Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-12Bitstream added on 2014-06-13T18:57:56Z : No. of bitstreams: 1 almeida_fe_me_guara.pdf: 3463520 bytes, checksum: 687003c1392e31477b62d4db52bb211e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Equipamentos aeronáuticos embarcados podem ser submetidos a elevados níveis de vibração durante o vôo. Normas internacionais especificam os níveis de vibração que os componentes de uso civil e militar devem ser capazes de suportar de acordo com o emprego e com o tipo de aeronave ao qual serão integrados. Em alguns equipamentos aeronáuticos considerações de geometria e massa limitam severamente as opções de projeto no sentido de evitar ressonâncias na faixa de freqüência de qualificação do equipamento, o que pode fazer com que componentes eletrônicos internos sofram níveis muito elevados de vibração. O presente trabalho visa à redução das cargas dinâmicas com a introdução de dispositivos do tipo passivo de isolamento de vibração. Para redução e amortecimento de vibrações foram utilizados materiais com baixa rigidez, mas resistência mecânica suficiente para suportar os esforços dinâmicos. Diversas configurações de isoladores fabricadas com vários materiais (poliuretano, silicone, polietileno e uma combinação de polietileno e silicone) foram ensaiadas. A solução adotada foi analisada também por simulações numéricas pelo método dos elementos finitos, obtendo-se respostas em freqüência (acelerações), deslocamentos e tensões. Os deslocamentos e os valores máximos de tensão calculados apresentaram valores inferiores aos máximos admissíveis. Os resultados numéricos e experimentais apresentaram boa correlação entre si. A combinação de polietileno e silicone obteve o melhor desempenho permitindo uma redução de aproximadamente 85% do nível de vibração RMS sobre o equipamento e os componentes eletrônicos. / Aeronautical systems can be submitted to high levels of vibration during flight. International standards specify the vibration levels that this kind of systems must withstand according to its function and the aircraft where it will be integrated. For some of these systems, geometry and mass properties are strictly defined by some design issues and therefore cannot be changed in order to achieve better dynamical properties and avoid resonance peaks or high vibrations level in internal electronic components. The main goal of this work is to reduce the dynamic loads acting on sensible electronic equipment using passive vibration isolators. Materials witch provide low suspension resonance frequencies but enough mechanical strength and a medium loss factor are used to build vibration isolators. Some simple vibration isolators devices made by polymers are evaluated by dynamic tests performed with an airborne equipment. The devices tested are made by polyurethane, silica, polyethylene and a combination of the two formers. The dynamical behavior of the configuration with better performance is also analyzed through numerical simulation by finite element method. The numerical results for the dynamic responses are compared with the experimental results and shown good agreement. The combination of silica and polyethylene have show the better performance supporting appropriately the dynamic loads and reducing the RMS vibration level measured in the electronic components in 85%.

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<p> In the past two decades or so. microsatellites have become a very widely used genetic tool in many disciplines of biology. Their major downfalL however. is that they often need to be isolated de novo before they can be applied to molecular studies. Traditional shotgun cloning can be successfuL but it is often overly costly and time consuming. Compounding this downfall, isolating microsatellites from some taxa has been shown to be difficult. For example. on average only 0.46% of all clones screened using avian genomes will yield positive clones. This is thought to be a result of a smaller avian genome, a requirement for flight. Several alternative methods have been developed for isolating microsatellites, but the choice as to which isolation method to use is often arbitrary. To address this. four species of birds. the smooth-billed ani (Crotophaga ani). herring gull (Larus argentatus), yellow-bellied elaenia (Elaenia flavogaster), and pukeko (Porphyria porphyria), representing four different orders were used to compare two alternative isolation methods. Enrichment via selective hybridization versus cloning with Lambda Zap phage vector were compared in terms of monetary requirements (total startup cost as well as per isolation attempt cost). and time requirements (total time from start to finish and hands-on experimentation time). No significant difference was detected in terms of number of polymorphic microsatellite loci isolated by each method (p = 0.57), with enrichment yielding more for the anis and elaenias, Lambda Zap yielding more for herring gulls. and both methods isolating equal numbers for pukekos. Nor was any difference found between the methods for dollars spent per sequence with repeat (SWR) using the startup cost (p = 0.30). Enrichment. however. proved to be significantly more effective in terms of dollars per SWR isolated using the per use cost (p = 0.004) as well as hands-on minutes per SWR (p = 0.01) and total minutes per SWR (p < 0.01 ). Based on these tindings. selective hybridization is the better choice for microsatellite isolation. </p> / Thesis / Master of Science (MSc)

Haldane's rule, which states that the heterogametic sex is preferentially afflicted if one of hybrid sexes is sterile or inviable, is a general pattern in all animals that possess sex chromosomes. The hybrid sterility component of this rule is especially important because hybrid sterility is involved in the onset of postzygotic isolation. Accumulating evidence on the fast evolution of individual sex genes have stimulated us to hypothesize that the fast evolution of sex genes may be the force underlying the excess of hybrid heterogametic sterility. This study tests the evolutionary patterns of sex genes in comparison to non-sex genes, as a general group. The divergences between a group of 19 sex genes and 20 non-sex genes from X chromosome were compared between D. melanogaster, D. mauritiana, D. simulans, and D. sechellia using PCR-RFLP. Within species polymorphism data were also obtained for D. simulans and D. mauritiana. The results show a significantly higher divergence for sex genes than non-sex genes, while a comparable level of intraspecific polymorphism was revealed in both groups. Among the sex gene group, genes related to male reproduction appear to evolve faster than femalereproductive genes. The evolution of both sex and non-sex genes conforms to the neutral theory under Tajima's test and HKA test. The faster evolution of sex genes supports the fast-sex theory as an explanation for the hybrid sterility component of Haldane's rule. Localization of some examples of hybrid sterility genes is crucial to ultimately untangle the genetics of hybrid sterility. The car region of D. mauritiana, which has been shown to harbor genes that confer full effect of hybrid sterility in the D. simulans genetic background, was introgressed into the D. simulans genome by continuous backcrosses. Recombination mapping analysis, taking advantage of molecular markers, revealed that at least two regions are capable of causing hybrid sterility in this species group. The phenotypes of hybrid testes were examined during the backcross process. / Thesis / Master of Science (MSc)

</p> I investigated the effects of habitat fragmentation in terms of spatial scale (enclosures of different sizes) and the degree of isolation (different mesh sizes) on benthic macroinvertebrates in the littoral zone of a shallow lake. I hypothesized that decreasing diversity and increasing temporal variation will occur with decreasing size and increasing isolation of enclosures. This hypothesis was tested by examining spatial and temporal variation (coefficient of variation) among replicate enclosures. Variation in benthic diversity was further examined within and among enclosures. The degree of isolation and habitat size interacted to determine variation of species abundance in the benthic community. Specifically, at higher levels of isolation (plastic enclosures), variance among enclosures of the same and of different sizes was the greatest compared to less isolated enclosures. We also investigated the persistence of benthic macroinvertebrates where persistence is defined as constancy in the number of organisms through time. We hypothesized that persistence is lower in small and more isolated enclosures as opposed to large less isolated ones. We simultaneously tested the hierarchical nature of community persistence as outlined by Rahel (1990) to determine if there is a difference in the assessment of persistence of the assemblage depending on the analytical scale used. There is a possible scale effect at the level of abundance rank since small (1 and 4 m2 ) enclosures had lower persistence than large (9 and 16m2 ) enclosures. Low persistence in both abundance and abundance rank over time prevented a conclusive test of the hierarchical nature of community persistence. I conclude that it is important for benthic enclosure experiments to be conducted at various spatial and analytical scales and that, where replication is possible, spatial and temporal variation allows a thorough examination of different community responses. </p> / Thesis / Master of Science (MSc)

Speciation can be viewed as the formation of reproductive barriers between different populations. This thesis investigates patterns of natural and sexual selection shaping reproductive barriers between two hybridizing flycatchers (i.e. collared – and pied flycatchers). Behaviorally driven sexual isolation depends on both the availability of conspecific mates and on discrimination ability of individuals. My results demonstrate that these two factors may also interact. Discrimination abilities may change in response to the relative frequency of two interbreeding species. The underlying reason appears to be that male pied flycatchers have a song that incorporates more elements of the song characteristics of male collared flycatchers into their own song repertoires when occurring in areas inhabited predominantly by collared flycatchers. I investigated selection pressures acting on hybrids. In migratory species, hybrid fitness might be reduced as a consequence of intermediate suboptimal migration routes (extrinsic post zygotic isolation). Comparison of stable isotope signatures of revealed that parental species have separate wintering grounds, but hybrids appear to winter at the same location as pied flycatchers. A possible dominance effect in the inheritance of migration direction may hence reduce this potential cost. This interpretation is supported by the absence of a reduction in juvenile to adult survival of hybrids. By further comparing male hybrid fitness to that of the parental species, using lifehistory data, I demonstrate that hybrid males experience a moderate reduction in fitness (mainly through a sexually selected disadvantage). Sexual selection acting on male hybrids can play a major role in the speciation process because when the same characters affect assortative mating as well as hybrid fitness, reinforcement of reproductive barriers becomes more likely. Even when reproductive isolation is completed- the fate of newly formed species may be uncertain since they may strongly compete for ecological space. Long-term persistence of ecologically similar, species requires that there are spatial or temporal variation in their relative fitness. The growth of nestling pied flycatchers is less affected by harsh environmental conditions. We suggest that a regional co-existence of the two flycatcher species is due to a lifehistory trade-off between interference competitive ability and robustness to a harsh conditions. Overall, the studies in this thesis reveal the complexity of the interactions between mate choice and competition in shaping sexual signals. Furthermore, it suggests that natural selection is moderate on hybrid males and that sexual selection may have strong implications for the maintenance of species integrity.

<p>The rolling isolation system (RIS) studied in this dissertation functions on the principle of a rolling pendulum; an isolated object rests on a steel frame that is supported at its corners by ball-bearings that roll between shallow steel bowls, dynamically decoupling the floor motion from the response of the object. The primary focus of this dissertation is to develop predictive models that can capture experimentally-observed phenomena and to advance the state-of-the-art by proposing new isolation technologies to surmount current performance limitations. To wit, a double RIS increases the system's displacement capacity, and semi-active and passive damped RISs suppress the system's displacement response.</p><p>This dissertation illustrates the performance of various high-performance isolation strategies using experimentally-validated predictive models. Effective modeling of RISs is complicated by the nonholonomic and chaotic nature of these systems which to date has not received much attention. Motivated by this observation, the first part of this dissertation addresses the high-fidelity modeling of a single, undamped RIS, and later this theory is augmented to account for the double (or stacked) configuration and the supplemental damping via rubber-coated bowl surfaces. The system's potential energy function (i.e. conical bowl shape) and energy dissipation model are calibrated to free-response experiments. Forced-response experiments successfully validate the models by comparing measured and predicted peak displacement and acceleration responses over a range of operating conditions.</p><p>Following the experimental analyses, numerical simulations demonstrate the potential benefits of the proposed technologies. This dissertation presents a method to optimize damping force trajectories subject to constraints imposed by the physical implementation of a particular controllable damper. Potential improvements in terms of acceleration response are shown to be achievable with the semi-active RIS. Finally, extensive time-history analyses establish how the undamped and damped RISs perform when located inside biaxial, hysteretic, multi-story structures under recorded earthquake ground motions. General design recommendations, supported by critical-disturbance spectra and peak-response distributions, are prescribed so as to ensure the uninterrupted operation of vital equipment.</p> / Dissertation

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