Interação do complexo luminescente [Eu(tta)3] com sílica mesoporosa

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Ecologia da ictiofauna do estuário do rio Paciência, Ilha do Maranhão - Brasil

Os sistemas estuarinos funcionam como importante habitat para várias especies de peixes, atraves das redes de canais de mare. Sob o ponto de vista ecologico, a comunidade ictiofaunística desempenham importante funcao no balanco energetico dos varios niveis tróficos dos ecossistemas estuarinos. Neste contexto, o presente estudo objetivou: determinar as distribuições espaco-temporais da ictiofauna; explicar suas características comportamentais e ecologicas; comparar a composicao da biomassa relativa, guildas ecologicas e funcionais em diferentes sistemas estuarinos da costa Norte; investigar a influencia das variaveis bioticas e abioticas e sua correlacao com os padroes biologicos da ictiofauna e identificar alteracoes na integridade biotica dos canais de mare estudados, utilizando a ictiofauna. Os dados foram obtidos a partir de amostragens bimestrais nos canais de mare Iguaiba, Grande e Cristovao, no periodo de janeiro/2006 a setembro/2007, utilizando redes de emalhar e tapagem. Paralelamente, foram tomadas amostras na camada superficial da agua para determinacao das variaveis fisico-quimicos e dos nutrientes inorganicos dissolvidos. Na caracterizacao ecologica das especies, foram empregados indices que estimam a diversidade, equitabilidade e riqueza. O Indice de Integridade Biotica foi aplicado para avaliar os efeitos das possiveis alteracoes ambientais na ictiofauna. Tecnicas univariadas (ANOVA, Kruskall-Wallis) e multivariadas (Cluster, nMDS, SIMPER, COIA e curvas ABC) foram usadas para comparar as especies e os locais de capturas. No total foram capturados 12.219 peixes distribuídos em 55 especies e 27 familias. As familias Sciaenidae, Ariidae, Carangidae, Engraulidae e Mugilidae apresentaram maior riqueza de especies. Ariopsis bonillai e Cetengraulis edentulus, apresentaram maior contribuicao para a formacao de grupos mais similares; Stellifer naso e Cynoscion acoupa foram responsaveis pela dissimilaridade entre os grupos formados. Cerca de 66% dos peixes capturados foram representados por individuos jovens, confirmando a condicao de bercario dos sistemas estuarinos. Os registros ictiofaunisticos entre o Golfao Marajoara e Maranhense apontam a ocorrência de 140 especies. Especies marinhas visitantes ocasionais e de agua doce ocorreram ocasionalmente. Marinhas estuarino-oportunistas e estuarino dependentes apresentaram maior contribuicao no Golfao Maranhense, ja as estuarino residentes apresentaram biomassa elevada em todos os sistemas estuarinos investigados. Detritivoros ocorreram principalmente no Pará e zoobentivoros no Maranhao. A ocorrencia de piscivoros foi inversamente proporcional a abundancia de juvenis. A co-estrutura formada entre variaveis ambientais-peixes foi significativa. As variaveis salinidade, pH, silicato, amonio, fosfato e nitrato influenciaram na estrutura da ictiofauna. Nenhuma especie se associou a ambientes com elevadas concentracoes de nutrientes inorganicos. As curvas ABC demonstraram que o ambiente estuarino encontra-se moderadamente perturbado, enquanto o indice de integridade caracterizou a qualidade ambiental dos canais de mare entre muito pobre a regular. O estudo mostrou que os canais de mare são importantes areas de criacao devido a dominancia de juvenis; a ictiofauna apresenta sazonalidade em relacao aos periodos hidrologicos; a comunidade peixes presente nos canais de mare pode atuar como indicadora da qualidade de ecossistemas submetidos a pulsos de mares. Considera-se, portanto, a protecao dos canais entre-mares dos manguezais uma ação essencial para o manejo dos recursos pesqueiros, uma vez que existe uma forte relacao entre abundancia da ictiofauna e a composição estrutural do habitat.

Modelagem numérica da influência do eletrojato equatorial em dados magnetotelúricos produzidos por estruturas tridimensionais

A América do Sul apresenta várias peculiaridades geomagnéticas, uma delas, é a presença do Eletrojato Equatorial, o qual se estende de leste para oeste no Brasil ao longo de aproximadamente 3500 km. Considerando-se o fato de que a influência do Eletrojato Equatorial pode ser detectada a grandes distâncias do seu centro, isto suscita o interesse em se estudar os seus efeitos na exploração magnetotelúrica no Brasil. A influência do eletrojato equatorial na prospecção magnetotelúrica tem sido modelada para meios geológicos uni e bidimensionais valendo-se para isto de soluções analíticas fechadas e de técnicas numéricas tais como elementos finitos e diferenças finitas. Em relação aos meios geológicos tridimensionais, eles tem sido modelados na forma de "camadas finas", usando o algoritmo "thin sheet". As fontes indutoras utilizadas para simular o eletrojato equatorial nestes trabalhos, tem sido linhas de corrente, eletrojatos gaussianos e eletrojatos ondulantes. Por outro lado, o objetivo principal da nossa tese foi o modelamento dos efeitos que o eletrojato equatorial provoca em estruturas tridimensionais próprias da geofísica da prospecção. Com tal finalidade, utilizamos o esquema numérico da equação integral, com as fontes indutoras antes mencionadas. De maneira similar aos trabalhos anteriores, os nossos resultados mostram que a influência do eletrojato equatorial somente acontece em frequências menores que 10^-1 Hz. Este efeito decresce com a distância, mantendo-se até uns 3000 km do centro do eletrojato. Assim sendo, a presença de grandes picos nos perfis da resistividade aparente de um semi-espaço homogêneo, indica que a influência do eletrojato é notável neste tipo de meio. Estes picos se mostram com diferente magnitude para cada eletrojato simulado, sendo que a sua localização também muda de um eletrojato para outro. Entretanto, quando se utilizam modelos geo-elétricos unidimensionais mais de acordo com a realidade, tais como os meios estratificados, percebe-se que a resposta dos eletrojatos se amortece significativamente e não mostra muitas diferenças entre os diferentes tipos de eletrojato. Isto acontece por causa da dissipação da energia eletromagnética devido à presença da estratificação e de camadas condutivas. Dentro do intervalo de 3000 km, a resposta eletromagnética tridimensional pode ser deslocada para cima ou para baixo da resposta da onda plana, dependendo da localização do corpo, da frequência, do tipo de eletrojato e do meio geológico. Quando a resposta aparece deslocada para cima, existe um afastamento entre as sondagens uni e tridimensionais devidas ao eletrojato, assim como um alargamento da anomalia dos perfis que registra a presença da heterogeneidade tridimensional. Quando a resposta aparece deslocada para baixo, no entanto, há uma aproximação entre estes dois tipos de sondagens e um estreitamento da anomalia dos perfis. Por outro lado, a fase se mostra geralmente, de uma forma invertida em relação à resistividade aparente. Isto significa que quando uma sobe a outra desce, e vice-versa. Da mesma forma, comumente nas altas frequências as respostas uni e tridimensionais aparecem deslocadas, enquanto que nas baixas frequências se mostram com os mesmos valores, com exceção dos eletrojatos ondulantes com parâmetros de ondulação α = —2 e —3. Nossos resultados também mostram que características geométricas próprias das estruturas tridimensionais, tais como sua orientação em relação à direção do eletrojato e a dimensão da sua direção principal, afetam a resposta devido ao eletrojato em comparação com os resultados da onda plana. Desta forma, quando a estrutura tridimensional é rotacionada de 90°, em relação à direção do eletrojato e em torno do eixo z, existe uma troca de polarizações nas resistividades dos resultados, mas não existem mudanças nos valores da resistividade aparente no centro da estrutura. Ao redor da mesma, porém, se percebe facilmente alterações nos contornos dos mapas de resistividade aparente, ao serem comparadas com os mapas da estrutura na sua posição original. Isto se deve à persistência dos efeitos galvânicos no centro da estrutura e à presença de efeitos indutivos ao redor do corpo tridimensional. Ao alongar a direção principal da estrutura tridimensional, as sondagens magnetotelúricas vão se aproximando das sondagens das estruturas bidimensionais, principalmente na polarização XY. Mesmo assim, as respostas dos modelos testados estão muito longe de se considerar próximas das respostas de estruturas quase-bidimensionais. Porém, os efeitos do eletrojato em estruturas com direção principal alongada, são muito parecidos com aqueles presentes nas estruturas menores, considerando-se as diferenças entre as sondagens de ambos tipos de estruturas. Por outro lado, os mapas de resistividade aparente deste tipo de estrutura alongada, revelam um grande aumento nos extremos da estrutura, tanto para a onda plana como para o eletrojato. Este efeito é causado pelo acanalamento das correntes ao longo da direção principal da estrutura. O modelamento de estruturas geológicas da Bacia de Marajó confirma que os efeitos do eletrojato podem ser detetados em estruturas pequenas do tipo "horst" ou "graben", a grandes distâncias do centro do mesmo. Assim, os efeitos do eletrojato podem ser percebidos tanto nos meios estratificados como tridimensionais, em duas faixas de freqüência (nas proximidades de 10^-1 Hz e para freqüências menores que 10^-3 Hz), possivelmente influenciados pela presença do embasamento cristalino e a crosta inferior, respectivamente. Desta maneira, os resultados utilizando o eletrojato como fonte indutora, mostram que nas baixas freqüências as sondagens magnetotelúricas podem ser fortemente distorcidas, tanto pelos efeitos galvânicos da estrutura tridimensional como pela presença da influência do eletrojato. Conseqüêntemente, interpretações errôneas dos dados de campo podem ser cometidas, se não se corrigirem os efeitos do eletrojato equatorial ou, da mesma forma, não se utilisarem algoritmos tridimensionais para interpretar os dados, no lugar do usual modelo unidimensional de Tikhonov - Cagniard.

Potential Application in Energy Harvesting of Intermodal Energy Exchange in a Frame: FEM Analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fingerprints of short-range and long-range structure in BaZr1-xHfxO3 solid solutions: an experimental and theoretical study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Protocolo para sinterização de zircônia odontológica por energia de micro-ondas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of parametric uncertainties on the performance of a piezoelectric energy harvesting device

The use of piezoelectric materials for the development of electromechanical devices for the harvesting or scavenging of ambient vibrations has been extensively studied over the last decade. The energy conversion from mechanical (vibratory) to electrical energy is provided by the electromechanical coupling between mechanical strains/stresses and electric charges/voltages in the piezoelectric material. The majority of the studies found in the open literature present a tip-mass cantilever piezoelectric device tuned on the operating frequency. Although recent results show that these devices can be quite effective for harvesting small amounts of electrical energy, little has been published on the robustness of these devices or on the effect of parametric uncertainties on the energy harvested. This work focuses on a cantilever plate with bonded piezoelectric patches and a tip-mass serving as an energy harvesting device. The rectifier and storage electric circuit was replaced by a resistive circuit (R). In addition, an alternative to improve the harvesting performance by adding an inductance in series to the harvesting circuit, thus leading to a resonant circuit (RL), is considered. A coupled finite element model leading to mechanical (displacements) and electrical (charges at electrodes) degrees of freedom is considered. An analysis of the effect of parametric uncertainties of the device on the electric output is performed. Piezoelectric and dielectric constants of the piezoelectric active layers and electric circuit equivalent inductance are considered as stochastic parameters. Mean and confidence intervals of the electric output are evaluated.

The firm. Techno-organizational changes, industrial relations and performances. An enquiry on Reggio Emilia local industrial system

It is not unknown that the evolution of firm theories has been developed along a path paved by an increasing awareness of the organizational structure importance. From the early “neoclassical” conceptualizations that intended the firm as a rational actor whose aim is to produce that amount of output, given the inputs at its disposal and in accordance to technological or environmental constraints, which maximizes the revenue (see Boulding, 1942 for a past mid century state of the art discussion) to the knowledge based theory of the firm (Nonaka & Takeuchi, 1995; Nonaka & Toyama, 2005), which recognizes in the firm a knnowledge creating entity, with specific organizational capabilities (Teece, 1996; Teece & Pisano, 1998) that allow to sustaine competitive advantages. Tracing back a map of the theory of the firm evolution, taking into account the several perspectives adopted in the history of thought, would take the length of many books. Because of that a more fruitful strategy is circumscribing the focus of the description of the literature evolution to one flow connected to a crucial question about the nature of firm’s behaviour and about the determinants of competitive advantages. In so doing I adopt a perspective that allows me to consider the organizational structure of the firm as an element according to which the different theories can be discriminated. The approach adopted starts by considering the drawbacks of the standard neoclassical theory of the firm. Discussing the most influential theoretical approaches I end up with a close examination of the knowledge based perspective of the firm. Within this perspective the firm is considered as a knowledge creating entity that produce and mange knowledge (Nonaka, Toyama, & Nagata, 2000; Nonaka & Toyama, 2005). In a knowledge intensive organization, knowledge is clearly embedded for the most part in the human capital of the individuals that compose such an organization. In a knowledge based organization, the management, in order to cope with knowledge intensive productions, ought to develop and accumulate capabilities that shape the organizational forms in a way that relies on “cross-functional processes, extensive delayering and empowerment” (Foss 2005, p.12). This mechanism contributes to determine the absorptive capacity of the firm towards specific technologies and, in so doing, it also shape the technological trajectories along which the firm moves. After having recognized the growing importance of the firm’s organizational structure in the theoretical literature concerning the firm theory, the subsequent point of the analysis is that of providing an overview of the changes that have been occurred at micro level to the firm’s organization of production. The economic actors have to deal with challenges posed by processes of internationalisation and globalization, increased and increasing competitive pressure of less developed countries on low value added production activities, changes in technologies and increased environmental turbulence and volatility. As a consequence, it has been widely recognized that the main organizational models of production that fitted well in the 20th century are now partially inadequate and processes aiming to reorganize production activities have been widespread across several economies in recent years. Recently, the emergence of a “new” form of production organization has been proposed both by scholars, practitioners and institutions: the most prominent characteristic of such a model is its recognition of the importance of employees commitment and involvement. As a consequence it is characterized by a strong accent on the human resource management and on those practices that aim to widen the autonomy and responsibility of the workers as well as increasing their commitment to the organization (Osterman, 1994; 2000; Lynch, 2007). This “model” of production organization is by many defined as High Performance Work System (HPWS). Despite the increasing diffusion of workplace practices that may be inscribed within the concept of HPWS in western countries’ companies, it is an hazard, to some extent, to speak about the emergence of a “new organizational paradigm”. The discussion about organizational changes and the diffusion of HPWP the focus cannot abstract from a discussion about the industrial relations systems, with a particular accent on the employment relationships, because of their relevance, in the same way as production organization, in determining two major outcomes of the firm: innovation and economic performances. The argument is treated starting from the issue of the Social Dialogue at macro level, both in an European perspective and Italian perspective. The model of interaction between the social parties has repercussions, at micro level, on the employment relationships, that is to say on the relations between union delegates and management or workers and management. Finding economic and social policies capable of sustaining growth and employment within a knowledge based scenario is likely to constitute the major challenge for the next generation of social pacts, which are the main social dialogue outcomes. As Acocella and Leoni (2007) put forward the social pacts may constitute an instrument to trade wage moderation for high intensity in ICT, organizational and human capital investments. Empirical evidence, especially focused on the micro level, about the positive relation between economic growth and new organizational designs coupled with ICT adoption and non adversarial industrial relations is growing. Partnership among social parties may become an instrument to enhance firm competitiveness. The outcome of the discussion is the integration of organizational changes and industrial relations elements within a unified framework: the HPWS. Such a choice may help in disentangling the potential existence of complementarities between these two aspects of the firm internal structure on economic and innovative performance. With the third chapter starts the more original part of the thesis. The data utilized in order to disentangle the relations between HPWS practices, innovation and economic performance refer to the manufacturing firms of the Reggio Emilia province with more than 50 employees. The data have been collected through face to face interviews both to management (199 respondents) and to union representatives (181 respondents). Coupled with the cross section datasets a further data source is constituted by longitudinal balance sheets (1994-2004). Collecting reliable data that in turn provide reliable results needs always a great effort to which are connected uncertain results. Data at micro level are often subjected to a trade off: the wider is the geographical context to which the population surveyed belong the lesser is the amount of information usually collected (low level of resolution); the narrower is the focus on specific geographical context, the higher is the amount of information usually collected (high level of resolution). For the Italian case the evidence about the diffusion of HPWP and their effects on firm performances is still scanty and usually limited to local level studies (Cristini, et al., 2003). The thesis is also devoted to the deepening of an argument of particular interest: the existence of complementarities between the HPWS practices. It has been widely shown by empirical evidence that when HPWP are adopted in bundles they are more likely to impact on firm’s performances than when adopted in isolation (Ichniowski, Prennushi, Shaw, 1997). Is it true also for the local production system of Reggio Emilia? The empirical analysis has the precise aim of providing evidence on the relations between the HPWS dimensions and the innovative and economic performances of the firm. As far as the first line of analysis is concerned it must to be stressed the fundamental role that innovation plays in the economy (Geroski & Machin, 1993; Stoneman & Kwoon 1994, 1996; OECD, 2005; EC, 2002). On this point the evidence goes from the traditional innovations, usually approximated by R&D investment expenditure or number of patents, to the introduction and adoption of ICT, in the recent years (Brynjolfsson & Hitt, 2000). If innovation is important then it is critical to analyse its determinants. In this work it is hypothesised that organizational changes and firm level industrial relations/employment relations aspects that can be put under the heading of HPWS, influence the propensity to innovate in product, process and quality of the firm. The general argument may goes as follow: changes in production management and work organization reconfigure the absorptive capacity of the firm towards specific technologies and, in so doing, they shape the technological trajectories along which the firm moves; cooperative industrial relations may lead to smother adoption of innovations, because not contrasted by unions. From the first empirical chapter emerges that the different types of innovations seem to respond in different ways to the HPWS variables. The underlying processes of product, process and quality innovations are likely to answer to different firm’s strategies and needs. Nevertheless, it is possible to extract some general results in terms of the most influencing HPWS factors on innovative performance. The main three aspects are training coverage, employees involvement and the diffusion of bonuses. These variables show persistent and significant relations with all the three innovation types. The same do the components having such variables at their inside. In sum the aspects of the HPWS influence the propensity to innovate of the firm. At the same time, emerges a quite neat (although not always strong) evidence of complementarities presence between HPWS practices. In terns of the complementarity issue it can be said that some specific complementarities exist. Training activities, when adopted and managed in bundles, are related to the propensity to innovate. Having a sound skill base may be an element that enhances the firm’s capacity to innovate. It may enhance both the capacity to absorbe exogenous innovation and the capacity to endogenously develop innovations. The presence and diffusion of bonuses and the employees involvement also spur innovative propensity. The former because of their incentive nature and the latter because direct workers participation may increase workers commitment to the organizationa and thus their willingness to support and suggest inovations. The other line of analysis provides results on the relation between HPWS and economic performances of the firm. There have been a bulk of international empirical studies on the relation between organizational changes and economic performance (Black & Lynch 2001; Zwick 2004; Janod & Saint-Martin 2004; Huselid 1995; Huselid & Becker 1996; Cappelli & Neumark 2001), while the works aiming to capture the relations between economic performance and unions or industrial relations aspects are quite scant (Addison & Belfield, 2001; Pencavel, 2003; Machin & Stewart, 1990; Addison, 2005). In the empirical analysis the integration of the two main areas of the HPWS represent a scarcely exploited approach in the panorama of both national and international empirical studies. As remarked by Addison “although most analysis of workers representation and employee involvement/high performance work practices have been conducted in isolation – while sometimes including the other as controls – research is beginning to consider their interactions” (Addison, 2005, p.407). The analysis conducted exploiting temporal lags between dependent and covariates, possibility given by the merger of cross section and panel data, provides evidence in favour of the existence of HPWS practices impact on firm’s economic performance, differently measured. Although it does not seem to emerge robust evidence on the existence of complementarities among HPWS aspects on performances there is evidence of a general positive influence of the single practices. The results are quite sensible to the time lags, inducing to hypothesize that time varying heterogeneity is an important factor in determining the impact of organizational changes on economic performance. The implications of the analysis can be of help both to management and local level policy makers. Although the results are not simply extendible to other local production systems it may be argued that for contexts similar to the Reggio Emilia province, characterized by the presence of small and medium enterprises organized in districts and by a deep rooted unionism, with strong supporting institutions, the results and the implications here obtained can also fit well. However, a hope for future researches on the subject treated in the present work is that of collecting good quality information over wider geographical areas, possibly at national level, and repeated in time. Only in this way it is possible to solve the Gordian knot about the linkages between innovation, performance, high performance work practices and industrial relations.

A numerical program for Railway vehicle-track-structure dynamic interaction using a modal substructuring approach

This work presents a program for simulations of vehicle-track and vehicle-trackstructure dynamic interaction . The method used is computationally efficient in the sense that a reduced number of coordinates is sufficient and doesn’t require high efficiency computers. The method proposes a modal substructuring approach of the system by modelling rails , sleepers and underlying structure with modal coordinates, the vehicle with physical lumped elements coordinates and by introducing interconnection elements between these structures (wheel-rail contact, railpads and ballast) by means of their interaction forces. The Frequency response function (FRF) is also calculated for both cases of track over a structure (a bridge, a viaduct ...) and for the simple vehicle-track program; for each case the vehicle effect on the FRF is then analyzed through the comparison of the FRFs obtained introducing or not a simplified vehicle on the system.

Spin polarised Heusler compounds

In der vorliegenden Dissertation dient ein einfaches Konzept zur Systematisierung der Suche nach neuen Materialien mit hoher Spinpolarisation. Dieses Konzept basiert auf zwei semi-empirischen Modellen. Zum einen kann die Slater-Pauling Regel zur Abschätzung magnetischer Momente verwendet werden. Dieses Modell wird dabei durch Rechnungen zur elektronischen Struktur unterstützt. Das zweites Modell kann insbesondere für die Co2YZ Heusler Verbindungen beim Vergleich ihrer magnetischen Eigenschaften gefunden werden. Für diese Verbindungen ergibt sich eine scheinbare lineare Abhängigkeit der Curie-Temperatur beim Auftragen als Funktion des magnetischen Momentes. Angeregt durch diese Modelle wurde die Heusler Verbindung Co2FeSi nochmals detailliert im Hinblick auf ihre geometrische und magnetische Struktur hin untersucht. Als Methoden dienten dabei die Pulver-Röntgenbeugung, die EXAFS Spektroskopie, Röntgen Absorptions- and Mößbauer Spektroskopie sowie Hoch- und Tieftemperatur Magnetometrie, XMCD and DSC. Die Messungen zeigten, dass es sich bei Co2FeSi um das Material mit dem höchsten magnetischen Moment (6 B) und der höchsten Curie Temperatur (1100 K) sowohl in der Klasse der Heusler Verbindungen als auch in der Klasse der halbmetallischen Ferromagnete handelt. Zusätzlich werden alle experimentellen Ergebnisse durch detaillierte Rechnungen zur elektronischen Struktur unterstützt. Die gleichen Konzepte wurden verwendet, um die Eigenschaften der Heusler Verbindung Co2Cr1-xFexAl vorherzusagen. Die elektronische Struktur und die spektroskopischen Eigenschaften wurden mit der voll-relativistischen Korringa-Kohn-Rostocker Methode berechnet, unter Verwendung kohärenter Potentialnäherungen um der zufälligen Verteilung von Cr und Fe Atomen sowie zufälliger Unordnung Rechnung zu tragen. Magnetische Effekte wurden durch die Verwendung Spin-abhängiger Potentiale im Rahmen der lokalen Spin-Dichte-Näherung mit eingeschlossen. Die strukturellen und chemischen Eigenschaften der quaternären Heusler Verbindung Co2Cr1-xFexAl wurden an Pulver und Bulkproben gemessen. Die Fernordnung wurde mit der Pulver Röntgenbeugung und Neutronenbeugung untersucht, während die Nahordnung mit der EXAFS Spektroskopie aufgeklärt wurde. Die magnetische Struktur von Pulver und Bulkproben wurde mitttels 57Fe-Mößbauer Spektroskopie gemessen. Die chemische Zusammensetzung wurde durch XPS analysiert. Die Ergebnisse dieser Methoden wurden verglichen, um eine Einsicht in die Unterschiede zwischen Oberflächen und Volumeneigenschaften zu erlangen sowie in das Auftreten von Fehlordnung in solchen Verbindungen. Zusätzlich wurde XMCD an den L3,2 Kanten von Co, Fe, and Cr gemessen, um die elementspezifischen magnetischen Momente zu bestimmen. Rechnungen und Messungen zeigen dabei eine Zunahme des magnetischen Momentes bei steigendem Fe-Anteil. Resonante Photoemission mit weicher Röntgenstrahlung sowie Hochenergie Photoemission mit harter Röntgenstrahlung wurden verwendet, um die Zustandsdichte der besetzten Zustände in Co2Cr0.6Fe0.4Al zu untersuchen. Diese Arbeit stellt außerdem eine weitere, neue Verbindung aus der Klasse der Heusler Verbindungen vor. Co2CrIn ist L21 geordnet, wie Messungen mittels Pulver Röntgenbeugung zeigen. Die magnetischen Eigenschaften wurden mit magnetometrisch bestimmt. Co2CrIn ist weichmagnetisch mit einer Sättigungsmagnetisierung von 1.2B bei 5 K. Im Gegensatz zu den bereits oben erwähnten Co2YZ Heusler Verbindungen ist Co2CrIn kein halbmetallischer Ferromagnet. Im Rahmen dieser Arbeit wird weiterhin eine Regel zur Vorhersage von halbmetallischen komplett kompensierten Ferrimagneten in der Klasse der Heusler Verbindungen vorgestellt. Dieses Konzept resultiert aus der Kombination der Slater-Pauling Regel mit der Kübler-Regel. Die Kübler Regel besagt, dass Mn auf der Y Position zu einem hoch lokalisierten magnetischen Moment tendiert. Unter Verwendung dieses neuen Konzeptes werden für einige Kandidaten in der Klasse der Heusler Verbindungen die Eigenschaft des halbmetallischen komplett kompensierten Ferrimagnetismus vorhergesagt. Die Anwendung dieses Konzeptes wird anhand von Rechnungen zur elektronischen Struktur bestätigt.

Einflussfaktoren der Studienfachwahl im Wandel: eine empirische Untersuchung auf Basis des Studierendensurveys

„Wer studierte was wann und warum?“ Diese Formulierung impliziert die Fragestellung und die Themenbereiche der Arbeit, die einen Beitrag zur Diskussion von Bildungsentscheidungen auf gesellschaftlicher, organisationaler und individueller Ebene leistet. Ausgangspunkt der Analyse ist eine ausführliche theoretische Einbettung des Themas anhand verschiedener Konzepte und der Aufarbeitung des Forschungsstandes. Dabei werden sozialstrukturelle Merkmale, die Bedeutung von Lebensorientierungen und der Komplex der individuellen Motivationslagen diskutiert und u.a. in Bezug zur handlungstheoretischen Unterscheidung der Um-zu- und Weil-Motive von Alfred Schütz gesetzt. Dieses Konzept und die daraus resultierenden Hypothesen werden in einer quantitativ-empirischen Analyse untersucht. Datengrundlage ist das Studierendensurvey der AG Hochschulforschung der Uni Konstanz. Anhand von binären logistischen Regressionsanalysen werden bestimmte Einflussstrukturen und fachspezifische Profile ermittelt. Insbesondere die Konzeption der intrinsischen und extrinsischen Motivationen zeichnet dabei deutliche Unterscheidungen zwischen den Fächern. Auch in der Betrachtung des Zeitraumes 1985-2007 werden Veränderungen der Einflussstrukturen der Studienfachwahl deutlich, wie z.B. die schwindende Bedeutung der sozialen Herkunft für die Studienfachwahl zeigt. Abschließend wird der Zusammenhang der Einflussstrukturen der Studienfachwahl mit der Studienzufriedenheit analysiert. Auch für die Zufriedenheit von Studierenden und damit den Studienerfolg sind bestimmte Strukturen der Studienfachwahl von Bedeutung.

Multilevel Domain Decomposition Algorithms for Monolithic Fluid-Structure Interaction Problems with Application to Haemodynamics

Finite element techniques for solving the problem of fluid-structure interaction of an elastic solid material in a laminar incompressible viscous flow are described. The mathematical problem consists of the Navier-Stokes equations in the Arbitrary Lagrangian-Eulerian formulation coupled with a non-linear structure model, considering the problem as one continuum. The coupling between the structure and the fluid is enforced inside a monolithic framework which computes simultaneously for the fluid and the structure unknowns within a unique solver. We used the well-known Crouzeix-Raviart finite element pair for discretization in space and the method of lines for discretization in time. A stability result using the Backward-Euler time-stepping scheme for both fluid and solid part and the finite element method for the space discretization has been proved. The resulting linear system has been solved by multilevel domain decomposition techniques. Our strategy is to solve several local subproblems over subdomain patches using the Schur-complement or GMRES smoother within a multigrid iterative solver. For validation and evaluation of the accuracy of the proposed methodology, we present corresponding results for a set of two FSI benchmark configurations which describe the self-induced elastic deformation of a beam attached to a cylinder in a laminar channel flow, allowing stationary as well as periodically oscillating deformations, and for a benchmark proposed by COMSOL multiphysics where a narrow vertical structure attached to the bottom wall of a channel bends under the force due to both viscous drag and pressure. Then, as an example of fluid-structure interaction in biomedical problems, we considered the academic numerical test which consists in simulating the pressure wave propagation through a straight compliant vessel. All the tests show the applicability and the numerical efficiency of our approach to both two-dimensional and three-dimensional problems.

Ab-initio study of hydrogen technology materials for hydrogen storage and proton conduction

This dissertation deals with two specific aspects of a potential hydrogen-based energy economy, namely the problems of energy storage and energy conversion. In order to contribute to the solution of these problems, the structural and dynamical properties of two promising materials for hydrogen storage (lithium imide/amide) and proton conduction (poly[vinyl phosphonic acid]) are modeled on an atomistic scale by means of first principles molecular dynamics simulation methods.rnrnrnIn the case of the hydrogen storage system lithium amide/imide (LiNH_2/Li_2NH), the focus was on the interplay of structural features and nuclear quantum effects. For these calculations, Path-Integral Molecular Dynamics (PIMD) simulations were used. The structures of these materials at room temperature were elucidated; in collaboration with an experimental group, a very good agreement between calculated and experimental solid-state 1H-NMR chemical shifts was observed. Specifically, the structure of Li_2NH features a disordered arrangement of the Li lattice, which was not reported in previous studies. In addition, a persistent precession of the NH bonds was observed in our simulations. We provide evidence that this precession is the consequence of a toroid-shaped effective potential, in which the protons in the material are immersed. This potential is essentially flat along the torus azimuthal angle, which might lead to important quantum delocalization effects of the protons over the torus.rnrnOn the energy conversion side, the dynamics of protons in a proton conducting polymer (poly[vinyl phosphonic acid], PVPA) was studied by means of a steered ab-initio Molecular Dynamics approach applied on a simplified polymer model. The focus was put on understanding the microscopic proton transport mechanism in polymer membranes, and on characterizing the relevance of the local environment. This covers particularly the effect of water molecules, which participate in the hydrogen bonding network in the material. The results indicate that these water molecules are essential for the effectiveness of proton conduction. A water-mediated Grotthuss mechanism is identified as the main contributor to proton conduction, which agrees with the experimentally observed decay on conductivity for the same material in the absence of water molecules.rnrnThe gain in understanding the microscopic processes and structures present in this materials can help the development of new materials with improved properties, thus contributing to the solution of problems in the implementation of fuel cells.

Thermal model for optimization of vascular laser tissue soldering

Laser tissue soldering (LTS) is a promising technique for tissue fusion based on a heat-denaturation process of proteins. Thermal damage of the fused tissue during the laser procedure has always been an important and challenging problem. Particularly in LTS of arterial blood vessels strong heating of the endothelium should be avoided to minimize the risk of thrombosis. A precise knowledge of the temperature distribution within the vessel wall during laser irradiation is inevitable. The authors developed a finite element model (FEM) to simulate the temperature distribution within blood vessels during LTS. Temperature measurements were used to verify and calibrate the model. Different parameters such as laser power, solder absorption coefficient, thickness of the solder layer, cooling of the vessel and continuous vs. pulsed energy deposition were tested to elucidate their impact on the temperature distribution within the soldering joint in order to reduce the amount of further animal experiments. A pulsed irradiation with high laser power and high absorbing solder yields the best results.

Assessment Of Dynamic Properties Of A Crowd Model For Human-Structure Interaction Modeling

As lightweight and slender structural elements are more frequently used in the design, large scale structures become more flexible and susceptible to excessive vibrations. To ensure the functionality of the structure, dynamic properties of the occupied structure need to be estimated during the design phase. Traditional analysis method models occupants simply as an additional mass; however, research has shown that human occupants could be better modeled as an additional degree-of- freedom. In the United Kingdom, active and passive crowd models are proposed by the Joint Working Group as a result of a series of analytical and experimental research. It is expected that the crowd models would yield a more accurate estimation to the dynamic response of the occupied structure. However, experimental testing recently conducted through a graduate student project at Bucknell University indicated that the proposed passive crowd model might be inaccurate in representing the impact on the structure from the occupants. The objective of this study is to provide an assessment of the validity of the crowd models proposed by JWG through comparing the dynamic properties obtained from experimental testing data and analytical modeling results. The experimental data used in this study was collected by Firman in 2010. The analytical results were obtained by performing a time-history analysis on a finite element model of the occupied structure. The crowd models were created based on the recommendations from the JWG combined with the physical properties of the occupants during the experimental study. During this study, SAP2000 was used to create the finite element models and to implement the analysis; Matlab and ME¿scope were used to obtain the dynamic properties of the structure through processing the time-history analysis results from SAP2000. The result of this study indicates that the active crowd model could quite accurately represent the impact on the structure from occupants standing with bent knees while the passive crowd model could not properly simulate the dynamic response of the structure when occupants were standing straight or sitting on the structure. Future work related to this study involves improving the passive crowd model and evaluating the crowd models with full-scale structure models and operating data.