T.D. Malevu

Bio: T.D. Malevu is an academic researcher from University of KwaZulu-Natal. The author has contributed to research in topics: Materials science & Scanning electron microscope. The author has an hindex of 4, co-authored 11 publications receiving 137 citations. Previous affiliations of T.D. Malevu include Sefako Makgatho Health Sciences University & University of the Free State.

A Summary of New Findings on the Biological Effects of Selenium in Selected Animal Species-A Critical Review.

Abstract: Selenium is an essential trace element important for many physiological processes, especially for the functions of immune and reproductive systems, metabolism of thyroid hormones, as well as antioxidant defense. Selenium deficiency is usually manifested by an increased incidence of retention of placenta, metritis, mastitis, aborts, lowering fertility and increased susceptibility to infections. In calves, lambs and kids, the selenium deficiency demonstrates by WMD (white muscle disease), in foals and donkey foals, it is associated with incidence of WMD and yellow fat disease, and in pigs it causes VESD (vitamin E/selenium deficiency) syndrome. The prevention of these health disorders can be achieved by an adequate selenium supplementation to the diet. The review summarizes the survey of knowledge on selenium, its biological significance in the organism, the impact of its deficiency in mammalian livestock (comparison of ruminants vs. non-ruminants, herbivore vs. omnivore) and possibilities of its peroral administration. The databases employed were as follows: Web of Science, PubMed, MEDLINE and Google Scholar.

Effect of annealing temperature on nano-crystalline TiO2 for solar cell applications

Abstract: This study investigates the effect of annealing temperature (AT) on structure, morphology and optical properties of hydrothermally synthesized TiO2 nanocrystals. Selected-Area Diffraction (SAED) confirmed high quality monocrystals. XRD and Raman spectroscopy indicate only anatase and rutile phases. At high temperature, the (101) and (001) are preferred. PL emission peaks appear at 407, 416 and 493 nm, which can be attributed to photo-excited electron-hole pairs, band-edge excitons and oxygen vacancy defects, respectively. UV–Vis spectroscopy indicates that AT over the 200–600 °C temperature range causes the band gap to decrease from 3.08 eV to 2.73 eV. Hydrothermal synthesis followed by annealing at 600 °C is found to be a good route for high-purity, nanocrystalline anatase-phase TiO2 with the preferred {001} orientation that is thought to enhance solar cell performance.

Developments on Perovskite Solar Cells (PSCs): A Critical Review

Abstract: This review provides detailed information on perovskite solar cell device background and monitors stepwise scientific efforts applied to improve device performance with time. The work reviews previous studies and the latest developments in the perovskite crystal structure, electronic structure, device architecture, fabrication methods, and challenges. Advantages, such as easy bandgap tunability, low charge recombination rates, and low fabrication cost, are among the topics discussed. Some of the most important elements highlighted in this review are concerns regarding commercialization and prototyping. Perovskite solar cells are generally still lab-based devices suffering from drawbacks such as device intrinsic and extrinsic instabilities and rising environmental concerns due to the use of the toxic inorganic lead (Pb) element in the perovskite (ABX3) light-active material. Some interesting recommendations and possible future perspectives are well articulated.

A Review of the Impact of Zinc Oxide Nanostructure Morphology on Perovskite Solar Cell Performance

Abstract: Zinc oxide (ZnO) has been widely studied over the last decade for its remarkable properties in optoelectronic and photovoltaic devices because of its high electron mobility and excitonic properties. It has probably the broadest range of nanostructured forms that are also easy and cheap to synthesize using a wide variety of methods. The volume of recent work on ZnO nanostructures and their devices can potentially overshadow significant developments in the field. Therefore, there is a need for a concise description of the most recent advances in the field. In this review, we focus on the effect of ZnO nanostructure morphologies on the performance of ZnO-based solar cells sensitized using methylammonium lead iodide perovskite. We present an exhaustive discussion of the synthesis routes for different morphologies of the ZnO nanostructure, ways of controlling the morphology, and the impact of morphology on the photoconversion efficiency of a given perovskite solar cell (PSC). We find that although the ZnO nanostructures are empirically similar, one-dimensional structures appear to offer the most promise to increasing photoconversion efficiency (PCE) by their proclivity to align and form vertically stacked layers. This is thought to favor electron hopping, charge mobility, and conductivity by allowing multiple charge conduction pathways and increasing the effective junction cross-sectional area. The combined effect is a net increase in PCE due to the reduced surface reflection, and improved light absorption.

Phase transformations of high-purity PbI2 nanoparticles synthesized from lead-acid accumulator anodes

Abstract: High-purity hexagonal lead iodide nanoparticles have been synthesized from a depleted sealed lead acid battery anode. The synthesized product was found to consist of the rare 6R polytype form of PbI 2 that is thought to have good potential in photovoltaic applications. We investigate the effects of annealing time and post-melting temperature on the structure and optical properties using 1.5418 A CuK α radiation. Photoluminescence measurements were done under 150 W/221 nm wavelength xenon excitation. Phase transformation was observed through XRD peaks when annealing time increased from 0.5–5 h. The nanoparticle grain size and inter-planar distance appeared to be independent of annealing time. PL measurements show three broad peaks in a range of 400 nm to 700 nm that are attributed to excitonic, donor–acceptor pair and luminescence bands from the deep levels.

Nutrient requirements of dairy cattle

Abstract: Nutrient requirements of dairy cattle , Nutrient requirements of dairy cattle , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

The Role of Selenium in Arsenic and Cadmium Toxicity: an Updated Review of Scientific Literature

Abstract: Arsenic (As) and cadmium (Cd) are elements arousing major public health concerns associated with environmental pollution, high toxicity potential, and carcinogenic nature. However, selenium (Se) at low doses and incorporated into enzymes and proteins has antioxidant properties and protects animals and humans from the risk of various diseases. It also has an exceptionally narrow range between necessary and toxic concentrations, which is a well-known hindrance in its use as a dietary supplement. The present article aims to update and expand the role of Se in As and Cd toxicity discussed in our earlier paper. In general, recent reports show that Se, regardless of its form (as selenite, selenomethionine, nanoSe, or Se from lentils), can reduce As- or Cd-mediated toxicity in the liver, kidney, spleen, brain, or heart in animal models and in cell culture studies. As was suggested in our earlier review, Se antagonizes the toxicity of As and Cd mainly through sequestration of these elements into biologically inert complexes and/or through the action of Se-dependent antioxidant enzymes. An increase in the As methylation efficiency is proposed as a possible mechanism by which Se can reduce As toxicity. However, new studies indicate that Se may also diminish As or Cd toxicity by activation of the Nrf2 pathway. In addition, this paper discusses possible signs of Se toxic effects, which may be a challenge for its future use in the therapy of As and Cd poisoning and provide future directions to address this issue.

The minerals

Abstract: Minerals are essential inorganic elements that have a significant impact on growth development and health of fish. Among vertebrates, fish are unique in their ability to absorb minerals from their diets but also from water across gills and skin. Although significant progress has been made in the past 2 decades on requirements of certain minerals (phosphorus, zinc, copper, and selenium), a major gap exists in the uptake, function, biological availability, and excretion of most minerals. Several deficiency signs including cataracts, skeletal deformities, and hatchability of eggs have been linked to trace element deficiencies. In recent years, major shifts from the use of fishmeal to plant ingredients have resulted in a focus on mineral bioavailability; however, interactions between minerals and their uptake from water justify a much broader approach in this area. This chapter provides a brief overview of the known functions, deficiencies, requirements, and bioavailability of minerals and identifies certain issues yet to be resolved.

Shifts in thioredoxin reductase activity and oxidant status in mononuclear cells obtained from transition dairy cattle.

Abstract: Measures of oxidative status were examined in 14 dairy cows during the transition period. Blood samples were obtained approximately 21 d before expected calving, at calving, and again at 21 d in milk (DIM). Plasma samples were used to determine lipid hydroperoxide concentrations. Total white blood cells were used to determine the oxidative status of glutathione. Peripheral blood mononuclear cell (PBMC) lysates were used to determine the total antioxidant potential and enzymatic activities of glutathione peroxidase (GPX) and thioredoxin reductase (TrxR1). Both plasma lipid hydroperoxide concentrations and GPX activity in PBMC increased at calving and during the first 21 DIM when compared with prepartum samples. Conversely, the total antioxidant potential and TrxR activity declined in PBMC during the first 21 DIM, even though both GPX activity and the glutathione-to-GSSG ratio remained elevated during this time period. Results from this study support previous findings that report increased GPX activity when reactive oxygen metabolites, including lipid hydroperoxides, increase in transition dairy cows. The significant decrease in TrxR activity with a concomitant decrease in total antioxidant potential in PBMC during this same stage of lactation, however, would suggest that this selenoprotein is not able to rebound during periods of oxidative stress to the same extent as GPX1. This study shows for the first time that TrxR may be an important antioxidant defense mechanism in PBMC that is compromised during the periparturient period.