1,721,094 research outputs found
Field demonstration for the solvent-based sampling method to perform compound-specific isotope analysis on gas-phase VOC
No full textThe solvent-based sampling method for collecting gas-phase volatile organic compounds (VOCs) and conducting compound-specific isotope analysis (CSIA) was deployed during a controlled field study. The solvent-based method used methanol as a sink to accumulate petroleum hydrocarbons during the sampling of soil air and effluent gas. For each gaseous sample collected, carbon isotope analysis (δ13C) was conducted for a selection of five VOCs (benzene, toluene, o-xylene, cyclopentane and octane) emitted by a synthetic hydrocarbon source emplaced in the subsurface. The δ13C values obtained for gaseous VOCs (collected from soil gas and effluent gas) were compared to measurements obtained for the same VOCs present in the source material (none aqueous phase liquid - NAPL) and dissolved in groundwater to evaluate the reliability of the solvent-based sampling method in providing accurate isotope measurements. Since the NAPL source was composed of only 12 VOCs, potential bias related to the analytical procedure (such as co-elution) were avoided, hence emphasizing on field-related bias. This field evaluation demonstrated the capacity of the solvent-based method to produce precise and accurate δ13C measurements. The isotopic discrepancies between the gaseous and the NAPL values were < 1 ‰ for 39 out of the 41 comparison points, thus deemed not statistically different based on a common isotopic uncertainty error of ±0.5 ‰. Moreover, the current field study is the first field study to report δ13C measurements for up to five gas-phase VOCs obtained from the same sample, which appears to be of interest for VOC fate or forensic studies. The possibility to use several VOC isotopic measurements enabled by the sampling method would contribute to strengthen the connection assessment between gaseous VOCs and the suspected emitting source. Accordingly, the field results presented herein support the application of this sampling methodology to conduct CSIA assessment in the frame of VOC vapor studies
Use of hydrogeological and geochemical methods to investigate the origin and fate of vinyl chloride in groundwater in an urban environment, Ferrara, Italy.
No full textVinyl chloride (VC) groundwater contamination around the city of Ferrara, Italy, is rather widespread and has created a serious environmental problem in this highly urbanized region. The paper discusses recent data derived from a geochemical and isotopic fingerprinting study carried out at the Pandora site, which is characterized by the existence of a long VC plume, and at the Caretti site where high concentrations of chlorinated compounds, including VC, occur. Data was also collected at an unconfined aquifer under¬neath a major petrochemical plant. The isotopes data show that the unusual negative δ13C values observed in the VC at both sites (Pandora –43 and
–65‰; Caretti: –62 and –72‰) could not be attributed to reductive dechlorination of manufactured primary PCE or TCE. Unusual negative δ13C values for PCE and TCE also characterise the impacted aquifer beneath the petrochemical plant and the Caretti site. Based on the industrial history of the region, which includes production of PVC and chloromethanes (ClM), it is postulated that contamination in the Ferrara region is linked to wastes originating from the production of chloromethanes. The primary organic compound used in ClM production is methane, which is strongly depleted in 13C similar to the values observed in VC, PCE and TCE at the investigated sites. It is also postulated that the contamination is linked to dumping of industrial waste in the abandoned lagoons used by the sugar industry and in clay pits associated with the clay industry
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
Origin and Fate of Vinyl Chloride as Primary Contaminant
No full textUsually vinyl chloride is considered to be the product of reductive dechlorination of chlorinated ethenes. However, at some sites vinyl chloride may also be present as primary contaminant. The goal of the study was to evaluate if stable carbon and chlorine isotopes can be used to identify vinyl chloride as primary contaminant and to trace the fate of the compound. The main study consists of a site where residues from PVC production were disposed and a plume of VC was detected in a sandy aquifer with absence of other chlorinated ethenes.
The VC plume was delineated using monitoring wells and profiling with a direct-push rig. VC concentrations of up to 11 mg/L were found. Carbon isotope analysis of the VC revealed very depleted 13C values between -61 and -73‰ in wells with the highest concentration. The depleted 13C value could be linked to the VC production processes or due to isotope fractionation associated with the polymerization process. The very depleted isotope values may serve as an indication of VC as primary contaminant for other sites with similar wastes.
Downgradient of the source, a substantial shift of the carbon isotope ratios was observed suggesting transformation of the compound. Currently, combined carbon and chlorine isotope analysis of VC is carried out. The dual isotope approach in conjunction with characterization of redox conditions should provide insight into the pathway of VC degradation, as oxidative and reductive transformation are expected to lead to different relative shifts for the two isotopes. Once the pathway of VC degradation is identified, biodegradation rates will be estimated based on shifts in isotope ratios and groundwater flow velocities, which help to predict the future evolution of the VC plume
Origin and fate of vinyl chloride in a groundwater plume
No full textChlorinated ethenes are one of the most common contaminants found in groundwater.
The presence of VC in groundwater is commonly considered as a byproduct of
reductive dechlorination of chlorinated ethenes. However, at some sites vinyl chloride
may also be present as primary contaminant. The goal of the study was to evaluate if
stable carbon and chlorine isotopes can be used to identify vinyl chloride as primary
contaminant and to trace the fate of the compound in a groundwater plume. The study
site is a sandy aquifer underlying the densely urbanized Pontelagoscuro northern part
of the city of Ferrara, Italy. A VC plume with absence of other chlorinated ethenes was
detected in the aquifer likely linked to infiltration of residues from a PVC production
facility.
The VC plume was delineated using monitoring wells and profiling with a direct-push
rig. VC concentrations of up to 11 mg/L were found in some part of the plume. Carbon
isotope analysis of the VC revealed very depleted 13C values between -61 and
–73 per mille in wells with the highest concentration. The depleted 13C value could
be linked to the VC production processes or due to isotope fractionation associated
with the polymerization process. The very depleted isotope values may serve as a fingerprint
to elucidate the presence of VC as primary contaminant for other sites with
similar wastes. Downgradient of the source along the groundwater flow system, a substantial
shift of the carbon isotope ratios was observed suggesting transformation of
the VC. The presence of CH4, C2H4 and C2H6 suggest the plume is under anaerobic
conditions. Currently, combined carbon and chlorine isotope analysis of VC and carbon
isotope analysis on CH4, C2H4 and C2H6 is been carried out. The dual isotope
approach in conjunction with characterization of redox conditions should provide insight
into the pathway of VC degradation, as oxidative and reductive transformation
are expected to lead to different relative shifts for the two isotopes. Once the pathway
of VC degradation is identified, biodegradation rates will be estimated based on
shifts in isotope ratios and groundwater flow velocities, which will be use to predict
the future evolution of the VC plume in the aquifer
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
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