Thesis (M. Phil.)--University of Hong Kong, 1991.

Thesis (M. Phil.)--University of Hong Kong, 1991.

Inaug.-diss.--Göttingen. / Lebenslauf.

Thesis (M.A.)--Boston University

Thesis (M.A.)--Boston University. / In Chapter 1 of this thesis we give some elementary definitions and prove the following three theorems: 1.1 Every positive integer n greater than one can be expressed in the form n=p1p2...pk where each of the pi is a prime number. 1.2 Every integer n greater than one can be expressed in standard form in one and only one way. If we write n=(p1^a1)(p2^a2).....(pj^aj), where p1< p2 <...< pj and each ai is greater than 0, then n is expressed in standard form. 1.3 The number of prime numbers is infinite [TRUNCATED]

Made available in DSpace on 2018-08-24T22:53:14Z (GMT). No. of bitstreams: 1 tese_4955_.pdf: 2595696 bytes, checksum: 9e5cf0372c78efe4f4b26fe602407955 (MD5) Previous issue date: 2011-04-15 / A presença de casas e prédios e outras construções próximas de fontes emissoras afeta o padrão de escoamento de ar e a dispersão dos contaminantes na camada limite superficial. Além disto, o tempo de média para o qual as concentrações médias do contaminante são determinadas depende da composição química do contaminante e do tempo de impacto causado. Por exemplo, para compostos odorantes, o tempo de média deve ser relacionado ao intervalo de tempo de uma inspiração (1 à 5s) ou ao intervalo de tempo para o qual os compostos odorantes causam efetivamente o incômodo. Uma das ferramentas empregadas nos estudos desses impactos são os modelos matemáticos que tem a capacidade de incluir o efeito da presença de obstáculos e de representar concentrações de curto período no escoamento. Devido à facilidade e rapidez em sua aplicação, os modelos gaussianos são muito empregados com adaptações incorporando o efeito de obstáculos e a representação de concentrações de curto período. O presente trabalho tem como objetivo avaliar os modelos CALPUFF e AERMOD, utilizando o modelo PRIME para considerar os efeitos da presença do obstáculo, e duas metodologias para a obtenção de concentrações de pico, uma que aplica um fator de ajuste no coeficiente de dispersão e outra que aplica um fator de ajuste diretamente nas concentrações para pequenos intervalos de tempo. Os resultados das modelagens foram comparados com dados obtidos em experimentos de túnel de vento, e mostraram os que os modelos tenderam a subestimar os valores de concentração próximos aos obstáculos, com o modelo AERMOD superestimando seus resultados em relação ao CALPUFF. Além disso, foi possível inferir que o modelo CALPUFF melhora o seu desempenho à medida que a distância em relação ao obstáculo aumenta. Já com relação ao modelo AERMOD, constatou-se que seus resultados melhores ocorrem parte nas regiões próximas do obstáculo, sendo superior ao CALPUFF na maioria dos casos. Entretanto, para maiores distâncias, os dois modelos estimaram resultados semelhantes. A análise das concentrações máximas médias para intervalos de tempo de curto período sugeriu que o ajuste aplicado diretamente nas concentrações nas previsões dos modelos AERMOD e CALPUFF não diferem substancialmente. Porém quando as duas metodologias são analisadas no CALPUFF, as maiores concentrações de pico são encontradas com o fator de ajuste aplicado diretamente nas concentrações, com uma diminuição da diferença entre as metodologias à medida que se tem intervalos de tempos maiores.

Commercial superalloys like Rene88DT are used in high temperature applications like turbine disk in aircraft jet engines due to their excellent high temperature properties, including strength, ductility, improved fracture toughness, fatigue resistance, enhanced creep and oxidation resistance. Typically this alloy's microstructure has L12-ordered precipitates dispersed in disordered face-centered cubic &#947; matrix. A typical industrially relevant heat-treatment often leads to the formation of multiple size ranges of &#947;¢ precipitates presumably arising from multiple nucleation bursts during the continuous cooling process. The morphology and distribution of these &#947;&#8242; precipitates inside &#947; matrix influences the mechanical properties of these materials. Therefore, the study of thermodynamic and kinetic factors influencing the evolution of these precipitates and subsequent effects is both relevant for commercial applications as well as for a fundamental understanding of the underlying phase transformations. The present research is primarily focused on understanding the mechanism of formation of different generations of &#947;&#8242; precipitates during continuous cooling by coupling scanning electron microscopy (SEM), energy filtered TEM and atom probe tomography (APT). In addition, the phase transformations leading to nucleation of &#947;&#8242; phase has been a topic of controversy for decades. The present work, for the first time, gives a novel insight into the mechanism of order-disorder transformations and associated phase separation processes at atomistic length scales, by coupling high angle annular dark field (HAADF) - STEM imaging and APT. The results indicate that multiple competing mechanisms can operate during a single continuous cooling process leading to different generations of &#947;&#8242; including a non-classical mechanism, operative at large undercoolings.

No description available.

The rapid increase in the use of embedded systems for performing secure transactions, has proportionally increased the security threat, faced by such devices. Security threats are an issue of concern at both software and hardware level. The field of cryptography has been intensively researched for secure implementation techniques, methods to attack secure systems and countermeasures to avoid such attacks. In this thesis, we provide solutions for two interesting problems in the field of hardware security using reconfigurable hardware. First, we discuss a countermeasure to prevent side-channel analysis (SCA) attacks on an embedded system. We present an SCA-resistant processor design in the context of an embedded design flow for FPGA. It integrates an SCA-resistant custom instruction set on a soft-core CPU and derives an SCA resistance from dual-rail precharge principle. The resulting countermeasure applies to a broad class of block ciphers that consist of lookup tables and logical operations. While many countermeasures have been proposed previously, we show that our solution achieves an excellent trade-off between SCA resistance, (software and hardware) design complexity, performance, and circuit area cost. Secondly, we present a system to attack a special type of cryptography called Elliptic Curve Cryptography(ECC). It targets the Elliptic Curve Discrete Logarithmic Problem (ECDLP) for a NIST-standardized ECC-curve over 112-bit prime field. We implement a successful demonstration of an ECC cryptanalytic engine using the Pollard rho algorithm on a hardware-software co-integrated platform. We propose a novel, generalized architecture for polynomial-basis multiplication over prime field and its extension to a dedicated square module. Its design strategy is portable to other prime field moduli. / Master of Science

在這篇論文中，我們將探討整函數與半純函數之分解。並且著重於質函數與擬質函數之研究。同時，我們證明某類多項式其次數為合成數且為質函數。 / In this thesis, we study some factorizations of entire and meromorphic functions, in particular, prime and pseudo-prime functions. Also, we obtain a new class of prime polynomials of composite degree.