Ultrasonic transducer modeling is important and fundamental research for nondestructive testing of materials. Traditionally, in most nondestructive evaluation applications, the ultrasonic transducers are modeled as point sources generating spherical wave fronts, line sources generating cylindrical wave fronts, or planar surfaces generating plane wave fronts. In reality, the transducer front face has finite dimensions; it is neither point source nor planar source. This study shows how the ultrasonic field in the neighborhood of a transducer with finite dimension varies in homogeneous and nonhomogeneous media. In this thesis, the pressure variation in front of a transducer face is computed for the following three situations: (1) the transducer is immersed in a homogeneous fluid; (2) the transducer is near a fluid-fluid interface; and (3) the transducer is near a fluid-solid interface using Distributed Point Source Method For the nonhomogeneous fluid medium, both normal incidence and oblique incidence cases have been studied.

Genetic algorithms are used to predict the size and location of an elliptical cavity within a solid half-space. The scattering of ultrasonic waves in the solid half-space with a cavity is modeled using Distributed Point Source Method (DPSM). DPSM which is a semi-analytical technique that utilizes Green’s function is used for modeling because this technique is more efficient than popular but not so efficient Finite Element Method (FEM). FEM is very inefficient for modeling ultrasonic wave propagation problems at high frequencies and for solving an inverse problem one needs an algorithm that can solve the forward problem efficiently. The inverse problem is solved by applying a genetic algorithm to the forward problem to determine the optimum solution. The optimum population size and number of generations are determined. Results and analysis are performed for 3 cases of unknown variables.

Experiments were conducted to examine the cause of lag-phase growth during phenol degradation by mixed microbial cultures that had been acclimated to one of four substrates. Four aerated Imhoff cones were inoculated with wastewater sludge and fed one of four substrates: acetate, egg albumin, vegetable oil, or phenol. Inocula from these cones were injected into batch reactors containing phenol. Time-dependent growth was measured by two methods: most probable number (MPN) and epifluorescence microscopy (EM). The MPN technique was used to distinguish two cell concentrations: total cells and a phenol-degrading community within the total; EM was also used to count total cells. The results indicated that a lag in phenol utilization for all cultures, except the phenol-acclimated cultures, was a result of growth of a phenol-degrading subpopulation, and not due to enzyme induction of the existing population. Similar experiments were conducted using 2,4-dichlorophenol (2,4-DCP), which resulted in no growth and no degradation of 2,4-DCP.

Unique features of behavior of granular materials make constitutive modeling of these materials a challenge that has not yet been answered completely. Because volume changes are so important for the type of behavior exhibited by frictional materials, it is important to correctly incorporate them in constitutive models, both in terms of their rate of development and their magnitude. In this study a number of consolidated drained triaxial tests are performed to find those features of sand behavior that can be considered "material parameters" and can be used for constitutive modeling of granular soils. Special attention is given to those features of material behavior that are related to dilatancy. A number of published experimental data are also analyzed and useful trends of soil behavior are found.

This thesis is based upon a need to re-examine the assumptions and expand upon the results arrived at in recent studies on the flexural stiffness of reinforced concrete columns. A survey is presented of concrete column design over the last 200 years. Elastic and plastic behavior of concrete columns is discussed with respect to stiffness and Euler's buckling load. Some limitations and applications of buckling load are considered. Various current code approximations of stiffness are presented. Four possible methods for computing a more exact stiffness (EI) and their advantages and disadvantages are discussed. The formula EI = M/φ provides the best solution. The two dimensional program RECTCOL which is based on the P-M-φ relationships is developed and explained. Then RECTCOL is used to show how the column flexural stiffness varies with axial load, reinforcement ratio, yield strength of the reinforcing steel, concrete strength, cover, and column dimensions. A flow chart and source code are included by RECTCOL.