Multiple Scattering and Attenuation Phenomena in Diffraction Imaging

The problem of cross sectional (tomographic) imaging bf objects with diffracting sources is addressed. Specifically the area of investigation is the effect of multiple scattering and attenuation phenomena in diffraction imaging. The validity of either the Born or the Rytov approximations is the basic assumption behind all the inverse scattering techniques in diffraction tomography. To test these techniques When these assumptions are not satisfied, we have developed a computational procedure for the calculation of the “ true” scattered fields from a multi-component object. Using this procedure, the performance of two available diffraction reconstruction techniques is examined in the presence of multiple scattering effects. The simulation results show the superiority of the Synthetic Aperture technique. We have also studied the role of attenuation in the reconstruction techniques. To calculate the scattered fields from an object in the presence of attenuation, new computer simulation programs are developed. These codes are used in a simulation study of the effect of the attenuation parameter on the object reconstuctions. [reconstruction

The CRC Plotting Package

The CRC Plotting Package is a device independent graphics system. Subroutines for generating graphics exist for programs written in FORTRAN or C. A program called Qplot exists to plot binary vectors generated as the output of any program

A New Method for Reliability Calculation of the Active Systems with Time-Dependent Failure Rates based on Weibull Distribution

Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the most studies in the reliability area, it is assumed that the failure rates of the system components are constant and have exponential distributions. This distribution and its attractive memory less property provide simple mathematical relationships in order to obtain the system reliability. But in real word problems, considering time-dependent failure rates is more realistic to model processes. It means that, the system components do not fail with a constant rate during the time horizon; but this failure rate changes over the time. One of the most useful statistical distributions in order to model the time-dependent failure rates is the Weibull distribution. This distribution is not a memory less one, so it was impossible to apply simple and explicit mathematical relationships as the same as exponential distributions for the reliability of a system. Therefore, researchers in this field have used simulation technique in these circumstances which is not an exact method to get near-optimum solutions. In this paper, for the first time, it is tried to obtain a mathematical equation to calculate the reliability function of a system with time-dependent components based on Weibull distribution. Also, in order to validate the proposed method, the results compared with exact solution that exists in literature

TOMOGRAPHIC IMAGING WITH DIFFRACTING SOURCES (SCATTERING, DOPPLER, ULTRASOUND)

The problem of cross sectional (tomograhic) imaging of objects with diffracting sources is addressed. Specifically the two areas of investigation are: the diffraction effects in Doppler ultrasonic imaging and the effect of multiple scattering and attenuation phenomena in diffraction imaging. The past theoretical contributions in Doppler ultrasonic imaging have borrowed heavily from the electromagnetic case. In these contributions most points of departure between the ultrasonic and electromagnetic cases were taken care of by heuristic incorporation of factors in the derived formulas. A theory is presented that is more complete in the sense that it specifically accounts for the diffracted fields of the transducer aperture (assumed to be a source of a Gaussian focussed beam), the interaction of these fields with the scattering sites, and the interaction of the transducer aperture with the back-scattered fields. The theoretical formulations are utilized in the implementation of a series of computer simulations of a typical Doppler ultrasound system to examine the role of different parameters of the system. The validity of either the Born or the Rytov approximations is the basic assumption behind all the inverse scattering techniques in diffraction tomography. To test these techniques when these assumptions are not satisfied, we have developed a computational procedure for the calculation of the true scattered fields from a multi-component object. Using this procedure, the performance of two available diffraction reconstruction techniques is examined in the presence of multiple scattering effects. The simulation results show the superiority of the Synthetic Aperture technique. We have also studied the role of attenuation in the reconstruction techniques. To calculate the scattered fields from an object in the presence of attenuation, new computer simulation programs are developed. These codes are used in a simulation study of the effect of the attenuation parameter on the object reconstructions

On the Estimation of Porosity in Composites by Oblique Angle Illumination

Reported here are some preliminary computer simulation results on the feasibility of using oblique incidence ultrasound for the detection and estimation of porosity in composites. In the oblique incidence approach, the composite is illuminated at off normal angles in such a manner that the reflected returns from the fibers are in directions away from the illuminating transducer. Since the scattered returns from porosity tend to be more omnidirectional than the fiber returns, there is a larger received signal in the presence of porosity.</p

Developing a mathematical programming model for dynamic facility layout problem using transportation utilities

The goal of the dynamic facility layout problem is to find the best layout for facilities at a multi period planning horizon so that the total cost of material handling and relocating the facilities is minimized. One of the most important aspects of this issue is to consider the transporters and minimizing material handling time. This paper developed a bi-objective mathematical model which is able to simultaneously minimize the material handling costs between facilities and the cost of rearrangement facilities and material handling time. Due to probabilistic characteristic of the transporters, such as the time of handling operation and existence of the failure, calculating the time required to carry the material using analytical relationships is impossible. Therefore, this paper uses the simulation approach and artificial neural networks. In this approach, a lot of scenarios are generated by combining of variables. Each scenario shows the location of the facilities and how to perform transportation operations in each period. Then each of these scenarios is implemented through computer simulation and simulation results are considered as the response variable. Finally, using input and response variable, an artificial neural network is trained so that it can accurately estimate the time of carrying out the transportation operations. Given that the above problem is a NP-hard; this paper proposes a new Multi-Objective meta heuristic algorithm to optimize the problem and compares the performance of the proposed algorithm with existing algorithms in literature

A new soft computing algorithm based on cloud theory for dynamic facility layout problem

This paper deals with dynamic facility layout problem (DFLP) in a plant which is concerned with determining the best position of machines in the plant during a multi-period planning horizon. The material handling costs and machines rearrangement costs (MRC) are used to determine the best layout. In addition to the positions of machines, the details of transportation such as type of transporters and sequence of transportation operations have a direct effect on material handling costs (MHC). Therefore, it is more realistic to consider the transportation details during DFLP optimization. This paper proposes a new mathematical model to simultaneously determine the best position of machines in each period and to plan the transportation operations. Minimizing sum of MHC and MRC is considered as the objective function. A new hybrid meta-heuristic approach has been developed by combining modified genetic algorithm and cloud-based simulated annealing algorithm to solve the model. Finally, the proposed methodology is compared with two meta-heuristics on a set of test problems