Induced polarization (IP) tomography measurements as a near-surface geophysical method can provide information about the degree of chargeability of subsurface materials, and are commonly used in mineral exploration, engineering studies (e.g., sediment/bedrock interface identification, crushed zones and faults detection, and landslide and soil properties imaging.), as well as in environmental investigations (contaminant plums identification and landfill characterization). The purpose of these measurements is to obtain the distribution of polarizability characteristics inside an object, generally below the surface, at the boundary of the object, or outside the area in question. The result of such measurements can be mathematically modeled for the specific polarizability properties by the solution of Poisson’s equation restricted by appropriate boundary conditions. In this paper, we focus on the importance of simulating induced-polarization responses and retrieving chargeability distributions in geo-materials to enhance the characterization of subsurface structures. We present the methods for forward modeling and nonlinear inversion of induced-polarization measurements. To this end, in the first step, Poisson’s equation for a two-dimensional ground with arbitrary distribution of conductivity is solved using the finite difference numerical method and in the next step, based on the existing relations between conductivity and chargeability (Siegel’s formulation), the apparent induced polarization response is calculated. Finally, we solve the nonlinear chargeability inversion problem following a nonlinear apparent resistivity inversion. This is achieved by imposing physical constraints to prevent the estimation of unrealistic model parameters, using a Newton-based optimization method. To evaluate the efficiency of the proposed methodology, we utilized the proposed algorithm to two simulated examples and a real data set. Our numerical results show that the algorithm reliably represents the main features and structure of the Earth’s subsurface in terms of the resistivity and chargeability models. All the algorithms presented in this paper have written in the MATLAB programming language.

In the paper a dynamic exact solution in the time domain for dynamic analysis dam-reservior interaction is presented. The dam structure is flexible with infinite reservoir Exact consideration of the radiation boundary condition of the infinite reservoir and deformation of dam structure are included in the formulation which explicitly expresses the physical phenomena of fluid-structure system. The hydrodynamic pressure in the fluid domain of the structure-reservoir system is assumed to be governed by the pressure wave equation. The upstream face of the dam is considered vertical. The dam structure is modeled as a cantilever Euler-Bernoulli beam. The thickness of the dam is assumed to be variable. A new method for analysis of non-prismatic beams is presented. This new method is based on using new functions namely Basic Displacement Functions (BDFs).These functions are obtained by solving the governing equation of motion of a non-prismatic Euler-Bernoulli beam. Using this method dynamic shape functions are efficiently obtained for non-prismatic beams. Interactive behavior of the dam-reservoir system with different geometrical properties is demonstrated by numerical examples when the system is subjected to ramp acceleration and El Centro earthquake ground motions. The results are compared with those of literature and the competency of the method is shown in both economy and exactness.

Low-frequency, high-amplitude surface wave (ground roll) is an old problem in land-based seismic field records. Conventional processing modules are to suppress ground- rolls, such as frequency and velocity filters, which use the Fourier transform. All of these techniques assume that the frequency contents of seismic trace are stationary, but in reality seismic traces have time varying frequency contents. In this study an alternative method to the Fourier transform known as the wavelet transform was used to suppress ground rolls. The key advantage of the wavelet transform over the Fourier transform is that it does not assume that the trace is stationary, and it can also localize the target information in the time-scale domain. The wavelet transform decomposes the seismic trace using basis functions that have finite extent in both frequency and time. In this research, an algorithm was prepared to take the wavelet transform of seismic traces of a shot record. Then a filter for ground roll suppression was designed based on the results of wavelet transform. Finally, the efficiency of this filter was compared to that of the band-pass and F-K filters.

Due to the spherical divergence and specifically absorption in the earth, amplitude of a propagating seism wave varies as a function of time. This stretches the wavelet in time and reduces the time (or vertical) resolution of the seismic sections. To overcome the problem one has to apply so called spatial migration or deconvolution on data. Usually the least square Wiener deconvolution is used to boost up the attenuated frequency components. Unfortunately, the Wiener based deconvolution methods assume that the source generated seismic wavelet is stationary (i.e. its frequency content remains unchanged within the record). A method of deconvolution in the Gabor domain is applied in this paper that considers the seismic data as a non-stationary phenomenon.The Gabor transform (Equation 1) is a windowed or short time Fourier transform, where the window used to isolate the frequency content of input record in time, is a Gaussian type. According to the uncertainty principle, the Gabor transform has the least uncertainty among other windowed Fourier transforms.Please clik on PDF icon to viwe the complet abstract.

This paper presents a time-domain comparator with low supply voltage and low power consumption for using in circuits that comparator’s input common-mode voltages swing is 0 to half supply voltage. To design the time-domain comparator, a delay element with a very high delay-voltage gain is proposed. The purpose of designing this comparator is to achieve high delay-voltage gain, which leads to an increase in the accuracy of the comparator, as well as a significant reduction in power consumption and occupied area compared to conventional time-domain comparators. This time-domain comparator utilizes subthreshold concept and also uses the bulk-voltage of transistor as a comparator input. The proposed comparator is simulated in 0.18µm TSMC technology at 1V supply voltage, which according to the intended application, the supply voltage can be reduced to about 0.4V. The simulation results show that with supply voltage of 1V the proposed comparator consumes 250nW at the clock frequency of 2.5MHz. The figure of merit of 0.1µW/MHz indicates the high performance of the proposed comparator. Based on the Monte Carlo simulation, the offset voltage of this comparator is obtained 2.8mV.

The initial model, Jacobian matrix, Frechet derivatives, and digital look-up tables are essential components in most time-domain electromagnetic (TEM) data modeling methods in layered earth. Computations of these components in the modeling process are time-consuming as their determinations need to use iterative operations. Zohdy introduced an alternative method for the rapid inversion of direct current (DC) resistivity data obtained using the Wenner and Schlumberger electrode configurations. The methodology allows for the inclusion of a flexible number of layers, which are chosen in conjunction with the initial model based on the data-derived knowledge, and avoids large and iterative calculations of Jacobian matrix and Frechet derivatives. This paper presents an endeavor to enhance the outcomes of TEM data modeling or inversion utilizing the Zohdy's technique through the elimination of the look-up tables. In this study, various synthetic models of stratified geological formations are examined using the the above-mentioned methodology. The modeling findings demonstrate robustness even when 5% and 10% noise levels are entered into the dataset. Hence, this approach can be considered as a worthy method for TEM data inversion accompanying some levels of noise in the data.

Numerical modeling has been largely developed in soil mechanics behavior by different methods. Among them, the development of the boundary element method, which is the most suitable one for domains with infinite boundary conditions like soils media, has been restricted by the necessity of deriving the Green's functions of the governing differential equations. Indeed, attempting to solve the three-dimensional boundary value problems for unsaturated soils leads one to search for the associated Green's functions of the governing differential equations.In this paper the governing differential equations of the phenomena are presented which consist of three main groups of equations: 1- equilibrium and constitutive equations of soil's solid skeleton, 2- conservation and transfer equations for air phase and 3- conservation and transfer equations for moisture phase.The associated Green's functions have been manipulated with a few assumptions to first linearize the completely non-linear governing differential equations and next to make possible deriving the results, mathematically. After applying the Laplace transform to eliminate the time variable, Green's functions of the governing differential equations have been derived using the straightforward Kupeadze's method. Then using the inverse Laplace transforms, the completely closed-form Green's functions have been derived in the time domain.Finally, for verification of the results it has been demonstrated that when the conditions approach to the poroelastostatic case, the Green's functions approach to the corresponding poroelastostatic Green's functions as well. As no analytical solutions are available in the literature for the mentioned Green's functions, it seems to be a new experience to introduce a set of fundamental solutions for the unsaturated case for the first time.

Correct information about a power system’s dynamic variables is important and necessary for protection and control issues. Today's power systems, which differ from past systems, face new challenges due to converter-based resources. A solution to these challenges is dynamic state estimation in short time intervals, such as the time domain. This paper simulates a standard 68-bus system in the presence of converter-based resources with a high penetration percentage in DIgSILENT software and compares the performance of four Bayesian filters in estimating the dynamic variables of the synchronous generators of the system using values in the time domain with each other. The four types of filters used include extended Kalman filter, unscented Kalman filter, ensemble Kalman filter, and particle filter.The MATLAB software suite was used for the comparison of the performance of the four filter types in different scenarios, including the presence of measurement and processing noise, extreme noise, network fault, data missing, state estimation time by each filter, and the comparison of time domain method with other methods such as phasor domain. Finally, the advantages and disadvantages of each were identified.