An object-oriented framework is presented for developing and simulating individual-based models of cell populations. The framework supplies classes to define objects called simulation channels that encapsulate the algorithms that make up a simulation model. These may govern state-updating events at the individual level, perform global state changes, or trigger cell division. Simulation engines control the scheduling and execution of collections of simulation channels, while a simulation manager coordinates the engines according to one of two scheduling protocols. When the ensemble of cells being simulated reaches a specified maximum size, a procedure is introduced whereby random cells are ejected from the simulation and replaced by newborn cells to keep the sample population size constant but representative in composition. The framework permits recording of population snapshot data and/or cell lineage histories. Use of the framework is demonstrated through validation benchmarks and two case studies based on experiments from the literature.

The public health and veterinary importance of Gulf Coast ticks, Amblyomma maculatum Koch (1844) have become more apparent during the last several decades. In addition, new records of this three-host ixodid tick presently show a geographic distribution throughout much of the southern United States. Rickettsia parkeri, a spotted fever group rickettsia (SFGR) that is commonly found infecting the Gulf Coast tick, was only recently recognized as a human pathogen. Over the last decade, more than 20 human cases of disease caused by R. parkeri have been recognized in the Americas, all of which were similar in presentation to mild Rocky Mountain spotted fever. In addition, a novel, poorly characterized SFGR, “Candidatus Rickettsia andeanae”, was recently identified in A. maculatum from Peru, United States, Chile and Argentina. As the recognition of R. parkeri as a pathogen and “Ca. R. andeanae” as an additional SFGR in A. maculatum only recently occurred, a general gap exists in our understanding of the biology of these SFGRs. The overall objective of this dissertation was to contribute to our knowledge of SFGR infecting A. maculatum. In Chapter 3, we present a prevalence study of R. parkeri, and “Ca. R. andeanae” in A. maculatum from Mississippi where we detected 15.2% R. parkeri-singly infected ticks and 3.1% total “Ca. R. andeanae” infected ticks of which 1.7% were co-infected with R. parkeri. In Chapter 4, we discuss finding four genetically different populations of A. maculatum from Mississippi infected with a homogenous population of R. parkeri, using Single Strand Conformation Polymorphism analysis. Those initial data relating to “Ca. R. andeanae” provided a foundation for studies described in Chapters 5 and 6. We report the first morphological study of “Ca. R. andeanae” using transmission electron microscopy in Chapter 5 and isolation of this SFGR in ,A. maculatum cell co-culture in Chapter 6. We anticipate that results presented in this dissertation will contribute to our understanding of the ecology of ,A. maculatum as a vector for the human pathogen, R. parkeri, and increase the current understanding of both R. parkeri and “Ca. R. andeanae” in A. maculatum.

[pt] Este artigo analisa o uso de crédito durante a pandemia Covid-19 no contexto de um programa de transferência de renda. Sob uma abordagem Diferença em Diferenças, eu mostro evidências causais de como a implementação de um programa de transferência de renda impactou os padrões de uso de crédito da população, usando um conjunto combinado de microdados: SISFOH (um sistema de focalização familiar), a pesquisa domiciliar nacional e o registro de crédito para o Perú. Explorando uma descontinuidade na regra de concessão de renda emergencial à população mais pobre, mostro que os indivíduos que receberam um subsídio monetário aumentaram seu total de empréstimos no sistema financeiro, ao contrário daqueles que não o fizeram. Isso é preocupante, pois também se apresenta um aumento nas taxas de juros e dias de atraso. Além disso, também exploro algumas dimensões da heterogeneidade populacional (educação, idade, gênero, informalidade, entre outras), encontrando um impacto diferenciado de acordo com certas características dos indivíduos. Fiz um esforço especial na análise da informalidade, pois, mesmo na ausência de uma identificação exógena, essa variável apresenta resultados significativos e passa em certos testes de identificação. / [en] This paper analyzes the use of credit during the Covid-19 pandemic in the context of a cash transfer program. Under a Difference-in-Differences approach, I show causal evidence of how the implementation of a cash transfer program impacted the population s credit use patterns, using a combined set of microdata: SISFOH (a household targeting system), the national household survey, and the credit register for Peru. Exploring a discontinuity in the rule for granting emergency income to the poorest population, I show that individuals who received a monetary subsidy increased their total lending in the financial system, in contrast to those individuals who did not. This is worrisome as it is also presented an increase in the interest rates and days of arrears. Furthermore, I also explore some dimensions of population heterogeneity (education, age, gender, informality, among others), finding a differentiated impact according to certain characteristics of individuals. I put a special effort into the informality analysis since, even in the absence of an exogenous identification, this variable presents significant results and passes certain tests of identification.