The human brain is considered to be the most complex and powerful information-processing device in the known universe. The fundamental concepts behind the physics of complex systems motivate scientists to investigate the human brain as a collective property emerging from the interaction of thousand agents. In this dissertation, I investigate the emergence of cooperation-induced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series of properties such as avalanche distribution in size and duration coinciding with the experimental results on neural networks both in vivo and in vitro. Focusing attention on temporal complexity and fractal index of the system, I discuss how to define an order parameter and phase transition. Criticality is assumed to correspond to the emergence of temporal complexity, interpreted as a manifestation of non-Poisson renewal dynamics. In addition, I study the transmission of information between two networks to confirm the criticality and discuss how the network topology changes over time in the light of Hebbian learning.

No description available.

The purpose of this thesis is to examine the accuracy of the RAPID (Real-Time Analysis for Particle Transport and In-situ Detection) eigenvalue algorithm based on a few problems from the ICSBEP (International Criticality Safety Benchmark Evaluation Project) Handbook. RAPID is developed based on the MRT (Multi-Stage Response-Function Transport) methodology and it uses the fission matrix (FM) method for performing eigenvalue calculations. RAPID has already been benchmarked based on several real-world problems including spent fuel pools and casks, and reactor cores. This thesis examines the accuracy of the RAPID eigenvalue algorithm for modeling the physics of problems with unique geometric configurations. Four problems were selected from the ICSBEP Handbook; these problems differ by their unique configurations which can effectively examine the capability of the RAPID code system. For each problem, a reference Serpent Monte Carlo calculation has been performed. Using the same Serpent model in the pRAPID (pre- and post-processing for RAPID) utility code, a series of fixed-source Serpent calculations are performed to determine spatially-dependent FM coefficients. RAPID calculations are performed using these FM coefficients to obtain the axially-dependent, pin-wise fission density distribution and system eigenvalue for each problem. It is demonstrated that the eigenvalues calculated by RAPID and Serpent agree with the experimental data within the given experimental uncertainty. Further, the detailed 3-D pin-wise fission density distribution obtained by RAPID agrees with the reference prediction by Serpent which itself has converged to less than 1% weighted uncertainty. While achieving accurate results, RAPID calculations are significantly faster than the reference Serpent calculations, with a calculation time speed-up of between 4x and 34x demonstrated in this thesis. In addition to examining the accuracy of the RAPID algorithm, this thesis provides useful information on the use of the FM method for simulation of nuclear systems. / Master of Science / In the modeling and simulation of nuclear systems, two parameters are of key importance: the system eigenvalue and the fission distribution. The system eigenvalue, known as kef f , is the ratio of neutron production from fission in the current neutron generation compared with the absorption and leakage of neutrons from the system in the previous neutron generation. When this ratio is equal to one, the system is critical and is a self-sustaining chain reaction. Knowledge of the fission distribution is important in the nuclear power industry, as it enables engineers to determine the best reactor core assembly configuration to maintain an even power distribution. Several methods have been developed over the years to effectively solve for a nuclear systems fission distribution and system eigenvalue. Aspects of both Monte Carlo and deterministic transport methods have been combined into RAPID’s MRT methodology. It is capable of accurately determining the system eigenvalue and fission distribution in real time. This thesis examines the accuracy of the RAPID algorithm using four unique problems from the ICSBEP handbook. These problems help us to test the limits of the FM method in RAPID through the modeling of small, unique geometric configurations not seen in large, uniformly configured power reactor cores and spent fuel pools. For comparison, each problem is modeled using the Serpent Monte Carlo code, an accurate code meant to serve as the industry standard for determination of the fission distribution of each problem. This model is then used to generate a set of FM coefficients for use in RAPID calculations. It is demonstrated that the eigenvalues calculated by RAPID and Serpent agree with the experimental data within the given experimental uncertainty. The fission distribution obtained by RAPID is also in agreement with the Serpent reference model. Finally, the RAPID eigenvalue calculation is significantly faster than the corresponding Serpent reference model, with speed-ups ranging from 4x to 34x demonstrated.

A hybrid Quasi-diffusion/Monte Carlo Method for solving multigroup criticality problems in slab geometry was investigated. Analog Monte Carlo was used to calculate functionals (Eddington Factors) that were then used in solution of the quasi-diffusion equations. The hybrid method was shown to accurately and precisely predict the k-eigenvalue and fission source distribution for loosely coupled problems with high dominance ratios and significant spatial gradients. The hybrid method was also shown to be computationally more efficient than analog Monte Carlo. / Graduation date: 2012

Submitted by Nadir Basilio (nadirsb@uninove.br) on 2015-07-17T14:17:18Z No. of bitstreams: 1 Walquiria Barcelos de Figueiredo.pdf: 11234029 bytes, checksum: dbf21e923a2bfae3e29f6be02048db53 (MD5) / Made available in DSpace on 2015-07-17T14:17:18Z (GMT). No. of bitstreams: 1 Walquiria Barcelos de Figueiredo.pdf: 11234029 bytes, checksum: dbf21e923a2bfae3e29f6be02048db53 (MD5) Previous issue date: 2014-11-19 / The present study aimed to point out the reasons of failure of supply of inputs to an Intensive Care Unit (ICU) of a tertiary public hospital, identifying the risks associated with lack of essential materials in patient care and the occurrence of Healthcare Associated Infection (HAI). For this purpose, a study delineated as action research was conducted, as well as surveys and document analysis of recorded cases of HAI in the studied unit between 2012 and 2013, apart from the content analysis of the spreadsheet input supply. A literature search was conducted on standards, legislation and scientific articles related to the subject. Aiming to understand the perception of the professional group, a survey instrument was applied to the staff of the unit in a form of a semi-structured questionnaire. Through opportunities for improvement related to the management and control of essential materials, care of patients, a scoring model to material considered essential to the ICU, based on the classification system into categories ABC and XYZ was proposed. According to the criticality of the missing material to be used in sector, it was possible to generate a report to the Sub Committee on Hospital Infection Control and the administrative sector, to help in emergency procurement and distribution of basic materials for the assistance and thus minimize the occurrence of adverse events and consequently increased professional satisfaction and patient safety. / O presente estudo objetivou levantar quais as razões das falhas de abastecimento dos insumos de uma Unidade de Terapia Intensiva (UTI) de um hospital público terciário, identificando os riscos associados à falta de materiais essenciais na assistência ao paciente e na ocorrência de infecções relacionadas à saúde (IRAS). Para isso, foi realizado um estudo delineado como pesquisa-ação, além de levantamentos e análise documental dos casos registrados de IRAS na unidade entre 2012 e 2013, bem como análise de conteúdo das planilhas de fornecimento de insumos. Uma pesquisa bibliográfica também foi realizada, sobre normas, legislações e artigos científicos relacionados ao assunto. Com o objetivo de compreender a percepção do grupo profissional, um instrumento de pesquisa foi aplicado na forma de questionário semiestruturado à equipe da unidade estudada. Através das oportunidades de melhoria relacionadas à gestão e controle de materiais essenciais para o cuidado de pacientes, foi proposto um modelo de pontuação a esses materiais considerados fundamentais para a UTI, baseado no sistema de classificação em categorias ABC e XYZ. De acordo com a criticidade do material em falta a ser utilizado no setor, foi possível gerar um relatório à Subcomissão de Controle de Infecção Hospitalar e ao setor administrativo, para auxiliar na aquisição emergencial e distribuição dos materiais básicos para a assistência, e desta forma minimizar a ocorrência de eventos adversos e aumentar, consequentemente, a satisfação dos profissionais e segurança dos pacientes.

No description available.

Experimentos têm revelado que redes de neurônios, tanto in vitro como in vivo, mantêm atividade descrita por avalanches e se organizam em um estado crítico no qual essas avalanches são distribuídas de acordo com leis de potência. Mostramos no presente trabalho que um modelo de rede de elementos excitáveis com sinapses dinâ- micas é capaz de exibir criticalidade auto-organizada para ampla região do espaço de parâmetros. Nossos resultados estão de acordo com outros estudos que indicam que a depressão sináptica de curto prazo constitui mecanismo suciente para produzir criticalidade em avalanches neuronais. No entanto, segundo diversos pesquisadores, embora o ajuste de parâmetros seja grosso para que haja criticalidade no modelo, é mais preciso dizer que o sistema não apresenta criticalidade auto-organizada genu ína, mas sim quasi-criticalidade auto-organizada, como os demais modelos não conservativos presentes na literatura. / Experiments have shown that neuronal networks, both in vitro and in vivo, maintain activity described by avalanches and they are organized into a critical state in which these avalanches are distributed according to power laws. We have demonstrated that a model based on a network of excitable elements with dynamical synapses is able to exhibit self-organized criticality for a wide range of the parameter\'s space. Our results are consistent with other studies that suggest short-term synaptic depression is enough to produce criticality in neuronal avalanches. However, according to several researchers, in spite of the tuning to be gross to ensure that there is criticality in the model, it is more accurate do not say that the system presents genuine self-organized criticality, but self-organized quasi-criticality as the other non-conservative models in the literature.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / Includes bibliographical references. / Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

No description available.

Many chaotic and complicated systems cannot be analysed by traditional methods. In 1987 P.Bak, C.Tang, and K.A.Wiesenfeld developed a new concept called Self-Organised Criticality (SOC) to explain the behaviour of composite systems containing a large number of elements that interact over a short range. In general this theory applies to complex systems that naturally evolve to a critical state in which a minor event starts a chain reaction that can affect any number of elements in the system. It was later shown that many complex phenomena such as flux pinning in superconductors, dynamics of granular systems, earthquakes, droplet formation and biological evolution show signs of SOC. The dynamics of complex systems in nature often occurs in terms of punctuation, or avalanches rather than following a smooth, gradual path. Extremal dynamics is used to model the temporal evolution of many different complex systems. Specifically the Bak-Sneppen evolution model, the Sneppen interface depinning model, the Zaitsev flux creep model, invasion percolation, and several other depinning models. This thesis considers extremal dynamics at constant flux where M>1 smallest barriers are simultaneously updated as opposed to models in the limit of zero flux where only the smallest barrier is updated. For concreteness, we study the Bak-Sneppen (BS) evolution model [Phys. Rev. Lett. 71, 4083 (1993)]. M=1 corresponds to the original BS model. The aim of the present work is to understand analytically through mean field theory the random neighbour version of the generalised BS model and verify the results against the computer simulations. This is done in order to scrutinise the trustworthiness of our numerical simulations. The computer simulations are found to be identical with results obtained from the analytical approach. Due to this agreement, we know that our simulations will produce reliable results for the nearest neighbour version of the generalised BS model. Since the nearest neighbour version of the generalised BS model cannot be solved analytically, we have to rely on simulations. We investigate the critical behaviour of both versions of the model using the scaling theory. We look at various distributions and their scaling properties, and also measure the critical exponents accurately verifying whether the scaling relations holds. The effect of increasing from M=1 to M>1 is surprising with dramatic decrease in size of the scaling regime.