Vol. 58, No. 10 (2009)
2009-05-20
GENERAL
2009, 58 (10): 6677-6681.
doi: 10.7498/aps.58.6677
Abstract +
Template match arithmetic（TMA） is vital to the template identification technology of nuclear warheads and components. This paper introduces a TMA of high-resolution gamma-ray spectral fingerprint based on mean vector test. Some trials on gamma-ray samples were conducted to check the validity of TMA. The validity of TMA was comfirmed by correctly distinguishing between samples of different intensities and components. Two pieces of advice are given on the design of template structure.
2009, 58 (10): 6682-6685.
doi: 10.7498/aps.58.6682
Abstract +
We study three special cases of simple generalized collaboration networks， namely the preferential attachment, random attachment and mixed attachment networks. Based on Markov chain theory, we provide a rigorous proof for the existence of the steady-state degree distribution of the network generated by this model and obtain its corresponding exact formula. In particular, for mixed attachment, if it has preferential attachment, degree distribution of the network obeys power-law distribution, and it is a scale-free network.
2009, 58 (10): 6686-6691.
doi: 10.7498/aps.58.6686
Abstract +
By using Lie’s invariance infinitesimal criterion, we obtain the continuous equivalence transformations of a class of nonlinear Gardner equations with variable coefficients. Starting from the equivalence algebra， we construct the differential invariants of order one and make group classification. Finally some general class of variable coefficient nonlinear Gardner equations can be mapped to constant-coefficient mKdV equation and KdV-mKdV equation. In particular, some exact solutions of the Gardner equation with variable coefficients are obtained.
2009, 58 (10): 6692-6695.
doi: 10.7498/aps.58.6692
Abstract +
A type of nonlinear model of the global climate is considered. By using the perturbation theory and method, solution to the asymptotic expansions of some related problems are constructed. The asymptotic expansions of the solution to the original problem have a higher degree of approximation. The perturbed asymptotic method is an analytic method, and the obtained solution can be analytically operated sequentially.
2009, 58 (10): 6696-6702.
doi: 10.7498/aps.58.6696
Abstract +
Power law phenomena generated by human activity can be explained by selective theory. More mechanisms are brought forward to generate power law phenomena through the extension of threshold probability. It was demonstrated that selective theory is universal in deducing the power law mechanisms. Therefore, it is significant to extend the theory for further research on the power law phenomena.
2009, 58 (10): 6703-6708.
doi: 10.7498/aps.58.6703
Abstract +
We used random matrix theory （RMT） to remove the noises in lung cancer gene expression data and used the modules approach and the hierarchical clustering approach to construct the gene networks. Comparing the results given by the two methods, we found that RMT-hierarchical clustering method gives true modules as well as the correlations between the modules. The results indicate that RMT-hierarchical clustering method is an effective new method for identifying gene networks.
2009, 58 (10): 6709-6718.
doi: 10.7498/aps.58.6709
Abstract +
Three-dimensional electromagnetic particle-in-cell （PIC） simulation is based on FDTD （finite-differential time-domain） and PIC methods. Based on the characteristics of these methods, the parallel algorithm was designed, which divided the whole simulation domain into a number of subdomains, and every computing process simulated a subdomain and transferred the boundary information. Then the influencing factors of speedup were analyzed. Finally, the parallel algorithm was implemented in CHIPIC3D software and the parallel version of CHIPIC3D was used to simulate a kind of magnetically insulated transmission line oscillator and the relative klystron amplifier. The results show that the parallel algorithm is correct and the speedup is increased.
2009, 58 (10): 6719-6724.
doi: 10.7498/aps.58.6719
Abstract +
In spectral resolution enhancement the linear prediction of exponentially decaying sinusoidal superposition signal is one of the key technologies. In this study, the direct calculating equations of forward and backward linear prediction coefficients, the relationship between forward and backward linear prediction coefficients, and the forward and backward linear predictability conditions are derived. It is shown that, for exponential decaying sinusoidal superposition signal, there is not simple conjugate symmetry between forward and backward linear prediction coefficients, but they are still related. This research provides a theoretical basis for spectral resolution enhancement about decaying interference signals.
2009, 58 (10): 6725-6728.
doi: 10.7498/aps.58.6725
Abstract +
The problem of constructing an acceleration-dependent Lagrangian from the equations of motion is studied. A method for the computation of an acceleration-dependent Lagrangian from the self-adjoint equations is presented. Two examples are given to illustrate the application of the results.
2009, 58 (10): 6729-6731.
doi: 10.7498/aps.58.6729
Abstract +
The differential equations of motion of a weakly nonholonomic system in which there is a small parameter are established. We develope the generators of infinitesimal transformations and the gauge function via the multiple power-series expansion of the parameter and substitute them into a generalized Noether identity. The Noether theorem is used to obtain an approximate conserved quantity.
Unified symmetry of mechanico-electrical systems with nonholonomic constraints of non-Chetaev’s type
2009, 58 (10): 6732-6736.
doi: 10.7498/aps.58.6732
Abstract +
The unified symmetry of mechanico-electrical systems with nonholonomic constraints of non-Chetaev’s type are studied, and the definition and the criterion of unified symmetry of mechanico-electrical systems are deduced from the Lagrange-Maxwell equations. The Noether conserved quantity, the Hojman conserved quantity and a new conserved quantity deduced from the unified symmetry are obtained. An example is given to illustrate the application of the results.
2009, 58 (10): 6737-6742.
doi: 10.7498/aps.58.6737
Abstract +
Stability of a straight Kirchhoff elastic rod with circular cross section acted by a pair of force screws is studied. Cartesian coordinate and Cardan angle are used to express the position and attitude of a cross section of the rod. Special solution which is a straight equilibrium state of the rod is derived from Kirchhoff equation of the rod, and the linear perturbation equation on this special solution is further solved. The stability of the solution for the straight equilibrium state of the rod is discussed according to the existence of non-zero solution of integration constants at various kinds of boundary conditions of the rod, such as that with two joints ends, two fixed ends, a fixed end and a free end, or a joint end and a fixed end. The critical loads are deduced and the stable ranges are plotted. Greehill formula is extended to other cases, and Euler formula for compression rod becomes its special case.
2009, 58 (10): 6743-6749.
doi: 10.7498/aps.58.6743
Abstract +
Wave generation by the falling rock in the two-dimensional wave tank is experimentally and numerically studied, where the numerical model utilizes the boundary element method to solve the fully nonlinear potential flow theory. The wave profiles at different times are measured in the laboratory, which are also used to test the numerical model. Comparisons show that the experimental and numerical results are in good agreement, and the numerical model can be used to simulate the wave generation due to the submarine rock falling. Further numerical tests on the influences of the rock size, density, initial position and the falling angle on the wave elevation of the generated waves are performed, respectively. The results show that the size and density of the rock have strong effects on the maximum elevation of the generated wave, while the effects of the initial position and the falling angle of the rock are also significant. When the size or the density of the rock increases, the maximum elevation of the generated wave increases. The same effect on the generated wave would be produced if the initial position of the rock becomes closer to the surface, or the falling angle between the falling route and the vertical direction turns larger. In addition, the present numerical tests reveal that the submarine rock falling provides a new generation method for the breaking wave in the wave tank.
2009, 58 (10): 6750-6760.
doi: 10.7498/aps.58.6750
Abstract +
An equivalent mass source is modeled as excited sources of internal waves generated by the displacement of fluid and the wake of vortex shedding or turbulence due to the body moving in a stratified fluid, a mathematical model for the vertical displacement of internal waves generated by such an equivalent mass source is presented by use of both the associated eigenvalue problem and the Fourier transform method, and the method for estimating the speed, length and diameter of the equivalent mass source is proposed. Calculations based on the proposed method are performed for the generation of internal waves by a towed sphere in a stratified fluid, and the numerical results are in good agreement with the available experimental results of Robey in the kinematic wave patterns and the maximum peak-to-peak amplitude of the internal waves. Such a method may have potentially important applications.
2009, 58 (10): 6761-6763.
doi: 10.7498/aps.58.6761
Abstract +
It is found that the solutions for the classical third-order standing and short-crested waves cannot satisfy the required amplitude equations, exerting a direct influence on the modern shore-crested wave theories which are related closely with the classical theories. For this reason, a set of theoretical criteria are put forward to eliminate the incompatibility between the solutions and the equations, fully ensuring the inherent harmony and correctness of the finally obtained solutions.
2009, 58 (10): 6764-6769.
doi: 10.7498/aps.58.6764
Abstract +
A unified boundary integral equation is proposed to solve the sound radiation and scattering from the open/closed thin-bodies with arbitrary acoustic impedance in two- and three-dimensional domain. The proposed integral equation has the same influence matrix for both acoustic radiation and scattering problems and can synchronously solve the sound radiation and scattering from non-compact thin-body with arbitrary acoustic impedance condition, which can be applied to predict the noise of turbomachinery, pipe, and the muffler performance. In further work, the effects of moving surface and moving medium on sound radiation and scattering should be considered.
2009, 58 (10): 6770-6771.
doi: 10.7498/aps.58.6770
Abstract +
The electromagnetic properties of the moving media interface in a high frequency range is analysed and the dependence of generalized refraction on frequency is obtained based on special relativity.
2009, 58 (10): 6772-6778.
doi: 10.7498/aps.58.6772
Abstract +
We show how a nonlocal and open-target destination quantum controlled-Not （CNOT） gate can be probabilistically implemented by using partially entangled pairs of particles. We first investigate the controlled implementation of a nonlocal and three-target destination CNOT gate using three partially entangled pairs, and then generalize the scheme to the case of N-target destination. In this scheme, Alice’s local generalized measurement described by a positive operator valued measurement （POVM） plays a key role. We construct the required POVM. It is worth noting that deterministic and exact implementation of a nonlocal CNOT gate can be realized using partially entangled pairs.
2009, 58 (10): 6779-6785.
doi: 10.7498/aps.58.6779
Abstract +
Quantum safety communications is a process of quantum key distribution （QKD）. Current QKD technology restricts transmission to a low bit rate. To improve the QKD bit rate and develope high rate and large capacity, we propose a multiple-input-multiple-output（MIMO） quantum key distribution system. The Wigner operator of multi-photon entangled states in MIMO quantum key distribution channel is presented. As a result, the Wigner function of multi-photon double-model squeezed entangled sates and MIMO quantum key distribution channel capacity are also obtained, which will provide theoretical support and technical basis for developing robust space-time processing algorithm of MIMO quantum safety communications and designing optimum high performance system of MIMO quantum key distribution.
2009, 58 (10): 6786-6790.
doi: 10.7498/aps.58.6786
Abstract +
Under the condition of electron-LO photon strong coupling, the eigenfunction and the eigenenergy of the ground state and the first excited state of the electron in quantum ring, are obtained by solving precisely the Schrdinger equation. A qubit is formed by overlaying both the ground state and the first excited state of the electron-LO phonon system.Numerical calculations indicate that the distribution of the probability density of electrons in quantum oscillates periodically with time and angle coordinate. The oscillating period decreases with the increase of the electron-LO phonon coupling strength, which shows that the existence of phonon can reduce the coherence of qubit, and that the oscillating period increases with the increasing inner（or outer） radius of quantum ring. Therefore, the coherence of qubit can be improved by choosing proper size of quantum ring.
2009, 58 (10): 6791-6797.
doi: 10.7498/aps.58.6791
Abstract +
Quantum chromodynamics with 2+1 flavor fermions at finite temperature and finite density was studied. Polyakov loop and chiral condensate were used to determine the dependence of the phase transition on the chemical potential and hop parameter. Finite volume scaling and Monte Carlo simulation were adopted to determine the type of phase transition. It was found that the transition between confined phase and deconfined phase varied from crossover to a first order one while the hop parameter κ1 increased from a small value to nearly the chiral limit. The phase diagram was also presented.
2009, 58 (10): 6798-6801.
doi: 10.7498/aps.58.6798
Abstract +
We extend the classical Damour-Ruffini method and discuss Hawking radiation in Schwarzschild -de Sitter black hole. Under the condition that the total energy of spacetime is conservative, considering the effect of radiation particle on the spacetime and the relevance between the black hole event horizon and cosmological horizon, we obtain the black hole radiation spectrum. The radiation spectrum is no longer a pure thermal spectrum. It is related to Bekenstein-Hawking entropy change corresponding to the black hole event horizon and cosmological horizon. The result is consistent with an underlying unitary theory.
2009, 58 (10): 6802-6808.
doi: 10.7498/aps.58.6802
Abstract +
We investigate the influence of complex network topological structure on the traffic delivery by the traffic awareness routing strategy. In order to characterize the efficiency of the packet delivery process, we introduce an order parameter to measure the network capacity by the critical value of phase transition from free flow to congestion. Here, we present two kinds of models, based on its degree or its betweenness that the delivery capacity of each node is proportional to. Simulation results show that, in the case of identical average degree, WS small-world network is significantly more susceptible to traffic congestion than ER random networks and BA scale-free networks in the first model, while the capacities of all kinds of networks are enhanced greatly in the second model, especially for WS small-world network. Finally, it is worth noting that which of the two models will be best suitable for handling traffic delivery depends on the structural characteristics of networks.
2009, 58 (10): 6809-6817.
doi: 10.7498/aps.58.6809
Abstract +
The adaptive synchronization of integration complex networks is studied,and a network division scheme is introduced according to the nature of different links. Using the Lyapunov stability theory and the adaptive feedback control method, the principle of global synchronization of rather general weighted complex dynamical networks for identical nodes and different nodes and their corresponding controllers is given. Finally, numerical results verify the effectiveness of the proposed method.
2009, 58 (10): 6818-6822.
doi: 10.7498/aps.58.6818
Abstract +
A new sixth-order hyperchaotic Chua’s circuit is presented, and the Lyapunov exponent, the dimension, and the phase diagram are computed by MATLAB. At the same time, the corresponding electronic circuit is realized,and our results are in agreement with the results of simulation, which proves that this system exists and can be realized in physics.
2009, 58 (10): 6823-6827.
doi: 10.7498/aps.58.6823
Abstract +
Based on the adaptive backstepping method, a kind of synchronization controller is proposed for multi-scroll chaotic systems with different initial states and unknown parameters. The synchronization controller can realize complete synchronization, anti-synchronization, and a kind of nonlinear generalized synchronization between two chaotic systems, and it is better for application. Simulations show the effectiveness of the controller.
2009, 58 (10): 6828-6832.
doi: 10.7498/aps.58.6828
Abstract +
Spatiotemporal chaos control in one-dimensional complex Ginzburg-Landau equation was described. We proposed a method of coupled feedback based on the flocking algorithms. By using the homogeneous-periodic solutions and the traveling wave solutions as our target, we showed numerically that the spatiotemporal chaos can be controlled to a regular state if appropriate control strength was chosen. The physical mechanism was analyzed based on the correlation function.
2009, 58 (10): 6833-6837.
doi: 10.7498/aps.58.6833
Abstract +
The effect of noise on a two-dimensional neural map with stable subthreshold oscillations is investigated by numerical simulation. It is found that noise can induce action potential and stochastic resonance. Furthermore, the influences of control parameter and input signal frequency on the dynamics of the system are also studied. Only when the parameters are chosen in or near to the regime of silence, we can observe the frequency-dependent stochastic resonance phenomenon.
2009, 58 (10): 6838-6844.
doi: 10.7498/aps.58.6838
Abstract +
On the assumption that the input voltage can be replaced by its RMS value and the frequencies of the inductor current and the output voltage are much lower than the switching frequency of the converter, the small-signal model of Boost PFC converter is constructed and the medium-frequency oscillation in Boost PFC converter is studied. The underlying mechanism of this nonlinear phenomenon is analyzed and the stability conditions are also given. These obtained results indicate that this type of nonlinear phenomenon is different from the fast- and slow-scale instabilities, and the main characteristic of this type of nonlinear phenomena is that its oscillation frequency lies between the line frequency and the switching frequency. Finally, an experimental circuit is designed, and its experimental results agree very well with the simulation results.
2009, 58 (10): 6845-6851.
doi: 10.7498/aps.58.6845
Abstract +
The impact of bus stop on the dynamics of traffic flow is studied by a cellular automata model. Two types of bus stops, non-harbor shaped and harbor shaped, are considered. The properties of traffic flow are investigated by analyzing the fundamental diagram and the spatial-temporal diagram. The influences of bus ratio and length of bus stop are analyzed in detail. The simulation results show that the non-harbor shaped bus stop has more influence on the traffic flow, and the flux cannot be effectively increased by extending the bus stop length; the harbor shaped bus stop has less influence on the traffic flow and the flux can be improved by extending the bus stop length.
2009, 58 (10): 6852-6857.
doi: 10.7498/aps.58.6852
Abstract +
A slide-type ultrahigh pressure apparatus with 6/8 anvils is described. The three-supporting pillars of the main framework and the slide-type multi-anvils have conformable mechanical symmetry. Under the loading uniaxial pressure, the first-stage anvils can be self-corrected and run with excellent synchronicity and reproducibility. In the present experiments, the edge length of pyrophyllite octahedron is 125 mm and the truncation edge length of tungsten carbide anvil is 8 mm. The cell pressure was calibrated at room temperature by means of the known pressure-induced phase transitions of Bi and ZnTe at 255, 77, 96 and 120 GPa. The cell temperature under 10 GPa was measured up to 1560 ℃ by WRe3-WRe25 thermocouple. The temperature calibration was reconfirmed and extended to the higher range by observation of diamond formation on the interface between graphite heater and steel plug, and by comparison of the variational details of recorded data and the Fe—C phase diagram, and then the axial temperature gradient was estimated to be about 21 ℃/mm.
2009, 58 (10): 6858-6862.
doi: 10.7498/aps.58.6858
Abstract +
Transparent Er3+/Yb3+ co-doped lead fluosilicate glass ceramics is prepared, which contains nano crystalline with size of 10—12 nm. The up-conversion emission in oxyfluoride glass ceramics is notably stronger than that in its glass counterpart. The green luminescence intensity of the 2 H11/2（4S3/2）→4I15/2 transition and the red luminescence intensity of 4F9/2→4I15/2 transition in the glass ceramics are 26 and 6 times stronger than those in its glass counterpart, respectively. The ratio of the green emission intensity to the red one for the lead fluosilicate glass ceramics decreases abviously, while it is almost a constant for the lead fluosilicate glass. It is believed that the low phonon energy in nanocrystallines and the changed energy transfer properties result in the enhancement of the up-conversion emission and the variation of the up-conversion spectra.
EDITOR'S SUGGESTION
2009, 58 (10): 6863-6872.
doi: 10.7498/aps.58.6863
Abstract +
A detailed investigation on dual-band （mid- and far-） infrared detection and photon frequency upconversion in GaN/AlGaN heterojunction structures is carried out. We deduce the Al composition in intrinsic AlGaN barrier layer through photoluminescence spectroscopy, and evaluate the conduction bandgap interfacial workfunction in GaN/AlGaN with different Al compositions. Based on the mid- and far-infrared responsivity simulation of single-period GaN/AlGaN heterojunction detector, we investigate the mid- and far-infrared photon frequency upconversion efficiencies of multi-period GaN/AlGaN heterojunction detectors integrated with GaN/AlGaN violet light emitting diodes in relation to the GaN emitter layer thickness, intrinsic AlGaN barrier layer thickness, violet photon extraction efficiency, internal quantum efficiency, spatial frequency, and GaN emitter doping concentration. The results show that GaN-based infrared upconversion devices have high upconversion efficiency and good optoelectronic application prospect.
ATOMIC AND MOLECULAR PHYSICS
2009, 58 (10): 6873-6878.
doi: 10.7498/aps.58.6873
Abstract +
The potential energy curves （PECs） for the ground state （X1Σ+） and six excited states （a3П, A1П, B1Σ+, b3Σ-,c3Σ+, and C′1Δ） of BH molecule have been computed using the multireference configuration interaction （MRCI） method and Dunning’s correlation consistent basis sets aug-cc-pV5Z. By employing the Murrell-Sorbie function （MS） and the least-square fitting method, the analytical potential energy functions （APEFs） of these states are obtained. The root means square （RMS） errors between the fitted results and the ab initio values are very small in comparison with the chemical accuracy （349755 cm-1）, which implies that the APEFs can well display the interactions between the two atoms of BH molecule. Based on the APEFs, we have calculated the spectroscopic parameters and compared them with the available theoretical and experimental values. The calculating results are in good agreement with the experimental values, which shows that the present APEFs are accurate. The double-well PEC for the B1Σ+ state has also been fitted accurately with MS function, which provides a sample for more wider application of MS function.
2009, 58 (10): 6879-6883.
doi: 10.7498/aps.58.6879
Abstract +
The Lα x-ray production cross sections of Ga, As, Pt, W and Au by electron impact are calculated using a modified version of the BELL formula by incorporating both ionic and relativistic corrections in it. The proposed modified Bell model with a single set of parameters can provide an excellent data in the reduced energy range 1≤E/Inl≤106（E and Inl are, respectively, the incident energy and ionization energy） with performance level at least as good as any of the existing methods and models. Experimental data are compared with the present results in cases of with and without the relativistic correction factor GR and the ionic correction factor Fion, with calculated cross sections obtained from the distorted wave Born approximation and with other experimental data available in the literature. The calculated results can be used to simulate the hot-electron energy spectrum and laser plasma yields and accordingly can provide accurate parameters for electron devices.
2009, 58 (10): 6884-6888.
doi: 10.7498/aps.58.6884
Abstract +
Using terahertz time domain spectroscopy （THz-TDS）, THz transmission spectrum of the array with sub-wavelength apertures on the Nb thin film has been studied in the temperature range of 5—300 K. The extraordinary transmission is observed and the peak positions are in agreement with the computer simulation technology simulation results. The transmission amplitude increases with the decreasing temperature.
2009, 58 (10): 6889-6893.
doi: 10.7498/aps.58.6889
Abstract +
Based on scattering theory of high-energy x-ray, the structure and extinction properties of Mg2Si crystal have been studied. It is shown that for Mg2Si with antifluorite structure extinction only occurs if the indices of diffraction H, K and L are neither all odd nor all even, and diffraction occurs if H, K and L are either all odd or all even. It is of great significance to study the crystal with antifluorite structure in application.
2009, 58 (10): 6894-6901.
doi: 10.7498/aps.58.6894
Abstract +
In order to meet the requirement of microchannel plate position-sensitive photon counting detector in the extreme ultraviolet region, the quantum efficiency of alkali halide photocathode was studied. Based on the fact that the photoemission from photocathode is formed by secondary electrons, the theoretical model of secondary electron emission for alkali halide photocathode was presented， and the formula of secondary electron yield was obtained. For photon energy ranging from 30 to 250 eV, the effect of the thickness of photocathode and the incidence angle on the secondary electron yield was calculated and analyzed，the result showed that when the thickness was higher than 100 nm and the grazing angle was larger than the critical angle of photocathode material, high secondary electron yield was obtained. Finally, according to the derived formula, the spectrum response of the secondary electron yield for twenty alkali halides was analyzed， and the result showed that the position of the peak yield was in accordance with the resonant absorption of photocathode materials.
2009, 58 (10): 6902-6907.
doi: 10.7498/aps.58.6902
Abstract +
We investigate the dynamical stability of a dark state of the atom-heteronuclear-trimer conversion system in a stimulated Raman adiabatic passage process. By casting the quantum Hamiltonian into an effective classical one and analyzing the eigenvalues of the Hamiltonian-Jacobi matrix obtained by linearizing the equations of motion around the fixed point corresponding to the dark state, we analytically obtain the condition for the occurrence of the dynamical instability of the atom-trimer dark state. Taking heteronuclear atoms of 87Rb and 41K as an example, we numerically give the unstable region. We find that the dynamical instability is induced by the interparticle interactions. Moreover，the occurrence of the dynamical instability depends on not only the emergence of the real or complex eigenvalues of the Hamiltonian-Jacobi matrix but also the scanning rate of the external fields.
2009, 58 (10): 6908-6912.
doi: 10.7498/aps.58.6908
Abstract +
The Raman cross-sections of β-carotene C=C double bond （1520 cm－1） and C—C single bond（1155 cm－1） vibration mode have been measured using cyclohexane as internal standard. The result shows that the Raman cross-section of β-carotene increases with the increase of refractive indexes of solvents. The difference of β-carotene Raman cross-section in different refractive indexes of solvents was explained by the dispersion and resonance Raman theory.
2009, 58 (10): 6913-6919.
doi: 10.7498/aps.58.6913
Abstract +
The close coupling calculation of rotationally inelastic collision of He with Na2 is first performed by employing a recently computed ab initio potential energy surface. The process of rovibrational energy excitation and relaxation of Na2 in collision with He has been studied in detail based on the single and double exitations coupled cluster with a noniterative perturbation treatment of triple excitations CCSD （T） potential energy surface. Our results are in good agreement with the experimental results. Our results show that: （1）The elastic cross section（Δj=0） is much larger than the inelastic cross section. （2）The largest amplitude occurs at small scattering angles. At low Δj transition, the He projectile is predominantly forward scattering. Backward scattering occurs as Δj increases. （3）For inelastic cross section, the most effective transition is that with Δj=2.（4）The fast narrow diffraction oscillations in the cross sections are the obvious characteristics for the low Δj inelastic transitions, which decreases with increasing j. （5）The elastic differential-cross-sections（DCS）provides a useful visualization of rotational rainbows at low translational energy. It is beneficial to reducing the loss in molecular cooling and trapping.
2009, 58 (10): 6920-6925.
doi: 10.7498/aps.58.6920
Abstract +
The highly charged ions129Xe27+ impacting on Ni surface are neutralized by resonant capturing of electrons of metallic conduction band and release of potential energies. The multiply excited Xe atoms are formed and the outer-shell electrons are de-excited by emitting infrared photons. In the process, within femtoseconds, the projectile total energies are deposited on the target surface （on the nanometers scale）, which excites and ionizes the target atoms. The characteristic transitions between complex configurations of atoms and ions occur, especially the characteristic forbidden transition （M1 and E2） of NiⅠand NiⅡ, and the X-ray emission. The increasing of X-ray yield per ion with kinetic energies of projectile was found.
2009, 58 (10): 6926-6931.
doi: 10.7498/aps.58.6926
Abstract +
The stereodynamics in the chemical reaction He+H+2 and its isotopic variants at the collision energy of 145 kJ/mol have been studied by using the quasi-classical trajectory （QCT） method on AQUILANTI surface. The correlated k-j′， k-k′-j′ angular distributions, and the product rotational alignment are discussed in detail. The calculations indicate that the stereodynamics of the reactions of He+HH+→HeH++H, He+HD+→HeH++D and He+HT+→HeH++T are sensitive to the mass factor and the repulsive energy of diatomic molecule.
2009, 58 (10): 6932-6937.
doi: 10.7498/aps.58.6932
Abstract +
The vibrational excitation integrated cross sections （ICSs） of the low-energy electron-H2 scattering are studied using the vibrational close-coupling （VCC） method. 18 Morse vibrational states, 5 partial waves and 4 molecular symmetries are used to converge the vibrational excitation ICSs. It is shown that the properties of the vibrational excitation scattering potentials and the accuracy of the vibrational excitation ICSs may be affected by the quality of the vibrational wavefunctions and the accuracy of the vibrational energies. The converged vibrational excitation （ν0=0→ν=0，1，2，3） ICSs agree well with the known experimental results.
2009, 58 (10): 6938-6945.
doi: 10.7498/aps.58.6938
Abstract +
The triple differential cross sections for electron impact ionization of helium in the special geometry of coplanar large energy loss are calculated by using the BBK model and the modified BBK model. The calculated results are compared with the experimental results of Catoire and the present experimental results of Stevenson. The previous theoretical deduction is proved and the exchange effects are analyzed and discussed.
2009, 58 (10): 6946-6950.
doi: 10.7498/aps.58.6946
Abstract +
This paper presents the positron study on carbon-Fe3O4 coaxial nanofibers, which is one kind of new promising functional materials. According to the positron annihilation lifetime spectra and the coincidence Doppler broadening spectra, we find in this material that positrons annihilate partly in monovacancies of Fe3O4, partly in microcavities of Fe3O4 and partly in shelled carbon nanotubes. We also estimate the annihilation proportion in each part, which reveals the nanofibers’ microstructure to a certain extent.
2009, 58 (10): 6951-6955.
doi: 10.7498/aps.58.6951
Abstract +
For Ar clusters produced by specifical jet, the Rayleigh scattering was employed to investigate the cluster formation process and to measure the cluster size along nozzle axis under different background gas pressures. The developing process of cluster and the axial distribution of cluster size were observed at pressures from 20 to 60 atm experimentally. The relationship between the cluster size and the pressure and axial distance from the jet nozzle was obtained. It was found that the largest clusters were formed at distance 5 mm from the nozzle.
2009, 58 (10): 6956-6961.
doi: 10.7498/aps.58.6956
Abstract +
The geometrical structures of Tin and TinLa（n=1—7） clusters are optimized by using density functional theory（B3LYP） and LANL2DZ basis sets, and the vibrational frequency and electronic properties are calculated. The effect of La atom on the pure Tin clusters is discussed by analyzing the changes of average bond length, binding energy, HOMO-LUMO gaps, and magnetic moments between TinLa and Tin clusters. Furthermore, the reason of the changes caused by La atom is also studied.
CLASSICAL AREA OF PHENOMENOLOGY
2009, 58 (10): 6962-6972.
doi: 10.7498/aps.58.6962
Abstract +
The eigen function of a bifrequency magnetically insulated transmission line oscillator （BFMILO） is deduced, and the dispersion characteristics and the field distribution are analyzed in detail. By dividing a traditional symmetrical coaxial disk loaded slow wave structures （SWS） into two different azimuthal partitions, the SWS of BFMILO becomes a two-dimensional SWS. In this structure, different electromagnetic modes are distributed in different azimuthal partitions, so that two different electromagnetic modes, which are competition modes in a traditional MILO, can interact with electrons separately and stably. This special SWS is the key point in designing a BFMILO. The proposed method can also be used in analyzing a mlti-frequency MILO.
2009, 58 (10): 6973-6978.
doi: 10.7498/aps.58.6973
Abstract +
For one-dimensional drift spaces with parallel and cylindrical structures, space-charge-limited currents are calculated, and the steady transmission of intense electron beams exceeding the currents with virtual cathodes are studied theoretically. The transmission characteristics, such as the position of virtual cathode, the transmission rate of electrons at virtual cathode, and the transit-time of electrons in the spaces, are given analytically.
2009, 58 (10): 6979-6984.
doi: 10.7498/aps.58.6979
Abstract +
Two-dimensional （2D） polarization holographic recordings were accomplished in azobenzene side-chain liquid-crystalline polymer thin films. The 2D polarization grating makes up of two orthogonal 1D polarization gratings, which were written at the same place by two orthogonally linearly polarized 532 nm beams. It is found that the diffraction efficiency of 2D grating is lower than that of 1D grating, and the 2D grating acts as the integration of its componential 1D gratings. Furthermore, we find that the polarization dependency of diffraction efficiency and the polarization conversions arise from the collaboration of linear and circular birefringence.
2009, 58 (10): 6985-6991.
doi: 10.7498/aps.58.6985
Abstract +
The squeezing properties of atom laser are investigated with and without rotating-wave approximation by means of quantum theory in the system of optical field interacting with Bose-Einstein condensate of two-level atoms. The influences of the atomic eigenfrequency, the interaction intensity between optical field and atoms，the initial squeezing factor of optical field and the virtual photon field on the squeezing properties are discussed. The results show that two quadrature components of atom laser can be squeezed periodically. The quantum Rabi frequency and the collapse and revival frequency of atom laser fluctuation depend on the atomic eigenfrequency and the interaction intensity between optical field and atoms respectively. When the initial squeezing factor of optical field increases and the virtual photon field is considered, the degree of squeezing of the atom laser also increases.
2009, 58 (10): 6992-6999.
doi: 10.7498/aps.58.6992
Abstract +
The rate equations of all-fiber acousto-optic Q-switched lasers were solved under different initial boundary conditions by numerical simulation, and the distribution of upper-level population density along the doped fiber under forward pumping and backward pumping, and the relations between pulse energy, average power, pulse width, stored energy and pulse repetition rate, signal transmittance of the pump coupler, and pump power, were obtained. The simulation was analyzed from the viewpoint of the amplified spontaneous emission light, and an all-fiber Y3+b-doped acousto-optic Q-switched laser was employed experimentally to test the effect of pumping manners on the average power and pulse width. The results show that pumping manners significantly affect the performance of all-fiber acousto-optic Q-switched lasers under different pulse repetition rates, so the lasers should be forward pumped for better characteristics of output pulses under lower pulse repetition rate, and they should be backward pumped under higher pulse repetition rate.
2009, 58 (10): 7000-7004.
doi: 10.7498/aps.58.7000
Abstract +
A diode-end-pumped Nd:YVO4 intracavity frequency-tripled continuous-wave 355 nm laser has been demonstrated. The laser cavity is the simple concave-to-plane linear cavity, which is short and compact. The laser cavity length is only 70 mm. The efficient second and third-harmonic waves are generated by two lithium triborate （LBO） crystals successfully. The 355 nm laser output power is 306 mW at a pump power of 2527 W with an optical-to-optical efficiency of 012% and the corresponding beam quality is satisfactory. The instability of the output power of 274 mW is less than 53%. By using the technology of intracavity frequency conversion and choosing the proper parameters in cavity design, the miniaturization and handiness of the all-solid-state continuous-wave ultraviolet lasers with the relatively low output powers are improved greatly, which will broaden the application fields of the ultraviolet lasers.
2009, 58 (10): 7005-7011.
doi: 10.7498/aps.58.7005
Abstract +
The dispersion properties of nanofibers was numerically simulated and caculated in details, and different dispersion properties in different diameters and materials were compared. The results show that, there are two zero dispersion wavelengths in nanofibers with silica core. With the increase of fiber diameter, the disperison curve tends to smooth and the zero dispersion wavelength also changes. When the core is silicon, it only have one zero dispersion wavelength. With the increase of diameter, its zero dispersion wavelength moves to the long-wavelength end. The generalized nonlinear Schrdinger equation is adopted to describe the evolution of ultra-short laser pulse propagating in nanofibers, and is solved by using the split-step Fourier method. The influence of dispersion on the generation of supercontinuum and the evolution of pulse profile in different dispersion regions are compared. In the normal dispersion region, the output spectral width is narrow. While in the zero dispersion region and the anomalous dispersion region, the super continuum spectrum can be obtained easily.
2009, 58 (10): 7012-7016.
doi: 10.7498/aps.58.7012
Abstract +
The concept of “moving beam” in near field is proposed. It is found that the device of smoothing by spectral dispersion （SSD） can generate “moving beam” in the near field. The mechanism and the condition for generating “moving beam”， the motion characteristics of the “moving beam”， and the suppression of small-scale self focusing are analyzed theoretically. The numerical simulations agree with the theoretical analyses.
2009, 58 (10): 7017-7024.
doi: 10.7498/aps.58.7017
Abstract +
A novel chirp elimination and pulse compression method is firstly proposed using reconstruction equivalent chirp superstructured fiber Bragg grating（REC-SSFBG）. Based on the feasibility of REC technology for any physical realizable target response， this novel chirp elimination method is suited for any model of chirped pulse. The simulation results show that the time bandwidth product decrease from 225， 265 and 250 to 0458， 0636 and 073 for linearly chirped， Gauss chirped and Lorentz chirped pulses， respectively. The original pulsewidth is 20 ps and the chirp coefficients is -5 for all the three cases. Further experiment is performed with a fabricated REC-SSFBG to compress a chirped pulse generated from commercial software with model of gain-switched distributed feedback laser diode. The pulsewidth decreases from 25 ps to 5 ps， which agrees well with the simulation.
2009, 58 (10): 7025-7029.
doi: 10.7498/aps.58.7025
Abstract +
HfO2 films were prepared by electron beam evaporation on K9 glass. The residual stresse was measured by viewing the substrate deflection using ZYGO interferometer. The influences of deposition rate and oxygen partial pressure on the residual stress were studied. The results show that all the residual stresses are tensile stresses. The packing density of films increases while the residual stress decreases with the increasing deposition rates and the decreasing oxygen partial pressure. The microstructure of the HfO2 films was inspected by X-ray diffraction （XRD）. The relationship between the stress and the microstructure was also discussed.
2009, 58 (10): 7030-7033.
doi: 10.7498/aps.58.7030
Abstract +
The transmission properties of terahertz （THz） wave in metal-coated hollow waveguide are studied. Based on the characteristic equation of THz electromagnetic wave in metallic hollow waveguide， the dependence of the transformation attenuation and phase constant on the frequency of THz wave， inner radius of the waveguide and conductance of the metal material is simulated by using the Newton-Raphson iterative method. The results show that， the transformation attenuation can be decreased effectively by using large radius waveguide and high conductance coating metal.
2009, 58 (10): 7034-7043.
doi: 10.7498/aps.58.7034
Abstract +
Response properties of the fourth-order acoustic low-pass filtering fiber-optic hydrophones are investigated theoretically and experimentally. A mechanical acoustic resistance， which is used to describe the system’s mechanical loss， is introduced into the previous lumped parameters model of the hydrophone， and an improved acoustic equivalent circuit is given. Phase frequency response is an important parameter for the hydrophone array applications. It has great effect on beamforming， which affects the abilities of locating， discerning， and tracking targets. Therefore， the phase response peroperties is studied with the amplitude response peroperties. Some results， which are instructive for designing of acoustic low-pass filtering hydrophone， are obtained by numerical simulation. The measured rsponse curves are in good agreement with the simulation results， which verifies the correctness of the theory and the model. The fourth-order acoustic low-pass filtering fiber-optic hydrophones are useful for improvement of the anti-aliasing ability of modern sonar arrays.
2009, 58 (10): 7044-7049.
doi: 10.7498/aps.58.7044
Abstract +
The lattice parameters， elastic properties and electronic density of state of the （59Cr-41Ti）100－xVx（x=5， 15， 30， 60， 80， 100） V-based solid solution hydrogen storage alloys were calculated using the first-principles plane-wave pseudo-potential method based on the density functional theory， and the calculated results were in agreement with the experimental results. It was found that the V-based alloy x=60 showing better elastic properties， with the Young modulus Yzz=14930 GPa， shear modulus Ct=5442 GPa and bulk elastic modulus B=19396 GPa. By combining the experimental cyclic durability performance， we found plastic deformations occurred in the alloys. Thus， we concluded that the elastic properties were not the primary factor that determines the cyclic durability of the V-based hydrogen storage alloys. The micromechanism of the elastic properties of the impure alloys were also explained with the electronic density of state.
2009, 58 (10): 7050-7056.
doi: 10.7498/aps.58.7050
Abstract +
The fractal characteristics of the surface roughness are investigated by using fractal geometry. A three-dimensional model of laminar flow in microchannels with surface roughness characterized by fractal geometry is developed and analyzed numerically. The Weierstrass-Mandelbrot function is introduced to characterize the multiscale self-affine roughness. The effects of Reynolds number Re， relative roughness， and fractal dimension on Poiseuille number are investigated and discussed. The results show that， different from the conventional channels， Poiseuille number in rough microchannels is no longer constant for different Re， but increases approximately linearly with Re， and is larger than the classical value. The flow over roughness features with high relative roughness induces recirculation and flow separation， which plays an important role in flow pressure drop. More specifically， roughness with larger fractal dimension， which yields more frequent variation in the surface profile， also results in a significant increase in pressure loss， even though at the same relative roughness. In addition， the accuracy of Poiseuille number calculated by the present model is verified by the experimental data available in the literature.
2009, 58 (10): 7057-7061.
doi: 10.7498/aps.58.7057
Abstract +
In direct drive inertial confinement fusion， surface perturbations seeded by imprint from laser intensity variations play an important role in Rayleigh-Taylor（RT） growth. Laser imprinting and consequent RT growth in planar CH targets driven by different pulse shapes have been investigated. The experimental results reveal that the range of density modulation induced by laser imprinting is larger when the driving laser has lower foot intensity and rises more slowly. Enhancing the pre-pulse intensity can restrain the effect of laser imprinting notablely.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2009, 58 (10): 7062-7066.
doi: 10.7498/aps.58.7062
Abstract +
A tunable filter is formed when a plasma defect is introduced in the one-dimensional dielectric-air microwave photonic crystal. Plasma is a dispersive medium and its equivalent refractive index is related to the frequency of the incident electromagnatic wave and the plasma frequency， so it is feasible to shift the syntonic frequency of plasma defect by changing the plasma parameters, which behaves as a tunable filter. In the numerical simulation， the finite-difference time-domain method and the piecewise linear current density recursive convolution finite-difference time-domain method are applied to the dielectric and plasma， respectively. The results show that the filter channel of this microwave photonic crystal can be tuned in a wide band in the photonic band-gap by changing the plasma frequency.
2009, 58 (10): 7067-7073.
doi: 10.7498/aps.58.7067
Abstract +
Single-shell gas-puff Z-pinch experiments were performed on “Yang” accelerator （peak current 500—850 kA， rise time ～85 ns）. The x-ray power and yield， the time-resolved and time-integrated images of plasma implosions were measured. Based on the corresponding diagnostics， the implosion time was defined and the implosion process was divided into four stages. the initial plasma status and the distribution of radiative intensity were studied. In addition， the implosion trajectories， load mass， radial convergence and magneto- Rayleigh-Taylor （MRT） instability were analyzed.
EDITOR'S SUGGESTION
2009, 58 (10): 7074-7078.
doi: 10.7498/aps.58.7074
Abstract +
At the SILEX-Ⅰlaser facility， penumbral imaging technique was used to record a Kα source in two dimensions. Due to the fact that the source was produced via the interaction between ultrashort-ultraintensity laser and ‘Velvet’ target， we can obtain high quality Kα source images. More details about the source spatial distributions can be deduced from the two-dimensional imaging than that from the one-dimensional imaging such as knife edge imaging.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2009, 58 (10): 7079-7082.
doi: 10.7498/aps.58.7079
Abstract +
Ga2（1-x）In2xO3（x=01—09） thin films were prepared on α-Al2O3 （0001） substrates by metalorganic chemical vapor deposition （MOCVD）. The structure， the optical and electrical properties as well as the effect of annealing on the properties of the films were investigated in detail. The results indicate that the film deposited with composition x=02 was polycrystalline with β-Ga2O3 structure， the film with x=05 was amorphous and transformed into body-centered cubic （bcc） structure of In2O3 with a preferred orientation of （222） after annealing. For x=08， the obtained film showed bcc structure of In2O3 and the crystalinity was improved after annealing treatment. The average transmittance for the films in the visible range was over 85%. The band-gap of the Ga2（1-x）In2xO3 films can be suitably tuned from 376 to 443 eV by controlling the gallium content and it is increased obviously by annealing.
2009, 58 (10): 7083-7087.
doi: 10.7498/aps.58.7083
Abstract +
We realized the growth of terahertz quantum-cascade laser （THz QCL） by gas source molecular beam epitaxy （GSMBE）. Electrochemical capacitance-voltage method， Hall measurement and high-resolution x-ray diffraction were used to evaluate the crystalline quality of the THz QCL active region. Meanwhile， we used an ensemble Monte Carlo method to investigate the carrier transport characteristics in a resonant-phonon THz QCL. Level alignment and electron motion under different applied biases are discussed in detail.
2009, 58 (10): 7088-7093.
doi: 10.7498/aps.58.7088
Abstract +
The structural properties of a quasicrystal model with twelve-fold rotational symmetry are studied. We correct the errors in the self-similar transformation of the square-rhombus-hexagon tiling model proposed by Socolar. Based on the Stampfli-Ghler square-rhombus-triangle tiling model， the quasi-unit cell is successfully constructed， which can describe the dodecagonal quasiperiodic structure by the covering theory.
2009, 58 (10): 7094-7100.
doi: 10.7498/aps.58.7094
Abstract +
Based on the adaptive finite element method， the phase-field model has been employed to simulate the free dendritic growth process governed by capillary anisotropy or kinetic anisotropy. It is illustrated that the free dendritic growth depends sensitively on the degree of the capillary anisotropy or kinetic anisotropy of the solid-liquid interface. As the anisotropies are enhanced， the dendrite tip growth velocity increases， but the dendrite tip radius decreases. These two kinds of anisotropies have different effects on the free dendritic growth behaviors. Under the capillary anisotropic condition， there is a power law relationship between the stability parameter and the capillary anisotropy parameter. And under the kinetic anisotropic condition， there is a linear relationship between the stability parameter and the capillary anisotropy parameter.
2009, 58 (10): 7101-7107.
doi: 10.7498/aps.58.7101
Abstract +
Thin film of tellurium was prepared by vacuum evaporation deposition on glass, polyethylene foils and Si under high magnetic field. The results show that the difference of the substrate can strongly affect the particle size, and a magnetic flux density of 4 T can accelerate the speed of growth of Te film, increase the particle size and the intensity of （011） peak of Te films.
2009, 58 (10): 7108-7113.
doi: 10.7498/aps.58.7108
Abstract +
Ti ions were implanted into ZnS films at a dose of 1×1017ions/cm2 and energy of 80 keV by vacuum evaporation. After ion implantation， the as-implanted sample was annealed in argon ambient at different temperatures from 500 ℃ to 700 ℃. The effects of ion implantation and post-thermal annealing on the structural and optical properties of ZnS films were investigated by x-ray diffraction （XRD）， photoluminescence （PL） and optical absorption. The results showed that the diffraction peak intensity was recovered by annealing at 500 ℃. The optical absorption in the visible region increased after Ti ion implantation and the absorption edge blueshifted with the increasing annealing temperature. The PL emission intensity increased with the increasing annealing temperature.
2009, 58 (10): 7114-7118.
doi: 10.7498/aps.58.7114
Abstract +
The Raman shifts of Si—Si， Ge—Ge and Si—Ge in Si（1-x）Gex alloys are calculated by Keating model. The calculated Raman shifts are 40275，41339 and 38815 cm-1 when the concentrations of Ge are 01， 05 and 09 respectively. These results are consistent with the reported experimental results， which indicates the validity of the Keating model for obtaining the Raman frequency of strained materials by changing the elastic coefficients of stretching and compression and bond-bending interaction. The single-phonon scattering peak at 477029 cm-1 in amorphous silicon is obtained for the first time by Keating model, which is in agreement with the result of 4800 cm-1 from the literature, indicating that the atoms of amorphous silicon as a whole are stretched compared with that of crystalline silicon.
2009, 58 (10): 7119-7123.
doi: 10.7498/aps.58.7119
Abstract +
The thermopower of decagonal AlCuCo quasicrystal was measured in the periodic and quasiperiodic direction by laser heating alternating current measurement method in the temperature range of from 300 K to 1200 K. We found that the thermopower is negative in the periodic direction and positive in the quasiperiodic direction. The thermopower hopps at 1123 K （850 ℃） along the periodic direction. The change of the thermopower is not monotonic at high temperature. The measurement method we used is sensitive to the phase transition point.
2009, 58 (10): 7124-7129.
doi: 10.7498/aps.58.7124
Abstract +
Base on the lumped resistance-capacitance （RC） tree power model，a novel distributed interconnect dynamic power analytical model was proposed，which considers the effect of non-uniform temperature distribution along the interconnect. The new model overtakes the defect that the lumped model cannot represent the effect of non-uniform temperature distribution on the resistance of interconnect，and estimates the total power consumption of RC tree under a non-ideal unit step input. The proposed model is used to calculate the total power consumption of interconnect under nanometer-scale complementary metal-oxide semiconductor （CMOS） typical process. The results show that the longer the interconnected line is，the greater the effect of non-uniform temperature distribution on the power consumption is，and the dynamic power per unit length keeps constant under different processes. The proposed model can accurately calculate the dynamic power of interconnects，thus can be used to optimize design of large scale interconnect router and clock network in network-on-chip structure.
2009, 58 (10): 7130-7135.
doi: 10.7498/aps.58.7130
Abstract +
Considering the via effect and the heat fringing effect simultaneously，we proposed a compact interconnect temperature distribution model that can be applied for single interconnect and multilevel interconnects. Based on the 65 nm complementary metal-oxide semiconcluctor （CMOS） interconnect and material parameter，the temperature distribution of multilevel interconnects and single interconnect with different lengths was calculated. The results show that the temperature rise of global interconnect is still large when the via effect is considered，while the temperature rise of intermediate line and local line is quite small. For multilevel interconnects，the temperature rise in the uppermost layer interconnect is the largest. The temperature rise is approximately proportional to the thickness of insulator，and will rise higher if the thermal conductivity of dielectric materials becomes smaller. The proposed interconnect temperature distribution model can be used in nanometer CMOS computer-aided design.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2009, 58 (10): 7136-7140.
doi: 10.7498/aps.58.7136
Abstract +
Under the same condition，ZnO models with different sizes are proposed by using the plane wave ultra-soft pseudopotential technique based on the density functional theory （DFT）. Al and N with different concentrations are heavily doped in ZnO semiconductor，and the density of states of Al and N doped ZnO is calculated by DFT mothod under the condition of low temperature. The relative average number of holes and the scattering mobility of holes in the valence band are calculated. We find that heavily doping of Al-2N atoms with low concentration can enhance the conducting of ZnO，which means that the conductivity of ZnO semiconductor is related with not only the concentration of heavy doped Al and N，but also the relative average number of holes and the scattering mobility of holes in the valence band. The calculated results agree with the experimental results.
2009, 58 (10): 7141-7146.
doi: 10.7498/aps.58.7141
Abstract +
The magnetic structure，energy band structure and electronic structure of BiFeO3 and BiFe075Co025O3 are investigated by using density functional theory combined with the projector augumented wave （PAW） method. Our numerical results show that the doping of Co does not destroy its perovskite structure and BiFe075Co025O3 keeps the obvious ferroelectricity. The ferromagnetism can be significantly improved since the doping of Co changes the G-type antiferromagnetic order into ferromagneti cone. However，the doping of impurity Co degrades the insulativity.
2009, 58 (10): 7147-7150.
doi: 10.7498/aps.58.7147
Abstract +
The interaction between a semiconducting single-walled carbon nanotube and its graphite substrate was studied by calculation based on the density functional theory. Between two contact configurations of the system energy minimum, a series of metastable contact configurations of the carbon nanotube on the graphite were optimized, and the atomic structures of these contact configurations and the related energy bands of the system were determined. It is found that the interaction makes the contacted graphite surface concave and the band gap of the carbon nanotube narrow, which may be significant to the carbon-based nanodevice strategy.
2009, 58 (10): 7151-7155.
doi: 10.7498/aps.58.7151
Abstract +
The electron field emission properties of C-doped capped single-walled BNNT （C@BNNT） are investigated by first-principles study. The results show that with the increase of the applied electric field, the electronic structure of C@BNNT changes significantly，the density of states （DOS） shifts towards the low energy position，the local density of states （LDOS） at the Fermi level increases dramatically，the energy gap between the lowest unoccupied molecular orbital （LUMO） and the highest occupied molecular orbital （HOMO） decreases drastically and the electrons congregate to the capped side. The investigations of DOS，HOMO/LUMO and Mulliken population analysis indicate that， compared with pristine BNNT, the field emission properties of C@BNNT, especially of C@BNmoreNT， are greatly improved.
2009, 58 (10): 7156-7161.
doi: 10.7498/aps.58.7156
Abstract +
Based on the π-electron energy dispersion relation of general compound lattices derived from the tight-binding model, and assuming that the transverse confinement potential of graphene nanoribbon is a infinite hard-wall potential，we obtain the energy dispersion relation of graphene nanoribbon and the conditions that determine whether it is metallic or semi-conducting. The results presented here show that the electronic structure of graphene nanoribbon is intimately related to its geometric structure （symmetry and width），so graphene nanoribbon can be modified as metallic or semi-conducting materials only by controlling its geometric configurations，which suggests that it is highly promising to use graphene nanoribbon to develop novel nano-scale devices.
2009, 58 (10): 7162-7167.
doi: 10.7498/aps.58.7162
Abstract +
The possibility of forming cascading energy levels in SrTiO3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.
2009, 58 (10): 7168-7175.
doi: 10.7498/aps.58.7168
Abstract +
Cluster-cluster aggregation model based on Monte Carlo method is used to simulate the structure of the fractal-like soot cluster agglomerates consisting of spherical primary particles，and Mueller-matrix elements of fractal-like soot cluster agglomerates are calculated based on the discrete dipole approximation method. The numerical relations between the Mueller-matrix elements and the total number and the diameter of the primary sphere in agglomerate are discussed for different incident wavelengths，which provides an effective theoretical method for studing the formation mechanism，structural characteristics and scattering characteristics of randomly distributed cluster agglomerates.
2009, 58 (10): 7176-7182.
doi: 10.7498/aps.58.7176
Abstract +
Based on the Neel-Brown relaxation time theory and the effective temperature model proposed by Li et al.，the thermal effect in current induced magnetic spin torque switching is theoretically studied. On the basis of Landau-Lifshitz-Gilbert equation and Fokker-Planck equation，through analyzing the current induced magnetic switching and potential change，a new model to explain the potential barrier reducing is proposed. Different from Lis model，this model is nonlinear. The model is used to discuss the relation between temperature，switching time and critical current. For the current induced temperature rise，our model does accord with the experiment well. The method for determining the intrinsic switch electric current，testing time and intrinsic potential barrier in magnetic switching is also proposed.
2009, 58 (10): 7183-7188.
doi: 10.7498/aps.58.7183
Abstract +
On the basis of the number fluctuation model of n-type metal oxide semiconductor field effect transistor （nMOSFET），non-Gaussianity of noise in nMOSFET was studied by the quadratic sum of the bicoherence，which belongs to higher order statistics. Comparing nMOSFETs test noise with Monte Carlo simulative noise，we proved that there is non-Gaussianity in nMOSFTs noise, that the noises non-Gaussian degree in small size devices is stronger than that in large size devices, and that the non-Gaussian degree of nMOSFTs noise in strong inversion and linear regime increase with the drain-source voltage. The physical mechanism of nMOSFET noise is discussed from Monte Carlo simulation and the central limit theorem.
2009, 58 (10): 7189-7193.
doi: 10.7498/aps.58.7189
Abstract +
The temperature characteristics of the forward voltage of GaN based blue light emitting diodes are studied. We find that the temperature coefficient decreases with the increasing temperature when the temperatures is relatively high. There is an inflection point as the temperature coefficient deceases，then the temperature coefficient changes from negative to positive. If the temperature still increases at this moment，the forward voltage will increase dramatically，resulting in the failure of the light emitting diodes. This phenomenon is not obvious when the current is low. When the current increases，this phenomenon becomes more and more obvious，and the temperature of inflection point becomes lower and lower. Moreover, the forward voltage increases more quickly when the temperature is higher than the inflection point temperature. By comparing the test result of another group light emitting diodes with the same package epoxy, we find that the influence of glass transition temperature of the package epoxy can be neglected. The appearance of this phenomenon is due to the rapid increment of the equivalent series resistance，of which the main reason is the rapid deterioration of the p-type layers of the GaN based blue light emitting diode. The result shows that we can judge the quality of the GaN based blue light emitting diodes p-type layers quickly by measuring the variation of the forward voltage with temperature，which is a rapid method for the researchers and producers.
2009, 58 (10): 7194-7198.
doi: 10.7498/aps.58.7194
Abstract +
Aluminum gallium indium nitride（AlGaInN） quaternary epilayers were prepared by metalorganic chemical vapor deposition （MOCVD） on c-plane sapphire （α-Al2O3） substrates. Three samples were grown under different temperatures of 800 ℃，850 ℃ and 900 ℃. It is found that the In composition monotonically decreases with the increasing growth temperature，while the Al composition is nearly invariable. The V-pits appeared when the growth temperature increases to 850 ℃, and the size and density of V-pits drastically decrease and the nucleation of V-pits is passivated when the growth temperature rises to 900 ℃ due to the desorption enhancement of segregated In atoms.
2009, 58 (10): 7199-7203.
doi: 10.7498/aps.58.7199
Abstract +
Al （Al2O3，2wt%） doped ZnO thin films （ZAO） with tunable band gap，alloyed with different Mg contents （1wt%，3wt% and 5wt%），were prepared by radio frequency magnetron sputtering on glass substrates and annealed at 500℃ in air. The optical and electrical properties of the films were measured by X-ray diffractometer，four-point probe method，Hall-effect configuration，and UV-VIS spectrophotometer. The results show that the Mg co-doped ZAO thin films have a wurtzite structure with （002） preferred orientation. Compared with ZAO film，the optical transmission of Mg co-doped ZAO thin films in the ultraviolet region increases and the average optical transmissions in the visible region is greater than 85%，except the 5wt% Mg doped films. The band gaps of ZAO and Mg co-doped ZAO thin films can be modulated from 344 eV to 351 eV by increasing the Mg content from 1wt% to 5wt%. For 1wt%，3wt% and 5wt% Mg doping，the Mg co-doped ZAO thin films have the resistivity of 12×10-3，37×10-3 and 85×10-3 Ω·cm，respectively. Stokes shifts of 20，14 and 50 meV were observed for doping of 1wt%，3wt%，and 5wt% Mg contents. We find that a large Mg doping content will degrade the crystal quality of Mg co-doped ZAO thin films，decrease the optical transmissions in the visible region and decrease the carrier mobility in the films. Therefore，the resistivity of Mg co-doped ZAO thin films increases with the Mg doping content.
2009, 58 (10): 7204-7210.
doi: 10.7498/aps.58.7204
Abstract +
Based on the structural characteristics of a molecular wire coupled to electrodes，the electronic tunneling process in a molecular device consisting of such a composite molecule under a bias is modeled by a simplified successive tunneling model with asymmetric multiple potential barriers in series. An analytical expression for the electronic transmission spectrum is obtained. Then，the relations between the transmission coefficient and various parameters，such as the width and height of the barrier，the distance between two neighboring barriers，the effective mass of electron, and the bias voltage, are calculated. It is found that when the electron energies are equal to some special values，obvious resonant tunneling occurs，and the transmission coefficient is very sensitive to the parameters mentioned above. The results presented here suggest that the transport behaviors of molecular electronic devices can be significantly modified in a controlled way, for example，by altering the constituents or/and the configurations of the composite molecule.
2009, 58 (10): 7211-7215.
doi: 10.7498/aps.58.7211
Abstract +
Three kinds of metal-oxide-semiconductor high-electron-mobility transistors （MOS-HEMTs） with different thickness of Al2O3 dielectric layer were fabricated on the same wafer by atomic layer deposition. The measurement results of MOS capacitance，gate leakage current，and the output and transfer characteristics indicate that the control capability of the gate on two-dimentional electron gas will be reduced，while the gate leakage current will be decreased and the breakdown voltage will be increased with the increase of the Al2O3 dielectric layer thickness. Our analysis shows that the thinner the dielectric layer is，the greater the gate capacitance will be，which leads to greater negative shift of threshold voltage and much poorer insulating performance in restraining gate leakage current. Otherwise，with the increase of dielectric layer，higher gate voltage will be applied to obtain higher maximum saturation current density. Moreover，a thorough analysis of the transconductance and the capacity-voltage （C-V） characteristic shows that better passivation effect and insulating performance can be obtained with thicker dielectric layers.
2009, 58 (10): 7216-7221.
doi: 10.7498/aps.58.7216
Abstract +
Tl-2212 bicrystal Josephson junctions on SrTiO3 substrates have been fabricated. The I-V characteristic of a Josephson junction under microwave radiation were measured，and microwave induced steps were observed in accordance with the Josephson frequency-voltage relationship. The RCSJ model including noise of bicrystal Josephson junction was constructed through numerical simulation，and the results of simulation were in good agreement with the experimental data. Using the RCSJ model，we investigated the effect of noise on the dynamic characteristics of Josephson junction through simulation，and explained the phenomenon of reduced height and increased breadth of the minima of microwave induced steps. We proposed that the effective noise temperature should be the sum of operational temperature and equivalent temperature of the external noise.
2009, 58 (10): 7222-7226.
doi: 10.7498/aps.58.7222
Abstract +
The structural and magnetic properties of Sm2Fe17-xCrx compound have been investigated by means of x-ray diffraction and magnetization measurements. The results show that the Sm2Fe17-xCrx （x=1—3） compounds annealed at 1050 ℃ for 5 days have a rhomhedral Th2Zn17-type structure，and the Sm2Fe17-xCrx（x=25, 30） compounds annealed at 1050 ℃ for 7 days have a monoclinic Nd3（Fe，Ti）29-type structure. Long annealing time and high content of Cr can make the Sm-Fe-Cr compound with a Nd3（Fe，Ti）29-type structure become very stable. This is quiet different from the R2Fe17-xCrx compound （R is a heavy rare earth element）. The analysis of unit-cell volume and unit-cell parameters show that there exists a strong anisotropic magneto-volume effect in Sm2Fe17-xCrx compounds. The result of magnetization measurement shows that the effects of the substituting Cr for Fe at dumbbell sites on the Curie temperature and the magneto-crystalline anisotropy of the compound with Th2Ni17-type structure are greater than that of the compound with Th2Zn17-type structure.
2009, 58 (10): 7227-7234.
doi: 10.7498/aps.58.7227
Abstract +
Considering the electrostrictive，magnetostrictive effects in the ferroelectric （FE） phase and ferromagnetic （FM） phase and the elastic stress arising from FE/FM and film/substrate interfaces，using the Landau-Devonshire thermodynamic theory，we investigate the magnetoelectric coupling effect in epitaxial 1-3 type multiferroic nanocomposite thin films. We renormalize the dielectric and magnetic coeffcients twice and obtain the quasi-intrinsic magnetoelectric coupling in Landau free energy function of this multiferroic system. Then，the electrical-field-induced magnetization and polarization for films of different thickness in 1-3 type BaTiO3-CoFe2O4 nanocomposite system are analyzed. Our results show that the relaxation of the in-plane compressive stress of the thin film makes magnetization and polarization both decrease with the increasing film thickness，and an applied electric field can result in the reversal of magnetization in step with the switching of the electric polarization due to the out-of-plane elastic coupling between the interface of the FE and FM phases. Our results agree well with the experimental results.
2009, 58 (10): 7235-7240.
doi: 10.7498/aps.58.7235
Abstract +
The structures and properties of Zr and Hf-modified SrBi4Ti4O15（SBTi） ceramics were investigated. We find that the basic crystal structure is not changed after the substitution of equal-valent cations Zr4+ and Hf4+ for the Ti4+ ions at B site in SBTi. Compared with the higher-valent cation doping （V, Nb）, Zr4+ and Hf 4+ substitution can also improve the ferroelectric property of SBTi. The enhancement of remnant polarization （2Pr） by Hf4+ doping is obviously larger than that by Zr4+ doping, though these two cations have almost the same radius. This indicates that the reduced concentration of oxygen vacancy is not the only reason responsible for the improvement of the 2Pr in the B site doping, and other uncertain reasons should also be considered. The piezoelectric properties of these ceramics are investigated briefly. The tendency of piezoelectric constant changing with the doping dosage is nearly consistent with the tendency of 2Pr. Meanwhile, the dielectric properties of these ceramics are investigated, the Curie temperature of the samples varieds slightly with the doping amount, which implies that the good thermal stability of SBTi is not sacrificed.
2009, 58 (10): 7241-7245.
doi: 10.7498/aps.58.7241
Abstract +
Optically injected semiconductor laser is applied to photonic microwave generation. The microwave is generated by the beat between the oscillation frequency of the slave laser and that of the external injection light. We find that the microwave frequency can be tuned from 61 GHz to 129 GHz by varying the injection optical power in experiment. The tunable ability in our scheme can also be achieved through adjustment of the frequency detuning. Numerical simulations indicate that the frequency of the optically generated microwave can be higher than 40 GHz by using the optical injection semiconductor laser technique.
2009, 58 (10): 7246-7249.
doi: 10.7498/aps.58.7246
Abstract +
We synthesized size-controlled，uniformly distributed, and thioglycolic-stabilized CdTe nanocrystals by wet chemistry method. The multilayer nanocrystals were assembled on Si substrate by bifunctional linker molecule and the resonance energy transfer between different sized CdTe nanocrystals embedded in gelatin film was investigated. The results showed that the multilayer nanocrystals were in a good order because the distance between the layers was nearly the same. The distance between different sized nanocrystals was relatively short in the directly dried sample. We can observe the resonance energy transfer by the red shift in its photoluminescence.
2009, 58 (10): 7250-7254.
doi: 10.7498/aps.58.7250
Abstract +
Ultrafast dynamics and its excitation-energy-density dependence of photoexcited carriers in amorphous Ge2Sb2Te5 film were studied at room temperature by femtosecond-time-resolved pump-probe reflectivity spectroscopy. It was found that the reflectivity reduced down to a minimum in 05 ps after pump excitation, and then started to increase sharply up to a new maximum value larger than the initial reflectivity in several picoseconds. Furthermore, the decreased and increased amplitudes of the reflectivity with respect to its initial value as well as its rising rate from the minimum to the maximum both increased with the increasing excitation energy density. The sharp rising process of the reflectivity was explained quantitatively based on the model of Auger recombination of high density plasma and Auger-recombination-induced heating of cyrstal lattice, which shows that the heating effect induced by Auger recombination in high density plasma should be the main mechanism of ultra-short laser pulse-induced phase change.
2009, 58 (10): 7255-7260.
doi: 10.7498/aps.58.7255
Abstract +
A new ultraviolet photodetector of employing p menus type GaN （p－-GaN） as the active layer is proposed. It is easy to obtain the p－-GaN layer with low carrier concentration. As a result, the depletion region can be increased and the quantum efficiency can be improved. The influence of some structure parameters on the performance of the new device is investigated. Through the simulation calculation, it is found that the quantum efficiency increases with the decrease of the barrier height between the metal electrode and the p－-GaN layer, and it is also found that the quantum efficiency can be improved by reducing the thickness of the p－-GaN layer. To fabricate the new photodetector with high performance, we should employ thin p－-GaN layer as the active layer and reduce the Schottky barrier height.
2009, 58 (10): 7261-7266.
doi: 10.7498/aps.58.7261
Abstract +
Co, Cu single doped and co-doped ZnO thin films were fabricated on the glass substrate by means of sol-gel process. The influence of Co and Cu doping on the surface morphologies of ZnO films was investigated. X-ray diffraction shows that all the ZnO thin film samples are well oriented and the grain size of Cu-doped ZnO film is the largest. Strong blue double emission and weak green emission were observed in the photoluminescence spectra of all samples at room temperature and both long wavelength blue peak and green peak could be modulated by doping. The blue double peaks are caused by transition of electrons from the bottom of the conduction band to zinc vacancy or from the zinc interstitial to the top of the valence band. However, the green peak is highly relevant to the oxygen slip formed by doping.
2009, 58 (10): 7267-7271.
doi: 10.7498/aps.58.7267
Abstract +
A series of nanophosphors of Y1-xPO4:xEu3+（005≤x≤030）were synthesized by a mild hydrothermal method with post heat treatment. The structure and morphology of the samples were characterized by X-ray diffraction （XRD） and scanning electron microscope （SEM）. The results show that these nanophosphors have tetragonal structure with spherical and fine rod-like morphologies in acidic and alkaline condition, respectively, but all are on the nanoscale. The photoluminescence （PL） properties were also investigated under vacuum ultraviolet （VUV） excitation. Compared with samples prepared by solid state reaction, the PO3-4 absorption band located at 142 nm in vacuum ultraviolet region shifts towards high-energy direction. The intensity of 5D0→7F2 （619 nm） emission peak of Eu3+ is higher than that of 5D0→7F1. After heat treatment, the color purity and luminous intensity of the phosphors can be greatly improved. The PL intensity of optimized phosphor is superior to that of samples prepared by solid state reaction. These phenomena can be attributed to the improved crystallinity and reduced defects.
2009, 58 (10): 7272-7277.
doi: 10.7498/aps.58.7272
Abstract +
Electrofluorescent organic light-emitting device with the structure of ITO/NPB/Alq3/LiF/Al and electrophosphorescent device with the structure of ITO/NPB/CBP: Ir（ppy）3/BCP/Alq3/LiF/Al were fabricated. Their electroluminescence properties were measured under an external magnetic field of 50 mT. Compared to the case of without magnetic field, the electroluminescent（EL） efficiencies of the above-mentioned two kinds of devices increase 44% and 7%, respectively. Based on the luminescence mechanism of organic light-emitting diodes （OLEDs）, the observed phenomena were explained. The origin of the improvement can be attributed to the Zeeman split of triplet state due to the external magnetic field influence, resulting in the conversion of triplets T+ into singlet S in the electrofluorescent device and an increase of the rate constants of triplet energy transfer from host to guest in electrophosphorescent device, respectively. At the same time, the reduced concentrations of triplet decreases the interaction of triplets with free carriers, resulting in an increase in the mobility of free carriers within the device and hence increasing the current.
2009, 58 (10): 7278-7281.
doi: 10.7498/aps.58.7278
Abstract +
The vertical-cavity surface-emitting laser（VCSEL） has proved to be a low cost light source with attractive properties such as surface emission, circular and low divergence output beam, and simple integration in two-dimensional array. Many new applications such as in spectroscopy, optical storage, short distance fiber optic interconnects, and in longer distance communication, are continuously arising. Many of these applications require stable and single-mode high output power. Several methods that affect the transverse guiding and/or introduce mode selective loss or gain have been developed. In this study, a method for improving the single mode output power by using metal surface plasmons nanostructure is proposed. Theoretical calculation shows that the outpout power is improved about 50% compared to the result of standard VCSELs.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2009, 58 (10): 7282-7287.
doi: 10.7498/aps.58.7282
Abstract +
GaN layers with AlGaN intermediate layers of different Al mole fraction steps were grown on 6H-SiC by metal organic vapour phase epitaxy system. The residual stress and surface morphology of these samples were compared with GaN/AlN/SiC structure in detail. High resolution X-ray diffraction indicates that the c-axis constant increases with the increasing number of AlGaN steps, while low-temperature photoluminescence measurement shows a blue-shift of the GaN peak. These results should be attributed to the decreased residual stress in GaN. Furthermore, surface morphology of samples with AlGaN intermediate layers is improved according to the results of atomic force microscope.
2009, 58 (10): 7288-7293.
doi: 10.7498/aps.58.7288
Abstract +
The deposition parameters of hydrogenated microcrystalline silicon （μc-Si:H） films were optimized for two factors, the siliane concentration and total flow rate, under high deposition power density and high deposition pressure by very high frequency plasma enhanced chemical vapor deposition（VHF-PECVD）.The device-grade film with activation energy of 047 eV was finally prepared at a rate of 142 nm/s when the siliane concentration was 45% and the total flow rate was 100 sccm.Meanwhile,the deposition rate of microcrystalline thin films has reached 21 nm/s under 600 Pa. We have researched the electronic property and the conductivity of thin films by use of grain boundary trapping model and statistical shift of Fermi level model respectively. Moreover, we analyzed the effect of post-oxygenation on the electronic performance of thin films.
2009, 58 (10): 7294-7299.
doi: 10.7498/aps.58.7294
Abstract +
The p-i-n type μc-Si:H solar cells were prepared in a single chamber using very high frequency plasma enhanced chemical vapor deposition technique. Boron cross-contamination between p-layer and subsequent i-layer seriously affects the device performance. The effects of p-seeding on the μc-Si:H i-layers and performance of μc-Si:H solar cells were investigated.The p-seeding method was mainly realized by relatively high hydrogen rich plasma. It has been demonstrated that p-seeding can improve the characteristics of p/i interface and the vertical uniformity of the intrinsic layer and reduce boron contamination. Through the optimization of p-seeding layer technique, a-Si:H/μc-Si:H tandem solar cell with 881% （1 cm2） conversion efficiency has been fabricated in single chamber.
Mechanism of surface nanocrystallization in pure nickel induced by high-current pulsed electron beam
2009, 58 (10): 7300-7306.
doi: 10.7498/aps.58.7300
Abstract +
High-current pulsed electron beam （HCPEB） technique was applied to irradiate the samples of polycrystalline pure nickel. Microstructures of the irradiated surface and sub-surface were investigated by using scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The experimental results show that the surface layer melted, and 2 μm depth remelted layer was formed on the top surface. Superfast solidification of melted layer results in the formation of nano-structure of 80 nm grain size in the remelted layer. In the sub-surface regions, the structures of dislocation walls and sub- dislocation walls in it with band shape were induced by severe plastic deformation, which become the dominant structures 5—15 μm below the irradiated surface. Those defect structures crossing with each other results in grain refinement, and nanocrystal grains about 10 nm in size were produced in the sub-surface layer.
2009, 58 (10): 7307-7312.
doi: 10.7498/aps.58.7307
Abstract +
Molecular dynamics simulations are utilized to study the deformation process in NiAl under uniaxial tension using embedded atom method （EAM） interatomic potential. Both the tensile stress-strain curve and the atomic configurations are analyzed. The martensitic phase transformation is observed and the initial B2 NiAl transforms to a face-centered cubic ordered phase （L10）. The investigation of atomic configuration evolution indicates that the martensitic phase transformation occurs by the propagation and annihilation of {110} twinning planes. The nucleation mechanism of stress induced martensile has also been discussed.
2009, 58 (10): 7313-7316.
doi: 10.7498/aps.58.7313
Abstract +
To deal with the problem that autosorb analyzer can only work under the condition of pressure below 0.1 MPa, we have designed and fabricated a new apparatus which is used to study the characteristics of adsorption in an extended range of pressure.Ideal gas equation of state and van der Waals equation are used to calculate the capacity of hydrogen storage of the materials of resorcinol-formaldehyde carbonized aerogel with the help of the new apparatus.
2009, 58 (10): 7317-7321.
doi: 10.7498/aps.58.7317
Abstract +
The chemical hydride NaMgH3 is considered to be a promising candidate for hydrogen storage materials with its high hydrogen gravimetric and volumetric densities. The mechanism of the improved dehydrogenating properties of NaMgH3 doped by F anion was investigated using plane-wave pseudopotential （PW-PP） approach based on the density functional theory （DFT）. Computational results show that the formation enthalpy and reaction enthalpy of the hydride decrease drastically with the substitution of F for H. This results in a favorable thermodynamic modification, and facilitates the dehydrogenation reaction of the hydrides.
2009, 58 (10): 7322-7329.
doi: 10.7498/aps.58.7322
Abstract +
Edelman has proposed that there are degeneracy phenomena in neural system. However, he did not discuss the modality and function about degeneracy in neuron network. In this paper, the phenomenon of degeneracy in neuron circuit of binaural localization is studied on the basis of the ordered space, and some methods of degeneracy for the neural networks are discussed. By combing the phenomenon of degeneracy with neuron coding, we can better understand the degeneracy phenomenon. Although the results we obtained are rationalistic, the Jeffress model, which is widely accepted, is covered by this circuit. Therefore, the theory proposed in the paper also has its biological basis.
2009, 58 (10): 7330-7338.
doi: 10.7498/aps.58.7330
Abstract +
Dimensionality and the corresponding physical characteristics of auditory attribute space for equal-loudness underwater noise are investigated. Firstly, cluster analysis and questionnaire surveys are performed to obtain a number of auditory attribute descriptors in Chinese language, and then based on paired comparison and semantic differential approach, a dissimilarity matrix and a subjective evaluation value of each descriptor are obtained. Finally, by use of multidimensional scaling and principal component analysis, auditory attribute space of underwater noise with equal-loudness and equal-duration is determined and then the five-dimensional space is composed by dark-roughness, fluctuation, fast-variety, sharpness and regularity.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2009, 58 (10): 7339-7350.
doi: 10.7498/aps.58.7339
Abstract +
The evaporation duct is a natural microwave trapping phenomenon over water surfaces, which has a strong impact on near-surface electromagnetic propagation. For radar and communication system designs and operations,it is of great significance to obtain the long-term mean features of evaporation duct in a large-scale sea. In order to overcome the shortcomings of single-point measurement at local sea, a method for calculating the statistical features of the evaporation duct in a large scale-sea based on the NCEP （National Centers for Environmental Prediction） reanalysis data was presented. This method was confirmed by using the weather buoy data at the Pacific Ocean and the measurement data on the Weizhou Island in the South Sea of China. With NCEP reanalysis data of 18 years, the spatio-temporal features of evaporation duct in the West Pacific Ocean were studied. The distribution features of the evaporation duct height for different seas and months were obtained. The evaporation duct database was established with spatial resolution of about 1875°×19°, which is 28 times higher than the existing 10°×10°database.
2009, 58 (10): 7351-7358.
doi: 10.7498/aps.58.7351
Abstract +
To analyze the regional characteristics of temperature changes in China, by using the daily mean temperature series from 1961 to 2002 of 435 weather stations in China, we set up the temperature fluctuant networks, calculate the topology statistics of every station, and present the special distribution graph of all stations. We find that the degrees of RRD, RDD, DRR, DDR, DrR are extraordinarily high, and the occurrence probability of temperature fluctuation represented by these 5 nodes is greater, which is helpful for forecasting the trend of temperature changes. Then,from the distribution graph of the degrees of these 5 nodes in all the 435 stations, we define them by the symbols as countrywide model, hypo-countrywide model, eastern model, blend model, and western with southern model. The coefficient between the degree distribution in every station and the national average degree distribution has a regional characteristics, which provide us with the feasibility for analyzing the regional characteristics in theory. From the regional characteristics of the national distribution of the average clustering coefficient, we define three kinds of significant regions of temperature changes in China: strong complex regions, weak complex regions and middle complex regions.
2009, 58 (10): 7359-7367.
doi: 10.7498/aps.58.7359
Abstract +
Based on the idea of using historical-analogue information to predict the prediction errors of model, a new method named analogue correction of errors by predictable component （FACEPC） was developed. This method is adopted to identify the predicable components for which the prediction result is relatively not quite sensitive to the initial values. And then for predicable components, an associated scheme is chosen for historical-analogue selection and error correction. This method was further applied to experiments on operational seasonal prediction model of National Climate Center. By selecting suitable analogues and prediction schemes for different regions, the results from cross-validation indicate that the predictive skill scores of summer precipitation and circulation have got significant improvement relative to systematic error correction, which looks more obvious in ENSO episodes and over regions with more predictable components. Especially, the skill scores over China area have also been clearly improved, exhibiting its potential application perspective to operational seasonal prediction. Besides, preliminary sensitive experiments show that the FACEPC-based predictions are also obviously influenced by the analogue-selected factors and the length of historical data.
2009, 58 (10): 7368-7375.
doi: 10.7498/aps.58.7368
Abstract +
The propagation and redistribution of radiation in surface-atmosphere medium can be fully described by vector radiative transfer equation, which is the basis of quantitative remote sensing. How to deal with the questions of multiple-scattering effect, the polarization effect of the scattered radiation and the surface reflectance model is essential to an accurate simulation of vector radiative transfer equation, which affects the precision of quantitative remote sensing. This paper solves the vector equation of radiative transfer by using the successive orders of scattering approach; it includes the bidirectional reflectance distribution function （BRDF） model and bidirectional polarized reflectance distribution function （BPDF） model of surface reflectance. The index of relative errors was used to quantitatively study the effect induced by the difference of surface reflectance models and the polarization effect. Based on the studies, the basic theory of quantitative remote sensing using vector radiative transfer equation is proposed.
2009, 58 (10): 7376-7381.
doi: 10.7498/aps.58.7376
Abstract +
Based on the geometrical analysis, the near-field overlapping area shape of an off-axis laser lidar, which is formed by the telescope field of view and the laser distribution, is divided into three types, and the analytical formula for calculating the overlapping factor of off-axis lidar is given. According to the formula and the Gaussian distribution of the laser mode, the curve of the overlapping factor with the altitude of the Mie scattering lidar in our Laboratory is obtained. Using the curve, the lidar return signal under different weather conditions in Chengdu is corrected, based on which the return signal is retrieved by the Klett inversion method, and the curves of the atmospheric extinction coefficient varying with the altitude are obtained. The results show that the atmospheric extinction coefficient obtained by the correction method in the study is accordant with the practical weather condition.
2009, 58 (10): 7382-7391.
doi: 10.7498/aps.58.7382
Abstract +
When the high-power high frequency （HF） wave is pumped into the ionosphere, the pump wave reflection region is another main heated area. We setup a two-dimensional model of HF ionospheric heating in the magnetic meridian at lower latitude, and obtain results according to the background parameters of the morning and evening. We find that the electronic temperature around the pump wave reflection region increases intensively, and the electronic density decreases in the same area. The electronic density increases in the areas above and under the magnetic line of the electronic density hole. The ionospheric heating effect in the evening is much obvious than that in the morning, for which the maximum change rates of electronic density are -13% and -3.6% respectively, and the maximum change rates of electronic temperature are 88% and 22%, respectively.
