Design and simulation of chiral negative refractive structure based on folded-wire
A new chiral structure working in microwave and optical frequency bands based on folded-wire is designed and simulated. Effective parameters of this structure, including polarization azimuth rotation angle, ellipticity angle, relative permittivity, relative permeability, chiral parameter and refractive index are obtained from simulated transmission and reflection spectra. The results show that the exceptionally strong polarization azimuth rotation angle and the ellipticity angle are found in microwave and optical frequency bands. Because this structure has a large chiral parameter, negative refractive index of a circularly polarized wave can be obtained without requiring permittivity and permeability to be negative simultaneously.
Design and study of miniaturized-element frequency selective surfaces
We propose a miniaturized-element frequency selective surface (MEFSS) by using the coupling mechanisms between capacitive surface and inductive surface, so the uint cell size will not be restricted by wavelength. In order to improve resonance stability performance with respect to different polarizations and incidence angles, according to the traditional FSS Y element, we create periodic elements of capacitive surface and inductive surface with "Y" shape and Y element array is in the form of equilateral triangle, The grid array and the effects of the parameteristics of Y loop element on the frequency response characteristics of MEFSS are calculated using the modal matching method. With filming technology and lithography, the corresponding capacitive surface and inductive surface between polyimide are produced and a prototype MEFFSS using freedom space method is examined. Both simulated and measured results obtained show that the MEFFSS constructed by using equilateral triangle "Y" element array has much better f0 resonance stability performance with respect to different polarizations and 60° incidence angles, and the -3 dB bandwidth reaches up to 7.6 GHz. We present a theoretical and experimental reference of MEFSS for the applications in large-angle incidence curved streamlined radome.
Synchrotron K-edge subtraction imaging and its application to metallic foams
On the basis of sudden change of linear absorption coefficient (LACs) in the vicinity of absorption edge, the synchrotron K-edge subtraction technique is developed to label the three-dimensional (3D) distribution of element. In this work, tomographic scans above and below the specific absorption edge of Zn are carried out and the subtracted image is used to identify and quantify the 3D distribution of Zn element inside the cell wall of Al-Zn-Mg foam. A non-uniform spatial distribution of Zn element is found in the cell wall of as-cast foam. After long solution tratment, the concentration of Zn element tended to be homogeneous. It is confirmed that the local agglomerated Zn-bearing particles exerta negative influence on the brittle cracking of the cell wall. The K-edge subtraction technique provides a powerful tool for the quantitative microstructure characterization of three-dimensional tissues.
Design of metamaterial frequency selective surface with polarization selectivity
Two kinds of frequency selective surfaces with polarization selective characteristics are proposed in this paper. According to the design method of metamaterial, frequency selectivity capability can be achieved by the combination of continuous conducting wire and cut-wire whose effective permittivity is Lorentz-type. By different dimensions and structures in the x-axis and the y-axis of frequency selective surface unit cells, the passband properties for TE and TM waves are separated, so a polarization selective surface in GHz band can be achieved. The design method demonstrates the feasibility of metamaterial frequency selective surface and is of great reference value in fabricating polarization filter and polarization wave generator of specified frequency.
Influence and simulated correction of tip/tilt phase error on fiber laser coherent beam combination
Near-field models of coherent beam combination (CBC) with different beam channels and fill factors are employed, and the influences of tip/tilt phase errors on CBC are studied. The key device for tilt-error correction, named adaptive fiber optics collimator(AFOC), is introduced. A MOPA-configuration fiber laser CBC system compensating both piston and tip/tilt phase errors is designed. Then, the dynamic courses of tilt-error correction using stochastic parallel gradient descent (SPGD) algorithm in a seven-channel system are simulated, and the effects of CBC at different tilt-error amplitudes and frequencies are investigated. Experimental results show that the tilt-error should be corrected to improve CBC effects, and algorithm's control ability drops off when tilt-error amplitude and frequency increase. The results in this paper present a reference for multi-channel high power fiber laser CBC systems in real atmospheric environments.
Shifts of beam centroid of Laguerre-Gaussian beams reflected and refracted at a dielectric interface
Extension characteristics of the depth of field for wavefront coding system
The wavefront coding extension of the depth of field (DOE) for an imaging system is achieved by inserting a third order phase plate into the pupil plane of a spatially incoherent imaging system. The encoded image can be digitally restored to produce a final image with improved depth-dependent details. The characteristics of the system are studied, and the modulation transfer function (MTF) varying with defocus and modulation coefficient,α, of the third order phase mask is analyzed, the results about the effects of α value on the extension of DOE and the bandwidth are obtained. The results are conducible to the design of wavefront coding optical system and the choice of an appropriate α velue.
Image fusion algorithm based on block-DCT in wavelet domain
A feature-level image fusion algorithm using wavelet transform combined with the discrete cosine transform (DCT) is proposed. The basic idea is to perform block-DCT of each source image first, and then to select the retained coefficients according to maximum variance; each image is compressed to 25 percent of the original size. The coordinates of the retained coefficients are used as private keys. Finally, the processed DCT coefficient matrixes are taken as the wavelet coefficients and the fused image is obtained by taking the inverse wavelet transform. The experimental results show that the algorithm realizes the fusion of images with different sizes. Furthermore, one single image can be reconstructed by one single private key.
Fiber-based narrow-band single-photon source with high heralding efficiency
According to the correlated photon pairs produced by spontaneous four-wave mixing in dispersion-shifted fiber, we present a telecom-band single-photon source by using mode-locked laser. Single-photons with a -3 dB bandwidth of 1.1 nm are heralded with more than 50% probability. The measured second-order correlation g(2)(0) is equal to 0.09±0.01. Our source is well suit for quantum communication systems.
Multiple electromagnetically-induced transparency of hyperfine levels in cesium 6S1/2 -6P3/2 -8S1/2 ladder-type system
Based on the cesium 6S1/2 -6P3/2 -8S1/2 ladder-type system, electromagnetically-induced transparency (EIT) is further investigated in a room-temperature vapor cell. When the probe laser is locked to one of the hyperfine transitions between the ground state 6S1/2 (F=3) and the intermediate state 6P3/2 while the coupling laser scans the transition between the intermediate state 6P3/2 and the excited state 8S1/2, the EIT spectrum has a flat background improving the spectral resolution. The theoretically calculated EIT spectral profiles from a multi-level ladder-type model are consistent well with the obtained experimental phenomena.
Entropy exchange and entanglement of a moving atom with k-photon Jaynes-Cummings model
The entropy correlation and the entanglement of a moving atom interacting with k-photon Jaynes-Cummings model are investigated. Entropy exchange between atomic and field subsystems, which is a form of anti-correlated behavior, is explored. Analytical results show that atomic motion, transition number k of field and field-mode structure can influence the entropy exchange between atom and light field. Moreover, the relationship between entropy correlations and entanglement is also discussed.
Hot-images induced by the random distribution defects in high power laser systems
Mechanism for long pulse laser-induced hard damage to the MOS pixel of CCD image sensor
The interaction process between 1.06 μm wavelength Nd:YAG long pulse laser with a millisecond pulse width and the MOS pixel of frame transfer area CCD image sensor and its hard damage mechanism are studied by the finite element method. The thermal-mechanical coupled modeling for long pulse laser irradiation of a MOS pixel is established, and the distributions of temperature and stress are obtained. The results show that the spallations between O layer and S layer appear due to the S layer radial stress on the surface exceeding the compressive strength under the action of the long pulse laser, then it will extend to the entire layer before melting by radial stress,axial stress and hoop stress. Hard damage of pixel occurs as spallation, and one pixel or an array of pixels in the laser irradiation area of CCD sensor is completely in failure. This paper could provide foundation for both laser-induced damage and protection of CCD image sensor.
Design of dispersion decreasing fiber for compressing stationary rescaled pulse
A ccording to the compression principle of stationary rescaled pulse (SRP) in the comb-like optical fiber (CPF), the design of dispersion decreasing fiber (DDF) for compressing stationary rescaled pulse is demonstrated in this paper. The dispersion profile of DDF is found to be decreased linearly. The compression ratio and the power ratio are both equal to the ratio between initial and final values of second order dispersion coefficient when the incident pulse is SRP. When the dispersion slope of the fiber is small enough, the fundamental soliton without chirp can be approximated as SRP. When the dispersion slope of the fiber is high, the fundamental soliton without chirp cannot be approximated as SRP. When the incident pulse is fundamental soliton with linear chirp, which is proportional to the dispersion slope of the fiber, the compression ratio and the power ratio are closer to the ratio between initial and final dispersion values,which indicates that the fundamental soliton with linear chirp is approximated as SRP with less error than fundamental soliton without chirp.
Effect of PbI2 on optical properties of Te-based far infrared transmitting chalcogenide glasses
A novel series of Ge-Te-PbI2 chalcogenide glasses is prepared by traditional melt-quenching method, and the glass-forming region is determined. X-ray diffraction, differential thermal analysis, visible/near-infrared absorption spectroscopy and infrared transmission spectra are adopted to analyze the composition, the structure, and the performance of the Te-based glasses system with an addition of PbI2. The Tauc equation is used to calculate the direct and the indirect optical band gaps, based on the metallization criterion and the band gap energy theory, the relationship between optical band gap and composition is investigated. The results show that with the addition of PbI2, the glasses-forming ability and the thermal stability are improved, Also, the density and the refractive index of glass sample both increase, the short-wavelength edges shift to ward a longer wavelength, the band gap decreases and the infrared cut-off wavelength of glass is 25 μm which keeps almost unchanged. The series of glasses can be adopted to fabricate the far-IR optical wave-guide devices.
Numerical study on the optical absorption of one dimension metallic gratings
We investigate the reflected response of one-dimensional metallic grating with rigid coupled-wave analysis. Three types of resonance absorptions, i.e., Rayleigh anomaly, surface plasmon polariton (SPP) standing wave resonance and geometric resonance, are identified in the gray-scale map of the reflectivity as a function of two structural parameters: grating period and groove depth. Furthermore, the interactions among these resonances are discussed. Our calculation reveals that a hybrid mode of SPP standing wave resonance and geometric resonance can be found, while no hybrid mode of Rayleigh anomaly and geometric resonance exists. In the analysis of compound gratings, we find phase resonance. How the phase resonance changes the reflection and the absorption of compound metallic gratings is also discussed. When the wavelength of incident light is less than grating period, sharp dip is found in reflectivity as a function of groove depth. In the other case, i.e. Wavelength greater than grating period, phase resonance results in a split of the hybrid absorption branch of SPP standing wave resonance and geometric resonance.
Diffraction property of broadband metal multi-layer dielectric gratings based on rigorous coupled-wave analysis
The rigorous coupled-wave analysis technique for describing the diffraction of metal multi-layer diffraction grating (MMDG) is built. Formulation for a stable and efficient numerical implementation of diffraction efficiency is presented for MMDG with TE polarization. With the merit function of the -1 order diffraction efficiency higher than 97% and working bandwidth, the parameters of MMDG are optimized to achieve broadband. The bandwidths used for 800 nm and 1053 nm can be 130 nm and 150 nm respectively. The manufacture latitude and the effective incident angle for the optimized structure of MMDG are discussed. The optimized grating should be useful for chirped pulse compress.
Multi-wavelength ultraviolet terawatt-order CPA system
We set up a multi-wavelength ultraviolet terawatt-order chirped pulse amplification(CPA) system according to the CPA technology and the frequency conversion technology. The system offers 1Hz, 5Hz and 10Hz high energy ultraviolet pulses by precise time synchronization among 5 repeat frequencies. The RMS of output energy fluctuation rate of CPA is less than 2% with using a pre-amplified system of energy fluctuation rate less than 0.3% RMS and a time synchronizer with time jitter less than 3 ns. The multi-wavelength high energy ultraviolet pulses with 64 mJ/400 nm,16 mJ/267 nm and 5 mJ/205 nm are obtained, and their corresponding peak powers reach the terawatt level.
Scattering of polarized light by randomly oriented coated spheroidal particle
A computer method is described to calculate the light-scattering properties of randomly oriented, axially symmetric coated particles, in the framework of the T-matrix theory. Both the core and the shell can be axially symmetric nonspheroidal particles. Based on the coated spheroidal particle model, light scattering characteristics of water aerosols with an absorptive core (black carbon) are calculated. The effects of cores with different sizes and shapes are analyzed on extinction efficiencies, scattering efficiencies, absorption efficiencies, single scattering albedos, asymmetric parameters.
Actuating frequency selection of single mode Lamb waves using single piezoelectric transducer
Evaporation induced solidification of cyclohexane drops under acoustic levitation condition
The evaporation process of a cyclohexane drop is investigated by single-axis acoustic levitation method. It is found that the evaporation of the cyclohexane drop results in the decrease of its temperature below the melting point, and leading to solidification. The real-time observation with a high speed camera shows that the cyclohexane nucleates near the equator of the drop surface and grows dendritically with an average velocity ranging from 12.5 to 160.4 mm/s. Further studies indicate that the ratio Sh/Nu of the average Sherwood number to Nusselt number under acoustic levitation condition is 1.3 times of that under natural convection condition. This suggests that the acoustic streaming boundary layer effectively strengthens the evaporation but has less promotion effect on the heat transfer. Therefore, the drop temperature declines to a lower value and the evaporation induced solidification occurs under acoustic levitation condition. Accordingly, a necessary condition for the occurrence of evaporation induced solidification of volatile liquids is proposed.
Experimental method of measuring sound velocity using ultrasonic flowmeter
In order to obtain sound velocity in liquid, an experimental method of measuring sound velocity is designed. A time-difference type ultrasonic flowmeter and normal flow checkout equipment are used to measure the flow speed of liquid in closed hydraulic pipeline simultaneously, then the measured value and the true value of the flow rate are measured, and the meter-factor of the ultrasonic flowmeter is determined. Furthermore, the relationship between the sound velocity and the meter-factor is derived under a certain condition. Based on the method, the velocity of sound in dinitrogen tetroxide (N2O4) at 7.6-19.4 ℃ and unsymmetric dimethyl hydrazine ((CH3)2NNH2) at 6.5-25.2 ℃ are measured at 0.17 MPa. It provides reference for measuring the sound velocity in other liquid.
Hologram pressure field weighted norm extrapolation method
Hologram pressure extrapolation is a key process of Patch nearfield acoustic holography. In this paper, a pressure extrapolation method based on the weighted norm extrapolation is proposed, in which the auto-power spectrum of hologram pressure estimated by the measured data is used as a weighting function to build the weighted norm, and the hologram pressure extrapolation is realized by minimizing the weighted norm. Because both the spectrum shape and the bandwidth information about hologram pressure are utilized during the extrapolation, a more accurate extrapolated result can be achieved. The validity of the proposed method is proved by a numerical simulation and an experiment study. The simulation results show that the proposed method has obviously advantages in accurcy and computational efficiency compared with the classic wave number domain extrapolation method. Furthermore, the proposed method is used to extrapolate a pressure field generated by a camped steel plate in experiment and a satisfactory result is obtained.
The delayed feedback control to suppress the vibration in a torsional vibrating system
We investigate the delayed feedback control to suppress the vibration in a torsional vibrating system. The delayed feedback control is applied to a torsional vibrating system with a nonlinear dynamical absorber.We investigate the effects of gain and delay on vibration suppression of the primary system. The results show that for a fixed gain, the vibration of the primary system can be suppressed at some values of the delay. As the delay varies for a fixed gain, the amplitude of the primary system can be suppressed to a minimum value. The vibration of the primary system is suppressed form 0.24 to 0.03 when the gain and the delay are chosen to be appropriate values. The analytical solutions are consistent well with the numerical simulation.
Threshold value of shear stress in H-22 cells generated sonoporation
Based on a spherically symmetric bubble model, the threshold shear stress for H-22 cells which are irradiated by continuous focused ultrasound is estimated. On the condition that the final concentration of the superparamagnetic iron oxide (SPIO) in the cell suspension is 410 μg/mL, the focused ultrasound sonication is at a frequency of 1.37 MHz, the power from amplifer is 2 W, and H-22 cells are exposed to the ultrasound for 60 s, the labeling efficiency is about 45.9%±13.5%. Prussian blue staining confirms iron uptake and shows numerous blue-stained iron particles in the cytoplasm, while more than 90% labeled cells remained viable. The results show that the reparable sonoporation arises in plasma membrane and SPIO nanoparticles enter into the H-22 cells. Numerical calculations show that the shear stress acting on the cell is 697 Pa, which is the threshold shear stress for H-22 cell sonoporation.
Thermal conductivity of mesoporous material MCM-41
In this paper, the mesoporous structural unit of MCM-41 is established first and the equilibrium molecular dynamics (EMD) numerical simulation is performed to obtain the shell thermal conductivity of MCM-41. Then, based on one-dimensional heat transfer analysis, the analytical expression for effective thermal conductivity of MCM-41 is obtained by coupling heat conduction in air-filled nano-pores and that in the shell. The effects of wall thickness, pore size and porosity on the thermal conductivities of the MCM-41 are further analyzed. It turns out that MCM-41 possesses good thermal insulation and the decrease of effective thermal conductivity is closely linear as porosity increases. Furthermore, the thermal conductivity shows that it is obviously anisotropic and its largest value is along the length of the pores, and that it has the quasi-one-dimensional characteristic.
Potential entransy and potential entransy decrease principle
In this paper, we analyze some kinds of potential energies, such as the geopotential energy, the electrostatic potential energy, the chemical potential energy, the mass entransy and so on. It is found that they all can be expressed as the product of a conservative extensive quantity and an intensity quantity. This kind of potential energy is named potential entransy. Based on the concept of potential entransy, the potential entransy decrease principle is developed. It is found that the potential entransy of an isolated system always decreases when the extensive quantity is transferred in the system. Furthermore, the criteria of equilibrium state for an isolated system and a common closed system are derived on the basis of the concept of potential entransy. It is found that when an isolated system reaches its equilibrium state, its potential entransy is a minimum value. When a common closed system reaches its equilibrium state, its quasi-free potential entransy is also a minimum value. In addition, when a closed system with prescribed potential is in its equilibrium state, its free potential entransy is also a minimum value. When the principles above are used in heat transfer, the entransy decrease principle for heat transfer and the thermal equilibrium criteria can be developed. We think that the new physical quantity, entransy in heat transfer, is the core concept of the subject, because it can be used to describe the irreversibility of heat transfer, optimize heat transfer processes, measure the disorder degree of one system, and set up the thermal equilibrium criteria.
The conserved quantities in general theorems ofthe Cosserat elastic rod dynamics
Conserved quantities of the Cosserat elastic rod dynamics are studied according to the general theorems of dynamics. The rod dynamical equation takes the cross section of the rod as its objective of study and is expressed by two independent variables, the arc coordinate of the rod and the time, so the conserved quantities are written in the integral forms and there exist the arc coordinate conservation and the time conservation. The existence conditions and the formulas of conservations of momentum and moment of momentum are derived from the theorem of momentum and the theorem of moment of momentum respectively, which contain two cases of conserved quanties, one is the time and the other is arc coordinate. Also existence conditions and formulas of conservations of energy about time and are coordinate, which contain mechanical energy conservation, are derived from energy equations about the time and arc coordinate of the rod respectively. All of conservative motions of the rod are explained by examples. The conserved quantities in the integral form are of practical significance in both theoretical and numerical analysis for the Cosserat elastic rod dynamics.
Investigation of sign spectrum sensing method
Spectrum measurement technology is widely used in wireless communication, electronic countermeasure, cognitive radio, smart absorbing structure, etc. In this paper we propose a new sign spectrum sensing approach which contains mainly data acquiring stage and spectrum sensing stage. In the former stage, based on the standard compression sensing, we propose a new sign data acquiring approach, in which we preserve only the sign information about the measurements, so that the data storage space is reduced. In the latter stage, we construct the spectrum sensing algorithm based on the consistent reconstruction principle and the gradient steepest descent algorithm. Simulation results demonstrate that this approach reduces the number of measurements and the data storage space, and at the same time this approach perfectly acquires the spectrum information. This approach can well be used in front spectrum measurement stage of wireless commucation, electronic countermeasure, smart absorbing structure and cognitive radio.
Mei symmetry and Mei conserved quantity of Appell equations for nonholonomic systems of Chetaev’s type with variable mass
Mei symmetry and Mei conserved quantity of Appell equation for a nonholonomic system of Chetaev’s type with variable mass are studied. The Appell equation and differential equation of motion of the system are set up. The expression of the total derivative of the function along the trajectory of the system with respect to t, the definition and criterion of Mei symmetry of Appell equation for a nonholonomic system of Chetaev’s type with variable mass under the infinitesimal transformation of group are given. The structural equation of Mei symmetry and the expression of Mei conserved quantity expressed by Appell equation are obtained. An example is given to illustrate the application of the results.
Another kind of conserved quantity induced by Mei symmetry of mechanico-electrical system
Another kind of conserved quantity deduced from Mei symmetry of mechanico-electrical system is studied. Under the infinitesimal transformation of groups, another kind of conserved quantity of Mei symmetry of mechanico-electrical system is obtained from the definition and the criterion of Mei symmetry of mechanico-electrical system. Finally, an example is given to illustrate the application of the result.
Influence of reduced electric field on the evolvement characteristics of plasma under conditions of N2/O2 discharge
Adopting the plasma kinetic model, we perform a numerical calculation of evolution characteristics in N2/O2 plasma with various reduced electric fields. The results show that there is an approximate linear relation between electron average energy and reduced electric field, the electron average energy is 2.6 eV and its maximum is 35 eV when reduced electric field is 100 Td, and reduced electric field has a strong influence on electron energy distributing function. The number densities of nitrogen molecules and atoms, oxygen atoms in electronic excited state reach their peaks when discharge is over, then drop off; but the number density of nitrogen molecules in vibrational excitation remains unchanged after discharge; oxygen atoms recombine into ozone molecules. With the increase of reduced electric field, the number density of vibration excitated nitrogen molecules reduces because of the decrease of the number of electrons with low energy, but other particles are increasing. The number densities of vibrational excitated nitrogen molecules are 3.83×1011cm-3, 1.98×1011cm-3 and 1.77×1011 cm-3 when reduced electric fields are set to be 50 Td, 75 Td and 100 Td respectively.
Influence of impurity on Mueller matrices of randomly distributed cluster agglomerates
The effects of impurity on the Mueller matrices of randomly distributed cluster agglomerates are analyzed. The equivalent complex refractive indees of silicate particle containing different volume fractions of amorphous carbon are obtained by the Bruggeman effective medium theory. Mueller-matrix elements of randomly distributed cluster agglomerates containing various chemical compositions are calculated by the discrete dipole approximation (DDA) method, and the profiles of Mueller-matrix elements are presented. The influence of the impurity on the Mueller matrices of randomly distributed cluster agglomerates is discussed. The results show that the influence of impurity on the Mueller matrices of randomly distributed cluster agglomerates is quite large, and it varies with the size parameters of the randomly distributed cluster agglomerates.
Shock experiment with sandwiched target in laser indirect-drive experiment
Laser indirect-drive has the potential to get ultra-high pressure which is very useful for shock physics. The sandwiched target is used to suppress the ionization effect which causes the blanking area in optical streak camera (OSC) in indirect-drive experiment. The blanking effect can be avoided by the time scale and the intensity. With the thick ablator, the blanking effect appears before the shock wave arrives at the transparent material. Then the blanking effect can be avoided in time scale. With the high Z material, the X-ray which causes the blanking effect can be blocked before the transparent material. For one shock experiment, the shock wave result in Al2O3 is achieved after using the thick ablator to stagger the blanking effect and shock wave signal. The shock wave result in quartz and polystyrene material is obtained after the block layer has been added to the ablator layer. The sandwiched target provides the technique support for the equation of state and shock timing experiment in indirect-drive.
Coupling characteristics research on Z-pinch driver and wire array load
Self-consistent circuit solution of Z-pinch driver discharging and wire array implosion is realized via Pspice analog behavioral modeling (ABM) based on the 0-dimensional implosion model. The influence of wire array and circuit parameters on implosion process is investigated using the method. Results show that wire array as its load is strongly coupled with Z-pinch driver. The maximum pinch current, the implosion time and the maximum kinetic energy (Ek) transferring to wire array are very sensitive to driver and wire array parameters. When the driver doesnot change and implosion time doesnot exceed a quarter of oscillation periods, the maximum pinch current, the implosion time and the maximum Ek increase while wire array mass increasing, and implosion time decreases as initial wire array radius increases. With keeping wire array unchanged, the implosion time decreases and implosion time increases as capacitance of driver increases, but the Ek efficiency firstly increases then decreases. The optimal array parameters for a given driver should make the implosion fully use the rising edge of current pulse, and make the pinch time close to a quarter of oscillation period, so that the implosion process could obtain maximum Ek efficiency.
Incremental regularized extreme learning machine based on Cholesky factorization and its application to time series prediction
In order to solve the hidden-layer neuron determination problem of regularized extreme learning machine (RELM) applied to chaotic time series prediction, a new algorithm based on Cholesky factorization is proposed. First, an RELM-based prediction model with one hidden-layer neuron is constructed and then a new hidden-layer neuron is added to the prediction model in each training step until the generalization performance of the prediction model reaches its peak value. Thus, the optimal network structure of the prediction model is determined. In the training procedure, Cholesky factorization is used to calculate the output weights of RELM. Experiments on chaotic time series prediction indicate that the algorithm can be effectively used to determine the optimal network strueture of RELM, and the prediction model trained by the algorithm has excellent performance in prediction accuracy and computational cost.
Study on bursting of pancreatic β cells in codimension-2 bifurcation regions
Electrical activities of insulin secretion in pancreatic islets are characterized by bursts of action potentials. With a simple but representative Vries-Sherman model, we determine the regions of different types of bursting in two-parameter plane through the two-parameter bifurcation analysis of the fast subsystem. Moreover, fast/slow analysis is used to reveal topological types of bursting patterns for different values of the parameter Vm and transition mechanisms between them.
New explicit exact solution of one type of the sine-Gordon equation with self-consistent source
This paper deals with one type of sine-Gordon with self-consistent source (SGESCS). The explicit exact solution of the equation is investigated using a generalized binary Darboux transformation. The complexiton solution for the equation is finally obtained.
Coupled KdV equation: similarity reduction and analytical solution
Using the CK direct method, we obtain the similarity reduction of coupled KdV equation, which is then explained in detail by group theory. To check the Painlevé integrability of coupled KdV equation, the reduction equation is also classified by means of the Painlevé test, and three types of P-integrable models are found. Finally, it is shown that the coupled KdV equation has kinds of traveling wave solutions, including conoidal periodic wave solution, soliton solution, and so on.
Asymptotic solution for fractal soliton of disturbed Nizhnik-Novikov-Veselov system
A class of nonlinear disturbed Nizhnik-Novikov-Veselov system is studied. Using the special asymptotic method, the asymptotic solution for fractal soliton of corresponding system is obtained.
Fault diagnosis for a class of output-coupling complex dynamical networks with time delay
Fault diagnosis is a challenging issue in complex dynamical networks. In the real-world complex dynamical networks, there exists much uncertain information, such as unknown topological structure and uncertain node parameters. Based on network outer synchronization, an approach to fault diagnosis is proposed for a class of output-coupling time delay complex dynamical networks with unknown node parameters. Output variables are used to construct the controllers. A few conditions satisfying outer synchronization are specified from Lyapunov stability theorem. The proposed approach can be used to monitor the online evolution of time-delay network topological structure. Numerical simulations are given to verify the effectiveness of the proposed approach.
A method of solving a class of disturbed Lorenz system
A solving problem for the Lorenz system in atmospheric physics is considered. First, a set of variational iterations is constructed by using the generalized variation principle. Then, the initial approximate solution is determined. Finally, using the variational iteration, each approximate solution for corresponding model is found. The generalized variational iteration method is an analytic method, and the obtained solution can be analytically operated further.
Detection of weak signal based on the sea clutter scattering
Sea clutter scattering is analyzed in the paper. The stochastic differential equations are given for the physical quality of sea clutter. The diffusion process model is built by using Ito formula. These processes are represented as Ito stochastic differential equations, which enables the identificating their stochastic volatilities with certain free functions that serve as calibrating the model. Finally the correlation detection method is used to detect weak signal from sea clutter.
Numerical simulation of negative oxygen ion generation and temporal evolution in atmospheric plasma
The generation process and temporal evolution of negative oxygen ions in a atmospheric plasma are numerically simulated in this paper. The results show that there exists a knee point in the attenuation process of negative oxygen ions, followed by a long time stationary phase. The density of negative oxygen ions in the stationary phase has a linear relation with the initial electron number density. Moisture content has a large effect on the temporal evolution of negative oxygen ions.
Dynamics of cubic and quintic nonlinear Schrödinger equations
We solve one-dimensional(1D) cubic and quintic nonlinear Schrödinger equations by the symplectic method. The dynamical property of the nonlinear Schrödinger equation is studied with using diffenent nonlinear coefficients. The results show that the system presents quasiperiodic solution, chaotic solution, and periodic solution with the cubic nonlinear coefficient increasing, and the breather solution reduced into a fundamental soliton solution under the modulation of the quintic nonlinear coefficient.
Entanglement and nonlocality for generalized Greenberger-Horne-Zeilinger state
With the help of Svetlichny's inequality, we obtain an analytical expression of the quantum nonlocality for generalized Greenberger-Horne-Zeilinger(GHZ) state composed of a (GHZ) state and a W state. The numerical results between tripartite entanglement and nonlocality for generalized GHZ state are discussed.
Wigner function of two-mode squeezed number state and its properties
By means of the entangled state representation as well as the Wigner operator in such a representation, the Wigner function of the two-mode squeezed number states is derived. The properties of corresponding Wigner function in the phase space are discussed by numerical calculation. The results indicate that Wigner function distribution in the phase space should be influenced by the correlation and the entanglement between two modes of two-mode squeezed number state.
Decoy-state quantum key distribution with practical light source
The performance of active decoy-state quantum key distribution (QKD) system with a practical light source is compared with that of passive decoy-state QKD. The effect of statistical fluctuation due to a finite data size on final secret key rate is analyzed. This procedure is based on the standard error analysis on the assumption that all the variables measured in the experiment fluctuate around their asymptotic values. The relation between key generation rate and secure transmission distance is shown with exchanged quantum efficiency of threshold detector (ηd=1 and ηd=0.4) under the condition of active decoy-state (or passive decoy-state ) QKD which we pick the data size to be N=6.0×109. This analysis will provide important parameters for practical QKD experiment.
Effects of external field parameters on conversion from ultracold atoms to heteronuclear triatomic molecules
We investigate the effects of external field parameters, including the strength of Rabi pulse, its width, and single-photon detuning, on conversion from ultracold atoms to heteronuclear triatomic molecules by two-photon stimulated Raman adiabatic passage. It is found that the conversion efficiency of the system decreases first with the strength of the Stokes pulse increasing, then oscillates, and finally approaches a stable value, which is less than 1. But for the pump pulse, the efficiency first increases with the increase of the pulse intensity, and then approaches 1 quickly. The results show that the two pulses play different roles in the conversion. The pulse width can not only determine the final conversion efficiency, but also be used to reflect the time needed for stable conversion. The system has a higher efficiency of conversion for red detuning pump laser, but the blue detuning is not conducive to the formation of the molecules. In addition, the differences of the adiabaticity and conversion efficiency among different reaction pathways are discussed.
Stochastic resonance of square wave signal in an overdamped harmonic oscillator
The output power and the signal-to-noise ratio of an overdamped harmonic oscillator are calculated in the case of square wave signal input. The corresponding stochastic resonance phenomenon and the comparison with the case of cosine signal input are discussed. Results reveal that there appear the stochastic resonances in these two cases, and the phenomenon in which the resonance and suppression are coexistent, but the coexistence phenomenon appears in the different stochastic resonance curves for these two models.
Realization of the discrete chaotic system based on SET-MOS circuits
A new method of realizing a discrete chaotic system using the hybrid architecture of single-electron transistor (SET) and metal oxide semiconductor (MOS) is proposed in this paper. The transfer characteristic for two parallel SETs with a biased current source is investigated and the corresponding S-shape piecewise linear function model is established. Based on this model a one-dimensional discrete mapping system is first constructed, and the dynamics of the system is then analyzed through one-dimensional mapping process bifurcation diagram and Lyapunov exponents, and the corresponding discrete chaotic system is finally designed through the electronic circuit of SET-MOS hybrid architecture. All these indicate that our approach not only is feasible but also has some advantages such as simple circuit structure and good integration compared with existing methods.
Global control of chaotic systems based on linear state feedback
By analyzing structural characteristics of nonlinear vector field for a class of chaotic systems, a new approach to controlling chaos globally and rapidly is put forward. Based on linear state feedback, an independent stable equation of some state variables is separated. Controlled chaotic systems degenerate gradually into stable linear systems. Nonlinear quivering phenomenon is eliminated completely further. The approach can be used to control Lorenz system families or new chaotic systems with similar structures. A class of simple controllers is designed to guarantee that closed-loop systems are globally asymptotically stable at the origin. Numerical examples illustrate the shortcut and the validity of the presented approach in this paper.
Research on impulsive synchronization approach ofparameter uncertain hyperchaotic systems with time-delay
In this paper, based on the Lyapunov stability theory, the impulsive synchronization asymptotic stability condition for different hyperchaotic systems with time delay and parameter uncertainty is first presented by using the linear feedback of state variable error between the slave system and the master system as the impulsive control signal. After the synchronization, a digital communication system with time delay is provided to achieve secure communication. This scheme is of high security and robustness. Moreover, computer simulations show that in the communication system, the synchronization of the systems could be achieved quickly, and by using chaotic cipher sequence to encrypt the digital signal, the useful information signal can be recovered effectively from the receiver.
A fast algorithm with convergence for generalized predictive function control of Hénon chaotic system
A kind of fast generalized predictive function control algorithm with convergence of tracking for Hénon chaotic system is proposed. First, based on the existing generalized predictive function control algorithm, the matrix inversion computation in the control law is avoided because special basis functions are selected according to the motion characteristics of chaotic system and the change trend of practical control input. Then, by introducing the determinate feedforward gain matrix into performance index function, it is convergent that the output of Hénon chaotic system follows reference signal. The simulated results show the effectiveness of this algorithm.
Control of chaos solely based on PSO-LSSVM without usiing an analytical model
For a chaotic system with nonlinear ity and uncertainty, it is difficult to obtain the satisfactory performance using general control methods. A least square support vector marchine (LSSVM) control method based on particle swarm optimigation(PSO), is proposed for chaos control. Optimizing two parameters of LSSVM model by PSO abilities of the fast convergence and whole optimization, thus aroiding the blindness of man-made choice, the LSSVM-PSO model can enhance the capability of forecasting. The proposed method does not need any analytic model, and it is still effective in the presence of measurement noises. Simulation results with a Logistic mapping and Henon attractor show the effectiveness and feasibility of this method.
Study on fast synchronization of chaos
In radar, communication and other engineering applications, fast synchronization is needed because of the limited time of transmitting signal. However, the convergence rate of conventional synchronization is slow. To resolve the problem, a fast synchronization algorithm is proposed. According to Taylor expansion, nonlinear controller is designed to make the control matrix of error equation satisfy critical conditions for synchronization and further to optimize the control matrix, so fast synchronization can be achieved with only one step operation. In addition, given the practical engineering launches only one state variable, in this paper are take the typical continuous Duffing system and discrete Logistic system as examples and design the fast synchronization driven by only one variable. Finally, simulation results show that compared with common single coupling and OPCL synchronization, the proposed algorithm has fast convergence rate, strong anti-noise cap ability, and strong engineering practice significance.
Image scrambling based on Logistic uniform distribution
Most algorithms of image scrambling transformation based on Logistic map are currently dedicated to permutation rules and methods without considering design philosophy. In this paper, we propose a new image bit permutation algorithm based on the Logistic map. This algorithm with firmly mathematic theory is designed by following the scientific course from theory to practice. According to the characteristics of chaotic sensitivity to initial condition and large key space, starting from Logistic map, the transformation which can generate uniformly distributed random variable in the interval based on Logistic at μ=4 is developed. Utilizing this generated uniform random variable, random permutation algorithm based on interchange position is obtained. For measuring permutation strength of the proposed random permutation algorithm, the corresponding permutation strength testing algorithm is designed. Based on this permutation algorithm, the image bit permutation algorithm is described. When used to image and compared with Baker Ye and Yoon algorithm, the proposed image bit permutation method exhibits large key space, extreme sensitivity to initial condition, effective capability for dissipating high correlation among pixels and increasing information about entropy value. Results show that this proposed scrambling scheme with firmly theoretical foundation can enhance image security significantly.
17.5 Gbit/s random bit generation using chaotic output signal of mutually coupled semiconductor lasers
Based on two mutually coupled semiconductor lasers linked by fiber, a chaotic seed signal with a 10 GHz ultra-broadband is obtained experimentally. Adopting an 8-bit analog-to-digital converter, the seed signal is converted into a binary bit stream. By an exclusive-OR operation and the most significant bit rejection, a random bit sequence at a rate up to 17.5 Gbit/s, which has passed both the National Institute of Standard and Technology statistical test and the Diehard test, is obtained.
Adaptive anti-synchronization of unified hyperchaotic system with fully unknown parameters
In this paper, We investigate the adaptive anti-synchronization in a unified hyperchaotic system with unknown parameters. First, according to the Lyapunov stability theory, We achieve an adaptive controller and show that the controller can make a unified hyperchaotic system with unknown parameters asymptotically stable at a fixed point. Second, by the adaptive anti-synchronization method, We design an adaptive anti-synchronous controller and thereby achieve the hyperchaotic system synchronization. Finally, numerical simulations show the effectiveness of the scheme.
The bound for a class of four-dimensional hyperchaotic system and its synchronization
In this paper, a class of four-dimensional continuous autonomous system is studied. It has only one balance under certain conditions but it shows a complicated dynamic behavior. The equilibrium points and lyapunov exponents of the system are analyzed. The bound of this system is estimated and the expression of the bound is presented. In addition, the complete synchronization is also discussed by designing a linear controller. Finally, the corresponding numerical simulations are performed.
Unified projective synchronization of chaotic system
A unified method for the projective synchronization of chaotic system is proposed in this paper. The universal model of chaotic projective synchronization is established by constructing a generalized proportion matrix and an appropriate response system. All kinds of synchronized schemes can be achieved by varying the generalized proportion matrix, including generalized projective synchronization, dislocated projective synchronization and generalized hybrid dislocated projective synchronization and so on. The stability analysis in the paper is proved using Lyapunov stability theory. Numerical simulations of generalized hybrid dislocated projective synchronization for multiscroll chaotic attractors system and hyperchaotic Qi system verify the effectiveness of the proposed method.
A new network structure entropy based node difference and edge difference
Entropy is a very important indicator which describes the heterogeneity of the networks. Two kinds of structure entropies, which are based on degree distribution and relative degree respectively, have some problems to describe the characteristics of network structure. Because they focus only on one of "node" or "edge" factors. In this paper, We consider the difference between "node" and "edge" to define a new network structure entropy. The theoretical analyses and the simulation experiments on regular network, random network and scale-free network prove that this new network structure entropy is more effective to reflect the characteristics of network structure, especially more reasonable to describe the sparse network and star network.
Phase transitions and the mean first passage time of an asymmetric bistable system with non-Gaussian Lévy noise
This paper aims to investigate an asymmetric bistable system driven by non-Gaussian Lévy noise. The stationary probability density functions are obtained by the Grünwald-Letnikov scheme, and the effects of noise intensity and stability index on the stationary probability density are examined. Phase transitions can be observed though a qualitative change of the stationary probability distribution, which indicates that the phase transitions are induced by the asymmetric parameter and the stability index of Lévy noise. Additionally, the mean first passage time is considered, and different mechanisms for the effects of asymmetric parameter, noise intensity and stability index on first passage time are also obtained.
Synchronizing fractional chaotic systems with different orders
To synchronize fractional chaotic systems with different orders, a method is proposed in which a fractional chaotic system with different orders is changed into a fractional chaotic system with the same order but different structures, according to the properties of fractional differential equation. This method is successfully used to synchronize fractional Lorenz chaotic systems. Numerical simulation demonstrates the effectiveness of the method.
Reduction of 1/f noise in semiconductor devices based on wavelet transform and Wiener filter
In order to reduce universal 1/f noise in semiconductor devices, a method with combining lifting wavelet transform and Wiener filter is presented. Firstly, the iteratively reweighted least square method is introduced to fit the power spectrum of 1/f noise and estimate its parameter, and then an appropriate wavelet can be selected. Secondly, the signal with 1/f noise is decomposed by lifting wavelet transform. Considering the fact that the wavelet transform whitens 1/f noise, Wiener filter is used to treat the wavelet coefficient of each layer. Allpass filter is optimized to adjust the phase frequency response of Wiener filter, and the phase of filtered wavelet coefficient is not changed. Finally, the useful signal embedded in 1/f noise is retrieved by the inverse lifting wavelet transform. Experimental study demonstrates the proposed procedure and verifies its effectiveness, and the experimental data are acquired from a force sensor developed for minimally invasive surgery robot. The results show that the method works very well in minimizing 1/f noise, and so the resolution of the sensor increases 25%.
A new pseudo-random number generator and application to digital secure communication scheme based on compound symbolic chaos
A new concept of compound symbolic chaotic series is proposed. According to the kneading pair series in symbolic dynamics, by compounding a pseudo-random series with sub-series on condition of kneading rules we obtain a new symbolic chaotic series which is then transformed into a pseudo-random binary number (PRN) series. The length of the new PRN series elongates at a speed of geometric procession with iteration number. Theoretical and experimental analyses both prove that the above algorithm provides an effective PRN generator. To apply the algorithm to digital secure communication, a new cellular automata is established. With the automata, the data expansion is avoided, the encryption is finished quickly, the obvious avalanche effect can be produced, and thus the security is improved.
Ground state properties of Rn isotopes within the relativistic mean field theory
The ground state properties of Rn isotopes are studied within the framework of relativistic mean field theory. The pairing correlation is treated by the BCS method. The calculation results are in good agreement with the experimental data. The quadrupole deformations can be founded mainly in the regions with neutron number far from magic number (N=110-124) and (N=129-142). In the regions where the neutron number is larger than the magic number(N=127-142), the hexadecapole deformations are also significant. The isotope shift for Rn isotope is also studied and a drastic change in the slope of the curve is found near the magic neutron nuclei.
First-principles calculation on electronic structure and optical properties of iron-doped SnO2
By the full-potential linearized augmented plane wave method (FP-LAPW), we investigate the electronic structures and optical properties of Fe-doped SnO2 system, including the density of states (DOS), band structure, dielectric function and other optical spectra. The calculation indicates that the Fe doped materials are all direct transition semiconductors with half-metallic property. With the increase of Fe-doping concentration, the Fermi level goes into valence band gradually, and the band gap reduces with the coupling of Fe atoms increasing. Moreover, impurity can change the property of the bond formation to some extent, and make it have metallic bond characteristic. Furthermore, we find that the optical spectrum (such as absorption spectrum), extinction coefficient, etc are blue shifted, corresponding to the imaginary part of dielectric function. The peaks are related to the transition of electrons, which indicates internal relationship between the electronic structures and optical properties theoretically.
The structure and analytical potential energy function of the ground state of HNO molecule
The ground electronic state and the reasonable dissociation limit of HNO molecule are determined based on the group theory and the atomic and molecular reaction statics. The energy, the equilibrium geometry and the harmonic frequency of the ground electronic state of HNO are calculated using the density functional theory B3LYP method in combination with the 6-311G ** basis set. The computational results show that the ground state of HNO molecule has CS symmetry, its ground electronic state is X1A', and the equilibrium parameters of the structure are RH—N=0.1065nm, RN—O=0.1200 nm,∠H—N—O=108.60°, dissociation energy De=15.379 eV, bending vibrational frequency ν1=1575.6351 cm-1, symmetric stretch frequency ν2=1673.2890 cm-1, and asymmetric stretch frequency ν3=2837.7856 cm-1. Then the analytic potential energy function of HNO molecule is derived by the many-body expansion theory. The potential curves correctly describe the configurations and the dissociation energy for the HNO molecule.
Control of atomic path in projectile cold atom gyroscope
Cold atoms possess low velocity, narrow velocity distribution as well as good matter wave coherence, thus they have been used to achieve cold atom interferometers. The interferometers with Sagnac effect form atom gyroscopes which can measure rotation rate accurately. Here we report our recent progress in building a projectile cold atom gyroscope. We achieve the accurate control of the bidirectional projectile cold atom motion through the use of a homemade direct digital frequency synthesizer.
Optical characterization of neutron detection crystal Li6Gd(BO3)3:Ce
Colorless and transparent Li6Gd(BO3)3:Ce crystals are grown with the Czoralski method. Their optical characteristics and luminescence processes are also investigated. The ultraviolet-vaccum ultraviolet (UV-VUV) transmittance spectra are measured and the result shows that absorption peaks due to Ce3+ ions and Gd3+ ions, and the absorption band related to charge transfer band of Ce4+ ions are present. According to the UV-VUV excitation and emission spectra, it is found that there appear luminescences of 5d→4f radiative transitions of Ce3+ ions and of 4f→4f radiative transitions of Gd3+ ions, and also Gd3+→Ce3+ energy transfer. The X-ray and γ-ray stimulated luminescence spectra show that the scintillation light of the crystal is mainly from Ce3+ ions.
Analysis of momentum and energy resolutions of the reaction microscope
Based on the working principle of the reaction microscope and the technical parameters employed in our setup, all the possible factors which affect the momentum resolutions of the recoil-ions and the electrons are analyzed. The resolution dependences on the parameters are discussed in detail. The target extension is critical to the momentum and energy resolutions. For electrons the energy resolution is sensitive to the momentum anti-parallel to the extraction electric field: the larger the momentum, the worse the resolution is. The results are applicable to both longitudinal and transverse reaction microscopes.
Simulations of one-dimensional transverse laser cooling of Cr atomic beam with Monte Carlo method
A well collimated atomic beam plays an important role in laser focused Cr atom deposition. The simulations of one-dimensional (1D) transverse laser cooling of Cr atomic beam is performed with the Monte Carlo method. Taking into account the stochastic initial conditions of each atom, isotopes other than 52Cr, longitudinal velocity distribution and transverse divergence, the atomic beam cooled by laser is optimized and evaluated. The obtained results are consistent with experimental. In addition, with picking out the trajectories of isotopes other than 52Cr that are not cooled by the laser the center maximum value can be reduced by 9.3%, and the FWHM is increased by 11% of the transverse distribution.
Cluster-plus-glue-atom model in bcc solid solution alloys
In the present work we propose the cluster-plus-glue-atom model for bcc solid solutions by establishing periodic packing geometries of CN14 basic clusters in bcc lattice to reflect the idealized chemical short-range order near solute atoms. The model is expressed by cluster formula (glue)x, where the cluster center is occupied by a solute having the largest negative enthalpy, mixed with the solvent, and other solute atoms serves as glues or substitute for the solvents in cluster shell. The 1 ∶1 cluster model (glue atom)1 is specially emphasized that guarantees to a maximum extent the glue-cluster nearest neighbors and hence forms a most efficient configuration. This 1 ∶1 model is conducible to the design of a low-V hydrogen-storage V1 alloy and a Nb1 alloy with low Young’s modulus combined with high strength.
Effect of Co+ implantation on structural and optical properties in single-crystal TiO2
Ion implantation technique is used for doping Co+ to single crystal TiO2(001). The implanted energies and the fluences of Co+ are 40keV and 1×1016cm-2; 80 keV and 5×1015, 1×1016, 5×1016, 1×1017cm-2; 120 keV and 1×1016cm-2, respectively. And then, the structural and the optical properties of all samples are characterized by using X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), UV - Vis diffuse reflectance spectroscopy (UV-Vis DRS), and these impurities in implanted samples are also analyzed. From the XRD spectra of implanted samples we observe that the greater damage is caused with the increase of the kinetic energy of incident ions. UV - Vis diffuse reflectance spectroscopy measurement shows that the absorbance of visible band is enhanced in all the implanted samples, and the optical band gap decreases with implanted ion fluence increasing from 5×1015cm-2 to 5×1016cm-2.
Total ionizing dose effect of 0.18 μm nMOSFETs
A 0.18 μm MOSFET with shallow trench isolation is exposed to a γ-ray radiation. The parameters such as off-state leakage current, threshold voltage, transconductance, gate leakage current, and subthreshold slope are analyzed for pre- and post-irradiation. By introducing constant sheet charges at the shallow trench isolation oxide sidewall, good agreement between 3D simulation and experiment result is demonstrated. We believe that the thin gate oxide is insensitive to radiation, and the radiation induced charge trapping in the shallow trench isolation still leads to macroscopic effects such as drain-to-source leakage current, ultimately limiting the tolerance of CMOS circuits.
Effects of controllable defects on thermal conductance in a nanowire with a quantum box
By using the scattering-matrix method and the scalar model of elasticity, we investigate the effect of controllable defects on low temperature thermal conductance in a nanowire with a quantum box geometry. It is found that the thermal conductance can be controlled by adjusting the parameters of the defects. The size and the position of the defect can induce the variation in thermal conductance. It is also found that the behavior of the thermal conductance versus temperature is different for different types of defects.
Phase transition of atomic chain in the one-dimensional Frenkel-Kontorova model
The effect of the initial velocity of boundary atom on the motion of an atomic chain is studied by the one-dimensional Frenkel-Kontorova model. The obatined results show that the three phases could be observed in our simulation, these being harmonic phase when v<v1, choatic phase when v1<v<v2 and uniformity phase when v>v2. It is aslo shown that the two critical velocites(v1,v2) are strongly influenced by the number of atoms and the depth of the substrate potential.
Effect of interface contacts between TiO2 particles on electron transport in dye-sensitized solar cells
Based on sol-gel and screen-printed method, nanoporous TiO2 thin films obtained under different sintering temperatures and times are adopted in dye-sensitized solar cells. According to FESEM, TiO2 particles tend to compact through touch contact under low sintering temperature, but touch contact is substituted by surface contact when the temperature is up to 510 ℃, which results in larger particle coordination number. Moreover, the influence of different contact ways between TiO2 particles on the electron transport is investigated by IMPS/IMVS technology. The results indicate that with the sintering temperature increasing from 420 ℃ to 510 ℃, the electron transport time (τ d) decreases while the electron effective diffusion length (L n) increases, owing to the increased contact surface between TiO2 particles. However, when the sintering temperature increases up to 550 ℃, the porous structure of the TiO2 electrode collapses and new surface state appears on the TiO2 surface, leading to the increase of τ d. It is suggested that the larger short-circuit current density (Jsc) and efficiency (η) can be obtained when the sintering temperature of nanoporous TiO2 film is in a range of 480-510 ℃.
STM tip-induced atomic motion on the top of film supported by a metal substrate
We investigate the scanning tunneling microscopy (STM) tip-modulated atomic motion on the top of Co island and interlayer mass transport on the island edge based on the molecular static (MS) method. Our results show that STM manipulation has an important effect on Co atomic diffusion on the top of Co island and on the island edge. The interaction of the STM tip with the adatom and the strong shape transitions in Co island and in the Cu(001) substrate result in the change of the jump diffusion barrier on the top of the island, the Ehrlich-Schwoebel(E-S) and exchange barrier on the island edge. It is found that by adjusting the distance between the tip and the substrate one can reduce the diffusion barrier of the above three diffusion processes and transform the growth mode of the Co films from 3D to 2D.
Mechanism of the influence of the interaction between interstitial H atom and doped atom on the dehydrogenation performance of LiNH2
The first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the mechanism of the influence of interaction between interstitial H atom defect and doped atom on the dehydrogenation performance of LiNH2. We obtain the most stable structure of LiNH2 by geometrical optimization, and calculate the binding-energies, interstitial H atom defect formation energies, densities of states (DOSs), and electric charge populations for LiNH2 and doped LiNH2. Studies show that the results of binding-energy cannot reflect the dehydrogenating properties of LiNH2 and doped LiNH2. In equilibrium, there are a number of interstitial H atom defects; the formation energy of interstitial H atom defect is reduced by doping Mg and Ti, which increases the concentration of interstitial H atoms. Interstitial H atoms can induce the defect energy level in the gap, which reduces the width of the gap, and improves the dehydrogenation performance of LiNH2. The strength of N-H bond in [NH2]- is weakened by interstitial H atom, so that hydrogen atoms in LiNH2 is relatively easy to release. The covalent bond between interstitial H atom and N atom of [NH2]- explains the escape of NH3 from the dehydrogenation reaction of LiNH2 system. The strengths of N-H bonds are not equal in doped LiNH2, a part of N-H bonds are weaker, and other N-H bonds are strong, the hydrogen atoms are easy to release from weaker N-H bonds.
Formation abilities and electronic properties of Mg-TM-H (TM = Sc, Ti, V, Y, Zr, Nb) crystal
Theoretical studies of structures, cohesive energies,reaction enthalpies and densities of states (DOSs) of Mg7TMH16 (TM=Sc, Ti, V, Y, Zr, Nb) compounds are performed using the first-principles method based on the density functional theory in the generalized gradient approximation. The cohesive energies are calculated to analyze the stability, and the formation abilities of Mg7TiH16 and Mg7NbH16 are stronger than others. The obtained formation enthalpy for hydride Mg7TMH16 is used to investigate the possible pathways of formation reaction. The calculated formation enthalpy changes show that the decomposition temperature of Mg7TMH16 is lower than that of MgH2. The electronic DOSs reveal that all the hydrides studied here exhibit metallic characteristics.
Theoretical investigation of elastic, electronic, and optical properties of zinc-blende structure GaN under high pressure
The elastic, electronic, and optical properties of zinc-blende structure GaN under high pressure are investigated by using a first-principles ultra-soft pseudo-potential approach of the plane wave based on the density functional theory. The calculated results show the dependences of the elastic constant, the bulk modulus, the young modulus, and the energy gap on the applied pressure, and the results are in good agreement with the experimental and theoretical values. Furthermore, the dielectric function, optical reflectivity, refractive index, absorption coefficient and energy-loss function of GaN are analyzed in terms of the accurately calculated band structure and density of state. The conclusions drawn from the calculations offer theoretical basis for the design and application of GaN.
Selective adsorption of small molecules on grafted polymers
A density functional approach to the description of the selective adsorption of a binary mixture of small molecules on a surface grafted with the square-well chains is proposed. The excess Helmholtz free energy functional of the system is divided into two contributions from the hard-sphere repulsion and the square-well attraction respectively. In the bulk phase, the equation of state of Liu and Hu (Liu H L, Hu Y 1996 Feuid Phase Equilibra 122 75) is used to calculate the free energy of the repulsive part and the equation of state of Li and He (Li J L and He H H 2009 Feuid Phase Equilibria 276 57) is used to calculate the free energy of the attractive part. A simple weighted density approximation is adopted on both parts to construct the functional. Using this theoretical approach, the structures of the grafted polymers and the selective adsorptions of binary square-well fluids on the grafted layer at different temperatures are investigated. The theory predicts that the brush thickness increases linearly with the grafting density but non-linearly with temperature and the brush thickness tends to sateration at high temperature. Given the chain length and grafting density, the theoretical calculation also reveals that the polymer brush has strong selective adsorption cap ability at low temperature and the cap ability will weaken greatly when the polymer brush is heated above the temperature of sateration.
First-principles study of influence of dopants Fe on the dehydrogenation properties of VH2
In this paper, the influence of doping Fe on the electronic structure and the dehydrogenation property of VH2 is investigated by using the plane wave ultrasofi pseudopotential method which is base on the first principles of density functional theory (DFT). The calculated results are as follows: (1)the unit cell volume, the cell parameter, and the alloy formation heat of VH2 gradually decrease with the increase of Fe; (2) the fermi level electron density increases by dopping Fe; (3)the population the and electron density of V-H bond both decrease with doped Fe. These results indicate that the stability is declined and the interaction between V and H atom is weakened by adding Fe into the VH2 system. So it comes to the conclusion that the hydrogen desorption property of VH2 can be improved by adding Fe.
Influence of doped PEDOT ∶PSS on performance of polymer solar cells
In this paper, we investigate the doping effect on conductivity of poly(3,4-ethylene dioxythiophene):poly (styrenesulphonic acid)(PEDOT ∶PSS)and its influence on performance of polymer solar cell. The experiment demonstrates that the conductivity of PEDOT ∶PSS is improved obviously by doping polar solvent dimethyl sulfoxide (DMSO). The maximum of the conductivity is 1.25 S/cm when the doping concentration reaches 10 wt%, which increases about three orders of magnitude compared with the undoped. Based on doped PEDOT ∶PSS used as an anode buffer layer, the polymer solar cell (ITO/PEDOT ∶PSS/P3HT:PCBM/LiF/Al) shows an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT ∶PSS. Consequently, it improves the whole performance of polymer solar cell. The short-circuit current density (Jsc) of 11.09 mA·cm-2, the open circuit voltage (Voc) of 0.63 V, and the fill factor (FF) of 63.7% are obtained under 100 mW/cm2 air-mass solar simulator illumination, yielding a 4.45% power conversion efficiency (η).
A study of CuPc-doping MEH-PPV/PCBM organic photovoltaic devices
We fabricate efficient bulk heterojunction organic photovoltaic (OPV) device based on poly(2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), with copper(Ⅱ) phthalocyanine (CuPc) used as a donor and -phenyl C61-butyric acid methyl ester (PCBM) serving as an acceptor. The power conversion efficiency of the MEH-PPV/PCBM OPV device with 15% CuPc (1.41%) increases by 12% compared with that of the standard MEH-PPV/PCBM device (1.26%). The efficiency improvement can be attributed to the CuPc supplemental absorption and higher mobility than MEH-PPV, leading to increased short-circuit current density.
Effects of gradient disorder on electronic transport in quasi-one-dimensional nanowires
Considering both the gradient decay of the real disorder and the contact scattering, we investigate the electronic transport in quasi-one-dimensional nanowires by developing a decomposition elimination method for Green's function matrix. In the presence the contact scattering, the conductance oscillates with energy. For some energies of incident electrons, an abnormal enhancement is obtained in the average conductance due to the destroyed coherence by the introduction of much low disorder, showing that there appears a new conductance peak. In the absence of disorder gradient, the average conductance firstly decreases then increases with disorder strength, indicating that there exists a localization-delocalization transition. In the presence of linearly decaying disorder, the average conductance increases slightly in a strong disorder region. In the case of the Gaussian-type decaying disorder, the average conductance decreases exponentially and the localization-delocalization transition disappears, which is different from previous thereotical result. The results are helpful for the design and the application of quasi-one-dimensional nanowires device.
The origin of EPIR effect in Nd0.7Sr0.3MnO3 ceramics
Polycrystalline ceramic Nd0.7Sr0.3MnO3 is synthesized using high-energy ball milling and post heat treatment method. The properties of electric transport are measured using direct current (DC) 4-wire and 2-wire methods. The results show that both the grain (phase) boundary and the electrode-bulk contact interface has interfacial resistance and space charge layer. The two kinds of space charge regions have greatly different effects on the DC transport: for the former, the I-V curve exhibits nonlinear characteristic and no EPIR effect takes place; for the later, however, an obvious EPIR effect is observed even if the I-V curve also shows nonlinear behaviour. It well suggests that for the ceramic Nd0.7Sr0.3MnO3, only the electrode-bulk contact interface can induce the EPIR effect although there is a similar nonlinear I-V characteristic for the grain (phase) boundary and the electrode-bulk contact interface.
Optical and electrical characterization of (BiFeO3)25/(La0.7Sr0.3MnO3)25 multilayered thin films
(001) oriented(BiFeO3)25/(La0.7Sr0.3MnO3)25 multilayered thin films are fabricated on (001)SrTiO3 substrate by rf-magnetron sputtering. UV-vis absorption spectrum analysis in a photon energy range of 1.2-6.4 eV is carried out, and the result shows that in a range of 1.3-2.1 eV the absorption is enhanced compared with that on SrTiO3 substrate. And the optical band gap of BiFeO3 is around 2.7 eV, which is in accordance with other reportsed results very well. Furthermore, the current-voltage curves are measured in a temperature range of 100-300 K, and the analyses according to several dielectric conduction models exhibite that the space-charge-limited conduction is dominated in the fabricated (BiFeO3)25/(La0.7Sr0.3MnO3)25 multilayered thin films.
Coherent controlling surface plasmon transport properties in Ag nanowire by classic optical field
Coherent controlling surface plasmon transport in metal nanowire coupled to quantum dot is investigated theoretically by real-space method. In the calculations, the dispersion relation of metal nanowire is supposed to be linear and the quantum dot is a cascaded three-level system. The calculations reveal that whether the surface plasmon is transmitted or reflected by turning off or on the classic field can be controlled. The surface plasmon transmission and reflection spectra can be controlled by adjusting the intensity and the circular frequency of classic optical field even the energy of surface plasmon and quantum dot is not matched. The dissipations affecting on the transport properties are also discussed.
Theoretical research on optical properties of gain-assisted plasmonic coupled resonator optical waveguides
Active materials are proposed to fill into plasmonic coupled resonator optical waveguide constructed with metal rings. Optical properties including transmission, dispersion relation and group index of the waveguide are illustrated by performing the transfer matrix method analysis and the finite difference time domain simulation. The results show that the anomalous and the normal dispersions of the active material near the resonance frequency will help to flatten or slope the dispersion relation produced by the geometric structure, leading to an amplified or attenuated group index of the waveguide. Additionally, we can real-time tune the optical properties of the waveguide by electrically or optically pumping the active material. Our results verify a feasible way for the application of such a waveguide in high desity integration of optical circuits.
Effects of end groups on the rectifying performance in D-B-A molecular rectifiers
Using the density-functional theory and the non-equilibrium Green’s function method, we investigate the electronic transport properties and rectifying performances of four different molecular devices based on different end groups from the same D-B-A molecule. The results show that the end groups can significantly affect the rectifying performances of such molecular rectifiers, because the end groups can influence the coupling effects between the molecule and the electrodes, thus changing the delocalization of molecular orbitals, and further changing their transport properties and rectifying performances. More interestingly, it is found that the rectifying directions and working mechanism for all of our studied systems are in disagreement with ones proposed originally by Aviram and Ratner. This property can be rationalized through the asymmetric shift of molecular levels under biases of different polarities.
Transport properties of two-dimensional electron gas in lattice-matched InAlN/GaN and InAlN/AlN/GaN materials
The lattice-matched InAlN/GaN structure is one kind of emerging material with high conductivity and used in GaN-based high electron mobility transistors (HEMTs). The transport properties of lattice-matched InAlN/GaN structure and InAlN/AlN/GaN structure are studied. The samples are grown using pulsed metal organic chemical vapor deposition on sapphire substates. Both structures show temperature-dependent Hall mobilities with a typical behavior of two-dimensional electron gas (2DEG). Theoretical analysis of the temperature dependence of mobility is carried out based on the comprehensive consideration of various scattering mechanisms such as acoustic deformation-potential, piezoelectric, polar optic phonon, dislocation, alloy disorder and interface roughness scattering. It is found that the dominant scattering mechanisms are the interface roughness scattering and the polar optic phonon scattering for both structures at room temperature. The insertion of AlN spacer layer into InAlN/GaN interface exempts 2DEG from alloy disorder scattering, more importantly results in a better interface, and restrains greatly interface roughness scattering. The influence of sheet density on 2DEG mobility is also considered, and the upper limit of density-dependent 2DEG mobility is given for lattice-matched InAlN/GaN and InAlN/AlN/GaN structures and compared with many reported experimental data.
High electron mobility lattice-matched InAlN/GaN materials
InAlN can be in-plane lattice matched (LM) to GaN, and the formed InAlN/GaN heterostructure is one kind of materials with high conductivity to be used in GaN-based high electron mobility transistors (HEMTs). It is reported that the high-mobility InAlN/GaN material is grown by using pulsed metal organic chemical vapor deposition (PMOCVD) on sapphire, and the Hall electron mobility reaches 949 and 2032 cm2/Vs at room temperature and 77 K, respectively. The two-dimensional electron gas (2DEG) is formed in the sample. When 1.2 nm thick AlN space layer is inserted to form InAlN/AlN/GaN structure, the Hall electron mobility increases to 1437 and 5308 cm2/Vs at room temperature and 77 K, respectively. It is shown by analyzing the results of X-ray diffraction and atomic force microscopy and the features of PMOCVD that the crystal quality of InAlN/GaN material is quite high, and the InAlN layer LM to GaN has smooth surface and interface. The high mobility characteristics of InAlN/GaN and InAlN/AlN/GaN materials are ascribed to the fact that the 2DEG has a comparatively low sheet density (1.6×1013-1.8×1013 cm-2), the alloy disorder scattering is weakened in the high-quality InAlN crystal since its compositions are evenly distributed, and the interface roughness scattering is alleviated at the smooth interface where the 2DEG is located.
Improvement of resistive switching in Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructures
Ti/Pr0.7Ca0.3MnO3/Pt and Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructures are prepared using a pulsed laser deposition (PLD) technique, and the resistive switching of the heterostructures is investigated. The Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructure, which has a La0.67Sr0.33MnO3 modulation layer, shows superior characteristics of resistive switching. In particular, the switching ratio and the fatigue properties are improved greatly in this heterostructure. The mechanism of resistive switching in Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructure is also discussed in this paper.
Electrical and optical properties of Cu-Al-O thin films sputtered using non-stoichiometric target
Taking account difference in sputtering rate between Cu and Al, we use a polycrystalline CuAlO2 target with a ratio between Cu and Al being 0.9 ∶1 to prepare the Cu-Al-O film by RF magnetron sputtering. The electrical and the optical properties of the thin film are influenced by the temperature of the substrate. When the substrate temperature is around 500 ℃, the film has a good transmission of 70% in the range of the visible light. Calculated by the fitted formula, the direct band gap is 3.52 eV,and it is in good agreement with the theoretical value. Near room temperature, the thin film conforms to the semiconductor thermal activation mechanism, when the substrate temperature is about 500 ℃, the film conductivity reaches 2.48×10-3 S·cm-1.
Effects of interfacial Ru, Pd, Ag, and Au insertion layers on the anisotropic magnetoresistance in Ta/NiFe/Ta trilayers
Ta/NiFe/Ta trilayers are commonly used in various commercial sensors based on anisotropic magnetoresistive(AMR) effect. Technologically it is desirable to reduce NiFe film thickness to diminish the demagnetization effect for the smaller and smaller devices. However, the AMR ratio of thin NiFe film decreases rapidly with film thickness decreasing when the NiFe film is thinner than 20 nm. Our previous work revealed that the AMR ratio and the thermal stability of Ta/NiFe/Ta trilayers can be significantly improved through interfacial Pt addition due to the enhanced interfacial spin-orbit scattering and the suppressed magnetic dead layers. In this paper, 4d and 5d elements including Ru, Pd, Ag and Au, are also introduced at the interfaces of Ta/NiFe/Ta films fabricated by DC magnetron sputtering. It is found that the insertion of interfacial Pd layers leads to an appreciable AMR enhancement in the as-sputtered state and after annealing. Insertion layers of Ag and Au with small surface energy and relatively low melting point suffer from thermal interdiffusion and seriously deteriorate the AMR of the annealed films, whereas Ru insertion layers exhibit improved thermal stability. The present results indicate that the AMR of Ta/NiFe/Ta films can be notably affected by the extremely thin interfacial insertion layers due to the changed interfacial spin-orbit scattering, magnetic dead layer and atomic interdiffusion.
Pressure induced band-gap changes in (Ba0.5Sr0.5)TiO3 (BST) from first-principles calculations
The high-pressure behaviors of crystalline (Ba0.5Sr0.5)TiO3 (BST) are investigated, using the first-principles calculations based on the density functional theory. The results show that as pressure increases, the band gap of BST first increases and peaks at around 55 GPa, and then gradually decreases. The analysis of density of states shows that in the low-pressure region (0<P<55 GPa), the increase in band gap is due to the formation of anti-bonding states and bonding states in the conduction band and valence band, respectively. In the high-pressure region (P>55 GPa), the delocalization phenomenon in dominant due to the fact that the delocaligation action exceeds the force of bonding state and anti-bonding state, which results in the decrease of the band gap.
Vibrational effect on external field control of charge transmission in molecular nano-junction
With the weak-coupling approach in molecular vibrational normal coordinate, the charge transmission under external optical field through molecular nano-junction is studied. From the charging energy point of view, the sequential charge transmission is analyzed and the current-voltage characteristics under external optical field are studied. It is found that the vibrational effect of molecule is the key factor of the removal of Franck-Condon blockage under external optical field. Furthermore, the effects of charging energy and intra-molecular vibrational energy redistribution (IVR) in charge transmission under external optical field are studied in detail.
Electric tunability of microwave permeability dispersion behaviors of metamaterials
By embedding a capacity-variable diode into a split ring resonator (SRR), it is found that the effective capacitance of such an SRR element can be varied by the biased voltage of diode. Therefore the resonance frequency and effective permeability of an SRR element can be tuned. Based on these results, a smart microwave magnetic metamaterial is proposed. Employing the finite-difference time-domain and retrieval method, the variations of resonance frequency and permeability of the SRR element are simulated and calculated by changing the biased voltage. It is found that with the decrease of capacitance due to the increase of biased voltage, the resonance frequencies are shifted towards lower values, and so are the resonance frequencies of permeability dispersion. Finally, the difference in permeability dispersion behavior between SRR structure and natural magnetic material (for instance, ferrite) has been pointed out.
Room-temperature ferromagnetism observed in Si-Al2O3 composite film
Room-temperature ferromagnetism (FM) is observed in Si-Al2O3 amorphous composite film. The magnetic moment is the highest in the case of the Si-Al2O3 composite films with the Si content being 15 vol.%, and distinct domains are detected in our films. The difference in magnetism property between sample annealed in Ar atmosphere and untreated composite film indicates that the observed ferromagnetism does not originate primarily from oxygen defects. It is concluded that the ferromagnetism arises from the direct coupling between defects. These defects orignate from the interface between Si particles and Al2O3 matrix. By varying the Si content in the film, one can change the defect density and thereby control the strength of the ferromagnetic coupling.
Integration of SRO/PZT/SRO/Ni-Al/Cu/Ni-Al/SiO2/Si ferroelectric capacitor with copper
To integrate ferroelectric capacitor with copper thin film, SRO/Ni-Al/Cu/Ni-Al/SiO2/Si stack is fabricated by magnetron sputtering with Ni-Al as the barriers between Cu and SiO2/Si and between Cu and SRO simultaneously in order to segregate Cu from its adjacent oxide layers for avoiding interdiffusions/reactions when samples are annealed at a high temperature. XRD and AFM are employed to study microstructure and surface morphology respectively. The Cu diffraction peaks and the uniform surfaces are found in SRO/Ni-Al/Cu/Ni-Al/SiO2/Si stack at a high temperature of 750 ℃, implying that the SRO/Ni-Al/Cu/Ni-Al/SiO2/Si stack possesses excellent stability. It is also found that growing at the lower temperature followed by annealing at a high temperature is better than current growing at the room temperature followed by annealing at a high temperature in that the former can relax stresses and reduced the roughness of interfaces to prevent the destruction of barrier and Cu layers at the high temperature. Moreover, PZT is grown on a SRO/Ni-Al/Cu/Ni-Al/SiO2/Si stack by the sol-gel method to construct a ferroelectric capacitor with copper, and the microstructure, the ferroelectric performance and leakage are investigated. The good ferroelectric properties of the capacitor with copper are presented, including a saturated hysteresis loop, remnant polarization ~42 μC/cm2, coercive voltage ~1.0 V, dielectric constant ~1600, leakage current ~1.83×10-4 A/cm2, excellent fatigue resistance, and good retention performance, indicating that high conductivity copper thin film has a promising application to high density and performance ferroelectric memory. Analysis of the leakage fitting also suggests that bulk-limited space-charge-limited conduction (SCLC) acts as the leakage current mechanism in the capacitor.
Design and manufacture of high dispersion mirror
The designed and manufactured high dispersion mirror combines the characteristics of chirped mirror and Gires-Tournois interferometer(GTI) mirror and provides high dispersion compensation with about -800fs2 GDD in a wavelength range of 780-830 nm and about -2500fs2 GDD in a wavelength range 1030-1050 nm, respectively. The dispersion mirror is manufactured by ion beam sputtering. The performance of the mirror has reached the designed values and can compensate the normal dispersion from ultrafst laser system effectively.
Influence of long lifetime absorption process on the measurement of ultrafast carrier dynamics
The wavelength dependence of ultrafast relaxation dynamics of photoexcited carriers in bulk GaAs is studied using femtosecond time-resolved pump-probe transmission spectroscopy under the same photoexcited carrier concentration and the ratio of pump to probe in intensity. Negative and oscillating time-delayed signals are observed at central wavelengths of 760 nm and 780 nm and judged to be incorrect physically by comparson with a simulated computation result. It is found by waveform analysis that they are caused by the phase reversal of the output waveforms from a photodetector, while the phase reversal originates from a long lifetime absorption process existing in GaAs sample. It is pointed out that the phase reversal of the waveform can be corrected by raising the ratio of pump to probe in intensity at the photodetector, so that right transient traces can be obtained. However, raising the ratio is incompatible with the viewpoint that the scattered contribution to the photodetector from pump light should be filtered as much as possible. This result has an important reference value for the acquisition of correct ultrafast dynamics using time-resolved pump-probe spectroscopy.
Photoluminescence enhancement of colloidal quantum dots embedded in a microcavity
We report on the study of CdSe quantum dot microcavity formed between two distributed Bragg reflectors (DBRs). The active region consisting of CdSe quantum dots is embedded in PMMA. We use the transfer matrix method (TMM) to simulate the reflectivity spectrum of the microcavity. We demonstrate an enhancement of the spontaneous emission from the colloidal CdSe quantum dots in the microcavity. After embedding the QDs in the cavity, the full width at half maximum (FWHM) is narrowed to 7.5 nm compared with 27.9 nm of QDs in free space. The emission of the quantum dots is enhanced by a factor of 3.7 due to the microcavity effect.
An analytical thermal model for 3D integrated circuit considering through silicon via
Based on the one-dimensional analytical thermal model for N strata stacked chips without through-silicon via (TSV), the equivalent thermal model for TSV is presented in this paper. And then, the corresponding analytical thermal model with considering TSV is deriveed. Finally, Matlab software is used to verify and analyze the influence of TSV on the thermal management of 3D IC intergration. The analysis results indicate that the TSV can effectively improve the heat dissipation of 3D IC circuits, and the increase of TSVs’s pitch can raise the temperature of the 3D IC circuit.
Influence of source gas flow ratio on the proteins adsorbability of F-DLC film
The fluorinated diamond-like carbon (F-DLC) films are prepared by reactive magnetron sputtering under different gas flow radios with trifluoromethane (CHF3 ) and argon (Ar) used as source gases and pure graphite as a target on the surface of 316L stainless steel (SU316L). Factors which influence the protein adsorbability are discussed by double-stilled water, BCA and FTIR spectra. The results show that the surface of SU316L coated with F-DLC film could obviously reduce the number of adherent platelets and dramatically relieves the deformation of platelets, leading to a ratio of higher albumin to fibrinogen adsorption higher than that with using the SU316L substrates, which indicates that the SU316L coated with F-DLC film can improve the blood compatibility. The film has the highest ratio of albumin to fibrinogen adsorption and the best hemocompatibility when the ratio of gas flow is 2 ∶1. Furthermore, the measurements of the contact angle, the surface energy of films and FTIR spectra show that the ratio of albumin to fibrinogen adsorption and the hemocompatibility of F-DLC coated SU316L depend on the surface energy (hydrophobic nature) of films and the quantity of -CFx bonds (the ratio of F/C) contained in film. The modulating of blood compatibility of the films can be realized by the control of the ratio of source gas flow.
Effects of codoping of Al and Sb on structure and optical properties of ZnO nanorod ordered array thin films
An Al and Sb codoped ZnO nanorod ordered array thin film is deposited on a glass substrate with a ZnO seed layer by hydrothermal method. The XRD, SEM, TEM, and SAED results indicate that the thin film consists of nanorods growing in the direction vertical to the ZnO seed layer, and that the nanorods with an average diameter of 27.8 nm and length of 1.02 μm consist of single crystalline wurtzite ZnO crystal growing along the  direction. Raman scattering analysis demonstrates that the Al and Sb codoped ZnO thin films with the concentrations of Al and Sb of 3.0 at%, 4.0 at%, 5.0 at%, 6.0 at% have Raman shifts of 3, 10, 14 and 12 cm-1 according to Raman shift 580 cm-1 of undoped ZnO nanorod thin film, respectively. Room temperature photoluminescence reveals that the emission intensity decreases at 545 nm and increases at 414 nm in ZnO film prepared by the codoping of Al and Sb. It is because the decrease of Oi and the increase of Zni are caused by the codoping of Al and Sb.
Principles of potential entransy in generalized flow
Some natural phenomena, such as heat transfer, molecular diffusion and electricity conduction, are very similar to each other to some extent. They all could be treated as generalized flows. Based on this kind of similarity, in this paper we generalize the theory of entransy, and define the concepts of potential entransy, potential entransy flux, and potential entransy dissipation. In the system where there is only one kind of generalized flow or two kinds of generalized flows, the conditions under which we can develop the principles of potential entransy are introduced. Furthermore, the minimum principle of potential entransy loss, the extremum principle of potential entransy dissipation and the generalized minimum flow resistance principle are developed and discussed.
Superlattice patterns in a coupled two-layer Lengel-Epstein model
Electrochemical property of Si-O-C composite anode materials prepared by pyrolyzing polysiloxane containing phenyl under different atmospheres
Silicon Oxycarbide (Si-O-C) composite anode materials are prepared by pyrolysis of polysiloxane containing phenyl under argon and hydrogen atmospheres, separately. They are characterized by element analysis, wide-angle powder X-ray diffraction, Raman spectroscopy for comparison with each other. It is found that the silicon oxycarbide composite anode pyrolyzed under a hydrogen atmosphere demonstrates lower irreversible capacity and larger reversible capacity which increases with temperature rising. The one pyrolyzed at 1000 ℃ shows a reversible capacity of 622 mAh/g, and first coulombic efficiency of 59%.The magnitude of the irreversible capacity is correlated with the content of oxygen, and the reversible capacity is related to the content and structure of free carbon, and also the structure of Si-O-C. It is believed that Si-O-C composite materials pyrolyzed under a hydrogen atmosphere could be promising anode materials for lithium ion batteries.
Influence of TiCl4 nanoporous TiO2 films on the performance of dye-sensitized solar cells
The mechanisms of electron transport and back-reaction in dye-sensitized solar cells (DSCSs) are investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The DSCSs with and without TiCl4-treated nanoporous TiO2 films are measured by IMPS/IMVS. The results indicate that the electron lifetime (τn), the diffusion coefficient (Dn), the diffusion length (Ln), the incident photon to current efficiency (IPCE) and the photoinduced charge (Qoc) increase markedly, while the dark current and the electron transit time (τd) decreases for the TiCl4-treated nanoporous TiO2 films. The influence of TiCl4-treatment of nanoporous TiO2 film on the electron generation, the transport and the recombination processes is investigated at a microscopic level.
Fiber-coupled laser-driven flyer plates experiments
A system for the launch of hypervelocity flyer plates is developed, characterized and applied. Laser-driven flyers are launched from substrate backed aluminum-alumina- aluminum sandwiched films. A laser-induced plasma is used to drive flyers with a thicknesses of a 5.5 μm and a diameter of less than 1 mm, and typically, the flyer plates can achieve velocities of a few kilometers per second. These flyer plates have several applications ranging from micrometeorite simulation to laser ignition. The flyer plates considered here have three layers: an ablation layer for forming plasma; an insulating layer; and a final thicker layer for forming the final flyer plate. The optical fiber delivery system determines the spatial profile of the laser spot and power capacity. A technique and procedure for coupling high power laser pulse into optical fiber is developed. The surface finish of the fiber is found to be a critical factor. This fiber optic system is successfully used to launch flyer plates. Measurements of the flyer performance including the mean velocities and planarity are made by an optical time-of-arrival (TOA) technique with using an optical fiber array probe. The flyer shows a good planarity and achieves an average velocity of 1.7 km/s. The relationship between flyer velocity and incident laser pulse energy is investigated.
Improved base-collector depletion charge and capacitance model for SiGe HBT on thin-film SOI
The SiGe heterojunction bipolar transistor (HBT) on thin film SOI is successfully integrated with SOI CMOS by "folded collector". This paper deals with the collector depletion charge and the capacitance of this structure. An optimized model is presented based on our previous research. The results show that the charge model is smoother, and that the capacitance model with considering different current flow areas, is vertical and horizontal depletion capacitances in series, showing that the depletion capacitance is smaller than that of a bulk HBT. The charge and capacitance vary with the increase of reverse collector-base bias. This collector depletion charge and capacitance model provides valuable reference to the SOI SiGe HBT electrical parameters design and simulation such as Early voltage and transit frequency in the latest 0.13 μm SOI BiCMOS technology.
Features extraction from EEG signals induced by acupuncture based on the complexity analysis
Time irreversibility analysis of ECG based on symbolic relative entropy
Popularity based network statistical analysis in peer-to-peer application
There are rich statistical characteristics in a peer-to-peer (p2p) network. The more refined statistical characteristics still need further understanding. In this paper we define the popularity threshold of the resource, and abstract the user network based on the popularity threshold to reflect the refined structure characteristics. Through the emprical study of a workload from a dominant peer-to-peer file sharing system, we confirm that the user network based on the popularity threshold has more clear cluster features than the original network. With the popularity threshold of resource increasing, the clustering is more evident. The homoplasy of users within the same cluster is enhanced. The clustering accuracy is inproved. Furthermore, in this paper we extract the cluster fingerprints which can provide a high representation accuracy in low dimensions.
Human dynamics analysis in online collaborative writing
Investigating the human online behavior has become a central issue for understanding human dynamics in recent years. In this paper we analyze the temporal and content-updating statistical properties of online collaborative writing based on Wikipedia data. Online collaborative writing is one of the important and widespread human online behaviors, which is of great apphication. Empirical result shows that the distribution of inter-event time in collaborative writing is on the multi-scale. That is to say, two time intervals that range from 1 min to 30 min and 30 min to 24 h both obey power-law distribution with exponents equal to 1.62 and 1.16 respectively, while the interval larger than 24 h obeys a distribution whose cumulative form is F(τ)∝τ－b－alog(τ). More investigatons show successive updating behavior and mutual updating behavior working together to lead to the multi-scale distribution of inter-event time. Successive updating behavior leads to the power-law distribution with an exponent 1.62 of interval within 30 min while mutual updating behavior leads to the power-law distribution with an exponent 1.16 of interval ranging from 30 min to 24 h. Furthermore, we find that reverse updating repeats frequently in collaborative writing. The proportions of reversing updating and the updating size are strongly relatively reflect that the updating size is a main reason leading to the relevant content to be preserved. The bigger the updating size, the harder it would be preserved. More statistical analyses imply that "watching dog" and "edit war" exist in Wikipedia editing. Those results are very helpful to deepen the understanding of the human collective behavior, especially of the collaborative developing behavior.
A modified optimal routing strategy based on random walk on complex networks
In our original contributions, we found that the time which a random walker spends in finding a given path is directly proportional to the continued product of the degrees of all the nodes which pass through the given path. In this paper, with our original contributions, we give a modified routing strategy to improve the capacity of the network when all nodes have the same packet-delivery rates. We define an average routing centrality degree of the node to analyze the traffic load on the node with different degrees, and then we analyze the transportation capacity by using the critical value of Rc, the average packet travel time, the average path length and the search information. Both theoretical and experimental results show that compared with the shortest path strategy and the efficient path strategy, the new strategy can enhance the network capability.
Propagation, distribution and detection principle of seismic precursory signals
The earth crust consists of tectonic plates, faults and the fault gouges at their boundaries. In the case of studying such an issue as quasi-static mechanics on the seismic precursory spreading, the crustal lithosphere must be treated as a granular system consisting of large-scale discrete grains. In the process of seismogeny, the rock blocks driven by tectonic forces induce a stick-slip motion by overcoming the friction and the boundary resistance. When the fault gouges between blocks are squeezed and their strength increases to a certain degree, the next block will be pushed to generate a stick-slip motion and the successive rock blocks move gradually in the same way. As in any granular system, the distribution and transfer of force and the movement of the rock blocks must be in the chain-like form. This model is not only reasonably deduced from the physical bases, but also supported by many actual observations. In this work the distribution of force-motion-deformation and the spreading time sequence are given with the simulated experiments and analysis. The main feature of the generated precursory information is described. The essential difference between the understanding of seismic precursor led by viewing the crustal lithosphere as granular system and that as continuum medium is presented. How to acquire effective seismic precursory information as well as how to associate it with the occurrence of earthquake is discussed. Some of the seismology problems are explained reasonably, which can be hardly understood from the continuum medium view point.
A review of the turbulent mixing by wind wave breaking
It is formidable task to provide a comprehensive investigation of wave breaking and its turbulence process. In this review paper, the observations of turbulence by wave breaking and its parameterizations since 1990 are presented. Among them, the following are the most important. (1)Wave breaking induced turbulent mixing process cannot be described by the wall-layer theory, that is, the rate of dissipation of turbulent kinetic energy is not proportional to the inverse of water depth. In fact, a significant turbulent mixing enhancement in near-surface layer for a depth of several meters is achived by wave breaking. The dissipation rate of turbulence kinet energy is one to three orders larger than the value predicted by the wall-layer scaling. (2)In the crest region above the mean waterline, the dissipation rate increases as εdis∝z-2.3, while in the region below the trough, the dissipation rate decreases as εdis∝exp(-αz) or εdis∝z-2. (3)The turbulent mixing length is a critical physical quantity to study the wave breaking. Up to now, however, there has been a large difference between the values given by the previous studies. Extensive work on the mixing depth and turbulent mixing length by wave breaking is also needed in the future.
A new method of retrieving typhoon's sea level pressure fields and central positions from scatterometer-derived sea surface winds
First, UWPBL model(the university of washington planetary boundary layer model) is used to retrieve YaGi typhoon sea level pressure from sea surface wind data of SeaWinds which are obtained from QuikSCAT(called direct retrieving) and these strength results are analyzed. Then the variational method is used to decompose the sea surface winds field into two parts: vortex and irrotational environmental flow field, the UWPBL model is used again to retrieve YaGi typhoon sea level pressure from the vortex flow field, the results of typhoon central positions are analyzed by comparing the results with the results of direct retrieving, NCEP data and typhoon annual reports. It turns out that the accuracy of the typhoon sea level pressure central position is obviously improved. This method offers a new idea for the study of typhoon from microwave scatterometer data.
Remote sensing of atmospheric refractivity from field measurements of vertical receiver array
In this paper we put forward a possibility of refractive index profile retrieval using field measurements at an array of radio receivers through the variational adjoint approach. The derivation of the adjoint model begins with the electromagnetic parabolic equation for a smooth, perfectly conducting surface and horizontal polarization conditions. To deal with the ill-posed difficulties of the inversion, the regularization idea is introduced into the establishment of the cost function. Based on the variational assimilation idea, the retrieval iterative format is constructed. Numerical experiments demonstrate the feasibility of theoretic algorithm for refractivity estimation. However, using the split-step Fourier algorithm to solve the forward model and the adjoint model, the intrinsic error of the solutions will increase with the extension of the propagation range, which reduces the inversion accuracy at long distance propagation. Through adopting a good initial refractivity profile and introducing the background fields in the cost function the inversions could generally be improved.
Tracking refractivity from radar clutter using extended Kalman filter and unscented Kalman filter
Since the traditional statistical and physical algorithms in the inversion of refractivity from radar clutter (RFC) cannot track omni directions in real time, a new filter algorithm (extended Kalman filter and unscented Kalman filter) is proposed. The parameter equation of atmospheric duct, observation operator, state equation of filter arithmetic are derived separately. Finally, the implementation of the iterative inversion filter algorithm is derived. On the theoretical basis, two algorithms above are tested separately with or without considering the variation of refractivity with time. The experimental result indicates that unscented Kalman filter is suited to solve the nonlinear inversion problem, which has significance in theoretical foundation and technological support for practical applications for the future.
X-ray pulsar-based navigation semi-physical simulation experiment system
For the huge costs, the space flight experiment cannot be realized in the preliminary step of X-ray pulsar based navigation (XPNAV) research. So, a kind of XPNAV semi-physical simulation experiment system is designed in this paper. This system is composed of two parts: the simulation of pulsar signal and the calculation of navigation parameters. In the first part, the time when X-ray photon arrives at the solar system barycenter is modeled by non-homogeneous Poisson process, then the output pulse of X-ray detector can be simulated by time transformation. In the second part, the navigation information included in the pulses which have been simulated in the first part can be reached by using the Delta-Correction method. This system can be used to simulate four pulsar signals simultaneously, and to study the process of signal processing and parameters calculation of XPNAV at photo level. This system has the advantage of low costs and high simulation accuracy, and provides a reference for the design of prototype in space flight experiment.
Classification of Blazar objects based on Logistic regression model
We collecte 205 Blazars (142 BL Lacertae objects and 63 flat spectrum radio quasars(FSRQs)),and investigate the correlation between the redshift, the fluxes in the radio band (5 GHz), optical (V band) , X-ray (1 keV), and the X-ray photon spectral index for the BL Lacertae objects and FSRQs by the correlation analysis and Logistic regression model. The results indicate that major influencing factors on Blazar object classification are the redshift, the fluxes in the radio band (5 GHz), and the X-ray photon spectral index. The derived equation is effective as a substantial criterion for Blazar objects classification, of which the accuracy is 91.2%. Our results strongly support the division of Blazar objects into BL Lacertae objects and FSRQs. We compare the properties of BL Lacertae objects and FSRQs from the fluxes in the optical (V band) and X-ray (1 keV), and find that BL Lacertae objects are not significantly different from FSRQs. The implications of these correlations, which support the evolutionary sequence of Blazar objects, are also discussed.