This dissertation is a study of the relationships between nitrogen (N) availability and spiraling (the paired processes of nutrient cycling and advective transport) in stream ecosystems. Anthropogenic activities have greatly increased rates of N loading to aquatic ecosystems. However, streams may be important sites for retention, removal, and transformation of N. In order to identify controls on NO3-N spiraling in anthropogenically impacted streams, I examined relationships among NO3-N spiraling and a suite of chemical, physical, and biological variables in streams spanning a gradient of N concentration. Across all streams, gross primary production (GPP) accounted for most NO3-N demand. Uptake of NO3-N was also related to GPP but was limited by N availability when N concentrations were low. A combination of GPP and NO3-N explained 80% of the variance in uptake. In chapter 3, I conducted a series of short-term nutrient releases in which streamwater NO3-N concentration was incrementally elevated to identify conditions leading to saturation of uptake capacity. Four of six study streams showed signs of N limitation whereas there was no significant change in uptake with increasing NO3-N amendment in two streams, suggesting N saturation. Proximity to saturation was generally correlated to N concentration but was also predicted by the ratio of N:P. My results suggest complex relationships between N spiraling and availability that depend on resident biota and other limiting factors. In chapter 4, I examined nutrient spiraling methodology by comparing differences between ambient and amendment-derived NO3-N spiraling metrics. I quantified spiraling metrics during a short-term NO3-N amendment and under ambient conditions using a stable isotope (15NO3-N) tracer. Uptake lengths measured during amendments were consistently longer than ambient uptake lengths. Amendment-derived NO3-N uptake velocity and uptake were underestimated relative to ambient conditions. Using a technique to estimate ambient uptake length extrapolated from the relationship between uptake length and nutrient amendment concentration for a series of amendments at different concentrations, I found that extrapolated uptake lengths were generally better predictors of ambient uptake lengths than amendment-derived uptake lengths but the technique was less effective in high N streams that showed signs of weak N limitation. / Ph. D.

To assess how urbanization impacts stream nutrient uptake, a series of instantaneous (i.e. slug) nutrient additions were conducted in 3 urban and 3 non-urban streams during open and closed canopy conditions. Single additions of N, P, and combined additions of N and P were performed at each site. These data were used to test the hypothesis that high N:P concentrations in urban streams would result in P-limited conditions, and to assess differences in nutrient uptake kinetics (i.e., the relationship between uptake and concentration) between urban and non-urban streams. The results show that there were no consistent differences in N vs. P limitation among urban and non-urban streams suggesting that ambient N:P ratios are not useful predictors of nutrient limitation at the ecosystem scale. Areal uptake rates of N in urban streams were greater than non-urban streams coinciding with elevated N concentrations. Conversely, areal uptake rates of P were similar between urban and non-urban streams because these systems have similar ambient concentrations of P. Urban and non-urban streams demonstrated similar uptake velocity and areal uptake rate responses to increasing nutrient concentrations. However, unique to this study, urban streams had greater uptake velocities at ambient nutrient concentrations. These findings suggest that urban streams could have a greater capacity for nutrient uptake over a broad range of nutrient concentrations, but prior work indicates that this capacity may be constrained by the duration of the nutrient addition.

We investigated the influence of multiple disturbances on ecosystem structure and function in a headwater stream adjacent to an abandoned arsenic mine using an upstream (reference) and downstream (mine-influenced) comparative reach approach. In this study, floods were addressed as a pulse disturbance, and the abandoned arsenic mine was characterized as a press disturbance. Chronically elevated levels of arsenic were specifically addressed as a ramp disturbance. Stream ecosystem structure and biogeochemical functioning were characterized monthly over a period from July to December 2004 by determining benthic organic matter standing stocks, ecosystem metabolism, and by using solute additions to examine differences in phosphorus uptake and hydrology over the monitoring period. Influences of the press disturbance were evident in the mine-influenced reach where arsenic concentrations (254 ± 39 µg/L) were >30 higher than in the reference reach (8 ± 1 µg/L). However, in almost all cases the presence of the abandoned arsenic mine appeared to exert little influence on reach-scale measures of ecosystem structure and function (e.g., organic matter standing crops, phosphorus uptake). Conversely, floods (i.e., pulse disturbances) influenced organic matter standing stocks and hydrologic interactions between the stream and transient storage zones in both study reaches. Interactions between press and pulse disturbances were evident in several cases and illustrated by phosphorus uptake responses. Phosphorus uptake was best predicted by coarse particulate organic matter standing stocks in the reference reach. However, in the reach exposed to the press disturbance (i.e., mine-influenced reach), both coarse particulate organic matter standing stocks and characteristics of the pulse disturbance regime (i.e., number of days post-flood) were significant predictors of phosphorus uptake. Within the mine-influenced reach, arsenic concentrations increased from 16–600 µg/L and were addressed as a ramp disturbance. Analysis of phosphorus uptake in the mine-influenced reach across a gradient of arsenic concentrations correlated with Michaelis-Menton models of enzyme kinetics in the presence of a competitive inhibitor. These results suggest that arsenic appears to competitively inhibit phosphorus uptake by microbial assemblages in the mine-influenced reach. Results from this study highlight the fact that ecotoxilogical studies at the ecosystem scale should consider not only contaminant influences, but rather place its implications within the extant disturbance regime generated from both natural and anthropogenic sources. / Master of Science

Feminism movements have questioned the notion of coherent identities in contemporary western societies. In particular, they hold that to consider a woman as a coherent and stable subject is contrary to feminist beliefs, as this refuses the multiplicity of cultural, social and political intersections within which this allegedly concrete array of women is constructed. According to Luce Irigaray and Judith Butler, individual identities are both socially and politically constructed. With this in mind, the objective of this thesis is to analyze Irish gender relations as represented in Anne Enrights contemporary work. In analyzing Enrights literary characters as representations of contemporary women, primarily with regard to motherhood, certain historical and cultural aspects specific to Ireland must be considered in order to understand how womens identities have been shaped by the political, religious, and social establishments in place from the turn of the century up to contemporary Irish society. This thesis argues that, in her literature, Enright defines her characters both tangentially and paradoxically thereby provoking a rupture in the established image of woman. Thus, she draws attention to the shift from the inner self to the external world in an aesthetic attempt to construct her own authentic space. This involves an aesthetic process in which the author uses narrative strategies to guide the reader on a circular-upward progression towards social self-awareness. The objective of Enrights literary texts is to guide the individual in a spiraling movement of thoughts which leads him or her to perceive a self-reflection in the narrative. Then, carried by the spiraling narrative, the outer social context of the narrative becomes involved with its inside world, promoting an elevation of the reader towards a self-awareness of his or her materiality immersed in human relations. / Os movimentos feministas têm questionado a postulação do conceito de identidades coerentes nas sociedades ocidentais contemporâneas pois, de acordo com tal ideia, considerar as mulheres como um sujeito coerente e estável significa ser contrário às crenças feministas, recusando a multiplicidade de interseções culturais, sociais e políticas nas quais o conjunto concreto de mulheres é construído. Segundo Luce Irigaray e Judith Butler, as identidades individuais são construídas social e politicamente. Tendo isso em mente, o objetivo desta tese é analisar as relações de gênero como representadas no trabalho da escritora contemporânea Anne Enright. Ao analisar as personagens literários de Enright como uma representação das mulheres atuais, principalmente no que diz respeito à maternidade, os aspectos históricos e culturais específicos da Irlanda devem ser considerados para entender como a identidade das mulheres foi moldada com base em um estabelecimento ideológico político, religioso e social desde a virada do século até os dias atuais. A hipótese é que, em sua literatura, Enright define seus personagens tangencialmente e paradoxalmente provocando uma ruptura na imagem das mulheres socialmente estabelecida. Assim, ela ilumina o movimento do eu interior para o mundo exterior em uma tentativa estética de construir seu próprio espaço. Isso significa um processo no qual a autora usa estratégias narrativas para orientar o leitor em uma tentativa ascendente para a autoconsciência social. O objetivo dos textos literários de Enright é o de guiar o indivíduo pelo movimento espiralado dos seus pensamentos e, em primeiro lugar, obter uma auto-reflexão através da narrativa que impulsiona o interior dos personagens para o exterior. Então, abrangido pela espiral, o contexto social envolve o mundo interior da narrativa, promovendo uma elevação do leitor para uma autoconsciência de sua materialidade imersa nas relações humanas.

Feminism movements have questioned the notion of coherent identities in contemporary western societies. In particular, they hold that to consider a woman as a coherent and stable subject is contrary to feminist beliefs, as this refuses the multiplicity of cultural, social and political intersections within which this allegedly concrete array of women is constructed. According to Luce Irigaray and Judith Butler, individual identities are both socially and politically constructed. With this in mind, the objective of this thesis is to analyze Irish gender relations as represented in Anne Enrights contemporary work. In analyzing Enrights literary characters as representations of contemporary women, primarily with regard to motherhood, certain historical and cultural aspects specific to Ireland must be considered in order to understand how womens identities have been shaped by the political, religious, and social establishments in place from the turn of the century up to contemporary Irish society. This thesis argues that, in her literature, Enright defines her characters both tangentially and paradoxically thereby provoking a rupture in the established image of woman. Thus, she draws attention to the shift from the inner self to the external world in an aesthetic attempt to construct her own authentic space. This involves an aesthetic process in which the author uses narrative strategies to guide the reader on a circular-upward progression towards social self-awareness. The objective of Enrights literary texts is to guide the individual in a spiraling movement of thoughts which leads him or her to perceive a self-reflection in the narrative. Then, carried by the spiraling narrative, the outer social context of the narrative becomes involved with its inside world, promoting an elevation of the reader towards a self-awareness of his or her materiality immersed in human relations. / Os movimentos feministas têm questionado a postulação do conceito de identidades coerentes nas sociedades ocidentais contemporâneas pois, de acordo com tal ideia, considerar as mulheres como um sujeito coerente e estável significa ser contrário às crenças feministas, recusando a multiplicidade de interseções culturais, sociais e políticas nas quais o conjunto concreto de mulheres é construído. Segundo Luce Irigaray e Judith Butler, as identidades individuais são construídas social e politicamente. Tendo isso em mente, o objetivo desta tese é analisar as relações de gênero como representadas no trabalho da escritora contemporânea Anne Enright. Ao analisar as personagens literários de Enright como uma representação das mulheres atuais, principalmente no que diz respeito à maternidade, os aspectos históricos e culturais específicos da Irlanda devem ser considerados para entender como a identidade das mulheres foi moldada com base em um estabelecimento ideológico político, religioso e social desde a virada do século até os dias atuais. A hipótese é que, em sua literatura, Enright define seus personagens tangencialmente e paradoxalmente provocando uma ruptura na imagem das mulheres socialmente estabelecida. Assim, ela ilumina o movimento do eu interior para o mundo exterior em uma tentativa estética de construir seu próprio espaço. Isso significa um processo no qual a autora usa estratégias narrativas para orientar o leitor em uma tentativa ascendente para a autoconsciência social. O objetivo dos textos literários de Enright é o de guiar o indivíduo pelo movimento espiralado dos seus pensamentos e, em primeiro lugar, obter uma auto-reflexão através da narrativa que impulsiona o interior dos personagens para o exterior. Então, abrangido pela espiral, o contexto social envolve o mundo interior da narrativa, promovendo uma elevação do leitor para uma autoconsciência de sua materialidade imersa nas relações humanas.

The ability to withstand a short circuit is the most essential feature of a power transformer. The most important reason to design short-circuits proof transformers is to ensure the reliability of the power grid (avoiding black outs etc.) and safety (fire and explosion in case of failure). During short circuit, the most effected winding is the LV winding due to the flow high currents even during the normal working condition. So during a short circuit large forces are generated which act on the winding and these forces can reach hundreds of tons in fraction of a second, so the transformer must be properly designed in order to withstand these forces or the transformer can fail in different ways. One of the possible failure modes called “Spiraling” is discussed and analyzed in this thesis. Spiraling Occurs when the LV winding twists tangentially in the opposite direction at the ends due to radial short circuit forces. From literature study the transient forces acting on the winding during a 3-phase short circuit was determined and these transient forces were used to perform simulations on the model. The axial and radial forces applied on the model were such that it has a uniform magnitude per each turn. Various analysis was performed on the model which includes the Static, Modal and Transient Structural analysis in Ansys Workbench and each analysis involved parametric analysis where the deformations and the torsional mode shapes were determined

Autotrophs and heterotrophs differ in their demand, acquisition and use of materials, but fundamentally nutrient demand is inherently linked to metabolism based on the stoichiometry of biochemical reactions. The differences between these two groups of organisms confound straightforward regression approaches to quantifying the relationship between nutrient demand and metabolism at an ecosystem level. We address how nutrient demand in headwater streams changes with shifts in organic matter supply and associated microbial activity by investigating these relationships in the predominantly heterotrophic conditions of a southern Appalachian stream. We measured litter input, organic matter standing crops, litter respiration rates and nitrate demand several times during the course of decomposition. There was a strong relationship between leaf standing crop and nitrate uptake efficiency across dates with maximal efficiency occurring when litter standing crops were highest. There was also an increase in nitrogen (N) uptake rate relative to respiration rates as breakdown progressed, which appears to be due to a shift in nutrient supply from the substrate to the water column associated with the depletion of labile, high quality organic matter in the substrate. It is our contention that streams establish a gradient of resource supply from particulate to dissolved sources that coincides with the movement of materials from terrestrial to marine systems. / Master of Science

Forested mountain watersheds provide essential resources and services (e.g., water supply) to downstream ecosystems and human communities. Fast-growing mountainside residential development not only modifies the terrestrial system but also aquatic systems by changing the nutrient input from the terrestrial to aquatic. However, the impacts of mountainside residential development on stream ecosystems are complex because interactions between in- stream process and hillslope soils control in-stream nutrient dynamics, and it is difficult to experimentally study these interactions at broad spatial scales. In my dissertation research, I first developed models for leaf decomposition in a forested headwater stream by synthesizing several important ecological concepts, including ecological stoichiometry, microbial nutrient mining, and microbe-substrate interaction. I then extended the single stream model to a stream network model and further linked the stream network model with a terrestrial model that simulates nutrient processes and hydrology in hillslope soils. With this complete modeling framework, I conducted a global sensitivity analysis to evaluate the importance of terrestrial nutrient input versus in-stream processes in modifying nitrogen export. I also conducted a simulation to investigate the impacts of housing density, buffer zone protection, and stream travel distance from the residential development to the catchment outlet on nitrogen export at the local and regional scale. The model for leaf decomposition performed better for predicting detritus decay and nutrient patterns when microbial groups were divided into immobilizers and miners and when leaf quality was included as a variable. The importance of terrestrial nutrient input versus in-stream nutrient processes greatly depended on the level of terrestrial nutrient input. When terrestrial nitrate input was low, nitrogen export was more sensitive to in-stream net microbial nitrogen flux (mineralization - immobilization) than nitrate input. However, when terrestrial nitrate input was high, nitrate input was more important than in-stream net nitrogen flux. Greater impacts, i.e., higher nitrogen export at the local scale or greater change in nitrogen export at the regional scale, were associated with higher residential density, a lack of buffer zone protection, and shorter stream travel distance from the residential development to the catchment outlet. Although subject to model assumptions and further validation through field experiments, this research provides a general modeling framework for in-stream processes and aquatic-terrestrial linkages and expands an understanding of interactions between terrestrial and in-stream nitrogen dynamics and the impacts of mountainside development on stream ecosystems, identifies directions for further research, and provides insights for land and river management in mountainous areas. / Ph. D.

I investigated how anthropogenic acidification influences stream metabolism and nitrogen (N) cycling by considering the stress response of microbial compartments responsible for these ecosystem processes. Microcosm incubations of leaf biofilms from streams of differing pH revealed greater rates of fungal biomass-specific respiration (i.e. the stress metric <i>q</i>CO₂) and biomass-specific N uptake (i.e. <i>q</i>N) with increasing acidity. The positive relationship between <i>q</i>CO₂ and <i>q</i>N indicated alternate fates for N other than structural biomass, possibly related to increased exoenzyme production as part of the stress response. Whole-stream ¹⁵N experiments and measurements of respiration and fungal standing crop across the pH gradient resulted in similar patterns in <i>q</i>CO₂ and <i>q</i>N found in microcosm experiments, supporting <i>q</i>CO₂ as an ecosystem-level stress indicator and providing insight towards controls over N cycling across the pH gradient. Fungal biomass and ecosystem respiration declined with increasing acidity while N uptake metrics were not related to pH, which suggested <i>q</i>N in acid streams was sufficiently high to counteract declines in fungal abundance. During spring, chlorophyll <i>a</i> standing crops were higher in more acidic streams despite lower nutrient concentrations. However, N uptake rates and gross primary production differed little between acid and circumneutral streams. Reduced heterotrophy in acid streams was apparent in lower whole-stream respiration rates, less ability to process organic carbon, and little response of N uptake to added carbon resources. Overall, acid-induced stress in streams was found to impair decomposer activity and caused a decoupling of carbon and nitrogen cycles in these systems. / Ph. D.

Dans cette thèse, on étudie les C2-feuilletages de codimension 1, dans les 3-variétés compactes connexes et orientables. Il est bien connu que l’on peut construire explicitement sur de telles variétés un feuilletage qui possède des composantes de Reeb. Vient alors le problème crucial d’existence des feuilletages tendus (toujours ouvert).Rappelons qu’un feuilletage tendu n’admet pas de composante de Reeb, mais que la réciproque est fausse.La première partie de ce travail, consiste à comprendre la différence entre un feuilletage non-tendu sans composante de Reeb et un feuilletage tendu. On verra que l’orientation transverse des feuilles toriques joue un rôle crucial, en donnant une condition nécessaire et suffisante sur cette orientation transverse pour qu’un feuilletage soit tendu. Pour cela on étudiera de près les procédés géométriques de tourbillonement et de spiralement, et on montrera qu’ils apparaissent toujours au voisinage d’une feuille torique.La seconde partie de ce travail se concentre sur le problème d’existence de feuilletages tendu. Rappelons que depuis les travaux de D. Gabai [1983], on sait que si une 3-variété admet une homologie non-triviale, alors elle admet un feuilletage tendu. Mais le problème d’existence est toujours ouvert parmi les sphères d’homologies, et on s’intéresse ici à celles qui sont fibrées de Seifert. On montre que toutes les sphères d’homologie entière fibrées de Seifert sauf S3 et la sphère d’homologie de Poincaré admettent un feuilletage tendu. Par contre, parmi les sphères d’homologie rationnelle non-entière, fibrées de Seifert, il existe une infinité de telles variétés qui admettent un feuilletage tendu, et une infinité qui n’en admettent pas. / In this thesis, we study codimension 1, C2-foliations, in compact, connected and orientable 3-manifolds. It is well known that we can explicitly construct on such manifolds a foliation admitting Reeb components. Then comes the crucial problem of existence of taut foliation (still opened).Recall that a taut foliation does not admit a Reeb component, but the converse is false. The first step of this work focuses on the difference between a non-taut and Reebless foliation, and a taut foliation. We will understand that the transverse orientation of the torus leaves plays a key-role, by giving a necessary and sufficient condition on the transverse orientation, for a foliation to be taut. For this, we will study the geometric processes of turbulization and spiraling with generalizations, and we see that they always appear in a neighborhood of a torus leaf.The second step of this work is concentrated on the problem of existence of taut foliations. Recall that since the work of D. Gabai [1983], we know that if a 3-manifold has non-trivial homology, then it admits a taut foliation. This problem is still opened among homology spheres and we focus here on Seifert fibered ones. We show that all Seifert fibered integral homology spheres (but S3 and Poincar &#769;e homology sphere) admit a taut foliation. Nevertheless, among Seifert fibered rational (and non-integral) homology spheres, there exist infinitely many which admit a taut foliation and infinitely many which do not admit one.