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Search Results: 1 - 10 of 467948 matches for " Ignacio A Rodriguez-Brenes "
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Cellular replication limits in the Luria-Delbrück mutation model
Ignacio A Rodriguez-Brenes,Dominik Wodarz,Natalia L. Komarova
Quantitative Biology , 2015,
Abstract: Originally developed to elucidate the mechanisms of natural selection in bacteria, the Luria-Delbr\"uck model assumed that cells are intrinsically capable of dividing an unlimited number of times. This assumption however, is not true for human somatic cells which undergo replicative senescence. Replicative senescence is thought to act as a mechanism to protect against cancer and the escape from it is a rate-limiting step in cancer progression. Here we introduce a Luria-Delbr\"uck model that explicitly takes into account cellular replication limits in the wild type cell population and models the emergence of mutants that escape replicative senescence. We present results on the mean, variance, distribution, and asymptotic behavior of the mutant population in terms of three classical formulations of the problem. More broadly the paper introduces the concept of incorporating replicative limits as part of the Luria-Delbr\"uck mutational framework. Guidelines to extend the theory to include other types of mutations and possible applications to the modeling of telomere crisis and fluctuation analysis are also discussed.
Pronóstico de la Concentración de Ozono en Guadalajara-México usando Redes Neuronales Artificiales
García,Ignacio; Marbán,Alonso; Tenorio,Yenisse M; Rodriguez,José G;
Información tecnológica , 2008, DOI: 10.4067/S0718-07642008000300013
Abstract: a forecasting model to predict the maximum ozone concentration in a specific day in the metropolitan area of guadalajara-mexico was developed. an artificial neuronal network fed with six meteorological variables and three chemicals was used. nodes in the hidden layer were varying in a number among 12 and 15. the transfer functions were log-sigmoid for the hidden layer and linear for the output layer. for the network training the levenberg-marquardt algorithm with historical dates from 1999 to 2004. data for 2005 were used to evaluate the predictive capabilities of the trained network, evaluating the quality of the air at three levels: good, moderate, and unhealthy. the model presented global efficiencies of around 50%, reaching and 65% for high ozone concentrations.
Pronóstico de la Concentración de Ozono en Guadalajara-México usando Redes Neuronales Artificiales Ozone Concentration Forecast in Guadalajara-Mexico using Artificial Neuronal Networks
Ignacio García,Alonso Marbán,Yenisse M Tenorio,José G Rodriguez
Información Tecnológica , 2008,
Abstract: Se desarrolló un modelo de pronóstico de la concentración de ozono máxima para el día de interés para la Zona Metropolitana de Guadalajara-México. Se uso una Red Neuronal Artificial alimentada con seis variables meteorológicas y tres químicas. Los nodos de la capa oculta se variaron entre doce y quince, las funciones de transferencia de la capa interna fueron log-sigmoidal, y de la de salida fue lineal. Para entrenar la red se empleó un algoritmo de Levenberg-Marquardt con datos históricos de 1999 a 2004. Datos del a o 2005 fueron usados para verificar la capacidad predictiva de la red ya entrenada, y evaluar la calidad del aire en tres niveles: buena, moderada y mala. El modelo tuvo eficiencias globales de alrededor del 50%, llegando a 65% para concentraciones elevadas de ozono. A forecasting model to predict the maximum ozone concentration in a specific day in the Metropolitan Area of Guadalajara-Mexico was developed. An Artificial Neuronal Network fed with six meteorological variables and three chemicals was used. Nodes in the hidden layer were varying in a number among 12 and 15. The transfer functions were log-sigmoid for the hidden layer and linear for the output layer. For the network training the Levenberg-Marquardt algorithm with historical dates from 1999 to 2004. Data for 2005 were used to evaluate the predictive capabilities of the trained network, evaluating the quality of the air at three levels: good, moderate, and unhealthy. The model presented global efficiencies of around 50%, reaching and 65% for high ozone concentrations.
LA POLíTICA AGRARIA COMUNITARIA Y LA REVISIóN DE 2008
García Brenes,David;
Revista de Economía Institucional , 2009,
Abstract: over time, the cap has had a very important role for the economic objectives of the eu. it is the institutional policy with the highest share of the community budget. this article examines the evolution of the cap since the nineties, with the aims of reducing surpluses, developing an agricultural sector which is sustainable and open in global markets and responding to the new priorities of consumers. the reform of the cap proposed by the european commission in may 2008 is also analyzed.
La Política Agraria Comunitaria y la revisión en 2008
David García Brenes
Revista de Economía Institucional , 2009,
Abstract: La Política Agraria Comunitaria (PAC) ha jugado a lo largo de la historia un importante papel en los objetivos económicos de la Unión Europea. Esto ha supuesto que sea la política institucional con mayor peso específico en el presupuesto comunitario. En este trabajo se describen los cambios que se han hecho en la PAC desde los a os noventa, para reducir los excedentes, conseguir una agricultura sostenible y abierta en los mercados globales, y responder a las nuevas prioridades de los consumidores. Además, se analiza la propuesta que la Comisión Europea presentó en mayo de 2008 para reformar la PAC.
Geometrical Structures of Space-Time in General Relativity
Ignacio Sanchez-Rodriguez
Physics , 2008, DOI: 10.1063/1.2958176
Abstract: Space-Time in general relativity is a dynamical entity because it is subject to the Einstein field equations. The space-time metric provides different geometrical structures: conformal, volume, projective and linear connection. A deep understanding of them has consequences on the dynamical role played by geometry. We present a unified description of those geometrical structures, with a standard criterion of naturalness, and then we establish relationships among them and try to clarify the meaning of associated geometric magnitudes.
G-Structures defined on pseudo-Riemannian manifolds
Ignacio Sanchez-Rodriguez
Mathematics , 2008,
Abstract: Concepts and techniques from the theory of G-structures of higher order are applied to the study of certain structures (volume forms, conformal structures, linear connections and projective structures) defined on a pseudo-Riemanniann manifold. Several relationships between the structures involved have been investigated. The operations allowed on G-structures, such as intersection, inclusion, reduction, extension and prolongation, were used for it.
Where Have All the Worriers Gone? Temporal Instability of the Abbreviated Penn State Worry Questionnaire Limits Reliable Screening for High Trait Worry  [PDF]
Tamara E. Spence, Terry D. Blumenthal, Gretchen A. Brenes
Psychology (PSYCH) , 2012, DOI: 10.4236/psych.2012.311141
Abstract: Participant selection is an important step in research on individual differences. If detecting an effect of a personality variable is predicated on the use of extreme groups, then mistakenly including participants who are not in the extremes may weaken the ability to see an effect. In this study, changes in trait worry were evaluated in 68 undergraduate students reporting low or high levels of worry. Participants completed the abbreviated Penn State Worry Questionnaire (PSWQ-A) three times: 1) at the beginning of the se- mester; 2) 3 - 13 weeks later; and 3) 1 hr later, following a psychophysiological assessment session. Test–retest reliability across the three administrations was high, but almost half of the sample no longer met the pre-defined criteria for classification as low or high worriers at the second administration. That is, scores were reliable, but not stable, across time. Instability of self-report worry was significantly greater for high worriers than for low worriers, and this effect was predicted by trait anxiety at the beginning of the semester. These findings suggest that the PSWQ-A is sensitive to factors other than trait worry, which may result in dilution of effects when participants are selected for extreme worry scores. This also sug- gests that screening participants weeks before the actual study should be supplemented by readministra- tion of the screening questionnaire, to identify participants who no longer meet criteria for inclusion.
A Prediction Study of Path Loss Models from 2-73.5 GHz in an Urban-Macro Environment
Timothy A. Thomas,Marcin Rybakowski,Shu Sun,Theodore S. Rappaport,Huan Nguyen,Istvan Z. Kovacs,Ignacio Rodriguez
Mathematics , 2015,
Abstract: It is likely that 5G wireless systems will encompass frequencies from around 500 MHz all the way to around 100 GHz. To adequately assess the performance of 5G systems in these different bands, path loss (PL) models will need to be developed across this wide frequency range. The PL models can roughly be broken into two categories, ones that have some anchor in physics, and ones that curve-match only over the data set without any physical anchor. In this paper we use both real-world measurements from 2.0 to 28 GHz and ray-tracing studies from 2.0 to 73.5 GHz, both in an urban-macro environment, to assess the prediction performance of the two PL modeling techniques. In other words, we look at how the two different PL modeling techniques perform when the PL model is applied to a prediction set which is different in distance, frequency, or environment from a measurement set where the parameters of the respective models are determined. We show that a PL model with a physical anchor point can be a better predictor of PL performance in the prediction sets while also providing a parameterization which is more stable over a substantial number of different measurement sets.
Transformaciones en la organización del trabajo en el cultivo del olivar: El caso de Andalucía
García Brenes,M. David;
Mundo agrario , 2007,
Abstract: the globalization process and the liberalization of the economic activity have had a noticeable incidence in the social and economic reality of andalusia, which is a region in the south of spain . this research studies the most important transformations in the work market based on the results obtained with semi structured interviews to agriculture labourers of four towns representatives of the olive industry of andalusia . the study points out how the process of reestructuration that this cultivates has followed had made that the olive industry lose a good portion of its social character and a growth of temporary labour. through it is studied the secondary place that have the women work and how a significant number of labourers have been substituted by immigrants who accept the new conditions of work.
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