Table of contents

30 January 2012, Volume 21 Issue 2 Previous issue    Next issue

RAPID COMMUNICATION

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A diagrammatic categorification of q-boson and q-fermion algebras Cai Li-Qiang(蔡立强), Lin Bing-Sheng(林冰生), and Wu Ke(吴可) Chin. Phys. B, 2012, 21 (2):  020201.  DOI: 10.1088/1674-1056/21/2/020201 Abstract ( 958 )   PDF (231KB) ( 703 )   In this paper, we study the diagrammatic categorification of q-boson algebra and also q-fermion algebra. We construct a graphical category corresponding to q-boson algebra. q-Fock states correspond to some kind of 1-morphisms, and the graded dimension of the graded vector space of 2-morphisms is exactly the inner product of the corresponding q-Fock states. We also find that this graphical category can be used to categorify q-fermion algebra.

GENERAL

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Finite symmetry transformation group of the Konopelchenko–Dubrovsky equation from its Lax pair Hu Han-Wei(胡瀚玮) and Yu Jun(俞军) Chin. Phys. B, 2012, 21 (2):  020202.  DOI: 10.1088/1674-1056/21/2/020202 Abstract ( 1052 )   PDF (122KB) ( 591 )   Starting from a weak Lax pair, the general Lie point symmetry group of the Konopelchenko-Dubrovsky equation is obtained by using the general direct method. And the corresponding Lie algebra structure is proved to be a Kac-Moody-Virasoro type. Furthermore, a new multi-soliton solution for the Konopelchenko-Dubrovsky equation is also given from this symmetry group and a known solution.

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Modified variational iteration method for an El Niño Southern Oscillation delayed oscillator Cao Xiao-Qun(曹小群), Song Jun-Qiang(宋君强), Zhu Xiao-Qian(朱小谦), Zhang Li-Lun(张理论), Zhang Wei-Min(张卫民), and Zhao Jun(赵军) Chin. Phys. B, 2012, 21 (2):  020203.  DOI: 10.1088/1674-1056/21/2/020203 Abstract ( 1072 )   PDF (108KB) ( 674 )   This paper studies a delayed air-sea coupled oscillator describing the physical mechanism of El Niño Southern Oscillation. The approximate expansions of the delayed differential equation's solution are obtained successfully by the modified variational iteration method. The numerical results illustrate the effectiveness and correctness of the method by comparing with the exact solution of the reduced model.

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An improved complex variable element-free Galerkin method for two-dimensional elasticity problems Bai Fu-Nong(白福浓), Li Dong-Ming(李东明) Wang Jian-Fei(王健菲), and Cheng Yu-Min(程玉民) Chin. Phys. B, 2012, 21 (2):  020204.  DOI: 10.1088/1674-1056/21/2/020204 Abstract ( 1253 )   PDF (324KB) ( 976 )   In this paper, the improved complex variable moving least-squares (ICVMLS) approximation is presented. The ICVMLS approximation has an explicit physics meaning. Compared with the complex variable moving least-squares (CVMLS) approximations presented by Cheng and Ren, the ICVMLS approximation has a great computational precision and efficiency. Based on the element-free Galerkin (EFG) method and the ICVMLS approximation, the improved complex variable element-free Galerkin (ICVEFG) method is presented for two-dimensional elasticity problems, and the corresponding formulae are obtained. Compared with the conventional EFG method, the ICVEFG method has a great computational accuracy and efficiency. For the purpose of demonstration, three selected numerical examples are solved using the ICVEFG method.

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Symmetry groups and Gauss kernels of Schrödinger equations Kang Jing(康静) and Qu Chang-Zheng(屈长征) Chin. Phys. B, 2012, 21 (2):  020301.  DOI: 10.1088/1674-1056/21/2/020301 Abstract ( 1004 )   PDF (151KB) ( 695 )   The relationship between symmetries and Gauss kernels for the Schrödinger equation iut=uxx+f(x)u is established. It is shown that if the Lie point symmetries of the equation are nontrivial, a classical integral transformations of the Gauss kernels can be obtained. Then the Gauss kernels of Schrödinger equations are derived by inverting the integral transformations. Furthermore, the relationship between Gauss kernels for two equations related by an equivalence transformation is identified.

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Photonic zitterbewegung and its interpretation Wang Zhi-Yong(王智勇), Xiong Cai-Dong(熊彩东), Qiu Qi(邱琪), and Liao-Yun(廖云) Chin. Phys. B, 2012, 21 (2):  020302.  DOI: 10.1088/1674-1056/21/2/020302 Abstract ( 889 )   PDF (109KB) ( 484 )   In terms of the volume-integrated Poynting vector, we present a quantum field-theory investigation of the zitterbewegung (ZB) of photons, and show that this ZB occurs only in the presence of virtual longitudinal and scalar photons. To present a heuristic explanation for such a ZB, by assuming that the space time is sufficiently close to the flat Minkowski space, we show that the gravitational interaction can result in the ZB of photons.

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State reconstruction of molecular spatial rotation Qin Xiao(覃晓) and Gao Jun-Yi(高军毅) Chin. Phys. B, 2012, 21 (2):  020303.  DOI: 10.1088/1674-1056/21/2/020303 Abstract ( 956 )   PDF (1657KB) ( 477 )   We establish a reconstruction approach for the rotational quantum state of linear molecules possessing a magnetic manifold. Our approximate method contains an iteration with generalized matrix inverses, processing the tomographic integral of the time-dependent molecular-axis distribution in a polar angle. As shown in a simulated example for an alignment state, the density matrix is determined in a high fidelity. An analytic tomographic formula is also derived for the symmetric top rotation. The state coherent in the quantum space of both the angular momentum and its magnetic projection can be approximately retrieved from the observable time-resolved solid-angle distribution of the molecular axis.

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Encoding entanglement-assisted quantum stabilizer codes Wang Yun-Jiang(王云江), Bai Bao-Ming(白宝明), Li Zhuo(李卓), Peng Jin-Ye(彭进业), and Xiao He-Ling(肖鹤玲) Chin. Phys. B, 2012, 21 (2):  020304.  DOI: 10.1088/1674-1056/21/2/020304 Abstract ( 1040 )   PDF (145KB) ( 717 )   We address the problem of encoding entanglement-assisted (EA) quantum error-correcting codes (QECCs) and of the corresponding complexity. We present an iterative algorithm from which a quantum circuit composed of CNOT, H, and S gates can be derived directly with complexity O(n2) to encode the qubits being sent. Moreover, we derive the number of each gate consumed in our algorithm according to which we can design EA QECCs with low encoding complexity. Another advantage brought by our algorithm is the easiness and efficiency of programming on classical computers.

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A 9×9 matrix representation of Temperley–Lieb algebra and corresponding entanglement Gou Li-Dan(苟立丹) and Zhu Rui-Han(朱瑞晗) Chin. Phys. B, 2012, 21 (2):  020305.  DOI: 10.1088/1674-1056/21/2/020305 Abstract ( 1138 )   PDF (107KB) ( 536 )   We present the matrix U. The $9\times9$ U matrix is a representation of specialized Temperley-Lieb algebra. Based on which, a unitary $\check{R}$ matrix is generated via the Yang-Baxterization approach. The  $9\times9$$\check{R}$  matrix, a solution of the Yang-Baxter equation, is universal for quantum entanglement.

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Dynamic stability and manipulation of bright matter-wave solitons by optical lattices in Bose–Einstein condensates Song Chang-Sheng(宋昌盛), Li Jing(黎菁), and Zong Feng-De(宗丰德) Chin. Phys. B, 2012, 21 (2):  020306.  DOI: 10.1088/1674-1056/21/2/020306 Abstract ( 994 )   PDF (4004KB) ( 763 )   An extended variation approach to describing the dynamic evolution of self-attractive Bose-Einstein condensates is developed. We consider bright matter-wave solitons in the presence of a parabolic magnetic potential and a time-space periodic optical lattice. The dynamics of condensates is shown to be well approximated by four coupled nonlinear differential equations. A noteworthy feature is that the extended variation approach gives a critical strength ratio to support multiple stable lattice sites for the condensate. We further examine the existence of the solitons and their stabilities at the multiple stable lattice sites. In this case, the analytical predictions of Bose-Einstein condensates variational dynamics are found to be in good agreement with numerical simulations. We then find a stable region for successful manipulating matter-wave solitons without collapse, which are dragged from an initial stationary to a prescribed position by a moving periodic optical lattice.

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Static spherically symmetric star in Gauss–Bonnet gravity Zhou Kang(周康), Yang Zhan-Ying(杨战营), Zou De-Cheng(邹德成), and Yue Rui-Hong(岳瑞宏) Chin. Phys. B, 2012, 21 (2):  020401.  DOI: 10.1088/1674-1056/21/2/020401 Abstract ( 1111 )   PDF (131KB) ( 894 )   We explore static spherically symmetric stars in Gauss-Bonnet gravity without a cosmological constant, and present an exact internal solution which attaches to the exterior vacuum solution outside stars. It turns out that the presence of the Gauss-Bonnet term with a positive coupling constant completely changes thermal and gravitational energies, and the upper bound of the red shift of spectral lines from the surface of stars. Unlike in general relativity, the upper bound of the red shift is dependent on the density of stars in our case. Moreover, we have proven that two theorems for judging the stability of equilibrium of stars in general relativity can hold in Gauss-Bonnet gravity.

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Number-phase quantization of a mesoscopic RLC circuit Xu Cheng-Lin(胥成林) Chin. Phys. B, 2012, 21 (2):  020402.  DOI: 10.1088/1674-1056/21/2/020402 Abstract ( 1049 )   PDF (82KB) ( 776 )   With the help of the time-dependent Lagrangian for a damped harmonic oscillator, the quantization of mesoscopic RLC circuit in the context of a number-phase quantization scheme is realized and the corresponding Hamiltonian operator is obtained. Then the evolution of the charge number and phase difference across the capacity are obtained. It is shown that the number-phase analysis is useful to tackle the quantization of some mesoscopic circuits and dynamical equations of the corresponding operators.

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Twofold hidden conformal symmetry of Kerr–Bolt black holes M. R. Setare and V. Kamali Chin. Phys. B, 2012, 21 (2):  020403.  DOI: 10.1088/1674-1056/21/2/020403 Abstract ( 950 )   PDF (106KB) ( 565 )   Previously we have shown that a four-dimensional Kerr-Bolt black hole in non-extremal and also in extremal cases could be described by a holographic two-dimensional (2D) conformal field theory (CFT) [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 074]. Motivated by recent work [Chen C M, Huang Y M, Sun J R, Wu M F and Zou S J 2010 Phys. Rev. D 82 066004], we show that there is another holographic description for these black holes. The first description is called the J-picture, whose construction is based on the black hole angular momentum. The new description is called the Q-picture, whose constructions originate from the nut charge of the black hole. Similar to the previous cases [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 074], we show that this new picture for a low frequency limit of the wave equation of a massless charged scalar field in the background of a Kerr-Bolt black hole can be written as the Casimir of SL(2,R) symmetry. Our result shows that the entropy of the black hole is reproduced by the Cardy formula. In addition, the absorption cross section is consistent with the finite temperature absorption cross section for a two-dimensional CFT.

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Stochastic synchronization for time-varying complex dynamical networks Guo Xiao-Yong(郭晓永) and Li Jun-Min(李俊民) Chin. Phys. B, 2012, 21 (2):  020501.  DOI: 10.1088/1674-1056/21/2/020501 Abstract ( 1218 )   PDF (290KB) ( 785 )   This paper studies the stochastic synchronization problem for time-varying complex dynamical networks. This model is totally different from some existing network models. Based on the Lyapunov stability theory, inequality techniques, and the properties of the Weiner process, some controllers and adaptive laws are designed to ensure achieving stochastic synchronization of a complex dynamical network model. A sufficient synchronization condition is given to ensure that the proposed network model is mean-square stable. Theoretical analysis and numerical simulation fully verify the main results.

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Feedback control in a coupled Brownian ratchet Gao Tian-Fu(高天附), Liu Feng-Shan(刘凤山), and Chen Jin-Can(陈金灿) Chin. Phys. B, 2012, 21 (2):  020502.  DOI: 10.1088/1674-1056/21/2/020502 Abstract ( 1060 )   PDF (284KB) ( 630 )   On the basis of the double-well ratchet potential which can be calculated theoretically and implemented experimentally, the influences of the time delay, the coupling constant, and the asymmetric parameter of the potential on the performance of a delayed feedback ratchet consisting of two Brownian particles coupled mutually with a linear elastic force are investigated. The centre-of-mass velocity of two coupled Brownian particles, the average effective diffusion coefficient, and the Pe number are calculated. It is found that the parameters are affected by not only the time delay and coupling constant but also the asymmetric parameter of the double-well ratchet potential. It is also found that the enhancement of the current may be obtained by varying the coupling constant of the system for the weak coupling case. It is expected that the results obtained here may be observed in some physical and biological systems.

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Bifurcations and chaotic threshold for a nonlinear system with an irrational restoring force Tian Rui-Lan(田瑞兰), Yang Xin-Wei(杨新伟), Cao Qing-Jie(曹庆杰), and Wu Qi-Liang(吴启亮) Chin. Phys. B, 2012, 21 (2):  020503.  DOI: 10.1088/1674-1056/21/2/020503 Abstract ( 1078 )   PDF (1568KB) ( 811 )   Nonlinear dynamical systems with an irrational restoring force often occur in both science and engineering, and always lead to a barrier for conventional nonlinear techniques. In this paper, we have investigated the global bifurcations and the chaos directly for a nonlinear system with irrational nonlinearity avoiding the conventional Taylor's expansion to retain the natural characteristics of the system. A series of transformations are proposed to convert the homoclinic orbits of the unperturbed system to the heteroclinic orbits in the new coordinate, which can be transformed back to the analytical expressions of the homoclinic orbits. Melnikov's method is employed to obtain the criteria for chaotic motion, which implies that the existence of homoclinic orbits to chaos arose from the breaking of homoclinic orbits under the perturbation of damping and external forcing. The efficiency of the criteria for chaotic motion obtained in this paper is verified via bifurcation diagrams, Lyapunov exponents, and numerical simulations. It is worthwhile noting that our study is an attempt to make a step toward the solution of the problem proposed by Cao Q J et al. (Cao Q J, Wiercigroch M, Pavlovskaia E E, Thompson J M T and Grebogi C 2008 Phil. Trans. R. Soc. A 366 635).

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A one-time one-key encryption algorithm based on the ergodicity of chaos Wang Xing-Yuan(王兴元) and Teng Lin(滕琳) Chin. Phys. B, 2012, 21 (2):  020504.  DOI: 10.1088/1674-1056/21/2/020504 Abstract ( 1026 )   PDF (604KB) ( 582 )   In this paper, we propose a new one-time one-key encryption algorithm based on the ergodicity of a skew tent chaotic map. We divide the chaotic trajectory into sub-intervals and map them to integers, and use this scheme to encrypt plaintext and obtain ciphertext. In this algorithm, the plaintext information in the key is used, so different plaintexts or different total numbers of plaintext letters will encrypt different ciphertexts. Simulation results show that the performance and the security of the proposed encryption algorithm can encrypt plaintext effectively and resist various typical attacks.

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Period-doubling bifurcation in two-stage power factor correction converters using the method of incremental harmonic balance and Floquet theory Wang Fa-Qiang(王发强), Zhang Hao (张浩), and Ma Xi-Kui(马西奎) Chin. Phys. B, 2012, 21 (2):  020505.  DOI: 10.1088/1674-1056/21/2/020505 Abstract ( 1242 )   PDF (919KB) ( 1113 )   In this paper, period-doubling bifurcation in a two-stage power factor correction converter is analyzed by using the method of incremental harmonic balance (IHB) and Floquet theory. A two-stage power factor correction converter typically employs a cascade configuration of a pre-regulator boost power factor correction converter with average current mode control to achieve a near unity power factor and a tightly regulated post-regulator DC-DC Buck converter with voltage feedback control to regulate the output voltage. Based on the assumption that the tightly regulated post-regulator DC-DC Buck converter is represented as a constant power sink and some other assumptions, the simplified model of the two-stage power factor correction converter is derived and its approximate periodic solution is calculated by the method of IHB. And then, the stability of the system is investigated by using Floquet theory and the stable boundaries are presented on the selected parameter spaces. Finally, some experimental results are given to confirm the effectiveness of the theoretical analysis.

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A novel block encryption scheme based on chaos and an S-box for wireless sensor networks Tong Xiao-Jun(佟晓筠), Wang Zhu(王翥), and Zuo Ke(左科) Chin. Phys. B, 2012, 21 (2):  020506.  DOI: 10.1088/1674-1056/21/2/020506 Abstract ( 1127 )   PDF (252KB) ( 1554 )   The wireless sensor network (WSN) has been widely used in various fields, but it still remains in the preliminary discovery and research phase with a lack of various related mature technologies. Traditional encryption schemes are not suitable for wireless sensor networks due to intrinsic features of the nodes such as low energy, limited computation capability, and lack of storage resources. In this paper, we present a novel block encryption scheme based on the integer discretization of a chaotic map, the Feistel network structure, and an S-box. The novel scheme is fast, secure, has low resource consumption and is suitable for wireless sensor network node encryption schemes. The experimental tests are carried out with detailed analysis, showing that the novel block algorithm has a large key space, very good diffusion and disruptive performances, a strict avalanche effect, excellent statistical balance, and fast encryption speed. These features enable the encryption scheme to pass the SP800-22 test. Meanwhile, the analysis and the testing of speed, time, and storage space on the simulator platform show that this new encryption scheme is well able to hide data information in wireless sensor networks.

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Fuzzy neural network based on a Sigmoid chaotic neuron Zhang Yi(张诣) and Wang Xing-Yuan(王兴元) Chin. Phys. B, 2012, 21 (2):  020507.  DOI: 10.1088/1674-1056/21/2/020507 Abstract ( 1027 )   PDF (301KB) ( 692 )   The theories of intelligent information processing are urgently needed for the rapid development of modem science. In this paper, a novel fuzzy chaotic neural network, which is the combination of fuzzy logic system, artificial neural network system, and chaotic system, is proposed. We design its model structure which is based on the Sigmoid map, derive its mathematical model, and analyse its chaotic characteristics. Finally the relationship between the accuracy of map and the membership function is illustrated by simulation.

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Application of local polynomial estimation in suppressing strong chaotic noise Su Li-Yun(苏理云), Ma Yan-Ju(马艳菊), and Li Jiao-Jun(李姣军) Chin. Phys. B, 2012, 21 (2):  020508.  DOI: 10.1088/1674-1056/21/2/020508 Abstract ( 1167 )   PDF (408KB) ( 605 )   In this paper, we propose a new method that combines chaotic series phase space reconstruction and local polynomial estimation to solve the problem of suppressing strong chaotic noise. First, chaotic noise time series are reconstructed to obtain multivariate time series according to Takens delay embedding theorem. Then the chaotic noise is estimated accurately using local polynomial estimation method. After chaotic noise is separated from observation signal, we can get the estimation of the useful signal. This local polynomial estimation method can combine the advantages of local and global law. Finally, it makes the estimation more exactly and we can calculate the formula of mean square error theoretically. The simulation results show that the method is effective for the suppression of strong chaotic noise when the signal to interference ratio is low.

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Synchronization of noise-perturbed optical systems with multiple time delays Tang Mao-Ning(唐矛宁) Chin. Phys. B, 2012, 21 (2):  020509.  DOI: 10.1088/1674-1056/21/2/020509 Abstract ( 1055 )   PDF (487KB) ( 540 )   In this paper, complete synchronization and generalized synchronization between two unidirectionally coupled optical systems with multiple time delays and noise perturbation are investigated. Sufficient conditions for both complete synchronization and generalized synchronization are rigorously established. Numerical simulations fully support the theoretical results. The effect of parameter mismatch on the quality of synchronization is also explored.

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Topology identification for a class of complex dynamical networks using output variables Fan Chun-Xia(樊春霞), Wan You-Hong(万佑红), and Jiang Guo-Ping(蒋国平) Chin. Phys. B, 2012, 21 (2):  020510.  DOI: 10.1088/1674-1056/21/2/020510 Abstract ( 1062 )   PDF (461KB) ( 614 )   A problem of topology identification for complex dynamical networks is investigated in this paper. An adaptive observer is proposed to identify the topology of a complex dynamical networks based on the Lyapunov stability theory. Here the output of the network and the states of the observer are used to construct the updating law of the topology such that the communication resources from the network to its observer are saved. Some convergent criteria of the adaptive observer are derived in the form of linear inequality matrices. Several numerical examples are shown to demonstrate the effectiveness of the proposed observer.

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Critical properties of mixed spin-1 and spin-5/2 with equal and unequal crystal fields Ali Yigit and Erhan Albayrak Chin. Phys. B, 2012, 21 (2):  020511.  DOI: 10.1088/1674-1056/21/2/020511 Abstract ( 1047 )   PDF (484KB) ( 616 )   The effects of assuming equal or unequal crystal fields (CF) on the phase diagrams of a mixed spin-1 and spin-5/2 system are investigated in terms of the recursion relations on the Bethe lattice (BL). The equal CF case was considered for the coordination numbers q=3, 4, and 6, while for q=3 the unequal CF case was also studied. It was found that for the equal CF case, the model exhibits second-order phase transitions and two compensation temperatures for all q, the reentrant behavior for q=4 and first-order phase transitions and tricritical point (TCP) for q=6. In the unequal CF case for q=3, the system yields first- and second-order phase transitions, TCP's, and three compensation temperatures. In addition, the TCP's in a very short range are classified as the stable and unstable ones depending on their free energies.

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Multiple flux difference effect in the lattice hydrodynamic model Wang Tao(王涛), Gao Zi-You(高自友), and Zhao Xiao-Mei(赵小梅) Chin. Phys. B, 2012, 21 (2):  020512.  DOI: 10.1088/1674-1056/21/2/020512 Abstract ( 1049 )   PDF (321KB) ( 607 )   Considering the effect of multiple flux difference, an extended lattice model is proposed to improve the stability of traffic flow. The stability condition of the new model is obtained by using linear stability theory. The theoretical analysis result shows that considering the flux difference effect ahead can stabilize traffic flow. The nonlinear analysis is also conducted by using a reductive perturbation method. The modified KdV (mKdV) equation near the critical point is derived and the kink-antikink solution is obtained from the mKdV equation. Numerical simulation results show that the multiple flux difference effect can suppress the traffic jam considerably, which is in line with the analytical result.

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Recent advance on the efficiency at maximum power of heat engines Tu Zhan-Chun(涂展春) Chin. Phys. B, 2012, 21 (2):  020513.  DOI: 10.1088/1674-1056/21/2/020513 Abstract ( 1125 )   PDF (770KB) ( 972 )   This review reports several key advances on the theoretical investigations of efficiency at maximum power of heat engines in the past five years. The analytical results of efficiency at maximum power for the Curzon-Ahlborn heat engine, the stochastic heat engine constructed from a Brownian particle, and Feynman's ratchet as a heat engine are presented. It is found that: the efficiency at maximum power exhibits universal behavior at small relative temperature differences; the lower and the upper bounds might exist under quite general conditions; and the problem of efficiency at maximum power comes down to seeking for the minimum irreversible entropy production in each finite-time isothermal process for a given time.

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Theoretical investigation of total-asymmetric simple exclusion processes with attachment and detachment Xiao Song(肖松), Liu Ming-Zhe(刘明哲), Shang Jing(商晶), and Wang Hua(王华) Chin. Phys. B, 2012, 21 (2):  020514.  DOI: 10.1088/1674-1056/21/2/020514 Abstract ( 1148 )   PDF (157KB) ( 741 )   In this paper, traffic systems with attachment and detachment have been studied by total-asymmetric simple exclusion processes (TASEPs). Attachment and detachment in a one-dimensional system is a type of complex geometry that is relevant to biological transport with the random update rule. The analytical results are presented and have shown good agreement with the extensive Monte Carlo computer simulations.

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Real time detection of antibody–antigen interaction using a laser scanning confocal imaging-surface plasmon resonance system Zhang Hong-Yan(张洪艳), Yang Li-Quan(杨立泉), Meng Lan(孟岚), Nie Jia-Cai(聂家财), Ning Ting-Yin(宁廷银), Liu Wei-Min(刘卫敏), Sun Jia-Yu(孙嘉宇), and Wang Peng-Fei(汪鹏飞) Chin. Phys. B, 2012, 21 (2):  020601.  DOI: 10.1088/1674-1056/21/2/020601 Abstract ( 1272 )   PDF (4448KB) ( 888 )   A laser scanning confocal imaging-surface plasmon resonance (LSCI-SPR) instrument integrated with a wavelength-dependent surface plasmon resonance (SPR) sensor and a laser scanning confocal microscopy (LSCM) is built to detect the bonding process of human IgG and fluorescent-labeled affinity purified antibodies in real time. The shifts of resonant wavelength at different reaction time stages are obtained by SPR, corresponding well with the changes of the fluorescence intensity collected by using LSCM. The instrument shows the merits of the combination and complementation of the SPR and LSCM, with such advantages as quantificational analysis, high spatial resolution and real time monitor, which are of great importance for practical applications in biosensor and life science.

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A method of measuring micro-impulse with torsion pendulum based on multi-beam laser heterodyne Li Yan-Chao(李彦超) and Wang Chun-Hui(王春晖) Chin. Phys. B, 2012, 21 (2):  020701.  DOI: 10.1088/1674-1056/21/2/020701 Abstract ( 920 )   PDF (324KB) ( 550 )   In this paper, we propose a novel method of multi-beam laser heterodyne measurement for micro-impulse. The measurement of the micro-impulse, which is converted into the measurement of the small tuning angle of the torsion pendulum, is realized by considering the interaction between pulse laser and working medium. Based on Doppler effect and heterodyne technology, the information regarding the small tuning angle is loaded to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, thereby obtaining many values of the small tuning angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, the small tuning angle can be obtained accurately and the value of the micro-impulse can eventually be calculated. Using Polyvinylchlorid+2%C as a working medium, this novel method is used to simulate the value of the micro-impulse by MATLAB which is generated by considering the interaction between the pulse laser and the working medium, the obtained result shows that the relative error of this method is just 0.5%.

RAPID COMMUNICATION

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Density functional theory study of the interaction of H2 with pure and Ti-doped WO3 (002) surfaces Hu Ming(胡明), Wang Wei-Dan(王巍丹), Zeng Peng(曾鹏), Zeng Jing(曾晶), and Qin Yu-Xiang(秦玉香) Chin. Phys. B, 2012, 21 (2):  023101.  DOI: 10.1088/1674-1056/21/2/023101 Abstract ( 1232 )   PDF (1109KB) ( 1019 )   Density functional theory (DFT) calculations are conducted to explore the interaction of H2 with pure and Ti-doped WO3 (002) surfaces. Four top adsorption models of H2 on pure and Ti-doped WO3 (002) surfaces are investigated respectively, they are adsorption on bridging oxygen O1c, absorption on plane oxygen O2c, absorption on 5-fold W5c (Ti), and absorption on 6-fold W6c. The most stable and H2 possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O2c site, while the favourable adsorption sites for H2 in a Ti-doped surface is not only an O2c site but also a W6c site. The adsorption energy, the Fermi energy level EF, and the electronic population are investigated and the H2-sensing mechanism of a pure-doped WO3 (002) surface is revealed theoretically: the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H2. It can be predicted that the method of Ti-doped into a WO3 thin film is an effective way to improve WO3 sensor sensitivity to H2 gas.

GENERAL

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Investigations of spectroscopic parameters and molecular constants for X1Σg+, w3Δu, and W1Δu electronic states of P2 molecule Wang Jie-Min(王杰敏), Feng Heng-Qiang(冯恒强), Sun Jin-Feng(孙金锋), and Shi De-Heng(施德恒) Chin. Phys. B, 2012, 21 (2):  023102.  DOI: 10.1088/1674-1056/21/2/023102 Abstract ( 1011 )   PDF (122KB) ( 579 )   The potential energy curves (PECs) of three low-lying electronic states (X1Σg+, w3Δu, and W1Δu)of P2 molecule are investigated using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the correlation-consistent basis set in the valence range. The PECs of the electronic states involved are modified by the Davidson correction and extrapolated to the complete basis set (CBS) limit. With these PECs, the spectroscopic parameters of the three electronic states are determined and compared in detail with the experimental data. The comparison shows that excellent agreement exists between the present results and the available experimental data. The complete vibrational states are computed for the w3Δu, and W1Δu electronic states when the rotational quantum number J equals zero and the vibrational level G(v), the inertial rotation constant Bv, and the centrifugal distortion constant Dv of the first 30 vibrational states are reported, which accord well with the experimental data. The present results show that the two-point extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants.

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Subluminal to superluminal light propagation in a V-type three-level atomic system interacting with squeezed vacuum Zhang Qin(张琴), Qu Guang-Hui(屈光辉), Tang Yuan-He(唐远河), Jin Kang(金康), and Ji Wei-Li(纪卫莉) Chin. Phys. B, 2012, 21 (2):  023201.  DOI: 10.1088/1674-1056/21/2/023201 Abstract ( 1071 )   PDF (210KB) ( 801 )   We study the light propagation properties in a V-type three-level atomic system interacting with two independent broadband squeezed baths. Using the graphic method, the dependences of the absorption and the dispersion of the system on the coupling field strength, the incoherent pumping field strength and the intensity of the squeezed vacuum are analysed. The result shows that the probe pulse propagation can be changed from subluminal to superluminal speed.

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P-branch emission spectra of the A1$\Pi$–X1Σ+ system of IrN Fan Qun-Chao(樊群超), Sun Wei-Guo(孙卫国), Li Hui-Dong(李会东), and Feng Hao(冯灏) Chin. Phys. B, 2012, 21 (2):  023301.  DOI: 10.1088/1674-1056/21/2/023301 Abstract ( 1213 )   PDF (157KB) ( 502 )   The P-branch emission spectra of (4,1) and (3,1) bands of the A1$\Pi$-X1Σ+ system of IrN molecule are studied using an analytical formula which is derived from elementary expression of molecular total energy by taking multiple spectral differences. It not only reproduces the known experimental transition lines, but also predicts the unknown spectral lines up to J= 80 for each band by using a group of fifteen known experimental transition lines.

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Autler–Townes splitting in photoelectron spectra of K2 molecule Yao Hong-Bin(姚洪斌) and Zheng Yu-Jun(郑雨军) Chin. Phys. B, 2012, 21 (2):  023302.  DOI: 10.1088/1674-1056/21/2/023302 Abstract ( 1025 )   PDF (419KB) ( 624 )   We investigate Autler-Townes splitting in the photoelectron spectra of K2 molecule driven by pump-probe pulses via employing the time-dependent wave packet approach. It is found that the magnitude of Aulter-Townes splitting varies with the wavelength of the intense laser pulse. In particular, the phenomenon of Aulter-Townes splitting vanishes for the far-off resonance of the pump pulse. Also, the split peaks of Autler-Townes in the case of resonant pump pulse give us an approach to directly obtaining the transition dipole moment of a molecule.

RAPID COMMUNICATION

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Orbital responses to methyl sites in CnH2n+2 (n=1–6) Yang Ze-Jin(杨则金), Cheng Xin-Lu(程新路), Zhu Zheng-He(朱正和), and Yang Xiang-Dong(杨向东) Chin. Phys. B, 2012, 21 (2):  023401.  DOI: 10.1088/1674-1056/21/2/023401 Abstract ( 1013 )   PDF (5875KB) ( 595 )   Orbital responses to methyl sites in CnH2n+2 (n=1-6) are studied by B3LYP/TZVP based on the most stable geometries using the B3LYP/aug-cc-pVTZ method. Vertical ionization energies are produced using the SAOP/et-pVQZ model for the complete valence space. The highest occupied molecular orbital (HOMO) investigations indicate the p-electron profiles in methane, ethane, propane, and n-butane. By increasing the number of carbon-carbon bonds in lower momentum regions, the s, p-hybridized orbitals are built and display strong exchange and correlation interactions in lower momentum space (P$\lesssim$0.50 a.u.). Meanwhile, the relative intensities of the isomers in lower momentum space show the strong bonding number dependence of the carbon-carbon bonds, meaning that more electrons have contributed to orbital construction. The study of representative valence orbital momentum distribution further confirms that the structural changes lead to evident electronic rearrangement over the whole valence space. An analysis based on the isomers reveals that the valence orbitals are isomer-dependent and the valence ionization energy experiences an apparent shift in the inner valence space. However, such shifts are greatly reduced in the outer valence space. Meanwhile, the opposite energy shift trend is found in the intermediate valence space.

GENERAL

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Influence of the reagent vibration on the stereo-dynamics of the reactions D- + H2 and H- + D2 Chen Xiao-Qiong(陈肖琼), Wang Mei-Shan(王美山), Yang Chuan-Lu(杨传路), and Wu Ji-Cheng(吴继成) % Chin. Phys. B, 2012, 21 (2):  023402.  DOI: 10.1088/1674-1056/21/2/023402 Abstract ( 1106 )   PDF (1164KB) ( 670 )   Employing the quasi-classical trajectory method and the potential energy surface of Panda and Sathyamurhy [Panda A N and Sathyamurthy N 2004 J. Chem. Phys. 121 9343], the effect of the reagent vibration on vector correlation of the ion-molecule reactions D- + H2 and H- + D2 is studied at a collision energy of 35.7 kcal/mol. Four generalized polarization-dependent differential cross sections (2$\pi$/σ)(dσ00/dωt),(2$\pi$/σ)(dσ20/dωt),(2$\pi$/σ)(dσ22/dωt), and (2$\pi$/σ)(dσ20/dωt) are presented in the centre-of-mass reference frame, separately. At the same time, the effects on the product angular distributions P(θr), P($\phi$r) and P(θr,$\phi$r) of the title reactions are also analysed. The calculated results show that the scattering tendencies of the product HD, the alignment and the orientation of j' sensitively depend on reagent molecule vibration.

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Demonstration of the approximation of eliminating atomic excited populations in an atom–cavity system Zhang Yu-Qing(张玉青), Huang Gang(黄刚), and Tan Lei(谭磊) Chin. Phys. B, 2012, 21 (2):  023701.  DOI: 10.1088/1674-1056/21/2/023701 Abstract ( 994 )   PDF (206KB) ( 593 )   Using the master equation approach to a V-type three-level atom inside a high-finesse single-mode cavity in the strong coupling condition, we demonstrate the approximation of eliminating populations of atomic excited states, which is widely used in the field of the atom-cavity systems [Hechenblaikner G, Gangl M, Horak P and Ritsch H 1998 Phys. Rev. A 58 3030]; Liu L W, Tan T and Xu Y 2008 J. Mod. Opt. 56 968; Cho J, Angelakis D G and Bose S 2008 Phys. Rev. A 78 062338. This is reflected in the deviation of the population δ, of which the value is 10-3～10-2. We further find the deviation of the dipole force and demonstrate that the deviation of atomic population will not notably affect the dipole force of the atom in the strong coupling condition. A relevant experimental case is also presented.

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Electron acceleration by tightly focused radially polarized few-cycle laser pulses Liu Jin-Lu(刘晋陆), Sheng Zheng-Ming(盛政明), and Zheng Jun(郑君) Chin. Phys. B, 2012, 21 (2):  024101.  DOI: 10.1088/1674-1056/21/2/024101 Abstract ( 984 )   PDF (281KB) ( 788 )   Within the framework of plane-wave angular spectrum analysis of the electromagnetic field structure, a solution valid for tightly focused radially polarized few-cycle laser pulses propagating in vacuum is presented. The resulting field distribution is significantly different from that based on the paraxial approximation for pulses with either small or large beam diameters. We compare the electron accelerations obtained with the two solutions and find that the energy gain obtained with our new solution is usually much larger than that with the paraxial approximation solution.

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Propagation dynamics and experimental observation of quadratic vortex beam Chen Zi-Yang(陈子阳) and Pu Ji-Xiong(蒲继雄) Chin. Phys. B, 2012, 21 (2):  024201.  DOI: 10.1088/1674-1056/21/2/024201 Abstract ( 993 )   PDF (9405KB) ( 478 )   The concept of a quadratic vortex beam is proposed, in which phase term of the beam is given by exp(i mθ2). The phase of the quadratic vortex beam increases with azimuthal angle nonlinearly. This change in phase produces several unexpected effects. Unlike the circularly symmetric beam spot of normal vortex beams, the intensity distribution of the quadratic vortex beam is shown to be asymmetric. The phase singularities will shift in the transverse beam plane on propagation.

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Non-Gaussianity and decoherence of generalized photon-added coherent state as a Hermite-excited coherent state Li Heng-Mei(李恒梅) and Xu Xue-Fen(许雪芬) Chin. Phys. B, 2012, 21 (2):  024202.  DOI: 10.1088/1674-1056/21/2/024202 Abstract ( 1093 )   PDF (1244KB) ( 651 )   Generalized photon-added coherent state (GPACS) is obtained by repeatedly acting the combination of Bose creation and annihilation operations on the coherent state. It is found that GPACS can be regarded as a Hermite-excited coherent state due to its normalization factor related to a Hermite polynomial. In addition, we adopt the Hilbert-Schmidt distance to quantify the non-Gaussian character of GPACS and discuss the decoherence of GPACS in dissipative channel by studying the loss of nonclassicality in reference of the negativity of Wigner function.

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Comparison of nonclassicality between photon-added and photon-subtracted squeezed vacuum states Ma Shan-Jun(马善钧) and Luo Wen-Wei(罗文葳) Chin. Phys. B, 2012, 21 (2):  024203.  DOI: 10.1088/1674-1056/21/2/024203 Abstract ( 1177 )   PDF (1028KB) ( 1194 )   In this paper, we introduce photon-added and photon-subtracted squeezed vacuum state (PASV and PSSV) and obtain their normalized factors, which have the similar forms involved in Lengendre polynomials. Moreover, we give the compact expressions of Wigner function, which are related to single-variable Hermite polynomials. Especially, we compare their nonclassicality in terms of Mandel Q-factor and the negativity of Wigner function.

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Enhancement and suppression of spatial splitting four-wave mixing in atomic medium Zhuang Yu-Ming(庄雨茗), Sang Su-Ling(桑苏玲), Li Pei-Ying(李培英), Yuan Chen-Zhi(袁晨智), Huo Shu-Li(霍淑利), Xue Xin-Xin(薛鑫鑫), Wang Zhi-Guo(王志国), Zheng Huai-Bin(郑淮斌), and Zhang Yan-Peng(张彦鹏) Chin. Phys. B, 2012, 21 (2):  024204.  DOI: 10.1088/1674-1056/21/2/024204 Abstract ( 916 )   PDF (1907KB) ( 490 )   We experimentally report on the evolution from singly-dressed to doubly-dressed four-wave mixing (FWM) process by controlling the powers of the probe, the pump and the dressing fields respectively. The differences in the enhancement and the suppression of FWM signal between the two-level and cascade three-level atomic systems are observed and explained by the multi-dressed effect theoretically. Both the x direction and the y direction spatial splittings of the degenerate-FWM (DWFM) beams are obtained. We also investigate the switch between the enhancement and the suppression of the DWFM signals and between its spatial splittings in x direction and y direction. The spatial splittings in x direction and y direction can be controlled by the relative position and the intensity of the involved laser beams. Such a study can be useful for optimizing the efficiency of the FWM process and providing potential applications in spatial signal processing.

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Generation and storage of double slow light pulses in a solid Fan Yun-Fei(范云飞), Wang Hai-Hua(王海华), Wang Rong(王荣), Zhang Xiao-Jun(张晓军), Kang Zhi-Hui(康智慧), Wu Jin-Hui(吴金辉), Zhang Han-Zhuang(张汉壮), and Gao Jin-Yue(高锦岳) Chin. Phys. B, 2012, 21 (2):  024205.  DOI: 10.1088/1674-1056/21/2/024205 Abstract ( 1045 )   PDF (176KB) ( 679 )   We experimentally study the generation and storage of double slow light pulses in a Pr3+:Y2SiO5 crystal. Under electromagnetically induced transparency, a single signal pulse is stored in the spin coherence of the crystal. By simultaneously switching on two control fields to recall the stored information, the spin coherence is converted into two slow light pulses with distinct frequencies. Furthermore, the storage and controlled retrieval of double slow light pulses are obtained by manipulating the control fields. This study of double slow light pulses may have practical applications in information processing and all-optical networks.

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Influence of Doppler broadening and spontaneously generated coherence on propagation effect in a quasi lambda-type four-level system Liu Zhong-Bo(刘中波), Liang Ying(梁颖), Jia Ke-Ning(贾克宁), and Fan Xi-Jun(樊锡君) Chin. Phys. B, 2012, 21 (2):  024206.  DOI: 10.1088/1674-1056/21/2/024206 Abstract ( 1005 )   PDF (474KB) ( 808 )   In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion (i.e. the probe field) in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.

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Compact, efficient diode-end-pumped Nd:GdVO4 slab continuous-wave 912-nm laser Liu Huan(刘欢) and Gong Ma-Li(巩马理) Chin. Phys. B, 2012, 21 (2):  024207.  DOI: 10.1088/1674-1056/21/2/024207 Abstract ( 1146 )   PDF (1235KB) ( 791 )   A fiber-coupled laser-diode (LD) end-pumped Nd:GdVO4 slab continuous-wave (CW) 912-nm laser and an LD bar end-pumped Nd:GdVO4 slab CW 912-nm laser are both demonstrated in this paper. Using the fiber-coupled LD of end-pumped type, a highest CW 912-nm laser output power of 10.17 W is obtained with a high optical-to-optical conversion efficiency of 24.6% and a slope efficiency of 34.5%. The measured M2 factors of beam quality in x and y directions are 5.3 and 5.1, respectively. Besides, an LD bar of end-pumped type is used to realize CW 912-nm laser output, which has the advantages of compactness and low cost. When the pump power is 38.8 W, the output power is 8.87 W and the measured M2 factors of beam quality in x and y directions are 16 and 1.31, respectively. In order to improve the beam quality of the 912-nm laser at x direction, a new quasi-concentric laser resonator will be designed, and an LD bar end-pumped Nd:GdVO4 slab high-power CW 912-nm TEM00 laser will be realized in the future.

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The thermal effect in diode-end-pumped continuous-wave 914-nm Nd:YVO4 laser Yan Ren-Peng(闫仁鹏), Yu Xin(于欣), Chen De-Ying(陈德应), Chen Fei(陈飞), Li Xu-Dong(李旭东), Ma Yu-Fei(马欲飞), and Yu Jun-Hua(于俊华) Chin. Phys. B, 2012, 21 (2):  024208.  DOI: 10.1088/1674-1056/21/2/024208 Abstract ( 1322 )   PDF (1017KB) ( 1000 )   The thermal effect and the heat generation in diode-end-pumped continuous-wave 914-nm Nd:YVO4 lasers are investigated in detail. A theoretical model of a diode end-pumped solid-state laser is constructed to analyse the influence of fractional thermal loading on the thermal effect in the Nd:YVO4 laser based on finite element analysis. The thermal focal lengths and the end-surface deformations of laser rods in Nd:YVO4 quasi-three-level and four-level lasers are measured and compared with the results obtained by ordinary interferometry for the demonstration of higher thermal loading in 914-nm laser. Finally the fractional thermal loading in the Nd:YVO4 quasi-three-level laser is calculated by matching the experimental and the simulated end deformations.

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Reconfigurable all-optical dual-directional half-subtractor for high-speed differential phase shift keying signal based on semiconductor optical amplifiers Zhang Yin(张印), Dong Jian-Ji(董建绩), Lei Lei(雷蕾), and Zhang Xin-Liang(张新亮) Chin. Phys. B, 2012, 21 (2):  024209.  DOI: 10.1088/1674-1056/21/2/024209 Abstract ( 1149 )   PDF (772KB) ( 750 )   All-optical digital logic elementary circuits are the building blocks of many important computational operations in future high-speed all-optical networks and computing systems. Multifunctional and reconfigurable logic units are essential in this respect. Employing the demodulation properties of delay interferometers for input differential phase shift keying signals and the gain saturation effect in two parallel semiconductor optical amplifiers, a novel design of 40 Gbit/s reconfigurable all-optical dual-directional half-subtractor is proposed and demonstrated. All output logic results show that the scheme achieves over 11=dB extinction ratio, clear and wide open eye diagram, as well as low polarization dependence (< 1 dB), without using any additional input light beam. The scheme may provide a promising candidate for future ultrafast all-optical signal processing applications.

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A scaling law of high-order harmonic generation Wu Yan(吴艳), Ye Hui-Liang(叶会亮), Shao Chu-Yin(邵初寅), and Zhang Jing-Tao(张敬涛) Chin. Phys. B, 2012, 21 (2):  024210.  DOI: 10.1088/1674-1056/21/2/024210 Abstract ( 1132 )   PDF (198KB) ( 604 )   Using a nonperturbative quantum electrodynamics theory of high-order harmonic generation (HHG), a scaling law of HHG is established. The scaling law states that when the atomic binding energy Eb, the wavelength $\lambda$ and the intensity I of the laser field change simultaneously to kEb, $\lambda$/k, and k3I, respectively. The characteristics of the HHG spectrum remain unchanged, while the harmonic yield is enhanced k3 times. That HHG obeys the same scaling law with above-threshold ionization is a solid proof of the fact that the two physical processes have similar physical mechanisms. The variation of integrated harmonic yields is also discussed.

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Equilateral pentagon polarization maintaining photonic crystal fibre with low nonlinearity Yang Han-Rui(杨汉瑞), Li Xu-You(李绪友), Hong Wei(洪伟), and Hao Jin-Hui(郝金会) Chin. Phys. B, 2012, 21 (2):  024211.  DOI: 10.1088/1674-1056/21/2/024211 Abstract ( 998 )   PDF (210KB) ( 750 )   A new pentagon polarization maintaining photonic crystal fibre with low nonlinearity is introduced. The full vector finite element method was used to investigate the distribution and the effective area of modal field, the nonlinear properties, the effective indices of two orthogonal polarization modes and the birefringence of the new PM-PCF effectively. It is found that the birefringence of the new polarization maintaining photonic crystal fibre can easily achieve the order of 10-4, and it can obtain higher birefringence, larger effectively mode-field area and lower nonlinearity than traditional hexagonal polarization maintaining photonic crystal fibre with the same hole pitch, same hole diameter, and same ring number. It is important for sensing and communication applications, especially has potential application for fibre optical gyroscope.

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The contrast between defect solitons in parity–time symmetric superlattice and simple-lattice complex potentials Hu Su-Mei(胡素梅) and Hu Wei(胡巍) Chin. Phys. B, 2012, 21 (2):  024212.  DOI: 10.1088/1674-1056/21/2/024212 Abstract ( 1126 )   PDF (2471KB) ( 579 )   The existence and stability of defect superlattice solitons in parity-time (PT) symmetric superlattice and simple-lattice complex potentials are reported. Compared with defect simple-lattice solitons in similar potentials, the defect soliton in superlattice has a wider stable range than that in simple-lattice. The solitons' power increases with increasing propagation constant. For the positive defect, the solitons are stable in the whole region where solitons exist in the semi-infinite gap. For the zero defect, the solitons are unstable at the edge of the band. For the negative defect, the solitons propagate with the shape of Y at low propagation constant and propagate stably at the large one.

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Maturing process of solitary wave train in a step-down chain Xia Ji-Hong(夏继宏), Wang Ping-Jian(王平建), and Liu Chang-Song(刘长松) Chin. Phys. B, 2012, 21 (2):  024501.  DOI: 10.1088/1674-1056/21/2/024501 Abstract ( 974 )   PDF (139KB) ( 560 )   In a step-down chain a solitary wave (SW) evolves into an SW train (SWT), but the formation of well-defined SWT takes time and space and little is known of the process from immature into mature SWT. We therefore perform a detailed numerical study of this process by analysing the local velocity amplitude and peak overlap of immature ordered SWs. The first SW continuously increases to maximal velocity amplitude and peak overlap until it is matured, but for following SWs there exist a minimal and maximal value of local velocity amplitude and, a minimal and maximal value of local peak overlap, clarifying the details of the energy propagation along the stepped chain. The immature and mature SWTs show the same dependence of the phase velocity on the SWs sequence. These provide guidelines for when or where the attention should be paid in the study of SWT.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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The effect of spherical aberration on temperature distribution inside glass by irradiation of a high repetition rate femtosecond pulse laser Dai Ye(戴晔), Yu Guang-Jun(余光军), Wu Guo-Rui(武国睿), Ma Hong-Liang(马洪良), Yan Xiao-Na(阎晓娜), and Ma Guo-Hong(马国宏) Chin. Phys. B, 2012, 21 (2):  025201.  DOI: 10.1088/1674-1056/21/2/025201 Abstract ( 999 )   PDF (3400KB) ( 776 )   In this paper, we study the effect of spherical aberrations on the light intensity and the temperature distribution in the focal region in a 250-kHz femtosecond laser irradiated Ag+-doped borosilicate glass. When a focused beam goes through an interface between air and glass, spherical aberration will result in the separation of the focal point and then cause a clear change of the light intensity distribution along the incident direction. That phenomenon will further influence the longitudinal cross-section temperature distribution in glass. Here we use Ag nanoparticle formation as a marker for establishing temperature distribution and we find that the formation of nanoparticle shows a strong dependence on the temperature field and the detailed precipitation process is also discussed.

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Dielectric layer-dependent surface plasmon effect of metallic nanoparticles on silicon substrate Xu Rui(徐锐), Wang Xiao-Dong(王晓东), Liu Wen(刘雯), Xu Xiao-Na(徐晓娜), Li Yue-Qiang(李越强), Ji An(季安), Yang Fu-Hua(杨富华), and Li Jin-Min(李晋闽) Chin. Phys. B, 2012, 21 (2):  025202.  DOI: 10.1088/1674-1056/21/2/025202 Abstract ( 1124 )   PDF (1246KB) ( 911 )   The electromagnetic interaction between Ag nanoparticles on the top of the Si substrate and the incident light has been studied by numerical simulations. It is found that the presence of dielectric layers with different thicknesses leads to the varied resonance wavelength and scattering cross section and consequently the shifted photocurrent response for all wavelengths. These different behaviours are determined by whether the dielectric layer is beyond the domain where the elcetric field of metallic plasmons takes effect, combined with the effect of geometrical optics. It is revealed that for particles of a certain size, an appropriate dielectric thickness is desirable to achieve the best absorption. For a certain thickness of spacer, an appropriate granular size is also desirable. These observations have substantial applications for the optimization of surface plasmon enhanced silicon solar cells.

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Spectroscopic properties of Er/Ce-codoped La3Ga5SiO14 Wang Qing-Guo(王庆国), Su Liang-Bi(苏良碧), Li Hong-Jun(李红军), Zheng Li-He(郑丽和), Xu Xiao-Dong(徐晓东), Tang Hui-Li(唐慧丽), Jiang Da-Peng(姜大朋), Wu Feng(吴锋), and Xu Jun(徐军) Chin. Phys. B, 2012, 21 (2):  026101.  DOI: 10.1088/1674-1056/21/2/026101 Abstract ( 961 )   PDF (2222KB) ( 757 )   The Er-single-doped and Er/Ce-codoped La3Ga5SiO14 polycrystalline powders are synthesized by the solid-phase synthesis method. The room-temperature luminescence spectra of the samples are investigated. The Near-infrared-region spectroscopic properties of Er3+ ions in the La3Ga5SiO14 systems are analysed with Judd-Ofelt theory and rate equations. The effective deactivating effect of Ce3+ ions on Er3+ ions is confirmed.

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High-pressure structures of InBi predicted by particle swarm optimization algorithm Liu Huan-Huan(刘欢欢) and Liu Yan-Hui(刘艳辉) Chin. Phys. B, 2012, 21 (2):  026102.  DOI: 10.1088/1674-1056/21/2/026102 Abstract ( 1135 )   PDF (1400KB) ( 727 )   We extensively explore the high-pressure structures of InBi by using a newly developed particle swarm optimization algorithm. An orthorhombic Imma structure is discovered to be stable from 43.7 GPa to 107.9 GPa, ruling out the previously speculated cubic structure. Further increasing the pressure, we find a tetragonal P4/nmm structure which is energetically more favourable from 107.9 GPa to 200 GPa. Especially, the tetragonal P4/nmm structure is known to occur at high pressure in the structures of ZnO and MgTe. We also predict this structure to be a high-pressure structure of ZnTe. Thus the tetragonal P4/nmm structure may be a universal high-pressure structure of the Ⅱ-Ⅵ and the Ⅲ-Ⅴ compounds.

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Molecular dynamics simulations of point defects in plutonium grain boundaries Ao Bing-Yun(敖冰云), Xia Ji-Xing(夏吉星), Chen Pi-Heng(陈丕恒), Hu Wang-Yu(胡望宇), and Wang Xiao-Lin(汪小琳) Chin. Phys. B, 2012, 21 (2):  026103.  DOI: 10.1088/1674-1056/21/2/026103 Abstract ( 1202 )   PDF (1450KB) ( 1058 )   A modified analytic embedded atom method (MAEAM) potential is constructed for fcc updelta-Pu. Molecular dynamics (MD) simulations with the potential are performed to investigate the interactions between two symmetrical tilt grain boundaries (GBs) and point defects such as He atom, vacancy and self-interstitial atom (SIA) in Pu. The calculated results show that point defect formation energies are on average lower than those in the lattice but variations from site to site along the GBs are very remarkable. Both substitutional and interstitial He atoms are trapped at GBs. Interstitial He atom is more strongly bound at the GB core than the substitutional He atom. The binding energy of SIA at GB core is higher than those of He atom and vacancy. GB core can bind many He atoms and SIAs due mainly to the fact that it contains many vacancies. Compared with He atom and SIA, the vacancy far from GB core is difficult to diffuse into the core. The GBs can act as sinks and sources of He atoms and SIAs, which may be a reason for the swelling of Pu after a period of self-irradiation because of the higher concentration of vacancy in the bulk.

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Effect of H impurity on misfit dislocation in Ni-based single-crystal superalloy: molecular dynamic simulations Yu Tao(于涛), Xie Hong-Xian(谢红献), and Wang Chong-Yu(王崇愚) Chin. Phys. B, 2012, 21 (2):  026104.  DOI: 10.1088/1674-1056/21/2/026104 Abstract ( 1056 )   PDF (2637KB) ( 815 )   The effect of H impurity on the misfit dislocation in Ni-based single-crystal superalloy is investigated using the molecular dynamic simulation. It includes the site preferences of H impurity in single crystals Ni and Ni3Al, the interaction between H impurity and the misfit dislocation and the effect of H impurity on the moving misfit dislocation. The calculated energies and simulation results show that the misfit dislocation attracts H impurity which is located at the $\gamma/\gamma'$ interface and Ni3Al and H impurity on the glide plane can obstruct the glide of misfit dislocation, which is beneficial to improving the mechanical properties of Ni based superalloys.

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Thermal conductance in a two-slit quantum waveguide Nie Liu-Ying(聂六英), Li Chun-Xian(李春先), Zhou Xiao-Ping(周晓萍), Wang Cheng-Zhi(王成志), and Cheng Fang(程芳) Chin. Phys. B, 2012, 21 (2):  026301.  DOI: 10.1088/1674-1056/21/2/026301 Abstract ( 1071 )   PDF (167KB) ( 496 )   Using the scattering-matrix method, we investigate the thermal conductance in a two-slit quantum waveguide at low temperature. The results show that the total thermal conductance decreases monotonically with temperature increasing. Moreover, we find that the behaviours of the thermal conductance versus temperature are different for different types of slits.

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Seeing time-reversal transmission characteristics through kinetic anti-ferromagnetic Ising chain Chen Ying-Ming(陈英明) and Wang Bing-Zhong(王秉中) Chin. Phys. B, 2012, 21 (2):  026401.  DOI: 10.1088/1674-1056/21/2/026401 Abstract ( 943 )   PDF (933KB) ( 498 )   As an example of our new approach to complex near-field (NF) scattering of electromagnetic waves, the time-reversal (TR) transmission process on an NF current-element array is mapped to the statistical process on a kinetic Ising transmission chain. Equilibrium statistical mechanics and non-equilibrium Monte Carlo (MC) dynamics help us to find signal jamming, aging, annihilating, creating, and TR symmetry breaking on the chain with inevitable background noises; and these results are general in NF systems where complex electromagnetic scattering arises.

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Atomistic simulation of fcc–bcc phase transition in single crystal Al under uniform compression Li Li(李莉), Shao Jian-Li(邵建立), Li Yan-Fang(李艳芳), Duan Su-Qing(段素青), and Liang Jiu-Qing(梁九卿) Chin. Phys. B, 2012, 21 (2):  026402.  DOI: 10.1088/1674-1056/21/2/026402 Abstract ( 1223 )   PDF (3711KB) ( 1510 )   By molecular dynamics simulations employing an embedded atom model potential, we investigate the fcc-to-bcc phase transition in single crystal Al, caused by uniform compression. Results show that the fcc structure is unstable when the pressure is over 250 GPa, in reasonable agreement with the calculated value through the density functional theory. The morphology evolution of the structural transition and the corresponding transition mechanism are analysed in detail. The bcc (011) planes are transited from the fcc (11$\bar{1}$) plane and the (1$\bar{1}$1) plane. We suggest that the transition mechanism consists mainly of compression, shear, slid and rotation of the lattice. In addition, our radial distribution function analysis explicitly indicates the phase transition of Al from fcc phase to bcc structure.

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Peptide friction in water nanofilm on mica surface Zhou Bo(周波), Xiu Peng(修鹏), Wang Chun-Lei(王春雷), and Fang Hai-Ping(方海平) Chin. Phys. B, 2012, 21 (2):  026801.  DOI: 10.1088/1674-1056/21/2/026801 Abstract ( 1140 )   PDF (2068KB) ( 1137 )   Peptide frictions in water nanofilms of various thicknesses on a mica surface are studied via molecular dynamics simulations. We find that the forced lateral motion of the peptide exhibits stick-slip behaviour at low water coverage; in contrast, the smooth gliding motion is observed at higher water coverage. The adsorbed peptide can form direct peptide-surface hydrogen bonds as well as indirect peptide-water-surface hydrogen bonds with the substrate. We propose that the stick-slip phenomenon is attributed to the overall effects of direct and indirect hydrogen bonds formed between the surface and the peptide.

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Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study Niu Wen-Xia(牛纹霞) and Zhang Hong(张红) Chin. Phys. B, 2012, 21 (2):  026802.  DOI: 10.1088/1674-1056/21/2/026802 Abstract ( 1026 )   PDF (553KB) ( 674 )   We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2$\times$2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.

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

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Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n+-layer Hu Sheng-Dong(胡盛东), Wu Li-Juan(吴丽娟), Zhou Jian-Lin(周建林), Gan Ping(甘平), Zhang Bo(张波), and Li Zhao-Ji(李肇基) Chin. Phys. B, 2012, 21 (2):  027101.  DOI: 10.1088/1674-1056/21/2/027101 Abstract ( 1293 )   PDF (580KB) ( 655 )   A novel silicon-on-insulator (SOI) high-voltage device based on epitaxy-separation by implantation oxygen (SIMOX) with a partial buried n+-layer silicon-on-insulator (PBN SOI) is proposed in this paper. Based on the proposed expressions of the vertical interface electric field, the high concentration interface charges which are accumulated on the interface between top silicon layer and buried oxide layer (BOX) effectively enhance the electric field of the BOX (EI), resulting in a high breakdown voltage (BV) for the device. For the same thicknesses of top silicon layer (10 μm) and BOX (0.375 μm), the EI and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI, respectively.

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Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study Xiao Jin(肖金), Yang Zhi-Xiong(杨志雄), Xie Wei-Tao(谢伟涛), Xiao Li-Xin(肖立新), Xu Hui(徐慧), and OuYang Fang-Ping(欧阳方平) Chin. Phys. B, 2012, 21 (2):  027102.  DOI: 10.1088/1674-1056/21/2/027102 Abstract ( 1227 )   PDF (3398KB) ( 1183 )   By using the first-principles calculations, the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.

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First-principles calculation of structural and electronic properties of pyrochlore Lu2Sn2O7 Chen Zhong-Jun(陈中钧) and Chen Tai-Hong(陈太红) Chin. Phys. B, 2012, 21 (2):  027103.  DOI: 10.1088/1674-1056/21/2/027103 Abstract ( 1093 )   PDF (227KB) ( 802 )   A Density functional theory method within generalized gradient approximation has been performed to obtain the static lattice parameters, oxygen positional parameter, bond length and bond angle and electronic properties of ideal Lu2Sn2O7 pyrochlore. The results are in excellent agreement with available experimental measurements. Density of states (DOS) of this compound was presented and analysed. We also notice the presence of the hybridization between oxygen and Lu metal. The band structure calculations show that the compound has direct band gap of 2.67 eV at the Γ point in the Brillouin zone and this indicates that the material has a semi-conducting feature.

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Role of Ga-doping in iron–gallium alloy clusters Tang Pei-Zhe(汤沛哲), Liu Hai-Tao(刘海涛), Zhu Jie(朱洁), Wang Shan-Ying(王山鹰), and Duan Wen-Hui(段文晖) Chin. Phys. B, 2012, 21 (2):  027104.  DOI: 10.1088/1674-1056/21/2/027104 Abstract ( 1193 )   PDF (1973KB) ( 904 )   The structural and magnetic properties of Fen-mGam (n=3～6, m=0～2; n=13, m=0～3) alloy clusters have been studied using density functional theory. The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites. The Ga-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters, along with a decrease of the local magnetic moments of Fe atoms around Ga dopants. These findings provide a microscopic insight into Fe-Ga alloys which are well-known magnetostriction materials.

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Characteristics of anomalous Hall effect in spin-polarized two-dimensional electron gases in the presence of both intrinsic, extrinsic, and external electric-field induced spin–orbit couplings Liu Song(刘宋), Yan Yu-Zhen(颜玉珍), and Hu Liang-Bin(胡梁宾) Chin. Phys. B, 2012, 21 (2):  027201.  DOI: 10.1088/1674-1056/21/2/027201 Abstract ( 1002 )   PDF (172KB) ( 533 )   The various competing contributions to the anomalous Hall effect in spin-polarized two-dimensional electron gases in the presence of both intrinsic, extrinsic and external electric-field induced spin-orbit coupling were investigated theoretically. Based on a unified semiclassical theoretical approach, it is shown that the total anomalous Hall conductivity can be expressed as the sum of three distinct contributions in the presence of these competing spin-orbit interactions, namely an intrinsic contribution determined by the Berry curvature in the momentum space, an extrinsic contribution determined by the modified Bloch band group velocity and an extrinsic contribution determined by spin-orbit-dependent impurity scattering. The characteristics of these competing contributions are discussed in detail in the paper.

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Signature of symmetry of laterally coupled quantum dots in far-infrared spectrum Gu Li-Ying(谷利英), Li Yan-Fang(李艳芳), Chu Wei-Dong(楚卫东), and Wei Ying-Hui(卫英慧) Chin. Phys. B, 2012, 21 (2):  027301.  DOI: 10.1088/1674-1056/21/2/027301 Abstract ( 1034 )   PDF (1165KB) ( 599 )   We study the effect of structure asymmetry on the energy spectrum and the far-infrared spectrum (FIR) of a lateral coupled quantum dot. The calculated spectrum shows that the parity break of coupled quantum dot results in more coherent superpositions in the low-lying states and exhibits unique anti-crossing in the two-electron FIR spectrum modulated by a magnetic field. We also find that the Coulomb correlation effect can make the FIR spectrum of coupled quantum dot without strict parity deviate greatly from Kohn theorem, which is just contrary to the symmetric case. Our results therefore suggest that FIR spectrum may be used to determine the symmetry of coupled quantum dot and to evaluate the degree of Coulomb interaction.

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Analytical study of surface states caused by the edge decoration Zhao Yuan-Yuan(赵媛媛), Li Wei(李炜), and Tao Rui-Bao(陶瑞宝) Chin. Phys. B, 2012, 21 (2):  027302.  DOI: 10.1088/1674-1056/21/2/027302 Abstract ( 1060 )   PDF (784KB) ( 764 )   Analytical studies of the effect of edge decoration on the energy spectrum of semi-infinite one-dimensional (1D) model and zigzag edged graphene (ZEG) are presented by means of transfer matrix method, in the frame of which the conditions for the existence of edge states are determined. For 1D model, the zero-energy surface state occurs regardless of whether the decorations exist or not, while the non-zero-energy surface states can be induced and manipulated through adjusting the edge decoration. On the other hand, the case for the semi-infinite ZEG model with nearest-neighbour interaction is discussed in the analogous way. The non-zero-energy surface states can be induced by the edge decoration and moreover, the ratio between the edge hopping and the bulk hopping amplitudes should be within a certain threshold.

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Quasibound states in graphene quantum-dot nanostructures generated by concentric potential barrier rings Jiang Zhao-Tan, Yu Cheng-Long, Dong Quan-Li Chin. Phys. B, 2012, 21 (2):  027303.  DOI: 10.1088/1674-1056/21/2/027303 Abstract ( 914 )   PDF (5329KB) ( 804 )   We study the quasibound states in a graphene quantum-dot structure generated by the single-, double-, and triple-barrier electrostatic potentials. It is shown that the strongest quasibound states are mainly determined by the innermost barrier. Specifically, the positions of the quasibound states are determined by the barrier height, the number of the quasibound states is determined by the quantum-dot radius and the angular momentum, and the localization degree of the quasibound states is influenced by the width of the innermost barrier, as well as the outside barriers. Furthermore, according to the study on the double- and triple-barrier quantum dots, we find that an effective way to generate more quasibound states with even larger energy level spacings is to design a quantum dot defined by many concentric barriers with larger barrier-height differences. Last, we extend our results into the quantum dot of many barriers, which gives a complete picture about the formation of the quasibound states in the kind of graphene quantum dot created by many concentric potential barrier rings.

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

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Quantum confinement effects and source-to-drain tunneling in ultra-scaled double-gate silicon n-MOSFETs Jiang Xiang-Wei(姜向伟) and Li Shu-Shen(李树深) Chin. Phys. B, 2012, 21 (2):  027304.  DOI: 10.1088/1674-1056/21/2/027304 Abstract ( 1327 )   PDF (748KB) ( 1253 )   By using the linear combination of bulk band (LCBB) method incorporated with the top of the barrier splitting (TBS) model, we present a comprehensive study on the quantum confinement effects and the source-to-drain tunneling in the ultra-scaled double-gate (DG) metal-oxide-semiconductor field-effect transistors (MOSFETs). A critical body thickness value of 5 nm is found, below which severe valley splittings among different X valleys for the occupied charge density and the current contributions occur in ultra-thin silicon body structures. It is also found that the tunneling current could be nearly 100% with an ultra-scaled channel length. Different from the previous simulation results, it is found that the source-to-drain tunneling could be effectively suppressed in the ultra-thin body thickness (2.0 nm and below) by the quantum confinement and the tunneling could be suppressed down to below 5% when the channel length approaches 16 nm regardless of the body thickness.

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A high mobility C60 field-effect transistor with an ultrathin pentacene passivation layer and bathophenanthroline/metal bilayer electrodes Zhou Jian-Lin(周建林), Yu Jun-Sheng(于军胜), Yu Xin-Ge(于欣格), and Cai Xin-Yang(蔡欣洋) Chin. Phys. B, 2012, 21 (2):  027305.  DOI: 10.1088/1674-1056/21/2/027305 Abstract ( 1116 )   PDF (1560KB) ( 1544 )   C60 field-effect transistor (OFET) with a mobility as high as 5.17 cm2/V·s is fabricated. In our experiment, an ultrathin pentacene passivation layer on poly-(methyl methacrylate) (PMMA) insulator and a bathophenanthroline (Bphen)/Ag bilayer electrode are prepared. The OFET shows a significant enhancement of electron mobility compared with the corresponding device with a single PMMA insultor and an Ag electrode. By analysing the C60 film with atomic force microscopy and X-ray diffraction techniques, it is shown that the pentacene passivation layer can contribute to C60 film growth with the large grain size and significantly improve crystallinity. Moreover, the Bphen buffer layer can reduce the electron contact barrier from Ag electrodes to C60 film efficiently.

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An extended chain Ising model and its Glauber dynamics Zhao Xing-Yu(赵兴宇), Huang Xin-Ru(黄心茹), Fan Xiao-Hui(樊小辉), and Huang Yi-Neng(黄以能) Chin. Phys. B, 2012, 21 (2):  027501.  DOI: 10.1088/1674-1056/21/2/027501 Abstract ( 1163 )   PDF (138KB) ( 880 )   It was first proposed that an extended chain Ising (ECI) model contains the Ising chain model, single spin double-well potentials and a pure phonon heat bath of a specific energy exchange with the spins. The extension method is easy to apply to high dimensional cases. Then the single spin-flip probability (rate) of the ECI model is deduced based on the Boltzmann principle and general statistical principles of independent events and the model is simplified to an extended chain Glauber-Ising (ECGI) model. Moreover, the relaxation dynamics of the ECGI model were simulated by the Monte Carlo method and a comparison with the predictions of the special chain Glauber-Ising (SCGI) model was presented. It was found that the results of the two models are consistent with each other when the Ising chain length is large enough and temperature is relative low, which is the most valuable case of the model applications. These show that the ECI model will provide a firm physical base for the widely used single spin-flip rate proposed by Glauber and a possible route to obtain the single spin-flip rate of other form and even the multi-spin-flip rate.

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Spin waves in the block checkerboard antiferromagnetic phase Hot! Lu Feng(卢峰) and Dai Xi(戴希) Chin. Phys. B, 2012, 21 (2):  027502.  DOI: 10.1088/1674-1056/21/2/027502 Abstract ( 1173 )   PDF (11109KB) ( 559 )   Motivated by the discovery of a new family of 122 iron-based superconductors, we present the theoretical results on the ground state phase diagram, spin wave, and dynamic structure factor obtained from the extended J1-J2 Heisenberg model. In the reasonable physical parameter region of K2Fe4Se5, we find that the block checkerboard antiferromagnetic order phase is stable. There are two acoustic spin wave branches and six optical spin wave branches in the block checkerboard antiferromagnetic phase, which have analytic expressions at the high-symmetry points. To further compare the experimental data on neutron scattering, we investigate the saddlepoint structure of the magnetic excitation spectrum and the inelastic neutron scattering pattern based on linear spin wave theory.

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Compact and broadband circularly polarized ring antenna with wide beam-width for multiple global navigation satellite systems Zhang Hong-Lin(张洪林), Hu Bin-Jie(胡斌杰), and Zhang Xiu-Yin(章秀银) Chin. Phys. B, 2012, 21 (2):  027701.  DOI: 10.1088/1674-1056/21/2/027701 Abstract ( 1175 )   PDF (1944KB) ( 1946 )   A compact and broadband circularly polarized (CP) annular ring antenna with wide beam-width is proposed for multiple global navigation satellite systems (GNSS) in the L1 band. The annular ring is excited by two modified L-probes with quadrature phase difference. It has a 36.3% 10-dB return loss bandwidth and a 13% 3-dB axial ratio bandwidth, because of the orthogonal L-probes with 90$^\circ$ phase difference. The measured peak gain of the antenna is 3.9 dBic. It can detect the satellites at lower elevation as its half power beam-width (HPBW) is 113$^\circ$ in both the x-z and y-z planes, achieving a cross-polarization level of larger than 25 dB. Noticeably, the antenna achieves 89% size reduction compared with the conventional half wavelength patch antennas. It can be used in hand-held navigation devices of multiple GNSS such as COMPASS, Galileo, GPS and GLONASS.

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Selective excitation of molecular mode in a mixture by femtosecond resonance-enhanced coherent anti-Stokes Raman scattering spectroscopy He Ping(贺平), Li Si-Ning(李思宁), Fan Rong-Wei(樊荣伟), Li Xiao-Hui(李晓晖), Xia Yuan-Qin(夏元钦), Yu Xin(于欣), and Chen De-Ying(陈德应) Chin. Phys. B, 2012, 21 (2):  027801.  DOI: 10.1088/1674-1056/21/2/027801 Abstract ( 1115 )   PDF (331KB) ( 592 )   Femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is used to investigate gaseous molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this broad spectroscopy. However, it can be demonstrated that by the electronic resonance enhancement optimization control a selective excitation of specific vibrational mode is possible. Using an electronically resonance-enhanced effect, iodine molecule specific CARS spectroscopy can be obtained from a mixture of iodine-air at room temperature and a pressure of 1 atm (corresponding to a saturation iodine vapour as low as about 35 Pa). The dynamics on either the electronically excited state or the ground state of iodine molecules obtained is consistent with previous studies (vacuum, heated and pure iodine) in the femtosecond time resolved CARS spectroscopy, showing that an effective method of suppressing the non-resonant CARS background and other interferences is demonstrated.

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Structural and optical investigation of nonpolar α-plane GaN grown by metal–organic chemical vapour deposition on r-plane sapphire by neutron irradiation Xu Sheng-Rui(许晟瑞), Zhang Jin-Feng(张金风), Gu Wen-Ping(谷文萍), Hao Yue(郝跃), Zhang Jin-Cheng(张进成), Zhou Xiao-Wei(周小伟), Lin Zhi-Yu(林志宇), and Mao Wei(毛维) Chin. Phys. B, 2012, 21 (2):  027802.  DOI: 10.1088/1674-1056/21/2/027802 Abstract ( 1106 )   PDF (1014KB) ( 688 )   Nonpolar (11$\bar{2}$0) α-plane GaN films are grown by metal-organic chemical vapour deposition (MOCVD) on r-plane (1$\bar{1}$02) sapphire. The samples are irradiated with neutrons under a dose of 1$\times$1015 cm-2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD) and photoluminescence (PL). The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.

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Temperature dependences of Raman scattering in different types of GaN epilayers Xue Xiao-Yong(薛晓咏), Xu Sheng-Rui(许晟瑞), Zhang Jin-Cheng(张进成), Lin Zhi-Yu(林志宇), Ma Jun-Cai(马俊彩), Liu Zi-Yang(刘子扬), Xue Jun-Shuai(薛军帅), and Hao Yue(郝跃) Chin. Phys. B, 2012, 21 (2):  027803.  DOI: 10.1088/1674-1056/21/2/027803 Abstract ( 1237 )   PDF (195KB) ( 1202 )   First-order Raman scatterings of hexagonal GaN layers deposited by the hydride vapour phase epitaxy and by metal-organic chemical vapour deposition on SiC and sapphire substrates are studied in a temperature range between 303 K and 503 K. The temperature dependences of two GaN Raman modes (A1 (LO) and E2 (high)) are obtained. We focus our attention on the temperature dependence of E2 (high) mode and find that for different types of GaN epilayers their temperature dependences are somewhat different. We compare their differences and give them an explanation. The simplified formulas we obtained are in good accordance with experiment data. The results can be used to determine the temperature of a GaN sample.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Double-layer microwave absorber of nanocrystalline strontium ferrite and iron microfibers Wei Chun-Yu(韦春余), Shen Xiang-Qian(沈湘黔), and Song Fu-Zhan(宋福展) Chin. Phys. B, 2012, 21 (2):  028101.  DOI: 10.1088/1674-1056/21/2/028101 Abstract ( 1042 )   PDF (2549KB) ( 1149 )   Microwave absorption properties of the nanocrystalline strontium ferrite (SrFe12O19) and iron ($\alpha$-Fe) microfibers for single-layer and double-layer structures are investigated in a frequency range of 2 GHz-18 GHz. For the single-layer absorbers, the nanocrystalline SrFe12O19 microfibers show some microwave absorptions at 6 GHz-18 GHz, with a minimum reflection loss (RL) value of -11.9 dB at 14.1 GHz for a specimen thickness of 3.0 mm, while for the nanocrystalline $\alpha$-Fe microfibers, their absorptions largely take place at 15 GHz-18 GHz with the RL value exceeding -10 dB, with a minimum RL value of about -24 dB at 17.5 GHz for a specimen thickness of 0.7 mm. For the double-layer absorber with an absorbing layer of α-Fe microfibers with a thickness of 0.7 mm and matching layer of SrFe12O19 microfibers with a thickness of 1.3 mm, the minimum RL value is about -63 dB at 16.4 GHz and the absorption band width is about 6.7 GHz ranging from 11.3 GHz to 18 GHz with the RL value exceeding -10 dB which covers the whole Ku-band (12.4 GHz-18 GHz) and 27% of X-band (8.2 GHz-12.4 GHz).

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InAs/GaAs submonolayer quantum dot superluminescent diode emitting around 970 nm Hot! Li Xin-Kun(李新坤), Liang De-Chun(梁德春), Jin Peng(金鹏), An Qi(安琪), Wei Heng(魏恒), Wu Jian(吴剑), and Wang Zhan-Guo(王占国) Chin. Phys. B, 2012, 21 (2):  028102.  DOI: 10.1088/1674-1056/21/2/028102 Abstract ( 1091 )   PDF (329KB) ( 1232 )   According to the InAs/GaAs submonolayer quantum dot active region, we demonstrate a bent-waveguide superluminescent diode emitting at a wavelength of around 970 nm. At a pulsed injection current of 0.5 A, the device exhibits an output power of 24 mW and an emission spectrum centred at 971 nm with a full width at half maximum of 16 nm.

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Spinel lithium titanate (Li4Ti5O12) as novel anode material for room-temperature sodium-ion battery Hot! Zhao Liang (赵亮),Pan Hui-Lin (潘慧霖),Hu Yong-Sheng (胡勇胜),Li Hong (李泓),Chen Li-Quan (陈立泉) Chin. Phys. B, 2012, 21 (2):  028201.  DOI: 10.1088/1674-1056/21/2/028201 Abstract ( 1889 )   PDF (686KB) ( 2297 )   This is the first time that a novel anode material, spinel Li4Ti5O12 which is well known as a “zero-strain” anode material for lithium storage, has been introduced for sodium-ion battery. The Li4Ti5O12 shows an average Na storage voltage of about 1.0 V and a reversible capacity of about 145 mAh/g, thereby making it a promising anode for sodium-ion battery. Ex-situ X-ray diffraction (XRD) is used to investigate the structure change in the Na insertion/deinsertion process. Based on this, a possible Na storage mechanism is proposed.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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An RLC interconnect analyzable crosstalk model considering self-heating effect Zhu Zhang-Ming(朱樟明) and Liu Shu-Bin(刘术彬) Chin. Phys. B, 2012, 21 (2):  028401.  DOI: 10.1088/1674-1056/21/2/028401 Abstract ( 1054 )   PDF (219KB) ( 672 )   According to the thermal profile of actual multilevel interconnects, in this paper we propose a temperature distribution model of multilevel interconnects and derive an analytical crosstalk model for the distributed resistance-inductance-capacitance (RLC) interconnect considering effect of thermal profile. According to the 65-nm complementary metal-oxide semiconductor (CMOS) process, we compare the proposed RLC analytical crosstalk model with the Hspice simulation results for different interconnect coupling conditions and the absolute error is within 6.5%. The computed results of the proposed analytical crosstalk model show that RCL crosstalk decreases with the increase of current density and increases with the increase of insulator thickness. This analytical crosstalk model can be applied to the electronic design automation (EDA) and the design optimization for nanometer CMOS integrated circuits.

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Characteristics analysis of acupuncture electroencephalograph based on mutual information Lempel–Ziv complexity Luo Xi-Liu(罗昔柳), Wang Jiang(王江), Han Chun-Xiao(韩春晓), Deng Bin(邓斌), Wei Xi-Le(魏熙乐), and Bian Hong-Rui(边洪瑞) Chin. Phys. B, 2012, 21 (2):  028701.  DOI: 10.1088/1674-1056/21/2/028701 Abstract ( 1240 )   PDF (4415KB) ( 883 )   As a convenient approach to the characterization of cerebral cortex electrical information, electroencephalograph (EEG) has potential clinical application in monitoring the acupuncture effects. In this paper, a method composed of the mutual information method and Lempel-Ziv complexity method (MILZC) is proposed to investigate the effects of acupuncture on the complexity of information exchanges between different brain regions based on EEGs. In the experiments, eight subjects are manually acupunctured at ‘Zusanli’acupuncture point (ST-36) with different frequencies (i.e., 50, 100, 150, and 200 times/min) and the EEGs are recorded simultaneously. First, MILZC values are compared in general. Then average brain connections are used to quantify the effectiveness of acupuncture under the above four frequencies. Finally, significance index P values are used to study the spatiality of the acupuncture effect on the brain. Three main findings are obtained: (ⅰ) MILZC values increase during the acupuncture; (ⅱ) manual acupunctures (MAs) with 100 times/min and 150 times/min are more effective than with 50 times/min and 200 times/min; (ⅲ) contralateral hemisphere activation is more prominent than ipsilateral hemisphere's. All these findings suggest that acupuncture contributes to the increase of brain information exchange complexity and the MILZC method can successfully describe these changes.

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Coherence resonance in globally coupled neuronal networks with different neuron numbers Ning Wei-Lian(宁维莲), Zhang Zheng-Zhen(张争珍), Zeng Shang-You(曾上游), Luo Xiao-Shu(罗晓曙), Hu Jin-Lin(胡锦霖), Zeng Shao-Wen(曾绍稳), Qiu Yi(邱怡), and Wu Hui-Si(吴慧思) Chin. Phys. B, 2012, 21 (2):  028702.  DOI: 10.1088/1674-1056/21/2/028702 Abstract ( 1201 )   PDF (315KB) ( 456 )   Because a brain consists of tremendous neuronal networks with different neuron numbers ranging from tens to tens of thousands, we study the coherence resonance due to ion channel noises in globally coupled neuronal networks with different neuron numbers. We confirm that for all neuronal networks with different neuron numbers there exist the array enhanced coherence resonance and the optimal synaptic conductance to cause the maximal spiking coherence. Furthermoremore, the enhancement effects of coupling on spiking coherence and on optimal synaptic conductance are almost the same, regardless of the neuron numbers in the neuronal networks. Therefore for all the neuronal networks with different neuron numbers in the brain, relative weak synaptic conductance (0.1 mS/cm2) is sufficient to induce the maximal spiking coherence and the best sub-threshold signal encoding.

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Detrended cross-correlation analysis of electroencephalogram Wang Jun(王俊) and Zhao Da-Qing(赵大庆) Chin. Phys. B, 2012, 21 (2):  028703.  DOI: 10.1088/1674-1056/21/2/028703 Abstract ( 1085 )   PDF (120KB) ( 646 )   In the paper we use detrended cross-correlation analysis (DCCA) to study the electroencephalograms of healthy young subjects and healthy old subjects. It is found that the cross-correlation between different leads of a healthy young subject is larger than that of a healthy old subject. It was shown that the cross-correlation relationship decreases with the aging process and the phenomenon can help to diagnose whether the subject's brain function is healthy or not.

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Constrained consensuses in disconnected topologies Song Hai-Yu(宋海裕), Yu Li(俞立), Hu Hong-Xiang(胡鸿翔), and Zhang Wen-An(张文安) Chin. Phys. B, 2012, 21 (2):  028901.  DOI: 10.1088/1674-1056/21/2/028901 Abstract ( 951 )   PDF (546KB) ( 572 )   This paper is concerned with the constrained consensuses problem for a group of agents in disconnected topologies. By dividing the communication topology into a combination of directed trees, some necessary and sufficient conditions are derived for all the agents to asymptotically reach a single consensus and multiple consensuses, respectively. The obtained results indicate that arbitrary anticipant consensuses can be achieved, if additional constrained controllers are added to those agents with specific indexes. Some illustrative examples are provided to demonstrate the effectiveness of the proposed theoretical results.

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Evaluating the AS-level Internet models: beyond topological characteristics Fan Zheng-Ping(范正平) Chin. Phys. B, 2012, 21 (2):  028902.  DOI: 10.1088/1674-1056/21/2/028902 Abstract ( 939 )   PDF (458KB) ( 606 )   A surge number of models has been proposed to model the Internet in the past decades. However, the issue on which models are better to model the Internet has still remained a problem. By analysing the evolving dynamics of the Internet, we suggest that at the autonomous system (AS) level, a suitable Internet model, should at least be heterogeneous and have a linearly growing mechanism. More importantly, we show that the roles of topological characteristics in evaluating and differentiating Internet models are apparently over-estimated from an engineering perspective. Also, we find that an assortative network is not necessarily more robust than a disassortative network and that a smaller average shortest path length does not necessarily mean a higher robustness, which is different from the previous observations. Our analytic results are helpful not only for the Internet, but also for other general complex networks.

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Analysis of the Chinese air route network as a complex network Cai Kai-Quan(蔡开泉), Zhang Jun(张军), Du Wen-Bo(杜文博), and Cao Xian-Bin(曹先彬) Chin. Phys. B, 2012, 21 (2):  028903.  DOI: 10.1088/1674-1056/21/2/028903 Abstract ( 1546 )   PDF (2314KB) ( 1425 )   The air route network, which supports all the flight activities of the civil aviation, is the most fundamental infrastructure of air traffic management system. In this paper, we study the Chinese air route network (CARN) within the framework of complex networks. We find that CARN is a geographical network possessing exponential degree distribution, low clustering coefficient, large shortest path length and exponential spatial distance distribution that is obviously different from that of the Chinese airport network (CAN). Besides, via investigating the flight data from 2002 to 2010, we demonstrate that the topology structure of CARN is homogeneous, howbeit the distribution of flight flow on CARN is rather heterogeneous. In addition, the traffic on CARN keeps growing in an exponential form and the increasing speed of west China is remarkably larger than that of east China. Our work will be helpful to better understand Chinese air traffic systems.

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An evolving network model with modular growth Zou Zhi-Yun(邹志云), Liu Peng(刘鹏), Lei Li(雷立), and Gao Jian-Zhi(高健智) Chin. Phys. B, 2012, 21 (2):  028904.  DOI: 10.1088/1674-1056/21/2/028904 Abstract ( 1087 )   PDF (345KB) ( 686 )   In this paper, we propose an evolving network model growing fast in units of module, according to the analysis of the evolution characteristics in real complex networks. Each module is a small-world network containing several interconnected nodes and the nodes between the modules are linked by preferential attachment on degree of nodes. We study the modularity measure of the proposed model, which can be adjusted by changing the ratio of the number of inner-module edges and the number of inter-module edges. In view of the mean-field theory, we develop an analytical function of the degree distribution, which is verified by a numerical example and indicates that the degree distribution shows characteristics of the small-world network and the scale-free network distinctly at different segments. The clustering coefficient and the average path length of the network are simulated numerically, indicating that the network shows the small-world property and is affected little by the randomness of the new module.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

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Collective behaviour of climate indices in the North Pacific air–sea system and its potential relationships with decadal climate changes Wang Xiao-Juan(王晓娟), Zhi Rong(支蓉), He Wen-Ping(何文平), and Gong Zhi-Qiang(龚志强) Chin. Phys. B, 2012, 21 (2):  029201.  DOI: 10.1088/1674-1056/21/2/029201 Abstract ( 1043 )   PDF (3086KB) ( 688 )   A climate network of six climate indices of the North Pacific air-sea system is constructed during the period of 1948-2009. In order to find out the inherent relationship between the intrinsic mechanism of climate index network and the important climate shift, the synchronization behaviour and the coupling behaviour of these indices are investigated. Results indicate that climate network synchronization happened around the beginning of the 1960s, in the middle of the 1970s and at the beginnings of the 1990s and the 2000s separately. These synchronization states were always followed by the decrease of the coupling coefficient. Each synchronization of the network was well associated with the abrupt phase or trend changes of annually accumulated abnormal values of North Pacific sea-surface temperature and 500-hPa height, among which the one that happened in the middle of the 1970s is the most noticeable climate shift. We can also obtain this mysterious shift from the first mode of the empirical orthogonal function of six indices. That is to say, abrupt climate shift in North Pacific air-sea system is not only shown by the phase or trend changes of climate indices, but also might be indicated by the synchronizing and the coupling of climate indices. Furthermore, at the turning point of 1975, there are also abrupt correlation changes in the yearly mode of spatial degree distribution of the sea surface temperature and 500-hPa height in the region of the North Pacific, which further proves the probability of climate index synchronization and coupling shift in air-sea systems.

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Inversion for atmosphere duct parameters using real radar sea clutter Sheng Zheng(盛峥) and Fang Han-Xian(方涵先) Chin. Phys. B, 2012, 21 (2):  029301.  DOI: 10.1088/1674-1056/21/2/029301 Abstract ( 1166 )   PDF (1396KB) ( 746 )   This paper addresses the problem of estimating the lower atmospheric refractivity (M profile) under nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled using five parameters and the horizontal structure is modeled using five parameters. The refractivity model is implemented with and without a priori constraint on the duct strength as might be derived from soundings or numerical weather-prediction models. An electromagnetic propagation model maps the refractivity structure into a replica field. Replica fields are compared with the observed clutter using a squared-error objective function. A global search for the 10 environmental parameters is performed using genetic algorithms. The inversion algorithm is implemented on the basis of S-band radar sea-clutter data from Wallops Island, Virginia (SPANDAR). Reference data are from range-dependent refractivity profiles obtained with a helicopter. The inversion is assessed (ⅰ) by comparing the propagation predicted from the radar-inferred refractivity profiles with that from the helicopter profiles, (ⅱ) by comparing the refractivity parameters from the helicopter soundings with those estimated. This technique could provide near-real-time estimation of ducting effects.

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Recovery of single event upset in advanced complementary metal–oxide semiconductor static random access memory cells Qin Jun-Rui(秦军瑞), Chen Shu-Ming(陈书明), Liang Bin(梁斌), and Liu Bi-Wei(刘必慰) Chin. Phys. B, 2012, 21 (2):  029401.  DOI: 10.1088/1674-1056/21/2/029401 Abstract ( 1200 )   PDF (1424KB) ( 1037 )   Using computer-aided design three-dimensional (3D) simulation technology, the recovery mechanism of single event upset and the effects of spacing and hit angle on the recovery are studied. It is found that the multi-node charge collection plays a key role in recovery and shielding the charge sharing by adding guard rings. It cannot exhibit the recovery effect. It is also indicated that the upset linear energy transfer (LET) threshold is kept constant while the recovery LET threshold increases as the spacing increases. Additionally, the effect of incident angle on recovery is analysed and it is shown that a larger angle can bring about a stronger charge sharing effect, thus strengthening the recovery ability.