A Composite Cylinder Model for the Prediction of Residual Stresses in Gamma-Titanium Composites

An experimental study of the residual stress formation and evolution in ␥-titanium-based composite material was completed for some important processing and heat treatment conditions. A concentric cylinder model based on Norton's creep law with the coefficients replaced by new terms related to time and temperature was developed by a combination of viscoplasticity and thermoelastic analysis of concentric cylinder domains representative for the matrix and the fiber. The x-ray diffraction (XRD) technique was used to measure average residual stresses at the neighborhood of Saphikon fibers. The composite was fabricated by hot isostatic pressing. The residual stress at the matrix decreased as the temperature of the heat treatment increased up to an optimum value, after which the residual stress started to build up despite the increase in the annealing temperature. This phenomenon was depicted through the numerical model as well as in the XRD

IMECE2005-81122 ADHESION ENERGY OF SINGLE WALL CARBON NANOTUBE-POLYETHYLENE COMPOSITE: EFFECT OF MAGNETIC FIELD

ABSTRACT In this paper, we investigate the adhesion energy at the interface between single wall carbon nanotubes and polyethylene matrix with and without an external magnetic field. The carbon nanotubes are of two different chiralities --armchair (10,10), and zigzag (10,0), and the external high magnetic field is of 25 Tesla intensity. The study employs molecular dynamics simulations and concludes that the magnetic field decreases the interfacial adhesion energy although it increases the individual potential energies of the nanotubes, the polyethylene, and the composite

Water-pipe smoking and serum testosterone levels in adult males in Qatar.

Water-pipe (WP) smoking is the most common method of tobacco consumption in the Middle-East and is rapidly spreading on a global scale. Although, water-pipe smoking is linked to various diseases, such as emphysema and various types of cancers, its effect on testosterone levels has yet to be investigated. This study explores the effect of water-pipe smoking on serum testosterone levels in males in Qatar. In this cross-sectional sample within a cohort study, we retrieved data for a total of 1000 male volunteers from the Qatar BioBank (QBB) project. A self-reported questionnaire was used to determine the water-pipe smoking status of participants. Moreover, participants were stratified based on the frequency of smoking. Total testosterone and sex hormone binding globulin (SHBG) were measured clinically, whereas free testosterone and bioavailable testosterone were calculated using Vermeulen's equation. Hormone values of 541 males (277 water-pipe smokers and 264 non-smokers) were compared using multiple regression analysis based on water-pipe smoking status after adjusting for confounding factors. No statistically significant difference was observed between WP smokers and non-water-pipe smokers in the likelihood of having lower or higher total testosterone, after adjustment for confounding factors. Similar results were found in free testosterone, bioavailable testosterone, and sex hormone binding globulin (all p>0.05). When compared with the reference group, both light and heavy water-pipe smokers had a similar likelihood of circulating low total testosterone levels (OR=0.83, 95% CI: 0.46-1.49; and OR=0.80, 95% CI: 0.43-1.49; respectively). Our results reveal, for the first time, that there is no significant change in total testosterone, free testosterone, bioavailable testosterone and sex hormone binding globulin in waterpipe smokers compared to non-water-pipe smokers. Therefore, we believe that further studies are needed to confirm the effect of water-pipe smoking on testosterone in different populations.This work was supported by the College of Medicine of Qatar University and grant QUST-2-CMED-2018-1 from Qatar University

Nanocharacterization of Proton Radiation Damage on Magnetically Oriented Epoxy

Abstract: In this study we investigate the shielding effectiveness of a structural epoxy against high-energy proton radiation. To study the influence of material texture on its radiation shielding effectiveness we induced orientations in the epoxy using a high magnetic field of 15 T and exposed it to proton beams of energy 6-15 MeV. The microstructure of the samples was characterized using ESEM and AFM microscopy. The effect of the radiation on the mechanical properties of the epoxy samples such as modulus and hardness was measured using nanoindentation tests

Building resilience in contemporary nursing practice

YesThe nursing profession is being threatened by staff shortages. Catherine Best explains why building resilience from within the profession is vital to safeguarding its future, by keeping newly qualified nurses in the job and preventing emotional ‘burnout’ across disciplines Resilience in nursing has been critiqued and challenged throughout the nursing literature. Trends in nursing have led to many nurses leaving the profession early in their career, often due to the immense pressures that they work under. There are many opinions on how nurses can develop the resilience needed to maintain professional integrity and continue to provide safe and effective care, while attempting to shoulder the considerable impact of political and professional drivers. This not only leaves nurses exhausted but often without hope. By taking collective action, this article argues that nurses may benefit from sharing ideas and learning from others, and in so doing rekindle hope and a belief that things can change

Telomere and telomerase in stem cells

Telomeres, guanine-rich tandem DNA repeats of the chromosomal end, provide chromosomal stability, and cellular replication causes their loss. In somatic cells, the activity of telomerase, a reverse transcriptase that can elongate telomeric repeats, is usually diminished after birth so that the telomere length is gradually shortened with cell divisions, and triggers cellular senescence. In embryonic stem cells, telomerase is activated and maintains telomere length and cellular immortality; however, the level of telomerase activity is low or absent in the majority of stem cells regardless of their proliferative capacity. Thus, even in stem cells, except for embryonal stem cells and cancer stem cells, telomere shortening occurs during replicative ageing, possibly at a slower rate than that in normal somatic cells. Recently, the importance of telomere maintenance in human stem cells has been highlighted by studies on dyskeratosis congenital, which is a genetic disorder in the human telomerase component. The regulation of telomere length and telomerase activity is a complex and dynamic process that is tightly linked to cell cycle regulation in human stem cells. Here we review the role of telomeres and telomerase in the function and capacity of the human stem cells

Development of a Surface Micromachined On-Chip Flat Disk Micropump

The paper presents research progress in the development of a surface micromachined flat disk micropump which employs the viscous and centrifugal effects acting on a layer of fluid sandwiched between a rotating flat disk and a stationary plate. The pump is fabricated monolithically on-chip using Sandia’s Ultraplanar Multilevel MEMS Technology (SUMMiT™) where an electrostatic comb-drive Torsional Ratcheting Actuator (TRA) drives the flat disk through a geared transmission. The paper reviews available analytical models for flow geometries similar to that of the described pump, and presents a set of experiments which depict its performance and possible failure modes. Those experiments highlight future research directions in the development of electrostatically-actuated, CMOS-compatible, surface micromachined pumps