Vol. 57, No. 11 (2008)
2008-06-05
GENERAL
2008, 57 (11): 6689-6693.
doi: 10.7498/aps.57.6689
Abstract +
A three dimentional equation for the equatoral sea-air oscillator Kelvin wave is considered. By using the variational iteration method，the approximate solution of the corresponding model is studied. The variational iteration method is an analytic method，the obtained solution can be used in further analytical operations.
2008, 57 (11): 6694-6698.
doi: 10.7498/aps.57.6694
Abstract +
The problem of solving the Lorenz equation is considered. Firstly，a set of homotopic mapping is constructed. Then the initial approximate solution is determined. Finally，using the homotopic mapping，the approximation for corresponding model is found. The homotopic mapping method is an analytic method，the obtained solution can be used in analytic operations subsequently.
2008, 57 (11): 6699-6703.
doi: 10.7498/aps.57.6699
Abstract +
Two types of conserved quantities deduced by Lie-Mei symmetry of variable mass mechanical system are studied in phase space in the paper. The definition and criterion of Lie-Mei symmetry for the system are given. A coordination function is introduced，and the conditions under which the Lie-Mei symmetry leads to the two types of conserved quantities and the forms of the two types of conserved quantities are obtained. An illustrative example is given. The coordination function can be selected according to the requirement for finding the gauge function，and the choice of the coordination function is multiformal，so more conserved quantities can be deduced from Lie-Mei symmetry of the system.
2008, 57 (11): 6704-6708.
doi: 10.7498/aps.57.6704
Abstract +
In this paper the conformal invariance under special infinitesimal transformations of Lagrange systems is studied. The necessary and sufficient conditions for the conformal invariance under infinitesimal transformations which is Lie symmetric at the same time are given. Finally we get the Hojman conserved quantities of the conformal invariance.
2008, 57 (11): 6709-6713.
doi: 10.7498/aps.57.6709
Abstract +
In this paper the conformal invariance under infinitesimal transformations of generalized Hamilton systems is studied. The necessary and sufficient conditions for the conformal invariance under infinitesimal transformations which has Lie symmetry are given. Then we get the Hojman conserved quantities from conformal invariance of generalized Hamilton systems. Finally，an illustrative example is given to verify the result.
2008, 57 (11): 6714-6717.
doi: 10.7498/aps.57.6714
Abstract +
The definition and the criterion of a Mei symmetry for a holonomic system are obtained in this paper.If the Mei symmetry is a Noether symmetry，the Noether conserved quantity is given，If the Mei symmetry is a Lie symmetry，the conserved quantity of Hojman type is obtained.An example is given to illustrate the application of the result.
2008, 57 (11): 6718-6721.
doi: 10.7498/aps.57.6718
Abstract +
In this article，Lie symmetry of Nambu mechanical systems is discussed and its determining equations are established. Consequently，the structure equation and the associated conserved quantities are obtained. The inverse problem of Lie symmetries of the systems is also studied. As an example，Euler equations are used to illustrate the application of the main results.
2008, 57 (11): 6722-6729.
doi: 10.7498/aps.57.6722
Abstract +
A least square particle finite element method is presented and used to simulate the impact and splash of 2D water droplets on the water surface. This algorithm is based on an upgraded Lagrangian framework. An extended Delaunay triangulation method is used to get the new mesh at every time step. An alpha-shape method is used to deal with the splash and impact of the free surface. The least square finite element method is applied to solve the Navier-Stokes equations. An adaptive time step algorithm is derived to improve the efficiency and the robustness of calculation，and a mesh pulling scheme is introduced to improve the conservation of the total mass. Finally，when compared with the commercial Flow-3d code，the computational results achieve good agreement. Moreover，the free surface is more accurate and more clearcut than that of the Eulerian description based Flow-3d code.
2008, 57 (11): 6730-6735.
doi: 10.7498/aps.57.6730
Abstract +
The Klein-Gordon equation of equal scalar and vector Manning-Rosen potentials with the centrifugal term is investigated in the spherical coordinates. Using a proper exponential approximate approach，the radial Klein-Gordon equation with the centrifugal term is transformed to the hypergeometric differential equation，and the analytical bound state radial wave functions of the arbitrary l-wave Klein-Gordon equation are obtained. Finally，two special cases for l=0 and α=0 or 1 are discussed briefly.
2008, 57 (11): 6736-6740.
doi: 10.7498/aps.57.6736
Abstract +
Based on the matrix of the time-dependent quantum transformation theory，we derive the analytic expression of the evolution operator for the time-dependent oscillators by using the time-dependent quantum transformation theory. Then the exact solution of the time-dependent oscillators is obtained.
2008, 57 (11): 6741-6750.
doi: 10.7498/aps.57.6741
Abstract +
In this paper，we consider the viscoelastic-plate equation under non-linear boundary conditions. Firstly，by the aid of Galerkin method，under non-linear boundary conditions (a) and the initial values w0∈W，and w1∈W，we prove the existence and uniqueness of a global weak solution w(t) for the initial boundary value problems. Secondly，under non-linear boundary conditions (b) and the initial values w0∈W，and w1∈W1，the existence and uniqueness of a global weak solution w(t) is also proved by using Galerkin method.
2008, 57 (11): 6751-6757.
doi: 10.7498/aps.57.6751
Abstract +
In recent years considerable attention is being paid to the blue-shift of photoluminescence due to quantum confinement in the nanostructure. By employing two simple models of one-dimensional crystal potential，we study the electronic energy spectra and confinement energies by solving the Schrdinger equation for the models. Based on the calculation of the confinement energies in the nanostructures，the size- and potential-dependence of the confinement energy and the blue shift are investigated. The results suggest that: with creasing size of the system the energy of electrons at the bottom of the conduction band decreases，but increases at the top of the valence band. Therefore，the confinement energies increased abruptly as the size of nano-particle (or nanostructures) decreases. Meanwhile，our results for the confinement energies show obvious difference from the ones calculated by the effective-mass approximation of ten used in the literature. Moreover，we also find that the band gap and blue shift depend on the crystal potential in the systems，and the confinement energies decrease as the potential increases.
2008, 57 (11): 6758-6762.
doi: 10.7498/aps.57.6758
Abstract +
On the condition of electric-LO phonon strong coupling in parabolic quantum dot，we obtain the eigenenergy and the eigenfuctions of the ground state and the first-excited state by using variational method of Pekar type. This system in quantum dot may be employed as a two-level quantum system-qubit. When the electron is in the superposition state of the ground state and the first-excited state，we obtain the space-time evolution of the electron density. It is shown that the electron density increases with the temperature when the temperature is lower，and the electron density decreases with the temperature when the temperature is higher. At the same time，we found that sometimes the electron density vibrates with the temperature，and its change is slowed down with the strength of coupling increasing.
2008, 57 (11): 6763-6770.
doi: 10.7498/aps.57.6763
Abstract +
Disasters threaten mankind and degrade our survival conditions，and have a serious impact on human society. Several previous disaster spreading models in complex networks are reviewed. Based on the evaluation of their advantages and disadvantages，a more realistic model in the networks with redundant systems is proposed. For different models in different network structures，the differences of spreading processes and the effects of some important parameters are analyzed by means of simulation. The disaster processes in the networks with redundant system become slow，which permits of longer rescue time to repair the system. It can explain the reason why large-scale disaster events rarely happen in real life.
2008, 57 (11): 6771-6776.
doi: 10.7498/aps.57.6771
Abstract +
We made a detailed，empirical analysis of the railway network of China (RNC)，in which the stations are treated as nodes and a link exists between every two nodes if there is a train stop at each node. Firstly，we explore the statistical properties of the directed and weighted RNC with respect to the distribution of degree and strength，clustering coefficient and the shorted path length. The results exhibit that the distribution of degree and strength are between the exponential distribution and scale-free. Moreover，the RNC is a hierarchical small-world network. Secondly，the construction of the railway is the result of balance between the economical cost and the degree of need such as the population density and the number of administrative divisions. So the topological properties constrained by the geographic factors are taken into consideration，such as the relation between railroad length and degree，the density distribution of the stations and the population and the community strength of the province. These results proved that the RNC is constrained by the geography and approaches to the optimal construction.
2008, 57 (11): 6777-6785.
doi: 10.7498/aps.57.6777
Abstract +
Under the condition of infinite dissemination of the network，it has been proved that the classical epidemic models do not give epidemic thresholds in the infinite scale-free networks. That is，a disease can always propagate on the network no matter how low its spread speed. However，the ability of individuals to spread virus in many real networks is not always infinite. If the maximum dissemination of individuals in the network is set finite，then there should exist a non-zero epidemic threshold for the above epidemic models. The relations between the epidemic threshold and the maximum dissemination，the relations between the degree of infection and the maximum dissemination are discussed，meanwhile the reason why classical epidemic models always over-predict the degree of infections in real networks is explained.
2008, 57 (11): 6786-6791.
doi: 10.7498/aps.57.6786
Abstract +
By developing the multiple-scale method，we study analytically the dynamical properties of soliton in a quasi-two-dimensional Bose-Einstein condensate. For the repulsive inter-atomic interaction，a unstable dark soliton can be found in the condensate，which would evolve into ring dark soliton with small amplitude. Especially，it is shown that the ring dark soliton has dynamic stability.
2008, 57 (11): 6792-6798.
doi: 10.7498/aps.57.6792
Abstract +
The simplified incidence function model with small delay time was employed to study the stability and mean extinction time of a metapopulation. By numerically computing the mean passage time and analyzing the stationary probability distribution function of the metapopulation，we found that：1) As delay time increases，the probability that pathe are occupied by a metapopulation decreases; 2) As delay time increases，the mean extinction time of a metapopulation decreases.
2008, 57 (11): 6799-6807.
doi: 10.7498/aps.57.6799
Abstract +
This paper presents a new three-dimensional continuous autonomous chaotic system. The new system has two system parameters and a nonlinear term which takes the form of arc tangent function. The stability of the new system is investigated based on linear matrix inequality (LMI) method. And the complex dynamic properties are studied by theoretical analysis，numerical simulation，Lyapunov exponents spectrum，bifurcation diagrams and Poincaré section diagrams.
2008, 57 (11): 6808-6814.
doi: 10.7498/aps.57.6808
Abstract +
A four-dimensional interrelated and switchable Lü hyperchaotic system is built by adding an additional state into the three-dimensional Lü chaotic system. When subsystems are hyperchaotic，an identical system parameter is determined according to the bifurcation diagrams of these subsystems. Some of its basic dynamical properties are studied detailedly，such as the feature of equilibrium，the phase portraits of hyperchaotic attractor，the Lyapunov exponent and fractal dimension. A practical circuit is designed to realize these systems. Experimental result shows the effectiveness and feasibility of the theoretical analysis and verifies the behavior of various attractors.
2008, 57 (11): 6815-6823.
doi: 10.7498/aps.57.6815
Abstract +
Using a Barkley model as an example，the pattern formation of spiral waves in inhomogeneous excitable medium is investigated. The normal distribution of parameters fluctuations is introduced to depict the inhomogeneous medium. It is found that the parameter fluctuations play an important role in the formation of spiral pattern. For a larger variance of the parameter fluctuations，the spiral waves are rough. In the case of the uniform distribution of fluctuations in two parameters，spiral wave cannot be observed for fluctuations beyond a certain range. It is conjectured that these results are induced by the rotating frequency of spiral wave for different parameters. For the larg rotating frequency，the spiral wave pattern is finely crowded，while it is sparse for small frequencies.
A new approach to synchronization between two different chaotic systems with parametric perturbation
2008, 57 (11): 6824-6829.
doi: 10.7498/aps.57.6824
Abstract +
The problem of chaotic synchronization between two different chaotic systems with parametric perturbation is studied. Based on Lyapunov stability law and norm theory，a sufficient condition to synchronize two different chaotic systems with parametric perturbation is given and a general way of choosing the controller is proposed. This method can realize the synchronization of two chaotic systems with parametric perturbation if the dimensions of the chaotic systems are equal and the state variables are measurable. And it is required that the control must decay to zero together with the errors as soon as the synchronization is reached. The proposed method is robust and can be used widely. Numerical simulations of synchronization between two chaotic systems，and synchronization between two hyperchaotic systems are provided to show the effectiveness and feasibility of the method.
2008, 57 (11): 6830-6836.
doi: 10.7498/aps.57.6830
Abstract +
Strong turbulence in the driven drift-wave equation of plasma can be suppressed successfully to a laminar flow by an external periodic signal with proper frequency and strength. In the driving wave coordinates，by transforming the wave system to a set of coupled oscillators (modes) moving in a periodic potential，generalized phase synchronization between these modes is regarded as one of the control mechanisms. In this paper，the effect of noise is studied in the course of the turbulence control. It is found that the laminar flow becomes disordered again with fairly weak bias noise，at the same time the generalized phase synchronization between the modes is lost. However，when the bias noise is quite strong，the quasi-period laminar state can be maintained and the modes can also reach generalized phase synchronization with each other.
2008, 57 (11): 6837-6843.
doi: 10.7498/aps.57.6837
Abstract +
Synchronization in a chaotic fractional-order differential system is studied. Three schemes are designed to achieve chaos synchronization of the fractional-order hyperchaotic system. Sufficient conditions on synchronization are also derived based on the Laplace transformation theory and stability theory of fractional-order linear systems. Numerical simulation or circuit simulation results are presented to demonstrate the effectiveness and feasibility of the proposed method.
2008, 57 (11): 6844-6851.
doi: 10.7498/aps.57.6844
Abstract +
A class of intermittent feedback scheme is proposed to eliminate the spiral wave in the excitable media, which is described by the Fitz-Hugh-Nagumo equation. The activators of the sites is observed and compared with the selected threshold (less than the maximum activator), a negative feedback is imposed on the whole system by inputting linear negative variable into the equation only when the sampled activator exceeds the threshold. It is found that the spiral wave is easier to be removed and the whole media becomes homogeneous when all the sites are monitored and smaller threshold is used, and the spiral wave just becomes sparse and breakup of spiral wave can be observed when the threshold is not small. On theother hand, weaker intensity of feedback still causes the spiral wave to be removed and the whole media still can become homogeneous when only one site is monitored. The controller will stop working as the whole media become homogeneous synchronically.
2008, 57 (11): 6852-6858.
doi: 10.7498/aps.57.6852
Abstract +
Based on stability theory of fractional-order linear systems, a novel method combining feedback control and active control is proposed for the synchronization between two different fractional-order chaotic systems. The controller is obtained, and the method can be applied to solve synchronization problems of several classes of fractional-order chaotic systems, e.g., Lorenz system, Rssler system, Chen system, Liu system, Lü system, Rssler hyperchaotic system and the new hyperchaotic system. Numerical simulation results are presented to demonstrate the effectiveness and feasibility of the proposed method.
2008, 57 (11): 6859-6867.
doi: 10.7498/aps.57.6859
Abstract +
A novel fifth-order hyperchaotic circuit is proposed. This circuit is composed by three linear inductors, two linear capacitors, one negative resistor, and two nonlinear elements, and has the π type circuit configuration. By switching the time constant of the circuit by the action of nonlinear element, the voltage and current is rapidly changed, and by using negative resistors, the condition for local divergence in the circuit is satisfied. The rapid change of voltage and current and local divergence are two primary conditions for generating chaos and hyperchaos in the circuit. Bifurcation and Lyapnuov exponent calculations demonstrate that the oscillation mechanism of the circuit evolves into chaos and hyperchaos from periodic with the change of bifurcation parameters. Furthermore, the fifth-order hyperchaotic circuit has been designed and the result of hardware experiment is reported.
2008, 57 (11): 6868-6877.
doi: 10.7498/aps.57.6868
Abstract +
Usually, pressure fluctuation in oil pipeline is assumed to be stochastic or as white noise, which hinders the improvement of fault diagnosis technology based on pressure fluctuation. To find the internal dynamics of pressure fluctuation in oil pipeline, the possibility of existing chaotic behavior is validated using the method of nonlinear analysis. Six experimental data sets are studied on which phase spaces are reconstructed, the fractal dimensions and Lyapunov exponents are computed and the stationary feature and nonlinearity are validated. By the analysis of the results, the rigorous chaotic character of pressure fluctuation in oil pipeline is found, which is a theoretical basis for the correlative investigation based on pressure time series of oil pipeline.
2008, 57 (11): 6878-6882.
doi: 10.7498/aps.57.6878
Abstract +
Control of chaos in an external cavity delay feedback semiconductor laser via modulating the feedback polarizing light is studied. The laser dynamic physical models of the delayed feedback of dual beams with orthogonal polarizating, with parallel polarizations, or with synchronous or arbitrary polarizing directions are presented, respectively. The delay time and feedback quantity of the feedback light can be adjusted by adjusting the mirror and the optical attenuator in the external optical path, or by adjusting the polarization plane of one beam of polarized light with respect to the polarization direction of the other beam, or at an arbitrary polarization direction to the other beam of polarizing light. In all these cases, the chaotic laser can be controlled. Numerical results show that the laser can be conducted to the single cycle or the multi-cycle, and at the same time be in the polarizing oscillation, polarizing anti-oscillation or stable states.
2008, 57 (11): 6883-6887.
doi: 10.7498/aps.57.6883
Abstract +
Exploiting the information provided by the number of ions in some fixed regions outside the matched radius boundary, the simulation of controlling the beam halo-chaos of a high intensity ion beam has been studied by applying the logarithm-function controller. Control results show that the halo-chaos and its regeneration can be eliminated effectively for five different initial distributions, respectively. The controlling method is easy to realize in experiment because it only needs to probe the control information in small and fixed regions.
2008, 57 (11): 6888-6895.
doi: 10.7498/aps.57.6888
Abstract +
The resonance of single-degree-of-freedom nonlinear impact oscillator to combined deterministic and random excitation is investigated. The method of harmonic balance, perturbation method and the method of stochastic averaging are used to determine the response of the system. The theoretical analyses are verified by numerical results. Theoretical analyses and numerical simulations show that when the intensity of the random excitation increases, the nontrivial steady state solution may change form a limit cycle to a diffused limit cycle. Under some conditions the system may have two steady state responses, one is a non-impact response, the other an impact response.
2008, 57 (11): 6896-6900.
doi: 10.7498/aps.57.6896
Abstract +
Study of the association between local and global behaviors is essential for self-organizing communication system design and system control. A cellular automaton-based model is proposed for addressing the topology control problem of wireless sensor networks which well captures the essential features of system behaviors. It is shown that the system behaviors vary with different local rules, and may have oscillating, decreasing or stable patterns. Moreover, this model can also reflect the tradeoff between different system requirements, which maybe inspiring for further study.
2008, 57 (11): 6901-6908.
doi: 10.7498/aps.57.6901
Abstract +
Simulations of bi-directional pedestrian flow with different direction splits and system sizes are presented based on cellular automata (CA) in this paper. It is well known that pedestrian movement is more flexible and adaptive to the dynamic conditions than vehicular flow, so four dynamic parameters are formulated to simplify tactically the decision-making process of pedestrians, which can reflect the pedestrian's judgment on the surrounding conditions and decide his her choice of action. The relationships of velocity-density and volume-density at different direction splits and on the different size system are studied and analyzed. It is found that there are phase transitions and a critical density point in the model and the relationships of velocity-density and volume-density are different in different phases. And the ratio of direction splits and system size affect the shapes of velocity-density curve, volume-density curve and the value of critical density point.
2008, 57 (11): 6909-6920.
doi: 10.7498/aps.57.6909
Abstract +
We extract the flow pattern complex network from the measured data. After detecting the community structure of the network through the community detection algorithm which is based on k-means clustering, we find that there are three communities in the network, which correspond to the bubble flow, slug flow and churn flow respectively, and the nodes of the network that are connected tightly between two communities correspond to the transitional flow. In this paper, from a new perspective, we not only achieve good identification of flow patterns in gas/liquid two-phase flow based on complex network theory, but also find the characteristics of flow pattern complex network that are sensitive to the flow parameters, which provide reference to the study of dynamic properties of two-phase flow.
2008, 57 (11): 6921-6925.
doi: 10.7498/aps.57.6921
Abstract +
An ytterbium-doped single polarization large-mode-area photonic crystal fiber laser amplifier is demonstrated, which can deliver average power of 16 W at a repetition rate of 50 MHz, corresponding to 320 nJ pulse energy. The length of the fiber is 3.5 m, and the pulse could be shorter since the spectrum is further broadened due to the SPM. The pulse duration is compressed to 85 fs after passing through a grating pair. The oscillator and amplifier of the system are composed of the same single polarization large-mode-area photonic crystal fiber, resulting in better environmental stability and compactness.
ATOMIC AND MOLECULAR PHYSICS
2008, 57 (11): 6926-6931.
doi: 10.7498/aps.57.6926
Abstract +
Based on the density functional theory (DFT) and non-equilibrium Green function (NEGF) method, we present calculations of the electron transport properties of a hydrogen molecule contacting two Pt micro-electrodes. The conductance we obtained agrees well with that of the experiment. The conceptual picture of Feynman path is used to explain our result. The local states of the contact are related to the peaks of the transmission spectrum.
2008, 57 (11): 6932-6938.
doi: 10.7498/aps.57.6932
Abstract +
For the first time, the interaction potentials of the He-HF(DF,TF) van der Waals complexes have been obtained by center of mass transformation and then employing Murrell-Sorbie potential function to fit the accurate interaction energy data, which have been computed at symmetry-adapted perturbation theory (SAPT) level. On the basis of the above results, the close coupling calculation of scattering cross sections for collision of He with HF(DF,TF) is performed by employing the fitted interaction potential. This calculation is performed at the incident energies of 50, 59.5, 86, 100 and 120 meV, respectively. The information of the elastic, inelastic and total integral cross sections were obtained, and the change tendency and characteristics of scattering cross section are discussed for He-HF(DF,TF)collision system.
CLASSICAL AREA OF PHENOMENOLOGY
2008, 57 (11): 6939-6945.
doi: 10.7498/aps.57.6939
Abstract +
An electrostatic dynamic model for wind-blown sand systems of dust devils or sand-dust storms was developed based on the electrochemistry of water molecular film on the surface of particles, in which water is ionized as H3O+/HO- and their concentration vary with temperature. The mobility of H3O+ from high concentration regime to low concentration regime is greater than that of HO-. The interaction of particles result in the change of particle kinetic energy and the particle surface temperature. The simulation of a three-sized particle system with diameters of 0.1, 0.2, and 0.4mm and particle numbers of 750, 100 and 50, respectively, shows that the small particles are charged negatively while the large particles are charged positively, which reasonably explains the electrostatic mechanism of dust devils and sand-dust storms. It was also found that the electrification is relevant to the humidity of granule system, which explains Guardiola's experiments. Coupled with gas-particle two-phase flow model, this electrostatic dynamic model will improve the accuracy of numerical simulation of the wind-blown sand system.
2008, 57 (11): 6946-6954.
doi: 10.7498/aps.57.6946
Abstract +
Basing on vector electromagnetic theory and the waveguide model, the vectorial Hopkins formula is deduced. It containes incidence angle and azimuth angle of off-axis illumination, which is different from the traditional scalar Hopkins formula. By simulating the aerial image of the three dimensional mask in actual lithography process, the optimal angular range of oblique incidence is analyzed, and the impact of oblique incidence angle on imaging quality is also discussed.
2008, 57 (11): 6955-6961.
doi: 10.7498/aps.57.6955
Abstract +
In this paper, a new method for color-image encryption using discrete quaternion fourier-transforms (DQFT) combined with doubled random-phase encryption as used in the optical implementation is proposed, by which color images can be processed as a whole, rather than as separated color components in three channels, so that the complexity of the encryption system can be effectively reduced without any reduction in its security. The principle of both encryption and decryption is detailed and the robustness of the system has been examined experimentally.
2008, 57 (11): 6962-6967.
doi: 10.7498/aps.57.6962
Abstract +
We demonstrated experimentally the generation of squeezed vacuum by a periodically poled KTP crystal in a continuous-wave optical parametric oscillator，which was pumped with 532nm field. The squeezed vacuum of 3.41 dB at 1064 nm was detected by a homodyne detection system. Moreover，the Wigner quasi-probability distribution function of the squeezed vacuum was reconstructed using quantum tomography technique.
2008, 57 (11): 6968-6975.
doi: 10.7498/aps.57.6968
Abstract +
The entanglement degree is investigated by means of the entropy theory between a two-level atom and a coherent field with varying frequency via two-photon transition. We restrict our attention to two cases, the field frequency varying with time in the forms of sine and rectangle. When the field frequency varies with time in the form of sine, the entanglement degree will increase sharply and maintain high values. By changing the amplitude α and angular frequency β of the field-frequency variation respectively, we find that the evolution process is more sensitive to the former. In the rectangular modulation case, different results will be produced when the pulses appear at different time. Comparing the pulses appearing at every minimum value with that at every maximum value, the entanglement degree will increase and reach stability more quickly and easily in the lattev case. The sudden change caused by the rectangular modulation is particularly beneficias to the control of the value of the field entropy.
2008, 57 (11): 6976-6981.
doi: 10.7498/aps.57.6976
Abstract +
We study a three-level atom assemble interacting with a pump field and a quantum probe field, and derive the Langevin quantum noise operators and quantum noise spectrum due to vacuum fluctuations via quantum theory. We calculate the output noise spectrum of active Raman scattering field through the medium when introducing one nonclassical squeezing field.
2008, 57 (11): 6982-6986.
doi: 10.7498/aps.57.6982
Abstract +
Efficient diode stack end-pumped slab lasers with a hybrid cavity were demonstrated. About 60 W of near-diffraction-limited output was obtained with Nd∶YVO4 slab crystals. The lower doped Nd∶YVO4 crystal shows the possibility of further power scaling with near-diffraction-limited output but it also increases the sensitivity of the wavelength to the temperature of the cooling water.
2008, 57 (11): 6987-6991.
doi: 10.7498/aps.57.6987
Abstract +
This paper reports a simple and accurate method for measuring thermal focal length of LD-side-pumped laser crystal. While applying the nonsymmetrical plane-plane-cavity to measure the thermal focal length, the distance from the end of the laser crystal to the end mirror need not be zero, and the reliability of this method is proved by experiments. Based on the obtained measurement results, folding configuration oscillators of yellow laser for intracavity sum frequency can be optimized, which ensures high space overlapping of two fundamental beams and high sum frequency efficiency.
2008, 57 (11): 6992-6997.
doi: 10.7498/aps.57.6992
Abstract +
Beam automatic alignment system is used to implement beam adjustment. Basing on the principle of matrix optics, the mathematical model for auto-alignment in four-pass amplifier is built by analyzing the properties of this system. Using this model, the scheme of beam alignment is designed, and the analytical solutions of the amounts of near field adjustment and far field adjustment are obtained, respectively.
2008, 57 (11): 6998-7004.
doi: 10.7498/aps.57.6998
Abstract +
All-optical time division was obtained in the frequency range from 9.0GHz to 19.8GHz. Nonlinear dynamics of a Fabry-Perot laser diode subjected to external optical injection is applied for all-optical clock division. The research results indicate that semiconductor laser subjected to external light injection performs period-one oscillation. We obtain the clock division of the signal pulses when the second harmonic frequency of the period-one oscillation approaches the repetition rate of the signal pulse, and the second harmonic and the fundamental frequency of the period-one oscillation were locked by the signal pulses simultaneously. Numerical simulation was performed on the all-optical time division with signal pulse injection using the rate equation of the semiconductor laser. The simulation result is in good agreement with the experiment. Phase noise level of the divided clock is observed to be smaller than -90 dBc/Hz over a frequency detuning range of 1.5GHz by changing the repetition rate of signal pulses under the fixed wavelength detuning value and input signal pulse power.
2008, 57 (11): 7005-7011.
doi: 10.7498/aps.57.7005
Abstract +
We present the research on the transmission characteristic of slow-light-mode in the photonic crystal line-defect waveguide bends on SOI. After optimizing the structure parameters in the vicinity of the bends, the normalized transmission efficiency of slow-light-mode through the photonic crystal 60 degree and 120 degree waveguide bends are as high as 80% and 60% respectively, which are 10 times higher than that in the undeformed case. To slow down light further, we design novel coupled cavity waveguide bend structures with high qulity-factor. High normalized transmission efficiency of 75% and low group velocity of c/170 (c is the light velocity in vacuum) are realized. These results are beneficial to enhance the slow light effect of photonic crystal structures and improve the miniaturization and integration of photonic crystal slow light devices.
2008, 57 (11): 7012-7016.
doi: 10.7498/aps.57.7012
Abstract +
The general expression of dispersion relation of microring coupled-resonator optical waveguides was obtained using transfer matrix method. Based on the dispersion relation the linear characteristics of optical pulse propagation in microring coupled-resonator optical waveguides was discussed with respect to the bandwidth, group velocity, dispersion and linear phase shift. These characteristics are important for applications of coupled-resonator optical waveguides in optical communications or as optical sensors.
2008, 57 (11): 7017-7021.
doi: 10.7498/aps.57.7017
Abstract +
A novel technique, based on wavelet-transform analysis, was introduced for the carrier-envelope phase extraction in this paper. With wavelet analysis technique, the carrier-envelope phases of amplified ultrashort optical pulses were directly extracted from the spectral interferences. The technique need no Fourier-transform and filter procedure, therefore, the uncertainty introduced from the filter is avoided naturally. Wavelet-transform technique extracted accurate carrier-envelope phase, therefore we hope it can find applications in the measurements and characterizations of few- to mono-cycle femtosecond optical pulses.
2008, 57 (11): 7022-7029.
doi: 10.7498/aps.57.7022
Abstract +
The acoustic characteristics of underwater cylindrical Helmholtz resonator are analyzed theoretically. Based on the theories of electro-acoustic analogy, a low frequency lumped-parameter model of the Helmholtz resonator is constructed with due consideration of the effects of the elasticity and the radiation impedance of the resonator. To our knowledge, this is the first time such a complete model is constructed. The input impedance and the transfer function of the system are given by circuit analysis. The effects of parameter values of the resonator on the acoustic characteristics are studied by numerical method. Some useful conclusions are drawn. A small aluminum cylindrical Helmholtz resonator is measured in a standing-wave tube filled with water. Error analysis is made in detail. The experimental results are in agreement with the simulation results considering the effect of the piezoelectric hydrophone. The validity of the theoretical analysis is testified. This paper supplies a theoretical and experimental basis for the design of underwater cylindrical Helmholtz resonators, and is useful for the estimation of underwater acoustic performance of Helmholtz resonators of other shapes.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2008, 57 (11): 7030-7037.
doi: 10.7498/aps.57.7030
Abstract +
Solutions of electron and ion density gratings at the linear stage are given. Deep plasma gratings produced by the ponderomotive force of the interference of the two intersecting laser pulses are investigated. Dependence of the plasma grating on the plasma density, duration and intensity of the laser pulses are studied with 1D particle-in-cell (PIC) simulation. It is found that the density of peaks of such gratings can be 8 times the initial plasma density and can last a few picoseconds. We have found stable, long-lifetime electromagnetic solitons by use of these gratings. It is shown that the intensity for the formation of relativistic EM solitons with two crossed-propagating pulses is reduced to a great extent.
2008, 57 (11): 7038-7043.
doi: 10.7498/aps.57.7038
Abstract +
Dual-frequency capacitively coupled plasma (DF-CCP) driven by two frequencies of 60MHz and 13.56MHz was studied using compensated Langmuir probe technique. The change of EEPF with radial position and low-frequency input power was obtained. The experimental result shows that the input power of 13.56MHz mainly affects the population of low-energy electrons and the effect becomes greater when the gas pressure increases. The EEPF exhibits a structure of bi-energy-peak beyond the centre of discharge. The second energy peak drifts to the region of higher electron energy from the centre to the edge of electrode. The emergence of second energy peak could be attributed to the enhanced heating of middle-energy electrons. The electron density and electron temperature were calculated using EEPF. The plasma electron heating mechanism was discussed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2008, 57 (11): 7044-7051.
doi: 10.7498/aps.57.7044
Abstract +
This paper discusses the influence of the polarization of incident X-vay on the reconstructed atomic image by numerical simulation and reconstruction, using a crystalstructure composed of 27 Fe atoms arranged in a cubic lattice as the model. Calculated results show that the choice of polarization is crucial for the atom observability. This paper proposes a new reconstructing algorithm which can eliminate the polarization effect of incident X-ray source and twin images inherent to holography at the same time. Numerical simulation and reconstruction results show that the reconstructing algorithm is effective and can be used to eliminate the influence of polarization of incident light source and twin image in experiments.
EDITOR'S SUGGESTION
2008, 57 (11): 7052-7056.
doi: 10.7498/aps.57.7052
Abstract +
This paper investigates a triple-gate single electron FET memory with a Si quantum dot floating gate and a Si quantum wire channel by establishing a numerical model of two-dimensional Schrdinger and Poisson equations. The electron concentration in the silicon quantum wire channel of different scales is investigated under conditions that diverse gate voltage and programming voltage are applied with a two-dimensional finite element solution. The influence of the quantum confinement effect and the electron distribution in the nano-scale channel on the structure is also investigated. Results of the simulation show that, the threshold voltage increases when the size of the channel decreases, and the voltage also increases as the number of electrons on the floating gate increases. However, a non-linear saturation tendency occurs when the number of injected electrons increases further, due to the high density of carriers in the nanoscale Si nanowire channel. Further research shows that the strong quantum confinement effect in the channel can effectively restrain the saturation tendency when the size of the channel is small enough. It's worth mentioning that the threshold voltage shift reflects the number of electrons stored on the floating gate.This effect implies a possibility of multi-level storage.
2008, 57 (11): 7057-7062.
doi: 10.7498/aps.57.7057
Abstract +
Two kinds of vertically aligned, well-ordered zinc oxide nanoneedle arrays were synthesized on silicon substrates without any catalyst by a simple thermal evaporation method. The nanoneedle arrays have uniform distribution and unique orientation and height. The field emission study shows that both of them have not only low turn-on field and threshold field, but also the ability of stable and long time emission. The low turn-on field and threshold field result from the high aspect ratio and thin apex of the nanoneedles. The stable and long time emission are due to the uniform distribution and good contact between the nanoneedles and the substrate. The results show that regular nanoneedle arrays are ideal candidates for flat panel field emission applications.
2008, 57 (11): 7063-7068.
doi: 10.7498/aps.57.7063
Abstract +
Monolithic TaN，NbN, TiN films and TaN/TiN, NbN/TiN multilayers with different modulation periods were prepared by reactive magnetic sputtering. The films were characterized by X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation. Results showed that there are coherent interfaces between the layers of TaN and TiN in TaN/TiN multilayers and the layers of NbN and TiN in NbN/TiN multilayers within a modulation period. The superhardness effect happened and the maximum hardness values of the two multilayers are nearly equal. The superhardness mechanism was discussed. The lattices mismatch between NbN/TiN and TaN/TiN multilayers is similar, but the difference in modulus of NbN/TiN multilayers is larger than that of TaN/TiN multilayers. It shows that stress field induced by coherent epitaxial growth is the main reason of superhardness effect.
2008, 57 (11): 7069-7077.
doi: 10.7498/aps.57.7069
Abstract +
On the basis of the atomistic simulations of electrowetting of single-walled carbon nanotubes by mercury, the electrowettings in double-walled carbon nanotubes are studied. Classical molecular dynamics simulations in conjunction with a macroscopic electrocapillarity model are carried out to clarify the effect of inner tube’s size on electrowetting. Results show that there is a great difference between electrowetting in single-walled and double-walled carbon nanotubes. The inner tube plays a key role in the electrowetting of double-walled carbon nanotube. Very different phenomenon occurs when the size of the inner tube is changed.
2008, 57 (11): 7078-7082.
doi: 10.7498/aps.57.7078
Abstract +
The single-phase polycrystalline Sm-filled skutterudites SmyFexCo4-xSb12 were investigated by Rietveld refinement and Raman scattering spectral analysis. The results of Rietveld refinement clarify that the SmyFexCo4-xSb12 compound has a filled skutterudite structure. The thermal parameter of Sm is larger than that of Sb, Fe and Co, and the Sb-Sb bond length of SmyFexCo4-xSb12 is longer than that of unfilled skutterudites. The results of Raman scattering study show a shift and broadening of the Sb4 ring breathing modes. These results indicate that Sm atoms fill the Sb-icosahedron voids of the skutterudites and rattle in them.
2008, 57 (11): 7083-7087.
doi: 10.7498/aps.57.7083
Abstract +
By internal friction technique，the behaviors of quenched-in vacancies and their influence on the reverse martensitic phase transformation (MT) temperature of the Cu-11.9Al-2.5Mn (wt%) shape memory alloy have been studied. Investigations on the specimens subjected to various cooling regimes indicate that rapid cooling rate leads to relatively high reverse MT temperature. For the water-quenched specimens，the reverse MT temperature bears a non-monotonic relationship to quenching temperature. This phenomenon may be related to the different formation energies of vacancies in ordered and disordered phases.
2008, 57 (11): 7088-7093.
doi: 10.7498/aps.57.7088
Abstract +
Real-time measurement of γ irradiation effect of Hg1-xCdx Te long-and mid-wavelength focal plane array photodiodes has been carried out. Through measuring the current-voltage characteristic during irradiation process, it has been found that mid-wavelength detectors are more radiation resistant than long-wavelength photodiodes. For long-wavelength detectors, the zero bias resistance, which is usually used to evaluate the performance of photodiodes, decreases with increased γ irradiation dosage. For mid-wavelength detectors, the zero biased resistance does not show a definite changing trend, and the irradiation mainly caused fluctuations of resistance-voltage curves with increased dosage. By numerically simulating the resistance-voltage curves of long-wavelength detectors on the basis of dark current mechanism, it was found that the lifetime ofminority carriers in the generation-recombination process was shortened and thedefects produced by irradiation increased as the dosage increased, and the affected dark current mechanism was mainly the generation-recombination current. Because the irradiated mid-wavelength detectors have much larger carrier mobility and much lower dopant density, and also a bandgap twice that of long-wavelength detectors, they showed a weaker irradiation effect. The fluctuations of the resistance-voltage curves caused by irradiation would lead to an increase on noise of the detectors.
The deformation mechanism of nanofilm with void under tensile loading: An atomistic simulation study
2008, 57 (11): 7094-7099.
doi: 10.7498/aps.57.7094
Abstract +
In this paper, we employ molecular static approach with quantum corrected Sutten-Chen many-body potential to study the mechanical behavior of nickel nanofilm during uniaxial loading, and investigate its microstructure by common neighbor analysis methods. The simulated results show that the existence of void significantly weakens the Young’s modulus and yield stress of nanofilm; with the increased strain, the shape of void changes from circular into elliptical, and the void is eventually entirely closed. The plastic deformation of nanofilm is characterized by {111} glide associated with Shockley partial dislocations, resulting in the formation of stacking faults.
2008, 57 (11): 7100-7107.
doi: 10.7498/aps.57.7100
Abstract +
The influence of the magnetic field and temperature on the properties of the strong-coupling magnetopolaron in an asymmetric quantum dot is studied by using the Tokuda’s linear-combination operator and the Lee-Low-Pines variational method. The expressions for the vibration frequency λ, ground state energy E0 and the effective mass m* of the magnetopolaron as a function of the transverse effective confinement strength ω1, the longitudinal effective confinement strength ω2, the electron-phonon coupling strength α, the cyclotron frequency ωc and the temperature parameter γ are derived. Numerical results indicate that λ and m* of the magnetopolaron will increase with increasing ω1,ω2,ωc and α, and will decrease with increasing temperature T. The value of E0 changing with ω1,ω2,ωc,α and γ are srongly related to the propties of the state of the magnetopolaron. The signs of positeve and negative E0 relate not only to the value of ω1,ω2,ωc and α but also to the value of γ. However, only on the condition of higher temperature (γλ,m* and E0 of the magnetopolaron is obvious.
2008, 57 (11): 7108-7113.
doi: 10.7498/aps.57.7108
Abstract +
Through the comparative investigation on oxygen precipitation behaviors in the heavily and lightly arsenic-doped n-type Czochralski (CZ) silicon wafers subjected to the two-step annealing successively at low temperature (450—800℃) and high temperature (1000℃), the effects of low-temperature annealing on oxygen precipitate nucleation in heavily arsenic-doped CZ silicon wafer have been elucidated. It was found that for the heavily arsenic-doped CZ silicon the oxygen precipitate nucleation during the 450 and 650℃ annealing was more significant than that during the 800℃ annealing, which was contrary to the case for lightly-doped CZ silicon. Moreover, in comparison with the lightly-doped CZ silicon, the oxygen precipitate nucleation at 450 and 650℃ was enhanced while that at 800℃ was suppressed in the heavily arsenic-doped CZ silicon. It is believed that in the heavily arsenic-doped CZ silicon the As-V-O complexes can be formed during the annealing at 450 and 650℃ so as to enhance the oxygen precipitate nucleation; while, during the 800℃ annealing the As-V-O complexes are not stable enough to act as the precursors of nuclei and, moreover, the heavy arsenic-doping leads to compressive lattice stress, therefore the oxygen precipitate nucleation is noticeably suppressed. Furthermore, it is revealed that the nitrogen-doping facilitates the oxygen precipitate nucleation during the annealing at low temperatures especially at 800℃, which is believed to be due to the heterogeneous nucleation centers induced by nitrogen-doping.
2008, 57 (11): 7114-7118.
doi: 10.7498/aps.57.7114
Abstract +
In this paper, amorphous, microcrystalline and polymorphous silicon films were prepared by plasma enhanced chemical deposition. Crystalline volume fraction of microcrystalline silicon was deduced from the Raman spectrum, and this fraction was validated using Bruggeman effective medium approximation (BEMA) model in spectroscopic ellipsometry measurement. The influence of thermal gradient on the deposition mechanism of microcrystalline and polymorphous silicon was investigated using a theoretical model. The dependence of crystalline volume fraction on film thickness shows there is a crystalline gradient between bottom and surface of microcrystalline film, and there is not such a gradient in polymorphous silicon film. Polymorphous and microcrystalline silicon have similar ordered state and density, which are signifieantly higher than those of amorphous silicon.
2008, 57 (11): 7119-7125.
doi: 10.7498/aps.57.7119
Abstract +
Precise measurement and control of GaN-film thickness is very important for GaN-based material epitaxy and device fabrication. However, GaN-films heteroepitaxially grown on large-mismatch substrates, such as sapphire, SiC and Si, etc., usually show a mosaic structure, which causes great difficulty to the GaN-film thickness measurement. Combining the advantages of Williamson-Hall plot method and diffraction profile shape analysis method, a new strategy was presented to effectively distinguish the X-ray diffraction broadening factors of finite crystallite size and inhomogeneous strain, which can be used to precisely and reliably determine the thickness of epitaxial films. The thickness of a series of GaN films grown on sapphire substrates in the range of 0.7—4.2 μm were measured by this method. Comparing with the thickness obtained from spectroscopic ellipsometry measurements, the difference was found to be within 4%, which shows the excellent performance of this method.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2008, 57 (11): 7126-7131.
doi: 10.7498/aps.57.7126
Abstract +
The Ca ion distribution in La1-xCaxMnO3(x≤1/3) has been studied using atomistic simulation. It is found that at low temperatures the doped Ca ions tend to be distributed in clusters with a size of about 6—19?. The stability of the clusters at high pressure and elevated temperature has also been studied, and the calculation results show that the Ca clusters are stable at 3 GPa and 120 K. This chemical phase separation may be one of the causes of the structure and electronic/magnetic inhomogeneity in La1-xCaxMnO3 found in experiments.
EDITOR'S SUGGESTION
2008, 57 (11): 7132-7138.
doi: 10.7498/aps.57.7132
Abstract +
Based on first-principles electronic structure and transport calculations, we have studied electronic structure and transport properties of graphene nanoribbons with single vacancy defects. It is shown that introduction of the single vacancy defects leads to a flat band belt at the Fermi energy level for graphene nanoribbons and the semiconductor-metal transition in zigzag semiconducting graphene nanoribbons, which is useful in the energy-band engineering. Armchair graphene nanoribbons with odd width are metallic with good electric conduction while armchair graphene nanoribbons with even width have metallic band structures with character of the group IV semiconductor. Single vacancy defects weakens the conduction of armchair graphene nanoribbons with odd width while obviously strengthens the conduction of armchair graphene nanoribbons with even width.
2008, 57 (11): 7139-7144.
doi: 10.7498/aps.57.7139
Abstract +
The adsorption of Au on the (110) surfaces of CeO2 and Zr-doped CeO2 were studied using projector-augmented wave (PAW) method based density-functional theory (DFT) within the gradient approximation (GGA) and with the inclusion of on-site Coulomb interaction (DFT+U). It is found that, due to the doping of Zr, the adsorption energies of Au are increased and the strongest adsorption geometry is altered. The doping of Zr results in larger distortion in the structure of the substrate, and enhances the catalytic activity of the Au/CeO2(110) system and the oxidization of Au. These results may lead to a better understanding for the Au/Zr-doped CeO2 catalysts and give some clues for improving the efficiency of the three-way catalysts (TWC).
2008, 57 (11): 7145-7150.
doi: 10.7498/aps.57.7145
Abstract +
Electronic structure, elastic constants and thermodynamic properties of Mg2Sn have been calculated by using the first-principles pseudopotential method. As shown by the calculated results, the band gap of Mg2Sn is 0.1198 eV. The linear response method is applied to determine the phonon dispersion relations and phonon density of states. The thermodynamic properties such as the constant-volume specific heat and Debye temperature are calculated. The calculated thermal conductivity is compared with the experimental data.
2008, 57 (11): 7151-7156.
doi: 10.7498/aps.57.7151
Abstract +
The electronic structures of potassium doped ZnO have been calculated by first principles plane wave-function psuedopotential approach based on density-functional theory and local density approximation. Properties of some defects were studied in order to explicate the conductivity mechanism of p-K:ZnO, including hydrogen interstitial (Hi), oxygen vacancy (VO), zinc interstitial (Zni) and zinc vacancy (VZn). The calculated results revealed that: (1) K-doping introduced a shallow acceptor,besides increasing the system total energy simultaneously. (2) K-H:ZnO decreased the system energy and increased the system stability. (3) Although the formation of VO was more difficult than that of Zni, both of them were electronegative centers and played a role in compensating for the acceptors. (4) VZn produceda shallow acceptor approximately 0.5 eV above the maximum valence band, which was beneficial for p-type conductivity. Finally, it was proposed that the realization of p-type conductivity in K:ZnO may be due to the formation of a KZn-O-Hi-O-VZn complex.
2008, 57 (11): 7157-7163.
doi: 10.7498/aps.57.7157
Abstract +
Molecular dynamics (MD) simulation is performed to study the diffusion and phase separation process in binary Lennard-Jones (LJ) liquid. It is found that the growth of phase separation with temperature can be divided into two stages. The first is the fast-growth at high temperatures and the second is the steady-growth at low temperatures. Diffusion activation energy in the phase separation system is not a constant, but a function of temperature and follows the relation of E=a+bTc. The influence of the sizes of the components on the phase separation is also discussed. The results shows that the diffusivity increases when the component size decreases. This facilitates the phase separation.
2008, 57 (11): 7164-7167.
doi: 10.7498/aps.57.7164
Abstract +
The electron field emission performance of CNT doped with one Boron atom and with one adsorbed H2O molecular (BCNT+H2O) was investigated through the calculations of density functional theory (DFT) in this paper. The results indicated that there is an atomic scale region of electron congregation near the top of BCNT+H2O, and the electronic density of states (DOS) round the Fermi level is enhanced obviously. It is expected that BCNT+H2O be suitable for the field emission of electrons,judging from the calculation results of DOS, HOMO/LUMO and Mulliken charge population.
2008, 57 (11): 7168-7172.
doi: 10.7498/aps.57.7168
Abstract +
La0.33Pr0.34Ca0.33MnO3 thin films have been grown on (100) LaAlO3 and (100) SrTiO3 substrates by pulsed laser deposition, and the physical properties of those thin films have been studied through magnetic and electric transport measurements. The results show that compressive strain between the film and substrate favors the formation of the ferromagnetic metallic phase while suppressing the charge ordered insulating phase. On the contrary, tensile strain tends to enhance the ferromagnetic metallic phase while eliminating the charge ordered insulating phase. The reason could be that the strain induces change in the Mn-O bonding angle in the crystal lattice and thus modify the double exchange interaction.
2008, 57 (11): 7173-7177.
doi: 10.7498/aps.57.7173
Abstract +
With the help of the floating sphere mirror image model and the Fowler-Nordheim equation, the emission current density from carbon nanotube was calculated in this paper. Taking the field enhancement factor and the emission current density into account, the field emission of carbon nanotube array was optimized in theory. The result shoved that the field emission from carbon nanotube array is maximal when the intertube distance is equal to one tenth of the tube height, which is a little smaller than the previous result. When the intertube distance is larger , the field enhancement factor increases, but the emission current density decreases even more rapidly with increasing intertube distance. For carbon nanotube arrays with higher array density, the field enhancement factor decreases greatly with the decreasing intertube distance due to the screening of the electric field.
2008, 57 (11): 7178-7184.
doi: 10.7498/aps.57.7178
Abstract +
The self-consistent effective-medium approximation is used to study the extraordinary magnetoresistance effect observed in nonmagnetic semiconductors. The inhomogeneous materials are treated as a three-dimensional resistor network of binary disorder, where the receptivity of each component is a tensor describing both the zero-field resistance and the Hall effect. The effective conductivity tensor of the total system is calculated with applied magnetic field. The resulting transversal magnetoresistance, longitudinal magnetoresistance and effective Hall coefficient are shown for different component concentrations and magnetic fields. When the components have two different types of charge carriers, and the mismatch between the zero-resistivity is enlarged, the macroscopic magnetoresisance exhibits complex behaviors which are related closely with the formation of the percolation structure in the inhomogeneous system.
2008, 57 (11): 7185-7189.
doi: 10.7498/aps.57.7185
Abstract +
A new kind of ultra-fast power photoconductive semiconductor switch with double-layer semi-insulating GaAs:EL2 is designed and prepared. Because the distribution of voltage between the triggered double GaAs layers is dynamic, when biased at a high electric field, the double layers go into the high-gain state one after the other but prevent each other from entering the Lock-on state, so the output electric pulse has double peaks and looks like a rectangular wave. This working mode not only has the strong points of the nonlinear mode, such as the required laser energy is far less and the rise time is shorter than that of the linear mode, but also has the merits of the linear mode, such as the repetition frequency is higher and the life is far longer than that of the nonlinear mode. Biased at 6500 V and triggered by an 8 ns, 3 mJ and 1064 nm laser pulse, the rise time of the output electric pulse is 13.2 ns, the fall time is 54.6 ns, the full width at half maximum is 148.4 ns, the first peak is 885 V and the second peak is 897 V. With the bias voltage increasing, the rise time nearly keeps a constant, the width and fall time decrease slightly and the double peaks increase obviously.
2008, 57 (11): 7190-7193.
doi: 10.7498/aps.57.7190
Abstract +
The m-plane GaN film is grown on LiAlO2 by metal organic chemical vapor deposition. The single crystal orientation of m-plane GaN is demonstrated, According to the X-ray diffraction results, and the anisotropy strain is calculated. X-ray rocking curve at different φ angle shows obvious in plane structural anisotropy. Polarized photoluminescence is employed for the investigation of optical anisotropy. Both the wavelength and the intensity for the emission peak near band edge vary with the rotation of polarization angle, and can be explained by the degeneration of the subbands in valence band under anisotropy strain.
2008, 57 (11): 7194-7199.
doi: 10.7498/aps.57.7194
Abstract +
A unified expression of magnetic susceptibility tensor is presented according to the magnetic-moment motion equation with Landau-Lifshitz damping term and Gilbert damping term. The application of equivalent magnetic permeability enables to transform the anisotropy problem to an isotropy one with the same electromagnetic solution in amorphous wire. By this transformation, the impedance of amorphous wire passing through an insulating or conducting magnetic ring are analyzed. Additionally, the magnetoimpedance effect in amorphous wire through a magnetic ring is simulated by the numerical analysis based on the finite element method. The results of theoretical analysis and numerical simulation, which agree with each other, indicate that the additional impedance caused by extra magnetic objects seriously reduces the magnetoimpedance change of amorphous wire and destroy the giant magnetoimpedance characteristic. Therefore, the return wire structure is proposed to diminish the additional impedance. The simulation results verified the effectiveness of this method.
2008, 57 (11): 7200-7203.
doi: 10.7498/aps.57.7200
Abstract +
Frequency selective surface (FSS) is a two-dimensional array structure, which can be used to improve the performance of radar absorbing materials. We design circular unit of FSS, and give a simulation research on the circular unit of FSS with the spectral domain approach. The result shows that the circular unit of FSS greatly widens the bandwidth of radar absorbing materials, and decreases the reflectivity of resonance frequency; the bandwidth of radar absorbing materials increases with the increasing radius of the unit, and the resonance frequency drifts to low frequency, which provides theoretical support to the application of FSS in wave absorbing materials.
2008, 57 (11): 7204-7209.
doi: 10.7498/aps.57.7204
Abstract +
A first principles plane-wave method is utilized to investigate the bulk properties of the NiTi alloy，such as the lattice parameters, formation energy and cohesive energy and the elastic constant. The results are in good agreement with experimental and other theoretical results.Furthermore,we have studied the geometric and electronic structures of NiTi (100) and(110)surfaces. As to the surface geometry, there are different relaxations in the surface layers. As for the cleaned NiTi(110) surface, outermost surface layer shows a large rippled relaxation in which Ni atoms contract into the bulk by 0.198? and Ti atoms expand to the vacuum by 0.122?. The calculation of the surface electronic structure shows that Ti-terminated surface is more reactive than Ni-terminated surface on (100) surface and the NiTi (110) surface is inert.
2008, 57 (11): 7210-7215.
doi: 10.7498/aps.57.7210
Abstract +
Transmission of electromagnetic wave in a heavily doped n-type GaAs film is studied theoretically. From the calculations, an extraordinary transmission of p-polarized waves through the film with subwavelength grooves on both surfaces at mid-infrared frequencies is found. This extraordinary transmission is attributed to the coupling of the surface-plasmon polariton modes and waveguide modes. By selecting a set of groove parameters, the transmission is optimized to a maximum. Furthermore, the transmission can be tuned by dopant concentrations. As the dopant concentration increases, the peak position shifts to higher frequency but the peak value decreases.
2008, 57 (11): 7216-7220.
doi: 10.7498/aps.57.7216
Abstract +
For the mesoscopic capacitance coupling LC circuit, the Hamiltonian is given by the canonical quantization. The Hamiltonian operator is diagonalized by a unitary transformation. The ensemble average energy and its fluctuations are derived by ensemble theory. In virtue of the generalized Hellmann-Feynman theorem, the quantum fluctuations of charge and self-conductance magnetic flux for the system at finite temperature are investigated. It is found that, the quantum fluctuations of charge and self-conductance magnetic flux depend on the temperature as well as the parameters of the circuit components.
2008, 57 (11): 7221-7227.
doi: 10.7498/aps.57.7221
Abstract +
We study the characteristics of the spin-tunneling time and the transmission coefficient in a ferromagnetic/semiconductor/ ferromagnetic heterojunction with a δ tunnel barrier. The effects of the quantum size and Rashba spin-orbit coupling are discussed. It is shown that the existence of the tunnel barrier will reduee the magnitude of the transmission coefficient and the variation of the barrier strength will change the phase of the transmission coefficient. The oscillation frequency of the transmission coefficient increases with the increasing of the Rashba spin-orbit coupling. When the spin-dependent electron tunnels through the heterojunction, the tunneling time becomes longer with the length of the semiconductor increasing. The Rashba spin-orbit coupling also affects the spin-tunneling time.
2008, 57 (11): 7228-7232.
doi: 10.7498/aps.57.7228
Abstract +
There has been much interest lately in the strained Si CMOS technology used for carrier mobility enhancement. The dispersion relation of valence band in strained Si is the theoretical basis for understanding and enhancing hole mobility. With in the frame of K.P theory, the dispersion relation is derived by taking strained Hamiltonian perturbation into account. The corresponding model obtained can be applied to calculate the valence band structure and hole effective mass along arbitrarily K wavevector direction in strained Si grown on arbitrarily oriented relaxed Si1－xGex(0≤x≤0.6) substrates, and hence is valuable as reference for the design of devices.
2008, 57 (11): 7233-7237.
doi: 10.7498/aps.57.7233
Abstract +
In this paper, GaN films are grown by metal organic vapor phase epitaxy. Different N2 carrier gas percentages were used in the high-temperature growth process of the bulk GaN, and the dependence of sheet resistance on N2 carrier gas percentage is studied. It is found that the sheet resistance of the GaN film increases dramatically with N2 carrier gas percentage. When N2 carrier gas percentage is 50%, the sheet resistance of the GaN film is 1.1×108Ω/sq, and the surface root-mean-square roughness is as small as 0.233 nm. Secondary ion mass spectroscopy measurements reveal that the concentration of carbon and oxygen impurities is almost the same in the samples with different N2 carrier gas percentage. The density of edge-dislocation-related defects increases with N2 carrier gas percentage, while the density of screw-dislocation-related defects shows no obvious difference for all the samples. Our results indicate that the increase of the sheet resistance of GaN film is mainly due to the increase of edge threading dislocations, which act as acceptor centers in the GaN material.
2008, 57 (11): 7238-7243.
doi: 10.7498/aps.57.7238
Abstract +
The influence of pit defects on AlGaN surface and dislocation defects in GaN buffer layer on the current collapse of MOVPE-grown AlGaN/GaN high electron mobility transistors (HEMTs) is studied in this paper. Pulsed gate voltage measurements show that the surface pit defects result in gate lag current collapse and increased of source/drain resistance. And the more pit defects exist, the more obvious current collapse and increased source/drain resistance are observed. Pulsed drain voltage measurements show that the drain lag current collapse, which is almost unaffected by the surface pit defects, can be associated with the dislocation defects in GaN buffer layer. Our experimental results indicate that pit defects on AlGaN surface and dislocation defects in GaN buffer layer can be one of the origins of gate lag and drain lag current collapse, respectively.
Study on doping and electrical properties of organic infrared semiconductor phthalocyanine erbium(Ⅲ)
2008, 57 (11): 7244-7251.
doi: 10.7498/aps.57.7244
Abstract +
The organic infrared semiconductor ErPc2 prepared by solid phase reaction method has been doped with iodine, the resistivity of ErPc2 has been successfully decreased by about three orders of magnitude by doping. The R-T relationships for intrinsic and iodine doped ErPc2 have been studied, it is found that compared with intrinsic ErPc2, the doped ErPc2 has a remarkable decrease in resistivity, the relationship between resistance and temperature for the doped ErPc2 has not been changed intrinsically, both intrinsic and doped ErPc2 exhibit an exponential dependence of R-T. It is also found that the heat activation energy (Ea) has been effectively reduced by doping, which leads to more carriers that may take part in conducting electricity for ErPc2. The decrease in pre-exponential factor (A) may also contribute to reducing resistivity of ErPc2. The exponential relationship between I and V under a strong electrical field strength has also been explained for the intrinsic organic infrared semiconductor ErPc2.
2008, 57 (11): 7252-7256.
doi: 10.7498/aps.57.7252
Abstract +
Using the coupled sine-Gordon equations，we investigate the motion of Josephson vortex in high-Tc superconductors. It is found that the oscillation behavior in the average voltage and resistance of Josephson vortex flow appear with the increasing of magnetic field in a fixed bias current. The period of the oscillation corresponds to the field, which has the magnitude of adding one Josephson vortex quantum per one intrinsic Josephson junction.
2008, 57 (11): 7257-7261.
doi: 10.7498/aps.57.7257
Abstract +
Highly c-oriented La1.85Sr0.15CuO4 (LSCO) films were successfully deposited on SrTiO3 (STO) substrates by on-axis magnetron sputtering. By using the standard four-probe technique and X-ray diffraction (XRD), we investigated the influence of film thickness on the structure and superconductivity of LSCO(x=0.15) films. The experiment results show that the full-width at half maximum (FWHM) of the (006) rocking curve decreases with increasing film thickness, which indicates that the crystal qualities of films are improved. Meanwhile, the superconducting transition temperature is higher for the thicker films.
2008, 57 (11): 7262-7266.
doi: 10.7498/aps.57.7262
Abstract +
Polycrystalline Si0.9654Mn0.0346 films codoped with boron have been prepared by rf magnetron sputtering deposition followed by fast thermal processing for crystallization. Magnetic property investigation indicated that the film consists of two ferromagnetic phases. The low Curie temperature ferromagnetic phase (TC～50K) is due to the Mn4Si7 phase in the film as detected by X-ray diffraction (XRD), while the high temperature phase (TC～250K) results from the incorporation of Mn into silicon. The polycrystalline thin films were treated by hydrogen passivation for about 4 minutes using radio-frequency plasma enhanced chemical vapor deposition (PECVD). After hydrogenation, the saturation magnetization increases with the increase of hole concentration in the films. The magnetic properties are closely related to the transport properties of the polycrystalline Si0.9654Mn0.0346 films, which suggests a mechanism of hole-mediated ferromagnetism in Si-based diluted magnetic semiconductors.
2008, 57 (11): 7267-7273.
doi: 10.7498/aps.57.7267
Abstract +
By using the density-matrix renormalization group method, the spin entanglement in the antiferromagnetic Heisenberg chain with the staggered Dzyaloshinskii-Moriya (DM) interactions is investigated. It is found that the staggered DM interactions remove the field-induced second order quantum phase transition of the system at the magnitude of magnetic field H＝2, and lead to the vanishing of the anomalous behavior of quantum entanglement. Also, the staggered DM interactions eliminate the divergence of entanglement range. It means the disappearance of the factorizing point in the model studied. Due to the presence of the staggered DM interactions, the system will never come to the state of saturated ferromagnetism under finite magnetic fields, thus maintaining the spin entanglement. The staggered DM interactions favor the tuning of the strength and range of spin entanglement.
2008, 57 (11): 7274-7278.
doi: 10.7498/aps.57.7274
Abstract +
The Perovskite BaFeO3 nano-powder has been synthesized by sol-gel method. The micro-structure and morphology of BaFeO3 nano-powder have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results showed that the samples annealed at 800 ℃ formed the perovskite-type BaFeO3 with grain size of about 20 nm and the (110) and (100) spacings of about 0.280 nm and 0.401 nm, respectively. The room temperature magnetic properties of samples have been measured on vibrating sample magnetometer (VSM). It is shown that the BaFeO3 nano-powder has a complete hysteresis loop, which means that BaFeO3 powder possess significant weak ferromagnetism at room temperature, and this property changes obviously with the annealing temperature. Ferromagnetism of perovskite BaFeO3 nano-powder mainly originates from oxygen vacancy among Fe3+-O-Fe4+.
2008, 57 (11): 7279-7286.
doi: 10.7498/aps.57.7279
Abstract +
The initial spontaneous magnetic domains in nanoscale Fe islands on W(110) substrates are studied numerically with micromagnetic simulations. The critical anisotropies separating different domain states for irregular, elliptic and rectangular shape islands are determined precisely. A full phase diagram of magnetic domain states as a function of anisotropy and thickness is obtained, in which there is a wide transition zone separating two domain states from vortex or diamond domains, and the boundaries on two sides of the transition zone are indefinite. The calculated results indicate that the initial spontaneous magnetic domains are determined mainly by anisotropies and thicknesses, and rim shapes have significant influences on vortex and diamond domain configurations. Further study is needed to determine the exact anisotropies of nanoscale Fe islands.
2008, 57 (11): 7287-7291.
doi: 10.7498/aps.57.7287
Abstract +
First order reversal curves (FORC) were simulated and experimentally measured for the first time for laminated antiferromagnetically coupled (LAC) media. Micromagnetic simulation was effectively utilized in order to understand correctly the various peaks in the FORC contours. The result of the simulation was used to assign the experimentally observed FORC contour peaks to different magnetization reversals. It was observed that the FORC could provide more information than the interactions measured by the conventional delta-M method.
2008, 57 (11): 7292-7297.
doi: 10.7498/aps.57.7292
Abstract +
The dynamic Young's modulus of elasticity and the dynamic piezomagnetic coefficient of magnetostrictive material are derived based on the nonlinear constitutive model of magnetostrictive material. Based on the equivalent circuit method, the relation between magnetoelectric effect of the laminated composite and the dynamic Young's modulus of elasticity, and the dynamic piezomagnetic coefficient of magnetostrictive material is established. The influences of bias magnetic field on the resonant frequencies and the resonant magnetoelectric voltage coefficients of the laminated composite are discussed. The theoretical analysis and the experimental results indicate that there is an optimal bias magnetic field at which the resonant magnetoelectric voltage coefficient of the laminated composite reaches its maximum.
2008, 57 (11): 7298-7304.
doi: 10.7498/aps.57.7298
Abstract +
A slim-loop ferroelectric ceramic of Pb (Zr0.42Sn0.40Ti0.18)O3(PZST42/40/18) was prepared by partially replacing Pb with Ba and La, and replacing (Zr, Sn, Ti) with Nb in low zirconiumn. The saturation polarization (Ps), the remnant polarization (Pr) and the area of the hysteresis loop (S) were measured to be 20.66 μC/cm2, 0.55 μC/cm2 and 0.0298J/cm3, respectively. Relative permittivity (ε)≈2840 can be reached in this ferroelectric ceramic at room temperature and frequency of 1kHz, but the energy density (w) is 0.319J/cm3. The results of the pulse charge-discharge measurements showed that a single piece of the PZST42/40/18 slim-loop ferroelectric ceramic can carry 2330 A and endures charge-discharge cycle over one thousand times. The released charge decreases with increasing cycle times according to second order exponential decay. These ferroelectric ceramics have potential for pulsed power capacitor applications.
2008, 57 (11): 7305-7309.
doi: 10.7498/aps.57.7305
Abstract +
High temperature Raman spectroscopy has been used to probe the growth units existing in PbMoO4 melt. According to the Raman spectra of PbMoO4 crystal at various temperatures and the melt just above the crystal melting point, we found that Pb2+ cations and ［MoO4］2－ groups acting as the growth units exist in the melt. Further, we have studied the interaction between the growth units and various low-index planes of PbMoO4 crystal. The crystal growth habit and the cause of dendrite growth are explained. Finally, we point out that the best seed orientations for the crystal growth are parallel to its {101} planes.
2008, 57 (11): 7310-7316.
doi: 10.7498/aps.57.7310
Abstract +
A three-dimensional model for the modulated free carrier absorption (MFCA) is developed to measure the electronic transport properties (the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity) of semiconductor wafers. The dependence of MFCA amplitude and phase on the electronic transport properties at different pump-probe-beam separation and different modulation frequencies is investigated. It is found that the sensitivities of MFCA signal to individual transport parameters increase with increasing two-beam separation. An experiment with a silicon wafer is performed and the carrier lifetime, carrier diffusivity, and front surface recombination velocity are determined simultaneously and unambiguously by fitting the observed values of the MFCA amplitude and phase as functions of the separation between the pump and probe laser spots, measured at several modulation frequencies covering an appropriate range.
2008, 57 (11): 7317-7321.
doi: 10.7498/aps.57.7317
Abstract +
The energy transfer process of phosphorescent dye PtOEP (2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) doped organic molecule Alq (tris(8- hydroxyquinoline) aluminum) thin films were studied by steady-state spectrum and time-resolved spectrum. The energy transfer efficiency and critical radius of the doped thin films were estimated from the overlap integral between the absorption spectra of PtOEP and the fluorescent spectra of Alq based on Frster theory. The experimental results from steady fluorescent spectra were approximately consistent with the estimation, which indicates that Frster energy transfer mechanism is operative in dye doped organic thin films. The experimental results from time-resolved fluorescent spectroscopy show that the fluorescent lifetime of Alq in the doped thin films decreases gradually with the doping concentration, indicating that there is an efficient energy transfer from Alq to PtOEP in the doped thin films.
2008, 57 (11): 7322-7326.
doi: 10.7498/aps.57.7322
Abstract +
We have prepared the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and researched their photoluminescence (PL). X-ray diffraction (XRD) revealed that the synthesized products are monoclinic gallium oxide, and its morphology as observed by the scanning electron microscope (SEM) revealed that Ga2O3 nanobelts with breadth less than 100nm and length of several micrometers are synthesized under low oxygen pressure, while nanoparticles are synthesized under high oxygen pressure. Room-temperature photoluminescence under excitation of 325 nm shows that the β-Ga2O3 nanostructures have stable emission at 516 nm, which may be related to the defects such as the oxygen vacancies and the gallium-oxygen vacancy pairs.
2008, 57 (11): 7327-7332.
doi: 10.7498/aps.57.7327
Abstract +
Amorphous aluminum oxide thin films doped with cerium have been deposited by middle frequency reactive magnetron sputtering. There exist Ce3+ ions in the Al2O3:Ce thin films as shown by XPS measurement. The photoluminescence emission from these films show peaks around 374 nm which are associated with 5d to 4f transitions of Ce3+ ions. The intensity of these peaks is strongly dependent on the amount of cerium incorporated in the films. The presence of cerium as well as the stoichiometry of these films have been determined by energy dispersive X-ray spectroscopy (EDS) measurements. It is proposed that the light emission observed is generated by luminescence centers associated with trivalent ionic cerium impurities. The crystalline structure of the sample was analysed by X-ray diffraction (XRD). Auger electron spectroscopy has been used to estimate the stoichiometry of the films. This luminescence feature is advantageous for display techniques which require a purer blue emission.
2008, 57 (11): 7333-7337.
doi: 10.7498/aps.57.7333
Abstract +
A series of MoO3/Al2O3 catalysts was prepared by the impregnation method. The positron annihilation lifetime spectra(PALS)and coincidence Doppler broadening (CDB) spectra of the samples were measured to study the pore structure and dispersion of MoO3. The PALS result shows that there are two types of pores with different size in the Al2O3 support. After MoO3 was loaded in the support, Mo species are mainly dispersed inside the large pores of the support, and thus decrease the volume of the large pores. The CDB spectrum shows significant change while MoO3 loading is just 3%. This indicates that the Mo species are dispersed into the pores, and cause the change of the electron momentum distribution seen by positrons. As the MoO3 loading exceeds 18%, the size of the large pores is decreased to the similar size of the small pores, and the positron annihilation parameters show nearly no change with further Mo loading, which indicates saturation of the dispersion of Mo species.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2008, 57 (11): 7338-7343.
doi: 10.7498/aps.57.7338
Abstract +
H2 and He gas mixture diluted very high frequency plasma assisted reactive thermal chemical vapor deposition (VHFPA-RTCVD) is used to prepare μc-SiGe:H thin films, and the optical emission spectrum is used to in situ monitor the reacting plasma during the growing process. It is observed that H2 and He gas mixture dilution is effective in increasing the number of Hα* and reducing the temperature of electrons in the plasma. X-ray diffraction (XRD) and photo- and dark-conductivity measurement show that by optimizing the fractions of H2 and He in the mixture the defect states are reduced, which prompted the growth of and improved the structure, and the optical-electronical properties of the film are enhanced.
2008, 57 (11): 7344-7348.
doi: 10.7498/aps.57.7344
Abstract +
In this paper, we report a kind of electrically tunable multiplexed grating which is prepared conveniently with a single step holographic exposure on the mixture of nematic liquid crystals and photosensitive monomers. The periods of two sub-gratings contained in the multiplexed grating are tested with scanning electronic microscopy (SEM), the results show that their periods are 1 μm and 4 μm, respectively. Diffraction properties of this multiplexed grating are tested, and it is found that there are two diffraction peaks when the testing beam incidents at two different incidence angles. The corresponding diffraction efficiencies of the two sub-gratings are 90% (for Λ=1μm) and 60% (for Λ=4μm), which have a good agreement with the theoretical results obtained by coupled wave theory (the theoretical values being 92.57% for Λ=1μm and 63.68% for Λ=1μm). In addition, the electro-optical performance indicates, that the threshold voltage for the sub-gratings are similar with each other, the V90 of Λ=1μm is 7V/μm and 6V/μm for Λ=4μm, respectively. Such results show the good synchronized electrically-tunable property of multiplexed grating.
2008, 57 (11): 7349-7353.
doi: 10.7498/aps.57.7349
Abstract +
Density functional theory was used to study the mechanism of the reaction of FC(O)O with NO. The geometric configurations of reactants, intermediates, transition states and products were optimized by B3LYP method at 6-311G(d,p) level. The energies of stationary points along the pathway were calculated at CCSD(T) level. Intermediates and transition states were confirmed by the results of vibrational analysis. From the results of the reaction mechanism of the reaction of FC(O)O with NO, one can see that the reaction of FC(O)O+NO has four pathways and several steps. Comparing the four pathways’activation energies, one can find that the pathway FC(O)O+NO→M3→TS6→M5→FNO+CO2 is the main reaction pathway and FNO radical and CO2 are the main products, which is in good agreement with the result reported in the literature.
2008, 57 (11): 7354-7359.
doi: 10.7498/aps.57.7354
Abstract +
The ultrafast energy transfer has been investigated in a porphyrin (TPP) and polypyridyl ruthenium (Ⅱ) (Ru) hybrid, which is linked by a butyl chain by using time-resolved fluorescence spectroscopic technique. The experimental result shows that，when the excitation wavelength is at the absorption peak (～453 nm) of the Ru moiety，an ultrafast energy transfer occurs from Ru to porphyrin moiety (～400ps). When the excitation wavelength (～400 nm) is at the absorption peak of the TPP moiety，no energy transfer is detected from TPP to Ru. The origin of the energy transfer has been analyzed by using Frster theory. The theoretical result shows that the energy transfer is attributed to dipole-dipole interaction based on the spectra overlap.
2008, 57 (11): 7360-7366.
doi: 10.7498/aps.57.7360
Abstract +
As height increases a vertical granular column in a bin can transfer its weight the side wall gradually, then pressure at bottom ceases to increase with the height and reaches to saturation. However it is notable that not every granular column will stay in this stress status with saturation, known as the silo-effect. For example, when mechanical environments of the side wall are modified such that it is unable to take on the weight of granular matter, the bottom pressure will evidently increase linearly with the height. This work analyzes using the assumptions given by Janssen the behavior of this rather unusual granular column, which is in static mechanical equilibrium but does not have a stress saturation as in conventional silos.
2008, 57 (11): 7367-7373.
doi: 10.7498/aps.57.7367
Abstract +
Characterization of colloidal crystals composed of two types of polystyrene particles of different sizes (94 nm and 141 nm respectively) at different number ratios is studied by means of Kossel diffraction and reflection spectra technique. The results showed the dependence of the mean interparticle distance (D0) and crystal structure on the number ratio of the two types of particles. The formation time of crystals lengthens as the number ratio of the two components approaches 1∶1. When the number ratio (9 4nm∶141 nm) decreases, the mean interparticle distance (D0) becomes larger. This study also shows that when the above number ratio equals 5:1, superlattice structure appears in the binary colloidal system.
2008, 57 (11): 7374-7379.
doi: 10.7498/aps.57.7374
Abstract +
A numerical model of organic bulk heterojunction solar cell based on Onsager's theory of geminate charge recombination and related theory of inorganic semiconductors is described. the correctness of the model is verified by experimental data. On the basis of this model, we analyzed the influence of effective voltage and operating temperature on the properties of organic solar cells and the factors that affect the photocurrent efficiency of the device.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2008, 57 (11): 7380-7389.
doi: 10.7498/aps.57.7380
Abstract +
To analyze the dynamics of the temperature data, using homogenous partition of coarse graining process, the series of Chinese daily main temperature from 1961 to 2002 is transformed into symbolic sequences consisting of 5 characters {R,r,e,d,D}. The vertices of the temperature fluctuation network is 125 3-symbol strings (i.e., 125 fluctuation patterns in durations of 4 days), linked in the network's topology by time sequence. It contains Integrated information about interconnections and interactions between fluctuation patterns of temperature in network topology. Random fluctuant network and chaos fluctuant network by using random sequence and chaos sequence of Lorenz system were built. We calculated the dynamical statistics of the degrees and the distribution of degrees, clustering coefficient and the shortest path length, and compared the difference of these three sequences from the view point of network. The result is that. The main vertices of temperature fluctuant network generally contain the 3 characters R, r and e, and corresponding the background of global warming, the feature of temperature fluctuation is mainly ascending. On all accounts, the temperature fluctuant network is similar with chaos network in its dynamical statistics, but is markedly different from random network, which reflects the complexity of temperature fluctuation. And besides, some vertices in temperature fluctuant network have high betweenness centrality (BC), 4% of vertices bear 71.9% of betweenness centrality of networks, these vertices of importance in topological statistics are helpful to understanding the inherent law and information transmission. The vertices' BC in chaos network is similar with that of the temperature network, but vertices in random network almost have identical betweenness centrality. As a result, the patterns of temperature fluctuation corresponding to the process of weather change have similar property with chaos rather than the random fluctuation process.
2008, 57 (11): 7390-7395.
doi: 10.7498/aps.57.7390
Abstract +
Lidar is a powerful tool for atmospheric monitoring. However, most lidars operate only in nighttime due to the interference of strong background skylight in daytime. We have developed the AML-1 lidar system, which can measure aerosol profiles in daytime also. In this paper, the structure and specifications of the lidar system are described. Various noise sources of the lidar and methods for rejecting these noises are discussed. It has been found that among these noises the sky radiation is the main background noise for daytime working lidars. This noise can be effectively eliminated by incorporating small divergence-angel of emitting laser beam, narrow-field-of-view receiver, and narrow-band filter with high transmittance. Some daytime boundary layer aerosol profiles measured by the AML-1 are presented.
2008, 57 (11): 7396-7407.
doi: 10.7498/aps.57.7396
Abstract +
Atmospheric aerosol particles, as one of the important members in the earth atmosphere, can influence the radiative transfer from violet and visible light to infrared in a wide wave band. On one hand, by scattering and absorption of electromagnetic waves, they can induce the energy attenuation of light waves; on the other hand, by turning the absorbed energy into the heat energy, they can heat up the atmosphere. This process directly or indirectly plays an important role in the simulation of radiate climate effect, the propagation of laser atmosphere, the high resolution spectrum, the ground and space remote sensing, the atmospheric correction, the environmental monitoring, the target detection and identification, and the overland traffics, aviation and navigation. We review the study of physics-optics characteristics of atmospheric aerosols, aiming at providing a reference for further study of atmospheric aerosols.
2008, 57 (11): 7408-7414.
doi: 10.7498/aps.57.7408
Abstract +
According to the prediction of the theory of Big Bang, the universe has gone through from the phase of inflation to the phase of radiation and to the phase of matter at last to the phase of acceleration expansion now. In the radiation phase, the rudimental free photons of decoupling become the Cosmologic Microwave Background Radiation which we observe by now. If there is not any perturbation, the CMB radiation will be isotropy, but in the earlier era of the universe, there exist all kinds of the perturbations, which caused the anisotropy the Cosmic Microwave Background radiation. This research will emphatic depict the influence of the relic gravitational wave for the Cosmic Microwave Background radiation in anisotropy of polarization, especially in E-mode and B-mode polarization.
