Vol. 61, No. 10 (2012)
The self-trapping of superfluid Fermi gases in the Bose-Einstein condensation regime and in unitarity
2012, 61 (10): 100301. doi: 10.7498/aps.61.100301
In the mean-field theory and two-mode approximation, we study the self-trapping of superfluid Fermi gases in the BEC regime and in unitarity by observing the evolution of the population imbalance with time and the variation of the average of population imbalance with several non-linear interaction parameters. The high-frequency modulations of both the symmetric double-well potential and the potential well are studied. The boundary conditions of the self-trapping and non-self-trapping are given. We find that high-frequency modulation in a certain range of modulation can make the self-trapping phenomenon easier to achieve. Finally, we study the influence of the initial value on self-trapping, and find that the increase of the absolute of the initial value can make the self-trapping more conducive to the realization.
Single photon wavelength modulation absorption spectrum of acetylene for 1.5 m laser wavelength stabilization
2012, 61 (10): 104205. doi: 10.7498/aps.61.104205
We describe a kHz single photon wavelength modulation technology to realize the locking reference signal of the laser frequency. By detecting the single photon acetylene gas absorption spectrum and by amplifying the lock-in the discrete single photon response pulse, we achieve the laser frequency stabilized in real time. The 1.5 m distribution feedback semiconductor laser output frequency is stabilized at acetylene gas absorption peaks, and the typical laser frequency fluctuation is less than 25 MHz within 175 s. This single photon wavelength modulated absorption spectrum technology eliminates the high background noise in low frequency range and can be used in the quantum communication system and optical wavelength division multiplex.
2012, 61 (10): 105202. doi: 10.7498/aps.61.105202
The characteristics of a real-time ion detectorplastic scintillator are experimentally investigated on an electrostatic accelerator. The sensitivity, the dynamic range, the energy response, and the spatial resolution of the plastic scintillator are calibrated, and then compared with those of other ion detectors. Meanwhile, the possibility for the plastic scintillator to be used as a diagnostic tool in laser-driven ion acceleration experiment is discussed. The plastic scintillator provides an efficient tool for online ion detection in the experiments of high-repetition-rate laser-driven ion accelerations.
2012, 61 (10): 100201. doi: 10.7498/aps.61.100201
The REST operation for multilevel storage in phase change random access memory cell is investigated via numerical simulation. A three-dimensional memory cell model is built, and the physical property variation is calculated by solving the Laplace equation and the heat conduction equation with finite element method. The phase distribution in phase change layer and the total resistance of the cell are examined. The influences of cell structure size variation on multilevel storage process and states are analyzed. The simulation results demonstrate that multilevel storage can be achieved through accurate electrical pulse control while the variations of phase change layer thickness and bottom electrode contact size have relatively large effect on the storage state. The storage states can all keep stable for more than 10 years at 80 ℃.
2012, 61 (10): 100202. doi: 10.7498/aps.61.100202
The control of amplitude of limit cycle emerging from the Hopf bifurcation in Langford system under a nonlinear feedback controller is investigate in this paper. Explicit nonlinear control formulae and amplitude approximations in terms of control gains are derived by utilizing the center manifold theory and normal form reduction. Gain-amplitude curves for controlled systems are drawn and verified by numerical simulations. The formulae and expressions for the Langford system present a convenient approach to obtaining an effective analytical control in this system.
Parameter joint estimation of phase space reconstruction in chaotic time series based on radial basis function neural networks
2012, 61 (10): 100501. doi: 10.7498/aps.61.100501
In this paper, we propose a joint estimation method of two parameters for phase space reconstruction in chaotic time series, based on radial basis function (RBF) neural networks. And we obtain the best estimation values, according to some objective standards. Furthermore, The single-step and multi-step RBF prediction model is used to estimate the best embedding dimension and delay time, and Lorenz system is selected as an example. Finally, the estimation values are tested in the original model. The simulations show that we can obtain the best estimation values through the method, and the prediction accuracy is significantly improved.
2012, 61 (10): 100502. doi: 10.7498/aps.61.100502
By choosing an appropriate damping kernel function of generalized Langevin equation, fractional Langevin equation (FLE) is derived in the case of overdamped condition. With the theory of anomalous diffusion and the memory of fractional derivatives, the physical meaning of FLE is discussed. Moreover, the internal mechanism of stochastic resonance about FLE is obtained. Finally, the numerical simulation shows that in a certain range of the order, stochastic resonance appears in FLE, and it is evident that the SNR gain in fractional Langevin equation is better than that of the integer-order situation.
2012, 61 (10): 100503. doi: 10.7498/aps.61.100503
By using theoretical analysis and numerical simulation, the stability and the paramagnetism of Fermi gas in a strong magnetic field at low temperatures are studied, and the influences of temperature and magnetic field on the stability and susceptibility of the system are analyzed. The results show that the strong magnetic field causes variation of a system stability, and such a change relates to temperature. While the effects of temperature on stability and susceptibility are relevant to the chemical potential (i.e. the particle number density) of free gas. When the chemical potential is even, the magnetic field weakens the stability of the system, and the increasing of temperature leads to the reduction in the susceptibility of the system. When the chemical potential is odd, the magnetic field strengthens the stability of the system, while the increasing of temperature can increase the susceptibility of the system. With temperature increasing, the effect of the magnetic field on the stability is weakened. With magnetic field increasing, the change of the stability of the system becomes oscillatory, and the oscillation center of the susceptibility shifts down.
2012, 61 (10): 100504. doi: 10.7498/aps.61.100504
Suppressions of spiral waves and spatiotemporal chaos in cardiac tissue are investigated by using the Luo-Rudy phase I model. Two control methods are proposed. (Ⅰ) A planar wave is generated by alternately changing the extracellular potassium ion concentration, and then a weak external electric field is used to help plane wave to suppress spiral waves and spatiotemporal chaos. (Ⅱ) The extracellular potassium ion concentration is first enhanced. Planar waves are then generated by the wave emission induced by an external electric field. We use the planar waves to suppress the spiral waves and spatiotemporal chaos. The results show that the control methods can effectively suppress spiral waves and spatiotemporal chaos when relevant parameters are appropriately chosen. When regional myocardial ischemia occurs, high extracellular potassium ion concentration will appear where myocardial ischemia occurs. The methods of wave emission can be used to suppress spiral waves and spatiotemporal chaos in heart in this case. The advantages and mechanism of the control methods are explained.
2012, 61 (10): 100505. doi: 10.7498/aps.61.100505
For studying the statistical properties of characteristic quantities in noise signal, such as the amplitude of extreme, the amplituds of the rising edge and the falling edge, the interval between extreme points and the product value of the quantities,the background noise signal sequence values of photoelectric sensor in suspended particle counter are recorded by using the high-speed data acquisition card. The results show that the statistical distribution of these characteristic quantities match well with the form of the log-normal distribution, with natural number l used as the independent variable. The statistical distributions of characteristic quantities show a high degree of similar characteristics. Based on this statistical similarity the transform relationship between the independent variables corresponding to different characteristic quantities by power function can be derived. The similarity between statistical distribution functions of characteristic quantities can be understood as a kind of performance of statistical fractal characteristics for noise signal collections.
Detection of weak target signal with least-squares support vector machine and generalized embedding windows under chaotic background
2012, 61 (10): 100506. doi: 10.7498/aps.61.100506
To extract weak signal from the chaotic background, in this paper we analyze the theory of state space reconstruction of complicated nonlinear system, and put forward an estimation method utilizing the least-squares support vector machine (LS-SVM) based on a generalized window function. In the algorithm the generalized embedded window is taken as a foundation and the correlation function method is used to determine the embedded dimension and time delay of Lorenz system and so the state space reconstruction is realized and by combining the error forecasting model in which the LS-SVM is used to estimate the errors, the detection of the weak target signal, such as transient and periodic signal, is achieved. It is illustrated in the simulation experiments that the model proposed can detect the weak signals effectively from a chaotic background and reduce the influence of noise on the target signals, which possesses minor forecasting error. Compared with those conventional methods, this method has a remarkable advantage in reducing detection threshold and improving the accuracy of prediction. When the signal-to-noise ratio is -87.41 dB in the chaotic noise background, the new method can reduce the root mean square error nearly two orders of magnitude, reach 0.000036123, while the traditional SVM can only reach 0.049 under the condition of -54.60 dB.
2012, 61 (10): 100507. doi: 10.7498/aps.61.100507
The improved impulsive control method is proposed to realize the complete synchronization of integral and fractional order hyperchaotic systems. Some effective sufficient conditions are produced to realize the asymptotical stability of synchronization error system. In particular, some simple and practical conditions are derived in synchronizing the chaotic systems by choosing constant impulsive distances and control gains. Compared with the existing results, the main results are less conservative by relaxing some unnecessary inequality constraints. Simulation results show the effectiveness and the feasibility of the proposed impulsive controller.
2012, 61 (10): 100508. doi: 10.7498/aps.61.100508
Serious interference between motor vehicles and pedestrians happens at crosswalk when pedestrian flow is large. In this paper, cellular automata models are used to model the behavior of mutual interferences between pedestrians and vehicles at crosswalk by introducing conflict interference rules between pedestrians and vehicles. Numerical simulations are carried out to study the fluxes of vehicle and pedestrian, influenced by the parameters, such as the arrival rates, pedestrian waiting time and the pedestrian's sensitivity coefficient to vehicle. Simulation results show that the model can reflect the interference characteristics between pedestrians and vehicles well. With the increase of threshold that pedestrians cross the traffic lane riskily, motor vehicle flow increases but pedestrian flow decreases. With the increase of pedestrian's sensitivity coefficient, pedestrian avoiding probability decreases, motor vehicle flow decreases, pedestrian flow increases. The results have certain significance for the control and management of mixed traffic.
2012, 61 (10): 100509. doi: 10.7498/aps.61.100509
The effects of correlated time between noises on the stability of unstable state in the Logistic system are investigated. Using the steepest-descent approximation, the analytic expression for the mean first-passage time from unstable state to stable state is derived. The numerically calculated results indicate that the additive noise, the multiplicative noise and the correlated time between the additive and the multiplicative noises weaken the stability of unstable state, but the correlation between the additive and the multiplicative noises enhances the stability of unstable state.
2012, 61 (10): 100601. doi: 10.7498/aps.61.100601
An improved method of step height measurement by optical frequency comb and tunable diode laser is presented. The tunable diode laser is phase locked to the optical frequency comb, so that the output wavelength of the laser can be locked and measured in a high accuracy. Based on the principle of variable synthetic wavelength chain, the step height can be measured by tuning the wavelength of the locked tunable diode laser. This method can be used to eliminate the effect of the synthetic wavelength error on the measurement uncertainty of the step height. The stability of the phase locked laser is tested by locking a tunable diode laser to an optical frequency comb for about 5000 s. It is shown that the frequency stability of the phase locked laser is 1.810-12. The uncertainty of the step height measurement by this method is estimated to be 7.9 nm accordingly. Moreover, the measurement result of the step height can be traced to the time and frequency standard.
Influence of mechanical configuration and hardness of last stage anvil on high pressure producing efficiency for octahedral cell
2012, 61 (10): 100701. doi: 10.7498/aps.61.100701
We analyse the loading force transmissions for two kinds of loading structures directed at multistage octahedral cell of high pressure device, and build a mechanical relationship for high pressure producing efficiency. The relationship between cell pressure and hydraulic load is calibrated at room temperature for 14/8, 12/6 and 10/4 cell assemblies using the phase transitions of Bi, ZnTe, ZnS and GaAs under high pressure. Also we discuss qualitatively the influences of both mechanical configuration and hardness of last stage anvil on high pressure producing efficiency of octahedral cell. The experimental results show that both mechanical configuration and hardness of last stage anvil are key factors for affecting high pressure producing efficiency, what is more, the mechanical configuration is more important. The larger the geometry configuration of octahedral cell, the higher the high pressure producing efficiency is; high pressure producing efficiency of 6-8 type loading configuration is higher than that of 2-6-8 type loading configuration; when the pressure of octahedral cell approaches to Vickers hardness of last stage anvil, the harder the last stage anvil, the higher the high pressure producing efficiency and the higher cell pressure is.
2012, 61 (10): 102101. doi: 10.7498/aps.61.102101
The relativistic mean field theory is used to investigate the shape evolution of Pt isotopes. The calculated binding energy and deformation parameter 2 are consistent with those obtained in experiment. The potential energy surfaces and the single particle levels show the shape evolution for Pt isotopes. From N=88 to N=126, the shapes for Pt nuclei evolve from spherical shapes to X(5), and then to shapes of stable quadruple deformation, finally back to the spherical shapes. In detail, 166-172Pt are spherical. 174Pt and 192-196Pt possess the X(5) symmetry. 176-190Pt are deformed nuclei. 204Pt holds spherical shape. These results in agreement with the experimental observations.
Measurement and analysis of neutron capture rate of U-238 in an alternate depleted uranium/polyethylene system
2012, 61 (10): 102801. doi: 10.7498/aps.61.102801
In order to check the conceptual design of subcritical reactor, an alternate depleted uranium/polyethylene-shell simulation device was established, to carry out uranium-238 neutron capture rate experiment using activation technique. The depleted uranium foils were activated at 90o to the incident. By measuring the 277.6 keV -ray emitted from 239Np generated by 238U (n, ) 239U reaction and correcting self-absorption of uranium experimentally, the 238U (n, ) reaction rate with an uncertainty between 3.5% and 3.7% and a total neutron capture of 2.24 0.09 of the system were obtained. The experiment was simulated using MCNP5 code with ENDF libraries. The simulations and measurements accord within 5% for the 238U (n, ) reaction rate and within 1% for the total neutron capture rate of 238U.
2012, 61 (10): 102901. doi: 10.7498/aps.61.102901
In a traveling wave tube, efficiency of multistage depressed collector (MDC) is very important because it is closely related to total efficiency. The correct estimate of the efficiencies of MDC and TWT can help us predict TWT's whole function and provide a theoretical guidance for developing pertinent software, which therefore plays an important role in optimizing MDC and improving TWT total efficiency. Although formula for predicting MDC efficiency was given by Kosmahl in 1980, whose estimation is much higher than the measured value, a more accurate formula is still necessary. Firstly, the concept of dissipated common difference is used in this paper to estimate the efficiencies of MDC and TWT and then new estimate formulas are obtained by making a model of arithmetic triangular energy distribution for spent beam. It is expected that new formulas give predictions closer to the measured values than the Kosmahl's evaluation. Finally, expression for optimal MDC electrodes is given on the basis of two extreme values, i.e., maximal MDC efficiency and minimal total dissipated energies on all electrodes. The prediction from the expression is reasonable and accurate.
2012, 61 (10): 102902. doi: 10.7498/aps.61.102902
A figure of merit (FOM) for thick pinhole imaging and its formula are developed. The FOM can describe the total spatial resolution and sensitivity of thick pinhole imaging. Based on the penetration model, the root-mean-square of point spread function and the effective diameter at the center are derived. FOMs at the total and effective field of view are calculated. Based on the figures, the characteristics of thick pinhole imaging are discussed.
ATOMIC AND MOLECULAR PHYSICS
2012, 61 (10): 103101. doi: 10.7498/aps.61.103101
The background blackbody radiation causes the shift of the hyperfine energy level and affects the accuracy of the optical frequency standard. The polarizabilities of the hyperfine energy levels 5d106s2S1/2 (F=0) and 5d96s2 2D5/2 (F=2) of 199Hg+ are evaluated and the relative frequency shift at room temperature due to blackboby radiation is calculated to be -5.410-17. Finally the effect of blackbody radiation on single 199Hg+ optical frequency standard is discussed at an ultralow temperature.
A theoretical study on electron impact excitation differential cross sections and Stokes parameters of Mg atom
2012, 61 (10): 103102. doi: 10.7498/aps.61.103102
Differential cross sections (DCSs) and Stokes parameters for electron impact excitation of 3s3p 1P1, 3s4p 1P1 states in magnesium are calculated by using the fully relativistic distorted-wave (RDW) program REIE06. In the calculations, the relativistic effects and electron correlations are considered systematically. The results are analyzed and compared with available experimental data and theoretical calculations, and they are in good agreement with each other.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (10): 104101. doi: 10.7498/aps.61.104101
An (AB)N(BA)N-type one-dimensional photonic crystal is made from common material A(SiO2) and electric single-negative material B. Numerical calculation results indicate that there is a very sharp tunneling model at 1907.3 nm of the original band. When the incident angle increases, the transmittance and the full-width half-maximum of the tunneling mode remains the same, but its position is blue shifted. The value of |d/d| turns larger when the incident angel is in a range from 15 to 65. When permeability of B medium B increases from 5 to 10, the position of the tunneling model is only red shifted. When geometric thickness of the dielectric increases, the transmittance of the tunneling model remains unchanged, but its position is red shifted obviously and its full-width half-maximum increase slightly.
2012, 61 (10): 104102. doi: 10.7498/aps.61.104102
The laue bent crystal is the most effective optical element of focusing, collimating and monochromating of high flux density hard X-rays (above 30 keV) from the insertion device radiation, because of reducing the high heat load effectively. So the study of the focusing optical properties is important for developing high performance and stability laue bent crystal monochromator. We give a systematic research of the focusing properties of laue bent crystal by X-ray trace program self-developed, analyze the effects of the mode of incident beam and crystal parameter on focusing spot size, focal length, diffracted beam divergence, etc., and obtain the following results: the higher the diffracted energy, the smaller the spot size is and the spot size tends to be a constant; the smaller the bend radius of crystal, the smaller the spot size is, and the spot size reaches a minimum when the bend radius is a threshold, then as the bend radius decreases, the spot size becomes larger because of aberration; the spot size is linearly directly proportional to the thickness of crystal. For the divergence of diffracted beam, it becomes smaller as the diffracted energy is high, and tends to be a constant; it is linearly directly proportional to the curvature of bent crystal. Also we obtain a reasonable range of bent crystal parameters from the study by ray-tracing.
2012, 61 (10): 104201. doi: 10.7498/aps.61.104201
Commonly, by virtue of the frequency selective surface (FSS) radome's shape, out-band signals are reflected to other directions to achieve a stealth radome. However, with the development of the anti-stealth of poly-state radar technology, such reflected signals can be still detected. In view of this problem, a novel frequency selective surface loaded with resistance film absorbers is proposed. Such an FSS not only has a stable performance for various incident angles and for different polarizations, but also possesses absorptive property to electromagnetic waves in out-band. By virtue of this advantage, the out-band signals can be absorbed and the risk of anti-stealth detection can be greatly reduced. In addition, because of the function of the absorber, grating lobes of the FSS are also restrained, which reduces the interference of operating band.
2012, 61 (10): 104202. doi: 10.7498/aps.61.104202
A new method of polarization imaging, based on Stokes parameter, is proposed by digital in-line holography. The idea is to reconstruct the spatial distribution of polarization state of light transmitted through anisotropic objects using a linearly polarized beam and an elliptically polarized reference beam. Stokes parameters of object wave are obtained and the distribution of polarization can be determined uniquely by obtaining digital holograms in both orthogonal orientations and measuring the information about amplitude and phase of object wave in these two directions. The results show that the method can be used to measure the polarized properties of objects. In addition, it is applicable to both in-line and off-axis holography, because it can remove a zero-order and conjugate image components while acquiring Stokes parameters of object wave.
2012, 61 (10): 104203. doi: 10.7498/aps.61.104203
Based on the theory of suface plasmon resonance and the special nano-optical effect of metal-dielectric composite, we study super-resolution photolithography using multilayer films. The main point is to use 365 nm exposal light to realize super-resolution imaging by using a mask with a period of 230 nm and linewidth of 100 nm. We discuss the selection of the parameters multi-film with equal thickness, and achieve a sufficient contrast and high intensity through numerical simulation, then verify the obtained results by the plasmon nanolithography technique. Choosing the best scheme, we achieve large-area super-resolution images with the subwavelength structure.
Theoretical research of the influence of operation mode of chemical oxygen-iodine laser on its pulsing
2012, 61 (10): 104204. doi: 10.7498/aps.61.104204
One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The influences of gas temperature of 150-450 K and pressure of 660-2660 Pa on single pulse energy, pulse duration and peak power are studied. The internal reason of the influences of pressure and temperature on laser characteristics is analyzed. The results show that the higher laser peak power can be obtained in the case of gas temperature of 150 K and pressure of 1330 Pa than in the case of 400 K and 2660 Pa. Thus an efficient pulsed chemical oxygen-iodine laser is promising if the abundant atomic iodine is generated instantaneously. The approach to atomic iodine generation does not disturb the state of supersonic flow.
2012, 61 (10): 104206. doi: 10.7498/aps.61.104206
At present, in most high-power laser drivers the phase modulation is used to suppress the effect of stimulated Brillouin scattering and meet the requirement for target surface light intensity uniformity. However, the modulated pulses show intense FM-to-AM effect after transmitted through a complex laser system. Analyzing the source of this effect is essential to the improvement of the output performance of whole laser system. In this paper, the theoretical analysis and the numerical simulation of the FM-to-AM conversion of the optical flat plates are investigated, which has been ignored by many researchers. The simulation results show that the more the laser passes through the optical flat plates, the deeper the modulation will be (for example, the modulation depth will be as high as 22.2% when transmitting ten times), and it follows a linearly increasing trend. What's more, the different flat optical elements have different spectral filtering effects. When the central wavelength of the front-end is chosen to be 1054 nm, the spectral filtering effect is very weak. To our knowledge, the reduction of the FM-to-AM conversion by changing the central wavelength is presented for the first time.
2012, 61 (10): 104207. doi: 10.7498/aps.61.104207
Chalcohalide glasses with compositions of (100-2x) GeS2-xGa2S3-xCsCl (x= 15, 20, 25) are synthesized by the conventional melt-quenching method. Third-order optical nonlinearities of these glasses are studied using the Z-scan technique. The relationship between photon energy and optical nonlinearity is analyzed. Moreover, the effect of glass composition on the third-order nonlinearity is investigated. The results show that just a small variation of the excitation photon energy causes the value of samples to change in a large range. The value increases with the enhancement of excitation photon energy. When the photon energy is close to 0.5 Eg, the value is close to 0 and the factor of quality of the glass reaches an optimal value. The increase of CsCl content enlarges the optical band gap Eg, which leads to the blue-shift toward the short edged wavelength, and lowers the value. However, the value varies little because of the opposite effect on the optical nonlinearity between the structure and the band gap Eg. In this work, the optical nonlinearity is shown to be dependent on band gap and structure, and the results have a certain directive significance and reference value for future research.
Morphology control of gold nanoparticles on glass surface realized by electric field assisted dissolution method
2012, 61 (10): 104208. doi: 10.7498/aps.61.104208
Noble metal nanoparticles have potential applications in photonics, catalysis, and bio-labeling, owing to their much unique optical properties and surface activities. Monodisperse spherical Au nanoparticles with sizes in a range of about 60-80 nm are formed on the glass surfaces via ion sputtering and follow-up heat treatment. At an appropriate temperature, the electric field assisted dissolution process of Au nanoparticles is realized by the strong direct current electric field in step-like feature. In the different color areas of glass surface, it can be found that the original spherical Au nanoparticles are dissolved into the particles with the shape of a lunar eclipse. From surface plasmon resonance absorption properties and scattering electron microscopy images of Au nanoparticles in the different color areas, the influence of experimental condition on property of gold nanoparticle is demonstrated. From the current-voltage characteristics in electric field assisted dissolution experimental process, the physical process of Au nanoparticle dissolution under strong direct current electric field is analysed: the tunneling process of ejected electrons from Au particles to the anode starts, then followed by transfer process of Au cations to the glass matrix and the combination process of electrons from cathode with a positive charge Au particles. The physical mechanism of morphology control of Au nanoparticles realized by electric field assisted dissolution method is discussed in detail.
2012, 61 (10): 104209. doi: 10.7498/aps.61.104209
According to the analysis of gain theory, the absorption or gain of medium depends on pump power. The coherent population oscillation leads the pulse to experience absorption saturation and propagation delay in a medium with absorption. This effect induces the pulse to experience gain saturation and propagation advance in a medium with gain. Making use of the transition rate equation of metastable state poplation, we develop the model of fast light in erbium-doped optical fiber and obtain the analytic expression of time advance. We demonstrate that there is a saturation effect of fast light in low frequency region, but the fast light is enhanced with pump power increasing in high frequency region.
The optical transmission and improvement of flux for the static polarization wind imaging interferometer
2012, 61 (10): 104210. doi: 10.7498/aps.61.104210
The static polarization wind imaging interferometer takes advantage of polarized-light beam to obtain interferogram, and beam transmission characteristic in core polarization components is a key issue. The Jones matrix is convenient and concise for analyzing the optics polarization state, and easy to obtain the relationship of key optical components in the system performance. The Jones matrix is introduced to describe the static polarization interferometer system respectively in a given case and in a general case. The variations of optical flux and interference fringe visibility are investigated as functions of polarization direction and wave plate azimuth associated with the key components, and their optimal values are ascertained. The optical flux can be improved by widening field of view and increasing the transmittance of the pyramid prism. The simulation results of the interference intensities confirm the theoretical expectations.The study provides a theoretical basis and practical guidance for the design, development and engineer of the static polarization wind imaging interferometer.
2012, 61 (10): 104301. doi: 10.7498/aps.61.104301
The traditional terrain contour matching (TERCOM) algorithm has worse reliability when velocity error or course error is larger. The extend Kalman filtering (EKF) algorithm based BUAA inertial terrain aided navigation (BITAN) algorithm fails to correctly position, leading to a decline of robustness when large initial position error or altimeter noise error occurs. In this paper, we introduce a Robust BUAA inertial terrain aided navigation (RBITAN) algorithm, which is an improved algorithm of BITAN. In the RBITAN algorithm a searching mode approach is designed by the statistic properties of mean absolute difference algorithm, mean square difference algorithm and cross correlation algorithm. The RBITAN gathers the advantages of both the TERCOM algorithm and the BITAN algorithm, and it adopts EKF based BITAN algorithm as the tracking approach. The algorithm is verified by both real digital altitude model and flight-test data. Compared with the BITAN algorithm, the RBITAN algorithm is robust, for it can achieve accurate positioning and tolerate large initial position error or altimeter noise error.
2012, 61 (10): 104302. doi: 10.7498/aps.61.104302
In this paper, by taking the acoustic property of a two-dimensional squarely arranged Helmholtz resonator array for example, we point out that there exist two kinds of couplings in the local resonance phononic crystal, which are the coupling between the resonator and background and the coupling among the resonators, respectively. The first coupling effect can be changed by changing the quality factor of the resonator. A local-resonant type of band gap can be converted into a Bragg-scattering type continually when this kind of coupling becomes larger and larger. The second one, which is based on the overlapping of the near filed around the resonators, can be enhanced by reducing the distance between the nearest resonators. As a result, a wider band gap, but a smaller penetration depth of the wave, can be obtained.
2012, 61 (10): 104501. doi: 10.7498/aps.61.104501
Point defects are implanted in an ordered granular system by randomly selecting granules and changing their stiffness coefficients. The discrete element method is used to research the normal force probability distribution. Simulation result shows that force network is almost homogeneous without defects whereas force network will become inhomogeneous with defects. The concepts of primary normal force and secondary normal force are proposed and their statistics are analyzed separately. As the rate of defects increases, the changing process of primary normal force distribution is complex, whereas the secondary normal force distribution is always exponential distribution. Our simulation shows that normal force distributions are different between randomly packing system and compositional disordered system of low defect rate. But when defect rate is large, the distributions are similar. These results are beneficial to the understanding of the relationship between inhomogeneous force network and disordered system.
2012, 61 (10): 104701. doi: 10.7498/aps.61.104701
Based on the consistence principle for the severe slugging formation condition, a computational fluid dynamics (CFD) method is proposed for numerically simulating the gas-liquid severe slugging in a pipeline-riser system by converting the three-dimensional pipeline-riser system into a two-dimensional equivalent one. Numerical simulation is conducted for the gas-liquid flow patterns of the severe slugging in a declination pipeline-riser system according to the experimental cases presented in the reference, and variations of characteristics of the flow parameters with gas-liquid superficial velocity due to such a severe slugging are obtained, including period, pressure fluctuation and blowout time, the numerical results are in good agreement with the experimental results. Moreover, the theoretical methods are obtained of determining the gas superficial velocity at the riser inlet, the gas volume fraction in the riser and the average velocity at the riser outlet during the severe slugging blowout stage, and the variations of characteristics of these flow parameters with time are presented. Besides, a theoretical predicting method of determining the flow patterns in the riser during the severe slugging blowout stage is further proposed, and the theoretical results are consistent with the CFD numerical results. The CFD method could save much time and computing resource, and the theoretical methods could be used to predict the damage of severe slugging quickly.
2012, 61 (10): 104702. doi: 10.7498/aps.61.104702
In this paper, an improved numerical scheme based on the lattice BGK method (LBM) is proposed for solving the advective transport equation coupled with an incompressible flow. We utilize the LBM to solve the equations of flow field and build a second order discrete scheme for the advective transport equations using the probability density function of LBM. Meanwhile, the validity of the method is verified by an advective transport in a planar channel flow. Numerical results show that the method reduces the numerical dissipation efficiently and it involves consistently smaller memory requirements compared with previous studies.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (10): 105201. doi: 10.7498/aps.61.105201
The thermophysical properties of arc plasma provide reliable micro-theoretical foundations and parameter inputs for the numerical simulation of the air arc discharge process. Based on the assumption of the local thermodynamic equilibrium, the computation of transport properties including electron diffusion coefficient, viscosity, thermal conductivity and electrical conductivity is performed by using the Chapman-Enskog method and expanding the sonine polynomial up to the third-order approximation (second-order for viscosity) in a pressure (0.120 atm) and temperature range (30040000 K) conditions which satisfy most thermal plasma modelling requirements. The most recent data on potential interactions and elastic differential cross sections for interacting particles are utilized to determine the collision integrals, resulting in more accurate and reliable values of transport properties than those given in the previous literature.
2012, 61 (10): 105203. doi: 10.7498/aps.61.105203
Plasma immersion ion implantation (PIII) of polymer materials is inherently difficult because the voltage across the sheath is reduced by the voltage drop across the insulator due to dielectric capacitance and charge accumulating on the insulator surface. The spatiotemporal evolutions of plasma sheath, energy and dose of ions are simulated by particle-in-cell (PIC) model for ion implantation into insulator materials. Statistical results can be achieved through scouting each ion motion in the plasma sheath. Based on the PIC model, the secondary electron emission (SEE) coefficient is determined according to the instant energy of implanting ions. Effects of thickness, dielectric constant and SEE coefficient on sheath evolution, dose and energy of incident ions are studied. The ion implantation doses and the share of high-energy incident ions are basically equivalent to the case of implantation of conductor ions, when the polymer thickness is less than 200 m, relative dielectric constant is more than 7, and SEE coefficient is less than 0.5. The numerical simulation of ion implantation into polymer can effectively provide a scientific and experimental basis for PIII of insulators and semiconductors.
The three-dimensional numerical simulation study of H transmission and negative hydrogen ions production
2012, 61 (10): 105204. doi: 10.7498/aps.61.105204
The negative hydrogen ion source neutral particle transmission characteristics and the physical processes of the negative hydrogen ion extracted from plasma grid surface are analyzed. The influence of the extraction hole transfer rate which leads to hydrogen atom transmission is studied. A physical phenomenon of collision and reflection between H and different attribution conductor walls is explored. Then based on CHIPIC software platform, a full three-dimensional PIC-MCC simulation algorithm, in which the H transmission and the physical process of negative hydrogen ion production can be simulated, is successfully developed. It is verified by the simulation of JAEA 10A model. While the simulation reaches a steady state, the average energy of H is about 0.57 eV and H presents +Y drift. The non-uniform H beam bombarding the extraction wall leads to the spatial nonuniformity of negative hydrogen ions. These simulation results are consistent with those given in the literature, thereby verifying the reliability of the algorithm.
Model analysis of experiments of implosion symmetry on Shenguang-Ⅱ and Shenguang-Ⅲ prototype laser facilities
2012, 61 (10): 105205. doi: 10.7498/aps.61.105205
The analysis and control of implosion symmetry of fuel capsule is one of the most important issues in inertial confinement fusion (ICF), and many experiments and simulations on it have been done. Here we use a simple model on implosion symmetry in ICF to analyze the best lengths of the hohlraum and distortions of capsule on Shenguang-Ⅱ and Shenguang-Ⅲ prototype laser facility. It is shown that the calculated best lengths agree with the ones obtained in experiment and the calculated capsule distortions are also close to experimental measurements. The validated model may give some references to the future experiments of implosion symmetry on Shenguang-Ⅲ laser facility.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2012, 61 (10): 106101. doi: 10.7498/aps.61.106101
The generalized gradient approximation based on the density functional theory is used to analyze the geometric and the electronic properties of C80H80. The geometric structure research indicates that between the two possible stable isomers, the isomer with 20 hydrogens connecting 12 pentagons and the 60 others outside is more stable structure. The analyses of the energy level, the orbital wavefunction, and the density of states of H20@C80H60, show that the atomic orbits of the H and C atoms have strong hybridization on the occupied molecular orbits. The low unoccupied molecular orbital of H20@C80H60 is occupied mainly by the H atoms inside the carbon cage, while the high occupied molecular orbital of H20@C80H60 are occupied partly by the H atoms outside the cage. Therefore, the H atoms inside and outside the cage will play different roles in the chemical reaction involving H20@C80H60. The H20@C80H60 shows the character of the closed-shell structures with no magnetic moment.
2012, 61 (10): 106102. doi: 10.7498/aps.61.106102
Within the framework of effective-mass approximation, exciton states confined in zinc-blende GaN/AlGaN quantum dot (QD) are investigated by a variational approach, including the three-dimensional confinement of electron and hole in the QD and the finite band offset. Numerical results show that both the exciton binding energy and the interband emission energy decrease when QD height (or radius) increases. Our theoretical results are in agreement with the experimental measurements.
Research on the total dose irradiation effect of partial-depletion-silicon-on insulator static random access memory
2012, 61 (10): 106103. doi: 10.7498/aps.61.106103
In this paper, the changes of electrical parameters and their functional errors with the total radiation dose are studied, when the PDSOI static random access memory (SRAM) is irradiated under different total doses. After the SOI SRAM is irradiated by the 60Co-γ ray, the total dose radiation damage mechanism and the correlation between the changes of device parameters and function errors are discussed. For the large-scale SOI integrated circuits, this provides a possible method to further study the total dose radiation hardening and the radiation damage assessment of the devices. It is indicated that the increase of current consumption is due mainly to the radiation-induced leakage current from both field oxygen and buried oxide. The drift of threshold voltage creates the decline in output high level, the slight increase in output low level, the significant reduction in peak-peak value, and the increase of transmission delay. When the total dose accumulates and reaches a certain amount of dose, the logic mutation error emerges, resulting in the failure of shutdown function. There is a certain correlation between the transmission delay, the output high and the logic error.
2012, 61 (10): 106501. doi: 10.7498/aps.61.106501
The influences of atomic number and shape on Debye temperature, surface energy, surface pressure and lattice are studied by means of Me-lennard jones potential, then the influences of anharmonicity and shape on surface character are discussed. The result shows that (1) the Debye temperature and surface energy increase as atomic number increases, and that of rod nanodiamond is lower than that of cubic one. (2) The surface pressure and the variation of lattice parameter at low temperature decrease with the atom number decreasing, and the rod sample change is more apparent. The harmonic atomic surface pressure is smaller than the anharmonic one. (3) The above case is obvious when less atom number is small.
2012, 61 (10): 106801. doi: 10.7498/aps.61.106801
Using the first-principles calculations within the density functional theory, we study the nanofriction between two graphene layers. The result shows that the friction of the graphene is isotropic, and the relationship between the load and the friction factor can be divided into three phases. For the smaller and larger loads, the friction factor does not increase as the load increases, which follows the Amonton's law; for the middle phase, with the increase of the load, the friction factor increases linearly. However, the nanofriction characteristics between the two incommensurate graphenes show that the incommensurate structure can reduce the friction factor between graphenes greatly, which is in agreement with experimental result. These studies provide a fundamental understanding about the nanofriction phenomenon between the graphene layers.
2012, 61 (10): 106802. doi: 10.7498/aps.61.106802
The magnetic properties of the Fe-based nanocrystalline alloys are determined mainly by their grain sizes, and the mechanism of the variation of grain size with annealing temperature is an important issue in the study of nanocrystalline alloys. In this paper, the relationships between grain size and annealing temperature for these alloys within the primary crystallization temperature (Tx1) and the secondary crystallization temperature (Tx2) for 1 h are investigated, and a corresponding model is proposed. The physical mechanism of the fact that the grain size first decreases and then increases with the increase of annealing temperature is explained by using this model. It is found that the grain size has a minimum value when these alloys are isochronally annealed at the temperature near 0.6 times that of the melting point. Theoretical analysis results are found to be in agreement with the experiments data within the investigated temperature range. This investigation provides a means to obtain the smallest grain size quickly.
The effect of nitrogen ion bombarding energy on the bonding structure of nitrogenated tetrahedral amorphous carbon film
2012, 61 (10): 106803. doi: 10.7498/aps.61.106803
The tetrahedral amorphous carbon (ta-C) films with more than 80% sp3 in fraction are deposited by the filtered cathode vacuum arc technique. Then the energetic nitrogen (N) ions are used to bombard the ta-C films to fabricate nitrogenated tetrahedral amorphous carbon (ta-C:N) films. The composition and the structure of the films are analyzed by visible Raman spectrum and X-ray photoelectron spectroscopy. The result shows that the bombardment of energetic nitrogen ions can form CN bonds, convert CC bonds into C＝C bonds, and increase the size of sp2 cluster. The CN bonds are composed of C＝N bonds and CN bonds. The content of C＝N bonds increases with the N ion bombardment energy increasing, but the content of CN bonds is inversely proportional to the increase of nitrogen ion energy. In addition, CN bonds do not exist in the films.
Influence of radio frequency power on the structure and optical properties of glow discharge polymer films
2012, 61 (10): 106804. doi: 10.7498/aps.61.106804
Taking advantage of triple radio frequency, hydrocarbon polymer films are fabricated at different powers by the glow discharge polymerization technology. The deposition rates, the chemical structures, the atomic ratios and the optical properties are studied. The thicknesses of glow discharge polymer (GDP) films are measured by the surface profiler technology. The chemical compositions of GDP films are characterized by FT-IR spectra and element analysis. The optical properties of GDP films are investigated by UV-VIS spectra. With RF power increasing from 20 W to 60 W, the deposition rate of GDP films first increases 0.34 μ m/h, then decreases after the RF power reaches 40 W. In visible light area more than 500 nm, the optical transmittances of all GDP films are more than 90%.The optical band gaps of GDP films first decrease, then reaches the minimum at the RF power of 50 W, then increases when the RF power increases from 20 W to 60 W.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Correlations between the valence electron structure and melt pointing and cohesive energies of rare earth metals
2012, 61 (10): 107101. doi: 10.7498/aps.61.107101
Rare earth element is one kind of strategic materials. Some rare earth elements have been industrialized. They play major roles in permanent magnetism material, lightening, catalysis and hydrogen storage material. In order to understand the rare earth elements more, it is necessary to study the structures of the valence electrons and atoms of them. The valence electron structures and properties of yttrium, scandium and lanthanum group rare earth elements are studied with the empirical electron theory (EET). Based on the valence electron parameters, the melting points and cohesive energies of these rare earth elements are calculated. The calculations accord with those of the measurements. According to the analyses of EET, the structures and the physical properties of rare earth elements depend on the electron emission or transformation between the lattice-electrons and coherent electrons in outer orbital. It is exhibited that the melting point tends to increase with the lattice electron-covalent electron transformation, however, the valence status of rare earth element affects significantly the electron distribution and property. The covalent electron hoppings occur at divalent europium, ytterbium and samarium, and their melting points are related to the electron transformation covalence-electrons. It is different from the others with trivalent status. The theoretical analysis reveals that the cohesive energy is related to the 4f electrons. The contribution to cohesive energy increases with the number of 4f electrons increasing, which may be due to the shrinking effect of the atomic radius for the lanthanum group. The study implies that the characteriscs of rare earth element are due to the relation between their melt pointing and conhesive energy and electronic structure.
2012, 61 (10): 107102. doi: 10.7498/aps.61.107102
Rare-earth orthoferrites (such as YFeO3) with orthorhombic perovskite-type structure are promising candidates in the fields of electrode materials, gas sensors and photocatalysts. The geometric structure, the electronic structure and the optical properties of YFeO3 crystal are investigated by using the plane-wave pseudo-potential method, with the scheme of generalized gradient approximation, revised Perdew-Burke-Emzerhof exchange-correlation potential and ultrasoft pseudopotential. The obtained lattice parameters are in good accordance with experimental results reported. The results confirm that YFeO3 crystal is a direct semiconductor with a gap (Eg) of about 2.22 eV, based on the analyses about band structure, density of state, dielectric function, absorption coefficient, and photoconductivity. It is clarified that YFeO3 crystal and nanocrystalline possess good photocatalytic activities for visible light.
2012, 61 (10): 107301. doi: 10.7498/aps.61.107301
Based on the analysis of Poly-Si1-xGex gate work function and by solving Poisson equation, the models of vertical electric field and potential distribution in strained Si NMOSFET with Poly-Si1-xGex gate are obtained; threshold voltage model and the gate depletion thickness and it's normalization model are established in strained Si NMOSFET based on the above results, with the gate depletion effect of Poly-Si1-xGex taken into account. Then the influences of device geometrical and physical parameters of device especially the Ge fraction on Poly-Si1-xGex gate depletion thickness are investigated. Furthermore, the effect of gate depletion thickness on threshold voltage is analyzed. It shows that the poly depletion thickness decreases with the increases of Ge fraction and gate doping concentration, while it increases with the increase of substrate doping concentration. Furthermore, the threshold voltage increases with the increase of gate depletion thickness. The results can provide theoretical references to the design of strained Si devices.
Study on transport characteristics of CNTFET with HALO-LDD doping structure based on NEGF quantum theory
2012, 61 (10): 107302. doi: 10.7498/aps.61.107302
A transport model of CNTFET is built by solving the Poisson equation and Schrödinger equation within the non-equilibrium Green's function theory. The simulation method can relate the CNTFET transport properties directly with the chiral index of CNT. For the first time, the influences of single HALO and double LDD (HLL) doping structures on the CNTFET are investigated. The results show that under the same gate-source and drain-source voltages, HLL-CNTFET reduces significantly the leakage current and the subthreshold swing and increases on-off current ratio as compared with conventional CNTFET, indicating that this new structure has better gate control ability than conventional CNTFET. HLL-CNTFET possesses a smaller drain-source conductance so that it is more suitable for analog integrated circuits application, and has a smaller threshold voltage shift so shat it can better suppress DIBL effect. The increase of channel electric field strength near the source is beneficial to the increase of the electron transport rate; and the reduction in electric field near the drain is more conductive to the suppression of hot electron effects. This study is helpful for understanding the working mechanism and exploring new features of CNTFET.
2012, 61 (10): 107501. doi: 10.7498/aps.61.107501
The dynamical properties of quantum spin systems have received a great deal of theoretical and experimental attention in the past decades. Only recently, has much attention been paid to the random quantum spin systems. In this paper the effect of random external field on the dynamics of one-dimensional Blume-Capel model with s = 1 in the high-temperature limit is investigated by using the recurrence relations method. The spin autocorrelation function as well as the corresponding spectral density of the system is calculated in the presence of the field that satisfies two types of distributions. When the single-ion anisotropy takes 0, for the bimodal distribution, the dynamics of the system behaves as a crossover from a central peak behavior to a collective mode one. For the Gaussian distribution, when the standard deviation is small, the dynamical behavior of the system also exhibits a crossover; when the standard deviation is large enough, the system only shows a disordered behavior. We also discuss the effect of the single-ion anisotropy on the dynamical property of the system, and find that the collective-mode behavior becomes weaker as the single-ion anisotropy exists.
Influences of the demagnetizing field on dynamic behaviors of the magnetic domain wall in ferromagnetic nanowires
2012, 61 (10): 107502. doi: 10.7498/aps.61.107502
Understanding of magnetic domain wall dynamic behavior is one of the important issues in the realization of spintronic device based on domain wall motion. We investigate the dynamic behaviors of the magnetic domain wall propagation in L-shaped ferromagnetic nanowires under external magnetic driving fields. By micromagnetic simulation, we observe a dynamic characteristic of the magnetic domain wall in a ferromagnetic nanowire with varying the external field. By changing the nanowire thickness, we examine the influence of the demagnetizing field from the nanowire surface on the domain wall dynamics under a magnetic driving field after Walker breakdown field. Using an auxilliary magnetic field perpendicular to the nanowires, we analyze the effect of the demagnetizing field on the domain wall dynamic behaviors. The results show that the stronger external field or the thicker nanowire can enhance the generation of the demagnetizing field on the nanowire surface, leading to the occurrence of the Walker breakdown phenomenon with the periodic change of the inner spin structure of the domain wall during the domain wall propagation in the nanowires. By using an auxilliary magnetic field perpendicular to the nanowires, we find that the strength and the direction of the demagnetizing field can be modulated. It implies that the dynamic behavior of domain wall propagation in the nanowire is controllable.
2012, 61 (10): 107601. doi: 10.7498/aps.61.107601
High-magnetic-field, high-frequency electronic spin resonance (ESR) facility has been first developed in Wuhan National High Magnetic Field Center, China. The facility can achieve a frequency range of 210370 GHz, a temperature range of 2300 K and magnetic fields up to 50 T. The ESR facility has been tested with a sample of ruby. Clear ESR spectra of Cr3+ ion are obtained.
2012, 61 (10): 107701. doi: 10.7498/aps.61.107701
Frequency dispersions of Lamb waves in c and c polarized lead zinc niobate-lead titanate crystal free infinite plates are studied based on the partial wave theory. Multiple crossings between symmetric and antisymmetric Lamb modes are found only in c polarized crystals, and most of the dispersion relations would exhibit the same rule as that in lead magnesium niobate-lead titanate crystals. It is found that multiple crossings between A0 and S0 modes are directly related to the multivalued quasishear vertical slowness curves. A pair of complex conjugate roots of the wave number in the x3 direction is found in a certain area. Equation of elastic constants is obtained when A0 and S0 modes cross under this condition, which can be conveniently used to judge whether A0 and S0 modes cross for crystals with orthogonal and tetragonal symmetries.
The transmission properties in one-dimensional piezoelectric Fibonacci-class quasi-periodical phononic crystals
2012, 61 (10): 107702. doi: 10.7498/aps.61.107702
The transmission properties of phononic crystals in one-dimensional piezoelectric Fibonacci quasi-periodical superlattices are studied using the transfer matrix method. The transmission coefficients in piezoelectric Fibonacci quasi-periodical superlattices are compared with those of the phononic crystals with periodical structure and with non-piezoelectric Fibonacci quasi-periodical structure. The results show that the band gap can also be found in the phononic crystals with both piezoelectric and non-piezoelectric Fibonacci quasi-periodical superlattices, and the frequency range of the gap in piezoelectric Fibonacci quasi-periodical superlattices is larger than those of periodical structure and non-piezoelectric Fibonacci quasi-periodical structure. Furthermore, the transmission coefficients are studied as a function of the properties of the material and incidence angle of the wave. The results show that the transmission coefficients in piezoelectric Fibonacci quasi-periodical superlattices are correlated with incidence angle of the wave.
2012, 61 (10): 107703. doi: 10.7498/aps.61.107703
Influences of dislocation distribution on the resistive switching effect of Ag doped SiO2 thin film are investigated under different sample preparation conditions. Stable resistance switching characteristics are observed for the samples annealed at 120 ℃ and prepared in Ar/O2 mixed atmosphere. It is shown that annealing process, electric field formation and atmosphere of preparation can change the intensity and the distribution of the dislocations (Ag interstitial atoms and oxygen vacancies) in the Ag-SiO2 structure, which leads to the resistive switching effect based on the formation and annihilation of the conducting filaments.
2012, 61 (10): 107801. doi: 10.7498/aps.61.107801
Raman spectra of benzene and chloroform with different relative concentrations are measured. The frequencies of CH stretching vibration in chloroform shift to lower wave number with the increase of benzene concentration, which can be explained by C/H interaction. This interaction is saturated when the chloroform volume fraction is less than 40%: the frequencies of CH stretching vibration remain the same. Taking the chloroform volume fraction of 70% chloroform and benzene mixed solution as the research object, the Raman spectra of binary solution and pure liquid are measured at different pressures and temperatures. According to the relationship between pressure and temperature of the frequencies of CH stretching vibration in chloroform, the regular pattern of C/H interaction is obtained.
The fabrication of Er3+/Ce3+ co-doped tellurite- bismuth glasses and the improvement of spectroscopic properties
2012, 61 (10): 107802. doi: 10.7498/aps.61.107802
A series of 80TeO2-10Bi2O3-10TiO2-0.5Er2O3-xCe2O3 (x=0, 0.25, 0.5, 0.75, 1.0 mol%) and (80-y) TeO2-10Bi2O3-10TiO2-yWO3-0.5Er2O3-0.75Ce2O3 (y=3, 6, 9, 12 mol%) tellurite-bismuth glasses are prepared by the conventional high-temperature melting and annealing method. The absorption spectra of 400-1700 nm, upconversion spectra and 1.53 m band fluorescence spectra under the excitation of 975 nm, the 4I11/2 and 4I13/2 level fluorescence lifetimes of Er3+ under the excitation of 808 nm, and the Raman spectra of doping-free glass samples are measured. Meanwhile, the spectroscopic parameters of Er3+ are calculated and analyzed with the help of Judd-Ofelt theory and McCumber theory. The results indicate that the upconversion fluorescence can be suppressed efficiently and the 1.53 m band fluorescence can be enhanced evidently, owing to the energy transfer from Er3 +: 4I11/2Ce3+:2F5/2 levels when the Ce3+ ions are introduced into the Er3+-doped tellurite-bismuth glasses. Moreover, the 1.53 m band fluorescence intensity can be improved and the fluorescence spectral width can be broadened further when an appropriate amount of WO3 component is introduced. The above research results are of theoretical significance for obtaining the tellurite-bismuth glasses with excellent spectroscopic properties, which are used for the 1.53 m broadband Erbium-doped optical fiber amplifier.
2012, 61 (10): 107803. doi: 10.7498/aps.61.107803
Based on the production kinetics of oxide-trapped charge and interface-trapped charge and the microscopic mechanism of radiation damage, a model of post-irradiation threshold voltage drift due to oxide trap and interface trap as a function of radiation dose is proposed. This model predicts that the post-irradiation threshold voltage drift due to oxide trap and interface trap would be linear in dose at low dose levels. At high dose levels, the post-irradiation threshold voltage drift due to oxide trap tend to be saturated, its peak value has no correlation with radiation dose, and the post-irradiation threshold voltage drift due to interface trap has an exponential relationship with radiation dose. In addition, the model indicates that the oxide-trapped charge and the interface-trapped charge start a saturation phenomenon at different radiation doses, and the saturation phenomenon of oxide-trapped charge appears earlier than interface-trapped charge. Finally, the experimental results accord well with the model. This model provides a more accurate prediction for radiation damage in metal-oxide-semiconductor field effect transistor.
2012, 61 (10): 107804. doi: 10.7498/aps.61.107804
Eu3+ doped CaWO4 phosphors of different concentrations are prepared by a co-precipitation method. The X-ray diffraction patterns and field emission scanning electron microscopy images are investigated. The excitation spectra, emission spectra and the curves of fluorescence decays of the samples are measured. The Judd-Ofelt (J-O) parameters, quantum efficiencies of the 5D0 level of Eu3+ and color coordinates are calculated. The dependences of relative intensity of charge transfer band, J-O parameter and quantum efficiency on doping concentration are discussed. The photoluminescence properties of Eu3+ doped CaWO4 luminescent material are studied. The results indicate that the 616 nm red emission of Eu3+5D07F2 transition can be effectively excited by 394.5 nm and 465 nm with high excitation efficiency and the concentration quenching is high. So the CaWO4: Eu red phosphor may have a potential application for white light emitting diode.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (10): 108101. doi: 10.7498/aps.61.108101
Based on the binary cellular automaton method, a modified cellular automaton model for ternary alloys is developed to simulate dendrite growth controlled by solutal effects and microsegregation in the low Peclet number regime by coupling PanEngine, which is a multicomponent thermodynamic and equilibrium calculation engine. The model can be used to calculate the interfacial equilibrium composition by considering the influence of Gibbs-Thomson effect induced curvature undercooling, and multicomponents contributed constitutional undercooling. Meanwhile, the growth velocity of interface is determined by solving the solute conservation equation simultaneously with dimensionless solute supersaturation equation for each alloying element. Moreover, equilibrium liquidus temperature and equilibrium solid concentration at the interface are derived by PanEngine. Free dendrite growth of Al-7%Si-xMg ternary alloys is simulated by the present model, which shows that the increase of solute Mg can suppress the growths of both primary and secondary dendrite arms. Meanwhile, constrained columnar dendrite growth of Al-7%Si-0.5%Mg with the increases of pulling velocity and constant thermal gradient during directional solidification is calculated. The results reveal the competitive growth of columnar dendrites, and demonstrate that the primary dendrite arm spacing would decrease as the pulling velocity increases, which accords well with the Hunt model.
2012, 61 (10): 108102. doi: 10.7498/aps.61.108102
In order to investigate the range of nucleation area of Si nanoparticles under different pressures, a single crystalline Si target with high resistivity is ablated by a XeCl excimer laser (wavelength 308 nm, laser fluence 3 J/cm2) in an ambient pressure range from 1 to 200 Pa of pure Ar gas. The Si nanocrystalline films are systemically deposited on glass or single crystalline Si substrates that are lined up at a distance of 2.0 cm under the ablation point. Raman and X-ray diffraction spectra indicate that the films are nanocrystalline. Scanning electron microscope images of the films show that the ambient pressure effect on the average size and the distributing range of Si nanoparticles on the substrate. According to the method of determining the location of nucleation area, it is found that the range of nucleation area of Si nanoparticles first broadens and then narrows with the increase of ambient pressure. The dynamics is analysed theoretically to explain the results.
Simulation of morphological evolution and crystallographic tilt in heteroepitaxial growth using phase-field crystal method
2012, 61 (10): 108103. doi: 10.7498/aps.61.108103
The phase-field crystal (PFC) model is employed to study the morphological evolution and the crystallographic tilt of heteroepitaxial growth on vicinal substrates. The results are as follows: for heterostructures with large misfit (ε > 0.08) the crystallographic tilt of epitaxial layer is approximately proportional to the substrate miscut angle, while the elastic strain energy of the film will lead to the nucleation of dislocation, which contributes to step-flow growth mode. As for the heterostructures with small misfit (ε < 0.04) the elastic strain energy will be released in the form of surface energy, and the surface profile of epitaxial film is dislocation-free island. When exposed to high undercooling, the substrate with large misfit and miscut angle will result in small-angle grain boundary between the substrate and the epitaxial layer. The small-angle grain boundary is composed of arranged dislocations, and it significantly changes the growth orientation of epitaxial layer.
2012, 61 (10): 108104. doi: 10.7498/aps.61.108104
In this paper, we investigate the magnetic and martensitic transformation properties of Cu doping partial Ni in Ni50Mn36In14 alloy. It is found that the critical temperature of the martensitic transformation decreases with Cu concentration x in Ni50-xCuxMn36In14 increases. While Cu concentration is less than 5% at., the magnetization of austenite phase is stronger than that of martensite phase, and ΔM of magnetization martensite and austenite increases with Cu doping. ΔM increases rapidly to 80 emu/g when x=4.5 and a field-induced transformation is observed in this alloy, predicting the application potential as the magnetic actuation and magnetoresistance materials. As Cu content increases to x > 5, the magnetization of austenite becomes weaker than that of martnensite, ΔM decreases to near zero.
2012, 61 (10): 108201. doi: 10.7498/aps.61.108201
The red-brown CdSe thin films are electrochemically deposited on conductive ITO/TiO2 film surfaces, and the multilayer TiO2/CdSe structures are constructed. The microstructures and the photoelectrochemical properties of multilayer TiO2/CdSe structures are investigated. The results show that the CdSe thin films are grown preferentially along the (111) direction. The thickness and UV-Vis absorbance intensity of multilayer films increase with the increase of layer number of TiO2/CdSe structure. The results obtained from photoelectrochemistry measurement indicate that the optimal photoelectrochemical current response and open-circuit voltage are obtained in a biolayer TiO2/CdSe system, which therefore demonstrates the favorable photoelectrochemical properties.
Research on characteristics degradation of n-metal-oxide-semiconductor field-effect transistor induced by hot carrier effect due to high power microwave
2012, 61 (10): 108501. doi: 10.7498/aps.61.108501
High power microwave (HPM) can disrupt the normal work of electronic systems through the effect of HPM on semiconductor devices. In this paper, the physical process and the physical model of the characteristic degradation of n-metal-oxide-semiconductor field-effect transistor (nMOSFET) induced by HPM are introduced. In device simulation results, the output characteristic curve of nMOSFET shows that HPM can induce the degradation of the characteristics of device, including the forward drift of threshold voltage, and the reduction of saturation current and transconductance. Based on the process and the model introduced in this paper, the voltage pulse generated by HPM makes nMOSFET be in depletion status and hot carrier increase; then the effect of hot carrier results in the characteristic degradation of device. The experimental result of MOS injected HPM shows the changes of output characteristics and model parameters are consistent with the device simulation results, proving that the physical process and the physical model introduced in the paper are correct.
2012, 61 (10): 108701. doi: 10.7498/aps.61.108701
A low-loss and broadband terahertz twin-core photonic band-gap fiber directional coupler is proposed, which consists of a cladding with a triangular lattice array of sub-wavelength air rods and two cores formed respectively by omitting seven nearby air rods. The group velocity dispersion, the coupling and the loss of the fibers are investigated by using a full-vector finite element method. The numerical simulations show that the loss coefficient of the coupler is less than 0.021 cm-1, and the coupling broadband of 0.14 THz can be realized. The directional coupler has potential applications in terahertz communication systems, such as filtering, wavelength-division multiplexing, polarization isolation, switching and so on.
2012, 61 (10): 108801. doi: 10.7498/aps.61.108801
The mechanical properties of MH2 (M= La, Nd, Gd, Tb, Y, Dy, Ho, Er, Lu, Sc, Ti, Zr, Hf) are studied by the first-principles calculations. The results show that the fluorite structures of MH2 (M= La, Nd, Gd, Tb, Y, Dy, Ho, Er, Lu, Sc) are stable at low temperatures. Their bulk moduli, shear moduli and Young's moduli increase in the order of LaH2, NdH2, GdH2, TbH2, YH2, DyH2, HoH2, ErH2, LuH2 and ScH2. However, the cubic phases of MH2 (M= Ti, Zr, Hf) are unstable at low temperatures. According to the densities of states and charge densities of TbH2, ErH2, TiH2 and HfH2, it can be found that the stabilities of metal dihydrides depend on the interaction between metal and hydrogen atoms.
Experimental investigation on open-circuit voltage of InGaP/InGaAs/Ge triple-junction solar cell influenced by the vibration direction of the electric vector of linearly polarized light
2012, 61 (10): 108802. doi: 10.7498/aps.61.108802
In this paper, it is investigated experimentally that the open-circuit voltage of InGaP/InGaAs/Ge triple-junction solar cell is influenced by the vibration direction of the electric vector of linearly polarized light. The results show that those voltages are subjected to periodic changes with the vibration direction of the electric vector, and the magnitude of change is about 1%4%. It is due to the effect of anisotropy of band structure in the three-junction solar cell,which is confirmed by theoretical analysis. In addition, through combining the experimental study with theoretical analysis, the relationship between open-circuit voltage and illumination, is studied, showing that they are related to each other logarithmically, which is different from characteristics of a single-junction solar cell. From fitting results, it is indicated that the triple-junction solar cells may be regarded as three diodes connected in series, of which the ideality factor is close to 6. This is due to many defects in three-junction solar cells.
2012, 61 (10): 108901. doi: 10.7498/aps.61.108901
How to guarantee the transport efficiency of the network and how to improve the network capacity are the main subject of the study presently. We investigate the gravity of the nodes to the transfer of data packets, and propose a routing method based on gravity constraint. In order to characterize the efficiency of the method, we introduce an order parameter H to measure the throughput of the network by a critical value of phase transition from free state to jammed state, and use the maximum travel time 〈Tmax〉 and the average travel time 〈Tavg〉 to test the transmission efficiency of the network. We simulate the network capacity under three different gravity constraints. Simulation results show that when only considering the path with shortest length, the network capacity is very small and the distribution of flow is extremely uneven; when only considering minimum waiting time, the excessive circuitous transfer of data packets occurs and most of the nodes will be in congestion state; when considering the gravity of path length and waiting time simultaneously and choosing a node with reasonable gravity, the network capacity will be improved greatly and the congestion level will be relieved to some extent.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Study of the stable components in extended-range forecasting for the coming 1030 days during the snow storm event in January 2008
2012, 61 (10): 109201. doi: 10.7498/aps.61.109201
In this paper we extract components in extended-range forecast for the coming 10-30 days by the Butterworth Band-pass filter using the NCEP/NCAR reanalysis daily data of geopotential height from 1978 to 2007 and from January 6th to February 4th, and at the same time extract the basic function of climate state by empirical orthogonal function (EOF). And we use the same way to deal with the daily data of geopotential height during the snow storm event in January 2008 by the Butterworth Band-pass Filter. We use the contribution rate to explain the variance of EOF and the elements which influence this weather process in a period of 1030 days. Stable components in extended-range forecast for the coming 1030 days can be divided into two parts according to the contribution rate analysis: climatic stable components and abnormal stable components. Results show that climatic stable components are in the subject status during the snow storm event in January 2008 while abnormal stable components are equivalent to a disturbed value superimposed on climatic stable components. The influence of abnormal stable components cannot be neglected, and they can play quite a significant role. The circulation patterns of abnormal stable components correspond well to anomalies in Pacific region. These conclusions deepen our understanding of 1030 days components and provide a new way to think and solve the problem of extended range forecast for the coming 1030 days.
Analysis of characteristics of a sharp turn from drought to flood in the middle and lower reaches of the Yangtze River in spring and summer in 2011
2012, 61 (10): 109202. doi: 10.7498/aps.61.109202
We use global reanalysis data probided by NCEP/NCAR, precipitation data at 740 observational stations of China provided by the National Climate Center of the China Meteorological Administration, and grid data of precipitation in 2011 provided by National Meteorological Information Center to analyze the phenomenon of a sharp turn from drought to flood in the middle and lower reacher of Yangtze River in early June 2011, and the characteristics of its circulation background and briefly conclude as follows: 1) the precipitation in the middle and lower reaches of the Yangtze River was less and its change rate was smaller than that of corresponding climatological normals from January to May in 2011, both surged suddenly in June, leading to the appearence of a sharp turn from drought to flood in June, and the kickpoint was at the 31st pentad (the 1st pentad in June); 2) around the sharp turn, both flood water vapor flux and the space-time evolution characteristics of the first and the second modes of EOF analysis represented the transform of water vapor transport from a weaker state to a stronger one; 3) before and after the turn, atmospheric circulation fields were significantly different. Before the sharp turn, winter monsoon in northern hemisphere was strong, and summer monsoon in southern hemisphere was weak, leading to the delay of monsoon tranform, stronger East Asian Trough, which went against warm-moist air blowing to the north. All of that eventually led to less rainfall in south China and occurance of this sharp turn. In early June, the period of turining, the circulation was adjusted quickly, which presented that the western Pacific subtropical high extended to west and jump to north abruptly, East Asian Trough kept strong and was maintained in the west, and blocking high located in the Okhotsk Sea weakened. Thus, cold and warm air converged in the middle and lower reaches of the Yangtze River and contributed to the occurance and continuation of precipitation. It is the main reason of the sharp turn from drought to flood in the middle and lower reaches of the Yangtze River.