Por conta da liberação de uma nova faixa de espectro as aplicações que utilizam transmissão em banda ultralarga se expandiram. Por conta disso, várias formas de transmissão pulsada ganharam destaque. Contudo, o projeto e estudo de antenas até então era majoritariamente feito em banda estreita e regime permanente senoidal. Além disso, para transmissão pulsada, a resposta impulsiva da antena passa a ser mais necessária do que sua resposta em banda estreita. Por isso, o objetivo desse estudo foi explorar o que ocorre com pulsos estreitos se propagando em uma antena de forma a se obter uma aproximação da resposta impulsiva de antenas. Mais especificamente, foi obtido um modelo analítico que explicita a relação entre a geometria e o funcionamento da antena. Através do estudo da espiral equiangular foi possível encontrar o decaimento do pulso de corrente ao longo da linha como também o campo radiado de forma quantitativa. Tal resultado, assim como os procedimentos para sua obtenção, poderá ser utilizado para outras antena filamentares. / The applications for Ultra Wide Band have grown since the new regulation allowed the use of a new large frequency band. Since then, systems for pulsed transmission entered the spotlight. However, the antenna\'s project and study were in big part done in narrowband and sinusoidal steady-state. Besides, the impulse response is of much more interest for these systems than the frequency response. For this reason, the main goal of this work is to explore how current pulses propagate on the antenna to obtain an approximate impulse response. Moreover, an analytical model that unveils the relation between the antenna geometry and its current decay is presented. Through the study of the equiangular spiral it is possible to find the pulse decay as a function of the line length and the radiated field in a quantitative fashion. This result as well as the methods used to obtain it can be used for other antennas.

The diffusion of a particle in a crowded environment typically proceeds through three regimes: for very short times the particle diffuses freely until it collides with an obstacle for the first time, while for very long times diffusion the motion is Fickian with a diffusion coefficient D that depends on the concentration and type of obstacles present in the system. For intermediate times, the mean-square displacement of the particle often increases approximately as t α , with α < 1, typical of what is generally called anomalous diffusion. However, it is not clear how one can identify or choose a time or displacement interval that would give a reliable estimate of α. In this paper, we use two exact numerical approaches to obtain diffusion data for a simple Lattice Monte Carlo model in both time limits. This allows us to propose an objective definition of the transient regime and a unique value for α. Furthermore, our methodology directly gives us the length scale over which the transient regime switches to the steady-state regime. We test our proposed approach using several types of obstacle systems, and we introduce the novel concept of excess diffusion lengths. Finally, we show that the values of the parameters describing the anomalous transient regime depend on the Monte Carlo moves used to describe the dynamics of the particle, and we propose a new algorithm that correctly models the short time diffusion of a particle on a lattice.

<div>Detecting hidden/smuggled special nuclear materials (SNM) is one of the unsolved problems in the safeguards industry. The biggest challenge is to quantify and track SNM and prevent the use of these materials for illicit purposes. The goal is to detect smallest quantity of SNM in large cargo containers, at the ports of entry, in the shortest amount of measurement time. Currently passive detection techniques, which is based on long-lived isotopes, are used to detect hidden SNM. This technique is not very reliable, as appropriate shielding of the SNM can reduce detection signals from these long-lived isotopes. Accelerator based active interrogation methods are proposed to solve the SNM problem. Besides SNM, another challenge in the nuclear industry is to meet the demand and supply of medical radioisotopes, particularly Tc-99m (half-life 6 hours). Mo-99, which decays to Tc-99m, is one of the fission products found in nuclear reactors. Because of short half-life of 66 hours, Mo-99 cannot be stockpiled. The shutdown of various research reactors globally disrupted the supply of Mo-99. Because of the financial and regulatory burden on the nuclear reactors, accelerator-based systems can be used to produce Mo-99.</div><div><br></div><div>With the aim to solve these two major challenges, a preliminary study is done to understand the neutrons behavior on milliseconds (or shorter) time steps in an accelerator driven subcritical system. A pulsed external neutron source, i.e. Deuterium-Deuterium (DD) generator, drives the assembly. Using first principles, the transient equations are derived and the neutron population at different time stamps is calculated. The Li-6 detector’s response to the neutron population is predicted. Experiments are performed to compare the predicted behavior with the observed behavior. The model is extended further to investigate the case of no uranium fuel inside the system. Transient measurements, in the absence of the uranium fuel, are made and the neutron die-away time is determined. This die-away time is compared with the predicted time.</div>

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O acidente vascular cerebral, doenÃa incapacitante e terceira causa de morte em paÃses desenvolvidos à caracterizada pela interrupÃÃo ou reduÃÃo do fluxo sangÃÃneo para o cÃrebro capaz de causar alteraÃÃo na funÃÃo cerebral. Sabe-se que o receptor A1 da adenosina possui um papel chave na neuroproteÃÃo devido à diminuiÃÃo da liberaÃÃo de glutamato e hiperpolarizaÃÃo neuronal. O objetivo desse trabalho foi determinar os efeitos do prÃ-condicionamento por estresse de contensÃo em ratos submetidos à isquemia cerebral transitÃria (ICT) por oclusÃo bilateral das carÃtidas e a participaÃÃo dos receptores A1 da adenosina nesse processo. Inicialmente, ratos Wistar machos, entre 200-240g, foram submetidos ao estresse de contensÃo (ST) em cilindros por 2h e imediatamente depois submetidos à ICT pela oclusÃo de ambas as artÃrias carÃtidas durante 30min. Um dos grupos dos animais foi prÃ-tratado com o antagonista do receptor A1 da adenosina, DPCPX, antes do estresse de contensÃo nas doses de 0,1mg/kg ou 1mg/kg. A temperatura retal foi monitorada e mantida a 37ÂC atravÃs de uma luz incandescente. Vinte e quatro horas depois do tÃrmino da ICT os animais foram sacrificados, tiveram seus cÃrebros dissecados, seccionados e imersos em soluÃÃo de Cloreto de 2,3,5-Trifeniltetrazol (TTC) a 1% por 30 min. para analise da viabilidade do tecido cerebral. Os testes comportamentais foram efetuados 72h apÃs a ICT e consistiram em Teste do Campo Aberto para a atividade locomotora, Labirinto em Y para a memÃria operacional ou de procedimento e Esquiva Passiva para aferiÃÃo da memÃria aversiva de curta e longa duraÃÃo. Os animais submetidos à ICT tiveram dano no tecido cerebral (FO= 10,36  0,75%; ISQ= 18,52  2,62%) alÃm de diminuiÃÃo no comportamento exploratÃrio de rearing (no de eventos: FO= 5,00 1,23; ISQ= 1,50  0,72) e dÃficit da memÃria aversiva de longa duraÃÃo (FO= 271,2  17,61s; ISQ= 108,4 67,64s). Nenhuma diferenÃa significativa foi encontrada no nÃmero de cruzamentos em Campo Aberto (FO= 15,71 2,02; ISQ= 11,00 2,13), na memÃria de procedimento (FO= 70,16  5,77; ISQ= 71,37  7,94), ou na memÃria aversiva de curta duraÃÃo (FO= 145,9  42,75; ISQ= 113,1  64,97).Os animais prÃ-condicionados por estresse tiveram uma reduÃÃo na taxa de infarto cerebral (FO= 10,36  0,75%; ISQ= 18,52  2,62%; ISQ+ST= 12,59  0,87%) e um retorno aos nÃveis normais do comportamento de rearing observado no teste do campo aberto (FO= 5,00 1,23; ISQ= 1,50 0,72; ISQ+ST= 6,091 1,443). No teste de esquiva passiva, observamos uma tendÃncia à melhora da memÃria aversiva de longa duraÃÃo (FO= 271,2  17,61s; ISQ= 108,4 67,64s; ISQ+ST= 156,1Â45,81s). Quando tratados com o DPCPX na dose de 1mg/kg, os animais tiveram um bloqueio da neuroproteÃÃo obtida com o prÃ-condicionamento (ISQ= 18,52  2,62%; ISQ+ST= 12,59  0,87%; ISQ+ST+DPCPX 1= 19,95  3,38%), aumento no nÃmero de rearings que havia sido normalizada pela contensÃo (ISQ= 1,50 0,72; ISQ+ST= 6,091 1,443; ISQ+ST+DPCPX 1= 3,20 0,90) e uma tendÃncia à reversÃo dos efeitos do prÃ-condicionamento na memÃria aversiva de longa duraÃÃo (ISQ= 108,4 67,64s; ISQ+ST= 156,1Â45,81s; ISQ+ST+DPCPX 1= 88,61 38,83s). O estresse de contensÃo conferiu neuroproteÃÃo aos animais submetidos à ICT e tal neuroproteÃÃo foi perdida pelo tratamento prÃvio com DPCPX. Esses achados apontam para a participaÃÃo do receptor A1 da adenosina na proteÃÃo conferida por estresse de contensÃo por mecanismos que ainda precisam ser esclarecidos. / Stroke,as disabling disease and as third cause death in developed countries, is characterized for the interruption of cerebral blood flow capable to cause alteration on brain functions. It is well established that the activation of A1 adenosine receptor confers neuroprotection against acute noxious brains stimuli. The aim of this study was to investigate the effects of preconditionnement by restraint stress on rats subjected to transient cerebral ischemia (TCI) and the participation of A1 receptor in this process. Firstly, Wistar male rats weighing 200-240g were exposed to immobilisation stress for 2 hours followed to TCI by occlusion of both carotid arteries for 30 minutes. Group of animals were pretreated with A1 receptor antagonist DPCPX (0,1mg/kg or 1 mg/kg. i.p.) before immobilisation stress. Retal temperature was monitored and 37ÂC were maintened during cirurgical procedure using a heating light. Infarct size was determined by TTC staining 24h after TCI and the behavioral tests were performed after 72 hours. Open field test were used to assess locomotor activity, Y-maze test for working memory and passive avoidance test to aversive short and long term memory evaluation. Our results showed that TCI caused damage on brain tissue (sham operated= 10.36  0.75%; ISC= 18.52  2.62%), decreased the vertical exploratory behavior (number of events: sham= 5.00  1.23; ISC= 1.50  0.72) and deficit on long term aversive memory (sham= 271.2  17.61s; ISC= 108.4  67.64s). No differences were found on the crossing behavior (sham= 15.71  2.02; ISC= 11.00  2.13), working memory (sham= 70.16  5.77; ISC= 71.37  7.94) neither short term memory (sham= 145.9  42.75; ISC= 113.1  64.97). The infarct volume rates on restraint stress (RS) group were significantly less than ischemic (ISC) group (sham= 10.36  0.75%; ISC= 18.52  2.62%; RS= 12.59  0.87%) while the number of rearing were significantly higher (sham= 5.00 1.23; ISC= 1.50 0.72; RS= 6.091 1.443). On the passive avoidance test, restraint stress tend to impair the ischemic damage on the long term memory (sham= 271.2  17.61s; ISC= 108.4  67.64s; RS= 156.1  45.81s). When treated with DPCPX (1mg/kg) the infarct size show an increase (ISC= 18.52  2.62%; RS = 12.59  0.87%; DPCPX= 19.95  3.38%) suggesting a blockade of neuroprotection action achieved by restraint stress. DPCPX also decreased the number of rearing on the open field test (ISC= 1.50  0.72; RS= 6.091 1.443; DPCPX = 3.20  0.90) and tend to reverse the improvement of long term aversive memory accessed by restraint stress (ISC= 108.4  67.64s; RS= 156.1  45.81s; DPCPX 1= 88.61 38.83s). This work showed a neuroprotection of pre conditioning restraint stress against cerebral ischemia and the blockade of this action by a previously administration of DPCPX, A1 adenosine antagonist. These findings point to the involvement of the A1 adenosine receptor in the protection conferred by restraint stress by mechanisms that still need to be clarified.

Por conta da liberação de uma nova faixa de espectro as aplicações que utilizam transmissão em banda ultralarga se expandiram. Por conta disso, várias formas de transmissão pulsada ganharam destaque. Contudo, o projeto e estudo de antenas até então era majoritariamente feito em banda estreita e regime permanente senoidal. Além disso, para transmissão pulsada, a resposta impulsiva da antena passa a ser mais necessária do que sua resposta em banda estreita. Por isso, o objetivo desse estudo foi explorar o que ocorre com pulsos estreitos se propagando em uma antena de forma a se obter uma aproximação da resposta impulsiva de antenas. Mais especificamente, foi obtido um modelo analítico que explicita a relação entre a geometria e o funcionamento da antena. Através do estudo da espiral equiangular foi possível encontrar o decaimento do pulso de corrente ao longo da linha como também o campo radiado de forma quantitativa. Tal resultado, assim como os procedimentos para sua obtenção, poderá ser utilizado para outras antena filamentares. / The applications for Ultra Wide Band have grown since the new regulation allowed the use of a new large frequency band. Since then, systems for pulsed transmission entered the spotlight. However, the antenna\'s project and study were in big part done in narrowband and sinusoidal steady-state. Besides, the impulse response is of much more interest for these systems than the frequency response. For this reason, the main goal of this work is to explore how current pulses propagate on the antenna to obtain an approximate impulse response. Moreover, an analytical model that unveils the relation between the antenna geometry and its current decay is presented. Through the study of the equiangular spiral it is possible to find the pulse decay as a function of the line length and the radiated field in a quantitative fashion. This result as well as the methods used to obtain it can be used for other antennas.

Bandpass filtered transient-evoked otoacoustic emission (TEOAE) waveforms are composed of short-latency (SL) and long-latency (LL) portions. The LL portion has latency consistent with generation through linear coherent reflection at the tonotopic place on the basilar membrane. The short-latency (SL) portion occurs earlier in time and exhibits less compressive growth. Several mechanisms have been hypothesized to explain generation of the SL portion, including 2f1-f2 intermodulation distortion and coherent reflection basal to the tonotopic place. Two experiments were designed to examine the generation mechanism and generation location of the SL portion. Experiment 1 tests the hypothesis that the SL portion results from low-side, cubic intermodulation distortion. Experiment 2 determines the region along the basilar membrane at which the SL portion of the TEOAE is generated. The null hypothesis that the SL portion of the TEOAE is generated through low-side, cubic intermodulation distortion requires stimuli with broad frequency content. Stimulus energy at different frequencies (f1 and f2) is presumed to interact simultaneously across the cochlear partition, generating a distortion-source OAE. To test this hypothesis, OAEs were evoked using 2 kHz tone-bursts with durations spanning the time-frequency continuum between a click and a pure tone. As tone-burst duration increases, stimulus energy at the primary frequencies (f1 and f2) decreases and the input to any nonlinear distortion source is reduced. Accordingly, if generated through 2f1-f2 distortion, the magnitude of the SL portion of the TEOAE was expected to decrease as tone-burst duration increased. Results were inconsistent with generation of the SL portion through intermodulation distortion. As tone-burst duration increased, the SL portion remained present in the TEOAE. The presence of the SL portion influenced the level-dependency of TEOAE latency and magnitude to the same extent across all tone-burst durations. The region of generation along the cochlear partition of the SL portion has implications for the mechanism through which it is generated. Generation through low-side, cubic intermodulation distortion (2f1-f2) would occur near the f2 tonotopic place. If generation is through coherent reflection, a generation region basal to that of the tonotopic place is hypothesized. To determine the cochlear region where the SL portion is generated, TEOAEs were evoked by 2 kHz tone-bursts in the presence of different suppressor stimuli. The amount of suppression induced by each suppressor on the OAE was measured, and the suppressor frequency causing greatest suppression of a given portion of the TEOAE was interpreted as corresponding to that portion's generation place along the basilar membrane. For analysis purposes, the SL portion was divided into two SL time-windows (SL1 and SL2). The LL portion of the TEOAE was maximally suppressed by a 2.07 kHz tone, consistent with generation at the tonotopic place. Both SL components were generated basal to the tonotopic place. The later-occurring SL portion of the TEOAE (SL1) was generated between 1/4-1/3-octave basal to the tonotopic place while the earlier-occurring SL portion (SL2) was generated 3/5-octave basal to the tonotopic place. The generation region of the SL1 portion of the TEOAE was too apical to be consistent with generation through 2f1-f2 distortion. Although the generation region of the SL2 portion was what would be expected for a 2f1-f2 distortion-source OAE, the latency was too early. Generation of both SL portions may be explained through basal linear coherent reflection. Per this mode of generation, the SL1 and SL2 portions of the TEOAE each likely mirror the underlying mechanics at different regions along the cochlear partition.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

The activity of glutamate transporters is essential for the temporal and spatial regulation of the neurotransmitter concentration in the synaptic cleft which is critical for proper neuronal signaling. Because of their role in controlling extracellular glutamate concentrations, dysfunctional glutamate transporters have been implicated in several neurodegenerative diseases and psychiatric disorders. Therefore, investigating the mechanism of substrate transport by these transporters is essential in understanding their behavior when they malfunction. A bacterial glutamate transporter homologue has been successfully crystallized revealing the molecular architecture of glutamate transporters. However, many important questions remain unanswered. In this thesis, I will address the role of D439 in the binding of Na+, and I will identify other electrogenic steps that contribute to the total electrogenicity of the transporter cycle. The role of D439 in the binding of Na+ to the transporter was explored previously in this lab. While it was proposed that the effect of D439 in Na+ binding is indirect, the results described in this thesis provides added support to this work. Here, I will show that the D439 mutation changed the pharmacology of EAAC1 such that THA was converted from a transported substrate to a competitive inhibitor. I will also show that Na+ binding to the substrate-bound mutant transporter occurred with the same affinity as that of Na+ to the substrate-bound wild-type transporter. Therefore, based on these results, D439 is not directly involved in the binding of Na+ to the substrate-bound transporter, but that its effect is rather indirect through changing the substrate binding properties. Na+ binding steps to the empty transporter and to the glutamate-bound EAAC1 contribute only 20% of the total electrogenicity of the glutamate transporter reactions cycle. While K+-induced relocation has been proposed to be electrogenic, there is no experimental evidence that supports it. In this work, I will show that the K+-induced relocation of the empty transporter is electrogenic. Moreover, the results in this work show that the K+-dependent steps are slower than the steps associated with the Na+/glutamate translocation suggesting that the K+-induced relocation determines the transporter?s properties at steady state.

The Purpose of this thesis is to experimentally demonstrate an inversion analysis technique, developed by Dr. Jay Frankel (UTK), that utilizes transient temperature data from probes embedded at known locations in a material. This allows one to determine thermal properties (thermal diffusivity and thermal conductivity) of the material, surface temperature, and the surface heat flux as they change with time. Dr. Frankel’s inversion method can be used to determine surface temperature and heat flux of a one-dimensional semi-infinite slab based on the transient data from one or two embedded probes, if the thermal conductivity and thermal diffusivity of the material are known. Frankel’s theory suggests that the thermal properties of the material can be determined if transient data from two thermocouple (TC) probes at known locations and the heat flux at the surface are known. This thesis investigates finding the thermal properties and surface temperature of materials using a two embedded thermocouple approach. As an initial check to the inversion analysis, the theoretical temperature solution for a one-dimensional semi-infinite slab was used. This validated that the analysis could converge to the constant thermal properties for the theoretical material. An experiment was run again to provide data for the materials copper and aluminum. Using a real material is fundamentally different from using theoretical determined (analytical) data, because the thermal properties for a real material vary with temperature. Since the inversion analysis converged to a constant solution for the theoretical temperatures, it was believed that the real material will converge to a solution. However, it was seen that the thermal diffusivity for the real materials never converged to the expected value. Although, when a constant handbook value for the thermal diffusivity is used to calculate the thermal conductivities from the experimental temperature data collected from the internal probes, the inversion analysis resulted in good agreement with experiment.

During this PhD thesis, cobalt (Co) catalysts have been prepared, characterized and studied in the carbon monoxide hydrogenation (CO+H2) reaction (also known as “Fischer-Tropsch” (FT) reaction). In industry, the FT synthesis aims at producing long chain hydrocarbons such as gasoline or diesel fuels. The interest is that the reactants (CO and H2) are obtained from other carbonaceous sources than crude oil: natural gas, coal, biomass or even petroleum residues. As it is well known that the worldwide crude oil reserves will be depleted in a few decades, the FT reaction represents an attractive alternative for the production of various fuels. Moreover, this reaction can also be used to produce high value specialty chemicals (long chain alcohols, light olefins…). Two different types of catalysts have been investigated during this thesis: cobalt with magnesia used as support or dispersant (Co/MgO) and cobalt with silica used as support (Co/SiO2). Each catalyst from the first class is prepared by precipitation of a mixed Co/Mg oxalate in acetone. This coprecipitation is followed by a thermal decomposition under reductive atmosphere leading to a mixed Co/MgO catalyst. On the other hand, Co/SiO2 catalysts are prepared by impregnation of a commercial silica support with a chloroform solution containing Co nanoparticles. This impregnation is then followed by a thermal activation under reductive atmosphere. The mixed Co/Mg oxalates and the resulting Co/MgO catalysts have been extensively characterized in order to gain a better understanding of the composition, the structure and the morphology of these materials: thermal treatments under reductive and inert atmospheres (followed by MS, DRIFTS, TGA and DTA), BET surface area measurements, XRD and electron microscopy studies have been performed. Moreover, an original in situ technique for measuring the H2 chemisorption surface area of catalysts has been developed and used over our catalysts. The performances of the Co/MgO and Co/SiO2 catalysts have then been evaluated in the CO+H2 reaction at atmospheric pressure. Chemical Transient Kinetics (CTK) experiments have been carried out in order to obtain information about the reaction kinetics and mechanism and the nature of the catalyst active surface under reaction conditions. The influence of several experimental parameters (temperature, H2 and CO partial pressures, total volumetric flow rate) and the effect of passivation are also discussed with regard to the catalyst behavior. Our results indicate that the FT active surface of Co/MgO 10/1 (molar ratio) is entirely covered by carbon, oxygen and hydrogen atoms, most probably associated as surface complexes (possibly formate species). Thus, this active surface does not present the properties of a metallic Co surface (this has been proved by performing original experiments consisting in switching from the CO+H2 reaction to the propane hydrogenolysis reaction (C3H8+H2) which is sensitive to the metallic nature of the catalyst). CTK experiments have also shown that gaseous CO is the monomer responsible for chain lengthening in the FT reaction (and not any CHx surface intermediates as commonly believed). Moreover, CO chemisorption has been found to be irreversible under reaction conditions. The CTK results obtained over Co/SiO2 are quite different and do not permit to draw sharp conclusions concerning the FT reaction mechanism. More detailed studies would have to be carried out over these samples. Finally, Co/MgO catalysts have also been studied on a combined DRIFTS/MS experimental set-up in Belfast. CTK and Steady-State Isotopic Transient Kinetic Analysis (SSITKA) experiments have been carried out. While formate and methylene (CH2) groups have been detected by DRIFTS during the FT reaction, the results indicate that these species play no role as active intermediates. These formates are most probably located on MgO or at the Co/MgO interface, while methylene groups stand for skeleton CH2 in either hydrocarbon or carboxylate. Unfortunately, formate/methylene species have not been detected by DRIFTS over pure Co catalyst without MgO, because of the full signal absorption.