Vol. 61, No. 22 (2012)

On the recharge-discharge oscillator model for El Niño-Southern Oscillation (ENSO)
Zhao Qiang, Liu Shi-Kuo, Liu Shi-Da
2012, 61 (22): 220201. doi: 10.7498/aps.61.220201
Abstract +
A kind of recharge-discharge oscillator model for the El Niño-Southern Oscillation (ENSO) is considered. By transforming the ENSO model into the van der Pol equation and analyzing its properties qualitatively, we proved that the ENSO recharge-discharge oscillator model possesses a stable limit cycle.
Group consensus analysis of multi-agent systems with delays
Ji Liang-Hao, Liao Xiao-Feng, Liu Qun
2012, 61 (22): 220202. doi: 10.7498/aps.61.220202
Abstract +
In this paper, a new consensus problem is investigated which is group consensus. It contains such consensus problem as a special case that all agents in a network reach a consistent value asymptotically. Consider a dynamic multi-agent system with connected undirected or connected bipartite graph topology and delays, two novel consensus protocols are introduced to solve the group consensus problem. The convergence analysis is discussed and the sufficient condition for system group convergence is obtained based on the frequency-domain analysis and generalized Nyquist criterion, respectively. And we know that the condition of group convergence is only depended on system's time delay and the adjacent weight between the agents, meanwhile, delay can affect the dynamic characteristics of the system. Finally, simulations are provided to demonstrate the effectiveness of our theoretical results.
Bifurcation analysis for a delayed sea-air oscillator coupling model for the ENSO
Xu Chang-Jin
2012, 61 (22): 220203. doi: 10.7498/aps.61.220203
Abstract +
In this paper, a delayed sea-air oscillator coupling model for the ENSO is investigated. We obtain the sufficient condition of stability in equilibrium. By choosing delay η as a bifurcation parameter, we show that Hopf bifurcation can occur when delay η passes through a sequence of critical values. Meanwhile, based on the center manifold theory and the normal form approach, we derive the formula for determining the properties of Hopf bifurcating periodic orbit, such as the direction of Hopf bifurcation, the stability of Hopf bifurcating periodic solution and the periodic of Hopf bifurcating periodic solution. Finally, numerical simulations are carried out to illustrate the analytical results.
Generation of correlated pseudorandom variables in Monte Carlo simulation
Wen De-Zhi, Zhuo Ren-Hong, Ding Da-Jie, Zheng Hui, Cheng Jing, Li Zheng-Hong
2012, 61 (22): 220204. doi: 10.7498/aps.61.220204
Abstract +
Correlated pseudorandom variables with prescribed marginal distribution functions sometimes are required in simulation such as in Monte Carlo studies. In this paper, we present a general procedure and a simple but effective numerical approach to generating correlated random variables sampling sequence with prescribed marginal probability distribution functions and correlation coefficient matrix based on linear transformation-nonlinear transformation with Choesky factor. Some simulation results are reported. Simulation results show that the collections of random numbers generated by the presented procedure have desired correlations and pass the Kolmogorov-Smirnov non-parametric hypothesis test of specified marginal distribution. Some restrictions on the application of this method are discussed.
The mechanism of energy input to bistable system to generate stochastic resonance
Lin Min, Huang Yong-Mei
2012, 61 (22): 220205. doi: 10.7498/aps.61.220205
Abstract +
According to the Langevin equation that describes the Brownian particle motion, the instantaneous power and average power of Brownian particle provided by periodic external force are analyzed. The mechanism of energy input to a bistable system to generate stochastic resonance is revealed. The theoretical analysis and numerical simulation manifest that the instantaneous power absorbed by Brownian particle changes periodically. The change frequency is twice that of periodical external force, and its amplitude and average are controlled by the noise intensity. The energy input form of periodic external force can be controlled effectively by changing the parameters of thermal environment where Brownian particle is located.
Analysis of lasing in gain medium based on four-energy level atomic model
Sun Bing-Bing, Wu Bo, Wang Hui, Huang Zhi-Xiang, Wu Xian-Liang
2012, 61 (22): 220206. doi: 10.7498/aps.61.220206
Abstract +
With the present interest in metamaterial, gain medium shows promise for complex system due to their amplification effect and wide potential application area. In this paper we present a model that simulates lasing in gain medium by using a model of four-energy level atomic system based on the finite-difference time-domain method.Meanwhile we propose a new pump mechanism, i.e., Gaussian Pump. It is found that results of the spectra, lasing threshold and population dynamics of the new pump mechanism are in good agreement with theoretical results. The results can also provide reference for caculating more complex metamaterial system.
Two-dimensional quantum spectra and classical orbits of isosceles- right triangular billiards
Liu Xiang-Long, Zhu Man-Zuo, Lu Lu
2012, 61 (22): 220301. doi: 10.7498/aps.61.220301
Abstract +
The quantum spectra are derived from the wave-functions and the energy-functions of the isosceles-right triangular model. Although the eigenstates of the billiard system are not separable, the problem of functions with two variables is exactly solvable. The numerical results of the Fourier transform of quantum spectral functions are compared with the results from the classical orbits whose lengths match well with the positions of the spectra peaks. This result gives a new evident for the correspondence of quantum and classical mechanics.
Berry phase and quantum phase transition in spin chain system with three-site interaction
Shan Chuan-Jia
2012, 61 (22): 220302. doi: 10.7498/aps.61.220302
Abstract +
In this paper, we diagonalize the Hamiltonian of the one-dimensional spin chain system with three-body interaction. Then we solve geometric phase of ground state in the system through a rotating operation. By the numerical calculation of the geometric phase and its derivative, we consider the three-body interaction effects on the geometric phase and quantum phase transition, the results show that the geometric phase can be well used to characterize quantum phase transition in this system, and find that three-body interaction not only can move the criticality region, but also can generate a new critical point.
Routing protocol for wireless ad hoc quantum communication network based on quantum teleportation
Yu Xu-Tao, Xu Jin, Zhang Zai-Chen
2012, 61 (22): 220303. doi: 10.7498/aps.61.220303
Abstract +
A concept of wireless ad hoc quantum communication network is proposed and a routing protocol is designed for wireless quantum communicaiton network with complex structure. The routing protocol is on-demand and the routing metric is based on the number of entangled particle pairs. The node that wants to send information carried by quantum state can initiate a route request and establishment procedure. The destination node chooses path by the routing metric and sends route reply message along the selected path. During the information transmission, if the quantum channel or the wirless channel between any neighbors in the selected path is broken, a route discovery process is reinitiated to set up a new route. Nodes in the selected path use a both-end approximation algorithm to establish a quantum channel. After the quantum channel is established, the quantum state is transferred by quantum teleportation and the information transfer between any two nodes in wireless ad hoc quantum communication network is finished.
Determing the entanglement of quantum nonbinary graph states
Xu Jian, Chen Xiao-Yu, Li Hai-Tao
2012, 61 (22): 220304. doi: 10.7498/aps.61.220304
Abstract +
Graph states are multipartite entangled states that correspond to mathematical graphs, where the vertices of the graph now play the role of quantum multilevel systems and edges represent interactions of the systems. Graph states are the basis of quantum error correction and one-way quantum computer. We systematically study the entanglement of non-binary graph states. Using iterative algorithm and entanglement bounds, we calculate the entanglement of all the ternary graph states up to nine vertices and parts of quaternary and quinary graph states modulo local unitary transformations and graph isomorphisms. The entanglement measure can be the geometric measure, the measure of relative entropy of entanglement or the measure of logarithmic robustness. We classify the graph states according to the entanglement values obtained. The closest product states obtained in the calculations are studied.
Many-body quantum fluctuation effects of Rosen-Zener transition in Bose-Einstein condensates
Wang Jian-Zhong, Cao Hui, Dou Fu-Quan
2012, 61 (22): 220305. doi: 10.7498/aps.61.220305
Abstract +
We investigate many-body quantum fluctuation effects of Rosen-Zener transition of Bose-Einstein condensate (BEC) in a symmetric double-well potential through the relation between the average population imbalance of the final state (APIFS) and scanning period. In the linear case, we deduce the analytical expression of the APIFS which has the same behavior as in the mean-field level. We also employ numerical calculation to demonstrate it. In the nonlinear case, numerical results show that the APIFS in the sudden limit also accords with that in the mean-field level whereas in the adiabatic limit the many-body result is quite different from that of the mean-field case: the behavior of APIFS with respect to scanning period is similar to sinusoidal rather than rectangular oscillation, besides the oscillation period increases with both the total number N and the nonlinear parameter c increasing.


Evolution of interference patterns of strongly interacting Fermi gases in a harmonic trap
Wen Wen, Li Hui-Jun, Chen Bing-Yan
2012, 61 (22): 220306. doi: 10.7498/aps.61.220306
Abstract +
We study the evolution of the interference patterns of strongly interacting Fermi gases in a harmonic trap after removal of the optical lattice, by numerically solving the superfluid order-parameter equation. We find that for the strongly interacting Fermi gas elastic collisions during the expansion blur the interference peaks. In order to obtain a nearly ballistic expansion, the fast magnetic field ramp technique is applied in experiment. We simulate the fast magnetic field ramp process before expansions of strongly interacting Fermi gases. We find that clear interference patterns are formed, and oscillate for a long time in the harmonic trap. We also calculate the interference patterns in different superfluid regimes, which accord with the experimental observations.
Ground state phase diagram of the quantum spin 1 Blume-Capel model: reduced density fidelity study
Zhao Jian-Hui
2012, 61 (22): 220501. doi: 10.7498/aps.61.220501
Abstract +
The reduced density fidelity is a measure of distance between two reduced density matrix, which can be used to characterize quantum phase transitions in quantum many-body systems. In this paper, we use the multi-scale entanglement reorganization ansatz (MERA) algorithm to simulate the spin 1 quantum Blume-Capel model and determine its ground-state phase diagram through calculating the reduced density fidelity. The qualitative relevant information contained in one site reduced density matrix is different from that contained two-site reduced density matrix, which can be detected by using the reduced density fidelity. In addition, we also characterize quantum phase transitions in quantum many-body systems by using the local parameters and energy gaps.
Dynamics of current controlled switching converters under wide circuit parameter variation
Bao Bo-Cheng, Yang Ping, Ma Zheng-Hua, Zhang Xi
2012, 61 (22): 220502. doi: 10.7498/aps.61.220502
Abstract +
With current-controlled buck-boost converter used as an example, through a detailed description of the switch state of the switching converter under wide circuit parameter variation, such as input voltage and load resistance variation, two inductor current borders in the current controlled switching converter are derived and an accurate discrete-time model is established. The validation of the discrete-time model is verified by a piecewise-linear model. Based on the discrete-time model, the complex dynamical behaviors existing in switching converter, such as period-double bifurcation, border-collision bifurcation, robust chaos and intermittent chaos, etc., are revealed. By formulating the Jacobian, the maximum Lyapunov exponent and the movement trajectories of eigvalues with the variations of circuit parameters are obtained. By utilizing the parameter-space maps, the operation-state regions corresponding to circuit parameter regions are estimated. Finally, an experimental setup is implemented, the corresponding observation results are consistent with those of theory analyses. In this paper the dynamics theory in switching converters is investigated systematically; the analysis methods and research results are helpful for designing and controlling switching converters.
Effects of nonlinearity on quantum resonance ratchet
Zhao Wen-Lei, Dou Fu-Quan, Wang Jian-Zhong
2012, 61 (22): 220503. doi: 10.7498/aps.61.220503
Abstract +
We investigate the effect of the nonlinear interaction on the quantum resonance ratchet for the periodically kicked Bose-Einstein condensate that is realized on a ring. In the noninteracting case, the wave packet spreads asymmetrically in momentum space, leading to a directed current. We show that for the weak nonlinear interaction, the probability density distribution in momentum space has two peaks which linearly shift to ward positive and negative momentum, respectively. The force periodically acting on each peak is a constant with time evolution. The competition between the motions of the two parts of cold atoms leads to the reduce or the revival of the momentum current. For the strong nonlinearity, the momentum distribution has only one peak which does not shift with time. The force on this peak is almost zero with time evolution, thus the directed current varnishes.
Active adaptive fuzzy integral sliding mode control for unified chaotic system with uncertainties and disturbance
Lu Yong-Kun
2012, 61 (22): 220504. doi: 10.7498/aps.61.220504
Abstract +
An active adaptive fuzzy integral sliding mode controller is proposed for a unified chaotic system with parametric uncertainties under external perturbation. An improved control method is designed to guarantee the stability, while maintaining the transient performances of the original nonlinear integral sliding mode control. The proposed method reduces the effects of both the uncontrollable state of unified chaotic system and approximation error of adaptive fuzzy compensator on system state error. The stability of the controller is analyzed by Lyapunov stability theorem. The simulation results show that the system states can be controlled to target points with parametric uncertainties under external perturbation. The effectiveness of this method is illustrated by the numerical simulation.
Synchronization of fractional order hyperchaotic Chen system based on PIα control
Chen Zhi-Wang, Wang Jing, Pang Shuang-Jie
2012, 61 (22): 220505. doi: 10.7498/aps.61.220505
Abstract +
In this paper, a kind of PIα controller is designed for the synchronization of fractional order hyperchaotic Chen system. The controller is designed according to the fractional order hyperchaotic Chen system. The stability of the system is proved by the improved double parameter Mittag-Leffler function estimate theorem and the extended Gronwall lemma. Furthermore, the condition of controller parameters is pointed out which makes the fractional order hyperchaotic Chen system synchronous. Numerical simulations are presented to verify the effectiveness of the method.
Parameter determination based on composite evolutionary algorithm for reconstructing phase-space in chaos time series
Zhang Wen-Zhuan, Long Wen, Jiao Jian-Jun
2012, 61 (22): 220506. doi: 10.7498/aps.61.220506
Abstract +
To improve the prediction accuracy of the chaotic time series prediction model, a composite optimization method of the differential evolution (DE) algorithm that is based on the phase space reconstruction and least square supported vector machine (LSSVM), is proposed. The phase space parameters and LSSVM model parameters are taken as differential evolution algorithm individuals while the prediction accuracy of the chaotic time series is used as the evaluation function of DE algorithm. The optimal parameters are obtained by mutation, crossover, and selection operators of DE algorithm. Several numerical simulation results show that not only four parameters are determined at the same time, but also the performance of chaotic time series prediction is improved.
Multi-scale strategy and data surrogating test: two elements for the detection of time irreversibility in heart rate variability
Hou Feng-Zhen, Huang Xiao-Lin, Zhuang Jian-Jun, Huo Cheng-Yu, Ning Xin-Bao
2012, 61 (22): 220507. doi: 10.7498/aps.61.220507
Abstract +
Based on the method of multi-scale space (Pm, Gm) and data surrogating test, time-irreversibility analysis is applied to the heart rate variabilities (HRVs) from different crowds and different states, awake and asleep respectively, of healthy youths. The results show that i) the HRVs of healthy crowed have irreversible dynamics prevailingly, while the irreversibility decreases but does not disappear with aging or heart disease appearing. For example, most (more than 75%) of the congestive heart failure (CHF) patients still have irreversible dynamics; ii) for HRVs of healthy crowd, irreversible dynamics presents the daytime/nighttime rhythms and their significant difference between in daytime and in nighttime. And a stronger irreversibility is detected in nighttime. HRV is generated by the cardiac dynamic system, in which regulations usually perform via multiple feedback loops with different delays. Therefore, in order to arrive at a reliable conclusion, multi-scale strategy and data surrogating test are suggested to serve as the two elements for the detection of time irreversibility in HRV. The proposed method combines these two elements and reaches a conclusion consistent with the conclusions in previous reports.
Chaos synchronization between complex networks with uncertain structures and unknown parameters
Zhang Meng, Lü Ling, Lü Na, Fan Xin
2012, 61 (22): 220508. doi: 10.7498/aps.61.220508
Abstract +
Chaos synchronization between complex networks with uncertain structures and unknown parameters is investigated. By designing appropriate control inputs, we achieve the synchronization between two complex networks. The unknown parameters of nodes at two networks and the coupling strength between the nodes are identified simultaneously in the process of synchronization. The CO2 laser equation with modulation loss is taken for example to simulate experiment. It is found that the synchronization performance between two networks is very stable.
Hybrid solutions of three functions to the (2+1)-dimensional sine-Gordon equation
Gao Mei-Ru, Chen Huai-Tang
2012, 61 (22): 220509. doi: 10.7498/aps.61.220509
Abstract +
Based on a constructed Wronskian form expansion method, a few new types of hybrid solutions to the (2+1)-dimensional sine-Gordon equation are obtained. These solutions are some various combinations of trigonometric functions, hyperbolic functions and Jacobi elliptic functions.
Study on the mean absolute growth of model error for chaos system
Yang Jin-Hui, Song Jun-Qiang
2012, 61 (22): 220510. doi: 10.7498/aps.61.220510
Abstract +
Mean absolute growth of model error which is used to describe the initial error growth for chaos system, is employed in this paper to investigate the model error growth, and some meaningful conclusions are drew from it. It is found that the mean absolute growth of model error is initially exponential with a growth rate which has no direct relationship with the largest Lyapunov exponent. Afterwards model error growth enters into a nonlinear phase with a decreasing growth rate, and finally reaches a saturation value. If the difference between the attractor of real system and that of the model system is very small, the model error saturation level is consistent with the initial error saturation level of real system. With these conclusions one can obtain the predictability limit of a model easily, which is meaningful for weather prediction models. Also the predictability limit of model can be used for model comparison. The exacter model has a higher predictability limit which is useful for new model development.
Extended Holme-Kim network model and synchronizability
Wang Dan, Jing Yuan-Wei, Hao Bin-Bin
2012, 61 (22): 220511. doi: 10.7498/aps.61.220511
Abstract +
The relations between two highly clustered scale-free network evolution mechanisms and synchronizability are studied in this paper. Firstly, we propose an extended Holme and Kim (EHK) model with adjustive clustering coefficients and power-law exponent based on the Holme and Kim (HK) model. Triad formation mechanism is extended among old nodes compared with the HK model. And the following shortages of HK modle are settled: there is no link evolution in old nodes and the numbers of links of a new node adding to network is fixed. Secondly, the effect of triad formation on synchronizability in an unweighted network is investigated. Finally, simulation results show that the triad formation mechanism can weaken the synchronizability of both types of networks.
A novel free-space method of mearsuring of electromagnetic parameters based on the resonance property of reflectivity
Ding Shi-Jing, Huang Liu-Hong, Li Yue-Bo, Xue Fan-Xi
2012, 61 (22): 220601. doi: 10.7498/aps.61.220601
Abstract +
The free-space method is a analysis method applicable for measuring electromagnetic parameters of materials, owing to its non-contact and non-destructibility. Base on the resonance property of reflectivity under sweep frequency mode, a novel free-space method is presented. For the study of constructive interference or destructive interference, the method is used to measure the real component of complex dielectric constant through the thickness of material and the interference frequency. The method can also measure the imaginary component of complex dielectric content by the positions of peaks and valleys of waveform or/and their correlation. The study also demonstrates the higher precision obtained by using the valley-to-valley ratio than by using the standing waveform ratio (peak-to-valley ratio).
Error synthesis and statistical analysis on stepped mirror array by Monte Carlo method
Lü Jin-Guang, Liang Jing-Qiu, Liang Zhong-Zhu
2012, 61 (22): 220701. doi: 10.7498/aps.61.220701
Abstract +
To achieve the miniaturization and the static state of the Fourier transform spectrometer, two stepped mirror arrays are introduced into the time-modulation Fourier transform spectrometer to replace of the plane mirrors. The two stepped mirrors can sample the interferogram data in two-dimensional space, which can reduce the size of the instrument and increase the stability of the system. Due to the precision restriction on the stepped mirrors in the fabrication process, the various sub-mirrors of the stepped mirrors may contain various thickness errors and angle errors, which can affect the distribution of the interferogram and the quality of the spectrum. We regard the thickness error and the angle error of all the sub-mirrors as random variables, and synthesize all the error terms into a Fourier transform integration function using Monte Carlo method. By means of statistic analysis on the spectrum error factor, we can appraise the recovered spectrum affected by the thickness error and the angle error of the sub-mirror. The statistical result indicates that the statistical mean of the spectrum error factor increases with thickness standard deviation and angle standard deviation increasing. According to the statistical analysis on spectrum error factor, the tolerances of the thickness standard deviation and the angle standard deviation of the sub-mirror can be determined in the fabrication process of the stepped mirrors.
The total dose irradiation effects of SOI NMOS devices under different bias conditions
Zhuo Qing-Qing, Liu Hong-Xia, Yang Zhao-Nian, Cai Hui-Min, Hao Yue
2012, 61 (22): 220702. doi: 10.7498/aps.61.220702
Abstract +
Based on 0.8 μm process, in the paper we investigate the total dose irradiation effects of SOI NMOS devices under different bias conditions. The devices are exposed to 60Co γ ray at a dose rate of 50 rad (Si)/s. In higher gate bias condition, the drain leakage current increases because more positive charges are trapped in the buried oxide. When the applied gate voltage is larger than the threshold voltage, its drain current of the front gate in ID-VG characteristic suddenly increases and the body current presents a unique upside down bell shape.
Electrical and mechanical properties of a Cu-Cr-Zr alloy aged under an imposed DC current and static magnetic field
Rao Xian-Jun, Zhong Yun-Bo, Zhang Zeng-Guang, Wang Zhi-Qiang, Deng Kang, Ren Zhong-Ming, Xu Kuang-Di
2012, 61 (22): 221301. doi: 10.7498/aps.61.221301
Abstract +
In this paper, Cu-0.41wt.%Cr-0.21wt.%Zr alloy is subjected to an isochronal aging treatment with a DC electric current (100A/cm2) and a static magnetic field simultaneously imposed. The alloy in the form of plate with a thickness of 2 mm is solid-solution-treated and cold deformed with a total area reduction of more than 98% before aging. The results indicate that the conductivity and micro hardness of the sample are significantly improved by the imposed electric-magnetic field. The conductivity of the sample increases with magnetic flux density (MFD) improving, especially at a lower aging temperature (350 ℃), and a maximum improvement of 22.1% IACS in conductivity could be obtained with a 10 T magnetic field. For the property of micro hardness, it increases with MFD increasing at a lower aging temperature (350 ℃), while at a higher aging temperature, it first increases and then decreases with MFD increasing. The effects of the DC current and magnetic field on the microstructure of the alloy are investigated by transmission electron microscopy. A lower dislocation density and more Cr precipitation are observed under electric-magnetic couple field than under the DC current only. It indicates that the electric and magnetic fields enhance the aging process of Cu-Cr-Zr alloy distinctly. According to the experimental results, we believe that the main mechanism of the influence of electric and magnetic fields on the Cu-Cr-Zr alloy is that the magnetic field enhances the interaction between solute atoms, vacancies, dislocations and electron wind force, thereby intensifing the effect of the dc current.
First-principles study on W-S co-doped anatase titanium dioxide
Wu Guo-Hao, Zheng Shu-Kai, Liu Lei, Jia Chang-Jiang
2012, 61 (22): 223101. doi: 10.7498/aps.61.223101
Abstract +
The electronic structures and optical properties of pure anatase TiO2, W doped, S doped and W-S co-doped anatase TiO2 are calculated using the plane-wave ultra-soft pseudo-potential (PWPP) method based on the density functional theory. The results indicate that the lattice is distorted and the lattice constant is enlarged due to doping. The doping also introduces impurity energy levels into the forbidden band. For the S-doped TiO2, its forbidden band width decreases and the introduction of impurity energy levels result in the red shift of the absorption band edge, but for the W-doped and W-S co-doped anatase TiO2, their obviously increased forbidden band gaps result in the blue shifts of the absorption spectra.
Influences of isotopic variant and collision energy on the stereodynamics of the N(4S)+H2 reactive system
Xia Wen-Ze, Yu Yong-Jiang, Yang Chuang-Lu
2012, 61 (22): 223401. doi: 10.7498/aps.61.223401
Abstract +
The influences of isotopic variant and collision energy on the stereodynamics in the N(4S)+H2 reaction are investigated by using the quasi-classical trajectory method on the calculated DMBE potential energy surface. The angular distributions of P(r), P(r) and P(r, r), which reflect the vector correlation of k-j' and k-k'-j', differential cross sections,integral cross sections are calculated and discussed in detail. Moreover,the influences of collision energy variant in a collision energy range of 25-80~kcal/mol in the three reactions N+H2,N+D2 and N+T2 are also studied The results indicate that the stereodynamic properties of the reactions are influenced by intermolecular isotope and collision energies.
A new mini-magnetic lens proposal for coverging the clod atoms
Xu Xin-Ping, Zhang Hai-Chao, Wang Yu-Zhu
2012, 61 (22): 223701. doi: 10.7498/aps.61.223701
Abstract +
A mini-magnetic lens for laser-cooled rubidium atoms is experimentally demonstrated in this paper. The key component of the mini-magnetic lens is a mini-coil with a radius of 2 mm. When the cold atomic clouds are transported in the vicinity of the coil along its axial, they are compressed in the longitudinal direction due to the interaction with the non-uniform magnetic field of the coil. Given a current carrying time of about 10 ms, the atomic clouds tend to be gradually compressed in the axial direction with the increase of the coil current. When the coil current is greater than 0.9 A, the atomic clouds begin to expand. At a threshold value of 0.9 A, the focus length of the mini-magnetic lens is determined to be about 1.3 mm. Compared with the case that no current passes through the mini-coil, the dimension of the focused atom clouds is one order of magnitude smaller. Moreover, the focus length can be controlled by both the coil current and its carrying time. Numerical simulations are also given which are in agreement with the experimental results.
Generation of the three-dimensional array of optical trap by spatial light modulator
Xu Shu-Wu, Zhou Qiao-Qiao, Gu Song-Bo, Ji Xian-Ming, Yin Jian-Ping
2012, 61 (22): 223702. doi: 10.7498/aps.61.223702
Abstract +
In this paper, a new scheme of generating a three-dimensional array of optical trap is proposed by using a composite phase grating that is fabricated by liquid crystal spatial light modulator. The composite phase grating is formed by combining the circular grating, which is generated by transforming a one-dimensional rectangular grating into a circular grating that can produce the longitudinal array of optical trap, with a two-dimensional rectangular grating. The grating that generates 5× 5× 5 array of optical trap is simulated according to the technical parameters of the spatial light modulator. The output intensity distribution is calculated by using the Gaussian light wave with ordinary power as input light and focusing the diffracting light with lens. The results show that three-dimensional array of optical trap with a very high peak value of intensity and an intensity gradient is obtained around the focus of the lens. The optical dipole potential of trapping cold atoms achieves the order of mK, and the interaction force between the atom and the optical field is much greater than the atom gravity. When the high power laser is used as input light, the generated array of optical trap can also be employed to trap the cold molecules produced by Stark deceleration.
Simulation and design of a W-band extended interaction klystron amplifier
Wu Yang, Xu Zhou, Zhou Lin, Li Wen-Jun, Tang Chuan-Xiang
2012, 61 (22): 224101. doi: 10.7498/aps.61.224101
Abstract +
Extended interaction klystron amplifier is a very important high power millimeter wave source with many actual and potential applications. Based on the electromagnetic simulation software and 3D PIC code, a W-band extended interaction klystron amplifier is designed. In the PIC simulation, when the beam voltage is 30 kV and current is 8 A, the device can generate a 43 kW output power at 96.8 GHz with an efficiency of 18% and a gain of 49.3 dB.
Design of waveguide array frequency selective surface filter in sub-millimeter wave band
Cui Guang-Bin, Miao Jun-Gang, Zhang Yong-Fang
2012, 61 (22): 224102. doi: 10.7498/aps.61.224102
Abstract +
In order to meet the low insertion loss of transmission band and the low reflection loss of reflection band in detection technology of millimeter and sub-millimeter wave, in this paper, we design a frequency selective surface (FSS) filter based on waveguide array structure in the sub-millimeter wave band. Through optimizing the structural parameters, the FSS filter overcomes the drawback that the insertion loss increases at large angle of incidence. Meanwhile the FSS filter is not sensitive to the change of angle of incidence, these make it satisfy the requirements of particular engineering. In addition, the frequency responses of the FSS filter to TE and TM are the same, so it can detect the dual-polarized radiation signals simultaneously. Firstly, we give initial values of structural parameter according to the indicator. Secondly, we simulate and optimized the structure by simulation software. Finally, a new FSS filter with a low insertion loss is given. Simulation results show that the FSS filter meets the system requirements and overcomes the shortcoming of large insertion loss at a large incident angle. Then, we analyze the main source of the insertion loss in transmission band. An error sensitivity analysis of structural parameters of FSS filter is also given, which provides a reference for fabrication.
Research of secondary fringes in field-widened achromatic, temperature-compensated wind, imaging interferometer (FATWindII)
Dai Hai-Shan, Zhang Chun-Min, Mu Ting-Kui
2012, 61 (22): 224201. doi: 10.7498/aps.61.224201
Abstract +
The accurate method to calculate secondary fringes of field-widened, achromatic, temperature-compensated wind imaging interferometer (FATWindII) is presented, and the distribution of secondary fringes on instrument detector is simulated. The effects of secondary fringes on inversion errors of temperature and wind velocity are calculated. The formulas of modulation functions and phase shifts are derived when the wedge compensating glasses with arbitrary tilt angles, and the optimal tilt angles of wedge compensating glasses are obtained in FATWindII. By adopting antireflection film and wedge compensating glasses, the relative intensity of secondary fringes is reduced to below 2.5%, and the inversion errors of temperature and wind velocity introduced by the effects of secondary fringes can be minimized to about 0.05 K and 0.045 m·s-1 respectively. The research has important theoretical significance and practical guidance for the FATWind instrument design, fabrication and calibration.
Large-diameter multi-level diffractive optical elements with high energy efficiency
Wu Rong, Hua Neng, Zhang Xiao-Bo, Cao Guo-Wei, Zhao Dong-Feng, Zhou Shen-Lei
2012, 61 (22): 224202. doi: 10.7498/aps.61.224202
Abstract +
When large-diameter (100 mm) multi-level diffractive optical elements are applied to high-power laser systems in order to solve the problem of low energy efficiency, the energy efficiency can be greatly improved within uniform focal spot by reducing high diffraction orders. In this paper, we show both theoretically and experimentally that more than 90% energy can be focused into a desired spot as predicted previously by theoretical estimation.
Bidirectional chaos communication based on two semiconductor lasers subjected to incoherent optical injection of common-chaotic-signal
Wei Yue, Fan Li, Xia Guang-Qiong, Chen Yu-Lin, Wu Zheng-Mao
2012, 61 (22): 224203. doi: 10.7498/aps.61.224203
Abstract +
Based on the chaotic synchronization between two response semiconductor lasers (RLs) subjected to incoherent optical injection of common-chaotic-signal from a driven laser (DL), a bidirectional chaos communication scheme is proposed, and the chaotic synchronization characteristics and the effects of intrinsic mismatched parameter on the synchronization performances are numerically investigated. The results show that high-quality chaos synchronization between the two RLs can be achieved while the cross-correlation coefficients between the two RLs and the DL are very low under proper operation condition; the intrinsic parameter mismatching between two RLs will destroy the synchronized quality to a certain extent, but the consequence is not severe. Additionally, the bidirectional transmission performances for two messages with 2Gbit/s and the security of the scheme are also analyzed.
Optical bistability via active Raman gain in an n-type atomic medium
Yang Jin-Jin, Li Hui-Jun, Wen Wen, Huang Guo-Xiang
2012, 61 (22): 224204. doi: 10.7498/aps.61.224204
Abstract +
We study the optical bistability (OB) in an active Raman gain atomic medium by means of a unidirectional ring cavity. The system considered is a resonant n-type four-level atomic ensemble, which can be realized at room temperature and not only have a lot of tunable parameters, such as detuning, atomic concentration, pump and control field, but also possess gain-free (or little gain) transparent windows. We discuss the conditions and the range of these parameters for realizing OB, and also the condition for realizing optical multistability. Our results will provide the theoretical basis for experimental realization.
Improvement on stress instability in smoothed particle hydrodynamics
Yang Xiu-Feng, Liu Mou-Bin
2012, 61 (22): 224701. doi: 10.7498/aps.61.224701
Abstract +
Smoothed particle hydrodynamics (SPH) is a Lagrangian meshfree particle method. It has special advantages in modeling large deformation and free surface flow, and has been widely applied to different problems in engineering and science. However, the classical SPH suffers from stress instability which resticts its further development and applications. The fundamental reason of stress instability is that the stress state and the kernel do not match each other. For frequently used bell-shaped kernel function, in tensile state the attraction between particles increases as particle spacing decreases, thereby leading to tensile instability. In a compressible state, the repulsive force between particles increases, and then decreases as particle spacing decreases, thereby leading to compressible instability. In this paper is presented an approach to removing stress instability in SPH by proposing a new kernel function and a modified SPH discrete form. In the modified SPH, the force between particles is always repulsive and it increases as particle spacing decreases. Two numerical examples are given to test the proposed approachs, and the obtained numerical results clearly demonstrate that the new approach can eliminate stress instability effectively.
Research on interaction between bubble and surface waves based on BEM
Liu Yun-Long, Zhang A-Man, Wang Shi-Ping, Tian Zhao-Li
2012, 61 (22): 224702. doi: 10.7498/aps.61.224702
Abstract +
In order to study the interaction between underwater explosion bubble and surface waves, numerical and analytical methods are combined in this paper to solve the singular problem of the opened free surface and to consider the influence of far field. Then we decompose the velocity potential into incident potential due to the waves and the disturbing potential due to the bubble to consider the influence of waves. With the numerical model, interaction between the underwater explosion bubble and surface waves and the influence of wavelength and initial phase on the bubble dynamics are analyzed in this paper. Through the analysis of the numerical results, following conclusions are reached. During the collapsing phase of the bubble, the existence of the waves would budge the upside bubble and the downward liquid jet, while for the spike of the free surface, the influences on its height and width are considerable besides its migration. These magnitudes of influence are changed with the initial phase periodically, and decrease with the increase of wavelength in the range considered in this paper.
Numerical simulation on the thermal deposition of optical surface irradiated by low energy ion beam in ion beam figuring
Yuan Zheng, Dai Yi-Fan, Xie Xu-Hui, Zhou Lin
2012, 61 (22): 225201. doi: 10.7498/aps.61.225201
Abstract +
Based on energy deposition theory of Sigmund, the model of thickness of energy perturbation layer caused by low energy ion bombarding optical surface is built up. Beam current density on the optical surface is obtained by theory analysis, and the model of thermal deposition caused by low energy ion bombarding optical surface is built up. TRIM program is used to simulate the collision between low energy ions and atoms on the optical surface. And then, contributions to the thermal deposition and energy perturbation layer thickness from parameters such as ion energy, ion type and incidence angle are discussed. Finally, by taking the thermal quantity of deposited workpiece as a heat source in ANSYS, temperature field, thermal gradient field and stress field of the workpiece are obtained. The temperature and thermal gradient of the surface radiated by ion beam each present a Gaussian profile, and decrease along the radius from the center to the edge. The stress on the surface is a compressive stress within the radius of Half Maxim, and it is a tension-tension stress from the radius of Half Maxim to the edge.
Heating mechanism of hot electrons in the interaction between laser and nanolayered target
Yu Jin-Qing, Jin Xiao-Lin, Zhou Wei-Min, Li Bin, Gu Yu-Qiu
2012, 61 (22): 225202. doi: 10.7498/aps.61.225202
Abstract +
The generation of hot electrons and the coupling efficiency from laser to hot electrons are very important issues in fast ignition of inertial confinement fusion, which are important for optimizing the parameters of laser pulse and plasma and reducing the requirement for laser pulse. Laser interaction with nanolayered target is considered to be one of available ways of enhancing the coupling efficiency of laser to hot electrons. In order to understand the heating mechanism of hot electrons in the interaction between laser and nanolayered target in great detail, two-dimensional particle-in-cell simulation is carried out in this paper. Reflux for cold electrons moving to the interaction-face and then being accelerated near the interaction-face is detected by observing the tracks of electrons in the nanolayered target. It is found that the energies of inverse electrons are far smaller than those of forward electrons and the most inverse electrons are from the reflux of cold electrons by investigating the variations of the electron density and the electron energy density in one laser period. The J B heating mechanism is found to be a dominate mechanism in the generation of hot electrons by comparing the field and the locations of hot electrons at different times.
Numerical simulation of enhanced glow discharge plasma immersion ion implantation using three-dimensional PIC/MC model
He Fu-Shun, Li Liu-He, Li Fen, Dun Dan-Dan, Tao Chan-Cai
2012, 61 (22): 225203. doi: 10.7498/aps.61.225203
Abstract +
Enhanced glow discharge plasma immersion ion implantation is self-consistently simulated using a three-dimensional PIC/MC model. The information about ion counts, space potential, plasma density and ion incident dose is obtained. The results show that the sheath has fully expanded at 5 μs. There is a stable equilibrium of ion counts at 15 μs, which corroborates the characteristic of self-sustaining glow discharge of EGD-PIII. In the space just below anode where is found a highest plasma density, verifying the electron focusing effect. The rate of implantation is steady and the incident dose is relatively uniform except at the rim of target. A higher pulse negative bias may increase the injection rate but reduce the dose uniformity at the same time.
Core condition analysis of radiation driven implosion for maximum compression
Dong Jian-Jun, Ding Yong-Kun, Cao Zhu-Rong, Zhang Ji-Yan, Cheng Bo-Lun, Yang Zheng-Hua, Deng Bo, Yuan Zheng, Jiang Shao-En
2012, 61 (22): 225204. doi: 10.7498/aps.61.225204
Abstract +
Core condition studies of radiation driven implosion for maximum compression time are the key contents of inertial confinement fusion research. Core conditions refer to the electron temperature and mass density in core region. The spatial distribution of core emission is calculated based on local thermal equilibrium by Multi one-dimensional simulation of core temperature and density. Assumption is made that the core temperature and density distributions each meet a Gauss distribution. Peak values and full widths at half maximum of temperature and density spatial distribution can be inferred by parameter optimization. The data-processing for implosion experiment on Sheng-GuangIII prototype facility indicates that the peak values of temperature and density are 1.7 keV and 1.2 g/cm3 respectively. The full widths at half maximum of temperature and density distribution are 20 μm and 18 μm respectively.
Experimental investigation of delayed double pulse laser produced plasma in air
Liu Ke, Yi You-Min, Li Liang-Bo
2012, 61 (22): 225205. doi: 10.7498/aps.61.225205
Abstract +
By using Mach-Zehnder interferometer, we gain time series interference patterns of delayed double pulse laser and three-monopulse laser produced air plasmas. And then we gain electron density values in the centre of plasma region at different moments. We compare electron density values of the plasmas produced, respectively, by delayed double pulse laser and three-monopulse laser. The results show that the electron density of the plasma produced by the delayed double pulse laser is greater than by the three-monopulse laser at the same time after the second laser effects. The electron density time change processes of the plasma produced by delayed double pulse laser and monopulse laser of the same injection energy are analyzed theoretically. The analysis results show that when the same laser energy is injected, the delayed double pulse method can increase the plasma existing time effectively.
Study on phase analysis of nanoparticles by high-voltage electrical explosion method of copper wire
Li Shi-Wen, Feng Guo-Ying, Li Wei, Han Jing-Hua, Zhou Sheng-Yang, Yin Jia-Jia, Yang Chao, Zhou Shou-Huan
2012, 61 (22): 225206. doi: 10.7498/aps.61.225206
Abstract +
Copper nanoparticles are produced by high-voltage electrical explosion of copper wires. The high-voltage breakdown experimental setup for copper is built. The morphology and composition of the breakdown material are tested by the transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and X-ray diffractometry (XRD) and energy dispersive spectroscopy(EDS) methods, respectively. Based on the morphology, size distribution, elemental spectrum (EDS), and XRD analysis of the breakdown material, the phase characteristics of high-voltage breakdown copper wire are studied. The results show that wire is fully ionized under high pressure, forming a filamentous distribution which is composed of condensation of nanoparticles. The diameters of copper nanoparticles are between 30 nm and 60 nm. The nanoparticles product is composed of Cu and O elements. The product is a mixture of metallic copper, cupric oxide and cuprous oxide. The particle size and its product composition are controlled by varying length and diameter of the copper wire, discharge voltage, etc.
Hole doping effects on structure and magnetic properties of Sr2FeMoO6
Hu Yan-Chun, Wang Yan-Wen, Zhang Ke-Lei, Wang Hai-Ying, Ma Heng, Lu Qing-Feng
2012, 61 (22): 226101. doi: 10.7498/aps.61.226101
Abstract +
Samples of Sr2-xKxFeMoO6 (x=0, 0.01, 0.02, 0.03, 0.04) are prepared by standard solid-state reaction. The crystal structures and magnetic properties for the ordered double perovskite oxides Sr2-xKxFeMoO6 (0 x 0.04) are investigated. X-ray powder diffraction studies reveal that all the samples are of single phase and each of them has a I4/m symmetry. The anti-site defects in double perovskite oxides of Sr2FeMoO6 may be adjusted by alkali metal element of K doping. The unit cell magnetizations at 280 K are 1.12B for x=0.00 and 1.26B for x=0.04. The cation-ordering and the variation of structure parameters play improtant roles in determining the magnetism in the doping system.
Insitu neutron diffraction study of micromechanical interaction and phase transformation in dual phase NiTi alloy during tensile loading
Sun Guang-Ai, Wang Hong, Wang Xiao-Lin, Chen Bo, Chang Li-Li, Liu Yao-Guang, Sheng Liu-Si, Woo Wanchuck, Kang Mi-Hyun
2012, 61 (22): 226102. doi: 10.7498/aps.61.226102
Abstract +
It is well known that the shape memory effect of NiTi alloy is closely related to the micro-structural characteristics. Neutron diffraction method can used to explore the changes of the phase transformation, lattice strain and twining reorientation of bulk NiTi alloy during deformation caused by the applied stress. In this paper, combining the four types of deformation characteristics in the macro stress-strain curves of dual phase NiTi alloy and using in-situ neutron diffraction measurement, the micromechanical interactions and phase transformation are determined. The volume fraction of the initial austenite before deformation is about 22%. The contrast transformation, which is corresponding to the lattice strain rapid decreasing of (110)B2 and increasing of (002)B19', reveals that the stress-induced transformation from austenite to martensite phase appears with the volume fraction of austenite decreasing rapidly and 011 II type twinning increases at the low strain hardening stage. At the same time, the initial martensite grains change their orientation to a favorable direction and the new {201} type martensite twinnings induced with the increase of applied stress cannot recover after unloading. At the high strain hardening stage, the twinning deformation is considered to be the main mechanism from the observing of the changes in the full width at half maximum (FWHM). Meanwhile, the slipping caused by dislocation is the main deformation mechanism corresponding to the obvious increas of the FWHM at the statured stage of the strain hardening.
Mechanical parameters selection in InSb focal plane array detector normal direction
Meng Qing-Duan, Yu Qian, Zhang Li-Wen, Lü Yan-Qiu
2012, 61 (22): 226103. doi: 10.7498/aps.61.226103
Abstract +
In order to learn the effects of front surface structural defects and back surface thinning process on the InSb chip deformation, its elastic modulus along normal direction is reduced in InSb structural modeling, and based on the typical strain character appearing under thermal shock, the mechanical parameter selection basis is deduced in this paper. Simulation results show that when the out-of-plane elastic modulus of InSb chip is set to be 30 percent Young's modulus, both the maximum Von Mises stress and Z component of strain appear in the N electrode zone, and the extremum values present non-continuous distribution. These are in good agreement with fracture origination zone and crack distribution in the fracture statistics results of 128 128 InSb infrared focal plane array under thermal shock. Besides, the region above the indium bump array is convex upward, and the domain above the isolation trough is concave downward, they are also identical with the scenario of Z component of strain in InSb chip under thermal shock. All these results indicate that the Z component of strain criterion can not only predict both crack origination zone and crack distribution, but also support both Z component of strain distribution in the central region and Z component of strain enhancement effect in the InSb chip N electrode zone.
The effects of stacking fault and temperature on deformation mechanism of nanocrystalline Mg
Song Hai-Yang, Li Yu-Longi
2012, 61 (22): 226201. doi: 10.7498/aps.61.226201
Abstract +
The effects of stacking fault (SF) and temperature on the mechanical properties of nano-polycrystal Mg under tension loading are investigated by molecular dynamics simulations. The interatomic potential of embedded atom method (EAM) is used as the Mg-Mg interaction. The computational results show that the yield strength of nano-polycrystal Mg can be obviously enhanced when stacking fault is introduced into grains, and the effect of SF on the Young's modulus of nano-polycrystal Mg is very small. The results also show that tensile twins and new grain at 300.0 K are nucleated and initiated at grain boundaries, growing continuously with the increase of strain. The dihedral angel between the (1000) plane of new grain and the X-Y plane is about 35. In other words, the nucleation and the growth of twins and new grains are the predominant deformation mechanism for nano-polycrystal Mg at 300.0K. We also find that at 10.0K the dislocation nucleation and slip are the predominant modes of the plastic deformation for nano-polycrystal Mg.
Mechanical resonance based acoustic spectrographic technique
Song Wei, Chen Yu-Hao, Li Xiao-Hui, Zhang Xian-Liang, Wang Jia-Hui, Cai Zhi-Gang
2012, 61 (22): 226202. doi: 10.7498/aps.61.226202
Abstract +
A model for the accurate measurement of low frequency sound spectrum is put forward and a simplified experimental device is built. Based on the principle of mechanical resonance, the natural frequency of the system is controlled, which realizes the function of both measuring frequency spectrum and monitoring noises at low frequency. The device is able to measure the acoustic source at a single frequency below 100 Hz as well as to analyze the spectra of acoustic sources at mixed frequencies, with a relatively high resolution of 1 Hz beyond 40 Hz.
Light emission mechanism of sapphire under shock loading from 40 to 60 GPa
Zhang Ning-Chao, Liu Fu-Sheng, Peng Xiao-Juan, Chen Yuan-Fu, Wang Jun-Guo, Zhang Ming-Jian, Xue Xue-Dong
2012, 61 (22): 226501. doi: 10.7498/aps.61.226501
Abstract +
The spontaneous spectroscopic and radiation pyrometer techniques are combined together to study the light emission of shocked sapphire and its time dependence under a compression of 41—87 GPa. The results are confirmed that the shock induced light emission from sapphire can be attributed to the thermal radiation from the shear bands because of partial dislocation damage. The spectral distribution matches well with the equilibrium thermal radiation of Planck grey-body feature. The fact that of the radiation color temperature is close to the corresponding melting temperature can be explained reasonably by the thermal equations of the plastic flow.
Phase transition and thermal expansion properties of ZrV2-xPxO7
Yuan Huan-Li, Yuan Bao-He, Li Fang, Liang Er-Jun
2012, 61 (22): 226502. doi: 10.7498/aps.61.226502
Abstract +
ZrV2-xPxO7 (x = 0, 0.4, 0.8, 1.0) solid solutions are prepared using a solid state reaction method. Powder X-ray diffraction (XRD) analysis reveals that the as-prepared solid solutions are of single-phase cubic type in crystal structure. Temperature dependent Raman spectroscopic studies demonstrate that the phase transition temperature of ZrV2-xPxO7 decreases with the increase of the content of P. ZrV2O7, ZrV1.6P0.4O7, ZrV1.2P0.8O7 and ZrVPO7 transform from a 3× 3× 3 superstructure to a 1× 1× 1 normal structure at about 373 K, 363 K 273 K and 213 K, respectively. The results of thermal expansion testing indicate that the temperature of positive thermal expansion changes to negative thermal expansion with the increase of P content. The temperatures of positive-to-negative thermal expansion of ZrV2-xPxO7 are 429 K, 403 K, 372 K, 390 K, 398 K and 435 K for x=0, 0.2, 0.4, 0.6, 0.8 and 1, respectively. Two phase change transformations are demonstrated in ZrV2-xPxO7 materials in our work, which is beneficial for preparing the negative thermal expansion materials at room temperature using ZrV2O7.
The vibration and dissociation of NO onPt (111) surface
Lü Bing, Linghu Rong-Feng, Song Xiao-Shu, Li Ying-Fa, Yang Xiang-Dong
2012, 61 (22): 226801. doi: 10.7498/aps.61.226801
Abstract +
The absorption of NO on the Pt (111) surface is investigated based on the density functional theory and the periodic slab model. The absorption structure is analyzed through scanning tunneling microscopy (STM) image. The calculated Pt-NO stretching vibration (2) frequency is almost unchanged, and the frequencies of blocked translation (3, 4) and blocked rotation (5, 6) are completely degenerate. The dissociation processes of NO on Pt (111) surface are discussed in detail using the CI-NEB method. The results show that the dissociation of NO on Pt (111) surface is difficult and it must overcome 2.29 eV energy barrier to achieve it.
Study of the evolution of helium bubbles in helium-containing titanium films
Wang Kang, Deng Ai-Hong, Liu Li, Li Yue, Zhou Yu-Lu, Hou Qing, Zhou Bing, Wang Shan-Lin
2012, 61 (22): 226802. doi: 10.7498/aps.61.226802
Abstract +
In this paper, the evolution of the He-related defects in the titanium film is experimentally investigated by combining slow positron beam analysis (SPBA) and transmission electron microscope (TEM) technique. The results indicate that small bubbles in the titanium film distribute uniformly at room temperature. With the increment of He concentration, the density of He bubbles in the sample increases correspondingly. Large bubbles are observed in the titanium film containing high He concentration after 973 K high temperature annealing, and it is found that both migration-coalescence and cascade-coalescence around the bigger He bubbles lead to the rapid growth of He bubbles.
Study on the lattice constants and energy band properties of Be and Ca doped wurtzite ZnO
Zheng Shu-Wen, Fan Guang-Han, Zhang Yong, He Miao, Li Shu-Ti, Zhang Tao
2012, 61 (22): 227101. doi: 10.7498/aps.61.227101
Abstract +
The lattice constants, energy band properties and formation energies of BexZn1-xO, CayZn1-yO and BexCayZn1-x-yO alloys of Be and Ca doped wurtzite ZnO alloys are calculated by the plan-wave pseudopotential method with GGA in density functional theory (DFT). The theoretical results show the lattice constants of BexZn1-xO alloy decrease with Be content increasing, which is contrary to the scenario of CayZn1-yO alloy. For the energy band properties of Be_xZn1-xO and CayZn1-yO alloys, the valence band maxima (VBM) are determined by O 2p states and the conduction band minima (CBM) is occupied by Zn 4s states, and their band gaps are broadened when Be or Ca content is increased. The lattice constant of Be0.125Ca0.125Zn0.75O alloy of Be and Ca co-doped ZnO is matched with that of ZnO and its energy bandgap is greater than that of ZnO, so Be0.125Ca0.125Zn0.75O /ZnO structure is suitable for high-quality ZnO based device. In addition, the stability of Be0.125Ca0.125Zn0.75O alloy is also analysed.
The effect of strain on band structure of single-layer MoS2: an ab initio study
Wu Mu-Sheng, Xu Bo, Liu Gang, Ouyang Chu-Ying
2012, 61 (22): 227102. doi: 10.7498/aps.61.227102
Abstract +
We study the electronic properties of single-layer MoS2 with biaxial tensile strain by using an ab initio method of plane wave potential technique based on the density function theory. Our results show that a small tensile strain (0.5%) will result in the transition from direct to indirect gap for ingle-layer MoS2. With the increase of strain, the feature of the indirect gap can be preserved but the gap decreases linearly. Based on the further analysis of the density of states and the projected charge density for single-layer MoS2, the reason of the change of band structure is revealed.
Preparation, structures and electrical properties of alkaline earth and transition metal-doped NdAlO3 conducting ceramics
Xiang Jun, Guo Yin-Tao, Zhou Guang-Zhen, Chu Yan-Qiu
2012, 61 (22): 227201. doi: 10.7498/aps.61.227201
Abstract +
Novel Nd0.9Sr0.1Al1-xMxO3-δ (M = Co, Fe, Mn; x =0, 0.15, 0.3, 0.5) conducting ceramics each with a hexagonal perovskite structure are prepared using organic-gel method combined with subsequent high temperature sintering. The influences of transition elements (Co, Fe, and Mn) and their dosages on the structure characteristics and electrical properties are investigated in detail. The experimental results reveal that well-crystallized Nd0.9Sr0.1Al1-xMxO3-δ perovskite oxide ultrafine powders can be obtained by calcining the gel precursors at 900 ℃ for 5 h. The lattice parameters of sintered ceramics increase with the increase of transition metal content (x), and they increase according to the order of Co, Mn, and Fe. All the samples are mixed conductors of oxygen ions and holes in air, and the oxygen ion transport number is enhanced monotonically from 0.32 at 500 ℃ to 0.63 at 850 ℃ for NdAlO3-δ ceramic single-doped with alkaline earth metal Sr, indicating that this material has an electronic-to-ionic dominant transition in electrical conductivity with measurement temperature increasing. Whereas the oxygen ion transport numbers are all below 0.001 for the samples co-doped with Sr and transition metals (Co, Fe, and Mn), and their electrical conductivities are absolutely dominated by p-type conduction. It is found that the conductivity values increase with the increase of x value, and they increase according to the order of Mn, Fe, and Co, while the change of corresponding apparent activation energies is just the opposite. Nd0.9Sr0.1Al0.5Co0.5O3-δ ceramic has the highest electrical conductivity, ~100.8 S/cm at 800 ℃, and the lowest apparent activation energy (0.135 eV) in all the synthesized samples. The observed changes in structure and electrical property in this study can be explained on the basis of the difference in ionic radii among the doped transition metals as well as the differences in bond energies and covalencies among the M-O bonds.
Scanning tunneling mircroscopy and X-ray photoelectron spectroscopy studies of MnSi film and MnSi1.7 nanowires grown on Si substrates
Shi Gao-Ming, Zou Zhi-Qiang, Sun Li-Min, Li Wei-Cong, Liu Xiao-Yong
2012, 61 (22): 227301. doi: 10.7498/aps.61.227301
Abstract +
Manganese silicides are promising industrial materials in optoelectronics and microelectronics fields. The study of electronic structures of manganese silicide film and nanowires is essential for a deeper understanding of their properties. In this paper, MnSi film and MnSi1.7 nanowires are prepared by molecular beam epitaxy method, and then observed by scanning tunneling microscopy (STM). The Mn 2p and Si 2p of MnSi film and MnSi1.7 nanowires are comprehensively studied using X-ray photoelectron spectroscopy (XPS). The results demonstrate that MnSi film with ~ 0.9 nm high is √3 × √3 reconstruction, and that the MnSi1.7 nanowires are about ~ 3 nm high, 16—18 nm wide and 500—1500 nm long. The binding energies of the Mn 2p1/2 level and Mn 2p3/2 level for MnSi film are 649.7 and 638.7 eV, respectively, which coincide with those of MnSi1.7 nanowires. The Mn 2p3/2 and Mn 2p1/2 peaks which are located at 640—645 eV and ~653.8 eV indicate that an oxide layer formed on the surfaces of film and nanowires because of short-time exposure to the atmosphere. The negative chemical shifts for MnSi film and MnSi1.7 nanowires from Si2p spectra indicate that with the formation of manganese silicides, the chemical state of Si is changed.
Breakdown voltage analysis for new Al0.25Ga0.75N/GaN HEMT with F ion implantation
Duan Bao-Xing, Yang Yin-Tang, Kevin J. Chen
2012, 61 (22): 227302. doi: 10.7498/aps.61.227302
Abstract +
In order to alleviate the leakage current of AlGaN/GaN High Electron Mobility Transistors (HEMT) device with the N-type GaN buffer, the new Al0.25Ga0.75N/GaN HEMT with the Fluoride ion implantation is proposed for the first time in this paper. Firstly, the output characteristic has the ohmic characteristic for the AlGaN/GaN HEMT without acceptor-type trap, which explains why Fe and Mg are doped into the GaN buffer layer as reported in the literature in theory and simulation. By using the output characteristics of the Ids-Vds for the AlGaN/GaN HEMTs with and without low density drain, the results are obtained that fluoride ion implantation can capture effectively the electrons emitted from the source to reduce the leakage current of the GaN buffer compared with fluoride ions in the gate and the drain regions. The breakdown voltage goes up to 262 V. The scientific basis is set up for desiging the new AlGaN/GaN HEMT with both the low leakage current and the high breakdown voltage.
Theoretical study of luminance of GaN quantum dots planted in quantum well
Wang Du-Yang, Sun Hui-Qing, Xie Xiao-Yu, Zhang Pan-Jun
2012, 61 (22): 227303. doi: 10.7498/aps.61.227303
Abstract +
A theoretical simulation of electrical and optical characteristics of quantum dot (QD) light-emitting diodes depending on the QD sizes is conducted with APSYS software. The electron and hole concentration in the LED and the radioactive recombination rate are studied. Simulation results show that with the increase of the QD size, the emission wavelength has a red shift. With the radius of QD increasing from 1.8 nm to 13 nm , the red shift of emission wavelength has reaches 309.6 meV. The use of the QDs with different sizes planted in quantum well can achieve full-color display with a single LED. When different quantum wells are planted with different QDs, the LED turns into a muti-wavelength luminescence even white LED. We can improve the intensity of each wavelength by adjusting the surface density of QDs. The luminous uniforming of the muti-wavelength LED can be effective improved by adjusting the QD surface density.
Density functional theory study on transparent conductive oxide CuScO2
Fang Zhi-Jie, Mo Man, Zhu Ji-Zhen, Yang Hao
2012, 61 (22): 227401. doi: 10.7498/aps.61.227401
Abstract +
Using the first-principle method within the generalized gradient approximation, in this paper we study the band structure, state density and doping level of transparent conductive oxide CuScO2. The calculated results show that the valence band of CuScO2 is composed mainly of 3d of Cu, and 2p of O; while the conduct band is comprised mainly of 3d of Sc. Through the +U correction, with the increase of the value of U, the conduct band of CuScO2 becomes split, and results in the enlarged band gap, which shows that the +U correction can improve the band gap of CuScO2. By comparing all kinds of dopant level in CuScO2, it found that the substitution of Mg for Sc can effectively improve the p-type conductivity in CuScO2.
Study on the structural and magnetic properties of La-doped barium ferrites
Li Jie, Zhang Huai-Wu, Li Yuan-Xun, Li Qiang, Qin Jun-Feng
2012, 61 (22): 227501. doi: 10.7498/aps.61.227501
Abstract +
Magnetic properties of La doped M-type barium ferrites are studied. The samples are prepared by the standard solid state reaction method. The influences of La3+ on structures and magnetic properties of barium ferrites (Ba1-xLaxFe12O19) are investigated. Single-phase M-type barium ferrites with chemical composition of Ba1-xLaxFe12O19 (x=0.0—0.6) are formed by sintering at 1100—1175 ℃ in air. Scanning electron microscopy (SEM) reveals that the La doping has no effect on the structure of barium ferrite. Vibrating sample magnetometer (VSM) shows that with the valaue of x increasing, the saturation magnetization (Ms) increases, reaching a maximum at x=0.2 and then decreases and the coercivity of the sample increases continuously. The value of Ms reaches a maximum value of 62.8 emu/g at x=0.2 and 1175 ℃, and the Hc reaches a maximum value of 3911.5 Oe at x=0.6 and 1125℃.
Preparation of ZrO2:Eu3+-Bi3+ phosphor and Bi3+ sensitizing characteristic emission of Eu3+ ions
Sang Shi-Jing, Lü Shu-Chen, Qu Xiu-Rong, Yang Xiao-Xu, Zhang Li-Li
2012, 61 (22): 227801. doi: 10.7498/aps.61.227801
Abstract +
Eu3+ and Bi3+ codoped ZrO2 nanocrystalline powders are prepared by chemical co-precipitation method. The room temperature characteristic emission of Eu3+ can be observed from each sample. We determine the crystal structures and luminescent properties of the samples. It is shown that the crystal phase of nanocrystalline ZrO2:Eu3+-Bi3+ powder calcined at 600 ℃ is tetragonal, and it turns into the mixture of tetragonal and monoclinic phase as temperature rises to 800, 950, and 1100 ℃. It is obvious that characteristic emission intensity of Eu3+ in the tetragonal phase is greater than in the mixed phase. Bi3+ can sensitize the room temperature characteristic emission of Eu3+ in nanocrystalline ZrO2.
Preparation and red long-lasting luminescence properties of Eu3+ doped CaO
Li Hai-Ling, Wang Yin-Hai, Zhang Wan-Xin, Wang Xian-Sheng, Zhao Hui
2012, 61 (22): 227802. doi: 10.7498/aps.61.227802
Abstract +
The red long-persistent phosphor CaO: Eu3+ is prepared by a co-precipitation method with further thermal decomposition. The X-ray diffraction analysis shows that the crystal structure of calcium carbonate sample transforms into a single-phase structure and then generates a single-phase calcium oxide structure with the increase of sintering temperature. The excitation spectrum of CaO: Eu3+ shows a broad band around 255 nm, which is attributed to the charge transfer of Eu3+-O2-, and a sharp peak at 393 nm. The emission spectral limes of sample correspond to Eu3+ transitions between 5D and 7FJ (J=0, 2, 3, 4) electron configurations. The red long afterglow is observed at room temperature. A trap level located at 0.69 eV is found by thermolumihnescence measurement, which arises from the fact that Eu3+ is substituted for Ca2+ and enters into the lattice The afterglow luminescence mechanism of sample was discussed according to quantum tunneling.
First-order and second-order infrared quantum cutting of Ho3+ Yb3+ doped oxyfluoride vitroceramics
Chen Xiao-Bo, Yang Guo-Jian, Li Song, Sawanobori N., Xu Yi-Zhuang, Chen Xiao-Duan, Zhou Gu
2012, 61 (22): 227803. doi: 10.7498/aps.61.227803
Abstract +
Infrared quantum cutting is an international hot research field nowadays. Comparitive research between first-order and second-order quantum cutting of Ho3+ Yb3+ doped oxyfluoride vitroceramics is reported in present paper. It is found that most population can easily non-radiativly relax to (5F45S2) energy level when the energy levels between 5G5 and 5S2 are excited. For (5F45S2) level, the population of Ho3+ ion can be cross-transferred to 5I6 level by strong ETr7-ETaYb {5F4(Ho) 5I6 (Ho), 2F7/2(Yb) 2F5/2(Yb)} cross energy transfer passage; meanwhile, Yb3+ ion is excited to 2F5/2 level from 2F7/2 ground state. It results in the two infrared photons which can be absorbed by crystal Si, that is, one is (1153 nm, 1188 nm) infrared photon and the other is (973.0 nm, 1002.0 nm) infrared photon. Therefore, it results in two-photon first-order infrared quantum cutting. Finally, the cross energy transfer efficiency tr, 1%Yb(5F45S2)=29.2%, tr, 10.5%Yb(5F45S2)=99.2%. and cooperative energy transfer efficiency tr, 1%Yb(5F3)=4.18%, tr, 10.5%Yb(5F3)=75.3% of Ho(0.5)Yb(1):FOV and Ho(0.5)Yb(10.5):FOV are calculated. Their quantum efficiency up-limits of two-photon quantum cutting are CR, 1%Yb(5F45S2)=129.2%, CR, 10.5% Yb(5F45S2)=199.2 and CO, 1%Yb(5F3)=104.18%, CO, 10.5% Yb(5F3)=175.3% respectively. That is to say, the probability of first-order infrared quantum cutting is larger than that of second-order infrared quantum cutting. The present research is of significance for enhancing solar cell efficiency.
A Monte Carlo simulation study on growth mechanism of horizontal nanowires on crystal surface
Lan Mu, Xiang Gang, Gu Gang-Xu, Zhang Xi
2012, 61 (22): 228101. doi: 10.7498/aps.61.228101
Abstract +
With the kinetic Monte Carlo simulation of smooth (001) surface of symmetry-broken simple cubic crystal in fluid with low supersatuaration rate, the mechanism of nanowire growth based on crystal nuclei on the surface is discovered and the morphology of nanowire is obtained. The dependences of nanowire morphology on thermal roughness in the longitudinal and latitudinal direction and growth time on the anisotropic surface of the crystal are further discussed. The relations of nanowire growth rate with thermal roughness, supersaturation rate, surface size and diffusion rate on the surface are then systematically studied.
Quantitative phase-field model for dendritic growth with two-sided diffusion
Pan Shi-Yan, Zhu Ming-Fang
2012, 61 (22): 228102. doi: 10.7498/aps.61.228102
Abstract +
A quantitative phase-field (PF) model with an anti-trapping current (ATC) is developed to simulate the dendritic growth with two-sided diffusion. The asymptotic analysis is performed at the second-order for the PF equations coupled with nonlinear thermodynamic properties and an ATC term under the equal chemical potential condition. The PF mobility and ATC are derived based on the asymptotic analysis in the thin interface limit, and the solute drag model. Then the model is reduced to the dilute solution limit for dendrite solidification of binary alloys. The test of convergence with respect to the interface width exhibits an excellent convergent behavior of the proposed model. The performance of the model is then validated by comparing PF simulations with the predictions of the Gibbs-Thomson relation, the linearized solvability theory, and the modified-Lipton-Glicksman-Kurz (M-LGK) analytical model, for the isothermal dendritic growth of an Fe-0.15 mol%C alloy. The results demonstrate quantitative capabilities of the model that effectively suppresses the abnormal solute trapping effect when the interface is taken artificially to be wide. It is also found that the present model can quantitatively describe dendrite growth with various solid diffusivities, ranging from the case with one-sided diffusion to the symmetrical model.
Growth and spectral properties of 5 at%Yb:YNbO4 crystal
Zhou Peng-Yu, Zhang Qing-Li, Yang Hua-Jun, Ning Kai-Jie, Sun Dun-Lu, Luo Jian-Qiao, Yin Shao-Tang
2012, 61 (22): 228103. doi: 10.7498/aps.61.228103
Abstract +
5 at%Yb3+:YNbO4 crystal is grown by Czochralski(CZ) method. Its transmission and emission spectra are measured. The absorption peaks are located at 933, 955, 974 and 1003 nm with their corresponding absorbtion cross section values 0.7310-20, 1.8510-20, 0.8610-20 and 0.4410-20 cm2; and the FWHM of 955 nm absorbtion peak is 17 nm. Its emission band centered at 1020 nm with the FWHM is 41 nm, which is over three times that of Yb3+:YAG crystal. The emission cross section values of 955, 974, 1005, 1021 and 1030 nm peaks are calculated to be 0.6910-20, 0.8610-20, 1.8110-20, 1.1110-20 and 0.5710-20 cm2, respectively, and the biggest one is comparable to that of Yb3+:YAG crystal. The laser parameters of 5 at% Yb3+:YNbO4 crystal are evaluated and the results suggest that it is a potential all-solid-state pumped laser crystal in tunable and ultrafast lasers field.
Synthesis and properties of multiple boride Pr1-xCexB6 cathodes by reactive spark plasma sintering
Li Xiao-Na, Zhang Xin, Zhang Jiu-Xing, Bao Li-Hong, Zhang Ning, Zhang Fan-Xing
2012, 61 (22): 228104. doi: 10.7498/aps.61.228104
Abstract +
The polycrystalline Pr1-xCexB6 (x = 0.2, 0.4, 0.6, 0.8) hexaborides are prepared by the reactive spark plasma sintering (SPS) method using mixed powder of CeH2, PrH2 and B. The effects of Ce doping on the phase composition, the mechanical properties and the thermionic emission properties of the hexaboride are investigated. The single-phased hexaborides CexPr1-xB6 bulks are sintered at a temperature of 1450℃, pressure of 50MPa and holding time of 5 min, and the sintered samples show high value of Vickers hardness (24.34 GPa) and bend strength (226.02 MPa). The thermionic emission results show that with the increase of Ce content, the thermionic emission current density increases linearly and the maximum value of Pr0.4Ce0.6B6 reaches 47.3 A·cm-2 under an applied voltage of 950 V at 1973 K, which is much higher than that obtained by traditional method. Thus, the SPS technique represents a suitable method to synthesize the dense rare-earth hexaborides with excellent properties.
Spectroscopic properties of cerium doped YVO4 crystals and analysis on valence state of cerium ion
Wang You-Fa, Wu Zhou-Li, Li Wen-Run, Wang Shuai, Tong Hong-Shuang, Ruan Yong-Feng
2012, 61 (22): 228105. doi: 10.7498/aps.61.228105
Abstract +
High-quality cerium doped YVO4 crystals are grown by the Czochralski method in a furnace heated by medium frequency induction. Cerium carbonate and ceria of 2 at% are respectively doped into the different crystals. The X-ray diffraction spectra show that all samples present YVO4 crystallographic phase. The absorption spectra, excitation spectra and photoluminescence spectra of the samples are measured. It is found that the spectroscopic properties of the samples doped with the different cerium impurities are similar. The two kinds of the samples each radiate a wideband blue light centered at 440 nm when excited by 325 nm light. This blue light emission is due to the 5d → 4f intrinsic emission of Ce3+ ions. In addition, the two kinds of the samples each radiate a wideband red light centered at 620 nm when excited by 460 nm light. The X-ray photoelectron spectroscopy (XPS) show that the O(1s) peak splits into two peaks at 529.8 eV and 531.8 eV, which indicate that there are two types of coordinate oxygen ions in the crystal. One kind of coordinate oxygen ion is normal coordinated oxygen ion (O2-) and another kind of coordinate oxygen ion is a hole (O-). According to recorded 5 peaks of Ce(3d) XPS, it is deduced that the Ce3+ ions and Ce4+ ions coexist in each of these samples. It is considered that the wideband red light emission of Ce:YVO4 crystal is due to the charge transfer transition of the Ce4+-O2- ion pairs, and Ce:YVO4 powders may become a novel red phosphor used for white LED.
Effect of surface tension anisotropy on the growth patterns of cellulars in directional solidification
Zhang Yun-Peng, Lin Xin, Wei Lei, Wang Meng, Peng Dong-Jian, Huang Wei-Dong
2012, 61 (22): 228106. doi: 10.7498/aps.61.228106
Abstract +
The growth patterns of cellulars in directional solidification are investigated numerically using the cellular automata (CA) model in two dimensions. A criterion which determine whether the cellulars reach stable state is derived from the analysis of simulated results. The simulated results also show that it is easy for tip splitting to appear for cellulars when the surface tention anisotropy is very small. So it is hard to obtain stable cellular arrays. However, if the amplitude of surface tention anisotropy is strong enough, it is easy to obtain stable cellular arrays. And the intensity of surface energy anisotropy can considerably influence the stable cellular patterns. The stronger the surface energy anisotropy, the smaller the stable cellular spacing and the cellular tip radius are, and the smaller the ratio between tip radius and cellular spacing, the smaller the tip concentration and the tip undercooling are.
Ag antidot array modified TiO2 film and its photocatalysis performance
Qi Hong-Fei, Liu Da-Bo, Cheng Bo, Hao Wei-Chang, Wang Tian-Min
2012, 61 (22): 228201. doi: 10.7498/aps.61.228201
Abstract +
Ag antidot arrays modified TiO2 films are obtained by PS colloidal crystal template technique and magnetron sputtering method, and the microstructure of Ag antidot array is modulated through controlling the sputtering power. And then, the structural and the photocatalysis performances of all samples are characterized by using scanning electron microscopy, X-ray diffraction, UV-Vis spectrophotometer, and four-point probe. The experimental results show that the microstructure of Ag antidot array significantly influences the photocatalysis performance of the sample. With the diameter of the antidot array decreasing, the photocatalysis performance of the sample is enhanced due to the increase of conducting ability. The photocatalysis performance is highest, when the diameter of the antidot array is 710 nm. Subsequently, with the diameter of the antidot array further decreasing, the photocatalysis performance decreases to a certain extent, which results from the increases of the carrier loss and the light shading area. The photocatalysis performance of Ag antidot array modified TiO2 film is superior to that of TiO2 film. This is attributed to the fact that the Ag antidot array could effectively promote the separation of surface photoinduced charge carrier of TiO2 nanoparticles, which is responsible for the remarkable increase in photocatalytic activity.
Forming efficiency of porous anodic oxide and formation mechanism of nanopores
Zhu Xu-Fei, Han Hua, Song Ye, Ma Hong-Tu, Qi Wei-Xing, Lu Chao, Xu Chen
2012, 61 (22): 228202. doi: 10.7498/aps.61.228202
Abstract +
Porous anodic alumina (PAA) and porous anodic TiO2 nanotubes have received considerable attention because of their applications in a number of fields. The formation mechanisms of nanopores and nanotubes in these porous anodic oxides, however, have remained unclear until now. The interactions between porous structural features and current-time transients in anodizing process cannot be successfully explained. Based on the mechanism of dielectric breakdown of the compact anodic alumina (CAA), the differences and internal relations in their forming processes between CAA and PAA are contrasted in detail. From this innovative standpoint, according to the divergence of PAA and CAA in their current-time curves (or voltage-time curves), two essential causes which induce the decrease of the forming efficiency of oxide in the anodizing process, that is, the generation of the electronic current and the oxygen evolution, are presented in the paper. The evidences of the round hollows within the CAA films, show that the regularly embryo pores result from the oxygen bubbles. According to the aluminum anodizing in the mixed-electrolyte, the results show that once oxygen evolution stopping, the pore growth must be stopped, and the pores must be sealed by the above compact oxide. A novel composite film of the anodic oxide is presented. All of the above conclusively show that in the forming process of PAA, an appropriate magnitude of electronic current ensures the oxygen evolution and the pores formation, an appropriate magnitude of ionic current ensures the oxide formation and growth of pore walls.
Investigation of suppression of non-working mode oscillation in a high gain relativistic klystron amplifier
Chen Yong-Dong, Jin Xiao, Li Zheng-Hong, Huang Hua, Wu Yang
2012, 61 (22): 228501. doi: 10.7498/aps.61.228501
Abstract +
Because non-working modes are very easy to excit in the high gain relativistic klystron amplifier, and seriously affect the beam-wave interactive action, the suppressing of non-working modes is very important. These modes can seriously degrade klystron performance and cause the pulse shortening, the normal operation of HGRKA will be affected greatly. This paper deals with the mechanism of non-working mode self-excitation by the PIC simulation, and it is obvious that the coupling between cavities is the main cause of non-working mode self-excitation. The coupling can form the positive feedback loop. The formula for starting current of non-working mode self-excitation is developed according to the coupling between cavities, and the corresponding measures are taken to avoid non-working mode self-excitation. Then the corresponding simulations and optimization are conducted. Finally non-working mode control is realized in the HGRKA experimentally when driven power is only few kilowatts. The RF output has a power of 0.98 GW and pulse width of 100 ns.
0—1 integer linear programming for actively shielded magnetic resonance image (MRI) superconducting magnet design
Zhang Guo-Qing, Du Xiao-Ji, Zhao Ling, Ning Fei-Peng, Yao Wei-Chao, Zhu Zi-An
2012, 61 (22): 228701. doi: 10.7498/aps.61.228701
Abstract +
Here introduced is an optimization design method for actively shielded magnetic resonance image (MRI) superconducting magnet based on the integer linear programming. The feasible coil space is densely divided by an array of candidate squares and, its size is determined by the size of actual superconducting wire. The 0—1 integer linear programming method is adopted to obtain the initial wire concentrated region of coils by comprehensivly considering superconductivity wire consumption, magnetic field intensity inside the superconductors, homogeneity in imaging region and the range of leak fields. Then by reasonably adjusting the position and section size of the wire concentrated region for the next calculation, the final MRI superconducting magnet structure with rectangular section coils is obtained. The method is based on the full size of the superconducting wire, which makes the MRI superconducting magnet design more feasible and has greater advantage for the actual fabriction. With different constraints, the method can also be used for other superconducting magnet design. Finally an example of the MRI magnet optimal design is presented.


Calibration of optical tweezers using time of flight method
Zhou Dan-Dan, Ren Yu-Xuan, Liu Wei-Wei, Gong Lei, Li Yin-Mei
2012, 61 (22): 228702. doi: 10.7498/aps.61.228702
Abstract +
Conventional method of calibrating optical trap stiffness is applicable for microspheres whose diameters range from hundreds of nanometer to several micrometers, but only have a slight advantage for those microspheres with diameters lager than five micrometers. To compensate this, we experimentally develop a time of flight method for measuring optical trap stiffness with larger microspheres. By comparing the optical trap stiffness of microspheres with different sizes and different materials at different laser powers, the time of flight method is confirmed to be more accurate and practical for microspheres larger than 5 μm; the result is of the same order of magnitude as the results of Brownian noise based analysis of 5 μm polystyrene bead. The results are higher than theoretical values due to the limited bandwidth of the camera. In comparison, the time of flight method is superior to other methods and does make sense in the fast calibration of optical trap stiffness on cell level. This method can be applied to optical traps with special field distributions. In the measurement of mechanical properties of cells, it can avoid using microspheres as force probe, thus providing a novel approach to the study of sophisticated single molecule process on the membrane of cells.
Structural analysis of Cu(In1-xGax)Se2 multi-layer thin film solar cells
Pan Hui-Ping, Bo Lian-Kun, Huang Tai-Wu, Zhang Yi, Yu Tao, Yao Shu-De
2012, 61 (22): 228801. doi: 10.7498/aps.61.228801
Abstract +
In this paper, the complex structure of CuInGaSe (CIGS), which is fabricated by a two-step progress (the deposition step and the salinization) or co-evaporation method, is analyzed in detail by several methods. Rutherford backscattering spectroscopy (RBS) shows unique advantage for investigating CIGS multi-layer. For the two-step CIGS thin films, both Ga and In atoms reveal a gradient distribution. Such a distribution that Ga atoms are more likely to be localized in a deeper layer of surface than in a shallow layer of surface, has no relation with the Mo layer. RBS and Auger electron spectroscopy (AES) prove that there appears diffusion in the interfaces of multi-layers, especially the interfaces of CdS and CIGS, Mo and CIGS. X-ray fluorescence (XRF) indicates that CIGS thin film presents the highest efficiency when the content ratio of In and Ga atoms is 0.7:0.3. Structural investigation by X-ray diffraction reveals the improved crystalline quality after annealing.
On weightd scale-free network model with tunable clustering and congesstion
Wang Dan, Jin Xiao-Zheng
2012, 61 (22): 228901. doi: 10.7498/aps.61.228901
Abstract +
We propose an evolutionary model for weighted network with tunable clustering coefficient according to characteristics of real network. The model gives power-law distributions of degree, weight, and strength, as confirmed in many real network. In particular, the weighted model has a nonlinear correlation between average clustering coefficient and degree, which is in good agreement with flat head real weighted technological network. Moreove, the effect of the weighted network structure on traffic delivery is studied. The packet traffic flow on the weighted scale-free network is investigated based on the local routing strategy using node strength, and the delivering ability of node is controlled by node strength. The simulations show that the traffic dynamics depends strongly on the controlled parameter.
Theoretical analysis on optimal navigation with total energy restriction in a two-dimensional lattice
Li Yong, Dou Fei-Ling, Fan Ying, Di Zeng-Ru
2012, 61 (22): 228902. doi: 10.7498/aps.61.228902
Abstract +
Recently, a certain total energy constraint =cN was introduced into the Kleinberg's navigation model, where is the total length of the long-range connections, c is a positive constant and N is the network size. The simulation results obtained in the one and two-dimensional cases indicate that with total cost restricted the optimal power-law exponent for adding extra long-range links between any two nodes seems to be =d+1, where d is the dimension of the underlying lattice in this paper. Based on mean field theory, the navigation process on the 2-dimensional cost constrained navigation model can be described by dynamical equations. Based on our theoretical analysis and the numerical results of the dynamical equations, we prove that for large networks and comparatively small total energy, the optimal power-law exponent is =3 for the two-dimensional case. Our results can perfectly correspond to simulations reported previously.
A novel local-world-like evolving bipartite network model
Tian Li-Xin, He Ying-Huan, Huang Yi
2012, 61 (22): 228903. doi: 10.7498/aps.61.228903
Abstract +
In complex networks, node degree values are limited by some practical factors. The saturation of node degree, which is a function of network evolution time, is defined first. We propose a novel evolving bipartite network model based on preferential attachment in local-world, which is generated by node saturation restrictions, not new node selection. So we also call it local-world-like model. However, the numerical simulation results display that the degree distribution does not obey the power-law distribution. We find that the degree value interval of this local-world-like bipartite network is small. There is no hub node. In addition to these, we analyze mixing coefficient of the network and find that the assortativities of the network are different when the network is generated by different initial parameters Such a result accords with our simulated result.
Comprehensive Survey for the Frontier Disciplines
Progress of the improved mobilities of organic field-effect transistors based on dielectric surface modification
Shi Wei-Wei, Li-Wen, Yi Ming-Dong, Xie Ling-Hai, Wei-Wei, Huang Wei
2012, 61 (22): 228502. doi: 10.7498/aps.61.228502
Abstract +
The surface property of the dielectric has a significant influence on growth, morphology, order of the organic semiconductor, and charge carrier transport. The relevant research shows that the mobility of organic field-effect transistor could be effectively improved via ameliorating the surface property of the dielectric. The purpose of this review is to introduce the main factors, including the roughness and the surface energy of dielectric, which exert a tremendous influence on the field effect mobility of OFET, and chiefly describe the progress of the two common methods used for the dielectric modification, viz., the self-assembled monolayer modification and the polymer modification. Finally, the novel applications at present are summarized in this review and some perspectives on the research trend are proposed.


Black hole mass and radiation pressure of Seyfert 1 galaxies
Xiong Ding-Rong, Zhang Xiong, Zheng Yong-Gang, Huang Bang-Rong, Mao Li-Sheng, Liu Wen-Guang, Cha Yong-Juan
2012, 61 (22): 229801. doi: 10.7498/aps.61.229801
Abstract +
We collect 214 Seyfert 1 galaxies(147 narrow line Seyfert 1 and 67 broad line Seyfert 1) and research black hole mass bulge velocity dispersion Eddington radio luminosity at 5100 Å and redshift. Our conclusions are follows: (1) when computing black hole mass, we should consider the effect of radiation pressure, especially for the narrow line Seyfert 1 galaxies; (2) when the effect of radiation pressure is considered, narrow line Seyfert 1 galaxies meet MBH-σ relation of normal galaxies and are in su-Eddington accretion; (3) in a large samples, the evolution of Seyfert 1 galaxies is from narrow line Seyfert 1 galaxies to broad line Seyfert 1 galaxies, which is consistent with other results obtained in different ways.