Papers by David Hernández
Marine Pollution Bulletin, 2014
1] Enterococci are the U.S. Environmental Protection Agency recommended fecal indicator bacteria ... more 1] Enterococci are the U.S. Environmental Protection Agency recommended fecal indicator bacteria for assessing recreational marine water quality. Traditional methods of enterococci analyses are time consuming, resulting in delays in issuing beach closures. Models can potentially circumvent these delays by forecasting times when beaches should be closed. The objective of this study is to develop an innovative coupled microbehydrodynamic-morphological model. The unique feature of this model is its capability of simulating the release of microbes attached to coastal beach sands as a result of combined wave and tidal forcing. A nearshore process model (XBeach) was coupled with a microbe transport-decay equation. This equation included source functions that accounted for microbial release from mobilized sand, groundwater flow, entrainment through pore water diffusion, rainfall-runoff loading, and a fate function that accounted for solar inactivation effects. The model successfully simulated observed spatial and temporal patterns of enterococci in the beach water, including the reproduction of diel and tidal fluctuations and the rapid decrease of enterococci levels from the waterline to offshore. Primary processes for enterococci loading to the water column included wave-induced sediment resuspension and tidal washing for the entrainment of enterococci from the pore water in the intertidal zone. Diffusion was the major mechanism to transport enterococci from the intertidal zone to offshore. Sunlight inactivation was a key process to reduce enterococci levels during the day and to produce the diurnal cycles. Rainfall runoff was found to be an intermittent source of enterococci to beach water, whereas groundwater exchange was of secondary importance. Sensitivity analyses suggested that the processes and coefficients related to enterococci loading have quasi-linear characteristics, whereas model results of enterococci levels were sensitive to both diffusion and sunlight inactivation coefficients, showing high nonlinearity and spatial and temporal dependence. Citation: Feng, Z., A. Reniers, B. K. Haus, and H. M. Solo-Gabriele (2013), Modeling sediment-related enterococci loading, transport, and inactivation at an embayed nonpoint source beach, Water Resour. Res., 49,
El método Sondeo Eléctrico Vertical (SEV), conocido desde 1912, ha cambiado sustancialmente duran... more El método Sondeo Eléctrico Vertical (SEV), conocido desde 1912, ha cambiado sustancialmente durante los últimos 10 años, apareciendo una nueva tecnología llamada Imagen de Resistividad (IR) con interpretación 2D de los datos de resistividad. Otra vía posible de desarrollo del método SEV es, partiendo de las relaciones existentes entre la resistividad eléctrica y los parámetros petrofísicos (PP), estimar estos últimos a partir de datos de IR. Para la realización práctica de este concepto fue desarrollada la teoría del problema directo e inverso que relaciona la resistividad eléctrica con los PP. Cada trabajo de campo deberá incluir un levantamiento de SEV (IR), mediciones de resistividad eléctrica del agua subterránea con el objetivo de determinar su salinidad y la recolección de algunas muestras representativas de suelo del sitio con mediciones hechas en laboratorio de la resistividad eléctrica como función de la salinidad del agua de poro, creando el modelo petrofísico del suelo de este sitio. Esta tecnología puede ser utilizada tanto para la caracterización de sitios limpios como contaminados por hidrocarburos. Para el caso de sitios contaminados, los valores de los PP determinados en laboratorio, salinidad de agua y los datos de IR, permiten establecer la frontera petrofísica entre suelo limpio y contaminado, y por consiguiente, configurar la pluma contaminante. En este trabajo se incluyen, como ejemplos prácticos, los resultados de la aplicación de esta tecnología en algunos sitios contaminados por hidrocarburos en México.
Contemporary Sociology, 2003
Page 1. 418 Review Essays Ethnic Prophecies: A Review Essay DAVID MANUEL HERNANDEZ University of ... more Page 1. 418 Review Essays Ethnic Prophecies: A Review Essay DAVID MANUEL HERNANDEZ University of California-Berkeley hernandz@uclink4 berkeley.edu EVELYN NAKANO GLENN University of California-Berkeley englenn 'socrates. berkeley. edu ...
American Quarterly, 2002
... musings on Los Angeles have given short shrift to the Latino contributions to El Pueblo de Nu... more ... musings on Los Angeles have given short shrift to the Latino contributions to El Pueblo de Nuestra Señora la Reina de los ... barrio or Oakland's current Fruitvale community); 2) polycentric barrios (such as Chicago's Pilsen, Little Village, Humboldt Park, and Logan Square); 3 ...
American Quarterly, 1999
... More self-reflexive and engaging than other authors, Castañeda's maturity-immaturity bin... more ... More self-reflexive and engaging than other authors, Castañeda's maturity-immaturity binary, however, dangerously parallels class theories of machismo and ... Dagoberto Gilb and Juan Felipe Herrera offer examples of thickly shelled and thinly articulated senses of male self. ...
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Papers by David Hernández