Vol. 62, No. 9 (2013)
2013-05-05
GENERAL
2013, 62 (9): 090201.
doi: 10.7498/aps.62.090201
Abstract +
Using Mawhin's continuation theorem, we discussed the existence of periodic solution for a class of nonlinear problem, and then investigated the problem of periodic solution of sport model of plasmas particle in the process of magnetosphere-ionosphere coupling. A result on the existence of periodic solution to the model is obtained.
2013, 62 (9): 090202.
doi: 10.7498/aps.62.090202
Abstract +
Firstly, the relative rotation nonlinear dynamic system is established, which contains time-varying stiffness, commonly damping force and compulsive periodic force. Secondly, some results of the existence and uniqueness of periodic solutions of the system are obtained by using the continuation theorem of coincidence degree theory. The significance is that we generalize the results published in the literature. Furthermore, an example is given to illustrate that our results are new.
2013, 62 (9): 090203.
doi: 10.7498/aps.62.090203
Abstract +
The nonlinear diffusion-convection equation f(x)ut=(g(x)D(u)ux)x+h(x)P(u)ux+q(x)Q(u) with variable coefficients and source term has been studied. This equation is symmetrically reduced by the generalized conditional symmetry method. Some exact solutions to the resulting equations are constructed, with the diffusion terms D(u)=um (m≠-1,0,1) and D(u)=eu. These exact solutions are also the generalized functional separable solutions. Solutions to the equation with constant coefficients are covered by those exact solutions to the equation with variable coefficients.
2013, 62 (9): 090204.
doi: 10.7498/aps.62.090204
Abstract +
In this paper, in order to obtain new solutions to nonlinear evolution equations, the auxiliary equation method and (G'/G)-expansion method are studied and extended. By using the method, many new exact solutions of the nonlinear (2+1)-dimensional Nizhnik-Novikov-Vesselov equations with variable coefficients are obtained. The interaction new solutions include Jacobi elliptic function, hyperbolic function, triangular function and rational function.
2013, 62 (9): 090205.
doi: 10.7498/aps.62.090205
Abstract +
We have investigated the internal relation among the first integral, Hojman's method and Birkhoff's equations. There is a special equivalent relationship between Birkhoffian and Birkhoffian functions constructed by Hojman's method, and from this we can derive a more general form of Hojman's method. Then, combining the special equivalent relationship and Birkhoff's equations, we can derive the cyclic integral in Birkhoffian sense. An example is given to illustrate the application of the results.
2013, 62 (9): 090206.
doi: 10.7498/aps.62.090206
Abstract +
A sufficient stability condition for time-domain magnetic field integral equations (TDMFIE) based on marching on-in time (MOT) algorithm is obtained through theoretical derivation using the norm. If the condition is satisfied, it can be ensured that the computational results will always be stable in late-time no matter what kind of incident wave is. Moreover, a factor expressing the recursive relationship of the currents is obtained, which can represent the constringency of the currents. Finally, the sufficient stability condition is validated by numerical results. Meanwhile, the numerical results also verify that the factor can be used to represent the stability of the currents.
2013, 62 (9): 090301.
doi: 10.7498/aps.62.090301
Abstract +
Continuous-time quantum random walk is constructed when photons propagate passing the branches of the waveguide array. It is possible to make quantum simulator, based on the quantum walk in waveguides, on a commercial scale firstly, but there are still some problems such as input state, the structure and boundary of the waveguides that should be treated at present. A nearest-neighbor coupling model is used to deal with the question of coupled waveguides and an explicit analytical solution can be derived. Using the analytical solution, we analyze the effects of input state on particle number probability distribution function and the second-order coherence degree of the quantum walk process in periodic waveguides. The results show that the symmetry properties of the input state would influence the distribution of second-order coherence degree, but have little effect on the probability distribution function.
2013, 62 (9): 090501.
doi: 10.7498/aps.62.090501
Abstract +
In this paper, a new detecting method for weak periodic signals with unknown periods and unknown forms, the so-called fractional stopping oscillation method, is presented. This new detecting method, which is based on the research of some dissipative system of single degree of freedom, is sensitive to periodic signal—even with unknown period and unknown form—and insensitive to noise. Compared with the known chaotic detections in which a built-in signal must be pre-set with the same frequency and the same form as the detected periodic signal, the fractional stopping oscillation method can not only be used even at lower SNR than chaotic detection, but also has some other notable advantages as follows: (1) it need not get the period and the form of detected signal before hand or pre-estimate them; (2) it need not pre-calculate the chaotic threshold value; (3) the existence of periodic signal in system input can be reliably and quantitatively judged by volatility index function, designed in this paper, for stopping oscillation method; (4) a more sensitive detection method can be achieved by the fractionalization of the detection system, especially, the detection threshold can reach -182 dB when the background noise is colored Gaussian noise.
2013, 62 (9): 090701.
doi: 10.7498/aps.62.090701
Abstract +
A highly sensitive torsion sensor, which can measure the torsion angle and determine the torsion direction simultaneously, is proposed and experimentally demonstrated by using side-leakage photonic crystal fiber (SLPCF) based Sagnac loop. When the SLPCF is turned in the clockwise direction, the transmission spectra of the torsion sensor shift towards the shorter wavelength side; whereas the transmission spectra of the torsion sensor shift towards the longer wavelength side when the SLPCF is turned in anticlockwise direction. Experimental results demonstrate that the length of the SLPCF inserted into Sagnac loop plays an important role for determining the torsion sensitivity and the torsion angle range. For the SLPCF with shorter length, the torsion sensor has the larger torsion sensitivity, but the torsion angle measuring range would be decreased. The opposite situation takes place for the SLPCF with longer length used in the torsion sensor. When the length of SLPCF is 14.85 cm, the torsion sensitivity of the sensor is up to 0.9354 nm/(°) and the torsion angle range from -90° to +90°; When we increase the length of SLPCF to 32 cm, the torsion sensitivity of the sensor gets down to 0.2132 nm/(°), but the torsion angle range can be expanded as from -180° to +180°. To eliminate the perturbation of environmental temperature, we adopt a two-dimensional measuring matrix to achieve simultaneous measurements of the torsion angle and temperature. In other words, using two-dimensional measuring matrix can also eliminate the perturbation of the environmental temperature to the measured result of torsion angle.
2013, 62 (9): 090702.
doi: 10.7498/aps.62.090702
Abstract +
Because a harmonic diffractive optical element has special achromatism and athermalization, it can be applied to infrared dual-band search and tracking optical system. In this paper, we make the device that can be used in the wavelength ranges 3.7—4.8 μm and 8.7—11.3 μm; It has an efficient focal length 200 mm, the F/number 2.5, the full field of view is 5°. The environment temperature can be changed between -80 ℃—200 ℃. The practical design shows that the system not only shows good image quality in mid-and long-wave, but also the advantages of compact structure, high rates of transmission and athermalization.
2013, 62 (9): 090703.
doi: 10.7498/aps.62.090703
Abstract +
Simultaneous measurement of the concentration and size of spray droplets plays an important role in understanding sprays. The global rainbow technique is applied to measure the concentration and size of bi-component droplets. Based on the modified Nussenzweig theory, the refractive index and size distribution are optimally evaluated, and then the concentration is retrieved with prior relationship between the refractive index and concentration. The inverse algorithm is verified by the simulated global rainbow signals; results shows that it can accurately retrieve the refractive index and size distribution of the droplets with an unimodal or bimodal particle size distribution. Sprays of water-ethanol solution with volume concentration from 0% to 100% are measured. Results show that the measured refractive indices agree well with the exact values, and the size distribution is stable. The global rainbow technique shows great potential in concentration measurement of spray droplets.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2013, 62 (9): 091401.
doi: 10.7498/aps.62.091401
Abstract +
The high performance nano-crystal Ni material was prepared by the pulse electrodeposition process; the intensity, composition and the microscopic structure of the nano-crystal Ni material were investigated by various measurements. In this paper, the 1 MeV electron was chosen as the irradiation source to investigate the energy loss of high energy electron in the nano-crystal Ni material and conventional bulk Ni material, and the energy deposition process during the electron irradiation was measured by the absorbed dose tablets. The results show that the grain size affects the energy loss process during the 1MeV electron irradiation seriously. The absorbed dose of 1 MeV electron in the nano-crystal Ni material is lower than that in the common Ni material with the same thickness, which indicates that the energy deposition of high energy electron in nano-crystal metal is lower than that in the conventional bulk metal, and the nano-crystal metal has an advantage of radiation resistance.
NUCLEAR PHYSICS
2013, 62 (9): 092301.
doi: 10.7498/aps.62.092301
Abstract +
The long life decay products 210Pb, 210Bi and 210Po of 222Rn are adsorbed in atmospheric particulate matters, thus making it possible to estimate the average residence time by measuring the specific activity or activity ratio of radon daughters. However, the existing research results are rather bad in consistency and the contradictory phenomena cannot be reasonably explained, which makes it inapplicable to atmospheric environmental monitoring. For this reason, starting with the basic attributes of lower atmosphere, based on the decay characteristics, transfer rates and other related information of radioactive nuclides in atmospheric particulates, a mathematical model is built to reflect the relationship among the particle numbers of the absorbed, decayed and transferred. Then, a new method is presented to estimate the average residence time of atmospheric aerosol. The method can solve the confusion that have appeared in the current research, reveal that the atmosphere has limited self-purification function, and provide the condition for nuclides in the same decaying chain to decay to the activity balance and the way to reduce the average residence time. All these conclusions will provide a scientific basis for further study and exploitation in atmospheric environment monitoring.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (9): 093101.
doi: 10.7498/aps.62.093101
Abstract +
The interaction potential energy of Mg-CO complex was calculated by employing ab initio method in the single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD (T)] and large basis sets. The potential energy surface expressed by an analytical function was obtained for the first time as far as we know. A single global minimum occurs at Re= 8.98a0 and θe= 119.09° at an energy of -72.21 cm-1, and the potential energy surface has a weak anisotropy. Based on the potential, the rovibrational energy level structure of the Mg-CO complex was investigated. The microwave transition frequencies and spectroscopic parameters for the Mg-CO complex were theoretically predicted.
2013, 62 (9): 093201.
doi: 10.7498/aps.62.093201
Abstract +
The state transfer of nS Rydberg atoms induced by external pulsed electric field has been investigated. Cold nS Rydberg atoms are prepared by the two-photon transition and the selective field-ionization method is used to detect the Rydberg atoms and "P" state due to the state mixing. The avoided crossing of nS and (n-4) manifold is studied and the dependence of the state transfer rate on the strength of pulsed field is obtained. Experimental result is interpreted by using Stark effect of electric field and it shows consistency between experiment and calculation.
2013, 62 (9): 093301.
doi: 10.7498/aps.62.093301
Abstract +
The multiphoton transition is investigated theoretically by using wave packet method for the ground electronic state of HF molecule. A laser field composed of two overlapping infrared pulses is used in our model, and the ratio of their frequencies is 1:2. States |4,0> and |4,2> are chosen as target states. Calculated results show that the population can be transferred to different target states as the corresponding resonant frequency is chosen. The probability of the population transfer can be controlled by the initial phase difference of the two pulses. When the initial phase difference is of an odd number of π/2, the probability of population transfer reaches the maximal value. When the initial phase difference is of an even number of π/2, the probability of population transfer reaches the minimum value. In comparison with the state |4,2>, the initial phase difference has a stronger in fluence on the population of the state |4,0>.
2013, 62 (9): 093601.
doi: 10.7498/aps.62.093601
Abstract +
The optimum valence bond scheme is a new theoretical method in generating the initial geometric configurations in molecular dynamics simulations of cluster systems. We will present the application of such a new method to the prediction of nano-structures and the study of matter properties, especially for the low-dimensional nano-structures, such as clusters and nano wires. The optimum valence bond scheme uses the atomic geometry of structures and the space distribution of the valence electrons (mainly the molecular orbitals near the Fermi levels, i.e., the generalized frontier orbitals) to determine the possible stable geometric configurations of nano-structures. Silicon clusters are used to demonstrate the features of the optimum valence bond scheme. Metallic clusters such as those of lithium, sodium, beryllium and magnesium are used as examples to illustrate the application of the scheme to the prediction of structures and the studies of the evolution of the material properties with the sizes of clusters. We will use the adsorption process of lithium ion and MoS nano wire to illustrate the application of the optimum valence bond scheme in the studies of the ionic conduction mechanism of the energy storage materials. We will finish the paper by summarizing the direction for further development of the optimum valence bond scheme.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2013, 62 (9): 094101.
doi: 10.7498/aps.62.094101
Abstract +
In this paper, we present a high-order generalized extended Born approximation (Ho-GEBA) algorithm for modeling 3D electromagnetic responses of an arbitrary anisotropic body in transverse anisotropic background medium based on integral equation method. First, generalized series solutions of the integral equation are obtained by successive iterative technique, and a contraction operator is introduced for the anisotropic medium based on the iterative dissipation principle to guarantee the convergence of high-order series. Then, we derive the Ho-GEBA solutions of 3D electromagnetic responses in the anisotropic medium using the abnormal body domain decomposition method combining with the extended Born approximation. Analytical solutions of dyadic Green's functions in the transverse isotropic medium are used, which can improve the efficiency of the algorithm greatly. Numerical results show the validity of the algorithm by comparing it with the full integral equation method and the classical Born approximation.
2013, 62 (9): 094102.
doi: 10.7498/aps.62.094102
Abstract +
A possibility of new structure for high harmonics high gain (HGHG) free electron laser is proposed, in which the structure of the optical klystron is placed in the resonance cavity to form the HGHG modulator. This particular modulator can remove seed laser of the conventional HGHG. Such a scheme will be beneficial to high-repetition-rate, full coherence and narrow bandwidth. Detail simulation by GINGER was given, showing that up to 12 harmonics the output of the oscillator is still very well.
2013, 62 (9): 094103.
doi: 10.7498/aps.62.094103
Abstract +
An explicit expression for the spectral distribution of the radiation energy from a relativistic electron with a magnetic moment is derived. Consequentially for an extreme relativistic electron moving along a planar circular orbit, the spectral distributions of synchrotron radiation in σ- and π- polarization are calculated including the modification from electron's magnetic moment. It is shown that for the synchrotron radiation with high critical frequency ωc with ħωc≥ 10 keV, the modification may be considerable. The relationship between the polarization of synchronous electrons and radiation fields is obtained, and thus the information about spin polarization of electron beam from measuring the polarization of radiation fields is provided.
2013, 62 (9): 094202.
doi: 10.7498/aps.62.094202
Abstract +
A new reflective grism, which combines together the grating and prism, is introduced in this paper. The numerical simulation, based on the ray tracing, shows that the grism pair can introduce minus GVD and GDD; therefore it can well compensate for the material dispersions in the chirped pulse amplifier (CPA). Compared to the conventional CPA with up-chirp, the new scheme with down-chirp can support a near Fourier Transform-limited compressed pulse due to much better compensation for high-order dispersion of materials in amplifier, in which the grism acts as the stretcher and the ZF7 bulk material as the compressor. In addition, the improved transmission efficiency and simplified configuration makes it a promising way to amplify femtosecond laser pulses to sub-mJ at a high repetition rate.
2013, 62 (9): 094203.
doi: 10.7498/aps.62.094203
Abstract +
The wave aberration theory of non-symmetrical optical systems is useful for understanding the misalignment in symmetrical systems and designing of off-axis mirror systems. A theory about the third-order aberrations for sub-aperture plane symmetric optical system is developed by using the aberration theory for full-aperture axially symmetric spherical systems. This paper proves the nodal aberration theory, namely, the points in the field with zero third-order aberration will deviate from the field center except for spherical aberration. It also reveals that the nodal aberrations arise from the transformation of the aberrations in full-aperture systems. This theory can be efficiently used in non-symmetric optical system designing process.
2013, 62 (9): 094204.
doi: 10.7498/aps.62.094204
Abstract +
Far-field speckle generated by weak scattering screen is a central bright spots, around which is a speckle structure similar to the normal speckle. According to the far-field speckle produced by weak scattering screen, it is assumed that the image plane speckle of weak scattering screen is the result of coherent superposition of both uniform background and normal speckle. However, there exists a discrepancy between the assumption and the actual image plane speckle. Based on the above circumstances, the statistical properties are studied about the image plane speckle fields produced by Gaussian correlation weak scattering screens in the 4f optical imaging system of high-pass filter. It is found that the above assumption is correct when the surface roughness of the weak scattering screen and the wavelength of the incident light wave are almost the same.
2013, 62 (9): 094205.
doi: 10.7498/aps.62.094205
Abstract +
Based on the cross-spectral density function of Gaussian Shell-Model and Huygens integral, the expression of partially coherent Airy beam was derived. The non-diffraction and acceleration characteristics of partially coherent Airy beam were theoretically studied and experimentally observed. The experimental observation was consistent with the theoretical prediction. Furthermore, the non-diffraction distance and the transversal acceleration decrease with decreasing coherent length.
2013, 62 (9): 094206.
doi: 10.7498/aps.62.094206
Abstract +
A novel method for measuring the diffusion coefficient of liquids is introduced in this paper. A transparency capillary is used as both diffusive pool and imaging element, spatially resolving ability of the capillary in measuring refractive index of liquid is utilized to observe and record diffusive process directly, diffusion coefficient of liquid is calculated based on Fick second law and acquired experimental data. With the new method, the diffusive process of pure glycerol in water at 25 ℃ is investigated, the obtained diffusion coefficient is 0.898×10-5 cm2/s, which is of a relative error 4.47% compared with the literature value measured by the holographic interference. The influence of measurement accuracy of refractive index and capillary viscosity on measuring result is also analyzed. The method is characterized by micro-quantity sample required, faster measurement and better stability, which opens a new way to measure diffusion coefficient of liquid medium.
2013, 62 (9): 094207.
doi: 10.7498/aps.62.094207
Abstract +
An interesting fact in digital holography is that the reconstruction process of the hologram recorded by the color camera may result in some periodic distribution of images in the image plane. In this paper we describe the production mechanism, characteristics and application of image periodicity in digital hologram reconstruction. Our study shows that the image distribution characteristics in the hologram reconstruction are strongly dependent on the option of RGB sampling mode due to a color filter array being used in the CCD camera, and the relevant demosaicing process of the sampling array reconstruction. The image and the dc noise from the hologram reconstruction may be of different distribution patterns due to the modulation function in the inverse Fourier transform of a full monochromatic sampling array (MSA) with demosaicing. Thus, this work reveals the potential relationship between the demosaicing algorithm for a full MSA reconstruction, the sampling frequency in the hologram recording, and the image periodicity in the hologram reconstruction. Finally the application of the image periodicity in zero-order noise suppression is discussed.
2013, 62 (9): 094208.
doi: 10.7498/aps.62.094208
Abstract +
Based on the reaction mechanism of non-chain pulsed DF laser and taking into consideration the deactivation of the stimulated DF molecules by ground state DF molecules, D2 molecules, D atoms, F atoms, the dynamical model for non-chain pulsed DF laser is established using the rate equation theory. Through solving this model with Runge-Kutta method, the dependence of species concentration in the gain area on time is obtained. Then the effects of the working gas ratio and the reflectance of output mirror on photon number density, single pulse energy, pulse width and output power are studied in light of this model. The optimum parameters of the working gas ratio and the reflectance of output mirror are attained based on the theoretical calculation. The pulse waveform and single pulse energy of non-chain pulsed DF laser calculated by using the rate equations theory agree well with experimental data based on electric-discharge. These results would provide a theoretical support for the optimization of non-chain pulsed DF laser.
EDITOR'S SUGGESTION
2013, 62 (9): 094209.
doi: 10.7498/aps.62.094209
Abstract +
We demonstrate a novel regenerative amplifier with a long ring cavity. Calculation on cavity parameters supports a large mode size. Based on the simulation with the cavity design software, we successfully established a 12 m ring regenerative amplifier. The amplified laser energy up to 20 mJ was obtained under 150 mJ green pump laser at a repetition rate of 10 Hz, corresponding to 13.3% conversion efficiency. The spectral bandwidth of the output pulse was 30 nm, which could support a sub 30 fs pulse duration. After seed injection, the ASE of the amplifier was effectively suppressed.
2013, 62 (9): 094210.
doi: 10.7498/aps.62.094210
Abstract +
Nanosecond pulse laser electrochemical etching can remove the electrolytic products of laser irradiated region and so improve the processing stability and processing efficiency. The stress-etching characteristics and the material removal mechanism for aluminum alloy workpiece were investigated theoretically and experimentally by the use of a laser electrochemical machining system. For comparison of processing topography between laser direct etching in air and laser electrochemical machining, the scanning electron microscopy and the optical profilometry were used to detect and analyze etching morphological characteristics of machining areas. Based on the principle of mechanics and electrochemistry, stress-etching principles of laser electrochemical machining were studied. In this study, the effects of processing parameters and machining method on machining quality were explored, and a complex microstructure was processed successfully with reasonable processing parameters. The results show that laser electrochemical machining with better stability can reduce surface roughness and improve machining quality effectively.
2013, 62 (9): 094211.
doi: 10.7498/aps.62.094211
Abstract +
A wavelength-tunable laser output at 589 nm with high conversion efficiency based on sum-frequency generation by using the technique of single-wavelength extra-cavity resonance is achieved. The two fundamental wavelengths are 1583 nm and 938 nm and the nonlinear crystal is the period-poled lithium niobate. After the frequency of 1583 nm laser was locked to the cavity mode and the frequency of 938 nm laser was scanned, a 589 nm laser output with power of 4.96 mW and wavelength tuning range of 7 GHz was obtained and the stability of the output power is improved effectively with the help of servo feedback loop technique of acousto-optic-modulator. Finally, based on this laser, the saturated fluorescence spectrum of sodium D2 line in the temperature range of 348—413 K (75—140 ℃) were measured. The Doppler-free structures of D2a, D2b and crossover lines on Doppler background were observed, which can provide reference signals for the frequency locking of 589nm laser.
2013, 62 (9): 094212.
doi: 10.7498/aps.62.094212
Abstract +
A new method for compressing ultra-short laser pulse has been proposed in which cascaded quadratic nonlinearity with tilt pulse is used. The pulse compression scheme with group velocity matching between fundamental harmonic (FH) and second harmonic (SH) pulses in a single BBO crystal has been analyzed theoretically. The compressed results have been investigated and compared between the cases of group velocity matching and mismatching. Furthermore, the influences of the phase mismatching between the FH and SH pulses, the length of the nonlinear crystal, the initial peak intensity and pulse-duration of the FH pulse on the pulse-duration compression have been analyzed and simulated. The results show that the matched group velocity between FH and SH pulses can improve significantly both the temporal profile and the spectrum distribution of the compressed pulse. High quality compression can be achieved by optimizing and selecting the parameters such as phase mismatch, length of the nonlinear crystal, initial intensity and so on. For the fundamental pulse with 800 nm central wavelength, 100 fs duration and 50 GW/cm2 peak intensity, the 20fs output FH pulse has been achieved, and at the same time the 14 fs SH pulse has also been generated in 25 mm-long BBO crystal with Δk=60 mm-1 (1.98° detuning angle) and external tilt angle γ0=74°.
2013, 62 (9): 094213.
doi: 10.7498/aps.62.094213
Abstract +
In this paper, the impacts of boundary on the surface bright soliton in (1+1)-dimensional nonlocal nonlinear media are investigated First the solution of the surface soliton under the given boundary conditions in a normalized system is derived, and then, the critical power and the balance position of the surface soliton are obtained. Next, in the numerical simulation, due to the impact of boundary, it is difficult to form stable solitons when the width of the sample is too small. And the impact of the boundary on the soliton can be ignored only if the width of the sample is large enough; then the stable soliton can exist, which is similar to the analytical results. In addition, the impact of the boundary on the surface soliton when beams do not input from its equilibrium position is also investigated. In this case, the beam will propagate oscillating periodically about the stationary position, which is equivalent to the interaction of two out-of-phase solitons in nonlocal bulk media. Both the oscillating trajectory and period dovetail coinsde nicely with each other.
2013, 62 (9): 094214.
doi: 10.7498/aps.62.094214
Abstract +
The influences of atmospheric turbulence and the beam coherence on the average intensity of tilted and off-axis laser beams propagating through a cat-eye optical lens in the turbulence are studied. It is shown that the oscillatory behavior and the skewness of average intensity may appear because there exist apertures and active detection laser beams are tilted or off-axis. The skewness is independent of turbulence, but the oscillatory behavior disappears due to turbulence. For a small positive defocus of a cat-eye optical lens, the on-axis average intensity reaches its maximum. The a positive defocus value becomes small as the focal length of the cat-eye optical lens decreases, but it is independent of atmospheric turbulence and the coherence of active detection laser beams. And the average intensity becomes an off-Gaussian-like profile when the propagation distance is large enough in turbulence. However, less beam spreading may occur with increasing propagation distance for active detection laser beams with less coherence, which is quite different from the behavior of laser beams propagating in free space. The better the coherence of active detection laser beams is, the more the average intensity is affected by the turbulence, but the difference is small. The results obtained in this paper are very useful for the applications is active laser detection.
2013, 62 (9): 094215.
doi: 10.7498/aps.62.094215
Abstract +
There has been great difference between the theoretical signals of the lidar's echo and its actual signals, due to the angles between the laser beam and its receiving optical axis, and the laser intensity distribution being asymmetrical. So the correction of the echo signal is necessary. According to the mathematical derivation and the software simulation, the mathematical expression of the lidar's overlap factor is given, and the overlap factor curves with detection range are drawn which express the characters over the total detection range, then the best angle between lidar's emitting axis and the receiving axis is obtained. The overlap factors are analyzed when the laser is Gaussian with a uniform intensity distribution. The lidar distance correction signal and Klett formula are corrected by the overlap factor, and the instrument parameters of the lidor are measured. In the range where the overlap factor is not zero, its correction echo signals and extinction coefficients can be obtained by using the corrected Klett formula. While in the range of the lidar's blind zone, the signals can be derived by a slope method. Finally, the total correction curve of the extinction coefficients is gained, and it is in accordance with the actual one correction cuive.
2013, 62 (9): 094216.
doi: 10.7498/aps.62.094216
Abstract +
In this paper, theoretical researches on the MgO:LN tunable hexagonal phase array grating based on the Talbot effect were presented. Researches revealed the effects on the intensity distribution of near-field diffraction from array grating duty cycle which is defined as D, phase difference which is defined as Δφ and the distance coefficient which is defined as β. The results obtained show that good near-field diffraction images can be achieved at D=52%, Δφ=0.75π, β=0.2. Based on the theoretical researches, the tunable hexagonal phase array grating is designed and fabricated from periodically poled MgO:LN crystal. Through experimental test, the Talbot effect diffraction imaging map is successfully obtained at different Δφ and β, which verifies the results of the theoretical researches.
2013, 62 (9): 094217.
doi: 10.7498/aps.62.094217
Abstract +
We have carried out experimentally the supercontinuum generation in GeO2-doped-core uniform photonic crystal fiber and zero-dispersion wavelength-decreasing photonic crystal fiber with pump pulses 1.8 ps operating at 1040 nm. Dispersion and nonlinear effects such as cross-phase modulation, four-wave mixing, modulation instability play a crucial role as they extend the supercontinuum towards short wavelength side. Zero-dispersion wavelength-decreasing photonic crystal fiber can improve group-velocity matching between solitons and dispersive waves deduced from numerical simulation of the evolution of spectra generated in a taper and uniform fiber. We obtained experimentally a spectrum expanding to the blue side and the power variation is indeed of 10 dB over a spectral range of 165.7 nm (between 4061 and 6718 nm) in the taper fiber.
2013, 62 (9): 094218.
doi: 10.7498/aps.62.094218
Abstract +
Bacillus subtilis, Aspergillus niger spore and Aspergillus niger mycelium are chosen for samples preparation. The above three samples' reflection spectra in 2.5—15 μm band are recorded by using infrared microscopic spectrometer. From Kramers-Kronig (K-K) relationship, microbe samples' complex refractive indexes in 6—14 μm band are calculated. According to the microbe samples' absorption spectra, their water contents are calculated using the absorption characteristics of water, protein and nucleic acid. Based on the above three microbe samples' water contents and complex refractive indexes in far infrared band, biologic particle's complex refractive index model in 6—14 μm band are constructed and the model's reliability is analyzed. The construction of biologic particle's complex refractive index model has important significance in the development of rapid analysis and identification method of biologic samples, and the detection and identification technologies of biologic aerosol.
2013, 62 (9): 094219.
doi: 10.7498/aps.62.094219
Abstract +
We have anelyzed the displacement damage effects on quantum dot lasers theoretically and deduced the relation between the radiation-induced threshold current change and the neutron fluence. The neutron radiation experiment for quantum dot lasers are also carried out to examine the displacement damage coefficient of the non-radioactive recombination rate. The formula fits the experimental data very well, and can describe the trend of the laser performance under electron irradiation. It can also predict the behavior of quantum dot lasers under radiation environment and is valuable for practical application.
2013, 62 (9): 094301.
doi: 10.7498/aps.62.094301
Abstract +
The interaction of ultrasound with an interface between two rough surfaces in contact has become a quite popular topic in many areas related to non-destructive evaluation (NDE). We proposed a theory of ultrasonic nonlinear interaction between some random rough elastic interfaces. The model of random elastic-contact interface is first described, and then the nonlinear ultrasonic interaction of interfaces with stress-strain relationship is studied, by using different models including linear simplified model, exponential model, and Gaussian model. Results of numerical simulations and experiments demonstrate that the Gaussian model is more suitable for describing the solid rough interfaces. This study provides an explanation of the ultrasonic interaction on mesoscopic level, which is a theoretical basis for practical application to detect cracks, defects and injuries in industrial ultrasonic NDE.
2013, 62 (9): 094302.
doi: 10.7498/aps.62.094302
Abstract +
The coupled-mode method based on the direct global matrix (DGMCM) approach for sound propagation in range-dependent waveguides [Luo et al., "A numerically stable coupled-mode formulation for acoustic propagation in range-dependent waveguides," Sci. China-Phys. Mech. Astron. 55, 572 (2012)] is further developed. The normal mode model KRAKEN is adopted to provide local modal solutions and their associated coupling matrices. As a result, the model DGMCM is capable of providing full two-way solutions for the two-dimensional realistic problems characterized by a penetrable bottom and a depth-varying sound speed profile. In addition, the closed-form expressions of coupling matrices for sound propagation in a range-dependent, two-layer waveguide are proposed. The numerical solutions of the coupling matrices by DGMCM agree well with the analytical solutions. Sound propagation in a penetrable wedge is solved by the updated DGMCM model. The numerical results indicate that the updated DGMCM model is numerically stable and accurate, and can provide benchmark solutions for realistic range-dependent problems.
2013, 62 (9): 094303.
doi: 10.7498/aps.62.094303
Abstract +
A method of range and depth estimation was studied using a single hydrophone based on the dispersive characteristic and time-frequency analysis for low frequency underwater acoustic pulse signals in shallow water environment. First, the signal received on a single hydrophone can be decomposed into a series of modes within the frame work of normal mode theory, and then the dispersive characteristic of the propagating modes can be analyzed using the time-frequency analysis. In order to improve the time-frequency resolution, the use of the time-frequency distribution with adaptive radial-Gaussian kernel extracts the arrival time difference of propagating modes in dispersion curve, which can be used to estimate source range. Mode energy can be extracted using binary time-frequency mask filtering based on multi-mode joint matching processing; and the source depth can be estimated by comparing the differences of the mode energy of the real data and simulated replica data, yielding a contrast function. Simulation results from a shallow-water Pekeris waveguide show that the time-frequency distribution with adaptive radial-Gaussian kernel represents well the dispersion characteristics of the underwater acoustic pulse signals, provides higher time-frequency resolution and overcomes the problem of the inherent limit for the time resolution and frequency resolution in the traditional short-time Fourier transform, so that the modes can be separated and identified more easily in the time-frequency plane. From the result of the range estimation, the different mode combinations have different results of the range estimation. The range estimation result can be obtained accurately by using the mode with high energy in the time-frequency plane. The relative error in range estimation is less than 2% by using the mode with high energy. In terms of the depth estimation, the more the number of joint matching mode, the more sharp peak and low fake peaks the contrast function has, so that the depth estimation is further improved by incorporating more modes. This research has great significance for studying the extraction and separation of low frequency underwater acoustic pulse signals.
2013, 62 (9): 094304.
doi: 10.7498/aps.62.094304
Abstract +
In this paper, a local resonant phononic crystal is designed and fabricated based on Helmholtz resonators. Experiment is carried out to study the defect mode of the structure, in which a point defect is introduced. Due to the coupling of the defect cell and perfect cells, a narrow pass band appears in the local resonant forbidden band. Meanwhile, acoustic energy localization effect is observed around the defect resonator at the frequency of defect mode which changes with the defect parameter. However, the defect mode is close to the edge of the forbidden band, the localized energy is high. In addition, if the resonant frequency of the defect unit is smaller than that of the perfect unit, the localized energy is mostly distributed in the waveguide. In contrast, the energy is mostly localized in the resonators when the defect unit frequency is larger than that of the perfect unit. This work will be of help for designing new acoustic functional devices of filters and concentrators.
2013, 62 (9): 094401.
doi: 10.7498/aps.62.094401
Abstract +
In this paper, a novel testing method for the assembled performances of the helix slow-wave structure (SWS) with a supported rod is proposed based on heat distribution of SWS. A distributed temperature testing platform using fiber Bragg grating (FBG) and thermocouple is designed, and the influence of thermal sensors on the heat dissipation capability of the SWS is analyzed means of ANSYS. The experimental system including a distributed micro FBG sensor array is set up to test the assembled performance of SWS of the X-band TWT. The results show that the assembled performances of the SWS can be effectively obtained by the tested curve of temperature difference.
2013, 62 (9): 094501.
doi: 10.7498/aps.62.094501
Abstract +
In this article, from the integral variational principles for embedded variation identity of high-order nonholonomic constrained systems, three kinds of dynamics for high-order nonholonomic constrained systems are obtained, including the vakonomic dynamical model, Lagrange-d'Alembert model and a new one if utilizing respectively three kinds of conditional variation to them. And the integral variational principles for embedded variation identity of high-order nonholonomic constrained systems is also fitted for the general nonholonomic systems when the constrained equation is reduced to a first-order one. Then, the vakonomic dynamic, Chetaev dynamics and a new model of general nonholonomic systems can also be obtained. Finally, two illustrated examples are used to verify the validity of the theory.
2013, 62 (9): 094502.
doi: 10.7498/aps.62.094502
Abstract +
The dynamic equation of some nonlinear relative rotation system with two masses has been established, which contains a kind of nonlinear sick-slip friction. Chaotic motion and the control effect of multi-delay feedbacks of the nonlinear relative rotation system under external excitation are investigated. When the system is in chaos under external excitation, the multi-time delay is applied to control the chaotic motion. The chaotic critical conditions of parameters about Smale commutation are given in terms of Melnikov theory, while the influence of multi-delay feedbacks on the system movement state and chaotic critical conditions is studied. The control impacts of multi-time delay parameters on chaotic motion are studied by phase diagram, Poincare map and power spectrum, separately.
2013, 62 (9): 094701.
doi: 10.7498/aps.62.094701
Abstract +
The influence of CO2 laser local irradiation (CLLI) on the laser damage resistance of fused silica was studied. It is found that CLLI has no evident effect on the laser-induced damage threshold (LIDT) of fused silica when the temperature of irradiation center is low (1139 K). However, the influence of CLLI on LIDT becomes important when the temperature of irradiation center is higher (1638 K). AT first, LIDT decreases with r increasing from zero to rM, where r is the distance to irradiation center, and rM is the distance at which the residual stress-induced phase retardance reaches the maximum. Then, LIDT increases a little when r is larger than rM. The origin of this phenomenon is discussed. Due to the residual stress, re-initiated damage in irradiation region can result in the formation of fractures. The fractures due to the re-initiated damage at irradiation center transport along radial direction firstly, and then transport along the tangential direction near rM. This may be due to the maximum tensile hoop stress and radial stress dependence of radius. Cares should be taken for the optical cleaning when thermal oven annealing is used to eliminate the residual stress. Otherwise, crystallization can be induced by contamination during annealing. The contamination also has negative impact on the light transmission and LIDT.
COMPREHENSIVE SURVEY FOR THE FRONTIER DISCIPLINES
2013, 62 (9): 094201.
doi: 10.7498/aps.62.094201
Abstract +
Micromaching by using femtosecond laser has been developing rapidly. This paper introduces the main developments in the last ten years on the formation mechanisms of periodic ripples in metals, semiconductors, and dielectrics induced by femtosecond lasers. By combining the methods of multi-beam interferences with the self-organized periodic nanostructures, two-dimensional periodic complex nanostructures can be fabricated on the surface of semiconductors. Compared with that of plane surface, the photoluminescence of nanostructures increases greatly.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (9): 095201.
doi: 10.7498/aps.62.095201
Abstract +
The modified screened Coulomb potential is obtained with considering the changes of plasma number density. Both the analytical results and molecular dynamical simulation show that the modification due to the changes of number density has a minor effect on the dynamical and structural properties of the two-dimensional dusty plasmas. However, further modifications including such as the particle size, ion drag force and pressure force possibly change the profile of the spherically asymmetric Coulomb potential. Motivated by the above speculation, the modified screened Coulomb potential with a set of margin parameters is used to investigate the dynamical and structural properties of the two-dimensional dusty plasmas. It is found that the diffusion of system is extensively decreased, particularly, a circle configuration is formed, which is similar ho the experimental observation of spherical assemble. Additionally, a uniform magnetic field is used to investigate the effects on the dynamical and structural properties of the two-dimensional dusty plasmas.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2013, 62 (9): 096101.
doi: 10.7498/aps.62.096101
Abstract +
Based on the influence of Kondo effect in carbon nanotubes, the Anderson model was used to characterize the system of carbon nanotubes/magnetic impurity at a finite temperature. The electric conductivity and the thermopower in the system of carbon nanotubes/magnetic impurity were researched by using the Landauer formula. The results of theoretical calculation agree well with that of experimental research.
2013, 62 (9): 096401.
doi: 10.7498/aps.62.096401
Abstract +
Due to its fitting the resistive switching behavior of memristor well, the percolation network model has recently attracted attention in the memristive mechanism field. However, the current 2D percolation network model lacks the pristine states analysis. In this paper, the original model is simplified to study the effects of pristine state on the forming process of conductive percolation channel with the increase of applied voltage. Intuitively, such a percolation network model not only demonstrates the dynamic process of local conducting channels formed in the physical meaning, which verifies that the resistance distribution of the memristor switching is not ideally bistable but can be fitted by Gauss curve; also it contributes to deciphering the unknown conductive mechanisms of memristor with the various types of percolation channel.
2013, 62 (9): 096801.
doi: 10.7498/aps.62.096801
Abstract +
The amorphous Ge20Sb15Se65 thin film was prepared by magnetron sputtering deposition technique. Effect of heat treatment temperature in the range of 150—400 ℃ on the optical properties of Ge20Sb15Se65 thin films has been investigated. The microstructure and optical properties of the films were characterized by UV-Vis, Raman spectroscopy and XRD, the optical constant was calculated using the Swanepoel method and Tauc's law from the optical transmission spectra. Results indicate that when the annealing temperature (Ta) is lower than the glass transition temperature (Tg), the optical band gap (Egopt) increases from 1.845 to 1.932 eV, and the refractive index decreases from 2.61 to 2.54, while the optical band gap decreases from 1.932 to 1.822 eV and the refractive index increases from 2.54 to 2.71 with a further increase of Ta. The results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structural transformations. It is well consistent with the results of structure analysis by XRD and Raman spectroscopy.
2013, 62 (9): 096802.
doi: 10.7498/aps.62.096802
Abstract +
CrN/ta-C composite coating on a high-speed steel substrate is performed by magnetic filtered cathodic arc technique and magnetron sputtering technique. Adheision of ta-C film on the high-speed steel substrate is studied by changing the preparation process of a buffer layer of CrN. The results are as follows. With the increase of nitrogen flow, the buffer layer chromium nitride experiences the phase transition of Cr-Cr2N-CrN; the adhesion of the coating is improved with the increase of nitrogen flow, but when the nitrogen flow exceeds 30 sccm, the adhesion of coating will decline; the preferred orientation and grain structure of chromium nitride are changed by adjusting the substrate bias; the adhesion of the coating is improved with the increases of the bias voltage, but when the bias voltage exceeds 200 V, the the coating adhesion characteristics will be slightly reduced. The abrasion resistance of the test also shows that CrN coating can significantly improve the adhesion of the ta-C film on a substrate of high speed steel, and can also significantly improve the wear characteristics.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (9): 097201.
doi: 10.7498/aps.62.097201
Abstract +
In order to explore the extinction and scattering characteristics of expanded graphite, which is a kind of 3 millimeter wave interference materials, the formula of extinction, scattering, absorption and backscattering cross sections (radar cross. section, RCS) are established based on the electromagnetic scattering theory of cylindrical conductor of finite length and finite conductivity by the method of moment. The extinction and scattering characteristics are calculated, and the influening factors of the characteristics including length, radius, conductivity and magnetic permeability of the expanded graphite are analyzed using Mathematica program. Results show that the expanded graphite has excellent extinction and scattering properties when its length and radius are 1.5 mm and 0.5 mm, respectively, and the properties can be improved when the conductivity and magnetic permeability of the expanded graphite are increased properly. This research provides a valuable insight into the improvement of interference performance of expanded graphite in 3 millimeter wave.
2013, 62 (9): 097202.
doi: 10.7498/aps.62.097202
Abstract +
We have studied the effect of population inversion associated with the electron and hole injection in graphene layer n-i-p structures with split gates at room temperature. Considering the transverse electric field screening of the n-section, we calculated the dependence of the electron-hole effective temperature and optical phonon effective temperature on the gate-voltage. It is shown that the injection can lead to cooling of the electron-hole plasma in n-section to the temperatures lower than the lattice temperature. The current-voltage characteristics, and the frequency-dependent dynamic conductivity are calculated, the frequency-dependent dynamic conductivity can be negative in the terahertz frequency range at a certain applied voltage. The study demonstrates that electron-hole plasma cooling can enhance the negative dynamic conductivity effect and improve the feasibility of terahertz lasing.
2013, 62 (9): 097301.
doi: 10.7498/aps.62.097301
Abstract +
Zinc oxide (ZnO) has attracted increasing attention as one of the most promising n-type thermoelectric materials. Although ZnO has been screened for high power factor, the ZT results were discouraging for its high thermal conductivity. Preparing nanocomposite is an effective way to reduce the thermal conductivity. The Ag-ZnO nanocomposites were synthesized by means of sol-gel method and their thermoelectric properties were investigated. Their XRD pattern and SEM miro graphs show that Ag nanoparticles are mainly lecated at the grain boundary of ZnO. Increasing Ag content leads to a significant decrease in absolute value of Seebeck coefficient (|S|). The electrical conductivity increases with increasing Ag content, while the thermal conductivity of Ag-ZnO nanocomposites is much lower than the bulk ZnO sample. The highest ZT (0.062) is found for 7.5 mol% Ag@ZnO nanocomposite at 750 K, thirty-five times of that of bulk ZnO. Since the Ag-ZnO junction leads to charge redistribution, the deflexed energy band obtained for ZnO should facilitate the electron transfer across the interface and thus accelerates the mobility of charge carriers. Thus increasing mobility of charge carriers would lead to the increase in electrical conductivity and a decrease in Seebeck coefficient. The difference of thermal conductivity comes from the lattice thermal conductivity. Due to the high density of interfaces and grain boundaries present in the nanocomposites, the scattering of phonons across a broad wavelength spectrum is enhanced. This suppresses the lattice thermal conductivity of the nanocomposites significantly.
EDITOR'S SUGGESTION
2013, 62 (9): 097302.
doi: 10.7498/aps.62.097302
Abstract +
Within the framework of the fraction-dimensional space approach, the binding energy and the effective mass of a polaron confined in a GaAs film deposited on Al0.3Ga0.7As substrate have been investigated. It is shown that the polaron binding energy and mass shift decrease monotonously with increasing film thickness. For the film thickness of Lw70 and the substrate thickness of Lb200 , the substrate thickness will influence the polaron binding energy and mass shift. The polaron binding energy and mass shift increase with increasing substrate thickness. In the region Lw70 or Lb200 , the substrate thickness has no influence on the polaron binding energy and mass shift.
2013, 62 (9): 097303.
doi: 10.7498/aps.62.097303
Abstract +
We have studied two batches of photovoltaic HgCdTe detectors irradiated by CW band-in laser, and discovered, two different over-saturation phenomena. It is shown that the over-saturation phenomenon associated with the open-circle voltage signals which decreases with increasing light intensity is of universal existence in the PV HgCdTe detectors irradiated by intense light. The regular and special phenomena of PV HgCdTe detectors under intense light radiation are definite and obvious. The generation conditions for the two typical over-saturation phenomena are analyzed in terms of the equivalent circuit model. These two kinds of over-saturation phenomena have been numerically simulated. Numerical results are in good agreement with experimental data. It is found that the two generation mechanisms of the over-saturation phenomena of PV detector under irradiation of the above-band gap laser do exist. One is the increasing dark current due to thermal effectm, and the other is the leak current due to the bugs in the detector material.
2013, 62 (9): 097401.
doi: 10.7498/aps.62.097401
Abstract +
In this paper, the evolution of vortex configuration for mesoscopic two-gap superconductor is investigated by the time-dependent Ginzburg-Landau theory in the presence of an externally applied field. The vortex configurations of s-wave and d-wave, and the distribution of magnetic field are given when the temperature is between critical temperatures of s-wave and d-wave. In theory, the over-cold and the over-hot field, and the boundary effect on vortex are simulated when the magnetic flux penetrates the superconductor.
2013, 62 (9): 097501.
doi: 10.7498/aps.62.097501
Abstract +
This paper deals with the exchange bias and its thermal stability in magnetic BiFeO3/Ni81Fe19 bilayer sputtered under an electromagnetic field. The results show that the BiFeO3/Ni18Fe19 bilayer presents an in-plane uniaxial magnetic anisotropy and a significant exchange bias effect, however the exchange bias field Hex in the BiFeO3/Ni18Fe19 bilayer does not show a visible training effect. The forward and recoil loop shifts towards positive fields, while holding the film in a negative saturation field. Hex decreases monotonously with the increase in the holding time (tsat), whereas Hc is almost the same. With increasing temperature Tm, Hex will not alter significantly, which means that Hex is not sensitive to the temperature, showing a good thermal stability. However, Hc may reduce rapidly with the increase in temperature. We believe that the good thermal stability may result from the coupling between ferroelectric and antiferromagnetic moments in BiFeO3.
2013, 62 (9): 097502.
doi: 10.7498/aps.62.097502
Abstract +
Multiferroic Bi0.95Dy0.05Fe1-xCoxO3 (x=0, 0.05, 0.1, 0.15) ceramics were prepared by rapid liquid phase sintering method. We studied the effect of (Dy+Co) doping on the structure, electrical and ferromagnetism properties of BiFeO3 ceramics. The structure and morphology of BiFeO3 ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopey (SEM). The results showed that all the peaks for Bi0.95Dy0.05Fe1-xCoxO3 samples can be indexed based on the crystal structure of pure BiFeO3. And XRD analysis revealed a phase transition in (Dy+Co) co-doped BiFeO3 when x was larger than 0.1 and grain sizes changed from 1 to 5 μm. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. Magnetic measurements showed that all samples possess strong ferromagnetism at room temperature expect BiFeO3 and Bi0.95Dy0.05FeO3, which are weakly ferromagnetic. The M'rs, of Bi0.95Dy0.05Fe1-xCoxO3 with x=0.05, 0.01 and 0.15 are 0.43, 0.489, 0.973 emu/g and the M'rs of them are 0.77, 1.65, 3.08 emu/g, respectively. The magnetic moment of BiFeO3 and B0.95Dy0.05Fe1-xCoxO3 ceramics varies with temperature from 300 to 900 K at an applied field of 5 kOe. It shows that the TN of BiFeO3 from 644 to 648 K with different content of Dy3+ can be changed by crystal structures and exchanges between Dy3+-Fe3+. The phase transition temperature of Bi0.95Dy0.05Fe1-xCoxO3 shifted to lower temperatures from 870 K to 780 K demonstrate that Co3+ doping causes a drop of TC as compared with BiFeO3. The change of TC of Bi0.95Dy0.05Fe1-xCoxO3 depends mainly on the Fe-O-Fe super-exchange strength and the relative stability of magnetic structure.
2013, 62 (9): 097801.
doi: 10.7498/aps.62.097801
Abstract +
In this paper, Gd2(WO4)3:Eu nanophosphors with different Eu3+ concentrations were synthesized through co-precipitation. The crystal structure and morphology of the nanophosphors were characterized by means of XRD and field emission scanning electron microscopy. Emission and excitation spectra (phonon sideband spectra) of each sample were measured, and concentration quenching curves were also drawn. The optimal doping concentration was confirmed to be 20 mol%. Huang-Rhys factor for each sample of different doping concentration was calculated by the phonon sideband spectra. Fluorescence lifetimes of the samples with different Eu3+ doping concentrations were measured. By fitting the fluorescence lifetime data of Eu3+ 5D0 level within the Auzel's model, the intrinsic lifetime for 5D0 level was determined and the generated phonon number in the quenching process was measured. The energy transfer rate of Eu3+ was derived from the fluorescence lifetime data, and the relationship between the energy transfer rate and the concentration was also given.
2013, 62 (9): 097802.
doi: 10.7498/aps.62.097802
Abstract +
Temperature-dependent Raman spectroscopic study on orthophosphates Ba3(PO4)2 and Sr3(PO4)2 were carried out up to 900 ℃. The change of Raman lines and crystal structure has been investigated at high-temperatures. It is found that all the Raman lines exhibit a decrease in frequency shifts and the width of the Raman lines increases with the increase in temperature. The P-O bond lengths in the crystal increase in high- temperature, but the O-P-O bond angles have less change. No phase changes have been observed under 900 ℃.
EDITOR'S SUGGESTION
2013, 62 (9): 097803.
doi: 10.7498/aps.62.097803
Abstract +
Nitrogen is one of the most commonly-observed impurities in diamond, and affects the luminescence of these defects greatly. The complexes could be obtained from the nitrogen atom trapping the native defects such as self-interstitials, vacancies. In this study, a high-pressure and high-temperature synthesized nitrogen-doped diamond was characterized by cathode luminescence (CL) image, and the results showed that the blue region of this sample is the {100} growth sector. The {100} sector was then electron-irradiated in transmission electron microscope (TEM) and subsequently annealed at high temperatures so as to introduce the native defects to further form the nitrogen-containing complexes. All the optical properties of these defects in diamond were investigated by the low temperature photoluminescence (PL) spectra. The PL of {100} sector dominated the strong luminescence of nitrogen-vacancy (NV) complexes together with a weak 503 nm signal.
2013, 62 (9): 097901.
doi: 10.7498/aps.62.097901
Abstract +
In order to understand the spectral response characteristic of the NEA GaN photocathodes at UVA band, three samples grown by MOCVD with different emission layer thickness and doping concentration were activated in the ultra-high vacuum system, and their spectral response were tested online. We fit the experimental quantum efficiency with illumination wavelength between 0.25—0.35 μ by the use of reflection-mode GaN photocathode quantum efficiency formula and the least square approximation method. The back-interface compound rate and the slope of fitting line L are gained and the reflection-mode GaN photocathodes quantum efficiency is simulated with incident light wavelength at 0.35 μ. The results show that the back-interface compound rate and the slope of the fitting line L can reflect GaN photocathode response performance. When the back-interface compound rate of GaN photocathode is less than 105 cm/s and the thickness of the emission layer is set between 0.174—0.212 μ, the photocathode has optimal spectral response performance.
Effect of synthesis temperature on preparation and field emission property of Ce-doped SiC nanowires
2013, 62 (9): 097902.
doi: 10.7498/aps.62.097902
Abstract +
In this paper, Ce doped-SiC nanowires were prepared by chemical vapor reaction technique at the different synthesis temperatures, and the field emission (FE) properties of the nanowires were measured. The products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED) and X-ray diffraction (XRD). The results suggested that the products were β-SiC, the nanowires become bending and the content of Ce reduces with increasing temperature; the values of the turn-on and threshold field increase at first and then decrease. When the synthesis temperature is 1250 ℃, the content of Ce is 0.27 at%, the turn-on and threshold fields of the product are 2.5 V/μm and 5.2 V/μm.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (9): 098201.
doi: 10.7498/aps.62.098201
Abstract +
SnSb/MCMB composite material was prepared by multi-step synthesis methods. Mesocarbon Microbeads (MCMB) powders were modified by acid treatment firstly, and then SnSb nano particles were deposited on the surface of MCMB through chemical reduction method forming a core-shell composite structure. To characterize the phase and morphology of the composites material, X-ray diffraction (XRD), scanning electron microscope (SEM) were used. The constant current charge and discharge (CD) and cyclic volt ampere (CV) methods were also used to test the electrochemical performance of SnSb/MCMB. The results demonstrated that SnSb/MCMB presents a multiphase system of nanocrystalline and amorphous structure. The capacity attenuation of SnSb alloy is faster than that of SnSb/MCMB. For the SnSb/MCMB composite, the tiny alloy particles were dispersed on the surface of MCMB powders, preventing from the serious agglomeration of nano particles. At the same time, the inner core MCMB can also buffering the volume effect of the alloy compoites to improve the elecrtochemical cycling stability. The composite material was a first discharge specific capacity of 936.161 mAh/g and the first Coulomb efficiency 80.3%. The specific capacity was still up to 498.221 mAh/g after 50 cycles.
2013, 62 (9): 098501.
doi: 10.7498/aps.62.098501
Abstract +
Noise suppression is a key technique in retrieving weak magnetic signal from human heart. In order to improve the signal-to-noise ratio (SNR) of magnetocardiography (MCG) signals, signal average method is widely used. However, due to the existence of local environmental interference, averaging the whole section data would unavoidable bring distortion to the average signal. In this paper, the authors proposed a kind of selective average method by using the template matching. The results showed that this method can effectively eliminate the data section with interference such as low frequency fluctuation, pulse burr etc. Thus averaging MCG signal with high SNR and fidelity will be obtained.
2013, 62 (9): 098502.
doi: 10.7498/aps.62.098502
Abstract +
Based on the principle of ultra-short channel MOSFET, a definite solution of potential is proposed by introducing two rectangular sources between the insulated gate and the space-charge region. By using the semi-analytical method and the spectral method, the 2D semi-analytical solution has been obtained for the first time as faras we know. The solution is a special function for the infinite series expressions. The most advantage of this model is that it can not only be calculated directly without numerical analysis but also keep the same accuracy as that of numerical solution. In addition, this model, which can be directly used in circuit simulation, has the characteristics that in its expression there is no adapter parameter with small calculating amount. The potential, surface potential and threshold of 45—22 nm MOSFET have been calculated in the frame of this model. It is shown that the calculated results are identical with Medici.
2013, 62 (9): 098503.
doi: 10.7498/aps.62.098503
Abstract +
Bipolar junction transistors (BJTs), as important electronic components in analog or mixed-signal integrated circuits (ICs) and BiCMOS (Bipolar Complementary Metal Oxide Semiconductor) circuits, are employed in the space environment. Therefore, the research on characteristics and mechanisms of ionization damage in the BJTs is very important. Lower energy electrons are used as irradiation source to study the ionization damage in NPN and PNP transistors. Various bias conditions are imposed on the emitter-base junction to reveal the different bias conditions that contribute to the radiation effect on NPN and PNP transistors during irradiation processing. The semiconductor parameter analyzer, Keithley 4200-SCS, is used to measure the change of electrical parameters of transistors with increasing electron irradiation fluence in situ. Based on the measurement results, we find the degradation of transistors is severe under reverse emitter-base bias, and is lowest under forward emitter-base bias, while it is medium under zero emitter-base bias at a given irradiation fluence.
2013, 62 (9): 098701.
doi: 10.7498/aps.62.098701
Abstract +
Neural system can characterize the information evoked in external stimulations by spatiotemporal encoding. Acupunctureas, as a mechanical actionis equivalent to an external stimulus to the neural system. In order to decipher how neural systems represent and transmit acupuncture information, experiments are designed such that different frequencies of manual acupuncture (MA) manipulations can be given to ‘Zusanli’ point of an experimental rat, and the induced electrical signals in spinal dorsal root ganglion are detected and recorded. First, the spike trains are obtained by data preprocessing and transformed into point process trains. Then a generalized linear model is introduced to encode the acupuncture information and produce the simulated neural spike train. In addition, a Bayesian decoding algorithm is used to reconstruct the displacement oscillograms of the acupuncture needle from the neural point process spike train. Finally, the quantile-quantile (Q-Q) plot based on the time-rescaling theorem is used to evaluate the agreement between the encoding model and the point process data. Results prove to be valid based on statistical analysis. These studies have offered new insights into neural processing underlying acupuncture and have implementations for constructing the interface between neural systems and machines and improving the clinical study.
2013, 62 (9): 098702.
doi: 10.7498/aps.62.098702
Abstract +
In circular cone-beam computed tomography (CT), to solve the 3D image reconstruction from truncated projection data which has no truncation along PI-line, backprojection-filtration (BPF) algorithm is a preferred choice. However, in its performance the integral interval of backprojection is variable for different PI-line, rendering the parallelism performance of backprojection low. So it cannot satisfy the requirement of fast image reconstruction in practical CT system. In this paper, a tent BPF (T-BPF) algorithm is developed based on the data rebinning method, which was performed by first rearranging the cone-beam data to tent-like parallel-beam data, and then applying the proposed BPF-type algorithm to reconstruct images from the rearranged data. T-BPF turns the variable view-angle integral interval of backprojection into a fixed integral interval, and there are no relations in the loops of backprojection calculation, which means the parallelism performance of T-BPF is an improvement over that of the original BPF algorithm. The results of experiments show that compared with the conventional CPU implementation, the GPU accelerated method provides images of the same quality with a speedup factor 1036 for the reconstruction of 2563 Shepp-Logan model. The speedup factor is an improvement in the original BPF algorithm. T-BPF provides a solution for the 3D fast reconstruction from truncated data.
2013, 62 (9): 098901.
doi: 10.7498/aps.62.098901
Abstract +
In this paper, we present the empirical investigation results for the urban subway networks in China. The results show that all the urban subway networks have high clustering coefficient and small character path length, which exhibit a small-world behavior, the degree distributions take multiplicative exponential function forms. Otherwise, these networks are hierarchically organized by overlapping cliques, which are all the globally coupled networks. To explain these results, we introduce a network model, which is in good agreement with the empirical results; in addition, this model can explain the evolutionary procedure of other networks, such as the urban bus transport networks or the film actor networks.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2013, 62 (9): 099201.
doi: 10.7498/aps.62.099201
Abstract +
Based on previous studies of the interaction between wave and flow, combining the vertical component of disturbance convective vorticity vector, the disturbance horizontal divergence and the vertical gradient of disturbance generalized potential temperature, We define a new disturbance thermodynamic shear advection parameter in this paper. This parameter means a typical wave action density, its equation of tendency is a typical wave action equation, which could describe the development or evolution of mesoscale disturbance. With the wave action density and the wave action equation, we have conducted a diagnostic analysis of the heavy-rainfall event caused by landfall typhoon "Morakot" in 2009. Results show that the abnormal values of the wave action density (namely the disturbance thermodynamic shear advection parameter) will always change with the development of the observed precipitation regions, both their horizontal distribution and their temporal evolution are quite similar. Statistical analysis reveals a certain correspondence between the wave action density and the observed 6-hour accumulated surface rainfall in the summer of 2009, and they are intimately related to each other. The wave action density may be used to describe the typical vertical structure of dynamic and thermodynamic fields of a precipitation system, so it is closely related to the occurrence and development of the precipitation system and may have certain relation with the surface rainfall regions. The calculation of the wave action flux divergence shows that at the time around the landing of typhoon "Morakot" in the southeastern China coastal region, the potential vorticity of disturbance ageostrophic wind is the main forcing term affecting the local variation of wave action density. The contribution of the coupled term between the first-order disturbance advection and disturbance shear to the local variation of wave action density is secondary. While the exchange of disturbance momentum and disturbance heat between the basic state and disturbance has relatively weak influence on the development and evolution of disturbance. After the landing of typhoon "Morakot" in the southeastern China coastal region, these forcing terms and the wave action itself are apparently weakened.
2013, 62 (9): 099202.
doi: 10.7498/aps.62.099202
Abstract +
The momentum and heat transfer coefficients used in the atmospheric numerical models usually are taken as constants. In fact, the bulk transfer coefficients change not only with atmospheric stabilities, but also with the air motion and thermodynamic properties of the surface boundary layer. In this paper, the bulk transfer coefficients of momentum and sensible heat are determined by using the data observed by the eddy correlation system and those of the average wind velocity and temperature gradients over the Xilin Guole semiarid grassland in May, 2008. The relations between the bulk transfer coefficients and the gradients in Richardson numbers are analyzed, and the relationship between the bulk transfer coefficients and atmospheric stabilities is also studied. Finally, the changes of momentum bulk transfer coefficients with wind speed and the relations between sensible heat transfer coefficients and temperature are determined. Comparison with the eddy correlation method for observing transfer coefficients, there is a great difference between the computational values of typical Businger-Dyer similarity functions. The revised Monin-Obukhov similarity functions could significantly improve the accuracy of the transfer coefficients. Under the near neutral stratification, there was an obvious interaction between the land surface and the flow condition over semiarid regions. The momentum bulk transfer coefficient varies with the mean wind speed at 10 m according to the quadratic curve laws. Under the low wind velocity condition, the influence of the air flow on the roughness was not significant and the momentum transfer coefficient will increase with increasing wind velocity. While at the high wind speed, the momentum transfer coefficient will decrease with increasing wind velocity, for the air flow changes the roughness height of surface boundary layer. Under the near neutral stratification, there was a quadratic curve law between the temperature and the sensible heat transfer coefficient, which provides a useful parameterization scheme for sensible heat transfer coefficient. The new schemes could parameterize the turbulent fluxes with average wind velocity and temperature gradients data, and does not need to compute the roughness.
2013, 62 (9): 099203.
doi: 10.7498/aps.62.099203
Abstract +
This paper examines the surface energy imbalance status over the semi-arid areas of the Loess Plateau, using the data collected by eddy covariance (EC) and boundary layer meteorological measurement systems at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The energy balance ratio is about 0.80 during the daytime in all seasons, while that is only about 0.20 in the night. For the observation time with no local circulation, the energy balance ratio is improved to more than 85% in the daytime. Even in the night of spring, summer or autumn, the energy balance ratio is also improved to 70%. However, the ratio in nighttime of winter is only 29.4%. After taking into consideration all the energy budget items, the surface energy is still not closed, which means that the eddy covariance system underestimated the turbulent heat flux. And the observation error changes with seasons, with maximum in winter and minimum in spring. The errors of sensible heat flux and latent heat flux may impact CO2 flux through the WPL correction, and cause the uncertainty of long term net ecosystem exchange (NEE), and the NEE throughout the year can be overestimated by 41.2%.
2013, 62 (9): 099204.
doi: 10.7498/aps.62.099204
Abstract +
Taking into account the variations of the refractivity gradient near the sea surface, We have used the curved wave spectral estimation (CWSE) technique to calculate the grazing angle. CWSE combined with the modified GIT reflectivity model and radar range equation, the radar sea clutter power modeling is performed under the atmospheric duct propagation conditions. Finally, the validation of CWSE is tested through numerical experiments and comparisons with the real measurement data.
2013, 62 (9): 099205.
doi: 10.7498/aps.62.099205
Abstract +
Considering the abnormal precipitation in north-west and drougtin south China during the summer of 2012, we have analyzed the decadal precipitation distribution and the chief probably-influencing factors in recent 50 years, in order to make a discussion of the possibility of decadal change of summer precipitation in East China since the summer of 2012. Research results show that the north Pacific decadal oscillation (PDO) is in cold phase, and the north cold air active and the west Pacific subtropical high (WPSH) are both in weak phase during the summer of 1961-1978. This situation is beneficial to the strong east Asia summer monsoon (EASM) and the north expansion of the low latitude water vapor, causing the summer precipitation in northern China more than normal in this decadal. While the situation is in quite opposite way during 1979-1992 (which causes the decadal change of summer precipitation in east China) that the precipitation is less than normal in northern China during the late period. Meanwhile, since in the late 2010 PDO changed from the warm phase to cold phase, the sea surface temperature was warmer in north Pacific and colder in west Pacific than normal, while the west Pacific subtropical high and the north region cold air active both changed from strong phase to weak phase, and the EASM became stronger, quite similar to that in 1961-1978. All of the cases showed that there might be once more a decadal change of summer precipitation in East China since the summer of 2012. Furthermore, the yearly variation of indices of PDO, EASM, WPSH and Baikal Height (BH) showed that the abnormal precipitation distribution and the chief influencing factors are not only the yearly variables but also the probable signal of decadal change in the following years.
2013, 62 (9): 099206.
doi: 10.7498/aps.62.099206
Abstract +
The blocking high in Eurasia mid-high latitudes (EMHBH) is one of the leading members of East Asian summer monsoon circulation system, which also has a crucial influence on the summer flood/drought in China, especially in the region of Yangtze River. However, the objective quantitative prediction of EMHBH is an urgent issue we are facing and also a complicated problem in the current short-term climate prediction. This paper, by using the dynamical and statistical prediction (DSP) methods and based on the forecast data of the numerical modal(CGCM) and the abundant historical observations, has carried out prediction experiments of the above three blocking high regions in the summer averaged 500 hPa geopotential height fields. The results show that the DSP methods can diminish the prediction errors to some extent, which is also suitable for operational application. In addition, sensitivity tests show that the selection of the number of similar targets or similar yeas has significant influences on the prediction results.
2013, 62 (9): 099401.
doi: 10.7498/aps.62.099401
Abstract +
The high negative amplitude rapid-charging events (RCEs), which were observed by the floating potential measurement unit (FPMU) on the International Space Station (ISS) and occurred at the eclipse exit, have attracted a lot of attention recently and are not yet understood. The RCEs are most serious of all types of ISS charging phenomena. Compared with the normal-charging events (NCEs) which occurred on morning sector, the RCEs are characteristic of rapid rise time (<10 seconds) and higher amplitude (30—70 V). In particular, their occurrence at the morning terminator indicates that they are related to the solar panel excitation process at the moment of receiving solar illumination. In this paper, an electric circuit model for the charging of the ISS structure and solar panel is established, based on which a differential equation is developed, with the different charging mechanisms included and also the way of solar panel excitation considered. The calculation results for the RCEs agree well with the typical waveforms.
2013, 62 (9): 099501.
doi: 10.7498/aps.62.099501
Abstract +
Edge detection is the focus and difficult point for speckle reduction anisotropic diffusion. Traditional methods typically rely on the estimation of mean and variance in edge detection. The precision of the estimations influences the accuracy of edge detection. In this paper, we present an anisotropic diffusion filter based on image entropy. This method uses image entropy as an edge detector to eliminate the error due to the estimation of mean and variance, and improves the edge detection capability. The experimental results show that the visual quality and evaluation indexes of the new method outperform those of the traditional methods.
