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Die Sachen mitgestalten
(2007)
Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro-acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided ploy(ethylene terephthalate) (PETP) films by means of foaming with CO2 biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoid PETP films foamed with supercritical CO2 at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflamation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF0 atmosphere. The new optimized PETP ferroelectric exhibit quite large piezoelectric coefficients up to almost 500 pCN(-1), for which unusually low elastic stiffness of only around 0.3 MPa are essential. The PETP foam ferroelectrics posses unclamped thickenss-extension resonance frequences between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic-transductant applications.
The paper presents a simulation and parameter-estimation approach for evaluating stochastic patterns of population growth and spread of an annual forest herb, Melampyrum pratense (Orobanchaceae). The survival of a species during large-scale changes in land use and climate will depend, to a considerable extent, on its dispersal and colonisation abilities. Predictions on species migration need a combination of field studies and modelling efforts. Our study on the ability of M. pratense to disperse into so far unoccupied areas was based on experiments in secondary woodland in NE Germany. Experiments started in 1997 at three sites where the species was not yet present, with 300 seeds sown within one square meter. Population development was then recorded until 2001 by mapping of individuals with a resolution of 5 cm. Additional observations considered density dependence of seed production. We designed a spatially explicit individual-based computer simulation model to explain the spatial patterns of population development and to predict future population spread. Besides primary drop of seeds (barochory) it assumed secondary seed transport by ants (myrmecochory) with an exponentially decreasing dispersal tail. An important feature of populationpattern explanation was the simultaneous estimation of both population-growth and dispersal parameters from consistent spatio-temporal data sets. As the simulation model produced stochastic time series and random spatially discrete distributions of individuals we estimated parameters by minimising the expectation of weighted sums of squares. These sums-ofsquares criteria considered population sizes, radial population distributions around the area of origin and distributions of individuals within squares of 25*25 cm, the range of density action. Optimal parameter values, together with the precision of the estimates, were obtained from calculating sums of squares in regular grids of parameter values. Our modelling results showed that transport of fractions of seeds by ants over distances of 1…2 m was indispensable for explaining the observed population spread that led to distances of at most 8 m from population origin within 3 years. Projections of population development over 4 additional years gave a diffusion-like increase of population area without any “outposts”. This prediction generated by the simulation model gave a hypothesis which should be revised by additional field observations. Some structural deviations between observations and model output already indicated that for full understanding of population spread the set of dispersal mechanisms assumed in the model may have to be extended by additional features of plant-animal mutualism.
The paper presents a simulation and parameter-estimation approach for evaluating stochastic patterns of population growth and spread of an annual forest herb, Melampyrum pratense (Orobanchaceae). The survival of a species during large-scale changes in land use and climate will depend, to a considerable extent, on its dispersal and colonisation abilities. Predictions on species migration need a combination of field studies and modelling efforts. Our study on the ability of M. pratense to disperse into so far unoccupied areas is based on experiments in secondary woodland in NE Germany. Experiments started in 1997 at three sites where the species was not yet present, with 300 seeds sown within 1m2. Population development was then recorded until 2001 by mapping of individuals with a resolution of 5 cm. Additional observations considered density dependence of seed production. We designed a spatially explicit individual-based computer simulation model to explain the spatial patterns of population development and to predict future population spread. Besides primary drop of seeds (barochory) it assumed secondary seed transport by ants (myrmecochory) with an exponentially decreasing dispersal tail. An important feature of population-pattern explanation was the simultaneous estimation of both population-growth and dispersal parameters from consistent spatio-temporal data sets. As the simulation model produced stochastic time series and random spatially discrete distributions of individuals we estimated parameters by minimising the expectation of weighted sum of squares. These sums of squares criteria considered population sizes, radial population distributions around the area of origin and distributions of individuals within squares of 25cm×25 cm, the range of density action. Optimal parameter values, together with the precision of the estimates, were obtained from calculating sum of squares in regular grids of parameter values. Our modelling results showed that transport of fractions of seeds by ants over distances of 1-2m was indispensable for explaining the observed population spread that led to distances of at most 8mfrom population origin within 3 years. Projections of population development over four additional years gave a diffusion-like increase of population area without any "outposts". This prediction generated by the simulation model gave a hypothesis which should be revised by additional field observations. Some structural deviations between observations and model output already indicated that for full understanding of population spread the set of dispersal mechanisms assumed in the model may have to be extended by additional features of plant-animal mutualism.
Die Magisterarbeit (im Studiengang Soziologie an der Universität Potsdam) knüpft an Beate Krais’ Gedankengang an, wonach durch die unreflektierte Präsenz des Parsonschen Rollenkonzepts innerhalb der (soziologischen) Theorie, theoretische Gegensätze von Individuum und Gesellschaft, Natur und Kultur, Körper und Geist, Irrationalismus und Rationalismus etc. konzeptionell reformuliert werden. Auf dieser strukturellen Grundlage, so Krais’ kritische Stoßrichtung, legitimiere auch die Frauen- und Geschlechterforschung nur wieder überkommene Stereotypen über Geschlechterrollen (Gender) innerhalb moderner, ausdifferenzierter Gesellschaften. Grundlegender jedoch werde so die Vorstellung eines natürlich gegebenen Unterschieds zwischen ‚zwei’ Geschlechtern (Sex) begründet. Feministische Theorie, so Regine Gildemeisters und Angelika Wetterers sozialkonstruktivistisch fundierte Betrachtung, konterkariere auf diesem Wege gerade ihren eigenen Anspruch, das Ideologem: „Biologie als Schicksal“ als solches zu entlarven. In theoretisch-methodischer Konsequenz vollziehe man vielmehr eine problematische Positivierung des Geschlechterdualismus. In Überwindung dieser Problematik sind zwei Richtungen theoretischer Entwicklung erkennbar. Einerseits wird im Anschluss an neuere modernistische bzw. poststrukturalistische Argumentationen die Möglichkeit einer kritisch orientierten Sozial- bzw. Geschlechterforschung grundsätzlich bezweifelt. Andererseits wird an dieser Stelle aber auch der paradigmatische Übergang von der Frauen- und Geschlechterforschung zur Geschlechterverhältnisforschung expliziert, welcher die für das feministische Projekt grundlegende Verbindung wissenschaftlicher und kritischer Ambitionen neu reflektiert und im Anspruch auf eine integrative, gendersensible Sozialwissenschaft forschungsstrategisch neu ausrichtet. Mit der Betrachtung der Soziologie Pierre Bourdieus tritt der Diskussion eine theoretische Position hinzu, die in eigener Weise Schwachstellen und Einseitigkeiten postmoderner und postfeministischer Ansätze herausstellt. Auf der Grundlage einer praxeologischen Theorie zeigen sich aber auch besondere Affinitäten zum feministischen Diskurs. Über eine Theorie der symbolischen Gewalt verdeutlicht Bourdieu, wie die Kategorie ‚Geschlecht’ in der sozialen Praxis der Akteure immer wieder konstruiert wird (doing gender). Gleichwohl verweist er, über bisherige Erkenntnisse hinausgehend, auf die soziale Mächtigkeit dieser Kategorie innerhalb der Dialektik sozialer und symbolischer Strukturen. Gegen die Kritik, die im deutschsprachigen Raum von Seiten der Frauen- und Geschlechterforschung an Bourdieus Buch: „Die männliche Herrschaft“ (1997) geübt wurde, versucht die Arbeit einer vorschnellen Lesweise und Aburteilung des Bourdieuschen Werks durch eine evaluative Betrachtung seiner soziologischen Konzepte im Hinblick auf die Herausforderungen feministischer Theorie und Kritik entgegenzuwirken.