Synthesis and properties of a new AB-cross-linked copolymer membrane system

The alcohol permeability and permselectivity properties as well as the morphology of membranes made of a newly developed AB-cross-linked copolymer system composed of elastomeric and glassy components were investigated. The copolymer was synthesized by a hydrosilylation reaction between poly(styrene-stat-isoprenes) (Mn from 40,000 to 100,000 g/mol) with high content in unsaturated side groups (≈ 60% of entire isoprene content) and polyhydrogen polysiloxanes with varying SiH content (0.75 10.7 mol %) and molecular mass, Mn, from 2,500 to 36,000 g/mol. A two-track approach was taken to determine the morphology of the copolymer system. The first employed the usual polymer characterization methods such as electron microscopy, DSC, IR spectroscopy, the density gradient method, and mechanical measurements. For the second approach, different copolymer permeability models were tested so as to give an insight into the copolymer morphology. As a final step, the permeability and permselectivity properties were correlated with the morphological structure of the copolymer system. It was observed that the respective continuous microphase dominated the copolymer's physical properties, as, e.g., permeability, permselectivity, and mechanical properties. The microphase inversion in the copolymer system was proved by the permeability/permselectivity as well as by the mechanical measurements

Perfect 3-Dimensional Lattice Actions for 4-Dimensional Quantum Field Theories at Finite Temperature

We propose a two-step procedure to study the order of phase transitions at finite temperature in electroweak theory and in simplified models thereof. In a first step a coarse grained free energy is computed by perturbative methods. It is obtained in the form of a 3-dimensional perfect lattice action by a block spin transformation. It has finite temperature dependent coefficients. In this way the UV-problem and the infrared problem is separated in a clean way. In the second step the effective 3-dimensional lattice theory is treated in a nonperturbative way, either by the Feynman-Bogoliubov method (solution of a gap equation), by real space renormalization group methods, or by computer simulations. In this paper we outline the principles for $\varphi ^4$-theory and scalar electrodynamics. The Ba{\l}aban-Jaffe block spin transformation for the gauge field is used. It is known how to extend this transformation to the nonabelian case, but this will not be discussed here.Comment: path to figures (in added uu-file) revised, no other changes 33 pages, 3 figures, late

Blockspin transformation for finite temperature field theories with gauge fields

A procedure is proposed to study QFT at zero or at finite temperature by a sequence of real space renormalization group (RG) or blockspin transformations. They transform to effective theories on coarser and coarser lattices.The ultimate aim is to compute constraint effective potentials, i.e. the free energy as a function of suitable order parameters.From the free energy one can read off the thermodynamic behaviour of the theory, in particular the existence and nature of phase transitions. In a finite temperature QFT one begins with either one or a sequence of transformations which transform the original theory into an effective theory on a three-dimensional lattice. Its effective action has temperature dependent coefficients. Thereafter one may proceed with further blockspin transformations of the three-dimensional theory. Assuming a finite volume, this can in principle be continued until one ends with a lattice with a single site. Its effective action is the constraint effective potential. In each RG-step, an integral over the high frequency part of the field has to be performed. This is done perturbatively and requires the knowledge of bare fluctuation field propagators and of interpolation operators which enter into the vertices. A detailed examination of these quantities is presented for scalar fields, abelian gauge fields and for Higgs fields, finite temperature is admitted.Comment: 88 pages, latex, 17 figures appende

Medien in der Erziehungswissenschaft: Status und Probleme

In allen Bildungskontexten sind in den letzten Jahren viele Medienprojekte initiiert worden, in denen die Möglichkeiten digitaler Medien für die Bildung untersucht werden und mit denen zum Teil weitreichende Hoffnungen auf die Erneuerung des Bildungswesens verknüpft sind. Zunehmend wird dabei deutlich, dass die neuen Medien keineswegs zuverlässig oder gar automatisch zu bestimmten Veränderungen im Bildungssektor führen und dass die Einführung neuer Medien nicht zu revolutionären Umwälzungen der Bildungsarbeit beitragen wird. Im Gegenteil – die Bildungspraxis - in allen Sektoren - hat «Lehrgeld» zahlen müssen: Viele Vorhaben haben ihre Erwartungen nicht vollständig erfüllen können, durchaus interessante und zukunftsweisende Vorzeigeprojekte stehen vor der Aufgabe der nachhaltigen Sicherung ihrer Entwicklungen

Open Educational Resources and Informational Ecosystems: «Edutags» as a connector for open learning

Teaching and learning in school essentially relies on analogous and digital media, artefacts and tools of all kinds. They are supported and provided by various players. The role of these players for providing learning infrastructures and the interaction between them are discussed in the following paper. Increasingly, Open Educational Resources (OER) become available and the question arises how the interaction between these players is impacted. On the one hand, some players implement closed informational ecosystems that might provide a rich and coherent environment for learning, but also lock the users into a defined and often restricted environment. On the other hand, other players are interested in developing an infrastructure that supports open learning without the boundaries of closed informational ecosystems. Such open informational ecosystems must provide interconnections to numerous, in principal, unlimited number of platforms for learning contents. In the context of the project «Edutags» a reference platform is being implemented by way in which the contents of various providers are being connected and enriched through user-generated tags, commentaries and evaluations. The discussion points out that such an independent reference platform, operated separately from content platforms, must be considered as an important element in an open and truly distributed infrastructure for learning resources. Hence, we do not only need open educational resources to support open learning, we also need to establish an open informational ecosystem that supports such approaches

Stoichiometry determination of chalcogenide superlattices by means of X-ray diffraction and its limits

In this paper we explore the potential of stoichiometry determination for chalcogenide superlattices, promising candidates for next-generation phase-change memory, via X-ray diffraction. To this end, a set of epitaxial GeTe/Sb2Te3 superlattice samples with varying layer thicknesses is sputter-deposited. Kinematical scattering theory is employed to link the average composition with the diffraction features. The observed lattice constants of the superlattice reference unit cell follow Vegard's law, enabling a straight-forward and non-destructive stoichiometry determination.Comment: physica status solidi (RRL) - Rapid Research Letters (2019

Repositioning Formative Assessment from an Educational Assessment Perspective: A Response to Dunn & Mulvenon (2009)

Within the recognized tensions between statewide testing and the process of teaching and learning, formative assessment’s potential for improving student learning and for shedding light “inside the black box,” has received increased attention from scholars in different countries. In their critical review, Dunn & Mulvenon (2009) pointed out the lack of agreed-upon definitions and limited empirical evidence concerning formative assessment. We contend that from the educational assessment field, there is a clear overlap among definitions of the concept and that the conceptual confusion may be coming from outside the field. We also argue that Dunn & Mulvenon’s claim of limited empirical evidence is basically inaccurate and based on misinterpretations of Black & Wiliam’s (1998) article and of social science research more broadly. Consequently, we start by distinguishing key concepts related to formative assessment. Second, we describe the paradigm of the educational assessment field, and summarize the different definitions they propose. Finally, the article addresses the issue of “limited” empirical evidence concerning formative assessment. Accessed 8,040 times on https://pareonline.net from December 10, 2012 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right

Mediendidkatik in der Lehrerbildung

Der Beitrag diskutiert Ziele und Inhalte der Aus- und Weiterbildung von Lehrpersonen im Bereich der Mediendidaktik. Vorliegende Angebote - vor allem in der Weiterbildung - sind oft entweder technisch oder medienerzieherisch ausgerichtet und als solches zu eng ausgeführt. Neben der Auseinandersetzung mit Möglichkeiten digitaler Medien im Unterricht sollte die didaktische Reflexion über die Bedeutung von Medien in Lehr-Lernprozessen im Mittelpunkt stehen. Dazu sind insbesondere die pädagogischen Ziele des Medieneinsatzes zu benennen, zu deren Analyse und Bewertung Leitfragen vorgestellt werden

Quo vadis Mediendidaktik? Zur theoretischen Fundierung von Mediendidaktik

Die mediendidaktische Forschung ist geprägt durch Einzelprojekte, in denen die Möglichkeiten neuer Lernmedien erprobt werden. Zur theoretischen Begründung und Einordnung der Vorhaben werden in der Regel die lerntheoretischen Ansätze des Behaviorismus, Kognitivismus und Konstruktivismus herangezogen. Im vorliegenden Beitrag sollen einige Probleme einer solchen Fundierung von Mediendidaktik diskutiert werden. Die bisherige Theoriebildung in der Mediendidaktik ist durch die Suche nach dem «einen» besten Ansatz des Lernens und Lehrens geprägt. Perspektivisch wären jedoch lerntheoretische und bildungstheoretische Ansätzen stärker zu verknüpfen. Dabei kann der Pragmatismus sensu Dewey als richtungsweisende Grundlage zur theoretischen Fundierung von Mediendidaktik dienen

Zur (Neu)Positionierung der Mediendidaktik. Handlungs- und Gestaltungsorientierung in der Medienpädagogik

Die Grenzziehung zwischen Mediendidaktik und Medienerziehung ist nicht zuletzt durch Veränderungen der Medien selbst mehr denn je fraglich geworden. Eine andere Betrachtung ergibt sich, wenn man eine handlungsorientierte mit einer gestaltungsorientierten Perspektive der Medienpädagogik verknüpft. Die handlungsorientierte Perspektive möchte das handelnde Individuum zu einem kompetenten Umgang mit Medien befähigen. Die gestaltungsorientierte Perspektive betrachtet in Ergänzung dazu die lern- und entwicklungsförderlichen Potenziale medialer Umwelt. In der Verknüpfung dieser beiden Perspektiven lässt sich die «Kompetenz für Medienhandeln» entwickeln, die auf die Verständigung von Menschen durch Teilhabe an Wissen und Kultur, durch Partizipation an gesellschaftlicher Kommunikation, und auf Entwicklung von Persönlichkeit abzielt