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Tunable femtosecond laser in the visible range with an intracavity frequency-doubled optical parametric oscillator
Zhu Jiang-Feng, Xu Liang, Lin Qing-Feng, Zhong Xin, Han Hai-Nian, Wei Zhi-Yi
Chin. Phys. B, 2013, 22 (5): 054210
Quenched Fe moment in the collapsed tetragonal phase of Ca1-xPrxFe2As2
Ma Long, Gi Gao-Feng, Dai Jia, Saha S R, Drye T, Paglione J, Yu Wei-Qiang
Chin. Phys. B, 2013, 22 (5): 057401
Optimized geometry and electronic structure of graphyne-like silicyne nanoribbons
Pei Yang, Wu Hai-Bin
Chin. Phys. B, 2013, 22 (5): 057303
Chin. Phys. B  
  Chin. Phys. B--2013, Vol.22, No.5
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TOPICAL REVIEW — Magnetism, magnetic materials, and interdisciplinary research

Review of magnetocaloric effect in perovskite-type oxides

Zhong Wei, Au Chak-Tong, Du You-Wei
Chin. Phys. B, 2013, 22 (5): 057501 doi: 10.1088/1674-1056/22/5/057501
Full Text: [PDF 1168 KB] (Downloads:1257)
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We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO3-type manganese oxides, A3B2O7-type two-layered perovskite oxides, and A2B'B''O6-type ordered double-perovskite oxides). Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal (Na or K) doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ (0 < x < 0.5), and double-perovskite Ba2Fe1+xMo1-xO6 (0 ≤ x ≤ 0.3) near their respective Curie temperatures. Compared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.

Magnetic nanoparticle-based cancer nanodiagnostics

Muhammad Zubair Yousaf, Yu Jing, Hou Yang-Long, Gao Song
Chin. Phys. B, 2013, 22 (5): 058702 doi: 10.1088/1674-1056/22/5/058702
Full Text: [PDF 4052 KB] (Downloads:1172)
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Diagnosis facilitates the discovery of an impending disease. A complete and accurate treatment of cancer depends heavily on its early medical diagnosis. Cancer, one of the most fatal diseases world-wide, consistently affects a larger number of patients each year. Magnetism, a physical property arising from the motion of electrical charges, which causes attraction and repulsion between objects and does not involve radiation, has been under intense investigation for several years. Magnetic materials show great promise in the application of image contrast enhancement to accurately image and diagnose cancer. Chelating gadolinium (Gd III) and magnetic nanoparticles (MNPs) have the prospect to pave the way for diagnosis, operative management, and adjuvant therapy of different kinds of cancers. The potential of MNP-based magnetic resonance (MR) contrast agents (CAs) now makes it possible to image portions of a tumor in parts of the body that would be unclear with the conventional magnetic resonance imaging (MRI). Multiple functionalities like variety of targeting ligands and image contrast enhancement have recently been added to the MNPs. Keeping aside the additional complexities in synthetic steps, costs, more convoluted behavior, and effects in-vivo, multifunctional MNPs still face great regulatory hurdles before clinical availability for cancer patients. The trade-off between additional functionality and complexity is a subject of ongoing debate. The recent progress regarding the types, design, synthesis, morphology, characterization, modification, and the in-vivo and in-vitro uses of different MRI contrast agents, including MNPs, to diagnose cancer will be the focus of this review. As our knowledge of MNPs’ characteristics and applications expands, their role in the future management of cancer patients will become very important. Current hurdles are also discussed, along with future prospects of MNPs as the savior of cancer victims.

Review on graphene-based strain sensors

Zhao Jing, Zhang Guang-Yu, Shi Dong-Xia
Chin. Phys. B, 2013, 22 (5): 057701 doi: 10.1088/1674-1056/22/5/057701
Full Text: [PDF 2279 KB] (Downloads:1880)
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In this paper, we review various types of grapheme-based strain sensors. Graphene is a monolayer of carbon atoms, which exhibits prominent electrical and mechanical properties and can be a good candidate in compact strain sensor applications. However, a perfect graphene is robust and has a low piezoresistive sensitivity. So scientist are driven to increase the sensitivity using different kinds of methods since the first graphene-based strain sensor was reported. We give a comprehensive review of graphene-based strain sensors with different structures and mechanisms. It is obvious that graphene offers some advantages and has potential for the strain sensor application in the near future.

Imperfect pitchfork bifurcation in asymmetric two-compartment granular gas

Zhang Yin, Li Yin-Chang, Liu Rui, Cui Fei-Fei, Pierre Evesque, Hou Mei-Ying
Chin. Phys. B, 2013, 22 (5): 054701 doi: 10.1088/1674-1056/22/5/054701
Full Text: [PDF 339 KB] (Downloads:336)
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The clustering behavior of a mono-disperse granular gas is experimentally studied in an asymmetric two-compartment setup. Unlike the random clustering in either compartment in the case of symmetric configuration when lowering the shaking strength to below a critical value, the directed clustering is observed, which corresponds to an imperfect pitchfork bifurcation. Numerical solutions of the flux equation using a modified simple flux function show qualitative agreements with the experimental results. The potential application of this asymmetric structure is discussed.

A single-event transient induced by a pulsed laser in a silicon-germanium heterojunction bipolar transistor

Sun Ya-Bin, Fu Jun, Xu Jun, Wang Yu-Dong, Zhou Wei, Zhang Wei, Cui Jie, Li Gao-Qing, Liu Zhi-Hong, Yu Yong-Tao, Ma Ying-Qi, Feng Guo-Qiang, Han Jian-Wei
Chin. Phys. B, 2013, 22 (5): 056103 doi: 10.1088/1674-1056/22/5/056103
Full Text: [PDF 595 KB] (Downloads:381)
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A study on single event transient (SET) induced by pulsed laser in silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) is presented in this work. The impacts of laser energy and collector load resistance on the SET are investigated in detail. The waveform, amplitude, and width of the SET pulse as well as collected charge are used to characterize the SET response. The experimental results are discussed in detail and it is demonstrated that the laser energy and load resistance significantly affect the SET in the SiGe HBT. Furthermore, the underlying physical mechanisms are analyzed and investigated, and a near-ideal exponential model is proposed for the first time to describe the discharge of laser-induced electrons via collector resistance to collector supply when both base-collector and collector-substrate junctions are reverse biased or weakly forward biased. Besides, it is found that an additional multi-path discharge would play an important role in the SET once the base-collector and collector-substrate junctions get strongly forward biased due to a strong transient step charge by the laser pulse.

Quenched Fe moment in the collapsed tetragonal phase of Ca1-xPrxFe2As2 Hot!

Ma Long, Gi Gao-Feng, Dai Jia, Saha S R, Drye T, Paglione J, Yu Wei-Qiang
Chin. Phys. B, 2013, 22 (5): 057401 doi: 10.1088/1674-1056/22/5/057401
Full Text: [PDF 428 KB] (Downloads:293)
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We report 75As NMR studies on single crystals of rare-earth doped iron pnictide superconductor Ca1-xPrxFe2As2. In both cases of x=0.075, 0.15, a large increase of νq upon cooling is consistent with the tetragonal-collapsed tetragonal structure transition. A sharp drop of the Knight shift is also seen just below the structural transition, which suggests the quenching of Fe local magnetism, and therefore offers important understanding of the collapsed tetragonal phase. At even low temperatures, the 1/75T1 is enhanced and forms a peak at T≈ 25 K, which may be caused by the magnetic ordering of the Pr3+ moments or spin dynamics of mobile domain walls.

Comparative study of travelling wave and numerical solutions for the coupled short pulse (CSP) equation

Vikas Kumar, R. K. Gupta, Ram Jiwari
Chin. Phys. B, 2013, 22 (5): 050201 doi: 10.1088/1674-1056/22/5/050201
Full Text: [PDF 253 KB] (Downloads:339)
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The Lie symmetry analysis is performed for coupled short plus (CSP) equation. We derive the infinitesimals that admit the classical symmetry group. Five types arise depending on the nature of the Lie symmetry generator. In all types, we find reductions in terms of system of ordinary differential equations, and exact solutions of the CSP equation are derived, which are compared with numerical solutions using classical fourth-order Runge-Kutta scheme.

Combine complex variable reproducing kernel particle method and finite element method for solving transient heat conduction problems

Chen Li, Ma He-Ping, Cheng Yu-Min
Chin. Phys. B, 2013, 22 (5): 050202 doi: 10.1088/1674-1056/22/5/050202
Full Text: [PDF 468 KB] (Downloads:311)
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In this paper, the complex variable reproducing kernel particle (CVRKP) method and the finite element (FE) method are combined as the CVRKP-FE method to solve transient heat conduction problems. The CVRKP-FE method not only conveniently imposes the essential boundary conditions, but also exploits the advantages of the individual methods while avoiding their disadvantages, then the computational efficiency is higher. A hybrid approximation function is applied to combine the CVRKP method with the FE method, and the traditional difference method for two-point boundary value problems is selected as the time discretization scheme. The corresponding formulations of the CVRKP-FE method are presented in detail. Several selected numerical examples of the transient heat conduction problems are presented to illustrate the performance of the CVRKP-FE method.

Painlevé integrability of generalized fifth-order KdV equation with variable coefficients: Exact solutions and their interactions

Xu Gui-Qiong
Chin. Phys. B, 2013, 22 (5): 050203 doi: 10.1088/1674-1056/22/5/050203
Full Text: [PDF 752 KB] (Downloads:638)
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By means of singularity structure analysis, the integrability of a generalized fifth-order KdV equation is investigated. It is proven that this equation passes the Painlevé test for integrability only for three distinct cases. Moreover, the multi-soliton solutions are presented for this equation under three sets of integrable conditions. Finally, by selecting appropriate parameters, we analyze the evolution of two solitons, which is especially interesting as it may describe the overtaking and the head-on collisions of solitary waves of different shapes and different types.

Exact solutions of (3+1)-dimensional nonlinear incompressible non-hydrostatic Boussinesq equations

Liu Ping, Li Zi-Liang
Chin. Phys. B, 2013, 22 (5): 050204 doi: 10.1088/1674-1056/22/5/050204
Full Text: [PDF 279 KB] (Downloads:456)
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The symmetries and the exact solutions of the (3+1)-dimensional nonlinear incompressible non-hydrostatic Boussinesq (INHB) equations, which describe the atmospheric gravity waves, are studied in this paper. The calculation on symmetry shows that the equations are invariant under the Galilean transformations, the scaling transformations, and the space-time translations. Three types of symmetry reduction equations and similar solutions for the (3+1)-dimensional INHB equations are proposed. Traveling and non-traveling wave solutions of the INHB equations are demonstrated. The evolutions of the wind velocities in latitudinal, longitudinal, and vertical directions with space-time are demonstrated. The periodicity and the atmosphere viscosity are displayed in the (3+1)-dimensional INHB system.

Simulation optimization for train movement on single-track railway

Ye Jing-Jing, Li Ke-Ping
Chin. Phys. B, 2013, 22 (5): 050205 doi: 10.1088/1674-1056/22/5/050205
Full Text: [PDF 235 KB] (Downloads:521)
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Optimizing train movement has a great significance for railway traffic. In this paper, based on the optimal velocity car-following model, we propose a new simulation model for optimizing train movement in railway traffic. Here a kind of single-track railway is considered. Our aim is to reduce the energy consumption of train movement and ensure the train being on time by controlling the velocity curve of train movement. The simulation results indicate that the proposed model is effective for optimizing train movement. And some major characteristics of train movement can be well captured. This method provides a new way to optimize train movement in railway traffic.

The discontinuous Petrov-Galerkin method for one-dimensional compressible Euler equations in the Lagrangian coordinate

Zhao Guo-Zhong, Yu Xi-Jun, Guo Peng-Yun
Chin. Phys. B, 2013, 22 (5): 050206 doi: 10.1088/1674-1056/22/5/050206
Full Text: [PDF 550 KB] (Downloads:437)
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In this paper, a Petrov-Galerkin scheme named Runge-Kutta control volume (RKCV) discontinuous finite element method is constructed to solve the one-dimensional compressible Euler equations in the Lagrangian coordinate. Its advantages include preserving the local conservation and a high resolution. Compared with the Runge-Kutta discontinuous Galerkin (RKDG) method, the RKCV method is easier to be implemented. Moreover, the advantages of the RKCV and the Lagrangian methods are combined in the new method. Several numerical examples are given to illustrate the accuracy and the reliability of the algorithm.

Prediction and experimental measurement of electromagnetic thrust generated by a microwave thruster system

Yang Juan, Wang Yu-Quan, Ma Yan-Jie, Li Peng-Fei, Yang Le, Wang Yang, He Guo-Qiang
Chin. Phys. B, 2013, 22 (5): 050301 doi: 10.1088/1674-1056/22/5/050301
Full Text: [PDF 1356 KB] (Downloads:6662)
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A microwave thruster system that can convert microwave power directly to thrust without gas propellant is developed. In the system, a cylindrical tapered resonance cavity and a magnetron microwave source are used respectively as the thruster cavity and the energy source to generate the electromagnetic wave. The wave is radiated into and then reflected from the cavity to form a pure standing wave with a non-uniform electromagnetic pressure distribution. Consequently, a net electromagnetic thrust exerted on the axis of the thruster cavity appears, which is demonstrated through theoretical calculation based on the electromagnetic theory. The net electromagnetic thrust is also experimentally measured in the range from 70 mN to 720 mN when the microwave output power is from 80 W to 2500W.

Quantum information entropies of the eigenstates for the Pöschl-Teller-like potential

Guo-Hua Sun, M. Avila Aoki, Shi-Hai Dong
Chin. Phys. B, 2013, 22 (5): 050302 doi: 10.1088/1674-1056/22/5/050302
Full Text: [PDF 308 KB] (Downloads:455)
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Shannon entropy for lower position and momentum eigenstates of Pöschl-Teller-like potential is evaluated. Based on the entropy densities demonstrated graphically, we note that the wave through of the position information entropy density ρ(x) moves right when the potential parameter V1 increases and its amplitude decreases. However, its wave through moves left with the increase in the potential parameter |V2|. Concerning the momentum information entropy density ρ(p), we observe that its amplitude increases with increasing potential parameter V1, but its amplitude decreases with increasing |V2|. The Bialynicki-Birula-Mycielski (BBM) inequality has also been tested for a number of states. Moreover, there exist eigenstates that exhibit squeezing in the momentum information entropy. Finally, we note that position information entropy increases with V1, but decreases with |V2|. However, the variation of momentum information entropy is contrary to that of the position information entropy.

Correlation dynamics of two-parameter qubit-qutrit states under decoherence

Yuan Hao, Wei Lian-Fu
Chin. Phys. B, 2013, 22 (5): 050303 doi: 10.1088/1674-1056/22/5/050303
Full Text: [PDF 324 KB] (Downloads:506)
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We investigate the dynamics of correlations for two-parameter qubit-qutrit states under various local decoherence channels including depahsing, phase-flip, bit- and trit-flip, bit- and trit-phase-flip, and depolarizing channels. We find that, under certain conditions, the classical correlations may not be affected by the noise or decay monotonically. The quantum correlations measured by measurement-induced disturbance (MID) show three types of dynamical behaviors: (i) monotonic decay to zero, (ii) monotonic decay to a nonzero steady value, (iii) increase from zero and then decrease to zero in a monotonic way. Consequently, we find that, differing from the dynamics of entanglement, the present classical and quantum correlations do not reveal sudden death behavior.

Finding symmetries of trees using continuous-time quantum walk

Wu Jun-Jie, Zhang Bai-Da, Tang Yu-Hua, Qiang Xiao-Gang, Wang Hui-Quan
Chin. Phys. B, 2013, 22 (5): 050304 doi: 10.1088/1674-1056/22/5/050304
Full Text: [PDF 306 KB] (Downloads:247)
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Quantum walk, the quantum counterpart of random walk, is an important model and widely studied to develop new quantum algorithms. This paper studies the relationship between the continuous-time quantum walk and the symmetry of a graph, especially that of a tree. Firstly, we prove in mathematics that the symmetry of a graph is highly related to quantum walk. Secondly, we propose an algorithm based on the continuous-time quantum walk to compute the symmetry of a tree. Our algorithm has better time complexity O(N3) than the current best algorithm. Finally, through testing three types of 10024 trees, we find that the symmetry of a tree can be found with an extremely high efficiency with the help of the continuous-time quantum walk.

Scheme for implementing economical phase-covariant quantum cloning machine of distant atomic qubits with single-photon interference

Zhou Yan-Hui, Wang Lei, Lai Xiao-Lei
Chin. Phys. B, 2013, 22 (5): 050305 doi: 10.1088/1674-1056/22/5/050305
Full Text: [PDF 213 KB] (Downloads:260)
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By means of the cavity-assisted photon interference, a simple scheme is proposed to implement symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our present scheme, a high-fidelity cloning machine is realized. Our scheme may be quite useful in terms of the distributed quantum information processing.

Implementation of unambiguous comparison for unknown pure quantum states with cavity-assisted interaction

Cheng Liu-Yong, Wang Hong-Fu, Zhang Shou, Yeon Kyu-Hwang
Chin. Phys. B, 2013, 22 (5): 050306 doi: 10.1088/1674-1056/22/5/050306
Full Text: [PDF 336 KB] (Downloads:233)
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We propose two effective schemes for local and remote unknown atomic state comparisons with cavity-assisted single photon input-output process without any initial entanglement or auxiliary resource. And the unambiguous state discrimination is considered using the state comparison process as the basic module. All the implementation schemes here just involve common quantum logic gates and the single qubit measurement. The analysis shows that our schemes are feasible under the current experimental conditions.

Generation of four-atom Greenberger-Horn-Zeilinger state via adiabatic passage

Zhang Chun-Ling, Chen Mei-Feng
Chin. Phys. B, 2013, 22 (5): 050307 doi: 10.1088/1674-1056/22/5/050307
Full Text: [PDF 339 KB] (Downloads:317)
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We propose a scheme to generate a Greenberger-Horn-Zeilinger (GHZ) state of four atoms trapped in a two-mode optical cavity via an adiabatic passage. The scheme is robust against moderate fluctuations of the experimental parameters. Numerical calculations show that the excited probabilities of both the cavity modes and the atoms are tiny and depend on the pulse peaks of the classical laser fields. For certain decoherence due to the atomic spontaneous emission and the cavity decay, there exits a range of pulse peaks to get a high fidelity.

Mesoscopic entangled coherent states implemented with a circuit quantum electrodynamics system

Zhao Ying-Yan, Jiang Nian-Quan
Chin. Phys. B, 2013, 22 (5): 050308 doi: 10.1088/1674-1056/22/5/050308
Full Text: [PDF 223 KB] (Downloads:246)
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We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system, which consists of a nanomechanical resonator, a superconducting Cooper-pair box (CPB), and a superconducting transmission line resonator. In the system, the CPB plays the role of nonlinear medium and can be conveniently controlled by a gate voltage including direct-current and alternating-current components. The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.

Quantum steganography with large payload based on dense coding and entanglement swapping of Greenberger-Horne-Zeilinger states

Ye Tian-Yu, Jiang Li-Zhen
Chin. Phys. B, 2013, 22 (5): 050309 doi: 10.1088/1674-1056/22/5/050309
Full Text: [PDF 206 KB] (Downloads:305)
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A quantum steganography protocol with a large payload is proposed based on the dense coding and the entanglement swapping of the Greenberger-Horne-Zeilinger (GHZ) states. Its super quantum channel is formed by building up a hidden channel within the original quantum secure direct communication (QSDC) scheme. Based on the original QSDC, secret messages are transmitted by integrating the dense coding and the entanglement swapping of the GHZ states. The capacity of the super quantum channel achieves six bits per round covert communication, much higher than the previous quantum steganography protocols. Its imperceptibility is good, since the information and the secret messages can be regarded to be random or pseudo-random. Moreover, its security is proved to be reliable.

Several teleportation schemes of an arbitrary unknown multi-particle state via different quantum channels

Peng Jia-Yin, Mo Zhi-Wen
Chin. Phys. B, 2013, 22 (5): 050310 doi: 10.1088/1674-1056/22/5/050310
Full Text: [PDF 210 KB] (Downloads:294)
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We first provide four new schemes for two-party quantum teleportation of an arbitrary unknown multi-particle state by using three-, four- and five-particle states as the quantum channel, respectively. The successful probability and fidelity of the four schemes reach 1. In the first two schemes, the receiver can only apply one of the unitary transformations to reconstruct the original state, making it easier for these two schemes to be directly realized. In the third and fourth schemes, the sender can preform Bell-state measurements instead of multipartite entanglement measurements of the existing similar schemes, which makes real experiments more suitable. It is found that the last three schemes may become tripartite controlled teleportation schemes of teleporting an arbitrary multi-particle state after a simple modification. Finally, we present a new scheme for three-party sharing an arbitrary unknown multi-particle state. In this scheme, the sender first shares three three-particle GHZ states with two agents. After setting up the secure quantum channel, an arbitrary unknown multi-particle state can be perfectly teleported if the sender performs three Bell-state measurements, and either of two receivers operates an appropriate unitary transformation to obtain the original state with the help of other receiver's three single-particle measurements. The successful probability and fidelity of this scheme also reach 1. It is demonstrated that this scheme can be generalized easily to the case of sharing an arbitrary unknown multi-particle state among several agents.

Superposition solitons in two-component Bose-Einstein condensates

Wang Xiao-Min, Li Qiu-Yan, Li Zai-Dong
Chin. Phys. B, 2013, 22 (5): 050311 doi: 10.1088/1674-1056/22/5/050311
Full Text: [PDF 456 KB] (Downloads:417)
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We develope the Hirota bilinear method and obtain the exact one and two superposition soliton solutions for two-component Bose-Einstein condensates. The conversion of three kinds of solitons including the superposition solitons, bright-bright solitons, and dark-bright solitons is discussed. With the energy analysis, we find that the superposition soliton state is an excitation state for this system. Moreover, the collision of two superposition solitons is found to be elastic.

The stability of a shearing viscous star with an electromagnetic field

M. Sharif, M. Azama
Chin. Phys. B, 2013, 22 (5): 050401 doi: 10.1088/1674-1056/22/5/050401
Full Text: [PDF 208 KB] (Downloads:269)
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We analyze the role of the electromagnetic field for the stability of a shearing viscous star with spherical symmetry. Matching conditions are given for the interior and the exterior metrics. We use a perturbation scheme to construct the collapse equation. The range of instability is explored in Newtonian and post Newtonian (pN) limits. We conclude that the electromagnetic field diminishes the effects of the shearing viscosity in the instability range and makes the system more unstable in both Newtonian and post Newtonian approximations.

Spectroscopy via adiabatic covariant action for the Bañados-Teitelboim-Zanelli (BTZ) black hole

Li Hui-Ling, Lin Rong, Cheng Li-Ying
Chin. Phys. B, 2013, 22 (5): 050402 doi: 10.1088/1674-1056/22/5/050402
Full Text: [PDF 211 KB] (Downloads:276)
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Very recently, via the covariant form of the adiabatic invariant I=f pidqi instead of I=∫ pidqi, an equally spaced spectroscopy of a Schwarzschild black hole was derived. The emphasis was given to the covariant of results. In this paper, we extend that work in a spherically symmetric spacetime to the case of a rotating Bañados-Teitelboim-Zanelli (BTZ) black hole. It is noteworthy that the adiabatic covariant action I=f pidqi gives the same value for the black hole spectroscopy in different coordinates. The result shows that the area spectrum is ΔA=8π lP2, which confirms the initial proposal of Bekenstein. And the result is consistent with that already obtained by other methods.

Feedback control of wave segments in excitable medium

Wu Ning-Jie, Gao Hong-Jun, Ying He-Ping
Chin. Phys. B, 2013, 22 (5): 050501 doi: 10.1088/1674-1056/22/5/050501
Full Text: [PDF 277 KB] (Downloads:434)
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Depending on the excitability of the medium, a propagating wave segment would either contract or expend to fill the medium with spiral waves. This paper aims to introduce a simple mechanism of feedback control to stabilize such an expansion or contraction. To do this, we lay out a feedback control system in a block diagram and reduce it into a bare, universal formula. Analytical and experimental findings are compared through a series of numerical simulations of the Barkley model.

New predication of chaotic time series based on local Lyapunov exponent

Zhang Yong
Chin. Phys. B, 2013, 22 (5): 050502 doi: 10.1088/1674-1056/22/5/050502
Full Text: [PDF 655 KB] (Downloads:456)
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A new method of predicting chaotic time series is presented based on local Lyapunov exponent, by quantitatively measuring the exponential rate of separation or attraction of two infinitely close trajectories in state space. After reconstructing state space from one-dimensional chaotic time series, neighboring multiple-state vectors of the predicting point are selected to deduce the prediction formula using the definition of local Lyapunov exponent. Numerical simulations are carried out to test its effectiveness and verify its higher precision than two older methods. Effects of number of referential state vectors and added noise on forecasting accuracy are also studied numerically.

Cryptanalysis and improvement of a digital image encryption method with chaotic map lattices

Wang Xing-Yuan, Liu Lin-Tao
Chin. Phys. B, 2013, 22 (5): 050503 doi: 10.1088/1674-1056/22/5/050503
Full Text: [PDF 3490 KB] (Downloads:606)
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A digital image encryption scheme using chaotic map lattices has been proposed recently. In this paper, two fatal flaws of the cryptosystem are pointed out. According to these two drawbacks, cryptanalysts could recover the plaintext by applying chosen plaintext attack. Therefore, the proposed cryptosystem is not secure enough to be used in the image transmission system. Experimental results show the feasibility of the attack. As a result, we achieve some improvements to enhance the encryption scheme, which can completely resist our chosen plaintext attack.

Exponential synchronization of coupled memristive neural networks via pinning control

Wang Guan, Shen Yi, Yin Quan
Chin. Phys. B, 2013, 22 (5): 050504 doi: 10.1088/1674-1056/22/5/050504
Full Text: [PDF 943 KB] (Downloads:383)
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This paper is concerned with the exponential synchronization problem of coupled memristive neural networks. In contrast to general neural networks, memristive neural networks exhibit state-dependent switching behaviors due to the physical properties of memristors. Under a mild topology condition, it is proved that a small fraction of controlled subsystems can efficiently synchronize the coupled systems. The pinned subsystems are identified via a search algorithm. Moreover, the information exchange network needs not to be undirected or strongly connected. Finally, two numerical simulations are performed to verify the usefulness and effectiveness of our results.

A new identification control for generalized Julia sets

Sun Jie, Liu Shu-Tang
Chin. Phys. B, 2013, 22 (5): 050505 doi: 10.1088/1674-1056/22/5/050505
Full Text: [PDF 556 KB] (Downloads:262)
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In this paper, we propose a new method to realize drive-response system synchronization control and parameter identification for a class of generalized Julia sets. By means of this method, the zero asymptotic sliding variables are applied to control the fractal identification. Furthermore, the problems of synchronization control are solved in the case of a drive system with unknown parameters, and the unknown parameters of the drive system can be identified in the asymptotic synchronization process. The results of simulation examples demonstrate the effectiveness of this new method. Particularly, the basic Julia set is also discussed.

Complexity analyses of multi-wing chaotic systems

He Shao-Bo, Sun Ke-Hui, Zhu Cong-Xu
Chin. Phys. B, 2013, 22 (5): 050506 doi: 10.1088/1674-1056/22/5/050506
Full Text: [PDF 804 KB] (Downloads:426)
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The complexities of multi-wing chaotic systems based on the modified Chen system and multi-segment quadratic function are investigated by employing statistical complexity measure (SCM) and spectral entropy (SE) algorithm. How to choose the parameters of the SCM and SE algorithms is discussed. The results show that the complexity of the multi-wing chaotic system does not increase as the number of wings increases, and it is consistent with the results of the Grassberger-Procaccia (GP) algorithm and the largest Lyapunov exponent (LLE) of the multi-wing chaotic system. This conclusion is verified by other multi-wing chaotic systems.

Markov transition probability-based network from time series for characterizing experimental two-phase flow

Gao Zhong-Ke, Hu Li-Dan, Jin Ning-De
Chin. Phys. B, 2013, 22 (5): 050507 doi: 10.1088/1674-1056/22/5/050507
Full Text: [PDF 1446 KB] (Downloads:379)
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We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas-liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitatively characterizing the dynamic flow behavior in the transitions among different gas-liquid flow patterns.

A novel image block cryptosystem based on spatiotemporal chaotic system and chaotic neural network

Wang Xing-Yuan, Bao Xue-Mei
Chin. Phys. B, 2013, 22 (5): 050508 doi: 10.1088/1674-1056/22/5/050508
Full Text: [PDF 4338 KB] (Downloads:523)
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In this paper, we propose a novel block cryptographic scheme based on spatiotemporal chaotic system and chaotic neural network (CNN). The employed CNN comprises a 4-neuron layer called chaotic neuron layer (CNL), where spatiotemporal chaotic system participates in generating its weight matrix and other parameters. The spatiotemporal chaotic system used in our scheme is the typical coupled map lattice (CML), which can be easily implemented in parallel by hardware. A 160-bit-long binary sequence is used to generate the initial conditions of the CML. The decryption process is symmetric relative to the encryption process. Theoretical analysis and experimental results prove that the block cryptosystem is secure and practical, and suitable for image encryption.

Integrability of extended (2+1)-dimensional shallow water wave equation with Bell polynomials

Wang Yun-Hu, Chen Yong
Chin. Phys. B, 2013, 22 (5): 050509 doi: 10.1088/1674-1056/22/5/050509
Full Text: [PDF 227 KB] (Downloads:257)
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We investigate the extended (2+1)-dimensional shallow water wave equation. The binary Bell polynomials are used to construct bilinear equation, bilinear Bäcklund transformation, Lax pair, and Darboux covariant Lax pair for this equation. Moreover, the infinite conservation laws of this equation are found by using its Lax pair. All conserved densities and fluxes are given with explicit recursion formulas. The N-soliton solutions are also presented by means of the Hirota bilinear method.

New exact solutions of (3+1)-dimensional Jimbo-Miwa system

Chen Yuan-Ming, Ma Song-Hua, Ma Zheng-Yi
Chin. Phys. B, 2013, 22 (5): 050510 doi: 10.1088/1674-1056/22/5/050510
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By using the (G'/G)-expansion method and the variable separation method, a new family of exact solutions of the (3+1)-dimensional Jimbo-Miwa system is obtained. Based on the derived solitary wave solutions, we obtain some special localized excitations and study the interactions between two solitary waves of the system.

Consensus of second-order multi-agent systems with nonuniform time delays

Zhang Wen-Guang, Liu Ji-Zhen, Zeng De-Liang, Hu Yong
Chin. Phys. B, 2013, 22 (5): 050511 doi: 10.1088/1674-1056/22/5/050511
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In this study, the consensus problem for a class of second-order multi-agent systems with nonuniform time delays is investigated. A linear consensus protocol is used to make all agents reach consensus and move with a constant velocity. By a frequency-domain analysis, a simplified sufficient condition is given to guarantee the consensus stability of the dynamic system. Finally, the effectiveness of the obtained theoretical results is illustrated through numerical simulations.

A thermal entangled quantum refrigerator based on a two-qubit Heisenberg model with Dzyaloshinskii-Moriya interaction in an external magnetic field

Wang Hao, Wu Guo-Xing
Chin. Phys. B, 2013, 22 (5): 050512 doi: 10.1088/1674-1056/22/5/050512
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Based on an isotropic two spin-1/2 qubits Heisenberg model with the Dzyaloshinskii-Moriya interaction in an external magnetic field, we have constructed an entangled quantum refrigerator. Expressions for the basic thermodynamic quantities, i.e., the heat exchanged, the net work input, and the coefficient of performance, are derived. Some intriguing features and their qualitative explanations in zero and non zero magnetic fields are given. The influence of the thermal entanglement on the refrigerator is investigated. The results obtained here have general significance and will be helpful to understand the performance of an entangled quantum refrigerator.

Spectral decomposition at complex laser polarization configuration

Yang Hai-Feng, Gao Wei, Cheng Hong, Liu Hong-Ping
Chin. Phys. B, 2013, 22 (5): 053201 doi: 10.1088/1674-1056/22/5/053201
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We study the role of laser polarization in the diamagnetic spectrum for the transition from the ground state to the highly excited Rydberg states through a single photon absorption. For simplicity, one usually polarizes the irradiation laser to the selected main quantum axis, which is along the applied external electric or magnetic field. The transition selection rule is simply expressed as Δm=0, which corresponds to the π transition. When the polarization is circularly polarized around the main axis, the σ+ or σ- transition occurs, corresponding to the selection rule of Δm=1 or Δm=-1, respectively. A slightly more complex case is that the laser is linearly polarized perpendicular to the main axis. The numerical calculation shows that we can decompose the transition into the sum of σ+ and σ- transitions, it is noted as the σ transition. For the more complex case in which the laser is linearly polarized with an arbitrary angle with respect to the main axis, we have to decompose the polarization into one along the main axis and the other one perpendicular to the main axis. They correspond to π and σ transitions, respectively. We demonstrate that these transitions in the diamagnetic spectrum and the above spectral decomposition well explain the experimentally observed spectra.

Spectrally selective optical pumping in Doppler-broadened cesium atoms

Zhang Jun-Hai, Zeng Xian-Jin, Li Qing-Meng, Huang Qiang, Sun Wei-Min
Chin. Phys. B, 2013, 22 (5): 053202 doi: 10.1088/1674-1056/22/5/053202
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The D1 line spectrally selective pumping process in Doppler-broadened cesium is analyzed by solving the optical Bloch equations. The process, described by a three-level model with the L scheme, shows that the saturation intensity of broadened atoms is three orders of magnitude larger than that of resting atoms. The |Fg =3>→|Fe =4> resonance pumping can result in the ground state |Fg =4, mF =4i sublevel having a maximum population of 0.157 and the population difference would be about 0.01 in two adjacent magnetic sublevels of the hyperfine (HF) state Fg =4. To enhance the anisotropy in the ground state, we suggest employing dichromatic optical HF pumping by adding a laser to excite D1 line |Fg =4>→jFe =3> transition, in which the cesium magnetometer sensitivity increases by half a magnitude and is unaffected by the nonlinear Zeeman effect even in Earth’s average magnetic field.

Cross section for impact single ionization of B2+ by H+

Ye Dan-Dan, Qi Yue-Ying, Hu Ya-Hua, Ning Li-Na
Chin. Phys. B, 2013, 22 (5): 053401 doi: 10.1088/1674-1056/22/5/053401
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The ionization process of B2+ by H+ impact is studied using the continuum-distorted-wave eikonal-initial-state (CDW-EIS) method and the modified free electron peak approximation (M-FEPA), respectively. Total, single-, and double-differential cross sections from 1s and 2s orbital are presented for the energy range from 10 KeV/u to 10 MeV/u. Comparison between the results from the two methods demonstrates that the total and single-differential cross sections for the high-energy incident projectile case can be well evaluated using the simple M-FEPA model. Moreover, the M-FEPA model reproduces the essential features of the binary-encounter (BE) bump in the double-differential cross sections. Thus, BE ionization mechanism is discussed in detail by adopting the M-FEPA model. In particular, the double- and single-differential cross sections from the 2s orbital show a high-energy hip, which is different from those from the 1s orbital. Based on Ref. [1], the Compton profiles of B2+ for 1s and 2s orbitals are given, and the hips in DDCS and SDCS from the 2s orbital are explained.

Theoretical study of stereodynamics for the D'+DS(ν = 0,j = 0)→D'D+S abstraction reaction

Guo Ya-Hui, Zhang Feng-Yun, Ma Hong-Zhang
Chin. Phys. B, 2013, 22 (5): 053402 doi: 10.1088/1674-1056/22/5/053402
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Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D' +DS(v = 0, j = 0)→D'D+S on a new LZHH potential energy surface (PES) of the adiabatic 3A'' electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θr), Pr), and P(θrr), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(ds00/dωt), (2π/σ)(ds20/dωt), (2π/σ)(ds22+/dωt), (2π/σ)(ds21-/dωt)) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.

First-principles study of electronic properties of interfacial atoms in metal-metal contact electrification

Zhang Yuan-Yue, Shao Tian-Min, Su Kang
Chin. Phys. B, 2013, 22 (5): 053403 doi: 10.1088/1674-1056/22/5/053403
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The mechanism of contact electrification between metals was studied using the first-principles method, taking the Ag-Fe contact as an example. Charge population, charge density difference, and the orbitals and densities of states (DOS) were calculated to study the electronic properties of the contacting interfacial atoms. Based on the calculation, the amount of contact charge was obtained. The investigation revealed that the electrons near Fermi levels with higher energies transfer between the outermost orbitals (s orbitals for Ag and d orbitals for Fe). Meanwhile, polarized covalent bonds form between the d electrons in the deep energy states. These two effects together lead to an increase of charge magnitude at the interface. Also, the electrons responsible for electrification can be determined by their energies and orbitals.

Orientation of KRb molecules in a switched electrostatic field

Huang Yun-Xia, Xu Shu-Wu, Yang Xiao-Hua
Chin. Phys. B, 2013, 22 (5): 053701 doi: 10.1088/1674-1056/22/5/053701
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We theoretically investigate the orientation of the cold KRb molecules induced in a switched electrostatic field by numerically solving the full time-dependent Schrödinger equation. The results show that the periodic field-free molecular orientation can be realized for the KRb molecules by rapidly switching off the electrostatic field. Meanwhile, by varying the switching times of the electrostatic field, the adiabatic and nonadiabatic interactions of the molecules with the applied field can be realized. Moreover, the influences of the electrostatic field strength and the rotational temperature to the degree of the molecular orientation are studied. The investigations show that, the increasing of the electrostatic field will increase the degree of the molecular orientation, both in the constant-field regime and in the field-free regime, while the increasing of the rotational temperature of the cold molecules will greatly decrease the degree of the molecular orientation.

Cloaking an object in a half space without reflection

Guo Peng-Fei, Li Du, Dai Qing, Fu Yun-Qi
Chin. Phys. B, 2013, 22 (5): 054101 doi: 10.1088/1674-1056/22/5/054101
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A novel cloaking scheme to hide an object in a half space from electromagnetic (EM) detection without reflection is firstly presented. The proposed cloaking scheme contains a couple of matching strips, which consist of an isotropic material layer and an anisotropic UPML layer, located right under the bottom surface of a semi-cylindrical cloaking shell. Simple expressions for the material parameters of the cloaking scheme are derived. Numerical simulations are also performed, and good cloaking effect is achieved. The cloaking scheme is effective to hide the local object with strong scattering characters placed on mobile carriers, such as the radar antenna system on the aircraft.

A cost-effective structure of a centralized-light-source WDM-PON utilizing inverse-duobinary-RZ downstream and DPSK upstream

Chen Long-Quan, Qiao Yao-Jun, Ji Yue-Feng
Chin. Phys. B, 2013, 22 (5): 054201 doi: 10.1088/1674-1056/22/5/054201
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In this paper, we propose a new structure of centralized-light-source wavelength division multiplexed passive optical network (WDM-PON) utilizing inverse-duobinary-return-to-zero (inverse-duobinary-RZ) downstream and DPSK upstream. It reuses downstream light for the upstream modulation, which retrenches lasers assembled at each optical network unit (ONU), and ultimately largely cuts down the cost of ONUs. Meanwhile, a 50-km-reach WDM-PON experiment with 10-Gb/s inverse-duobinary-RZ downstream and 6-Gb/s DPSK upstream is demonstrated here. It is revealed to be a novel cost-effective alternative for the next generation access network.

Continuous imaging space in three-dimensional integral imaging

Zhang Lei, Yang Yong, Wang Jin-Gang, Zhao Xing, Fang Zhi-Liang, Yuan Xiao-Cong
Chin. Phys. B, 2013, 22 (5): 054202 doi: 10.1088/1674-1056/22/5/054202
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We report an integral imaging method with continuous imaging space. This method simultaneously reconstructs real and virtual images in the virtual mode, with a minimum gap that separates the entire imaging space into real and virtual space. Experimental results show that the gap is reduced to 45% of that in a conventional integral imaging system with the same parameters.

OH- absorption and nonvolatile holographic storage properties in Mg:Ru:Fe:LiNbO3 crystal as a function of Mg concentration

Xu Chao, Zhang Chun-Lei, Dai Li, Leng Xue-Song, Xu Lei, Xu Yu-Heng
Chin. Phys. B, 2013, 22 (5): 054203 doi: 10.1088/1674-1056/22/5/054203
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Mg:Ru:Fe:LiNbO3 crystals with various concentrations of MgO (in mole) and fixed content of RuO2 and Fe2O3 (in mass) are grown with the Czochralski method from the congruent melt. Their infrared transmission spectra are measured and discussed to investigate the defect structure. With the increase of Mg2+ concentration the blue nonvolatile holographic storage capability is enhanced. The nonvolatile holographic storage properties of dual-wavelength recording of Mg(7 mol%):Ru:Fe:LiNbO3 nonvolatile diffraction efficiency, response time and nonvolatile sensitivity reach 59.8%, 70 s, and 1.04 cm/J, respectively. Comparing Mg(7 mol%):Ru:Fe:LiNbO3 with Ru:Fe:LiNbO3 crystal, the response time is shortened apparently. The nonvolatile diffraction efficiency and sensitivity are raised largely. The mechanism in blue photorefractive nonvolatile holographic storage is discussed.

Emission spectrum of a harmonically trapped Λ-type three-level atom

Guo Hong, Tang Pei
Chin. Phys. B, 2013, 22 (5): 054204 doi: 10.1088/1674-1056/22/5/054204
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We theoretically investigate the emission spectrum for a Λ -type three-level atom trapped in the node of the standing wave. We show that the atomic center-of-mass motion not only directly affects the peak number, peak position, and peak height in atomic emission spectrum, but also influences the effects of the cavity field and the atomic initial state on atomic emission spectrum.

The single-longitudinal-mode operation of a ridge waveguide laser based on two-dimensional photonic crystals

Wang Hua-Yong, Xu Xing-Sheng
Chin. Phys. B, 2013, 22 (5): 054205 doi: 10.1088/1674-1056/22/5/054205
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An electrically driven, single-longitudinal-mode GaAs based photonic crystal (PC) ridge waveguide (RWG) laser emitting at around 850 nm is demonstrated. The single-longitudinal-mode lasing characteristic with a single wavelength is achieved by introducing the PC to the RWG laser. The triangle PC is etched on both sides of the ridge by photolithography and inductive coupled plasma (ICP) etching. The lasing spectra of the RWG lasers with and without the PC are studied, and the result shows that the PC purifies the longitudinal mode. The power/facet and current-voltage characteristics have also been studied and compared.

Laser diode end-pumped Nd:YVO4 regenerative amplifier for picosecond pulses

Zhang Zi-Long, Liu Qiang, Yan Ping, Xia Paketi, Gong Ma-Li
Chin. Phys. B, 2013, 22 (5): 054206 doi: 10.1088/1674-1056/22/5/054206
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A diode dual-end-pumped Nd:YVO4 regenerative amplifier was reported. The influence of the cavity stability on the performance of the regenerative amplifier was studied. The experimental results matched well with the analysis at high pump power. The mode locking seed pulses with 15 ps pulse width and 10 nJ single pulse energy at 86 MHz were amplified up to 4.7 mJ at 1 kHz, corresponding to the maximum amplification about 0.5×106, by our regenerative amplifier. And an average power of 4.7 W was obtained at the repetition rate from 1 kHz to 10 kHz.

Effect of fused silica subsurface defect site density on light intensification

Li Li, Xiang Xia, Yuan Xiao-Dong, He Shao-Bo, Jiang Xiao-Dong, Zheng Wan-Guo, Zu Xiao-Tao
Chin. Phys. B, 2013, 22 (5): 054207 doi: 10.1088/1674-1056/22/5/054207
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The effect of defect density on the modulation of incident laser waves is investigated. First, based on the actual defect distribution in the subsurface of fused silica, a three-dimensional (3D) grid model of defect sites is constructed. The 3D finite-difference time-domain method is developed to solve the Maxwell equations. Then the electrical field intensity in the vicinity of the defect sites in the subsurface of fused silica is numerically calculated. The relationships between the maximal electrical field intensity in fused silica and the geometry of the defect sites are given. The simulated results reveal that the modulation becomes more remarkable with an increase of the defect density. In addition, the effect of the distribution mode of defects on modulation is discussed. Meanwhile, the underlying physical mechanism is analyzed in detail.

Dynamics of optical rogue waves in inhomogeneous nonlinear waveguides

Zhang Jie-Fang, Jin Mei-Zhen, He Ji-Da, Lou Ji-Hui, Dai Chao-Qing
Chin. Phys. B, 2013, 22 (5): 054208 doi: 10.1088/1674-1056/22/5/054208
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We propose a unified theory to construct exact rogue wave solutions of the (2+1)-dimensional nonlinear Schrödinger equation with varying coefficients. And then the dynamics of the first- and the second-order optical rogues are investigated. Finally, the controllability of the optical rogue propagating in inhomogeneous nonlinear waveguides is discussed. By properly choosing the distributed coefficients, we demonstrate analytically that rogue waves can be restrained or even be annihilated, or emerge periodically and sustain forever. We also figure out the center-of-mass motion of the rogue waves.

Determination of temporal structure of femtosecond laser pulses by means of the laser-induced air plasma

Zhang Nan, Bao Wen-Xia, Yang Jing-Hui, Zhu Xiao-Nong
Chin. Phys. B, 2013, 22 (5): 054209 doi: 10.1088/1674-1056/22/5/054209
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A new approach is presented to reveal the temporal structure of femtosecond laser pulses by recording the corresponding time-resolved shadowgraphs of the laser-induced air plasma. It is shown that the temporal structures of femtosecond laser pulses, normally not observable by the ordinary intensity autocorrelator, can be detected through intuitively analyzing the ultrafast evolution process of the air plasma induced by the femtosecond laser pulses under examination. With this method, existence of pre- and post-pulses has been clearly unveiled within the time window of ± 150 fs in reference with the main 50-fs laser pulses output from a commercial 1-kHz femtosecond laser amplifier. The unique advantage of the proposed method is that it can directly provide valuable information about the pulse temporal structures' effect on the laser-induced ionization or material ablation.

Tunable femtosecond laser in the visible range with an intracavity frequency-doubled optical parametric oscillator Hot!

Zhu Jiang-Feng, Xu Liang, Lin Qing-Feng, Zhong Xin, Han Hai-Nian, Wei Zhi-Yi
Chin. Phys. B, 2013, 22 (5): 054210 doi: 10.1088/1674-1056/22/5/054210
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We demonstrated experimentally a synchronously pumped intracavity frequency-doubled femtosecond optical parametric oscillator (OPO) using a periodically-poled lithium niobate (PPLN) as the nonlinear material in combination with a lithium triborate (LBO) as the doubling crystal. A Kerr-lens-mode-locked (KLM) Ti:sapphire oscillator at the wavelength of 790 nm was used as the pump source, which was capable of generating pulses with a duration as short as 117 fs. A tunable femtosecond laser covering the 624-672 nm range was realized by conveniently adjusting the OPO cavity length. A maximum average output power of 260 mW in the visible was obtained at the pump power of 2.2 W, with a typical pulse duration of 205 fs assuming a sech2 pulse profile.

Four distributed feedback laser array integrated with multimode-interference and semiconductor optical amplifier

Ma Li, Zhu Hong-Liang, Liang Song, Zhao Ling-Juan, Chen Ming-Hua
Chin. Phys. B, 2013, 22 (5): 054211 doi: 10.1088/1674-1056/22/5/054211
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Monolithic integration of four 1.55-μ InGaAsP/InP distributed feedback (DFB) lasers using varied ridge width with a 4×1 multimode-interference (MMI) optical combiner and a semiconductor optical amplifier (SOA) is demonstrated. The average output power and the threshold current are 1.8 mW and 35 mA, respectively, when the injection current of the SOA is 100 mA, with a side mode suppression ratio (SMSR) exceeding 40 dB. The four channels have a 1-nm average channel spacing and can operate separately or simultaneously.

Benchmark solutions for sound propagation in an ideal wedge

Luo Wen-Yu, Yang Chun-Mei, Qin Ji-Xing, Zhang Ren-He
Chin. Phys. B, 2013, 22 (5): 054301 doi: 10.1088/1674-1056/22/5/054301
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Sound propagation in a wedge-shaped waveguide with perfectly reflecting boundaries is one of the few range-dependent problems with an analytical solution, and hence provides an ideal benchmark for a full two-way solution to the wave equation. An analytical solution for the sound propagation in an ideal wedge with a pressure-release bottom was presented by Buckingham and Tolstoy [Buckingham and Tolstoy 1990 J. Acoust. Soc. Am. 87 1511]. The ideal wedge problem with a rigid bottom is also of great importance in underwater acoustics. We present an analytical solution to the ideal wedge problem with a perfectly reflecting bottom, either rigid or pressure-release, which may be used to provide a means for investigating the sound field in depth-varying channels, and to establish the accuracy of numerical propagation models. Closed-form expressions for coupling matrices are also provided for the ideal waveguides characterized by a homogeneous water column bounded by perfectly reflecting boundaries. A comparison between the analytical solution and the numerical solution recently proposed by Luo et al. [Luo W Y, Yang C M and Zhang R H 2012 Chin. Phys. Lett. 29 014302] is also presented, through which the accuracy of this numerical model is illustrated.

Cross-diffusive effects on the onset of the double-diffusive convection in a horizontal saturated porous fluid layer heated and salted from above

Rajib Basu, G. C. Layek
Chin. Phys. B, 2013, 22 (5): 054702 doi: 10.1088/1674-1056/22/5/054702
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Double-diffusive stationary and oscillatory instabilities at the marginal state in a saturated porous horizontal fluid layer heated and salted from above are investigated theoretically under the framework of Darcy for porous medium. The contributions of Soret and Dufour coefficients are taken into account in the analysis. Linear stability analysis shows that the critical value of the Darcy-Rayleigh number depends on cross-diffusive parameters at marginally stationary convection, while the marginal state characterized by oscillatory convection does not depend on the cross-diffusion terms even if the condition and frequency of oscillatory convection depends on the cross-diffusive parameters. The critical value of the Darcy-Rayleigh number increases with increasing value of the solutal Darcy-Rayleigh number in the absence of cross-diffusive parameters. The critical Darcy-Rayleigh number decreases with increasing Soret number, resulting in destabilization of the system, while its value increases with increasing Dufour number, resulting in stabilization of the system at the marginal state characterized by stationary convection. The analysis reveals that the Dufour and Soret parameters as well as the porosity parameter play an important role in deciding the type of instability at the onset. This analysis also indicates that the stationary convection is followed by the oscillatory convection for certain fluid mixtures. It is interesting to note that the roles of cross-diffusive parameters on the double-diffusive system heated and salted from above are reciprocal to the double-diffusive system heated and salted from below.

Impacts of air pressure on the evolution of nanosecond pulse discharge products

Yu Jin-Lu, He Li-Ming, Ding Wei, Wang Yu-Qian, Du Chun
Chin. Phys. B, 2013, 22 (5): 055201 doi: 10.1088/1674-1056/22/5/055201
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Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge (NPD) plasma under different air pressures are calculated. The results show that air pressure has a significant impact on the NPD products and on the peak value of particle number density for particles such as O atoms, O3 molecules, N2(A3) molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N2(B3) and N2(C3) molecules in excited states are only slightly affected by the air pressure.

The internal propagation of fusion flame with the strong shock of a laser driven plasma block for advanced nuclear fuel ignition

B. Malekynia, S. S. Razavipour
Chin. Phys. B, 2013, 22 (5): 055202 doi: 10.1088/1674-1056/22/5/055202
Full Text: [PDF 249 KB] (Downloads:299)
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The accelerated skin layer may be used to ignite solid state fuels. The detailed analyses were clarified by solving the hydrodynamic equations for nonlinear force driven plasma block ignition. In this paper, the complementary mechanisms are included for the advanced fuel ignition: external factors such as laser, compression, shock waves, and spark. The other category is created within the plasma fusion as reheating of alpha particle, the Bremsstrahlung absorption, expansion, conduction, and shock waves generated by explosions. With the new condition for the control of shock waves, the spherical deuterium-tritium fuel density should be increased to 75 times of the solid state. The threshold ignition energy flux density for the advanced fuel ignition may be obtained using temperature equations, including the ones for the density profile obtained through the continuity equation and the expansion velocity for the r≠0 layers. These thresholds are significantly reduced in comparison with the ignition thresholds at x=0 for the solid advanced fuels. The quantum correction for the collision frequency is applied in the case of the delay in ion heating. Under the shock wave condition, the spherical proton-boron and proton-lithium fuel densities should be increased to densities 120 and 180 times of the solid state. These plasma compressions are achieved through a longer duration laser pulse or X ray.

Numerical study of physical properties of resistive wall modes in tokamaks

Xia Xin-Nian, Liu Yue, Liu Chao, He Yu-Ling, Xia Guo-Liang
Chin. Phys. B, 2013, 22 (5): 055203 doi: 10.1088/1674-1056/22/5/055203
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The effect of the plasma with toroidal rotation on the resistive wall modes in tokamaks is studied numerically. An eigenvalue method is adopted to calculate the growth rate of the modes for changing plasma resistivity and plasma density distribution, as well as the diffusion time of magnetic field through the resistive wall. It is found that the resistive wall mode can be suppressed by the toroidal rotation of the plasma. Also, the growth rate of the resistive wall mode decreases when the edge plasma density is the same as the core plasma density, but it changes only slightly with the plasma resistivity.

Synthesis of TiN/a-Si3N4 thin film by using a Mather type dense plasma focus system

T. Hussain, R. Ahmad, N. Khalid, Z. A. Umar, A. Hussnain
Chin. Phys. B, 2013, 22 (5): 055204 doi: 10.1088/1674-1056/22/5/055204
Full Text: [PDF 580 KB] (Downloads:458)
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A 2.3 kJ Mather type pulsed plasma focus device was used for the synthesis of a TiN/a-Si3N4 thin film at room temperature. The film was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The XRD pattern confirms the growth of polycrystalline TiN thin film. The XPS results indicate that the synthesized film is non-stoichiometric and contains titanium nitride, silicon nitride, and a phase of silicon oxy-nitride. The SEM and AFM results reveal that the surface of the synthesized film is quite smooth with 0.59 nm roughness (root-mean-square).

Effect of H3BO3 on the phase stability and long persistence properties of Sr3.96Al14O25:Eu0.012+, Dy0.023+ phosphor

Xie Wei, Wang Yin-Hai, Zou Chang-Wei, Liang Feng, Quan Jun, Zhang Jun, Shao Le-Xi
Chin. Phys. B, 2013, 22 (5): 056101 doi: 10.1088/1674-1056/22/5/056101
Full Text: [PDF 593 KB] (Downloads:514)
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Sr3.96Al14O25:Eu2+,Dy3+ long persistent materials with different weight of H3BO3 prepared by the high temperature solid-state reaction method were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence spectra (PL), and thermoluminescence (TL). The results of XRD indicate that the 3% addition of H3BO3 is in favor of the formation of pure phase Sr4Al14O25, and SrAl12O19 was generated when H3BO3 is in low content or high content. The average grain sizes of samples grow bigger during the increasing of H3BO3. PL spectra show that the emission peak does not shift evidently and the emission intensity changes a little, indicate that the different amount of H3BO3 have a little inference to the crystal field. The decay characteristics and TL measurement show that H3BO3 affect the afterglow properties of Sr3.96Al14O25:Eu2+,Dy3+, because the increasing of H3BO3 lead to more defects in Sr4Al14O25 matrix.

Structures and physical properties of R2TX3 compounds

Pan Zhi-Yan, Cao Chong-De, Bai Xiao-Jun, Song Rui-Bo, Zheng Jian-Bang, Duan Li-Bing
Chin. Phys. B, 2013, 22 (5): 056102 doi: 10.1088/1674-1056/22/5/056102
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Rare-earth compounds have been a subject of intensive research based on the unique electronic structures of the rare-earth elements. Novel ternary intermetallic compounds R2TX3 (R=rare-earth element or U, T=transition-metal element, X=Si, Ge, Ga, In) is a significant branch of this research field due to their complex and intriguing physical properties, such as magnetic order at low temperature, spin-glass behavior, Kondo effect, heavy fermion behavior, and so on. The unique physical properties of R2TX3 compounds are related to distinctive electronic structures, crystal structures, micro-interaction, and external environment. Most R2TX3 compounds crystallize in AlB2-type or derived AlB2-type structure and exhibit many similar properties. This paper gives a concise review of the structures and physical properties of these compounds. Spin glass, magnetic susceptibility, resistivity, and specific heat of R2TX3 compounds are discussed.

Ruby fluorescence pressure scale: Revisited

Liu Lei, Bi Yan, Xu Ji-An
Chin. Phys. B, 2013, 22 (5): 056201 doi: 10.1088/1674-1056/22/5/056201
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Effect of non-hydrostatic stress on X-ray diffraction in diamond anvil cell (DAC) is studied. Pressure gradient in sample chamber leads to the broadening of the diffraction peaks, which increase with the hkl index of the crystal. It is found that the difference between the determined d-spacing compressive ratio d/d0 and the real d-spacing compressive ratio dr/d0 is determined by the yield stress of the pressure transmitting media (if used) and the shear modulus of the sample. On the basis of the corrected experiment data of Mao et al. (MXB86), which was used to calibrate the most widely used ruby fluorescence ruby scale, a new relationship of ruby fluorescence pressure scale is corrected, i.e., P=(1904/9.827)[(1+Δλ/λ0)9.827-1].

Microstructure and properties of Nb/Ta multilayer films irradiated by high current pulse electron beam

Ma Xin-Xin, Guo Guang-Wei, Tang Guang-Ze, Sun Ming-Ren, Wang Li-Qin
Chin. Phys. B, 2013, 22 (5): 056202 doi: 10.1088/1674-1056/22/5/056202
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Nb/Ta multilayer films deposited on Ti6Al4V substrate with Nb and Ta monolayer thicknesses of 30 nm, 120 nm, and 240 nm were irradiated by high current pulse electron beam (HCPEB) to prepare Nb-Ta alloyed layers. The microstructure and the composition of the outmost surface of melted alloyed layers were investigated using transmission electron microscope (TEM) equipped with X-ray energy dispersive spectrometer (EDS) attachment. The Ta content of the alloyed surface layer prepared from the monolayer of thickness 30 nm, 120 nm, and 240 nm was ~ 27.7 at.%, 6.37 at.%, and 0 at.%, respectively. It was found that the Ta content in the alloyed layer plays a dominant role in the microstructure of the films. The hardness and the wear rate of the alloyed layers decrease with the increasing content of Ta in the surface layer.

Diffusion of aluminum in MgO: A thermodynamic approach study

Zhang Bao-Hua, Wu Xiao-Ping
Chin. Phys. B, 2013, 22 (5): 056601 doi: 10.1088/1674-1056/22/5/056601
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We have applied a thermodynamical model to calculate the diffusion coefficient of aluminum in MgO with the aid of bulk elastic properties. Our calculated diffusivities as a function of temperature and pressure are compared with the existing results derived from the experimental or theoretical investigations. We find that the present model provides a satisfactory estimation for the activation volume and the activation enthalpy.

Production of 87Rb Bose-Einstein condensates in a hybrid trap

Duan Ya-Fan, Jiang Bo-Nan, Sun Jian-Fang, Liu Kang-Kang, Xu Zhen, Wang Yu-Zhu
Chin. Phys. B, 2013, 22 (5): 056701 doi: 10.1088/1674-1056/22/5/056701
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We report a rapid evaporative cooling method using a hybrid trap which is composed of a quadrupole magnetic trap and a one-beam optical dipole trap. It contains two kinds of evaporative coolings to reach the quantum degeneracy: previously radio-frequency (RF) enforced evaporative cooling in the quadrupole magnetic trap and further runaway evaporative cooling in the optical dipole trap. The hybrid trap does not require a very high power laser such as that in the traditional pure optical trap, but still has a deep trap depth and a large trap volume, and has better optical access than the normal magnetic trap like the quadrupole-Ioffe-configuration (QUIC) cloverleaf trap. A high trap frequency can be easily realized in the hybrid trap to enhance the elastic collision rate and shorten the evaporative cooling time. In our experiment, pure Bose-Einstein condensates (BECs) with about 1×10^5 atoms can be realized in 6 s evaporative cooling in the optical dipole trap.

Demagnetizing factors in patterned CoNiFe films with rectangular elements

Zhang Yu, Zhang Dong, Wang Yu-Kun, Yin Yu-Li, Huang Zhao-Cong, Luo Chen, Zhai Ya
Chin. Phys. B, 2013, 22 (5): 056801 doi: 10.1088/1674-1056/22/5/056801
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CoNiFe patterned films with rectangular elements, all 600 nm wide but of different lengths, were fabricated and investigated by ferromagnetic resonance experiment and micromagnetic simulation. An in-plane magnetic uniaxial anisotropy was exhibited, and its value increases with an increase in the aspect ratio of the elements, which was fitted by the model, including a quasi-ellipsoid demagnetizing field and a non-uniform demagnetizing field. The relative importance of the non-uniform demagnetizing field decreased from 0.26 to 0.16 with an increase in the length-width aspect ratio of the patterned element from 1.5 to 10. The demagnetizing factors in the three principal axes were determined from the experimental data of ferromagnetic resonance, which agreed reasonably well with the values calculated by micromagnetic simulation. The calculation also indicated that the interaction between elements could be neglected when the edge to edge spacing between neighboring elements was larger than 3 μ in our patterned films.

First-principles study on nonlocal ferromagnetism in (Cu, N)-codoped ZnO

Qin Guo-Ping, Wang Xin-Qiang, Zheng Ji, Kong Chun-Yang, Ruan Hai-Bo, Li Wan-Jun, Zhao Yong-Hong, Meng Xiang-Dan
Chin. Phys. B, 2013, 22 (5): 057101 doi: 10.1088/1674-1056/22/5/057101
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First-principles calculations based on spin density functional theory are performed to study the spin-resolved electronic properties of ZnO codoped with Cu and N. (Cu, N)-codoped ZnO exhibits magnetism, and the total magnetic moment mainly originates from the p-d hybridization of Cu-N and Cu-O as well as p-p coupling interaction between N and O at the Fermi level. The Zn34Cu2O35N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the (Cu, N)-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.

Structures and phase transitions of ScH3 under high pressure

Kong Bo, Zhou Zhu-Wen, Chen De-Liang, Ling-hu Rong-Feng
Chin. Phys. B, 2013, 22 (5): 057102 doi: 10.1088/1674-1056/22/5/057102
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The structures and the phase transitions of ScH3 under high pressure are investigated using first-principles calculations. The calculated structural parameters at zero pressure agree well with the available experimental data. With increasing pressure, the transition sequence hcp (GdH3-type)→C2/m→fcc→hcp (YH3-type)→Cmcm of ScH3 is predicted first; the corresponding transition pressures at 0 K are 23 GPa, 25 GPa, 348 GPa, and 477 GPa, respectively. The C2/m symmetry structure is a possible candidate but not a good one as the intermediate state from hexagonal to cubic in ScH3. On the other hand, via the analysis of the structures of hexagonal ScH2.9, cubic ScH3, and cubic ScH2, we find that the repulsive interactions of H-H atoms must play an important role in the transition from hexagonal to cubic.

Structural, magnetic, electronic, and elastic properties of face-centered cubic PuHx (x = 2, 3):GGA (LSDA) + U + SO

Guo Yong, Ai Juan-Juan, Gao Tao, Ao Bing-Yun
Chin. Phys. B, 2013, 22 (5): 057103 doi: 10.1088/1674-1056/22/5/057103
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We perform first-principles calculations to investigate the structural, magnetic, electronic, and mechanical properties of face-centered cubic (fcc) PuH2 and fcc PuH3 using the full potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) and the local spin density approximation (LSDA) taking account of both relativistic and strong correlation effects. The optimized lattice constant a0= 5.371 Å for fcc PuH2 and a0= 5.343 Å for fcc PuH3 calculated in the GGA + sp (spin polarization) + U (Hubbard parameter) + SO (spin-orbit coupling) scheme are in good agreement with the experimental data. The ground state of fcc PuH3 is found to be slightly ferromagnetic. Our results indicate that fcc PuH2 is a metal while fcc PuH3 is a semiconductor with a band gap about 0.35 eV. We note that the SO and the strong correlation between localized Pu 5f electrons are responsible for the band gap of fcc PuH3. The bonds for PuH2 have mainly covalent character while there are covalent bonds in addition to apparent ionicity bonds for PuH3. We also predict the elastic constants of fcc PuH2 and fcc PuH3, which were not observed in the previous experiments.

Energy transfer and correlation dynamics in a three-quasi-spin-pigment system

Zhang Yin-Ping, Li Hong-Rong, Fang Ai-Ping, Chen Hao, Li Fu-Li
Chin. Phys. B, 2013, 22 (5): 057104 doi: 10.1088/1674-1056/22/5/057104
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In this paper, the effects of quantum and classical correlations on the excitation energy transfer in a three-quasi-spin-pigment system are investigated. We first study the dependence of the energy transfer efficiency on various initial correlations of the donor pigments, and find that the initial concurrence is crucial to the efficiency no matter whether the initial states are pure or mixed. We then demonstrate the dynamics of correlations of the system and observe the appearance of sudden death of quantum correlations in the donor pigments. The relation between the energy transfer efficiency and the dynamics of correlations in the donor pigments is also discussed.

Effect of high-temperature buffer thickness on quality of AlN epilayer grown on sapphire substrate by metalorganic chemical vapor deposition

Liu Bo, Zhang Sen, Yin Jia-Yun, Zhang Xiong-Wen, Dun Shao-Bo, Feng Zhi-Hong, Cai Shu-Jun
Chin. Phys. B, 2013, 22 (5): 057105 doi: 10.1088/1674-1056/22/5/057105
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The effect of an initially grown high-temperature AlN buffer (HT-AlN) layer's thickness on the quality of an AlN epilayer grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD) in a two-step growth process is investigated. The characteristics of AlN epilayers are analyzed by using triple-axis crystal X-ray diffraction (XRD) and atomic force microscopy (AFM). It is shown that the crystal quality of the AlN epilayer is closely related to its correlation length. The correlation length is determined by the thickness of the initially grown HT-AlN buffer layer. We find that the optimal HT-AlN buffer thickness for obtaining a high-quality AlN epilayer grown on sapphire substrate is about 20 nm.

High sensitivity Hall devices with AlSb/InAs quantum well structures

Zhang Yang, Zhang Yu-Wei, Wang Cheng-Yan, Guan Min, Cui Li-Jie, Li Yi-Yang, Wang Bao-Qiang, Zhu Zhan-Ping, Zeng Yi-Ping
Chin. Phys. B, 2013, 22 (5): 057106 doi: 10.1088/1674-1056/22/5/057106
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AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm2·V-1·s-1 has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films.

Electrical transport and thermoelectric properties of Ni-doped perovskite-type YCo1-xNixO3 (0≤ x ≤0.07) prepared by sol-gel process

Liu Yi, Li Hai-Jin, Zhang Qing, Li Yong, Liu Hou-Tong
Chin. Phys. B, 2013, 22 (5): 057201 doi: 10.1088/1674-1056/22/5/057201
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Electrical transport and thermoelectric properties of Ni-doped YCo1-xNixO3 (0≤ x ≤0.07), prepared by using sol-gel process, are investigated in a temperature range from 100 to 780 K. The results show that with the increase of Ni doping content, the values of DC resistivity of YCo1-xNixO3 decrease, but carrier concentration increases. The temperature dependences of the resistivity for YCo1-xNixO3 are found to follow a relation of lnρ ∝ 1/T in a low-temperature rang (LTR) (T<~304 K for x=0; ~ 230 K < T <~500 K for x=0.02, 0.05, and 0.07) and high-temperature range (HTR) (T > ~ 655 K for all compounds), respectively. The estimated apparent activation energies for conduction Ea1 in LRT and Ea2 in HTR are both found to decrease monotonically with doping content increasing. At very low temperatures (T < ~ 230 K), Mott's law is observed for YCo1-xNixO3 (x ≥ 0.02), indicating that considerable localized states form in the heavy doping compounds. Although the Seebeck coefficient of the compound decreases after Ni doping, the power factor of YCo1-xNixO3 is enhanced remarkably in a temperature range from 300 to 740 K, i.e., a 6-fold increase is achieved at 500 K for YCo0.98Ni0.02O3, indicating that the high-temperature thermoelectric property of YCoO3 can be improved by partial substitution of Ni for Co.

Combined frequency- and time-domain photocarrier radiometry characterization of ion-implanted and thermally annealed silicon wafers

Ren Sheng-Dong, Li Bin-Cheng, Gao Li-Feng, Wang Qian
Chin. Phys. B, 2013, 22 (5): 057202 doi: 10.1088/1674-1056/22/5/057202
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A combined frequency-swept and quasi-time-domain photocarrier radiometry (PCR) technique was developed to characterize thermally annealed silicon wafers with B+, P+, and As+ ion implantation at doses ranging from 1×1011 cm-2 to 1×1016 cm-2. The implantation dose dependence of the PCR amplitude, the frequency dependencies of the PCR amplitude and phase, as well as the quasi-time-domain PCR waveforms were simultaneously employed to analyze all the ion-implanted silicon samples. The dependence of the effective lifetime on the implantation dose has been investigated and shown to be related to the trap density and lifetime extracted from the transient PCR signals.

Effects of a bar on optical transmission through Z-shaped metallic slit arrays

Wu Cai-Ni, Li Hong-Jian, Peng Xiao, Cao Guang-Tao, Liu Zhi-Min
Chin. Phys. B, 2013, 22 (5): 057301 doi: 10.1088/1674-1056/22/5/057301
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We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switch.

Effects of polarization on intersubband transitions of AlxGa1-xN/GaN multi-quantum wells

Tian Wu, Yan Wei-Yi, Xiong Hui, Dai Jian-Nan, Fang Yan-Yan, Wu Zhi-Hao, Yu Chen-Hui, Chen Chang-Qin
Chin. Phys. B, 2013, 22 (5): 057302 doi: 10.1088/1674-1056/22/5/057302
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The effects of polarization and related structural parameters on the intersubband transitions of AlGaN/GaN multi-quantum wells (MQWs) have been investigated by solving the Schrödinger and the Poisson equations self-consistently. The results show that the intersubband absorption coefficient increases with increasing polarization while the transition wavelength decreases, which is not identical to the case of the interband transitions. Moreover, it suggests that the well width has a greater effect on the intersubband transitions than the barrier thickness, and the intersubband transition wavelength of the structure when doped in the barrier is shorter than that when doped in the well. It is found that the influences of the structural parameters differ for different electron subbands. The mechanisms responsible for these effects have been investigated in detail.

Optimized geometry and electronic structure of graphyne-like silicyne nanoribbons Hot!

Pei Yang, Wu Hai-Bin
Chin. Phys. B, 2013, 22 (5): 057303 doi: 10.1088/1674-1056/22/5/057303
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Silicyne, a silicon allotrope, which is closely related to silicene and has the graphyne-like structure, is theoretically investigated in this work. Its optimized geometry and electronic band structure are calculated by means of the first-principles frozen-core projector-augmented wave method implemented in the Vienna ab initio simulation package (VASP). We find that the lattice parameter is 9.5 Å, the silicon chain between hexagons is composed of disilynic linkages (-Si≡Si-) rather than cumulative linkages (=Si=Si=), and the binding energy is -3.41 eV per atom. The band structure is calculated by adopting the generalized gradient approximation and hybrid functionals. The band gap produced by the HSE06 functional is 0.73 eV, which is nearly triple as much as that by the generalized gradient approximation of Perdew-Burke-Ernzerhof functional.

Fabrication and characterization of V-gate AlGaN/GaN high electron mobility transistors

Zhang Kai, Cao Meng-Yi, Chen Yong-He, Yang Li-Yuan, Wang Chong, Ma Xiao-Hua, Hao Yue
Chin. Phys. B, 2013, 22 (5): 057304 doi: 10.1088/1674-1056/22/5/057304
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V-gate GaN high electron mobility transistors (HEMTs) are fabricated and investigated systematically. A V-shaped recess geometry is obtained using an improved Si3N4 recess etching technology. Compared with standard HMETs, the fabricated V-gate HEMTs exhibit a 17% higher peak extrinsic transconductance due to a narrowed gate foot. Moreover, both the gate leakage and current dispersion are dramatically suppressed simultaneously, although a slight degradation of frequency response is observed. Based on a two-dimensional electric field simulation using Silvaco "ATLAS" for both standard HEMTs and V-gate HEMTs, the relaxation in peak electric field at gate edge is identified as the predominant factor leading to the superior performance of V-gate HEMTs.

Strong perpendicular magnetic anisotropy in Co2FeAl0.5Si0.5 film sandwiched by MgO layers

Wang Sheng, Li Xiao-Qi, Bai Li-Juan, Xu Xiao-Guang, Miao Jun, Jiang Yong
Chin. Phys. B, 2013, 22 (5): 057305 doi: 10.1088/1674-1056/22/5/057305
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Co2FeAl0.5Si0.5 (CFAS) based multilayers sandwiched by MgO layers have been deposited and annealed at different temperatures. Perpendicular magnetic anisotropy (PMA) with the magnetic anisotropy energy density Ku ≈ 2.5×106 erg/cm3 and the coercivity Hc=363 Oe has been achieved in the Si/SiO2/MgO (1.5 nm)/CFAS (2.5 nm)/MgO (0.8 nm)/Pt (5 nm) film annealed at 300 ℃. The strong PMA is mainly due to the top MgO layer. The structure can be used as top magnetic electrodes in half-metallic perpendicular magnetic tunnel junctions.

Temperature-controllable spin-polarized current and spin polarization in a Rashba three-terminal double-quantum-dot device

Hong Xue-Kun, Yang Xi-Feng, Feng Jin-Fu, Liu Yu-Shen
Chin. Phys. B, 2013, 22 (5): 057306 doi: 10.1088/1674-1056/22/5/057306
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We propose a Rashba three-terminal double-quantum-dot device to generate a spin-polarized current and manipulate the electron spin in each quantum dot by utilizing the temperature gradient instead of the electric bias voltage. This device possesses a nonresonant tunneling channel and two resonant tunneling channels. The Keldysh nonequilibrium Green's function techniques are employed to determinate the spin-polarized current flowing from the electrodes and the spin accumulation in each quantum dot. We find that their signs and magnitudes are well controllable by the gate voltage or the temperature gradient. This result is attribute to the change in the slope of the transmission probability at the Fermi levels in the low-temperature region. Importantly, an obviously pure spin current can be injected into or extracted from one of the three electrodes by properly choosing the temperature gradient and the gate voltages. Therefore, the device can be used as an ideal thermal generator to produce a pure spin current and manipulate the electron spin in the quantum dot.

Energy gap suppression and excess current in Tl2Ba2CaCu2O8 intrinsic Josephson junctions

Wang Pei, Xie Wei, Hu Lei, Liu Xin, Zhao Xin-Jie, He Ming, Ji Lu, Zhang Xu, Yan Shao-Lin
Chin. Phys. B, 2013, 22 (5): 057402 doi: 10.1088/1674-1056/22/5/057402
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Intrinsic Josephson junctions in misaligned Tl2Ba2CaCu2O8 thin film were fabricated on LaAlO3 substrate. The temperature dependence of the critical current is investigated around liquid nitrogen temperature. In the current voltage characteristic, large voltage jump and free of resistive branch are observed, which shows good consistency with the intrinsic Josephson junctions. By analyzing the large gap voltage in the curve, great suppression of the energy gap is found. Through discussing the temperature dependence of the gap voltage in liquid nitrogen temperature, it is showed that this phenomenon can be caused by the nonequilibrium quasiparticle injection. The temperature influence on the excess current also confirms the nonequlibrium effect.

Large reversible magnetocaloric effect in HoMn2O5

Ge Heng, Zhang Xiang-Qun, Ke Ya-Jiao, Jin Jin-Ling, Liao Zhi-Xin, Cheng Zhao-Hua
Chin. Phys. B, 2013, 22 (5): 057502 doi: 10.1088/1674-1056/22/5/057502
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Magnetocaloric effect (MCE) in polycrystalline HoMn2O5 was investigated by isothermal magnetization curves from 2 K to 50 K. A relatively large magnetic entropy change, ΔSM = 7.8 J/(kg·K), was achieved with the magnetic field up to 70 kOe. The magnetic entropy change is reversible in the whole range of temperature. The contributions of elastic and magnetoelastic energy to the changing of the magnetic entropy are discussed in terms of the Landau theory. The reversibility of MCE with maximal refrigerant capacity RC = 216.7 J/kg makes polycrystalline HoMn2O5 be promising as a magnetic refrigerant.

Oscillation of coercivity between positive and negative in MnxGe1-x:H ferromagnetic semiconductor films

Qin Yu-Feng, Yan Shi-Shen, Xiao Shu-Qin, Li Qiang, Dai Zheng-Kun, Shen Ting-Ting, Yang Ai-Chun, Pei Juan, Kang Shi-Shou, Dai You-Yong, Liu Guo-Lei, Chen Yan-Xue, Mei Liang-Mo
Chin. Phys. B, 2013, 22 (5): 057503 doi: 10.1088/1674-1056/22/5/057503
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Amorphous MnxGe1-x:H ferromagnetic semiconductor films prepared in mixed Ar with 20% H2 by magnetron co-sputtering show global ferromagnetism with positive coercivity at low temperatures. With increasing temperature, the coercivity of MnxGe1-x:H films first changes from positive to negative, and then back to positive again, which was not found in the corresponding MnxGe1-x and other ferromagnetic semiconductors before. For Mn0.4Ge0.6:H film, the inverted Hall loop is also observed at 30 K, which is in consistence with the negative coercivity. The negative coercivity is explained by the antiferromagnetic exchange coupling between the H-rich ferromagnetic regions separated by the H-poor non-ferromagnetic spacers. Hydrogenation is a useful method to tune the magnetic properties of MnxGe1-x films for the application in spintronics.

Monte Carlo study of nanowire magnetic properties

R. Masrour, L. Bahmad, A. Benyoussef
Chin. Phys. B, 2013, 22 (5): 057504 doi: 10.1088/1674-1056/22/5/057504
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In this work, we use Monte Carlo simulations to study the magnetic properties of a nanowire system based on a honeycomb lattice, in the absence as well as in the presence of both an external magnetic field and crystal field. The system is formed with NL layers having spins that can take the values σ =± 1/2 and S=± 1,0. The blocking temperature is deduced, for each spin configuration, depending on the crystal field Δ. The effect of the exchange interaction coupling Jp between the spin configurations σ and S is studied for different values of temperature at fixed crystal field. The established ground-state phase diagram, in the plane (Jp, Δ), shows that the only stable configurations are: (1/2,0), (1/2,+1), and (1/2,-1). The thermal magnetization and susceptibility are investigated for the two spin configurations, in the absence as well as in the presence of a crystal field. Finally, we establish the hysteresis cycle for different temperature values, showing that there is almost no remaining magnetization in the absence of the external magnetic field, and that the studied system exhibits a super-paramagnetic behavior.

First-principle study on optical properties of N-La-codoped anatase TiO

Wang Qing, Liang Ji-Feng, Zhang Ren-Hui, Li Qiang, Dai Jian-Feng
Chin. Phys. B, 2013, 22 (5): 057801 doi: 10.1088/1674-1056/22/5/057801
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The electronic structures, deformation charge density, dipole moment, and optical properties of N-La-codoped anatase titanium dioxide (TiO2) are studied using the plane-wave ultrasoft pseudopotential method based on density functional theory (DFT). The optical properties of two-ion-doped TiO2are analyzed via electronic structures, deformation charge density, and dipole moment. For the model of N-La-doped TiO2, smaller atom fraction of N and La atoms induces better optical properties. The absorption edges of two doped TiO2 models redshift to the visible-light region.

Electronic Raman scattering in double semi-parabolic quantum wells

N. Zamani, A. Keshavarz, M. J. Karimi
Chin. Phys. B, 2013, 22 (5): 057802 doi: 10.1088/1674-1056/22/5/057802
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The differential cross-section for electronic Raman scattering in double semi-parabolic quantum wells of typical GaAs/AlxGa1-xAs is investigated numerically with the effective-mass approximation. The dependence of the differential cross-section on structural parameters such as the barrier width and the well widths are studied. Our results indicate that the electronic Raman scattering is affected by the geometrical size and can be negligible in the symmetric double-well case.

Near-infrared downconversion in Eu2+ and Pr3+ co-doped KSrPO4 phosphor

Sun Jia-Yue, Sun Yi-Ning, Zhu Ji-Cheng, Zeng Jun-Hui, Du Hai-Yan
Chin. Phys. B, 2013, 22 (5): 057803 doi: 10.1088/1674-1056/22/5/057803
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A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4:Eu2+, Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KSrPO4 host. With broadband near-ultraviolet light excitation induced by the 4f→5d transition of Eu2+, the characteristic NIR emission of Pr3+, peaking at 974 nm and 1019 nm due to 3P01G4 and 1G43H4 transitions, is generated as a result of the energy transfer from Eu2+ to Pr3+. The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2+ prove the energy transfer from Eu2+ to Pr3+. This Eu2+ and Pr3+ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.

Surface plasmon enhanced photoluminescence in amorphous silicon carbide films by adjusting Ag island film sizes

Yu Wei, Wang Xin-Zhan, Dai Wan-Lei, Lu Wan-Bing, Liu Yu-Mei, Fu Guang-Sheng
Chin. Phys. B, 2013, 22 (5): 057804 doi: 10.1088/1674-1056/22/5/057804
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Ag island films with different sizes have been deposited on hydrogenated amorphous silicon carbide (α -SiC:H) films, and the influences of Ag island films on the optical properties of the α -SiC:H films are investigated. Atomic force microscope images show that Ag nanoislands are formed after Ag coating, and the size of the Ag islands increase with increasing Ag deposition time. The extinction spectra indicate that two resonance absorption peaks which correspond to out-of-plane and in-plane surface plasmon modes of the Ag island films are obtained, and the resonance peak shifts toward longer wavelength with increasing Ag island size. The photoluminescence (PL) enhancement or quenching depends on the size of Ag islands, and PL enhancement by 1.6 times on the main PL band is obtained when the sputtering time is 10 min. Analyses show that the influence of surface plasmons on the PL of α-SiC:H is determined by the competition between the scattering and absorption of Ag islands, and PL enhancement is obtained when scattering is the main interaction between the Ag islands and incident light.

Tunneling effect in cavity-resonator-coupled arrays

Ma Hua, Qu Shao-Bo, Liang Chang-Hong, Zhang Jie-Qiu, Xu Zhuo, Wang Jia-Fu
Chin. Phys. B, 2013, 22 (5): 057805 doi: 10.1088/1674-1056/22/5/057805
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The quantum tunneling effect (QTE) in a cavity-resonator-coupled (CRC) array was analytically and numerically investigated. The underlying mechanism was interpreted by treating electromagnetic waves as photons, and then was generalized to acoustic waves and matter waves. It is indicated that for the three kinds of waves, the QTE can be excited by cavity resonance in a CRC array, resulting in sub-wavelength transparency through the narrow splits between cavities. This opens up opportunities for designing new types of crystals based on CRC arrays, which may find potential applications such as quantum devices, micro-optic transmission, and acoustic manipulation.

Formula for average energy required to produce a secondary electron in an insulator

Xie Ai-Gen, Zhan Yu, Gao Zhi-Yong, Wu Hong-Yan
Chin. Phys. B, 2013, 22 (5): 057901 doi: 10.1088/1674-1056/22/5/057901
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Based on a simple classical model specifying that the primary electrons interact with the electrons of a lattice through the Coulomb force and a conclusion that the lattice scattering can be ignored, the formula for the average energy required to produce a secondary electron (ε) is obtained. On the basis of the energy band of an insulator and the formula for ε, the formula for the average energy required to produce a secondary electron in an insulator (εi) is deduced as a function of the width of the forbidden band (Eg) and electron affinity χ. Experimental values and the εi values calculated with the formula are compared, and the results validate the theory that explains the relationships among Eg, χ, and εi and suggest that the formula for εi is universal on the condition that the primary electrons at any energy hit the insulator.

Enhancement of microwave absorption of nanocomposite BaFe12O19/α-Fe microfibers

Yang Xin-Chun, Liu Rui-Jiang, Shen Xiang-Qian, Song Fu-Zhan, Jing Mao-Xiang, Meng Xian-Feng
Chin. Phys. B, 2013, 22 (5): 058101 doi: 10.1088/1674-1056/22/5/058101
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Nanocomposite BaFe12O19/α-Fe microfibers with diameters of about 1-5 μm are prepared by the organic gel-thermal selective reduction process. The binary phase of BaFe12O19 and α-Fe is formed after reduction of the precursor BaFe12O19/α-Fe2O3microfibers at 350 ℃ for 1 h. These nanocomposite microfibers are fabricated from α-Fe (16-22 nm in diameter) and BaFe12O19 particles (36-42 nm in diameter) and basically exhibit a single-phase-like magnetization behaviour, with a high saturation magnetization and coercive force arising from the exchange-coupling interactions of soft α-Fe and hard BaFe12O19. The microwave absorption characteristics in a 2-18 GHz frequency range of the nanocomposite BaFe12O19/α-Fe microfibers are mainly influenced by their mass ratio of α-Fe/BaFe12O19 and specimen thickness. It is found that the nanocomposite BaFe12O19/α-Fe microfibers with a mass ratio of 1:6 and specimen thickness of 2.5 mm show an optimal reflection loss (RL) of -29.7 dB at 13.5 GHz and the bandwidth with RL exceeding -10 dB covers the whole Ku-band (12.4-18.0 GHz). This enhancement of microwave absorption can be attributed to the heterotructure of soft, nano, conducting α-Fe particles embedded in hard, nano, semiconducting barium ferrite, which improves the dipolar polarization, interfacial polarization, exchange-coupling interaction, and anisotropic energy in the nanocomposite BaFe12O19/α-Fe microfibers.

Role of chelating agent in chemical and fluorescent properties of SnO2 nanoparticles

He Shao-Bo, Wang Shi-Fa, Ding Qing-Ping, Yuan Xiao-Dong, Zheng Wan-Guo, Xiang Xia, Li Zhi-Jie, Zu Xiao-Tao
Chin. Phys. B, 2013, 22 (5): 058102 doi: 10.1088/1674-1056/22/5/058102
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A modified polyacrylamide gel route is applied to synthesize SnO2 nanoparticles. High-quality SnO2 nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λex = 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.

Optoelectronic characteristics of CuO nanorods

Xie De-Hua, Wang Fei-Fei, Lü Hao, Du Min-Yong, Xu Wen-Jie
Chin. Phys. B, 2013, 22 (5): 058103 doi: 10.1088/1674-1056/22/5/058103
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Optoelectronic characteristics of p-type CuO nanorods, synthesized by a simple hydrothermal method, were investigated at different atmospheres and oxygen pressures. The CuO nanorods have lower resistance in air than in vacuum, unlike the n-type semiconductors. This is explained in terms of the surface accumulation conduction. Measurements at different oxygen pressures indicate that oxygen has an important effect on the optoelectronic properties of p-type nanomaterials.

Density behaviors of Ge nanodots self-assembled by ion beam sputtering deposition

Xiong Fei, Yang Tao, Song Zhao-Ning, Yang Pei-Zhi
Chin. Phys. B, 2013, 22 (5): 058104 doi: 10.1088/1674-1056/22/5/058104
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Self-assembled Ge nanodots with areal number density up to 2.33×1010 cm-2 and aspect ratio larger than 0.12 are prepared by ion beam sputtering deposition. The dot density, a function of deposition rate and Ge coverage, is observed to be limited mainly by the transformation from two-dimensional precursors to three-dimensional islands, and to be associated with the adatom behaviors of attachment and detachment from the islands. An unusual increasing temperature dependence of nanodot density is also revealed when high ion energy is employed in sputtering deposition, and is shown to be related with the breaking down of the superstrained wetting layer. This result is attributed to the interaction between energetic atoms and the growth surface, which mediates island nucleation.

Growth and characterization of single crystals of the quaternary TlGaSeS compound

S. R. Alharbi
Chin. Phys. B, 2013, 22 (5): 058105 doi: 10.1088/1674-1056/22/5/058105
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The electrical conductivity and Hall effect for TlGaSeS crystals have been investigated over a wide temperature range. The crystals we used are grown by a modified Bridgman technique and possess p-type conductivity. The energy gap has been found to be 1.63 eV, whereas the ionization energy is 0.25 eV. The variations of the Hall mobility as well as the carrier concentration with temperature have been investigated. The scattering mechanisms of the carrier are checked over the whole investigated temperature range. Furthermore, the diffusion coefficient, relaxation time, and diffusion length of holes are estimated.

Fabrication of ZnO nanoparticles-embedded hydrogenated diamond-like carbon films by electrochemical deposition technique

Zhang Pei-Zeng, Li Rui-Shan, Pan Xiao-Jun, Xie Er-Qing
Chin. Phys. B, 2013, 22 (5): 058106 doi: 10.1088/1674-1056/22/5/058106
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ZnO nanoparticles-embedded hydrogenated diamond-like carbon (ZnO-DLC) films have been prepared by electrochemical deposition in ambient conditions. The morphology, composition, and microstructure of the films have been investigated. The results show that the resultant films are hydrogenated diamond-like carbon films embedded with ZnO nanoparticles in wurtzite structure, and the content and size of the ZnO nanoparticles increase with increasing deposition voltage, which are confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and transmission electron microscope (TEM). Furthermore, a possible mechanism used to describe the growth process of ZnO-DLC films by electrochemical deposition is also discussed.

Dynamic aggregation evolution of competitive societies of cooperative and noncooperative agents

Lin Zhen-Quan, Ye Gao-Xiang
Chin. Phys. B, 2013, 22 (5): 058201 doi: 10.1088/1674-1056/22/5/058201
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We propose an evolution model of cooperative agent and noncooperative agent aggregates to investigate the dynamic evolution behaviors of the system and the effects of the competing microscopic reactions on the dynamic evolution. In this model, each cooperative agent and noncooperative agent are endowed with integer values of cooperative spirits and noncooperative spirits, respectively. The cooperative spirits of a cooperative agent aggregate and the noncooperative spirits of a noncooperative agent aggregate change via four competing microscopic reaction schemes: the win-win reaction between two cooperative agents, the lose-lose reaction between two noncooperative agents, the win-lose reaction between a cooperative agent and a noncooperative agent (equivalent to the migration of spirits from cooperative agents to noncooperative agents), and the cooperative agent catalyzed decline of noncooperative spirits. Based on the generalized Smoluchowski's rate equation approach, we investigate the dynamic evolution behaviors such as the total cooperative spirits of all cooperative agents and the total noncooperative spirits of all noncooperative agents. The effects of the three main groups of competition on the dynamic evolution are revealed. These include: (i) the competition between the lose-lose reaction and the win-lose reaction, which give rise to respectively the decrease and increase in the noncooperative agent spirits; (ii) the competition between the win-win reaction and the win-lose reaction, which give rise to respectively the increase and decrease in the cooperative agent spirits; (iii) the competition between the win-lose reaction and the catalyzed-decline reaction, which give rise to respectively the increase and decrease in the noncooperative agent spirits.

Coupling effects of depletion interactions in three-sphere colloidal system

Chen Ze-Shun, Dai Gang, Gao Hai-Xia, Xiao Chang-Ming
Chin. Phys. B, 2013, 22 (5): 058202 doi: 10.1088/1674-1056/22/5/058202
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In a three-sphere system, the middle sphere is acted by two opposite depletion forces from the other two spheres. It is found that, in this system, the two depletion forces are coupled with each other and result in a strengthened depletion force. So the difference of the depletion forces of the three-sphere system and its corresponding two two-sphere systems is introduced to describe the coupling effect of the depletion interactions. The numerical results obtained by Monte-Carlo simulations show that this coupling effect is affected by both the concentration of small spheres and the geometrical confinement. Meanwhile, it is also found that the mechanisms of the coupling effect and the effect on the depletion force from the geometry factor are the same.

Dependence of effective screening length in granular columns on bead and silo sizes and their ratio

Ali Shah, Ahmed Khan, Saeed Ahmed Khan
Chin. Phys. B, 2013, 22 (5): 058301 doi: 10.1088/1674-1056/22/5/058301
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Apparent mass measurements at the bottom of silo have been carried out. An important parameter in the Janssen model known as the effective screening length has been investigated for different bead and silo diameters as well as of their ratios. It is found that the effective screening length augments with the grain diameter d in addition to the granular column size. It is also revealed that λ exhibits stronger correlation with the bead diameter than that of silo. This phenomenon is attributed to the reduced-shielding of the vertical stresses to the horizontal ones.

Analytical models of lateral power devices with arbitrary vertical doping profiles in drift region

Hua Ting-Ting, Guo Yu-Feng, Yu Ying, Gene Sheu, Jian Tong, Yao Jia-Fei
Chin. Phys. B, 2013, 22 (5): 058501 doi: 10.1088/1674-1056/22/5/058501
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By solving 2D Poisson's equation, analytical models are proposed to calculate the surface potential and electric field distributions of lateral power devices with arbitrary vertical doping profiles. The vertical and the lateral breakdown voltages are formulized to quantify the breakdown characteristic in completely-depleted and partially-depleted cases. A new reduced surface field (RESURF) criterion which can be used in various drift doping profiles is further derived for obtaining the optimal trade-off between the breakdown voltage and the on-resistance. Based on these models and the numerical simulation, the electric field modulation mechanism and the breakdown characteristics of lateral power devices are investigated in detail for the uniform, linear, Gaussian, and some discrete doping profiles along the vertical direction in the drift region. Then, the mentioned vertical doping profiles of these devices with the same geometric parameters are optimized, and the results show that the optimal breakdown voltages and the effective drift doping concentrations of these devices are identical, which are equal to those of the uniform-doped device, respectively. The analytical results of these proposed models are in good agreement with the numerical results and the previously experimental results, confirming the validity of the models presented here.

Advantages of an InGaN-based light emitting diode with a p-InGaN/p-GaN superlattice hole accumulation layer

Liu Chao, Ren Zhi-Wei, Chen Xin, Zhao Bi-Jun, Wang Xing-Fu, Yin Yi-An, Li Shu-Ti
Chin. Phys. B, 2013, 22 (5): 058502 doi: 10.1088/1674-1056/22/5/058502
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P-InGaN/p-GaN superlattices (SLs) are developed for hole accumulation layer (HAL) of blue light emitting diode (LED). Free hole concentration as high as 2.6×1018 cm-3 is achieved by adjusting the Cp2Mg flow rate during the growth of p-InGaN/p-GaN SLs. The p-InGaN/p-GaN SLs with appropriate Cp2Mg flow rates are then incorporated between the multi-quantum well and AlGaN electron blocking layer as an HAL, which leads to the enhanced light output power by 29% at 200 mA, compared with the traditional LED without such SL HAL. Meanwhile, the efficiency droop is also effectively alleviated in the LED with the SL HAL. The improved performance is attributed to the increased hole injection efficiency, and the reduced electron leakage by inserting the p-type SL HAL.

Performance improvement of blue light-emitting diodes with an AlInN/GaN superlattice electron-blocking layer

Zhao Fang, Yao Guang-Rui, Song Jing-Jing, Ding Bin-Bin, Xiong Jian-Yong, Su Chen, Zheng Shu-Wen, Zhang Tao, Fan Guang-Han
Chin. Phys. B, 2013, 22 (5): 058503 doi: 10.1088/1674-1056/22/5/058503
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The characteristics of a blue light-emitting diode (LED) with an AlInN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically. The carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results suggest that the LED with an AlInN/GaN SL EBL has better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region than the LED with a conventional rectangular AlGaN EBL or a AlGaN/ GaN SL EBL. The results also indicate that the efficiency droop is markedly improved when an AlInN/GaN SL EBL is used.

The effect of dimerization on the magnetoresistance in organic spin valves

Wang Hui, Hu Gui-Chao, Ren Jun-Feng
Chin. Phys. B, 2013, 22 (5): 058504 doi: 10.1088/1674-1056/22/5/058504
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The effect of lattice dimerization on the magnetoresistance (MR) in organic spin valves is investigated based on the Su-Schrieffer-Heeger (SSH) model and the Green's function method. By comparing with the results for a uniform chain, we find that the dimerization of the molecular chain modifies the monotonic dependence of the MR on the bias to an oscillatory one. A sign inversion of the MR is observed when the amplitude of the dimerization is adjusted. The results also show that at a low bias, the MR through a dimerized chain decreases with the increasing bias as well as the increasing chain length, which is consistent with the experimental reports. A further understanding can be achieved by analyzing the electronic states and the spin-dependent transmission spectrum with the parallel and antiparallel magnetization orientations of the two ferromagnetic electrodes.

Adaptive synchronization control of coupled chaotic neurons in the external electrical stimulation

Yu Hai-Tao, Wang Jiang, Deng Bin, Wei Xi-Le, Chen Ying-Yuan
Chin. Phys. B, 2013, 22 (5): 058701 doi: 10.1088/1674-1056/22/5/058701
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In this paper we present a combined algorithm for the synchronization control of two gap junction coupled chaotic FitzHugh-Nagumo (FHN) neurons in the external electrical stimulation. The controller consists of a combination of dynamical sliding mode control and adaptive backstepping control. The combined algorithm yields an adaptive dynamical sliding mode control law which has advantages over static sliding mode-based controller of chattering-free, i.e., a sufficiently smooth control input signal is generated. It is shown that the proposed control scheme can not only compensate for the system uncertainty, but also guarantee the stability of the synchronized error system. In addition, numerical simulations are also performed to demonstrate the effectiveness of the proposed adaptive controller.

An LCOR model for suppressing cascading failure in weighted complex networks

Chen Shi-Ming, Pang Shao-Peng, Zou Xiao-Qun
Chin. Phys. B, 2013, 22 (5): 058901 doi: 10.1088/1674-1056/22/5/058901
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Based on the relationship between capacity and load, cascading failure on weighted complex networks is investigated, and a load-capacity optimal relationship (LCOR) model is proposed in this paper. Compared with other three kinds of load-capacity linear or non-linear relationship models in model networks as well as a number of real-world weighted networks including the railway network, the airports network and the metro network, the LCOR model is shown to have the best robustness against cascading failure with less cost. Furthermore, theoretical analysis and computational method of its cost threshold are provided to validate the effectiveness of the LCOR model. The results show that the LCOR model is effective for designing real-world networks with high robustness and less cost against cascading failure.

An adaptive strategy based on linear prediction of queue length to minimize congestion in Barabási-Albert scale-free networks

Shen Yi
Chin. Phys. B, 2013, 22 (5): 058902 doi: 10.1088/1674-1056/22/5/058902
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In this paper, we propose an adaptive strategy based on linear-prediction of queue length to minimize congestion in Barabási-Albert (BA) scale-free networks. This strategy uses local knowledge of traffic conditions and allows nodes to be able to self-coordinate their accepting probability to the incoming packets. We show that the strategy can delay remarkably the onset of congestion and systems avoiding the congestion can benefit from hierarchical organization of accepting rates of nodes. Furthermore, with the increase of prediction orders, we achieve larger values for the critical load together with a smooth transition from free-flow to congestion.

A thermal flux-diffusing model for complex networks and its applications in community structure detection

Shen Yi
Chin. Phys. B, 2013, 22 (5): 058903 doi: 10.1088/1674-1056/22/5/058903
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We introduce a thermal flux-diffusing model for complex networks. Based on this model, we propose a physical method to detect the communities in the complex networks. The method allows us to obtain the temperature distribution of nodes in time that scales linearly with the network size. Then, the local community enclosing a given node can be easily detected for the reason that the dense connections in the local communities lead to the temperatures of nodes in the same community being close to each other. The community structure of a network can be recursively detected by randomly choosing the nodes outside the detected local communities. In the experiments, we apply our method to a set of benchmarking networks with known pre-determined community structures. The experiment results show that our method has higher accuracy and precision than most existing globe methods and is better than the other existing local methods in the selection of the initial node. Finally, several real-world networks are investigated.

In-situ high-pressure behaviors of double-perovskite Sr2ZnTeO6

Han Dan-Dan, Gao Wei, Li Na-Na, Tang Rui-Lian, Li Hui, Ma Yan-Mei, Cui Qi-Liang, Zhu Pin-Wen, Wang Xin
Chin. Phys. B, 2013, 22 (5): 059101 doi: 10.1088/1674-1056/22/5/059101
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Structural and spectroscopic properties of Sr2ZnTeO6 (SZTO) were investigated by angle-dispersive synchrotron X-ray powder diffraction and Raman spectroscopy in a diamond anvil cell up to 31 GPa at room temperature. Although SZTO remained stable up to the highest pressure, the different pressure coefficients of the normalized axial compressibility were obtained as βab=8.16×10-3 GPa-1 and βc=7.61×10-3 GPa-1. The bulk modulus B0 was determined to be 190(1) GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. All the observed Raman modes exhibited a broadening effect under high pressure. The vibrational band ϒ 1 around 765 cm-1, which is associated with the Te-O stretching mode in the basal plane of the TeO6 octahedron, had the largest pressure coefficient, and the Grüneisen parameters for all the observed phonon modes also were calculated and presented. These parameters could be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for monitoring the magnitude of the shift of phonon frequencies with strains.

Channel characterization at 120 GHz for future indoor communication systems

Chen Zhen, Cao Jun-Cheng
Chin. Phys. B, 2013, 22 (5): 059201 doi: 10.1088/1674-1056/22/5/059201
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We present a simulation on the spatial and temporal characteristics of the indoor propagation channel at 120 GHz. The simulation, applied to a dynamic scenario with randomly placed objects and moving people in a room, is based on a three-dimensional ray-tracing method. Propagation and reflection mechanisms of electromagnetic waves are discussed in the channel model. The received power in a 0.95-m-height plane is obtained. Comparison between walls and ceiling covered with dielectric mirrors and those with three common wall and ceiling materials are presented. The result shows that the holistic received power level with dielectric mirrors is about 10 dB higher than with other materials.

Monte Carlo evaluation of spatial multiple-bit upset sensitivity to oblique incidence

Geng Chao, Liu Jie, Xi Kai, Zhang Zhan-Gang, Gu Song, Hou Ming-Dong, Sun You-Mei, Duan Jing-Lai, Yao Hui-Jun, Mo Dan
Chin. Phys. B, 2013, 22 (5): 059501 doi: 10.1088/1674-1056/22/5/059501
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We investigate the impact of heavy ion irradiation on hypothetical static random access memory (SRAM) device. Influences of the irradiation angle, critical charge, drain-drain spacing, and dimension of device structure on the device sensitivity have been studied. These prediction and simulated results are interpreted with MUFPSA, a Monte Carlo code based on Geant4. The results show that the orientation of ion beams and device with different critical charge exert indispensable effects on multiple-bit upsets (MBUs), and that with the decrease in spacing distance between adjacent cells or the dimension of the cells, the device is more susceptible to single event effect, especially to MBUs at oblique incidence.

Inflationary dynamics in the braneworld scenarios

Zhang Kai-Yuan, Wu Pu-Xun, Yu Hong-Wei
Chin. Phys. B, 2013, 22 (5): 059801 doi: 10.1088/1674-1056/22/5/059801
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We analyze the attractor behaviour of the inflation field in braneworld scenarios using the Hamilton-Jacobi formalism, where the Friedmann equation has the form of H2=ρ+ε2ρ0ρ or H2=ρ+ερ2/2σ, with ε=±1. We find that in all models the linear homogeneous perturbation can decay exponentially as the scalar field rolls down its potential. However, in the case of a -ρ2 correction to the standard cosmology with ρ < σ, the existence of an attractor solution requires (σ-ρ)/φ2 > 1. Our results show that the perturbation decays more quickly in models with positive-energy correction than in the standard cosmology, which is opposite to the case of negative-energy correction. Thus, the positive-energy modification rather than the negative one can assist the inflation and widen the range of initial conditions.
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