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Search Results: 1 - 10 of 593713 matches for " Marcos A. Capistrán "
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First Principles Modeling of Nonlinear Incidence Rates in Seasonal Epidemics
José M. Ponciano ,Marcos A. Capistrán
PLOS Computational Biology , 2011, DOI: 10.1371/journal.pcbi.1001079
Abstract: In this paper we used a general stochastic processes framework to derive from first principles the incidence rate function that characterizes epidemic models. We investigate a particular case, the Liu-Hethcote-van den Driessche's (LHD) incidence rate function, which results from modeling the number of successful transmission encounters as a pure birth process. This derivation also takes into account heterogeneity in the population with regard to the per individual transmission probability. We adjusted a deterministic SIRS model with both the classical and the LHD incidence rate functions to time series of the number of children infected with syncytial respiratory virus in Banjul, Gambia and Turku, Finland. We also adjusted a deterministic SEIR model with both incidence rate functions to the famous measles data sets from the UK cities of London and Birmingham. Two lines of evidence supported our conclusion that the model with the LHD incidence rate may very well be a better description of the seasonal epidemic processes studied here. First, our model was repeatedly selected as best according to two different information criteria and two different likelihood formulations. The second line of evidence is qualitative in nature: contrary to what the SIRS model with classical incidence rate predicts, the solution of the deterministic SIRS model with LHD incidence rate will reach either the disease free equilibrium or the endemic equilibrium depending on the initial conditions. These findings along with computer intensive simulations of the models' Poincaré map with environmental stochasticity contributed to attain a clear separation of the roles of the environmental forcing and the mechanics of the disease transmission in shaping seasonal epidemics dynamics.
An analysis of the interaction between influenza and respiratory syncytial virus based on acute respiratory infection records
Yendry N. Arguedas-Flatts,Marcos A. Capistrán,J. Andrés Christen,Daniel E. Noyola
Quantitative Biology , 2013,
Abstract: Under the hypothesis that both influenza and respiratory syncytial virus (RSV) are the two leading causes of acute respiratory infections (ARI), in this paper we have used a standard two-pathogen epidemic model as a regressor to explain, on a yearly basis, high season ARI data in terms of the contact rates and initial conditions of the mathematical model. The rationale is that ARI high season is a transient regime of a noisy system, e.g., the system is driven away from equilibrium every year by fluctuations in variables such as humidity, temperature, viral mutations and human behavior. Using the value of the replacement number as a phenotypic trait associated to fitness, we provide evidence that influenza and RSV coexists throughout the ARI high season through superinfection.
Towards Uncertainty Quantification and Inference in the stochastic SIR Epidemic Model
Marcos A. Capistrán,J. Andrés Christen,Jorge X. Velasco-Hernández
Statistics , 2011,
Abstract: In this paper we introduce a novel method to conduct inference with models defined through a continuous-time Markov process, and we apply these results to a classical stochastic SIR model as a case study. Using the inverse-size expansion of van Kampen we obtain approximations for first and second moments for the state variables. These approximate moments are in turn matched to the moments of an inputed generic discrete distribution aimed at generating an approximate likelihood that is valid both for low count or high count data. We conduct a full Bayesian inference to estimate epidemic parameters using informative priors. Excellent estimations and predictions are obtained both in a synthetic data scenario and in two Dengue fever case studies.
A Generic Multivariate Distribution for Counting Data
Marcos Capistrán,J. Andrés Christen
Statistics , 2011,
Abstract: Motivated by the need, in some Bayesian likelihood free inference problems, of imputing a multivariate counting distribution based on its vector of means and variance-covariance matrix, we define a generic multivariate discrete distribution. Based on blending the Binomial, Poisson and Negative-Binomial distributions, and using a normal multivariate copula, the required distribution is defined. This distribution tends to the Multivariate Normal for large counts and has an approximate pmf version that is quite simple to evaluate.
Bayesian Analysis of ODE's: solver optimal accuracy and Bayes factors
Marcos Capistrán,J. Andrés Christen,Sophie Donnet
Statistics , 2013,
Abstract: In most relevant cases in the Bayesian analysis of ODE inverse problems, a numerical solver needs to be used. Therefore, we cannot work with the exact theoretical posterior distribution but only with an approximate posterior deriving from the error in the numerical solver. To compare a numerical and the theoretical posterior distributions we propose to use Bayes Factors (BF), considering both of them as models for the data at hand. We prove that the theoretical vs a numerical posterior BF tends to 1, in the same order (of the step size used) as the numerical forward map solver does. For higher order solvers (eg. Runge-Kutta) the Bayes Factor is already nearly 1 for step sizes that would take far less computational effort. Considerable CPU time may be saved by using coarser solvers that nevertheless produce practically error free posteriors. Two examples are presented where nearly 90% CPU time is saved while all inference results are identical to using a solver with a much finer time step.
Estatus micorrízico de Jacaratia mexicana y hongos formadores de micorriza arbuscular presentes en selvas bajas caducifolias del Golfo de México
Zulueta Rodríguez, Ramón;Varela, Lucía;Aguilar Espinosa, Sergio;Trejo Aguilar, Dora;Lara Capistrán, Liliana;
Revista mexicana de micología , 2010,
Abstract: we evaluated the mycorrhizal status of jacaratia mexicana a. dc. and the presence of arbuscular mycorrhizal fungi (amf) in three patches of dry deciduous forests located on the slope of the gulf of mexico. there were no mycorrhizal structures in any of the materials collected in field, and therefore the susceptibility of this specie to amf was determined. the study revealed the presence of arbuscles and vesicles 15 days after inoculation. six morphospecies were identified: glomus intraradices, g. constrictum,g. sinuosum, glomus sp. 1, glomus sp. 2. and entrophospora infrequens. the only related morphospecies in sampled sites were g. intraradices and g. sinuosum, and they were also fairly abundant in veracruz (8, 870 and 5), campeche (958 and 448) and yucatán (3, 708 and 16). all of them have not been reported associated with j. mexicana in our country before.
New method for Gamma/Hadron separation in HAWC using neural networks
T. Capistrán,I. Torres,L. Altamirano,for the HAWC collaboration
Physics , 2015,
Abstract: The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is located at an altitude of 4100 meters in Sierra Negra, Puebla, Mexico. HAWC is an air shower array of 300 water Cherenkov detectors (WCD's), each with 4 photomultiplier tubes (PMTs). Because the observatory is sensitive to air showers produced by cosmic rays and gamma rays, one of the main tasks in the analysis of gamma-ray sources is gamma/hadron separation for the suppression of the cosmic-ray background. Currently, HAWC uses a method called compactness for the separation. This method divides the data into 10 bins that depend on the number of PMTs in each event, and each bin has its own value cut. In this work we present a new method which depends continuously on the number of PMTs in the event instead of binning, and therefore uses a single cut for gamma/hadron separation. The method uses a Feedforward Multilayer Perceptron net (MLP) fed with five characteristics of the air shower to create a single output value. We used simulated cosmic-ray and gamma-ray events to find the optimal cut and then applied the technique to data from the Crab Nebula. This new method is tuned on MC and predicts better gamma/hadron separation than the existing one. Preliminary tests on the Crab data are consistent with such an improvement, but in future work it needs to be compared with the full implementation of compactness with selection criteria tuned for each of the data bins.
Sugarcane Transcript Profiling Assessed by cDNA-AFLP Analysis during the Interaction with Sugarcane Mosaic Virus  [PDF]
Cibele N. F. Medeiros, Marcos C. Gon?alves, Ricardo Harakava, Silvana Creste, Paula M. Nóbile, Luciana R. Pinto, Dilermando Perecin, Marcos G. A. Landell
Advances in Microbiology (AiM) , 2014, DOI: 10.4236/aim.2014.49057
Abstract:

Sugarcane mosaic caused by Sugarcane Mosaic Virus (SCMV) is one of the most important virus diseases of sugarcane. In the present study, changes in the transcription profile obtained by cDNA-AFLP analysis were investigated in two sugarcane varieties contrasting to SCMV resistance, when challenged with a severe virus strain. Healthy plants derived from meristem tip tissue culture were mechanically inoculated under greenhouse controlled conditions and sampled at 24, 48 and 72 hours after inoculation. A total of 392 transcript-derived fragments (TDFs) were verified in the resistant variety against 380 in the susceptible one. The two sugarcane genotypes showed differential behavior in the number of induced and repressed TDFs along the time-course samplings. Ten out of 23 sequenced TDFs (unique from the resistance variety), showed identity with known plant sequences, mostly related to plant defense mechanisms against pathogens. The cDNA-AFLP technique was effective in revealing changes in the transcription profile within and between contrasting varieties when challenged by SCMV.

Stratifying systems over hereditary algebras
Paula A. Cadavid,Eduardo do N. Marcos
Mathematics , 2013,
Abstract: This paper deals with stratifying systems over hereditary algebras. In the case of tame hereditary algebras we obtain a bound for the size of the stratifying systems composed only by regular modules and we conclude that stratifying systems can not be complete. For wild hereditary algebras with more than 2 vertices we show that there exists a complete stratifying system whose elements are regular modules. In the other case, we conclude that there are no stratifing system over them with regular modules. In one example we built all the stratifying systems, with a specific form, having maximal number of regular summads.
Impacto del fracaso de la ventilación no invasiva en el pronóstico de los pacientes: Subanálisis de un estudio multicéntrico Impact of noninvasive ventilation failure upon patient prognosis: Subanalysis of a multicenter study
M. Delgado,A. Marcos,A. Tizón,A. Carrillo
Medicina Intensiva , 2012,
Abstract: Objetivo: La ventilación no invasiva (VNI) constituye la primera línea de tratamiento en las exacerbaciones de la enfermedad pulmonar obstructiva crónica y el edema cardiogénico. Algunos estudios sugieren que el fracaso de la VNI incrementaría el riesgo de mortalidad, principalmente debido al retraso en la intubación. Pretendemos analizar si el fracaso de la VNI se asocia con un peor pronóstico en condiciones de práctica clínica diaria. Pacientes: Subanálisis del estudio de validación multicéntrico Sabadell Score, analizando los pacientes con insuficiencia respiratoria aguda que requieren ventilación mecánica invasiva (VMI) o VNI, tras excluir los pacientes con limitación terapéutica. Variables: Estudio de cohortes prospectivo. Recogimos datos demográficos, tratamientos específicos y complicaciones (fracaso renal agudo e infecciones adquiridas en UCI). Los pacientes se siguieron hasta el alta hospitalaria o muerte. El análisis estadístico incluyó regresión logística múltiple de Cox. Resultados: Analizamos 4.132 pacientes, de los cuales 1.602 (39%) recibieron solo VMI y 529 (13%) VNI. La VNI fue exitosa en el 50%, y el otro 50% requirió intubación, siendo más frecuente en pacientes neurológicos y postoperados. La mortalidad real fue similar a la predicha en los pacientes tratados solo con VMI (27 vs 29%, p=NS), pero inferior en los pacientes tratados con VNI (22 vs 33%, p<0,001), siendo muy inferior a la predicha en el grupo VNI-éxito (12 vs 28%, p<0,001), y solo ligeramente inferior en el grupo VNI-fracaso (32 vs 38%, p=NS). Conclusiones: El fracaso de la VNI y la necesidad de intubación no parecen empeorar el pronóstico de los pacientes. Objective: Noninvasive ventilation (NIV) constitutes first-line treatment for the exacerbation of obstructive pulmonary disease and cardiogenic lung edema. Several studies suggest that NIV failure could increase the risk of mortality, mainly due to the delay in tracheal intubation. We aimed to evaluate the negative impact of NIV failure in routine practice among Spanish ICUs. Patients: A subanalysis was made of the multicenter validation of the Sabadell Score study, extracting patients with acute respiratory failure requiring either invasive or noninvasive mechanical ventilation, with the exclusion of patients presenting "do not resuscitate and/or do not intubate" orders. Variables: We recorded demographic parameters, ICU-specific treatments and the development of acute renal failure or infections during ICU stay. Patients were followed-up on until hospital discharge or death. The statistic analysis included Cox multip
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