Student teachers’ perception of dilemmatic demands and the relation to epistemological beliefs

Teaching is characterized by contradictory demands, resulting in teaching dilemmas. For example, to promote the continuous learning of students, teachers need to set up rules and control them, which in turn can undermine students’ intrinsic motivation. Teachers have to become aware of these contradictions and need to understand that not all aspects of good teaching can be maximized at the same time. An adequate representation of the dilemmatic nature of problems of teaching is therefore crucial for judging different teaching situations. Also, an adequate epistemological understanding is needed. We assessed student teachers’ (N = 122) perceptions of demands in teaching in general and in regards to specific situations, as well as their epistemological beliefs. Perception of demands in general influenced the judgment of specific situations, but there was also a situation-specific component. Epistemological beliefs were related to the perceptions of demands in general, especially in situations in which the dilemmatic content was highly visible. Together, findings suggest that epistemological beliefs shape the perception of demands in teaching in general, and that the perception of demand in general again influences perception in specific situations

Modern middleware for the data acquisition of the Cherenkov Telescope Array

The data acquisition system (DAQ) of the future Cherenkov Telescope Array (CTA) must be ef- ficient, modular and robust to be able to cope with the very large data rate of up to 550 Gbps coming from many telescopes with different characteristics. The use of modern middleware, namely ZeroMQ and Protocol Buffers, can help to achieve these goals while keeping the development effort to a reasonable level. Protocol Buffers are used as an on-line data for- mat, while ZeroMQ is employed to communicate between processes. The DAQ will be controlled and monitored by the Alma Common Software (ACS). Protocol Buffers from Google are a way to define high-level data structures through an in- terface description language (IDL) and a meta-compiler. ZeroMQ is a middleware that augments the capabilities of TCP/IP sockets. It does not implement very high-level features like those found in CORBA for example, but makes use of sockets easier, more robust and almost as effective as raw TCP. The use of these two middlewares enabled us to rapidly develop a robust prototype of the DAQ including data persistence to compressed FITS files.Comment: In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions at arXiv:1508.0589

Potassium self-diffusion in a K-rich single-crystal alkali feldspar

The paper reports potassium diffusion measurements performed on gem-quality single-crystal alkali feldspar in the temperature range from $1169$ to 1021 \, \mbox{K}. Natural sanidine from Volkesfeld, Germany was implanted with \mbox{}^{43}\mbox{K} at the ISOLDE/CERN radioactive ion-beam facility normal to the (001) crystallographic plane. Diffusion coefficients are well described by the Arrhenius equation with an activation energy of 2.4 \, \mbox{eV} and a pre-exponential factor of 5\times10^{-6} \, \mbox{m}^{2}/\mbox{s}, which is more than three orders of magnitude lower than the \mbox{}^{22}\mbox{Na} diffusivity in the same feldspar and the same crystallographic direction. State-of-the-art considerations including ionic conductivity data on the same crystal and Monte Carlo simulations of diffusion in random binary alloy structures point to a correlated motion of K and Na through the interstitialcy mechanism

From eating to discovering: How metaphors of learning change during students' enculturation

During their enculturation process students need to adapt their conceptions of learning to the learning culture at the university. However, conceptions are usually implict and thus difficult to assess. Metaphors have been proposed as a possibility to examine conceptions. Therefore, in a longitudinal study (N=30), changes to metaphors of learning were examined over the course of the first year of studies. In general, we found that metaphors were more congruent with university learning culture in the 2nd year of studies than in the 1st year, indicating that students undergo a complex enculturation process changing their conceptions of learning. 16.12.2015 | Elisabeth Wegner & Matthias Nückles (Freiburg

Kompetenzerwerb oder Enkulturation? Lehrende und ihre Metaphern des Lernens

Das Ziel eines Studiums kann sowohl im Erwerb von Wissen und Fähigkeiten ("Aneignungsmetapher des Lernens") als auch in der Enkulturation in eine Fachcommunity verstanden werden ("Partizipationsmetapher", vgl. SFARD, 1998). Der Kompetenzbegriff beinhaltet beide Aspekte des Lernens. In der Studie wurde daher in strukturierten Interviews (N=36) untersucht, in welchen Metaphern Lehrende über Lehren und Lernen denken und welche Ziele sie in ihrer Lehre verfolgen. Die Ergebnisse zeigen, dass ein beträchtlicher Anteil von Lehrenden Lernen im Sinne der Enkulturation ins Fach verstehen. Dies deutet darauf hin, dass die alleinige Auslegung des Kompetenzbegriffs im Sinne des Erwerbs von Fähigkeiten bei vielen Lehrenden nicht anschlussfähig ist und in der Umsetzung von kompetenzorientierter Lehre auch die Perspektive der Enkulturation berücksichtigt werden muss. 23.01.2013 | Elisabeth Wegner & Matthias Nückles (Freiburg

Towards negative cycle canceling in wind farm cable layout optimization

Abstract In the Wind Farm Cabling Problem (WCP) the task is to design the internal cabling of a wind farm such that all power from the turbines can be transmitted to the substations and the costs for the cabling are minimized. Cables can be chosen from several available cable types, each of which has a thermal capacity and cost. Until now, solution approaches mainly use Mixed-integer Linear Programs (MILP) or metaheuristics. We present our current state of research on a fast heuristic specifically designed for WCP. We introduce an algorithm that iteratively improves a cable layout by finding and canceling negative cycles in a suitably defined network. Our simulations on publicly available benchmark sets show that the heuristic is not only fast but it tends to produce good results. Currently our algorithm gives better solutions on large wind farms compared to an MILP solver. However, on small to medium instances the solver performs better in terms of solution quality, which represents a starting point for future work

Engineering Negative Cycle Canceling for Wind Farm Cabling

In a wind farm turbines convert wind energy into electrical energy. The generation of each turbine is transmitted, possibly via other turbines, to a substation that is connected to the power grid. On every possible interconnection there can be at most one of various different cable types. Each cable type comes with a cost per unit length and with a capacity. Designing a cost-minimal cable layout for a wind farm to feed all turbine production into the power grid is called the Wind Farm Cabling Problem (WCP). We consider a formulation of WCP as a flow problem on a graph where the cost of a flow on an edge is modeled by a step function originating from the cable types. Recently, we presented a proof-of-concept for a negative cycle canceling-based algorithm for WCP [Sascha Gritzbach et al., 2018]. We extend key steps of that heuristic and build a theoretical foundation that explains how this heuristic tackles the problems arising from the special structure of WCP. A thorough experimental evaluation identifies the best setup of the algorithm and compares it to existing methods from the literature such as Mixed-integer Linear Programming (MILP) and Simulated Annealing (SA). The heuristic runs in a range of half a millisecond to under two minutes on instances with up to 500 turbines. It provides solutions of similar quality compared to both competitors with running times of one hour and one day. When comparing the solution quality after a running time of two seconds, our algorithm outperforms the MILP- and SA-approaches, which allows it to be applied in interactive wind farm planning

Arctic in Rapid Transition (ART) : science plan

The Arctic is undergoing rapid transformations that have brought the Arctic Ocean to the top of international political agendas. Predicting future conditions of the Arctic Ocean system requires scientific knowledge of its present status as well as a process-based understanding of the mechanisms of change. The Arctic in Rapid Transition (ART) initiative is an integrative, international, interdisciplinary pan-Arctic program to study changes and feedbacks among the physical and biogeochemical components of the Arctic Ocean and their ultimate impacts on biological productivity. The goal of ART is to develop priorities for Arctic marine science over the next decade. Three overarching questions form the basis of the ART science plan: (1) How were past transitions in sea ice connected to energy flows, elemental cycling, biological diversity and productivity, and how do these compare to present and projected shifts? (2) How will biogeochemical cycling respond to transitions in terrestrial, gateway and shelf-to-basin fluxes? (3) How do Arctic Ocean organisms and ecosystems respond to environmental transitions including temperature, stratification, ice conditions, and pH? The integrated approach developed to answer the ART key scientific questions comprises: (a) process studies and observations to reveal mechanisms, (b) the establishment of links to existing monitoring programs, (c) the evaluation of geological records to extend time-series, and (d) the improvement of our modeling capabilities of climate-induced transitions. In order to develop an implementation plan for the ART initiative, an international and interdisciplinary workshop is currently planned to take place in Winnipeg, Canada in October 2010

Die Wirkung hochschuldidaktischer Weiterbildung auf den Umgang mit widersprüchlichen Handlungsanforderungen

Die Tätigkeit des Lehrens ist mit in sich widersprüchliche Anforderungen verbunden (z. B. Förderung von selbstgesteuertem Lernen vs. Unterstützung von Lernenden). Lehrende müssen sich der Antinomien didaktischen Handelns bewusst sein, um adäquat mit ihnen umzugehen zu können. 36 Lehrende (16 ohne vs. 20 mit hochschuldidaktischer Weiterbildung) wurden im strukturierten Interview mit dilemmatischen Entscheidungsszenarios konfrontiert. Es wurden fünf Typen im Umgang mit Widersprüchen identifiziert, wobei Weiterbildungsteilnehmer/innen in zwei von vier Szenarios komplexeren Auffassungen zugeordnet werden konnten. Lehrerfahrung hingegen hatte keinen Effekt. Weiterbildung trägt also offenbar zu einem verbesserten Verständnis von Lehren bei. 02.11.2011 | Elisabeth Wegner & Matthias Nückles (Freiburg

Power management in a hydro-thermal system under uncertainty by Lagrangian relaxation

We present a dynamic multistage stochastic programming model for the cost-optimal generation of electric power in a hydro-thermal system under uncertainty in load, inflow to reservoirs and prices for fuel and delivery contracts. The stochastic load process is approximated by a scenario tree obtained by adapting a SARIMA model to historical data, using empirical means and variances of simulated scenarios to construct an initial tree, and reducing it by a scenario deletion procedure based on a suitable probability distance. Our model involves many mixed-integer variables and individual power unit constraints, but relatively few coupling constraints. Hence we employ stochastic Lagrangian relaxation that assigns stochastic multipliers to the coupling constraints. Solving the Lagarangian dual by a proximal bundle method leads to successive decomposition into single thermal and hydro unit subproblems that are solved by dynamic programming and a specialized descent algorithm, respectively. The optimal stochastic multipliers are used in Lagrangian heuristics to construct approximately optimal first stage decisions. Numerical results are presented for realistic data from a German power utility, with a time horizon of one week and scenario numbers ranging from 5 to 100. The corresponding optimization problems have up to 200,000 binary and 350,000 continuous variables, and more than 500,000 constraints