United Arab Emirates University

About: United Arab Emirates University is a education organization based out in Al Ain, United Arab Emirates. It is known for research contribution in the topics: Population & Diabetes mellitus. The organization has 6227 authors who have published 14170 publications receiving 321143 citations. The organization is also known as: University of the United Arab Emirates & UAEU.

Effect of aspect ratio on the elastic buckling of uniaxially loaded plates with eccentric holes

Abstract: The Finite Element Method (FEM) has been employed to determine the elastic buckling load of uniaxially loaded rectangular perforated plates with length a and width b. Plates with simply supported edges in the out-of-plane direction and subjected to uniaxial end compression in their longitudinal direction are considered. Integer plate aspect ratios, a/b=1, 2, 3 and 4, have been chosen to assess the effect of aspect ratio on the plate buckling load. Two perforation shapes of different sizes are considered; circular, and rectangular with curved corners. The rectangular perforation is oriented such that either its long or its short side is parallel to the longitudinal direction of the plate. The center of perforation was chosen at different locations of the plate. The study shows that the buckling load of a rectangular perforated plate that could be divided into equal square panels is not the same as that of the square panel that contains the perforation when treated as a separate square plate. For rectangular plates, the study recommends not to have the center of a circular hole placed in a critical zone defined by the end half of the outer square panel, to try always to put the hole in an interior panel of the plate, and to have the distance between the edge of a circular hole and the nearest unloaded edge of the plate not less than 0.1b. The study concludes also that the use of a rectangular hole, with curved corners, with its short dimension positioned along the longitudinal direction of the plate is a better option than using a circular hole, from the plate stability point of view.

Kinetics and mechanisms of decomposition reaction of hydrogen peroxide in presence of metal complexes

Abstract: Hydrogen peroxide was discovered in 1818 and has been used in bleaching for over a century [1]. H2O2 on its own is a relatively weak oxidant under mild conditions: It can achieve some oxidations unaided, but for the majority of applications it requires activation in one way or another. Some activation methods, e.g., Fenton's reagent, are almost as old [2]. However, by far the bulk of useful chemistry has been discovered in the last 50 years, and many catalytic methods are much more recent. Although the decomposition of hydrogen peroxide is often employed as a standard reaction to determine the catalytic activity of metal complexes and metal oxides [3,4], it has recently been extensively used in intrinsically clean processes and in end-of-pipe treatment of effluent of chemical industries [5,6]. Furthermore, the adoption of H2O2 as an alternative of current industrial oxidation processes offer environmental advantages, some of which are (1) replacement of stoichiometric metal oxidants, (2) replacement of halogens, (3) replacement or reduction of solvent usage, and (4) avoidance of salt by-products. On the other hand, wasteful decomposition of hydrogen peroxide due to trace transition metals in wash water in the fabric bleach industry, was also recognized [7]. The low intrinsic reactivity of H2O2 is actually an advantage, in that a method can be chosen which selectively activates it to perform a given oxidation. There are three main active oxidants derived from hydrogen peroxide, depending on the nature of the activator; they are (1) inorganic oxidant systems, (2) active oxygen species, and (3) per oxygen intermediates. Two general types of mechanisms have been postulated for the decomposition of hydrogen peroxide in the presence of transition metal complexes. The first is the radical mechanism (outer sphere), which was proposed by Haber and Weiss for the Fe(III)-H2O2 system [8]. The key features of this mechanism were the discrete formation of hydroxyl and hydroperoxy radicals, which can form a redox cycle with the Fe(II)/Fe(III) couple. The second is the peroxide complex mechanism, which was proposed by Kremer and Stein [9]. The significant difference in the peroxide complex mechanism is the two-electron oxidation of Fe(III) to Fe(V) with the resulting breaking of the peroxide oxygen-oxygen bond. It is our intention in this article to briefly summarize the kinetics as well as the mechanisms of the decomposition of hydrogen peroxide, homogeneously and heterogeneously, in the presence of transition metal complexes. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 643–666, 2000

The prevalence of psychological consequences of COVID-19: A systematic review and meta-analysis of observational studies.

Abstract: A systematic review and a meta-analysis were conducted to examine the overall prevalence of psychological health outcomes during COVID-19. Seven databases were systematically searched to include studies reporting on at least one psychological outcome. The pooled prevalence of primary psychological outcomes was 26% (95%CI: 21-32). Pooled prevalence for symptoms of PTSD was 33% (0-86), anxiety 28% (21-36), stress 27% (14-43), and depression 22% (13-33). The prevalence of psychological outcomes was similar in healthcare workers and in the general population (34% [24-44] and 33% [27-40] respectively). High prevalence figures support the importance of ensuring adequate provision of resources for mental health.

Antimicrobial peptide defenses of the mountain yellow-legged frog (Rana muscosa).

Abstract: The mountain yellow-legged frog (Rana muscosa) inhabits high elevation lakes in California that are largely undisturbed by human activities. In spite of this habitation in remote sites, populations continue to decline. Although predation by non-native fish is one cause for declines, some isolated populations in fishless lakes are suffering new declines. One possible cause of the current wave of declines is the introduction of the pathogenic chytrid fungus (Batrachochytrium dendrobatidis) which invades the adult skin to cause chytridiomycosis. In many amphibian species, the skin is protected by antimicrobial peptides secreted into the mucous. Here we show that R. muscosa produces three previously unknown antimicrobial peptides belonging to the ranatuerin-2 and temporin-1 families of antimicrobial peptides. These three peptides, along with bradykinin, are the most abundant peptides in the skin secretions detected by mass spectrometry. Natural mixtures of peptides and individual purified peptides strongly inhibit chytrid growth. The concentration of total peptides recovered from the skin of frogs following a mild norepinephrine induction is sufficient to inhibit chytrid growth in vitro. A comparison of the species susceptibility to chytridiomycosis and the antichytrid activity of peptides between R. muscosa and R. pipiens suggest that although R. muscosa produces more total skin peptides, it appears to be more vulnerable to B. dendrobatidis in nature. Possible differences in the antimicrobial peptide repertoires and life history traits of the two species that may account for differences in susceptibility are discussed.

Prospective chemistry teachers' conceptions of the conservation of matter and related concepts

Abstract: This study investigated the quality and extent of understanding of certain well-known theoretical concepts which prospective teachers of chemistry in Yemen possess. In addition to the concepts of the conservation of atoms and mass, and the mole, the concepts of atomic mass and balancing chemical equations were chosen for this study. An instrument was built first, then administered to 173 junior and senior prospective chemistry teachers. The results showed that the prospective teachers' understandings of most of the concepts ranged from a partial understanding with specific misconception to no understanding. Only on balancing chemical equations did the prospective teachers show good understanding. The results showed that most prospective teachers depended on mere memorization of the concepts without meaningful understanding. It also found that the prospective teachers' knowledge about the concepts was fragmented and not correlated. The study attributed the prospective teachers' misconceptions to defective instruction. Finally, the study concluded that more effective teaching methods are needed to ensure a sound understanding of these concepts. © 1997 John Wiley & Sons, Inc. J Res Sci Teach 34: 181–197, 1997.