Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010. / Committee Chair: El-Sayed, Mostafa; Committee Member: Perry, Joseph; Committee Member: Wang, Zhong; Committee Member: Whetten, Robert; Committee Member: Zhang, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.E.)--University of Canterbury, 2007. / Typescript (photocopy). "March 2007." Includes bibliographical references (p. 123-127). Also available via the World Wide Web.

Eutectic Fe-C, Ni-C and Fe-C-Si alloys have been solidified directionally in an electron-beam floating zone apparatus under carefully controlled conditions and the resulting morphologies in these alloy systems have been studied as a function of rate. In addition, the transition from the stable iron-graphite (grey iron) to the metastable iron-iron carbide (white iron) mode has been observed and has been related to the iron-carbon/iron-iron carbide double phase diagram by means of undercooling measurements. Interlamellar spacing measurements carried out on both the graphitic and carbidic modes using material of the same composition and purity under identical experimental conditions showed a λaR-1/2 and a λaR-1/3 relationship in the iron-graphite and iron-iron carbide eutectic systems, respectively. / Thesis / Doctor of Philosophy (PhD)

<p> The major purpose of the work described in this thesis has been the development of an analytical model for the electron-beam pumped semiconductor laser system consistent with the main dynamic effects observed experimentally in the stimulated emission. The lasing mat4:!rials used in this study were single crystals of CdS, CdS1e and GaAs. The choice was made on the basis of the availability of high purity single crystals and for representation of both II-VI and III-V materials in the study. </p> <p> Generally, the light output from a pulse-excited semiconductor laser changes in both wavelength and far-field pattern as a function of time during the excitation pulse. The effects investigated divide naturally into two parts. The first part deals with the tuning of the peak output of the stimulated emission toward lower energies during the excitation pulse. The second part deals with a deviation of the far-field radiation pattern of the spatial laser mode with respect to the cavity axis and the changes of this angle with time during the pump pulse. </p> <p> In parallel with these investigations, a theoretical model of the semiconductor laser was developed. This model takes into account spatial variations in the gain and refractive index in the semiconductor material and changes in these profiles with time. The analysis, in terms of the experimental parameters, leads to a prediction of angular tuning of the far-field mode and can account for certain features of faster-than-bandgap wavelength tuning in a number of disparate laser materials. A particularly significant consequence of the model is the prediction of dramatic variations in cavity loss as a function of time. The major consequences of this effect for laser dynamics are discussed. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

Nanopore-based single-molecule analysis of biomolecules such as DNA and proteins is a subject of strong scientific and technological interest. In recent years, solid state nanopores have been demonstrated to possess a number of advantages over biological (e.g., ion channel protein) pores due to the relative ease of tuning the pore dimensions, pore geometry, and surface chemistry. However, solid state fabrication methods have been limited in their scalability, automation, and reproducibility. In this work, a wafer-scale fabrication method is first demonstrated for reproducibly fabricating large arrays of solid-state nanopores. The method couples the high-resolution processes of electron beam lithography (EBL) and atomic layer deposition (ALD). Arrays of nanopores (825 per wafer) are successfully fabricated across a series of 4' wafers, with tunable pore sizes from 50 nm to sub-20 nm. The nanopores are fabricated in silicon nitride films with thicknesses varying from 10 nm to 50 nm. ALD of aluminum oxide is used to tune the nanopore size in the above range. By careful optimization of all the processing steps, a device survival rate of 96% is achieved on a wafer with 50 nm silicon nitride films on 60- 80 micron windows. Furthermore, a significant device survival rate of 88% was obtained for 20 nm silicon nitride films on order 100 micron windows. In order to develop a deeper understanding of nanopore fabrication-structure relationships, a modeling study was conducted to examine the physics of EBL, in particular: to investigate the effects of beam blur, dose, shot pattern, and secondary electrons on internal pore structure. Under the operating conditions used in pore production, the pores were expected to taper to a substantially smaller size than their apparent size in SEM. This finding was supported by preliminary conductance readings from nanopores.

Commercial sterilization of medical devices may be performed using electron beam irradiators, which operate at various electron energies. The potential for activating components of the devices has been discussed, with current standards stating that an electron energy greater than 10 MeV requires assessment of potential induced radioactivity. There does not appear to be a literature citation for this energy limit, but it is the accepted default assumption within the industry. This research was directed at evaluating potential activation in medical products sterilized in electron beam as a function of the electron maximum energy. Monte Carlo simulation of a surrogate medical device was used to calculate photon and neutron fields resulting from electron irradiation, which were used to calculate concentrations for several radionuclides. The predominant mechanism for inducing radioactivity is photoneutron production in metal elements. Other mechanisms, including photoneutron production in deuterium with subsequent neutron capture, neutron capture of the photoneutrons produced in metal elements, and isomeric excitation, are all possible means of inducing radioactivity in similar conditions, but none made a perceptible contribution to activation in these experiments. The experiments confirmed that 10 MeV is a conservative assumption that any lower energy does not create significant activation. However, in the absence of a limited number of elements, the amount of induced radioactivity at 11 MeV and 12 MeV could also be considered insignificant. When based on an estimate of the amount of metal present in a medical device, the sum-of-fractions comparison to the US Nuclear Regulatory Commission exempt concentration limits is less than unity for all energies below 12.1 MeV, which suggests that there is minimal probability of significant induced activity at energies above the generally-accepted standard 10 MeV upper energy limit. / text

This thesis describes several techniques for the optimization of the manufacturing of relief diffractive structures used as optical elements by Electron beam lithograph BS600 in the Electron beam laboratory of the Institute of Scientific Instruments of the Academy of Sciences of the Czech Republic. The Electron beam lithograph BS600 was originally developed and constructed in the Institute of Scientific Instruments of the Academy of Sciences of the Czech Republic for Tesla in 1983, but is still developing, which was published. The Electron been lithograph BS600 is specific in these days because of its accelerating potential and is unique in the world because of the possibility to shape the beam. The optimization of manufacturing of relief diffractive structures, used as optical elements, was mostly reached by analysis, bringing optimal solution for the required effect. Moreover, an algorithm was developed for driving the electron beam position, shape, size and the time of each elementary exposition. The analysis showed that is convenient to use mathematical description of separate lines of diffractive structures. A separate subject was carried out for the calibration of the exposition field of the Electron beam lithograph BS600.

No description available.

The common manufacturing process of prosthetic sockets is usually a time- and labor consuming activity. This project’s purpose was to look for alternative manufacturing methods that could speed up the process and enhance the experience for the patient for example make some personal design or make the socket lighter. The main goal was to investigate which properties could be achieved by applying Electron Beam Melting as an alternative manufacturing process for prosthetic sockets by applying an earlier developed methodology. An investigation of earlier scientific works with the keywords (additive manufacturing, free form fabrication, orthopedic, prosthetic sockets and rapid manufacturing) was done as well as gathering knowledge how to operate and handle the machines necessary to carry out the project. An updated version of the methodology was developed where the design was verified using finite element analysis. With the updated version the methodology contained nine steps, which in short was as follows. First apprehend an inner socket from an orthopedic clinic with a pattern drawn up on it, the pattern is then transferred to a computer environment and manipulated to the desired shape and thickness. A compressive strength test, both virtual and experimental, was designed by a modified version of the ISO-10328 standard and the virtual design was verified before the socket was manufactured in the Electron Beam Melting machine. The manufactured socket was tested in the experimental set-up to verify the virtual one. The result was a personal designed socket of Ti6Al4V including the male pyramid for connection and a suspension system, which consisted of an inner socket and a one-way valve. It was concluded that Electron Beam Melting could be used as an alternative manufacturing process of prosthetic sockets.