Made available in DSpace on 2015-05-15T11:46:18Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 899692 bytes, checksum: d08b5615c89c2ad179f1f6dda0a8c410 (MD5) Previous issue date: 2014-06-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, we study issues related the existence, nonexistence and regularity of solutions to semilinear Schrödinger equations of type u + a(x)u = jujp2u; u 2 H1(RN); where N 2, p > 2 if N = 2 and 2 < p < 2N=(N 2) if N 3 and the potential a(x) is a positive function that belongs to L1(RN). To obtain the results, we use a Linking Theorem and the Principle of Symmetric Criticality. / Neste trabalho, estudamos questões relacionadas a existência, não-existência e regularidade de soluções para equações de Schrödinger semilineares do tipo u + a(x)u = jujp2u; u 2 H1(RN); onde N 2, p > 2 se N = 2 e 2 < p < 2N=(N 2) se N 3 e o potencial a(x) é uma função positiva que pertence a L1(RN). Para obtenção dos resultados, usamos um Teorema de Linking e o Princípio da Criticalidade Simétrica.

Neste trabalho estudamos o modelo Olami-Feder-Christensen (OFC). Fortes correlações espaciais e temporais dificultam a obtenção de resultados analíticos para este modelo. Assim, nossas investigações foram realizadas através de simulações computacionais. A fim de identificar o regime estacionário de forma eficiente e econômica desenvolvemos algumas estatrégias. Também percebemos que a escolha adequada da configuração inicial pode antecipar ou retardar o início do regime estacionário. Por fim, a criticalidade do modelo foi estudada através de uma abordagem totalmente nova. Em vez de tentarmos identificar o comportamento crítico do sistema por meio da distribuição de avalanches, definimos uma grandeza , que em um processo ramificado simples seria a taxa de ramificação do sistema. Analisando o comportamento dessa variável em um espaço de fases verificamos que o modelo OFC e sua versão aleatória (que de antemão sabemos que só apresenta criticalidade no regime conservativo) tem um comportamento bastante similar. Obtivemos, ao contrário do que se acreditava, fortes evidências de que o modelo OFC apenas exibe criticalidade no regime conservativo. / We have investigated the Olami-Feder-Christensen model. The model presents strong temporal and spatial correlations what makes it very difficult to perform analytical calculations. So our treatment was numerical. We developed strategies to identify the regime with high level of accuracy. We noticed that depending on the initial configurations, the statistical stationary state can be reached faster. Finally we have investigated the criticality of the model through new strategy. Instead of looking for powers laws, we defined a quantity , very similar to the branching ratio in a simple branching process. We were able to show the behavior of the Olami-Feder-Christensen and the random version of this model are similar. We got strong numerical evidences that, in opposition to previous results, the Olami-Fedel-Christensen model is critical only in the conservative regime.

Orientadores: José Antônio Brum, Marcus Aloizio Martinez de Aguiar / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-26T08:49:23Z (GMT). No. of bitstreams: 1 PinheiroNeto_Joao_M.pdf: 16027257 bytes, checksum: ff0a08fdba027bd6f2bc28198e34d482 (MD5) Previous issue date: 2014 / Resumo: Nesta dissertação de mestrado estudamos a dinâmica e estrutura de redes complexas. Começamos com uma revisão da literatura de redes complexas, apresentando as métricas de rede e modelos de conectividade mais comuns. Estudamos então em detalhe a dinâmica do modelo das Random Threshold Networks (RTN). Desenvolvemos uma nova aproximação de campo médio para a dinâmica de RTNs, consideravelmente mais simples que aproximações anteriores. Esta nova aproximação é útil de um ponto de vista prático, pois permite a geração de RTNs onde a atividade média da rede é controlável. Fazemos então uma revisão da literatura de redes adaptativas, apresentando alguns modelos de redes adaptativas com características interessantes. Por fim, desenvolvemos dois modelos de redes adaptativas inspirados pela evolução da estrutura neuronal no cérebro. O primeiro modelo utiliza regras simples e uma evolução baseada na remoção de links para controlar a atividade sobre a rede. A inspiração é a remoção de neurônios e conexões neuronais após a infância. Este modelo também consegue controlar a atividade de grupos individuais dentro de uma mesma rede. Exploramos uma variante deste modelo em um espaço bidimensional, onde conseguimos gerar redes modulares e small-world. O segundo modelo utiliza inputs externos para controlar a evolução da topologia da rede. A inspiração neste caso é o desenvolvimento das conexões neuronais durante a infância, que é influenciado por interações com o ambiente. O modelo gera avalanches finitas de atividade, e é capaz de gerar topologias especificas e modulares utilizando regras simples / Abstract: In this Masters Dissertation we study the structure and dynamics of complex networks. We start with a revision of the literature of complex networks, presenting the most common network metrics and models of network connectivity. We then study in detail the dynamics of the Random Threshold Network (RTN) model. We develop a new mean-field approximation for the RTN dynamics that is considerably more simple than previous results. This new approximation is useful from a practical standpoint, since it allows the generation of RTNs where the average activity of the network is controlled. We then review the literature of Adaptive Networks, explaining some of the adaptive models with interesting characteristics. At last, we develop two models of adaptive networks inspired by the evolution of neuronal structure in the brain. The first model uses simple rules and a link-removing evolution to control the activity on the network. The inspiration is the removal of neurons and neuronal connections after infancy. This model can also control the activity of individual groups within the same network. We explore a variant of this model in a bi-dimensional space, where we are able to generate modular and small-world networks. The second model uses external inputs to control the topological evolution of the network. The inspiration in this case is the development of neuronal connections during the infancy, which is influenced by interactions with the environment. The model generates finite avalanches of activity, and is capable of generating specific and modular topologies using simple rules / Mestrado / Física / Mestre em Física

In this thesis I will outline various quantum phase transitions in 2D models of magnets that are amenable to simulation with quantum Monte Carlo techniques. The key player in this work is the theory of deconfined criticality, which generically allows for zero temperature quantum phase transitions between phases that break distinct global symmetries. I will describe models with different symmetries including SU(N), SO(N), and "easy-plane" SU(N) and I will demonstrate how the presence or absence of continuous transitions in these models fits together with the theory of deconfined criticality.

The vision of automated driving demands a highly available system, especially in safety-critical functionalities. In automated driving when a driver is not binding to be a part of the control loop, the system needs to be operational even after failure of a critical component until driver regain the control of vehicle. In pursuit of such a fail-operational behavior, the developed design process with software redundancy in contrast to conventional dedicated backup requires the support of automatic configurator for scheduling relevant parameters to ensure real-time behavior of the system. Multiple implementation methods are introduced to provide an automatic service which also considers task criticality before assigning task to the processor. Also, a generic method is developed to generate adaptation plans automatically for an already monitoring and reconfiguration service to handle fault occurring environment.

M. Sc. / The substitution series CeCu5−xAlx where x 2 {1.0, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4} was synthesized and characterized via x-ray diffraction and scanning electron microscope analysis. All the compounds formed single phase in the P6/mmm hexagonal crystal structure, which pushed the solubility limit of Al within this structure from CeCu3Al2 to CeCu2.6Al2.4. The ascast samples were annealed, but the annealing process had no visible effect on the crystalline nature nor on the physical properties of the samples. The electric, magnetic and thermal properties were measured on Quantum Design’s Physical Properties Measurement System and Magnetic Properties Measurement System. The electrical resistivity showed single-ion Kondo scattering at intermediate temperatures with no signs of coherence for x 2 {1.0, 1.5, 2.0, 2.1, 2.2, 2.3} CeCu2.6Al2.4 on the other hand showed a weak maximum at 2 K, which was the onset of antiferromagnetic ordering confirmed by other measurements. The magnetoresistance was fitted by the Beth´e ansatz spin-1/2 model and the obtained Kondo temperatures had a maximum at CeCu3Al2, with linear dependencies on Al concentration on either side of this point. The Kondo moments followed an exponential dependence on the Al concentration, but these effective moments were far lower than the free-ion value, due to the Kondo interaction. The thermal conductivity in this series was phonon dominated with the magnitude of the electronic component being inversely proportional to the Kondo temperature, showing the effect that the Kondo scattering mechanism has on the availability of the conduction electrons to participate in heat transport. The magnitude of the peak in the thermoelectric power S(T) was strongly dependent on the Al concentration, having a maximum at CeCu2.8Al2.2. Below the peak there were two temperature dependencies: S(T) / T for x 2 {1.0, 1.5, 2.4} which is metallic and for x 2 {2.0, 2.1, 2.2, 2.3} S(T)/T /−ln(T) which is characteristic of a quantum critical point. The data were also fitted with a phenomenological model and the obtained Kondo temperatures were quantitatively similar to those obtained from the Beth´e ansatz. The heat capacity Cp(T) data confirmed these compounds to be heavy fermions and also showed Cp(T)/T /−ln(T) below 10 K, which is the hallmark for a magnetically tuned quantum critical point. The magnetic susceptibility showed a Curie-Weiss temperature dependence at temperatures above 100 K, with magnetic moments close to the free-ion value, indicating the presence of localized magnetic moments. The low temperature data found (T) /−ln(T) for Al concentrations near CeCu3Al2 and the ordering present in CeCu2.6Al2.4 was suppressed by 0.3 K in going from 0.01 T to 2 T, suggesting that the ground state is antiferromagnetic in this compound.

Cette thèse explore plusieurs sujets fondamentaux pour les circuits mésoscopiques qui incorporent un faible nombre de canaux de conduction électroniques. Les premières expériences concernent le caractère quantifié (discret) de la charge dans les circuits. Nous démontrons le critère de quantification de la charge, nous observons la loi d’échelle prédite pour cette quantification ainsi qu’une transition vers comportement universel à mesure que la température augmente. Le second ensemble d’expériences concerne la physique critique quantique non-conventionnelle qui émerge du modèle Kondo à multi-canaux. Par l’implémentation d’une impureté Kondo avec un pseudo-spin de valeur ½ constitué de deux états de charge dégénérés d’un circuit, nous explorons la physique Kondo à deux- et trois-canaux. Au point critique quantique symétrique, nous observons les points fixes Kondo universels prédits, des exposants universels de lois d’échelle et nous validons les courbes complètes obtenues par le groupe de renormalisation numérique. En s’écartant du point critique quantique, nous explorons la transition depuis la zone critique quantique : par une visualisation directe du development d’une transition de phase quantique, par l’espace des paramètres de la zone critique quantique ainsi que par les comportements d’universalité et d’échelle. / This thesis explores several fundamental topics in mesoscopic circuitry that incorporates few electronic conduction channels. The first experiments address the quantized character (the discreteness) of charge in circuits. We demonstrate the charge quantization criterion, observe the predicted charge quantization scaling and demonstrate a crossover toward a universal behavior as temperature is increased. The second set of experiments addresses the unconventional quantum critical physics that arises in the multichannel Kondo model. By implementing a Kondo impurity with a pseudo-spin of ½ constituted by two degenerate charge states of a circuit, we explore the two- and three-channel Kondo physics. At the symmetric quantum critical point, we observe the predicted universal Kondo fixed points, scaling exponents and validate the full numerical renormalization group scaling curves. Away from the quantum critical point, we explore the crossover from quantum criticality: direct visualization of the development of a quantum phase transition, the parameter space for quantum criticality, as well as universality and scaling behaviors.

<p>More than twenty-five percent of the risk of failure for the 9-1-1 system can be contributed to blocked lines. The second major failure mode is unhelpful or improperly trained telecommunicators. The quick dispatch of emergency response teams in the event of any disaster or accident through the use of the 9-1-1 system is crucial to the well-being of the public. These potential failure modes prevent desperately awaited help from arriving as soon as possible. Therefore, the reliability and effectiveness of the system must be evaluated.</p> <p> The objective of this report is to identify failure modes of the 9-1-1 system, calculate their criticality, prioritize them in order of risk, and propose economical and feasible alternative solutions.</p> <p> Failure mode, effects, and criticality analysis (FMECA) is an evaluation tool that proves extremely useful when a system is desired to be kept highly effective and reliable. In this report, it is applied within the Systems Engineering Process to analyze areas of weakness throughout the New Jersey 9-1-1 system. FMECA is widely used throughout the military and commercial industry. It illustrates the interrelationships between causes and effects of failure modes, and helps to focus attention on high risk areas so that proper precautions may be taken.</p> <p> First, the use of FMECA is reviewed. The step-by-step procedures are next illustrated, and it is noted that FMECA must be tailored to each system relative to its characteristics and desired application. The New Jersey 9-1-1 system is analyzed in detail and is found to be an effective emergency communications network. However, technology has not yet provided solutions to all possible failures. In fact, technology adds to the failure possibilities. Possible future areas of development are included.</p> <p> / Master of Science

Second-order phase transitions involve critical fluctuations just below and above the transition temperature. Macroscopically, they manifest in the power-law behaviour of many physical properties such as the susceptibility and the specific heat. The power-laws are predicted to be universal, i.e. the same exponents are expected for a certain class of transitions irrespective of the microscopic details of the system. The underlying commonality of such transitions is the divergence of the correlation length ξ and the correlation time ξ_τ of the critical fluctuations at the transition temperature. Both ξ and ξ_τ can be directly observed by neutron scattering experiments, making them an ideal tool for the study of critical phenomena. At classical phase transitions, the critical fluctuations will be thermal in nature. However, if a second-order transition occurs at T = 0, thermal fluctuations are frozen, and the transition is driven by quantum fluctuations instead. This is called a quantum critical point. The quantum nature of the fluctuations influences observable properties, also at finite temperatures, and causes unusual behaviour in the vicinity of the quantum critical point or the existence of exotic phases, e.g. unconventional superconductivity. Heavy-fermion compounds are a class of materials that is well suited for the study of quantum criticality. They frequently show second-order transitions into a magnetically ordered state at very low temperatures, which can easily be tuned to T = 0 by the application of pressure, magnetic fields or element substitution. In this thesis, fluctuations near a quantum critical point are investigated for three heavy-fermion systems. CeCu2Si2 shows unconventional superconductivity close to an antiferromagnetic quantum critical point. Results from single-crystal neutron spectroscopy and thermodynamic measurements are discussed and some details are also given about the synthesis of large single crystals. The focus of the study is the comparison of the inelastic response of magnetic and superconducting samples, which are found to be very similar for ΔE > 0.2 meV. CePdAl has an antiferromagnetic state with partial magnetic frustration. The ordering temperature can be suppressed by Ni substitution towards a quantum critical point. Single-crystal neutron diffraction experiments of three members of the substitution series were analysed. They revealed several unusual effects of the frustrated state in the pure sample, and show that magnetic order and frustration persist in the substituted samples. YbNi4P2 is a rare example of a compound with ferromagnetic quantum criticality, which has only been studied in the last few years. The aim of the powder neutron spectroscopy experiments presented here was to obtain an overview of the relevant energy scales, i.e. the crystal electric field, local magnetic fluctuations and ferromagnetic fluctuations. Simulations using the program McPhase were performed for a thorough understanding of the crystal electric field.

General purpose graphics processing units (GP-GPU), owing to their enormous thread-level parallelism, can significantly improve the power consumption at the near-threshold (NTC) operating region, while offering close to a super-threshold performance. However, process variation (PV) can drastically reduce the GPU performance at NTC. In this work, choke points—a unique device-level characteristic of PV at NTC—that can exacerbate the warp criticality problem in GPUs have been explored. It is shown that the modern warp schedulers cannot tackle the choke point induced critical warps in an NTC GPU. Additionally, Choke Point Aware Warp Speculator, a circuit-architectural solution is proposed to dynamically predict the critical warps in GPUs, and accelerate them in their respective execution units. The best scheme achieves an average improvement of ∼39% in performance, and ∼31% in energy-efficiency, over one state-of-the-art warp scheduler, across 15 GPGPU applications, while incurring marginal hardware overheads.