THE ROLE OF THERMAL INPUT ON SQUAT TYPE DEFECTS IN RAILS

The recently discovered squat type defect which is understood as a thermal defect has renewed interest in rolling contact fatigue damage in railway studies. These defects were reported to appear in several locations across the globe where the cost incurred for their removal leads to a major increase of track maintenance cost. While the growth mechanism for classical rolling contact fatigue squat is well understood, limited research has so far been undertaken for squat type defects leaving them poorly understood, especially in their initiation and propagation mechanism. The presence of white etching layer in all locations where these defects have been found strongly suggests that thermal input is responsible for their development rather than fluid assisted growth that is responsible for the development of classical rolling contact fatigue squats. In this thesis, research is reported that combines morphological analysis data with a boundary element model to understand the direct influence of these thermally transformed layers on the initiation and propagation of squat type defects in rail. Furthermore, the work has been extended to explore the possibilities for defect detection in rails reaching a positive proof of concept outcome. It is expected that this approach could serve as a basis for maintenance schedules in order to avoid rail failure due to inadequate understanding of this type of defect

Giving Families a Voice for Equitable Healthy Food Access in the Wake of Online Grocery Shopping

Understanding the views of families from low-income backgrounds about inequities in healthy food access and grocery purchase is critical to food access policies. This study explored perspectives of families eligible for the Supplemental Nutrition Assistance Program (SNAP) on healthy food access in physical and online grocery environments. The qualitative design used purposive sampling of 44 primary household food purchasers with children (aged ≤ 8), between November 2020–March 2021, through 11 online focus groups and 5 in-depth interviews. Grounded theory was used to identify community-level perceived inequities, including influences of COVID-19 pandemic, SNAP and online grocery services. The most salient perceived causes of inequitable food access were neighborhood resource deficiencies and public transportation limitations. Rural communities, people with disabilities, older adults, racially and ethnically diverse groups were perceived to be disproportionately impacted by food inequities, which were exacerbated by the pandemic. The ability to use SNAP benefits to buy foods online facilitated healthy food access. Delivery fees and lack of control over food selection were barriers. Barriers to healthy food access aggravated by SNAP included social stigma, inability to acquire cooked meals, and inadequate amount of monthly funds. Findings provide a foundation for policy redesign to promote equitable healthy food systems

An assessment of the high-entropy alloy system VCrMnFeAlx

A major consideration when choosing materials for nuclear reactors is the future radioactive waste produced by the irradiation of their component parts. Only a handful of structural metals can be considered ‘low activation’ in a fusion environment. In recent work, we showed that the low-activation multicomponent equiatomic alloy VCrMnFe comprises a single BCC (A2) phase at 1200°C. Here, we examine its stability on ageing at lower temperatures, and the effect of Al additions (to create VCrMnFeAlx alloys) to destabilise the sigma phase and form strengthening superlattice structures. It is found that substantial volume fractions of sigma phase form after ageing VrCrMnFe at 600°C and 800°C for 1000 h. The addition of Al was found to destabilise the sigma phase, as predicted using thermodynamic modelling, with it being eliminated at all temperatures with additions of 6.6 at% Al. Increasing Al additions also led to the formation of superlattice structures: B2 and L21 (Heusler). Higher Al content had a slight increasing effect on the alloys’ hardness, but also embrittled the alloys (at room temperature). Significant hardening was produced by nano-segregation induced in the higher Al x = 0.25, 0.5 and 1.0 alloys after aging at 600 °C. This alloy system presents an attractive opportunity to fine-tune the composition to obtain a balance of ductility and high-temperature strength and stability. Of particular interest was the formation a two-phase basket weave cube-on-cube orientated, coherent, microstructure in VCrMnFeAl1.0 after aging at 800 °C

Shape memory characteristics of a nanocrystalline TiNi alloy processed by HPT followed by post-deformation annealing

A martensitic TiNi shape memory alloy was processed by high-pressure torsion (HPT) for 1.5, 10 and 20 turns followed by post-deformation annealing (PDA) at 673 and 773 K for various times in order to study the microstructural evolution during annealing and the shape memory effect (SME). Processing by HPT followed by the optimum PDA leads to an appropriate microstructure for the occurrence of a superior SME which is attributed to the strengthening of the martensitic matrix and grain refinement. A fully martensitic structure (B19’ phase) with a very small grain size is ideal for the optimum SME. The results indicate that the nanocrystalline microstructures after PDA contain a martensitic B19’ phase together with an R-phase and this latter phase diminishes the SME. Applying a higher annealing temperature or longer annealing time may remove the R-phase but also reduce the SME due to grain growth and the consequent decrease in the strength of the material. The results show the optimum procedure is a short-term anneal for 10 min at 673 K or only 1.5 min at 773 K after 1.5 turns of HPT processing to produce a maximum recovered strain of ~8.4% which shows more than 50% improvement compared with the solution-annealed condition

Conceptual framework for a cardiac surgery simulation laboratory and competency-based curriculum in Pakistan - a short innovation report

Simulation is a commonly utilized technique in healthcare education as it provides trainees a realistic, but safe, environment to learn a variety of skills. Trainees belonging to fields known for high stakes with low margins for error, such as cardiac surgery, can greatly benefit from simulation-based education. We propose the establishment of the first multi-tier high fidelity cardiac surgery simulation lab with a structured curriculum that will eventually provide multidisciplinary training to promising cardiac surgeons across Pakistan. The simulation lab may also be used for research, grant acquisition and patent development. Our setup will include the following levels of simulation: a simple bench model, a virtual reality simulator and a unique human performance simulator. Our multitiered approach allows for appropriate sequential trainee skill progression. Finally, we hope that our model inspires the development of similar curricula and modules for trainees belonging to other surgica

Effect of Cu on Amorphization of a TiNi Alloy during HPT and Shape Memory Effect after Post‐Deformation Annealing.

A ternary TiNiCu memory alloy was subjected to high‐pressure torsion (HPT) followed by post‐deformation annealing (PDA) to study the effect of Cu (5 at%) on amorphization after HPT processing and also the microstructural evolution and shape memory effect (SME) after PDA. The results show that even after 20 revolutions the ternary alloy contains nanocrystalline areas and the microstructure is not fully amorphous. An easier martensite to austenite transformation and minor remaining austenite in the ternary alloy are responsible for suppressing amorphization. PDA at 673 K provides nanocrystalline microstructures containing an R‐phase with a minor martensitic B19' phase in the ternary alloy. The SME of this alloy after PDA is not as satisfactory as for the binary alloy processed through similar conditions because of the existence of a high volume fraction of the R‐phase. Nevertheless, the total recovered strain of the ternary alloy after PDA for 30 min has a maximum value of 6.5%

Comparative trends in ischemic heart disease admissions, presentation and outcomes due to the COVID-19 pandemic: First insights from a tertiary medical center in Pakistan

Introduction: COVID-19 has manifested a striking disarray in healthcare access and provision, particularly amongst patients presenting with life-threatening ischemic heart disease (IHD). The paucity of data from low-middle income countries has limited our understanding of the consequential burden in the developing world. We aim to compare volumes, presentations, management strategies, and outcomes of IHD amongst patients presenting in the same calendar months before and during the COVID-19 pandemic.Methods: We conducted a retrospective cross-sectional analysis at the Aga Khan University Hospital, one of the premier tertiary care centres in Pakistan. Data were collected on all adult patients (\u3e18 years) who were admitted with IHD (acute coronary syndrome (ACS) and stable angina) from March 1 to June 30, 2019 (pre-COVID) and March 1 to June 30, 2020 (during-COVID), respectively. Group differences for continuous variables were evaluated using student t-test or Mann-Whitney U test. The chi-squared test or Fisher test was used for categorical variables. Values of p less than 0.05 were considered statistically significant. P-value trend calculation and graphical visualization were done using STATA (StataCorp, College Station, TX).Results: Data were assimilated on 1019 patients, with 706 (69.3%) and 313 (30.7%) patients presenting in each respective group (pre-COVID and during-COVID). Current smoking status (p=0.019), admission source (p\u3c0.001), month of admission (p\u3c0.001), proportions ACS (p\u3c0.001), non-ST-elevation-myocardial-infarction (NSTEMI; p\u3c0.001), unstable angina (p=0.025) and medical management (p=0.002) showed significant differences between the two groups, with a sharp decline in the during-COVID group. Monthly trend analysis of ACS patients showed the most significant differences in admissions (p=0.001), geographic region (intra-district vs intracity vs outside city) (p\u3c0.001), time of admission (p=0.038), NSTEMI (p=0.002) and medical management (p=0.001).Conclusion: These data showcase stark declines in ACS admissions, diagnostic procedures (angiography) and revascularization interventions (angioplasty and coronary artery bypass graft surgery, CABG) in a developing country where resources and research are already inadequate. This study paves the way for further investigations downstream on the short- and long-term consequences of untreated IHD and reluctance in health-seeking behaviour

Micromechanical Properties of Injection-Molded Starch–Wood Particle Composites

The micromechanical properties of injection molded starch–wood particle composites were investigated as a function of particle content and humidity conditions. The composite materials were characterized by scanning electron microscopy and X-ray diffraction methods. The microhardness of the composites was shown to increase notably with the concentration of the wood particles. In addition,creep behavior under the indenter and temperature dependence were evaluated in terms of the independent contribution of the starch matrix and the wood microparticles to the hardness value. The influence of drying time on the density and weight uptake of the injection-molded composites was highlighted. The results revealed the role of the mechanism of water evaporation, showing that the dependence of water uptake and temperature was greater for the starch–wood composites than for the pure starch sample. Experiments performed during the drying process at 70°C indicated that the wood in the starch composites did not prevent water loss from the samples.Peer reviewe

Severe plastic deformation for producing superfunctional ultrafine-grained and heterostructured materials: An interdisciplinary review

Ultrafine-grained and heterostructured materials are currently of high interest due to their superior mechanical and functional properties. Severe plastic deformation (SPD) is one of the most effective methods to produce such materials with unique microstructure-property relationships. In this review paper, after summarizing the recent progress in developing various SPD methods for processing bulk, surface and powder of materials, the main structural and microstructural features of SPD-processed materials are explained including lattice defects, grain boundaries and phase transformations. The properties and potential applications of SPD-processed materials are then reviewed in detail including tensile properties, creep, superplasticity, hydrogen embrittlement resistance, electrical conductivity, magnetic properties, optical properties, solar energy harvesting, photocatalysis, electrocatalysis, hydrolysis, hydrogen storage, hydrogen production, CO2 conversion, corrosion resistance and biocompatibility. It is shown that achieving such properties is not limited to pure metals and conventional metallic alloys, and a wide range of materials are currently processed by SPD, including high-entropy alloys, glasses, semiconductors, ceramics and polymers. It is particularly emphasized that SPD has moved from a simple metal processing tool to a powerful means for the discovery and synthesis of new superfunctional metallic and nonmetallic materials. The article ends by declaring that the borders of SPD have been extended from materials science and it has become an interdisciplinary tool to address scientific questions such as the mechanisms of geological and astronomical phenomena and the origin of life

Formation and significance of topologically close-packed Laves phases in refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) inherently have a high potential to form topologically close-packed (TCP) Laves phases. Phase engineering to control the amount and type of TCP-Laves phases plays an important role in physical and mechanical properties of RHEAs. The present investigation addressed key parameters to TCP-Laves phase formation in RHEAs by considering thermodynamic calculations and empirical relations. Two novel TiVCrZrCo and TiVCrZrFe RHEAs were designed and fabricated as alloy models with high melting points (>2000 K) and relatively low density (~6.5 g.cm-3) with multiphase microstructure including BCC matrix together with C14 and C15 Laves phases. Existence of atoms such as V, Co, Cr and Fe together with Zr, Ti, Nb and Hf refractory elements promote TCP-Laves phase formation. Very negative values for mixing enthalpy of atom pairs (ΔHmix) and remarkable differences between atomic sizes of the constitutive elements (δ) are key factors in Lave phase formation in multicomponent alloys. The empirical parameters including ΔHmix and δ must be in the defined range of −20 ≤ ΔHmix ≤ -3 kJ.mol-1 and 4 <δ < 10 to appear Laves phase in the microstructures of HEAs. TCP-Laves phase formation led to increase and decrease in hardness and fracture toughness, significantly. The understanding of key factors in RHEAs design can lead to phase engineering and the fabricated alloys with a desirable amount of TCP-Laves phase, which are suited for hydrogen storage applications or for applications in harsh operating environments exposed to high temperatures, irradiations, wear, and erosion