Vol. 59, No. 6 (2010)
2010, 59 (6): 3720-3726. doi: 10.7498/aps.59.3720
With considering Bose-Einstein condensates to be confined in a periodic dichromatic optical lattice, Bloch energy band structure and Landau-Zener tunneling behaviors of the first and second band gaps are studied in this paper. It is shown that when the relative phase between the two lattices increases from 0 to π, the width of the first band gap in the Bloch energy band increases, while the width of the second band gap decreases. Meanwhile, it is found that the depth and the relative phase between the two lattices have both an important effect on Landau-Zener tunneling properties.
2010, 59 (6): 4014-4017. doi: 10.7498/aps.59.4014
It is revealed in the present paper that the reflectance around the defect mode of one-dimensional defective photonic crystal (PC) in an asymmetric structure approaches to 1, while the phase-shift depends on the number of the coupled-defect layers, i.e., the phase shift is 2π for every sub-peak of the defect mode. When the defect layer is a temperature sensitive material, very small change of temperature will cause a significant phase change. Secondly, it is demonstrated that the relationship of phase and temperature has a linear range. According to the above characteristics, a highly sensitive temperature sensor is designed based on the phase property of photonic crystal. Moreover, this principle of PC phase sensing can be extended to study other sensors, such as the two-dimensional PC, which is suitable for optical integration.
2010, 59 (6): 3627-3632. doi: 10.7498/aps.59.3627
We study the motion of a particle in a bistable potential in the presence of single frequency signal and dual-frequency signal, and give the approximate analytical relationship between response peak-to-peak value and driven peak-to-peak value of the bistable system under the control of dual-frequency signal. The paper also reveals a peculiar phenomenon of the non-linear system, that is frequency coupling of different frequencies and the energy infiltration from the frequency of input to the other. The analysis is carried out from the view point of dynamics mechanism and the frequency spectrum distribution. It deepens the understanding of the mechanism of stochastic resonance in the bistable system. The results of numerical simulation prove the validity of theoretical analysis.
Finding conserved quantities of three-dimensional second-order nonlinear coupled dynamics systems by the extended Prelle-Singer method
2010, 59 (6): 3633-3638. doi: 10.7498/aps.59.3633
In this paper, the extended Prelle-Singer (P-S) method is employed to finding the conserved quantities of three-dimensional second-order nonlinear coupled dynamic systems, the determining equations, the constraint equations of integral factors and the general expression of conserved quantities are obtained. The calculation method of integral factors is disscussed. Finally, two conserved quantities of three-particles Tada crystal lattice problem are found by extended P-S method.
2010, 59 (6): 3639-3642. doi: 10.7498/aps.59.3639
The Lie-Mei symmetry and conserved quantities of Appell equation for a holonomic mechanical system are studied. On the basis of the Appell equation, we first obtain the Lie symmetry and the Mei symmetry for the equation and the conserved quantities deduced from them, then the definition and the criterion for Lie-Mei symmetry of Appell equation are presented. Lastly, the Mei conserved quantity and the Hojman conserved quantity are deduced from the Lie-Mei symmetry. An example is given to illustrate the application of the result.
2010, 59 (6): 3643-3647. doi: 10.7498/aps.59.3643
The Hojman method for construction of the Birkhoffian representation is discussed. By using Hojman method, the Birkhoff symmetry is restudied. A new idea of this symmetry is presented. A new proof of the Birkhoff conserved quantity is given. It is shown that the Birkhoff symmetry depends only on the Birkhoff tensors. An example is given to show the application of the result.
Precise periodic solutions and uniqueness of periodic solutions of some relative rotation nonlinear dynamic system
2010, 59 (6): 3648-3653. doi: 10.7498/aps.59.3648
The precise periodic solution and uniqueness of periodic solutions of some relative rotation nonlinear dynamical system possessing linear rigidity and nonlinear damping force and forcing periodic force is investigated. Firstly, the stability and uniqueness of limit cycles of a kind of autonomous nonlinear dynamical system are discussed. Secondly, the necessary condition of uniqueness of periodic solutions of the system is presented by using qualitative analysis method. The precise periodic solution of the system is obtained under certain conditions.
2010, 59 (6): 3654-3662. doi: 10.7498/aps.59.3654
Smoothed particle hydrodynamics(SPH) is a Lagrangian meshfree particle method, and has been widely applied to different areas including incompressible or pseudo-incompressible flows with multiphase interfaces and moving boundaries. In this paper, an instability problem has been identified when the conventional SPH method is applied to modeling the Poiseuille flow problem at long-term simulations. It is found that this instability resulted from the particle inconsistency inherent to the SPH method, which originates from the discrete particle approximation and is a fundamental cause for poor approximation accuracy. A new particle approximation approach has been used to restore the particle consistency. We show that this particle consistency restoring approach can produce stable solutions for both regular and irregular particle distributions even at long-term simulations.
2010, 59 (6): 3663-3667. doi: 10.7498/aps.59.3663
A new solution for classical monochromatic short-crested waves in finite water depth is presented by including the ambient uniform currents. With the aid of the original classical solution, we obtain a complete solution and show a variety of interaction mechanisms for the second-and third-order solution structures.
2010, 59 (6): 3668-3673. doi: 10.7498/aps.59.3668
We extend the homotopy analysis method to solving the discrete modified KdV equation. The bright soliton solution expressed by a series of exponential functions is obtained, which agrees well with the exact solution. It indicates the validity and great potential of the homotopy analysis method in solving complicated nonlinear problems.
Stochastic functional analysis of propagation and localization of cylindrical wave in a two-dimensional random medium
2010, 59 (6): 3674-3685. doi: 10.7498/aps.59.3674
Propagation and localization of cylindrical wave in a two-dimensional isotropic and homogeneous random medium is studied. By expanding the random permittivity fluctuation in the form of a Wiener integral equation in the frequency domain, and representing the wave fields by a linear combination of outgoing and incoming waves, the scalar Helmholtz equation is solved by means of stochastic functional approach to obtain the analytical expression of cylindrical wave. The spatial wave energy distribution is derived to demonstrate the localization phenomenon, and the localization length is also calculated. Compared with the waves in non-random medium, the wave transfer equation between plane wave and cylindrical wave in random medium shows an additional exponential factor to indicate the modulation effects due to the medium randomness in both the amplitude and the phase. Numerical simulations are presented to illustrate the functional dependence of the localization phenomenon.
Convergence analysis of quantum-behaved particle swarm optimization algorithm and study on its control parameter
2010, 59 (6): 3686-3694. doi: 10.7498/aps.59.3686
Based on the analysis of particle swarm optimization algorithm, the particle is described in the quantum space and the potential energy field model is created. And then according to the swarms gregariousness, the quantum-behaved particle swarm optimization (QPSO) algorithm is derived. Within the framework of random algorithms global convergence theorem, the convergence of QPSO algorithm is discussed and is proved to be a kind of global convergence algorithm. Three kinds of control strategy are proposed for the unique parameter of QPSO algorithm and they are tested on five benchmark functions. According to the test results, some conclusions concerning the selection of the parameter are drawn.
2010, 59 (6): 3695-3699. doi: 10.7498/aps.59.3695
The Dicke model displays quantum chaotic dynamic properties in the without-rotating-wave approximation. We explore the dynamic properties of the single-particle coherence in Dicke model by using the first-order temporal correlation function and numerical simulation. The results reveal that the first-order temporal correlation function decays very rapidly when the initial coherent state is centered in chaotic regions, but rather slowly when the initial coherent state is centered in regular regions. This indicates that the single-particle coherence is highly sensitive to initial states, and the classical chaos suppresses quantum coherence. The mean single particle coherence during the evolution is studied, and a better quantum-classical correspondence is obtained. Finally, the dynamics of single-particle coherence in the whole phase space is investigated, which reveals the chaotic and regular structures of the phase space more clearly.
2010, 59 (6): 3700-3703. doi: 10.7498/aps.59.3700
This paper introduces the Wheeler-Dewitt (W-D) equation in the five-dimensional R+R2 theory of gravity, and gets solutions of the W-D equation by separation of variables. Using the Kaluza-Klein theory, the Robertson-Walker metric is extended to the five-dimensional spacetime. With the field equations of the spacetime, the relationship between energy and the cosmological term can be obtained.
Complexity of multi-architecture type of deterministic weighted generalized Farey organized network pyramid
2010, 59 (6): 3704-3714. doi: 10.7498/aps.59.3704
Three types of deterministic weighted generalized Farey organized network pyramids(so-called WGFONP-1,WGFONP-2, WGFONP-3) are constructed, and the topological characteristics (degree distribution, average path length, clustering coefficient, assortative coefficient and so on) of network pyramids are studied by theoretical and numerical analyses. Using Farey sequence as determinacy, randomicity and hybrid weights of network nodes, we calculate and fit the strength distribution and the weight distribution of the network pyramids, as well as tentatively reveal the complexities and the diversities of the WGFONP-1,WGFONP-2 and WGFONP-3. These results can conduce to the understanding of complexities and diversities of a number of practical networks.
2010, 59 (6): 3715-3719. doi: 10.7498/aps.59.3715
Using the methods of numerical simulation and quantum statistics, based on the thermodynamic quantities of Fermi gas trapped in a general external potential, we studied the thermodynamic properties of a relativistic Fermi gas trapped in hard-sphere potential, gave the analytical expressions of the energy and heat capacity of the relativistic Fermi system, and analyzed the influence of the relativistic effect on the energy and heat capacity. The results showed the energy and heat capacity of the relativistic Fermi system is larger than those of the nonrelativistic case. The larger the relativistic eigenvalue, the lower the change temperature of heat capacity. As the temperature rises, the larger the relativistic eigenvalue, the greater the energy.
The mean first-passage time for a cancer development system driven by colored cross-correlated noises
2010, 59 (6): 3727-3732. doi: 10.7498/aps.59.3727
In this paper, the mean first-passage times for a cancer development system driven by colored cross-correlated noises are investigated. Based on the Novikov theorem and the Fox approach, the approximate Fokker-Planck equation and the explicit expressions of the mean first-passage time are derived. Numerical results show that: if the coupling strength between the two noises is negative, the mean first-passage time is a decreasing function of the two noise intensities, but an increasing function of the correlation time; if the coupling strength between the two noises is positive, then the value of the monotonic mean first-passage time versus the additive noise intensity depends on the transition direction. And in addition, the mean first-passage time is a non-monotonic function of the multiplicative noise intensity, but a decreasing function of the correlation time.
Control and analysis of a third-order nonautonomous ferroresonance chaotic circuit with a transformer
2010, 59 (6): 3733-3739. doi: 10.7498/aps.59.3733
In this paper, the chaos dynamics behavior of a third-order nonautonomous ferroresonance chaotic circuit with single phase transformer has been analyzed and simulated. We drew the conclusion that there is only a nonlinear flux-controlled inductance in this circuit, which has been investigated and simulated by using a fourth-order autonomy improved system. We confirm that the chaotic behavior exists in this circuit by computer simulation and circuit experiment. A simple method of controlling chaos is proposed by varying the linear capacitance parameters.
Function projective synchronization of quntum cellular neural network and Lorenz hyperchaotic system with uncertain parameters
2010, 59 (6): 3740-3746. doi: 10.7498/aps.59.3740
In the paper, function projective synchronization of quantum cellular neural network with uncertain system parameters and Lorenz hyperchaotic system is studied. The adaptive controllers are proposed to make the states of two different chaotic systems asymptotically synchronized up to a desired scaling function. We also present the relevant proof by applying Lyapunov stability theory. Moreover, linear independence of coefficient vector of uncertain system parameters in quantum cellular neural network is analyzed theoretically, which aims to realize the unknown parameter identification and estimation. Numerical simulations are made to show the effectiveness of the function projective synchronization and parameter estimation.
2010, 59 (6): 3747-3755. doi: 10.7498/aps.59.3747
Stability and dynamic behavior of negative differential conductivity in thyristors are studied in this paper, which aims to clarify the mechanism of chaotic phenomena in the thyristor. Firstly, a spatio-temporal model of the thyristor is established, and the boundary condition of the system is obtained based on the linear stability analysis. The results show that the instability of thyristor is not only determined by the characteristics of negative differential conductivity, but also depends on the external conditions. Computer simulation is made to verify the proposed view for different external control parameters. The theoretical results are also confirmed by experimental measurements. So, the mechanism of chaotic phenomena in thyristor is clearly explained.
2010, 59 (6): 3756-3762. doi: 10.7498/aps.59.3756
The converter topologically conjugates with its symbol time series. The research of converter can be reduced to the research of symbol time series, and more common results can be gotten. The complexity of converter is studied based on arithmetic complexity of symbol time series, characteristics are gotten from its inner structure. Compared with statistics complexity, arithmetic complexity can describe working cycling and catastrophe point, thus the theoretical basis for understanding the complexity characteristics of converter is provided.
2010, 59 (6): 3763-3768. doi: 10.7498/aps.59.3763
Measure synchronization is an interesting phenomenon found in coupled Hamiltonian systems. By taking Poincaré section analysis, it is found that the separatrix crossing behaviors is the dynamical mechanism behind measure synchronization transition in both time-discrete and time-continuous coupled Hamiltonian systems.
Dynamical modeling and analysis of current mode controlled switching converter with ramp compensation
2010, 59 (6): 3769-3777. doi: 10.7498/aps.59.3769
Buck, boost and buck-boost converters are three basic switching DC-DC converters. Current mode controlled switching DC-DC converters have two boundaries in a wide circuit parameters variation range. Based on the ramp up and ramp down slopes of the inductor current before and after the turn on of power switch for switching DC-DC converters, a unified model of the current mode controlled switching DC-DC converters with ramp compensation is established in this paper. Only three parameters appear in this model after dimensionless normalization, from which the dynamical behaviors of switching DC-DC converters in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) can be effectively illustrated. By utilizing the proposed unified model, two orbit state shifting borderline equations are derived, from which three operation state regions namely the stable period-one region, CCM robust chaos region, and DCM weak chaos and strong intermittence region, of switching DC-DC converters can be determined. The two-dimensional parameter bifurcation diagrams of switching DC-DC converters and circuit experimental observations of current mode controlled buck converter verify the analysis results of the partitioning of operation state regions by two borderline equations.
2010, 59 (6): 3778-3784. doi: 10.7498/aps.59.3778
The Monte-Carlo method is used to investigate the effect of random noise on empirical mode decomposition of the nonlinear signals. The simulation results show that, the influence of noise is obvious for the low-level intrinsic mode function and unabvious for the high-level intrinsic mode function. With the increase of the intensity of white noise, the intrinsic mode function pure noise level will increase. When the intrinsic mode function pure noise levels is subtracted from the noise signal, about 80% of the noise influence will be reduced. The noise signals largest Lyapunov exponent is smaller than that of the noise-free signal.
2010, 59 (6): 3785-3793. doi: 10.7498/aps.59.3785
Memristor, which is a nonlinear resistor with memory function, is the fourth fundamental two-terminal circuit element besides the resistor, capacitor and inductor. A memristor based oscillator circuit, directly derived from Chuas oscillator by replacing Chuas diode with a flux-controlled memristor characterized by a smooth monotonically increasing nonlinearity, is presented in this paper. By using conventional dynamical analysis method, the dynamical behaviors of the new smooth memristor oscillator with the variations of circuit parameters and initial conditions are investigated. The research results demonstrate that the dynamical behavior of the smooth memristor oscillator not only depends on the circuit parameters, but also closely depends on the initial conditions of the circuit. Different from general chaotic systems, some novel nonlinear phenomenas, such as the transient chaos and state transitions and so on, can be found in the proposed system.
Analysis of coupling nonlinear dynamical behaviors between two stages in a cascade power-factor-correction converter
2010, 59 (6): 3794-3801. doi: 10.7498/aps.59.3794
A cascade power-factor-correction (PFC) converter is a nonlinear system cascaded by a PFC converter and a direct current-direct current (DC-DC) converter. According to the nonlinear model of the cascade PFC converter derived, we simulate the interstage coupling nonlinear dynamical behaviors of the system, and the simulation results are verified experimentally. The results shows that with the decrease of the PFC output capacitance the bifurcation may appear, which results in the change of the DC-DC output voltage. Likewise, the dynamical behavior of the PFC stage may change with DC-DC load resistance. When the duty ratio of the DC-DC stage becomes saturated, the coupling process between the PFC stage and the DC-DC stage is very complicated.
2010, 59 (6): 3802-3809. doi: 10.7498/aps.59.3802
For the periodically excited Chens system, when there exists order gap between the natural frequency of the original system and the excited frequency, dynamical behaviors associated with the two different time scales can be observed. Bifurcations of the system have been presented by considering the variation of the excited term. Fast-slow analysis is employed to explore the evolution of the system with different parameter conditions, which gives different types of bursters such as symmetric fold bursting, symmetric subHopf bursting and symmetric Hopf-homoclinic bursting, as well as the bifurcation mechanism. Furthermore, the influence of both the amplitude and the frequency of the excitation on the bursting is discussed in detail.
2010, 59 (6): 3810-3816. doi: 10.7498/aps.59.3810
A novel method of bandwidth enhancement of a chaotic carrier from a semiconductor laser transmitter is studied by cross-phase modulation (XPM). And a physical model of laser dynamics is presented under the condition of XPM effect of optical fiber path. A frequency detuning formula with optical dual-feedback and XPM effect is deduced. The nonlinear phase shift arisen from XPM effect impacts on the gain and bandwidth enhancement factor of the laser. The second order nonlinear effect of the fiber enriches the varieties in the amplitude and the phase of the laser while the nonlinear phase shift produces a lot of new frequencies, which spread the bandwidth. Numerical results reveal that, with XPM effect, the new bandwidth is the quadruple of the bandwidth without XPM effect, and the relaxation oscillation frequency of the chaotic laser is increased to 285 times that of the laser without XPM effect. It is found that the enhancement of the chaotic bandwidth depends evidently on the optical fiber length, the power input into the optical fiber, the mirror reflectance and the second order nonlinear coefficient.
2010, 59 (6): 3817-3823. doi: 10.7498/aps.59.3817
Based on the lattice hydrodynamic model with bidirectional pedestrian flow, the lattice hydrodynamic model which considered the interaction of the next-nearest-neighbor pedestrians was proposed in this paper. By the linear stability analysis, the stability condition was obtained. By nonlinear analysis, the modified Korteweg-de Vries equation to describe the density wave of pedestrian congestion was given. Furthermore, numerical simulation was carried out to examine the performance of such a model and it shows consistency with the theoretical analysis results.
2010, 59 (6): 3824-3830. doi: 10.7498/aps.59.3824
An improved coupling lattice model of two-lane traffic flow is proposed by taking into account the effect of the two-lane coupling and lane changing. And the lane changing rate of traffic flow is modified. The analysis of the modified lane changing rate shows that it is in better accordance with the real traffic than the previous ones. The linear stability condition of the extended model is obtained by using the linear stability theory. Numerical simulation also shows that our model can better reproduce the lane changing of traffic flow than previous ones by considering the information of two-lane coupling interaction. And there is unavoidable effect on the two-lane traffic flow from the coupling effect between the two lanes.
2010, 59 (6): 3831-3840. doi: 10.7498/aps.59.3831
In this paper, we propose a new cellular automaton model for studying the temporary bottleneck induced by a special accident. The difference in driver behavior between before and after the accident occurrences is taken into account to investigate the effect of the bottleneck on driving character. Simulation results show that the new model can reproduce some complicated traffic phenomena, such as the asymmetrically lane-changing and grabbing the entrance on the bottleneck, and a reasonable asymmetrically gear-alternating control regulation can enhance the outflow of the bottleneck.
2010, 59 (6): 3841-3845. doi: 10.7498/aps.59.3841
In this article, a global routing method is proposed for weighted scale-free networks. To bypass the central nodes and alleviate the congestion, it chooses the best route according to the minimum value of the cost function which is based on the node strength. Simulation results show that the network capacity is improved more than 10 times by our method than by the shortest path strategy at the cost of a slightly growth in the average path-length.
2010, 59 (6): 3846-3850. doi: 10.7498/aps.59.3846
In this paper, the electron transport through a double-barrier InAs /InP nanowire heterostructure between two reservoirs at different temperatures and chemical potentials is studied. The transport probability of electron is obtained by using transfer matrix method, and the heat flow carried by the electrons transfer is derived. The performance characteristic curves of the refrigerator are plotted by numerical calculation. The influence of the barrier width and well width on the operation performance of the refrigerator is analyzed. It is found that when the well width is fixed, the position of resonance energy level increases while the width of resonance energy level decreases as the barrier width increases, and for the same bias the larger the barrier width, the smaller the cooling rate, while the larger the relative coefficient of performance. When the barrier width is fixed, for the same bias, the relative coefficient of performance will decrease as the well width increases. The curve obtained when both the well width and barrier width vary, is similar to the curve obtained when the well width varies and barrier width is fixed. Thus we can see that cooling rate and the relative cooling factor are mainly affected by the well width.
2010, 59 (6): 3851-3855. doi: 10.7498/aps.59.3851
Baraba′si has proposed a queue model of the human behavior. In this paper we compare the Baraba′si results and Va′zquez results. We proposed a model of human behavior dynamics by taking into consideration the service-time distribution. We obtained exact results for the model by calculating the waiting time distribution and sojourn time distribution of active tasks. The results show that the waiting time distribution of the model is a power-law distribution with exponent 2 for the highest priority first selection protocol. This exponent approximates to degree exponent 2.1 observed in Hsue-Shen Tsien correspondence pattern.
2010, 59 (6): 3856-3862. doi: 10.7498/aps.59.3856
The thermal wave phenomenon induced by the ultrafast laser heating in metal films has been studied by different experimental methods in the past. In our experiment, a femtosecond laser pump-probe system is used to study the ultrafast energy transport between the electrons and phonons. The experiments showed a weak wave peak in the electron temperature curve following the main peak caused by the laser pulse. The reproducibility of the results has been tested for different laser intensities and different film samples. This weak peak in electron temperature could be explained by the reflection of the thermal wave from the rear surface. The experimental results agree with the theoretical curves calculated by the hyperbolic two-step model. The speed of the thermal wave is about 5×105 m/s and the electron relaxation time is about 60 fs.
A new method of polarization measurement based on the novel polarization interference imaging spectrometer
2010, 59 (6): 3863-3870. doi: 10.7498/aps.59.3863
A new spaceborne remote sensing principle and method of two-dimensional object polarization measurement, which is based on the novel polarization interference imaging spectrometer (NPIIS) using the field of view compensated Savart polariscope, is presented. Without modification of the optical system of the NPIIS, the Stokes vector, the degree of polarization and polarization direction expressions are derived by measuring the intensity of one pixel on the image plane after three rotations of the polarization interferometer. The method and principle is verified by computer simulation, and the results appear to be well consistent with the theoretical analysis. The research extends the measurement function of the interference imaging spectrometer. Compared with the existing imaging spectrometers which can measure the two-dimensional image information and one-dimensional spectral information, another method to acquire the object information by measuring the polarization state is developed.
ATOMIC AND MOLECULAR PHYSICS
Theoretical study of radiative recombination and the sub-sequent radiative decay processes in highly charged Au ions
2010, 59 (6): 3871-3877. doi: 10.7498/aps.59.3871
Using multi-configuration Dirac-Fock method and the corresponding packages GRASP92 and RATIP, as well as the newly developed RERR06, we have calculated the radiative recombination (RR) spectra for capturing a continuum electron into n| (n=4—8, l=0—3) subshell of Ni-like Au51+, Cu-like Au50+ and Zn-like Au49+ ions and their corresponding radiative decay spectra. The calculated RR spectra reproduce the experimental spectra excellently. It was found that for the Ni-like Au51+, Cu-like Au50+ and Zn-like Au49+ ions, the probability of capturing a free electron to n=4 subshell is the largest. Furthermore, the main characteristics of the relative decay spectra is the domination of the lines from the captured electrons radiatively decaying from the n=4 subshell.
Energies, fine structures, and Auger widths of the high-lying triply excited states of 2S(m) and 2D(m) (m=2—7) for the “hollow atom” lithium
2010, 59 (6): 3878-3884. doi: 10.7498/aps.59.3878
The relativistic energies and fine structures of the high-lying triply excited states 2l2l′nl″ 2S(m) and 2D(m) (m=2—7) for the “hollow atom” lithium are studied using the saddle-point variational method and the saddle-point complex-rotation method, including the mass polarization and relativistic corrections. The partial Auger widths and the total widths are also calculated. By the discussion of relativistic effect, we recalibrated the configurations of 2S(7) , 2D(6) and 2D(7).
Influence of the collision energy and isotopic variant on the stereodynamics of reaction H+BrF→HBr+F
2010, 59 (6): 3885-3891. doi: 10.7498/aps.59.3885
Quasi-classical trajectory calculations are carried out for the exothermic reaction H+BrF→HBr+F on the latest London-Eyring-Polanyi-Sato potential energy surface. The product angular distributions which reflect the vector correlation are calculated. Polarization dependent differential cross sections which are sensitive to many photoinitiated bimolecular reactions are presented in the center of mass frame. The calculated results suggest that the product rotational polarization becomes stronger as collision energy increases and the products were mainly backward scatteried. By comparing the product polarization of reactions D+BrF→DBr+F and H+BrF→HBr+F, the isotope effects have also been revealed.
Cross section invertion between double electron capture and transfer ionisation in low energy collision of highly charged ion(4≤q≤7) with He
2010, 59 (6): 3892-3896. doi: 10.7498/aps.59.3892
Based on the potential parameter Ω, which was defined as energy deposits ratio of incidence ion with target ion after double electron capture, the selection rule between double electron capture and transfer ionization of helium target induced by Aq+ (q=4,5,6,7) ions was studied. It is found that there is a cross point for the cross-section ratio curve of double electron capture and transfer ionization at Ω=10, and for ΩΩ≥10 the transfer ionization is a key reaction channel of double electron transfer.
Optimized structure and thermodynamic properties of atomic clusters in the framework of the extended Hubbard model
2010, 59 (6): 3897-3904. doi: 10.7498/aps.59.3897
By using a numerical exact diagonalization method, the properties of atomic clusters with atom number N=5 and N=6 are investigated in the framework of the extended Hubbard model. The optimized structure and the corresponding total spin S are obtained both as a function of Hubbard onsite interaction U, nearest-neighbor Coulomb repulsion V and filling number of electrons. Results show that with V increasing, the optimized structure of cluster turns into a chain or star-like structure with fewer bonds. The thermodynamic properties are also analyzed based on the distribution of energy levels of cluster with an optimized structure.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (6): 3905-3911. doi: 10.7498/aps.59.3905
Two inversion methods for electromagnetic scattering, the deterministic gradient search method and the Monte Carlo random search method， are proposed in this paper. Firstly, the fundamental principles of the two methods are introduced. Inversion properties including the positioning capability of the scattering body, inversion accuracy and inversion time of the two methods are analyzed and compared. Simulation results demonstrates that the deterministic gradient search method can be used for scattering body positioning and the results using Monte Carlo random search method have high-precision at the same time have high speed. Successive applications of both methods fully realize the advantages of the two methods and improve the inversion result.
Ocean duct inversion from radar clutter using variation adjoint and regularization method (Ⅱ): inversion experiment
2010, 59 (6): 3912-3916. doi: 10.7498/aps.59.3912
On the theoretical basis, using simulated and measured radar clutter data, we tested the inversion algorithm respectively. In simulated radar clutter data inversion, inversion results with and without considering the regularization item are discussed. In real radar clutter data inversion, dependence of the inversion results on the precision of the first guess values is discussed, in which the first guess values are either emperical model values or statistics inversion results, respectively. Finally, the advantages and disadvantages are compared between the variation adjoint regularization algorithm and the traditional statistical inversion algorithm, pointing out the direction of improvement in future work.
2010, 59 (6): 3917-3923. doi: 10.7498/aps.59.3917
The characteristics of Q-switched Nd:YAG laser induced damage to fused optical fibers has been investigated experimentally. A scheme of laser induced damage to optical fiber in a vacuum chamber was presented and carried out.With this scheme, the air pressures on the input face of optical fiber was reduced to 10—100 Pa, laser-induced breakdown on the optical fiber end face was significantly suppressed, the breakdown threshold increased to 185 times that in the atmosphere. The damage morphology of optical fiber end face was analyzed, which was the result of the combined actions of laser pulses standing wave and ablation. The existence of a large number of defects on or under the fiber end face reduces the anti-laser-induced damage ability of the optical fibers. Under the vacuum condition, another damage mode——the fiber “entry” segment damage occurred. This “entry” segment damage mode occurred at 5—30 mm distances from the input end face of optical fiber, the blasting damage area was 1—3 mm long along the fiber core axis. That the initial reflection of laser beam at the interface of fiber cladding and core causes laser focusing which induced the entry damage, was proved by theory and simulations.
2010, 59 (6): 3924-3929. doi: 10.7498/aps.59.3924
In this work, the terahertz transimission spectrum through a one-demensional (1D) photonic crystal made from doped semiconductor n-GaAs/polycarbonate is studied by the transfer-matrix method. We show that, compared with most photonic crystals made from two different dielectrics, the doped semiconductor/dielectrics 1D photonic crystals can not only form the photonic gap, but also enhance the terahertz transmission through n-GaAs. We also propose and research a terahertz modulator based on the 1D photonic crystals, the transimitted terahertz waves through which can be modulated by different carrier densities in the semicondutor by varying the applied voltage.
2010, 59 (6): 3930-3935. doi: 10.7498/aps.59.3930
A phase plate was fabricated on a quartz crystal using ion beam etching technique with a predesigned angular phase mask, which can modulate the phase of light illuminating the phase plate by 0 and π rad. Analyzed the field distribution of the diffracted light by angular diffraction theory, which shows the resulting beam is a superposition of two Laguerre-Gaussian(LG) beams with opposite topological charges. Illuminating the phase plate using the expanded beam with diameter 4 mm generates the superposition of two LG beams with the same radian index p=0 and opposite angular index l=20 and l=-20 By increasing the aperture of the illuminating beam, LG beam with higher p index can be acquired, while the l index remains opposite.
Experimental study on all-normal-dispersion mode-locked fiber laser with optimal spectral filtering position
2010, 59 (6): 3936-3941. doi: 10.7498/aps.59.3936
Employing nonlinear polarization rotation, an all-normal-dispersion mode-locked fiber ring laser was constructed, in which a fiber filter with 10 nm bandwidth was used in the cavity to provide the additional self-amplitude modulation. The important role of the filter position plays in the high-chirped pulse shaping in the laser has been experimentally demonstrated by choosing different locations of the filter in the cavity. A mode-locked pulse series, with the averaged power of 922 mW, output pulse duration of 62 ps, and pulse repetition frequency of 266 MHz, corresponding to the pulse energy of 35 nJ, was obtained in the optimized filter position under a pump power of 320 mW. By the numerical simulation, the propagation dynamics of pulses in the three cases of spectral filter (SF) position in the cavity are obtained and analyzed. The optimal location of the SF is found, which is in agreement with our experimental result.
High power narrow linewidth single-frequency line-polarized fiber amplifier based on master-oscillator power amplifier technology
2010, 59 (6): 3942-3947. doi: 10.7498/aps.59.3942
High power single-frequency (SF) lasers are of great significance in science, industry, and defense applications such as gravitational wave detection, free apace optical communication, range finding, lidar, parametric wavelength conversion in resonant cavities. We report on a high power single-frequency linearly polarized radiation with a nearly diffraction-limited beam quality by use of a two-stage fiber master-oscillator power amplifier system. The master oscillator is an SF distribution feedback fiber laser with polarization maintaining (PM) and single mode (SM) fiber pigtailed output power of about 10 mW at 1064 nm, and its line-width is of 20 kHz. This light power is amplified to about 1 W by the first stage of all-fiber SM/PM amplifier and then seeded at the second stage of high power main amplifier with large mode area (LMA) ytterbium-doped fiber (YDF). The pumping diode laser of the main amplifier is fiber-coupled (the core diameter is 400 μm and corresponding numerical aperture is 022) with a max emitting power as high as 190 W at 976 nm. By employing the co-pump configuration with a space coupling efficiency of about 85%, we demonstrate that the power output from the LMA/PM YDF (core diameter is 20 μm, inner cladding diameter is 400 μm) reaches 128 W and its corresponding overall slope-efficiency is 85% of the launched pump power. The beam profile is diffraction-limited and linearly polarized with a polarization extinction ratio over 12 dB. There is observed neither amplified spontaneous emission nor stimulated Brillouin scattering phenomenon, which means that the substitution of the pump source with the more powerful one can further enhance power output if LMA YDF with a larger core size, shorter fiber length and higher doping efficiency is used.
Influence of current aperture size on threshold in double oxide confined vertical-cavity surface-emitting lasers
2010, 59 (6): 3948-3952. doi: 10.7498/aps.59.3948
In this paper, the coupling equations for electric field, carrier density, optical-field and temperature are simulated self-consistently in double oxide confined vertical cavity surface emitting laser therefore the characteristics threshold are studied. The potentials near the oxide layers and the activity region are obtained and the effect of current aperture edge is simulated. The distributions of threshold injected current density, carrier density, fundamental mode and temperature for different radii of double oxide confined current aperture are obtained. An appropriately confined radius of current aperture for minimum threshold injected current is found, and the structure of vertical cavity surface emitting laser is designed.
Effective radius of curvature of partially coherent flat-topped beam propagating through atmospheric turbulence
2010, 59 (6): 3953-3958. doi: 10.7498/aps.59.3953
The analytical expression for the effective radius of curvature R of a partially coherent flat-topped beam propagating through atmospheric turbulence is derived. It is shown that R decreases due to turbulence. However, position zmin where R reaches its minimum will change due to the turbulence when the strength of turbulence is strong enough. The effective radius of curvature R increases with the increase of beam coherence parameter β when the strength of turbulence is weak, while R decreases with β increasing when the strength of turbulence is strong. The R decreases slowly with the increase of beam order M(N). The R of partially coherent flat-topped beam with larger β and smaller M(N) is more sensitive to turbulence. In addition, in free space the wavefront of partially coherent flat-topped beam can be regarded as a spherical surface in the far-field, which is independent of the beam parameters. However, in turbulence the effective radius of curvature depends on the beam parameters in the near field and also in the far field.
Radiation force of highly focused cosine-Gaussian beam on a particle in the Rayleigh scattering regime
2010, 59 (6): 3959-3964. doi: 10.7498/aps.59.3959
The radiation force of highly focused cosine-Gaussian beam acting on a particle in the Rayleigh scattering regime is theoretically investigated in this paper. The results show that it is feasible to utilize cosine-Gaussian beam in optical trapping system. Unlike the conventional optical beams, the cosine-Gaussian beam could simultaneously trap particles whose refractive index is lower or higher than the ambient.
2010, 59 (6): 3965-3972. doi: 10.7498/aps.59.3965
Based on nonlinear Kerr effect model of erbium-doped ring fiber laser, the influences of pump power and nonlinear coefficient on chaotic bandwidth are investigated. The results indicate that, with fixed nonlinear coefficient, the bandwidth of the chaos increases first and then decreases with the increasing of pump power. Fixing the pump power at 01 W, the chaotic bandwidth rises up to 153 GHz with the nonlinear coefficient increased to 45 W-1km-1. On further increasing the nonlinear coefficient the chaotic bandwidth is reduced gradually.
2010, 59 (6): 3973-3978. doi: 10.7498/aps.59.3973
When collinear dual-color intense laser pulses are overlapped in time, a strong coupling interaction occurs between their plasma filaments. Due to the cross phase modulation, strong non-linear effects are generated and the spectrum width of the ultrafast ultraviolet (UV) pulse is further broadened. The original UV pulse with a bandwidth of 15 nm and energy of 045 mJ is obtained by tripling the frequency of a Ti:sapphire laser system. The UV pulse and the near inferred pulse of 71 mJ can induce plasma filaments separately after focusing within an argon gas cell, leading to an obvious modulation of the UV spectrum. The full width at half maximum of UV spectrum increases to 64 nm which is 4 times the width of spectrum before focusing and 25 times the width of single ultraviolet filament broadening. In this experiment, we mainly study the frequency spectrum evolution of dual-color co-filament in argon gas under the condition of different time delays, coupling locations and gas pressures. Optimizing these factors can yield a valid approach to achieving extremely ultrafast pulses in the range of ultraviolet.
2010, 59 (6): 3979-3985. doi: 10.7498/aps.59.3979
High-power and high-repetition-rate multi-wavelength femtosecond pulses are obtained by the nonlinear frequency up-conversion of large mode area photonic crystal fiber femtosecond system. Effects of focal length on the transverse mode of second harmonic are theoretically analyzed and experimentally demonstrated, showing that the longer the focal length, the better the mode quality. Under the condition of fundamental average power of 218 W, pulse duration of 110 fs and repetition rate of 50 MHz, generation of the second, third and fourth harmonics are achieved at the wavelengths of 520, 347, and 261 nm, with the maximum average power of 105, 47, and 214 W, respectively. The conversion efficiencies of frequency doubling and frequency tripling are 482% and 216%, and the conversion efficiency of frequency quadrupling from the second harmonic is 204%. Pulse duration of the fourth harmonic pulse is 408 fs, as measured by the cross-correlation technique.
Experimental study of slow light based on four-wave mixing wavelength conversion and dispersion in optical fibers
2010, 59 (6): 3986-3991. doi: 10.7498/aps.59.3986
Slow light based on four-wave mixing (FWM) wavelength conversion and dispersion is experimentally studied. The FWM bandwidth of the highly nonlinear fiber is measured to be 40 nm, which is also the slow light tunable bandwidth. A 34 ns delay of 500 MHz sine signal is achieved in standard single mode fiber, and 198 ns delay of short pulses with 100 ps width is achieved in dispersion compensation fiber (DCF). An advancement of 209 ns for the 100 ps short pulses is also achieved in the DCF. The method to increase the slow light delay is discussed, and large delay up to microseconds is expected when wideband FWM wavelength conversion and large dispersion fibers are used. The expected large delay will help us realize high efficiency fiber delay lines and all-fiber buffers.
2010, 59 (6): 3992-4000. doi: 10.7498/aps.59.3992
Based on the nonlocal nonlinear Schrdinger equation, which is the evolution equation of propagation of spatial soliton in the nonlocal media, the pulsating propagation of spatial solitons in one-dimensional strongly nonlocal optical lattice are researched numerically by the split-step Fourier method. The pulsating propagation period of spatial soliton is analyzed for different parameters of propagation, such as the initial energy of the beam, the nonlocality degree, the modulation degree of lattice, the period of the transverse modulation and the asymptotic rate of the longitudinal modulation of linear refractive index. And the inherent physical mechanisms of pulsating propagation of spatial soliton are discussed for the different parameters of lattice structure. Furthermore, the controllable switching behavior of spatial optical soliton has been achieved in the strongly nonlocal optical lattice with longitudinal modulation of linear refractive index.
2010, 59 (6): 4001-4007. doi: 10.7498/aps.59.4001
The expressions of average refractive index in a helix pitch of ferroelectric liquid crystal（FLC） were derived by theoretical approximation computation of the helix structure at chiral smectic C phase of FLC. A conclusion that FLC molecules in a helix pitch as a whole can be considered as a model of nematic liquid crystal in terms of the expressions of average refractive index was obtained. When the thickness of FLC with a vertical alignment along the helical axis is integer times long as the helix pitch, FLC molecules can be considered as a group composed of nematic liquid crystal models. The comparisons of experiment results of ZLI-3654 FLC with 5CB nematic liquid crystal confirmed the above conclusion. The theory and experiment are in good agreement. Theoretical guidance and a deeper understanding can be provided by this theory for preparation of deformed helix FLC and vertical alignment deformed helix FLC devices, as well as application of ferroelectric liquid crystal.
2010, 59 (6): 4008-4013. doi: 10.7498/aps.59.4008
Transmission properties of the system of dielectric spheres periodically mounted in a metal slab are investigated. The electromagnetic wave can enter the dielectric spheres by tunneling effect and exists as a cavity mode. The surface plasmon polaritons can occur at certain frequency because of the periodically mounted dielectric spheres, which effectively modulate the metal surface to a periodical structure. When the frequencies of the cavity mode and that of the surface plasmon polaritons are close to each other, the coupling between them can greatly enhance both the electromagnetic modes, which results in a very strong electric field in the dielectric spheres of the upper layer. This strong electric field can further enter partially the dielectric spheres at the lower layer by tunneling effect, and can propagate out of the metal slab by the similar mechanism at the upper side of the metal slab, which causes additional increment in the transmission.
2010, 59 (6): 4018-4022. doi: 10.7498/aps.59.4018
A method of designing left-handed metamaterials based on inter-unit-cell coupling was proposed in this paper. A theoretical model was established using equivalent circuit theory. By properly setting the geometrical parameters of adjacent unit cells, the electric resonance frequency can be made equal to the magnetic resonance frequency. Thus, the left-handed bandwidth reaches its maximum. A typical left-handed metamaterial based on inter-unit-cell coupling was fabricated and tested. The experimental results show that the test sample has equal electric and magnetic resonance frequencies and the left-handed bandwidth is 24 GHz. This verifies the design method proposed in this paper.
2010, 59 (6): 4023-4029. doi: 10.7498/aps.59.4023
In this paper are described three composite structures of visible light metamaterials, i.e. dendritic structures and dendritic structures, dendritic structures and silver film, dendritic structures and indium tin oxide slice, based on the physical model of “double-fishnet” structure. By double template-assisted electrochemical deposition, silver dendritic structure arrays and silver films are fabricated, which is useful for achieving the above three composite structures. It is revealed that all of the three composite structures have the same effects according to the transmission spectra and reverberation spectra.A comparison among all of the three composite structures clealy shows that the composite structure of dendritic structures and indium tin oxide slice has the best performance, such as low loss and distinct planar focus effect. Through adjusting the experiment conditions, three kinds of visible light metamaterials are prepared which can realize planar focus effects at red, green and blue light frequencies, separately.
Extraordinary transmission through one-dimensional metallic gratings with sub-wavelength slits under transverse electric wave excitation
2010, 59 (6): 4030-4035. doi: 10.7498/aps.59.4030
To show how to achieve the extraordinary transmission of one-dimensional metallic gratings with sub-wavelenghth slits, the transmission distribution of transverse electric (TE) wave through one-dimensional metallic gratings with sub-wavelenghth slits with a dielectric substance applied on it in different ways has been simulated by the finite-difference time-domain method. The relations between the refractive index of dielectric and the transmission efficiency is elicited from simulation, which show that the extraordinary transmission can be produced at several special wavelengths. Then, a new theory named the guided-mode-like resonance theory is put forward based on the guided-mode resonance theory, which is well suited for the extraordinary transmission under the TE-polarized wave excitation, and it is concluded that the guided-mode-like resonance is the main reason for the extraordinary transmission of TE-polarized wave. Thus, the new theory can explain the problems which cant be explained by the traditional theory. In a word, the guided-mode like resonance theory reveals the physical nature of the extraordinary transmission phenomenon which provides a theoretical basis for the further study of the extraordinary transmission phenomenon.
2010, 59 (6): 4036-4041. doi: 10.7498/aps.59.4036
In this paper, a novel all-solid octagonal Yb3+-doped photonic crystal fiber (PCF) with large mode area and low loss is proposed. The air holes in the cladding are replaced by the B2O3-doped quartz rods，which increases the thermal damage threshold of the PCF and simplifies the fabrication process. The properties of the PCF are investigated by multi-pole method. Simulation results show that the effective mode area of this PCF is up to 2000 μm2, and the bending loss for a bending radius of 5 cm is as low as 05 dB/m at 1064 μm. Also, this PCF can support effectively single-mode operation. The design results of this paper are highly meaningful for the development of fiber lasers and fiber amplifiers.
Signal impairment analysis of optical controlled apparatus caused by semiconductor optical amplifier
2010, 59 (6): 4042-4049. doi: 10.7498/aps.59.4042
This paper analyzes the signals impairment in the semiconductor optical amplifier (SOA) based optical buffer for optical packets switching networks, including the shape distortion of single pulse and the pattern dependent distortion of the continuous bit stream due to the SOAs nonlinearity and the limitation of its carrier lifetime, the deterioration of signal-to-noise ratio caused by the accumulation of amplified spontaneous emmision noise of the SOA, and the power leakage. The theoretical analysis and experimental results indicate that the buffered circle is restricted to 20—30, as determined by the signals impairment when a negative control optical pulse with high power is injected into SOA.
Low-dispersion high-birefringence effect of squeezed hexagonal lattice elliptical hole photonic crystal fiber
2010, 59 (6): 4050-4055. doi: 10.7498/aps.59.4050
A new type of photonic crystal fiber for realizing the effect of low dispersion high birefringence is proposed. The fiber is composed of a solid silica core and a cladding with squeezed-hexagonal-lattice elliptical air-hole along the fiber length. Dispersion and birefringence are investigated simultaneously by using the full vectorial plane wave method. Simulations indicate that the wavelength for realizing low-dispersion high-birefringence can be controlled by artificially choosing the structure parameters of photonic crystal fiber, such as the hexagonal lattice squeezing ratio, the relative air hole spacing and the air hole ellipticity. The optimal and feasible parameters of the fiber with low-dispersion high-birefringence are given, with the result of the total dispersion being within ±5 ps·nm-1km-1 over an ultra broad wavelength range from 1360 to 1670 nm and the corresponding high birefringence being about 15×10-2 at 1550 nm.
Effect of pinhole diameter on measurement accuracy of self-referencing interferometer wavefront sensor
2010, 59 (6): 4056-4064. doi: 10.7498/aps.59.4056
The diameter of pinhole is a critical element that affects the measurement accuracy of self-referencing interferometer wavefront sensor (SRIWFS), and its dimension is determined by the accuracy requirement of practical measurement and the intensity transmission. The effects of pinhole diameter on quality and intensity transmission of reference wave are analyzed on the basis of the Fourier optics theory, and then they are verified by numerical simulation and experiment. These results demonstrate that to obtain a good approximation to a reference wave, the pinhole diameter should equal half of the Airy-disk diameter produced by an unaberrated optic. In this way, the root-mean-square value of the reference wavefront is less than λ/100 for all aberrations with the peak-to-valley value of not smaller than one wavelength. These theoretical analyses and experimental results provide a valuable reference and illumination for determining the dimension of pinhole along with the analysis or design of SRIWFS for various testing tasks.
2010, 59 (6): 4065-4070. doi: 10.7498/aps.59.4065
Based on the theoretical study of the dry friction isolation system under the random vibration, a formula for the description of the acceleration response of metal rubber (MR) isolation system under random vibration was derived. An experimental research for the MR isolator subject to random vibration excitation was carried out, and the effects of the relative density, the preliminary deformation, and the acceleration level of excitation on the root mean square of acceleration response for the isolation system were analyzed and depicted in curves. The theoretical root mean square of acceleration response was compared with the experimental ones, and the range for the practical use was determined.
2010, 59 (6): 4071-4083. doi: 10.7498/aps.59.4071
Nonlinear vibration phenomena including superharmonics, subharmonics, quasi-subharmonics and chaos in metal plate excited by intensive ultrasonic pulses are studied experimentally and theoretically. In the experiments, the plates are excited by the ultrasonic pulse modulated high frequency vibration, and the nonlinear vibration velocities of the plates are measured by laser vibrometer for different sizes and fixing conditions of the plates. The analysis of time series, frequency spectrum and phase space are also performed to characterize the nonlinear vibration of the plate. According to the experimental conditions, a vibro-impact model with nonlinear contact damping is presented to explore the generation mechanism of the complicated nonlinear vibration in the plate. In the dynamic model, the intermittent vibro-impact between the ultrasonic transducer horn and plate are considered as the main source for generating the strongly nonlinear vibration in the plate. The numerical calculation results are in agreement with the observed experimental phenomena.
2010, 59 (6): 4084-4092. doi: 10.7498/aps.59.4084
The nucleation and coagulation of nanoparticles in the binary system of water vapor (relative humidity 70%) and sulfuric acid vapor (5×10-6) were detailedly studied by performing numerical simulation in a planar jet (Re=8300). The large eddy simulation was utilized to calculate the flow field, and the particle field is obtained by using the direct quadrature method of moment to solve the particle general dynamic equation. The distributions of particle number concentration, volume concentration and average diameter were discussed. The result shows that the growth of the calculated momentum thickness is consistent with the previous experimental data. The interface of the jet will roll up and generate the coherent vortices which will lead to an obvious decrease of the specie concentration of sulfuric acid vapor and increase of number concentration of nanoparticles in the vortex core. The appearance of the coherent vortices increases the possibility of particle collision and enhances the particle coagulation. The nanoparticle nucleation is enhanced in the vortex core where high particle number concentration will accelerate the particle coagulation.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2010, 59 (6): 4093-4099. doi: 10.7498/aps.59.4093
The plasma surface wave propagation in a rectangular structured device is simulated using the finite-difference time-domain method. The effect of device parameters on the propagation of plasma surface wave excited by slot antenna array is investigated. The parameters considered include the relative permittivity and thickness of dielectric slab, and the air gap on the top of dielectric slab. Appropriate parameters for the relative permittivity and thickness of dielectric slab are obtained through simulations, and it is found that the existence of air gap would greatly weaken the excitation of surface wave. The simulation results provide a good reference for the design optimization of large-scale rectangular surface-wave plasma source.
2010, 59 (6): 4100-4109. doi: 10.7498/aps.59.4100
Penumbral imaging of the neutron production in laser-driven inertial confinement fusion experiment is an important diagnostic technique. In order to meet the resolution requirement, we simulate the point spread function (PSF) under the conditions of different source-aperture distances, different thicknesses, different outer radii, and different shapes of the aperture. Base on the sharpness and the isoplanaticity of PSF, the diagnostic system can be optimized. According to the simulation results, tolerant misalignment of system is analysed: a resolution of 15 μm can be satisfied by the linear reconstruction method, and a resolution of 5 μm can be achieved by using the nonlinear reconstruction method.
2010, 59 (6): 4110-4116. doi: 10.7498/aps.59.4110
An atmospheric-pressure argon plasma discharge with a length of 63 cm is generated in a quartz capillary by using a pair of hollow needle electrodes. The discharge mode transition from abnormal glow to arc is investigated by means of electrical measurement and optical emission spectroscopy. The effects of the distance between two needle electrodes and the operating frequency of power supply on the voltage-current characteristics are discussed. The plasma electron density was estimated to be the order of 1014 cm-3 in the arc discharge. Moreover, the variation of gas temperature with the applied voltage is also studied, which is closely associated with the power dissipation. Furthermore, in measuring the oxygen atoms generated in argon/oxygen arc plasma discharge by optical actinometry, we found that the amount of oxygen atoms almost does not change with the rise of oxygen concentration.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
By solving Schrdinger equation exactly, we obtain the neutron wave function in the slit. With the Kirchhoff’s law, we obtain the neutron diffraction function. Finally, we obtain the mathematical relation between the relative diffraction intensity of neutron double-slit diffraction and the diffraction position. The calculation result is in accordance with the experimental data.
Theoretical investigation of the electronic structure and thermoelectric transport property of Mg2Si
2010, 59 (6): 4123-4129. doi: 10.7498/aps.59.4123
Full-potential linearized augmented plane wave method and Boltzmann transport properties have been used to investigate the crystal structure and electronic structure of Mg2Si. Electronic conductivity, Seebeck coefficient and power factor are calculated. Energy band structure shows that Mg2Si is an indirect semiconductor with energy band gap of about 020 eV. Transport properties versus the doping level have been calculated for the n type and p type doped materials at 700 K. The optimal carrier concentration corresponding to the maxima of power factor are obtained, which are 7749×1019 cm-3 and 1346×1020 cm-3 for the p-doping and n-doping respectively. Maximum ZT value of 093 has been estimated in combination with experimental data of thermal conductivity. From the transport properties at different temperatures, we found that the ratio of power factor to relaxation time is enhanced when the temperature increases. Optimum doping level of materials used in middle and high temperature range is higher than that of materials used in low temperature.
The hardness of 4H-SiC, which was high-temperature (500 K) helium-implanted to fluences of 3×1016 ions cm-2 and subsequently thermally annealed at the temperature ranging from 773 to 1273 K, was studied by nanoindentation. It is found that the hardness of the implanted 4H-SiC increases at the first, then decreases, and then increases again with increasing annealing tempeature in the temperature range of 500—1273 K, and significant increase in hardness is observed at 773 K. The behavior is ascribed to the changes of the density, length, and tangling of the covalent Si—C bond through the recombination of point defects, clustering of He-vacancy, and growth of helium bubbles during the thermal annealing.
Experimental analysis of charge transfer efficiency degradation of charge coupled devices induced by proton irradiation
2010, 59 (6): 4136-4142. doi: 10.7498/aps.59.4136
The experiments on charge coupled devices (CCD) irradiated by protons were carried out. The charge transfer efficiency (CTE) of CCD was measured before and after proton radiation. The radiation damage mechanism of CTE degradation was analyzed. The CTE degradation induced by irradiation of protons of different energies was compared. The experimental results were explained by the theoretical analysis based on the calculation by radiation particle transport simulation software.
2010, 59 (6): 4143-4149. doi: 10.7498/aps.59.4143
Aluminium adsorptions on Pt(111),Ir(111) and Au(111) surface are studied systematically by using the density function theory. Four highly symmetric sites, namely face-centered cubic(fcc)-hollow,hexagonal close-packed(hcp)-hollow, top and bridge sites, are adopted. We calculate atomic geometry， average binding energy and differences in electron density among the three systems. The Mulliken charge population analyses and the projected densities of states of the three systems are also discussed. It is found that the hcp-hollow site is the energetically favorable site for Pt(111)and Ir(111) surfaces, but the energetically favorable site is the fcc-hollow site for Au(111) surface.
2010, 59 (6): 4150-4155. doi: 10.7498/aps.59.4150
Monolithic AlN，NbN films and AlN/NbN multilayers with different modulation periods were prepared by reactive magnetic sputtering. The films were characterized by X-ray diffraction, X-ray reflectivity and high-resolution transmission electron microscopy. The results showed that the crystal structure of monolithic AlN and NbN films is close-packed hexagonal (hcp) and face-centered cubic (fcc), respectively. The crystal structure of AlN and NbN is hcp and fcc, respectively, in AlN/NbN multilayers. The interfaces between AlN layers and NbN layers are coherent， i.e., c-NbN (111)∥h-AlN(0002). The lattice mismatch of AlN/NbN multilayers is 013%. The thermodynamic calculation revealed that no matter how thickness of AlN or NbN layer is, the AlN layer does not form nonequilibrium structure of fcc, but the equilibrium structure of hcp. The AlN layers grow in the way of hetero-epitaxial coherent growth with NbN layers.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effects of the concentration of Ga high doping on electric conductivity and red shift of ZnO from frist-principles
2010, 59 (6): 4156-4161. doi: 10.7498/aps.59.4156
We present the band structures and densities of states and calculation of absorption spectrum as well as the relative number of electrons and mobility ratio of electrons scattering from Zn1-xGaxO with different concentration of Ga， and in the condition of high concentration of Ga heavily doped in ZnO semiconductor at low temperature， by adopting the ab-initio plane wave ultra-soft pseudo potential technique based on the density functional theory. It was found that the relative number of electrons increases with the concenteation of Ga increasing， but the mobility ratio of electrons of Zn1-xGaxO decreases. The conductivity and minimum band gaps of the doped and undoped ZnO have been compared respectively，from which we draw the conclusion that the conductivity of Zn1-xGaxO semiconductor decreases with the concentration of Ga increasing. When the concentration of Ga reaches a certain value， the minimum band gap dreases with the concentration of Ga increasing， and the phenomenon of red shift happens in the high energy zone. Calculations is in agreement with the experimental results obtained in Zn1-xGaxO with atomic Ga doping in excess of x=004.
2010, 59 (6): 4162-4169. doi: 10.7498/aps.59.4162
Based on the local atomic-orbital density functional theory plus the nonequilibrium Green’s function approach, we study the transport sensitivities of a carbon atomic wire attached, respectively with seven kinds of commonly seen side-groups NO2, CN, CHO, Br, C6H5, C5H4N, NH2. The calculated results show that the transport current is most sensitive to attached C6H5 and CHO groups, less sensitive to attached CN and C5H4N groups. Under certain bias values, the currents have a substantial decline and would reached to 1/2, or even 1/3 the magnitude as the unattached system C6. But the transport of the carbon atomic wire is little influenced by the attached NO2, NH2, and Br. The intrinsic origins of side-group effects on the transport current in the wire are the suppression of the transmission eigen-channel, change of the Mulliken population, diminution of the delocalization of highest occupied molecular orbital or lowest unoccupied molecular orbital, and alteration of the resonant molecular orbital.
2010, 59 (6): 4170-4177. doi: 10.7498/aps.59.4170
Structural and electronic properties of clean polar ZnO surfaces are studied by using the first-principles ultra-soft pseudo-potential approach to the plane wave, based on the density functional theory. Furthermore, the relaxations, bandstructures, and densities of states for ZnO(0001) and ZnO(0001) surfaces and the N adsorption for ZnO(0001) surface are studied. The calculation results reveal that the relaxation of ZnO(0001) surface is stronger than that of ZnO(0001) surface, so ZnO(0001) surface has a better integrity. Compared with the ZnO bulk, the ZnO(0001) surface has a narrow bandgap, and big conductivity due to the delocalizing characters. However, the bandgap of the ZnO(0001) surface widens, the empty energy levels appear near the top of bandgap due to the existence of O-2p states, and the body electrons transite easily to the surface, under the thermal excitation, and resulting in negative charges.We find that the face-centered site is the stablest adsorption position of ZnO (0001) surface, and the formation energy is lowest in the first layer when N atoms are embeded in the ZnO (0001) surface. Therefore, N atoms easily accumulate on the surface layer rather than occupy the positions in the body.
2010, 59 (6): 4178-4185. doi: 10.7498/aps.59.4178
The cell parameters, electron localization function and density of states of pure and Zr-doped NaAlH4 and Na3AlH6 are investigated using plane-wave pseudo-potential method based on density functional theory. The results show that NaAlH4 and Na3AlH6 are insulators characterized by a band gap of 46 and 31 eV, respectively. The Al and H atoms form covalent bonds and the Na and H atoms form ionic bonds in NaAlH4 and Na3AlH6 When Zr replaces Na, the interaction between Zr and H is stronger than the primary Na—H bond, and the interaction between Al and H becomes weaker; when Zr replaces Al, the bond between Zr and H is weaker than the primary Al—H bond. Our calculations indicate that Zr-doped NaAlH4 and Na3AlH6 are more stable than that of the pure alanates, and the energy to remove H atom is significantly decreased.
2010, 59 (6): 4186-4193. doi: 10.7498/aps.59.4186
By performing first principles electronic structure calculations, we have revealed the effect of boron/nitrogen pairs doping in armchair single-walled carbon nanotubes (SWCNT). It is shown that for two kinds of sites in the armchair SWCNT, the doping of B/N pairs can more easily happen on the P1 site which is at 30° angle to the tube axis. An energy gap is opened in metallic SWCNT by doping B/N pairs, and the energy gap increases with raising the axial concentration of the B/N pairs. Moreover, when two couples of B/N pairs are doped in SWCNT, the electronic structure is sensitive to the relative positions of B/N pairs in the couple along the circumference of tubes. It’s due to that the original charge distribution is changed by B/N pairs doping, and the effect of B/N pairs is localized. When the distance between B/N pairs increases, the extent of the effect is increased. This result may contribute to preparing pure semiconductor and effectively controlling the electronic structure.
By using the tight-binding energy band theory, we study the band structures of BC3 nanotubes under stretching and compressing deformations, the conductivity band turns more and more close to the valence band of the BC3 nanotubes and eventually they overlap each other with the increase of tension. Furthermore, the results obtained show that the overlap under compressing is bigger than that under stretching. The biggest overlap under compressing is up to 05 eV, but it is only 02 eV under stretching. In addition, for armchair BC3 nanotubes, the results of band structures show that with the increase of tension, the BC3 nanotube transforms into an indirect semiconductor from a direct semiconductor, and then leads to the band overlap. The armchair BC3 nanotube is an unstable narrow-gap semiconductor, because a little compress (et=-0003) can convert it transform into an indirect semiconductor from a direct semiconductor. For zigzag BC3 nanotubes, a slight deformation can turn into a direct semiconductor having only one allowed wave vector from a direct semiconductor having all wave vectors, owing to the existence of two flat conductivity and valence bands.
2010, 59 (6): 4202-4210. doi: 10.7498/aps.59.4202
For the Fibonacci sequence constructed by following the inflation rule A→AB and B→A, using the one-dimensional random walk model and Hurst’ analysis, we calculate numerically the auto-correlation function, the pseudo standard deviation of displacement defined by ourselves and the rescaled range function and investigate systematically the statistical properties. The results are compared with that of one-dimensional random binary sequence. We show that the Fibonacci sequence presents correlated behavior as well as scaling invariability and self-similarity. In addition, basing on the tight-binding model of the single electron and transfer matrix method, we study the charge transfer properties of Fibonacci sequence and discuss specially the dependence of electron transmission on energy and the length of the sequence. We find some resonant peaks can survive in relatively longer Fibonacci sequences than in random sequences, which also implies that there are long-range correlations in Fibonacci sequences.
2010, 59 (6): 4211-4215. doi: 10.7498/aps.59.4211
The electrical transport properties of Ca3Co4O9 could be modified by doping in the Ca site. The Ca site doped Ca3-xAgxCo4O9(x=0—005) bulk samples were fabricated by citric acid sol-gel and spark plasma sintering method. The resulting samples were analyzed by X-ray power diffraction, scanning electron microscopy and electrical constant measurement. The results showed that all samples were single phased, the prefered orientation was lowered by Ag doping for Ca. The x=003 sample exhibited highest grain orientation among doped samples, which exhibited layered microstructure. Its electrical resistivity was increased and then decreased slightly by Ag doping, but the transport mechanism was not changed. However, the doped samples exhibited high electrical resistivity caused by changed electronic structure by Ag doping for Ca. The x=004 sample exhibited highest electrical resistivity in the measuring temperature region with the highest value 146 mΩ·cm at 973 K.
2010, 59 (6): 4216-4220. doi: 10.7498/aps.59.4216
Co-doped nano-absorbent is prepared by the sol-gel method. The effect of the fabrication condition on physical property and absorbing property are analyzed. The optimum fabrication condition is found. The influence of particle size on absorbing property is compared with that of the conventional absorbent. Radar absorbing measurement shows that nano-absorbent has a good absorbing property.
Magneto-tunneling effect in weakly coupled GaAs/AlGaAs/InGaAs double quantum well tunneling structure
2010, 59 (6): 4221-4225. doi: 10.7498/aps.59.4221
We report on the magnetic tunneling properties of weakly coupled GaAs/AlGaAs/InGaAs double quantum well tunneling structure at low temperature (15 K) in a magnetic field applied parallel to the tunneling current. The device is in resonance at zero bias voltage. From an analysis of the oscillations in magneto-conductivity for different bias voltages, the change in ground-state energy levels in two quantum wells with the bias can be confirmed and thus the tunneling mechanism was studied. The results reported in this paper provide the basis for the successful fabrication of weakly coupled double quantum dot system.
2010, 59 (6): 4226-4234. doi: 10.7498/aps.59.4226
Starting from the Keating model, a semi-continuum atomistic lattice model, with directly taking into account the discrete nature in width and thickness direction, is proposed to calculate the elastic constants and Youngs modulus of single crystal silicon nanowires (SiNWs). Based on the six-band k·p theory and the deformation potential concept, and taking into account the quantum-size effect and spin-orbit coupling, a numerical model for the valence band structures of SiNWs in various transport orientations is established by using the finite difference method. Then we use a top-of-the-barrier ballistic field-effect transistor (FET) model to investigate the effects of the uniaxial stress and the elastic constants on ballistic transport properties of the p-type SiNW FETs in combination with the calculation results from the two models mentioned above. It is found that the elastic constants and Youngs modulus of the SiNW are highly size-dependent, which is in good agreement with the available molecular dynamics result. Furthermore, our calculations indicate that the effect of size-dependent elastic constants on ballistic transport current of the SiNW FET strongly depends on the effect of the uniaxial stress on ballistic transport current, because when the uniaxial stress induces a significant change in valence band structures of SiNWs, the size-dependent elastic constants can obviously modify the valence band structure.
2010, 59 (6): 4235-4239. doi: 10.7498/aps.59.4235
Using the diamond anvil cell（DAC）method and the technology of sputtered film， photoetch and chemical etching， the conductivity of micron dimension ZnO were measured successfully under high pressure with molybdenum electrodes on DAC. The samples conductivity was minimal at 919 GPa pressure， which showed the beginning of structural phase transition from wurtzite to rocksalt. Contining compression as far as 1122 GPa， the conductivity increased rapidly and then slowly， which indicated the phase transformation pressure spot was 1122 GPa and the whole example was of rocksalt structure. In addition， it was found that the oxygen holes caused conductivity change by experimentally comparing the samples annealed at 500 ℃ in air， in argon and unannealed respectively.
2010, 59 (6): 4240-4244. doi: 10.7498/aps.59.4240
White polymer light-emitting diode with a single layer of fluorescent polymer blend was fabricated. The structure of the device is indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)/emission layer/1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene/Ba/Al, and the emission layer is a blend of poly［2,7-(9,9-dioctyl)fluorene-co-2,3-bis(4-phenyl)-6-fluoroquinoxaline］ (PF-BPFQ5), phenyl-substituted poly(p-phenylene vinylene) derivative (P-PPV) and poly［2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene］ (MEH-PPV), which, respectively, emits blue, green and red light. When the blend weight ratio of PF-BPFQ5∶P-PPV∶MEH-PPV is 100∶06∶06, a pure white light emission is obtained with CIE coordinates of (0331,0329). The maximal luminance efficiencies is 564 cd/A. Meanwhile, the electroluminescence spectrum of white-light emission is stable under different current densities.
2010, 59 (6): 4245-4252. doi: 10.7498/aps.59.4245
Using the full-potential linearized augmented plane wave method, we studied the electronic structure and magnetic properties of SrFeAsF and Co-doped superconductor SrFe0.875Co0.125AsF. It is found that SrFeAsF exhibits a stripe antiferromagnetic ground state, and in SrFe0.875Co0.125AsF the checkboard antiferromagnetic state become a competitive candidate. The Co-doping drastically suppresses the antiferromagnetic order, increases the density of states near the Femi level and enhances the itineranly of 3d electrons. These results show that the superconductivity is induced by the magnetic fluctuations in SrFe0.875Co0.125AsF.
Study on the microstructures and electrical properties of Bi0.5Ba0.5Fe0.5Ti0.49Nb0.01O3 thermistor ceramic
2010, 59 (6): 4253-4260. doi: 10.7498/aps.59.4253
The Bi0.5Ba0.5Fe0.5Ti0.49Nb0.01O3 thermistor has been prepared by the standard solid-state reaction method, and the microstructures, direct current resistivity, dielectric property, impedance and electric modulus were investigated by the X-ray diffraction, scanning electron microscopy, resistivity-temperature measurement and alternating current impedance spectroscopy. The results show that the material, with an average grain size of about 10 μm, still has cubic perovskite structure, and the lattice constant of the material becomes larger compared with that of the BaTiO3. The resistivity and thermistor contant B value of the material are about 107 Ω·cm and 7690 K, respectively, and the phase transition occurs twice (at 403 and 523 K), which are confirmed by the dielectric spectrum as a function of temperature. The complex impedance spectroscopy shows the non-ideal Debye type with two incomplete overlapping Cole-Cole semicircles corresponding to the grain and grain boundary resistance. The imaginary part of alternating current resistance as a function of frequency indicates there are two relaxation effects observable in the grain and grain boundary. The phase transition has little effect on the conduction property of bulk grain, but a great impact on that of the grain boundary.
2010, 59 (6): 4261-4266. doi: 10.7498/aps.59.4261
Micro-Raman scattering from the nitrogen doped n-SiC is performed at the temperatures ranging from 100 to 450 K. The temperature dependences of the first-order Raman scattering, electronic Raman spectra and the second-order Raman features are obtained. These measurements reveal that most of the first-order Raman phonon frequencies decrease with temperature increasing, but the redshifts of the acoustic phonon modes are smaller than those of the optical phonon modes. Meanwhile, the longitudinal optical phonon-plasma coupled (LOPC) mode manifests different features with temperature increasing. The LOPC mode tends to have a blueshift at a lower temperature but a redshift at a higher temperature. This indicates that the temperature dependence of LOPC mode is affected not only by the anharmonic effects, but also by the ionized donor concentration. With the increase of the measurement temperature, the intensity of the electronic Raman spectrum decreases, and the linewidth gradually broadens, but the electronic Raman signal is almost not shifted. The redshift of the second-order Raman spectrum is smaller than that of the first-order Raman spectrum, but the intensity of the second-order Raman spectrum substantially decreases with the increase of temperature.
2010, 59 (6): 4267-4278. doi: 10.7498/aps.59.4267
Binary β-FeSi2 phase is an important semiconductor metal silicide with narrow band-gaps. The formation of this phase in ternary alloys was investigated for the search of ternary semiconductor silicides. Using the cluster line approach as the theoretical guideline, a structure model is established with one cluster and one glue atom, and alloy series of Fe3Si8M(M=B, Cr, Ni, Cu, Co, Al) were designed by replacing the glue atom Fe in binary β-FeSi2. To obtain homogenous alloys, high vacuum suction casting and melt spinning method were used for the preparation of alloy rods and ribbons. Microstructure and composition analysis showed that the β phase could dissolve 15%—20% Ni, 4%—13% Cu, 7%—10%Co and 7%—10%Cr (molar content). However, in contrary to the designed formula, the added Al replaces Si rather than Fe. There were trace amounts of amorphous particles in Fe3Si8B and Fe3Si8Cr ribbon samples, which showed under the rapid cooling conditions, the addition of B and Cr was favorable for the amorphous phase formation.
2010, 59 (6): 4279-4282. doi: 10.7498/aps.59.4279
By using photoluminescence (PL) and time-resolved PL spectra， the optical properties of single InAs quantum dot (QD) embedded in the p-i-n structure have been studied under an applied electric field. With the increasing of electric field， the exciton lifetime increases due to the Stark effect. We noticed that the decrease or quenching of PL intensity with increasing the electric field is mainly due to the decrease of the carriers captured by QD.
2010, 59 (6): 4283-4289. doi: 10.7498/aps.59.4283
The organic light emitting diode with inserted LiF layer has been fabricated. Tris-(8-hydroxyquinoline) aluminum (Alq3) was used as electron-transport layer and N, N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) was used as hole-transport layer. By changing the thickness of LiF deposited between Alq3 and NPB, the optoelectrical properties and the magnetic field effect on electroluminescence were studied at different temperatures. The measurement results show that using LiF layer enables the transport of carrier and the formation of excited states inside the device. A thick LiF layer blocks the transport of holes, lowering the efficiency of the device. However, use of LiF layer can effectively tune the magnetic field effect of electroluminescence. Compared with conventional devices, the magnetic field effect of device with inserted LiF layer was strengthened within low-field range (the magnetic induction BB≥40 mT) decrease of electroluminescence, and the thicker the LiF layer, the smaller the magnitude of decrease. These observations indicate that the concentration of the triplet excitons offects the high magnetic field decrease of electroluminescence at low temperatures.
2010, 59 (6): 4290-4295. doi: 10.7498/aps.59.4290
The difference between the diffusion drift length of photoelectrons in exponential-doping GaAs photocathode and that in uniform-doping GaAs photocathode is studied. According to quantum equations, the optimized thickness of transmission-mode exponential-doping GaAs photocathode is simulated to be 20 μm. Two transmission-mode exponential-doping GaAs samples with the thickness of 16 and 20 μm are activated by (Cs,O) alternation technique. Integral sensitivities of the two samples are 1228 and 1547 μA/lm, respectively. The ratio of integral sensitivities of the two samples is 0796∶1, which agrees with the simulation result.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (6): 4296-4302. doi: 10.7498/aps.59.4296
High quality C-N-V films with different compositions were prepared on cemented carbide substrate using pulsed bias arc ion plating. The surface morphology, composition, microstructure and properties of C-N-V films were investigated by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, grazing incident X-ray diffraction, and nano-indentation, respectively. The results show that the deposited films were nanocomposite films with VN nanocrystalline phase imbedded within diamond-like carbon(DLC) amorphous matrix. The hardness and elastic modulus, which are closely related to the composition and structure of the film, first increase and then decrease with increasing V and N contents and have the highest values of 368 and 5697 GPa exceeding that of pure DLC film prepared under the same condition when nitrogen content is 204% and vanadium content is 218%. The variation of V and N contents has significant influence on the phase structure, relative concentration of VN crystalline phase and DLC amorphous phase, and induces the formation of nano-diamond phase, hence has great effect on the properties of the films.
The mechanism of structure phase transition from α Fe to ε Fe under uniaxial strain: First-principles calculations
2010, 59 (6): 4303-4312. doi: 10.7498/aps.59.4303
We performed first-principles calculations for the pressure-induced martensitic phase transition from the ground state ferromagnetic body-center cubic (bcc) phase to a nonmagnetic hexagonal close-packed (hcp) phase of Fe under uniaxial strain along the ［001］ direction of bcc phase based on density-functional theory, employing the pseudopotentional and plane-wave method. The calculated results show that the transition path under unixial strain is significantly different from that under hydrostatic pressure. A sudden drop of the magnetic moment is observed at a critical point on the transition path, which results in a discontinuous derivative in the total energy and volume curve. This is a feature of a magnetic first-order phase transition, which indicates that magnetism is the primary stabilizing mechanism of the bcc structure. The enthalpy barrier for bcc-to-hcp transformation decreases as the uniaxial strain (the pressure) increases. The physical origin of the influence of uniaxial strain on the phase transition is discussed.
Molecular dynamics simulation of CO2 separation from integrated gasification combined cycle syngas via the hydrate formation
2010, 59 (6): 4313-4321. doi: 10.7498/aps.59.4313
Molecular dynamics (MD) simulation is used to study the microscopic mechanism of CO2 separation from integrated gasification combined cycle(IGCC) syngas (CO2/H2) via the hydrate formation. The stable structures and microscopic properties of CO2 hydrate, H2 hydrate, and CO2/H2 hydrate from one stage separation for IGCC syngas are investigated systematically. The binding energy for loading the hydrate structure with the guest molecules, ΔEn, was analyzed. It was shown that the binding between CO2 and water is more stable than that between H2 and water. That is, CO2 can more easily form the hydrate. Therefore, CO2 in the CO2/H2 gas mixture more easily transfers into the hydrate phase. Based on this, CO2 can be separated from the IGCC syngas. The binding energy for loading the single cavity with the guest molecules, ΔEGH, was analyzed. It was found that the gas mixture can form structure Ⅰ(SⅠ) hydrate, in which CO2 molecules preferably occupy the big cavity and then occupy the small cavity, and H2 molecules only occupy the small cavity. The simulation was carried out at pressure of 85 MPa and temperature of 2737 K for the stable structure of the CO2/H2 hydrate in one stage separation for IGCC syngas. From the ΔEn and ΔEGH of the systems with H2 single and double occupancy in the small cavity, it is concluded that the configurations with the single occupancy is most stable. The stable structure of the hydrate in one stage separation is attained by MD. It provides a theoretical evidence of CO2 separation for formation hydrate in IGCC syngas.
Influence of Fe-B pairs on minority carrier lifetime, trapping density and internal quantum efficiency in mono-crystal Si solar cells
2010, 59 (6): 4322-4329. doi: 10.7498/aps.59.4322
Solar-grade p-type Czochralski silicon wafers are doped with phosphorus by single-face and double-face diffusions, and the influence of Fe-B pairs on the minority carrier lifetime, the trapping centers density and the internal quantum efficiency （IQE） of cells （fabricated from the wafers） is analyzed by measuring microwave-detected photo-conductance decay minority carrier lifetime. In the doped wafers with single-face diffusion, the minority carrier lifetime is determined mainly by the density distribution of Fe-B pairs. However, in the doped wafers with double-face diffusion, the minority carrier lifetime is less influenced by the concentration distribution of Fe-B pairs than by other impurities and defects. Numerical calculation based on the combination of the transient voltage signal and the trapping model indicates that the density of trapping centers is reduced by either of diffusion process. On the other hand, detailed analysis of selected specific spots in one wafer with single-face diffusion shows that Fe-B pairs are not the major factor influencing the density of trapping centers. The wafers with different diffusion processes are fabricated into c-Si solar cells and the IQE is measured by using a light beam induced current. The results show that the IQEs of cells with double-face diffusion are higher than those with single-face diffusion, which demonstrates the negative effect of Fe-B pairs on the IQE of solar cells.
Influence of n-type layer structure on performance and light-induced degradation of n-i-p microcrystalline silicon solar cells
2010, 59 (6): 4330-4336. doi: 10.7498/aps.59.4330
A series of n-i-p microcrystalline silicon thin film solar cells with different values of crystalline volume fraction Xc of n-type layers are prepared by radio frequency plasma enhanced chemical vapor deposition. It is found that the structure of intrinsic layer is strongly dependent on the structure of n-type layer, especially the incubation layer thickness at n/i interface and Xc of intrinsic layer. This series of solar cells were light-soaked under 100 mW/cm2 for 400 h. The experiment results demonstrate that the solar cell with the highest Xc of intrinsic layer (Xc(i)=65%) has the lowest light-induced degradation ratio. Then the solar cell with n-type layer deposited in an amorphous silicon/microcrystalline silicon transition region (Xc(i) =54%) is light-soaked under the irradiations of white light, red light and blue light with the same light intensities, separately. After 400 h light-soaking, the light degradation ratio is only 2% for the red light irradiation, while it is 8% for the blue light irradiation.
2010, 59 (6): 4337-4342. doi: 10.7498/aps.59.4337
The dynamics of the translocation of single-stranded desoxyribonucleic acid (DNA) chains through a nanopore under the driving of an applied field is studied by three-dimensional Langevin dynamics simulations. It was found that different monomers correspond to different residence times. With the increase of the length of nanopore, the difference in residence time becomes smaller and smaller. Based on the simplified model, a new method is proposed to discriminate between the poly(dA) and poly(dC) of single-stranded DNA chains by recording the residence time of monomer. The method is utilized to predict the sequence of seventeen different chains, and the average accuracy is about 951%. If the residence time of monomer can be well recorded in the DNA translocation experiment, the sequence of the whole DNA will be predicted once and for all. With the improvement of the method, it will provide a low-cost high-throughput way to predict the sequence of DNA.
2010, 59 (6): 4343-4350. doi: 10.7498/aps.59.4343
The wavelet transform was applied to process the accelerometer signals derived from human walking. The accelerometer signals were first decomposed at different levels utilizing the multi-scale and multi-resolution characteristics of the discrete wavelet transform. After the determination of both the mother wavelet and the optimal decomposition level, human gait series can thus be extracted from the eigen scale of the accelerometer signal. Compared with the method that detects peak values directly from accelerometer signals by thresholding, the wavelet transform gives higher detection rate of peak values on the eigen scale of the accelerometer signals. Even when the accelerometer signals are exposed to serious noise, experimental results still demonstrate that the wavelet approach can guarantee the precision of the extracted gait series, which is of vital importance for the subsequent analyses. It can be concluded that wavelet transform is an effective tool for the extraction of gait rhythmicity. The wavelet transform will be helpful in identifying the characteristics of other physiological signals.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The trend of seismic activities in China and adjacent regions after Wenchuan earthquake——Research of seismic energy release with “oscillation analogy”
2010, 59 (6): 4351-4358. doi: 10.7498/aps.59.4351
According to the geological structure and characteristics of seismic activity in the eastern segment of Eurasian seismic zone, China and adjacent regions are chosen as the research regions, where earthquakes of Ms≥60 happened 824 times in total from 1897 to 2008 The sum of the yearly released energy is filtered and studied systematically. The results show that the release of seismic energy features a periodic damped oscillation. Through the oscillation analogy, we can forecast quantitatively the long-term and medium- and short- term seismic situations in China and adjacent regions. Theoretical analysis confirms that the earthquake vibrancy in the continental plates should last 1537 a, namely, 1897—2050 Such a result is consistent with the conclusions from the analysis of Chinese historical seismic data collected for more than 2000 a, and it may be regarded as a theoretical basis that the periodic seismic activity lasts about 150 a in China and adjacent regions. According to the periodic characteristic of the seismic activity, we can forecast theoretically that the current active duration will close in 2010—2012, furthermore, the next active duration will begin near 2020—2021, and then end in 2040 around. Subsequently, the earthquake process will completely enter into a relatively quiet duration for over one century after 2050
2010, 59 (6): 4359-4368. doi: 10.7498/aps.59.4359
Meteorological observation data have observational errors inevitably. It is an ill-posed inverse problem to perform the derivation of discrete data with observation errors. In order to solve the perplexing problem, this paper puts forward the new algorithm which reconstructs the first-order partial derivatives of the two-dimensional observation data in the rectangular region， which is based on the idea of Tikhonov regularization . We test the performance of the algorithm with a series of simulating observation data, the results show that the algorithm is effective and has higher accuracy. It is feasible to analyze meteorological observation data with the algorithm and can enhance the recognizing ability for the small-scale weather systems.
2010, 59 (6): 4369-4379. doi: 10.7498/aps.59.4369
The principle of a novel static polarization wind imaging interferometer is described, and the Jones matrix of the system is derived in general case. The theoretical measurement errors of the wind and temperature, introduced by some important parameter errors of all the polarization components in the system, is calculated and analyzed by computer simulation. The tolerances of the parameters are proposed according to accuracy of the system. The study provides a theoretical basis and practical guidance for the development, calibration and data post-processing of the novel static polarization wind imaging interferometer.
2010, 59 (6): 4380-4384. doi: 10.7498/aps.59.4380
In the Parikh-Wilczeks semiclassical tunneling framework, the Hawking radiation of particles with electrical and magnetic charges tunneling across the event horizon of black hole is investigated. Taking the Reissner-Nordstrǒm black hole with topological defects and with magnetic charges for an example, the calculation shows that the tunneling process of the outgoing particle is consistent with an underlying unitary theory, and supports Parikh-Wilczeks conclusion. The emission spectrum is no longer precisely thermal.
2010, 59 (6): 4385-4389. doi: 10.7498/aps.59.4385
We study thermodynamic properties of the effective right and left systems of Reissner-Nordstrm-anti-de Sitter black hole. Then, we analyze the case of Kerr-Newman-anti-de Sitter(KN-AdS) black hole and calculate the corresponding thermodynamic quantities of the right and the left systems. For the nearly extremal case, it can be seen that the effective right system of KN-AdS black hole satisfies the Nernst theorem and the effective left system has a finite temperature.
2010, 59 (6): 4390-4394. doi: 10.7498/aps.59.4390
In accordance with the holographic principle， by calculating the entropy of the quantum field just on the event horizon of the Gibbons-Maeda dilaton black hole， the holographic entropy and the Bekenstein-Hawking entropy of the black hole are obtained. By using the non-commutative quantum field theory， the divergence of the state density near the event horizon in usual quantum field theory is removed and the ultraviolet cutoff in the heat gas method of black hole entropy is avoided.Using the residue theorem, the integral difficulty in the calculation is overcome and the results here are obtained quantitatively. The results show that black hole entropy is identical with the statistical entropy of the quantum states at the horizon. Black hole entropy may be obtained by calculating the quantum states only at the event horizon, and in the calculation the influences of quantum states outside the horizon should be avoided.
REVIEW OF FRONTIER AREA
2010, 59 (6): 4395-4402. doi: 10.7498/aps.59.4395
With the reduction of feature size of integrated circuits, higher current density has been introduced in electronic devices which produces a significant Joule heating effect. This also brings about an increase of the temperature which induces a very high temperature gradient in some local regions of micro interconnects. As a result, thermomigration will occur and metal atoms will move opposite to the direction of the temperature gradient. Thermomigration is one of common modes in reliability failures in electronic devices. This paper reviews and analyzes the previous researches on the thermomigration theory and experiment in stripe and solder interconnects under the temperature loading and the current/temperature loading. The challenges of thermomigration are discussed for interconnects in electronic devices in the future.