Oxygen isotope effect on the in-plane penetration depth in underdoped La_{2-x}Sr_{x}CuO_{4} single crystals

We report measurements of the oxygen isotope effect (OIE) on the in-plane penetration depth \lambda_{ab}(0) in underdoped La_{2-x}Sr_{x}CuO_{4} single crystals. A highly sensitive magnetic torque sensor with a resolution of \Delta \tau ~ 10^{-12} Nm was used for the magnetic measurements on microcrystals with a mass of ~ 10 microg. The OIE on \lambda_{ab}^{-2}(0) is found to be -10(2)% for x = 0.080 and -8(1)% for x = 0.086. It arises mainly from the oxygen mass dependence of the in-plane effective mass m_{ab}*. The present results suggest that lattice vibrations are important for the occurrence of high temperature superconductivity.Comment: 4 pages, 3 figures, submitted to PR

Die Moderation von Klassengesprächen im Schnittbereich von Naturwissenschaft und Gesellschaft

Das Atelier verfolgte das Ziel, den Teilnehmenden einen Einblick in Inhalt und Methoden des laufenden NF-Projekts „ReflecT“ (2004 – 2007) zu vermitteln. Es wurde die Frage erörtert, unter welchen Bedingungen Klassengespräche zu Themen, die im Schnittbereich von Naturwissenschaften und Gesellschaft liegen, am ehesten gelingen könnten. Anhand eines 10-minütigen Unterrichtsvideos sowie Zwischenergebnissen aus der Forschung wurden verschiedene Perspektiven vorgestellt und diskutiert. Der Fokus lag insbesondere auf der Moderation von Klassengesprächen

Studies on a socio-ecological approach to environmental education – a contribution to a critical position in the education for sustainable development discourse

This paper outlines a critical position in relation to education for sustainable development referring to a socio-ecological approach to environmental education. This approach was developed in a cooperative research process with pre-academic secondary schools over several years in Switzerland. For 13 years our research group has been the one in Switzer-land to systematically research on curriculum and professional development in environ-mental education in secondary schools. The group was established at the Swiss Federal Institute of Technology in Zurich (ETHZ) supported by funding of the Swiss National Foundation for Scientific Research, and from 1998 proceeded with research projects at the Institute for Teacher Education (upper secondary level) at the University of Zurich. Case studies were carried out to explore the potentials and constraints which teachers and students meet when working with environmental issues. Two case studies from different research phases are shown which illustrate how both teachers and learners are challenged to cope with increasingly unstructured and unknown situations, pluralistic and controversial perspectives, and with the critical role of science in society. Outcomes are discussed in the light of the social process of sustainable development

Self-organized Vortex State in Two-dimensional Dictyostelium Dynamics

We present results of experiments on the dynamics of Dictyostelium discoideum in a novel set-up which constraints cell motion to a plane. After aggregation, the amoebae collect into round ''pancake" structures in which the cells rotate around the center of the pancake. This vortex state persists for many hours and we have explicitly verified that the motion is not due to rotating waves of cAMP. To provide an alternative mechanism for the self-organization of the Dictyostelium cells, we have developed a new model of the dynamics of self-propelled deformable objects. In this model, we show that cohesive energy between the cells, together with a coupling between the self-generated propulsive force and the cell's configuration produces a self-organized vortex state. The angular velocity profiles of the experiment and of the model are qualitatively similar. The mechanism for self-organization reported here can possibly explain similar vortex states in other biological systems.Comment: submitted to PRL; revised version dated 3/8/9

Modelling the evolution of the Sun's open and total magnetic flux

Solar activity in all its varied manifestations is driven by the magnetic field. Particularly important for many purposes are two global quantities, the Sun's total and open magnetic flux, which can be computed from sunspot number records using models. Such sunspot-driven models, however, do not take into account the presence of magnetic flux during grand minima, such as the Maunder minimum. Here we present a major update of a widely used simple model, which now takes into account the observation that the distribution of all magnetic features on the Sun follows a single power law. The exponent of the power law changes over the solar cycle. This allows for the emergence of small-scale magnetic flux even when no sunspots are present for multiple decades and leads to non-zero total and open magnetic flux also in the deepest grand minima, such as the Maunder minimum, thus overcoming a major shortcoming of the earlier models. The results of the updated model compare well with the available observations and reconstructions of the solar total and open magnetic flux. This opens up the possibility of improved reconstructions of sunspot number from time series of cosmogenic isotope production rate

Developing critical thinking in environmental education: a video study of classroom discussions on socio-ecological issues in secondary schools

An important task of science education is to develop the ability to judge the meaning and significance of scientific progress and future perspectives. It is widely agreed that students should be enabled to deal with scientific innovations and to utilize them in a critical and responsible way. This process demands integrating scientific knowledge, knowledge about social processes and awareness of personal and social values. Increasing judgement skills by applying critical thinking is thus a relevant element of science education today

Performance Characteristics of a Cluster of 5-kW Laboratory Hall Thrusters

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76117/1/AIAA-19752-159.pd

Isotope effects in underdoped cuprate superconductors: a quantum phenomenon

We show that the unusual doping dependence of the isotope effects on transition temperature and zero temperature in - plane penetration depth naturally follows from the doping driven 3D-2D crossover, the 2D quantum superconductor to insulator transition (QSI) in the underdoped limit and the change of the relative doping concentration upon isotope substitution. Close to the QSI transition both, the isotope coefficient of transition temperature and penetration depth approach the coefficient of the relative dopant concentration, and its divergence sets the scale. These predictions are fully consistent with the experimental data and imply that close to the underdoped limit the unusual isotope effect on transition temperature and penetration depth uncovers critical phenomena associated with the quantum superconductor to insulator transition in two dimensions.Comment: 6 pages, 3 figure

Developing a multiple-document-processing performance assessment for epistemic literacy

The LAK15 theme “shifts the focus from data to impact”, noting the potential for Learning Analytics based on existing technologies to have scalable impact on learning for people of all ages. For such demand and potential in scalability to be met the challenges of addressing higher-order thinking skills should be addressed. This paper discuses one such approach – the creation of an analytic and task model to probe epistemic cognition in complex literacy tasks. The research uses existing technologies in novel ways to build a conceptually grounded model of trace-indicators for epistemic-commitments in information seeking behaviors. We argue that such an evidence centered approach is fundamental to realizing the potential of analytics, which should maintain a strong association with learning theory

Remarks on Causality in Relativistic Quantum Field Theory

It is shown that the correlations predicted by relativistic quantum field theory in locally normal states between projections in local von Neumann algebras \cA(V_1),\cA(V_2) associated with spacelike separated spacetime regions $V_1,V_2$ have a (Reichenbachian) common cause located in the union of the backward light cones of $V_1$ and $V_2$. Further comments on causality and independence in quantum field theory are made.Comment: 10 pages, Latex, Quantum Structures 2002 Conference Proceedings submission. Minor revision of the order of definitions on p.