2,716 research outputs found
Phase diagram of a polydisperse soft-spheres model for liquids and colloids
The phase diagram of soft spheres with size dispersion has been studied by
means of an optimized Monte Carlo algorithm which allows to equilibrate below
the kinetic glass transition for all sizes distribution. The system
ubiquitously undergoes a first order freezing transition. While for small size
dispersion the frozen phase has a crystalline structure, large density
inhomogeneities appear in the highly disperse systems. Studying the interplay
between the equilibrium phase diagram and the kinetic glass transition, we
argue that the experimentally found terminal polydispersity of colloids is a
purely kinetic phenomenon.Comment: Version to be published in Physical Review Letter
Separation and fractionation of order and disorder in highly polydisperse systems
Microcanonical Monte Carlo simulations of a polydisperse soft-spheres model
for liquids and colloids have been performed for very large polydispersity, in
the region where a phase-separation is known to occur when the system (or part
of it) solidifies. By studying samples of different sizes, from N=256 to N=864,
we focus on the nature of the two distinct coexisting phases. Measurements of
crystalline order in particles of different size reveal that the solid phase
segregates between a crystalline solid with cubic symmetry and a disordered
phase. This phenomenon is termed fractionation.Comment: 8 pages, 5 figure
Organic Molecules in the Galactic Center. Hot Core Chemistry without Hot Cores
We study the origin of large abundances of complex organic molecules in the
Galactic center (GC). We carried out a systematic study of the complex organic
molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO, and CS toward
40 GC molecular clouds. Using the LTE approximation, we derived the physical
properties of GC molecular clouds and the abundances of the complex
molecules.The CH3OH abundance between clouds varies by nearly two orders of
magnitude from 2.4x10^{-8} to 1.1x10^{-6}. The abundance of the other complex
organic molecules relative to that of CH3OH is basically independent of the
CH3OH abundance, with variations of only a factor 4-8. The abundances of
complex organic molecules in the GC are compared with those measured in hot
cores and hot corinos, in which these complex molecules are also abundant. We
find that both the abundance and the abundance ratios of the complex molecules
relative to CH3OH in hot cores are similar to those found in the GC clouds.
However, hot corinos show different abundance ratios than observed in hot cores
and in GC clouds. The rather constant abundance of all the complex molecules
relative to CH3OH suggests that all complex molecules are ejected from grain
mantles by shocks. Frequent (similar 10^{5}years) shocks with velocities >6km/s
are required to explain the high abundances in gas phase of complex organic
molecules in the GC molecular clouds. The rather uniform abundance ratios in
the GC clouds and in Galactic hot cores indicate a similar average composition
of grain mantles in both kinds of regions. The Sickle and the Thermal Radio
Arches, affected by UV radiation, show different relative abundances in the
complex organic molecules due to the differentially photodissociation of these
molecules.Comment: 18 pages, 10 Postscript figures, uses aa.cls, aa.bst, 10pt.rtx,
natbib.sty, revsymb.sty revtex4.cls, aps.rtx and aalongtabl.sty. Accepted in
A&A 2006. version 2. relocated figures and tables. Language editor
suggestions. added reference
EpidemiologÃa de las fracturas de perfil osteoporótico
Las fracturas osteoporóticas de cadera van acompañadas de una morbimortalidad altas. Entre los factores de riesgo de padecer una fractura de este tipo se encuentra el haber sufrido otra fractura de este tipo con anterioridad.
Objetivo: conocer las caracterÃsticas epidemiológicas de los pacientes con fractura de perfil osteoporótico en el área sanitaria dependiente del Hospital "Virgen de la Victoria" de Málaga.
Pacientes y métodos: se incluyen a las mujeres que han sufrido una fractura de tipo osteoporótico en cualquier localización anatómica.
Estudio de tipo indagatorio estadÃstico. Se utiliza a base de datos del programa GIOS (MSD®), en la que se recogen caracterÃsticas antropomórficas de las pacientes, asà como los hábitos, factores de riesgo y toma de medicación previa
Equilibrium fluid-solid coexistence of hard spheres
We present a tethered Monte Carlo simulation of the crystallization of hard
spheres. Our method boosts the traditional umbrella sampling to the point of
making practical the study of constrained Gibb's free energies depending on
several crystalline order-parameters. We obtain high-accuracy estimates of the
fluid-crystal coexistence pressure for up to 2916 particles (enough to
accommodate fluid-solid interfaces). We are able to extrapolate to infinite
volume the coexistence pressure (p_{co}=11.5727(10) k_B T/\sigma^3) and the
interfacial free energy (\gamma_{100}=0.636(11) k_B T/\sigma^2).Comment: 6 pages, 4 pdf figures. Version to be published in PRL. Appendices
contain Supplemental Materia
Evaluación de la citotoxicidad de una mezcla de ocho contaminantes a concentraciones de relevancia ambiental
The ubiquitous presence of pollutants and the accurate evaluation of their potential risks for environmental and human health is an area of major concern. We have simulated an in vitro scenario of long-term exposure to a mixture of eight pollutants at real environmental concentrations using mammalian Vero cells. Our results demonstrate that cellular proliferation rates were significantly altered, either by inhibition or stimulation, depending on the mixture composition and the exposure time. We encourage the urgency of reviewing safety levels for emerging contaminants accepted by regulatory agencies, considering that mixtures of pollutants represent a threat for environmental and human healthThis work was supported by grants from the Spanish Ministry of Science and Innovation (CTM2008-00311; CTM2012-31344
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