Particle accelerators produce beams of high-energy particles, which are used for both fundamental and applied scientific research and are critical to the development of accelerator driven sub-critical reactor systems. An effective magnetic shield is very important to achieve higher quality factor (Qo) of the cryomodule of a particle accelerator. The allowed value of field inside the cavity due to all external fields (particularly the Earth’s magnetic field) is ~15 mG or less. The goal of this PhD dissertation is to comprehensively study the magnetic properties of commonly used magnetic shielding materials at both cryogenic and room temperatures. This knowledge can be used for the enhanced design of magnetic shields of cryomodes (CM) in particle accelerators. To this end, we first studied the temperature dependent magnetization behavior (M-H curves) of Amumetal and A4K under different annealing and deformation conditions. This characterized the effect of stress or deformation induced during the manufacturing processes and subsequent restoration of high permeability with appropriate heat treatment. Next, an energy based stochastic model for temperature dependent anhysteretic magnetization behavior of ferromagnetic materials was proposed and benchmarked against experimental data. We show that this model is able to simulate and explain the magnetic behavior of as rolled, deformed and annealed amumetal and A4K over a large range of temperatures. The experimental results for permeability are then used in a finite element model (FEM) in COMSOL to evaluate the shielding effectiveness of multiple shield designs at room temperature as well as cryogenic temperature. This work could serve as a guideline for future design, development and fabrication of magnetic shields of CMs.

Thesis advisor: Susanto Basu / Thesis advisor: Peter Ireland / This dissertation consists of three independent chapters analyzing the role that information and credit frictions play in goods and financial markets. Within these chapters, I develop dynamic stochastic general equilibrium (DSGE) models to study the implications of these frictions on the macroeconomy, both at the national and international level. In the first chapter, I provide a novel explanation for the observed large and persistent fluctuations in real exchange rates using a model with noisy, dispersed information among price-setting firms. Chapter two studies how entrepreneurs' attitudes towards risk affect business cycles in a framework with agency frictions between borrowers and lenders. Finally, chapter three introduces a liquidity channel in a business cycle model with agency frictions to rationalize the highly volatile behavior of default recovery rates observed in the data. Real exchange rates have been extremely volatile and persistent since the end of the Bretton Woods system. For many developed economies, real exchange rates are as volatile as nominal exchange rates, and their fluctuations exhibit a half-life in the range of three to five years. Traditional sticky-price models struggle to jointly account for these features under plausible nominal rigidities (Chari, Kehoe, and McGrattan, 2002). Is it possible to reconcile, in a single framework, the enormous short-term volatility of the real exchange rate with its extremely long half-life? The first chapter of this dissertation addresses this question within a framework in which information is noisy and heterogeneous among price-setting firms. In this context, the continuing uncertainty that firms face about the state of the economy and about the beliefs of their competitors, slows down the price adjustment in response to nominal shocks, generating large and long-lived real exchange rate movements. I estimate the model using real output and output deflator data from the US and the Euro Area and show, as an out-of-sample test, that the model successfully explains the observed volatility and persistence of the Euro/Dollar real exchange rate. In a Bayesian model comparison, I show that the data strongly favor the dispersed information model relative to a sticky-price model à la Calvo. The model also accounts for the persistent effects of monetary shocks on the real exchange rate that I document using a structural vector autoregression. The second chapter, joint with Mikhail Dmitriev, studies how entrepreneurs' attitudes towards risk affect business cycles in a model with agency frictions. Entrepreneurs are inevitably exposed to non-diversified risk, which likely affects their willingness to borrow and to invest in risky projects. Nevertheless, the financial friction literature has paid little attention to how entrepreneurs' desire to take on this risk affects their investment choices in a general-equilibrium setting. Indeed, business cycle models with credit market frictions that feature idiosyncratic risk assume, for tractability, that entrepreneurs are risk neutral (Bernanke, Gertler, and Gilchrist, 1999, BGG). In this chapter, we generalize the BGG framework to the case of entrepreneurs with constant-relative-risk-aversion preferences. In doing so, we overcome the aggregation challenges of this setup and maintain an analytically tractable, log-linear framework. Our main result is that higher risk aversion stabilizes business cycle fluctuations in response to financial shocks, such as wealth redistribution or risk shocks, without significantly affecting the dynamic responses to technology and monetary shocks. Our findings suggest that, within this class of models, the ability of financial shocks to account for a large portion of short-run output fluctuations found in previous work (e.g., Christiano, Motto, and Rostagno (2014)) crucially hinges on borrowers' risk neutrality. The third chapter, joint with Mikhail Dmitriev, examines the implications of the cyclical properties of default recovery rates for aggregate fluctuations. We document that recovery rates after default in the United States are highly volatile and strongly pro-cyclical. These facts are hard to reconcile with the existing financial friction literature. Indeed, models with limited enforceability à la Kiyotaki and Moore (1997) do not feature defaults and recovery rates in equilibrium, while agency costs models following Bernanke, Gertler, and Gilchrist (1999) underestimate the volatility of recovery rates by one order of magnitude. In this chapter, we extend the standard agency costs model allowing liquidation costs for creditors to depend on the tightness of the market for physical capital. Creditors do not have expertise in selling entrepreneurial assets, but when buyers are plentiful, this disadvantage is minimal. Instead when sellers are abundant, the disadvantage of being an outsider is higher. Following a negative shock, entrepreneurs sell capital and liquidation costs for creditors increase, driving down recovery rates. With higher liquidation costs, creditors cut lending and cause entrepreneurs to sell even more capital. This liquidity channel works independently from standard balance sheet effects, and amplifies the impact of financial shocks on output by up to 50 percent. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Economics.

No presente trabalho medimos e analisamos distribuições angulares para o processo de espalhamento elástico do núcleo radioativo de 12B em alvo de 58Ni. As medidas foram realizadas nas energias de Elab=30.0 e 33.0 MeV no laboratório do acelerador Pelletron. Essas energias são próximas a barreira Coulombiana (VB=28.0 MeV) para esse sistema. Para a produção do feixe radioativo de 12B utilizamos o sistema RIBRAS instalado nesse laboratório. As distribuições angulares foram analisadas com o modelo ótico, utilizando potenciais de Woods-Saxon e Potencial de São Paulo. Para uma interpretação física mais consistente e um estudo da influência de outros canais de reação no espalhamento elástico analisamos também considerando o método de canais acoplados. Considerando o acoplamento dos canais de espalhamento inelásticos, reorientação e spin-órbita pudemos descrever a distribuição angular na energia de 30.0 MeV. No entanto esses canais não foram suficientes para descrever a distribuição angular na energia de 33.0 MeV, indicando que outros canais como de transferência e/ou break-up possam ser importes. A partir da análise das distribuições angulares com modelo ótico obtivemos também a seção de choque total de reação. Essas seções de choque foram comparadas com a de outros sistemas utilizando métodos de redução, indicando que o projétil 12B segue uma sistemática intermediária entre núcleos fortemente ligados e fracamente ligados. Finalmente, discutimos a sistemática dos resultados de canais acoplados para o espalhamento elásticos dos isótopos de Boro 8,10,11,12B no alvo 58Ni em termos da configuração de clusters dos projéteis. / In the present work we measure and analyzed angular distributions for the process of elastic scattering of the radioactive nucleus of 12B in a target of 58Ni. The measurements were performed in the energies of Elab = 30.0 and 33.0 MeV in the Pelletron accelerator laboratory. These energies are close to the Colombian barrier (VB = 28.0 MeV) for this system. For the production of the radioactive beam of 12B we used the RIBRAS system installed in this laboratory. The angular distributions were analyzed with the optical model, using potentials of Woods-Saxon and Potential of São Paulo. For a more consistent physical interpretation and a study of the influence of other reaction channels in the elastic scattering we also analyze the coupled channel method. Considering the coupling of the inelastic scattering channels, reorientation and spin-orbit we could describe the angular distribution in the energy of 30.0 MeV. However, these channels were not enough to describe the angular distribution in the energy of 33.0 MeV, indicating that other channels as transfer and / or break-up can be amounts. From the analysis of the angular distributions with optical model we also obtained the section of total reaction shock. These cross sections were compared with those of other systems using reduction methods, indicating that projectile 12B follows a systematic intermediate between tightly bound and weakly bonded cores. Finally, we discuss the systematics of the results of elastic scattering channels of the Boron isotopes 8,10,11,12B in the 58Ni target in terms of the cluster configuration of the projectiles.

Foram determinadas de maneira absoluta seções de choque duplamente diferenciais de produção de bremsstrahlung, para elétrons com energia cinética de 20, 50, 75 e 100~keV, nos elementos C, Al, Ag, Te, Ta e Au, e nos ângulos de emissão dos fótons $35^{\\mathrm}$, $90^{\\mathrm}$ e $131^{\\mathrm}$. As medidas foram realizadas na linha de feixe de baixa energia do Acelerador Microtron, do Instituto de Física da Universidade de São Paulo, em um arranjo que contou com três detetores de Ge hiperpuro, dois planares e um coaxial. Os alvos finos foram confeccionados pela técnica de deposição física de vapores, enquanto suas espessuras foram caracterizadas a partir da espectrometria de retroespalhamento de Rutherford. Foi desenvolvido um modelo analítico para descrever a função reposta de detetores de Ge, que permitiu a deconvolução dos espectros de bremsstrahlung entre os 12~keV e o ponto de máxima transferência de energia, com uma resolução de 1~keV. As seções de choque obtidas apresentam uma incerteza relativa entre 3\\% e 5\\%, e foram comparadas com os cálculos teóricos que constituem o estado da arte na temática, e com os poucos dados experimentais encontrados na literatura. / Bremsstrahlung doubly dierential cross sections were absolutely determined for electrons with kinetic energies of 20, 50, 75 and 100 keV, in the elements C, Al, Ag, Te, Ta e Au, and the photon emission angles of 35o, 90o and 131o. The measurements were performed at the low energy beam line of the S~ao Paulo Microtron Accelerator, using three high purity Ge detectors: two planar and one coaxial. Thin targets were obtained by the Physical Vapor Deposition technique, and their thicknesses were characterized through Rutherford Backscattering Spectroscopy. An analytical model was developed to describe the response function of Ge detectors, which allowed to unfold the bremsstrahlung spectra between 12 keV and the maximum energy transfer point, with an energetic resolution of 1 keV. The obtained cross sections present relative uncertainties between 3% and 5%. These results were compared with the higher accurate theoretical calculations and also with the experimental reports found in literature.

With the amount of users on the web steadily increasing websites must at times endure heavy loads and risk grinding to a halt beneath the flood of visitors. One solution to this problem is by using HTTP reverse proxy caching, which acts as an intermediate between web application and user. Content from the application is stored and passed on, avoiding the need for the application produce it anew for every request. One popular application designed solely for this task is Varnish; another interesting application for the task is Nginx which is primarily designed as a web server. This thesis compares the performance of the two applications in terms of number of requests served in relation to response time, as well as system load and free memory. With both applications using their default configuration, the experiments find that Nginx performs better in the majority of tests performed. The difference is however very slightly in tests with low request rate.

No presente trabalho medimos e analisamos distribuições angulares para o processo de espalhamento elástico do núcleo radioativo de 12B em alvo de 58Ni. As medidas foram realizadas nas energias de Elab=30.0 e 33.0 MeV no laboratório do acelerador Pelletron. Essas energias são próximas a barreira Coulombiana (VB=28.0 MeV) para esse sistema. Para a produção do feixe radioativo de 12B utilizamos o sistema RIBRAS instalado nesse laboratório. As distribuições angulares foram analisadas com o modelo ótico, utilizando potenciais de Woods-Saxon e Potencial de São Paulo. Para uma interpretação física mais consistente e um estudo da influência de outros canais de reação no espalhamento elástico analisamos também considerando o método de canais acoplados. Considerando o acoplamento dos canais de espalhamento inelásticos, reorientação e spin-órbita pudemos descrever a distribuição angular na energia de 30.0 MeV. No entanto esses canais não foram suficientes para descrever a distribuição angular na energia de 33.0 MeV, indicando que outros canais como de transferência e/ou break-up possam ser importes. A partir da análise das distribuições angulares com modelo ótico obtivemos também a seção de choque total de reação. Essas seções de choque foram comparadas com a de outros sistemas utilizando métodos de redução, indicando que o projétil 12B segue uma sistemática intermediária entre núcleos fortemente ligados e fracamente ligados. Finalmente, discutimos a sistemática dos resultados de canais acoplados para o espalhamento elásticos dos isótopos de Boro 8,10,11,12B no alvo 58Ni em termos da configuração de clusters dos projéteis. / In the present work we measure and analyzed angular distributions for the process of elastic scattering of the radioactive nucleus of 12B in a target of 58Ni. The measurements were performed in the energies of Elab = 30.0 and 33.0 MeV in the Pelletron accelerator laboratory. These energies are close to the Colombian barrier (VB = 28.0 MeV) for this system. For the production of the radioactive beam of 12B we used the RIBRAS system installed in this laboratory. The angular distributions were analyzed with the optical model, using potentials of Woods-Saxon and Potential of São Paulo. For a more consistent physical interpretation and a study of the influence of other reaction channels in the elastic scattering we also analyze the coupled channel method. Considering the coupling of the inelastic scattering channels, reorientation and spin-orbit we could describe the angular distribution in the energy of 30.0 MeV. However, these channels were not enough to describe the angular distribution in the energy of 33.0 MeV, indicating that other channels as transfer and / or break-up can be amounts. From the analysis of the angular distributions with optical model we also obtained the section of total reaction shock. These cross sections were compared with those of other systems using reduction methods, indicating that projectile 12B follows a systematic intermediate between tightly bound and weakly bonded cores. Finally, we discuss the systematics of the results of elastic scattering channels of the Boron isotopes 8,10,11,12B in the 58Ni target in terms of the cluster configuration of the projectiles.

La complexité des systèmes embarqués et des applications impose des besoins croissants en puissance de calcul et de consommation énergétique. Couplé au rendement en baisse de la technologie, le monde académique et industriel est toujours en quête d'accélérateurs matériels efficaces en énergie. L'inconvénient d'un accélérateur matériel est qu'il est non programmable, le rendant ainsi dédié à une fonction particulière. La multiplication des accélérateurs dédiés dans les systèmes sur puce conduit à une faible efficacité en surface et pose des problèmes de passage à l'échelle et d'interconnexion. Les accélérateurs programmables fournissent le bon compromis efficacité et flexibilité. Les architectures reconfigurables à gros grains (CGRA) sont composées d'éléments de calcul au niveau mot et constituent un choix prometteur d'accélérateurs programmables. Cette thèse propose d'exploiter le potentiel des architectures reconfigurables à gros grains et de pousser le matériel aux limites énergétiques dans un flot de conception complet. Les contributions de cette thèse sont une architecture de type CGRA, appelé IPA pour Integrated Programmable Array, sa mise en œuvre et son intégration dans un système sur puce, avec le flot de compilation associé qui permet d'exploiter les caractéristiques uniques du nouveau composant, notamment sa capacité à supporter du flot de contrôle. L'efficacité de l'approche est éprouvée à travers le déploiement de plusieurs applications de traitement intensif. L'accélérateur proposé est enfin intégré à PULP, a Parallel Ultra-Low-Power Processing-Platform, pour explorer le bénéfice de ce genre de plate-forme hétérogène ultra basse consommation. / Emerging trends in embedded systems and applications need high throughput and low power consumption. Due to the increasing demand for low power computing and diminishing returns from technology scaling, industry and academia are turning with renewed interest toward energy efficient hardware accelerators. The main drawback of hardware accelerators is that they are not programmable. Therefore, their utilization can be low is they perform one specific function and increasing the number of the accelerators in a system on chip (SoC) causes scalability issues. Programmable accelerators provide flexibility and solve the scalability issues. Coarse-Grained Reconfigurable Array (CGRA) architecture consisting of several processing elements with word level granularity is a promising choice for programmable accelerator. Inspired by the promising characteristics of programmable accelerators, potentials of CGRAs in near threshold computing platforms are studied and an end-to-end CGRA research framework is developed in this thesis. The major contributions of this framework are: CGRA design, implementation, integration in a computing system, and compilation for CGRA. First, the design and implementation of a CGRA named Integrated Programmable Array (IPA) is presented. Next, the problem of mapping applications with control and data flow onto CGRA is formulated. From this formulation, several efficient algorithms are developed using internal resources of a CGRA, with a vision for low power acceleration. The algorithms are integrated into an automated compilation flow. Finally, the IPA accelerator is augmented in PULP - a Parallel Ultra-Low-Power Processing-Platform to explore heterogeneous computing.

Esse trabalho consistiu na medida e análise de distribuições angulares do espalhamento elástico e inelástico para núcleos de massa A=10 em alvos de 58Ni e no desenvolvimento de novos feixes secundários radioativos para o sistema RIBRAS. As distribuições angulares do sistema 10B+58Ni foram medidas nas energias E(lab)= 19, 20, 21, 23, 24, 25 e 35 MeV, no laboratório Tandar na Argentina, enquanto a distribuição angular do sistema 10C+58Ni foi medida na energia E(lab)= 35.3 MeV, utilizando o sistema TWINSOL, da Universidade de Notre Dame, Estados Unidos. O formalismo de canais acoplados foi utilizado para estudar a influência da estrutura deformada do núcleo 10B e da estrutura Bruniana do núcleo 10C. Os resultados indicaram a importância desses efeitos, bem como a possível influência dos canais de transferências e breakup. / This work consisted in the analysis and measurement of angular distributions for elastic and inelastic scattering of mass A=10 projectiles in 58Ni target, as well as in the development of new secondaries radioactive ion beams for the RIBRAS system. Angular distributions for the 10B+58Ni system were measured at E(lab)= 19, 20, 21, 23, 24, 25 and 35 MeV, at Tandar Laboratory in Argentina, while an angular distribution at E(lab)= 35.3 MeV for the 10C+58Ni was measured at the University of Notre Dame, USA, using the Twinsol system. The coupled channel formalism was used to investigate the influence deformed structure of the 10B and Brunian structure for 10C nucleus. The results indicated the importance of these effect as well as the possible influence of transfer and breakup channels. In this work the development of 10C, 14C and 12B beams were investigated for future use in the RIBRAS system.

A utilização da técnica de teleterapia para tratamento de câncer tem sido usada por anos com bons resultados clínicos. Em meados da década de 90, a remoção do filtro aplainador, item que compõe o cabeçote de um acelerador linear de uso clínico, tem sido objeto de estudos por demonstrar bons resultados no tratamento de alguns tipos de câncer. Técnicas utilizadas como Radioterapia de Intensidade Modulada (IMRT) e Radioterapia Estereotáxica (SRT), mostram-se mais eficazes quando não se utiliza o filtro aplainador. A empresa Varian Oncology lançou em 2012 um acelerador linear de uso clínico capaz de operar com o filtro aplainador (FF) e sem o filtro aplainador (FFF), o TrueBeam. Os objetivos desse trabalho são avaliar a homogeneidade de dois importantes parâmetros utilizados para o cálculo de dose nos pacientes submetidos ao tratamento com esse modelo de acelerador linear, a porcentagem de dose profunda (PDP) e índice de qualidade do feixe (TPR20/10). Os dados fornecidos para a análise foram cedidos pelo Hospital Israelita Albert Einstein (HIAE), Real Hospital Português (RHP) e 3 instituições norte-americanas. Através de uma análise estatística dos dados das instituições citadas pode-se observar melhor o comportamento desses parâmetro que demonstraram-se muito homogêneos e com erros menores que 1% na maioria dos casos, confirmando desse modo que os aceleradores lineares do modelo TrueBeam mantém na maioria das vezes uma boa concordância dos parâmetros analisados. / Teletherapy, radiation therapy with linear accelerators, for cancer treatment has being used for years with good clinical results.Since the 90\'s the removal of the flattening filter, item placed at the gantry of the machine, has shown better results for the treatment of some cancers thus being extensively studied. Treatments with Intensity Modulated RadioTherapy (IMRT) and Sthereotaxic RadioTherapy (SRT) were more efficient without the flattening filter. Varian Oncology released the TrueBeam in 2012, a accelerator capable of operating with or without the flattening filter. The aim of this work is to access homogeneity of the percentage depth dose (PDP) and beam quality index (TPR20/10), two important parameters used in patient dose calculations. The data used for analysis were obtained with the Israelita Albert Einstein Hospital (HIAE), Real Português Hospital (RHP) and 3 more institutions located in the United States. The statistical data analysis allowed to observe the parameters behaviors. In general, they were very homogeneous, with errors smaller than 1% confirming the conformance of the TrueBeam accelerators.

"This thesis describes a co-processor system that has been designed to accelerate computations associated with Singular Value Array Reconciliation Tomography (SART), a method for locating a wide-band RF source which may be positioned within an indoor environment, where RF propagation characteristics make source localization very challenging. The co-processor system is based on field programmable gate array (FPGA) technology, which offers a low-cost alternative to customized integrated circuits, while still providing the high performance, low power, and small size associated with a custom integrated solution. The system has been developed in VHDL, and implemented on a Virtex-4 SX55 FPGA development platform. The system is easy to use, and may be accessed through a C program or MATLAB script. Compared to a Pentium 4 CPU running at 3 GHz, use of the co-processor system provides a speed-up of about 6 times for the current signal matrix size of 128-by-16. Greater speed-ups may be obtained by using multiple devices in parallel. The system is capable of computing the SART metric to an accuracy of about -145 dB with respect to its true value. This level of accuracy, which is shown to be better than that obtained using single precision floating point arithmetic, allows even relatively weak signals to make a meaningful contribution to the final SART solution."