51,431 research outputs found
Nonequilibrium Phase Transitions in Directed Small-World Networks
Many social, biological, and economic systems can be approached by complex
networks of interacting units. The behaviour of several models on small-world
networks has recently been studied. These models are expected to capture the
essential features of the complex processes taking place on real networks like
disease spreading, formation of public opinion, distribution of wealth, etc. In
many of these systems relations are directed, in the sense that links only act
in one direction (outwards or inwards). We investigate the effect of directed
links on the behaviour of a simple spin-like model evolving on a small-world
network. We show that directed networks may lead to a highly nontrivial phase
diagram including first and second-order phase transitions out of equilibrium.Comment: 4 pages, RevTeX format, 4 postscript figs, uses eps
Nanowires: A route to efficient thermoelectric devices
Miniaturization of electronic devices aims at manufacturing ever smaller
products, from mesoscopic to nanoscopic sizes. This trend is challenging
because the increased levels of dissipated power demands a better understanding
of heat transport in small volumes. A significant amount of the consumed energy
is transformed into heat and dissipated to the environment. Thermoelectric
materials offer the possibility to harness dissipated energy and make devices
less energy-demanding. Heat-to-electricity conversion requires materials with a
strongly suppressed thermal conductivity but still high electronic conduction.
Nanowires can meet nicely these two requirements because enhanced phonon
scattering at the surface and defects reduces the lattice thermal conductivity
while electric conductivity is not deteriorated, leading to an overall
remarkable thermoelectric efficiency. Therefore, nanowires are regarded as a
promising route to achieving valuable thermoelectric materials at the
nanoscale. In this paper, we present an overview of key experimental and
theoretical results concerning the thermoelectric properties of nanowires. The
focus of this review is put on the physical mechanisms by which the efficiency
of nanowires can be improved. Phonon scattering at surfaces and interfaces,
enhancement of the power factor by quantum effects and topological protection
of electron states to prevent the degradation of electrical conductivity in
nanowires are thoroughly discussed
The INTEGRAL-OMC Scientific Archive
The Optical Monitoring Camera (OMC) on-board the INTEGRAL satellite has, as
one of its scientific goals, the observation of a large number of variable
sources previously selected. After almost 6 years of operations, OMC has
monitored more than 100 000 sources of scientific interest. In this
contribution we present the OMC Scientific Archive
(http://sdc.laeff.inta.es/omc/) which has been developed to provide the
astronomical community with a quick access to the light curves generated by
this instrument.We describe the main characteristics of this archive, as well
as important aspects for the users: object types, temporal sampling of light
curves and photometric accuracy.Comment: 4 pages, 5 figures. "Highlights of Spanish Astrophysics V"
Proceedings of the VIII Scientific Meeting of the Spanish Astronomical
Society (SEA) held in Santander, July 7-11, 200
Coherent Pion Production by Neutrinos
In this talk I review the main features of the coherent/diffractive pion
production by neutrinos on nuclei. The method is based on PCAC and relates the
reaction to elastic pion-nucleus scattering. Estimates for the
expected rates and distributions in neutrino reactions are presented with the
help of hadronic data. The absolute rates are significantly smaller than the
older estimates which brings theory in agreement with the neutral current
measurements and the bounds in charged current reactions.Comment: 5 pages, 7 figures, Proceedings of the Sixth International Workshop
on Neutrino-Nucleus Interactions in the Few-GeV Region (NuInt09), May 18-22,
Sitges, Barcelona, Spai
Reliable First-Principles Alloy Thermodynamics via Truncated Cluster Expansions
In alloys cluster expansions (CE) are increasingly used to combine
first-principles electronic-structure and Monte Carlo methods to predict
thermodynamic properties. As a basis-set expansion in terms of lattice
geometrical clusters and effective cluster interactions, the CE is exact if
infinite, but is tractable only if truncated. Yet until now a truncation
procedure was not well-defined and did not guarantee a reliable truncated CE.
We present an optimal truncation procedure for CE basis sets that provides
reliable thermodynamics. We then exemplify its importance in NiV, where the
CE has failed unpredictably, and now show agreement to a range of measured
values, predict new low-energy structures, and explain the cause of previous
failures.Comment: 4 pages, 2 figure
Symmetries and exact solutions of the BPS Skyrme model
The BPS Skyrme model is a specific subclass of Skyrme-type field theories
which possesses both a BPS bound and infinitely many soliton solutions
(skyrmions) saturating that bound, a property that makes the model a very
convenient first approximation to the study of some properties of nuclei and
hadrons. A related property, the existence of a large group of symmetry
transformations, allows for solutions of rather general shapes, among which
some of them will be relevant to the description of physical nuclei.
We study here the classical symmetries of the BPS Skyrme model, applying them
to construct soliton solutions with some prescribed shapes, what constitutes a
further important step for the reliable application of the model to strong
interaction physics.Comment: Latex, 17 page
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