Vol. 61, No. 20 (2012)

The renormalization solution for a class of relative rotation nonlinear dynamic model with multi-frequency excitation
Tang Rong-Rong
2012, 61 (20): 200201. doi: 10.7498/aps.61.200201
Abstract +
Using the perturbation theory, a class of relative rotation nonlinear dynamical model possessing nonlinear elastic force, friction force and multi-frequency excitation is investigated. The relations for the frequency syntheses are investigated, and the conditions under which multi-typical resonance happens at the same time are given. Using the renormalization method, the asymptotic expansions for the solutions of the model under corresponding conditions are obtained.
Conformal invariance, Mei symmetry and the conserved quantity of the Kepler equation
Liu Hong-Wei, Li Ling-Fei, Yang Shi-Tong
2012, 61 (20): 200202. doi: 10.7498/aps.61.200202
Abstract +
In this paper, the conformal invariance and Mei symmetry of Kepler system under infinitesimal transformations are discussed in detail. The new conserved quantity of the system is given, which is different from the total energy and the angular momentum. The independences of these conserved quantities are discussed in the space which is composed of general ordinates and general speed.
Mei symmetry and Mei conserved quantity of Nielsen equation in a dynamical system of the relative motion with nonholonomic constraint of Chetaev's type
Wang Xiao-Xiao, Zhang Mei-Ling, Han Yue-Lin, Jia Li-Qun
2012, 61 (20): 200203. doi: 10.7498/aps.61.200203
Abstract +
Mei symmetry and Mei conserved quantity of Nielsen equations in a dynamical system of the relative motion with nonholonomic constraint of Chetaev's type are studied. The differential equations of motion of Nielsen equation for the system, the definition and criterion of Mei symmetry, and the expression of Mei conserved quantity deduced directly from Mei symmetry for the system are obtained. An example is given to illustrate the application of the results.
A type of new conserved quantity of Mei symmetry for Appell equations in a holonomic system
Sun Xian-Ting, Han Yue-Lin, Wang Xiao-Xiao, Zhang Mei-Ling, Jia Li-Qun
2012, 61 (20): 200204. doi: 10.7498/aps.61.200204
Abstract +
A type of new conserved quantity of Mei symmetry for Appell equations in a holonomic system is investigated. Based on the definition and criterion of Mei symmetry for Appell equations in a holonomic system, a type of new structural equation and new conserved quantity of Mei symmetry for Appell equations in a holonomic system expressed by Appell function under the infinitesimal transformations of groups are obtained. An example is given to illustrate the application of the results.
Infinite sequence new exact solutions of K(m,n) equation and B(m,n) equation
Bai Yu-Mei, Taogetusang, Han Yuan-Chun
2012, 61 (20): 200205. doi: 10.7498/aps.61.200205
Abstract +
New solutions of several kinds of auxiliary equations, Bcklund transformation and nonlinear superposition formula of the solutions are presented by studying a highly auxiliary equation method. Based on this and different m and n, the method of combining transformation and direct integration is used to obtain infinite sequence new exact solutions of K(m,n) equation and B(m,n) equation, which include infinite sequence smooth soliton solutions, peak soliton solutions and compact soliton solutions.
Unsteady dynamic evolution adjoint design method
Gao Ying-Ying, He Feng, Shen Meng-Yu
2012, 61 (20): 200206. doi: 10.7498/aps.61.200206
Abstract +
On the basis of studying the traditional adjoint method based on the steady flow solution and the steady solution of the adjoint equation, a new optimal aerodynamic design method called the dynamic evolution adjoint method is presented in this paper. This new method is based on the instantaneous solution of the unsteady flow governing equation and the instantaneous solution of the unsteady adoint equation. The dynamic evolution adjoint method has the advantage of both the adjoint method and the dynamic evolution method. The numerical results of many examples show that this new method is much more time saving than the traditional adjoint method and the accuracy of this new method can be the same as that of the traditional adjoint method.
Relaxation properties of graphene nanoribbons at different ambient temperatures: a molecular dynamics study
Wang Wei-Dong, Hao Yue, Ji Xiang, Yi Cheng-Long, Niu Xiang-Yu
2012, 61 (20): 200207. doi: 10.7498/aps.61.200207
Abstract +
At different thermodynamic temperatures (between 0.01 and 4000 K), the relaxation properties of three kinds of graphene nanoribbons with different aspect ratios are simulated by molecular dynamics method based on Tersoff-Brenner and AIREBO potential functions separately. Then we compare the energy curves and surface morphologies of nanoribbon relaxation with two kinds of potential functions, and study the dynamic equilibrium process of the graphene nanoribbons during their relaxation simulation. The simulation results show that the single layer graphene nanoribbon is not of a perfect planar structure and that a certain degree of fluctuations and folds occur at the edges and inside of nanoribbons, which are consistent with the existing experimental results; the surface fluctuation level of graphene nanoribbons decreases with the reduction of the aspect ratio, and the system kinetic energy has a dramatic influence on the relaxation deformation of the graphene nanoribbons at different temperatures, which indicates that the higher the system temperature, the greater the deformation is. Curl phenomenon could appear even on the surface of the nanoribbon with a high aspect ratio at a certain temperature. Finally, the simulations of graphen molecular dynamics by using the Tersoff-Brenner and AIREBO potential are deeply analyzed.
Singular perturbation solution of a class of sea-air oscillator for the El Niño/La Niña-southern oscillation
Han Xiang-Lin, Du Zeng-Ji, Mo Jia-Qi
2012, 61 (20): 200208. doi: 10.7498/aps.61.200208
Abstract +
The EI Niño/La Niña and southern oscillation is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interactions. In this paper, the aim is to create a method of asymptotically solving the nonlinear singularly perturbed problem for the ocean-atmosphere oscillator models. And according to a class of ocean-atmosphere oscillator models, employing the singular perturbation method, we study the approximate solution of corresponding problem. The obtained results from singular perturbation method can be used for analyzing the sea surface temperature anomaly and the thermocline depth anomaly in the equatorial Pacific of the atmosphere-ocean oscillator for the EI Niño/La Niña and southern oscillation model.
Dynamical patterns of epidemic outbreaks on scale-free networks with traffic flow
Hu Heng-Kai, Wang Kai, Yang Guang, Liu Qian, Pei Wen-Jiang, Qiu Shen-Wei, Wei Cheng-Jian, Zhang Yi-Feng
2012, 61 (20): 200209. doi: 10.7498/aps.61.200209
Abstract +
A modified susceptible-infected (SI) model is developed in this paper. The mean field approximation method is further adopted. This present research is based on traffic-driven epidemic spreading behavior. Take MIP routing for example, diffusion coefficient τ, traffic generation rate λ, infection rate β and their relationship with the actual betweenness bk are re-explored under the SI model. Both the theoretical and experimental results indicate that under the same internet topology and routing strategy, the diffusion coefficient τ is inversely proportional to average traffic generation rate λ and infection rate β.


The physical significances and applications of Schmidt decompositions of continuum bipartile entangled state representation
Fan Hong-Yi, Li Xue-Chao
2012, 61 (20): 200301. doi: 10.7498/aps.61.200301
Abstract +
According to the continuum bipartite entangled state representation |η> we derive the Schmidt decomposition of |η>, respectively in the coordinate representation, momentum representation and the particle number representation, and explain their physical significances. As the applications of the Schmidt decomposition, we directly derive the action of the single-mode squeeze operator on |η>, the two-mode squeeze operator's entangled state representation, as well as the matrix element of displacement operator in the Fock space. Generalization of our discussion in this paper to the multipartite entangled state cases is feasible.
Study on the dynamics of an inelastic bouncing ball
Zhou Zhi-Gang, Shi Yu-Ren, Liu Cong-Bo, Wang Guang-Hui, Yang Hong-Juan
2012, 61 (20): 200501. doi: 10.7498/aps.61.200501
Abstract +
Considering the case of air damping, we use the method of numerical simulation to study dynamic behavior of inelastic bouncing ball. By changing the value of control parameter V0, the motion of the bouncing ball exhibits nonlinear phenomena of period doubling bifurcation, chaos, etc. These phenomena are confirmed by both 0-1 test and maximal Lyapunov exponent.
The distribution functions of characteristic quantities for random noise signal of photodetector
Yan Zhen-Gang, Lin Ying-Lu, Yang Juan, Li Zhen-Hua, Bian Bao-Min
2012, 61 (20): 200502. doi: 10.7498/aps.61.200502
Abstract +
Based on the random process of the photodetector noise signals {Vi}, the different characteristics of the two parts of the random measurementstability constant part and random fluctuation part are analyzed. A new mathematical model of the random noise signal is established. The theoretical analysis shows that the statistical distributions must obey the relationship of nonlinear transform. The distribution laws of the different characteristic quantities in the same random process are studied experimentally, such as, the amplitude of extreme, the amplitudes of the rising edge and falling edge, the interval between extreme points, the difference between adjacent amplitudes, the product value of the quantities and the quotient value of the quantities. And the statistical distribution of these characteristic quantities matches well with the form of the lognormal distribution. From the theoretical and experimental results we can conclude that the lognormal distribution plays an important role in describing the random fluctuation part characteristic of random process.
Exact solution for mean trapping time of random walk on a scale-free Koch network
Xing Chang-Ming, Liu Fang-Ai, Xu Ru-Zhi
2012, 61 (20): 200503. doi: 10.7498/aps.61.200503
Abstract +
As a basic dynamical process, random walk on networks is fundamental to many branches of science, and has attracted much attention. A difficult problem in the study of random walk is how to obtain the exact solution for the mean trapping time (MTT) of this process. The MTT is defined as the mean time for the walker staring from any node in the network to first reach the trap node. In this paper, we study random walk on the Koch network with a trap located at the highest degree node and calculate the solution for MTT. The accurate expression for the MTT is obtained through the recurrence relation and the structure properties of the Koch network. We confirm the correctness of the MTT result by direct numerical calculations based on the Laplacian matrix of Koch network. It can be seen from the obtained results that in the large limit of network size, the MTT increases linearly with the size of network increasing. Comparison between the MTT result of the Koch network with that of the other networks, such as complete graph, regular lattices, Sierpinski fractals, and T-graph, shows that the Koch has a high transmission efficiency.
Research on the entropy of logistic chaos
Pan Xin-Yu, Zhao He-Ming
2012, 61 (20): 200504. doi: 10.7498/aps.61.200504
Abstract +
As a simple one-dimensional chaotic system, logistic map has some important applications in many fields. The stable entropy characteristic of logistic function is proposed in this paper. A series of logistic sequence entropy, calculated under different initial values and values of parameter μ, is found to have some special distributions. A great number of numerical simulations prove that the entropy is determined by parameter μ, and it is irrelevant with initial value. The logistic sequence becomes a uniform distribution, and its entropy is close to a maximum, when μ is increased to 4. Thereby the stationary quality of logistic chaos can be speculated to some extent.
Bifurcations in coupled electrical circuit systems
Li Qun-Hong, Yan Yu-Long, Yang Dan
2012, 61 (20): 200505. doi: 10.7498/aps.61.200505
Abstract +
A coupled system composed of two nonlinear circuit systems is investigated. In this paper, the existence condition and the analytical expressions of equilibrium in higher-dimensional system are derived, and the co-dimension 1 and co-dimension 2 bifurcations of equilibrium are also studied. Furthermore, the complicated bifurcations are obtained through the continuation of limit cycles. It may lead to various dynamical behaviors such as periodic motion, chaos, etc., for the interaction of two subsystems with periodic motions under different coupling parameters. Using the qualitative analysis of equilibrium before and after coupling, the relation between the discontinuity of bifurcation diagram and occurrence of neutral saddle in the case of weak coupling is presented.
A new grid multi-wing chaotic system and its circuit implementation
Zhou Xin, Wang Chun-Hua, Guo Xiao-Rong
2012, 61 (20): 200506. doi: 10.7498/aps.61.200506
Abstract +
In this paper, a new three-dimensional autonomous chaotic system is proposed. However, the structural form of the new chaotic system is limited to a double-wing like most Lorenz-like systems. According to the equilibrium points and topological structure of this double-wing chaotic system we design some appropriate nonlinear functions for it. Then, the new double-wing chaotic system can be modified into a grid multi-wing chaotic system. Basic dynamical properties of the system are studied by theoretical analysis and numerical simulation, which proves the chaotic behaviors of this new grid multi-wing chaotic system. Finally, an oscillator circuit is designed for implementation. The circuit simulation results are in good agreement with the numerical simulation results.
Oscillations and their mechanism of compound system with periodic switches between two subsystems
Yu Yue, Zhang Chun, Han Xiu-Jing, Bi Qin-Sheng
2012, 61 (20): 200507. doi: 10.7498/aps.61.200507
Abstract +
Complicated behaviors of the compound system with periodic switches between two nonlinear systems are investigated in detail. Through the local analysis, the critical conditions such as fold bifurcation and Hopf bifurcation are derived to explore the bifurcations of the compound systems with different stable solutions in the two subsystems. Different types of oscillations of the switched system are observed of which, the mechanism is presented to show that the trajectories of the oscillations can be divided into several parts by the switching points, governed by the two subsystems, respectively. With the variation of the parameters, cascading of doubling increase of the switching points can be obtained, leading to chaos via period-doubling bifurcations. Furthermore, because of the non-smooth characteristics at the switching points, different forms of bifurcations may occur in the compound system, which may result in complicated dynamics such as chaotic oscillations, instead of the simple connections between the trajectories of the two subsystems.
Research of Lyapunov exponent of S-boxes
Zang Hong-Yan, Fan Xiu-Bin, Min Le-Quan, Han Dan-Dan
2012, 61 (20): 200508. doi: 10.7498/aps.61.200508
Abstract +
In the design of cryptographic algorithms, S-boxes provide the cryptosystems with the information confusion function. The traditional cryptography indexes of the S-boxes generally include linear deviation, differential characteristics, algebraic immunity, fixed point mumber, snowslide effect, and so on. In 2006, Kocarev et al. (Kocarev L, Szczepanski J, Amigo J M and Tomovski I 2006 IEEE Transactions on Circuits and Systems-I: regular papers 53 6 1300) set up a discrete chaos theory based on the finite set. In light of the theory in this paper, we introduce the definition of the Lyapunov exponent with Hamming distance, calculate and compare the Lyapunov exponent values of the S-boxes in several cryptographic algorithms. In this paper we prove that a map defined on the Euclidean distance has a maximal Lyapunov exponent value of 0. In this paper it is shown that the relationship between the Lyapunov exponent and the snowslide effect of the S-box is the relationship between the butterfly effect in chaos theory and the snowslide effect in cryptography. The definition of the Lyapunov exponent of the proposed S-boxes may be complementary to the traditional cryptography indexes of the S-box.
Detection of a coupled vibration by mechanical resonant absorption spectra
Yang Yue-Bin, Zuo Wen-Long, Bao Yan-Xiang, Liu Shu-Yu, Li Long-Fei, Zhang Jin-Xiu, Xiong Xiao-Min
2012, 61 (20): 200509. doi: 10.7498/aps.61.200509
Abstract +
In this paper, we propose a novel scheme of measuring a coupled but uneasy detected vibration mode through surveying another much easier detected vibration mode in a complex mechanical system. Through measuring the frequency dependence of phase lag of strain behind stress, i.e., the apparent mechanical dissipation-frequency spectrum, for the easy detected vibration mode, we are able to obtain the corresponding resonant absorption peak for the coupled vibration mode in addition to the expected main system resonance. By studying the observed resonant absorption peak: peak position, peak width and peak height, we can obtain the detailed information about the coupled vibration mode: the intrinsic resonant frequency, dissipation and coupling coefficient. Through measuring the apparent mechanical dissipation frequency spectrum of torsion vibration, the detection of the progression vibration about the pendulum axis is presented as a representative example of our scheme.
Nanoscale stabilization of metastable phase: thermodynamic model and experimental studies
Song Xiao-Yan, Xu Wen-Wu, Zhang Zhe-Xu
2012, 61 (20): 200510. doi: 10.7498/aps.61.200510
Abstract +
A thermodynamic model, into which the nanoscale effect is introduced, is established to describe the thermal parameters of metastable phase, as well as their changes with the concentration, temperature and grain size. Based on the model calculations and experiments, the thermodynamic properties and dependence on the grain size are disclosed. Taking the metastable SmCo7 phase for example, the conditions for the single-phase stability and the phase decomposition are studied. The results are important for the control of the phase stability and phase transformation of the metastable-phase alloy.
Sum-of-square-based impulsive control for chaotic system based on polynomial model
Yang Jun, Sun Qiu-Ye, Yang Dong-Sheng
2012, 61 (20): 200511. doi: 10.7498/aps.61.200511
Abstract +
In this paper, we present a novel impulsive control method based on polynomial model for a large class of chaotic systems. First, the polynomial model is used to model the chaotic system, in which the state equation of the system is composed of the polynomial matrix of the system and the column vector of monomials in state. Compared with others modeling methods, any pre-defined hypothesis is removed. Next, a sum-of-square (SOS)-based impulsive control method is investigated to guarantee that the chaotic system is asymptotically stable. It can obtain larger impulsive interval using SOS-based optimization algorithm over linear matrix inequality technique, which means the same control performance can be realized by less control action. Finally, the simulation is provided to demonstrate the effectiveness of the proposed method.
Chaos analysis of high-frequency harmonics of locomotive LCI
Zhang Kun, Zhang Yang, Zha Xiao-Ming, Xiong Yi, Peng Guang-Qiang, Fan You-Ping
2012, 61 (20): 200512. doi: 10.7498/aps.61.200512
Abstract +
Considering typical AC-DC-AC multiple units, CRH2 motor car, in this paper we deduce its parametric equations under sine pulse width modulation, and set up a new nonlinear parameter model. Fractal situation of higher harmonic is analyzed based on chaos theory. Aiming at typical traction substations, calculation and simulation are conducted, and the result is verified based on data from actual wave records, which proves that high-frequency harmonic can lead to system resonance and expands the application of chaos analysis method.
Design of extraordinary-optical-transimission refractive-index sensor of subwavelength metallic slit array based on a Fabry-Perot model
Zeng Zhi-Wen, Liu Hai-Tao, Zhang Si-Wen
2012, 61 (20): 200701. doi: 10.7498/aps.61.200701
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The refractive index sensing properties of a period array of subwavelength metallic slits in water environment are investigated. The transmission spectra of the slit array are calculated with a rigorous fully-vectorial method. A simple semi-analytical Fabry-Perot model that can accurately reproduce the rigorous fully-vectorial data is built up. We find that the transmission peak becomes sharpest as it is exactly located at the Rayleigh anomaly position, which is explained based on the resonance condition derived from the model. The method to design the slit array to achieve this sharpest transmission peak is presented. The full width at half-maximum (δλ) of the designed transmission peak can be as low as 0.01 nm, which corresponds to a refractive-index measurement uncertainty (δns) of 2× 10-6 RIU. The influences of array period, slit width and incident angle on the designed sensitivity, δλ, δns and peak transmittance of the sensor are systematically provided.
Broadband single-peak filtering characteristics of coated long-period fiber gratings
Chen Hai-Yun, Gu Zheng-Tian, Yang Ying
2012, 61 (20): 200702. doi: 10.7498/aps.61.200702
Abstract +
A coated long-period fiber grating (LPFG) operating at the phase-matching turning point couples the fundamental core mode to a higher-order cladding mode, producing a single broad-band whose 3dB-bandwidth is dependent on the difference in dispersion between the core mode and a cladding mode, grating length and central wavelength. The variations of film refractive index and thickness influence the difference in dispersion between the core mode and cladding mode and thus, the bandwidth of loss peak. The central wavelength of loss peak also varies with the changes of film parameters. When the film refractive index is 1.57 and the film thickness is 350 nm, the bandwidth of loss peak reaches 302 nm. The bandwidth can be further improved to 334 nm by reducing the grating length based on the fact that the loss at the central wavelength is guaranteed to be more than 6 dB. A further investigation shows that introducing a π phase shift into a uniform LPFG at a proper position that is away from the grating center can increase the bandwidth to 372 nm and more.
Study on Lagrangian analysis for solving the stress gradually along the time
Tao Wei-Jun, Huan Shi
2012, 61 (20): 200703. doi: 10.7498/aps.61.200703
Abstract +
Lagrangian analysis method is re-analyzed, in which by measuring the physical variables of each Lagrangian positions the other physical variables of these positions of the material is analyzed, and then the dynamic mechanical properties of materials can be determined. However, the existing Lagrangian analysis methods are still inadequate when the particle velocity is known. In this paper, a new Lagrangian analysis method, with only particle velocity known, is developed, which is called step by step method along the time. The method does not make any assumption, and it can solve the problem when only particle velocity wave profiles are measured. A set of experimental data of concrete under impact is processed with the method, and the corresponding strain wave, stress wave, and stress-strain relations of the whole process of loading and unloading are calculated. Thus the strain rate dependent elastic-elastic constitutive characteristics of the concrete are revealed.
Optical model potential of antiproton atoms with nuclear polarization correction
You Yang-Ming, Wang Bing-Zhang, Wang Ji-You
2012, 61 (20): 202401. doi: 10.7498/aps.61.202401
Abstract +
According to SIC-X, a more rigorous calculating method, we propose a self-consistent field mode with the Rydberg exchange parameters. Using this method to calculate nuclear polarization, the result is more accurate than that given by Chen et al. Besides, when they calculated P238U energy level transition, their model is likely to be imperfect and maybe has some defects that are hard to overcome. And their result is likely to be inaccurate. In the early 70s of 20th century, Batty performed the exploration of optical model potential, and after more than twenty times of exploring and improving, he finally presented a correct form of optical model potential. When a self-consistent field model for Rydberg exchange parameters is used to calculate nuclear polarization, we use this method to correct Batty's nuclear polarization under optical model potential and the P238U energy level transition. We obtain the energy levels of antiproton atoms. The result is exactly the same as the experimental result. This result together with the case of -, K-, - and - atoms supports the correctness of optical model potential of Batty's description of the strong interaction between nucleons. At the same time, it also shows the correctness of the method of calculating nuclear polarization. It provides a theoretical basis for further study and application of antiparticle atoms and exoticac atoms.
Research of the early debris expansion from high-altitude nuclear explosions
Yang Bin, Niu Sheng-Li, Zhu Jin-Hui, Huang Liu-Xing
2012, 61 (20): 202801. doi: 10.7498/aps.61.202801
Abstract +
Based on magnetohydrodynamic theory a shell model is developed to describe debris motion of high-altitude nuclear explosion. The debris motion parameter of Starfish is simulated. The model is verified by comparison with the results available from the literature. For the comparison between typical high-yield and low-yield nuclear explosion, the debris motions of kiloton and megaton at 100 km, 400 km and 1500 km are especially simulated. The difference in expansion law, caused by explosion yield, is analyzed. The results show that explosion condition and atmospheric environment have a significant influence on the expansion of the law of the debris cloud, and the debris environmental parameters in different directions are significantly different from each other.
Study on spectroscopic properties of B2 (X3g-, A3u) molecule
Liu Hui, Xing Wei, Shi De-Heng, Sun Jin-Feng, Zhu Zun-Lue
2012, 61 (20): 203101. doi: 10.7498/aps.61.203101
Abstract +
The X3g- and A3u states of B2 molecule are studied using highly accurate valence internally contracted multireference configuration interaction approach including the Davidson modification. The Dunning's correlation-consistent basis sets, aug-cc-pV6Z and aug-cc-pV5Z, are used in the study. To obtain more reliable results, the potential energy curves (PECs) of two electronic states are extrapolated to the complete basis set limit by the two-point total-energy extrapolation scheme. The effects of the core-valence correlation and relativistic correction on PEC are taken into account. Employing these PECs, the spectroscopic parameters (Te, Re, e, exe, eye, Be, e, e and e) of the X3g- and A3u states of two main isotopes (11B2, 10B11B) are determined and compared with those reported in the literature. Comparison with the experimental data demonstrates that the present results are accurate. With the PECs determined here, the whole vibrational states for 11B2 (X3g-, A3u) and 10B11B (X3g-, A3u) are determined when the rotational quantum number J equals zero (J=0) by numerically solving the radical Schrdinger equation of nuclear motion. For each vibrational state of every isotope species, the vibrational level and inertial rotation constants are obtained, which are in excellent accordance with the experimental findings.
The nonsequential double ionization of argon atoms with elliptically polarized laser pulse
Yu Ben-Hai, Li Ying-Bin, Tang Qing-Bin
2012, 61 (20): 203201. doi: 10.7498/aps.61.203201
Abstract +
With elliptically polarized laser pulse, the nonsequential double ionization (NSDI) of argon atoms is investigated using fully classical ensemble. The results show that the yield of NSDI decreases with increase of the ellipticity, that the momentum spectrum of the correlated electron from double ionization events in the final state shows a correlated behavior along the long axis of the laser polarization plane and an anticorrelated behavior along the short axis of the laser polarization plane, and that the momentum spectrum distribution of Ar2+ ion exhibits a single-peak structure at the zero along the short axis of the laser polarization plane, which becomes broader with the increase of the ellipticity. Trajectory back analyses show that the happening of NSDI is still due to recollision, and that the delay time between the collision and the single ionization increases with ellipticity increasing, which is because that the first electron needs more trips shuttling back and forth, so that it can recollide with the parent ion under the more ellipticity.
Effects of additional pulse wavelength at different frequencies on attosecond pulse generation in multicycle two-color laser field
Meng Jian, Chen Gao, Liu Sheng-Nan
2012, 61 (20): 203202. doi: 10.7498/aps.61.203202
Abstract +
We theoretically investigate the effects of additional pulse wavelength at different frequencies on attosecond pulse generation from the hydrogen atom exposed to multicycle two-color laser field, by numerically solving the one-dimensional time-dependent Schrödinger equation. The results show that when the wavelength of the additional pulse is set to be 1600 nm, the cutoff position of the harmonic spectra is extended dramatically compared with the scenario in the case of 533 nm pulse in visible waveband, accordingly the bandwidth of supercontinuum is widened, finally 78 attosecond pulse is obtained by wavelet transform. In this paper, we explain the effects of additional pulse wavelength in different wavebands on high order harmonic generation for the first time according to the optical oscillation frequency of the synthesized field. Also, such a result is conducible to choosing the appropriate additional pulse frequency in order to obtain the isolated attosecond pulse.
Scattering of electrons in linearly polarized high-intensity laser standing waves
Tian Mi, Zhang Qiu-Ju, Bai Yi-Ling, Cui Chun-Hong
2012, 61 (20): 203401. doi: 10.7498/aps.61.203401
Abstract +
We investigate the motion of electrons in linear polarization relativistic laser standing wave field. The dependences of scattering electron incident in laser polarization plane on the electron initial position, energy and the laser intensity are analyzed. The results indicate that the interaction between electron scattering and sanding wave has a close relationship with the electron relative energy γ0/a0. The initial energy of electron has a critical value by which the forward and backward scattering can be distinguished from each other. The critical energy needed for electron forward scattering increases by the laser intensity. Measured by electronic relative energy, the critical value is in a about 1.0-1.25 range. For the same initial energy, the extent of electron incident plane leading to the forward scattering reduces when the laser intensity becomes higher. Moreover, electrons with low energy easily tend to pass through the standing wave from node planes. Electron oscillation-center and ponderomotive force reversal effect exist merely when the electron relative energy is in a certain range. The electron initially rest on optical axis. The inelastic scattering in which the energy can be exchanged between the electron and the field is also discussed.
Transferring single-atoms between two red-detuned far-off-resonance optical dipole traps
Wang Cheng, Xu Peng, He Xiao-Dong, Wang Jin, Zhan Ming-Sheng
2012, 61 (20): 203701. doi: 10.7498/aps.61.203701
Abstract +
The preparation and manipulation of single neutral atoms in optical dipole traps have important applications in quantum simulation and information. For this purpose, a single neutral atom, trapped in a static optical dipole trap which is formed by a strongly focused red-detuned far-off-resonance laser, can be transferred to a movable optical dipole trap when the movable trap crosses the static trap and the transfer efficiency can reach about 94%, meanwhile this transferred atom could be located at given position in the focal plane. This experimental result has potential applications in realizing entanglement of two individual neutral atoms in an optical dipole trap array.
Design and study of elliptical cylinder external cloak based on line-transformation
Wang Zhan, Dong Jian-Feng, Liu Jin-Jing, Luo Xiao-Yang
2012, 61 (20): 204101. doi: 10.7498/aps.61.204101
Abstract +
Electromagnetic external cloak is an important device, which can make an object outside its domain invisible, meanwhile the object can exchange information with the outer region. Based on line-transformation and the concept of complementary medium, an elliptical cylindrical external cloak with only axial parameter changed is designed in this paper. The expressions of material parameters are derived, and then the performance of the elliptical cylindrical external cloak is simulated using the full wave simulation software. The results obtained confirm the correctness of constitutive parameters tensor. In addition, the effects of loss on performation of external cloak are investigated. Finally, the distribution of constitutive tensors is also investigated. This work provide a feasible way to fabricate matematerial-assisted elliptical cylindcial external cloak.
Research on scattering properties of phosphor for high power white light emitting diode based on Mie scattering theory
Qian Ke-Yuan, Ma Jun, Fu Wei, Luo Yi
2012, 61 (20): 204201. doi: 10.7498/aps.61.204201
Abstract +
Based on Mie scattering theory, the phosphor particle's scattering effect were simulated including light excitation and absorption. The light intensity proportion changes of forward and backward scattering light with different white light emitting diode (LED) color temperature were calculated. We also analyzed the phosphor particle size effecting the luminous flux of white LED and light color distribution of angle. Devices' excitation and emission spectrums used in our simulation were real measured spectrums of the material, rather than assuming a single spectrum. Our investigation discloses that when a conformal phosphor layer was adapted, phosphor particle diameter of 0.5 μm, makes maximum luminous flux and phosphor particles smaller, light color distribution of angel is better. While for given package structure, the best spatial color uniformity can be achieved with a phosphor layer thickness of 0.8 mm.
Scattering properties of non-spherical particles in the CO2 shortwave infrared band
Fan Meng, Chen Liang-Fu, Li Shen-Shen, Tao Jin-Hua, Su Lin, Zou Ming-Min, Zhang Ying, Han Dong
2012, 61 (20): 204202. doi: 10.7498/aps.61.204202
Abstract +
Based on the T-matrix method and the generalized multiparticle Mie-solution (GMM) method combined with diffusion-limited aggregation simulator, the scattering properties of non-spherical particles and aggregates are simulated at 1.6 μm and 2.0 μm. And the effects of the equal-volume sphere radius, the complex refractive index, the particle shape and the relative humidity (RH) on the scattering characteristics parameters of non-spherical aerosol are analyzed. The results show that besides the equal-volume sphere radius and the particle shape, the RH could also lead to a large change of the scattering properties. And the relative differences in back scattering between spherical particles and non-spherical particles in different relative humidities are all larger than 18%. If the RH increases, the back scattering will increase for small-size particles, while the back scattering of large-size ones will decrease. The asymmetry factors of the smaller aggregates are 0.023 averagely greater than those of the single equal-volume non-spherical particles, which the asymmetry factors of the bigger aggregates are 0.055 averagely less than those of the single equal-volume non-spherical particles. The differences in single scattering albedo between the two wavelengths 1.6 μm and 2.0 μm are all much larger for either aggregates or single equal-volume particles, and the biggest difference reaches 0.226. This research has scientific significance for studying the aerosol multiple scattering influencing on the accuracy of CO2 satellite retrieval.


Fabry-Perot cavity locked by using single photon modulation
Wang Jing-Jing, He Bo, Yu Bo, Liu Yan, Wang Xiao-Bo, Xiao Lian-Tuan, Jia Suo-Tang
2012, 61 (20): 204203. doi: 10.7498/aps.61.204203
Abstract +
Fabry-Peort (FP) cavity-based quantum key distribution has some advantages in the phase-coded quantum key distribution (QKD). Locking the frequency of the FP cavity transmission to the frequency of single photon carrying the key information determines the security of QKD. In this paper, we propose an FP cavity locked to a single photon (the mean photon number is about 0.1) frequency using single-photon modulation/demodulation method. The single photon detector working in the Geiger mode is used to detect modulated single photons then direactly demodulated by the lock-in amplifier. The discrete single photon response pulses accumulated fulfills the phase sensitive detection, and the signal-to-noise ratio of signal frequency discrimination is up to 112. The transmission frequency fluctuation of the locked FP is limited to 2 MHz.
Optimal working point of a Brillouin amplifier for a weak input signal in the transient regime
Gao Wei, Lü Zhi-Wei, He Wei-Ming
2012, 61 (20): 204204. doi: 10.7498/aps.61.204204
Abstract +
In order to improve the working performances of a transient Brillouin amplifier, the dependences of the signal-noise-ratio, sensitivity, energy extraction efficiency and signal amplification factor on exponential gain G are numerically studied based on the theoretical model of transient Brillouin amplification including distributed noise, and an optimal working point of a Brillouin amplifier is obtained. Experimental verifications are performed by choosing CS2 and FC-72 as nonlinear media. A frequency-doubled Nd:YAG pulse laser is used. Results show that when the pump pulse lags behind the Stokes signal pulse by an amount of time equal to half the pulse width, Gopt can be set to be above the SBS threshold exponential gain Gth. For a collinear Brillouin amplifier, Gopt is 1.1-1.3 times Gth; while for a non-collinear structure, Gopt can be set to be over 1.3 times Gth. Nearly saturated amplification is achieved.
Numerical implementation of deformation and motion of droplet at the interface between vapor and solid surface with smoothed particle hydrodynamics methodology
Qiang Hong-Fu, Liu Kai, Chen Fu-Zhen
2012, 61 (20): 204701. doi: 10.7498/aps.61.204701
Abstract +
In order to simulate the deformation and motion of droplet at the interface between vapor and solid surface, the smoothed particle hydrodynamics method with continuum surface force model for surface tension is modified in this paper. A surface tension algorithm with boundary conditions of wall adhesion is derived using a new treatment of boundary conditions and a corrective algorithm of particle interface normal. The colours of virtual solid particles are set according to the position of fluid surface to assure that the interface normal of particles at the junction of vapor, fluid and solid phase is normal to the contact line. By introducing Brackbill's treatment of boundary conditions of wall adhesion, the interface normal between fluid particles and some virtual solid particles at the junction of vapor, fluid and solid phase is corrected. However the module of the interface normal is kept constant. Finally, based on the new algorithm, the changing process of fluid surface in a tank, wetting process of a droplet and distortion process of a droplet on solid surface driven by shear flow are simulated. The results are compared with those obtained by volume of fluid method, showing that the new method has higher accuracy and better stability, and it is adapted to deal with the engineering problems such as the deformation and motion of droplets at the interface between vapor and solid surface.
Preliminary behavior studies of edge localized modes on HL-2A
Liu Chun-Hua, Nie Lin, Huang Yuan, Ji Xiao-Quan, Yu De-Liang, Liu Yi, Feng Zhen, Yao Ke, Cui Zheng-Ying, Yan Long-Wen, Ding Xuan-Tong, Dong Jia-Qi, Duan Xu-Ru
2012, 61 (20): 205201. doi: 10.7498/aps.61.205201
Abstract +
The edge-localized modes (ELMs) are often excited in an H-mode plasma, and they are helpful for cleaning the H-mode plasma to sustain a steady state for a longer time by controlling plasma density and exhausting impurities, but energy and particles carried by ELM burst will badly damage the first-wall of fusion device, thus the characteristics of and the control and mitigation of ELM are studied necessarily prior to the basic operational regime operating on ITER. ELMs of different perturbation amplitudes are observed experimentally on HL-2A tokamak. The frequency of small perturbation amplitude ELM decreases with the increase of net heating power, and it is about 300-400 Hz, and energy loss induced by per ELM is usually less than 3% of the plasma energy. The small ELM is type Ⅲ ELM. While for large (type-I) ELM, besides that the energy loss induced by an ELM is generally more than 10%, they also exert an obvious perturbation on other plasma parameters, such as plasma current and electron density, and the tELM may be longer than 30 ms. ELM precursors are poloidally asymmetric, which can be measured by Mirnov probes on the low field side, but not on the high field side; the frequency of ELM precursors is about 45 kHz, and the longest precursors last approximately 10 ms prior to the ELM bursts.
Effect of electron temperature anisotropy on plasma-wall interaction in Hall thruster
Qing Shao-Wei, E Peng, Duan Ping
2012, 61 (20): 205202. doi: 10.7498/aps.61.205202
Abstract +
To further reveal the physical mechanism of the saturated electron temperature which is about 50-60 eV in the discharge channel of Hall thruster, the effect of electron temperature anisotropy (ETA) on plasma-wall interaction in Hall thruster is studied by using a 2D3V particle-in-cell sheath dynamic model. Some important physical parameters such as electron-wall collision frequency, electron energy deposition at wall and the cooling effect of near-wall sheath on channel electron are calculated. Numerical results indicate that the influence of ETA on plasma-wall interaction is neglectable when electron temperature is low. However, when Te>24 eV, the ETA can significantly reduce electron-wall collision frequency, thereby reducing the electron energy deposition at wall and weakening the cooling effect of near-wall sheath on channel electron. It suggests that the anisotropy of electron temperature tends to increase the saturated electron temperature in the discharge channel of Hall thruster through remarkably weakening the interaction between channel electron and wall.
Wall cleanings for pre-treatment on EAST
Li Jia-Hong, Hu Jian-Sheng, Wang Xiao-Ming, Yu Yao-Wei, Wu Jin-Hua, Chen Yue, Wang Hou-Yin
2012, 61 (20): 205203. doi: 10.7498/aps.61.205203
Abstract +
Wall cleaning has been used popularly on tokamaks to reduce impurities and fuel recycling. Since 2008, the plasma facing components of EAST have been all of graphite. Due to the special crystal structure of graphite, high outgassing rate and strong absorption of hydrogen gas are induced. The wall cleaning is in particular important for the pre-treatment before the plasma operation of the machine. In this article, we introduce the wall conditioning system on EAST, and study the removal efficiency of device baking and glow discharge cleaning in different working gases and at different operating parameters. The long duration baking and GDC cleaning in EAST notably reduce the wall outgassing, and impurity radiation. After the cleanings, plasma is easily obtained, which is beneficial for the plasma physics experiment.
Synthesis and photonics characteristics research of CdS:Cu 1D nanostructures
Liu Jun, Zhou Wei-Chang, Zhang Jian-Fu
2012, 61 (20): 206101. doi: 10.7498/aps.61.206101
Abstract +
One-dimensional (1D) Cu-doped CdS nanostructure is synthesized via the chemical vapor deposition. The growth mechanism of Cu-doped CdS nanoarchitecture is disclosed. Some novel photonic properties are discovered. The experimental results indicate that the preparation of Cu-doped CdS 1D nanostructure could be achieved by controlling the experiment conditions. With the effect of doped ions, the nanoarchitecture has different radiant spectra when it is excitated by lasers of different powers. Doping concentration is considered to be an evident factor to affect the position and relative power of the illuminant peaks but not to influence spectrum shapes evidently. The result may be conducible to extending the application of CdS nanoarchitectures in the research field of nanophotonics.
Back-gate bias effect on partially depleted SOI/MOS back-gate performances under radiation condition
Zhou Xin-Jie, Li Lei-Lei, Zhou Yi, Luo Jing, Yu Zong-Guang
2012, 61 (20): 206102. doi: 10.7498/aps.61.206102
Abstract +
According to the partially depleted SOI/MOS device's band gap, starting with the electric field, which is a factor of back-gate charge stack, we combine SOI device capacitance model and flat capacitance model for finding the way to keep electric field at the interface of Si/SiO2, and build a back-gate bias model. For validating the new model, we use alloy-agglomeration at the back gate. After radiation experiments, we compare the results of back-gate effect on NMOS with those on PMOS. It is concluded that as far as NMOS is concerned, negative voltage at back-gate can eliminate the back-gate effect which influence the performance of device, and improves the performance of front-gate. However negative voltage at back-gate makes the performance of PMOS worse. Therefore, when we use the back-gate bias to improve the performance of device, we must consider the performances of NMOS and PMOS and compromise the choice of the voltage which is applied to the back-gate. This research supplies not only a design scheme for hardening back-gate effect of SOI devices under radiation condition, but also a support in theory for integrated circuit design and manufacture, which is used in space.
Elastic properties of β-HMX under extra pressure: a first principles study
Su Rui, Long Yao, Jiang Sheng-Li, He Jie, Chen Jun
2012, 61 (20): 206201. doi: 10.7498/aps.61.206201
Abstract +
The elastic properties of the β-HMX under an extra pressure are studied from density functional theory calculations using the projector augmented wave method. The calculated bulk modulus and shear modulus under zero pressure are 12.7 GPa and 4.4 GPa which are in good agreement with the available experimental results. A detailed analysis of the pressure-dependent stiffness tensor shows that the bulk modulus and shear modulus both increase as the pressure increases. As the pressure goes up to 7 GPa, the lattice is unstable along the direction of the shear strain. This result agrees well with the results of Raman scattering experiment.
Ejecta on Pb surface below and above melting pressure
Chen Yong-Tao, Ren Guo-Wu, Tang Tie-Gang, Li Qing-Zhong, Wang De-Tian, Hu Hai-Bo
2012, 61 (20): 206202. doi: 10.7498/aps.61.206202
Abstract +
In this paper, Asay-F-window diagnostic technology for high density and large mass ejecta measurement is designed. By Asay-F-window technology, the mass and the density-velocity distribution of ejecta from Pb surface are presented. The difference in ejecta between below and above Pb melting pressure is particularly studied. Moreover, the physical causation inducing the ejecting difference is well explained through theory analysis.
Multiphase equation of states of solid and liquid phases for bismuth
Li Ying-Hua, Chang Jing-Zhen, Li Xue-Mei, Yu Yu-Ying, Dai Cheng-Da, Zhang Lin
2012, 61 (20): 206203. doi: 10.7498/aps.61.206203
Abstract +
Element bismuth (Bi) will experience complex phase transitions under high temperature and high pressure, which means significant changes in physical properties, such as density, energy, etc. Multiphase equations of states (EOSs) of both solid and liquid phases for Bi are presented. The EOSs are based on the three-term expression for Helmholtz free energy, where the ion vibration free energy is evaluated from the mean field potential model we recently proposed. The calculated results show that our multiphase EOSs can well reproduce the experimental data, including phase diagram, isotherms of solid phases, density measurements of liquid phase and shock-wave compression data, which proves the rationality of the parameter values and the universal nature of this model.
Numerical study of shock-induced phase transformation of cerium under low pressure
Pan Hao, Hu Xiao-Mian, Wu Zi-Hui, Dai Cheng-Da, Wu Qiang
2012, 61 (20): 206401. doi: 10.7498/aps.61.206401
Abstract +
The dynamic responses of cerium under low pressure, including γ →α phase transition, are numerically studied in this paper. The velocity profiles of shock experiments show that the transition process between the two phases is smooth and there is no obvious disconnection between the two plastic waves of the particle velocity profiles. Three important problems in the dynamic response, including constitutive model, Hugoniot relation and phase transition/reversal, are discussed. A multi-phase equation of state and constitutive model of Ce are presented in this paper after analyzing the typical wave configuration of cerium under the shock loading and releasing. The dynamic phase transition model is built for the non-equilibrium course in the phase γ → α transition induced by shock wave. The numerical results accord with the experimental data of the plane impact tests, indicating that the dynamic phase transition model can describe the dynamic response under low pressure of cerium more reasonably.
Non-Gaussian analysis of noise for metal interconnection electromigration
He Liang, Du Lei, Huang Xiao-Jun, Chen Hua, Chen Wen-Hao, Sun Peng, Han Liang
2012, 61 (20): 206601. doi: 10.7498/aps.61.206601
Abstract +
Based on scattering theory, the resistance of polycrystalline interconnection originates mainly from vacancies and voids scattering at grain boundary. Through using the free volume concept, the scattering process at grain boundary is simulated, and a non-Gaussian model of noise is establised. The model shows the earlier electromigration noise is gaussian, through electromigration process, noise turns non-Gaussian, which reflects the change of dynamic mechanism. Bicoherence coefficient is used to characterize the non-Gaussian noise. Finally, experimental result validates the model.
Theoretical study on boundary distributions and flow-metal heat transfer during melt treatment by cooling sloping plate
Guan Ren-Guo, Zhao Zhan-Yong, Huang Hong-Qian, Lian Chao, Chao Run-Ze, Liu Chun-Ming
2012, 61 (20): 206602. doi: 10.7498/aps.61.206602
Abstract +
In this paper, according to the principle of grain refining and semisolid forming by cooling sloping plate process, the distributions of boundary layers during melt treatment by the sloping plate are studied, and mathematic models of heat transfer and cooling rate are established. Calculation results show that the change time from laminar flow to turbulent flow decreases with the increases of the sloping angle and initial flow velocity. The thickness of temperature boundary layer decreases with the increases of initial flow velocity. The effect of the sloping angle on the thickness of temperature boundary is small. The boundary layer thicknesses of the both temperature and velocity increase with the increase of the flow distance gradually. In the laminar flow region, the thickness of the temperature boundary layer is much bigger than that of the velocity boundary layer, while the two layers coincide with each other in the turbulent flow zone. The melt cooling rate on the sloping plate and the melt thickness have an inverse proportion relationship between each other. When the initial flow velocity is lower than 1 m/s the cooling rate increases along the sloping plate gradually. While the initial flow velocity is 1 m/s, the cooling rate dose not change approximately. However, when the initial flow velocity is larger than 1m/s the cooling rate decreases along the sloping plate gradually. The melt cooling rate on the cooling sloping plate is between 100 K/s and 1000 K/s, which belongs to meta-rapid solidification scope.
The optimization of lithography process on the deep muti-stepped surface
Sun Li-Yuan, Gao Zhi-Yuan, Zou De-Shu, Zhang Lu, Ma Li, Tian Liang, Shen Guang-Di
2012, 61 (20): 206801. doi: 10.7498/aps.61.206801
Abstract +
In this article, we investigate the problems existing in the lithography on the deep multi-stepped surface. Different photoresist thicknesses above and under the step are measured in experiment. The relationship between step height and photoresist thickness is discussed and numerically described. Based on the description of Beer model about the light absorption coefficient, the curves of different light transmittances at different times are analysed. Reasons why the light transmittance changes with time are explained, and the light absorption coefficient is believed to be related to photoresist thickness. On this basis, the lithography process is optimized. The patterns with narrow line-width under the deep step on the wafer are obtained.
Ordered mesoporous antireflective films for 1053 nm high power pulse laser
Sun Jing-Hua, Xu Yao, Yan Liang-Hong, Lü Hai-Bing, Yuan Xiao-Dong
2012, 61 (20): 206802. doi: 10.7498/aps.61.206802
Abstract +
Single-layer silica films are prepared via evaporation-induced-self-assembling process using triblock copolymer surfactant F127 as template and tetraethoxysiliane as precursor under acidic condition. After ammonia pretreatment, the as-deposited films undergo a thermal decomposition process to remove the surfactant, and the mesopores are formed in film. Three techniques are used to characterize the mesoscopic structure of film, i.e., grazing-incidence X-ray diffraction, nitrogen adsorption/desorption and transmission electron microscopy. The results indicate that the film has an ordered cage-like porous structure and can be indexed as the body-centered-cubic arrangement. The optical properties of the films are investigated via ellipsometry and UV-VIS-NIR transmission spectrometer. The transmitance can reach up to 99.9% at 1053 nm wavelength. The refractive index varies with the molar ratio of F127/Si. Atomic force microscope is used to probe the surface morphology, and the surface roughness Ra is 1.2 nm. A 1053 nm laser is used to determine the laser damage threshold of film and all the thresholds are higher than 25 J· cm-2 (1 ns). This method has a potential application in the preparation of large-aperture antireflective films.
Ge and Nb co-doped TiO2 films with narrow band gap and low resistivity prepared by sputtering
Luo Xiao-Dong, Di Guo-Qing
2012, 61 (20): 206803. doi: 10.7498/aps.61.206803
Abstract +
Ge and Nb co-doped anatase TiO2 films are prepared by using radio frequency magnetron sputtering. The structures, resistivities and band gap properties of the films, which depend on Ge and Nb doping amounts, sputtering power and annealing temperature, are discussed. It is found that the band gap and resistivity of TiO2 film can be simultaneously tailored by co-doping with Ge and Nb. With doping volume fractions of 6% Nb and 20% Ge, the resistivity of the film can be reduced from 104 Ω/cm to 10-1 Ω/cm, and the band gap from 3.2 eV to 1.9 eV. After annealing, the Ge and Nb co-doped TiO2 film shows not only a lower resistivity but also a stronger absorption for visible and infrared light. As a result, Ge and Nb co-doped TiO2 film with adjustable band gap and resistivity can be prepared with magnetron sputtering by choosing proper Ge and Nb doping amounts and annealing conditions.
Investigation of polarons in perovskite manganites
Yi Ding, Qin Wei, Xie Shi-Jie
2012, 61 (20): 207101. doi: 10.7498/aps.61.207101
Abstract +
Perovskite manganites have aroused a great interest in their outstanding electrical and magnetic properties, but the characteristics of carriers in these materials are still under debate. According to the Mn-O chain, we build a one-dimensional tight-binding model to study the characteristics of charge carriers in manganites. It is obtained that at doping concentration x=0.5, the system shows a ferromagnetic state and the energy bands of spin up and spin down are completely splitted. A gap exists between valence band and conduction band, and all the electronic states are extended. With further doping, a localized electronic state appears, which we call a polaron. Accompanied with the electronic state, local distortions of the lattice and deep levels appear in the gap. The depth of the polaron increases with the doping quantity of electrons. It is also found that the polaron is spin polarized and has a maximum electronic charge of 0.621 e in the present parameters, beyond which the polaron will be divided into two separate states called solitons.
Electronic structures and dielectric properties of BaCoxZn2-xFe16O27 from first principles
Ri Chung-Ho, Li Lin, Qi Yang
2012, 61 (20): 207102. doi: 10.7498/aps.61.207102
Abstract +
On the basis of the crystal structure model of BaCoxZn2-xFe16O27 , their ground electronic states and dielectric properties have been investigated using the generalized gradient approximation plus Hubbard U approach. The co-substitutions of cobalt and zinc cause the electrical conductivity of BaFe18O27 to change from a half-metallic to semiconductive. With the increase of Co content x, the energy gap of BaCoxZn2-xFe16O27 increases but the lattice constants and the magnetic moment of the unit cell decrease. The calculations of dielectric constants show that the static dielectric constants increase with x, lie in a range of 6.2-7.2 and appear to be anisotropic. Through the Born electric charge analysis it is shown that the polarization of Co and Zn itself has little effect on the polarization of the material and the main polarization may be related to the polarization of the iron and oxygen ions, caused by the crystal distortion.
First-principles study of N-doped and N-V co-doped anatase TiO2
Xu Jin-Rong, Wang Ying, Zhu Xing-Feng, Li Ping, Zhang Li
2012, 61 (20): 207103. doi: 10.7498/aps.61.207103
Abstract +
The ground state atomic configurations and electronic structures of anatase TiO2, N-doped TiO2 and N-V co-doped TiO2 are studied by the projector augmented wave method and the generalized gradient approximation plus U (Hubbard correction) (GGA+U) based on the density functional theory. The results indicate that the volume of cell is slightly larger and the ground state configuration has no change significantly for N-doped TiO2, but the symmetry of cell is broken and the position of V atom is more close to N atom after co-doping with N and V. The band gap of anatase TiO2 is calculated to be 3.256 eV, which is in agreement with experimental value (3.23 eV). When N is doped, the gap is reduced by more than 0.4 eV. but for N-V co-doped system, the gap reduces to 2.555 eV. Moreover, the acceptor level and donor level, which can be formed between the valence band maximum and the conduction band minimum because of co-doping with N and V, are more favorable to the separation of photoelectron-hole pairs and reduce the rate of recombination. Therefore, the co-doping of anatase TiO2 with N and V can effectively improve the photocatalytic performance of anatase.
Influence of magnetic anisotropy thermoelectric effect on spin-dependent devices
Chen Jia-Luo, Di Guo-Qing
2012, 61 (20): 207201. doi: 10.7498/aps.61.207201
Abstract +
While researching the thermoelectric effect of the nanocontact, we find that the thermoelectric voltage between both ends of the "Γ"-shaped Ni wire changes significantly by applying an external magnetic field, which we attribute to the influence of magnetic anisotropy of Ni wire. The effect of the external magnetic field always produces an extra force whose direction goes against the temperature gradient. And the extra force clearly corresponds to the magnetic field and temperature difference between both ends of the Ni wire. These results suggest that during studying spin-dependent devices, the testing methods and the configuration of magnetic material need to be noticed seriously in order to avoid interfusing additional electromagnetic signals which may bring about a miscarriage of justice to the experimental results.
Room-temperature ultrafast spin dynamics in colloidal CdSe quantum dots
Li Xia, Feng Dong-Hai, Pan Xian-Qun, Jia Tian-Qing, Shan Lu-Fan, Deng Li, Sun Zhen-Rong
2012, 61 (20): 207202. doi: 10.7498/aps.61.207202
Abstract +
Time-resolved Faraday rotation spectroscopy is used to study the spin coherence in colloidal CdSe quantum dots at room temperature. Spin dephasing time and relevant dephasing mechanisms are analyzed in different transverse magnetic fields. The exciton spin-dephasing time is 102 ps in a zero magnetic field, which is affected by hyperfine interaction between electron and nuclear spins. In a transverse magnetic field of 250 mT, the exciton spin-dephasing time becomes 294 ps due to the fact that the presence of magnetic field makes the nuclear spin fluctuations unimportant. Further increasing the external magnetic field, the spin dephasing time becomes shorter. The magnetic field dependence of the exciton spin dynamics shows that the spin dynamics is dominated by the inhomogeneous dephasing in high magnetic fields (≥ 250 mT).
Analysis of the light absorption enhancement in polymer solar cell with TiO2 optical spacer
Li Guo-Long, Li Jin, Zhen Hong-Yu
2012, 61 (20): 207203. doi: 10.7498/aps.61.207203
Abstract +
The thickness of the active layer is limited by its low carrier mobility in the polymer solar cell composed of the blend bulk-heterojunction formed by conjugated polymer as donor material and fullerene as acceptor material, which can affect the light absorption in the polymer solar cell. TiO2 inserted into polymer solar cell as optical spacer can redistribute the electromagnetic field inside the device and enhance the light absorption of it. In this paper, light intensity and absorption inside the devices with different thicknesses of P3HT:PCBM layer and TiO2 layer are calculated based on transfer matrix method. Theoretical analysis shows that inserting 10 nm TiO2 into the device can increase 16.3% light absorption, simultaneously thinning the active layer by 25 nm and the thickness of active layer will not apparently reduce the dissociation rate of the excitons. With the device structure of ITO (100 nm)/PEDOT:PSS (40 nm)/P3HT:PCBM/TiO2/LiF (1 nm)/Al (120 nm), the optimal thicknesses of the active layer and TiO2 are 75 nm and 10 nm respectively, which is confirmed by the experimental results from the devices with three different structures.
The light absorption enhancement in polymer solar cells with periodic nano-structures gratings
Li Guo-Long, Li Jin
2012, 61 (20): 207204. doi: 10.7498/aps.61.207204
Abstract +
The thickness of the active layer is limited by its low carrier mobility in the polymer solar cell composed of the blend bulk-heterojunction formed by P3HT as donor material and PCBM as acceptor material, which can affect the light absorption in the polymer solar cell. Nano-structure gratings inserted into polymer layer can redistribute the electrical field inside the device and improve its light absorption. Two-dimensional electrical field distributions inside the polymer solar cell are simulated with the grating period of 1 μ, fill ratio of 0.5 and incident wavelengths of 500 nm and 700 nm based on finite difference time domain. The light absorptions by the devices with different grating depths and fill ratios are calculated based on rigorous coupled wave. The analysis illustrates that light spots occur in the device due to the light diffraction caused by the gratings and the light absorption is increased by 4.2% with a grating fill ratio of 0.5, depth of 10 nm and an incident light wavelength of 512 nm. In experiment, nano-structure gratings are introduced into the devices by the micro-printing technology with PDMS and polymer solar cell is structured with ITO/ PEDOT:PSS gratings/ P3HT:PCBM/ LiF/ Al. The experimental results from the planar and the grating devices prove that the nano-structure gratings embedded in PEDOT:PSS layer increase the power conversion efficiency by 31%.
Investigation on the current collapse effect of AlGaN/GaN/InGaN/GaN double-heterojunction HEMTs
Yu Chen-Hui, Luo Xiang-Dong, Zhou Wen-Zheng, Luo Qing-Zhou, Liu Pei-Sheng
2012, 61 (20): 207301. doi: 10.7498/aps.61.207301
Abstract +
A series of AlGaN/GaN/InGaN/GaN double-heterojunction high-electron-mobility-transistors (DH-HEMT) is fabricated with GaN channel layer thicknesses from 6 nm to 20 nm by two-dimensional (2D) numerical simulations. A new idea for optimizating of DH-HEMT structure is proposed. The hot electron effect and self-heating effect are investigated by using hydrodynamic model. Current collapse and negative differential conductance are observed to be directly relevant to GaN channel layer thickness. DH-HEMT with thicker GaN channel layer can confine electrons better in channel, which significantly diminishes the penetration ability of hot electrons from channel layer to buffer layer under high voltage. Increasing the thickness of GaN channel layer appropriately can effectively restrict current collapse and negative differential conductance, and consequently improve device performance under high voltage condition.
Effects of B additive on structure and magnetic properties of Co-Zr-Mo alloys
Hou Zhi-Peng, Zhang Jin-Bao, Xu Shi-Feng, Wu Chun-Ji, Wang Zi-Han, Yang Kun-Long, Wang Wen-Quan, Du Xiao-Bo, Su Feng
2012, 61 (20): 207501. doi: 10.7498/aps.61.207501
Abstract +
The phases and magnetic properties of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5, and 4.0) are studied by X-ray diffraction analysis and magnetic measurements. Proper addition of Ti could improve the magnetic properties of Co-Zr alloy significantly. The largest value of Hc=7.0 kOe (1 Oe =79.5775 A/m) is obtained in the Co77Zr16Mo5B2 melt-spun ribbon. The grain size of Co5Zr phase decreases with the increase of B content, which contributes significantly to the enhancement of exchange-coupling effect. The coercivity values of the Co77Zr18-xMo5Bx (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are affected mainly by the grain size of the Co5Zr phase. The coercivity value first increases and then decreases with the decrease of the Co5Zr phase. On the other hand, the coercivity mechanisms of Co77Zr18-xBxMo5 (x=1.0, 1.5, 2.0, 2.5) melt-spun ribbons are found to be of the pinning type.
Synthesis and magnetic properties of CoFe2O4 and MnFe2O4 nano composites
Gao Ruo-Rui, Yu Wei, Fei Chun-Long, Zhang Yue, Xiong Rui, Shi Jing
2012, 61 (20): 207502. doi: 10.7498/aps.61.207502
Abstract +
Highly dispersed granular nano-composite material of CoFe2O4 and MnFe2O4 with an average size of 20 nm is synthesized through thermal decomposition. The soft-hard magnet exchange-spring effect is observed in magnetization measurements at low temperatures, and is found to be strongly affected by the temperature of the reaction and the composition ratio between soft and hard magnetic phases. Magnetization measurements at different temperatures show that at 20 K, the saturation magnetization increases significantly, which is attributed to the freezing of the spin-glass like state at the surface of the nano-composite material. A Henkel Plot measurement on our sample shows that for the dispersed composite material of CoFe2O4 and MnFe2O4, the dipole interaction is dominant among magnetic interactions.
A band Jahn-Teller effect in the martensitic phase transition of the Heusler alloy Mn2NiGe
Luo Li-Jin, Zhong Chong-Gui, Dong Zheng-Chao, Fang Jing-Huai, Zhou Peng-Xia, Jiang Xue-Fan
2012, 61 (20): 207503. doi: 10.7498/aps.61.207503
Abstract +
The changes of crystal structure, magnetic structure, electronic structure in the martensitic phase transition for magnetic shape memory alloy Mn2NiGe are calculated by first-principles method. The results show that in the martensitic phase transition for Mn2NiGe, there is produced a Jahn-Teller distortion, in which the c-axis becomes longer but a-axis and b-axis turn shorter, forming an elongated octahedral geometry. There is a significant change in magnetic moment for Mn ion in the centre of octahedron, but a little change happens to the Ni and Ge ions that are regarded as a ligand. The energy levels of eg and t2g are split by redistributing the density of states for d electrons and so opening a pseudogap near the fermi energy due to lattice distortion.
Dielectric properties of CaCu3Ti4O12 ceramics prepared by a simplified coprecipitation method
Jia Ran, Gu Fang, Wu Zhen-Hua, Zhao Xue-Tong, Li Jian-Ying
2012, 61 (20): 207701. doi: 10.7498/aps.61.207701
Abstract +
Precursor powder of CaCu3Ti4O12 is prepared by a simplified coprecipitation process, in which an optimum reaction condition with ammonium acetate is used as buffer solution and pH=3.0 is proved by X-ray diffraction and scanning electron microscope. The CaCu3Ti4O12 ceramics samples are prepared by sintering the calcined powder at different temperatures (1040℃-1100℃). It is found that higher sintering temperature of CaCu3Ti4O12 ceramics will lead to lager grain size, higher dielectric constant and lower dielectric loss. The dielectric loss of CaCu3Ti4O12 ceramics is suggested to be due to DC electric conductivity, low-frequency relaxation loss and high-frequency relaxation loss. The low-frequency and high-frequency relaxations are related to grain boundary and oxygen vacancy defects respectively.
Influences of Y- and La-dopant on the thermal conductive properties and dielectric relaxation of Al2O3-based ceramics
Wu Jun-Bo, Tang Xin-Gui, Jia Zhen-Hua, Chen Dong-Ge, Jiang Yan-Ping, Liu Qiu-Xiang
2012, 61 (20): 207702. doi: 10.7498/aps.61.207702
Abstract +
Al2O3 ceramics doping with Y3+ and La3+ are synthesized by conventional solid state reaction method. The structures, thermal conductivities properties and the effects of sintering temperature on the electrical properties of the samples are measured. X-ray diffraction results indicate that all the ceramics are formed to be of pure solid solution when the samples are sintered at 1500℃. Thermal conductivities of Al2O3 ceramics reach up to 8.60 W/(m· K). All the ceramics show temperature-stable dielectric characteristics. Typical dielectric relaxation behaviors are observed in Y- and La-doped Al2O3 ceramics, and the relaxation mechanism is also analyzed.
The influence of central metal Ga atom on triplet-state dynamics and singlet oxygen generation of Corrole
Shao Wen-Li, Lin Yong-Feng, Lin Feng-Can, Peng Kai-Mei, Zhang Lei, Wang Hui, Liu Hai-Yang, Ji Liang-Nian
2012, 61 (20): 207801. doi: 10.7498/aps.61.207801
Abstract +
In this paper, the triplet-state transient absorption spectra and the dynamic processes of 5, 15-bis (pentafluorophenyl)-10-(phenyl) corrole, 5, 10, 15-tris (pentafluorophenyl) corrole and their corresponding free-base corroles are measured by the laser flash photolysis technique. The measurement results show that the wavelength region of triplet-state absorption of these corroles ranges from 440 nm to 540 nm and the absorption peak wavelength of each sample is 450 nm. The insertion of metal Ga atom into corrole ring shortens the triplet lifetime of corrole under anaerobic condition and makes triplet lifetime longer under aerobic condition, which reduces oxygen quenching rate. The steady-state emissions of singlet oxygen of these corroles are also measured by the infrared luminescence method. The results show that the insertion of metal Ga atom makes singlet oxygen quantum yield of corroles slightly decrease. The results indicate that the heavy atom effect generated from metal Ga atom influences the triplet-state dynamics and singlet oxygen generation of corrole.
Stability of organic light-emitting device
Zhang Xin-Wen, Hu Qi
2012, 61 (20): 207802. doi: 10.7498/aps.61.207802
Abstract +
Organic light-emitting device (OLED) has well-recognized advantages in simple structure, low-driving voltage, flexibility, large area and availablity. It shows tremendous commercial applications in optical communication, information display and solid-state lighting, and has been one of the most attractive projects in optoelectronic information field over the last decade. Since 1987, OLED has rapidly developed, its brightness and efficiency has reached the practical demands. However, one of the main challenges to the industrialization is the stability of the device. In this paper, some of the extrinsic and intrinsic degradation mechanisms in OLEDs are summarized and discussed, such as the dark-spot formation, morphological instability of organic thin film, metal-atom diffusion, Alq3 cationic and positive charge accumulation. After that, we summarize the approaches to obtaining the long lifetime OLED. Finally, some perspectives on the stability of OLED are proposed.
Polarization dependence of carrier-induced refractive index change
Miao Qing-Yuan, Cui Jun, Hu Lei-Lei, He Jian, He Ping-An, Huang De-Xiu
2012, 61 (20): 207803. doi: 10.7498/aps.61.207803
Abstract +
The influences of carrier density, tensile strain, well width and barrier material component on the refractive index changes of TE mode and TM mode in quantum well are analyzed. Then the quantum wells having characteristics of both large refractive index change (on the order of 10-2) and low polarization dependence (on the order of 10-4) in a wavelength range from 1530 nm to 1570 nm are designed by comprehensively integrating the parameters above. The result shows that almost the same spectra of refractive index change can be acquired by integrating different groups of parameters.
Microstructure of spray-formed FGH4095 after static recrystallization
Zhang Yu, Ge Chang-Chun, Shen Wei-Ping, Qiu Cheng-Jie
2012, 61 (20): 208101. doi: 10.7498/aps.61.208101
Abstract +
For the study of solution heat treatment characteristic of spray-formed FGH4095 after near iso thermal forging, the superalloy specimens, which have been hot isostatically pressed (HIPed) and forged with a 75% compression ratio, are solution heat treated at 1120℃, 1140℃ and 1160℃ for 10, 20 and 40 min respectively, and oil quenched. The characteristics of static recrystallization process including grain size and precipitated phase after heat treatment are discussed. The results show that the temperature of solution heattreatment has a great influence on the microstructure. In heat treatment at 1120℃ the recrystallization is slow, and the necklace structure is formed due to the localized incomplete recrystallization; at 1140℃ for 40 min, the static recrystallization is basically completed, the average grain size is about 8 μm; at 1160℃, the recrystallization is finished in 10 min, and the grains grow up to about 18 μm.
High frequence structure simulator simulation and performance analysis for nearfield and wide band electric coupling antenna
Yang Yong, Sun Wei-Qiang, Zhuang Qian-Wei, Feng Tao, Xu Sheng-Yong, Xie Si-Shen
2012, 61 (20): 208401. doi: 10.7498/aps.61.208401
Abstract +
Electric field coupling antenna is a new type of antenna that can be used in high speed wireless communication at a very short distance. It is the working antenna for TransferjetTM technology promoted by Sony Corporation. In this paper, we use the high frequency structure simulator to design a typical antenna of this kind with parametric structures. We analyze the influences of the length (Ls) and width (Ws) of the short stub, the height (H) of coupling electrode on the performance of the antenna corresponding to the centre frequency and bandwidth. We also analyze the effects of the distance (d) and angle () between two antennas and the size of coupling electrode (Lc) on transmission loss. Finally, we design an antenna satisfying the technology standards of TransferjetTM, thus demonstrate its working performance.
A time-dependent nonlinear theory and simulation for gyroklystron amplifier
Ma Jun-Jian, Zhu Xiao-Fang, Jin Xiao-Lin, Hu Yu-Lu, Li Jian-Qing, Yang Zhong-Hai, Li Bin
2012, 61 (20): 208402. doi: 10.7498/aps.61.208402
Abstract +
A time-dependent nonlinear theory for gyroklystron amplifier is presented. The theory includes a time-dependent description of the electromagnetic fields and a self-consistent analysis of the electrons. The generalized telegrapher equations represent the electromagnetic fields. The equations of motion of the electrons are described in the framework of the guiding-center approximation. All trajectories are calculated and used as current sources for the fields. The nonlinear theory of interaction is investigated in which mode coupling is taken into account in varying wall radius. Transverse velocity of the electrons from the gyroklystron amplifier satisfies Gaussian distribution. Distribution model of the velocity spread in the gyroklystron amplifier beam-wave interaction is established. A code for the self-consistent nonlinear beam-wave interaction is developed based on the presented theory. The electron beam-wave interaction of a Kα band gyroklystron amplifier is thoroughly studied and analyzed by the code. Numerical verification using MAGIC simulation is also given. The numerical results are in good agreement with the self-consistent nonlinear simulations.


Response properties of NbN superconductor nanowire for multi-photon
Zhou Yu, Zhang La-Bao, Jia Tao, Zhao Qing-Yuan, Gu Min, Qiu Jian, Kang Lin, Chen Jian, Wu Pei-Heng
2012, 61 (20): 208501. doi: 10.7498/aps.61.208501
Abstract +
In this paper, we study the response properties of multi-photon of NbN superconductor nanowire in superconducting single photon detector (SSPD). We measure the NbN nanowire device's DC characteristics and detection probability for single and multi-photon light pulse signal at a temperature of 3.5 K. The measured results show that the superconducting transition current of superconductor nanowire decreases as light irradiation intensity increases. The photon number detected by SSPD is derived from the slope of detection probability versus light intensity. We find that the detected photon number increases as superconducting nanowire bias current decreases. Moreover, based on quantum optics and hotspot theory, we analyze the mechanism of the multi-photon response of superconducting nanowire semi-quantitatively. This result may be of benefit to understanding SSPD and developing the SSPD with the capability of resolving photon number.
Study on the light extraction efficiency of GaN-based light emitting diode by using the defects of the photonic crystals
Yue Qing-Yang, Kong Fan-Min, Li Kang, Zhao Jia
2012, 61 (20): 208502. doi: 10.7498/aps.61.208502
Abstract +
Many studies have shown that the photonic crystals and surface nanostructures can improve the light extraction efficiency of light emitting diode (LED). The defects and disorders exist in photonic crystals inevitably as the manufacturing technology limitations, and so the light extraction efficiency of LED will be changed correspondingly. In this work we perform a simulation study on defects and disorder of photonic crystals by the finite-difference time-domain (FDTD) method, and we speed up the FDTD by GPU acceleration technology. Simulation results show that a small number of defects in photonic crystals LED do not reduce the LED light extraction efficiency. Instead, the light extraction efficiency of LED will be increased by adding some defects into the photonic crystals. We give a detailed analysis of its physical mechanism. We design a kind of photonic crystals with defects, and its light extraction efficiency achieves 1.6 times that of the perfect photonic crystals.
Changes of entropy and power spectrum in circadian rhythm for heart rate variability signals
Li Jin, Liu Da-Zhao
2012, 61 (20): 208701. doi: 10.7498/aps.61.208701
Abstract +
Physiologic systems generate complex fluctuations in their output signals that reflect the underlying dynamics. In order to detect the effect of circadian rhythm for heart rate variability signals, we apply base-scale entropy method and power spectral analysis to the 24-hour heart rate variability signals. The results show that 1) such profound circadian- and pathologic-dependent changes are accompanied by changes in base-scale entropy and power spectral distribution, but by little changes in approximate entropy; 2) the circadian regulating ability of vagal nerve is clearly decreasing for congestive heart failure subjects; 3) the base-scale entropy is more sensitive than spectral analysis method to distinguishing wake/sleep states and identifying patterns generated from healthy and pathologic states, meanwhile, the base-scale entropy changes reflect corresponding changes in autonomic nerve outflow. With the suppression of vagal tone and dominance of sympathetic tone in congestive heart failure subjects, there are more variabilities in the m-words form π due to the trends in the data. So the higher base-scale entropy belongs to congestive heart failure subjects. With the decrease of sympathetic tone during sleep, the base-scale entropy drops in both healthy and congestive heart failure subjects. Finally, in order to further investigate the effect of series length, we calculate the base-scale entropy for different length series and find that the series length nearly has no influence on the result.
Study of the stable components in extended-range forecasting for the coming 10-30 days during the snow storm event in November 2009
Wang Kuo, Feng Guo-Lin, Sun Shu-Peng, Zheng Zhi-Hai
2012, 61 (20): 209201. doi: 10.7498/aps.61.209201
Abstract +
In this paper, we extract stable components in extended-range forecasting for the coming 10-30 days by using empirical orthogonal function analysis and some other methods during the snow storm event in November 2009. At the first time, stable components in extended-range forecasting for the coming 10-30 days can be divided into two parts: climatic stable components and abnormal stable components, by contribution rate analysis, similarity coefficient and so on. We combine climatic stable components and low-pass filter components to obtain climatological background field. The results show as follows. 1) The circulation pattern of climatological background field persists for a long time and changes slowly. It provides climatological background for the weather event mainly. 2) The climatological background field can indicate the fluctuations of semi-permanent or permanent center with a large space scales. The climatological background field cooperates well in vertical divisions. 3) The abnormal stable components reflect abnormal circulation, and the circulation pattern of abnormal stable components corresponds to the snow storm event in November 2009 well on the time scale. The climatological background field represents circulation pattern background and the abnormal stable components represent the relative strength of weather system.
The preliminary research about the precursory signals of abrupt climate change based on critical slowing down phenomenon
Wu Hao, Hou Wei, Yan Peng-Cheng, Feng Guo-Lin
2012, 61 (20): 209202. doi: 10.7498/aps.61.209202
Abstract +
In recent years, critical slowing down phenomenon has shown great potentials in the area of disclosing whether complex dynamic system tends to critical cataclysm. Based on the concepts of critical slowing down, the observed data of pacific decadal oscillation (PDO) index and the national average monthly temperature are processed in this article to study the precursory signals of abrupt climate change. Take the abrupt climate change in a period from the late1970s to the early 1980s for example, the variances and autocorrelation coefficients which can characterize critical slowing down are calculated separately. The results show that the PDO index and the national average monthly temperature both have obviously a critical slowing down phenomenon before the abrupt climate change takes place, which indicates that critical slowing down phenomenon is a possible early warning signal for abrupt climate change. The introduction of critical slowing down theory into abrupt climate change precursory signals and study on it have practical significance and important scientific value for thoroughly understanding the abrupt climate change and for catching the precursory signals of abrupt climate change.
The interaction of H2D+ with thin solid foils and the detection of its structure
Zhu Zhou-Sen, Yuan Xue-Dong, Miao Jing-Wei, Shi Mian-Gong, Liao Xue-Hua, Fang Cai-Jin
2012, 61 (20): 209203. doi: 10.7498/aps.61.209203
Abstract +
The Interaction between molecular ion H2D+ and ultra-thin solid film is reported for the first time. The importance of H2D+ in the areas such as astrophysics is stated and the study on H2D+ of recent years is outlined. The formation mechanism for the H2D+ under laboratory conditions is also analysed. The structural pattern of H2D+ and the mean internuclear separation are determined using Coulomb explosion technique. Once again, the existence of wake effects in the interaction of molecular ions with solid is confirmed and three-body wake effect module is used to determine the geometric structure of H2D+. Finally, the unusual structure of the wake of energy spectrum for the heavier ions in the H2D+ Coulomb explosion is discussed.
Properties of rapidly rotating hybrid stars with non-Newtonian gravity
Fu Hong-Yang, Wen De-Hua, Yan Jing
2012, 61 (20): 209701. doi: 10.7498/aps.61.209701
Abstract +
The properties of rapidly rotating hybrid stars are calculated and discussed with an equation of state considering non-Newtonian gravity (described by the Yukawa contribution). The said properties include the mass-radius relationship, the Kepler rotating frequency, the moment of inertia, the gravitational redshift and the ratio of the rotational energy to the gravitational energy. It is shown that at the Kepler frequency, the maximum stellar mass increases up to about 20% compared with that from the static model at the same central density. It is also shown that for a rapidly rotating hybrid star, the rotation has an obvious influence on the bulk properties, such as the mass-radius relationship, the moment of inertia, the ratio of the rotational energy and gravitational energy, but has a faint effect on the polar gravitational redshift.
Research of the navigation accuracy for the X-ray pulsar navigation system
Wang Peng, Zhao Bao-Sheng, Sheng Li-Zhi, Hu Hui-Jun, Yan Qiu-Rong
2012, 61 (20): 209702. doi: 10.7498/aps.61.209702
Abstract +
In order to improve the navigation accuracy of the X-ray pulsar navigation system, in this paper we propose a constant fraction timing method based on the low-pass filter to measure the arrival time of the X-ray pulse in X-ray pulsar navigation. According to the technical scheme, the timing accuracies and dead times of original peaking timing and the improved constant fraction timing are measured. Experimental results indicate that the timing accuracy and the dead time of the peaking timing system are 18 ns and 4750 ns, the timing accuracy and the dead time of the constant fraction timing system are 0.78 ns and 105 ns. The timing accuracy and the dead time of constant fraction timing system are significantly improved compared with those of the peaking timing system. In the X-ray pulsar navigation system, the cumulative pulse profile of the X-ray pulse is constructed in the two different timing systems through measuring the arrival time of the X-ray photon. Experimental results indicate that compared with using the peaking timing system, the cumulative pulse profile of the X-ray pulse using the improved constant fraction timing system is improved obviously, therefore, the navigation accuracy could be improved by using the constant fraction timing system.