Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Latent hardening/softening behavior in tension and torsion combined loadings of single crystal FCC micropillars

In metallic materials, the activation of one slip system increases the flow strength of other slip systems, which is phenomenon known as latent hardening. This latent hardening behavior has been understood by the &quot;forest hardening&quot; mechanism arising from mutual dislocation interactions at the continuum length scale. As the size of a sample decreases to the submicron scale, the interactions between dislocations become increasingly sparse, so plastic deformation is instead governed mainly by dislocation sources. In this paper, we use three-dimensional dislocation dynamics (DD) simulations to examine plastic deformation in single crystalline Cu micropillars subjected to two types of combined loading conditions: tension after torsion and torsion after tension. These combined loadings are then compared with simple tension and pure torsion, respectively. We find that there exists a transition from latent hardening to latent softening in 600 nm samples undergoing tension after torsion. The systematic computational and theoretical model described here suggests explosive multiplication causes dislocation density to greatly increase, giving rise to latent softening in those micropillars under tension after torsion. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.N

The effect of advanced treatment of sewage effluents on metal speciation and (bio)availability

The bioavailability of metals can be strongly influenced by dissolved organic carbon (DOC). Wastewater treatment effluents add considerable quantities of DOC and metals to receiving waters, and as effluent controls become more stringent advanced effluent treatments may be needed. We assessed the effects of two types of advanced treatment processes on metal availability in wastewater effluents. Trace metal availability was assessed using diffuse gradients in thin films and predicted through speciation modelling. The results show little difference in metal availability post advanced treatment. EDTA-like compounds are important metal complexants in the effluents

Dislocation interactions at the grain boundary in FCC bicrystals: An atomistically-informed dislocation dynamics study

To understand the underlying mechanisms that control the mechanical properties of nanostructured metals, an insight into the role of the grain boundary in dislocation-driven plastic deformation is vital. The grain boundary has been observed as a dislocation source, sink, or having no effect, which in turn, gives rise to different macroscopic mechanical responses. With this motivation, atomistic simulations and three-dimensional dislocation dynamics simulations were performed to investigate dislocation interactions at various grain boundaries and their role in the plastic deformation of face-centered cubic (FCC) bicrystalline micropillars. The atomistically-informed dislocation dynamics simulations show that bicrystalline samples containing a high angle grain boundary (HAGB) display hardening and higher flow stresses compared to single crystals, while micropillars with a coherent twin boundary (CTB) show similar flow stresses to the reference single crystalline samples. This is due to the transparency of the grain boundary to slip transmission, which is observed in the atomistic simulations. Interestingly, allowing dislocation glide on the grain boundary exhibits a decrease in flow stress as slip transmission becomes easier. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.N

Effect of size and orientation on stability of dislocation networks upon torsion loading and unloading in FCC metallic micropillars

At the continuum length scale, mechanical properties of metals show relatively weak orientation dependence; however, they exhibit strong anisotropic behaviors as the size of sample decreases to micron and nanometer length scales. In this study, three-dimensional dislocation dynamics (DD) simulations are performed to investigate the orientation-dependent plasticity in submicron face-centered cubic (FCC) micropillars subjected to torsion. Accommodating results from atomistic modeling, updated surface nucleation schemes in DD models have been developed for three orientations ([001], [101], and [111]), allowing investigation of the dislocation microstructure evolution and the corresponding anisotropic mechanical response upon torsional loading and unloading. The DD simulation results show that the coaxial and hexagonal networks formed in [101] and [111] oriented nanopillars, respectively, exhibited excellent plastic recovery, while the rectangular network formed in the [001] crystal orientation was more stable and did not experience as much plastic recovery. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.N

Intrinsic size dependent plasticity in BCC micro-pillars under uniaxial tension and pure torsion

The mechanical behavior of submicron body-centered cubic (BCC) micro-pillars is investigated by three-dimensional dislocation dynamics (DD) simulations to better understand the governing mechanisms for size dependent plasticity under uniaxial tension and pure torsion. A formula is developed to compute the incremental plastic twist due to dislocation motion in DD simulations. The DD simulations show that different dislocation microstructures are created depending on the loading conditions, which leads to different size dependent mechanical behavior. While in tension plasticity is mainly governed by the kinetics of dislocation motion controlled partly by the surface dislocation sources, plastic flow in torsion is controlled by dislocation pile-ups associated with strain gradients. The simulation results also reveal a Bauschinger effect and plastic recovery under cyclic twist, which have been observed in recent experiments. (C) 2020 Elsevier Ltd. All rights reserved.Y