Repositorio IPICYT
Not a member yet
1534 research outputs found
Sort by
Richness and abundance of granivorous vertebrates determine acorn removal patterns in a human modified oak forest
Get PDF"Most forests of the Earth have been affected by human activities and this can alter the plant-animal interactions on which depend the functional integrity of these ecosystems. In this study, we assessed the relationships between acorn removal rates and the richness and abundance of granivorous vertebrates along a forest-edge-clearing gradient. We also evaluated whether removal rates differed among oak species with different acorn size. To this purpose, a field experiment was performed including acorns of five oak species, which were exposed to seed consumers in the three different habitats (forest interior, man-made clearings and the edge between these habitats). The experimental units consisted in five paper trays containing 50 acorns of each oak species located at different distances from the edge towards the forest and the man-made clearing (0, 20 and 50 m). Experimental sites were equipped with phototraps to record the identity of the visiting granivorous vertebrates. Richness and abundance of granivores increased from the edge towards the forest interior, while the converse patterns were observed in the man-made clearing. For most oak species, acorn removal patterns was positively correlated with richness and abundances of granivores, though in all habitats small-sized acorns were removed much faster and in larger proportions than big-sized acorns. Although these results are specific for the study site, they suggest that man-made clearings reduce the richness and abundance of granivores, thus negatively affecting the secondary dispersion of zoochoric tree species towards open habitats. Further, it also seems that large-seeded oak species face greater dispersal limitations than small-seeded oaks, because of the lack of animals able to scatter them from the forest to the clearings.
Prueba de irreversibilidad en el análisis de Electrocardiogramas
Get PDF"El desarrollo de métodos para el análisis de señales biomédicas ha sido objeto de estudio en las últimas décadas; en el área de las investigaciones biomédicas hay una necesidad constante por mejores herramientas de diagnóstico. En el presente trabajo se propone analizar electrocardiogramas mediante la producción de entropía en modelos markovianos. El objetivo es exhibir evidencia numérica de la diferencia en producción de entropía promedio entre pacientes sanos y pacientes con arritmia cardíaca. Los electrocardiogramas analizados se obtuvieron de la base de datos PhysioBank. Las secuencias simbólicas se generaron a partir de tres particiones del espacio de estados y dos tiempos de muestreo. Las secuencias simbólicas permitieron calcular la probabilidad estacionaria de los estados, estimar las probabilidades de transición entre los estados y así obtener el modelo markoviano del sistema. La producción de entropía promedio en pacientes sanos y pacientes con arritmia se estimó a partir del modelo markoviano y a partir de un estimador de irreversibilidad empírico. En general, la probabilidad empírica de los estados converge en un tiempo promedio de 15 minutos para los dos grupos de pacientes, a lo que suponemos es el vector de probabilidad estacionario. La probabilidad empírica de los estados, como función del número de datos, presenta mayor fluctuación en los pacientes con arritmia cardíaca que en los pacientes sanos. Respecto a la producción de entropía, los resultados numéricos exhiben una diferencia en la producción de entropía promedio entre los dos grupos de pacientes, teniendo una mayor producción de entropía los pacientes sanos. Los resultados respecto al comportamiento de la producción de entropía, fueron consistentes para los dos enfoques que adoptamos, a saber: el enfoque del modelo markoviano y el enfoque de un estimador de irreversibilidad empírico. En este trabajo se presenta evidencia numérica de que la producción de entropía puede ser una cantidad relevante para distinguir entre electrocardiogramas generados por pacientes con arritmia y aquellos generados por pacientes sanos. Sin embargo, para dar resultados más contundentes, es necesario un estudio más exhaustivo, aumentando la estadística y restringiendo más las condiciones, además de proponer una forma de estadarización de los datos, entre otros.""Recently there has been an important development of the methods employed for the analysis of biomedical data, since there is an increasingly need for better diagnostic tools. In this manuscript, we propose analyze electrocardiograms by usingMarkov models. The purpose is to show numerical evidence in the mean entropy production between healthy patients and patients with cardiac arrhythmia. The analyzed electrocardiograms were obtained from the PhysioBank database. From the time-series we have generated symbolic sequences using three different partitions of the state space and two sampling times, trying to encode the physiological meaning of the data. The symbolic sequences allowed calculating the stationary probability of the states, and estimating the transition probabilities, in this way the markovian model was obtained. The mean entropy production in healthy patients and in patients with arrhythmia was estimated from the inferred markovian model and using an empirical irreversibility estimator. We observed, that, the empirical probability of the states generally converges in an average time of 15 minutes for the two groups of patients. We assume the empirical probability converges to the stationary probability vector. The empirical probability states exhibit greater fluctuations in patients with cardiac arrhythmia than in the healthy ones. Regarding the entropy production, the numerical results show a difference in the mean entropy production between both groups of patients, having a higher entropy production the healthy patients, as expected. The results obtained with the two approaches we adopted, namely: the approach of theMarkovmodel and the empirical irreversibility estimator approach, are consistent. In this thesis we show numerical evidence that entropy production might be a relevant quantity to distinguish between electrocardiograms generated by patients with cardiac arrhythmia and those generated by healthy patients. However, to give more conclusive results, a more comprehensive study is necessary, let say, by increasing the statistics and by further restricting the conditions, proposing a formof standardization for data, among others."CONACY
Dinámica atmosférica en la topografía ondulante de la Curvatura de Monterrey
Get PDF"La circulación sobre una topografía ondulante resulta en flujos complejos condicionados por la forma del terreno provocando procesos locales y cambios en el comportamiento del viento, la temperatura, la humedad, la presión, entre otras variables. La zona conocida como Curvatura de Monterrey, se caracteriza por un conjunto de cuencas orográficas y un marcado gradiente altitudinal que generan un relieve ondulatorio complejo e idóneo para investigar la interacción de diferentes perturbaciones atmosféricas (huracanes, ondas tropicales, frentes fríos y condiciones normales estacionales) con dicha topografía. Los casos analizados fueron: el huracán “Alex” que tuvo lugar del 25 de junio al 2 de julio del 2010 y que de acuerdo con el Servicio Meteorológico Nacional produjo la mayor cantidad de precipitación acumulada (600 mm en 72 horas) sobre la región en más de 50 años. También se eligieron condiciones extremas de frentes fríos (Frente Frío #25 presentado en enero del 2012) y de ondas cálidas (Onda de calor registrada en mayo del 2012). Se presentan resultados obtenidos a través de las simulaciones numéricas realizadas aplicando el modelo WRF. Los datos indicaron que la topografía es un factor inequívoco de cambios en los patrones de viento generando ondulaciones por encima de las cuencas. También se observó que las cuencas almacenan calor. Además, se observó que los eventos extremos generan mecanismos conocidos como: transporte descendente de momento horizontal, canalización forzada, canalización inducida por gradiente de presión y flujos inducidos térmicamente, provocando cambios en las condiciones locales sobre todo en las porciones más altas de los escarpes.""Circulation on an undulating topography results in complex flows conditioned by the
shape of the terrain causing local processes and changes in wind behavior, temperature,
humidity, pressure, among other variables. The area known as Curvatura de Monterrey,
is characterized by a set of orographic basins and a marked altitudinal gradient that
generate a undulatory complex and ideal relief to investigate the interaction of different
atmospheric disturbances (hurricanes, tropical waves, cold fronts and normal seasonal
conditions) with this kind of topography. The cases analyzed were: the hurricane "Alex"
which took place from June 25 to July 2nd, 2010 and which according to the National
Meteorological Service produced the highest amount of accumulated precipitation (600
mm in 72 hours) over the region in more than 50 years. Extreme cold fronts were also
chosen (Cold Front # 25 presented in January 2012) and warm waves (Heat wave
recorded in May 2012). Results obtained through the numerical simulations carried out
by applying the WRF model are presented. The data indicate that the topography is an
unambiguous factor of changes in the wind patterns generating ripples above the basins.
It was also observed that the basins keep heat. In addition, it was observed that extreme
events generate mechanisms known as: horizontal moment descending transport, forced
channeling, channeling induced by pressure gradient and thermally induced flows,
causing changes in local conditions especially in the higher portions of the escarpments.
Isolation and characterization of mercury resistant trichoderma strains from soil with high levels of mercury and its effects on Arabidopsis thaliana mercury uptake
Get PDF"Traditional mining activities are usually correlated with high levels of soil pollution, which is a major environmental concern. Extensive mining activities have taken place in the San Joaquin region in the State of Querétaro, México resulting in high levels of mercury soil pollution (up to 1532 ± 300 mg/kg). We isolated mercury-resistant fungal strains from the San Joaquin region soils and identified them through morphologic characteristics and ITS rDNA region sequence analysis. We determined that fungi isolated belong to the genus Trichoderma. All the isolates selected showed the ability to catalyze the volatilization of Hg. For air sampling, an active sampling device was constructed and using acid KMnO4 as an absorbent, the concentration of mercury in solution was determined through the cold vapor atomic absorption method. The results show mercury volatilization from the fungal species assay, with a maximum of 213.04 ± 32.6 µg/m3 while mycelium accumulation ranged from less than 17.5 ± 2.9 to 20.0 ± 3.4 µg/g. The fungal isolates were also evaluated for their ability to reduce mercury uptake in Arabidopsis thaliana. These observations suggest the utility of Trichoderma for the mobilization of mercury in those contaminated soils.
Stabilisation of small mono- and bimetallic gold–silver nanoparticles using calix[8]arene derivatives
No full text"In this paper, we report the synthesis of octa(hydroxy)-octa(mercaptobutoxy)calix[8]arene and its use as a stabiliser of nanoparticles (NPs). We show that the reduction of gold and/or silver ions in the presence of this calix[8]arene in ethanolic solutions leads to the formation of very small spherical nanoparticles (NPs) that are homogeneous in size. Confinement and cooperative effects due to the macrocyclic structure of the calix[8]arenes account for the obtained small sizes and the homogeneity. In the case of the simultaneous reduction of gold and silver ions, STEM-EDX mappings provide evidence of the formation of alloyed Au-Ag NPs stabilised by calix[8]arenes. The surface accessibility and potential catalytic applications of the NPs are tested using the reduction of 4-nitrothiophenol by NaBH4 as a model reaction.
Tuning the dedoping process of PEDOT:PSS films using DBU-solvent complexes
Get PDF"In this study, we report a successful simple technique to dedope pristine PEDOT:PSS films at room temperature by dipping the films into 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) mixes with different solvents such as dimethyl sulfoxide (DMSO), acetonitrile (MeCN) and deionized (DI) water. The treated PEDOT:PSS films presented a strong ?-?* absorption band centered at 630?nm, which indicated that the PEDOT chains were being reduced to their neutral state. The dedoping efficiency of the PEDOT chains depended on the used DBU complex, the DBU concentration in the mixture as well as the immersion time, which was quantified comparing the relative intensities between the ?-?* and the polaronic (centered around 900?nm) bands. The best dedoping efficiencies of PEDOT:PSS films were obtained using MeCN/DBU or DI water/DBU complexes, as the polaronic band almost disappeared, whereas using DMSO/DBU complex the polaronic band was always present. This difference was mainly related to the degree of basicity of the DBU complexes and solubility extent of PEDOT:PSS in the various solvents. Finally, thick dedoped PEDOT:PSS films showed a strong yellow emission when they were excited with a 488?nm laser. The encapsulated dedoped thick films endured up to 50?mW of laser power without impacting their luminescent and physical properties.
Robust fringe pattern analysis method for transient phenomena
Get PDF"We propose a method for analysing a sequence of noisy interferograms with closed fringes acquired at a high–speed frame rate. Our method is appropriate for analysing ESPI sequences of transient phenomena such as deformations caused by vibrations. Firstly, we compute a differential phase between frames using a procedure based on a Gabor filter bank. We then refine this initial phase with a regularised quadratic cost function that keeps the consistency of the restored phase with the fringe patterns. In addition, we also present the robust version of our phase refining method. This prevents the introduction of phase deformations by the smoothing process. We demonstrate by means of numerical and real–data experiments that our method is appropriate for analysing ESPI sequences of transient phenomena.
Analysis of a class of complex system without equilibria via switched control law
Get PDF"In this article we introduce a new class of complex system without equilibria which exhibits a chaotic multiscroll attractor in each node. The number of scrolls in the attractor is determined by a switched control law to allow the operation of different linear affine systems. Thus, the system is composed of many subsystems which interact with each other to generate a multiscroll attractor. This new class of piecewise linear (PWL) system presents no positive real part in the eigenvalues of the Jacobian matrix as opposed to the reported systems with multiscrolls. The scrolls present a complex behavior since these don’t unwrap and don’t appear close to an unstable manifold of a saddle-focus equilibrium point. A particular case is taken as case study and simulation plots of the attractor are provided.
Validación experimental analógica de un atractor multienroscado en 1-D generado por un sistema lineal conmutado
Get PDF"En este artículo se presenta la implementación física de un atractor caótico multienroscado en una dirección (1-D) basado en un sistema lineal conmutado (SLC). A partir de este SLC se lleva a cabo una síntesis de circuitos para obtener un circuito electrónico analógico basado en amplificadores operacionales. Las variables de estado se obtienen midiendo el voltaje de la solución analógica del sistema implementado experimentalmente. Las pruebas experimentales se comparan contra la simulación numérica y la del circuito implementado. El circuito electrónico es simple, utiliza componentes comerciales y puede ser construido por cualquier estudiante a nivel licenciatura.
Magnetite nanoparticles as adsorbent material for Cu2+ ions from aqueous solution
Get PDF"Cu2+ ions can cause serious injuries to human health, at both high and low concentrations. Therefore, it is important not only to remove Cu2+ ions from aqueous media, but also to develop analytical methods for their accurate determination at low concentrations. Magnetite is one of the most used sorbents for Cu2+ removal. This work aims at synthesizing magnetite nanoparticles and at evaluating their adsorption capacity toward Cu2+ ions in aqueous solution by means of atomic absorption spectroscopy. Magnetite nanoparticles were characterized by means of a vibrational magnetometer, Fourier transformer infrared spectrum (FTIR), x-ray diffraction (XRD) and Thermal gravimetric analysis (TGA). Magnetic nanoparticles showed Ms values of 52 and 62 emu/g. By taking into consideration the precipitation of Cu(OH)2 as a function of pH in the evaluation of the adsorption capacity of magnetite, we found that the maximum Cu2+ adsorption occurs at pH = 7 and that the adsorption equilibrium of the two samples is reached at 490 and 445 min. The use of blank solution avoids the overestimation of the adsorption capacity due to the presence of insoluble Cu(OH)2. Finally, two models are considered as a liquid/solid phase reaction, pseudo-first- and pseudo-second-order reaction. Batch adsorption kinetics agrees with a pseudo-second-order model, suggesting that chemisorption is the rate-limiting step.