Vol. 56, No. 7 (2007)
2007-04-05
GENERAL
2007, 56 (7): 3637-3641.
doi: 10.7498/aps.56.3637
Abstract +
In order to expand the solid angle for imaging of electrons in ion-atom collisions, we designed a complex Helmholtz coils composed of four single coils. Theoretical simulations were carried out to optimize the arrangement of the coils. The complex is constructed according to the theoretical analysis, and the magnetic fields were measured for interested regions. The measured results show that the relative uniformity of the magnetic fields is ±0.6%, which satisfies the requirements of collision experiments.
2007, 56 (7): 3642-3648.
doi: 10.7498/aps.56.3642
Abstract +
The research showed that the probability density curve of residential trip distribution is very similar to the probability density curve of electron in ground state of hydrogen atom. The characteristics of residential trip distribution can be well described by the electron cloud model in quantum mechanics. In this paper a residential trip distribution model is built by simulating electron cloud according to the radial probability density function of electron in hydrogen atom. Then the model is validated by the sample survey data in Changchun city and San Francisco area. The application model is further put forward and its calibration method and process are given by using an example. The model can quantitatively describe the state of residential trip distribution in urban planning and urban traffic planning.
2007, 56 (7): 3649-3654.
doi: 10.7498/aps.56.3649
Abstract +
A Chebyshev generalized finite spectral method is proposed for 2-D linear and nonlinear waves. To attain high accuracy in time discretization, the fourth-order Adams-Bashforth-Moulton predictor and corrector scheme was used. The proposed numerical scheme is validated by applications to the linear shallow water equations and extended Boussinesq equations, where analytical solution and experimental data are available for comparison respectively. Numerical results agree very well with the corresponding analytical solution or experimental data in all cases.
2007, 56 (7): 3655-3661.
doi: 10.7498/aps.56.3655
Abstract +
Algebraic dynamical algorithm is used to solve numerically the artificial earth satellite motion equation for the first time, and the result is compared with Runge-Kutta algorithm and symplectic algorithm under the forth order. The result shows that algebraic dynamical algorithm has higher accuracy than the others in the long-term calculation of satellite orbit. We also discussed the quadrupole and octupole deformation of the Earth's impact on the satellite orbit.
2007, 56 (7): 3662-3666.
doi: 10.7498/aps.56.3662
Abstract +
In this paper, a class of wading wave equations are considered. Using the homotopic mapping theory and method, the corresponding approximate solution of the system is obtained.
2007, 56 (7): 3667-3674.
doi: 10.7498/aps.56.3667
Abstract +
In this paper we introduce one type of generalized dispersive Camassa-Holm model and make its singularity analysis. We prove that the model is Painlevé integrable by an alternative WTC-Kruskal test and obtain the Painlevé-Bcklund systems and the Bcklund transformation. Many new types of regular soliton, singular soliton, kink soliton, compacton and anti-compacton are explored. Particularly, we have found singular structures of periodic cuspon waves in kink solitons, which occur in their central regions. Based on the regular solitonic system, we do Bcklund transformation and obtain three sorts of singular solitons, namely the periodic blow-up wave with hump structure, kink soliton for the blow-up wave structure and the compacton.
2007, 56 (7): 3675-3677.
doi: 10.7498/aps.56.3675
Abstract +
The Lie symmetries and Hojman conserved quantities of one kind of differential equations of motion of nonholonomic systems are studied. The determining equations and the restriction equations of Lie symmetries of the system are obtained. The condition under which a conserved quantity exists is established and the form of the conserved quantity is given. An example is given to illustrate the application of the result.
2007, 56 (7): 3678-3682.
doi: 10.7498/aps.56.3678
Abstract +
The stability of nonlinear dynamical system of relative rotation is studied. Firstly, the dynamics equation of relative rotation autonomous nonlinear dynamical system with commonly damped force and forced excitation is deduced. Secondly, the stability of relative rotation nonlinear dynamical system is studied. For the nonlinear dynamical system, it is proved that the closed orbit bifurcation can occur under some conditions. Finally, The approximate solution of the equation under forced excitation is obtained by the method of multiple scales.
2007, 56 (7): 3683-3687.
doi: 10.7498/aps.56.3683
Abstract +
For relativistic particles with spin-0 (satisfying the Klein-Gordon equation) and spin-1/2 (satisfying the Dirac equation) in infinitely deep potential well, matrix elements for the coordinate, momentum and the velocity operators are calculated. In the limit of large quantum numbers, these matrix elements give the corresponding classical quantities (nowbeing related quantities in special relativity) and satisfy exact classical relations. These results show that the Heisenberg correspondence principle is applicable to such relativistic systems.
2007, 56 (7): 3688-3692.
doi: 10.7498/aps.56.3688
Abstract +
In this paper, a new ring-shaped non-harmonic oscillator potential is proposed. Under the condition of equal scalar and vector potentials, the exact bound solutions and energy equations of both the Klein-Gordon equation and Dirac equation for this oscillator potential are obtained. It is shown that the angular wave functions of Klein-Gordon equation are given by the hypergeometric functions and the radial wave functions are expressed in terms of the confluent hypergeometric functions or general Laguerre polynomial. The spinner wave functions of the Dirac equation are constructed with the of the Klein-Gordon equation.
2007, 56 (7): 3693-3694.
doi: 10.7498/aps.56.3693
Abstract +
The oscillation of electron between two quantum wells has been studied by exactly solving the time-dependent Schrdinger equation(Acta Phys. Sin. 52 1862). The oscillation behaviour for a general case was given and the case for ω=0 was specially discussed. In this paper, we obtained the same solution more simply for the ω＝0 case using a new method.
2007, 56 (7): 3695-3702.
doi: 10.7498/aps.56.3695
Abstract +
Phase drift caused by environment is the main source of quantum bit error rate and instability in the double M-Z interferometer quantum key distribution(QKD) system. The phase drift consists of both high-frequency and low-frequency vibrations, the former, which is due to environment noise, is usually conducted via the atmosphere and can be isolated by technological measures (e.g. using foamed-plastics wrapping or rubber pillow ), the latter comes from building-vibration, which vibrates slowly with a serious impact on M-Z interferometer, with a period of 3±0.32 min (min level). A novel real-time tracking and compensation method for phase drift caused by low-frequency vibration is proposed. With the improved scheme, the QKD system based on double M-Z interferometers can operate stably for 24 hours, and key exchange with an error below 6% over 75 kilometers has been achieved in the lab.
2007, 56 (7): 3703-3708.
doi: 10.7498/aps.56.3703
Abstract +
By introducing orthogonal basis，the entangled coherent states are converted to discrete ones. We calculate their entanglement by concurrence their nonclassical effects，such as squeezing and antibunching. We find that the entanglement always follows either one of squeezing or antibunching and the entanglement increases with the increase of one of the nonclassical effects.
2007, 56 (7): 3709-3718.
doi: 10.7498/aps.56.3709
Abstract +
The stability of quantum computating of the kicked Harper model with various perturbations is investigated. Above a certain threshold of the imperfections, quantum chaos sets in. The effects of the noise errors and the static imperfections on the quantum computation are analyzed by comparing the statistical ergodic properties and the Husimi functions of the perturbed eigenstates with the ideal eigenstates of the Floquet operator. It is shown that the fidelity decay with static imperfections is exponential while it is Gaussian with noise errors. The time scales of reliable computation with these perturbations are obtained through numerical simulations. Due to the errors in classical computation the distance of two initial states increases exponentially, while the stability of quantum computation is independent of the integrable or chaotic nature of the underlying dynamics.
2007, 56 (7): 3719-3722.
doi: 10.7498/aps.56.3719
Abstract +
Recently, Hawking radiation of the black hole was studied by tunnel effect method. It was found that the radiation spectrum of the black hole is not a strictly pure thermal spectrum. How the deviation between the radiation spectrum from pure thermal spectrum affect the entropy is a very interesting problem. In this paper, we calculate the partition function using the energy spectrum derived by tunnel effect, then obtain the entropy of the black hole. When we take first order approximation, the logarithmic term of entropy correction is consistent with the one considering the generalized uncertainty relation. However, in our calculation, there is no uncertain factor. And the coefficient of logarithmic correction term is the same one after considering the correction to the black hole entropy due to the thermal fluctuation. There are no divergent terms in our result when the thermal capacity of the black hole is negative. So our discussion has universality.
2007, 56 (7): 3723-3726.
doi: 10.7498/aps.56.3723
Abstract +
The quantum tunneling framework is adopted to investigate tunneling radiation of Barriola-Vilenkin black hole with a global monopole. We obtain a conclusion that the emission rate of massive particles is related with the change of Bekenstein-Hawking entropy. The emission rates of massless and massive particles take the same functional form. It is consistent with the underlying unitary theory.
2007, 56 (7): 3727-3732.
doi: 10.7498/aps.56.3727
Abstract +
A simple analysis for the behavior of a completely inelastic ball bouncing on a vertically vibrating plate has been given. Controlled by the normalized vibration acceleration, the ball undertakes a serials of subharmonic bifurcations. Several typical bifurcation processes are discussed.
2007, 56 (7): 3733-3738.
doi: 10.7498/aps.56.3733
Abstract +
We investigate adiabatic Landau-Zener tunnelling in nonlinear three-level system. The levels and tunnelling probability are studied with respect to the nonlinearity. For weak nonlinearity, the structures of the levels are smooth and similar to their linear counterparts. However the eigenstates of the middle-level will be unstable for some system parameters, which leads to the adiabaticity to break down and the tunnelling probability chaotic. For strong nonlinearity, the structures of the levels are distorted, including double-ring-like distortion in lower-level and butterfly-like distortion in upper-level. The adiabaticity will be broken down more badly. Finally we give a possible application of the system in triple-well trapped Bose-Einstein condensates.
2007, 56 (7): 3739-3743.
doi: 10.7498/aps.56.3739
Abstract +
By adopting the gain-noise model of the single-mode laser in which the pump noise is subject to amplitude modulation wave and the action of biased signal, we use the linear approximation to calculate the power spectrum and signal-to-noise ratio (SNR) of the laser intensity, which is driven by two colour noises correlated in the form of an exponential function. The result shows that the SNR shows stochastic resonance with the variation of the noise intensity, the self-correlation time of the pump noise, the parameter of the laser system, the carrier frequency and the signal frequency of the amplitude modulation wave.
2007, 56 (7): 3744-3752.
doi: 10.7498/aps.56.3744
Abstract +
This paper studies the problem of robust H∞ guaranteed cost control for a class of time-varying uncertain continuous systems with both state and input delays. Suppose that the time-varying uncertain parameters are norm-bounded, but the matched conditions are not required to satisfy. A new sufficient condition of H∞ robust stabilization which satisfies guaranteed cost index is given for the systems by constructing the generalized Lyapunov function and taking the linear matrix inequality approach. Robust H∞ guaranteed cost controllers can be realized simply by solving the corresponding linear matrix inequalities so that a guaranteed cost function for the closed-loop systems has an upper bound irrespective of all admissible parameter uncertainties. Then, by iterative approach, the optimal robust H∞ guaranteed cost controllers can be obtained through the corresponding convex optimization. A numerical example is given to show the potential of the proposed technique.
2007, 56 (7): 3753-3758.
doi: 10.7498/aps.56.3753
Abstract +
We further studied the cross-focus system and found direct experimental evidence for the truncation error induced intermittency. The experiment demonstrated that, the numerical solution of the cross-focus system shows features of on-off intermittency, while the analytical solution of the cross-focus system is only a simple limited sequence, and the shadowability controls the system evolution. The accumulation of truncation errors imply the shadowing distances of evolving orbits, and the shadowing distance increases on approaching the fixed point and decreases on leaving the fixed point, and the increment equals the decrement in the cycles statistically. In the vicinity of nonhyperbolic fixed point, there is a threshold value, when the accumulation surpasses this threshold value, a tailure of the shadowability takes place, the system jumps from the attraction phase to the repulsion phase. It is reasonably conjectured that a new extended dimension may occur locally in the vicinity of nonhyperbolic fixed point due to truncation errors.
2007, 56 (7): 3759-3765.
doi: 10.7498/aps.56.3759
Abstract +
The proportional-integral-derivative (PID) control algorithm with two degrees of freedom are easy and useful. But when they are applied to nonlinear systems, the parameters are difficult to tune. Using improved genetic algorithm to optimize parameters of PID controller with two degrees of freedom, the convergence rate of parameter optimization is rapid and accurate. When applied to Chen's chaotic system and synchronous motor chaotic system, good results are obtained in simulation experiments.
2007, 56 (7): 3766-3770.
doi: 10.7498/aps.56.3766
Abstract +
In this paper, we consider a symbolic dynamic method, based on going athwart the coupled map lattices, to estimate unknown initial conditions of nonlinear dynamical system from the given symbolic vector sequence. It is proved that any value taken from the interval IN will converge to the initial conditions with the iteration of athwart-coupled map lattices function, and an initial condition detection method from symbolic vector sequence is presented. Both theoretical and experimental results show that the estimation method can establish one-to-one correspondence between the initial conditions of coupled map lattices and their symbolic vector sequence; therefore this technique appears to be ideally suited for information estimation.
2007, 56 (7): 3771-3776.
doi: 10.7498/aps.56.3771
Abstract +
A method for detecting weak signals embebed in chaotic noise by neural networks based on the theory of phase space reconstruction of the complicated nonlinear system is presented. One-step predictive model for chaotic background is built by neural network that possess powerful cap ability of learning and nonlinear processing. Then the weak transient signal or periodic signal which is embedded in the chaotic background can be detected from the predictive error. And the detecting ability of this method when the chaotic background is mixed with white noiseis studied. The difference in the detecting principle for the transient signal and periodic signal is pointed out. The experiment which takes the Lorenz system as chaotic background shows this method can effectively detect very weak signals embedded in the chaotic background.
2007, 56 (7): 3777-3781.
doi: 10.7498/aps.56.3777
Abstract +
Adding a suitable scalar controller to a class of chaotic systems, we can realize the synchronization for these chaotic systems. The method of obtaining the scalar controller from chaotic systems is established. The sufficient and necessary condition of chaos synchronization is obtained, which is irrelative to the chaotic system.
2007, 56 (7): 3782-3788.
doi: 10.7498/aps.56.3782
Abstract +
A method of chaos control using half period delayed-nonlinear feedback based on stability criterion is proposed in present paper. By a suitable separation of chaotic system, a special nonlinear function is obtained. Using the sum of nonlinear function about the chaotic output signal and its half period delayed output signal a continuous feedback input perturbation is constructed. Self-symmetric directly unstable periodic orbits can be stabilized by the method without using any external force. The method retains the advantages of performing the self-control of delay feedback control and overcomes its limitations. Beside, the validity of control is ensured due to the stability criterion. The control can be started at any moment, and it is convenient and flexible. The coupled coupling Duffing oscillator is taken as a numerical example. The results of numerical simulation show the validity of the method.
2007, 56 (7): 3789-3795.
doi: 10.7498/aps.56.3789
Abstract +
Chaotification is an inverse process of chaos control. This paper addresses the mechanism of chaotification of buck converter. A new chaotification model of buck converter is established. Then the chaotification rule of buck converter is discussed. The fact that using time-delay feedback at the input can realize chaotification in buck converter is proved. The ranges of control parameters are determined using nonlinear dynamics stability theory. Computer simulation is made to verify the proposed method and analyze the influence of different control parameters. The theoretical results are verified by experimental measurements.
2007, 56 (7): 3796-3802.
doi: 10.7498/aps.56.3796
Abstract +
In this paper, an impulsive control for synchronization of a class of unified chaotic systems with channel time-delay and parameter uncertainty is proposed. The practical stability of impulsive synchronization between two nonautonomous chaotic systems is studied. This practical stability is equivalent to that of the synchronization error system at the origin. Based on the theory of impulsive differential equation, the criterion for the practical stability of the synchronization error system at the origin is presented. Numerical simulations show the effectiveness of the method.
2007, 56 (7): 3803-3812.
doi: 10.7498/aps.56.3803
Abstract +
Phase synchronization(PS) and generalized synchronization(GS) of a chaotic oscillator driven by two chaotic signals is investigated. Anti-biased PS and biased GS in the presence of biased coupling are found, i.e., the response oscillator can be phase synchronized (generally synchronized) by the drive with a weaker (stronger) coupling rather than the stronger (weaker) driver. The mechanism for these behaviors are explored.
2007, 56 (7): 3813-3819.
doi: 10.7498/aps.56.3813
Abstract +
This paper presents a method of controlling gyro system based on bounded damping feedback. Firstly，using LaSalle invariable theorem，a stability analysis is given theoretically. Then by introducing a two order Butterworth lowpass filter，a feedback controller is proposed on the basis of measured signals. The chaotic gyro system can be stabilized to different periodic obits or fixed points in the numerical simulation. Furthermore，the effects of control parameter and noise are investigated. The results show that the implementation of this control method is simple and easy. In addition，the controller has strong robustness against weak external noise.
2007, 56 (7): 3820-3826.
doi: 10.7498/aps.56.3820
Abstract +
Using high temperatures and ultrasonic, ultrasonic bonding is one of the main methods in the wire bonding technology of the MEMS. The vibrations of transducer were tested. Based on the phase reconstruction theory, identification of the nonlinear characteristics was developed. In comparison with the time series along the axial direction, pitching direction and the horizontal direction, the correlated dimensions have been calculated, clearly describing the nonlinear dynamic characteristics of the transducer. It is helpful for understanding of transducer and can be used as a guide for modeling of this complicated structure.
2007, 56 (7): 3827-3832.
doi: 10.7498/aps.56.3827
Abstract +
We study the trajectories and escaping problem in the Hénon-Heiles system using a new fourth order symplectic algorithm and the Runge-Kutta-Fehlberg algorithm. Starting from the same initial point，we found the distance between the two numerical trajectories calculated by the two algorithms increases exponentially in time in the chaotic region. We show this result can be used to measure chaos. We also calculate the escape rate as a function of energy above threshold in the Hénon-Heiles system. The results calculated with two different algorithms agree very well.
2007, 56 (7): 3833-3838.
doi: 10.7498/aps.56.3833
Abstract +
Hydrophobic AR SiO2 coating was deposited on the K9 substrate with sol-gel dipping technique，and laser-conditioning was done in “R on 1" mode with Nd:YAG laser (1064nm，7.5ns). Laser-induced damage thresholds (LIDT) were measured by “1 on 1" mode，and fore-and-aft changes of the surface morphology and fractal structure of the coating caused by laser conditioning were investigated with atomic force microscope (AFM) and multi-fractal spectrum (MFS), respectively. The results showed that after laser-conditioning the LIDT of the coating increased obviously，the mean-square roughness decreaseds lightly and the surface of the coating became more smooth，and that width of MFS shrinked and the uniformity of distribution of fractal framework was improved. It means that the micro-structure of the surface of the coating become, so regular that the coating could resist more powerful laser irradiation. Further more，MFS is an effective method to research mechanism of high power laser irradiation on optical coating because we can acquire more information about the change of the surface structure of the coating.
2007, 56 (7): 3839-3844.
doi: 10.7498/aps.56.3839
Abstract +
We calculate the single-particle resonances in a one-dimensional model potential and isotropic three-dimensional harmonic and Woods-Saxon potentials using the real stabilization method in coordinate space. The results of the real stabilization method are in good agreement with those from the scattering phase shift method and the analytical continuation in the coupling constant method.
2007, 56 (7): 3845-3850.
doi: 10.7498/aps.56.3845
Abstract +
In this paper，different methods are used to simulate the dipole characteristic of terahertz (THz) wave emitted from low-temperature grown GaAs (LT-GaAs) and Semi-insulting GaAs (SI-GaAs) photoconductive semiconductor switches. The results indicate that the main cause of the dipole characteristic of THz wave emitted from LT-GaAs is the lifetime of optical-generated carriers being shorted than the generation time. For SI-GaAs photoconductive semiconductor switches with lifetime of optical-generated carriers longer than 100ps，the dipole characteristic of THz waveforms is mainly caused by intra-valley scattering and space charge field screening under different experimental conditions (different bias field and different optical pulse energy).
2007, 56 (7): 3851-3860.
doi: 10.7498/aps.56.3851
Abstract +
The precipitated grains in molten metal are to migrate due to the magnetization force. A model describing the migration of a single grain in motlen metal has been proposed in terms of the classical dynamics of rigid body, in which the grain is regarded as a sphere. The theoretical expressions about effective viscosity of the conducting melt, the velocity and distance of migrating grains were derived. The effective viscosity increases linearly with the increment of B2 (the square of the magnetic flux density). The migrating velocity is accelerated to the final value in several ms. The final speed decreases sharply with the increment of the magnetic flux density, which demonstrates that the migration of the grain is suppressed by the high magnetic field. The migration distance is closely relative with the distribution of the magnetic flux density. In order to examine the situation of the primary Si, the sample of Al-18wt%Si alloy was held at 650℃ for an hour and then a high gradient magnetic field (Bz=5T，BzdBz/dz=-224T2/m) was imposed for a certain time before quenching the sample from the melt. The experimental results indicated that the grains withradii larger than or equal to 40μm were mostly migrated in 120s，in good agreement with the theoretical calculation.
2007, 56 (7): 3861-3866.
doi: 10.7498/aps.56.3861
Abstract +
The new assumption that a photon cannot be split is made in the Monte Carlo simulation for optical scattering response function is made，which eliminates the uncertainly in arbitrarily choosing the threshold of photon death. A hyperbolic method is proposed to simulate the Gaussian beam used in optical coherence tomography systems where curved sample interfaces are encountered. Comparison between the calculated OCT pictures of a microscope slide (flat interface) and a cornea (curved interface) with the corresponding experimental ones indicates the effectiveness and the relative advantage of our new simulation method.
2007, 56 (7): 3867-3872.
doi: 10.7498/aps.56.3867
Abstract +
Tunable diode laser absorption spectroscopy (TDLAS) with wavelength modulation is used to measure the NH3 concentration at normal temperature and pressure near 1531.7nm in near-infrared region. The concentration of 25ppm can be obtained by 10m long-path cell，and concentration from 25ppm to 400ppm has good linear relationship with 2f signal. The effect of particles on 2f signal is discussed in this paper，and a solution of the problem using laser intensity linear fit to make the concentration measurement immune to particle disturbance is suggested.
NUCLEAR PHYSICS
2007, 56 (7): 3873-3879.
doi: 10.7498/aps.56.3873
Abstract +
The proton and neutron 1S0 pairing gaps and their isospin dependence in isospin asymmetric nuclear matter have been studied by the isospin dependent Brueckner-Hartree-Fock approach and the BCS theory. We have focused on investigating and discussing the effect of three-body force. The calculated results indicate that as the isospin asymmetry increases，the density range of the 1S0 neutron superfluidity is narrowed slightly and the maximum value of the neutron pairing gap increases，while the density domain for the proton superfluidity enlarges rapidly and the peak value of the proton gap decreases remarkably. The three-body force turns out to affect only weakly the neutron 1S0 superfluidity and its isospin dependence，i.e.，it leads to a small reduction of the neutron 1S0 paring gap. However, the three-body force not only reduces largely the strength of the proton 1S0 gaps at high densities in highly asymmetric nuclear matter but also suppresses strongly the density domain for the proton 1S0 superfluidity phase.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (7): 3880-3886.
doi: 10.7498/aps.56.3880
Abstract +
A full relativistic multi-configuration Dirac-Fock theory with quantum electrodynamical (QED) effect and Breit corrections is used to calculate the magnetic quadrupole M2 2s21S0—2s2p3P2(Z=10—103) transition energy level, transition probabilities and oscillator strengths for Be-like ions for the first time. The results with Breit and QED corrections included are in good agreements with current experimental data and other theoretical values. The results show that the magnetic quadrupole transition probabilities of highly ionized atoms are comparable with those of neutral atomic allowed transitions and cannot be ignored in the laser plasma of high temperatures in ICF and MCF fusions. The effect of the magnetic quadrupole transition of highly ionsized atoms should be considered in the calculation of dielectronic recombination process, opacity, free path and so on.
2007, 56 (7): 3887-3892.
doi: 10.7498/aps.56.3887
Abstract +
Based on the conclusion that the contribution of correlated decay of two vacancies in atoms is small，the de-excitation process of Mg1+(1s-1) hollow magnesium ions with single K-vacancy and Mg2+(1s-2) double K-vacancy were treated by applying the radiative-single Auger - double Auger cascade model（RACDA）. The final-charge-state distribution(FCSD) of these hollow ions were calculated，and compared with that obtained with the radiative-single Auger cascade model（RAC）. The probability of tetravalent ion production via the de-excitation of Mg1+(1s-1) obtained by RACDA model is considerable，but tetravalent ion is not produced in the by RAC model. The probability of hexavalent ion production via the de-excitation of Mg2+(1s-2) obtained by RACDA model is very large，but hexavalent ion is not produced in the RAC model.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (7): 3893-3899.
doi: 10.7498/aps.56.3893
Abstract +
The diamond stylus extrudes the metal film and causes coupled elastic-plastic deformation which shapes the profile of the ruled grating. The grating profile function which is hard to get would influenced accurate analysis of the diffraction characteristic. An analytical method of the diffraction characteristic of the mechanically ruled grating is presented based on the profile fitting function. The problem of excessive departure between the measured and theoretical value of the diffraction efficiency of high density ruled grating is solved by this method. We take a 1200l/mm UV grating，the grating profile is scanned in the principal section and then the profile curve function is got. The reason why the diffraction efficiency wasn't high is found by calculation. And then the diffraction efficiency increased about 20% by improving the technology.
2007, 56 (7): 3900-3905.
doi: 10.7498/aps.56.3900
Abstract +
Conformal dome may enhance the velocity and effective range of the missile systems by providing better aerodynamical surfaces than traditional domes. However，the highly aspheric surface may introduce serious aberration which changes with the field of regard，and the fixed corrector can be used to correct these higher aberrations in the big field. This paper analysis the performance of the conformal dome and proposes a way for the optical corrector design by adding diffractive element into the fixed corrector. The simulation proves it's an effective way to improve the imaging quality of the conformal dome.
2007, 56 (7): 3906-3910.
doi: 10.7498/aps.56.3906
Abstract +
Based on the diffusive equation of incoherent-feedback random lasers，whose gain is modified by adding a saturation factor，the evolution of the emitted light intensity in two-photon pumping random lasers varying with time is studied by use of finite difference method. Numerical results show how the intensity of emitted light varies from the spontaneous radiation，which undergoes amplification at small-signal gain，to the steady output due to the saturation effect. It is noted that the nonlinear effect，e.g. saturation of gain，in such laser system can be achieved under low intensity conditions due to the disorder of media. Our results give a theoretical support to obtaining the steady output of the two-photon pumping random lasers.
2007, 56 (7): 3911-3916.
doi: 10.7498/aps.56.3911
Abstract +
Photoacoustics as a potential and noninvasive medical imaging technology，it combines the advantages of ultrasound imaging and optical imaging to provide high ultrasonic resolution and high optical contrast tissue images. A reconstruction algorithm named the modified simultaneous iterative reconstruction technique (MSIRT) using in limited-view data in photoacoustic imaging was studied. The simulation and experiments result demonstrated that MSIRT has good performance in photoacoustic imaging for limited-view data at angles 90°，135° and 180°. It works much better than traditional algebraic reconstruction algorithm in rectification of the measurement and the speed of convergence. A circular scan with a single-element transducer system was used to obtain photoacoustic signals through 180° in the experiment. This technique provides a high contrast and high resolution (about 60μm) photoacoustic imaging of blood vessels of a chicken embryo based on MSIRT. It greatly reduced the data acquisition time. This method could be potentially used to realtime monitoring of cerebral blood flow and the vascular damage during photodynamic therapy.
2007, 56 (7): 3917-3923.
doi: 10.7498/aps.56.3917
Abstract +
By means of numerical analysis，the distribution of pump light and the output laser power along the fiber with different fiber length has been investigated. The experimental research of the Nd3+-doped polarization-maintaining fiber laser is reported，which is pumped by 808nm semiconductor laser. The influence of different fiber winding radius on output power and polarization characteristic of the laser are studied. Double wavelength peaks at 1060nm and 1092nm are obtained. The maximum output power of the laser is 7.35W at 1060nm，the slope efficiency is 58.3%.
2007, 56 (7): 3924-3930.
doi: 10.7498/aps.56.3924
Abstract +
This paper analyzes the security of double random phase encoding in fresnel domain from the viewpoint of cryptoanalysis. We demonstrate the encryption system is vulnerable to chosen-plaintext attack with a prior knowledge of diffraction distance and wavelength. With this attack an opponent can access double random phase keys with the help of the impulse functions as chosen plaintext. The significant feature of proposed attack is that the decryption process is lossless. Numerical simulations show good agreement with theoretical analysis.
2007, 56 (7): 3931-3936.
doi: 10.7498/aps.56.3931
Abstract +
We present an improved differential phase shift quantum key distribution schemewhich features auto-compensation，high efficiency，and excellent practicality. Alice modulates continuous laser using an intensity modulator based on polarization to generate coherent pulse train. Bob employs a Fraday-Michelson interferometer instead of a traditional M-Z interferometer，which automatically compensates for the polarization mode dispersion caused by the changes of environment and improves the stability of the interference visibility. The present scheme not only has a simpler configuration，but also offers a higher key creation efficiency than traditional schemes. Furthermore，it enhances the security of the system. With the proposed experimental setup，a stable quantum key distribution was performed over 80km fiber with a quantum bit-error rate of less than 4%.
2007, 56 (7): 3937-3944.
doi: 10.7498/aps.56.3937
Abstract +
From negative quantum conditional entropy point of view this paper intestigates the entanglement measure of the prue state and a kind of mixed state of bipartite quantum system. Also this paper gives a definition of quantum conditional entropy of entanglement EA｜B(ρAB) and proves that it satisfies the four fundamental conditions of a entanglement measure for a kind of mixed state of 2×2 quantum system by this negative quantum conditional entropy Using conditional entropy of entanglement, this paper investigates the quantum entanglement between the two identical two-level atoms simultaneously interacting with vacuum cavity field as an application. This paper compares conditional entropy of entanglement and concurrence at the same condition, and the result shows that the curves of their evolvements are identical. These obtained results test and verifys that conditions of an entanglement measure may be taken as the entanglement measure of the prue state and a kind of mixed state of bipartite quantum system.
2007, 56 (7): 3945-3949.
doi: 10.7498/aps.56.3945
Abstract +
A novel high-power semiconductor laser diode (LD) with very large cavity using multi-active -layer cascaded by tunnel-junction was developed. The window size of the LD was enlarged extremely and less than 20 degree of the lasing beam divergency was obtained，which benefits the coupling between the LD and the optical fiber. Many types of lensed fibers were used to test with the LD and the coupling efficiencies were increased over 30% compared with the conventional LD.
2007, 56 (7): 3950-3954.
doi: 10.7498/aps.56.3950
Abstract +
A new LD end pumped Nd：LuVO4 microchip laser was reported for the first time. Study of laser properties was carried out on the effects of different Nd3+ doped concentration，different cavity length and different 1064nm transmission. The relationship between the maximum output power and LD performance temperature was measured at different pump power. 923mW of continuous output at 1064nm with TEM00 mode was obtained at 2W pump power，the pump threshold being 48mW. The slope efficiency was 52%，and increased to 59% when the microchip was cooled.
2007, 56 (7): 3955-3960.
doi: 10.7498/aps.56.3955
Abstract +
We present a method to obtain a laser pulse train at high repetition rate for the Ti：sapphire laser system based on the chirped pulse amplification technique. The conventional working mode of the Pockels cell in the Ti：regenerative amplifier is modified. At a certain dumping time, a portion of the amplified seed pulse is dumped out of the cavity by a certain dumping ration every time the pulse runs around the cavity. Thenceforward, the chirped pulses at high repetition rate are generated. Based on the Franz-Nodvik amplification theory，a theoretical model of the regenerative amplifier is established and the analysis of the dependence of the pulse sequence on the dumping time and dumping ratio is given by numerical computation. With a pumping energy of 35mJ and a dumping ratio of 1/2, a fourteen-pulse sequence at 100MHz with pulse energy of 0.02mJ is obtained at a finite period of time in a pumping cycle.
2007, 56 (7): 3961-3965.
doi: 10.7498/aps.56.3961
Abstract +
The effect of La2O3 doping on the spectroscopic properties of transparent Yb：Y2O3 ceramics was studied. After doping La2O3，the shapes and positions of the absorption and emission peaks of transparent (Yb0.05Y0.95-xLax)2O3 ceramics were almost the same as those of Yb：Y2O3. When La2O3 was added into Yb：Y2O3，the lattice constant of (Yb0.05Y0.95-xLax)2O3 became large and the crystal field strength weaker due to introducing of larger radius of La3+ ion, simultaneously its degree of order is decreased, which results in the decrease of the emission intensities and the emission cross-sections. The emission intensities were reduced greatly for the excessive doping of La2O3 (16at%) in (Yb0.05Y0.95-xLax)2O3 ceramics. On the whole the fluorescent lifetimes of the samples are increased by 45%—60% after doping La2O3.
2007, 56 (7): 3966-3971.
doi: 10.7498/aps.56.3966
Abstract +
Using interference method fabricate photonic lattices in self-defocus photorefractive crystal LNbO3:Fe. We had find the phenomenons that dual-beam interference fringe one divides into two,four-beam interference fringe one divides into four. We had proved it is a kind of phenomena of spacial frequency-doubling, this kind of phenomenon is the result of the interaction between the interfere field and the interfere field fabricative photonic lattices. This experiment had showed that spacial second-harmonic generation and high-order harmonics generation can be easy achieved by photorefractive effect crystal,that second-harmonic can fabricate spacial frequency-doubling photonic lattices, that high-order harmonics can fabricate spacial frequency-high photonic lattices.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2007, 56 (7): 3972-3976.
doi: 10.7498/aps.56.3972
Abstract +
At present, the methods using parallel plates and probes for detecting the plasma in the strong field have some limitations in measuring the charged particles produced by gas with high flow rate at atmospheric pressure. In this paper, a new detector with a spherical probe was proposed and was used to measure the charged particle concentration under the conditions of various gas velocities, electric field intensities and distances, as well as to study the spatial distribution of plasma. The result of the new method when was compared with that of DLY air ion detector indicates that the concentration detected by the former is near to the real value. Moreover, the detector with a spherical probe has advantages of as simple operation, small volume and convenience of local test, which contribute to the research of spatial distribution of plasma.
2007, 56 (7): 3977-3983.
doi: 10.7498/aps.56.3977
Abstract +
In this paper, the properties of soliton structures in a hot, unmagnetized dusty plasma which consists of a negatively charged hot dust fluid with variable dust charge, non-thermal distribution of ions and Boltzmann distribution of electrons have been studied. A modified KdV (mKdV) equation which describes the dust acoustic waves in this system is derived by the reductive perturbation method. The effects of dusty plasma parameters on the dust-acoustic solitary waves is studied theoretically. It is found that the soliton structures is determined by the dusty plasma parameters. Furthermore, the soliton only exists in certain regions where these parameters are specially chosen.
2007, 56 (7): 3984-3989.
doi: 10.7498/aps.56.3984
Abstract +
A soft X-ray laser Mach-Zehnder interferometer was used to diagnose electron density Ne of spot-focused CH plasma on Shengguang II facility, and the experimental results were presented in this paper. Density reconstruction was performed by making Abel transform, 2D distribution of Ne was obtained, and the highest Ne was about 3.2×1021cm-3. Comparing with simulation results of JB19 code (1.5D) and XRL2D code (2D), it was found that the theoretical result with flux-limited factor of 0.05 agreed with reconstructed result in high density area, but experimental result gave an Ne distribution declining faster. Furthermore, 2D Ne distribution of simulation differed much from that of experiment in details. A brief error analysis showed that flatness error of interferometer dominated the experimental error.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2007, 56 (7): 3990-3995.
doi: 10.7498/aps.56.3990
Abstract +
A novel back-gate reduced bulk field concept which makes a breakthrough in improving the vertical breakdown voltage of high voltage SOI transistors is proposed. The mechanism of the improved breakdown characteristics is that the electric field distributions of the active region are modulated by the interface charges induced by the back-gate voltage. The bulk electric field at the drain side is reduced, the bulk electric field at the source side is increased, and the breakdown voltage of the high voltage SOI device is improved. The impact of the back-gate bias on thick film SOI LDMOS (over 600 V) is discussed via two-dimensional simulations. When the back-gate bias is 330V, the breakdown voltage of the three-zone SOI double RESURF LDMOS is 1020V, which is 47.83% greater than that of a conventional LDMOS. The novel concept presents a new method for realizing over 600 V high voltage power device and high voltage integrated circuit.
2007, 56 (7): 3996-4003.
doi: 10.7498/aps.56.3996
Abstract +
The rapid solidification and microstructure formation of Cu-Pb monotectic alloy were investigated by melt spinning method. The relationship between liquid separation and physical parameters such as cooling rate and solidification time etc. was analyzed theoretically by coupling the heat transfer equation and Navier-Stokes equation. It is revealed that the rapid cooling of the melt has more remarkable effect on microstructure forming of the monotectic alloys than liquid flow under rapid solidification. The rapid solidification can suppress the liquid separation, which results in the formation of uniform microstructure for various Cu-Pb monotectic alloys. With the rise of cooling rate, the grain size clearly decreases, the microstructure was markedly refined and the microstructural morphology changes from coarse dendrite to uniform and fine equiaxial crystallites. Increasing the cooling rate and shortening solidification time are the essential conditions to suppress liquid phase separation and obtain the uniform monotectic microstructure in gravity field.
2007, 56 (7): 4004-4008.
doi: 10.7498/aps.56.4004
Abstract +
The glass transition and crystallization behavior of Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk amorphous alloy are investigated by X-ray diffraction and differential scanning calorimetry under high temperature and high pressure. The results show that the free volume and enthalpy and crystallization activation energy decrease with increasing pressure.
2007, 56 (7): 4009-4016.
doi: 10.7498/aps.56.4009
Abstract +
The mesostructure in Fe-based (Fe73.5Cu1Nb3Si13.5B9) nanocrystalline ribbons annealed under different stress (FNRAS) was investigated by observation of the cross section images of the ribbons with atomic force microscopy (AFM) and X-ray diffraction. The longitudinally driven giant magneto-impedance and transversal magnetic anisotropy field (Hk) were measured. The mechanism of the transversal magnetic anisotropy field can be explained by the mesostructure of the directional preference of crystalline grain (coated with amorphous shell) gathering, along the transverse direction, induced in the course of annealing of the Fe-based alloy ribbons under stress.
2007, 56 (7): 4017-4023.
doi: 10.7498/aps.56.4017
Abstract +
Structural stability for selenium and tellurium nanowires is studied by combining first-principles method and empirical approach. This is an interesting topic due to the fact that the Se and Te crystals are composed of triangular Se and Te chains and that the chain-chain interaction is relatively weak. Nanowires of small diameters (<30?) are studied by first-principles calculations. Meanwhile, an empirical method that considers only the interaction between chains is also proposed in order to study the nanowires of larger diameters. The nanowires with hexagonal cross section are more stable, though the hexagon is not always perfect in shape due to the limitation of chain number. This result agrees with the widely accepted stable structures of selenium and tellurium nanowires.
2007, 56 (7): 4024-4031.
doi: 10.7498/aps.56.4024
Abstract +
On the basis of measurements and theoretical analysis, linear and nonlinear optical properties on the Ag:Bi2O3 composite films with different Ag concentrations were investigated. The relationship between the Ag concentrations and the surface plasmon resonance (SPR) of Ag:Bi2O3 composite films were characterized by UV-VIS-NIR spectroscopy, and the dependence of third-order nonlinear susceptibility of composite films on Ag concentrations was investigated by picosecond Z-scan technique with different excitation wavelength (532nm and 1064nm). The analysis of optical properties of these films was carried out using the theories of surface plasmon resonance and localized field enhancement respectively. From the experimental and theoretical results, the dependence of third-order nonlinear susceptibilities χ(3) on Ag concentration was shown. With Ag concentration around 35％ and the excitation wavelength at 532nm near the surface plasmon resonance (560nm—622nm), the third-order nonlinear susceptibility χ(3) showed a maximum value of 2.4×10-9 esu.
2007, 56 (7): 4032-4038.
doi: 10.7498/aps.56.4032
Abstract +
In this paper, porous silicon (PS) was prepared by electrochemical etching method, its two-dimensional microstructure was observed by field emission scanning electron microscope (FESEM) and the three-dimensional topological image of PS was captured by Nano-Profilometry (NP), thus the reason for the difference of PS microstructures was discussed and the effect of microstructure on its mechanical property was investigated. Using MTS Nano Indenter XP, the relationship between hardness and Youngs modulus and the indentation displacement was studied and the mechanical property of PS with various porosities was compared. The experimental result showed that the porosity of PS prepared under various etching current densities (40,60,80 and 100mA/cm2) ranges from 60%—80%, which is increasing with the rising etching current density. The thickness of PS prepared under 20% HF is approximately 40—50μm; the average value of hardness and Youngs modulus of PS ranges from 0.478GPa—1.171GPa and 10.912GPa—17.15GPa， respectively； and the values decrease with the etching current density rising, and decrease or keep constant with the displacement increasing in the range of nano_hardness and micro_hardness, respectively. The impact on PS mechanical property of its surface condition, thickness, microstructure and environment was analyzed and the relationship between PS mechanical property and microstructure was obtained.
2007, 56 (7): 4039-4043.
doi: 10.7498/aps.56.4039
Abstract +
The thermodynamic equilibrium relationship of the hydrogen storage of LaNi5 is analyzed. An equilibrium formula describing the P-C-T relationship for covering all the available experimental data is derived. The experimental P-C-T relationship is analyzed using the equilibrium formula. The thermodynamic functions for the equilibrium of the hydrogen storage are calculated and discussed.
2007, 56 (7): 4044-4048.
doi: 10.7498/aps.56.4044
Abstract +
Nonpolar a-plane (1120) ZnO films were successfully grown on (302) γ-LiAlO2 substrate by pulsed laser deposition. When the temperature of the substrate was 350℃, the film was mix-oriented(a and c) with a wide distribution of crystal grain size, and the c-plane ZnO was dominant. When the temperature of the substrate was 500℃, pure (1120) ZnO film was formed，with the FWHM of ZnO (1120) rocking curve ～0.65° and the grain size distribution narrowed. Its in-plane anisotropy was demonstrated by polarized transmission spectrum. The FWHM of the peak of near band emission in the PL spectra was found to be only 105meV for the sample with substrate temperature of 650℃，indicating the large size and uniform distribution of crystal grains which was also confirmed by AFM.
2007, 56 (7): 4049-4055.
doi: 10.7498/aps.56.4049
Abstract +
The macro-texture, grain boundary distribution and surface morphology in CVD free standing diamond films deposited with different methane concentrations were observed by X ray diffraction, electron backscatter diffraction and SEM. The atom stacking process of twins on {111} planes of diamond crystal were studied. It is shown that the twins form easily on {111} planes because of the 〈111〉 60° orientation relationship of first order twin and the stacking structure of {111} planes. At low methane concentration, carbon atoms tend to deposit on {111} planes with lower surface energy, which facilitates the formation of twins by means of rotating deposition of carbon atoms, while the high twinning frequency weakens the texture. With increasing methane concentration the {001} planes with lower growing activation energy become the main frontal growth fronts, and only those grains with 〈001〉 crystal direction which is parallel to the surface normal can continuously grow, so that the probability of twin nucleation decreases. In addition, second_order twins were found in diamond film, and their formation mechanism was analyzed.
2007, 56 (7): 4056-4061.
doi: 10.7498/aps.56.4056
Abstract +
Residual stresses of galvanized passive film were measured by X-ray diffraction (XRD), at the same time, the residual stress distribution of galvanized passive film in the thickness direction was measured with electro-analysis polishing method, and the effect of residual stress on bonding strength of the film were analyzed. The experimental results show that residual stress of galvanized passive film is always compressive, which decreases as the residual stresses on the substrate surface increases. Residual stress of galvanized passive film in the thickness direction of 2—10μm is -274.5—-428.3MPa, and the residual stress distribution of galvanized passive film in the thickness direction has a gradient. Interfacial bonding strength of galvanized passive film/substrate is inversely proportional to the residual stress, and the decrease of the film stress improves the bonding strength.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2007, 56 (7): 4062-4067.
doi: 10.7498/aps.56.4062
Abstract +
The geometrical structure of Mg,Zn,Cd doped 32-atom supercell of InN was optimized using the ultra-soft pseudopotential method of total-energy plane wave based upon the density functional theory (DFT). Cell parameters of both doped and undoped cells were calculated theoretically. The binding energy, partial density of states, Mulliken charges, electron density differences of doped InN crystals were calculated and discussed in detail. The results revealed that compared with Zn and Cd, Mg substituting for In has the greatest solubility and yield more states of holes.So Mg is suitable for p-type doping of InN.
2007, 56 (7): 4068-4074.
doi: 10.7498/aps.56.4068
Abstract +
Using the discrete-dipole approximation (DNA) method, after calculating optical characteristics of the single soot aggregation particle, we obtained the relationships of scattering cross section, absorption cross section and asymmetry parameter of soot aggregation particle with the changing incident angles, which provide an efficient approach for the research of radiative transportation of wave in soot particles. We propose the angular distribution of scattering matrix elements of soot particles at different incident angles, which provides a theoretical approach for the research of scattering characteristics, polarization characteristics, and the structural characteristics of the scatterer.
2007, 56 (7): 4075-4078.
doi: 10.7498/aps.56.4075
Abstract +
The interface binding energy has been defined according to the atomic binding energy. The interface electronic structures of ZA27/CNT have been calculated by recursive method in zinc-aluminum composite reinforced by carbon nanotube. The microphysics of carbon nanotube distribution at grain boundaries of ZA27 alloy and the cause of weak interface binding in ZA27/CNT at electronic level were made clear. The research showed that the metal matrix has great effect on the density of states of carbon atoms on the nanotube, but the nanotube has little effect on the density of states of aluminum or zinc atoms in the matrix. The density of states of carbon on nanotube tends to become assimilated with matrix atoms and combine with the matrix, but as the assimilation degree is low, the interface binding strength is very weak. It is believed that similar property of atoms with matrix decorating or plated on carbon nanotube may help to reinforce the interface binding strength and improve the performance of ZA27 composite.
2007, 56 (7): 4079-4084.
doi: 10.7498/aps.56.4079
Abstract +
We have calculated the electronic structure of zinc blende structure ZnS under different high pressures by means of plane wave pseudo-potential method(PWP) with generalized gradient approximation (GGA) in this paper. We have found that the lattice constants and bond length decrease with pressure increasing. The charge transfer from S atoms to Zn atoms becomes less, and the covalence nature of Zn-S bond becomes stronger. Secondly, the peak of density of states of Zn atoms and S atoms change to some degree. Furthermore, it has a shifting tendency towards lower energy. On the other hand, ZnS turns from direct band gap to indirect band gap semiconductor when ambient pressure reaches 24GPa. The indirect band gap narrows and the direct band gap widens with pressure increasing.
2007, 56 (7): 4085-4088.
doi: 10.7498/aps.56.4085
Abstract +
Pentacene crystallizes in a layered structure with a herringbone arrangement within the layers. There exist several polymorphs of pentacene. Identification of these pentacene polymorphs is especially important as the electronic properties depend strongly on the stacking of the molecules within the layers. In this paper the intermolecular potential energy of the pentacene crystal is represented by Born-Mayer-Haggins pair potential model. We have performed electronic band structure calculation based on the tight-binding model for the two polymorphic crystal structures of pentacene. The calculated bandwidth reduction in going from 0K to room temperature is of the order of 8%—14%.
2007, 56 (7): 4089-4093.
doi: 10.7498/aps.56.4089
Abstract +
The electronic structure of CaWO4 crystal containing F-type color centers are studied within the framework of the fully relativistic self-consistent Direc-Slater theory, using a numerically discrete variational (DV-Xα) method. We come to a conclusion that F and F+ color centers exhibit donor energy level located in the forbidden band. The optical transition energies are 1.92eV and 2.42eV, respectively, which correspond to the 650nm and 515nm absorption bands. It is predicted that the 650nm and 515nm absorption bands originate from the F and F+ centers in CaWO4 crystals.
2007, 56 (7): 4094-4098.
doi: 10.7498/aps.56.4094
Abstract +
Molecular dynamics simulations based on a coarse-grained, bead-spring model are adopted to investigate the stability of both nonfunctional and functional perfluoropolyether (PFPE) on solid substrates. For nonfunctional PFPE, the surface morphology changes little with time. The film is stable. For functional PFPE, part of lubricant molecules show local dewetting which causes the increase of surface roughness with time. The film is unstable. Besides, the changes in surface morphology with different endbeads are compared, which indicate that the endbead-endbead interaction is the principal reason for the film instability and the endbead-substrate interaction has little effect on the film stability.
2007, 56 (7): 4099-4104.
doi: 10.7498/aps.56.4099
Abstract +
Magneto-transport measurements have been carried out on three heavily Si δ-doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As single quantum well samples in which two subbands were occupied by electrons. The weak anti-localization (WAL) has been found in such high electron mobility systems. The strong Rashba spin-orbit (SO) coupling is due to the high structure inversion asymmetry (SIA) of the quantum wells. Since the WAL theory model is so complicated in fitting our experimental results, we obtained the Rashba SO coupling constant α and the zero-field spin splitting Δ0 by an approximate approach. The results are consistent with that obtained by the Shubnikov-de Haas (SdH) oscillation analysis. The WAL effect in high electron mobility system suggests that finding a useful approach for deducing α and Δ0 is important in designing future spintronics devices that utilize the Rashba SO coupling.
2007, 56 (7): 4105-4112.
doi: 10.7498/aps.56.4105
Abstract +
We present a review on the noise in mesoscopic physics. The main sources of noise are briefed. The fluctuations in the occupation number give rise to thermal noise, while shot noise is a consequence of the quantization of charge. We introduce the main theory of noise——scattering theory, which has been applied to saddle-shaped semiconductor quantum wires and ferromagnetic/insulator/semiconductor double heterojunctions. The physical significance of the study of noise are pointed out.
Grown-in oxygen precipitates in czochralski silicon investigated by transmission electron microscopy
2007, 56 (7): 4113-4116.
doi: 10.7498/aps.56.4113
Abstract +
The grown-in oxygen precipitates in conventional Czochralski (CZ) silicon and nitrogen-doped Czochralski (NCZ) silicon have been investigated by means of transmission electron microscopy (TEM). Tiny oxygen precipitates about 5nm in size were observed in the NCZ specimens. It is believed that the oxygen precipitates may have grown from the heterogeneous nuclei of nitrogen-related complexes formed at a low temperature of 650℃.
2007, 56 (7): 4117-4121.
doi: 10.7498/aps.56.4117
Abstract +
Density gradient quantum model has been used to analyse the breakdown characteristic of InP-based composite channel HEMT(high electron mobility transistor). The collision ionization in composite channel and quantum effect has been taken into consideration. We payed great attention to the relationship of on-state breakdown voltage with respect to the thickness of In0.7Ga0.3As channel, and promoted a method to enhance the on-state breakdown voltage. A commercial 2D-device simulation program. Sentaurus has been used to simulate the on-state breakdown voltage of the device. A comparison has been made between the result of simulated and measured data. The result shows that with the reduction of the thickness of In0.7Ga0.3As channel, on-state breakdown voltage of the device will be enhanced greatly without reducing saturation current, which has a significant meaning for promoting the power performance of InP-based HEMT.
2007, 56 (7): 4122-4126.
doi: 10.7498/aps.56.4122
Abstract +
Undoped hydrogenated silicon films have been prepared from a gas mixture of silane and hydrogen, at deposition temperature varying from 200—450℃ in an ultrahigh vacuum system using RFPECVD technique. Raman scattering, SEM and UV spectrophotometer are used to analyse the structure changes of microcrystalline silicon films throughout the deposition temperature range. Results show that at lower deposition temperature, the crystalline volume fraction of μc-Si:H films increased with the increasing of deposition temperature. Exceeding a certain temperature, the crystalline volume fraction decreased with further increasing of deposition temperature. This is attributed to a change in the dominant film growth process from surface-diffusion-limited at low deposition temperatures to flux-limited at higher deposition temperatures.
2007, 56 (7): 4127-4131.
doi: 10.7498/aps.56.4127
Abstract +
The thickness and refractive index of Zn1-xMgxO film grown on A-sapphire substrate by molecular beam epitaxy were measured by ellipsometry. Combined with Mg content measured by inductively coupled plasma (ICP), the curves showing the relationships of thickness with film growth condition and the refractive index with the Mg content in the film were deduced by numerical analysis, which may serve as a theoretical basis for controlling the thickness and the refractive index in Zn1-xMgxO film growth process.
2007, 56 (7): 4132-4136.
doi: 10.7498/aps.56.4132
Abstract +
La1-xSrxMnO3(LSMO)/TiO2 pn heterojunctions have been successfully synthesized by RF magnetron sputtering and they exhibit good rectifying properties. The diffusion potentials increase with increasing Sr concentration, which may be attributed to the increased carrier concentration. And the diffusion potential increases with decreasing measurement temperature, which may have resulted from modification of the interface electronic structure of La1-xSrxMnO3/TiO2 pn heterojunction with changing temperatures. It is worth noting that the metal-insulator (M-I) transition of LSMO can also be observed in pn heterojunctions and the increased sheet-resistance of pn heterojunctions at low temperature is related to the introduction of TiO2.
2007, 56 (7): 4137-4142.
doi: 10.7498/aps.56.4137
Abstract +
This paper introduces in detail the working principle of Si/SiGe Quantum cascade laser(QCL). Appropriate parameters are used to calculate the hole subband structure of Si/Si1-xGex quantum well using a six-band k·p method.The dispersion relation and energy band for different layer thickness and compositions are investigated. Meanwhile,the energy separations between hole subbands in Si/Si1-xGex/Si quantum wells are also analyzed. Finally the calculated results are used for the Si/SiGe QCL design，which will be beneficial to the structure optimization of Si/SiGe QCL.
2007, 56 (7): 4143-4147.
doi: 10.7498/aps.56.4143
Abstract +
Magneto-transport measurements have been carried out on a Si δ-doped In0.65Ga0.35As/In0.52Al0.48As metamorphic high-electron-mobility transistor with InP substrate in a temperature range between 1.5 and 60K under magnetic field up to 13T. We studied the Shubnikov-de Haas(SdH) effect and the Hall effect for the In0.65Ga0.35As/In0.52Al0.48As single quantum well occupied by two subbands and obtained the electron concentration and energy levels respectively. We solve the Schrdinger-Kohn-Sham equation in conjunction with the Poisson equation self-consistently and obtain the configuration of conduction band, the distribution of carriers concentration, the energy level of every subband and the Fermi energy. The calculational results are well consistent with the results of experiments. Both experimental and calculational results indicate that almost all of the δ-doped electrons transfer into the quantum well in the temperature range between 1.5 and 60K.
2007, 56 (7): 4148-4151.
doi: 10.7498/aps.56.4148
Abstract +
Based on the Kosterlitz-Thouless (KT) phase transition model of two-dimensional systems, by introducing the thermal activation energy and the mean height of the pinning landscape into the correlation length, a modified KT transition model has been proposed to study the temperature dependence of the resistivity transition in anisotropic superconductors. This modified KT transition model is consistent with the Coulomb-Gas (CG) scaling law and the Halperin-Nelson relation. And it is applied to study the scaling behavior of the resistivity transition of Tl2Ba2CaCu2Ox (Tl-2212) thin film under various intensities of magnetic field. The calculated mean height of the pinning landscape from the resistivity curve depends on the temperature linearly, which supports the proposed model.
2007, 56 (7): 4152-4157.
doi: 10.7498/aps.56.4152
Abstract +
The NiFeCoP/CuBe composite wire is produced by electroless-deposition. The composite wire shows distinct magnetoimpedance effect at low frequency. The maximal GMI ratio is 40% at 20kHz and about 97% at 180kHz. The frequency dependence of magnetization in NiFeCoP composite wire is analyzed in terms of equivalent circuits and complex permeability. The relaxation frequency of the composite wire is about 1MHz. The displacement of domain wall can be damped by the DC applied field. So the effect of the DC applied field is to eliminate the parallel RL circuit.
2007, 56 (7): 4158-4168.
doi: 10.7498/aps.56.4158
Abstract +
Based on the energy structure of quasi-three-level Yb-ion, the pumping and lasing rate equations are set up. The pumping dynamics of Yb-ion is investigated analytically and numerically, which includes the pumping excitation efficiency, the minimum pumping intensity, and the stored energy extraction efficiency. The laser performances of three typical Yb-doped laser materials are compared, i.e., Yb:S-FAP, Yb:YAG and Yb:FP-glass. Based on the criterion of amplified spontaneous emission (ASE), the design principles of pulsed energy-storage Yb lasers are investigated specifically, which includes the optimum thickness and doping concentration of the gain medium. Finally, based on our model, the baseline parameters are presented for a 100J-class diode-pumped solid-state laser based on either Yb:S-FAP or Yb:YAG. This paper would be helpful for designing the pulsed energy-storage Yb-based DPSS lasers.
2007, 56 (7): 4169-4174.
doi: 10.7498/aps.56.4169
Abstract +
Copper nitride (Cu3N) thin films were deposited on glass substrates by reactive radio frequency magnetron sputtering under different radio frequency power (P) and nitrogen partial pressure r(r=N2/［N2+Ar］). The thickness, crystalline structure and surface morphology of films were characterized by profilometer, X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The optical transmission spectrum was obtained by an ultraviolet-visible (UV-VIS) spectrophotometer and the optical band gap (Eg) was calculated. The results suggest that the films' deposition rate increases with P and r. The surface of the films reveals a compact structure, and the grain size of Cu3N is about 30nm. Meanwhile, with increasing r, the grain size and optical band gap of Cu3N increase, of which Eg ranges from 1.47 to 1.82eV, and the films' growth prefers the (111) direction at low r and the (100) direction at high r.
2007, 56 (7): 4175-4179.
doi: 10.7498/aps.56.4175
Abstract +
The characteristics of small signal gain are studied in a one-dimensional periodically arranged amplifying media. It is proved that the small signal gain characteristics shows special features with the increase of gain material length. The variation in gain is determined by the mutual competition between the photonic band gap formed by the refractive index of amplifying media and gain reaction under the resonant Bragg condition. Furthermore, we investigated the gain on the parameters of excitons and resonant atoms.
2007, 56 (7): 4180-4186.
doi: 10.7498/aps.56.4180
Abstract +
The multi-shock Hugoniot and shock temperatures of gaseous hydrogen-helium equimolar mixture with initial pressure and temperature of～30MPa and～90 K have been measured up to 140 GPa using two-stage light gas gun and shock reverberation technique. Two kinds of multi-channel pyrometer systems with different sensitivities, were used in experiment for diagnostics, because the thermal radiation of the sample in the first-shock state is lower than that in the multi-shocked states by a magnitude of one to two orders. The measured pressure, volume and temperature are respectively 5GPa, 12.0cm3/mol and 3030 K in the first-shock state, 27GPa, 6.7cm3/mol and 5070K in the second -shock state, and 105GPa, 4.0cm3/mol and 5090K in the fourth-shock state. The results for the first- and second-shock states are well described by the fluid perturbation theory and dissociation model. It demonstrates that the dissociation of molecular hydrogen of the compressed sample is negligible in the first-shock state, while about 7% and 32% of molecular hydrogen undergo dissociation in the second-and fourth-shock states, respectively. The fourth-shock temperature measured was lower than the prediction for～2000K.
2007, 56 (7): 4187-4193.
doi: 10.7498/aps.56.4187
Abstract +
Upconversion blue emissions of Tm3+ ions with different doping (0.5at.%, 3 at.%, 5 at.%) in NaY(WO4)2 crystals are investigated under 800nm diode laser excitation. The upconversion mechanism and the dependence of upconversion efficiency on ion concentration are analyzed with respect to the absorption spectra, fluorescence spectra, and parameters calculated by Judd-Ofelt theory. Four ion-ion interaction processes: 3H5+1G4→3H6+1D2, 3H5+3H5→3H6+3F3, 1G4+3H6→3F4+3F3,1G4+3H6→3F3+3F4, which influence the upconversion dominantly in Tm3+ heavy-doped system, are demonstrated theoretically and experimentally. The results indicate that cross-relaxation and cooperative upconversion are the dominant processes affecting the blue emission efficiency.
2007, 56 (7): 4194-4199.
doi: 10.7498/aps.56.4194
Abstract +
This paper reports on upconversion properties of Tm3+/Yb3+ co-doped TeO2-Ga2O3-R2O (R=Li, Na, K) glasses pumped by 808 and 977 nm laser diodes (LD). An intense upconversion emission centered at 476-nm (blue) along with a weak emission at 650 nm (red) has been observed when pumped by 977 nm LD, assigned to the transitions of 1G4→3H6 and 1G4→3H4 and/or 3F2，3→3H6 of Tm3+, respectively. The 476-nm upconversion intensity has a nearly cubic dependence on incident pump laser power, indicating a three-photon process. However, a quadratic dependence of the 476-nm upconversion intensity on the incident pump laser power has been observed when pumped by 808 nm LD, due to two-photon absorption process. It is noticed that the intensity of the blue-upconversion emission increases signifieantly with increasing radius of alkali metal of samples when pumped by 977 nm LD, while no obvious change has been observed when pumped by 808 nm LD.
2007, 56 (7): 4200-4206.
doi: 10.7498/aps.56.4200
Abstract +
This paper reports on spectroscopic properties and energy transfer of Tm3+/Ho3+-codoped ZnO-WO3-TeO2 glass upon excitation of 808nm diode laser. The J-O strength parameters， spontaneous emission probability and radiative lifetime of Ho3+ were calculated using Judd-Ofelt theory. The absorption cross-section and stimulated emission cross-section were also investigated. Our result indicates that the highest gain of 2.0 μm emission, which comes from 5I7 to 5I8 transition of Ho3+, might be achieved from the glass at the rare-earth ion concentration of 0.5 mol% of Tm2O3 and 0.15 mol% of Ho2O3. It is found that coefficients of the forward Tm3+→Ho3+ energy transfer is about 18 times that for the backward Tm3+←Ho3+ energy transfer. The calculated fluorescence lifetime of the 5I7 level of Ho3+ is 3.9 ms and the emission cross section of the 5I7→5I8 transition of Ho3+ exhibits a maximum of 9.15×10-21 cm2 at 2027 nm. We also found that Tm3+/Ho3+-codoped tellurite glass is a promising host material for potential 2.0 μm laser by comparing the quantum efficiencies, the values of σe×τm and gain coefficients of fluoride and heavy metal oxide glasses respectively.
2007, 56 (7): 4207-4212.
doi: 10.7498/aps.56.4207
Abstract +
The Er3+, Yb3+-doped CaO-Y2O3-Al2O3-SiO2 glasses were prepared by melting, and then annealed. The emission spectra and upconversion spectra of glass-ceramics have been investigated. The upconversion luminescence mechanisms of Er3+ in YAG glass-ceramics were analyzed. The results show that the Er,Yb:YAG glass-ceramics are obtained after annealing of the glasses. A broad emission spectrum of width 200nm in the wavelength range of 1450—1650nm was obtained in Er,Yb:YAG glass-ceramics at room temperature. The full width at half-maximum (FWHM) of the 4I13/2→4I15/2 transition is ～180nm. This may be as a result of the luminescence of the Er3+ ions in YAG crystal phase and the remnant Er3+ ions in glass phase acting together. The upconversion luminescence intensity increases because the phonon energy of YAG crystallite is lower than that of aluminosilicate glass. The infrared to green or to red upconversion luminescence intensities for the glass-ceramics are evaluated to be nearly 7 or 3 times as high as that of aluminosilicate glasses, respectively. The relative intensities of green and red upconversion emission changed because the microscopic environment around Er3+ and Yb3+ ions changed upon heat treatment.
2007, 56 (7): 4213-4217.
doi: 10.7498/aps.56.4213
Abstract +
Using micro-photoluminescence technique, we observed a new photoluminescence peak about 0.348eV above the bandgap of GaAs (E0). By analyzing its optical characteristics, we assigned this peak to the nonequilibrium luminescence emission from the E0＋Δ0 bandgap in semi-insulated GaAs, which was further verified by Raman results. The observed polarization, excitation power dependence and temperature dependence of the photoluminescence spectra from the E0＋Δ0 energy level were very similar to those from the E0 of GaAs. This mainly resulted from the common conduction band around Γ6 that was involved in the two optical transition processes, and indicated that the optical properties of bulk GaAs were mainly determined by the intrinsic properties of the conduction band. Our results demonstrated that the micro-photoluminescence technique is a powerful tool to investigate the high energy states above the fundamental bandgap in semiconductor materials.
Instantaneous relaxation of photoconductivity in GaN film grown on vicinal sapphire substrate by MBE
2007, 56 (7): 4218-4223.
doi: 10.7498/aps.56.4218
Abstract +
By optimizing the technique and conditions experimentally, we have grown GaN film on vicinal sapphire (0001) substrates by radio frequency plasma-assisted molecular beam epitaxy (MBE). It was found that the films grown on vicinal sapphire (001) substrates have better quality than that grown on conventional substrate, as shovn by XRD and AFM characterization. Through investigation of the instantaneous relaxation behaviors of photoconductivity in GaN films grown on vicinal and common sapphire substrates, three stages of carrier recombination in the conventional MBE GaN film were discovered. The stages consist of bimolecular, monomolecular and persistent recombination phases in which the relaxation times are 0.91, 7.7 and 35.5ms, respectively. In comparison, only bimolecular and monomolecular recombination processes of photo-generated carriers were found in the GaN film grown on vicinal sapphire (0001) substrate, the relaxation time was measured to be 0.78 and 14 ms, respectively. Theoretical considerations directly show that the persistent conductivity mainly originates from the native dislocation defects in GaN film grown by MBE.
2007, 56 (7): 4224-4228.
doi: 10.7498/aps.56.4224
Abstract +
Silicon doped Sb2Te3 films were deposited by three target (Si, Sb and Te) co-sputtering. For comparison, Ge2Sb2Te5 and Sb2Te3 films were also prepared. Memory cells (pore size=10 μm×10 μm) were fabricated by micro-fabrication to further study their storage performance. Results indicate that silicon doping increases the crystallization temperature. Meanwhile, silicon doping drastically enhances the resistivity ratio (high resistance state/low resistance state) to 106 by increasing both amorphous resistivity and crystal resistivity so as to further increasing the ON/OFF ratio of memory cell. Compared with Ge2Sb2Te5 film, 16at%Si-Sb2Te3 film has a higher crystalline resistivity and lower melting temperature, which are helpful to the reduction of RESET current. Memory cell with silicon doped Sb2Te3 film poccesses memory storage characteristics, and it can be reversibly switched between the high resistance state (RESET status) and the low resistance state (SET status). The SET status can be triggered by electrical pulse of 3V, 500ns and it comes back to the RESET status when 4V, 20ns pulse is applied, while Ge2Sb2Te5 cells, with the same structure can't be switched back to RESET state.
2007, 56 (7): 4229-4234.
doi: 10.7498/aps.56.4229
Abstract +
The Concorde MicroPET Rodent R4 system designed by Concorde Microsystems Inc. is the dedicated positron emission tomography (ECT) for studies of rodents. The scanner has 32 detector rings and a 120mm animal aperture. The transversal field of view(FOV) is 100mm, and the axial FOV is 78mm. The spatial resolution at the center of FOV is smaller than 1.8mm. This paper designs a series of experiments to evaluate the performance parameters (spatial resolution, sensitivity, scatter ets.) of the scanner. In the center FOV the transversal spatial resolution is 1.9mm, the axial spatial resolution is 1.88mm. The absolute sensitivity of the system is 39.88 cps/kBq for an energy window of 250KeV-750KeV. For the same energy window the 2D-reconstructed scatter fractions is 50.6%, the 3D-reconstructed scatter fractions is 32.3%.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2007, 56 (7): 4235-4241.
doi: 10.7498/aps.56.4235
Abstract +
The organic ionic salt of trans-4-［4-(dimethylamino) styryl］-1-methylpyridium p-toluenesulfonate (DAST) is a kind of nonlinear optical crystal. Large and high-quality DAST crystals were grown in a saturated DAST-methanol solution from seed crystals by controlling the temperature. The effects of preparation method, temperature and cooling speed on the growth of DAST crystals were investigated in detail. The light transmittance and thermal stability of prepared DAST crystals were studied. The sample of DAST crystal heated at 265℃ was characterized by X-ray diffraction (XRD) and Fourier transformation infra-Red spectroscopy (FT-IR), and it was proved that the phase transition temperature of DAST crystal is 260℃, and it is feasible to prepare DAST crystal from the melt. At the same time, the process of weight loss of DAST crystal at 37—800℃ was discussed preliminarily.
2007, 56 (7): 4242-4246.
doi: 10.7498/aps.56.4242
Abstract +
2D ordered, size-controlled nano-pillar was fabricated onto silicon substrate by direct nanosphere lithography with a mask of colloidal spheres. First, an ordered single layer of polystyrene (PS) nanosphere with a diameter of 200 nm was obtained by self-assembly on silicon surface. Then, the size of PS nanosphere on silicon substrate was reduced by reactive ion etching(RIE) with oxygen to form size-controllable PS nanosphere templates. Finally，these samples with nanosphere templates were etched by RIE with carbon fluoride to fabricate 2D ordered silicon pillar. The size of pillar is determined by the PS sphere diameter reducedby RIE and is controlled easily by choosing appropriate etching time. The period of silicon pillar arrays is determined by the initial diameter of PS spheres.
2007, 56 (7): 4247-4251.
doi: 10.7498/aps.56.4247
Abstract +
Through studying the microstructure of AZ61 alloy solidified in different external fields, it is found that when solidified in single magnetostatic field , the grain boundaries were composed of matrix Mg and meshy Mg-Al-Zn compounds. When solidified in the field composed of magnetostatic field and alternating current , the grain boundaries were composed of matrix Mg and Mg-Al-Zn compounds which existed as isolated spots as well as a certain amount in the meshy state. But when solidified in the field composed of magnetostatic field and direct current, the mesh disappeared and together with matrix Mg a little Mg-Al-Zn compound appeared as discontinuous flakes. Compared with single magnetostatic field, solidification in magnetostatic field and currenmakes the solute content in grains to increase and the solute content in grain boundaries to decrease.
2007, 56 (7): 4252-4255.
doi: 10.7498/aps.56.4252
Abstract +
There are important applications of metal in metamaterials. Three methods for dealing with metal in FDTD are analyzed and compared. ADE(auxiliary differential equation method) and PLRC(piecewise linear recursive convolution) have the same numerical result. However, there is a little difference between Sakoda's method and ADE. It is due to the error in calculation of convolution integral with Sakoda's method. Improving the convolution integral with the method used in PLRC, these three methods give the same results.
2007, 56 (7): 4256-4261.
doi: 10.7498/aps.56.4256
Abstract +
The high density PPy films (HD-PPy，ρ>1.4g/cm3) doped with p-toluenesulfonate (TOS-) counterions were electropolymerized by a facile approach in H2O and acetonitrile (AN) mixed solvent. The structure and electrochemical properties of the HD-PPy films were measured by X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that appropriate ratio of AN/H2O (99/1) could be favorable to increase the density of PPy films. Further enhancement of the density could be obtained by using higher current density (such as 10mA/cm2), as it favors the formation of two-dimensional structure. Generally, low temperature of polymerization, Tp (e.g. -20℃), is advantageous to the enhancement of density and conductance of PPy films. But if Tp is too low, it beesmes disadvantageous in case of the high current density of polymerization. The HD-PPy films (1.42g/cm3) were obtained at 0 ℃ with 10mA/cm2 in AN/H2O(99/1) solution. Furthermore, HD-PPy films were characterized not only by high electronic conductivity (～220S/cm) and high thermal stability, but also by low electrochemical activity. It was indicated that the HD-PPy would be not only an excellent electrode material but also a promising corrosion protection material.
2007, 56 (7): 4262-4269.
doi: 10.7498/aps.56.4262
Abstract +
The electronic states of tetracene adsorbed on Ru (1010) surface as well as their adsorption sites and directions has been studied by using ultraviolet photoelectron spectroscopy (UPS), angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) and scanning tunneling microscopy (STM). The UPS measurements show that the six peaks from the tetracene are 2.1, 3.5, 4.8, 6.0, 7.1 and 9.2 eV below the Fermi level. The ARUPS measurements suggest that the plane of tetracene molecule is parallel to the Ru(1010) surface. The STM image shows that the tetracene molecule is adsorbed on Ru (1010) surface with its longer axis lying in the direction of either ［0001］ or ［1210］. The adsorption structure was confirmed with an ab initio calculation based on density functional theory (DFT). The short-bridge site and the hollow site are the most favorable sites when the molecule has its longer axis oriewted along ［0001］ and ［1210］, respectively.
2007, 56 (7): 4270-4276.
doi: 10.7498/aps.56.4270
Abstract +
Solid-state dye-sensitized solar cells (DSCs) were prepared using polaniline (PANI) as hole- transport material. The charge transport and recombination in the cells were studied by means of intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS). On the basis of lifetime (τn) and mean transit time (τd) of the electrons in nanoporous TiO2 film and fitting of the IMPS response, the effective diffusion coefficient (Dn) and the diffusion length (Ln) of electrons in the TiO2 film were acquired. The electron lifetime in the PANI-based DSCs was about 10 times lower than their liquid counterparts, indicating a much more serious recombination of photogenerated electrons in the TiO2 film, very likely mainly with holes of oxidized dye molecules. With increase in the thickness of TiO2 film, both τn and τd decreased, whereas Ln and Dn increased; and the better performance of the solid-state cells was available only in a suitable thickness range of TiO2 films.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (7): 4277-4280.
doi: 10.7498/aps.56.4277
Abstract +
There is a pronounced antisymmetry with respect to the equator for the middle stratospheric methane, and it has been attributed to the anomalous annual cycle of vertical motions. The NCAR interactive chemical, dynamical and radiative two-dimensional model (SOCRATES) has been used to simulate and explore the possible cause of the anomalous annual cycle of vertical motions. The simulation results indicate that the quasi-biennial shift to the equator of high concentration ozone center plays an important role in the interannual anomaly of annual cycle. Ashigh concentration of ozone leaves the equator for the summer Hemisphere, there more solar radiation is absorbed in the middle stratosphere, while in the winter Hemisphere the situation is the contrary. Thus enhanced ascending motion is promoted by greater short-wavelength radiation heating in the middle stratosphere over the summer Hemisphere and strengthens the descending motion over the winter Hemisphere as well, which results in a stronger annual cycle. On the contrary, when high concentration of ozone is located close to the equator, there is a relatively weaker annual cycle.
2007, 56 (7): 4281-4288.
doi: 10.7498/aps.56.4281
Abstract +
Based on the extended Huygens-Fresnel principle, the analytical expression for the spectrum of ultrashort pulsed Hermite-Gaussian (H-G) beams propagating through the turbulent atmosphere is derived. The spectral shift and spectral transition are studied, and reasonable physical explanations are given. It is shown that the spectrum depends on the structure constant of the refractive index, order of the Hermite polynomial, pulse duration and position of the observation point. The on-axis spectrum is blue-shifted, the off-axis spectrum becomes red-shifted with increasing transverse coordinate, and the position with null spectral shift is independent of pulse duration. Furthermore, there exists an off-axis spectral transition when the turbulence reaches a certain degree. The behavior of the off-axis spectral transition in turbulence is very different from that in free space, which is analyzed in detail.
2007, 56 (7): 4289-4296.
doi: 10.7498/aps.56.4289
Abstract +
Two field-of-view shifted Shack-Hartmann wavefront sensors (FSWFS) are proposed, which are used to measure the wavefront information of object signal under daytime conditons. The experimental results on the sky background's non-uniformity characteristics are obtained, the detecting error of the dual focal-plane FSWFS is analyzed in this paper and its principle has been proven by experiments with a single focal-plane array. The measuring results indicate that FSWFS can precisely and stably measure the wavefront information of object signal with strong background. At the same time, the detection capacity of FSWFS is estimated and its restraining factors are analyzed, and the estimation results show that the adaptive optics system with FSWFS in Yunnan observatory can precisely measure the wavefront information of object signal whose V magnitude is 5 when the brightness of the sky background is 10 W/m2·sr.
2007, 56 (7): 4297-4304.
doi: 10.7498/aps.56.4297
Abstract +
Low-altitude and high-altitude nuclear explosions are sources of intensive additional ionization in ionosphere. In this paper, in terms of the ionization equilibrium equation system and the equation of energy deposition of radiation in atmosphere, and considering the influence of atmosphere, the temporal and spacial distribution of ionization effects caused by atmospheric nuclear detonation are investigated. The calculated results show that the maximum of additional free electron density produced by low-altitude nuclear explosion is greater than that by the high-altitude nuclear burst. As to the influence of instant nuclear radiation, there is obvious difference between the low-altitude and the high-altitude explosions. The influence range and the continuance time caused by delayed nuclear radiation is less for the low-altitude nuclear detonation than that for the high-altitude one.
2007, 56 (7): 4305-4311.
doi: 10.7498/aps.56.4305
Abstract +
From a large volume of literature we have collected a total of 16818 datapoints of effective observation of BL Lac object S5 0716+714 in the optical band, and constructed its long-term light curve from 1994 to 2006 AD. The light curve shows that S5 0716+714 is very active and exhibits very complicated non-sinusoidal variations. We used power spectrum method to analyze the period of light curve variation. Our results show that the long-term period of variation is 1.1 year. Time of coincidence is possible, Raiteri et al. have found the period of 3.3 year, which may be a multiple of 1.1-year periods. We expect next burst in 2006 July.
