1,721,015 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
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
Evaluation of the phytotoxic effects of pharmaceuticals in aquatic higher plants
No full textPharmaceuticals are biologically active, ubiquitous, low-level contaminants which are continuously introduced into the environment at volumes comparable to pesticides. Typically detected in the ng/L to [mu]g/L range, the effects of these contaminants in the aquatic environment are largely uncharacterized. In order to address this data gap, over 30 pharmaceuticals were screened through laboratory assays with 'Lemna gibba', 12 in aquatic microcosms with 'L. gibba, Myriophyllum sibiricum' and/or 'Myriophyllum spicatum', and 2 at the molecular/biochemical level in 'L. gibba'. Among the pharmaceuticals initially screened, only fluoroquinolone, sulfonamide, and tetracycline antibiotics proved to be phytotoxic between 10-1000 [mu]g/L, however, no significant risks were found using conservative assumptions. Similarly, a microcosm assessment with an eight pharmaceutical mixture indicated no significant risks for either 'L. gibba' or 'M. sibiricum', though fluoroquinolone (levofloxacin) and sulfonamide (sulfamethoxazole) antibiotics, as well as a blood lipid regulator (atorvastatin) were identified as phytotoxic components. Tylosin, a macrolide antibiotic heavily used as a prophylactic in Canadian agriculture, was found to cause no statistically significant inhibition in any endpoint measured in 'L. gibba' or 'M. spicatum' evaluated singly in aquatic microcosms. Although a mixture of tetracyclines was found to pose little risk to the floating macrophyte 'L. gibba', the submerged macrophyte 'M. sibiricum' showed significant inhibition and potential risks, largely because of the reduction in light penetrating the water column by as much as 99.8% at a depth of 70 cm caused by parent compounds and/or metabolites. A probabilistic ecological hazard assessment designed to address the unique data availability of pharmaceuticals revealed low probability for risk to aquatic macrophytes in all cases, with the exception of tetracyclines. Statin class blood lipid regulators were found to significantly reduce metabolite levels (sterols) downstream of the target enzyme (3-hydroxy-3methylglytaryl coenzyme-A reductase) in the mevalonic acid pathway by as much as 90%. However, no significant hazards were identified, though these pathway-specific endpoints were on average 3 times more sensitive than gross morphological endpoints. Therefore, from the subset of pharmaceuticals tested, these compounds appear to pose little risk to aquatic higher plants, evaluated in the laboratory, microcosms or using pathway-specific endpoints
Evaluation of probabilistic ecological risk assessment methodology using aquatic microcosms and azinphos-methyl
No full textThe general trend toward probabilistic risk assessment in aquatic toxicology relies on some key assumptions, several of which are questionable. At present, only a few studies have been carried out to evaluate the probabilistic approach. To this end, a multi-species outdoor microcosm study was conducted using the organophosphorus insecticide azinphos-methyl, the freshwater fish ' Pimephales promelas' and 'Lepomis gibbosus', as well as zooplankton. A regression design was used with 5 treatment levels (0.1-100 [mu]g/L) and a control. Comparison of the 96 hr LC50s for fish (31.7 and 3.2 [mu]g/L, respectively) with the 10th percentile of the acute sensitivity distribution (0.9 [mu]g/L) indicates that this extrapolated value would not correspond to acute toxicity in these species. Based on literature data, the multi-species no observable effect concentration (NOEC) for ' Daphnia' sp. (0.1 [mu]g/L) coincides with the chronic and acute 10 th centiles (0.092 and 0.15 [mu]g/L) of the single species invertebrate sensitivity distributions. For fish, the multi-species NOEC for survival (0. 17 [mu]g/L is below the acute 10th centile of 0.9 [mu]g/L, which is not protective. Probabilistic risk assessment of azinphos-methyl in Southern Ontario surface waters indicates that up to 30% of fish and 50-70% of invertebrate species may be acutely impacted. The applicability of probabilistic extrapolation to ecosystem level effects is highly uncertain and thus difficult to reconcile
Chlorophyll fluorescence as a mechanistic bioindicator of photosynthetic inhibition in aquatic plants
No full textThis thesis describes an investigation of a chlorophyll fluorescence assay used to estimate the efficiency of photosynthetic electron transport in plants exposed to environmental stress from polycyclic aromatic hydrocarbons (PAHs) and solar ultraviolet radiation. A series of experiments were performed to validate pulse amplitude modulated chlorophyll fluorescence in aquatic plants as a rapid biological indicator of exposure to environmental contaminants and stressors. Chlorophyll fluorescence endpoints were measured in the macrophytes ' Lemna gibba' and 'Myriophyllum spicatum' upon exposure to creosote, a mixture of polycyclic aromatic hydrocarbons. In laboratory exposures, the concentration-dependent response of chlorophyll fluorescence was closely related to conventional endpoints such as frond production, shoot length, root length and leaf chlorophyll concentration. Chlorophyll fluorescence was similarly diminished in plants exposed to creosote in outdoor aquatic microcosms, at concentrations which inhibited seasonal plant population biomass. Chlorophyll fluorescence was therefore predictive of effects at higher levels of biological organization. To examine the applicability of this assay in the field, chlorophyll fluorescence was measured from natural assemblages of Lake Erie phytoplankton exposed to the PAHs anthracene and 1,2-dihydroxyanthraquinone. It was found that inhibition of photosynthetic electron transport could be detected with short exposures to low chemical concentrations. The ability of chlorophyll fluorescence to detect inhibition of photosynthesis by sunlight (photoinhibition) was examined in 'Myriophyllum' plants in microcosms screened to remove specific wavelengths of sunlight. The ultraviolet-B, ultraviolet-A and visible regions of sunlight had specific but minor effects on the various chlorophyll fluorescence parameters. No clear relationship between chlorophyll fluorescence and plant growth was found. However, when chlorophyll fluorescence was examined in Lake Erie phytoplankton exposed to the same sunlight treatments, a rapid and dose-dependent effect was observed. A nonlinear statistical model based on the cumulative energy received by the phytoplankton was used to estimate biological effectiveness coefficients for photoinhibition by each waveband. It was found that ultraviolet-B radiation was much more damaging than other wavelengths of sunlight. Chlorophyll fluorescence is therefore a suitable endpoint for detecting inhibition of photosynthetic electron transport in aquatic plants exposed to various environmental stresses, which is linked to effects at higher levels of biological organization
Ecotoxicological and chemical evaluation of motor gasoline and BTEX compounds in soil
No full textThe toxicity of motor gasoline, benzene, toluene, ethylbenzene, and xylenes (collectively referred to as BTEX compounds), to terrestrial organisms (plants, soil invertebrates) in various soils (artificial sandy-loam soil, and field-collected clay loam and sandy-loam soils) was examined. As these compounds are highly volatile, sub-samples of the spiked soils were collected along a concentration gradient and the measured concentrations were used to derive estimated effect concentrations (EECs) to better reflect the concentrations to which the organisms were actually exposed. Adverse effects were most pronounced in the acute toxicity tests. Acute effects were generally predictive of longer-term effects. Reproduction and growth were unaffected in adults that survived initial acute exposures ( toluene > benzene. Long-term (234 days) studies of the fate and effects of motor gasoline on earthworms demonstrated no toxicity following one month of exposure in the clay loam soil, and two months following exposure in the sandy-loam soils. The decline in toxicity was a function of reduced bioavailability as a result of aging (sequestration), biodegradation, and volatilization. The derived data will contribute to the understanding of the fate and effects of fresh or weathered gasoline spill events to terrestrial ecosystems
Population-level and suborganismal responses in fish due to chronic creosote exposure in aquatic microcosms
No full textCreosote is a wood preservative typically comprised of approximately 85% polycyclic aromatic hydrocarbons (PAHs), 10% phenolics, and 5% heterocyclic compounds. The toxicity of liquid creosote and leachate from creosote-impregnated pilings to fathead minnows ('Pimephales promelas' R.) (FHM) and goldfish ('Carassius auratus' L.) was assessed in subchronic exposures in 12 m3 outdoor aquatic microcosms. Effects in fish were assessed immediately following treatment or following 35 days of "aging" from phase partitioning and degradation. The 7-day LC50 values for adult FHMs during the 0 to 30 day leachate exposure and the 0 to 30 day liquid creosote exposures were 88.1 [mu]g/L and 196 [mu]g/L respectively, in terms of total average measured aqueous concentrations of priority PAH compounds throughout the exposure periods. No hepatic microsomal ethoxy-o-deethylase induction was observed. Synchronous scan bile fluorescence responses were a sensitive and consistent indicator of exposure concentrations of total aqueous priority PAHs. (Abstract shortened by UMI.
The use of growth and membrane integrity assays as bioindicators of creosote effects in Myriophyllum spicatum L.
No full textThe use of membrane integrity as a bioindicator of creosote effects in the aquatic macrophyte, Myriophyllum spicatum L. was investigated using both laboratory and microcosm studies. The effects of creosote on Myriophyllum growth was determined. In the laboratory, adverse effects were first observed at approximately 1.5 mg/L, though creosote concentrations 13 mg/L stimulated shoot growth. A decrease in plant biomass was also observed in the microcosms. Myriophyllum membrane fluidity and permeability were determined following creosote exposure. In the laboratory, the membrane fluidity results were invalid, but a dose-dependent increase in membrane permeability at concentrations 0.1 mg/L was observed. This increase occurred at concentrations below those at which effects were observed in the growth study. The results of the membrane studies conducted in microcosms were unclear. Further study is required before membrane integrity can be used as a bioindicator
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