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2016年, 第25卷, 第6期　刊出日期：2016-06-05 上一期    下一期

GENERAL

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Nonlocal symmetry and exact solutions of the (2+1)-dimensional modified Bogoyavlenskii-Schiff equation 黄丽丽, 陈勇 2016 (6):  60201-060201.  doi: 10.1088/1674-1056/25/6/060201 摘要 ( 888 )   HTML ( 0 )   PDF(11463KB) ( 1393 )   In this paper, the truncated Painlevé analysis, nonlocal symmetry, Bäcklund transformation of the (2+1)-dimensional modified Bogoyavlenskii-Schiff equation are presented. Then the nonlocal symmetry is localized to the corresponding nonlocal group by the prolonged system. In addition, the (2+1)-dimensional modified Bogoyavlenskii-Schiff is proved consistent Riccati expansion (CRE) solvable. As a result, the soliton-cnoidal wave interaction solutions of the equation are explicitly given, which are difficult to find by other traditional methods. Moreover figures are given out to show the properties of the explicit analytic interaction solutions. 参考文献 | 相关文章 | 计量指标

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Degree distribution of random birth-and-death network with network size decline 张晓军, 杨会兰 2016 (6):  60202-060202.  doi: 10.1088/1674-1056/25/6/060202 摘要 ( 830 )   HTML ( 0 )   PDF(376KB) ( 282 )   In this paper, we provide a general method to obtain the exact solutions of the degree distributions for random birth-and-death network (RBDN) with network size decline. First, by stochastic process rules, the steady state transformation equations and steady state degree distribution equations are given in the case of m ≥ 3 and 0< p< 1/2, then the average degree of network with n nodes is introduced to calculate the degree distributions. Specifically, taking m=3 for example, we explain the detailed solving process, in which computer simulation is used to verify our degree distribution solutions. In addition, the tail characteristics of the degree distribution are discussed. Our findings suggest that the degree distributions will exhibit Poisson tail property for the declining RBDN. 参考文献 | 相关文章 | 计量指标

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Anonymous voting for multi-dimensional CV quantum system 施荣华, 肖伊, 石金晶, 郭迎, 2016 (6):  60301-060301.  doi: 10.1088/1674-1056/25/6/060301 摘要 ( 636 )   HTML ( 0 )   PDF(282KB) ( 285 )   We investigate the design of anonymous voting protocols, CV-based binary-valued ballot and CV-based multi-valued ballot with continuous variables (CV) in a multi-dimensional quantum cryptosystem to ensure the security of voting procedure and data privacy. The quantum entangled states are employed in the continuous variable quantum system to carry the voting information and assist information transmission, which takes the advantage of the GHZ-like states in terms of improving the utilization of quantum states by decreasing the number of required quantum states. It provides a potential approach to achieve the efficient quantum anonymous voting with high transmission security, especially in large-scale votes. 参考文献 | 相关文章 | 计量指标

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Analysis of weak signal detection based on tri-stable system under Levy noise 贺利芳, 崔莹莹, 张天骐, 张刚, 宋莹 2016 (6):  60501-060501.  doi: 10.1088/1674-1056/25/6/060501 摘要 ( 812 )   HTML ( 0 )   PDF(1443KB) ( 391 )   Stochastic resonance system is an effective method to extract weak signal. However, system output is directly influenced by system parameters. Aiming at this, the Levy noise is combined with a tri-stable stochastic resonance system. The average signal-to-noise ratio gain is regarded as an index to measure the stochastic resonance phenomenon. The characteristics of tri-stable stochastic resonance under Levy noise is analyzed in depth. First, the method of generating Levy noise, the effect of tri-stable system parameters on the potential function and corresponding potential force are presented in detail. Then, the effects of tri-stable system parameters w, a, b, and Levy noise intensity amplification factor D on the resonant output can be explored with different Levy noises. Finally, the tri-stable stochastic resonance system is applied to the bearing fault detection. Simulation results show that the stochastic resonance phenomenon can be induced by tuning the system parameters w, a, and b under different distributions of Levy noise, then the weak signal can be detected. The parameter intervals which can induce stochastic resonances are approximately equal. Moreover, by adjusting the intensity amplification factor D of Levy noise, the stochastic resonances can happen similarly. In bearing fault detection, the detection effect of the tri-stable stochastic resonance system is superior to the bistable stochastic resonance system. 参考文献 | 相关文章 | 计量指标

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Interaction function of coupled bursting neurons 石霞, 张佳栋 2016 (6):  60502-060502.  doi: 10.1088/1674-1056/25/6/060502 摘要 ( 447 )   HTML ( 0 )   PDF(14222KB) ( 273 )   The interaction functions of electrically coupled Hindmarsh-Rose (HR) neurons for different firing patterns are investigated in this paper. By applying the phase reduction technique, the phase response curve (PRC) of the spiking neuron and burst phase response curve (BPRC) of the bursting neuron are derived. Then the interaction function of two coupled neurons can be calculated numerically according to the PRC (or BPRC) and the voltage time course of the neurons. Results show that the BPRC is more and more complicated with the increase of the spike number within a burst, and the curve of the interaction function oscillates more and more frequently with it. However, two certain things are unchanged: φ=0, which corresponds to the in-phase synchronization state, is always the stable equilibrium, while the anti-phase synchronization state with φ=0.5 is an unstable equilibrium. 参考文献 | 相关文章 | 计量指标

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Exploring the relationship between fractal features and bacterial essential genes 余永明, 杨立才, 周茜, 赵璐璐, 刘治平 2016 (6):  60503-060503.  doi: 10.1088/1674-1056/25/6/060503 摘要 ( 604 )   HTML ( 0 )   PDF(1834KB) ( 314 )   Essential genes are indispensable for the survival of an organism in optimal conditions. Rapid and accurate identifications of new essential genes are of great theoretical and practical significance. Exploring features with predictive power is fundamental for this. Here, we calculate six fractal features from primary gene and protein sequences and then explore their relationship with gene essentiality by statistical analysis and machine learning-based methods. The models are applied to all the currently available identified genes in 27 bacteria from the database of essential genes (DEG). It is found that the fractal features of essential genes generally differ from those of non-essential genes. The fractal features are used to ascertain the parameters of two machine learning classifiers: Naïve Bayes and Random Forest. The area under the curve (AUC) of both classifiers show that each fractal feature is satisfactorily discriminative between essential genes and non-essential genes individually. And, although significant correlations exist among fractal features, gene essentiality can also be reliably predicted by various combinations of them. Thus, the fractal features analyzed in our study can be used not only to construct a good essentiality classifier alone, but also to be significant contributors for computational tools identifying essential genes. 参考文献 | 相关文章 | 计量指标

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H∞ synchronization of the coronary artery system with input time-varying delay 李晓蒙, 赵占山, 张静, 孙连坤 2016 (6):  60504-060504.  doi: 10.1088/1674-1056/25/6/060504 摘要 ( 868 )   HTML ( 0 )   PDF(11233KB) ( 311 )   This paper investigates the H∞ synchronization of the coronary artery system with input delay and disturbance. We focus on reducing the conservatism of existing synchronization strategies. Base on the triple integral forms of the Lyapunov-Krasovskii functional (LKF), we utilize single and double integral forms of Wirtinger-based inequality to guarantee that the synchronization feedback controller has good performance against time-varying delay and external disturbance. The effectiveness of our strategy can be exhibited by simulations under the different time-varying delays and different disturbances. 参考文献 | 相关文章 | 计量指标

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An exclusion process with dynamic roadblocks 郭宁, 陈金邕, 胡茂彬, 姜锐 2016 (6):  60505-060505.  doi: 10.1088/1674-1056/25/6/060505 摘要 ( 702 )   HTML ( 2 )   PDF(2362KB) ( 279 )   We study an exclusion process with multiple dynamic roadblocks. Each roadblock can move diffusively forward or backward with different rates, as well as unbind from/rebind to a free site. By Monte Carlo simulations, the two moving types are investigated in combination of roadblock number. The case of only diffusive roadblocks shows an asymmetric current-density relation. The case of only long-range jumping roadblocks presents that flux decreases with increasing roadblock number. 参考文献 | 相关文章 | 计量指标

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Stability analysis of traffic flow with extended CACC control models 郑亚周, 程荣军, 卢兆明, 葛红霞 2016 (6):  60506-060506.  doi: 10.1088/1674-1056/25/6/060506 摘要 ( 787 )   HTML ( 0 )   PDF(18712KB) ( 353 )   To further investigate car-following behaviors in the cooperative adaptive cruise control (CACC) strategy, a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models. In this control system, some vital comprehensive information, such as multiple preceding cars' speed differences and headway, variable safety distance (VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods. Local and string stability criterion for the velocity control (VC) model and gap control (GC) model are derived via linear stability theory. Numerical simulations are conducted to study the performance of the simulated traffic flow. The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion. 参考文献 | 相关文章 | 计量指标

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Analyses of an air conditioning system with entropy generation minimization and entransy theory 吴艳秋, 蔡黎, 吴鸿娟 2016 (6):  60507-060507.  doi: 10.1088/1674-1056/25/6/060507 摘要 ( 708 )   HTML ( 0 )   PDF(492KB) ( 407 )   In this paper, based on the generalized heat transfer law, an air conditioning system is analyzed with the entropy generation minimization and the entransy theory. Taking the coefficient of performance (denoted as COP) and heat flow rate Qout which is released into the room as the optimization objectives, we discuss the applicabilities of the entropy generation minimization and entransy theory to the optimizations. Five numerical cases are presented. Combining the numerical results and theoretical analyses, we can conclude that the optimization applicabilities of the two theories are conditional. If Qout is the optimization objective, larger entransy increase rate always leads to larger Qout, while smaller entropy generation rate does not. If we take COP as the optimization objective, neither the entropy generation minimization nor the concept of entransy increase is always applicable. Furthermore, we find that the concept of entransy dissipation is not applicable for the discussed cases. 参考文献 | 相关文章 | 计量指标

SPECIAL TOPIC—Soft matter and biological physics (Review)

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Microwave interrogation cavity for the rubidium space cold atom clock 任伟, 高源慈, 李唐, &;吕德胜, 刘亮 2016 (6):  60601-060601.  doi: 10.1088/1674-1056/25/6/060601 摘要 ( 928 )   HTML ( 0 )   PDF(2663KB) ( 391 )   The performance of space cold atom clocks (SCACs) should be improved thanks to the microgravity environment in space. The microwave interrogation cavity is a key element in a SCAC. In this paper, we develop a microwave interrogation cavity especially for the rubidium SCAC. The interrogation cavity has two microwave interaction zones with a single feed-in source, which is located at the center of the cavity for symmetric coupling excitation and to ensure that the two interaction zones are in phase. The interrogation cavity has a measured resonance frequency of 6.835056471 GHz with a loaded quality factor of nearly 4200, which shows good agreement with simulation results. We measure the Rabi frequency of the clock transition of the rubidium atom in each microwave interaction zone, and subsequently demonstrate that the distributions of the magnetic field in the two interaction zones are the same and meet all requirements of the rubidium SCAC. 参考文献 | 相关文章 | 计量指标

GENERAL

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Study of the optimal duty cycle and pumping rate for square-wave amplitude-modulated Bell-Bloom magnetometers 王美玲, 王梦冰, 张桂迎, 赵凯锋 2016 (6):  60701-060701.  doi: 10.1088/1674-1056/25/6/060701 摘要 ( 682 )   HTML ( 0 )   PDF(868KB) ( 312 )   We theoretically and experimentally study the optimal duty cycle and pumping rate for square-wave amplitude-modulated Bell-Bloom magnetometers. The theoretical and the experimental results are in good agreement for duty cycles and corresponding pumping rates ranging over 2 orders of magnitude. Our study gives the maximum field response as a function of duty cycle and pumping rate. Especially, for a fixed duty cycle, the maximum field response is obtained when the time averaged pumping rate, which is the product of pumping rate and duty cycle, is equal to the transverse relaxation rate in the dark. By using a combination of small duty cycle and large pumping rate, one can increase the maximum field response by up to a factor of 2 or π/2, relative to that of the sinusoidal modulation or the 50% duty cycle square-wave modulation respectively. We further show that the same pumping condition is also practically optimal for the sensitivity due to the fact that the signal at resonance is insensitive to the fluctuations of pumping rate and duty cycle. 参考文献 | 相关文章 | 计量指标

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Spectroscopic measurements and terahertz imaging of the cornea using a rapid scanning terahertz time domain spectrometer 刘文权, 鲁远甫, 焦国华, 陈险峰, 周志盛, 佘荣斌, 李金瑛, 陈四海, 董玉明, &;吕建成 2016 (6):  60702-060702.  doi: 10.1088/1674-1056/25/6/060702 摘要 ( 696 )   HTML ( 0 )   PDF(1614KB) ( 289 )   Spectroscopic measurements and terahertz imaging of the cornea are carried out by using a rapid scanning terahertz time domain spectroscopy (THz-TDS) system. A voice coil motor stage based optical delay line (VCM-ODL) is developed to provide a rather simple and robust structure with both the high scanning speed and the large delay length. The developed system is used for THz spectroscopic measurements and imaging of the corneal tissue with different amounts of water content, and the measurement results show the consistence with the reported results, in which the measurement time using VCM-ODL is a factor of 360 shorter than the traditional motorized optical delay line (MDL). With reducing the water content a monotonic decrease of the complex permittivity of the cornea is observed. The two-term Debye relaxation model is employed to explain our experimental results, revealing that the fast relaxation time of a dehydrated cornea is much larger than that of a hydrated cornea and its dielectric behavior can be affected by the presence of the biological macromolecules. These results demonstrate that our THz spectrometer may be a promising candidate for tissue hydration sensing and practical application of THz technology. 参考文献 | 相关文章 | 计量指标

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Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame 陈爽, 苏铁, 郑尧邦, 陈力, 刘亭序, 李仁兵, 杨富荣 2016 (6):  60703-060703.  doi: 10.1088/1674-1056/25/6/060703 摘要 ( 558 )   HTML ( 0 )   PDF(485KB) ( 257 )   The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF (laser-induced fluorescence) in flame. The detailed physical models of spectral absorption lineshape broadening, collisional transition and quenching at elevated pressure are built. The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation, which include collisional quenching, rotational energy transfer (RET), and vibrational energy transfer (VET). Based on these, some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure. These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor. 参考文献 | 相关文章 | 计量指标

ATOMIC AND MOLECULAR PHYSICS

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Correlation between valence electronic structure and magnetic properties in RCo5 (R= rare earth) intermetallic compound 薛智琴, 郭永权 2016 (6):  63101-063101.  doi: 10.1088/1674-1056/25/6/063101 摘要 ( 789 )   HTML ( 0 )   PDF(263KB) ( 364 )   The magnetisms of RCo5 (R=rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules (EET). The theoretical moments and Curie temperatures agree well with experimental ones. The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo5 intermetallic compounds. The moments of RCo5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth, and the s electrons also affect the magnetic moments by the hybridization of d and s electrons. It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons. In the heavy rare-earth-based RCo5 intermetallics, the contribution to magnetic moment originates from the 3d and 4f electrons. The covalence electrons and lattice electrons also affect the Curie temperature, which is proportional to the average moment along the various bonds. 参考文献 | 相关文章 | 计量指标

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Density function theoretical study on the complex involved in Th atom-activated C-C bond in C2H6 王青青, 李鹏, 高涛, 王红艳, 敖冰云 2016 (6):  63102-063102.  doi: 10.1088/1674-1056/25/6/063102 摘要 ( 672 )   HTML ( 0 )   PDF(795KB) ( 277 )   Density functional theory (DFT) calculations are performed to investigate the reactivity of Th atom toward ethane C-C bond activation. A comprehensive description of the reaction mechanisms leading to two different reaction products is presented. We report a complete exploration of the potential energy surfaces by taking into consideration different spin states. In addition, the intermediate and transition states along the reaction paths are characterized. Total, partial, and overlap population density of state diagrams and analyses are also presented. Furthermore, the natures of the chemical bonding of intermediate and transition states are studied by using topological method combined with electron localization function (ELF) and Mayer bond order. Infrared spectrum (IR) is obtained and further discussed based on the optimized geometries. 参考文献 | 相关文章 | 计量指标

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Structures, stabilities, and magnetic properties of the FenAu (n= 1-12) clusters 吕瑾, 张江燕, 梁瑞瑞, 武海顺 2016 (6):  63103-063103.  doi: 10.1088/1674-1056/25/6/063103 摘要 ( 688 )   HTML ( 0 )   PDF(2711KB) ( 421 )   The configurations, stabilities, electronic, and magnetic properties of FenAu (n= 1-12) clusters are investigated systematically by using the relativistic all-electron density functional theory with the generalized gradient approximation. The substitutional effects of Au in Fen+1 (n= 1, 2, 4, 5, 10-12) clusters are found in optimized structures which keep the similar frameworks with the most stable Fen+1 clusters. And the growth way for FenAu (n= 6-9) clusters is that the Au atom occupies a peripheral position of Fen cluster. The peaks appear respectively at n= 6 and 9 for FenAu clusters and at n= 5 and 10 for Fen+1 clusters based on the size dependence of second-order difference of energy, implying that these clusters possess relatively high stabilities. The analysis of atomic net charge Q indicates that the charge always transfers from Fe to Au atom which causes the Au atom to be nearly non-magnetic, and the doped Au atom has little effect on the average magnetic moment of Fe atoms in FenAu cluster. Finally, the total magnetic moment is reduced by 3 μB for each of FenAu clusters except n= 3, 11, and 12 compared with for corresponding pure Fen+1 clusters. 参考文献 | 相关文章 | 计量指标

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Photoionization microscopy of Rydberg hydrogen atom in a non-uniform electrical field 程绍昊, 王德华, 陈召杭, 陈强 2016 (6):  63201-063201.  doi: 10.1088/1674-1056/25/6/063201 摘要 ( 708 )   HTML ( 0 )   PDF(1696KB) ( 260 )   In this paper, we investigate the photoionization microscopy of the Rydberg hydrogen atom in a gradient electric field for the first time. The observed oscillatory patterns in the photoionization microscopy are explained within the framework of the semiclassical theory, which can be considered as a manifestation of interference between various electron trajectories arriving at a given point on the detector plane. In contrast with the photoionization microscopy in the uniform electric field, the trajectories of the ionized electron in the gradient electric field will become chaotic. An infinite set of different electron trajectories can arrive at a given point on the detector plane, which makes the interference pattern of the electron probability density distribution extremely complicated. Our calculation results suggest that the oscillatory pattern in the electron probability density distribution depends sensitively on the electric field gradient, the scaled energy and the position of the detector plane. Through our research, we predict that the interference pattern in the electron probability density distribution can be observed in an actual photoionization microscopy experiment once the external electric field strength and the position of the electron detector plane are reasonable. This study provides some references for the future experimental research on the photoionization microscopy of the Rydberg atom in the non-uniform external fields. 参考文献 | 相关文章 | 计量指标

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Experimental optimum design and luminescence properties of NaY(Gd)(MoO4)2: Er3+ phosphors 孙佳石, 徐赛, 李树伟, 石琳琳, 翟梓会, 陈宝玖 2016 (6):  63301-063301.  doi: 10.1088/1674-1056/25/6/063301 摘要 ( 894 )   HTML ( 0 )   PDF(933KB) ( 244 )   Three-factor orthogonal design (OD) of Er3+/Gd3+/T (calcination temperature) is used to optimize the luminescent intensity of NaY(Gd)(MoO4)2:Er3+ phosphor. Firstly, the uniform design (UD) is introduced to explore the doping concentration range of Er3+/Gd3+. Then OD and range analysis are performed based on the results of UD to obtain the primary and secondary sequence and the best combination of Er3+, Gd3+, and T within the experimental range. The optimum sample is prepared by the high temperature solid state method. Photoluminescence excitation and emission spectra of the optimum sample are detected. The intense green emissions (530 nm and 550 nm) are observed which originate from Er3+ 2H11/2→4I15/2 and 4S3/2→4I15/2, respectively. Thermal effect is investigated in the optimum NaY(Gd3+)(MoO4)2:Er3+ phosphors, and the green emission intensity decreases as temperature increases. 参考文献 | 相关文章 | 计量指标

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Intense source of cold cesium atoms based on a two-dimensional magneto-optical trap with independent axial cooling and pushing 黄家强, 颜学术, 吴晨菲, 张建伟, 王力军 2016 (6):  63701-063701.  doi: 10.1088/1674-1056/25/6/063701 摘要 ( 840 )   HTML ( 0 )   PDF(11366KB) ( 334 )   We report our studies on an intense source of cold cesium atoms based on a two-dimensional (2D) magneto-optical trap (MOT) with independent axial cooling and pushing. The new-designed source, proposed as 2D-HP MOT, uses hollow laser beams for axial cooling and a thin pushing laser beam to extract a cold atomic beam. With the independent pushing beam, the atomic flux can be substantially optimized. The total atomic flux maximum obtained in the 2D-HP MOT is 4.02×1010 atoms/s, increased by 60 percent compared to the traditional 2D+ MOT in our experiment. Moreover, with the pushing power 10 μW and detuning 0Γ, the 2D-HP MOT can generate a rather intense atomic beam with the concomitant light shift suppressed by a factor of 20. The axial velocity distribution of the cold cesium beams centers at 6.8 m/s with an FMHW of about 2.8 m/s. The dependences of the atomic flux on the pushing power and detuning are studied in detail. The experimental results are in good agreement with the theoretical model. 参考文献 | 相关文章 | 计量指标

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Electromagnetic backscattering from one-dimensional drifting fractal sea surface I: Wave-current coupled model 谢涛, 赵尚卓,,方贺, 于文金, 何宜军 2016 (6):  64101-064101.  doi: 10.1088/1674-1056/25/6/064101 摘要 ( 659 )   HTML ( 0 )   PDF(661KB) ( 258 )   To study the electromagnetic backscattering from a one-dimensional drifting fractal sea surface, a fractal sea surface wave-current model is derived, based on the mechanism of wave-current interactions. The numerical results show the effect of the ocean current on the wave. Wave amplitude decreases, wavelength and kurtosis of wave height increase, spectrum intensity decreases and shifts towards lower frequencies when the current occurs parallel to the direction of the ocean wave. By comparison, wave amplitude increases, wavelength and kurtosis of wave height decrease, spectrum intensity increases and shifts towards higher frequencies if the current is in the opposite direction to the direction of ocean wave. The wave-current interaction effect of the ocean current is much stronger than that of the nonlinear wave-wave interaction. The kurtosis of the nonlinear fractal ocean surface is larger than that of linear fractal ocean surface. The effect of the current on skewness of the probability distribution function is negligible. Therefore, the ocean wave spectrum is notably changed by the surface current and the change should be detectable in the electromagnetic backscattering signal. 参考文献 | 相关文章 | 计量指标

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Optical bistability and multistability via double dark resonance in graphene nanostructure Seyyed Hossein Asadpour, G Solookinejad, M Panahi, E Ahmadi Sangachin 2016 (6):  64201-064201.  doi: 10.1088/1674-1056/25/6/064201 摘要 ( 675 )   HTML ( 0 )   PDF(10713KB) ( 344 )   Electrons in graphene nanoribbons can lead to exceptionally strong optical responses in the infrared and terahertz regions owing to their unusual dispersion relation. Therefore, on the basis of quantum optics and solid-material scientific principles, we show that optical bistability and multistability can be generated in graphene nanostructure under strong magnetic field. We also show that by adjusting the intensity and detuning of infrared laser field, the threshold intensity and hysteresis loop can be manipulated efficiently. The effects of the electronic cooperation parameter which are directly proportional to the electronic number density and the length of the graphene sample are discussed. Our proposed model may be useful for the nextgeneration all-optical systems and information processing based on nano scale devices. 参考文献 | 相关文章 | 计量指标

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Optical control of light propagation in photonic crystal based on electromagnetically induced transparency 王丹, 武晋泽, 张俊香 2016 (6):  64202-064202.  doi: 10.1088/1674-1056/25/6/064202 摘要 ( 829 )   HTML ( 0 )   PDF(1138KB) ( 362 )   A kind of photonic crystal structure with modulation of the refractive index is investigated both experimentally and theoretically for exploiting electromagnetically induced transparency (EIT). The combination of EIT with periodically modulated refractive index medium gives rise to high efficiency reflection as well as forbidden transmission in a three-level atomic system coupled by standing wave. We show an accurate theoretical simulation via transfer-matrix theory, automatically accounting for multilayer reflections, thus fully demonstrate the existence of photonic crystal structure in atomic vapor. 参考文献 | 相关文章 | 计量指标

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Single-photon scattering by two separated atoms in a supercavity 朱伟, 肖骁, 周端陆, 张芃 2016 (6):  64203-064203.  doi: 10.1088/1674-1056/25/6/064203 摘要 ( 744 )   HTML ( 0 )   PDF(3542KB) ( 304 )   We study the single-photon scattering along a one-dimensional cavity array with two distant two-level atoms in a supercavity, which aims to simulate a recent x-ray experiment [Nature 482, 199 (2012)]. Without introducing dissipation, we find that when one atom is exactly located at a node of a mode of the supercavity and the other is at the antinode of that mode, no splitting of the reflectivity peak can appear. Nevertheless, the atom at the node significantly changes the positions of the reflectivity valleys. On the other hand, when the atom is shifted a little from the exact node, then the splitting can appear. We also explain these results with an analysis based on the general formal scattering theory. Our result implies the importance of non-resonant modes of the supercavity in our problem. 参考文献 | 相关文章 | 计量指标

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Control of dispersion in fiber coupled resonator-induced transparency structure 田赫, 掌蕴东, 戚大伟, 苏润洲, 白岩, 徐强 2016 (6):  64204-064204.  doi: 10.1088/1674-1056/25/6/064204 摘要 ( 601 )   HTML ( 0 )   PDF(486KB) ( 227 )   Induced transparency phenomena and strong dispersion can be produced in a coupled resonator induced transparency (CRIT) structure. In this paper, we investigate the influences of structure parameters, such as amplitude reflection coefficient and loss, on transmission spectrum and dispersion of CRIT structure, and further study the control of dispersion in the structure. The results show that in the CRIT structure, adjusting the loss of resonators is an effective method of controlling dispersion and producing simultaneous normal and abnormal dispersion. When we choose approximate amplitude reflection coefficients of the two couplers, the decrease of transmittance due to loss could be effectively made up. In the experiment, we achieve the control of dispersion and simultaneous strong normal and abnormal dispersion in the CRIT structure comprised of fiber. The results indicate the CRIT structure has potential applications in optical signal processing and optical communication. 参考文献 | 相关文章 | 计量指标

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Analysis of algebraic reconstruction technique for accurate imaging of gas temperature and concentration based on tunable diode laser absorption spectroscopy 夏晖晖, 阚瑞峰, 刘建国, 许振宇, 何亚柏 2016 (6):  64205-064205.  doi: 10.1088/1674-1056/25/6/064205 摘要 ( 717 )   HTML ( 0 )   PDF(490KB) ( 557 )   An improved algebraic reconstruction technique (ART) combined with tunable diode laser absorption spectroscopy(TDLAS) is presented in this paper for determining two-dimensional (2D) distribution of H2O concentration and temperature in a simulated combustion flame. This work aims to simulate the reconstruction of spectroscopic measurements by a multi-view parallel-beam scanning geometry and analyze the effects of projection rays on reconstruction accuracy. It finally proves that reconstruction quality dramatically increases with the number of projection rays increasing until more than 180 for 20×20 grid, and after that point, the number of projection rays has little influence on reconstruction accuracy. It is clear that the temperature reconstruction results are more accurate than the water vapor concentration obtained by the traditional concentration calculation method. In the present study an innovative way to reduce the error of concentration reconstruction and improve the reconstruction quality greatly is also proposed, and the capability of this new method is evaluated by using appropriate assessment parameters. By using this new approach, not only the concentration reconstruction accuracy is greatly improved, but also a suitable parallel-beam arrangement is put forward for high reconstruction accuracy and simplicity of experimental validation. Finally, a bimodal structure of the combustion region is assumed to demonstrate the robustness and universality of the proposed method. Numerical investigation indicates that the proposed TDLAS tomographic algorithm is capable of detecting accurate temperature and concentration profiles. This feasible formula for reconstruction research is expected to resolve several key issues in practical combustion devices. 参考文献 | 相关文章 | 计量指标

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Spectral broadening induced by intense ultra-short pulse in 4H-SiC crystals 徐春华, 闫腾飞, 王刚, 王文军, 梁敬魁, 陈小龙 2016 (6):  64206-064206.  doi: 10.1088/1674-1056/25/6/064206 摘要 ( 580 )   HTML ( 0 )   PDF(335KB) ( 318 )   We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H-SiC single crystals. It is demonstrated that the full width at half maximum of output spectrum increases linearly with the light propagation length and the peak power density, reaching a maximum 870 cm-1 on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm2. Such spectral broadening can be well explained by the self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index. The nonlinear refractive index n2 is estimated to be 1.88×10-15 cm2/W. The intensity-dependent refractive index is probably due to both the nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process. Super continuum spectra could arise as crystals are long enough to induce the self-focusing effect. The results show that SiC crystals may find applications in spectral broadening of high power lasers. 参考文献 | 相关文章 | 计量指标

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Ultra-broadband modulation instability gain characteristics in As2S3 and As2Se3 chalcogenide glass photonic crystal fiber 王河林, 吴彬, 王肖隆 2016 (6):  64207-064207.  doi: 10.1088/1674-1056/25/6/064207 摘要 ( 789 )   HTML ( 0 )   PDF(1525KB) ( 394 )   Based on the designed As2Se3 and As2S3 chalcogenide glass photonic crystal fiber (PCF) and the scalar nonlinear Schrödinger equation, the effects of pump power and wavelength on modulation instability (MI) gain are comprehensively studied in the abnormal dispersion regime of chalcogenide glass PCF. Owing to high Raman effect and high nonlinearity, ultra-broadband MI gain is obtained in chalcogenide glass PCF. By choosing the appropriate pump parameter, the MI gain bandwidth reaches 2738 nm for the As2Se3 glass PCF in the abnormal-dispersion region, while it is 1961 nm for the As2S3 glass PCF. 参考文献 | 相关文章 | 计量指标

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Effect of turbulent atmosphere on the on-axis average intensity of Pearcey-Gaussian beam F Boufalah, L Dalil-Essakali, H Nebdi, A Belafhal 2016 (6):  64208-064208.  doi: 10.1088/1674-1056/25/6/064208 摘要 ( 703 )   HTML ( 1 )   PDF(9477KB) ( 237 )   The propagation characteristics of the Pearcey-Gaussian (PG) beam in turbulent atmosphere are investigated in this paper. The Pearcey beam is a new kind of paraxial beam, based on the Pearcey function of catastrophe theory, which describes diffraction about a cusp caustic. By using the extended Huygens-Fresnel integral formula in the paraxial approximation and the Rytov theory, an analytical expression of axial intensity for the considered beam family is derived. Some numerical results for PG beam propagating in atmospheric turbulence are given by studying the influences of some factors, including incident beam parameters and turbulence strengths. 参考文献 | 相关文章 | 计量指标

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Use of a plane jet for flow-induced noise reduction of tandem rods 赵鲲, 杨希祥,,张为华 2016 (6):  64301-064301.  doi: 10.1088/1674-1056/25/6/064301 摘要 ( 705 )   HTML ( 0 )   PDF(2486KB) ( 452 )   Unsteady wake from upstream components of landing gear impinging on downstream components could be a strong noise source. The use of a plane jet is proposed to reduce this flow-induced noise. Tandem rods with different gap widths were utilized as the test body. Both acoustic and aerodynamic tests were conducted in order to validate this technique. Acoustic test results proved that overall noise emission from tandem rods could be lowered and tonal noise could be removed with use of the plane jet. However, when the plane jet was turned on, in some frequency range it could be the subsequent main contributor instead of tandem rods to total noise emission whilst in some frequency range rods could still be the main contributor. Moreover, aerodynamic tests fundamentally studied explanations for the noise reduction. Specifically, not only impinging speed to rods but speed and turbulence level to the top edge of the rear rod could be diminished by the upstream plane jet. Consequently, the vortex shedding induced by the rear rod was reduced, which was confirmed by the speed, Reynolds stress as well as the velocity fluctuation spectral measured in its wake. This study confirmed the potential use of a plane jet towards landing gear noise reduction. 参考文献 | 相关文章 | 计量指标

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Biphasic behavior of energy in a stepped chain 王平建, 何爱香, 林忠海, 魏广芬, 刘燕丽 2016 (6):  64501-064501.  doi: 10.1088/1674-1056/25/6/064501 摘要 ( 568 )   HTML ( 0 )   PDF(257KB) ( 193 )   The impact energy decay in a step-up chain containing two sections is numerically studied. There is a marked biphasic behavior of energy decay in the first section. Two sections close to the interface are in compression state. The degree of compression of the first section first decreases and becomes weakest at “crossing” time of biphasic behavior of energy, then increases. The further calculations provide the dependence of the character time on mass ratio (m1/m2), where m1 and m2 are the particle mass in the first and second section respectively. The bigger the α (α =[(Ωm1-m2)/(Ωm1+m2)]2 with Ω =1.345), the bigger the energy ratio is. The multipulse structure restricts the transport of energy. 参考文献 | 相关文章 | 计量指标

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Gradient-augmented hybrid interface capturing method for incompressible two-phase flow 付峥, 吴士玉, 刘凯欣 2016 (6):  64701-064701.  doi: 10.1088/1674-1056/25/6/064701 摘要 ( 709 )   HTML ( 0 )   PDF(1550KB) ( 256 )   Motivated by inconveniences of present hybrid methods, a gradient-augmented hybrid interface capturing method (GAHM) is presented for incompressible two-phase flow. A front tracking method (FTM) is used as the skeleton of the GAHM for low mass loss and resources. Smooth eulerian level set values are calculated from the FTM interface, and are used for a local interface reconstruction. The reconstruction avoids marker particle redistribution and enables an automatic treatment of interfacial topology change. The cubic Hermit interpolation is employed in all steps of the GAHM to capture subgrid structures within a single spacial cell. The performance of the GAHM is carefully evaluated in a benchmark test. Results show significant improvements of mass loss, clear subgrid structures, highly accurate derivatives (normals and curvatures) and low cost. The GAHM is further coupled with an incompressible multiphase flow solver, Super CE/SE, for more complex and practical applications. The updated solver is evaluated through comparison with an early droplet research. 参考文献 | 相关文章 | 计量指标

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Laser-induced breakdown spectroscopy applied to the characterization of rock by support vector machine combined with principal component analysis 杨洪星, 付洪波, 王华东, 贾军伟,,董凤忠 2016 (6):  65201-065201.  doi: 10.1088/1674-1056/25/6/065201 摘要 ( 751 )   HTML ( 0 )   PDF(502KB) ( 297 )   Laser-induced breakdown spectroscopy (LIBS) is a versatile tool for both qualitative and quantitative analysis. In this paper, LIBS combined with principal component analysis (PCA) and support vector machine (SVM) is applied to rock analysis. Fourteen emission lines including Fe, Mg, Ca, Al, Si, and Ti are selected as analysis lines. A good accuracy (91.38% for the real rock) is achieved by using SVM to analyze the spectroscopic peak area data which are processed by PCA. It can not only reduce the noise and dimensionality which contributes to improving the efficiency of the program, but also solve the problem of linear inseparability by combining PCA and SVM. By this method, the ability of LIBS to classify rock is validated. 参考文献 | 相关文章 | 计量指标

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Investigation of impurity transport using laser blow-off technique in the HL-2A Ohmic and ECRH plasmas 张凯, 崔正英, 孙平, 董春凤, 邓玮, 董云波, 宋绍栋, 蒋敏, 李永高, 卢平, 杨青巍 2016 (6):  65202-065202.  doi: 10.1088/1674-1056/25/6/065202 摘要 ( 797 )   HTML ( 1 )   PDF(2566KB) ( 311 )   Impurity transports in two neighboring discharges with and without electron cyclotron resonance heating (ECRH) are studied in the HL-2A tokamak by laser blow-off (LBO) technique. The progression of aluminium ions as the trace impurity is monitored by soft x-ray (SXR) and bolometer detector arrays with good temporal and spatial resolutions. Obvious difference in the time trace of the signal between the Ohmic and ECRH L-mode discharges is observed. Based on the numerical simulation with one-dimensional (1D) impurity transport code STRAHL, the radial profiles of impurity diffusion coefficient D and convective velocity V are obtained for each shot. The result shows that the diffusion coefficient D significantly increases throughout the plasma minor radius for the ECRH case with respect to the Ohmic case, and that the convection velocity V changes from negative (inward) for the Ohmic case to partially positive (outward) for the ECRH case. The result on HL-2A confirms the pump out effect of ECRH on impurity profile as reported on various other devices. 参考文献 | 相关文章 | 计量指标

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Simulation of nanoparticle coagulation in radio-frequency C2H2/Ar microdischarges 刘相梅, 李奇楠, 李瑞 2016 (6):  65203-065203.  doi: 10.1088/1674-1056/25/6/065203 摘要 ( 557 )   HTML ( 0 )   PDF(1864KB) ( 241 )   The nanoparticle coagulation is investigated by using a couple of fluid models and aerosol dynamics model in argon with a 5% molecular acetylene admixture rf microdischarges, with the total input gas flow rate of 400 sccm. It co-exists with a homogeneous, secondary electron-dominated low temperature γ-mode glow discharges. The heat transfer equation and flow equation for neutral gas are taken into account. We mainly focused on investigations of the nanoparticle properties in atmospheric pressure microdischarges, and discussed the influences of pressure, electrode spacing, and applied voltage on the plasma density and nanoparticle density profiles. The results show that the characteristics of microdischarges are quite different from those of low pressure radio-frequency discharges. First, the nanoparticle density in the bulk plasma in microdischarges is much larger than that of low pressure discharges. Second, the nanoparticle density of 10 nm experiences an exponential increase as soon as the applied voltage increases, especially in the presheath. Finally, as the electrode spacing increases, the nanoparticle density decreased instead of increasing. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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In-situ study of precipitates in Al-Zn-Mg-Cu alloys using anomalous small-angle x-ray scattering 杨春明, 边风刚, 熊柏青, 刘冬梅, 李怡雯, 滑文强, 王劼 2016 (6):  66101-066101.  doi: 10.1088/1674-1056/25/6/066101 摘要 ( 719 )   HTML ( 0 )   PDF(853KB) ( 301 )   In the present work, the precipitate compositions and precipitate amounts of these elements (including the size distribution, volume fraction, and inter-precipitate distance) on the Cu-containing 7000 series aluminum alloys (7150 and 7085 Al alloys), are investigated by anomalous small-angle x-ray scattering (ASAXS) at various energies. The scattering intensity of 7150 alloy with T6 aging treatment decreases as the incident x-ray energy approaches the Zn absorption edge from the lower energy side, while scattering intensity does not show a noticeable energy dependence near the Cu absorption edge. Similar results are observed in the 7085 alloy in an aging process (120℃) by employing in-situ ASAXS measurements, indicating that the precipitate compositions should include Zn element and should not be strongly related to Cu element at the early stage after 10 min. In the aging process, the precipitate particles with an initial average size of ～8Å increase with aging time at an energy of 9.60 keV, while the increase with a slower rate is observed at an energy of 9.65 keV as near the Zn absorption edge. 参考文献 | 相关文章 | 计量指标

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Thermodynamic and transport properties of spiro-(1,1')-bipyrrolidinium tetrafluoroborate and acetonitrile mixtures: A molecular dynamics study 张庆印, 谢鹏, 王欣, 于学文, 时志强, 赵世怀 2016 (6):  66102-066102.  doi: 10.1088/1674-1056/25/6/066102 摘要 ( 931 )   HTML ( 2 )   PDF(2713KB) ( 537 )   Organic salts such as spiro-(1,1')-bipyrrolidinium tetrafluoroborate ([SBP][BF4]) dissolved in liquid acetonitrile (ACN) are a new kind of organic salt solution, which is expected to be used as an electrolyte in electrical double layer capacitors (EDLCs). To explore the physicochemical properties of the solution, an all-atom force field is established on the basis of AMBER parameter values and quantum mechanical calculations. Molecular dynamics (MD) simulations are carried out to explore the liquid structure and physicochemical properties of [SBP][BF4] electrolyte at room temperature. The computed thermodynamic and transport properties match the available experimental results very well. The microscopic structures of [SBP][BF4] salt solution are also discussed in detail. The method used in this work provides an efficient way of predicting the properties of organic salt solvent as an electrolyte in EDLCs. 参考文献 | 相关文章 | 计量指标

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Phenomenological description of semi-soft nematic elastomers 刁文文, 孟庆田, 叶方富 2016 (6):  66103-066103.  doi: 10.1088/1674-1056/25/6/066103 摘要 ( 627 )   HTML ( 0 )   PDF(821KB) ( 224 )   Nematic elastomers are new materials that have many remarkable properties. In this article, we study how nonlinear elasticity of semi-soft nematic elastomers can be described phenomenologically. We start with a theory based on strain tensor only, and then continue to develop a phenomenological description with the liquid crystal order tensor included explicitly. Such a description has the virtue of being able to treat the strain tensor and the liquid crystal order tensor equally and thus making the complicated symmetries of nematic elastomers easier to understand. 参考文献 | 相关文章 | 计量指标

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Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries 葛勇, 孙宏祥, 管义钧, 曾赣鹤 2016 (6):  66104-066104.  doi: 10.1088/1674-1056/25/6/066104 摘要 ( 793 )   HTML ( 0 )   PDF(2407KB) ( 341 )   The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures. The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries. More interestingly, at high temperatures, the ultimate strengths of the graphene with the zigzag-orientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures, which is determined by inner initial stress in grain boundaries. The results indicate that the finite temperature, especially the high one, has a significant effect on the ultimate strength of graphene with grain boundaries, which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications. 参考文献 | 相关文章 | 计量指标

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Understanding of surface pit formation mechanism of GaN grown in MOCVD based on local thermodynamic equilibrium assumption 高志远, 薛晓玮, 李江江, 王勋, 邢艳辉, 崔碧峰, 邹德恕 2016 (6):  66105-066105.  doi: 10.1088/1674-1056/25/6/066105 摘要 ( 797 )   HTML ( 1 )   PDF(729KB) ( 281 )   Frank's theory describes that a screw dislocation will produce a pit on the surface, and has been evidenced in many material systems including GaN. However, the size of the pit calculated from the theory deviates significantly from experimental result. Through a careful observation of the variations of surface pits and local surface morphology with growing temperature and V/III ratio for c-plane GaN, we believe that Frank's model is valid only in a small local surface area where thermodynamic equilibrium state can be assumed to stay the same. If the kinetic process is too vigorous or too slow to reach a balance, the local equilibrium range will be too small for the center and edge of the screw dislocation spiral to be kept in the same equilibrium state. When the curvature at the center of the dislocation core reaches the critical value 1/r0, at the edge of the spiral, the accelerating rate of the curvature may not fall to zero, so the pit cannot reach a stationary shape and will keep enlarging under the control of minimization of surface energy to result in a large-sized surface pit. 参考文献 | 相关文章 | 计量指标

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Comparative study on beryllium and magnesium as a co-doping element for ZnO:N 苏宇泉, 陈明明, 苏龙兴, 祝渊, 汤子康 2016 (6):  66106-066106.  doi: 10.1088/1674-1056/25/6/066106 摘要 ( 669 )   HTML ( 0 )   PDF(279KB) ( 335 )   Stable nitrogen doping is an important issue in p-type ZnO research for device applications. In this paper, beryllium and magnesium are systematically compared as a dopant in ZnO to reveal their nitrogen-stabilizing ability. Secondary ion mass spectrum shows that Be and Mg can both enhance the stability of nitrogen in ZnO while Be has a better performance. Zn 2p and O 1s electron binding energies change in both MgZnO and BeZnO thin films. Donor-acceptor luminescence is observed in the BeZnO samples. We conclude that Be is a better co-doping element than Mg for p-type ZnO:N. 参考文献 | 相关文章 | 计量指标

RAPID COMMUNICATION

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Bismuth-content-dependent polarized Raman spectrum of InPBi alloy 魏冠男, 谭青海, 戴兴, 冯琦, 骆文刚, 盛宇, 王凯, 潘文武, 张立瑶, 王庶民, 王开友 2016 (6):  66301-066301.  doi: 10.1088/1674-1056/25/6/066301 摘要 ( 728 )   HTML ( 0 )   PDF(2257KB) ( 349 )   We systematically investigate the optical properties of the InP1-xBix ternary alloys with 0≤ x≤ 2.46%, by using high resolution polarized Raman scattering measurement. Both InP-like and InBi-like optical vibration modes (LO) are identified in all the samples, suggesting that most of the Bi-atoms are incorporated into the lattice sites to substitute P-atoms. And the intensity of the InBi-like Raman mode is positively proportional to the Bi-content. Linear red-shift of the InP-like longitudinal optical vibration mode is observed to be 1.1 cm-1/Bi%, while that of the InP-like optical vibration overtone (2LO) is nearly doubled. In addition, through comparing the Z(XX)Z and Z(XY)Z Raman spectra, longitudinal-optical-plasmon-coupled (LOPC) modes are identified in all the samples, and their intensities are found to be proportional to the electron concentrations. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Numerical modeling of condensate droplet on superhydrophobic nanoarrays using the lattice Boltzmann method 张庆宇, 孙东科, 张友法, 朱鸣芳 2016 (6):  66401-066401.  doi: 10.1088/1674-1056/25/6/066401 摘要 ( 671 )   HTML ( 2 )   PDF(845KB) ( 350 )   In the present study, the process of droplet condensation on superhydrophobic nanoarrays is simulated using a multi-component multi-phase lattice Boltzmann model. The results indicate that three typical nucleation modes of condensate droplets are produced by changing the geometrical parameters of nanoarrays. Droplets nucleated at the top (top-nucleation mode), or in the upside interpillar space of nanoarrays (side-nucleation mode), generate the non-wetting Cassie state, whereas the ones nucleated at the bottom corners between the nanoarrays (bottom-nucleation mode) present the wetting Wenzel state. Time evolutions of droplet pressures at the upside and downside of the liquid phase are analyzed to understand the wetting behaviors of the droplets condensed from different nucleation modes. The phenomena of droplet condensation on nanoarrays patterned with different hydrophilic and hydrophobic regions are simulated, indicating that the nucleation mode of condensate droplets can also be manipulated by modifying the local intrinsic wettability of nanoarray surface. The simulation results are compared well with the experimental observations reported in the literature. 参考文献 | 相关文章 | 计量指标

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Properties of n-Ge epilayer on Si substrate with in-situ doping technology 黄诗浩, 李成, 陈城钊, 王尘, 谢文明, 林抒毅, 邵明, 聂明星, 陈彩云 2016 (6):  66601-066601.  doi: 10.1088/1674-1056/25/6/066601 摘要 ( 709 )   HTML ( 0 )   PDF(1693KB) ( 283 )   The properties of n-Ge epilayer deposited on Si substrate with in-situ doping technology in a cold-wall ultrahigh vacuum chemical vapor deposition (UHVCVD) system are investigated. The growth temperature of ～500℃ is optimal for the n-Ge growth in our equipment with a phosphorus concentration of ～1018 cm-3. In the n-Ge epilayer, the depth profile of phosphorus concentration is box-shaped and the tensile strain of 0.12% confirmed by x-ray diffraction measurement is introduced which results in the red shift of the photoluminescence. The enhancements of photoluminescence intensity with the increase of the doping concentration are observed, which is consistent with the modeling of the spontaneous emission spectrum for direct transition of Ge. The results are of significance for guiding the growth of n-Ge epilayer with in-situ doping technology. 参考文献 | 相关文章 | 计量指标

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Mechanism of contact angle saturation and an energy-based model for electrowetting 赵瑞, 梁忠诚 2016 (6):  66801-066801.  doi: 10.1088/1674-1056/25/6/066801 摘要 ( 793 )   HTML ( 0 )   PDF(635KB) ( 261 )   Electrowetting, as a well-known approach to increasing droplet wettability on a solid surface by electrical bias, has broad applications. However, it is limited by contact angle saturation at large voltage. Although several debated hypotheses have been proposed to describe it, the physical origin of contact angle saturation still remains obscure. In this work, the physical factors responsible for the onset of contact angle saturation are explored, and the correlated theoretical models are established to characterize electrowetting behavior. Combination of the proper 3-phase system employed succeeds in dropping the saturating contact angle below 25°, and validates that the contact angle saturation is not a result of device-related imperfection. 参考文献 | 相关文章 | 计量指标

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Effects of grinding-induced grain boundary and interfaces on electrical transportation and structure phase transition in ZnSe under high pressure 杨洁, 汪沛, 张国召, 周晓雪, 李静, 刘才龙 2016 (6):  66802-066802.  doi: 10.1088/1674-1056/25/6/066802 摘要 ( 668 )   HTML ( 0 )   PDF(304KB) ( 305 )   Interface and scale effects are the two most important factors which strongly affect the structure and the properties of nano-/micro-crystals under pressure. We conduct an experiment under high pressure in situ alternating current impedance to elucidate the effects of interface on the structure and electrical transport behavior of two ZnSe samples with different sizes obtained by physical grinding. The results show that (i) two different-sized ZnSe samples undergo the same phase transitions from zinc blend to cinnabar-type phase and then to rock salt phase; (ii) the structural transition pressure of the 859-nm ZnSe sample is higher than that of the sample of 478 nm, which indicates the strong scale effect. The pressure induced boundary resistance change is obtained by fitting the impedance spectrum, which shows that the boundary conduction dominates the electrical transport behavior of ZnSe in the whole experimental pressure range. By comparing the impedance spectra of two different-sized ZnSe samples at high pressure, we find that the resistance of the 478-nm ZnSe sample is lower than that of the 859-nm sample, which illustrates that the sample with smaller particle size has more defects which are due to physical grinding. 参考文献 | 相关文章 | 计量指标

TOPICAL REVIEW—Low-dimensional complex oxide structures

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Aberration-corrected scanning transmission electron microscopy for complex transition metal oxides 张庆华, 肖东东, 谷林 2016 (6):  66803-066803.  doi: 10.1088/1674-1056/25/6/066803 摘要 ( 851 )   HTML ( 0 )   PDF(3859KB) ( 770 )   Lattice, charge, orbital, and spin are the four fundamental degrees of freedom in condensed matter, of which the interactive coupling derives tremendous novel physical phenomena, such as high-temperature superconductivity (high-Tc SC) and colossal magnetoresistance (CMR) in strongly correlated electronic system. Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it, and also indispensable for designing new materials and devices. Scanning transmission electron microscopy (STEM) integrating multiple techniques of structure imaging and spectrum analysis, is a comprehensive platform for providing structural, chemical and electronic information of materials with a high spatial resolution. Benefiting from the development of aberration correctors, STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization; many improvements have been achieved in recent years, thereby giving an in-depth insight into material research. Here, we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides; atomic-scale mapping of ferroelectric polarization, octahedral distortions and rotations, valence state, coordination and spin ordering are presented. We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Interactions between vacancies and prismatic Σ3 grain boundary in α-Al2O3: First principles study 王飞, 赖文生, 李如松, 何彬, 黎素芬 2016 (6):  66804-066804.  doi: 10.1088/1674-1056/25/6/066804 摘要 ( 811 )   HTML ( 0 )   PDF(520KB) ( 206 )   Interactions between vacancies and Σ3 prismatic screw-rotation grain boundary in α-Al2O3 are investigated by the first principles projector-augmented wave method. It turns out that the vacancy formation energy decreases with reducing the distance between vacancy and grain boundary (GB) plane and reaches the minimum on the GB plane (at the atomic layer next to the GB) for an O (Al) vacancy. The O vacancy located on the GB plane can attract other vacancies nearby to form an O-O di-vacancy while the Al vacancy cannot. Moreover, the O-O di-vacancy can further attract other O vacancies to form a zigzag O vacancy chain on the GB plane, which may have an influence on the diffusion behavior of small atoms such as H and He along the GB plane of α-Al2O3. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Band-gap engineering of La1-xNdxAlO3 (x = 0, 0.25, 0.50, 0.75, 1) perovskite using density functional theory: A modified Becke Johnson potential study Sandeep, D P Rai, A Shankar, M P Ghimire, Anup Pradhan Sakhya, T P Sinha, R Khenata, S Bin Omran, R K Thapa 2016 (6):  67101-067101.  doi: 10.1088/1674-1056/25/6/067101 摘要 ( 833 )   HTML ( 2 )   PDF(23943KB) ( 459 )   The structural, electronic, and magnetic properties of the Nd-doped Rare earth aluminate, La1-xNdxAlO3 (x = 0% to 100%) alloys are studied using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory. The effects of the Nd substitution in LaAlO3 are studied using the supercell calculations. The computed electronic structure with the modified Becke-Johnson (mBJ) potential based approximation indicates that the La1-xNdxAlO3 alloys may possess half-metallic (HM) behaviors when doped with Nd of a finite density of states at the Fermi level (EF). The direct and indirect band gaps are studied each as a function of x which is the concentration of Nd-doped LaAlO3. The calculated magnetic moments in the La1-xNdxAlO3 alloys are found to arise mainly from the Nd-4f state. A probable half-metallic nature is suggested for each of these systems with supportive integral magnetic moments and highly spin-polarized electronic structures in these doped systems at EF. The observed decrease of the band gap with the increase in the concentration of Nd doping in LaAlO3 is a suitable technique for harnessing useful spintronic and magnetic devices. 参考文献 | 相关文章 | 计量指标

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Numerical simulation study of organic nonvolatile memory with polysilicon floating gate 闫兆文, 王娇, 乔坚栗, 谌文杰, 杨盼, 肖彤, 杨建红 2016 (6):  67102-067102.  doi: 10.1088/1674-1056/25/6/067102 摘要 ( 823 )   HTML ( 0 )   PDF(701KB) ( 331 )   A polysilicon-based organic nonvolatile floating-gate memory device with a bottom-gate top-contact configuration is investigated，in which polysilicon is sandwiched between oxide layers as a floating gate. Simulations for the electrical characteristics of the polysilicon floating gate-based memory device are performed. The shifted transfer characteristics and corresponding charge trapping mechanisms during programing and erasing (P/E) operations at various P/E voltages are discussed. The simulated results show that present memory exhibits a large memory window of 57.5 V, and a high read current on/off ratio of ≈ 103. Compared with the reported experimental results, these simulated results indicate that the polysilicon floating gate based memory device demonstrates remarkable memory effects, which shows great promise in device designing and practical application. 参考文献 | 相关文章 | 计量指标

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Comparisons between adsorption and diffusion of alkali, alkaline earth metal atoms on silicene and those on silicane: Insight from first-principles calculations 徐波, 卢欢胜, 刘波, 刘刚, 吴木生, 欧阳楚英 2016 (6):  67103-067103.  doi: 10.1088/1674-1056/25/6/067103 摘要 ( 652 )   HTML ( 0 )   PDF(1333KB) ( 386 )   The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory. Silicane is staler against the metal adatoms than silicene. Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene. Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed. However, the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate. Combining the adsorption energy with the diffusion energy barriers, it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage. In order to avoid forming a metal cluster, we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane. Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials. 参考文献 | 相关文章 | 计量指标

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First principles study of the diffusional phenomena across the clean and Re-doped γ-Ni/γ'-Ni3Al interface of Ni-based single crystal superalloy 孙敏, 王崇愚 2016 (6):  67104-067104.  doi: 10.1088/1674-1056/25/6/067104 摘要 ( 838 )   HTML ( 0 )   PDF(19025KB) ( 300 )   Density functional theory calculations in conjunction with the climbing images nudged elastic band method are conducted to study the diffusion phenomena of the Ni-based single crystal superalloys. We focus our attention on the diffusion processes of the Ni and Al atoms in the γ and γ ' phases along the direction perpendicular to the interface. The diffusion mechanisms and the expressions of the diffusion coefficients are presented. The vacancy formation energies, the migration energies, and the activation energies for the diffusing Ni and Al atoms are estimated, and these quantities display the expected and clear transition zones in the vicinity of the interface of about 3-7 (002) layers. The local density-of-states profiles of atoms in each (002) layer in the γ and γ ' phases and the partial density-of-states curves of Re and some of its nearest-neighbor atoms are also presented to explore the electronic effect of the diffusion behavior. 参考文献 | 相关文章 | 计量指标

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Compton profiles of NiO and TiO2 obtained from first principles GWA spectral function S M Khidzir, M F M Halid, W A T Wan Abdullah 2016 (6):  67105-067105.  doi: 10.1088/1674-1056/25/6/067105 摘要 ( 537 )   HTML ( 0 )   PDF(8857KB) ( 327 )   In this work, we first use momentum density studies to understand strongly correlated electron behavior, which is typically seen in transition metal oxides. We observe that correlated electron behavior as seen in bulk NiO is due to the Fermi break located in the middle of overlapping spectral functions obtained from a GW (G is Green's function and W is the screened Coulomb interaction) approximation (GWA) calculation while in the case of TiO2 we can see that the origin of the constant momentum distribution in lower momenta is due to a pile up of spectra before the Fermi energy. These observations are then used to compare our calculated Compton profiles with previous experimental studies of Fukamachi and Limandri. Our calculations for NiO are observed to follow the same trend as the experimental profile but it is seen to have a wide difference in the case of TiO2 before the Fermi break. The ground state momentum densities differ significantly from the quasiparticle momentum density, thus stressing the importance of the quasiparticle wave function as the input for the study of charge density and the electron localization function. Finally we perform a calculation of the quasiparticle renormalization function, giving a quantitative description of the discontinuity of the GWA momentum density. 参考文献 | 相关文章 | 计量指标

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Hybrid density functional study on lattice vibration, thermodynamic properties, and chemical bonding of plutonium monocarbide 杨荣, 唐斌, 高涛, 敖冰云 2016 (6):  67106-067106.  doi: 10.1088/1674-1056/25/6/067106 摘要 ( 522 )   HTML ( 0 )   PDF(6020KB) ( 251 )   Hybrid density functional theory is employed to systematically investigate the structural, magnetic, vibrational, thermodynamic properties of plutonium monocarbide (PuC and PuC0.75). For comparison, the results obtained by DFT, DFT+U are also given. For PuC and PuC0.75, Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic (AFM) structure. The calculated phonon spectra suggest that PuC and PuC0.75 are dynamically stable. Values of the Helmholtz free energy ΔF, internal energy ΔE, entropy S, and constant-volume specific heat Cv of PuC and PuC0.75 are given. The results are in good agreement with available experimental or theoretical data. As for the chemical bonding nature, the difference charge densities, the partial densities of states and the Bader charge analysis suggest that the Pu-C bonds of PuC and PuC0.75 have a mixture of covalent character and ionic character. The effect of carbon vacancy on the chemical bonding is also discussed in detail. We expect that our study can provide some useful reference for further experimental research on the phonon density of states, thermodynamic properties of the plutonium monocarbide. 参考文献 | 相关文章 | 计量指标

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Alternating current characterization of nano-Pt(II) octaethylporphyrin (PtOEP) thin film as a new organic semiconductor M Dongol, M M El-Nahass, A El-Denglawey, A A Abuelwafa, T Soga 2016 (6):  67201-067201.  doi: 10.1088/1674-1056/25/6/067201 摘要 ( 815 )   HTML ( 0 )   PDF(3930KB) ( 420 )   Alternating current (AC) conductivity and dielectric properties of thermally evaporated Au/PtOEP/Au thin films are investigated each as a function of temperature (303 K-473 K) and frequency (50 Hz-5 MHz). The frequency dependence of AC conductivity follows the Jonscher universal dynamic law. The AC-activation energies are determined at different frequencies. It is found that the correlated barrier hopping (CBH) model is the dominant conduction mechanism. The variation of the frequency exponent s with temperature is analyzed in terms of the CBH model. Coulombic barrier height Wm, hopping distance Rω, and the density of localized states N(EF) are valued at different frequencies. Dielectric constant ε1(ω,T) and dielectric loss ε2(ω,T) are discussed in terms of the dielectric polarization process. The dielectric modulus shows the non-Debye relaxation in the material. The extracted relaxation time by using the imaginary part of modulus (M") is found to follow the Arrhenius law. 参考文献 | 相关文章 | 计量指标

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Alternating-current relaxation of a rotating metallic particle 聂国熹, 田文佳, 黄吉平, 顾国庆 2016 (6):  67202-067202.  doi: 10.1088/1674-1056/25/6/067202 摘要 ( 639 )   HTML ( 0 )   PDF(2048KB) ( 216 )   Based on a first-principles approach, we establish an alternating-current (AC) relaxation theory for a rotating metallic particle with complex dielectric constant εα = εα-σα/ω0. Here εα is the real part, σα the conductivity, ω0 the angular frequency of an AC electric field, and i=√-1. Our theory yields an accurate interparticle force, which is in good agreement with the existing experiment. The agreement helps to show that the relaxations of two kinds of charges, namely, surface polarized charges (described by εα) and free charges (corresponding to σα), contribute to the unusually large reduction in the attracting interparticle force. This theory can be adopted to determine the relaxation time of dynamic particles in various fields. 参考文献 | 相关文章 | 计量指标

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Control of Hall angle of Skyrmion driven by electric current 刘高斌, 李达,,王健, 刘伟, 张志东 2016 (6):  67203-067203.  doi: 10.1088/1674-1056/25/6/067203 摘要 ( 748 )   HTML ( 0 )   PDF(298KB) ( 355 )   Skyrmions are very promising for applications in spintronics and magnetic memory. It is desired to manipulate and operate a single skyrmion. Here we report on the thermal effect on the motion of current-driven magnetic Skyrmions in magnetic metal. The results show that the magnon current induced by the thermal gradient acts on Skyrmions via magnonic spin-transfer torque, an effect of the transverse and longitudinal Skyrmions drift velocities, thus leading to the effective manipulation of the Hall angle through the ratio of thermal gradient to electric current density, which can be used as a Skyrmion valve. 参考文献 | 相关文章 | 计量指标

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Finite size effects on the helical edge states on the Lieb lattice 陈锐, 周斌 2016 (6):  67204-067204.  doi: 10.1088/1674-1056/25/6/067204 摘要 ( 860 )   HTML ( 0 )   PDF(40691KB) ( 347 )   For a two-dimensional Lieb lattice, that is, a line-centered square lattice, the inclusion of the intrinsic spin--orbit (ISO) coupling opens a topologically nontrivial gap, and gives rise to the quantum spin Hall (QSH) effect characterized by two pairs of gapless helical edge states within the bulk gap. Generally, due to the finite size effect in QSH systems, the edge states on the two sides of a strip of finite width can couple together to open a gap in the spectrum. In this paper, we investigate the finite size effect of helical edge states on the Lieb lattice with ISO coupling under three different kinds of boundary conditions, i.e., the straight, bearded and asymmetry edges. The spectrum and wave function of edge modes are derived analytically for a tight-binding model on the Lieb lattice. For a strip Lieb lattice with two straight edges, the ISO coupling induces the Dirac-like bulk states to localize at the edges to become the helical edge states with the same Dirac-like spectrum. Moreover, it is found that in the case with two straight edges the gapless Dirac-like spectrum remains unchanged with decreasing the width of the strip Lieb lattice, and no gap is opened in the edge band. It is concluded that the finite size effect of QSH states is absent in the case with the straight edges. However, in the other two cases with the bearded and asymmetry edges, the energy gap induced by the finite size effect is still opened with decreasing the width of the strip. It is also proposed that the edge band dispersion can be controlled by applying an on-site potential energy on the outermost atoms. 参考文献 | 相关文章 | 计量指标

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A self-powered sensitive ultraviolet photodetector based on epitaxial graphene on silicon carbide 黄郊, 郭丽伟, 芦伟, 张永晖, 史哲, 贾玉萍, 李治林, 杨军伟, 陈洪祥, 梅增霞, 陈小龙 2016 (6):  67205-067205.  doi: 10.1088/1674-1056/25/6/067205 摘要 ( 1192 )   HTML ( 0 )   PDF(510KB) ( 478 )   A self-powered graphene-based photodetector with high performance is particularly useful for device miniaturization and to save energy. Here, we report a graphene/silicon carbide (SiC)-based self-powered ultraviolet photodetector that exhibits a current responsivity of 7.4 mA/W with a response frequency of over a megahertz under 325-nm laser irradiation. The built-in photovoltage of the photodetector is about four orders of magnitude higher than previously reported results for similar devices. These favorable properties are ascribed to the ingenious device design using the combined advantages of graphene and SiC, two terminal electrodes, and asymmetric light irradiation on one of the electrodes. Importantly, the photon energy is larger than the band gap of SiC. This self-powered photodetector is compatible with modern semiconductor technology and shows potential for applications in ultraviolet imaging and graphene-based integrated circuits. 参考文献 | 相关文章 | 计量指标

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High temperature characteristics of bilayer epitaxial graphene field-effect transistors on SiC Substrate 何泽召, 杨克武, 蔚翠, 刘庆彬, 王晶晶, 李佳, 芦伟立, 冯志红, 蔡树军 2016 (6):  67206-067206.  doi: 10.1088/1674-1056/25/6/067206 摘要 ( 712 )   HTML ( 0 )   PDF(941KB) ( 412 )   In this paper, high temperature direct current (DC) performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃. At a gate voltage of -8 V (far from Dirac point), the drain-source current decreases obviously with increasing temperature, but it has little change at a gate bias of +8 V (near Dirac point). The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies. Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures. The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience, demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices. 参考文献 | 相关文章 | 计量指标

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Topological charge pump by surface acoustic waves 郑一, 冯世平, 杨师杰 2016 (6):  67301-067301.  doi: 10.1088/1674-1056/25/6/067301 摘要 ( 799 )   HTML ( 0 )   PDF(2042KB) ( 302 )   Quantized electron pumping by the surface acoustic wave across barriers created by a sequence of split metal gates is interpreted from the viewpoint of topology. The surface acoustic wave serves as a one-dimensional periodical potential whose energy spectrum possesses the Bloch band structure. The time-dependent phase plays the role of an adiabatic parameter of the Hamiltonian which induces a geometrical phase. The pumping currents are related to the Chern numbers of the filled bands below the Fermi energy. Based on this understanding, we predict a novel effect of quantized but non-monotonous current plateaus simultaneously pumped by two homodromous surface acoustic waves. 参考文献 | 相关文章 | 计量指标

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Quantum transport through a multi-quantum-dot-pair chain side-coupled with Majorana bound states 江兆潭, 仲成成 2016 (6):  67302-067302.  doi: 10.1088/1674-1056/25/6/067302 摘要 ( 787 )   HTML ( 2 )   PDF(885KB) ( 295 )   We investigate the quantum transport properties through a special kind of quantum dot (QD) system composed of a serially coupled multi-QD-pair (multi-QDP) chain and side-coupled Majorana bound states (MBSs) by using the Green functions method, where the conductance can be classified into two kinds: the electron tunneling (ET) conductance and the Andreev reflection (AR) one. First we find that for the nonzero MBS-QDP coupling a sharp AR-induced zero-bias conductance peak with the height of e2/h is present (or absent) when the MBS is coupled to the far left (or the other) QDP. Moreover, the MBS-QDP coupling can suppress the ET conductance and strengthen the AR one, and further split into two sub-peaks each of the total conductance peaks of the isolated multi-QDPs, indicating that the MBS will make obvious influences on the competition between the ET and AR processes. Then we find that the tunneling rate ΓL is able to affect the conductances of leads L and R in different ways, demonstrating that there exists a ΓL-related competition between the AR and ET processes. Finally we consider the effect of the inter-MBS coupling on the conductances of the multi-QDP chains and it is shown that the inter-MBS coupling will split the zero-bias conductance peak with the height of e2/h into two sub-peaks. As the inter-MBS coupling becomes stronger, the two sub-peaks are pushed away from each other and simultaneously become lower, which is opposite to that of the single QDP chain where the two sub-peaks with the height of about e2/2h become higher. Also, the decay of the conductance sub-peaks with the increase of the MBS-QDP coupling becomes slower as the number of the QDPs becomes larger. This research should be an important extension in studying the transport properties in the kind of QD systems coupled with the side MBSs, which is helpful for understanding the nature of the MBSs, as well as the MBS-related QD transport properties. 参考文献 | 相关文章 | 计量指标

TOPICAL REVIEW—Low-dimensional complex oxide structures

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Modulation of physical properties of oxide thin films by multiple fields 杨华礼, 王保敏, 朱小健, 尚杰, 陈斌, 李润伟 2016 (6):  67303-067303.  doi: 10.1088/1674-1056/25/6/067303 摘要 ( 557 )   HTML ( 0 )   PDF(9560KB) ( 674 )   Recent studies of the modulation of physical properties in oxide thin films by multiple fields are reviewed. Some of the key issues and prospects of this area of study are also addressed. Oxide thin films exhibit versatile physical properties such as magnetism, ferroelectricity, piezoelectricity, metal-insulator transition (MIT), multiferroicity, colossal magnetoresistivity, switchable resistivity. More importantly, the exhibited multifunctionality can be tuned by various external fields, which has enabled demonstration of novel electronic devices. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Piezoelectric polarization and quantum size effects on the vertical transport in AlGaN/GaN resonant tunneling diodes Dakhlaoui H, Almansour S 2016 (6):  67304-067304.  doi: 10.1088/1674-1056/25/6/067304 摘要 ( 778 )   HTML ( 0 )   PDF(305KB) ( 275 )   In this work, the electronic properties of resonant tunneling diodes (RTDs) based on GaN-AlxGa(1-x)N double barriers are investigated by using the non-equilibrium Green functions formalism (NEG). These materials each present a wide conduction band discontinuity and a strong internal piezoelectric field, which greatly affect the electronic transport properties. The electronic density, the transmission coefficient, and the current-voltage characteristics are computed with considering the spontaneous and piezoelectric polarizations. The influence of the quantum size on the transmission coefficient is analyzed by varying GaN quantum well thickness, AlxGa(1-x)N width, and the aluminum concentration xAl. The results show that the transmission coefficient more strongly depends on the thickness of the quantum well than the barrier; it exhibits a series of resonant peaks and valleys as the quantum well width increases. In addition, it is found that the negative differential resistance (NDR) in the current--voltage (I-V) characteristic strongly depends on aluminum concentration xAl. It is shown that the peak-to-valley ratio (PVR) increases with xAl value decreasing. These findings open the door for developing vertical transport nitrides-based ISB devices such as THz lasers and detectors. 参考文献 | 相关文章 | 计量指标

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Influence of surface states on deep level transient spectroscopy in AlGaN/GaN heterostructure 朱青, 马晓华, 陈伟伟, 侯斌, 祝杰杰, 张濛, 陈丽香, 曹艳荣, 郝跃 2016 (6):  67305-067305.  doi: 10.1088/1674-1056/25/6/067305 摘要 ( 812 )   HTML ( 0 )   PDF(508KB) ( 385 )   Deep level transient spectroscopy (DLTS) as a method to investigate deep traps in AlGaN/GaN heterostructure or high electron mobility transistors (HEMTs) has been widely utilized. The DLTS measurements under different bias conditions are carried out in this paper. Two hole-like traps with active energies of Ev+0.47 eV, and Ev+0.10 eV are observed, which are related to surface states. The electron traps with active energies of Ec-0.56 eV are located in the channel, those with Ec-0.33 eV and Ec-0.88 eV are located in the AlGaN layer. The presence of surface states has a strong influence on the detection of electron traps, especially when the electron traps are low in density. The DLTS signal peak height of the electron trap is reduced and even disappears due to the presence of plentiful surface state. 参考文献 | 相关文章 | 计量指标

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Heterogeneous integration of GaAs pHEMT and Si CMOS on the same chip 吴立枢, 赵岩, 沈宏昌张有涛, 陈堂胜 2016 (6):  67306-067306.  doi: 10.1088/1674-1056/25/6/067306 摘要 ( 789 )   HTML ( 0 )   PDF(1284KB) ( 333 )   In this work, we demonstrate the technology of wafer-scale transistor-level heterogeneous integration of GaAs pseudomorphic high electron mobility transistors (pHEMTs) and Si complementary metal-oxide semiconductor (CMOS) on the same Silicon substrate. GaAs pHEMTs are vertical stacked at the top of the Si CMOS wafer using a wafer bonding technique, and the best alignment accuracy of 5 μm is obtained. As a circuit example, a wide band GaAs digital controlled switch is fabricated, which features the technologies of a digital control circuit in Si CMOS and a switch circuit in GaAs pHEMT, 15% smaller than the area of normal GaAs and Si CMOS circuits. 参考文献 | 相关文章 | 计量指标

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Critical current density behaviors across a grain boundary inclined to current with different angles in YBa2Cu3O7-δ bicrystal junctions 花涛, 许伟伟, 吉争鸣, 郭大元, 王青云, 马湘蓉, 梁瑞宇 2016 (6):  67401-067401.  doi: 10.1088/1674-1056/25/6/067401 摘要 ( 752 )   HTML ( 0 )   PDF(935KB) ( 268 )   The critical current density behaviors across a bicrystal grain boundary (GB) inclined to the current direction with different angles in YBa2Cu3O7-δ bicrystal junctions in magnetic fields are investigated. There are two main reasons for the difference in critical current density in junctions at different GB inclined angles in the same magnetic field: (i) the GB plane area determines the current carrying cross section; (ii) the vortex motion dynamics at the GB affects the critical current value when the vortex starts to move along the GB by Lorentz force. Furthermore, the vortex motion in a bicrystal GB is studied by investigating transverse (Hall) and longitudinal current-voltage characteristics (I-Vxx and I-Vxy). It is found that the I-Vxx curve diverges from linearity at a high driving current, while the I-Vxy curve keeps nearly linear, which indicates the vortices inside the GB break out of the GB by Lorentz force. 参考文献 | 相关文章 | 计量指标

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Structural stabilities and electrical properties of Ba8Ga16-xCuxSn30 single crystals under high temperatures 王劲松, 程峰, 刘红霞, 李德聪, 申兰先, 邓书康 2016 (6):  67402-067402.  doi: 10.1088/1674-1056/25/6/067402 摘要 ( 658 )   HTML ( 1 )   PDF(926KB) ( 219 )   Single crystalline samples of type-I and type-VIII Ba8Ga16-xCuxSn30 (x = 0, 1) clathrates are prepared by the Sn-flux method. Effects of Cu-doping on stability and electrical properties of Ba8Ga16Sn30 single crystal are explored by first-principle and experiment. All samples are heated to different high temperatures and maintained at these temperatures for 120 min and then cooled to room temperature to explore their structural stabilities. Results from DTA and powder x-ray diffraction analysis indicate that type-I Ba8Ga16Sn30 structure is transformed into type-VIII phase after the sample has been heated to 185℃. Type-VIII BGS is stable during heating and cooling, but type-VIII Ba8Ga15CuSn30 decomposes into Sn and Ba(Ga/Sn)4 during cooling. Meanwhile, the electrical properties of type-I samples are measured, their electrical conductivities are enhanced, and the Seebeck efficient is reduced with Cu substitution. The type-I samples after phase transformations show the electrical characteristics of type-VIII samples. 参考文献 | 相关文章 | 计量指标

SPECIAL TOPIC—Non-equilibrium phenomena in soft matters

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Superconductivity in Sm-doped CaFe2As2 single crystals 陈东云, 阮彬彬, 于佳, 郭琦, 王小川, 穆青隔, 潘伯津, 刘通, 陈根富, 任治安 2016 (6):  67403-067403.  doi: 10.1088/1674-1056/25/6/067403 摘要 ( 949 )   HTML ( 0 )   PDF(8560KB) ( 543 )   In this article, the Sm-doping single crystals Ca1-xSmxFe2As2 (x=0～0.2) were prepared by the CaAs flux method, and followed by a rapid quenching treatment after the high temperature growth. The samples were characterized by structural, resistive, and magnetic measurements. The successful Sm-substitution was revealed by the reduction of the lattice parameter c, due to the smaller ionic radius of Sm3+ than Ca2+. Superconductivity was observed in all samples with onset Tc varying from 27 K to 44 K upon Sm-doping. The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples. Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x >0.10. The doping dependences of the c-axis length and onset Tc were summarized. The high-Tc observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Pressure effect on magnetic phase transition and spin-glass-like behavior of GdCo2B2 胡光辉, 李领伟, 2016 (6):  67501-067501.  doi: 10.1088/1674-1056/25/6/067501 摘要 ( 728 )   HTML ( 0 )   PDF(1589KB) ( 270 )   We systematically investigate the effect of pressure on the magnetic properties of GdCo2B2 on the basis of alternating current (AC) susceptibility, AC heat capacity and electrical resistivity measurements under pressures up to 2.2 GPa. A detailed magnetic phase diagram under pressure is determined. GdCo2B2 exhibits three anomalies that apparently reflect magnetic phase transitions, respectively, at temperatures TC = 20.5 K, T1 = 18.0 K and TN = 11.5 K under ambient pressure. Under pressures up to 2.2 GPa, these anomalies are observed to slightly increase at TC and T1, and they coincide with each other above 1.6 GPa. Conversely, they decrease at TN and disappear under pressures higher than 1.4 GPa. The results indicate that the low-temperature magnetic phases can be easily suppressed by pressure. Moreover, the spin-glass-like behavior of GdCo2B2 is examined in terms of magnetization, aging effect and frequency dependence of AC susceptibility. A separation between the zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves becomes evident at a low magnetic field of 0.001 T. A long-time relaxation behavior is observed at 4 K. The freezing temperature Tf increases with frequency increasing. 参考文献 | 相关文章 | 计量指标

TOPICAL REVIEW—Low-dimensional complex oxide structures

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Electrical control of magnetism in oxides 宋成, 崔彬, 彭晶晶, 毛海军, 潘峰 2016 (6):  67502-067502.  doi: 10.1088/1674-1056/25/6/067502 摘要 ( 591 )   HTML ( 0 )   PDF(4992KB) ( 1112 )   Recent progress in the electrical control of magnetism in oxides, with profound physics and enormous potential applications, is reviewed and illustrated. In the first part, we provide a comprehensive summary of the electrical control of magnetism in the classic multiferroic heterostructures and clarify the various mechanisms lying behind them. The second part focuses on the novel technique of electric double layer gating for driving a significant electronic phase transition in magnetic oxides by a small voltage. In the third part, electric field applied on ordinary dielectric oxide is used to control the magnetic phenomenon originating from charge transfer and orbital reconstruction at the interface between dissimilar correlated oxides. At the end, we analyze the challenges in electrical control of magnetism in oxides, both the mechanisms and practical applications, which will inspire more in-depth research and advance the development in this field. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Role of vacancy-type defects in magnetism of GaMnN 邢海英, 陈雨, 纪骋, 蒋盛翔, 苑梦尧, 郭志英, 李琨, 崔明启, 张国义 2016 (6):  67503-067503.  doi: 10.1088/1674-1056/25/6/067503 摘要 ( 703 )   HTML ( 0 )   PDF(845KB) ( 270 )   Role of vacancy-type (N vacancy (VN) and Ga vacancy (VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation. Theoretical results show that both the VN and VGa influence the ferromagnetic state of a system. The VN can induce antiferromagnetic state and the VGa indirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN. The transfer of electrons between the vacancy defects and Mn ions results in converting Mn3+ (d4) into Mn2+ (d5). The introduced VN and the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing, as well as the coexistence of Mn3+ (d4) and Mn2+ (d5) are found in GaMnN films grown by metal--organic chemical vapor deposition. The analysis suggests that a big proportion of Mn3+ changing into Mn2+ will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material. 参考文献 | 相关文章 | 计量指标

TOPICAL REVIEW—Low-dimensional complex oxide structures

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Nanoscale control of low-dimensional spin structures in manganites 王静,,梁仁荣, 黄文, 郑仁奎, 张金星 2016 (6):  67504-067504.  doi: 10.1088/1674-1056/25/6/067504 摘要 ( 866 )   HTML ( 0 )   PDF(3256KB) ( 606 )   Due to the upcoming demands of next-generation electronic/magnetoelectronic devices with low-energy consumption, emerging correlated materials (such as superconductors, topological insulators and manganites) are one of the highly promising candidates for the applications. For the past decades, manganites have attracted great interest due to the colossal magnetoresistance effect, charge-spin-orbital ordering, and electronic phase separation. However, the incapable of deterministic control of those emerging low-dimensional spin structures at ambient condition restrict their possible applications. Therefore, the understanding and control of the dynamic behaviors of spin order parameters at nanoscale in manganites under external stimuli with low energy consumption, especially at room temperature is highly desired. In this review, we collected recent major progresses of nanoscale control of spin structures in manganites at low dimension, especially focusing on the control of their phase boundaries, domain walls as well as the topological spin structures (e.g., skyrmions). In addition, capacitor-based prototype spintronic devices are proposed by taking advantage of the above control methods in manganites. This capacitor-based structure may provide a new platform for the design of future spintronic devices with low-energy consumption. 参考文献 | 相关文章 | 计量指标

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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First-principles studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7 胡朝浩, 殷学辉, 王殿辉, 钟燕, 周怀营, 饶光辉 2016 (6):  67801-067801.  doi: 10.1088/1674-1056/25/6/067801 摘要 ( 610 )   HTML ( 0 )   PDF(870KB) ( 346 )   The detailed theoretical studies of electronic, optical, and mechanical properties of γ-Bi2Sn2O7 are carried out by using first-principle density functional theory calculations. Our calculated results indicate that γ-Bi2Sn2O7 is the p-type semiconductor with an indirect band gap of about 2.72 eV. The flat electronic bands close to the valence band maximum are mainly composed of Bi-6s and O-2p states and play a key role in determining the electrical properties of γ-Bi2Sn2O7. The calculated complex dielectric function and macroscopic optical constants including refractive index, extinction coefficient, absorption coefficients, reflectivity, and electron energy-loss function show that γ-Bi2Sn2O7 is an excellent light absorbing material. The analysis on mechanical properties shows that γ-Bi2Sn2O7 is mechanically stable and highly isotropic. 参考文献 | 相关文章 | 计量指标

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Broadband, polarization-insensitive, and wide-angle microwave absorber based on resistive film 布丹丹, 岳春生, 张广求, 胡永涛, 董胜 2016 (6):  67802-067802.  doi: 10.1088/1674-1056/25/6/067802 摘要 ( 828 )   HTML ( 0 )   PDF(3957KB) ( 287 )   A simple design of broadband metamaterial absorber (MA) based on resistive film is numerically presented in this paper. The unit cell of this absorber is composed of crossed rectangular rings-shaped resistive film, dielectric substrate, and continuous metal film. The simulated results indicate that the absorber obtains a 12.82-GHz-wide absorption from about 4.75 GHz to 17.57 GHz with absorptivity over 90% at normal incidence. Distribution of surface power loss density is illustrated to understand the intrinsic absorption mechanism of the structure. The proposed structure can work at wide polarization angles and wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves. Finally, the multi-reflection interference theory is involved to analyze and explain the broadband absorption mechanism at both normal and oblique incidence. Moreover, the polarization-insensitive feature is also investigated by using the interference model. It is seen that the simulated and calculated absorption rates agree fairly well with each other for the absorber. 参考文献 | 相关文章 | 计量指标

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Raman scattering studies on the collapsed phase of CaCo2As2 籍建葶, 张安民, 杨润, 田勇, 金峰, 邱祥冈, 张清明 2016 (6):  67803-067803.  doi: 10.1088/1674-1056/25/6/067803 摘要 ( 876 )   HTML ( 0 )   PDF(648KB) ( 363 )   In this work, Raman scattering measurements have been performed on the collapsed phase CaCo2As2 crystals. At least 8 Raman modes were observed at room temperature though CaCo2As2 is structurally similar to other 122 compounds like BaFe2As2. Two Raman modes are assigned to the intrinsic A1g and B1g of this material system respectively. The other ones are considered to originate from the local vibrations relevant to cobalt vacancies. Careful polarized measurements allow us to clearly resolve the four-fold symmetry of the B1g mode, which put strong constraints on possible point group symmetries of the system with Co vacancies. The temperature-dependent measurements demonstrate that the anomalies in both frequency and width of the B1g mode occur around Neel temperature TN. The anomalies are considered to be related to the gap opening near the magnetic transition. The study may shed light on the structural and magnetic changes and their correlations with superconductivity in 122 systems. 参考文献 | 相关文章 | 计量指标

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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All-dielectric frequency selective surface design based on dielectric resonator 王正斌, 高超, 李波, 吴知航, 张华美, 张业荣 2016 (6):  68101-068101.  doi: 10.1088/1674-1056/25/6/068101 摘要 ( 879 )   HTML ( 0 )   PDF(2517KB) ( 493 )   In this work, we propose an all-dielectric frequency selective surface (FSS) composed of periodically placed high-permittivity dielectric resonators and a three-dimensional (3D) printed supporter. Mie resonances in the dielectric resonators offer strong electric and magnetic dipoles, quadrupoles, and higher order terms. The re-radiated electric and magnetic fields by these multipoles interact with the incident fields, which leads to total reflection or total transmission in some special frequency bands. The measured results of the fabricated FSS demonstrate a stopband fractional bandwidth (FBW) of 22.2%, which is consistent with the simulated result. 参考文献 | 相关文章 | 计量指标

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Coalbed methane adsorption and desorption characteristics related to coal particle size 冯艳艳, 杨文, 储伟 2016 (6):  68102-068102.  doi: 10.1088/1674-1056/25/6/068102 摘要 ( 626 )   HTML ( 0 )   PDF(1154KB) ( 290 )   Effects of particle size on CH4 and CO2 adsorption and desorption characteristics of coals are investigated at 308 K and pressures up to 5.0 MPa. The gas adsorption and desorption isotherms of coals with particle sizes ranging from 250 μm to 840 μm are measured via the volumetric method, and the Langmuir model is used to analyse the experimental results. Coal particle size is found to have an obvious effect on the coal pore structure. With the decrease of coal particle size in the process of grinding, the pore accessibility of the coal, including the specific surface area and pore volume, increases. Hence, coal with smaller particle size has higher specific surface area and higher pore volume. The ability of adsorption was highly related to the pore structure of coal, and coal particle size has a significant influence on coal adsorption/desorption characteristics, including adsorption capacity and desorption hysteresis for CH4 and CO2, i.e., coal with a smaller particle size achieves higher adsorption capacity, while the sample with a larger particle size has lower adsorption capacity. Further, coal with larger particle size is also found to have relatively large desorption hysteresis. In addition, dynamic adsorption performances of the samples are carried out at 298 K and at pressures of 0.1 MPa and 0.5 MPa, respectively, and the results indicate that with the increase of particle size, the difference between CO2 and CH4 adsorption capacities of the samples decreases. 参考文献 | 相关文章 | 计量指标

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Electronic transport properties of silicon junctionless nanowire transistors fabricated by femtosecond laser direct writing 马刘红, 韩伟华, 王昊, 吕奇峰, 张望, 杨香, 杨富华 2016 (6):  68103-068103.  doi: 10.1088/1674-1056/25/6/068103 摘要 ( 783 )   HTML ( 1 )   PDF(1793KB) ( 389 )   Silicon junctionless nanowire transistor (JNT) is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate. The performances of the transistor, i.e., current drive, threshold voltage, subthreshold swing (SS), and electron mobility are evaluated. The device shows good gate control ability and low-temperature instability in a temperature range from 10 K to 300 K. The drain currents increasing by steps with the gate voltage are clearly observed from 10 K to 50 K, which is attributed to the electron transport through one-dimensional (1D) subbands formed in the nanowire. Besides, the device exhibits a better low-field electron mobility of 290 cm2·V-1·s-1, implying that the silicon nanowires fabricated by femtosecond laser have good electrical properties. This approach provides a potential application for nanoscale device patterning. 参考文献 | 相关文章 | 计量指标

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Generalized model for laser-induced surface structure in metallic glass 叶林茂, 武振伟, 刘凯欣, 汤秀章, 熊向明 2016 (6):  68104-068104.  doi: 10.1088/1674-1056/25/6/068104 摘要 ( 706 )   HTML ( 2 )   PDF(2532KB) ( 343 )   The details of the special three-dimensional micro-nano scale ripples with a period of hundreds of microns on the surfaces of a Zr-based and a La-based metallic glass irradiated separately by single laser pulse are investigated. We use the small-amplitude capillary wave theory to unveil the ripple formation mechanism through considering each of the molten metallic glasses as an incompressible viscous fluid. A generalized model is presented to describe the special morphology, which fits the experimental result well. It is also revealed that the viscosity brings about the biggest effect on the monotone decreasing nature of the amplitude and the wavelength of the surface ripples. The greater the viscosity is, the shorter the amplitude and the wavelength are. 参考文献 | 相关文章 | 计量指标

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Bound states of Dirac fermions in monolayer gapped graphene in the presence of local perturbations Mohsen Yarmohammadi, Malek Zareyan 2016 (6):  68105-068105.  doi: 10.1088/1674-1056/25/6/068105 摘要 ( 695 )   HTML ( 1 )   PDF(12593KB) ( 352 )   In graphene, conductance electrons behave as massless relativistic particles and obey an analogue of the Dirac equation in two dimensions with a chiral nature. For this reason, the bounding of electrons in graphene in the form of geometries of quantum dots is impossible. In gapless graphene, due to its unique electronic band structure, there is a minimal conductivity at Dirac points, that is, in the limit of zero doping. This creates a problem for using such a highly motivated new material in electronic devices. One of the ways to overcome this problem is the creation of a band gap in the graphene band structure, which is made by inversion symmetry breaking (symmetry of sublattices). We investigate the confined states of the massless Dirac fermions in an impured graphene by the short-range perturbations for “local chemical potential” and “local gap”. The calculated energy spectrum exhibits quite different features with and without the perturbations. A characteristic equation for bound states (BSs) has been obtained. It is surprisingly found that the relation between the radial functions of sublattices wave functions, i.e., fm+(r), gm+(r), and fm-(r), gm-(r), can be established by SO(2) group. 参考文献 | 相关文章 | 计量指标

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An efficient multipaction suppression method in microwave components for space application 崔万照, 李韵, 杨晶, 胡天存, 王新波, 王瑞, 张娜, 张洪太, 贺永宁 2016 (6):  68401-068401.  doi: 10.1088/1674-1056/25/6/068401 摘要 ( 643 )   HTML ( 0 )   PDF(1630KB) ( 304 )   Multipaction, caused by the secondary electron emission phenomenon, has been a challenge in space applications due to the resulting degradation of system performance as well as the reduction in the service life of high power components. In this paper we report a novel approach to realize an effective increase in the multipaction threshold by employing micro-porous surfaces. Two micro-porous structures, i.e., a regular micro-porous array fabricated by photolithography pattern processing and an irregular micro-porous array fabricated by a direct chemical etching technique, are proposed for suppressing the secondary electron yield (SEY) and multipaction in components, and the benefits are validated both theoretically and experimentally. These surface processing technologies are compatible with the metal plating process, and offer substantial flexibility and accuracy in topology design. The suppression effect is quantified for the first time through the proper fitting of the surface morphology and the corresponding secondary emission properties. Insertion losses when using these structures decrease dramatically compared with regular millimeter-scale structures on high power dielectric windows. SEY tests on samples show that the maximum yield of Ag-plated samples is reduced from 2.17 to 1.58 for directly chemical etched samples. Multipaction testing of actual C-band impedance transformers shows that the discharge thresholds of the processed components increase from 2100 W to 5500 W for photolithography pattern processing and 7200 W for direct chemical etching, respectively. Insertion losses increase from 0.13 dB to only 0.15 dB for both surface treatments in the transmission band. The experimental results agree well with the simulation results, which offers great potential in the quantitative anti-multipaction design of high power microwave components for space applications. 参考文献 | 相关文章 | 计量指标

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Improvement of sintering, nonlinear electrical, and dielectric properties of ZnO-based varistors doped with TiO2 Osama A Desouky, K E Rady 2016 (6):  68402-068402.  doi: 10.1088/1674-1056/25/6/068402 摘要 ( 637 )   HTML ( 0 )   PDF(8769KB) ( 439 )   The effects of TiO2 on sintering and nonlinear electrical properties of (98.5-x)ZnO-0.5MnO2-0.5Co2O3-0.5Bi2O3-xTiO2 (x = 0.3, 0.5, 0.7, 0.9 mol%) ceramic varistors prepared by the ceramic technique are investigated in this work. The optimum sintering temperature of the prepared samples is deduced by determining the firing shrinkage and water absorption percentages. The optimum sintering temperature is found to be 1200 ℃, at which each of the samples shows a maximum firing shrinkage and minimum water absorption. Also minimum water absorption appears in a sample of x=0.9 mol%. Higher sintering temperature and longer sintering time give rise to a reduction in bulk density due to the increased amount of porosity between the large grains of ZnO resulting from the rapid grain growth induced by the liquid phase sintering. The crystal size of ZnO decreases with increasing TiO2 doping. The addition of TiO2 improves the nonlinear coefficient and attains its maximum value at x = 0.7 mol% of TiO2, further addition negatively affects it. A decrease in capacitance consequently in the dielectric constant is recorded with increasing the frequency in a range of 30 kHz-200 kHz. The temperature and composition dependences of the dielectric constant and AC conductivity are also studied. The increase of temperature raises the dielectric constant because it increases ionic response to the field at any particular frequency. 参考文献 | 相关文章 | 计量指标

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Perpendicularly oriented barium ferrite thin films with low microwave loss, prepared by pulsed laser deposition 陈大明, 李元勋, 韩莉坤, 龙超, 张怀武 2016 (6):  68403-068403.  doi: 10.1088/1674-1056/25/6/068403 摘要 ( 796 )   HTML ( 0 )   PDF(544KB) ( 278 )   Barium ferrite (BaM) thin films are deposited on platinum coated silicon wafers by pulsed laser deposition (PLD). The effects of deposition substrate temperature on the microstructure, magnetic and microwave properties of BaM thin films are investigated in detail. It is found that microstructure, magnetic and microwave properties of BaM thin film are very sensitive to deposition substrate temperature, and excellent BaM thin film is obtained when deposition temperature is 910℃ and oxygen pressure is 300 mTorr (1 Torr=1.3332×102 Pa). X-ray diffraction patterns and atomic force microscopy images show that the best thin film has perpendicular orientation and hexagonal morphology, and the crystallographic alignment degree can be calculated to be 0.94. Hysteresis loops reveal that the squareness ratio (Mr/Ms) is as high as 0.93, the saturated magnetization is 4004 Gs (1 Gs=104 T), and the anisotropy field is 16.5 kOe (1 Oe=79.5775 A·m-1). Ferromagnetic resonance measurements reveal that the gyromagnetic ratio is 2.8 GHz/kOe, and the ferromagnetic resonance linewith is 108 Oe at 50 GHz, which means that this thin film has low microwave loss. These properties make the BaM thin films have potential applications in microwave devices. 参考文献 | 相关文章 | 计量指标

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An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils 李华, 张树林, 张朝祥, 孔祥燕, 谢晓明 2016 (6):  68501-068501.  doi: 10.1088/1674-1056/25/6/068501 摘要 ( 701 )   HTML ( 0 )   PDF(499KB) ( 300 )   For a practical superconducting quantum interference device (SQUID) based measurement system, the Tesla/volt coefficient must be accurately calibrated. In this paper, we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils. The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil. By applying magnetic fields through a three-dimensional Helmholtz coil, the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields. Calibration with alternating current (AC) field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current (DC) calibration to avoid possible effects due to eddy current. In our experiment, a calibration relative error of about 6.89×10-4 is obtained, and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils. The method does not need precise alignment of the magnetometer inside the Helmholtz coil. It can be used for the multichannel magnetometer system calibration effectively and accurately. 参考文献 | 相关文章 | 计量指标

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A local fuzzy method based on “p-strong” community for detecting communities in networks 沈毅, 任刚, 刘洋, 徐家丽 2016 (6):  68901-068901.  doi: 10.1088/1674-1056/25/6/068901 摘要 ( 582 )   HTML ( 0 )   PDF(291KB) ( 225 )   In this paper, we propose a local fuzzy method based on the idea of “p-strong” community to detect the disjoint and overlapping communities in networks. In the method, a refined agglomeration rule is designed for agglomerating nodes into local communities, and the overlapping nodes are detected based on the idea of making each community strong. We propose a contribution coefficient bvci to measure the contribution of an overlapping node to each of its belonging communities, and the fuzzy coefficients of the overlapping node can be obtained by normalizing the bvci to all its belonging communities. The running time of our method is analyzed and varies linearly with network size. We investigate our method on the computer-generated networks and real networks. The testing results indicate that the accuracy of our method in detecting disjoint communities is higher than those of the existing local methods and our method is efficient for detecting the overlapping nodes with fuzzy coefficients. Furthermore, the local optimizing scheme used in our method allows us to partly solve the resolution problem of the global modularity. 参考文献 | 相关文章 | 计量指标