Thesis (M. Sc.)--University of Canterbury, 2006. / Typescript (photocopy). "August 2006." Includes bibliographical references (leaves 105-108). Also available via the World Wide Web.

Thesis (Ph.D.)--Baylor University, 2006. / Includes bibliographical references (p. 201-208).

Glow discharge electron guns are used to generate continuous electron beams at 0.5keV-3.0keV in the intermediate range of gas pressures (0.1mb-10.0mb). Cathodes incorporating internal cavities are used to generate distinct electron beam filaments in both Helium and Argon. The formation of such beam filaments has been investigated using a number of different cathode types, and criteria for the production of stable electron beams are established. The production of an electron beam in a glow discharge is largely determined by the motion of electrons in the Cathode dark space sheath region next to the cathode, and other discharge processes in this region. A theoretical model has been developed to simulate electron motion in the sheath region, and in the Negative glow plasma region, of a Helium discharge with a Cathode fall of between 150V and 1000V. It is shown that the electron flux at the 'sheath/Negative glow boundary becomes increasingly monoenergetic as the Cathode fall rises to 1000V. The results are also compared with experimental spatial emission profiles of the glow in the Cathode dark space and Negative glow regions of a helium discharge. In particular, properties of the Cathode glow region in the sheath are discussed. Aspects of the theoretical model and results from the experimental measurements are also used to discuss discharge processes in the sheath region of cathodes incorporating internal cavities, and mechanisms leading to the formation of the electron beam filaments. The production of fast electrons in a glow discharge has a number of applications, including the excitation of gases leading to laser action. Aspects relating to the excitation of high lying energy states in gases, corresponding to known laser transitions, are discussed. It is shown that the production of helium ions, which are responsible for the excitation of metal atoms via asymmetric charge transfer in metal ion lasers, is theoretically more efficient in an electron beam discharge. The results are compared with the theoretical ion production rates in Hollow cathode discharges, and high-voltage Hollow cathode devices. Several electrode geometries using multiple arrays of electron gun cathodes have been developed. Investigations of an electron beam excited argon plasma suggest that Ar II excited states are pumped directly by single electron impacts, even at very low current densities (~10^-3 A cm^-2). From previous calculations using the 'sudden perturbation' approximation, those ion states known to have large cross-sections for direct electron impact excitation (3p44p2P) appear to be favourably pumped in the electron beam plasma.

Axially-moving materials arise in problems associated with spacecraft antennas, pipes conveying fluid and telescopic robotic manipulators. Flexible extendible beams are a special class of axially-moving materials, in which the axially-moving material is modelled as a slender beam and the mechanism of elastic deformation is transverse bending. Hamilton's principle is used to derive the governing differential equation of motion and system invariant properties of a flexible extendible beam protruding from a rigid wall with prescribed extrusion profile. The mass of the system is not constant and the general analytical solution to the equation of motion is not known. In this study, numerical solutions are obtained using finite-element analysis. However, instead of following the obvious (but cumbersome) approach of using fixed-size elements and increasing their number, in a stepwise fashion, as mass elements enter the domain of interest, a more elegant approach is followed wherein the number of elements is fixed, while the sizes of the elements change with time. To this end, a variable-domain beam finite element whose size is a prescribed function of time is formulated. The accuracy of this variable-domain beam element is demonstrated through the time-integration of equations of motion using various extrusion profiles. Additional verification is performed by the evaluation of the system's invariant quantities, comparison with a special analytical solution, and the dynamic stability analysis of pipes conveying fluid. The effects of wall flexibility, tip mass, and high-frequency axial-motion perturbations to the transverse response of the flexible extendible beam are also examined. In order to gain a deeper insight into the mechanics of this system, the dynamic stability characteristics of the flexible extendible beam are also investigated using various extrusion profiles. The effects of physical damping, tip mass, tip support and wall flexibility on the stability characteristics of this system are examined. The power and versatility of this finite-element formulation is demonstrated in a simulation of an extruding flexible extendible beam which carries a tip mass and protrudes from a flexible envelope beam which imparts three-dimensional rigid-body rotations to the system. / Graduate

The Stark field perturbed spectra of near infrared vibrational overtones of hydrogen fluoride and acetylene have been measured with a high resolution molecular beam laser spectrometer. A high performance laser power build-up cavity (optical resonator) was constructed to measured the weak ro-vibrational transitions of the v₂ + 3v₃ vibrational combination band of acetylene. The measured gain of the build-up cavity was found to be at least 300 out of a potential 2000. The primary reason for the lower than expected gain was attributed to losses induced by the extreme heat build-up on the mirror surfaces. The electric dipole moment for the v = 3 vibrational overtone of hydrogen fluoride was determined to be 1.9614 ± 0.0021 Debye. This result was compared with predictions from the available theoretical models and some theoretical constants were revised based on the current contribution to dipole moment function of hydrogen fluoride. The Stark field perturbed spectra of the v₁ + 3v₃ and v₂ + 3v₃ vibrational combination bands of acetylene were analysed for their polarisability tensors. In order to complete the study, the ground electronic state static polarisability and anisotropy of the polarisability were also determined. They were found to be 3.96A³ and 1.071 ± 0.014A³, respectively. The |1030⁰0⁰> state (v₁ + 3v₃) was observed to be coupled with the |0040⁰0⁰> infrared forbidden state (4v₃) in the presence of the Stark electric field. The resultant analysis produced values of 4.62 ± 0.09A³ for the polarisability and 1.15 ± 0.03A³ for the polarisability anisotropy of the |1030⁰0⁰> state. The difference in energy between |1030⁰0⁰> and |0040⁰0⁰> was determined to be 4.133 cm⁻¹, which compares well with local mode calculations. The measurements of the v₂ + 3v₃ band indicated that the |0130⁰0⁰> state was strongly coupled with another infrared allowed, unidentified (rogue), state in the absence of the Stark field as well as with the infrared forbidden, |1120⁰0⁰> state in the presence of the Stark field. The previously unobserved J = 5 ← 4 transition of the infrared allowed rogue state was recorded here for the first time. The Stark field perturbed spectra of the R(3) and R(5) ro-vibrational transitions of the v₂ + 3v₃ band also showed evidence of rogue transitions. The ensuing analysis determined that the |0130°0°) state has a polarisability of 3.5 ± 0.3A³ and a polarisability anisotropy of 5.6 ± 1.8A³. The Stark field perturbed spectra of the R(3) and R(5) transitions were fit to a non-crossing model and the energy levels of the rogue J = 4 and J = 6 states were determined. The energy level difference between |0130°0°) and |1120°0°) was determined to be -11.88±0.22 cm⁻¹. This does not compare well with local mode calculations and it is possible that the perturbations due to the presence of the rogue state impeded the accurate determination of the energy level difference. The identity of the rogue vibrational state could not be determined from the data presented in this thesis alone. However, collaborative work with another research group suggests that the rogue vibrational state is |0306°3¹) (see Chapter 7). / Graduate

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This thesis focuses on the dynamic and static behavior of steel fiber-reinforced concrete (SRFC) beams. As part of this study a total of eighteen (18) beams are tested, including fourteen (14) SFRC beams, and a companion set of four (4) beams built without fibers. Seven (7) of the beams are tested under quasi-static (slowly applied) loading with the remaining eleven (11) beams tested under simulated blast loading using the University of Ottawa shock-tube. The variables considered in this study include: concrete type (SFRC vs. conventional concrete), fiber content, fiber type, as well as the effect of transverse reinforcement. The criteria used to evaluate the blast performance of the beams includes: overall blast capacity, maximum and residual mid-span displacement, secondary fragmentation and damage control. Static results confirm the beneficial effect of fibers on improving the shear and flexural capacity of beams. Dynamic results show that use of steel fibers at a sufficient content can increase shear capacity and effectively replace transverse reinforcement in beams tested under blast loads. The results also show that increasing fiber content can improve the blast response of the beams by reducing maximum and residual mid-span displacement, improving damage tolerance and minimizing secondary blast fragments. However, at high fiber contents, problems with workability of the concrete mix can occur, resulting in a reduction of improvements when compared to SFRC specimens with lower fiber content. The analytical research program aimed at predicting the response of the test beams using dynamic inelastic single-degree-of-freedom (SDOF) analysis. Overall the analytical results demonstrate that SDOF analysis can be used to predict the blast response of beams built with SFRC.

A beam of polarized ³He⁺ ions has been produced using atomic beam method techniques. This method has the attraction of being capable of producing an ion beam with polarizations up to 100%. The polarization of ³He beams presently produced by optical pumping techniques is of the order of 5%. The apparatus is composed of three main sections, the atomic beam source consisting of a supersonic nozzle cooled to liquid helium temperatures to produce a low velocity atomic beam, the tapered hexapole magnet to spatially separate the particles in the two magnetic spin substates, and the electron bombardment ionizer to produce ³He⁺ ions from the neutral ³He atomic beam. The low velocity beam is required because the nuclear magnetic moment of ³He is of the order of 1000 times smaller than the electronic magnetic moment used to separate beams in conventional Stern-Gerlach magnets and to achieve a high ionization efficiency. The measured intensity of the beam produced by the atomic beam source cooled to liquid helium temperature was 1 x 10¹⁸ atoms/sr-sec, the most probable velocity was 310 m/sec, and the velocity full width at half maximum was 50 m/sec. The beam flux through the ionizer increases by a factor of 1.3 when the hexapole field is turned on, in good agreement with the theoretically expected increase. This increase corresponds to a polarization of 65% of the atomic beam. A 12nA³He⁺ ion beam was obtained corresponding to an ionization efficiency of approximately 0.15%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A wide variety of inelastic scattering and electron attachment phenomena have been studied by directing an electron beam into a gas filled chamber and by observing the results of the interaction. The use of a "monoenergetic" electron beam has permitted the relative cross sections for such processes to be examined in some detail. Three instruments were used to make the measurements, and these instruments were designed and constructed during the course of the work to be described. All three employed a 127° electrostatic electron velocity selector to filter the electron beam. An electron energy analyzer permitted the observation of inelastically scattered electrons, and a monopole or a quadrupole mass filter permitted the measurement of the relative amounts of positive or negative ionization generated by the electron beam in its interaction with the gas. The measurement of the energy dependence of the cross sections was the prime objective of the work, and much care was taken in the design of the instruments to ensure that the cross section curves were not distorted by spurious effects. The forward inelastic scattering spectra of helium and ethylene were recorded using an electron beam having an incident energy of 50 eV . The ionization efficiency curves of singly and doubly charged helium were obtained, and the results are compared with several theoretically derived expressions for electron impact threshold laws. The positive ionization efficiency curves for nitrogen and oxygen were also obtained. An examination of the dissociative capture, non-dissociative capture and ion pair processes has been made by determining the energy dependence of the cross sections for the production of the parent and/or fragment negative ions from nine molecules. Finally, the generation of zero energy electrons from inelastic scattering events has been studied by using sulfur hexafluoride as an electron scavenger in a mixture with the sample gas. The threshold electron impact spectra were obtained for six atomic and molecular species. In all cases, such measurements were carried out below and above the ionization potential of the sample. / Science, Faculty of / Chemistry, Department of / Graduate