1,720,954 research outputs found
Heavy metals and antioxidant responses in the soil ciliate Cyrtoymena tetracirrata: a preliminary analysis
Full text linkIn the last decades, the discharge of anthropogenic heavy metals to the ecosystems has increased worldwide. These heavy metals do not degrade, but get accumulated in the food chain and additionally, some of them produce carcinogenic and toxic effects in human and animals. Ciliated protozoa are cosmopolitan eukaryotic microorganisms which are adapted for life in soil, aquatic, and marine ecosystems. In addition, they are very sensitive to diverse pollutants and toxic agents, and some of them, share a higher degree of functional conservation with human genes than other microbial model microorganisms. In general, bioassays are good tool to assess metal pollution because they have the ability to react and detect only the available fraction of the metal ions. In indirect mechanisms, essential and non-essential metals can generate reactive oxygen species (ROS), e.g., superoxide radical (O-2), hydrogen peroxide (H2O2), hydroxyl radical (HO-), and singlet oxygen (1O2), in living organisms. Heavy metal induced ROS causes adverse effect by attacking cellular macromolecules, resulting in protein denaturation, lipid peroxidation, DNA damage, and alteration of calcium and redox homeostasis, thus, generating oxidative stress in the organisms. The main aim of our study was to evaluate the cytotoxic effect of the heavy metals Cd, Zn and Cu by means of a combination of ecotoxicological and antioxidant activity assays in the ciliate Cyrtoymena tetracirrata isolated from the soil of an agriculture farm located in Marche region (Italy). We have measured the 24-hrs LC50 and LC20 values for single metal exposures as well as, the effects of binary metal mixtures (Cd + Zn, Cd + Cu, and Cu + Zn) on C. tetracirrata viability, applying the Concentration Addition model based on the Toxic Unit approach to assess the type of interaction (i.e. synergistic, antagonistic etc.) between heavy metals. Furthermore, we applied different antioxidant in vitro tests, such as total phenol content (TPC), a,adiphenyl- b-picrylhydrazyl (DPPH), Metal chelating assay (MCA) and Hydroxyl Radical Scavenging Assay (HRSA), to evaluate the presence of antioxidant activity in the ciliates exposed to heavy metals. Our preliminary results showed, the LC50 values to Cd, Cu, and Zn were 1.16, 0.37 and 32.7 mg L-1, respectively and LC20 values were 0.53, 0.22 and 23.0 mg L-1, respectively. The order of toxicity was Cu > Cd >> Zn. In most of the cases, bimetallic (Cd + Zn, Cd + Cu, and Cu + Zn) treatments produced antagonistic effects. The activity of intra- and extra-cellular antioxidant capacity of ciliate cells exposed to different heavy metals conditions was found to be significantly increased with respect to the untreated cells (control). Thus, C. tetracirrata seem to have a good potential to be used as a model organism in ecotoxicological studies of soil contaminated with heavy metals. In the long run, our goals will be to analyse the antioxidant enzymes and the expression of potential stress related genes (antioxidant genes) of C. tetracirrata
The soil ciliated protozoa Cyrtoymena tetracirrata as bioindicators of soil health: cytotoxicity of single and bimetallic mixtures of heavy metals and antioxidant defenses
Full text linkAs far as we known, the releases of heavy metals (HMs) to the environments and particularly in agricultural soils, has increased globally in the last few years. Although, a number of reviews have analysed the effects of HM contaminated soils using various microbial test organisms, few studies have focused on soil ciliated protozoa as potential bioindicators of soil health. Thus, in this study we have evaluated the cytotoxic effects and the presence of antioxidant activities in the soil ciliate Cyrtoymena tetracirrata exposed for 24hrs to both single (Cd, Cu, and Zn) and bimetallic mixtures (Cd + Zn, Cd + Cu, and Cu + Zn) of HMs. Ecotoxicological tests showed, LC20 values to Cd, Cu, and Zn of 0.53, 0.22 and 23.0 mg L-1, respectively and, LC50 values of 1.16, 0.37 and 32.7 mg L-1, respectively. The order of toxicity was Cu > Cd >> Zn. Using the Concentration Addition model approach we found that the Cd + Zn bimetallic mixtures treatments were able to prevalently produce antagonistic effects in comparison to the other mixtures (Cd + Cu, and Cu + Zn). With regards to the analysis of the antioxidant activities, the total phenolic contents (TPC) were significantly higher in the ciliates exposed to Cu at the LC20 value previously identified (extracellular: P ≤ 0.01) and to Cd at the LC20 value (intracellular: P ≤ 0.001). Higher α,α-diphenyl-β-picrylhydrazyl (DPPH) scavenging activities were found at the Cd and Zn LC50 values for both the extracellular and intracellular contents (P ≤ 0.05). Hydroxyl scavenging activity (HRSA), unveiled that higher levels of antioxidants were produced following exposures to Cd LC50 (extracellular: P ≤ 0.001) and Cu LC50 values (intracellular: P ≤ 0.001). Overall the present study reveals, that C. tetracirrata has the potential to be used as bio-indicator of HM polluted soils
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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