1,721,007 research outputs found
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
Characterization of Antibiotic Resistance Profiles of Surface Water Bacteria in an Urbanizing Watershed
Get PDFWastewater treatment plants (WWTP) are typically incapable of addressing the influx of antibiotics (AB), and may act as a harbor for the selection and proliferation of antibiotic resistant bacteria (ARB). In order to examine the influence of WWTP discharge on the AB resistance profiles of surface water bacteria in an urban stream setting, E. coli isolates and total heterotrophic bacteria populations were cultivated from 6 sampling sites up and downstream of WWTPs, and evaluated for resistance to selected ABs. Samples were collected over a 9-month period in the Carter���s Creek watershed of College Station, TX. E. coli isolates were tested for resistance to ampicillin, tetracycline, sulfamethoxazole, ciprofloxacin, cephalothin, cefoperazone, gentamycin, and imipenem using the Kirby-Bauer disc diffusion method. HPCs were cultivated on R2A amended with ampicillin, ciprofloxacin, tetracycline, and sulfamethoxazole. Significant associations (p < 0.05) were observed between the locations of sampling sites relative to WWTP discharge points and the rate of E. coli isolate resistance to tetracycline, ampicillin, cefoperazone, ciprofloxacin, and sulfamethoxazole; and an increased rate of isolate multi-drug resistance. The abundance of AB-resistant HPCs was significantly greater (p < 0.05) downstream of WWTPs for all treatments; however, there was no spatially significant difference when normalized to total HPCs cultivated with no AB. Results suggest that the effects of human development, specifically the discharge of treated WWTP effluent into surface waters, are potentially significant contributors to the spread and persistence of AB resistance in the surrounding watershed
Phytoremediation of Hydrocarbon-Contaminated Soil Using Phenolic-Exuding Horticultural Plants
Get PDFA greenhouse experiment was designed to test phenolic-exuding horticultural plant species for their phytoremediation potential in soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Species included high-phenolic-exuding plants: Malus sp., Osmanthus fragrans, Sambucus nigra, Castanea pumila, Morus alba, and Myrica cerifera and low-polyphenol-exuding plants: Ziziphus jujube, Ribes aureum, and Cassia fistula. The species were planted in soil amended with benzo[a]pyrene, phenanthrene, and pyrene. After 7 months, nitrogen, phosphorus, and potassium amendments were added each month for three months. Plant roots were harvested; polyphenols were ethanol-extracted and quantified using the Folin-Ciocalteu method. Rhizosphere DNA was extracted, quantified, and the 16S rRNA gene and ITS region were sequenced for bacteria and fungi, respectively. In addition, qPCR was conducted that targeted the 16S rRNA and ITS region of bacteria and fungi, respectively. The highest and lowest concentrations of phenolics were from Sambucus nigra and Ribes aureum, respectively. There were no significant differences between 16S rRNA and ITS abundance among treatments. Sequencing showed a significant difference between the rhizosphere bacterial community compositions on a global level. Specifically, several Actinobacteria were over-represented in the low-phenolic-exuding plants, while high-phenolic-exuding plants were over-represented by several Proteobacteria. There were no significant differences between the fungal populations of treatments and all were dominated by Ascomycota. However, high-phenolic exuders had a higher abundance of Basidiomycota, than the low-phenolic exuders. Results showed that different microbial communities were selected for by high polyphenol-exuding plants and low polyphenol-exuding plants. This selection was more pronounced in bacteria than in fungi. The drastic ways in which bacteria respond to phenolic inputs highlight their importance in phytoremediation
Cover- and Double-Cropping Impacts on Soil Health and Moisture of a Dryland Winter Wheat System in the Texas Rolling Plains
Get PDFConstraints on food, land and water resources pose a need for conservation practices to maintain viable agricultural lands. Wheat - a staple cereal grain for humans and animals worldwide - has been heavily cultivated in the Great Plains of the United States well before the 1900s. Historically in this region, tillage and fallow periods were implemented as a means to conserve soil moisture during summer months. However, almost 100 years ago, these practices in conjunction with long periods of drought followed by large wind events resulted in the Dust Bowl of the 1930s and brought immense erosion and loss of topsoil to the southern Great Plains. Advances in conservation management to provide crop cover to soil surfaces and reduction in tillage have helped protect the soil in the Great Plains; however, adoption of these practices remains low in part due to concerns for soil moisture preservation.
Although the potential for no-tillage and cover crops to protect the soil, build organic matter, and improve soil health has been demonstrated across much of the USA, little research has focused on the application of these techniques to the Texas Rolling Plains region. The objective of this study was to evaluate cover and double cropping practices in a wheat monocropping system under no-till management and their effects on soil health and soil moisture. A wheat-fallow control was compared to seven treatments with various cover crops in rotation including legumes and mixtures treated as cover crops or double crops. Soils were collected and analyzed for biological, chemical and physical properties including microbial biomass, mineralizable carbon, soil carbon and nitrogen fractions, soil aggregate distribution and water content. After three years of cover crops in rotation, there was generally greater soil microbial biomass and activity with treatments receiving cover. In addition, by implementing cover and double crops, soil moisture was not negatively impacted during the study period and those treatments had greater volumetric water content following precipitation events compared to the wheat-fallow control. Some parameters of soil health did not respond to the intensified wheat system; however, many soil characteristics (such as soil organic carbon) change on decadal time scales, and longer-term studies may be needed to more fully evaluate their potential responses. Results indicate cover and double crops can be a viable method to build soil health and sustainability without reducing soil moisture in wheat-monocropping systems in the Texas Rolling Plains
Impact of Winter Cover Crops and Tillage on Soil Microbial Populations and Mycorrhizal Colonization in Dryland Cotton
Get PDFCotton producers are interested in adopting conservation tillage for potential soil health benefits such as increasing soil microbial biomass. However, little is known about the resulting impacts of cover crops and tillage practices on soil microorganisms, especially plant beneficial microbes such as AMF abundance and interactions with cotton plants under dryland conditions. The objectives of this study were to evaluate soil microbial biomass and soil parameters in different tillage systems and cover crop rotations with dryland cotton, and to evaluate root colonization and AMF diversity in these treatments. A multi-year field study was conducted with a randomized-complete block design, with four replicates. Treatments included conventional tillage, no-till, and no-till with a variety of different cover crops. Prior to planting in year 2, soil samples (0-7.5 cm depth) were collected and characterized for microbial biomass using phospholipid fatty acid analysis (PLFA). Mycorrhizal colonization of cotton roots was determined at multiple time points during the growing season. Individual root fragments were isolated from cotton roots, DNA extracted and used to identify mycorrhizal community structure in cotton roots by ribosomal RNA gene sequencing. The PLFA results showed little difference in microbial biomass levels between conventional tillage and no-till samples Inclusion of a cover crop increased microbial biomass by up to 2-fold. In August, the use of cover crops increased percentage of mycorrhizal colonization of cotton, as higher root colonization was observed in hairy vetch, Austrian winter field pea and crimson clover. Root colonization was lowest in conventionally tilled plots. In October, the differences in root-colonization among the treatments had largely disappeared. Principal coordinate analyses of relative abundance of AMF species (operational taxonomic units) indicated that different cover crop treatments influenced AMF community structure in cotton roots. In August, AMF species colonizing cotton roots were similar in most treatments. The AMF community structure appeared distinct between conventional tillage and cover crop treatments by October. The results indicated that cover crops demonstrated positive legacy effects by increasing soil microbial biomass and AMF colonization of cotton roots, especially at the initial growth stages of cotton. These impacts could translate to higher drought tolerance and productivity under dryland conditions
- …
