4,932 research outputs found
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 have a (Reichenbachian) common cause located in the union of
the backward light cones of and . 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.
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