Quantitative Analysis of Arterial Spin Labeling FMRI Data Using a General Linear Model

Arterial spin labeling techniques can yield quantitative measures of perfusion by fitting a kinetic model to difference images (tagged-control). Because of the noisy nature of the difference images investigators typically average a large number of tagged versus control difference measurements over long periods of time. This averaging requires that the perfusion signal be at a steady state and not at the transitions between active and baseline states in order to quantitatively estimate activation induced perfusion. This can be an impediment for functional magnetic resonance imaging task experiments. In this work, we introduce a general linear model (GLM) that specifies Blood Oxygenation Level Dependent (BOLD) effects and arterial spin labeling modulation effects and translate them into meaningful, quantitative measures of perfusion by using standard tracer kinetic models. We show that there is a strong association between the perfusion values using our GLM method and the traditional subtraction method, but that our GLM method is more robust to noise

Formulación e implantación de modelos de daño para la simulación de la evolución al colapso en sólidos

83 páginas. Maestría en Ingeniería Estructural.La mecánica de daño es una herramienta atractiva para describir el deterioro progresivo de las propiedades mecánicas de los materiales. Estudia a nivel microscópico la degradación de un material cuando se somete a distintas cargas y efectos en el tiempo. Existen cuatro aproximaciones para describir la degradación en materiales como son: agrietamiento distribuido, mecánica de fractura, discontinuidad de interiores y la mecánica de daño. En esta investigación se realizaron dos tipos de algoritmos matemáticos basados en la mecánica de daño para la simulación numérica de sólidos que fallan en esfuerzos de sólo tensión y de sólo cortante, respectivamente. La formulación de estos dos se fundamenta en el modelo de daño isotrópico con umbral de falla de igual tensión-compresión y considerando algunas propuestas realizadas por otros autores. Se realizan, para un entendimiento sencillo del daño, formulaciones uniaxiales las cuales se extienden, por medio de algebra y cálculo tensorial, en modelos de daño bidimensionales y tridimensionales.Finalmente se hace la validación de estos dos modelos de daño propuestos mediante ejemplos de aplicación que constan de resultados experimentales y numéricos reportados en la literatura.Consejo Nacional de Ciencia y Tecnología (México)

DE CONVENTO DE SAN FRANCISCO A PORTALES DE TOLUCA. ANÁLISIS SOCIOHISTÓRICO DEL LUGAR

La creación de edificios depende de dos rubros importantes: la construcción y la edificación. Lo invisible soporta lo visible, sin las historias y narrativas de la sociedad no sería posible la generación de referentes urbanos. Con esta inferencia se generó un análisis sociohistórico del Convento de San Francisco y su transformación en los Portales de Toluca, observando los comportamientos sociales e históricos que confluyeron en un lugar durante los siglos XVI al XX, entendiendo al lugar como ese espacio con una alta densidad espacio-tiempo, el espacio en donde se gesta la intensidad del ser

Patterns, localized structures and fronts in a reduced model of clonal plant growth

A simplified model of clonal plant growth is formulated, motivated by observations of spatial structures in Posidonia oceanica meadows in the Mediterranean Sea. Two levels of approximation are considered for the scale-dependent feedback terms. Both take into account mortality and clonal, or vegetative, growth as well as competition and facilitation, but the first version is nonlocal in space while the second is local. Study of the two versions of the model in the one-dimensional case reveals that both cases exhibit qualitatively similar behavior (but quantitative differences) and describe the competition between three spatially extended states, the bare soil state, the populated state, and a pattern state, and the associated spatially localized structures. The latter are of two types, holes in the populated state and vegetation patches on bare ground, and are organized within distinct snaking bifurcation diagrams. Fronts between the three extended states are studied and a transition between pushed and pulled fronts identified. Numerical simulations in one spatial dimension are used to determine front speeds and confront the predictions from the marginal stability condition for pulled fronts.Comment: 14 pages, 18 figures. To appear in Physica

Numerical and experimental characterization of the hydrodynamics and drying kinetics of a barbotine slurry spray

Spray drying is a basic unit operation in several process industries such as food, pharmaceutical, ceramic, and others. In this work, a Eulerian-Lagrangian three-phase simulation is presented to study the drying process of barbotine slurry droplets for the production of ceramic tiles. To this end, the simulated velocity field produced by a spray nozzle located at the Institute of Ceramic Technology in Castelló (Spain) is benchmarked against measurements obtained by means of laser Doppler anemometry in order to validate the numerical model. Also, the droplet size distribution generated by the nozzle is obtained at operating conditions by means of laser diffraction and the data obtained are compared qualitatively to those found in the literature. The characteristic Rosin-Rammler droplet size from the distribution is introduced thereafter in the three-phase simulation to analyse the drying kinetics of individual droplets. The model predicts the theoretical linear evolution of the square diameter (D2-law), and the temperature and mass exchange with the environment. The proposed model is intended to support the design and optimization of industrial spray dryers

Effect of Chitosan Edible Coating on the Biochemical and Physical Characteristics of Carp Fillet (Cyprinus carpio) Stored at −18ºC.

The effect of an edible coating (EC) with 1.5% chitosan as an additive, on common carp (Cyprinus carpio) fillet, was determined evaluating the biochemical, physicochemical, textural, microbiological, and nutritional characteristics periodically during its hydroperoxides content (HPC) (0.8324 nM hydroperoxides/mg of protein versus 0.5540 nM/mg with regard to the EC sample), as well as protein carbonyl content (PCC) (0.5860 nM versus 0.4743 nM of reactive carbonyl groups/mg of protein of noncoated material), keeping properties for a longer period of time, and a lower protein solubility (7.8 mg of supernatant protein/mg of total microbialgrowth,thecountwas2.2×10 CFU/gofsampleinmesophilesversus4.7×10 intheECsample.Theresultsindicatethat the use of EC added with chitosan maintains the quality of the product regarding lipid and protein oxidation until fourth month of storage, maintaining moisture content without variation for at least 3 months, and inhibits microbial growth up to 2 logarithmic units, during five months of frozen storage

Consumo de agua subterránea en Guanajuato, México

El problema de sobreexplotación de acuíferos en México se agudiza debido a la baja eficiencia en el uso del recurso y a la contaminación de las fuentes de abastecimiento. La situación del estado de Guanajuato es grave y requiere alternativas de solución que pueden darse mediante recomendaciones de política que contribuyan a hacer más eficiente y racional el uso del vital líquido. En este trabajo se determinaron los factores que afectan el consumo de agua en los sectores urbano, pecuario, agrícola de riego e industrial del estado, para lo cual se estimó un modelo de ecuaciones simultáneas compuesto de cuatro ecuaciones de demanda y cuatro identidades para el período 1980-2004. El análisis de los resultados muestra que la cantidad consumida de agua responde de manera inelástica a cambios en el precio, con elasticidades de -0.0150 para el sector urbano, -0.0038 para el pecuario, -0.052 para la agricultura de riego (se utilizó la cuota de mantenimiento de la infraestructura del Distrito de Riego más el efecto del costo de la energía eléctrica para uso agrícola, ya que el agua es gratuita) y -0.126 para el sector industrial. Estas elasticidades indican que el consumo de agua en los sectores urbano y pecuario es más insensible a cambios en el precio, que en el industrial y agrícola de riego. Por tanto, las políticas de administración del consumo deberán considerar aumentos en estos sectores, pues se puede reducir en 1 % la cantidad consumida de la industria y la agricultura de riego aumentando el precio del agua en 7.93 y 19.2 %

Effects of types and doses of yeast on gas production and in vitro digestibility of diets containing maize (Zea mays) and lucerne (Medicago sativa) or oat hay

Two yeast products formulated with Saccharomyces cerevisiae were evaluated at the same colonyforming units (CFUs) per gram of substrate. Samples of maize, lucerne and oat hays were mixed (0.5 kg) to a proportion of 80% forage (lucerne or oat) with 20% maize (DM basis) and combined with each yeast to obtain 1.5 x 107 or 3.0 x 107 CFU/g DM. There was also a control without yeast. In vitro gas production was measured at 0, 2, 4, 6, 8, 10, 14, 18, 24, 30, 36, 42, 48, 60, and 72 h incubation. There was no forage/yeast interaction. Both yeast products tended to reduce the maximum volume produced quadratically and lag time linearly, while in vitro dry matter digestibility (IVDMD) increased linearly. Ruminal ammonia N and lactic acid were not affected, whereas methane and carbon dioxide tended to be reduced with the intermediate dose of yeast. When the mixture included oat hay, the total volume of gas increased, the lag time decreased, and there was higher IVDMD than in the lucerne-based mixtures, which were associated with lower methane production. Ammonia and lactic acid remained unchanged. The two yeast products showed the same effects on the dynamics of gas production and in vitro digestibility when dosed at the same number of viable cells or CFUs, and there was no interaction with forage quality