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Vol. 61, No. 13 (2012)

2012-07-05
GENERAL
Simulation of reflection spectrum of FBG with uniaxial anisotropic crystal cladding
Li Li-Jun, Ma Hui, Zhang Yan-Liang, Sui Tao, Lai Yong-Zheng, Li Jing, Cao Mao-Yong
2012, 61 (13): 130201. doi: 10.7498/aps.61.130201
Abstract +
In this paper, the ideal normal mode characteristic equation of the optical fiber with uniaxial anisotropic crystal cladding is derived. Using mean value theorem and combining Matlab numerical method, a solving algorithm of this transcendental equation is proposed. Therefore, the relationship between FBG reflect spectrum characteristic and cladding reflective index is simulated. The simulation results show that kcl has a strong influence on the spectrum, different values of kcl can lead to different reflectivities and different Bragg wavelengths.
A method of constructing infinite sequence soliton-like solutions of nonlinear evolution equations
Taogetusang, Bai Yu-Mei
2012, 61 (13): 130202. doi: 10.7498/aps.61.130202
Abstract +
The auxiliary equation method is used to construct the finite new exact solutions of nonlinear evolution equations. To search for infinite sequence soliton-like exact solutions of nonlinear evolution equations, characteristics of constructivity and mechanization of auxiliary equation method are analyzed and summarized. Therefore, the quasi-Bcklund transformation between new solutions of a kind of auxiliary equation with Riccati equation is presented, then (2+1)-dimensional modified dispersive water-wave system is taken as an applicable example to find infinite sequence soliton-like new exact solutions by choosing two kinds of formal solutions of nonlinear evolution equations with the help of symbolic computation system Mathematica, where included are the infinite sequence smooth soliton-like solutions, compact soliton solutions and peak soliton-like solutions.
The stability of solitay wave solution to a modified Kadomtsev-Petviashvili equation
Zhang Juan, Zhou Zhi-Gang, Shi Yu-Ren, Yang Hong-Juan, Duan Wen-Shan
2012, 61 (13): 130401. doi: 10.7498/aps.61.130401
Abstract +
The reductive perturbation method is employed to describe the behaviour of ion-acoustic waves for plasmas in the absence of magnetic field, leading to a type of modified Kadomtsev-Petviashvili equation. The stability of a special type of solitary wave solutions for the modified Kadomtsev-Petviashvili equation is investigated with a finite difference scheme. The numerical results show that this solitary wave is unstable under two particular initial perturbations.
The influence of the disorderded substrate potential on static friction force
Yang Yang, Wang Cang-Long, Duan Wen-Shan, Shi Yu-Ren, Chen Jian-Min
2012, 61 (13): 130501. doi: 10.7498/aps.61.130501
Abstract +
In order to better simulate a real model which can be realized in experiment, we study a two-dimensional(2D) Frenkel-Kontorova(FK) model driven by the disordered substrate potential which is charactered by the sum of identical Gaussian functions. Commensurate and incommensurate interfaces are discussed. In the paper, we mainly analyse the mechanism of friction, and the effects of static friction force on the disordered substrate potential.
Stochastic resonance in FHN neural system driven by non-Gaussian noise
Zhang Jing-Jing, Jin Yan-Fei
2012, 61 (13): 130502. doi: 10.7498/aps.61.130502
Abstract +
Stochastic resonance (SR) is studied in the FitzHugh-Nagumo (FHN) neural system subject to multiplicative non-Gaussian noise, additive Gaussian white noise and a periodic signal. Using the path integral approach and the two-state theory, the expression of the signal-to-noise ratio (SNR) is derived. The simulation results show that conventional SR and double SR occur in the FHN neural model under different values of system parameters. The effects of the additive and multiplicative noise intensities on SNR are different. Moreover, the addition of non-Gaussian noise is conductive to the enhancement of the response to the output signal of the FHN neural system.
Stochastic resonance in an over-damped linear oscillator driven by multiplicative quadratic noise
Zhang Lu, Zhong Su-Chuan, Peng Hao, Luo Mao-Kang
2012, 61 (13): 130503. doi: 10.7498/aps.61.130503
Abstract +
For an over-damped linear oscillator driven by multiplicative quadratic noise and periodic modulated noise, the exact analytical expressions of the first two moments, the amplitude and variance of the system steady-state response are obtained. We find that this system has richer dynamic behaviors than the traditional linear systems driven by linear noise; when the coefficients of the quadratic noise satisfy certain conditions, both the amplitude and the variance of the system steady-state response present stochastic resonance.
Control of fast-scale bifurcation in single-phase SPWM inverter and its stability analysis
Hu Nai-Hong, Zhou Yu-Fei, Chen Jun-Ning
2012, 61 (13): 130504. doi: 10.7498/aps.61.130504
Abstract +
H bridge inverter is a basic nonlinear topology in power electronic circuits. However it is prone to the generation of fast-scale instability phenomenon due to the variation of some parameters in the operation process, which can be eliminated with the slope compensation simply and effectively. Experience plays the leading role and common engineering design is lacking in necessary design criteria. Accrording to the bifurcation control theory of nonlinear system, in this paper we analyze the implementation of slope compensation on H bridge inverter under peak current mode control in detail, thereby obtaining the accurate amplitude requirements of the compensated slope signal and realize the optimization. The results of the analysis are consistent with those of simulation experiment, and the inverter circuit under appropriate slope compensation can operate in stable regime especially with the performances being enhanced remarkably. The research method is also applicable for the stability analysis of other power electronic circuits.

EDITOR'S SUGGESTION

The normalized KLD coefficient and its application in detection of correlation and synchronization from multivariable series
Xie Xiao-Ping, Chen Hong-Ping, Cao Zhi-Tong, He Guo-Guang
2012, 61 (13): 130505. doi: 10.7498/aps.61.130505
Abstract +
The KLD coefficient and the normalized KLD coefficient are proposed to characterize the correlation of multivariable series in order to overcome the intrinsic limitations of the KLD dimension density. Using the uncorrelated or perfectly correlated multivariable series, the upper and the lower bound functions of the KLD dimension density, and furthermore the upper and the lower bounds of the KLD coefficient are analytically deduced. Then, the normalized KLD coefficient is proposed in the paper. The analyses and numerical simulations prove that the changes of correlation of multivariable series can lead to linear variation of the normalized KLD coefficient. The simulations also prove that the normalized KLD coefficient can detect the changes of correlation sensitively, even if these are induced by only two channels of multivariable series. Furthermore, the normalized KLD coefficient can be used to analyze the nonstationary time series. The simulation results of coupled map lattice prove that the normalized KLD coefficient can also be used for the nonlinear system analysis.
Amplitude spiral wave in coupled complex Ginzburg-Landau equation
Gao Ji-Hua, Xie Wei-Miao, Gao Jia-Zhen, Yang Hai-Peng, Ge Zao-Chuan
2012, 61 (13): 130506. doi: 10.7498/aps.61.130506
Abstract +
A novel amplitude spiral wave in coupled complex Ginzburg-Landau equation (CGLE) system is proposed. The stability conditions and the relevant factors are investigated via numerical simulations. On the tip of an amplitude spiral wave there exist no topological defect, which is different from the commonly observed phase spiral wave, and in its amplitude part (instead of phase part) there is a spiral structure. In this research, the stability of amplitude spiral wave is studied by considering the different initial patterns in the case of the system parameter mismatches.
Application of FuzzyEn algorithm to the analysis of complexity of chaotic sequence
Sun Ke-Hui, He Shao-Bo, Yin Lin-Zi, Duo Li-Kun
2012, 61 (13): 130507. doi: 10.7498/aps.61.130507
Abstract +
To analyze the complexity of chaotic sequence correctly, complexity of systems, including typical discrete chaotic systems and continuous chaotic systems, are investigated based on the FuzzyEn algorithm. Compared with ApEn, SampEn and Intensive statistical complexity algorithm, the FuzzyEn algorithm is an effective measure algorithm for analyzing chaotic sequence complexity, and it has low sensitivity to and slight dependences on phase space dimension (m), similar tolerance (r) and sequence length (N), better robustness and measure value continuities. Results of the complexities of chaotic systems show that the complexity of continuous chaotic systems are much smaller than those of the discrete chaotic systems. However, having been disturbed by high complex discrete chaotic pseudo-random sequences or classical m-series, the pseudo-random sequences of continuous chaotic systems increase their complexities significantly. Our result provides a theoretical basis for the application of chaotic sequences to the field of cryptography and secure communication.
Research of Chaotic encryption system based on FPGA technology
Liu Qiang, Fang Jin-Qing, Zhao Geng, Li Yong
2012, 61 (13): 130508. doi: 10.7498/aps.61.130508
Abstract +
In this paper, a kind of chaos encryption system is presented based on chaotic encryption algorithm and traditional encryption algorithm, and hardware is implemented by using the FPGA technology. According to discrete and digital technologies, Henon Map and Logistic Map are applied, and chaotic iteration sequence is generated by using Verilog HDL language and FPGA technology. By combining the traditional iteration algorithm, the files are encrypted and decrypted. Based on Xilinx FPGA exploitation platform, secret communication experiments on Internet are successefully. The devise has potential prospective applications in internet secrecy communication.
Simulation of pedestrian evacuation with asymmetrical pedestrian layout
Yue Hao, Zhang Xu, Chen Gang, Shao Chun-Fu
2012, 61 (13): 130509. doi: 10.7498/aps.61.130509
Abstract +
Simulation of pedestrian evacuation from a room with multi-exit and asymmetrical pedestrian layout is presented based on an improved dynamic parameter model in this paper. The computation and the count-area of imaginary distance are improved based on the Max-Min evacuation path selection of actual and imaginary distance in order to reduce evacuation imbalance caused by the asymmetry of pedestrian layout. An imbalance coefficient is introduced to describe the asymmetry of pedestrian layout. The effects of pedestrian layout asymmetry on the evacuation time are analyzed respectively from fixed and unfixed pedestrian initialization site. The simulation results of the improved and original models are compared and analyzed, and the improved model can effectively reduce evacuation imbalance. Simulation results show that under normal evacuation condition with considerring reasonable pedestrian and jam around exits, evacuation time is hardly affected by pedestrian and exit layout and depends mainly on cognition coefficient, total width of exits and pedestrian initialization amount.
Structures and melting behaviors of ultrathin platinum nanowires
Xia Dong, Wang Xin-Qiang
2012, 61 (13): 130510. doi: 10.7498/aps.61.130510
Abstract +
The amorphous-like structures and melting behaviors of ultrathin platinum nanowires are studied by EAM potential by using empirical molecular-dynamic simulation and the dependence of nanowire melting temperature pm soze os pntaomed. When the Lindeman criterion is 0.03, we find that the melting temperature for Pt nanowires is well consistent with the result obtained from the potential energy. Through comparing the Lindemann indexes on each shell, the thermal stability is studied. The results indicate that melting of the cylindrical helical structures starts from the interior atoms and that of the bulklike rectangular structure starts from the surface. We also observe the positions of the atoms at different temperatures to obtain the atomic diffusion and mobility.
ATOMIC AND MOLECULAR PHYSICS
Molecular dynamics simulation on friction process of silicon-doped diamond-like carbon films
Lan Hui-Qing, Xu Cang
2012, 61 (13): 133101. doi: 10.7498/aps.61.133101
Abstract +
Silicon-doped diamond-like carbon (Si-DLC) film is of significant interest for tribological effects, because it has a very low friction coefficient and possesses the potential to improve wear performance in humid atmospheres and at high temperatures. Many experimental results of the Si-DLC film show that its tribological property changes greatly with silicon content. In this paper, we use molecular dynamics (MD) simulation to study sliding friction processes between DLC and Si-DLC films under dry friction and oil-lubricated conditions separately. The results show that after sliding, a transfer film between the DLC and Si-DLC films is formed under the dry friction condition. In contrast, a boundary lubrication layer is found under the oil-lubricated condition. Therefore the friction forces on the dry friction condition are larger than those on the oil-lubricated condition. Small addition of silicon atoms can reduce the friction force of DLC films indeed, but it has little effect to the friction force when the silicon content is larger than 20%. There is a obvious effect of the silicon content on the bond number of transfer films under the dry friction condition, and CC bond and CSi bond both first increase and then decrease, there is almost no little CSi bond at the end of the sliding.
Maximum correlation at the transition to the saturation regime of nonsequential double ionization
Xin Guo-Guo, Zhao Qing, Liu Jie
2012, 61 (13): 133201. doi: 10.7498/aps.61.133201
Abstract +
The nonseqential double ionization of helium in the laser with intensities ranging from blow the recolliding ionization threshold to near the sequential double ionization regime is studied systematically. We obtain the probability ratio between correlation and anti-correlation of the two final electrons, and find the maximum ratio is in the transition region to the saturation regime of nonsequential double ionization. The maximum ratio generation course is shown in correlated two-electron longitudinal momentum spectrum, and the deep mechanism is investigated by orbit back-trace analysis. The rescattering of one electron after recollision and the high speed recollision of the tunneled electron lead to the increases of anticorrelation ratio in low- and high- intensity laser fields respectively.
Investigations of vibrational levels and dissociation energies of diatomic systems using a variational algebraic method
Zhang Yi, Sun Wei-Guo, Fu Jia, Fan Qun-Chao, Feng Hao, Li Hui-Dong
2012, 61 (13): 133301. doi: 10.7498/aps.61.133301
Abstract +
The algebraic method (AM) suggested by Sun et. al. is developed into a nodal variational AM (VAM) to offset the possible experimental errors by using an energy variational part δE after analyzing the error amplification effect. The VAM is used to study the full vibrational levels {Eυ} and the dissociation energies De for 51Πu7Li2, (6d)1Δg Na2, (7d)1ΔgNa2 and 51∑+ NaK alkali metal diatomic molecular electronic systems. The results reproduce all known experimental vibrational energies, predict correct dissociation energies and all unknown high-lying levels that may not be given if one uses original AM or other numerical methods or experimental methods. These theoretical analyses and results not only show that the VAM is feasible and correct for many diatomic systems, but also provide constructive reference for other numerical calculations or simulations.
A theoretical study on double differential cross sections for (e, 2e) process of hydrogen
Yang Huan, Zhang Sui-Meng, Xing Ling-Ling, Wu Xing-Ju, Yuan Hao
2012, 61 (13): 133401. doi: 10.7498/aps.61.133401
Abstract +
The double differential cross sections for electron impact ionization of hydrogen at incident energies of 15.6 eV, 17.6 eV, 25 eV and 40 eV are calculated by use of BBK model and modified BBK model. The results of the present work are compared with the absolute experimental date. The structure of the cross sections is analysed and the contributions of exchange effects to corss sections are discussed.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Design of a thin wide-band absorber based on metamaterials and resistance frequency selective surface
Cheng Yong-Zhi, Nie Yan, Gong Rong-Zhou, Zheng Dong-Hao, Fan Yue-Nong, Xiong Xuan, Wang Xian
2012, 61 (13): 134101. doi: 10.7498/aps.61.134101
Abstract +
Three kinds of absorbers, based on square metal patch structure(SMP) metamaterials, resistance frequency selective surface (RFSS), and the combined SMP with RFSS structures, are designed, respectively. The absorptivities of these absorbers are simulated and analyzed by FDTD method. The simulation results indicate that in a frequency range of 230 GHz, SMP absorber can achieve stronger multi-bands absorption by the proper design of geometrical parameters of unit cell; RFSS absorber can achieve stronger high-frequency broadband absorption by the proper design of the square resistance of unit cell. However, the bandwidth of stronger absorption is limited; the absorption of the composite absorber combined with SMP and RFSS structure is greater than 90% in a frequency range of 325 GHz, which has a characteristic of better impedance matching to the free space in a wide frequency range.
Design of a low-frequency broadband metamaterial absorber based on resistance frequency selective surface
Cheng Yong-Zhi, Wang Ying, Nie Yan, Zheng Dong-Hao, Gong Rong-Zhou, Xiong Xuan, Wang Xian
2012, 61 (13): 134102. doi: 10.7498/aps.61.134102
Abstract +
A low-frequency broadband, polarization-insensitive and wide-angle metamaterial absorber is presented, which is based on resistance frequency selective surface (RFSS). The unit cell of this absorber consists of cave cross planar metamaterial (CCPM), RFSS, dielectric substrate and metal backboard. The simulated results based on FDTD method indicate that with the absorptions of compared to the individual CCPM absorber and RFSS absorber, the absorption of the composite structure absorber of CCPM and RFSS is enhanced greatly, and it is greater than 80% and the absorption peak is over 98% in the whole frequency range of 15 GHz. The simulated absorptions under the conditons of different polarization and incident angles indicate that this composite structure absorber has polarization-insensitive and wide-angle absorption.
The study of asymmetric energy transmission based on the nonlinear supratransmission
Tao Feng, Chen Wei-Zhong, Xu Wen, Du Si-Dan
2012, 61 (13): 134103. doi: 10.7498/aps.61.134103
Abstract +
In this paper, the phenomenon of the asymmetric energy transmission is numerically investigated in the forbidden band of the electrical transmission line formed by two nonlinear segments which are identical in structure but different in inductor parameter. By considering the driving voltage at the frequency within the forbidden bands of both segments, the carrier of the asymmetric energy flux is the nonlinear wave beyond the band, instead of the linear wave in the passband, and the mechanism is closly related to the nonlinear supratransmission. To further understand this phenomenon in electrical transmission line, we also study the correlations between the energy intensity and the circuit parameters. Finally, we investigate the dependency of the voltage threshold on the driving frequency in physical experiment, and the result is qualitatively identical with that calculated by using equation.
Electromagnetic coupling and shielding effectiveness of apertured rectangular cavity under plane wave illumination
Jiao Chong-Qing, Qi Lei
2012, 61 (13): 134104. doi: 10.7498/aps.61.134104
Abstract +
Based on the Bethe's theory for small aperture coupling and the eigen-mode expansion method, an approximate analytic model for the field distribution inside a rectangular cavity with apertures under plane wave illumination is presented. The effects of aperture shape, dimensions, number, position, and the wave incidence and polarization angles on cavity mode excitation can be taken into consideration in this model with clear physical explanation. The calculation results from this model are in better agreement with experimental data than those from the equivalent circuit model. The effects of various factors on the shielding effectiveness of the cavity are analyzed, and the obtained results are useful for guiding the design of electromagnetic shielding enclosures.
Ray ellipse method of analyzing the power and polarization state of partially polarized light
Liu Chao, Cen Zhao-Feng, Li Xiao-Tong, Xu Wei-Cai, Shang Hong-Bo, Neng Fen, Chen Li
2012, 61 (13): 134201. doi: 10.7498/aps.61.134201
Abstract +
It is difficult to cope with the changes in power and polarization for partially polarized light. The light polarization will also affect the image quality, especially for imaging with large numerical aperture. A novel method of analyzing the power and the polarization state of partially polarized light is proposed in this paper. This method has a good intuitiveness and requires much smaller computation. An aplanatic lens system is simulated. Polarization effect caused is analyzed with this method. The results show that for the imaging light the intensity of TM polarized light relatively increases because of large numerical aperture, which will influence image contrast. Imaging in high refractive index medium can be used to improve this problem.
The electric and magnetic polarization singularities of Gaussian vortex beam in the free-space propagation
Luo Ya-Mei, Lü Bai-Da, Tang Bi-Hua, Zhu Yuan
2012, 61 (13): 134202. doi: 10.7498/aps.61.134202
Abstract +
Using the Fresnel vector diffraction integral and taking the Gaussian vortex beam as an example, the analytical expressions for the electric and magnetic components of Gaussian vortex beam propagating in the free-space are derived, and used to study the variations of electric and magnetic polarization singularities in free space. It is found that there exist two-dimensional (2D) and three-dimensional (3D) electric and magnetic polarization singularities in the free-space, which do not coincide in general. By varying waist width ratio, amplitude ratio, and propagation distance, the motion of polarization singularities takes place. In the 2D and the 3D electric and magnetic fields, the V-point may appear under a certain condition.
Focal depth research of digital holographic reconstructed image
Li Jun-Chang
2012, 61 (13): 134203. doi: 10.7498/aps.61.134203
Abstract +
Regarding the object scattering light as a superposition of light waves emitting from a lots of point sources on object surface of which phases have random values, in the paper, wee investigate the diffracted field of digital holographic reconstructed image and defocused image. The definition of depth of focal (DOF) is also given based on the feature that the reconstructed image is displayed in pixels. According to the characteristic that the physical dimensions of pixel are associated with computation method, focal depth expressions are deduced when image is reconstructed with different algorithms. Finally, experimental verification is given.
Generation and control of electromagnetically induced double photonic band-gaps
Yu Miao, Zhang Yan, Fang Bo, Gao Jun-Yan, Gao Jin-Wei, Wu Jin-Hui
2012, 61 (13): 134204. doi: 10.7498/aps.61.134204
Abstract +
By using the technique of electromagnetically induced transparency and solving density matrix equations for atoms and transfer matrix equations of fields, we study the steady optical properties of a four-level system of cold atoms driven by a traveling-wave field and a standing-wave field. It is found that a nearly perfect structure of double photonic band-gap can be generated with specific parameters. In particular, the reflectivity inside each photonic band-gap is homogeneous over 95%. It is convenient to modulate the positions and widths of both photonic band-gaps by changing intensities and frequencies of the driving fields. The double photonic band-gaps can be used to achieve all-optical routing and switching and therefore may have applications in all-optical information networks.
Precise frequency control of an Er-doped fiber comb
Cao Shi-Ying, Meng Fei, Lin Bai-Ke, Fang Zhan-Jun, Li Tian-Chu
2012, 61 (13): 134205. doi: 10.7498/aps.61.134205
Abstract +
The repetition rate and the carrier-envolope offset frequency of a home-made Er-doped fiber comb are precisely phase-locked. The residual fluctuations of the stabilized repetition rate and the carrier-envolope offset frequency are 0.515 mHz and 93.13 mHz respectively
Study on characteristics of acoustic modes via stimulated Brillouin scattering in photonic crystal fiber
Hou Shang-Lin, Xue Le-Mei, Li Suo-Ping, Liu Yan-Jun, Xu Yong-Zhao
2012, 61 (13): 134206. doi: 10.7498/aps.61.134206
Abstract +
The effects of optical fiber parameters, pump wavelength and the fiber core refractive index in small-core photonic crystal fibers on characteristics of acoustic modes and the dependency of the acoustic modes coupling are investigated by the effective index method. The results indicate that both the mixed longitudinal acoustic mode and transverse acoustic mode jointly produce the acoustic fields, and their coupling forms the mixed acoustic mode; the propagation constant of acoustic mode can be changed by tailoring the pump wavelength or the PCF core refractive index in the process of SBS; the acoustic mode coupling increase and the phase velocity of the acoustic mode decreases with the increase of the PCF core diameter, and there is also a growing trend of the number of the acoustic modes at the same propagation constant. The velocity decreases with the increase of the frequency of the pump wave.
Discrete soliton interaction in quasi one-dimensional optically induced photonic lattice
Xiao Fa-Jun, Zhang Peng, Liu Sheng, Zhao Jian-Lin
2012, 61 (13): 134207. doi: 10.7498/aps.61.134207
Abstract +
The coherent and the incoherent interactions of discreet solitons in quasi one-dimensional optically induced photonic lattice are theoretically and numerically analyzed. It is found that in-phase solitons attract each other and out-of-phase solitons repel one other. Due to the anisotropy of the nonlinearity, two initially attractive incoherent solitons will repel each other as their interval waveguide number increasing. Moreover, the pendulum-like intertwist of discrete solitons is observed during the incoherent interaction due to the interplay between soliton transverse motions resulting from the soliton interaction and the Bragg reflection of the lattice structure. These results help us to understand how the anisotropy of the nonlinearity response plays a role in discrete soliton interaction and offers the theoretical support for the experimental investigation.
Research on one-dimensional function photonic crystals
Wang Guang-Huai, Wang Qing-Cai, Wu Xiang-Yao, Zhang Si-Qi, Wang Jing, Liu Xiao-Jing, Ba Nuo, Gao Hai-Xin, Guo Yi-Qing
2012, 61 (13): 134208. doi: 10.7498/aps.61.134208
Abstract +
In the paper, we present a new kind of function photonic crystal of which the refractive index is a function of space position. According to Fermat principle, we give the motion equations of light in one-dimensional, two-dimensional and three-dimensional function photonic crystals. For one-dimensional function photonic crystal, we give the dispersion relation, the band gap structure and the transmissivity, and we obtain wider or narrower band gap structure than that of conventional photonic crystal. We study the effects of the refractive index, the number of period, the incidence angle and the thickness of medium layer on photonic crystal band gap, and obtain some valuable laws. Our results give the theoretical support designing the photonic crystals of different band gap structures.
Ultrahigh-Q small-V photonic crystal nanobeam cavities based on parabolic-shaped width and taper holes
Feng Chen, Feng Guo-Ying, Chen Nian-Jiang, Zhou Shou-Huan
2012, 61 (13): 134209. doi: 10.7498/aps.61.134209
Abstract +
One-dimensional (1-D) photonic crystal (PhC) nanobeam cavity based on parabolic-shaped width and tapered holes was proposed and analyzed. Finite-difference time-domain simulations show that both an ultrasmall modal volume (V~ 0.04(λ /n)3) and ultrahigh quality factor (Q~ 1.8× 107) can be obtained in PT PhC nanobeam cavity. In addition, the PT PhC nanobeam have one order lower V comparing to parabolic and tapered nanobeam. With compactness, lower fabrication requirements to achieve ultrahigh Q/V, the proposed nanobeam could be versatile platforms of interest for optical communications, optomechanics, cavity QED, etc.
Properties of photonic quantum well structures containing left-handed materials
Liu Li-Xiang, Dong Li-Juan, Liu Yan-Hong, Yang Cheng-Quan, Shi Yun-Long
2012, 61 (13): 134210. doi: 10.7498/aps.61.134210
Abstract +
According to the technology of LC-load transmission lines photonic quantum well structures are fabricated. Two kinds of structures are act as quantum well. While the left-handed materials works as well, the number of resonance modes increase with the thickness of left-handed materials. Compared with the condition of photonic crystals work as well, the left-handed materials act as well has the advantage of smaller size and adjusting. Experimental results are consistent with theory.
Viscosity coefficient in granular medium
Qian Zu-Wen
2012, 61 (13): 134301. doi: 10.7498/aps.61.134301
Abstract +
A granular medium can be regarded as an equivalent uniform medium, of which the attenuation coefficient and the acoustic speed are obtained from the author's theory published elsewhere. The equivalent static density can be given by the mixed rule. According to the author's sound propagation theory in the granular medium, furthermore, the secondary waves are plane waves as well when the incidental sound wave is plane wave. In these cases, the three-dimensional equations can be simplified into a one-dimensional equation, and an expression for the viscosity coefficient in concentrated granular medium can be obtained. The theoretical results show that the viscosity coefficient depends on not only the volume fraction of the grains, but also sound frequency. On the other hand, the theory given in this paper can be used in the realistic cases, where less restrictions will be imposed on the applications than the Einstein's theory.
Sectorial oscillation of acoustically levitated viscous drops
Shao Xue-Peng, Xie Wen-Jun
2012, 61 (13): 134302. doi: 10.7498/aps.61.134302
Abstract +
The sectorial oscillation of acoustically levitated viscous drops is investigated by applying a series of aqueous glycerol solutions (viscosity = 0.9475.65 mPas). It is found that there exists a critical viscosity c for a definite mode of sectorial oscillation, and that mode can be excited only when c. The critical viscosities for the l = 29th mode sectorial oscillation are experimentally determined with a modulation amplitude to the acoustic field reaching = 0.23. It is found that ln c decreases approximately linearly with l. Analysis based on the parametric resonance theory indicates that in order to excite the sectorial oscillation, the equatorial radius of the drop must be perturbed overs a threshold hc, which is proportional to the viscosity and increases with l. Therefore, the sectorial oscillations can hardly be excited to those drops with high viscosity and large oscillation modes. Both the amplitude and resonant modulating frequency width decrease with the enlargement of viscosity. No obvious effect of viscosity is found on the eigenfrequency of sectorial oscillation.
Research on a cylindrical cloak with active acoustic metamaterial layers
Shen Hui-Jie, Wen Ji-Hong, Yu Dian-Long, Cai Li, Wen Xi-Sen
2012, 61 (13): 134303. doi: 10.7498/aps.61.134303
Abstract +
Enlightened by the tunable properties of effective density of the active acoustic metamaterial, we design an active infinite cylinder acoustic cloak according to the idea of the multilayer structured acoustic cloak with homogeneous isotropic materials. Utilizing the electrical analog, the dynamical equation of the acoustic cavity with Piezo-Diaphragm is presented. By analyzing the circuit diagram, the control strategy of achieving various effective densities which are used for constructing the acoustic cloak is given. Based on the necessary parameters such as the wide range values of the relative densities gained by active control, and the acoustic speed of each composite layer, the acoustic pressure field of the plane wave incident on the cloak is calculated, via the FEM model. Also the pressure map of a rigid cylinder scatterer with surrounded fluid is performed for comparison. Results show that outside the cloaking shell, the plane wave field is almost undisturbed. However inside the shell, the plane wavefronts are gradually deflected, and guided around the cloaked domain, returning to the original plane shape with small perturbation. This phenomenon making the cloak acoustically invisible in some frequency ranges has useful values in engineering applications. Finally, the total scattering cross section of the cloak is calculated to investigate the invisible effect according to the frequency domain. The total number of the composite active metamaterial layers is 15, which is much easier to realize in experiment.
Study of bone fatigue evaluation with ultrasonic guide waves based on elastic modulus
Zhang Zheng-Gang, Ta De-An
2012, 61 (13): 134304. doi: 10.7498/aps.61.134304
Abstract +
How to diagnose the bone fatigue damage at early stages is one of the hot research subjects in bone evaluation field. In this study, the propagation characteristics of ultrasonic guide wave in a long bone under different elastic moduli are analyzed using theoretical calculation and simulation methods. First, theoretical solutions of guided wave in a long bone are calculated. Then, a finite difference time-domain (FDTD) numerical method of simulating the propagation of guide wave in a long bone is presented. The simulation results are in good agreement with the theoretical values. And, the relationship between elastic modulus and the propagation characteristics, including group velocity, central frequency and attenuation, is discussed. The results show that group velocity and central frequency increase with the increase of elastic modulus. However, attenuation decreases with the increase of elastic modulus. Those results demonstrate that the propagation of guide wave can reflect the variation of elastic modulus of long bone, which provides a theoretical basis for evaluating the early stages of fatigue damage in long bone.
Experimental study and improvement of frequency lowering algorithm in Chinese digital hearing aids
Liang Rui-Yu, Xi Ji, Zhao Li, Zou Cai-Rong, Huang Cheng-Wei
2012, 61 (13): 134305. doi: 10.7498/aps.61.134305
Abstract +
Frequency lowering algorithms are the most effective and secure for improving the auditory identification capability of hearing-impaired patients. Through analyzing the current algorithms by the test of subjective auditory approach, in the paper we propose an adaptive algorithm combining slow playback algorithm with frequency transition algorithm. The algorithm can adaptively adjust playback ratio according to the signal spectrum structure to reduce the desynchronization in time region. Furthermore, a method of evaluating the playback ratio in noise is designed based on the frequency spectrum relation between noise and noisy signal. Results showed that compared with other frequency lowering algorithms, the proposed algorithm can improve the auditory identification capability from 15% to 20%. In addition, in the test for hearing-impaired person, the significant improvement on the average auditory identification capability is also obtained compared with the conventional hearing aid device.
Effects of Ge profile in base region on thermal characteristics of SiGe HBTs
Zhao Xin, Zhang Wan-Rong, Jin Dong-Yue, Fu Qiang, Chen Liang, Xie Hong-Yun, Zhang Yu-Jie
2012, 61 (13): 134401. doi: 10.7498/aps.61.134401
Abstract +
As is well known, the base Ge composition can improve the DC characteristics, frequency characteristics and noise characteristics of SiGe HBTs. However, the reports about the effects of Ge profile on HBTs thermal characteristics are rare. In this paper, by use of SILVACO simulator, the effects of different Ge gradients on thermal and electrical characteristics of SiGe HBT are investigated. It is found that under the same total Ge amount condition, as Ge gradient increases, the fT of device increases significantly, the uniformity of temperature distribution becomes better, the influences of temperature on the and fT are weakened, but the gain becomes smaller. For the device with uniform Ge composition, the is high, but the influence of temperature on the is enormous, the uniformity of temperature distribution is poor. Based on these results, in order to make a tradeoff among thermal, gain and frequency characteristics, a novel Ge composition structure with the combination of the uniform and graded Ge composition is proposed. The results show that the novel Ge composition structure SiGe HBT has good performances lower peak temperature, better uniform temperature profile, smaller variabilities of and fT with temperature, sufficient high and fT compared with the uniform Ge composition device. These new results provide valuable reference for the device thermal design, and are supplemental to the research and application of SiGe HBTs.
Study on ultra fast nonequilibrium heat transfers in nano metal films by femtosecond laser pump and probe method
Zhu Li-Dan, Sun Fang-Yuan, Zhu Jie, Tang Da-Wei
2012, 61 (13): 134402. doi: 10.7498/aps.61.134402
Abstract +
The reduction in size and the increase in speed of microelectronic device make the probability of nonequilibrium electron-phonon phenomena become greater, leading to the increase of thermal resistance in the device. The measurement of electron-phonon coupling factor in material resistance increasingly becomes important for accurate thermal treatment. The femtosecond laser pump and probe method is used for studing the nonequilibrium heat transfer in nano metal films with different thicknesses. Exploring parabolic two-step model (PTS) to fit the experimental data. During the fitting process, we considered the proportional relationship between the changes of electron temperature and phonon temperature, which affects the reflectivity. By studying the different thicknesses of Ni and Al films electron-phonon coupling factors, we find that the electron-phonon coupling factor does not change with film thickness. In addition, the experimental result verifies that the reflectivity of probe laser is affected by electron temperature and phonon temperature at the same time. Through the data analysis, we also get the influence coefficients of electron temperature and phonon temperature on reflectivity.
Experimental and theoretical investigations of the effect of “Brazil Nut” segregation in vibrating granular matters
Peng Ya-Jing, Zhang Zhuo, Wang Yong, Liu Xiao-Song
2012, 61 (13): 134501. doi: 10.7498/aps.61.134501
Abstract +
Size segregation is one of important properties of vibrating granular matters. It is significant to understand and study the segregation mechanisms and parameter range of controlling factors of mixed granular matters for the development of industry, agriculture and pharmaceutical. In this paper, we investigate the influence factors and physical mechanisms of "Brazil Nut" segregation experimentally and theoretically. The influences of vibrating acceleration, sizes and densities of large and small granules on the segregation time are analyzed. The hydro-model is used to evaluate segregation time and explain the experimental results qualitatively. Results show that the vibration acceleration is a main controlling factor for "Brazil Nut" segregation in the case of fixed frequency. There is a critical acceleration. When the acceleration is larger then its critical value the main physical mechanism changes from convection to filling voids, and the effect of acceleration on segregation decreases, while the effect of size of large granule on it increases. Furthermore, "Brazil Nut" segregation still arises when the density ratio is equal to 1. The increase of the size or density of small granular may enhance "Brazil Nut" segregation.
Low speed water-entry of cylindrical projectile
He Chun-Tao, Wang Cong, He Qian-Kun, Qiu Yang
2012, 61 (13): 134701. doi: 10.7498/aps.61.134701
Abstract +
Experimental studies of the water-entry of cylinder bodies are conducted using high-speed camera to capture the splashes over the water surface and the subsurface cavity shapes during water entry and the cavity-running phase. Cavity evolution is discussed on single 140 conical cylinder body such as formation, development, and pinch-off of vertical and oblique entry. The dependence of the pinch-off type on the entry velocity is discussed for various entry speeds. The phenomena of two-body water entry in series and side-by-side are discussed in the end of this paper, and the data show that the spatial distance between the two bodies has a great influence on the development and the stability of the cavity and the dynamics of both bodies themselves.
Research on simultaneous reconstruction of the temperature distribution of a 3D participating medium and its boundary
Feng Yu-Xiao, Huang Qun-Xing, Liang Jun-Hui, Wang Fei, Yan Jian-Hua, Chi Yong
2012, 61 (13): 134702. doi: 10.7498/aps.61.134702
Abstract +
In-situ and nonintrusive 3D temperature measurement is very important for combustion diagnosis and controlling of pollutants. The temperature reconstruction technique based on radiation inverse analysis has received intensive attention. In order to reduce the computation cost and take boundary temperature into consideration, a discrete method is presented for 3D temperature distribution determination for an absorbing, emitting and scattering combustion medium and its boundary by using the emission image measured by four CCD cameras. First the radiative source term is retrieved through the discrete transfer method. Then, the temperature is inferred from the blackbody intensity obtained by subtracting the media scattering and boundary reflecting contribution from the source term by the discrete ordinate approximation. The least squares minimum residual algorithm is improved to solve the ill-posed reconstruction equations. The performance of the proposed method is examined by numerical test. The effects of measurement noise and radiative properties on the reconstruction accuracy are investigated. The results show that the method proposed in this paper is capable of reproducing the temperature of the medium and its boundary accurately, even with noise. The reconstruction time cost is reduced significantly compared with those of other methods.
Elecrohydrodynamical characteristics of liquid film motor driven by a square-wave electrophoresis electric field
Liu Zhong-Qiang, Gan Kong-Yin, Li Ying-Jun, Jiang Su-Rong
2012, 61 (13): 134703. doi: 10.7498/aps.61.134703
Abstract +
Liquid film motor as a novel experimental device will play an important role in basic research and technology applications. In-depth theoretical studies on its electro-hydrodynamics (EHD) motions under various conditions are of great significance. In current paper, the dynamical characteristics of the liquid film motor driven by a square-wave electrophoresis electric field perpendicular to a uniform constant external electric field are investigated. Space-time dependence of the film's rotation linear velocity is derived analytically. The theoretical results indicate that a symmetrical reciprocating rotation in the film gradually converts to a vibration as the frequency of the electrophoresis electric field increases. This not only helps us understand the physical origin of the vibration of the liquid film motor, but also provides a new option to design a liquid film mixer in the application.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Shock timing experiment based on imaging velocity interferometer system for any reflector
Wang Feng, Peng Xiao-Shi, Mei Lu-Sheng, Liu Shen-Ye, Jiang Xiao-Hua, Ding Yong-Kun
2012, 61 (13): 135201. doi: 10.7498/aps.61.135201
Abstract +
The timing of multiple shock waves is crucial technique to the performance of inertial confinement fusion ignition targets. With the requirement for shock timing, the timing ability of Shen Guang-III prototype is analyzed by experimental data of two shots. The laser pulse in Shen Guang-III prototype is shaped in time scale, and the window material is z-cut quartz. The stream lines of two shock waves in quartz target are presented with Multi-1D program. Two steps of radiation drive two shock waves that coalesce in the quartz target, the resulting history, coalesce times, and transit times are observed in the stream lines. With the experiment results of two shots, the consistence of resulting history and coalesce times of two shock waves is provided under the same condition of laser pulse, target and diagnostic parameter. The differences in shock wave velocity, fringe contrast and quality occur at coalesce times of two shock waves. And the reflectivity of second shock wave does not increase compared with that of first shock wave. These experimental results and method provide the strong support for shock timing technique.
The effects of local density of states on surface plasmon polaritons
Han Qing-Yao, Tang Jun-Chao, Zhang Chao, Wang Chuan, Ma Hai-Qiang, Yu Li, Jiao Rong-Zhen
2012, 61 (13): 135202. doi: 10.7498/aps.61.135202
Abstract +
Surface plasmon polariton (SPP) is a kind of electromagnetic oscillation coupling due to the undulation of charge intensity, which is excited at the interface between metal and dielectric. With the help of near-field enhancement, surface plasmon polariton plays an important role in nano-photonics. When the effect of SPP is used to fabricate the single photon resource, not only the volume can be miniaturized, but also the single photon radiation and collection efficiency can be effectively improved. According to the relationship between the factor of Purcell effect and the density of states, we calculate the local density of electromagnetic states(LDOS) and Purcell factor. By analyzing the local densities of electromagnetic states of different metallic materials, we find that silver is the most suitable metal. For a certain metal, the detection distance and the dielectric material also have influences on local density of electromagnetic states and Purcell factor, and they provide important parameters for the designing of single photon resource based on surface plasmon resonances.
3D simulation optimization and design of multicusp ion source
Yang Chao, Liu Da-Gang, Chen Ying, Xia Meng-Zhong, Wang Xue-Qiong, Wang Xiao-Min
2012, 61 (13): 135203. doi: 10.7498/aps.61.135203
Abstract +
In this paper, a permanent magnet of multicusp ion source is calculated in theory, using the binary collision model to deal with coulomb collision between electrons. Collision between electrons and hydrogen species is treated with the null-collision model. Therefore, the three-dimensional PIC-MCC simulation algorithm is developed. Two optimization design models of multicusp ion source, ET-60U, are simulated by the software. Also, the spatial distribution characteristics and the relevant issues of the volume negative hydrogen ion production rate of the two kinds of ion sources are explored. Finally, The basic idea about the design of the negative hydrogen ion source is proposed. indicating that appropriately regulating the magnetic field distribution of the multicusp ion source can produce uniform ion beam, and that appropriately adjusting the size of the extraction magnetic field and the ion source structure can obtain both the ion beam spatial uniformity and the high production rate.
Laser-driven reservoir target for quasi-isentropic compression in aluminum
Shan Lian-Qiang, Gao Yu-Lin, Xin Jian-Ting, Wang Feng, Peng Xiao-Shi, Xu Tao, Zhou Wei-Min, Zhao Zong-Qing, Cao Lei-Feng, Wu Yu-Chi, Zhu Bin, Liu Hong-Jie, Liu Dong-Xiao, Shui Min, He Ying-Ling, Zhan Xia-Yu, Gu Yu-Qiu
2012, 61 (13): 135204. doi: 10.7498/aps.61.135204
Abstract +
The quasi-isentropic compression of material with high strain rate can be obtained by the ramp wave loading of plasma jet produced by laser-driven reservoir target. The quasi-isentropic compression experiments of aluminum are carried out on the high power laser facility of SG-III prototype. The smooth and continuous speed history of free surface of specimen is recorded with a line-imaging velocity interferometer (VISAR). The peak pressure (60 GPa), the rise time of the load (~ 10 ns) and the strain (~ 108 s-1) are derived by the back-integrating method, and the reverberation of compression wave at the rear surface of the sample is observed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
A small-angle X-ray scattering study of micro-defects in thermally treated HMX
Yan Guan-Yun, Tian Qiang, Huang Chao-Qiang, Gu Xiao-Min, Sun Guang-Ai, Chen Bo, Huang Ming, Nie Fu-De, Liu Yi, Li Xiu-Hong
2012, 61 (13): 136101. doi: 10.7498/aps.61.136101
Abstract +
The defects in HMX, induced by thermal expansion, phase transition and chemical decomposition, have large effects on the performance of HMX. In this work, the defects of HMX samples under heat treatment are characterized by small angle X-ray scattering (SAXS) and atomic force microscopy. A large number of pores with an average size of 10 nm are found during the - phase transition of HMX (180℃), and the pores increase in size and decrease in number with time increasing. A new population of small pores with sizes of 58 nm are produced in HMX during the thermal decompositions (190℃ and 200℃). The size and the number of the small pores increase with temperature increasing.
Research on the influences of point defects on the thermal conductivity of carbon nanotube by simulation with orthogonal array testing strategy
Li Wei, Feng Yan-Hui, Chen Yang, Zhang Xin-Xin
2012, 61 (13): 136102. doi: 10.7498/aps.61.136102
Abstract +
In the preparation process of carbon nanotubes, various point defects inevitably come into being in the lattice structures. The defects strongly affect the thermal transport properties of carbon nanotubes. Thermal conduction in carbon nanotube is simulated by using nonequilibrium molecular dynamics method with reactive bond order (REBO) potential. Thermal conductivities of carbon nanotubes with and without defects are calculated for comparison. An orthogonal array testing strategy is employed. In the calculation it greatly saves the experimental effort and identifies the degrees of influence of such structural factors as defect type, tube length, tube radius, etc. on thermal conductivity of tube. The effects of three types of point defects: vacancy, doping and adsorption are primarily studied, and the ambient temperature factor is also analyzed. Simulation results show that the thermal conductivity of carbon nanotubes with defects decreases significantly due to point defects compared with that of perfect carbon nanotubes. The defect type has the first greatest influence on the decrease of thermal conductivity, and hvae the second third greatest infuluences respeetively the radius and the length of carbon nanotubes. The degrees of influence of the above types of point defect are in the order of vacancydopingadsorption. Different types of point defects have different effects on tubes at different ambient temperatures.
Simulation study on thermodynamic, dynamic and structural transition mechanisms during the formation of Ca70Mg30 metallic glass
Xu Chun-Long, Hou Zhao-Yang, Liu Rang-Su
2012, 61 (13): 136401. doi: 10.7498/aps.61.136401
Abstract +
The rapid quenching process of Ca70Mg30 alloy is simulated by using the molecular dynamics method. During the liquid-glass transition process, the thermodynamic, dynamic and structural transition mechanisms are investigated deeply, and the relations between glass transition temperatures determined by different methods are discussed. It is found that both the simulated structural factor of Ca70Mg30 metallic glass and glass transition temperature are consistent with the experimental results, and the icosahedral local configuration plays a critical role in the formation of Ca70Mg30 metallic glass. The dynamic property of supercooled liquid gradually deviates from the Arrhenius law and satisfies the MCT power law due to the cage effect formed by neighbor atoms. It is also found that the structural glass transition temperature is close to the dynamic one, and they are higher than the calorimetric glass transition temperature. The relationship between them and the ideal dynamic glass transition temperature satisfies the Odagaki relation.
Vibrational dynamics of water confined in mesoporous silica under low temperature
Huang Xiu-Feng, Pan Li-Qing, Li Chen-Xi, Wang Qiang, Sun Gang, Lu Kun-Quan
2012, 61 (13): 136801. doi: 10.7498/aps.61.136801
Abstract +
The Raman vibrational spectra of water inside mesoporous silicate are measured in a temperature range of 100 T 303 K. It is found that the Raman spectrum of confined water becomes more different from that of bulk water with the decrease of water content in pores. For samples with high water content in pore, the main peak position of the Raman spectrum of water changes abruptly in a narrow temperature range. However, when water content decreases down to 20%, the red shift of the main peak of the Raman spectrum is continuous with temperature decreasing. At the same time, its temperature-dependence is the same as that of bulk amorphous ice.
Geometric structures and nitrogen adsorption properties of BaO adlayer on Ru(0001) surface
Zhao Xin-Xin, Tao Xiang-Ming, Mi Yi-Ming, Ji Xin, Wang Li-Li, Wu Jian-Bao, Tan Ming-Qiu
2012, 61 (13): 136802. doi: 10.7498/aps.61.136802
Abstract +
First principles calculations are performed to study the geometric structures and the nitrogen adsorption properties of BaO adlayer on Ru(0001) surface. It is suggested that BaO adlayer is more stable on Ru(0001) surface at low coverage. A configuration is observed in surface phase at low coverage. In this structure oxygen is adsorbed on the hcp site of one p(1 1) cell, and barium is adsorbed close to the top site of the same p(1 1) cell. Bond length of oxygen and ruthenium is calculated to be 0.209 nm, longer than the EXAFS experimental value about 0.018 nm. Nitrogen prefers to be adsorbed on the sites close to barium. Nitrogen adsorption energies at those sites are calculated to be in a range from 0.70 to 0.87 eV, which are bigger than those at the sites close to oxygen. Adsorption sites near barium atoms have more activities to weaken nitrogen. The lowest N-N stretching vibrational frequency on the sites is about 1946 cm-1, less than the highest frequency on sites around oxygen (about 130 cm- 1). Bond strengths of nitrogen on Ru(0001) /BaO surface are between those on clean Ru(0001) and Ru(0001) /Ba surface. The adsorption properties of sites around BaO layer are determined by chemical characteristic of barium and oxygen. Electron transfer from barium to ruthenium enhances the hybridization between ruthenium and nitrogen by reducing and increasing the occupation of * and * orbitals respectively.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Modification of zigzag graphene nanoribbons by patterning vacancies
Zhang Yu, Liu Lian-Qing, Jiao Nian-Dong, Xi Ning, Wang Yue-Chao, Dong Zai-Li
2012, 61 (13): 137101. doi: 10.7498/aps.61.137101
Abstract +
The transport properties of zigzag graphene nanoribbons (ZGNRs) with different patterns of vacancies are investigated by using the density functional theory and nonequilibrium Green's function (NEGF) formalism. It is found that the transport properties vary with lattice type vacancy. For two vacancies, A-B type vacancies have the most significant influence on the conductance of ZGNRs, while A-A type vacancies have the most slightly influence on the conductance. More importantly, the pattern of vacancies has enormous influence on electron transport around the Femi energy. As hexagon carbons are removed, the ZGNRs will be modified, changing from metallic to semiconducting. This lays the theoretical foundation for tuning the electron properties of ZGNRs by patterning vacancies.
First-principles study of FeAl(B2) microalloyed with La, Ac, Sc and Y
Zhao Rong-Da, Zhu Jing-Chuan, Liu Yong, Lai Zhong-Hong
2012, 61 (13): 137102. doi: 10.7498/aps.61.137102
Abstract +
The effects of FeAl(B2) microalloyed with rare earth element (REEs) La, Ac, Sc and Y on structural, elastic and electronic properties are investigated by first-principles calculation based on the density function theory (DFT). The calculation results show that the REEs Y tend to be substituted for Fe site, while La, Ac and Sc tend to be substituted for Al site, and Ac causes the largest lattice distortion. The calculation results of elastic properties show that the ductility of FeAl(B2) is improved by the addition of La, Ac, Sc and Y. The Fe7Al8Sc has better ductility and hardness. The effect of REEs on the performance of alloy is attributed to the variation of hybridization between Fe and Al electrons. The calculation results are in accordance with experimental and theoretical results.
Quasiparticle band structure calculation for SiC using self-consistent GW method
Gao Shang-Peng, Zhu Tong
2012, 61 (13): 137103. doi: 10.7498/aps.61.137103
Abstract +
Quasiparticle band structures of 3C-SiC and 2H-SiC were calculated using ab initio many body perturbation theory with GW approximation. Quasiparticle energies along high symmetry lines in the first Brillouin zone were evaluated using quasiparitcle self-consistent GW (QPscGW) method and the Maximally-localized Wannier Function interpolation. Both 3C-SiC and 2H-SiC have an indirect band gap with valence band maximum locating at point. The conduction band maximum of 3C-SiC is at X point. As a comparison, band gaps of 3C-SiC calculated by DFT-LDA, one-shot G0W0 and QPscGW are 1.30 eV, 2.23 eV and 2.88 eV respectively. The conduction band minimum of 2H-SiC locates at K point with a band gap of 2.12 eV, 3.12 eV and 3.75 eV predicted by DFT-LDA, one-shot G0W0 and QPscGW respectively. Lattice parameters calculated by DFT-LDA were used in this work. The QPscGW calculations are based on pseudopotential method, predicting slightly larger bandgaps for both 3C-SiC and 2H-SiC comparing with experiments.
The model of valence-band dispersion for strained Ge/Si1-xGex
Dai Xian-Ying, Yang Cheng, Song Jian-Jun, Zhang He-Ming, Hao Yue, Zheng Ruo-Chuan
2012, 61 (13): 137104. doi: 10.7498/aps.61.137104
Abstract +
Based on the kp theory, the valence-band dispersion model for biaxial strained Ge/Si1-xGex is derived by taking strained Hamiltonian perturbation into account. The model can be used to calculate the valence band structure and hole effective mass along arbitrarily k wavevector direction in strained Ge grown on arbitrarily oriented relaxed Si1-xGex virtual substrate. The MATLAB simulation results of the model show that by comparison with relaxed Ge, the more anisotropy of the hole effective mass occurs in strained Si1-xGex and the hole effective mass of the top valence band decreases with the increase of Ge fraction. The results can supply valuable references to the conduction channel design related to stress and orientation in the Si-based strained Ge MOS devices and integrated circuits.
Synthesis and characteristic research of nanoparticles KY3F10: Yb, RE (RE=Er, Ho, Tm) by thermal decomposition
Peng Yong, Xing Ming-Ming, Luo Xi-Xian, Wang Li-Qiang
2012, 61 (13): 137201. doi: 10.7498/aps.61.137201
Abstract +
Organic dyes and quantum dots possess the defects: wide emission spectrum and the poor photothermal stability and cytotoxicity, which restricts their applications in biological studies. Lanthanide-doped upconversion fluorescent materials in which there exists neither autofluorescence nor light bleaching phenomenon, has high sensitivity and good long-term stability, which are conducive to in vivo detection. KY3F10: Yb, RE(RE=Er, Ho, Tm) nanocrystals are synthesized by the thermal decomposition method and oleic acid as surface coating agent. The effects of the oleic acid content on morphology and particle size are studied. Optimal ratio of oleic acid to octadecene is 3:1 for the preparation of spherical monodisperse nanocrystals. Strong yellow green, green and blue emissions from the prepared samples are observed at 980 nm laser excitation. These results show that KY3F10: Yb, RE (RE=Er, Ho, Tm) nanoparticles as biological probes have excellent features in multiple fluorescent markers.
Large-deviation analysis for counting statistics in double-dot Aharonov-Bohm interferometer
Li Jun, Liu Yu, Ping Jing, Ye Yin, Li Xin-Qi
2012, 61 (13): 137202. doi: 10.7498/aps.61.137202
Abstract +
The Coulomb correlation and quantum coherence in a double-dot Aharonov-Bohm interferometer can result in two distinct transport channels: a fast channel and a slow one, while their coupling is tunable by changing the magnetic flux passing through an interference loop. However, these effects cannot be manifested by the conventional transport current. In this work, employing the large-deviation method which was originally developed in the nonequilibrium statistical mechanics, we perform a large-deviation analysis for the transport through this double-dot interferometer system and reveal a clear dynamical phase transition behavior.
The effect of electrostatic discharge on the I-V and low frequency noise characterization of Schottky barrier diodes
Liu Yu-Dong, Du Lei, Sun Peng, Chen Wen-Hao
2012, 61 (13): 137203. doi: 10.7498/aps.61.137203
Abstract +
Based on the analysis of thermal electron emission, the model of the carrier mobility fluctuation and the white noise theory, the effect of electrostatic discharge (ESD) on the I-V and low frequency noise of Schottky barrier diode (SBD) is discussed in this paper. The different Human Body Model(HBM) ESD injected times with the same voltage peaks are applied to the cathode and anode separately. It is found that the diode subjected to the cathode stress shows greater degradation than subjected to the anode stress, and the magnitude of noise shows significant change. With the increase of ESD injected times, the forward characteristic has no change, while reverse current almost increases at each time. The magnitudes of forward and reverse 1/f noise increase all the time. In view of the relationship between defects and damage, and the noise sensibility, the low frequency noise can serve as a tool for researching the sensitivity to the electrostatic discharge damage of SBD.
Investigation of the nonlinear response mechanism of photovoltaic HgCdTe detector irradiated by CW band-in laser
Jiang Tian, Cheng Xiang-Ai, Zheng Xin, Xu Zhong-Jie, Jiang Hou-Man, Lu Qi-Sheng
2012, 61 (13): 137302. doi: 10.7498/aps.61.137302
Abstract +
The medium wave HgCdTe photovoltaic detector (band gap ~0.33 eV) is irradiated by a CW band-in laser. The experimental results are shown that the detector enter into nonlinear response state as the incidence laser power increase. When the detector entered into nonlinear response state, the open circle voltage (Voc) signal decreased with the laser power. The Voc signal rapidly decreased when the laser turned on and the Voc signal rapidly increased when the laser turned off. The effect of laser induced temperature field and temperature dependence built-in field of pn junction were considered. The laser power variation of laser turn on and turn off were aslo considered. The analytical model of photovoltaic detector irradiated by above-band gap CW laser was built up. The calculation results agree well with the experiment results. It is shown that the temperature dependence built-in field of pn junction is the main mechanism induced the nonlinear response. The magnitude of Voc signals with laser turn on and turn off is decided by light intensity and temperature.
The effect of ITO annealing on electrical characteristic of GaN based LED
Liu Jian-Peng, Zhu Yan-Xu, Guo Wei-Ling, Yan Wei-Wei, Wu Guo-Qing
2012, 61 (13): 137303. doi: 10.7498/aps.61.137303
Abstract +
In the recent years,more and more light-emitting diodes use indium tin oxide (ITO) as the current spreading layer. But if there is not any treatment, the electrical properties of light emitting diode are very poor. So to get excellent electrical properties of light emitting diode, annealing is an effective method to improve the electrical properties of light emitting diode using indium tin oxide as the current spreading layer. However, the annealing time and temperature can affect the electrical property of light emitting diode individually. In order to investigate this problem,we measured the series resistance and ideality factor of the light emitting diode got under different annealing time and annealing temperature. According to the model proposed by Jay M. Shah,we can inferred the characteristics of indium tin oxide and P-type GaN contact. The results showed that: the electrical properties of the light-emitting diode can reach an excellent value with increasing annealing temperature and time, and if continuing to increase in temperature or time, it can lead to a decline in light-emitting diode electrical properties. It is very helpful to optimize the annealing temperature and time and manufacture excellent electrical properties of devices.

EDITOR'S SUGGESTION

The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and levitation force of single domain GdBCO bulk superconductor
Ma Jun, Yang Wan-Min, Li Jia-Wei, Wang Miao, Chen Sen-Lin
2012, 61 (13): 137401. doi: 10.7498/aps.61.137401
Abstract +
The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and the levitation force of single domain GdBCO bulk superconductor are investigated with a cubic permanent magnet in their coaxial configuration in zero field cooled state at liquid nitrogen temperature in three different ways. It is found that when the N pole of the cubic permanent magnet, for the levitation force measurement, is placed above the GdBCO bulk superconductor and in the downward direction, the maximal levitation force can be improved to 31.8 N, and that when the N pole of the additional cubic permanent magnet points to upward and sticks to the bottom of the GdBCO bulk, the maximal levitation force is increased up to about 222% of the levitation force of 14.3 N for the system without additional permanent magnet. The maximal levitation force can be improved to 21.6 N (or reduced to 8.6 N), when the GdBCO bulk superconductor is closely placed below and magnetized by the additional cubic permanent magnet with N pole in the upward (or downward) direction, and the additional permanent magnet is removed away after the magnetization, the maximal levitation force is about 151% (or 60%) of 14.3 N for the system without the additional permanent magnet. The results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on the scientific and reasonable designing of the system configurations, which is very important for the practical design and application of superconducting magnetic levitation system.
Phonon softening and superconductivity of -pyrochlore oxide superconductors AOs2O6 (A=K, Rb)
Sun Jia-Fa, Wang Wei
2012, 61 (13): 137402. doi: 10.7498/aps.61.137402
Abstract +
Using the first-principles calculational method based on the density functional theory, we study the structural instabilities, phonon softenings, and their relation to the superconductivities of two -pyrochlore oxide superconductors AOs2O6(A=K, Rb). It is found that there are structural instabilities of alkali ions along the 〈111〉 direction in the two -pyrochlore oxide superconductors AOs2O6(A=K, Rb), especially in KOs2O6. Meanwhile, a comparison of the phonon frequency at zone-center between KOs2O6 and RbOs2O6 shows that the frequency of KOs2O6 is lower in general than that of RbOs2O6, leading to the stronger electron-phonon coupling. We conclude that K atom located in a large oxygen cage has an unusual large atomic displacement parameter and strong activity, thereby resulting in strong phonon softening. This is the foundamental cause for stronger electron-phonon coupling and higher superconducting transition temperature of KOs2O6. These are of significance for explaining the superconductivities in -pyrochlore oxide superconductors AOs2O6(A=K, Rb).
Influence of annealing ambience on the magnetic properties of doped ZnO films
Li Zhi-Wen, Qi Yun-Kai, Gu Jian-Jun, Sun Hui-Yuan
2012, 61 (13): 137501. doi: 10.7498/aps.61.137501
Abstract +
The non-magnetic element Al and magnetic element Co doped ZnO films are prepared by dc magnetron sputtering The films were annealed first in vacuum and then in air. The crystal structures are analyzed by x-ray diffraction (XRD) and magnetic properties are measured by Physical Properties Measurement System (PPMS). The results show that annealing ambience has a great influence on structure and magnetic property of sample Al doped ZnO films annealed in vacuum show no room temperature ferromagnetism, but the ones annealed in air show room temperature ferromagnetism. The room temperature ferromagnetism may be associated with enhanced charge transfer between Al and ZnO films annealed in air. And for Co doped ZnO films annealed in air annealed, the ferromagnetism is weakened. The change of magnetism may be related to the competition between enhanced magnetism resulting from charge transfer between Al and ZnO and reduced magnetism resulting from interstitial Co atoms oxygenated.
Effects of Fe doping on the crystal structures and photoluminescences of ZnO: Ni thin films prepared by sol-gel method
Wu Zhong-Hao, Xu Ming, Duan Wen-Qian
2012, 61 (13): 137502. doi: 10.7498/aps.61.137502
Abstract +
Zn0.95-xNi0.05FexO (x=0, 0.005, 0.01, 0.03, 0.05) thin films are fabricated on the glass substrates by the sol-gel method. The surface morphologies and crystal structures of the films are investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal that preferential orientations are all along the (002) direction in all films. the qualities of ZnO: Ni films for low or high Fe concentration become worse, the crystal grain sizes of ZnO: Ni film are reduced, but moderate Fe doping seems to improve the film quality. XPS results reveal that Ni elements exist as Ni2+, and Fe elements exist as Fe2+ and Fe3+. Strong ultraviolet emission peaks, blue double emission peaks and green emission peaks are observed in the photoluminescence spectra of all samples at room temperature. It is found that the PL intensities of (Ni, Fe) co-doped ZnO films could be well modulated by Fe doping. In combination with other reports, we think that the ultraviolet emission peaks are due to exciton recombination; while the blue double peaks are caused by transition of electrons from the zinc interstitial to the top of the valence band or from the oxygen vacancy to the zinc vacancy. However, the green peak is highly dependent on oxygen vacancy and zinc vacancy formed by doping.
Fabrication and magnetic properties of Co70Cu30 alloy nanowire arrays with high coercivity
Liu Xiao-Xu, Zhao Xing-Tao, Zhang Ying, Zhu Yan, Wu Guang-Heng
2012, 61 (13): 137503. doi: 10.7498/aps.61.137503
Abstract +
CoCu solid solution alloy nanowire arrays which exhibit the face-centered cubic structure with strong [220] orientation along the nanowire axes are fabricated for first time in the anodic aluminum oxide template by electrodeposition. The proportion of Co ingredient in CoCu alloy nanowire arrays is up to 70%. Transmission electron microscopy revealts that the nanowire arrays are uniform and continuous and have a large aspect ratio of about 300. The magnetic hysteresis loop demonstrates that the Co70Cu30 alloy nanowire arrays have a large coercivity of about 2438 Oe and relatively large squareness of about 0.76 parallel to nanowire arrays which greatly exceeds the value previousely reported. Good magnetic properties are achieved due mainly to the larger proportion of Co ingredient than that in the normal CoCu alloy nanowire arrays and the large shape anisotropy. The results of magnetic measurement and the calculations from formula demonstrate that the symmetric fanning mechanism of sphere chains model could be employed to explain the magnetization reversal process which is related to the structure of the Co70Cu30 nanowire arrays.
Effect of adjustable bias voltage on magnetoelectric properties of magnetostrictive/piezoelectric laminated transducer structure
Li Ping, Huang Xian,  Wen Yu Mei
2012, 61 (13): 137504. doi: 10.7498/aps.61.137504
Abstract +
The magnetoelectric properties of PZT5/Terfenol-D/PZT8 laminated transducer structure are analyzed and detected for adjusting the bias voltage across PZT5. A control method of one-order resonant frequency for a magnetostrictive/piezoelectric laminated magnetoelectric transducer structure is proposed. The resonant frequency and the prestrain of the magnetoelectric laminated structure can be adjusted by changing the bias voltage across PZT5. The relationships between the control voltage, the strain, the Young's modulus, the resonant frequencies and the resonant magnetoelectric coefficient are analyzed. Theoretical analyses show that the resonant frequency of the laminated structure is almost a linear function of the applied dc bias voltage at a small strain. The magnetoelectric coefficient is hardly related to the control voltage. The experimental results verify the theoretical analyses. For a control voltage of 170 V to +170 V, the resonant frequency can be linearly adjusted. The adjusted maximum of the resonant frequency is 1 kHz. The ratio of the adjusted value to the bias control voltage is 2.94 Hz/V. For a bias magnetic field from 0 Oe to 225 Oe, the resonant frequency is almost unrelated to the bias magnetic field. The magnetoelectric voltage coefficient changes with the bias magnetic field. A maximum magnetoelectric voltage coefficient of 1.65 V/Oe is obtained at a bias magnetic field of 178 Oe.
Application of high-k dielectrics in novel semiconductor devices
Huang Li, Huang An-Ping, Zheng Xiao-Hu, Xiao Zhi-Song, Wang Mei
2012, 61 (13): 137701. doi: 10.7498/aps.61.137701
Abstract +
As the feature size of MOSFET scales beyond 45 nm, SiO2 as gate dielectric fails to meet the performance requirement because of the high gate oxide leakage current. It is necessary to replace SiO2 with high-k materials. However, high-k materials as gate dielectric have some limitations and are not expectedly compatible with the conventional structure, inducing new challenges such as bad interfacial quality, increased threshold voltage, mobility degradation, etc. In this paper we review the problems encountered in the introduction of high-k gate dielectric into planar devices and the solutions in terms of material, device structure and process integration. Some novel applications of high-k materials in new devices and the future trend are also reviewed.

EDITOR'S SUGGESTION

Theoretical and experimental investigation of W doped ZnO
Wang Yan-Feng, Huang Qian, Song Qing-Gong, Liu Yang, Wei Chang-Chun, Zhao Ying, Zhang Xiao-Dan
2012, 61 (13): 137801. doi: 10.7498/aps.61.137801
Abstract +
The properties of high valence difference W doped ZnO films (WZO) are investigated by means of plane wave pseudo-potential method based on the density-functional theory (DFT) and pulsed DC magnetron sputtering technique. The theoretical result shows after incorporation of W the Fermi level enters into the conduction band, showing that a typical n-type metallic characteristic and the optical band gap Eg* increase significantly. The carriers originate from the orbits of W 5d, O 2p and Zn 3d. Moreover, the increase of the lattice constant is due to the longer bond length of W-O and lattice distortion. The experimental results demonstrate that the deposited WZO film grows preferentially in the (002) crystallographic direction but the lattice constant increases. The resistivity decreases from 1.35 10-2 cm to 1.55 10-3 cm and the optical bandgap extends from 3.27 eV to 3.48 eV compared with those of ZnO. The average transmittance is over 83 % in a wavelength range from 400 to 1100 nm. The experimental results are in good agreement with the theoretical results, showing that the WZO thin film has a great potential application as transparent conductive oxide.
Comprehensive Survey for the Frontier Disciplines
Progress in terahertz surface plasmonics
Wang Yue, Wang Xuan, He Xun-Jun, Mei Jin-Shuo, Chen Ming-Hua, Yin Jing-Hua, Lei Qing-Quan
2012, 61 (13): 137301. doi: 10.7498/aps.61.137301
Abstract +
Plasmonics, which deals with the unique optical properties of metallic and semiconductor nanostructure, is one of the most fascinating and fast-moving areas of photonics. Its board scale research in the visible, infrared, terahertz and microwave frequencies has driven by the advances in the micro/nano fabrication and the computational simulation technologies, as well as the potential applications in areas of high sensitivity bio-chemical sensing, sub-wavelength light-guiding, near-field microcopy, and nanolithography. Especially, the development of the artificial metamaterial has laid the good foundation for the material and devices in the terahertz frequency range, which is barely responded by the nature materials, and furthermore, has promoted the progress of terahertz surface plasmonics. In this paper the generation, propagation, new applications, and perspective of terahetz surface plamonics are reviewed and discussed.
Solvothermal recrystallized synthesis of one-dimensional CdS nanorods self-assembled from nanoparticles
Zhang Bao-Hua, Guo Fu-Qiang, Sun Yi, Wang Jun-Jun, Li Yan-Qing, Zhi Li-Li
2012, 61 (13): 138101. doi: 10.7498/aps.61.138101
Abstract +
Two different solvothermal synthesis routines are used to fabricate CdS nanocrystals with different morphologies and sizes. Anhydrous ethylenediamine (en) is chosen as solvent, CdCl2. 2.5H2O and thiourea (H2NCSH2N) as the cadmium source and sulfur source respectively in the first method. CdS Nanocrystals are prepared at different reaction temperatures (160 ℃-220 ℃) and the influence of the reaction temperature on the growth of CdS nanocrystals is discussed. In the other routine, anhydrous ethylenediamine (en) is also chosen as solvent. The synthesized products at 160 ℃ are recrystallized under 200 ℃ for 2-8 h. The influence of the recrystallisation time on the growth of CdS Nanocrystal is discussed. The in-situ analysis of effect of the growth time on the growth of CdS nanocrystals is performed. The phase, morphology and crystallographic structure of CdS nanocrystals are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) respectively. The results show that both products exhibit pure hexagonal structures, the morphology of the product is nanoparticles at the temperatures below 160 ℃, when the temperature is rasied to higher than 160 ℃, the products are CdS nanorods. Meanwhile, the morphologies of the recrystallisation products under 200 ℃ for different times are found to convert from nanoparticles into nanorods gradually. The nanorods are composed of zero-dimensional particles through self-assembly process which could be demonstrated by field emission scanning electron microscopy (HRTEM) analysis. Finally, the factors that influence the morphology changes of CdS nanocrystals and the mechanism of the growth of nanorods are discussed.
Influence of surface fluorination temperature on space charge accumulation in polyethylene
Chen Xuan, An Zhen-Lian, Liu Chen-Xia, Zhang Ye-Wen, Zheng Fei-Hu
2012, 61 (13): 138201. doi: 10.7498/aps.61.138201
Abstract +
Polyethylene (PE) discs prepared by hot-pressing, each with a thickness of 0.8 mm, are surface fluorinated in a laboratory vessel by an F2/N2 mixture containing 12.5% F2 by volume at different temperatures of 35, 55, and 70 ℃ for the same time of 2 h. The influence of fluorination temperature on space charge accumulation in PE is investigated by the pressure wave propagation method. The results show an obvious decrease in space charge accumulation in the fluorinated sample subject to a direct current high voltage with the increase of fluorination temperature, and there exists almost no charge accumulation in the sample fluorinated at 70 ℃. Attenuated total reflection infrared analyses indicate a substantial change in chemical composition of the sample surface layers by the fluorinations and an obvious increase in degree of fluorination with fluorination temperature increasing. Contact angle measurements and surface energy calculations indirectly indicate a significant increase in permittivity of the fluorinated layers by the fluorinations. Open-circuit thermally stimulated discharge current measurements further reveal different charge trapping properties of the fluorinated layers and the improved barrier properties of the fluorinated layer to the diffusion of the chemical species from the semi-conductive electrode to the PE with increase of fluorination temperature, thus indicating a corresponding decrease in free volume of the surface layer. The decrease in the free volume plays a more important role in suppressing the space charge accumulation, compared with the increase in permittivity and the change in charge trap.
Improving the light-soaking stability of a-Si: H/μc-Si: H tandem solar cells
Hou Guo-Fu, Lu Peng, Han Xiao-Yan, Li Gui-Jun, Wei Chang-Chun, Geng Xin-Hua, Zhao Ying
2012, 61 (13): 138401. doi: 10.7498/aps.61.138401
Abstract +
Improving the light-soaking stability of silicon-based thin film solar cells is a very important issue for industrial production. In order to obtain high-efficiency a-Si:H/μc-Si:H tandem solar cells with good light-soaking stability, In this paper we first present the results about a-Si:H top solar cell with high light-soaking stability. Then we mainly investigate the influences of N/P tunnel junction and silane concentration (SC) profiling of μc-Si:H i-layer on the light-soaking stability of a-Si:H/μc-Si:H tandem solar cells. Up to now we have been able to obtain a-Si:H/μc-Si:H tandem solar cell with a light-soaking degradation ratio of only 7%.
High-speed and high-power uni-traveling-carrier photodetector
Zhang Ling-Zi, Zuo Yu-Hua, Cao Quan, Xue Chun-Lai, Cheng Bu-Wen, Zhang Wan-Chang, Cao Xue-Lei, Wang Qi-Ming
2012, 61 (13): 138501. doi: 10.7498/aps.61.138501
Abstract +
The drift-diffusion theory is adopted to simulate the bandwidth and the saturation characteristics of InGaAs/InP uni-traveling-carrier (UTC) photodetector. According to the experiment results, we analyze the physical mechanisms in high speed and high power UTC photodetector. It is shown that introducing the cliff layer and the gradually doped absorption layer can enhance the saturation characteristic obviously. Electric field collapse in the absorption layer leads to the saturation, and RC constant is still a limitation factor for device with diameter larger than 20 μm. In this paper we point out the effective methods to improve device performance.
The preparation and performance analysis of GaN-based high-voltage DC light emitting diode
Cao Dong-Xing, Guo Zhi-You, Liang Fu-Bo, Yang Xiao-Dong, Huang Hong-Yong
2012, 61 (13): 138502. doi: 10.7498/aps.61.138502
Abstract +
The design and the preparation of GaN-based high-voltage DC light emitting diode are realized. It is found that the device, whose chip structure is truncated pyramid using the epitaxial wafer whose subsrate is a patterned sapphire substrate, has a higher luminous efficiency than other chip structures. The luminous efficiency increases up to 116.06 lm/W when the device is packaged into white LED at a color temperature of 4500 K which is driven by 20 mA, and the corresponding voltage is 50 V. The I-V curve shows that the threshold voltage is 36 V, corresponding to a drive current of 1.5 mA. The optical power increases approximately linearly with the increase of driving current when the driving current increases from 15 mA to 50 mA, and the luminous efficiency in this range decreases more slowly with the increase of driving current, indicating that the GaN-based high-voltage DC LED is favourably driven by large current density, and severe efficiency droop will not appear as the drive current density increases, which offers a new idea for studying and solving the efficiency droop problem from the chip level.
Numerical study of spectrum-control in dual-wavelength LED with doped quantum well barriers of different doping concentration
Liu Xiao-Ping, Fan Guang-Han, Zhang Yun-Yan, Zheng Shu-Wen, Gong Chang-Chun, Wang Yong-Li, Zhang Tao
2012, 61 (13): 138503. doi: 10.7498/aps.61.138503
Abstract +
Dual-wavelength LEDs with doped quantum well barriers of different doping concentrations are numerically investigated by using the APSYS simulation software. The carrier concentrations, radiative recombination rates, energy band diagrams and spectra are investigated at different doping types and different doping concentrations. The results show that through adjusting the doping concentration of the quantum well barrier a suitable spectrum can be obtained, which will satisfy the need of application. And the effect of spectrum-control in dual-wavelength LED is due to the blocking effect of electrons and holes by doped quantum well barriers.
Optimization of quantum dot solar cells based on structures of GaAs/InAs-GaAs/ZnSe
Jiang Bing-Yi, Zheng Jian-Bang, Wang Chun-Feng, Hao Juan, Cao Chong-De
2012, 61 (13): 138801. doi: 10.7498/aps.61.138801
Abstract +
Based on the structures of GaAs/InAs-GaAs/ZnSe P-i-N quantum dot solar cells, according to the optical principle and diffusion theory, mathematic model describing the relationship between photogenerated electron current density and thickness of layer is proposed, and the effect of the quantum dot layer on the characteristics of solar cell is analyzed quantitatively for improving the power conversion efficiency of quantum dot solar cells. Simulations show that the optimal thicknesses of P(GaAs) and N(ZnSe) are 1541 nm and 78 nm respectively when the i layer thickness is 3000 nm, and the power conversion efficiency of solar cell is 20.1% at a single wavelength; At the same time, the volume of quantum dot and the temperature affect I-V property of quantum dot solar cell, and the value of open voltage reduces with the increase of the volume of quantum dot and temperature, so that the power conversion efficiency will be reduced.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Dynamical identification of a heavy sauna weather event in northern China in 2009
Yang Shuai, Gao Shou-Ting, Chen Bin
2012, 61 (13): 139201. doi: 10.7498/aps.61.139201
Abstract +
A sauna weather event in northern China in July 2009 is numerically simulated and diagnostically analyzed. The atmospheric circulation characteristics, the horizontal and vertical distributions of temperatures and moistures, and the distribution of potential vorticities are studied. It is found that anticyclone dominates the upper troposphere during the sauna weather event. In the horizontal chart, the relative humidity in the lower troposphere is large. From the vertical sections, descending airflow dominates the moist and warm sectors at the middle and lower levels. There are clear humidity gradient, evident vertical gradient of temperature, and slanting distribution of potential vorticity. The sauna weather event occurs in the generally high-temperature environment of summertime, so it is difficult to dynamically identify and diagnose the sauna weather depending on some single factor, e.g., temperature or moisture. According to the high-temperature, large-moisture, and strong-potential vorticity characteristics during the sauna weather in northern China, a moist thermal potential vorticity parameter MTPV, may be expressed as ▽ q (▽ ▽ Q), where q is the sum of water vapor and all hydrometeors including cloud water, rain water, cloud ice, snow and graupel; is potential temperature; Q is potential vorticity) which is appropriate for sauna weather, is introduced. Then it is used to dynamically diagnose sauna weather event. And it is simplified by calculation analysis in case study. It is found that the MTPV anomaly is accompanied by the sauna weather process. Although high temperature, large moisture and strong slanting potential vorticity development present in the sauna weather process in northern China in July 2009, their coverages for these single variables are larger than our target region of this sauna weather event. While for the MTPV and its simplified form combining these variables, their anomalies maintain in the lower troposphere around Beijing and its peripheral areas in northern China, viewing from either zonal or meridional section. Therefore, both MTPV and its simplified form can better dynamically identify this high-temperature and high-humidity sauna weather event.
The analysis of the influence of globe SST anomalies on 500 hPa temperature field based on Bayesian
Yan Peng-Cheng, Hou Wei, Qian Zhong-Hua, He Wen-Ping, Sun Jian-An
2012, 61 (13): 139202. doi: 10.7498/aps.61.139202
Abstract +
In this paper, we break down sea surface temperature(SST) anomaly field by using the empirical orthogonal function (EOF) to obtain a rebuilding space made up of different patterns which are orthogonal to each other, then we unfold 500 hPa temperature field in this space. Furthermore, with the method of Bayesian analysis, we define the impact index of different patterns on 500 hPa air temperature field and research the variation characteristic of index with the change of spatial pattern of SST. It is found that SST field has a great effect on 500 hPa temperature field between April to June. Besides, after the abrupt climate change, different patterns of SST have different effects on temperature field.
A differentiable thresholding function and an adaptive threshold selection technique for pulsar signal denoising
Gao Guo-Rong, Liu Yan-Ping, Pan Qiong
2012, 61 (13): 139701. doi: 10.7498/aps.61.139701
Abstract +
Because of the extremely low signal-to-noise ratio of pulsar signals, it is difficult to suppress noise while preserving details by the traditional denoise methods. Therefore, a wavelet domain pulsar signal denoising method based on a differentiable thresholding function and an adaptive threshold selection technique is presented. The signal-to-noise ratio(SNR), the root mean square error(RMSE), the relative error of the peak value (REPV) and the error of the peak position (EPP) are used to evaluate the performance of the proposed denoising method. Experimental results show that the proposed method can remove the pulsar signal noise and keep the useful information effectively. At the same time, it can achieve a higher PSNR, a lower RMSE, a lower REPV and a lower EPP than the soft thresholding and hard thresholding methods.