5,965 research outputs found
Statistical Mechanics of finite arrays of coupled bistable elements
We discuss the equilibrium of a single collective variable characterizing a
finite set of coupled, noisy, bistable systems as the noise strength, the size
and the coupling parameter are varied. We identify distinct regions in
parameter space. The results obtained in prior works in the asymptotic infinite
size limit are significantly different from the finite size results. A
procedure to construct approximate 1-dimensional Langevin equation is adopted.
This equation provides a useful tool to understand the collective behavior even
in the presence of an external driving force
Comment on "Soliton ratchets induced by excitation of internal modes"
Very recently Willis et al. [Phys. Rev. E {\bf 69}, 056612 (2004)] have used
a collective variable theory to explain the appearance of a nonzero energy
current in an ac driven, damped sine-Gordon equation. In this comment, we prove
rigorously that the time-averaged energy current in an ac driven nonlinear
Klein-Gordon system is strictly zero.Comment: 3 pages, 1 figure, Submitted to Phys. Rev.
Modelling a two-dimensional spatial distribution of mycotoxin concentration in bulk commodities to design effective and efficient sample selection strategies
Mycotoxins in agricultural commodities are a hazard to human and animal health.
Their heterogeneous spatial distribution in bulk storage or transport makes it
particularly difficult to design effective and efficient sampling plans. There
has been considerable emphasis on identifying the different sources of
uncertainty associated with mycotoxin concentration estimations, but much less
on identifying the effect of the spatial location of the sampling points. This
study used a two-dimensional statistical modelling approach to produce detailed
information on appropriate sampling strategies for surveillance of mycotoxins in
raw food commodities. The emphasis was on deoxynivalenol (DON) and ochratoxin A
(OTA) in large lots of grain in storage or bulk transport. The aim was to
simulate a range of plausible distributions of mycotoxins in grain from a set of
parameters characterising the distributions. For this purpose, a model was
developed to generate data sets which were repeatedly sampled to investigate the
effect that sampling strategy and the number of incremental samples has on
determining the statistical properties of mycotoxin concentration. Results
showed that, for most sample sizes, a regular grid proved to be more consistent
and accurate in the estimation of the mean concentration of DON, which suggests
that regular sampling strategies should be preferred to random sampling, where
possible. For both strategies, the accuracy of the estimation of the mean
concentration increased significantly up to sample sizes of 40-60 (depending on
the simulation). The effect of sample size was small when it exceeded 60 points,
which suggests that the maximum sample size required is of this order. Similar
conclusions about the sample size apply to OTA, although the difference between
regular and random sampling was small and probably negligible for most sample
sizes
Phase-dependent exciton transport and energy harvesting from thermal environments
Non-Markovian effects in the evolution of open quantum systems have recently
attracted widespread interest, particularly in the context of assessing the
efficiency of energy and charge transfer in nanoscale biomolecular networks and
quantum technologies. With the aid of many-body simulation methods, we uncover
and analyse an ultrafast environmental process that causes energy relaxation in
the reduced system to depend explicitly on the phase relation of the initial
state preparation. Remarkably, for particular phases and system parameters, the
net energy flow is uphill, transiently violating the principle of detailed
balance, and implying that energy is spontaneously taken up from the
environment. A theoretical analysis reveals that non-secular contributions,
significant only within the environmental correlation time, underlie this
effect. This suggests that environmental energy harvesting will be observable
across a wide range of coupled quantum systems.Comment: 5 + 4 pages, 3 + 2 figures. Comments welcom
Asterias: a parallelized web-based suite for the analysis of expression and aCGH data
Asterias (\url{http://www.asterias.info}) is an integrated collection of
freely-accessible web tools for the analysis of gene expression and aCGH data.
Most of the tools use parallel computing (via MPI). Most of our applications
allow the user to obtain additional information for user-selected genes by
using clickable links in tables and/or figures. Our tools include:
normalization of expression and aCGH data; converting between different types
of gene/clone and protein identifiers; filtering and imputation; finding
differentially expressed genes related to patient class and survival data;
searching for models of class prediction; using random forests to search for
minimal models for class prediction or for large subsets of genes with
predictive capacity; searching for molecular signatures and predictive genes
with survival data; detecting regions of genomic DNA gain or loss. The
capability to send results between different applications, access to additional
functional information, and parallelized computation make our suite unique and
exploit features only available to web-based applications.Comment: web based application; 3 figure
Vacuum fluctuations and the conditional homodyne detection of squeezed light
Conditional homodyne detection of quadrature squeezing is compared with
standard nonconditional detection. Whereas the latter identifies
nonclassicality in a quantitative way, as a reduction of the noise power below
the shot noise level, conditional detection makes a qualitative distinction
between vacuum state squeezing and squeezed classical noise. Implications of
this comparison for the realistic interpretation of vacuum fluctuations
(stochastic electrodynamics) are discussed.Comment: 14 pages, 7 figures, to appear in J. Opt. B: Quantum Semiclass. Op
Linking tourism, retirement migration and social capital
A general trend in the study of international retirement migration has been the increased attention paid to the social contacts and network connections of the migrants in both the destination and the origin areas. These studies have examined the extent to which migrants build social relationships with their neighbours and the host society while also maintaining social links with their countries of origin, addressing the central role that leisure travel plays in sustaining increasingly dispersed social networks and maintaining the social capital of these networks and of the individuals involved in them. Using a case study approach to examine British retirement migration to Spain, we explore the relevance of transnational social networks in the context of international retirement migration, particularly the intensity of bidirectional visiting friends and relatives (VFR) tourism flows and the migrants' social contacts with friends and/or family back in their home country. Building on the concept of social capital and Putnam's distinction between bonding and bridging social capital, we propose a framework for the analysis of the migrants' international social networks. The results of a study conducted based on a sample of 365 British retirees living in the coast of Alicante (Spain) show both the strength of the retirees' international bonding social capital and the role of 'VFR's travel and communication technologies in sustaining the migrants' transnational social practices and, ultimately, their international bonding social capital. It also provides evidence for the reinforcing links between tourism-related mobility and amenity-seeking migration in later life. © 2013 © 2013 Taylor & Francis
Population analysis of the late hercynian faulting in the Spanish Central System
[Resumen] En la región comprendida entre Cercedilla, El Espinar y Robleao de Chavela (Sistema Central), se han observado una serie de zonas de cizalla ductiles que cortan a las estructuras Hercínicas anteriores; son de dirección N80-NIIOE y poseen movimientos de tipo normal. Este tipo de régimen distensivo concuerda con tipos deformacionales descritos por otros autores en el Sistema Central Español. En la misma zona están también presentes una serie de diques y fallas frágiles que corresponden a un régimen deformacional inicialmente de tipo distensión uniaxial, según NS-NIOE. Las principales direcciones de fraturación se concretan en dos familias muy próximas (N80E y NIOOE), o en una única familia según N90E. A favor de esta última dirección, yen régimen de tipo extensión uniaxial se emplazan una serie de porfidos graníticos, muy característicos del área estudiada. Debido al temprano emplazamiento de estos diques ya los planos de movimiento deducibles para unos y otros tipos de fallas, pensamos que ambos eventos han de tener una cierta relación temporal. La distensión uniaxial pasa en el tiempo, mediante aumento de las compresiones de dirección N9S-NIOO E, a tectónica de tipo de desgarre. A toda esta evolución deformacional se le denomina «Etapa Malagon». Estos desgarres afectan de una manera dúctil, si bien sin recristalizaciones posteriores, a los diques de porfido granítico, que aun se están emplazando. Posteriormente, y ya dentro de la tectónica netamente de tipo frágil, se produce un régimen deformacional de tipo desgarre, con dirección de compresión NSOE que termina en distensión radial, que hemos denominado «Etapa Hiendelaencina ». En esta fase se emplazan diques de cuarzo y baritina de direcciones N20E' y N80E.[Abstract] In the region between Cercedilla, El Espinar and Robledo de Chavela (Middle Occidental Sector of the Central System) a series of ductile shear zones have been observed that cut to the former Hercynian structures with Nao-NIOO trends and having normal movement. This extensive regime agrees with other previous works. There are, in the same area, a series of dykes and brittle faults that correspond .to a deformational regime with uniaxial extension (initially from N5 to NIO). The main fault trends are Nao and NIOO (or only one with N90 trend). Following this last direction a series of granitic dykes are emplaced. This dyke emplacement and the movement scheme make us think in a certain temporal relation between them. The uniaxial extension changes, with an increase of the compresive axis (N95-NIOO), to a strike-slip fault tectonics. We will call this deformational evolution, «Malagon Phase». Subsequently, and in a clear brittle tectonics, it is produced a deformational regime of strike slip type with a direction of compression of N50E, ending in a radial extension named «Hiendelaencina Phase», with emplacement of quartz and baryte dykes with N20 and Nao trends
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