An electromagnetic inverse scattering approach based on support vector machine
Zero-index metamaterial based on double-negative structure
We present a new kind of zero-index metamaterial composed of periodic array of dendritic cells with continuous long pole, and investigate its electromagnetic characteristics. First, we study the one-level dendritic cell with continuous long pole. The retrieved effective permittivity and permeability of the unit cell simultaneously tend to be zero from their negative values at a frequency of 9.5 GHz, which leads to a near-zero refractive index. Then by changing the geometric parameters of the unit, we find the influences of the branch length and the separation angle on the electromagnetic parameters. Finally, increasing the level number of the branch gives rise to two-level and three-level dendritic cells respectively with continuous long pole. Adjusting the geometric parameters of each unit cell to appropriate values, the zero-index matematerials with zero permittivity and permeability can be obtained at the same frequency.
Isotropic negative permeability metamaterials and left-handed metamaterials based on miniature structure
Multiple scattering spectra through fog particles in the ellipsoidal model
Because of the properties of non-sphericity and multiple scattering of fog particles and the effects of geometrical optics, the light scattering through fog has become a difficult problem. In this paper, we establish an ellipsoidal model of fog particles. On the basis of radiative-transfer equation and with the consideration of the effects of geometrical optics, we obtain a formula of calculating multiple light scattering intensity through the fog particles with different sizes and different shape distributions. Our results are in agreement with the earlier results in two special cases, which verifies that our method is reliable. The calculations show that scattering spectra through the ellipsoidal fog particles present elliptical feature, which is different from circular feature for random orientation non-spherical particles. At the different orientation angles the angular distributions of the light intensity are different, and this difference becomes smaller with the shape ratio approaching to 1. The stripes of the scattering spectra progressively disappear with the increase of optical thickness, which is different from the case of single-scattering. At different orientation angles and observation angles, the scattering intensities always first increase then decrease with the increase of optical thickness for the fog particles of the different size distributions and different shape ratio distributions, and a maximal intensity occurs at τ =1.0–3.0. The calculations also indicate that the scattering spectra of actual fog particles present the turbid pattern around the central light speckle because of wide size distribution in many cases.
The ratio choice method of the pinhole aperture to the waist of the Gaussian laser in the fabrication of holographic gratings
In the fabrication of the holographic diffraction gratings, the scatter light which is produced by the reflection of the granule in air or the diffraction defect of the optical apparatus will be recorded simultaneously in the resist. Those noises not only reduce the diffraction efficiency of gratings, but also give rise to the scattered light in diffraction. So an appropriate spatial filter should be used to stop the higher spatial frequencies corresponding to the Gaussian beam. Because the diffraction effect after the pinhole aperture can demolish the wavefronts of laser, it is the most important to choose the optimal pinhole for adjusting the waist of the laser. On the basis of standard scalar diffraction theory, the field amplitude is given by the convolution calculation, the phase distortion of diffraction wavefronts is also analyzed, and the lower limit ratio of the aperture size with respect to the beam radius is given when the phase transitions are further away from the center. Using the energy conservation of Gaussian beam and comparing the characteristics change of diffraction beam, the effect of diffraction is presented and the upper limit ratio of the spatial filter is given by the critical condition of the diffraction. The conclusion shows that if the ratio of the aperture radius to beam waist is between 1.52< a/ω0<2.2, the phase is invariable in the area of the exposal, and the power transmitting the spatial-filter pinhole aperture is slightly more than 99%, so spatial filter performs its function only in this range of the radio.
An image hiding and blind extraction algorithm based on block discrete wavelet transform
Photonic generation and transmission of chaotic ultra wideband signals
Research on linewidth characteristics and broadening mechanism of distributed feedback fiber laser
The linewidth characteristics of distributed feedback fiber laser (DFB-FL) is fully explored in this paper. The linewidth broadening effect of DFB-FL induced by self-pulsation, phase-shifted grating, especially lasing window, external disturbance, etc. are extensivly investigated in the paper based on the theoretical derivation and experiment. An effective linewidth compression method is proposed, and a self-injection system of DFB-FL comes up to reduce its linewidth from 35 kHz to less than 10 kHz.
Influence of temporal error with different pulse shapes on coherent beam combination system
Coherent beam combination of fiber laser array is an important technology for high-power output fiber laser systems. However, the coherent beam combination is influenced by temporal error, which always exists in the laser array. The coherent beam combination of pulse fiber lasers in the presence of temporal error is investigated in theory in this paper. The effects of pulse shape and temporal error on the coherently combined beam are studied. The characteristics of combined beam, i.e. pulse shape, peak power, far-field pattern and power in barrel (PIB) are calculated and analyzed when the pulse shapes (including square, triangle and sine) and temporal errors are different. It is revealed that for coherently combining square pulse lasers, the pulse shape of the combined beam changes acutely because of temporal error, and the far-field pattern and PIB change proportionally with temporal error increasing; for coherently combining triangle pulse lasers, the pulse shape and the peak power of the combined beam are acutely influenced by temporal error, and the far-field pattern and the PIB change acutely when temporal error is large. It is revealed that coherently combined beam of sinusoidal pulse lasers has good characteristics when two pulse laser with sinusoidal pulse shapes are coherently combined and the time delay between the two pulses is less than 10% of pulse duration.
Near-field modulation of lateral cracks
Light intensification caused by cracks in fused silica subsurface is one of main factors of laser-induced damage to optical materials. Three-dimensional finite-difference time-domain method is used to simulate parabola-section-model lateral cracks. Moreover, the relationship between light intensification and breadth-to-depth ratio R is discussed. The results show that the morphology change after acid etching is an important cause of damage mitigation. Modulation is very weak and close to each other when R is greater than 10.0 and it increases rapidly when R less than 5.0. The electric field intensity reaches a maximal value when R ranges from 1.0 to 3.0, and the maximal electric field is 4.3 V/m. The electric field intensity of more than 80% samples exceed 2 times than the incident light when R ranges from 1.0 to 3.5. Intensified area has the skin effect with depth increasing. It is demonstrated that enhanced area lying directly below the crack firstly shifts to left and right sides, then it moves to parabola-section interface and the horizontal interface. Finally, the whole subsurface will be enhanced. In addition, electric field modulation firstly increases and then decreases in the z direction when depth is large enough.
Analysis of thermal effect and its influence on output power of thin disk laser
Theoretical investigation of orthogonal dual-pump four-wave mixing in semiconductor optical amplifier
A comprehensive broad-band model of orthogonal dual-pump four-wave mixing (FWM) in semiconductor optical amplifier (SOA) is presented in the case of the polarization state of the input signal being arbitrary. By performing numerical simulation and taking the all-optical wavelength conversion based on orthogonal dual-pump FWM in an SOA for example, the effects of the input light powers, frequency detuning and polarization state of the input signal on the orthogonal dual-pump FWM and the performances of wavelength conversion are theoretically investigated.
Theoretical and experimental investigations of spatial optical dark soliton filamentization in nonlocal self-defocusing Kerr medium
Sol-gel co-assembly of inverse opal film and research on its optical properties
Comparison of the resolutions of integral imaging three-dimensional display based on human vision
Design and optimization of low-loss low-nonlinear high negative-dispersion photonic crystal fiber
A novel hexangular lattice dual-concentric-core photonic crystal fiber is proposed, which is composed of a central defect core, an outer ring core by introducing small air-holes on the forth ring and double cladding circle air-holes along the direction of fiber length. Based on full vector finite element method with anisotropic perfectly matched layers, its dispersion, nonlinear, leakage loss and mode field are numerically investigated. Numerical results indicate that the proposed fiber shows higher negative dispersion tunable effect and stronger confinement ability of guided mode, which the leakage loss is close to 10-2 dB·m-1. The wavelength for high negative dispersion value can be adjusted by artificially choosing the parameters of proposed fiber, i.e. Λ, d1 and f. Both its dispersion and dispersion slope are negative, the dispersion slope values are between-1–-6 ps·km-1nm-2 over C band, and its negative dispersion value is-3400 ps·km-1nm-1, the nonlinear coefficient is only 3.6 km-1W-1, and the corresponding area of mode field is 43 μm2 at wavelength of 1.55 μm, if the parameter is selected as Λ=1.2 μm, f=0.917, d1=0.515 μm. Obviously, it has a good dispersion compensation, therefore it has admirable applications in the field of high-speed large-capacity high-power pulses long-distance communication system.
All-optical logic gates based on nonlinear polarization rotation in high nonlinear fiber
A novel scheme to realize all-optical logic gates is proposed based on nonlinear polarization rotation (NPR) in high nonlinear fiber (HNLF). Two optical signals A and B together with a continuous wave are injected into the HNLF. Due to the optical power variation in HNLF, nonlinear birefringence will be induced between the two polarization axes. Both the optical signal and the continuous wave are filtered out at the output of HNLF. By controlling the optical power and the polarization of the optical signal as well as the polarization of the polarizer with respect to the polarization of optical signal/continuous wave, multiple all-optical logic gates can be realized. The theoretical analysis of the optical logic gates based on NPR in HNLF is provided. And the feasibility of the scheme is demonstrated by realizing all optical“and”,“not”,“or”,“xor”,“nxor”,“A· B”,“A·B”, half-adder and half-subtracter at 10 Gbit/s operation.
Preparation and spectral characteristics of Bi-doped double cladding fiber
Bi-doped double cladding fiber preform is prepared by modified chemical vapor deposition and solution doping process. The absorption spectrum of preform and the near-infrared (NIR) luminescence spectrum of fiber are experimentally investigated. The luminescence spectrum of the fiber shows a peak emission band at 1140 nm with a full-width at half-maximum (FWHM) of 130 nm under 976 nm LD exciting. Under 808 or 793 nm LD exciting, an ultra-broad NIR emission with an FWHM of more than 250 nm is observed in the Bi-doped fiber, and the range of luminescence spectrum is from 1000 to 1700 nm. After the heat treatment of the Bi-doped fiber preform slice under 900 ℃ for 1 h, under 808 nm LD exciting, the fluorescence intensity is about 4 times higher than that of the perform slice without heat treatment. The results indicate that the Bi-doped double cladding fiber is a promising gain medium used for ultrashort fiber lasers and tunable fiber lasers.
Research on the temporal-spatial distributions and the physical mechanisms for the sound speed profiles in north-central Indian Ocean
The structure of sound speed in ocean has a strong influence on underwater sound propagation. For underwater target detection and underwater acoustic communication, it is of great significance to obtain the temporal and spatial distribution of sound speed profile. Since the limitations and applicability of vertical grads method in structural analysis of sound speed in the Indian Ocean, optimal partition method is developed to calculate the sound spring layer. The study focuses on analysing the eigenvalues of sound speed profiles (SSPs) in the north-central Indian Ocean based on the last 10 year data of array for real-time geostrophic oceanography. The vertical structure characteristics of sound speed are investigated in the Indian Ocean, and the laws of temporal and spatial variation are obtained. The distribution of the fitting accuracy with the order of empirical orthogonal functions (EOF) are found. The physical mechanisms of the temporal and spatial variation of SSPs are revealed with the marine physical environment in Indian Ocean. The simulation results show that optimal partition method is suitable for the area to judge the structure of spring layer, and the parameters of the corresponding criterion is also proposed. The regional distributions of the fitting accuracy with the order of EOF are more obvious than with the seasonal variations. The deep channel axis exists at south 5°S and there are three spring layers between 15°S and 25°S. The structures of SSPs in the Indian Ocean can be classified into four types: single spring layer, double spring layer type Ⅰ, double spring layer type Ⅱ and three spring layer, and for seasonal models: spring model, summer model, autumn model and winter model. The analysis results of the SSPs can provide some reference value for acoustic propagation and the sonar systems.
Experimental study of interaction between bubble and free surface
Phase stability, crystal structure and thermoelectric properties of Cu doped AgSbTe2
CuxAg1-xSbTe2 samples with x = 0–0.3 are prepared by a combined process of melt-quenching and spark plasma sintering (SPS). X-ray powder diffraction (XRD) analysis indicates that single phase samples with the NaCl-type structure are obtained for the Cu-doped samples before SPS treatment, whereas a small quantity of Ag2Te impurities coexist with the main cubic phase for the sample without Cu. According to our thermoanalysis and XRD results, the substitution of Cu for Ag can effectively prevent the precipitation of Ag2Te, but this also leads to the presence of a minor amorphous phase in the melt-quenched sample. The amorphous phase crystallizes into Sb7Te metastable phase at about 540 K, which finally transforms into the stable Sb2Te3 compound. After the SPS treatment of the melt-quenched sample, the sample with x=0.1 remains a single phase with the face-centered-cubic crystal structure, while Sb7Te and Sb2Te3 are precipitated as the second phases for the samples with x = 0.2 and 0.3, respectively. The electrical conductivity increases and the Seebeck coefficient decreases with the addition of Cu due to the existence of the second phase in the samples with x = 0.2 and 0.3. Accordingly, thermal conductivities also increase with the addition of Cu, leading to the reduced thermoelectric performance of the x= 0.2 and 0.3 samples. For the sample with x = 0.1, its power factor is comparable to that of the literature reported AgSbTe2 compound. As a result of so-called alloying effect, the phonon scattering effect is enhanced due to the partial replacement of Ag by Cu, leading to the reduced thermal conductivity of the x = 0.1 sample. Therefore, the Cu0.1Ag0.9SbTe2 sample exhibits the promising thermoelectric performance and a dimensionless thermoelectric figure of merit (ZT) value of 1 is achieved at 620 K.
Bi-doped germanium niobate glasses with near-infrared broad-band emission
The Bi2O3 doped glasses with concentrations δ of (0.9-x) GeO2-xNb2O5-0.1BaO (x=0.04, 0.07, 0.1) glasses are prepared by the conventional melting method. The differential thermal analysis (DTA) curves, the absorption spectra, the fluorescence decay curve and the X-ray photoelectron spectra are measured. The difference between glass crystallization onset temperature and transition temperature (Tx-Tg) of the glasses is up to 200℃ from the DTA curve. Absorption peaks at 500, 700, and 1000 nm are observed. The absorption edges show a red-shift with the increase of Nb2O5 content x. The emission band at 1300 nm with the full width at half maximum near 200 nm is observed under the excitation of 808 nm laser. The fluorescence intensity increases with the increase of the concentration δ of Bi2O3. The fluorescence intensity reaches a maximal value when the concentration δ of Bi2O3 is about 0.01. The peaks of binding energy in XPS are located at 159.6 and 164.7 eV respectively. The binding energy peaks are located between those of Bi3+ and Bi5+ by comparing with those of Bi2O3 (Bi3+) and NaBiO3 (Bi5+). According to the XPS results, one may conclude that Bi3+ and Bi5+ ions co-exist in the glass. The near infrared broadband emission may be assigned to Bi5+ ion based on the results of emission spectra and X-ray photoelectron spectra. The broadband intensity is gradually weakened as the Nb2O5 content x increases from 0.04 to 0.1. As GeO2 is substituted by Nb2O5, complex NbGe defects are formed and the lower valence state of Bi ions will be inevitably formed to compensate the extra electric charge from Nb5+, thus resulting in the inhibition of Bi5+ and weakening the fluorescence aforementioned.
A screw dislocation interacting with a wedge-shaped crack in one-dimensional hexagonal quasicrystals
The interaction between a screw dislocation and a semi-infinite wedge-shaped crack in one-dimensional hexagonal quasicrystal is investigated by the conformal transformation method and the perturbation technique. Analytical solutions are obtained for the stress intensity factor of crack, and the force on dislocation. The effects of the dislocation location and the wedge angle on the image force of the dislocation are revealed. At the same time the influence of the dislocation on crack behaviour is also discussed in detail. The corresponding results of the sharp crack can be obtained as a special case of the present solutions (i.e. λ=1/2).
The effects of point-defects on the dynamic scaling of growing surfaces
The dynamic scaling properties of growing surfaces with point-defects are studied by applying the dynamic renormalization-group approach to the noisy Kuramoto-Sivashinsky equation with an additional term of point-defects potential. From the roughness and the dynamic exponents α and z obtained here it follows that point-defects tend to roughen the growing surface and shorten its dynamic relaxation process to a steady-growth state.
The phase diagram of the Gauss model on a decorated square lattice
Using equivalent transformation and spin-rescaling methods, the Gauss model on a decorated square lattice is studied. It is found that the square decorated Gauss lattice could be transformed into a regular square Gauss lattice with nearest-neighbor, and next-nearest-neighbor interactions. By calculating the regular square-lattice Gauss model, the critical temperature of the Gauss model is obtained on a decorated square lattice, and the exact phase diagram of this system can also be obtained.
The first principles and experimental study on Mn-doped LiFePO4
The electronic structures of pure and Mn-doped LiFePO4 are studied using density functional theory (DFT). The results demonstrate that the pure LiFePO4 has a band gap of 0.725 eV, while the 25% Mn doped LiFe0.75Mn0.25PO4 has the smallest band gap (0.469 eV), and the weakest Fe–O and Li–O bond, which indicates that the electronic conductivity and the ionic conductivity of the doped LiFePO4 are improved due to doping. On the other hand, the experimental results also show that the LiFe0.75Mn0.25PO4 has the best electrochemical performance and it delivers a very high capacity of 158 mAh? g-1 and a high energy density of 551 Wh·kg-1.
Free volume evolution of pre-annealed Zr55Al10Ni5Cu30 bulk metallic glass during rolling
Traces of nanocrystals are introduced into Zr55Al10Ni5Cu30 bulk metallic glass through isothermally annealing the glass at 715 K for 30 min. The pre-annealed samples are rolled at different strain rates up to 95% thickness reduction at room temperature. The thermal stability and the free volume of the deformed sample are examined by differential scanning calorimetry. It is found that the thermal stability does not change with deformation degree. At any strain rate, free volume content increases continuously with the increase of deformation degree without saturation. As strain rate increases, however, the free volume content with the same deformation degree first increases and then decreases, which is significantly different from the case of the metallic glass with monolithic amorphous structure under plastic deformation.
Influence of optical-phonon scattering on electron mobility in wurtzite AlGaN/AlN/GaN heterostructures
Adopting a numerical method of solving self-consistently the Schrödinger equation and Poisson equation through taking into account the realistic heterostructure potential, which includes the influences of energy band bending and the finite thickness of barriers, and through considering the built-in electric field induced by spontaneous and piezoelectric polarization, the eigenstates and eigenenergies of electrons in two-dimensional electron gas (2DEG) are obtained for wurtzite AlxGa1-xN/AlN/GaN heterostructures with an inserted AlN layer. Based on the continuous dielectric model and the Loudon's uniaxial crystal model, optical-phonon modes and their ternary mixed crystals effect are discussed using the transfer matrix method. Furthermore, the Lei-Ting balance equation is extended in order to investigate the distribution of 2DEG and its size effect as well as ternary mixed crystals effect on electron mobility, which under the influence of each branch of optical-phonon modes are analyzed at room temperature. The results show that the increases of the thickness of inserted AlN layer and the Al component of AlxGa1-xN in the barrier enhance the built-in electric field in the GaN layer, leading 2DEG to be much closer to the interface of a heterostructure. In addition, it can also be found that the scattering from the interface phonons is stronger than from other optical-phonons, the interface phonons play a dominant role in the total mobility. A higher electron mobility can be obtained by adjusting appropriately the thickness of inserted AlN layer and Al component.
Thermoelectric properties of (AgSbTe2)100-x (GeTe)x fabricated by hot pressing method
Using pure metal Ag, Te, Ge and Sb powders as raw materials, (AgSbTe2)100-x-(GeTe)x (x=80–90) (TAGS) are synthesized by vacuum reaction. X-ray diffraction (XRD) analysis results show that after sintering the alloys each have a rhombohedral structure. TAGS power is sintered by hot pressing method. Their phase compositions, crystal structures and morphologies are characterized by XRD and scanning electron microscope analysis methods. Their electric conductivities are measured by direct current method. Their Seebeck coefficients are measured when a temperature difference (ΔT=1–4℃) is applied along two ends of sample. Through testing the thermoelectric properties of materials, the variations of different performance parameters of the sample are investigated in a temperature range of 30–500℃. The results show that the sample is nano crystals and its thermoelectric properties change as the composition changes. We can see that TAGS-80 has a good thermal performance, with ZTmax=1.8 at 530℃.
The effect of the interdot Coulomb interaction on Kondo resonance in series-coupled double quantum dots
We theoretically investigate the effect of the interdot coulomb interaction on Kondo resonance in series-coupled double quantum dots. The Anderson Hamiltonian of our system is solved by means of the slave-boson mean-field approximation, and the variations of the density of states, the transmission probability, the occupation number and the Kondo temperature with interdot Coulomb interaction are discussed in the Kondo regime, and the densities of states are calculated in the Kondo regime for various interdot Coulomb repulsions with parallel and antiparallel lead-polarization alignments. Our results reveal that the interdot Coulomb interaction between quantum dots greatly influences the physical property of this system, and relevant underlying physics of this problem is discussed.
Measurement of the hole mobility in the blend system by space charge limited current
The measurement of carrier mobility in organic semiconductor material and device is one of important study contents. The hole-only devices based on the different solvent blends of poly (3-hexylthiophene) (P3HT) and [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) as acceptor are fabricated, the structures of the devices are all ITO/PEDOT:PSS/P3HT:PCBM/Au. The hole mobilities in the blend systems with different solvents and various annealing treatments are measured by the space charge limited current method. The results show that the J-V curves of charge transfer in the devices meet Mott-Gurney equation, the hole mobilities in the active layer with different solvents are different, the active layer formed with high boiling point solvent 1, 2-dichlorobenzene possesses higher hole mobility, heat treatment contributes to the improvement of the hole mobility in the devices. The reason of change of hole mobility is analyzed.
Density functional study on the adsorption of C atoms on Ni (111) surface
With the density functional first-principles calculations, we investigate the structures and electronic properties of transition metal nickel and its (111) surface. The adsorption behavior of single C atom on Ni (111) surface and its co-adsorption with the another C atom on Ni (111) surface are studied. The calculations on band structure and density of states show that significant spin polarization exists at the Fermi level of both nickel and its (111) surface. By comparing the adsorption energy, we find that the hollow site of hexagonal close-packed on the second layer of Ni atoms is the most stable position for the first C atom adsorption, and the hollow site of face-centered cubic on the third layer of Ni atoms is the most stable site for the co-adsorption of second C atom. Charge analysis shows that 1.566e charge transfers from each C atom to the adjacent Ni atom, which is similar to the 1.68e charge transfer in the first C atom adsorption case. The calculations on magnetism show that the magnetic moments of the two C atoms in co-adsorption are 0.059μB and 0.060μB, respectively, which are larger than the magnetic moment 0.017μB of single C atom in Ni (111) surface.
Nonlinear Landau-Zener transition of Fermi superfluid gases
By using the analysis of phase, fixed point and tunneling rate between two wells, we study the nonlinear Landau-Zener transition of Fermi superfluid gases in a two-mode system. We find that the interaction between fermi pairs can affect the quantum transition. We also find that when the interaction parameter c is less than the critical value c*, in the adiabatic limit, the quantum adiabatic transition theorem is still satisfied, but when the interaction parameter c is greater than this critical value, the quantum adiabatic transition theorem will not be satisfied. Finally, we obtain the relationship between the tunneling rate and the scan rate by comparing with the linear case.
Distributions of the threshold voltage and the temperature in the channel of amorphous silicon thin film transistors
Based on the double exponential distributions of trap states in the channel of the hydrogenated amorphous silicon thin film transistor, characteristic temperatures of tail state and deep state are distinguished. Besides, series resistances are used to be associated with characteristic lengths of the source and the drain with trap states. By taking advantage of the Poisson equation and Gauss theorem, the expression of the threshold voltage distribution is obtained. The results show that with the increase of the distance between the point and the source, the threshold voltage decreases. Moreover, under the degradation of the self-heating effect, the distribution of the temperature in the channel is non-uniform and its variation in the channel center is the biggest.
The mechanism of negative magnetoresistance in nondegenerate p-type Hg1-xMnxTe (x>0.17) monocrystal
It is important to study the mechanism of negative magnetoresistance (MR) in magnetic semiconductors for the correct understanding of the sp-d interactions between carriers and magnetic ions. In this work, temperature-dependent Hall effect (10–300 K) and magnetic susceptibility (5–300 K) are measured for the study of negative MR and paramagnetic enhancement of nondegenerate p-type Hg1-xMnxTe (x>0.17) monocrystal. As temperature decreases, both negative MR and susceptibility show the same behaviors, each of which contains an exponentially changing temperature function \exp(-K/T). According to the theory of impurity energy level in semimagnetic semiconductor, magnetic field can lead to the spin-splitting of acceptor level and result in reducing the binding energy of acceptors, which is responsible mainly for the negative MR in nondegenerate p-type Hg1-xMnxTe monocrystal.
Study on conducting characteristics of electrical trees in cross-linked polyethylene cable insulation
The conducting characteristics of two typical electrical trees in cross-linked polyethylene (XLPE) cable insulation are studied by a combination of optical microscopy observation, partial discharge measurement and con-focal Raman spectroscopy analysis. Although they are grown under similar conditions, these two trees display very different shapes. One is a typical branch-pine tree grown at 9 kV, and the other is a branch tree grown at 11 kV. The growth and the partial discharge regularities show obvious differences. The disordered graphitic carbon is condensed in the main tree channels of the branch-pine tree. From the relative intensity of the graphitic carbon G band to D band, the graphitic domain is estimated to be about 8 nm in size. The tree channel resistance per unit length is less than 10 Ω· μm-1, which is sufficient to prevent the partial discharge from developing within the tree structure. The branch-pine tree shows the features of the conducting tree. The fluorescence background is observed in the channels of branch tree, which shows the existence of the products of the material degradation, but no disordered graphitic carbon is observed in these tree channels. These tree channels display obvious non-conducting characteristics, which is not sufficient to prevent the continuous effect of the partial discharges. Finally, a single channel growth model is proposed for the conducting and non-conducting trees grown in XLPE cable insulation. Based on the equivalent circuit theory, the growth mechanisms of the two trees with different conducting characteristics in XLPE cable insulation are discussed.
The influence of variable quantity of polarization on the current intensity of the electron emission from La-doped Pb(Zr, Sn, Ti)O3 ferroelectric cathode
Ferroelectric cathodes exhibit huge potentials in high-power microwave tube electron beam source, panel display, and the propeller space navigation, due to their superior properties. The material properties of the ferroelectric cathode have been proved to have a significant influence on electron emission, which is indicated in recent research work. In the course of electron emission, the variation of polarization can be caused by non-shielded surface charge which is induced by high trigger voltage. A certain relationship may be found between polarization variation and current intensity of electron emission. To study the relationship between current intensity of electron emission and polarization variation in ferroelectric cathodes, the samples of lanthanum-doped lead zirconate stannate titanate ferroelectric and antiferroelectric ceramics are prepared by the method of solid state calcinations, and the polarization variations of the material under different voltages are measured in the positive half cycle test of hysteresis loop. The curve of the electron emission current intensity versus the trigger voltage is measured, and then the relationship between electron emission current intensity and polarization variation is investigated. The results show that the electron emission current intensities of the two samples are both directly proportional to the polarization variation.
Top-emitting white organic light-emitting diodes based on a ZnS light outcoupling layer
Top-emitting white organic light-emitting diode (TEWOLED) has potential applications in lighting and full color displays. Microcavity effect in TEWOLED restrains the realization of the white emission with excellent optical and electric performances. In this paper, a ZnS film with a high refractive index used as a light outcoupling layer is introduced into the metal cathode to enhance its transmittivity to a maximal value in the blue light wavelength region. In addition, transfer matrix theory is utilized to optimize the thicknesses of the cathode and the ZnS outcoupling layer and the wide-angle interference is used to design the position of the blue emission layer inside the organic light-emitting diode. Based on the above work, the white light with relatively high luminous efficiency, good color purity, and small CIE coordinate change is acquired. The corresponding luminance and current efficicency are 9213 cd/m2 and 3 cd/A, respectively. The CIE coordinates belong to the white emission and are near the white light equal-energy point. The white emission also shows stable spectra with respect to the observation angle, with a limited CIE coordinate change of (0.02, 0) for a large observation angle change from 0° to 60°.
Design and fabrication of SiO2/Si3N4 dielectric distributed Bragg reflectors for ultraviolet optoelectronic applications
In this paper, we design a SiO2/Si3N4 dielectric distributed Bragg reflector (DDBR) by the transfer-matrix method, which is grown by plasma-enhanced chemical vapor deposition on sapphire (0001). There exists a slight difference between theoretical and experimental results in peak wavelength (～ 10 nm). The peak wavelength is blue shifted with the number of DDBR pairs increasing. The 13-pair DDBR provides a 58 nm wide stop band centered at 333 nm with a maximal reflectivity of higher than 99%, as the refractive index ratio of Si3N4 to SiO2 is relatively high. It is proved by the scanning electron microscope and atomic force microscope measurements that the variations of thickness and roughness of Si3N4 layer with respect to SiO2 layer during growth contribute to the blue shift of peak wavelength. The X-ray reflectivity measurements indicate that the interfacial degradation of the samples has little effect on the maximum reflectivity, and the relatively poor quality of SiO2 compared with Si3N4 may be one of the reasons that cause the difference between the measurements and simulations.
The fabrication and field emission properties of ZnO nanoparticles-doped diamond-like carbon films by electrochemical deposition
The formation of ZnO nanoparticles embedded in diamond-like carbon (DLC) thin film, deposited by electrochemical technique without post-processing, is observed. The effect of ZnO doping on the field emission (FE) property of DLC film is investigated. The chemical composition, the microstructure, and the surface morphologies of the sample are characterized by X-ray photoelectron microscopy, transmission electron microscopy, Raman spectrum, and atomic force microscope (AFM). It is shown that the ZnO nanoparticles are of a wurtzite structure and the content of ZnO increases with Zn source increasing in electrolyte. The ZnO doping enhances both the graphitization and the surface roughness of the DLC film, which is verified by Raman spectrum and AFM. By the ZnO doping, the FE properties of the DLC film are improved. An emission current density of 1 mA/cm2 is obtained at an electric field of 20.7 V/μm for the film with a Zn/(Zn+C) ratio of 10.3at%. The improvement on the FE properties of the ZnO-doped DLC film is analyzed in the context of microstructure and chemical composition.
Preparation and characterization of multilayered titanium/titanium-diamond-like carbon films
The titanium/titanium diamond-like carbon (Ti/Ti-DLC) multi-layered films are deposited by combined electron cyclotron resonance microwave plasma enhanced chemical vapor deposition method and mid-frequency magnetron sputtering method using acetylene as the reactive gas and Ti target with a purity of 99.99%. The structures, compositions and surface morphologies of the samples are characterized by X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectrometer. The mechanical properties of Ti/Ti-DLC multilayer films are investigated by microhardness tester, friction wear test instrument and surface roughmeter. The results show that TiC phase appears in multilayered film. The main growth mode of the film is island mode and there exists columnar crystal structure neither in Ti layer nor Ti-DLC layer. The properties of the multi-layered film, including composite hardness, friction coefficient, surface morphology and surface roughness are affected by the modulation period Λ. It is shown that nano-hardening effect takes place when Λ is small while large particles appear on the surface of the film, leading to a large surface roughness and friction coefficient. The layered structure of the film is not clear when Λ≤ 50 nm.
Preparation and characteristic study of nanometer thickness depleted uranium / Au multilayer
Modeling and experimental results show that the depleted uranium (DU) and Au"cocktail" nanometer multilayer will improve the X-ray conversion efficiency by reducing energy loss to penetration of the X-ray into the hohlraum wall. DU/Au multilayer plane film is deposited by magnetron sputtering through alternately rotating substrate in front of separate DU and Au sources. The geometry parameter, surface topography, atomic concentration and interface structure of DU/Au multilayer are characterized by white light interferometer, scanning electronic microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Au film becomes continuous when its thickness reaches 8 nm. Combining with theoretical modeling results, 30 nm DU and 8 nm Au multilayer is chosen. The periodic thickness of DU/Au is measured to be about 37 nm. Well-defined Du/Au interface is observed by SEM. Diffusion at DU/Au interface is observed by XPS. The atomic concentration ratio of DU, Au, O is 73:26:1. The binding energy of Au 4f of 8 nm thickness Au film shifts toward high-energy tail about by 0.6 eV. Similar phenomena are unfound in 30 nm thickness DU film.
A model for releasing of stored energy and microstructure evolution during recrystallization by phase-field simulation
A format of f(ηik,ηjk ) = Es (ηide )2(1-(ηjre )2) to express cold deformed stored energy is suggested in a phase-field model for simulating recrystallization in alloys. Using AZ31 magnesium alloy as an example, the recrystallization process is simulated by the new model, and the simulation results are in good agreement with experimental measurements. The nucleation process of recrystallization is realized for the first time by the model based on the physical background. The simulation results show that the grain growth of a cold deformed alloy in the annealing process indicates automatically two stages: recrystallization driven by the restored energy and thermal growth driven by boundary energy. A theoretical time spent in finishing recrystallization, obtained by simulation, is found to be 2/3 of that obtained by industrial practice. The mechanism and the experimental results about the influence of cold deformation on subgrain size and stored energy are examined, and the experimental results are introduced into the simulation. The common experimental phenomenon shows that there is a peak at the critical strain on the curve of recrystallized grain size versus cold strain. A theoretical explaination to the mechanism of the peak occurrence is also discussed.
Analytical modeling of coil impedance based on truncated region eigenfunction expansion method in eddy current tube inspection
In order to calculate theoretically the coil impedance, the separation of variables method and the Cheng matrix method are used to establish the analytical model by applying the magnetic insulation condition in eddy current tube detection with encircling probes inside and outside respectively. In the established model, there exists a definite integral related to modified Bessel function. Gaussian integral algorithm is proposed to accurately perform the numerical calculation. Simulations are carried out on the thinning of a copper tube wall thickness using the presented model, traditional Dodd model and finite element model. Their results are in good agreement with each other, demonstrating that the derived analytical model is correct. Compared with the Dodd and finite element models, the improved model has some advantages such as good efficiency, easy adjustment of accuracy and so on.
Terahertz broadband antireflection photonic device with graded refractive indices
High resistivity silicon is a very common optical component in a terahertz system. However, its high relative refractive index of 3.42 causes a large impedance mismatch at the silicon-to-air interface. This severely reduces the available power in a terahertz system which motivates researchers to find a good anti-reflection solution. In the terahertz region, the lack of proper materials for broadband anti-reflection severely hinders such a research development. A photonic grating with graded refractive indices is demonstrated on silicon. Compared wich the case of planar silicon wafer, the transmission is observed to increase from 0.2 THz to over 7.3 THz for a device with 15 μm period, which covers most of the terahertz band. With a striking relative 3 dB bandwidth of 116.3%, the device is polarization-independent and can be used under a wide incidence angle.
Study of the effect of lithography deviation on 4H-SiC floating junction junction barrier Schottky diode
The breakdown voltage of 4H-SiC junction barrier schottky diode with floating junction is larger than that of traditional junction barrier Schottky diode under the condition of the same fixed on-resistance. It is a crucial technology that the alignment of lithography between p+ region of floating junction and main junction. The simulation results obtained using two-dimensional simulator ISE show that the breakdown voltage obviously drops with the deviation of lithography increasing. Although the breakdown characteristics of the dislocation and the alignment structure are similar, the series resistance of the dislocation structure is larger than the latter when the forward voltage is larger than 2 V.
Investigation of spectral regulation in dual- wavelength light-emitting diodes by using the selective p-doped barriers
The electrical and the optical characteristics of dual-wavelength light-emitting diode (LED) with the newly designed selective p-doped barriers are investigated numerically. The simulation results show that the selective p-doped barriers can improve the distribution equilibria of electron and hole concentrations in each quantum well (QW). The radiative recombination rate of QW is enhanced remarkably when specific number of p-doped barriers is adopted, and the electron leakage current is suppressed obviously with this new design. Therefore, the internal quantum efficiency is improved and the trend of efficiency drooping with the increase of current injection is also alleviated. Moreover, the curve peaks of the spectrum become quite uniform when the specific number of vertically-stacked QWs is adopted, and the spectral regulation of the dual-wavelength LED is more effective.
Enlargement of current spin polarization in organic spintronic device
Using the spin diffusion-drift equation and considering the effects of the electric fields and the special carriers in organic semiconductors, the enlargement ratio of current spin polarization in a simple T-shaped organic spintronic device is theoretically studied. It is found that the significant enlargement ratio of the current spin polarization can be acquired by adjusting the electric field and the polaron ratio in organic semiconductor.
Photoelectricity performance research based on the sol-modified thin film electrode of dye-sensitized solar cells
Nanoporous film electrode is a crucial composition of dye-sensitized solar cells, which influences the photoelectric conversion performance. To improve the property of the photoelectrode, different modification methods by using different concentrations of TiO2 sol are investigated. The crystallite size and phase of the nanoporous TiO2 particles and the TiO2 sol after sintering are studied with X-ray diffraction. The microstructure morphologies of the conductive glass and the films are determined by the high resolution transmission electron microscopy and the field emission scanning electron microscopy. The influences on electron lifetime τn and the electron transit time τd are analyzed by intensity-modulated photocurrent spectroscopy and photovoltage spectroscopy from the mechanisms of electron transport and back reaction kinetics. It is found that the back reactions are well suppressed under dark conditions after sol modifications. τn is effectively extended and τd is also shorten correspondingly by any kind of sol treatment. The short-current density and the photoelectric conversion efficiency are increased by 10.9% and 11.9% separately, when 0.10 mol·L-1 sol modification is applied both to the conductive glass and to the nanoporous TiO2 film at the same time.
Analysis of organic photovoltaic devices with MoOx doped 4,4′,4″-tris(N-(3-methylphenyl)-N- phenylamin) triphenylamine as hole transport layer
MoOx doped 4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamin) triphenylamine (m-MTDATA) is used as a hole transport layer to improve the efficiency of CuPc/C60 small molecular organic photovoltaics. A series of devices is fabricated in a high vacuum system. One of the devices with the structure of indum tin oxides (ITO)/m-MTDATA:MoOx(3:1)(30 nm)/CuPc(20 nm)/C60(40 nm)/Bphen (8 nm)/LiF(0.8 nm)/Al(100 nm) shows that the following parameters are achieved: the open circuit voltage Voc = 0.40 V, short-circuit current Jsc=6.59 mA/cm2, fill factor of 0.55, and power conversion efficiency ηp=1.46% under AM1.5 solar illumination. The efficiency of the device is improved by 38% compared with that of the device without hole transport layer ITO/CuPc(20 nm)/C60(40 nm)/Bphen(8 nm)/LiF(0.8 nm)/Al(100 nm). The improvement of the device performance may be attributed to the addition of m-MTDATA:MoOx (3:1) (30 nm) hole transport layer that reduces the contact resistance between the ITO electrode and the organic layer, thus reducing the overall device series resistance and improving the efficiency of the device.
Riemann θ function solutions to modified Korteweg de Vries-sine-Gordon equation
Based on some Riemnan theta function solutions to a elliptical equation, together with its Backlund transformation, infinite sequences Riemann θ function solutions are derived, then regarding this elliptical equation as an auxiliary equation, with the help of computer software (Mathematica), infinite sequences Riemann θ function solutions to the modified Korteweg de Vries sine-Gordon equation are obtained.
Approximate functional variable separation for the porous medium equation with perturbed nonlinear source
Internal layer solution of singularly perturbed optimal control problem
Asymptotic solving method of soliton for El Niño/La Niña-southern oscillation nonlinear disturbed model
A class of El Niño/La Niña-southern oscillation (ENSO) stochastic disturbed model is considered. Firstly, using the special method of undetermined coefficients, the exact solution of the non-disturbed ENSO model is obtained. Then the approximate solutions of stochastic disturbed ENSO model are constructed by using the asymptotic theory and method. And it is illustrated with example that the asymptotic solutions have the better degree of accuracy.
Interpolating reproducing kernel particle method for elastic mechanics
The practical security and performance analysis of the quantum data stream cipher system by the αη protocol
Variable space scale factor spherical coordinates and time-space metric
The time-space metric is a fundamental concept of general relativity, and it is the logical foundation of cosmology and astrophysics. A time-related space scale factor is introduced into a 4-dimensional time-space interval model. The transformations among the flat metric, the Schwarzschild metric and the Robertson-Walker (R-W) metric are obtained in spherical coordinate system. Based on the time-space interval of the time-related scale factor coordinate, the solutions of R-W metric with parameter k=±1 and the non-vacuum metric outside stars are deduced. A new point of view is advanced to comprehend the modern physical non-flat time-space.
The analysis of stochastic resonance of periodic signal with large parameters
Stochastic resonance of linear harmonic oscillator subjected to simple harmonic force with frequency fluctuation
Research of one-dimensional discrete chaotic system constructed by the hybrid circuits of single-electron transistor and metal oxide semiconductor
Identification of a stochastic neural firing rhythm lying in period-adding bifurcation and resembling chaos
To identify non-periodic neural rhythm to be chaos or stochasticity has been an important scientific thesis. A kind of non-periodic spontaneous firing pattern, whose behavior is transition between period-k burst in a string and period-k+1 burst in a string (k=1,2), lying between period-k bursting pattern and period-k+1 bursting pattern, is found in the experimental neural pacemaker. The deterministic structures of the firing are identified by nonlinear prediction and first return map of the interspike intervals (ISIs) series. The co-existence of the period-k bursting and period-k+1 bursting is manifested in the deterministic theoretical neuronal model, Chay model. Non-periodic firing patterns similar to the experimental observation are simulated in the co-existing parameter region, implying that the firing pattern is transition between two kinds of bursts induced by noise. A binary series can be acquired by transforming two kinds of bursts to symbols 0 and 1, respectively. The stochastic dynamics within the transitions between two kinds of bursts are detected by probability analysis on the binary series. It not only shows that the rhythm is stochastic firing with deterministic structures instead of chaos, but also provides the typical examples and effective methods to intensively identify the chaotic and stochastic firing patterns in a real nervous system.
Non-smooth bifurcation analysis of Chen system via impulsive force
Chaotic time series prediction based on wavelet echo state network
Chaos is widespread in nature and human society, so the prediction of chaotic time series is very important. In this paper, we propose a new chaotic time series prediction model– echo state network based on wavelet, which can effectively overcome the ill-posed problem that exists in traditional echo state networks. And it also has a good generalization ability. Three time series are used to test the new model, i.e., Lorenz time series, Lorenz time series with added noise and batch reactor vessel temperature time series. Results suggest that the new proposed method can achieve a higher predictable accuracy, better generalization and more stable prediction results than traditional echo state networks.
Multivariate chaotic time series prediction based on extreme learning machine
For multivariate chaotic time series prediction problem, a prediction based on input variable selection and extreme learning machine is proposed in this paper. The multivariate chaotic time series is reconstructed in phase space, and a mutual information based method is used to select the input variables, which have high statistics information with the output variables. The extreme learning machine is conducted to model the multivariate chaotic time series in the phase space by utilizing its approximation capability. In order to improve the prediction accuracy, a model selection algorithm is conducted for extreme learning machine to choose an expected minimum risk prediction model. Simulation results based on Lorenz, Rössler multivariate chaotic time series and Rössler hyperchaotic time series show the effectiveness of the proposed method.
A chaos synchronization method based on amplitude
Performance analysis of a quantum heat engine working with a particle in a one-dimensional harmonic trap
A zero-watermarking algorithm of stereoscopic image based on hyperchaotic system
In order to protect the copyright of stereoscopic images in the condition of the image quality, a zero-watermarking stereoscopic image algorithm is presented based on hyperchaotic system. In the proposed algorithm, disparity zero-watermark is constructed according to the stability of disparity between low frequency bands of wavelet decomposition of the left and the right views and direct coefficients of discrete cosine transform; in the process of zero-watermark construction, the zero-watermark position mapping according to the features of the sensitivity of hyperchaotic discrete system initial value, ampleness of parameter key space and complexity of dynamic behavior, enhances the security of algorithm. The relationship between security and watermark capacity is also analyzed. Experimental results show that the proposed algorithm is strong robust to noise, filtering, compression, and the shearing of asymmetrical and symmetrical attacks.
Performances of a boron-lined ionization chamber used in neutron/γ-ray mixed field of reactors
Boron-lined ionization chambers (BLICs) have gradually become one of radiation detectors which are used to monitor the neutron/γ-ray mixed field with large flux around reactors in recent years. In this paper a BLIC with high sensitivity is fabricated and the internal structure is detailed. By using a weak current amplifier with an accuracy of fA, the leakage current of the BLIC is less than 1.0 pA when the high voltage is below 700 V; under the irradiation by the Am-Be neutron source, on the I-V curve of the BLIC there appears a current plateau with a length of 500 V and a slope of 3.72×10-4 V-1; when the operating voltage is 400 V, the leakage current of the BLIC is 0.4 pA. Experiments show that neutron signal current measured by the BLIC depends on the relative position of the BLIC with repect to the radiation source; a maximum of 2.0 pA is obtained when the source is 8 cm away from the bottom of the hole in the paraffin moderator. Under the exposure by 137Cs and 90Sr, γ-ray signal current measured by the BLIC is 1.0–2.0 pA, but the current plateau is not obvious in γ-ray field. The neutron sensitivity of the BLIC reaches a level of 1.0×10-15 Acm2s and the γ-ray sensitivity reaches a level of 9.0×10-22 Acm2s·eV-1. The BLIC shows small leakage current, high sensitivity, and good plateau characteristics, which can be used to monitor the neutron/γ-ray mixed field around reactors.
Numerical simulation of X-ray ionization and atmospheric temporal evolutions with high-altitude nuclear explosions
The X-ray ionizations and the atmospheric temporal evolutions with different altitude nuclear explosions are numerically simulated in this paper. It is concluded that the density of electrons generated by X-ray ionization has a peak value at 100 ns after the X-rays have arrived, and the peak density reduced with the increase of distance from the stripped nucleus area. The life time of electrons is long, and increases with the distance from the stripped nucleus area. O+, O2+, N2+ are generated by X-ray ionization. The distance of X-ray ionization in atmosphere is within a few tens of kilometers. The peak density of explosion at 80 km high is larger than at 120 km high in the area close to stripped nucleus area, but the scenario is opposite in the area far from stripped nucleus area.
Density functional study on the geometric property of MnxSny(x=2,3,4; y=18,24,30)
The geometric structures of the MnxSny (x=2,3,4; y=18,24,30) clusters are studied using the density functional theory method. The geometric optimization shows that the favourite structures of MnxSn6x+6 (x=2,3,4) are D3d single-cage structures which encapsulate Mn atoms, i.e. Mn2Sn18, Mn3Sn24 and Mn4Sn30.However the favourite structures of MnxSn6x+12 (x=2,3) are two-cage structures, i.e. MnSn12-MnSn12 and MnSn12-Mn2Sn18.Thus, it is promising to form new one-dimensional nonawires of MnxSny heterostructures by controlling the number of Mn atoms.
Parameterized inversion of frequency sounding data in horizontally stratified transverse isotropic medium
In this paper, we advance a fast iterative inversion algorithm of frequency electromagnetic sounding data to simultaneously reconstruct the horizontal and the vertical conductivities and interface each bed in the horizontally stratified transversely isotropic (TI) medium. First, applying the analytic expression of the electromagnetic dyadic Green's functions in the TI medium, we realize the forward modeling of the frequency sounding via the fast algorithm of Sommerfeld integral. Then using the perturbation principles and Fourier inversion transform, we establish an efficient computation of Fréchet derivatives of the frequency sounding data with respective to all the model parameters. And we use the least square criterion, the normalization and singular value decomposition to iteratively recovery all model parameters. Finally, numerical results validate the inversion algorithms and their antinoise ability.
Numerical simulation on the early dynamics of barium clouds released in the ionosphere
Based on a neutral barium cloud diffusion model, considering the oxidation and ionization loss of barium atoms, the early (t ≤ 100 s) evolution characeristics, morphologies, brightnesses and electronic density distributions of barium clouds released in the ionosphere are discussed in this paper. The numerical simulation results are presented for the early dynamics of barium clouds with different released masses (1, 10 kg), different release altitudes (250, 300 km), and different initial shape factors (1, 10).
Dynamic wavefront correction with a fast liquid-crystal on silicon device of pure phase