Vol. 62, No. 22 (2013)
The study of conserved quantities and symmetries for two-dimensional isotropic harmonic charged oscillator moving in homogeneous magnetic field
2013, 62 (22): 220201. doi: 10.7498/aps.62.220201
The kinematic differentiation equations of two-dimensional isotropic harmonic charged oscillator moving in a homogeneous magnetic are obtained by using Newton’s second law. Two integrals (conserved quantities) are obtained by directly integrating the kinematic differentiation equations. The relationship between the Lagrangian and the conserved quantity is established through the Legendre transformation, thereby obtaining a Lagrangian function of the system. The Noether symmetry and Lie symmetry of the infinitesimal transformations corresponding to the conserved quantities are studied. Finally, the kinematical equations of the system are obtained.
The first order approximate Lie symmetries and approximate conserved quantities of the weak nonlinear coupled two-dimensional system
2013, 62 (22): 220202. doi: 10.7498/aps.62.220202
A real weak nonlinear coupled two-dimensional system is constructed first by using coupling spring with variable force constant. The first-order approximate Lie symmetries and approximate conserved quantities of the system are studied. The system possesses six first-order approximate Lie symmetries and approximate conserved quantities, of which one is an exact conserved quantity, four are trivial conserved quantities, and only one is a stable conserved quantity.
2013, 62 (22): 220301. doi: 10.7498/aps.62.220301
We study the entanglement properties in a one-dimensional Ising chain with a tilted magnetic field that is capable of showing both integrable and nonintegrable behaviors. Here the pairwise entanglement is characterized by concurrence and the multipartite entanglement is characterized by the Q measure. According to the entanglement properties of the ground state in the Ising mode, which have tilt angle, we can find that the Q measure decreases with the increasing of the strength of external field. And the phase transition property of the system is changed with the increase of tilt angle for the external magnetic field. We also consider the evolution of entanglement in this model, and find that the nonintegrability can suppress the pairwise entanglement but promotes the multipartite entanglement with the integrable system.
Entanglement properties of two atoms interacting with weak coherent states trapped in two distant cavities connected by an optical fiber
2013, 62 (22): 220302. doi: 10.7498/aps.62.220302
Considering a system comprised of two-level atoms resonantly interacting with weak coherent states trapped in two distant cavities connected by an optical fiber initially, we study the entanglement properties of the atom-atom, the cavity-cavity and the atom-cavity. Then the influences of the ratio between fiber-cavity and atom-cavity coupling intensity, the intensity and the phase of the cavity field on the entanglement properties are investigated numerically. It is shown that the entanglements of the atom-atom, the cavity-cavity and the atom-cavity vary with time in the periodical or approximately periodical manner; the entanglement can be transferred from cavity-cavity to atom-atom reciprocally. Compared with the entanglements of atom-atom and cavity-cavity, the varying period of atom-cavity entanglement is short. The ratio of fiber-cavity coupling intensity to atom-cavity coupling intensity and the phase of cavity field affect the entanglement properties greatly. The great entanglement can be achieved by using a smaller ratio of coupling intensity between fiber-cavity and atom-cavity.
2013, 62 (22): 220501. doi: 10.7498/aps.62.220501
In the paper, the chaotic characteristics of two functions are studied by a quadratic surface mapping in spatial unit area. When a surface is the standard surface in spatial unit area and another surface is generated randomly, the probability that the two functions are in the chaos can be greater than one-tenth, so this is a better method of generating chaos. The chaotic characteristics are analyzed by calculating the Lyapunov exponent and drawing the bifurcation diagram. According to the bifurcation diagram of the changing parameter and the characteristics of the regional distribution of the chaotic surface control points, the chaotic mapping function can be found and a lot of two-dimensional chaotic attractor graphics can be obtained. Besides, gray scale image is regarded as a discrete two-dimensional function for the first time. The study of image as an iteration expression shows some chaotic characteristics. The study shows that the same or similar image converges to the cycle point easily, which can be used in some research areas such as image recognition.
2013, 62 (22): 220502. doi: 10.7498/aps.62.220502
By introducing periodically alternate current source as well as suitable values for the parameters to ensure that there exists order gap between the natural frequency and the exited frequency, a two-time scale namely, a fast-slow coupled non-smooth generalized Chua’s circuit model is established. Based on the corresponding generalized autonomous system, the stabilities of the equilibrium points in different regions are investigated, from which the critical conditions related to different types of bifurcation forms are obtained. At the same time, combining the theory of Clarke derivative, different types of non-conventional bifurcation models which may occur when the trajectory passes across the non-smooth boundaries are explored. Furthermore, with the combination of the generalized phase portraits, two typical periodic bursting phenomena namely, the Fold/Fold and Fold/Hopf periodic bursters, and their associated bifurcation mechanisms are analysed in detail.
2013, 62 (22): 220503. doi: 10.7498/aps.62.220503
The influence of Turing modes in two subsystems on pattern formation is investigated by the two-layer non-linearly coupled Brusselator model. It is found that the coupling coefficient and wave number ratio between two Turing modes take an important role in the pattern formation and pattern selection. The kind of pattern changes from simple pattern to complex one with the increase of wave number ratio. When nonlinear coupling coefficient is smaller than 0.1, the short wave mode in system 1 under the action of instability mode in system 2 can form not only simple pattern (such as simple hexagon and quadrilateral and stripe pattern), but also complex pattern due to the resonance coupling between the two Turing modes (such as honeycomb hexagon and super hexagon and complex black-eye pattern), and the transformation process of pattern from quadrilateral to superlattice pattern is observed for the first time under the specific parameters. When nonlinear coupling coefficient is more than 0.1, the simple patterns such as simple hexagon and stripe pattern are obtained only in system 1, because there is no resonance coupling between the two Turing modes in system 1.
2013, 62 (22): 220504. doi: 10.7498/aps.62.220504
Ion channels in the membrane of neuron can be blocked by some toxic chemicals. Blocking ion channels will reduce the conductivity and the number of activated channels, and affect the electrical activity of neurons. And then the spatiotemporal patterns of neuronal network would be changed. In this paper, the nearest-neighbor coupled Hodgkin-Huxley neuronal network with periodic boundary is adapted to the investigation of the evolution of spatiotemporal patterns of neuronal network when the sodium and potassium ion channels are blocked randomly, by using numerical method. The results indicate that sodium ion and potassium ion channel random blockage could lead to the breakup of spiral wave. Furthermore, we analyze the firing probability of neuronal network and find that sodium ion channel random blockage reduces the excitability of neuronal network, which is sensitive to noise; but potassium ion channel random blockage enhances the excitability of neuronal network. Compared with uniform blockage of ion channels, the random blockage of ion channels makes neuronal network have rich dynamics phenomena. Finally, the no-flux boundary condition is applied and the results are similar to the above ones.
Characteristics of time-delay complex Lorenz chaotic system and its self-synchronization of time delay
2013, 62 (22): 220505. doi: 10.7498/aps.62.220505
Self-synchronization of time delay implies that the synchronization between the time-delay system and the original system keeps the structure and parameters of systems unchanged, thus these various problems produced by time-delay in practice are avoided. Taking a time-delay complex Lorenz system for example, we investigate its dynamic characteristics and the influence of of time lag factor. A nonlinear feedback controller is designed to realize the self-synchronization of time delay of the complex Lorenz system. Numerical simulations verify the effectiveness of the presented controller. The controller adopts some states to realize the synchronization of all states. It is simple in principle and easy to implement in engineering.
2013, 62 (22): 220506. doi: 10.7498/aps.62.220506
The detecting of clusters or communities in large real-world networks such as large social or information networks is of considerable significance. We propose a new weighted evolving model of high clustering scale-free network incorporating a community structure mechanism, which means the addition of the new node depends on not only a single node but also a community. In the process of the evolution, a new node with probability p and a new community with the probability 1–p are added to the network. Different from the existing studies where new links are additionally established, some links with probability φ according to the triad formation mechanism and other links with the probability 1–φ according to the random selection mechanism are connected between neighbors in the model. The topology and weights of links of the network evolve as time goes on. Moreover, the evolving model gives power-law distributions of degree, weight, and strength as confirmed in several real world systems. Especially, the average clustering coefficient exhibits power-law decay as a function of degree of node. Both the community structure and the triad formation can enhance the average clustering coefficient of scale-free networks. Furthermore, we investigate how the synchronization of the network is influenced by the evolution mechanism of the network. Numerical simulation results show that the network synchronizability is optimized when the average clustering coefficient decreases in the model.
2013, 62 (22): 220701. doi: 10.7498/aps.62.220701
A trace gas sensor based on all optical quartz-enhanced photoacoustic spectroscopy (QEPAS) is designed and demonstrated. An extra detection light beam is added to the traditional QEPAS setup to convert the amplitude of vibration of the quartz tuning fork, which is proportional to the concentration of the target gas, into the variation of the detection light intensity. As a result, there are not any electrical components near the measurement position. Such a design makes it immune to electromagnetic interference and provides a compact sensor head, which can be used in a tiny space or an adverse environment. Using the new setup to measure the water concentration in air, the obtained noise equivalent absorption coefficient is 1.13×10-6 cm-1W/√Hz. The approaches to further optimizing the system and improving the sensitivity are also discussed in detail.
2013, 62 (22): 220702. doi: 10.7498/aps.62.220702
The effective transmittance of the Fabry-Perot (F-P) etalon in the case of the atmospheric backscatter light incidence is deduced. In the single F-P etalon-based dual-frequency Doppler lidar system, the wind retrieval accuracy with Rayleigh-induced effect for average method is analyzed quantitatively. A nonlinear iterative algorithm is proposed which can retrieve both wind speed and backscatter ratio, and its effectiveness is verified by simulation test. At the same time, the specific expressions of the radial wind speed error and backscatter ratio error are deduced. According to these expressions, the radial wind speed error and backscatter ratio error are simulated. The simulation results show that on the assumption that the total number of backscattering photons received by telescope is 50000, the radial wind speed measurement error decreases rapidly with the increase of backscatter ratio; when Rβ >1.2, the radial wind speed error is below 3 m/s within the wind speed measurement dynamic range of ±25 m/s; the backscatter ratio measurement error increases with the increase of backscatter ratio, but it is almost irrelative to the magnitude of radial wind; when Rβ<10, the backscatter ratio relative error is less than 13%.
2013, 62 (22): 220703. doi: 10.7498/aps.62.220703
In the theoretical analysis of the optical readout IR imaging, the incoherent area light source with a certain size is typically simplified into an ideal point light source, which leads to analytical errors. In this paper an area light source model is established, and using the Fraunhofer diffraction theory the influence of the optical detection sensitivity on area light source is studied. The dependence of the optical detection sensitivity on light source radius and reflector length of the focal plane array is found. And optimized design criteria for the size of light source and the length of the reflector are proposed. According to theoretical analysis, the experimental verification is carried out, and the results are consistent with theoretical analyses.
2013, 62 (22): 220704. doi: 10.7498/aps.62.220704
The machined workpiece has high mechanical storage energy because of the defect structures formed in nanocutting and their evolution from high energy state to the low energy state by adjusting atom positions automatically is called surface-energy aging. The effect of surface-energy aging on the surface properties of monocrystalline silicon workpiece is analyzed by Monte Carlo simulations of machined surface. It is shown that the surface-energy aging effect can increase the surface roughness and the degree of order of damaged layer, however reduce the residual stress and the average potential energy of workpiece. Amorphous silicon structure in metamorphic layer decreases and recrystallization phenomenon occurs in the surface-energy aging process. It is found that some β-Si phase structures and BCT5-si phase structures transform into the diamond cubic structure of Si in the surface-energy aging process. Surface-energy aging effect has a great influence on the surface properties of the machined surface of monocrystalline silicon workpiece, and can improve the mechanical properties of micro/nanostructures.
2013, 62 (22): 222401. doi: 10.7498/aps.62.222401
MCNP program is used to calculate the neutron transmission coefficient of 3–9 cm-thick neutron absorber material B4C/Al composite with 5%–15% B4C content in air, water, 200–1400 ppm (1 ppm=10-6) H3BO3 solution, irradiated by 0.5–20 MeV neutrons and 235U thermal neutron fission source. The results show that the transmission coefficient of B4C/Al composite decreases with the increase of the content of B4C and the thickness of material, but increases with the increase of neutron energy, and has little influence from the variation in H3BO3 solution concentration. A better shielding effect of B4C/Al composite is displayed in water than in H3BO3 solution, and a “reversal” phenomenon of the shielding effect occurs in air. The neutron transmission coefficient is almost unchanged with neutron energy when neutron energy is higher than the 5–15 MeV. The neutron transmission coefficient of B4C/Al composite irradiated under a fission source is lower than under a steady 20 MeV neutron source. Ranking the shielding performances of media, the sequence is H3BO3 solution > water > air, and the exponential decay relationships between neutron transmission coefficient and thickness of medium can be expressed as e-0.71x and e-0.669x, where x is thickness of medium in cm.
Study of nuclear stopping in Au+Au collisions at alternating gradient synchrotron energies by the ultra-relativistic quantum molecular dynamic model
2013, 62 (22): 222402. doi: 10.7498/aps.62.222402
Nuclear stopping in Au+Au collisions at alternating gradient synchrotron energies is studied in the framework of the modified ultra-relativistic quantum molecular dynamics transport model, in which mean field potentials of both formed and “preformed” hadrons (from string fragmentation), medium-modified nucleon-nucleon elastic cross sections, and cluster recognition criteria are considered. It is found that nuclear stopping is influenced by both the mean field potentials of formed and “preformed” hadrons and the medium modification of nucleon-nucleon elastic cross section. The free proton number is higher than that from the experimental rapidity distribution in the central region of rapidity distribution, which can be understood by considering the new criteria of judging fragments.
2013, 62 (22): 222801. doi: 10.7498/aps.62.222801
Through using the basic probability theory and establishing the law of finite chains near the prompt criticality, we deduce the formula of relation between the neutrons number and time in the process of persistent chains initiated by a single-pulse neutron source in burst reaction. The formula is validated by the experiments of CFBR-Ⅱ. The formula is the development of Hansen theory model because it can describe not only the developing tendency in the later stages but also the rapid increasing of neutron number in the early stage. Furthermore, according to the relation between the initial time of burst reaction and the intensity of neutron source, we illustrate that the initial time is hardly dependent on the intensity of weak neutron source.
ATOMIC AND MOLECULAR PHYSICS
2013, 62 (22): 223101. doi: 10.7498/aps.62.223101
By applying the first-principles method based on the density functional theory, we study the non-dissociative adsorption of C3H7SH molecule and the dissociated adsorption of C3H7S group both on Au(111) surface at five kinds of coverages (1/16, 2/16, 3/16, 4/16, 1/3). It is found that both the tilt angle and the adsorption energy are affected by coverage. When the coverage increases to 1/3, the tilt angle of the molecular axis reduces 6°–10°, and the adsorption energy reduces 0.21 eV. At a saturated coverage, the absorption properties are especially studied for three Au(111) surface structures of (3×3), (2√3×2√3 ight)R30° and 2√3×3. For the non-dissociative adsorption of C3H7SH at the saturated coverage, both the adsorption configurations and adsorption energies are almost the same for the three surface structures. But for the dissociated C3H7S group, the adsorption energies of surface structures of (2√3×2√3 ight)R30° and 2√3×3 are about 0.05-0.07 eV higher than that of the (3×3) surface structure. Effects of the van der Waals interaction on the adsorption configuration and energy are investigated by the DFT-D2 method. For the non-dissociative adsorption of C3H7SH/Au(111) system at a saturated coverage of 1/3, the van der Waals interaction reduces the interaction distance between the adsorbate and the substrate, and corrects the adsorption energy by 0.53 eV, which is close to experimental result.
Molecular structure and electronic spectrum of 2, 2, 5, 5-tetrachlorobiphenyl under the extenal electric field
2013, 62 (22): 223102. doi: 10.7498/aps.62.223102
Polychlorinated biphenyls (PCBs) are persistent organic pollutant, and 2, 2, 5, 5-tetrachlorobiphenyl is generally used as a model molecule of PCBs in some studies. PCB52 molecule is degraded under external electric fields. The molecular structure of PCB ground state is optimized by density functional theory (B3LYP) method with 6-311+g(d) basis sets. The effects of electric fields ranging from-0.04 a.u. to 0.04 a.u. are investigated on structural parameters, total energy, dipole moment and charges distribution. The transition wavelengths, oscillator strengths and excitation energies of the first six excited states under external electric fields are calculated by the time dependent density functional theory method. The result shows that the bond lengths of 1C21Cl and 14C20Cl increase with external electric field increasing. The dihedral angle of two benzene rings of PCB52 molecule increases under the electric fields, and the PCB52 molecule reduces toxicity. PCB52 molecule energy gaps decrease, leading to the fact that the molecule is susceptible to excitation to an excited state and reductive dechlorination reaction. As the increase of the applied electric field, the excitation energies rapidly decrease, absorption wavelengths are red-shifted toward longer wavelength and oscillator strength is no longer zero, which indicates that the PCB52 molecule is easily excited and dissociated.
Precise measurements of rotational constants of the pure long range state of ultracold cesium molecules
2013, 62 (22): 223301. doi: 10.7498/aps.62.223301
The high resolution spectrum of ultracold Cs2 pure long range 0g- state is experimentally measured using modulated trap loss spectroscopic technology. Based on Double photoassociation spectroscopic technique, precise frequency difference reference signals are constructed to accurately calibrate the resonant frequency intervals of the ro-vibrational levels, thus obtaining the relationship between the frequency interval of rotational level and the rotational quantum number. The experimental data are fitted by the non-rigid rotational model, and the molecular rotational constants corresponding to different vibrational levels in the ultracold Cs2 pure long range 0g- state are acquired. The experimental results demonstrate a linear decrease of the rotational constant with the increase of vibrational quantum number, and the linear decreasing rate is -0.41m MHz0.01 MHz.
2013, 62 (22): 223401. doi: 10.7498/aps.62.223401
The high-energy H++H impact excitation process in Debye plasma is investigated using impact parameter Born approximation method. In the cases of several different values of Debye length D, the inter-nuclear distance R of matrix elements, the weighted probability at a collision energy of 160 keV/u, and impact excitation cross sections in an energy range of 100–1000 keV/u for direct 1s → 2p transition in H for both the unscreened and screened Coulomb interactions are calculated. It is demonstrated that the magnitude of impact excitation cross section gradually reduces as screening parameter increases. According to the excitation cross section formula and the calculated results, a detailed analysis of the reason for the reduction caused by excitation cross section is given in this paper. The effects of screened Coulomb interaction on the potential of between incident particles and excited electronic and on the hydrogenatomic structure (wave function and energy level) have very important influence on the excitation cross section.
2013, 62 (22): 223402. doi: 10.7498/aps.62.223402
Sulfur in hydrogen combustion reaction chemistry, which plays an important role in meteorology, combustion reactions, and atmospheric pollution, has been extensively investigated recently. And its reverse reaction has also been a research object gradually. The research in this paper is based on the exact potential energy surface (L S J, Zhang P Y, Han K L, He G Z 2012 J. Chem. Phys. 136 094308), with using the method of quasi-classical trajectory on the exchange reaction of H (D)+SH/SD dynamic properties. In this paper, the scalar properties are calculated, including the cross section, rate constant, opacity function, product vibrational, rotational distributions, product scattering direction, rotational angular momentum orientation, and alignment properties. In this paper, how the collision energy and the isotope affect the reaction H (D)+SH/SD kinetic properties is analyzed in detail. The results show that as collision energy increases, the reaction cross section increases, product backscatter weakens gradually while the product rotational angular momentum alignment and orientation nature strengthen gradually. In addition, the isotope effect has a significant influence on the reaction kinetics. The reaction mechanism which is shown in the title and based on the reaction kinetics and the potential energy surface, is also discussed in this paper.
ELECTROMAGENTISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Simulation of marine controlled-source electromagnetic response in horizontally layered transversely isotropic formation by using improved transmission line method
2013, 62 (22): 224101. doi: 10.7498/aps.62.224101
In this paper, the two-dimensional Fourier transform and wave decomposition technique are used to transform Maxwell’s equation in transversely isotropic (TI) formation into two independent sets of transmission line equations about transverse magnetic (TM) wave and transverse electric (TE) wave. According to both transmission line theory and superposition principle, an improved transmission line method is advanced to simplify the computational process of TM wave and TE wave only by introducing the transmission line Green’s functions of the current source. Thus, the new algorithm and the new expressions of current source electromagnetic (EM) dyadic Green’s functions in frequency-wavenumber domain are established for realizing the efficient simulation of marine controlled-source electromagnetic (MCSEM) responses in the horizontally layered TI formation. On this base, the basic solutions of the transmission line Green’s functions and EM boundary conditions are utilized to derive the recursive formula of the generalized reflections and amplitudes of the TE and TM waves, and the analytic solutions of the Green’s functions in each bed are obtained. Then, by using Fourier inverse transform and Bessel integral formula, the MCSEM responses in frequency-spatial domain are expressed in the Sommerfeld integral form. A combination of the cubic spline interpolation with the Lommel integral is used to efficiently compute the MCSEM responses. Finally, we validate the modeling algorithm and investigate the influences of changes in operation frequency and anisotropic coefficient on the MCSEM response in the TI formation.
2013, 62 (22): 224102. doi: 10.7498/aps.62.224102
Looking for a new light source, especially short-wavelength coherent light source has attracted much attention. A possibility and basic conditions are discussed by using crystalline undulator field radiation as a short-wavelength laser; it is pointed out that the short-wavelength laser has not yet been available so far which is due to not only technical reasons, but also physical reasons. In this paper, the physical problem is analyzed by using parametric excitation method. Introducing the sine-squared potential, the particle motion equation is reduced to a pendulum equation with a damping term and parameter excitation term in the framework of classical mechanics and the dipole approximation. A stability of the system is discussed using Melnikov method, and the critical condition of the system is also analyzed. The results show that the stability of the system relates to its parameters. By adjusting these parameters appropriately, the stability of the system can be ensured in principle.
2013, 62 (22): 224201. doi: 10.7498/aps.62.224201
According to the feature of receptor system of coherent field imaging technique, also known as Fourier telescope, the influence of the deviation of receptors on optical transfer function (OTF) of coherent field imaging technique is investigated, and the relation between OTF and optical distance mean square deviation of receptor is also derived, which indicates that the OTF of coherent field imaging technique is a negative index function of square of product of optical distance mean square deviation and frequency difference. It can provide theoretical basis of determining the accuracy of receptor system.
Experimental study on coherent beam combination of fiber amplifiers using adaptive power-in-the-bucket cost function
2013, 62 (22): 224202. doi: 10.7498/aps.62.224202
Beam combination (BC) of fiber amplifiers based on master-oscillator-power-amplifier configuration is an outstanding way to generate high power and high beam quality laser output, where the tip/tilt aberrations among beamlets are considered as a serious influence factor to BC effects. In this paper, a new tip/tilt control method based on adaptive power-in-the-bucket (PIB) cost function is proposed to solve the problem of restricted tip/tilt correcting value in current BC systems. Experimental setup of coherent BC of two-channel 2 W fiber amplifier array is established. Home-made piezoelectric-ring fiber-optic phase-modulator and adaptive fiber-optics collimator are employed to correct piston-and tip/tilt-type aberrations, respectively. The feasibility of proposed tip/tilt control method using adaptive-PIB is demonstrated and nice effect of coherent BC is achieved.
Investigation on coherence characteristics of Gauss-Schell model beam propagating in atmospheric turbulence
2013, 62 (22): 224203. doi: 10.7498/aps.62.224203
The change in coherence length of Gauss-Schell model beam propagating in atmospheric turbulence is studied by comparing with propagation in free space. The coherence length change only depends on source parameters in free space while its change in turbulence is governed by source parameters and turbulence. Beam spreading results in an increase in the coherence length in vacuum. For propagation in turbulence, the coherence length increases due to beam spreading over relatively short distance while decreases on account of the enhancement of turbulence over a sufficiently long distance. Thus, the simple analysis of the influence of turbulence on the coherence length is not mature enough. In order to exclude the effect of beam spreading, the ratio of coherence length to beam size is employed. It is found that atmospheric turbulence always leads to the decline of ratio. The explanations, based on numerical simulation, of above-mentioned results are given in this paper.
2013, 62 (22): 224204. doi: 10.7498/aps.62.224204
Based on digital holography recording system, it is proposed to use both polarization and angular multiplexing techniques to detect a polarization state. Reference beam is divided into two beams with orthogonal polarization directions and equal initial phases. And the beams interfere with the two orthogonal components of object wave respectively, which generates two holograms recorded in one frame. The use of angular multiplexing separates the two orthogonal components of object wave in the Fourier domain by respectively introducing carriers towards different directions. By numerical filtering, inverse Fourier transform and then diffraction calculation, complex amplitude of object wave can be obtained at different distances to the holograms. With the obtained complex amplitude, it is possible to work out both the Stokes parameters and Jones vector, which describe the polarization state of the object wave. The measuring of elliptical polarization state and the characterizing of polarization states at different locations on axis prove the validity of this real-time full-field detection method.
2013, 62 (22): 224205. doi: 10.7498/aps.62.224205
Based on the coherent population trapping theory, a new physical model of the electromagnetically induced grating (EIG) is proposed. Analytical expression of the dielectric susceptibility is derived using this model. Owing to the atomic coherence, introduced by the coherent population trapping, three regions of dielectric susceptibility, i.e., a gain region, a region with no absorption and high-refraction index, and a dark region, are formed. Based on this model and the energy level of 87Rb, a novel scheme to implement the diffraction grating is proposed. Moreover, theoretical analysis and calculation of this grating are carried out. The results show that in the region with no absorption and high refractive index, the grating presents a pure phase grating and the first-order diffraction intensity can reach 0.4. In the gain region, however, the grating is a combination of phase grating and amplitude grating, and at its largest-gain point, the maximum of the first-order diffraction efficiency arrives at 1.26, and the second-order diffraction efficiency can also increase to 0.31.
2013, 62 (22): 224206. doi: 10.7498/aps.62.224206
Reliable spectroscopic parameters of probed species at high temperature, such as line strengths, self-broadening coefficients, air-broadening coefficients, and temperature exponents, are important in absorption spectroscopy for accurately studying species properties, such as temperature, concentration, speed, and their corresponding field distributions. However, parameters from widely used database such as HITEMP are mainly theoretical calculation results, and there exist considerable errors compared with the results in actual situations. In order to validate spectroscopic parameters of CO2 lines used in combustion diagnosis, CO2 spectrum is recorded as a function of temperature in a range between 700 K and 1300 K in experiment using a distributed feed-back diode laser. Parameters of each line are deduced, such as line strengths, self-broadening coefficients and temperature exponents. The relative errors between measured and calculated line-strengths are less than 11% at 5006.978 cm-1 and 5007.7874 cm-1. The measured self-broadening coefficients at different temperatures and temperature exponents are conducive to the detection of CO2 concentration in combustion diagnostics.
2013, 62 (22): 224207. doi: 10.7498/aps.62.224207
High-quality-factor microspheres with smooth surface are fabricated through surface tension by heating and fusing a single tapered fiber using arc of electrodes discharge. Stimulated Raman scattering of the third order nonlinear phenomena of microspheres with high power density whispering gallery modes was studied by coupling 976 nm laser into microspheres through tapered fiber as evanescent wave. The total six cascaded Raman lasers were observed in the experiment. At each order, single longitudinal mode and multi longitudinal mode Raman lasers were observed. The Raman laser at around 1200 nm was measured with pump power less than 582.6 μW. The sixth-order Raman laser at around 1287.04 nm was observed when pump power is 3.014 mW.
2013, 62 (22): 224208. doi: 10.7498/aps.62.224208
By virtue of Liouville Theorem and unified colored-noise approximation approach, an approximate Fokker-Planck equation for a tree growth Logistic model subjected to cross-correlated colored noises is derived, and the steady-state probability distribution (SPD) function is obtained. The steady-state properties of the Logistic model are analyzed. We find the following: (1) the position of peak of SPD moves toward left side as D increases while the position of the peak moves toward the contrary direction with Q increasing; (2) the peak of SPD becomes narrow and grows in height as |λ| increases, and for the case of λ >0, the position of peak moves toward right as D increases, but it is opposite for the case of λQ increases.
2013, 62 (22): 224209. doi: 10.7498/aps.62.224209
The mechanism of laser-induced surface acoustic wave (SAW) on annular stator is theoretically and experimentally studied. An annular stator with groove arrays is specifically designed. The physical model of laser-induced SAW on the stator is established, and the key factors influencing the wave amplitude are disclosed. We introduce a new kind of visualization method to detect laser-induced SAW on the copper-made annular stator, under a pulsed laser of 1053 nm wavelength, 30 ns pulse width and 1 mJ pulse energy. The results show that when the location of the irradiating laser spot is near the groove arrays, the SAW propagating towards the groove will be attenuated and absorbed immediately by the groove arrays, while the SAW away from the groove can keep propagating along the stator surface. In this way, the one-way propagation of laser-induced SAW is successfully acquired. In the contrast experiments, the laser-induced SAW travels in both directions on a copper ring without groove arrays, resulting in a chaotic state of the surface acoustic wave. The one-way SAW induced by pulsed laser on the annular stator will be used in the laser-driven SAW motor in the future.
Optical single sideband modulation with continuously tunable optical carrier-to-sideband ratio by employing a dual-parallel Mach-Zehnder modulator
2013, 62 (22): 224210. doi: 10.7498/aps.62.224210
We propose and demonstrate an optical single sideband (OSSB) modulation approach with continuously tunable optical carrier-to-sideband ratio (OCSR) theoretically and experimentally. In the proposal, one dual-parallel Mach-Zehnder modulator (DP-MZM) acts as a key component. By properly setting the modulator, three separate sub-modulators inside the DP-MZM can be used to realize the OSSB modulation, optical carrier phase-shift, and lightwave interference. By adjusting the bias voltage of one sub-modulator, the OCSR can be tuned continuously. In the experiment, the tuning range of OCSR is found to be between-20.8 dB and 23.5 dB at modulation index m=0.2. We also analyze the relationship between the OCSR and RF power after detection. It is found that with properly adjusting the OCSR, the receiver sensitivity can be greatly improved.
Study on the emission spectrum of AlO radical B2+X2+ transition using laser-induced breakdown spectroscopy
2013, 62 (22): 224211. doi: 10.7498/aps.62.224211
Based on laser-induced breakdown spectroscopy, a short pulse laser is used to excite Al2O3 (content of 99%) ceramic to produce ceramic plasma. The plasma emission spectrum is collected, and 33 spectral lines of AlO radical B2+X2+ transition are obtained. The time-resolved AlO radical spectrum and its relationship with laser pulse energy are investigated. The results show that the emission spectrum of AlO radical appears later and lasts longer than those of Al atom and Al ion. With the increase of the laser pulse energy, the spectral intensity of AlO radical decreases and the time when the maximum spectral intensity appears moves backward. Finally, the ceramic plasma produced in air is compared with that produced in Ar environment. The results prove that the formation of AlO radical spectrum has an important relationship with O2 in air.
Research on bionic underwater acoustic communication technology based on differential Pattern time delay shift coding and dolphin whistles
2013, 62 (22): 224301. doi: 10.7498/aps.62.224301
Regarding the performance degradation caused by the traditional method of covert underwater acoustic communication, in this paper we propose a bionic underwater acoustic communication technology on the basis of differential Pattern time delay shift coding system and dolphin whistles. The signal band of dolphin whistles is narrow and the intervals between information signals are different, and the cross-correlation is very weak. Dolphin whistles are used for synchronization and Patterns, for the time interval between dolphin whistles conveys the information bits. The mimicked version of communication signal is not easy to detect and intercept, and the special encoding method of differential Pattern time delay shift also makes the information not easy to decipher, so this bionic underwater acoustic communication technology has strong covert and confidential nature and it also has an excellent performance in anti inter-symbol interference and anti Doppler effect. A tank experiment is conducted for this system. At SNR 0 dB and relative movement, the user message is recovered at an effective data rate of 67 bit/s with low bit error. It is proved that the system has an effectiveness, robustness and covert nature.
2013, 62 (22): 224302. doi: 10.7498/aps.62.224302
To solve the problem of low bandwidth efficiency of underwater acoustic spread spectrum communication, a multicarrier modulation scheme combined with M-ary spread spectrum and cycle shift keying (CSK) is proposed in this paper. The code sequences chosen by M-ary modulation are then modulated by CSK, simultaneously, they are modulated by the orthogonal multicarrier. The approach enhances the bandwidth efficiency greatly. The performances of the system with m-sequence, Kasami-sequence, and Gold sequence as the code sequence are compared over the underwater acoustic multipath channel with the same data rate and the same bandwidth. The simulations and the results of pool experiment show that m-sequence as the code sequence performs best and Gold sequence performs worst. The number of the m-sequence is limited. In order to increase the data rate further and make the performances of other sequences close to the m-sequence, a new approach to suppressing the inter-carrier interference (ICI), named multiple sequences, is proposed. The approach can greatly suppress the ICI caused by multipath and make the performance close to the performance of the m-sequence.
2013, 62 (22): 224303. doi: 10.7498/aps.62.224303
Compared with multi-dimension inversion, the single parameter inversion has the main advantages that inversion complexity decreases with the number of parameters increasing. Firstly, the slop of bottom loss versus grazing angle FdB is proposed to serve as a single parameter. Secondly, in terms of mode and ray paths, the relation between impulse response and seabed reflection loss property FdB is discussed. Finally, a time-domain inversion method using least-squares fitting to intensity decay rate is designed accordingly. Experimental data in North Yellow Sea are inverted. The inverted results are evaluated by the core samples. Good agreement is also obtained between measurement and predictions of transmission losses with using the inverted result. As this method only requires single hydrophone and comparatively few measurements, it is believed to provide a rapid but robust estimation of FdB which can meet the need for many applications.
Numerical study of collision process between two equal diameter liquid micro-droplets using a modified smoothed particle hydrodynamics method
2013, 62 (22): 224701. doi: 10.7498/aps.62.224701
In this work, the dynamical collision process between two miscible/immiscible micro-droplets is simulated by a modified smoothed particle hydrodynamics (C-SPH) method. In order to improve the numerical accuracy and stability of traditional SPH method, a kernel gradient modified scheme without kernel derivative is considered. Meanwhile, an improved surface tension technique based on the van der Waals model is adopted to deal with the moving interface. The reliability of C-SPH method of simulating the deformation process between two droplet collisions is tested through the numerical simulations of coalescence process between two miscible Newtonian droplet collisions. Subsequently, the coalescence process of miscible polymer droplet collision and the deformation process of bouncing and separation between two immiscible droplet collisions are investigated, in which the control equations of droplets are all based on the van der Waals model. The influences of the collision velocity, collision angle and the density ratio on the deformation process of collision are discussed, and the changes of liquid bridge and rotation angle are analyzed.
Study on continuous vortices induced by sub-microsecond pulsed surface dielectric barrier discharge plasma
2013, 62 (22): 224702. doi: 10.7498/aps.62.224702
The experiments to generate vortices continuously using sub-microsecond pulsed surface dielectric barrier discharge (SDBD) actuator are conducted by particle image velocimetry (PIV). The double-frequencies actuation mode is presented which includes repetitive pulse frequency and vortex frequency. It is found that the empty zone of PIV particles appears in the place where the particles are quite few even nil during the experiments. When discharges occur the primary empty zone is produced by the micro explosion due to the released heat of plasma, and when discharges end the secondary empty zone appears. The induced flow is farther apart form wall and the influence of wall friction should be suppressed due to primary empty zone. When the secondary empty zone on the left side of actuator exposed electrode is blown away completely, the next actuation can start. In order to control the flow more effectively, the pulse voltage with higher repetitive frequency should be applied. The pulse number during one vortex time should be more than 10. As the pulse number increases, the maximal velocity of induced flow increases but the momentum transfer efficiency decreases. The mechanisms releasing heat and body force can be triggered by using the sub-microsecond pulse SDBD actuator.
2013, 62 (22): 224703. doi: 10.7498/aps.62.224703
The appearance of gas bubbles in a valve-less micropump is generally undesirable as they can lead to performance deterioration, life reduction and even complete failure of the micropump. In order to predict influence of gas bubbles in valve-less micropump chamber on periodic driving pressure, the mathematical models, including volume change of chamber, continuity equation, effective bulk modulus and resistance coefficients of the nozzle and diffuser, are given to describe dynamic characteristics of piezoelectric valve-less nozzle/diffuser micropump. The influence of different gas bubble volume in chamber on the valve-less micropump periodic driving pressure is analyzed. Pressure pulsations with two gas bubbles into the valve-less micropump chamber are simulated and tested. Simulation and experimental results are given. Comparison of the results shows that the mathematical model and simulation method can handle the prediction of pressure pulsations accompanying gas bubble in the valve-less micropump.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2013, 62 (22): 225201. doi: 10.7498/aps.62.225201
To investigate the mechanism of electrification from aero-engine jet and the electrification effect on the overall charging characteristics of vehicle, a simulation model of concentration of charged particles in aero-engine is build based on the equations of fluid motion. And concentration changes of various particles are simulated. To verify the simulation result, a special electrostatic induction sensor for detecting the electrification of engine jet is designed, according to the principle of the Faraday cup, to measure the dynamic potential when the turbofan engine starts, operates steadily, accelerates, decelerates and stops. The simulation and experimental results show that the aircraft is negatively charged by the electrification from aero-engine jet and the mechanism of electrification from aero-engine jet is described specifically. The research may provide a guidance to the further study on analyzing the overall charging characteristics of vehicle during the flight.
According to the theory of nonlinear Rosen-Zener tunneling, we investigate the nonlinear Ramsey interference of Bose-Einstein condensate in a double-well potential with Gaussian pulse. Rich Ramsey fringes are shown by the numerical simulations. The influences on the fringes of the atom-atom interaction and the period of Gaussian pulse are discussed. We obtain the analytical expression for the fundamental frequency of Ramsey fringes by using Hamilton equation. The relation of the frequency to the interaction strength and the Gaussian-pulse period is found by analyzing the fringes through Fourier transformation. The numerical simulations are consistent with our theoretical predictions.
A high transmittance, flat energy spectrum response detector is designed. The relationship between the image and absolute intensity of the pulse radiation is established via a detector, which simplifies the calibration of the absolute measurement in the imaging system. And a new technical approach to the absolute imaging diagnosis for the pulsed radiation is developed. The experiments show that the uncertainty of the absolute intensity measured by this technology is 33%.
Variations of implosion asymmetry with hohlraum length and time in indirect-drive inertial confinement fusion
2013, 62 (22): 225204. doi: 10.7498/aps.62.225204
In order to achieve the high density compression in laser indirect-drive inertial confinement fusion, the implosion symmetry and hohlraum radiation uniformity are strictly required. To study the variations of implosion asymmetry with hohlraum length and time, three kinds of hohlraum lengths are adopted in experiment. X-ray emission from capsule fuel is measured by an X-ray framing camera. Based on measured capsule compression process and ellipticity variation, it is preliminarily judged that the medium hohlraum of 1700 μm long is the closest to implosion symmetry demand of Shenguang Ⅲ prototype laser facility. Time-resolved implosion asymmetry is derived from a simplified analytic model, in which used is the time-resolved hohlraum radiation nonuniformity derived from a view-factor code. The derived results of the time-resolved implosion asymmetry are basically in agreement with experimental results. The physical mechanism for how hohlraum radiation nonuniformity evolution induces the variations of implosion asymmetry with hohlraum length and time is analyzed.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Diffusion of order reconstruction induced by 1/2 wedge disclination in a thin hybrid nematic liquid-crystal cell
2013, 62 (22): 226101. doi: 10.7498/aps.62.226101
Based on the Landau-de Gennes theory, the diffusion of order reconstruction induced by 1/2 wedge disclination in a thin hybrid cell is investigated by the relaxation iterative method. The core structure, the biaxial structure, and the diffusion of order reconstruction as the cell thickness decreases, are explored. The defect structure and the range of order reconstruction do not change when the cell thickness is larger than 15. As the thickness decreases from 15, the defect range broadens along the substrate direction, and the biaxial region as well as the range of order reconstruction also enlarges. When the thickness further decreases to below the critical value of 10, the biaxial region and the order reconstruction range merge into an entire cell, where the planar orientation is abruptly converted into the perpendicular one across the biaxial wall. The results obtained in this paper are important for further studying the regulating effect of topological defect on submicron colloidal particles in nematics.
2013, 62 (22): 226102. doi: 10.7498/aps.62.226102
For single-wall carbon nanotubes filled with gold nanowires, a kind of carbon nanotube cable type composite material, its thermal conductivity is simulated by non-equilibrium molecular dynamics method. The Tersoff potential is employed for C-C bonding interactions, the Lennard-Jones potential for C-Au interactions and the embedded atom method potential for Au-Au interactions. It turns out that the electronic thermal conductivity (ETC) of gold nanowire is much lower than that of the composite with the same size, so the ETC of metal nanowire could be ignored. The carbon atoms tend to vibrate along the axial direction of the tube because of the interaction between gold and carbon atoms. Furthermore, the umklapp scatterings among phonons are reduced and the phonon mean free path is increased. Therefore, the thermal conductivity of the composite is 20%45% higher than the bare carbon nanotubes in a temperature range of 100500 K, but the growth rate decreases with the rise of temperature. The thermal conductivity of the composite rises with the increasing of length but in a sharper rate, and decreases with the increasing of diameter in the same rate, which is similar to the bare carbon nanotubes.
2013, 62 (22): 226103. doi: 10.7498/aps.62.226103
The effects of different precipitants (NH4HCO3 and NaOH) on the performances of ZnO varistor ceramics which were prepared by coprecipitation method were analyzed. There are noticeable influences for different precipitants to the microstructure and electrical performances of ZnO varistor ceramics. The change of microstructure is caused by the properties of precipitants themselves while the change of electrical performance is caused by the influence of precipitants to the grain boundary potential barrier properties. Besides, the donor impurity ion Na+ introduced by NaOH in the ZnO varistor ceramic will increase the free electron concentration in the grain. So the densities of intrinsic defects (zinc interstitial and oxygen vacancy) are restrained. The density of zinc interstitial is more sensitive to donor impurity ions compared with oxygen vacancy. Therefore the choice of precipitant is important when using coprecipitation method to prepare the powder of ZnO varistor ceramics. Even little impurity ions will result in the obvious change of the performance of varistor ceramics. The impurity ions should be avoided in the powder of ZnO varistor ceramics.
2013, 62 (22): 226201. doi: 10.7498/aps.62.226201
In this paper, the damage evolution of high purity aluminum under shock loading is investigated experimentally. The surface profile measurement technique based on white light axial chromatic aberration is used to measure the cross-section of sample which is soft-recovered from dynamic impact experiments. Then, the cross-section image and 3-D surface topography are obtained by reconstruction of the data, the quantified damage is also calculated based on the data. The results show that in the early stage of damage evolution the spatial distribution of relative void volume is not continuous, which results from nucleation affect, size affect and stress relaxation. The damage curves show not only the maximum damage but also a second peak. In the late stage of damage evolution, the spatial distribution of damage increment is discontinuous, which results from the coalescence of voids. The damage of the coalescence region rapidly increases and the secondary peak of the damage curve disappears.
2013, 62 (22): 226301. doi: 10.7498/aps.62.226301
Within the framework of effective mass approximation, the values of energy eigenvalue En in Ga1-xInxNyAs1-y/GaAs quantum well are theoretically calculated using shooting method. In addition, we calculate the electron-LO phonon scattering and mean scattering rate at different temperatures, well width, N concentrations and In concentrations for an electron initially in the second subband and finally in the ground state using Fermi’s golden rule. It is shown that the electron-LO phonon scattering and mean scattering rate increase with the increase of N concentration under the In concentration constant. The electron-LO phonon scattering and mean scattering rate decrease with the increase of In concentration under the In concentration constant. The electron-LO phonon scattering increases monotonically with the increase of temperature. When the temperature is relatively low, the variation of mean scattering rate is not obvious with the increase of temperature When the temperature is relatively high, mean scattering rate increases with the increase of temperature. The scattering and mean scattering rate increase up to their maxima and then begin to decrease as the well width increases. The maximum value is reached when the well width is about 200 Å. Our calculated results are meaningful and can be used for designing the optoelectronic devices based on Ga1-xInxNyAs1-y/GaAs quantum well.
2013, 62 (22): 226801. doi: 10.7498/aps.62.226801
Reflection high energy electron diffraction (RHEED) is used to monitor the two-step desorption of oxides on InAs(001) surface in the vacuum chamber, and the high temperature indium-assisted desorption processes of surface oxides under high arsenic pressure and low arsenic pressure are compared. The first step of two-step deoxidation method for InAs substrate is to heat the substrate slowly at high temperature. The second step is high temperature indium beam-assisted desorption of surface oxides. The RHEED patterns of sample at high temperature desorption of oxides show that the high temperature indium beam-assisted desorption of InAs surface oxide method could eventually clear residual oxide that the traditional slow heating method cannot remove. The scanning tunneling microscope images of sample after homogeneous epitaxial growth prove the viability of high-heat indium beam-assisted desorption of InAs surface oxide under high arsenic pressure. Finally, we analyse the mechanism of high-heat indium beam assisted desorption of surface oxides of substrate.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2013, 62 (22): 227101. doi: 10.7498/aps.62.227101
The lattice parameters, total energy, magnetism, density of states, and band structure in the multiferroic material DyMnO3 with orthorhombic structure are investigated by using different magnetic models, and the non-collinear magnetism and the collinear magnetism are taken into account by using density functional theory combined with the projector augmented wave method via the software package of VASP. The generalized-gradient approximation (GGA) pseudo potential is used in the calculation, and the local spin density approximation +U method is also adopted to deal with the strong correlation effect of the 3d electrons. The results show that Mn ion in the AAFM magnetic model has the lowest energy and is the most stable, while the weak magnetism of the rare earth ion Dy can be neglected, and that the total energy and the magnetic moment of DyMnO3 in orthorhombic structure increase when the non-collinear magnetic structure of Mn ion is considered and that the DyMnO3 material is an indirect-gap insulator with an energy gap value of 0. 38 eV obtained from GGA or 1.36 eV from GGA+U, and the lattice distortion should be considered to be due to the hybridization between Mn-3d and O-2p electrons, which can be analyzed from the density of state.
2013, 62 (22): 227201. doi: 10.7498/aps.62.227201
Owning to its sharp metal-insulator transition at ～340 K, VO2 is becoming an attractive candidate for the electrical and optical material. Here we report on the fabrication and characterization of VO2 thin film obtained from the V2O5 thin film annealed in Ar/H2 ambience. V2O5 thin film is fabricated by using the pulsed laser deposition system on the R-sapphire substrate under several different conditions by varying the substrate temperature and the pressure of the growth atmosphere to optimize the growth condition. Then we carry out the annealing treatment on the V2O5 thin film in different annealing conditions. The VO2 thin films are characterized using X-ray diffraction, X-ray photoelectron spectroscopy and R-T measurement. When annealed in a temperature range of 500–525 ℃ for 3 h in H2(5%)/Ar ambience, the V2O5 thin film can be converted into the mixed-structures of metastable monoclinic structure (B) and the monoclinic rutile structure (M) which is responsible for the phase-change property. And under the same conditions, when the annealing time reaches 4.5 h, the pure VO2(B) is obtained. Further we anneal the VO2(B) in pure Ar ambience and tentatively realize the resistivity reduced by nearly four orders with the temperature increasing from 25 ℃ to 105 ℃. The transition temperature is nearly 350 K. And the transition between VO2 (B) and VO2 (M) is realized.
The effect of additional permanent magnet magnetizing methods on magnetic field distribution and the levitation force of single domain GdBCO bulk superconductor
2013, 62 (22): 227401. doi: 10.7498/aps.62.227401
It has been investigated that the interaction force between a cubic permanent magnet PM1 and a GdBCO bulk (HTSC) superconducting permanent magnet (SCPM) magnetized by a cubic permanent magnet PM2 under different configurations at 77 K. Two configurations were used for the magnetization of the GdBCO bulk, one is that the North pole of the PM2 is in upward direction, the other is in downward direction, so that the North pole of the SCPM is in two states SCPM↑ and SCPM↓; the vertical distance between the bottom surface of PM1 and the top surface of SCPM is kept as a constant value, but the PM2 can be fixed at any positions (x) along a diameter of the GdBCO bulk during the magnetization process. It is found that: for the PM1↓-SCPM↑ configuration, the maximum levitation force is increasing from 16.7 N to 23.1 N when x increases from –15 mm to 0, and then decreases to 16.6 N when x further increases to 15 mm; but for the PM1↓-SCPM↓ configuration, the maximum levitation force is decreasing from 17.7 N to 7 N when x increases from –15 mm to 0, and then increases to 17.6 N when x further increases to 15 mm. These results are not only much different in the two configurations, but also much different from the maximum levitation force 17.1 N of the sample under zero field cooled condition, which is closely related with the trapped field distribution of the SCPM at different x values. These results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on scientific and reasonable designing of the system configurations, which is very important during the practical design and applications of superconducting magnetic levitation systems.
Effects of high magnetic field on the microstructure and magnetic properties of Fe80Ni20 thin films with different thickness values
2013, 62 (22): 227501. doi: 10.7498/aps.62.227501
Fe80Ni20 thin films with different thickness values are prepared by the molecular beam vapor deposition technique, respectively, in the cases with applying no magnetic field and with applying a 6 T magnetic field perpendicular to the surface of substrates. Film property studies show that as film thickness value increases, the coercive force in-plane decreases, which is in accordance with Neel theory, and that the squareness ratio first quickly increases, and then slowly decreases. The 6 T magnetic field restrains coalescence and abnormal growth of grains, and reduces surface roughness. Therefore, with 6 T magnetic field applied during the film preparation, the coercive force of thin film is less and the squareness ratio is larger than that with no magnetic field applied. The thin films are anisotropic in-plane with applying no magnetic field, but isotropic with applying a 6 T magnetic field.
Micromagnetic analysis of the effect of the easy axis orientation on demagnetization process in Nd2Fe14B/α-Fe bilayers
2013, 62 (22): 227502. doi: 10.7498/aps.62.227502
The hysteresis loops and energy products in the magnetization reversal process are investigated by one-and three-dimensional micromagnetic methods for a Nd2Fe14B/α-Fe bilayer system with an angle β between the applied field and the easy axis, and the results are compared with available experimental results. The calculation shows that the deviation of the easy axis affects the magnetization reversal process seriously. When β≠0°, there is no obvious nucleation in the magnetization reversal process. The remanence decreases as β decreases, and the squareness of the hysteresis loops is weakened, leading to the sharp decrease of energy product. For Nd2Fe14B(10 nm)/α-Fe(8 nm), the energy product decreases by 30.3% when β=10°. In the magnetization reversal process, as the total energy reaches the maxium, Zeeman energy decreases with increasing of β, and the exchange energy first increases and then decreases slightly, and the anisotropic energy increases with the increasing of β. The deviation of easy axis has a greater influence on the energy product of the bilayer system with larger soft thickness. The out-of-plane deviation of easy axis has a similar effect.
Transmission and application of electron spin wave function in alternating ferromagnetic and nonmagnetic layers
2013, 62 (22): 227701. doi: 10.7498/aps.62.227701
We establish a general model of a finite periodic system by n pairs of alternating ferromagnetic and nonmagnetic (FNF) layers. Using Bloch spin wave quantum theory, the basic properties of alternating FNF layers and the dependence of property of electron wave scattering in alternating layers on the number of layers are investigated. It is found that an electron wavefunction in the system can be expressed as the superposition of eigenvectors of a transfer matrix or Bloch-like functions in an infinite periodic system. Form this function we can obtain an exact solution for monochromatic wave scattering of a system with an arbitrary number of layers. On this basis, the dependences of reflection and transmission coefficients on energy for the electron wavefunction in a periodic system are determined. The calculation of spectral window shows that its energy position and width are the same as those of almost full reflection region. The system can be used as spin filter due to high-energy dispersion and dependence of exchange energy on electron spin direction.
Molecular dynamics simulation of low-energy hydrogen atoms bombarding tungsten (001) surface at different angles and their depth distribution
2013, 62 (22): 227901. doi: 10.7498/aps.62.227901
Molecular dynamics simulations are performed to study the diffusion behavior of low-energy hydrogen atoms in bcc tungsten (001). The simulation results show that when the energy of vertically incident hydrogen atoms is in a range of 0–20.0 eV, their retention probability increases rapidly; in the whole incident energy range 0.5–50.0 eV, the reflection probability gradually drops, but still exceeds 60%. By varying the incident angle, the retention probability may increase in some energy ranges compared with those in the case of vertical incidence, but the reflection probability still dominates. In this paper, we also obtain the depth distribution of energy deposition of incident hydrogen and its isotopes. It is found that tritium deposits more energies in the surface region than hydrogen.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2013, 62 (22): 228101. doi: 10.7498/aps.62.228101
A three-dimensional quasi-steady state mathematical model for the coupled arc in double electrode tungsten inert gas (TIG) welding is established based on the fluid dynamic equations and Maxwell equations under the reasonable boundary conditions. By solving these equations, the distributions of temperature, velocity, arc pressure and current density of the coupled arc are obtained. The results accord well with previous experimental results. It is found that the maximum temperature and plasma velocity of the coupled arc decrease compared with those of the TIG arc in the similar conditions. The peak value of arc pressure and current density at the anode surface decline sharply. Both the electrode spacing and arc length have significant influences on temperature and flow field, current density, and arc pressure of the coupled arc. Furthermore, coupled arc pressure and current density at the anode cannot be described by Gaussian assumption.
2013, 62 (22): 228501. doi: 10.7498/aps.62.228501
An InP/InGaAsP uni-traveling-carrier double heterojunction phototransistor (UTC-DHPT) photodetector is simulated and analyzed in a two-dimensional (2D) model utilizing a numerical device simulator (Atlas). The effects of device structure parameters on operational performance, such as responsivity and characteristic frequency, are studied in detail. Simulation results indicate that the UTC-DHPT can ease the contradiction between detection efficiency and working speed, which exists in traditional heterojun-ction phototransistor and achieve both high responsivity (≥17.93 A/W) and high characteristic frequency (≥121.68 GHz) simultaneously.
2013, 62 (22): 228502. doi: 10.7498/aps.62.228502
In this paper the resistive mechanism of the device with structure of ITO/PMMA/Al and the relevant SPICE simulation circuit are investigated. By optimizing the annealing temperature of PMMA, the devices can achieve continuous erasable-readable-writeable-readable operation. Based on the surface morphology researches of PMMA with different annealing temperatures, a physics model of nonlinear charge-drift mechanism in doping system is established to explain the resistance characteristics of the organic device. And the state equations are established to describe the interface movement of different doping regions in the model. Then, the SPICE simulation circuit is set up with feedback control integrator. Finally, substituting the measured parameters of device into the simulation circuit, we obtain the current-voltage simulation curve which is in good agreement with the actual results of the device. The results verify the resistance mechanism of nonlinear charge-drift in our device, and the applicability of the SPICE simulation of nonlinear charge-drift model based on inorganic memristors to the organic resistive memory.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The classification of winter regional extreme low temperature events in China and their corresponding relationship to climatic indices extreme anomaly
2013, 62 (22): 229201. doi: 10.7498/aps.62.229201
We identify China regional low temperature extreme events (RELTEs) in winter during the periods from 1951 to 2010 using objective identification technique for regional low temperature extreme events (OITRELTEs). The 559 RELTEs are identified and classified into 6 types, i.e., nationwide style, east style, northeast-north China style, north-south China style, south style, and northwest-south China style, according to the spatial distribution of these events. The circulation backgrounds of different styles of low temperature events are also analyzed. In addition, taking the classical event that began from January 21st in 1971 for example, anomaly characteristics of sea surface temperature, geopotential height and winds vectors are investigated specifically. Based on these analyses, the corresponding relationships between different types of events and anomalies of climatic indices are further studied, and the relations between mainly influencing index and event are obtained for different types of events. On the whole, when the NINO3.4, the Pacific decadal oscillation, and the Arctic oscillation are small and the winter wind index is strong, the probability with which the RELTE happens is high; in the years in which the winter average values of the four indices reach 15% of extreme threshold, the percentages of occurrence of RELTE reach up to 80.0%, 77.8%, 60.0% and 62.5%, respectively. Therefore, certain signals can be offered for diagnosing and predicting the RELTE from the index anomalies.
2013, 62 (22): 229401. doi: 10.7498/aps.62.229401
The rapidly charging event (RCE) is a new category of spacecraft charging, which was first observed at an international space station in 2006. It occurred in the presence of the eclipse, with the floating potential increasing abruptly to tens of volts, well beyond the safety level of –40 V, within a few seconds. The RCE has not yet been understood thoroughly until now. Based on Ferguson and Craven’s theory, we developed a physical model for the rapidly charging events recently and gave satisfactory predictions compared with the observations. In this paper, we investigate the physical process and mechanism in detail, and explain the statistical characteristics and the underlying physics through the model calculations. It is shown that the rapidly charging event is a non-equilibrium charging process and driven by the high voltage solar arrays. The rapid charging is mainly due to the fact that the cover glass blocking effect cannot follow the rapid increasing of the solar voltage when it is abruptly turned on at the exit of eclipse. As the RCE reaches equilibrium it acts as a normal charging event. The rapidly charging amplitudes depend on many factors, such as the switch-on time of the solar arrays, the pattern of switch-on, etc., which play key roles, and so that the floating potential data exhibit a spread to a certain extent. The maximum potential decreases with electron density increasing, which is in good agreement with observations.
2013, 62 (22): 229402. doi: 10.7498/aps.62.229402
ELF/VLF waves are generated via amplitude-modulated heating of the lower ionosphere. Based on the modulated heating theory, the directional radiation models of dual beam amplitude modulation (DAM) and circle geometric modulation (CGM) are established by introducing the phased array ideas, which are validated by comparison with the experimental data. According to the models, differences between the above two directional radiation models and the normal amplitude modulation (AM) are analyzed with parameters of HARRP phased-array HF facility, and the influences of the modulation frequency (fELF/VLF) and elevation of the heating waves on mode are investigated as well. Compared with the AM mode, DAM and CGM can realize the directional radiation, and enhance the radiant intensity by properly setting the initial phase, the modulation frequency (fELF/VLF) and angle of inclination of the heat wave to the vertical direction. The ELF/VLF radiant intensity may be increased by 11.3 dB when replacing AM with CGM.
2013, 62 (22): 229601. doi: 10.7498/aps.62.229601
Small space debris impact the surface of spacecraft frequently at a velocity of about 10 km/s, thereby creating plasma cloud clusters during the impact. If the impact happens in the area with high voltage, then the plasma can induce discharge. This mechanism of spacecraft discharging has been widely accepted but research about it is rare. In this paper we present the experimental results of 200 micron glass ball particles impact induced discharge carried out on a plasma drag small space debris accelerator. The experimental results and characteristics of the discharging signals are also analyzed in this paper.