to imprecision of pulse length, finite Rydberg interaction, and atomic spontaneous emission are discussed.

Deterministic implementations of fermionic quantum SWAP and Fredkin gates for spin qubits based on charge detection

Wang Hong-Fu,Zhang Shou,Zhu Ai-Dong
Chin. Phys. B 2012, 21 (4): 040306;  doi: 10.1088/1674-1056/21/4/040306
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We propose a scheme to implement fermionic quantum SWAP and Fredkin gates for spin qubits with the aid of charge detection. The scheme is deterministic without the need of qubit-qubit interaction, and the proposed setups consist of simple polarizing beam splitters, single-spin rotations, and charge detectors. Compared with linear optics quantum computation, this charge-measurement-based qubit scheme greatly enhances the success probability for implementing quantum SWAP and Fredkin gates and greatly simplifies the experimental realization of scalable quantum computers with noninteracting electrons.

Flux qubit with a large loop size and tunable Josephson junctions Hot!

Deng Hui,Yu HaiFeng,Xue Guang-Ming,Tian Ye,Ren Jian-Kun,Wu Yu-Lin,Huang Ke-Qiang,Zhao Shi-Ping,Zheng Dong-Ning
Chin. Phys. B 2012, 21 (4): 040307;  doi: 10.1088/1674-1056/21/4/040307
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We present the design of a superconducting flux qubit with a large loop inductance. The large loop inductance is desirable for coupling between qubits. The loop is configured into a gradiometer form that could reduce the interference from environmental magnetic noise. A combined Josephson junction, i.e., a DC-SQUID is used to replace the small Josephson junction in the usual 3-JJ (Josephaon junction) flux qubit, leading to a tunable energy gap by using an independent external flux line. We perform numerical calculations to investigate the dependence of the energy gap on qubit parameters such as junction capacitance, critical current, loop inductance, and the ratio of junction energy between small and large junctions in the flux qubit. We suggest a range of values for the parameters.

Linear instability and adiabaticity of a dark state during conversion of two species of fermionic atoms to stable molecules Hot!

Meng Shao-Ying,Chen Xi-Hao,Wu Wei,Fu Li-Bin
Chin. Phys. B 2012, 21 (4): 040308;  doi: 10.1088/1674-1056/21/4/040308
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In the present paper, we investigate the linear instability and adiabaticity of a dark state during conversion of two species of fermionic atoms to stable molecules through the stimulated Raman adiabatic passage aided by Feshbach resonance. We analytically obtain the regions for the appearance of linear instability. Moreover, taking 40K and 6Li atom-molecule conversion systems as examples, we give the unstable regions numerically. We also attempt to obtain the adiabatic criterion for this nonlinear system with classical adiabatic dynamics and study the adibaticity of the dark state with the adiabatic condition.

Analytic solutions of the ground and excited states of the spin-weighted spheroidal equation in the case of s=2

Sun Yue,Tian Gui-Hua,Dong Kun
Chin. Phys. B 2012, 21 (4): 040401;  doi: 10.1088/1674-1056/21/4/040401
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By using the super-symmetric quantum mechanics (SUSYQM) method, this paper obtains the analytical solutions for the spin-weighted spheroidal wave equation in the case of s=2. Based on the derived W0 to W4 the general form for the n-th-order super-potential is summarized and is proved correct by mathematical induction. Hence the ground eigenvalue problem is completely solved. Particularly, the novel solutions of the excited state are investigated according to the shape-invariance property.

Verification of the spin-weighted spheroidal equation in the case of s=1

Zhang Qing,Tian Gui-Hua,Sun Yue,Dong Kun
Chin. Phys. B 2012, 21 (4): 040402;  doi: 10.1088/1674-1056/21/4/040402
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The spin-weighted spheroidal equation in the case of s=1 is studied. By transforming the independent variables, we make it take the Schrödinger-like form. This Schrödinger-like equation is very interesting in itself. We investigate it by using super-symmetric quantum mechanics and obtain the ground eigenvalue and eigenfunction, which are consistent with the results previously obtained.

Holographic superconductor models in the non-minimal derivative coupling theory

Chen Song-Bai,Pan Qi-Yuan,Jing Ji-Liang
Chin. Phys. B 2012, 21 (4): 040403;  doi: 10.1088/1674-1056/21/4/040403
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We study a general class of holographic superconductor models via the Stückelberg mechanism in the non-minimal derivative coupling theory in which the charged scalar field is kinetically coupling to Einstein's tensor. We explore the effects of the coupling parameter on the critical temperature, the order of phase transitions and the critical exponents near the second-order phase transition point. Moreover, we compute the electrical conductivity using the probe approximation and check the ratios wg/Tc for the different coupling parameters.

Scattering and absorption of particles by a black hole involving a global monopole

Shao Jian-Zhou,Wang Yong-Jiu
Chin. Phys. B 2012, 21 (4): 040404;  doi: 10.1088/1674-1056/21/4/040404
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Under the conditions that the wavelength of a particle is much larger than its radius of central mass, and the Schwarzschild field is weak, the scattering of a particle has been studied by many researchers. They obtained that scalar and vector particles abide by Rutherforďs angle distribution by using the low level perturbation method and the scattered fielďs approximation in a weak field. The scattering cross section of a photon coincides with the section in Newton's field of point mass. We can obtain the photon's polarization effect by calculating the second-order perturbation in the linear Schwarzschild field. This article discusses the scattering and absorption of a particle by a black hole involving a global monopole by using the aforesaid method.

Dispersion compensation in an open-loop all-optical chaotic communication system

Liu Hui-Jie,Ren Bin,Feng Jiu-Chao
Chin. Phys. B 2012, 21 (4): 040501;  doi: 10.1088/1674-1056/21/4/040501
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The optical chaotic communication system using open-loop fiber transmission is studied under strong injection conditions. The optical chaotic communication system with open-loop configuration is studied using fiber transmission under strong injection conditions. The performances of fiber links composed of two types of fiber segments in different dispersion compensation maps are compared by testing the quality of the recovered message with different bit rates and encrypted by chaotic modulation (CM) or chaotic shift keying (CSK). The result indicates that the performance of the pre-compensation map is always worst. Two types of symmetrical maps are identical whatever the encryption method and bit-rate of message are. For the transmitting and the recovering of message of lower bit rate (1 Gb/s), the post-compensation map is the best scheme. However, for the message of higher bit rate (2.5 Gb/s), the parameters in communication system need to be modified properly in order to adapt to the high-speed application. Meanwhile, two types of symmetrical maps are the best scheme. In addition, the CM method is superior to the CSK method for high-speed applications. It is in accordance with the result in a back-to-back configuration system.

Novel criteria for exponential synchronization of inner time-varying complex networks with coupling delay

Zhang Qun-Jiao,Zhao Jun-Chan
Chin. Phys. B 2012, 21 (4): 040502;  doi: 10.1088/1674-1056/21/4/040502
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This paper mainly investigates the exponential synchronization of an inner time-varying complex network with coupling delay. Firstly, the synchronization of complex networks is decoupled into the stability of the corresponding dynamical systems. Based on the Lyapunov function theory, some sufficient conditions to guarantee its stability with any given convergence rate are derived, thus the synchronization of the networks is achieved. Finally, the results are illustrated by a simple time-varying network model with a coupling delay. All involved numerical simulations verify the correctness of the theoretical analysis.

Exponential networked synchronization of master-slave chaotic systems with time-varying communication topologies

Yang Dong-Sheng,Liu Zhen-Wei,Zhao Yan,Liu Zhao-Bing
Chin. Phys. B 2012, 21 (4): 040503;  doi: 10.1088/1674-1056/21/4/040503
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The networked synchronization problem of a class of master-slave chaotic systems with time-varying communication topologies is investigated in this paper. Based on algebraic graph theory and matrix theory, a simple linear state feedback controller is designed to synchronize the master chaotic system and the slave chaotic systems with a time-varying communication topology connection. The exponential stability of the closed-loop networked synchronization error system is guaranteed by applying Lyapunov stability theory. The derived novel criteria are in the form of linear matrix inequalities (LMIs), which are easy to examine and tremendously reduce the computation burden from the feedback matrices. This paper provides an alternative networked secure communication scheme which can be extended conveniently. An illustrative example is given to demonstrate the effectiveness of the proposed networked synchronization method.

Cryptanalysis of an ergodic chaotic encryption algorithm

Wang Xing-Yuan,Xie Yi-Xin,Qin Xue
Chin. Phys. B 2012, 21 (4): 040504;  doi: 10.1088/1674-1056/21/4/040504
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In this paper, we present the results for the security and the possible attacks on a new symmetric key encryption algorithm based on the ergodicity property of a logistic map. After analysis, we use mathematical induction to prove that the algorithm can be attacked by a chosen plaintext attack successfully and give an example to show how to attack it. According to the cryptanalysis of the original algorithm, we improve the original algorithm, and make a brief cryptanalysis. Compared with the original algorithm, the improved algorithm is able to resist a chosen plaintext attack and retain a considerable number of advantages of the original algorithm such as encryption speed, sensitive dependence on the key, strong anti-attack capability, and so on.

Bound states of spatial optical dark solitons in nonlocal media

Ou-Yang Shi-Gen,Hu Wei,Guo Qi
Chin. Phys. B 2012, 21 (4): 040505;  doi: 10.1088/1674-1056/21/4/040505
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It is shown that multiple dark solitons can form bound states in a series of balance distances in nonlocal bulk media. Dark solitons can either attract or repel each other depending on their separated distance. The stability of such bound states are studied numerically. There exist unstable degenerate bound states decaying in different ways and having different lifetimes.

Characteristics of synchronized traffic in mixed traffic flow

Ning Hong-Xin,Xue Yu
Chin. Phys. B 2012, 21 (4): 040506;  doi: 10.1088/1674-1056/21/4/040506
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In this paper, the characteristics of synchronized traffic in mixed traffic flow are investigated based on the braking light model. By introducing the energy dissipation and the distribution of slowdown vehicles, the effects of the maximum velocity, the mixing ratio, and the length of vehicles on the synchronized flow are discussed. It is found that the maximum velocity plays a great role in the synchronized flow in mixed traffic. The energy dissipation and the distribution of slowdown vehicles in the synchronized flow region are greatly different from those in free flow and a traffic jamming region. When all of vehicles have the same maximum velocity with Vmax > 15, the mixed traffic significantly displays synchronized flow, which has been demonstrated by the relation between flow rate and occupancy and estimation of the cross-correlation function. Moreover, the energy dissipation in the synchronized flow region does not increase with occupancy. The distribution of slowdown vehicles shows a changeless platform in the synchronized flow region. This is an interesting phenomenon. It helps to deeply understand the synchronized flow and greatly reduce the energy dissipation of traffic flow.

Further improvement of the Lyapunov functional and the delay-dependent stability criterion for a neural network with a constant delay

Qiu Fang,Zhang Quan-Xin,Deng Xue-Hui
Chin. Phys. B 2012, 21 (4): 040701;  doi: 10.1088/1674-1056/21/4/040701
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This paper investigates the asymptotical stability problem of a neural system with a constant delay. A new delay-dependent stability condition is derived by using the novel augmented Lyapunov-Krasovskii function with triple integral terms, and the additional triple integral terms play a key role in the further reduction of conservativeness. Finally, a numerical example is given to demonstrate the effectiveness and lower conservativeness of the proposed method.

Measurements, characteristics, and origin of new electromagnetic interference on magnetocardiographic measurements

Gu Hong-Fang,Cai Wen-Yan,Wei Yu-Ke,Liu Zheng-Hao,Wang Qian,Wang Yue,Dai Yuan-Dong,Ma Ping
Chin. Phys. B 2012, 21 (4): 040702;  doi: 10.1088/1674-1056/21/4/040702
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In order to eliminate the influence of the large-amplitude magnetic field noise that has complicated magnetocardiographic studies since October 2009, we have performed high-accuracy measurement of the environmental magnetic field noise in the vicinity of Beijing Subway Line 4 using a three-component height Tc radio frequency (rf) superconducting quantum interference device (SQUID). By analysing the spatial form and other characteristics of the time and the frequency domains and by calculating the circumferential magnetic field distribution based on a duel-end feeding system model, we reach the following conclusions: (i) the main source of magnetic field noise is the magnetic field generated by the subway trains, and (ii) the magnetic field interference results mainly from the imbalance between traction current and return rail current that is caused by the leakage current.

An improved two-dimensional unstructured CE/SE scheme for capturing shock waves

Fu Zheng,Liu Kai-Xin
Chin. Phys. B 2012, 21 (4): 040202;  doi: 10.1088/1674-1056/21/4/040202
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In this paper, the accuracy of Chang's unstructured space-time conservation element and solution element (CE/SE) scheme is analysed for the first time. Based on a redefinition of conservation elements and solution elements, an improved two-dimensional (2D) unstructured CE/SE scheme with an adjustable parameter β is proposed to accurately capture shock waves. The new scheme can be applied to any type of grid without special treatment. Compared with Chang's original parameter α, larger β dose not cost extra computational resources. Numerical tests reveal that the new scheme is not only clear in physical concept, compact and highly accurate but also more capable of capturing shock waves than the popular fifth-order accurate weighted essentially non-oscillatory scheme.

Improved atom number with a dual color magneto–optical trap

Cao Qiang,Luo Xin-Yu,Gao Kui-Yi,Wang Xiao-Rui,Chen Dong-Min,Wang Ru-Quan
Chin. Phys. B 2012, 21 (4): 043203;  doi: 10.1088/1674-1056/21/4/043203
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We demonstrate a novel dual color magneto-optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose-Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.

Spin excitations in a K0.84Fe1.99Se2 superconductor as studied by Mössbauer spectroscopy Hot!

Li Zhi-Wei,Ma Xiao-Ming,Pang Hua,Li Fa-Shen
Chin. Phys. B 2012, 21 (4): 047601;  doi: 10.1088/1674-1056/21/4/047601
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Mössbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, ΔE ≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron-selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.

Polymer nanofibers prepared by low-voltage near-field electrospinning

Zheng Jie,Long Yun-Ze,Sun Bin,Zhang Zhi-Hua,Shao Feng,Zhang Hong-Di,Zhang Zhi-Ming,Huang Jia-Yin
Chin. Phys. B 2012, 21 (4): 048102;  doi: 10.1088/1674-1056/21/4/048102
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Electrospinning is a straightforward method to produce micro/nanoscale fibers from polymer solutions typically using an operating voltage of 10 kV-30 kV and spinning distance of 10 cm-20 cm. In this paper, polyvinyl pyrrolidone (PVP) non-woven nanofibers with diameters of 200 nm-900 nm were prepared by low-voltage near-field electrospinning with a working voltage of less than 2.8 kV and a spinning distance of less than 10 mm. Besides the uniform fibers, beaded-fibers were also fabricated and the formation mechanism was discussed. Particularly, a series of experiments were carried out to explore the influence of processing variables on the formation of near-field electrospun PVP nanofibers, including concentration, humidity, collecting position, and spinning distance.

Stereodynamics of the reactions Ne+H2+ /Ne+D2+/Ne+T2

Xiao Jing,Yang Chuan-Lu,Wang Mei-Shan
Chin. Phys. B 2012, 21 (4): 043101;  doi: 10.1088/1674-1056/21/4/043101
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The vector correlations between products and reagents for the reactions Ne+H2+, Ne+D2+, and Ne+T2+ are calculated by means of the quasi-classical trajectory method on a new potential energy surface constructed by Lü et al. [J. Chem. Phys. 2010 132, 014303]. The polarization-dependent differential cross-sections (2π /σ )(dσ 00/dωt), (2π /σ )(dσ20/dωt), (2π /σ )(dσ22+ /dωt), and (2π /σ )(dσ21-/dωt), and the distributions of P(θr), P(φr), and P(θr, Pφr) are calculated. The isotoπc effect, which is associated with the difference in mass factor among the three reactions, is revealed.

Structural, electronic, and magnetic properties of boron cluster anions doped with aluminum: BnAl- (2≤n≤9)

Gu Jian-Bing,Yang Xiang-Dong,Wang Huai-Qian,Li Hui-Fang
Chin. Phys. B 2012, 21 (4): 043102;  doi: 10.1088/1674-1056/21/4/043102
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The geometrical structures, relative stabilities, electronic and magnetic properties of small BnAl- (2≤n ≤ 9) clusters are systematically investigated by using the first-principles density functional theory. The results show that the Al atom prefers to reside either on the outer-side or above the surface, but not in the centre of the clusters in all of the most stable BnAl- (2≤n ≤ 9) isomers and the one excess electron is strong enough to modify the geometries of some specific sizes of the neutral clusters. All the results of the analysis for the fragmentation energies, the second-order difference of energies, and the highest occupied-lowest unoccupied molecular orbital energy gaps show that B4Al- and B8Al- clusters each have a higher relative stability. Especially, the B8Al- cluster has the most enhanced chemical stability. Furthermore, both the local magnetic moments and the total magnetic moments display a pronounced odd-even oscillation with the number of boron atoms, and the magnetic effects arise mainly from the boron atoms except for theB7Al- and B9Al- clusters.

The analytical potential energy function of flue gas SO2(X1A1)

Wu Dong-Lan,Xie An-Dong,Yu Xiao-Guang,Wan Hui-Jun
Chin. Phys. B 2012, 21 (4): 043103;  doi: 10.1088/1674-1056/21/4/043103
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The equilibrium structure of flue gas SO2 is optimized using the density functional theory (DFT)/ B3P86 method and CC-PV5Z basis. The result shows that it has a bent (C2V, X1A1) ground state structure with an angle of 119.1184circ. The vibronic frequencies and the force constants are also calculated. Based on the principles of atomic and molecular reaction statics (AMRS), the possible electronic states and reasonable dissociation limits for the ground state of SO2 molecule are determined. The potential functions of SO and O2 are fitted by the modified Murrell-Sorbie+c6 (M-S+c6) potential function and the fitted parameters, the force constants and the spectroscopic constants are obtained, which are all close to the experimental values. The analytic potential energy function of the SO2(X1A1) molecule is derived using the many-body expansion theory. The contour lines are constructed, which show the static properties of SO2(X1A1), such as the equilibrium structure, the lowest energies, the most possible reaction channel, etc.

Photonic generation of power-efficient FCC-compliant ultra-wideband waveforms using semiconductor optical amplifier (SOA): theoretical analysis and experiment verification

Dong Jian-Ji,Luo Bo-Wen,Huang De-Xiu,Zhang Xin-Liang
Chin. Phys. B 2012, 21 (4): 043201;  doi: 10.1088/1674-1056/21/4/043201
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We theoretically design a power-efficient ultra-wideband pulse generator by combining three monocycle pulses with different weights. We also experimentally demonstrate a feasible scheme to generate such power-efficient ultra-wideband waveforms using cross-phase modulation in a single semiconductor optical amplifier. The designed ultra-wideband pulse fully satisfies the requirements for the spectral mask specified by the Federal Communications Commission with high power efficiency. In the experiment, a power-efficient ultra-wideband waveform with a pulse duration of 310 ps is achieved, and the power efficiency is greatly improved compared with that of a single monocycle pulse or a mixture of two monocycles.

Quantum calculations for photodetachment cross sections of H- in an inhomogeneous electric field

Wu Xiao-Qing,Du Meng-li,Zhao Hai-Jun
Chin. Phys. B 2012, 21 (4): 043202;  doi: 10.1088/1674-1056/21/4/043202
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We calculate the photodetachment cross sections of H- in a gradient electric field based on traditional quantum approach. The system provides a rare example that the formulas for the cross sections can be explicitly derived by both the quantum approach and closed-orbit theory. The quantum results are compared with those of the closed-orbit theory. The correct phase values in the closed-orbit theory are essential and necessary to produce accurate cross sections. Our quantum results remove some previous ambiguities in assigning the phase values in the closed-orbit theory (G. C. Yang and M. L. Du 2007 Phys. Rev. A 75 029904E).

The structural and spectroscopic properties for uranium oxides

Li Peng,Jia Ting-Ting,Gao Tao,Li Gan
Chin. Phys. B 2012, 21 (4): 043301;  doi: 10.1088/1674-1056/21/4/043301
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The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO2, UO3, and U2O3 molecules are systematically investigated using the density functional theory (DFT) with the method of generalized gradient approximation (GGA). The bond lengths and the vibrational frequencies of the ground states of UO, UO2, and UO3 molecules are all in agreement with available experimental data. For U2O3 molecules, our calculations indicate that the ground state of the U2O3 molecule is an X7A1 state with D3h (trigonal bipyramid) symmetry (R1(U-O)=0.2113 nm, R2(U1-U2)=0.2921 nm, angleU1OU2=87.5°,dihedral angle θ(U,O1,O2,O3)=62.40°). The harmonic frequency, the IR intensity and the spin density of the U2O3 molecule are all obtained for the first time in theory. For the ground state of U2O3 molecules, the vibrational frequencies are 178.46 (A1), 276.79 (E1), 310.77 (E1), 396.63 (A2), 579.15 (E1), and 614.98 (A1) cm-1. The vibrational modes corresponding to the IR maximum peaks are worked out for UO3 and U2O3 molecules. Besides, the results of Gophinatan-Jug bond order indicate that UO, UO2, and UO3 molecules possess U=O double bonds and that the U2O3 molecule possesses U-O single bonds and a U-U single bond.

Spectroscopic properties in Er Er3+/Yb3+Co-doped fluorophosphate glass

Zheng Tao,Qin Jie-Ming,Jiang Da-Yong,L&#; Jing-Wen,Xiao Sheng-Chun
Chin. Phys. B 2012, 21 (4): 043302;  doi: 10.1088/1674-1056/21/4/043302
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Using the technique of high-temperature melting, a new Er3+/Yb3+ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er3+ and Yb3+ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd-Ofelt theory, the oscillator strength was computed. The lifetime of 4I13/2 level (τm) of Er3+ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 τm. The large stimulated emission cross section of the Er3+ was calculated by the McCumber theory. The spectroscopic properties of Er3+ ion were compared with those in different glasses. The full width at half maximum and σe are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.

Photodetachment of negative ion in a gradient electric field near a metal surface

Liu Tian-Qi,Wang De-Hua,Han Cai,Liu Jiang,Liang Dong-Qi,Xie Si-Cheng
Chin. Phys. B 2012, 21 (4): 043401;  doi: 10.1088/1674-1056/21/4/043401
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Based on closed-orbit theory, the photodetachment of H- in a gradient electric field near a metal surface is studied. It is demonstrated that the gradient electric field has a significant influence on the photodetachment of negative ions near a metal surface. With the increase of the gradient of the electric field, the oscillation in the photodetachment cross section becomes strengthened. Besides, in contrast to the photodetachment of H- near a metal surface in a uniform electric field, the oscillating amplitude and the oscillating region in the cross section of a gradient electric field also become enlarged. Therefore, we can use the gradient electric field to control the photodetachment of negative ions near a metal surface. We hope that our results will be useful for understanding the photodetachment of negative ions in the vicinity of surfaces, cavities, and ion traps.

Vibrational relaxation dynamics in transient grating spectroscopy studied by rate equations based on time-dependent correlation function

Yu Guo-Yang,Song Yun-Fei,He Xing,Zheng Xian-Xu,Tan Duo-Wang,Chen Jun,Yang Yan-Qiang
Chin. Phys. B 2012, 21 (4): 043402;  doi: 10.1088/1674-1056/21/4/043402
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A modified model, a set of rate equations based on time-dependent correlation function, is used to study vibrational relaxation dynamics in transient grating spectroscopy. The dephasing, the population dynamics, and the vibrational coherence concerning two vibrational states are observed respectively in organic dye IR780 perchlorate molecules doped polyvinyl alcohol matrix. The result shows that in addition to the information concerning system-environment interaction and vibrational coherence, the vibrational energy transfer can be described by this modified model.

10BaF2:NaF, Na3AlF6/TiO2 composite as a novel visible-light-driven photocatalyst based on upconversion emission

Liu En-Zhou,Fan Jun,Hu Xiao-Yun,Hou Wen-Qian,Dai Hong-Zhe
Chin. Phys. B 2012, 21 (4): 043403;  doi: 10.1088/1674-1056/21/4/043403
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A rare-earth free upconversion luminescent material, 10BaF2:NaF, Na3AlF6/TiO2, is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light (550 nm-610 nm) into ultraviolet light (290 nm-350 nm), and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF2:NaF, Na3AlF6/TiO2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO2 under visible light irradiation (λ>515nm). The results show that 10BaF2:NaF, Na3AlF6/TiO2 is a more effective photocatalyst for CO2 reduction than pure TiO2, their corresponding methanol yields are 179 and 0 upmumol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO2 on 10BaF2:NaF, Na3AlF6/TiO2 is proposed.

High sensitive detection of high-order partial wave scattering in photoassociation of ultralcold atoms

Li Yu-Qing,Ma Jie,Wu Ji-Zhou,Zhang Yi-Chi,Zhao Yan-Ting,Wang Li-Rong,Xiao Lian-Tuan,Jia Suo-Tang
Chin. Phys. B 2012, 21 (4): 043404;  doi: 10.1088/1674-1056/21/4/043404
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We report on the observation of enhanced high-order partial wave scattering from atom-atom interaction via changing the temperature of a magneto-optical trap in the process of photoassociation. The high-order scattering partial wave is directly manifested through the large signal amplitude of the rovibrational resonance levels of trap-loss spectroscopy from photoassociation.

A comparative study on geometries, stabilities, and electronic properties between bimetallic AgnX (X=Au, Cu; n=1-8) and pure silver clusters

Ding Li-Ping,Kuang Xiao-Yu,Shao Peng,Zhao Ya-Ru,Li Yan-Fang
Chin. Phys. B 2012, 21 (4): 043601;  doi: 10.1088/1674-1056/21/4/043601
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Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geometric structures, the relative stabilities, and the electronic properties of bimetallic AgnX (X=Au, Cu; n=1-8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n=6 for the Ag_nAu clusters, and at n=5 for AgnCu clusters. For different-sized AgnX clusters, one X (X=Au or Cu) atom substituted Agn + 1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps show interesting odd-even oscillation behaviours, indicating that Ag2, 4, 6, 8 and Ag1, 3, 5, 7X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Ag_n host to the impurity atom except for the Ag2Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd-even oscillations are found for the VIP and η of the AgnX (X=Au, Cu; n=1-8) clusters.

Three-dimensional surface current loops in broadband responsive negative refractive metamaterial with isotropy

He Xun-Jun,Wang Yue,Mei Jin-Shuo,Gui Tai-Long,Yin Jing-Hua
Chin. Phys. B 2012, 21 (4): 044101;  doi: 10.1088/1674-1056/21/4/044101
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We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.

Simplified triangular ground plane cloak by oblique multilayer dielectrics

Wang Shen-Yun,Liu Shao-Bin
Chin. Phys. B 2012, 21 (4): 044102;  doi: 10.1088/1674-1056/21/4/044102
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Based on the effective medium theory, the triangular ground plane cloak can be realized by thin layered systems. Two solutions of parameter setting of the layered cloak are suggested to demonstrate the invisibility performance of a hybrid incoming wave. The hybrid parameters are derived from the equivalent of both anisotropies of permittivity and permeability to the alternating layers. The performance of the designed layered cloak is validated by both TM and TE wave simulations with near-field distributions and average scattering power outflows on an observation semicircle. From the simulation results, the layered cloak with both hybrid parameters and improved hybrid parameters can reflect the incoming TM/TE waves in a specular direction, and the latter behaves with a better overall invisibility performance.

Cutting of nonmetallic materials using Nd:YAG laser beam

Bashir Ahmed Tahir,Rashid Ahmed,M. G. B. Ashiq,Afaq Ahmed,M. A. Saeed
Chin. Phys. B 2012, 21 (4): 044201;  doi: 10.1088/1674-1056/21/4/044201
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This study deals with Nd:YAG laser cutting nonmetallic materials, which is one of the most important and popular industrial applications of laser. The main theme is to evaluate the effects of Nd:YAG laser beam power besides work piece scanning speed. For approximate cutting depth, a theoretical study is conducted in terms of material property and cutting speed. Results show a nonlinear relation between the cutting depth and input energy. There is no significant effect of speed on cutting depth with the speed being larger than 30 mm/s. An extra energy is utilized in the deep cutting. It is inferred that as the laser power increases, cutting depth increases. The experimental outcomes are in good agreement with theoretical results. This analysis will provide a guideline for laser-based industry to select a suitable laser for cutting, scribing, trimming, engraving, and marking nonmetallic materials.

Nonlinear performances of dual-pump amplifiers in silicon waveguides

Meng Fan,Yu Chong-Xiu,Deng Yun-Yi,Yuan Jin-Hui
Chin. Phys. B 2012, 21 (4): 044202;  doi: 10.1088/1674-1056/21/4/044202
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The performances of a dual-pump parametric and Raman amplification process and the wavelength conversion in silicon waveguides are investigated. By setting the Raman contribution fraction f to be 0.043 in our analytical model, the amplification gain of the probe signal can be obtained to be over 10 dB. The pump transfer noise (PTN), the quantum noise (QN), and the total noise figure (TNF) are discussed, and the TNF has a constant value of about 4 dB in the gain bandwidth. An idler signal generated during the parametric amplification (PA) process can be used to realize the wavelength conversion in wavelength division multiplexing (WDM) systems. In addition, the pump signal parameters, the generated free carrier lifetime and effective mode area (EMA) of the waveguide are analysed for the optimization of signal gain and noise characteristics.

The two-mode quantum Fresnel operator and the multiplication rule of 2D Collins diffraction formula

Xie Chuan-Mei,Fan Hong-Yi
Chin. Phys. B 2012, 21 (4): 044203;  doi: 10.1088/1674-1056/21/4/044203
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By using the two-mode Fresnel operator we derive a multiplication rule of two-dimensional (2D) Collins diffraction formula, the inverse of 2D Collins diffraction integration can also be conveniently derived in this way in the context of quantum optics theory.

Over exposed image information recovery via stochastic resonance

Yang Yi-Bing,Tao Wei-Ming,Huang Jia-Min,Xu Bo-Hou
Chin. Phys. B 2012, 21 (4): 044204;  doi: 10.1088/1674-1056/21/4/044204
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Over exposure is rather annoying in photo taking. However, in some severe light conditions over exposure is inevitable using conventional cameras due to the limitation of dynamic range of the image sensor. The over exposed information would be completely lost and unrecoverable. In order to cope with this problem, we propose a novel technique in which the noise is used to enlarge the dynamic range of the image sensor. The essential mechanism that noise contributes to the information recovery is investigated. It is also proved that the visibility of regained information can reach the peak when specifically added noise is synchronized with the image sensor, thus activating the phenomenon of stochastic resonance (SR). Four different types of noises are investigated to show the effects of variant distributions on the quality of recovered information. The experimental outcomes are consistent with our theoretical results, which indicates that the SR-based lost information recovery is quite promising.

Generating a four-photon polarization-entangled cluster state with homodyne measurement via cross-Kerr nonlinearity

Su Shi-Lei,Wang Yuan,Guo Qi,Wang Hong-Fu,Zhang Shou
Chin. Phys. B 2012, 21 (4): 044205;  doi: 10.1088/1674-1056/21/4/044205
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We propose a protocol to generate a four-photon polarization-entangled cluster state with cross-Kerr nonlinearity by using the interference of polarized photons. The protocol is based on optical elements, cross-Kerr nonlinearity, and homodyne measurement, therefore it is feasible with current experimental technology. The success probability of our protocol is optimal, this property makes our protocol more efficient than others in the applications of quantum communication.

Noise analysis in ghost imaging from the perspective of coherent-mode representation

Bai Yan-Feng,Yang Wen-Xing,Yu Xiao-Qiang
Chin. Phys. B 2012, 21 (4): 044206;  doi: 10.1088/1674-1056/21/4/044206
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First we present a theoretical analysis of classical noise in ghost imaging system based on the coherent-mode representation theory. The classical noise depends crucially on the distribution of the eigenvalues of the coherent-mode representation of the source and the decomposition coefficients of the object imaged. We show that both decreasing the distribution of the decomposition coefficients and increasing the distribution of the eigenvalues can lead to the decrease of classical noise.

Geometric phases in qubit-oscillator system beyond conventional rotating-wave approximation

Wang Yue-Ming,Du Guan,Liang Jiu-Qing
Chin. Phys. B 2012, 21 (4): 044207;  doi: 10.1088/1674-1056/21/4/044207
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In this work we investigated the geometric phases of a qubit-oscillator system beyond the conventional rotating-wave approximation. We find that in the limiting of weak coupling the results coincide with that obtained under rotating-wave approximation while there exists an increasing difference with the increase of coupling constant. It was shown that the geometric phase is symmetric with respect to the sign of the detuning of the quantized field from the one-photon resonance under the conventional rotating-wave approximation while a red-blue detuning asymmetry occurs beyond the conventional rotating-wave approximation.

The mechanism of producing energy-polarization entangled photon pairs in the cavity-quantum electrodynamics scheme

Shu Chang-Gan,Xin Xia,Liu Yu-Min,Yu Zhong-Yuan,Yao Wen-Jie,Wang Dong-Lin,Cao Gui
Chin. Phys. B 2012, 21 (4): 044208;  doi: 10.1088/1674-1056/21/4/044208
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We investigate theoretically two photon entanglement processes in a photonic-crystal cavity embedding a quantum dot in the strong-coupling regime. The model proposed by Johne et al. (Johne R, Gippius N A, Pavlovic G, Solnyshkov D D, Shelykh I A and Malpuech G 2008 Phys. Rev. Lett. 100 240404), and by Robert et al. (Robert J, Gippius N A and Malpuech G 2009 it Phys. Rev. B 79 155317) is modified by considering irreversible dissipation and incoherent continuous pumping for the quantum dot, which is necessary to connect the realistic experiment. The dynamics of the system is analysed by employing the Born-Markov master equation, through which the spectra for the system are computed as a function of various parameters. By means of this analysis the photon-reabsorption process in the strong-coupling regime is first observed and analysed from the perspective of radiation spectrum and the optimal parameters for observing energy-entangled photon pairs are identified.

A simple scheme to generate χ-type four-charge entangled states in circuit QED

Gao Gui-Long,Song Fu-Quan,Huang Shou-Sheng,Wang Hui,Yuan Xian-Zhang,Wang Ming-Feng,Jiang Nian-Quan
Chin. Phys. B 2012, 21 (4): 044209;  doi: 10.1088/1674-1056/21/4/044209
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We propose a simple scheme to generate χ-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator (TLR). The coupling between the superconducting qubit and the TLR can be effectively controlled by properly adjusting the control parameters of the charge qubit. The experimental feasibility of our scheme is also shown.

Nonclassicality of a two-variable Hermite polynomial state

Tan Guo-Bin,Xu Li-Juan,Ma Shan-Jun
Chin. Phys. B 2012, 21 (4): 044210;  doi: 10.1088/1674-1056/21/4/044210
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The nonclassicality of the two-variable Hermite polynomial state is investigated. It is found that the two-variable Hermite polynomial state can be considered as a two-mode photon subtracted squeezed vacuum state. A compact expression for the Wigner function is also derived analytically by using the Weyl-ordered operator invariance under similar transformations. Especially, the nonclassicality is discussed in terms of the negativity of the Wigner function. Then violations of Bell's inequality for the two-variable Hermite polynomial state are studied.

Medium performance effect on the high output energy from a xenon lamp-pumped pyrromethene-567 solid-state dye laser

Wang Lei,Chen De-Ying,Fan Rong-Wei,He Wei-Ming
Chin. Phys. B 2012, 21 (4): 044211;  doi: 10.1088/1674-1056/21/4/044211
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In order to obtain a high output energy from a xenon lamp-pumped solid-state dye laser, homogeneities of laser mediums and flatnesses of medium faces with different processing treatments are discussed in the paper. The mediums without aging treatment, which are prepared by using a prepolymer process and have diamond-machined end faces to produce the required optical finish, give a highest laser output of 281.9 mJ with 0.215% slope efficiency at 2.0?10-4 mol/L. The best medium lifetime is 21 shots to 50% of original output equating 74.6 kJ/liter.

Incident laser modulation of a repaired damage site with a rim in fused silica rear subsurface

Li Li,Xiang Xia,Zu Xiao-Tao,Yuan Xiao-Dong,He Shao-Bo,Jiang Xiao-Dong,Zheng Wan-Guo
Chin. Phys. B 2012, 21 (4): 044212;  doi: 10.1088/1674-1056/21/4/044212
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Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of optics in high fluence laser systems. However, the CO2 laser induced ablation crater is often surrounded by a raised rim at the edge, which can also result in the intensification of transmitted ultraviolet light that may damage the downstream optics. In this work, the three-dimensional finite-difference time-domain method is developed to simulate the distribution of electrical field intensity in the vicinity of the CO2 laser mitigated damage site located in the exit subsurface of fused silica. The simulated results show that the repaired damage sites with raised rims cause more notable modulation to the incident laser than those without rims. Specifically, we present a theoretical model of using dimpled patterning to control the rim structure around the edge of repaired damage sites to avoid damage to downstream optics. The calculated results accord well with previous experimental results and the underlying physical mechanism is analysed in detail.

Low group velocity in a photonic crystal coupled-cavity waveguide

Zhang Chang-Xin,Xu Xing-Sheng
Chin. Phys. B 2012, 21 (4): 044213;  doi: 10.1088/1674-1056/21/4/044213
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A two-dimensional photonic crystal coupled-cavity waveguide is designed and optimized, the transmission spectrum is calculated by using the finite-difference time-domain method, and the group velocity of c/1856 is obtained. To our knowledge, this value of group velocity is the lowest group velocity in a photonic crystal waveguide calculated from its transmission spectrum so far. The result is confirmed by the photonic band structure calculated by using the plane wave expansion method, and it is found that the photonic crystal waveguide modes in a photonic band structure are in accordance with those in the transmission spectrum by using the finite-difference time-domain method. The mechanism of slow light in the coupled-cavity waveguide of photonic crystal is analysed.

Tortuosity for streamlines in porous media

Kou Jian-Long,Tang Xue-Ming,Zhang Hai-Yan,Lu Hang-Jun,Wu Feng-Min,Xu You-Sheng,Dong Yong-Sheng
Chin. Phys. B 2012, 21 (4): 044701;  doi: 10.1088/1674-1056/21/4/044701
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An analysis of tortuosity for streamlines in porous media is presented by coupling the circle and square models. It is assumed that some particles in porous media do not overlap and that fluid in porous media is incompressible. The relationship between tortuosity and porosity is attained with different configurations by using a statistical method. In addition, the tortuosity fractal dimension is expressed as a function of porosity. Those correlations do not include any empirical constant. The percolation threshold and tortuosity fractal dimension threshold of porous media are also presented as: φc=0.32, DTc=1.07. The predicted correlations of the tortuosity and the porosity agree well with the existing experimental and simulated results.

Transport properties of a binary mixture of CO2–N2 from the pair potential energy functions based on a semi-empirical inversion method

Song Bo,Wang Xiao-Po,Yang Fu-Xin,Liu Zhi-Gang
Chin. Phys. B 2012, 21 (4): 045101;  doi: 10.1088/1674-1056/21/4/045101
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The potential energy surface of a CO2-N2 mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. Ref. Data 19 1179 (1990)]. With the new invert potential, the transport properties of CO2-N2 mixture are presented in a temperature range from 273.15 K to 3273.15 K at low density by employing the Chapman-Enskog scheme and the Wang Chang-Uhlenbeck-de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient.

Equation of state for pure fluids at critical temperature

S. B. Khasare
Chin. Phys. B 2012, 21 (4): 045102;  doi: 10.1088/1674-1056/21/4/045102
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In this paper, we employ the concept of probability for creating a cavity with diameter d in fluid along with the perturbation and variation approach, and develop an equation of state (EOS) for a hard sphere (HS) and Lennard-Jones (LJ) fluids. A suitable axiomatic form for surface tension S(r) is assumed for the pure fluid, with r as a variable. The function S(r) has an arbitrary parameter m. S(r)=A+B(d/r)/[1+m(d/r)]. We use the condition in terms of radial distribution function G(λ d, η) containing the self-consistent parameter λ and the condition of continuity at r=d/2 to determine A and B. A different EOS can be obtained with a suitable choice of m and the EOS has a lower root-mean-square deviation than that of Barker-Henderson BH2 for LJ fluids.

Perturbation and variational approach for the equation of state for hard-sphere and Lennard–Jones fluids

Chin. Phys. B 2012, 21 (4): 045103;  doi: 10.1088/1674-1056/21/4/045103
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The present work uses the concept of a scaled particle along with the perturbation and variation approach, to develop an equation of state (EOS) for a mixture of hard sphere (HS), Lennard-Jones (LJ) fluids. A suitable flexible functional form for the radial distribution function G(R) is assumed for the mixture, with R as a variable. The function G(R) has an arbitrary parameter m and a different equation of state can be obtained with a suitable choice of m. For m= 0.75 and m= 0.83 results are close to molecular dynamics (MD) result for pure HS and LJ fluid respectively.

The effects of relativistic broadening and frequency down-shift on electron–cyclotron emission measurements in EAST

Liu Yong,Han Xiang,Ti Ang,Wang Yu-Min,Ling Bi-Li,Hu Li-Qun,Gao Xiang
Chin. Phys. B 2012, 21 (4): 045201;  doi: 10.1088/1674-1056/21/4/045201
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This paper presents a theoretical calculation of the effects of relativistic broadening and frequency down-shift on the electron cyclotron emission measurements for a wide range of plasma parameters in the Experimental Advanced Superconducting Tokamak (EAST). The calculation is based on the radiation transfer equation, with the reabsorption and reemission processes taken into account. The broadening effect contributes to the radial resolution of the measurement, and the calculation results indicate that it is ~2 cm in the case of the central electron temperature 10 keV. A pseudo radial displacement of the obtained electron temperature profile occurs if the relativistic frequency down-shift effect is not taken into account in the determination of the emission layer position. The shift could be a few centimeters as the electron temperature increases, and this effect should be taken into account.

Experimental investigation of nanosecond discharge plasma aerodynamic actuation

Wu Yun,Li Ying-Hong,Jia Min,Liang Hua,Song Hui-Min
Chin. Phys. B 2012, 21 (4): 045202;  doi: 10.1088/1674-1056/21/4/045202
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In this paper we report on an experimental study of the characteristics of nanosecond pulsed discharge plasma aerodynamic actuation. The N2 (C3u) rotational and vibrational temperatures are around 430 K and 0.24 eV, respectively. The emission intensity ratio between the first negative system and the second positive system of N2, as a rough indicator of the temporally and spatially averaged electron energy, has a minor dependence on applied voltage amplitude. The induced flow direction is not parallel, but vertical to the dielectric layer surface, as shown by measurements of body force, velocity, and vorticity. Nanosecond discharge plasma aerodynamic actuation is effective in airfoil flow separation control at freestream speeds up to 100 m/s.

Self-consistent diverted tokamak equilibria with nonzero edge current

Shi Bing-Ren
Chin. Phys. B 2012, 21 (4): 045203;  doi: 10.1088/1674-1056/21/4/045203
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The semi-analytical method, previously used to construct model double-null and single-null diverted tokamak equilibria (Bingren Shi, Plasma Phys. Control Fusion/ 50 (2008) 085006, 51 (2009) 105008, Nucl. Fusion/ 51 (2011) 023004), is extended to describe diverted tokamak equilibria with nonzero edge current, including the Pfirsch-Schlüter(PS) current. The PS current density is expressed in a way suitable to describe a diverted tokamak configuration in the near separatrix region. The model equilibrium is expressed by only two terms of the exact separable solutions of the Grad-Shafranov equation, one of which is governed by a homogeneous ordinary differential equation, and the other by an inhomogeneous one. The particular merits of such a model configuration are that the internal region inside the separatrix and a suitable scrape-off layer can be simultaneously described by this exact solution. To investigate the physics in the region near the X-point, the magnetic surfaces can be satisfactorily described by approximate hyperbolic curves.

Aspects of the upstream region in a plasma jet with dielectric barrier discharge configurations

Li Xue-Chen,Jia Peng-Ying,Yuan-Ning,Chang Yuan-Yuan
Chin. Phys. B 2012, 21 (4): 045204;  doi: 10.1088/1674-1056/21/4/045204
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A plasma column with a length of about 65 cm is generated in the upstream region of a plasma jet using dielectric barrier discharge configurations. The effects of experimental parameters such as the amplitude of the applied voltage and the driving frequency are investigated in aspects of the plasma column by the optical method. Results show that both the plasma length and the propagating velocity, as well as the discharge current, increase with the increase in the applied voltage or its frequency. The discharge mechanism is analysed qualitatively based on streamer theory, where photo-ionization is important. Furthermore, optical emission spectroscopy is used to investigate the electric field intensity of the upstream region.

The interplay between the lattice and magnetism in La(Fe11.4Al1.6)C0.02 studied by powder neutron diffraction

Wang Zhi-Cui,He Lun-Hua,Wang Hai,Liu Rong-Deng,Wang Fang-Wei
Chin. Phys. B 2012, 21 (4): 046101;  doi: 10.1088/1674-1056/21/4/046101
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The crystallographic structure and magnetic properties of La(Fe11.4Al1.6)C0.02 are studied by magnetic measurement and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La(Fe11.4Al1.6)C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites: FeI (8b) and FeII (96i), and that Al atoms preferentially occupy the FeII site. A ferromagnetic state can be induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La(Fe11.4Al1.6)C0.02 has no net magnetization in the paramagnetic (T>TN=182 K) or antiferromagnetic states, and thus keeps its small lattice. Analysis of the Fe-Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.

Hcp-icosahedron structural transformation induced by the change in Ag concentration during the freezing of (CoAg)561 clusters

Xiao Xu-Yang
Chin. Phys. B 2012, 21 (4): 046102;  doi: 10.1088/1674-1056/21/4/046102
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The synergy effect of alloy elements in bimetallic clusters can be used to tune the chemical and physical properties. Research on the influences of alloy concentration and distribution on the frozen structure of bimetallic clusters plays a key role in exploring new structural materials. In this paper, we study the influence of Ag concentration on the frozen structure of the (AgCo)561 cluster by using molecular dynamics simulation with a general embedded atom method. The results indicate that the structure and chemical ordering of the (AgCo)561 cluster are strongly related to Ag concentration. Hcp-icosahedron structural transformation in the frozen (CoAg)561 cluster can be induced by changing Ag concentration. The chemical ordering also transforms to Janus-like Co-Ag from core-shell Co-Ag.

Surface segregation of InGaAs films by the evolution of reflection high-energy electron diffraction patterns

Zhou Xun,Luo Zi-Jiang,Guo Xiang,Zhang Bi-Chan,Shang Lin-Tao,Zhou Qing,Deng Chao-Yong,Ding Zhao
Chin. Phys. B 2012, 21 (4): 046103;  doi: 10.1088/1674-1056/21/4/046103
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Surface segregation is studied via the evolution of reflection high-energy electron diffraction (RHEED) patterns under different values of As4 BEP for InGaAs films. When the As4 BEP is set to be zero, the RHEED pattern keeps a 4×3/(n×3) structure with increasing temperature, and surface segregation takes place until 470 ℃. The RHEED pattern develops into a metal-rich (4×2) structure as temperature increases to 495 ℃. The reason for this is that surface segregation makes the In inside the InGaAs film climb to its surface. With the temperature increasing up to 515 ℃, the RHEED pattern turns into a GaAs(2×4) structure due to In desorption. While the As4 BEP comes up to a specific value (1.33×10-4 Pa-1.33×10-3 Pa), the surface temperature can delay the segregation and desorption. We find that As4 BEP has a big influence on surface desorption, while surface segregation is more strongly dependent on temperature than surface desorption.

The phase transition, hygroscopicity, and thermal expansion properties of Yb2-xAlxMo3O12

Li Qiu-Jie,Yuan Bao-He,Song Wen-Bo,Liang Er-Jun,Yuan Bin
Chin. Phys. B 2012, 21 (4): 046501;  doi: 10.1088/1674-1056/21/4/046501
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Materials with the formula Yb2-xAlxMo3O12 (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8) were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffraction, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3O12 solid solutions crystallize in a single monoclinic phase for 1.7≤ x≤ 2.0 and in a single orthorhombic phase for 0.0le xle 0.4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhombic phase transition temperature of Al2Mo3O12 can be reduced by partial substitution of Al3+ by Yb3+, and the Yb2-xAlxMo3O12 (0.0< x≤ 2.0) materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of Al3+ for Yb3+ in Yb2Mo3O12 decreases its hygroscopicity, and the linear thermal expansion coefficients after complete removal of water species are measured to be -9.1× 10-6/K, -5.5× 10-6/K, 5.74× 10-6/K, and -9.5× 10-6/K for Yb1.8Al0.2(MoO4)3, Yb1.6Al0.4(MoO4)3, Yb0.4Al1.6(MoO4)3, and Yb0.2Al1.8(MoO4)3, respectively.

Temperature dependence of the thickness and morphology of epitaxial graphene grown on SiC (0001) wafers

Hao Xin,Chen Yuan-Fu,Li Ping-Jian,Wang Ze-Gao,Liu Jing-Bo,He Jia-Rui,Fan Rui,Sun Ji-Rong,Zhang Wan-Li,Li Yan-Rong
Chin. Phys. B 2012, 21 (4): 046801;  doi: 10.1088/1674-1056/21/4/046801
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Epitaxial graphene is synthesized by silicon sublimation from the Si-terminated 6H-SiC substrate. The effects of graphitization temperature on the thickness and surface morphology of epitaxial graphene are investigated. X-ray photoelectron spectroscopy spectra and atomic force microscopy images reveal that the epitaxial graphene thickness increases and the epitaxial graphene roughness decreases with the increase in graphitization temperature. This means that the thickness and roughness of epitaxial graphene films can be modulated by varying the graphitization temperature. In addition, the electrical properties of epitaxial graphene film are also investigated by Hall effect measurement.

The stabilities, electronic structures and elastic properties of Rb–As systems

Havva Bogaz Ozisik,Kemal Colakoglu,Engin Deligoz,Haci Ozisik
Chin. Phys. B 2012, 21 (4): 047101;  doi: 10.1088/1674-1056/21/4/047101
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The structural, electronic and elastic properties of Rb-As systems (RbAs in NaP, LiAs and AuCu structures, RbAs2 in the MgCu2 structure, Rb3As in Na3As, Cu3P and Li3Bi structures, and Rb5As4 in the A5B4 structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghan's equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young's modulus, the shear modulus, Poisson's ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.

Oxygen vacancy formation and migration in Sr- and Mg-doped LaGaO3: a density functional theory study

Zhang Jie,Liang Er-Jun,Sun Qiang,Jia Yu
Chin. Phys. B 2012, 21 (4): 047201;  doi: 10.1088/1674-1056/21/4/047201
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Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O0.3-δ (LSGM) with various crystal symmetries (cubic, rhombohedral, orthorhombic, and monoclinic) are studied by employing first-principles calculations based on density functional theory (DFT). It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In our calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O1 and O2 oxygen sites. The migration energies along the migration pathway linking the two O2 sites are obviously lower than those along the pathway linking the O1 and O2 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications.

The electrical properties of sulfur-implanted cubic boron nitride thin films

Deng Jin-Xiang,Qin Yang,Kong Le,Yang Xue-Liang,Li Ting,Zhao Wei-Ping,Yang Ping
Chin. Phys. B 2012, 21 (4): 047202;  doi: 10.1088/1674-1056/21/4/047202
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Cubic boron nitride (c-BN) thin films are deposited on p-type Si wafers using radio frequency (RF) sputtering and then doped by implanting S ions. The implantation energy of the ions is 19 keV, and the implantation dose is between 1015 ions/cm2 and 1016 ions/cm2. The doped c-BN thin films are then annealed at a temperature between 400 ℃ and 800 ℃. The results show that the surface resistivity of doped and annealed c-BN thin films is lowered by two to three orders, and the activation energy of c-BN thin films is 0.18 eV.

Charge transport and shot noise on the surface of a topological insulator with a magnetic modulation

Yuan Jian-Hui,Cheng Ze,Zhang Jian-Jun,Zeng Qi-Jun,Zhang Jun-Pei
Chin. Phys. B 2012, 21 (4): 047203;  doi: 10.1088/1674-1056/21/4/047203
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In this paper, we investigate the transport features and the Fano factor of Dirac electrons on the surface of a three-dimensional topological insulator with a magnetic modulation. We consider a hard wall bounding condition on the edge of the topological insulator, which implies that a surface state of the topological insulator is insulating. We find that a valley of conductivity at the Dirac point is associated with a Fano factor peak, and more interestingly, this topological metal changes from insulating to metallic by controlling the effective exchange field.

Homogeneous interface-type resistance switching in Au/La0.67Ca0.33MnO3/SrTiO3/F:SnO2 heterojunction memories

Zhang Ting,Ding Ling-Hong,Zhang Wei-Feng
Chin. Phys. B 2012, 21 (4): 047301;  doi: 10.1088/1674-1056/21/4/047301
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La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunctions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field-induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3?104% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.

The influence of interfacial barrier engineering on the resistance switching of In2O3:SnO2/TiO2/In2O3:SnO2 device

Liu Zi-Yu,Zhang Pei-Jian,Meng Yang,Li Dong,Meng Qing-Yu,Li Jian-Qi,Zhao Hong-Wu
Chin. Phys. B 2012, 21 (4): 047302;  doi: 10.1088/1674-1056/21/4/047302
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The I-V characteristics of In2O3:SnO2/TiO2/In2O3:SnO2 junctions with different interfacial barriers are investigated by comparing experiments. A two-step resistance switching process is found for samples with two interfacial barriers produced by specific thermal treatment on the interfaces. The nonsynchronous occurrence of conducting filament formation through the oxide bulk and the reduction in the interfacial barrier due to the migration of oxygen vacancies under the electric field is supposed to explain the two-step resistive switching process. The unique switching properties of the device, based on interfacial barrier engineering, could be exploited for novel applications in nonvolatile memory devices.

A unified charge-based model for SOI MOSFETs applicable from intrinsic to heavily doped channel

Zhang Jian,He Jin,Zhou Xing-Ye,Zhang Li-Ning,Ma Yu-Tao,Chen Qin,Zhang Xu-Kai,Yang Zhang,Wang Rui-Fei,HanYu,Chan Mansun
Chin. Phys. B 2012, 21 (4): 047303;  doi: 10.1088/1674-1056/21/4/047303
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A unified charge-based model for fully depleted silicon-on-insulator (SOI) metal-oxide semiconductor field-effect transistors (MOSFETs) is presented. The proposed model is accurate and applicable from intrinsic to heavily doped channels with various structure parameters. The framework starts from the one-dimensional Poisson-Boltzmann equation, and based on the full depletion approximation, an accurate inversion charge density equation is obtained. With the inversion charge density solution, the unified drain current expression is derived, and a unified terminal charge and intrinsic capacitance model is also derived in the quasi-static case. The validity and accuracy of the presented analytic model is proved by numerical simulations.

The effect of a non-aligned unit on double-screen frequency-selective surface transmission characteristics

Wang Jian-Bo,Lu Jun,Sun Guan-Cheng,Chen Xin-Yi,Chen Gui-Bo
Chin. Phys. B 2012, 21 (4): 047304;  doi: 10.1088/1674-1056/21/4/047304
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Double-screen frequency-selective surfaces (FSSs) can bring about a better flattened effect and a rapidly declining edge. They are therefore an effective means to achieve outer-zone stealth of the radar cabin to detect radar waves. In this article, a double-screen wide-bandpass FSS structure is designed and the transmission characteristics of the units under alignment and non-alignment are simulated by means of the spectral domain approach. Meanwhile, the experimental parts fabricated by vacuum evaporation and lithography are tested in a microwave chamber. The results show that the aligned unit structure has good incident angle stability and can achieve high transmittance when the bandwidth is 3.3 GHz, and the transmission loss is less than -1 dB. When the units have a non-aligned structure, the bandwidth decreases and transmission loss increases with increasing incident angle.

The effects of post-thermal annealing on the optical parameters of indium-doped ZnO thin films

Peng Li-Ping,Fang Liang,Wu Wei-Dong,Wang Xue-Min,Li Li
Chin. Phys. B 2012, 21 (4): 047305;  doi: 10.1088/1674-1056/21/4/047305
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Indium-doped ZnO thin films are deposited on quartz glass slides by RF magnetron sputtering at ambient temperature. The as-deposited films are annealed at different temperatures from 400 ℃ to 800 ℃ in air for 1 h. Transmittance spectra are used to determine the optical parameters and the thicknesses of the films before and after annealing using a nonlinear programming method, and the effects of the annealing temperatures on the optical parameters and the thickness are investigated. The optical band gap is determined from the absorption coefficient. The calculated results show that the film thickness and optical parameters both increase first and then decrease with increasing annealing temperature from 400 ℃ to 800 ℃. The band gap of the as-deposited ZnO:In thin film is 3.28 eV, and it decreases to 3.17 eV after annealing at 400 ℃. Then the band gap increases from 3.17 eV to 3.23 eV with increasing annealing temperature from 400 ℃ to 800 ℃.

Conductance of metallic nanoribbons with defects

Deng Shi-Xian,Liang Shi-Dong
Chin. Phys. B 2012, 21 (4): 047306;  doi: 10.1088/1674-1056/21/4/047306
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The conductances of two typical metallic graphene nanoribbons with one and two defects are studied using the tight binding model with the surface Green's function method. The weak scattering impurities, U~1> eV, induce a dip in the conductance near the Fermi energy for the narrow zigzag graphene nanoribbons. As the impurity scattering strength increases, the conductance behavior at the Fermi energy becomes more complicated and depends on the impurity location, the AA and AB sites. The impurity effect then becomes weak and vanishes with the increase in the width of the zigzag graphene nanoribbons (150 nm). For the narrow armchair graphene nanoribbons, the conductance at the Fermi energy is suppressed by the impurities and becomes zero with the increase in impurity scattering strength, U >100 eV, for two impurities at the AA sites, but becomes constant for the two impurities at the AB sites. As the width of the graphene nanoribbons increases, the impurity effect on the conductance at the Fermi energy depends sensitively on the vacancy location at the AA or AB sites.

Preparation and the physical properties of antiperovskite-type compounds Cd1-xInxNNi3 (0≤x≤0.2) and Cd1-yCuyNNi3 (0≤y≤0.2)

He Bing,Dong Cheng,Yang Li-Hong,Ge Lin-Hui,Mu Li-Bin,Chen Xiao-Chao
Chin. Phys. B 2012, 21 (4): 047401;  doi: 10.1088/1674-1056/21/4/047401
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Two series of Cd1-xInxNNi3 (0≤x≤0.2) and Cd1-yCuyNNi3 (0≤y≤0.2) samples were prepared from CdO, In2O3, CuO, and nickel powders under NH3 atmosphere at 773 K. The structural and physical properties were investigated by means of X-ray powder diffraction temperature-dependent resistivity and magnetic measurements. X-ray powder diffraction results showed that the Cd1-xInxNNi3 and Cd1-yCuyNNi3 compounds have a typical antiperovskite structure, and the CdNNi3, Cd0.9In0.1NNi3, and Cd0.9Cu0.1NNi3 compounds show metallic temperature-dependent resistivity and exhibit a Fermi liquid behavior at low temperature. In contrast to the paramagnetism previously reported, the CdNNi3 sample exhibits very soft and weak ferromagnetism, and no superconductivity was found in the Cd1-xInxNNi3 and Cd1-yCuyNNi3 samples down to 2 K. Each sample exhibited very soft and weak ferromagnetism, and the temperature dependence of the magnetization of the Cd1-xInxNNi3 and Cd1-yCuyNNi3 samples can be well fitted to the combination of a Bloch term and a Curie-Weiss term.

The magnetic properties of diluted CoFe2O4 nanomaterials

R. Masrour,M. Hamedoun,A. Benyoussef
Chin. Phys. B 2012, 21 (4): 047501;  doi: 10.1088/1674-1056/21/4/047501
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The magnetic properties of (CoxFe1-x)A(Zn1-xFe<1-x)BO4 are studied using mean-field theory and the probability distribution law to obtain the saturation magnetization, the coercive field, the critical temperature, and the exchange interactions with different values of D (nm) and x. High-temperature series expansions (HTSEs) combined with the Padé approximant are used to calculate the critical temperature of (CoxFe1-x)A(Zn1-xFe<1-x)BO4, and the critical exponent associated with magnetic susceptibility is obtained.

The doping effects of BiFe1-xCoxO3 (x=0.0-0.8) in layered perovskite Bi4Ti3O12 ceramics

Yang Wen-Lu,Chen Chun-Yan,Mao Xiang-Yu,Chen Xiao-Bing
Chin. Phys. B 2012, 21 (4): 047502;  doi: 10.1088/1674-1056/21/4/047502
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Bi5Fe1-xCoxTi3O15 (x= 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8) multiferroic ceramics are synthesized in two steps using the solid state reaction technique. X-ray diffraction patterns show that the samples have four-layer Aurivillius phases. At room temperature (RT), the samples each present a remarkable coexistence of ferromagnetism (FM) and ferroelectricity (FE). The remnant polarization (2Pr) reaches its greatest value of 14 μC/cm2 at x = 0.6. Remnant magnetization (2Mr) first increases and then decreases, and the greatest 2Mr is 7.8 menu/g when x= 0.5. The magnetic properties for x = 0.4 are similar to those for x= 0.6, indicating that the magnetic properties originate mainly from the coupling between Fe3+ and Co3+ ions, rather than from their own magnetic moments.

Effects of oxygen vacancy location on the electronic structure and spin density of Co-doped rutile TiO2 dilute magnetic semiconductors

Sun Yun-Bin,Zhang Xiang-Qun,Li Guo-Ke,Cheng Zhao-Hua
Chin. Phys. B 2012, 21 (4): 047503;  doi: 10.1088/1674-1056/21/4/047503
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According to density functional theory (DFT) using the plane wave base and pseudo-potential, we investigate the effects of the specific location of oxygen vacancy (VO) in a (Ti,Co)O6 distorted octahedron on the spin density and magnetic properties of Co-doped rutile TiO2 dilute magnetic semiconductors. Our calculations suggest that the VO location has a significant influence on the magnetic moment of individual Co cations. In the case where two Co atoms are separated far away from each other, when the VO is located at the equatorial site of a Co-contained octahedron, the ground state of the two Co cations is d6(t2g3 ↑,t2g3 ↓) without any magnetic moment. However, if the VO is located at the apical site, these two Co sites have different ground states and magnetic moments. The spin densities are also observed to be modified by the exchange coupling between the Co cations and the location of VO. Some positive spin polarization is induced around the adjacent O ions.

A first-principles study of the magnetic properties in boron-doped ZnO

Xu Xiao-Guang,Yang Hai-Ling,Wu Yong,Zhang De-Lin,Jiang Yong
Chin. Phys. B 2012, 21 (4): 047504;  doi: 10.1088/1674-1056/21/4/047504
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First-principles calculations based on density functional theory are performed to study the origin of ferromagnetism in boron-doped ZnO. It is found that boron atoms tend to reside at Zn sites. The induced Zn vacancy is a key factor for ferromagnetism in Zn1-xBxO (0

First principles study of the magnetism driven by cation defects in CeO2: the important role of O2p states

Lu Zhan-Sheng,Ma Dong-Wei,Zhang Jing,Xu Guo-Liang,Yang Zong-Xian
Chin. Phys. B 2012, 21 (4): 047505;  doi: 10.1088/1674-1056/21/4/047505
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The magnetism driven by cation defects in undoped CeO2 bulk and thin films is studied by the density functional theory corrected for on-site Coulomb interactions (DFT+U) with U=5 eV for the Ce4f states and U=7 eV for the O2p states. It is found that the Ce vacancies can induce a magnetic moment of the ~4μB/supercell, which arises mainly from the 2p hole state of the nearest neighbouring O atom (~1μB on per oxygen) to the Ce vacancy. The effect of the methodology is investigated, indicating that U=7 eV for the O2p state is necessary to obtain the localized O2p hole state in defective ceria with cation vacancies.

Spectroscopic characterization of Yb:Sc2O3 transparent ceramics

Lu Shen-Zhou,Yang Qiu-Hong
Chin. Phys. B 2012, 21 (4): 047801;  doi: 10.1088/1674-1056/21/4/047801
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Yb:Sc2O3 transparent ceramics are fabricated by a conventional ceramic process and sintering in H2 atmosphere. The room-temperature spectroscopic properties are investigated, and the Raman spectrum shows an obvious vibration characteristic band centred at 415 cm-1. There are three broad absorption bands around 891, 937, and 971 nm, respectively. The strongest emission peak is centred at 1.04 μm with a broad bandwidth (11 nm) and an emission cross-section of 1.8×10-20 cm2. The gain coefficient implies a possible laser ability in a range from 990 nm to 1425 nm. The energy-level structure shows that Yb:Sc2O3 ceramics have large Stark splitting at the ground state level due to their strong crystal field. All the results show that Yb:Sc2O3 transparent ceramics are a promising material for short pulse lasers.

Characterization of 4H–SiC substrates and epilayers by Fourier transform infrared reflectance spectroscopy

Dong Lin,Sun Guo-Sheng,Zheng Liu,Liu Xing-Fang,Zhang Feng,Yan Guo-Guo,Zhao Wan-Shun,Wang Lei,Li Xi-Guang,Wang Zhan-Guo
Chin. Phys. B 2012, 21 (4): 047802;  doi: 10.1088/1674-1056/21/4/047802
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The infrared reflectance spectra of both 4H-SiC substrates and epilayers are measured in a wave number range from 400 cm-1 to 4000 cm-1 using a Fourier-transform spectrometer. The thicknesses of the 4H-SiC epilayers and the electrical properties, including the free-carrier concentrations and the mobilities of both the 4H-SiC substrates and the epilayers, are characterized through full line-shape fitting analyses. The correlations of the theoretical spectral profiles with the 4H-SiC electrical properties in the 30 cm-1-4000 cm-1 and 400 cm-1-4000 cm-1 spectral regions are established by introducing a parameter defined as error quadratic sum. It is indicated that their correlations become stronger at a higher carrier concentration and in a wider spectral region (30 cm-1-4000 cm-1). These results suggest that the infrared reflectance technique can be used to accurately determine the thicknesses of the epilayers and the carrier concentrations, and the mobilities of both lightly and heavily doped 4H-SiC wafers.

The concentration quenching and crystallographic sites of Eu2+ in Ca2BO3Cl

Li Pan-Lai,Xu Zheng,Zhao Su-Ling,Wang Yong-Sheng,Zhang Fu-Jun
Chin. Phys. B 2012, 21 (4): 047803;  doi: 10.1088/1674-1056/21/4/047803
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A yellow phosphor, Ca2BO3Cl:Eu2+, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f,65d1→4f,7 transition of Eu2+. Eu2+ ions occupy two types of Ca2+ sites in the Ca2BO3Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2+ in Ca2BO3Cl. The emission intensity of Eu2+ in Ca2BO3Cl is influenced by the Eu2+ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.

Size-dependent nonlinear absorption and refraction of Ag nanoparticles excited by femtosecond lasers

Fan Guang-Hua,Qu Shi-Liang,Guo Zhong-Yi,Wang Qiang,Li Zhong-Guo
Chin. Phys. B 2012, 21 (4): 047804;  doi: 10.1088/1674-1056/21/4/047804
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Silver (Ag) nanoparticles with different average sizes are prepared, and the nonlinear absorption and refraction of these nanoparticles are investigated with femtosecond laser pulses at 800 nm. The smallest Ag nanoparticles show insignificant nonlinear absorption, whereas the larger ones show saturable absorption. By considering the previously reported positive nonlinear absorption of 9 nm Ag nanoparticles, the nonlinear absorptions of Ag nanoparticles are found to be size-dependent. All these nonlinear absorptions can be compatibly explained from the viewpoints of electronic transitions, energy bands and electronic structures in the conduction band of Ag nanoparticles. The nonlinear refraction is attributed to the effect of hot electrons arising from the intraband transition in the s-p conduction band of Ag nanoparticles.

Step instability of the In0.2Ga0.8As (001) surface during annealing

Zhang Bi-Chan,Zhou Xun,Luo Zi-Jiang,Guo Xiang,Ding Zhao
Chin. Phys. B 2012, 21 (4): 048101;  doi: 10.1088/1674-1056/21/4/048101
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Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8As/GaAs(001) surface has been investigated by scanning tunneling microscopy (STM). The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton-Cabrera-Frank (BCF) model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.

The influences of model parameters on the characteristics of memristors

Zhou Jing,Huang Da
Chin. Phys. B 2012, 21 (4): 048401;  doi: 10.1088/1674-1056/21/4/048401
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As the fourth passive circuit component, a memristor is a nonlinear resistor that can “remember” the amount of charge passing through it. The characteristic of “remembering” the charge and non-volatility makes memristors great potential candidates in many fields. Nowadays, only a few groups have the ability to fabricate memristors, and most researchers study them by theoretic analysis and simulation. In this paper, we first analyse the theoretical base and characteristics of memristors, then use a simulation program with integrated circuit emphasis as our tool to simulate the theoretical model of memristors and change the parameters in the model to see the influence of each parameter on the characteristics. Our work supplies researchers engaged in memristor-based circuits with advice on how to choose the proper parameters.

Linear matrix inequality approach for synchronization control of fuzzy cellular neural networks with mixed time delays

P. Balasubramaniam,M. Kalpana,R. Rakkiyappan
Chin. Phys. B 2012, 21 (4): 048402;  doi: 10.1088/1674-1056/21/4/048402
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Fuzzy cellular neural networks (FCNNs) are special kinds of cellular neural networks (CNNs). Each cell in an FCNN contains fuzzy operating abilities. The entire network is governed by cellular computing laws. The design of FCNNs is based on fuzzy local rules. In this paper, a linear matrix inequality (LMI) approach for synchronization control of FCNNs with mixed delays is investigated. Mixed delays include discrete time-varying delays and unbounded distributed delays. A dynamic control scheme is proposed to achieve the synchronization between a drive network and a response network. By constructing the Lyapunov-Krasovskii functional which contains a triple-integral term and the free-weighting matrices method an improved delay-dependent stability criterion is derived in terms of LMIs. The controller can be easily obtained by solving the derived LMIs. A numerical example and its simulations are presented to illustrate the effectiveness of the proposed method.

An open-styled dielectric-lined azimuthally periodic circular waveguide for a millimeter wave traveling-wave tube

Liu Yang,Wei Yan-Yu,Xu Jin,Yin Hai-Rong,Yue Ling-Na,Gong Yu-Bin,Wang Wen-Xiang
Chin. Phys. B 2012, 21 (4): 048403;  doi: 10.1088/1674-1056/21/4/048403
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An open-styled dielectric-lined azimuthally periodic circular waveguide (ODLAP-CW) for a millimeter-wave traveling-wave tube (TWT) is proposed, which is a modified form of a dielectric-lined azimuthally periodic circular waveguide (DLAP-CW). The slow-wave characteristics of the open-styled DLAP-CW are studied by using the spatial harmonics method, which includes normalized phase velocity and interaction impedance. The complicated dispersion equations are numerically solved with MATLAB and the results are in good agreement with the simulation results obtained from HFSS. The influence of structural parameters on the RF properties is investigated based on our theory. The numerical results show that the optimal thickness of the metal rod can increase the interaction impedance, with the dielectric constant held fixed. Finally, the slow-wave characteristics and transmission properties of an open-styled structure are compared with those of the DLAP-CW. The results validate that the mode competition is eliminated in the improved structure with only a slight influence on the dispersion characteristics, which may significantly improve the stability of an open-styled DLAP-CW-based TWT, and the interaction efficiency is also improved.

Analytical model including the fringing-induced barrier lowering effect for a dual-material surrounding-gate MOSFET with a high-κ gate dielectric

Li Cong,Zhuang Yi-Qi,Zhang Li,Bao Jun-Lin
Chin. Phys. B 2012, 21 (4): 048501;  doi: 10.1088/1674-1056/21/4/048501
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By solving Poisson's equation in both semiconductor and gate insulator regions in the cylindrical coordinates, an analytical model for a dual-material surrounding-gate (DMSG) metal-oxide semiconductor field-effect transistor (MOSFET) with a high-kappa gate dielectric has been developed. Using the derived model, the influences of fringing-induced barrier lowering (FIBL) on surface potential, subthreshold current, DIBL, and subthreshold swing are investigated. It is found that for the same equivalent oxide thickness, the gate insulator with high-kappa dielectric degrades the short-channel performance of the DMSG MOSFET. The accuracy of the analytical model is verified by the good agreement of its results with that obtained from the ISE three-dimensional numerical device simulator.

A novel superjunction MOSFET with improved ruggedness under unclamped inductive switching

Ren Min,Li Ze-Hong,Deng Guang-Min,Zhang Ling-Xia,Zhang Meng,Liu Xiao-Long,Xie Jia-Xiong,Zhang Bo
Chin. Phys. B 2012, 21 (4): 048502;  doi: 10.1088/1674-1056/21/4/048502
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The ruggedness of a superjunction metal-oxide semiconductor field-effect transistor (MOSFET) under unclamped inductive switching conditions is improved by optimizing the avalanche current path. Inserting a P-island with relatively high doping concentration into the P-column, the avalanche breakdown point is localized. In addition, a trench type P+ contact is designed to shorten the current path. As a consequence, the avalanche current path is located away from the N+ source/P-body junction and the activation of the parasitic transistor can be effectively avoided. To verify the proposed structural mechanism, a two-dimensional (2D) numerical simulation is performed to describe its static and on-state avalanche behaviours, and a method of mixed-mode device and circuit simulation is used to predict its performances under realistic unclamped inductive switching. Simulation shows that the proposed structure can endure a remarkably higher avalanche energy compared with a conventional superjunction MOSFET.

Density waves in a lattice hydrodynamic traffic flow model with the anticipation effect

Zhao Min,Sun Di-Hua,Tian Chuan
Chin. Phys. B 2012, 21 (4): 048901;  doi: 10.1088/1674-1056/21/4/048901
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By introducing the traffic anticipation effect in the real world into the original lattice hydrodynamic model, we present a new anticipation effect lattice hydrodynamic (AELH) model, and obtain the linear stability condition of the model by applying the linear stability theory. Through nonlinear analysis, we derive the Burgers equation and Korteweg-de Vries (KdV) equation, to describe the propagating behaviour of traffic density waves in the stable and the metastable regions, respectively. The good agreement between simulation results and analytical results shows that the stability of traffic flow can be enhanced when the anticipation effect is considered.

Competition between two kinds of information among random-walking individuals

Liu Zhen-Zhen,Wang Xing-Yuan,Wang Mao-Ji
Chin. Phys. B 2012, 21 (4): 048902;  doi: 10.1088/1674-1056/21/4/048902
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A model is proposed to describe the competition between two kinds of information among N random-walking individuals in an L times L square, starting from a half-and-half mixture of two kinds of information. Individuals remain or change their information according to their neighbors' information. When the moving speed of individuals v is zero, the two kinds of information typically coexist, and the ratio between them increases with L and decreases with N. In the dynamic case (v>0), only one information eventually remains, and the time required for one information being left scales as TvαLβNγ.

Cosmological applications in Kaluza–Klein theory

M.I. Wanas,Gamal G.L. Nashed,A.A. Nowaya
Chin. Phys. B 2012, 21 (4): 049801;  doi: 10.1088/1674-1056/21/4/049801
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The field equations of Kaluza-Klein (KK) theory have been applied in the domain of cosmology. These equations are solved for a flat universe by taking the gravitational and the cosmological constants as a function of time t. We use Taylor's expansion of cosmological function, Λ(t), up to the first order of the time t. The cosmological parameters are calculated and some cosmological problems are discussed.
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