Vol. 61, No. 7 (2012)
2012-04-05
GENERAL
2012, 61 (7): 070201.
doi: 10.7498/aps.61.070201
Abstract +
Homotopy analysis method is a new method to form approximate analytical solution for non-linear system by using various base functions, which is different from traditional analytical methods. So far, the analytical solution of the point reactor neutron kinetics equations with six-group delayed neutrons has not been obtained yet. In this paper the homotopy analysis method is employed for solving the point reactor neutron kinetics equations with six-group delayed neutrons. The series analysis solutions are obtained using the homotopy analysis method, and the relevant algorithm is given and analyzed. The results show that the computation time and accuracy satisfy the engineering requirements. This analysis method can be applied to the design, the analysis and the simulation of reactor control.
2012, 61 (7): 070202.
doi: 10.7498/aps.61.070202
Abstract +
Instability of satellite platform will seriously affect the quality of spectral imaging. The degradation mechanism of interferential and dispersive imaging spectrometers caused by satellite vibrations is studied in this paper. A simulation algorithm of degradation based on differential dynamic spectral imaging is presented. And the concept of mean mixing ratio (MMR) is proposed, which builds the bridge between the parameters of satellite vibration and the influences on spectral imaging. The quantitative relationship between them is also deduced in detail. Spectral degradation results are simulated by taking the typical spectra and the generated spectrums of surface features as the ideal original data. Simulation results show that the effects caused by pitch and roll are much greater than that by yaw, and the vibrations affect not only spatial resolution but also spectrum, and the regions of rich species are influenced seriously.
2012, 61 (7): 070401.
doi: 10.7498/aps.61.070401
Abstract +
The semi-inverse method is proposed by He to establish generalized variational principles for mathematical and physical problems, in which the variational crisis brought by the Lagrange multiplier method can be eliminated. with He's semi-inverse method, a family of variational principles is constructed for Rossby wave, atmospheric acoustic wave and gravity wave respectively. The obtained variational principles have also proved correct.
2012, 61 (7): 070501.
doi: 10.7498/aps.61.070501
Abstract +
Owing to the fact that standard particle filter and ensemble Kalman filter can not efficiently represent the posterior probability density function (PDF), an improved particle filter is proposed. In this algorithm, an innovation step is introduced after the prediction step, and the analyses of non-observation time and observation time are treated separately. The numerical simulations of a low- and a high-dimensional systems show that this new particle filter can follow the true state of a highly nonlinear non-Gaussian system very well.
2012, 61 (7): 070502.
doi: 10.7498/aps.61.070502
Abstract +
The complicated dynamical evolution of a circuit system composed of two Rayleigh-types subsystems, which are switched by a periodic switch and a threshold controller, is investigated. Through the analysis of the subsystem equilibrium points, the conditions for Fold bifurcation and Hopf bifurcation in the parameter space are given respectively. The distribution of the generalized Jacobian eigenvalues varying with auxiliary parameter at the switching boundary is presented. Then the possible bifurcation behaviors of the system at the switching boundary are obtained. The mechanisms of the different behaviors of the system are discussed. It is pointed that the trajectories of the system have two kinds of turning points, which are determined by the periodic switch and the threshold controller respectively. Meanwhile, the multiple collisions between the trajectories and the non-smooth boundary may lead the system to change from chaos to period-adding bifurcation.
2012, 61 (7): 070503.
doi: 10.7498/aps.61.070503
Abstract +
A chaotic vibration isolation device under the condition of small displacement is designed according to the chaotic vibration theory.The device can generate strong nonlinearity under small displacement. The linear part and the nonlinear part are completely separated. The overall stiffness, the ratio of linear term to nonlinear term can be easily adjusted. The engineering application scope of the device turns wider. The numerical simulation is carried out with specific parameters. The design is confirmed.
EDITOR'S SUGGESTION
2012, 61 (7): 070504.
doi: 10.7498/aps.61.070504
Abstract +
To study the effect of noise on the network and the influence of noise on the spatio-temporal behaviors of the network, a homogeneous network of excitable cells is constructed, in which the classical Morris-Lecar neuron model behaves as a unit by electric coupling to neighbouring ones. The deterministic behavior of each unit is a resting state corresponding to class Ⅱ excitability. Under the action of white Gaussian noise in the network, spiral wave can be induced within a large range of noise intensity, while disordered spatiotemporal structure is induced within a certain small intensity range. With the increase of noise intensity, spiral wave is characterized by a transition back and forth between simple structure and complex structure, or appears alternately with the disordered structure. By calculating spatial structure function and signal-to-noise ratio (SNR), it is found that the SNR of spiral wave with a simple structure is higher and the SNR becomes lower when the spiral wave has a complex or an even disordered structure. The SNR curve shows that multiple peaks appear with the increase of noise intensity, which indicates that white Gaussian noise can induce the multiple spatial coherence resonance in an excitable cellular network, and suggests that there are many opportunities to select diverse intensity noises to be rationally used in a realistic excitable system.
2012, 61 (7): 070505.
doi: 10.7498/aps.61.070505
Abstract +
The synchronization of a two-dimensional (2D) neuronal network is investigated, based on the dynamical model of Hindmarsh-Rose neuron. In order to know the effects of different types of coupling on the synchronization of a network, we propose three coupling schemes. They are the general feedback coupling, the hierarchical feedback couplings with and without local mean field. The numerical results show that when the neighbor coupling strength is small, the hierarchical feedback couplings with and without local mean field can achieve local and global synchronizations of the network, whereas the general feedback coupling cannot achieve global synchronization. Different couplings generate different patterns in the corresponding network, so that the processes of the transition from asynchronization to synchronization in the networks are different. With the increase of coupling strength, the synchronization in the network with the general feedback or hierarchical feedback couplings is suddenly established, and the networks exhibit different coherent patterns that are aperiodic before the global synchronization occurs. However, the network with hierarchical feedback couplings and local mean field exhibits the different synchronous processes. The neurons in the same layer first achieve the transition from bursting synchronization to global synchronization, leading to the formation of target wave. Then, the synchronization region gradually expands from the center of the network. Finally, the whole networks can achieve synchronization. These results show that the lossless signal transmission can be achieved only if the appropriate coupling is applied. In addition, we find that the hierarchical feedback coupling with local mean field can facilitate synchronization.
2012, 61 (7): 070506.
doi: 10.7498/aps.61.070506
Abstract +
Surface roughening has been extensively studied in many fields of science and technology. In order to investigate the influence of imperfection of the randomly diluted lattices on dynamic scaling behavior of the surfaces, the etching model growing on diluted squares is simulated by kinetic Monte Carlo (KMC) simulation. It is found that although the scaling behavior of the etching model can be affected by imperfections of the randomly diluted lattices, the roughness and the growth exponent are larger than those of the growth on perfect squares. The scaling behavior still satisfies the Family-Vicsek dynamic scaling. In addition, the finite system size effect of the randomly diluted lattice is also calculated and analyzed.
2012, 61 (7): 070701.
doi: 10.7498/aps.61.070701
Abstract +
A new feedback neural network model is proposed. The network has the sinusoidal basis functions as its weights. Neuronal activation function is a linear function. The network connection form is feedback structure. An energy function is defined for the feedback neural network. And then, the network stability issue in operation is analyzed. In the Liapunov sense, the proposed feedback network stability is proved. During the operation of the network, the network states are changed ceaselessly but network weights vary according to time-dependent sinusoidal law. As the network state changes continuously, its energy will be reduced. Finally, when network comes to a stable state, its energy arrivs at a minimum value. The network is particularly suited for the adaptive approximation and the detection for periodic signals because of its sinusoidal basis function weights. It is, in practice, a new and effective way for periodic signal detection and processing. The very good detection results are obtained in the detection of power system voltage sag characteristics. Simulation examples show that the dynamic response speed of the network is very high.
2012, 61 (7): 070702.
doi: 10.7498/aps.61.070702
Abstract +
In this paper, stable Li-doped ZnO solid solution (ZnO: Li) is successfully prepared by sintering the mixture of ZnO and Li2O powders under a pressure of 5 GPa and at temperatures between 1200 ℃ and 1500 ℃. It is found that the high pressure and temperature conditions have significant effects on the electrical conductivity and the structure of the ZnO solid solution. The best p-type ZnO doping 4.5 at.% Li with a resistivity of 3.1 10-1cm, carrier concentration of 3.3 1019cm-3, and mobility of 27.7 cm/Vs is achieved at 1500 ℃. The p-type conduction formed in ZnO is due to acceptor formed by one substitutional Li atom at Zn site, which has an acceptor level of 110 meV. Furthermore, the effects of pressure on formation and electrical properties of the p-type ZnO are discussed.
2012, 61 (7): 070703.
doi: 10.7498/aps.61.070703
Abstract +
Mode competition induces non-stationary oscillations during the operation of a gyrotron backward-wave oscillator (gyro-BWO), which severely reduces its tunable bandwidth and output power. Self-consistent nonlinear theory is used to study the modes-competition mechanism of a W-band fundamental TE01 mode gyro-BWO. Tapered non-resonant interaction circuit structure and loading lossy ceramic are employed to suppress the competing modes, as a way of preventing non-stationary oscillation in the circuit. Systematically optimized interaction circuit is capable of suppressing all the competing modes and can stably operate in the fundamental axial mode of the TE01 mode. Calculation indicates that a peak power of 105 kW and a -3 dB tunable bandwidth of 5.4% are attainable. This is meaningful and provides a theoretical foundation for developing broadband millimeter gyro-BWOs in the applications of counter-measure system, non-destructive detection, plasma diagnosis, material processing, and so on.
2012, 61 (7): 070704.
doi: 10.7498/aps.61.070704
Abstract +
The spectral resolution can be increased by detecting the optical signal in a narrowband spectrum for the Fourier transform spectrometer based on spatial modulated in our study. In this paper, to study the effect of the radiant source on the interference system, we regard the radiant noise as a narrowband stationary Gaussian random process. Using the linear system analysis method and the statistical theory, we deduce the input signal-to-noise ratio (SNR) and the output SNR after the optical signal and the radiant noise have passed through the interference system. Then we simulate the system and compare the obained result with a narrowband rectangle spectrum, and obtain the SNR gains along the optical path difference (OPD) in different autocorrelation degree and cross-correlation degree values. The simulation result indicates that the SNR gains at different OPDs in the correlation degree space each are a monotonic smooth surface. The SNR gain maximum moves along the radius and the contour of the correlation degree circle, and it returns to the initial position. after an OPD According to the analysis of the SNR gain, the autocorrelation degree and cross-correlation degree values can be controlled in a certain area, which can serve as a criterion for the design and the test of the radiant source.
NUCLEAR PHYSICS
EDITOR'S SUGGESTION
2012, 61 (7): 072601.
doi: 10.7498/aps.61.072601
Abstract +
The rapid neutron-capture process (r-process), which is an interdisciplinary field of astrophysics and nuclear physics, is bound up with various characteristics of thousands of neutron-rich exotic nuclei, such as nuclear masses, and the relevant reactions. By employing the WLW microscopic-macroscopic nuclear mass model developed recently, the solar r-process abundance distribution is well reproduced in the classical r-process approach. In comparison with the well known FRDM model, the present calculation better pictures the nuclear region of A135 and A180, and especially avoids the abundance peaks at A135 often obtained in other calculations. The improvement in the r-process calculation may indicate a more suitable description of the evolution of shell structure and symmetry energy towards the drip line in the WLW model.
2012, 61 (7): 072901.
doi: 10.7498/aps.61.072901
Abstract +
In order to study the properties of the carbon nanotube(CNT) cathode with intense pulsed emission, the outgassing property of cathode is investigated on the 2MeV linear induction accelerator(LIA) injector. Results show that the cathode has a capability of desorbing gases from the CNT cathode under pulsed high voltage. The outgassing plays an important role in the formation of the cathode plasma. The amounts of outgassing for the several experiments are estimated to be 0.081.12PaL, the corresponding ratios between outgassing amount and electron number are roughly calculated to be in a range of 254203atoms/e- by numerical integral of pressure, showing that the cathode plasma is weakly ionized. The relationship between diode voltage, emission current density, outgassing amount, and the outgassing molecule number per electron are analyzed.
2012, 61 (7): 072902.
doi: 10.7498/aps.61.072902
Abstract +
A kind of fusion dianostics based on proton recoil method and magnetic analyzing technology is introduced. It can be used for the accurate diagnoses of plama tempreture, fuel density and neutron yield. A prototype is designed, using a high-powered Nd-Fe-B permanent dipole for magnetic analyzer, and proton position distribution in the focal plane is measured by CR-39 trajectory detector or PIN detector. The system is calibrated with a 239 Pu source, and a corresponding particle transport simulation program is worked out. The performance of the spectrometer is investigated with the Monte Carlo simulation, and neutron experiments are taken on the K-400 accelerator.
2012, 61 (7): 072903.
doi: 10.7498/aps.61.072903
Abstract +
Based on the basic principle of four-quadrant-based tracking sensor, the energy detecting rate, centroid detecting error and the displacement sensitivity of four-quadrant detector caused by noise or dead zone are analyzed in detail. The tracking error formula of four-quadrant-based tracking senor is put forward theoretically and verified experimentally. The results show that when the noises are constant, the tracking error of four-quadrant-based tracking senor depends on the ration between the width of Gauss facula and the width of dead zone of four-quadrant detector.
2012, 61 (7): 072904.
doi: 10.7498/aps.61.072904
Abstract +
Double layers of 150 mm?150 mm plastic scintillator arrays are used to locate the cosmic ray. Both layers of arrays are read out by wavelength-shifting fibers, which are bundled and coupled to image intensifier and ICCD camera. The light signal is delayed more than 200 ns by the image intensifier, so the ICCD can be pre-triggered by an external fast coincident signal. This cosmic ray positioning system is used to measure the time resolution and photon transfer time of the time-of-fly detector for the common test platform based on cosmic ray. Compared with traditional cosmic rays test, the data-taking efficiency of this system increases more than 30 times because of multi-point readout and higher position resolution. The test results show that the time resolution of the time-of-fly detector is better than 200 ps, which satisfies the requirement of the common platform based on cosmic ray.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (7): 073101.
doi: 10.7498/aps.61.073101
Abstract +
The adsorption property of hydrogen molecules on YmSi@Al12 (m=13) cluster is investigated using the density functional theory. The results show that yttrium atoms do not suffer from clustering on the Si@Al12 cluster. The 18-electron rule can be used to design these systems, and Si@Al12 cluster coated with three yttrium atoms can adsorb 16 H2 molecules with a gravimetric density of up to 5.0 wt%. The calculated adsorption energy of 0.324-0.527 eV/H2 molecule is suited for reversible hydrogen storage in near-ambient conditions.
2012, 61 (7): 073102.
doi: 10.7498/aps.61.073102
Abstract +
It is necessary to investigate the characteristics and the evolution law of metal deformation by using the appropriate strain analysis method. The deformation of metal is complex, so there exists no useful method to amalyze the local deformation characteristics and to describe the global equivalent deformation of deformed metal. In this paper, we propose a statistical moment method of strain analysis. Statistical moment method builds up the relationship between micro quantities and macro strain. For instance, it is used to study the deformations of monocrystal under uniaxial load and the nanocrystalline under shear and shock, showing that moment method can not only describe and evaluate the local and the global deformation of metal but also distinguish elastic and plastic deformation by nonuniform coefficient. Moment method is a general and effective way to investigate the deformation mechanism of complex structure material.
2012, 61 (7): 073601.
doi: 10.7498/aps.61.073601
Abstract +
This paper focuses on the Li-storage performances and the stabilities of the hybrid structure of different lattice planes of the silicon clusters and graphene by the first-principles theory. In this paper, we calculate the binding energy, the adsorption energy, and the PDOS of the hybrid structure of the different heights and sizes of the silicon clusters and graphene. We figure out that strong Si-C bonds between the silicon cluster and graphene can form. Especially, the hybrid structure of the silicon clusters with plane (111) and graphene performs best with the highest formation energy and the outstanding stability. According to the calculation of Li-absorption energy, we conclude that the location of the silicon cluster near the graphene has higher possibility and higher absorption energy of the Li storage, owing to the charge transfers between lithium and carbon, and between lithium and silicon. Because the graphene is used, the deformation of the interface of the silicon cluster can be obviously reduced during the absorption of Li, which brings about a good future for the hybrid structure used as the battery anode materials.
2012, 61 (7): 074101.
doi: 10.7498/aps.61.074101
Abstract +
A novel resonant-type composite right/left handed transmission line (CRLH TL) and its correlative lumped-element equivalent circuit model are presented based on complementary single split ring resonator pair (CSSRRP). The circuit model is investigated in depth through the Bloch theory, and the condition for balanced CRLH TL is derived. The negative refractive index and the backward wave propagation are demonstrated by the effective electromagnetic parameter retrieval. After that, a balanced electrically small CRLH TL with zero phase shift is designed at WiMAX (Worldwide Interoperability for Microwave Access) band by introducing the Koch fractal geometry into CSSRRP. For application, a series power divider is fabricated and measured. Consistent simulated and measured results confirm the design concept. The bandwidth of the proposed power divider is broadened by 56%, and the overall dimension is only 58% of its conventional counterpart based on meandered line. Thus novel CRLH TL based on fractal shape CSSRRP can be found to have an extensive application in future small-size wireless communication system.
2012, 61 (7): 074102.
doi: 10.7498/aps.61.074102
Abstract +
With the full time-domain electromagnetic simulation technique, the time-domain propagation properties such as the temporal pulse waveform, the pulse compression and the electric field distribution inside the material are comparably investigated by transmitting the time-reversal pulsed electromagnetic wave and the pulsed electromagnetic wave through the double negative material of the Smith structure, respectively. The results show that after the time-reversal pulsed electromagnetic wave passes through the double negative material, the received electromagnetic wave exhibits remarkable spatial and temporal focusing at the location of the initial excitation. The most interesting physical phenomenon is that the peak values of the electric field inside the double negative material become smaller and tend to be uniform in the magnitude. These novel physical phenomena would be very helpful for developing new electronic devices and systems with double negative materials for the purpose of high power applications.
2012, 61 (7): 074103.
doi: 10.7498/aps.61.074103
Abstract +
The thermal and the ultraviolet radiation degradation mechanisms of lamp used BaMgAl10O17:Eu2+, Mn2+ phosphor are investigated in a comparative way. Thermal and the ultraviolet radiation treatments can both seriously damage the luminous efficiency of BaMgAl10O17:Eu2+,Mn2+. It is revealed that the thermal degradation is involved in the oxidation and migration of Eu2+ ions. The ultraviolet radiation makes the Eu2+ in metastable state, which weakens the direct absorption of Eu2+ and thus reduces the relative luminescence intensity of BaMgAl10O17:Eu2+,Mn2+.
2012, 61 (7): 074104.
doi: 10.7498/aps.61.074104
Abstract +
Based on the electron optics theory, through a massive numerical calculation by programming, a double-anode magnetron injection gun (MIG) for a 1THz gyrotron is designed. The method of calculation and design of MIG is expounded, and the problem that high magnetic compression ratio in THz gyrotron(compression ratio of 125 in electron gun for 1THz gyrotron in this paper)could lead to the reversal of direction of electron flow is also detailedly analyzed and simulated. Through simulation and optimization, an MIG with a modest velocity ratio of the beam (=1.3) and a low velocity spread (8%) is designed.
2012, 61 (7): 074105.
doi: 10.7498/aps.61.074105
Abstract +
In this paper, the interference of wave packets reflected from a stationary boundary and a moving boundary respectively are discussed. The present theory is based on the boundary value problem of classical electrodynamics, especially with the moving boundary which gives rise Doppler effect. Various distinguished interference properties are investigated and a rigorous expression for the velocity measurement of the moving mirror is provided. At the end, the paper points out that many similar and important problems are waiting for us to explore.
2012, 61 (7): 074201.
doi: 10.7498/aps.61.074201
Abstract +
The amplitude of speckles which are in the extremely deep Fresnel diffraction region and generated by weak scattering screens is extracted. It is found that when scattering distance is fixed, the property of phase distribution varies with weak scattering screen roughness. For a weak scattering screen, the phase distribution property changes with scattering distance. The phase votex phenomenon does not appear until the surface of weak scattering screen is rough enough. It is interesting that there are phase vortices on scattering screen surface. The phase votex density will rise when scattering screen becomes rougher or scattering distance turns larger. Experimental results are helpful to realize that the phase and the phase votex distribution property vary with roughness of weak scattering screen and scattering distance which lies in the extremely deep Fresnel diffraction region. Moreover, the results contribute to the understanding of the speckle field evolution with scattering distance.
2012, 61 (7): 074202.
doi: 10.7498/aps.61.074202
Abstract +
The effect of two beam combination schemes, i.e. combination of coherent and incoherent beam, on the radiation force and stability in trapping metallic Rayleigh particles is studied, where the dependences of the radiation force on beam combination scheme, off-axis distance, coherence parameter and particle radius are stressed and illustrated by numerical examples. It is shown that there exist critical values dc and c for different combination schemes. For 0ddc or 0cthe Gaussianthe Gaussian-like intensity profile takes place in the geometrical focal plane, so that the transverse gradient force can act as a restoration force to provide stable equilibrium point. Fordd0,c or00,cthe transverse gradient force can not trap metallic Rayleigh particles. For 0ddc the intensity, the radiation force, the trapping stiffness, and the longitudinal trapping range of coherently combined beam are larger than those of incoherently combined beams. Therefore, a suitable choice of combination scheme, smaller off-axis distance and coherence parameter is beneficial to trapping metallic Rayleigh particles in the use of combined beams.
2012, 61 (7): 074203.
doi: 10.7498/aps.61.074203
Abstract +
By adding periodic signal into single-mode laser, and taking the first-order approximation to the multiplication noise of the laser gain-noise model,we find that the output signal is of the Lorentz type when we obtain power spectrum by calculating the correlated function. The signal-to-noise ratio shows the stochastic resonance occurs with the variations of intensities of the pump noise and quantum noise, and the noise intensity of resonant peak is smaller than that under the zeroth approximation.
2012, 61 (7): 074204.
doi: 10.7498/aps.61.074204
Abstract +
Single-frequency fiber Raman amplifier (SF-FRA) is known for the ability of all-band amplification, and it is very attractive for the amplification of single-frequency seed light at a special wavelength, such as 1178nm and 1271nm. The 1080nm single-frequency signal light is amplified by a 1031nm pump source, and the influences of seed power of single-frequency signal light, length of Raman gain fiber, pump scheme are experimentally investigated. The results show that the efficiency of SF-FRA increases with the enhancement of the single-frequency signal power and the length of Raman gain fiber. The efficiency of co-pump SF-FRA is higher than that of the counter-pump SF-FRA. The measure ments show that the linewidth of single-frequency signal light is not broadened obviously in the process of Raman amplification. The visibilities of the rapid-exposure pattern of far-field interference of single-frequency seed light and the amplified light are 0.814 and 0.719, respectively. The results show that the coherence of single-frequency signal light is affected by the SF-FRA more or less. These experimental results can provide a reference for designing other special wavelength SF-FRA.
2012, 61 (7): 074205.
doi: 10.7498/aps.61.074205
Abstract +
The incoherently coupled soliton families are predicted in photovoltaic photorefractive crystals illuminated by E-polarized incoherent uniform back-ground irradiation with a divider resistance under steady-state conditions. These soliton families can be established provided that the incident optical beams share the same polarization and wavelength, and are mutually incoherent. When these incoherent coupled soliton families propagate together, all components can propagate stably in photorefractive crystal. Moreover, such soliton families reduce into spatial soliton or incoherently coupled soliton pairs when they contain only one or two components. The 14 kinds of incoherently coupled spatial soliton families can be obtained from this theory by adjusting the value of the divider resistance, E-polarized back-ground irradiation, the biased electric field and photovoltaic electric field. Previous theories advanced individually elsewhere for these soliton families can be obtained by simplifying this theory under appropriate conditions.
2012, 61 (7): 074206.
doi: 10.7498/aps.61.074206
Abstract +
A scanning spectral filter method to improve the signal-noise-ratio in the femtosecond chains is proposed by using the characteristic that the instantaneous frequency varies with the time approximately linearly for the chirped pulse in the time-frequency domain. The scanning spectral filtering for reduing the amplification of spontaneous emission (ASE) intensity is analyzed in the time-frequency domain by using the Short-Time Fourier Transform method. The results show that the pulse contrast can be improved by two orders, and the transmission efficiency of the chirped pulse can exceed 90% when the synchronizing time jitter ranges from -2ps to 2ps and the chirp rate p from 0.9C/T2 to 1.10C/T2. Adopting the cascaded scanning filter to improve the pulse contrast is investigated too, which can improve the pulse contrast effectively. The great advantage of this novel nonlinear spectral filter technology is high energy and high peak intensity femtosecond chains for it filters out the ASE in the near field in temporal domain.
2012, 61 (7): 074207.
doi: 10.7498/aps.61.074207
Abstract +
Wavefront coding system with a cubic phase mask is one of important methods to extend depth of the field. This paper analyzes the characteristics of the system based on stationary phase method in space domain. By analyzing the point spread function of an arbitrary strip of the cubic phase mask, this paper points out that two stationary phase points lead to oscillations in point spread function while one stationary phase point causes a smooth curve in point spread function. Theoretical analysis illustrates that the oscillations exist in point spread function if and only if there are symmetrical components about the optical symmetrical axis. Furthermore, different areas of the point spread function correspond to different positions of symmetrical components of the mask, which is useful in the manufacture and test of the cubic phase mask. In addition, the optical symmetrical axis does not coincide with the geometrical symmetrical axis in the defocused system, causing smooth curve in defocused point spread function. As a contrast, smooth curve can not be observed in focused point spread function because of the coincidence of the symmetrical axis and the geometrical symmetrical axis.
2012, 61 (7): 074501.
doi: 10.7498/aps.61.074501
Abstract +
To find the characteristics of curved road traffic flow, we propose a new car-following model based on the typical full velocity difference model, and analyze the model stability condition with system state space method and control system stability criteria. With numerical simulation, the stability and feasibility of the model are proved. Under the condition of same initialization traffic flow density, with the increase of road curve, traffic flow stability decreases. Our study is greatly helpful for traffic control and management at road curve site.
2012, 61 (7): 074701.
doi: 10.7498/aps.61.074701
Abstract +
Experiments are conducted for the characteristics of both body and wake-generated internal waves due to a revolution body (aspect ratio 7:1) in a stratified fluid with a pycnocline where the revolution body is horizontally towed in forward and backward ways. Results show that the body-generated internal waves are a type of stationary multiple-mode Lee wave structures, and the wake-generated internal waves are a type of non-stationary quasi-Lee structures produced by the large-scale coherent structure in the turbulent wake acting as a moving excitation with respect to the towed revolution body. The transition between Lee and quasi-Lee waves occurs at a critical Froude number Frc which is shown to be linearly dependent on the aspect ratios of the revolution bodies where the wave patterns for FrFrc are dominated byLee waves,whereas the wave patterns forFrFrcare dominated by quasi-Lee waves,Fr is the Froude number for the characteristic diameter of the revolution body. For the quasi-Lee waves, the dimensionless peak-to-peak amplitudes linearly increase with Fr and the Froude numbers relative to the correlation velocities remain at a relatively constant value of approximately 0.8 regardless of the aspect ratios. Moreover, the head and the tail shapes of the revolution body have no remarkable influence on the critical Froude number Frc, as well as both the Froude numbers relative to the correlation velocities and the dimensionless peak-to-peak amplitudes of the quasi-Lee waves.
2012, 61 (7): 076101.
doi: 10.7498/aps.61.076101
Abstract +
In this paper, we design and fabricate a new test structure of bipolar device. A gate is deposited on the oxide layer covering the base region of normal lateral pnp bipolar transistor. The characteristic of drain current (collector current) versus the gate voltage is recorded by sweeping the voltage applied to the gate, then the subthreshold-current technique is used to separate the radiation induced oxide trapped charges and interface traps in the gate controlled lateral pnp bipolar transistor during 60Co- irradiation. The test structure and the measurement of the bipolar transistor used in the experiment are introduced in detail in this paper.
2012, 61 (7): 076102.
doi: 10.7498/aps.61.076102
Abstract +
The typical neutral density filter is a metal film plated on a K9 glass to achieve the effective absorption of laser. Its lower damage threshold severely restricts its application to high energy laser systems. Experimental study on damage morphology and damage mechanism of filter in a higher laser energy density is carried out. The variation characteristics of damage morphology are as follows: with the increase of laser energy density, damage spots first appear on the filter, then develop into cracks, and the cracks grow gradually longer and eventually connect into linear and block forms, resulting in a large area of film dropping off. A model of defect absorption leading to film damage on neutral density filter is established. And temperature and stress distributions on the film surface are calculated, separately. The inhomogeneous temperature rise on film surface leads to radial, hoop and axial thermal stress distributions. Theoretical analysis shows that cracks along the radial direction are caused by hoop stress. When laser energy density is larger than about 2.2 J/cm2, impurity particle radius is larger than 140 nm and the distance between impurity particles is less than 10 m. A large number of cracks can connect together to cause a large area of film to drop off.
2012, 61 (7): 076103.
doi: 10.7498/aps.61.076103
Abstract +
The initial damage threshold, the damage growth threshold and the damage growth laws of K9 glass and fused silica glass are tested respectively in the same experimental condition with 1 nanosecond laser. The comparison of the laser induced damage performance between the two glass materials is performed. The results show that the initial damage thresholds of the two glass materials are the same, the damage area growths both obey the exponential increase rule and their damage depth growths obey the linear increase rule. However, there is apparent difference in the rule of damage growth. For example, the damage growth threshold is lower and the damage growth coefficient is higher for K9 glass. This can be explained by the difference in the material mechanical strength between the two glass materials. The present research is very important for choosing transparent optical materials used in high power laser.
2012, 61 (7): 076501.
doi: 10.7498/aps.61.076501
Abstract +
Graphene has become one of the most exciting topics of nano-material research in recent years because of its unique thermal properties. Nitrogen doping and vacancy defects are utilized to modify the characteristics of graphene in order to understand and control the heat transfer process of graphene. We use nonequilibrium molecular dynamics to calculate the thermal conductivity of armchair graphenenanoribbon affected by nitrogen doping concentration and nitrogen doping location, and analyze theoretically the cause of the change of thermal conductivity. The research shows that the thermal conductivity drops sharply when graphenenanoribbon is doped by nitrogen. When nitrogen doping concentration is up to 30%, the thermal conductivity drops by 75.8%. When the location of nitrogen doping moves from the cold bath to the thermal bath, the thermal conductivity first decreases and then increases. And it is also found that the structure of triangular single-nitrogen-doped graphenenanoribbon is inhibited more strongly in the heat transfer process than that of parallel various-nitrogen-doped graphenenanoribbon. Vacancy defects reduce the thermal conductivity of graphenenanoribbon. When the location of vacancy moves from the cold bath to thermal bath, the thermal conductivity first decreases and then increases. When the vacancy position is located at 3/10 of the entire length relative to the edge of the cold bath, the thermal conductivity reaches a minimum value. This is because of the phonon velocity and phonon mean free path varying with the concentration and the location of nitrogen doping and the location of vacancy defect. These results are useful to control the heat transfer process of nanoscalegraphene and provide theoretical support for the synthesis of new materials.
2012, 61 (7): 076502.
doi: 10.7498/aps.61.076502
Abstract +
Polyparaphenylene/LiNi-ferrite nanocomposites are prepared by a novel rheological phase reaction method. The thermoelectric properties of the as-prepared nanocomposites are characterized and the effect of spark plasma sintering (SPS) conditions is investigated. The TEM images show that the size of LiNi-ferrite is around 100300 nm and the polyparaphenylene has diffused boundaries outside it. The negative value of Seebeck coefficient confirms the n-type conduction, and the n-type conduction is attributed to hopping of electrons from Fe2+ to Fe3+ ions. It is found that the electrical conductivity of nanocomposite does not change with sintering time whereas the Seebeck coefficient decreases and thermal conductivity increases with sintering time. Therefore the figure of merit decreases. Because of the high electrical conductivity and low thermal conductivity of organic material and high Seebeck coefficient of inorganic material, the figure of merit of nanocomposites is improved.
2012, 61 (7): 076801.
doi: 10.7498/aps.61.076801
Abstract +
The surface structure of platinum nanoparticle in a fuel cell is the key factor to determine the catalytic efficiency. In this paper, we apply our recently established condensation potential model [2009 Acta. Phys. Sin. 58 3293; 2009 J. Chem. Phys. 130 164711] to predict the surface structure of platinum nanoparticle, and the reliability of the model is verified by molecular dynamics simulations. By first-principles calculations based on this model, we show that for various shapes of platinum particles the surfaces are mainly composed of fcc (111) facets (about 80%), and the ratio of (100) faces is about 10%. The results are consistent with existing experimental observations. Owing to the simplicity of the calculations, this condensation potential model is widely used to predict the surface structure of common nanoparticles.
2012, 61 (7): 076802.
doi: 10.7498/aps.61.076802
Abstract +
The adsorption and the diffusion of oxygen on the Pt (111) surface and subsurface are basic issues to understand oxidation and corrosion, which are investigated based on the density functional theory and the periodic slab model. The absorption structure is analyzed through scanning tunneling microscopy (STM) image. The diffusion processes of oxygen atoms on Pt (111) surface and subsurface are discussed in detail using the CI-NEB method. The results show that the diffusion of oxygen atoms over Pt (111) surface is easier than the diffusion into the subsurface, which is mainly because the diffusion of the subsurface needs to go through a layer of Pt atoms and must overcome a certain energy barrier. Transition metal Pt is indicated to have a strong antioxidant activity.
Electronic structures and optical properties of transition metals (Fe, Co, Ni, Zn) doped rutile TiO2
2012, 61 (7): 077101.
doi: 10.7498/aps.61.077101
Abstract +
The geometric structures of transition metals (Fe, Co, Ni and Zn) doped rutile TiO2 are studied using the first-principles method based on the density functional theory. The lattice parameters, the electronic energy band structure, and the optical properties are calculated and discussed. The results show that the errors between calculated and experimental values of lattice parameters are less than 3.6%. Appropriate dopants of transition metal ions not only influence the band structure of rutile TiO2 system and broaden the scope of light absorption, but also play an important role in trapping electrons, improving the effective separation of electronic-hole pair and enhancing light absorption ability. The optimum Fe, Co, Ni, Zn doped rutile TiO2 systems in theory are Ti0.75Fe0.25O2, Ti0.75Co0.25O2, Ti0.75Ni0.25O2, Ti0.17Zn0.17O2, respectively. The 3d orbits of Fe, Co, Ni split into two groups of energy bands, t2g and eg states contribute to the higher level of valence band and the lower level of conduction band, respectively, which is conducive to the generation of electronic-hole pair and the enhancement of photocatalytic performance of rutile TiO2. Zn 3d orbit is completely filled with electrons, and the electrons are hardly excited, so the photocatalytic activity of rutile TiO2 is not obviously improved.
2012, 61 (7): 077102.
doi: 10.7498/aps.61.077102
Abstract +
Based on first principles within the density-functional theory, we establish three different concentration Eu-doping anatase TiO2 models by using the plane-wave ultrasoft pseudopotential method. We calculate the density of states, the electron density difference, the band structure and the absorption spectrum. The results show that Eu creates an impurity level in the band gap of TiO2 and a redshift in absorption spectrum of anatase TiO2. By comparing the bands of anatase TiO2, with two different Eu-doping concentrations (1.39 at% and 2.08 at%) we find that more Eu atoms make the impurity level deeper, the recombination rate bigger, and the electron lifespan shorter.
2012, 61 (7): 077103.
doi: 10.7498/aps.61.077103
Abstract +
In this paper, we report on the magnetism and the thermomagnetic power generation performance of a first-order phase transition material Mn1.2Fe0.8P0.4Si0.6,which can be used for thermomagnetic power generation that turns heat directly into electricity. The compound is synthesized by using the high-energy ball milling and solid state reaction method. Magnetic measurements show that the compound undergoes a ferromagnetic-to-paramagnetic first-order phase transition at 337 K, accompanied by a giant magnetization change. According to this feature of the material, we design a demonstration device for thermomagnetic power generation, and study the electric current generated by heat induced phase transition. The current increases with the increase of the heat-flow temperature and the mass of material. This study shows that the Mn1.2Fe0.8P0.4Si0.6 compound possesses the high performance of thermomagnetic power generation.
2012, 61 (7): 077201.
doi: 10.7498/aps.61.077201
Abstract +
According to a tight-binding model and the Green's function formalism, we investigate the electronic transport in hybrid contact of doubly stacked zigzag graphene nanoribbons. Our study shows that the next nearest neighbor interlayer coupling, the hybrid contact length and gate voltage each have a significant modulation effect on the electron transmission spectrum. Due to the next nearest neighbor interlayer coupling, the transmission spectrum of the hybrid contact exhibits an electron-hole asymmetry, which is consistent with the experimental result. There exist some transmission gap (T=0) and quantum step (T=1) within the first subband below the Fermi energy, meaning that electrons can reflect and/or transmit completely. It is also observed that the transmission coefficient oscillates within 1 as the contact length increases, showing a quantum interference effect. Under a gate voltage in the bilayer regime, the transmission coefficient can be changed from 1 to 0, showing that a switching effect exists here. The results is useful for the design and the application of the graphene-based device.
2012, 61 (7): 077301.
doi: 10.7498/aps.61.077301
Abstract +
The organic thin film photovoltaic device with a structure of tin indium oxide (ITO)/organic semiconductor/metal is fabricated. A rectifying behavior of the device is observed from the current-voltage characteristics. However, it is hard to judge the direction of internal electric field between the organic semiconductor and electrodes under Schottky contacts. In order to investigate the characteristics of Schottky contacts between the organic semiconductor and electrodes, the devices with the structures of ITO/organic insulator layer/organic semiconductor/metal and ITO/organic semiconductor/organic insulator layer/metal are fabricated. It is easy to judge the direction of internal electric field between the organic semiconductor and electrodes under Schottky contacts by the direction of transient photocurrent which is produced under the irradiation from the modulated laser. The correctness of judgement is further proved by the change of transient photocurrent intensity with a bias voltage applied.
2012, 61 (7): 077302.
doi: 10.7498/aps.61.077302
Abstract +
Electron density is an important parameter for the macroscopic properties of metal. The reflectance spectrum measurement and the Hall Effect measurement are basic experiments for obtaining electron density and carrier density. Two samples (sample 1:100 nm, sample 2:10 nm) of nanostructure block rare earth metal Tm are studied. Their reflectivity spectra show that the surface reflection of Tm metal possess metallic optical properties in a region of infrared-ultraviolet, the electronic densities np of 6s band are 2.434 1028/m3 and 1.7011028/m3 similar to that of alkali. The carriers measured by Hall Effect experiment are of cavity tipe in the two samples, and the carrier densities nH are 8.0321024/m3 and 7.6791024/m3 respectively. They are only states near the Fermi surface. In addition, the conductance of Tm block is three orders of magnitude higher than one of semiconductor. The grain nanostructurization makes electronic density np, conductance , and carrier density nH decrease, but Hall coefficient RH increase.
2012, 61 (7): 077303.
doi: 10.7498/aps.61.077303
Abstract +
By using nonequilibrium Green's functions in combination with the density-functional theory, we investigate the effects of B and N doping on the transport properties in phenalenyl molecular device. The calculated results show that negative differential resistance behavior can be observed in phenalenyl molecular device where the device current can decrease with the base voltage increasing particularly in a bias voltage region, and the peak-to-valley current ratio reaches up to 5.12. The device current can be increased before 0.8 V when the molecular center atom is replaced by B or N atom. But, the negative differential resistance behavior can be weakened and the peak-to-valley current ratio can decrease to 3.83 and 3.61, respectively. The doping effects of B and N, which are induced by the difference in extranuclear electron number between them, can make the orbitals and corresponding transmission peaks move toward high or low energy to modulate the electronic transport ability and the negative differential resistance behavior of the device.
2012, 61 (7): 077701.
doi: 10.7498/aps.61.077701
Abstract +
In order to induce the general behaviors of the orientation correlations between molecules from the variation of static dielectric constant of liquid with temperature, we filtrate the experimental data of 18 kinds of liquids with the contribution of the electronic polarizations much smaller than that of the orientation correlations between molecules from the present references. The results indicate that there is a universal crossover for the varication of the static dielectric constants of the liquids with temperature, and for such a kind of crossover, there exist at least two kinds of orientation correlation orders between molecules, one increases but the other decreases with temperature.
Electronic structure and optical properties of 0.5NdAlO3-0.5CaTiO3 from first-principles calculation
2012, 61 (7): 077702.
doi: 10.7498/aps.61.077702
Abstract +
The optimized crystal structure, energy band, density of states, and optical properties of 0.5NdAlO3-0.5CaTiO3 are calculated by the plane wave ultrasoft pseudopotential method based on the first-principles density functional theory. The optimized crystal parameters are in good agreement with the experimental ones and the errors are less than 1%. The calculated energy band results indicate that 0.5NdAlO3-0.5CaTiO3 has an indirect band gap of 0.52 eV. The energy band near Fermi level is determined by the density of states of Nd-4f, O-2p, Nd-4p, Al-3p, Ti-4d electrons. Moreover, the dielectric function, reflectivity and refractive index of 0.5NdAlO3-0.5CaTiO3 are also calculated.
2012, 61 (7): 077801.
doi: 10.7498/aps.61.077801
Abstract +
This paper deals with the retrieving of the bidirectional reflectance distribution functions (BRDFs) of the distinct urban cover in the Pearl River Delta (PRD) region employing the high-spatial-resolution multi-angle polarized measurements made by the directional polarimetric camera (DPC). The results show that three BRDF models (RPV, Ross-Roujean and Ross-Li) describe the DPC measurements well. Forest is best fitted by Ross-Li and bare soil is best fitted by Ross-Roujean. Urban and shrub are best fitted by RPV. The results demonstrate that the reflectances of different types of surfaces are different and increase with the increase of scattering angle. The basic theory of investigating surface properties using multi-angle measurements is proposed.
2012, 61 (7): 077802.
doi: 10.7498/aps.61.077802
Abstract +
The CaWO4:Eu3+ phosphors with different doping concentrations and different sintered temperatures are synthesized using the microemulsion reaction method. After sintered at different temperatures, the samples with doping concentration of 30 or 50 mol% can obtain the brightest characteristic emissions from Eu3+ ions. At 800 ℃, moreover, the samples with doping concentrations of 0.52 mol% can emit the strongest light. It is therefore concluded that more intense emissions enable the CaWO4:Eu3+ phosphors with high doping concentrations to have great potential to be used as efficient phosphors in the future.
2012, 61 (7): 077901.
doi: 10.7498/aps.61.077901
Abstract +
Plasma-sprayed scandia-doped oxide cathode is prepared by doping a small amount of scandia into the triple carbonates and employing the air plasma spraying technique. In the preparation process, a small amount of scandia is added in the shaping process of mixing the triple carbonates with an additional 12%22% of BaCO3 (molar ratio). The shape and the distribution of the feed material analyzed by using scanning electron microscope show that the size and the shape of the feed material meet the requirement for plasma-spraying and that it fully compensates the loss of barium in the plasma-spraying process. The analysis of the decomposition process shows that scandia-doped plasma-sprayed oxide cathode has a shorter process of decomposition and less exhausted gas amount than the commonly-used oxide cathode. The test on the emission performance of the new type oxide cathode shows that the emission performance of scandia-doped plasma-sprayed oxide cathode is much better than that of commonly-used oxide cathode and that the life time of the former is longer than that of the latter.
2012, 61 (7): 078101.
doi: 10.7498/aps.61.078101
Abstract +
Metal rubber (MR) material is a new-type of damping material. Its raw material and fabrication process have same unique features. Wire helix is considered as the unit cell geometry of MR. Combining cylindrical compression coil spring theory, a mechanical model is established for individual wire helix which is located in the horizontal or longitudinal direction. Three contact statuses are analyzed for the neighboring helixes and mechanical models are derived for these cases according to the Kulun model. The arrangement and the spatial distribution of the microelements are assumed to be located evenly and periodically inside the MR. A mathematic model is established to characterize the damping behavior of MR. It came from the unit cell geometry and the fabrication process of MR materials. It is easy to explain the mechanism of hysteresis loop and the nonlinear stiffness and damping characteristic of MR by analyzing contact states and contact number of unit cell wire helixes. Finally, a comparison is made between theoretical results and experimental results. This model is valuable for the analysis of the material mechanics and the design of MR. It provides theoretical support for the further engineering application of MR in the field of vibration reduction.
2012, 61 (7): 078102.
doi: 10.7498/aps.61.078102
Abstract +
To extend the kind of diamond and solve the low life of diamond tools because of the insufficiency of holding force, the strip-shape diamond with more than 2.5 in length-diameter ratio and 0.81.0 mm in length is synthesized by optimizing FeNi based catalyst composition and using the technology in the China-type cubic anvil high pressure apparatus. Because of the unique morphology, the threshing phenomenon appearing in the using of diamond tools is controlled effectively. Furthermore, we find that the growth rate of strip-shape diamond is much faster than that of the conventional diamond. Strip-shape diamond morphology and catalyst composition around the growing diamond crystal are characterized by SEM and EDS. The results indicate that the facets of diamond crystal are elongated along {100} and {111} faces and catalyst compositions around the growing diamond crystal become segregated. On this basis, we illustrate the growth mechanism of strip-shape diamond.
2012, 61 (7): 078103.
doi: 10.7498/aps.61.078103
Abstract +
Different types of nanostructures of an organic dye compound, perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA), are prepared on anodic alumina oxide (AAO) at different values of substrate temperature (Ts) by a facile physical vapor deposition (PVD) method in a molecular beam epitaxy (MBE) system. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) techniques are applied to the systematical characterization of the nanostructures. It is found that the PTCDA nanofibers, nanoneedles, nanobelts, and nanorods are produced at 330 ℃Ts; Only nanorods are formed at 280 ℃, 230 ℃, and 180 ℃, and their lengths become short asTs decreases; the continuous films are obtained on 50 ℃ AAOs substrates. HRTEM and SAED results show that the nanoneedle and nanorods are of single crystal. According to SEM results, the formation of PTCDA nanostructures should be mainly affected by surface curvature andTs.
2012, 61 (7): 078104.
doi: 10.7498/aps.61.078104
Abstract +
Thick Ge epitaxial layers are grown on Si(001) substrates in the ultra-high vacuum chemical vapor deposition system by using the method of low temperature buffer layer combining strained layer superlattices. The microstructure and the optical properties of the Ge layers are characterized by double crystal X-ray diffraction, HRTEM, AFM and photoluminescence spectroscopy. The root-mean-square surface roughness of the Ge epilayer with a thickness of 880nm is about 0.24 nm and the full-width-at-half maximum of the Ge peak of the XRD profile is about 273. The etch pit density related to threading dislocations is less than 1.5106 cm-2. The direct band transition photoluminescence is observed at room temperature and the photoluminescence peak is located at 1540 nm. It is indicated that the Ge epitaxial layer is of good quality and will be a promising material for Si-based optoelectronic devices
2012, 61 (7): 078105.
doi: 10.7498/aps.61.078105
Abstract +
In the process of nanopowder production by the wire electrical explosion, the ablation of electrodes and the formation of micron-size particles are directly influenced by the way the current is injected into the metal wire from the electrodes. Through the channels which are provided by the contact between the electrodes and the wire ends, as well as the breakdown between them, a series of experiments of electrical explosion is carried out. Results show that the photocurrent detected by photodiodes at the wire ends almost occurs simultaneously with the circuit discharge current, however it at the central section lags behind the circuit discharge current obviously. The initial explosion product of the wire ends is liquid, and that of the other parts of wire is gas. Those results indicate that when the current folows into the contact, the phenomenon of gas discharge also occurs at the wire ends. Because the plasma provides another current path, the energy density of the wire ends is decreased. Hence, the wire ends cannot explode and form remainder on the electrodes. When the current flows into the breakdown, the electrodes ablated is slightly obvious, and there was no remainder on the electrodes.
2012, 61 (7): 078106.
doi: 10.7498/aps.61.078106
Abstract +
In this study, zinc chloride, chromic chloride, ammonium hydroxide and ammonium chloride are used as the source materials to prepare the crystalline Cr-doped ZnO diluted magnetic semiconductor by the hydrothermal method under a 4-T pulsed magnetic field. The structures and the morphologies of the samples are characterized by X-ray diffraction and scanning electron microscope. The magnetic analysis of the specimens is performed by vibrating sample magnetometer. The effects of pulsed magnetic field on the microstructure and the magnetic properties of the Cr-doped ZnO are discussed. The result indicates that all the samples still have hexagonal wurtzite structures. The pulsed magnetic field is conducive to promote the crystal growth orientation. The sample fabricated under pulsed magnetic field exhibits good room temperature ferromagnetism. The saturation magnetization is 0.068 emu/g. However, the sample synthesized without magnetic field shows paramagnetism at room temperature. The Curie temperature (Tc) of the Cr-doped ZnO is increased by 16 K through the pulsed magnetic field processing.
2012, 61 (7): 078501.
doi: 10.7498/aps.61.078501
Abstract +
Combining self-heating effect, mobility degradation in high electric field and avalanche generation effect, a two-dimensional electro-thermal model of the typical silicon-based n+-p-n-n+ structure bipolar transistor induced by high power microwave is established in this paper. By analyzing the variations of device internal distributions of the electric field, the current density and the temperature with time, a detailed investigation of the damage effect and the mechanism of the bipolar transistor under the injection of 1GHz equivalent voltage signals from the base and collector is performed. The results show that temperature elevation occurs in the negative half-period and the maximum temperature falls slightly in the positive half-period when the signals are injected from the collector. Compared with the former, device damage occurs easily with the signals injected from the base. Specifically, the base-emitter junction is susceptible to damage. The damage results caused by two large-amplitude signals with initial phases of 0 and respectively indicate that the injected signal with an initial phase of is liable to cause device damage. Meanwhile, the emitter series resistance can enhance the capability of the device to withstand microwave damage effectively.
2012, 61 (7): 078502.
doi: 10.7498/aps.61.078502
Abstract +
Although the grid with film sphere and porous structure plays a very important role in sphere grid-controlled electron gun, its cut-off amplification factor can be obtained only in the plane-square-mesh approximation. Due to the lack of consideration for non-uniformity of cut-off amplification factor and information about cathode half-angle and radius of curvature of grid, the designs of sphere grid and electron gun cannot be related by the plane-square-mesh approximation, which is unusable as theory basis for fabricating thinner grid wires. In this paper, we model the grid with film sphere and porous structure and obtain the new expression for cut-off amplification factor by recalculating the screening factors and the ratios of the radius of grid wire to the area of this single mesh in different ring areas. In combination with the conclusion of cut-off amplification factor given in Spangenberg's book, the effects of grid wire's radius, sphere center angle and the number of radial grid wires on the cut-off amplification factor, and the variation of the cut-off amplification factor with temperature rising are obtained. Finally, the steps for the design of grid with film sphere and porous structure and some specific examples are presented. The results show that the grid devised by new expression is more stable and reliable, and problems existing in plane-square-mesh approximation are solved.
2012, 61 (7): 078503.
doi: 10.7498/aps.61.078503
Abstract +
The diamond-amplifier photocathode (DAP) offers a new widely applicable way to generate high average-current, high brightness, and low thermal emittance electron beams. Physical processes with multiple parameters are important for the design of a reliable and efficient DAP. To perfom a study in-depth, a 2D Monte Carlo model in MATLAB frame is built to simulate the secondary electron transport in diamond. This simulation gives some proofs that the drift velocity is sensitive to diamond temperature and electric field applied, but not sensitive to the low impurity density(1017/cm-3). As an appropriate result, the saturation velocity of secondary electron reaches 1.88?107 cm/s, and mobility without applied field is 3732 cm2 /V.s. In addition, some properties of a secondary electron bunch transported in diamond are discussed, which indicate that the effect of space charge under our considered electron cloud density is small.
2012, 61 (7): 078504.
doi: 10.7498/aps.61.078504
Abstract +
A novel asymmetric HALO-doped surrounding-gate MOSFET with gate overlapped lightly-doped drain is presented. The performance of the new structure is studied by developing physics-based analytical models for surface potential, threshold voltage, and subthreshold current. It is found that the new structure can effectively suppress the short-channel effects and the hot-carrier effects, and simultaneously reduce the off-state current. It is also revealed that subthreshold current is a slight function of doping concentration of overlapped region, while work-function of gate electrode has a strong influence on subthreshold current. The accuracy of the analytical model is verified by its good agreement with the three-dimensional numerical device simulator ISE.
EDITOR'S SUGGESTION
2012, 61 (7): 078701.
doi: 10.7498/aps.61.078701
Abstract +
Weak absorption is the main condition of conventional phase retrieval of in-line X-ray phase-contrast CT. The absorption of most samples, however, cannot be neglected in practice, it is needed to find new algorithms of attaining quantitative information. The phase retrieval algorithm of phase-attenuation duality (PAD) is used to realize the quantitative imaging of different density parts in a mixed contrast sample, and the digital simulation and experimental investigation are carried out in order to prove its feasibility in this paper. The simulated results show that the reconstructive errors of three materials are less than 1%, and the values decrease with the increase of refractive index. The experiment was carried out in the X-ray imaging and biological application beam-line of Shanghai Synchrotron Facility, and the results show that the PAD method can attain the sample quantitative information and the reconstructive accuracy is relatively low compared with that of simulation. Through the analysis of experimental data, ring artifact is mostly the primary cause. One single projection data set is used only in simulation and experiment. So the PAD approach can be applied to the quantitative information research of mixed contrast objects. In addition, because of the relatively low radiation dose, it should be suited to investigate the quantitative phase-contrast CT of biomedical sample with soft tissue and bone together.
2012, 61 (7): 078801.
doi: 10.7498/aps.61.078801
Abstract +
Based on some physical and geometric parameters, the influence of internal resistance on the cell performance is analyzed and a semi-empirical mathematical model of the efficiency is built for some configurations of large-scale dye-sensitized solar cells. Three configurations of large-scale cells are investigated, in which the independent units are connected in series and in parallel, as well as in series-parallel. The efficiencies of the three-type large-scale cells are calculated according to their physical and geometric parameters. The applicability of the model is analyzed by comparing the calculated efficiencies with the measured ones. The influences of the physical and geometric parameters on the cell performance are investigated based on the semi-empirical mathematical model. It is found that the optimization of the performance of large-scale cells can be carried by analyzing the influences of physical and geometric parameters using the semi-empirical mathematical model.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (7): 075101.
doi: 10.7498/aps.61.075101
Abstract +
The dielectric surface breakdown has become a major factor of restricting the output power of high power microwave source. And the multipactor is the key phase of the process of the dielectric surface breakdown. In this paper, the multipactors in external magnetic fields with different strengths are simulated by using the particle-in-cell method. And the effect of the external magnetic field on multipactor is also studied. The results show that when the external magnetic field reaches a certain value, the multipactor is suppressed in the half time of the microwave transmission. So the power capability can be increased to more than four times through the suppression of the multipactor by the external magnetic field under the ideal condition.
2012, 61 (7): 075201.
doi: 10.7498/aps.61.075201
Abstract +
Based on the variations of the static pressure along the magnetic field line in different divertor operation regimes, the effects of the divertor operation regimes on the plasma parallel flow at the edge of a tokamak are investigated using a one-dimensional fluid model. In low recycling regime, the variation of the static pressure along the field line is obvious from the scrape-off layer (SOL) region near the X-point, and the variation tendency is the same as that of the density. The Mach number of the plasma parallel flow increases along the magnetic field line and the variation is from gentle to sharp. In high recycling regime, the static pressure does not change much except in the near divertor plate region, as a result, the Mach number of the plasma parallel flow varies gently in the SOL region and the most of the divertor region, and it increases rapidly in the near divertor plate region. The variation of the static pressure in weak divertor detachment regime is similar to that in high recycling regime, but the static pressure shows decrease tendency in the SOL region near the X-point, consequently, the Mach number of the plasma parallel flow at X-point is larger than that in high recycling regime. In strong divertor detachment regime, static pressure decreases obviously in the SOL region and away from the divertor plate region, where the static pressure decreases rapidly, and a high Mach plasma parallel flow is observed. Static pressure decreasing while dynamic pressure increasing to keep the total pressure conservation is shown to be a possible cause of the high Mach parallel flow.
2012, 61 (7): 075202.
doi: 10.7498/aps.61.075202
Abstract +
In tokamak plasma, the discharge will turn into runaway discharge from normal discharge if the plasma density becomes very low. The discharge will enter into slide-away discharge if the density decays to a critical one, in which the confinement of plasma (exactly supper thermal electrons) is better than that in normal discharge. The confinement of plasma and the anomalous Doppler instability during slide-away discharge gas puffing are investigated. The effect of gas puffing on runaway electrons during slide-away discharge is also studied in this paper. It is found that the anomalous Doppler instability can be suppressed by the gas puffing during slide-away discharge, while the confinement of plasma becomes poor, and many high energy runaway electrons occur during gas puffing.
2012, 61 (7): 075203.
doi: 10.7498/aps.61.075203
Abstract +
Superconducting photonic crystals are artificial periodic structures composed of superconductors and dielectric structures. In this paper, the transfer matrix method(TMM) is used to study the transmittance of one-dimensional photonic crystals consisting of cryogenic superconductor and lossless dielectric for TM wave. It is shown that a stop band staring from zero frequency can be apparently observed, whose cutoff frequency is adjusted by varying the temperature and the magnetic field. However, because of the contribution of the normal conducting electrons (NCEs) , taking no account of external magnetic field, the width of the low frequency photonic band gap (PBG) is no longer influenced by the temperature of the superconductor. The cutoff frequency of PBG adjusted by the temperature and the external magnetic field with the contribution of NCEs are compared with those obtained by neglecting them. However, when superconductors are in a normal state, the low frequency PBG of photonic crystals disappears.
2012, 61 (7): 075204.
doi: 10.7498/aps.61.075204
Abstract +
In electronegative or reactive plasmas, the problems such as negative ions floating near the sheath edge or deposition contamination cause more challenges for the diagnosis of conventional Langmiur probe. The electron density measured by microwave resonance probe is only a function of dielectric constant of plasma, there should be less or no influence of electronegative or reactive plasma. In this paper, a floating microwave resonator probe is proposed to measure electron density of capacitively coupled Ar plasma. A comparison with Langmuir double probe measurement shows that microwave resonance probe is applicable for measuring low electron density of plasma. The experimental results from the measurements of Ar/SF6 and SF6/O2 capacitively discharge driven by 40.68 MHz show that addition of SF6 into Ar plasma reduces the electron density significantly, with further increase of SF6 flow rate, electron density shows a gradual decrease. While for the addition ofO2 into SF6 discharge, the electron density continuously decreases with the increase ofO2 flow rate. Additionally, the electron density does not vary with lower frequency input power for SF6/O2 capacitively discharge driven by 40.68 MHz/13.56 MHz. The preliminary interpretations of the above experimental phenomena are presented.
2012, 61 (7): 075205.
doi: 10.7498/aps.61.075205
Abstract +
Collisionless steady plasma sheath model is taken into account to study the interaction between dusty particles and plasma sheath as well as the density distributions of electrons, ions and dusty particles. Numerical simulation results are obtained, showing that the ability of an isolated charge to absorb electrons weakens with the increase of dusty particle density and its temperature, while the collective effect strengthens with the radius of dusty particle. Simultaneously, Bohm velocity and the sheath thickness are also greatly affected. The sheath potential decreases significantly and the E-field is stronger near the electrode. In addition, the densities of electrons and ions reduce exponentially but the dusty particle has a critical value. The three particles satisfy the quasi-neutrality condition.
2012, 61 (7): 075206.
doi: 10.7498/aps.61.075206
Abstract +
BrightK-shell X-ray emissions are generated through the interaction between intense femtosecond laser pulses and Ar clusters. The total yield ofK-shell X-ray photons reaches 1 1011 photons/shot with a conversion efficiency of 2.8 10-5 in 4. When Ar clusters are irradiated by a laser pulse with intense prepulse, the yield ofK-shell X-ray photos will decrease due to prepulse ionization. Keeping high-density plasmas interacting with the main pulse is essential for obtaining the highest X-ray yield.
2012, 61 (7): 075207.
doi: 10.7498/aps.61.075207
Abstract +
We generalize the Layzer's bubble model to the cases of two-dimensional and three-dimensional analytical models of an arbitrary interface Atwood number and obtain self-consistent equations. The generalized model provides a continuous bubble evolution from the earlier exponential growth to the nonlinear regime. The asymptotic bubble velocities are obtained for the Rayleigh-Taylor(RT) and Richtmyer-Meshkov(RM) instabilities. We also report on the two-dimensional and the three-dimensional analytical expressions for the evolution of the RT bubble velocity.
2012, 61 (7): 075208.
doi: 10.7498/aps.61.075208
Abstract +
In inertial confinement fusion experiments, a fiducial system is established in order to correlate the signals from different channels of one spectrometer and the signals from different spectrometers to obtain time-related experimental data. The constitution, the principle and the data processing method, together with the uncertainty analysis are introduced. Signals from different channels and from three spectrometers diagnosing from different directions are correlated with an uncertainty of 70 ps. The time-related historical radiation fluxes from a cylinder target, measured from three different directions, are obtained in the experiments on Shenguang Ⅲ prototype laser facility, offering the physical information about the heat wave propagation along the axis of the cylinder and the attenuation of soft X-ray radiation flux.
2012, 61 (7): 075209.
doi: 10.7498/aps.61.075209
Abstract +
Experimental results indicate that there exist two stable discharge operation points in a self-excited mode Hall effect thruster. During the operation, the discharge operation point jumps to and fro between two values, which greatly influences the physical process of plasma discharge in the thruster channel and the comprehensive performance of thrusters. In this paper, by using the relationship between discharge magneto-ampere characteristic curve and magnetic field coil current curve, we propose the physical mechanism of forming the discharge bistable characteristic. On the basis of the mechanism, a method of stabilizing the single discharge operation point is presented through changing the slope of magnetic field coil current curve. The physical explanation is given through established one-dimensional dynamic fluid model for self-excited mode, and the results are approved by the self-excited experiment.
2012, 61 (7): 075210.
doi: 10.7498/aps.61.075210
Abstract +
The Hall drift of electrons in anode layer plasma accelerator is analyzed based on Lorentz transformation. It is shown that Hall drift does not exist always in the cross-field. If the ratio of E to B is lager than light speed, Hall drift will disappear. The further analysis shows that the Hall drift is not always in the form of gyration. It is also in the forms of wave and straight line, depending on electric-magnetic field configuration and initial energy of electrons. The electric-magnetic configuration determines the speed of drift, and then affects electron energy. This can determine the ionization efficiency in discharge. A numerical simulation using the Particle-in-Cell method is performed. The result indicates that a nice ratio of E and B will produce high ionization efficiency (for argon, this value is about 4106). This value will change with working gas according to the ionization cross section determined by electron energy.
2012, 61 (7): 075211.
doi: 10.7498/aps.61.075211
Abstract +
Dielectric barrier discharge is an important method of producing nonequilibrium low-temperature plasma. Measurement of the plasma parameters is highly valuable for its industrial application. Plasma parameters of square superlattice pattern are investigated by optical emission spectroscopy in a dielectric barrier discharge by using a two-liquid-electrode dielectric barrier discharge device in argon at atmospheric pressure. It is found that the light intensity of the large diameter microdischarge channel(big dot) is different from that of the small diameter channel (small dot). Vibrational temperature is investigated by using the N_{2} second positive spectrum. Electronic excitation temperature is measured by means of spectral line intensity ratio. Electron density is obtained by using the stark broadening of Ar atom 696.54 nm spectral line. The results show that the electron density and the vibrational temperature of the small dot are larger than those of the big dot but the electronic excitation temperature is lower than that of the big dot. It is suggested that the plasma state of the big dot is different from that of the small dot in the stable square superlattice pattern.
2012, 61 (7): 075212.
doi: 10.7498/aps.61.075212
Abstract +
Effects of focusing conditions on femtosecond laser induced plasma fluorescence in air are investigated by using different focal length lenses. Under the tightly focusing condition, the fluorescence spectra are composed mainly of continuous spectrum and line spectra from N and O atoms, which is due to the higher laser intensity and corresponding higher electron density than those in the case of weakly focused laser beam. In the latter case, only line spectra from air molecules are observed. Besides, the intensity of line spectrum as a function of propagation distance is measured, which reveals the evolution of the plasma filaments.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2012, 61 (7): 075213.
doi: 10.7498/aps.61.075213
Abstract +
Using high dynamic range X-ray framing camera, the radiation driven ablative Rayleigh-Taylor instability facing backlight radiography on SHENGUANH (SG) II device is studied. In the SG II that has eight beams with the 2 ns laser pulse and the ninth beam for Mo backlight, two-dimensional space-time ablation RT growth process for the cycle 20 m and the initial perturbation 1 m are observed clearly, and the non-linear growth process is also observed by the doping Br ratio of 1.1% in samples. The result lays a good foundation for quantitative characterization and numerical simulation of RT instability in inertial confinement fusion (ICF) experiments.
