Synchrotron radiography studies of shear-induced dilation in semi-solid Al alloys and steels

An improved understanding of the response of solidifying microstructures to load is required to further minimize casting defects and optimize casting processes. This article overviews synchrotron radiography studies that directly measure the micromechanics of semisolid alloy deformation in a thin sample direct-shear cell. It is shown that shear-induced dilation (also known as Reynolds’ dilatancy) occurs in semisolid alloys with morphologies ranging from equiaxed-dendritic to globular, at solid fractions from the dendrite coherency point to ~90% solid, and it occurs in both Al alloys and carbon steels. Discrete-element method simulations that treat solidifying microstructures as granular materials are then used to explore the origins of dilatancy in semisolid alloys

Ethnic and racial differences in children and young people with respiratory and neurological post-acute sequelae of SARS-CoV-2: an electronic health record-based cohort study from the RECOVER Initiative

BackgroundChildren from racial and ethnic minority groups are at greater risk for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, but it is unclear whether they have increased risk for post-acute sequelae of SARS-CoV-2 (PASC). Our objectives were to assess whether the risk of respiratory and neurologic PASC differs by race/ethnicity and social drivers of health.MethodsWe conducted a retrospective cohort study of individuals <21 years seeking care at 24 health systems across the U.S, using electronic health record (EHR) data. Our cohort included those with a positive SARS-CoV-2 molecular, serology or antigen test, or with a COVID-19, multisystem inflammatory disease in children, or PASC diagnosis from February 29, 2020 to August 1, 2022. We identified children/youth with at least 2 codes associated with respiratory and neurologic PASC. We measured associations between sociodemographic and clinical characteristics and respiratory and neurologic PASC using odds ratios and 95% confidence intervals estimated from multivariable logistic regression models adjusted for other sociodemographic characteristics, social vulnerability index or area deprivation index, time period of cohort entry, presence and complexity of chronic respiratory (respectively, neurologic) condition and healthcare utilization.FindingsAmong 771,725 children in the cohort, 203,365 (26.3%) had SARS-CoV-2 infection. Among children with documented infection, 3217 children had respiratory PASC and 2009 children/youth had neurologic PASC. In logistic regression models, children <5 years (Odds Ratio [OR] 1.78, 95% CI 1.62-1.97), and of Hispanic White descent (OR 1.19, 95% CI 1.05-1.35) had higher odds of having respiratory PASC. Children/youth living in regions with higher area deprivation indices (OR 1.25, 95% CI 1.10-1.420 for 60-79th percentile) and with chronic complex respiratory conditions (OR 3.28, 95% CI 2.91-3.70) also had higher odds of respiratory PASC. In contrast, older (OR 1.57, 95% CI 1.40-1.77 for those aged 12-17 years), non-Hispanic White individuals and those with chronic pre-existing neurologic conditions (OR 2.04, 95% CI 1.78-2.35) were more likely to have a neurologic PASC diagnosis.InterpretationRacial and ethnic differences in healthcare utilization for neurologic and respiratory PASC may reflect social drivers of health and inequities in access to care.FundingNational Institutes of Health

Adjuvant nab-Paclitaxel + Gemcitabine in Resected Pancreatic Ductal Adenocarcinoma: Results From a Randomized, Open-Label, Phase III Trial

PURPOSE: This randomized, open -label trial compared the efficacy and safety of adjuvant nabpaclitaxel + gemcitabine with those of gemcitabine for resected pancreatic ductal adenocarcinoma (ClinicalTrials.gov identifier: NCT01964430). METHODS: We assigned 866 treatment -naive patients with pancreatic ductal adenocarcinoma to nab-paclitaxel (125 mg/m2) + gemcitabine (1,000 mg/m(2)) or gemcitabine alone to one 30-40 infusion on days 1, 8, and 15 of six 28 -day cycles. The primary end point was independently assessed disease -free survival (DFS). Additional end points included investigator-assessed DFS, overall survival (OS), and safety. RESULTS: Two hundred eighty-seven of 432 patients and 310 of 434 patients completed nabpaclitaxel + gemcitabine and gemcitabine treatment, respectively. At primary data cutoff (December 31, 2018; median follow-up, 38.5 [interquartile range [IQR], 33.8-43 months), the median independently assessed DFS was 19.4 (nab-paclitaxel + gemcitabine) versus 18.8 months (gemcitabine; hazard ratio [HR], 0.88; 95% CI, 0.729 to 1.063; P =.18). The median investigator-assessed DFS was 16.6 (IQR, 8.4-47.0) and 13.7 (IQR, 8.3-44.1) months, respectively (HR, 0.82; 95% CI, 0.694 to 0.965; P=.02). The median OS (427 events; 68% mature) was 40.5 (IQR, 20.7 to not reached) and 36.2 (IQR, 17.7-53.3) months, respectively (HR, 0.82; 95% CI, 0.680 to 0.996; P =.045). At a 16 -month follow-up (cutoff, April 3, 2020; median follow-up, 51.4 months [IQR, 47.0-57.0]), the median OS (511 events; 81% mature) was 41.8 (nab-paclitaxel + gemcitabine) versus 37.7 months (gemcitabine; HR, 0.82; 95% CI, 0.687 to 0.973; P =.0232). At the 5 -year follow-up (cutoff, April 9, 2021; median follow-up, 63.2 months [IQR, 60.1-68.7]), the median OS (555 events; 88% mature) was 41.8 versus 37.7 months, respectively (HR, 0.80; 95% CI, 0.678 to 0.947; P =.0091). Eighty-six percent (nab-paclitaxel + gemcitabine) and 68% (gemcitabine) of patients experienced grade >= 3 treatment -emergent adverse events. Two patients per study arm died of treatment -emergent adverse events. CONCLUSION: The primary end point (independently assessed DFS) was not met despite favorable OS seen with nab-paclitaxel + gemcitabine

An X-ray microtomographic and finite element modeling approach for the prediction of semi-solid deformation behaviour in Al-Cu alloys

There is a dearth of published experimental measurements of flow stress behaviour of semi-solids, yet it is critical for simulating phenomena ranging from the processing of metals to the flow of magma. In this paper, a method for calculating flow stress behaviour of semi-solids was developed using a combination of high-temperature compression testing, X-ray microtomography (XMT) imaging and direct finite element modeling (DFEM). This novel methodology was applied to columnar dendritic structures in semi-solid Al-Cu alloys via first quantifying the complex geometry of the semi-solid using XMT. Then these three-dimensional datasets were meshed and their behaviour was simulated using DFEM to derive the stress-strain relationship with a fraction solid (fS) dependency term. The mechanical behaviour of the solid dendrites near the liquidus temperature was not available in the literature; therefore, samples were fabricated and compression tested using a Gleeble 3500 thermomechanical simulator. The resulting XMT-DFEM-derived constitutive equation predicts the flow stress behaviour of semi-solid in the range of fS equal to 0.1-0.9, showing good correlation to prior experimental data for both other aluminium and ferrous alloys. © 2009 Acta Materialia Inc

Microtomographic characterization of columnar Al–Cu dendrites for fluid flow and flow stress determination

During the twin roll casting of Al alloys, the interdendritic liquid may flow as the two solidification fronts are compressed together between the rolls. This can lead to defects such as centerline segregation. To understand the flow properties of the interdendritic liquid, samples of Al–12 wt.% Cu were solidified directionally in a Bridgman furnace and quenched to capture the growing columnar dendritic structures. The quenched samples were scanned using a laboratory X-ray microtomography (XMT) unit to obtain the 3D structure with a voxel resolution of 7.2 μm. Image analysis was used to separate the Al dendrite from the interdendritic Al–Al2Cu eutectic. Flow between the dendrites was simulated by solving the Stokes equation to calculate the permeability tensor as a function of the fraction solid. The results were compared to prior experimental measurements and calculations using synchrotron tomography observations of equiaxed structures. Elasto–plastic finite element (FE) simulations were performed on the dendritic structures to determine flow stress behavior as a function of fraction solid. It was found that the standard approximations for the reduction in flow stress in the semi-solid have a variation in excess of 100% from that calculated using the true structure. Therefore, it is critical to simulate the actual dendrite for effective flow stress determination