Vol. 62, No. 16 (2013)
Conformal invariance and conserved quantity of Mei symmetry for Appell equations in holonomic system
2013, 62 (16): 160201. doi: 10.7498/aps.62.160201
For a holonomic system, the conformal invariance and conserved quantity of Mei symmetry for Appell equations are studied. Firstly, by the infinitesimal one-parameter transformation group and the infinitesimal generator vector, we define Mei symmetry and conformal invariance of differential equations of motion for holonomic system, and the determining equation of Mei symmetry and conformal invariance for holonomic system are given. Then, taking advantage of a structure equation that gauge function satisfies, the system corresponding Mei conserved quantity is derived. Finally, an example is given to illustrate the application of the result.
Hopf bifurcation and the problem of periodic solutions in a recharge-discharge oscillator model for El Niño and southern oscillation with time delay
2013, 62 (16): 160202. doi: 10.7498/aps.62.160202
In this paper, a recharge-discharge oscillator model for El Niño and southern oscillation with time delay is investigated. We obtain the critical time delay associated with Hopf bifurcation, and discuss the problem of periodic solutions for the model by using Maehin’s continuation theorem.
2013, 62 (16): 160203. doi: 10.7498/aps.62.160203
In this paper, using the modified Clarkson-Kruskal direct method, the symmetries and the reductions of (2+1) dimensional Broer-Kau-Kupe-rshmidt (BKK) are obtained. At the same time, a great many of solutions are derived by solving the reduction equations, including the rational functions hyperbolic functions, the trigonometric functions, the power series solution, and the Airy function solution.
Recent experiments about the circuit cavity quantum electrodynamics have realized the ultrastrong couplings between the artificial atom and the photon, in which the coupling strengths have the same order of the photon frequency. In such a regime, the well-known rotating wave approximation is invalid, and the system dynamics is thus governed by the Rabi model. In this paper, we investigate the photon squeezing of the Rabi model. We find numerically that with the increase of the atom-photon coupling strength, the photon squeezing does not increase linearly, but displays a maximum in the ultrastrong coupling regime. In addition, we also reveal that the photonsqueezing can be enhanced by the counter-rotating terms of the Rabi model. Our results are of benefit to preparing the required squeezing state of the photon in experiment.
Quantum voting protocols based on the non-symmetric quantum channel with controlled quantum operation teleportation
2013, 62 (16): 160302. doi: 10.7498/aps.62.160302
In the paper, we present a kind of quantum voting protocol, which is based on controlled quantum teleportation of local unitary operations in non-symmetric quantum channel. In this protocol, the umpire CA with zero knowledge proof quantum identity authentication ensures voter’s anonymous identity authentication. The counting institution Bob generates a high-dimensional Greenberger-Horne-Zeilinger entangled state to establish a high-dimensional quantum communication channel. Performing the local unitary operation on their low-dimensional quantum ballot, voter’s quantum vote is teleportated by asymmetric matrix measurement and scrutineer Charlie auxiliary measuring. With the scrutineer Charlie’s help, Bob achieves the voting result by the output of unitary operation. Compared with other general quantum operation teleportation quantum voting protocol, the protocol utilizes the quantum information and transmission of quantum channel, which have different dimensions, so single particle information cannot be stolen, and can prevent forgery. The electoral process is fair and undeniable, owing to Charlie’s supervision. Since the success probability of quantum teleportation of local unitary operations is 1, the quantum voting is reliable.
2013, 62 (16): 160303. doi: 10.7498/aps.62.160303
In this paper, we study the self-trapping of a Bose-Fermi mixture in a periodic modulation field by adjusting fermionic number and interaction parameter in a double-well potential. We find that the self-trapping of bosons can be affected by interatomic self-interaction and interspecific interaction parameter. Moreover, we notice that the self-trapping of bosons gives rise to a critical phenomenon with the variation of interaction strength and fermionic number.
2013, 62 (16): 160401. doi: 10.7498/aps.62.160401
In this paper, we use the wave equation of charged mass point to prove the existence of magnetic monopole. And according to Rubakov-Callan model there could be a lot of magnetic monopoles in neutron stars. Then using the structure equation of neutron stars we obtain upper limit and lower limit of mass-radius ratio for magnetic charged neutron star.
2013, 62 (16): 160501. doi: 10.7498/aps.62.160501
The two inductor current boundaries are derived, and segmented smooth iteration mapping model of current controlled quadratic boost converter is established based on the detailed description of switching states. The comparative analyses of the nonlinear bifurcation behaviors are performed with input inductor current and the storage inductor current as current feedback respectively. Two boundary conditions for the transition from stable period-one state to sub-harmonic oscillation state and for the transition from discontinuous conduction mode to continuous conduction mode are derived by analyzing stability and operation mode. The operation-state regions corresponding to circuit parameter regions are estimated by utilizing the parameter-space maps. An experimental circuit is built and the results show that both different bifurcation routes and operation mode transition phenomenon are changed with parameter variation, the current controlled quadratic boost converter exhibits complicated dynamical behaviors. The experimental results verify the correctness of the theoretical analysis.
2013, 62 (16): 160502. doi: 10.7498/aps.62.160502
Many real excitable systems can be descibed as inhomogeneous media, where the inhomogeneity is an important factor for the formation of spiral waves and the changing of their dynamics. In this paper, we investigate the effect of excitability obstacles on spiral-wave dynamics. For an excitability-reduced obstacle, the neighbor spiral tip is attracted into the obstacle. When more localized obstacles are placed, the attactive case depends on the distribution, size and excitability of the obstcales. On the basis of analyzing the small-value area of the inhibitor variable, we illustrate the mechanism of these behaviors occuring. For an excitability-enhanced obstacle, the nearby spiral tip is repelled. The tip motion after the repelsive effect depends on the type of the initial spiral wave, i.e. rigidily rotating spiral wave or meandering spiral wave. In the present of more localized obstacles, there exist different behaviors for different distributions, sizes and excitabilities of the obstcales, and different types of initial waves.
2013, 62 (16): 160503. doi: 10.7498/aps.62.160503
For fault prognosis of rotating machinery under variable operation, a fault tracking method based on phase space warping and smooth orthogonal decomposition (SOD) is presented to describe the degradation process of rotating machinery. Firstly, phase space is reconstructed using vibration time-series, and a tracking function of damage evolution is built by quantifying phase space warping. To compensate for cumulative model error and the error caused by variation of local probability distribution of the reference phase space points, the original time-series is partitioned into several data segments and the phase space is partitioned into several subspaces correspondingly. Several feature vectors are concatenated into tracking matrix. Secondly, the different trends caused by actual damage degradation and operation variety in the tracking matrix are separated by smooth orthogonal decomposition. According to smooth orthogonal values, dominant smooth orthogonal coordinates which reflect actual fault degradation trends are extracted. Finally, fault degradation process of bearing out-race is simulated. Rotating speed is varied during the degradation process. Applying the presented method to the degradation process tracking, the tracking matrix is built and decomposed by SOD, and the results show that the proposed method can track the evolution trend of the rotating machinery fault without the influence of operation condition variety.
2013, 62 (16): 162801. doi: 10.7498/aps.62.162801
Polarized neutron radiography allows the direct and real-space visualization of magnetic field distribution by detecting the polarization change in the transmitted beam. Spin polarizer/analyzer apparatus is important in polarized neutron imaging system, whose polarization efficiency directly affects the imaging quality of magnetic field. In this paper, the relation between the registered neutron intensity and magnetic field distribution is re-calculated after introducing the polarization efficiency parameter. Bender polarizers and 3He spin filters are simulated by Monte Carlo software VITESS to verify the calculation. The quantification ability with low beam polarization is also analyzed by considering the beam monochromaticity and bender geometry. The results will be helpful for processing image data and designing instrument.
Accurate Rutherford backscattering spectrocsopy measurement of aluminium composition in AlxGa1-xN crystal film
2013, 62 (16): 162901. doi: 10.7498/aps.62.162901
The AlxGa1-xN epitaxial film is grown on (0001)-oriented sapphire with a 20 nm thick aluminium nitride buffer layer by metal organic chemical vapor deposition. The thickness of AlxGa1-xN layer with high crystal quality is about 2 μrm determined by ultraviolet visible light transmittance spectrum analysis. The homogeneity of aluminium in AlxGa1-xN epitaxial film is tested through the energy Eg at the peak intensity in the deep ultraviolet photoluminescence spectrum. The epitaxial wafer with good homogeneity is used to determine aluminium composition by Rutherford backscattering spectroscopy (RBS). Six samples are measured by tow ion beam analysis laboratories, and the experimental data of RBS random spectrum are simulated by the software. The source of measurement uncertainty is analyzed including the sample homogeneity, pileup correction and counting statistics and so on. The research results show that when the alpha particle is used as incident ion, with 2000 keV energy and 165° scattering angle, the measurement uncertainty of RBS for the determination of aluminium composition (x=0.8) is 2.0% and the coverage factor k=2.
Application of mean value theorem of integrals in the efficiency callibration technology of radioactive xeon sample
2013, 62 (16): 162902. doi: 10.7498/aps.62.162902
The radioxenon from environmental samples is usually measured by the HPGe detector. The relative measurement method is used in the analysis process. However, the half-life of radioactive isotopes of xenon is too short to be used as a standard, so the calibration of the HPGe detector is difficult. In order to resolve this problem, the mixed disk sources are used to simulate the efficiencies of four radioactive xenon isotopes, and the mean value theorem of integrals is adopted, thereby improving the accuracy and simplifying the process. The samples are obtained by the xenon system under environment of high activity of radon, then the γ spectrum with regions of interest for 133Xe are obtained by the sample measurement. The activity of 133Xe is given by using the detection efficiency of disk source at a certain source-detector distance. The detection efficiency simulated by disk source is consistent with the detection efficiency of gas cell. Therefore, the simulated technology of disk source and mean value theorem of integrals are identified to be correct and effective.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (16): 163101. doi: 10.7498/aps.62.163101
According to ab initio calculations, the differential scattering cross sections between He and HF, HCl, HBr are calculated and compared with experimental data. The results show that the calculation method can calculate comparatively accurate interactional potential. As halogen atom radius increases, at 0°, the minimum of interactional potential shallows, the position of potential well moves into the distance, and anisotropic property becomes prominent, while at 180°, the minimum of interactional potential depens, the position of potential well moves into the distance, and the isotropic property becomes obvious. The potential well depth under T structure is larger than that of linear structure. With the increases of halogen atoms radius, a more spherical symmetry is exhibited, and it can be seen obviously that contributions of radial coefficients V0, V1, V2, V3, ··· decrease gradually, which is important to understand the study of excited state dynamics.
2013, 62 (16): 163102. doi: 10.7498/aps.62.163102
Electronic structure and optical properties of RDX are calculated by the first-principle density function theory pseudopotential method. The calculated results show that RDX is an insulator with a band gap of 3.43 eV, that the valence band of RDX is mainly composed of C-2s, C-2p, N-2s, N-2p and O-2s, O-2p, and that the conduction bands are mainly composed of N-2p and O-2p. The static dielectric function ε1(0) is 1.38, the imaginary part of dielectric function has five peaks and the largest peak is at the position corresponding to 4.6 eV of photon energy. The electronic direct transitions for these peaks are analyzed in detail. The absorption, reflectivity and loss function of RDX are analyzed in terms of calculated band structure and density of states. The results indicate that the RDX is not sensitive to the optical absorption nor to reflectivity nor to energy loss.
2013, 62 (16): 163103. doi: 10.7498/aps.62.163103
The potential energy curves (PEC) for the ground state (X2∏) and three excited states (4∑-, 2∑-, 2Δ) of SF molecule are computed using the multireference configuration interaction method and the basis sets aug-cc-pV6Z where the Davidson correction is considered as an approximation to full CI. The separation parameters (Re, ωe, ωeχe, D0, De, Be and αe) are evaluated using the PEC of SF. The spectroscopic parameters are compared with those reported in the literature, and excellent agreement is found between them. With the PEC of SF, some vibrational states of SF are predicted when J=0 by numerically solving the radical Schrödinger equation of nuclear motion. For each vibrational state, the vibrational levels and inertial rotation constants are reported.
2013, 62 (16): 163301. doi: 10.7498/aps.62.163301
The low mode energy of deuterium is calculated by quantum mechanics theory and deuterium zero-point vibration energy. The smooth, uniformity, euphotic solid deuterium film is obtained by home-made planar cryotarget system. The infrared absorption spectrum of solid deuterium film is studied by infrared spectroscopy system. The strong absorption peaks mostly result from the Q1(0)+S0(0), Q1(0)+S0(1), Q1(0)+S0(0)+S0(1) vibration, rotation modes. The experimental data are in good agreement with the analysis results.
2013, 62 (16): 163302. doi: 10.7498/aps.62.163302
Spectra of H+, 35Cl+, H35Cl+ and their isotopologues, due to resonance enhanced multiphoton ionization (REMPI) of HCl via the F1Δ2 (v’=1) Rydberg and V1∑+ (v’=13, 14) ion-pair states are recorded in a range of 84800-85700 cm-1. Perturbation effects indicate the resonance interaction between the F1Δ2 (v’=1) and V1∑+ (v’=14) states. An improved model for analyzing relative signal intensity of spectrum, based on state interaction and photofragmentation process, is used to analyze the F1Δ2 (v’=1) spectral data. Interaction strength (W’=0.6 cm-1) and a predissociation parameter (γ=0.025) are derived. Comparable interaction strength and unperturbed spectroscopic parameters are derived from the deperturbation analysis of line positions for the F1Δ2 (v’=1) and V1∑+ (v’=13, 14) spectra. The study indicates that the formation of the H+ and Cl+ ions via two-photon resonance excitation of F1Δ2 (v’=1) state is associated with the state interaction. An indication of the line-shift of F1Δ2 (v’=1) state spectrum due to Rydberg-to-Rydberg state interaction is also found. The nonzero γ value suggests that the predissociation of the F1Δ2 state is important.
2013, 62 (16): 163401. doi: 10.7498/aps.62.163401
The double differential cross sections for electron impact ionization of hydrogen at different incident energies are calculated by use of the Brauner-Briggs-Klar (BBK) model and first order born approximation model. The results are compared with experimental data and other theoretical results. The non-first-order effects of the BBK model are analyzed and discussed in detail.
2013, 62 (16): 163402. doi: 10.7498/aps.62.163402
The triple differential cross sections for electron impact ionization hydrogen (e, 2e) reactions are calculated as an example by use of the impulse approximation and Born approximation model at different coplanar asymmetric geometries. The results of the present work are compared with experimental data. The structures of the cross sections and the physical nature of these structures are discussed in detail. Moreover, the exchange effect contribution to the cross section is also discussed, which supports our earlier conclusions.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (16): 164101. doi: 10.7498/aps.62.164101
In this paper, a new method of using the electric field numerical weight to process the inhomogeneous cells is proposed, which is to resolve the problems such as high errors and parallel direction excluded in the existing finite-difference time-domain method. Instead of deriving average dielectric constant, the new method weights the electric field strength, which is the true solving variables, according to the mean value theorem, and then the length of the integral path is multiplied by the weight. In the new method both the discontinuous effects of inhomogeneous Ampere cell and the ones of inhomogeneous Faraday cell are taken into account, so it is accurate, easy to implement, versatile, and applicable to any of the various positional relationships between the dielectric interface and the electric field strength variable. A numerical model of dielectric filled circular waveguide is used for the numerical calculation and simulation, in which the deviations of the characteristic roots in two-dimensional TE mode solved by different methods from the theoretical ones are compared, and the anisotropies of different methods are also compared. The numerical result shows that the characteristic roots solved by the presented method are closer to the theoretical ones and the anisotropy caused by the proposing method is lower, which proves that this method is more efficient to process the inhomogeneous cells.
2013, 62 (16): 164102. doi: 10.7498/aps.62.164102
When solving electromagnetic scattering problem with T-matrix method, if the scattering obstacles have point-group symmetry, i.e. remaining unchanged under the group transformation, we can obtain the relationship between geometric symmetry and symmetry of elements in T matrix by the usage of group theory. In this way we can foresee the exact values of some matrix elements, as well as relations between elements, which would save numerous running time in numerical calculation.
Investigation on the reconstruction of objects buried in layered media based on the equivalent current source
2013, 62 (16): 164201. doi: 10.7498/aps.62.164201
In this paper, a new algorithm based on the equivalent current source is proposed to reconstruct the objects buried in layered media. In this method the radiating current source from the scattering data is first reconstructed and the reconstruction of equivalent current source and objects are then achieved efficiently by solving an optimization problem in a lower dimensional linear space using the conjugate gradient method. The effects of the frequency of incident wave, sampling interval, length of measurement line level of noise, and the estimation of background on the reconstructed results are studied and analyzed in detail. Numerical results show that the proposed method has a high ability to reconstruct the objects buried in layered media. Therefore, the method can be used to solve the problems in the areas of through-the-wall imaging and geophysical exploration and so on.
Diffraction barrier breakthrough in coherent anti-Stokes Raman scattering microscopy and detection limitanalysis
2013, 62 (16): 164202. doi: 10.7498/aps.62.164202
We provide an approach to breaking the diffraction limit in coherent anti-Stokes Raman scattering (CARS) microscopy and report a theoretical analysis of detection limit (DL) forit. The additional probe beam, whose profile is doughnut shaped and wavelength is different from the size of Gaussian probe beam, interacts with the coherent phonons at the rim of the diffraction-limited spot to increase theresolution by re-engineering the point spreadfunction of the system. The signal strength reduces with the size of focal volume decreasing, besides, when CARS is used in biology, the molecules of interest are usually in low concentration, which makes the signal detection more difficult. Accordingly, a remaining crucial problem is whether the reduced signal generated in the suppressed focal volume can be detected from the noise background and the analysis of DL, so it is an important precise in implementation of CARS nanoscopy. We describe T-CARS process with full quantum theory and estimate the extreme power density levels of the pump and Stokes beams determined by saturation behavior of coherent phonons. When the pump and Stokes intensities reach such extreme values and total intensity of the excitation beams arrives at a maximum tolerable by most biological samples in acertain suppressed focal volume, the DL of T-CARS nanoscopy correspondingly varies with the exposure time. For an attainable spatial resolution of ～40 nm in three dimension and areasonable exposure time of 20 ms, the DL in the suppressed focal volume is approximately ～103. The signal can be well detected from the noise fluctuation only if the number of molecules of interest exceeds this limit.
According to the relevant theory of optical transfer function (OTF), the OTF and point spread function of coherent field imaging technology (also known as Fourier telescopy) are derived. The formulas for calculating the resolution power of coherent field imaging system with T type and O type transmitter arrangement are given, which provides a theoretic basis of analyzing the limited angle resolution of coherent field imaging system. Based on this study, the relationship between resolutions of the coherent field imaging system with T type and O type transmitter arrangement is investigated.
2013, 62 (16): 164204. doi: 10.7498/aps.62.164204
We present a joint spectral and depth domain spectral domain phase microscopy for high-sensitive and high-dynamic-range quantitative phase imaging, where phase information retrieved in spectral domain is used to overcome the limitation of 2π ambiguity and phase information in depth domain is used to achieve a high phase sensitivity. By theoretical derivation and simulation, the sensitivity advantage of phase information in depth domain over phase information in spectral domain is investigated. The theoretical derivation of joint spectral and depth domain spectral domain phase microscopy is presented in detail. The performance of the proposed joint spectral and depth domain spectral domain phase microscopy is illustrated by phase imaging of a coverslip and a resolution target.
2013, 62 (16): 164205. doi: 10.7498/aps.62.164205
The all fiber sources of photon pairs in the 1550 nm telecom band have the advantages of low cost and compatibility with the fiber network. Further improving the purity will improve the practicality of the quantum light sources. For the pulsed pump field propagating through the optical fiber, a certain amount of chirp will be inevitably induced due to the effects of chromatic of dispersion and Kerr nonlinearity, but its influence on the purity has not been studied yet. In this paper, using photon pairs produced by the spontaneous four wave mixing in dispersion shifted fiber, we study the influence of pump chirp on the purity of photon pairs by varying the chirp of the pulsed pump. For the pump with a given bandwidth, our results demonstrate that the purity of photon pairs having a certain production rate, decreases with the increase of the absolute quantity of pump chirp. Therefore, the purity of the photon pairs with relatively small detuning can be improved by using the transform limited pump pulses due to the suppressed Raman scattering.
2013, 62 (16): 164206. doi: 10.7498/aps.62.164206
We demonstrate experimentally the short pulse amplitude squeezed light from a singly resonant synchronously pumped optical parametric oscillator (SPOPO). The SPOPO operates in the frequency degenerate case and below threshold, with using a periodically poled potassium titanyl phosphate crystal. The pump laser is the second harmonic of a ultrashort mode-locked femtosecond pulse at 850 nm. The reduction of quantum noise of 2.58 dB is obtained experimentally. The squeezing extent is deduced to be 4.48 dB.
2013, 62 (16): 164207. doi: 10.7498/aps.62.164207
We provide a four-level double-V type atomic system driven by two week probe fields and two strong coupling laser beams. In the condition of resonant four-wave mixing, the two probe fields can be amplified without population inversion. Due to the fact that the two excited states are close- lying upper levels of hyperfine structure, the spontaneously generated coherence (SGC) effect must be considered. Interestingly, the amplitude of gain is sufficiently enhanced with the same parameters as those in the case without considering SGC. In addition, we find that the probe gain is sensitive to the phase of two laser fields which interact with the same lower level. To be more specific, the amplitude of gain is modulated by the phase periodically but restricted by θ (the angle between two induced dipole moments). At the same time, we also analyze the influence of the coherence pumping (strong coupling fields) detuning.
2013, 62 (16): 164208. doi: 10.7498/aps.62.164208
Fluorescent nanodiamonds containing nitrogen vacancy centers are created by electron irradiation. The values of spin echo coherence time T2 of nitrogen vacancy centers in nanodiamonds are very small, which are between 0.86 s and 5.6 s. The results of Ramsey interference fringes show that the values of dephasing time T2* differ from each other and the T2* of nitrogen vacancy center NV1 is biggest (0.7 s). Its inhomogeneous linewidth obtained from Fourier transform frequency spectrum of Ramsey interference fringes is 1.05 MHz. The hyperfine structure for the nitrogen vacancy center electron spin coupled to the host nitrogen-14 nuclear spin can be detected by the electron spin resonance spectrum in nitrogen vacancy center NV1. It is important for the realization of the manipulation of nuclear spins and quantum gates of multiqubit in nanodiamonds.
Dual-channel chaos synchronization and communication based on a vertical-cavity surface emitting laser with double optical feedback
2013, 62 (16): 164209. doi: 10.7498/aps.62.164209
Using two orthogonal polarization mode outputs from a vertical-cavity surface emitting lasers (VCSEL) with double optical feedback as two chaotic carriers, a dual-channel chaos secure communication system is established, and the synchronization and communication performances of such a system are numerically investigated. The results show that under suitable operated condition, the time-delay signatures of two chaotic carriers originating from two linear polarization modes in the T-VCSLE with double optical feedback can be suppressed efficiently. Under the strong injection locking case, high-quality chaos synchronization between two corresponding modes of T-VCSEL and R-VCSEL can be realized by polarization-preserved optical injection from T-VCSEL to R-VCSEL. Moreover, the tolerance of the synchronization quality on the frequency detuning between T-VCSEL and R-VCSEL is enhanced with the increase of the injection strength. Adopting additive chaos modulation encryption scheme, two pieces of 500 Mbit/s encoded message can be hidden efficiently in the two chaotic carriers in the propagation process and can be successfully extracted at the receiver. Although Q factor decreases with the increase of message transmission rate, the values of Q factor for two channels are still larger than 6 for 6 Gbit/s message.
2013, 62 (16): 164210. doi: 10.7498/aps.62.164210
Rytov theory combined with the ABCD ray matrix is used to analyzes the statistical property of a reflected wave from a retro-reflector caused by atmospheric turbulence. The covariance function and the scintillation index of the receiving field caused by the combined effect of the turbulence and the random shaking of the reflector array are deduced on the basis of the mutual statistical independence of the two kinds of effects. The aperture factor and the scintillation of a receiving aperture with a finite size are calculated, and those of the retro-reflector and the array are compared to prove that the array does not change distribution of the intensity fluctuation but amplifies the fluctuation by a factor of 2.
2013, 62 (16): 164211. doi: 10.7498/aps.62.164211
Some radiometric and photometric measurements need high accuracy knowledge of the area of the aperture. So the accurate knowledge of the area of the limiting aperture is very important. There are two types of methods to measure the aperture areas. Type-one contains contract method, and no-contract method, and type-two contains geometrical method and effective area method. In this paper we first describe all the methods briefly, then emphatically explain the no-contract method, geometrical method and effective area method. Finally, a comparison of measurement accuracy, degree of difficulty in measurement, and equipment cost among different methods, indicates that the geometric method and the effective area method are very promising. In order to improve the uncertainty of the measurement, more stable laser and accurate translation stage are needed.
2013, 62 (16): 164212. doi: 10.7498/aps.62.164212
Design rules for liquid crystal (LC) lens with low driving voltage are studied in this paper. Many rules are obtained from simulations of five kinds of LC materials. If normalized Δneff of the LC material is less than 95%, the driving voltage of LC lens will be less than 10 V. On the premise that the performance of LC lens is satisfied and fabrication process is permitted, the smaller the normalized Δneff, the lower the driving voltage of the designed LC lensis. The results in can guide people in this paper designing and preparing the LC lens with high performance.
2013, 62 (16): 164501. doi: 10.7498/aps.62.164501
The problem of perturbation to Noether symmetry and adiabatic invariant for a nonconservative dynamic system is studied under a dynamic model presented by El-Nabulsi. First of all, the fractional action-like variational problem proposed by El-Nabulsi under the framework of the fractional calculus and based on the definition of the Riemann-Liouville fractional integral is introduced, and the Euler-Lagrange equations of the nonconservative system are given. Secondly, the definition and criterion of the Noether quasi-symmetric transformation are given, the relationship between the Noether symmetry and the invariant is established, and the exact invariant is obtained. Finally, the perturbation to the Noether symmetry of the system after the action of a small disturbance and corresponding adiabatic invariant are proposed and studied, the conditions for the existence of adiabatic invariant and the formulation are given. An example is given to illustrate the application of results.
2013, 62 (16): 164502. doi: 10.7498/aps.62.164502
A normal distribution random force field is introduced into the study of granular flow, and its effect is observed by computer simulations. The results show that the random force almost does not cause changes in average density and velocity in a uniform granular flow, and affects little the fluctuation of the density. The main effect of the random force field is that it increases the fluctuation of the granular velocity and maintains the granular flow at a certain dispersed kinetic energy by competing with the dissipation of the granular system. It is also shown that the dispersed kinetic energy obtained by the random force field is not equally distributed in each degree of freedom, and that the equipartition of energy is difficult to realize in granular system because of its dissipation property.
2013, 62 (16): 164503. doi: 10.7498/aps.62.164503
We experimentally measure the local equation of state for two-dimensional horizontal fluidize granular gases confined in a rectangle box. Local equation of state can be seen as a local constitutive equation of temperature, pressure and the number density. Except the kinetic parts, the collision parts of the stress tensor are included. The diagonal components of the stress tensor are almost constant, which is consistent with the results from the simulation and hydrodynamic theory. Furthermore, the spacial profiles of the temperature and the number density are shown to be consistent with the experimental results of micro-gravity. Finally the local equations of state for different area fractions are found to have great discrepancies with the theoretical predictions no matter how the low or dense the density is.
2013, 62 (16): 164601. doi: 10.7498/aps.62.164601
In the paper, we propose a new nucleation rate function, which combines grain size, and models for nucleation and growth of voids in a ductile polycrystalline metal. The proposed model is used to analyse the effects of grain size on the dynamic tensile damage of high purity Cu samples with different grain sizes. Numerical results show that pull-back minima and void number decrease with grain size increasing, slope after pull-back and average void diameter increase with grain size increasing. The computed results are in qualitative agreement with experimental results.
Composition analysis and mechanism approach of the electrorheological fluids based on the precursor of TO2
2013, 62 (16): 164701. doi: 10.7498/aps.62.164701
We synthesize the powder of the precursor of TiO2, which shows the giant electrorheological effect but does not include the component of CaC2O4H2O. By use of X-ray diffraction, scanning electron microscope, inductively-coupled plasma spectrometer, themogravimetry-mass spectrum, etc, it is found that the precursor of TiO2 is amorphous powder with nanosize, and its components include TiOC2O42H2O and TiO(OH)2. The electrorheological fluid made by the powder shows a similar temperature characteristic to that made by the precursor of CaTiO3, i.e., when the powder is heated to the temperature above 160℃, the yield stress of the electrorheological fluid made by it decreases gradually, and when it is heated to 200℃, the giant electrorheological effect disappears completely. It is also found that the chemical reaction accompanies with the disappearance of the giant electrorheological effect is that the crystalized water in TiOC2O42H2O is volatilized in heating process. These characteristics can be observed in all electrorheological fluids made by the precursor of other titanate, so we conclude that TiOC2O42H2O is the key component for this series of giant electrorheological fluids.
2013, 62 (16): 164702. doi: 10.7498/aps.62.164702
A one-dimensional model about the ignition process of boron particle in boron-based propellant ducted rocket is systemically investigated. The gas flow around the boron particle, the heat transfer and the mass transfer between the boron particle and the surrounding are included in the model. And the effects of Stefan flow are also proposed. The changing regularities of important parameters in the two typical cases, viz., the successful ignition case and the degenerate ignition case are studied in detail. And their reasons are analyzed. The result shows that both the evaporation of the liquid boric oxide layer and the oxidation of the boron are remarkably accelerated as the result of the self-heating exothermic oxidation in the successful ignition case, and the mass fraction profiles of the oxygen gas and those of the B2O3 gas also dramatically change in that case. However, both the mass flux of the evaporation of the liquid boric oxide layer and that of the consumption of the oxygen gas are relatively small, and both of them tend to be nearly constant in the degenerate ignition case. The mass fraction profile of the oxygen gas and that of the B2O3 gas change little in the degenerate ignition case. In the two typical cases, Stefan flow on the boron particle surface undergoes the change of flow direction, viz., Stefan flow initially comes from the surrounding and then it flows from the particle surface to the surrounding.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Origin of energetic carbon ions with different charge states in ultrashort laser-thin foil interactions
2013, 62 (16): 165201. doi: 10.7498/aps.62.165201
High charge state carbon ions are observed from the rear surface of thin foil irradiated by intense femtosecond laser pulse at intensities up to 6.4×1018 W/cm2. The origin of the ions is studied by analyzing the basic ionization process occurring at the rear surface. It is shown that the normally dominant ionization process is field ionization by barrier suppression for charge states less than He-like (C4+), while collisional ionization is significant for C5+ and C6+.
2013, 62 (16): 165202. doi: 10.7498/aps.62.165202
Numerous football-shaped Zinc micro-spheres on inner surface of the crater are produced by pulsed laser ablation of Zn metals in vacuum condition (～2 Pa). Pulsed laser induced plasma emission spectrum is measured to reveal the effects of macro- and micro-structures on subsequent pulse laser ablation. The intensity of spectral line at 334.5 nm originating from Zn atoms by subsequent laser ablation of the ablated spot is 10.3% higher than that created over a smooth surface. The intensity of the same spectral line produced over a ablated spot with a great number of micro-spheres is 1.343 times higher than that produced by the plasma generated over the ablated spot. The Zn micro-sphere completely covered with nano-scaled regular pentagonal and hexagonal facets can lead to an enhanced absorption of the following laser energy. The total number of Zn micro-spheres increases as the number of laser shots increses, which can result in hotter and dense plasma by subsequent laser ablation. The proposed results are of importance for developing the laser micro-drilling technique.
2013, 62 (16): 165203. doi: 10.7498/aps.62.165203
In this paper, molecular dynamics simulation is used to study the interactions between H atoms and the crystalline Si surface when H atoms bombard the Si surface in different incident energies. The results show that the adsorption rate of H atoms first increases and then reaches an equilibrium value with the increase of incident energy, which is consistent with the experimental results. The results also reveal that the H atoms are deposited on the Si surface, forming hydrogenated amorphous silicon film. The etching products (H2, SiH2, SiH3 and SiH4) influence the adsorption rate of H atoms, and determine the surface roughness of the hydrogenated amorphous silicon film. The surface roughness reaches a minimal value when the incident energy is 1 eV. However, both the yield and the distribution of the composition (SiH, SiH2, SiH3) in the hydrogenated amorphous silicon film change with the increase of incident energy.
2013, 62 (16): 165204. doi: 10.7498/aps.62.165204
In this work, gas phase processes in a high pressure (～100 Torr) DC hydrocarbon plasma are investigated in situ by optical emission spectroscopy and mass spectroscopy. In the high pressure plasma, optical emission characteristics of glow layers are obviously different. C2, CH dominated band spectra and discrete spectra are distinctively observed in the positive column, whereas the emission intensity is found to decrease in the anode region. In the cathode region, a large number of complicated spectra are detected, which indicates the intensive interaction between the cathode and plasma under high pressure induces complicated atomic and molecular processes. With the the increase of pressure, electron excitation temperature decreases while gas rotational temperature goes up. High methane concentration causes increases in C2, C2H2 and C2H4 but a reduction in C2H6. Those suggest that the effect of gas temperature on gas phase process is significantly enhanced under high pressure.
Investigation on the characteristics of dielectric barrier discharge with fairly large volume generated in air at atmospheric pressure
2013, 62 (16): 165205. doi: 10.7498/aps.62.165205
By using a tri-electrode dielectric barrier discharge device, a uniform discharge with fairly large volume is realized in the main discharge region in atmospheric pressure air. The characteristics of the main discharge are investigated by optical and electrical methods. Results show that the main discharge includes two discharge modes with changing the input power of the source, which are a plasma plume discharge and a plasma column discharge. The inception voltage decreases with the increase of the peak value of the applied voltage for plume discharge. It can be deduced that the pre-ionization of air in the main discharge region is important for the main discharge, which results from the UV emitted from the coaxial dielectric barrier discharge. Spatially resolved measurements are conducted on the plasma plume and the plasma column with photomultiplier tubes. It is found that the plasma plume behaves like a plasma bullet that corresponds to a fast moving layer of light emission zone. Comparatively, the discharges at different positions of the plasma column almost volley, which means that the plasma column is of continuous discharge. Through analyzing the optical spectrum emitted from the main discharge, the vibrational temperature and rotational temperature are calculated. Results indicate that both the vibrational temperature and the rotational temperature decrease with the increase of peak value of the applied voltage. These results are of significance for the industrial applications of dielectric barrier discharge.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Simulation study of effect of initial melt temperature on microstructure evolution of liquid metal Ni during solidfication process
2013, 62 (16): 166101. doi: 10.7498/aps.62.166101
A molecular dynamics simulation study is performed on the effect of the thermal history of initial melt temperature on the microstructure evolution in solidification process of liquid metal Ni by means of quantum Sutton-Chen n-body potential. The pair distribution function g(r) curves, the bond-type index method, the cluster-type index method and the three-dimensional (3D) visualization method are used to analyze the microstructure evolution in the solidification process. It is found that the initial melt temperature plays a critical role in the evolution of microstructures, but it is not obvious in liquid and supercooled states and the effects can be fully displayed only near the crystallization transition temperature Tc. The 1421 and 1422 bond-types or the FCC (12 0 0 0 12 0) and HCP (12 0 0 0 6 6) cluster in the system play the critical role in the microstructure evolution. The results show that at a cooling rate of 11012 K/s with different initial melt temperatures, the solidification structures of liquid metal Ni are always crystallized, but the numbers of the main bond-types and clusters have a vast varying range, and it does not vary linearly with the decrease of initial melt temperature. However, the system energy changes linearly with the decrease of initial melt temperature. Through the 3D visualization method, it is also found that atoms of the same cluster are gathered in the same layer when the system has a higher initial temperature, and these layers would be scattered when the initial melt temperature decreases. The 3D visualization method would help to deeply investigate the evolution mechanisms of microstructures in liquid metals during solidification.
We perform the first-principles calculations to investigate the roles of C vacancy and nitrogen impurity in the magnetic properties of diamond. The coupling is ferromagnetic between the C vacancies in -2e charged state, whereas they prefer to interact antiferromagnetically in -e charged state. Substituting C with N atoms can manipulate the charge states of C vacancies and the magnetic interactions between them. Our work offers a possible route toward high Curie temperature ferromagnetism in metal-free diamond.
2013, 62 (16): 166801. doi: 10.7498/aps.62.166801
Productions of transmute elements (hydrogen and helium) have great influences on the resistance to irradiation damage in structural materials for fusion reactor. The evolution of irradiation damage in bcc iron is investigated with ion implantation and electron irradiation. Pure iron implanted by He+ or D+ ions at room temperature are aged at 500℃ for 1 h, then irradiated by electrons under high voltage electron microscope. The results show that interstitial loops (i-loop) and vacancy loops (v-loop) are formed in He+-implanted iron and D+-implanted iron respectively. Under electron irradiation, due to the absorption of interstitials atom, i-loop grows up while v-loop shrinks. According to the rate of variation of dislocation loop, v-loop absorbs more interstitial atoms, i.e., the dislocation bias of D+-implanted iron is larger than that of He+-implanted iron, which means that the v-loop has the more contributions to irradiation swelling than i-loop. The causes of the different natures of dislocation loops formed in D+-implanted iron and He+-implanted iron are analyzed by the structures of He-V and D-V complexes.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effects of the concentration of heavily oxygen vacancy of rutile TiO2 on electric conductivity performance from first principles study
2013, 62 (16): 167201. doi: 10.7498/aps.62.167201
The band structures and the total densities of states of pure and the different concentrations of heavily oxygen vacancy of rutile TiO2-x (x=0, 0.125, 0.25) supercell are studied by using the plane-wave ultrasoft pseudopotential method based on the the density functional theory. Local density approximation +U is used to correct band gaps. The results show that the higher the concentration of heavy oxygen vacancy, the narrower the gap of rutile TiO2 is, the smaller the effective mass of electron is, the lower the electron mobility is, and the lower the electron conductivity is. The calculation results are in agreement with the experimental results.
2013, 62 (16): 167202. doi: 10.7498/aps.62.167202
Polaron transport process in conjugated polymer with intrachain disorder is simulated using a nonadiabatic evolution method. The simulations are performed within the framework of an extended version of the Su-Schrieffer-Heeger model modified to include intrachin disorder and an external electric field. It is found that the polaron transport mechanism is determined by both the electric field and the intrachain disorder. The effects of intrachin disorder are negative in most cases, but with the increase of the electric field, the influence of intrachin disorder on polaron transport decreases.
2013, 62 (16): 167301. doi: 10.7498/aps.62.167301
Surface plasmon polaritons can localize the photons near the metal surface, forming a strong near-field energy density, which affects the efficiency of illumination for molecules and the coefficient of utilization for optical-voltage materials near the metal surface. We analyze the absorption spectrum for the metal-insulator hybrid structure grating and give out the surface plasmon coupling condition according to structure and filling factor. We prove that when filling factor is high enough to form a tiny gap between grating elements, the efficiency for photons to be coupled into surface plasmon polaritons can reach above 94%.
Polarization properties of plasmonic color filters comprised of arrays of subwavelength size holes on Au films
2013, 62 (16): 167302. doi: 10.7498/aps.62.167302
Plasmonic color filters comprised of metal films can be adjusted easily. Periodic arrays of subwavelength size holes with circle, square and rectangular shape are fabricated on 200 nm thick Au films by using focused ion beam. The structures are utilized as plasmonic color filters for exhibiting color variation under the illumination of white light in different polarization directions. We find that for rectangular hole arrays, the color of the transmitted light changes greatly with polarization direction. However, for arrays of circle and square holes, color of the transmitted light is not sensitive to the polarization direction of incident light. We conclude that localized surface plasmon around a single hole is a key factor in influencing the color of transmission light, rather than surface plasmon polaritons induced by periodic arrays. If incident light does not excite the localized surface plasmon around the holes, the effect of surface plasmon polariton will disappear, Based on different display colors of transmitted light of the subwavelength holes with polarization, a composite color display sample is prepared, which will exhibit different color patterns as the polarization direction of incident light changes.
2013, 62 (16): 167303. doi: 10.7498/aps.62.167303
As a special metal surface state, optical Tamm state (OTS) has been widely used in designing the new generation of optical devices for its unique advantages in light control and operation. Based on distribute Bragg reflector (DBR)-metal-DBR (DMD)structure, asymmetric mechanism is introduced by mismatching central frequencies of the two DBRs to design and control the generation of OTS. Through the analysis of reflection spectrum and the electric field distribution characteristics, the interaction and variation rules of OTS on each side of metal are revealed. The results indicate that the DMD structure can support the presence of two OTSs with different intrinsic wavelengths. Besides, the mismatch will affect the strengths and intrinsic wavelengths of the two OTSs, i.e., the upper and lower branches of OTS appear with the variation of . In addition, polarization state and injection angle of incident light have a considerable influence on the strength and intrinsic wavelength of OTS.
2013, 62 (16): 167304. doi: 10.7498/aps.62.167304
Large contact resistance due to Fermi level pinning effect at the interface between metal and n-type Ge strongly restricts the performance of Ge device on Si substrate. In this paper, the contacts of metal Al and Ni with n-type Ge and p-type Ge epitaxial layers grown by UHV/CVD are comparatively studied. It is found that the contact of NiGe/n-Ge is better than that of Al/n-Ge at the same dopant concentration. When the concentration of P is 21019 cm-3, the ohmic contact of NiGe/n-Ge with c down to 1.4310-5 cm2 is demomstrated, which is about one order of magnitude lower than that of Al/n-Ge contact. The specific contact resistance of NiGe/p-Ge is 1.6810-5 cm2 when the B concentration is 4.21018 cm-3, corresponding to that of Al/p-Ge. Compared with Al/n-Ge contact, P segregation at the interface between NiGe and Ge, rather than lowering Schottky barrier height, is the main reseaon for achieving the low specific contact resistance. NiGe/Ge contact should be a good choice for contact electrode for Ge devices at present.
Flat-roof of dynamic equilibrium phenomenon in static negative biase temperature instability effect on power metal-oxide-semiconductor field-effect transistor
2013, 62 (16): 167305. doi: 10.7498/aps.62.167305
The effect of static negative bias temperature instability stress on p-channel power metal-oxide-semiconductor field-effect transistor (MOSFET) is investigated by experiment and simulation. The time evolution of the negative bias temperature instability degradation presents the trend which follows the reaction-diffusion (R-D) theory on the exaggerated time scale. A flat-roof section is observed under the varying stress condition, which can be considered as the dynamic equilibrium phase through the simulation verification based on the R-D model. The analysis of the simulated results also provides the explanation for the difference in the time duration of the dynamic equilibrium phase under the condition of varying stress voltage.
2013, 62 (16): 167306. doi: 10.7498/aps.62.167306
Separating the load impedance of the resonant frequency selective surface (FSS) can form the complementary frequency selective surface (CFSS), whose filtering feature is based on the coupling mechanism. The resonance of CFSS can be tuned by controlling the rotation angle of the element on the capacitive surface. Taking tripole element for example, the frequency response of the CFSS is calculated by using the coupled integral equation method. A 250 mm250 mm prototype is tested via free space method. Calculation and test results show that the resonance of the CFSS can be tuned actively as the rotation angle changes. This study provides reference to the active FSS design.
2013, 62 (16): 167307. doi: 10.7498/aps.62.167307
In order to make the dual-band frequency-selective surface (FSS) used in the engineering conditions of thick substrate, wide band spacing and large incident angle, an FSS structure with dual-band at Ku-band and Ka-band is presented. The stable filtering condition of the FSS is analyzed by using the grating lobe diagram, and the transmission of the FSS with combination or fractal elements is calculated using the vector modal matching method. The design method of the dual-band FSS with thick substrate is obtained by analyzing the resonance mode of the element and the transmission of the FSS. By using those methods, an FSS with combination elements of the square and Y loops is designed. The simulated and tested results show that the dual-bands of the structure at Ku-band and Ka-band are stable and the transmissions of the two pass-bands are larger than 75% when the incident angle is varied from normal to 45. This paper provides some theoretical and experimental references for the design of the dual-band FSS with thick substrate, wide band spacing and large incident angle.
Proximity-effect-induced superconductivity by granular Pb film on the surface of Bi2Te3 topological insulator
2013, 62 (16): 167401. doi: 10.7498/aps.62.167401
The appearance of topological insulators provides us with a chance of finding topological superconductors and Majorana fermions. To pursue these findings one might need to induce large areas of proximity superconductivity on the surface of Bi2Te3 by depositing granular and discrete Pb film. In this experiment, a superconducting state over a distance of 9.5 rm is observed below 0.25 K on a Bi2Te3 crystal whose surface is deposited with Pb grains with a thickness of less than 20 nm and separated at a distance of 20-30 nm.
2013, 62 (16): 167501. doi: 10.7498/aps.62.167501
The structure, magnetism and magnetocaloric effect in Mn42Al50-xFe8+x are studied in this paper. The Curie temperature (TC) is tunable in a wide temperature range around the ambient temperature by varying the Fe and Al concentration. The values of TC are 270 K, 341 K and 370 K, respectively corresponding to the values of x of 8, 10 and 12. The magnetization has a sharp drop around the respective phase transition temperature and no obvious thermal or magnetic hysteresis is found, suggesting that a typical reversible second order phase transition occurs. The maxima of the magnetic entropy change (Sm) under an applied field change of 0-5 T are 2.48 (Mn42Al42Fe16), 2.52 (Mn42Al40Fe18) and 2.40 Jkg-1K-1 (Mn42Al38Fe20), which are almost independent of composition. The simple and easy preparation process, the good corrosion resistance and ductility, the reversible second order phase transition, and the low cost of raw material make them attractive candidate for the magnetic refrigerant, although their values of Sm are not very large compared those that of the rare earth based compounds.
Influences of strain on electronic structure and magnetic properties of CoFe2O4 from first-principles study
2013, 62 (16): 167502. doi: 10.7498/aps.62.167502
Spinel ferrites, such as CoFe2O4, can be used in various fields such as computer technology, aerospace, and medical biotechnology due to their good electromagnetic properties. Although, CoFe2O4 thin films have good application prospects in the magnetoelectric composites, the effects of strain on the electronic structure and magnetic properties of cobalt ferrite film have not been reported. Through the use of two-dimensional strain model closer to the epitaxial growth experiments, the films of Cobalt ferrite are simulated on various substrates with a realistic biaxial strain model by first-principles plane-wave pseudopotential method based on density functional theory, and combined with the generalized gradient approximation in the paper. And the structural stabilities, electronic structures and magnetic properties of CoFe2O4 films are studied. The results show that the inverse spinel is still energetically favored under strain, but the energy difference decreases, thus Fe3+ions in the tetrahedral sites and Co2+ ions in the octahedral sites are easier to exchange their positions. As the strain increases, the band gap of cobalt ferrite becomes narrower, and the magnetic moment of atom in the lattice changes, while the net magnetic moment changes little.
Gaussian type inhomogeneous stress and strain effects on the magnetic properties in ferromagnetic thin films
2013, 62 (16): 167503. doi: 10.7498/aps.62.167503
The effects of Gaussian type inhomogeneous stress and strain on the magnetic properties in ferromagnetic thin films are studied by Monte-Carlo simulation. The results show that the coercive field could be enhanced by the strain parallel to the easy axis and stress perpendicular to the easy axis, on the other hand, it could also be weakened by the stress parallel to the easy axis and strain perpendicular to the easy axis. The coercive field increases (or decreases) in the system, meanwhile, the remanent magnetization and squareness increase (or decrease) as well. More interestingly, the easy axis will rotate within the centralized region under stress parallel to the initial easy axis and strain perpendicular to the initial easy axis. The range of centralized region with easy axis rotation is strongly dependent on the magnitude of stress or strain and the width of its distribution.
2013, 62 (16): 167701. doi: 10.7498/aps.62.167701
The formation energies and ionization energies of Ag-N dual-doped ZnO and interstitial N and H monodoped ZnO:(Ag,N) are investigated from the firstprinciples pseudo-potential approach based on density functional theory. It is found that AgZn-NO accepter pair has lower formation energy and ionization energy than Ag-N related to acceptor clusters, which demonstrates that the p-type conductivity of Ag-N dual-doped ZnO system is mainly attributed to the formation of the accepter pairs. Moreover, when ZnO:(Ag,N) system has additional N atoms in some interstitial sites of ZnO crystal, interstitial N atom and AgZn-NO accepter pair prefer to bind together to form AgZn-(N2)O donor complex which lowers doping efficiency, which is not conducive to p-type conductivity. For H doping in the ZnO:(Ag,N) system, the interstitial H atoms also prefer to bind to the AgZn-NO accepter pair, forming acceptor-donor-acceptor (AgZn-H#em/em#-NO) triplet, which not only enhances the incorporation of acceptors (AgZn-NO) but also gives rise to a shallower acceptor level in the band gap in p-type ZnO crystal. Thus, it is suggested that H-assisted Ag-N codoping is an effective method of p-type doping in ZnO.
2013, 62 (16): 167702. doi: 10.7498/aps.62.167702
Piezoelectrets are made from cellular polypropylene(pp)foam sheets by using a pressed-gas expansion followed by corona charging process. The elastic modulus, piezoelectricity and the acoustic response of such fabricated films are investigated. The results show that the Youngs modulus in the thickness direction is more than two orders of magnitude higher than those in the transverse directions. The d33 coefficient remains linear in an applied pressure range from 15 to 35 kPa. As measuring frequency increases from 2 to 300 Hz, d33 coefficient decreases to 81%, which is probably associated with the enhancement of elastic modulus of the film with pressure increasing. In a range from 100 Hz to 100 kHz, the PP piezoelectric films exhibit flat frequency response curves. The open circuit voltage sensitivity and d33 coefficient at 1 kHz are 0.84 mV/Pa and 164 pC/N, respectively.
Nano surface two-dimensional periodic half-round grooves enhanced light absorption in silicon film solar cell
2013, 62 (16): 167801. doi: 10.7498/aps.62.167801
The influence of nano surface two-dimensional periodic half-round grooves on the enhancement of light absorption in silicon film solar cell is studied with the finite-difference time-domain method. The result shows that the broadband solar spectrum absorption is enhanced. The light optical absorption in Si thin-film cell is enhanced by optimizing the thickness of SiO2 anti-reflection film and the radius of half-round grooves, and the total integrated absorption of solar spectrum wavelength in a range from 300 nm to 1000 nm is about 117% greater than that of single silicon thin film.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (16): 168101. doi: 10.7498/aps.62.168101
We have investigated the motion of dislocations originating from Vicker indentations in single-crystalline silicon wafers subjected to high temperature rapid thermal processing (RTP) under different ambients. It is found that the dislocations move very rapidly due to the release of residual stress around the indentations during the RTP. Moreover, as the RTP temperature exceeds 1100 °C, the dislocation gliding distances in the specimens subjected to the RTP in N2 atmosphere are much shorter than in Ar ambient. We believe that the nitrogen atoms injected into the indentation by the RTP under N2 ambient exhibit a pinning effect on dislocation motion. It is thus shown that the high temperature RTP in N2 ambient can improve the mechanical strength of silicon wafer.
The fabrication of the antireflective periodic nano-arrary structure on Si surface using nanoimprint lithography and the study on its properties
2013, 62 (16): 168102. doi: 10.7498/aps.62.168102
The intrinsic Fresnel reflection of Si surface, which causes more than 30% of the incident light to be reflected back from the surface, seriously influences the photoelectric conversion efficiency of Si-based semiconductor photoelectric device, such as solar cell and infrared detector. Recently, how to find a simple and efficient method, which is also suitable for mass production, aiming to suppress the undesired reflectivity and therefore improving the efficiency of the device, has become a research focus. In this work, we successfully convert a 2D nanopillar array structure into the Si surface via the nanoimprint lithography. The nanopillar has a flat surface and a paraboloid-like side wall profile. The period and the height of the hexagonal array structure are 530 nm and 240 nm, respectively. The cut-paraboloid nanopillar structure generates a relatively smooth gradient of the refractive index in the optical interface, which plays a key role in suppressing the Fresnel reflection in a wide range of wavelength. The reflectivity of the nanopillar arrayed Si surface is tested in a wavelength range from 400 to 2500 nm at an incident angle of 8° during the measurement. Compared with the unstructured Si, the structured Si has a reflectivity that significantly decreases in the test area: in a wavelength range from 400 to 1200 nm, and the reflectivity of the silicon surface is less than 10%. Specifically, the reflectivity is almost zero at a wavelength of about 1360 nm. The results are confirmed with the effective medium and rigorous coupled-wave theory.
Analysis on steady plasma process of high-rate microcrystalline silicon by optical emission spectroscopy
2013, 62 (16): 168103. doi: 10.7498/aps.62.168103
The ratio of I(Hα*)/I(SiH*), obtained from the real time optical emission spectroscopy (OES) measurement in the high-rate microcrystalline silicon deposition process, as a function of time is used to analyze the cause of increasing crystallinity along the growth direction. Hydrogen dilution gradient method which means silane concentration gradient and hydrogen flow gradient method is adopted to improve vertical structure uniformity of the material. High-quality microcrystalline material around 53%-62% of Xc can be prepared through silane concentration gradient compared with 55%-75% of Xc prepared in the traditional method. In the silane depleted cases, by increasing the hydrogen flow the longitudinal uniformity of the material can be effectively improved. The vertical crystallinity around 53%-60% can be obtained. This is mainly due to the increase of the hydrogen flow that makes the collision probability increased, as a result, electron temperature of plasma reduced. Thus, the decomposition of hydrogen decreases and the reaction of hydrogen annihilation is suppressed. At the same time, the influence of back diffusion of SiH4 is suppressed. The gradually increasing trend of the ratio of I(Hα*)/I(SiH*) is controlled during the deposition of microcrystalline silicon film.
Output short-circuit spark discharging energy and output intrinsic safety criterion of Buck converters
2013, 62 (16): 168401. doi: 10.7498/aps.62.168401
To obtain the output intrinsic safety criterion of Buck converters, the experimental research on its output-short circuit discharge characteristics is conducted by using the safety spark test apparatus. It is found that its spark discharge process can be divided into four stages, i.e., the dielectric-breakdown, spark-generation, spark-keeping and spark-extinguishment. According to the obtained spark discharge characteristics, the output short-circuit spark discharging energy (OSSDE) is deeply analyzed. It is indicated that the OSSDE of the Buck converter with a given inductance is a concave function of load resistance RL when RL is less than the critical resistance RLC corresponding to this inductance, while that is a convex function of RL in the case of RL > RLC. Considering the actual parameter range of the Buck converter, it is further pointed out that when RL RLC, the OSSDE increases with the increase of RL and reaches its maximum in the case of RL=RLC; when RL > RLC, the OSSDE first increases and then decreases with the increase of RL and reaches its maximum in the case of RL, DCM. The most dangerous operating conditions of the converter in whole dynamic range are obtained, i.e., the converter operates in DCM when the input voltage is the highest and RL=RL, DCM. Meanwhile, the maximum OSSDE is achieved. According to the energy equivalence, an output intrinsic safety criterion for Buck converter is proposed by modeling the output short-circuit discharging behaviour as a simple capacitive circuit. The theoretical analysis and proposed criterion are verified by the simulation and experimental results.
2013, 62 (16): 168402. doi: 10.7498/aps.62.168402
Optimal design method of high-power microwave source based on particle simulation and parallel genetic algorithm is presented in this paper. The output power of the high-power microwave device, simulated by the fully electromagnetic particle simulation code UNIPIC, is given as a fitness function, and the float-encoding genetic algorithm is used to optimize the high-power microwave device. Using this method, we encode the position and height of the Bragg reflector of the relativistic backward wave oscillator (RBWO), and optimize the parameters for a massively parallel processor. Simulation results demonstrate that we can obtain the global optimal parameters of the Bragg reflector of the RBWO.
2013, 62 (16): 168701. doi: 10.7498/aps.62.168701
In order to improve the performance of the wavelet analysis in the process of the heart sound signals, in this paper, we construct a wavelet basis which is exclusively used for processing the heart sound signals on the basis of wavelet theory construction. Firstly, we propose a general method of constructing a compactly supported biorthogonal wavelet which has even length filter banks, Secondly, according to the characteristics of heart sound signals, we discuss the structure principle of heart sound wavelet and a synthesis model of heart sound signals based on the heart sound wavelets. Finally, we construct the heart sound wavelet on the basis. In order to highlight the advanced nature and practical application of heart sound wavelet in processing heart sound signals, the theory and numerical simulation of heart sound wavelet are analyzed more comprehensively. Experimental results show that compared with commonly using the db and bior series wavelets, using the heart sound wavelet to process the heart sound signals can obtain good denoising effect, accurate classified information about heart sound and low reconstruction error rate. So the heart sound wavelet provides a new method of deep studying of heart sound feature extraction and identification and has a positive significance in describing the details of the individual characteristics of the heart sounds. The paper designs a method of the special wavelet which is based on the application object, which provides a new approach to the selection of wavelet basis in engineering applications.
An efficient reconstruction algorithm for flat object based on backprojection filtration method in circular half-cover computed tomography
2013, 62 (16): 168702. doi: 10.7498/aps.62.168702
In circular full-cover cone-beam computed tomography (CT), the field-of-view (FOV) is limited by the width of planar detector, resulting in low imaging efficiency for large object. The FOV can be doubled by half-cover scanning, in which the back-projection filtration (BPF) algorithm based on the concept of PI-line is the best choice for image reconstruction. However, the integral intervals of different PI-lines are unequal in the BPF algorithm, leading to heavy communication consuming and calculation. As a result, the reconstruction efficiency by use of the BPF algorithm is low. In this paper, an efficient image reconstruction strategy based on the BPF algorithm for flat object is proposed. With the method, we demonstrate that the inequality of integral interval of PI-line can be ignored in the discrete implementation of the BPF algorithm when the thickness of flat object is less than 2Rsin(2π/Np) (R is the scanning radius and Np is the number of uniform sampled projections in a full circle). Compared with the original BPF algorithm for half-cover scanning, our method has two major advantages: the first one is that the outer loop is the sample angle while the inner loop is the PI-line, which reduces the communication consuming for computer significantly; the second one is that the derivative of projection, back-projection and inverse Hilbert transform along the PI-line can be computed using parallel computing techniques readily. The results of numerical simulation and real data experiment indicate that the computational efficiency of the proposed method is 5.6 times that for original BPF algorithm and the reconstruction errors of the two methods are comparable.
A pair of high resolution magnetic tweezers with illumination of total reflection evanescent field and its application in the study of DNA helicases
2013, 62 (16): 168703. doi: 10.7498/aps.62.168703
The resolution of conventional magnetic tweezers is limited by the Brown motion of magnetic beads. When the force is lower than ～10 pN, the resolution of magnetic tweezers decreases significantly because of the increased Brown motion. To improve the resolution of magnetic tweezers under low forces, we combine the total internal reflection fluorescence techniques with magnetic tweezers, and design a novel single molecule connection: magnetic bead-DNA linker-fluorescent bead-single molecule. With the improved magnetic tweezers, we study the folding dynamics of a DNA hairpin. The results reveal that a nanometer-scale resolution is obtained. By analyzing these results, we calibrate the penetration depth of the total internal reflection field. Finally, we investigate the unwinding dynamics of a BLM helicase core protein. Some preliminary results of the helicase unwinding experiments confirm the practicability of the improved magnetic tweezers in the field of single molecular research.
A detailed study of the effect of Schottky barrier on the dark current density-voltage characteristics of CdS/CdTe solar cells
2013, 62 (16): 168801. doi: 10.7498/aps.62.168801
Numerical modeling is used to obtain insight into the details of the effect of back contact barrier height (φb) on the dark current density-voltage characteristics of CdS/CdTe solar cell. And relation between the roll-over and the barrier height is obtained. Analytic simulations are fitted to the measured current density-voltage curve in a temperature range from 220 to 300 K. And the influence of barrier height on J-V of the CdS/CdTe thin film solar cell with Cu/Mo back contact fitted parameters is discussed. The equation between back contact barrier height (φb) and the reverse saturation current density (Jb0) is revised and the experimental data are consistent with the simulation results very well.
2013, 62 (16): 168802. doi: 10.7498/aps.62.168802
One layer SiNx:H films with different thickness are deposited by plasma enhanced chemical vapor deposition to prepare several kinds of polycrystalline silicon color solar cells. The optical and electrical properties are tested by instruments and simulated by PC1D. And the analysis shows that 1) when the antireflection film thickness is less than 50 nm, the deficiencies of color solar cells and solar modules are mainly influenced by open circuit voltage (Voc) and short circuit current (Isc); when the antireflection film thickness is greater than 50 nm, the passivation of H ions is stable and the deficiencies are mainly influenced by Isc; 2) the efficiency of most color solar cells is lower than that of blue ones, but the color solar cell will have some gains after packaging, which is because of the better optical matching of reflective film with ethylene-vinyl acetal copo and glass.
2013, 62 (16): 168901. doi: 10.7498/aps.62.168901
Microscopic traffic models are developed to simulate traffic phenomena. However, current models are usually based on the fact that vehicles travel in the middle of a single lane and make a lateral movement only when the driver wants to change lane. They are incapable of describing driving behavior in a complex traffic environment with a lot of lateral separations which may cause traffic flow to be unstable on a single lane. In order to solve the problem, in this paper we first build up the equations of motion based on target steering angle (TSA) and then establish a series of rules for determining TSA by considering the lateral separation characteristics between the follower and the leader. Finally a new vehicular behavior model is developed. The properties of the model are investigated by simulating two scenarios. It is found that the proposed model is capable of describing complex phenomena which cannot be described by existing models and explaining the perturbation caused by bus near bus stations. The results also imply that this model with taking the lateral separation characteristic into account greatly enhances the effectiveness of vehicular behavior.
2013, 62 (16): 168902. doi: 10.7498/aps.62.168902
Research collaboration network has become an essential part in our academic activities. We can keep or develop collaboration relationships with other researchers or share research results with them within the research collaboration network. It is well generally accepted that different relationships have essentially different influences on the collaboration of researchers. Such a scenario also happens in our daily life. The advisor-advisee relationship plays an important role in the research collaboration network, so identification of advisor-advisee relationship can benefit the collaboration of researchers. In this paper, we aim to conduct a systematic investigation of the problem of indentifying the social relationship types from publication networks, and try to propose an easily computed and effective solution to this problem. Based on the common knowledge that graduate student always co-authors his papers with his advisor and not vice versa, our study starts with an analysis on publication network, and retrieves these features that can represent the advisor-advisee relationship. According to these features, an advisor-advisee relationship identification algorithm based on maximum entropy model with feature selection is proposed in this paper. We employ the DBLP dataset to test the proposed algorithm. The results show that 1) the mean of deviation of estimated end year to graduation year is 1.39; 2) the accuracy of advisor-advisee relationship identification results is more than 95%, and it is better than those of other algorithms obviously. Finally, the proposed algorithm can be extended to the relationship identification in online social network.
Networks with links representing different relationships have attracted much attention in recent years. Previous studies mostly focused on the analyses of network topology and evolution, multi-relation pattern mining, detection of overlapping communities, and cascading failure. However, epidemic spreading on multi-relation networks remains a largely unexplored area. We propose a binary-relation network model, representing working and friendship relationships, to reveal the effect of multiple relationships on the epidemic spreading. A link representing a closer relationship carries a higher weight. For reactive infection process in a multi-relation network, the threshold of outbreak is suppressed, making the epidemic harder to control. Comparing the networks with different structural heterogeneities such as the Watts-Strogatz (WS), Erdös-Rènyi and Barabási-Albert networks, the WS network is affected most significantly. Interestingly, the relative changes in the thresholds on the three networks are found to be independent of the structure. For contact infection process, an increase in the weight of the closer relationship can raise the outbreak threshold significantly and reduce the prevalence. As the fraction of closer relationship varies, an optimal fraction corresponding to a maximum outbreak threshold and minimum prevalence emerges. With an increase in the weight of the closer relationship, the proportion of links corresponding to the optimal value decreases. Most interestingly, the optimal proportions of closer-relation links on the three networks are almost the same, and thus they are independent of the network topology. This study not only contributes to the better understanding of epidemic spreading dynamics on multi-relation networks, but also provides a new perspective for research on multi-relation networks.
According to the existence of motif in complex network topology structure, the motif-based node degree and edge degree are proposed to measure the importance of node and edge in the network on the basis of the traditional node degree and edge clustering coefficient. The Rand-ESU algorithm is used for motif detection of eight different scale networks, and the result demonstrates the existence of motif. The Rand-ESU algorithm is also used for analyzing the motif structures and characteristics in Karate network and Dolphin network. The Pearson correlation coefficient is used to measure the correlations of motif-based node degree and traditional node degree, motif-based edge degree and edge clustering coefficient. The results of simulation analysis show that the correlations are related to the motif species. The definitions of motif-based node degree and edge degree are the improvement and development of original definitions, and they comprehensively depict the importance of node and edge in the network.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (16): 169501. doi: 10.7498/aps.62.169501
Three-dimensional (3D) wavefront sensing of atmosphere turbulence is a key step to realize multi-conjugate adaptive optics technology. In this article, model tomography, which is one of the most important algorithms for 3D wavefront sensing, is analyzed in theory, the principle limitation of model tomography is proposed. Based on this view the reason for tomography error is discussed, and the simulation results for different errors are produced finally. The analysis shows that part Zernike model basis is used as a new basis of polynomial decomposition in model tomography, which leads to modal coupling error and aliasing error. The un-correlation of part Zernike model basis is the prerequisite to avoid modal aliasing error, but modal coupling error cannot be removed and we can only restrain its influence. Combined with simulation result a method with large field of view (FOV) sensing and small FOV reconstruction is proposed and gives a good performance to control modal coupling error.