Vol. 61, No. 2 (2012)
Temporal evolution and controllable factors for self-deflection of screening photovoltaic solitons in LiNbO3 crystal
2012, 61 (2): 020201. doi: 10.7498/aps.61.020201
According to the band transport model theory, we establish the temporal evolution for dynamic equations concerning screening photovoltaic solitons in LiNbO3 crystal in this paper. By using the finite difference method, we find that there exist large self-deflection bright and dark screening photovoltaic solitons in LiNbO3 crystal, where the shape of the solitons becomes asymmetry ic with the increase of time. In addition, the absolute value of slope of the curve in deflection direction turns larger, while it tends to be smaller in the opposite direction as time increases. On the other hand, analysis shows that the factors related to the degree of self-deflection and deformation include acceptor concentration NA, dark radiation Id and applied electric field E0. When NA rises, the self-deflection degree and the deformation of bright soliton become smaller and the counterpart of dark soliton has opposite tendency while Id and E0 keep invariant. Moreover, for the bright and dark solitons, the space charge field induced in crystals is easier to reach saturation as Id diminishes and there is no saturation phenomenon in both cases when the ratio between center light intensity and dark radiation intensity is 10-1. With the E0 increases, the bright soliton self-deflection degree and deformation decrease, while the dark soliton self-deflection degree and deformation increase.
2012, 61 (2): 020202. doi: 10.7498/aps.61.020202
A class of higher-dimensional disturbed nonlinear Burgers system in physical model is studied. By using the modifying generalized variational iteration method, the corresponding iteration expansions are constructed. And the approximate solutions of the solitary wave by using the iteration method are obtained.
Variational iteration solution method of soliton for a class of nonlinear disturbed Burgers equation
2012, 61 (2): 020203. doi: 10.7498/aps.61.020203
The problem of solving a class of nonlinear disturbed Burgers equation is studied. Using the variational iteration method, a functional is introduced, then its variational is computed, and the iteration expansion is constructed. The soliton solutions of the approximate expansion are obtained from the corresponding equation.
Analytical mechanics representations of a moving charged particle in a magnetic field with radiation friction
2012, 61 (2): 020204. doi: 10.7498/aps.61.020204
The anatylical mechanics representations of a charged particle moving in a uniform magnetic field with radiation friction are studied. First, by solving the inverse problem of Birkhoffian mechanics for the differential equations of motion the 4 Birkhoffian representations of the charged particle are obtained. Secondly, 4 Lagrangian representations in the state space and 4 Lagrangian representations in the configuration space are derived, and then 4 Hamiltonians are constructed. Lastly, 4 first integrals are obtained from the analytical mechanics representations of the moving particle, and the solutions of the equations of motion are presented.
Numerical simulation of temperature field of DE-GMAW and its comparison with experimental measurements
2012, 61 (2): 020205. doi: 10.7498/aps.61.020205
Based on the features of DE-GMAW (double electrode gas metal arc welding), a new hybrid heat-source model that is suited for the DE-GMAW is established. Using this heat-source model, the temperature fields of DE-GMAW wtih different welding parameters are simulated. According to the simulation results with different welding parameters, in this article we analyze the influence of welding parameters on the heat input of base metal in DE-GMAW. To verify the rationality of the hybrid heat-source model of DE-GMAW, the simulation results of the temperature field are compared with the results obtained from the experiment that is carried out under the same condition. The research results indicate that under the same total current, the heat input of base metal decreases gradually with the increase of by-pass current. Moreover, the closer to the welding line the greater the decrease rate of the heat input of base metal is. The study and the comparison of the thermal cycle curve of measured points show that the simulation results are in good agreement with the experimental results. These results indicate that the temperature field model is accurate and the hybrid heat-source model is reasonable.
2012, 61 (2): 020206. doi: 10.7498/aps.61.020206
For an inhomogeneous quantum magnetoplasma system with density and temperature gradients, a two-dimensional nonlinear fluid dynamic equation is derived in the case where the collision frequency between ions and neutrals is minor. The shock, explosion and vortex solutions of the potential for this system are obtained. The changes of the potential in the dense astrophysical environment are discussed. It is shown that the strength of the shock and the width of the explosion are both enhanced with the density increasing (equivalently, the normalized quantum parameter decreasing), but with the drift velocity decreasing (equivalently, the density and temperature gradients decreasing); the potential always tends to a stable value with the spatiotemporal phase increasing, and the system approaches finally to a stable state. Besides, the temporal and spatial distributions of the vortex potential display a stable and period vortex street.
Experimental study of tungsten and tungsten alloy coating produced by cold gas dynamic spray and tungsten particles calculation and simulation
2012, 61 (2): 020207. doi: 10.7498/aps.61.020207
Results of optical microscopy, scanning electron microscopy, AFM are presented for tungsten coating produced by low and high cold gas dynamic spraying, respectively. The critical velocity of tungsten powder was calculated, what is more, tungsten particles collision was also simulated by soft ANSYS/LS-DYNA. Cold gas dynamic spray (CGDS) is a rapidly developing coating technology, in which spray particle are deposited through plastic impact on substrate at high velocities at low temperature. In these experiments, the process produced a reasonably dense tungsten coating and tungsten alloy coating. This paper reports the effect of deposition parameters which including temperature, spraying distance, particle size, etc. on the structures formed.
2012, 61 (2): 020301. doi: 10.7498/aps.61.020301
Quantum dot is a typical nano functional device, which has a very attractive prospect in biotechnology, semiconductor technology, quantum optics and other fields. In this paper, we construct a cavity containing a two-level atom to simulate a nano cavity coupling a two-level quantum dot, and study the electrical transmission in the cavity. We solve the transfer function of a single electron and obtain the formulas of transportation and reflection. By adjusting the intrinsic properties of the cavity and the atom and coupling between them, we study the transmission characteristics of a single electron in the cavity and understand the role of the two-level atom and the cavity in the electrical transport. The results can provide some theoretical support for quantum control of the electron transport in a nano device.
2012, 61 (2): 020302. doi: 10.7498/aps.61.020302
By expanding the density matrix of the open system in terms of Gell-mann matrix in a three-level system, we parameterize coefficients of expansion by some azimuthal angles and find an identity mapping of the density matrices onto interior points of the unit Poincaré sphere. Thus, the relations between the points on the unit Poincaré sphere and wave functions are extended to connect the interior points in the sphere with the nonunit vector rays corresponding to an open system in complex Hilbert space. Thus,the geometric phases for the open system are proposed to be observed by the nonunit vector rays,where the geometric phase of the pure state is the limiting case of our definition. The results show that this geometric phase merely with duplicate three-dimensional Hilbert projection space geometry structure related, has nothing to do with the open system concrete evolution way; and it depends on population inversion and is a slippy and single-value curve of Bloch radius. Therefore, the mixed state of open system retains indeed a memory of its motion in the form of a geometric phase factor.
2012, 61 (2): 020303. doi: 10.7498/aps.61.020303
In this paper we study the quantum selective repeat protocol of data link layer based on quantum teleportation. When two sites are communicating in the physical layer, the sender divides a series of qubits intom frames by adding auxiliary qubits. After continuously transmitting m quantum frames, the receiver judges whether he receives the correct quantum frame according to the classical information provided by the sender. If the receiver receives the correct quantum frames, he returns confirmed frames using the quantum channel. If the correct quantum frames are not received, the receiver does not return denial frames. The sender judges quantum frames which he must resend according to the received confirm frames in setting time. Because the sender resends only the quantum frames which are lost or mistaken, this protocol reduces the transmission delay and improves communication efficiency. In the entire course of communications, the classical channel is used only to transmit the survey information, thus its burden is reduced.
2012, 61 (2): 020501. doi: 10.7498/aps.61.020501
The limit induced bifurcation (LIB) in AC/DC power system caused by converter transformer tap and extinction angle limit under the control mode of constant current in rectifier and constant voltage in inverter is studied in this paper. The reason why the singularity induced bifurcation does not occur while the hard limit encounters is analyzed. The transformer ratio should be larger than a critical value while LIB occurs and the formulas for critical value of LIB in defferent types are derived in this paper. The sensitivities of critical value to parameters are calcaulated, from which some bifurcation points are eliminated and the stable region is augmented. And, the effects of field voltage limit on critical value and stable region are discussed. Finally, a mechanism of limit induced bifurcation is proposed. The increase of reactive power consumed in converter transformer and the decrease of the reactive power compensation in converter AC bus and the transform of control mode result in the system destabilization due to the lack of reactive power.
2012, 61 (2): 020502. doi: 10.7498/aps.61.020502
The dynamics of spiral wave in a three-layer excitable medium with circular feedback coupling is studied, based on the Bär model. The numerical results show that the drifting or meandering of spiral waves in the subsystems can be observed when the coupling strength is small. When the coupling strength is slightly big, the interaction between subsystems may cause spiral waves in some subsystems to move out of the boundaries of the subsystems. The subsystems return to rest state. In addition, the interaction may generate the transition from spiral wave state to target wave or turbulence states in some subsystems. The phenomenon that the asymptotic state of a subsystem depends on the initiation condition is observed. With the further increase of the coupling strength, the approximate generalized synchronization of the spiral waves in three subsystems is established. When the coupling strength is bigger, the spiral waves evolve into turbulence.
Effects of sodium and potassium ion channel fluctuation on the spatiotemporal patterns of neuronal network
2012, 61 (2): 020503. doi: 10.7498/aps.61.020503
Taking into account sodium and potassium ion channel noises, the evolution of the patterns of neuronal networks is investigated. No matter what kind of ion channel noise is working, with coupling coefficient increasing, the spatiotemporal patterns of the neuronal network can be evolved into spiral waves when temperature and noise strength are given, and there is a coupling coefficient threshold for forming a spiral wave. The analysis shows that sodium ion channel noise contributes to the formation of spiral waves in neurons network, while the potassium ion channel noise is not conducive to the formation of spiral waves. In addition, it is found that lower temperature can make the neurons network more sensitive to noise. Finally, the transformation of spiral waves into target waves, in the case of specific parameters is discussed.
2012, 61 (2): 020504. doi: 10.7498/aps.61.020504
Applying the regression analysis to the measured data in CO oxidation on platinum group metals, a analytical theory model with different time scales is established in this paper. The stabilities of equilibria are discussed in detail, and different types of the solutions may bifurcate from the equilibria with the change of the parameters. With a certain parameter, the system can exhibit periodic oscillations via the saddle-node homoclinic orbit bifurcation, which can evolve into periodic bursting, owing to Hopf bifurcation of the fast subsystem. The bifurcation connecting the quiescent state and the repetitive spikes is presented to account for the occurrence of the Nk oscillations. Furthermore, the mechanism of sequence of the period-adding bifurcations is explored to reveal why the length of the sequences become longer with the variation of the parameters.
New equivalence method of integrated three-phase AC-DC system based on differential homology and chaotic analysis
2012, 61 (2): 020505. doi: 10.7498/aps.61.020505
Integrated three-phase AC-DC system is widely used in modern society with series of base units. In this paper we deduce a general equation of the system in an affine coordination in order to use the differential geometry. Firstly, a new approximate equivalence method is presented by differential homology, including the judgment criterion and the main parameters of the equivalent model. Besides, the chaotic analysis relates different parameters to different situations which can accurately be simulated by PSCAD/EMTDC. And then calculation of eigenvalue indicates that the equivalence method is useful and simple. Finally, a simulation shows the accuracy and the applicability of the method.
In this paper we propose a new simple four-dimensional (4D) chaotic system by introducing a nonlinear state feedback controller. There is a fully qualified four-wing type in all directions of the chaotic attractor. With a larger positive Lyapunov exponent, some interesting and complex dynamic behaviors are obtained. Basic dynamical properties of the four-wing attractor are studied by numerical and theoretical analyses, such as dissipativity equilibria, Poincaré map, spectrum map, continuous spectrum and chaotic behaviors. The sensitivities of system parameters to the chaotic behaviors are further explored by calculating, in detail, its Lyapunov exponent spectrum and bifurcation diagrams. Finally, an oscillator circuit is designed for implementation. The EWB observation results are in reasonable agreement with the numerical simulation results.
2012, 61 (2): 020507. doi: 10.7498/aps.61.020507
In this paper a method is proposed to estimate the unknown parameters of nonlinear map based on the discrete variational principle, which can be applied to all map chaotic systems governed by the following equation: xk+1 = F(xk,). Numerical simulations on the well-known Logistic map and Henn map are conducted and all unknown parameters of the two discrete chaotic systems are identified respectively. Simulation results show that the discrete variational method is effective for parameter identification of the map chaotic system.
Parameter modulation digital communication and its circuit implementation using fractional-order chaotic system via a single driving variable
2012, 61 (2): 020508. doi: 10.7498/aps.61.020508
Based on the sliding mode variable structure control theory and the adaptive control technique, a single-state adaptive-feedback controller containing a novel fractional integral sliding surface is developed to synchronize a class of fractional-orderchaotic systems. According to the modulation-parameter principle, using single driving variable for a fractional order chaotic system, a kind of digital communication scheme is presented. The results of the circuit stimulation and the circuit experiment show that the information can be received and sent successfully, which demonstrates the feasibility and the effectiveness of the scheme.
Adaptive generalized synchronization between two different complex networks with time-varying delay coupling
2012, 61 (2): 020509. doi: 10.7498/aps.61.020509
This paper deals deals with the problem of generalized synchronization (GS) between two different complex networks with time-varying delay coupling. By designing a nonlinear adaptive controller, the GS between these two networks is achieved based on Barbalat's lemma. Furthermore, when the topological structures of two networks are fully unknown, the GS problem is also discussed. Numerical simulations are provided to demonstrate the effectiveness of the proposed methods.
2012, 61 (2): 020510. doi: 10.7498/aps.61.020510
With the help of the symbolic computation system Maple and the improved projective method and variable separation method, a new family of solitory wave solutions for (3+1)-dimensional Burgers system is derived. Based on the derived solution, some novel soliton structures and soliton evolvements are investigated.
2012, 61 (2): 020511. doi: 10.7498/aps.61.020511
In order to investigate the effect of the structure of fractal substrates on dynamic scaling behavior of the surfaces, the etching model growing on the Sierpinski arrowhead and crab fractal substrates is simulated by means of Kinetic Monte Carlo (KMC). It is found that the etching model evolving on two kinds of fractal substrates can exhibit dynamic scaling behavior, and can still be described by the Family-Vicsek scaling relation. Although the Sierpinski arrowhead and crab fractal substrates have the same fractal dimension, the obvious different values of roughness exponent and dynamic exponent z, however, are obtained on these two substrates, and they neither of them satisfy the scaling relation +z=2, which is satisfied in the usual Euclid space. It can be seen from the results obtained here that the scaling exponents of the etching model growing on fractal substrate are determined by not only the fractal dimension but also the fractal structure.
2012, 61 (2): 020601. doi: 10.7498/aps.61.020601
We observe the fluorescence and the saturated fluorescence spectra of (5s2)1S0(5s5p)3P1 intercombination transition of thermal strontium atomic beam. Experimental investigation of 88Sr(5s2)1S0(5s5p)3P1 intercombination transition is performed on the different experimental conditions. Our study indicates that experimental parameters affect spectra largely, including temperature, intensity of laser and scanning frequency of laser. Intensity of spectrum is reciprocal of scanning frequency of laser due to long lifetime of (5s5p)3P1 state of Sr atom. Owing to Doppler broadening, transit broadening and other experimental factors, the linewidth of (5s2)1S0(5s5p)3P1 fluorescence spectrum is far more than its natural linewidth and proportional scanning frequency of laser.
Detection of brain auditory evoked magnetic field based on low-Tc superconducting quantum interface device
2012, 61 (2): 020701. doi: 10.7498/aps.61.020701
Superconducting quantum interface devices (SQUID) is widely used in human brain signal detection. As one of the applications of magnetoencephalography (MEG) system, the detection of the auditory evoked response is useful for the development of MEG system and the research into auditory mechanism of human brain. Generally, the auditory evoked response includes three peaks which are P50m, N100m and P200m. We develop a single-channel MEG system in a magnetically shielded room based on the superconducting quantum interface device (SQUID) and second-order axial gradiometer. The responses of the main peak N100m under different tone frequencies are preliminarily studied by using our system. The typical evoked response of N100m to 1 kHz pure tone and 100 ms duration is measured to be 0.4 pT. Under the tone stimulus at low frequency, the delay of the peak N100m to the tone onset is 125 ms at 100 Hz, which is longer than the typical value of 100 ms. In comparison with the response to 1 kHz pure tone stimulus, the amplitude of the evoked response in a random frequency range from 1 kHz to 4 kHz is stronger and the delay is several milliseconds. This work lays the foundation of the studies of the auditory mechanism and multichannel MEG system by using software gradiometers.
2012, 61 (2): 020702. doi: 10.7498/aps.61.020702
Color vision is based on a three-color colorimeter of colorimetric principle, and the colorimetric properties of illumination is the key factor for color imaging. Therefore based on the principle of colorimetry, in this paper we analyse and calculate the colorimetric properties of LED array sources for color vision application. By comparison with the standard D65 light source, the adjustment principle and range of correlated color temperature are studied for LED array sources. Chromaticity coordinates and relevant color temperature of white balance are also studied. The LED array source has a large range for adjusting the correlated color temperature and has a better ability of color display. Chromaticity coordinates and relevant color temperature of white balance R:G:B=254:237:90 are closer to those of the standard chromaticity. The ability of color reproduction reaches a better result of color reproduction. Therefore, the colorimetric properties of LED array sources are more appropriate for color vision application.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2012, 61 (2): 021101. doi: 10.7498/aps.61.021101
In this paper are study the symmetry of Lagrangians and the conserved quantities for a nonholonomic variable mass system. Firstly, the criterion of the symmetry of Lagrangians for a nonholonomic variable mass system is given. Secondly, the conditions under which there exist a conserved quantity and the form of the conserved quantity, are obtained. Finally, an example is given to illustrate the application of the results.
Conformal invariance, Noether symmetry and Lie symmetry for holonomic mechanical system with variable mass
2012, 61 (2): 021102. doi: 10.7498/aps.61.021102
The conformal invariance of holonomic mechanical system with variable mass is studied. Firstly, the definition of conformal invariance for holonomic mechanical system with variable mass is given; secondly, the relation between the conformal invariance and the Noether symmetry is discussed, and the Noether conserved quantity led by the conformal invariance is obtained; finally, the relation between the conformal invariance and the Lie symmetry is discussed, and the Hojman conserved quantity caused by the conformal invariance of the systems is obtained. In the paper, an example is given to illustrate the application of the results.
Magnetronlike structure is a non-cathode magnetron waveguide structure. It is the basic configuration of relativistic magnetron with axial extraction (MDO). First, the dispersion relation and the field expression of the magnetronlike structure are obtained by the field matched method. Then, the results are proved by the high electromagnetic field analysis software, and the cutoff frequency is studied by changing the structure parameters. The final results show that with keeping the other parameters constant, the π mode cutoff frequency can be promoted by reducing the outer radius, enlarging the inner radius or increasing the number of the cavities. Enlarging the cavity angle will reduce the π mode cutoff frequency. The outcomes produced in this paper will play a fundamental role in the theoretical analysis on the mode conversion and transmission of the relativistic magnetron with axial extraction.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (2): 023101. doi: 10.7498/aps.61.023101
Tin oxide has become one of hot points in transparent conductive materials due to its excellent electrical and optical properties. Based on the full-potential linearized augmented plane wave method (FP-LAPW), we investigate the electronic structure and the optical properties of the material Fe-S co-doped SnO2. The results show that the two co-doped compounds are all direct transition semiconductors with half-metallic properties. Fe-S co-doping can narrow the band gap, and the density of states (DOS) shifts toward the low energy with the increase of S concentration. The charge density of co-doped system is redistributed, and the degree of Fe polarization and the capacity of bonding are enhancd with the increase of S. What is more, the peaks of imaginary part of dielectric function and optical absorption are red shifted, and the absorption edge decreases with the increase of S concentration.
2012, 61 (2): 023102. doi: 10.7498/aps.61.023102
By performing first-principles calculations, we demonstrate the electronic structure, the transport properties, and the adsorption effect of A-Z-A graphene nanoribons field effect transistor. It is concluded that the pure A-Z-A GNR-FET has typical bipolar characteristics, and energy gaps will become smaller due to the adsorbed molecule. For the adsorption of H, N2, NO2, H2O, SO2, O2 and NO, A-Z-A GNR-FET remains typical bipolar characteristic, but shows a little difference in transport property after it has adsorbed different types of molecles. For the adsorption of OH, transport property changes totally and does not have a bipolar characteristic any more. These results may contribute to the implementation of gas detector based on GNRs and the design of GNR-FET applied in complex environments.
2012, 61 (2): 023103. doi: 10.7498/aps.61.023103
We employ ab initio plane-wave pseudo potential density functional theory to calculate the equilibrium lattice parameters, elastic constants, anisotropies, Poisson's ratios, and the Cauchy violation under hydrostatic pressures of 060 GPa for BC5 with hexagonal P3m1 and tetragonal I4m2 structures. The results show that two structures are stable under high pressure and the incompressibility increases with pressure. In addition, the electron structures, the total and the partial densities of states are also calculated. BC5 is found to be metallic with band gap, unlike other B-C compounds. The material properties of BC5 are mainly determined by B 2p1 and C 2p2 electronic states together. All these show that BC5 is an unusual super hard material, and it may be a potential candidate for diamond at high temperature. The given density of states indicates the covalent hybridization between B and C atoms in this compound. The pressure slightly influences the density of states and the band gap, indicating stability under high pressure. We also find that pressure has no influence on the density of states near Fermi level and the band gap, except for slight shifts of the bands. It can be further inferred that BC5 will have good stability under high pressure.
Theoretical study of the Rydberg series energy levels of ns2S1/2,np2P1/2,3/2, nd2D3/2,5/2 and nf2F5/2,7/2 for alkali-metal Li, Na, K, Rb, Cs and Fr
2012, 61 (2): 023104. doi: 10.7498/aps.61.023104
In the frame work of multi-channel quantum defect theory, the energy levels of Rydberg series of ss2S1/2, np2P1/2, np2P3/2, nd2D3/2, nd2D5/2, nf2F5/2 and nf2F7/2 of alkali-metal atom are calculated by the relativistic multi-channel theory, in five different approximations, i.e., frozen core approximation, with consideration of l=-1 dipole polarization effect, l=+1 dipole polarization effect, l = 1 dipole polarization effect, stretch effect, and both dipole polarization effects and stretch effect, respectively. The present calculations show that electron correlation effect plays an important role in the energy level of Rydberg series. In summary, dipole polarization effect is more important than the stretch effect, and the l = + 1 dipole polarization effect is more important than l = - 1 dipole polarization effect. However, stretch effect is more important for energy levels of both Rydberg series ns2S1/2,(nd2D3/2,nd2D5/2) of Na, and Rydberg series (np2P1/2,np2P3/2) of Li.
2012, 61 (2): 023201. doi: 10.7498/aps.61.023201
One-dimensional Bose-Hubbard model is studied in detail. Soliton solutions in infinite space is presented, The elliptic function wave solutions and its nenergy and effective mass are also found under the periodic boundary condition.
A new method based cross-correlation technique (CD-OCT) is proposed to acquire and analyse the information about flow velocity with low signal-to-noise ratio(SNR) in spectral-domain optical coherence tomography(SD-OCT). We theoretically study the procedure of this method, and analyse the correlation between the noises by computer simulation and experiment. The Doppler flow images reconstructed by CD-OCT are compared with those reconstructed by Joint spectral and time-domain optical coherence tomography (STD-OCT). The results demonstrate that CD-OCT can significantly improve the SNR, thus rendering it suitable for the flow measurement in low SNR.
2012, 61 (2): 023402. doi: 10.7498/aps.61.023402
Backward trajectories computed using the NOAA HYSPLIT model and global NOAA-NCEP/NCAR pressure level reanalysis data from November 2007 to October 2010, are used to trace air history and analyze the atmospheric transportation properties over SACOL. The cluster analysis has the advantage of providing highly disaggregated trajectory clusters, from which fifteen significant clusters arriving at the SACOL, which reflect the main feature of air mass trajectories, are obtained during this period. It is found that the air mass trajectories from Sichuan province and Chongqing account for 16% of all trajectories and have the biggest influence, those from local and Shanxi province have the second biggest influence, and those from the Eastern Europe and Bangladesh have the smallest influence. The Aerosol Optical Depth (AOD) at 870nm and ngstrm exponent acquired by a Multi-Filter Rotating Shadowband Radiometer (MFRSR) at SACOL are employed to analyze aerosol optical properties and particle characteristics under the control of different air mass sources. The maximum average AOD of 0.29 0.12 (mean standard deviation of mean) corresponds to the air mass originating from Taklimakan Desert, whereas the minimum average AOD is 0.14 0.02 from Bangladesh. According to ambient conditions of the studied site and the geographical conditions and moved track of air mass, the quantitative contributions of different sources to the three-year average AOD of 0.22 are investigated. The results show that the greatest contribution to the average AOD, accounting for almost 41.1%, came from local and regional sources, an additional important contribution from dust areas is about 28.4% of the average AOD, the contribution from the Central Asia source occupies 17.9%, that from Eastern Europe and Middle East is 12.6%.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (2): 024101. doi: 10.7498/aps.61.024101
Time-reversed system with a sub-wavelength structure is one of the necessary conditions for the system to show spatial super-resolution characteristics. In the near field zone, Coulomb field predominates the transmission of signals. The resolution limit of Coulomb field is characterized only by the sizes and the spatial distribution of scatterers, which is useful for obtaining the super-resolution beyond the diffraction limit.
2012, 61 (2): 024102. doi: 10.7498/aps.61.024102
We systematically investigate the transmission characteristics of the split ring resonator (SRR) for propagation perpendicular to the plane of the ring resonator. Both the vertical polarization and the horizontal polarization are considered. A retrieval procedure is used to obtain permittivity and permeability . It is found that in the normal incidence case the SRR also has strong electric and magnetic responses. The electric response occurs when electric field is parallel to the side of the SRR (vertical polarization) and the frequency band is often higher than that of magnetic resonance. The magnetic response needs a polarization rotation (horizontal polarization) and the magnetic resonant frequency is the same as that of parallel incidence. The conclusions are demonstrated and the reasons for the electric and magnetic resonances are also discussed theoretically.
2012, 61 (2): 024201. doi: 10.7498/aps.61.024201
The near-field diffraction characteristics when a high-power laser beam traverses contaminant particles are studied by using the designing software of high-power laser drivers-Laser designer. The modulations generated by contaminant particles are sorted. Then the influence of contaminant particles with amplitude or phase modulation on the near-field intensity distribution in vacuum or in fused silica is analyzed in great detail. The results show that in both vacuum and fused silica, the phase modulated contaminant particles have a greater influence on the near-field properties of high-power laser. Moreover, it is found that in fused silica, the small-scale self-focusing hot-image modulation of high-power laser induced by phase modulated hard-edge contaminant particles is momentous. But the lateral shift of high-power laser beam caused by contaminant particles maybe inhibits the small-scale self-focusing effect to some extent, thereby reducing the laser injury risk of optical component.
This work aims at developing a new excitation method for thermal wave nondestructive test(NDT)-Terahertz excitation. In the paper we introduce a theoretical model of heat conduction for periodical THz excitation. BWO (backward wave oscillator) terahertz source is employed to heat a carbon fiber plate with wave absorbing coating, surface temperature variations and distributions are captured by an infrared camera, and Canny edge algorithm is used to process thermal images to show the defects. Result of flash pulse thermography serves as comparison, and the advantages of THz thermal wave NDT are discussed. The combination of THz technology and infrared thermal wave NDT is realized.
2012, 61 (2): 024203. doi: 10.7498/aps.61.024203
Based on the chaotic synchronization of two response semiconductor lasers (RLs) under the injection from a common chaotic signal of a drive laser (DL), a new type of secure communication system, which allows bidirectional and long-distance information transmissions, is proposed. A corresponding theoretical model is established to study the bidirectional transmission performance, security performance and the system performance under different transmission distances. The results show that when two RLs receive chaotic light injected from a DL, the chaotic outputs of two RLs achieve a fairly good isochronal synchronization without any time delay, while there is a big difference between the signals of RLs and the signal of DL; the system owns high security level after having analyzed the various ways from which eavesdropper may obtain message; if the ordinary single mode optical fiber is used as a transmission channel, the Q factor of decoded message can reach more than 6 after a propagation over 50km; if the dispersion-shifted fiber is employed, the Q factor of decoded message can still reach more than 6 after a propagation over 200km.
Determination of tropospheric NO2 by airborne multi axis differential optical absorption spectroscopy
2012, 61 (2): 024204. doi: 10.7498/aps.61.024204
The airborne multi axis differential optical absorption spectroscopy (AMAXDOAS) is employed to retrieve tropospheric vertical columns of NO2. The differential slant columns of NO2 are retrieved combined with the spectra in different viewing directions by the DOAS method and the vertical columns are calculated with the radiative transfer model SCIATRAN. The dependences of AMF on altitude, surface albedo, and solar zenith angle are studied. The measurement campaign in pearl region delta region on December 10 in 2008 is reported. The NO2 vertical column distribution is obtained in zenith and nadir directions. The results from airborne multi axis DOAS are compared with those from a ground-based multi axis DOAS in Zhuhai, with a deviation of 0.08. The results show that AMAXDOAS can be used to measure the tropospheric NO2 in a large area within a short time.
Selection of regularization parameters using an atmospheric retrievable index in a retrieval of atmospheric profile
2012, 61 (2): 024205. doi: 10.7498/aps.61.024205
Using an atmospheric retrievable index and The Nelder-Mead simplex method, a dynamic regularization parameter selection method for the retrieval of atmospheric profile with remote sensing data. And a series of test is carried out with four typical regional profiles. The results show that the ranges of the optimal regularization parameter for different profiles are small. And to improve computational efficiency in the actual retrieval process, the regularization parameter can be approximately taken as a constant. The results provide a valuable method of selecting the regularization parameters in the retrieval of atmospheric profiles using the remote sensing data.
Surface crystallization of amorphous fused silica during electron cyclotron resonance plasma etching
2012, 61 (2): 024206. doi: 10.7498/aps.61.024206
After low pressure fluorine plasma ecthing and oxygen ion passivation, a crystallized layer composed of SiO2 nano-crystal grains is observed in an amorphous fused silica surface. The depth of crystallized layer is at least several hundreds nanometers. Fluorine and carbon ion are generated from Ar/CF4 by the method of electron cyclotron resonance (ECR). F ion breaks Si-O band of initial silica surface layer and releases O ion. Carbon ion combines with oxygen ion, and turns into CO2, and SiF4 is generated from fluorine and silicon. After initial surface layer is removed, unsaturated Si atom remains. Si dangling bond recombines with new O ion and then creates crystallized -cristobalite nano-crystal grains under a high temperature.
Super-resolution optical microscopic imaging method based on annular illumination with high numerical aperture
2012, 61 (2): 024207. doi: 10.7498/aps.61.024207
On the basis of narrow-band filtered annular light-cone illumination with high numerical aperture, a new far-field super-resolution optical microscopic imaging method is proposed, and its physical model is established. Using the scalar diffraction theory, the formula of diffraction intensity in the image plane is derived for annular light-cone illumination and imaging under different numerical apertures. The diffraction patterns are further simulated through the Matlab program, which demonstrates that such a method may significantly increase the microscopic imaging resolution. Experiments have been carried out on a self-build microscopic system, showing that a resolution can be achieved to be better than 150 nm under 450 nm light wavelength and 1.125-1.25 annular numerical apertures. The experimental results are in good agreement with the theoretical predictions, thus proving the feasibility of this microscopic imaging method.
2012, 61 (2): 024208. doi: 10.7498/aps.61.024208
Based on the method of stationary phase and the theorem of the vectorial structure, the analytical expressions for the vectrorial terms, namely the TE and TM terms, of a linearly polarized Laguerre-Gauss beam are derived in the far-field. According to the far-field energy flux distributions of the TE and TM terms, the ratios of the powers of the TE and TM terms to the power of the Laguerre-Gauss beam are given. The analytical formulae of the far-field divergence angles of the Laguerre-Gauss beam and its TE and TM terms are presented, respectively. A relation among the far-field divergence angles of the TE term, the TM term, and the Laguerre-Gauss beam is also derived. The formulae obtained are applicable not only to the paraxial case, but also to the non-paraxial case. The dependences of the ratios of the powers of the TE and TM terms to the whole power onf-parameter and mode number are numerically examined. The effects of thef-parameter, the mode number, and the linearly polarized angle on the far-field divergence angle of the Laguerre-Gauss beam and its TE and TM terms are also analyzed. This research reveals the far-field divergent properties of the linearly polarized Laguerre-Gauss beam from the vectorial structure, and enriches the recognition of the propagation characteristics of the linearly polarized Laguerre-Gauss beam.
2012, 61 (2): 024301. doi: 10.7498/aps.61.024301
Recently piezoelectric shunt damping has attracted a lot of attention in vibration and noise control. In this article, piezoelectric shunt damping is used in underwater sound absorption in order to enhance the sound absorption of the coating. A one-dimensional electro-acoustic model is established for the calculation by combining the equivalent circuit of thickness mode of a piezoelectric composite coating with the transfer matrix of plane wave propagation. This model can be used to calculate the sound absorption of multiple layers of piezoelectric and non-piezoelectric mediums. Underwater sound absorption of the 0-3 type piezoelectric composite coatings is theoretically analyzed. Elastic, piezoelectric and dielectric constants of the 0-3 type piezoelectric composites are calculated by Furukawa's model. Results show that the negative capacitance circuit can adjust the surface acoustic impedance of the piezoelectric composite coating at broadband frequencies. Suitable shunt resistances can make it match the characteristic acoustic impedance of water better. Therefore, the sound absorption can be greatly promoted.
2012, 61 (2): 024401. doi: 10.7498/aps.61.024401
The influence on the motion of single solid particles in a Newtonian fluid by melting and convection is direcly simulated. The fluid motion is computed from the conservation laws. Density and viscosity change with fluid temperature, and the particle moves according to the equation of motion of a rigid body under the action of gravity and hydrodynamic forces arising from the motion of the fluid. In the process of melting, a distinctive morphology develops due to the different heat fluxes around the particle's surface, and the thermal gradient determines the melting rate. The phases are coupled by the fluid-particle mutual force , force moment and the boundary conditions. In our study, two different situations are carried out, which are sedimentation in isothermal fluid without thermal convection and melting; sedimentation with thermal convection and melting, two double particles are simulated separately. The results show that the vortex shedding arising by the natural convection, mass losing by melting and melting morphology change the sedimentation velocity and induce horizontal oscillation.
Analysis of dynamic properties of a spatial flexible beam with large overall motion and nonlinear deformation in non-inertial reference frame
2012, 61 (2): 024501. doi: 10.7498/aps.61.024501
In this paper, the dynamic properties of a spatial flexible beam with large overall motion and nonlinear deformation in non-inertial reference frame are investigated. The dynamic response of the present model is compared with those of zero-order approximate model and one-order coupling model. Then changing of dynamic stiffening terms due to the new coupling terms is discussed according to different models. At the same time, the effect of initial static deformation on the tip is considered to study the vibrant deformation of flexible beam. In addition, when the overall motion is free, the rigid-flexible coupling dynamic theory is extended to spatial structure from planar structure. The difference among zero-order approximate model, one-order coupling model and the present exact model is revealed by the frequency spectrum analysis method and concludes that the speed of overall motion is a vital cause for the difference among different models. And the dynamic stiffening phenomenon still exists in a rigid-flexible coupling system while the overall motion is free.
2012, 61 (2): 024502. doi: 10.7498/aps.61.024502
A gradient representation and a second order gradient representation of the mechanics system are studied. The differential equations of motion of the holonomic and nonholonomic mechanics systems are expressed in the canonical coordinates. A condition under which the system can be considered as a gradient system is given. A condition under which the system can be considered as a second order gradient system is obtained. Two examples are given to illustrate the application of the result.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Density functional calculations of geomatric structure, electronic structure, stability, and magnetic properties of transitional atom endohedral unclassical fullerene M@C22(M=Sc,Ti, V, Cr, Mn, Fe, Co and Ni)
2012, 61 (2): 026101. doi: 10.7498/aps.61.026101
The generalized gradient approximation (GGA) based on density functional theory(DFT) is used to analyze the structural and electronic properties of the unclassical endohedral fullerene M@C22(M=Sc, Ti, V, Cr, Mn, Fe, Co and Ni). It is found that the ground-state structure of the unclassical fullerene C22 is a spin singlet cage containing one four-membered ring and the doping of transition metal atom can obviously enhance the stability. It is discovered that the C-M bond have both the covalent and the ionic characteristics. The analyses of magnetism, energy levels, orbital wave functions and density of states show the hybridization between the 3d orbital ofM atom and the C atomic orbital in C22. In addition, Ti, Cr, Fe and Ni atoms become non-magnetic after they have been doped into the C22.
The influence of channel size on total dose irradiation and hot-carrier effects of sub-micro NMOSFET
2012, 61 (2): 026102. doi: 10.7498/aps.61.026102
Total dose irradiation and the hot-carrier damages are two of the important factors for the application of sub-micro and even smaller MOS devices. Therefore, how to prevent the device from being damaged attracts much attention. Total dose irradiation and hot-carrier effects of sub-micro NMOSFET with various channel sizes are studied. Electronic parameters are measured and the results show that though the principles of damages are somewhat similar, the total dose irradiation and the damage behavior and their dependences on the width-to-length(W/L) ratio of channel size for these two effects are different. The most notable damage of radiation lies in the great increase of the off-state leakage current, and the damage increases withW/L reducing. While for hot-carrier effect, several parameters such as trans-conductance change a lot, except for the off-state leakage current. And the damage increases as channel length and channel width decrease. The different damage behaviors and different relations to channel size are attributed to the different location of charges induced. Therefore, different aspects should be considered when the device is hardened against these two effects.
2012, 61 (2): 026701. doi: 10.7498/aps.61.026701
The shock properties of C100 concrete are investigated by the gas gun planar impact technique. The manganin pressure gauge is used to measure the pressure-time curves of the samples. The physical quantities are all obtained by the Lagrange method. Moreover, it is observed from the measured pressure-time curves that the rate-sensitivity of dynamic response for C30 concrete is not negligible, showing marked stress relaxation and dissipation. The damage factor is introduced into the state equation. The material parameters in the Grüneisen-type equation of state are determined.
First-principles predictions for the tensile strength of Al metal with dislocations of twist grain boundaries
2012, 61 (2): 026801. doi: 10.7498/aps.61.026801
By the first-principles calculations based on the density functional theory, the tensile strength of Al metal with dislocations of twist grain boundaries (GBs) is predicted from its electronic structure to its essential mechanical properties. The results show that the theoretical tensile strength for Al twist GB is about 8.73GPa and it is less than that for Al glide GB(9.5GPa) (Phys. Rev. B 75, 174101 (2007)). However, its fracture strain for Al twist GB is 24% and 16% more than that for Al glide GB. It suggests that the mechanical properties of the metal can be greatly improved by experimentally modulating its defect or dislocation. Furthermore, the physics of the fracture of Al twist GB is analyzed by the distributions of charge density and the changes of bond length, and it is found that the facture appears in the GB. Our theoretical predictions can play an important role in guiding the improvement of mechanical properties and structural designs for Al metal.
2012, 61 (2): 026802. doi: 10.7498/aps.61.026802
NiO films are prepared with radio frequency magnetron sputtering. Ellipsometric experiment results show that NiO film is transparent for visible light,and its refractive index can be modified by changing Tsub and annealing temperature. Scanning electron microscopy and X-ray diffraction experiment results show that Tsub and annealing temperature can modify the morphology and crystal structure of NiO film which can further modify the conductivity of NiO. The optimized NiO film is used in polymer solar cell (PSC) as an anode blocking layer. The experimental results show that NiO is a better candidate than the PEDOT:PSS often used as an anode blocking layer for PSC. The power conversion efficiency of PSC with NiO reaches 2.26% which is three times as high as that with PEDOT:PSS.
2012, 61 (2): 026803. doi: 10.7498/aps.61.026803
We propose a novel approach for the study of rheological properties of silica nanoparticle monolayers at the air-water interface. The layers are deformed by indenting and raising a titanium cone. The surface pressure variations in these down-up cycles are recorded and analysed. The oscillation amplitude of surface pressure d results from the tensile deformation of the particle layer. d and the relaxation time are strongly dependent on the adsorption energy of particles at the interface, thereby significantly changing the particle hydrophobicity. The results provide a deeper insight into the viscoelastic behaviour of particle layer, suggesting that the proposed method can be utilized for the rheological study of the layers of this kind.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2012, 61 (2): 027101. doi: 10.7498/aps.61.027101
Based on the density function theory, the electronic structure, densities of states, and optical properties of -AlON are calculated by using the local density approximation and plane-wave pseudoptential method. The complex dielectric functions and the optical properties including refractive index, reflection spectra, absorption spectra of -AlON are analyzed in terms of calculated density of state. As shown by the theoretical calculation, the static dielectric function of -AlON is 1(0)=2.60, and the refractive index is n0=1.61, its absorptions in a range from IR to NUV and a UV range up to 20.23eV all approach to zero, showing the optical transparent behaviors . The calculated results are consistent with relevant experimental values, providing theoretical basis and reference for the application of the optical material to windows and domes.
2012, 61 (2): 027102. doi: 10.7498/aps.61.027102
Using the first-principles method based on the density functional theory, we study the doping effect of B impurity in HgCdTe (MCT).We find that the most stable configuration of the impurity is at the B hexagonal interstitial position, rather than at the in-situ substitution. The electronic structures and the density of states of B hexagonal interstitial doped MCT are systematically investigated. Near neighbour (NN) and next-near-neighbor (NNN) atoms around the B impurity are obviously relaxed. The relaxation induces the breaking of NN Te-Hg covalent bond. Moreover, B hexagonal interstitial behaves as triple n-type dopant. The charged state analysis indicates that Bih(2Hg1Cd) with three positive charges is most stable and forms an effecient donor. However, as long as the Hg vacancy exists, complex impurity between Hg vacancy and B impurity can be easily formed, its binding energy reaches up to 0.96 eV. Such complex behaves as single n-type dopant. Considering radiation damage of B ion implantation, the complex is a main factor restricting the activation of B ion in MCT.
Study of Rashba spin splitting and intersubband spin-orbit coupling effect in AlGaN/GaN quantum wells
2012, 61 (2): 027103. doi: 10.7498/aps.61.027103
Rashba spin splitting coefficients for the first two subbands1,2 and intersubband spin-orbit coupling coefficient 12 are obtained by projecting the characteristic equation into the subspace of conduction band. Then Schrdinger and the Poisson equations are solved self-consistently to calculate1,2 and 12 under different gate voltages. Then contributions to the spin-orbit coupling coefficients from the well, the left and the right heterointerfaces and the left and the right barriers of the quantum well are discussed. Resulsts show that the spin-orbit coupling coefficient can be modulated by the gate voltage, and the intersubband spin-orbit coupling coefficients calculated here are a little smaller than the Rashba coefficients1,2, but they are basically of the same order.
2012, 61 (2): 027104. doi: 10.7498/aps.61.027104
The platinum-doped graphene has been achieved in our previous experiments. To further study the effects of metal doping on the band structures of graphene, and provide theoretical guidance for the next step of the experiment, we analyze the electronic properties of armchair graphene nanoribbons (AGNRs) with platinum atoms doping in the divacancy positions using first principle calculation based on density functional theory. The results show that the band structures of AGNRs can be effectively tailored by controlling the doping position on ribbons. Edge position is the most stable position for platinum atom. The band gaps of edge doped AGNRs can be shown in three curves like that of pristine AGNRs. However, they degenerate into two curves at large width, inhibiting the vibration of band gaps to some extent. In addition, several narrow platinum-doped AGNRs with width index Na = 3p and 3p + 1 have impurity level(s) in the band gap, reducing the large band gap effectively. Furthermore, band characteristics of platinum doped AGNRs are not sensitive to doping concentration, thus reducing the challenge of experimental precision. Our results will promote the application of graphene nanoribbons in the field of nano-electronics.
Heterojunction structure forming in the polymer film doped with small-molecule organic semiconductors
2012, 61 (2): 027201. doi: 10.7498/aps.61.027201
Blends and doping of organic semiconductors are generally employed to improve effectively the charge transfer and dissociation performance. The absorption spectrum may be optimized making use of the different energy states of the components in the blends, which may favor the development of the photovoltaic or solar cell devices. Excellent type-II heterojunction structures can be produced by mixing the small-molecule perylene (EPPTC) and a copolymer of polyfluorene (F8BT). Actually, F8BT and EPPTC exhibit absorptions in the blue region and in the green region, respectively. Thus, the blend will have a much broadened absorption spectrum. In the experiment, the blend solution of these two materials in chloroform is spin-coated onto a piece of glass substrate, so that EPPTC is doped into the polymer of F8BT and the heterojunction structure forms in the final solid film. Then, steady-state absorption and fluorescence spectroscopy, as well as the transient photoluminesence spectroscopy (time-correlated single-photon counting), is used to investigate the formation and the photoluminescence properties of exciplex in the heterojunction film of F8BT doped with EPPTC. The photoluminscence (PL) spectrum and the life-time are measured to characterize the exciplex in the blend film, where the longer life-time of the red-shifted PL spectrum confirms the formation of the exciplex. This provides various experimental data for understanding the formation and the photophysical properties of the heterojunction structures in organic semiconductor blends. Futhermore, the absorption of the blend film covers a large range of the visible spectrum. Therefore, this kind of doping of organic semiconductor is important for the development of photovoltaic and solar cell devices.
Improvement in breakdown characteristics of 4H-SiC MESFET with a gate-drain surface epi-layer and optimization of the structure
2012, 61 (2): 027202. doi: 10.7498/aps.61.027202
A novel SiC MESFET structure with a p-type surface epi-layer is proposed and 4H-SiC MESFET models are presented which precisely describe the working mechanism of the device. Considering carrier velocity saturation, impact ionization and electric field modulation, the effect on distribution of electric field is analyzed. Also, the output current (Ids) and breakdown voltage (VB) dependences on the dimensions of the p-type epi-layer are studied based on abrupt junction approximation. The high electric field peak at the gate edge is suppressed by introducing a new electric field peak at the drain side, and the built-in field of p-n junction formed along channel surface further weakens the electric field peaks, leading to smoother distribution of electric field. By comparison with the conventional and the fieldplated MESFETs, it is shown that the proposed structure greatly improves the characteristic of SiC MESFET. In addition, the optimized dimensions are obtained and the results show that VB is greatly increased by 33% with Ids unchanged (less than 3%) when the thickness and the doping concentration of the surface epi-layer are chosen as 0.12 upm and 5 1015 cm-3, respectively.
2012, 61 (2): 027301. doi: 10.7498/aps.61.027301
HgCdTe-based metal-insulator-semiconductor field effect transistor is fabricated by low-cost liquid phase epitaxy technique. Clear SdH oscillation in xx and quantum Hall plateaus of xy are observed, indicating that it is a good transistor. By measuring the magnetoresistance near zero field, we observe the weak antilocalization effect in our sample, suggesting a relatively strong spin-orbit coupling. The experimental data can be well fitted by the ILP theory. The fitting-obtained spin-splitting energy increases with increasing electron concentration, and the maximum reaches up to 9.06 meV. From the obtained spin-splitting energy, we calculate the spin-orbit coupling parameter and find that it increases with increasing electron concentration, which is contrary to the observations in a wide quantum well.
2012, 61 (2): 027302. doi: 10.7498/aps.61.027302
Based on a three-dimensional self-consistent numerical model with consideration of electron scattering, trapping and transport, the charging effects due to low-energy defocused electron beam irradiation are simulated for a SiO2 thin film with a grounded conductive substrate. The results show that because of electron drift and diffusion, electrons can transit the electron scattering region, forming negative space charges. The space charge is, therefore, positive and negative within and outside the scattering region, respectively. Some electrons can flow to the conductive substrate, forming the leakage current, and the transient negative charging process tends to equilibrium as the leakage current increases. In comparison, the transient positive charging process approaches equilibrium with the number of returned electrons increasing due to the positive surface potential. In the equilibrium state, the surface potential of the film negatively charged decreases with film thickness and trap density increasing; it increases with electron mobility and dielectric constant. However, the equilibrium surface potential of the film positively charged varies slightly with film parameter.
Effect of internal stress on sructure, martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Mn2NiGa
2012, 61 (2): 027501. doi: 10.7498/aps.61.027501
The structures, the martensitic transformations and the magnetic properties of ferromagnetic shape memory alloy Mn2NiGa with the loading and the unloading of the external compressive stress are investigated. The plastic deformation occurring during the stressing causes a high level of dislocation defects existing in the sample. The residual internal stress results in a significant increase of the reversed transformation temperature. The threshold value of compressive pressure for causing the completely martensitic transformation at room temperature is identified to be 1.0 GPa based on the experimental measurements of XRD and magnetic coercivity. The coercivity of the martensitic phase increases from 50 Oe to 350 Oe due to the application of the external stress up to 2.0 GPa. It is also observed that the reversed martensitic transformation occurrs, when the sample is treated by heating up to about 730 K. This is attributed to the elimination of the dislocation by the annealing effect. Such a high reverse martensitic transformation temperature allows the measurement of the Curie temperature of martensitic phase and the obtained value is 530 K.
2012, 61 (2): 027502. doi: 10.7498/aps.61.027502
The KKR-CPA-LDA method was used to calculate the electronic and the magnetic structures of Fe2CrGa alloy. The results indicate that Fe2CrGa alloy prefers to crystallize in Hg2CuTi-type structure rather than L21 one. The analysis of density of states reveals that the intra-atomic exchange splitting affected by crystal field plays an important role in forming the Hg2CuTi-type structure. The molecular magnetic moments measured experimentally are in a range of 2.282.48B/f.u., which is very close to that expected theoretically by the calculations based on the Hg2CuTi-type structure, but not based on the L21 structure. The experimental results also show that the Curie temperature of Fe2CrGa alloy can be continuously manipulated from 308K to 445K by heat-treating under the various conditions, indicating a high sensitivity of the exchange interaction to the atomic ordering in this system.
2012, 61 (2): 027503. doi: 10.7498/aps.61.027503
Dilute magnetic semiconductors have auracted much attention because of their potential applications in spintronics. In this paper, the effects of oxygen vacancy on total energy and magnetism in Co-doped TiO2 are investigated using the density functional theory. The energy of the system with a shorter Co-Co distance is higher than that with larger Co-Co distance after introducing oxygen vacancy. Oxygen vacancy trends to congregate around the Co cations. Moreover, the strength of exchange couple reduces in the system with a shorter Co-Co distance after introducing oxygen vacancy. For the system with a larger Co-Co distance, the exchange couple between two Co impurities is anti-ferromagnetic if oxygen vacancy is located at the basal site of octahedron containing Co, and ferromagnetic if oxygen vacancy is located at the apical site of octahedron containing Co.
2012, 61 (2): 027504. doi: 10.7498/aps.61.027504
Arrays of FexCo1-x( 0 x 0.51) binary alloy nanowires are fabricated into the (anodic aluminum oxide) AAO template pores by AC electrodeposition. The XRD pattern indicates that the crystallite structure of Co nanowire is hcp with existence of strong (100) orientation along the nanowire axis. While the crystallites structure of FeCo binary alloy nanowires is bcc with existence of strong (110) orientation along the nanowire axes. The peaks shift toward the lower angle when the Fe content of nanowire increases. At room temperature, magnetic measurement results show that FeCo alloy nanowires exhibit excellent magnetic properties. The introduction of Fe improves the magnetic property of Co nanowire compared with that of the Co nanowire. FeCo binary alloy nanowire has a larger coercive force and squareness ratio. The coercivity of the FeCo alloy nanowire is calculated by using a magnetization reversal model based on chains of spheres with coherence rotation mechanism and symmetric fanning mechanism. The magnetization reversal mechanism is supported by chains of spheres with symmetric fanning mechanism.
Theoretical research of correlation of electronic structure with birefringence and anisotropy of TiO2
2012, 61 (2): 027801. doi: 10.7498/aps.61.027801
The crystal structure, the band structure, and the density of states of anatase TiO2 are analysed by using the plane-wave ultrasoft pseudopotential method of the first principles based on the density functional theory. Then we calculate optical properties such as dielectric function, energy loss function, photoconductivity systematically based on the results of electronic structure, and analyse the correlation of electronic structure with birefringence and anisotropy. The obtained results are consistent well with the reported results in the literature, revealing the natures of electronic structure of TiO2 and its birefringence as well as anisotropy theoretically.
One-step hydrothermal process for self-assembly of zinc oxide nanorods array on Al-doped ZnO nanoplate surface
2012, 61 (2): 027802. doi: 10.7498/aps.61.027802
Self-assembly ZnO nanorod array on Al-doped ZnO nanoplate surface is directly synthesized via a simple one-step hydrothermal approach, without using any template, surfactant or pretreated substrates. The morphology of the ZnO nanostructure observed by the scanning electron microscopy shows that the thickness and size of ZnO nanoplate are 200 nm and 2 m, respectively. The diameter and the length of ZnO nanorods are respectively 150 nm and 1.5 m. A possible growth mechanism is proposed for the selective growth of ZnO nanorods array on the nanoplate substrate, which contains two stage nucleation-growth processes. Finally, the influence of Al on the photoluminescence of the sample is been discussed.
2012, 61 (2): 027803. doi: 10.7498/aps.61.027803
The extinction spectra and the electric field distributions of the cross-shaped nanostructures are calculated by the discrete dipole approximation method. Compared with the individual nanorod, the cross-shape nanostructure can generate high local electric fields at the lateral surface. Because of the electric field couplings between adjacent protruding parts, much enhanced electric fields always occur at the lateral surface of the cross-shape nanostructure, with the incident polarization direction varied. In addition, the effects of the structural parameters of the cross-shape nanostructures on their plasmonic properties are also investigated. These results would guide the preparation of the cross-shape nanostructures for their applications in surface enhanced Raman scattering.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
A comparative study between MEAM and Tersoff potentials on the characteristics of melting and solidification of carborundum
2012, 61 (2): 028101. doi: 10.7498/aps.61.028101
Molecular dynamic simulations of bulk melting, surface melting and crystal growth of SiC are carried out. The atomic interactions in SiC are calculated by MEAM and Tersoff potentials separately. The results show that the bulk melting of SiC with MEAM potential exhibits its relations to temperature similar to that with Tersoff potential, while can be indicated by the mean atomic energy, Lindemann index and structure order parameter. The difference between them is the bulk melt point: MEAM is 4250 K, while Tersoff is 4750 K. At the same superheat degree, the velocities of surface melting of SiC separately, with MEAM and Tersoff potentials are in substantial agreement. But at the same absolute temperature, the surface melting of SiC with MEAM potential is faster than that which the Tersoff potential, which is due to the difference in thermodynamic melting point. The Measured value of the thermodynamic melting point of MEAM is 3338 K compared with 3430 K of Tersoff. On the crystal growth side, the crystal growth velocity of SiC with MEAM potential is related to the undercooling. The fastest velocity corresponds to the undercooling of 400 K. However, the crystal of SiC with Tersoff potential cannot grow in the undercooling of 0 K1000 K. Overall, the MEAM potential is better than Tersoff potential in the sense of describing the melting and solidification of carborundum.
2012, 61 (2): 028102. doi: 10.7498/aps.61.028102
In surface roughening of the growth process, the shadowing effect generated by non-normal incidence of particles is a kind of long-range interaction. It is found that the surface morphology and the bulk property in non-normal incidence are nontrivially affected by shadowing effect. In this paper, the effects of the oblique-incidence angle on scaling exponent, skewness and kurtosis in surface statistics and bulk porosity are investigated by simulating the oblique-incidence ballistic deposition model. The results illustrate that there are a non-monotonic relation between scaling exponents and oblique-incidence angle, and the finite size effects of skewness and kurtosis depend on oblique-incidence angle. The simulation results are also analyzed qualitatively in the paper.
2012, 61 (2): 028103. doi: 10.7498/aps.61.028103
Shape memory effect and superelasticity are studied in this paper. At room temperature, perfect strain plateaus of 3.3%, 2% and 3% are obtained in the ,  and  directions. The energies required to induce the martensitic transformation in different crystallographic directions are estimated from the stress-strain results. Each of the magnetization curves in the martensitic phase indicates that a magnetic anisotropy energy density Ku = (1/2)MsHa =4.8× 105 erg/cm3, which is far smaller than the mechanical driving force for variants twinning. This interpretes why only a little magnetic field induced strain in NiFeGa alloy has been observed so far.
Hydrogenated poly-crystalline silicon thin films deposited by inductively coupled plasma assisted pulsed dc twin magnetron sputtering
2012, 61 (2): 028104. doi: 10.7498/aps.61.028104
Hydrogenated poly-crystalline silicon thin films are deposited by inductively coupled plasma assisted pulsed dc twin magnetron sputtering at a temperature below 300 ℃. The samples are characterized by X-ray diffraction, Raman scattering, transmission electron microscopy, and Fourier transform infrared spectroscopy. The relationship between hydrogen dilution ratio and the characteristic of thin film is studied systematically. The mechanism of crystallization is discussed on the basis of the results of diagnosis of plasma by Langmuir probe and optical emission spectra.
Influence of gate voltage on gate-induced drain leakage current in ultra-thin gate oxide and ultra-short channel LDD nMOSFET's
2012, 61 (2): 028501. doi: 10.7498/aps.61.028501
The influence of gate voltage VG on gate induced drain leakage (GIDL) current is studied in LDD nMOSFET with a gate oxide of 1.4nm and a channel length of 100nm. It is found that the split phenomena of ln(Id/(VDG-1.2))-1/(VDG-1.2) curves under different VG values occurs, which are different from the large MOSFET. Through comparing varieties of ln(Id/(VDG-1.2)) of different VG values, the mechanism of this split phenomenon is obtained. This is ascribed to the change of the hole-tunneling part of GIDL current under different VG values. The absolute value of ln(Id/(VDG-1.2)) curve slope decrease with |VG| value decreasing . It is further found that the values of slope c and intercept d of ln(Id/(VDG-1.2)) curves are linear with VG and the slopes of c and d are 3.09 and -0.77, respectively. The values of c and d quantificationally show the influence of VG on the GIDL current in an ultra-thin ultra-short MOSFET. On the basis of these results, a new GIDL current model including VG is proposed.
2012, 61 (2): 028701. doi: 10.7498/aps.61.028701
Molecular dynamics simulation is used to study the friction of mixed Langmuir-Blodgett film composed of hydrocarboxylic acid (CnH2n+1COOH, n=12,13,14,15,16,17) and the C17H31COOH, in order to investigate the influence of the structure on friction. The results show that the restiction of long chain molecules by the neighbor molecules increases and the monolayers become more steady as n increases, while the shear pressure between the monolayers decreases and reaches a minimum when n=17. The hydrogen-bond formed in the mixed monolayers is the main reason why the monolayers become more steady, espatially,the hydrogen-bonds are most steady when n=16, but the monolayer composed that just of C17H31COOH molecules has the best sliding effect; there is no hydrogen-bond between the two monolayers. The shear pressure is hardly affected by the molecular deformation.
2012, 61 (2): 028801. doi: 10.7498/aps.61.028801
By analyzing engine decision of cognitive wireless network, the mathematical model of engine decision is given, and then it is converted into a multi-objective optimization problem. A Chaos quantum clonal algorithm is proposed to solve the problem, and the algorithm convergent with probability 1 is proved, in which the quantum coding and logistic mapping are used to initialize the population. A quantum mutation scheme is designed with chaotic disturbances. Finally, the simulation experiments are done to test the algorithm under a multi-carrier system. The results show that compared with QGA-CE (quantum genetic algorithm based cognitive engine), this algorithm has a good convergence and an objective function value. It can adapt the parameter configuration and meet the real-time requirement for cognitive engine.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2012, 61 (2): 029201. doi: 10.7498/aps.61.029201
In this paper, the soil moisture is simulated by RegCM3 over the Tibetan Plateau. The obtained results are as follows:(1) The simulated annual cycle of soil moisture is consistent with the observation, but the simulations of soil moisture with different land surface conditions are different. (2) In the area with sparse vegetation , the simulated soil moisture is larger than observation in summer and consistent with that in winter, while in the area with lush vegetation, simulated soil moisture is consistent with observation in summer and larger than that in winter. (3) The larger deviation of simulated soil moisture is corresponding to a large deviation of simulated precipitation and temperature.The soil moisture is revised with revised method, and the results show that the debiations of soil moisture and temperature are reduced. The systematic errors of temperature and precipitation are eliminated after revision. We believe that the revised soil moisture and temperature can provide more accurate data over Tibetan Plateau, and be used to calculate the permafrost distribution.
2012, 61 (2): 029202. doi: 10.7498/aps.61.029202
We construct a complex network of the middle latitude circulation system of north hemisphere (NCNH). The decadal characteristic of leading teleconnection and its probable correlation with abrupt climate change are analyzed base on the circulation system network. Results show that (1) action centres of NAO, EUPA and WP have all moved during different periods in the recent 40 years and there has been a common abrupt change process as the end of the 1970s and beginning of the 1990s separately; (2) the new index which denotes the importance of teleconnection is defined using the node degree of NCNH. The temporal change of new index shows that the leading modes were PNA, EUPA and WP before the 1980s; index of NAO notably increased and all the five teleconnections were comparatively robust after 1980s; the index of AO notably increased and other modes comparatively decreased after 1987. So, center and index changes of decadal leading teleconnections may be another important phenomenon of abrupt climate change.
2012, 61 (2): 029501. doi: 10.7498/aps.61.029501
In this paper we present an algorithm of computing two-dimensional (2D) stable and unstable manifolds of hyperbolic fixed points of nonlinear maps. The 2D manifold is computed by covering it with orbits of one-dimensional (1D) sub-manifolds. A generalized Foliation condition is proposed to measure the growth of 1D sub-manifolds and eventually control the growth of the 2D manifold along the orbits of 1D sub-manifolds in different directions. At the same time, a procedure for inserting 1D sub-manifolds between adjacent sub-manifolds is presented. The recursive procedure resolves the insertion of new mesh point, the searching for the image (or pre-image), and the computation of the 1D sub-manifolds following the new mesh point tactfully, which does not require the 1D sub-manifolds to be computed from the initial circle and avoids the over assembling of mesh points. The performance of the algorithm is demonstrated with hyper chaotic three-dimensional (3D) Hnon map and Lorenz system.
2012, 61 (2): 029502. doi: 10.7498/aps.61.029502
In order to improve the resolution of an imaging system and make the system as simple as possible, the wavefront sensing and the image post-processing using phase diversity are combined to form a new method, i.e., phase diversity hybrid method, in this paper. The performance of this method is simulated for a point source and also for an extended source. An experimental platform is built based on a point source. The experimental results demonstrate that the acceptable results cannot be achieved by using single post-processing for large aberration. The full width half maximum of the light spot descends from 5.1 pixels, 5.1 pixels, and 5.0 pixels which are corrected by adaptive optics to 3.3 pixels, 3.2 pixels, and 3.0 pixels respectively. We can see that the quality of the image processed by phase diversity hybrid method is much better than that restored by post-processing method or corrected by adaptive optics only. It has a great potential application in the filed of high resolution imaging.
2012, 61 (2): 029601. doi: 10.7498/aps.61.029601
The cumulated impacts of the space micro debris on the solar cells is experimentally simulated on the plasma dynamic accelerator in CSSAR. For a duration of ten years on the typical sun synchronous orbit, the solar cell functional degradation due to the micro impacts is measured, and the result accords well with the predicted result according to the impacting damage equation.