Vol. 62, No. 12 (2013)
2013-06-20
GENERAL
2013, 62 (12): 120101.
doi: 10.7498/aps.62.120101
Abstract +
In both PIN-type and NIP-type thin film silicon solar cells, textured light trapping substrates are used to enhance light absorption and improve energy conversion efficiencies. Scalar scattering theory is used to simulate the light trapping performance of textured substrates. The results indicate that in order to get good light trapping performance, the root mean square (RMS) for front reflectors in PIN-type solar cells should be at least 160 nm, while it is only 40 nm for back reflectors in NIP-type solar cells. A series of a-SiGe:H single-junction solar cells is deposited on back reflectors with different RMS values. It is found that a-SiGe:H solar cells deposited on back reflectors with RMS values of 40 and 61.5 nm demonstrate similar short current density values and quantum efficiencies. These results indicate that RMS value of 40 nm is enough to get good light trapping performance, which is consistent with the numerical simulation.
2013, 62 (12): 120201.
doi: 10.7498/aps.62.120201
Abstract +
Using an invariance of differential equations under the infinitesimal transformations of group, we study the Lie-Mei symmetry of Nielsen equations for a singular nonholonomic system of Chetaev'type. We establish the Lie-Mei symmetry equations. The definitions of weak and strong Lie-Mei symmetry are given, and Hojman conserved quantities and Mei conserved quantities are obtained. An example is given to illustrate the application of the results.
2013, 62 (12): 120202.
doi: 10.7498/aps.62.120202
Abstract +
Based on a kind of new Lie superalgebras, we introduce the general method of constructing the nonlinear integrable couplings of super soliton hierarchy. Super trace identity over the corresponding loop superalgebras is used to obtain the super Hamiltonian structures for the resulting nonlinear integrable couplings of the super soliton hierarchy. As an application, we give the nonlinear integrable couplings of super Kaup-Newell hierarchy and its super Hamiltonian structures. This method can be generalized to other super soliton hierarchy.
2013, 62 (12): 120203.
doi: 10.7498/aps.62.120203
Abstract +
Molecular dynamics simulation is performed to investigate the wetting behaviors of Pb droplet on Ni(100), Ni(110) and Ni(111) substrates. It has been shown that the wetting behavior of precursor film is isotropic for Pb droplet on Ni(100) and Ni(111) substrates, but anisotropic for Pb droplet on Ni(110) substrate. The demonstrated anisotropy is attributed to the differences in diffusion mechanism and rate along different crystal orientations for Pb atoms with corresponding anisotropic structure of the crystal lattice on Ni(110) substrate. The spreading dynamics of precursor film on different lattice surfaces are also investigated, which shows that there is no surface alloy formed for Pb droplet on Ni(111) surface and the spreading dynamics can be described by R2 t, but surface alloy forms for Pb droplet on Ni(100) and Ni(110) surface and the spreading dynamics satisfies R4 t, at the same time the spreading rate of droplet on Ni(100) is higher than that of Ni(110) substrate.
2013, 62 (12): 120301.
doi: 10.7498/aps.62.120301
Abstract +
In this paper, we theoretically study the relation between concurrence and nonlocality depicted by Bell-type inequality violation of quantum mechanics prediction versus local realism prediction for the GHZ (Greenberger -Horne-Zeilinger) class states. Analytical expressions of concurrence, violations of the Mermin inequality and the Svetlichny inequality are obtained. Through numerical calculations, the relationship between entanglement and nonlocality of GHZ-class states is discussed. Our results show that the concurrence is consistent with the degree of nonlocality described by violations of the two Bell-type inequalities of GHZ-class states. The Bell operator and its parameters can obviously reveal the nonlocal features of quantum states.
2013, 62 (12): 120501.
doi: 10.7498/aps.62.120501
Abstract +
In this paper, a class of topologically conjugated maps of tent map is established, and the sampling rule is proved to generate the independently and uniformly distributed key streams. One example is given to show that the established chaotic system does not converge into zero in each parameter due to its nonlinear characteristic. Another example with different initial values and lengths of sequence is illustrated, in which the chaotic key stream generated by the proposed theorem is independently and uniformly distributed chaotic system and can successfully satisfy the randomness requirements in Federal Information Processing Standard 140-2(FIPS PUB 140-2) and National Institute of Standards and Technology Special Publication 800-22 (NIST SP800-22) test. The result in this paper can provide the theoretical foundation and more selections of systems to generate independently and uniformly distributed chaotic key stream.
2013, 62 (12): 120502.
doi: 10.7498/aps.62.120502
Abstract +
A two-dimensional (2D) two-component and two-phase lattice Boltzmann method (LBM) with large density ratio is developed based on a modified Shan-Chen pseudopotential model combined with the deferent time step method. The present LBM model can simulate the gas-liquid two-phase flow with density ratio up to around 800. To validate the model, the pressure difference between the inside and outside of a bubble varying with its radius is simulated with different gas-liquid interact parameters and density ratios. The results are found to obey the Laplace law. Then, the LBM is coupled with the cellular automaton (CA) method used for simulating the solid phase growth, and the finite difference method (FDM) used for calculating the temperature field. The LBM-CA-FDM coupled model is used to simulate the interaction between bubble and the solidification interface. The results show that the existence of adiabatic bubble influences the distribution of temperature field in front of solidification interface, which leads to a bulge of the solid-liquid interface when it is close to the bubble. Under the conditions of different growth rates, the bubble is either engulfed or pushed away by the growing solid-liquid interface. The simulation results agree reasonably well with those observed experimentally.
2013, 62 (12): 120503.
doi: 10.7498/aps.62.120503
Abstract +
Based on fractional Langevin equation and random walk theory, a numerical algorithm that can be applied to non-Markov long-memory system is established in this paper. In addition, the evolution behaviour of random variable ruled by fractional sub-diffusion equation is numerically studied in three conditions: no dissipation, no fluctuation and both being present. The results show that competition exists between dissipation and fluctuation. As time goes by, the effect of Guassian fluctuation weakens and damping plays a main role in the evolution of system; however, because of the existance of "rare-though-dominant" events, long-tail fluctuation makes the evolution of system abrupt change at a certain probability.
2013, 62 (12): 120504.
doi: 10.7498/aps.62.120504
Abstract +
The mass of Brownian particle is fluctuant in a viscous medium, because the molecules of surrounding medium may randomly stick on it. This mass fluctuation influence on the system resonant behavior is studied by modeling it as a symmetric dichotomous noise. Using Shapiro-Loginov formula and Laplace transformation, the analytical expression of system steady response amplitude is presented. The corresponding numerical results are used to discuss system resonant behavior. Furthermore, the reliability of theoretical results is tested by simulation experiments. All the research results show that: 1) the system steady response is a simple harmonic vibration which has the same frequency as the driving signal; 2) with the variations of driving frequency, oscillator mass and noise parameters, the system presents real resonance, parameter induced resonance and stochastic resonance phenomenon, respectively; 3) because of the mass fluctuation, some new resonant forms are observed, such as one-peak and one-valley resonance, two-peak resonance, etc.
2013, 62 (12): 120505.
doi: 10.7498/aps.62.120505
Abstract +
A kind of one-degree-of-freedom nonlinear moving belt system is considered. The analytical research of sliding region and existence conditions of equilibrium are first derived by the theory of piecewise-smooth dynamical system. Then, using numerical method, one- or two-parameter continuation of several types of periodic orbits of the system is calculated. We obtain codimension-1 sliding bifurcation curves, codimension-2 sliding bifurcation points, and global bifurcation diagram in parameter space for the system. The investigation of bifurcation behavior shows that the speed of moving belt and amplitude of friction have a great influence on dynamic behavior, and reveals the complex nonlinear dynamic phenomenon of the moving belt system.
2013, 62 (12): 120506.
doi: 10.7498/aps.62.120506
Abstract +
Global property of a Duffing-van der Pol oscillator with two external periodic excitations is investigated by generalized cell mapping digraph method. As the bifurcation parameter varies, a chaotic transient appears in a regular boundary crisis. Two kinds of transient boundary crises are discovered to reveal some reasons for the discontinuous changes for domains of attraction and boundaries. A chaotic saddle collides with the stable manifold of a periodic saddle at the fractal boundary of domains when the crisis occurs, if the chaotic saddle lies in the basin of attraction, the basin of attraction decreases suddenly while the boundary increases after the crisis; if the chaotic saddle is at a boundary, the two boundaries merge into one because of the crisis. In addition, two chaotic saddles can be merged into a new one, when they touch each other in a transient merging crisis. Finally the chaotic transient disappears in an interior crisis. The characteristics of these generalized crises are quite important for the study of chaotic transients.
2013, 62 (12): 120507.
doi: 10.7498/aps.62.120507
Abstract +
Corresponding to two strange Lorenz attractors, in the Lorenz model there exist two opposite regimes which can be called as positive and negative regimes. Despite the trajectory of the Lorenz system changing between the two regimes back and forth with an unfixed period, the regime change is predictable. In this paper, with the help of the Lorenz map, three rules for predicting regime change are obtained. In particular, besides two generic predictable rules for the condition of regime transition and duration in new regime, a new rule about length for reaching transition condition, which has not been reported in previous work, is also very important. It provides another approach to forecasting the evolution of the nonlinear dynamical system. The results show that the position for highest point in cusps is the critical value for regime change. When the value of variable z is greater than the corresponding critical value, the current regime is about to end, and the Lorenz model will move to other regime in the next cycle. The length for reaching transition condition in the current regime decreases monotonically with local maximum value zmax, and the smaller zmax in current status implies the bigger length for reaching transition condition. The duration in new regime increases monotonically with the maximum value zM in the previous regime, and the bigger the value of zM, the larger the range for the duration increase is. In addition, the forcing is also associated with the prediction rules for regime change. It not only makes transition conditions for positive and negative regimes different, but also determines the speed of decrease in length for reaching transition condition and the range of increase for duration in new regime.
2013, 62 (12): 120508.
doi: 10.7498/aps.62.120508
Abstract +
The complex dynamics of the Logistic map via two types of periodic impulsive forces is investigated in this paper. With the parameter varying, the system produces the phenomenon such as equilibrium solutions, periodic solutions, and chaotic solutions. Furthermore the system can evolve into chaos by a cascading of period-doubling bifurcations. The Poincaré map of the Logistic map via periodic impulsive force is constructed and its bifurcation is analyzed. Finally, the Floquet theory is used to explore the bifurcation mechanism for the periodic solutions.
2013, 62 (12): 120509.
doi: 10.7498/aps.62.120509
Abstract +
For a class of continuous time different structure chaotic systems, due to the strong robustness and adaptability of active disturbance rejection controller (ADRC), we put forward a kind of the anti-synchronization of different structure chaotic systems with auto-disturbance-rejection control strategy. Because there are many parameters in ADRC and they are very difficult to set, in this paper we propose a chaotic particle swarm optimization algorithm to optimize the parameters of controller. Using Lorenz system and Chua system with different structures as an example to perform the simulation test, the results of the simulation verify that the proposed method can realize the anti-synchronization control of the different structure chaos systems faster and has a very strong anti-interference ability.
2013, 62 (12): 120510.
doi: 10.7498/aps.62.120510
Abstract +
Considering the problem that simply modifying the reservoir algorithm cannot significantly improve the prediction accuracy of chaotic multivariate time series, in this paper we propose a hybrid prediction model based on error correction. The observed data includes both linear and nonlinear features. First, we use autoregressive and moving average model to capture the linear features, then build a regularized echo state network to portray the dynamic nonlinear features. Finally, we add the predicted nonlinear value to the predicted linear value, in order to improve forecasting accuracy achieved by either of the models used separately. The experimental results of Lorenz and Sunspot-Runoff in the Yellow River time series demonstrate the effectiveness and characteristics of the proposed model herein.
2013, 62 (12): 120511.
doi: 10.7498/aps.62.120511
Abstract +
When the traditional strategy of sliding window (SW) deals with the flowing data, the data far from current position are mechanically and briefly moved out of the window, and the nearest ones are moved into the window. To solve the shortcomings of this forgetting mechanism, the strategy of filtering window (FW) is proposed, in which adopted is the mechanism for selecting the superior and eliminating the inferior, thus resulting in the data making more contributions to the will-built model to be kept in the window. Merging the filtering window with least squares support vector regression (LSSVR) yields the filtering window based LSSVR (FW-LSSVR for short). As opposed to traditional sliding window based LSSVR (SW-LSSVR for short), FW-LSSVR cuts down the computational complexity, and needs smaller window size to obtain the almost same prediction accuracy, thus suggesting the less computational burden and better real time. The experimental results on classical chaotic time series demonstrate the effectiveness and feasibility of the proposed FW-LSSVR.
2013, 62 (12): 120512.
doi: 10.7498/aps.62.120512
Abstract +
Multiscale multivariate sample entropy can test the multivariate complexity, which is accepted as a kind of reflection of nonlinear dynamical interactions in multichannel data. It is however relatively unstable due to the rigid ranking scheme used in comparison among different patterns. It is not applicable to the nonlinear and non-stationary data because the multiscale framework used is in fact handled by moving average succeeded by down-sampling, which actually has a premise of stationary data. We substitute a fuzzy membership function for the original rigid one and compare the performances of different kinds of fuzzy membership functions. In addition, we employ the multivariate empirical mode decomposition (MEMD) to capture different scales. Results show that the substitution of fuzzy membership function brings in significant stability. It is much more obvious by using the introduced physical fuzzy membership function (PFMF). Also MEMD could capture scales more robustly. In conclusion, the introduced PFMF- and MEMD-based MMFE perform best. Final analysis on the interactions between heart rate variability (HRV) and heart diastolic time interval variability (DIV) validates it. In addition, the results show that the multivariate complexity between HRV and DIV decreases in aging or heart failure group but in a distinctly different decreasing manner–it deceased at low scales with aging, indicating a loss of short-range correlation but both at low and high scales with heart failure, which shows the losses of both short- and long-range correlations. Studies in noninvasive detection of cardiovascular diseases should benefit from the above conclusions.
2013, 62 (12): 120513.
doi: 10.7498/aps.62.120513
Abstract +
In this paper we consider the issues of chaos synchronization and chaos-based secure communication when the so-called observer matching condition is not satisfied. An auxiliary drive signal vector is introduced such that the observer matching condition is satisfied. High-gain observers are employed to estimate the auxiliary drive signals as well as their derivatives in a finite time by using the drive signals of original system. Then, a kind of reduced-order observer is constructed which can directly eliminate the influence of the non-linear part and the disturbances of the system. Based on the estimates of states as well as the estimates of the auxiliary signals and their derivatives, a kind of message information recovery method is proposed. Finally, the Rössler chaotic system is used as a simulation example to verify the effectiveness of the proposed method.
2013, 62 (12): 120701.
doi: 10.7498/aps.62.120701
Abstract +
A new ultraviolet Raman lidar system is proposed and developed for detecting atmospheric water vapor and aerosol study. The combination of dichroic mirrors and narrow-band interference filters is used as high-performance spectroscopic system to obtain the fine-separation and high-efficiency extraction of Mie-Rayleigh scattering signals, the vibrational Raman scattering signal of H2O and N2. By the American standard model and a set of atmospheric scattering signal model, the signal-to-noise ratio (SNR) and the water vapor measurement error are simulated and analyzed. The preliminary experiments are carried out at nighttime in Xi'an area for detecting the atmospheric water vapor and aerosols. Taking a set of the atmospheric returned signals measured under cloudy weather for example, the profiles of atmospheric backscatter ratio and water vapor mixing ratio are retrieved, and the SNR profiles of the three channels are discussed and verify that this configuration can achieve a high rejection rate (10-7) to Mie-Rayleigh scattering. The theoretical and experimental results show that water vapor detection error of less than 15% can be obtained under a backscatter ratio of 17, which demonstrates the feasibility of the system for the atmospheric aerosol and water vapor measurements.
2013, 62 (12): 120702.
doi: 10.7498/aps.62.120702
Abstract +
The determination and mathematical descriptions of the difference between the imaging radiation measurement and the non-imaging radiation measurement which is of maturity are necessary for extending the radiation measurement from non-imaging technology to imaging technology. In this paper, the mathematical descriptions of the imaging and non-imaging radiation measurement are deduced based on the basic equations of radiation measurement and the correspondence between the infinitesimal planes of the target and sensor array. Because the imaging plane does not change the radiation transfer between the target and sensor, the mathematical descriptions of the imaging effect can be obtained by comparing the two mathematical descriptions. A concrete analysis of the imaging effect based on pinhole imaging and lens imaging is carried out. The results show that the primary cause of the imaging effect is the imaging optical axis angle while the subsidiary cause is the imaging zenith angle, and the influence of the subsidiary cause is determined by the difference between the imaging optical axis angle and the imaging zenith angle.
2013, 62 (12): 120703.
doi: 10.7498/aps.62.120703
Abstract +
Based on surface-wave oscillator (SWO), the high power 0.34 THz source using over-moded structure is studied. The attention is paid to the influence of the parameters of the slow-wave structure (SWS) on the dispersion curve, and then the SWS is optimized. According to the simulation results, the size of SWS and the requirements for the accuracy in the SWS machining are confirmed. Finally, the source is simulated by the particle-in-cell method. Numerical results show that the structure is capable of radiating a terahertz signal with a frequency of 0.34 THz and a maximum output power of about 7.8 MW. Moreover, the structure works in the state of an SWO stably. The research of the SWS is the foundation of the design of 0.34 THz source, and it is also very meaningful for the realization of the source in engineering.
2013, 62 (12): 120704.
doi: 10.7498/aps.62.120704
Abstract +
Among many terahertz wave generation methods, nonlinear optical collinear difference frequency generation (CDFG) is always regarded as a promising way to achieve the high power, broadband, continual tunable terahertz wave emission. Theoretical analysis shows that a big coherent length (on millimeter scale) in isotropic GaP crystal could be realized by the laser wavelength near 1064 nm in the CDFG process, which meets the condition of high power and broadband terahertz generation. In the experiment, a high power and broadband terahertz wave is achieved from GaP crystal, with its tunable terahertz range 95.9-773.4 μm (0.39-3.13 THz) and the highest terahertz peak power 7 W at 2 THz. The experimental result is generally consistent well with its theoretical calculation.
NUCLEAR PHYSICS
2013, 62 (12): 122801.
doi: 10.7498/aps.62.122801
Abstract +
Compact accelerator based neutron source has lower cost and better flexibility than nuclear reactor. Neutron imaging using such a neutron source has attracted more and more attention in recent years, in spite of its relatively low neutron fluence. In order to keep a definite neutron flux above a reasonable level on a compact accelerator based neutron imaging system, one could not set the collimation ratio to be as high as the reactor neutron source to obtain a high resolution. Coded source could increase the collimation ratio without reducing the neutron flux much. It may benefit neutron imaging system in the case of low yield neutron source. Since 2005, several laboratories in Germany and USA have carried out simulation and experiments of coded source neutron imaging. Those experiments are based on the reactor neutron sources, which have high neutron yield and low scattered neutron background. Recently, a preliminary coded source neutron imaging experiment was carried out on PKUNIFTY (Peking University Neutron Imaging Facility), which is based on a 2 MeV deuteron RFQ accelerator. It is the first time that coded source neutron imaging has been applied to an accelerator-based neutron source. Projections of coded neutron source are taken with a neutron yield of 2.6×1011 s-1. With Wiener filter deconvolution and Lucy-Richardson maximum likelihood iteration algorithm, the experimental projections are reconstructed successfully. Because the accumulated neutron fluence is low and the neutron background is high, the signal-to-noise ratio of reconstructed images is not good enough, which will be improved by reducing the neutron background.
2013, 62 (12): 122901.
doi: 10.7498/aps.62.122901
Abstract +
With the continuous development of the micro-structure of gas detectors, many different new detection requirements have been proposed. For more stable working time, lower discharge rate with long term and high effective gain, a new structure detector has been designed. Combined with the detection's advantages of MicroMegas and gas electron multiplier (GEM), it is composed of a MicroMagas chamber with one GEM foil as preamplifier. In this paper, the structure of the detector and detection principle are presented in detail. Using a 55Fe X-ray radioactive source in the operation mixtures gas of argon and isobutene (Ar/Iso =95/5), the performances of the detector gain, discharge rate, energy resolution and stable working time are investigated. Compared with standard MicroMegas detectors with no GEM foil, our detector show that a stable working time could reach more than 30 h of continuous work, the gain of the detector could exceed 106 and the discharge rate could be reduced by nearly 100 times at the same gain.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (12): 123101.
doi: 10.7498/aps.62.123101
Abstract +
The first-principles density-functional theoretical calculations are performed to investigate the effects of N doped and N, M (Cd, Mg) codoped on the geometrical structures and field emission properties of capped (9, 0) zinc oxide nanotubes (ZnONT). The results show that the N could improve the stability of the structure of capped side. With the increase of the applied electric field, the density of states (DOS) shifts towards the low energy position, the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap and the effective work function decrease drastically, and the electrons congregate to the capped side. The analyses of DOS/local DOS, HOMO/LUMO, and Mulliken population indicate that the field emission properties of N, Cd-Codoped ZnONT are improved, but those of N, Mg-codoped ZnONT are worsened.
2013, 62 (12): 123201.
doi: 10.7498/aps.62.123201
Abstract +
The photodetached electron flux of H- in magnetic field near a metal surface is studied with a semi-classical open theory, and the relation between the electron flux distribution and classical trajectory is also revealed. The electron flux distributions are calculated at various magnetic field strengths, with a ion-surface distance given. The results show that with the increase of magnetic field strength, the interference pattern in the flux distribution becomes much more complicated because the number of the classical trajectories of the detached electrons contributing to the electron flux distribution increases. In addition, we find that as the energy of detached electron changes, the detached-electron flux distribution changes accordingly. Therefore, the interference pattern in the detached-electron flux distribution can be controlled by adjusting the magnetic field strength and the energy of detached electron. Our study will provide a new understanding of photo-detachment microscopy of anion in external field and surface, and can be used to guide the future experimental research on the anion photo-detachment microscopy.
2013, 62 (12): 123202.
doi: 10.7498/aps.62.123202
Abstract +
As a powerful tool to deal with multi-electron dynamics in strong laser field, multi-configuration time-dependent Hartree Fock (MCTDHF) method has attracted great attention. In this paper, the strategy of the implement of the MCTDHF theory is illustrated in the paper in detail. We develop three types of Fortran source soft packages based on three different bases to study correlated dynamics of atoms and molecules in strong laser field. The calculated soft-packages based on the theory are introduced in detail. The calculations are performed by using the soft-package. The prospect of the MCTDHF approach to simulating the multi-electron dynamics in strong laser field are also presented.
2013, 62 (12): 123301.
doi: 10.7498/aps.62.123301
Abstract +
The Voigt profile function which is the convolution of the Doppler and Lorentzian function is investigated analytically and its maximum is obtained. The results indicate that the maximum of the Voigt profile function is smaller than maxima of Doppler and Lorentzian profile function, which is determined by the half-widths of Doppler and Lorentzian profile function. The Voigt profile function is a symmetric function about the central frequency. A new technique is presented, with which the Doppler and Lorentzian profile function can be obtained by using the maximum and half-width of the Voigt profile function, and the technique is verified by the Monte Carlo method.
2013, 62 (12): 123302.
doi: 10.7498/aps.62.123302
Abstract +
Combining the time-dependent density functional theory with molecular dynamics of ions the excitation of the carbon wire C5 is explored. It is found that the stronger the laser intensity, the more energies are absorbed by C5 and the earlier the ionization takes place and the more electrons are emitted when considering the effect of the laser intensity on the excitation of the carbon wire C5. The study of the influence of the polarization of the laser pulse on the excitation of C5 indicates that the ionization is enhanced and the dipole moment along the laser polarization is strengthened when the laser polarization is along the molecular axis, and the x-direction polarized laser pulse can only excite the dipole oscillation along the x axis, and the y-direction polarized one can only excite Dy. Furthermore, it is found that the synchronicity of the vibration of carbon bonds changes a little due to the enhanced ionization when the laser polarization is along the molecular axis, while the vibration modes of ionized carbon wire C5 are the same as those of the neutral carbon wire C5.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (12): 124101.
doi: 10.7498/aps.62.124101
Abstract +
In order to reduce the radar cross section (RCS) of antenna, a wideband-enhanced ultra-thin metamaterial absorber is designed by reducing the distance between the two absorption peaks due to the double resonances. The absorber is composed of two metallic layers separated by a lossy dielectric spacer. The top layer consists of a single-square loop with four splits on the four sides and a square metal patch in the center and the bottom one is of a solid metal. A dipole resonance and an LC resonance are caused by the structure of the metamaterial absorber. By fine adjusting geometry parameters of the structure, we can obtain a polarization-insensitive and wide-incident-angle ultra-thin absorber whose absorption values are 91.6% and 96.5%. On condition that thickness is less than 0.01λ the absorber has a full-width at half-maximum of 8.2%. The absorber is applied to the circularly polarized tilted beam antenna for reducing RCS. Simulated and experimented results show that the RCS reduction of antenna is above 3 dB within the operation band from 5.5 GHz to 6.5 GHz, the gain is not changed and the bandwidth is increased due to the improvement of axial ratio. At the resonance, the most reduction values exceed 8 dBsm and 11 dBsm while the absorber has a good characteristic of RCS reduction at the boresight direction from -36° to +36°.
2013, 62 (12): 124102.
doi: 10.7498/aps.62.124102
Abstract +
Bandgap properties of one-dimensional superconducting photonic crystals containing metamaterials are investigated by the transfer matrix method. It is shown that the low-frequency band gap can also be present in this superconducting photonic crystal similar to the usual superconducting photonic crystal containing dielectric materials. The low-frequency band gap can be widened considerably when the suitable structure parameters are chosen. However, in certain structural parameters, the low-frequency band gap can not be found in this superconducting photonic crystal just as in one-dimensional dielectric-dielectric photonic crystal. The polarization properties and the influences of the operating temperature and the structure parameters of superconducting photonic crystals on the photonic band gap are also investigated in this paper.
EDITOR'S SUGGESTION
2013, 62 (12): 124201.
doi: 10.7498/aps.62.124201
Abstract +
Double helix point spread function possesses continuously rotating invariant features with defocus, and it can be used for performing nano-resolution image of thick samples and for studying singleparticle tracking by combining the single-molecule localization method. However, the inadequacy of the original double helix point spread function is that the transfer function efficiency is very low, so it is difficult to achieve photon limited applications for the bio-imaging. The double-helix point spread function is optimized by introducing an iterative algorithm so that the constraints of the point spread function can be optimized best in three different domains: the Laguerre-Gauss modal plane, the spatial domain, and the Fourier domain. The simulation results show that the peak intensity of high efficiency double helix point spread function is 30 times higher than the original one. The design and fabrication of the phase plate are also proposed. The experimental results are in good agreement with the theoretical predictions, thus proving the feasibility of this method.
EDITOR'S SUGGESTION
2013, 62 (12): 124202.
doi: 10.7498/aps.62.124202
Abstract +
Sample information-extracting with diffraction enhanced imaging (DEI) has been one of the interesting areas for many years. Using cosine curve to fit rocking curve in DEI, we deduce the equations described by cosine functions for peak-position image, low- and high-angle image. The analytical expressions of absorption image, refractive angle image and scattering image are also developed. Then a simple method is proposed for sample information-extracting with DEI based on those deductions. This method can extract the absorption information, refractive angle information and scattering information of a sample using only three images, i.e. one peak-position, one low-angle image and on high-angle image, resulting in simple experimental process and low radiation dose introduced to sample by imaging process. The experiments are carried out on a standard sample and a real biological sample. For comparison, experiments are also carried out on the same two samples using the common multiple-image radiography (MIR) method, in which at least seven images should be used to extract sample information. Experimental results show that our new method does extract sample information successfully, and the results from our new method are comparable to those from the MIR method.
2013, 62 (12): 124203.
doi: 10.7498/aps.62.124203
Abstract +
There are two sampling models of digital hologram in digital holographic research. The complex mathematical operation is involved in these two models, thereby leading to different results frequently and inconvenient theoretical analysis and practical application. Based on the analysis of physical processes in recording digital hologram and the study on geometry structure of CCD detector, the two sampling models are simplified into the same mathematical expression in this paper. Through studying the simplified model with cosine series expansion of digital hologram and sampling theorem, it is shown that the model has clear physical meanings and can be used for application study conveniently. Using the simplified model, we study digital holographic recording system with optical system and exact wavefront reconstruction expression verified in experiment.
2013, 62 (12): 124204.
doi: 10.7498/aps.62.124204
Abstract +
For the non-uniform pumping and cooling to the thin disk-type laser medium, the district cooling method for thin disk-type laser medium is proposed and examined both experimentally and theoretically. Based on heat conduction equation, the distributions of temperature and stress in end pumping thin disk-type laser medium with evenly cooling and district cooling are calculated. The results show that the tensile stresses on the edge of gain medium with evenly cooling are changed into the low values of compressive stresses for the case of district cooling, and the distribution of temperature in medium with district cooling is much more uniform than with evenly cooling, the ranges of temperature reduces about 86%, and this result is consistent well with the experimental result. The district cooling method could provide a new way of thermal management for thin disk-type laser.
2013, 62 (12): 124205.
doi: 10.7498/aps.62.124205
Abstract +
Based on the approach of mode decomposition, the influence of the longitudinal shift of the entrance plane on the propagation properties of beams in strongly nonlocal nonlinear medium is analyzed. The shift of the entrance plane changes the order and the longitudinal position of beam patterns in a period, the size of patterns, and the radius of the cophasal surface. These properties can be described with a simple mathematical equation, therefore the beam solution after the entrance plane is shifted can be easily obtained from that before the entrance plane is shifted.
2013, 62 (12): 124206.
doi: 10.7498/aps.62.124206
Abstract +
The concentration of carbon dioxide in the atmosphere has been increasing continuously. This is a big concern with respect to the environment and climate changes and so on. A kind of ground-based low-resolution remote sensing system and a real-time spectral inversion method are presented for the real-time remote sensing column concentration of carbon dioxide. Based on continuous observation of this system in Hefei, the total atmospheric transmittance is real-timely obtained from the solar absorption spectrum. The column concentrations of carbon dioxide and oxygen are inversed from total atmospheric transmittance by line-by-line nonlinear least squares spectral inversion algorithm. The column concentration of oxygen is used as internal standard function to obtain the column average volume mixing ratio of carbon dioxide in total dry air column, and the precision is better than 3%.The average volume mixing ratio of carbon dioxide in dry-air column, from 12: 00 to 15:00 on September 25, 2012, is compared with observation results by Japanese greenhouse-gases satellite over the site in this period, showing that the relative deviation is less than 1%. Obviously, it is an effective way to measure greenhouse gases concentration with high precision and accuracy.
2013, 62 (12): 124207.
doi: 10.7498/aps.62.124207
Abstract +
A fiber-optic surface plasmon resonance sensor (SPR) based on tapered structure probe is studied. The incentive mode of tapered probe calculated by finite-difference time-domain method serves as design references, and the tapered structure of sensor probe fabricated by polishing and grinding at the end of a fiber is similar to Kretschmann prism SPR model, which can realize the modulation of SPR wave. The results show that in the refractive index detection range from 1.3330 to 1.4215, tapered structure FO-SPR sensor has a sensitivity of 1-6 times higher than common FO-SPR sensor and it still keeps a limiting resolution level of 10-5 RIU. The designed tapered structure SPR sensor, which has the advantages of tapered incentive mode, design flexibility, user practical applicability, simple preparation process, a relatively small sample need, and high stability, will fulfill different environment and measuring conditions of biochemical testing and environment monitoring.
2013, 62 (12): 124208.
doi: 10.7498/aps.62.124208
Abstract +
Theoretical and experimental studies of stimulated Raman spectrum with the D1 line of an 85Rb atomic vapor system are performed. In this Λ-type system, we discover that the influence of the pump on the probe field includes two parts: stimulated Raman excitation and optical pumping. Depending on the pump frequency detuning and field intensity conditions, the Raman spectrum can display either gain or loss. When the optically pumped absorption spectrum is taken as background, either a narrow transparent window or an absorption doublet with widely different linewidths appears. Our theoretical analysis agrees well with our experimental observations. Based on these studies, we present an interpretation from a new viewpoint of the physics of electromagnetically induced transparency (with on-resonance pumping) and Autler-Townes splitting (with far off-resonance pumping) in a Λ-type level atomic system, giving the relationship between these two important phenomena and the Raman spectrum.
2013, 62 (12): 124301.
doi: 10.7498/aps.62.124301
Abstract +
The active triple sound insulation structure using planar loudspeaker as the secondary actuator can be easily implemented and has better sound insulation performance in the low frequency range. The key problem encountered when implementing such a control system is to sense the error signal which should be highly correlated with the radiated sound power. In this paper, the theory of sensing the radiation modes of simply supported beam using polyvinylidene fluoride (PVDF) arrays used in one-dimensional case is extended to two-dimensional structure, and then it is used in triple panel structure to optimally design the error sensing strategy. Based on the specific rule of sound energy transmission through triple panel structure, some key problems encountered in realizing the sensing system such as selection of the objective function, optimization of the number of PVDFs and implementing the sensing system, are analyzed thoroughly. The results obtained demonstrate that due to the fact that the majority of vibrating energy of radiated panel is stored in several limited number of panel modes, the amplitude of the first three order radiation modes can be obtained by simply summing the limited number of weighted PVDF film current output. And the weighted coefficient is fixed. The amplitudes of the radiation modes sensed by the proposed method are in good agreement with the theoretical value. The sensing accuracy of the error sensing system can be guaranteed, and this approach highly simplify the implementation of the error sensing system.
2013, 62 (12): 124302.
doi: 10.7498/aps.62.124302
Abstract +
The traditional measurements for environmental noise exposure-dose are inapplicable to the sound samples with fixed playing duration used in subjective evaluation experiment. In this paper, we propose a method for exposure-dose measurement of sound samples with fixed duration. The method based on the short-term exposure-dose values during the playing time of the sound samples. An entire analysis on the potential influencing factors are carried out, including the short-term analysis period, the statistical properties of the short-term exposure-dose values and four different frequency weightings. Then 11 indices are used to measure the exposure-dose of the fixed duration sound sample, which lays the groundwork for establishing the dose-annoyance relationships via subjective evaluating experiments.
2013, 62 (12): 124401.
doi: 10.7498/aps.62.124401
Abstract +
Spherical ZnO nanoparticles each with a uniform size are synthesized by a hydrothermal method. These ZnO nanoparticles are then dispersed into water by ultrasonic vibrating to form stable nanofluids. The electrical conductivity of water-based ZnO nanofluids with a variety of temperature and volumetric fractions are investigated. The volumetric-fraction-dependent thermal conductivity is also measured at room temperature. Experiments indicate that the electrical conductivity of ZnO nanofluid reveals a non-linear relationship versus volumetric fraction. However, it presents a quasi linear relationship versus temperature. The thermal conductivity is enhanced nearly linearly with volumetric fraction increasing. Moreover, a modified model is established based on Maxwell thermal conductivity model and Brownian dynamics theory by considering boundary adsorption layer, aggregation and Brownian motion of nanoparticles in the fluid. The expected thermal conductivity values based on the modified model are in good agreement with our experimental data, suggesting that our modified model might be more accurately adapted to the nanofluids thermal conductivity.
2013, 62 (12): 124701.
doi: 10.7498/aps.62.124701
Abstract +
macromolecular solutions under Poiseuille flow in microchannels are investigated using the dissipative particle dynamics (DPD) approach. The results show that the macromolecular solutions are non-Newtonian fluids which can be described by power-law fluids, and the power-law index decreases with the increase of the macromolecular concentration. The DPD simulations show that the hydrodynamic interaction between the macromolecular chains and the wall, and the gradient of Brownian diffusivity of the chains govern the cross-stream migration of the macromolecules. However, the chain-wall hydrodynamic interaction may not be fully developed and are partly screened in conventional DPD approach. Hence, the chains migrate toward the wall during flow. Simulation results also indicate that the migration toward the wall increases with the increase of the driving force. The competition between the unscreened chain-wall hydrodynamic interaction and Brownian diffusivity leads to two symmetric off-center peaks and a local minimum in the channel centerline in the chain center-of-mass distribution. Under strong confinement, the chain-wall hydrodynamic interaction may be fully screened and the Brownian motion is weak, thus the chains weakly move toward the wall for channel of small width.
2013, 62 (12): 124702.
doi: 10.7498/aps.62.124702
Abstract +
A projection-based incompressible smooth particle hydrodynamics (ISPH) is applied to the simulation of the deformation process of viscous liquid drop. In our numerical computation, the particle shifting technique is used to overcome particle clustering due to the tensile instability in SPH. In order to verify the proposed ISPH, numerical simulations of a viscous circle drop stretching and a viscous square drop rotating are carried out. The pressure distribution in the drop is obtained, and the deformation process of viscous liquid drop is correctly captured. Comparisons between numerical results and the analytical solutions in the literature are presented. The simulation results show that the projection-based ISPH with particle shifting technique can be used to simulate the deformation process of viscous liquid drop with stability and accuracy.
2013, 62 (12): 124703.
doi: 10.7498/aps.62.124703
Abstract +
In this paper, we investigate the streamer discharge process in transformer oil under positive nanosecond pulse voltage through developing a two-dimensional axially symmetric fluid model and simulating the physics of discharge inception and propagation. The streamer discharge profile and distributions of electric field and space charge density are obtained under different conditions such as the amplitude of applied voltage, rise time and gap distance. Simulation results show that space charges enhance the front field of streamer head, which is conducive to the longer propagation of discharge channel, therefore "ionization wave" is formed. The magnitude and rise time of applied voltage have evident influences on the average speed of streamer propagation. It can be observed that the higher the applied impulse voltage, the faster the streamer propagates, and the steeper the rise time of applied impulse, when streamer arrives at the same position, the larger the discharging radius will be and the smaller maximal electric field will be. The cases of different gap distances indicate that longer gap distance corresponds to a faster average speed of streamer. It is considered that field-dependent molecular ionization predominates the charge generation mechanism of streamer discharge process in transformer oil, and space charge effect contributes to further developing ionization until the whole gap eventually breakdowns. The study is dedicated to the better understanding of the process from inception to breakdown of discharging in transformer oil, as well as ionization mechanism in liquid dielectric.
2013, 62 (12): 124704.
doi: 10.7498/aps.62.124704
Abstract +
Under potential flow assumption, a numerical method is established to simulate the nonlinear movement of the free surface after the breakup of a bubble, with taking the surface tension and viscous into consideration. A method to handle the splitting of the jet or drop is put forward. Besides, an experiment of rising bubble bursting at the free surface is conducted, and the numerical result is in good agreement with the experimental result. In order to study the mechanism and law of the free surface movement after bubble breakup, the dynamic behavior of different sizes of bubble breakup is studied with the program developed, including the jet from the bottom of the bubble, the splitting of the jet or drop and so on. The variation law of the size and time of the first splitting drop, and the maximum velocity of the jet is studied and summarized. Finally, the influences of Reynolds number and Weber number on the free surface after bubble breakup are also analyzed.
2013, 62 (12): 124705.
doi: 10.7498/aps.62.124705
Abstract +
The flow in microchannel involves many microscale effects, because of its large ratio of superficial area to volume. And it further causes the density profiles of flow in microchannel to be greatly different from in the macro-channel. In this paper we investigate the effects of three factors (εLL, σLL, σLS) on density profile of micro-flow via the Poiseuille flow in a nanochannel using none-equilibrium molecular dynamics simulation method. In our study, we selected NVE as the statical ensemble, LJ/126 model as the potential energy function. We also adopt the Rigid-atom model to describe the wall and the temperature thermostat through using the time/rescale methods. The motion equations are solved using Verlet algorithm. The results show that as the interaction between flow atoms decreases, the oscillation degree of density profiles near the wall increases. The balance distance (σLL) between flow atoms affects the existence state and density profiles of flow in the micro channel: the greater σLL causes the flow atoms to be arranged as the fcc structure liking a solid, while smaller σLL results in the flow atoms moving as a changeable "cluster". The balance distance (σLS) between wall atoms and flow atoms also has a significant influence on flow density. As σLS increases, the oscillation degrees of density profile near the wall and the distance between the starting point of density profile and wall increase. Besides, we analyze the mechanism of effects of the interaction between the flow atoms on density distribution based on the "capture-escape " behavior of atoms adjoining the wall.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (12): 125201.
doi: 10.7498/aps.62.125201
Abstract +
The quantitative analysis models of multiple linear regression, neural network regression and support vector machine regression with laser-induced breakdown spectroscopy are established in this paper. Heavy metal Ni in water selected as research object is tested and comparativly analyzed. The average relative standard deviations of multiple linear regression, neural network regression and support vector machine regression are 7.60%, 4.86% and 2.35%, and the maximum standard deviations are 23.35%, 15.20% and 8.29% respectively, the average relative errors are 25.98%, 10.58% and 2.72%, and the maximum relative errors are 116.47%, 47.38% and 9.89% respectively. Methods and reference data are provided for the further study of fast measurement of tracing heavy metals in water by laser induced breakdown spectroscopy technique.
2013, 62 (12): 125202.
doi: 10.7498/aps.62.125202
Abstract +
The high-precise opacity of the dense plasma has important applications in the design and simulation of fusion research, and in plasma diagnostics. Base on the novel technique of point-projection backlighting, a broadband high-resolution elliptical crystal X-ray spectrometer, which is used to measure simultaneously the self-emission spectrum, the backlighting source spectrum, and the transmission spectrum in one shot, is designed on the Shengguang-II laser facility. The process of the colliding-shock-compressed sample by laser-driven shock waves is also investigated using a one-dimensional radiation hydrodynamics code MULTI. In the measurement, the dense plasma, produced in aluminum by colliding shocks driven by laser beams, reaches a peak density several times that of a solid, and the short backlighting from the 3d-4f transition bands of ytterbium is used as an absorption source for time- and space-resolving diagnostics. Several experimental results are obtained, they are the X-ray source spectrum, the transmission spectrum, and the self-emission spectrum of the dense Al sample in one shot obtained by using the point-projection method, as well as X-ray-absorption fine-structure spectra, and the changes in the K-shell photo-absorption edge of aluminum as it was compressed by a laser-driven shock waves. The transmissivity distribution and red- shift around 80 m (with respect to the cold value of 1.56 keV) of the dense aluminum are also obtained. The data obtained are further analysed. As a result, a new theoretical model is developed.
2013, 62 (12): 125203.
doi: 10.7498/aps.62.125203
Abstract +
Traditional implosion backlight imaging experiment has disadvantages of nonuniform X-ray source, low contrast ablator interface and high requirement for diagnostic device tuning precision. A novel design of multi-point X-ray source combined with phase contrast imaging developed and optimized based on experimental research performed on Shenguang-II facility is presented. The novel design can obtain high-quality experimental result with uniform X-ray source, clear interface between ablator and inner DD gas and large image view. At the same time, the new design using diagnostic silt instead of diagnostic hole improves tuning precision. The experimental result proposes that novel design of laser driven plasma point x-ray source combined with phase contrast imaging has advantage of area X-ray source combined with absorb imaging and can be widely used in inertial confinement fusion and high energy density physics.
2013, 62 (12): 125204.
doi: 10.7498/aps.62.125204
Abstract +
In this paper, a 0.14 THz relativistic backward-wave oscillator (RBWO) filled with neutral argon gas is simulated by using the UNIPIC code. The effects of plasma on the output power, frequency, and the start-oscillation time of the RBWO filled with different-pressure gases are studied. The simulation result shows that the background plasma can cause the pulse-shortening and new frequency appearing in the 0.14 THz RBWO. Appropriate plasma infusion can reduce the start-oscillation time and increase the output power of 0.14 THz RBWO.
2013, 62 (12): 125205.
doi: 10.7498/aps.62.125205
Abstract +
In this paper we study the effects of transverse profile of incident laser on trapping of electrons in an electron bow-wave injection regime. By using the particle-in-cell code, we find that the super-gaussian profile laser pulse can drive more energetic electrons of the electron bow-wave into the bubble with higher longitudinal injection velocity. At last, the total number of trapped electrons increases almost 5 times. And the quality of electron beam is also improved obviously.
2013, 62 (12): 125206.
doi: 10.7498/aps.62.125206
Abstract +
By one-dimensional particle-in-cell simulations, the relativistic electron sheets generated by interaction between the ultra-relativistic intense laser pulse with intensity above 1022 W/cm2 and the thin foil target, as well as the attosecond X-ray pulses induced by Thomson backscattering from electron bunch are studied in this paper. The results indicate that increasing the intensity of the driving laser, reducing the density and thickness of foil target corresponding make the longitudinal momentum of the electrons enhanced and the wavelength of X-ray radiation reduced. Attosecond X-ray pulse with wavelength 1.168 nm can be obtained through optimizing correlated parameters. Especially, using probing laser pulse with doubling frequency and optimizing parameters of the drive light and thin film target can make the wavelength of coherent attosecond X-ray radiation reduced obviously, even below 0.4 nm, and the energy of the scattered photons can achieve more than 2 keV.
2013, 62 (12): 125207.
doi: 10.7498/aps.62.125207
Abstract +
Based on the Joule heating effect of gas discharge in the working process of the plasma actuator, the plasma synthetic jet is simulated with a three-dimensional phenomenological model, under the assumption of local thermodynamic equilibrium plasma.The flow field evolution process of the plasma synthetic jet during a whole cycle is obtained. The results show that in the self-sustained periodical jet built by a single energy deposition, there is a maxium pulse frequency–saturated frequency which could relaize that the cavity is recovered sufficiently. Large energy deposition, small exit orifice diameter and high diameter-height ratio with the same cavity volume could induce higher speed jet, and the increase of the jet speed occurs concurrently with the decrease of the saturated frequency. During a saturated cycle, up to 16% of the mass in the cacity is expelled, but the recovery can only achieve about 90% of the initial mass in the cavity. Plasma synthetic jet actuator is supplied by a capacitive power supply at atmospheric pressure, the fractions of power that go into gas heating and jet kinetic energy are 5% and 1.6% respectively.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (12): 126101.
doi: 10.7498/aps.62.126101
Abstract +
In this paper, we have examined the thermal stability of Pt-Au core-shell nanoparticle by using molecular dynamics simulations with embedded-atom potential. The results show that the melting point of Pt-Au core-shell nanoparticle is significantly higher than that of pure Au one but lower than that of Pt one. By the analyses of Lindemann index, it is discovered that the melting first occurs in Au shell, then spreads into interior, finally the overall melting of Pt core appears. The temperature range of melting is much broader for Pt-Au core-shell nanoparticle than for Au and Pt nanoparticles. Moreover, Pt-Au core-shell nanoparticle exhibits a distinct two-stage melting during continuous heating, and the structure of solid (core)-liquid (shell) coexistence has been observed between two meltings.
2013, 62 (12): 126801.
doi: 10.7498/aps.62.126801
Abstract +
Silicon-rich silicon nitride (SiNx) thin films are deposited at 220 ℃ on n-type monocrystalline silicon substrates by plasma enhanced chemical vapor deposition using NH3 and SiH4 as the reaction gases. The samples are annealed at temperature in a range of 500-1100 ℃ in N2 atmosphere. We analyze the crystalline states of silicon quantum dots (Si-QDs) and calculate the crystalline ratios of samples under different annealing conditions according to the Raman spectra. The crystalline ratio is less than 18% when the annealing temperature is lower than 950 ℃, when the temperature reaches 1100 ℃, the crystalline ratio is increased to 53%, which indicates that most of the Si-QDs have been converted into crystallines. Fourier transform infrared spectra are measured at room temperature to investigate the evolutions of the bonding structures within the SiN_x matrix. We find that the wavelengths of Si-N and Si-H bond shift toward higher wavelength, which manifests the formation of near stoichiometric silicon nitride. Photoluminescence generated from all samples is investigated in detail. We find five luminescence peaks, whose origins are analyzed. We conclude that the obvious green luminescence (centred at 500-550 nm) oringinates from Si-QDs and the others come from different defects in the films. The effects of sizes and distribution of Si-QDs on the shift of the luminescence peak are discussed. We acquire that the sizes of Si-QDs are in a rang from 1.6 nm to 3 nm, which have an obvious confinement effect. These results are useful for fabricating contronllable Si-QDs and achievement of luminescent devices based on Si-QDs.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (12): 127101.
doi: 10.7498/aps.62.127101
Abstract +
The geometrical structures, electronic structures, densities of states and optical properties of undoped ZnO, and Yb2+- and Yb3+-doped ZnO are calculated based on the first-principles density function theory pseudopotential method. The calculated results show that the system exhibits lower energy and better stability after the ytterbium incorporation, and a new localized band appears between the valance and conduct. The ytterbium with different valences has different influences on the electronic structure and optical properties. The imaginary parts of dielectric function of Yb2+- and Yb3+-doped ZnO both exhibit a new peak of 0.46 eV compared with that of undoped ZnO, Their static dielectric constants increase obviously, the absorption band edges are shifted toward the longer wavelengths, and strong absorption peaks appear at 0.91 eV. The reason for the phenomena is also discussed in this paper.
2013, 62 (12): 127102.
doi: 10.7498/aps.62.127102
Abstract +
The gate capacitance-voltage (C-V) characteristic of strained SiGe pMOSFET is very different from that of bulk Si pMOSFET, and can be strongly affected by the channel doping. In this paper, we first study the formation mechanism of the "plateau" which can be observed in the gate C-V characteristics of strained SiGe pMOSFET, and then present a physics based analytical model to predict the gate C-V characteristic of strained SiGe pMOSFET. It is found that this plateau is channel doping dependent. The results from the model are compared with the experimental results and they are found to be in excellent agreement with each other, giving the evidence for its validity.
2013, 62 (12): 127301.
doi: 10.7498/aps.62.127301
Abstract +
The surface relaxations, band structures, densities of states and surface energies of BiOCl{001} surfaces containing {001}-1Cl, {001}-BiO and {001}-2Cl are studied using first-principles based on density functional theory. The calculated results indicate that there exist obvious relaxations for the three types of {001} surfaces, especially for their double chlorine layers. The relaxation result of {001}-1Cl surface is the minimum one in the BiOCl{001} surfaces. Compared with the electronic structure of bulk BiOCl, BiOCl{001} surfaces exhibit the smaller band gap and stronger localized energy levels. Besides, both conduction and valence band of {001}-BiO shift towards the lower energy and there exist surface states at the bottom of conduction band. For {001}-2Cl, surface states are located at the top of valence band. The occurrences of these surface states can lead to the obvious reductions of band gaps for {001}-BiO and {001}-2Cl. Furthermore, the surface energy of BiOCl{001} is calculated and investigated. The analysis results show that surface energies of {001}-1Cl, {001}-BiO and {001}-2Cl are 0.09206 J·m-2, 2.392 J·m-2 and 2.461 J·m-2, respectively. Thus the {001}-1Cl possesses the minimum surface energy and the highest stability, while {001}-BiO and {001}-2Cl exhibit the higher reaction activities and are difficult to be exposed in the growth process of BiOCl crystal. Our obtained results provide the theoretical guidance for the further understanding of the facet-dependent photoreactivity of BiOCl, the fine manipulation of their photoreactivity, and the progress of actual application for BiOCl photocatalytic material.
2013, 62 (12): 127302.
doi: 10.7498/aps.62.127302
Abstract +
The non-resonantly enhanced optical transmission phenomenon of sub-wavelength metallic slits on a thin film is significant for broadband light harvesting devices. To improve the efficiency of transmission, in this paper, we propose a compound structure of the tapered metallic slit embedded with rectangular cavity, and its optical properties are investigated by the finite element method. The results show that the compound structure leads to a higher transmission than the tapered metallic slit without rectangular cavity. In addition, the effects of the structure parameters and the position of the rectangular cavity on the transmission property are also studied. These results would be helpful for designing metallic slits with high transmission.
EDITOR'S SUGGESTION
2013, 62 (12): 127401.
doi: 10.7498/aps.62.127401
Abstract +
We fabricate MgB2 ultra-thin films via hybrid physics-chemical vapor deposition technique (HPCVD). Under the same background pressure, the same H2 flow rate and the same deposition time, by changing the B2H6 flow rate, we fabricate a series of ultra-thin films with thickness values ranging from 10 nm to 40 nm. These films grow on MgO(111) substrate, and are all c-axis epitaxial. These films show the good connectivity, a very high Tc(0) ≈ 35-38 K and a very low residual resistivity ρ(42 K) ≈ 1.8-20.3 μΩ·cm-1. As the thickness increases, critical transition temperature also increases and the residual resistivity decreases. The 20 nm film also shows an extremely high critical current density Jc (0 T, 5 K) ≈ 2.3×107 A/cm2, which indicates that the films fabricated by HPCVD are well qualified for device applications.
2013, 62 (12): 127501.
doi: 10.7498/aps.62.127501
Abstract +
In this paper, we systematically investigate the dynamics of non-magnetic spheres (polystyrene spheres) and magnetic nanoparticles dispersed in Fe3O4 magnetic colloid under an externally applied magnetic field. It is found that the polystyrene spheres form chain-like structures when the direction of magnetic field is parallel to the sample cell. The whole dynamic process of polystyrene spheres in the magnetic field can be characterized by a fast interaction between polystyrene spheres and magnetic nanoparticles and a slow interaction among polystyrene chain-like structures respectively. When a magnetic field is applied in the direction perpendicular to the sample cell, polystyrene spheres can be assembled into a short-range ordered two-dimensional structure due to the repulsive interaction among polystyrene spheres. Once the applied magnetic field excesses a critical level, a flower-shaped complex structure can be formed due to the attractive interaction between the polystyrene sphere and the magnetic cluster.
2013, 62 (12): 127502.
doi: 10.7498/aps.62.127502
Abstract +
The study on magnetoelectric effect in hexagonal perovskite structure HoMnO3 has become a very important aspect in the research of multiferroic materials. In this paper, using the first principles based on the generalized gradient approximation of density functional theory and considering the noncollinear magnetic structure calculation, the effects of the interation between on-site Coulomb of d electron and spin-orbit coupling on the electronic density of states and energy band structure of HoMnO3 are calculated and investigated. The calculations show that due to the on-site Coulomb interaction, the strong hybridization of Ho 5d with O(3, 4) 2p and Mn 3d with O(1, 2) 2p orbits are considered as the origin of driving force for the ferroelectric distortion. At the same time, the distributions of the energy gap and energy band provide a theoretical support for the explanation of strong optical absorption peak in experiment. In addition, the spin-orbit coupling makes the orbital hybridization of Mn 3d with O(3, 4) 2p within the ab plane strengthened, and the partial energy degeneracy in the ab plane is eliminated. The HoMnO3 is shown to possess the insulator characteristics of typical indirect energy gap.
2013, 62 (12): 127701.
doi: 10.7498/aps.62.127701
Abstract +
Based on reversion motion of dipoles in ferroelectrics under the electric field in the random field Ising model, the relationship between electric field and polarization in order-disorder transition is investigated, and the function tanh(x) for the electric field in order-disorder transition is coincident with the experimental relationship between electric field and polarization in the second order ferroelectric transition. Therefore, increases in polarization and internal poling field are due to the collective motion of dipoles, where electric field and temperature are critical in the polarization and Gibbs free energy. By distinguishing the contributions between optic mode and polarization portion with a gaussian-type distribution of Curie-temperature, and considering a complex dispersion form of dielectric permittivity contributed by dipoles, the relationships between dielectric permittivity and temperature, as well as frequency, are derived.
2013, 62 (12): 127801.
doi: 10.7498/aps.62.127801
Abstract +
Using a polycarbonate membrane (PCM) as a template, and combining with the electrochemical deposition method, we prepare gold nanorods each with about 36 nm in diameter and 1 μrm in length. We measure transmission spectra, and find that the resonant absorption peak is at around 540 nm. Subsequently, the enhancement effects of the nanorods are investigated with 514 nm and 633 nm laser excitations. Comparing the spectra under resonant condition with those under non-resonant condition, we conclude that the field enhancement effect under the resonant excitation is more prominent than under the non-resonant excitation. The enhancement factor under the resonant excitation is increased to 7 times of the factor under the non-resonant excitation. Comparing with similar researches, we achieve the following two improvements: 1) with a resonant excitation, we significantly increase the enhancement factor of gold nanorods; 2) we eliminate the fluorescence of PCM molecules, thus make the template method more feasible for transparent surface-enhanced Raman scattering substrate applications.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (12): 128101.
doi: 10.7498/aps.62.128101
Abstract +
An analytical bond-order potential based on Tersoff-Brenner model for Sn is developed using the Levenberg-Marquardt optimization algorithm with the first-principles calculations on fundamental physical properties of five configurations of Sn, and with the available experimental results. The potential is used to determine the crystal structures, binding energies, bond distances and strengths, and bulk modulus of the β-Sn and body-centered-tetragonal Sn, and to predict the changes in free energy of the α and β phase with temperature. Result indicate that the calculated basic properties of the phases and the predicted transition temperature from α to β phase are in good agreement with the reported experimental data. The proposed interatomic potential is short-ranged and quickly evaluated, and it could be used to distinguish covalent bond from metallic bond in the phases, so it is very useful for large-scale molecular dynamics simulations of Sn-based solder.
2013, 62 (12): 128201.
doi: 10.7498/aps.62.128201
Abstract +
The interaction between two spiral waves in two-layer excitable medium coupled indirectly through a passive medium and with time-delayed coupling is investigated by using the Bär model. The numerical results show that time-delayed coupling can either facilitate the synchronization of two spiral waves or lead to the transition from spiral wave to collective oscillation, different target waves, spatiotemporal chaos or rest state. Period-2 and period-3 spiral waves and the meander or drift of spiral wave are observed in the coupled excitable medium. The physical mechanism underlying these phenomena is discussed.
2013, 62 (12): 128501.
doi: 10.7498/aps.62.128501
Abstract +
By analyzing the variations of the internal distributions of the temperature with time and the current density and the burnout time with the signal amplitude, we study the internal damage process and mechanism of the typical silicon-based n+-p-n-n+ structure bipolar transistor induced by three kinds of high power microwaves such as triangular wave, sinusoidal wave and square wave. The results show that the base-emitter junction is the damage position and the device is more susceptible to damage under the injection of the square waves. The displacement current and the burnout time increase but the proportion of the displacement current in the total current decreases with signal amplitude increasing. The injected power plays a determinative role in the damage process compared with the displacement current. Adopting the data analysis software, the relation equation between the burnout time t and the signal frequency f is obtained. It is demonstrated that the burnout time increases with signal frequency increasing, and the equations of the three kinds of high power microwaves all agree with the formula t= afb.
2013, 62 (12): 128801.
doi: 10.7498/aps.62.128801
Abstract +
According to single-walled carbon nanotube good conductivity, baryon transmission performance, and high photoelectric conversion performance of quantum dot composite material, in this letter, we use in situ condensation method to prepare polymer/poly (2-methoxy, 5-oc-toxy)-1, 4-phenylenevinylene (MOPPV)-single walled carbon nanotubes/PbSe quantum dot composites and use X-ray diffraction, transmission electron microscope, UV-vis absorption spectroscopy to study their characteristics. The results indicate that MOPPV, SWNT and PbSe quantum dots can be effectively combined, especially the SWNT and MOPPV form a network structure in MOPPV matrix, and PbSe quantum dots, each with an average size of 5.75 nm, can be dispersed to form a coating or mosaic structure in the polymer substrate of MOPPV-SWNT, producing the light induced charge transfer phenomenon. The study of composite photoelectric performance shows that when the polymer MOPPV, SWNT, PbSe have their mass ratio of 1: 0.3: 1, the composite photoelectric performance is best: open circuit voltage is 0.556 V, short circuit current is 2.133 mA, fill factor is 34.48%, conversion efficiency is 0.452%. Compared with the polymer MOPPV-PbSe quantum dots composite materials, the optoelectronic properties are increased by 2-3 times.
2013, 62 (12): 128802.
doi: 10.7498/aps.62.128802
Abstract +
An adaptive resource allocation algorithm is proposed for the adaptive resource allocation problem of orthogonal frequency division multiple access, in which a novel subcarrier and power allocation algorithms based on fish swarm algorithm are proposed. Subcarrier allocation is first implemented on condition that the m total power is distributed uniformly on each subcarrier. The fish swarm algorithm is then used to fulfill power allocation through the global search ,including a fitness function of the user's fairness and system capacity. Computer simulation results show that the proposed algorithm not only guarantees user fairness but also achieves maximal system capacity.
2013, 62 (12): 128803.
doi: 10.7498/aps.62.128803
Abstract +
Organic solar cell (OSC) with an inverted structure based on subphthalocyanine (SubPc)/C60 is fabricated by using Cs2CO3, graphene:Cs2CO3 mixed system and ZnO nanoparticles as cathode modifying materials, and its influences on the performance and stability of OSC are investigated. The results show that the OSC with an appropriate thickness of cathode modifying layer exhibits higher performance and it is more stable than those unmodified ones. The power conversion efficiency (PCE) of the Cs2CO3 and graphene:Cs2CO3 mixed material modified device is enhanced by a factor of two. Meanwhile, the ZnO nanoparticle modified device shows a highest open-circuit voltage (VOC) of 0.89 V, and the PCE increases more than 4 times. Besides, the adoptions of different cathode modifying materials and the inverted structures can effectively prevent the series resistance of the device from increasing, thereby improving the stability of the device.
2013, 62 (12): 128901.
doi: 10.7498/aps.62.128901
Abstract +
The node importance measurement plays an important role in analyzing the robustness of the network. Most researchers use the degree or clustering coefficient to measure the node importance. However, the degree can only take into account the neighbor size, regardless of the clustering property of the neighbors. The clustering coefficient could only measure the closeness among the neighbors and neglect the activity of the target node. In this paper, we present a new method to measure the node importance by combining neighbor and clustering coefficient information. The robustness results measured by the network efficiency through removing the important nodes for the US Air network, the power grid of the western United States and Barabasi-Albert networks show that the new method can more accurately evaluate the node importance than the degree, neighbor information and k-shell indices.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (12): 129201.
doi: 10.7498/aps.62.129201
Abstract +
This paper focuses on the mechanism of the trend and oscillation in precipitation records in northwestern China over the past 60 years. The results from regression and orthogonal wavelet decomposition show a clearly ascending in annual precipitation since 2000, which is contributed mostly by significant increase in autumn and winter precipitations, while almost no trend can be identified in spring and summer time, which shows a weak descending in non-linear form. This may be in connection with different warming rates in seasons. There is a significant anti-correlation between the precipitation and the North Atlantic oscillation (NAO) on the inter-annual scale. About 80% of their variances concentrate on inter-annual and multi-decadal scales. The multi-decadal components of NAO index have a phase leading about 10 years to corresponding precipitation, about 4-5 years leg for AMO. Hence, NAO index can be used as an indicator for inter-decadal change of the precipitation. Other results from combination-difference analysis show that the NAO in extreme negative phase could lead to the precipitation increase in central Asia and northwestern China, owing to increase in eastward water-vapor transport from south Europe to Northwestern China, which causes an increase in column water vapor content in the above areas, and meanwhile the transient eddy activity becomes intensified in the areas or north with a further south route moving from Europe, Central Asia throughout northwestern China. On the contrary, a dry climate might appear in the areas when meet extreme positive phase of NAO. Thus, NAO's oscillation is one of the most important mechanisms for inter-annual change in precipitation of northwestern China.
2013, 62 (12): 129202.
doi: 10.7498/aps.62.129202
Abstract +
In order to realize the fusion of altimeter wind speed and radiometer wind speed, the Kriging method is used to interpolate radiometer wind speed to the altimeter path to obtain the altimeter wind speed observation operator, a cost function is established, and then the variational method is adopted to construct and analyze wind speed and derive fusion results. Simulation tests are carried out when only altimeter wind speed contains error, only radiometer wind speed contains error, both altimeter and radiometer wind speed contain error. The results show that through the variational fusion, the accuracy is improved, especially in the altimeter path. The Jason-1 altimeter cycle 241 wind speed data and spatial temporally matched Special Sensor Microwave Imager Sounder wind speed data (carried by Defense Meteorological Satellite Program F17) are selected to carry out the real test, and the results show that the fused wind speed is more close to the buoy observation, so it is confirmed that the variational fusion method is effective, statics shows that 60% altimeter and radiometer data matched, which means that fusion is an important theory and has application value. The variational fusion method can be applied to the fusion of HY-2 satellite altimeter and radiometer wind inversion results.
2013, 62 (12): 129203.
doi: 10.7498/aps.62.129203
Abstract +
By the transfer entropy method, in this article we analyze the transfer of information between x, y, z component of Lorenz system and Walker circulation with temperature difference and vertical velocity. It is found that y is the information source and x is the information sink between x and y component of Lorenz system, also y is the information source and z is the information sink between x and z component. But the direction of information transfer depends on the control parameter r between x and z component, even if the direction of information transfer between x, y and z component of Lorenz system does not vary when the initial value changes. In western Pacific, the information transfers from the temperature difference to the vertical velocity, while the information transfers from the vertical velocity to the temperature difference in the eastern equatorial Pacific, which is consistent with the physical mechanism of Walker circulation. And land-sea thermal plays an important role in the information transfer between temperature difference and vertical velocity. In winter, the information transfer between temperature difference and vertical velocity is strongest, in summer and autumn it is weaker, and in spring it is weakest, which may be the reasons of spring predictability barrier. These results suggest that transfer entropy is proved to be an effective method and tool of measuring the transfer direction of the kinetic system information, and has broad application prospects in the field of meteorology.
2013, 62 (12): 129204.
doi: 10.7498/aps.62.129204
Abstract +
Lyapunov exponent is an important physical quantity indicating a system is in regular motion or in chaotic motion. In view of this, in this paper, we use the Lyapunov exponent to study the chaotic properties of the system, and the mutations in climate. The results show that the Lyapunov exponent is a reliable mutation detection method. For the ideal sequence or actual atmosphere sequence the method can be used to accurately find out the mutation position; the predictability of nonlinear local Lyapunov exponent is used to evidence the reliability of the early warning signals of abrupt climate change based on the phenomenon of critical slowing down, through calculating the largest Lyapunov exponent of each time the system intrinsic properties can be reflected and the chaos characteristics can be studied, thereby providing a theoretical basis for the wide applications of the present method in real observation data.
2013, 62 (12): 129701.
doi: 10.7498/aps.62.129701
Abstract +
BL Lacertae object OJ 287 is one of the Blazars, which shows convincing evidence of periodic variations. We have collected the 4.8, 8.0 and 14.5 GHz data for OJ 287 from the University of Michigan Radio Observatory database over three decades. Due to the complexity of the variability data, some algorithms for period searching are not ideal yet. An alternative to traditional periodicity analysis is the ensemble empirical mode decomposition (EEMD). This method can analyze the cyclic components of complicated nonlinear and non-stationary processes. Using the EEMD analysis, the light curve of OJ 287 at radio frequency can be resolved into six independent intrinsic mode functions that have different average periods and trends. We find possible periods of 18.9, 11.9, 5.7 and 2.4 years in 4.8 GHz, 12.2 , 5.2 and 2.4 years in 8.0 GHz and 21.8, 12.0, 4.3 and 2.4 years in 14.5 GHz. The most common periods are 12.0 years and 2.4 years, which imply that the emissions in these bands may originate from the same radiative process. The results also confirm that a radio variability period of OJ 287 is in agreement with the optical variability period of about 12.0 years. The result shows that the components of different variability periods can be separated properly with the EEMD that is a nonlinear and non-stationary signal processing method.
2013, 62 (12): 129702.
doi: 10.7498/aps.62.129702
Abstract +
As an autonomous navigation method, X-ray pulsar navigation can provide position, timing and attitude information for various spacecrafts. Since the X-rays (1-20 keV) from the pulsar can not penetrate the earth atmosphere, an X-ray source in laboratory needs to be set up to test and calibrate the detector. In this paper an arbitrary X-ray pulse source to simulate the neutron pulsar signal is proposed. The main components of the simulation source are a grid controlled X-ray tube and arbitrary pulse generation electronics. With the arbitrary pulse voltage applied to the tube grid, the X-ray intensity is controlled. Through electron optics design, the tube electrode parameters are optimized. A grid controlled X-ray tube is fabricated and tested. Using a micro-channel plate detector to detect and reconstruct the generated X-ray pulses, the similarity between the accumulated profile and the original pulsar profile is better than 95%. The frequency stability of the pulsar source emulator is about 2×10-11.
