With first-principles calculations, we investigate characteristics of n-and p-type impurities by means of group V and VII atoms substituting selenide atoms in GeSe monolayer. It shows that formation energy increases with increasing impurity atomic size. For group V atom-doped GeSe monolayer systems, calculated transition levels indicate that F, Cl, Br or I dopant provides n-type deeper donor impurity states. However, for group VII atom-doped cases, N, P or As dopant provides n-type shallow acceptor impurity states. It provides theoretical reference for related experimental research.

Sound relaxation frequency is frequency of peak point in sound absorption spectrum, which contains information of gas composition, ambient temperature, and pressure in excitable gases. With characteristics of sound relaxation frequency is linearly in proportion to gas pressure, we propose an algorithm for synthesizing gas pressure by acoustic relaxation frequency calculated with absorption coefficients and sound speeds at two frequencies. Measurement error of sound relaxation frequency is proportional to acoustic measurement error. Specially, as sound absorption measurement errors at the two frequencies are equal, error of synthesized pressure is zero. For methane and its mixtures at a certain temperature, simulation results demonstrate effectiveness of the algorithm and its robustness to acoustic measurement errors. Thus, a novel acoustic method, which is simple, robust, and capable of on-line to detect pressure of excitable gas vessel, is provided.

Analytic relations between acoustic relaxation frequency and external temperature and pressure in multi-component excitable gases are deduced. Theoretical and calculational results show that relaxation frequency is inversely proportional to relaxation time of primary relaxation process, proportional to vibration coupling heat capacity of primary relaxation process, and inversely proportional to external heat capacity. Increase of temperature is related to increase of heat transfer capacity and energy transfer rate of internal and external degrees of freedom, which leads to decrease of relaxation time. It results that relaxation frequency is proportional to ambient temperature. Increase of pressure increases molecular collision rate and causes relaxation time to decrease, which brings about relaxation frequency being linearly proportional to ambient pressure.

Ground states of BrCl in different electric fields from 0 to 0.035 a.u. are optimized by HF(Hartree-Fock) theory at 6-31+G(d,p) basis sets. Optimized parameters, dipole moment, total energy, bond length, charge distribution, the highest occupied molecular orbital energies, the lowest unoccupied molecular orbital energies, energy gap, infrared spectrum and dissociation potential energy surface(PES) are obtained. It shows that with increasing external field from 0 to 0.035 a.u. along molecular axis Z (Br-Cl bond direction), molecular total energy increasing firstly, then decreasing, while bond length and dipole moment decreases at beginning and then increases. Energy gap decreases and atomic charge distribution increases with increasing electric field. IR vibration spectrum of BrCl molecule shows an observable blue shift firstly and then red shift with increasing of external electric field. External electric field of 0.045 a.u. is enough to induce degradation of BrCl with Br-Cl bond breaking. It provides reference for degradation of BrCl in external electric field.

The core philosophy of Material Genome Initiative is transition of way of new material design from traditional "try-and-error" approach to in-silico material design approach where intensive computing and material informatics are employed. It aims to effectively speed up discovery, development, production and deployment of new material two times faster as it is now. It means a culture shift of new material discovery:simulation and prediction first, followed by experiment. An integrated computational material platform that can facilitate high-throughput quantum mechanical simulations and manage simulation lifecycle data is therefore vital. This paper depicts a high throughput computational material platform and software framework, namely, MatCloud, which effectively integrates individual quantum mechanical simulation tasks, data extraction and data storage into an automatic flow in an end-to-end manner without direct human control. Especially, core data curation activities are also integrated into this flow rather than happening at post-simulation stage separately. MatCloud is demonstrated in an example of disorder binary alloy design to be valid and effective.

Burton-Miller method, a complex linear combination of conventional boundary element method (CBIE) and hypersinglar boundary element method (HBIE), is widely used to deal with exterior acoustic problems. The difficult in implementing Burton-Miller method is computing strongly singular integrals (2D problems). Although, many weakly singular/regularization methods have been presented to evaluate these integrals, these methods are still difficult or extremely time consuming. In this paper, analytical integration of strongly singular boundary integral equations discretized with constant element for 2D Helmholtz problems is presented. All singular and strongly singular integrals are analytically evaluated in finite part sense as constant elements are applied to discretize boundary. Contour integral is used for singular and strongly integrals. Validity of formulas is demonstrated with numerical examples.

An isogeometric analysis based on a kind of local bivariate B-spline function and Burton-Miller method is introduced in boundary element method (BEM) for 3D Helmholtz problems.The method avoid efficiently computation of singular and nearly singular integrals aroud singular point of parametric surface.Numerical examples show that the algorithm has good performance in accuracy, efficiency and convergence.The algorithm performs isogeometric BEM (IBEM) with traditional global B-spline shape functions on CPU time and accuracy.The method has potential in engineering applications.

By introducing conductive burning process into classical deflagration-to-detonation transition (DDT) model, transition process from low speed conductive burning to convective burning to detonation was proposed. Transition process in HMX granular bed with 85% loading density was simulated. Development of conductive burning, convective burning and detonation was analyzed. In early stage combustion propagation rate is very slow. It propagates no more than 0. 2mm within 8. 16ms. After onset of convective burning, it tooks 20 ms to form a steady detonation with a velocity of 8 165 m·s^-1. Time to form detonation increases with decrease of particle diameter and ignition pressure.

To study influence of run-time on dynamic characteristics of water/oil separation, a mathematical model is established to describe flow field in vacuum oil purifier. Evaporation of droplet phase transition equations are established, considering effect of three-phase flow of oil/water/vapor and water droplets evaporation phase change. Influences of run-time on oil/water/vapor three-phase volume fraction distribution and axial dehydration rate are analyzed. Dynamic characteristics of oil/water/vapor three-phase flow at different run-time is indicated. Efficiency of dehydration of water/oil separation is enhanced with run-time. It provides a foundation for further research on water/oil separation mechanism in vacuum oil purifier.

With finite-differences approach,we investigate electronic properties of 2DEG in periodic magnetic field modulation. It shows that the system exhibits rich band structures with presence of magnetic field. Width of sub-bands becomes narrower as k_y increases,because the greater k_y is the deeper the potential well is. Due to different effective potential in two regions,k_y > 0 and k_y < 0,band structure in two areas are not consistent. More bound states are in the area of k_y > 0. In addition,we study effect on energy band structure of period,distance of magnetic stripes and strength of magnetization.

Dual-channel 4H-SiC MESFET is optimized for high power microwave applications.Physics-based analytical models for the device are obtained by solving one- and two-dimensional Poisson's equations.Direct-current (DC) and alternating-current (AC) performances of the 4H-SiC MESFET are calculated.The result is in agreement with experimental data.Calculated maximum saturation current density and breakdown voltage are about 420 μA·μm^-1 and 155 V,respectively,which are greater than those of dual-channel structure,275 μA·μm^-1 and 141 V.Resultant maximum output power density is 7.4 W·mm^-1,which is 64% higher than that of dual-channel structure.Cutoff frequency and the maximum oscillation frequency are slightly improved.The power performance is significantly improved while its AC characteristics are not degraded.

Particle finite element method (PFEM) is used to incompressible multi-fluid flows include arbitrary numbers of fluids. Identification of internal interfaces is a key. It is solved by subdivision of mixed elements which are divided into single-fluid elements. To adapt to different fluid properties, a stabilized formulation based on finite calculus procedure is used in fractional step method. Boundary point birth, particle velocity control, and automatically penetration check are used for preventing penetration. Accuracy and reliability of PFEM and interface identification measure are demonstrated with Rayleigh-Taylor instability test and collapse of water column. Finally, seven fluids mixing shows that mixing of an arbitrary number of immiscible fluids could be simulated easily.

A modified PEBI grid generation method with frontal approach is proposed,which is used to investigate reservoir modeling.Validity of the PEBI grid generation method is shown by comparing results of a self-developed reservoir simulator with that of a software CMG.A synthetic case with irregular boundary is investigated.It shows that PEBI grids reduce influence of grid orientation compared with conventional Cartesian grids.It is favorable to describe complex reservoir boundaries accurately and to implant internal constraints such as vertical well,fault in PEBI grid generation method.

Du Fort-Frankel differential format for mode calculation of unstable resonator is presented.A fast finite differential method based on matrix motion and coordinate system transformation is used to calculate output field of a bare cavity and an active cavity.Calculated results are compared with references.It shows that the method is good both in precision and speed in calculating modes of an active unstable resonator with large Fresnel numbers.It can be 20 to 40 times faster compared with a conventional method.With this method,output power of a HF chemical laser is calculated.It shows that the output power increase with decrease of distance between gain medium and concave mirror.This result is valuable to the design of high power DF chemical laser.

Two-phase detonation of RDX particles suspended in air was numerically studied with CE/SE method.Behind leading shock front of detonation,explosive particles are accelerated and heated by the gas flow.Energy is released to support propagation of detonation wave.Dust detonation in a shock tube was numerically simulated.Distribution of physical quantity behind leading shock front was calculated.Parameters of detonation were obtained and they agree well with those in a reference.Dust detonation in a complex channel was numerically simulated.It shows that CE/SE method simulates gas-solid two-phase detonation successfully.

Threshold gain of laser mode in terahertz quantum cascade laser is calculated with finite element method. It shows that contact layer thickness and doping density have far greater impact on threshold gain than waveguide width and lasing wavelength. As thickness and density becoming smaller (greater), threshold gain of TM₁ (TM₀) mode becomes smaller. Far-field characteristics of the beam are analyzed using vector diffraction theory. The beam spot is basically elliptical. With increase of waveguide width or lasing wavelength, far-field divergence angles at x direction decrease or increase linearly. Though the contact layer thickness and doping density for TM₀ mode are different from that for TM₁, their far-field divergence angles at x direction are same. Moreover, far-field divergence angles at y direction are unaffected by waveguide width, and less affected by lasing wavelength. In terms of threshold gain and beam quality, TM₁ is more desirable than TM₀ mode.

A visco-elasticity polymer flooding mathematical model with three phases and five components is established with mass conservation principle.IMPES method is used to simulate the polymer flooding considering tackffying effect of elasticity,action of decreasing residual oil and visco-elasticity of heavy crude.It indicates that visco-elasticity polymer flooding decreases saturation of residual oil and increases viscosity of flooding system effectively,and then enhances oil recovery.As polymer concentration increases, oil recovery rises qucikly,and then tends stable.An optimal value is about 2 000mg·L^-1.As injection rate grows.oil recovery increases and then declines.There exists an optimum value.Oil recovery increases rapidly with the increasing of injection volume,and then tends stable.The best volume is 0.6PV.

Density reconstruction of inhomogeneous dense DT plasmas is studied with simultaneous iterative reconstruction technique(SIRT).In simulation of density diagnostics of a two-dimensional(2D) slice plasma,fast protons used fordiagnostics can be generated with laser-plasma interaction and energy loss of fast protons going through plasmas is crucial.As original and final energies of protons are given,density reconstruction by SIRT method is done without noise level of final energies.Accuracy of the method is better than that of the Tikhonov regularization method based on deviation principle of L-curve.In addition,the SIRT method is available with incomplete data.

Electronic transport of a two-probe system consisting of Au (111) electrodes and two base pairs sandwiched between Au (111) contacts is investigated with density functional theory combined with non-equilibrium Green's function method.It shows that conductance of base pairs is sensitive to distance between electrodes and oscillates.At a fixed gap between electrodes,transverse transport of base pairs under low bias is calculated and is compared with base pairs with a silver ion.It shows that conductive capability of G-C decreases and that of A-T increases as silver ions are combined with base pairs.

Two-dimensional and three-dimensional simulations are performed to investigate supersonic cold gas flows in micro-nozzles using continuum-based no-slip and slip models,respectively.The validity of continuum-based models is examined by DSMC method.The study focuses on low Reynolds number effects,three-dimensional effect and propulsive performance of the micro-nozzle flow.It shows that compared to the prediction of propulsive performance,the simulation of local flow fields needs a more stringent model.The no slip N-S equations are able to predict propulsive performance of micro-nozzles with Kn < 0.03.Reynolds number is a key parameter in governing low Reynolds number effect and propulsive performance.The strong viscous losses can be mitigated and better propulsive performance can be achieved at higher chamber pressures.The micro-nozzle with the ratio of etch depth to throat width more than 13 has a good 2D characteristic as Re > 1000.

The positive and negative frequency expressions of quasi-monochromatic optical fields of a pulse in fiber-optic communication and the positive and negative frequency forms of Fourier transformations and nonlinear Schrödinger(NLS) equations are discussed.Especially,in the solution of pulse spectrum,the negative frequency form of NLS equation should be solved by the negative frequency form of Fourier transformation,while the positive frequency form of NLS equation is solved by the positive frequency form of Fourier transformation.An example is given using split step Fourier method.

We develop a general-purpose two-dimensional semiconductor simulator (GSS),by which the drift-diffusion model and hydrodynamic model are calculated.It calculates steady-state and transient responses of the devices with different materials structures and is applied to an NPN transistor and MESFET.IV curves,electron density distribution and temperature variation are obtained.

We introduce FD-BPM to three-dimensional waveguides and calculate the refractive index of Er³⁺-Yb³⁺ co-doped phosphate glass waveguides.The simulation for a signal light (1.54 μm) and a pump light (0.98 μm) is performed in a Er³⁺-Yb³⁺ co-doped phosphate glass waveguide with FD-BPM.It shows that the scatter loss can be neglected and the optical field is symmetric in a buried waveguide.A buried Er³⁺-Yb³⁺ co-doped phosphate glass waveguide is demonostrated the best to make Er³⁺-Yb³⁺ co-doped phosphate glass waveguide lasers and amplifiers.

A fast simulation annealing (SA) algorithm for the design of diffractive optical elements (DOE) for uniform illumination is presented.The Tsallis statistic and corresponding utility function are introduced into a hybrid algorithm in which the self-iterative and SA algorithms are combined to enhance the efficiency.Compared with traditional SA algorithm,simulated results show that it saves 99% of time to converge the incident energy into a desired region with the same mean square error (MSE).

Ion bombardment affects the stability and lifetime of micro-tip field emission devices. In the Si field emission array (FEA), the atoms in the residual gas may collide with electrons and be ionized, so many ions could be produced. Due to the electrical field in the FEA device, the ions bombard on the Si tips. This paper analyzes the mechanism of ion bombardment on the Si tip. The process concerning ion generation and ion bombardment is numerically simulated. The damage to the tip is analyzed quantitatively, and related conclusions are given.

A 9-bits lattice gas model with temperature effect is applied into the simulation of thermoacoustic prime movers. The self-excited oscillation in a thermoacoustic resonant tube has been simulated. The distribution of two-dimensional temperature field and the evolution process of temperature are presented as well. The effects of the length of stack and of its position on acoustic pressure have also been investigated numerically. The simulation results are valuable to the optimum design of stack. The validity of the lattice gas model for a thermoacoustic engine has been verified by the comparison of the simulated and experimental results, which demonstrates that the lattice gas method is suitable for the thermoacoustic simulation.

Relationships between the choice of the positive and negative frequency expression of optical waves, adoption of Fourier transformation form and form of nonlinear Schrödinger equation are discussed. The generally accepted form of nonlinear Schrödinger equation is the result of choosing the negative frequency expression. In accord with the negative frequency expression, the form of Fourier transformation cannot be chosen at will. When the nonlinear Schrödinger equation is solved using numerical methods based on Fourier transformation, the form of fast Fourier transformation must be paid attention in the programming languages used. In most programming languages, the adopted forms of fast Fourier transformation and inverse transformation are opposite to the forms adopted in nonlinear optics. It is also pointed out that some related numerical errors existed in some references.

Based on many body potential model,the crystallizing processes of Au and Ag are investigated by means of molecular dynamics simulation technique.The pairs analysis method is applied to compare the difference of the local symmetry of molecular cluster between both atoms.In the process of crystallization, the rebuild of the local cluster and the transformation of pairs is found to be from 1661、1441 to 1421、1422.The other important information given is about the microstructure of Au,Ag.

A volume weighting CIC method is developed to compute the node charges and currents in PIC simulation of axial symmetrical plasmas.A set of formulae for computing the node charges and currents is derived.The results given here can be applied to 2(1/2) dimensional electrostatic and electromagnetic PIC simulation of axial symmetrical plasmas.

Monte Carlo method has been used to calculate neutral atom density distributions in Tokamaks. Numerical results for HT-6B, HT-6M are in good agreements with the experimental data.