Thesis (Ph.D.)--Murdoch University, 2005. / Thesis submitted to the Division of Science and Engineering. Includes bibliographical references (p. 175-182).

Thesis (M.S.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references (leaves 55-58). Online version available on the World Wide Web.

The detection of sound sources with microphone arrays can be enhanced through processing individual microphone signals prior to the delay and sum operation. One method in particular, the Phase Transform (PHAT) has demonstrated improvement in sound source location images, especially in reverberant and noisy environments. Recent work proposed a modification to the PHAT transform that allows varying degrees of spectral whitening through a single parameter, andamp;acirc;, which has shown positive improvement in target detection in simulation results. This work focuses on experimental evaluation of the modified SRP-PHAT algorithm. Performance results are computed from actual experimental setup of an 8-element perimeter array with a receiver operating characteristic (ROC) analysis for detecting sound sources. The results verified simulation results of PHAT- andamp;acirc; in improving target detection probabilities. The ROC analysis demonstrated the relationships between various target types (narrowband and broadband), room reverberation levels (high and low) and noise levels (different SNR) with respect to optimal andamp;acirc;. Results from experiment strongly agree with those of simulations on the effect of PHAT in significantly improving detection performance for narrowband and broadband signals especially at low SNR and in the presence of high levels of reverberation.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 27, 2009) Includes bibliographical references (p. 70-74).

Electron impact excitation phenomena play an important role in atomic and molecular physics. The different energy levels of an atom or molecule interact differently with incoming electrons with different energies and that affects the excitation of the energy levels of the atoms and molecules. Studies involving electron impact excitation process are generally conducted with optical emission techniques or by the electron energy loss method. In the present study, for the first time, cavity ringdown spectroscopy (CRDS) has been used to investigate electron impact excitation phenomena of electronatom collision processes. The technique, i.e., electron impact excitation-cavity ringdown spectroscopy (EIE-CRDS), was employed for the purposes of fundamental study and of real-time applications. The fundamental study which was carried out in terms of determining electron impact excitation cross section (EIECS) has been demonstrated by measuring EIECS of a few excited levels of mercury (Hg) atom. For the application side, the EIE-CRDS technique has been employed for trace element detection. This dissertation first describes the fundamentals of electron impact excitationcavity ringdown spectroscopy (EIE-CRDS); afterwards its applications are demonstrated. A novel method of measuring excitation cross sections using this EIE-CRDS technique has been explained. In this method, first the excitation of atoms are achieved by electron impact excitation process, subsequently, CRDS measured absolute number density is utilized to determine the absolute EIECS values. Steps of the method are described in detail. Applicability of the method is demonstrated by measuring EIECS of three different energy levels of Hg, namely 6s6p 3P0, 6s6p 3P1, and 6s7s 3S1, and the obtained values are in agreement with those reported in the literature. Secondly, the EIE-CRDS technique was employed to investigate the absorption spectrum of mercury atom in the vicinity of 404.65 nm, corresponding to the transition 6s7s 3S1 -> 6s6p 3P0 levels of mercury. Elemental mercury was measured using a laser of wavelength 404.65 nm. The technological feasibility of developing a portable size instrument for mercury detection was explored. Subsequently, a portable size, dual-mode, plasma-CRDS based prototype instrument, capable of real-time trace element monitoring, was developed. The design, functioning, and specifications of the instrument are also explained.

Incident 0.5 to 2.5 MeV charged particle beams were used to ionize the inner-shells of selected targets and study their subsequent emission of characteristic x-rays. ⁹Be⁺ ions were used to examine K-shell x-ray production from thin F, Na, Al, Si, P, Cl, and K targets, L-shell x-ray production from thin Cu, An, Ge, Br, Zr and Ag targets, and M-shell x-ray production from thin Pr, Nd, Eu, Dy, Ho, Hf, W, Au, Pb and Bi targets. L-shell x-ray production cross sections were also measured for ²⁷Al⁺ ions incident upon Ni, Cu, Zn, As, Zr, and Pd targets. M-shell x-ray production cross sections were measure for ²⁷Al⁺ and ⁴⁰Ar⁺ ions incident upon Pr, Nd, Gd, Dy, Lu, Hf, Au, Pb, Bi, and U targets. These measurements were performed using the 2.5 MV Van de Graaff accelerator at North Texas State University. The x-rays were detected with a Si(Li) detector whose efficiency was determined by fitting a theoretical photon absorption curve to experimentally measure values. The x-ray yields were normalized to the simultaneously measured Rutherford backscattered (RBS) yields which resulted in an x-ray production cross section per incident ion. The RBS spectrum was obtained using a standard surface barrier detector calibrated for to account for the "pulse height defect." The experimental results are compared to the predictions of both the first Born and ECPSSR theories; each of which is composed of two parts, the direct ionization (DI) of the target electron to the continuum and the capture (EC) of the target electron to the projectile. The first Born describes DI by the Plane-Wave-Born-Approximation (PWBA) and EC by the Oppenheimer-Brinkman-Kramers treatment of Nikolaev (OBKN). ECPSSR expands upon the first Born by using perturbed (PSS) and relativistic (R) target electron wave functions in addition to considering the energy loss (E) of the projectile in the target and its deviation from straight line trajectory (Coulomb deflection (C)). The measurements presented show that the first Born theories overestimate the measured results rather significantly for all experiments using the ⁹Be beams to examine the inner shell x-rays, while the ECPSSR predictions fir the measured data much better. For incident ²⁷Al and ⁴⁰Ar ions, the measured results are not predicted by the theories. The first Born generally over-predicts the data for low target atomic numbers while under-predicting at high atomic numbers. The ECPSSR theory greatly under-predicts the results (factors of 10³ to 10²⁰). Reasons for this behavior are discussed as well as suggestions for future experiments.

This Thesis describes the development of an electron-impact microfocus x-ray source and its application for phase-contrast imaging. The source is based on a novel, liquid-jet target concept. Stable and continuous operation can be achieved at substantially higher electron-beam power densities than conventional solid target based systems. The maximum x-ray brightness can potentially be increased by a factor of 10-1000, which would provide significantly improved performance in applications such as imaging. In order to reach the high x-ray brightness, comparable performance from the electron gun is needed. A LaB6-cathode-based electron gun is analyzed in terms of achievable e-beam brightness and beam quality and is found capable to deliver power densities in the 10-100 MW/mm2 range using optimized electro-optics. A proof-of-principle microfocus source has been developed. Experiments show that the liquid-metal-jet target can be operated at more than an order of magnitude higher e-beam power densities than modern solid-metal targets. This brightness enhancement has been utilized to acquire in-line phase-contrast images of weakly absorbing objects. The source potentially enables the application of high-resolution phase-contrast x-ray imaging with short exposure times in clinics and laboratories. Different liquid-jet-target materials have been tested. The Sn-jet (Ka=25.3 keV) could be suitable for mammography, whereas the Ga-jet ((Ka=9.2 keV) may be utilized for x-ray diffraction studies. In addition, a non-metallic methanol jet has been the demonstrated in stable x-ray operation. All materials and compounds found in liquid form can, thus, potentially be used for electron-impact liquid-jet-target x-ray generation. Scaling to higher e-beam power density and x-ray brightness levels is discussed and is determined to be feasible. Potential difficulties, such as debris emission and instabilities of the x-ray emission spot, are investigated in some detail. Larger and/or faster jets could overcome the present limitations because of their inherently higher heat load capacities. Dynamic-similarity experiments show that liquid jets can in principle be operated in a stable manner at much higher speeds than previously shown. / QC 20100915

No description available.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-06-27T18:11:39Z No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-07T21:06:14Z (GMT) No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) / Made available in DSpace on 2017-08-07T21:06:14Z (GMT). No. of bitstreams: 1 ritadecassiapolitovitaalessio.pdf: 1515814 bytes, checksum: ec2256bcf074df2e72a53fe6c0a62c6f (MD5) Previous issue date: 2009-06-09 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O estudo de ressonâncias, através de estados metaestáveis pelo impacto de elétrons, permite observar estruturas bem definidas nos espectros, gerando informações diretas sobre as energias de formação das ressonâncias, bem como suas formas e larguras. A investigação destas ressonâncias é muito importante em vários ramos da ciência, possuindo inúmeras aplicações biológicas e tecnológicas. Um espectrômetro por impacto de elétrons foi construído e implantado no Laboratório de Física Atômica e Molecular, permitindo a obtenção das funções de excitação do Argônio, do Hélio e da molécula de Nitrogênio, sendo esta técnica inédita no Brasil. Neste espectrômetro aplica-se a técnica dos feixes cruzados, que consiste basicamente de um canhão de elétrons monocromatizado, um feixe de gás efusivo, uma gaiola de Faraday para a blindagem da região de colisão, um detector de íons metaestáveis, devidamente posicionado, e um coletor de Faraday. O canhão de elétrons monocromatizado apresenta uma alta eficiência, cobrindo continuamente uma faixa de energia de 7 a 200 eV, com uma resolução em torno de 50 meV. Para a aquisição dos espectros, a energia do canhão foi varrida a partir do limiar de excitação metaestável até uma energia menor que o primeiro potencial de ionização do alvo estudado. / The study of resonances through metastable states of atoms and molecules by electron impact shows spectra with well-defined structures, providing direct information on the energies of resonances formation, as well as its shapes and widths. The investigation of these resonances is important in several branches of science, such as many technological and biological applications. In this work we have assembled at Laboratory of Atomic and Molecular Physics an electron impact spectrometer which allowed us to collect metastables excitations functions of Argon, Helium and the Nitrogen molecules. As far we know, that was the first time that this technique was performed in Brazil. That spectrometer applies the cross beam technique, and consists of a monochromatized electron gun, an effusive gas beam, a cage to shield the collision region, a metastable detector properly positioned and a Faraday cup. The monocromatized electron gun built has a high efficiency, covering continuously the energy range from 7 to 200 eV, with a resolution of about 50 meV. The three spectras recorded in this work cover the energy range from the excitation metastable threshold up to energy lower than the first ionization potential of the targets studied.

No / The Raman and electron impact mass spectra of synthetic indigo and its four 6,6'-dihalogeno analogues are reported and discussed. The influence of varying the halogen on these Raman spectra is considered. Particular emphasis is laid on distinguishing indigo from 6,6'-dibromoindigo and differentiating between the dihalogenocompounds, so as to develop protocols for determining whether artefacts are coloured with dyes of marine or terrestrial origin and whether such artefacts are dyed with genuine Tyrian Purple or with dihalogenoindigo substitutes that do not contain bromine. The value of even low resolution electron impact mass spectrometry in a forensic context as a means of identifying authentic 6,6'-dibromoindigo and distinguishing it from its dihalogenoanalogues is emphasised.