Chin. Phys. B

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The periodic oscillations in the ENSO recharge–discharge oscillator model

Zhang Wu-Fan, Zhao Qiang

Chin. Phys. B, 2013, 22 (12): 120201 doi: 10.1088/1674-1056/22/12/120201
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A class of recharge–discharge oscillator model for the El Niño/Southern Oscillation (ENSO) is considered. A stable limit cycle is obtained by transforming the ENSO model into the van der Pol-Duffing equation. We proved that there exists periodic oscillations in the ENSO recharge–discharge oscillator model.

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A self-adaptive stochastic resonance system design and study in chaotic interference

Lu Kang, Wang Fu-Zhong, Zhang Guang-Lu, Fu Wei-Hong

Chin. Phys. B, 2013, 22 (12): 120202 doi: 10.1088/1674-1056/22/12/120202
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The us of stochastic resonance (SR) can effectively achieve the detection of weak signal in white noise and colored noise. However, SR in chaotic interference is seldom involved. In view of the requirements for the detection of weak signal in the actual project and the relationship between the signal, chaotic interference, and nonlinear system in the bistable system, a self-adaptive SR system based on genetic algorithm is designed in this paper. It regards the output signal-to-noise ratio (SNR) as a fitness function and the system parameters are jointly encoded to gain optimal bistable system parameters, then the input signal is processed in the SR system with the optimal system parameters. Experimental results show that the system can keep the best state of SR under the condition of low input SNR, which ensures the effective detection and process of weak signal in low input SNR.

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An improved interpolating element-free Galerkin method for elasticity

Sun Feng-Xin, Wang Ju-Feng, Cheng Yu-Min

Chin. Phys. B, 2013, 22 (12): 120203 doi: 10.1088/1674-1056/22/12/120203
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Based on the improved interpolating moving least-squares (ⅡMLS) method and the Galerkin weak form, an improved interpolating element-free Galerkin (ⅡEFG) method is presented for two-dimensional elasticity problems in this paper. Compared with the interpolating moving least-squares (IMLS) method presented by Lancaster, the ⅡMLS method uses the nonsingular weight function. The number of unknown coefficients in the trial function of the ⅡMLS method is less than that of the MLS approximation and the shape function of the ⅡMLS method satisfies the property of Kronecker δ function. Thus in the ⅡEFG method, the essential boundary conditions can be applied directly and easily, then the numerical solutions can be obtained with higher precision than those obtained by the interpolating element-free Galerkin (IEFG) method. For the purposes of demonstration, four numerical examples are solved using the ⅡEFG method.

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A meshless model for transient heat conduction analyses of 3D axisymmetric functionally graded solids Suggested by editors

Li Qing-Hua, Chen Shen-Shen, Zeng Ji-Hui

Chin. Phys. B, 2013, 22 (12): 120204 doi: 10.1088/1674-1056/22/12/120204
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A meshless numerical model is developed for analyzing transient heat conductions in three-dimensional (3D) axisymmetric continuously nonhomogeneous functionally graded materials (FGMs). Axial symmetry of geometry and boundary conditions reduces the original 3D initial-boundary value problem into a two-dimensional (2D) problem. Local weak forms are derived for small polygonal sub-domains which surround nodal points distributed over the cross section. In order to simplify the treatment of the essential boundary conditions, spatial variations of the temperature and heat flux at discrete time instants are interpolated by the natural neighbor interpolation. Moreover, the using of three-node triangular finite element method (FEM) shape functions as test functions reduces the orders of integrands involved in domain integrals. The semi-discrete heat conduction equation is solved numerically with the traditional two-point difference technique in the time domain. Two numerical examples are investigated and excellent results are obtained, demonstrating the potential application of the proposed approach.

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GGA+U study of the electronic energy bands and state density of the wurtzite In_1-xGa_xN

Wang Wei-Hua, Zhao Guo-Zhong, Liang Xi-Xia

Chin. Phys. B, 2013, 22 (12): 120205 doi: 10.1088/1674-1056/22/12/120205
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The electronic band structures, densities of states (DOSs), and projected densities of states (PDOSs) of the wurtzite In_1-xGa_xN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation (GGA) and GGA+U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In_1-xGa_xN. The conduction band minimum (CBM) energy increases, while the valence band maximum (VBM) energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap (BG) and the valence band width (VBW). Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.

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Simulating train movement in an urban railway based on an improved car-following model

Ye Jing-Jing, Li Ke-Ping, Jin Xin-Min

Chin. Phys. B, 2013, 22 (12): 120206 doi: 10.1088/1674-1056/22/12/120206
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Based on the optimal velocity car-following model, in this paper, we propose an improved model for simulating train movement in an urban railway in which the regenerative energy of a train is considered. Here a new additional term is introduced into a traditional car-following model. Our aim is to analyze and discuss the dynamic characteristics of the train movement when the regenerative energy is utilized by the electric locomotive. The simulation results indicate that the improved car-following model is suitable for simulating the train movement. Further, some qualitative relationships between regenerative energy and dynamic characteristics of a train are investigated, such as the measurement data of regenerative energy presents a power-law distribution. Our results are useful for optimizing the design and plan of urban railway systems.

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New approach to Q-P (P-Q) ordering of quantum mechanical operators and its applications

Hu Li-Yun, Zhang Hao-Liang, Jia Fang, Tao Xiang-Yang

Chin. Phys. B, 2013, 22 (12): 120301 doi: 10.1088/1674-1056/22/12/120301
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In this paper, we introduce a new way to obtain the Q-P (P-Q) ordering of quantum mechanical operators, i.e., from the classical correspondence of Q-P (P-Q) ordered operators by replacing q and p with coordinate and momentum operators, respectively. Some operator identities are derived concisely. As for its applications, the single (two-) mode squeezed operators and Fresnel operator are examined. It is shown that the classical correspondence of Fresnel operator’s Q-P (P-Q) ordering is just the integration kernel of Fresnel transformation. In addition, a new photo-counting formula is constructed by the Q-P ordering of operators.

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Spin and pseudospin symmetries of the Dirac equation with shifted Hulthén potential using supersymmetric quantum mechanics

Akpan N. Ikot, Elham Maghsoodi, Eno J. Ibanga, Saber Zarrinkamar, Hassan Hassanabadi

Chin. Phys. B, 2013, 22 (12): 120302 doi: 10.1088/1674-1056/22/12/120302
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In this paper, we obtain approximate analytical solutions of the Dirac equation for the shifted Hulthén potential within the framework of spin and pseudospin symmetry limits for arbitrary spin–orbit quantum number κ using the supersymmetry quantum mechanics. The energy eigenvalues and the corresponding Dirac wave functions are obtained in closed forms.

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The squeezing dynamics of two independent atoms by detuning in two non-Markovian environments ^Hot! Suggested by editors

Zou Hong-Mei, Fang Mao-Fa, Yang Bai-Yuan

Chin. Phys. B, 2013, 22 (12): 120303 doi: 10.1088/1674-1056/22/12/120303
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The squeezing dynamics of two independent two-level atoms off-resonantly coupled to two non-Markovian reservoirs is studied by the time-convolutionless master-equation approach. We find that the squeezing of two atoms is dependent on both detuning and the non-Markovian effect. Our results show that, in the non-Markovian regime, the bigger the detuning and the stronger the non-Markovian effect are, the larger the strength of the squeezing is. And the squeezing of two atoms can be effectively protected for a long time when both the non-Markovian effect and detuning are present simultaneously. The physical mechanism is that the detuning not only can promote the feedback of information from the environment into the atomic system but also can greatly suppress the atomic decay in the non-Markovian regime.

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The dynamics of three coupled dipolar Bose–Einstein condensates Suggested by editors

Wu Jian-Hua, Xu Sheng-Nan

Chin. Phys. B, 2013, 22 (12): 120304 doi: 10.1088/1674-1056/22/12/120304
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The dynamics of the three coupled dipolar Bose–Einstein condensates containing N bosons is investigated within a mean-field semiclassical picture based on the coherent-state method. Varieties of periodic solutions (configured as vortex, single depleted well, and dimerlike states) are obtained analytically when the fixed points are identified on the N=constant. The system dynamics are studied via numeric integration of trimer motion equations, thus revealing macroscopic effects of population inversion and self-trapping with different initial states. In particular, the trajectory of the oscillations of the populations in each well shows how the dynamics of the condensates are effected by the presence of dipole–dipole interaction and gauge field.

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Conserved charges of Kerr–Ads spacetime using Poincaré gauge version

Gamal G. L. Nashed

Chin. Phys. B, 2013, 22 (12): 120401 doi: 10.1088/1674-1056/22/12/120401
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The process of covariant conserved charge of gravitational theory, which is covariant under general coordinate and local Lorentz transformations, has been applied to many tetrad fields, which reproduce Kerr-Ads spacetime, to calculate their conserved charges. It is shown that this process gives an infinite value of the conserved charges for Kerr–Ads spacetime. Therefore, the method of “regularization through relocalization”, i.e., modification of the Lagrangian of the gravitational field through a total derivative, is used. This method gaves a finite and a consistent result of total energy and angular momentum for Kerr–Ads spacetime.

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High-frequency gravitational waves having large spectral densities and their electromagnetic response Suggested by editors

Li Fang-Yu, Wen Hao, Fang Zhen-Yun

Chin. Phys. B, 2013, 22 (12): 120402 doi: 10.1088/1674-1056/22/12/120402
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Various cosmology models, brane oscillation scenarios, interaction of interstellar plasma with intense electromagnetic radiation, and even high-energy physics experiments (e.g., Large Hadron Collider (LHC)) all predict high frequency gravitational waves (HFGWs, i.e., high-energy gravitons) in the microwave band and higher frequency region, and some of them have large energy densities. Electromagnetic (EM) detection to such HFGWs would be suitable due to very high frequencies and large energy densities of the HFGWs. We review several typical EM detection schemes, i.e., inverse Gertsenshtein effect (G-effect), coupling of the inverse G effect with a coherent EM wave, coupling of planar superconducting open cavity with a static magnetic field, cylindrical superconducting closed cavity, and the EM sychro-resonance system, and discuss related minimal detectable amplitudes and sensitivities. Furthermore, we give some new ideas and improvement ways enhancing the possibility of measuring the HFGWs. It is shown that there is still a large room for improvement for those schemes to approach and even reach up the requirement of detection of HFGWs expected by the cosmological models and high-energy astrophysical process.

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Scheduling of high-speed rail traffic based on discrete-time movement model

Sun Ya-Hua, Cao Cheng-Xuan, Xu Yan, Wu Chao

Chin. Phys. B, 2013, 22 (12): 120501 doi: 10.1088/1674-1056/22/12/120501
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In this paper, a new simulation approach for solving the mixed train scheduling problem on the high-speed double-track rail line is presented. Based on the discrete-time movement model, we propose control strategies for mixed train movement with different speeds on a high-speed double-track rail line, including braking strategy, priority rule, travelling strategy, and departing rule. A new detailed algorithm is also presented based on the proposed control strategies for mixed train movement. Moreover, we analyze the dynamic properties of rail traffic flow on a high-speed rail line. Using our proposed method, we can effectively simulate the mixed train schedule on a rail line. The numerical results demonstrate that an appropriate decrease of the departure interval can enhance the capacity, and a suitable increase of the distance between two adjacent stations can enhance the average speed. Meanwhile, the capacity and the average speed will be increased by appropriately enhancing the ratio of faster train number to slower train number from 1.

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Codimension-two bifurcation of axial loaded beam bridge subjected to an infinite series of moving loads

Yang Xin-Wei, Tian Rui-Lan, Li Hai-Tao

Chin. Phys. B, 2013, 22 (12): 120502 doi: 10.1088/1674-1056/22/12/120502
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A novel model is proposed which comprises of a beam bridge subjected to an axial load and an infinite series of moving loads. The moving loads, whose distance between the neighbouring ones is the length of the beam bridge, coupled with the axial force can lead the vibration of the beam bridge to codimension-two bifurcation. Of particular concern is a parameter regime where non-persistence set regions undergo a transition to persistence regions. The boundary of each stripe represents a bifurcation which can drive the system off a kind of dynamics and jump to another one, causing damage due to the resulting amplitude jumps. The Galerkin method, averaging method, invertible linear transformation, and near identity nonlinear transformations are used to obtain the universal unfolding for the codimension-two bifurcation of the mid-span deflection. The efficiency of the theoretical analysis obtained in this paper is verified via numerical simulations.

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Control of the patterns by using time-delayed feedback near the codimension-three Turing–Hopf–Wave bifurcations

Wang Hui-Juan, Wang Yong-Jie, Ren Zhi

Chin. Phys. B, 2013, 22 (12): 120503 doi: 10.1088/1674-1056/22/12/120503
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Control of the spatiotemporal patterns near the codimension-three Turing–Hopf–Wave bifurcations is studied by using time-delayed feedback in a three-variable Brusselator model. Linear stability analysis of the system shows that the competition among the Turing-, Hopf- and Wave-modes, the wavenumber, and the oscillation frequency of patterns can be controlled by changing the feedback parameters. The role of the feedback intensity P_u played on controlling the pattern competition is equivalent to that of P_w, but opposite to that of P_v. The role of the feedback intensity P_u played on controlling the wavenumber and oscillation frequency of patterns is equivalent to that of P_v, but opposite to that of P_w. When the intensities of feedback are applied equally, changing the delayed time could not alter the competition among these modes, however, it can control the oscillation frequency of patterns. The analytical results are verified by two-dimensional (2D) numerical simulations.

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Effects of switching frequency and leakage inductance on slow-scale stability in a voltage controlled flyback converter

Wang Fa-Qiang, Ma Xi-Kui

Chin. Phys. B, 2013, 22 (12): 120504 doi: 10.1088/1674-1056/22/12/120504
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The effects of both the switching frequency and the leakage inductance on the slow-scale stability in a voltage controlled flyback converter are investigated in this paper. Firstly, the system description and its mathematical model are presented. Then, the improved averaged model, which covers both the switching frequency and the leakage inductance, is established, and the effects of these two parameters on the slow-scale stability in the system are analyzed. It is found that the occurrence of Hopf bifurcation in the system is the main reason for losing its slow-scale stability and both the switching frequency and the leakage inductance have an important effect on this slow-scale stability. Finally, the effectiveness of the improved averaged model and that of the corresponding theoretical analysis are confirmed by the simulation results and the experimental results.

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Modified projective synchronization with complex scaling factors of uncertain real chaos and complex chaos

Zhang Fang-Fang, Liu Shu-Tang, Yu Wei-Yong

Chin. Phys. B, 2013, 22 (12): 120505 doi: 10.1088/1674-1056/22/12/120505
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To increase the variety and security of communication, we present the definitions of modified projective synchronization with complex scaling factors (CMPS) of real chaotic systems and complex chaotic systems, where complex scaling factors establish a link between real chaos and complex chaos. Considering all situations of unknown parameters and pseudo-gradient condition, we design adaptive CMPS schemes based on the speed-gradient method for the real drive chaotic system and complex response chaotic system and for the complex drive chaotic system and the real response chaotic system, respectively. The convergence factors and dynamical control strength are added to regulate the convergence speed and increase robustness. Numerical simulations verify the feasibility and effectiveness of the presented schemes.

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Stability of operation versus temperature of a three-phase clock-driven chaotic circuit

Zhou Ji-Chao, Hyunsik Son, Namtae Kim, Han Jung Song

Chin. Phys. B, 2013, 22 (12): 120506 doi: 10.1088/1674-1056/22/12/120506
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We evaluate the influence of temperature on the behavior of a three-phase clock-driven metal–oxide–semiconductor (MOS) chaotic circuit. The chaotic circuit consists of two nonlinear functions, a level shifter, and three sample and hold blocks. It is necessary to analyze a CMOS-based chaotic circuit with respect to variation in temperature for stability because the circuit is sensitive to the behavior of the circuit design parameters. The temperature dependence of the proposed chaotic circuit is investigated via the simulation program with integrated circuit emphasis (SPICE) using 0.6-μm CMOS process technology with a 5-V power supply and a 20-kHz clock frequency. The simulation results demonstrate the effects of temperature on the chaotic dynamics of the proposed chaotic circuit. The time series, frequency spectra, bifurcation phenomena, and Lyapunov exponent results are provided.

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Dynamic magnetic behavior of the mixed spin (2, 5/2) Ising system with antiferromagnetic/antiferromagnetic interactions on a bilayer square lattice

Mehmet Ertaş, Mustafa Keskin

Chin. Phys. B, 2013, 22 (12): 120507 doi: 10.1088/1674-1056/22/12/120507
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Using the mean-field theory and Glauber-type stochastic dynamics, we study the dynamic magnetic properties of the mixed spin (2, 5/2) Ising system for the antiferromagnetic/antiferromagnetic (AFM/AFM) interactions on the bilayer square lattice under a time varying (sinusoidal) magnetic field. The time dependence of average magnetizations and the thermal variation of the dynamic magnetizations are examined to calculate the dynamic phase diagrams. The dynamic phase diagrams are presented in the reduced temperature and magnetic field amplitude plane and the effects of interlayer coupling interaction on the critical behavior of the system are investigated. We also investigate the influence of the frequency and find that the system displays richer dynamic critical behavior for higher values of frequency than that of the lower values of it. We perform a comparison with the ferromagnetic/ferromagnetic (FM/FM) and AFM/FM interactions in order to see the effects of AFM/AFM interaction and observe that the system displays richer and more interesting dynamic critical behaviors for the AFM/AFM interaction than those for the FM/FM and AFM/FM interactions.

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The Korteweg-de Vires equation for the bidirectional pedestrian flow model considering the next-nearest-neighbor effect

Xu Li, Lo Siu-Ming, Ge Hong-Xia

Chin. Phys. B, 2013, 22 (12): 120508 doi: 10.1088/1674-1056/22/12/120508
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This paper focuses on a two-dimensional bidirectional pedestrian flow model which involves the next-nearest-neighbor effect. The stability condition and the Korteweg-de Vries (KdV) equation are derived to describe the density wave of pedestrian congestion by linear stability and nonlinear analysis. Through theoretical analysis, the soliton solution is obtained.

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Magnetic transition of ferromagnetic material at high pressure using a novel system ^Hot! Suggested by editors

Hu Tian-Li, Wang Xin, Han Bing, Li Yan, Huang Feng-Xian, Zhou Qiang, Zhang Tao

Chin. Phys. B, 2013, 22 (12): 120701 doi: 10.1088/1674-1056/22/12/120701
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A system for the investigation of the magnetic properties of materials under high pressure is fabricated based on diamond anvil cell (DAC) technology. The system is designed with an improved coil arranged around the diamond of a non-magnetic DAC. Using this system, the magnetic transition of ferromagnetic (Fe) sample under increasing pressure can be observed. We successfully obtain the evolution of magnetic properties as a function of applied pressure reaching 26.9 GPa in the Fe sample. A magnetic transition is observed at approximately 13 GPa, which is consistent with the theoretical prediction.

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A laser pump-re-pump atomic magnetometer

Yang Ai-Lin, Yang Guo-Qing, Cai Xun-Ming, Xu Yun-Fei, Lin Qiang

Chin. Phys. B, 2013, 22 (12): 120702 doi: 10.1088/1674-1056/22/12/120702
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We demonstrate experimentally an atomic magnetometer based on optical pumping theory, a magnetic resonance that is induced by a radio frequency field and dependent on the magnetic field strength. Compared with the conventional method using one radiation field, which is used not only as the probe beam but also as a pump beam, the additional re-pump beam can increase remarkably the amplitude of the signal. It is shown that the amplitude of the magnetic field resonance signal can increase more than 55% by using an additional re-pump beam, which makes the sensitivity of the magnetometer higher. Finally, we investigate the relation between amplitude of the signal and re-pump laser power, and calculate the atomic population in the trapping states with rate equations.

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Rotating polarizer, compensator, and analyzer ellipsometry

Sofyan A. Taya, Taher M. El-Agez, Anas A. Alkanoo

Chin. Phys. B, 2013, 22 (12): 120703 doi: 10.1088/1674-1056/22/12/120703
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In this paper we propose theoretically a set of ellipsometric configurations using a rotating polarizer, compensator, and analyzer at a speed ratio of N₁ω:N₂ω:N₃ω. Different ellipsometric configurations can be obtained by giving different integral values to N₁, N₂, and N₃. All configurations are applied to bulk c-Si and GaAs to calculate the real and imaginary parts of the refractive index of the samples. The accuracies of all ellipsometric configurations are investigated in the presence of a hypothetical noise and with small misalignments of the optical elements. Moreover, the uncertainties in the ellipsometric parameters as functions of the uncertainties of the Fourier coefficients are studied. The comparison among different configurations reveals that the rotating compensator–analyzer configuration corresponds to the minimum error in the calculated optical parameters.

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Molecular properties and potential energy function model of BH under external electric field

Wu Dong-Lan, Tan Bin, Wan Hui-Jun, Zhang Xin-Qin, Xie An-Dong

Chin. Phys. B, 2013, 22 (12): 123101 doi: 10.1088/1674-1056/22/12/123101
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Using the density functional B3P86/cc-PV5Z method, the geometric structure of BH molecule under different external electric fields is optimized, and the bond lengths, dipole moments, vibration frequencies, and other physical properties parameters are obtained. On the basis of setting appropriate parameters, scanning single point energies are obtained by the same method and the potential energy curves under different external fields are also obtained. These results show that the physical property parameters and potential energy curves may change with external electric field, especially in the case of reverse direction electric field. The potential energy function without external electric field is fitted by Morse potential, and the fitting parameters are obtained which are in good agreement with experimental values. In order to obtain the critical dissociation electric parameter, the dipole approximation is adopted to construct a potential model fitting the corresponding potential energy curve of the external electric field. It is found that the fitted critical dissociation electric parameter is consistent with numerical calculation, so that the constructed model is reliable and accurate. These results will provide important theoretical and experimental reference for further studying the molecular spectrum, dynamics, and molecular cooling with Stark effect.

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Structure and magnetic properties of Os_n (n=11～22) clusters

Zhang Xiu-Rong, Zhang Fu-Xing, Chen Chen, Yuan Ai-Hua

Chin. Phys. B, 2013, 22 (12): 123102 doi: 10.1088/1674-1056/22/12/123102
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The structure and magnetic properties of Os_n (n=11～22) clusters are systematically studied by using density functional theory (DFT). For each size, the average binding energy per atom, the second-order differences of total energies and the highest occupied molecular orbital (HOMO)–the lowest unoccupied molecular orbital (LUMO) gaps are calculated to analyze the stability of the cluster. The structures of Os₁₄ and Os₁₈ clusters are based on a close-packed hexagonal structure, and they have maximum stabilities, so n=14, 18 are the magic numbers. The 5d electrons play a dominant role in the chemical reaction of Os_n clusters. The magnetic moments of Os_n clusters are quenched around n=12, and when n=18～22 the value approximates to zero, due to the difference of electron transfer.

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Ab initio MRCI+Q study on potential energy curves and spectroscopic parameters of low-lying electronic states of CS⁺

Li Rui, Wei Chang-Li, Sun Qi-Xiang, Sun Er-Ping, Jin Ming-Xing, Xu Hai-Feng, Yan Bing

Chin. Phys. B, 2013, 22 (12): 123103 doi: 10.1088/1674-1056/22/12/123103
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Carbon monosulfide molecular ion (CS⁺), which plays an important role in various research fields, has long been attracting much interest. Because of the unstable and transient nature of CS⁺, its electronic states have not been well investigated. In this paper, the electronic states of CS⁺ are studied by employing the internally contracted multireference configuration interaction method, and taking into account relativistic effects (scalar plus spin–orbit coupling). The spin–orbit coupling effects are considered via the state-interacting method with the full Breit–Pauli Hamiltonian. The potential energy curves of 18 Λ–S states correlated with the two lowest dissociation limits of CS⁺ molecular ion are calculated, and those of 10 lowest Ω states generated from the 6 lowest Λ–S states are also worked out. The spectroscopic constants of the bound states are evaluated, and they are in good agreement with available experimental results and theoretical values. With the aid of analysis of Λ–S composition of Ω states at different bond lengths, the avoided crossing phenomena in the electronic states of CS⁺ are illuminated. Finally, the single ionization spectra of CS (X¹Σ⁺) populating the CS⁺(X²Σ_1/2⁺, A²Π_3/2, A²Π_1/2, and B²Σ_1/2⁺) states are simulated. The vertical ionization potentials for X²Σ_1/2⁺, A²Π_3/2, A²Π_1/2, and B²Σ_1/2⁺ states are calculated to be 11.257, 12.787, 12.827, and 15.860 eV, respectively, which are accurate compared with previous experimental results, within an error margin of 0.08 eV~0.2 eV.

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Relativistic R-matrix studies of photoionization processes of Ar⁵⁺

Li Chuan-Ying, Han Xiao-Ying, Wang Jian-Guo, Qu Yi-Zhi

Chin. Phys. B, 2013, 22 (12): 123201 doi: 10.1088/1674-1056/22/12/123201
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The 3s–np photoionization processes of the ground state ²P_1/2 and the metastable state ²P_3/2 of Ar⁵⁺ are investigated using our recently developed relativistic R-matrix code, where the interactions between the bound states and the continuum states are included. Both resonance positions and the oscillator strengths are in much better agreement with the absolute experimental measurements by Wang et al.[Wang J C, Lu M, Esteves D, Habibi M, Alna’washi G and Phaneuf R A 2007 Phys. Rev. A 75 062712] with a resolution of 80 meV than their theoretical results. The contributions of the two experimental unresolved transitions are distinguished in our calculations, which show that the transitions from the ground state also make significant contributions to some resonances. Our theoretical results are also in good agreement with the measurements for the first resonance with a higher resolution of 20 meV.

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Potential energy curve study on the ³Π electronic states of GaX (X=F, Cl, and Br) molecules

Cao Yun-Bin, Yang Chuan-Lu, Wang Mei-Shan, Ma Xiao-Guang

Chin. Phys. B, 2013, 22 (12): 123401 doi: 10.1088/1674-1056/22/12/123401
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The potential energy curves (PECs) of the ³Π states of GaX (X=F, Cl, and Br) molecules are calculated using the multireference configuration interaction method with a large contracted basis set aug-cc-pV5Z. The PECs are accurately fitted to analytical potential energy functions (APEFs) using the Murrell–Sorbie potential function. The spectroscopic parameters for the states are determined using the obtained APEFs, and compared with the theoretical and experimental data available presently in the literature.

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Investigation of energy transfer from pyrromethene dye to cresyl violet 670 in ethanol Suggested by editors

Li Xiao-Hui, Fan Rong-Wei, Yu Xin, Chen De-Ying

Chin. Phys. B, 2013, 22 (12): 123402 doi: 10.1088/1674-1056/22/12/123402
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[PDF 414 KB] (Downloads:417)

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In this paper, radiative and nonradiative energy transfer from laser dye pyrromethene 567 (PM567) and pyrromethene 580 (PM580) as donors to cresyl violet 670 (CV670) as acceptor in ethanol are investigated by using the steady-state emission measurement and the second harmonic generation (532 nm, ～ 13 ns) of a Q-switched Nd:YAG laser as the pumping source. The fluorescence intensity of the acceptor is improved due to the introduction of the donors, and the largest enhancement is obtained to be 128% in the PM567:CV670 dye mixture system. Energy transfer parameters, including the radiative and nonradiative energy transfer rate constants (K_R and K_NR), critical distance (R₀), and half quenching concentration ([A]_1/2) are investigated using the Stern–Volmer plots, and the acceptor concentration dependencies of radiative and nonradiative transfer efficiencies are also obtained. The values of K_R for PM567:CV670 and PM580:CV670 systems are 2032.0×10⁹ L·mol^-1·s^-1 and 2790.4×10⁹ L·mol^-1·s^-1, respectively, and the values of corresponding K_NR are 3.3×10⁹ L·mol^-1·s^-1 and 4.2×10⁹ L·mol^-1·s^-1, respectively. The results indicate that the dominant mechanism responsible for the energy transfer in the dye mixture systems is of the radiative type.

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Structures, stabilities, and electronic properties of F-doped Si_n (n=1～12) clusters：Density functional theory investigation

Zhang Shuai, Jiang Hua-Long, Wang Ping, Lu Cheng, Li Gen-Quan, Zhang Ping

Chin. Phys. B, 2013, 22 (12): 123601 doi: 10.1088/1674-1056/22/12/123601
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[PDF 976 KB] (Downloads:409)

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The geometries, stabilities, and electronic properties of FSi_n (n=1～12) clusters are systematically investigated by using first-principles calculations based on the hybrid density-functional theory at the B3LYP/6-311G level. The geometries are found to undergo a structural change from two-dimensional to three-dimensional structure when the cluster size n equals 3. On the basis of the obtained lowest-energy geometries, the size dependencies of cluster properties, such as averaged binding energy, fragmentation energy, second-order energy difference, HOMO–LUMO (highest occupied molecular orbital–lowest unoccupied molecular orbital) gap and chemical hardness, are discussed. In addition, natural population analysis indicates that the F atom in the most stable FSi_n cluster is recorded as being negative and the charges always transfer from Si atoms to the F atom in the FSi_n clusters.

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Computer study of the spectral characteristics of the disperse water–methane system

A. Y. Galashev

Chin. Phys. B, 2013, 22 (12): 123602 doi: 10.1088/1674-1056/22/12/123602
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[PDF 390 KB] (Downloads:275)

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The interaction of water clusters that adsorbed methane molecules with infrared radiation is studied by molecular dynamics. The presence of methane molecules in the disperse water system leads to an increase in absorption and emission of infrared radiation and a strong depletion of the Raman spectrum. In this case, the reflection coefficient of a monochromatic plane electromagnetic wave increases and its frequency spectrum significantly changes. The comparison of experimental data for similar characteristics of water, methane, or their mixtures is presented.

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Effects of self-fields on dispersion relation and growth rate in two-stream electromagnetically pumped free electron laser with axial guide magnetic field

S. Saviz, H. Rajabalinia

Chin. Phys. B, 2013, 22 (12): 124101 doi: 10.1088/1674-1056/22/12/124101
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[PDF 1202 KB] (Downloads:299)

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A theory for a two-stream free-electron laser (FEL) with an electromagnetic wiggler (EMW) and axial guide magnetic field is developed. In the analysis, the effects of self-fields are taken into account. The growth rate is derived. The characteristics of the growth rate are studied numerically. The dependence of the normalized wave number, which corresponds to the maximum growth rate, on the cyclotron frequency is presented. The comparisons between the normalized maximum growth rate and its corresponding wave number normalized by employing the axial magnetic field, for the cases with and without self-fields in the two-stream FEL are studied numerically.

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Effects of density profile and multi-species target on laser-heated thermal-pressure-driven shock wave acceleration

Wang Feng-Chao

Chin. Phys. B, 2013, 22 (12): 124102 doi: 10.1088/1674-1056/22/12/124102
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[PDF 1184 KB] (Downloads:332)

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The shock wave acceleration of ions driven by laser-heated thermal pressure is studied through one-dimensional particle-in-cell simulation and analysis. The generation of high-energy mono-energetic protons in recent experiments (D. Haberberger et al., 2012 Nat. Phys. 8 95) is attributed to the use of exponentially decaying density profile of the plasma target. It does not only keep the shock velocity stable but also suppresses the normal target normal sheath acceleration. The effects of target composition are also examined, where a similar collective velocity of all ion species is demonstrated. The results also give some reference to future experiments of producing energetic heavy ions.

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Controlling the photoluminescence spectroscopy of quinacrine dihydrochloride by SiO₂ inverse opal photonic crystal Suggested by editors

Li Chao-Rong, Yang Zhao-Ting, Xu Qing, Dong Wen-Jun

Chin. Phys. B, 2013, 22 (12): 124201 doi: 10.1088/1674-1056/22/12/124201
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[PDF 461 KB] (Downloads:512)

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Manipulation of the photoluminescence spectra of light-emitting materials doped in three-dimensional (3D) inverse opal photonic crystals is investigated. Quinacrine dihydrochloride molecules doped highly ordered SiO₂ inverse opal is successfully synthesized by co-assembly combined with double-substrate vertical infiltrate method. The quinacrine dihydrochloride-doped and-undoped SiO₂ inverse opals each exhibit an apparent photonic band gap (PBG) in the visible light region. Significant suppression of the emission is observed when the PBG is overlapped with the quinacrine dihydrochloride emission bands. The mechanism of suppression effect of PBG in inverse opal on the fluorescence intensity of quinacrine dihydrochloride molecules is studied.

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A planar chiral nanostructure with asymmetric transmission of linearly polarized wave and huge optical activity in near-infrared band

Liu Dao-Ya, Luo Xiao-Yang, Liu Jin-Jing, Dong Jian-Feng

Chin. Phys. B, 2013, 22 (12): 124202 doi: 10.1088/1674-1056/22/12/124202
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[PDF 569 KB] (Downloads:414)

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Just like an electronic diode that allows the electrical current to flow in one direction only, a kind of chiral metamaterial structure with a similar functionality for the electromagnetic wave is proposed. The designed nanostructure that consists of twisted metallic split-ring resonators on both sides of a dielectric substrate achieves asymmetric transmission for a forward and backward propagating linearly polarized wave by numerical simulation in near-infrared band. Difference in transmission efficiency of the optimized structure between the same polarized waves incident from opposite directions can reach a maximum at the communication wavelength (1.55 μm). Moreover, the simulation results of this structure also exhibit strong optical activity and circular dichroism.

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Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Wu Jian, Cui Huai-Yang, Huang Meng, Ma Ming-Lei

Chin. Phys. B, 2013, 22 (12): 124203 doi: 10.1088/1674-1056/22/12/124203
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[PDF 701 KB] (Downloads:338)

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Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors (DBRs), the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.

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Mid-IR dual-wavelength difference frequency generation in uniform grating PPLN using index dispersion control Suggested by editors

Chang Jian-Hua, Sun Qing, Ge Yi-Xian, Wang Ting-Ting, Tao Zai-Hong, Zhang Chuang

Chin. Phys. B, 2013, 22 (12): 124204 doi: 10.1088/1674-1056/22/12/124204
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[PDF 369 KB] (Downloads:416)

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A novel widely tunable dual-wavelength mid-IR difference frequency generation (DFG) scheme with uniform grating periodically poled lithium niobate (PPLN) is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching (QPM) peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.

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A sensitive method of determining optic axis azimuth based on laser feedback

Wu Yun, Zhang Peng, Chen Wen-Xue, Tan Yi-Dong

Chin. Phys. B, 2013, 22 (12): 124205 doi: 10.1088/1674-1056/22/12/124205
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[PDF 653 KB] (Downloads:426)

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A sensitive method to determine the optic axis azimuth of the birefringence element is presented, which is based on laser feedback. The phase difference between the two intensities in birefringence feedback changes with the angle between the optic axis of the birefringence element and laser original polarization. The phase difference is highly sensitive to the relative position of the optic axis and the laser original polarization. This method is used to highly precisely determine the optic axis azimuth, and is able to distinguish between the fast axis and the slow axis of the birefringence element. Theoretical analysis and experimental results are both demonstrated.

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Investigation of stimulated rotational Raman scattering of the high-power broadband laser with applied angular dispersion

Fan Xin-Min, Lü Zhi-Wei, Lin Dian-Yang, Liu Ying, Zhu Cheng-Yu, He Wei-Ming, Ding Lei

Chin. Phys. B, 2013, 22 (12): 124206 doi: 10.1088/1674-1056/22/12/124206
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[PDF 399 KB] (Downloads:385)

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Smoothing by spectral dispersion (SSD) leads to considerable improvement on laser-irradiation uniformity in far field for fusion lasers. Phase modulation in time and spectral angular dispersion (SAD) across the beam introduced by SSD will affect the stimulated rotational Raman scattering (SRRS) gain in the near field. This paper focuses on the influence of SAD on SRRS gain under different laser conditions. Results show that the SAD will aggravate the generation of SRRS when the laser initial additional phase is constant. On the contrary, the SAD can reduce the SRRS gain if appropriate SSD parameters are adopted when the laser initial additional phase is variable. SSD has a certain application prospect in SRRS suppression.

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Resisting shrinkage properties of volume holograms recorded in TiO₂ nanoparticle-dispersed acrylamide-based photopolymer Suggested by editors

Zhao Lei, Han Jun-He, Li Ruo-Ping, Wang Long-Ge, Huang Ming-Ju

Chin. Phys. B, 2013, 22 (12): 124207 doi: 10.1088/1674-1056/22/12/124207
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[PDF 1476 KB] (Downloads:351)

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A novel organic–inorganic nanoparticle–photopolymer composite system is developed, and its fundamental holographic recording characteristics are studied. In this hydrophilic TiO₂-nanoparticle-dispersed acrylamide photopolymer composite system, the counter-diffusion of monomers and nanoparticles plays a fundamental and key role in hologram grating formation. The experimental results indicate that the volume shrinkage of the nanoparticle–photopolymer film during the holographic recording can be drastically reduced compared with the undoped photopolymer film. It is also found that the diffraction efficiency of the grating recorded in the nanoparticle–photopolymer film depends strongly on the concentration of the TiO₂-nanoparticles, and there exists an optimal TiO₂-nanoparticle-doping concentration to make the diffraction efficiency and the refractive index modulation reach their maxima. Additionally, the digital data page is stored and reconstructed in the nanoparticle–photopolymer film.

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Polarization readout analysis for multilevel phase change recording by crystallization degree modulation Suggested by editors

Lin Jin-Cheng, Long Guo-Yun, Wang Yang, Wu Yi-Qun

Chin. Phys. B, 2013, 22 (12): 124208 doi: 10.1088/1674-1056/22/12/124208
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[PDF 421 KB] (Downloads:304)

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Four different states of Si₁₅Sb₈₅ and Ge₂Sb₂Te₅ phase change memory thin films are obtained by crystallization degree modulation through laser initialization at different powers or annealing at different temperatures. The polarization characteristics of these two four-level phase change recording media are analyzed systematically. A simple and effective readout scheme is then proposed, and the readout signal is numerically simulated. The results show that a high-contrast polarization readout can be obtained in an extensive wavelength range for the four-level phase change recording media using common phase change materials. This study will help in-depth understanding of the physical mechanisms and provide technical approaches to multilevel phase change recording.

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Efficient evanescent coupling design for GeSi electro-absorption modulator

Li Ya-Ming, Cheng Bu-Wen

Chin. Phys. B, 2013, 22 (12): 124209 doi: 10.1088/1674-1056/22/12/124209
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[PDF 402 KB] (Downloads:464)

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Efficient coupling from the silicon waveguide to the GeSi layer is the key to success in the GeSi electro-absorption (EA) modulator based on evanescent coupling. A lateral taper in the upper GeSi layer has room for increasing the modulating efficiency and alleviating the sensitivity of the extinction ratio (ER) and insertion loss (IL) to the length of the active region. The light behavior and the effect of the taper are explored in detail using the beam propagation method (BPM). After optimization, the light can nearly be totally confined in the GeSi layer without any oscillation. The modulator with the designed taper can achieve low IL and high ER.

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Investigation of long-range sound propagation in surface ducts

Duan Rui, Yang Kun-De, Ma Yuan-Liang

Chin. Phys. B, 2013, 22 (12): 124301 doi: 10.1088/1674-1056/22/12/124301
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[PDF 1155 KB] (Downloads:904)

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Understanding the effect of source-receiver geometry on sound propagation in surface ducts can improve the performance of near-surface sonar in deep water. The Lloyd-mirror and normal mode theories are used to analyze the features of surface-duct propagation in this paper. Firstly, according to the Lloyd-mirror theory, a shallow point source generates directional lobes, whose grazing angles are determined by the source depth and frequency. By assuming a part of the first lobe to be just trapped in the surface duct, a method to calculate the minimum cutoff frequency (MCF) is obtained. The presented method is source depth dependent and thus is helpful for determining the working depth for sonar. Secondly, it is found that under certain environments there exists a layer of low transmission loss (TL) in the surface duct, whose thickness is related to the source geometry and can be calculated by the Lloyd-mirror method. The receiver should be placed in this layer to minimize the TL. Finally, the arrival angle on a vertical linear array (VLA) in the surface duct is analyzed based on normal mode theory, which provides a priori knowledge of the beam direction of passive sonar.

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Numerical analysis of the resonance mechanism of the lumped parameter system model for acoustic mine detection

Wang Chi, Zhou Yu-Qiu, Shen Gao-Wei, Wu Wen-Wen, Ding Wei

Chin. Phys. B, 2013, 22 (12): 124601 doi: 10.1088/1674-1056/22/12/124601
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[PDF 850 KB] (Downloads:455)

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The method of numerical analysis is employed to study the resonance mechanism of the lumped parameter system model for acoustic mine detection. Based on the basic principle of the acoustic resonance technique for mine detection and the characteristics of low-frequency acoustics, the “soil-mine” system could be equivalent to a damping “mass-spring” resonance model with a lumped parameter analysis method. The dynamic simulation software, Adams, is adopted to analyze the lumped parameter system model numerically. The simulated resonance frequency and anti-resonance frequency are 151 Hz and 512 Hz respectively, basically in agreement with the published resonance frequency of 155 Hz and anti-resonance frequency of 513 Hz, which were measured in the experiment. Therefore, the technique of numerical simulation is validated to have the potential for analyzing the acoustic mine detection model quantitatively. The influences of the soil and mine parameters on the resonance characteristics of the soil–mine system could be investigated by changing the parameter setup in a flexible manner.

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Effects of transpiration on unsteady MHD flow of an upper convected Maxwell (UCM) fluid passing through a stretching surface in the presence of a first order chemical reaction

Swati Mukhopadhyay, M. Golam Arif, M. Wazed Ali Pk

Chin. Phys. B, 2013, 22 (12): 124701 doi: 10.1088/1674-1056/22/12/124701
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[PDF 440 KB] (Downloads:355)

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The aim of this article is to present the effects of transpiration on the unsteady two-dimensional boundary layer flow of non-Newtonian fluid passing through a stretching sheet in the presence of a first order constructive/destructive chemical reaction. The upper-convected Maxwell (UCM) model is used here to characterize the non-Newtonian behavior of the fluid. Using similarity solutions, the governing nonlinear partial differential equations are transformed into ordinary ones and are then solved numerically by the shooting method. The flow fields and mass transfer are significantly influenced by the governing parameters. The fluid velocity initially decreases as the unsteadiness parameter increases and the concentration decreases significantly due to the increase in the unsteadiness. The effect of increasing values of transpiration (suction) and the Maxwell parameter is to suppress the velocity field; however, the concentration is enhanced as transpiration (suction) and the Maxwell parameter increase. Also, it is found that the fluid velocity decreases as the magnetic parameter increases; however, the concentration increases in this case.

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Simultaneous effects of magnetic field and space porosity on compressible Maxwell fluid transport induced by a surface acoustic wave in a microchannel

Khaled S. Mekheimer, Soliman R. Komy, Sara I. Abdelsalam

Chin. Phys. B, 2013, 22 (12): 124702 doi: 10.1088/1674-1056/22/12/124702
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[PDF 355 KB] (Downloads:523)

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Peristaltic motion induced by a surface acoustic wave of a viscous, compressible and electrically conducting Maxwell fluid in a confined parallel-plane microchannel through a porous medium is investigated in the presence of a constant magnetic field. The slip velocity is considered and the problem is discussed only for the free pumping case. A perturbation technique is employed to analyze the problem in terms of a small amplitude ratio. The phenomenon of a “backward flow” is found to exist in the center and at the boundaries of the channel. In the second order approximation, the net axial velocity is calculated for various values of the fluid parameters. Finally, the effects of the parameters of interest on the mean axial velocity, the reversal flow, and the perturbation function are discussed and shown graphically. We find that in the non-Newtonian regime, there is a possibility of a fluid flow in the direction opposite to the propagation of the traveling wave. This work is the most general model of peristalsis created to date with wide-ranging applications in biological, geophysical and industrial fluid dynamics.

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Modelling the unsteady melt flow under a pulsed magnetic field

Chen Guo-Jun, Zhang Yong-Jie, Yang Yuan-Sheng

Chin. Phys. B, 2013, 22 (12): 124703 doi: 10.1088/1674-1056/22/12/124703
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[PDF 1500 KB] (Downloads:293)

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A numerical model for the unsteady flow under a pulsed magnetic field of a solenoid is developed, in which magnetohydrodynamic flow equations decouple into a transient magnetic diffusion equation and unsteady Navier–Stokes equations in conjunction with two equations of the k–ε turbulent model. A Fourier series method is used to implement the boundary condition of magnetic flux density under multiple periods of a pulsed magnetic field (PMF). The numerical results are compared with the theoretical or experimental results to validate the model under a time-harmonic magnetic field; it is found that the toroidal vortex pair is the dominating structure within the melt flow under a PMF. The velocity field of a molten melt is in a quasi-steady state after several periods; changing the direction of the electromagnetic force causes the vibration of the melt surface under a PMF.

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Investigation of impurity transport using supersonic molecular beam injected neon in HL-2A ECRH plasma

Cui Xue-Wu, Cui Zheng-Ying, Feng Bei-Bin, Pan Yu-Dong, Zhou Hang-Yu, Sun Ping, Fu Bing-Zhong, Lu Ping, Dong Yun-Bo, Gao Jin-Ming, Song Shao-Dong, Yang Qing-Wei

Chin. Phys. B, 2013, 22 (12): 125201 doi: 10.1088/1674-1056/22/12/125201
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[PDF 1049 KB] (Downloads:440)

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In this paper, we describe the behavior of impurity transport in the HL-2A electron cyclotron resonance heating (ECRH) L-mode plasma. The neon as a trace impurity is injected by the supersonic molecular beam injection (SMBI) technique, which is used for the first time to study the impurity transport in HL-2A. The progression of neon ions is monitored by the soft X-ray camera and bolometer arrays with good temporal and spatial resolutions. The convection and diffusion process of the neon ions are investigated with the one-dimensional impurity transport code STRAHL. The results show that the diffusion coefficient D of neon ions is a factor of four larger than the neoclassical value in the central region. The value of D is larger in the outer region of the plasma (ρ > 0.6) than in the central region of the plasma (ρ < 0.6). The convective velocity directs inwards with a value of ～-1.0 m/s in the Ohmic discharge, but it reverses to direct outwards with a value of ～ 8.0 m/s in the outer region of the plasma when ECRH is applied. The result indicates that the impurity transport is strongly enhanced with ECRH.

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Determinations of plasma density and decay time in the hollow cathode discharge by microwave transmission

Zhang Lin, He Feng, Li Shi-Chao, Ouyang Ji-Ting

Chin. Phys. B, 2013, 22 (12): 125202 doi: 10.1088/1674-1056/22/12/125202
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[PDF 517 KB] (Downloads:550)

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The microwave (MW) transmission method is employed to measure both the plasma density and the plasma decay time in the hollow cathode discharge (HCD) in argon at low pressure. The plasma density in DC-driven or pulsed HCD is on the order of 10¹² cm^-3, which can block the X-band MW effectively. In the case of pulsed HCD, the MW transmittance shows the same waveform as the pulsed current during the rising edge if the driving frequency is low, but with a longer delay during the falling edge. The MW transmittance reaches a constant low level when the driving frequency is high enough. The plasma decay time in the HCD system is measured to be about 100 μs around a pressure of 120 Pa. The ambipolar diffusion is considered to be the major mechanism in the decay process.

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XPS and Raman studies of electron irradiated sodium silicate glass

Chen Liang, Wang Tie-Shan, Zhang Gen-Fa, Yang Kun-Jie, Peng Hai-Bo, Zhang Li-Min

Chin. Phys. B, 2013, 22 (12): 126101 doi: 10.1088/1674-1056/22/12/126101
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[PDF 322 KB] (Downloads:780)

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The microstructure modifications of sodium silicate glass induced by 1.2-MeV electron irradiation are studied by x-ray photoelectron spectroscopy and Raman spectroscopy. Depth profile analyses are also performed on the irradiated glass at 10⁹ Gy. A sodium-depleted layer with a thickness of a few tens of nanometers and the corresponding increase of network polymerization on the top surface are observed after electron bombardment, while the polymerization in the subsurface region has a negligible variation with the irradiation dose. Moreover, the formation of molecular oxygen after electron irradiation is evidenced, which is mainly aggregated in the first two-micron-thick irradiated glass surface. These modifications are correlated to the network relaxation process as a consequence of the diffusion and desorption of sodium species during electron irradiation.

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A novel method to prepare Au nanocage@SiO₂ nanoparticle Suggested by editors

Jiang Tong-Tong, Yin Nai-Qiang, Liu Ling, Lei Jie-Mei, Zhu Li-Xin, Xu Xiao-Liang

Chin. Phys. B, 2013, 22 (12): 126102 doi: 10.1088/1674-1056/22/12/126102
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[PDF 696 KB] (Downloads:696)

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Gold (Au) nanocage@SiO₂ nanoparticles are prepared by a novel approach. The silver (Ag) nanocube@SiO₂ structure is synthetized firstly. Next, the method of etching a SiO₂ shell by boiling water is adopted to change the penetration rate of AuCl₄^- through the SiO₂ shell. AuCl₄^- can penetrate through silica shells of different thickness values to react with the Ag nanocube core by changing the incubation time. The surface plasma resonance (SPR) peak of synthetic Au nanocage@SiO₂ can be easily tuned into the near-infrared region. Besides, CdTeS quantum dots (QDs) are successfully connected to the surface of Au nanocage@SiO₂, which testifies that the incubation process does not change the property of silica.

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Effects of Cu on the martensitic transformation and magnetic properties of Mn₅₀Ni₄₀In₁₀ alloy

Li Ge-Tian, Liu Zhu-Hong, Meng Fan-Yan, Ma Xing-Qiao, Wu Guang-Heng

Chin. Phys. B, 2013, 22 (12): 126201 doi: 10.1088/1674-1056/22/12/126201
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[PDF 2454 KB] (Downloads:454)

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The structures, the martensitic transformations, and the magnetic properties are studied systematically in Mn₅₀Ni_40-xCu_xIn₁₀, Mn_50-xCu_xNi₄₀In₁₀, and Mn₅₀Ni₄₀In_10-xCu_x alloys. The partial substitution of Ni by Cu reduces the martensitic transformation temperature, but has little influence on the Curie temperature of austenite. Comparatively, the martensitic transformation temperature increases and the Curie temperature of austenite decreases with the partial replacement of Mn or In by Cu. The magnetization difference between the austenite phase and the martensite phase reaches 70 emu/g in Mn₅₀Ni₃₉Cu₁In₁₀; a field-induced martensite-to-austenite transition is observed in this alloy.

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Investigations of high-pressure and high-temperature behaviors of the newly-discovered willemite-Ⅱ and post-phenacite silicon nitrides

Chen Dong

Chin. Phys. B, 2013, 22 (12): 126301 doi: 10.1088/1674-1056/22/12/126301
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[PDF 300 KB] (Downloads:372)

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Using the first-principles method of the plane-wave pseudo-potential, the structural properties of the newly-discovered willemite-Ⅱ Si₃N₄ (wⅡ phase) and post-phenacite Si₃N₄ (δ phase) are investigated. The α phase is predicted to undergo a first-order α→wⅡ phase transition at 18.6 GPa and 300 K. Within the quasi-harmonic approximation (QHA), the α→wⅡ phase boundary is also obtained. When the well-known β→γ transition is suppressed by some kinetic reasons, the β→δ phase transformation could be observed in the phase diagram. Besides, the temperature dependences of the cell volume,thermal expansion coefficient, bulk modulus, specific heat, entropy and Debye temperature of the involved phases are determined from the non-equilibrium free energies. The thermal expansion coefficients of wⅡ-Si₃N₄ show no negative values in a pressure range of 0-30 GPa, which implies that the wⅡ-Si₃N₄ is mechanically stable. More importantly, the δ-Si₃N₄ is found to be a negative thermal expansion material. Further experimental investigations may be required to determine the physical properties of wⅡ- and δ-Si₃N₄ with higher reliability.

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Molecular dynamics study of thermal stress and heat propagation in tungsten under thermal shock

Fu Bao-Qin, Lai Wen-Sheng, Yuan Yue, Xu Hai-Yan, Li Chun, Jia Yu-Zhen, Liu Wei

Chin. Phys. B, 2013, 22 (12): 126601 doi: 10.1088/1674-1056/22/12/126601
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[PDF 1228 KB] (Downloads:524)

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Using molecular dynamics (MD) simulation, we study the thermal shock behavior of tungsten (W), which has been used for the plasma facing material (PFM) of tokamaks. The thermo-elastic stress wave, corresponding to the collective displacement of atoms, is analyzed with the Lagrangian atomic stress method, of which the reliability is also analyzed. The stress wave velocity corresponds to the speed of sound in the material, which is not dependent on the thermal shock energy. The peak pressure of a normal stress wave increases with the increase of thermal shock energy. We analyze the temperature evolution of the thermal shock region according to the Fourier transformation. It can be seen that the “obvious” velocity of heat propagation is less than the velocity of the stress wave; further, that the thermo-elastic stress wave may contribute little to the transport of kinetic energy. The heat propagation can be described properly by the heat conduction equation. These results may be useful for understanding the process of the thermal shock of tungsten.

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Expressions of the radius and the surface tension of surface of tension in terms of the pressure distribution for nanoscale liquid threads

Yan Hong, Wei Jiu-An, Cui Shu-Wen, Zhu Ru-Zeng

Chin. Phys. B, 2013, 22 (12): 126801 doi: 10.1088/1674-1056/22/12/126801
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[PDF 185 KB] (Downloads:265)

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The expressions of the radius and the surface tension of surface of tension R_s and γ_s in terms of the pressure distribution for nanoscale liquid threads are of great importance for molecular dynamics (MD) simulations of the interfacial phenomena of nanoscale fluids; these two basic expressions are derived in this paper. Although these expressions were derived first in the literature[Kim B G, Lee J S, Han M H, and Park S, 2006 Nanoscale and Microscale Thermophysical Engineering, 10, 283] and used widely thereafter, the derivation is wrong both in logical structure and physical thought. In view of the importance of these basic expressions, the logic and physical mistakes appearing in that derivation are pointed out.

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Tensile properties of phase interfaces in Mg–Li alloy：A first principles study

Zhang Cai-Li, Han Pei-De, Wang Xiao-Hong, Zhang Zhu-Xia, Wang Li-Ping, Xu Hui-Xia

Chin. Phys. B, 2013, 22 (12): 126802 doi: 10.1088/1674-1056/22/12/126802
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[PDF 349 KB] (Downloads:475)

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Employing density functional theory, we study the tensile and fracture processes of the phase interfaces in Mg–Li binary alloy. The simulation presents the strain–stress relationships, the ideal tensile strengths, and the fracture processes of three phase interfaces. The results show that the α/α and α/β interfaces have larger tensile strength than that of β/β interface. The fractures of both α/α and β/β interfaces are ductile fractures, while the α/β fractures abruptly._Further analyses show that the fracture of the α/β occurs at the interface.

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Pits and adatoms at the interface of 1-ML C₈₄/Ag (111)

Wang Peng, Zhang Han-Jie, Li Yan-Jun, Sheng Chun-Qi, Li Wen-Jie, Xing Xiu-Na, Li Hai-Yang, He Pi-Mo, Bao Shi-Ning, Li Hong-Nian

Chin. Phys. B, 2013, 22 (12): 126803 doi: 10.1088/1674-1056/22/12/126803
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We prepare a well-defined C₈₄ monolayer on the surface of Ag (111) and study the geometric structure by scanning tunneling microscopy (STM). The C₈₄ molecules form a nearly close-packed incommensurate R30° lattice. The lattice is long-distance ordered with numerous local disorders. The monolayer exhibits complex bright/dim contrast; the largest height difference between the molecules can be greater than 0.4 nm. Annealing the monolayer at 380 ℃ can desorb part of the molecules, but more than sixty percent molecules stay on the Ag (111) surface even after the sample has been annealed at 650 ℃. Our analyses reveal that the 7-atom pits form beneath many molecules. Some other molecules sit at the 1-atom pits. Ag adatoms (those removed substrate atoms, accompanying the pit formation) play a very important role in this system. The adatoms can either stabilize or destabilize the monolayer, depending on the distribution manner of the adatoms at the interface. The distribution manner is determined by the co-play of the following factors: the dimension of the interstitial regions of the C₈₄ overlayer, the number of the adatoms, and the long-distance migration of part adatoms.

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Defect-induced ferromagnetism in rutile TiO₂：A first-principles study

Zhang Yong, Qi Yue-Ying, Hu Ya-Hua, Liang Pei

Chin. Phys. B, 2013, 22 (12): 127101 doi: 10.1088/1674-1056/22/12/127101
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Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO₂ have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO₂ and the magnetic moment mainly comes from p orbitals of O atoms around the Ti vacancy. However, the Ti vacancy under normal conditions is very difficult to form due to its high formation energy. Our calculations indicate that Li-doped TiO₂ can reduce the formation energy while keeping the magnetism. The large magnetization energy indicates that Li-doped TiO₂ is a promising room-temperature diluted magnetic semiconductor.

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Ab initio investigation of the structural and unusual electronic properties of α-CuSe (klockmannite)

Ali Reza Shojaei, Zahra Nourbakhsh, Aminollah Vaez, Mohammad Dehghani

Chin. Phys. B, 2013, 22 (12): 127102 doi: 10.1088/1674-1056/22/12/127102
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In this article, a computational analysis has been performed on the structural properties and predominantly on the electronic properties of the α-CuSe (klockmannite) using density functional theory. The studies in this work show that the best structural results, in comparison to the experimental values, belong to the PBEsol-GGA and WC-GGA functionals. However, the best results for the bulk modulus and density of states (DOSs) are related to the local density approximation (LDA) functional. Through utilized approaches, the LDA is chosen to investigate the electronic structure. The results of the electronic properties and geometric optimization of α-CuSe respectively show that this compound is conductive and non-magnetic. The curvatures of the energy bands crossing the Fermi level explicitly reveal that major charge carriers in CuSe are holes, whose density is estimated to be 0.86×10²² hole/cm³. In particular, the Fermi surfaces in the first Brillouin zone demonstrate interplane conductivity between (001) planes. Moreover, the charge carriers among them are electrons and holes simultaneously. The conductivity in CuSe is mainly due to the hybridization between the d orbitals of Cu atoms and the p orbitals of Se atoms. The former orbitals have the dual nature of localization and itinerancy.

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In situ electronic structural study of VO₂ thin film across the metal–insulator transition

Emin Muhemmed, Abduleziz Ablat, Wu Rui, Wang Jia-Ou, Qian Hai-Jie, Kurash Ibrahim

Chin. Phys. B, 2013, 22 (12): 127103 doi: 10.1088/1674-1056/22/12/127103
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The in situ valence band photoemission spectrum (PES) and X-ray absorption spectrum (XAS) at V L_Ⅱ-L_Ⅲ edges of the VO₂ thin film, which is prepared by pulsed laser deposition, are measured across the metal–insulator transition (MIT) temperature (T_MIT=67 ℃). The spectra show evidence for changes in the electronic structure depending on temperature. Across the T_MIT, pure V 3d characteristic d_‖ and O 2p-V 3d hybridization characteristic π_pd, σ_pd bands vary in binding energy position and density of state distributions. The XAS reveals a temperature-dependent reversible energy shift at the V L_Ⅲ-edge. The PES and XAS results imply a synergetic energy position shift of occupied valence bands and unoccupied conduction band states across the phase transition. A joint inspection of the PES and XAS results shows that the MIT is not a one-step process, instead it is a process in which a semiconductor phase appears as an intermediate state. The final metallic phase from insulating state is reached through insulator–semiconductor, semiconductor–metal processes, and vice versa. The conventional MIT at around the T_MIT=67 ℃ is actually a semiconductor–insulator transformation point.

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Anisotropic localization behavior of graphene in the presence of diagonal and off-diagonal disorders ^Hot! Suggested by editors

Wang Li-Min, Shi Shao-Cong, Zhang Wei-Yi

Chin. Phys. B, 2013, 22 (12): 127201 doi: 10.1088/1674-1056/22/12/127201
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[PDF 389 KB] (Downloads:345)

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Anisotropic localization of Dirac fermions in graphene along both the x and y axes was studied using the transfer-matrix method. The two-parameter scaled behavior around the Dirac points was observed along the x axis with off-diagonal disorder. In contrast, the electronic state along the y axis with armchair edges was delocalized, which can be described well by single parameter scaling theory. This implies that the breakdown of the single-parameter scaling is related to the zigzag edge along the x axis. Furthermore, dimerization induced by the substrate suppresses the two-parameter scaling behavior along the x axis and preserves the delocalized state along the y axis. Our results also demonstrate anisotropic localization in graphene with diagonal disorder that can be tuned by dimerization.

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Transport and magnetoresistance effect in an oxygen-deficient SrTiO₃/La_0.67Sr_0.33MnO₃ heterojunction

Wang Jing, Chen Chang-Le, Yang Shi-Hai, Luo Bing-Cheng, Duan Meng-Meng, Jin Ke-Xin

Chin. Phys. B, 2013, 22 (12): 127302 doi: 10.1088/1674-1056/22/12/127302
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An oxygen-deficient SrTiO₃/La_0.67Sr_0.33MnO₃ heterojunction is fabricated on an SrTiO₃ (001) substrate by a pulsed laser deposition method. The electrical characteristics of the heterojunction are studied systematically in a temperature range from 80 K to 300 K. The transport mechanism follows I ∝ exp (eV/nkT) under small forward bias, while it becomes space charge limited and follows I ∝ V^m(T) with 1.49< m <1.99 under high bias. Such a heterojunction also exhibits magnetoresistance (MR) effect. The absolute value of negative MR monotonically increases with temperature decreasing and reaches 26.7% at 80 K under H=0.7 T. Various factors, such as strain and oxygen deficiency play dominant roles in the characteristics.

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Influence of annealing temperature on passivation performance of thermal atomic layer deposition Al₂O₃ films Suggested by editors

Zhang Xiang, Liu Bang-Wu, Zhao Yan, Li Chao-Bo, Xia Yang

Chin. Phys. B, 2013, 22 (12): 127303 doi: 10.1088/1674-1056/22/12/127303
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Chemical and field-effect passivation of atomic layer deposition (ALD) Al₂O₃ films are investigated, mainly by corona charging measurement. The interface structure and material properties are characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. Passivation performance is improved remarkably by annealing at temperatures of 450 ℃ and 500 ℃, while the improvement is quite weak at 600 ℃, which can be attributed to the poor quality of chemical passivation. An increase of fixed negative charge density in the films during annealing can be explained by the Al₂O₃/Si interface structural change. The Al–OH groups play an important role in chemical passivation, and the Al–OH concentration in an as-deposited film subsequently determines the passivation quality of that film when it is annealed, to a certain degree.

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Increased performance of an organic light-emitting diode by employing a zinc phthalocyanine based composite hole transport layer

Guo Run-Da, Yue Shou-Zhen, Wang Peng, Chen Yu, Zhao Yi, Liu Shi-Yong

Chin. Phys. B, 2013, 22 (12): 127304 doi: 10.1088/1674-1056/22/12/127304
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We demonstrate that the electroluminescent performances of organic light-emitting diodes are significantly improved by employing a zinc phthalocyanine (ZnPc)-based composite hole transport layer (c-HTL). The optimum ris-(8-hydroxyquinoline)aluminum (Alq₃)-based organic light-emitting diode with a c-HTL exhibits a lower turn-on voltage of 2.8 V, a higher maximum current efficiency of 3.40 cd/A and a higher maximum power efficiency of 1.91 lm/W, which are superior to those of the conventional device (turn-on voltage of 3.8 V, maximum current efficiency of 2.60 cd/A, and maximum power efficiency of 1.21 lm/W). We systematically studied the effects of different kinds of N’-diphenyl-N,N’-bis(1-naphthyl)(1,1’-biphenyl)-4,4’diamine (NPB):ZnPc c-HTL. Meanwhile, we also investigate their mechanisms different from that in the case of using ZnPc as buffer layer. The specific analysis is based on the absorption spectra of the hole transporting material and current density–voltage characteristics of the corresponding hole-only devices.

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Dependence of electron dynamics on magnetic fields in semiconductor superlattices

Yang Gui, Wang Lei, Tian Jun-Long

Chin. Phys. B, 2013, 22 (12): 127305 doi: 10.1088/1674-1056/22/12/127305
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Numerical simulation results are presented for a drift-diffusion rate equation model which describes electronic transport due to sequential tunneling between adjacent quantum wells in weakly coupled semiconductor superlattices (SLs). The electron dynamics is dependent on the external magnetic field perpendicular to the electron motion direction, and a detailed explanation is given. Using different parameters, the system shows different dynamic behaviors, and three distinct phenomena are observed and controlled by increasing magnetic field. (i) For a lower doping density, the system state transfers from stable state to oscillationary state. (ii) An opposite result is obtained to that in the case (i) for an intermediate value of the doping density, and the state changes from oscillationary to stationary. (iii) The state varies between oscillationary and stationary when doping density is large. Then, a detailed theoretical analysis is given to explain these surprise phenomena. The distribution of the electric-field domain along the SLs is plotted. We find the structure of the domain is almost uniform for a lower doping density, and no domain occurs in the SLs. By adding an external ac signal, complex nonlinear behaviors are observed from the Poincaré map and the corresponding phase diagrams when the driving frequency changes.

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Post-annealing effect on the structural and mechanical properties of multiphase zirconia films deposited by a plasma focus device

I. A. Khan, R. S. Rawat, R. Ahmad, M. A. K. Shahid

Chin. Phys. B, 2013, 22 (12): 127306 doi: 10.1088/1674-1056/22/12/127306
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Nanostructured multiphase zirconia films (MZFs) are deposited on Zr substrate by the irradiation of energetic oxygen ions emanated from a plasma focus device. The oxygen operating gas pressure of 1 mbar (1 bar=10⁵ Pa) provides the most appropriate ion energy flux to deposit crystalline ZrO₂ films. X-ray diffraction (XRD) patterns reveal the formation of polycrystalline ZrO₂ films. The crystallite size (CS), crystal growth, and dislocation densities are attributed to increasing focus shots, sample axial distances, and working gas pressures. Phase and orientation transformations from t-ZrO₂ to m-ZrO₂ and c-ZrO₂ are associated with increasing focus shots and continuous annealing. For lower (200 ℃) annealing temperature (AT), full width at half maximum (FWHM) of diffraction peak, CS, and dislocation density (δ) for (020) plane are found to be 0.494, 16.6 nm, and 3.63×10^-3 nm^-2 while for higher (400 ℃) AT, these parameters for (111) plane are found to be 0.388, 20.87 nm, and 2.29×10^-3 nm^-2, respectively. Scanning electron microscope (SEM) results demonstrate the formation of rounded grains with uniform distribution. The estimated values of atomic ratio (O/Zr) in ZrO₂ films deposited for different axial distances (6 cm, 9 cm, and 12 cm) are found to be 2.1, 2.2, and 2.3, respectively. Fourier transform infrared (FTIR) analysis reveals that the bands appearing at 441 cm^-1 and 480 cm^-1 belong to m-ZrO₂ and t-ZrO₂ phases, respectively. Maximum microhardness (8.65±0.45 GPa) of ZrO₂ film is ～ 6.7 times higher than the microhardness of virgin Zr.

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A monolithic distributed phase shifter based on right-handed nonlinear transmission lines at 30 GHz

Huang Jie, Zhao Qian, Yang Hao, Dong Jun-Rong, Zhang Hai-Ying

Chin. Phys. B, 2013, 22 (12): 127307 doi: 10.1088/1674-1056/22/12/127307
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The epitaxial material, device structure, and corresponding equivalent large signal circuit model of GaAs planar Schottky varactor diode are successfully developed to design and fabricate a monolithic phase shifter, which is based on right-handed nonlinear transmission lines and consists of a coplanar waveguide transmission line and periodically distributed GaAs planar Schottky varactor diode. The distributed-Schottky transmission-line-type phase shifter at a bias voltage greater than 1.5 V presents a continuous 0°–360° differential phase shift over a frequency range from 0 to 33 GHz. It is demonstrated that the minimum insertion loss is about 0.5 dB and that the return loss is less than-10 dB over the frequency band of 0–33 GHz at a reverse bias voltage less than 4.5 V. These excellent characteristics, such as broad differential phase shift, low insertion loss, and return loss, indicate that the proposed phase shifter can entirely be integrated into a phased array radar circuit.

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Switching effects in superconductor/ferromagnet/superconductor graphene junctions

Li Xiao-Wei, Liu Dan, Bao Yan-Hui

Chin. Phys. B, 2013, 22 (12): 127401 doi: 10.1088/1674-1056/22/12/127401
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[PDF 266 KB] (Downloads:358)

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The Josephson effect in the superconductor/ferromagnet/superconductor (SFS) graphene Josephson junction is studied using the Dirac Bogoliubov-de Gennes (DBdG) formalism. It is shown that the SFS graphene junction drives 0–π transition with the increasing of p=h₀L/v_Fħ, which captures the effects of both the exchange field and the length of the junction; the spin-down current is dominant. The 0 state is stable for p < p_c (critical value p_c ≈ 0.80) and the π state is stable for p > p_c, where the free energy minima are at φ_g=0 and φ_g=π, respectively. The coexistence of the 0 and π states appears in the vicinity of p_c.

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Phase transition in a two-dimensional Ising ferromagnet based on the generalized zero-temperature Glauber dynamics

Meng Qing-Kuan, Feng Dong-Tai, Gao Xu-Tuan, Mei Yu-Xue

Chin. Phys. B, 2013, 22 (12): 127501 doi: 10.1088/1674-1056/22/12/127501
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[PDF 257 KB] (Downloads:408)

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At zero temperature, based on the Ising model, the phase transition in a two-dimensional square lattice is studied using the generalized zero-temperature Glauber dynamics. Using Monte Carlo (MC) renormalization group methods, the static critical exponents and the dynamic exponent are studied; the type of phase transition is found to be of the first order.

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Phase shift of polarized light through sculptured thin films：Experimental measurements and theoretical study

Hou Yong-Qiang, Qi Hong-Ji, Li Xu, He Kai, Yi Kui, Shao Jian-Da

Chin. Phys. B, 2013, 22 (12): 127801 doi: 10.1088/1674-1056/22/12/127801
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[PDF 754 KB] (Downloads:637)

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A slanted columnar TiO₂ sculptured anisotropic thin film (ATF) is prepared via the glancing angle deposition technique and used as the phase retardation plate. The tilted nanocolumn microstructures of thin film induce the optical anisotropy. With the biaxial birefringent model, the optical constants dispersion equations of TiO₂ ATF are derived by fitting the transmittance spectra for s-and p-polarized waves measured at normal and oblique incidence within 400 nm–1200 nm. The phase shift of polarized light after reflection and/or transmission through the TiO₂ ATF is analyzed with the characteristic matrix employing the extracted structure parameters. The theoretical studies reasonably well accord with the experimental results measured with spectroscopic ellipsometry. In addition, the dependences of the phase shift on the coating physical thickness and oblique incidence angle are also discussed. Birefringence of the biaxial ATF provides a sophisticated phase modulation by varying incidence angles over a broad range to have a wide-angle phase shift.

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Interplay between out-of-plane magnetic plasmon and lattice resonance for modified resonance lineshape and near-field enhancement in double nanoparticles array

Ding Pei, Wang Jun-Qiao, He Jin-Na, Fan Chun-Zhen, Cai Gen-Wang, Liang Er-Jun

Chin. Phys. B, 2013, 22 (12): 127802 doi: 10.1088/1674-1056/22/12/127802
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[PDF 557 KB] (Downloads:445)

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Two-dimensional double nanoparticle (DNP) arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the nanoparticle height or the array period due to the height-dependent magnetic resonance and the periodicity-dependent lattice resonance. The interplay between the two plasmon modes can lead to a remarkable change in resonance lineshape and an improvement on magnetic field enhancement. Simultaneous electric field and magnetic field enhancement can be obtained in the gap region between neighboring particles at two resonance frequencies as the interplay occurs, which presents “open” cavities as electromagnetic field hot spots for potential applications on detection and sensing. The results not only offer an attractive way to tune the optical responses of plasmonic nanostructure, but also provide further insight into the plasmon interactions in periodic nanostructure or metamaterials comprising multiple elements.

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Fabrication and performance optimization of Mn–Zn ferrite/EP composites as microwave absorbing materials

Wang Wen-Jie, Zang Chong-Guang, Jiao Qing-Jie

Chin. Phys. B, 2013, 22 (12): 128101 doi: 10.1088/1674-1056/22/12/128101
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Magnesium-substituted Mn_0.8Zn_0.2Fe₂O₄ ferrite is synthesized by the sol–gel combustion method using citrate acid as the complex agent. The electromagnetic absorbing behaviors of ferrite/polymer coatings fabricated by dispersing Mn–Zn ferrite into epoxy resin (EP) are studied. The microstructure and morphology are characterized by X-ray diffraction and scanning electron microscope. Complex permittivity, complex permeability, and reflection loss of ferrite/EP composite coating are investigated in a low frequency range. It is found that the prepared ferrite particles are traditional cubic spinel ferrite particles with an average size of 200 nm. The results reveal that the electromagnetic microwave absorbing properties are significantly influenced by the weight ratio of ferrite to polymer. The composites with a weight ratio of ferrite/polymer being 3:20 have a maximum reflection loss of –16 dB and wide absorbing band. Thus, the Mn–Zn ferrite is the potential candidate in electromagnetic absorbing application in the low frequency range (10 MHz–1 GHz).

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Size-dependent thermal stresses in the core–shell nanoparticles

Astefanoaei I, Dumitru I, Stancu Al

Chin. Phys. B, 2013, 22 (12): 128102 doi: 10.1088/1674-1056/22/12/128102
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The thermal stress in a magnetic core–shell nanoparticle during a thermal process is an important parameter to be known and controlled in the magnetization process of the core–shell system. In this paper we analyze the stress that appears in a core–shell nanoparticle subjected to a cooling process. The external surface temperature of the system, considered in equilibrium at room temperature, is instantly reduced to a target temperature. The thermal evolution of the system in time and the induced stress are studied using an analytical model based on a time-dependent heat conduction equation and a differential displacement equation in the formalism of elastic displacements. The source of internal stress is the difference in contraction between core and shell materials due to the temperature change. The thermal stress decreases in time and is minimized when the system reaches the thermal equilibrium. The radial and azimuthal stress components depend on system geometry, material properties, and initial and final temperatures. The magnitude of the stress changes the magnetic state of the core–shell system. For some materials, the values of the thermal stresses are larger than their specific elastic limits and the materials begin to deform plastically in the cooling process. The presence of the induced anisotropy due to the plastic deformation modifies the magnetic domain structure and the magnetic behavior of the system.

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Theoretical prediction of the optimal conditions for observing the stereodynamical vector properties of the C(³P)+OH (X²∏)→CO(X¹S⁺)+H(²S) reaction

Wang Yuan-Peng, Zhao Mei-Yu, Yao Shun-Huai, Song Peng, Ma Feng-Cai

Chin. Phys. B, 2013, 22 (12): 128201 doi: 10.1088/1674-1056/22/12/128201
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[PDF 318 KB] (Downloads:339)

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The best optimal initial reactant state and collision energy for observing the stereodynamical vector properties of the title reaction in the ground electronic state X²A’ potential energy surface (PES)[Zanchet et al. 2006 J. Phys. Chem. A 110 12017] are theoretically predicted using the quasi-classical trajectory (QCT) method for the first time. The calculated results reveal that the smallest value of the rotational quantum number j, larger vibrational quantum number v, and the lower strength of collision energy should be selected for offering the most obvious picture about the stereodynamical vector properties. Polarization-dependent differential cross sections and the angular momentum alignment distribution, P(θ_r) and P(Φ_r) in the center-of-mass frame, are obtained to gain an insight into the alignment and orientation of the product molecules. The rotational angular momentum vector j’ of CO is aligned to be perpendicular to reagent relative velocity k. The product polarizations align along the y axis, pointing to the positive direction of the y axis. A new method is developed to investigate massive reactions with various initial states and to further study the vector properties of the fundamental reactions in detail.

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Cubature Kalman filters：Derivation and extension

Zhang Xin-Chun, Guo Cheng-Jun

Chin. Phys. B, 2013, 22 (12): 128401 doi: 10.1088/1674-1056/22/12/128401
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This paper focuses on the cubature Kalman filters (CKFs) for the nonlinear dynamic systems with additive process and measurement noise. As is well known, the heart of the CKF is the third-degree spherical–radial cubature rule which makes it possible to compute the integrals encountered in nonlinear filtering problems. However, the rule not only requires computing the integration over an n-dimensional spherical region, but also combines the spherical cubature rule with the radial rule, thereby making it difficult to construct higher-degree CKFs. Moreover, the cubature formula used to construct the CKF has some drawbacks in computation. To address these issues, we present a more general class of the CKFs, which completely abandons the spherical–radial cubature rule. It can be shown that the conventional CKF is a special case of the proposed algorithm. The paper also includes a fifth-degree extension of the CKF. Two target tracking problems are used to verify the proposed algorithm. The results of both experiments demonstrate that the higher-degree CKF outperforms the conventional nonlinear filters in terms of accuracy.

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Effects of NPB anode buffer layer on charge collection in ZnO/MEH-PPV hybrid solar cells

Gong Wei, Xu Zheng, Zhao Su-Ling, Liu Xiao-Dong, Fan Xing, Yang Qian-Qian, Kong Chao

Chin. Phys. B, 2013, 22 (12): 128402 doi: 10.1088/1674-1056/22/12/128402
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[PDF 451 KB] (Downloads:522)

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We investigate the effects of (N,N’-diphenyl)-N,N’-bis(1-naphthyl)-1,1’-biphenyl-4,4’-diamine (NPB) buffer layers on charge collection in inverted ZnO/MEH-PPV hybrid devices. The insertion of a 3-nm NPB thin layer enhances the efficiency of charge collection by improving charge transport and reducing the interface energy barrier, resulting in better device performances. S-shaped light J–V curve appears when the thickness of the NPB layer reaches 25 nm, which is induced by the inefficient charge extraction from MEH-PPV to Ag. Capacitance–voltage measurements are performed to further investigate the influence of the NPB layer on charge collection from both simulations and experiments.

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Alternating-current losses in two-layer superconducting cables consisting of second-generation superconductors coated by U-shaped ferromagnetic materials

Ahmet Cicek, Fedai Inanir, Fedor Gömöry

Chin. Phys. B, 2013, 22 (12): 128403 doi: 10.1088/1674-1056/22/12/128403
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[PDF 853 KB] (Downloads:278)

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Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.

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Multichannel fetal magnetocardiography using SQUID bootstrap circuit Suggested by editors

Zhang Shu-Lin, Zhang Guo-Feng, Wang Yong-Liang, Liu Ming, Li Hua, Qiu Yang, Zeng Jia, Kong Xiang-Yan, Xie Xiao-Ming

Chin. Phys. B, 2013, 22 (12): 128501 doi: 10.1088/1674-1056/22/12/128501
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[PDF 486 KB] (Downloads:557)

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Fetal magnetocardiography (MCG) is a sophisticated non-invasive technique for the fetal heart diagnosis. We constructed a multichannel fetal MCG system based on a novel superconducting quantum interference device (SQUID) direct readout scheme called SQUID bootstrap circuit (SBC). The system incorporates four SBC gradiometers for the signal detection and three SBC magnetometers as the references. The fetal MCG signal at a 28-weeks’ gestation was measured. By the fetal MCG signal separation and average, the P-wave and QRS complex can be clearly identified. These results indicate that the SBC is one of the most promising techniques for the fetal MCG recordings.

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Improvement in electroluminescence performance of n-ZnO/Ga₂O₃/p-GaN heterojunction light-emitting diodes

Zhang Li-Chun, Zhao Feng-Zhou, Wang Fei-Fei, Li Qing-Shan

Chin. Phys. B, 2013, 22 (12): 128502 doi: 10.1088/1674-1056/22/12/128502
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[PDF 487 KB] (Downloads:1023)

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n-ZnO/p-GaN heterojunction light-emitting diodes with and without a Ga₂O₃ interlayer are fabricated. The electroluminescence (EL) spectrum of the n-ZnO/p-GaN displays a single blue emission at 430 nm originating from GaN, while the n-ZnO/Ga₂O₃/p-GaN exhibits a broad emission peak from ultraviolet to visible. The broadened EL spectra of n-ZnO/Ga₂O₃/p-GaN are probably ascribed to the radiative recombination in both the p-GaN and n-ZnO, due to the larger electron barrier (ΔE_C=1.85 eV) at n-ZnO/Ga₂O₃ interface and the much smaller hole barrier (ΔE_V=0.20 eV) at Ga₂O₃/p-GaN interface.

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0.15-μm T-gate In_0.52Al_0.48As/In_0.53Ga_0.47As InP-based HEMT with f_max of 390 GHz

Zhong Ying-Hui, Zhang Yu-Ming, Zhang Yi-Men, Wang Xian-Tai, Lü Hong-Liang, Liu Xin-Yu, Jin Zhi

Chin. Phys. B, 2013, 22 (12): 128503 doi: 10.1088/1674-1056/22/12/128503
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[PDF 1012 KB] (Downloads:414)

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In this paper, 0.15-μm gate-length In_0.52Al_0.48As/In_0.53Ga_0.47As InP-based high electron mobility transistors (HEMTs) each with a gate-width of 2×50 μm are designed and fabricated. Their excellent DC and RF characterizations are demonstrated. Their full channel currents and extrinsic maximum transconductance (g_m,max) values are measured to be 681 mA/mm and 952 mS/mm, respectively. The off-state gate-to-drain breakdown voltage (BV_GD) defined at a gate current of-1 mA/mm is 2.85 V. Additionally, a current-gain cut-off frequency (f_T) of 164 GHz and a maximum oscillation frequency (f_max) of 390 GHz are successfully obtained; moreover, the f_max of our device is one of the highest values in the reported 0.15-μm gate-length lattice-matched InP-based HEMTs operating in a millimeter wave frequency range. The high g_m,max, BV_GD, f_max, and channel current collectively make this device a good candidate for high frequency power applications.

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Open critical area model and extraction algorithm based on the net flow-axis

Wang Le, Wang Jun-Ping, Gao Yan-Hong, Xu Dan, Li Bo-Bo, Liu Shi-Gang

Chin. Phys. B, 2013, 22 (12): 128504 doi: 10.1088/1674-1056/22/12/128504
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[PDF 588 KB] (Downloads:374)

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In the integrated circuit manufacturing process, the critical area extraction is a bottleneck to the layout optimization and the integrated circuit yield estimation. In this paper, we study the problem that the missing material defects may result in the open circuit fault. Combining the mathematical morphology theory, we present a new computation model and a novel extraction algorithm for the open critical area based on the net flow-axis. Firstly, we find the net flow-axis for different nets. Then, the net flow-edges based on the net flow-axis are obtained. Finally, we can extract the open critical area by the mathematical morphology. Compared with the existing methods, the nets need not to divide into the horizontal nets and the vertical nets, and the experimental results show that our model and algorithm can accurately extract the size of the open critical area and obtain the location information of the open circuit critical area.

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Organic photovoltaic cells with copper (Ⅱ) tetra-methyl substituted phthalocyanine

Xu Zong-Xiang, Roy V. A. L.

Chin. Phys. B, 2013, 22 (12): 128505 doi: 10.1088/1674-1056/22/12/128505
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[PDF 308 KB] (Downloads:490)

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Efficient heterojunction organic photovoltaic (OPV) cells are fabricated based on copper tetra-methyl phthalocyanine (CuMePc) as donor and fullerene (C₆₀) as acceptor. The power conversion efficiency of CuMePc/C₆₀ OPV cell (2.52%) is increased by 88% compared with that of the non-peripheral substituted copper phthalocyanine (CuPc)/C₆₀ OPV cell (1.34%). The introduction of methyl substituent leads to stronger π–π interaction of CuMePc (～ 3.5 Å) than that of CuPc (～ 3.8 Å). The efficiency improvement is attributed to the enhanced carrier mobility of CuMePc thin film (1.1×10^-3 cm²/V·s) and better film morphology by introducing methyl groups into the periphery of CuPc molecule.

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Flexible white top-emitting organic light-emitting diode with a MoO_x roughness improvement layer

Chen Shu-Fen, Guo Xu, Wu Qiang, Zhao Xiao-Fei, Shao Ming, Huang Wei

Chin. Phys. B, 2013, 22 (12): 128506 doi: 10.1088/1674-1056/22/12/128506
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[PDF 1668 KB] (Downloads:474)

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In this paper, an MoO_x film is deposited on a polyethylene terephthalate (PET) substrate as a buffer layer to improve the surface roughness of the flexible PET substrate. With an optimized MoO_x thickness of 100 nm, the surface roughness of the PET substrate can be reduced to a very small value of 0.273 nm (much less than 0.585 nm of the pure PET). Flexible white top-emitting organic light-emitting diodes (TEOLEDs) with red and blue dual phosphorescent emitting layers are constructed based on a low-reflectivity Sm/Ag semi-transparent cathode. The flexible white emission exhibits the best luminance and current injection characteristics with the 100-nm-thick MoO_x buffer layer and this result indicates that a smooth substrate is beneficial to the enhancement of device electrical and electroluminescence performances. However, the white TEOLED with a 50-nm-thick MoO_x buffer layer exhibits a maximum current efficiency of 4.64 cd/A and a power efficiency of 1.9 lm/W, slightly higher than those with a 100-nm MoO_x buffer layer, which is mainly due to an obvious intensity enhancement but limited current increases in 50-nm MoO_x-based white TEOLED. The change amplitudes of the Commission International de l’Eclairage (CIE) chromaticity coordinates are less than (0.016, 0.005) for all devices in a wide luminance range over 100 cd/m², indicating an excellent color stability in our white flexible TEOLEDs. Additionally, the flexible white TEOLED with an MoO_x buffer layer shows excellent flexibility to withstand more than 500 bending times under a curvature radius of approximately 9 mm. Research demonstrates that it is mainly attributed to the high surface energy of the MoO_x buffer layer, which is conducible to the improvement of the surface adhesion to the PET substrate and the Ag anode.

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Symmetrical adhesion of two cylindrical colloids to a tubular membrane Suggested by editors

Niu Yu-Quan, Wei Wei, Zheng Bin, Zhang Cai-Xia, Meng Qing-Tian

Chin. Phys. B, 2013, 22 (12): 128701 doi: 10.1088/1674-1056/22/12/128701
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[PDF 471 KB] (Downloads:290)

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With the full treatment of the Helfrich model we theoretically study the symmetrical adhesion of two cylindrical colloids to a tubular membrane. The adhesion of the rigid cylinders with different radius from the membrane tube surface can produce both shallow wrapping with relatively small wrapping angle and deep wrapping with big wrapping angle. These significant structural behaviors can be obtained by analyzing the system energy. A second order adhesion transition from the desorbed to weakly adhered states is found, and a first order phase transition where the cylindrical colloids undergo an abrupt transition from weakly adhered to strongly adhered states can be obtained as well.

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Species diversity in rock–paper–scissors game coupling with Levy flight Suggested by editors

Wang Dong, Zhuang Qian, Fan Ying, Di Zeng-Ru

Chin. Phys. B, 2013, 22 (12): 128702 doi: 10.1088/1674-1056/22/12/128702
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[PDF 587 KB] (Downloads:365)

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The rock–paper–scissors (RPS) game is a nice model to study the biodiversity in an ecosystem. However, in the previous studies only the nearest-neighbor interaction among the species was considered. In this paper, taking the long-range migration into account, the effects of the interplay between nearest-neighbor-interaction and long-range-interaction given by Levy flight with distance distribution l^h (-3 ≤ h <-1) in the spatial RPS game are investigated. Taking the probability, exchange rate, and power-law exponent of Levy flight as parameters, the coexistence conditions of three species are given. The critical curves for stable coexistence of three species in the parameter space are presented. It is also found that Levy flight has interesting effects on the final spatiotemporal pattern of the system. The results reveal that the long-range-interaction given by Levy flight exhibits pronounced effects on biodiversity of the ecosystem.

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Stochastic bounded consensus tracking of leader-follower multi-agent systems with measurement noises based on sampled data with general sampling delay

Wu Zhi-Hai, Peng Li, Xie Lin-Bo, Wen Ji-Wei

Chin. Phys. B, 2013, 22 (12): 128901 doi: 10.1088/1674-1056/22/12/128901
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[PDF 357 KB] (Downloads:519)

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In this paper we provide a unified framework for consensus tracking of leader-follower multi-agent systems with measurement noises based on sampled data with a general sampling delay. First, a stochastic bounded consensus tracking protocol based on sampled data with a general sampling delay is presented by employing the delay decomposition technique. Then, necessary and sufficient conditions are derived for guaranteeing leader-follower multi-agent systems with measurement noises and a time-varying reference state to achieve mean square bounded consensus tracking. The obtained results cover no sampling delay, a small sampling delay and a large sampling delay as three special cases. Last, simulations are provided to demonstrate the effectiveness of the theoretical results.

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Ground-based remote sensing of atmospheric total column CO₂ and CH₄ by direct sunlight in Hefei Suggested by editors

Cheng Si-Yang, Xu Liang, Gao Min-Guang, Li Sheng, Jin Ling, Tong Jing-Jing, Wei Xiu-Li, Liu Jian-Guo, Liu Wen-Qing

Chin. Phys. B, 2013, 22 (12): 129201 doi: 10.1088/1674-1056/22/12/129201
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[PDF 1660 KB] (Downloads:348)

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Fourier transform spectrometry has played an important role in the three-dimensional greenhouse gas monitoring as the focus of attention on global warming in the past few years. In this paper, a ground-based low-resolution remote sensing system measuring the total columns of CO₂ and CH₄ is developed, which tracks the sun automatically and records the spectra in real-time and has the advantages of portability and low cost. A spectral inversion algorithm based on nonlinear least squares spectral fitting procedure for determining the column concentrations of these species is described. Atmospheric transmittance spectra are computed line-by-line in the forward model and observed on-line by direct solar radiation. Also, the wavelength shifts are introduced and the influence of spectral resolution is discussed. Based on this system and algorithm, the vertical columns of O₂, CO₂, and CH₄ are calculated from total atmospheric observation transmittance spectra in Hefei, and the results show that the column averaged dry-air mole fractions of CO₂ and CH₄ are measured with accuracies of 3.7% and 5%, respectively. Finally, the H₂O columns are compared with the results observed by solar radiometer at the same site and the calculated correlation coefficient is 0.92, which proves that this system is suitable for field campaigns and used to monitor the local greenhouse gas sources under the condition of higher accuracy, indirectly.

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Analysis of stable components in the extended-range forecast for the coming 10–30 days in winter 2010 and 2011

Wang Kuo, Feng Guo-Lin, Zeng Yu-Xing, Wang Xu-Jia

Chin. Phys. B, 2013, 22 (12): 129202 doi: 10.1088/1674-1056/22/12/129202
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[PDF 2581 KB] (Downloads:435)

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In this paper we try to extract stable components in the extended-range forecast for the coming 10–30 days by using empirical orthogonal function (EOF) analysis, similarity coefficient, and some other methods based on the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis daily data. The comparisons of the coefficient of variance of climatological background field and truth data in winter between 2010 and 2011 are made. The method of extracting stable components and climatological background field can be helpful to increase forecasting skill. The forecasting skill improvement of air temperature is better than geopotential height at 500 hPa. Moreover, this method improves the predictability better in the Pacific Ocean. In China, the forecast in winter in Northeast China is more uncertain than in the other parts.

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Modulational instability of optically induced nematicon propagation

L. Kavitha, M. Venkatesh, S. Dhamayanthi, D. Gopi

Chin. Phys. B, 2013, 22 (12): 129401 doi: 10.1088/1674-1056/22/12/129401
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[PDF 3995 KB] (Downloads:537)

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We report the modulational instability (MI) analysis for the modulation equations governing the propagation of coherent polarized light through a nematic liquid crystal (NLC) slab, in the limit of low light intensity and local material response. The linear stability analysis of the nonlinear plane wave solutions is performed by considering both the wave vectors (k,l) of the basic states and wave vectors (K,L) of the perturbations as free parameters. We compute the MI gain, and the MI gain peak is reduced and the stable bandwidth is widened with the increase of the strength of the applied electric field. Further, we invoke the extended homogeneous balance method and Exp-function method aided with symbolic computation and obtain a series of periodic solitonic humps of nematicon profiles admitting the propagation of laser light in the NLC medium.

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Transcription’s bubble under the influence of long-range interactions and helicoidal coupling

Mirabeau Saha, Timoléon C. Kofané

Chin. Phys. B, 2013, 22 (12): 129402 doi: 10.1088/1674-1056/22/12/129402
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[PDF 965 KB] (Downloads:426)

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The influence of power-low long-range interactions (LRI) and helicoidal coupling (HC) on the properties of localized solitons in a DNA molecule when a ribonucleic acid polymerase (RNAP) binds to it at the physiological temperature is analytically and numerically investigated in this paper. We have made an analogy with the Heisenberg model Hamiltonian of an anisotropic spin ladder with ferromagnetic legs and anti-ferromagnetic rung coupling. When we limit ourselves to the second-order terms in the Taylor expansion, the DNA dynamics is found to be governed by a completely integrable nonlinear Schrödinger (NLS) equation. In this case, results show that increasing the value of HC force or LRI parameter enhances the bubble height and reduces the number of base pairs which form the bubble. For the fourth-order terms in a Taylor expansion, results are closely resembling those of second-order terms, and are confirmed by numerical investigation. These results match with some experimental data and thus provide a better representation of the base pairs opening in DNA which is essential for the transcription process.

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Electron capture rates for iron group nuclei at the surface of magnetar Suggested by editors

Luo Xia, Du Jun, Li Ping-Ping

Chin. Phys. B, 2013, 22 (12): 129701 doi: 10.1088/1674-1056/22/12/129701
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[PDF 231 KB] (Downloads:284)

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Effects of an ultra-strong magnetic field on electron capture rates for ⁵⁵Co are analyzed in the nuclear shell model and under the Landau energy levels quantized approximation in the ultra-strong magnetic field, and the electron capture rates on 10 abundant iron group nuclei at the surface of a magnetar are given. The results show that electron capture rates on ⁵⁵Co are increased greatly in the ultra-strong magnetic field, by about 3 orders of magnitude generally. These conclusions play an important role in future study of the evolution of magnetars.