Progress of white organic light-emitting device
White organic light-emitting device (OLED) has potential of producing highly efficient saturated white light with the advantages of low-driving voltage, large area available, and flexible display, hence presenting many potential applications in solid state lighting and display industry. At present, the architecture of white OLED device includes mainly single emission layer, multilayer, down-conversion, stacked OLED, etc. which possess their own benefits, and it has attracted much attention respectively. In this paper after introducing the performance standards of white light, we review the development of white OLED in the aspects of architecture and performance. After that, we summarize the approaches to obtaining the high-performance white OLED. Meanwhile, we discuss the challenges to improving white OLED performance. Finally we look forward to the development of white OLED in the future.
Research and development of GaN photocathode
Negative electron affinity GaN photocathode with greatly advanced photoelectricity performance is described. The research of GaN photocathode focuses on the three points, i. e. , quantum yield, electron energy distribution and surface model, in the last decade. The domestic research of GaN photocathode is still in its infancy, the basic theory is not established, and preparation technology is not mature. In this paper we review emission mechanism, material growth, surface cleaning, activation process optimization, varied-doping structure design and stability of GaN photocathode. The latest experimental results confirm that the fabrication technology of GaN photocathode is feasible.
Experimental study on X-band repetitively oversized backward wave oscillator
A new type of high power microwave device is developed based on bitron and backward wave oscillator. The device is composed of two parts: the modulation cavity and the extraction cavity (which is similar to slow wave structure). The modulation cavity acts as electron beam modulator and microwave reflector, which forms a microwave resonator in combination of the extraction cavity. The electron is modulated when it passes through the modulation cavity, and the high power microwave is generated when the modulated beam passes through the extraction cavity. An X-band high power microwave device is designed for a 20 GW accelerator, and the simulation results are frequency 8.25 GHz and output power 5.70 GW. Using superconducting magnet as guiding magnet, a microwave power of 5.20 GW at X-band (frequency (8.25±0.01)GHz) is obtained in single pulse mode. The radiation power is 5.06 GW when the repetition rate is 30 Hz, and the pulse length is 13.8 ns.
Three-dimensional particle-in-cell simulation studies on a new radial three-cavity coaxial virtual cathode oscillator
A new radial three-cavity structure of the coaxial virtual cathode oscillator is proposed and studied numerically in this paper. Using the radial three-cavity structure, the beam-wave conversion efficiency is enhanced by modulating the electric field in the beam-wave interaction area, while the resonator composed of the radial three-cavity configuration and the mesh anode helps restrain mode competition effectively . And then the coaxial extraction structure benefits the energy extraction, and it can also absorb the used electrons entering into the drifting tube. Therefore, this new kind of virtual cathode oscillator can achieve a high output power. With an electron beam of 50 kA at 400 kV, a peak power of about 6 GW is achieved by simulation at 4.5 GHz. The mean power reaches 3.1 GW and the beam-wave conversion efficiency is about 15%.
Influence of longitudinal radio frequency electric field on multipactor effect on a dielectric surface
Based on the multipactor dynamic model and the secondary electron emission yield curves, the multipactor phenomenon of the secondary electron emission subjected to the longitudinal radio frequency (RF) electric field existing on a dielectric surface is simulated using the Monte Carlo method. The susceptibility curve of the electric field on the surface and the temporal evolution image of the multipactor discharge are investigated. The power deposited on the dielectric surface by the multipactor is also obtained in terms of an S-band RF dielectric window. The results show that the longitudinal RF electric field may intensify the single-surface multipactor effect, which is likely to result in dielectric crack and detrimental to RF transmission.
Magnetic metamaterial based on connected split and closed rings
Through connecting split and closed rings together, a three-dimensional magnetic metamaterial is proposed in this paper. When the electric field of the induced electromagnetic wave is perpendicular to the dielectric board, this construction exhibits negative effective permeability. Its magnetic resonant frequency is insensitive to the variation of the width of the metallic wires, which facilitates practical fabrications and applications. Meanwhile this construction is of significance for designing polarization-independent and isotropic magnetic and left-handed metamaterials.
Investigation on focus and transport characteristics of high transmission rate sheet electron beam
The investigation on focus and transport characteristics of sheet electron beam has been a key technique for the development of high-power microwave and millimeter-wave vacuum electronic devices. Compared with the period permanent magnetic system to transport the sheet electron beam, the uniform magnetic focusing system has many advantages, such as easily adjusting and matching the magnet with the beam, focusing the intensity electron beam, no cut off beam voltage restriction, etc. However, the Diocotron instability of the sheet electron beam in the uniform magnetic field can produce the distortion, deformation, vortex and oscillation to destroy the beam transportation. In this paper, the single-particle model and the cold-fluid model theory and calculation are used to indicate that if the electron optics system parameters of the sheet beam are designed more carefully, the magnitude of uniform magnetic field and the filling factor of the beam in transport tunnel are increased appropriately, the Diocotron instability can be reduced, even vanished completely to transport the sheet beam effectively in a long distance. To verify the above conclusion, the electron gun with the ellipse cathode and the electron optics system are designed and optimized with the three-dimensinal simulation software in detail. After the complex assembly and weld process with the small geometry and high precision, the W-band sheet electron beam tube is manufactured and tested. The sheet beam cross section of 10 mm×0.7 mm is achieved experimentally with the one-dimensional compression and formation of electron gun. Also, with a beam voltage of 20—80 kV, and beam current of 0.64—4.60 A,the experimental transmission rate of sheet beam electron tube manufactured is more than 95% with a drift length of 90 mm, which is higher than the periodic cusp magnetic field transport experiment result of 92% obtained recently.
Diffraction characteristic of a misaligned vortex beam through a phase-hologram grating
We study the analytical features of the output beam diffracted from a phase-hologram grating when the incident vortex beam is misaligned with respect to the grating. The analytical representation describing the diffracted beam of the 1st order is derived theoretically. Based on the representation, the central of gravity and the central intensity of the diffracted beam are investigated in the cases of the alignment, lateral displacement, angular tilt and simultaneous lateral misalignment and angular tilt, separately. It is shown that the diffracted beam is described through confluent hypergeometrical function. The misalignment of the incident vortex beam can give rise to the displacement of the beam center of gravity, which is independent of the misalignment direction and azimuth angle. The displacement is more obvious for the lager misalignment. In the case of angular tilt, the direction of beam center of gravity is nearly identical to the misalignment direction, whatever the topological charge of the incident beam and the fork number of the grating are. Besides, if the sum of the topological charge of the incident beam and the fork number of the grating is zero, with radial displacement and deflection angule increasing, the central intensity of the diffracted beam decreases gradually, otherwise, the central intensity is non-zero value any more. That means the misalignment between the phase-hologram grating and the incident vortex beam can influence the measurement of the topological charge of the vortex beam.
Analysis and measurement for passive tag modulationperformance of backscatter link
Optimal conditions for maximizing the effectively received power of reader receiver in passive ultra high frequency radio-frequency identification system are analyzed in this paper. The mismatched impendence affecting modulation index of tag backscatter link is discussed. Expressions of backscattered modulation indexes for calculating normalized effective received power of reader receiver, lower boundary of signal-to-noise ratio for demodulated output signal, and bit error rate are derived. Modulation indexes of backscatter link under different parameters are measured in open indoor environment. The measurement results show that the tag can be detected successfully when the modulation index of backscatter link is in a range from 5% to 10%.
Phase noise detection method in fiber lasers based onphase modulation and demodulation
In coherent combination of active phase control, there have existed three main phase detection techniques until now, they are heterodyne phase detection technique, multi-dithering technique and stochastic parallel gradient descent algorithm. A new phase detection method based on phase modulation and demodulation is proposed according to the principle of heterodyne phase detection and multi-dithering technique. Periodic phase modulation signal is implemented on a reference laser, and the coherent detection is carried on between the reference laser and the signal laser. With some processing of the modulation signal and the coherent detected optoelectronic signal, the phase noise is detected and the noise compensation can be realized. Numerical simulation and experimental studies are conducated. Experimental results show that the phase detection accuracy is higher than 1/50 wavelength and the average phase compensation residual error is less than 1/50 wavelength in the case of a 2 kHz sine wave phase noise with a phase region of
Experiment and simulation of time lens using electro-opticphase modulation and cross phase modulation
Temporal imaging is one of the important research issues of time lens. The theory of temporal imaging is investigated briefly. The experiment using electro-optic phase modulation to perform optical pulses compression is demonstrated. And the simulation and the discussion using electro-optic phase modulation and cross phase modulation to perform temporal imaging system are presented. The experimental results show that the temporal imaging system which consisits of time lens basing electro-optic phase modulation can effectively compress the optical pulses. However, the compression coefficient is restricted by the aperture of the time lens, and the resolution of the temporal imaging system is low. Further more, the simulation results and the analysis results indicate that the temporal imaging system which consists of time lens basing cross phase modulation has a bigger compression coefficient and a higher resolution. However, this temporal imaging system is difficult to realize.
Stereoscopic visualization based on splitting of two-way polarized image beams
A thin metal film is introduced to split two-way polarized image beams, thereby accomplishing a stereoscopic three-dimensional display. Linearly polarized beams emitted by two uniform liquid crystal displays (LCDs) are reflected and transmitted by ultrathin aluminum film separately. Since optical constant of ultrathin metal film depends on film thickness, a piecewise linear function is used to obtain the relationship between the volume fraction of aluminum and the thickness of the film, and then the optical constant can be estimated by the Sheng Model. Following this procedure it is proved that both the reflected and the transmitted beams become elliptically polarized light beams and their principal axes are approximately vertical. Thus two orthogonal polarizers can be used to separate them and then make the observer have a perception of depth in LCD image. In order to keep the quantities of light entering the observer’s two eyes balanced, the thickness of the aluminum film is optimized. Experimental results are in agreement with the theoretical analyses, so the correctness of the method is verified.
Analysis and correction of object wavefront reconstruction errorsin two-step phase-shifting interferometry
The method of calculating and correcting object wave reconstruction errors caused by phase shift errors in two-step phase-shifting interferometry is studied systematically. Based on the principle of random distribution and the amplitude-phase independence of diffractive object wave, the expression of objective wave reconstruction error is introduced and the formula for that in the two-step standard algorithm is deduced. The automatic error correction method is suggested by further analyzing the structures, the characters of those errors caused by phase shift errors, and the objective expression. By the proposed method, the reconstructive amplitude and phase errors can be corrected at the same time through simple operation on the objective complex amplitude reconstructed by the standard two-step method without the additional measurement or the acknowledge of phase shift. The computer simulations are carried out to verify the effectiveness of this method, and the results show that the method is robust and reduces the effect of phase shift error on object wave-front reconstruction by about 2 orders of magnitude. Optical experiments also indicate that this method is effective and efficient.
Statistics property of polarized photon emission driven bya pair of pulses in single quantum dot
We study the properties of the x- and the y-polarized photons of the single quantum dot system driven by a pair of pulses using the generating function approach. Our results show that the quantum interference effects on the line shapes and the Mandels parameter Q of the x- and y-polarized photons and the linear and the nonlinear cross correlations are important.
Wavelet transform of odd- and even-binomial states
In the context of quantum mechanics the classical wavelet transform of a function f with the mother wavelet ψ can be recast into a matrix element of the squeezing-displacing operator U(μ,s) as 〈ψ|U(μ,s) |f〉. The technique of integral within an ordered product of operators is used to support this theory. Based on this, wavelet transforms are done for even- and odd-binomial states, and the corresponding numerical calculation leads to the spectrum of wavelet transform, which is helpful for recognizing the difference between even- and odd-states.
Mapping between multi-photon polarization state and single-photon spatial qudit and its applications
Based on a special controlled-NOT gate, a multi-photon state encoded in polarizations of photons could be transformed into the corresponding single photon qudit encoded in spatial mode. It will make the processing on multi-photon change into the operation on a single-photon, if the inverse transformation from a single photon qudit back to a multi-photon state could be realized also. Associated with linear optical multi-port interferometer for single-photon unitary operation, the positive-operator value measurement and the universal unitary operation for multi-photon state are realized. This approach is more efficient than the previous one with decomposition into two-qubit gates in the circuit-based quantum computation, and it is feasible with using the current experimental technology.
Theoretical analysis of two-stage pumping technology for high power fiber lasers
The problems of direct pumping and two-stage pumping for high power fiber lasers are theoretically analyzed. The simulation results show that 1070 nm laser directly pumped by 975 nm laser provides a theoretical slope efficiency up to 80%. But it is hard to make the highest temperature of the fiber core reduce below 150 ℃ by forced water cooling when pump power is 10 kW. For the two-stage pumping technology, if the conventional cladding pumping technology is used the slope efficiency is less than 20% when a 1070 nm laser is pumped by a 1018 nm laser. With the pump power filling factor increasing from 0.0025 to 0.1, the slope efficiency can be raised from 18.5% to 80.9%, thus the total slope efficiency is raised from 15.5% to 68%. Two-stage pumping is inferior to direct pumping in terms of slope efficiency, but it has the obvious advantage of thermal management. How to raise the pump power filling factor to achieve high slope efficiency and good temperature characteristics at the same time is the key technology of the two-stage pumping.
Enhancing stimulated Raman scattering of benzene high-order Stokes lines by fluorescence of 4-sulfphenyl porphyin in liquid-core optical fiber
Stimulated Raman scattering of benzene is studied in liquid-core fiber. Owing to fluorescence and third-order nonlinear 4-sulfphenyl porphyin, the high-order stimulated Raman scattering, such as sixth-order Stokes line of benzene, can be observed at a relatively low input-laser power. The threshold of high Stokes line is lowered with the addition of the 4-sulfphenyl porphyin when the concentration of solution is within 10-6 and 10-9 mol/L. At the same time, the Stokes line width becomes narrow with Stokes line order increasing. These results are expected to be applied to tunable laser, seeding laser, biological molecular structures and biological molecule used in none biological area.
Interactions of Laguerre-Gaussian solitons instrongly nonlocal nonlinear media
Based on the modified Snyder-Mitchell model, the optical fields that are produced by two collinear Laguerre-Gaussian solitons (LGS) in a strongly nonlocal nonlinear medium are studied. Various novel kinds of solitons on the profiles which depend on the model-index and the relative amplitude of LGS are shown. It is the phase vortices of the LGS that lead to the optical singularities. The many-ring soliton is produced first with the collinear component LGS. The optical field may rotate in propagation, and the angular velocity of the spiral soliton is given.
Influence of nonlocalization degree on the interaction between spatial dark solitons
The interaction between dark solitons in nonlocal self-defocusing media is investigated. Numerical results show that there is a critical condition for interaction between dark solitons in nonlocal self-defocusing medium. Under the critical condition, dark solitons will neither attract nor repell each other because the attractive force and repulsive force between them are identical. Beyound the critical condition, dark solitons may attract or repell each other depending on the nonlocalization degree and distance between them. The value of the critical condition is found.
Mutual-induced fractional Fourier transform in strongly nonlocal nonlinear medium
The effect of mutual-induced fractional Fourier transform (FRFT) between a weak signal beam and a strong pump beam in a strongly nonlocal nonlinear medium is described. The signal beam is an FRFT during propagation and the order of FRFT is dependent on the propagation distance and the power of the pump beam. When the propagation distance is fixed, the order of FRFT of the signal beam is proportional to the square root of the power of the pump beam. Mutual-induced FRFT is another method of light controlling light, and its properties contribute to the development of new type FRFT devices, optical information processing and optical imaging.
Theoretical and experimental studies on ultra-broad-bandwavelength tunableness by optical soliton mechanism
It is crucial but challengeable that the generation of optical exact by synchronized seed pulses both for the main amplifier chain and for the pump-laser chain of an optical parametric chirped pulse amplification system, which are tried to be developed by the soliton mechanism. Detailed numerical simulation of the soliton propagation mechanism are accomplished. So the evolutions of solitons in time-domain and frequency-domain as well as the reciprocity characteristic with other nonlinear effects are clarified. Experiments are carried out, for validating the method of using soliton mechanism to generate ultra-broad band tunable ultra-short laser pulses. Forming, breaking up and self-frequency shift of a soliton are observed. The favorable tunablenesses of the wavelength between the visible and the near-infrared regions are exhibited. All these experimental results are well consistent with the theoretical analyses.
Experimental determination of scattering matrix of fire smoke particles at 532 nm
Based on polarization modulation and lock-in detection, an experimental apparatus is built to determine several important angular dependent scattering matrix elements at 532 nm. The apparatus is tested by water droplets through comparing measurement results with Mie calculations. Measurement results of scattering matrix elements and element ratios between smoke particles produced by smoldering cotton test fire and those produced from flaming n-heptane test fire are presented. We find that results of Mie calculations are able to describe the experimental data of smoldering cotton test fire smoke, which indicates that the particles generated by smoldering cotton test fire are mostly spherical in shape with considering the particle size relative to the wavelength. Using the optimization method, we estimate the refractive index (m=1.49+i0.01) and size distribution (lognormal distribution, σg=2.335 and dg=0.17 μm) of smoldering cotton test fire smoke. Contrarily, the experimental data of flaming n-heptane fire smoke cannot be described by Mie scattering, which is interpreted by the nonspherical, fractal aggregate morphology of the particulates.
Model of quench cooling and experimental analysis of cylindrical infrared chalcogenide glass
The tapping temperature and the cooling rate are the key parameters during the development process of chalcogenide glass. Based on the theory of heat conduction equation, a model for calculating the temperature distribution of cylindrical chalcogenide glass is established using the least square fitting method in this paper. The tapping temperature, the temperature distribution and the cooling rate are simulated by using the model. The simulation results are compared with experimental data. The results show that the glass temperature stays in a non-steady non-uniform distribution, the surface cooling is the fastest, and the temperature decreases exponentially with time when the glass is tapped off from the furnace; the temperature of glass rod from the center to the edge is approximately of parabola distribution; the crystallization is the most difficult when the glass is tapped off at 50—100 ℃ higher than crystallization temperature and a surface heat exchange coefficient of 180 W ·m-2K-1. Under the guidance of the theoretical model the uniform and transparent chalcogenide glass with a diameter of 110 mm and height of 80 mm is obtained. The glass transmission spectrum range is 0.8—17 μm. The 2 mm thick flat sheet has the average transmittance higher than 65% in a 8—12 μm range.
Frequency properties of the defect mode inside a photonic crystal band-gap with zero average refractive index
Left-handed metamaterial has been designed based on transmission line technology. A left-handed and a normal materials are studied alternately to form a one-dimensional photonic crystal with an average refractive index of zero but a special band-gap emerges. The two band-edge frequencies of this gap are insensitive to the incident angle and lattice constant. These characteristics can be used in the miniaturization of filters and high-quality coupling. Studies show that we can regulate the mode frequency by controlling the thickness of the defect layer, which can provide a method for the adjusting frequency in applications. The experimental results are consistent with numerical simulation.
Magnetically tunable magneto-photonic crystals for multifunctional terahertz polarization controller
A multifunctional terahertz polarization controller is designed based on the two-dimensional photonic crystal structure and the ferrite material. The different working devices including a controllable polarizer, a polarization beam splitter and a tunable phase retarder with continuous phase retardations of -π—π at 1 THz are controlled by the shift of photonic band gap with different external magnetic fields. By using the plane wave expansion method and the rigorous coupled wave analysis, we calculate the band gap positions and transmittances of device with the variation of magnetic field. The field distribution and phase are simulated by the finite difference time domain method.
Core-shape transitions in photonic crystal fiber
The mode field and the translational efficiency are studied by the finite difference beam propagation method in an anamorphic photonic crystal fiber. Selective hole collapse is realized in laboratory and anamorphic fibers with circular to rectangular cores and small to large mode fields are made. The loss at wavelength 1550 nm is below 0.05 dB during each translation. The calculated and the experimental results are consistent with each other.
Effect of finite-amplitude acoustic wave nonlinear interaction on farfield directivity of sound source
The acoustic radiation pressure expression of a multi-frequency sound source is obtained on the basis of the Fenlon theory. Then using the solution method of a monochromatic source harmonic wave directivity, farfield directivity of second-order approximate is obtained in the case of the dual-frequency sound source interaction. Subsequently, the effect of two-wave interaction on the farfield of first-order and second-order wave of either wave is studied and discussed when the initial radiation pressures and frequencies are different. The conclusion is that there are some different effects of sound wave interaction on the farfield directivity of a sound source, when the relative initial radiation pressure and frequency between the sound waves is changed.
Dynamical behaviors of hydrodynamic cavitation bubble under ultrasound field
Considering liquid viscosity, surface tension, liquid compressibility and turbulence, the dynamical behaviors of cavitation bubble in venturi cavitation reactor are numerically investigated with using acoustic field regarding water as a work medium. The effects of acoustic frequency, acoustic pressure and ratio of throat to pipe diameter on cavitation bubble dynamics, bubble temperature and pressure pulse by rapid collapse of cavitation bubble are analysed. The results show that bubble motion of hydrodynamic cavitation modulated by ultrasound, becomes the high energy stable cavitation. It is favorable for enhancing the cavitation effect.
Symplectic symmetry feature of thermoacoustic network
Symplectic mathematics is introduced into the thermoacoustic network model. The transferring matrix of thermoacoustic system is analyzed, and the transferring matrix of working gas in isothermal fluid pipe of thermoacoustic system is a symplectic matrix. The transferring matrix of working gas in regenerator of thermoacoustic system is not a symplectic matrix, but it can be converted into a symplectic matrix by variable transformation. With variable transformation, the whole transferring matrix of thermoacoustic system can be represented by a symplectic matrix. The form of symplectic matrix is conducible to analyzing and calculating the thermoacoutic network model.
A type of new conserved quantity of Mei symmetry for Nielsen equations
A type of new conserved quantity of Mei symmetry of Nielsen equations for a holonomic system is studied. Under the infinitesimal transformation of groups, new structural equation and new conserved quantity of Mei symmetry of Nielsen equations for a holonomic system are obtained from the definition and the criterion of Mei symmetry of Nielsen equations. Finally, an example is given to illustrate the application of the results.
A two-lane cellular automaton traffic flow model with the influence of driving psychology
A two-lane cellular automaton model is developed to analyze the urban traffic flow with considering the influence of driving psychology. In order to show the different psychological characters of drivers when changing lane and braking, lane-changing choice probability and safety parameter are introduced. By computer simulation, the relationships among speed, density and traffic volume are given to show the influence of driving psychology on the traffic flow. The simulation results indicate that the lane-changing choice probability has little effect on the average speed, but it makes the variance of speed larger. And the safety parameter can increase the average speed and the traffic volume.
The analysis of effects and theories for electromagnetic hydrodynamics propulsion by surface
The electromagnetic hydrodynamics(EMHD) propulsion by surface is performed through the reaction of electromagnetic body force, which is induced in conductive flow fluid (such as seawater, plasma and so on) around the propulsion unit. Based on the basic governing equations of electromagnetic field and hydrodynamics, by numerical simulations obtained by the finite volume method, the characteristics of flow field structures near the navigating and the strength variation of propulsion force are investigated at varying positions (the angle of attack). The results show that surface electromagnetic body force can modify the structure and the input energy of flow boundary layer, which enables the navigation to obtain the thrust. With the increase of interaction parameter the effect of viscous resistance and pressure drag to navigating decrease and the nonlinear relationship between propulsion coefficient and interaction parameter tends to be linear gradually. The strength of propulsion force depends mainly on the electromagnetic body force. The lift force can be improved effectively through the EMHD propulsion by surface at an angle of attack for navigating. The navigating surface can be designed as working space of propulsion units, which is of certain significance for optimizing the whole struction and improving the efficiency.
Direct method of determining the lattice parameters of a phase from X-ray diffraction pattern of multi-phase
A new method of determining lattice parameters by peak fitting of X-ray diffraction pattern, without involving structure parameters, is introduced. The method can be applied to a single phase and one phase in multi-phase diffraction patterns. It can avoid getting different fitting results caused by using different extrapolation functions, and can get a more accurate result in a short time. The application program of the method has been used in the practical work. For improving the fitting accuracy, the program can also adjust off-axis deviation of the sample surface and the goniometric mechanical zero.
Neutron diffraction study of aging process effect on phase structure of single crystal superalloy
The neutron diffraction results obtained by oscillating and fixing φ during data collection show that the high ageing temperature is effective to eliminate dendrite crystals and the microstrain exists mainly in the γ' phase. Based on the microstructure obtained by neutron diffraction and scanning electron microscope, the influence of ageing temperature and time on γ' phase are evaluated. The unique misorientations among γ' phase grains are observed from superlattice measurements. According to the neutron diffractions of different crystal planes, the crystal symmetry is slightly changed from cubic to quartet (a < c) due mainly to the γ matrix phase and the experimental results also prove the strain deviation in difference orientations, thus providing the basis for the existence of driving force for the raft model. The calculation based on the superlattice diffraction shows that in the interfaces between the γ and γ' phases exists a complex distortion: the mismatch varies from -0.1% to -0.3% and the mismatch value can be reduced by high temperature during the first ageing and long time during the second ageing.
All-organic two-dimensional photonic crystal laser based on holographic polymer dispersed liquid crystals
In this paper, we report a kind of dye-doped two-dimensional photonic crystal based on holographic polymer dispersed liquid crystals (HPDLC) with a lattice constant of 582nm, which is prepared conveniently with a single step holographic exposure. Under the excitation of a frequency-doubled Nd:yttrium-aluminum-garnet laser operating at a wavelength of 532nm, optically pumped lasing with narrow bandwidth and low threshold is observed from a 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye-doped two-dimensional photonic crystal. The results show that the emitted lasing peak is centered at about 603nm with a full width at half maximum of only 0.4nm, and the threshold energy is about 22.7 μJ, which is evidently lower than the reported previously. The laser bandwidth decreases by a factor of three from 1.4nm to 0.4nm compared with that of the dye-doped HPDLC transmission grating. This result exhibits a bright prospect in application of tunable photonic crystal laser.
Effects of thermal evaporation and electron beam evaporation on two-dimensional patterned Ag nanostructure during nanosphere lithography
In the process of fabricating two-dimensional Ag nano-arrays via nanosphere lithography, different deposition methods present different lattice point shapes of Ag nanostructure. Nano-triangles are produced by thermal evaporation whereas nano-rings are obtained by electron beam evaporation although they are both of hexagonal lattice. It is indicated that the sizes, the surface nanocurvature, the thermal and the kinetic energies of the particles deposited are key factors controlling the formation of the shape of Ag lattice point.
Long-range Finnis-Sinclair potential for Zn-Mg alloy
A set of optimal long-range Finnis-Sinclair (F-S) potential parameters of single Mg are achieved by fitting the lattice energy, lattice constants, and elastic constants to experimental results. With the same method, the set of the F-S potential parameters of single Zn are obtained through the introduction of modifying factor to the repulsive term. Finally, the lattice energy and lattice constants of Mg21 Zn25, MgZn2 and Mg2Zn11 alloys are further fitted to achieve the F-S potential parameters of Zn-Mg based on the previous F-S potential parameters of Mg-Mg and Zn-Zn. After that, a series of molecular dynamics simulations of single Mg, Zn, and Mg21 Zn25, MgZn2, Mg2Zn11 alloys is performed at 300 K with the achieved F-S potential parameters, thereby proving the F-S potential parameters to be appropriate for the description of Zn-Mg alloys. The long-range F-S potential parameters of Zn and Zn, Mg and Mg, Zn and Mg are obtained.
Microstructures in polycrystalline pure copper induced by high-current pulsed electron beam——deformation structures
In order to investigate the superfast deformation mechanism of metal, the high-current pulsed electron beam (HCPEB) technique is employed to irradiate the polycrystalline pure copper. The microstructure of the irradiated sublayer is investigated by using transmission electron microscopy. It is suggested that the stress with very high value and strain rate is introduced within the sublayer after HCPEB irradiation. The dislocation cell and the tangle dislocation formed by cross slip are the dominant defects after one-pulse HCPEB irradiation, whereas, dense dislocation walls and twins are the central microstructures after five- and ten-pulse irradiation. The diffusion and the climb of the atomic plane can cause the formation of the steps at the grain boundary and (or) the twin boundary. Based on the structure characteristics of the irradiated surface, the possible deformation mechanism induced by HCPEB irradiation is discussed.
Influence of interface traps of p-type metal-oxide-semiconductor field effect transistor on single event charge sharing collection
Due to negative bias temperature instability and hot carrier injection, p-type metal-oxide-semiconductor field effect transistor (MOSFET) will degrade with time, and the accumulation of interface traps is one major reason for the degradation. In this paper, the influence of the accumulation of pMOSFET interface traps on single event charge sharing collection between two adjacent pMOSFET is studied based on three-dimensional numerical simulations on a 130 nm bulk silicon complementary metal-oxide-semiconductor process, the results show that with the accumulated interface traps increasing, the charge sharing collection reducs for both the two pMOSFETs. The influence of the accumulation of pMOSFET interface traps on single event charge sharing induced multiple transient pulses between two adjacent inverters is also studied, the results show that the multiple transient pulses induced by the two pMOSFET charge sharings will be compressed, while multiple transient pulses induced by the two nMOSFET charge sharing will be broadened.
Research on the conductivity of KAg4 I5-AgI composite
KAg4I5(10%AgI) composite is prepared by the solid-state reaction method in the dark and dry conditions, and its structure, morphology, ion conductivity properties, and phase transition temperature are studied by X-ray diffraction, scanning electron microscope, impedance spectroscopy, differential scanning calorimetry and other analytical tools. The results show that when the two phases (AgI and KAg4I5 phases) in the composite are both fast ionic conductor phases, ionic conductivity of composite is higher than that of the single phase, and the heating and cooling of the conductivity curves form a hysteresis loop.During heating and cooling, AgI phase transition temperature lags 5 and 10 ℃ respectively.We use the interaction interface, the interface stress phase and Gouy-Chapman model to analyze the mechanism for the improved conductivity of this composite and phase transition temperature change when the two phases are both the fast ionic conductive.
First principles study of H2 molecule adsorption on Li3 N(110) surfaces
The adsorption of H2 on a Li3N(110) crystal surface is studied by first principles. Preferred adsorption sites, adsorption energy, dissociation energy and electronic structure of the H2/Li3N(110) systems are calculated separately. It is found that H2 is adsorbed on the N bridge site more favorably than on the other sites, while two —NH radicles are formed on the Li3N(110) crystal surface. The calculated adsorption energy on the N bridge site is 1.909 eV, belonging to a strong chemical adsorption. The interaction between H2 and Li3N(110) surface is due mainly to the overlapping among H 1s, N 2s and N 2p states, through which covalent bonds are formed between N and H atoms. An activation barrier of 1.63 eV is found for the dissociation of H2 molecule in N bridge configuration, which indicates that the dissociative adsorption of H2 on Li3N(110) surface is favorable under the certain heat activation condition; —NH2 radicle is formed after the optimization of H2 adsorbed on the N top site. The adsorption energy on the N top site is negative. In other words, this adsorption is unstable. So it is concluded that it is not easy to produce the LiNH2 between Li3N(110) face and H2 directly.
Microstructure and mechanical properties of Ti-B-C-N nanocomposite coatings
Ti-B-C-N nanocomposite coatings with different C quantities are deposited on Si(100) and high speed steel (W18Cr4V) substrates by the closed-field unbalanced reactive magnetron sputtering in the mixture of argon, nitrogen and acetylene gases. The microstructures of Ti-B-C-N nanocomposite coatings are characterized by X-ray diffraction and high-resolution transmission electron microscopy; while the nanohardness and elastic modulus values are measured by the nano-indention method. The results indicate that in the studied composition range, the deposited Ti-B-C-N nanocomposite coatings are found still only in the TiN base nanocrystalline. When the C2H2 flux is small, adding C can promote crystallization of Ti-B-C-N nanocomposite coatings, and the grain can be increased to improve the mechanical properties, when the grain size of about 6 nm (C2H2 flux rate 2 cm3/min), hardness, elastic modulus and fracture toughness of Ti-B-C-N nanocomposite coatings achieve the maximum, respectively, 35.7 GPa, 363.1 GPa and 2.46 MPa ·m1/2; the further increase of the C content of Ti-B-C-N nanocomposite coating can reduce mechanical properties of coating dramatically.
Structure and mechanical property of glow discharge polymer
Different glow discharge polymer (GDP) thin-films are prepared at various working pressures and flux ratios of trans-2-butune (T2B) to H2 by using low-pressure plasma enhanced chemical vapor deposition technology. Hydrogen atomic content and network structure of GDP thin-film are characterized by element analysis and Fourier transform infrared spectrum. The hardness and modulus of GDP coating are measured by nanoindentation. It is found that when working pressure and flux ratio between T2B and H2 gradually decrease, hydrogen content and sp3 CH3 groups decrease, sp2 CH2 and sp3 CH1,2 groups increase and hardness H and Young’s modulus E of GDP coating and the cross-linking degree of carbon network inerease.
Calculation of valence band structure of uniaxial 〈111〉 stressed silicon
The valence band structure of uniaxial 〈111〉 stressed silicon is calculated in the frame of k·p perturbation method and compared with that of unstressed silicon. The valence band energy level shifting, splitting, and variation of the effective mass in the vicinity of the Γ point are presented for different uniaxail 〈111〉 stresses. The effective masses for the heavy and light hole bands in unstressed, our calculation results are in good agreement with the obtained published results of bulk silicon. The study extends the selective range of optimum stresses and crystal direction configuration of conduction channels for uniaxial stressed silicon devices. The obtained results of splitting energy and effective mass may serve as the reference for the calculation of other physical parameters of uniaxial 〈111〉 stressed silicon.
Helicity effects on Rh adsorption behavior inside and outside the single-wall carbon nanotubes
The curvature and the helicity of single-wall carbon nanotube (SWCNT) are the important factors which influence the adsorption behaviors of metal atoms inside and outside carbon tubes. However, it is difficult to investigate the separate effects of SWCNT helicity on the adsorption behaviors of metal atoms. In the present work, the armchair (6, 6), zigzag (10, 0), and chiral (8, 4) tubes with similar curvature are selected, then the Rh adsorption behaviors inside and outside the tubes are systematically investigated using the density functional theroy. Due to the different SWCNT helicities, the stable configurations of Rh atoms on tubes are different. The neighbor carbon atoms interacting with Rh atoms vary with tube helicity, therefore, the Rh adsorption energies for a similar configuration are also different. It indicates that the outer charge density of SWCNT is higher than the inner one. Different helicities lead to different charge density variations along the radial direction. Charge density difference shows that the orbital orientations of Rh adatom and the electrons obtained and lost are slightly different due to the different helicities. The bandstructure indicates that the doping band appears near the Fermi energy level. The (6, 6) tube with Rh adatom still exhibits metallicity. When Rh atoms are adsorbed inside the (10, 0) tube, the nanotube transforms from the semiconducting into the metallic one. However, the band gap reduces when Rh atoms adsorbed outside the tube. After the Rh adsorption, the (8, 4) tube band gap reduces.
Effects of Mn and N codoping on microstructure and performance of anatase TiO2
The effects of Mn and N codoping on the crystal structure, defect formation energy, electronic structure, optical property and redox ability of anatase TiO2 are investigated by first-principles calculations of plane-wave ultrasoft pseudopotential. The calculation results show that the octahedral dipole moment of anatase TiO2 increases due to its lattice distortion after Mn, N codoping, which is favorable for effective separation of photogenerated electron-hole pairs. Some impurity bands appear in the band gap, which leads to the red-shift of optical absorption edge and to the increase in coefficient of light absorption, thereby facilitating the enhancement of the photocatalytic efficiency. If the impurity band is not taken into account, the band edge redox potential of codoped TiO2 is only slightly changed compared with that of pure TiO2 . All of these results can explain the better photocatalytic performances of Mn, N codoped anatase TiO2 under visible-light irradiation.
Lattice dynamical, dielectric and thermodynamic properties of LiNH2 from first principles
The lattice dynamical, dielectric properties and thermodynamic properties of LiNH2 are investigated by first principles calculations. Based on the density functional perturbation theory within the framework of linear response theory, the phonon dispersion curves and the phonon density of phonon states throughout the Brillouin zone are obtained. The calculated frequencies of the Raman active and infrared active modes are compared with previous experimental and theoretical results, and Born effective charge tensor as well as electronic dielectric permittivity tensor is presented. We find that the Born effective charge tensor of LiNH2 has quite small anisotropy. These calculated results are in good agreement with available experimental and theoretical values. Furthermore, the thermodynamic functions are predicted using the phonon density of states.
First principles study of structural, electronic and elastic properties of Mg2 Si polymorphs
The structural and the elastic properties of the Mg2Si polymorphs are calculated. The calculations are performed by using the plane-wave pseudo-potential method within the framework of first principles. The anti-fluorite structure, the anti-cotunnite structure and the Ni2In-type structure of Mg2Si can retain their mechanical stability in the pressure intervals 0—7 GPa,7.5—20.2 GPa and 21.9—40 GPa, separately. The relationships between pressure and the elastic moduli (elastic constant, bulk modulus, shear modulus, Young’s modulus, Poisson ratio and anisotropy factor) are discussed. The electron density distribution, the density of states, the bond length and the Mulliken population of these polymorphs are systemically investigated. Our results show that the anti-fluorite Mg2Si is a semiconductor and the other two polymorphs are metallic materials. The interaction between Mg 2p, 3s and Si 3p plays a dominant role in the stability of the Mg2Si polymorphs. The strongest interactions in the anti-fluorite Mg2Si and the Ni2In-type Mg2Si are Mg-Mg and Mg-Si interactions, respectively. Our results are concordant with the experimental data and the previous results.
Investigation on the dynamic conductance of mesoscopic system based on the self-consistent transport theory
According to the self-consistent electronic dynamic transport theory of mesoscopic system, we present the dynamic conductance of mesoscopic structure. As an application of this theory, we employ a coherent mesoscopic parallel-plate capacitor model in the present study. The results show that the dynamic conductance of system depends on the frequency of external field and Fermi energy of system, and is a complex with a finite imaginary part. For a smaller frequency, the conductance shows a similar feature to dc case, but with the increase of the frequency of external fields, substantial deviations between dc case and ac case are observed, the dynamic conductance of system presents a peak structure with Fermi energy varying. For a given Fermi energy, the dynamic conductance is oscillatory with frequency varying, moreover some negative imaginary parts of conductance are observed. The negative imaginary part implies the capacitive behavior, and positive imaginary part refers to the inductive behavior.
Transport characteristic of photoelectrons in uniform-doping GaAs photocathode
The transport of photoelectrons in a uniform-doping transmission-mode GaAs photocathode is calculated by establishing the models of atomic configuration and ionized impurity scattering. And the influence of the doping concentration of photocathode, the photocathode thickness, the electron diffusion length on the diffused circle and the ratio of the number of photoelectrons reaching the emit-surface to the number of exited photoelectrons at the back-interface of GaAs photocathode are analyzed. The calculated results show that the limiting linear resolution is 769 mm-1 with the cathode thickness being 2 μm, the electron diffusion length 3.6 μm and the uniform-doping concentration 1×1019 cm-3. The research on the transport of photoelectrons is worthwhile for preparing the high-performance GaAs cathode and improving the resolution of intensifier image.
Synthesis and electrical properties of dual doped CaMnO3 based ceramics
Different Nb doped Ca0.9Yb0.1Mn1-xNbxO3 ceramics are successfully synthesized by the conventional solid state reaction technique. The crystal structures are of orthorhombic phase, belonging to the Pnma space group. The lattice constant and the volume increase with the increase of Nb content. Relatively high density is around 97%. Scanning electron microscope (SEM) images show that samples are well crystallized. The electrical resistivity and the Seebeck coefficient are measured in a temperature range between 300 and 1100 K. At low temperatures, the electrical resistivity shows a semiconductive-like behavior. At high temperatures, the electrical resistivity exhibits a typical metallic conductive behavior. The semiconductor-metal transition temperature shifts toward a higher temperature with the increase of Nb content. The electrical resistivity increases with Nb dopant, except that the electrical resistivity for x=0.03 is slight lower than that fox x=0.00 sample at high temperature range. This conductivity behavior can be understood as the fact that though Nb doping can introduce more carriers, it also distorts the MnO6 octahedra, and causes the carrier localization. The values of Seebeck coefficient are all negative, indicative of an n-type electrical conduction. The absolute value of Seebeck coefficient increases with temperature increasing, but decreases with the increase of Nb content. The highest power factor is obtained to be 297 μW/K2m at 497 K in the x=0.00 sample, and the power factor of this sample is less independent of temperature in the whole measured temperature range.
Influence of niobium doping on crystal structure and thermoelectric property of reduced titanium dioxide ceramics
Titanium oxide ceramics doped with niobium is synthesized in reduced atmosphere at 1200 ℃ by conventional solid-state reaction technique. From their crystal structures determined by the powder X-ray diffraction(XRD), the samples have multiple-phase with low Nb concentration, but they have single tetragonal rutile phase when Nb content is larger than 0.02. The electrical conductivities, the Seebeck coefficients and the thermal conductivities of the samples with single phase are measured at a temperature range between room temperature and 900 K. The electrical conductivity and the Seebeck coefficient show non-metallic behaviors. According to the fitting, it is found that the samples show thermal-activation mechanism at low temperatures and small-polaron hopping conduction mechanism at high temperatures. Moreover, the analyses of XRD, electrical conductivity and Seebeck coefficient show that the concentration of oxygen vacancy decreases with Nb content increasing. Thermal conductivity decreases with temperature increasing, dominating by lattice thermal conductivity. In the measurement region, the figure of merit (ZT) reaches a highest value of 0.19 at 873 K in the Ti0.98Nb0.02O2-δ sample.
Preparation and electrical transport properties of Fe doped Ca1-xFexMnO3(x=0—0.12) oxide
The Fe doped Ca1-xFexMnO3(x=0—0.12) powder and bulk samples are fabricated by citric acid sol-gel and ceramic preparation process, the samples are analzed by X-ray diffraction pattern and electrical constant measurement. The results show that all samples are of single phase, the lattice constants are gradually lowered by Fe doping for Ca site, and the crystalline grain growth is restrained. All the bulk samples have semiconductor transporting characteristics in the whole temperature range of measurement. The transportation mechanism is not changed. The energy for polarons to hop is increased for doped samples and thus the electrical resistivity is increased by increasing Fe doping concentration.
Relationship between light efficiency and juction temperature of high power AlGaInP light-emitting diode
One of the main problems of high power AlGaInP light-emitting diode (LED) is the heat generated seriously at large working current, which is caused by the weak current spreading, the photon blocking and absorbing of p-type or n-type electrode, and the critical reflection at the interface between the device and air. The heat inside can lead to the restriction on light output, and gives rise to low light efficiency and the low luminous intensity. In this paper, we introduce a new LED structure which is composed of compound current spreading layers and compound distribute Bragg reflector (DBR) layers. For the new structure LED, the injected current spreads adequately and the reflectivity is improved by the compound DBR layers. The testing results show that the performance of new structure LED is much better than that of the conventional LED, and that at a working current of 350 mA, the output powers of the two kinds of LEDs (which are unpackaged) are 17 and 49.48 mW respectively. At the same time, the heat testing results show the relationship between LED light efficiency and juction temperature, and the consistence between the juction temperature ratio and the ratio of light efficiency for the two kinds LEDs, which implies that LED light efficiency can be improved by reducing heat generated inside and reducing the juction temperature.
Surface-plasmon-mediated emission enhancement from Ag-capped ZnO thin films
Ag/ZnO bilayer thin films are fabricated on Si substrates via two-step approach of "ZnO sputtering + Ag evaporation". The enhancement of the near band edge (NBE) emission of the ZnO film is realized through coupling between the surface plasmon resonating energy at Ag/ZnO interface and the photonic energy of ZnO NBE emission. The dependence of the emission enhancement ratio η of ZnO on the thickness and the growth temperature T of Ag cap-layers are investigated. By evaporating Ag(8 nm) cap-layer onto ZnO(100 nm) film at high substrate temperatures (T≥300 ℃), the η value reaches about 18,i.e., η≈18, which is more than twice that of Ag(8 nm)/ZnO(100 nm) bilayer films grown at low temperatures (T≤200 ℃). It is found that the realization of the larger η can be ascribed to the bigger surface roughness of Ag/ZnO bilayer samples prepared under higher growth temperatures.
Effect of palladium adsorption on the electrical transport of semiconducting carbon nanotubes
Properties of MgB2 ultra-thin films grown by hybrid physical-chemical vapor deposition
We fabricate MgB2 ultra-thin films via hybrid physical-chemical vapor deposition technique. Under the same background pressure, the same H2 flow rate, by changing B2H6 flow rate and deposition time, we fabricate a series of ultra-thin films with thickness ranging from 5 nm to 80 nm. These films grow on SiC substrate, and are all c-axis epitaxial. We study the Volmer-Weber mode in the film formation. As the thickness increases, critical transition temperature Tc(0) also increases and the residual resistivity decreases. Especially, a very high Tc(0) ≈ 32.8 K for the 7.5 nm film, and Tc(0) ≈ 36.5 K, low residual resistivity ρ(42 K)≈ 17.7 μΩcm, and extremely high critical current density Jc (0 T,4 K) ≈ 107 A/cm2, upper critical field Hc2(0) for 10 nm film are achieved. Moreover, by optimizing the H2 flow rate, we obtain relatively smooth surface of the 10 nm epitaxial film, with a root-mean-square roughness of 0.731 nm, which makes them well qualified for device applications.
Preparation and electric field driven magnetoelectric effect for multiferroic La2/3Sr1/3MnO3/BaTiO3 composite films
Using pulsed laser deposition, multiferroic La2/3Sr1/3MnO3(LSMO)/BaTiO3(BTO) composite films are deposited on LaAlO3 (LAO)(001) substrate. X-ray diffraction results show that LSMO and BTO films exhibit only (001) orientation. Film smoothness is verified by their low root-mean-square surface roughness values as 1.4 nm from atomic force microscope study. The magnetic and the electric properties of these composite films are investigated. Furthermore, the variations of resistivity and metal-insulator transition temperature TMI of LSMO, induced by the external electric field, are studied. The resisitivity is reduced while the TMI is enhanced for hole accumulation state which is induced by negative electric field across BTO layer. In contrast, the resistivity is enhanced while the TMI is reduced for hole depletion state, which shows coupling between magnetic and electric order parameters, i.e., there is a magnetoelectric effect induced by electric field.
Local lattice structure and spin singlet contribution to zero-field splitting of ZnS:Cr2+
Using the unified ligand-field-coupling scheme, the 210×210 complete energy matrices including all the spin states for d4 configuration transition metal ions are constructed within a strong field representation. By diagonalizing the complete energy matrices, the local lattice structure and the Jahn-Teller energy of Cr2+ ions doped into ZnS are investigated. It is found that the theoretical results are in good agreement with the experimental data. Moreover, the contribution of the spin singlet to the zero-field splitting (ZFS) parameter of Cr2+ ions doped into ZnS is also investigated. The results indicate that the spin singlet contribution to ZFS parameter D is negligible, but the contribution to ZFS parameters a and F may not be neglected.
Design of a wide-band metamaterial absorber based on loaded magnetic resonators
A wide-band, polarization-insensitive and wide-angle metamaterial absorber based on loaded magnetic resonator is proposed. A single unit cell of the absorber is comprised of a magnetic resonator loaded with lumped elements, a substrate and a back metal board. Simulated absorbances of the one-dimensional-array absorber under loading and unloading conditions indicate that compared with under the unloading condition, the one-dimensional absorber under the loading condition can realize a wide-band absorption. Simulated absorbances of the one-dimensional-array absorber with lossy and loss-free substrates indicate that the power loss in the absorber results from lumped resistances in magnetic resonators, and is insensitive to the loss of the substrate. Simulated absorbances of the one-dimensional-array absorber with different lumped resistances and capacitances indicate that there exist optimal values for lumped resistances and capacitances, where the absorbance is highest and the bandwidth is widest. Simulated absorbances of the two-dimensional-array absorber under different polarization angles and different incident angles indicate that the absorber is polarization-insensitive and angle-wide.
Design of a wide-band metamaterial absorber based on resistance films
A wide-band, polarization-insensitive and wide-angle metamaterial absorber is presented, which is based on resistance films. A unit cell of the absorber consists of a hexagonal resistance film, a substrate and a metal backboard. Simulated reflectances and absorbances indicate that this absorber has a wide-band strong absorption for the incedent wave from 7.0 GHz to 27.5 GHz, indicating that electrocircuit resonances are more suited to realize a wide-band strong absorption than electromagnetic resonances. Simulated absorbances under different polarization angles and different incident angles show that this absorber is polarization-insensitive and angle-wide. Simulated influence of substrate and resistance film on the absorbance of the absorber indicates that there exist optimal values for the capacitance between the resistance film and the metal backboard and for the resistance of the resistance film, where electrocircuit resonances are strongest and the absorption band is widest.
Femtosecond photoinduced magnetization of terbium gallium garnet crystal
The photoinduced magnetization in magneto-optical crystal terbium gallium garnet (TGG) is investigated by time-resolved pump-probe spectroscopy. When the pump pulse is elliptically polarized, the rotation signal and the ellipticity signal of the probe pulse are observed at zero time delay, resulting from the optical Kerr effect and the inverse Faraday effect. The direction of the effective magnetic field is dominated by the helicity of the pump pulse, so the rotation signal and the ellipticity signal of the probe pulse can be triggered selectively by modifying the helicity of the pump pulse. The full widths at half maximum of the rotation signal and the ellipticity signal both can be as fast as about 500 fs, which indicates that TGG crystal is expected to be a candidate material of ultrafast all-optical magnetic switching.
Excitation spectrum intensity adjustment of SrWO4:Eu3+ red phosphors for light-emitting diode
The SrWO4:Eu3+ red phosphors with different Eu3+ doping concentrations and different sintering temperatures are prepared by the co-precipitation method. The powders as-prepared exhibit sharply red characteristic emissions of Eu3+ ions at room temperature. The near-ultraviolet and blue light absorption intensities are controlled by adjusting sintering temperature and doping concentration and so the red emission intensities under the 395 or 465 nm excitation can be adjusted. Our results show that the SrWO4:Eu3+ red phosphors can be effectively excited by the ultraviolet light, the near-ultraviolet (395 nm) light and 465 nm blue light. Therefore the SrWO4:Eu3+ red phosphors may have a potential application to white light-emitting diodes.
Effect of spin-coating process on the performance of passive-matrix organic light-emitting display
Effects of incident polarization and electric field coupling on the surface plasmon properties of square hollow Ag nanostructures
Square hollow nanostructure can induce a large-area enhanced electric field at the main plasmon peak. Therefore, it can be used as a substrate for the surface enhanced Raman scattering. The effects of the incident polarization on the extinction spectrum and the electric field distribution of the square Ag nanostructure are studied by the discrete dipole approximation method. The results show that the plasmon peaks do not shift with the variation of incident polarization. However, the electric field distribution is strongly dependent on the direction of incident polarization. Additionally, the effect of the electric field coupling between adjacent square Ag nanostructures on the plasmon mode is also studied. It is found that the plasmon resonance can be tuned by varying the separation between adjacent squares. These results could be used to guide the preparation of such closed nanostructures for specific plasmonic applications.
Investigation on the band structures of AlN/InN and AlN/GaN superlattices
The band structures of wurtzite-AlN/InN and AlN/GaN superlattices are calculated by the Krönig-Penney model and the deformation potential theory under considering the lattice strain. Our calculations include the variation of band structure with the parameters for the sublayers, and the energy dispersion relations. It is found that by varying the sublayer thickness, the band structures can be well designed in different ways. The strain will change the bandgaps, reduce the band offsets and the sub-bands obviously, and make the valence band more complex. In comparison with the experimental results, our model is rather suited for simulating the narrow-quantum-well structures, while for the wide-quantum-well structures, the build-in field should be considered.
Preparation of lamina-shape TiO2 nanoarray electrode and its electron transport in dye-sensitized solar cells
Lamina-shape TiO2 nanoarrays (LTNA) film electrode which is vertically grown on the surface of a Ti sheet by the means of hydrogen peroxide oriented etching at low temperature. X-ray diffraction shows that amorphous phase transforms to highly-crystalline anatase phase of the LTNA film after having been calcined at 500 ℃ for 1 h. Field emission scanning electron microscope exhibits a vertically oriented lamina-shape array with the morphology uniformly distributed and perfectly coated on the surface of Ti sheet, and the average height (film thickness), width and thickness of the leave are 1.35 μm, 30—80 nm and 10—15 nm respectively, after 1 d etching in hydrogen peroxide at 80 ℃. The LTNA electrodes exhibit similar morphologies except for the film with a thickness of 2.12 μm by hydrogen peroxide etching for 2 d. Using the LTNA film electrode as photoanode based on dye C106 fabricate back-illumination type dye-sensitized solar cell (DSC), a power conversion efficiency can reach 3.2% under an irradiation of air mass 1.5 global (100 mW·cm-2) simulated sunlight. Mesoporous TiO2 films are also used in the fabrication of DSC under similar conditions. The devices are compared with each other by transient photoelectric attenuation and electrical impedance technique. The results demonstrate that the LTNA-electrode DSC has a much lower recombination rate and a longer electron life time.
Growth of Ge quantum dot at the mix-crystal interface self-induced on the ion beam sputtering deposition
The dense domes of Ge quantum dots on Si (001) substrate with a monomodal morphology distribution are deposited at different temperatures by ion beam sputtering (IBS). The areal density of the Ge quantum dots is observed to increase with elevating temperature, but the dots size to decrease. As the deposition temperature increases to 750 ℃, the smaller Ge quantum dots each with a height of 14.5 nm and base width of 52.7 nm are obtained by sputtering 15 monolayer Ge coverage, and the dots areal density is up to 1.68×1010 cm-2 at the same time. Thus the evolution of Ge quantum dot prepared by IBS is very different from that by vapor deposition at thermal equilibrium condition. The stable shape and the size distribution are demonstrated to result from the kinetic behavior of the surface atoms which is restricted by the thermodynamic limitations. A mix-crystal interface including amorphous and crystal components is revealed by Raman spectrum, and this special interface is demonstrated to contribute to the high density of Ge quantum dots, since the boundaries between the two different components can provide more preferential centers for the nucleation. As the density increases at high deposition temperature, the elastic repulsion between islands is enhanced, resulting in the surface atoms growing along the orientation of high index during the IBS deposition, and inducing the increase in aspect ratio and the reduction in island size.
Preparation and structure characterization of Pd thin films by supercritical fluid deposition
Pd films are deposited on the Si wafers by the reduction of palladium(Ⅱ) hexafluoroacetylacetonate, which is used as the precursor, in the supercritical CO2 solution at temperature 100 ℃ and pressures between 12 and 18 MPa, and with reaction for 10—20 h. The films are continuous, uniform and 0.3—1.5 μm thick. The analyses of the Pd films by X-ray photoelectron spectroscopy and X-ray diffraction indicate that the structures of the deposited films are of single matter and nanocrystalline. The scanning electron microscope images show that pressure is a factor of affecting the size of the grain of the deposited film. At a pressure of 12 MPa, the size of grain is between 30 and 60 nm, at a pressure of 15 MPa, it is between 90 and 120 nm. Moreover, at a pressure of 18 MPa, it is between 150 and 180 nm. At the same temperature, with higher pressures, the size of the grain is bigger. On the same conditions, Pd thin films are deposited on the inner and the outer surfaces of cylindrical cavity.
Simulation of multi-grain solidification and subsequent spinodal decomposition by using phase field crystal model
The phase field crystal model (PFCM) is employed to simulate the process of multi-grain solidification and its subsequent spinodal decomposition in a binary alloy system. Simulation results show that the PFCM can reproduce the whole process of the important material processing phenomena of multi-grain solidification, including nucleation, growth, coarsening and grain boundary formation. Furthermore, the PFCM can also successfully simulate the full course of the multi phase transformation process from solidification to spinodal decomposition.
Detection of seam tracking offset based on infrared image during high-power fiber laser welding
Seam tracking is a significant precondition to obtain good welding quality. During the laser welding, the laser beam focus must be controlled to follow the welding seam accurately. A novel approach to detecting the offset between the laser beam focus and the welding seam based on infrared image processing is investigated during high-power fiber laser butt-joint welding of type 304 austenitic stainless steel plates at a continuous wave fiber laser power of 10 kW. The joint gap width is less than 0.1 mm. An infrared sensitive high speed camera arranged in off-axis direction of laser beam is used to capture the dynamic thermal images of a molten pool. The characteristics of thermal distribution and infrared radiation of the molten pool, when the laser beam focus is deviated from the welding seam center, are analyzed. Two parameters called the keyhole morphological parameter and the heat accumulation effect parameter are defined as the characteristic values of seam tracking offset to determine the offset between the laser beam focus and the desired welding seam. Also, the image processing technique is used to analyze the infrared images of the molten pool, which indicates the presence of mathematic correlation between the defined two parameters and the seam tracking offset. The welding experiments confirm that the offset between the laser beam focus and the welding seam can be estimated by the keyhole morphological parameter and the heat accumulation effect parameter effectively.
Influence of annealing on thermal stability of IrMn-based magnetic tunnel juctions
The magnetic tunnel junction with a structure of IrMn/CoFe/AlOx/CoFe is deposited by magnetron sputtering and annealed at different temperatures in a magnetic field of parallel to the orienting field. Vibrating sample magnetometer is used to record the magnetic hysteresis loop at room temperature, and scanning probe microscope is used to record the interface morphology. The influence of annealing on thermal stability of the magnetic tunnel junction is investigated by holding the film in its negative saturation field. After annealing, the exchange bias increases due to the enhancement of unidirectional anisotropy of antiferromagnetic layer. The recoil loop of the pinned ferromagnetic layer shifts towards the positive field, and the exchange bias field decreases monotonically, with the film held in a negative saturation field, whereas annealing reduces the reduction speed of Hex.
Molecular dynamics simulation of low-energy sputtering of Pt (111) surface by oblique Ni atom bombardment
The low-energy sputtering on Pt (111) surface by Ni atom at incident angle in a range of 0°— 80° (with respect to the direction normal to the surface) is studied by molecular dynamics simulations. The atomic interaction potential obtained with embedded atom method is used in the simulation. The dependence of sputtering yield, energy and angular distribution of sputtered particles as well as sticking probability of Ni atom on incident angle are discussed. The dependence of sputtering yield on incident angle θ can be divided into three different regions in θ, i.e., θ ≤ 20°, 20° ≤ θ ≤ 60°, and θ ≥ 60°. Based on sticking probability and movement of incident atom, physical mechanism of low-energy sputtering at oblique particle bombardment is suggested. When the incident angle θ is smaller than 20°, the reflection of incident atom by target atom dominates the sputtering process of surface atom, which is similar to the sputtering mechanism for the case of θ = 0°. While for 20° ≤ θ ≤ 60°, the reflection of incident atom is no longer important for the low-energy sputtering. For the case of θ ≥ 60°, there occurs no sputtering.
A quasi transverse electromagnetic mode waveguide developed by using metal-patch electromagnetic bandgap structure
To solve the narrow operation-band of the electromagnetic bandgap (EBG) waveguide, a quasi transverse electromagnetic (TEM) mode waveguide using the metal-patch EBG structure as sidewall is proposed in this paper. Theoretical analysis and numerical calculation show that broader bandwidth, better transportation property, and more uniform electric field distribution of the quasi-TEM mode can be reached. Simulation results using Ansoft HFSS indicate that the metal-patch EBG structure can convert TE10 mode into quasi-TEM mode in the central frequency of 14 GHz with a bandwidth of 1.7 GHz and the uniformity of electric field distribution reaches 84.7% in 83.9% cross section area.
An X band synthesizer for a few hundred megawatt level power microwaves
A synthesis method for a few hundred megawatt level power microwave is presented in this paper. Based on the coupling wave theory and the polarized wave orthogonal theory, the pulse series of one gigawatt level power microwave and one hundred megawatt level power microwave can be put in two separate ports and put out from one common port. The synthesizer is unitized by two cylindrical waveguides which are back to back combined; the cylindrical waveguide which is joined with the output port is named main channel, and the other cylindrical waveguide is called associate channel. The main channel transmits horizontally polarized TE011 mode microwave, and the operation frequency band is only limited to the barrier frequency λc. The associate channel transmits vertical polarized TE011 mode microwave, and the operation frequency band can reach up to several hundred mega hertz. High power experiment indicates that the transmission energy efficiency of the main channel is nearly 100% and the coupling energy efficiency of the associate channel is above 87%, the power capacity of the main channel is more than 1GW and that of the associate channel is about 300 MW.
Radiation-resistant bipolar n-p-n transistor
Bipolar n-p-n transistor geometrical parameters are optimized based on the principle of minimizing the perimeter-to-area ratio (P/A). Three types of radiation-resistant n-p-n transistors are developed and fabricated in the 20 V bipolar process. The first is emitter-base junction hardened n-p-n transistor. The second has heavily boron doped base ring. And the last uses both radiation-resistant measurements. The experimental results indicate that after irradiated by the radiation of total dose of 1 kGy, in current gain, the common n-p-n(unhardened) transistor reduces about 60%—65%, while the first two hardened n-p-n transistors increases 10%—15%: the last hardened n-p-n transistors are 15%—20% greater than the common n-p-n transistors in current gain.
Efficient white polymeric light-emitting diodes by doping ionic iridium complex
A series of white polymer light-emitting diodes (WPLEDs) each with a single emitting layer using ionic iridium complex is fabricated. The white light is obtained via two complementary colors of orange light emitter ionic iridium complexe PF6 (Hnpy: 2-(naphthalen-1-yl)pyridine, c-phen: 1-ethyl-2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)-1H-imidazo phenanthroline) and sky-blue light emitter Firpic (iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C(2)) picolinate. The emtting layer consists of poly(N-vinylcarbzole) (PVK) as host polymer, 1,3-bis -phenylene (OXD-7) as electron-transporting materials, Firpic and PF6. The structure of the WPLED is indium-tin-oxide/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)(40 nm)/emtting layer (80 nm)/CsF(1.5 nm)/Al(120 nm). When the mass ratio of PVK, OXD-7, Firpic, PF6 is 67 ∶23 ∶10 ∶0.25, the most efficient white light is obtained with a color coordinate of (0.31,0.40), a maximal luminance efficiency of 13.3 cd/A and a maximal luminance of 6032 cd/m2. Meanwhile, the color coordinate is unchanged with current density. The mechanism of the WPLED is discussed.
Dynamic properties of bilayer membrane
We study the dynamics of bilayer membrane using the Fourier space Brownian dynamical equation. The surface of the bilayer membrane is demonstrated directly by using three-dimensional figure. Our results demonstrate that the slipping between the up-monolayer and bottom-monolayer is a very important dynamical process in the membrane dynamics, which strongly affects the height-height correlation function.
Oxygen and carbon behaviors in multi-crystalline silicon and their effect on solar cell conversion efficiency
Understanding and controlling the impurity behavior are important for low-cost and high-efficiency of multi-crystalline silicon solar cells. We employ the infrared spectroscopy to study the change of oxygen and carbon concentrations after thermal treatment in different parts of multi-crystalline silicon ingots grown by directional solidification technology. In correlation with the solar cell performances such as the minority carrier lifetime, photoelectric conversion efficiency and internal quantum efficiency, we investigate the physical mechanism of the effects of various concentrations of oxygen and carbon on cell performance. We propose an oxygen precipitation growth model considering the influence of carbon to simulate the size distribution and concentration of oxygen precipitation after the thermal treatment. It is found that carbon not only deteriorates the efficiency of the cells made from the silicon from the top part of the ingot, but also plays an important role in the effect of oxygen precipitation: enhancing the size and the quantity of oxygen precipitation in the silicon from the middle part of the ingot, which induces the defect and increases the recombination; while resulting in the small size and low quantity of oxygen precipitation in the silicon from the bottom part due to the low carbon content, thereby improving the cell efficiency through gettering impurities. We further demonstrate the complex behaviors of oxygen and carbon by a two-step thermal treatment technique, from which we point out that the two-step thermal treatment is applicable only to the improvement of the efficiency of solar cells from the bottom part of multi-crystalline silicon ingots.
Design of a highly efficient light-trapping structure for amorphous silicon solar cell
A highly efficient light-trapping structure consisting of a diffractive grating, a MgF2 film, a ZnS film and Ag reflector, is used for a-Si:H solar cell. Using the rigorous coupled wave theory, the weighted absorptance photon number (ξAM1.5) of a 1 μm thick a-Si:H solar cell is calculated in a wavelength range from 400 to 1000 nm for the AM1.5 solar spectrum at 25 ℃. It is used to design the optimal parameters of the light-trapping structure. Results indicate that ξAM1.5 of the solar cell can reach 74.3%, if the period, the depth and the duty cycle of the diffractive grating, and the height of the MgF2 film and the ZnS film are 800 nm, 160 nm, 0.6125, 90 nm and 55 nm, respectively. If a ZnS/Ag film is fabricated on the rear surface of the solar cell, a larger ξAM1.5 (76.95%) can be obtained. It is demonstrated that the trapping structure is useful for elevating the efficiency of the solar cell.
Effect of 3,4,9,10-perylenetetracarboxylic dianhydride on the performance of ZnO nanorods/polymer hybrid solar cell
ZnO nanoroods/poly (MEH-PPV) hybrid solar cells are fabricated and their properties are discussed. In order to improve the absorption of sunlight, a layer of 3,4,9,10-perylenetetracarboxylic dianhydride(PTCDA) is inserted between ZnO nanorods and MEH-PPV, and cells with the structure ITO/ZnO nanorods/PTCDA/MEH-PPV/Au are prepared with different thickness values of PTCDA. After introducing PTCDA, the devices show a strong and broad absorption in visible region, which increases the number of photo-induced excitons and thus results in an enlarged photocurrent. When the thickness of PTCDA is 40 nm, we can observe the smooth morphology of thin layer surface, and achieve the best performance of the device.
Some new integrable nonlinear dispersive equations and their solitary wave solutions
Under different system parameters, some new integrable models of the generalized modified Dullin-Gottwald-Holm are obtained by Painlevé analysis. Using the auto-Backlund transformation, solitary wave solutions of these integrable models are obtained.
Asymptotic solution to the delay sea-sir oscillator for El Niño/La Niña-southern oscillation mechnism
A class of coupled system of the El Niño/La Niña-southern oscillation mechanism is studied. Using the asymptotic analytic perturbation method and the simple and valid technique, the asymptotic expansions of solution to the El Niño/La Niña-southern oscillation model are obtained and the asymptotic behavior of solution to the corresponding problem is considered.
Fidelity of the photon subtracted (or added) squeezed vacuum state and squeezed cat state
In this paper, the fidelity of photon subtracted (or added) squeezed vacuum state with arbitrary number of photons and squeezed cat state is derived analytically. The result shows that whether the photon is added or subtracted, the maximum fidelity increases with the increase of the change of photon number, and the amplitude of the superposition state corresponding to the maximum fidelity also increases. In addition, for the same number of subtracted or added photons, the amplitude of the superposition state corresponding to the maximum fidelity in the case of added photon is larger than in the case of subtracted photon, but the maximum fidelity in the case is smaller. Although it is more difficult to make photon added than photon subtracted the photon added can be used as an important method to obtain cat state of large amplitude.
Arbitrated quantum signature scheme based on entanglement swapping
An arbitrated quantum signature scheme based on entanglement swapping is proposed in this paper. On the foundation of Bell states, the message to be signed is coded with a unitary sequence, and consequently the unitary sequence is used to calibrate the Bell states between the signer and the arbitrator, finally the signature is generated through quantum cryptography. Using the correlation states generated through entanglement swapping on the arbitrator’s side, the receiver can verify the signature through Bell measurement on his own side. In this scheme, anyone except the authentic signer cannot forge a legal signature and the true receiver cannot deny his recipient because the security of underling quantum cryptography and the participants’privacy are effectively protected in this scheme.
Error correction and decoding for quantum stabilizer codes
Mapping the error syndromes to error operators is the core of quantum decoding network and the key step to realize quantum error correction. The definitions of the bit flip error syndrome matrix and the phase flip error syndrome matrix are presented, and then the error syndromes of Pauli errors are expressed in terms of the columns of the bit flip error syndrome matrix and the phase flip error syndrome matrix. It is also shown that the error syndrome matrix of a stabilizer code is determined by its check matrix, which is similar to the relationship between the classical error and the parity check matrix of classical codes. So, the techniques of error detection and error correction for classical linear codes can be applied to quantum stabilizer codes after some modifications. The error correction circuits are constructed based on the relationship between the error operator and error syndrom. The decoding circuit is constructed by reversing the encoding circuit because the encoding operators are unitary.
Generalized variational principles for Boussinesq equation systems
The semi-inverse method is proposed by He to establish the generalized variational principles for physical problems, which can eliminate variational crisis brought by the Lagrange multiplier method. Via the He ’s semi-inverse method, a family of variational principles is constructed for the Boussinesq equation systems and variant Boussinesq equation systems of fluid dynamics. The obtained variational principles have also proved to be correct.
The brick-wall model unapplicable to the calculating of black hole entropy
The brick-wall model is widely used to calculate the entropies of static or stationary black holes. An ultraviolet cutoff factor needs to be introduced to remove the divergence of the result in brick-wall model. The cutoff factor has not been explained reasonably up to now. A study indicated that when the brick-wall model or thin film model was used to calculate the black hole entropy, the ultraviolet cutoff factor could be discarded if the generalized uncertainty relation was adopted. In this paper, it is proved that since the first term of Schwarzschild black hole entropy formula in the brick-wall model is not only the Bekenstein-Hawking term but also the term containing the ultraviolet cutoff factor, when the cutoff factor is removed, the Bekenstein-Hawking term is lost and the black hole entropy cannot be obtained by using the generalized uncertainty relation in brick-wall model.
A new global embedding approach to study Hawking and Unruh effects for higher-dimensional rotation black holes
First, we effectively reduce the higher-dimensional rotation metric to a 2-dimensional metric near the event horizon which contains only the (t-r) sector. Then, we study the Unruh/Hawking temperature for (1+1)-dimensional space-time with the new global embedding method. It is shown that the viewpoint of Banerjee and Majhi is correct. We also extend the study to the case of higher-dimensional rotation black hole.
Thermodynamic properties of a weakly interacting Fermi gas in a strong magnetic field
Based on the "pseudopotential" method and the local-density approximation, the thermodynamic properties of a weakly interacting Fermi gas in a strong magnetic filed are studied, the integrated analytical expressions of thermodynamic quantities of the system are derived, and the effects of magnetic field as well as interparticle interactions on the thermodynamic properties of the system are analyzed. It is shown that at both high and low temperatures, magnetic field may adjust the effects of interacting. At low temperatures, magnetic field can lower the chemical potential, total energy and heat capacity of the system compared with the situation of Fermi gas in the absence of the magnetic field. The repulsive interactions may increase the chemical potential, but reduce the total energy and heat capacity of the system compared with the situation of non-interacting Fermi gas. At high temperatures, magnetic field as well as repulsive interactions can reduce the total energy and increase heat capacity of the system, moreover, strong magnetic field may change the effects of interaction on the total energy and the heat capacity of the system.
Merging crisis of chaotic saddle in a Duffing unilateral vibro-impact system
A computational investigation of chaotic saddles in a Duffing vibro-impact system is presented. Chaoctic saddle crisis is investigated in a duffing vibro-impact system considered. This crisis is due to the tangency of the stable and unstable manifolds of period saddle connecting two chaotic saddles. The threshold of tangency induces the merging crisis of chaotic saddle, that is, as the system parameter crosses the critical value, a larger boundary chaotic saddle appears due to the merging of two chaotic saddles located on the basin boundary and in the internal basin respectively. In fact, this chaotic saddle crisis is responsible for the merging crisis of chaotic attractors eventually.
Control of spiral waves in FitzHugh-Nagumo systems
Control of spiral wave in two-dimensional FitzHugh-Nagumo equation is studied. The phase space compression approach is used to confine the system trajectory into a finite area and to annihilate spiral wave in the numerical simulation. Three stages are found in the control process. The spiral is driven to a homogenous stationary state when the compress limit is small; the spiral is stable with a fixed frequency when the compression limit is large; in the intermediate controlling parameter regime, the spatiotemporal turbulent state is observed. The controlling process is investigated by considering system pattern, variable evolution, phase space trajectory, etc, and the characteristics of amplitude function and oscillatory frequency are summarized as well.
Selective forgetting extreme learning machine and its application to time series prediction
Cellular automaton simulation with directed small-world networks for the dynamical behaviors of spiral waves
In this paper, we study the influence of the rewiring probability p of the directed small-world network on dynamical behavior of spiral wave using the Greenberg-Hastings cellular automaton model. The computer simulation results show that when p is small enough, the stable spiral wave under the regular networks keeps its stability unchanged, and when p is increased, the phenomenon such as meandering, breakup and disappearance of the spiral waves appears. The relation between the excitability and p leads to the conclusion that the occurrence of the above phenomenon originates from the reducing of the excitability. On the other hand, the period of cell is also related to p.
Spread spectrum communication based on hardware encryption
The scheme of 1 Gbit/s random sequence generated by chaotic laser as spreading code is proposed. Theoretical analysis indicates that the pseudo random sequence exhibited periodic behavior is eliminated by the random sequence and the capability of spreading code is enlarged. Meanwhile, the communication security can be improved by variable spreading code. The corresponding spread spectrum system is numerically simulated by Simulink software and the results demonstrate that the greater the used spreading gain, the lower the obtained error rate will be when the information speed is constant, which is consistent with the theoretical results. The anti-jamming ability of the spread spectrum system is strengthened and the security is enhanced compared with those of the traditional spreading system.
Modified function projective synchronization of a class of chaotic systems
A general method of modifying function projective synchronization of a class of chaotic systems is proposed in this paper by designing a suitable response system. The two schemes of obtaining the response system from chaotic system are established based on unidirectional coupled synchronization. Since chaos synchronization can be achieved by transmitting only a single variable from driving system to response system, this method is more practical. The stability analysis in the paper is proved using Lyapunov stability theory. Numerical simulations of a hyperchaotic system verify the effectiveness of the proposed method.
Considering two-velocity difference effect for coupled map car-following model
Based on the pioneer work of Konishi et al, a new coupled map car-following model is presented by considering the headway distance of two successive vehicles in front. The feedback control method presented by Zhao-Gao is utilized to suppress the traffic congestion in the coupled map car-following model. According to the control theory, the condition under which the traffic jam can be suppressed is analyzed. The results are compared with that presented by Konishi et al. The simulation results show that the new model with the feedback control method presented by Zhao-Gao could suppress the traffic jam effectively.
The stochastic energetics resonance of bistable systems and efficiency of doing work
The interaction of work and heat between Brownian particles in a bistable system, the external periodic force and the thermal stochastic force are analyzed. The stochastic energy balance equation based on Langevin equation is established. For the Langevin equation subjected to periodic force, stochastic force and damping force, the method of combining dynamics and non-equilibrium thermodynamics is used. From force as the foothold changed into energy as the research core, the exchange of energy between system and environment and the efficiency of doing work are deeply analyzed with this method when the Brownian particle motion is along single trajectories, which reveals that the bistable system exhibits stochastic energetic resonance phenomenon.
Epidemic spreading in complex networks with spreading delay based on cellular automata
In this paper, based on the cellular automata, we propose a new susceptible-infected-susceptible (SIS) model to study epidemic spreading in the networks with spreading delay. Theoretical analysis and simulation results show that the existence of spreading delay can significantly reduce the epidemic threshold and enhance the risk of outbreak of epidemics. It is also found that both the epidemic prevalence and the propagation velocity increase obviously with the spreading delay increasing. Moreover, the SIS model proposed in this paper describes not only the average propagation tendency of epidemics, but also the dynamic evolution process over the time of epidemics and the probability events such as outbreak and extinction of epidemics, and thus can overcome the limitations of the differential equation model based on mean-field method that describes only the average transmitting tendency of epidemics. Meanwhile, some suggestions of how to effectively control the propagation of epidemics are presented.
Ti:sapphire femtosecond comb with two spectral broadening parts
The first generation of femtosecond optical frequency comb (FOFC) based on the Ti:sapphire femtosecond laser in National Institute of Metrology of China, is improved and optimized in this paper. By changing the repetition rate of the femtosecond laser, the spectral broadening parts and the beat frequency signal detection, the complexity of spectral broadening is reduced and the stability of FOFC and the convenience for the frequency measurement are improved. With such an FOFC, the absolute frequencies of the I2-stabilized Nd:YAG 532 nm laser and I2-stabilized He-Ne 633 nm laser are measured. The experimenal results are in accordance with the recommended values by the International Committee for Weights and Measures.
A novel large-orbit electron gun with gradually-changing reversal magnetic field
A novel approach to achieve a large-orbit electron beam is demonstrated using a gradually-changing reversal magnetic field. On the basis of analyzing the general regularities of electron movement and various factors which lead to eccentricity and velocity spread in the gradually-changing reversal magnetic field, we design a large-orbit electron gun. Different from the traditional three-step method, our design does not pursuit the formation of thin tubular electron beam and the utilization of mutation reversal magnetic field, which reduces the difficulties in structure complexity and tube-making process. In addition, the cathode emission band can be placed in the axial magnetic field before the magnetic reversal point where its magnitude decreases gradually, by controlling the angular momentum difference between every trajectory starting points and using the offset effect of various unfavorable factors to reduce eccentricity and velocity spread. The simulation results are consistent with the theoretical analyses, which shows that the beam quality can be improved remarkably by fine-tuning electromagnetic fields, confirms that the efficiency and the applicability of the adjusting method we proposed, and provides a new technical way to obtain a high-quality large-orbit electron beam for high-efficiency large-orbit millimeter-wave devices.
Outgassing mass spectrum analysis with intense pulsed emission of carbon nanotube cathode
The outgassing mass spectrum property with intense pulsed emission of the carbon nanotube(CNT) cathode is investigated on a 2 MeV linear induction accelerator injector by using the quadrupole mass spectrometer. The results show that the cathode has a capability of desorbing gases from the CNT cathode under pulsed high voltage. There are significant CO2, N2(CO) and H2 desorbing gases which play an important role in the formation of the cathode plasma. The mechanism of electron emission of CNT cathode is plasma-induced field emission, rather than explosive field emission, which is proved by analyzing the desorbed gases component.
X-ray Zernike apodized photon sieves for phase-contrast microscopy
We present a kind of diffractive lens Zernike apodized photon sieves (ZAPS) whose structure is based on the combination of two concepts: apodized photon sieves and Zernike phase-contrast. Combined with the synchrotron light source, the ZAPS can be used as an objective for high-resolution phase-contrast X-ray microscopy in physical and life sciences. The ZAPS is a single optic unit that integrates the appropriate ±π/2 radians phase shift through selective zone placement shifts in an apodized photon sieve. The focusing properties of the ZAPS can be easily controlled by apodizing its pupil function. An apodized photon sieve with Gaussian pupil is fabricated by lithographic technique and shows that the side-lobes are significantly suppressed at the expense of slightly widening the width of the main lobe.
Research of Kramers-Krönig relationship for reconstruction of ultrashort electron longitudinal bunch profile by means of frequency domain measurements
Kramers-Krönig (K-K) relationship is widely used in diagnostics of longitudinal bunch distribution with frequency domain measurement, and it has been used as a powerful tool in analysis of bunch profile and length. The study results show that the bunching beam parameters are severely affected by the choosing of the baseline of autocorrelation curve, power loss at low frequency and cutoff at high frequency, as well as extrapolation point, etc. As an example, the longitudinal bunching length is measured by means of coherent transition radiation in accelerator laboratory of Tsinghua University. We analyze the influence of the choice of parameters on measured experiment results and discuss the method of choosing the key parameters for the K-K transform.
High order harmonic generation from a two-dimensional model H atom in arbitrary polarized laser
The two-dimensional time-dependent Schrödinger equation of arbitrary polarized laser pulse interacting with a model H atom is solved by using the two-dimensional asymptotic boundary condition (ABC) and symplectic algorithm. In order to investigate the influence of ellipticity on high order harmonic generation (HHG) of atom in arbitrary polarized laser field, we consider different ellipticities, and then compute the HHG for two-dimensional model H atom. Finally, we analyze the characteristics of HHG under different polarized laser fields. So it is reasonable and effective to extend the one-dimensional ABC and symplectic algorithm to the problem of laser interacting with a two-dimensional model atom.
Cross sections of Cq+(q=1—4)electron loss in collision with He, Ne and Ar investigating
Electron-loss cross sections in Cq+(q=1—4)collisions with He,Ne,Ar are measured in the intermediate-velocity regime, and the ratio of the two-electron-loss cross section to the one-electrom-loss cross section, R21, are calculated. It is shown that a single-channel analysis is not sufficient to explain the results, and that projectile electron loss, electron capture by the projectile, and target ionization must be considered together to interpreter the data. The screening and antiscreening theory can annalyse the threshold velocity, but cannot totally explain the data of R21 with velocity increasing. The effective charge of target increases with velocity increasing. Ne and Ar have the same effective charges in the velocity regime, but He has a smaller one at the same velocity. The correlation between loss electrons is also analyzed.
Theoretical study of electronic structure and optical properties of OsnN0,±(n=1 — 6) clusters
The possible geometrical and electronic structures of (OsnN)0,±(n=1—6) clusters are optimized by using the density functional theory (B3LYP) at the LANL2DZ level. For the ground state structures of (OsnN)0,±(n=1—6) clusters, The magnetic properties, the natural bond orbit (NBO), the spectrum and the aromatic characteristics are analyzed. The calculated results show that the magnetic moment of OsnN- cluster is quenched at n=1 and 5. Reversed ferromagnetic coupling between Os atom and N atom takes place in Os2N and Os4N0,± clusters. The NBO charge distribution of clusters depends on the relative position of the atom, for example, the charge transfer happening to N atoms in the endpoint is more obvious than that happening to the N atoms in the middle. There are obvious vibration peaks in IR and Raman spectra of (OsnN)0,±(n=1—6) clusters. The aromaticity of Os5N- cluster is the strongest.
Computational study on thermal stability of an AuCu249 alloy cluster on the atomic scale
Structural change of an AuCu intermetallic alloy cluster including 249 atoms during heating is studied by molecular dynamics simulation within the framework of embedded atom method. The analyses of pair-distribution function, atomic density function, and pair analysis technique show that the structural change of this cluster involves different stages from the outer part into the inner part owing to continuously interchanging positions among atoms at elevated temperature. During the change of the atom packing structure, gold atoms move from the inner part to the outer part of this cluster, whereas copper atoms move from the outer part into the inner part.
Numerical simulation of multipactor on dielectric surface in high direct current field
The numerical simulation of multipactor in the dielectric surface breakdown in high direct current field is realized by using the particle-in-cell method. And the influence of the strength of the high direct current field, smoothness of the dielectric surface and secondary electron yield coefficient on the multipactor are researched through the simulation of multipactor. Finally, the influence of the tilting of high direct current field and external magnetic field on the multipactor are also investigated. The results show that selecting of the dielectric with low secondary electron yield coefficient and tilting of high direct current field can reduce the degree of multipactor, and for the external magnetic field the degree of multipactor decreases effectively only when the external magnetic field exceeds a certain value.
Analysis of formation mechanism of Li-like satellites in aluminum plasma and experimental application
Base on the code of steady K-shell model for collision radiative balance, we analyze the main mechanism of populating the Li-like satellite of aluminum plasma in detail. The evolutions of the Li-like satellite intensity ratios of 1s2p2 2P—1s22p2P, 1s2s2p(1S)2P—1s22s2S and 1s2p2 2D—1s22p2P with electron temperature and density are depicted from which we find that the intensity ratio is density sensitive and temperature unsensitive, which can be used to diagnose the electron density in hot dense plasma. At the same time, the evolution of the intensity ratio of He-like to He-like resonant with electron density is also given. The value of the ratio is large in the high electron density region due to the influence of the undistinguished Li-like statellite around the He-like intercombination. Finally, we simulate the spectra emitting from the hot dense aluminum plasmas generated by the "Shengguang-Ⅱ" equipment and give the electron temperature and density.
Magnetic shear effect on zonal flow generation in ion-temperature-gradient mode turbulence
By decoupling the nonlinear fluid equations of ion-temperature-gradient (ITG) mode, the zonal flow-drift wave nonlinear dynamical equation including magnetic shear is derived. The role of magnetic shear for zonal flow generation by ITG mode turbulence is studied using a four-wave interaction model of modulational instability. Finally we can draw the conclusion that within a smaller range of k//, as |k//| increases, the growth rate of zonal flow is also increased.
Shock timing experiment in polystyrene target based on imaging velocity interferometer system for any reflector
Simulation of protective effect of the buffer on the first mirror in HL-2A tokamak
How to improve the protective effect of the first mirror is urgent for tokamaks at present. Buffer is one of the efficient methods to reduce the impurity redeposition on the first mirror. In order to study the protective effect of the buffer, the physical model of the particle redeposition on the first mirror is established with the Monte Carlo method on the basis of the parameters and experiments of the HL-2A tokamak. Particle redepositions on the first mirror are simulated under different conditions, including the cases without buffer and with cone buffer. The simulation results match well with the experimental results. The accuracy of the model is verified, and the simulation is efficient for providing theoretical basis for the protection of the first mirror.
Experimental study on emission spectra of air plasma induced by femtosecond laser pulses
The emission spectra produced in ambient air with focused strong femtosecond laser pulses are studied experimentally. The results show the emission spectrum presents the short-wavelength continuum spectrum with stronger intensity(cutoff wavelength 340 nm) and long-wavelength line spectrum with less weak intensity(near 800 nm). A similar spectrum shape can be acquired with fixed pulse width 50 fs and adjustable laser pulse energy. When the pulse energy is 1 mJ and the pulse width increases from 50 fs to 1ps, the peak value of continuum spectrum located in 500 nm wavelength becomes strong and gradually presents the line spectrum characteristics.
Numerical simulation of plasma immersion ion implantation for cubic target with finite length using three-dimensional particle-in-cell model
Plasma immersion ion implantation (PIII) of the square target with finite length is simulated using a three-dimensional particle-in-cell (PIC) plasma simulation in this paper. The incident dose, the impact angle and the implanted energy on the target surface are investigated. The results show that the sheath around the square target with finite length becomes spherical rapidly during PIII. And the three-dimensional sheath width is small apparently compared with the one simulated by two-dimensional PIC. And it is found that the three-dimensional ion dose is not evenly distributed on the target surface during simulation time (50ω-1pi) in this work. The dose is smallest in the center of the target, and it is largest near the corner. This is due to spherical sheath where ions are focused and accelerated into near the corner. In the central zone, the ion incidence is nearly normal to the surface, and the impact average energy exceeds 90% of the maximum. But the impact angle near the corner is always nearly 45°, and the implanted energy is only about 50% of the maximum.
Development of percentile estimation formula for skewed distribution
Order statistics establishes a relation between the position of the ranked data and corresponding cumulative probability, so it can be used to estimate the cumulative probability. Owing to the fact that different climatological data have different skewness degrees, in this paper, according to the cumulative probability function under the skewed distribution conditions, we perform theoretical analysis and numerical simulation to establish the position parameters of the regression model which are related to skewness index, then give an amperic percentile formula under the skewed distribution. By using the data about the summer temperature in global from 1980 to 2009, we compare the positions of ranked data corresponding to the 90th percentile, which are obtained by this formula and Jenkinson’s formula.
Influence of time delay on global temperature correlation
Modeling of ultraviolet characteristics of deep space target
Ultraviolet detection has advantages of high sensitivity and low false alarm rate. Analysis of ultraviolet characteristics has great significance for space target detection. An accurate modeling method is proposed for the ultraviolet characteristics of space target. Based on the background environment and material properties of space target, region and grid division are generated, and the mathematical model of ultraviolet characteristics of space target is established by introducing bidirectional reflectance distribution function. The position relations of target, detector and background radiation source are determined by coordinate transformation algorithm. The calculation flow for ultraviolet characteristics of space target is derived. Finally, the observed ranges and irradiation distributions of Ziyuan-1 and Fengyun-3 satellite are calculated by the given parameters. The simulation results demonstrate the validity of the modeling method.
Characteristic periodicity analysis of the X-ray flux variability of quasar PKS 1510-089
We present the X-ray light curve (1.5—12 keV) for quasar PKS 1510-089 with the observation of the all-sky monitor on the Rossi X-ray Timing Explorer from January 1996 to December 2009. Using the discrete correlation function method, the wavelet analysis method and the power spectrum method to analyze the data, we find that the light curve variability period of quasar PKS 1510-089 is (0.94±0.08)a. The super massive binary black hole model in used to analyze this source, and the results show that the orbit period of the super massive binary black hole system is (1.85±0.10)a and the super massive binary black hole model is the better model for describing the light curve periodic behaviour of quasar PKS 1510-089 at present.