1,720,984 research outputs found
Assessing the bioavailability of organic pollutants in surfactant solutions using a novel bioluminescent biosensor
No full textBioavailability is often considered to be the rate limiting process in the bioremediation of sites contaminated with hydrophobic organic compounds (HOCs). In order to meet the need for a direct measurement technique for microbial bioavailability, the whole-cell bioluminescent biosensor PpF1G4 was developed. To create PpF1G4, bioluminescent reporter genes (lux) were placed under the control of the promoter region of the solvent efflux pump genes (sep) in Pseudomonas putida F1. In screening experiments, it was determined that biosensor PpF1G4 produced a bioluminescent response to a wide range of aromatic compounds.PpF1G4 was used to evaluate how three nonionic surfactants (Triton X-100, Brij 30 and Brij 35) influence the bioavailability of three different HOCs (toluene, naphthalene, and phenanthrene). Nonionic surfactants were used because they are in general less toxic to bacteria. The increased bioluminescent response of PpF1G4 in micellar solutions of Triton X-100 and Brij 35 indicated higher intra-cellular concentrations of the test compounds, toluene, naphthalene and phenanthrene, compared to control systems with no surfactants present. In contrast, Brij 30 caused a decrease in the bioluminescent response to the test compounds. The effect of the micellar solutions on the toluene biodegradation rate was consistent with the bioluminescent response. Thus, the bioluminescent response of PpF1G4 was an accurate indicator of bioavailability. The results suggest that nonionic surfactants enhance biodegradation in two ways: (1) by augmenting membrane permeability through binding of surfactant monomers; and (2) by increasing the mass flux of substrates present in the micellar pseudophase to the cells.PpF1G4 was also employed to evaluate the bioavailability of HOCs partitioned from multicomponent NAPLs (gasoline, crude oil, and creosote) into surfactant solutions. All three surfactants tested increased the bioavailability of HOCs partitioned from creosote and crude oil. None of the surfactants significantly enhanced the response to gasoline-equilibrated solutions. The suppression of bioluminescence in Brij 30 solutions containing single test compounds did not occur in Brij 30 solutions containing multiple HOCs. This research sheds some light on how certain nonionic surfactants may increase the bioavailability of HOCs and thus enhance bioremediation
The effect of interfacial films on mass transfer of benezene and naphthalene from NAPLs to water /
No full textThe dissolution of aromatic hydrocarbon compounds and polycyclic aromatic hydrocarbons from petroleum phases into water results in groundwater contamination at petroleum contaminated sites. The objective of the research is to investigate whether aging of oil-water interfaces and the formation of interfacial films retard dissolution of solutes from petroleum phases.The equilibrium partitioning and mass transfer rates of benzene and naphthalene in oil-water systems were evaluated experimentally. The research demonstrated that: (i) the mass transfer of the solutes from Brent Blend crude oil to water is retarded when the oil-water interface is aged; (ii) visually observable interfacial films are formed between gasoline and water when amended with asphaltenes or asphaltenes and resins; (iii) the mass transfer of solutes from gasoline amended with asphaltenes or asphaltenes and resins decreased by a factor of 2.3 to 66 between 4 to 35 days of interface aging and (iv) equilibrium partitioning is not significantly affected by amending the gasoline
Mass Transfer and biodegradation of polycyclic aromatic hydrocarbons from non-aqueous phase liquids
No full textOrganic liquids such as crude oils, creosotes and coal tar often remain in contact with groundwater or surface waters for long periods of time before or during any attempted remediation. Potentially toxic solutes such as polycyclic aromatic hydrocarbons (PAHs) are continuously released from pollutant oil phases described above to the water phase. The research was aimed at understanding how physicochemical as well as biological phenomena affect dissolution and biodegradation of PAH compounds from pollutant oil phases. These phenomena were investigated for a simple two-component non-aqueous phase liquid (NAPL) and for creosote, a multi component NAPL.Mass transfer experiments of naphthalene from a synthesized two-component NAPL were conducted to assess the extent of variation of mass transfer rate coefficients between column and completely mixed flow-through (CMFT) systems. The differences in the hydrodynamics between column and CMFT systems, employed in this study, resulted in a difference in the mass transfer rate coefficients of a factor of 3. Several reported empirical correlations for the estimation of mass transfer coefficients in batch and column systems were verified. Good agreement between Sherwood numbers, a dimensionless quantity reflecting the magnitude of the mass transfer coefficient, predicted by the reported correlations and those calculated from mass transfer coefficients obtained from the experiments was obtained in all cases.The biodegradation kinetic coefficients mumax and Ks for the biodegradation of naphthalene from a two-component NAPL, coated onto uniformly sized nonporous particles, were evaluated in completely mixed batch reactor (CMBR) systems and in flow-through column systems. The values obtained for mumax and Ks from column systems were very close to those obtained from CMBR systems. This suggests that both coefficients estimated from CMBR or column systems can be applied for modeling studies. The development of biofilms at the NAPL-water interface reduced mass transfer rates of naphthalene by 70% in column systems and 60% in CMBR systems.Viscous interfacial films develop at the creosote-water interface when creosote is aged in water for a period of time. The mass transfer rate coefficient of naphthalene from creosote to water was reduced by 30% over a one-week aging period. Minor additional reductions were observed with further aging. Hindered diffusion through the bulk creosote phase and changes in composition of creosote as a result of extended dissolution did not account for the observed reductions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
