Vol. 59, No. 2 (2010)
2010-01-20
GENERAL
2010, 59 (2): 699-704.
doi: 10.7498/aps.59.699
Abstract +
The phenomenon of coherence resonance in a nonlinear integrate-and-fire neuronal model subject to correlated multiplicative synaptic and additive voltage-gated channel noise are investigated. Based on the adiabatic approximation theory and the unified colored approximation method，the analytic expression of the probability distribution of the first fire （FPD） and the coefficient of variation （CV） of the inter-spike interval of firing are obtained. It is shown that the FPD and the CV are functions of the intensity of the multiplication synaptic colored noise，the additive voltage-gated channel white noise，the correlation time of multiplicative noise and the strength of the correlation between noises. By choosing appropriate noise parameters，the phenomenon of coherence resonance can occur. Meanwhile，the effects of intensity of the multiplication synaptic noise，the additive voltage-gated channel noise，the correlation time of multiplicative noise and the strength of the correlation between noises on coherence resonance are discussed.
2010, 59 (2): 705-711.
doi: 10.7498/aps.59.705
Abstract +
Considering the nodes with different anti-attack abilities in scale-free networks，we investigated the probabilistic behaviors of malware propagation in scale-free complex networks. Using the cellular automata，we proposed a model of malware propagation in complex networks with the nodes having different anti-attack abilities. In particular，a vulnerability function related to node’s degree is firstly introduced into the model to describe the different anti-attack abilities of nodes. Then，the epidemic threshold and time evolution of malware propagation are investigated through analysis and simulation for the various vulnerability functions. The results show that different anti-attack abilities of nodes can produce significant effects on the behaviors of propagation. For example，different anti-attack abilities of nodes can change the value of epidemic propagation，and slow down the spreading speed of malware. Finally，it is pointed out that the vulnerability function is very important for adopting appropriate immunization strategies to control the malware propagation.
2010, 59 (2): 712-715.
doi: 10.7498/aps.59.712
Abstract +
According to Penrose-Hawkings theorem on the singularity of cosmology，the singularity exists in the case when the source havs no rotation or acceleration，and the energy density satisfies the condition ρ+3p≥0. In this paper we study some singularity-free cosmological models under the conditions that the source has rotation. Some cosmological solutions without singularity are obtained.
2010, 59 (2): 716-718.
doi: 10.7498/aps.59.716
Abstract +
The Noether symmetry and the Hojman conserved quantities of the Kepler equation are studied. The determining equations of Noether symmetry for the system are given. A theorem asserting that the Noether symmetry for the system leads to the Hojman conserved quantity is presented.
2010, 59 (2): 719-723.
doi: 10.7498/aps.59.719
Abstract +
The extended Prelle-Singer method is used to find the conserved quantities of second-ordinary nonlinear coupled dynamics systems such as x=1（x，y），y=2（x，y），and the differential equations of integral factors and the general expression of conserved quantities are obtained. The Noether symmetry and Lie symmetry of the systems are also discussed. Finally，two conserved quantities of quartic anharminic oscillator are obtained by the extended Prelle-Singer method，and the symmetries of this system are discussed.
2010, 59 (2): 724-728.
doi: 10.7498/aps.59.724
Abstract +
We study the Lie symmetries and Hojman conserved quantities of generalized linear nonholonomic mechanical systems. Under special infinitesimal transformations in which the time is invariable，the determining equations，the constrained restriction equations and the additional restriction equations of the nonholonomic mechanical systems are obtained. The Hojman conserved quantity of the corresponding holonomic systems，the weakly Hojman conserved quantity and the strongly Hojman conserved quantity of the linear nonholonomic systems are obtained. An example to illustrate the application of the result is given.
2010, 59 (2): 729-734.
doi: 10.7498/aps.59.729
Abstract +
The model of rain-wind-induced vibration of continuous stay cable is built on the basis of the dAlembert principle. This model can describe the dynamic characteristics of continuous stay cable better than the truncated model. By analyzing the static bifurcation behaviors according to the singularity theory，we describe the bifurcation problem as a one-codimensional unfolding with Z2 symmetry. The transition set and bifurcation diagrams for the singularity are presented，while the stability of the zero solution is studied using the eigenvalues in various parameter regions. The corresponding relationship between the unfolding parameters and the physical parameters will facilitates further analysis of the bifurcation behaviors of the stay cable，and it also provides theoretical basis for the design of cable stayed bridge. Meanwhile，it is helpful to the development and application of the engineering projects.
EDITOR'S SUGGESTION
2010, 59 (2): 735-739.
doi: 10.7498/aps.59.735
Abstract +
Based on a recently established third-order theory for surface capillary-gravity short-crested waves，a second-order solution for the bottom boundary-layer velocities in the waves is presented by solving the Prandtl boundary layer equations，which provids an essential theoretical basis in advance for determining the resulting mass transport.
2010, 59 (2): 740-743.
doi: 10.7498/aps.59.740
Abstract +
Based on total investigation, analysis and judgment of one main class of coastal wave models, the mild-slope equations， an operator representing the wide wave-current interactions in coastal waters is introduced to develop a time-dependent theoretical hierarchy of the mild-slope equations for wave-current interactions by means of the universal Hamiltonian variational principle for water waves, which reaches a comparatively high degree of harmony and unity of form and content.
2010, 59 (2): 744-749.
doi: 10.7498/aps.59.744
Abstract +
LS method，a new method for solving nonlinear evolution equations，is proposed. It is based on the （G′/G）–expansion method and the extended hyperbolic tangent function method，and the Poincaré’s qualitative theory is also led in. Then Fisher equation is tested as an example. The properties of integral curves for traveling wave system of Fisher equation are obtained through qualitative analysis，and then a monotonically decreasing wave-front solution of Fisher equation as a dissipative system and a monotonically increasing wave-front solution of Fisher equation as an expansion system are obtained too. Some results agree with that of Ablowitz et al. and some new results for Fisher equation are also obtained as an expansion system. The LS method is used to look for the exact solutions under the condition that the property of solution curves have been obtained through the qualitative analysis，and the target is clear. The LS method also reveals that a linear system can also be used as auxiliary equations to solve nonlinear systems.
2010, 59 (2): 750-753.
doi: 10.7498/aps.59.750
Abstract +
Ultra-long waves in the modified Burger model are studied by using the method of travelling-wave solution. Taylor series expansion is used to isolate the characteristics of linear waves and identify the nonlinear waves. The analytical solutions to nonlinear ultra-long waves with the complete Coriolis force and heating，which can be approximately described by the KdV equation and the combined KdV and mKdV （KdV-mKdV） equation，are obtained. The cnoidal waves，solitary waves，and soliton-like solutions are also obtained.
2010, 59 (2): 754-758.
doi: 10.7498/aps.59.754
Abstract +
The effect of basis configuration on acoustic band structure in two-dimensional complex phononic crystals （PCs） was investigated. We found that when the basis configuration was changed, the irreducible Brillouin zone （BZ） of PCs might be changed too，and part of band extrema were no longer on the high-symmetry lines. In particular，the PCs with some basis configurations were forced to render the whole first BZ irreducible. Therefore，besides the high symmetrical PCs，only by throughout investigation of the BZ can we obtain the authentic band structures and band gaps for the lower symmetrical PCs with complex crystal lattice.
2010, 59 (2): 759-764.
doi: 10.7498/aps.59.759
Abstract +
Using a special rotational transformation of coordinates and momentum，we solve successfully the diagonalization of Hamiltonian. Furthermore，we obtain the exact wave function of dual-coupled two-dimensional harmonic oscillators with time-dependent and anisotropic mass and frequency by means of trial function methed. The wave function is also verified.
2010, 59 (2): 765-770.
doi: 10.7498/aps.59.765
Abstract +
The optical properties of quantum dots have a close relationship with the size fluctuation，density，strain filed distribution of the dots and the spacer layer thickness. InAs/GaAs quantum dot with GaNXAs1-X strain compensation layers （SCL） is theoretically investigated for improving the crystal quality. The reduction effects of the spacer thickness are discussed quantitatively. The influence of the location and the N concentration of the GaNXAs1-X SCL on compensation of the strain formed on quantum dots （QDs） and the system is also discussed. The reduction effect of SCL on strain of system is analyzed and the vertical alignment probability between the adjacent layers is calculated. Our results can provide a theoretical basis for finding the optimal properties of SCL to realize the high quality multi-QD layer.
2010, 59 (2): 771-777.
doi: 10.7498/aps.59.771
Abstract +
As its classical counterpart，quantum Gaussian noise is an important noise model in quantum information theory. The study of capacity of quantum Gaussian channel plays an important role in quantum communications. Based on the definition of quantum Gaussian state，the entropy of quantum Gaussian state，and Holevo bound theorem，the classical capacity of quantum Gaussian channel is given at first in the paper，where the classical capacity is defined as the capacity when only classical messages are transmitted through the quantum channel. Then，the classical capacities of quantum multiple access Gaussian channels are deduced according to the classical capacity theorem of multiple access quantum channels. For simplicity and generality，a multiple access quantum channel with two senders and one receiver is used for computation. The results can be generalized to the quantum channel with n senders and one receiver.
2010, 59 (2): 778-782.
doi: 10.7498/aps.59.778
Abstract +
Using entropy density of scalar field near event horizon in an arbitrarily accelerating black hole with electric charge and magnetic charge, we study the law for the thermal radiation of black hole and the instantaneous radiation energy flux is obtained. It is found that the thermal radiation of a black hole always satisfies the generalized Stefan-Boltzmann’s law. The proportional coefficient of generalized Stefan-Boltzmann is no longer a constant, and it becomes a dynamic coefficient that is related to the parameters of the black hole. For different dynamic black holes, the obtained generalized Stefan-Boltzmann’s dynamic proportional coefficient is different from each other, because the gravitation field and electromagnetic field around black holes is not the same.
2010, 59 (2): 783-791.
doi: 10.7498/aps.59.783
Abstract +
Based on the further evolvement of the improved chaotic system with constant Lyapunov exponent spectrum, by introducing an absolute term in the dynamic equation, a novel chaotic attractor is found in this paper. Firsty, the existence of chaotic attractor is verified by simulation of phase portrait, Poincaré mapping, and Lyapunov exponent spectrum. Secondly, the basic dynamical behaviour of the new system is investigated and expounded. Simulation of Lyapunov exponent spectrum, bifurcation diagram and numerical analysis on amplitude evolvement of state variables show that the state variables of the chaotic system can be modified linearly by a global linear amplitude adjuster while the Lyapunov exponent spectrum keeps on stable and the chaotic attractor displays the same phase portrait. Finally, an analog circuit is designed to implement the new system, the chaotic attractor is observed and the action of global linear amplitude adjuster is verified, all of which show a good agreement between numerical simulation and experimental results.
2010, 59 (2): 792-800.
doi: 10.7498/aps.59.792
Abstract +
A cascaded encryption scheme using physical chaos is realized primarily, which combines chaotic encryption with data encryption standard. The difference of statistical properties of cipher text is studied for two cases. One case is that the ciphertexts come from different schemes, i.e. the cascaded and the single-stage ones, respectively. The other is that the ciphertexts are generated by chaotic signals with different unpredictability in the same scheme. Because physical chaos is adopted in this system, there is no assured relationship between plaintexts and ciphertexts, and the statistical characteristics of ciphertexts should be better than （or about equal to） that of any other encryption system. The experimental results support this conclusion, and show that the stronger unpredictability of chaotic signals causes the weaker correlation of ciphertexts.
2010, 59 (2): 801-815.
doi: 10.7498/aps.59.801
Abstract +
The existence of special piecewise-linear structure, global linear amplitude adjuster and phase-reverse controller in improved chaotic system with constant Lyapunov exponent spectrum contributed much to finding new synchronization methods and new adjusting parameters. According to the principle of generalized synchronization, by constructing appropriate driving system and response system, generalized synchronization of the improved chaotic system with constant Lyapunov exponent spectrum then can be achieved. By changing the parameter of response system, the complete synchronization and generalized projective synchronization can be further realized. The amplitude of the state variable of the driving system and the response system can be controlled to increase and decrease synchronously by the global linear amplitude adjuster, while the phase of certain variables can be controlled to reverse synchronously by the phase-reverser. This synchronization system dispenses with other special controllers, possesses simple structure and so can be implemented easily. Finally, the implement circuit of synchronization system is designed. It is validated by experiment simulation that the synchronization methods are feasible, the amplitude and the phase of the state variable in the synchronization system can be controlled by special parameters of the improved chaotic system.
2010, 59 (2): 816-825.
doi: 10.7498/aps.59.816
Abstract +
We use the extreme frequency sensitivity of Duffing’s equation to produce intermittent chaos（we call it “breather”） and propose a new method to quantitatively detect the parameters of unknown weak periodic signals. The theoretical analysis and instance simulation have proved its feasibility. We also put forward a way to improve the detection results and enhance the accuracy.
2010, 59 (2): 826-831.
doi: 10.7498/aps.59.826
Abstract +
Based on the extended closed-orbit theory with the combination recurrence induced by the nuclear core scattering，we calculate the time-dependent auto-ionization rate of lithium atoms in parallel electric and magnetic fields, and the chaotic behavior in the auto-ionization process is explained. A qualitative description of the shape of the ionizing trajectories from the nesting distinct fractal epistrophes is given.In particular, some special escape trajectories induced by core-scattering is obtained in configuration space. The escape time and the auto-ionization rate that exhibit a series of chaotic pulse train are discussed for different magnetic fields. We find that, with the increase of the magnetic field, the ionizing electron pulse train along with the corresponding ionized electron trajectories become more and more complicated, showing the sensitive dependence of the dynamic properties on the initial conditions.
2010, 59 (2): 832-841.
doi: 10.7498/aps.59.832
Abstract +
The similarities as well as the differences of the optimal velocity model（OV model） and the Nagel-Schreckenberg model （NS model） are compared by both analytical and numerical approaches. By analyzing the rules of both models, we prove that the NS model is a discrete form model of OV model. By numerical simulations, OV model with different parameters and stochastic NS model are compared from two aspects, namely the fundamental diagram and their dynamics under open boundary conditions. The results show that these two models have very similar behaviors. However, they are different in essence, and each model has their own advantages, which makes it useful. This study provides a basis for the application and improvement of traffic flow models.
2010, 59 (2): 842-850.
doi: 10.7498/aps.59.842
Abstract +
The relationships between positive （negative） eigenspectrums and the structure properties of community （anti-community） of complex networks are investigated, and some corresponding definitions are given. By using the multieigenspectrums of modularity matrix of networks, a kind of structural centrality measure called the community centrality, is introduced. This individual centrality measure describes the strength that the individual adheres to the corresponding community. The measure is illustrated and compared with the standard centrality measures using several artificial networks and real world networks data. The results show that the community centrality has better discrimination, and it has positive correlation with the degree centrality.
2010, 59 (2): 851-858.
doi: 10.7498/aps.59.851
Abstract +
We present an analytical analysis of the actors’ degree distribution of collaboration networks by the rate equation approach. The results show that the actors’ degree follows a Yule-Simon distribution and this distribution can be well approximated by a shifted power law function. We find that the actors’ degree distribution has a large deviation from power-law with the increase of the growth speed of actors. It indicates that the growth speed of actors is another key factor influencing the topological properties of collaboration networks besides preferential attachment. The results of our analytical analysis can be well fitted with the empirical data from some public transport networks and scientists collaboration networks. Furthermore, we discuss the generating mechanism of the growth speed of actors in evolution of collaboration networks and its potential value of application in real-world networks.
2010, 59 (2): 859-866.
doi: 10.7498/aps.59.859
Abstract +
According to analysis of discrete cosine transform （DCT） coefficients of video sequence, a new DCT coefficients statistical model based on Weibull probability density function（PDF） is introduced. Compared with Laplacian PDF and Cauchy PDF, the model can describe properties of DCT of video sequences much better. In addition, according to the new statistical model and theory of entropy coding, the rate quantization （RQ） and distortion quantization （DQ） functions are proposed separately. Based on the simplified and approximate RQ and DQ which are obtained by the theory of rate distortion （RD） model and the properties of real video sequence, the novel RD model is presented. The experimental results show that the real video sequence encoded by intra or inter can be described much better by using rate distortion model based on Weibull PDF.
2010, 59 (2): 867-876.
doi: 10.7498/aps.59.867
Abstract +
We present a three-phase four-leg matrix converter circuit topology, which can be used as three-phase four-wire AC voltage source to power the load imbalance. For the matrix converter topology, a novel indirect space vector modulation strategy is proposed, and the switch vector synthetic formula are deduced, giving a range of options, duty-cycle calculation and output reference voltage settings. Finally the new circuit topology for the simulation is studied. The results show that the circuit topology under three-phase unbalanced load can ensure sinusoidal output voltage waveform and stability.
EDITOR'S SUGGESTION
2010, 59 (2): 877-882.
doi: 10.7498/aps.59.877
Abstract +
An all-optical high sensitivity atomic magnetometer is investigated and demonstrated experimentally, of which the principle is based on the interaction between laser beam and rubidium atoms in magnetic field. This interaction is dependent on the magnetic field surrounding the Rb atom cell, therefore the magnetic field information can be obtained simply by measuring the changes of the laser power transmitted through the Rb atom cell. The principle of the atomic magnetometer is analyzed and the performance of the experimental setup is investigated. The experimental result agrees well with the theoretical predictions. Furthermore, some important factors that may affect the performance of the magnetometer are discussed, and the ways to improve the sensitivity of the atomic magnetometer are also put forward.
2010, 59 (2): 883-892.
doi: 10.7498/aps.59.883
Abstract +
The magnetoelastic damping in magnetostrictive material is investigated. It is noted that the quality factor （the inverse measure of damping） of giant magnetostrictive material Terfenol-D is strongly dependent on bias direct current （DC） magnetic field. Taking advantage of the DC field dependence of magnetoelastic damping in magnetostrictive material, a DC or quasistatic magnetic sensor is proposed. The sensor is designed as a composite piezoelectric transformer （CPT） which is fabricated by bonding magnetostrictive material and piezoelectric transformer in layers. Theoretical analysis shows that the output voltage of the CPT is directly proportional to the quality factor of the CPT. Therefore, the output voltage of the CPT also strongly depends on DC field due to the strong field dependence effect of quality factor in magnetostrictive material. In addition, the ΔE effect of magnetostrictive material has little influence on the magnitude of the output voltage. A Terfenol-D/PZT8 composite transformer is fabricated for experiment. The experimental results show that the output sensitivity to DC field achieves ~5.12 mV·Oe-1 when the CPT is driven near resonance by an AC voltage with amplitude of 0.5 V.
2010, 59 (2): 893-898.
doi: 10.7498/aps.59.893
Abstract +
The basic conditions for designing a wide field Michelson interferometer with chromatic and thermal compensation, which is used to measure the upper atmospheric wind field，is briefly described. Comparing with the current method for designing the wide field Michelson interferometer with chromatic and thermal compensation, we present a method uses four media for the compensation of the MI to eliminate the monochromatic thermal aberration. The result shows that, by using this method, the polychromatic thermal aberration is ten to hundred times smaller than the method now in use. The research has important theoretical significance and practical value both for the research and development of the wide field Michelson interferometer with chromatic and thermal compensation for detection of the upper atmospheric wind field.
2010, 59 (2): 899-906.
doi: 10.7498/aps.59.899
Abstract +
Taking the aurora in upper atmosphere as the detection source, we propose a new principle of passive detection of emission rate in upper atmosphere wind based on the Lorentzian line shape profile. Using this principle, we can detect not only the physical parameter of upper atmospheric wind such as velocity, temperature and pressure, but aslo the emission rate, which resolves the problem of detecting emission rate at present. The calculation formula of the distribution of the velocity, temperature, pressure and emission rate are deduced based on the Lorentzian line shape profile, and by using computer simulation, the error curve is described. This study provides a theoretical basis for further study of detection of upper atmospheric wind field. It will play a significant role and has a wide application prospect in aerospace, space exploration, and environmental protection.
2010, 59 (2): 907-912.
doi: 10.7498/aps.59.907
Abstract +
A micro-spectrometer without moving parts that can be manufactured through micro-opto-electro-mechanical system techniques is developed, and the interference system is introduced. The fabrication of the micro multi-mirrors, which is the core part of the system, is investigated and wet etching of silicon in KOH solution is testified to be a good method. The root mean square surface roughness of the reflect surface made up of Si planes （111） through wet etching is less than 10 nm.
NUCLEAR PHYSICS
2010, 59 (2): 913-917.
doi: 10.7498/aps.59.913
Abstract +
The temporal statistics of multiple scattered broadband terahertz pulses through a highly scattering medium is analyzed. The probability distribution function of the scattered field varies with the delay time. The probability distributions of the scattered field, and the real and imaginary components are discussed. Due to the broad bandwidth and the transient nature of the terahertz pulses, the statistics of the scattered field evolves over time and is therefore nonstationary. This analysis emphasizes that these measured fields are not stationary. We demonstrate that the nonstationary process is a direct consequence of the time dependence of the averaged intensity.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (2): 918-924.
doi: 10.7498/aps.59.918
Abstract +
The electron impact excitation （EIE） cross sections from the ground state to all of the 2s22p53 and 2s2p63（=s, p, d） states along the Ne-like isoelectronic sequence of ions （Z=50—57） have been calculated by using the multi-configuration Dirac-Fock package GRASP92 and the fully relativistic distorted-wave program REIE06. In the calculations, the relativistic effects and electron correlation effects are considered systematically. Based on those calculations, the EIE cross sections along the Ne-like isoelectronic sequence of ions for different incident electron energies are discussed, and some important conclusions are drawn. We also study the influence of the correlation effects on the values of the 3C/3D line-intensity ratio ［3C: （2p1/23d3/2）1→2s22p6 1S0, 3D: （2p3/23d5/2）1→2s22p6 1S0］ along the Ne-like sequence. A comparison is made between the present results and previous theoretical calculations and experimental results for the EIE cross sections in Ba46+ ions, and a good agreement is obtained.
2010, 59 (2): 925-931.
doi: 10.7498/aps.59.925
Abstract +
Based on special relativity, the formation mechanism of characteristic X\|ray was studied, and the influence of the spin-orbit coupling on the characteristic X\|ray wavelength was analyzed. A calculation formula of the X\|ray wavelength based on special relativity is obtained. Error analysis is carried out systematically for the calculation values of wavelength, and the rules of relative error are obtained. It is shown that the results of the calculation are very close to the experimental results, which have some reference meaning for spectrum analysis of characteristic X\|ray in application.
2010, 59 (2): 932-936.
doi: 10.7498/aps.59.932
Abstract +
Using the closed orbit theory, we calculate the photodetachment cross section of H-ion in a uniform electric field near a metal surface. The results show that the photodetachment cross section of H- near the threshold has a significant change after the metal surface has been placed in the uniform electric field. Compared with the situation of the photodetachment of H- ion in a single uniform electric field, the oscillating amplitude of the photodetachment cross section of this system is increased and the oscillating frequency is decreased. If we keep the electric field strength at a given value, we find that with the increase of the distance between the metal surface and the H- ion, the oscillating amplitude of the photodetachment cross section decreases and the oscillating frequency increases. When the ion-to-surface distance increases to a certain value, the influence of the metal surface disappeared, and the photodetachment cross section approaches the photodetachment cross section of H- in a uniform electric field.
2010, 59 (2): 937-942.
doi: 10.7498/aps.59.937
Abstract +
The momentum transfer cross sections （MTCSs） of low-energy electron scattering from H2 molecule are studied using the body frame vibrational close coupling method and the electrostatic potential, the exchange potential,and the correlated polarization potential calculated based on ab initio method. By considering the contributions of 18 Morse vibrational wave functions, 8 partial waves, and 16 molecular symmetries, we obtain the converged MTCSs of ν=0→ν′=0,1,2,3,4 transition excitations. The converged total MTCSs agree well with the recommended values of Elford et al., and are better than the previous theoretical studies in the eletron energy range of 1 eV
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (2): 943-948.
doi: 10.7498/aps.59.943
Abstract +
The numerical reconstruction scheme of equivalent electromagnetic parameters for composite material is proposed based on the finite difference time domain（FDTD） method. To study the relationship between equivalent electromagnetic parameters and the bulk density of mixed medium, the reflection coefficient and transmission coefficient were firstly calculated by the FDTD method, and then the equivalent electromagnetic parameters were reconstructed by genetic algorithm and propagation matrix method under different blending ratios. When the blending ratio of composite material is low or high,the equivalent electromagnetic parameters calculated by the equivalent constitutive parameter formulas and numerical reconstruction scheme agree well with each other. The results are somewhat different only for the middle blending ratio. The results show the feasibility of the proposed numerical scheme for the reconstruction of equivalent electromagnetic parameters of composite material.
2010, 59 (2): 949-957.
doi: 10.7498/aps.59.949
Abstract +
The principle of the polarization interference imaging spectrometer （PIIS） developed in our laboratory is described. The principle of the beam splitting of Glan-Taylor prism which is one of the key components in the PIIS is analyzed. Using the ray-tracing method, we obtain the transmittance of Glan-Taylor prism at full angle of view. By computer simulation, we analyze the influence of the incidence plane, incidence angle and thickness of air gap on transmittance, and the dependence of the transmittance on wavelength is given in the spectral range which is required by the instrument system using Sellmeier dispersion equation. The transmittance of Grand-Taylor prism is tested in experiment, and the results are in good agreement with the theoretical results, so the correctness of the theory is verified.
2010, 59 (2): 958-963.
doi: 10.7498/aps.59.958
Abstract +
The methods for improving the focusing properties of subwavelength metallic lens by optimizing the groove width and depth of the structure simultaneously are presented. We investigate how the variations of the width and depth of the groove affect the half width at half maximum of the focus, intensity, normal focusing efficiency of the focal spot and the focal length, based on the finite-difference and time-domain method. The optimum design methods of metal lens are put forth through discussing the focusing regularity and physical mechanism, which can provide a theoretical basis for realizing the nano-focusing and flexible manipulation of light wave based on metallic lens.
2010, 59 (2): 964-972.
doi: 10.7498/aps.59.964
Abstract +
The speckle fields and their phase singularities produced respectively by the square loop aperture and circular ring aperture are studied. It is found that the zero-contour of the real and imaginary parts occurs in the complicated tangential and intersectional situations. The tangential and intersectional points can also form phase singularities, around which the phase distribution shows the characteristics of symmetry and discontinuity，which differs from the spiral distribution around the traditional singular points formed by the zero crossings of the real and imaginary parts. The speckle particle distributions in the speckle fields produced by the square loop aperture and circular ring aperture is different from those by the traditional square aperture, and the speckle particle distributions are modulated by the scattering aperture, in stripes of horizontal or vertical outlines and circular outlines respectively. In addition, an interesting phenomenon occurs that a lot of disc-like dark regions appear in the intensity pattern of the speckle fields. We call it “light intensity dark nucleus”, whose center corresponds to a vortex with homogeneous phase distribution.
2010, 59 (2): 973-979.
doi: 10.7498/aps.59.973
Abstract +
Stochastic parallel gradient descent （SPGD） algorithm is one of the effective ways to realize high power fiber laser coherent combining of master oscillator power amplifier. The basic principle of the SPGD algorithm in the coherent combining is introduced, the SPGD phase controller has been designed and manufactured, and the representative experiment results are presented. Theoretical analysis shows that the iteration rate is 200000 per second, the average compensation bandwidth is about 12500 Hz, the minimal phase control error is 1/179 wavelength. Experiment shows that the SPGD controller can perform well in phase locking of two lasers, the average phase residual error is less than 1/25 wavelength when the amplitude of the phase noise is greater than λ/10, and the frequency is 3 kHz.
2010, 59 (2): 980-988.
doi: 10.7498/aps.59.980
Abstract +
Automatic target detection is always difficult in complex background. The Wigner-Ville distribution has a good characteristic that the images can be represented in spatial/spatial-frequency domains. Through the pseudo Wigner-Ville distribution, the statistical property of Rényi entropy is studied. The change of Rényi entropy’s statistical property in natural images when the man-made objects appear is analysed. Then a novel method for generating saliency map based on pseudo Wigner-Ville distribution and Rényi entropy is proposed. Target detection is performed when the saliency map is segmented using a simple and convenient threshold method. Experimental results show the proposed method can detect the military vehicles from complex earth background effectively.
2010, 59 (2): 989-997.
doi: 10.7498/aps.59.989
Abstract +
The principle of the polarizing atmospheric Michelson interferometer is introduced, the influence of the polarization directions of all the components on its interferential intensity and modulation depth is discussed, and the dependence of intensity and modulation depth on the deviation is calculated with the polarization direction deviating from the ideal direction. We analyze the influence on the intensity and modulation depth when the polarization directions of the polarizer, the three quarter-wave plates and the analyzer deviate from the ideal direction. The changing curves of modulation depth, wind velocity and the temperature with the deviation of the polarization direction are obtained. We also give the tolerances of all the polarization directions. These results would be helpfull for theoretical research and development of the new polarizing atmospheric Michelson interferometer. It also has scientific value and wide prospect for measuring winds in the thermosphere and for space measurement.
2010, 59 (2): 998-1008.
doi: 10.7498/aps.59.998
Abstract +
Statistical distributions of synthetic aperture radar （SAR） images based on central limit theorem cannot reflect the statistical characteristics of sharp peak and heavy tail of high-resolution SAR images. By using the generalized central limit theorem, the heavy-tailed distributions （heavy-tailed Rayleigh distribution for amplitude image and heavy-tailed exponential distribution for intensity image） are obtained from the symmetric stable distributions of real and imaginary parts of echoes. Taking the heavy-tailed Rayleigh distribution as an example, the algebraic tails of heavy-tailed distributions are explained as well as the statistical properties of sharp peak and heavy tail. In order to model the high-resolution SAR images with the heavy-tailed distributions, based on second-kind statistical, Characteristics the log-cumulant estimator is proposed to efficiently estimate the parameters of the heavy-tailed distributions. Modeling experiments on real SAR images demonstrate that the heavy-tailed distributions based on the generalized central limit theorem can accurately describe the sharp-peaked and heavy-tailed statistical characteristics of high-resolution SAR images.
2010, 59 (2): 1009-1016.
doi: 10.7498/aps.59.1009
Abstract +
Based on the geometric theory of concave grating, we deduce the mathematical expressions of the meridional curve, Sagittal curve and the relational expression for the holographic flat-field image concave grating. We also propose a new optimal method in all used range for correcting the meridional and sagittal aberrations. Different from the design method using CODE V or ZEMAX, we use mathematical expression and adopt grating optimal factor instead. By fitting the meridional focusing curve and Sagittal focusing curve of concave grating, we find an image surface in theory to ensure that the meridional and also the Sagittal aberrations tend to zero, and then design and fabricate the grating based on the fitting parameters. We solve the problem that the meridional curve transcendental equation cannot solve by Matlab, and discuss the influence of two curves for different grating constants and different incidence angles. We find that the aberrations in a wide spectral range can be corrected by diminishing the incidence angle and increasing the grating scribed lines.
2010, 59 (2): 1017-1020.
doi: 10.7498/aps.59.1017
Abstract +
We propose a scheme for generating four-photon polarization-entangled cluster states based on the cross-Kerr nonlinear interaction between field-modes. Compared with other schemes, our scheme introduces the idea of parity gate and uses the non-destructive measurement method based on homodyne detection, which is easier to implement in experiment.
2010, 59 (2): 1021-1029.
doi: 10.7498/aps.59.1021
Abstract +
A single semiconductor optical amplifier （SOA） assisted by optical filter is exploited to realize high-speed all-optical wavelength conversion, in which, the filter is employed to optimize output spectrum. We propose a spectrum optimizer which contains a band pass filter （BPF） and a delay interferometer （DI）. Based on this configuration, 80 Gbit/s all-optical non-inverted conversion has been numerically simulated. Furthermore, the quality of output signal has been improved greatly using genetic algorithms to optimize the parameters of the spectrum optimizer. Additionally，the effect of ultra-fast carrier dynamics in SOA on the output signal is analyzed theoretically. The dependence of the signal extinction ratio （ER） and pattern effect （PE） on variations of the BPF’s ER and DI’s ER is also studied.
2010, 59 (2): 1030-1034.
doi: 10.7498/aps.59.1030
Abstract +
A erbium-doped fiber ring laser, which utilizes a single-stage polarization-independent acousto-optic tunable filter by use of quasi-collinear coupling as the tuning component, is proposed and a continuously tunable lasing wavelength is realized. The filtering principle of the polarization-independent quasi-collinear filter is introduced briefly, and then the compensation of frequency-shift is analyzed. The experimental results are that the output power of the laser pumped at 13 mW is measured to be 322 μW at a lasing wavelength of 1550 nm, the threshold pump power is 7.65 mW, and the slope efficiency is 6.02%; the tuning range of 38 nm, starting from 1524.7 nm ending at 1562.4 nm, is observed.
2010, 59 (2): 1035-1039.
doi: 10.7498/aps.59.1035
Abstract +
The control of the photonic crystal waveguide over the beam profile of vertical-cavity surface-emitting lasers is investigated. The symmetric slab waveguide model is adopted to analyze the control parameters of the beam profile in the photonic-crystal vertical-cavity surface-emitting laser （PC-VCSEL）. The filling factor （the ratio of the hole diameter to the lattice constant） and the etching depth control the divergence angle of the PC-VCSEL, and the low filling factor and the shallow etching depth are beneficial to achieve the low-divergence-angle beam. Two types of PC-VCSELs with different filling factors and etching depths are designed and fabricated. The experimental results show that the device with a lower filling factor and a shallower etching depth has a lower divergence angle, which agrees well with the theoretical predictions.
2010, 59 (2): 1040-1046.
doi: 10.7498/aps.59.1040
Abstract +
Based on the theoretical analysis of the conditions of the fast or slow light without distortion for arbitrary signal, a universal formula of an optimized Brillouin comb gain is obtained in accordance with the spectrum characteristics of the periodic signal. According to the amount of delay or advancement required, each Brillouin gain intensity and frequency detuning between Brillouin gain peak and the corresponding harmonic frequency of periodic signal can be found conveniently using this universal formula, then the whole Brillouin comb gain is identified. Numerical calculation for sinusoidal signal, Gaussian periodic signal and square periodic signal is performed. The results show that zero-broadening slow and fast light is achieved using this optimized Brillouin comb gain for the three types of periodic signals, and the validity of the universal formula is proved. Moreover, the magnitude of the delay or advancement can be tuned continuously by adjusting the Brillouin gain intensity and frequency detuning.
2010, 59 (2): 1047-1051.
doi: 10.7498/aps.59.1047
Abstract +
Using the characteristic that a time delay between the signal of stimulated Brillouin scattering （SBS） and the pump beam during amplification of SBS signal is allowed, a controller is devised to control the polarizations of two pulses propagating collinearly with orthogonal polarizations. It makes the two beams have the same polarization when the SBS signal meets the pump beam. Therefore, amplification of the SBS signal is realized.
2010, 59 (2): 1052-1062.
doi: 10.7498/aps.59.1052
Abstract +
Intrinsic optical bistability （IOB） in Tm3+/Yb3+ codoped laser crystal under 650 nm laser excitation is theoretically studied. Based on the theory of nonlinear coupled rate equations, we numerically analyze IOB evolutions of the populations at Tm3+/Yb3+ energy levels, and the influence of system parameters on IOB and the dynamic operation of bistable hysteresis loop. The simulation result shows the fluorescence IOB in visible-infrared spectra of Tm3+/Yb3+ codoped laser crystal under photon avalanche pumping scheme. It is found that IOB phenomena can be largely enhanced by optimizing the Tm3+/Yb3+ concentration ratio, choosing low phonon-energy crystal host and using crystal cooling technology, and also by tuning the pump laser to match the resonant frequency of Tm3+ excited-state absorption transition. Through tuning the pump laser wavelength and adjusting the rate of change in pump intensity, the controllable IOB switching can be achieved.
2010, 59 (2): 1063-1068.
doi: 10.7498/aps.59.1063
Abstract +
We use spectral renormalization method to solve the nonlocal nonlinear Schrdinger equation, which gives accurate waveform of nonlocal optical spatial soliton. The relation between critical power and critical beamwidth is acquired in different nonlocal conditions. We discovered that optical spatial soliton exists stably in any nonlocal degree. Comparing analytic solution with numerical solution for different response functions, we find that they are consistent only under strong nonlocal and weak nonlocal conditions. The effective range of analytic solution is also given.
2010, 59 (2): 1069-1074.
doi: 10.7498/aps.59.1069
Abstract +
We solve the two-dimensional strongly nonlocal nonlinear Schrdinger equation in polar coordinates. An exact analytical solution of self-similar waves, namely Kummer-Gaussian soliton clusters, is obtained. Numerical simulations confirm the validity of the analytical solutions. It is shown that the nonlocal optical spacial solitons have large phase shift.
2010, 59 (2): 1075-1081.
doi: 10.7498/aps.59.1075
Abstract +
We investigate the power controlled short-range interactions between spacial optical solitons in the strongly nonlocal nonlinear media. For the short-range interactions, the trajectory of mass center of solitons will deflect because of the phase difference under the condition of momentum conservation. We verify by experiment that the degree of deflection depends on the ratio of the power of two solitons, and the case of equal power corresponds to the maximum deflection. Using the characteristics of power control on the interaction between solitons, we measure the photic-induced response time of nematic liquid crystals, and find that it is much shorter than the bias-voltage-induced response time.
2010, 59 (2): 1082-1087.
doi: 10.7498/aps.59.1082
Abstract +
SiO2 colloidal crystal template was fabricated by the solvent vaporization convection self-assembly method. The low pressure chemical vapor deposition method was then used to fill the voids of the silica colloidal crystal template with high refractive index silicon, thus silicon inverse opal photonic crystal was obtained. The modality structure silicon inverse opal was characterized by scanning electron microscopy. Its photonic bandgap structure was calculated based on plane wave expansion method. Its photonic bandgap properties were characterized by Fourier transform infrared spectroscopy. The results showed that silicon is homogeneously distributed inside the voids of silica template. The wavelength and bandwidth of photonic bandgap measured by microscopic infrared spectrometer agree with the calculated one. The tilt-angle reflectance spectra along the different incidence angles showed that the refection peaks with the band center wavelength of 3319 nm always existed. This result proved that silicon inverse opal has the complete photonic bandgap. The bandgap lies in the range of mid infrared atmosphere window.
2010, 59 (2): 1088-1094.
doi: 10.7498/aps.59.1088
Abstract +
Precise physical experiments place strict requirements on target illumination uniformity in inertial confinement fusion research. Currently, the main stream of beam smoothing technology adopted in solid-state laser driver combines smoothing by spectral dispersion （SSD）, phase plate and beam overlapping. A new smoothing method aimed at indirect-drive laser fusion is studied here, which uses linearly modulated light and angular spectral dispersion. After using this technique, high frequency modulations on the far field could be smoothed. In the meantime, near field after the dispersion grating could be smoothed too. Experimental results show that the measured spectrum is similar to the simulated one. Phase modulator is not necessary in this method, while it is a crucial element in traditional SSD method.
2010, 59 (2): 1095-1100.
doi: 10.7498/aps.59.1095
Abstract +
When the hexagonal structure parameters are changed, the dispersion coefficient and nonlinear coefficient with two zero-dispersion of photonic crystal fiber as a function of wavelength is investigated from the near infrared wavelength to the range of communication band by multipole method. We compare photonic crystal fiber of hexagonal structure with that of octagonal structure, both of which have the same structural parameters. The two zero-dispersion wavelengths of photonic crystal fiber with hexagonal structure are much flatter and the nonlinear coefficient of photonic crystal fiber with hexagonal structure is significantly increased, so the photonic crystal fiber with hexagonal structure is more accessible to flattened high nonlinearity and two zero-dispersion wavelengths. It is shown from numerical results that it is possible to design photonic crystal fiber of hexagonal structure with two zero-dispersion and high nonlinear coefficient around 800 nm.
2010, 59 (2): 1101-1107.
doi: 10.7498/aps.59.1101
Abstract +
A kind of high birefringence and highly nonlinear nano-structured photonic crystal fibers （N-PCFs） is proposed. The birefringence, fundamental mode field, dispersion and nonlinear characteristics of the fiber have been studied by electromagnetic scattering theory of multipole. It is found that the birefringence becomes larger by increasing the dissymmetry level of fiber core and air holes in cladding, and the largest birefringence reaches up to 1.918×10-2. With this type of high birefringence and highly nonlinear N-PCFs, the peak of birefringence can be moved to the required wavelength by adjusting the pitch value. The non-linear coefficient of N-PCF with pitch 400 nm reaches up to 0.2 m-1·W-1 in the wavelength of 800 nm.Meanwhile, the birefringence value is also very large in the wavelength range of 750—1000 nm. A perfect combination of high birefringence and high nonlinearity is realized in N-PCF. It is useful for manufacturing new type of nano-photonic apparatus and development of integrated optics.
2010, 59 (2): 1108-1115.
doi: 10.7498/aps.59.1108
Abstract +
In the conventional nearfield acoustic holography （NAH）, only the pressure or particle velocity is used as the input quantity, and it cannot separate the waves from the two sides of the hologram surface. Therefore, all sources are assumed to be on one side of the hologram surface, i.e. the sound field is assumed to be free. This assumption limits the practical applications of NAH. In the NAH using pressure and particle velocity measurements, both pressure and particle velocity are used as the input quantities. By establishing and solving the coupling relationship on the hologram surface between the waves from the two sides of the hologram surface, the waves from the two sides can be separated. On the basis of the previous studies on sound field separation techniques and based on the Euler formula and the finite difference approximation technique, a new theoretical formula of NAH using pressure and particle velocity measurements is given, and then an experiment is performed to validate the method.
2010, 59 (2): 1116-1122.
doi: 10.7498/aps.59.1116
Abstract +
The oscillation phenomena for granular mixture within a vertically vibrated container are investigated with the event-driven method. The container consists of two rooms with equal size separated by a clapboard with certain height，and two kinds of granules with the radius of one twice as larger as the other are used. Investigation results indicate that the period of oscillation of granula sharply increases with the decrease of the ratio of density between two kinds of particles. The relations of the ratio of density to the ratio of vertical height of the two kinds of particles are calculated, which shows that the main factor of granular oscillation is not the “Brazil nut effect” or “reverse Brazile nut effect”. The granular temperature is calculated and found to be relevant to oscillations of mixture. When the temperature of the small particle is above a certain value, oscillations of granular mixture occur. According to hydromechanical equations proposed by Viridi et al., these equations are correspondly modified and may explain the relations between the period of oscillation and the ratio of granular density.
2010, 59 (2): 1123-1129.
doi: 10.7498/aps.59.1123
Abstract +
Considering two-layer fluid bounded by the thermocline, under the condition of weak nonlinearity, based on the dynamic equations of two-layer fliud, the nonlinear Schrdinger equation for internal waves in deep sea is obtained by adopting hierarchical method. The coefficients of dispersion and nonlinearity are analysed, the soliton solution of the nonlinear Schrdinger equation is obtained, and the exactitude of the theory is demonstrated by a numerical experiment.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (2): 1130-1136.
doi: 10.7498/aps.59.1130
Abstract +
We demonstrate an all fiber multi-laser pulse generation system that can output broadband chirped pulse, nano-second shaped pulse and narrowband pump pulse for optical parametric chirped pulsed amplifiers system with precise synchronization. Yb3+-doped fiber mode-locked laser and single longitudinal oscillator are used as the optical source for the fiber system. The ultra-short pulse train generated from the mode locked fiber laser was split into two beam-lines and both were chirp-stretched to 0.9 ns. One of them was directly amplified to a magnitude of 10 μJ to provide the high-energy petawatt laser facility with seed pulse. The other was tailored by a 1.2 nm bandwidth filter to form a 140 ps unit pulse. It was then stacked in a fiber stacker and formed a 2.3 ns arbitrarily shaped pulse. The shaped pulse was amplified to 10 μJ to provide seed pulse for the pellet compression. Simultaneously, we sampled part of the ultra-short pulse train from the mode locked laser. The sampled pulse train was converted to electrical signal and phase-locked to generate trigger pulse that precisely synchronized with the mode locked pulse for an amplitude modulator. The continuous-wave laser generated from the fiber single longitudinal oscillator was tailed by the amplitude modulator and then amplified to provide seed pulse for the OPCPA system. The output of the fiber system can switch between different kinds of pulses with flexibility according to the physical experimental requirement.
2010, 59 (2): 1137-1142.
doi: 10.7498/aps.59.1137
Abstract +
A class of wide band-gap semiconductor offers an attractive alternative to Si and X-ray diode detector technologies for X-ray detection in inertia contract fusion （ICF） experiments, because diamond has high thermal conductivity, resistivity and breakdown field, fast charge collection, low leakage current, wide band-gap, low dielectric constant, large carrier drift velocity and outstanding radiation hardness. Using chemical vapor deposition （CVD）, diamond of 1 mm×1 mm×2 mm，1 mm×1 mm×3 mm was synthesized. The quality of diamond has been examined by Ramma spectrum and X-ray diffraction. And the detectors were fielded. Characteristics of these detectors have been studied on an 8 ps pulse-wide laser equipment and SGIII-prototype equipment. The results indicate that the rise time and full width at half maximum of the detector system reach 60 ps and 120 ps, respectively. The measured spectrum is consistent with the result of soft X-ray spectrometer. There is no response to 3ω0 laser for the CVD detector. The applications of CVD diamond for X-ray measurement in ICF experiments are reviewed.
2010, 59 (2): 1143-1147.
doi: 10.7498/aps.59.1143
Abstract +
We analyze, separately, the effects of the microwave magnetic field and the oblique microwave field on multipactor discharge on a dielectric surface. Using particle-in-cell/Monte Carlo simulation, we obtain the temporal evolution of the number of electrons, direct current electric field, mean kinetic energy of electrons，and power deposited in the dielectric in the cases of the microwave magnetic field and the oblique microwave field. The numerical results show that the oblique microwave field and the microwave magnetic field can significantly affect the mean kinetic energy of electrons, but do not qualitatively change the number of electrons and the power deposited in the dielectric, so the microwave magnetic field and the oblique microwave field do not significantly affect the multipactor.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2010, 59 (2): 1148-1154.
doi: 10.7498/aps.59.1148
Abstract +
The rare-earth doped strontium aluminate phosphors SrxCa4-xAl14O25:Eu2+,Dy3+（x＝0，0.8，1.6，2.4，3.2，4） were synthesized by a high temperature solid-state reaction method. The X-ray diffraction studies show that phase of the phosphors is orthorhombic Sr4Al14O25 for x4O7 for x > 2.4. The results indicate that the phase structure of the samples changes from Sr4Al14O25 to CaAl4O7 when the value of x changes from 0 to 4. In addition, a blue shift was found in the emission spectra due to the change in nature of the Eu2+ surroundings. The decay characteristics show that the phosphor samples with different Ca2+ contents have different afterglow time, and the afterglow time also changes with the value of x. The measurement of thermoluminescence reveals that the trap depth of the phosphor samples with different Ca2+ contents is different. The samples with deeper traps have longer afterglow time.
2010, 59 (2): 1155-1162.
doi: 10.7498/aps.59.1155
Abstract +
Polycrystalline samples of Sr14Cu24O41 and Sr14（Cu0.97M0.03）24O41（M=Zn, Ni, Co） were synthesized by standard solid state reaction method. All samples are single phase as identified by X-ray diffraction, no regular shift of lattice parameters a, c is found, but the lattice parameter b increases slightly with doping magnetic ions Ni and Co, and has no change with doping non-magnetic ion Zn, respectively. Selected area electron diffraction experiments show that Zn,Ni and Co ions may substitute for Cu ions in the chain. All the doping compounds are still semiconductors and have a crossover temperature Tρ like the parent phase Sr14Cu24O41. The influence of magnetic ion Ni or Co doping on the resistivity is smaller than that of non-magnetic ion Zn doping, while the influence of non-magnetic ion Zn doping on crossover temperature is smaller than that of magnetic ion Ni or Co doping.
2010, 59 (2): 1163-1168.
doi: 10.7498/aps.59.1163
Abstract +
Atom probe tomography characterization and thermal aging method have been employed to investigate the precipitation of Cu-rich clusters in reactor pressure vessel （RPV） model steels with and without the addition of Ni alloying element. It is observed that the number density of Cu-rich clusters in the PRV model steel with the addition of Ni （0.84 wt%） is higher than that without the addition of Ni. The segregation of nickel in the Cu-rich clusters and at the boundaries of clusters/matrix was also observed. It is found that the nickel alloying element can promote the precipitation of Cu-rich clusters in RPV model steel. An analytical embedded atom method model of Fe-Cu and Fe-Cu-Ni system is constructed on the basis of the physical properties of pure constituents Fe, Cu and Ni. The calculation results show that the nickel （1 at%） can promote the precipitation of Cu-rich clusters. The calculation results agree with the results of experiments.
2010, 59 (2): 1169-1174.
doi: 10.7498/aps.59.1169
Abstract +
High quality silicon nanowires （SiNWs） were grown directly from n-（111） silicon single crystal substrate by using Au film as a metallic catalyst. The diameter and length of the formed nanowires are 30—60 nm and from several micrometers to sereral tens of micrometers, respectively. The effects of Au film thickness, annealing temperature, growth time and N2 gas flow rate on the formation of the nanowires were experimentally investigated. The results confirmed that the silicon nanowires with controlled diameter, length, shape and orientation can be obtained via reasonably choosing and optimizing various technical conditions. The formation process of the silicon nanowires is analyzed qualitatively based on solid-liquid-solid growth mechanism.
2010, 59 (2): 1175-1179.
doi: 10.7498/aps.59.1175
Abstract +
Aiming at solving the “snap back” problem in the stiction, the sine rough surface model is established. Based on the Casimir effect, the Casimir force is obtained. Based on the micro scopic Wigner-Seitz principle, the Hanaker force is derived, which includes the repulsive force. The stiction force is simulated and the two “snap back” points are found. The curve of the stiction force has two break points, which is in agreement with the experiment.
2010, 59 (2): 1180-1184.
doi: 10.7498/aps.59.1180
Abstract +
The dispersion relation of transverse magnetic（TM） wave and transverse electric（TE） wave for surface plasmon at a metal-Kerr nonlinear medium interface are analyzed based on the Maxwell equations and the boundary conditions. The dispersion relation of TM wave is complex, due to the nonlinearity, and it has a dielectric coefficient and intensity-dependent expression. However, the TE wave does not exist at this interface as in the linear case.
2010, 59 (2): 1185-1189.
doi: 10.7498/aps.59.1185
Abstract +
Molecular dynamics was employed to study the migration and coalescence of He atom and He dimmer in Ti lattice which contains He-vacancy cluster. The influence of the ratio of helium to vacancy （He density） of the cluster and the He number of the cluster on coalescence of He and He-vacancy cluster in Ti lattice is studied. It is found that anisotropic diffusion is independent of the He-vacancy cluster in Ti lattice. The coalescence of helium and He-vacancy cluster is mainly along the ［001］ direction. The coalescence of He dimmer and He-vacancy cluster is faster than the coalescence of He atom and He-vacancy cluster.
2010, 59 (2): 1190-1195.
doi: 10.7498/aps.59.1190
Abstract +
Three sets of hydrogenated microcrystalline silicon （μc-Si:H） films for different deposition time were prepared by very high frequency-plasma enhanced chemical vapor deposition with different deposition rates. The surface roughness evolution of μc-Si:H has been investigated using spectroscopic ellipsometry. For films with the deposition rate of 0.08 nm/s and 0.24 nm/s, the surface roughness of films changes a little, and the growth exponent β is about 0.20. Similar β values ascribed to the adatoms have enough time to move to the site with lower energy under lower deposition rate. However, when the deposition rate increases to 0.66 nm/s, the surface roughness of films increases obviously, and the exponent β is about 0.81, which is much higher than 0.5 for zero diffusion limit in the scaling theory. The growth mode of high-rate deposited μc-Si:H is clearly different from that of lower-rate deposited μc-Si:H. This is due to the fact that the adatoms have no enough time to diffuse before being covered by the radicals of the next layer under high deposition rate, which decreases the surface diffusion of the adatom, and therefore increases the film surface roughening which results in a larger β. The case of β>0.5 is related to the shadowing effect.
2010, 59 (2): 1196-1201.
doi: 10.7498/aps.59.1196
Abstract +
The solar cell light absorber Cu（In,Ga）（Se,S）2（CIGSS） thin films were prepared by annealing the electrodeposited Cu（In,Ga）Se2（CIGS） precursors in H2S ambient at 500 ℃. The precursors and annealed films were characterized by energy dispersive X-ray spectroscopy, Auger electron spectroscopy, scanning electron microscopy, X-ray diffraction and Raman scattering. The results show that the complete removal of oxygen atom from the film and a substitution of Se by S can be achieved by H2S-annealing. Furthermore, the depth profiles of constituent elements become more uniform, and the Cu-Se micro-phase can be eliminated by H2S-annealing. Moreover, the CIGSS films have good crystallinity and smaller crystal lattice parameters with S and Ga incorporation into the chalcopyrite structure.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (2): 1202-1211.
doi: 10.7498/aps.59.1202
Abstract +
Using plane-wave pseudopotential methods based on the density functional theory, we have studied the structural and the electronic properties of gold doped Hg1-xCdxTe （MCT）. The results indicate that the in situ gold impurity maintains stabile bonds with the host atoms. Moreover, the in situ gold impurity creates a shallow acceptor level behaving as an efficient p-type dopant. For all mole fractions under molecular beam epitaxy （MBE） cation-rich growth condition, for 0.75＜x≤1 under MBE Te-rich growth condition, and for 0.75≤x≤1 under liquid phase epitaxy cation rich growth condition, the self-compensating effect occurs and the gold impurity cannot behave as an efficient p-type dopant in MCT.
2010, 59 (2): 1212-1218.
doi: 10.7498/aps.59.1212
Abstract +
The formation of B defect, the crystal structure, formation energies, density of states and electronic structure of B-N codoped ZnO were studied using first-principles pseudo-potential approach of the plane wave based upon the density functional theory（DFT）.The study reveals that most of the B atom will present in as-doped ZnO in the form of BZn, which could result in the shrinkage of ZnO unitcell.Compared with N doped ZnO, B-N codoped ZnO has a lower formation energy, correspondingly a higher chemical stability, so its formation is more realizable. Moreover, the acceptor levels of B-N doped ZnO are shallower, resulting in a decreased ionization energy as well as a higher acceptor density.The bonding power of Zn-N is increased in as-doped ZnO, the properties of acceptors are also improved, therefore B-N codoping is expected to be a more efficient way to fabricate p-type ZnO.
2010, 59 (2): 1219-1224.
doi: 10.7498/aps.59.1219
Abstract +
Geometric structures, density of states and band structures of zinc blend structure and rock salt structure of ZnSe at different pressures （from 0 to 20 GPa） have been calculated by means of plane wave pseudo-potential method with generalized gradient approximation. The structural phase transitions, elastic constants, bonding and electronic structures of ZnSe under pressure have been discussed. From the principle of enthalpy for the zincblende and rocksalt ZnSe, the pressure at the phase transition is 15.3 GPa, which is higher than the result of 11.52 GPa deduced from the elastic constants of the phase transition criterion. The change of phase to simple cubic has not been found at the pressure of 9.5 GPa; and the sp3 hybrid orbital has not been eliminated during the structure phase transition, while the 4s electronic state of Zn atom has a major contribution to the conductivity in rocksalt phase.
2010, 59 (2): 1225-1232.
doi: 10.7498/aps.59.1225
Abstract +
The propagation of shockwave in nanocrystalline copper has been studied by means of molecular dynamics simulation. The samples are prepared by Voronoi method and crystalline orientations of each grain are limited by three conditions. The result shows for the first time that nanocrystalline copper shows the phenomenon of multi-yield under shock loading, and the shockwave has a multi-wave structure. The profiles of shock-front suggest grain boundary sliding and dislocation emmision in sequence. The shock-front consists of an elastically deforming area, a plastically deforming area dominated by grain boundary sliding and a plastically deforming area dominated by dislocation movement. There are irregularities on both elastic wave and plastic wave, and the former is obvious than the latter.
2010, 59 (2): 1233-1236.
doi: 10.7498/aps.59.1233
Abstract +
GaN: Mg films have been grown on sapphire at low temperature by metal-organic chemical vapor deposition, the properties of different source flux GaN: Mg materials were studied. When the molar ratio of CP2Mg and TMGa is between 1.4×10-3 and 2.5×10-3, the quality of crystal was improved with the increasing molar ration, and the hole concentration was increased linearly. When the molar ratio is 2.5×10-3，the concentration is equal to that of the film grown at higher temperature, and the surface morphology is more coarser. Taking the p-GaN layer with molar ratio of CP2Mg and TMGa of 2.5×10-3 as the light-emitting diode, when the inject current is 20 mA, the output light power was increased by 17.2%.
2010, 59 (2): 1237-1242.
doi: 10.7498/aps.59.1237
Abstract +
We discuss the capacitance of a coherent mesoscopic parallel-plate capacitor based on the self-consistent theory of dynamic response for mesoscopic systems. The results show that the capacitance is a complex function of frequency which is strongly dependent on the frequency of the external field. The capacitance-frequency curve shows a significant characteristic that a peak in the imaginary part of the capacitance corresponds to the minimum in the real part, and further study shows that they are related to a plasmon-like excitation. In addition,we discuss the size effect of the capacitor, and find that the capacitance approaches geometric capacitance when the distance between two plates of the capacitor is very large.
2010, 59 (2): 1243-1247.
doi: 10.7498/aps.59.1243
Abstract +
Antimony and tellurium were deposited alternatively on the substrates by ion beam sputtering with 11 periodic layers of Sb/Te deposited. The films were then annealed at the vacuum chamber. The properties of the thin films were tested by X-ray diffraction （XRD）, Hall measurement and Seebeck coefficient measurement systems. XRD results indicate that the major diffraction peaks of the film match those of Sb2Te3. The film growth is apparently at the ［101］/［012］ orientation and many Te peaks are observed. Hall measurement reveals that all the samples are p-type and the resistivities are low. The electric conductivity of the films approaches that of the bulk metal and the carrier concentration is of 1023 cm-3. Seebeck coefficient measurement shows that the samples have nice thermoelectrical properties and the seebeck coefficients are in the range of 7.8—62 μV/K. Among all, the samples annealed at 200 ℃ for 6 h have the highest seebeck coefficient of about 62 μV/K and the lowest resistivity.
2010, 59 (2): 1248-1251.
doi: 10.7498/aps.59.1248
Abstract +
Organic solar cells with structure of ITO/MoO3（5 nm）/Rubrene（50 nm）/C60（45 nm）/Rubrene（0, 3, 5.5, 9.5 nm）/Al（130 nm） were prepared. The rubrene layer near the Al cathode was used as the electron transporting layer. Compared with that of the control device without the electron transporting layer, the open circuit voltage, fill factor and power conversion efficiency of the device with 5.5 nm rubrene layer were increased from 0.68 V, 0.488, 0.315% to 0.86 V, 0.574, 0.490%, respectively. The analysis of the experimental results shows that when hot Al atoms are directly deposited on C60 layer, the C60 layer is undermined and a high work function is formed, which leads to a weaker built-in electric field and a poorer performance. When the rubrene layer is inserted, a significant improvement in device performance is achieved due to the formation of defect states in rubrene layer during Al deposition. Further experimental results of single-electron devices show that energy levels of the defect states are lower than that of the lowest unoccupied molecular orbital of C60.
2010, 59 (2): 1252-1257.
doi: 10.7498/aps.59.1252
Abstract +
A novel composite-channel AlxGa1-xN/AlyGa1-yN/GaN high electron mobility transistor has designed and optimized. The influence of the two-dimensional electron gas and electric field on device structure parameter is obtained from the self-consistent solution based on the theory of semiconductor energy band and quantum well. The influence of the layer structure of the device on its performance is obtained from simulation using TCAD software. Combining the results of theoretical analysis and simulation, the optimized structure Al0.31Ga0.69N/Al0.04Ga0.96N/GaN HEMT is proposed. The simulation results show that the device with gate length of 1 μm and gate width of 100 μm has the maximum transconductance of 300 mS/mm and small fluctuation in the gate voltage of from -2 V to 1 V, which shows the excellent linearity of the device. The maximum current density of 1300 mA/mm, the cut-off frequency of 11.5 GHz and a maximum oscillation frequency of 32.5 GHz are obtained.
2010, 59 (2): 1258-1262.
doi: 10.7498/aps.59.1258
Abstract +
We study the irradiation effects of the GaN-based blue light-emitting diodes（LEDs） with InGaN/GaN multi-quantum well irradiated by five doses of 60Co （4×104 Ci） at room temperature. From the analyses of the characteristics of the current-voltage （I-V） relation, current-luminous flux （F-L） relation, chromatic purity, luminous intensity, luminous flux, the full width at half maximum, and the wavelength of LEDs samples before and after irradiation, we obtain the effects of γ irradiation on the devices. It shows that the consistency and uniformity of the samples become worse after irradiation. At the 20 mA working current, the luminous intensity reduces by 90% and the luminous flux falls by 40% at the maximum total dose. The quantity τ0Kγ describing the radiation hardness of the LEDs is equal to 4.039×10-7 rad·s-1, and the saturation current increases at lower positive bias （<2.6 V） with the increasing total dose.
2010, 59 (2): 1263-1267.
doi: 10.7498/aps.59.1263
Abstract +
ZnO and ZnO thin films doped with different Mg contents （0.81at%,2.43at% and 4.05at%） were fabricated by radio frequency-magnetron sputtering （RF-MS） on glass substrates at 450 ℃. The microstructure, photoluminescence （PL）, optical and electrical properties were investigated. The results show that ZnO and diluted Mg doped ZnO thin films present a hexagonal wurtzite structure with high crystal quality. In the short wavelength side of near band emission （NBE）, a high energy emission band for 0.81at% and 2.43at% Mg doped thin films occurs together with NBE. The increasingly high energy band peak gradually covers the NBE peak with Mg doping increasing to 4.05at%. It is suggested that the energy of the electrons near the substituted Mg2+ increases, and these electrons occupy a higher energy level. However, the energy gap between conduction band and valance band still exists because the electrons energy near the un-substituted Zn2+ does not change. With the increasing doped Mg content, electrons in the higher energy level increase and predominate. Therefore, the reason for the increase in the band gap of Mg doped ZnO thin films can be attributed to the increase in the energy of electrons after Mg doping, together with the Burstein-Moss effect. Incidentally, all films exhibit a high average optical transmission （≥85%）. The optical band gap of Mg doped ZnO thin films increases with the increasing Mg doping content and changes from 3.36 to 3.52 eV. The resistivity of the Mg doped films are 2.2×10-3, 3.4×10-3 and 8.1×10-3 Ω·cm for 0.81at%, 2.43at% and 4.05at% Mg contents, respectively.
2010, 59 (2): 1268-1274.
doi: 10.7498/aps.59.1268
Abstract +
We increase the hole concentration of the p-GaN contact layer of the epitaxial wafer of conventional GaN-based devices by laser-induced Zn doping. Improvement of the photoelectric property of light-emitting diodes （LED） is confirmed. Compared with LED with no laser-induced doping, the forward voltage under 20 mA current is decreased from 3.33 V to 3.13 V, the series resistance is decreased from 30.27 Ω to 20.27 Ω， and the degradation coefficient at room temperature is reduced from 1.68×10-4 to 1.34×10-4. In addition, the reverse leakage current of the LED is reduced from over 0.2 μA to less than 0.025 μA after an aging time of 1600 h by accelerated lifetime testing, and the lifetime is increased about 41％. These results are attributed to the improvement of p-type ohmic contact and the decrease of the thermal resistance due to laser-induced doping of Zn to the p-GaN contact layer.
2010, 59 (2): 1275-1281.
doi: 10.7498/aps.59.1275
Abstract +
We investigated the technology and the related physical problems for integrating organic thin-film transistor （OTFT） and polymer light-emitting diode （PLED）. The OTFT uses Pentacene as the active medium, Ta2O5 as dielectric layer, Ta as gate electrode and Au as source/drain electrodes. The structure of PLED device is ITO/PEDOT:PEO （polyethylene oxide）/P-PPV or MEH-PPV/Ba/Al. The PEDOT:PEO, P-PPV and MEH-PPV film layers were obtained by using screen printing technology. The transistors have a threshold voltage of -7.1 V and carrier mobility of 0.91 cm2/（V·s）. The luminance of the PLEDs with P-PPV and MEH-PPV emissive layer when were driven by OTFT could reach 124 and 22 cd/m2, and the maximal luminous efficiency are 12.4 and 1.1 cd/A, respectively.
2010, 59 (2): 1282-1287.
doi: 10.7498/aps.59.1282
Abstract +
The millimeter wave irradiation characteristics of a Tl-2212 high-temperature superconducting thin film bicrystal Josephson junction embedded in a hemispherical Fabry-Perot resonator was studied. The coupling characteristics of the bicrystal Josephson junction with the Fabry-Perot resonator have been investigated experimently, showing that it was greatly affected by the factors such as the location of the sample in the open resonator, the angle between them, the pattern of the junction and the distance between the two reflecting mirrors of the resonator. The optimized coupling between Josephson junction and applied microwave was achieved by refined adjustment of the factors. In this case, 9 orders distinct Shapiro steps were observed. Taking advantage of the Fabry-Perot resonator technique, the coupling problem between high-temperature superconducting thin film Josephson junction and applied millimeter wave was well solved, which is of significance for the research on radiation and detection of millimeter wave and terahertz wave of high-temperature superconducting Josephson junction.
2010, 59 (2): 1288-1293.
doi: 10.7498/aps.59.1288
Abstract +
Considering the dependence of the gap on the exchange energy in ferromagnetic d-wave superconductor, we use an extended Blonder-Tinkham-Klapwijk approach to investigate the shot noise in semiconductor/ferromagnetic d-wave superconductor junction by solving the Bogoliubov-de Gennes（BdG） equation. It is shown that the exchange energy h0 in the ferromagnetic d-wave superconductor may induce a split of the shot noise double-peak at zero-bias and the energy gap peak, and the interval between the two split peaks is equal to 2h0; furthermore, with the increasing exchange energy h0, the shot noise and the ratio of shot noise power to average current are restrained.
2010, 59 (2): 1294-1301.
doi: 10.7498/aps.59.1294
Abstract +
Appling high temperature optical microscopy （HTOM）, the in-situ observations on the melting process of RBa2Cu3Oz（RBCO） oxide thin films were carried out. Combined the X-ray diffraction （XRD） pole figures with the scanning electron microscope （SEM）, the microstructure of RBCO thin films with different in-plane and out-of-plane orientations were studied. The relationship between the thermal stability of RBCO thin film and its microstructure was investigated. The conclusions of semi-coherent interface energy theory is in good agreement with the experimental results from HTOM, SEM and XRD. It is evident that the thermal stability of 0° in-plane YBCO grain surpasses the 45° one in the air. Additionally, it was found that a very small volume percentage of a-axis grain has an obvious influence on the decomposition behavior and thermal stability of SmBCO film.
2010, 59 (2): 1302-1307.
doi: 10.7498/aps.59.1302
Abstract +
Bi4Ti3O12（BIT） and Bi3.25La0.75Ti2.97V0.03O12（BLTV） thin films were fabricated on the Pt/TiO2/SiO2/p-Si（100） substrate using sol-gel method. The effect of La and V codoping on the structural and electrical properties of BIT thin films was investigated. BIT thin film exhibits predominantly c-axis orientation while BLTV thin film shows random orientation. Raman spectroscopy shows that TiO6 （or VO6） symmetry decreases and Ti—O （or V—O） hybridization increases with V substitution. The residual polarization of BLTV thin film is 25.4 μC/cm2, which is larger than that of BIT thin film （9.2 μC/cm2）. BLTV thin film also shows excellent fatigue endurance and low leakage current characteristics, which implies the oxygen vacancies are suppressed by La and V codoping in the thin films.
2010, 59 (2): 1308-1313.
doi: 10.7498/aps.59.1308
Abstract +
To study the effect of the thermal stresses on the optics, experiment is performed to measure the damage threshold of the two fused silica samples with one annealed to eliminate thermal stresses while the other not. The measurement includes the effects of the thermal stresses on the initial damage threshold of the fused silica, the damage growth threshold, and the damage growth laws. The results show that the damage threshold decreases as the thermal stresses increase, and the damage induced by the laser is accelerated by the thermal stresses. For the same laser intensity, the damage growth factor is higher for the area with higher thermal stresses, but the damage growth still obeys the exponential increase rule and no obvious effect of the thermal stresses is found on the damage growth threshold. The study here will determine to some extent whether the technology of the CO2 laser pretreatment can be applied to the large-aperture optics or not.
2010, 59 (2): 1314-1320.
doi: 10.7498/aps.59.1314
Abstract +
The electronic structure and optical properties of transition metals （TM）-doped （Fe, Co or Ru） titanate nanotubes （TNTs） have been investigated by using the plane-wave ultrasoft pseudopotential method. TM atom intercalation into the interlayer region of the layered TNTs structure has great influence on the geometry of the original structure and the formation energy of Co-doping or Ru-doping is lower after geometry optimizations. Doped atoms bond with the surrounding O atoms to form a kind of solid solution. The results show that, Fe,Co or Ru intercalation reduces the band gap of TNTs and introduces new energy levels in the band gap, extending the absorption edge of the doped TNTs well into the visible region, which is due to the appearance of the b1g（dx2－y2） and a1g（dz2） states; partial impurity bands are in semi-filled states, which act as the capture centers of holes to reduce the recombination of electrons and holes; the valence bands of the doped TNTs move towards low energy, making the holes more oxidative. Finally, the absorption spectrum of the doped TNTs shows that Ru-doped TNTs has a stronger absorptive capacity in the visible region.
2010, 59 (2): 1321-1327.
doi: 10.7498/aps.59.1321
Abstract +
Energy transfer processes of Tm3+ singly doped and Tm3+/Ho3+-codoped TeO2-WO3-ZnO glass have been investigated under excitation of 808 nm diode laser and the involved mechanisms are discussed. The microscopic parameters and critical radii are calculated by using Dexter model and their characteristics are analyzed. The Inokuti-Hirayama model improved by Vila et al. is utilized to fit the fluorescence decay curves of Tm3+. The results indicate that there are not only Inokuti-Hirayama-type solution but also localized interaction solution in the energy transfer processes of Tm3+ and Ho3+. Furthermore, the contribution of the localized interaction increases with the increasing of the concentrations of Tm3+ and Ho3+.
2010, 59 (2): 1328-1332.
doi: 10.7498/aps.59.1328
Abstract +
A series of samples about Eu3+ doped, Bi3+∶Eu3+-codoped borosilicate glasses have been prepared by high-temperature sintering. The excitation spectra, emission spectra and the phonon sideband spectra of the samples were measured. The influence on the luminescence of Eu3+ ions was discussed with Eu3+ ions as probe when Bi3+ions were doped. The results show that the electron-phonon coupling coefficient calculated in this study is smaller than those of borate-lead glasses and others reported before, but the probability of non-radiative transition of Eu3+ ions is increased by the doping of Bi3+ ions. The Bi3+ ions can sensitize Eu3+ ions, and when Bi3+ ions are doped, the covalent property becomes bigger with the symmetry becoming smaller ，which enhances the luminescence intensity of Eu3+ ions on the whole. Therefore, in the borosilicate glasses, the increase of luminescence intensity about Eu3+ ions is the result of the combined action between the above factors，not simply because of the energy transition from Bi3+ ions to Eu3+ ions.
2010, 59 (2): 1333-1337.
doi: 10.7498/aps.59.1333
Abstract +
Transparent polycrystalline α-Al2O3 ceramics were fabricated by conventional solid-state processing with MgO as additive. The absorption, excitation, emission spectra and thermoluminescence of α-Al2O3 transparent ceramics were investigated. There are two characteristic absorptions, one is centered at 192 nm, and the other at from 230 to 250 nm, which are caused by F+ and F color centers, respectively. There is one obvious emission peak located at 410 nm. Based on the excitation spectra, it is shown that the emission peaks are caused by the absorption of F+ and F color centers. The thermoluminescence curves show three peaks centered at 368, 456 and 614 K, respectively. The peak centered at 456 K may be caused by F and F+ centers.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (2): 1338-1343.
doi: 10.7498/aps.59.1338
Abstract +
Silicon oxide films were deposited in electron cyclotron resonance-radio frequency dual hybrid plasmas using a mixture of HMDSO and oxygen as source gases, and optical emission spectroscopy was employed to investigate the gas phase species in the plasma. It is found that both the deposition rate and the chemical bonds of films are significantly affected by the radio frequency bias. The deposition rate is slightly increased when a low direct current self-bias is applied, and is reduced with the increasing self-bias due to strengthened ion bombardment. The ratios of O to Si in the films deposited under the bias frequency of 400 kHz are above 2∶1, nearly the same as that under 13.56 MHz. However, the content of carbon under 400 kHz bias is much higher than that under 13.56 MHz. The reason is that the application of the high frequency bias of 13.56 MHz not only strengthens ion bombardment on the material surface, but also induces the variations of the bulk plasmas including the increase of O atom density, while the main effect of the bias of 400 kHz is only to strengthen ion bombardment.
2010, 59 (2): 1344-1348.
doi: 10.7498/aps.59.1344
Abstract +
In-situ hydrogen plasma treating technique and burial method using microcrystalline silicon layer were used respectively to reduce the boron contamination in intrinsic layer for the p-i-n type microcrystalline silicon thin film solar cells deposited in single chamber. The measurement results of J-V relation and the quantum efficiency of solar cells proved that both of them improve the short circuit current density of solar cells to some extent. However, each method showed different effects on the other characteristic parameters of solar cells. By optimizing the hydrogen treating time and light trapping structure, single junction microcrystalline silicon thin film solar cell with 6.39% conversion efficiency has been fabricated in single chamber.
2010, 59 (2): 1349-1356.
doi: 10.7498/aps.59.1349
Abstract +
A comprehensive error analysis is carried out for a 256-element annular spherical-section phased array when used for synthesizing three\|dimensional multi-focus acoustic fields. The influence of array excitation errors on field patterns is summarized for both amplitude and phase errors. References to the design of driving module are provided for phased array with hundreds of elements. The simulation results show that the phased array with hundreds of elements has a robust ability of acoustic field synthesizing. Five-bit digitalization of phase signal can ensure the validity of the abstained acoustic fields. The array excitation errors affect the focal energy distribution mostly. The effect of amplitude errors can be weakened by reducing the error ratio through increasing the overall excitation energy.
2010, 59 (2): 1357-1365.
doi: 10.7498/aps.59.1357
Abstract +
The spatial resolution of pinhole single photon emission computed tomography （SPECT） imaging is usually estimated according to Anger’s empirical formula, which could result in a large inaccuracy in experimental measurement. We present a more accurate formula based on the analysis of physical processes of pinhole imaging. The effectiveness of the proposed formula was evaluated by accurate Monte Carlo simulations and experiments of the phantom imaging. The images were reconstructed using three\|dimensional iterative OSEM algorithm. Then the effects of the voxel size, the geometrical mapping of the projection matrix and the ratio of detector size to imaging object size, on the spatial resolution were discussed. The experiment results show that the spatial resolution estimated by the proposed formula is about 10% smaller than the experimental value while the estimation by the Anger’s formula is about 60% larger than the experimental value. Therefore, our proposed formula is more accurate than Anger’s formula for predicting the spatial resolution of pinhole SPECT imaging, and it can be utilized for design and use of pinhole SPECT system.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Advective vorticity equation and its application to the vorticity variation of typhoon Bilis in 2006
2010, 59 (2): 1366-1377.
doi: 10.7498/aps.59.1366
Abstract +
The vorticity equation in the form of momentum cross multiplication is derived in pressure coordinate, in which the divergence term in the classic vorticity equation （CVE） does not appear. This vorticity equation in momentum cross multiplication form involves the rotation effect of the horizontal wind advection, which can be called the advective vorticity equation （AVE）. Because the rotational effect of horizontal wind advection can be directly analyzed on the synoptic charts, this equation is easily applied to operational weather analysis. The vorticity and its tendency of typhoon Bilis occurred in July 2006, it is analyzed and the results show that the distributions of the vertical vorticity tendencies from the two equations are similar except that the values of AVE is larger than that of CVE, and positive vorticity tendency from AVE is more concentrated than that of CVE. The detailed analyses of the three terms on the right hand side of AVE indicated that the advective term is a leading factor in determining the change of vertical vorticity for the development of the typhoon Bilis. When the vorticity induced by the rotational effect of horizontal wind advection plays a dominant role, AVE shows advantages for the diagnosis and analysis of synoptic systems. Thus, the AVE is useful for analysis of the change of vorticity and diagnosis of the movement for typhoon Bilis. Furthermore, the tendency of the term related to geostrophic vorticity and divergence always accords with the track of Bilis, which means this term can be used as an indicator for track prediction of typhoon.
2010, 59 (2): 1378-1384.
doi: 10.7498/aps.59.1378
Abstract +
The effects of defocus and astigmatism aberration of the turbulent atmosphere on the intensity distribution of a focused vortex carrying Gaussian beam are investigated. The integral expression of the intensity distribution on the focal plane in slant path is derived from the extended Fresnel-Kirchhoff diffraction integral and the quadratic approximation of phase structure function. And the influences of the three factors, turbulent strength, the propagation distance and the topological charge of the initial beam, are investigated by numerical calculation. Our results show that in weak turbulent region, the effects of defocus and astigmatism aberration in turbulent atmosphere on the intensity distribution of a vortex carrying Gaussian beam are very small and can be ignored. However, in the middle turbulent region, the effects of defocus and astigmatism are pronounced. As the propagation distance and the turbulent strength increase, both aberrations cause the decrease of the intensity peak value, the spreading of the beam, and the stretching of the dark core. For the beams with single topological charge, under the influence of astigmatism, the peak value of the intensity decreases more seriously, the intensity of the secondary maximum stripe increases much faster, and the focal spot expands more than the effect of defocus aberration. Compared with single topological charge, the effects of defocus and astigmatism of vortex beam with double topological charge are more obvious. The focal spots are expanded, and the secondary maximum stripes are more obvious. However, under the effect of astigmatism, because of the reduction of the coherence and the deflection effect of the beam, the dark core on the focal plane tends to break into two dark regions separated by a bright region.
2010, 59 (2): 1385-1390.
doi: 10.7498/aps.59.1385
Abstract +
Hypervelocity impact can produce instantaneous plasma during the impact． Through two kind of sensor designed in this paper to collect the plasma to attain the arriving time of the particle, we use the time of flight method to obtain the velocity of the particle． During the elementary experiment in the plasma drag particle accelerator, the impact signal was captured and the measurement of the particle velocity was achieved．The experiment result proves that this method has a high precision in time survey and a high signal to noise ratio．
EDITOR'S SUGGESTION
2010, 59 (2): 1391-1395.
doi: 10.7498/aps.59.1391
Abstract +
We investigate a weak electron screening effect on the electron capture of proton in the neutrino-driven wind of proto-neutron stars. Our results show that the electron screening has little influence on specific heating rate, entropy and other physical parameters in the wind. However, it improves electron fraction obviously, which strongly supports the latest nucleosynthesis of rapid neutron capture process.
REVIEW OF FRONTIER AREA
2010, 59 (2): 1396-1401.
doi: 10.7498/aps.59.1396
Abstract +
The advantages of using Monte Carlo method for simulating radiative transfer in complex turbid random media like biological tissues are well recognized. However, in most biophotonic applications, the wave nature of probing optical radiation is ignored, and its propagation is considered in terms of neutral particles, the so-called photon packets. Nevertheless, when the fundamental principle of some particular optical techniques for revealing the physiological and pathological information of tissues are based on the interference and polarization or coherent effects of scattering of optical/laser radiation, the wave nature of optical radiation must be considered. In this paper, latest development of Monte Carlo method for simulating light transmission in tissues is reviewed and its bio-photonic applications are presented.
