Local dynamics and bending mechanics of mesostructured materials

Die vorliegende Arbeit behandelt die Anwendung der Rasterkraftmikroskopie auf die Untersuchung mesostrukturierter Materialien. Mesostrukturierte Materialien setzen sich aus einzelnen mesoskopen Bausteinen zusammen. Diese Untereinheiten bestimmen im Wesentlichen ihr charakteristisches Verhalten auf äußere mechanische oder elektrische Reize, weshalb diesen Materialien eine besondere Rolle in der Natur sowie im täglichen Leben zukommt. Ein genaues Verständnis der Selbstorganisation dieser Materialien und der Wechselwirkung der einzelnen Bausteine untereinander ist daher von essentieller Bedeutung zur Entwicklung neuer Synthesestrategien sowie zur Optimierung ihrer Materialeigenschaften. Die Charakterisierung dieser mesostrukturierten Materialien erfolgt üblicherweise mittels makroskopischer Analysemethoden wie der dielektrischen Breitbandspektroskopie, Thermogravimetrie sowie in Biegungsexperimenten. In dieser Arbeit wird gezeigt, wie sich diese Analysemethoden mit der Rasterkraftmikroskopie verbinden lassen, um mesostrukturierte Materialien zu untersuchen. Die Rasterkraftmikroskopie bietet die Möglichkeit, die Oberfläche eines Materials abzubilden und zusätzlich dazu seine quantitativen Eigenschaften, wie die mechanische Biegefestigkeit oder die dielektrische Relaxation, zu bestimmen. Die Übertragung makroskopischer Analyseverfahren auf den Nano- bzw. Mikrometermaßstab mittels der Rasterkraftmikroskopie erlaubt die Charakterisierung von räumlich sehr begrenzten Proben bzw. von Proben, die nur in einer sehr kleinen Menge (<10 mg) vorliegen. Darüberhinaus umfasst das Auflösungsvermögen eines Rasterkraftmikroskops, welche durch die Größe seines Federbalkens (50 µm) sowie seines Spitzenradius (5 nm) definiert ist, genau den Längenskalenbereich, der einzelne Atome mit der makroskopischen Welt verbindet, nämlich die Mesoskala. In dieser Arbeit werden Polymerfilme, kolloidale Nanofasern sowie Biomineralien ausführlicher untersucht.rnIm ersten Projekt werden mittels Rasterkraftmikroskopie dielektrische Spektren von mischbaren Polymerfilmen aufgenommen und mit ihrer lokalen Oberflächenstruktur korreliert. Im zweiten Projekt wird die Rasterkraftmikroskopie eingesetzt, um Biegeexperimente an kolloidalen Nanofasern durchzuführen und so ihre Brucheigenschaften genauer zu untersuchen. Im letzten Projekt findet diese Methode Anwendung bei der Charakterisierung der Biegeeigenschaften von Biomineralien. Des Weiteren erfolgt eine Analyse der organischen Zusammensetzung dieser Biomineralien. Alle diese Projekte demonstrieren die vielseitige Einsetzbarkeit der Rasterkraftmikroskopie zur Charakterisierung mesostrukturierter Materialien. Die Korrelation ihrer mechanischen und dielektrischen Eigenschaften mit ihrer topographischen Beschaffenheit erlaubt ein tieferes Verständnis der mesoskopischen Materialien und ihres Verhaltens auf die Einwirkung äußerer Stimuli.rn

Sustainable regional development: Reconciling global and local dynamics and stakes in the Swiss Alps

This article explores how global and local dynamics and stakes can be brought together when trying to combine conservation and regional development. For this purpose we analyse a series of studies carried out in the area of the Swiss Alps Jungfrau-Aletsch World Heritage Site (WHS). The approaches used in these studies to analyse the diversity and development of the region included data collection and evaluation of indicators such as population development, number of working places, occupation rates in various economic sectors and commuter balance, as well as interviews with key informants and assessment of existing planning tools. The major challenge of the newly declared World Heritage Region is that it is neither a political or administrative nor a cultural unit but constitutes a completely new type of space that breaks up and crosses traditional boundaries. The studies revealed an economic tertiarisation process and migration of the population from remote areas to regional centres. Tourism was identified as the key economic sector in the region. Regarding regional sustainability, the studies identified a need for quality dialogue and negotiation of interests and stakes. It was shown that in dealing with sustainability at the local level, many key issues cannot be resolved on the ground, as they depend on regional or national decisions, e.g. the conditions for tourism promotion in the region or economic validation of agricultural activity. We conclude from these findings that national or even international factors do not provide a basis for location-specific solutions, as they are often too general, and that the global label does not ensure sustainability in a designated WHS region; this depends entirely on local and regional dynamics.

Random walks in local dynamics of network losses

We suggest a model for data losses in a single node (memory buffer) of a packet-switched network (like the Internet) which reduces to one-dimensional discrete random walks with unusual boundary conditions. By construction, the model has critical behavior with a sharp transition from exponentially small to finite losses with increasing data arrival rate. We show that for a finite-capacity buffer at the critical point the loss rate exhibits strong fluctuations and non-Markovian power-law correlations in time, in spite of the Markovian character of the data arrival process.

Secular dynamics and family identification among highly inclined asteroids in the Euphrosyne region

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

Structure, organization and dynamics of functional supramolecular materials studied by solid-state NMR

Functional materials have great importance due to their many important applications. The characterization of supramolecular architectures which are held together by non-covalent interactions is of most importance to understand their properties. Solid-state NMR methods have recently been proven to be able to unravel such structure-property relations with the help of fast magic-angle spinning and advanced pulse sequences. The aim of the current work is to understand the structure and dynamics of functional supramolecular materials which are potentially important for fuel-cell (proton conducting membrane materials) and solar-cell or plastic-electronic applications (photo-reactive aromatic materials). In particular, hydrogen-bonding networks, local proton mobility, molecular packing arrangements, and local dynamics will be studied by the use of advanced solid-state NMR methods. The first class of materials studied in this work is proton conducting polymers which also form hydrogen-bonding network. Different materials, which are prepared for high 1H conduction by different approaches are studied: PAA-P4VP, PVPA-ABPBI, Tz5Si, and Triazole-functional systems. The materials are examples of the following major groups; - Homopolymers with specific functional groups (Triazole functional polysiloxanes). - Acid-base polymer blends approach (PAA-P4VP, PVPA-ABPBI). - Acid-base copolymer approach (Triazole-PVPA). - Acid doped polymers (Triazole functional polymer doped with H3PO4). Perylenebisimide (PBI) derivatives, a second type of important functional supramolecular materials with potent applications in plastic electronics, were also investigated by means of solid-state NMR. The preparation of conducting nanoscopic fibers based on the self-assembling functional units is an appealing aim as they may be incorporated in molecular electronic devices. In this category, perylene derivatives have attracted great attention due to their high charge carrier mobility. A detailed knowledge about their supramolecular structure and molecular dynamics is crucial for the understanding of their electronic properties. The aim is to understand the structure, dynamics and packing arrangements which lead to high electron conductivity in PBI derivatives.

Shelf and estuarine transport mechanisms affecting the supply of competent larvae in a suite of brachyuran crabs with different life histories

Supply of competent larvae to the benthic habitat is a major determinant of population dynamics in coastal and estuarine invertebrates with an indirect life cycle. Larval delivery may depend not only on physical transport mechanisms, but also on larval behavior and physiological progress to the competent stage. Yet, the combined analysis of such factors has seldom been attempted. We used time-series analyses to examine tide- and wind-driven mechanisms responsible for the supply of crab megalopae to an estuarine river under a major marine influence in SW Spain, and monitored the vertical distribution of upstream moving megalopae, their net flux and competent state. The species Panopeus africanus (estuarine), Brachynotus sexdentatus (euryhaline) and Nepinnotheres pinnotheres (coastal) comprised 80% of the whole sample, and responded in a similar way to tide and wind forcing. Tidal range was positively correlated to supply, with maxima 0 to 1 d after spring tides, suggesting selective tidal stream transport. Despite being extensively subjected to upwelling, downwind drift under the effect of westerlies, not Ekman transport, explained residual supply variation at our sampling area. Once in the estuary, net flux and competence state matched the expected trends. Net upstream flux increased from B. sexdentatus to P. africanus, favoring transport to a sheltered coastal habitat (N. pinnotheres), or to the upper estuary (P. africanus). Competence state was highest in N. pinnotheres, intermediate in B. sexdentatus and lowest in P. africanus, as expected if larvae respond to cues from adequate benthic habitat. P. africanus megalopae were found close to the bottom, not above, rendering slower upstream transport than anticipated.

Plano de revitalização do centro histórico de Braga

Dissertação de mestrado em Políticas Comunitárias e Cooperação Territorial

Mass effects mediate coexistence in competing shrews.

Recent developments in metacommunity theory have raised awareness that processes occurring at regional scales might interfere with local dynamics and affect conditions for the local coexistence of competing species. Four main paradigms are recognized in this context (namely, neutral, patch-dynamics, species-sorting, and mass-effect), which differ according to the role assigned to ecological or life-history differences among competing species, as well as to the relative time scale of regional vs. local dynamics. We investigated the patterns of regional and local coexistence of two species of shrews (Crocidura russula and Sorex coronatus) sharing a similar diet (generalist insectivores) over four generations, in a spatially structured habitat at the altitudinal limit of their distributions. Local populations were small, and regional dynamics were strong, with high rates of extinction and recolonization. Niche analysis revealed significant habitat differentiation on a few important variables, including temperature and availability of winter resting sites. In sites suitable for both species, we found instances of local coexistence with no evidence of competitive exclusion. Patterns of temporal succession did not differ from random, with no suggestion of a colonization-competition trade-off. Altogether, our data provide support for the mass-effect paradigm, where regional coexistence is mediated by specialization on different habitat types, and local coexistence by rescue effects from source sites. The strong regional dynamics and demographic stochasticity, together with high dispersal rates, presumably contributed to mass effects by overriding local differences in specific competitive abilities.

Carabid beetle assemblages in three environments in the Araucaria humid forest of southern Brazil

Carabid beetle assemblages in three environments in the Araucaria humid forest of southern Brazil. Carabidae is composed mainly by ground-dwelling predator beetles. It is the fourth most diverse group within Coleoptera, but its diversity in the Neotropical region is understudied. Here we describe and analyze the diversity of carabid beetles in a region of subtropical rain forest dominated by Araucaria angustifolia with different landscapes. Three areas were chosen in an environmental integrity gradient: primary forests, secondary forests and old Pinus plantations. Pitfall traps were taken monthly, in a total of 14 samples per area. 1733 adult carabid beetles, belonging to 18 species, were sampled. There were differences in richness and abundance between the sampled areas. The total scores followed the same tendency: primary forests (14 species/747 individuals), secondary forests (13/631) and Pinus forests (10/355). An analysis of similarity shows differences in species composition, for both areas and seasons. Galerita lacordarei was the most abundant species for all samples and seasons. Carabid species show similar responses in accordance with habitat heterogeneity and disturbance. The abundance of Galerita lacordarei was influenced by temperature, for all sampled sites. Environmental changes affect the carabid assemblages and decrease diversity, possibly interfering in local dynamics. Seasonality patterns seem to indicate an increase in individual movement during summer, probably in search of resources. It is suggested that microhabitat patchiness is probably an important factor affecting carabid beetle diversity at small spatial scales.

A fully adaptive numerical approximation for a two-dimensional epidemic model with nonlinear cross-diffusion

An epidemic model is formulated by a reactionâeuro"diffusion system where the spatial pattern formation is driven by cross-diffusion. The reaction terms describe the local dynamics of susceptible and infected species, whereas the diffusion terms account for the spatial distribution dynamics. For both self-diffusion and cross-diffusion, nonlinear constitutive assumptions are suggested. To simulate the pattern formation two finite volume formulations are proposed, which employ a conservative and a non-conservative discretization, respectively. An efficient simulation is obtained by a fully adaptive multiresolution strategy. Numerical examples illustrate the impact of the cross-diffusion on the pattern formation.

Les oscillations torsionnelles dans la zone de convection solaire

Nous analysons les oscillations torsionnelles se développant dans une simulation magnétohydrodynamique de la zone de convection solaire produisant des champs magnétiques de type solaire (champs axisymétriques subissant des inversions de polarités régulières sur des échelles temporelles décadaires). Puisque ces oscillations sont également similaires à celles observées dans le Soleil, nous analysons les dynamiques zonales aux grandes échelles. Nous séparons donc les termes aux grandes échelles (force de Coriolis exercée sur la circulation méridienne et les champs magnétiques aux grandes échelles) de ceux aux petites échelles (les stress de Reynolds et de Maxwell). En comparant les flux de moments cinétiques entre chacune des composantes, nous nous apercevons que les oscillations torsionnelles sont maintenues par l’écoulement méridien aux grandes échelles, lui même modulé par les champs magnétiques. Une analyse d’échange d’énergie confirme ce résultat, puisqu’elle montre que seul le terme comprenant la force de Coriolis injecte de l’énergie dans l’écoulement. Une analyse de la dynamique rotationnelle ayant lieu à la limite de la zone stable et de la zone de convection démontre que celle-ci est fortement modifiée lors du passage de la base des couches convectives à la base de la fine tachocline s’y formant juste en-dessous. Nous concluons par une discussion au niveau du mécanisme de saturation en amplitude dans la dynamo s’opérant dans la simulation ainsi que de la possibilité d’utiliser les oscillations torsionnelles comme précurseurs aux cycles solaires à venir.

Estrategias de control ciudadano: una aproximación a la intervención megaminera en Cajamarca Tolima. (2007-2013)

El presente estudio de caso busca describir y analizar a la luz de los conceptos de resistencia civil y acción colectiva cómo las movilizaciones sociales en el Tolima han logrado generar cambios en el modo de operar de la transnacional minera Anglogold Ashanti en la mina la Colosa entre el año 2007 y el año 2013. Con este fin, se realizaron una serie de entrevistas y visitas de campo que permitieron un acercamiento al movimiento de los Comités Ambientales y Campesinos del Tolima. Este acercamiento dio como resultado una reconstrucción del panorama de la problemática que enfrentan las comunidades locales cuando las empresas megamineras llegan a sus territorios transformando, en diferentes aspectos, la dinámica del lugar. Dicho panorama se constituye en un insumo que puede ser utilizado por las comunidades para empoderarse frente al derecho de decidir sobre el uso que le quieren dar a su territorio.

Diplomacia transfronteriza en tiempos de revolución: el Alto Río Negro iberoamericano, 1815-1820 (Estudios)

This article studies the impacts of the independence war in the regional border of the High Negro River, taking as it’s object of analysis the existing multiples connections between the inhabitants of both sides of the imaginary boundary line. From July 1817, the independence war in Venezuela changed the coordinates: the struggles between the republican patriots and those obedient to the King (Realistas), faithful to the restoration of the Spanish monarchy of Fernando VII, managed the great border region, and influenced the political, social and local dynamics, mainly the existing cross-border relations between both, impacted the ordinary life of the local population and affected the diplomacy between the Portuguese and Spanish American authorities, those faithful to the King (Realistas) and patriots.

Decomposition in tropical forests: a pan-tropical study of the effects of litter type, litter placement and mesofaunal exclusion across a precipitation gradient

1. Litter decomposition recycles nutrients and causes large fluxes of carbon dioxide into the atmosphere. It is typically assumed that climate, litter quality and decomposer communities determine litter decay rates, yet few comparative studies have examined their relative contributions in tropical forests. 2. We used a short-term litterbag experiment to quantify the effects of litter quality, placement and mesofaunal exclusion on decomposition in 23 tropical forests in 14 countries. Annual precipitation varied among sites (760-5797 mm). At each site, two standard substrates (Raphia farinifera and Laurus nobilis) were decomposed in fine- and coarse-mesh litterbags both above and below ground for approximately 1 year. 3. Decomposition was rapid, with >95% mass loss within a year at most sites. Litter quality, placement and mesofaunal exclusion all independently affected decomposition, but the magnitude depended upon site. Both the average decomposition rate at each site and the ratio of above- to below-ground decay increased linearly with annual precipitation, explaining 60-65% of among-site variation. Excluding mesofauna had the largest impact on decomposition, reducing decomposition rates by half on average, but the magnitude of decrease was largely independent of climate. This suggests that the decomposer community might play an important role in explaining patterns of decomposition among sites. Which litter type decomposed fastest varied by site, but was not related to climate. 4. Synthesis. A key goal of ecology is to identify general patterns across ecological communities, as well as relevant site-specific details to understand local dynamics. Our pan-tropical study shows that certain aspects of decomposition, including average decomposition rates and the ratio of above- to below-ground decomposition are highly correlated with a simple climatic index: mean annual precipitation. However, we found no relationship between precipitation and effects of mesofaunal exclusion or litter type, suggesting that site-specific details may also be required to understand how these factors affect decomposition at local scales.