A three-Dimensional deflection of the electron-beam resulting a missed joint due to thermoelectric magnetism generated in welding dissimilar metal is experi- mentally and analytically investigated. In theoretical analyisis a narrow welding cavity is assumed to be a paraboloid of revolution. Applying a three-dimensional analytical solution of thermolectric currents, magnetic fiux densities, and deflections of the electron beam are determined from Maxwell's electromagnetic equations. The computed magnetic fields,thermoelectric currents and beam deflection will be compared to experimental results. Factors affect-ing deflection are discussed. The major advantage of welding with a high-power-density-electron-beam is the ability to weld dissimilar metals, unfortunately, can be missed. when the beam from the electron gun is properly aligned with the joint, subsequent deflection of the beam can result in nonsymmetric fusion along a joint, or the fusion zone may miss the joint .One reason responsible for the beam deflection is due to thermoelectric magnetic fields. Since temperature gradients exist between the top and bottom and in front and be-hind the deep and narrow cavity ,thermoelectric currents due to the Seebeck effect are produced in dissimilar metals. The induced magnetic field above and below the top surface therefore deflects the electron-beam and induces a missed joint in S-shaped. In this study, experiments will be conducted to measure missed joints. A three-dimensional thermoelectric and heat conduction model is also to predict deflection of an electron-beam From the surroundings and to bulk workpieces, the entire trajectory of the beam can be determined.a more systematical and realistic understanding on missed joint parameters.

Spiking representing a periodic melting and solidification in the depth of fusion zone during high-intensity beam welding is experimentally and theorectically investigated in this work . A spike is a sudden increase in penetration beyond what might be called the average penetration line. Many spikes have voids in their lower portions because molten metal does not fuse to the sides of the hole, producing a condition similar to a cold shut in a casting. These defects seriously reduce the strength of the joint. Due to the significant role of specular reflection on absorption, an investigation of the beam characteristics, especially the focal location, on spiking is important. Furthermore, as the cavity base oscillates upward and downward relatively from the focal location, a central region subject to direct irradiation changes instantaneously from maximum to zero and vice versa. This leads to several hundred time difference in energy absorption and strongly periodic melting at the cavity base. Physical phenomenon of spiking is obtained by comparing between the measured and predicted data based on scale anlaysis of transport process near the cavity base and energy absorption as a function of focal location.

Cracked beam problem is an elliptic boundary value problem with singularity. It is often used as a testing model for numerical methods. We use numerical and symbolic boundary approximation methods and boundary collocation method to compute its extremely high accurate solution with global error $O(10^{-100})$. This solution then can be regarded as the exact solution. On the other hand, we vary the boundary conditions of this problem to obtain several related models. Their numerical solutions are compared to those of cracked beam and Motz problems, the prototypes of singularity problems. From the comparison we can conclude the advantage of each model and decide the best testing model for numerical methods.

In this thesis, we study the array theory and the array synthesis methods to design a sector antenna composed of a broadside collinear array and a corner reflector that is suitable for base stations. The antenna produces a sector beam in the horizontal plane to reduce the co-channel interference. In the elevation plane the antenna produces a narrower beam in order to achieve a higher gain. A uniform array is known to produce a high side lobe level which will cause serious interference. Therefore, Dolph-Tchebyscheff linear array method and Taylor line source method are utilized for the antenna design. We also design the structure of corner reflector which is combined with an array to form the sector antenna. We also study the switched-beam system, design and fabricate a 4¡Ñ1 microstrip patch antenna array to simulate the operation of the system and measure its performance.

Abstract The occurrence of ripples on the workpiece surface after solidification in electron-beam weld or melting is experimentally and analytically investigated. The maximum accelerating voltage and welding current of electron-beam welder are 60kV and 50mA, respectively, while the workpieces are four different materials containing different quantities of sulfur. Using a scale analysis to account for heat transfer and fluid flow induced by different quantities of surface active element in the molten pool. The result predicted results show good agreement with experimental data.

Increase in consumption of fresh produce over the past decade has resulted in a rise in incidents of foodborne outbreaks due to pathogens. Chemical sanitizers have been extensively used in the industry for decontamination of fresh produce. However, they are ineffective in certain commodities and under certain processing conditions, necessitating the evaluation of alternative technologies. Electron beam irradiated sliced cantaloupe were tested for 21 days of storage for total aerobic bacterial counts, texture, color and sensory parameters as a function of irradiation doses 0, 0.7 and 1.4 kGy and the wash treatments, water and 200 mg/L chlorine applied to the melons before cutting. Melons washed only with water prior to cutting had total aerobic bacterial counts of 4.0, 2.0 and 0.8 log cfu/g on day 0 at irradiation doses of 0, 0.7 and 1.4 kGy respectively. On day 0, melons washed with chlorine prior to cutting had total aerobic bacterial counts of 2.7, and 0.7 log cfu/g at irradiation doses of 0 and 0.7 kGy and below detection limit at 1.4 kGy. Texture measured as compression force was lower only for cantaloupe irradiated at 1.4 kGy. Irradiation did not affect objective color and descriptive attribute flavor and texture sensory attributes of cantaloupe. Irradiation reduced Salmonella Poona by 1.1 log cfu/g at 0.7 kGy and 3.6 log cfu/g at 1.5 kGy. The D-value of S. Poona on irradiated sliced cantaloupe was found to be 0.211 kGy. Among the spoilage organisms, lactic acid bacteria and mold were reduced effectively by irradiation but there was no significant effect on reduction of yeasts. Our results show that electron beam irradiation in combination with chemical sanitizers is effective in decontamination of fresh-cut produce. Electron microscopy images provided valuable information on attachment sites of S. Poona on cantaloupe rind. The ineffectiveness of chemical sanitizers due to possible inaccessibility to pathogens in these attachment sites provides the basis for application of irradiation in decontamination of fresh produce.

A chemical solution composed of paraffin wax, chloroform, and methyl yellow biological indicator was shaped into a solid 3-D apple phantom to determine absorbed dose from e-beams and X-rays. The purpose of this research was to determine the most uniform irradiation treatment on apple-phantoms (a complex shaped target) and GAFCHROMIC® HD-810 films using electron beams from (1) a 2 MeV Van de Graaff (VDG) accelerator, (2) a 10 MeV Linear Accelerator (LINAC), and (3) X-rays from a 5 MeV LINAC. Irradiation with the VDG accelerator confirmed that tilting the apple-phantom yaxis towards the e-beam source by 90 degrees, 45, and 22.5 degrees resulted in more uniform treatment in both the methyl yellow apple phantom and HD-810 film. The phantoms were over-exposed at the top and bottom regions when their y-axis was oriented exactly parallel to the e-beam at 22.5-degrees. The 45-degree orientation ensured uniformity throughout the whole apple surface without overexposing it at the top and bottom. In contrast, the 90-degree orientation resulted in the least effective treatment with the bottom and top region not receiving any radiation. A 10 MeV dual e-beam showed uniform penetration from top to bottom in the HD-810 film and apple phantoms. The HD-810 film responded linearly with doses up to 1.5 kGy while the methyl yellow response was non-linear up to 0.5 kGy maximum. The X-ray irradiation completely penetrated the apple phantoms from top to bottom showing excellent lateral uniformity at different penetration depths.

Research is performed to assess the viability of applying the least squares model to one-dimensional heat transfer and Euler-Bernoulli Beam Theory problems. Least squares models were developed for both the full and mixed forms of the governing one-dimensional heat transfer equation along weak form Galerkin models. Both least squares and weak form Galerkin models were developed for the first order and second order versions of the Euler-Bernoulli beams. Several numerical examples were presented for the heat transfer and Euler- Bernoulli beam theory. The examples for heat transfer included: a differential equation having the same form as the governing equation, heat transfer in a fin, heat transfer in a bar and axisymmetric heat transfer in a long cylinder. These problems were solved using both least squares models, and the full form weak form Galerkin model. With all four examples the weak form Galerkin model and the full form least squares model produced accurate results for the primary variables. To obtain accurate results with the mixed form least squares model it is necessary to use at least a quadratic polynominal. The least squares models with the appropriate approximation functions yielde more accurate results for the secondary variables than the weak form Galerkin. The examples presented for the beam problem include: a cantilever beam with linearly varying distributed load along the beam and a point load at the end, a simply supported beam with a point load in the middle, and a beam fixed on both ends with a distributed load varying cubically. The first two examples were solved using the least squares model based on the second order equation and a weak form Galerkin model based on the full form of the equation. The third problem was solved with the least squares model based on the second order equation. Both the least squares model and the Galerkin model calculated accurate results for the primary variables, while the least squares model was more accurate on the secondary variables. In general, the least-squares finite element models yield more acurate results for gradients of the solution than the traditional weak form Galkerkin finite element models. Extension of the present assessment to multi-dimensional problems and nonlinear provelms is awaiting attention.

We have grown the high quality AlGaN/GaN heterostructure by plasma-assisted molecular beam epitaxy. We obtained the mobility of two-dimensional electron gas of the AlGaN/GaN is 9300 cm2/Vs and carrier concentration is 7.9¡Ñ1012 cm-2 by conventional van der Pauw Hall measurement at 77K. The samples made of the AlGaN/GaN heterostructure were patterned to Hall bar geometry with a width of 20£gm by conventional photolithography. After the photolithography, the nanowire was fabricated by the process of focus ion beam (FIB), and the widths of nanowire were reduced to 900 nm, 500 nm, 300 nm, 200nm, 100 nm, 80 nm and 50 nm respectively. The SiO2 layer and Al electrode were deposed on the samples to form nanowired MOSFETs. We have studied the leakage current measurement on the AlGaN/GaN nanowired MOSFETs at 300K. On the 100 nm and 200 nm width of nanowires, we did not observe the leakage current for the gate voltage work range from -2.5 to 3.0 V and from -0.5 to 0.5 V respectively.

The major purpose of LED is the electroluminescence. We use the time-resolved electroluminescence (TR-EL) method to measure the response time of LED in our experiments. In addition, typical diode has optical beam induced current (OBIC) characteristic in its depletion region. Combining upon physical reaction we can compare TR-EL and OBIC in the same LED. We are using the high frequency function generator, pulsed laser with high repetition rate, laser scanning confocal microscopy and a high frequency phase sensitive lock-in loop to achieve temporal resolution. The response time of LED can be measured in two different physical characteristic.