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Effects of Velocity Gradients and Secondary Flow on the Dispersion of Solutes in a Meandering Channel
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Application of the transient storage model to analyze advective hyporheic exchange with deep and shallow sediment beds
No full textHydrodynamics of vertical subsurface flow constructed wetlands: Tracer tests with rhodamine WT and numerical modelling
No full textTypical unsteady unsaturated conditions can profoundly affect the hydrodynamics of vertical subsurface flow constructed wetlands. In this study we analyzed the hydrodynamics of a 33 m(2) vertical flow pilot plant, treating municipal secondary effluents. Three different saturation conditions were analyzed under several constant flux regimes: complete saturation, partial saturation with the free water table 20 cm over the bottom of the bed, and complete drainage. Tracer tests were performed in steady state conditions by dosing rhodamine WT as square input signals. Breakthrough curves were analyzed by means of both a classical residence time distribution analysis and an originally developed numerical plug-flow model with longitudinal dispersion adapted to the unsaturated conditions. We found that the degree of global mixing in the vertical flow constructed wetland increased as the water content increased; this effect was controlled by the hydraulic residence time of the system. Conversely, the degree of local mixing was inversely affected by water content; the dispersivity was 4.5, 10, and 14 cm for fully saturated, partially saturated and draining conditions, respectively. We explain the dependency of dispersivity on water content in physical terms; however, further studies are needed to mathematically include this relationship in numerical models that describe the behaviour of vertical flow constructed wetlands. (C) 2008 Elsevier B.V. All rights reserved
Grade 3 anal intraepithelial neoplasia in an HIV-infected african girl
No full textWomen with HIV infection are at increased risk of anogenital dysplasia and cancer, related to human papillomavirus infection. These neoplasms are rare in perinatally HIV-infected girls before onset of sexual activity. We report a case of high-grade anal dysplasia in a 10-year-old African girl with untreated perinatal HIV infection
Hysteresis in streamflow-water table relation provides a new classification system of rainfall-runoff events
Full text linkRainfall-runoff event types can be used to better understand the hydrological functioning of catchments. In this study, we propose a framework to characterize and classify runoff events relying on the hysteresis analysis of the relation between streamflow (independent variable) and depth to water table (dependent variable). We evaluated hysteresis for 112 rainfall-runoff events occurred in the period 2012-2016 in a small forested catchment in the Italian Pre-Alps. Three main groups of rainfall-runoff events were identified, each associated with specific hydro-meteorological characteristics of the events. A first group, identified by a faster response of streamflow compared to the groundwater level (which led to a clockwise hysteretic loop), was characterized by dry antecedent conditions, short rainfall events, low streamflow peaks and small runoff coefficients. A second group had characteristics similar to the first group, that is, faster response of streamflow compared to the groundwater level (clockwise hysteretic loop), but on average displayed a narrower hysteretic loop. A third group, identified by a faster response of the groundwater level compared to streamflow (which led to an anti-clockwise loop), was characterized by wet antecedent conditions, long rainfall events, high streamflow peaks and large runoff coefficients. Results showed statistically significant differences among the groups, corroborated by an analysis based on environmental tracers (H-2 and electrical conductivity). This study shows how the analysis of the hysteretic relation between streamflow and depth to water table can be used for grouping rainfall-runoff events and to better identify the catchment's hydrological response to rainfall inputs
Nanoscale supramolecular probes for the naked-eye detection of illicit drugs
Full text linkThe identification of psychoactive substances, in particular of designer drugs, on the site of their discovery is crucial to contrast the diffusion of drugs of abuse. We report here the first example of a nanoscale colorimetric probe, based on the nanoconfinement of a tricyclic dye and the target analytes in the cavity of cucurbit[8]uril. The probe selectively responds to N-(2methoxybenzyl)phenethylamines, with a limit of detection of 3 μM. The sensing system can be deposited on paper, thus obtaining a colorimetric strip test capable of discriminating illegal drugs from other substances of common use
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