7,696 research outputs found
Non-Arrhenius ionic conductivities in glasses due to a distribution of activation energies
Previously observed non-Arrhenius behavior in fast ion conducting glasses
[\textit{Phys.\ Rev.\ Lett.}\ \textbf{76}, 70 (1996)] occurs at temperatures
near the glass transition temperature, , and is attributed to changes in
the ion mobility due to ion trapping mechanisms that diminish the conductivity
and result in a decreasing conductivity with increasing temperature. It is
intuitive that disorder in glass will also result in a distribution of the
activation energies (DAE) for ion conduction, which should increase the
conductivity with increasing temperature, yet this has not been identified in
the literature. In this paper, a series of high precision ionic conductivity
measurements are reported for
glasses with compositions ranging from . The impact of the
cation site disorder on the activation energy is identified and explained using
a DAE model. The absence of the non-Arrhenius behavior in other glasses is
explained and it is predicted which glasses are expected to accentuate the DAE
effect on the ionic conductivity.Comment: 2 figure
Encountering and Countering Tribal Conflict With Film and Dialogue
Martin explores the ability of group leaders to overcome resistance to reconciliation in group conflicts, whether innate or otherwise. He uses an example of a group conflict that occurred across religious lines with the pending release of a movie titled Theologians Under Hitler. Even if out-group biases make group conflicts harder to resolve, offsetting that complication might be a predisposition to attend to the views of a respected leader of the in-group
Meta-evaluation of the impacts and legacy of the London 2012 Olympic Games and Paralympic Games : Developing methods paper
This report brings together the interim findings from the Developing Meta-Evaluation Methods study, which is being undertaken in conjunction with the Meta-Evaluation of the Impacts and Legacy of the London 2012 Olympic Games and Paralympic Games.
The work on methods is funded by the Economic and Social Research Council (ESRC). The aim of this paper is to review the existing evidence on conducting meta-evaluation, and provide guidance appropriate to the Meta Evaluation of the Games as well as other meta-evaluation studies
Coherence Constraints for Operads, Categories and Algebras
Coherence phenomena appear in two different situations. In the context of
category theory the term `coherence constraints' refers to a set of diagrams
whose commutativity implies the commutativity of a larger class of diagrams. In
the context of algebra coherence constrains are a minimal set of generators for
the second syzygy, that is, a set of equations which generate the full set of
identities among the defining relations of an algebraic theory.
A typical example of the first type is Mac Lane's coherence theorem for
monoidal categories, an example of the second type is the result of Drinfel'd
saying that the pentagon identity for the `associator' of a quasi-Hopf algebra
implies the validity of a set of identities with higher instances of this
associator.
We show that both types of coherence are governed by a homological invariant
of the operad for the underlying algebraic structure. We call this invariant
the (space of) coherence constraints. In many cases these constraints can be
explicitly described, thus giving rise to various coherence results, both
classical and new.Comment: 29 pages, LaTeX209, article 12pt + leqno style. A substantially
revised versio
Revising Z: part I - logic and semantics
This is the first of two related papers. We introduce a simple specification logic ZC comprising a logic and a semantics (in ZF set theory) within which the logic is sound. We then provide an interpretation for (a rational reconstruction of) the specification language Z within ZC. As a result we obtain a sound logic for Z, including a basic schema calculus
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