1,720,973 research outputs found
Mechanisms behind the cholesterol-reducing effect of cereal soluble dietary fibres: (1,3:1,4) beta glucan & arabinoxylan
No full textEpidemiological, clinical and animal studies have shown a positive relationship between diets rich in soluble dietary fibres (SDF) such as -glucan (βG), pectin, guar gum, psyllium and arabinoxylan (AX), and reduced serum cholesterol leading to a decreased risk of cardiovascular disease (CVD). Three mechanisms have been proposed to explain the cholesterol-reducing effects of SDF: prevention of bile salts (BS) reabsorption from the small intestine leading to an excess faecal BS excretion; reduced glycemic response leading to lower insulin stimulation of hepatic cholesterol synthesis; and fermentation products of SDF, mainly propionate causing a reduced hepatic cholesterol synthesis via enzyme inhibition. The most convincing evidence has been reported for the BS “binding” mechanism; however the nature of the interactions between the BS-cholesterol mixed micelles and SDF are poorly defined. Therefore in this thesis, three physicochemical mechanisms have been postulated and in vitro experiments carried out to test these hypotheses on simple systems made up of mono-molecular BS micelles and different sources and molecular weights SDFs. These hypotheses are: Hypothesis 1: SDF increases the barrier properties of the unstirred layer between BS micelles & intestinal absorptive cells Hypothesis 2: SDF & BS are associated / complexed at a molecular level Hypothesis 3: SDF forms a local matrix that entraps BS micelles. Further, an animal experiment in which pigs were used as a human model was carried out to investigate whether a wheat soluble arabinoxylan rich fraction (AXRF) added to a typical Western diet lowers blood cholesterol and triglycerides by the same mechanisms as βGs. The passage kinetics of a model bile salt and complete porcine bile across a dialysis membrane of 20 KDa MWCO in the presence and absence of two cereal SDF polysaccharides barley βG and wheat AX has been studied as a model for passage across the unstirred water layer that lines the small intestine. A first-order kinetic analysis was used to calculate the rate coefficients (K) which quantified the effectiveness of barley βG and wheat AX in retarding the transport of bile salts. For both the model bile salt and porcine bile, steady state viscosity was shown to be more related to rate coefficients than concentration. These results suggest that both polymers delay the passage of BS, with effectiveness determined by solution viscosity. The 2nd and 3rd hypotheses have been studied using 13C nuclear magnetic resonance (NMR) spectroscopy and small angle X-ray scattering (SAXS). Investigation of molecular interactions were carried out between model BS (taurochenodeoxycholate: TCDC or glycochenodeoxycholate: GCDC) micelles with each of bG and AX. The results showed that the SDFs interact differently with the BS depending not only on the source but also on their molecular weights. In the presence of oat and barley bG, small chemical shift changes were observed in the BS resonances, but not in the bG resonances, without any apparent change in line widths. The SAXS results showed that the X-ray scattering of the BS and bG were not additive and consistent with changed dimensions of bG in the presence of BS. The combined results from NMR and SAXS suggest that the BS micelles form dynamic interactions leading to temporary adsorption to the polymer. In contrast, in the presence of low and medium molecular weights wheat AX, no systematic chemical shift changes for either TCDC/GCDC or AX resonances were found, but line broadening with decreased intensities of the TCDC/GCDC signals was observed. The SAXS results showed that the scattering of the BS and AX were additive with no change in the dimensions of either component in the presence of the other. These results suggest that the AX polymers form local networks entrapping the micelles and restricting their mobility. High molecular weight barley and oat βG and rye AX form both close molecular interactions and network with the micelles. In the animal trial, 40 male pigs were separated by weight into 4 groups and each group was fed on one of 4 experimental diets for 4 weeks. They were then anesthetised and blood and intestinal samples were collected. The diets were comprised of a typical Western diet containing low or high red meat content with and without added wheat arabinoxylan-rich fraction (AXRF). The blood samples were analysed for total BS in the jugular (JV) and hepatic portal (HP) veins while total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and triglycerides (TAG) were analysed in the JV. The intestinal samples taken from 4 sections of the small intestine and the caecum were analysed for individual BS and fatty acids (FA) apparent digestibility. The pigs fed the AXRF diets had significantly decreased blood BS from both locations (P-values: HPV=0.003; JV=0.001) and TAG (P=0.02) but with no effect on cholesterol (P-values: TC=0.28; LDL-C=0.45), the latter probably because the Western-style diet did not induce hypercholesterolemia. The reduced blood TAG levels were consistent with the reduced/delayed TAG digestion in the small intestine found in the presence of AXRF (P-values: total fat=0.02; SFA=0.08; MUFA=0.01; unsaturated FA=0.02)
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
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
- …
