Vol. 61, No. 19 (2012)
2012, 61 (19): 190201. doi: 10.7498/aps.61.190201
In order to overcome the disadvantages of existing complex network robustness research models in which only the local influences of disabled nodes and topological robustness are considered, the node load, utmost load and disabled model are defined by node efficiency and a new method to evaluate complex network functional robustness is proposed in which the whole influence of disabled nodes is considered. The complex network functional robustness is evaluated by the final disabled node proportion after beat and the optimized evaluation arithmetic is given. Experiments show that this method is effective and feasible in evaluation of complex network functional robustness in which the node load is considered, and it is applicable for large scale complex networks.
2012, 61 (19): 190202. doi: 10.7498/aps.61.190202
Using three-order symplectic integrators and fourth-order collocated spatial differences, a high-order symplectic finite-difference time-domain (SFDTD(3, 4)) scheme is proposed to solve the time-dependent Schrdinger equation. First, high-order symplectic framework for discretizing the Schrdinger equation is described. The numerical stability and dispersion analyses are provided for the FDTD(2, 2), FDTD(2, 4) and SFDTD(3, 4) schemes. The results are demonstrated in terms of theoretical analyses and numerical simulations. The spatial high-order collocated difference reduces the stability that can be improved by the high-order symplectic integrators. The SFDTD(3, 4) scheme and FDTD(2, 4) approach show better numerical dispersion than the traditional FDTD(2, 2) method. The simulation results of a two-dimensional quantum well and harmonic oscillator strongly confirm the advantages of the SFDTD(3, 4) scheme over the traditional FDTD(2, 2) method and other high-order approaches. The explicit SFDTD(3, 4) scheme, which is high-order-accurate and energy-conserving, is well suited for long-term simulation.
2012, 61 (19): 190203. doi: 10.7498/aps.61.190203
In order to expand the engineering application area of nonlinear standing waves in acoustic resonators, a new numerical algorithm is proposed for simulating nonlinear standing waves in resonators. It also can be used to overcome the shortages of the existing numerical methods, which restrict the solution to the nonlinear standing waves in cylindrical resonators and exponential resonators. The numerical algorithm is constructed based on the Navier-Stokes equations in the resonators with variable cross-section for an unsteady compressible thermoviscous fluid without truncation, and the space conservation law. The numerical algorithm-finite volume method for solving the nonlinear standing waves in acoustic resonators by piston driving is built based on the semi-implicit method for pressure-linked equations-consistent algorithm and staggered grid technique. Simulations for solving the nonlinear standing waves in cylindrical resonators, exponential resonators and conical resonators are carried out. By comparison with the existing experimental results and numerical simulation results, the accuracy of the developed finite volume algorithm is verified. Some new physical results are obtained, including unsteady velocity, density and temperature. The shock-like pressure wave shapes are found in cylindrical resonators, simultaneously, and the results show that the sharp velocity spikes appear in the cylindrical resonators. High amplitude acoustic pressures are generated in exponential resonators and conical resonators. Shock-like pressure waves and the sharp velocity spikes are not found. The strong dependence of the physical properties of nonlinear standing waves on resonator shape is demonstrated through the simulative results.
2012, 61 (19): 190501. doi: 10.7498/aps.61.190501
Cardiac memory effect, which exhibits the time-delayed coupling of membrane voltage, is introduced into Luo-Rudy phase I cardiac model. The effect of the cardiac memory on spiral waves is investigated. The numerical results show that the cardiac memory can lead to irregular meandering of spiral waves. When the delay-time is properly chosen, the increase of memory strength causes the decrease of spiral wave frequency. If memory strength exceeds the critical value, the cardiac memory results in the disappearances of both spiral waves and spatiotemporal chaos in system because the time-dependent potassium ion current is over suppressed by cardiac memory.
2012, 61 (19): 190502. doi: 10.7498/aps.61.190502
There are many non-smooth objects in nature, such as coastline, rock fracture, cross section, whose differentiabilities cannot be described by ordinary calculus and methods in Euclidean geometry. The local fractional derivative is one of the potential tools to investigate the non-smooth problems. This study revisits the non-smooth curves generated from the fractional integrals and Cantor-like set. From the view of the fractional differentiable functions, the differentiabilities of the non-smooth curves are derived by using a binomial expansion.
2012, 61 (19): 190503. doi: 10.7498/aps.61.190503
In this paper we mainly study the application of piecewise fractional Brownian motion (PFBM) to modeling radar sea clutter. Because the research objects in nature and man-made systems are usually not perfectly fractal in mathematics, the fractal properties of these researched objects cannot hold in the whole scale interval. Traditionally, the mono-fractal model of sea clutter only makes use of the self-similarity of sea clutter within the scale-invariant interval for parameter estimation but ignores the information contained in the scales outside the scale-invariant interval. The PFBM describes the sea clutter piecewisely in frequency domain, which corresponds to describing the sea clutter in time domain respectively on the large scale and on the fine scale. Combining the physical background, the PFBM model can explain the mechanism of the different roughnesses of a sea clutter time sequence respectively on the large scale and on the fine scale. Subsequently, in the paper, we study the effects of moving targets with different Doppler frequencies on sea clutter. The results show that moving targets can cause different effects on sea clutter respectively on the large scale and on the fine scale.
2012, 61 (19): 190504. doi: 10.7498/aps.61.190504
In this paper, a chaotic impulse synchronization is proposed by using opti-electronic feedback. The laser chaos dynamical equations are numerically calculated, and the different chaotic states are obserred by modulating the coefficient of feedback or impulse which realizes the control of chaotic dynamics. Then, the impulse synchronization equations are numerically calculated, and the simulation image of synchronization is plotted. Experiments show the scheme can achieve the chaotic synchronization.
2012, 61 (19): 190505. doi: 10.7498/aps.61.190505
In the Chen-Lai and Wang-Chen algorithm , the modular functions are both defined in (-∞,+∞). A modular function, however, in the implementation of electronic circuit, is more reasonable in line with the actual situation if it is defined in a finite region. We take for example the anti-control of a discrete time system, of which the modular function is sine function on the basis of a finite region. And in the sense of Li-Yorke, the chaotic sufficient condition and the rigorous theory proof are provided. As a result, ranges of specific circuit parameters can be determined by both the sufficient conditions resulting from the theorem, and a finite region defined by the device, or the constraint conditions of a dynamic range. Therefore, this provides a fundamental basis for the circuit design and its technology. Based on this method, the anti-control circuit of the discrete time system is designed, of which the modular function is sine function in a finite region. And the experimental results are given for confirming the feasibility of the method. The method presented in this paper can also be applied to the circuit implementation and the anti-control of a discrete time system, of which the modular function is other nonlinear function.
2012, 61 (19): 190506. doi: 10.7498/aps.61.190506
Poincaré plot is an important method in nonlinear analysis of heart rate variability(HRV). Based on the modified Poincaré plot, two arguments-the regional distribution entropy and regional distribution coefficient are put forward for the quantitative description of the scatter distribution trends in the studied area. And the distributions of the Poincaré plot in the four quadrants are calculated separately. Through the analysis of the HRV sample data from healthy young people, older people and congestive heart failure(CHF) sufferers in MIT-BIH database, we find that the two parameters show a significant difference between the groups. Meanwhile, the analysis results in different quadrants show that the sensitivities of the four quadrants are different, and especially in the first quadrant, the sensitivity is best. This phenomenon shows that the changes of vagal control function are most significant between healthy people and CHF sufferers, which is consistent with previous physiological research conclusion. Experimental results also show that the method can be used for short-term data, and thus is easier to extend to clinical applications.
2012, 61 (19): 190507. doi: 10.7498/aps.61.190507
In order to reveal the internal dynamic property of wind power time series the nonlinear analysis method is used to identify the chaotic property of wind power set which is the basis for the prediction of the wind power time series. Firstly day correlation property on wind power time series of a certain wind farmer is analyzed. Secondly the largest Lyapunov exponent of wind power set is calculated on the basis of phase space construction to verify the presence of chaos in wind power time series. The ultra-short-term predicted of wind power would produce larger errors by using the Volterra filter multi-step prediction so the predicted results of Volterra filter are corrected by combining the results predicted by Local-region Multi-steps Method and the largest Lyapunov exponent method with weighted Markov chain and ordered operator. Finally the prediction on wind power of a certain wind farmer is presented and the simulation results illustrate that the correction forecasting model improves high predictive accuracy effectively, which provides a useful reference for wind power prediction by the Volterra filter multi-step method.
Rational solutions and spatial solitons for the (2+1)-dimensional nonlinear Schrdinger equation with distributed coefficients
2012, 61 (19): 190508. doi: 10.7498/aps.61.190508
The nonlinear Schrdinger equation is one of the most important nonlinear models with widely applications in physics. Based on a similarity transformation, the (2+1)-dimensional nonlinear Schrdinger equation with distributed coefficients is transformed into a traceable nonlinear Schrdinger equation, and then two types of rational solutions and several spatial solitons are derived.
2012, 61 (19): 190509. doi: 10.7498/aps.61.190509
Opinion formation is the result of co-evolution of individual behavior and environment. Individual behavior is determined by its rational cognition and irrational emotion. Environment includes culture, cognitive and behavioral patterns and social interactions. Culture and cognitive patterns are usually related to the spatial factors. In this paper, a social network with geographical factors is constructed. Together with the Ising model in networks, the effects of both spatial and social factors on opinion formation are investigated. The phase transition in the process of opinion formation is studied. The results indicate that both spatial cultural background and global preference for public opinion are crucial to opinion formation.
2012, 61 (19): 190510. doi: 10.7498/aps.61.190510
To analyze the topological properties of Beijing public transport network, until July 2010, we have collected 1165 bus lines and 9618 bus stops of Beijing City (14 districts and 2 counties) as the sample data to build up a directed and weighted complex network model based on neighboring stops by applying the complex network theory. In this model, bus stops are considered as nodes of the complex network, while bus lines connecting two neighboring stops as edges. Consequently, the network has the topological properties of a complex network and meanwhile the nodes (bus stops) have clear geographic coordinates. The complexity of Beijing public transport is then verified through analyzing the topological properties of node degree, node strength, strength distribution, average shortest path, clustering coefficient in the complex network. We find that the distributions of node degrees and node strengths are extremely uneven and the cumulative strength distributions of the top 5% and 10% nodes reach 22.43% and 43.02% respectively. The results also show that the node strength, ordinal number and cumulative strength distribution of the nodes all follow the power-law distribution, showing the network characteristics of scale-free and small world. Some "key nodes" play an important role in network connection. We find two kinds of "key nodes" by using high carrying pressure node analysis and extract regional central analysis. These rules provide new references for optimizing the urban transport network, managing traffic congestion and planning and developing the traffic.
Method of identifying the relative position between standing wave of laser light and substrate in atom lithography
2012, 61 (19): 190601. doi: 10.7498/aps.61.190601
Standing wave of laser light acts as an array of lenses to focus the moving atoms in atom lithography. The position between standing wave and substrate plays an important role in determining the quality of depositional nanometer lines. Using the rule of Gaussian beam, a method of accurately identifying the position of standing wave of laser light is reported. By adjusting accurately the displacement stage which carries the beam focus lens and reflective mirror, the laser beam is subsequently shielded by depositional substrate. Signal of photoelectric detector is changed because of shielding the standing wave, so we can convert the displacement of standing wave into electrical signal. Positioning the standing wave against substrate is achieved by using the value of waist diameter of standing wave of laser light. Theoretical model is developed according to the experimental process. The result of numerical computation coincides well with the experimental record. This method realizes accurately positioning standing wave of laser light against substrate, and it provides the experimental basic for deeply studying the influence of the distance between standing wave and substrate on the quality of depositional nanometer lines.
2012, 61 (19): 190701. doi: 10.7498/aps.61.190701
Higher fracture probability appearing in InSb infrared focal plane array (IRFPA) subjected to thermal shock test, restricts its final yield. In order to understand the fracture mechanism, in light of the proposed equivalent method, where a 32× 32 array is employed to replace the real 128× 128 array, to a three - dimensional structural model of IRFPA is developed by taking into account the temperature dependence of thermal expansion coefficient, anisotropic mechanical strength of InSb chip, damaging effects of the surface of the InSb chip, and a reduction of 90% the out-of-plane elastic modulus. Simulation results show that a maximum Von Mises stress appears in the N electrode zone in InSb chip, and the extremum values present a non-continuous distribution. This means that the cracks is most likely to emerge in the region of N electrode, besides, the number of crack tracks is more than one. These are well consistent with the 128× 128 InSb IRFPA fracture statistics results under thermal shock test. All these are beneficial to the further study of fracture inducing factors and structural reliability design of InSb IRFPA.
2012, 61 (19): 192901. doi: 10.7498/aps.61.192901
The SiO2-B2O3-Al2O3-Gd2O3 system based samples doping with rare earth Ce3+ ions (cations) are synthesized by high-temperature melting method. The effects on their density, transmission and scintillating properties are investigated. The results indicate that all the samples, especially those that have high densities, have good physical properties. The emission peak wavelengths of all samples excited by X-ray are at 390 nm. Increasing the concentrations of Ce3 + and Gd3+ ions has a positive effect on luminescence properties. However, when the concentration of Ce3+ ions arrives at 1 mol%, with the increase of the concentration of Ce3+, the emission peak decreases. When Gd3+ ions concentration reaches a certain value scintillating properties decreases with Gd3+ ion concentration increasing. The X-ray-induced luminescence intensity of the sample of SBAG4 is about 90% that of BGO crystal. Gd3+ ions can sensitize the luminescence of Ce3+, the best concentration of Ce3+ ions is 1 mol% and the best concentration of Gd3+ ions is 15 mol%. These samples are attractive for some physical applications.
ATOMIC AND MOLECULAR PHYSICS
The study of dielectronic recombination (DR) rate coefficient for ground state of Ne-like isoelectronic sequence ions
2012, 61 (19): 193101. doi: 10.7498/aps.61.193101
The dielectronic recombination (DR) rate coefficients for Ne-like isoelectronic sequence ions in the ground state 2s22p6 are calculated by using relativistic configuration interaction (RCI) method over a wide temperature ranging from 0.1EI to 10EI where EI is the ionization energy of corresponding Na-like ion. The (2s2p)73ln'l', (2s2p)74l4l' and (2s2p)74l5l' complexes are considered as autoionizing doubly excited states of Ne-like ions in the calculation. The contribution of (2s2p)73ln'l' complex with l' >8 is found to be negligible. The contribution of high Rydberg states of (2s2p)73ln'l' complex obeys the complex-complex n'-3 extrapolation, and the larger the nuclear charge, the smaller the value of n' is. On the basis of the detailed level-by-level results, a general analytic formula for the total DR rate coefficient for all the ions along the Ne-like isoelectronic sequence is constructed. This formula can generally reproduce the calculated DR rate coefficients within 2% for electron temperature between 0.1EI and 10EI. Burgess-Merts semiempirical formula is found to be inadequate for predicting the DR rates of Ne-like ions at low electron temperatures (kTeEI) and may be used for high electron temperatures (kTe > 2EI).
2012, 61 (19): 193102. doi: 10.7498/aps.61.193102
In recent years, many theoretical and experimental researches have reported that different atoms doping TiO2 is one of the effective methods to reduce the gap. In this paper, the band structure, density of states and optical property of C-Zn co-doped rutile TiO2 are studied by the plane-wave ultrasoft pseudopotential method based on the first-principles density functional theory. The calculations show that C-Zn co-doped TiO2 results in the conductor band apparently shifted down to the Fermi level. Some impurity energy levels of co-doped TiO2 are below the conduction band minimum, and others are above the valence band maximum. The distance between them narrows down, which results in the redshift of the optical absorption edges to visible-light region. These impurity energy levels can reduce the recombination rate of photoexcited carriers and improve the photocatalytic efficiency of TiO2. Besides, the optical absorption coefficient becomes larger in visible-light region and the energy loss decreases clearly.
2012, 61 (19): 193201. doi: 10.7498/aps.61.193201
The M X-ray spectra of Ta induced by H+, He2+, Ar11+ and Xe20+ are measured in Heavy Ion Research Facility in Lanzhou. The intensities of M (M3N5) and N (M4,5N6,7), i.e. I and I, are also derived from the spectra. It is found that the intensity ratio of I/I increases with the increase of projectile atomic number. The results show that the M3-subshell fluorescence yield 3 of Ta target is greatly enhanced, owing to multiple ionization effect in collision with heavy ions.
2012, 61 (19): 193301. doi: 10.7498/aps.61.193301
Depletion of atmospheric ozone layers is more and more serious. Alkyl halides dissociate under the solar UV radiation with the product of free halogen atoms, which greatly damages the ozone layer and is the main culprit for the depletion of ozone layers. In this paper, methyl iodide is chosen as a calibration system of velocity map imaging. Velocity map images of iodine atom I (2P3/2) at different focus voltages are obtained in the dissociation of methyl iodine under an UV radiation of ～266 nm by techniques of velocity map imaging and REMPI (Resonance Enhanced Multiphoton Ionization). The magnification factor N of velocity map imaging system is measured to be 1.13. Photodissociation dynamics of 1, 4-C4H8BrCl under an UV radiation of ～234 nm is investigated on this velocity map imaging system. The speed and angular distributions of the fragments Br(2P3/2) and Br* (2P1/2) atoms in the dissociation are obtained and analyzed. Experimental results suggest that the dissociation of 1, 4-C4H8BrCl to both Br(2P3/2) and Br* (2P1/2) atoms under an UV radiation of ～234 nm happens promptly along the C-Br bond via repulsive surfaces after excitation. The anisotropy coefficient values are obtained from angular distributions of imaging of the fragments Br (2P3/2) and Br* (2P1/2) atoms, by which the ratio between perpendicular transition and parallel transition for those two dissociation channels are calculated. In addition, photodissociation mechanisms of CH2BrCl, 1, 2-C2H4BrCl, 1, 3-C3H6BrCl and 1, 4-C4H8BrCl at an UV radiation of ～234 nm are compared, and the dependences of dissociation mechanisms of dihalogen alkyl compounds on size of the alkyl radical are obtained.
The ladder three-level system including ground state, excited state and high excited state is investigated by using the density matrix equations. The coherence effect of ladder three-level system is analyzed, and absorption and dispersion curves of weak probe laser are obtained. The effects of interaction between high excited atoms and external electric field on the coherence effect are also investigated. The result shows that the interaction between high excited atoms or the external field can make the absorption curve and the dispersion curve shifted.
2012, 61 (19): 193601. doi: 10.7498/aps.61.193601
Using density functional theory and non-equilibrium Green's function technique, we investigate the magnetic and quantum transport properties of Tan(B3N3H6)n+1 (n ≤ 4) clusters. The results show that these clusters have sandwich structures as the ground states and their stabilities are all very high, and that the total magnetic moment increases linearly with cluster size increasing. When these sandwich clusters are coupled to Au electrodes, the Au-Tan(B3N3H6)n+1-Au system could exhibit high spin-filter capability under finite bias voltage and can be viewed as a new kind of low-dimensional spin filter.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2012, 61 (19): 194201. doi: 10.7498/aps.61.194201
Split ring resonator arrays are difficult to achieve miniaturization because of their big sizes, while complementary split ring resonators are easy to damage the other parts of the microwave circuit because it is etched on the ground layer. In order to solve these problems, a novel double-layer dielectric composite right/left-handed transmission line structure is proposed and its equivalent relative permittivity and permeability are calculated. Then the influence of dimension parameters of this novel structure on transmission characteristics is analyzed. Finally two dual-band bandpass filters are designed and fabricaled by applying a new Minkowski fractal curve to this structure, and meanwhile the dual-band characteristic of this composite right/left transmission line is demonstrated.
2012, 61 (19): 194202. doi: 10.7498/aps.61.194202
From the angular spectrum theory of beam, we obtain a transmission model in the paraxial approximation which describes the spin Hall effect of light, and we use this model to analyze the cross-polarization characteristics in spin Hall effect of light. By analyzing the change of cross-polarization intensity and incident angles we find that the spin splitting in spin Hall effect of light becomes stronger when cross-polarization effect is stronger. In order to facilitate the experimental observation, we choose the incident angle near the Brewster angle where it's spin Hall effect of light is much more evident, and from where we observe a strong cross-polarization effect. If we increase the cross-polarization components and reduce the light of original polarization direction at the same time, the spin Hall effect of light can be greatly enhanced. This is a promising method to develop new optical devices based on spin Hall effect of light.
2012, 61 (19): 194203. doi: 10.7498/aps.61.194203
Time lens based on cross phase modulation can realize accurate quadratic phase modulation. However, its application in optical pulse compression is restricted by the pump pulse with a high peak power. The formula of the peak power is deduced. It is proposed to use an output fiber with positive dispersion to lower the high peak power requirement for the pump pulse. It is also proposed to use a 4f system which consists of two time lenses to realize optical pulse compression, thereby more effectively lowering the peak power of the pump pulse. The formulas of the peak power and the resolution of the 4f system are deduced. The optical pulse compression is simulated and analysed. The research results demonstrate that in a 4f system based on cross phase modulation, femtosecond pulses can be generated by using pump pulses with small peak power; With compression factor increasing, the pulse width of the output pulse is restricted mainly by the solution of the 4f system. The method of improving the solution of the 4f system is discussed.
2012, 61 (19): 194204. doi: 10.7498/aps.61.194204
Effective fusion method of remote sensing multispectral and panchromatic image must ensure maximizations of spectrum and space information. Using the fusion algorithm framework with combining HIS transformation and wavelet transform (HIS-wavelet), in this paper we propose a new method to extract high frequency coefficients and a new multispectral and panchromatic image fusion method by using multi-objective particle swarm optimization (MOPSO) algorithm. According to the physical characteristics that the edge information in the high frequency has the nature of direction and noise points in the high frequency are generally isolated, a high frequency coefficient extraction method based on Gauss first order differential is proposed. The final resulting image is optimally combined by two images obtained by using different fusion rules in HIS-wavelet. Multiple fusion evaluation indicators are used as object functions and the MOPSO algorithm is used to find the optimal weights. The experiments on TM multi-spectral image and SPOT panchromatic image are carried out. Experimental results demonstrate that the improved method has a better improvement in spectral and spatial information. At the same time, the resulting image which is obtained using MOPSO algorithm has obvious advantages in retaining the spectral information and the spatial information is also greatly improved.
A novel simple fiber nonlinearity suppression method in fiber-optic transmission systems using an all optical phase pre-emphasis
2012, 61 (19): 194205. doi: 10.7498/aps.61.194205
In this paper we propose, simulate and experimentally verify a novel and simple optical phase pre-emphasis method, which is capable of mitigating fiber nonlinearity in dense wavelength division mult-DWDM optical translation systems. In our simple method, each transmitted wavelength is modulated by a phase modulator driven by a periodic parabolic electric driving signal. Both of the simulations and experimental results verify that the proposed method can effectively mitigate the fiber Kerr nonlinearity.
Pair coherent state evolutions through parametric frequency conversion and the realization of quantized vortex states
2012, 61 (19): 194206. doi: 10.7498/aps.61.194206
The pair coherent state evolution during a parametric frequency conversion is analyzed. And the wavefunction of the evolving pair coherent state in configuration space is obtained. It is found that the state may become a modified Bessel-Gaussian vortex state with topological charge index q which is a new non-Gaussian state. In coherent state representation such a modified Bessel-Gaussian vortex state is an eigenstate of sum of squared two-mode annihilation operators a2 + b2. The result obtained in this paper provides a new scheme for generating quantized vortex states in experiment with currently available technology.
The theoretical study on abnormal experimental phenomenon of the elongated rod Nd:glass pulsed laser
2012, 61 (19): 194207. doi: 10.7498/aps.61.194207
According to the principle of laser and a large number of experimental data proved and also considering the influence of the ignored spontaneous emisson, we study the abnormal phenomenon that the Nd: glass rod which was longer than the optical pump cavity is optically amplified without pumping. The theoretical result is almost the same as experimental result.
2012, 61 (19): 194208. doi: 10.7498/aps.61.194208
The absorption spectrum of NO is analyzed in a range of 12530-12850 cm-1 using optical heterodyne concentration modulation spectroscopy in an AC glow discharge of He/NO mixture. Among all the spectral lines, 324 lines are assigned to the (4, 0) band and 267 ones are fitted to the Hamiltonians of the b4Σ--a4Πi system by a non-linear least-square fitting procedure. A residual (0.0071 cm-1) comparable to system error (0.0071 cm-1) is obtained. The main molecular constants are consistent with those reported in the literature and the fine structure constants are fitted.
2012, 61 (19): 194209. doi: 10.7498/aps.61.194209
According to the nonlinear coupled equation under the joint action of Raman scattering and parametric amplification when the optical pulse propagats in the birefringent fiber, based on Lorentzian model of parallel Raman gain spectrum, the gain spectrum is obtained by combining Raman scattering and parametric amplification when the pump wave polarization direction is along the two orthogonal birefringence axes. The gain spectrum is discussed as a function of input parameters (input power, the group velocity mismatch) in different dispersion regimes. The result shows that the balance between non-linearity and dispersion is destructed by Raman scattering. Stokes and anti-stokes gain spectrum are asymmetric because of Raman effect. The structure of gain spectrum is confirmed when input power is constant. The intensity and width of gain spectrum change with dispersion and nonlinear parameter.
2012, 61 (19): 194210. doi: 10.7498/aps.61.194210
The dispersion characteristics of photonic crystal fibers are computed using the multipole method. Single-mode fiber with three zero-dispersion wavelengths is obtained by properly designing fiber structure parameters. The dispersion characteristics of photonic crystal fiber with a small air hole in the core are analyzed. Fibers with four zero-dispersion wavelengths are designed. The variation rules of zero-dispersion wavelength with fiber structure parameter are found. The locations and spacings of the zero-dispersion wavelengths can be adjusted flexibly in a large wavelength range. Closing to zero and flattened dispersion can be obtained in the fibers with multiple zero-dispersion wavelengths. The multiple zero-dispersion wavelengths can create a rich phase-matching topology, and enable better controlling the spectral locations of the four-wave-mixing and resonant-radiation bands emitted by solitons and short pulses.
2012, 61 (19): 194211. doi: 10.7498/aps.61.194211
The streak cameras which with an internal or external microchannel plate (MCP) image amplification has a significant enhancement on the detect signal threshold, but also induces the saturation effect of MCP to limit the dynamic range of streak camera. The saturation effect of MCP is described through the channel multiplier model of a discrete resistance capacitance dynode chain, explaining that the input output linear range of MCP which in both the two amplification method is depend on the charge restored in the channels the contribution of compensate effect which comes from the bias current is very limited, even using a low restistance MCP in the external method streak camera, so the streak cameras with an internal and external MCP image amplification should have equivalent dynamic range, low resistance MCP only function if a rapid sequence shots is required, and MCP gain was set up properly is critical for the dynamic range of streak camera.
Generation of photonic microwave based on the period-one oscillation of an optically injected semiconductor lasers and all-optical linewidth narrowing
2012, 61 (19): 194212. doi: 10.7498/aps.61.194212
Based on the single period dynamics of optically injected semiconductor laser, the generation of photonic microwave and its linewidth narrowing effect by introducing optical feedback are experimentally demonstrated. The experimental results show that the photonic microwave frequency can be continuously and widely tuned in a range of several ten GHz by adjusting the injection parameters. By introducing an optical feedback and properly adjusting the feedback strength, the photonic microwave linewidth is reduced by about two orders of magnitude from a range of 40-100 MHz to a range of 300-900 kHz. The influence of optical feedback length on the microwave linewidth is not obvious except that the photonic microwave frequency exhibits an periodical variation in a small range when the feedback length is finely varied in a small range.
2012, 61 (19): 194301. doi: 10.7498/aps.61.194301
In this paper, we study the propagation of elastic longitudinal wave in one-dimensional (1D) finite periodic phononic crystal with exponential section, and obtain the expression of frequency response function. Comparing the 1D phononic crystal with constant section, we find that the value of attenuation inside the band gap decreases quickly as the cross-sectional area of output and increases, at the same time, the initial frequency decreases and the cut-off frequency increases, i.e. the width of the band gap will increase. The effects of the lattice constant and the filling fraction on band gap are also analyzed. The change trends of the initial frequency and cut-off frequency are consistent with those of constant section. We hope that the investigation of this paper will be helpful for the phononic crystal in practical application such as vibration shield.
2012, 61 (19): 194302. doi: 10.7498/aps.61.194302
The radiation impedance expressions of flexural vibration rectangular plate with simply supported boundary are derived, and the numerical results are obtained by using the Gauss numerical integral method. Some conclusions can be obtained on the basis of the curves of relative radiation impedances versus frequency in the different modes and those corresponding to different aspect ratios. The lower the mode, the greater the radiation impedance in the low frequency is, so are the acoustic radiated power and the quality with vibration. For a rectangular plate of certain area and mode, the more the value of r (r = a/b, aspect ratio) approximates to 1, that is, the closer the square is, the greater the radiation resistance and the radiation reactance are. The method offers a reference for determining magnitude of the radiation impedance of the rectangular plate in other complicated boundary conditions (they may be no analytical displacement solutions). The method of calculating the radiation impedance of flexural vibration can be naturally transplanted into the case of piston vibration.
2012, 61 (19): 194303. doi: 10.7498/aps.61.194303
Based on the model for the one-dimensional coupled oscillation of bubble-liquid column in tube, a theoretical investigation of the forced oscillation of a cylindrical gaseous bubble in a microtubule is presented. For the case that the two acoustic pressures of microtubule ends are not homogenous, the linear natural frequency is not affected, but its oscillating amplitude is influenced by the effective acoustic pressure amplitude. The relations between the amplitudes of fundamental, third and one third harmonic oscillations and the acoustic frequency are analyzed using the succession-level approximation method. Numerical results show that the bubble oscillates nonlinearly if the effective value of acoustic pressure exceeds 0.1MPa. It is found that the amplituds of fundamental, third and one third harmonic oscillations are multivalued, and the response of third harmonic oscillation is stronger in the region of lower frequencies. Furthermore, the third harmonic oscillation may be probably induced in the region of ω/ω0 ≥ 1.
Lyapunov-Schmidt reduction and singularity analysis of a high-dimensional relative-rotation nonlinear dynamical system
2012, 61 (19): 194501. doi: 10.7498/aps.61.194501
The dimensionality reduction and bifurcation of some high-dimensional relative-rotation nonlinear dynamical system are studied. Considering the nonlinear influence factor of a relative-rotation nonlinear dynamic system, the high-dimensional relative-rotation torsional vibration global dynamical equation is established based on Lagrange equation. The equivalent low-dimensional bifurcation equation, which can reveal the low-dimensional equivalent bifurcation equation between the nonlinear dynamics and parameters, can be obtained by reducing the dimensionality system using the method of Lyapunov-Schmidt reduction. On this basis, the bifurcation characteristic is analyzed by taking universal unfolding on the bifurcation equation through using the singularity theory. The simulation is carried out with actual parameters. The parameter region of torsional vibration and the effect of the parameters on the vibration are discussed.
2012, 61 (19): 194502. doi: 10.7498/aps.61.194502
In the process of indoor pedestrian evacuation, the game between pedestrians greatly influence evacuation efficiency. In this paper, we introduce the boycott strength into the updated game strategy coefficient in order to investigate the influence of boycott strength on the evacuation efficiency. The relations between the evacuation time and boycott strength for different pedestrian densities and exit widths are obtained by numerical simulations based on cellular automaton model. The results show that the vying behaviors are extremely easy to spread and the crowd will turn into a vying state when the boycott strength is small. When the pedestrian density is low and the exit is wide, we encourage the pedestrians to imitate the winners to update their game strategies via offering the information about standardizing roles about rapid evacuation. When the pedestrian density is high and the exit is narrow, the information about standardizing roles about avoiding to congestion is provided. Thus, the evacuation efficiency can be enhanced. Finally, the optimal boycott strength corresponding to the shortest evacuation time in different conditions is yielded. Our study provides a new perspective to enhance the efficiency of indoor pedestrian evacuation.
2012, 61 (19): 194701. doi: 10.7498/aps.61.194701
The dispersive periodic structures are simulated by the split-field finite difference time domain (FDTD) method. According to the Floquet theorem, a set of auxiliary elements are introduced into the FDTD iteration to deal with electromagnetic simulation of oblique incidence on periodic structures, by combining the periodic and absorption boundary condition. We here extend the split-field method to the study of periodic dispersive structures by combining the Z transformation method. The iterative equations of the Drude dispersive model are also provided. By Comparing analytical and other numerical results, the efficiency and wide applicability of our method are demonstrated.
2012, 61 (19): 194702. doi: 10.7498/aps.61.194702
Short groove arranged in one-dimensional quasicrystal structure is designed by mechanical method in this paper and drag reduction experiments are performed by viscometer. The results show that there is a novel drag reduction effect compared with periodic structure of one-dimensional short groove, in which 12-fold quasicrystal structure of one-dimensional short groove has the best drag reduction, and has an equal effect compared with one-dimensional periodic groove structure. An two-dimensional grating model is proposed to investigate the mechanism. It is found that in comparison with two-dimensional periodic grating, the intensity spectrum of coherent wave passing through two-dimensional quasiperiodic grating has several characteristic structure factors. Corresponding to the quasicrystal structures of one-dimensional short groove, the quasiperiodic structure in spanwise direction can activate little disturbance on boundary layer and make the secondary vortex more uniform, which restrains the strong disturbance in spanwise, consequently reducing the drag.
Tunable negative refraction properties of photonic crystals based on silicon columns arranged in magnetic liquids
2012, 61 (19): 194703. doi: 10.7498/aps.61.194703
Tunable negative refraction of two-dimensional photonic crystal made of silicon cylinders hexagonally arranged in a MnFe2O4 magnetic liquid is studied. The plane wave expansion and finite-difference time-domain method are used to calculate and simulate its band structure, equi-frequency surface and negative refraction property. For the TE mode, the negative refraction of the two-dimensional photonic crystal made of the silicon column-magnetic liquid system can be tuned by a magnetic field. When the volume fraction of magnetic nanoparticles within the magnetic liquid and the frequency of the incident light are fixed, the deflection angle of the refraction light and the absolute value of the negative refractive index increase gradually with the external magnetic field increasing. When the volume fraction of magnetic nanoparticles within the magnetic liquid and the strength of the external magnetic field are fixed, the absolute value of the negative refractive angle and negative refractive index decrease with the normalized frequency of the incident light increasing. In addition, when the external magnetic field and the normalized frequency of the incident light are fixed, the negative refraction weakens with the increase of magnetic nanoparticle volume fraction of background solution.
Comprehensive Survey for the Frontier Disciplines
2012, 61 (19): 194213. doi: 10.7498/aps.61.194213
Polymer photovoltaic cells with organic polymer materials as the active layers for an increasing power conversion efficiency have become a research hotspot in the field of photovoltaic devices in recent years. In this paper, Internal mechanism of polymer/fullerene solar cells are elaborated exhaustively, including light absorption, exciton diffusion and dissociation and charge carrier transport as well as extraction. Furthermore, the optimization of device structure, morphology control and interface modification are introduced to improve performance of polymer/fullerene solar cells. Power conversion efficiency and the various structures which can be achieved are discussed in detail. The future prospects of polymer photovoltaic cells are also expected.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2012, 61 (19): 195201. doi: 10.7498/aps.61.195201
A U-shape plasma antenna is established by a 5—20 kHz alternating current(AC) source. The structure of the antenna is described, and part of electrical characteristics are measured. Results show that in a frequency range from 50 to 400 MHz, the noise level of 5—20 kHz AC plasma antenna is close to that of a metal antenna, but much lower than that of frequency AC plasma antenna. Besides, the antenna shows good impendance and gain bandwith characteristics.
Atmospheric pressure streamer and glow-discharge generated alternately by pin-to-plane dielectric barrier discharge in air
2012, 61 (19): 195202. doi: 10.7498/aps.61.195202
Performance of producing a high energy electron can be improved, if the glow discharge is generated in a system of dielectric barrier discharge. In this paper, different discharge modes of pin-to-plane dielectric barrier discharge are investigated in atmospheric pressure. Different discharge modes are observed in the positive half-period and negative half-period of the discharge. When and applied voltage is 3 kV, a streamer mode appear in the positive half-period and a corona (or Trichel discharge) mode occurs in negative half-period. When the applied voltage is 6 kV, a streamer emerges in the positive half-period and a micro glow discharge is present in the negative half-period. The micro glow discharge has hierarchical structure like that typical low pressure glow discharge produces. The generation of micro glow discharge is due to, enough strong cathode electric field strength and effective secondary electron emission process around naked negative electrode. The glow discharge transforming to arc discharge is avoided due to dielectric layer.
2012, 61 (19): 195203. doi: 10.7498/aps.61.195203
The knowledge of two-temperature transport coefficients over wide temperature and pressure range is essential to model the flow and heat transfer in plasma process. In this study, the plasma composition is calculated using the Saha equation and the transport coefficients are worked out using Chapman-Enskog method expanded up to higher approximation. The electron temperature Te is assumed to be different from that of heavy species Th. The evolutions of viscosity, thermal conductivity, and electric conductivity of helium plasma are presented in elctron temperature range from 300 K to 40 000 K. It is shown that the transport coefficients strongly depend on pressure and non-equilibrium parameter (θ= Te/Th). These values in local thermodynamic equilibrium state accord well with previously reported data.
2012, 61 (19): 195204. doi: 10.7498/aps.61.195204
The effect of cooling rate on layering the deuterium ice inside inertial confinement fusion (ICF)spherical cryotarget is studied by backlit shadowgraphy. Experimentally, the temperature of ice is first determined by the calibration of temperature field around ICF cryotarget. The solidification process of deuterium in the cryotarget is in- situ characterized by backlit shadowgraphy. The power-spectrum density of the bright ring in shadowgraphy at different cooling rates is obtained. Experimental results demonstrate that the step-gradient slow cooling is favorable for forming uniform fuel ice in comparison with the rapid cooling. Furthermore, the validity of characterizing the ICF cryotarget layering by the backlit shadowgraphy is also verified.
2012, 61 (19): 195205. doi: 10.7498/aps.61.195205
Implosion and radiation characteristics of conical wire array in different regimes of implosion are investigated at the 1 MA Qiangguang-1 facility by X-ray self-emission diagnostics. Experimental results show that the shape of precursor plasma is also conical. The initial implosion takes place near the cathode by a stronger Lorenz force, forming a triangle-like structure that produces harder X ray. The current crossing the bubble in the front of the wire array near the anode persists in persist ablating, thereby leading to a zippered stagnation. The initial implosion of a bubble near the cathode is followed by the implosion zippering upwards as the zipper implosion speed is 2.59 107 cm/s. The results shows that the conical array has a broader X-ray power pulse than cylinderical wire array due to the zippered stagnation and zippered implosion of the array. The study of implosion characteristics of specialized axis symmetric wire array Z-pinch-like conical wire array can provide a valuable test bed for understanding the regime of implosion as well as theoretical model and magneto-hydrodynamic (MHD) codes, both of which primarily develop for the modeling of cylindrical wire array Z pinches.
2012, 61 (19): 195206. doi: 10.7498/aps.61.195206
We do some research on E-H mode transition of inductively coupled plasma (ICP) in the interlayer chamber, using the microwave phase and plasma spectrum diagnotic technique. The mode transition between E and H mode is a sudden changes phenomenon. The input power of the transition varies as the pressure changes in the chamber. The transition power from H to E is less than from E to H, so the hysteresis in power hence is established. The change of the relative spectral intensity is basically the same the variation of the electron density with input power. We obtain a stable plasma source, with an electron density ranging from 3.85× 1011 cm-3 to 4.68× 1011 cm-3, an outer surface area of 0.3 m2, and a thickness of 2 cm.
2012, 61 (19): 195207. doi: 10.7498/aps.61.195207
The current within imploding multiwire tungsten arrays is measured using micro magnetic probes in the Qiangguang-1 facility at a current of 1.3 MA and rise time of about 70 ns. Difference in current distribution in multiwire arrays between with and without foam cylinder on the array axis is studied. Stable and reliable results are obtained for tungsten wire array Z-pinch with a wire diameter of 4.2 μm and an annular diameter of 12 mm. The results shows that the output of magnetic probe at a radius of 3.2 mm lags about 20 ns behind the discharge current pulse. After that, the ratio of inside current to the total current increases 20% within 20 ns and keeps steady for 30-40 ns. It is found that the foam cylinder has no appreciable influence on the inside current value in the initial stage of implosioin.
Experimental and theoretical studies on gas discharge and plasma oscillation at atmospheric pressure
2012, 61 (19): 195208. doi: 10.7498/aps.61.195208
The gas discharge and plasma oscillation between the electrodes of high-voltage alternating current arc generator are studied, and the nanosecond pulsed phenomenon in the gas discharge process is observed at atmospheric pressure. Electron accumulation phenomenon under the action of alternating electric field is described by using a function. Based on the equation of electron fluid motion and Maxwell equations, the discharge voltage between the electrodes is depicted theortically. Theoretical and experimental results are consistent with each other basically, and the electron density is estimated to be 1.3 1012/m3.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Spray-forming technology can produce billets with similar microstructure and higher productivity compared with the P/M process. The nickel based superalloy FGH4095 billet was produced by spray-forming with nitrogen as atomization gas. The pressure of the atomization gas and the temperature of the deposit zone were recorded. The compactness of the deposit was characterized by quantitative metallography and Archimedes method. The grain structure of substrate and the size and morphology of ' phase were observed. Results show that the density of the deposit produced by nitrogen spray forming reaches about 99% and little amount of pores with diameters about 12 m could be detected in the deposit matrix. While, pores could be enclosed by HIP and near iso-thermal forging process; Nitrogen was existed as carbonitride with diameters less than 1 m. The average grain size of the equiaxed grains in the interior of the deposit is about 2040 m, while the grains near the surface of the deposit are finer with average grain size about 13um; the primary ' phase which has diameters about 0.30.5 m possesses irregular block feature. The microstructure of the spray deposit is related to the temperature history of the alloy during the spray forming process.
The effects of different particle size Y2Ba4CuBiOy nanoparticles doped on the properties of single domain YBCO bulk superconductors by TSIG process
2012, 61 (19): 196102. doi: 10.7498/aps.61.196102
Single domain YBCO bulk superconductors are fabricated by the top-seeded infiltration and growth process(TSIG). The effects of different particle size Y2Ba4CuBiOy nanoparticles doped on the growth morphology, microstructure and levitation force of single domain YBCO bulk superconductors are investigated. The mean diameters of the initial Y2Ba4CuBiOy nanoparticles respectively are 283 nm, 170.4 nm and 82.5 nm, and the amount of Y2Ba4CuBiOyadded to Y2BaCuO5 is 2 wt%. The results show that the single domain YBCO bulk superconductors can be fabricated, and the surface of the sample has significant cross pattern and four single domain sectors become smooth and flat. The second phase Y2Ba4CuBiOy nanoparticles are well-distributed into the single domain YBCO bulk samples, and the particles sizes of Y2Ba4CuBiOy nanoparticles in the YBCO bulk sample are respectively 270 nm, 150 nm and 50 nm, smaller than that the initial powder. The magnetic levitation forces of the samples increase gradually with the decrease of initial powders of Y2Ba4CuBiOy nanoparticles, which are respectively 10 N, 17 N and 22 N. The results are very important for further studying the method of flux pinning of nanoparticles and improving the properties of YBCO bulk superconductors.
2012, 61 (19): 196103. doi: 10.7498/aps.61.196103
With feature size scaling down, the influence of crosstalk on single event effect becomes more important. In order to analytically describe the influence of crosstalk effect on single event transient (SET), based on the equivalent circuits of SET and 6-node template model for interconnects, by using defined four rules of point admittance to simplify the calculation, the analytical model for single event crosstalk (SEC) is deduced. Through differentiating and Taylor series expansion theorem, the expression for the peak value of crosstalk voltage is achieved. The simulation results show that the analytical model is well consistent with SPICE circuits and average relative error is 2.51%, and max error is 5.11%.
The structural transition of water at quartz/water interfaces under shock compression in phase region of liquid
2012, 61 (19): 196201. doi: 10.7498/aps.61.196201
We investigate the structural transformations of water at the water/quartz interface under shock compression in ranges from 0.5 to 2 GPa and from 335 to 375 K by techniques of a gas-gun and light transmission tests. The results show that the structural transformation of water occurs in the region of liquid phase, which starts from water/quartz interface at high pressures and temperatures. The transformation rate is related to the property of quartz interface. This structural evolution indicates that a lager number of water molecules undergone transitions in equilibrium behavior. The kinetic process of liquid water structure can be divided into four stages while the structure continues growing to saturation. This new mechanism of structural transformation has immediate implications for water structure transformation in diverse natural environments.
2012, 61 (19): 196202. doi: 10.7498/aps.61.196202
Planar shock compression experiments are performed on a Zr-based bulk metallic glass (BMG), Zr51Ti5Ni10Cu25Al9 at peak shock stresses from 10 GPa to 27 GPa to investigate its plastic behavior under high pressure and high strain-rate. The particle velocity profiles measured at the free surface of the samples are analyzed to estimate longitudinal stresses of the Zr-based BMG in the shock loading process,and then shear stresses are obtained by comparing longitudinal stresses with a hydrostat. Though there is an obvious relaxation effect after elastic front, the Hugoniot elastic limit of the Zr-based BMG is found to increase with shock stress increasing. However, the shear stresses across the plastic shock front display stress hardening above the Hugoniot elastic limit followed by a stress relaxation (softening) to Hugoniot state, and the relaxation level also increases with shock stress increasing. The changes of shear stresses under planar shock compression are consistent with the results from molecular dynamic simulations, but obviously different from the pressure-shear impact experimental results or uniaxial stress impact experimental results.
Effect of 4 GPa pressure treatment on the solid state transformation kinetics of T8 steel in heating process
2012, 61 (19): 196203. doi: 10.7498/aps.61.196203
The transformation temperatures and durations of solid state transformation in T8 steel before and after 4 GPa pressure treatment are measured using differential scanning calorimetry, and the transformation activation energy and Avrami exponent are also calculate. Then the effects of 4 GPa pressure treatment on solid state transformation kinetics in T8 Steel are investigated based on the kinetic parameters and the observation of microstructure. The results show that the solid state transformation in T8 steel shifts toward the low temperature region after 4 GPa pressure treatment. The high pressure treatment can reduce the phase transformation time and Avrami exponent and enhance the phase transformation activation energy, which is favorable for refining the grains but has little effect on the phase transformation mechanism.
2012, 61 (19): 196301. doi: 10.7498/aps.61.196301
During the past decade, a growing attention has been paid to the Lamb waves propagating in composite plates due to a variety of applications for nondestructive evaluation, vibration attenuation and Lamb wave sensors. We present a revised plane wave expansion method and a finite element method to study the large partial band-gaps of a multiple Lamb wave phononic crystal thin plate with a symmetric mirror plane The results show that lots of partial stopbands of lower-order Lamb waves exist and can be substantially enlarged by using multiple heterostructures which consist of several pieces of phononic crystal with different ratios of the thickness (H) to the lattice period (L). These contribute to good mode choice for lower-order Lamb waves, which is believed to have much significance for optimially choosing models in Lamb wave nondestructive test and the one-way Lamb wave mode transmission.
2012, 61 (19): 196401. doi: 10.7498/aps.61.196401
Spinodal decomposition and nucleation process are realized by using three transparent solutions: SCN-30 wt%H2O, SCN-50 wt%H2O, and SCN-80 wt%H2O, and the migration characteristics of minor phase droplets (MPDs) was investigated when uni-direction temperature field is applied. It is find that spinodal decomposition takes place in SCN-50 wt%H2O system and nucleation processes occur in SCN-30 wt%H2O and SCN-50 wt%H2O systems. The period during which the minor droplets of the same size in spinodal decomposition are formed is 1/3—1/2 of that in nucleation process. Moreover, the temperature interval in the system with critical composition is larger than those in other systems, therefore, the minor phase droplet formed in spinodal decomposition is longer than that in nucleation process. Under uni-direction temperature field conditions, the migration velocity of MPDs in SCN-80 wt%H2O system is measured experimentally. It is revealed that the experimental results agree well with the calculated Marangoni velocity, indicating that the Marangoni migration plays a key role in the motion of MPDs.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
First-principles calculations of optical and mechanical properties of LiBX2 (B= Ga, In; X= S, Se, Te)
2012, 61 (19): 197101. doi: 10.7498/aps.61.197101
First-principles calculations of optical and mechanical properties of LiBX2 (B= Ga,In; X= S,Se,Te) are performed using plane-wave pseudopotential method. According to the order of band gaps, the order of laser induced damage thresholds is LiGaS2 > LiInS2 > LiGaSe2 > LiInSe2 > LiGaTe2 > LiInTe2. The elastic constants of these crystals can all meet the mechanical stability conditions at normal pressure, and the plasticitics and ductilities of indium compounds are better than those of gallium compounds. Theoretical values of average static electronic dielectric constant ε1(0), average ordinary refraction index n0 and birefringence index Δn of these crystals are in good agreement with the experimental data. LiGaS2, LiInS2, LiGaSe2, LiInSe2 and LiGaTe2 compounds have the large birefringences and their absorption and reflectivity spectra are transmissible through mid- and far-IR region, so the five crystals are likely to be promising materials for nonlinear optical applications in the mid- and far-IR region.
2012, 61 (19): 197102. doi: 10.7498/aps.61.197102
The high-temperature lattice constants and elastic moduli of the silicon nitrides are calculated using the plane-wave pseudo-potential method combined with the vibrational Debye-like model. β-Si3N4 is ductile at low temperature and brittle at high temperature. γ-Si3N4 is found to be brittle and covalent in nature. We find a positive slope of the β→γ phase boundary, hence, at higher temperatures it requires higher pressures to synthesize γ -Si3N4. The α → γ phase boundary may be expressed as P=16.29-1.835-10-2 T+9.33945-10-5T2-2.16759-10-7 T3+2.91795-10-10T4. We also obtain the electronic structures and energy bands of Si3N4 with and without pressure. The interaction between Si-s, p and N-s, p plays a dominant role in the stability of α-Si3N4. The α- and β-Si3N4 have the ΓV-ΓC indirect band gaps (4.9~eV and 4.4~eV) while γ-Si3N4 has a direct band gap(3.9~eV). The tops of the valence bands for α- and β-Si3N4 are along the Γ-M and Γ-A direction, respectively. Our results are consistent with the experimental data and the theoretical results.
2012, 61 (19): 197201. doi: 10.7498/aps.61.197201
Bottom-gate junctionless thin-film transistors (TFTs) based on indium-tin-oxide (ITO) are fabricated at room temperature. Source/drain electrodes and channel layer are the same ITO thin films without source/drain junction formation, hence the fabrication process is greatly simplified and the fabrication cost is reduced. We employ electric-double-layer (EDL) SiO2 with large capacitance as the gate dielectric, and find that the drain current can be effectively modulated by the gate bias when the thickness of ITO film decreases to about 20 nm. These junctionless TFTs show excellent electrical performances with a small subthreshold swing of 0.13 V/dec, a high mobility of 21.56 cm2/V·s and a large on/off ratio of 1.3× 106. The performances of these junctionless TFTs do not show significant degradation even after 4 months in air ambient, the subthreshold swing is still 0.13 V/dec, the mobility slightly decreases to 18.99 cm2/V·s and the on/off ratio is still larger than 106. Such TFTs are very promising for the applications in low-cost low-power portable electronic products and novel sensors.
2012, 61 (19): 197301. doi: 10.7498/aps.61.197301
We investigate the relationships between the nonlinear Ramsey interference pattern of the angular frequency and system parameters of fermi superfluid gase in unitarity regime in three limited cases. We find that the interaction between fermions and the difference in energy between double-well potentials have a significant influence on the angular frequency of the interference pattern. Through numerical simulation and theoretical analysis, the relationship between angular frequency of the interference pattern and the system parameters is given, and the numerical simulations and theoretical analyses are in good agreement.
2012, 61 (19): 197401. doi: 10.7498/aps.61.197401
High-quality MgB2 films are fabricated via hybrid physical-chemical vapor deposition (HPCVD) and irradiated by Ti ions. Compared with the unirradiated film, the Ti-irradiated MgB2 film shows a high critical current density (Jc) in magnetic field and also a high upper critical field (Hc2), while the superconducting transition temperature (Tc) does not decrease significantly. The Ti-irradiated film with a best fluence at 1 1013/cm2 shows a high Jc of 1.72 105 A/cm2 in 4 T perpendicular field at a temperature of 5 K and a moderately decreased Tc at 39.9 K.
2012, 61 (19): 197501. doi: 10.7498/aps.61.197501
Electrochemical method is used to fabricate nano-fiber coating absorbent. The effect of the fiber length on electromagnetic property is analyzed. Radar absorbing coating is prepared preferentially. The measurements show that nano-fiber coating absorbent has good absorbing properties.
Phenomenological analysis for dielectric dispersion of donor doped barium titanate based relaxor ferroelectric
2012, 61 (19): 197701. doi: 10.7498/aps.61.197701
Dielectric dispersion of relaxor ferroelectric in diffusion region is related to the doping of extrinsic ions or ordering arrangement of intrinsic ions. The further explanation and unitive characterization of the dispersion property are required. Focusing on the facts that cation vacancies and dielectric dispersion in barium titanate based relaxor ferroelectric can be caused by donor doping in high concentration, three equivalently correlated Gaussian distributions of doping dopants, Curie temperature, and cation vacancy are obtained. The relevant Gibbs free energy and relation between dielectric constant and temperature of the relaxors with donor doping are deduced. The result demonstrates an increase in concentration of cation vacancy with temperature decreasing in diffusion transition region. The unipole charges caused by the cation vacancies are probably responsible for the dielectric dispersion and loss by their hopping motion.
2012, 61 (19): 197702. doi: 10.7498/aps.61.197702
Dielectric properties of three different CaCu3Ti4O12 ceramic samples sintered, respectively, in vacuum, air and oxygen are investigated. Three plateaus are detected in the dielectric temperature spectra within 10—300 K for all the three samples, meanwhile the three corresponding peaks of the real impedance and imaginary capacitance occur at a certain temperature. However, the sample sintered in vacuum presents a higher dielectric and clearer real impedance and imaginary capacitance peak, which indicates that oxygen concentration and oxygen vacancy have a great influence on the dielectric property of CaCu3Ti4O12. The results reveal that the three plateaus observed in the dielectric temperature spectra come from the grain, grain boundary and the oxygen vacancy sitting in grain boundary, respectively. The analysis of dielectric spectra indicates that the activation energy of the grain is related to the sintering atmosphere and the oxygen vacancy results in a variable-range-hopping conductivity and polarization for the grain. The activation energy of oxygen vacancy trapper is about 0.46 eV and is nearly independent of sintering atmosphere. The high dielectric constant at low-frequency or high temperature is caused by oxygen vacancy trapping carriers in CaCu3Ti4O12.
2012, 61 (19): 197703. doi: 10.7498/aps.61.197703
Using conventional solid-phase sintering technique combined with a special atmosphere controlling technique, KNN-based lead-free transparent ceramics, xBa(Sc0.5Nb0.5)O3-(1-x) (K0.5N0.5)NbO3 (xBSN-(1-x) KNN), are prepared and investigated. Their microstructure, dielectric performance, ferroelectric performance and optical transparency are investigated. The results show that such ceramics are each with a pseudocubic-Perovskite structure, without any other impure phase. Their grain size is comparable to the light wavelength and the grains are highly condensed without evident crystal borders. For x=0.05, the d33 reaches up to 110 pC/N maximally and the 2Pr =25.4 C/cm2. Moreover, such ceramics are each with an excellent transparency. Their optical transparency reaches about 54%, In the near-infrared wavelength 2500 nm, their optical transparency is near 83%. Such ceramics are a type of environment-friendly lead-free transparent ceramics which may be promising in replacing lead-based transparent ceramics.
2012, 61 (19): 197801. doi: 10.7498/aps.61.197801
On the basic of the synthesis of CdTe/CdS core/shell quantum dots (QDs) in aqueous phase, we study ultrafast carrier dynamic behaviors of CdTe/CdS QDs with different shell thicknesses, by using femtosecond time-resolved transmission spectroscopy. The results show that both the buildup time of the lowest exciton state and its following relaxation time become longer as CdS shell thickness increases. The results also indicate that the buildup rate of a space-separate exciton is slower than that of a space-overlapped exciton, and that carrier relaxation changes from surface-defect related mechanism into surface-passivated charge separation regime, which is consistent with steady-state absorption and photoluminescence experiments.
2012, 61 (19): 197901. doi: 10.7498/aps.61.197901
The blind holes processing experiment is conducted on the silicon under the radiation of a 355 nm nanosecond UV repetitive pulse laser. With the increase of the laser pulse number, the variations of the silicon morphology,the depth and aperture of the blind holes are observed, and the thermodynamic process of UV laser irradiating silicon is analyzed. The results show that the formation of the blind silicon hole in the laser ablation process is due to the interaction between thermal effect and force effect. Thermal effect results in fusion, vaporization and even producing laser plasma by ionization in silicon, which is essential to the removal of the material. The molten material is compressed by the plasma shock wave and the expansion of the high-temperature gaseous material,and then ejection outward, which will benefit the further ablation; the force propagates along the laser transmission direction,perpendicular to the silicon surface, so the removal parts are distributed mainly along the depth direction of the hole, reaching a high aperture ratio, which is up to 8:1 in our experiments. In addition, the laser-induced plasma also prevents the effect of laser on the target surface, and with the increase of hole depth, laser defocusing occurs. The two aspects finally restrict the ablation depth. The results shows that in the process of laser irradiation on the material, the ablation efficiency is much higher when the former 100 pulses arrived than the sequent laser pulses.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2012, 61 (19): 198101. doi: 10.7498/aps.61.198101
In this paper, an a-Si/Ge thin film with a buried layer of Ge and an a-Si thin film are prepared on Si substrates at a temperature of 500 ℃ by magnetron sputtering. The prepared films are annealed for 5h at different temperatures in vacuum. The annealed films are characterized by Raman scattering, X-ray diffraction, atomic force microscope and field emission scanning electron microscope. The results reveal that Ge can induce amorphous Si (a-Si) growing at a temperature of 500 ℃ by magnetron sputtering crystallize after annealing at a temperature of 600 ℃ for 5h. And in the a-Si/Ge thin film the degrees of crystallization of a-Si are 44% and 54% at the annealing temperatures of 600 ℃ and 700 ℃, respectively. By comparison, a-Si thin film without Ge is crystallized at an annealing temperature of 800 ℃ for 5h and the degree of crystallization is 46%. The crystallization temperature of a-Si/Ge is reduced by 200 ℃ compared with that of a-Si film without buried Ge layer in the film. The prepared poly-Si thin film possesses high Si(200) orientation with a grain size of 76 nm. The preparation of poly-Si film by Ge-induced crystallization might be a useful technology for developing high-quality poly-Si film.
2012, 61 (19): 198102. doi: 10.7498/aps.61.198102
CuInS2 thin films are deposited on Pyrex slide glass substrates by direct current triode sputtering using CS2 as a reactive gas and Cu/In mixed metal plate as sputtering target. The effects of substrate temperature and area ratio of Cu to In on the crystalline structure and composition of CuInS2 films are discussed under the same growth condition (0.02 Pa of CS2 partial pressure). When sputtering time is 2 h, their thickness are obtained to be 1-2 μm. The CuInS2 films are characterized by EPMA, XRD, and so on. The results show that the optimal CuInS2 films are obtained at a ratio of 1.4 and growth temperatures of 150 ℃, 250 ℃ and 350 ℃, and that these films each have a chalcopyrite structure. The content of carbon impurity in each of the as-deposited CuInS2 films is found to be about 8.9%.
Effects of pulsed magnetic field on Mn-doped ZnO diluted magnetic semiconductor prepared by hydrothermal method
2012, 61 (19): 198103. doi: 10.7498/aps.61.198103
In this study, zinc acetate, manganese acetate, ammonium hydroxide and ammonium chloride are used as the source materials to prepare crystalline Mn-doped ZnO diluted magnetic semiconductor by hydrothermal method under a 4 T pulsed magnetic field. The microstructures, morphologies and magnetic properties of the samples are characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman scattering spectra, Photoluminescnce and vibrating sample magnetometer. The effect of pulsed magnetic field on the microstructure and magnetic property of the Mn-doped ZnO diluted magnetic semiconductor are discussed. The result indicates that all the samples are still of hexagonal wurtzite structure. The pulsed magnetic field promotes the crystal growth, and improves room temperature ferromagnetism. The saturation magnetization (0.028 emu/g) of the sample fabricated under 4 T pulsed magnetic field is more than two times that of the sample synthesized without pulsed magnetic field. The Curie temperature (Tc) of the Mn-doped ZnO increases 15 K through the pulsed magnetic field processing.
Effect of electromigration on interfacial reaction in Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P flip chip solder joints
2012, 61 (19): 198104. doi: 10.7498/aps.61.198104
The effect of electromigration (EM) on the interfacial reaction in the Ni/Sn3.0Ag0.5Cu/Au/Pd/Ni-P flip chip solder joint is investigated under a current density of 1.0× 104 A/cm2 at 150℃. The (Cu,Ni)6Sn5 intermetallic compounds (IMCs) form at both solder/Ni and solder/Ni-P interfaces in the as-reflowed state. During aging at 150℃, the (Cu,Ni)6Sn5 interfacial IMCs grow thicker and transform into (Ni,Cu)3Sn4 type after 200 h at solder/Ni interface and 600 h at solder/Ni-P interface, respectively. During EM, the current direction plays an important role in Ni-P layer consumption. When electrons flow from Ni-P to Ni, EM enhances the consumption of Ni-P, i.e., the Ni-P s completely consumed and transforms into Ni2SnP after EM for 600 h. There is no Cu-Sn-Ni ternary IMC at the solder/Ni-P interface (cathode). Crack forms at the Ni2SnP/Cu interface due to the weak bonding force between Ni2SnP and Cu. When electrons flow from Ni to Ni-P, no obvious consumption of Ni-P is observed during EM; the current crowding effect induces a rapid and localized dissolution of Ni UBM and Cu pad at the chip side (cathode). The dissolved Ni and Cu atoms are driven along the flowing direction of electrons and form a large number of IMC particles in the solder matrix. During EM, the (Au,Pd,Ni)Sn4 phase prefers to be redistributed only at the anode interface, regardless of the direction of electron flow.
2012, 61 (19): 198701. doi: 10.7498/aps.61.198701
Circadian rhythm makes physiology and behaviors of organisms adapt to the day and night cycle in the environment. Recent experiment indicated a PER-TIM interval timer in Drosophila melanogaster cytoplasm. In this paper, we present a possible mathematical model for this interval timer. The characters of the model are the formation of big clusters, fast exchange and different functions of phosphorylation of different sites. The experimental results on features of the PER-TIM interval timer of mild type and perL mutant and on the existence of three different types of temporal profiles of nuclear accumulation of PER and TIM in single cells are reproduced by our simulations.
Research on sodium incorporation methods of growing Cu(In-Ga)Se2 thin film by low-temperature deposition
2012, 61 (19): 198801. doi: 10.7498/aps.61.198801
Sodium is proved to be able to improve the performance of Cu(In,Ga)Se2 solar cell grown on flexible polyimide substrate by a low-temperature deposition. Different sodium incorporation methods affect the film in different ways. Comparing the deposition of a NaF precursor with post deposition NaF treatment, different mechanisms can be found. In NaF precursor approach, Na is available during the Cu(In,Ga)Se2 growth and acts as a surfactant at the grain boundary which adds up an energy barrier for adatom to across. Thus, a small grain size as well as double-peak reflection pattern can be observed and the formation probability of donor defects is reduced. In post deposition NaF treatment, incorporation of NaF does not affect the growth and microstructure but passivates donor defects in the Cu(In,Ga)Se2 film. Moreover, according to the experimental results, external energy assistance is necessary during NaF incorporation through post deposition treatment. It is verified that Na incorporation is able to improve the properties of the film effectively when substrate temperature reaches above 350 ℃. Finally, the conversion efficiency of flexible Cu(In,Ga)Se2 thin film solar cell on polyimide substrate is achieved to be 10.4% by optimizing the sodium incorporation.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
A mechanism analysis of the interdecadal precipitation change in Northwestern China for the last 30 years of twentieth century
2012, 61 (19): 199201. doi: 10.7498/aps.61.199201
There took place an inter-decadal climate change over the west part of Northwestern China at mid-1980s. One of the significant characteristics is the increase in precipitation with more extreme rainfall or snowfall event. For understanding its mechanism our calculation focuses on the difference of the geo-potential height on 500 hPa, transient eddy activity, column water vapor content or precipitable water, moisture transport and its divergence between 1987-2000 and 1973-1986. The results show that the change in height field is favorable for the increase in moisture transport to the region with moisture convergence, leading to more water vapor over the region. Meanwhile the eddy activity became weak in wintertime and strong in summertime, leading to more synoptic processes in summertime and less in wintertime. A further decomposition shows that the increase in the transport with convergence was contributed mainly by its stationary-wave part along the west-east direction, while the transient eddy played a positive role in summertime and a negative one in wintertime for precipitation. It turns out that the increase in precipitation in the region resulted from the moisture convergence and the increase in eddy activity in summertime while the moisture convergence played a dominant role in wintertime. Besides, the warming climate also played a positive role in increasing air water-vapor content in the region since the warm air can hold more water vapors than the cold one.
2012, 61 (19): 199202. doi: 10.7498/aps.61.199202
In the moist lower troposphere, traditional phase-locked loop tracking of GPS (Global Position System) signal will introduce errors in the retrieved results. Both internal and external method can be used to remove navigation data modulation (NDM) and accurately recover the phase of GPS signals recorded in open-loop mode. The internal method removes the NDM using relationship between adjacent samples, while the external method removes the NDM using the externally recorded NDM bit data. Both above-mentioned methods are used to process the constellation observing system for meteorology, ionosphere and climate (COSMIC) radio occultation data. COSMIC case study shows that internal method may include half-cycle slip in the recovered phase, which will lead to error in the retrieved refractivity. About 3130 COSMIC radio occultation soundings recorded in open-loop mode are processed by the internal and external method, and statistical comparison results of retrieved refractivity with that from the European Centre for medium-range weather forecasts (ECMWF) analyses show that the external method has a better penetration ability than the internal method in the lower moist troposphere. The mean of fractional difference in refractivity retrieved by external method is smaller than that by internal method below about 3 km.
2012, 61 (19): 199203. doi: 10.7498/aps.61.199203
Ensemble prediction is an effective approach to accounting for uncertainties of initial conditions and model error. By combining the predictability of extended-range, both predictable components and unpredictable random components with different characteristics are treated with different ensemble prediction schemes and strategies. A new predictability-based extended-range ensemble prediction method (PBEP) is proposed. In this method, for predictable component, the uncertainty of model is taken into account through the use of multiple error correction scheme; while the random component probability distribution is obtained from the climate probability distribution of historical data, for the sake of avoiding the influence of model error. Prediction results show that the ensemble prediction method can improve the forecast skill in all regions of the world, and the extents of improvement are different for waves with different spatial scales compared with the operational dynamical extended-range ensemble prediction system of NCC/CMA, exhibiting its potential application perspective to operational extended-range prediction.
Raytracing of extreamely low frequency waves radiated from ionospheric artificial modulation at low latitude
2012, 61 (19): 199401. doi: 10.7498/aps.61.199401
Powerful high-frequency radio waves modulated at extremely low frequency (ELF) and very low frequency (VLF) can efficiently modify the lower ionospheric current which can act as an equivalent ionospheri'c antenna for the generation of ELF/VLF wave and these signals can propagate into the magnetosphere and the investigation of the propagation properties is of significance for understanding of radiation belt energetic electrons precipitation. In this paper, based on the raytracing theory, the ray paths of ELF waves in the magnetosphere are obtained using numerical modeling and the properties are analyzed. The results shows that the ELF waves generated from the low latitude reflect between the southern and northern hemisphere and propagate to the farther place gradually. For the signals with different frequencies, the higher their frequencies, the shorter their propagation distances are, the lower their frequencies, the longer their propagtion distances are. In the process, ELF waves tend to reflect near a fixed region. The normal angel increases to 90° gradually and ray direction tends to propagate along the direction of geomagnetic field.