1,721,087 research outputs found
Biodegradation of PAHs in aggregates of a low permeability soil
No full textIn the bioremediation of low-permeability soils, pollutant and, especially, the oxygen bioavailability are often the rate limiting steps. In cases when a biopile treatment can represent an applicable technique, pretreatment of the excavated soil is often necessary to attain an adequate air-filled porosity in the soil and to avoid the presence of large soil aggregates. The present work was performed to evaluate the influence of soil aggregate size in the bioremediation of a silt-clay type soil contaminated by PAHs. Microcosms were arranged with spherical soil aggregates of different diameter in near water-saturation conditions. Concentration of two and three aromatic ring PAHs, total biomass, and respiration rates were monitored. PAH concentration profiles inside the particles were also obtained. A simple and quick way to estimate the critical dimension of the soil aggregates was developed based on the evaluation of an oxygen penetration depth, that is, the distance from the external surface to the aggregate core beyond which oxygen concentration is practically zero. A very different time course of PAHs consumption was found in the external layer and the inner core of the aggregates as well as in aggregates of different dimensions. The results suggest that only the 3 mm external layer of the sphere is not limited by oxygen diffusion
Solids distribution in stirred slurry reactors: Influence of some mixer configurations and limits to the applicability of a simple model for predictions
No full textThe features of solids concentration distribution were investigated in baffled and unbaffled tanks of high aspect ratio, stirred with multiple radial, mixed-flow or axial impellers. In the baffled tanks the average profiles can be predicted with the sedimentation-dispersion model regardless of impeller type - in spite of slight systematic departures from the average trend at the impeller plane and/or midway between the impellers. This is hardly possible for the unbaffled tanks due to lack of physical foundation of this simple model. When the unbaffled tank is stirred with hydrofoil impellers, an inverted profile is even obtained. The mentioned departures and this last anomalous behaviour are qualitatively discussed with reference to particle-turbulence interaction
In situ bioremediation of a soil contaminated by mineral oil: A case study
No full textLaboratory tests were conducted to study the feasibility of a bioremediation treatment. The first phase of the work was exploratory and comprised slurry condition microcosm tests. The second phase consisted of solid-phase microcosm tests to evaluate the effectiveness of the treatment and to estimate the time needed to reach the target level of 100 mg.kg fixed by the local environmental agency. The third phase consisted of helping the remediation company to select the appropriate technology, of choosing the strategy for its application in the field and of monitoring the site during treatment. From the microcosm tests data, the depletion rate became slower as a residual concentration of pollutants of ~ 500 mg/kg was reached. This residual contamination part was hardly bioavailable to the microorganisms that proved to be very active in using hydrocarbons as a carbon source. The results of the tests showed very low contaminant depletion rates. All the attempts to increase the bioremediation rate failed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
