Vol. 59, No. 8 (2010)
2010-04-20
GENERAL
2010, 59 (8): 5175-5181.
doi:10.7498/aps.59.5175
Abstract +
Based on scale free network, the public opinion evolution model is constructed, in which the public opinion changes with topology (the relationship and the influence between the individual). The model features that the network structure constantly changes in the process of evolution with evolution parameter φ0. It is found that the evolution of the public opinion not only is controlled by the topological structure, but also induces the change of the topological structure: the network structure is no longer the initial scale-free network,but it has a Poisson distribution. With the time evolution in system, there is obvious convergence effect of the public opinions. The dozens of opinions in initial state evolve with time, but most of them perish and only a few of them can survive and develop for a long time. The evolution trend is coincident with that of the public opinions, views and beliefs in society.
2010, 59 (8): 5182-5189.
doi:10.7498/aps.59.5182
Abstract +
In this paper, combining the moving Kriging interpolation method and meshless local Petrov-Galerkin method, an improved meshless local Petrov-Galerkin method is presented, in which the Heaviside step function is used as test function over the local weak form. The present method is applied to two-dimensional potential problems and the corresponding discrete equations are derived. Because the shape functions so-obtained possess the Kronecker delta property, the essential boundary conditions can be enforced as the FEM; furthermore, the Heaviside step function is used as the test function, there is no domain integral, and only a regular boundary integral is involved. In this paper, the choice of the important parameters is studied. Numerical examples show that the present method has simpler numerical procedures and lower computation cost, in addition, the essential boundary conditions can be implemented directly.
2010, 59 (8): 5190-5193.
doi:10.7498/aps.59.5190
Abstract +
The approximate solution for a class of disturbed mKdV coupled system is considered taking a simple and valid technique. We first solve approximate solution of the 2-soliton for a corresponding complex-valued differential equation using the variational iteration method. And then the approximate solution of the 2-soliton for a original disturbed mKdV coupled system is obtained.
2010, 59 (8): 5194-5201.
doi:10.7498/aps.59.5194
Abstract +
The auxiliary equation of triangular function type including the first kind of elliptic equation and the formula of superposition of the solutions are given. Then based on general function transformation, new Jacobi elliptic exact solutions to (n+1)-dimensional double sine-Gordon equation are constructed with aid of symbolic computation system Mathematica. And the solutions include Jacobi elliptic function exact solutions, exact solitary wave solutions and triangular functions.
2010, 59 (8): 5202-5208.
doi:10.7498/aps.59.5202
Abstract +
The numerical and the analytical studies of the opening-up vesicles have become hot topics since the experimental observation by A. Saitoh et al. This paper deals with how to obtain the analytical solution of an opening-up shape from the Ouyang biconcave analytical solution. We find only two of the three boundary conditions for the vesicle rims to be independent. The second boundary condition can be satisfied by the Gaussian bending modulus kg=-2, then we obtain the geometric equation for the rims of an opening-up vesicle from the first boundary condition. By analyzing the Ouyang analytic solutions for a closed circular biconcave vesicle and periodic noduloidlike vesicle, we obtain three kinds of shapes with tube topology, which are the convex tube, the toruslike tube, and the catenoidlike tube.
2010, 59 (8): 5209-5212.
doi:10.7498/aps.59.5209
Abstract +
Another kind of conserved quantity deduced from Mei symmetry of Tzénoff equations for holonomic systems is studied. The expression of this conserved quantity and the determining equation to induce this conserved quantity are presented. The results indicate that this new method is easier to find conserved quantities than methods reported previously. Finally, application of this new result is presented by a practical example.
2010, 59 (8): 5213-5218.
doi:10.7498/aps.59.5213
Abstract +
In this paper a Lie point symmetry- preserving difference schemes approximating holonomic constrained mechanical systems is presented. The procedure is as follows: Firstly we find the Lie point symmetry groups of the original equation, and prolong them to three points of the lattice. Secondly the discrete invariants are obtained by solving discrete characteristic equations, then the invariant difference scheme is constructed by using these discrete invariants; and this invariants difference scheme will give the original equation under the continuous limit. Finally an example is presented to illustrate the applications of the result.
2010, 59 (8): 5219-5222.
doi:10.7498/aps.59.5219
Abstract +
The generalized canonical transformations of a kind of generalized Birkhoff systems are studied in this paper. The differential equations of motion of the generalized Birkhoff systems are estallished. The condition under which the transformations of the system are canonical is obtained. An example is given to illustrate the application of the result.
2010, 59 (8): 5223-5228.
doi:10.7498/aps.59.5223
Abstract +
A coupled nonlinear relative-rotation system is studied, and the Hopf bifurcation is analyzed under the condition of primary resonance and 1:1 internal resonance. In order to control the Hopf bifurcation point, the stability and amplitude of limit cycle, a nonlinear feedback controller is proposed, and numerical calculation can confirm the validity of the method.
2010, 59 (8): 5229-5234.
doi:10.7498/aps.59.5229
Abstract +
In this paper, using the homogeneous balance method, the (2+1) dimensional Konopelchenko-Dubrovsky equations are converted into two variable-separated linear partial differential equations. for three different function assumptions, the constant coefficient differential equations are obtained, respectively. By solving the eigenequations, new multisoliton solutions of the KD equations are constructed conveniently.
2010, 59 (8): 5235-5240.
doi:10.7498/aps.59.5235
Abstract +
Under the frame of classical electrodynamics, the electromagnetic radiation in magnetic anisotropic medium is investigated in this paper. The radiation power expressions for magnetic dipole and electronic quadrupole in magnetic anisotropic medium are in derived. Furthermore, the results, which are achieved by inserting the μr in isotropic medium into the obtained expressions, are agreed with the references. And the correctness of the obtained expressions is verified. The research results demonstrate that the radiation powers of magnetic dipole and electronic quadrupole are related to the μr in magnetic anisotropic medium. This conclusion is very helpful for determining the radiation effects of magnetic dipole and electronic quadrupole in magnetic anisotropic medium.
2010, 59 (8): 5241-5245.
doi:10.7498/aps.59.5241
Abstract +
Using the method developed by Gurvitz of solving Schrdinger equations and the numerical calculation, we investigate the oscillation and the entanglement of the two opposite-spin electrons in coupled quantum dots, and show how to read out the entanglement by quantum point-contact detector. The results show that the two electrons start to entangle due to Coulomb interaction, and then they move together with Coulomb interaction augmenting, similar to the oscillation of an electron in a qibit. In this case, we locate a quantum point contact detector near one of the quantum dots, and the entanglement information can be obtained by changing the current.
2010, 59 (8): 5246-5250.
doi:10.7498/aps.59.5246
Abstract +
In this paper the dynamical entanglements of anharmonic vibrations in the linear triatomic molecules are researched by the Lie algebraic approach. The linear entropy and the Von Neumann entropy are analytically obtained for both initial Fock states and coherent states. The dynamical properties of entanglement in molecules HCN and DCN are discussed.
2010, 59 (8): 5251-5255.
doi:10.7498/aps.59.5251
Abstract +
The schemes are presented for realizing optical Bell-state and GHZ-state analyzers through the Faraday rotation, which results from polarization photon reflected by optical cavity with trapped atom. They can be extended to the case of completely distinguishing photon Bell-state and GHZ-state without destroying quantum qubit. In the schemes, strong-coupling condition is not needed and the analyzers can be implemented in low-Q cavity, which further lower the diffculty in experiment.
2010, 59 (8): 5256-5260.
doi:10.7498/aps.59.5256
Abstract +
The goal of the Daya Bay reactor experiment is to determine unknown neutrino mixing angle θ13. The non-standard interactions (NSIs) of the neutrinos will affect the neutrino oscillation probability. In this paper we check the Daya Bay experimental sensitivity to θ13 in the presence of NSIs. Clearly, in this single experiment the values of θ13 and NSIs cannot be determined. The experimental observation of neutrino oscillation indicates a non-zero θ13. But if we do not observe the neutrino oscillation, it will not be meant that the value of θ13 must be zero.
2010, 59 (8): 5261-5265.
doi:10.7498/aps.59.5261
Abstract +
In this paper, the effect of Hubble parameter on the propagation of electromagnetic wave in Robertson-McVittie spacetime is discussed by using the post-Newtonian approximation method. To the bending test of light ray, the deflection angle caused by Hubble parameter H0 is calculated to its maximum amendatory term. Besides, the effects of finite distances of light source and receiver (d1 and d2 ) on deflection angle are also considered in this work. To the radar echo delay test, the maximum amendatory term to the formulae, induced by Hubble parameter, is given. The paper focuss on the study of influence of cosmological expansion on the propagation of electromagnetic wave. The work can be checked in the current high-precision gravity experiments in space and provides a theoretical basis for these experiments.
2010, 59 (8): 5266-5270.
doi:10.7498/aps.59.5266
Abstract +
Using the method beyond semiclassical approximation, the tunneling behavior of the arbitrary spin particles at the event horizon of Kerr-de Sitter black hole is researched, and the corrected Hawking temperature and the quantum tunneling rate are obtained. By the corrected temperature and the trace anomaly theory, the corrected entropy of Kerr-de Sitter black hole is derived.
2010, 59 (8): 5271-5275.
doi:10.7498/aps.59.5271
Abstract +
The density of states for an ideal Bose gas in a γ-dimensional potential is obtained. Morever, the spatial distribution of particle numerical density is derived in the Thomas-Fermi semiclassical approximation. On this basis, the valid gain range of space for atom laser (that is the valid trapped range of ideal Bose gas in γ-dimensional potential) is given, and the influence of some important factors is also discussed.
2010, 59 (8): 5276-5280.
doi:10.7498/aps.59.5276
Abstract +
In this paper,the mean first-passage time (MFPT) in a biased mono-stable system is investigated on the basis of the theory used in an asymmetric bistable system. The effects of parameters on MFPT are also analyzed based on the generalized potential function. The results show that, first,with parameter a and additive noise intensity Q increasing,the MFPTs in two directions both decrease on condition that bias parameter b is equal to zero; second,the time in which the particle jumps from xs1 to xs2 linearly decreases while the time in which the particle jumps from xs2 to xs1 linearly increases,owing to the fact that the symmetry of potential well is broken by the increase of bias parameter b; finally,the MFPTs in two directions monotonically increase as the ratio of multiplicative noise intensity to the additive noise intensity increases.
2010, 59 (8): 5281-5287.
doi:10.7498/aps.59.5281
Abstract +
In order to enhance the encryption speed and secrecy of the current chaotic secure communication system,a scheme of digital secure communication based on the stream cipher produced by real-time synchronization is presented. A improved cellular automata is used for encryption in the secure communication scheme while the expanded key technology and confusion technology are adopted. Numerical results show that the secure communication scheme can produce good pseudo-randomness stream ciphers while it has very fast speeds of encryption and decryption and high anti-attack ability.
2010, 59 (8): 5288-5292.
doi:10.7498/aps.59.5288
Abstract +
Recently,most of works had studied the impulsive stabilization of networks with time-varying delays. But there are few results about synchronization criterion of networks with time-varying delays via adaptive-impulsive control. In this paper,by adaptive-impulsive control method,projective synchronization in the drive-response complex network of partially linear systems with time-varying coupling is investigated. An adaptive-feedback controller,updating laws and a linear impulsive controller are proposed. An adaptive-impulsive projective synchronization criterion of network with time-varying coupling is established. And the coupling configuration matrix in network is not required irreducible. Moreover,numerical simulation is used to verify the effectiveness of the scheme.
2010, 59 (8): 5293-5298.
doi:10.7498/aps.59.5293
Abstract +
The linear control and the anti-control of a class of chaotic systems with only one nonlinear term are studied. Based on the Routh- Hurwitz stability condition,the chaotic system is controlled and the stable state is reached. Then,the chaotic state is recovered through changing controlled coefficient and a new chaotic system follows. The basic dynamical behavior of the new chaotic system is investigated and numerical simulation shows the chaotic nature of this new system.
2010, 59 (8): 5299-5306.
doi:10.7498/aps.59.5299
Abstract +
A new method is proposed for the stabilization of spatio temporal chaos in a thyristor device. The valid control of unstable periodic orbits (UPOs) of the chaotic system is achieved by combining time-delayed feedback control (TDFC) with the use of phase space compression. Based on the stability theory of linear periodic system,the linear stability analysis of the controlled system is discussed by using the Floquets theorem,and the feedback gain of TDFC was optimized through the Floquet exponents. The results show that the spatio temporally unstable periodic orbits embedded in a chaotic attractor of the spatially extended system can be stabilized by using the proposed method,and the spiking current filaments can also be inhibited well.
2010, 59 (8): 5307-5312.
doi:10.7498/aps.59.5307
Abstract +
We used a threshold controlling method to control chaos of chaotic neuron and constructed a threshold coupled chaotic neuronal map. The synchronization of the threshold coupled chaotic neuronal map was investigated. Simulation results show that the value of threshold determines the temporal period of outputs of the threshold coupled chaotic neuronal map. The spatial behavior of outputs of the threshold coupled chaotic neuronal map is determined by a relaxation time. A cluster character exists in the threshold coupled chaotic neuronal map. The synchronization of outputs of the threshold coupled chaotic neuronal map is achieved if the relaxation time is big enough.
2010, 59 (8): 5313-5318.
doi:10.7498/aps.59.5313
Abstract +
The formation of self-sustained target wave in a two-dimensional excitable medium into which a ring-like heterogeneous excitable medium is introduced is investigated. The numerical results show that the initial perturbation can produce a self-sustained target wave in an excitable medium when the excitabilities of two media and the size of the ring are appropriately chosen. The physical mechanism responsible for the formation of self-sustained target wave is analyzed.
2010, 59 (8): 5319-5324.
doi:10.7498/aps.59.5319
Abstract +
Transitions of different neuronal firing patterns in the Chay model are explored by numerical simulation of three firing sequences observed in experiments on neural pacemakers, and the bifurcation analysis of limit cycle. Firstly,the transitions of periodic firing patterns through a pair of period-doubling bifurcations are obtained. Secondly,a supercritical and a subcritical period-doubling bursting sequences with different appearances lead to chaos,and then transit to an inverse period-doubling spiking sequence in different ways,separately. Finally,we reveal the true nature of period-adding bursting sequence without chaotic bursting,which is closely related to period-doubling bifurcation.
2010, 59 (8): 5325-5331.
doi:10.7498/aps.59.5325
Abstract +
Base on the NaSch model, an improved single-lane cellular automaton traffic flow model for especial road is proposed via considering effects of curvature radii, arc length and friction factor on the vehicle movement. By numerical simulation for the traffic flow with different curvature radii, arc length and friction factor, it is found that our improved model can reflect accurately the influence of special sections of a road on the running vehicles, meanwhile visualize the complex nonlinear phenomenon traffic waves of alternate running and stopping as in actual traffics. The reflecting phenomenon in actual traffics indicates that traffic accidents and congestion can be avoided by increase the curvature radii, friction factor of road turning, the capacity of road can be enhanced also.
2010, 59 (8): 5332-5337.
doi:10.7498/aps.59.5332
Abstract +
Perovskite-type BiMnO3, in which ferroelectricity and ferromagnetism co-exist,has potential applications in sensor and information storage. Usually, BiMnO3 is synthesized under high temperature and high pressure in a gold capsule,which restricts its application and development extremely. In this paper, we synthesize the BiMnO3 nanopowders with MnCl2·4H2O,Bi2O3, NaOH,HNO3 and polyglycol at 100 ℃ by the co-precipitation method successfully, in which the conditions of temperature and pressure are reduced, thereby economizing the energy sources and lowering the cost. Their microstructure and magnetic properties are measured by using X-ray diffraction (XRD), transmission electron microscope(TEM) and vibration sample magnetometer(VSM). The effects of synthetical condition and the calcined temperature are also discussed.
2010, 59 (8): 5338-5344.
doi:10.7498/aps.59.5338
Abstract +
In this paper are analyzed the characteristics of the single photon detector (SPD) with using coaxial cables as reflection lines to cancel transient spikes noises, particularly,the characteristics of variations in bias voltage of the avalanche photodiode (APD) and output signal. Based on the theoretical analyses,the principle of the timing relation between single photon pulses and the two gate pluses is discussed. Also, the condition and the effect of transient spikes cancellation are achieved. And the minimal detecting period is obtained. Finally,we conduct some experiments to verify our theory. In our experiment,the noise rejection ratio is 25.1dB. The results accord with our theory satisfactorily. Our results will be helpful in designing and optimizing single photon detectors.
2010, 59 (8): 5345-5350.
doi:10.7498/aps.59.5345
Abstract +
In order to understand the structures of automobile exhaust particles and the components of nitrogen inside them,automobile exhaust particles from Santana 3000 and Golcars are investigated with scanning transmission X-ray microscopy (STXM) and the near edge X-ray absorption fine structure (NEXAFS) spectra. The results of STXM show that single particulate has a size of 500 nm and a nonuniform mass distribution with an empty hole inside it. Compared with the NEXAFS spectra,(NH4)2SO4 and NaNO3 spectra show many different σ* resonances at 406 eV,the spectrum of ammonium has a shoulder structure. NaNO3 and automobile exhaust particles show significant σ resonances at 412 eV and 418.5 eV. However,(NH4)2SO4 shows wider σ resonances 413.5 eV and 421.8 eV. Nitrates are main chemical species of nitrogen in automobile exhaust particles. In an energy range from 395 eV to 418 eV,Santana 3000 automobile exhaust particles are stack scanned. The principal component analysis and cluster analysis indicate that there exist nitrates in surface layer and minor ammonium inside it.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2010, 59 (8): 5351-5357.
doi:10.7498/aps.59.5351
Abstract +
Neutron penumbral imaging is an important diagnosis technique in laser-driven inertial confinement fusion experiment. In order to refine the resolution of 5 μm, it is necessary to develop nonlinear methods in reconstructing the detected imaging. In this paper, the authors improve the molecular dynamics method by using the Leap-frog format to increase convergence, and adding the edge-preserving regularization to suppress the edge-diffusion. Furthermore, the conjugate gradient method is also studied, and the relationship and differences between these two methods are revealed. Comparing the reconstruction results of the two methods, the advantages and disadvantages are analyzed for detecting images with noise.
NUCLEAR PHYSICS
2010, 59 (8): 5358-5363.
doi:10.7498/aps.59.5358
Abstract +
A method of estimating residence time of atmospheric aerosol (RTAA) is established based on the relationship between specific activity ratio of radon daughters in atmospheric particles and average life of the particles. The method is further testified in a standard radon chamber. When specific activity of radon is 1.816 kBq/m3 in the chamber,the RTAA is estimated to be 112.17 min,which is in agreement with the mean-ventilation time in the chamber,104.17 min. Therefore,the residence time of the atmospheric aerosol can be estimated by using the specific activity ratios of radionuclide in the same decay chain,such as 214Bi/214Pb, 210Bi/210Pb and 210Po/210Pb.
2010, 59 (8): 5364-5368.
doi:10.7498/aps.59.5364
Abstract +
The cross sections of fragments produced in the 140 A MeV 40,48Ca+9Be and 58,64Ni+9Be reactions have been calculated by the statistical abrasion-ablation model. The calculated cross sections of fragments are compared to the experimental results. Adopting the free space nucleus-nucleus cross sections in the calculations, the cross sections of fragments produced in the non-central collisions are well reproduced, but the cross sections of fragments produced in the central collisions are overestimated. If adopting the saturate density related nucleus-nucleus cross sections in the calculation, the cross sections of fragments produced in the non-peripheral collisions are well reproduced, but the cross sections of fragments produced in the peripheral collision are underestimated. It's suggested that the cross sections of fragments will be better reproduced by the SAA model if the nucleus-nucleus cross sections are related to the density distributions of projectile and target nuclei precisely.
2010, 59 (8): 5369-5373.
doi:10.7498/aps.59.5369
Abstract +
Accuracy in the measurement of an intense high-energy proton beam is generally disturbed by high energy proton induced secondary electron emission. In the present work,the compensation mechanism for secondary electron emission is investigated for the accurate measurement of high-energy proton beam. An experimental approach with using three metal foils to compensate for secondary electron emission is implemented and described. The experiment is carried out on the HI-13 tandem accelerator. The current detected from the middle metal foil is 0.7% of the proton beam. The experimental results show that the measured current of the high-energy proton beam is reliable within 1%.
2010, 59 (8): 5374-5381.
doi:10.7498/aps.59.5374
Abstract +
In the THz frequency range,several new high effects will restrict diode high-frequency performance. With the thermionic emission theory and the tunnel theory,the high-frequency performance of epitaxial Schottky diodes is re-evaluated and the structure parameters are optimized with using the cut-off frequency as a figure of merit. The results show that when the operation frequency is higher than the plasma frequency,the diode is equivalent to a capacitance with losing the frequency mixing performance. With the increase of frequency,increasing the doping density of substrate can reduce the substrate plasma resonance effect. The plasma resonance frequency of epitaxial layer is an important factor but transit time effect must be considered. The higher operation frequency can be obtained through reducing the anode diameter and the epilayer thickness,and increasing the epilayer doping density. The results have an important reference value in developing the room temperature THz mixing diodes.
ATOMIC AND MOLECULAR PHYSICS
2010, 59 (8): 5382-5386.
doi:10.7498/aps.59.5382
Abstract +
The formation of excited atom state 5s' D7/2 and its transition process in the copper plasma induced by nanosecond pulse laser are studied by the time-resolved spectrum technology. The experimental results indicate the recombination of electron and ion and the collisions among particles each play a dominent role in forming excited atom state 5s'D7/2 at different tims during its evolvement. When the collisions among particles are severe, the excited atom state 5s' D7/2 mainly transits to low energy atom state 4p' 4 Fo9/2. 500 ns after the peak of laser pulse arriving at target surface, the excited state 5s'D7/2 transited to 4p' 4 Fo9/2 and 4p' 4 D7/2 with the same probabilities by emitting lines CuI465.11 nm and CuI529.25 nm respectively.
2010, 59 (8): 5387-5391.
doi:10.7498/aps.59.5387
Abstract +
The SrAl2B2O7:Dy3+ phosphor is synthesizd through a general high temperature solid-state reaction, and its luminescence properties are investigated. The emission spectrum of SrAl2B2O7:Dy3+ shows the bands at 480nm,573nm and 678nm under the 365nm excitation, corresponding to the 4F9/2→6H15/2,4F9/2→6H13/2 and 4F9/2→6H11/2 typical transitions of Dy3+ respectively. The excitation spectrum for 573nm emission has excitation bands at 295 nm,325 nm,350 nm,365 nm and 400nm. The influence of doped Dy3+ contentration on the emission spectrum and the luminescent intensity of SrAl2B2O7:Dy3+ is investigated. The result shows that the intensity ratio of yellow emission (573nm) to blue emission (483 nm), Iy/Ib, increases with the increase of Dy3+ concentration, which may be explained by the Judd-Ofelt theory. The luminescent intensity increases first with the increase of Dy3+ concentration, then decreases. The concentration self-quenching is attributed to the d-d interaction according to the Dexter theory. The introducing of charge compensation agents of Li+, Na+ and K+ ions can augment the emission intensity. It is found that Li+ ions are the best to enhance the emission intensity.
2010, 59 (8): 5392-5396.
doi:10.7498/aps.59.5392
Abstract +
The technology of laser-focused atomic deposition can be used to develop the nanostructure transfer standard of length. In this paper, a novel method is used to fabricate the nanometer structure through chromium atomic deposition. By the designed pre-collimated hole with three apertures, the chromium atomic beam may be divided into three parts. The middle part is for the atom beam to react with the standing wave and the deposition on the substrate with periodic distribution and the other two parts which can not be blocked by the substrate are for the atom beam to react with the detecting laser beam, and can be used to inspect the characteristic of atomic beam. This can provide some guidance for the progress of deposition. The simulatiion results show that the full width of half maximum is 6.2 nm and the contrast is 28:1 by using this special pre-collimated hole. On the other hand, the full width of half maximum and contrast are 32 nm and 8∶1 without using this special hole.
2010, 59 (8): 5397-5405.
doi:10.7498/aps.59.5397
Abstract +
Method of solar occultation flux infrared spectroscopy to detect the pollution emission flux of sources is presented in detail. It is developed based on the FTIR technique. A Two-layer radiative transfer model is established theoretically. Algorithm of transmissivity calculation of pollution gas is expatiated. The method to obtain the absorption coefficient of molecules from HITRAN, NIST and QAsoft databases is mentioned. Levenberg-Marquardt algorithm is used to calculate column concentration of pollution gas from pollution source. The distribution of column concentration is drawn by software developed by our group. The total system and the sun tracker are shown in the paper. The distribution of column concentration of NH3 is measured in a chemical plant in Hefei China. The calculated distribution of column concentration of NH3 is consistent with the measured one in the chemical plant.
2010, 59 (8): 5406-5411.
doi:10.7498/aps.59.5406
Abstract +
In this paper, we present the development and experimental results of a time-resolved coherent anti-Stokes Raman scattering (CARS) experiment setup that is based on supercontinuum excitation and precise time-delay control. The output of a Ti-sapphire femtosecond laser is divided into two parts. One part is used to pump a photonic crystal fiber (PCF) to generate supercontinuum spectrum which is used as pump and stokes beams. The other part of the femtosecond laser is used as the probe light. Dimethyl sulfoxid, a sample with broad range of Raman spectrum was tested. Experimental results show that this system can inhibit the non-resonant background noise effectively and obtain CARS spectrum of dimethyl sulfoxide in the frequency range of 690—3200 cm-1 in one measurement, which means that spectrum range of the acquired CARS spectrum of dimethyl sulfoxide is 2500 cm-1. We also present experimental results of supercontinuum generation using a PCF.
2010, 59 (8): 5412-5417.
doi:10.7498/aps.59.5412
Abstract +
Considering the effect of molecular vibrational levels, inelastic currents through the "metal/single molecule/metal" in the frame of normal vibrational mode are studied. The results show that the Franck-Condon blockage is strongly dependent on the stable energy configuration of molecule in the charge transmission, thus the relation between stationary state and Franck-Condon blockage and the relations of intra molecular vibrational redistribution as well as the relative position of molecule and electrodes to the current-voltage character of the stationary molecule state are further studied theoretically.
2010, 59 (8): 5418-5423.
doi:10.7498/aps.59.5418
Abstract +
Ultracold atom photoassociation spectroscopy is significant for studying the long-range molecular potential energy structure. The signal-noise ratio of ultracold Cesium Molecule photoassociation Rovibronic Spectrum is one of the indicators as a measure of detection technology which directly affect the distinguishing ability and detection sensitivity of the spectra. We obtain an long-range ultracold cesium molecular hyperfine rovibration spectra by modulating the fluorescence spectroscopy. We find that demodulation parameters have a significant impact to the signal-noise ratio of spectra by studying the demodulation parameters such as integration time and sensitivity, which show nonlinear relation with the ratio. We achieve the optimal control of the signal-noise ratio for spectrum according to our experiment, which laid an important foundation for further studying the long-range state rovibration level of ultracold cesium molecule.
2010, 59 (8): 5424-5428.
doi:10.7498/aps.59.5424
Abstract +
In this paper, the Fuchs potential model and the Close-coupling method are used to calculate the low-energy cross sections for a He-Li2 scattering system. The dependences of total cross section on energies, differential section on angles, and partial wave cross section on quantum number of total angular momentum are discussed . The quantum effect on energy obtained.
2010, 59 (8): 5429-5438.
doi:10.7498/aps.59.5429
Abstract +
Possible geometrical structures of WnNim (n+m≤7; m=1, 2) clusters have been optimized by using the density functional theory (B3PW91) at the LANL2DZ level. For the ground state structures, the NBO,vibration frequencies, spectrum and polarizability are studied. The calculated results show: the hybrid phenomenon is very strong within W and Ni atoms, while weak in the W-Ni atoms. In the process of forming alloy clusters, the charge transfer happens owing to the interaction of W and Ni so that most of Ni atom is positive and while W atom is negative. The optical properties indicated, the number of the vibrational peak is the most in the IR and Raman of W6Ni cluster, the IR and raman absorption peak of W5Ni2 is the strongest and the IR absorption peak of W2Ni has only one; the bonding between atoms shows stronger with the increasing of W content in the WnNim (n+m≤7; m=1, 2) clusters.
CLASSICAL AREA OF PHENOMENOLOGY
2010, 59 (8): 5439-5443.
doi:10.7498/aps.59.5439
Abstract +
A 2D nonlinear beam-wave interaction is built to simulate the backward-wave oscillation(BWO) in a Helical traveling wave tube, based on the 1D beam-wave interaction model by taking into account the angular speed which is affected by magnetic field. The normalized oscillation start-up length with different space charge parameter is compared with that obtained from a equivalent circuit model in small signal, showing that they are close to each other. Also, the simulated results are in accordance with the measurements in a 8—18 GHz Helical TWT. The factors affecting the BWO are studied, by which some methods to suppress the BWO are improved.
2010, 59 (8): 5444-5449.
doi:10.7498/aps.59.5444
Abstract +
Traditional C-shaped split resonant ring(SRR) composite metal wire periodic structure is studied through simulation and experiment. Comparing the simulation result of negative permeability material based on periodic structure of octagonal SRR with that of closed split resonant rings (CSRRs), we ind that octagonal SRRs can produce negative permeability. A new kind of left-handed material combined with octagonal resonators and copper wires is de signed, and the simulation result shows that the structure has good left-hand property in a certain frequency band. Experimental samples of two different sizes are fabricated, in which negative refraction happens in ranges of 9.8—15 GHz and 9.5—15 GHz separately: small size sample has more broad negative band but lower transmission rate.By comparison with the experiment result of C-shaped sample we ind that the octagonal SRR hasa high transmission rate , but energy transmitting through new designed structure shows a more proportion in negative field, which demonstrates better negative behavior. This has important significance on design and study on new periodic structures of left-handed materials.
2010, 59 (8): 5450-5458.
doi:10.7498/aps.59.5450
Abstract +
In the present paper, based on the practical electron ray equation and the electron motion equation,for a bi-electrode concentric spherical system with electrostatic focusing, the spatial-temporal trajectories of moving electrons emitted from the photocathode are obtained, the exact and the approximate formulae for image position and flight time of electrons are deduced. Starting from the solutions of spatial-temporal trajectories, the electron optical spatial-temporal properties of this system are then discussed. A unified definition of spatial-temporal aberrations is given, in which the lateral aberration can be regarded as a combination of paraxial lateral aberration and geometrical lateral aberration; and the temporal aberration can be regarded as a comibination of paraxial temporal aberration and geometrical temporal aberration. All expressions of these corresponding aberrations are deduced.
2010, 59 (8): 5459-5466.
doi:10.7498/aps.59.5459
Abstract +
In this paper, we use the paraxial equations to study the spatial-temporal trajectories and their aberrations for a bi-electrode concentric spherical system with electrostatic focusing. In the present paper, starting from the paraxial ray equation and the paraxial motion equation, the paraxial spatial-temporal trajectory of moving electron emitted from the photocathode is obtained for a bi-electrode concentric spherical system with electrostatic focusing. The paraxial static and dynamic electron optics, as well as the paraxial spatial-temporal aberrations in this system are then discussed, the general regularity of imaging in paraxial optical system has been explored. The paraxial spatial aberrations, as well as the paraxial temporal aberrations with different orders, have been defined and deduced. Thus we get same conclusions about paraxial spatial and temporal aberrations as it has been given in paper[1], and it completely shows that the paraxial spatial-temporal aberrations can be investigated directly from the paraxial ray equation and paraxial motion equation.
2010, 59 (8): 5467-5473.
doi:10.7498/aps.59.5467
Abstract +
The propagation of the electromagnetic field in anisotropic relief gratings has been analysis, and the recursive algorithm of RTRA has been extended to the anisotropic medium in this paper. The numerical calculation shows that the space distribution of the electromagnetic field in each sub-micro-layer changes with the varying transmission depth in the relief grating, the space distribution in each sub-micro-layer is more uniformed than that in isotropic grating and the optical parameters of the anisotropic relief grating and the incident beam have a large impact on the space distribution of the electromagnetic field in relief grating and so on.
2010, 59 (8): 5474-5478.
doi:10.7498/aps.59.5474
Abstract +
Owing to the restriction of the stimulated Brillouin scattering (SBS) and other nonlinear effects, the output power of the single frequency amplifier is ar a level of about hundred watts. Multi-wavelength and non-single frequency seed laser will mitigate the SBS and improve the output power of the fiber laser amplifier. The coherent beam combining of the non-single frequency and/or multi-wavelength laser will greatly increase the total output power of the coherent beam combining as compared with the coherent beam combining of a single frequency laser. Based on the stochastic parallel gradient descent (SPGD) algorithm, coherent combining of four channel four-wavelength lasers is realized. In the close loop state, the mean power of the main-lobe is four times higher than that of the open-loop, approaching 75% of its ideal value. The coherent combining of the multi-wavelength and non-single frequency laser is demonstrated and an approach to the high power coherent beam combining is provided.
2010, 59 (8): 5479-5486.
doi:10.7498/aps.59.5479
Abstract +
The principle of home-designed novel polarization interference imaging spectrometer is discussed. The noise of novel polarization interference imaging spectrometer is analyzed, and the expression of total noise related to system throughput is deduced. The noise induced by imaging spectrometer system and CCD image sensor is extracted from spectrometer image. The signal-to-noise ratio of novel polarization interference imaging spectrometer based on such noise analyses is discussed, which proves that though luminous throughput of imaging spectrometer system has a crucial effect on the total noise, it does not affect the trend of variation in signal-to-noise ratio. A new practical guidance is thereby provided for the accurate calculation of the signal-to-noise ratio of imaging interference and the application of denoising method effectively.
2010, 59 (8): 5487-5495.
doi:10.7498/aps.59.5487
Abstract +
In view of the obvious wrong segmentation in commonly used region division of 2-D histogram and the non- universality of oblique segmentation method for image thresholding proposed recently, in this paper a much more widely suitable thresholding method is proposed based on the θ-division of 2-D histogram and the maximum Shannon entropy criterion. Firstly, the θ-division method of 2-D histogram is given. The region is divided by four parallel oblique lines and a line, where the angle between its normal line and gray level axis is θ degrees. Image thresholding is performed according to pixel's weighted average value of gray level and neighbour average gray level. The oblique segmentation method can be regarded as a special case of the proposed method at θ=45°. Then the formulae and its fast recursive algorithm of the method are deduced. Finally the segmented results and the running time at different values of θ are listed, which show that the segmented images achieve more accurate borders at smaller values of θ and the anti-noise is better at larger values of θ. The value of θ can be selected according to the real image characteristics and the requirements of segmented results. Compared with the algorithm of conventional 2-D maximum Shannon entropy method, the proposed method not only achieves more accurate segmentation results and more robust anti-noise, but also reduces the running time and memory space significantly.
2010, 59 (8): 5496-5507.
doi:10.7498/aps.59.5496
Abstract +
X-ray phase contrast microscopy (XPCM) achieves the high contrast imaging of low electron density materials with the spatial coherence peculiarity of X-rays. Considering that ginsengs are mainly composed of C, H, O, N and other low-Z elements, XPCM is an ideal tool to nondestructively investigate the characteristic microstructures of ginsengs in principle. Owing to the higher fluxes and luminance of the third generation of synchrotron radiation facility, it can present clearer and finer microstructures of ginsengs with better spatial and temporal resolutions. In this paper, the characteristic microstructures of wild ginseng ware investigated systemically by XPCM at Shanghai Synchrotron Radiation Facility (SSRF). For comparison, the characteristic structures of cultivated ginseng are also studied correspondingly. Moreover, a kind of new microstructure is found in young ginsengs, which is possibly a new characteristic structure of ginsengs. The results demonstrates that XPCM is a promising new method of identifying wild ginseng.
2010, 59 (8): 5508-5513.
doi:10.7498/aps.59.5508
Abstract +
By the method of coherent-state orthogonalization expansion, the evolution of atomic population inversion is investigated in the non-rotating-wave approximation. The numerical results indicate that, when field frequency and coupling do not change with time, the collapse-revival period of population inversion increases with the mean photon number of the field increasing, and the quick oscillation due to virtual photon process increases with couplings strengthening. When the frequency changes with time in the sine form, amplitude α and angle frequency β of the field both have a great influence on atomic population inversion. The sudden jumping of the field frequency can lead to some new collapses and rebibals in the evolution of atomic population inversion. Both of the field frequency forms can have an influence on quick oscillation due to virtual photon process.
2010, 59 (8): 5514-5522.
doi:10.7498/aps.59.5514
Abstract +
Optical pulse will reach the receiver not at exact time instance due to the transmission through the long trunk fiber, and this phenomenon will effect on the bits error rate in the Quantum key distribution (QKD) system to some extend. The time jitter based on the differential phase shift quantum key distribution system and two asymmetric Mach-Zehnder interferometers is measured outdoors in different transmission distance and the physical model of the relationship between the time jitter and the quantum bit error rate is proposed. According to this relationship, the quantum bit error rate can be estimated for some optical pulse shape and some statistical distribution function.
2010, 59 (8): 5523-5527.
doi:10.7498/aps.59.5523
Abstract +
We report a Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification in this paper. With the bi-directional Raman amplification, the loss of the optical fiber and the depletion of Brillouin pump light can be compensated for efficiently, hence the measurement resolution is improved at the end of the optical fiber significantly. The detected signal is stable along the whole length of the sensing fiber, free from the spectral broadening caused by the modulation instability and the problem of uneven ness of detected signals of the conventional BOTDA. The Raman amplification is very useful for enhancing the measurement accuracy. With the bi-directional Raman pump, a temperature resolution of 0.6 ℃ was achieved over a sensing distance of 50 km with a 50 m spatial resolution. The signal-to-noise ratio and the optical signal power distribution characteristics of the system have been studied by experiment.
2010, 59 (8): 5528-5532.
doi:10.7498/aps.59.5528
Abstract +
Periodically poled lithium niobate (PPLN) is investigated by micro-Raman spectrum and luminescence in a confocale microscopy configuration. It is observed that there exists a different in fluorescence strength between reversed domain and non reversed domain. And the Raman result shows that a Raman forbidden line occurs in the interface between the two domains. Results suggests a new non-destructive method to image polarisation gratings and provide important information about the mechanism involved in the polarisation reversal process.
2010, 59 (8): 5533-5540.
doi:10.7498/aps.59.5533
Abstract +
Based on the conduction band electron density and the expression of the effective dielectric function, the absorption coefficient at 532nm of KTP crystal is deduced. The evolution law of conduction band electron density, absorption coefficient and second harmonic generation (SHG) conversion efficiency are comparatively studied. The results are as follows. The 532 nm absorption coefficient of KTP crystal is increasing with conduction band electron density, and the SHG conversion efficiency is decreasing with conduction band electron density. When the power density of fundamental frequency laser is a fixed value, conduction band electron density shows accumulation effects a different repetition rates, which caused the 532 nm transmission and the SHG conversion efficiency of KTP crystal to vary exponentially with acting time, and the accumulation effect is increasing obviously with repetition rate, but conduction band electron density and absorption coefficient approach thir steady values.
2010, 59 (8): 5541-5546.
doi:10.7498/aps.59.5541
Abstract +
In this paper, a bidirectional chaos communication system based on semiconductor lasers with incoherent optical feedback is presented, and the synchronization characteristics and the communication performances of such a system are numerically investigated. The results show that when the parameters of the two lasers are matched, the good-quality chaos synchronization with zero lag time and simultaneously bidirectional message transmission can be realized and when the parameters of the two lasers are mismateched, the synchronization quality and communication performance are affected to a certain extent, but this system possesses good robustness against mismatched parameters and can still realize bidirectional chaos communication within a certain mismatched parameter range.
2010, 59 (8): 5547-5552.
doi:10.7498/aps.59.5547
Abstract +
We present the design and the simulation of an ultracompact high efficiency polarization beam splitter(PBS) based on the properties of the light waves propagating in straight waveguide and composite structure photonic crystal. The splitting properties of the PBS are numerically simulated and analyzed by using the plane wave expansion (PWE)method and finite difference time domain(FDTD) method. The PBS consists of three parts, namely, input waveguide, beam structure and output waveguide. It is shown that a high efficiency and a large separating angle for TE mode and TM mode can be achieved. Owing to these excellent features, including small size and high rate, the PBS makes a promising candidate in the future photonic integrated circuits.
2010, 59 (8): 5553-5558.
doi:10.7498/aps.59.5553
Abstract +
In this paper, a 2D photonic crystal (PC) with negative refractive index at multi-band is designed. Plane wave expansion method (PWEM) is used to obtain the band diagram and the equal-frequency surface (EFS). And the finite difference time domain (FDTD) simulation method is also used to analyze the equivalent refractive index of the PC. The results from both methods show that the equivalent refractive index of the PC at specifical band is negative.
2010, 59 (8): 5559-5563.
doi:10.7498/aps.59.5559
Abstract +
A new type of THz photonic crystal fiber with super-flattened dispersion and air hole varying cladding is designed in this paper. Its dispersion properties are analyzed by using the finite-difference time-domain (FDTD) method. The results show that the new THz photonic crystal fiber is better than THz photonic crystal fiber with air hole unarying cladding in controlling the dispersion, and that the new THz photonic crystal fiber has the flattened dispersion when the third ring diameter has the same value as the forth ring diameter. When the air hole diameters are d1=0.85d4, d2=0.95d4,d3=d4(d1,d2,d3,d4 are the diameters of air hole from the inter clad to the outer clad), the new THz photonic crystal fiber can have almost super-flattened dispersion at a level of -0.1±0.3 ps/(nm·km), a good ability to restrict the THz wave and a low loss in a wavelength reange between 60 μm and 65 μm.
2010, 59 (8): 5564-5571.
doi:10.7498/aps.59.5564
Abstract +
By the wave superposition approach a method of enhancing the spatial resolution of the nearfield acoustic holography is proposed. According to wave superposition approach, the source strengths of fictitious sources placed on the fictitious surface which is near the hologram surface are obtained by measuring the hologram pressure signal, then these fictitious sources are used to realize the interpolation of acoustic pressure, finally, the reconstruction can be done by the interpolated hologram pressure. By this method the spatial resolution of the reconstructed image can be improved, the measurement workload is reduced, and the measurement process is simplified. The parameters affecting the interpolated result are reasonably chosen by numerical simulations and the availability of this method is proved by numerical simulations and experimental resuets.
2010, 59 (8): 5572-5580.
doi:10.7498/aps.59.5572
Abstract +
An efficient approach for discrete particles coupled with the continuous fluid based on unstructured meshes is developed by reorganizing gas phase governing equations. The bubble formation caused by a single central jet pulse in a two-dimensional Pulsed Fluidized Bed (PFB) is simulated. The calculation results show good agreement with the experimental observations. Then our work concentrates on the study of the microscopic structures of two PFBs with different width. Pressure drop pulse and force chain breaks to overcome the inter-particle locking are found just as the jet starts. The simulations show that the gas flows in the bed experience from two-main-vortices to multi-vortices then to two-secondary-vortices. Particles in the bed demonstrate three types of characterized behaviors, i.e., raising, downslide along the bubble's boundary, and creeping motion in the corner.
2010, 59 (8): 5581-5587.
doi:10.7498/aps.59.5581
Abstract +
The packing structure of identical spheres poured into a narrow cylindrical container will be influenced by the curvature of the container wall. This has been known as the wall effect. Our experiments reveal that under the action of vertical vibration, the wall effect can be enhanced, that the spheres, initially in a random packed state, can be organized through convection into a stable ordered packing consisting of a concentric array of cylindrical "shells" of spheres. In each shell the spheres are hexagonally arrayed. During such a structure transition, the packing density distribution, initially with a damped oscillatory variation along the radial direction, turns into an undamped one. The effects of interstitial air and inhomogeneity in the packing on the convection of particles, and thereby on the dynamics for the formation of "shell" structure, are analyzed. In addition, some discussions on the stability of the "shell" structure are made.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
An extended model for ion charge state distribution of plasmas in collisional radiative steady state
2010, 59 (8): 5588-5595.
doi:10.7498/aps.59.5588
Abstract +
A non-Boltzmann distribution is constructed in terms of ion excitation-deexcitation equilibrium in plasmas, over which the rate coefficients of atomic processes are averaged, and an extended numerical model for charge state distribution of plasmas in collisional radiative steady state is established. The model is used to compute mean ion charge for various plasmas, ranging from low Z to high Z elements, as a function of electron temperature and density. Furthermore, the effects of non-Boltzmann distribution on mean ion charge and ion excited configuration population are investigated. The results show that the ion excited configuration population is evidently affected by the non-Boltzmann distribution.
2010, 59 (8): 5596-5601.
doi:10.7498/aps.59.5596
Abstract +
In tokamak plasmas, the discharge will turn into "runaway" discharge if the density decays to a critical one. The discharge will enter into "slide-away" discharge if the density reaches a lower level. The slide-away discharge is characterized by high confinement of superthermal electrons which constitute a large part of plasma current. In HT-7 Tokamak, the slide-away discharge is achieved by reducing the plasma density. The relationship between plasma current and critical density of slide-away discharge is investigated. It is also find that the increase of density in slide-away discharge can make the confinement of superthermal electrons poor and lots of superthermal electrons lost from the vacuum chamber.
2010, 59 (8): 5602-5605.
doi:10.7498/aps.59.5602
Abstract +
In order to study the attenuation of shock waves induced by a high-power pulsed laser in magnesium alloy, an AZ31B magnesium alloy sample is processed with an Nd:Glass laser with a wavelength of 1054 nm and pulse width of 23 ns, and the relative pressures of the shock waves are measured on time by a polyvinglidene fluoride (PVDF) gauge with a short rise time and a wide linear response range, combined together with an oscilloscope. The law of attenuation of laser shock wave is obtained by measuring the intensity pressures on the rear surface of the target for different thicknesses through which the shock waves pass each time. The experimental results show that the average velocity of the shock wave attenuation in magnesium alloy is 5.83×103 m/s with using a laser pulsed energy of 5 J is in good agreement with the propagation velocity of stress longitudinal wave; the law of the shock wave attenuation is exponential. The experimental result can be very useful for the laser shock processing on magnesium alloy.
2010, 59 (8): 5606-5612.
doi:10.7498/aps.59.5606
Abstract +
The signal transmission and measurement method of the passive UHF radio-frequency identification(RFID) system are discussed in this paper. Part of tags communication performance which conforms with the ISO/IEC 18000-6 Type C was obtained by using the software-defined radio test platform. The received power by the platform changes with the communication parameters. Sensitivity of different tags was tested. All experiments were conducted under normal conditions.The measurement results show that the small Tari, half duty cycle (PW) and higher modulation index in baseband signal encoding allow the RFID system to receive larger power, also the RFID system to have larger read range.
2010, 59 (8): 5613-5619.
doi:10.7498/aps.59.5613
Abstract +
Confined cathode micro-arc oxidation (CCMAO) has been investigated in Na2SiO3-KOH solution with industrial pure aluminum as substrate materials. The effects of the electrode distance (ED) on working current, potential distribution, arcing voltage and so on have been focused on. The energy efficiency as a function of ED has also been evaluated. The results show the working current decreases with increasing ED for the same exposure area of confined cathode and anode. However, the working current increases with increasing ED with only the cathode confined. It is attributed to different electrical field on the anode surface. With increasing ED, the electrical field beneath the confined cathode decreases while that far from the cathode increases. This leads to a different total working current. The arcing voltage increases with increasing ED while the effective voltage on anode surface nearly keeps constant. The thickness of the ceramic coating produced at a small ED is much higher than that at a larger ED. The energy consumption per unit volume of oxides by CCMAO indicates that smaller ED leads to higher energy efficiency.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Single crystal growth and magnetic properties of spinel structure and spin ordering compound CaTi2O4
2010, 59 (8): 5620-5625.
doi:10.7498/aps.59.5620
Abstract +
High quality and large-size single crystals of CaTi2O4 were prepared by the molten salt flux method. The X-ray diffraction and the EDS results showed that all the CaTi2O4 crystals have the rom temperature lattice parameters a=9.781 ?,b=9.966 ? and c=3.148 ?, and all the samples have perfect stoichiometric composition. Through the magnetic susceptibility measurement, we first obtained the Van-Vleck paramagnetic parameter of CaTi2O4 of 6.85×10－5cm3/mol, and Cure-Weiss temperature of -0.44 K, revealing that CaTi2O4 is a weak ferromagnetic compound. Further more, the existence of Ti-Ti dimer was confirmed by anisotropy measurement, the structure and direction of the antiferromagnetic dimer chains were also determined.
2010, 59 (8): 5626-5634.
doi:10.7498/aps.59.5626
Abstract +
Plate impact experiments are conducted on high density glass (HDG) with an initial density of ～4.817g/cm3 (Brand ZF6) at a two-stage light gas gun facility. A copper flyer plate is used as a standard sample. Experimental shock pressure is between 52.1GPa and 167.8GPa. A multi-wavelength pyrometer and optical analyzer technique are used to determine the Hugoniot curve, sound velocity and shock temperature of HDG. The experiment results reveal that polymorphism phase transitions occur in HDG under compression, and the onset pressures are ～23, ～78 and ～120GPa, respectively. The measured sound velocity first increases and arrives at about 78GPa, then decreases rapidly, and increases again with pressure increasing. Beyond ～120 GPa, the longitudinal sound velocity turns in to bulk sound velocity, indicating the melting of HDG. Measured shock temperatures also show discontinuities at ～78 and ～120GPa, after which its increase rate becomes small and consistent with the calculated Lindemann melting line, confirming the above HDG phase transformation behaviors. Our Hugoniot data are consistent well with LASL shock Hugoniot data of HDG, which shows discontinuity only at about 23GPa, indicating that the phase transitions at 78 and 120GPa are not first-order ones. Our shock data and the gained knowledge of dynamic response behavior of HDG are valuable for improving the accuracies in sound velocity measurements for metals and non-metals at pressures over a megabar range.
2010, 59 (8): 5635-5640.
doi:10.7498/aps.59.5635
Abstract +
The influence of temperature on micro-friction at point contact was studied on the basis of analysis of micro interfacial friction. Based on Towle's experimental relationship between sheer strength and temperature and the theory of thermal effect on mechanical properties of material, the relationship between the friction force and temperature is deduced. Theoretical analysis shows that the friction decreases as the temperature increases when the interfacial temperature is lower than the material's Debye temperature. Theoretical calculation and experimental results of atomic force microscopy show the same trend, indicating that the theory and the method presented in this paper is feasible.
2010, 59 (8): 5641-5645.
doi:10.7498/aps.59.5641
Abstract +
A new vacancy model by using periodic density functional theory was used to describe the process of In segregation from clean Al surfaces via atomic movement through vacancies. The detailed segregation mechanism of impurity metal In to Al (001) surface planes is examined, carefully evaluating energy barriers for each step in the segregation process. The results show that the system energy is decreased by 0.46 eV and the highest energy barrier is 0.34 eV when the impurity atom In moves from the second layer to the topmost layer in the Al (001) slab. The system energy is almost constant when impurity atoms segregate from the third layer to the second layer. Higher energy (0.65 eV) was needed to overcome the energy barriers. So, In showing a strong segregation to the clean Al (001) surface is thermodynamically favorable.
2010, 59 (8): 5646-5651.
doi:10.7498/aps.59.5646
Abstract +
Based on the influence of the nonuniform temperature distribution and the inductance effect of the wires on the interconnect delay time, a zero-clock-skew construction method of RLC interconnect clock tree is presented in this paper. The proposed analytical model has closed form expression and takes temperature distribution, inductance effect and unsymmetrical interconnect structure into consideration. Adopting parameters of 65 nm process technology, the proposed model is compared with the other available similar models. Results show that the new model is more accurate with maximum 1% error.
2010, 59 (8): 5652-5660.
doi:10.7498/aps.59.5652
Abstract +
The geometrical and electronic structures, the dopant formation energies, lattice constants, band structure and density of states of p-type SiC are calculated by the first principles of plane wave ultra-soft pseudo-potential method based on density functional theory. The band structures of different concentrations of B, Al and Ga are calculated. The results of the electronic structure show that the band gap narrows with the increase of doping concentration of B and the band gap widens with the increase of doping concentration of Al and Ga. At the same concentration the band gap of Ga doped SiC is wider than that of Al doped SiC, the band gap of Al doped SiC is wider than B doped SiC.
2010, 59 (8): 5661-5666.
doi:10.7498/aps.59.5661
Abstract +
We investigate theoretically the technologically essential Auger recombination lifetime in narrow-gap semiconductor superlattices by means of a completely first-principles formalism, based on accurate energy bands and wave functions provided by the full-potential linearized augmented plane wave scheme. The minority carrier Auger lifetimes are determined by two correlated approaches: (1) direct evaluation in Fermi's golden rule, and (2) indirect evaluation, based on a detailed balance formulation relating Auger recombination and its inverse process, impact ionization, in a unified framework. Lifetimes determined by the direct and indirect methods for n -doped HgTe/CdTe and InAs/InxGa1－xSb superlattices exhibit excellent consistency with experimentally measured values. This justifies the computational formalism as a new sensitive tool in performance optimization of the synthetic narrow-gap semiconductor superlattice systems.
2010, 59 (8): 5667-5671.
doi:10.7498/aps.59.5667
Abstract +
We have calculated the structure, electronic and elastic properties of MAlH4(M=Na,K) based on density functional theory. We found both NaAlH4 and KAlH4 are insulators and are characterized by Al—H covalent bond and M—AlH4 ionic bond. The elastic constants are small compared with those of other compounds (e.g MgH2) and decrease in the MAlH4(M=Li,Na,K,Rb,Cs) series. We explain this phenomenon according to the volume change of MAlH4(M=Li,Na,K,Rb,Cs) .
2010, 59 (8): 5672-5680.
doi:10.7498/aps.59.5672
Abstract +
The ground-state structures and energies of the bimetallic clusters ConCu55－n(n=0—55) were obtained by using the semi-empirical Gupta potential combined with a genetic algorithm. The ground-state geometries of those bimetallic clusters can be characterized by the basic Mackay icosahedron of the pure Co55 (Cu55) cluster. Beginning with n=0 (Cu55), the Cu atom(s) is(are) replaced in order and continuously by the Co atom(s) from the center to the surface and from the edge to the vertex. The ground-state structure depends on the number of the Co—Co bonds which have the largest energy, the number of the Co-Cu bonds with large energy and the average bond length of those bonds. Co13Cu42 is a magic cluster with an icosahedral core formed by 13 Co atoms, which plays a key role in the high stability of those bimetallic clusters.
EDITOR'S SUGGESTION
2010, 59 (8): 5681-5686.
doi:10.7498/aps.59.5681
Abstract +
Laser crystallization of amorphous Si thin films is one of reliable method of preparing nanocrystalline silicon with high density and controllable size. In the present work, molecular dynamics simulation based on Tersoff potential was used to study the laser crystallization process of ultrathin amorphous silicon film (2.7 nm) on amorphous silicon nitride substrate. The influence of laser fluences on the crystallization and formation of nanocrystalline Si was investigated. It was found that there exists a laser fluence window in which nucleation and growth of nanocrystalline Si can be realized, which is in agreement with our previous experimental observations. The nucleation and growth processes in microscopic scale were simulated and the size of formed nanocrystalline Si was limited in both vertical and lateral directions by the film thickness and the formation of grain boundaries.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2010, 59 (8): 5687-5691.
doi:10.7498/aps.59.5687
Abstract +
The mechanical property of diamond-like carbon films with different hydrogen concentration is studied using molecular dynamical simulation based on REBO potential energy functions. The stiffness, hardness, and elastic modulus of the films are calculated from the load-unload curve. It is shown that both of the fraction of sp3 carbon and the concentration of H in the films have strong influence on the film hardness. When H concentration in the film is lower than 39%, the hardness is mainly determined by sp3 carbon, when H concentration further increases, the hardness decreases greatly despite the increase of the sp3 fraction.
2010, 59 (8): 5692-5699.
doi:10.7498/aps.59.5692
Abstract +
Based on fractal theory, the Monte Carlo method is used to simulate the structures of fractal soot aggegates in random distribution. The radiative properties of randomly distributed soot aggregates are studied using the discrete dipole approximation (DDA), and the effects of the fractal dimension ,the monomer diameters , the number of monomers in the soot aggregates and the refractive index on the radiative properties of aggregated soot particles are analyzed. The results show that the radiative properties of randomly distributed soot aggregates of a given fractal dimension are complex functions of the monomer diameters, the number of monomers in the aggregates,and the refractive index. For small values of the monomer diameters, the absorption cross section of soot aggregates tends to be relatively constant when the fractal dimension is small, but increases rapidly when the fractal dimension exceeds two. However, a monotonical reduction in light absorption with the increase of the fractal dimension is observed for soot aggregates with sufficiently large monomer diameters, number of monomers,and refractive index. The scattering cross section , extinction cross section and single-scattering albedo increase monotonically with the increase of the fractal dimension. In a word, the results for soot aggregates differ profoundly from those calculated for the equivalent spherical particles, and the discrepancies between them change litte with the increase of the fractal dimension.This research is of scientific value in studying the radiative properties of aerosols and their climatic effects.
2010, 59 (8): 5700-5705.
doi:10.7498/aps.59.5700
Abstract +
Results of experiments of the 4 mm gap semi-insulating(SI) GaAs photoconductive switch triggered by 1064 nm, 1.0 mJ pulse laser showed the nonlinear mode when the bias field was 3800 V. Under the same bias electric field and trigger light energy conditions, the switch outputs stably nonlinear electrical pulses, and the switch surface injury mark is caused by filamentation after 1500 times triggering. Analysis shows that under given conditions of trigger energy and electric field, two transient thermal effects occur in the switch chip, namely the thermal relaxation and photoactivated charge domain-phonon drag, respectively. Thermal relaxation time is shortened to the order of picoseconds or subpicoseconds, thermal relaxation process leads to the thermal conduction relaxation. When photoactivated charge domain moves at 107cm/s speed from cathode to anode, switch chip transient temperature makes relaxation oscillations owing to these effects, and the rapid increase of temperature in the chip is constrained. Photoactivated charge domain-phonon drag effect transmits in the direction of the dislocation movement, the temperature in mobile region increases when the flow of thermal energy carried by the phonons was concentrated in the movement plane, the injury of filamentation is produced by superposition and cumulation of mobile tracks.
2010, 59 (8): 5706-5709.
doi:10.7498/aps.59.5706
Abstract +
Ti/Al contacts have been deposited by electron beam Evaporation onto N-polar n-type surfaces of GaN-based vertical structure LED on Si substrate. The effect of AlN buffer layer on ohmic contact of these chips has been investigated through I-V characteristic. The results shown Ti/Al contacts prepared on N-polar n-type surface without AlN buffer layer became ohmic contact after annealing in the temperature range of 500—600℃. The as-deposited Ti/Al contacts on N-polar n-type surface with AlN buffer layer shown ohmic behaviors with a specific contact resistivity of 2×10-5 Ωcm2 and maintained ohmic contact characteristics until anneal at 600℃. Therefore, The exsiting of AlN buffer layer is the key to forming highthermal stability ohmic contact for GaN-based vertical structure LED on Si substrate.
2010, 59 (8): 5710-5714.
doi:10.7498/aps.59.5710
Abstract +
(La0.7Sr0.3MnO3)m(BiFeO3)n superlattices were grown in situ on SrTiO3(001) substrates by rf magnetron sputtering. The current-voltage measurements were performed under the temperature of 50—150℃ for the superlattices specimens. The analysis showed that the leakage current increased with increasing the temperature or decreasing the BFO thickness in the samples. And the conduction mechanisms of the prepared (La0.7Sr0.3MnO3)m(BiFeO3)n superlattices were analyzed according to common insulator conduction models. It exhibited that the space-charge-limited current were dominated in the as fabricated (La0.7Sr0.3MnO3)m(BiFeO3)n superlattices in high temperature or high electrical field.
2010, 59 (8): 5715-5719.
doi:10.7498/aps.59.5715
Abstract +
In this paper, two kinds of ring-type microwave electric resonant structures were proposed, which were appropriately assembled with metal wires to form electromagnetic coupling units. The coupled structures have resonance response to the incident electromagnetic wave, and absorb the electric and magnetic fields strongly. We simulated these two kinds of coupled structures, and then optimized the simulation results to achieve the best absorption properties. The electromagnetic properties (the reflection coefficients S11 and the transmission coefficients S21) of metamaterial absorber sample were measured using free space method in microwave frequency from 8 to 12 GHz. At 10.7 GHz and 10.07 GHz, the absorptivity reaches 95% and 98%, respectively.
2010, 59 (8): 5720-5723.
doi:10.7498/aps.59.5720
Abstract +
We have demonstrated a two-color quantum well infrared photodetector (QWIP) exhibiting simultaneous photoresponse with cutoff wavelengths at 11.8 and 14.5 μm, respectively. Strong photocurrent signals are observed at temperature of 77 K. The simultaneous two-color photoresponse is achieved by utilizing a simple design by broadening the width of the quantum well and selecting an appropriate doping density. The two peaks are attributed to the intersubband transitions from the ground state to the first excited state (bound state) and to the fifth excited state (continuum state), respectively.
EDITOR'S SUGGESTION
Growth and character stics of AlGaN/GaN HEMT structures with AlN/GaN superlattices as barrier layers
2010, 59 (8): 5724-5729.
doi:10.7498/aps.59.5724
Abstract +
We report the growth and characterization of AlGaN/GaN heterostructures with AlN/GaN superlattices as the barrier layer.It is found that the surface morphology of the heterostructure is greatly improved compared with those using the conventional alloy AlGaN barrier layer.Meanwhile, electric properties of samples with high Al composition (≥40%) are superior to the conventional alloy sanples.Low sheet resistance (251 Ω/□) is obtained for our samples with 40% Al content.
2010, 59 (8): 5730-5737.
doi:10.7498/aps.59.5730
Abstract +
In this article, we comprehensively showed the impact of barrier layer traps, buffer layer traps and surface charge on current collapse and knee voltage change, pointed out that the change in the concentration of surface charge and barrier layer traps have little influence on the 2DEG density in the channel.When the concentration of surface charge changes, the knee voltage drift and strength of current collapse are in close connection with the change of potential energy in quantum well.Buffer layer has stronger local effect than barrier layer, when the concentration of bulk traps change in these layers, knee voltage drift is mainly caused by the change of 2DEG density, but has less change compared with the situation of surface charge.Potential energy changes in the quantum well is an important reason for the change of knee voltage, the strength of current collapse is determined by the size of potential energy and 2DEG density.
EDITOR'S SUGGESTION
2010, 59 (8): 5738-5742.
doi:10.7498/aps.59.5738
Abstract +
Self-assembled InAs/GaAs quantum dot structures with different cap layers are grown by metal-organic chemical vapor deposition.The structure and optical properties of quantum dots are investigated using atomic force microscopy and photoluminescence.The cap layers sandwiched between quantum dots are composed of a low-temperature layer and a high-temperature layer.The comparative studies on low-temperature cap layer show that In graded InGaAs layer structure improves the uniformity of quantum dots,decreases coalescent islands and enhances photoluminescence intensity.Emission wavelength shifts from 1256.0 nm to 1314.4 nm when the thickness of graded InGaAs low-temperature cap layer increases form 6.8 nm to 12 nm.The research on high-temperature cap layer structure indicates that In graded InGaAs layer can increase photoluminescence intensity.
2010, 59 (8): 5743-5748.
doi:10.7498/aps.59.5743
Abstract +
In the light of energy balance and screw dislocation formation model,a detailed analysis is presented on strain relaxation mechanism of pseudomorphic SiGe based on the experimental result that shear modulus of low-temperature Si (LT-Si) is less than that of SiGe.The mechanism shows that strain is relaxed by dislocation formed in LT-Si buffer layer when the thickness of pseudomorphic SiGe film is smaller than the critical thickness, and dislocations prefecentially form in LT-Si layer then the thickness of the film is equal or exceeds the critical thickness,which agrees with the experimental results reported in the literature.At the same time,an experiment was carried out to grow relaxed Si0.8Ge0.2 virtual substrate using LT-Si technology.The results indicated that dislocations were resmicted to the LT-Si layer and the relaxation degree was 85.09% without threading dislocations in Si0.8Ge0.2.The experimental results proved that the strain of pseudomorphic Si0.8Ge0.2 is relaxed by dislocations formed in the LT-Si buffer layer.
2010, 59 (8): 5749-5754.
doi:10.7498/aps.59.5749
Abstract +
ZnS thin films were prepared on glass substrate by RF magnetron sputtering technique.The quality of ZnS films formed at different deposition pressures,annealing temperatures and substrate temperatures were studied.The change of the film microstructure was analyzed by XRD and the lattice stress was evaluated.The spectral transmittance was measured by a spectrometer.From the spectrum,the band gap and Urbach energy were calculated.Scanning electron microscopy (SEM) was used to study the morphology of the surface of the sample.The result showed that there is big stress in the lattice when the substrate is at room temperature,and the value of stress increases with the pressure.After annealing at 300 ℃,the stress is minimal.When the substrate temperature is 350 ℃,the stress decreases,at the same time,ZnS films have good transmittance,and annealing at 300 ℃ improves the film quality.
2010, 59 (8): 5755-5758.
doi:10.7498/aps.59.5755
Abstract +
The experimental results of mm-wave coherent emission from a high temperature superconducting bicrystal Josephson junction array embedded in a Fabry-Perot resonator are reported in this paper.The mm-wave coherent emission from the series junction array results from the interaction of the junctions with the substrate serving as the dielectric resonator as well as the Fabry-Perot resonator.The central frequency of emission of a Josephson junction array containing 166 bicrystal junctions was 75.84 GHz,and the detected emission power was about 10 pW at 77 K.
2010, 59 (8): 5759-5765.
doi:10.7498/aps.59.5759
Abstract +
The influence of V doping at Mn site on charge order and spin order of La0.3Ca0.7MnO3 system has been studied by the measurement of magnetization-temperature (M-T) curves,resistivity-temperature (ρ-T) curves and electron spin resonance (ESR) spectra of samples La0.3Ca0.7Mn1－xVxO3 (x=0.05,0.10,0.134,0.20).The results show that, when 0.05≤3≤0.134,charge ordering (CO) phase exists in the system,and the spin order of the system exhibits the serial changes of paramagnetism (PM)—charge ordering (CO)—antiferromagnetism (AFM) with the decrease of temperature.When x=0.20,the charge ordering melts,and the system exhibits second-entering-type spin glass behavior.
2010, 59 (8): 5766-5771.
doi:10.7498/aps.59.5766
Abstract +
The dynamic behaviour in the vicinity of the interface for the strained superlattice is discussed in the classical mechanics frame based on the Seeger equation. We found that the motion and the accumulation of the dislocations by the non-linear resonance may give rise to the lamination or the fracture of the superlattice. At first, byintroducing the damping term,the Seeger equation describing the dislocation motion is reduced to the generalized Duffing equation describing superlattice in the small amplitude aproximation. Secondly,the main resonance, the super-harmonic resonance and the sub-harmonic resonance of the system are analysed by the multiscale method. The critical condition for the system to enter into resonance is found. It shows that the critical condition is related to the parameters of the system,by adeguately regulating the parameters of the system,the resonance can be avoided in principle,then the stability and the perfection of the superlattice materials may be bellev ensured.
2010, 59 (8): 5772-5776.
doi:10.7498/aps.59.5772
Abstract +
The Bi0.85Nd0.15FeO3 thin films were prepared on the Pt/Ti/SiO2/Si substrates by Sol-gel method.The effect of annealing temperature on formation of Bi0.85Nd0.15FeO3 phase was investigated. It was found that the Bi0.85Nd0.15FeO3 phase was formed and coexisted with the impurity phase when the films annealed at 450 ℃. The single-phase Bi0.85Nd0.15FeO3 films were obtained,when they were annealed at 500—600 ℃. Bi0.85Nd0.15FeO3 films annealed at 600 ℃ had saturated magnetization about 44.8 emu/cm3, remnant polarization (2Pr) about 16.6 μC/cm2,dielectric constant 145 and dielectric loss 0.032(1 MHz), respectively.
2010, 59 (8): 5777-5783.
doi:10.7498/aps.59.5777
Abstract +
Texturing of silicon surface is a major way to increase short circuit current and then improve the efficiency of silicon solar cells by effective light trapping.The anisotropic texturing of a (100) silicon surface was performed using tetramethyl ammonium hydroxide (TMAH) solution and NaClO additive in combination with continual ultrasonic wave treatment.The effect of ultrasonic wave and NaClO on the nucleation and growth of finc pyramids during the anisotropic texturing, and the effect of size of pyramids on the minority carrier lifetime of textured silicon wafer after the high temperature process were investigated.The enhancement of homogeneity of the smaller pyramids in the textured structure of silicon crystalline is obtained by adding continnal ultrasonic wave treatment to control the time of H2 bubble staying on the silicon surface and the speed of H2 detaching from the surface.The weighted mean reflectance for the solar spectrum AM 1.5G is 12.4% for the silicon surface with the optimal size of pyramids.After high temperature oxidation, the size of pyramid has an obvious exponential relation with the minority carrier lifetime of textured silicon wafer.
2010, 59 (8): 5784-5790.
doi:10.7498/aps.59.5784
Abstract +
In this paper the temperature and thermal stress distribution in a simplified-mode transparent slab is calculated and then variation of refractive index is acquired based on the photo-elastic theory. Using the vector differential algorithm the refractive behavior of rays in such media is simulated, and luminous intensity distribution and shape of fringes at the receiving plane is predicted. The output of the program is in coincidence with the check experiment based on photo-elasticity technique, which indicates the correctness of our analysis method and light transmission calculation method. This research provides a practical means for improving the imaging quality of optical instruments.
2010, 59 (8): 5791-5795.
doi:10.7498/aps.59.5791
Abstract +
We investigate in this paper the influence of the localized plasmon resonance of gold nano-island structure on the photoluminescence of the exciplex in the polymer blends. The experimental results show that when the particle plasmon resonance overlaps the photoluminescence spectrum of the exciplex,the corresponding emission intensity is enhanced significantly. Furthermore, alonger lifetime is observed with the exciplex emission. We propose that the localized electrical field induced by the particle plasmon resonance increaseds the exciton diffusion length and thus conduces to the formation of the exciplex in the phase separation interface.
2010, 59 (8): 5796-5802.
doi:10.7498/aps.59.5796
Abstract +
The influence of mixed former effect on the thermal stability,1.53 μm emission and the infrared to visible upconversion emission of the Er3+-doped tellurite glasses are investigated.The inhomogeneous broadening of emission spectrum of Er3+ ion with several network formers (WO3,Nb2O5 and GeO2)is discussed by Raman spectra.The results indicate that for Er3+-doped tellurite glass,besides improving the thermal stability of glasses,introducing the network former with appropriate phonon energy is helpful for the improvement of 1.53 μm emission via decreasing the lifetime of Er3+ ∶4 I11/2 level,and lowering the upconversion luminescence in visible wavelength.The present glasses exhibit a large emission cross section ((9.64—10.96)×10-21 cm2)and broad full width at half maximum (FWHM)(50—67 nm),which make them promising host materials for broadband Er3+-doped fiber.
2010, 59 (8): 5803-5807.
doi:10.7498/aps.59.5803
Abstract +
A series of chalcogenide glasses based on Ge25Ga10Se65 system co-doped with Ho3+/Pr3+ ions of different ratios were synthesized by melt-quenching technique. The absorption spectra,mid-infrared fluorescence and lifetime of glass samples under 908 nm laser excitation were measured. The emission cross section of Ho3+:5I7→5I8 and absorption cross section of Pr3+:3H4→3F2 were calculated. The energy transfer efficiency between Ho3+ and Pr3+ ions with different Pr3+ ion concentrations have been discussed. Through fitting the 2.0 μm fluorescence decay curves of Ho3+ ions,the energy transfer regime was judged. The results prove thatTm3+ is an efficient sensitizer which enhances the Ho3+: 2.9 μm fluorescence intensity significantly.
2010, 59 (8): 5808-5816.
doi:10.7498/aps.59.5808
Abstract +
Glasses with the compositions of (90-x)GeO2-xNb2O5-10Na2O(x=1,2,4,6,8 molar ratio)doped with Tm2O3 at the same concentration (4wt%) and 86GeO2-4Nb2O5-10Na2O dore at different concentrations were fabricated respectively by conventional melting method.The effects of Nb2O5 content on glass stability,fluorescence strength and J-O strength parameters were studied.According to the Judd-Ofelt theory,the J-O strength parameters (Ω2, Ω4, Ω6) of Tm3+ in different Nb2O5 concentration were calculated,with which the radiative transition probabilities,branching ratios and radiative lifetime were obtained.Meanwhile,according to the McCumber theory,the absorption and emission cross-sections corresponding to the 3F4→3H6 transitions of Tm3+ at 1.8 μm were obtained.The gain cross section was calculated by using the emission cross-section,absorbtion cross section and Tm3+ concentration.The fluorescence features (under 808 nm LD excitation) at ～1.47 and ～1.8 μm of Tm3+-doped glasses of different concentrations were studied.The fluorescence intensity at ～1.8 μm reached to the maximum when the Tm2O3-doping concentration was about 3wt%,and then decreased as the doping concentration increased further.The fluorescence intensity at ～1.8 μm reached to the maximum when the Nb2O5 content in glass composition was about 2 mol%.The effects of Nb2O5 content on the glass structure and the spectra properties were also discussed.
2010, 59 (8): 5817-5822.
doi:10.7498/aps.59.5817
Abstract +
Organic light-emitting diode (OLED) with structure of ITO/CuPc/NPB/Alq3/LiF/Al was fabricated,and the magnetic field effect on the injection current (magnetoconductance or MC effect) at 300 K,260 K,220 K,and 180 K were measured at constant voltage bias. During the transition of injection current from bipolar current to unipolar current,the MC of the device increased firstly and fell with the decreasing current. The MC became smaller at the lower temperatures. However,under all measurement conditions,the values of the MC were always positive. The inversion of MC from positive to negative as reported in literatures was not observed. The experimental results demonstrate that the ±MC effects in OLED not only depend on the unipolar or bipolar current. It is also related with the organic materials and device structure. Using the magnetic field modulated electron-hole pair mechanism and bipolaron model,the positive MC effects in bipolar and unipolar injection current are interpreted, respectively.
2010, 59 (8): 5823-5827.
doi:10.7498/aps.59.5823
Abstract +
SiN-based multilayers were prepared in a plasma enhanced chemical vapor deposition system followed by subsequently thermal annealing and laser irradiation with the aim of fabrication three-dimensional constrained, size-controlled and well-regulated Si nanocrystals. The experimental results show that Si nanocrystals grow in the Si-rich SiN sublayer. Furthermore, the grain size can be controlled according to the thick of Si-rich SiN. It is also found that the crystalline fraction of the multilayers irradiated by laser is significantly higher than that by thermal annealing. The devices that employing the laser-irradiated multilayer as luminescent active layer exhibit an enhanced visible electroluminescence and the external quantum efficiency is improved by 40% in comparison with the device without annealing.
2010, 59 (8): 5828-5832.
doi:10.7498/aps.59.5828
Abstract +
Here, we calculated theoretically the positron bulk lifetime of cuprous halide (except CuI,which has not the blende structure) and some borides with the method of atomic superposition approximation (ATSUP) on the basis of the theory of local density approximation (LDA) and general gradient approximation (GGA),the calculated results are in good agreement with the experiment. On the other hand, the positron lifetime of many other compounds which have blende structure are calcualted,and the results agree with the results published in literatur. Here we take the CuCl as an example,the pictures of the electron potential energy distribution, probability density of positron and positron annihilation rate are given. Finally the systematic results were fitted with curve as a function of lattice constants, and the fitted results are compared with the outcomes of other articles.
2010, 59 (8): 5833-5838.
doi:10.7498/aps.59.5833
Abstract +
The ZnS:Cu,Tm X-ray phosphor fine particles synthesized by hydrothermal method has been reported for first time and its photoluminescence (PL) and X-ray excited luminescence (XEL) properties have been studied in detail also. The direct hydrothermal treatment at 200 ℃ for 12h samples average gain size is about 15 nm; the synthesized spherical-like nanocrystals with well dispersity and narrow gain size distribution show cubic structure. The after annealing in Argon at 900 ℃ for 1h samples agglomerate size is about 200—600 nm and roughly spherical fine particles show pure hexagonal structure. The PL and XEL spectra of all of samples show a broad emission band and an intense emission band in the range of 400—600 nm. The maximum XEL intensity of sample directly synthesized by hydrothermal treatment is observed for Cu/Zn and Tm/Cu are 3×10-4 and 2, respectively. In this condition, the strongest PL and XEL emission is observed for the direct synthesized sample further annealing in Argon at 900℃ for 1h sample and the XEL peak center about 453 nm and 525 nm, respectively. The Samples with highly luminescence efficiencies and the smaller size could enhance the resolution of imaging systems. The difference between PL and XEL spectrum is due to its different excitation mechanism. The luminescence mechanism and different excitation mechanism of PL and XEL have been discussed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2010, 59 (8): 5839-5844.
doi:10.7498/aps.59.5839
Abstract +
The ZnO nanorods, primarily aligned perpendicular to the substrate, have been fabricated by hydrothermal decomposition. The scanning electron microscopy and photoluminescence method were used to characterize their morphology and optical properties, respectively. The field emission properties were also studied. The results indicate that the ZnO nanorods present good morphology, structure and good field emission property. The on-set field is 2.8 V/μm at a current density of 1 μA/cm2. The emission current density can reach 0.67 mA/cm2 at 6.4 V/μm. The field emission enhancement factor is 3660. Fluctuation of the current density is less than 25% at 4.5 V/μm for 5 hours. In the organic/inorganic electroluminescence heterostructure, with the ZnO nanorods as the electron transport layer and the m-MTDATA(4,4',4″-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine) as the hole transport layer, the ultra-violet emission of ZnO nanorods was obtained with a 40 nm blue-shift compared with the photoluminescence of the ZnO nanorods.
2010, 59 (8): 5845-5850.
doi:10.7498/aps.59.5845
Abstract +
In this study, numerical experiments are carried out to quantitatively investigate the effects of limited-view scanning on the resolution of photoacoustic tomography. An empirical formula is provided to approach our numerical results.The results of the study are helpful for the design of scanning trajectory and the evaluation of reconstruction.
2010, 59 (8): 5851-5856.
doi:10.7498/aps.59.5851
Abstract +
On the basis of the first oxide prepared anodized aluminum oxide template (AAO), the second, third and fourth oxidation preparation are implemented in turn. Then, the surface morphology and current curve changes of the AAO template with multiple oxidation preparation were compared and analyzed systemically. The apertures of nanopore made by the second, third and forth oxidation increase in order, the intervals between neighboring apertures reduce. However, the scale of ordered distribution of nanopores on the whole template surface does not change significantly. Then, carefully controlling the working conditions for the membrane-removed of the one-step oxidation AAO, the nanoporous with regular apertures and highly ordered was obtained after getting rid of the top oxidation layer about 10 minutes. Finally, based on those prepared AAO templates, integrated with the thermal nanoimprint lithography, we achieved the PMMA nano-pillar arrays with controllable lengths and diameters.
2010, 59 (8): 5857-5862.
doi:10.7498/aps.59.5857
Abstract +
IMPS(intensity-modulated photocurrent spectroscopy) and IMVS(intensity–modulated photovoltage spectroscopy) measurements are utilized to analyse different mechanisms for enhancing the performance of dye-sensitized solar cells(DSC) based on modified anode. Electron transport and back reaction in DSC are investigated under different illumination intensities. The modifications of anode, blocking layer and modified TiO2films, are performed by electrodeposition. It is found that short-current density Jsc and efficiency η of DSC are improved, but different mechanisms are obtained: the optimization of TCO by coating a blocking layer can effectively extend electron lifetime τ n, but it has little influence on electron transport. On the other hand, the optimization of TiO2 film can enhance electron transport, finally shorten transit time τ d and extend τ n.
Influence of surface effect to the performance of LiMn2O4 cathode material for lithium ion batteries
2010, 59 (8): 5863-5869.
doi:10.7498/aps.59.5863
Abstract +
The surface geometrical and electronic structure of LiMn2O4 (001) are investigated via a density functional approach within the spin-dependent generalized gradient approximation (GGA). Large relaxations perpendicular to the (001) plane of surface and subsurface atoms are observed, which is partly responsible for the Mn dissolution problem of the material when used as cathode material for lithium ion batteries. Because of the surface effect, only Mn3+ ions are observed at the LiMn2O4 (001) surfaces, which is very active for the disproportionation reaction occurs at the electrode/electrolyte interface. The calculated results are also in good agreements with experimental observations.
2010, 59 (8): 5870-5879.
doi:10.7498/aps.59.5870
Abstract +
Robustness is one of the most important requirements when digital watermarking is applied. Different from the StirMark test and various simulation tests, a mutual information function is defined as a criterion to measure the robustness of watermarking algorithm. Taking the additive spread spectrum watermarking scheme and quantization index modulation (QIM) watermarking scheme as two examples, the calculation formulas of mutual information function are derived to evaluate the robustness of the algorithms. Numerical computation of mutual information is performed with change of watermark noise rate (WNR). In the experiment, spread spectrum watermarking is implemented in discrete cosine transform (DCT) and QIM watermarking is implemented in discrete wavelet transform (DWT). The statistic bit error rate (BER) is derived against Gaussian distribution noise and JPEG compression. Experiment results show that the evaluation conclusion of mutual information method is in accordance with the empirical BER. Mutual information can be selected as a cost function to predict the BER.
2010, 59 (8): 5880-5887.
doi:10.7498/aps.59.5880
Abstract +
Neural system generates various kinds of fire patterns when stimulated by external or internal inputs. Acupuncture, as a mechanical action, is equivalent to an external stimulus to the neural system. When stimulated by the acupuncture, the neural system can evoke irregular electrical signals. Neural system is a complex nonlinear dynamic system that possesses strong nonlinear characteristic, so it is necessary to introduce the nonlinear time series analysis method to study the neural electrical signal. In this paper, an experiment is designed in which acupuncture is made at Zusanli with four different acupuncture manipulations to obtain action potentials on dorsal spinal nerve root. The concept of the interspike interval (ISI) is used for the study of the acupuncture electrical signals. Several nonlinear characteristic parameters are extracted, such as the Lyapunov exponent, correlation dimension and Lempel-Ziv complexity, and the neural coding of the electrical signal evoked by different acupuncture manipulations is obtained. It is also shown that under the effect of the acupuncture, the electrical signals of dorsal spinal nerve root based on acupuncture at Zusanli point has distinguished chaotic features.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2010, 59 (8): 5888-5895.
doi:10.7498/aps.59.5888
Abstract +
The surface energy imbalance problem has been an important challenge in the study of surface land process since it was found in the late 1980s. By utilizing the observed data in the land surface process experiment carried out over the Loess Plateau region in the middle part of Gansu, the characteristics of climate unclosure and short-term unclosure of the surface energy balance are analyzed and the relationship between surface energy balance unclosure and vertical velocity is studied in the paper. It is found that there is a good correlation between surface energy balance unclosure and vertical velocity. Furthermore, the paper estimates the values of vertical sensible heat advection in the surface layer. After considering the vertical sensible heat advection, characteristics of the surface energy balance condition are analyzed again and there is a significant improvement in the surface energy balance unclosure.This means vertical velocity plays an important role in the surface energy buget and the vertical sensible heat advection has a significant influence on the surface energy balance unclosure over the Loess Plateau region.
2010, 59 (8): 5896-5903.
doi:10.7498/aps.59.5896
Abstract +
We investigate precursors and predictability of extreme events of Lorenz system with different percentile. The precursors and predictability of Palmer Drought Severity Index (PDSI) extremes in China are analyzed, and obtained how the quality of the prediction depends on the size of the extreme events and on the correlation strength. Results indicate that for extreme events of Lorenz system and PDSI series, the stronger the extreme, the higher the predictablility. Moreover, we analyzed precursors and predictability of eight regions in China and provide some due scientific basis for flood and drought predictions.
2010, 59 (8): 5904-5913.
doi:10.7498/aps.59.5904
Abstract +
The detection error of Hartmann-Shack (H-S) wavefront sensor is one of the main errors in adaptive optical systems. In this paper, the detection error of H-S wavefront sensor based on the electron multiplying charge-coupled devices (EMCCD) is firstly analyzed and the detection error formula is established. Furthermore, the numerical simulation and experimental results show that the centroid detection error is related to the gain of EMCCD. The centroid detection error decreases with gain increasing when the gain is lower than Pmax/(Q·Nmean). When the gain is higher than Pmax/(Q·Nmean), the centroid detection error increases with the gain increasing, where Pmax is the peak electric charge value of EMCCD, Q is quantum efficiency, Nmean is the mean number of incident photons.
2010, 59 (8): 5914-5920.
doi:10.7498/aps.59.5914
Abstract +
In this paper, the Monte Carlo method is used to simulate atmospheric ionization effects of the prompt radiation from high altitude nuclear explosion (HANE). Simulation gives the instantaneous spatial distributions of the electron density in atmosphere. The atmosphere is a kind of non-uniform media, whose density drops rapidly with the increase of height. Therefore, a method, which samples the mass distance to replace the step length of the particle, is used to considerably increase the computing speed. The simulation results show that there is an obvious difference between additional ionization regions of different height of nuclear explosion. As the explosion-height increases, influence range of the prompt nuclear radiation will be wider, but the electron density will be lower.
2010, 59 (8): 5921-5924.
doi:10.7498/aps.59.5921
Abstract +
In Kasner space-time, we calculate the interference phase and oscillation length of the mass neutrinos in some special cases and find that the phase along the null is equivalent to the half phase along the geodesic in the high energy limit. When the parameter a in line element fulfils a=0, the interference phase is the same as that in Schwarzschild space-time. Research on this subject has impact on cosmology.