1,720,955 research outputs found
Speciation and persistence of tetracycline antibiotics in the aquatic environment: Characterization in terms of a linear rate model
No full textThe present work aimed at studying the degradation of tetracycline antibiotics in the aquatic environment with a view of arriving at a linear rate model taking into account microbial, photolytic and hydrolytic degradation, as well as adsorption/desorption equilibria. The degradation of the antibiotics was monitored both in river water and sediment of the aquatic microcosm experiments, as well as in control experiments consisting of distilled water over a period of 90 days. Ultrasonic assisted dispersive solid phase extraction was used to extract the antibiotics from water and sediment samples. High performance liquid chromatography coupled to a variable ultra violet detector was used to determine the changes in concentration of antibiotics over the period of 90 days. An initial loss of up to 35% at most, due to adsorption by the sediment was observed in the microcosm experiments soon after charging. Triphasic linear rates attributed to microbial degradation of free and sediment or colloidal particle 1 and 2 adsorbed antibiotic for both water phase and sediment phase of the aquatic microcosm experiments were observed for oxytetracycline, chlortetracycline and tetracycline, while biphasic kinetics attributed to degradation of free, colloidal or sediment particle bound antibiotic were observed for doxycycline. The initial rates of degradation ranged from 1.35 - 3.07 x 10-2 μg/g/day (water phase), and 7.90 x 10-3 to 4.79 x 10-2 μg/g/day (sediment phase). Oxytetracycline exhibited the highest rate of degradation while that for tetracycline was the least. The covered distilled water control experiments for all the antibiotics showed a biphasic degradation pattern attributed to hydrolysis ranging from 2 x 10-6 to 5 x 10-4μg/g/day and microbial degradation ranging from 1.8 - 2.7 x 10-3 μg/g/day. In the distilled water exposed to natural light experiments, monophasic degradation (6.9 x 10-3μg/g/day) was observed for oxytetracycline, while biphasic degradation was observed for the other antibiotics. Addition of nitrates increased slightly the initial degradation rates for the light exposed distilled water experiments while the rates increased significantly in the microcosm experiments. The slight increase observed in the control experiments consisting of distilled water is attributed to photosensitization by the nitrate ions, which form hydroxyl radicals that further degrade the antibiotics while the huge increase in the microcosm experiments is attributed to increased population of microorganisms, due to availability of nutrients (added nitrates). The addition of nitrates did not affect the subsequent slow degradation rates. This is because the degradation rates depend on the rate of desorption of the antibiotic from colloidal and sediment particle surfaces. A kinetic model taking into account hydrolysis, photolysis, microbial degradation, as well as adsorption/ desorption equilibrium is presented to explain the observed zero order kinetics in the present study
Effects of 15 Local Medicinal Plant Species on Protein Tyrosine Phosphatase 1B and Dipeptidyl Peptidase 1V Activity as Herbal Antidiabetic Type 2 Remedies
Get PDFThis study aimed at investigating plant species that are used locally in Zimbabwe to manage diabetes type 2 and their respective modes of action using in vitro studies. The plants for this study were identified by ethnobotanical studies and their respective antidiabetic potentials were evaluated using protein tyrosine phosphatase 1B (PTP 1B) and dipeptidyl peptidase IV (DPP IV) inhibition assays. Out of the 15 plant species used to manage diabetes in traditional practices, 9 inhibited PTP 1B with half maximal inhibitory concentrations (IC50) ranging from 0.03 ± 0.00 to 61.31 ± 0.70 μg/mL. The mechanism of inhibition deduced from Lineweaver-Burk plot was non-competitive inhibition for Bridelia micrantha, Brachylaena discolor, Artemisia afra, Sutherlandia frutescens and Euclea undulate, while Ziziphus mucronta extract inhibited PTP 1B enzyme in a competitive pattern. The inhibition mechanism was demonstrated by decreasing or constant Km and Vmax values. Km values ranged from 1.00 to 3.33 mM. Also 9 plant species out of the 15 studied showed DPP IV inhibition activity. Four plant species, Sutherlandia frutescens, Momordica balsamina, Bulbine latifola, and Spirostachys africanus exhibited inhibitory activity that was comparable to the approved DPP IV tight binding drug, sitagliptin with percentage inhibition ≥ 73.55 ± 0.32%. The present results provide a scientific base for the current uses of the plant species in local management of diabetes type 2. Thus these plants are not only useful in polyherbal formulations for management of diabetes type 2, but also serve as sources of lead compounds for further studies toward developing drugs for treating diabetes type 2.
Keywords: Diabetes type 2; traditional medicinal plants; enzyme inhibition; polyherbal remedies
Isolation and Quantification of Flavonoids from Kigelia africana (Lam.) Benth Fruit and Bark and their Antiradical and Antibacterial Activities
Get PDFKigelia africana is an evergreen deciduous tree used in Zimbabwe folklore medicine for wound and diabetes ulcers healing. This paper reports the isolation and quantification of flavonoids from stem barks and fruits of K. africana as well as their antibacterial and antiradical activities. Flavonoids in ethanol and ethyl-acetate extracts were quantified using UV-Vis spectrophotometry and were found to be 213.490 ± 0.001 mg/L and 36.614 ± 0.001 mg/L, respectively per quercetin equivalent. The preparative and analytical thin layer chromatography was used to profile the flavonoids from fruits and barks using ethyl-acetate and petroleum ether (3:7 v/v) mobile solvent systems. Ethanol extract yielded three flavonoids with Rf values of 0.05; 0.79 and 0.93, while the ethyl-acetate extract yielded two flavonoids with Rf values of 0.21 and 0.73. The antiradical activities of the extracts were determined using DPPH radical scavenging method using quercetin as reference, and the activities were found to be over 80% at 150 mg/L. The disc diffusion method was used for antibacterial activity determination, and flavonoids from both ethanol and ethyl-acetate extracts showed zones of inhibition ranging from 0 to 22 mm against Staphylococcus aureus and Pseudomonas aeruginosa. Although the present study revealed that flavonoids from K. africana possess significant antibacterial and antioxidant activities, more studies are necessary for them to be incorporated in polyherbal formulations for wound and diabetic ulcer topical treatments.
Keywords: Diabetic foot ulcers; Kigelia africana; Antibacterial activity; Flavonoids; Antioxidant activity
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
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