Effective Dielectric Response of Composites with Graded Material

The effective dielectric response of linear composites containing graded material is investigated under an applied electric field E_0.For the cylindrical inclusion with gradient dielectric function,ει(r)=b+cr,randomly embedded in a host with dielectric constant εm,we have obtained the exact solution of local electric potential of the composite media regions,which obeys a linear constitutive relation D=εE,using hypergeometric function.In dilute limit,we have derived the effective dielectric response of the linear composite media.Furthermore,for larger volume fraction,the formulas of effective dielectric response of the graded composite media are given.

Effective Medium Approximation for Nonlinear Composite Media

We build the perturbation expansion method for nonlinear composite media and extend the EMA for nonlinear effective conductivity. Using the solutions of boundary-value problems of a cylindrical in- clusion, we derive formulae for nonlinear effective conductivity.

Effect of hydrostatic pressure and polaronic mass of the binding energy in a spherical quantum dot

Simultaneous effect of hydrostatic pressure and polaronic mass on the binding energies of the ground and excited states of an on-center hydrogenic impurity confined in a GaAs/GaA1As spherical quantum dot are theoretically investigated by the variational method within the effective mass approximation. The binding energy is calculated as a function of dot radius and pressure. Our findings proved that the hydrostatic pressure led to the decrease of confined energy and the increase of donor binding energy. Conduction band non-parabolicity and the polaron masses are effective in the donor binding energy which is significant for narrow dots not in the confined energy. The maximum donor binding energy achieved by the polaronic mass in the ground and excited states are 2%-19% for the narrow dots. The confined and donor binding energies approach zero as the dot size approaches infinity.

Microwave backscattering from the sea surface with breaking waves

Based on the effective medium approximation theory of composites, the whitecap-covered sea surface is treated as a medium layer of dense seawater droplets and air. Two electromagnetic scattering models of randomly rough surface are applied to the investigation of microwave backscattering of breaking waves driven by strong wind. The shapes of seawater droplets are considered by calculating the effective dielectric constant of the whitecap layer. The responses of seawater droplets shapes, such as sphere and ellipsoid, to the backscattering coefficient are discussed. Numerical results of the models are in good agreement with the experimental measurements of horizontally and vertically polarized backscattering at microwave frequency 13.9GHz and different incidence angles.

Fabrication and characterization of rugate structures composed of SiO_(2) and Nb_(2)O_(5)

Gradient index layers and rugate structures were fabricated on a Leybold Syrus pro deposition system by plasma-assisted coevaporation of the low index material silica and the high index material niobium pentoxide.To obtain information about the compositional profiles of the produced layers,cross sectional transmission electron microscopy was used in assistance to deposition rate data recorded by two independent crystal monitors during the film preparation.The depth dependent concentration profiles were transformed to refractive index gradients by means of effective medium approximation.Based on the refractive index gradients the corresponding samples`transmission and reflection spectra could be calculated by utilizing matrix formalism.The relevance of the established refractive index profiles could be verified by comparison of the calculated spectra with the measured ones.

Vapor Sensing Theoretical Study on Optical Microcavities

When the organic vapors absorbed to the surface of porous silicon(PS), capillary condensation takes place due to the porous structure of the PS layer, accordingly resulting in the effective refractive index changing. For PS multi-layer microcavities, the different resonant peaks shift in the reflectivity spectrum of porous silicon microcavities(PSMs). The optical sensing model is set up by applying Bruggeman effective medium approximation theory, capillary condensation process and transfer matrix theoretically analytical method of one-dimensional photonic crystals. At the same time, comprehensively researched on are the sensing characteristics of PSMs which are exposed to give concentration organic vapors. At last, made is the theoretical simulation for sensing model of the PSMs in case of saturation by using computer numerical calculation, and found is the linearity relation between the refractive index of organic solvent and the peak-shift. At the same time deduced is the peak-shift as a function of the concentration of ethanol vapors.

Numerical simulation of flow and bed morphology in the case of dam break floods with vegetation effect

The purpose of this study is to establish a depth-averaged 2-D hydrodynamic and sediment transport model for the dambreak flows with vegetation effect. The generalized shallow water equations are solved using an explicit finite volume method with unstructured quadtree rectangular grid, and in the hydrodynamic model, a Harten-Lax-Van Leer（HLL） approximate Riemann solver is used to calculate the intercell flux for capturing the dry-to-wet moving boundary. The sediment transport and bed variation equations in a coupled fashion are calculated by including the bed variation and the variable flow density in the flow continuity and momentum equations. The drag force of vegetation is modeled as the sink terms in the momentum equations. The developed model is tested against lab experiments of the dam-break flows over a fix bed and a movable bed in vegetated and non-vegetated channels. The results are compared with experimental data, and good agreement is obtained. It is shown that the reduced velocity under vegetated conditions leads to a decrease of the peak discharge and a rise of the water level of rivers and also an enhancement of the sediment deposition.

Geoacoustic inversion based on reflection model of effective density fluid approximation

In order to obtain the physical and geoacoustic properties of marine sediments,an inverse method using reflection loss of different grazing angles is presented.The reflection loss is calculated according to the reflection model of effective density fluid approximation.A two-step hybrid optimization algorithm combining differential evolution and particle swarm optimization along with Bayesian inversion is employed in estimation of porosity,mean grain size,mass density and bulk modulus of grains.Based on the above physical parameters,geoacoustic parameters,including sound speed and attenuation,are further calculated.According to the numerical simulations,we can draw a conclusion that all the parameters can be well estimated with the exception of bulk modulus of grains.In particular,this indirect inverse method for bottom geoacoustic parameters performs high accuracy and strong robustness.The relative errors are 0.092%and 17%,respectively.Finally,measured reflection loss data of sandy sediments at the bottom of a water tank is analyzed,and the estimation value,uncertainty and correlation of each parameter are presented.The availability of this inverse method is verified through comparison between inverse results and part of measured parameters.

Complex effective depth approximation for soft solid bottom

In this paper, the approximate equation of Chapman's (real) effective depth for Pekeris guide is extended to the complex effective depth approximation whose real and imaginary parts explicate respectively the phase change and energy loss on reflection. It is shown that the homogeneous acoustic field, which comprises the complex effective depth approximation,closely reproduces the character of low modes at small grazing angles, and calculates effectively the acoustic field at longer ranges in shallow water. Application of the complex effective depth approximation can be extended to bottoms having two soft solid layers.