5,169 research outputs found
Parameter estimation and model selection for stochastic differential equations for biological growth
In this paper, we consider stochastic versions of three classical growth
models given by ordinary differential equations (ODEs). Indeed we use
stochastic versions of Von Bertalanffy, Gompertz, and Logistic differential
equations as models. We assume that each stochastic differential equation (SDE)
has some crucial parameters in the drift to be estimated and we use the Maximum
Likelihood Estimator (MLE) to estimate them. For estimating the diffusion
parameter, we use the MLE for two cases and the quadratic variation of the data
for one of the SDEs. We apply the Akaike information criterion (AIC) to choose
the best model for the simulated data. We consider that the AIC is a function
of the drift parameter. We present a simulation study to validate our selection
method.
The proposed methodology could be applied to datasets with continuous and
discrete observations, but also with highly sparse data. Indeed, we can use
this method even in the extreme case where we have observed only one point for
each path, under the condition that we observed a sufficient number of
trajectories. For the last two cases, the data can be viewed as incomplete
observations of a model with a tractable likelihood function; then, we propose
a version of the Expectation Maximization (EM) algorithm to estimate these
parameters. This type of datasets typically appears in fishery, for instance
Volúmenes molares aparentes de los anestésicos procaína-HCl y lidocaína-HCl en agua a temperaturas entre 278,15 y 313,15 K
La lidocaína-HCl y procaína-HCl son anestésicos locales ampliamente usados en procedimientos quirúrgicos menores, sin embargo la información fisicoquímica acerca de su comportamiento volumétrico, así como de otras propiedades fisicoquímicas, aún es incompleta en la actualidad. Por esta razón, en este artículo se presentan los valores de densidad de algunas soluciones acuosas de estos dos fármacos en función de la concentración (desde 0,0500 hasta 0,5000) mol kg–1 a diferentes temperaturas (278,15, 283,15, 288,15, 293,15, 298,15, 303,15, 308,15 y 313,15 K). Así mismo se presentan los volúmenes molares aparentes y volúmenes molares parciales a dilución infinita de los fármacos como electrolitos, y de otro lado, los volúmenes molares parciales a dilución infinita de los fármacos moleculares y las expansibilidades molares, los cuales fueron calculados a partir de los valores de densidad y composición de las mezclas. Los resultados obtenidos se interpretan en términos de interacciones soluto-solvente.Lidocaine-HCl and procaine-HCl are local anesthetic drugs widely used in minor chirurgic procedures, nevertheless, physicochemical information about their volumetric behavior, as well as for other aqueous properties, is not complete at present. In this context, in this article, densities of aqueous solutions of both drugs have been measured as a function of concentration (from 0.0500 to 0.5000) mol kg–1 at several temperatures, i.e. 278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. The apparent molar volumes and partial molar volumes at infinite dilution for the electrolyte drugs were calculated, whereas, the partial molar volumes at infinite dilution and partial molar expansibilities for the molecular forms were also calculated. The dependence of these properties with temperature is shown. The results are interpreted in terms of interaction solute-solvent.Fil: Delgado, Daniel R.. Universidad Nacional de Colombia; ColombiaFil: Jimenez Kairuz, Alvaro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Farmacia; ArgentinaFil: Manzo, Ruben Hilario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Departamento de Farmacia; ArgentinaFil: Vargas, Edgar F.. Universidad de los Andes; ColombiaFil: Martinez, Fleming. Universidad Nacional de Colombia; Colombi
Apparent molar volumes of sodium naproxen in water at several concentrations and temperatures
Densities of aqueous solutions of sodium naproxen have been measured as functions of concentration (from 0.0250 to 0.5000 mol kg-1
) and temperature (from 278.15 to 313.15 K). The apparent molar volumes, partial molar volumes at infinite dilution and partial molar expansibility were calculated. The
dependence of these properties with temperature is also shown. The results are interpreted in terms of solute-solvent interactions.Colegio de Farmacéuticos de la Provincia de Buenos Aire
Synthetic spectra of H Balmer and HeI absorption lines. II: Evolutionary synthesis models for starburst and post-starburst galaxies
We present evolutionary stellar population synthesis models to predict the
spectrum of a single-metallicity stellar population, with a spectral sampling
of 0.3 A in five spectral regions between 3700 and 5000 A. The models, which
are optimized for galaxies with active star formation, synthesize the profiles
of the hydrogen Balmer series (Hb, Hg, Hd, H8, H9, H10, H11, H12 and H13) and
the neutral helium absorption lines (HeI 4922, HeI 4471, HeI 4388, HeI 4144,
HeI 4121, HeI 4026, HeI 4009 and HeI 3819) for a burst with an age ranging from
1 to 1000 Myr, and different assumptions about the stellar initial mass
function. Continuous star formation models lasting for 1 Gyr are also
presented. The input stellar library includes NLTE absorption profiles for
stars hotter than 25000 K and LTE profiles for lower temperatures. The
temperature and gravity coverage is 4000 K <Teff< 50000 K and 0.0< log g$< 5.0,
respectively.
The models can be used to date starburst and post-starburst galaxies until 1
Gyr. They have been tested on data for clusters in the LMC, the super-star
cluster B in the starburst galaxy NGC 1569, the nucleus of the dwarf elliptical
NGC 205 and a luminous "E+A" galaxy. The full data set is available for
retrieval at http://www.iaa.es/ae/e2.html and at
http://www.stsci.edu/science/starburst/, or on request from the authors at
[email protected]: To be published in ApJS. 48 pages and 20 figure
The AMS-02 RICH Imager Prototype - In-Beam Tests with 20 GeV/c per Nucleon Ions -
A prototype of the AMS Cherenkov imager (RICH) has been tested at CERN by
means of a low intensity 20 GeV/c per nucleon ion beam obtained by
fragmentation of a primary beam of Pb ions. Data have been collected with a
single beam setting, over the range of nuclear charges 2<Z<~45 in various beam
conditions and using different radiators. The charge Z and velocity beta
resolutions have been measured.Comment: 4 pages, contribution to the ICRC 200
The Ring Imaging Cherenkov detector (RICH) of the AMS experiment
The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the
International Space Station (ISS) will be equipped with a proximity focusing
Ring Imaging Cherenkov (RICH) detector for measuring the electric charge and
velocity of the charged cosmic particles. A RICH prototype consisting of 96
photomultiplier units, including a piece of the conical reflector, was built
and its performance evaluated with ion beam data. Preliminary results of the
in-beam tests performed with ion fragments resulting from collisions of a 158
GeV/c/nuc primary beam of Indium ions (CERN SPS) on a Pb target are reported.
The collected data included tests to the final front-end electronics and to
different aerogel radiators. Cherenkov rings for a large range of charged
nuclei and with reflected photons were observed. The data analysis confirms the
design goals. Charge separation up to Fe and velocity resolution of the order
of 0.1% for singly charged particles are obtained.Comment: 29th International Conference on Cosmic Rays (Pune, India
Principales riesgos en el uso de tecnologías de la información en adolescentes
A principios del año 2020 el mundo se enfrentó a una de las más grandes pandemias en la historia y, con esto, a un cambio en el modo de vida de las personas. Este cambio tuvo como elemento central el uso de las tecnologías de la información. Si bien su uso había evolucionado rápidamente, aún se tenían muchos sectores de la población que no las integraban por completo. Además, con la llegada de la pandemia, el mundo entero tuvo la necesidad de adaptarse a una nueva forma de interactuar, desde la forma de convivir con la familia hasta la forma de impartir y tomar clases, por mencionar algunas actividades. En este sentido, la educación básica fue uno de los sectores más afectados, ya que tuvo que pasar del trabajo presencial a una enseñanza completamente en línea. Sin embargo, gran parte de esta población, integrada por adolescentes, niñas y niños no están familiarizados con los riesgos que conlleva la convivencia diaria con Internet. Esto dejó ver que las instituciones educativas no tuvieron tiempo de educar a sus estudiantes en materia de ciberseguridad. Con base en lo anterior, este artículo muestra algunos de los principales riesgos a los que se enfrentan los adolescentes, derivados principalmente de una cada vez mayor exposición a Internet. Para esto, no se contemplaron medidas mínimas de seguridad y prevención. Finalmente, se presentan algunas estrategias que ayudan a mitigar dichos problemas
Identification of candidate genes associated with fibromyalgia susceptibility in southern Spanish women: the al‑Ándalus project
Candidate-gene studies on fibromyalgia susceptibility often include a small number of single nucleotide
polymorphisms (SNPs), which is a limitation. Moreover, there is a paucity of evidence in Europe. Therefore, we
compared genotype frequencies of candidate SNPs in a well-characterised sample of Spanish women with fibromyalgia
and healthy non-fibromyalgia women.This work was supported by the Spanish Ministry of Economy and Competitiveness
[I+D+i DEP2010-15639, I+D+i DEP2013-40908-R to M.D.-F.;
BES-2014-067612 to F.E.-L.]; the Spanish Ministry of Education [FPU2014/02518
to M.B.-C.]; the Consejería de Turismo, Comercio y Deporte, Junta de Andalucía
[CTCD-201000019242-TRA to M.D.-F.]; Consejería de Salud, Junta de Andalucía
[PI-0520-2016 to M.D.-F.], and the University of Granada, Plan Propio de
Investigación 2016, Excellence actions: Units of Excellence; Unit of Excellence
on Exercise and Health (UCEES). This work is part of a Ph.D. Thesis conducted
in the Biomedicine Doctoral Studies of the University of Granada, Spai
The AMS-RICH velocity and charge reconstruction
The AMS detector, to be installed on the International Space Station,
includes a Ring Imaging Cerenkov detector with two different radiators, silica
aerogel (n=1.05) and sodium fluoride (n=1.334). This detector is designed to
provide very precise measurements of velocity and electric charge in a wide
range of cosmic nuclei energies and atomic numbers. The detector geometry, in
particular the presence of a reflector for acceptance purposes, leads to
complex Cerenkov patterns detected in a pixelized photomultiplier matrix. The
results of different reconstruction methods applied to test beam data as well
as to simulated samples are presented. To ensure nominal performances
throughout the flight, several detector parameters have to be carefully
monitored. The algorithms developed to fulfill these requirements are
presented. The velocity and charge measurements provided by the RICH detector
endow the AMS spectrometer with precise particle identification capabilities in
a wide energy range. The expected performances on light isotope separation are
discussed.Comment: Contribution to the ICRC07, Merida, Mexico (2007); Presenter: F.
Bara
Ultraviolet-Optical observations of the Seyfert 2 Galaxies NGC 7130, NGC 5135 and IC 3639: Implications for the Starburst-AGN Connection
We present and discuss HST (WFPC2 and FOC) images and UV GHRS spectra plus
ground-based near UV through to near IR spectra of three Seyfert 2 nuclei (NGC
7130, NGC 5135 and IC 3639). These galaxies, together to Mrk 477, were selected
from a bigger sample that comprises the 20 brightest Seyfert 2 nuclei, with the
goal to study the origin of the UV-optical-near IR featureless continuum in
Seyfert 2 nuclei. These four galaxies have bolometric luminosities, as computed
with the four IRAS bands, of 10^11 Lsol. They are close enough to be resolved
with HST the nuclear zone. This makes these Seyfert 2 galaxies benchmarks to
study the Starburst-AGN connection in more distant galaxies.
The data provide direct evidence of the existence of a central nuclear
starburst that dominates the UV light, and that seem to be responsible for the
origin of the so called featureless continuum. These starbursts are dusty and
compact. They have sizes (from less than 100 pc to a few hundred pc) much
smaller and closer to the nucleus than that seen in the prototype Seyfert 2
galaxy NGC 1068. The bolometric luminosity of these starbursts is similar to
the estimated bolometric luminosities of their obscured Seyfert 1 nuclei, and
thus they contribute in the same amount to the overall energetics of these
galaxies.Comment: to be published in ApJ 505, September issue. The figures are in a tar
files at: http://www.iaa.es/~rosa/Seyfert
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