Comprehensive Survey for the Frontier Disciplines
Morphologies of one-dimensional ZnO nanostructures (nanowires, nanobelts, etc.) and their characteristics are introduced. Methods of growing one-dimensional ZnO nanostructures and the relevant devices are demonstrated comprehensively, e.g. hydrothermal and chemical vapor deposition and so on. Progress in applications including light-emitting diodes and nanogenerators is provided. Finally, the future developing trend of one-dimensional ZnO nanostructures is presented and some novel means, techniques, etc. are also proposed.
The present status of research on negative electron affinity (NEA) GaN vacuum surface electron source is discussed with considering the latest research conclusions from our country and foreign country. Some valuable results about GaN vacuum electron source have been obtained including the theory of photoemission, the surface depuration method, the activation technique for GaN photocathode, the measurement of spectral response, the characteristics of material etc. The mechanism of photoemission for NEA GaN vacuum electron source is studied preliminarily. The depuration method of obtaining the atom cleanness surface is given. The GaN material is effectively activated with Cs or Cs/O. The spectral response of GaN vacuum electron source material is measured. The material characteristics affecting the quantum efficiency of the electron source are analyzed. The next investigation is also mentioned.
Influential factors of time reversal Mirror on focusing property of time-reversed electromagnetic wave
A novel method to calculate transient response of thin-wire structure above the layered lossy half-space
A novel hybrid method combining time domain integral equation(TDIE) with finite difference time domain(FDTD) is proposed to calculate transient response of thin wire structure above a layered lossy half-space. The time domain reflections of electromagnetic waves from layered half-space are obtained by one-dimensional FDTD method. Then, transient response of thin-wire induced by two excitation sources (incident wave and reflected wave) is achieved by employing the TDIE. The computed results illustrate the feasibility and high efficiency of the presented scheme.
Design of a quasi-optical mode converter for 94 GHz gyrotron
Based on geometry optics theory and vector diffraction theory, mode converter is studied to convert the gyrotron and other high-power microwave oscillator output mode into quasi-optical Gaussian beam, using Vlasov launcher and two quasi-optical reflector achieved quasi-Gaussian mode TEM00 transverse output.The working mechanism of Vlasov launcher in analyzed, the radiation field is calculated by using vector diffraction theory, and the surface radiation field is also calculated by using the surface current distribution method. A built-in quasi-optical mode converter is designed to convert the 94GHz, TE62 model millimeter wave into quasi-optical Gaussian beam through programming.
The influence of root mean square phase gradient of continuous phase plate on smoothing focal spot
In order to satisfy uniform irradiation requirement in inertial confinement fusion(ICF) system, the influence of surface characteristics of continuous phase plate on beam quality is studied in this paper. Based on wave optics and geometrical optics, theoretical analysis model is established, respectively. And the parameter, root mean square gradient, is used to unify both theoretical models. Meanwhile, the smoothing effects of root mean square phase gradient of continuous phase plate on laser beam with low-frequency aberrant wavefront are simulated. Numerical simulations show that the radius of focus spot will increase with the increase of root mean square phase gradient of continuous phase plate, and nonuniformity of beam top will decrease quickly, then reduce slowly and tend to be unchanged finally. So smoothing effect of continuous phase plate is obvious. In addition, energy availability factor has little change, then decreases gradually and reduces slowly. Spot size, nonuniformity of beam top and energy availability factor are all in a good range when the correlation length of continuous phase plate is not changed and root mean square gradient is 0.2—0.8 wave/mm.
Changes in the degree of paraxiality for Laguerre-Gaussian beams
Taking the Laguerre-Gaussian (L-G) beam for example, the changes in the degree of paraxiality for monochromatic beams are studied in detail. It is shown that the beam parameters, including mode indiex, relative waist width, propagation through a paraxial ABCD optical system, and diffraction by an aperture may change the degree of paraxiality. But the degree of paraxiality remains unchanged in free-space propagation. The results are illustrated by numerical examples and interpreted in physics by relating the degree of beam paraxiality with the far-field divergence angle.
Characteristics of spontaneous emission from a two-level atom in a very high Q cavity
In this paper we investigate a coupled system of an initially excited two-level atom coupled to a monomode cavity,and compute spontaneous emission spectrum and mean population density emitted by the atom and the cavity using the quantum theory that accounts for theoretical derviation and numerical calculation.The spectra emitted separately by the atom and the cavity in of strong coupling region are dramatically different from those in weak coupling region at resonance.The cavity spectrum line splitting in the strong coupling region,however,a hole exists in the atomic spectrum in the weak coupling region.We study systematically the emission spectra when the atom and the cavity are detuned,and the results show that if the cavity linewidth is much smaller than the atomic linewidth(good cavity regime),photons are emitted at the cavity frequency even if the atom and the cavity are strongly detuned,and provide theoretic foundation for the apparently puzzling feature observed in the recent experiment.In this paper we computate the atomic and the cavity mean population densities each as a function of time and their relation to the luminous intensity, and offer a new insight into civity induced transparency effect.
Phase-dependent electromagnetically induced transparency in a four-level atom system
Generation of Raman light source with an anti-reflection-coated edge-emitting laser diode in an external cavity
Phase locked two laser beams with a tunable and controllable frequency difference in a range of several GHz play a major role in the stimulated Raman transition, coherent population trapping, quantum states preparation and other quantum manipulation researches. We demonstrate such leaser beams with a tunable frequency difference in a range of 6.0—9.3GHz. In particular, the frequency differences of 6.835GHz and 9.192GHz corresponding to the ground state's hyperfine splitting in Rb87 and Cs133 respectively are realized experimentally. The power of the modulated beam is measured to be 6.87mW. With an antireflection-coated edge-emitting diode placed in an external cavity, we can suppress the carrier completely when the modulation frequency is lower than 4.0GHz by adjusting the external cavity length, the temperature, the current of the diode, and the power of the modulation. When the modulation is higher than 4.0GHz we cannot fully suppress the carrier, but we can also obtain the laser beams each with a high modulation depth due to modulation enhancement by external cavity resonance.
Output intensity of Ne-like Ge soft X-ray laser with double-pass amplification
Ne-like germanium soft X-ray lasers driven by nanosecond laser have very good applications, due to their stable output and strong intensity. The double-pass amplification mode, with a multi-layer reflective mirror added is investigated. The estimate and the experiment show that the output intensity of Ne-like germanium soft X-ray laser is enhanced by double-pass amplification. For 24mm length of double-pass amplification, the total output intensity is enhanced by 2.3 times as against that with no mirror added. Meanwhile, this mode results in quality decline of soft X-ray laser beam. So this mode is not entirely beneficial to the applied study.
Optical quality of high-power fiber laser beams propagating through collimating systems
Temperature dependent Raman spectra and micro-structure study of hexagonal MgTiO3 crystal
Hexagonal MgTiO3 crystal powder is prepared by solid-phase sintering method and characterized by X-ray diffraction method. Temperature dependent crystal cell parameters (293—1473 K) are deduced from the results of in-situ X-ray diffraction measurement with temperature increasing. In-situ Raman spectra are recorded (293—1623 K) at various temperatures and all the vibrational modes were assigned with the aid of theoretical calculation of first principles. It is demonstrated that temperature dependent Raman spectra are sensitive and can show the delicate variations of different bond lengths and angles between various atoms of local structure. But the relationship between Raman shift and bond length and angle can be independent of temperature. Those observed Raman vibrational bands being wider and overlapped with the increasing temperature reveals the enhanced amplitude of atomic instantaneous movement, which leads atoms to diffuse more heavily and the stability of the crystal to decrease, although MgTiO3 remains hexagonal crystal type.
The Hansch-Couillaud frequency locking mechanism of dual-wavelength external cavity resonance system based on diffusion bonded KTP crystal
Dual-wavelength external cavity resonance is achieved by Hansch-Couillaud(HC) frequency locking technology based on diffusion bonded KTP crystal. The HC frequency locking scheme based on diffusion bonded KTP crystal is analyzed theoretically and experimentally. The results show that the laser frequency can be locked to the resonance peak of e1-light or e2-light, compared with the results of a single KTP crystal. The longitude mode frequency of bow-tie cavity is locked at the frequency of 938nm laser firstly, and then the longitude mode frequency of bow-tie cavity is locked at the frequency of 1583 nm laser. The phase correlated locking of three components is realized.
Influence of optical simple pulse coding on the Brillouin optical time domain analyzer based on bi-directional Raman amplification
We report the influence of optical simple pulse coding on the Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification. This method is proposed to reduce the frequency uncertainty in long-distance BOTDA under higher spatial resolution. The experimental characterization of 49.6 km temperature sensing with a measurement accuracy of ~1 ℃ under ~2.5 m spatial resolution over the whole length of sensing fiber is demonstrated. The signal-to-noise ratio (SNR) and the optical signal power distribution characteristics of the system are studied experimentally in this paper.
Investigation of optical limiting based on the combination of stimulated Brillouin scattering and metal-phthalocyanine complexes
In order to improve the optical limiting performance based on stimulated Brillouin scattering (SBS), an optical limiter based on the combination of SBS and metal-phthalocyanine complexes (MPCs) is proposed in this paper. The output energy of the combination optical limiting designed based on SBS followed by MPCs shows flatter characteristic. The dependence of the output energy of optical limiting based on this combination approach on the input light intensity is numerically simulated, and validated in a continuum Nd:YAG seed-injected laser system. The theoretical and the experimental results indicate that the output energy based on this approach has a flatter characheristie than based on a single SBS.
Control and synchronization of phase-conjugate wave spatiotemporal chaos system driven by CO2 laser
Two-dimensional photonic crystal band gap characteristics
Proposal of novel and efficient polarization beam splitter
Soliton pulse propagation and optical delay properties in photonic crystal waveguide
The bright soliton pulse propagation and the slow light delay time properties of 2D cubic and triangular lattice photonic crystal line defect waveguide (PCW) with circular Si-rods near the left edge of the guidedmode are investigated. By using the plane-wave expansion (PWE) method, the ralues of soliton required peak power P0 and delay time TS of the waveguided with different radii of the first two rows of Si-rods adjacent to the waveguide, r1 and r2, and waveguide width D are numerically investigated. Adjusting the waveguide structure can bring in optimized cubic and triangular lattice waveguide, of which P0 is reduced by 81.17% and TS is increased by 66.32% for cubic lattice waveguide; P0 is reduced by 73.7% and TS is increased by 67.63% for triangular lattice waveguide. These results show that the soliton transmission performance in the photonic crystal line defect waveguide can be effectivly optimized.
Propagation properties of light in multimode photonic crystal waveguides with triangular lattices based on total internal reflection
The properties of the propagating field in multimode photonic crystal waveguides exhibiting no photonic band gaps with triangular lattices are investigated. By the effective refractive index method, these structures are regarded as three layer planar dielectric waveguides. And the multimode interference effect is numerically analyzed and simulated based on the self-imaging principle. The results show that the field can propagates effectively and resembles index-guided mode due to the combination of total internal reflection and distribution Bragg reflection. High transmission region shifts toward the shorter wavelength region, the bandwidth and the transmissivity increase with the increase of filling ratio, which provides a theoretical reference for selecting an appropriate filling ratio in practical applications.
Intensity-modulated bending sensors based on rare-earth-doped fibers
Design and study of high birefringent terahertz photonic crystal fiber with hybrid crystal lattice
In this paper, we propose a novel high birefringent terahertz (THz) photonic crystal fiber (PCF) with subwavelength circular air hole pairs in the core which are arranged as a hybrid crystal lattice structure. And its high mode birefringence is realized by reducing structure symmetry in core. A professional software COMSOL Multiphysics 4.0 is used for modeling, and the simulation results show that this kind of THz PCF exhibits a high birefringence on a level of 10-2and low confinement loss over a wide THz frequency range. Moreover, the birefringence or confinement loss can be controlled flexibly by adjusting some fiber parameters. Compared with a similar structure PCF for the optical communication, the THz PCF is easier to practically fabricate, owing to its large wavelength size.
High speed real-time optical sampling system based on optical parametric amplification
We propose a novel technique to achieve a high speed real-time optical sampling system based on optical parametric amplification in high nonlinear fiber (HNLF). Linearly chirped pulses are obtained by the dispersive propagation of short pulses emitted by a mode-locked fiber laser. The pulses are then fed into an HNLF together with signal under sampling. Thanks to the optical parametric amplification effect in the HNLF, the amplitude information will be modulated onto the linearly chirped pulses. By employing optical band-pass filters or wavelength division multiplexing (WDM) technology before the receivers, simultaneous high speed optical sampling and optical serial-to-parallel conversion are achieved. We demonstrate the feasibility of the scheme by optical sampling a 10 Gb/s on-off keying (OOK) signal at a sampling rate of 40GS/s and simultaneously converting it into four 10 GS/s sampling outputs. And the 10 Gb/s OOK signal is reconstructed later by the four sampling outputs. The scheme is simple and of low cost, which makes it a good candidate in high speed real-time sampling system.
Theoretical investigation on refractive index sensor basedon Bragg grating in micro/nanofiber
Subwavelength and nanometer diameter optical fibers have the optical property of enhanced evanescent fields, which makes them very sensitive to the index change of the ambient medium. In this paper, a novel refractometric sensor based on fiber Bragg grating in micro/nano-fiber (MNFBG) is proposed, integrating the enhanced evanescent fields of micro/nano-fiber (MNF) with wavelength choice feature of FBG, and the fabrication about MNFBG is discussed. Refractive index sensing characteristics is comprehensively investigated in theories, and the simulation of sensing the variation of ambient refractive index is performed by using the software of OptiGrating. Results show the sensitivity of the MNFBG is increasing with the decrease of the radium of the MNF. MNFBG with the radius of 400nm can achieve the sensitivity as high as 993nm/RIU. This value is enhanced by 170 times over that of the FBG with etched cladding, which demonstrates that MNFBG has great potential of application in miniaturized, high-sensitivity refractometric sensors.
An improved design method for C-band photonic crystal fibers with flat near-zero dispersion
The innermost air holes of photonic crystal fibers deform easily during the draw process, resulting in serious influcence on the practical fiber dispersion. Based on the multipole method, the simulation in the paper only changes the air holes in the secondlayer and the third layer to adjust the dispersion, while the innermost air holes each are set to have a smaller parameter. The simulation shows that this simple dispersion control method can also make zero-dispersion point quickly move and keep the dispersion flat. Based on the detailed analysis, we propose C-band near-zero flat dispersion photonic crystal fiber with the dispersion coefficient varying from -0.24ps/(km ·nm) to 0.33 ps/(km ·nm). Simulation shows that the air holes increasing from the fifth layer have little influence on the dispersion of previously proposed fiber, So by increasing the layers of air holes we can obtain an ideal confinement loss. This method is also applicable for the design of PCF operating in S and L bands with similar properties.
Characteristic study of polymer electro-optic modulator based on extended wheeler's conforming mapping method
An extended Wheeler's conforming mapping method is proposed to analyze the characteristic parameters of the multilayer based on the simple Wheeler's transformation. The explicit expression between the microwave characteristic parameter and the each layer parameter is obtained. Compared with the results obtained by the quasi-static finite element method (QS-FEM), our results show that the present approach can not only accurately evaluate the characteristic parameters of the multilayer but also have a great computational efficiency. Based on this method, a modified structure of the typical electro-optic modulator is given. The velocity matching and the impedance matching can be achieved simultaneously by adding a compensation layer.
Properties of infrasonic wave nonlinear propagation in the inhomogeneous moving atmosphere
A difference wave equation is obtained by discretizing a nonlinear acoustic wave equation in atmosphere in the second-order miniterm approximation based on the finite-difference time-domain method. And the pulsed infrasonic wave radiated by a linear array vertical or oblique propagation in moving inhomogeneous atmosphere is numerical simulated in the two-dimensional space, and sound pressure distribution after the different propagation times is investigated in the Wuhan(114 ∶20°E, 30 ∶37°N) of China and the initial time UT=29000s of summer and winter. The atmospheric inhomogeneity caused by the change of temperature and density, and the atmospheric motion caused by the presence of wind is considered by using the Msise00 and HWM93 models. The pressure difference pr obtained by subtracting no-windy pressure from the windy-pressure in above two seasons indicates that the wind has more influence on the sound field in the infrasonic propagation. The distribution waveform of pr is dependent on season because the "actual acoustic velocity" depends on season and propagation distance; The influence of wind on the nonlinear propagation is bigger than on the linear propagation.
Chaotic characteristics of gas bubble motion in acoustic field
Analysis of Lamb waves propagation in functional gradient materials using Taylor expansion method
Using delayed feedback to control the band of saturation control in an auto-parametric dynamical system
We investigate the band of the saturation control in an auto-parametric dynamical system by using the delayed feedback. In an original system without delay feedback, some unstable regions may occur in the band of the saturation control for some internal resonance detuning parameters. The band of the saturation control is distributed unreasonably. The delay feedback control is used to control the distribution of the band for saturation control. The effects of the gain and delay on the band of the saturation control are studied. The results show that the unstable regions of the saturation control can be eliminated by choosing the values of the gain and delay appropriately. Moreover, the bandwidth of the saturation control does not narrow. Consequently, the distribution band of the saturation control can be improved by using the delay feedback control.
Research on localization of the source of cyclostationary sound field
Nonlinear Rossby envelope waves under the influence of forcing dissipation and β effect topographic effect
In barotropic fluids, based on the quasi-geostrophic potential vorticity equation, an inhomogeneous nonlinear Schrödinger equation including topographic forcing and an external source is derived by employing the perturbation method and stretching transforms of time and space. With the inspection of the evolution of the amplitude of Rossby envelope solitary waves, it is found that β effect, topography effect and an external source are the important factors, the solitary Rossby wave is induced though the basic stream function has a shear flow. On the assumption that nonlinear and topographic effects are balanced, an inhomogeneous equation is derived, and the results show that the topography and Rossby waves interact in the barotropic flow. The inhomogeneous nonlinear Schrödinger equation describing the evolution of the amplitude of solitary Rossby envelope solitary waves as the change of Rossby parameter β(y) with latitude y, topographic forcing and the external source is obtained.
Measurements of rotational and vibrational temperatures based on flame emission spectroscopy
This study addresses emission spectra of Air-ethanol and Air-kerosene flames by using optical multichannel analysis system (OMA). Experimental results show that there are several bands of molecular spectrum in a range from 275 to 600nm. Among them, the OH A2Σ+→X2Πr(300—330 nm), the CH A2Δ→X2Π(410—440 nm), and C2 A3Πg→X3Πu (500— 520 nm) emissions have the strongest intensity. In turn, the fine structures of OH (A2Σ+→X2Πr) and CH (A2Δ→X2Π) emission are studied by using a high resolution grating in experiment, and the distributions of spectra intensity are calculated at different rotational and vibrational temperatures based on the molecular spectroscopy. Moreover, by comparing the simulated spectra with the experimental spectra of OH (A2Σ+→X2Πr) and CH (A2Δ→X2Π) emissions, the rotational and the vibrational temperatures of Air-ethanol flame are determined in this paper.
Multiscale analysis of defect initiation on the atomistic crack tip in body-centered-cubic metal Ta
The quasi-continuum method (QC), a multiscale method, is used to analyze body-centered-cubic (bcc) metal tantalum (tantalum, Ta) type Ⅱ crack-tip dislocation nucleation. Based on the relationship curves between dislocations emission position and stress intensity factor, the processes of dislocation defect initiation and development are investigated. Dislocation travels forward with different characteristics in different stages and the new nucleated dislocations expedite the already nucleated dislocation to move away from the crack tip. The analysis of initiation of the crack tip defects shows that they are the local defects that first appear, and with loading, more local defects emerge, which eventually move to the boundary, and lead to the type Ⅱ fracture. Furthermore, dislocation dissociation as well as extended dislocation is discussed. The partial dislocation nucleating before the perfect dislocation nucleation and emission is full proof that the dissociation of perfect dislocation takes place step by step, which means that the two minimum points on the energy curve have different formation mechanisms.
A density functional theory study of absorption behavior of CO on Au-doped single-walled carbon nanotubes
The absorption behaviors of CO on the (8,0) semiconducting intrinsic and gold doped (Au-doped) single-walled carbon nanotubes (SWCNTs) are investigated by the density functional theory because superior sensitivity of carbon nanotube to many toxic gases becomes a field of growing interest. It is shown that CO molecules can be absorbed to Au atoms on the wall of Au-doped SWCNT with a bingding energy as high as 2.1eV,and can attract lager charge transfer 0.23. Compared with the intrinsic SWCNT, the Au-doped SWCNT presents a high sensitivity to CO in terms of the calculated geometrical structures and electronic properties, Furthermore, the calculated electron densities of two representative adsorption positions show that Au-doped SWCNT electron clouds overlap more on the top of carbon adsorbed CO. By comparison with the oxygen absorption on SWCNT, we infer that the molecular CO absorbed on Au-doped SWCNT can induce significant change in the conductivity of SWCNT. So Au-doped SWCNT is expected to be a potential candidate for detecting the presence of CO.
Influence of defect states on band gaps of the 4340 steel in epoxy in two-dimensional phononic crystal
The band gaps of a two-dimensional phononic crystal are studied by using the plane-wave expansion method and the supercell calculations. The two-dimensional phononic crystal is formed by square-shape arrangement of 4340 steel inserted into epoxy resin. The band gaps of different structures are calculated such as defect-free, 45° crystal defect states, 90° crystal defect states, 135° crystal defect states and 180° crystal defect states. It is found that the bandwidth of defect state is about 31 times larger than that of the defect-free crystal; with F=0.1—0.9 the band gaps occur in different defect structures and increase with defect state angle increasing. In addition, the influences of filling fraction on the band gap number and the relative width of the minimum band gap are also discussed.
Manipulations of properties of the W-line emitting from the Si+ Self-ion-implanted Si thin films on insulated oxide layer
The Si+ self-ion-implanted and annealing experiments are conducted on the Si film based on the silicon-on-insulator wafers. The photoluminescence (PL) spectroscopy is used to investigate the luminescence properties of these Si film samples. Plentiful optical structures are observed in the PL spectra, including the D1, D2, D3, X, and the sharp W lines. By comparing the normalized PL intensities recorded by the same spectral experiments, we obtain the optimum self-ion-implanted and thermal annealing parameters. In addition, the defect origins and optical properties of the series of the D peaks and W line are well discussed.
Measurement of low-pressure Hugoniot data for bismuth with reverse-impact geometry
Hugoniot data for Bi are determined through measuring the impact velocity and the particle velocity at the sample/window interface on a powder gun or a two-stage light gas gun in a shock pressure range from 10 to 45 GPa, using reverse-impact geometry. The used experimental technique avoids the difficulty in accurately measuring the shock wave velocity resulting from the poor start synchronigm of electric pins under low shock pressure. The obtained Hugoniot data (shock wave velocity D versus particle velocity u) indicates that the D-u curve does have a discontinuity at a particle velocity of ~0.9 km/s, which is likely to be caused by the shock-induced solid-liquid phase transformation.
Floating zone growth and emission properties of single crystal LaB6cathode
The high quality, high purity and large size Lanthanum hexaborides (LaB6) single crystals have been successfully grown by optical floating zone method. The optimum crystal growth parameters are listed as follow: sample rotation rate is 30 r/min and the growth rate is 8—10 mm/h. The largest thermionic emission current density of (100) crystal surface is 44.36 A/cm2 at 1873 K. The work function at absolute zero is calculated to be 1.99 eV by Richardson line method, and the average value of effective work functions at different temperatures are calculated to be 2.59 eV. The field emission characteristic of single crystal LaB6 field emitting single tip show that the maximum field emission current density is 4.9×106 Acm-2 and the field enhancement factor is calculated to be 41500 cm-1, indicating excellent field emission performance. Thus, the single crystal is a promising cathode material for practical applications regarding to its excellent thermionic emission or field emission properties.
Molecular dynamics simulation of helium behavior in tungsten matrix
The helium behavior in tungsten matrix is investigated by means of molecular dynamics. Firstly, the He-W potential is created by combining the ZBL potential with the data from an ab intio method. The formation energy calculations predict that the most stable configuration for helium in interstitial position is the tetrahedral site, which is in good agreement with recent research results. The helium diffusion is simulated in great detail in a temperature range from 400 K to 1200 K, and the migration energy is obtained to be between the experimental data and the ab intio calculation result. Finally, the mechanism of helium accumulation in its initial stage is investigated from the viewpoint of energy. It is found that as the helium cluster grows, the binding energy of each additional helium atom to the cluster tends to increase, which is conducible to the further growth of the helium cluster.
Theoretical research of TiO2 adsorption on GaN(0001) surface
The adsorption of molecule TiO2 on GaN(0001) surface is theoretically explored by using a plane wave ultrasoft pseudo-potential method based on the density functional theory. The bonding processing of TiO2molecule on the surface of GaN(0001), the adsorption energy, and the adsorption orientation are investigated. The results indicate that Ti atom is adsorbed on fcc site or on hcp site, and two O atoms are combined with two Ga atoms on the GaN surface after adsorption. The chemical bonding of Ga—O shows a covalent feature, and the chemical bonding energy is achieved to be 7.932—7.943 eV. The O—O line directions lie along the GaN  directions, in accordance with experimental reports of (100)  TiO2// (0001) GaN. From ab initio dynamics calculation, the adsorption process can be divided into physical adsorption, chemical adsorption and superficial stable state,and the stable adsorption site is in accordance with the optimized results.
First principles study of the electronic structure and photoelectric properties of rutile vanadium dioxcide
The electronic structure and the photoelectric properties of rutile based VO2 are investigated using the FP-LAPW method which is combined with the DFT+U method. The calculated density of statas (DOS) shows that the DFT+U method can describe the conductive band properly. The V-O bonding in VO2 is induced mainly through the strong hybridization of V3d orbital and O2p orbital. The calculated plasma frequency is 3.44 eV when the applied light field is perpendicular to the c axis and 2.74 eV when the applied light field is along the c axis. The optical conductivity spectrum shows a Drude-like peak is between 0 eV and 1 eV while in upper area the interband contribution is more important. Finally, the reflection spectrum and the election energy loss spectrum (EELS) are calculated and analyzed.
First-principles study of the electronic structure and electric conductivity in W-type hexagonal ferrite BaFe18O27
The electronic ground state and the electric conductivity of W-type hexagonal ferrite BaFe18O27 are investigated in the generalized gradient approximation (GGA) as well as the GGA plus Hubbard U(GGA+U) scheme. The ionic relaxation calculation of the experimental crystal structure shows that oxygen ions at 6h site in the BaO layer move away from the "surface" position in the unit cell, resulting in a structural distortion. The magnetic moment of the cell is calculated to be 28 μB/f.u., in agreement with previous experimental results. By taking account of electronic band structure and crystal ionic configuration it is found that the material is a weak half-metal and the effective mass of conduction electrons along the c axis is much heavier than that perpendicular to this axis. Fe ions on octahedral 6 g sites and O ions around them of the spinel block form a "conductive layer". Therefore the electric conductivity perpendicular to the c axis is much greater than that parallel to the c axis.
First-principles study on the electronic structures, magnetism, and half-metallicity of full-Heusler X2YGa (X=Co, Fe, Ni; Y=V,Cr, Mn) alloys
Using the full-potential linearized augmented plane wave method within the generalized gradient approximation, we investigatete the electronic structures, magnetisms and half-metallicities of the full-Heusler X2YGa (X=Co, Fe, Ni; Y=V, Cr, Mn) alloys. It is found that the spin-orbit coupling has little effect on the electronic structures, magnetisms and half-metallicities of the full-Heusler X2YGa (X=Co, Fe, Ni; Y=V, Cr, Mn) alloys. Without spin-orbit coupling the Co2VGa,Co2CrGa,and Fe2CrGa alloys are half-metallic or nearly half-metallic ferromagnets. With including the spin-orbit coupling, the spin-polarizations are lowered by about 1%, thus they still remain high spin-polarizations. The Fe2MnGa, Co2MnGa, Ni2CrGa, and Ni2MnGa alloys are conventional ferromagnets, whereas the Fe2VGa and Ni2VGa alloys are paramagnets.
p-type transparent conductive BaSnO3: A first-principles calculations
Based on density functional theory calculations, the electronic properties of N-doped BaSnO3 and N and Sb codoping are investigated. It is found that codoping with N acceptors and Nb donors in a ratio of 2 ∶1 is suitable for the fabrication of low-resistivity p-type BaSnO3. Our results indicate that codoping with N acceptors and Nb donors is a prospective candidate as a p-type transparent conductive material.
Qualitative analysis of excess noise in nanoscale MOSFET
Investigation on the low-freauency noise physical models and the defects' characterization of the PbS infrared dectector
In order to characterize the defects of PbS thin film photoconductive infrared detector materials, The physical model of 1/f noise and g-r noise are deduced and verified. The surface trap densities under different voltages are calculated by the relation between 1/f noise and surface trap in this model. The phenomenon that the surface trap density increases with bias voltage is observed. Therefore, the conclusion that 1/f noise is proportional to bias voltage is drawn, and it is consistent with the experimental measurements. In addition, the relation between g-r noise and deep-level defect characterization parameters is investigated based on this model, and the method of using low frequency noise to characterize defect parameters including defect activate energy, degeneracy factor and capture section is presented.
High-efficiency blue fluorescence organic light-emitting diodes with DPVBi inserted in the doping emmision layer
We have fabricated high-efficiency blue fluorescence organic light-emitting diodes(OLEDs) with DPVBi inserted in the doping emmision layer(EML). The OLEDs with a configuration of ITO/2T-NATA/NPB/DPVBi:DSA-ph(inserted with DPVBi thin layer)/Alq3/LiF/Al are fabricated, using 2T-NATA as hole injection layer, NPB as hole transport layer, DPVBi:DSA-ph as emission layer and Alq3 as electron transport layer, respectively. The DPVBi thin layer inserted in EML leads to an increase in device efficiency as a results of an improvement of the balanced carrier injection, which results in an efficient radiative recombination in the emission zone. In addition, DPVBi ability of hole blocking can also be another reason for the improvement on the luminous gain. Hence, high radiative recombination is expected to take place in DPVBi:DSA-ph emission layer. This high efficient recombination results in high brightness and enhanced efficiency in our OLEDs. By optimizing the location and the number of layers of DPVBi thin layer, a maximum current efficiency of 6.77 cd/A is achieved at a current density 6.84 mA/cm2, which is nearly 67.6% more than that of non-inserted device. At a luminance of 1000 cd/m2, the current efficiency of the optimizing device is 6.49 cd/A at 6.7 V with a CIE (0.179, 0.317).
Structural phase transition and magnetic properties of Co50Fe50-xSix alloys
The structural and the magnetic properties of Co50Fe50-xSix alloys are investigated by carrying out experimental measurements and electron structure calculation. The alloy series exhibits the highly chemical ordering structure, showing a strong covalent bonding effect. The lattice parameters, molecular moment and Curie temperature linearly decrease with the increase of the Si content. The deviation of the structure is attributed to the atomic size effect. Based on Stearns theories, the decrease of the itinerant 3d (di) electron results in the decrease of Curie temperature due to the substitution of Si for Fe. The change of molecular moment follows the Slater-Pauling rule, but the calculation indicates that the change of the atomic moments is not linear. It implies that the covalent bonding effect is responsible for the magnetic changes. The molecular moment and Curie temperature of Heusler alloy Co2FeSi are measured to be 5.92 μB and 777 ℃, respectively. The calculation results also indicate that the half-metallic property of Co2FeSi may not be so perfect as reported, which requires a new design of energy band for the practical application. The investigation also shows that the structural transition and the magnetic structure transition accumulate in a narrow interval of Si content, which may become a good object for studying the interaction between the magnetization and the structure.
Scaling law of quantum Hall plateau-to-plateau transition in single layer graphene
Scaling law of quantum Hall plateau-to-plateau transition in single layer graphene is studied in a temperature range from 2 K to 50 K. We find that the scaling exponent κ is not universal. In a low temperature range, κ is about 0.13, while in a high temperature range, κ is about 0.33. The result indicates the dominance of long range scattering in graphene.
Properties of terahertz surface plasmon ploaritons on carbon nanotube film with periodic grating
Based on the dielectric property of carbon nanotube film, the surface plasmon ploariton propagation and localization phenomena on the carbon nanotube film are investigated using THz time-domain spectroscopy technique. The simulation results show that in the gate period of 168um, the resonance peaks of surface plasmon mode are at 0.99THz and 1.95 THz, which are consistent with the theoretical results. Further analysis demonstrates that both the gate thickness and the width have an important effect on the properties of surface plasmon ploaritons.
Fabrication of graphene nanoribbons through mechanical cleavage and their electronic transport properties at low temperature
We have fabricated graphene nanoribbons (GNRs) of length up to tens of microns through mechanical cleavage, and performed electron transport measurements on devices made of the GNRs down to a low temperature of 0.3 K. Fabry-Perot interference was observed in the conductance of the devices as functions of both bias voltage and gate voltage. The result indicates that our mechanically cleaved GNRs are of high quality, in which the electrons form an ideal one-dimensional system at low temperatures.
Decoupled states and anti-resonance in the Aharonov-Bohm interferometer with embodied quantum-dot ring
Using the Anderson model Hamiltonian and the non-equilibrium Green's function method, the decoupled states and antiresonance presenting in the electronic transport through N-quantum-dot ring embodied in A-B interferometer are studied theoretically. We find that the symmetry of the coupled-dot system and the magnetic flux through the Aharonov-Bohm (A-B) interferometer are two physical mechanisms responsible for the decoupled states. Even-odd parity oscillations occur in linear conductance spectra of such a highly symmetric quantum dot ring, due to even or odd molecular state decoupling from the leads by tuning the structure parameters, i.e., the magnetic flux. The results provide a new model for the designing of the nano-device.
Power characteristics of SiC bipolar-mode JFET
The operational mechanism of normally-off type bipolar-mode SiC junction field effect transistor (BJFET) is studied by using a two-dimensional numerical model. Compared with the unipolar-mode SiC JFET, the bipolar-mode can reduce the on-state resistor of the SiC JFET effectively and compromise between the on-state and off-state characteristic of the device. The simulation resluts also show that switching time of BJFET increases remarkably.
Investigation of the response mechanism of photovoltaic semiconductor with sub-bandgap photons
The photovoltaic HgCdTe detectors with band gaps 0.91 and 0.33 eV are irradiated by 10.6 μm laser (0.12 eV photon energy), separately. It is found that output voltage of detector (0.91 eV band gap) is positive, while the response voltage of detector (0.33 eV band gap) is opposite to it. To investigate this phenomenon, the detector with a band gap of 0.91 eV is irradiated by a given power 10.6 μm laser under different initial open-circuit voltags. It is experimentally demonstrated that the phenomenon is caused by the initial open-circuit voltage. With further investigation, the open-circuit voltage of the photovoltaic detector is determined by both the thermovoltage caused by thermoexcited carrier and the crystal thermal effect produced by free carrier absorption under sub-bandgap laser irradiation.
Structure and electromagnetic transport properties of compound NdNi2Ge2
The sample of compound NdNi2Ge2 is prepared by arc melting. The crystal structure is analyzed using powder X-ray diffraction and refined with Rietveld is method. It is shown that NdNi2Ge2 intermetallic compound crystallizes into a tetragonal structure with space group of I/4mmm and its lattice constant is a=4.120(1),c=9.835(0), Z=2. Nd atoms occupy 2a positions, Ni atoms 4d positions and Ge atom 4e positions. NdNi2Ge2 intermetallic compound has a Curie-Weiss constant of 25.8 and Curie-Weiss temperature of 6.24 K. The effective magnetic moment is 3.69μB, which is very close to that of Nd3+. It implies that the magnetic moment originates mainly from Nd3+ ion. The resistivity varies from 0.3 Ω ·μm—1.1 Ω ·μm. Fitting results show that this intermetallic compound is semimetal.
Magnetic entropy change and magnetic-field-induced strain in polycrystalline Ni47Mn32Ga21 alloy
The Ni47Mn32Ga21 polycrystalline alloy is prepared by the directional solidification technique. The components and the microstructure of the alloy are investigated using SEM, metallography and EDS methods. The magnetic entropy change in the process of the structural and magnetic phase transition, and magnetic-field-induced strains with pressure are also studied through analyzing the magnetization as a function of temperature, and the isotherm magnetization and magnetic field-induced strain curves. The results show that there is little difference between the component and the designed component. The alloy is comprised mainly of martensitic phase at room temperature. In the heating process, the magnetic entropy change reaches a maximum value and has a larger peak half width near Curie temperature(365 K). The maximum value of the magnetic entropy change is -1.45 J/kg ·K in a magnetic field of 747 kA/m and its peak half width is 21 K. The Ni47Mn32Ga21 alloy exhibits excellent free recoverability of the magnetic-field-induced strains at room temperature(298 K). The magnetic-field-induced strain reaches a saturated value of -670×10-6 without extra stress in a field of 480 kA/m. When the compressive stressis parallel to the direction of the magnetic field, the magnetic-field-induced strain increases evidently with the increase of the pressure, which reaches -1300×10-6 under a pressure of 27.3 MPa. Meanwhile the strain does not reach the saturated value.
Study of Ni4PrB electronic structure and magnetism
Considering the Coulomb potential and the exchange action, electronic structure, band structure and magnetic properties of the compound Ni4PrB within the local spin-density approximation (LSDA) and the LSDA+U approximation are studied through numerical simulation. The simulation results show that this system is a metallic semi-conductor and has Pr-Ni ferromagnetic coupling. The added Coulomb U effect can strongly affect magnetic properties and stable structure, and the total magnetic moment is provided by the local Ni magnetic moment before adding U effect, when the U effect is added to the system, the total magnetic moment is provided by the local Pr magnetic moment, and the system has a high structure stability. So U effect affects strongly the strong correlation, then it can describe reasonably the strong correlation and the exclusion effect caused by the spin exclusion.
Irreversible exchange-spring processes of antiferromagnetically exchange coupled hard-soft-hard trilayer structures
The demagnetization processes of antiferromagnetically exchange-coupled hard-soft-hard trilayer structures are studied based on the one-dimensional atomic chain model. It is found that when the magnetic anisotropy of soft layer is taken into account, the change of the soft layer thickness or the interfacial exchange coupling strength may lead to a transition from the reversible exchange-spring process to the irreversible process. For the trilayer structures with very thin soft layer, the demagnetization process exhibits typical reversible magnetic exchange-spring behavior. However as the thickness of soft layer increases, there appears a crossover point tc, after which the process becomes irreversible. There occurs also a critical interfacial exchange constant Ashc, above which the exchange-spring process is reversible. When Ash<Ashc, the irreversible exchange-spring process is realized. The phase diagrams of reversible and irreversible exchange-spring process are mapped in the plane of the interfacial exchange coupling Ash and soft layer thickness Ns. The dependences of the bending field on the soft layer thickness for different interfacial exchange couplings are numerically examined.
First-principles calculations of structure and magnetic properties of α-Fe(Si)phase precipitated in the Finemet alloy
The structure and the magnetic properties of α-Fe(Si) phase precipitated in the Finemet alloy, and some factors influencing the magnetic properties of α-Fe(Si) phase are investigated by first-principles calculation based on the density functional theory. From the angle of electron spin, the magnetic properties of α-Fe(Si) phases with different solubilityies of Si located at the different sites of the α-Fe superlattice are investigated. The calculation results show that the spin-state density is a critical factor influencing the magnetic properties. It is found that α-Fe(Si) phase with Si at the vertex sites shows better magnetic properties than those with Si at the core sites. It is concluded that with the solubility of Si in the α-Fe(Si) phase increasing, the probability of Si occurring at the vertex sites increases, which results in better magnetic properties. The calculation results accord with the previous experimental results. The present work is helpful for understanding the magnetism of the Finemet alloy.
Effects of A-site equivalence and non-equivalence substitution on polarization properties of K0.5Na0.5NbO3 lead-free piezoelectric ceramics
The effects of A-site equivalence and non-equivalence substitution on polarization temperature and electric field of K0.5Na0.5NbO3 lead-free piezoelectric ceramics are studied, and the results show that the ceramics sample of A-site equivalence is independent of polarization temperature and electric field, which can improve the piezoelectric constant. On the contrary, the ceramics sample of A-site non-equivalence substitution is sensitive to polarization temperature and electric field, constraining the piezoelectric properties.
Magnetocapacitance effect of magnetoelectric laminated composite at resonant frequency
A sandwich-like laminated composite of TbxDy1-xFe2-y/Pb(Zr, Ti)O3/TbxDy1-xFe2-y is prepared with a bonding method. The experimental study shows that the capacitance of the sample has several resonant peaks in the range of the frequency manipulated, and the resonant points shifte with the increase of applied magnetic field. The impedance of the sample also varies from capacitive to inductive ones at about the resonant point by changing the magnetic field. Giant positive and negative magnetocapacitance effects are observed simultaneously near the resonant frequency. From the constitutive equations of magnet and piezoelectrics involved, the capacitances as functions of frequency and magnetic field were theoretically modeled respectively. The results show that the experimental results are in good agreement with the theoretical ones, suggesting that the magnetocapacitance effect of the layered composite of magnetostriction/ piezoelectric originates from the magnetic field-controlled compliance coefficient of the ferromagnetic phase in the sample.
Phase transformation and dielectric properties of lead zirconate stannate titanate ferroelectric ceramic under hydraulic compression
Nb-doped lead zirconate stannate titanate ferroelectric ceramic with composition Pb0.99Nb0.02[(Zr0.90Sn0.10)0.96Ti0.04]0.98O3 (PZST 90/10-4-2Nb) is studied in a hydraulic pressure range of 0—300 MPa by released charge and dielectric measurements. Pressure-induced low temperature phase transition from ferroelectric rhombohedral (FR(LT)) structure to antiferroelectric orthorhombic (AO) strueture is investigated. Unpoled, poled and pressure-depolarized PZST 90/10-4-2Nb ferroelectric ceramics are used. The released charge quantity is 29.3 μC/cm2 and the threshold pressure is 140 MPa during the phase transformation from FR(LT) structure to AO strueture. Dielectric properties show that the threshold pressure of the phase transformation from FR(LT) structure to AO structure is 136 MPa for poled ceramic and 104 MPa for unpoled ceramic. Obvious characteristic of phase transformation is not observed in pressure-depolarized ceramic.
Micro-morphology and dielectric properties for (K0.45Na0.55)NbO3 lead-free piezoelectric crystal
Lead-free piezoelectric 〈001〉-oriented KNN crystals each with a dimension of 5 mm×3 mm×1 mm are obtained by melt grown technique. The room temperature crystal structure of orthorhombic perovskite-type lattice is determined from XRD measurment. The SEM observation reveals the growth steps aligning approximately along the  direction. Base on the model of negative ion coordination polyhedrons, it is explained that the layer growth mechanism is dominant for the 〈001〉 face. Two phase transition temperatures of orthorhombic-to-tetragonal (O-to-T) and tetragonal-to-cubic (T-to-C) are around 240 ℃ and 405 ℃ for KNN crystals according to the dielectric measurements, respectively. A linear fitting of the modified Curie-Weiss law to experimental data shows that the normal ferroelectric property is dominant for KNN crystal.
A polarization-insensitive and double-face-absorption chiral metamaterial absorber
A polarization-insensitive and double-face-absorbing metamaterial absorber is presented, which is based on chiral structure. The unit cell of this absorber is comprised of a chiral structure and a dielectric substrate. Simulated absorbances under frontal and reverse incident directions indicate that the structure of this absorber is reciprocal, and thus this absorber has double-face-absorption property. Simulated absorbances under different polarization angles indicate that this absorber is polarization-insensitive. Simulated absorbances under different angles of incidence indicate that this absorber is narrow-angled. Simulated surface currents and magnetic energy density of the unit cell indicate that there exists cross coupling between electric field and magnetic field, and that the absorption is related to chirality. Simulated absorbances under different loss conditions indicate that dielectric loss of the substrate is dominant in the absorbing process, and that metal loss can be neglected. This absorber may have potential applications in some double-face-absorbing fields.
Research on quantum efficient fitting and structure of high performance transmission-mode GaAs photocathode
To explore the structural feature of high performance transmission-mode GaAs photocathode, the optical properties and shortwave limitation for the transmission-mode quantum efficient formula is modified. By using the modified formula, a high quantum efficient (≈43%) curve of ITT is well fitted. A series of structural parameters is obtained with in a relative error less than 5%, which indicates that the thickness of the Ga1-xAlxAs window layer is 0.3—0.5 μm, the Al mole value is 0.7, and the thickness of the GaAs active layer is 1.1—1.4 μm. In addition, an optimized structure for the uniform-doping transmission-mode GaAs photocathode is suggested based on the fitted results. When the thickness of the Ga1-xAlxAs (x=0.7) layer and the GaAs layer are 0.4 μm and 1.1—1.5 μm respectively, the integral sensitivity can exceed 2350 μA/lm.
Host sensitized infrared quantum cutting of Er0.1Gd0.9VO4 crystal
The infrared quantum cutting phenomena of Er0.1Gd0.9VO4 crystal are studied in the present article. An interesting host sensitized infrared quantum cutting phenomenon is found, that is, there is a strong and broad excitation peak at 337.0 nm wavelength for its excitation spectrum of 1537.5 nm 4I13/2→4I15/2 infrared fluorescence. It can be recognized that the 337.0 nm excitation peak corresponds to the absorption of host GdVO4 crystal. Meanwhile, it is found that the integral fluorescence intensity of 1537.5 nm 4I13/2→4I15/2 infrared fluorescence, when the host absorption band is excited by 337.0 nm light, is about ten times larger than that of the sum of all other fluorescence intensities. Its infrared quantum cutting efficiency is similar to that of the excited 2H11/2 energy level and larger than that of others.
Numerical study of effect of geometrical parameters on the passband of left-hand material
Positron annihilation study of the microstructure of Co doped ZnO nanocrystals
ZnO nanopowders are mechanically mixed with a certain quantity of Co3O4 nanopowders to obtain 10at.% Co doped Co3O4/ZnO composites. The nanocomposites are annealed in argon atmosphere at different temperatures between 100 ℃ and 1200 ℃. The structure and the grain size of the nanocomposite are investigated by X-ray diffraction 2θ scans. With annealing temperature increasing up to 700 ℃, Co3O4 phase gradually disappears, and ZnO grain size begins to increase significantly. After annealing at above 1000 ℃, Co3O4 phase completely disappears, and CoO phase (rock-salt crystal structure) appears. Positron annihilation lifetime measurements reveal a large number of Zn vacancies and vacancy clusters existing in the interface region of the Co3O4 /ZnO nanocomposites. These defects are gradually recovered after annealing at above 700 ℃, and their number is under the detection limit after annealing at 900 ℃. The same conclusion can be drawn from the coincidence Doppler broadening (CDB) measurements.
Formation mechanism of layered microstructure and monotectic cell within rapidly solidified Fe62.1Sn27.9Si10 alloy
Ternary Fe62.1Sn27.9Si10 monotectic alloy is rapidly solidified in drop tube with the freely-falling-body techniqual and with melt spinning method separately. The phase separation, the microstructure characteristics, and the heat transfer of this alloy are investigated theoretically. Under free fall condition, the core-shell structure with two layers is formed because of Marangoni migration and surface segregation, where the Sn-rich phase is always located at droplet surface and the Fe-rich phase in the center. With the decrease of droplet diameter, both cooling rate and temperature gradient increase quickly, which facilitates the rapid growth of monotectic cell. With the increase of wheel speed, the cooling rate of alloy ribbon increases from 1.1×107 to 6.5×107 K/s, the fluid flow and the phase separation are suppressed to a great extent, and the "nine layers → two layers → no layer" structural transition occurs during the rapid solidification of Fe62.1Sn27.9Si10 alloy obtained by the melt spinning method. Meanwhile, the FeSn+L2→FeSn2 peritectic transformation is also suppressed, thus resulting in different phase constitutions as compared with the case of free fall condition. The energy dispersive spectroscopy (EDS) analysis reveals that the αFe phase exhibits a conspicuous solute trapping effect during rapid solidification.
Ni-FUSI metal gate work function modulation technology
Through fabricating Ni-FUSI metal gate capacitors and analyzing their C-V and Vfb-EOT characteristics, it is found that Ga or Yb has more favorable modulation ability than conventional dopants. The work function of Ni-FUSI metal gate is modulated close to the top of valince band and the bottom of conduction band, which meets the requirement of high performance CMOS devices. The high modulation abilities of Ga and Yb are explained by dipole theory. Moreover, it is found that the capacitance value of Ni-FUSI metal gate capacitor increases after incorporating Ga or Yb into Ni-FUSI metal gate, but the gate leakage current decreases. And the detailed explanation for the above phenomena is also included in this article by analyzing C-V and gate leakage current characteristics.
A physics-based model of insulated gate bipolar transistor with all free-carrier injection conditions in base region
A physics-based model of insulated gate bipolar transistor (IGBT) with all free-carrier injection conditions in a base region is presented, from which the ambipolar transport equations (ATEs) in high-level injection and low-level injection are deduced separately. Moreover, the boundary conditions of ATE are determined. In a more compact solution a Fourier-series solution for the ATE is used in this paper. Simulation and experimental results given by manufacturers are presented and compared with each other to validate the modeling approach. Physics-based IGBT model is used which is proved accurate.
A new research on sea surface wind direction retrieval of synthetic aperture radar image
A new method to retrieve sea surface wind direction using synthetic aperture radar image is presented. Some pretreatment steps such as suppressing noise, down sampling and dividing into several sub-images are presented first. The method of two-dimensional numerical differentiation based on Tikhonov regularization is introduced to compute the gradient direction in the sub-image intensity of every point. The distance weighted objective function is used to compute the overall gradient direction in the sub-images. The retrieved wind direction is orthogonal to the overall gradient. When adding 10% of random errors, numerical simulations show that the result of numerical differentiation is better than that from the Sobel operator which is based on the finite difference method: the former error is 0.7293 °, and the latter error is 13.5069 °. Finally, an experiment based on real SAR data shows that the wind direction deviates from the overall direction determined by the method of Sobel operator, and the direction determined by the method of numerical differentiation is consistent well with the overall wind direction. Comparing the ship board wind direction and the corresponding location wind direction retrieved from the synthetic aperture radar sub-images with the two methods, the average result error of Sobel operator method is 9.0331°, while that of numerical differentiation method is 1.1148°. This new method is an effective and high accurate method to retrieve the sea surface wind direction of synthetic aperture radar image.
Superparamagnetic nanoparticles formed in Fe-implanted ZnO
Due to its potential application to diluted magnetic oxides, transition metal doped ZnO has been under intensive investigation. We present a correlation between the structural and the magnetic properties of Fe implanted ZnO bulk crystals. Crystalline damage recovery, structural and magnetic properties are studied by Rutherford backscattering spectrometry and channelling (RBS/C), synchrotron radiation X-ray diffraction (SR-XRD), and superconducting quantum interference device magnetometer (SQUID), respectively. The 623 K Fe ion implantation and the high vacuum annealing at 823 K lead to the formation of secondary phase α-Fe and γ-Fe nanoparticles. The discrepancy between the zero-field cooling and the field cooling curves further indicates that Fe-implanted ZnO is superparamagnetic and the observed ferromagnetism originates from the Fe nanoparticles.
Mean response time of FitzHugh-Nagumo model in the presence of non-Gaussian noise and a periodic signal
The dynamics of the FitzHugh-Nagumo (FHN) model in the presence of non-Gaussian noise and a periodic signal is analyzed in this paper. We observe the resonant activation (RA) and the noise enhanced stability (NES) phenomena and analyze the effect of the non-Gaussian noise on the neuron dynamics by the mean response time (MRT) of the neuron. Some significant changes of the resonant activation (RA) and noise enhanced stability (NES) phenomena due to the correlation time of the noise are found. We observe that the NES effect is suppressed and RA phenomenon is unchanged, i.e., the non-Gaussian noise effectively enhances the efficiency of the neuronal response, for the case of strongly correlated noise. We report on the MRT as a function of q, and find that MRT is nonmonotonicaly dependent on q with a minimum at a finite q value which is smaller than 1. Finally we obtain that in certain situations, the non-Gaussian noise causes rescaling phenomenon, then the effect of non-Gaussian noise can be reproduced by a white noise.
Design and preparation of a radar-absorbing material based on metamaterial
A kind of radar-absorbing material (RAM) based on metamaterial, which contains resistive patches, dielectric substrate and metal backing, is designed. The reflectivity of the RAM is calculated using the finite difference time-domain method (FDTD) and optimized by genetic algorithm(GA). Then RAMs with a reflectivity bandwidth of 8—18 GHz below -10 dB is obtained. Moreover, its thickness is only 3mm. To confirm the design results, the RAM is prepared by fabricating a hollow quartz fibre reinforced epoxy resin substrate through using hand lay-up process and making the resistive patches by screen painting. The reflectivity of the absorber is measured, showing that the experimental result is consistent with the design value.
Kinetic property analysis of emergent behaviors in Swarm model
Emergence is one of the important characteristics of complex systems. At present, there is no definite conclusion on what emergence is and how it happens. Swarm model is selected for theoretical research. For convenience of doing so, its specific definition is given, and then the kinetic properties of this model are analyzed. By viewing the energy property, it is proven that under special circumstances the mean square deviation of each kinetic parameter would fall into a certain value space. Experimental results show that under certain conditions, by setting the initial state and parameters of the control equations, the behavior of Swarm can be effectively constrained.
Chaotic time series prediction based on robust echo state network
Focusing on the problem that the echo state network is easily influenced by outliers, in this paper we propose a robust model based on the Laplace prior distribution. This is achieved by replacing the Gaussian distribution with the Laplace distribution as the prior of the model output, the Laplace prior is less sensitive to the outliers and can enhance the capbility of the model to restrict outliers. Furthermoer, to solve the problem arising from the introduction of the Laplace distribution, which makes the solving process of the method difficlut, the bound optimization algorithm is employed and a suitable surrogate function is established. Based on the bound optimization algorithm, the Laplace prior can be equivalently transformed into the form of Gaussian prior, which is easily computed, and it can also be use to estimate the model parameters adaptively. Simulation results illustrate that the proposed method can be robust when outliers exist, while remaining acceptable prediction accuracy.
Matched asymptotic solution to a class of singularly perturbed thin plate bending problem
The thin plate-bending problem is studied. Introducing the stretched variables, the internal layer solutions near the boundary are constructed for the fourth order singularly perturbed boundary problem. Then matching the solutions with outer solution and using the theory of the composite expansion, the asymptotic solution is obtained finally.
Control of Hopf bifurcation in the one-cycle controlled Boost converter and its experimental implementation
The one-cycle controlled Boost converter is analyzed by using its averaged model. The results show that the one-cycle controlled Boost converter loses stability via a supercritical Hopf bifurcation, which may jeopardize the performance of the converter. A washout filter is proposed in this paper to suppress the Hopf bifurcation. This method can be easily implemented due to the structure of the one-cycle controlled Boost converter. The averaged model of the washout filter-aided one cycle controlled Boost converter is derived. Two new parameters in the washout filter can be chosen by Routh-Hurwitz stability criterion. The washout filter-aided method is verified by simulation and experiment.
Approximate finite-time stable control of Lorenz Chaos system
In the paper, the finite-time stability control problem for the Lorenz chaos system is studied. Considering the existence of uncertainty and nonlinearity in the Lorenz chaos system, a control method is proposed, which makes the controlled Lorenz system achieve approximate finite-time stability. And one kind of extended state observer is improved and designed to solve the unknown problem of uncertainty and nonlinearity for the controlled Lorenz system. The approximate finite-time stability of the closed-loop system is analysed by introducing the singular perturbation theary. Simulation results show the effectiveness of the control method and observer.
Numerical investigation of x-ray energy spectrum of rod-pinch diode
By particle-in-cell (PIC) simulation and theoretically analysis, electron spatial distribution and energy distribution in the rod surface of rod-pinch diode(RPD) are obtained separately, as input parameters for Monte Carlo simulation of photon energy spectrum of X-ray emitted from RPD. The Monte Carlo simulation results show that the average photon energy of shot 09006 is 0.441 MeV. Taking account of Pb attenuator, the simulation results accord with experiment data detected by PIN detectors array.
Multiscale simulation of nanometric cutting of single crystal Cu based on bridging domain method
One of the significant methods of multiscale simulation named bridging domain method which is a mixed atomistic-continuum formulation is reviewed. The mode related to atomistic/continuum coupling is introduced. The coupled method with the treatment of the overlapping subdomain is discussed, in which different scaling parameters (weigh factors) are adopted to calculate the energy of the system in the overlapping subdomain and to constrain the atomic and the continuum displacements by the Lagrange multiplier method. A bridging domain model is set up to investigate the effect of cutting speed on chip and workpiece atom force distribution in the nanometric cutting of single crystal copper. Simulation results show the cutting deformation coefficient decreases and the workpiece atom force increases with the increase of cutting speed. In addition, the machined surface qualities at different cutting speeds are investigated. The multiscale model and simulation of nanometric cutting are accomplished based on the bridging domain method, which lays a theoretical foundation for exploring the trans-scale simulation of nanometric cutting.
Nonorthogonal passive decoy-state quantum key distribution with a weak coherent state source
A nonorthogonal passive decoy-state method is presented with a reconstructive weak coherent state source. The method dose not prepare decoy states actively and divides the receiver detection events into two groups, i.e., triggered components and nontriggered components, according to triggering situation of the sender detector. Both triggered and nontriggered components, as signal states and decoy states, are used to do some estimations and to generate secure key. The simulation results show that a better key generation rate and a longer secure transmission distance can be obtained with the nonorthogonal passive decoy-state method than with the existing passive methods, and that the performance is comparable to the theoretical limit of an active infinite decoy-state protocol. Furthermore, the nontriggered component contribution to key generation offsets the limitation of the detector low efficiency, and the performance of the method dose not depend on the detector efficiency of sender. Because decoy states need not be prepared actively, and our protocol is easy to implement and apply to quantum key distribution at high transmission rates.
Bi-directional pedestrian flow model with traffic convention
In this paper, we extend a cellular-automata model recently proposed by Baek et al. to simulate traffic dynamics of the bi-direction pedestrians. And we present two improved strategies for the moving rules of the pedestrians. Numerical studies of average velocity-density diagram, spatial density distribution and position distribution of the pedestrians are given. We find that the two improved strategies can not only increase the average velocity of pedestrian flow, but also improve the utilization of the road, especially for the central region, reduce the degree of congestion, and avoid the occurrence of serious congestion. The two improved strategies have more comprehensive considerations of psychological and behavioral characteristics of pedestrians, which are also proper to simulate bi-directional pedestrian dynamics under a high traffic density.
Relativistic effect of ultracold Fermi gas in a strong magnetic field
Based on the single particle energy spectrum of weak relativity and Poisson’s formula,the thermodynamic potential function of Fermi gas in a strong magnetic field is derived. Furthermore, by using the thermodynamic relationships, the analytical expressions of statistic characteristic quantities of the system at low temperatures are obtained, and the influence mechanism of relativistic effect on the statistic properties of the system is analysed. It is shown that the relativistic effect becomes more significant with the magnetic field increasing. Compared with the corresponding oscillating amplitude, the monotonic term, which is caused by the relativistic effect, is much larger than the amplitude for the total energy, however, for the chemical potential and magnetic moment, they are almost of the same order.
A chaotic system with invariable Lyapunov exponent and its circuit simulation
A novel three-dimensional chaotic system with invariable Lyapunov exponent is proposed. The new system contains six system parameters, one quadratic cross-product term, and one square term. The dynamic properties of the new system are investigated via theoretical analysis, numerical simulation, Lyapunov dimension, Poincare diagrams, Lyapunov exponent spectrum, and bifurcation diagrams. The different dynamic behaviors of the new system are analyzed when each system parameter is changed. When the parameter of the square term varies, the Lyapunov exponent spectrum keeps invariable, the amplitudes of the signals of the first two dimensions change each as a power function with a minus half index, but the third one keeps its amplitude in the same range. Finally, the circuit of this new chaotic system is designed and realized by Multisim software, which confirms that the chaotic system can be achieved.
Nonlinear propagation and supercontinuum generation of a femtosecond pulse in silicon waveguide
Propagation of femtosecond pulse and supercontinuum generation in silicon waveguide are investigated numerically by solving the generalized nonlinear Schrödinger equation. The effects of dispersive effect and nonlinear loss on supercontinuum generation are simulated and analyzed. It is found that soliton fission is the main mechanism of supercontinuum generation in silicon waveguide. The relative position between the central wavelength of femtosecond pulse and zero-dispersive wavelength (ZDW) of silicon waveguide significantly affects the generation of supercontinuum. When the input pulse falls in the anomalous dispersion regime, soliton fission phenomenon is most obvious. It is also found that the high-order dispersion plays an important role in supercontinuum generation. When the absolute value of third-order dispersion is smaller, a broader supercontinuum can be obtained. Besides, two-photon absorption (TPA) effect in silicon induces high loss, and reduces the spectral width of the supercontinuum.
Dynamics of a novel chaotic neural firing pattern discovered in experiment and simulated in mathematical model
A special chaotic firing pattern lying between period-1 and period-2 firing pattern simulated in theoretical neuronal firing model, Hindmarsh-Rose (HR) model, has not been adequately understood for a long time. The non-periodic neural firing patterns lying between period-1 and period-2 firing pattern discovered in the biological experiments on neural pacemakers of rats are identified to be chaotic bursting and divided into three styles in appearance, according to the deterministic structures of the first return map and the short-term predictability of nonlinear predication. One style of the experimental chaos exhibits characteristics similar to the numerical simulations of the theoretical model, verifying the theoretical participation of HR model, while other styles display different characteristics. The characteristics of the three styles and the relationship and distinction among 3 styles of the chaotic rhythms are identified, and compared with those lying between period-2 and period-3 firing pattern, and between period-3 and period-4 firing pattern. In addition, the distinction between the transition procedure from period-1 to chaos and then to period-2 and other bifurcation scenarios from period-1 to period-2 firing pattern is also identified. The results confirm the novel chaos lying between period-1 and period-2 and the corresponding novel bifurcation scenario, enriching the kinds of the chaotic rhythms and bifurcation scenarios of neural firing. Finally simulations of the diversity and non-smooth characteristics of the chaotic rhythms discovered in the experiment and identification of the routine to chaos are also discussed.
Fractal characteristics of characteristic parameter statistical distributions of typical random signals
A two-parameter statistical model of the pulsed signals which can be used to describe the basic structural characteristics of the random signals is established in this paper. As a result, the random signal counting distributions of amplitude q(lV) and width p(lτ), as well as the different signal subset counting distributions under given width εlτ(lV) and amplitude δlV(lτ), all match well with the form of the lognormal distribution with a natural numberused as an independent variable. Besides, it is also found that there are internal relations between the counting distribution statistical characteristic parameters μlnV, μlnτ, σlnV, σlnτ and the corresponding signal characteristic parameters lV and lτ. In essence, these relations are the representations of random signal fractal characteristics. In a word, two characteristic parameter statistical distributions of the random signals each have a non-integral dimensional fractal feature.
A finite-time stable theorem about fractional systems and finite-time synchronizing fractional super chaotic Lorenz systems
Chaotic property analysis and prediction model study for heating load time series
In order to reveal the internal dynamics characteristics of heating load time series, the existing chaotic behavior is validated by use of nonlinear analysis method. The data sets taken from heat source and substation of district heat supply are studied by which phase spaces are reconstructed, and the correlation dimensions and the largest Lyapunov exponent are computed to identify the presence of chaos in heat load time series. By the analysis of the results, chaotic characteristics obviously exist in the heat load time series, which is a theoretical basis for the correlative investigation of heat load prediction. According to the existing heat load predictive method almostly based subjective models, a novel predictive approach based on Volterra adaptive filter, which avoids the subjective model assumptions, is presented for heat load prediction. Finally the predictive results are presented, and the simulation results illustrate that the second-order Volterra adaptive filter has high predictive accuracy which can meet the demands of heat energy-saving control and heat dispatching in practical applications.
Transient synchronization mutation of ring coupled Duffing oscillators driven by pulse signal
The dynamic behavior of ring coupled Duffing oscillators driven by non-periodic signal is investigated, a phenomenon is discovered, which shows that when ring coupled Duffing oscillators are in the period-doubling bifurcation phase state and one of the oscillators is driven by pulse signal under certain parameter conditions, this oscillator and the other oscillators suddenly change from synchronization to transient non-synchronization and then rapidly return to synchronization, which is defined as transient synchronization mutation. This phenomenon can be used to accurately detect weak pulse signal in strong noise environments, which can further extend the weak signal detection range based on the Duffing oscillator.
Synchronization of new Lü chaotic system via three methods
Study of the femtosecond fiber comb and absolute optical frequency measurement
An optical frequency comb is built by using a commercial femtosecond laser and signal-noise (S/N) ratio of the fceo signal is obtained to be about 30 dB. Its repetition rate frequency and offset frequency are highly stable and the tracking stability is verified. An absolute frequency measurement of a 1064 nm Nd: YAG laser is realized by using this stabilized optical frequency comb. The tracking stability of the repetition rate frequency is superior to 3.7×10-14 at 100 s and the absolute frequency of the laser is 281630111757362 Hz. The experimental result is in accordance with the recommended value by International Committee of Weights & Measures(CIPM).
Effect of temperature gradient on grain growth behavior from phase field simulations
A 2D model is developed to investigate the grain growth behavior under the influence of temperature gradient using the phase field method. The model is used to simulate the effect of temperature gradient on the nonuniform and directional grain growth behavior during annealing of polycrystalline materials. The results show that the static temperature gradient leads to the nonumiform grain growth, and that the grain growth exponent deviates from that of normal grain growth. In the case of annealing with a moving temperature gradient, the columnar grains may develop towards the locations with the highest temperature in the heated zone. Moreover, the grain growth behavior is closely related to the moving speed of the moving heated zone. Columnar grains occur only when the moving speed of the heated zone is higher than the minimum grain growth rate but lower than the maximum grain growth rate.
Analysis of comprehensive effects of piston error and sub-aperture aberrations on the image quality of sparse-optical-synthetic-aperture system
To improve the image quality of sparse-optical-synthetic-aperture system, the effects of sub-aperture self aberrations and piston errors among different sub-apertures should be considered comprehensively. Based on the pupil of sparse-optical-synthetic-aperture system, the system Strehl Ratio (SR) is deduced using the principle of Fourier optics, which leads to the theoretical result of the systems SR metric with the form of separated sub-aperture aberration and piston error. As for the bi-aperture system, the variances of the system SR metric are calculated and analyzed with different sub-apertures’ aberrations for conditions of corrected piston error and un-corrected piston error. Therefore, the comprehensive effects of sub-aperture aberrations and the piston errors among different sub-apertures on the system image quality are analyzed theoretically. From these analyses, the physical mechanism for the comprehensive effect of sub-aperture aberration and the piston error on the sparse-optical-synthetic-aperture system image quality is revealed, and it could be seen that the compensation of piston error is meaningful only if the sub-aperture self aberration is corrected to be in a certain limit.
Mass spectrum and mixing angle of axial-vector mesons
In this work, using the formula for hyperfine splittings, we first calculate the mass of the bottomonium member for the axial-vector multiplet (11P1). Then, the masses of the axial-vector mesons Bc1,(ss and K1B are extracted in Regge phenomenology. After that, we estimate the nonet mixing angle and the mixing angle for K1A - K1B. We suggest restudying h1(1380) near 1478 MeV and searching Bc1(1P) near 6774 MeV. The predictions may be useful for the discovery of the unobserved doubly heavy meson Bc1 and useful for understanding the K1A - K1B mixing and the axial-vector (11P1) nonet mixing.
Shell model study of Gamow-Teller transitions of nuclei 13N
Recent researches show that the beta decay of 13N can affect the electron abundance before the collapse of SNe Ia supernovae. Based on the shell model, the Gamow-Teller transition strengths from ground state to ground state and trom ground state to excited state of 13N are calculated and the results are compared with theoretical results and also with experimental data. The electron capture rates at different temperatures and densities are calculated and the effect of ground state on excited state transition is discussed. It is shown that due to the transition from ground state to excited state, the electron abundance of the SNe Ia supernovae decreases and the contributions are determined mainly by the low-lying excited states.
Particle-in-cell simulation of outer magnetically insulated transmission line of Z-pinch accelerator
In order to implement the particle-in-cell(PIC) simulation of four outer magnetically insulated transmission lines(MITL) of Z-pinch accelerator, we adopt the backward-going transmission line voltage wave at the double post-hole convolute(DHPC) travelling in the outer MITL direction, which is gained in circuit simulation to model the part from DHPC to Z-pinch load. For the purpose of enhancing the accuracy of equivalent circuit model of DHPC and Z-pinch load, the backward-going transmission line voltage wave that is computed by circuit simulation is rescaled by PIC simulation. The insulator voltage and current waves that are obtained in the PIC simulation of four outer MITLs of PBFA Z can match the electrical measurements better than those obtained by the circuit simulation. Moreover, the influence of Z-pinch load implosion on the process of pulsed power coupling in the outer MILT is analyzed and explained.
Experimental study of the secondary neutron angular spectra emitted from polyethylene slabs with D-T neutron source
An experimental method of measuring the secondary neutron angular spectrum from polyethylene slab assembly with D-T neutron source based on the proton-recoil method is developed. In order to ensure the energy linearity of the detector and obtain a good neutron-gamma discrimination capability in the case of a low effective neutron threshold (0.5MeV), neutron energy spectrum is measured in two parts: one is in a high energy region and the other in a lower energy region. The pulse shape discrimination (PSD) and the pulse height distribution (PH) two-dimensional information of the secondary neutron and the associated gamma rays are recorded event-by-event simultaneously. The selection and the deduction of the gamma ray events and the joining of the two-segment energy spectra are carried out by using the off-line data analysis programs written in the ROOT data analysis framework. Furthermore, an artificial neural network technique is used to accomplish the unfolding of the neutron spectra successfully. The experimental results of the second neutron angular spectra from 9cm and 18cm thick polythene slab assemblies with D-T neutron source in an energy region of 0.5 MeV to 15 MeV are obtained. The Monte Carlo calculations of the experimental models are accomplished by using the MCNP5 code with ENDF-VI data library. The experimental results are in agree ment with the calculation results within the experimental uncertainties.
Study on geometrical structure and spectrum ofpolymerization borohydride (BH3)n(n=1—3)
The possible geometrical structures of polymerization borohydride (BH3)n(n=1—3) are optimized in computation, based on different methods of B3P86、B3LYP,MP2,LSDA and by combining the Dunning relevant and consistent base group cc-PVTZ. The configuration geometric parameter, the electronic structure, the vibrational frequency and spectrum of the most stable structure are obtained, and the total energy (ET), binding energy (EBT), the average binding energy (Eav), the ionization potential (EIP), the energy crack (Eg), the Fermi level (EF) and so on are also given. The results indicate that the total energy is lowest and its value is close to the reported values from B3P86 method. The ground state of the three kinds of borohydride are all singlet states, the ir electronic states respectively are 1A',1A, and 1A. The stable geometry configuration of BH3 molecule is the planar triangle, B2H6 has a symmetrical ethylene type D2h spatial structure, and between H-B produces the hydrogen bridge type with three-center double electronic key, B3H9 has a C3νspatial structure, also produces a hydrogen bridge type of three-center double electronic key, but the three hydrogen bridge types are isolated from each other. Finally the infrared and the Raman spectrum, the average binding energy, the ionization potential, the energy gap, Fermi level and so on are analyzed. B2H6 is shown to be the most stable molecule in (BH3)n(n=1—3), the H-B bridge bond key long is longer than the terminal lond, the infrared intensity of strongest peak is a maximal value.
The study on structures and properties of Run and Run Au(n=1—12) clusters by density functional theory
The geometries, the stabilities, and the electronic properties of Run Au and Run (n=1—12) clusters are systematically investigated by the density functional theory. The results suggest that the lowest energy structures for Run Au clusters can be obtained by substituting one Ru atom in Run+1 clusters with Au atom. The geometries of Run Au clusters are similar to those of Run+1 clusters except local structural distortions. The second-order difference and fragmentation energy show that Ru5, Ru8, Ru5Au, and Ru8Au clusters are the most stable among these studied clusters, the doped Au atoms do not change the relative stabilities of Run clusters; the Au impurities increase the chemical activities of Run clusters, and the value of gap is determined mainly by the electron-pairing effect; the doped Au atoms increase the total magnetic moments of Run Au in most cases.
Density functional study on hydrogenation and non-hydrogenation graphene nanoribbon
Based on density functional theory and first-principles method, we investigate the structure and the electronic property of graphene nanoribbion with width N=8 and with or without hydrogen saturation on their edge. Our results show that the carbon atoms on the edge of armchair graphene nanoribbon without the hydrogen saturation are bonded together by triple bonding, which is stronger and more sensitive than that in the case of hydrogen saturation. This type of graphene nanoribbon can serve as a kind of basic material for nano-sensor. Our band structure calculations indicate that both armchair and zigzag nanoribbions are of semiconductor possessing an energy gap. Furthermore, the energy gap of nanoribbon without hydrogen saturation is larger than that with hydrogen saturation, which implies that hydrogen saturation has distinct decoration to the property of the nanoribbon. By the calculation of the paramagnetism, ferromagnetism and anti-ferromagnetism states of the zigzag graphene nanoribbon, we find that anti-ferromagnetism state is the most stable among them, and its magnetism on the edge is strongest, which is suitable for the application in spinelectronics.
Influence of electron correlation on Au ions
We present a comprehensive theoretical study of atomic characteristics of nine isoelectron sequences of gold ions in a broad range of wavelengths and transitions. The calculation is performed by the multiconfiguration Dirac-Fock(MCDF) method. The valence-valence, the core-valence and the core-core correlations are also considered. The calculated values including core-valence correlation are found to be consistent very well with other theoretical and experimental values. We believe that our calculated values can guide experimentalists in identifying the fine-structure levels in their future work.
Measurement of velocity distribution for strontium atom beam by Zeeman Scanning technology
We measure the velocity distribution of the strontium atomic beam directly by Zeeman scanning technology. The most probable velocities of atomic beam before and after Zeeman deceleration are 420 m/s and 60 m/s respectively. Zeeman scanning method is much convenient than other detect ways. Because of its direct fluorescence observation, it has a high accuracy relatively.
Macroscopic effects of high-order harmonic and isolated attosecond pulse generation driven by two-color laser field
Chromium atom deposition in elliptical standing wave filed
Direct-write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms deposit on a substrate. The motorial characteristics of chromium atoms in an elliptical standing wave filed are discussed, and the simulation results are given with different deflective angles of elliptical standing wave. The full width at half maximum (FWHM) is 3.2 nm and the contrast is 36 ∶1 with a deflective angle of 0°. The FWHM is 6.5nm and the contrast is 24 ∶1 with a deflective angel of 15°, but when the deflective angle reaches 30°, the stripe splits and two-peak configuration is formed.
Wave packet dynamics of the photodetachment ofH- near a metal surface
The wave packet dynamics of the photodetachment of H- near metal surface is studied by using the wave packet evolution and the autocorrelation function. The results show that the evolution and the revival structure of the detached electron depend not only on the ion-surface distance, but also on pulse width and initial pulse momentum. Therefore, we can control the wave packet dynamics of H- near a metal surface by changing the ion-surface distance and the parameter of the pulse laser. Besides, the electronic image state lifetime can also affect the wave packet evolution and the autocorrelation function. We find that with considering the electronic state lifetime,the amplitude of the quantum probability density decreases gradually with time,the whole wave packet structure has a significant attenuation and the lifetime can weaken the interference phenomenon in the process of wave packet evolution. Through the research on the autocorrelation function of electronic wave packet, we find that the wave packet exhibits a good revival structure without considering the lifetime of the state lifetime; however, with considering the lifetime of the state lifetime, the wave packet periodically collapses and expands with time,but after a period of time, the revival structure disappears. We hope that our theoretical study will provide some references for the experimental research of wave packet dynamics of negative ion near surfaces.
Theoretical study on (e,2e) process for helium in perpendicular geometry
The triple differential cross section for electron impact ionization of helium in the perpendicular geometry is calculated by use of BBK model and modified BBK model. The results of the present work are compared with experimental data. The structure of the cross section is analysed and the exchange effects are discussed systematically.
Theoretical study on structural and electronic properties of WnNim(n+m=8) clusters
The possible equilibrium geometries of WnNim(n+m=8) clusters are optimized by using the density functional theory at the B3LYP/LANL2DZ level. For the ground state structures, the average binding energy, the wiberg bond index(WBI), the magnetism and the natural bond orbital(NBO) method are analyzed. The calculated results show that with the increase of the W atom number, the cluster becomes more stable. The strength in WBI is in the following order: W-W>W-Ni>Ni-Ni. When n≥5, the WnNim(n+m=8) clusters include the basic structure of Wn cluster. The magnetic moments of WnNim(n+m=8) clusters are quenched at n=5 and 6.Inside W and Ni atoms, the hybrid phenomenon happens, owing to the charge transfer. And the charge transfer also occurs between W and Ni atoms, thereby forming a strong chemical bond between W and Ni.
Bright metastable noble gas atomic beam and atom trap using laser cooling
Metastable noble gas atomic beam is widely used in atomic and molecular physics studies.Using radio-frequency discharge and transverse laser cooling, we produced a well-collimated intense meta-stable Krypton beam.Numerical simulation is also used to analyze the trajectories of atoms in an optic field produced by transverse cooling laser beams.The charactersisticl of the atomic beam are determined by measuring the laser induced fluorescence.The atomic beam flux measured at 230 cm downstream is 1.6×1016 atoms/(s*sr), which is enhanced by two orders of magnitude.The Kr atoms are finally trapped in a magneto-optic trap.A total of 1.3×1010 meta-stable 84Kr atoms can be simultaneously trapped with a loading rate of 3.0×1011 atoms/s.The same setup is also successfully used to obtain a bright metastable atomic argon beam and trap.
Design of X-band backward wave oscillator with 10 GW output power
An efficient high power relativistic backward wave oscillator (RBWO) is designed. To enhance the beam-wave conversion efficiency and output power, an overmoded slow wave structure (SWS) is used and an inner conductor is inserted into the SWS. When electron energy is 1.3 MeV while the beam current is 17 kA, the simulated output microwave power is 10.4 GW at 8.8 GHz frequency for the RBWO.
Theoretical and numerical study on optimization of diode parameters in virtual cathode oscillator
The dependences of microwave efficiency and frequency on the parameters of diode in virtual cathode oscillator (VCO) are studied with particle-in-cell simulations, which further gives the effects of diode impedance on microwave efficiency and frequency. The characteristic impedance of microwave mode in virtual cathode oscillator is derived as in other high power microwave generators with slow-wave configurations and is used to analyze the optimization of diode parameters. It is shown that the optimal values of diode parameters are obtained when the diode impedance matches with the characteristic impedance of microwave mode in VCO with coaxial wave guide as well as in VCOs with other configurations. This is a good theoretical explanation for the optimization of diode in VCO and can be used to guide the design of devices.
Spatially-resolved measurement of conductivity of plasma single filament generated by femtosecond laser
Electric conductivity and high voltage breakdown threshold of single plasma filament generated by femtosecond laser are spatio resolved measured. The results show that the resistance of the single filament is in a range of 280—630 kΩcm after eliminating the contact resistance, and the breakdown threshold can be reduced down to ~50% of the original value in air. Furthermore, the variations of resistance and discharge threshold follow the same trend as that for the same part filament. The relation between breakdown threshold and resistance of the single filament is established.
Magnetoelectric heating in the ECR plasma
The magnetoelectric heating is investigated on an ECR plasma device. The ion temperatures are measured by ion sensitive probe (ISP) before and after magnetoelectric heating. The influences of bias voltage of electrical ring, magnet field and pressure on ion temperature and the efficiency of ion heating are studied. The results indicate that the whole heating of the plasma is accomplished through the magnetoelectric heating of the ions in the sheath of the electric ring and the radial transport of the heated ions. The ion temperature in the axial area increases with the bias voltage of electric ring, and their relationship is nonlinear. The ion temperature increases more than 20 eV when the bias voltage is 1000 V. A heating efficiency is achieved to be as high as 2%—2.5% and increases with the bias voltage increasing. The magnetic field strength plays an important role in the limitation and heating of the ions. The efficiency of the magnetoelectric heating increases with the increase of the magnetic field strength when the magnetic field strength changes from 6.3×10-2T to 8.7×10-2T. The efficiency of the magnetoelectric heating increases with the pressure decreasing when the pressure chenges in a range of 0.02—0.8Pa.
One-dimensional imaging diagnostics of imploding dynamics for planar wire array Z pinch
The primary experiment results of imploding dynamics for single and double planar wire arrays, acquired by optical streak camera, are presented and analyzed. The results show that the interaction of adjacent single wire plasma for single planar wire array is not dus entirely to inelastic collisions, while a part of plasma can move into the center and form precursor plasma across the plane of wire array; the current of outer wire is larger than that of the interior of wire, the time of ablation stage is ~65% of the total imploding time, and only a part of mass participates in the imploding stage.
Multi-component induction logging response in large dielectric formation
Wireline induction logs operating at a frequency of some tens of kHz are used to detect the resistivity of hydrocarbon reservoir. The dielectric constant of typical formation is usually smaller than that of pure water and its effect is negligible for induction log. However some peculiar rocks including organic matter named source rock have large dielectric permittivities caused by polarization, which can lead the traditional induction logging to have an nusual log response. Multi-component induction logging is new log method and has been developed in nearly ten years, which can provide more information about formation than traditional axial instrument and has large potential applications. In this paper, we study the effect of large dielectric constant on multi-component induction logging response and extract the information about resistivity and dielectric permittivity through the different combinations, there by realizing the formation parameters reconstruction and intuitive recognition for the hydrocarbon source rock.
Season division and its temporal and spatial variation features of General atmospheric circulation in East Asia
Using the NCEP-DOE Reanalysis 2 data of air temperature, geopotential height, relative humidity and wind field of 17 pressure levels from 1979 to 2009, and the Multi-factor Fisher optimal dissection method, the seasons of the general atmospheric circulation in East Asia are diuided. The main results are as follows. (1)The seasonal establishment of atmospheric general circulation is initiated from subtropic of the stratosphere in East Asia. In the troposphere the spring and the summer first start from the tropical regions, and then extend into middle latitudes. The autumn and the winter first start from middle latitudes, and then extend into low latitudes. (2) In the troposphere the seasonal establishment of atmospheric general circulation is more consistent, and it is very different from that in the stratosphere. And the seasonal establishments of the middle and the low level of the stratosphere are not very consistent. (3)In the past 30 years, the four seasons have started much earlier in about 6 years, in which years some stronger El Niño phenomena just happened. That implies that the El Niño phenomenon causes abnormal seasonal variation.
Stochastially re-sorting detrended fluctuation analysis: a new method to define the threshold of extreme event
By combining detrended fluctuation analysis (DFA) method with surrogate data method, and using the Heuristic segmentation algorithm as well as Chi-Square statistics, we develop a new method to determine the threshold of extreme events, e.g. stochastically re-sorting detrended fluctuation analysis (S-DFA) method. The S-DFA method has a certain phsical background, when the occurrence rate of the data is small, then these data belong to little-probability events and they contain so little information about the dynamic system, the states corresponding to these data are abnormal states or extreme states of the system. When the occurrence rate of the data is large or even in distribution these data do not belong to little-probability events and they contain much information about the system, the states corresponding to these data are normal states of the system. Compared with the Percentile curves method, the S-DFA method gives the critical value between extreme event and non-extreame event, which is definite and unique. We also extensively validate the effectiveness of S-DFA method through extreme event detection.
Extremely low temperature and its composite index based on stochastically re-sorting detrended fluctuation analysis
By combining the detrended fluctuation analysis (DFA) method with surrogate data method, and using the heuristic segmentation algorithm as well as Chi-Square statistics, we develop a new method to determine the threshold of extreme events, e.g. stochastically re-sorting detrended fluctuation analysis(S-DFA) method. By using the S-DFA method, we obtain the thresholds of extremely low temperature events from 1961 to 2006 in China and analyze their spatiao temporal characteristics of distribution. We also validate the effectiveness of the S-DFA method through extreme event detection using the temperature series. By defining the composite index of extremely low temperature events from the angle of predictability, this composite index is integrated with the information about the frequency and the strength of the extremely low temperature events, with considering the characteristic of regional climate system. Based on the composite index, we divide the extremely low temperature events during 1961—2006 in China into four different zones according to their own rank. The composite index of extremely low temperature tends to be katabatic on the whole, Before the the early 80's in the 20th century, the composite index changed according to two distinct 10-year quasi-periods, and after that the composite index was in a downward trend and was well below the average. Until after the mid-90's in the 20th century, it rose to about average value once again.
Characteristics of spatiotemporal distribution of extreme temperature events over China mainland in different climate states against the backdrop of most probable temperature
Daily max temperature records of National Meteorological Information Center from 1961 to 2009 over China mainland are divided into three climate states of 1961—1990,1971—2000,1981—2009 (just called StateⅠ, StateⅡ, State Ⅲ respectively). Most probable temperature(MPT) and extreme temperature events are defined according to the skewed function. The spatiotemporal distribution characteristics of frequency and strength of extreme temperature events over China mainland in different climate sates against the backdrop of MPT are analyzed. Spatially, frequency and strength of extremly high temperature in summer decrease significantly in the Yangtze-Huaihe river valley and the Yellow river and Huaihe River valley in StateⅠ and increase significantly in the arid-semiarid region and the econormically developed Yangtze River delta in State Ⅲ. The frequency of extremely low temperature in winter reduces remarkably in the north part and the Yangtze River delta in StateⅡ and in the Qinghai-Tibet Plateau, the southeast part of northeast China, the Yangtze River delta in State Ⅲ. The strength of extremely low temperature in winter reduces on the whole and provincial characteristics are not obvious. The frequency and the strength of extreme temperature events are consistont spatially. Temporally, the frequency and the strength of extremely high temperature in summer increase obviously both in StateⅡ and State Ⅲ. The frequency and the strength of extremely low temperature in winter reduce obviously in StateⅡ and the reducing trend slows down in State Ⅲ. Extremely high temperature in summer occurs frequently and extremely low temperature in winter remains stable. Extremity of high temperature in summer is stronger while in winter is stable relatively. The frequency and the strength of extreme temperature events are consistent temporally. During the common time period of States Ⅰ,Ⅱ and Ⅲ, the frequency of extremely high temperature events in the last state was always less than the former while the low temperature events are more, which is in accordance with the fact that the background temperature steps up with the states; the strength of extremely high temperature events in the latter state is less than that of the former while the strength of extremely low temperature events is stronger. For the abrupt change of climate at the end of the 1970 s and the beginning of the 1980 s, the frequency of extreme high temperature events decreases before the change and increases obviously after the change while the ones of extremely low temperature do not change significantly correspondingly; the strength of extremely high temperature events decreassd slightly before the change and increases obviously after the change while the strength of extremely low temperature does not change significantly for the change but the whole strength after the change is slightly lower than the one before the change.
Hawking radiation of dynamical Kinnersley black hole under the new tortoise coordinate transformation