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Chin. Phys. B  
  Chin. Phys. B--2012, Vol.21, No.3
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Asymptotic solving method for sea–air coupled oscillator ENSO model

Zhou Xian-Chun,Yao Jing-Sun,Mo Jia-Qi
Chin. Phys. B, 2012, 21 (3): 030201 doi: 10.1088/1674-1056/21/3/030201
Full Text: [PDF 113 KB] (Downloads:521)
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The ENSO is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interaction. In this article, we create an asymptotic solving method for the nonlinear system of the ENSO model. The asymptotic solution is obtained. And then we can furnish weather forecasts theoretically and other behaviors and rules for the atmosphere-ocean oscillator of the ENSO.

Solving coupled nonlinear Schrödinger equations via a direct discontinuous Galerkin method

Zhang Rong-Pei,Yu Xi-Jun,Feng Tao
Chin. Phys. B, 2012, 21 (3): 030202 doi: 10.1088/1674-1056/21/3/030202
Full Text: [PDF 181 KB] (Downloads:1199)
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In this work, we present the direct discontinuous Galerkin (DDG) method for the one-dimensional coupled nonlinear Schrödinger (CNLS) equation. We prove that the new discontinuous Galerkin method preserves the discrete mass conservations corresponding to the properties of the CNLS system. The ordinary differential equations obtained by the DDG space discretization is solved via a third-order stabilized Runge-Kutta method. Numerical experiments show that the new DDG scheme gives stable and less diffusive results and has excellent long-time numerical behaviors for the CNLS equations.

Fractal structures in a generalized square map with exponential terms

Li Xian-Feng,Chu Yan-Dong,Zhang Hui
Chin. Phys. B, 2012, 21 (3): 030203 doi: 10.1088/1674-1056/21/3/030203
Full Text: [PDF 492 KB] (Downloads:622)
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Fractal structures in a generalized squared map with exponential terms are expanded in this paper. We describe how complex behaviors can arise as the parameters change. The appearances of different kinds of fractal structures, in both the attractive and the divergent regions, and most interestingly, on small regular islands embedded in the chaotic region, are manifested to have a variety of extraordinary geometries in the parameter plane.

Novel stability and stabilization criteria for Takagi–Sugeno fuzzy time-delay systems

Gong Da-Wei,Zhang Hua-Guang,Wang Zhan-Shan
Chin. Phys. B, 2012, 21 (3): 030204 doi: 10.1088/1674-1056/21/3/030204
Full Text: [PDF 145 KB] (Downloads:592)
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We study the problems of stability and stabilization for Takagi-Sugeno (T-S) fuzzy time-delay systems. First, by constructing a less-redundant Lyapunov-Krasovskii function and introducing a useful inequality, an innovative stability criterion is obtained, which gives a significant improvement on the performance. Compared with the exiting references, our result can use fewer unknown variables and get better results. Furthermore, based on the derived stability criteria, a new stabilization condition is developed, in which the controller gain and the maximum allowable delay bound can be obtained simultaneously. The conditions are all derived in the form of linear matrix inequality, which are easy to verify. Finally, numerical examples are given to show the effectiveness of the proposed methods.

Word diversity can accelerate consensus in naming game

Zhang Xiao-Dan,Wang Zhen,Zheng Fei-Fei,Yang Miao
Chin. Phys. B, 2012, 21 (3): 030205 doi: 10.1088/1674-1056/21/3/030205
Full Text: [PDF 225 KB] (Downloads:475)
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In this paper, we introduce word diversity that reflects the inhomogeneity of words in a communication into the naming game. Diversity is realized by assigning a weight factor to each word. The weight is determined by three different distributions (uniform, exponential, and power-law distributions). During the communication, the probability that a word is selected from speaker's memory depends on the introduced word diversity. Interestingly, we find that the word diversity following three different distributions can remarkably promote the final convergency, which is of high importance in the self-organized system. In particular, for all the ranges of amplitude of distribution, the power-law distribution enables the fastest consensus, while uniform distribution gives the slowest consensus. We provide an explanation of this effect based on both the number of different names and the number of total names, and find that a wide spread of names induced by the segregation of words is the main promotion factor. Other quantities, including the evolution of the averaging success rate of negotiation and the scaling behavior of consensus time, are also studied. These results are helpful for better understanding the dynamics of the naming game with word diversity.

Dual-band frequency selective surface with quasi-elliptic bandpass response

Zhou Hang,Qu Shao-Bo,Peng Wei-Dong,Wang Jia-Fu,Ma Hua,Zhang Jie-Qiu,Bai Peng,Xu Zhuo
Chin. Phys. B, 2012, 21 (3): 030301 doi: 10.1088/1674-1056/21/3/030301
Full Text: [PDF 240 KB] (Downloads:557)
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Based on the substrate integrated waveguide technology, we present a dual-band frequency selective surface (FSS) with a quasi-elliptic bandpass response. The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes, with the same slots on both sides of the metal surfaces. Four cavities of different sizes and two slots of different sizes are used to design the novel FSS. Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance. The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles. Moreover, it is easy to fabricate.

Scattering states of modified Pöschlben–Teller potential in D-dimension

Chen Chang-Yuan,Lu Fa-Lin,You Yuan
Chin. Phys. B, 2012, 21 (3): 030302 doi: 10.1088/1674-1056/21/3/030302
Full Text: [PDF 166 KB] (Downloads:913)
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We present a new approximation scheme for the centrifugal term, and apply this new approach to the Schrödinger equation with the modified Pöschl-Teller potential in the D-dimension for arbitrary angular momentum states. The approximate analytical solutions of the scattering states are derived. The normalized wave functions expressed in terms of the hypergeometric functions of the scattering states on the k/2π scale and the calculation formula of the phase shifts are given. The numerical results show that our results are in good agreement with those obtained by using the amplitude-phase method (APM).

Optomechanical entanglement in a whispering-gallery cavity

Mi Xian-Wu,Bai Jiang-Xiang,Li De-Jun
Chin. Phys. B, 2012, 21 (3): 030303 doi: 10.1088/1674-1056/21/3/030303
Full Text: [PDF 172 KB] (Downloads:795)
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The dynamics of the optomechanical entanglement between optical cavity field modes and a macroscopic mechanical breathing mode in a whispering-gallery cavity as well as the continuous variable entanglement between the phase-quadrature amplitudes of the two whispering-gallery modes have been analysed. Simulated results indicate that under state-of-the-art experimental conditions, optomechanical entanglement is obvious and can occur even at temperatures of above 40 K. Compared with the entanglement of the mechanical oscillator at the ground state temperature, optomechanical entanglement is more intense by several orders of magnitude.

Generation of a new bipartite coherent-entangled state and its applications

Zhang Bao-Lai,Meng Xiang-Guo,Wang Ji-Suo
Chin. Phys. B, 2012, 21 (3): 030304 doi: 10.1088/1674-1056/21/3/030304
Full Text: [PDF 109 KB] (Downloads:443)
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A new bipartite coherent-entangled state is introduced in the two-mode Fock space, which exhibits the properties of both a coherent state and an entangled state. The set of coherent-entangled states makes up a complete and partly nonorthogonal representation. A simple experimental scheme to produce the coherent-entangled state using an asymmetric beamsplitter is proposed. Some applications of the coherent-entangled state in quantum optics are also presented.

Controlling quantum discord dynamics in cavity QED systems by applying a classical driving field with phase decoherence

Qian Yi,Xu Jing-Bo
Chin. Phys. B, 2012, 21 (3): 030305 doi: 10.1088/1674-1056/21/3/030305
Full Text: [PDF 1275 KB] (Downloads:579)
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We investigate a two-level atom interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence and find that a stationary quantum discord can arise in the interaction of the atom and cavity field as the time turns to infinity. We also find that the stationary quantum discord can be increased by applying a classical driving field. Furthermore, we explore the quantum discord dynamics of two identical non-interacting two-level atoms independently interacting with a quantized cavity field and a classical driving field in the presence of phase decoherence. Results show that the quantum discord between two atoms is more robust than entanglement under phase decoherence and the classical driving field can help to improve the amount of quantum discord of the two atoms.

Cryptanalysis of fair quantum blind signatures

He Li-Bao,Huang Liu-Sheng,Yang Wei,Xu Rui
Chin. Phys. B, 2012, 21 (3): 030306 doi: 10.1088/1674-1056/21/3/030306
Full Text: [PDF 116 KB] (Downloads:748)
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We investigate the fair quantum blind signature scheme proposed by Wang and Wen [Wang T Y and Wen Q Y 2010 Chin. Phys. B 19 060307], which uses the fundamental properties of quantum mechanics and the availability of a trusted arbitrator. However, in this paper, we find that the protocol cannot satisfy the property of non-forgeability even under the condition that the trusted arbitrator is totally credible. Moreover, a simple feasible suggestion for improving the protocol is proposed.

Efficient entanglement purification in quantum repeaters

Sheng Yu-Bo,Zhou Lan,Cheng Wei-Wen,Gong Long-Yan,Zhao Sheng-Mei,Zheng Bao-Yu
Chin. Phys. B, 2012, 21 (3): 030307 doi: 10.1088/1674-1056/21/3/030307
Full Text: [PDF 152 KB] (Downloads:666)
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We present an efficient entanglement purification protocol (EPP) with controlled-not (CNOT) gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy F>1/2. If the initial state is not entangled, it still can be purified. With the linear optics, this protocol can get pure maximally entangled pairs with some probabilities. Meanwhile, it can be used to purify the entanglement between the atomic ensembles in distant locations. This protocol may be useful in long-distance quantum communication.

Quantum communication via controlled holes in the statistical distribution of excitations in a nanoresonator coupled to a Cooper pair box Hot!

C. Valverde,A.T. Avelar,B. Baseia
Chin. Phys. B, 2012, 21 (3): 030308 doi: 10.1088/1674-1056/21/3/030308
Full Text: [PDF 625 KB] (Downloads:488)
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We propose a scheme to transmit information via the statistical distribution of excitations of a nanomechanical resonator. It employs a controllable coupling between this system and a Cooper pair box. The success probability and the fidelity are calculated and compared with those obtained in an atom-field system in different regimes. Addtionaly, the scheme can also be applied to prepare low excited Fock states.

Dispersion relation of excitation mode in spin-polarized Fermi gas

Liu Ke,Chen Ji-Sheng
Chin. Phys. B, 2012, 21 (3): 030309 doi: 10.1088/1674-1056/21/3/030309
Full Text: [PDF 169 KB] (Downloads:397)
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We study the dispersion relation of the excitation mode in a spin-polarized Fermi gas. In the frame of the imaginary-time finite temperature field theory, the polarization tensor is calculated by taking the random phase approximation. The population imbalance effects on the dispersion relation of the excitation mode and the spin-spin correlation susceptibility are investigated. The numerical results in terms of the imbalance ratio indicate the polarization effects on the dispersion relation and susceptibility χ.

Energy, momentum and angular momentum in the dyadosphere of a charged spacetime in teleparallel equivalent of general relativity

Gamal G.L. Nashed
Chin. Phys. B, 2012, 21 (3): 030401 doi: 10.1088/1674-1056/21/3/030401
Full Text: [PDF 121 KB] (Downloads:397)
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We apply the energy momentum and angular momentum tensor to a tetrad field, with two unknown functions of radial coordinate, in the framework of a teleparallel equivalent of general relativity (TEGR). The definition of the gravitational energy is used to investigate the energy within the external event horizon of the dyadosphere region for the Reissner-Nordström black hole. We also calculate the spatial momentum and angular momentum.

Pitchfork bifurcation and circuit implementation of a novel Chen hyper-chaotic system

Dong En-Zeng,Chen Zeng-Qiang,Chen Zai-Ping,Ni Jian-Yun
Chin. Phys. B, 2012, 21 (3): 030501 doi: 10.1088/1674-1056/21/3/030501
Full Text: [PDF 517 KB] (Downloads:868)
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In this paper, a novel four dimensional hyper-chaotic system is coined based on the Chen system, which contains two quadratic terms and five system parameters. The proposed system can generate a hyper-chaotic attractor in wide parameters regions. By using the center manifold theorem and the local bifurcation theory, a pitchfork bifurcation is demonstrated to arise at the zero equilibrium point. Numerical analysis demonstrates that the hyper-chaotic system can generate complex dynamical behaviors, e.g., a direct transition from quasi-periodic behavior to hyper-chaotic behavior. Finally, an electronic circuit is designed to implement the hyper-chaotic system, the experimental results are consist with the numerical simulations, which verifies the existence of the hyper-chaotic attractor. Due to the complex dynamic behaviors, this new hyper-chaotic system is useful in the secure communication.

Design of an adaptive finite-time controller for synchronization of two identical/different non-autonomous chaotic flywheel governor systems

Mohammad Pourmahmood Aghababa
Chin. Phys. B, 2012, 21 (3): 030502 doi: 10.1088/1674-1056/21/3/030502
Full Text: [PDF 221 KB] (Downloads:773)
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The centrifugal flywheel governor (CFG) is a mechanical device that automatically controls the speed of an engine and avoids the damage caused by sudden change of load torque. It has been shown that this system exhibits very rich and complex dynamics such as chaos. This paper investigates the problem of robust finite-time synchronization of non-autonomous chaotic CFGs. The effects of unknown parameters, model uncertainties and external disturbances are fully taken into account. First, it is assumed that the parameters of both master and slave CFGs have the same value and a suitable adaptive finite-time controller is designed. Second, two CFGs are synchronized with the parameters of different values via a robust adaptive finite-time control approach. Finally, some numerical simulations are used to demonstrate the effectiveness and robustness of the proposed finite-time controllers.

Adaptive projective synchronization of different chaotic systems with nonlinearity inputs

Niu Yu-Jun,Wang Xing-Yuan,Pei Bing-Nan
Chin. Phys. B, 2012, 21 (3): 030503 doi: 10.1088/1674-1056/21/3/030503
Full Text: [PDF 452 KB] (Downloads:545)
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We investigate the projective synchronization of different chaotic systems with nonlinearity inputs. Based on the adaptive technique, sliding mode control method and pole assignment technique, a novel adaptive projective synchronization scheme is proposed to ensure the drive system and the response system with nonlinearity inputs can be rapidly synchronized up to the given scaling factor.

Adaptive synchronization of chaos in permanent magnet synchronous motors based on passivity theory

Wei Du-Qu,Zhang Bo,Luo Xiao-Shu
Chin. Phys. B, 2012, 21 (3): 030504 doi: 10.1088/1674-1056/21/3/030504
Full Text: [PDF 603 KB] (Downloads:705)
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An adaptive synchronization control method is proposed for chaotic permanent magnet synchronous motors based on the property of a passive system. We prove that the controller makes the synchronization error system between the driving and the response systems not only passive but also asymptotically stable. The simulation results show that the proposed method is effective and robust against uncertainties in the systemic parameters.

Modified adaptive controller for synchronization of incommensurate fractional-order chaotic systems

Zhang Ruo-Xun,Yang Shi-Ping
Chin. Phys. B, 2012, 21 (3): 030505 doi: 10.1088/1674-1056/21/3/030505
Full Text: [PDF 629 KB] (Downloads:677)
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We investigate the synchronization of a class of incommensurate fractional-order chaotic systems, and propose a modified adaptive controller for fractional-order chaos synchronization based on the Lyapunov stability theory, the fractional order differential inequality, and the adaptive strategy. This synchronization approach is simple, universal, and theoretically rigorous. It enables the synchronization of0 fractional-order chaotic systems to be achieved in a systematic way. The simulation results for the fractional-order Qi chaotic system and the four-wing hyperchaotic system are provided to illustrate the effectiveness of the proposed scheme.

Synchronization of spatiotemporal chaos in complex networks via backstepping

Chai Yuan,Lü Ling,Chen Li-Qun
Chin. Phys. B, 2012, 21 (3): 030506 doi: 10.1088/1674-1056/21/3/030506
Full Text: [PDF 331 KB] (Downloads:751)
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A backstepping approach is proposed for the synchronization of chain networks of multi-spatiotemporal chaotic systems with topologically equivalent structures. The synchronization of multi-spatiotemporal chaotic systems is implemented by adding the control only to a terminal node, and the controller is designed via a corresponding update law. The control law is applied to spatiotemporal Gray-Scott systems. Numerical results demonstrate the effectiveness and the feasibility of the proposed approach.

Analytical solutions and rogue waves in (3+1)-dimensional nonlinear Schrödinger equation

Ma Zheng-Yi,Ma Song-Hua
Chin. Phys. B, 2012, 21 (3): 030507 doi: 10.1088/1674-1056/21/3/030507
Full Text: [PDF 353 KB] (Downloads:978)
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Analytical solutions in terms of rational-like functions are presented for a (3+1)-dimensional nonlinear Schrödinger equation with time-varying coefficients and a harmonica potential using the similarity transformation and a direct ansatz. Several free functions of time t are involved to generate abundant wave structures. Three types of elementary functions are chosen to exhibit the corresponding nonlinear rogue wave propagations.

Spatiotemporal self-similar solutions for the nonautonomous (3+1)-dimensional cubic–quintic Gross–Pitaevskii equation

Dai Chao-Qing,Chen Rui-Pin,Wang Yue-Yue
Chin. Phys. B, 2012, 21 (3): 030508 doi: 10.1088/1674-1056/21/3/030508
Full Text: [PDF 1486 KB] (Downloads:545)
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With the help of similarity transformation, we obtain analytical spatiotemporal self-similar solutions of the nonautonomous (3+1)-dimensional cubic-quintic Gross-Pitaevskii equation with time-dependent diffraction, nonlinearity, harmonic potential and gain or loss when two constraints are satisfied. These constraints between the system parameters hint that self-similar solutions form and transmit stably without the distortion of shape based on the exact balance between the diffraction, nonlinearity and the gain/loss. Based on these analytical results, we investigate the dynamic behaviours in a periodic distributed amplification system.

In-situ multi-information measurement system for preparing gallium nitride photocathode

Fu Xiao-Qian,Chang Ben-Kang,Qian Yun-Sheng,Zhang Jun-Ju
Chin. Phys. B, 2012, 21 (3): 030601 doi: 10.1088/1674-1056/21/3/030601
Full Text: [PDF 125 KB] (Downloads:545)
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We introduce the first domestic in-situ multi-information measurement system for a gallium nitride (GaN) photocathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity (NEA) status. Information including the heat cleaning temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency (QE) can be obtained during preparation. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 ℃. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the it in-situ multi-information measurement system the NEA GaN photocathode can be successfully prepared.

Density functional theory study of MgnNi2 (n=1–6) clusters

Li Jing,Liu Xiao-Yong,Zhu Zheng-He,Sheng Yong
Chin. Phys. B, 2012, 21 (3): 033101 doi: 10.1088/1674-1056/21/3/033101
Full Text: [PDF 182 KB] (Downloads:614)
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The geometries of MgnNi2 (n=1-6) clusters are studied by using the hybrid density functional theory (B3LYP) with LANL2DZ basis sets. For the ground-state structures of MgnNi2 clusters, the stabilities and the electronic properties are investigated. The results show that the groundstate structures and symmetries of Mg clusters change greatly due to the Ni atoms. The average binding energies have a growing tendency while the energy gaps have a declining tendency. In addition, the ionization energies exhibit an odd-even oscillation feature. We also conclude that n=3, 5 are the magic numbers of the MgnNi2 clusters. The Mg3 Ni2 and Mg5Ni2 clusters are more stable than neighbouring clusters, and the Mg4Ni2 cluster exhibits a higher chemical activity.

The effect of polymer type on electric breakdown strength on a nanosecond time scale

Zhao Liang,Su Jian-Cang,Pan Ya-Feng,Zhang Xi-Bo
Chin. Phys. B, 2012, 21 (3): 033102 doi: 10.1088/1674-1056/21/3/033102
Full Text: [PDF 137 KB] (Downloads:771)
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Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength (EBD) on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE (polyethylene), PTFE (polytetrafluoroethelene), PMMA (organic glass) and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD (PTFE) > EBD (PMMA) > EBD (Nylon) > EBD (PE). This result is consistent with the theoretical prediction.

First-principles study of the electronic and optical properties of the (Y, N)-codoped anatase TiO2 photocatalyst

Lin Yan-Ming,Jiang Zhen-Yi,Hu Xiao-Yun,Zhang Xiao-Dong,Fan Jun,Miao Hui,Shang Yi-Bo
Chin. Phys. B, 2012, 21 (3): 033103 doi: 10.1088/1674-1056/21/3/033103
Full Text: [PDF 439 KB] (Downloads:1035)
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First-principles plane-wave pseudopotential calculations are performed to study the geometrical structures, formation energies, and electronic and optical properties of Y-doped, N-doped, and (Y, N)-codoped TiO2. The calculated results show that Y and N codoping leads to lattice distortion, easier separation of photogenerated electron-hole pairs and band gap narrowing. The optical absorption spectra indicate that an obvious red-shift occurs upon Y and N codoping, which enhances visible-light photocatalytic activity.

The near-infrared spectra and distribution of excited states of electrodeless discharge rubidium vapour lamps

Sun Qin-Qing,Miao Xin-Yu,Sheng Rong-Wu,Chen Jing-Biao
Chin. Phys. B, 2012, 21 (3): 033201 doi: 10.1088/1674-1056/21/3/033201
Full Text: [PDF 287 KB] (Downloads:635)
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The population ratio between the excited states of rubidium in the electrodeless discharge rubidium vapour lamp is calculated according to the near-infrared spectra in the region of 780-1550 nm. By using a 1529 nm laser, we measure the density of natural rubidium atoms at the 5P3/2 level. The populations of different excited states are then clarified.

High-order harmonic generation with a two-color laser pulse

Luo Lao-Yong,Du Hong-Chuan,Hu Bi-Tao
Chin. Phys. B, 2012, 21 (3): 033202 doi: 10.1088/1674-1056/21/3/033202
Full Text: [PDF 839 KB] (Downloads:593)
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We theoretically investigate the electron dynamics of the high-order harmonics generation process by combining a near-infrared 800 nm driving pulse with a mid-infrared 2000 nm control field. We also investigate the emission time of harmonics using time-frequency analysis to illustrate the physical mechanisms of high-order harmonic generation. We calculate the ionization rate using the Ammosov-Delone-Krainov model and interpret the variations in harmonic intensity for different control field strengths and delays. We find that the width of the harmonic plateau can be extended when the control electric field is added, and a supercontinuum from 198 to 435 eV is generated, from which an isolated 61-as pulse can be directly obtained.

The influence of divergence angle on the deposition of neutral chromium atoms using a laser standing wave

Zhang Wen-Tao,Zhu Bao-Hua,Huang Jing,Xiong Xian-Ming,Jiang Qu-Bo
Chin. Phys. B, 2012, 21 (3): 033301 doi: 10.1088/1674-1056/21/3/033301
Full Text: [PDF 395 KB] (Downloads:480)
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The characteristics of neutral chromium atoms in the standing wave field are discussed. Based on a semi-classical model, the motion equation of neutral atoms in the laser standing wave field is analyzed, and the trajectories of the atoms are obtained by simulations with the different divergence angles of the atomic beam. The simulation results show that the full width at half maximum (FWHM) of the stripe is 2.75 nm and the contrast is 38.5:1 when the divergence angle equals 0 mrad, the FWHM is 24.1 nm and the contrast is 6.8:1 when the divergence angle equals 0.2 mrad and the FWHMs are 58.6 and 137.8 nm, and the contrasts are 3.3:1 and 1.6:1 when the divergence angles equal 0.5 and 1.0 mrad, respectively.

Laser guiding of cold molecules in a hollow optical fiber and continuous-wave cold molecular beam generation

Liu Run-Qin,Yin Ya-Ling,Yin Jian-Ping
Chin. Phys. B, 2012, 21 (3): 033302 doi: 10.1088/1674-1056/21/3/033302
Full Text: [PDF 424 KB] (Downloads:425)
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A novel scheme for guiding arbitrary buffer-gas cooled neutral molecules in a hollow optical fiber (HOF) using a red-detuned HE11 mode is proposed and analysed theoretically. We give the electromagnetic field distribution of the HE11 mode in the HOF and calculate the optical potential of an I2 molecule, and study the molecule guiding mechanism using a classical Monte Carlo simulation. Using a 6 kW input laser, an S-shape HOF with a 2 cm curvature radius for both bends, and an input molecular beam with a transverse temperature of 0.5 K and longitudinal temperature of 5 K, we obtain a guiding efficiency of ~0.126% for the scheme, and the transverse and longitudinal temperatures of the guided molecular beam are 1.9 mK and 0.5 K, respectively.

Sequential over-barrier ionization of multi-electron atoms in the tens-to-hundreds keV/u energy range

Zou Xian-Rong,Liu Lan-Diao,Ji Ming-Chao,Feng Dong,Chen Xi-Meng,Shao Jian-Xiong
Chin. Phys. B, 2012, 21 (3): 033401 doi: 10.1088/1674-1056/21/3/033401
Full Text: [PDF 121 KB] (Downloads:418)
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Our previous work on the classical over-barrier ionization model for helium double ionization is extended to the complex multi-electron system of Ne. The total and q-fold ionization cross sections are calculated at energies ranging from a few tens to several hundred keV/u. The calculation results are in good agreement with the experimental data, and the energy dependence of the cross sections suggests that the multi-ionization of a strong perturbated complex atom is probably the sequential over-barrier ionization process.

A molecular dynamics study of the structural change differences between Au225 and Au369 clusters on MgO surfaces at low temperature

Zhang Lin,Wang Shao-Qing,Chen Nan-Xian
Chin. Phys. B, 2012, 21 (3): 033601 doi: 10.1088/1674-1056/21/3/033601
Full Text: [PDF 398 KB] (Downloads:570)
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The differences in structural change between Au225 and Au369 clusters with their (111) facets supported on MgO(100) surfaces at 5 K are studied by using molecular-dynamics simulations with the atomic interchange potentials of the Au/MgO interface. The parameters are obtained from the ab initio energies using the Chen-Möbius inversion method. Analyses of the pair distribution functions show that the two Au clusters use different deformation processes to adjust the distances between the interface atoms, owing to the misfit between the atom distances among the clusters and the substrates. The local structural changes are identified by atomic density profiles.

Efficiency enhancement of a two-beam free-electron laser using a nonlinearly tapered wiggler

Maryam Zahedian,B. Maraghechi,M.H. Rouhani
Chin. Phys. B, 2012, 21 (3): 034101 doi: 10.1088/1674-1056/21/3/034101
Full Text: [PDF 965 KB] (Downloads:540)
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A nonlinear and non-averaged model of a two-beam free-electron laser (FEL) wiggler that is tapered nonlinearly in the absence of slippage is presented. The two beams are assumed to have different energies, and the fundamental resonance of the higher energy beam is at the third harmonic of the lower energy beam. By using Maxwell's equations and the full Lorentz force equation of motion for the electron beams, coupled differential equations are derived and solved numerically by the fourth-order Runge-Kutta method. The amplitude of the wiggler field is assumed to decrease nonlinearly when the saturation of the third harmonic occurs. By simulation, the optimum starting point of the tapering and the slopes for reducing the wiggler amplitude are found. This technique can be applied to substantially improve the efficiency of the two-beam FEL in the XUV and X-ray regions. The effect of tapering on the dynamical stability of the fast electron beam is also studied.

The Wigner distribution functions of coherent and partially coherent Bessel–Gaussian beams

Zhu Kai-Cheng,Li Shao-Xin,Tang Ying,Yu Yan,Tang Hui-Qin
Chin. Phys. B, 2012, 21 (3): 034201 doi: 10.1088/1674-1056/21/3/034201
Full Text: [PDF 760 KB] (Downloads:569)
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Based on the integral representation of the Bessel functions and the generating function of the Tricomi function, an analytical expression of the Wigner distribution function (WDF) for a coherent or partially coherent Bessel-Gaussian beam is presented. The reduced two-dimensional WDFs are also demonstrated graphically, which reveals the dependence of the reduced WDFs on the beam parameters.

Fano resonance and wave transmission through a chain structure with an isolated ring composed of defects

Zhang Cun-Xi,Ding Xiu-Huan,Wang Rui,Zhou Yun-Qing,Kong Ling-Min
Chin. Phys. B, 2012, 21 (3): 034202 doi: 10.1088/1674-1056/21/3/034202
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We consider a discrete model that describes a linear chain of particles coupled to an isolated ring composed of N defects. This simple system can be regarded as a generalization of the familiar Fano-Anderson model. It can be used to model discrete networks of coupled defect modes in photonic crystals and simple waveguide arrays in two-dimensional lattices. The analytical result of the transmission coefficient is obtained, along with the conditions for perfect reflections and transmissions due to either destructive or constructive interferences. Using a simple example, we further investigate the relationship between the resonant frequencies and the number of defects N, and study how to affect the numbers of perfect reflections and transmissions. In addition, we demonstrate how these resonance transmissions and refections can be tuned by one nonlinear defect of the network that possesses a nonlinear Kerr-like response.

The Fourier slice transformation of the Wigner operator and the quantum tomogram of the density operator

Wang Tong-Tong,Fan Hong-Yi
Chin. Phys. B, 2012, 21 (3): 034203 doi: 10.1088/1674-1056/21/3/034203
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Using the Weyl quantization scheme and based on the Fourier slice transformation (FST) of the Wigner operator, we construct a new expansion formula of the density operator ρ, with the expansion coefficient being the FST of ρ's classical Weyl correspondence, and the latter the Fourier transformation of ρ's quantum tomogram. The coordinate-momentum intermediate representation is used as the Radon transformation of the Wigner operator.

The difference in noise property between the Autler–Townes splitting medium and the electromagnetically induced transparent medium

Li Zhong-Hua,Li Yuan,Dou Ya-Fang,Zhang Jun-Xiang
Chin. Phys. B, 2012, 21 (3): 034204 doi: 10.1088/1674-1056/21/3/034204
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The quantum noise of squeezed probe light passing through an atomic system with different electromagnetically induced transparency and Autler-Townes splitting effects is investigated theoretically. It is found that the optimal squeezing preservation of the outgoing probe beam occurs in the strong-coupling-field regime rather than in the weak-coupling-field regime. In the weak-coupling-field regime, which was recently recognized as the electromagnetically induced transparency regime (Abi-Salloum T Y 2010 Phys. Rev. A bf81 053836), the output amplitude noise is affected mainly by the atomic noise originating from the random decay process of atoms. While in the strong-coupling-field regime, defined as the Autler-Townes splitting regime, the output amplitude noise is affected mainly by the phase-to-amplitude conversion noise. This is useful in improving the quality of the experiment for efficient quantum memory, and hence has an application in quantum information processing.

Highly efficient four-wave mixing induced by quantum constructive interference in rubidium vapour

Wang Gang,Xue Yan,Cui Cui-Li,Qu Yi,Gao Jin-Yue
Chin. Phys. B, 2012, 21 (3): 034205 doi: 10.1088/1674-1056/21/3/034205
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We demonstrate efficient four-wave mixing with an intensity conversion efficiency of nearly 100% in theory without considering the Doppler-broadening effect in a four-level double-Λ system of hot 87Rb gas. The corresponding experimental value of about 73% was reported in our earlier work under the same conditions. This dramatic efficiency is critically dependent on the constructive interference between two four-wave mixing processes relevant to the internally generated four-wave mixing signal.

Single-mode low threshold current multi-hole vertical-cavity surface-emitting lasers

Zhao Zhen-Bo,Xu Chen,Xie Yi-Yang,Zhou Kang,Liu Fa,Shen Guang-Di
Chin. Phys. B, 2012, 21 (3): 034206 doi: 10.1088/1674-1056/21/3/034206
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A multi-hole vertical-cavity surface-emitting laser (VCSEL) operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-reflector of an oxidation-confined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10? are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter-hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes.

A 168-W high-power single-frequency amplifier in an all-fiber configuration

Xiao Hu,Dong Xiao-Lin,Zhou Pu,Xu Xiao-Jun,Zhao Guo-Min
Chin. Phys. B, 2012, 21 (3): 034207 doi: 10.1088/1674-1056/21/3/034207
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We present a high-power, single-frequency, narrow linewidth fiber amplifier based on master oscillator power amplification chains in an all-fiber configuration. The effect of the delivery fiber on the maximum output power is studied. A home-made 1064-nm seed laser with a 20-kHz linewidth is boosted to 129 W, and limited by stimulated Brillouin scattering (SBS) when the delivery fiber is 1.2 m long. By shortening the delivery fiber length to 0.7 m, the SBS threshold is increased efficiently and the maximum output power rises to 168 W with an 82.9% power conversion efficiency. The experimental results indicate that the output power can be further raised by shortening the delivery fiber length and increasing the pump power.

The effects of heat treatment on microfluidic devices fabricated in silica glass by femtosecond lasers

Li Yan,Qu Shi-Liang
Chin. Phys. B, 2012, 21 (3): 034208 doi: 10.1088/1674-1056/21/3/034208
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We fabricated complex microfluidic devices in silica glass by water-assisted femtosecond laser ablation and subsequent heat treatment. The experimental results show that after heat treatment, the diameter of the microchannels is significantly reduced and the internal surface roughness is improved. The diameters of the fabricated microchannels can be modulated by changing the annealing temperature and the annealing time. During annealing, the temperature affects the diameter and shape of the protrusions in microfluidic devices very strongly, and these changes are mainly caused by uniform expansion and the action of surface tension.

A new method for measuring the pulse-front distortion of arbitrary shapes in high-power ultrashort laser systems

Zuo Yan-Lei,Jiang Dong-Bin,Zhu Qi-Hua,Dong Jun,Zen Xiao-Ming,Huang Xiao-Jun,Huang Zheng
Chin. Phys. B, 2012, 21 (3): 034209 doi: 10.1088/1674-1056/21/3/034209
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We present a new method that can be used to calculate pulse-front distortion by measuring the spectral interference of two point-diffraction fields in their overlapped district. We demonstrate, for the first time, the measurement of the pulse-front distortion of the pulse from a complex multi-pass amplification system, which exists in almost all high-power laser systems, and obtain the irregular pulse-front distribution. The method presented does not need any reference light or assumption about the pulse-front distribution, and has an accuracy of several femtoseconds.

Coherent coupling between vibrational modes of C–H bonds at different positions studied by femtosecond time-resolved coherent anti-Stokes Raman scattering

Du Xin,He Xing,Liu Yu-Qiang,Wang Ying-Hui,Yang Yan-Qiang
Chin. Phys. B, 2012, 21 (3): 034210 doi: 10.1088/1674-1056/21/3/034210
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We performed femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C-H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.

The stimulated Raman scattering competition between solute and solvent in Rhodamine B solution

Fang Wen-Hui,Li Zuo-Wei,Sun Cheng-Lin,Li Zhan-Long,Song Wei,Men Zhi-Wei,He Li-Qiao
Chin. Phys. B, 2012, 21 (3): 034211 doi: 10.1088/1674-1056/21/3/034211
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The competition between the stimulated resonance Raman scattering (SRRS) of Rhodamine B (RhB) and the stimulated Raman scattering (SRS) of ethanol (C2H5OH) is observed at the RhB in C2H5OH solution. For different concentrations of the solution, the peak wavelengths of the SRRS, the amplified spontaneous emission (ASE), the fluorescence and the absorption of RhB are different. The SRRS of RhB and the SRS of C2H5OH are simultaneously generated when the concentration of the solution is 10-5 mol/L and the energy of the excitation laser is 20.4 mJ. Otherwise, only either the SRRS of RhB or the SRS of C2H5OH is generated. The SRRS can be amplified by the ASE gain when the SRRS is near the peak of the ASE, and the peak wavelength of the SRRS coincides with the wavelength of the maximal intensity ASE.

Stimulated Brillouin scattering-induced phase noise in an interferometric fiber sensing system

Chen Wei,Meng Zhou,Zhou Hui-Juan,Luo Hong
Chin. Phys. B, 2012, 21 (3): 034212 doi: 10.1088/1674-1056/21/3/034212
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Stimulated Brillouin scattering-induced phase noise is harmful to interferometric fiber sensing systems. The localized fluctuating model is used to study the intensity noise caused by the stimulated Brillouin scattering in a single-mode fiber. The phase noise structure is analyzed for an interferometric fiber sensing system, and an unbalanced Michelson interferometer with an optical path difference of 1 m, as well as the phase-generated carrier technique, is used to measure the phase noise. It is found that the phase noise is small when the input power is below the stimulated Brillouin scattering threshold, increases dramatically at first and then gradually becomes flat when the input power is above the threshold, which is similar to the variation in relative intensity noise. It can be inferred that the increase in phase noise is mainly due to the broadening of the laser linewidth caused by stimulated Brillouin scattering, which is verified through linewidth measurements in the absence and presence of the stimulated Brillouin scattering.

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Yao Bao-Quan,Li Gang,Zhu Guo-Li,Meng Pei-Bei,Ju You-Lun,Wang Yue-Zhu
Chin. Phys. B, 2012, 21 (3): 034213 doi: 10.1088/1674-1056/21/3/034213
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Long-wave infrared (IR) generation based on type-II (o→e+o) phase matching ZnGeP2 (ZGP) and CdSe optical parametric oscillators (OPOs) pumped by a 2.05 μm Tm,Ho:GdVO4 laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency (PRF) with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.

Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

Chen Liang,Qian Yun-Sheng,Zhang Yi-Jun,Chang Ben-Kang
Chin. Phys. B, 2012, 21 (3): 034214 doi: 10.1088/1674-1056/21/3/034214
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Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future.

A photonic crystal side-coupled waveguide based on a high-quality-factor resonator array

Cui Nai-Di,Liang Jing-Qiu,Liang Zhong-Zhu,Wang Wei-Biao
Chin. Phys. B, 2012, 21 (3): 034215 doi: 10.1088/1674-1056/21/3/034215
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Based on the present coupled mode theory of the photonic crystal resonator array in this paper, we propose a novel side-coupled waveguide to achieve highly efficient coupling of photonic crystal devices. It is found that the coupling efficiency is sensitive to the interval, the total number and the quality factor of the resonator. Considering the coupling efficiency and the coupling region, we select five resonators with an interval of six lattice periods. By optimizing the structure parameters of the waveguide and resonator, the quality factors of the resonator can be modulated and the coupling efficiency of the side-coupled waveguide reaches 95.47% in theory. Compared with other coupling methods, the side-coupled waveguide can realize efficient coupling with a compact structure, a high level of integration and a low degree of operational difficulties.

Thermal modeling and the optimized design of metal plate cooling systems for single concentrator solar cells

Cui Min,Chen Nuo-Fu,Deng Jin-Xiang
Chin. Phys. B, 2012, 21 (3): 034216 doi: 10.1088/1674-1056/21/3/034216
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A metal plate cooling model for 400× single concentrator solar cells was established. The effects of the thickness and the radius of the metal plate, and the air environment on the temperature of the solar cells were analyzed in detail. It is shown that the temperature of the solar cells decreased sharply at the beginning, with the increase in the thickness of the metal plate, and then changed more smoothly. When the radius of the metal plate was 4 cm and the thickness increased to 2 mm or thicker, the temperature of the solar cell basically stabilized at about 53 ℃. Increasing the radius of the metal plate and the convective transfer coefficient made the temperature of the solar cell decrease remarkably. The effects of Al and Cu as the metal plate material on cooling were analyzed contrastively, and demonstrated the superiority of Al material for the cooling system. Furthermore, considering cost reduction, space holding and the stress of the system, we optimized the structural design of the metal plate. The simulated results can be referred to the design of the structure for the metal plate. Finally, a method to devise the structure of the metal plate for single concentrator solar cells was given.

Coupling characteristics of high birefringence dual-core As2S3 rectangular lattice photonic crystal fiber

Liu Shuo,Li Shu-Guang,Yin Guo-Bing,Wang Xiao-Yan
Chin. Phys. B, 2012, 21 (3): 034217 doi: 10.1088/1674-1056/21/3/034217
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A type of As2S3 chalcogenide glass mid-infrared dual-core photonic crystal fiber has been proposed. The dual-core photonic crystal fiber (PCF) consists of two asymmetric cores. The high polarization property and the coupling characteristics have been studied by using the finite element method and mode coupling theory. Numerical results show that the birefringence at wavelength λ = 10 μm is up to 0.01386 and the coupling length can reach wavelength λ = 5 μm, 261 μm and 271.44 μm for x-polarized mode and y-polarized mode, respectively. It demonstrates that a 6.786-mm-long fiber can exhibit an extinction ratio of better than -10 dB and a bandwidth of 180 nm.

Biomechanical behaviors of dragonfly wing: relationship between configuration and deformation

Ren Huai-Hui,Wang Xi-Shu,Chen Ying-Long,Li Xu-Dong
Chin. Phys. B, 2012, 21 (3): 034501 doi: 10.1088/1674-1056/21/3/034501
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In this paper, the natural structures of a dragonfly wing, including the corrugation of the chordwise cross-section, the sandwich microstructure veins, and the junctions between the vein and the membrane, have been investigated with experimental observations, and the morphological parameters of these structural features are measured. The experimental result indicates that the corrugated angle among the longitudinal veins ranges from 80? to 150?, and the sandwiched microstructure vein mainly consists of chitin and protein layers. Meanwhile, different finite element models, which include models I and I* for the planar forewings, models II and II* for the corrugated forewings, and a submodel with solid veins and membranes, are created to investigate the effects of these structural features on the natural frequency/modal, the dynamical behaviors of the flapping flight, and the deformation mechanism of the forewings. The numerical results indicate that the corrugated forewing has a more reasonable natural frequency/modal, and the first order up-down flapping frequency of the corrugated wing is closer to the experimental result (about 27.00 Hz), which is significantly larger than that of the planar forewing (10.94 Hz). For the dynamical responses, the corrugated forewing has a larger torsional angle than the planar forewing, but a lower flapping angle. In addition, the sandwich microstructure veins can induce larger amplitudes of torsion deformation, because of the decreasing stiffness of the whole forewing. For the submodel of the forewing, the average stress of the chitin layer is much larger than that of the protein layer in the longitudinal veins. These simulative methods assist us to explain the flapping flight mechanism of the dragonfly and to design a micro aerial vehicle by automatically adjusting the corrugated behavior of the wing.

Controlling the transition between Turing and antispiral patterns by using time-delayed-feedback

He Ya-Feng,Liu Fu-Cheng,Fan Wei-Li,Dong Li-Fang
Chin. Phys. B, 2012, 21 (3): 034701 doi: 10.1088/1674-1056/21/3/034701
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The controllable transition between Turing and antispiral patterns is studied by using a time-delayed-feedback strategy in a FitzHugh-Nagumo model. We treat the time delay as a perturbation and analyse the effect of the time delay on the Turing and Hopf instabilities near the Turing-Hopf codimension-two phase space. Numerical simulations show that the transition between the Turing patterns (hexagon, stripe, and honeycomb), the dual-mode antispiral, and the antispiral by applying appropriate feedback parameters. The dual-mode antispiral pattern originates from the competition between the Turing and Hopf instabilities. Our results have shown the flexibility of the time delay on controlling the pattern formations near the Turing-Hopf codimension-two phase space.

Approximate solution of the magneto-hydrodynamic flow over a nonlinear stretching sheet

Chin. Phys. B, 2012, 21 (3): 035201 doi: 10.1088/1674-1056/21/3/035201
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The approximate solution of the magneto-hydrodynamic (MHD) boundary layer flow over a nonlinear stretching sheet is obtained by combining the Lie symmetry method with the homotopy perturbation method. The approximate solution is tabulated, plotted for the values of various parameters and compared with the known solutions. It is found that the approximate solution agrees very well with the known numerical solutions, showing the reliability and validity of the present work.

Molecular dynamics simulations of displacement cascades in Fe–10%Cr systems

Yu Gang,Ma Yan,Cai Jun,Lu Dao-Gang
Chin. Phys. B, 2012, 21 (3): 036101 doi: 10.1088/1674-1056/21/3/036101
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Molecular dynamics simulations of the displacement cascades in Fe-10%Cr systems are used to simulate the primary knocked-on atom events of the irradiation damage at temperatures 300, 600, and 750 K with primary knocked-on atom energies between 1 and 15 keV. The results indicate that the vacancies produced by the cascade are all in the central region of the displacement cascade. During the cascade, all recoil Fe and Cr atoms combine with each other to form Fe-Cr or Fe-Fe interstitial dumbbells as well as interstitial clusters. The number and the size of interstitial clusters increase with the energy of the primary knocked-on atom and the temperature. A few large clusters consist of a large number of Fe interstitials with a few Cr atoms, the rest are Fe-Cr clusters with small and medium sizes. The interstitial dumbbells of Fe-Fe and Fe-Cr are in the lan111ran and lan110ran series directions, respectively.

Theoretical prediction of structural, electronic and optical properties of quaternary alloy Zn1-xBexSySe1-y

Hacini K,Meradji H,Ghemid S,El Haj Hassan F
Chin. Phys. B, 2012, 21 (3): 036102 doi: 10.1088/1674-1056/21/3/036102
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Within density functional theory based on the full potential-linearized augmented plane wave method, we carry out the first-principles calculation of the structural, electronic, and optical properties of the zinc blende quaternary alloy Zn1-xBexSySe1-y. The Perdew-Burke-Ernzerhof generalized gradient approximation based on the optimization of total energy and the Engel-Vosko generalized gradient approximation based on the optimization of the corresponding potential are used. Our investigation on the effect of the composition on lattice constants, bulk modulus, band gap, optical dielectric constant, and refractive index shows a non-linear dependence. The energy gap Eg(x, y) has been determined over the entire compositions x and y. In addition, the energy band gap of the technologically important quaternary alloy Zn1-xBexSySe1-y in conditions of being lattice matched to ZnS substrate has been investigated. It is noteworthy that the present work is the first theoretical study of the quaternary alloy of interest.

First-principles calculation of the lattice compressibility, elastic anisotropy and thermodynamic stability of V2GeC

Yang Ze-Jin,Guo Yun-Dong,Linghu Rong-Feng,Yang Xiang-Dong
Chin. Phys. B, 2012, 21 (3): 036301 doi: 10.1088/1674-1056/21/3/036301
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We investigate the elastic and the thermodynamic properties of nanolaminate V2GeC by using the ab initio pseudopotential total energy method. The axial compressibility shows that the c axis is always stiffer than the a axis. The elastic constant calculations demonstrate that the structural stability is within 0-800 GPa. The calculations of Young's and shear moduli reveal the softening behaviour at about 300 GPa. The Possion ratio makes a higher ionic or a weaker covalent contribution to intra-atomic bonding and the degree of ionicity increases with pressure. The relationship between brittleness and ductility shows that V2GeC is brittle in ambient conditions and the brittleness decreases and ductility increases with pressure. Moveover, we find that V2GeC is largely isotropic in compression and in shear, and the degree of isotropy decreases with pressure. The Gr黱eisen parameter, the Debye temperature and the thermal expansion coefficient are also successfully obtained for the first time.

Electronic structures and vibrational properties of coronene on Ru(0001): first-principles study Hot!

Zhang Yu-Yang,Du Shi-Xuan,Gao Hong-Jun
Chin. Phys. B, 2012, 21 (3): 036801 doi: 10.1088/1674-1056/21/3/036801
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We calculate the configurations, electronic structures, vibrational properties at the coronene/Ru(0001) interface, and adsorption of a single Pt atom on coronene/Ru(0001) based on density functional theory calculations. The geometric structures and electronic structures of the coronene on Ru(0001) are compared with those of the graphene/Ru(0001). The results show that the coronene/Ru(0001) can be a simplified model system used to describe the interaction between graphene and ruthenium. Further calculations of the vibrational properties of coronene molecule adsorbed on Ru(0001) suggest that the phonon properties of differently corrugated regions of graphene on Ru(0001) are different. This model system is also used to investigate the selective adsorption of Pt atoms on graphene/Ru(0001). The configurations of Pt on coronene/Ru(0001) with the lowest binding energy give clues to explain the experimental observation that a Pt cluster selectively adsorbs on the second highest regions of graphene/Ru(0001). This work provides a simple model for understanding the adsorption properties and vibrational properties of graphene on Ru(0001) substrate.

First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

Yildirim A,Koc H,Deligoz E
Chin. Phys. B, 2012, 21 (3): 037101 doi: 10.1088/1674-1056/21/3/037101
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The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.

First-principles study of the local structure and crystal field of Yb2+ in sodium and potassium halides

Wen Jun,Duan Chang-Kui,Yin Min,Yu. V. Orlovskii,Xia Shang-Da,Zhang Yong-Fan
Chin. Phys. B, 2012, 21 (3): 037102 doi: 10.1088/1674-1056/21/3/037102
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The local coordination structures around the doping Yb2+ ions in sodium and potassium halides were calculated by using the first-principles supercell model. Both the cases with and without the charge compensation vacancy in the local environment of the doping Yb2+ were calculated to study the effect of the doping on the local coordination structures of Yb2+. Using the calculated local structures, we obtained the crystal-field parameters for the Yb2+ ions doped in sodium and potassium halides by a method based on the combination of the quantum-chemical calculations and the effective Hamiltonian method. The calculated crystal-field parameters were analyzed and compared with the fitted results.

Isothermal bulk modulus and its first pressure derivative of NaCl at high pressure and high temperature

Song Ting,Sun Xiao-Wei,Liu Zi-Jiang,Li Jian-Feng,Tian Jun-Hong
Chin. Phys. B, 2012, 21 (3): 037103 doi: 10.1088/1674-1056/21/3/037103
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The isothermal bulk modulus and its first pressure derivative of NaCl are investigated using the classical molecular dynamics method and the quasi-harmonic Debye model. To ensure faithful molecular dynamics simulations, two types of potentials, the shell-model (SM) potential and the two-body rigid-ion Born-Mayer-Huggins-Fumi-Tosi (BMHFT) potential, are fully tested. Compared with the SM potential based simulation, the molecular dynamics simulation with the BMHFT potential is very successful in reproducing accurately the measured bulk modulus of NaCl. Particular attention is paid to the prediction of the isothermal bulk modulus and its first pressure derivative using the reliable potential and to the comparison of the SM and the BMHFT potentials based molecular dynamics simulations with the quasi-harmonic Debye model. The properties of NaCl in the pressure range of 0-30 GPa at temperatures up to the melting temperature of 1050 K are investigated.

Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

L? Ling,Zhang Jin-Cheng,Xue Jun-Shuai,Ma Xiao-Hua,Zhang Wei,Bi Zhi-Wei,Zhang Yue,Hao Yue
Chin. Phys. B, 2012, 21 (3): 037104 doi: 10.1088/1674-1056/21/3/037104
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AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 ? 1015 cm-2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance-voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.

Improving InGaN-LED performance by optimizing the patterned sapphire substrate shape

Huang Xiao-Hui,Liu Jian-Ping,Fan Ya-Ming,Kong Jun-Jie,Yang Hui,Wang Huai-Bing
Chin. Phys. B, 2012, 21 (3): 037105 doi: 10.1088/1674-1056/21/3/037105
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The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates (PSSes) with different values of fill factor (f) and slanted angle (θ) are investigated in detail. The threading dislocation (TD) density is lower in the film grown on the PSS with a smaller fill factor, resulting in a higher internal quantum efficiency (IQE). Also the ability of the LED to withstand the electrostatic discharge (ESD) increases as the fill factor decreases. The illumination output power of the LED is affected by both θ and f. It is found that the illumination output power of the LED grown on the PSS with a lower production of tanθ and f is higher than that with a higher production of tanθ and f.

Thermospin effects in parallel coupled double quantum dots in the presence of the Rashba spin–orbit interaction and Zeeman splitting

Xue Hui-Jie,Lü Tian-Quan,Zhang Hong-Chen,Yin Hai-Tao,Cui Lian,He Ze-Long
Chin. Phys. B, 2012, 21 (3): 037201 doi: 10.1088/1674-1056/21/3/037201
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The thermoelectric and the thermospin transport properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit, of a parallel coupled double-quantum-dot Aharonov-Bohm interferometer are investigated by means of the Green function technique. The periodic Anderson model is used to describe the quantum dot system, the Rashba spin-orbit interaction and the Zeeman splitting under a magnetic field are considered. The theoretical results show the constructive contribution of the Rashba effect and the influence of the magnetic field on the thermospin effects. We also show theoretically that material with a high figure of merit can be obtained by tuning the Zeeman splitting energy only.

Adsorption behavior of iron phthalocyanine on a Ag(110) surface

Wu Ke,Huang Qi-Huan,Zhang Han-Jie,Liao Qing,He Pi-Mo
Chin. Phys. B, 2012, 21 (3): 037202 doi: 10.1088/1674-1056/21/3/037202
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An investigation on the growth behavior of FePc on a Ag (110) surface is carried out by using scanning tunneling microscopy (STM). At an FePc coverage of 3.5 ML, an ordered superstructure (densely packed) with a lateral shift is observed. The densely packed superstructure can be attributed to the substrate commensuration and the intermolecular van der Waals attractive interaction. The in-plane lateral shift in the superphase is specifically along the direction of [110] azimuth. The results provide a new perspective to understanding the intermolecular and the molecule-substrate interactions.

Topological structure effect on far-infrared spectra in a GaAs/InAs nanoring Hot!

Gu Li-Ying,Li Yan-Fang,Chu Wei-Dong,Wei Ying-Hui
Chin. Phys. B, 2012, 21 (3): 037301 doi: 10.1088/1674-1056/21/3/037301
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On the basis of the growth mechanism of a GaAs/InAs nanoring, we propose a fine model which reflects the confinement details of real nanoring. Through calculations of the two-electron energy and far-infrared (FIR) spectra, we find that the ring topological structure and electron-electron interaction have great influence on the FIR spectra. The two unknown transition peaks in the experiment are determined theoretically. The theoretical results are in good agreement with the experiments.

Field-assisted spin-polarized electron transport through a single quantum well with spin–orbit coupling

Ding Xiu-Huan,Zhang Cun-Xi,Wang Rui,Zhou Yun-Qing,Kong Ling-Min
Chin. Phys. B, 2012, 21 (3): 037302 doi: 10.1088/1674-1056/21/3/037302
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We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling. The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron. The splitting of the Fano-type resonance induces the spin-polarization dependent electron current. The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron, the oscillation frequency, and the amplitude of the external field. These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.

Modeling of the drain-induced barrier lowering effect and optimization for a dual-channel 4H silicon carbide metal semiconductor field effect transistor

Zhang Xian-Jun,Yang Yin-Tang,Duan Bao-Xing,Chai Chang-Chun,Song Kun,Chen Bin
Chin. Phys. B, 2012, 21 (3): 037303 doi: 10.1088/1674-1056/21/3/037303
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A new analytical model to describe the drain-induced barrier lowering (DIBL) effect has been obtained by solving the two-dimensional (2D) Poisson's equation for the dual-channel 4H-SiC MESFET (DCFET). Using this analytical model, we calculate the threshold voltage shift and the sub-threshold slope factor of the DCFET, which characterize the DIBL effect. The results show that they are significantly dependent on the drain bias, gate length as well as the thickness and doping concentration of the two channel layers. Based on this analytical model, the structure parameters of the DCFET have been optimized in order to suppress the DIBL effect and improve the performance.

Temperature-dependent characteristics of 4H–SiC junction barrier Schottky diodes

Chen Feng-Ping,Zhang Yu-Ming,Zhang Yi-Men,Tang Xiao-Yan,Wang Yue-Hu,Chen Wen-Hao
Chin. Phys. B, 2012, 21 (3): 037304 doi: 10.1088/1674-1056/21/3/037304
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The current-voltage characteristics of 4H-SiC junction barrier Schottky (JBS) diodes terminated by an offset field plate have been measured in the temperature range of 25-300 ℃. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H-SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.

Analysis of the breakdown mechanism for an ultra high voltage high-side thin layer silicon-on-insulator p-channel lateral double-diffused metal oxide semiconductor

Zhuang Xiang,Qiao Ming,Zhang Bo,Li Zhao-Ji
Chin. Phys. B, 2012, 21 (3): 037305 doi: 10.1088/1674-1056/21/3/037305
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This paper discusses the breakdown mechanism and proposes a new simulation and test method of breakdown voltage (BV) for an ultra-high-voltage (UHV) high-side thin layer silicon-on-insulator (SOI) p-channel lateral double-di?used metal oxide semiconductor (LDMOS). Compared with the conventional simulation method, the new one is more accordant with the actual conditions of a device that can be used in the high voltage circuit. The BV of the SOI p-channel LDMOS can be properly represented and the effect of reduced bulk field can be revealed by employing the new simulation method. Simulation results show that the off-state (on-state) BV of the SOI p-channel LDMOS can reach 741 (620) V in the 3-μm-thick buried oxide layer, 50-μm-length drift region, and at -400 V back-gate voltage, enabling the device to be used in a 400 V UHV integrated circuit.

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

Feng Wei
Chin. Phys. B, 2012, 21 (3): 037306 doi: 10.1088/1674-1056/21/3/037306
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We carry out a theoretical study of nonlinear dynamics in terahertz-driven n+nn+ wurtzite InN diodes by using time-dependent drift diffusion equations. A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect, which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ1 valley. The appearance of different nonlinear oscillatory modes, including periodic and chaotic states, is attributed to the competition between the self-sustained oscillation and the external driving oscillation. The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods, such as the bifurcation diagram, the Fourier spectrum and the first return map. The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.

Single-particle distribution function of a quantum dot system at finite temperature

Wen Rui,Zhang De-Ping,Tian Guang-Shan
Chin. Phys. B, 2012, 21 (3): 037401 doi: 10.1088/1674-1056/21/3/037401
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In the present paper, we shall rigorously re-establish the result of the single-particle function of a quantum dot system at finite temperature. Unlike the proof given in our previous work (Phys. Rev. B 74 195414 (2006)), we take a different approach, which does not exploit the explicit expression of the Gibbs distribution function. Instead, we only assume that the statistical distribution function of the quantum dot system is thermodynamically stable. As a result, we are able to show clearly that the electronic structure in the quantum dot system is completely determined by its thermodynamic stability. Furthermore, the weaker requirements on the statistical distribution function also make it possible to apply the same method to the quantum dot systems in non-equilibrium states.

Highly sensitive giant magnetoimpedance in a solenoid containing FeCo-based ribbon

Fang Yun-Zhang,Xu Qi-Ming,Zheng Jin-Ju,Wu Feng-Min,Ye Hui-Qun,Si Jian-Xiao,Zheng Jian-Long,Fan Xiao-Zhen,Yang Xiao-Hong
Chin. Phys. B, 2012, 21 (3): 037501 doi: 10.1088/1674-1056/21/3/037501
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The highly sensitive giant magneto-impedance effect in a solenoid containing a magnetic core of Fe36Co36Nb4Si4.8B19.2 (FeCo-based) ribbon under a weak magnetic field (WMF) is presented in this paper. The FeCo-based amorphous ribbon is prepared by single roller quenching and annealed with Joule heat in a flowing nitrogen atmosphere. The giant magnetoimpedance effect in solenoid (GMIES) profiles are measured with an HP4294A impedance analyzer. The result shows that the GMIES responds to the WMF sensitively (as high as 1580 %/A穖-1). The high sensitivity can be obtained in a moderate narrow range of annealing current density (30-34 A/mm2) and closely depends on the driven current frequency. The highest sensitivity (1580 %/A穖-1) is obtained when the FeCo-based amorphous ribbon is annealed at 32 A/mm2 for 10 min and then driven with an alterning current (AC) at the frequency of 350 kHz. The highly sensitive GMIES under the WMF may result from the multiple magnetic-anisotropic structure, which is induced by the temperature gradient produced during Joule-heating the ribbon.

Excellent soft magnetic properties realized in FeCoN thin films

Zhang Lu-Ran,Lü Hua,Liu Xi,Bai Jian-Min,Wei Fu-Lin
Chin. Phys. B, 2012, 21 (3): 037502 doi: 10.1088/1674-1056/21/3/037502
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FeCoN soft magnetic thin films are prepared by using the reactive direct-current magnetron sputtering technique. It is found that the addition of N2 can reduce the coercivity of the FeCoN film, and excellent soft magnetic properties can be obtained when the ratio of N2 flow to total gas flow is 10%. The influences of texture, grain size, and stress on the magnetic properties and the high-frequency behaviors of the films are also discussed.

Magnetocaloric and barocaloric effects in a Gd5Si2Ge2 compound

Zou Jun-Ding
Chin. Phys. B, 2012, 21 (3): 037503 doi: 10.1088/1674-1056/21/3/037503
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The first-order phase transition in Gd5Si2Ge2 is sensitive to both magnetic field and pressure. It may indicate that the influences of the magnetic field and the pressure on the phase transition are virtually equivalent. Moreover, theoretical analyses reveal that the total entropy change is almost definite at a certain Curie temperature no matter whether the applied external field is a magnetic field or a pressure. The entropy change curve can be broadened dramatically under pressure, and the refrigerant capacity is improved from 284.7 J/kg to 447.0 J/kg.

Magnetocaloric effects in Mn1.35Fe0.65P1-xSix compounds

Geng Yao-Xiang,Tegus O,Bi Li-Ge
Chin. Phys. B, 2012, 21 (3): 037504 doi: 10.1088/1674-1056/21/3/037504
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The structural and magnetocaloric properties of Mn1.35Fe0.65P1-xSix compounds are investigated. The Si-substituted compounds, Mn1.35Fe0.65P1-xSix with x = 0.52, 0.54, 0.55, 0.56, and 0.57, are prepared by high-energy ball milling and the solid-state reaction. The X-ray diffraction shows that the compounds crystallize into the Fe2P-type hexagonal structure with space group P62m. The magnetic measurements show that the Curie temperature of the compound increases from 253 K for x = 0.52 to 296 K for x = 0.56. The isothermal magnetic-entropy change of the Mn1.35Fe0.65P1-xSix compound decreases with the Si content increasing. The maximal value of the magnetic-entropy change is about 7.0 J/kg稫 in the Mn1.35Fe0.65P0.48Si0.52 compound with a field change of 1.5 T. The compound quenched in water possesses a larger magnetic entropy change and a smaller thermal hysteresis than the non-quenched samples. The thermal hysteresis of the compound is less than 3.5 K. The maximum adiabatic temperature change is about 1.4 K in the Mn1.35Fe0.65P0.45Si0.55 compound with a field change of 1.48 T.

Microwave reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites

Wei Jian-Qiang,Zhang Zhao-Qi,Han Rui,Wang Tao,Li Fa-Shen
Chin. Phys. B, 2012, 21 (3): 037601 doi: 10.1088/1674-1056/21/3/037601
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The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range. The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy, and can be further enhanced by using a rotational orientation method. The complex permeability can be considered as the superposition of two types of magnetic resonance. The resonance peak at high frequency is attributed to the natural resonance, while the peak at low frequency is attributed to the domain-wall resonance. The simulated results of the microwave reflectivity show that the matching thickness, peak frequency, permeability, and permittivity are closely related to the quarter wavelength matching condition. The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band (1-2 GHz).

Effects of (LiCe) co-substitution on the structural and electrical properties of CaBi2Nb2O9 ceramics

Tian Xiao-Xia,Qu Shao-Bo,Du Hong-Liang,Li Ye,Xu Zhuo
Chin. Phys. B, 2012, 21 (3): 037701 doi: 10.1088/1674-1056/21/3/037701
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The piezoelectric, dielectric, and ferroelectric properties of the (LiCe) co-substituted calcium bismuth niobate (CaBi2Nb2O9, CBNO) are investigated. The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tanδ decreased. This makes poling using (LiCe) co-substitution easier. The ceramics (where □ represents A-site Ca2+ vacancies, possess a pure layered structure phase and no other phases can be found. The Ca0.88(LiCe)0.040.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties, with piezoelectric coefficient (d33) and Curie temperature (TC) found to be 13.3 pC/N and 960 ℃, respectively. The dielectric and piezoelectric properties of the (LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours. This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.

Guided-mode resonant Brewster filter consisting of two homogenous layers and a single grating with an equal refractive index

Ma Jian-Yong,Fan Yong-Tao
Chin. Phys. B, 2012, 21 (3): 037801 doi: 10.1088/1674-1056/21/3/037801
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In this paper, a new type of resonant Brewster filter (RBF) consisting of two homogenous layers and a single grating with an equal refractive index is presented. The properties are studied by using the plane waveguide method (PWM) and rigorous coupled-wave analysis (RCWA). It is found that the variation of the grating thickness does not effectively change the position of the resonant wavelength, however it has a remarkable effect on the line width, and the resonant peak can be adjusted back to its original position by slightly tuning the grating period. Moreover, by simultaneously tuning the thicknesses of the homogeneous layers above and beneath the grating structure, multiple channels can also be obtained when the RBF is illuminated at the Brewster angle calculated with the effective medium theory (EMT) of subwavelength grating. The adjacent optical thickness for acquiring the multiple channels is about three-quarters of the resonant wavelength. Furthermore, it is demonstrated that the line width at the operating resonant wavelength can be appreciably narrowed by tuning the thickness of the homogenous layer to its corresponding thickness without fine tuning the grating period or the thickness. Therefore, it is very useful for designing filters with different line widths at the desired wavelength. In addition, it is shown from our calculations that the symmetrical line feather can be obtained if the total optical thickness for the homogeneous layer meets the special condition.

An effective reflectance method for designing broadband antireflection films coupled with solar cells

Zhan Feng,He Ji-Fang,Shang Xiang-Jun,Li Mi-Feng,Ni Hai-Qiao,Xu Ying-Qiang,Niu Zhi-Chuan
Chin. Phys. B, 2012, 21 (3): 037802 doi: 10.1088/1674-1056/21/3/037802
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The solar spectrum covers a broad wavelength range, which requires that antireflection coating (ARC) is effective over a relatively wide wavelength range for more incident light coming into the cell. In this paper, we present two methods to measure the composite reflection of SiO2/ZnS double-layer ARC in the wavelength ranges of 300-870 nm (dual-junction) and 300-1850 nm (triple-junction), under the solar spectrum AM0. In order to give sufficient consideration to the ARC coupled with the window layer and the dispersion effect of the refractive index of each layer, we use multi-dimensional matrix data for reliable simulation. A comparison between the results obtained from the weighted-average reflectance (WAR) method commonly used and that from the effective-average reflectance (EAR) method introduced here shows that the optimized ARC through minimizing the effective-average reflectance is convenient and available.

Nanoscaled ZnO films used as enhanced substrates for fluorescence detection of dyes

Liu Yan-Song,Yi Fu,Ramachandram Badugu,Joseph R. Lakowicz,Xu Xiao-Liang
Chin. Phys. B, 2012, 21 (3): 037803 doi: 10.1088/1674-1056/21/3/037803
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The ability of nanoscaled ZnO films to enhance fluorescence was studied. We found that the fluorescence intensities of Cy5, rhodamine 6G, and fluorescein can be enhanced about 10-fold on nanoscaled ZnO films as compared to that on glass substrates. The lifetimes of all samples were measured, and no obvious change in lifetime was observed for dyes on different substrates. The mechanism for the nanoscaled ZnO film enhanced fluorescence appears to be different from that for the metal-fluorophore systems.

Terahertz wave generation in coupled quantum dots

Ma Yu-Rong,Guo Shi-Fang,Duan Su-Qing
Chin. Phys. B, 2012, 21 (3): 037804 doi: 10.1088/1674-1056/21/3/037804
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Based on coupled quantum dots, we present an interesting optical effect in a four-level loop coupled system. Both the two upper levels and the two lower levels are designed to be almost degenerate, which induces a considerable dipole moment. The terahertz wave is obtained from the low-frequency component of the photon emission spectrum. The frequency of the terahertz wave can be controlled by tuning the energy levels via designing the nanostructure appropriately or tuning the driving laser field. A terahertz wave with adjustable frequency and considerable intensity (100 times higher than that of the Rayleigh line) can be obtained. It provides an effective scheme for a terahertz source.

Zn/O ratio and oxygen chemical state of nanocrystalline ZnO films grown at different temperatures

Fan Hai-Bo,Zheng Xin-Liang,Wu Si-Cheng,Liu Zhi-Gang,Yao He-Bao
Chin. Phys. B, 2012, 21 (3): 038101 doi: 10.1088/1674-1056/21/3/038101
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ZnO nanocrystalline films are prepared on Si substrates at different temperatures by using metal-organic chemical vapour deposition (MOCVD). It is observed that when the growth temperature is low, the stoichiometric ratio between Zn and O atoms has a large deviation from the ideal ratio of 1:1. The ZnO grains in the film have small sizes and are not well crystallized, resulting in a poor photoluminescence (PL) property. When the temperature is increased to an appropriate value, the Zn/O ratio becomes optimized, and most of Zn and O atoms are combined into Zn-O bonds. Then the film has good crystal quality and good PL property. If the temperature is fairly high, the interfacial mutual diffusion of atoms between the substrate and the epitaxial film appears, and the desorption process of the oxygen atoms is enhanced. However, it has no effect on the film property. The film still has the best crystal quality and PL property.

Comparison of the formation process and properties of epitaxial graphenes on Si- and C-face 6H–SiC substrates

Wang Dang-Chao,Zhang Yu-Ming,Zhang Yi-Men,Lei Tian-Min,Guo Hui,Wang Yue-Hu,Tang Xiao-Yan,Wang Hang
Chin. Phys. B, 2012, 21 (3): 038102 doi: 10.1088/1674-1056/21/3/038102
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In this paper, the epitaxial graphene layers grown on Si- and C-face 6H-SiC substrates are investigated under a low pressure of 400 Pa at 1600 ℃. By using atomic force microscopy and Raman spectroscopy, we find that there are distinct differences in the formation and the properties between the epitaxial graphene layers grown on the Si-face and the C-face substrates, including the hydrogen etching process, the stacking type, and the number of layers. Hopefully, our results will be useful for improving the quality of the epitaxial graphene on SiC substrate.

Synthesis and characterization of a single diamond crystal with a high nitrogen concentration

Zhang Zhuang-Fei,Jia Xiao-Peng,Liu Xiao-Bing,Hu Mei-Hua,Li Yong,Yan Bing-Min,Ma Hong-An
Chin. Phys. B, 2012, 21 (3): 038103 doi: 10.1088/1674-1056/21/3/038103
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In this paper, we explore diamond synthesis with a series of experiments using an Fe-Ni catalyst and a P3N5 additive in the temperature range of 1250-1550 ℃ and the pressure range of 5.0-6.3 GPa. We also investigate the influence of nitrogen on diamond crystallization. Our results show that the synthesis conditions (temperature and pressure) increase with the amount of P3N5additive increasing. The nitrogen impurity can significantly influence the diamond morphology. The diamonds stably grow into strip and lamellar shapes in the nitrogen-rich environment. The Fourier-transform infrared spectrum shows that the nitrogen concentration increases rapidly with the content of P3N5additive increasing. By spectrum analysis, we find that with the increase of the nitrogen concentration, the Ib-type nitrogen atoms can aggregate in the A-centre form. The highest A-centre nitrogen concentration is approximately 840 ppm.

Slow-rise and fast-drop current feature of ultraviolet response spectra for ZnO-nanowire film modulated by water molecules

Ren Shou-Tian,Wang Qiang,Zhao Feng,Qu Shi-Liang
Chin. Phys. B, 2012, 21 (3): 038104 doi: 10.1088/1674-1056/21/3/038104
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This study describes the fabrication of ZnO-nanowire films by electro-chemical anodization of Zn foil. The ZnO films are characterized by field emission scanning electron microscopy, X-ray diffraction patterns, and transmission electron microscopy, respectively. The ultraviolet (UV) photo-response properties of the surface-contacted ZnO film are studied through the current evolution processes under different relative humidities. Unlike the usually observed current spectra of the ZnO films, the drop time is shorter than the rise time. The photo-conductivity gain G and the response time τ are both increased with the increase of the applied bias. The photo-conductivity gain G is lowered with the increase of the environmental humidity, while the response time τ is increased. These results can be explained by considering three different surface processes: 1) the electron-hole (e-p) pair generation by the UV light illumination, 2) the following surface O2- species desorption, and 3) the photo-catalytic hydrolysis of water molecules adsorbed on the ZnO surface. The slow-rise and fast-drop current feature is suggested to originate from the sponge-like structure of the ZnO nanowires.

Doctor-bladed Cu2ZnSnS4 light absorption layer for low-cost solar cell application

Chen Qin-Miao,Li Zhen-Qing,Ni Yi,Cheng Shu-Yi,Dou Xiao-Ming
Chin. Phys. B, 2012, 21 (3): 038401 doi: 10.1088/1674-1056/21/3/038401
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The doctor-blade method is investigated for the preparation of Cu2ZnSnS4 films for low-cost solar cell application. Cu2ZnSnS4 precursor powder, the main raw material for the doctor-blade paste, is synthesized by a simple ball-milling process. The doctor-bladed Cu2ZnSnS4 films are annealed in N2 ambient under various conditions and characterized by X-ray diffraction, ultraviolent/vis spectrophotometry, scanning electron microscopy, and current-voltage (J-V) meansurement. Our experimental results indicate that (i) the X-ray diffraction peaks of the Cu2ZnSnS4 precursor powder each show a red shift of about 0.4?; (ii) the high-temperature annealing process can effectively improve the crystallinity of the doctor-bladed Cu2ZnSnS4, whereas an overlong annealing introduces defects; (iii) the band gap value of the doctor-bladed Cu2ZnSnS4 is around 1.41 eV; (iv) the short-circuit current density, the open-circuit voltage, the fill factor, and the efficiency of the best Cu2ZnSnS4 solar cell obtained with the superstrate structure of fluorine-doped tin oxide glass/TiO2/In2S3/Cu2ZnSnS4/Mo are 7.82 mA/cm2, 240 mV, 0.29, and 0.55%, respectively.

Tunable broadband metamaterial absorber consisting of ferrite slabs and a copper wire

Yang Yong-Jun,Huang Yong-Jun,Wen Guang-Jun,Zhong Jing-Ping,Sun Hai-Bin
Chin. Phys. B, 2012, 21 (3): 038501 doi: 10.1088/1674-1056/21/3/038501
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A tunable broadband metamaterial absorber is demonstrated at microwave frequencies in this paper. The metamaterial absorber is composed of ferrite slabs with large resonance beamwidths and a copper wire. The theoretical analysis for the effective media parameters is presented to show the mechanism for achieving the perfect absorptivity characteristic. The numerical results of transmission, reflectance, and absorptivity indicate that the metamaterial absorber exhibits a near perfect impedance-match to free space and a high absorptivity of 98.2% for one layer and 99.97% for two layers at 9.9 GHz. The bandwidth with the absorptivity above 90% is about 2.3 GHz. Moreover, the absorption band can be shifted linearly in a wide frequency range by adjusting the magnetic bias. This metamaterial absorber opens a way to prepare perfectly matched layers for engineering applications.

Two-dimensional model of elastically coupled molecular motors

Zhang Hong-Wei,Wen Shu-Tang,Chen Gai-Rong,Li Yu-Xiao,Cao Zhong-Xing,Li Wei
Chin. Phys. B, 2012, 21 (3): 038701 doi: 10.1088/1674-1056/21/3/038701
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A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins. Extensive Langevin simulations of the model are performed. We discuss the dependences of motion and efficiency on the model parameters, including the external force and the temperature. A good qualitative agreement with the expected behavior is observed.

Effect of channel–protein interaction on translocation of a protein-like chain through a finite channel

Sun Ting-Ting,Ma Hai-Zhu,Jiang Zhou-Ting
Chin. Phys. B, 2012, 21 (3): 038702 doi: 10.1088/1674-1056/21/3/038702
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We study the translocation of a protein-like chain through a finite cylindrical channel using the pruned-enriched Rosenbluth method (PERM) and the modified orientation-dependent monomer-monomer interaction (ODI) model. Attractive channels (εcp=-2.0, -1.0, -0.5), repulsive channels (εcp=0.5, 1.0, 2.0), and a neutral channel (εcp =0) are discussed. The results of the chain dimension and the energy show that Z0=1.0 is an important case to distinguish the types of the channels. For the strong attractive channel, more contacts form during the process of translocation. It is also found that an external force is needed to drive the chain outside of the channel with the strong attraction. While for the neutral, the repulsive, and the weak attractive channels, the translocation is spontaneous.

Chaotic diagonal recurrent neural network

Wang Xing-Yuan,Zhang Yi
Chin. Phys. B, 2012, 21 (3): 038703 doi: 10.1088/1674-1056/21/3/038703
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We propose a novel neural network based on a diagonal recurrent neural network and chaos, and its structure and learning algorithm are designed. The multilayer feedforward neural network, diagonal recurrent neural network, and chaotic diagonal recurrent neural network are used to approach the cubic symmetry map. The simulation results show that the approximation capability of the chaotic diagonal recurrent neural network is better than the other two neural networks.

Exact scaling for the mean first-passage time of random walks on a generalized Koch network with a trap

Zhang Jing-Yuan,Sun Wei-Gang,Chen Guan-Rong
Chin. Phys. B, 2012, 21 (3): 038901 doi: 10.1088/1674-1056/21/3/038901
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In this paper, we study the scaling for the mean first-passage time (MFPT) of the random walks on a generalized Koch network with a trap. Through the network construction, where the initial state is transformed from a triangle to a polygon, we obtain the exact scaling for the MFPT. We show that the MFPT grows linearly with the number of nodes and the dimensions of the polygon in the large limit of the network order. In addition, we determine the exponents of scaling efficiency characterizing the random walks. Our results are the generalizations of those derived for the Koch network, which shed light on the analysis of random walks over various fractal networks.

First-principles study of atomic and electronic structures of kaolinite in soft rock

He Man-Chao,Zhao Jian,Fang Zhi-Jie
Chin. Phys. B, 2012, 21 (3): 039101 doi: 10.1088/1674-1056/21/3/039101
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Kaolinite is a kind of clay mineral which often causes large deformations in soft-rock tunnel engineering and thus causes safety issues. To deal with these engineering safety issues, the physical/chemical properties of the kaolinite should be studied from basic viewpoints. By using the density-functional theory, in this paper, the atomic and the electronic structures of the kaolinite are studied within the local-density approximation (LDA). It is found that the kaolinite has a large indirect band gap with the conduction band minimum (CBM) and the valence band maximum (VBM) being at the Γ and the B points, respectively. The chemical bonding between the cation and the oxygen anion in kaolinite is mainly ionic, accompanied by a minor covalent component. It is pointed that the VBM and the CBM of kaolinite consist of oxygen 2p and cation s states, respectively. The bond lengths between different cations and anions, as well as of the different OH groups, are also compared.
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