Granular flow through an aperture: Influence of obstacles near the outlet.

We study how the presence of obstacles in a confined system of monodisperse disks affects their discharge through an aperture. The disks are driven by a horizontal conveyor belt that moves at constant velocity. The mean packing fraction at the outlet decreases as the distance between the obstacles and the aperture decreases. The obstacles organize the dynamics of the stagnant zones in two characteristic behaviors that differ mainly in the magnitude of the fluctuations of the fraction of stagnant disks in the system. It is shown that the effective aperture is reduced by the presence of obstacles.

Suspension flow: do particles act as mixers?

Recently, Roht et al. [J. Contam. Hydrol., 2013, 145, 10-16] observed that the presence of suspended non-Brownian macroscopic particles decreased the dispersivity of a passive solute, for a pressure-driven flow in a narrow parallel-plate channel at low Reynolds numbers. This result contradicts the idea that the streamline distortion caused by the random diffusive motion of the particles increases the dispersion and mixing of the solute. Therefore, to estimate the influence of this motion on the dispersivity of the solute, and investigate the origin of the reported decrease, we experimentally studied the probability density function (pdf) of the particle velocities, and spatio-temporal correlations, in the same experimental configuration. We observed that, as the mean suspension velocity exceeds a critical value, the pdf of the streamwise velocity of the particles markedly changes from a symmetric distribution to an asymmetric one strongly skewed to high velocities and with a peak of the most probable velocity close to the maximum velocity. The latter observations and the analysis of the suspension microstructure indicate that the observed decrease in the dispersivity of the solute is due to particle migration to the mid-plane of the channel, and consequent flattening of the velocity profile. Moreover, we estimated the contribution of particle diffusive motion to the solute dispersivity to be three orders of magnitude smaller than the reported decrease, and thus negligible. Solute dispersion is then much more affected by how particles modify the flow velocity profile across the channel than by their random diffusive motion.

Granular flow through an aperture: influence of the packing fraction.

For the last 50 years, the flow of a granular material through an aperture has been intensely studied in gravity-driven vertical systems (e.g., silos and hoppers). Nevertheless, in many industrial applications, grains are horizontally transported at constant velocity, lying on conveyor belts or floating on the surface of flowing liquids. Unlike fluid flows, that are controlled by the pressure, granular flow is not sensitive to the local pressure but rather to the local velocity of the grains at the outlet. We can also expect the flow rate to depend on the local density of the grains. Indeed, vertical systems are packed in dense configurations by gravity, but, in contrast, in horizontal systems the density can take a large range of values, potentially very small, which may significantly alter the flow rate. In the present article, we study, for different initial packing fractions, the discharge through an orifice of monodisperse grains driven at constant velocity by a horizontal conveyor belt. We report how, during the discharge, the packing fraction is modified by the presence of the outlet, and we analyze how changes in the packing fraction induce variations in the flow rate. We observe that variations of packing fraction do not affect the velocity of the grains at the outlet, and, therefore, we establish that flow-rate variations are directly related to changes in the packing fraction.

Flow of a thin liquid film coating a horizontal stationary cylinder.

An experimental and theoretical study of the flow of liquid films around a stationary horizontal cylinder is reported. The film presents two different behaviors: The flow is stable in the upper zone (up to ∼150° with the vertical) and Rayleigh-Taylor-like instabilities appear in the lower zone. For the stable region, film thickness evolution could be described by numerically integrating an evolution equation obtained using a lubrication approximation. For the unstable region, a linear stability analysis allows us to determine the maximum growth wavelength for the Rayleigh-Taylor instability. Approximate analytical solutions were obtained for generatrices at an angle with the vertical θ=0 (stable region) and θ=π (where the instability appears).

Pressure independence of granular flow through an aperture.

We experimentally demonstrate that the flow rate of granular material through an aperture is controlled by the exit velocity imposed on the particles and not by the pressure at the base, contrary to what is often assumed in previous work. This result is achieved by studying the discharge process of a dense packing of monosized disks through an orifice. The flow is driven by a conveyor belt. This two-dimensional horizontal setup allows us to independently control the velocity at which the disks escape the horizontal silo and the pressure in the vicinity of the aperture. The flow rate is found to be proportional to the belt velocity, independent of the amount of disks in the container and, thus, independent of the pressure in the outlet region. In addition, this specific configuration makes it possible to get information on the system dynamics from a single image of the disks that rest on the conveyor belt after the discharge.

Rearrangements in a two-dimensional packing of disks.

Several aspects of the dynamics of a granular two-dimensional (2D) packing of disks slowly tilted until the system loses stability and an avalanche takes place are discussed. The evolution of the system, constructed with monodisperse disks placed on a thin cell, is studied by image analysis. As in the 3D case (packing of spheres), the system undergoes several rearrangements of different magnitude before the avalanche takes place. For thick systems, not only are small rearrangements detected but also displacements of large clusters of disks are observed in the bulk and on the free surface of the packing. In particular, characteristic angles and the avalanche mass were determined for samples of different heights. On thick systems, velocity fields of large rearrangements are presented and changes in the internal structure of the packing produced by these rearrangements are analyzed. It is found that the main effects of rearrangements is to increase the disorder of the system. Also, as the disorder of the system increases its stability threshold decreases.

Instabilities in slowly driven granular packing.

In this work, a digital imaging technique is used to study the superficial fluctuations observed when a granular packing is slowly driven to the threshold of instability. The experimental results show the presence of three types of events. Small superficial rearrangements of grains are observed during all the experiments. They present a power-law behavior although the system is not in a critical state as predicted by self-organized criticality models. In thick granular piles, large rearrangements are detected at regular angular intervals. They are related to the threshold of instability of the contact network that relaxes to stable configurations producing internal rearrangements of the grains. Finally, an avalanche is triggered when the superficial beads that are set in motion acquire enough momentum to destabilize grains from layers below.

Tratamiento del aneurisma poplíteo mediante prótesis intraluminal colocada por vía percutánea: reporte de un caso / Popliteal aneurysms: percutaneous endo-graft stenting

Los aneurismas poplíteos son infrecuentes, pero tienen una alta tendencia a complicaciones potencialmente catastróficas. La recomendación prácticamente universal de repararlos electivamente se ha facilitado recientemente con la colocación percutánea de injertos/stents vasculares, como una forma de terapia alternativa a la cirugía tradicional para casos seleccionados. Presentamos un caso de un aneurisma poplíteo gigante, tratado exitosamente por esta vía mínimamente invasiva

[Biomass and density of 2 seagrass species in southern Quintana Roo, Mexico]. / Biomasa y densidad de dos especies de pastos marinos en el sur de Quintana Roo, México.

The biomass and productivity of a seagrass community are useful for determining the ecological status of the coast. Leaf biomass and shoot density in beds of Thalassia testudinum Banks & Sol. ex K. D. Koenig, were compared for two environments in the Mexican Caribbean coast (N = 6 quadrants/site) in November 1998. Shoot and leaf biomass values were lower in the mangrove-associated meadow than in the reef lagoon meadow. This could be related to the higher percentage of epiphytes on the leaves. In addition, T. testudinum had more biomass than Syringodium filiforme Kütz in the reef lagoon.

Ethnic differences in insulin resistance and its consequences in older Mexican American and non-Hispanic white women.

BACKGROUND: This study was initiated to test the hypothesis that older, healthy, nondiabetic Mexican American women would be relatively resistant to insulin-mediated glucose disposal, hyperinsulinemic, and dyslipidemic as compared to a matched group of non-Hispanic White (NHW) women. METHODS: The study, cross-sectional in nature, involved 14 Mexican American and 19 NHW healthy, normotensive nondiabetic, postmenopausal women of similar age and body mass index. It took place in the General Clinical Research Center at Stanford Medical Center. Measurements were made of fasting plasma glucose, insulin and lipid concentrations, and plasma glucose and insulin concentrations following a 75 gram oral glucose challenge. Resistance to insulin-mediated glucose disposal was estimated by the steady-state plasma glucose (SSPG) concentration achieved at the end of a 3-hour constant infusion of glucose, insulin, and somatostatin. RESULTS: Mexican American women had significantly greater glucose (p < .001) and insulin (p < .001) responses to the oral glucose challenge than did the NHW women. Resistance to insulin-mediated glucose disposal was increased in Mexican American women (SSPG 195 +/- 25 mg/dl compared to 137 +/- 18 mg/dl in NHW; p < .001). While total cholesterol, low density lipoprotein (LDL)-cholesterol, and triglyceride concentrations were not significantly different in the two ethnic groups, high density lipoprotein (HDL)-cholesterol was significantly lower in the Mexican American women (51 mg/dl vs 61 mg/dl; p = .04). CONCLUSION: Older Mexican American women are more insulin resistant, glucose intolerant, and hyperinsulinemic, and have a lower HDL-cholesterol than a matched group of non-Hispanic White peers. These results were observed despite the exclusion of individuals with non-insulin dependent diabetes mellitus (NIDDM).

Diabetes mellitus e intolerancia a la glucosa en hipertensos. Hospital de Villarrica. / Diabetes mellitus and glucose intolerance in hypertensive patients. Hospital of Villarrica

Se analizan los resultados de las glicemias en ayunas y postingesta de 75 gramos de glucosa a los 120 minutos en 199 hipertensos del Hospital de Villarrica. Se precisan algunas caracteristicas del grupo estudiado como presencia de obesidad, tipo de hipertension, antecedentes hereditarios de diabetes, existencia de glicemia previas, ruralidad.Se encuentran once pacientes diabeticos y nueve con intolerancia a la glucosa, segun criterios diagnosticos propuestos por el DATA Group.Se destaca el factor obesidad en los casos de diabetes e intolerancia a la glucosa. Se enfatiza la necesidad de efectuar pesquisa de diabetes en los hipertensos, especialmente obesos entre los cincuenta y setenta anos

Tuberculosis infantil en Arica. / Infantile tuberculosis in Arica

Se analizaron 68 ninos tuberculosos controlados en la Unidad Broncopulmonar Infantil del Hospital Dr. Juan Noe, de Arica, entre el 1o.de enero y el 31 de diciembre de 1979. Se valoran aspectos epidemiologicos, clinicos, radiologicos y bacteriologicos. Se deduce la relevancia que reviste la TBC en la poblacion rural aymara y la conveniencia de mejorar el cumplimiento del programa de vacunacion BCG y el control con prueba de tuberculina

[Nutrition surveys in children attending kindergartens in the city of Cordoba]. / Encuesta nutricional realizada en niños concurrentes a jardines de niños de la ciudad de Córdoba.

A nutritional inquest was carried out in 1857 children attending kindergartens in Córdoba, Argentina, in 1974. Determinations were made for the socioeconomical level each child belonged (NES) and clinical and anthropometric examinations. Nutritional inquests were carried out in 414 of these children, psychological examinations in 51, and biochemical inquests in 61 children.