Controlling the interstitial element concentration in Ti-6Al-4V using calciothermic reduction

The production of Ti-6Al-4V components via powder metallurgy routes is looked upon as an efficient production method that reduces wastage, but leaves finished products with high interstitial oxygen concentrations that do not meet industrial standards. The ability to control the interstitial oxygen concentration in Ti-6Al-4V powder metallurgy would improve the viability of near net shape processing for the production of industrial components. One process that has demonstrated the ability to remove oxygen from titanium alloys is calciothermic reduction, which is a reduction process originally developed to reduce titanium dioxide to commercial purity titanium using a molten flux of calcium and calcium chloride. The aim of this thesis is to examine whether calciothermic reduction can be used to control the interstitial concentration of oxygen and nitrogen in powder metallurgy Ti-6Al-4V and understand the reaction mechanisms that enable this process to work. By understanding these mechanisms, the process can then be optimised to improve the properties of powder metallurgy Ti-6Al-4V components, and provide a basis to extend this to other alloy systems. Calciothermic reduction was demonstrated to be effective at reducing the interstitial oxygen concentration in powder metallurgy Ti-6Al-4V to acceptable industrial standards (< 2,000 wt .ppm). The optimisation of the process required the balance of thermodynamics and kinetics to be controlled; thermodynamics was important to ensuring the reaction would begin, with the kinetics becoming more important during the reduction process because the removal of interstitial oxygen concentration relied upon a diffusion based mechanism. Evaluation of the mechanism that underpins the removal of oxygen via calciothermic reduction, was assessed using a FIB-SIMS based technique. This method of analysis was developed during this research and demonstrated to be effective at quantifying interstitial oxygen concentrations in titanium alloy, which was used to confirm the formation of oxygen concentration gradients from titanium alloy bulk to the surface during calciothermic reduction. Further investigation of the reduction process indicated that calciothermic reduction could facilitate the nitriding of Ti-6Al-4V in a sealed air environment, forming a wear resistant surface layer in a novel process referred to as “Calciothermic Assisted Immersion Nitriding” (CAIN). The nitriding process produced a consistent TiCxNyOZ surface layer where the chemical composition of the layer developed in a three stage reaction involving the inward diffusion of interstitial carbon and nitrogen, whilst oxygen was removed from the surface. This surface layer improved the tribological properties of the Ti-6Al-4V samples by changing the wear mechanism from adhesive to abrasive, which resulted in an increased wear resistance, which was comparable to a commercial produced, physical vapour deposition TiCN coating.Open Acces

Rental externality, tenure security, and housing quality

This paper considers two tenure modes—owner- and renter-occupied housing—and models the effect of the rental externality and tenure security on single-family housing quality. We show that both rental externality and tenure security reduce renter-occupied housing quality when the user’s utilization, which reduces the quality of the accommodation, and the owner’s maintenance, which raises quality, are substitutes. Using singlefamily housing data in Japan, we obtain empirical results that are consistent with theoretical predictions. These results indicate that conventional wisdom—that the quality of renter-occupied housing is lower than that of owner-occupied housing—is supported for single-family housing in Japan

Comprehensive investigation of sources of misclassification errors in routine HIV testing in Zimbabwe.

INTRODUCTION: Misclassification errors have been reported in rapid diagnostic HIV tests (RDTs) in sub-Saharan African countries. These errors can lead to missed opportunities for prevention-of-mother-to-child-transmission (PMTCT), early infant diagnosis and adult HIV-prevention, unnecessary lifelong antiretroviral treatment (ART) and wasted resources. Few national estimates or systematic quantifications of sources of errors have been produced. We conducted a comprehensive assessment of possible sources of misclassification errors in routine HIV testing in Zimbabwe. METHODS: RDT-based HIV test results were extracted from routine PMTCT programme records at 62 sites during national antenatal HIV surveillance in 2017. Positive- (PPA) and negative-percent agreement (NPA) for HIV RDT results and the false-HIV-positivity rate for people with previous HIV-positive results ("known-positives") were calculated using results from external quality assurance testing done for HIV surveillance purposes. Data on indicators of quality management systems, RDT kit performance under local climatic conditions and user/clerical errors were collected using HIV surveillance forms, data-loggers and a Smartphone camera application (7 sites). Proportions of cases with errors were compared for tests done in the presence/absence of potential sources of errors. RESULTS: NPA was 99.9% for both pregnant women (N = 17224) and male partners (N = 2173). PPA was 90.0% (N = 1187) and 93.4% (N = 136) for women and men respectively. 3.5% (N = 1921) of known-positive individuals on ART were HIV negative. Humidity and temperature exceeding manufacturers' recommendations, particularly in storerooms (88.6% and 97.3% respectively), and premature readings of RDT output (56.0%) were common. False-HIV-negative cases, including interpretation errors, occurred despite staff training and good algorithm compliance, and were not reduced by existing external or internal quality assurance procedures. PPA was lower when testing room humidity exceeded 60% (88.0% vs. 93.3%; p = 0.007). CONCLUSIONS: False-HIV-negative results were still common in Zimbabwe in 2017 and could be reduced with HIV testing algorithms that use RDTs with higher sensitivity under real-world conditions and greater practicality under busy clinic conditions, and by strengthening proficiency testing procedures in external quality assurance systems. New false-HIV-positive RDT results were infrequent but earlier errors in testing may have resulted in large numbers of uninfected individuals being on ART

Guidelines for the vaccination of HIV-infected adolescents and adults in South Africa

No abstract available

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Boletín Oficial de la Provincia de Oviedo: Número 260 - 1971 noviembre 13

Since the eruption of Surtsey (1963 - 1965) many studies have been made of the resulting island, but the pre-emergent base remains submarine, un-incised and little studied. The same is true for many recently studied Surtseyan volcanoes, and means the pre-emergent parts of subaqueous eruptions are not well documented. This thesis presents an in depth study of the superb deposits of Surtseyan-style eruptions preserved in the South Island of New Zealand in Otago sea-cliffs along the coastline between Oamaru and Moeraki. These Eocene-Oligocene intraplate basaltic field deposits erupted in Surtseyan-style onto a submerged continental shelf and have since been exposed above sea level. They are inferred to be typical products of submarine processes such as those that built Surtsey to the sea surface. Volcanic fields typically include many small, monogenetic, volcanoes formed by single eruptions fed by short-lived magma plumbing systems that solidify after eruption. However, the stratigraphy of Cape Wanbrow suggests that eruptions produced multiple volcanoes whose edifices overlapped within a small area, but separated by millions of years. The small Cape Wanbrow highland is shown to include the remnants of 6 volcanoes that are distinguished by discordant to locally concordant inter-volcano contacts marked by biogenic accumulations or other slow-formed features. This discovery challenges the traditional view of monogenetic volcanoes and calls for researchers in monogenetic fields to start evaluating both unstudied and previously studied monogenetic volcanoes with this in mind. The 6 volcanoes contain several lithofacies associations: (a) the dominantly pyroclastic E1 comprising well-bedded tuff and lapilli-tuff, emplaced by traction dominated unsteady, turbulent high-density currents; (b) E2, massive to diffusely laminated block-rich tuff deposited by grain-dominant cohesionless debris flows; (c) E3, broadly cross stratified tuff with local lenses of low to high-angle cross-stratification which was deposited by either subaerial pyroclastic currents or subaqueously by unstable antidune and chute-and-pool forming supercritical flows; (d) E4, very-fine- to medium-grained tuff deposited by turbidity currents; (e) E5, bedded bioclast-rich tuff with increasing glaucony content upward, emplaced by debris flows; (f) E6, pillow lava and inter-pillow bioclastic sediment; and (g) E7, hyaloclastite breccia. These lithofacies associations aid interpretation of the eruptive evolution of each separate volcano, which in turn grew and degraded during build-up of the overall volcanic pile. Sedimentary processes played a prominent role in the evolution of the volcanic pile with both syn- and post-eruptive remobilization of debris from the growing pile of primary pyroclastic deposits of multiple volcanoes separated by time. An increase in bioclastic detritus up-sequence suggests that the stack of deposits from overlapping volcanoes built up into shallow enough waters for colonization to occur. This material was periodically shed from the top of the edifice to form bioclast-rich debris flow deposits of volcanoes 4, 5 and 6. Bedform geometries of volcanogenic sedimentary structures produced in both subaqueous and subaerial environments can be incredibly similar, if not identical, and this has resulted in a long history of difficulties in unambiguously distinguishing primary from reworked deposits, and gas-deposited from water-deposited ones. Sedimentary structures such as dunes and low- and high-angle cross-stratification produced by numerous flow types make interpretation of setting difficult. In particular the architecture of such deposits and often field observations of contextual detail can be extremely difficult to interpret based on their ubiquitous presence in many settings and flow types. This is made increasingly difficult when structures are poorly preserved, exposures are limited and independent palaeoenvironmental indicators are absent or ambiguous. However correct interpretation of such sedimentary structures along with the deposits they are part of can be crucial to understanding the host volcanic sequences. The origins of dunes and associated structures that occur within the pyroclastic deposits at Cape Wanbrow serve as an example, and have long been debated. To determine the depositional setting of dune-bearing deposits, careful analysis of contextual information has been completed along with the examination of well-described examples of; (1) subaerial dry pyroclastic deposits, (2) subaerial moist pyroclastic deposits, (3) deposits of gaseous fluid-gravity flow (e.g. eolian currents), (4) unidirectional fluid-gravity water flow deposits (e.g. rivers, tides) and (5) aqueous sediment-gravity flow deposits split into those comprising pyroclastic material and those with non-pyroclastic material. This includes examination of the physical controls that shape each example and the factors controlling bedform deposition in that environment with the aim of being able to distinguish between major flow types in each environment. For Cape Wanbrow, this analysis showed that ambiguous bedforms were formed subaerially, which thus provides direct evidence for emergence and subaerial growth of one of the the volcanoes represented in the succession. To understand multiple eruptions of monogenetic volcanoes at one site at Cape Wanbrow a study of peridotite xenoliths from Kakanui and Boatmans Harbour revealed that the peridotitic portions of sub-continental lithospheric mantle (SCLM) beneath North Otago contains a degree of compositional variation but is relatively fertile. The origins of the xenoliths indicate that the magmas are from either the base of the spinel facies lithosphere, from within the predicted narrow zone of garnet facies lithosphere or from within the asthenosphere. The xenoliths indicate that the magma source was fairly deep, and therefore the process that led to multiple eruptions over a small geographical area has to be one that affected the asthenosphere or the lower lithosphere

Students’ Experiences of English-Medium Instruction at the Postgraduate Level: Challenges and Sustainable Support for Success

More and more students are exploring overseas destinations and English-Medium Instruction (EMI) environments for their postgraduate studies. While it is known that students can often struggle in an EMI environment, the challenges faced by postgraduate students, and the support they receive or need, are not fully understood. By adopting a two-stage qualitative sequential data collection approach, this study explored the experiences and perceptions of full-time postgraduate students from Mainland China studying in a one-year Master of Education programme at a Hong Kong university during their first semester. Data were collected through an online survey (N = 73) and three in-depth group interviews (N = 12). The analysis of data offered a holistic understanding of the students’ challenges, needs, and struggles. The findings provide suggestions for support that teachers and programmes can provide to postgraduate students, as well as student self-help support strategies. Several sustainable support strategies are proposed to assist students in adjusting and succeeding in the EMI context at the postgraduate level