8,327 research outputs found
Group Importance Sampling for Particle Filtering and MCMC
Bayesian methods and their implementations by means of sophisticated Monte
Carlo techniques have become very popular in signal processing over the last
years. Importance Sampling (IS) is a well-known Monte Carlo technique that
approximates integrals involving a posterior distribution by means of weighted
samples. In this work, we study the assignation of a single weighted sample
which compresses the information contained in a population of weighted samples.
Part of the theory that we present as Group Importance Sampling (GIS) has been
employed implicitly in different works in the literature. The provided analysis
yields several theoretical and practical consequences. For instance, we discuss
the application of GIS into the Sequential Importance Resampling framework and
show that Independent Multiple Try Metropolis schemes can be interpreted as a
standard Metropolis-Hastings algorithm, following the GIS approach. We also
introduce two novel Markov Chain Monte Carlo (MCMC) techniques based on GIS.
The first one, named Group Metropolis Sampling method, produces a Markov chain
of sets of weighted samples. All these sets are then employed for obtaining a
unique global estimator. The second one is the Distributed Particle
Metropolis-Hastings technique, where different parallel particle filters are
jointly used to drive an MCMC algorithm. Different resampled trajectories are
compared and then tested with a proper acceptance probability. The novel
schemes are tested in different numerical experiments such as learning the
hyperparameters of Gaussian Processes, two localization problems in a wireless
sensor network (with synthetic and real data) and the tracking of vegetation
parameters given satellite observations, where they are compared with several
benchmark Monte Carlo techniques. Three illustrative Matlab demos are also
provided.Comment: To appear in Digital Signal Processing. Related Matlab demos are
provided at https://github.com/lukafree/GIS.gi
Odd Triplet Pairing in clean Superconductor/Ferromagnet heterostructures
We study triplet pairing correlations in clean Ferromagnet (F)/Superconductor
(S) nanojunctions, via fully self consistent solution of the Bogoliubov-de
Gennes equations. We consider FSF trilayers, with S being an s-wave
superconductor, and an arbitrary angle between the magnetizations of
the two F layers. We find that contrary to some previous expectations, triplet
correlations, odd in time, are induced in both the S and F layers in the clean
limit. We investigate their behavior as a function of time, position, and
. The triplet amplitudes are largest at times on the order of the
inverse ``Debye'' frequency, and at that time scale they are long ranged in
both S and F. The zero temperature condensation energy is found to be lowest
when the magnetizations are antiparallel.Comment: Four pages, including four figure
Valoración económica de los servicios ecosistémicos asociados al Parque Natural del Turia (Valencia)
[EN] The objective of this paper is to obtain the monetary value of ecosystem services provided by the Turia Natural Park (TNP). This paper proposes the use of the Analytic Multicriteria Valuation Method (AMUVAM) by replacing the Analytical Hierarchy Process (AHP) with the Analytic Network Process (ANP), since the ANP method allows to analyze interdependence relationships between the services provided by a system. The results express that the economic value of the ecosystem services associated to the TNP ranges between 163,946,752 € and 481,549,597 €. The results reveal distinct patterns in the valuation of the existing services due to ethical issues.[ES] El objeto de este trabajo es la obtención de un intervalo de valor de los servicios ecosistémicos proporcionados por el Parque Natural del Turia (PNT). La metodología empleada ha sido el método analítico de valoración multicriterio (Analytic Multicriteria Valuation Method, AMUVAM) sustituyendo el Proceso Analítico Jerárquico por el proceso analítico en red (Analytic Network Process, ANP), dado que este permite analizar relaciones de interdependencia entre los servicios del sistema. El valor económico de los servicios ecosistémicos asociados al PNT oscila entre 163.946.752 € y 481.549.597 € en función de las diferentes sensibilidades éticas de los expertos.Estruch-Guitart, V.; Valls-Civera, A. (2019). An economic valuation of ecosystem services provided by the River Turia Natural Park (Valencia). Economía Agraria y Recursos Naturales - Agricultural and Resource Economics. 18(2):93-115. https://doi.org/10.7201/earn.2018.02.05SWORD9311518
Proximity effects and triplet correlations in Ferromagnet/Ferromagnet/Superconductor nanostructures
We report the results of a study of superconducting proximity effects in
clean Ferromagnet/Ferromagnet/Superconductor ()
heterostructures, where the pairing state in S is a conventional singlet
s-wave. We numerically find the self-consistent solutions of the Bogoliubov-de
Gennes (BdG) equations and use these solutions to calculate the relevant
physical quantities. By linearizing the BdG equations, we obtain the
superconducting transition temperatures as a function of the angle
between the exchange fields in and . We find that
the results for in systems are clearly different
from those in systems, where monotonically increases
with and is highest for antiparallel magnetizations. Here,
is in general a non-monotonic function, and often has a minimum
near . For certain values of the exchange field and
layer thicknesses, the system exhibits reentrant superconductivity with
: it transitions from superconducting to normal, and then returns to a
superconducting state again with increasing . This phenomenon is
substantiated by a calculation of the condensation energy. We compute, in
addition to the ordinary singlet pair amplitude, the induced odd triplet
pairing amplitudes. The results indicate a connection between equal-spin
triplet pairing and the singlet pairing state that characterizes . We find
also that the induced triplet amplitudes can be very long-ranged in both the S
and F sides and characterize their range. We discuss the average density of
states for both the magnetic and the S regions, and its relation to the pairing
amplitudes and . The local magnetization vector, which exhibits reverse
proximity effects, is also investigated.Comment: 14 pages including 11 figure
Primera cita de Mauremys leprosa (Sauropsida: Testudines) a Sant Mateu del Maestrat
La tortuga de rierol, Mauremys leprosa (Scheigger, 1812), és citada per primer cop a Sant Mateu del Maestrat (el Baix Maestrat). Es fa una primera valoració de l'estat de la població, que es considera bona, amb una estructura d'edat normal i amb abundants exemplars juvenils que asseguren el reemplaçament. No s'han observat altres torugues d'aigua a la zona.First record of the Mauremys leprosa (Sauropsida: Testudines) in Sant Mateu del Maestrat.Terrapin, Mauremys leprosa (Schegger, 1812), is mentioned for the first time in Sant Mateu del Maestrat (el Baix Maestrat, Spain). A first assessment of he state of the population is made. That is considered good, with a natural age structure and abundant young speciments that ensure replacement. No other turtles were observed in the are
Time Scales for transitions between free energy minima of a hard sphere system
Time scales associated with activated transitions between glassy metastable
states of a free energy functional appropriate for a dense hard sphere system
are calculated by using a new Monte Carlo method for the local density
variables. We calculate the time the system,initially placed in a shallow
glassy minimum of the free energy, spends in the neighborhood of this minimum
before making a transition to the basin of attarction of another free energy
minimum. This time scale is found to increase with the average density. We find
a crossover density near which this time scale increases very sharply and
becomes longer than the longest times accessible in our simulation. This scale
shows no evidence of dependence on sample size.Comment: 25 pages, Revtex, 6 postscript figures. Will appear in Phys Rev E,
March 1996 or s
Intoxicación por paraquat : revisión
En este trabajo se revisan las características de la intoxicación por paraquat, y se presentan 15 casos clínicos altamente sugestivos de dicha intoxicación. El paraquat es un compuesto bipiridilo ampliamente usado en agricultura. Debido a que la intoxicación tiene efectos progresivos e irreversibles, es importante conocer la posibilidad de acceso al tóxico, pero ello muchas veces no es posible. Dado que el diagnóstico muchas veces es difícil para el clínico, la observación de un distress respiratorio severo, que empeora progresivamente en ausencia de signos radiológicos significativos, justifica un diagnóstico presuntivo de intoxicación por paraquat.In this work, we review the characteristics of paraquat poisoning and compare it with 15 clinical cases highly suggestive of this poisoning. Paraquat is a bipyridzlium compound, widely used as a contact herbicide in agriculture. Because the poisoning has progressive and irreversible effects, it's important to know a definitive history of acces to paraquat, but it 's difficult. Because the problem of diagnosis remains difficult for the practitioner; a clinical features of progressively worsening respiratory distress, in absence of radiógraphic demonstration of adequate cause of dyspnoea, justify a pressumptive diagnosis of paraquat poisoning
Nonlinear Hydrodynamics of a Hard Sphere Fluid Near the Glass Transition
We conduct a numerical study of the dynamic behavior of a dense hard sphere
fluid by deriving and integrating a set of Langevin equations. The statics of
the system is described by a free energy functional of the
Ramakrishnan-Yussouff form. We find that the system exhibits glassy behavior as
evidenced through stretched exponential decay and two-stage relaxation of the
density correlation function. The characteristic times grow with increasing
density according to the Vogel-Fulcher law. The wavenumber dependence of the
kinetics is extensively explored. The connection of our results with
experiment, mode coupling theory, and molecular dynamics results is discussed.Comment: 34 Pages, Plain TeX, 12 PostScript Figures (not included, available
on request
Open chain pseudopeptides as hydrogelators with reversible and dynamic responsiveness to pH, temperature and sonication as vehicles for controlled drug delivery
A new family of open chain-pseudopeptidic compounds displaying a pendant carboxylic group have been prepared with excellent yields. Their self-assembly has been studied under different conditions and in different media. Some of the compounds obtained have revealed to act as very efficient hydrogelators at low concentrations (CGC 1 mg mL−1). The resulting hydrogels show some interesting properties, including a high thermal stability, with the hydrogels maintaining their structure at temperatures above 65 °C, and their reversible dynamic sol–gel behavior being responsive to thermal and sonochemical inputs and to changes in the basic/acidic properties of the medium. Preliminary studies for controlled drug delivery have been carried out using a Franz Cell and employing a skin pig membrane, confirming that these Low Molecular Weight Gelators (LMWGs) can be appropriate vehicles for the controlled transdermal delivery of small-molecule drugs.Funding for open access charge: CRUE-Universitat Jaume
Effect of a Diet Supplemented with α-Tocopherol and β-Carotene on ATP and Antioxidant Levels after Hepatic Ischemia-Reperfusion
Ischemia-reperfusion injury associated with liver transplantation remains a serious complication in clinical practice. In the present study the effect of intake of α-tocopherol or β-carotene to limit liver injury by oxidative stress in ischemia and reperfusion was explored. Wistar rats were fed with diets enriched with α-tocopherol (20 mg/day) or β-carotene (3 mg/day) for 21 days. After 21 days, their livers were subjected to 15 and 30 min of ischemia and afterwards were reperfused for 60 min. The recovery of levels of ATP during reperfusion was better in the group of rats whose diets were supplemented with α-tocopherol or β-carotene than in the group control. The supplementation of the diet induced changes in the profile of enzymatic antioxidants. The supplementation with α-tocopherol and β-carotene resulted in a decreased of superoxide dismutase during the ischemia and a recovery was observed after reperfusion. Not changes were observed for the enzymes catalase and glutathione peroxidase and glutathione but their values were higher to those of the group control. In conclusion, the supplementation with α-tocopherol and β-carotene improve the antioxidant and energetic state of liver after ischemia and reperfusion injury
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