1,720,980 research outputs found
Ecology and modelling of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in cattle manure and soil
Get PDFThe number of food poisoning cases caused by enteropathogens has increased in recent years. A significant part of the outbreaks associated with the consumption of raw vegetables has been attributed to Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium. Bovine manure and slurry are the main environmental sources of these pathogens. Thus, reduction of the multiplication of E. coli O157:H7 and Salmonella serovar Typhimurium in cattle and their survival in manure and slurry are important tasks to minimize the risks of contamination of plant products and outbreaks of food-borne diseases. This thesis describes the influence of various environmental factors on survival of E. coli O157:H7 and Salmonella serovar Typhimurium in manure, slurry and soil amended with manure or slurry. The results presented in this thesis can be used for risk assessment of E. coli O157:H7 and Salmonella serovar Typhimurium in dairy farming systems and will help to identify and evaluate potential control strategies to minimize the chance of pathogen spread in the vegetable production chain
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
Tick tactics : interactions between habitat characteristics, hosts and microorganisms in relation to the biology of the sheep tick Ixodes ricinus
No full textThe sheep tick Ixodes ricinus (L.) is known to transmit a large number of pathogens of medical and veterinary importance, including the bacterium Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis. Ixodes ricinus is found predominantly in woodlands, which provide suitable hosts and microclimates for tick survival. Three blood meals from a wide array of possible hosts are needed to complete the tick life cycle within 2 to 6 years. Ticks can acquire B. burgdorferi s.l. during a blood meal on an infected host and can infect a new host during the next blood meal. In this thesis, interactions between hosts, habitat characteristics, and microorganisms in relation to the biology of I. ricinus were investigated. A longitudinal study that was initiated at 24 sites across The Netherlands revealed that ticks infested with B. burgdorferi s.l. were found at all sites, but with strong spatial and temporal variation. This variation could be partially attributed to habitat characteristics. Substantial variations in the bacterial diversity within I. ricinus nymphs were also observed between habitats. Molecular genetic analyses indicated the presence of several potentially pathogenic and non-pathogenic bacteria. The interactions of these bacteria with hosts, ticks and other micro-organisms that reside in the tick need to be established in the future. It is known that rodent populations can mediate B. burgdorferi s.l. circulation in nature. Therefore, we studied the potential effects of rodents on the spatial variation of Borrelia infections in host-seeking ticks. Wood mice (Apodemus sylvaticus) and bank voles (Myodes glareolus) were abundant at most sites, but had varying tick burdens and Borrelia-infection prevalence between sites. It is argued that the infection prevalence in host-seeking I. ricinus ticks in the vegetation depends on the degree of contact between ticks and mice, which is, in turn regulated by habitat characteristics.Larger hosts, such as ruminants, are important for tick reproduction. Because domestic cattle is frequently used in the management of forested areas in The Netherlands, the effect of such management on tick populations was addressed. Results from this thesis show that the presence of cattle in a woodland resulted in a locally reduced tick density, whereas Borrelia infection prevalence remained the same compared to ungrazed woodlands. The tick-reducing effect of cattle was attributed to the negative effect of cattle on rodent populations. Effects of other mechanisms such as habitat alteration by the cattle are arguable and require further study. A central issue in the ecology of Lyme borreliosis is the mechanism by which Borrelia species circulate between the life stages of ticks and their hosts. This circulation is strongly affected by the chance that the tick will find a host. It was found that that B. burgdorferi s.l.-infected I. ricinus nymphs displayed increased walking activity and had a greater resistance to desiccation than uninfected ticks. These Borrelia-mediated effects can contribute to increased chances of host finding by the tick, and thereby to an increased transmission of Borrelia species. In conclusion, Borrelia-infected ticks were present at all locations studied, but with a dynamic heterogeneity, which is partly influenced by habitat characteristics and rodent hosts. The introduction of large herbivores could become an advantageous management strategy to help reduce the incidence of Lyme borreliosis, and further experiments confirming the mechanisms underlying this relationship would be valuable. The established B. burgdorferi s.l.-mediated behavioural changes in I. ricinus contribute to the understanding of the ecology of Lyme borreliosis, and create opportunities for future studies on tick-parasite interactions
Ecology and modelling of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in cattle manure and soil
No full textThe number of food poisoning cases caused by enteropathogens has increased in recent years. A significant part of the outbreaks associated with the consumption of raw vegetables has been attributed to Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium. Bovine manure and slurry are the main environmental sources of these pathogens. Thus, reduction of the multiplication of E. coli O157:H7 and Salmonella serovar Typhimurium in cattle and their survival in manure and slurry are important tasks to minimize the risks of contamination of plant products and outbreaks of food-borne diseases. This thesis describes the influence of various environmental factors on survival of E. coli O157:H7 and Salmonella serovar Typhimurium in manure, slurry and soil amended with manure or slurry. The results presented in this thesis can be used for risk assessment of E. coli O157:H7 and Salmonella serovar Typhimurium in dairy farming systems and will help to identify and evaluate potential control strategies to minimize the chance of pathogen spread in the vegetable production chain
Oligotrophic bacteria and root disease suppression in organically managed soils
No full text The objective of this thesis was to obtain a better understanding of soil health in terms of microbial and chemical characteristics as well as suppression of soil borne plant pathogens. Organic soils were chosen as an appropriate model for studying soil health. Four different organic amendments were applied on two experimental fields with different crop history, providing a diverse range of soil quality levels. Many soil microbial variables were measured, including copiotrophic and oligotrophic bacterial populations, the abundance and diversity of Eubacteria, Alphaproteobacteria, Pseudomonas and fungal communities, as well as several microbial genes involved in nitrogen cycling. Plant disease suppressiveness was used as a quantitative integrative parameter reflecting the health status of soils. Rhizoctonia solani on beet and Fusarium oxysporum on flax were selected as pathosystems; areas under disease progress curves were measured in bioassays with differentially amended field soils and were related to soil parameters. Combined rather than single amendments enhanced Fusarium suppression, but Rhizoctonia suppression was more related to crop history than organic amendments. No universal correlations were found between disease suppression and microbial and chemical parameters, although pH and organic matter affected microbial communities and Fusarium wilt. A significant relation between ammonia oxidizing bacteria and disease suppression was observed for both pathogens; this relation was likely indirect via nitrogen availability and pH. No direct relationship was found between quantities of N cycling genes and disease suppression. A specific emphasis was put on the potential role of oligotrophic bacteria in soil health and disease suppression. Bacteria isolated on low carbon medium (10 mg C/L) were repeatedly transferred onto this medium to select true oligotrophic bacteria. Most isolates could grow on both low carbon and higher carbon (1000 mg C/L) media and belonged to Streptomyces, Rhizobium, Bradyrhizobium and Mesorhizobium. A new oligotrophic isolate was identified as Collimonas sp. IS343 and its interaction with R. solani was studied. This strain was better adapted to oligotrophic conditions than a copiotrophic Collimonas reference strain and was more effective in controlling R. solani. This thesis provided a better understanding of some aspects of soil health and emphasized the role of oligotrophic bacteria, a poorly understood but very important group of soil inhabitants.</p
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
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