Vol. 64, No. 2 (2015)

Stochastic resonance of an underdamped linear harmonic oscillator with fluctuating mass and fluctuating frequency
Zhong Su-Chuan, Yu Tao, Zhang Lu, Ma Hong
2015, 64 (2): 020202. doi: 10.7498/aps.64.020202
Abstract +
When Brownian particle moves in a viscoelastic medium, the surrounding molecules not only collide with the Brownian particle but also adhere to the Brownian particle randomly, thereby changing the mass of the Brownian particle. We investigate the stochastic resonance phenomenon in an underdamped linear harmonic oscillator with fluctuating mass and fluctuating frequency under an external periodic force. The exact expressions of the first moment and the amplitude of the output signal are obtained by using the Shapiro-Loginov formula and the Laplace transform technique. We establish the necessary and sufficient conditions for the emergence of the stochastic resonance phenomenon induced by the mass fluctuation noise intensity and frequency fluctuation noise intensity. Furthermore, based on the necessary and sufficient conditions, the output amplitude shows a non-monotonic dependence on the noise intensity, which means that the stochastic resonance phenomenon happens.
A blending crossover differential evolution approach to camera space manipulation parameter optimization
Xie Yu, Zhao Chun-Xia, Zhang Hao-Feng, Yan Xue-Jun, Chen De-Bao
2015, 64 (2): 020701. doi: 10.7498/aps.64.020701
Abstract +
A blending crossover differential evolution algorithm is proposed to increase the precision of camera-space manipulation (CSM) system. In this approach, six view parameters and flattening parameter are assembled into a single parameter of blending crossover differential evolution; the positioning precision of camera-space manipulation is set to be a fitness function.The CSM system can obtain the optimal parameter combination by evolutionary iteration.Experimental results of a virtual robot system show the robot positioning precision is improved by blending crossover differential evolution algorithm.
Investigation on the influences of linear chirp with different input pulse intensities on BaF2 cross-polarized wave generation
Li Gang, Liu Hong-Jie, Lu Feng, Wen Xian-Lun, He Ying-Ling, Zhang Fa-Qiang, Dai Zeng-Hai
2015, 64 (2): 020602. doi: 10.7498/aps.64.020602
Abstract +
Cross-polarized wave (XPW) generation based on BaF2 crystal is one of the most important tools in improving the contrast of ultra-intense femtosecond laser pulses at present. In this paper, the influences of linear chirp with different input pulse intensities on BaF2 XPW generation, including conversion efficiency, spectrum broadening, and pulse duration reduction are in detail simulated and discussed. Especially, the influence of linear chirp on spectrum broadening is comparatively investigated under unsaturated and intense input pulses. While the amount of spectrum broadening relative to linear chirp is symmetrical with respect to the zero chirp point under unsaturated input pulse, the results show that it is no longer those in the case under intense input pulse, and the intrinsic reason is explained in detail in this paper.
New complexion two-soliton solutions of a class of nonlinear evolution equation
Taogetusang, Yi Li-Na
2015, 64 (2): 020201. doi: 10.7498/aps.64.020201
Abstract +
New infinite sequence complexion two-soliton solutions of a kind of nonlinear evolution equation are constructed with the help of function transformations and two kinds of elliptic equations. Step one,according to two function transformations, a kind of nonlinear evolution equation is changed into a nonlinear ordinary differential equation of second order. Step two, using function transformation, the nonlinear ordinary differential equation of second order is transformed into a set of nonlinear ordinary differential equations of first order, and the first integral of the set of equations is obtained. Finally, the first integral with new solutions and Bäcklund transformation of two kinds of elliptic equations are used to search for new infinite sequence complexion two-soliton solutions of a kind of nonlinear evolution equation.
A novel frequency stabilization method for the seed laser of the pulse optical parametric oscillator in differential absorption lidar
Ge Ye, Hu Yi-Hua, Shu Rong, Hong Guang-Lie
2015, 64 (2): 020702. doi: 10.7498/aps.64.020702
Abstract +
A novel frequency stabilization method for the seed laser of the pulse optical parametric oscillator (OPO) in differential absorption lidar (DIAL) is proposed in this paper. The operating principle and the experimental setups are introduced in detail, and the accuracy of the frequency stabilization method and influence factors are also analyzed. The frequency of the seed laser is locked to an absorption line of water vapor (935.6849 nm) in the experiment, and the measured standard deviation of the frequency jitter is less than 8 MHz. The frequency of the seeded OPO signal is recorded thereafter. The standard deviation less than 28.7 MHz with the same frequency according to the seed laser is achieved, which is well applicable to DIAL.
Stochastic resonance of asymmetric bistable system with α stable noise
Jiao Shang-Bin, Yang Rong, Zhang Qing, Xie Guo
2015, 64 (2): 020502. doi: 10.7498/aps.64.020502
Abstract +
In this paper we take the asymmetric bistable system excited by weak periodic signal as a model and regard signal-to-noise ratio gain as an index to investigate the stochastic resonance phenomenon stimulated by additive and multiplicative α stable noise. Stochastic resonance phenomenon stimulated by only additive α stable noise is also investigated here. The laws for the resonance system parameters a, b, asymmetric skewness r and intensity amplification factor Q or D of α stable noise to act on the resonant output are explored under different stability index α and skewness parameter β of α stable noise. The results show that no matter whether under the joint action of additive and multiplicative α stable noise or under the action of only additive α stable noise, weak signal detection can be realized by tuning the system parameters a, b and r. The intervals of a, b and r which can induce stochastic resonances are multiple, and do not change with α nor β. Moreover, when investigating the noise-induced stochastic resonance, it is found that stochastic resonance can also be realized by tuning the intensity amplification factor of α stable noise. And the interval of D does not change with α nor β. The results will contribute to a reasonable selection of parameter-induced stochastic resonance system parameters and noise intensity of noise-induced stochastic resonance under α stable noise.
Spectral interferometry based absolute distance measurement using frequency comb
Wu Han-Zhong, Cao Shi-Ying, Zhang Fu-Min, Qu Xing-Hua
2015, 64 (2): 020601. doi: 10.7498/aps.64.020601
Abstract +
Spectral interferometry using frequency comb has become a powerful approach to absolute distance measurement. In this paper, we analyze the principle of spectral interferometry in detail. With the consideration of dispersion, pulse chirp and the power ratio of the reference pulse and the measurement pulse, we develop a Gaussian model, which can be used to determine distances. The frequency of the spectral interference fringe is of key importance. The distances can be directly determined by the frequency of the spectral interference fringe through one-step fast Fourier transform with no filters during the data processing. The simulation results show that the maximum deviation is 1.5 nm when the distance is 1.5 mm theoretically. The comb consists of hundreds of thousands of teeth in the spectral domain, and each tooth can be regarded as a cw laser. We propose a method based on the phases of two close modes. The principle is introduced, and the maximum deviation is 8.7 nm with a distance of 1.5 mm while the minimum deviation is 0.3 nm corresponding to distance of 0.5 mm. We theoretically show that the linear pulse chirp can be used for distance measurement. The measurement principle is analyzed, and the simulation shows that the maximum deviation is 5.3 nm when the distance is 1.2 mm.
An improved high performance Lorenz system and its application
Guan Guo-Rong, Wu Cheng-Mao, Jia Qian
2015, 64 (2): 020501. doi: 10.7498/aps.64.020501
Abstract +
Lorenz system is one of the most typical chaotic system models, and it has been well studied and widely applied. In order to obtain more complex structure and dynamic behavior of chaotic attractor for Lorenz system, improving the Lorenz system has become one of the important tasks in chaotic dynamical system. Therefore, an improved Lorenz system with complex dynamic behavior is proposed and used to protect image information security. Based on the existing various improvement Lorenz systems, firstly, a new Lorenz chaotic system is constructed by increasing the control parameters and modifying nonlinear expression in the existing Lorenz chaotic system; secondly, the mathematical properties of dissipation, symmetry, and stability in the proposed Lorenz system, which are similar to those in the existing Lorenz system, Bao system, Tee system and Y system, are investigated by modern differential dynamical system, and the experimental results of Lyapunov index and random sequence correlation of five different Lorenz systems show that the proposed Lorenz system has a more complex structure and chaotic dynamic behavior; finally, the discrete pseudo random sequences generated by five different Lorenz chaotic systems are used for scrambling the pixel position and diffusing the pixel value to protect image information security. The analyses of correlation and statistic histogram entropy of adjacent pixels, anti-differential attack and key sensitivity of the encrypted image, indicate that the improved Lorenz system proposed in this paper has much better potential advantages than other existing improved Lorenz system in image encryption application.
Leveraging neighborhood “structural holes” to identifying key spreaders in social networks
Su Xiao-Ping, Song Yu-Rong
2015, 64 (2): 020101. doi: 10.7498/aps.64.020101
Abstract +
The identifying of influential nodes in large-scale complex networks is an important issue in optimizing network structure and enhancing robustness of a system. To measure the role of nodes, classic methods can help identify influential nodes, but they have some limitations to social networks. Local metric is simple but it can only take into account the neighbor size, and the topological connections among the neighbors are neglected, so it can not reflect the interaction between the nodes. The global metrics is difficult to use in large social networks because of the high computational complexity. Meanwhile, in the classic methods, the unique community characteristics of the social networks are not considered. To make a trade off between affections and efficiency, a local structural centrality measure is proposed which is based on nodes' a nd their ‘neighbors’ structural holes. Both the node degree and “bridge” property are reflected in computing node constraint index. SIR (Susceptible-Infected-Recovered) model is used to evaluate the ability to spread nodes. Simulations of four real networks show that our method can rank the capability of spreading nodes more accurately than other metrics. This algorithm has strong robustness when the network is subjected to sybil attacks.
Method of identifying consitutive parameter in Tb0.3Dy0.7Fe2 Alloy
Yan Bai-Ping, Zhang Cheng-Ming, Li Li-Yi, Tang Zhi-Feng, Lü Fu-Zai, Yang Ke-Ji
2015, 64 (2): 027501. doi: 10.7498/aps.64.027501
Abstract +
In this paper, a simple consititutive parameter identification method for the application of domain model in Tb0.3Dy0.7Fe2 alloy is studied, the magnetization and hystersis characteristics are summarized. Targeting the problem of unclarity and difficulty in directly testing the constitutive parameters in Tb0.3Dy0.7Fe2 alloy, numerical calculation and experimental test are used to propose a parameter identification method. Coordinate transformation and graphic solution technique are used in this paper to simplify the minimization solutions of domain rotation in alloy. The dependence of parameters in magnetic rotation model is studied. On this basis, combined with simple experimental test, the method of indentifying Tb0.3Dy0.7Fe2 alloy is established, and the influences of anisotropy constants K1 and K2, energy distribution factor ω, axis orientation distribution in domain rotation are discussed. The method can simply and rapidly identify the constitutive parameters of Tb0.3Dy0.7Fe2 alloy in magnetic domain model, which is significant to improve the numerical calculation of domain rotation in magnetostrictive material. The above theoretical computations are significant for establishing magnetomechanical model of magnetostrictive material, and results are helpful for perfecting the identification of constitutive parameters.
Influences of sound speed profile on the source localization of different depths
Su Lin, Ma Li, Song Wen-Hua, Guo Sheng-Ming, Lu Li-Cheng
2015, 64 (2): 024302. doi: 10.7498/aps.64.024302
Abstract +
It is found in the data processing of matched filed source localization experiment that in the case of the slight mismatch of sound speed profile, the louder source below disappears while the weaker source above comes out. Based on the experimental phenomenon, the influences of the sound speed profile on the source localization of different depths are investigated. Firstly, the simulation is conducted in order to extract the influence of the uncertain factors in the sea test, from which it is further concluded that the deeper source is greatly affected. Then another simulation about the mismatch of the depth of the thermocline is conducted in the typical shallow-water negative gradient environment, from which a preliminary conclusion is drawn that the most sensitive depth to the mismatch of the sound speed profile is around 10 meters below the lower boundary thermocline. Finally, this pheonomenon is reasonably explained through a theoretical analysis from two aspects of the normal mode theory.
Chaotic randomness of mutually coupled vertical-cavity surface-emitting laser by optical injection
Liu Qing-Xi, Pan Wei, Zhang Li-Yue, Li Nian-Qiang, Yan Juan
2015, 64 (2): 024209. doi: 10.7498/aps.64.024209
Abstract +
In this paper, a randomness-enhanced chaotic system model of mutually coupled vertical-cavity surface-emitting lasers (VCSELs) is established by adding anothor injected VCSEL with variable polarizer optical feedback (VPOF). The randomness of chaotic signals is evaluated quantitatively by an information-theory-based quantifier, the permutation entropy (PE). The influences of VPOF-VCSEL rotating polarizer degree, feedback strength, injection strength, mutual coupling strength, path time delay and frequency detuning about injected VCSEL and coupled VCSELs on chaotic signal permutation entropy are numerically studied. It is shown that the chaotic signal permutation entropy of mutually coupled VCSEL system driven by the third VCSEL is much higher than the mutual system with no-driving VCSEL. That is to say, the randomness of coupled system chaotic signal can be enhanced by optical injection. When the rotating polarizer degree is approximately 45 degrees and the injection strength is saturated at a constant level, the system PE can be increased by coupled strength, which is set to be higher than feedback strength. In addition, unequal delay time between both coupled time and feedback time, and higher detuning frequency between driving VCSEL and coupled VCSELs can contribute to randomness-enhanced chaotic signals.
Experimental research of boresight error correction using returning signals from the illuminated targets through atmosphere
Tan Yi, Geng Chao, Li Xin-Yang, Luo Wen, Luo Qi
2015, 64 (2): 024216. doi: 10.7498/aps.64.024216
Abstract +
The relationship between boresight error and returning signal from the illuminated target is studied theoretically. The operating principle of a new-style adaptive-optics device, which is named adaptive fiber-optics collimator with the abilities to correct both laser beam transmission error and pointing error, is introduced. The laser beam pointing experimental setup with a laser propagation distance of 200 m through horizontal atmosphere is established. Based on returning signals from the illuminated two-dimensional and three-dimensional targets, the beam pointing closed loop using stochastic parallel gradient descent algorithm (SPGD) algorithm is achieved under different initial boresight errors. The experimental results indicate that the evaluation parameters of the residual boresight errors are less than 6% and 10.8% for the two-dimensional target and three-dimensional target, respectively, which are within the tolerance of theoretical analysis. Finally, the influence of SPGD parameter on moving-target pointing is analyzed.
A low radar cross-section artificial magnetic conductor reflection screen covering X and Ku band
Zheng Yue-Jun, Gao Jun, Cao Xiang-Yu, Li Si-Jia, Yang Huan-Huan, Li Wen-Qiang, Zhao Yi, Liu Hong-Xi
2015, 64 (2): 024219. doi: 10.7498/aps.64.024219
Abstract +
Based on the properties of the artificial magnetic conductor (AMC), a broadband low radar cross-section (RCS) reflection screen covering X and Ku band is designed and fabricated. The reflection screen is formed by combining two AMC cells, i.e., AMC1 with a dual band Jerusalem cross structure, and AMC2 with a wideband metal square patch structure. By optimizing the structures of these AMC cells, it is achieved that the frequency corresponding to the inversion point of the AMC1 reflection phase curve is equal or close to the frequency corresponding to the null point of the AMC2 reflection phase curve. Therefore, the valid reflection phase difference band is broadened and the RCS is reduced in a wider band. In addition, presented in this paper is a theoretical formula to calculate the reflection energy peak direction. When the incident angle, chessboard unit dimension and observed frequency are fixed, the reflection energy peak direction can be calculated by the formula. The calculation results from the theoretical formula are consistent with the HFSS simulation results, so the theoretical formula is valid. The simulation results indicate that, compared with the same-dimension metal RCS, the backscattering RCS is reduced by more than 10 dB in a frequency range of 7.4-17.0 GHz, except minority frequencies close to 9.8 GHz. The 10 dB-reducing RCS bandwidth covers the entire X band and most of Ku band, and the relative bandwidth is 78.7%. The largest reduction reaches 40.3 dB at 11.6 GHz. The simulations and the measurements are in good agreement. The results validate the broadband low RCS property of the reflection screen.
A closed-loop aberration compensating method of optics system based on holography
Tang Yan-Qiu, Sun Qiang, Zhao Jian, Yao Kai-Nan
2015, 64 (2): 024206. doi: 10.7498/aps.64.024206
Abstract +
We propose a holographic adaptive optics system based on holographic wavefront sensor and 21-element deformable mirror, and analyze the wavefront correction ability of the system in this paper. The principle of holographic wavefront sensor is described, and its numerical model is provided by fast Fourier transform algorithm in the thin hologram approximation. Then, the wavefront correction ability of 21-element deformable mirror is analyzed with its numerical model. Finally, the aberration compensation of the system is simulated and an experimental device is set up to verify the feasibility of the proposed adaptive optics system.
Multiple polarization switching in mutually coupled vertical-cavity surface emitting lasers
Zhou Zhen-Li, Xia Guang-Qiong, Deng Tao, Zhao Mao-Rong, Wu Zheng-Mao
2015, 64 (2): 024208. doi: 10.7498/aps.64.024208
Abstract +
Based on the spin-flip model, the characteristics of multiple polarization switching (PS) in mutually-coupled vertical-cavity surface emitting laser (VCSEL) are investigated by continuously changing some important parameters. The simulated results show that multiple PS can be generated through continuously varying the mutually-coupled strength, the oscillation frequency of one VCSEL or the oscillation frequencies of two VCSELs. The characteristics of multiple PS under the above three scenarios are analyzed, and the influence of the delay-coupled time on the performance of multiple PS is also discussed.
Analysis of ionizing and department damage mechanism in proton-irradiation-induced scientific charge-coupled device
Wen Lin, Li Yu-Dong, Guo Qi, Ren Di-Yuan, Wang Bo, Maria
2015, 64 (2): 024220. doi: 10.7498/aps.64.024220
Abstract +
A sort of homemade buried scientific charge-coupled device (CCD) is injected by 10 MeV protons, and measurements are carried out primarily on change of dark signal, charge transfer efficiency. Results show that parameters of CCD presented significantly decrease. Post-irradiation annealing is implemented and the results revel that CCD parameters recover to different extents. In this paper, analysed are the mechanism for the decrease of CCD parameters, and their dependences on process and structure in manufacture. The results above will provide helpful reference in characterization evaluation and technique development of future CCD.
Analysis of waveguide time-frequency based on Warping transform
Lu Li-Cheng, Ma Li
2015, 64 (2): 024305. doi: 10.7498/aps.64.024305
Abstract +
Sound propagation in underwater will induce dispersion due to the natural sea waveguide, and then it will degrade the results of the signal processing. Based on the waveguide invariant, a general warping transform is presented. This warping transform could extract the waveguide mode dispersion curve and remove the effect of the waveguide dispersion. Results from the simulation and experiment show that the transform woks well.
Characteristics on drag reduction of bionic jet surface based on earthworm's back orifice jet
Gu Yun-Qing, Mou Jie-Gang, Dai Dong-Shun, Zheng Shui-Hua, Jiang Lan-Fang, Wu Deng-Hao, Ren Yun, Liu Fu-Qing
2015, 64 (2): 024701. doi: 10.7498/aps.64.024701
Abstract +
In order to reduce the drag reduction of the fluid on the solid wall, based on the biology characteristics of earthworm, the earthworm's back orifice jet characteristic is analyzed. The bionic jet surface is modeled by imitating the earthworm's back orifice jet, and the SST k-ω turbulent model is used for numerically simulating the drag reduction characteristics of bionic jet surface, simultaneously the result of the numerical simulation is verified experimentally. On this account, the drag reduction mechanism of bionic jet surface is studied based on the imitation of the earthworm's back orifice jet. The results show that under certain conditions, the drag reduction characteristics of bionic jet surface for imitating the earthworm's back orifice jet are very effective. At the same angle of jet direction, the drag reduction rate increases with the increase of jet velocity; at the same jet speed, the drag reduction rate presents a tendency to increase after the first decrease with increasing the angle of the jet direction. The maximum drag reduction rates obtained from numerical simulation and experimental measurement both on condition that jet velocity is 1 m·s-1 and the angle of jet direction angel is -30°, are 8.69% and 7.86%, respectively. Jet surface changes the original boundary layer structure in smooth wall, thereby effectively controlling the wall boundary layer, and reducing the wall shear stress and also the velocity of the wall boundary layer.
On the accuracy and robustness of a new flux splitting method
Xie Wen-Jia, Li Hua, Pan Sha, Tian Zheng-Yu
2015, 64 (2): 024702. doi: 10.7498/aps.64.024702
Abstract +
The high speed flow problems usually involve complex flow phenomena, such as strong shock waves, shock-shock interactions, and shear layers. Prediction of these problems requires robust, efficient and accurate numerical methods. A robust flux splitting method capable of capturing crisp shock profile and exact contact surface is presented. Here, the flux vector of the Euler equation is split into convective and pressure parts according to the Toro's formulation. The accuracy of the numerical method at the contact discontinuity is examined first. Sufficient conditions of shock stability for this new method are obtained through a linear perturbation analysis. Several carefully chosen test problems are numerically investigated, and the numerical results demonstrate the accuracy and robustness of the proposed scheme.
Mode and hysteresis of laminar methane/oxygen inverse diffusion flame
Li Xin-Yu, Dai Zheng-Hua, Xu Yue-Ting, Li Chao, Wang Fu-Chen
2015, 64 (2): 024704. doi: 10.7498/aps.64.024704
Abstract +
Flame modes and liftoff hysteresis of the methane/oxygen inverse diffusion flame (IDF) are experimentally studied in still air. The effects of gas velocity on flame mode and liftoff hysteresis are investigated by changing the gas flow rate, and the influences of gas velocity on OH* distribution in different modes of flame are investigated using an ultraviolet camera. The results show that methane velocity, oxygen velocity and history of the flame mode are the key factors in determining the flame mode. Flame mode regimes are identified according to the three factors. The OH* profile along the axis of the nozzle in the IDF indicates that the reaction zone is narrow in fuel rich condition and broad in fuel lean condition. The hysteresis characteristics of the IDF are significantly influenced by the coaxial methane velocity. With the increase of coaxial methane velocity, the liftoff velocity and attachment velocity of the IDF decrease linearly, while the transition velocity increases linearly from partly premixed flame to IDF.
One-dimensional cellular automaton model of traffic flow considering dynamic headway
Zhang Ning-Xi, Zhu Hui-Bing, Lin Heng, Huang Meng-Yuan
2015, 64 (2): 024501. doi: 10.7498/aps.64.024501
Abstract +
Based on the NaSch cellular automaton traffic model, a modified single lane traffic model is proposed by considering the dynamic headway of successive vehicles, in which the complex characteristic and driving behavior difference between drivers are taken into account. The relationship between the flow rate and the traffic density is obtained by the numerical simulation, and it shows a two-dimensional region in the flow density plane. The three traffic phases, i.e., free flow, synchronized flow, and wide moving jams, are exhibited. It indicates that the synchronized flow and traffic jams can appear even if there is no traffic bottleneck. Besides, the high speed car-following phenomenon is indicated when the traffic is in the synchronized flow. The rate of the high speed car-following is in good agreement with the measured result.
Terahertz scattering property for the coated object of rough surface
Jiang Yue-Song, Nie Meng-Yao, Zhang Chong-Hui, Xin Can-Wei, Hua Hou-Qiang
2015, 64 (2): 024101. doi: 10.7498/aps.64.024101
Abstract +
The scattering of the radar signal by the coated target of a rough surface in the terahertz wave is studied. Considering the roughness of the surface, reflection coefficient is modified for the rough surface. The modified equivalent current can be obtained by using the reflection coefficient. Then using the modified equivalent current and the physical optics solution, the radar cross section of the coated object with the rough surface is obtained. And combining the graphical electromagnetic computing method, simulations to validate the formulation are performed. Numerical results for several coated bodies such as cylinder and cone-sphere geometry are given and discussed from different angles of incidence, different frequencies, different materials, different roughness values, and different coating thickness values.
Double cross-shape broadband low-loss and small units left-handed metamaterials based design and experimental verification
Dong Huai-Jing, Geng You-Lin
2015, 64 (2): 024102. doi: 10.7498/aps.64.024102
Abstract +
A method of designing a single side left-handed structure based on the integration of electric resonator and magnetic resonator is proposed in this paper. The left-handed units are composed of two cross types of metal mirrors that are parallel-placed on the same side of the substrate and then arranged into a periodic structure. The results of HFSS software simulation and a series of effective electromagnetic parameters extraction show that the left-handed structure exhibits negative effective permittivity and permeability simultaneously in a frequency range from 9.4 GHz to 16 GHz. Its relative passband reaches 52%, and the unit electrical length and loss are less than those of the same type of structures. The periodic structure is fabricated and tested using the waveguide method. The fine left-handed feature is proved again. This new structure lays a foundation for the wide applications of left-handed metamaterials.
Electromagnetic scattering characteristics of double S-shape exhaust nozzle with different coating medium parts
Gao Xiang, Shi Yong-Qiang, Yang Qing-Zhen, Chen Li-Hai
2015, 64 (2): 024103. doi: 10.7498/aps.64.024103
Abstract +
As one of the strong electromagnetic scattering source of the aircraft, the radar cross section (RCS) of the nozzle can be reduced by the special geometry and coating microwave absorbing material at the backward direction of the aircraft. In order to simulate the radar scattering characteristics of six coating models and one metal surface model of double S-shape nozzle, the mode combining impedance boundary condition with iterative physical optics (IPO) method is built. Forward and back-forward IPO method and open MP, MPI parallel computing technology are added to accelerate the convergence and reduce computational time. Besides, the ray tracing method is also adopted to improve the efficiency of geometric blanking judgment. The RCS variation regulations of 7 models under X waveband are obtained. The results indicate that coating medium can effectively diminish the RCS of double S-shape exhaust system. Proper coating method can not only reduce the RCS of exhaust system significantly, but also be economical, easy to coat and light-weight. Compared with all parts coating medium model, the model which is only coated at nozzle outlet can reduce microwave absorbing material cost by 73.6% and ensure that the maximal increment of RCS is less than 15.6%. Comparing with the metal model case, The RCS will decrease by at least 18.5%. The improved IPO method can be applied to the RCS evaluation of cavity and the study of coating absorbing material method, and provide technical support for the coating medium model experiment.
Progress in gain-guided and index-antiguided large mode area fiber laser pump technology
Shen Xiao, Zou Hui, Zheng Rui-Lin, Zheng Jia-Jin, Wei Wei
2015, 64 (2): 024210. doi: 10.7498/aps.64.024210
Abstract +
In this paper, we introduce a new type of gain guided and index antiguided (GG-IAG) large mode area (LMA) fiber structure, basic theory and its important applications in fiber laser fields. We draw a conclusion that the side pump technology is the most appropriate scheme for GG-IAG LMA fiber after comprehensively analyzing the laser output characteristics and the thermal effect of the fiber under different pump conditions. The theoretical simulations of GG-IAG fiber side pump technology and the side pump experiment process are performed by the V groove technology, which is conducible to the experiment research in relevant fields. Finally, the suggestion of how to reduce the difference between the experimental results and the theoretical results is made and its relevant reason is also discussed.
Detection of metal element in water using laser-induced breakdown spectroscopy assisted by nebulizer
Zhu Guang-Zheng, Guo Lian-Bo, Hao Zhong-Qi, Li Chang-Mao, Shen Meng, Li Kuo-Hu, Li Xiang-You, Liu Jian-Guo, Zeng Xiao-Yan, Lu Yong-Feng
2015, 64 (2): 024212. doi: 10.7498/aps.64.024212
Abstract +
In order to improve the limit of detection and linearity without losing the advantage of on-line and in-situ measurement, laser-induced breakdown spectroscopy assisted by nebulizer is investigated. The influences of the main experimental parameters, namely the defocusing amount, the distance between the nebulizer and the central of laser beam, the ablation energy and the delay are studied to maximize the signal-to-noise ratio. Using laser-induced breakdown spectroscopy assisted by nebulizer, we demonstrate that the detection limits are 1.2, 3.2, 19.1, 3.4, 2.8, and 15.9 ppm for Ca, Cr, K, Mg, Na, Pb respectively, and the linearities are all above 0.99. The results show that laser-induced breakdown spectroscopy assisted by nebulizer is an effective method to detect the tracing metal element in liquid on-line and in-situ.
Stochastic multi-resonance of the single-mode laser system driven by the noise with periodic force modulation
Zhang Rui-Fang, Cheng Qing-Hua, Xu Da-Hai
2015, 64 (2): 024211. doi: 10.7498/aps.64.024211
Abstract +
Using the linear approximation method, we calculate the intensity correlation function and the output signal-tonoise ratio (SNR) by adding a modulated wave to light intensity equation of a single mode laser system driven by the periodic force of modulating noise. Through the numerical calculation and analysis of the SNR, we find that the lowfrequency modulation frequency Ω, the high-frequency carrier frequency ω, and the frequency of periodic force Ωλ have a significant effect on the SNR. In particular, multi-peak stochastic resonances and strong single-peak resonance with low-frequency modulation frequency Ω appear in the SNR. When Ω ω, the system exhibits multi-peak resonance and the distance between the resonance peaks increases with the increase of Ωλ, but the position of peak is invariant. When Ω → ω, the output SNR R increases rapidly, the effect of Ωλ becomes weak or negligible, and multi-peak resonance disappears. When Ω = ω, a strong single-peak resonance appears in the system. In addition, the SNR varies with the decrease of amplitude of the multi-peak stochastic resonance, and with the SNR changes with carrier frequency the single-peak stochastic resonance appears in the system.
Propagation evolution of the off-axis ellipse vector beam
Li Yang, Zhu Zhu-Qing, Wang Xiao-Lei, Gong Li-Ping, Feng Shao-Tong, Nie Shou-Ping
2015, 64 (2): 024204. doi: 10.7498/aps.64.024204
Abstract +
The propagation characteristics of the off-axis ellipse vector beam (OEVB) are studied in this paper. The analytic expressions of the electric field and the intensity after OEVB propagating in free-space are derived. Numerical results indicate that the intensity distribution of OEVB is asymmetric and the intensity distribution after propagating is determined by propagation distance, dislocation displacement and ellipticity. In addition to expanding, the intensity distribution of OEVB tends to steady-state distribution finally and the dark core of vector beam disappears gradually during propagation. The major axis and minor axis of the ellipse intensity distribution in the steady-state are exchanged with each other as compared with in the initial plane. The results can help us to understand the dynamic propagation characteristics of the ellipse vector beam under the off-axis situation, and they can also guide the calibration of the ellipse vector beam in practice.
Image denoising model based on the improved Demons algorithm
Zhou Xian-Chun, Wang Mei-Ling, Zhou Lin-Feng, Wu Qin
2015, 64 (2): 024205. doi: 10.7498/aps.64.024205
Abstract +
According to image registration, we build a new Demons model of image denoising, in which the diffusion access is regarded as image registration. The experimental results indicate that the performance of the model is better than that of the Perona-Malik model: the ill-condition of the model is removed. It is not enough to describe local characteristics only by using the gradient information in the access of image denoising, so a level set curvature which is the driving force of image structure controlling is introduced into the denoising model. Therefore we propose a new model of image denoising based on two driving forces of gradient and curvature. The simulation results show that the two improved models can both suppress noise effectively, their definitions are enhanced obviously, the performance of image denoising model of two driving forces is more greatly improved.
Design and study of Fresnel lens for an antenna in indoor visible light communication system
Li Xiang, Lan Tian, Wang Yun, Wang Long-Hui
2015, 64 (2): 024201. doi: 10.7498/aps.64.024201
Abstract +
Indoor visible light communication is a novel wireless communication based on white LED technology. For its application needs, equal-pitch flat Fresnel lens is designed. Compared with traditional lens, Fresnel lens has several advantages including strong focus ability, short focal length, thin thickness, light weight, low cost, etc. The optical concentration ratio, the optical efficiency and the spot size of these Fresnel lenses are analyzed respectively with different parameters by means of Trace pro. Furthermore, the concentration performance is discussed at different incident angles. The results indicate that this kind of Fresnel lens could be used as an antenna of high-gain and small field, and the optical efficiency could be obtained to be 92.1%.


Theoretical model of phase-matching angles for KDP crystals and its verification analysis
Zhang Yang, Li Ting, Yuan Xiao-Dong, Xiong Zhao, Xu Xu, Ye Lang, Zhou Hai, Zhang Bin
2015, 64 (2): 024213. doi: 10.7498/aps.64.024213
Abstract +
In final optics assembly of high-power solid-state laser, in order to improve the third harmonic generation efficiency, the accurate assembly and calibration of ultra-thin KH2PO4 (KDP) crystal with large-aperture is one of the key technologies to realize inertial confinement fusion. In order to meet the requirements for high efficiency and precision crystal of online installation, it is necessary to measure crystalline phase matching angle for achieving the highest third harmonic conversion efficiency of high power laser. In this paper, for the third harmonic conversion by ultra-thin type Ⅰ/Ⅱ KDP crystals with large-aperture, the relationship between phase matching angles at different locations on the crystal is obtained according to the nonlinear optical properties of the crystal. Based on the analysis of the propagation path of the laser beam in the crystal, the relationship among the crystal surface shape, the phase matching angle and the best deflection angle is given. On this basis, the theoretical model for phase-matching angle of type Ⅰ/Ⅱ KDP crystal is proposed, and verified by the experimental results. The results show that the difference in phase matching angle between the prediction values and the experimental results is within 10.0 rad, showing that the theoretical model for phase-matching angles of type Ⅰ/Ⅱ KDP crystals is valid. This model provides a simple and efficient prediction method to obtain the phase matching angle distribution in full aperture of KDP crystal.
Phase singularities in femtosecond laser pulses transmitting through optical fiber probes
Liu Gui-Yuan, Song Hong-Sheng, Zhang Ning-Yu, Cheng Chuan-Fu
2015, 64 (2): 024203. doi: 10.7498/aps.64.024203
Abstract +
The near-field distribution of a light wave in a metal-coated optical fiber probe under the illumination of femtosecond laser pulses is numerically simulated. By choosing the maximum of the calculated light field data and the time when the light field reaches the maximum in a time period of one light wave cycle at each spatial point, we obtain the amplitude and phase distributions of the light field near the probe. We find that the output amplitude distribution of y-polarization has roughly a circled-cross-like pattern with two arc-like zero-amplitude zones. The zeros of light intensity are the phase singularities at which the phase is undefined. By analyzing the output phase distribution of y-polarization, we obtain the temporal evolution of the phase singularities and their characteristics
Transform relations between squeezed coherent state representation and quantum phase space distribution functions
Liang Xiu-Dong, Tai Yun-Jiao, Cheng Jian-Min, Zhai Long-Hua, Xu Ye-Jun
2015, 64 (2): 024207. doi: 10.7498/aps.64.024207
Abstract +
A new operator representation, called squeezed coherent state representation, is introduced since Husimi operator has the form of squeezed coherent state. We fisrt introduce its specific integral expression. When κ = 1, this representation is reduced to the usual P function. As an example, we calculate the squeezed coherent state representation for thermal field to illustrate a difference between P function and the squeezed coherent state representation. Especially, in order to better apply this representation to quantum optics, we reveal the integral transformations between the squeezed coherent state representation, respectively, and the following three functions: Wigner function, Q function, and Husimi function.
F-state based permanent optical data storage in bacteriorhodopsin film
Yu Xiang-Hua, Yao Bao-Li, Li Xin-Yu, Liu Shi-Lei, Lei Ming, Li Run-Ze, Liang Yan-Sheng, Zhou Xing, Wu Di, Dan Dan, Min Jun-Wei, Yan Shao-Hui
2015, 64 (2): 024218. doi: 10.7498/aps.64.024218
Abstract +
Upon excitation of high intensity linearly polarized femtosecond laser, a blue-shifted two-photon induced photoproduct named F540 state with permanent photo-induced anisotropy is observed in bacteriorhodopsin (BR) films. Based on the F-state, permanent optical data storage can be realized with spatial field modulation of femtosecond laser. By using a phase-only spatial light modulator to modulate the spatial phase distribution of the incident femtosecond laser beam, we generate spot-patterns in the focal plane of the microscopic objective lens, and the patterns are recorded in the BR film. At the same time, by varying the polarization direction of the excitation laser beam, polarization-multiplexed optical data storage in the BR film is demonstrated, which is applicable to high-density optical data storage and optical information encryption.
Influences of temperature, humidity and pressure on the attenuation characteristics of laser beam in water
Shi Jiu-Lin, Guo Peng-Feng, Huang Yu, Qian Jia-Cheng, Wang Hong-Peng, Liu Juan, He Xing-Dao
2015, 64 (2): 024215. doi: 10.7498/aps.64.024215
Abstract +
In this paper, the attenuation characteristics of 532 nm laser beam in water under different atmospheric conditions (temperature, humidity, air pressure) are investigated experimentally. Experimental results show that the attenuation coefficient of laser beam in water is significantly influenced by the atmospheric environment. The attenuation coefficient decreases with the increase of air pressure, and increases with the increase of temperature. The maximum value of attenuation coefficient of light appears in the case of high temperature and low air pressure, while the minimum value appears in the high air pressure and low temperature. The maximum attenuation coefficient of laser in water is about three times the minimum value. The mechanisms of these phenomena are discussed. These results are valuable for Brillouin lidar to achieve the remote sensing of ocean.


Ultrasonic enhancement of the porosity of alginate scaffold
Lu Lu, Ji Hong-Fei, Guo Ge-Pu, Guo Xia-Sheng, Tu Juan, Qiu Yuan-Yuan, Zhang Dong
2015, 64 (2): 024301. doi: 10.7498/aps.64.024301
Abstract +
Alginate scaffold with a three-dimensional (3D) porous structure can provide sufficient space for the cell to adhere, and has a good biocompatibility and mechanical strength. In this work, low-intensity pulsed ultrasound (LIPUS) is used to enhance the porosity of alginate scaffold based on acoustic cavitation. In the experiment, the alginate-calcium-based 3D scaffold culture system is fabricated with an optimum CaCl2/sodium alginate ratio of 3:5. The mechanical properties of alginate scaffold are measured and scanning electron microscopy is used to analyze the porosity of the scaffold. In addition, the microscopy observation of green fluorescent protein expression and the CCk-8 assessment are adapted to analyze the cell proliferation effect. Experimental results show that with LIPUS treatment under appropriate driving parameters (acoustic pressure 0.055 MPa and treatment time 20 min), the porosity of the 3D scaffold can be significantly improved, which would benefit the cell growth in the scaffold.
A geometric calibration mehtod of hydrophone array with known sources in near field under strong multipath
Wang Yan, Zou Nan, Liang Guo-Long
2015, 64 (2): 024304. doi: 10.7498/aps.64.024304
Abstract +
In order to meet the demand of underwater acoustic array calibration in near field with strong reflection, a high-precision geometric calibration method with known sources is proposed. Colligating the principles of non-plane wave model of point source and the Taylor approximation, a two-dimensional geometry error model for near field is established. And then the line mapping relationship is obtained between geometric error of sensors and signal eigen vector. Cramer-Rao bound (CRB) of this mode is deduced and analyzed. The influence of multipath on geometric calibration is studied. The strong reflections are compared to the coherent sources at a known position, and the compensation strategy is realized. The results from theory and simulation show that the precision of geometry calibration technique with accessorial sources in near field is high and it is close to the CRB in the case of low SNR. The method has a certain tolerance for the position error of accessorial sources. And it is applicable for multipath. Pool test results further verify the correctness of these results.
Influence factors of quantitative analysis precision of greenhouse gases and carbon isotope ratio based on infrared spectroscopy
Li Xiang-Xian, Xu Liang, Gao Min-Guang, Tong Jing-Jing, Feng Ming-Chun, Liu Jian-Guo, Liu Wen-Qing
2015, 64 (2): 024217. doi: 10.7498/aps.64.024217
Abstract +
The quantitative analysis based on Fourier transform infrared (FTIR) technology is affected by the temperature and pressure properties of gas and the H2O cross section, so the applications of FTIR technology to high-precision measurement area of the greenhouse gases and isotope ratio are restricted. Firstly, the methods of correcting the gas property sensitivities and H2O cross sensitivity are studied, then the standard gas measurements are corrected with these sensitivity correcting functions established through experimental study. The standard deviations of CO, CO2, N2O, CH4 and δ13CO2 are all improved after correcting the sensitivities, and reduced by 1.80-3.38 times. These studies are significant for the applications of FTIR technology to the high-precision measurement area of greenhouse gases and isotope ratio.
A robust localization method for source localization based on the auto-correlation function of wide-band signal
Zhang Tong-Wei, Yang Kun-De, Ma Yuan-Liang, Wang Yong
2015, 64 (2): 024303. doi: 10.7498/aps.64.024303
Abstract +
It is very difficult to estimate the relative arrival delay of the eigenrays for an unknown source in shallow water. The effects of a source position changing in the neighborhood and sound speed profile perturbation on arrival time of eigenvays are similar. In this paper, we present a robust localization method based on the auto-correlation function of wide-band signal of single hydrophone. By designing neighboring location constraints, a weighting function is constructed to change the peak cross-interference of the auto-correlation function to useful information that is conducible to the improving of targeting performance. In this method there is no need to estimate the relative arrival delay of the eigenray. Computer simulation shows that the robust method can achieve better localization performance, and even has tolerences of environment mismatch and searching grid mismatch. The performance of the robust method is validated through the broad-band data collected on a vertical line array during the Shallow Water 2006 experiments.
Numerical simulation of natural convection of square enclosure filled with Cu/Al2O3-water mixed nanofluid based on lattice Boltzmann method
Qi Cong, He Guang-Yan, Li Yi-Min, He Yu-Rong
2015, 64 (2): 024703. doi: 10.7498/aps.64.024703
Abstract +
As an effective heat transfer medium, Nanofluid is used widely in heat transfer field. However, due to the contradiction between the heat conductivity coefficient of nanofluid and the cost of nanoparticles, a new mixed nanofluid is developed. In order to investigate the natural convection heat transfer characteristics and the interaction mechanism between nanoparticles, the lattice Boltzmann equations of nanofluid flow and temperature fields are deduced by multi-scale technique based on considering the interaction forces between nanoparticles, and the lattice Boltzmann model of Cu/Al2O3-water mixed nanofluid is established by coupling the evolution equations of flow with temperature fields. Nanoparticles distribution in enclosure and interaction forces between nanoparticles are investigated, it is found that Brownian motion force is far bigger than any other forces, and the effects of temperature difference driving force and Brownian motion force on nanoparticles distribution are biggest. In addition, the effects of nanoparticles fractions and Rayleigh number on natural convection are investigated, and the natural convection heat transfer characteristics of mixed nanofluid (Cu/Al2O3-water) are compared with those of single metal nanoparticle nanofluid (Al2O3-water). It is found that the mixed nanofluid has a higher heat transfer characteristic than other common nanofluid.
Fingerprint data extraction from Chinese herbal medicines with terahertz spectrum based on second-order harmonic oscillator model
Zhao Feng, Long Shu-Ming, Zhang Yuan-Yuan, Wang Xin-Ke, Ye Jia-Sheng, Zhang Yan
2015, 64 (2): 024202. doi: 10.7498/aps.64.024202
Abstract +
Terahertz time-domain spectroscopy provides a new method of identifying and studying Chinese herbal medicines. We utilize a second-order terahertz filter to describe the samples of Chinese herbal medicines, and the behaviors of terahertz filter are characterized by a second-order differential equations with three parameters {α, β, γ} or the corresponding frequency domain system function H(f). The results of data analysis show that five kinds of Chinese herbal medicines which are used in the experiments have unique filter parameters. Thus, if these filter parameters are used as the fingerprint data of Chinese herbal medicines, we can effectively determine the types and origins of Chinese herbal medicines.
“Inverted-image” frequency chirp induced by self-phase modulation in highly noninstantaneous medium
Hong Wei-Yi
2015, 64 (2): 024214. doi: 10.7498/aps.64.024214
Abstract +
Nonlocal nonlinearity is one of the hottest topics in the nonlinear optics and even the nonlinear science. In this paper, the frequency chirp induced by the self-phase modulation (SPM) in a high noninstantaneous medium is investigated. It is found that the temporal distribution of the SPM-induced chirp can be approximated by the “inverted image” of the pulse intensity in the highly noninstantaneous limit. Moreover, this property does not depend on the envelope of the pulse. By using these properties, the temporal characteristics of the pulse propagation in a highly noninstantaneous medium is analyzed.
Stack-through silicon via dynamic power consumption optimization in three-dimensional integrated circuit
Dong Gang, Wu Wen-Shan, Yang Yin-Tang
2015, 64 (2): 026601. doi: 10.7498/aps.64.026601
Abstract +
Stack-through silicon via (TSV) used in three-dimensional integrated circuit has good temperature and heat transfer characteristics. A novel model for optimizing the dynamic power consumption based on stacked-TSV is proposed in this paper, in which delay, area and minimum aperture are comprehensively considered. After extracting single TSV parasitic electrical parameters, we analyze the influences of TSV size on multilayer TSV power consumption and delay performance, thereby building the hierarchical reduction TSV structure step by step. Moreover, the influences of TSV height and thickness of oxide layer are discussed. Results show that the model can significantly improve the dynamic power consumption at the expense of little delay. The power consumption optimization reduction is up to 19.52% with 5% delay penalty.
Irradiation effect of deuterium or hydrogen on Cr/W mixed transitional layers prepared by double ion beam deposition
Feng Hong-Li, Gou Cheng-Ling, Yu Jian-Gang, Han Wen-Jia, Chen Zhe, Cai Ya-Nan, Zhu Kai-Gui
2015, 64 (2): 026101. doi: 10.7498/aps.64.026101
Abstract +
Cr films with different thickness values on W substrates are prepared by double-ion-beam-deposition(DIBD) method. The deep distributions of Cr and W are analyzed by energy dispersive spectrometer. Hydrogen and deuterium irradiation of high energy and low flux are carried out in heavy ion accelerator. The changes of the sample surface morphology are analyzed by scanning electron microscopy. The injection range of hydrogen particles in double layers of Cr/W is simulated by simulation software SRIM. The experimental results demonstrate that a Cr/W mixture transitional layer is formed at the interface between Cr and W using DIBD method; hydrogen and deuterium of high energy and low flux tend to be retained in the Cr/W mixture transitional layer and form gas bubbles, while the Cr film is not easy to retain enough hydrogen or deuterium to form gas bubbles.
First-principles calculations of the diffusion behaviors of C, N and O atoms in V metal
Yang Biao, Wang Li-Ge, Yi Yong, Wang En-Ze, Peng Li-Xia
2015, 64 (2): 026602. doi: 10.7498/aps.64.026602
Abstract +
Based on the density functional theory, the diffusion behaviors of C, N and O atoms in V metal are studied by using the first-principles calculation method. Firstly, the site occupations of C, N and O atoms in the interstitials of the bcc V lattice are discussed. The interactions of interstitial C, N and O atoms with V lattice are analyzed, and the influence of the electronic structure on the interaction is explored. The study results show that C, N and O atoms are more stable in octahedral interstice of V metal, and a relatively strong bonding interaction is formed between their 2p-electron and the 3d-electron of V metal. The diffusion barriers of C, N and O atoms are 0.89 eV, 1.26 eV and 0.98 eV, respectively. Thus, the expressions of their diffusion coefficients are obtained. Finally, the diffusion coefficients of C, N and O atoms are compared by the Arrhenius plot. Their diffusion coefficients are calculated at 500-1100 K, and the calculation results are consistent with experimental values.
Detection of significant external trend in long-term air temperature records
Huang Yan, Yuan Nai-Ming, He Wen-Ping
2015, 64 (2): 029201. doi: 10.7498/aps.64.029201
Abstract +
Long-term historical air temperature records of four stations from Global Historical Climatology Network-Daily are analyzed in this study. By applying detrended fluctuation analysis of the second order to the monthly anomalies, different long-term correlations are found in different time periods at both the maximum and minimum temperatures, which indicate the existence of internal stochastic trend. By generating surrogate data with the same long-term correlations and data length, internal stochastic trends are estimated with confidence probability intervals of 95% and 99% provided. We find the longer data length, the shorter confidence probability interval we have; the stronger long-term correlation, the wider confidence probability interval is obtained. By comparing the temperature trends observed from the historical temperature records with the corresponding confidence probability intervals of the internal stochastic trends, significant external trends can be detected. We find that except for the maximum temperature in SAGINAW MBS INTL AP, temperatures from the four stations all show significant external trends when long historical data (>100 years) are considered. However, if only the past 30 years are taken into account, the observed trends are still not strong enough to exceed the confidence probability interval. Although we cannot exclude the existence of external trends, considering the possible influence from internal stochastic trends, the external trends are not significant. From this detection method, we can judge, in the context of global warming, whether an observed trend is significantly induced by external forcing. Therefore, it is useful for our further study targeting the internal (external) climatic impact factors.
Optically tuned wideband terahertz wave amplitude modulator based on gold-doped silicon
Tian Wei, Wen Qi-Ye, Chen Zhi, Yang Qing-Hui, Jing Yu-Lan, Zhang Huai-Wu
2015, 64 (2): 028401. doi: 10.7498/aps.64.028401
Abstract +
In this paper, we present a broadband terahertz wave amplitude modulator based on optically-controlled gold-doped silicon. Gold dots with a diameter of 40 μm are used as a dopant source. Experimental results indicate that interstitial Au atoms provide effective recombination centers for photo-generated electron-hole pairs in Si body, leading to a significant decrease of the minority carrier lifetime from more than 10 μs to about 110 ns. Dynamic modulation measurement at 340 GHz carrier shows a modulation depth of 21% and a maximum modulation speed of 4.3 MHz. This modulator has advantages such as wideband operation, high modulation speed, polarization insensitivity, and easy manufacture by using the large-scale integrated technology, and thus can be widely used in terahertz technology.
Preparation of the high-quality highly (100) oriented diamond films with controllable growth
Liu Cong, Wang Jian-Hua, Weng Jun
2015, 64 (2): 028101. doi: 10.7498/aps.64.028101
Abstract +
The high-quality highly (100) oriented diamond films each with controllable surface morphology, quality, orientation, and growth rate are prepared at low pressure by microwave plasma chemical vapor deposition. The results show that there is a coupled effect between substrate temperature and methane concentration on the growth of (100) oriented diamond films. The substrate temperature should be increased with increasing the methane concentration in order to obtain similar surface morphologies. When the methane concentration is 3.0%, the results indicate that there are five states for the orientation change with the substrate temperature increasing from 740 ℃ to 1100 ℃, and the diamond films with (100) orientation can be deposited at the substrate temperatures ranging from 860 ℃ to 930 ℃. Moreover, the quality and growth rate of each of (100) oriented diamond films are proportional to the substrate temperature and methane concentration, respectively. In order to obtain the high-quality highly (100) oriented diamond films, the substrate temperature and methane concentration should be both appropriate.
Biased random walks in the scale-free networks with the disassortative degree correlation
Hu Yao-Guang, Wang Sheng-Jun, Jin Tao, Qu Shi-Xian
2015, 64 (2): 028901. doi: 10.7498/aps.64.028901
Abstract +
Random walk has been applied to exploring the effective transport strategy of data package in complex networks. Because the disassortative degree correlation is ubiquitous in technical networks including the internet, we study the biased random walks in the scale-free networks with the disassortative degree correlation. Computer simulation shows that the degree correlation changes the behavior of the random walk. Random walkers are located on small degree nodes with a low probability, and they can be distributed homogeneously on other nodes. We find out the optimal biased coefficient that ensures the most homogeneous distribution on large nodes. In the optimal case, the degree-correlated network exhibits a more efficient random walk than degree-uncorrelated networks. We propose the mechanism for the effect of the disassortative mixing on the random walk.
Investigation of atom-attaching process of three-dimensional body-center-cubic dendritic growth by phase-field crystal model
Guo Can, Wang Jin-Cheng, Wang Zhi-Jun, Li Jun-Jie, Guo Yao-Lin, Tang Sai
2015, 64 (2): 028102. doi: 10.7498/aps.64.028102
Abstract +
On the basis of the Gaussian kernel phase field crystal model (PFC), we propose a modified PFC model. The atom-attaching process of three-dimensional body-center-cubic (BCC) dendritic growth is examined by using the modified PFC model. Our simulations indicate that in the process of the morphology evolution from regular dodecahedron to dendrite shape, the nucleation position of new layer is transferred from the center of {110} planes into the region of {110} plane near the tips, and then the BCC dendritic morphology is obtained. In the process of dendritic growth, first, new solid atom absorption takes place near dendrite tips, then liquid atoms start to grow up on the existing solid phase rapidly. After the dendrite tips are completely occupied by new atoms, new nuclei begin to form again. Increasing the initial atom density n will increase the velocity coefficient C and the anisotropy of C.
Beamforming design based on energy harvesting proportional fairness in a simultaneous wireless information and power transfer system
Zhang Hai-Yang, Huang Yong-Ming, Yang Lü-Xi
2015, 64 (2): 028402. doi: 10.7498/aps.64.028402
Abstract +
In this paper, we propose a beamforming design based on energy harvesting proportional fairness to overcome the unbalance of energy harvesting in a simultaneous wireless information and power transfer system. We aim at achieving the energy harvesting proportional fairness while guaranteeing the signal to interference plus noise ratio constraints at the information receivers and total power constraint at the transmitter by optimizing the beamforming vectors. This optimization problem is of non-convex and hence difficult to solve. In order to solve it, in this paper, we first use the semi-definite relaxation technique as a tool to transform it into a semi-definite program problem, and then propose an iterative algorithm based on bisection method to obtain the optimal beamforming vectors. Besides, we also extend our result to a robust case where the transmitter only knows a part of the channel state information and the bound of channel errors, and propose an iterative algorithm based on worst-case method to obtain the corresponding beamforming vectors. Finally, the simulation results show that the proposed algorithms can achieve both the energy harvesting proportional fairness and global optimum.
Effect of wafer bonding and laser liftoff process on residual stress of GaN-based vertical light emitting diode chips
Wang Hong, Yun Feng, Liu Shuo, Huang Ya-Ping, Wang Yue, Zhang Wei-Han, Wei Zheng-Hong, Ding Wen, Li Yu-Feng, Zhang Ye, Guo Mao-Feng
2015, 64 (2): 028501. doi: 10.7498/aps.64.028501
Abstract +
Residual stress conditions in GaN-based LEDs will have a significant influence on device performance and reliability. In this paper, GaN-based vertical LEDs under different stress conditions are fabricated by bonding with three types of submounts (Al2O3 submount, CuW submount and Si submount), changing the soak temperature (290 ℃, 320 ℃, 350 ℃ and 380 ℃) and using different laser energy densities (875, 945 and 1015 mJ·cm-2). The warpage and Raman scattering spectra of those GaN-based LEDs are measured. The experimental results show that the residual stress conditions in GaN-based vertical LEDs are a consequence of the bonded submounts and bonded metal, and the soak temperature is the primary factor that determines the degree of residual stress in LED chips. In the laser lift-off process, changing laser energy density in an appropriate range has little influence on residual strain of LED chips, and the micro-cracks in GaN layer caused by LLO process will play a role in releasing the residual stress. The warpage of epitaxial sapphire substrate becomes large after boding with Si submount, the residual stress in GaN-based vertical LEDs is tensile stress and becomes larger with the soak temperature rising. When GaN epi wafer bonds with Al2O3 submount and CuW submount, the warpages becomes small and large respectively and the residual stress in chips is compressive stress. Because of the mismatch of coefficient of thermal expansion, the compressive stress in GaN-based LED chips increases for Al2O3 submount and drops for CuW submount with the soak temperature rising.
A real-time axial activeanti-drift device with high-precision
Huo Ying-Dong, Cao Bo, Yu Bin, Chen Dan-Ni, Niu Han-Ben
2015, 64 (2): 028701. doi: 10.7498/aps.64.028701
Abstract +
In a fluorescent nano-resolution microscope based on single molecular localization, drift of focal plane will bring an additional deviation to the accuracy of single molecular localization. Consequently, this will reduce the final resolution of the reconstructed image and cause image degradation. Therefore, it is vital to control the system drift to a minimum level as much as possible. In recent years, the anti-drift ways emerged in endlessly. In this paper we made a systematic study aiming at the method in which optical measurement and negative feedback control are used. The basic principle and its implementation of the system are analyzed, and possible error is also evaluated. Finally, the precision of the system is tested experimentally. With this device, axial drift can be detected and corrected automatically in time, and the axial anti-drift accuracy as high as 9.93 nm can be achieved, which is one order higher than that of the existing commercial microscopies.


Spontaneous evolution of Cs 47D Rydberg atoms at different fine levels
Duan Jun-Yi, Wang Yong, Zhang Lin-Jie, Zhao Jian-Ming, Li Chang-Yong, Jia Suo-Tang
2015, 64 (2): 023201. doi: 10.7498/aps.64.023201
Abstract +
The spontaneous evolution from Rydberg atoms in different fine states to plasmas is investigated. Two-photon excitation is used to excite ultracold cesium atoms from 6S1/2 to 47D3/2 and 47D5/2 Rydberg states, respectively. The ramp electric field is used to ionize the Rydberg atoms and drive the ions to the micro-channel plate detector. In this experiment, The atom number of 47D5/2 state, which has a high oscillator strength compared with 47D3/2, is about 7 times larger than that of 47D3/2 state. Based on the different initial atom numbers of two fine states, the evolutions of plasma and Rydberg atoms are observed. The initial ionization time of Rydberg atoms and avalanche ionization rate of different states are presented. The initial ionization of Rydberg atoms is ascribed to the combining effect of state transfer from repulsive interaction to attractive interaction induced by the blackbody radiation and superradiation and Rydberg atoms collision. Moreover, the avalanche ionization and production of plasma are explained as being due to the rapid collision between Rydberg atoms and electrons in a local potential trap produced by positive ions.