Univ., Diss.--Hamburg, 2003. / Literaturverz. S. 203 - 219.

Nonequilibrium statistical physics involves the study of many-particle systems that break time reversibility|also known as detailed balance|at some scale. For states in thermal equilibrium, which must respect detailed balance, the comprehensive theory of statistical mechanics was developed to explain how their macroscopic properties arise from interactions between their microscopic constituent particles; for nonequilibrium states no such theory exists. The study of active matter, made up of particles that individually transduce free energy to produce systematic movement, provides a paradigm in which to develop an understanding of nonequilibrium behaviours. In this thesis, we are interested in particular in the microscopic interactions that generate the clustering of active particles that has been widely observed in simulations, and may have biological relevance to the formation of bacterial assemblages known as biofilms, which are an important source of human infection. The focus of this thesis is a microscopic lattice-based model of two random walkers interacting under mutual exclusion and undergoing the run-and-tumble dynamics that characterise the motion of certain species of bacteria, notably Escherichia coli. I apply perturbative and exact analytic approaches from statistical physics to three variants of the model in order to find the probability distributions of their nonequilibrium steady states and elucidate the emergent interactions that manifest. I first apply a generating function approach to the model on a one-dimensional periodic lattice where the particles perform straight line runs randomly interspersed by instantaneous velocity reversals or tumbles, and find an exact solution to the stationary probability distribution. The distribution can be interpreted as an effective non-equilibrium pair potential that leads to a finite-range attraction in addition to jamming between the random walkers. The finite-range attraction collapses to a delta function in the limit of continuous space and time, but the combination of this jamming and attraction is suffciently strong that even in this continuum limit the particles spend a finite fraction of time next to each other. Thus, although the particles only interact directly through repulsive hard-core exclusion, the activity of the particles causes the emergence of attractive interactions, which do not arise between passive particles with repulsive interactions and dynamics respecting detailed balance. I then relax the unphysical assumption of instantaneous tumbling and extend the interacting run-and-tumble model to incorporate a finite tumbling duration, where a tumbling particle remains stationary on its site. Here the exact solution for the nonequilibrium stationary state is derived using a generalisation of the previous generating function approach. This steady state is characterised by two lengthscales, one arising from the jamming of approaching particles, familiar from the instant tumbling model, and the other from one particle moving when the other is tumbling. The first of these lengthscales vanishes in a scaling limit where continuum dynamics is recovered. However, the second, entirely new, lengthscale remains finite. These results show that the feature of a finite tumbling duration is relevant to the physics of run-and-tumble interactions. Finally, I explore the effect of walls on the interacting run-and-tumble model by applying a perturbative graph-theoretic approach to the model with reflecting boundaries. Confining the particles in this way leads to a probability distribution in the low tumble limit with a much richer structure than the corresponding limit for the model on a periodic lattice. This limiting probability distribution indicates that an interaction over a finite distance emerges not just between the particles, but also between the particles and the reflecting boundaries. Together, these works provide a potential pathway towards understanding the clustering of self-propelled particles widely observed in active matter from a microscopic perspective.

Made available in DSpace on 2014-06-12T22:58:05Z (GMT). No. of bitstreams: 2 arquivo1446_1.pdf: 4391997 bytes, checksum: cf2f9970dc31e357b9bdb19b4ffdf45b (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O ambiente costeiro é berçário natural para um grande número de espécies marinhas, principalmente onde ocorrem mangues e recifes, que funcionam como abrigo natural para a desova e início de vida de muitas espécies marinhas. A linha de costa está inserida nesse ambiente, pois representa o limite entre o mar e o continente, no alcance máximo das ondas, onde cessa a ação marinha efetiva. Entretanto, a dinâmica de movimentação das marés torna esse limite uma zona de fronteira de difícil demarcação e monitoramento. Além disso, as alterações geomorfológicas, muitas vezes catalisadas pelas interferências antrópicas, diminuem a capacidade de regeneração natural das praias, dificultando o gerenciamento desse ambiente. Em virtude disso, essa tese desenvolveu alguns experimentos para localizar e monitorar linhas de costa nas praias de Sauaçui e Japaratinga, localizadas no Estado de Alagoas Brasil, aplicando tecnologia de posicionamento dos sistemas GNSS (Global Navigation Satellite System), com base em um indicador de linha de costa com representação matemática, correspondente à máxima altura alcançada pelas marés nos últimos 20 anos, acrescida do run-up, correspondente ao espraio das ondas. O GPS (Global Positioning System), que a partir deste ponto será designado apenas GPS, consiste em um sistema de posicionamento por satélite pertencente ao GNSS e pode gerar posicionamentos no modo dinâmico relativo, com precisão de poucos centímetros e suas técnicas já vem sendo aplicadas em programas de gerenciamento costeiro em várias partes do mundo. Entretanto, as alturas geradas pelo GPS são elipsoidais e representam um problema para o uso desse sistema em aplicações que envolvem altitudes, como é o caso das linhas de costa, que são relacionadas com o nível do mar. A técnica proposta nessa tese gera o modelo de elevação digital da praia, com base em perfis de praia, no mesmo referencial de nível das marés e nele identifica a linha de costa. Para isso, os referenciais verticais de maré e do GPS são correlacionados através de um artifício apropriado que requer o conhecimento das alturas de maré e do GPS em um mesmo local. Os perfis de praia aqui referidos são constituídos de pontos coordenados gerados pelo deslocamento de uma antena GPS em ziguezague ao longo da praia. Essa metodologia mostrou-se adequada para localizar e monitorar linhas de costa com precisão sub-métrica e tem como principal vantagem o fato desse modelo facilitar a visualização do comportamento da linha d´água, sendo apropriado para simular o deslocamento do mar sobre o continente. Os resultados mostram a localização geográfica das linhas de costa das praias objeto desse estudo, expressas no Sistema de Projeção Cartográfica Universal Transverso de Mercator (UTM). O monitoramento da linha de costa provém da comparação do seu traçado, superpondo-se os modelos produzidos em diferentes épocas e indica comportamento sazonal das linhas de costas tanto nas praias de Japaratinga (máximo de 6,0 m), como na praia de Sauaçui (máximo de 8,0 m). Além disso, como o referencial do GPS tem grande estabilidade, ele pode ser usado no monitoramento da estabilidade dos marcos de apoio, cujas coordenadas são suscetíveis de alterações, em havendo subsidências do solo e/ou movimentações de placas da crosta terrestre

The change of topography with time and the consequent structure of Earth's surface is dependent on the production and transport of weathered bedrock. I use measurements of in-situ cosmogenic 10Be to investigate erosion rates and exposure ages of boulders, streams, and hillslope sediments in central Pennsylvania, a landscape shaped by glacial/interglacial climate cycles and changes in base level. I measure rates of landscape change at three separate sites, Hickory Run boulder field, Young Womans Creek watershed, and Garner Run, a small upland catchment bounded by two ridgelines. Hickory Run Boulder field is the largest of its kind in the eastern United States. This enigmatic, 1-km-long field of boulders has been attributed to frost-induced processes during the last glacial maximum, when the Laurentide ice sheet margin was nearby. My isotopic data demonstrate that Hickory Run, and likely many other similar boulder fields in eastern North America are ancient, multigenerational features that have persisted over many glacial-interglacial cycles. These findings add nuance to the conventional view of periglaciation as a force that "wiped the slate clean" in the Appalachian Mountains -- in upland areas with resistant lithologies, I show that the landscape was reworked, but not reset by repeated periglaciation. Young Womans Creek is a 230 km2 drainage basin in the headwaters of the Appalachian Plateau physiographic province, where I investigate the role of non-equilibrium topography on the rates of erosion at a basin scale. Here, I use in-situ 10Be to understand the influence of fluvial incision into the landscape, contrasting erosion rates in undissected uplands with those in incised valleys. Erosion rates are positively correlated with slope, but correlate negatively with normalized channel steepness, ksn, and downstream distance. My results demonstrate the effects of lithology and base level on erosion rate are difficult to disentangle, and that when studied on a small scale, lithology exerts the strongest control over the spatial variability of erosion in a transient landscape. Resistant sandstone ridgelines such as those at Garner Run are common features in the Ridge and Valley province of central Pennsylvania. At this site, I strive to understand the influence of periglacial activity on the generation and movement of sediment downslope. My measurements demonstrate that sediment in small upland catchments such as Garner Run can have cosmogenic nuclide concentrations equal to and exceeding 100,000 years of surface exposure history. Despite perturbations by multiple glacial/interglacial cycles throughout the Pleistocene these sandstone-underlain environments are not young, and the exposure of surficial materials predates the last major advance of the Laurentide Ice Sheet at ˜26,000 years ago.

Gene loss is the obverse of novel gene acquisition by a genome through a variety of evolutionary processes. It serves a number of functional and structural roles, compensating for the energy and material costs of gene complement expansion. A type of gene loss widespread in the lineages of plant genomes is ``fractionation" after whole genome doubling or tripling, where one of a pair or triplet of paralogous genes in parallel syntenic contexts is discarded. Based on previous mathematical work on the distribution of gap sizes caused by fractionation in synteny blocks, we studied fractionation in the evolutionary history of the allotetraploid Coffea arabica (CA) and its two diploid progenitors, C. canephora (CC) and C. eugenioides (CE), annotated genome assemblies being provided by the Arabica Coffee Genome Consortium. By taking advantage of synteny blocks produced by SynMap, we studied the fractionation process after speciation and tetraploidization events, including visualization and modelling the distribution of deletion segments, and mechanisms of deletion events. We also expanded the research to eight other plant species to verify the dominance of DNA excision over pseudigenization during the fractionation and other gene loss.

Diploma thesis is focused on implementation of logistics system Milk Run for automotive lines in selected manufacturing company, which allows to deliver raw material for production effectively and on time. The theoretical part deals with the logistics principles, which are supporting lean manufacturing. The practical part is focused mainly on description of new supplying process and steps needed for implementation of Milk Run system in the company. The thesis is concluded with evaluation of project’s expected benefits.

Diploma thesis presents project about improving transportation of input material for assembly workplaces within the production department. Theoretical part is focused on the definition of production and logistics processes in general. Practical part is first devoted to analysis of original way of supplying materials. Then there is presented a lean supplying concept with Milk run followed by conclusions about the project benefits. At the end, there is also presented a way of improvement of informational flows by using informational technologies.

Tesis para optar al grado de Magíster en Ciencias, Mención Geofísica / En el presente trabajo se analiza la respuesta del agua al proceso temporal de ruptura de terremotos submarinos. Dicho comportamiento es estudiado por medio de la modelación de tsunamis generados por distintos tipos de fuentes sísmicas. Esto construyendo modelos de fallas finitas que permiten aislar los parámetros cinemáticos de las rupturas, para luego ser usados como entrada de la modelación de tsunamis. Los resultados muestran que desde el punto de vista cinemático las grandes amplitudes de tsunamis son una respuesta del agua a las bajas velocidades de ruptura, al tamaño de la columna de agua sobre la fuente y la ubicación del hipocentro en el plano de falla. Este estudio fue hecho considerando dos tipos de escenarios; se utilizó una batimetría simple, compuesta por un fondo plano y un talud que se eleva desde el fondo del mar hasta la costa y una batimetría realista del Norte de Chile, de iguar resolución espacial. Estas dos batimetrías contaron con dos superficies de falla asociadas; para el caso simple, se tuvo una superficie plana rectangular y para el caso del Norte de Chile, se construyeron muchos planos superpuestos sobre el slab en esa zona. Cada superficie de falla utilizó una distribución de slip uniforme y estocástica y para la simulación del terremoto se construyó un modelo cinemático de fuente que permitió controlar la velocidad de ruptura y el Rise Time. Entre los resultados obtenidos se destaca el hecho de que las bajas velocidades de ruptura pueden amplificar hasta 8 veces la altura del Run-Up, con respecto al caso de una fuente instantánea. También se observa que para velocidades lentas, el efecto de la directividad de la fuente controla la distribución espacial de las amplitudes del tsunami, haciendo que las mayores amplitudes del Run-Up se concentren en las costas más cercanas a la proyección horizontal de la dirección de propagación de la ruptura. También se observa que las amplitudes del tsunami dependen de la relación entre la velocidad de ruptura y la profundidad de la batimetría, por lo que se concluye que los terremotos tsunamigénicos de distintas partes del mundo logran excitar tsunamis que se propagan a diferentes velocidades de ruptura, dependiendo de la profundidad de la batimetría sobre la fuente. Finalmente, se observa que los terremotos tsunamigénicos que propagan sus rupturas con cambios abruptos de velocidad, de rápido a lento, logran amplificar la altura de los tsunamis más que las rupturas que se propagan a una velocidad constante.

MESHWR / Department of Hydrology and Water Resources / See the attached abstract below

This dissertation consists of three essays investigating the historical roots of economic development and inequality in the US South. The first essay examines the impact of slavery on long-run development. Using county-level data from the US South, I show that slavery has impeded long-run development through the human capital channel. The mechanism involves labor market institutions and their impact on demand for human capital. I find that the history of slavery hindered integration of black workers into the labor market. Moreover, border-county analyses show that selective application of laws and regulations was a primary tool for impeding labor market integration. Through estimating the relative return to education for each county, I further argue that blacks in a region with a greater legacy of slavery had fewer incentives to invest in human capital. The second essay studies the long run effects of cotton agriculture focusing on a novel aspect of structural change. I show that cotton specialization in the late 19th century had long-run negative impact on local development, and the negative relationship became only evident in the second half of the 20th century. I argue that the change was caused by the mechanization of cotton production. After cotton mechanization, cotton labor with low human capital was relocated to local manufacturing. In response to the inflow of cotton labor, there was a decline in labor productivity in manufacturing which persisted through directed technical change. Using census data, I show that initial cotton specialization reduces demand for skills in manufacturing even to this day. The third essay addresses the legacy of cotton agriculture on economic inequality. Using the Gini index of household income, I show that initial cotton specialization increased long-run economic inequality at the county level. Moreover, evidence from the census data indicates that cotton specialization increased wage inequality exclusively in the local service sector, without any effects on the other non-agricultural sectors. As an explanation, I argue that wage inequality in the service sector increased due to expansion of employment in low-wage occupations followed by a decrease in their wage level.