Using Monte Carlo simulations and analytic methods, we examine the dynamics of inter-species competition using the Penna bit-string model. We begin with a study of the steady state with a single species, then proceed to the dynamics of competition between two species. When the species are not evenly matched in fitness, a simple differential equation provides a satisfactory model of the behavior of the system. However, when the species are equally fit, we show that a model, originally proposed to describe population genetics [Fisher,Wright], is required. When mutations are allowed between the competing species, the dynamics becomes more interesting. The mutation rate becomes a parameter that dictates the steady state behavior. If the two species are not equally fit, the value of the mutation rate determines whether the longer-lived or faster reproducing species is favored. With two species that are equally fit, the steady state varies with mutation rate from a single peaked to a double peaked distribution. This behavior is shown to be well described by an extension to the Fisher-Wright model mentioned above. Finally, we describe the preliminary results of a few new lines of investigation, and suggest ideas for further study of the dynamics of this model. / Ph. D.

Bridges with external post-tensioned tendons are considered to be more durable than bridges with internal tendons (tendons within the webs and flanges), because external tendons are easier to inspect. In addition, in the event that extensive corrosion damage is detected, it is possible to replace an external tendon. However, an appropriate inspection for detecting damage needs to be determined for external tendons. This investigation focuses on the vibration technique, which uses the dynamic properties of the external tendon to infer the effective prestress force. Four large-scale external tendons, designed to simulate one section of an external tendon between two deviators in a post-tensioned bridge, were tested. In the study, damage to the tendons was induced in a quantifiable fashion at a specific location and the tensile force was measured directly. In addition, free-vibration tests were conducted periodically. This provided a direct means of measuring the sensitivity of measured natural frequencies and measured tensile force to local damage. The measured data were correlated with an approximation of the stiff string vibration model. In addition to the laboratory specimens, field testing was conducted on a bridge with external post-tensioned tendons. The findings from the study show that a loss in tensile force was not linear with a loss in the cross-sectional area of the strand, which results from stress redistribution within the tendon. Also, the natural frequencies were much less sensitive to the level of induced damage than the tensile force. While the measured data from the laboratory data compared very well with the analytical model, the field measurements exhibited a much greater deviation from the model. Due to several factors, the difference between the laboratory specimens and the bridge tendons are believed to be caused by larger levels of inherent error in the model. The findings from the investigation support the notion that vibration testing is most appropriately used in comparing relative differences between peer tendons. / text

O modelo não linear supersimétrico em l+l dimensões é acoplado à supergravidade. Ao quantizarmos a teoria, os campos de matéria adquirem massa dinamicamente, o que ocasiona a quebra da invariança de Weyl. Este fato implica em que as funções de dois pontos do Gravitino e do Graviton, obtidas a partir da ação efetiva, não sejam triviais. Em particular a função de dois pontos do Gravitino apresenta um polo no infravermelho. Nós conjeturamos que este polo está ligado com o confinamento dos graus de liberdade supersimétricos da teoria. Isto porque, ao restringirmos o domínio de integração de x IND. 1 à uma medida finita L (quebrando as invarianças da teoria), aparece na função de dois pontos do Gravitino um termo de massa, que decresce exponencialmente em função de L. Neste contexto relacionamos este model o como da corda supersimetrica e definimos um critério de estabilidade para a mesma. / The nonlinear o supersymmetric model in l+l dimensions is coupled to supergravity. When we quantize the theory, the matter fields acquire mass dynamically, which leads to the breaking of the Weyl invariance. This fact implies that the two point functions of the Gravitino and the Graviton, obtained from the effective action, become non trivial. Particularly, the two point function of the Gravitino presents a pole in the infrared region. We conjecture that this pole is related to the confinement of all supersymmetric degrees of freedom of the theory. If we restraind the integration domain of x1 to a finite lengh L (breaking all invariances of the theory), there appears a mass term in two point function of the Gravitino, which decreases exponentially with L. In this context we relate this model with that of the supersymmetric string and define a stability criteria for the latter.

O modelo não linear supersimétrico em l+l dimensões é acoplado à supergravidade. Ao quantizarmos a teoria, os campos de matéria adquirem massa dinamicamente, o que ocasiona a quebra da invariança de Weyl. Este fato implica em que as funções de dois pontos do Gravitino e do Graviton, obtidas a partir da ação efetiva, não sejam triviais. Em particular a função de dois pontos do Gravitino apresenta um polo no infravermelho. Nós conjeturamos que este polo está ligado com o confinamento dos graus de liberdade supersimétricos da teoria. Isto porque, ao restringirmos o domínio de integração de x IND. 1 à uma medida finita L (quebrando as invarianças da teoria), aparece na função de dois pontos do Gravitino um termo de massa, que decresce exponencialmente em função de L. Neste contexto relacionamos este model o como da corda supersimetrica e definimos um critério de estabilidade para a mesma. / The nonlinear o supersymmetric model in l+l dimensions is coupled to supergravity. When we quantize the theory, the matter fields acquire mass dynamically, which leads to the breaking of the Weyl invariance. This fact implies that the two point functions of the Gravitino and the Graviton, obtained from the effective action, become non trivial. Particularly, the two point function of the Gravitino presents a pole in the infrared region. We conjecture that this pole is related to the confinement of all supersymmetric degrees of freedom of the theory. If we restraind the integration domain of x1 to a finite lengh L (breaking all invariances of the theory), there appears a mass term in two point function of the Gravitino, which decreases exponentially with L. In this context we relate this model with that of the supersymmetric string and define a stability criteria for the latter.

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