1,721,037 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
An evaluation of the microbial contamination of carcasses at a local red meat type C abattoir
No full textThesis (MSc (Microbiology)--PU for CHE, 1997.The hygiene practices at a local abattoir were monitored. The main microbial spoilage organisms associated with red meat carcasses were enumerated and characterized from ten bovine carcasses. Instead of evaluating the final product
only, samples were taken at regular positions (four) along the carcass processing/dressing line from just after skin removal (flaying) until after a chilling period of between eighteen and twenty four hours. Total aerobic plate counts, Gram-negative counts and lactic acid bacterial counts were determined. The highest microbial numbers were consistently obtained from the total aerobic plate counts (approximately 3 log10 numbers per cm2) followed by the Gram negative counts (approximately 2 log10 numbers per cm2 ) and there were no
growths observed on the lactic acid bacteria agar. Characterization of the 104 predominant bacterial isolates from total aerobic plate counts of the carcasses
indicated the presence of Pseudomonas spp. (25%), Aeromonas spp (13%), Acinetobacter and Micrococcaceae (10% each) and fewer amounts of species of Moraxella(8%) , Alteromonas (5%) , Brochothrix and Corynebacterium (4% each), Enterobacteriaceae and Staphylococcus (3% each). The microflora from the Gram-negative counts of the carcasses was also dominated by the Pseudomonas spp. (50%),
Enterobacteriaceae (15%), Aeromonas spp. (10%) the Moraxella group (5%) and non-reculturable (20%). The possible effects of the carcass dressing procedures and the chilling process on the bacterial counts were
determined. Despite the apparent observable trends where the bacterial numbers seemed to decrease after the chilling process they were of no statistical significance.Master
Veranderinge van die plasmaproteïene, proteïengebonde-jodium en die lipogram tydens eksperimentele aterosklerose
Get PDFMSc, North-West University, Potchefstroom CampusThe object of this study was to
determine what changes the plasma proteins
and thyroid function exhibit during experimental
generation of atherosclerosis in experimental
animals and how this corresponded with the
measurable changes of these phenomena during
the natural development of this disease in man.
Experimental animals were fed on a
diet rich in fat and the plasma proteins were
determined over periods of four months with the
aid of electrophoresis (chapter 5). The protein
bound iodine (P .B.I.) of the animals was also
determined over periods of four months and
compared (see chapter 5). Together with this the
changes in the lipogram over the same periods
were also correlated.
From the experiments which were
conducted, it was established that the albumin
fraction of the plasma proteins showed a drop
during the experimental generation of
atheroschlerosis while the globulins (especially
globulin) showed a rising tendency.
In this experiment the P.B. I. showed
a falling tendency which implies that the thyroid
hormone synthesis mechanism was depressed.
The blood pattern changes in a few
experimental animals were compared with each
other. It was apparent that there was a close
relationship between lipaemia, an increase in
the albumin fraction of the plasma proteins on
the one hand and a decrease in thyroid function
on the other. These changes were interpreted in
terms of disturbances of the metabolic regulating
mechanisms of the body.
It was concluded that both these
criteria could be useful in the early diagnosis
of the development of atherosclerosis - also in man.Master
A study of the early DNA methylation events in oxidative stressed cultured mammalian cells
No full textThesis (MSc (Biochemistry))--North-West University, Potchefstroom Campus, 2013Cells are continuously exposed to reactive oxygen species (ROS) causing oxidative stress. Cells can withstand and counteract ROS using defence mechanisms which range from free radical scavengers, antioxidant enzymes and DNA repair systems. Prolonged exposure of cells to oxidant species leads to the accumulation of genetic as well as epigenetic alterations. Exposure of cells to the non-radical hydrogen peroxide (H2O2) leads to the generation of hydroxyl radicals (˙OH) by Fenton reactions when H2O2 reacts with a metal iron in the vicinity of DNA. These OH are very reactive and attack DNA giving rise to lesions such as single stand breaks and base modifications, which could influence DNA methylation. DNA methylation is the post synthetic addition of methyl groups to the carbon 5 position of cytosine when cytosines are in the CpG dinucleotide context and is involved in gene expression. DNA methylation is considered to be very stable. Aberrant DNA methylation influences cancer related gene expression and genomic stability. The aim of this study was to investigate early changes in the global DNA -and gene specific methylation patterns of cultured mammalian cells when cells were exposed to H2O2. The term early refers to how soon following exposure to H2O2 over a six hour period changes in the DNA methylation pattern can be observed when exposing cells to H2O2 concentrations that causes oxidative DNA damage. Changes in the hOGG1 promoter methylation status and gene expression were evaluated as this gene plays a crucial role in the initiation of the base excision repair pathway for the repair of oxidative DNA damage caused by H2O2 exposure. Results obtained with the
alkaline comet assay showed that H2O2 exposure led to oxidative DNA damage and decreased DNA repair capacity when cells were exposed to H2O2 in fully supplemented medium (DMEM + 10% FBS). A change in the global DNA methylation pattern was evaluated with the cytosine extension assay and an enzyme based methylation sensitive PCR was used to evaluate the change in the promoter methylation status of hOGG1. Changes in the global DNA- and gene (promoter) specific methylation patterns could be observed where; a degree of global DNA hypomethylation and hypermethylation of the hOGG1 promoter could be observed within the six hour period of exposure to a
concentration of H2O2 that was also associated with a high level of oxidative DNA damage. Finally, a decrease in the expression of the hOGG1 gene was also observed following exposure to this concentration of H2O2 within the six hour exposure period. These findings
suggests that oxidative DNA damage influences DNA methylation (both globally and gene specific) and that the expression of the hOGG1 gene is possibly influenced by promoter hypermethylation which is associated with oxidative DNA damage. Results were generated in human osteosarcoma (143B) cells. This cell line was used in order to investigate the effect of oxidative stress on the global DNA methylation pattern as well as the promoter methylation- and expression of the hOGG1 gene in wild type 143B cells (uncompromised complex III). Previous studies reported that in 143B cells in which complex III of the respiratory chain was compromised, by a knockdown system, deviations in the global DNA methylation pattern as well as the promoter methylation and expression of genes involved in DNA repair pathways could be observed.Master
Diversity in the applications of the single cell gel electrophoresis (comet) assay
Get PDFThesis (M.Sc. (Biochemistry))--North-West University, Potchefstroom Campus, 2005.The development of the single cell gel electrophoresis assay (Comet assay) as a
powerful method for measuring DNA strand breakage and repair, has lead to a broader understanding of the impact of certain internal and external factors on DNA damage. This study describes the establishment of the Comet assay in our
laboratory and its application in a diversity of studies. These studies include the monitoring of the effect of exercise on DNA damage and repair with the purpose of establishing the optimal exercise program for middle aged men; in the analysis of DNA repair in a breast cancer patient after chemotherapy, we demonstrated that to get a really informative picture of baseline DNA damage, it is necessary to invoke some type of insult to the DNA; we also studied the antioxidant activity of plant extract and finally an industrial application of the Comet assay where we studied DNA damage and repair in the lymphocytes of people exposed to a variety of chemicals. The Comet assay was made even more informative by
incorporating additional steps by digesting the DNA on the microscope slides with enzymes that recognize particular kinds of damage to the nucleic acid (formamidopyrimidine DNA glycosylase (Fpg) and Endonuclease lll (Endo lll). From these applications we can safely conclude that we have established the Comet assay as reproducible assay with proven diversity in its applications. The most significant contribution of this study is the quite novel modification of the Comet assay to monitor the methylation status of DNA. In this we applied the restriction endonuclease enzymes, Hpa ll and Msp I, which have different sensitivities to methylation of their common target site. Changes in the
methylation levels of DNA after treatment of animals and isolated cells with chemicals with known effects on DNA, were convincingly demonstrated and indications of cell specificity in DNA methylation were observed. We believe that this modification opens a new field of applications for the Comet assay.Master
Determining DNA damage and repair in human cells exposed to metabolites characteristic for tyrosinemia
Get PDFThesis (M.Sc. (Biochemistry))--North-West University, Potchefstroom Campus, 2005.Hereditary Tyrosinemia (HTI) is an autosomal recessive disorder caused by a deficiency of fumarylacetoacetate hydrolase (FAH) but the mechanism by which the hepatic and renal symptoms of HTI arise is largely unknown. The current hypothesis is that the final metabolites of tyrosine catabolism
(maleylacetoacetate and fumarylacetoacetate, and their derivatives,
succinylacetone and succinylacetoacetate) are toxic, and can possibly act as alkylating agents and/or disrupt sulfhydryl metabolism. In addition, aminolevulinic acid (ALA) accumulates under pathological conditions. Development of hepatic tumours is a characteristic of this inherited disease. The aim of this study was to use the comet assay (single cell gel electrophoresis) with isolated lymphocytes and primary hepatic cells to study the genotoxicity of the accumulating metabolites to contribute towards a better understanding of the underlying mechanisms responsible for the pathophysiology of this disease. From the results it was seen that the exposure of both isolated lymphocytes and hepatocytes to SA, ALA and pHPPA separately, caused DNA damage but a high degree of DNA repair in the exposed cells was also observed. Upon further investigation it was seen that the damage caused by SA and ALA inhibited the
cells' capacity to repair damaged DNA but some repair was still possible as was reflected in the low calculated repair capacity. The marked increase in DNA
damage in isolated lymphocytes and the much lower calculated repair capacity in
the hepatocytes, however, suggested that specific damage caused by pHPPA may have had an effect on the repair mechanisms of the cell. Contrary to previous reports (Mitchell et a/, 2001), pHPPA could have a definitive role in contributing to the clinical features such as the hepatocarcinogenesis
characteristic of HT1.Master
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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