13,775 research outputs found
c-axis transport and phenomenology of the pseudo-gap state in
We measure and analyze the resistivity of
crystals for different doping . We obtain the fraction of carrier
that do not participate to the c-axis
conductivity. All the curves collapse onto a universal curve
when plotted against a reduced temperature
. We find that at the superconducting
transition is doping independent. We also show that a magnetic field up
to 14 T does not affect the degree of localization in the (a,b) planes but
widens the temperature range of the x-scaling by suppressing the
superconducting phase coherence.Comment: 11 pages, 5 figures, submitted to Phys.Rev.
Bifurcation structures and transient chaos in a four-dimensional Chua model
A four-dimensional four-parameter Chua model with cubic nonlinearity is
studied applying numerical continuation and numerical solutions methods.
Regarding numerical solution methods, its dynamics is characterized on Lyapunov
and isoperiodic diagrams and regarding numerical continuation method, the
bifurcation curves are obtained. Combining both methods the bifurcation
structures of the model were obtained with the possibility to describe the {\it
shrimp}-shaped domains and their endoskeletons. We study the effect of a
parameter that controls the dimension of the system leading the model to
present transient chaos with its corresponding basin of attraction being
riddled.Comment: 9 figures, to appear in PL
Currents and Superpotentials in classical gauge theories: II. Global aspects and the example of Affine gravity
The conserved charges associated to gauge symmetries are defined at a
boundary component of space-time because the corresponding Noether current can
be rewritten on-shell as the divergence of a superpotential. However, the
latter is afflicted by ambiguities. Regge and Teitelboim found a procedure to
lift the arbitrariness in the Hamiltonian framework. An alternative covariant
formula was proposed by one of us for an arbitrary variation of the
superpotential, it depends only on the equations of motion and on the gauge
symmetry under consideration. Here we emphasize that in order to compute the
charges, it is enough to stay at a boundary of spacetime, without requiring any
hypothesis about the bulk or about other boundary components, so one may speak
of holographic charges. It is well known that the asymptotic symmetries that
lead to conserved charges are really defined at infinity, but the choice of
boundary conditions and surface terms in the action and in the charges is
usually determined through integration by parts whereas each component of the
boundary should be considered separately. We treat the example of gravity (for
any space-time dimension, with or without cosmological constant), formulated as
an Affine theory which is a natural generalization of the Palatini and
Cartan-Weyl (vielbein) first order formulations. We then show that the
superpotential associated to a Dirichlet boundary condition on the metric (the
one needed to treat asymptotically flat or AdS spacetimes) is the one proposed
by Katz, Bi\u{c}{\'a}k and Lynden-Bell and not that of Komar. We finally
discuss the KBL superpotential at null infinity.Comment: 16 pages, minor corrections and references added. Final version to
appear in CQ
Estimating Self-Sustainability in Peer-to-Peer Swarming Systems
Peer-to-peer swarming is one of the \emph{de facto} solutions for distributed
content dissemination in today's Internet. By leveraging resources provided by
clients, swarming systems reduce the load on and costs to publishers. However,
there is a limit to how much cost savings can be gained from swarming; for
example, for unpopular content peers will always depend on the publisher in
order to complete their downloads. In this paper, we investigate this
dependence. For this purpose, we propose a new metric, namely \emph{swarm
self-sustainability}. A swarm is referred to as self-sustaining if all its
blocks are collectively held by peers; the self-sustainability of a swarm is
the fraction of time in which the swarm is self-sustaining. We pose the
following question: how does the self-sustainability of a swarm vary as a
function of content popularity, the service capacity of the users, and the size
of the file? We present a model to answer the posed question. We then propose
efficient solution methods to compute self-sustainability. The accuracy of our
estimates is validated against simulation. Finally, we also provide closed-form
expressions for the fraction of time that a given number of blocks is
collectively held by peers.Comment: 27 pages, 5 figure
Validation of Phonon Physics in the CDMS Detector Monte Carlo
The SuperCDMS collaboration is a dark matter search effort aimed at detecting
the scattering of WIMP dark matter from nuclei in cryogenic germanium targets.
The CDMS Detector Monte Carlo (CDMS-DMC) is a simulation tool aimed at
achieving a deeper understanding of the performance of the SuperCDMS detectors
and aiding the dark matter search analysis. We present results from validation
of the phonon physics described in the CDMS-DMC and outline work towards
utilizing it in future WIMP search analyses.Comment: 6 Pages, 5 Figures, Proceedings of Low Temperature Detectors 14
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