Preclinical single-photon emission computed tomography (SPECT) is an essential tool for studying progression, response to treatment, and physiological changes in small animal models of human disease. The wide range of imaging applications is often limited by the static design of many preclinical SPECT systems. We have developed a prototype imaging system that replaces the standard static pinhole aperture with two sets of movable, keel-edged copper-tungsten blades configured as crossed (skewed) slits. These apertures can be positioned independently between the object and detector, producing an anamorphic image in which the axial and transaxial magnications are not constrained to be equal. We incorporated a 60 mm x 60 mm, millimeter-thick megapixel silicon double-sided strip detector that permits ultrahigh-resolution imaging. While the stopping power of silicon is low for many common clinical radioisotopes, its performance is sufficient in the range of 20-60 keV to allow practical imaging experiments. The low-energy emissions of ¹²⁵I fall within this energy window, and the 60-day half life provides an advantage for longitudinal studies. The flexible nature of this system allows the future application of adaptive imaging techniques. We have demonstrated ~225-μm axial and ~175-μm transaxial resolution across a 2.65 cm³ cylindrical field of view, as well as the capability for simultaneous multi-isotope acquisitions. We describe the key advancements that have made this system operational, including bringing up a new detector readout ASIC, development of detector control software and data-processing algorithms, and characterization of operating characteristics. We describe design and fabrication of the adjustable slit aperture platform, as well as the development of an accurate imaging forward model and its application in a novel geometric calibration technique and a GPU-based ultrahigh-resolution reconstruction code.

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Given a C*-algebra $A$ endowed with an action $\alpha$ of $\R$ and an $\alpha$-invariant trace $\tau$, there is a canonical dual trace $\widehat \tau$ on the crossed product $A \rtimes_\alpha \R$. This dual trace induces (as would any suitable trace) a real-valued homomorphism $\widehat \tau_* : K_0(A \rtimes_\alpha \R) \to \R$ on the even $K$-theory group. Recall there is a natural isomorphism $\phi_\alpha^i : K_i(A) \to K_{i+1}(A \rtimes_\alpha \R)$, the Connes-Thom isomorphism. The attraction of describing $\widehat \tau_* \circ \phi_\alpha^1$ directly in terms of the generators of $K_1(A)$ is clear. Indeed, the paper where the isomorphisms $\{\phi_\alpha^0,\phi_\alpha^1\}$ first appear sees Connes show that $\widehat \tau_* \phi_\alpha^1[u] = \frac{1}{2 \pi i} \tau(\delta(u) u^*)$, where $\delta = \frac{d}{dt} \big|_{t=0} \alpha_t(\cdot)$ and $u$ is any appropriate unitary. A careful proof of the aforementioned result occupies a central place in this thesis. To place the result in its proper context, the right-hand side is first considered in its own right, i.e., in isolation from mention of the crossed-product. A study of 1-parameter dynamical systems and exterior equivalence is undertaken, with several useful technical results being proven. A connection is drawn between a lemma of Connes on exterior equivalence and projections, and a quantum-mechanical theorem of Bargmann-Wigner. An introduction to the Connes-Thom isomorphism is supplied and, in the course of this introduction, a refined version of suspension isomorphism $K_1(A) \to K_0(\susp A)$ is formulated and proven. Finally, we embark on a survey of unbounded traces on C*-algebras; when traces are allowed to be unbounded, there is inevitably a certain amount of hard, technical work needed to resolve various domain issues and justify various manipulations. / Graduate / 0280

Research Doctorate - Doctor of Philosophy (PhD) / (**Note: this abstract is a plain text version of the author's abstract, the original of which contains characters and symbols which cannot be accurately represented in this format. The properly formatted abstract can be viewed in the Abstract and Thesis files above.**) Let (G,G+) be a quasi-lattice-ordered group with positive cone G+ Laca and Raeburn have shown that the universal C*-algebra C*(G,G+)introduced by Nica is a crossed product BG+ Xɑ G+ by a semigroup of endomorphisms. Subsequent research centered on totally ordered abelian groups. We generalize the results in [2], [3] and [5] to extend it to the case of discrete lattice-ordered abelian groups. In particular given a hereditary subsemigroup H+ of G+ we introduce a closed ideal IH+ of the C*-algebra BG+. We construct an approximate identity for this ideal and show that IH+ is extendibly a-invariant. It follows that there is an isomorphism between C*-crossed products (BG+/IH+) XɑG+ and B(G/H)+ XβG+. This leads to one of our main results that B(G/H)+ XβG+ is realized as an induced C*-algebra IndG-H (B(G/H+ Xt(G/H)+). Then we use this result to show the existence of the following short exact sequence of C*-algebras 0-IH+ XɑG+ → BG+ XɑG+ → IndG-H (B(G/H+ Xt(G/H)+) → 0. This leads to show that the ideal IH+ XɑG+ is generated by {iBG+(1-1u):u∊H+} and therefore contained in the commutator ideal CG of the C*-algebra BG+ XɑG+. Moreover, we use our short exact sequence to study the primitive ideals of the C* algebra BG+ XɑG+ which is isomorphic to the Toeplitz albebra T(G) of G.

Research Doctorate - Doctor of Philosophy (PhD) / (**Note: this abstract is a plain text version of the author's abstract, the original of which contains characters and symbols which cannot be accurately represented in this format. The properly formatted abstract can be viewed in the Abstract and Thesis files above.**) Let (G,G+) be a quasi-lattice-ordered group with positive cone G+ Laca and Raeburn have shown that the universal C*-algebra C*(G,G+)introduced by Nica is a crossed product BG+ Xɑ G+ by a semigroup of endomorphisms. Subsequent research centered on totally ordered abelian groups. We generalize the results in [2], [3] and [5] to extend it to the case of discrete lattice-ordered abelian groups. In particular given a hereditary subsemigroup H+ of G+ we introduce a closed ideal IH+ of the C*-algebra BG+. We construct an approximate identity for this ideal and show that IH+ is extendibly a-invariant. It follows that there is an isomorphism between C*-crossed products (BG+/IH+) XɑG+ and B(G/H)+ XβG+. This leads to one of our main results that B(G/H)+ XβG+ is realized as an induced C*-algebra IndG-H (B(G/H+ Xt(G/H)+). Then we use this result to show the existence of the following short exact sequence of C*-algebras 0-IH+ XɑG+ → BG+ XɑG+ → IndG-H (B(G/H+ Xt(G/H)+) → 0. This leads to show that the ideal IH+ XɑG+ is generated by {iBG+(1-1u):u∊H+} and therefore contained in the commutator ideal CG of the C*-algebra BG+ XɑG+. Moreover, we use our short exact sequence to study the primitive ideals of the C* algebra BG+ XɑG+ which is isomorphic to the Toeplitz albebra T(G) of G.

abstract: In this thesis, I investigate the C*-algebras and related constructions that arise from combinatorial structures such as directed graphs and their generalizations. I give a complete characterization of the C*-correspondences associated to directed graphs as well as results about obstructions to a similar characterization of these objects for generalizations of directed graphs. Viewing the higher-dimensional analogues of directed graphs through the lens of product systems, I give a rigorous proof that topological k-graphs are essentially product systems over N^k of topological graphs. I introduce a "compactly aligned" condition for such product systems of graphs and show that this coincides with the similarly-named conditions for topological k-graphs and for the associated product systems over N^k of C*-correspondences. Finally I consider the constructions arising from topological dynamical systems consisting of a locally compact Hausdorff space and k commuting local homeomorphisms. I show that in this case, the associated topological k-graph correspondence is isomorphic to the product system over N^k of C*-correspondences arising from a related Exel-Larsen system. Moreover, I show that the topological k-graph C*-algebra has a crossed product structure in the sense of Larsen. / Dissertation/Thesis / Ph.D. Mathematics 2011

Aujourd’hui, il semble que la méthode la plus prometteuse pour intensifier la combustion repose sur l’excitation hors-équilibre du mélange gazeux, qui permet ainsi de modifier la cinétique chimique. Pour obtenir une excitation efficace des degrés de liberté électronique et vibrationnel des molécules, l’utilisation d’une alimentation pulsée associée à une énergie des électrons adéquate est proposée. Ce travail de thèse porte sur l’application de générateur d’impulsion électrique haute fréquence capable de délivrer des pulses de 20 kilovolts pendant 20 nanosecondes ayant des temps de montée de l’ordre de 5 nanosecondes en combustion. Cette étude s’articule autour de deux grands axes de recherche. Le premier est la génération, à pression atmosphérique et à pression réduite, d’espèces excitées (oxygène électroniquement excité O2(a1?g), O2(b1Sg+) et oxygène atomique excité) ainsi que leur caractérisation par spectroscopie d’émission. Le second axe de recherche concerne leur utilisation pour l’intensification de la combustion. La première partie expérimentale s’est focalisée sur la génération d’oxygène électroniquement excité par plasma décharge à barrière diélectrique et décharge croisée dans des mélanges O2/He et O2/Ar. La décharge croisée est une cellule à barrière diélectrique pulsée qui est croisée avec une composante continue (DC). Dans ce cas, l’étape d’ionisation est réalisée par la DBD pulsée alors que la composante continue supporte le courant électrique entre chaque pulse. Le gaz produit par cette installation est étudié de manière exhaustive par spectroscopie d’émission. Ce travail, indispensable pour caractériser l’installation et obtenir les conditions initiales nécessaires pour les calculs de flamme, repose sur différents spectromètres et caméras. La première des applications potentielles dans le domaine de la combustion concerne l’intensification de la combustion par activation de l’oxygène. La conception de prototypes de brûleurs hybrides, intégrant un réacteur plasma nous a permis de valider cette technique d’intensification de la combustion et de la comparer à une flamme classique sans plasma. Finalement, la modélisation des paramètres fondamentaux d’une flamme de prémélange et de diffusion est entreprise par le logiciel CHEMKIN. L’effet promoteur de l’oxygène excité sur une flamme d’hydrogène a pu être modélisé. / Nowadays it seems that the most promising method for accelerating combustion is the non-equilibrium excitation of the gas mixture components, which allows one to affect the chemical reaction kinetics. To enable more efficient excitation of the electronic and vibrational degrees of freedom, one should use short-duration (nanosecond) pulses with a high reduced electric field. The present work focuses on the application of high frequency high voltage pulse discharges capable of delivering an electric pulse of 20 kV during 20 ns with controlled voltage rise time of 5 ns and at a frequency up to 25 kHz in combustion. This study articulates around two major research axis; that of the generation of excited species and particularly the feasibility to produce excited oxygen species in its singlet electronic states O2(a1?g) and O2(b1Sg+) by a non-thermal electric discharge, at reduced pressure until atmospheric pressure and its characterization by emission spectroscopy. The second research axis concerns their use for the intensification of combustion. The experimental part of the study concerns investigation of singlet oxygen production in the application of a dielectric barrier discharge in O2/He and O2/Ar binary mixtures. The second discharge is a special crossed discharge plasma-chemical reactor that has been developed. This crossed discharge consists of a hybrid discharge in which short high voltage pulses produce ionization while a comparatively low electric field supports the electric current between ionizing pulses. The gas produced by this installation is intensively studied by emission spectroscopy. This work, indispensable to characterize the installation and to obtain initial conditions necessary for flame calculations, relies on different spectrometers and intensified camera. The first potential in the combustion field is to significantly improve combustion efficiency and reduce pollutant emissions using oxidizer “activation”. Conception and development of hybrid plasma burner prototypes, integrating crossed discharge plasma reactor allows us to validate this application by comparing with a classical flame without plasma activation. Finally, modelling of premixed flame fundamental parameters is undergone with CHEMKIN software. The promoting effect of excited oxygen on hydrogen flame has been characterized.

viii, 107 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation consists of two related parts. In the first portion we use the tracial Rokhlin property for actions of a finite group G on stably finite simple unital C *-algebras containing enough projections. The main results of this part of the dissertation are as follows. Let A be a stably finite simple unital C *-algebra and suppose a is an action of a finite group G with the tracial Rokhlin property. Suppose A has real rank zero, stable rank one, and suppose the order on projections over A is determined by traces. Then the crossed product algebra C * ( G, A, à à ±) also has these three properties. In the second portion of the dissertation we introduce an analogue of the tracial Rokhlin property for C *-algebras which may not have any nontrivial projections called the projection free tracial Rokhlin property . Using this we show that under certain conditions if A is an infinite dimensional simple unital C *-algebra with stable rank one and à à ± is an action of a finite group G with the projection free tracial Rokhlin property, then C * ( G, A, à à ±) also has stable rank one. / Adviser: Phillips, N. Christopher

Orientador: Fabio Cesar Gozzo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-15T20:28:06Z (GMT). No. of bitstreams: 1 Figueiredo_AlanadosReis_M.pdf: 3529338 bytes, checksum: 3761ab750ec289d682a00aae3d02ea4b (MD5) Previous issue date: 2010 / Resumo: A espectrometria de massas (MS) desempenha um papel fundamental na proteômica, pois permite a identificação de proteínas, seqüenciamento de peptídeos, determinação de modificações pós-traducionais e análise quantitativa de expressão. Além das análises envolvendo a estrutura primária, há um grande interesse em se aplicar MS para análise de estruturas superiores (terciárias e quaternárias) de proteínas e uma das abordagens promissoras nesta área é a MS acoplada à ligação cruzada. Nesta abordagem, um reagente bifuncional liga covalentemente resíduos de aminoácidos espacialmente próximos e a distância máxima entre esses resíduos é dado pelo tamanho do agente de ligação cruzada (ALC). Nesse trabalho avaliou-se a extensão e exatidão das distâncias interresíduos tanto por simulações de dinâmica molecular quanto por experimentos de MS. As faixas de distâncias calculadas mostram que há sempre uma distância mínima entre resíduos ao qual o ALC pode se ligar, além de determinar o valor máximo para cada um dos ALC estudados (DSG, DSS e DSSeb). Os dados experimentais com proteínas modelo (Ubiquitina, Citocromo C e Mioglobina) mostraram ainda que todos dos peptídeos que apresentavam ligações cruzadas estavam dentro da faixa de alcance determinadas pelas simulações de dinâmica molecular, confirmando a exatidão do método. Os novos valores de tamanho das moléculas de ALC estudados podem agora ser utilizados para a determinação de estruturas superiores de proteínas através da técnica de MS acoplada a ligação cruzada / Abstract: Mass spectrometry (MS) plays a key role in proteomics because it allows the identification of proteins, peptide sequencing, determination of post-translational modifications and quantitative expression analysis. There is a great interest in using MS to perform analysis beyond the primary structure, i. e. tertiary and quaternary structures, and one of the most promising approaches in this filed is MS coupled to cross-linking technique. In this approach, a bifunctional reagent covalently binds amino acid residues that are close in space and the maximum distance between these residues is given by the arm length of the cross-linking agent. In this study we evaluated the extent and accuracy of the inter-residues distances by both molecular dynamics simulations and MS experiments. Simulated distance ranges showed that there is a minimum distance between residues to which the reagent can bind and a maximum value for each of the studied reagents (DSG, DSS and DSSeb). The experimental data from model proteins (Ubiquitin, Cytochrome C and Myoglobin) also showed that all the detected modified peptides were within the ranges determined by the molecular dynamics simulations, confirming the accuracy of the method. The new space arm length values of the reagent molecules can now be used for the determination of proteins higher structures by the MS coupled to cross-linking technique / Mestrado / Quimica Organica / Mestre em Química