Vol. 56, No. 4 (2007)
2007, 56 (4): 1843-1846. doi: 10.7498/aps.56.1843
A strongly nonlinear evolution equation is studied. Using the variational principle, firstly, the corresponding functional is constructed. Next, its Lagrange operator is selected; and then, using the generalized variational iteration method, the approximate solution of arbitrary degree of accuracy for the solitary wave is obtained.
The variational iteration method for the soliton solution of nonlinear generalized Landau-Ginzburg-Higgs equation
2007, 56 (4): 1847-1850. doi: 10.7498/aps.56.1847
Using the perturbation method, a class of nonlinear generalized Landau-Ginzburg-Higgs equations are studied. Firstly, by introducing a varitational iteration, the Lagrange multiplicator is accounted for. Then the iteration of the solution for original equation is constructed and the approximate solution is obtained.
2007, 56 (4): 1851-1854. doi: 10.7498/aps.56.1851
A class of higher power nonlinear systems with higher order singular point are discussed in the paper. A series recursive equations for the calculation of focus value are obtained. An application on power-5 system are given and the concrete simulation verifies the theory.
Perturbation of symmetries and Hojman adiabatic invariants of discrete mechanical systems in the phase space
2007, 56 (4): 1855-1859. doi: 10.7498/aps.56.1855
The perturbation of symmetries and adiabatic invariants of discrete mechanical systems in the phase space are studied. The Hojman exact invariants introduced by the special Lie symmetries of discrete mechanical systems in the phase space without perturbation are given. Based on the definition of high-order adiabatic invariants of a mechanical system in the phase space, the perturbation of Lie symmetries of the system by the action of small disturbance is investigated, and a type of new adiabatic invariants of the system are obtained, which can be called the Hojman adiabatic invariants. An example is given to illustrate the application of the results.
New explicit exact solutions of one type of generalized Boussinesq equations and the Boussinesq-Burgers equation
2007, 56 (4): 1860-1869. doi: 10.7498/aps.56.1860
In this paper, explicit exact solutions of one type of generalized Boussinesq equations (B(m，n) equations) and the Boussinesq-Burgers equation (B-B equation) are investigated using a generalized algebraic method. A variety of explicit exact solutions, such as solitary wave, triangular periodic, rational, Jacobi and Weierstrass elliptic function periodic solutions are obtained.
2007, 56 (4): 1870-1874. doi: 10.7498/aps.56.1870
An expanded method for constructing nonlinear differential-difference equation is presented. With this method and computer algebra system Maple, many exact soluions of a modified Volterra lattice have been obtained. The method can also be used for other nonlinear differential-difference equations.
2007, 56 (4): 1875-1880. doi: 10.7498/aps.56.1875
In accordance with the principle of superposition，for the teleportation of an arbitrary three-particle state via three pair nonmaximally entangled particles, the system state of particles can be expanded by Bell bases and transformation operator, and the teleportation can be realized only by performing a inverse transformation. The relation of transformation operators with unitary operation is discussed. The necessary condition to realize the teleportation is that the transformation operators have inverse operators.
2007, 56 (4): 1881-1887. doi: 10.7498/aps.56.1881
We may make three-particle entanglement using the source of three-particle W states. Put this particle entanglement down as quantum channel, and transfer information of Bell states measurement and von Neumann measurement using classical channel, the quantum teleportation net may then be realized. Based on this idea, we investigate the physical principle for building the quantum teleportation net using three-particle W states, find out the unitary transformation matrix for quantum teleportation of three-particle W states, and design a quantum teleportation net. We propose a scheme for quantum communications net and its protocol. If all stations work as schemed, quantum communications between any two stations may be realized.
Teleportation of arbitrary three-particle GHZ state using single three-particle maximal GHZ state or two EPR states
2007, 56 (4): 1888-1894. doi: 10.7498/aps.56.1888
Two schemes, using respectively the single three-particle maximal Greenberger-Horne-Zeilinger (GHZ) state and the two Einstein-Podolsky-Rosen (EPR) states as quantum channels, for deterministic teleportation of arbitrary three-particle GHZ state are proposed. These schemes are also generalized into the case of teleportation of arbitrary n-particle GHZ state (n≥4). The fidelity of teleportation when the quantum channels are affected by noise is discussed. It is found that when using single three-particle GHZ state which is affected by noise as quantum channel, the fidelity of teleportation is only related to the entanglement of the channel. However, when using two EPR states which is affected by noise as quantum channels, the fidelity of teleportation is related to the entanglement of both the channels and the unknown state to be delivered. Compared with previous proposals, our schemes require a reduced number of entangled states as quantum channels to achieve the same task.
2007, 56 (4): 1895-1905. doi: 10.7498/aps.56.1895
Classification and quantification of bipartite qubit, tripartite qubit, and bipartite qutrit entanglement are studied in detail based on the entanglement measure of multipartite pure states. The results show that different ways of pure state entanglement can be characterized by extremal values of the corresponding entanglement measure under the stochastic local operation and classical communication(SLOCC). Detailed analysis shows that there are three different kinds of entanglement under the SLOCC in both tripartite qubit and bipartite qutrit pure state systems. Comparison of the measure with the recently proposed entropy-product measure is made and briefly discussed.
2007, 56 (4): 1906-1910. doi: 10.7498/aps.56.1906
The two-level atom is described by Pauli sign and the environment is described by infinite harmonic particle thermal reservoir. We have studied the problem of fidelity of quantum states of two-level atoms located in strongly thermal radiation field. The two-level atoms' reducible density rectangular array is obtained. We discuss the properties of fidelity. It is shown that for the two two-level atoms initially situated in different coherent superposition states, quantum information may partly lose fidelity or may not lose fidelity during evolution in transmission process.
2007, 56 (4): 1911-1918. doi: 10.7498/aps.56.1911
Cnoidal wave solutions and soliton solutions in a one-dimensional ferromagnetic chain with anisotropy exchange interaction and single-ion anisotropy are obtained through travelling wave solution method and the influence of single-ion anisotropy on cnoidal waves and solitons is discussed. The results indicate that single-ion anisotropy makes the cnoidal waves and solitons easy to excite in an easy-plane ferromagnetic chain but difficult in an easy-axis one, and makes them more stable in the easy-axis ferromagnetic chain but less stable in the easy-plane one. The influence of single-ion anisotropy on soliton excitations in a one-dimensional isotropic ferromagnet is also discussed.
2007, 56 (4): 1919-1923. doi: 10.7498/aps.56.1919
We develop the fast-Fourier-transformation path-integral approach to investigate the quantum decay of a nonlinear dissipative system. The action of the bounce trajectory, i.e. the exponential factor of decay rate, is obtained. In the case of the nonlinear coupling f(x)=tanh［λ(x-xb)］ between the system and its environment, we find that the nonlinear coupling suppresses the decay rate. In contrast to the usual linear coupling, the action will not abide by the law SB=a［1-b(T/Tc)2］ and the crossover temperature rebounds, which means that the system steps into the quantum tunneling region at a higher temperature.
2007, 56 (4): 1924-1927. doi: 10.7498/aps.56.1924
We present a quantum key distribution scheme based on hyperentanglement swapping, which can simultaneously generate deterministic and random keys without the loss of security. The scheme only requires two\|photon states entangled both in spatial (path) and polarization modes, and such a photon pair can create 4 bit of secure keys (2 bit of random keys and 2 bit of deterministic keys). Our protocol can be implemented with linear optics under current technology.
The renormalized energy-momentum tensor and Casimir effect of Dirac field in two-dimensional static spacetime
2007, 56 (4): 1928-1937. doi: 10.7498/aps.56.1928
The renormalized energy-momentum tensor and Casimir effect of Dirac field in general asymptotic flat two-dimensional black hole backgrounds with Dirichlet boundary conditions are calculated using the general properties of the renormalized energy-momentum tensor. The general formulas of the renormalized energy-momentum tensor is given and the corresponding Casimir forces in many specific asymptotic flat black hole backgrounds are obtained. The relations of the renormalized energy-momentum tensors and Casimir effect with vacuum，Hawking radiation and trace anomaly are investigated respectively and the corresponding computation results are obtained.
2007, 56 (4): 1938-1943. doi: 10.7498/aps.56.1938
A general dynamical model for disaster spreading is established in this paper, aiming at some common characteristics of key lifeline systems such as power supply network, water supply network, gas supply network, traffic network and communications network, etc. This model considers self-healing function, disaster spreading mechanism and internal stochastic noise of nodes. And the effects of three key parameters,namely the self-healing factor, duration delay factor and noise intensity, on recovery rate and number of damaged nodes for three different network topologies, i.e. Erdos-Renyi network, scale-free network and small world network are investigated. Simulation results are consistent with the characteristics of these true lifeline systems, showing that the presented model can effectively model disaster evolving dynamics for lifeline systems.
The stochastic resonance (SR) in an optical bistable system under the simultaneous action of multiplicative and additive noises and periodic signal is studied using the adiabatic approximation theory. The signal-to-noise ratio(SNR)is a non-monotonic function of intensity of additive noise, in which the SR phenomenon appears. The SNR decreased with the intensity of multiplicative noise, and SR phenomenon does not appear. So the effects of additive and multiplicative noise on the output SNR are different.
2007, 56 (4): 1948-1951. doi: 10.7498/aps.56.1948
We use the synergetics to study how to allocate input probability in the binary symmetric discrete channel in order to maximize average mutual information for memoryless and memory channels with interference. We obtained the result that for the memoryless channel, the maximal average mutual information is in accordance with that the equivalent input probability can give according to the information theory. Moreover, we also studied the binary discrete memory channel with interference (noise), taking into account the input and output symbols having different memory degree and interference factor, and finally obtained the symbol optimized input probability. This a new method for studying information theory is presented.
2007, 56 (4): 1952-1957. doi: 10.7498/aps.56.1952
Power laws are ubiquitous in the complex communication networks of today. Network nodes are correlated. According to the correlation, network fixed point theory is proposed and analyzed. Banach fixed point theory was used to explain the operation of networks. In this way, the validity of network fixed point theory is proved. The iterative node sequences of Markov-like chains are generated by algorithms of routing. Communication network can be considered as a space formed by the node sequences. Based on the correlation of nodes, the more nodes in the sequence, the more accurately reflected the searching object node. The property makes location finding and data mining more accurate in communication. The object node mapped from the source node by some routing rule corresponds to Banach fixed point. The fixed point in network space is the object node. The physical character of network fixed point theory will be highly evident, when the network can provide ubiquitous connection for users. The reason is that when the network scale becomes greater, the colony action of nodes is more obvious, and network fixed point theory can show its physical character better. It has great significant theoretical and practical meaning for the organic and dynamic characters and congestion analysis of complex traffic communication network.
Decentralized output feedback robust stabilization and impulse analysis of uncertain generalized large-scale composite system
2007, 56 (4): 1958-1965. doi: 10.7498/aps.56.1958
This paper considers a class of uncertain generalized large-scale composite system and studies the decentralized stabilization problem for the system by employing Lyapunov method and using the matrix norm properties. We design a kind of decentralized output feedback robust controllers and obtain the norm bounds of system uncertainties which ensure robust stabilization for the system. Meanwhile, we analyse the impulse control problem of uncertain generalized composite system and its isolated subsystems. We give the norm bounds of system uncertainties which ensure the closed loop system impulse free. Finally, we obtain the norm bounds of being asymptoticly stable and impulse free for the closed loop of uncertain generalized composite system and its isolated subsystems.
In this paper a new chaotic system is presented. Some basic dynamical properties are investigated. The oscillator circuit relizing the new chaotic system is simulated using Electronics Workbench (EWB). Continuous spectrum, Lyapunov exponents, fractal dimension and strange attractor of the system are studied.
2007, 56 (4): 1971-1974. doi: 10.7498/aps.56.1971
The dynamic behavior of phase synchronization in coupled oscillators is investigated using Lyapunov exponents and correlation function. A strongest chaotic phase synchronization——complete synchronization was observed, in which the first two transverse Lyapunov exponents are made equal and the projective structures of oscillators become exactly the same.
Adaptive neural Legendre orthogonal polynomial nonlinear channel equalization for chaos-based communications systems
2007, 56 (4): 1975-1982. doi: 10.7498/aps.56.1975
The performance of chaos-based communications systems is greatly affected by many sorts of nonlinear distortions. If nonlinear distortions in the channel can be removed, the performance of chaos-based communications systems can be improved. According to analysis of Volterra filter, a novel structure of neural network Legendre orthogonal polynomial equalizer is proposed based on the theory of chaotic signal reconstruction. Combining the characteristic of single layer neural network and structure of Legendre orthogonal polynomial, the equalizer is designed and realized after the analysis of a few parameter nonlinear filters, and adaptive algorithm is deduced using the normalized least mean square algorithm. To support the analysis, simulation results for nonlinear chaos-based communication channel are provided.
2007, 56 (4): 1983-1987. doi: 10.7498/aps.56.1983
A new type of multi-folded torus and multi-scroll chaotic generator is studied by constructing a new nonlinear function. With the natural number n increasing, the characteristic of this chaotic system is that it can generate the 2n-folded torus and 2n+1-scroll chaotic attractors which are of the same size and evenly distributed, and the folded torus chaotic attractors alternated with the scroll attractors. The leaftmost and the rightmost of this chaotic system are scroll attractors. Finally, the circuitry is designed and simulated on Electronics Workbench (EWB).
2007, 56 (4): 1988-1993. doi: 10.7498/aps.56.1988
We present a systematic design procedure to anti-synchronize a class of chaotic systems based on techniques from the state observer design and the pole placement technique. In contrast to the conventional anti-synchronization approaches, the proposed method is rather simple and convenient to realize anti-synchronization. Furthermore, the rate of achieving anti-synchronization is very fast. Numerical simulations show the effectiveness of the proposed scheme.
2007, 56 (4): 1994-2004. doi: 10.7498/aps.56.1994
Theory of chaotic signal transmission in optical fiber and physical mechanism of chaotic signal acting on optical fiber transmission medium are theoretically studied. A physical model of nonlinear evolution of chaotic signal propagation in optical fiber is presented by coupling chaotic laser system with optical fiber channel. Action of self-phase modulation of optical fiber on propagation and evolution of chaotic signal is analyzed in detail. Self-phase modulation of fiber does not affect the pulse shape of chaotic signal, however, its product of nonlinear phase shift can widen the chaotic signal spectrum. Self-phase modulation does not affect the power distribution and field intensity distribution of chaotic pulse signal. However, it can affect the power spectrum distribution, the transformation of optical field of chaotic signal and field's slow-variying part. A frequency chipped model of nonlinear evolution of chaotic signal in fiber is presented. The evolution and characteristic of the phase, spectrum, field and field's slow-varying part in fiber are numerically simulated.
Bifurcations of safe basins and chaos in softening Duffing oscillator under harmonic and bounded noise excitation
2007, 56 (4): 2005-2011. doi: 10.7498/aps.56.2005
The erosion of the safe basins and related chaotic motions of a softening Duffing oscillator under harmonic and bounded random noise are studied. By the Melnikov method, the system's Melnikov integral is computed and the parametric threshold for the onset of chaos is obtained. Using the Monte-Carlo and Runge-Kutta method, the erosion of safe basins is also discussed. As an alternative definition, stochastic bifurcation may be defined as a sudden change in the character of stochastic safe basins when the bifurcation parameter of the system passes through a critical value. This definition applies equally well to either randomly perturbed motions or purely deterministic motions. It is found that random noise may destroy the integrity of the safe basins, bringing forward the stochastic bifurcation and making the threshold for onset of chaos vary to a large extent, which makes the system less safe and chaotic motion easier to occur.
2007, 56 (4): 2012-2017. doi: 10.7498/aps.56.2012
We proposed a five-speed lattice Boltzmann method to investigate the evolutionof the reaction-diffusion system. As an example, the production mechanism and evolution of the spiral wave were studied. We found that the system may evolve to three final states: homogenous, chaotic, and spiral waves-like, depending on the parameter of the system, and the crushing of the spiral waves in Selkov reaction-diffusion system belongs to the Doppler class.
2007, 56 (4): 2018-2023. doi: 10.7498/aps.56.2018
In this paper, by choosing an ansatz consistent with the asymptotic forms of the correlation and response function, the self-consistent mode-coupling theory is generalized to the analysis of the dynamic scaling of the nonlocal Sun-Guo-Grant equation and the values of the dynamic exponent depending on nonlocal parameter ρ are calculated numerically for the substrate dimension d=1, 2 dimensions，respectively. The results obtained are compared with that of dynamic renormalization-group theory and scaling analysis.
2007, 56 (4): 2024-2029. doi: 10.7498/aps.56.2024
In this paper we extend the single-lane feedback control model to the two-lane case, named as the two-lane optimal velocity feedback control (OVFC) model. Compared with the two-lane optimal velocity model, simulation results indicate that no serious traffic jams occur in the OVFC system when the feedback signal is introduced, and the oscillation of velocity becomes weaker or vanishes. This means that the two-lane OVFC model can suppress the traffic jams effectively.
Granular stream was created with Gaussian horizontal velocity distribution, and the granules pile up when falling on the ground. The ideal model predicts the pile should be Gaussian in shape but certain properties of granular matter can deform this ideal accumulation. After taking these factors into account, the pile surface evolution equation was acquired, and the theoretical prediction accorded with the experimental data very well. Finally, a new approach of mixing granular materials was proposed.
2007, 56 (4): 2037-2041. doi: 10.7498/aps.56.2037
We investigate the growing process and topological features of the short message networks (SMN). Simulations show that the networks' degree distribution，average degree and the correlation between the node's degree and its time in the network are different from those of the former networks models. With due consideration of some of the characteristics of the SMN, we suggest a new type of network growing protocol,namely the local-preference connecting protocol. The numerical results show that the networks generated from our model are more representative in simulating real networks represented by SMN when compared with other network models.
Two-dimensional Monte Carlo simulation of screening of the bias field in terahertz generation from semi-insulated GaAs photoconductors
2007, 56 (4): 2042-2046. doi: 10.7498/aps.56.2042
Ensemble-Monte Carlo model is used to simulate the time-resolved spatial electric field distribution and the influence on terahertz emission by screening of the bias field by the space charge in semi-insulated GaAs (SI-GaAs) photoconductive switches under different experimental conditions. The time-resolved spatial electric field distribution of photo-generated carriers shows that space charge screening is one of the important factors that limit high-power terahertz radiation of the biased SI-GaAs photoconductors triggerd by high optical energy pulses, and space charge screening can produce bipolar terahertz waveforms. When large-aperture biased photoconductors are triggerd by uniform gap illumination of high optical energy pulse, the effect of space-charge screening on terahertz radiation is small.
2007, 56 (4): 2047-2052. doi: 10.7498/aps.56.2047
Based on the concept of dinuclear system, considering the strong competition between fusion and quasiffision processes, by solving the master equation numerically to calculate the fusion probability of superheavy nuclei, we have estimated the excitation functions for the reactions 50Ti,58Fe+208Pb,209Bi, and the experimental data are basically reproduced. For different incident energies and different angular momentum, the effects on fusion and survival probability and the contribution to evaporation residue cross section have been given. These results help to further understand the mechanism for synthesizing superheavy nuclei.
ATOMIC AND MOLECULAR PHYSICS
2007, 56 (4): 2053-2060. doi: 10.7498/aps.56.2053
On the basis of the improved averaged atomic model, the distribution of the free electrons is dealt with by the partial-wave method to improve the precision of determination of the energy level, electron populations and atomic inner energy. The obtained results of atomic energy for ground state are in rather good agreement with that of Hartree-Fock method. As samples, the total electron energies of W, Au, Rn and Am are calculated respectively.
2007, 56 (4): 2061-2066. doi: 10.7498/aps.56.2061
We propose a novel scheme to build an all-optical surface atomic (or molecular) funnel using an optical system consisting of three cylindrical lenses, which can be used to produce a funnel-shaped intensity distribution near the focal plane of the last lens when the optical system is illuminated by a red-detuned Gaussian laser beam. We calculate the corresponding intensity distribution, the optical dipole potential and its dipole force for 23Na atoms. Our study shows that the proposed atom (or molecular) funnel can be used for the efficient loading of cold atoms in the surface optical guid, beam splitter and interferometer and surface microtrap, and so on. So our funnel has important applications in the integrated atom optics and its atom chip.
2007, 56 (4): 2067-2072. doi: 10.7498/aps.56.2067
An anisotropic intermolecular potential of the He-NO complex has been obtained by utilizing the Huxley analytic function to fit the intermolecular energy data, which have been calculated at the theoretical level of the RCCSD(T)/aug-cc-pVTZ+bf. Then the total differential cross section, elastic differential cross section and inelastic differential cross section for collision between He atom and NO molecule have been calculated using close-coupling approximation. Finally, the law governing the change of the differential scattering cross section has been given. This study shows that the fitted anisotropic intermolecular potential not only possesses the advantage of a simpler function form but also offers a better description of the characteristic of interaction in He-NO system. At the same time, the difficult problem of determining the intermolecular potential parameters can be solved on the basis of the results of ab initio calculation for the collision systems. Therefore, the result obtained may be helpful for probing collision mechanism between atoms and molecules.
2007, 56 (4): 2073-2078. doi: 10.7498/aps.56.2073
The S, T, U parameters of sodium from S→P state excited by electron, which can describe the changes of spin moment before and after collision, are calculated using the distorded wave Born approach with the scattering amplitudes and phases. We analyze the S,T,U parameters under the incident electron energy from 2.2 to 60 eV. The Sp parameter better coincides with reported experiment at 10 eV incident electron energy. All results show that the distribution changes are more obvious at lower incident energy than at higher energy.
Investigation of the processes in the collisions of partially stripped carbon ions with helium atom at low to intermediate energies
2007, 56 (4): 2079-2084. doi: 10.7498/aps.56.2079
he cross-section ratios for the double-to-single ionization of He associated with no projectile charge change (Rq,q), single-electron capture (Rq,q-1) and single-electron loss (Rq,q+1) were measured using coincidence technique. The coincidences resulted from the signals of recoil ions and scattered projectiles. For a given incoming projectile charge state the double-to-single ionization ratios vary strongly with the outgoing reaction channel. It is found that Rq,qRq,q+1Rq,q-1. For direct ionization, Rq,q is nearly independent of the incident projectile charge state. However, for ionization associated with single-electron capture and single-electron loss by the projectile, Rq,q-1 and Rq,q+1 depend strongly on the incident charge state of the projectile. These ionization ratios are interpreted in terms of theories of the atomic polarization effect and the screening and antiscreening effect of the electrons around the core.
Investigation of analytic potential energy function, harmonic frequency and vibrational levels for the 23Σ+g state of spin-aligned dimer 7Li2
2007, 56 (4): 2085-2091. doi: 10.7498/aps.56.2085
Using the symmetry adapted cluster/symmetry adapted cluster-configuration interaction(SAC/SAC-CI) method in Gaussian03 program package, the equilibrium geometry of the 23Σ+g state of spin-aligned dimer 7Li2 is calculated at a number of basis sets. At the same time, the single-point energy scanning calculation is also made at each basis set near the equilibrium internuclear separation obtained by the geometry optimization so as to attain the more accurate result. A disagreement between the result obtained by the geometry optimization and that obtained by the single-point energy scanning calculation is found. Our analysis shows that the result obtained by the single-point energy scanning calculation should be more reasonable. We drew the conclusion that the basis sets 6-311++G(3df,3pd), 6-311++G(2df,2pd) and 6-311++G(2df,pd) are the most suitable ones for the 23Σ+g state calculation. The complete potential energy curve is further scanned at SAC-CI/6-311++G(3df,3pd) level of theory for the state over the internuclear separation range from 2.5a0 to 37a0, then a least squares fit to the Murrell-Sorbie function is made, at last the harmonic frequency is calculated, which is in good agreement with other theoretical results. At the same time, the same calculations are made for the ground state for comparison. In addition, we have also calculated the vibrational levels and the classical turning points.
2007, 56 (4): 2092-2097. doi: 10.7498/aps.56.2092
In the frame of time-dependent density functional theory, the dynamical polarizabilities of Na5, Na6 and Na7 clusters are calculated using a time-dependent local density approximation. By using Fourier transformation, the optical absorption spectra of Na5, Na6 and Na7 clusters are obtained from their dynamical polarizabilities. It is shown that experimentally measured optical absorption spectra of Na5, Na6 and Na7 clusters are reproduced in our calculations. Furthermore, the calculations of Na6 and Na7 clusters are in good agreement with the results of configuration interaction method. Compared with the three-dimensional structure of Na6, the calculated optical absorption spectra of Na6 with the two-dimensional structure are more close to the experimental data.
CLASSICAL AREA OF PHENOMENOLOGY
2007, 56 (4): 2098-2105. doi: 10.7498/aps.56.2098
The melting snow particles on top of clouds form the melting layer of precipitation. The melting process starts with the snow particles falling, so the microphysical characteristics of the melting layer vary continuously in vertical direction. In this paper, a Monte Carlo simulation model for the melting layer is developed, and the melting snow particles are modeled by more practical three-layered spherical particles. The size distribution of the melting snow particles is derived from the raindrops size distribution. Vertical profiles of radar reflectivity and specific attenuation factor are computed at 5, 10, 35 and 94 GHz using the Mie theory at rain rates below 12.5 mm/h. It is shown that the radar bright band can be absent in the melting layer at frequencies above 20 GHz. This agrees with radar observations at 35 and 94 GHz. Base on the radiative transfer theory, the Monte Carlo method is used to compute the reflectivity of the melting layer whose microphysical characteristics are continuous in vertical direction. We compared the reflectivity of the melting layers with two different size-distributions (Gamma size distribution and Marshall-Palmer size distribution). These provided theoretical and numerical basis for radar remote sensing of the melting layer with high frequencies electromagnetic waves.
Study of electromagnetic scattering from fractal sea surface based on non-fully developed sea spectrum
2007, 56 (4): 2106-2114. doi: 10.7498/aps.56.2106
The non-fully developed full-range sea spectrum (NDFSS) is reconstructed, and a fractal sea model based on NDFSS (NDFFM) is presented, witch is well applicable to the real sea surface. The two-scale method is used to calculate the backward radar cross section (BRCS) of the NDFFM sea surface, and the relationship between the model parameters and the BRCS is discussed in detail. Compared with the conventional fractal model and the real radar data, this model is proved to be accurate and efficient.
2007, 56 (4): 2115-2118. doi: 10.7498/aps.56.2115
In this paper, a high-order symplectic finite difference time domain schemes is constructed for Hamilton system, using the symplectic Runge-Kutta-Nystrom (SYRKN) method. On the basis of fixed phase space and total energy in the Hamilton system, a formula of iterative algorithm is proposed which can be used to calculate the radar cross section of a metal cylinder. Calculation results have shown that the SYRKN method is accurate and fast.
2007, 56 (4): 2119-2123. doi: 10.7498/aps.56.2119
Spatially resolved reflectance close to the source is dependent on high-order optical parameters of the media. In order to investigate the influence of high-order parameters on the diffuse reflectance, we define sensitivities of the spatially-resolved diffuse reflectance to the second- and third-order optical parameters. The sensitivity denotes the relative change of diffuse reflectance due to a change in the optical parameter. Expressions of the sensitivities are derived from P3 approximation theory, and numerical analyses are performed. We show that the sensitivity changes with source-detector separation and reaches a maximum in the region between one transport mean free path and two transport mean free paths, and is positive in the region beyond one transport mean free path. The influence of third-order optical parameter on the diffusing reflectance can be ignored in comparison with the influence of second-order optical parameter.
2007, 56 (4): 2124-2130. doi: 10.7498/aps.56.2124
The multi-modes hopping in Nd:YAG lasers induced by optical feedback is presented. The threshold gains of different longitudinal modes are modulated by optical feedback. The mode which has the lowest threshold gain can oscillate. During the tuning of the external cavity length, when the threshold gain of the oscillating mode is higher than that of the adjacent mode, mode hopping occurs, and the intensity modulation curve fluctuates correspondingly. The different positions of hopping modes in the gain curve lead to different mode hopping points and intensity modulation curves. The closer to the center frequency, the larger intensity amplitude and the longer oscillating period the mode has. When the frequencies of two hopping modes are symmetric about the center frequency, the intensity amplitudes of them are equal, and their oscillating periods are equal too.
2007, 56 (4): 2131-2138. doi: 10.7498/aps.56.2131
The vectorial properties of paraxial beams propagating along the optical axis of uniaxial left-handed materials are studied. On the basis of a suitable plane-wave angular spectrum representation of the electromagnetic field, we obtain the analytical expressions of the optical field. The longitudinal component is expressible in terms of the firest correction of the transverse field. Moreover, the transverse field varies when either of the polarization and the distributing of the initial electromagnetic field is changed. But the longitudinal component is only dependent on the initial distributing of the field.
Entanglement evolution and Bell inequality violation of two atoms in Tavis-Cummings model with intrinsic decoherence
2007, 56 (4): 2139-2147. doi: 10.7498/aps.56.2139
Considering the interaction between two two-level atoms and a single-model field, we find an exact solution of the Milburn equation for the system. We investigate the time evolution of the entanglement between the two atoms and the maximal violation of Bell-CHSH inequality. The influence of dipole-dipole interaction and detuning between the caving and the atom on the entanglement and Bell violation is discussed. The effect of dipole-dipole interaction between two atoms on the entanglement and Bell inequality violation is obvious; with the detuning increasing, the entanglement between two atoms and Bell inequality violation becomes larger and we find that the stationary value of the entanglement between two atoms only depends on the difference between the dipole-dipole coupling intensity and the detuning. The Bell inequality violation and the entanglement does not satisfy the monotonic relation, a large Bell inequality violation may correspond to a small amount of entanglement.
2007, 56 (4): 2148-2153. doi: 10.7498/aps.56.2148
Some investigations have been made on the evolution of the linear entropies of atom-field system, in which two identical two-level atoms simultaneously interact with a single-mode dissipative cavity field under large detuning. The effects of the initial atom states and the dissipative factors of the cavity on all linear entropies are also discussed. The results show that the influence of the cavity decay constant on different kinds of Bell states is completely different, and the state |Ψ〉12 is a robust entangled state against the decoherence while the state |Φ〉12 is a fragile entangled state.
2007, 56 (4): 2154-2159. doi: 10.7498/aps.56.2154
A new kind of even and odd nonlinear coherent states (EONLCS) is constructed. Using the numerical computation method, the non-classical properties such as squeezing, amplitude-squared squeezing, anti-bunching and phase probability distribution of the new EONLCS are investigated. The results show that, in the different ranges of the parameter |λ|, the new EONLCS exhibits amplitude-squared squeezing in the directions Y1 and Y2. The squeezing effect is shown in the direction X2 for new even nonlinear coherent states, and the anti-bunching effect is shown for new odd nonlinear coherent states. Moreover, we find that the new EONLCS exhibit different quntum interference properties by studying the probability distributions of the states.
2007, 56 (4): 2160-2167. doi: 10.7498/aps.56.2160
Using the coherent state representation of the Wigner operator, the Wigner function for the photon-added even and odd coherent state (PAEOCS) is obtained. In terms of the variations of the Wigner function with the complex parameter α in the phase space, the non-classical properties of the PAEOCS are discussed. It is found that the PAEOCS always exhibits the non-classical properties, and the photon-added even (or odd) coherent state exhibits the non-classical properties more easily when m is odd (or even). By virtue of the marginal distributions of the Wigner function for the PAEOCS, we illuminate the physical meaning of the Wigner function. Finally, based on the intermidate coordinate-momentum presentation the quantum tomogram function for the PAEOCS is obtained.
2007, 56 (4): 2168-2174. doi: 10.7498/aps.56.2168
The interactions between a two-level atom and a squeezed field of time-varying frequency have been investigated. The properties of the atomic population inversion for two typical cases——the frequency of the field varying with time in the forms of sine function and rectangular pulses——have been considered. For the frequency changing with time in sinusoidal form, the collapse-revival phenomenon of the atomic population inversion is deformed not only by the frequency-modulation but also by the squeeze coefficient and the squeeze phase of the field. The sudden jumping of the field with rectangular pulsed frequency-modulation can lead to new collapses and revivals in the evolution of the atomic population inversion. The rectangular pulsed frequency-modulation can also lead to small-amplitude fast oscillations of the atomic population inversion during the pulse. There is no relation between the latter phenomena and the squeeze coefficient of the field.
2007, 56 (4): 2175-2179. doi: 10.7498/aps.56.2175
Differential phase shift quantum key distribution(DPSQKD) experiment based on weak coherent pulses have been performed in the laboratory. We encoded the bit information between the consecutive pulses. The bit information was decoded at Bob's side by Michelson-Faraday interferometer and single photon detector. This kind of quantum key distribution system can provide stable key distribution process, high efficiency of key creation, and high security key. So it is easily implemented in optical fibers using readily available optical telecommunication tools. We experimented DPSQKD over 76 km on fiber, the error rate of the sifted key is 5.3%. The quantum key distribution process is controlled by micro-computer based on ARM (advanced RISC(reduced instruction set computing) machines) processor.
2007, 56 (4): 2180-2183. doi: 10.7498/aps.56.2180
The influence of dispersion and loss on quantum bit error rate of a quantum key distribution system is analytically studied via quantum Schrdinger equation. The results show that the haul of quantum key distribution system can be increased by using the dispersion shift fiber and weak pulse with short pulse width in wavelength of 1.55 μm.
Generation of twisted stigmatic beam and transfer of orbital angular momentum during the beam transformation
2007, 56 (4): 2184-2190. doi: 10.7498/aps.56.2184
The twisted stigmatic beam with orbital angular momentum generated by transforming the Hermite-Gaussian beam through a rotated cylindrical lens system was studied. By utilizing of method of mode decomposition, the theory of transformation was analyzed. The transfer of orbital angular momentum during beam transformation was analyzed using beam transforming matrix and Collins integral. It was found that the angular momentum transfer takes place at the first cylindrical lens and remains constant after that.
2007, 56 (4): 2191-2195. doi: 10.7498/aps.56.2191
We present a source of soliton pulses in an erbium-doped fiber ring laser. The passive mode-locking is achieved by using the nonlinear polarization rotation technique. The system generates 352 fs pulses with repetition rate of 12.5 MHz and the 3dB spectrum width of about 7.8 nm at the central wavelength of 1563.3 nm. A low-cost erbium-doped fiber amplifier is employed to boost the peak power of the pulses. Single-mode supercontinuum is obtained by passing the amplified pulses through a photonic crystal fiber with the length of 101 nm. Further more, we show the evolution process of the supercontinuum with different optical pump power. It is shown that, with the low-intensity femtosecond pulses, the spectrum broadening is caused by the fission of the higher-order solitons. With the increase of the pump power, the threshold of stimulated Raman scattering (SRS) is achieved, and the energy transfer through SRS spreads toward the long wavelength and the short wavelength sides. On further increasing the pump power, the coupling between SRS and parametric four-wave mixing will result in the appearance of waves with new wavelengths, and the spectrum will become broader and more smooth.
2007, 56 (4): 2196-2201. doi: 10.7498/aps.56.2196
Based the energy transfer between ions and the transition between energy levels of diode-end-pumped Tm,Ho:YLF laser, and considering the energy transfer up-conversion and ground state re-absorption, the rate equations are set up. The analytical formula of fractional thermal loading is deduced from the rate-equations, and the results show that the fractional thermal loading critically depends on the pump-to-mode size ratio. The focal length of the thermal lens as a function of pump power is obtained in experiment. The experimental results are compared with theoretical results, which shows that the theoretical results are reasonable.
2007, 56 (4): 2202-2206. doi: 10.7498/aps.56.2202
Intensity fluctuation and phase noise are key factors limiting the applications of the diode lasers is many fields. The intensity noise of a free-running diode laser was investigated experimentally. Tens of longitudinal modes from the diode laser were successfully separated and identified by a self-made monochromator with 0.01 nm resolution. The noise of either the individual mode or the jointed modes of main mode and the sideband modes was detected using a low-noise radio frequency photodetector. The properties of the intensity noise between either the main mode and the side modes, or the side modes themselves were investigated systematically. The anticorrelation between main mode and side modes was confirmed, and the periodical anticorrelations between small longitudinal modes were found. These results can help us to understand the mechanism of the intensity noise of the diode lasers as well as the noise suppression for intensity-squeezed light generation.
2007, 56 (4): 2207-2211. doi: 10.7498/aps.56.2207
Yb3+/Er3+ co-doped yttrium lanthanum oxide transparent ceramics were fabricated and their spectroscopic properties were investigated. The specimens have large absorption and emission cross section. Because of the additive La2O3, the fluorescence lifetime of the specimens were close to that of the glasses. When the Yb3+ and Er3+ contents were 5at% and 0.5at%, the lifetime reached 9.65 ms. The properties of the specimens such as long lifetime, high emission cross section and narrow line width are favorable for the microminiaturization, integration and high power output of lasers.
Investigation of supercontinuum generation in normal dispersion-flattened fiber by picosecond seed pulses
2007, 56 (4): 2212-2217. doi: 10.7498/aps.56.2212
The evolution of picosecond seed pulses in the normal dispersion-flattened fiber to generate supercontinuum (SC) is investigated. The appearance of wave breaking during the process and the effect of the revealed four-wave mixing on the char acteristics of SC are also analyzed. The research indicates that the broadening of the pulse spectrum in the initial stage is dominated by the self-phase modulation. Afterwards, self-phase modulation is impaired while four-wave mixing is enhanced due to energy in the inner spectrum region being transferred continuously to the outside wings by dispersion, and the pulse spectrum further broadens remarkably. The characteristic of SC noise manifests the dynamic responses of typical SC spectral structures to the seed pulse amplitude noise that are closely related to the evolution.
2007, 56 (4): 2218-2222. doi: 10.7498/aps.56.2218
Stimulated Brillouin scattering(SBS) is one of important nonlinear optical phenomena, which is widely used in the areas of phase conjugation, pulse compression and beam combination. In this paper, a single axial and single transverse mode Q switched laser system is used as pump source and SBS is investigated experimentally in small bulk fused silica. Damage free operation is observed with SBS reflectivity up to 60%. The self-Stokes-seeding effect, which has been reported elsewhere, is verified. To improve reflected energy and SBS efficiency, two SBS samples connected in series is configured, but the SBS reflectivity cannot exceed 60% due to surface damage.
Experimental and theoretical investigation on novel all-optical format conversion based on a folded ultrafast nonlinear interferometer
2007, 56 (4): 2223-2228. doi: 10.7498/aps.56.2223
Pattern conversion is the key technology for all-optical clock recovery from non-return-to-zero (NRZ)signal. A novel scheme for all-optical NRZ to pseudo-return-to-zero (PRZ)conversion using a folded ultrafast nonlinear interferometer (UNI) has been put forward and demonstrated for the first time. Based on the segmented semiconductor optical amplifier model and the transmittance of the UNI, theoretical model for this scheme is established and the output characteristics are calculated theoretically. Stable format conversion from NRZ data to PRZ data has been achieved at 10, 20 and 40 Gbit/s. The influences of the input signal characteristics on the performance of the format conversion are investigated. Experimental results are in agreement with the numerical simulation results.
2007, 56 (4): 2229-2236. doi: 10.7498/aps.56.2229
In photoisomerization polymer, the perpendicular optical control of the optical spatial soliton interaction is simulated by numerical method. Under control, the properties of two interacting solitons are damaged, the signal beam can give birth to phenomena such as the two beams to join together, or to detach and so on. We also give a physical explanation of the phenomena, that they are determined by the difference in the initiatial phases of the beams, the incident position of control-beam and so on. The effect of perpendicular optical control of interaction solitons can be applied to optical interlinkage, optical waveguide and so on.
2007, 56 (4): 2237-2242. doi: 10.7498/aps.56.2237
Using Gaussian decomposion method, we analyze the characteristics of Z-scan curves for nonlocal nonlinear materials in this paper.We provide the normalized transmittance expression for determinating the nonlinear refractive index of nonlocal nonlinear medium based on Gaussian nonlinear response, analyze the influence of the degree of nonlocality on the Z-scan curves, show the methods of measuring the nonlinear refractive index of nonlocal nonlinear medium and the degree of nonlocality, discuss the adjustment brought about by the degree of nonlocality and suggest some feasible measurements. In addition, the numerical results on the base of sech response are obtained and compared with the results on the assumption that the nonlinear response of the nonlocal media is Gaussian.
2007, 56 (4): 2243-2249. doi: 10.7498/aps.56.2243
When intense infrared laser and extreme ultraviolet (XUV) attosecond pulse interact with an atom or molecule, the released electrons generally suffer a spread of energies due to the absorption and emission of laser photons. The nondipole effects in the high-order harmonic generation caused by the short wavelength of XUV attosecond pulse which is comparable to the scale of spreading electron wavepacket are discussed in this paper. The H+2 ion as a model molecule is assumed to be aligned along the propagation direction of the laser field. By solving the two-dimensional time-dependent Schrdinger equation and comparing the results taking account of nondipole effects with those under the dipole approximation, we find that intensity of the former harmonic yield is lower than that of the latter with a shift of the frequency towards lower order harmonics, and that more photoelectron peaks appear in the energy band of the photoelectron spectrum and the difference of their signal intensity at the same photoelectron energy is 2—5-fold. The results of numerical simulation also show that the nondipole effects are enhanced with the infrared laser field strength increasing and are weakened with the wavelength of attosecond pulse increasing.
Investigation on inverted and non-inverted wavelength conversion based on transient cross phase modulation of semiconductor optical amplifier
2007, 56 (4): 2250-2255. doi: 10.7498/aps.56.2250
All-optical wavelength conversion based on transient cross phase modulation of semiconductor optical amplifier (SOA) is a promising approach to achieve high-speed all-optical signal processing. We experimentally demonstrate inverted and non-inverted wavelength conversion (WC) based on single SOA and an optical bandpass filter with 0.4 nm bandwidth. When the central wavelength of the following filter is blue shifted by 0.25 nm or red shifted by 0.05 nm with respect to the wavelength of probe signal, the WC is inverted. When the filter detuning is blue shifted 0.29 nm or red shifted 0.25 nm, the WC is non-inverted. The polarity evolution from inverted WC to non-inverted WC is also presented with numerical simulation. The obtained results are in good agreement with the experiment.
2007, 56 (4): 2256-2260. doi: 10.7498/aps.56.2256
Based on the coupled mode theory, the bistability performance of nonlinear Bragg gratings is analyzed theoretically in terms of elliptic integration. The analytical expression describing the relation between the input intensity and the output intensity is presented. Consequently, the dependence of the bistability on the gratings inner parameters is investigated numerically. The results show that, the bistability performance of the nonlinear Bragg gratings depends not only on the product of the couple coefficient and the grating length but also on the couple coefficient and the gratings length respectively.
Energy transfer and upconversion luminescence of Tm3+/Yb3+ co-doped lanthanum-zinc-lead-tellurite glasses
2007, 56 (4): 2261-2267. doi: 10.7498/aps.56.2261
Tm3+/Yb3+ codoped lanthanum-zinc-lead-tellurite glasses were prepared. Infrared spectrum and upconversion luminescence spectra under 980 nm excitation were studied, and the upconversion luminescence mechanisms were discussed. Rate equations based on energy levels of Tm3+ and Yb3+ and the upconversion mechanisms were developed, and population density in different levels and coefficients of the energy transfer rate Cbi(i=0, 1,3) between Tm3+ and Yb3+ were obtained. The results indicated that, with increasing PbO content in the glass, the energy transfer between Yb3+:2F5/2 and Tm3+:3H4 was intensified, and upconversion luminescence intensity of blue emission was enhanced significantly.
Application of full vectorial mode matching method to the calculation of eigenmodes of three-dimensional bent waveguide
2007, 56 (4): 2268-2274. doi: 10.7498/aps.56.2268
The eigenmodes of bent rib and bent strip waveguides are calculated by accurate and rigorous full vectorial mode matching method. Mode index and bending loss are presented as functions of bending radius. The computation result shows an excellent agreement with that obtained by finite difference method. Comparison of the strip waveguides with radius of 12 and 50 μm indicates that the phenomena of TE-TM coupling occurring on the side wall will become very strong when the bending radius is decreased, and this is the reason why the modes in the bend waveguide with small radius are hybrid mode instead of TE mode or TM mode in the traditional sense. The difference between transverse components of hybrid mode will be abated if the bending loss decreased, and when the two components are comparable, the polarization dependence of bent waveguide will decrease greatly.
2007, 56 (4): 2275-2280. doi: 10.7498/aps.56.2275
The relation of normalized core radius (p/Λ) with hole-to-pitch ratio (d/Λ) and normalized frequency (Λ/λ) is obtained using full-vectorial effective index method. The illogical fixed valve of p/Λ is modified, and an improved full-vectorial effective index method is proposed. The modal properties computed using this method, such as the effective index and total dispersion, closely agree with those of the multi-pole method as well the experimental values, and the error of effective index was reduced by two to three orders. The dispersion of photonic crystal fiber is analyzed in detail, and the relations of dispersion with wavelength, hole pitch and d/Λ is obtained.
2007, 56 (4): 2281-2285. doi: 10.7498/aps.56.2281
The formation of a photonic quantum well structure by sandwiching a graded-index photonic crystal between two symmetrical constant-index photonic crystals is demonstrated. The transmission spectra of various quantum wells with different refractive index profiles in the well region are calculated by finite-difference time-domain method. The results show that the observed fine peaks are quantized states of a photonic band, provided the photonic band of the photonic crystal in the well region is just located in the photonic band gap of the photonic crystal in the barrier region. It is found that the number of the quantized states are equal to the number of periods of the well region, the un-folded new confined states can be obtained by adjusting profile exponent in a given frequency region, in this way the multiple photon confined states can be gained without increasing the size of quantum well structures within limited forbidden band gap region. This method can lead to the maximization of channel density and optimization of the use of effective bandwidth. This structure can be applied to built super-narrow band optical filter and multi-channel narrow band optical filter, it may find application in super-dense wavelength division multiplexing for optical communication and precise optical measurement.
Effect of initial frequency chirp on the linear propagation characteristics of the hyperbolic secant optical pulse
2007, 56 (4): 2286-2292. doi: 10.7498/aps.56.2286
The linear propagation characteristics of the hyperbolic secant optical pulse with initial linear and nonlinear frequency chirps are numerically studied in the anomalous-dispersion regime of a single mode fiber by use of the split-step Fourier method. It is found that the linear chirped hyperbolic secant pulse gradually evolves into near Gaussian pulse for |C|>0.1, and evolves into near hyperbolic secant pulse for 0≤|C|≤0.1. The smaller |C| is, the more the waveform approaches to hyperbolic secant curve. The effect of the negative linear chirp on the pulse broadening is greater than that of the positive chirp. The effect of the initial linear chirp on broadening of hyperbolic secant pulse is greater than that of Gaussian pulse for |C|≥0.5. The temporal waveform splitting of the hyperbolic secant pulse with nonlinear chirp is more obvious than that of Gaussian pulse during linear propagation. Furthermore, the expression of the time-bandwidth product of the pulse with the linear chirp is given.
2007, 56 (4): 2293-2297. doi: 10.7498/aps.56.2293
Coupling between nonparallel waveguides is studied by coupling mode theory, and the coupling equations and coupling coefficients are obtained. Using small angle approximation, results under several conditions are obtained,which are then compared with that of another method. Although both methods indicate that the optical power approaches to a stable value at positions far from the input,yet the values of optical power obtained by them are quite different. To be specific, near the input, optical power changes more violently with propagation distance for the method used by us. Since the effects of both optical amplitude and phase on the coupling equations and coupling coefficients are considered fully in the present method, our results are more comprehensive in describing the coupling of nonparallel waveguides and should be more meaningful for practical applications.
2007, 56 (4): 2298-2304. doi: 10.7498/aps.56.2298
The characteristics of wave propagation in laminated grid structure are analyzed using the lumped-mass method to yield the phase constant surface. The directions and regions of wave propagation in this grid structure for certain frequencies during pass bands are predicted with the iso-frequency contour lines of the phase constant surface, which are also validated with the calculated harmonic responses of a finite two-dimensional grid structure with 15×15 unit cells.
2007, 56 (4): 2305-2310. doi: 10.7498/aps.56.2305
The dynamical behavior of an elastic helical rod with circular cross section are discussed on the basis of Kirchhoff's theory. The dynamical equations of the rod described by the Euler's angles are established in the Frenet coordinates of the centerline. The helical state without twisting of the rod under the action of axial force and torque is discussed. The stability of the helical equilibrium is analyzed in the fields of statics and dynamics respectively. The difference and relationship between Lyapunov's and Euler's stability concepts of the rod equilibrium are discussed. We proved in the sense of first approximation that the Euler's stability conditions of the helical rod in the space domain are the necessary conditions of Lyapunov's stability in the time domain. The free frequency of three-dimensional flexural vibration of the helical rod is derived in analytical form as a function of the pitch angle of the helix and the wave number of the perturbed elastica.
2007, 56 (4): 2311-2317. doi: 10.7498/aps.56.2311
The density functional theory on the level of generalized gradient approximation and full-potential linearized augmented plane wave, and the two-dimensional cubic fitting method have been used to calculate the geometrical and elastic property of LaNi3.75Al1.25 compound. The results indicate that the substitutional Al atoms in this compound are most likely to occupy part of the equivalent positions of 3g and 2c. The optimized lattice parameters a=b=0.5137 nm，c=0.4018 nm, the elastic constants C11+C12=281.2, C13=82.3, C33=227.3, the bulk modulus B＝124.5 and shear modulus G＝68.2 GPa have also been worked out. The density of state, band structure and charge density have been presented, and the electronic specific heat 23.45 mJ/molK2 for LaNi3.75Al1.25 has been estimated.
2007, 56 (4): 2318-2322. doi: 10.7498/aps.56.2318
Experiments are designed to explore the maximum static friction F on a dragged probing rod in a granular pile contained in a cylindrical vessel. The results show that F decreases with the radius R of the cylindrical vessel increasing when R is smaller than 0.040 m, and F scarcely changes with R for R >0.045 m. Curve fitting shows that F is as a function of h (the height of the granular pile), namely F=A［h+B(e-h/B-1)］, here the parameter A relates to the shape of probing rod and the flow rate of injecting granules into the cylindrical vessel, and parameter B depends on the flow rate of injecting granules into the cylindrical vessel.
2007, 56 (4): 2323-2329. doi: 10.7498/aps.56.2323
By considering the effect of intermolecular force, the apparent viscosity of non-polar-molecular liquid flowing in microchannels with isotropic solid wall is studied. The molecular theory of apparent viscosity in microchannel taking into account the effects of channel walls is proposed. Numerical results show that the effect of the wall on liquid apparent viscosity can be very strong. The intensity of effect is determined by the intermolecular force between the liquid and the wall. Meanwhile, the effect of the wall decreases rapidly with the increase of distance from the wall. For liquid argon, the extent of influence is within 10 layers of molecules, which is about 4 nm from the wall.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
The techniques of single probe and emission spectroscopy diagnostics in low temperature argon plasmas
2007, 56 (4): 2330-2336. doi: 10.7498/aps.56.2330
Electric probe and analytical emission spectroscopy were used to acquire I-V curve and spectra of cylindrical plasmas produced by dc high-voltage discharge in the laboratory. The electron excitation temperature, electron temperature and electron density were obtained using respectively the electron energy probability function, Fermi-Dirac model and Schottky diffusion theory of low pressure discharge. The inherent relationships between the method of emission spectroscopy for determination of electron excitation temperatures, method of low-pressure discharge theory for estimation of electron density, and method of electric probe for calculation of electron temperature and density were explored. Further more, the spcial features of different diagnostic techniques were discussed. It was pointed out that the methods described in the article have preferential applications in plasma diagnostics under special environments.
Plasma electrolytic oxidation (PEO), also called micro-arc oxidation or anode spark deposition, is a novel technique to produce hard ceramic coatings on metals, such as aluminum, titanium, magnesium and their alloys (called by a joint name of valve metals). Up to now, almost all the researchers focused attention on the PEO process for samples of regular shapes such as cubes, discs or rods, and no one paid attention to the irregular samples such as tubes. In this work, the PEO behavior of aluminum tubes was investigated. The potential difference, which had a liner relation with the coating thickness inside the tube, was measured. A central axial accessorial electrode was used to eliminate the effect of potential decay inside tubes, which was effective for obtaining axially uniform coating on the inner surface of the tube.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2007, 56 (4): 2342-2346. doi: 10.7498/aps.56.2342
InN nanowires were prepared on Si substrates by low pressure chemical vapor deposition using Au as the catalyst. Scanning electron microscopy showed that the diameter of these nanowires is 60—100 nm, and the length is larger than 1 μm. High resolution transmission electron microscopy showed that the synthesized nanowires are a mixture of hexagonal and cubic phase. The field electron emission characteristics of these InN nanowires are good and the field emission current is stable. The turn-on electric field was 10.02 V/μm(the current density being 10 μA/cm2)，and at the high electric field of 24 V/μm，the current density was as high as to 5.5 mA/cm2. The field electron emission mechanism of these nanowires is discussed.
2007, 56 (4): 2347-2352. doi: 10.7498/aps.56.2347
The intermetallic compound PrMn6Sn6 was prepared by arc-melting and showed a HoFe6Sn6-type (group space: Immm) structure. The compound is ferromagnetic, where the Mn- and Pr-sublattices are ferromagnetically coupled,and has a Curie temperature of 325 K. The 119Sn Mssbauer spectra between 15 and 360 K were measured, and were analyzed by a simplified model according to the eight Sn crystallographic sites with different nearest-neighbors environment, and the corresponding transferred hyperfine fields and the average value dependence on temperature were obtained. The magnetic structure of the two sublattice is discussed.
2007, 56 (4): 2353-2358. doi: 10.7498/aps.56.2353
A horizontal annular temperature field has been designed on the basis of similarity principle to investigate the formation mechanism of core-shell microstructures of monotectic alloys during free fall. The phase separation process of transparent succino-dinitrile-52.6mol%H2O monotectic solution was observed directly. The H2O phase separated from the parent liquid at first, then moved to the center of the sample, and at last occupied the core part. The moving velocities of H2O droplets were measured according to the photographic pictures, which are in good agreement with the theoretical prediction of Marangoni migration velocities. The experiment reproduced the liquid phase separation process of monotectic alloy under microgravity condition.
Structure and growth behavior of low N-doped diamond film by microwave plasma assisted chemical vapor deposition
2007, 56 (4): 2359-2368. doi: 10.7498/aps.56.2359
Two-step growth of ZnO films deposited by reactive radio-frequency magnetron sputtering on Si(001) substrate
2007, 56 (4): 2369-2376. doi: 10.7498/aps.56.2369
Using reactive radio-frequency magnetron sputtering, ZnO films have been deposited on Si(001) substrate with a two-step growth method. The first step: depositing a ZnO buffer layer at low temperature and annealing at 800 ℃, the second step: growing the ZnO at the temperature of 750 ℃. In this paper, we discuss the dependence of the ZnO film growth on the etching time of Si chips and the deposition time of the buffer layer. It is found that different deposition time of the buffer layer results in the difference in the morphology of ZnO films. The difference can be related to the coverage of the buffer layer. When the buffer layer does not cover the substrate, the ZnO film has small grains similar to the film without buffer layer and quite large roughness and internal stress. When the substrate is completely covered by the buffer layer, a ZnO film can be obtained with large-sized grains, smooth surface and low internal stress. The growth behavior of the ZnO films is also related to the etching time of Si chip. With the increase of etching time, both the roughness of the ZnO films and the correlation length of the self-affine morphology decrease.
Influences of acetylene gas flow rate on mechanical properties and chemical structure of nanocomposite TiC diamond-like carbon films
2007, 56 (4): 2377-2381. doi: 10.7498/aps.56.2377
Nanocomposite TiC diamond-like carbon (DLC) films were prepared on silicon (100) wafer and Ti alloy samples by reactive magnetron sputtering combining with plasma source ion implantation. The hardness of the films was evaluated using nanoindentation. Micro-nick was employed to investigate the critical loading of the films. X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the chemical structure of the DLC films containing Ti. The results showed that changing acetylene gas flow rate could control Ti concentration in the films. Many nanometer TiC crystalline grains and nanocomposite TiC/DLC structure were formed by choosing proper C and Ti ratio, and the mechanical properties of the films were distinctly improved. In addition, ion implantation formed the transition layer which enhanced the adherence of the films.
Numerical analysis of thermal response of mid-infrared high reflectance coating under different laser irradiation angles
2007, 56 (4): 2382-2387. doi: 10.7498/aps.56.2382
Thermal response of mid-infrared high reflectance coating exposed to laser beam of wavelength of 4.3 μm at different incident angles was studied by numerical method. In this paper, the incident beam was modeled as a tapered wave with a Gaussian spectrum. Joule loss due to absorption in the absorptive layers was calculated analytically and temperature profile in the multilayer was presented. The temperature distributions of high reflectance coating with different incident angles of transverse electric (TE) mode and transverse magnetic (TM) mode laser beams were compared. For the TE mode laser, the highest temperature peak appears at the incident angle of 35°, for the TM mode, the magnitude of the temperature peak decreases with increasing incident angle.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
The effect of Ⅲ-family element doping on electronic structures and electrical characteristics of SnO2
2007, 56 (4): 2388-2392. doi: 10.7498/aps.56.2388
The electronic structures of SnO2 doped by Al, Ga and In were examined using density functional theory. Density of states (DOSs) calculation showed that the Fermi levels of all Ⅲ-family doped SnO2 systems shift to lower energy and therefore a partially occupied valence band was formed near the valence maxima, which indicates that substitional Ⅲ-group atoms act as acceptors in SnO2. Partial DOSs indicates that compared with substitional Al, substitional Ga or substitional In contribute much more because of the d states, Ga3d or In4d, which suggests that Ga and In is better than Al for p-type doping of SnO2. Ionization energy calculation further indicates that,of the substitional In, Ga and Al, substitional In has the smallest ionization energy of 0.06 eV, which means that substitional In gives the shallowest acceptor level in SnO2, and thus the highest hole concentration at the same doping concentrations.
2007, 56 (4): 2393-2398. doi: 10.7498/aps.56.2393
In order to study the local structure distortion and spin-Hamiltonian parameters of Al2O3:V3+ crystal, a new model has been proposed. On the basis of it, the relationship between the crystal structure parameters and spin-Hamiltonian (SH) parameters is established using Newman crystal-field superposition model. the lattice distortion and SH parameters of Al2O3:V3+ crystal, taking into account the slight magnetic interactions, including spin-spin, spin-other-orbit and orbit-orbit interactions, have been studied using the complete diagonalization method. The calculated results are in good agreement with experimental ones. It is found that the distance between upper and lower ligand oxygen plane increases by 0.0060 nm when V3+ is doped into Al2O3 crystal. Based on the local structure distortion model, at the same time, the microscopic origins of the SH parameters have been investigated for 3d2 ions in trigonal-symmetry crystal field. The results show that the SH parameters are mainly depend on spin triplets, and the contributions to SH parameters from slight magnetic interactions are related to spin triplets only.
Development and behavior study of a ZnO nanowire-based electroluminescence device with double insulating-layer structure
2007, 56 (4): 2399-2404. doi: 10.7498/aps.56.2399
ZnO nanowire thin film was prepared by chemical solution method and a ZnO nanowire-based electroluminescence device has been successfully developed. The device was driven by the alternating current and presented a good RC behavior. Under the action of applied bias, light emission in the ultraviolet region with the wavelength of 387 nm and in the visible region with 552 nm has been observed. The mechanism of electroluminescence and its frequency dependence are discussed in this paper by analyzing the electric properties of the device and the structure of energy band of ZnO semiconductor.
Using the method of density matrix, the rate equation of electron transport in mesoscopic systems are obtained from many-body Schrdinger equation. From those equations, we deduce expressions of spin current and charge current of single quantum well. It is found that there exists only spin current under certain conditions. Then we derive connection between the left current and the right one. The result shows that when the frequency of the rf field matches the Zeeman frequency of the electron in the quantum well, the spin current has a maximum value, which decreases with spin decoherence time.
Performance improvement of polymer light-emitting diodes based on fluorene copolymer with cesium fluoride/aluminum cathode
2007, 56 (4): 2409-2414. doi: 10.7498/aps.56.2409
Polymer light-emitting diodes with saturated red emission were fabricated using the copolymer, poly ［2,7-(9,9-dioctyl)fluorene-co-5,5′-(4,7-diselenophenyl)-2,2′-yl-2,1,3-benzothiadiazole］ (PFO-SeBT). Special attention was paid to polymer/electrode interface modification. The highest electroluminescence external quantum efficiency of 1.79%, which was more than twice that of devices with low work function metal cathode Ba/Al, was achieved by incorporation of CsF/Al cathode with carefully optimized thickness of CsF, and insertion of PVK layer in the PFO-SeBT1/anode interface. Efficient improvement of electron injection of CsF/Al cathode and blocking effect of PVK to electrons were proposed to be responsible for the improved performances of the device.
2007, 56 (4): 2415-2421. doi: 10.7498/aps.56.2415
We have carried out an in-depth investigation on the reflectivity R and phase shift φ of a novel semiconductor mirror, which can be applied in the far-infrared (FIR) spectral range. By fitting FIR reflection spectra of the GaAs material with different doping concentrations, empirical formulas are obtained for the doping concentration-dependent carrier relaxation time τ of n-GaAs and p-GaAs. The effects of structure and material parameters on the reflectivity and the phase shift of the mirror are analytically studied on the basis of the deduced formulas. All the related parameters of the mirror are further optimized, and the corresponding wavelength selectivity is calculated according to the highest absorption in the detector cavity. The experimental FIR reflection result confirms the theoretical simulation, revealing the unique properties of this mirror, which establishes the basis of optimum designing of various FIR mirrors.
Studies on surface roughness and growth mechanisms of microcrystalline silicon films by grazing incidence X-ray reflectivity
2007, 56 (4): 2422-2427. doi: 10.7498/aps.56.2422
The microcrystalline silicon films at different growth stages were deposited by plasma-enhanced chemical vapor deposition (PECVD). The reflectivity of grazing incidence X-ray from synchrotron radiation has been applied to investigate the evolution of surface roughness of these thin films. By study of surface morphology of microcrystalline silicon (μc-Si:H), we understand their growth kinetics and growth mechanism. The results show that the growth exponent β is 0.21±0.01 and 0.24±0.01 for μc-Si:H films deposited on glass substrate at fixed substrate temperature, Under the following condition of electrode distance, pressure, rf power density, H2 dilutied at 200 ℃ to be 2 cm, 6.66×102 Pa and 0.22 W/cm2, 99% and 98%, respectively. According to the KPZ model in the PECVD case the growth mechanism of the μc-Si:H films is a finite diffusion growth.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Dispersion feature in arbitrary direction of surface acoustic wave applied to property characterization of ultra-large-scale integrated circuit interconnect films
2007, 56 (4): 2428-2433. doi: 10.7498/aps.56.2428
The ultrasonic surface acoustic wave (SAW) technique is becoming attractive for accurate and nondestructive property determination for thin low-k films employed in the modern ultra-large-scale integrated circuit (ULSI). In this paper, the dispersive characteristics of SAW propagating along arbitrary directions on the layered films deposited on Si(100) were studied in detail. The computation time was reduced greatly by appling coodinate transformation. The calculation of 9×9 Christoffel matrix was simplified to 6×6 matrix for one film layer structure, and from 15×15 matrix to 10×10 matrix for two-layered structure. This work will benefit the on-line test of low-k film properties during ULSI fabrication. Furthermore, the limitation on the propagating direction of SAW can be eliminated in the measurement.
2007, 56 (4): 2434-2441. doi: 10.7498/aps.56.2434
The weakly charged colloidal system consisting of one or two charged large-spheres immersed in charged small-spheres confined between two charged plates are studied through Monte Carlo simulation. The electrostatic energy of the system is analytically calculated using the hyper-sphere method, and the depletion interactions between the charged large-sphere and the charged plate, and that between two charged large-spheres, are obtained using the acceptance ratio method. Compared with the corresponding uncharged hard sphere systems, it is found that, in the charged systems, the depletion forces between the charged spheres and the two charged plates are strengthened by the electrostatic interactions.
2007, 56 (4): 2442-2447. doi: 10.7498/aps.56.2442
The recent experiments on the dynamics of a common biological network motif, p53-Mdm2 feedback loop in population and individual cells shows two different kinds of oscillatory behaviors, namely the damped and sustained oscillations, for the activities of p53 and Mdm2 proteins in response to DNA damage. By exploiting the nonlinear dynamics in the negative feedback loop and through analyzing the dynamical relation between the DNA damage and the activities of p53 and Mdm2 proteins, we propose a nonlinear dynamical model to describe the oscillatory behaviors for the activities of p53 and Mdm2 proteins both in individual and in population of cells in a self-consistent and unified way.
2007, 56 (4): 2448-2455. doi: 10.7498/aps.56.2448
Acutely isolated rat hippocampal CA3 pyramidal neurons were irradiated with a semiconductor laser of wavelength 670 nm and power 5 mW. The properties of transient outward potassium (K+) channel were investigated using the whole-cell patch clamp technique. The experiment revealed that low level laser reduced the amplitudes of IA in a voltage-dependent and reversible manner. The steady-state activation and inactivation processes of IA were significantly affected by laser irradiation. And the steady-state activation curve shifted towards positive potential direction, altering the slope factor of curve and increasing the half-activation voltage. However, the steady-state inactivation curve shifted towards negative potential direction, reducing the half-inactivation voltage without changing the slope factor. The results show that low level laser irradiation could change the characteristics of transient outward K+ channel. Accordingly, the firing of action potential and the physiological function of neurons were adjusted as a result of low level laser irradiation, which might contribute to the recovery and regeneration of injured neurons.
Suppression of meandering spiral waves in the excitable media due to a perturbation with stochastic phase
2007, 56 (4): 2456-2465. doi: 10.7498/aps.56.2456
A new scheme is proposed to suppress the meandering spiral waves in the excitable media, which is described with two-dimensional variables. An external electronic signal with stochastic phase is imposed on a local area; few grids of the system are perturbed, for example, 4×4 and/or 5×5 grid nodes among all the 256×256 nodes, so that a new target wave may occur and competition between the newly generated target wave and the intrinsic meandering spiral waves develops dynamically. The numerical simulation results confirm that it is effective to suppress the meandering spiral wave in the Barkley model. Compared with a simple periodical driving in a local area, it shows some advantages such as shorter transient period to kill the spiral wave, and it is robust to spatiotempaoral noise. A new target wave could come into being and will kill the meandering spiral wave even in the anisotropic media,of which the diffusion coefficient is a function of space, when the intensity of the spatiotemporal noise is not too strong.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2007, 56 (4): 2466-2474. doi: 10.7498/aps.56.2466
The characteristics of accelerating coronal mass ejection (CME) and decelerating CME happening during 1997—2003 are analyzed. Prediction tests are made for geomagnetic disturbance events caused by the gradually accelerating CME-associated interplanetary shock waves and the decelerating CME-associated interplanetary shock waves, which can be identified by interplanetary scintillation (IPS) observation during 1997—2003. New membership functions and new correctional item of onset time of geomagnetic disturbances are respectively constituted for two kinds of CME. The main results are: for the onset time of the geomagnetic disturbance in the accelerating CME, the relative error between the observation,Tobs, and the prediction,Tpre,ΔTpre/Tobs≤10% for 21.86% of all events, ≤30% for 78.13% and ≥50% for only 9.36%; for the decelerating CME, ΔTpre/Tobs≤10% for 25.00% of all events, ≤30% for 84.37% and ≥50% for only 3.13%.These results show that the method has good feasibility for the geomagnetic disturbance predictions.