2,756 research outputs found
Thermal treatment of the minority game
We study a cost function for the aggregate behavior of all the agents
involved in the Minority Game (MG) or the Bar Attendance Model (BAM). The cost
function allows to define a deterministic, synchronous dynamics that yields
results that have the main relevant features than those of the probabilistic,
sequential dynamics used for the MG or the BAM. We define a temperature through
a Langevin approach in terms of the fluctuations of the average attendance. We
prove that the cost function is an extensive quantity that can play the role of
an internal energy of the many agent system while the temperature so defined is
an intensive parameter. We compare the results of the thermal perturbation to
the deterministic dynamics and prove that they agree with those obtained with
the MG or BAM in the limit of very low temperature.Comment: 9 pages in PRE format, 6 figure
Dynamical quenching and annealing in self-organization multiagent models
We study the dynamics of a generalized Minority Game (GMG) and of the Bar
Attendance Model (BAM) in which a number of agents self-organize to match an
attendance that is fixed externally as a control parameter. We compare the
usual dynamics used for the Minority Game with one for the BAM that makes a
better use of the available information. We study the asymptotic states reached
in both frameworks. We show that states that can be assimilated to either
thermodynamic equilibrium or quenched configurations can appear in both models,
but with different settings. We discuss the relevance of the parameter that
measures the value of the prize for winning in units of the fine for losing. We
also provide an annealing protocol by which the quenched configurations of the
GMG can progressively be modified to reach an asymptotic equlibrium state that
coincides with the one obtained with the BAM.Comment: around 20 pages, 10 figure
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A case of atypical disseminated herpes simplex virus 1 with hepatitis in a liver transplant recipient: the need for dermatologic evaluation
Disseminated herpes simplex virus (HSV) is mainly seen in immunocompromised individuals. Atypical lesions can be present in both primary infection and reactivation disease. Compared with the general population, inmunocompromised hosts are at greater risk of increased persistency and severity of clinical manifestations, including severe systemic involvement such as esophagitis, meningitis, and hepatitis. Herein, we report the case of a liver transplant recipient with atypical disseminated herpes simplex virus-1 complicated by HSV-related hepatitis. Dermatological consultation and histological assessment were crucial for a correct diagnosis and treatment
A Method to Determine the In-Air Spatial Spread of Clinical Electron Beams
We propose and analyze in detail a method to measure the in-air spatial
spread parameter of clinical electron beams. Measurements are performed at the
center of the beam and below the adjustable collimators sited in asymmetrical
configuration in order to avoid the distortions due to the presence of the
applicator. The main advantage of our procedure lies in the fact that the dose
profiles are fitted by means of a function which includes, additionally to the
Gaussian step usually considered, a background which takes care of the dose
produced by different mechanisms that the Gaussian model does not account for.
As a result, the spatial spread is obtained directly from the fitting procedure
and the accuracy permits a good determination of the angular spread. The way
the analysis is done is alternative to that followed by the usual methods based
on the evaluation of the penumbra width. Besides, the spatial spread found
shows the quadratic-cubic dependence with the distance to the source predicted
by the Fermi-Eyges theory. However, the corresponding values obtained for the
scattering power are differing from those quoted by ICRU nr. 35 by a factor ~2
or larger, what requires of a more detailed investigation.Comment: 11 pages, 5 Postscript figures, to be published in Medical Physic
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
Diseño y evaluación de un sistema inmunoenzimático rápido de tercera generación para la detección de anticuerpos antiVlH
This paper describes the development of a third generation method for the detection of specific antibodies against the Human lmmunodeficiency Virus (VIH) types 1 and 2. The method uses a Microelisa, based on the use of a mixture of synthetic peptides as antigens derived from gp41 and p24 of HIV 1 and p36 of HIV 2. This system requires a total of twenty minutes (20') in order to obtain a result with 100% specificity and 99% sensitivity, comparable to the new third - generation commercially available systems.Una mezcla de péptidos sintéticos correspondientes a regiones conservadas e inmunodominantes de las proteínas gp41 y p24 del virus de inmunodeficiencia humana tipo 1 (VIH 1) y de p36 del VIH tipo 2, se emplearon como antígenos para el desarrollo de un sistema de microelisa para la detección de anticuerpos específicos antiVlH en suero de pacientes infectados. Este abordaje multiepitópico permite la elaboración de un ELlSA rápido (20 minutos) con una sensibilidad del 99% y una especificidad del 100% cuando se enfrenta con un panel de 300 sueros: 100 de pacientes seropositivos y pacientes con SlDA y 200 muestras de donantes sanos. Estos resultados sugieren que el sistema de microelisa rápido posee una sensibilidad y especificidad comparables a la de los estuches comerciales de tercera generación disponibles actualmente
New Superhard Phases for 3D C60-based Fullerites
We have explored new possible phases of 3D C60-based fullerites using
semiempirical potentials and ab-initio density functional methods. We have
found three closely related structures - two body centered orthorhombic and one
body centered cubic - having 52, 56 and 60 tetracoordinated atoms per molecule.
These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and
shear moduli around 240 GPa, which make them good candidates for new low
density superhard materials.Comment: To be published in Physical Review Letter
Low Energy Electron and Nuclear Recoil Thresholds in the DRIFT-II Negative Ion TPC for Dark Matter Searches
Understanding the ability to measure and discriminate particle events at the
lowest possible energy is an essential requirement in developing new
experiments to search for weakly interacting massive particle (WIMP) dark
matter. In this paper we detail an assessment of the potential sensitivity
below 10 keV in the 1 m^3 DRIFT-II directionally sensitive, low pressure,
negative ion time projection chamber (NITPC), based on event-by-event track
reconstruction and calorimetry in the multiwire proportional chamber (MWPC)
readout. By application of a digital smoothing polynomial it is shown that the
detector is sensitive to sulfur and carbon recoils down to 2.9 and 1.9 keV
respectively, and 1.2 keV for electron induced events. The energy sensitivity
is demonstrated through the 5.9 keV gamma spectrum of 55Fe, where the energy
resolution is sufficient to identify the escape peak. The effect a lower energy
sensitivity on the WIMP exclusion limit is demonstrated. In addition to recoil
direction reconstruction for WIMP searches this sensitivity suggests new
prospects for applications also in KK axion searches
First measurement of the Head-Tail directional nuclear recoil signature at energies relevant to WIMP dark matter searches
We present first evidence for the so-called Head-Tail asymmetry signature of
neutron-induced nuclear recoil tracks at energies down to 1.5 keV/amu using the
1m^3 DRIFT-IIc dark matter detector. This regime is appropriate for recoils
induced by Weakly Interacting Massive Particle (WIMPs) but one where the
differential ionization is poorly understood. We show that the distribution of
recoil energies and directions induced here by Cf-252 neutrons matches well
that expected from massive WIMPs. The results open a powerful new means of
searching for a galactic signature from WIMPs.Comment: 4 pages, 6 figures, 1 tabl
Multiparticle Reactions with Spatial Anisotropy
We study the effect of anisotropic diffusion on the one-dimensional
annihilation reaction kA->inert with partial reaction probabilities when
hard-core particles meet in groups of k nearest neighbors. Based on scaling
arguments, mean field approaches and random walk considerations we argue that
the spatial anisotropy introduces no appreciable changes as compared to the
isotropic case. Our conjectures are supported by numerical simulations for slow
reaction rates, for k=2 and 4.Comment: nine pages, plain Te
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