On an Application of the Improved Maximum Product Criterion to Inverse Acoustic Scattering in a Layered Medium

In this paper, we consider the numerical treatment of an inverse acoustic scattering problem that involves an impenetrable obstacle embedded in a layered medium. We begin by employing a modified version of the well known factorization method, in which a computationally effective numerical scheme for the reconstruction of the shape of the scatterer is presented. This is possible, due to a mixed reciprocity principle, which renders the computation of the Green function at the background medium unnecessary. Moreover, to further refine our inversion algorithm, an efficient Tikhonov parameter choice technique, called Improved Maximum Product Criterion (IMPC) is exploited. Our regularization parameter is computed via a fast iterative algorithm which requires no a priori knowledge of the noise level in the far-field data. Finally, the effectiveness of IMPC is illustrated with various numerical examples.

Occam Inversion of Transient Electromagnetic Data in a Layered Medium with Azimuthal Anisotropy

In recent years, the anisotropic study has become a hot topic in the field of electromagnetics. Currently, inversion technologies of transient electromagnetic sounding data are mainly based on the case of an isotropic medium. However, the actual underground electrical structure tends to be complicated and anisotropic. It is often found that the isotropic inversion technologies do not lead to good results for field transient electromagnetic sounding data. We have developed an algorithm for calculating the transient electromagnetic response in a layered medium with azimuthal anisotropy. An occam inversion algorithm has also been implemented to invert the transient electromagnetic data induced by a grounded horizontal electric dipole in a layered medium with azimuthal anisotropy. Synthetic examples demonstrate the stability and validity of the inversion algorithm. Experimental results show different data for inverting have great influence on the inversion results.

Investigation on electromagnetic scattering from rough soil surface of layered medium using the small perturbation method

Electromagnetic scattering from a rough surface of layered medium is investigated, and the formulae of the scattering coefficients for different polarizations are derived using the small perturbation method. A rough surface with exponential correlation function is presented for describing a rough soil surface of layered medium, the formula of its scattering coefficient is derived by considering the spectrum of the rough surface with exponential correlation function; the curves of the bistatic scattering coefficient of HH polarization with variation of the scattering angle are obtained by numerical calculation. The influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the roughness surface parameters and the frequency of the incident wave on the blstatic scattering coefficient is discussed. Numerical results show that the influence of the permittivity of layered medium, the mean layer thickness of intermediate medium, the rms and the correlation length of the rough surface, and the frequency of the incident wave on the bistatic scattering coefficient is very complex.

Electromagnetic Scattering in a Two-layered Medium

The object of this paper is to investigate the three-dimensional electro- magnetic scattering problems in a two-layered background medium. These problems have an important application in today＇s technology, such as to detect objects that are buried in soil. Here, we model both the exterior impedance problem and the inhomogeneous medium problem in R3. We establish uniqueness and existence for the solution of the two scattering problems, respectively.

Propagation Characteristics of Elastic Wave in Layered Medium and Applications of Impact Imaging Method

It is an important subject to probe the structure in the medium by various kinds of detection methods in the geotechnical engineering. Based on the propagation theory of elastic wave in half-space layered medium, the propagation characteristics of elastic wave in layered medium with different elastic parameters are discussed using dynamic analysis of finite element method. It is known that the S-wave velocity, density and thickness of layer are related to the properties of the elastic wave including waveform characteristics, spectral characteristics and time-frequency characteristics. We pay special attention to the structure with low velocity interlayer. The impact imaging method is applied to the grouting construction of the immersed tube tunnel. Data acquisition and analytical method are introduced in detail. The grouting effects can be qualitatively evaluated by comparing the characteristics of elastic wave before grouting with those after grouting. Finally, a quantitative evaluation is obtained according to the relationship between energy response of elastic wave and impedance ratio.

Accurate evaluation of Green's functions in a layered medium by SDP-FLAM

Based on local Taylor expansions on the complex plane, a method for fast locating all modes （FLAM） of spectral-domain Green＇s Functions in a planar layered medium is developed in this paper. SDP-FLAM, a combination of FLAM with the steepest descent path algorithm （SDP）, is employed to accurately evaluate the spatial-domain Green＇s functions in a layered medium. According to the theory of complex analysis, the relationship among the poles, branch points and Riemann sheets is also analyzed rigorously. To inverse the Green＇s functions from spectral to spatial domain, SDP-FLAM method and discrete complex image method （DCIM） are applied to the non-near field region and the near filed region, respectively. The significant advantage of SDP-FLAM lies in its capability of calculating Green＇s functions in a layered medium of moderate thickness with loss or without loss. Some numerical examples are presented to validate SDP-FLAM method.

An inverse algorithm for reconstructing the acoustic parameters of layered medium

The inverse problem in geophysics is to infer the vertical structure from the observed data. The crucial assumption in deriving inversion algorithms obtained for different elementary layer structures. Much of the previous work on this problem for the case of plane wave at normal incidence has consisted of deriving a Schrodinger equation from the basic acoustic and stress-strain equations, and then reconstructing the potential appearing in this equation by using the Gelfand-Levitan procedure. We shall be concerned with structures in which the unknown coefficient has jump discontinuities. Here the unknown potential in the corresponding Gelfand-Levitan framework is highly singular, so much so that the theory breaks down. In this paper it is presented an inversion algorithm based on the Riccati equation,which avoids to solve the problem of singularity. The model experiment was conducted in a sewage pool of a factory. The final result of inversion agrecd well with the direct experimental observation.

Probe frequency- and field intensity-sensitive coherent control effects in an EIT-based periodic layered medium

A periodic layered medium, with unit cells consisting of a dielectric and an electromagnetically-induced transparency （EIT）-based atomic vapor, is designed for light propagation manipulation. Considering that a destructive quantum interference relevant to a two-photon resonance emerges in EIT-based atoms interacting with both control and probe fields, an EIT-based periodic layered medium exhibits a flexible frequency-sensitive optical response, where a very small variation in the probe frequency can lead to a drastic variation in reflectance and transmittance. The present EIT-based periodic layered structure can result in controllable optical processes that depend sensitively on the external control field. The tunable and sensitive optical response induced by the quantum interference of a multi-level atomic system can be applied in the fabrication of new photonic and quantum optical devices. This material will also open a good perspective for the application of such designs in several new fields, including photonic microcircuits or integrated optical circuits.

Model and Emulation of the System for the Passive Electrostatic Detecting People Through the Medium

The plane medium and point charge are regarded as an integral system. The static field＇s distribution situation of the point charge is studied in the medium structure of plane division layers by using mirror image method, drawing the point charge＇s calculation expression of the electric potential in every medium space. The mathematics model of passive electrostatic detecting people through the medium （regular distance between the goal point charge and the medium） is established, using MATLAB software to carry out emulation of the model and analysing the result, establishing the theoretical foundation for studying the technology of the passive static detecting people through the wall.

The Near-Field Microwave Focusing in the Layer Mediums

This paper deals with the microwave focusing in the layer mediums near the antenna aperture. Based on the plane-wave spectrum theory, the relationship between the Hertz potential and the electromagnetic field is discussed. An approach to the description of the field distribution in the layer mediums in case of an arbitary field source is proposed. Given the focusing current distribution over the antenna aperture, the field distribution of the focal region is worked out. In describing the field distribution over the focal region, the integration of spectrum functions in the spectrum domain (kx,ky) is carried out instead of the complicated Fresnel integral. The approximations are obtained by the saddle-point integration. Comparison with experimental results demonstrates the validity of the approach.

Effects of Solid Matrix and Porosity of Porous Medium on Heat Transfer of Marangoni Boundary Layer Flow Saturated with Power-Law Nanofluids

The effect of the solid matrix and porosity of the porous medium are first introduced to the study of power-law nanofluids, and the Marangoni boundary layer flow with heat generation is investigated. Two cases of solid matrix of porous medium including glass balls and aluminum foam are considered. The governing partial differential equations are simplified by dimensionless variables and similarity transformations, and are solved numerically by using a shooting method with the fourth-fifth-order Runge-Kutta integration technique. It is indicated that the increase of the porosity leads to the enhancement of heat transfer in the surface of the Marangoni boundary layer flow.

Mathematical Modeling Algorithms for Creating New Materials with Desired Properties Using Nano-Hierarchical Structures

In the enormous and still poorly mastered gap between the macro level, where well developed continuum theories of continuous media and engineering methods of calculation and design operate, and atomic, subordinate to the laws of quantum mechanics, there is an extensive meso-hierarchical level of the structure of matter. At this level unprecedented previously products and technologies can be artificially created. Nano technology is a qualitatively new strategy in technology: it creates objects in exactly the opposite way—large objects are created from small ones [1]. We have developed a new method for modeling acoustic monitoring of a layered-block elastic medium with several inclusions of various physical and mechanical hierarchical structures [2]. An iterative process is developed for solving the direct problem for the case of three hierarchical inclusions of l, m, s-th ranks based on the use of 2D integro-differential equations. The degree of hierarchy of inclusions is determined by the values of their ranks, which may be different, while the first rank is associated with the atomic structure, the following ranks are associated with increasing geometric sizes, which contain inclusions of lower ranks and sizes. Hierarchical inclusions are located in different layers one above the other: the upper one is abnormally plastic, the second is abnormally elastic and the third is abnormally dense. The degree of filling with inclusions of each rank for all three hierarchical inclusions is different. Modeling is carried out from smaller sizes to large inclusions;as a result, it becomes possible to determine the necessary parameters of the formed material from acoustic monitoring data.

Sound reflection from layered solid medium with rigid and slip interfaces

In this paper, a general model on sound reflection from a layered solid medium with rigid and slip interfaces is proposed by using matrix method. Analytical expressions for reflection coefficients of both longitudinal and transverse waves from the layered solid medium with one or two slip interfaces are derived. Numerical results of sound reflection coefficients from some typical adhesive joints with slip and rigid interfaces are presented, which may be useful for correct choice of technical parameters in ultrasonic evaluation of their interface properties.

Uncoupled state space solution to layered poroelastic medium with anisotropic permeability and compressible pore fluid

This paper presents an uncoupled state space solution to three-dimensional consolidation of layered poroelastic medium with anisotropic permeability and compressible pore fluid.Starting from the basic equations of poroelastic medium,and introducing intermediate variables,the state space equation usually comprising eight coupled state vectors is uncoupled into two sets of equations of six and two state vectors in the Laplace-Fourier transform domain.Combined with the continuity conditions between adjacent layers and boundary conditions,the uncoupled state space solution of a layered poroelastic medium is obtained by using the transfer matrix method.Numerical results show that the anisotropy of permeability and the compressibility of pore fluid have remarkable influence on the consolidation behavior of poroelastic medium.

The quasi-Rayleigh waves in a layered solid medium with a weak interface

The Rayleigh waves in a layered solid medium is dispersive. Using the 'spring' model for a weak interface between two solids, the characteristic equation for the quasi-Rayleigh waves in an isotropic layered solid medium with a weak interface is presented. The numerical results for the typical coating structure with the rigid, slip and weak interface are shown. The influence of the interface stiffness constants on the velocity of the quasi-Rayleigh waves is considered. The numerical results show that the interface characteristics of the coating structure can be nondestructively evaluated by employing the quasi-Rayleigh waves in the low frequency band.

On Estimating Magnitude of a Maximum Sequent Earthquake by Viscoelastic Coulomb Stress Change and a Discussion of the Relationship between the M_S7.3 Earthquakes in Yutian 2008 and 2014

On the basis of the previous studies of the layered crustal model in the Yutian area,combined with the field GPS continuous observation data,we roughly estimate the viscous coefficient of each layer. With the viscoelastic horizontal layer model,we calculate the viscoelastic co-seismic Coulomb stress change caused by the Yutian M_S7. 3 earthquakes 2008 and 2014 respectively. Based on the Coulomb stress change,using the calculation method of "direct "aftershock frequency,we come up with the theoretical earthquake frequency directly related to the mainshock and the co-seismic Coulomb stress change in the study area. Then we put forward a method,based on the comparison of theoretical and actual earthquake frequency or the comparison between theoretical and practical earthquake frequency-distance decay curve fitting residuals,to estimate the magnitude of a maximum sequent earthquake,directly related to the mainshock co-seismic Coulomb stress change. Results calculated by different methods show that the maximum follow-up earthquake magnitude caused by the coseismic Coulomb stress change lies from M_S7. 2 to M_S7. 5 following Yutian M_S7. 3 earthquake in 2008; but that of the 2014 Yutian M_S7. 3 earthquake is M_S6. 3. The former is very close to the Yutian M_S7. 3 earthquake in 2014.Because of the same magnitude,relatively close spatial distance,short time interval,the same region of the external force,the strong correlation between two seismic tectonic and a clear stress interaction,we thus consider that the two Yutian M_S7. 3 earthquakes in 2008 and 2014 constitute a pair of generalized double shock type earthquake. This is consistent with the sequence type characteristic of past "double shock"earthquakes in the region. In this paper,the influence of the magnitude lower limit and the b-value in the relationship of G-R on the results is discussed. As a result,when the viscoelastic coseismic Coulomb stress variation is determined,the lower limit of magnitude has little effect on the maximum sequent earthquake magnitude estimation,but b-value of G-R has a greater impact on the results.

Survey of multi-channel MAC protocols for IEEE 802.11-based wireless Mesh networks

This paper reviews multi-channel media access control（MAC） protocols based on IEEE 802.11 in wireless Mesh networks（WMNs）.Several key issues in multi-channel IEEE 802.11-based WMNs are introduced and typical solutions proposed in recent years are classified and discussed in detail.The experiments are performed by network simulator version 2（NS2） to evaluate four representative algorithms compared with traditional IEEE 802.11.Simulation results indicate that using multiple channels can substantially improve the performance of WMNs in single-hop scenario and each node equipped with multiple interfaces can substantially improve the performance of WMNs in multi-hop scenario.