1,721,027 research outputs found
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
Naphthenic acids: identification of structural properties that influence acute toxicity
No full textThe oil sands of north-eastern Alberta, Canada contain the second largest oil reserve on Earth, with an estimated 173.2 billion barrels of recoverable bitumen. The primary method for the extraction of bitumen from oil sand has been the Clark hot water extraction, a procedure that uses 80°C water and sodium hydroxide. The alkaline water used for the extraction is recycled, resulting in the release and concentration of naphthenic acids (NAs) from the sediment. NAs, a natural constituent of oil sand, have been identified as the principal toxic components of oil sands process-affected water (OSPW). Field studies have demonstrated that microbial degradation of lower molecular weight (MW) NAs leads to decreased acute toxicity, although the mechanism by which lower MW NAs would elicit a greater toxic response has not been described. Prior to the start of toxicity testing in this project, a time-efficient method for the extraction, purification, and concentration of NAs from OSPW was developed. In place of using ultrafiltration, diethylamoniethyl (DEAE) cellulose was used to remove humic-like materials from the organic acid extract, shortening the time required by approximately 90%. Kugelrohr distillation was used to separate a mixture of methylated NAs by differences in boiling point. Higher boiling NAs had a greater MW, as confirmed by electrospray ionization mass spectrometry (ESI-MS). Subsequent toxicity tests with 'Vibrio fischeri' using the Microtox assay revealed that toxicity decreased from the lowest MW fraction (41.9 ± 95% confidence interval (CI) of 5.5 mg L-1) to the highest (64.9 ± 95% CI of 14.5 mg L-1). Proton nuclear magnetic resonance (1H NMR) analysis of the Kugelrohr distilled methylated NA fractions revealed an increasing ratio of methyl ester hydrogen atoms to remaining aliphatic hydrogen atoms from the lowest MW fraction (0.130) to the highest MW fraction (0.214). These results, coupled with analysis by ESI-MS, indicate greater carboxylic acid content within NAs of higher MW and a greater degree of cyclicity. To investigate the influence of multiple carboxylic acid groups as well as increased MW on NA toxicity, eight NA-like surrogates (four mono-carboxylic; four di-carboxylic) were assayed in 'V. fischeri' and ' Daphnia magna.' The acute toxicity of the NA-like surrogates increased with higher MW, however, the toxicity significantly decreased with the presence of an additional carboxylic acid group. These results suggest that acute toxicity of NAs is dependent upon hydrophobicity, therefore the probable mode of action is narcosis, also referred to as membrane disruption. To determine the practicality of utilizing a (Quantitative) Structure-Activity Relationship ((Q)SAR) model to predict NA toxicity, the eight NA-like surrogates were entered into USEPA's ECOSAR model. The model's predicted toxicities were similar to observed toxicities in 'V. fischeri' and 'D. magna' assays, indicating that the model has potential to serve as a prioritization tool for identifying NA structures likely to have an increased toxicity. The ECOSAR model predicted increased toxic potency for NAs of equal MW containing fewer carbon rings. Furthermore, NA structures with a linear grouping of carbon rings had a greater predicted toxic potency than structures containing carbon rings in a clustered grouping
Effects of climate change on mercury concentrations in Arctic char, Salvelinus alpinus, in the high Arctic.
Full text linkThis thesis is an investigation of linkages of climate change and mercury concentrations in landlocked Arctic char and underlying food webs in Canadian Arctic lakes. Although the neurotoxin mercury is globally present in all environments, temporal and spatial trends in aquatic biota are often inconsistent, or do not exist for remote environments. Knowledge gaps include the influence of abiotic factors, possibly climate, and food web parameters on mercury accumulation in top predators. Furthermore, anthropogenic and natural mercury present in the environment are not well differentiated. To address these research needs, we collected landlocked Arctic char from 27 systems and food web organism from 18 lakes, and recorded abiotic lake characteristics expected to influence mercury cycling. Total mercury (THg) and monomethylmercury (MeHg) concentrations, and stable isotopes of carbon ([delta]13C), nitrogen ([delta]15N), and mercury ([delta]xHg) were determined. Relationships among these measures and with environmental characteristics were investigated. A temporal trend of mercury in Arctic char (muscle tissue) from the largest lake in the Canadian High Arctic from an existing dataset and newly collected char was investigated. Two abundant char morphotypes from Lake Hazen differed in mercury concentrations, and the resulting variability was accounted for using a statistical adjustment. Mercury concentrations did not change over the 16-year period (1990-2006), which is consistent with nearby measurements of gaseous elemental mercury at Alert (Nunavut, Canada). Food chain lengths (FCL) of 18 lakes were characterized, biomagnification of mercury was investigated using [delta]15N, and results compared among regions. Food web biomagnification was confirmed using trophic magnification factors (TMFs) in 18 Arctic char bearing lakes (TMFs 3.5 - 64.3). Benthic coupling was apparent from char [delta]13C signatures that resembled [delta]13C in chironomid midges. TMFs and FCL partly explained THg in adult char, but no latitudinal or other climatic trend was apparent. Mercury concentrations in adult Arctic char were positively related to catchment-to-lake area, and intra-regional, and regional differences in Hg in Arctic char were determined. No climatic factor we investigated was found to affect Hg in char directly; however, predicted climatic changes could affect THg in char indirectly through changes in the catchment (such as melting of permafrost). Stable isotope ratios of mercury revealed region specific mass-independent fractionation (MIF) of up to ~ 4.5 in Arctic char, which did reflect sediment ratios with a constant offset (MIF-factor). High MIF in zooplankton possibly reflected mercury assimilated from the water column. Char from Lake Pingualuk, known pelagic feeders, had high MIF, possibly reflecting an atmospheric Hg signal
Myriophyllum spp. in ecological risk assessment: a case study with haloacetic acids
No full textThis thesis describes the utility of 'Myriophyllum' spp. ecological risk assessment. 'Myriophyllum sibiricum' and ' M. spicatum' are rooted aquatic macrophytes occurring in a variety of ecosystems as natural and invasive species. 'M. sibiricum' has been recommended as a new test species for the registration of pesticides in North America. There is a paucity of field level testing with these plants and laboratory to field testing. Studies were conducted to evaluate the ability of these plants to develop and exhibit toxicity from haloacetic acid (HAA) exposure under field conditions using microcosms. 'Myriophyllum' spp. developed well under field conditions and were comparable in their sensitivity to toxicants under both laboratory and field conditions. Pigments were the least sensitive endpoints as compared to morphological endpoints such as mass and root measures. Laboratory data was a reasonable surrogate for effects observed in the field with these plants. HAAs were found to degrade readily, with the exception of trifluoracetic and chlorodifluoroacetic acids, and be relatively non-toxic to aquatic macrophytes. Using toxicity data from both field and laboratory tests to create effect measure distributions for these plants, HAAs were deemed to not pose a significant risk to these organisms under current environmental conditions. The use of effect measure distributions in the risk assessment process is promising, especially for threatened ecosystems and species. Overall, the use of 'Myriophyllum' spp in ecological risk assessment holds substantial benefits for protecting aquatic environments
Risk assessment of selective serotonin reuptake inhibitors: comparing methods in tiered environmental risk assessment
No full textEnvironmental detection of pharmaceuticals, including the selective serotonin reuptake inhibitor (SSRI) fluoxetine, has reinforced the need for environmental exposure, fate, effects, and hazard assessment of these chemicals. Environmental concentrations of SSRIs were predicted using current methodologies and compared to available measured environmental concentrations. The environmental fate of SSRIs fluoxetine, fluvoxamine, and sertraline was evaluated in microcosm model ecosystems; toxicity to algae and fish was evaluated at different tiers consisting of (quantitative) structure activity relationships, acute laboratory toxicity assays, and in microcosm model ecosystems. Hazard to fish and algae was evaluated using predicted environmental concentrations and toxicity values determined at each tier. The hazard at each tier was then compared to generate data-driven uncertainty factors (UFs) for extrapolation between tiers which were then used to extrapolate the additional hazard of the remaining SSRIs: citalopram and paroxetine. Furthermore, the utility of species sensitivity distributions (SSDs) and interspecies correlation estimation (ICE) was investigated as extrapolation methods and compared to pragmatic UFs. Overall, algae were found to be more sensitive than fish to SSRIs with sertraline being the most toxic of the SSRIs tested followed by fluoxetine and fluvoxamine. However, the hazard of SSRIs at current environmental concentrations is low. Moreover, SSDs and ICE show promise as extrapolation tools as they generated conservative hazard estimates that were more accurate than those derived using pragmatic UFs
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
An assessment of the contamination and effects of lampricide formulations of 3-trifluoromethyl-4-nitrophenol (TFM)
No full textThis thesis investigates the sources of hepatic mixed function oxygenase (MFO) enzyme induction and disruptions in circulating hormonal levels in fish exposed to lampricide formulations of 3-trifluoromethyl-4-nitrophenol (TFM). Methodology was developed for the isolation and recovery of chemicals associated with biological activity. Formulation impurities causing MFO induction were isolated using solid phase extraction and HPLC into two fractions. The major constituents in both fractions were identified as nitro-, trifluoromethyl- and/or chloro-substituted diphenyl ethers, which did not elevate MFO activity after in vivo exposures. Three chloro-nitro-trifluoromethyl-substituted dioxin isomers containing these substituents in the most potent fraction were confirmed by characterizations of synthetic isomers. The average concentration of these compounds in previous batches was which translates into loadings of 40 g/year to the Great Lakes Basin. Short-term waterborne exposures to a mixture of 2-trifluoromethyl-3-nitro-7-(and 8)-chloro-dibenzo-p-dioxin isomers elevated MFO activity in rainbow trout (Oncorhynchus mykiss), with a threshold between 0.148-0.745 nM (4.1-20.5 ng/L). Using mammalian (H4IIE) and fish (PLHC-1) in vitro assays, a 2,3,7-substituted isomer was 4-5 times more potent than 2,3,7-trichlorodibenzo-p-dioxin. It was further concluded that the formulation isomers are not substituted exclusively in the 2,3,7-positions. Chemical fractionations directed by competitive binding to rainbow trout estrogen receptors were used in a mechanistically linked approach to identify compounds associated with disruptions in endocrine homeostasis. Virtually all binding potential to the receptor was associated with fractions containing TFM and TFM isomers. Relative to estradiol, TFM demonstrated a competitive affinity of 5.03\times 10\sp{-5}. Vitellogenin induction in primary cultures of rainbow trout hepatocytes indicated TFM acts as an estradiol agonist in vitro but protein production was not detected in plasma of caged trout after a lampricide treatment. Following treatment, MFO induction in fish was rapid, peaking within 2-3 d, and was persistent after 18 d in caged rainbow trout, wild white sucker (Catostomus commersoni) and longnose dace (Rhinichthys cataractae) sampled downstream. Induction was highest in fish exposed closest to the application points. Chloro-nitro-trifluoromethyl dioxins were not detected in sediments after treatment and diphenyl ether impurities were ng/g after 18 d
Emerging organohalogen contaminants in bottlenose dolphins (Tursiops truncatus)
No full textIn this study, polyfluoroalkyl compounds (PFCs), polychlorinated biphenyls (PCBs) and hydroxylated-PCB metabolites (OH-PCBs) were investigated in live-captured and released bottlenose dolphins from the Western Atlantic and the Gulf of Mexico. Spatial trends in plasma contamination were observed for PFCs, PCBs, and OH-PCBs with the highest concentrations detected in plasma of dolphins sampled around Charleston, South Carolina. The detection of fluorotelomer carboxylic acids in dolphin plasma supported the hypothesis that fluorotelomer alcohols could be responsible for the long-range transport of PFCs. The concentrations of PFCs in plasma were not associated with gender but decreased with the age of animals. Sexually immature and developing calves were indeed more contaminated than mothers. The reproductive history of females was found to be associated with PFC concentrations and PFCs were found in milk of dolphins. These chemicals were detected in all organs of dolphins analyzed. The lack of temporal or seasonal trends in the concentrations suggested a continuous exposure of dolphins to these contaminants. The detection of PFCs in urine indicated excretion through the urinary system. Seawater and sediment from South Carolina and western Florida were contaminated with PFCs and the bioaccumulation and biomagnification of numerous PFCs in the bottlenose dolphin food web was observed. The results have also shown that, compared to the whole body burden estimation, using plasma or liver concentrations in dolphins tended to overestimate the biomagnification of PFCs. The measurements of PCBs and OH-PCBs in plasma confirmed the results previously reported for PCBs in marine mammals and showed that OH-PCBs are major environmental contaminants in dolphins. The profile of PCB and OH-PCB contamination were similar within contaminant groups among locations suggesting similar biotransformation processes, albeit at different intensities. The analysis of plasma has shown that a wide spectrum of OH-PCBs is found in blood of bottlenose dolphins. However, only around 20% of OH-PCBs could be identified by comparison to authentic standards. In addition, a large proportion of OH-PCB (<54% of the total [Sigma]OH-PCBs) were composed of monochloro- to trichloro-OH-PCBs which have rarely, if ever, been measured in biota. These findings indicated that OH-PCB concentrations are likely underestimated in samples. Further investigation is needed to better understand the fate and effects of these emerging organohalogen contaminants in marine mammals
- …
