2,849 research outputs found
Arsenic speciation in plants by HPLC-(UV)-HG-AFS: Optimisation of the extraction method and application to native plant species from soils polluted by mining activities
Se ha optimizado el método de extracción de especies de arsénico hidrosolubles en muestras de plantas terrestres procedentes de suelos contaminados por actividad minera. La especies extraÃdas se han determinado mediante HPLC-(UV)-HG-AFS
Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices
We examine how the current--voltage characteristics of a doped weakly coupled
superlattice depends on temperature. The drift velocity of a discrete drift
model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated
as a function of temperature. Numerical simulations and theoretical arguments
show that increasing temperature favors the appearance of current
self-oscillations at the expense of static electric field domain formation. Our
findings agree with available experimental evidence.Comment: 7 pages, 5 figure
Application of ultrasound probe sonication for arsenic and heavy metal extraction in soils
Se ha optimizado un método de extracción de arsénico y metales pesados en suelos contaminados procedentes de actividad minera, mediante la aplicación de la sonda de ultrasonidos focalizada
Arsenic and heavy metal uptake and accumulation in native plant species from soils polluted by mining activities
Arsenic and heavy metal (specifically Cd, Cr, Cu, Ni, Pb, and Zn) uptake, translocation, and accumulation in ten native plant species spontaneously growing in soils polluted by mining activities were studied, with a focus on future phytoremediation work in polluted soils. Plant and soil samples were collected in the vicinity of the Mónica mine (NW Madrid, Spain). Soil analysis showed the ability of native plants for growing in soils with high concentration levels of Cd, Cu, Pb, Zn, and especially As. From these elements, the highest percentage of extractable elements was found for Cd and the lowest for Pb. A highly significant correlation was observed between total and extractable element concentrations in soils, except for Cu, indicating that total concentration is the most relevant factor for element mobility in these soils. Extractable elements in soils were better correlated with concentrations in plants than total elements in soils; thus, extraction methods applied are suitable to estimate the element phytoavailable fraction in soils, which depends on the plant species and not only on the element mobility in soils. High element concentrations were found in the aboveground parts of Corrigiola telephiifolia (As and Pb), Jasione montana (Cd and Zn), and Digitalis thapsi (As, Cd, Cu, Pb and Zn). However, considering the translocation and accumulation factors, together with the concentration levels found in roots and aboveground parts, only C. telephiifolia could be considered a Pb accumulator and an As hyperaccumulator plant, which could be used for future phytoremediation work in soils polluted with As
Quasiperiodic time dependent current in driven superlattices: distorted Poincare maps and strange attractors
Intriguing routes to chaos have been experimentally observed in semiconductor
superlattices driven by an ac field. In this work, a theoretical model of time
dependent transport in ac driven superlattices is numerically solved. In
agreement with experiments, distorted Poincare maps in the quasiperiodic regime
are found. They indicate the appearance of very complex attractors and routes
to chaos as the amplitude of the AC signal increases. Distorted maps are caused
by the discrete well-to-well jump motion of a domain wall during spiky
high-frequency self-sustained oscillations of the current.Comment: 10 pages, 4 figure
A Distributed Solution to Synchronous Multiparty Interaction
Multiparty interactions are the key to describe problems where three or more processes need to collaborate simultaneously in order to solve a problem, and this paper aims to show the way we have implemented this mechanism in a network computer. The main feature of our solution is that it is not bound up with the underlying network, so it is highly portable. We also report some experimental results that showthat our prototype
performs quite well on low cost computers
Metal content determination in biodiesel samples by microwave mineralization and ICP-AES
El trabajo comprende la puesta a punto de un método de digestión, mediante calentamiento de microondas, de muestras de biodiesel obtenidas mediante catálisis homogénea de aceites vegetales, para la determinación de 20 elementos mediante ICP-AES
Biodisponibilidad, acumulación y traslocación de arsénico y metales pesados en plantas autóctonas procedentes de suelos afectados por la actividad minera
Se han evaluado los factores de biodisponibilidad, acumulación y traslocación de arsénico y metales pesados, en plantas autóctonas procedentes de suelos contaminados por actividades mineras, mediante el análisis de dichas muestras por ICP-AES
Chemostat culture systems support diverse bacteriophage communities from human feces
BACKGROUND: Most human microbiota studies focus on bacteria inhabiting body surfaces, but these surfaces also are home to large populations of viruses. Many are bacteriophages, and their role in driving bacterial diversity is difficult to decipher without the use of in vitro ecosystems that can reproduce human microbial communities. RESULTS: We used chemostat culture systems known to harbor diverse fecal bacteria to decipher whether these cultures also are home to phage communities. We found that there are vast viral communities inhabiting these ecosystems, with estimated concentrations similar to those found in human feces. The viral communities are composed entirely of bacteriophages and likely contain both temperate and lytic phages based on their similarities to other known phages. We examined the cultured phage communities at five separate time points over 24Â days and found that they were highly individual-specific, suggesting that much of the subject-specificity found in human viromes also is captured by this culture-based system. A high proportion of the community membership is conserved over time, but the cultured communities maintain more similarity with other intra-subject cultures than they do to human feces. In four of the five subjects, estimated viral diversity between fecal and cultured communities was highly similar. CONCLUSIONS: Because the diversity of phages in these cultured fecal communities have similarities to those found in humans, we believe these communities can serve as valuable ecosystems to help uncover the role of phages in human microbial communities
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