<p> It is known in the case of an electron gas that the Coulomb force between electrons is screened due to the density variation around the electrons. In a similar way the force acting between nucleons in nuclear matter may be appreciably different from the free nucleon-nucleon interactions. The main theme of this thesis is to examine the "Screening" effect of the nuclear force. To this end, first the dielectric formulation of the theory of an electron gas is reviewed. Relationship among the chain-diagram approximation, the random phase approximation and the dieledtric formulation is discussed in detail. These techniques are then applied to nuclear matter taking the one-pion exchange potential as an example. It is found that the screening effect on the nuclear force in nuclear matter is indeed quite appreciable. The validity of the approximations is discussed. </p> / Thesis / Master of Science (MSc)

We explore the dynamics of integrable and chaotic quantum many-body systems with a focus on universal structures known as caustics, which are a type of singularity categorized by catastrophe theory. Papers I and II study light cones in quantum spin chains, which we show are caustics and therefore inherits specific functional forms. For integrable systems, the edge of the cone is a fold catastrophe, making the wavefunction locally of Airy form. We also identify the cusp catastrophe in the XY model, thus the secondary light cone is a Pearcey function. Vortex pairs appear in the dynamics, are sensitive to phase transitions, and permit the extraction of critical scaling exponents. In paper II we use a Gaussian wavefront form to distinguish integrable and chaotic models. Writing the wavefront as exp[−m(x)(x − vt)2 + b(x)t], the scaling of coefficients m(x) and b(x) is the diagnostic. The local Airy function description in free models leads to a power-law ∼ x^{−n/3} scaling, while for the chaotic case the scaling is exponential ∼ e^{−cx}. In Paper III, we study the function Fn(t) = <(A(t)B)^n>, a generalization of the four-point out-of-time ordered correlator (OTOC) F2(t), for an integrable system and show that the function Fn(t) can be recast as the return amplitude of an effective time dependent chaotic system, exhibiting signals of chaos such as a positive Lyapunov exponent, spectral statistics consistent with random matrix theory, and relaxation. In Paper IV we perform a comprehensive investigation of caustics in many-body systems in (1+1)- and (2+1)-dimensional Fock space and time. We show how a hierarchy of caustics appear in the dynamics of many-body models, using two- and three-mode Bose-Hubbard models as guiding systems. We show that, in the case of the trimer, high dimensional caustics appear and are organized by the catastrophe X9. / Thesis / Doctor of Philosophy (PhD)

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This thesis explores the effects singularities have on stationary and dynamical properties of many-body quantum systems. In papers I and II we find that the ground state suffers a Z2 symmetry breaking phase transition (PT) when a single impurity is added to a Bose-Einstein condensate (BEC) in a double well (bosonic Josephson junction). The PT occurs for a certain value of the BEC-impurity interaction energy, Λc . A result of the PT is the mean-field dynamics undergo chaotic motion in phase space once the symmetry is broken. We determine the critical scaling exponents that characterize the divergence of the correlation length and fidelity susceptibility at the PT, finding that the BEC-impurity system belongs to the same universality class as the Dicke and Lipkin-Meshkov-Glick models (which also describe symmetry breaking PTs in systems of bosons). In paper III we study the dynamics of a generic two-mode quantum field following a quench where one of the terms in the Hamiltonian is flashed on and off. This model is relevant to BECs in double wells as well as other simple many-particle systems found in quantum optics and optomechanics. We find that when plotted in Fock-space plus time, the semiclassical wave function develops prominent cusp-shaped structures after the quench. These structures are singular in the classical limit and we identify them as catastrophes (as described by the Thom-Arnold catastrophe theory) and show that they arise from the coalescence of classical (mean-field) trajectories in a path integral description. Furthermore, close to the cusp the wave function obeys a remarkable set of scaling relations signifying these structures as examples of universality in quantum dynamics. Within the cusp we find a network of vortex-antivortex pairs which are phase singularities caused by interference. When the mean-field Hamiltonian displays a Z2 symmetry breaking PT modelled by the Landau theory of PTs we calculate scaling exponents describing how the separation distance between the members of each pair diverges as the PT is approached. We also find that the cusp becomes infinitely stretched out at the PT due to critical slowing down. In paper IV we investigate in greater detail the morphology of the vortex network found within cusp catastrophes in many-body wave functions following a quench. In contrast to the cusp catastrophes studied so far in the literature, these structures live in Fock space which is fundamentally granular. As such, these cusps represent a new iii type of catastrophe, which we term a ‘quantum catastrophe’. The granularity of Fock space introduces a new length scale, the quantum length lq = N −1 which effectively removes the vortex cores. Nevertheless, a subset of the vortices persist as phase singularities as can be shown by integrating the phase of the wave function around circuits in Fock-space plus time. Whether or not the vortices survive in a quantum catastrophe is governed by the separation of the vortex-antivortex pairs lv ∝ N −3/4 in comparison to lq , i.e. they survive if lv lq . When particle numbers are reached such that lq ≈ lv the vortices annihilate in pairs. / Thesis / Doctor of Philosophy (PhD)

Hardware-acceleration techniques continue to be used to boost the performance of scientific codes. To do so, software developers identify portions of these codes that are amenable for offloading and map them to hardware accelerators. However, offloading such tasks to specialized hardware accelerators is non-trivial. Furthermore, these accelerators can add significant cost to a computing system. Consequently, this thesis proposes a framework called GePSeA (General Purpose Software Acceleration Framework), which uses a small fraction of the computational power on multi-core architectures to offload complex application-specific tasks. Specifically, GePSeA provides a lightweight process that acts as a helper agent to the application by executing application-specific tasks asynchronously and efficiently. GePSeA is not meant to replace hardware accelerators but to extend them. GePSeA provide several utilities called core components that offload tasks on to the core or to the special-purpose hardware when available in a way that is transparent to the application. Examples of such core components include reliable communication service, distributed lock management, global memory management, dynamic load distribution and network protocol processing. We then apply the GePSeA framework to two applications, namely mpiBLAST, an open-source computational biology application and Reliable Blast UDP (RBUDP) based file transfer application. We observe significant speed-up for both applications. / Master of Science

Submitted by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-06-23T14:59:40Z No. of bitstreams: 1 TES_GUILHERME_AFONSO_MADALOZZO_COMPLETO.pdf: 2690462 bytes, checksum: f0014136baae215c473fedda8527433f (MD5) / Made available in DSpace on 2017-06-23T14:59:40Z (GMT). No. of bitstreams: 1 TES_GUILHERME_AFONSO_MADALOZZO_COMPLETO.pdf: 2690462 bytes, checksum: f0014136baae215c473fedda8527433f (MD5) Previous issue date: 2017-01-12 / Funda??o de Amparo ? Pesquisa do Estado do Rio Grande do Sul (FAPERGS) / The evolution of integrated circuit manufacturing process allowed the SoC (System-on- Chip) design in the 90?s, and currently the design of multiprocessors systems on chip ? MPSoCs (Multiprocessor System-on-Chip). Embedded systems use these devices, due to the offered computational power. The MPSoC design is a challenging task. Specify the MPSoC characteristics, define the components that compose the system and analyze their features are decisions that may change over the product development. Traditional design methods do not favor the design space exploration, leading to expensive products due to required hardware simulation at the gate level, which is only available at the end of the design flow. To solve the design problems of traditional methods, Platform Based Design (PBD) techniques is a design choice. The basis of PBD is a virtual platform model, enabling fast simulations, software debugging and reusability of hardware components. This Thesis comprises the study and development in two research axes: (1) modeling of virtual platforms; (2) analytical methods for software heuristics targeting embedded real-time applications. Virtual platforms are modeled by using ADLs (Architecture Description Languages). This work presents the modeling of several virtual platforms, using different abstraction levels (from RTL to untimed models) and memory architectures (shared and distributed). Based on the evaluations performed in each architecture, the HeMPS platform was adapted to execute real-time applications. The results showed that using the proposed scheduling mechanism and RTA mapping, the results meet the constraints defined by the applications. Comparing platforms with mapping and schedule heuristics on literature, the proposed platform met 100% of the restrictions resulting from the test cases. / A evolu??o no processo de fabrica??o de circuitos integrados permitiu o projeto de SoCs na d?cada de 1990, e atualmente o projeto de sistemas multiprocessados em um ?nico chip - MPSoCs (Multiprocessor System-on-Chip). Estes dispositivos s?o amplamente utilizados em sistemas embarcados, dado o poder computacional oferecido pelos mesmos. Aplica??es com restri??es de tempo-real v?m sendo utilizadas constantemente, sendo um desafio para o projeto de SoCs. O projeto de MPSoCs ? altamente complexo. Especificar as caracter?sticas do MPSoC, definir os componentes que comp?e o sistema e analisar suas funcionalidades s?o decis?es que podem apresentar altera??es ao longo do desenvolvimento do produto. M?todos tradicionais de projeto n?o favorecem as tomadas de decis?es e encarecem o produto, pois requerem simula??o em n?vel de hardware, estando dispon?vel apenas no final do fluxo de projeto. Para solucionar os problemas apresentados pelos m?todos tradicionais de projeto, adotou-se a t?cnica de projeto baseado em plataforma (PBD ? Platform Based Design). O m?todo de projeto PBD adota a modelagem de plataformas virtuais em n?vel de sistema possibilitando r?pidas simula??es, depura??o de software e reuso de componentes de hardware. Esta Tese tem por objetivo realizar estudos e desenvolvimentos em 2 eixos de pesquisa: (1) modelagem de plataformas virtuais com diferentes organiza??es de mem?ria; (2) estudo de m?todos anal?ticos para mecanismos de software em sistemas com restri??es de tempo-real. Para a modelagem de plataformas virtuais usa-se as ADLs (Architecture Description Language) OVP e ArchC. Neste tema de trabalho, diversas plataformas foram modeladas em diferentes n?veis de abstra??o (de RTL a modelos sem temporiza??o) e com diferentes arquiteturas de mem?ria (compartilhada e distribu?da). Com base nas avalia??es realizadas em cada arquitetura, adequou-se a plataforma HeMPS para executar aplica??es com restri??es de tempo-real. Os resultados apresentaram que, com a utiliza??o do mecanismo de escalonamento e do mapeamento RTA propostos, os dados resultantes das aplica??es com restri??es de tempo-real aconteceram dentro do per?odo de tempo definido pela aplica??o. Comparando plataformas com heur?sticas de mapeamento e escalonamento presentes na literatura, a plataforma desenvolvida na presente Tese atende as restri??es de aplica??es Hard-RT, garantindo 100% das restri??es resultantes dos casos de testes.

Um dos principais desafios em Redes Centradas em Informação (ICN) é como prover controle de acesso à publicação e recuperação de conteúdos. Apesar das potencialidades, as soluções existentes, geralmente, consideram um único usuário agindo como publicador. Ao lidar com múltiplos publicadores, elas podem levar a uma explosão combinatória de chaves criptográficas. As soluções projetadas visando a múltiplos publicadores, por sua vez, dependem de arquiteturas de redes específicas e/ou de mudanças nessas para operar. Nesta dissertação é proposta uma solução, apoiada em criptografia baseada em atributos, para controle de acesso a conteúdos. Nessa solução, o modelo de segurança é voltado a grupos de compartilhamento seguro, nos quais todos os usuários membros podem publicar e consumir conteúdos. Diferente de trabalhos anteriores, a solução proposta mantém o número de chaves proporcional ao de membros nos grupos e pode ser empregada em qualquer arquitetura ICN de forma gradual. A proposta é avaliada quanto ao custo de operação, à quantidade de chaves necessárias e à eficiência na disseminação de conteúdos. Em comparação às soluções existentes, ela oferece maior flexibilidade no controle de acesso, sem aumentar a complexidade do gerenciamento de chaves e sem causar sobrecustos significativos à rede. / One of the main challenges in Information-Centric Networking (ICN) is providing access control to content publication and retrieval. In spite of the potentialities, existing solutions often consider a single user acting as publisher. When dealing with multiple publishers, they may lead to a combinatorial explosion of cryptographic keys. Those solutions that focus on multiple publishers, on the other hand, rely on specific network architectures and/or changes to operate. In this dissertation, it is proposed a solution, supported by attribute-based encryption, for content access control. In this solution, the security model is focused on secure content distribution groups, in which any member user can publish to and retrieve from. Unlike previous work, the proposed solution keeps the number of cryptographic keys proportional to the number of group members, and may even be adopted gradually in any ICN architecture. The proposed solution is evaluated with respect to the overhead it imposes, number of required keys, and efficiency in the content dissemination. In contrast to existing solutions, it offers higher access control flexibility, without increasing key management process complexity and without causing significant network overhead.

Framväxten av en ny kundlogik, orsakad av teknikens framfart, har tvingat företag och organisationer att hitta nya tillvägagångssätt för att nå potentiella medlemmar eller kunder. Sociala medier är ett fenomen som har utvecklats från att vara ett kommunikationsverktyg för privatpersoner, till att bli ”ett nödvändigt ont” och en viktig del av marknadskommunikationen för många företag. Med denna uppsats vill vi utforska hur en ideell förening använder sociala medier för sin marknadsföring, vilka risker detta medför och vad som kan göras för att undvika dessa. Uppsatsen är en fallstudie som bygger på metodtriangulering och karaktäriseras av en abduktiv ansats. Studien baseras på två kvalitativa personliga intervjuer och en kvantitativ undersökning i form av enkät. Den teoretiska referensramen utgörs av word-of-mouth marketing, word-of-mouse marketing och many-to-many marketing.  Resultatet påvisar att fördelar med användandet av sociala medier för marknadsföring överträffar nackdelarna. För ideella organisationer borde nätverkande med hjälp av sociala medier vara en del av det vardagliga arbetet, både av ekonomiska och strategiska skäl. / The emergence of a new customer logic, caused by technological progress, has forced businesses to find new ways to reach potential members or customers. Social media is a phenomenon that has evolved from being a communication tool for individuals, to become a “necessary evil” and an important part of marketing communication for many businesses.  In this paper we explore how nonprofit organizations use social media in marketing, the risks involved in the process and what can be done to avoid these risks. The essay is a case study based on a quantitative survey and two qualitative interviews. The study shows that the benefits of the use of social media marketing surpass the disadvantages. For nonprofit organization, social media networking should be an integral part of the marketing efforts, for both economic and strategic reasons.