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Chin. Phys. B  
  Chin. Phys. B--2015, Vol.24, No.5
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Augmented Lyapunov approach to H state estimation of static neural networks with discrete and distributed time-varying delays

M. Syed Ali, R. Saravanakumar
Chin. Phys. B 2015, 24 (5): 050201;  doi: 10.1088/1674-1056/24/5/050201
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This paper deals with H state estimation problem of neural networks with discrete and distributed time-varying delays. A novel delay-dependent concept of H state estimation is proposed to estimate the H performance and global asymptotic stability of the concerned neural networks. By constructing the Lyapunov–Krasovskii functional and using the linear matrix inequality technique, sufficient conditions for delay-dependent H performances are obtained, which can be easily solved by some standard numerical algorithms. Finally, numerical examples are given to illustrate the usefulness and effectiveness of the proposed theoretical results.

Generalized symmetries of an N=1 supersymmetric Boiti–Leon–Manna–Pempinelli system

Wang Jian-Yong, Tang Xiao-Yan, Liang Zu-Feng, Lou Sen-Yue
Chin. Phys. B 2015, 24 (5): 050202;  doi: 10.1088/1674-1056/24/5/050202
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The formal series symmetry approach (FSSA), a quite powerful and straightforward method to establish infinitely many generalized symmetries of classical integrable systems, has been successfully extended in the supersymmetric framework to explore series of infinitely many generalized symmetries for supersymmetric systems. Taking the N=1 supersymmetric Boiti–Leon–Manna–Pempinelli system as a concrete example, it is shown that the application of the extended FSSA to this supersymmetric system leads to a set of infinitely many generalized symmetries with an arbitrary function f(t). Some interesting special cases of symmetry algebras are presented, including a limit case f(t)=1 related to the commutativity of higher order generalized symmetries.

Numerical solution of the imprecisely defined inverse heat conduction problem

Smita Tapaswini, S. Chakraverty, Diptiranjan Behera
Chin. Phys. B 2015, 24 (5): 050203;  doi: 10.1088/1674-1056/24/5/050203
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This paper investigates the numerical solution of the uncertain inverse heat conduction problem. Uncertainties present in the system parameters are modelled through triangular convex normalized fuzzy sets. In the solution process, double parametric forms of fuzzy numbers are used with the variational iteration method (VIM). This problem first computes the uncertain temperature distribution in the domain. Next, when the uncertain temperature measurements in the domain are known, the functions describing the uncertain temperature and heat flux on the boundary are reconstructed. Related example problems are solved using the present procedure. We have also compared the present results with those in [Inf. Sci. (2008) 178 1917] along with homotopy perturbation method (HPM) and [Int. Commun. Heat Mass Transfer (2012) 39 30] in the special cases to demonstrate the validity and applicability.

Effects of two types of noise and switching on the asymptotic dynamics of an epidemic model

Xu Wei, Wang Xi-Ying, Liu Xin-Zhi
Chin. Phys. B 2015, 24 (5): 050204;  doi: 10.1088/1674-1056/24/5/050204
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This paper mainly investigates dynamics behavior of HIV (human immunodeficiency virus) infectious disease model with switching parameters, and combined bounded noise and Gaussian white noise. This model is different from existing HIV models. Based on stochastic Itô lemma and Razumikhin-type approach, some threshold conditions are established to guarantee the disease eradication or persistence. Results show that the smaller amplitude of bounded noise and R0<1 can cause the disease to die out; the disease becomes persistent if R0>1. Moreover, it is found that larger noise intensity suppresses the prevalence of the disease even if R0>1. Some numerical examples are given to verify the obtained results.

A local energy-preserving scheme for Klein–Gordon–Schrödinger equations

Cai Jia-Xiang, Wang Jia-Lin, Wang Yu-Shun
Chin. Phys. B 2015, 24 (5): 050205;  doi: 10.1088/1674-1056/24/5/050205
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A local energy conservation law is proposed for the Klein–Gordon–Schrödinger equations, which is held in any local time–space region. The local property is independent of the boundary condition and more essential than the global energy conservation law. To develop a numerical method preserving the intrinsic properties as much as possible, we propose a local energy-preserving (LEP) scheme for the equations. The merit of the proposed scheme is that the local energy conservation law can hold exactly in any time–space region. With the periodic boundary conditions, the scheme also possesses the discrete change and global energy conservation laws. A nonlinear analysis shows that the LEP scheme converges to the exact solutions with order O(τ2+h2). The theoretical properties are verified by numerical experiments.

Exponential B-spline collocation method for numerical solution of the generalized regularized long wave equation

Reza Mohammadi
Chin. Phys. B 2015, 24 (5): 050206;  doi: 10.1088/1674-1056/24/5/050206
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The aim of the present paper is to present a numerical algorithm for the time-dependent generalized regularized long wave equation with boundary conditions. We semi-discretize the continuous problem by means of the Crank–Nicolson finite difference method in the temporal direction and exponential B-spline collocation method in the spatial direction. The method is shown to be unconditionally stable. It is shown that the method is convergent with an order of O(k2+h2). Our scheme leads to a tri-diagonal nonlinear system. This new method has lower computational cost in comparison to the Sinc-collocation method. Finally, numerical examples demonstrate the stability and accuracy of this method.

Ponderomotive squeezing and entanglement ina ring cavity with two vibrational mirrors

Feng Xiao-Min, Xiao Yin, Yu Ya-Fei, Zhang Zhi-Ming
Chin. Phys. B 2015, 24 (5): 050301;  doi: 10.1088/1674-1056/24/5/050301
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We investigate the properties of the ponderomotive squeezing and the entanglements in a ring cavity with two vibrational mirrors. In the part about squeezing, we find that the squeezing spectrum of the transmitted field shows a distinct feature when the two vibrational mirrors have different frequencies. We also study the effects of some external parameters such as the temperature and the laser power on the degree of squeezing. In the part concerning entanglement, we study the entanglements between the cavity field and one of the vibrational mirrors, and that between the two vibrational mirrors, with emphasis focusing on the robustness of entanglements with respect to the environment temperature.

Rotation of Bloch sphere induced by Lamb shift in open two-level systems

Wang Guo-You, Tang Ning, Liu Ying, Zeng Hao-Sheng
Chin. Phys. B 2015, 24 (5): 050302;  doi: 10.1088/1674-1056/24/5/050302
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From a quite general form of the Lindblad-like master equation of open two-level systems (qubits), we study the effect of Lamb shift on the non-Markovian dynamics. We find that the Lamb shift can induce a non-uniform rotation of the Bloch sphere, but that it does not affect the non-Markovianity of the open system dynamics. We determine the optimal initial-state pairs that maximize the backflow of information for the considered master equation and find an interesting phenomenon–the sudden change of the non-Markovianity. We relate the dynamics to the evolution of the Bloch sphere to help us comprehend the obtained results.

Generating function of product of bivariate Hermite polynomialsand their applications in studying quantum optical states

Fan Hong-Yi, Zhang Peng-Fei, Wang Zhen
Chin. Phys. B 2015, 24 (5): 050303;  doi: 10.1088/1674-1056/24/5/050303
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By virtue of the operator-Hermite-polynomial method, we derive some new generating function formulas of the product of two bivariate Hermite polynomials. Their applications in studying quantum optical states are presented.

Bidirectional quantum teleportation of unknown photons using path-polarization intra-particle hybrid entanglement and controlled-unitary gates via cross-Kerr nonlinearity

Jino Heo, Chang-Ho Hong, Jong-In Lim, Hyung-Jin Yang
Chin. Phys. B 2015, 24 (5): 050304;  doi: 10.1088/1674-1056/24/5/050304
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We propose an arbitrary controlled-unitary (CU) gate and a bidirectional quantum teleportation (BQTP) scheme. The proposed CU gate utilizes photonic qubits (photons) with cross-Kerr nonlinearities (XKNLs), X-homodyne detectors, and linear optical elements, and consists of the consecutive operation of a controlled-path (C-path) gate and a gathering-path (G-path) gate. It is almost deterministic and feasible with current technology when a strong coherent state and weak XKNLs are employed. Based on the CU gate, we present a BQTP scheme that simultaneously teleports two unknown photons between distant users by transmitting only one photon in a path-polarization intra-particle hybrid entangled state. Consequently, it is possible to experimentally implement BQTP with a certain success probability using the proposed CU gate.

One-dimensional lazy quantum walks and occupancy rate

Li Dan, Michael Mc Gettrick, Zhang Wei-Wei, Zhang Ke-Jia
Chin. Phys. B 2015, 24 (5): 050305;  doi: 10.1088/1674-1056/24/5/050305
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In this paper, we discuss the properties of lazy quantum walks. Our analysis shows that the lazy quantum walks have O(tn) order of the n-th moment of the corresponding probability distribution, which is the same as that for normal quantum walks. The lazy quantum walk with a discrete Fourier transform (DFT) coin operator has a similar probability distribution concentrated interval to that of the normal Hadamard quantum walk. Most importantly, we introduce the concepts of occupancy number and occupancy rate to measure the extent to which the walk has a (relatively) high probability at every position in its range. We conclude that the lazy quantum walks have a higher occupancy rate than other walks such as normal quantum walks, classical walks, and lazy classical walks.

A novel quantum information hiding protocol based on entanglement swapping of high-level Bell states

Xu Shu-Jiang, Chen Xiu-Bo, Wang Lian-Hai, Niu Xin-Xin, Yang Yi-Xian
Chin. Phys. B 2015, 24 (5): 050306;  doi: 10.1088/1674-1056/24/5/050306
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Using entanglement swapping of high-level Bell states, we first derive a covert layer between the secret message and the possible output results of the entanglement swapping between any two generalized Bell states, and then propose a novel high-efficiency quantum information hiding protocol based on the covert layer. In the proposed scheme, a covert channel can be built up under the cover of a high-level quantum secure direct communication (QSDC) channel for securely transmitting secret messages without consuming any auxiliary quantum state or any extra communication resource. It is shown that this protocol not only has a high embedding efficiency but also achieves a good imperceptibility as well as a high security.

Robust quantum secure direct communication and authentication protocol against decoherence noise based on six-qubit DF state

Chang Yan, Zhang Shi-Bin, Yan Li-Li, Han Gui-Hua
Chin. Phys. B 2015, 24 (5): 050307;  doi: 10.1088/1674-1056/24/5/050307
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By using six-qubit decoherence-free (DF) states as quantum carriers and decoy states, a robust quantum secure direct communication and authentication (QSDCA) protocol against decoherence noise is proposed. Four six-qubit DF states are used in the process of secret transmission, however only the |0'> state is prepared. The other three six-qubit DF states can be obtained by permuting the outputs of the setup for |0'>. By using the |0'> state as the decoy state, the detection rate and the qubit error rate reach 81.3%, and they will not change with the noise level. The stability and security are much higher than those of the ping–pong protocol both in an ideal scenario and a decoherence noise scenario. Even if the eavesdropper measures several qubits, exploiting the coherent relationship between these qubits, she can gain one bit of secret information with probability 0.042.

Quantum information transmission in the quantum wireless multihop network based on Werner state

Shi Li-Hui, Yu Xu-Tao, Cai Xiao-Fei, Gong Yan-Xiao, Zhang Zai-Chen
Chin. Phys. B 2015, 24 (5): 050308;  doi: 10.1088/1674-1056/24/5/050308
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Many previous studies about teleportation are based on pure state. Study of quantum channel as mixed state is more realistic but complicated as pure states degenerate into mixed states by interaction with environment, and the Werner state plays an important role in the study of the mixed state. In this paper, the quantum wireless multihop network is proposed and the information is transmitted hop by hop through teleportation. We deduce a specific expression of the recovered state not only after one-hop teleportation but also across multiple intermediate nodes based on Werner state in a quantum wireless multihop network. We also obtain the fidelity of multihop teleportation.

A long-distance quantum key distribution scheme based on pre-detection of optical pulse with auxiliary state

Quan Dong-Xiao, Zhu Chang-Hua, Liu Shi-Quan, Pei Chang-Xing
Chin. Phys. B 2015, 24 (5): 050309;  doi: 10.1088/1674-1056/24/5/050309
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We construct a circuit based on PBS and CNOT gates, which can be used to determine whether the input pulse is empty or not according to the detection result of the auxiliary state, while the input state will not be changed. The circuit can be treated as a pre-detection device. Equipping the pre-detection device in the front of the receiver of the quantum key distribution (QKD) can reduce the influence of the dark count of the detector, hence increasing the secure communication distance significantly. Simulation results show that the secure communication distance can reach 516 km and 479 km for QKD with perfect single photon source and decoy-state QKD with weak coherent photon source, respectively.

Effect of interaction and temperature on quantum phase transition in anisotropic square-octagon lattice

Bao An, Zhang Xue-Feng, Zhang Xiao-Zhong
Chin. Phys. B 2015, 24 (5): 050310;  doi: 10.1088/1674-1056/24/5/050310
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We investigate the effect of interaction, temperature, and anisotropic parameter on the quantum phase transitions in an anisotropic square-octagon lattice with fermions under the framework of the single band Hubbard model through using the combination of cellular dynamical mean field theory and a continuous time Monte Carlo algorithm. The competition between interaction and temperature shows that with the increase of the anisotropic parameter, the critical on-site repulsive interaction for the metal–insulator transition increases for fixed temperature. The interaction–anisotropic parameter phase diagram reveals that with the decrease of temperature, the critical anisotropic parameter for the Mott transition will increase for fixed interaction cases.

A multiple-relaxation-time lattice Boltzmann method for high-speed compressible flows

Li Kai, Zhong Cheng-Wen
Chin. Phys. B 2015, 24 (5): 050501;  doi: 10.1088/1674-1056/24/5/050501
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This paper presents a coupling compressible model of the lattice Boltzmann method. In this model, the multiple-relaxation-time lattice Boltzmann scheme is used for the evolution of density distribution functions, whereas the modified single-relaxation-time (SRT) lattice Boltzmann scheme is applied for the evolution of potential energy distribution functions. The governing equations are discretized with the third-order Monotone Upwind Schemes for scalar conservation laws finite volume scheme. The choice of relaxation coefficients is discussed simply. Through the numerical simulations, it is found that compressible flows with strong shocks can be well simulated by present model. The numerical results agree well with the reference results and are better than that of the SRT version.

Complex transient dynamics of hidden attractors in a simple4D system

Dang Xiao-Yu, Li Chun-Biao, Bao Bo-Cheng, Wu Hua-Gan
Chin. Phys. B 2015, 24 (5): 050503;  doi: 10.1088/1674-1056/24/5/050503
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A simple four-dimensional system with only one control parameter is proposed in this paper. The novel system has a line or no equilibrium for the global control parameter and exhibits complex transient transition behaviors of hyperchaotic attractors, periodic orbits, and unstable sinks. Especially, for the nonzero-valued control parameter, there exists no equilibrium in the proposed system, leading to the formation of various hidden attractors with complex transient dynamics. The research results indicate that the dynamics of the system shows weak chaotic robustness and depends greatly on the initial states.

Directional region control of the thermalfractal diffusion of a space body

Qiao Wei, Sun Jie, Liu Shu-Tang
Chin. Phys. B 2015, 24 (5): 050504;  doi: 10.1088/1674-1056/24/5/050504
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We present a directional region control (DRC) model of thermal diffusion fractal growth with active heat diffusion in three-dimensional space. This model can be applied to predict the space body heat fractal growth and study its directional region control. When the nonlinear interference term and the inner heat source term are generalized functions, the relationship between the particle aggregation probability and the interference terms can be obtained using the norm theory. We can then predict the aggregation form of particles in different regions. When the nonlinear interference terms in the model are expressed as a trigonometric function and its composite function, our simulations show that the DRC method of thermal fractal diffusion is effective and has reference value for the directional control of actual fractal growth systems.

Complex transitions between spike, burst or chaos synchronization states in coupled neurons with coexisting bursting patterns

Gu Hua-Guang, Chen Sheng-Gen, Li Yu-Ye
Chin. Phys. B 2015, 24 (5): 050505;  doi: 10.1088/1674-1056/24/5/050505
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We investigated the synchronization dynamics of a coupled neuronal system composed of two identical Chay model neurons. The Chay model showed coexisting period-1 and period-2 bursting patterns as a parameter and initial values are varied. We simulated multiple periodic and chaotic bursting patterns with non-(NS), burst phase (BS), spike phase (SS), complete (CS), and lag synchronization states. When the coexisting behavior is near period-2 bursting, the transitions of synchronization states of the coupled system follows very complex transitions that begins with transitions between BS and SS, moves to transitions between CS and SS, and to CS. Most initial values lead to the CS state of period-2 bursting while only a few lead to the CS state of period-1 bursting. When the coexisting behavior is near period-1 bursting, the transitions begin with NS, move to transitions between SS and BS, to transitions between SS and CS, and then to CS. Most initial values lead to the CS state of period-1 bursting but a few lead to the CS state of period-2 bursting. The BS was identified as chaos synchronization. The patterns for NS and transitions between BS and SS are insensitive to initial values. The patterns for transitions between CS and SS and the CS state are sensitive to them. The number of spikes per burst of non-CS bursting increases with increasing coupling strength. These results not only reveal the initial value- and parameter-dependent synchronization transitions of coupled systems with coexisting behaviors, but also facilitate interpretation of various bursting patterns and synchronization transitions generated in the nervous system with weak coupling strength.

Cascading failure in the wireless sensor scale-free networks

Liu Hao-Ran, Dong Ming-Ru, Yin Rong-Rong, Han Li
Chin. Phys. B 2015, 24 (5): 050506;  doi: 10.1088/1674-1056/24/5/050506
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In the practical wireless sensor networks (WSNs), the cascading failure caused by a failure node has serious impact on the network performance. In this paper, we deeply research the cascading failure of scale-free topology in WSNs. Firstly, a cascading failure model for scale-free topology in WSNs is studied. Through analyzing the influence of the node load on cascading failure, the critical load triggering large-scale cascading failure is obtained. Then based on the critical load, a control method for cascading failure is presented. In addition, the simulation experiments are performed to validate the effectiveness of the control method. The results show that the control method can effectively prevent cascading failure.
TOPICAL REVIEW—Precision measurement and cold matters

Understanding many-body physics in one dimension from the Lieb-Liniger model

Jiang Yu-Zhu, Chen Yang-Yang, Guan Xi-Wen
Chin. Phys. B 2015, 24 (5): 050311;  doi: 10.1088/1674-1056/24/5/050311
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This article presents an elementary introduction on various aspects of the prototypical integrable model the Lieb- Liniger Bose gas ranging from the cooperative to the collective features of many-body phenomena. In 1963, Lieb and Liniger first solved this quantum field theory many-body problem using Bethe's hypothesis, i.e., a particular form of wavefunction introduced by Bethe in solving the one-dimensional Heisenberg model in 1931. Despite the Lieb-Liniger model is arguably the simplest exactly solvable model, it exhibits rich quantum many-body physics in terms of the aspects of mathematical integrability and physical universality. Moreover, the Yang-Yang grand canonical ensemble description for the model provides us with a deep understanding of quantum statistics, thermodynamics, and quantum critical phenomena at the many-body physical level. Recently, such fundamental physics of this exactly solved model has been attracting growing interest in experiments. Since 2004, there have been more than 20 experimental papers that reported novel observations of different physical aspects of the Lieb-Liniger model in the laboratory. So far the observed results are in excellent agreement with results obtained using the analysis of this simplest exactly solved model. Those experimental observations reveal the unique beauty of integrability.

Micro-Gal level gravity measurements with cold atom interferometry

Zhou Min-Kang, Duan Xiao-Chun, Chen Le-Le, Luo Qin, Xu Yao-Yao, Hu Zhong-Kun
Chin. Phys. B 2015, 24 (5): 050401;  doi: 10.1088/1674-1056/24/5/050401
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Developments of the micro-Gal level gravimeter based on atom interferometry are reviewed, and the recent progress and results of our group are also presented. Atom interferometric gravimeters have shown high resolution and accuracy for gravity measurements. This kind of quantum sensor has excited world-wide interest for both practical applications and fundamental research.

Three-dimensional spin–orbit coupled Fermi gases: Fulde–Ferrell pairing, Majorana fermions, Weyl fermions, and gapless topological superfluidity

Xia-Ji Liu, Hui Hu, Han Pu
Chin. Phys. B 2015, 24 (5): 050502;  doi: 10.1088/1674-1056/24/5/050502
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We theoretically investigate a three-dimensional Fermi gas with Rashba spin–orbit coupling in the presence of both out-of-plane and in-plane Zeeman fields. We show that, driven by a sufficiently large Zeeman field, either out-of-plane or in-plane, the superfluid phase of this system exhibits a number of interesting features, including inhomogeneous Fulde–Ferrell pairing, gapped or gapless topological order, and exotic quasi-particle excitations known as Weyl fermions that have linear energy dispersions in momentum space (i.e., massless Dirac fermions). The topological superfluid phase can have either four or two topologically protected Weyl nodes. We present the phase diagrams at both zero and finite temperatures and discuss the possibility of their observation in an atomic Fermi gas with synthetic spin–orbit coupling. In this context, topological superfluid phase with an imperfect Rashba spin–orbit coupling is also studied.

Superfluidity of Bose–Einstein condensates in ultracold atomic gases

Zhu Qi-Zhong, Wu Biao
Chin. Phys. B 2015, 24 (5): 050507;  doi: 10.1088/1674-1056/24/5/050507
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Liquid helium 4 had been the only bosonic superfluid available in experiments for a long time. This situation was changed in 1995, when a new superfluid was born with the realization of the Bose–Einstein condensation in ultracold atomic gases. The liquid helium 4 is strongly interacting and has no spin; there is almost no way to change its parameters, such as interaction strength and density. The new superfluid, Bose–Einstein condensate (BEC), offers various advantages over liquid helium. On the one hand, BEC is weakly interacting and has spin degrees of freedom. On the other hand, it is convenient to tune almost all the parameters of a BEC, for example, the kinetic energy by spin–orbit coupling, the density by the external potential, and the interaction by Feshbach resonance. Great efforts have been devoted to studying these new aspects, and the results have greatly enriched our understanding of superfluidity. Here we review these developments by focusing on the stability and critical velocity of various superfluids. The BEC systems considered include a uniform superfluid in free space, a superfluid with its density periodically modulated, a superfluid with artificially engineered spin–orbit coupling, and a superfluid of pure spin current. Due to the weak interaction, these BEC systems can be well described by the mean-field Gross–Pitaevskii theory and their superfluidity, in particular critical velocities, can be examined with the aid of Bogoliubov excitations. Experimental proposals to observe these new aspects of superfluidity are discussed.

High-precision spectroscopy of hydrogen molecular ions

Zhong Zhen-Xiang, Tong Xin, Yan Zong-Chao, Shi Ting-Yun
Chin. Phys. B 2015, 24 (5): 053102;  doi: 10.1088/1674-1056/24/5/053102
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In this paper, we overview recent advances in high-precision structure calculations of the hydrogen molecular ions (H2+ and HD+), including nonrelativistic energy eigenvalues and relativistic and quantum electrodynamic corrections. In combination with high-precision measurements, it is feasible to precisely determine a molecular-based value of the proton-to-electron mass ratio. An experimental scheme is presented for measuring the rovibrational transition frequency (v,L):(0,0)→(6,1) in HD+, which is currently underway at the Wuhan Institute of Physics and Mathematics.

Optical determination of the Boltzmann constant

Cheng Cun-Feng, Sun Y. R., Hu Shui-Ming
Chin. Phys. B 2015, 24 (5): 053301;  doi: 10.1088/1674-1056/24/5/053301
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The Boltzmann constant kB is a fundamental physical constant in thermodynamics. The present CODATA recommended value of kB is 1.3806488(13)× 10-23 J/K (relative uncertainty 0.91 ppm), which is mainly determined by acoustic methods. Doppler broadening thermometry (DBT) is an optical method which determines kBT by measuring the Doppler width of an atomic or molecular transition. The methodology and problems in DBT are reviewed, and DBT measurement using the sensitive cavity ring-down spectroscopy (CRDS) is proposed. Preliminary measurements indicate that CRDS-based DBT measurement can potentially reach an accuracy at the 1 ppm level.

Precision measurement with atom interferometry

Wang Jin
Chin. Phys. B 2015, 24 (5): 053702;  doi: 10.1088/1674-1056/24/5/053702
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Development of atom interferometry and its application in precision measurement are reviewed in this paper. The principle, features and the implementation of atom interferometers are introduced, the recent progress of precision measurement with atom interferometry, including determination of gravitational constant and fine structure constant, measurement of gravity, gravity gradient and rotation, test of weak equivalence principle, proposal of gravitational wave detection, and measurement of quadratic Zeeman shift are reviewed in detail. Determination of gravitational redshift, new definition of kilogram, and measurement of weak force with atom interferometry are also briefly introduced.

Precision spectroscopy with a single 40Ca+ ion in a Paul trap

Guan Hua, Huang Yao, Liu Pei-Liang, Bian Wu, Shao Hu, Gao Ke-Lin
Chin. Phys. B 2015, 24 (5): 054213;  doi: 10.1088/1674-1056/24/5/054213
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Precision measurement of the 4s 2S1/2–3d 2D5/2 clock transition based on 40Ca+ ion at 729 nm is reported. A single 40Ca+ ion is trapped and laser-cooled in a ring Paul trap, and the storage time for the ion is more than one month. The linewidth of a 729 nm laser is reduced to about 1 Hz by locking to a super cavity for longer than one month uninterruptedly. The overall systematic uncertainty of the clock transition is evaluated to be better than 6.5× 10-16. The absolute frequency of the clock transition is measured at the 10-15 level by using an optical frequency comb referenced to a hydrogen maser which is calibrated to the SI second through the global positioning system (GPS). The frequency value is 411 042 129 776 393.0(1.6) Hz with the correction of the systematic shifts. In order to carry out the comparison of two 40Ca+ optical frequency standards, another similar 40Ca+ optical frequency standard is constructed. Two optical frequency standards exhibit stabilities of 1× 10-14τ-1/2 with 3 days of averaging. Moreover, two additional precision measurements based on the single trapped 40Ca+ ion are carried out. One is the 3d 2D5/2 state lifetime measurement, and our result of 1174(10) ms agrees well with the results reported in [Phys. Rev. A 62 032503 (2000)] and [Phys. Rev. A 71 032504 (2005)]. The other one is magic wavelengths for the 4s 2S1/2–3d 2D5/2 clock transition; λ|mj|= 1/2= 395.7992(7) nm and λ|mj|= 3/2= 395.7990(7) nm are reported, and it is the first time that two magic wavelengths for the 40Ca+ clock-transition have been reported.

Magnetocaloric effect study of SrFe0.8Co0.2O3 single crystal prepared under high pressure

Xia Hai-Liang, Qin Xiao-Mei, Yang Jun-Ye, Yin Yun-Yu, Dai Jian-Hong, Shi Wang-Zhou, Long You-Wen
Chin. Phys. B 2015, 24 (5): 050701;  doi: 10.1088/1674-1056/24/5/050701
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A high-quality SrFe0.8Co0.2O3 single crystal is prepared by combining floating-zone and high-pressure treatment methods. Its Magnetocaloric effect is investigated by magnetic measurements. A paramagnetism-to-ferromagnetism transition is found at about 270 K and this transition is a second-order one in nature as confirmed by Arrott plots. The saturated moment obtained at 2 K and 7 T is 3.63 μB/f.u. The maximal value of magnetic entropy change measured at 5 T is about 4.0 J·kg-1·K-1. The full wide at half maximum for a magnetic entropy change peak observed in SrFe0.8Co0.2O3 is considerably large. As a consequence, the relative cooling power value of SrFe0.8Co0.2O3 obtained at 5 T is 331 J/kg, which is greatly higher than those observed in other perovskite oxides. The present work therefore provides a promising candidate for magnetic refrigeration near room temperature.

Two waveguide layers in lithium niobate crystal formed by swift heavy Kr ion irradiation

Liu Tao, Huang Qing, Zhao Jin-Hua, Kong Wei-Jin, Liu Peng, Zhang Lian, Zhou Yu-Fan, Yu Xiao-Fei, Wang Lei, Wang Xue-Lin
Chin. Phys. B 2015, 24 (5): 056102;  doi: 10.1088/1674-1056/24/5/056102
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We report the formation of two waveguide layers in a lithium niobate crystal by irradiation with swift heavy Kr ions with high (GeV) energies and ultralow fluences. The micro-Raman spectra are measured at different depths in the irradiated layer and show that the high electronic energy loss can cause lattice damage along the ion trajectory, while the nuclear energy loss causes damage at the end of the ion track. Two waveguide layers are formed by confinement with two barriers associated with decreases in the refractive index that are caused by electronic and nuclear energy losses, respectively.

Asymmetric resistive switching processes in W:AlOx/WOy bilayer devices

Wu Hua-Qiang, Wu Ming-Hao, Li Xin-Yi, Bai Yue, Deng Ning, Yu Zhi-Ping, Qian He
Chin. Phys. B 2015, 24 (5): 058501;  doi: 10.1088/1674-1056/24/5/058501
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Asymmetric resistive switching processes were observed in W:AlOx/WOy bilayer RRAM devices. During pulse programming measurements, the RESET speed is in the range of hundreds of microseconds under -1.1 V bias, while the SET speed is in the range of tens of nanoseconds under 1.2 V bias. Electrical measurements with different pulse conditions and different temperatures were carried out to understand these significant differences in switching time. A redox reaction model in the W:AlOx/WOy device structure is proposed to explain this switching time difference.


Piezoelectricity in K1-xNaxNbO3: First-principles calculation

Li Qiang, Zhang Rui, Lv Tian-Quan, Zheng Li-Mei
Chin. Phys. B 2015, 24 (5): 053101;  doi: 10.1088/1674-1056/24/5/053101
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The piezoelectric properties of K1-xNaxNbO3 are studied by using first-principles calculations within virtual crystal approximation. To understand the critical factors for the high piezoelectric response in K1-xNaxNbO3, the total energy, piezoelectric coefficient, elastic property, density of state, Born effective charge, and energy barrier on polarization rotation paths are systematically investigated. The morphotropic phase boundary in K1-xNaxNbO3 is predicted to occur at x = 0.521, which is in good agreement with the available experimental data. At the morphotropic phase boundary, the longitudinal piezoelectric coefficient d33 of orthorhombic K0.5Na0.5NbO3 reaches a maximum value. The rotated maximum of d33* is found to be along the 50° direction away from the spontaneous polarization (close to the [001] direction). The moderate bulk and shear modulus are conducive to improving the piezoelectric response. By analyzing the energy barrier on polarization rotation paths, it is found that the polarization rotation of orthorhombic K0.5Na0.5NbO3 becomes easier compared with orthorhombic KNbO3, which proves that the high piezoelectric response is attributed to the flattening of the free energy at compositions close to the morphotropic phase boundary.

Relativistic atomic data for W XLVII

Sunny Aggarwal, A. K. S. Jha, Indu Khatri, Narendra Singh, Man Mohan
Chin. Phys. B 2015, 24 (5): 053201;  doi: 10.1088/1674-1056/24/5/053201
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Energy levels, radiative rates, and lifetimes are calculated for all levels of 3s23p, 3s23d, 3s3p2, 3s3d2, 3s3p3d, 3p23d, 3s3d2, 3p3d2, 3p3, and 3d3 configurations of Al-like tungsten ion (W XLVII). Multiconfigurational Dirac–Fock (MCDF) method is adopted for calculating energy levels and radiative rates. Oscillator strengths, radiative rates, and line strengths are reported for some E1 transitions from the ground level. Comparisons are made with the available data in the literature and good agreement has been found which confirms the reliability of our results.

Stereodynamics of the reactions: F+H2/HD/HT→FH+H/D/T

Chi Xiao-Lin, Zhao Jin-Feng, Zhang Yong-Jia, Ma Feng-Cai, Li Yong-Qing
Chin. Phys. B 2015, 24 (5): 053401;  doi: 10.1088/1674-1056/24/5/053401
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Among many kinds of ways to study the properties of atom and molecule collision, the quasi-classical trajectory (QCT) method is an effective one to investigate the molecular reaction dynamics. QCT calculations have been carried out to investigate the stereodynamics of the reactions F+H2/HD/HT→FH+H/D/T, which proceed on the lowest-lying electronic states of the FH2 system based on the potential energy surface (PES) of the 12A' FH2 ground state. Although the QCT method cannot describe all quantum effects in the process of the reaction, it has unique advantages when facing a three-atoms system or complicated polyatomic systems. Differential cross sections (DCSs) and three angle distribution functions P(θr), P(ør), P(θr, ør) on the PES at the collision of 2.74~kcal/mol have been investigated. The isotope effect becomes more obvious with the reagent molecule H2 turning into HD and HT. P(θr, ør), as the joint probability density function of both polar angles θr and ør, can reflect the properties of three-dimensional dynamic more intuitively.

Cooling and trapping polar molecules in an electrostatic trap

Wang Zhen-Xia, Gu Zhen-Xing, Deng Lian-Zhong, Yin Jian-Ping
Chin. Phys. B 2015, 24 (5): 053701;  doi: 10.1088/1674-1056/24/5/053701
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An electrostatic trap for polar molecules is proposed. Loading and trapping of polar molecules can be realized by applying different voltages to the two electrodes of the trap. For ND3 molecular beams centered at ~ 10 m/s, a high loading efficiency of ~ 67% can be obtained, as confirmed by our Monte Carlo simulations. The volume of our trap is as large as ~ 3.6 cm3, suitable for study of the adiabatic cooling of trapped molecules. Our simulations indicate that trapped ND3 molecules can be cooled from ~ 23.3 mK to 1.47 mK by reducing the trapping voltages on the electrodes from 50.0 kV to 1.00 kV.


Influence of obstacle on electromagnetic wave propagation in evaporation duct with experiment verification

Shi Yang, Yang Kun-De, Yang Yi-Xin, Ma Yuan-Liang
Chin. Phys. B 2015, 24 (5): 054101;  doi: 10.1088/1674-1056/24/5/054101
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In this paper, the influence of obstacle on electromagnetic wave propagation in an evaporation duct is investigated, both from numerical simulation and experimental observation. A comparison of electromagnetic wave propagation in evaporation duct with and without obstacle for a typical case is presented. The presence of obstacle causes a significant increase in path loss. The obstacle has significant impact on electromagnetic wave propagation when the frequency is higher than 5 GHz and when the evaporation duct height is higher than 10 m. The influence of an island on electromagnetic wave propagation was observed in the experiment held in the South China Sea, October 2012. The experiment result shows that the island causes about 30–40 dB increase in path loss. The discrepancy between model and measurement is analyzed and the errors of transmitting antenna height and relative humidity are the possible causes of the discrepancy.

Realizing high photovoltaic efficiency with parallel multijunction solar cells based on spectrum-splitting and -concentrating diffractive optical element Hot!

Wang Jin-Ze, Huang Qing-Li, Xu Xin, Quan Bao-Gang, Luo Jian-Heng, Zhang Yan, Ye Jia-Sheng, Li Dong-Mei, Meng Qing-Bo, Yang Guo-Zhen
Chin. Phys. B 2015, 24 (5): 054201;  doi: 10.1088/1674-1056/24/5/054201
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Based on the facts that multijunction solar cells can increase the efficiency and concentration can reduce the cost dramatically, a special design of parallel multijunction solar cells was presented. The design employed a diffractive optical element (DOE) to split and concentrate the sunlight. A rainbow region and a zero-order diffraction region were generated on the output plane where solar cells with corresponding band gaps were placed. An analytical expression of the light intensity distribution on the output plane of the special DOE was deduced, and the limiting photovoltaic efficiency of such parallel multijunction solar cells was obtained based on Shockley–Queisser's theory. An efficiency exceeding the Shockley–Queisser limit (33%) can be expected using multijunction solar cells consisting of separately fabricated subcells. The results provide an important alternative approach to realize high photovoltaic efficiency without the need for expensive epitaxial technology widely used in tandem solar cells, thus stimulating the research and application of high efficiency and low cost solar cells.

Phase and direction dependence of photorefraction in a low-frequency strong circular-polarized plane wave

Huang Yong-Sheng, Wang Nai-Yan, Tang Xiu-Zhang
Chin. Phys. B 2015, 24 (5): 054202;  doi: 10.1088/1674-1056/24/5/054202
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Contrary to the superposition principle, it is well known that photorefraction exists in the vacuum with the presence of a strong static field, a laser field, or a rotational magnetic field. Different from the classical optical crystals, the refractive index also depends on the phase of the strong electromagnetic field. We obtain the phase and direction dependence of the refractive index of a probe wave incident in the strong field of a circular-polarized plane wave by solving the Maxwell equations corrected by the effective Lagrangian. It may provide a valuable theoretical basis to calculate the polarization evolution of waves in the strong electromagnetic circumstances of pulsar or neutron stars.

Ghost imaging based on Pearson correlation coefficients

Yu Wen-Kai, Yao Xu-Ri, Liu Xue-Feng, Li Long-Zhen, Zhai Guang-Jie
Chin. Phys. B 2015, 24 (5): 054203;  doi: 10.1088/1674-1056/24/5/054203
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Correspondence imaging is a new modality of ghost imaging, which can retrieve a positive/negative image by simple conditional averaging of the reference frames that correspond to relatively large/small values of the total intensity measured at the bucket detector. Here we propose and experimentally demonstrate a more rigorous and general approach in which a ghost image is retrieved by calculating a Pearson correlation coefficient between the bucket detector intensity and the brightness at a given pixel of the reference frames, and at the next pixel, and so on. Furthermore, we theoretically provide a statistical interpretation of these two imaging phenomena, and explain how the error depends on the sample size and what kind of distribution the error obeys. According to our analysis, the image signal-to-noise ratio can be greatly improved and the sampling number reduced by means of our new method.

A novel phase-sensitive scanning near-field optical microscope

Wu Xiao-Yu, Sun Lin, Tan Qiao-Feng, Wang Jia
Chin. Phys. B 2015, 24 (5): 054204;  doi: 10.1088/1674-1056/24/5/054204
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Phase is one of the most important parameters of electromagnetic waves. It is the phase distribution that determines the propagation, reflection, refraction, focusing, divergence, and coupling features of light, and further affects the intensity distribution. In recent years, the designs of surface plasmon polariton (SPP) devices have mostly been based on the phase modulation and manipulation. Here we demonstrate a phase sensitive multi-parameter heterodyne scanning near-field optical microscope (SNOM) with an aperture probe in the visible range, with which the near field optical phase and amplitude distributions can be simultaneously obtained. A novel architecture combining a spatial optical path and a fiber optical path is employed for stability and flexibility. Two kinds of typical nano-photonic devices are tested with the system. With the phase-sensitive SNOM, the phase and amplitude distributions of any nano-optical field and localized field generated with any SPP nano-structures and irregular phase modulation surfaces can be investigated. The phase distribution and the interference pattern will help us to gain a better understanding of how light interacts with SPP structures and how SPP waves generate, localize, convert, and propagate on an SPP surface. This will be a significant guidance on SPP nano-structure design and optimization.

Double optomechanical transparency with direct mechanical interaction

Li Ling-Chao, Rao Shi, Xu Jun, Hu Xiang-Ming
Chin. Phys. B 2015, 24 (5): 054205;  doi: 10.1088/1674-1056/24/5/054205
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We present a mechanism for double transparency in an optomechanical system. This mechanism is based on the coupling of a moving cavity mirror to a second mechanical oscillator. Due to the purely mechanical coupling and the radiation pressure, three pathways are established for excitations of the probe photons into the cavity photons. Destructive interference occurs at two different frequencies, leading to double transparency to the probe field. It is the coupling strength between the mechanical oscillators that determines the locations of the transparency windows. Moreover, the normal splitting appears for the generated Stokes field and the four-wave mixing process is inhibited on resonance.

Controllable optical response in hybrid opto-electromechanical systems

Jiang Cheng, Cui Yuan-Shun, Liu Hong-Xiang, Li Xiao-Wei, Chen Gui-Bin
Chin. Phys. B 2015, 24 (5): 054206;  doi: 10.1088/1674-1056/24/5/054206
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We theoretically investigate the analog of electromagnetically induced absorption and parametric amplification in a hybrid opto-electromechanical system consisting of an optical cavity and a microwave cavity coupled to a common mechanical resonator. When the two cavity modes are driven by two pump fields, a weak probe beam is applied to the optical cavity to monitor the optical response of the hybrid system, which can be effectively controlled by adjusting the frequency and power of the two pump fields. We find that the analog of electromagnetically induced absorption and parametric amplification can appear in the probe transmission spectrum when one cavity is pumped on its red sideband and another is pumped on its blue sideband. These phenomena can find potential applications in optical switching and signal amplification in the quantum information process.

Tunable and broadband microwave frequency combs based on a semiconductor laser with incoherent optical feedback

Zhao Mao-Rong, Wu Zheng-Mao, Deng Tao, Zhou Zhen-Li, Xia Guang-Qiong
Chin. Phys. B 2015, 24 (5): 054207;  doi: 10.1088/1674-1056/24/5/054207
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Based on a semiconductor laser (SL) with incoherent optical feedback, a novel all-optical scheme for generating tunable and broadband microwave frequency combs (MFCs) is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 dB amplitude variation. For a fixed bias current, the line spacing (or repetition frequency) of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing increases with the increase in the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. In addition, mappings of amplitude variation, repetition frequency, and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.

Possible generation of a γ-ray laser by electrons wiggling in a background laser

Zhang Qi-Ren
Chin. Phys. B 2015, 24 (5): 054208;  doi: 10.1088/1674-1056/24/5/054208
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The possibility of γ-ray laser generation by the radiation of wiggling electrons in a usual background laser is discussed.

General design basis for a final optics assembly to decrease filamentary damage

Sun Xiao-Yan, Lu Xing-Qiang, Lü Feng-Nian, Zhang Guo-Wen, Zhang Zhen, Yin Xian-Hua, Fan Dian-Yuan
Chin. Phys. B 2015, 24 (5): 054209;  doi: 10.1088/1674-1056/24/5/054209
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The high-power laser beam in the final optics assembly of high-power laser facilities is often modulated by contamination particles, which may cause local high light intensity, thereby increasing the filamentary damage probability for optical components. To study the general design basis for a final optics assembly to decrease the risk of filamentary damage, different-sized contamination particles deposited on a component surface are simulated to modulate a 351-nm laser beam based on the optical transmission theory, and the corresponding simulation results are analyzed statistically in terms of the propagation characteristic and the light field intensity distribution of the modulated laser beam. The statistical results show that component thickness and distance between components can to some extent be optimized to reduce the appearance of local high light intensity, and the general design basis of component thickness and arrangement are given for different control levels of particle sizes. Moreover, the statistical results can also predict the laser beam quality approximately under the existing optics design and environmental cleanliness. The optimized design for final optics assembly based on environmental cleanliness level is useful to prolong the lifetime of optics and enhance the output power of high-power laser facilities.

Generation of isolated attosecond pulses in bowtie-shaped nanostructure with three-color spatially inhomogeneous fields

Xue Shan, Du Hong-Chuan, Xia Yue, Hu Bi-Tao
Chin. Phys. B 2015, 24 (5): 054210;  doi: 10.1088/1674-1056/24/5/054210
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We theoretically investigate high-order harmonic generation in a two-color multi-cycle inhomogeneous field combined with a 27th harmonic pulse. By considering a bowtie-shaped gold nanostructure, the spatiotemporal profiles of enhanced plasmonic fields are obtained by solving the Maxwell equation using finite-domain time-difference method. Based on quantum-mechanical and classical models, the effect of 27th harmonic pulse, temporal profile of enhanced plasmonic field and inhomogeneity on supercontinuum generation are analyzed and discussed. As a result, broadband supercontinuum can be generated from our approach with optimized gap size of nanostructure. Moreover, these results are not sensitively dependent on the relative phase in the two-color field.

Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal

Wu Ri-Na, Wu Jie, Wu Xiao-Jiao, Dai Qin
Chin. Phys. B 2015, 24 (5): 054211;  doi: 10.1088/1674-1056/24/5/054211
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In this work, negative dielectric nematic liquid crystal SLC12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap (PBG) is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 ℃ to 662.8 nm at 67 ℃, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation.

An improved transmitting multi-layer thin-film filter

Zhang Ying, Qi Hong-Ji, Yi Kui, Wang Yan-Zhi, Sui Zhan, Shao Jian-Da
Chin. Phys. B 2015, 24 (5): 054212;  doi: 10.1088/1674-1056/24/5/054212
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The angular resolutions of the phase-shifted Rugate thin-film filters, the ultra-narrow bandpass filters, and a cutoff filter-combination device are discussed, and the electric field distributions of the filters are compared. The results show that the three transmitting multi-layer thin-film filters can realize the same angular resolution, but the electric field in the cutoff filter-combination device is the lowest. Because a lower electric-field distribution corresponds to a higher laser-induced damage threshold of the thin films, the cutoff filter-combination device may replace the traditional spatial filters in high power laser systems.

Interface-guided mode of Lamb waves in a two-dimensional phononic crystal plate

Huang Ping-Ping, Yao Yuan-Wei, Wu Fu-Gen, Zhang Xin, Li Jing, Hu Ai-Zhen
Chin. Phys. B 2015, 24 (5): 054301;  doi: 10.1088/1674-1056/24/5/054301
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We investigate the interface-guided mode of Lamb waves in a phononic crystal heterostructures plate, which is composed of two different semi-infinite phononic crystal (PC) plates. The interface-guided modes of the Lamb wave can be obtained by the lateral lattice slipping or by the interface longitudinal gliding. Significantly, it is observed that the condition to generate the interface-guided modes of the Lamb wave is more demanding than that of the studied fluid–fluid system. The interface-guided modes are strongly affected not only by the relative movement of the two semi-infinite PCs but also by the thickness of the PC plate.

Flow aeroacoustic damping using coupled mechanical–electrical impedance in lined pipeline

Chen Yong, Huang Yi-Yong, Chen Xiao-Qian, Bai Yu-Zhu, Tan Xiao-Dong
Chin. Phys. B 2015, 24 (5): 054302;  doi: 10.1088/1674-1056/24/5/054302
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We report a new noise-damping concept which utilizes a coupled mechanical–electrical acoustic impedance to attenuate an aeroacoustic wave propagating in a moving gas confined by a cylindrical pipeline. An electrical damper is incorporated to the mechanical impedance, either through the piezoelectric, electrostatic, or electro-magnetic principles. Our numerical study shows the advantage of the proposed methodology on wave attenuation. With the development of the micro-electro-mechanical system and material engineering, the proposed configuration may be promising for noise reduction.

Spectral enhancement of thermal radiation by laser fabricating grating structure on nickel surface

Liu Song, Liu Shi-Bing
Chin. Phys. B 2015, 24 (5): 054401;  doi: 10.1088/1674-1056/24/5/054401
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Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared (FTIR) spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance (SPR) and Kirchhoff's law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis (RCWA) to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.

Bifurcation for the generalized Birkhoffian system

Mei Feng-Xiang, Wu Hui-Bin
Chin. Phys. B 2015, 24 (5): 054501;  doi: 10.1088/1674-1056/24/5/054501
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The system described by the generalized Birkhoff equations is called a generalized Birkhoffian system. In this paper, the condition under which the generalized Birkhoffian system can be a gradient system is given. The stability of equilibrium of the generalized Birkhoffian system is discussed by using the properties of the gradient system. When there is a parameter in the equations, its influences on the stability and the bifurcation problem of the system are considered.

Effect of supercritical water shell on cavitation bubble dynamics

Shao Wei-Hang, Chen Wei-Zhong
Chin. Phys. B 2015, 24 (5): 054701;  doi: 10.1088/1674-1056/24/5/054701
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Based on reported experimental data, a new model for single cavitation bubble dynamics is proposed considering a supercritical water (SCW) shell surrounding the bubble. Theoretical investigations show that the SCW shell apparently slows down the oscillation of the bubble and cools the gas temperature inside the collapsing bubble. Furthermore, the model is simplified to a Rayleigh–Plesset-like equation for a thin SCW shell. The dependence of the bubble dynamics on the thickness and density of the SCW shell is studied. The results show the bubble dynamics depends on the thickness but is insensitive to the density of the SCW shell. The thicker the SCW shell is, the smaller are the wall velocity and the gas temperature in the bubble. In the authors' opinion, the SCW shell works as a buffering agent. In collapsing, it is compressed to absorb a good deal of the work transformed into the bubble internal energy during bubble collapse so that it weakens the bubble oscillations.

Low-frequency oscillations in Hall thrusters

Wei Li-Qiu, Han Liang, Yu Da-Ren, Guo Ning
Chin. Phys. B 2015, 24 (5): 055201;  doi: 10.1088/1674-1056/24/5/055201
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In this paper, we summarize the research development of low-frequency oscillations in the last few decades. The findings of physical mechanism, characteristics and stabilizing methods of low-frequency oscillations are discussed. It shows that it is unreasonable and incomplete to model an ionization region separately to analyze the physical mechanism of low-frequency oscillations. Electro-dynamics as well as the formation conditions of ionization distribution play an important role in characteristics and stabilizing of low-frequency oscillations. Understanding the physical mechanism and characteristics of low- frequency oscillations thoroughly and developing a feasible method stabilizing this instability are still important research subjects.

Structure and chemical valence study of Srn+1RunO3n+1 (n=1, 2, ∞) series

Zheng Long, Zhu Xiao-Qin, Sui Yong-Xing, Xue Jian-Zhong, Liu Bo, Pei Ming-Xu
Chin. Phys. B 2015, 24 (5): 056101;  doi: 10.1088/1674-1056/24/5/056101
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Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn+1RunO3n+1 (n=1, 2, ∞) are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Srn+1RunO3n+1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn+1RunO3n+1 (n=1, 2, ∞).

Influence of heavy ion irradiation on DC and gate-lag performance of AlGaN/GaN HEMTs

Lei Zhi-Feng, Guo Hong-Xia, Zeng Chang, Chen Hui, Wang Yuan-Sheng, Zhang Zhan-Gang
Chin. Phys. B 2015, 24 (5): 056103;  doi: 10.1088/1674-1056/24/5/056103
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AlGaN/GaN high electron mobility transistors (HEMTs) were irradiated by 256 MeV 127I ions with a fluence up to 1× 1010 ions/cm2 at the HI-13 heavy ion accelerator of the China Institute of Atomic Energy. Both the drain current Id and the gate current Ig increased in off-state during irradiation. Post-irradiation measurement results show that the device output, transfer, and gate characteristics changed significantly. The saturation drain current, reverse gate leakage current, and the gate-lag all increased dramatically. By photo emission microscopy, electroluminescence hot spots were found in the gate area. All of the parameters were retested after one day and after one week, and no obvious annealing effect was observed under a temperature of 300 K. Further analysis demonstrates that swift heavy ions produced latent tracks along the ion trajectories through the hetero-junction. Radiation-induced defects in the latent tracks decreased the charges in the two-dimensional electron gas and reduced the carrier mobility, degrading device performance.

Characterization of CoPt nanowire fabricated by glancing angle deposition

Satoshi Kitai, Zhang Zheng-Jun, Shi Ji, Yoshio Nakamura
Chin. Phys. B 2015, 24 (5): 056201;  doi: 10.1088/1674-1056/24/5/056201
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CoPt and Co nanowire films were deposited by the Glancing Angle Deposition (GLAD) method. All samples are deposited on Si substrates that were covered by polystyrene spheres to assist the alignment of nanowires. SEM observation results show that the length and diameter of nanowires are uniform for all samples. According to the result of XRD, the crystal structure of CoPt is fcc. The angular dependence of magnetization of the nanowires shows that the easy axis of magnetization is along the growth direction of the nanowires.

An analytical model of thermal mechanical stress induced by through silicon via

Dong Gang, Shi Tao, Zhao Ying-Bo, Yang Yin-Tang
Chin. Phys. B 2015, 24 (5): 056601;  doi: 10.1088/1674-1056/24/5/056601
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We present an accurate through silicon via (TSV) thermal mechanical stress analytical model which is verified by using finite element method (FEM). The results show only a very small error. By using the proposed analytical model, we also study the impacts of the TSV radius size, the thickness, the material of Cu diffusion barrier, and liner on the stress. It is found that the liner can absorb the stress effectively induced by coefficient of thermal expansion mismatch. The stress decreases with the increase of liner thickness. Benzocyclobutene (BCB) as a liner material is better than SiO2. However, the Cu diffusion barrier has little effect on the stress. The stress with a smaller TSV has a smaller value. Based on the analytical model, we explore and validate the linear superposition principle of stress tensors and demonstrate the accuracy of this method against detailed FEM simulations. The analytic solutions of stress of two TSVs and three TSVs have high precision against the finite element result.

Spin excitation spectra of spin–orbit coupled bosons in an optical lattice

Li Ruo-Yan, He Liang, Sun Qing, Ji An-Chun, Tian Guang-Shan
Chin. Phys. B 2015, 24 (5): 056701;  doi: 10.1088/1674-1056/24/5/056701
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Spin-wave excitation plays important roles in the investigation of the magnetic phases. In this paper, we study the spin-wave excitation spectra of two-component Bose gases with spin–orbit coupling in a deep square optical lattice using the spin-wave theory. We find that, while the excitation spectrum of the vortex crystal phase is gapless with a linear dispersion in the vicinity of the minimum point, the spectra of the commensurate spiral spin phase and the skyrmion crystal phase are gapped. Significantly, the spin fluctuations strongly destabilize the classical ground state of the skyrmion phase with the appearance of an imaginary part in the eigenfrequencies of spin excitations. Such features of the spin excitation spectra provide further insights into the exotic spin phases.

Pattern transition from nanohoneycomb to nanograss on germanium by gallium ion bombardment

Zheng Xiao-Hu, Zhang Miao, Huang An-Ping, Xiao Zhi-Song, Paul K Chu, Wang Xi, Di Zeng-Feng
Chin. Phys. B 2015, 24 (5): 056801;  doi: 10.1088/1674-1056/24/5/056801
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During the irradiation of Ge surface with Ga+ ions up to 1017 ions·cm-2, various patterns from ordered honeycomb to nanograss structure appear to be decided by the ion beam energy. The resulting surface morphologies have been studied by scanning electron microscopy and atomic force microscopy. For high energy Ga+ irradiation (16–30 keV), by controlling the ion fluence, we have captured that the equilibrium nanograss morphology also originates from the ordered honeycomb structure. When honeycomb holes are formed by ion erosion, heterogeneous distribution of the deposited energy along the holes leads to viscous flow from the bottom to the plateau. Redistribution of target atoms results in the growth of protuberances on the plateau, and finally the pattern evolution from honeycomb to nanograss with an equilibrium condition.

Molecular dynamic simulations of surface morphology and pulsedlaser deposition growth of lithium niobate thin filmson silicon substrate

Liu Yue, Zhu Hao-Nan, Pei Zi-Dong, Kong Yong-Fa, Xu Jing-Jun
Chin. Phys. B 2015, 24 (5): 056802;  doi: 10.1088/1674-1056/24/5/056802
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The molecular dynamic simulation of lithium niobate thin films deposited on silicon substrate is carried out by using the dissipative particle dynamics method. The simulation results show that the Si (111) surface is more suitable for the growth of smooth LiNbO3 thin films compared to the Si(100) surface, and the optimal deposition temperature is around 873 K, which is consistent with the atomic force microscope results. In addition, the calculation molecular number is increased to take the electron spins and other molecular details into account.

Adsorption of glycine on diamond (001): Role of bond angle ofcarbon atoms

Li Lin, Xu Jing, Xu Li-Fang, Lian Chao-Sheng, Li Jun-Jie, Wang Jian-Tao, Gu Chang-Zhi
Chin. Phys. B 2015, 24 (5): 056803;  doi: 10.1088/1674-1056/24/5/056803
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The adsorption behaviors of glycine on diamond (001) are systematically investigated by first-principles calculations. We have considered all possible adsorption configurations without a surface dangling bond and give a quantitative analysis for the relationship between the deviation of carbon bond angle and adsorption energy. We found that a smaller distortion of carbon covalent bond angle results in a more stable adsorption structure, and the most stable adsorption has a benzene-ring-like structure with the highest adsorption energy of 5.11 eV per molecule and the minimum distortion of carbon covalent bond angle.

Structural characteristics of surface-functionalized nitrogen-doped diamond-like carbon films and effective adjustment to cell attachment

Liu Ai-Ping, Liu Min, Yu Jian-Can, Qian Guo-Dong, Tang Wei-Hua
Chin. Phys. B 2015, 24 (5): 056804;  doi: 10.1088/1674-1056/24/5/056804
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Nitrogen-doped diamond-like carbon (DLC:N) films prepared by the filtered cathodic vacuum arc technology are functionalized with various chemical molecules including dopamine (DA), 3-Aminobenzeneboronic acid (APBA), and adenosine triphosphate (ATP), and the impacts of surface functionalities on the surface morphologies, compositions, microstructures, and cell compatibility of the DLC:N films are systematically investigated. We demonstrate that the surface groups of DLC:N have a significant effect on the surface and structural properties of the film. The activity of PC12 cells depends on the particular type of surface functional groups of DLC:N films regardless of surface roughness and wettability. Our research offers a novel way for designing functionalized carbon films as tailorable substrates for biosensors and biomedical engineering applications.

Effect of thermal pretreatment of metal precursor on the properties of Cu2ZnSnS4 films

Wang Wei, Shen Hong-Lie, Jin Jia-Le, Li Jin-Ze, Ma Yue
Chin. Phys. B 2015, 24 (5): 056805;  doi: 10.1088/1674-1056/24/5/056805
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Zn/Sn/Cu (CZT) stacks were prepared by RF magnetron sputtering. The stacks were pretreated at different temperatures (200 ℃, 300 ℃, 350 ℃, and 400 ℃) for 0.5 h and then followed by sulfurization at 500 ℃ for 2 h. Then, the structures, morphologies, and optical properties of the as-obtained Cu2ZnSnS4 (CZTS) films were studied by x-ray diffraction (XRD), Raman spectroscopy, UV–Vis–NIR, scanning electron microscope (SEM), and energy-dispersive x-ray spectroscopy (EDX). The XRD and Raman spectroscopy results indicated that the sample pretreated at 350 ℃ had no secondary phase and good crystallization. At the same time, SEM confirmed that it had large and dense grains. According to the UV–Vis–NIR spectrum, the sample had an absorption coefficient larger than 104 cm-1 in the visible light range and a band gap close to 1.5 eV.

Efficiency droop suppression in GaN-based light-emitting diodes by chirped multiple quantum well structure at high current injection

Zhao Yu-Kun, Li Yu-Feng, Huang Ya-Ping, Wang Hong, Su Xi-Lin, Ding Wen, Yun Feng
Chin. Phys. B 2015, 24 (5): 056806;  doi: 10.1088/1674-1056/24/5/056806
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Gallium nitride (GaN) based light-emitting diodes (LEDs) with chirped multiple quantum well (MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells (QWs), LEDs with chirped MQW structures have better internal quantum efficiency (IQE) and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 mA/mm2, reduced down from 28.6% (conventional uniform LEDs) to 23.7% (chirped MQWs-a) and 18.6% (chirped MQWs-b), respectively. Meanwhile, the peak IQE increases from 76.9% (uniform LEDs) to 83.7% (chirped MQWs-a) and 88.6% (chirped MQWs-b). The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop.


Antiferromagnetism and Kondo screening on a honeycomb lattice Hot!

Lin Heng-Fu, Tao Hong-Shuai, Guo Wen-Xiang, Liu Wu-Ming
Chin. Phys. B 2015, 24 (5): 057101;  doi: 10.1088/1674-1056/24/5/057101
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Magnetic adatoms in the honeycomb lattice have received tremendous attention due to the interplay between Ruderman–Kittel–Kasuya–Yosida interaction and Kondo coupling leading to very rich physics. Here we study the competition between the antiferromagnetism and Kondo screening of local moments by the conduction electrons on the honeycomb lattice using the determinant quantum Monte Carlo method. While changing the interband hybridization V, we systematically investigate the antiferromagnetic-order state and the Kondo singlet state transition, which is characterized by the behavior of the local moment, antiferromagnetic structure factor, and the short range spin-spin correlation. The evolution of the single particle spectrum are also calculated as a function of hybridization V, we find that the system presents a small gap in the antiferromagnetic-order region and a large gap in the Kondo singlet region in the Fermi level. We also find that the localized and itinerant electrons coupling leads to the midgap states in the conduction band in the Fermi level at very small V. Moreover, the formation of antiferromagnetic order and Kondo singlet are studied as on-site interaction U or temperature T increasing, we have derived the phase diagrams at on-site interaction U (or temperature T) and hybridization V plane.

Experimental and theoretical study on field emission properties of zinc oxide nanoparticles decorated carbon nanotubes

Li Xin, Zhou Wei-Man, Liu Wei-Hua, Wang Xiao-Li
Chin. Phys. B 2015, 24 (5): 057102;  doi: 10.1088/1674-1056/24/5/057102
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Field emission properties of zinc oxide (ZnO) nanoparticles (NPs) decorated carbon nanotubes (CNTs) are investigated experimentally and theoretically. CNTs are in situ decorated with ZnO NPs during the growth process by chemical vapor deposition using a carbon source from the iron phthalocyanine pyrolysis. The experimental field emission test shows that the ZnO NP decoration significantly improves the emission current from 50 μA to 275 μA at 550 V and the reduced threshold voltage from 450 V to 350 V. The field emission mechanism of ZnO NPs on CNTs is theoretically studied by the density functional theory (DFT) combined with the Penn–Plummer method. The ZnO NPs reconstruct the ZnO–CNT structure and pull down the surface barrier of the entire emitter system to 0.49 eV so as to reduce the threshold electric field. The simulation results suggest that the presence of ZnO NPs would increase the LDOS near the Fermi level and increase the emission current. The calculation results are consistent with the experiment results.

A novel x-ray circularly polarized ranging method

Song Shi-Bin, Xu Lu-Ping, Zhang Hua, Gao Na, Shen Yang-He
Chin. Phys. B 2015, 24 (5): 057201;  doi: 10.1088/1674-1056/24/5/057201
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Range measurement has found multiple applications in deep space missions. With more and further deep space exploration activities happening now and in the future, the requirement for range measurement has risen. In view of the future ranging requirement, a novel x-ray polarized ranging method based on the circular polarization modulation is proposed, termed as x-ray circularly polarized ranging (XCPolR). XCPolR utilizes the circular polarization modulation to process x-ray signals and the ranging information is conveyed by the circular polarization states. As the circular polarization states present good stability in space propagation and x-ray detectors have light weight and low power consumption, XCPolR shows great potential in the long-distance range measurement and provides an option for future deep space ranging. In this paper, we present a detailed illustration of XCPolR. Firstly, the structure of the polarized ranging system is described and the signal models in the ranging process are established mathematically. Then, the main factors that affect the ranging accuracy, including the Doppler effect, the differential demodulation, and the correlation error, are analyzed theoretically. Finally, numerical simulation is carried out to evaluate the performance of XCPolR.

Spin transport in a Zigzag normal/ferromagnetic graphene junction

Shi Hao-Sheng, Vahram L. Grigoryan
Chin. Phys. B 2015, 24 (5): 057202;  doi: 10.1088/1674-1056/24/5/057202
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We study magnetic proximity effect induced low-energy spin transport in the normal/ferromagnetic junction of a semi-infinite zigzag graphene nanoribbon. Due to the absence of a spin flip in a single interface, the spin transfer in this model can be described by the “two-spin channel” model. We identify each spin channel as either a perfect conducting or a non-conducting channel. This feature leads to spin filter in symmetric zigzag graphene nanoribbon and spin precession in antisymmetric zigzag graphene nanoribbon, and helps to directly determine the exchange-splitting intensity directly, even without an external auxiliary bias.

Modified method of surface plasmons in metal superlattices

Zhang Yu-Liang, Wang Xuan-Zhang
Chin. Phys. B 2015, 24 (5): 057301;  doi: 10.1088/1674-1056/24/5/057301
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We present a modified method to solve the surface plasmons (SPs) of semi-infinite metal/dielectric superlattices and predicted new SP modes in physics. We find that four dispersion-equation sets and all possible SP modes are determined by them. Our analysis and numerical calculations indicate that besides the SP mode obtained in the original theory, the other two SP modes are predicted, which have either a positive group velocity or a negative group velocity. We also point out the possible defect in the previous theoretical method in accordance to the linear algebra principle.

Heat generation by spin-polarized current in a quantum dot connected to spin battery and ferromagnetic lead

Bai Xu-Fang, Sun Lian-Liang, Chi Feng
Chin. Phys. B 2015, 24 (5): 057302;  doi: 10.1088/1674-1056/24/5/057302
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We study theoretically the heat originated from electron–phonon coupling in a spintronic device composed of a semiconductor quantum dot attached to one spin battery and one ferromagnetic lead. It is found that the phenomenon of the negative differential of the heat current, which has previously been predicted in the charge-based device, disappears due to the Pauli exclusion principle resulted from the presence of the spin battery. Under some conditions, huge heat in the heat generation induced by resonant phonon emitting processes also disappears in this spin-based device. Furthermore, we find that the ferromagnetism of the lead can be used to effectively adjust the magnitude of the heat current in different dot level ranges. The proposed system is realizable by current technology and may be useful in designing high-efficiency spintronic components.

Si and Mg pair-doped interlayers for improving performance of AlGaN/GaN heterostructure field effect transistors grown on Si substrate

Ni Yi-Qiang, He Zhi-Yuan, Yao Yao, Yang Fan, Zhou De-Qiu, Zhou Gui-Lin, Shen Zhen, Zhong Jian, Zheng Yue, Zhang Bai-Jun, Liu Yang
Chin. Phys. B 2015, 24 (5): 057303;  doi: 10.1088/1674-1056/24/5/057303
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We report a novel structure of AlGaN/GaN heterostructure field effect transistors (HFETs) with a Si and Mg pair-doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio (~ 109). Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current.

Anisotropic transport properties of charge-ordered La5/8-yPryCa3/8MnO3 (y=0.43) film

Liu Yuan-Bo, Wang Shuan-Hu, Sun Ji-Rong, Shen Bao-Gen
Chin. Phys. B 2015, 24 (5): 057304;  doi: 10.1088/1674-1056/24/5/057304
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The anisotropic resistances along [001] and [1-10] axes are investigated for an La5/8-yPryCa3/8MnO3 (y=0.43) (LPCMO) film grown on (110)-oriented LaAlO3 substrate. It is found that the charge order (CO) transition is much stronger and the resistance is larger along the [001] direction than that along the [1-10] direction. Special attention has been paid to the different effects of a magnetic field on the resistances of the two axes. The resistance is more susceptible to the magnetic field along the [001] direction compared with that along the [1-10] direction. Our results demonstrate that the anisotropic transport properties can be ascribed to the intrinsic anisotropic strain field in the film, which changes the shape of metallic domains for the phase separation manganite film. We also provide a feasible method to rule out the Joule heat effect from the electric current effect. This could be useful for future construction and application of materials and devices.

Effects of thickness on superconducting properties and structures of Y2O3/BZO-doped MOD-YBCO films

Ding Fa-Zhu, Gu Hong-Wei, Wang Hong-Yan, Zhang Hui-Liang, Zhang Teng, Qu Fei, Dong Ze-Bin, Zhou Wei-Wei
Chin. Phys. B 2015, 24 (5): 057401;  doi: 10.1088/1674-1056/24/5/057401
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We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7-x (YBCO) films with BaZrO3 (BZO) and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). Comparing with pure YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

Structural and magnetic properties of La0.7Sr0.1AgxMnO3-δ perovskite manganites

Hou Xue, Ji Deng-Hui, Qi Wei-Hua, Tang Gui-De, Li Zhuang-Zhi
Chin. Phys. B 2015, 24 (5): 057501;  doi: 10.1088/1674-1056/24/5/057501
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Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3-δ (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol–gel method. X-ray diffraction patterns indicated that the samples had two phases with the R3c perovskite being the dominant phase and Mn3O4 being the second phase. X-ray energy dispersive spectra indicated that the ratio of Ag to La was very close to that of the nominal composition in the samples. The specific saturation magnetizations at 300 K increased from 32.0 A·m2/kg when x = 0.00 to 46.8 A·m2/kg when x = 0.10. The Curie temperature, TC, of the samples increased from 310 K when x = 0.00 to 328 K when x = 0.10. Because the atomic concentration ratios of La, Sr, and Mn in the five samples were all the same and only the Ag concentration changed, the variations of the specific saturation magnetizations at 300 K and the Curie temperatures suggested that the Ag cations have been doped into the A sites of the perovskite phase in the samples.

Magnetic and mechanical properties of Ni–Mn–Ga/Fe–Ga ferromagnetic shape memory composite

Tan Chang-Long, Zhang Kun, Tian Xiao-Hua, Cai Wei
Chin. Phys. B 2015, 24 (5): 057502;  doi: 10.1088/1674-1056/24/5/057502
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A ferromagnetic shape memory composite of Ni–Mn–Ga and Fe–Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni–Mn–Ga alloy, the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe–Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved.

Room temperature ferromagnetism in un-doped amorphous HfO2 nano-helix arrays

Xie Qian, Wang Wei-Peng, Xie Zheng, Zhan Peng, Li Zheng-Cao, Zhang Zheng-Jun
Chin. Phys. B 2015, 24 (5): 057503;  doi: 10.1088/1674-1056/24/5/057503
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Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.

Transparent ZnO/glass surface acoustic wave based high performance ultraviolet light sensors

Wang Wen-Bo, Gu Hang, He Xing-Li, Xuan Wei-Peng, Chen Jin-Kai, Wang Xiao-Zhi, Luo Ji-Kui
Chin. Phys. B 2015, 24 (5): 057701;  doi: 10.1088/1674-1056/24/5/057701
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Surface acoustic wave (SAW) resonators are a type of ultraviolet (UV) light sensors with high sensitivity, and they have been extensively studied. Transparent SAW devices are very useful and can be developed into various sensors and microfluidics for sensing/monitoring and lab-on-chip applications. We report the fabrication of high sensitivity SAW UV sensors based on piezoelectric (PE) ZnO thin films deposited on glass substrates. The sensors were fabricated and their performances against the post-deposition annealing condition were investigated. It was found that the UV-light sensitivity is improved by more than one order of magnitude after annealing. The frequency response increases significantly and the response becomes much faster. The optimized devices also show a small temperature coefficient of frequency and excellent repeatability and stability, demonstrating its potential for UV-light sensing application.

Threshold switching uniformity in In2Se3 nanowire-based phase change memory

Chen Jian, Du Gang, Liu Xiao-Yan
Chin. Phys. B 2015, 24 (5): 057702;  doi: 10.1088/1674-1056/24/5/057702
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The uniformity of threshold voltage and threshold current in the In2Se3 nanowire-based phase change memory (PCM) devices is investigated. Based on the trap-limited transport model, amorphous layer thickness, trap density, and trap depth are considered to clarify their influences upon the threshold voltage and threshold current through simulations.

Effect of pressure on the semipolar GaN (10-11) growth mode on patterned Si substrates

Liu Jian-Ming, Zhang Jie, Lin Wen-Yu, Ye Meng-Xin, Feng Xiang-Xu, Zhang Dong-Yan, Steve Ding, Xu Chen-Ke, Liu Bao-Lin
Chin. Phys. B 2015, 24 (5): 057801;  doi: 10.1088/1674-1056/24/5/057801
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In this paper, we investigate the effect of pressure on the growth mode of high quality (10-11) GaN using an epitaxial lateral over growth (ELO) technique by metal organic chemical vapor deposition (MOCVD). Two pressure growth conditions, high pressure (HP) 1013 mbar and low pressure growth (LP) 500 mbar, are employed during growth. In the high pressure growth conditions, the crystal quality is improved by decreasing the dislocation and stack fault density in the strip connection locations. The room temperature photoluminescence measurement also shows that the light emission intensity increases three times using the HP growth condition compared with that using the LP growth conditions. In the low temperature (77 K) photoluminescence, the defects-related peaks are very obvious in the low pressure growth samples. This result also indicates that the crystal quality is improved using the high pressure growth conditions.

High color rendering index white organic light-emitting diode using levofloxacin as blue emitter

Miao Yan-Qin, Gao Zhi-Xiang, Zhang Ai-Qin, Li Yuan-Hao, Wang Hua, Jia Hu-Sheng, Liu Xu-Guang, Tsuboi Taiju
Chin. Phys. B 2015, 24 (5): 057802;  doi: 10.1088/1674-1056/24/5/057802
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Levofloxacin (LOFX), which is well-known as an antibiotic medicament, was shown to be useful as a 452-nm blue emitter for white organic light-emitting diodes (OLEDs). In this paper, the fabricated white OLED contains a 452-nm blue emitting layer (thickness of 30 nm) with 1 wt% LOFX doped in CBP (4,4'-bis(carbazol-9-yl)biphenyl) host and a 584-nm orange emitting layer (thickness of 10 nm) with 0.8 wt% DCJTB (4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran) doped in CBP, which are separated by a 20-nm-thick buffer layer of TPBi (2,2',2"-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole). A high color rendering index (CRI) of 84.5 and CIE chromaticity coordinates of (0.33, 0.32), which is close to ideal white emission CIE (0.333, 0.333), are obtained at a bias voltage of 14 V. Taking into account that LOFX is less expensive and the synthesis and purification technologies of LOFX are mature, these results indicate that blue fluorescence emitting LOFX is useful for applications to white OLEDs although the maximum current efficiency and luminance are not high. The present paper is expected to become a milestone to using medical drug materials for OLEDs.

Fluorescence enhancement of radix angelica dahurica by binding to single silver sphere

Wang Qing-Ru, Shi Qiang, Li Shu-Hong, Wang Wen-Jun
Chin. Phys. B 2015, 24 (5): 057803;  doi: 10.1088/1674-1056/24/5/057803
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We present a theoretical study of the influence of a single silver sphere on the fluorescence of radix angelica dahurica, which is a kind of traditional Chinese medicine. The enhancement factors of the excitation and the relaxation processes are deduced. The excitation can be enhanced more than 100 times at 315 nm. The enhancement factor of the emission can reach up to 9 at a center wavelength of 400 nm.

Thin film micro-scaled cold cathode structures of undoped and Si-doped AlN grown on SiC substrate with low turn-on voltage

Shi Ming, Chen Ping, Zhao De-Gang, Jiang De-Sheng, Zheng Jun, Cheng Bu-Wen, Zhu Jian-Jun, Liu Zong-Shun, Liu Wei, Li Xiang, Zhao Dan-Mei, Wang Qi-Ming, Liu Jian-Ping, Zhang Shu-Ming, Yang Hui
Chin. Phys. B 2015, 24 (5): 057901;  doi: 10.1088/1674-1056/24/5/057901
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The field emission characteristics of the AlN thin films with micro-scaled cold cathode structures are tested in the high vacuum system. The aluminum nitride (AlN) thin films with a thickness of about 100 nm are prepared on the n-type 6H-SiC (0001) substrate at 1100 ℃ by metal organic chemical vapor deposition (MOCVD) under low pressure. The I–V curves and surface micro-images of undoped and Si-doped AlN films are investigated. From the I–V and Fowler–Nordheim plots, it can be seen that the Si-doped AlN shows better field emission characteristics compared with the undoped AlN sample. The obtained turn-on field is 6.7 V/μm and the maximum emission current density is 154 mA/cm2 at 69.3 V for the Si-doped AlN film cathode after proper surface treatment. It is proposed that the relatively low electric resistivity of Si-doped AlN films is significant for electron migration to the surface region, and their rougher surface morphology is beneficial to a higher local electric field enhancement for the field emission.
SPECIAL TOPIC --- Non-equilibrium phenomena in soft matters

Analysis of the third harmonic for class-F power amplifiers with an I–V knee effect

Zhao Bo-Chao, Lu Yang, Wei Jia-Xing, Dong Liang, Wang Yi, Cao Meng-Yi, Ma Xiao-Hua, Hao Yue
Chin. Phys. B 2015, 24 (5): 058401;  doi: 10.1088/1674-1056/24/5/058401
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The appearance of third-generation semiconductors represented by gallium nitride (GaN) material greatly improves the output power of a power amplifier (PA), but the efficiency of the PA needs to be further improved. The Class-F PA reduces the overlap of drain voltage and current by tuning harmonic impedance so that high efficiency is achieved. This paper begins with the principle of class-F PA, regards the third harmonic voltage as an independent variable, analyzes the influence of the third harmonic on fundamental, and points out how drain efficiency and output power vary with the third harmonic voltage with an I–V knee effect. Finally, the best third harmonic impedance is found mathematically. We compare our results with the Loadpull technique in advanced design system environment and conclude that an optimized third harmonic impedance is open in an ideal case, while it is not at an open point with the I–V knee effect, and the drain efficiency with optimized third harmonic impedance is 4% higher than that with the third harmonic open.

Determining the influence of ferroelectric polarization on electrical characteristics in organic ferroelectric field-effect transistors

Fu Zong-Yuan, Zhang Jian-Chi, Hu Jing-Hang, Jiang Yu-Long, Ding Shi-Jin, Zhu Guo-Dong
Chin. Phys. B 2015, 24 (5): 058502;  doi: 10.1088/1674-1056/24/5/058502
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Organic ferroelectric field-effect transistors (OFeFETs) are regarded as a promising technology for low-cost flexible memories. However, the electrical instability is still a critical obstacle, which limits the commercialization process. Based on already established models for polarization in ferroelectrics and charge transport in OFeFETs, simulation work is performed to determine the influence of polarization fatigue and ferroelectric switching transient on electrical characteristics in OFeFETs. The polarization fatigue results in the decrease of the on-state drain current and the memory window width and thus degrades the memory performance. The output measurements during the ferroelectric switching process show a hysteresis due to the instable polarization. In the on/off measurements, a large writing/erasing pulse frequency weakens the polarization modulation and thus results in a small separation between on- and off-state drain currents. According to the electrical properties of the ferroelectric layer, suggestions are given to obtain optimal electrical characterization for OFeFETs.

Effect of persistent high intraocular pressure on microstructure and hydraulic permeability of trabecular meshwork

Mei Xi, Ren Lin, Xu Qiang, Zheng Wei, Liu Zhi-Cheng
Chin. Phys. B 2015, 24 (5): 058701;  doi: 10.1088/1674-1056/24/5/058701
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As the aqueous humor leaves the eye, it first passes through the trabecular meshwork (TM). Increased flow resistance in this region causes elevation of intraocular pressure (IOP), which leads to the occurrence of glaucoma. To quantitatively evaluate the effect of high IOP on the configuration and hydraulic permeability of the TM, second harmonic generation (SHG) microscopy was used to image the microstructures of the TM and adjacent tissues in control (normal) and high IOP conditions. Enucleated rabbit eyes were perfused at a pressure of 60 mmHg to achieve the high IOP. Through the anterior chamber of the eye, in situ images were obtained from different depths beneath the surface of the TM. Porosity and specific surface area of the TM in control and high IOP conditions were then calculated to estimate the effect of the high pressure on the permeability of tissue in different depths. We further photographed the histological sections of the TM and compared the in situ images. The following results were obtained in the control condition, where the region of depth was less than 55 μ with crossed branching beams and large pores in the superficial TM. The deeper meshwork is a silk-like tissue with abundant fluorescence separating the small size of pores. The total thickness of pathway tissues composed of TM and juxtacanalicular (JCT) is more than 100 μ. After putting a high pressure on the inner wall of the eye, the TM region progressively collapses and decreases to be less than 40 μ. Fibers of the TM became dense, and the porosity at 34 μ in the high IOP condition is comparable to that at 105 μ in the control condition. As a consequent result, the permeability of the superficial TM decreases rapidly from 120 μm2 to 49.6 μm2 and that of deeper TM decreases from 1.66 μm2 to 0.57 μm2. Heterogeneity reflected by descent in permeability reduces from 12.4 μ of the control condition to 3.74 μ of the high IOP condition. The persistently high IOP makes the TM region collapse from its normal state, in which the collagen fibers of the TM are arranged in regular to maintain the physiological permeability of the outflow pathway. In the scope of pathologically high IOP, the microstructure of the TM is sensitive to pressure and hydraulic permeability can be significantly affected by IOP.

Evaluation of influences of frequency and amplitude on image degradation caused by satellite vibrations

Nan Yi-Bing, Tang Yi, Zhang Li-Jun, Zheng Cheng, Wang Jing
Chin. Phys. B 2015, 24 (5): 058702;  doi: 10.1088/1674-1056/24/5/058702
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Satellite vibrations during exposure will lead to pixel aliasing of remote sensors, resulting in the deterioration of image quality. In this paper, we expose the problem and discuss the characteristics of satellite vibrations, and then present a pixel mixing model. The idea of mean mixing ratio (MMR) is proposed. MMR computations for different frequencies are implemented. In the mixing model, a coefficient matrix is introduced to estimate each mixed pixel. Thus, the simulation of degraded image can be performed when the vibration attitudes are known. The computation of MMR takes into consideration the influences of various frequencies and amplitudes. Therefore, the roles of these parameters played in the degradation progress are identified. Computations show that under the same vibration amplitude, the influence of vibrations fluctuates with the variation of frequency. The fluctuation becomes smaller as the frequency rises. Two kinds of vibration imaging experiments are performed: different amplitudes with the same frequency and different frequencies with the same amplitude. Results are found to be in very good agreement with the theoretical results. MMR has a better description of image quality than modulation transfer function (MTF). The influence of vibrations is determined mainly by the amplitude rather than the frequency. The influence of vibrations on image quality becomes gradually stable with the increase of frequency.

Transportation-cyber-physical-systems-oriented engine cylinder pressure estimation using high gain observer

Li Yong-Fu, Kou Xiao-Pei, Zheng Tai-Xiong, Li Yin-Guo
Chin. Phys. B 2015, 24 (5): 058901;  doi: 10.1088/1674-1056/24/5/058901
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In transportation cyber-physical-systems (T-CPS), vehicle-to-vehicle (V2V) communications play an important role in the coordination between individual vehicles as well as between vehicles and the roadside infrastructures, and engine cylinder pressure is significant for engine diagnosis on-line and torque control within the information exchange process under V2V communications. However, the parametric uncertainties caused from measurement noise in T-CPS lead to the dynamic performance deterioration of the engine cylinder pressure estimation. Considering the high accuracy requirement under V2V communications, a high gain observer based on the engine dynamic model is designed to improve the accuracy of pressure estimation. Then, the analyses about convergence, converge speed and stability of the corresponding error model are conducted using the Laplace and Lyapunov method. Finally, results from combination of Simulink with GT-Power based numerical experiments and comparisons demonstrate the effectiveness of the proposed approach with respect to robustness and accuracy.

A cellular automata model of traffic flow with variable probability of randomization

Zheng Wei-Fan, Zhang Ji-Ye
Chin. Phys. B 2015, 24 (5): 058902;  doi: 10.1088/1674-1056/24/5/058902
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Research on the stochastic behavior of traffic flow is important to understand the intrinsic evolution rules of a traffic system. By introducing an interactional potential of vehicles into the randomization step, an improved cellular automata traffic flow model with variable probability of randomization is proposed in this paper. In the proposed model, the driver is affected by the interactional potential of vehicles before him, and his decision-making process is related to the interactional potential. Compared with the traditional cellular automata model, the modeling is more suitable for the driver's random decision-making process based on the vehicle and traffic situations in front of him in actual traffic. From the improved model, the fundamental diagram (flow–density relationship) is obtained, and the detailed high-density traffic phenomenon is reproduced through numerical simulation.

Cross-correlation matrix analysis of Chinese and American bank stocks in subprime crisis

Zhu Shi-Zhao, Li Xin-Li, Nie Sen, Zhang Wen-Qing, Yu Gao-Feng, Han Xiao-Pu, Wang Bing-Hong
Chin. Phys. B 2015, 24 (5): 058903;  doi: 10.1088/1674-1056/24/5/058903
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In order to study the universality of the interactions among different markets, we analyze the cross-correlation matrix of the price of the Chinese and American bank stocks. We then find that the stock prices of the emerging market are more correlated than that of the developed market. Considering that the values of the components for the eigenvector may be positive or negative, we analyze the differences between two markets in combination with the endogenous and exogenous events which influence the financial markets. We find that the sparse pattern of components of eigenvectors out of the threshold value has no change in American bank stocks before and after the subprime crisis. However, it changes from sparse to dense for Chinese bank stocks. By using the threshold value to exclude the external factors, we simulate the interactions in financial markets.

Identifying influential nodes based on graph signal processing in complex networks

Zhao Jia, Yu Li, Li Jing-Ru, Zhou Peng
Chin. Phys. B 2015, 24 (5): 058904;  doi: 10.1088/1674-1056/24/5/058904
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Identifying influential nodes in complex networks is of both theoretical and practical importance. Existing methods identify influential nodes based on their positions in the network and assume that the nodes are homogeneous. However, node heterogeneity (i.e., different attributes such as interest, energy, age, and so on) ubiquitously exists and needs to be taken into consideration. In this paper, we conduct an investigation into node attributes and propose a graph signal processing based centrality (GSPC) method to identify influential nodes considering both the node attributes and the network topology. We first evaluate our GSPC method using two real-world datasets. The results show that our GSPC method effectively identifies influential nodes, which correspond well with the underlying ground truth. This is compatible to the previous eigenvector centrality and principal component centrality methods under circumstances where the nodes are homogeneous. In addition, spreading analysis shows that the GSPC method has a positive effect on the spreading dynamics.

Dielectric behaviors at microwave frequencies and Mössbauer effects of chalcedony, agate, and zultanite

Levent Parali, İsrafil Şabikoğlu, Jiri Tucek, Jiri Pechousek, Petr Novak, Jakub Navarik
Chin. Phys. B 2015, 24 (5): 059101;  doi: 10.1088/1674-1056/24/5/059101
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In this study, dielectric properties within 8–12 GHz microwave frequencies, inductively coupled plasma-atomic emission spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57Fe Mössbauer spectroscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm-1 to 4000 cm-1 range, ε' values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, ε' and ε" values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57Fe Mössbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanoparticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.

A pseudoenergy wave-activity relation for ageostrophic and non-hydrostatic moist atmosphere

Ran Ling-Kun, Ping Fan
Chin. Phys. B 2015, 24 (5): 059201;  doi: 10.1088/1674-1056/24/5/059201
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By employing the energy-Casimir method, a three-dimensional virtual pseudoenergy wave-activity relation for a moist atmosphere is derived from a complete system of nonhydrostatic equations in Cartesian coordinates. Since this system of equations includes the effects of water substance, mass forcing, diabatic heating, and dissipations, the derived wave-activity relation generalizes the previous result for a dry atmosphere. The Casimir function used in the derivation is a monotonous function of virtual potential vorticity and virtual potential temperature. A virtual energy equation is employed (in place of the previous zonal momentum equation) in the derivation, and the basic state is stationary but can be three-dimensional or, at least, not necessarily zonally symmetric. The derived wave-activity relation is further used for the diagnosis of the evolution and propagation of meso-scale weather systems leading to heavy rainfall. Our diagnosis of two real cases of heavy precipitation shows that positive anomalies of the virtual pseudoenergy wave-activity density correspond well with the strong precipitation and are capable of indicating the movement of the precipitation region. This is largely due to the cyclonic vorticity perturbation and the vertically increasing virtual potential temperature over the precipitation region.

Extra-seasonal prediction of summer 500-hPa height field in the area of cold vortices over East Asia with a dynamical-statistical method

Zhao Jun-Hu, Yang Liu, Hou Wei, Liu Gang, Zeng Yu-Xing
Chin. Phys. B 2015, 24 (5): 059202;  doi: 10.1088/1674-1056/24/5/059202
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The cold vortex is a major high impact weather system in northeast China during the warm season, its frequent activities also affect the short-term climate throughout eastern China. How to objectively and quantitatively predict the intensity trend of the cold vortex is an urgent and difficult problem for current short-term climate prediction. Based on the dynamical-statistical combining principle, the predicted results of the Beijing Climate Center's global atmosphere–ocean coupled model and rich historical data are used for dynamic-statistical extra-seasonal prediction testing and actual prediction of the summer 500-hPa geopotential height over the cold vortex activity area. The results show that this method can significantly reduce the model's prediction error over the cold vortex activity area, and improve the prediction skills. Furthermore, the results of the sensitivity test reveal that the predicted results are highly dependent on the quantity of similar factors and the number of similar years.

Orbit optimization and time delay interferometry for inclined ASTROD-GW formation with half-year precession-period Hot!

Wang Gang, Ni Wei-Tou
Chin. Phys. B 2015, 24 (5): 059501;  doi: 10.1088/1674-1056/24/5/059501
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ASTROD-GW (ASTROD [astrodynamical space test of relativity using optical devices] optimized for gravitational wave detection) is a gravitational-wave mission with the aim of detecting gravitational waves from massive black holes, extreme mass ratio inspirals (EMRIs) and galactic compact binaries together with testing relativistic gravity and probing dark energy and cosmology. Mission orbits of the 3 spacecrafts forming a nearly equilateral triangular array are chosen to be near the Sun–Earth Lagrange points L3, L4, and L5. The 3 spacecrafts range interferometrically with one another with arm length about 260 million kilometers. For 260 times longer arm length, the detection sensitivity of ASTROD-GW is 260 fold better than that of eLISA/NGO in the lower frequency region by assuming the same acceleration noise. Therefore, ASTROD-GW will be a better cosmological probe. In previous papers, we have worked out the time delay interferometry (TDI) for the ecliptic formation. To resolve the reflection ambiguity about the ecliptic plane in source position determination, we have changed the basic formation into slightly inclined formation with half-year precession-period. In this paper, we optimize a set of 10-year inclined ASTROD-GW mission orbits numerically using ephemeris framework starting at June 21, 2035, including cases of inclination angle with 0° (no inclination), 0.5°, 1.0°, 1.5°, 2.0°, 2.5°, and 3.0°. We simulate the time delays of the first and second generation TDI configurations for the different inclinations, and compare/analyse the numerical results to attain the requisite sensitivity of ASTROD-GW by suppressing laser frequency noise below the secondary noises. To explicate our calculation process for different inclination cases, we take the 1.0° as an example to show the orbit optimization and TDI simulation.

Resonant behavior of stochastic oscillations of general relativistic disks driven by a memory-damped friction

Wang Zhi-Yun, Chen Pei-Jie, Zhang Liang-Ying
Chin. Phys. B 2015, 24 (5): 059801;  doi: 10.1088/1674-1056/24/5/059801
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By using a generalized Langevin equation to describe the vertical oscillations of a general relativistic disk subjected to a memory-damped friction and a stochastic force, we derive the power spectrum density (PSD) of accretion disk oscillating luminosity by the method of Laplace transform, and discuss the influence of the system parameters on the resonant behavior in PSD curves. The results show that as the damping strength α and memory time τ of the friction increase, the variation of PSD with spectrum frequency f from monotonous decreasing to occurring maximums, and the phenomenon of a general stochastic resonance (SR) with a single peak and multi-peaks can be found in PSD curves. The radial distance parameter n, the mass M, and spin parameter a* of the black hole determine the inherent frequency of vertical oscillations in the disk, and they have significant influences on the SR phenomena in a system of black hole binaries.
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