Uniaxial-deformation behavior of ice Ih as described by the TIP4P/Ice and mW water models

Using molecular dynamics simulations, we assess the uniaxial deformation response of ice Ih as described by two popular water models, namely, the all-atom TIP4P/Ice potential and the coarse-grained mW model. In particular, we investigate the response to both tensile and compressive uniaxial deformations along the [0001] and [01̄10] crystallographic directions for a series of different temperatures. We classify the respective failure mechanisms and assess their sensitivity to strain rate and cell size. While the TIP4P/Ice model fails by either brittle cleavage under tension at low temperatures or large-scale amorphization/melting, the mW potential behaves in a much more ductile manner, displaying numerous cases in which stress relief involves the nucleation and subsequent activity of lattice dislocations. Indeed, the fact that mW behaves in such a malleable manner even at strain rates that are substantially higher than those applied in typical experiments indicates that the mW description of ice Ih is excessively ductile. One possible contribution to this enhanced malleability is the absence of explicit protons in the mW model, disregarding the fundamental asymmetry of the hydrogen bond that plays an important role in the nucleation and motion of lattice dislocations in ice Ih.Fil: Santos Flórez, Pedro Antonio. Universidade Estadual de Campinas; BrasilFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: de Koning, Maurice. Universidade Estadual de Campinas; Brasi

Nonequilibrium Processes in Repulsive Binary Mixtures

We consider rapid cooling processes in classical, 3-dimensional, purely repulsive binary mixtures in which an initial infinite-temperature (ideal-gas) configuration is instantly quenched to zero temperature. It is found that such systems display two kinds of ordering processes, the type of which can be controlled by tuning the interactions between unlike particles. While strong inter-species repulsion leads to chemical ordering in terms of an unmixing process, weak repulsion gives rise to spontaneous crystallization, maintaining chemical homogeneity. This result indicates the existence of a transition in the topography of the underlying potential-energy landscape as the intra-species interaction strength is varied. Furthermore, the dual-type behavior appears to be universal for repulsive pair-interaction potential-energy functions in general, with the propensity for the crystallization process being related to their behavior in the neighborhood of zero separation

Atomistic Simulation of Nanoindentation of Ice Ih

Using molecular dynamics simulations, we study the nanoindentation response of the ice Ih basal surface using two popular water models, namely, the all-atom TIP4P/Ice potential and the coarse-grained mW model. In particular, we consider two markedly different temperatures at which a quasi-liquid layer (QLL) is or is not present. We discuss loading curves, hardness estimates, deformation mechanisms, and residual imprints, considering the effect of the QLL, indenter size, and penetration rate. At very low temperatures, in the absence of a QLL, both potentials produce similar loading curves and deformation mechanisms. Close to the melting temperature, however, important differences were found, including deviations in the QLL thickness and fraction as well as the presence of a competition between pressure-induced melting and recrystallization events. Nevertheless, both potentials exhibit similar deformation mechanisms and steady-state hardness estimates that are consistent with experimental data. In addition to contributing to the discussion regarding the interpretation of experimental AFM loading curves, the present results provide valuable information concerning the simulation of contact problems involving ice and the behavior of these two popular water models under such circumstances.Fil: Santos Flórez, Pedro Antonio. Universidade Estadual de Campinas; BrasilFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: De Koning, Maurice. Universidade Estadual de Campinas; Brasi

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Phase diagram of the Uhlenbeck-Ford model

Orientador: Maurice de KoningDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: O modelo de Uhlenbeck-Ford, que é um sistema artificial caracterizado por um potencial interatômico logarítmico e repulsivo, foi definido originalmente para o estudo teórico de gases imperfeitos, baseado no fato de que todas as integrais de muitos corpos, envolvidas no cálculo de coeficientes viriais, podem ser calculadas analiticamente. Assim, este modelo possui uma expressão exata para a equação de estado e a energia livre de Helmholtz na fase fluida. Um potencial escalonado deste modelo já foi proposto como sistema de referência na implementação de métodos de simulação atomística, para cálculos de energia livre de sistemas na fase fluida. Neste trabalho, é construído o diagrama de fase do modelo de Uhlenbeck-Ford dependente deste fator de escalonamento, delimitando as fases fluida e sólida, com estruturas cristalinas (BCC e FCC). A estabilidade das diferentes fases foi estudada analisando as curvas de energia livre, que foram obtidas utilizando a técnica de simulação atomística da Dinâmica Molecular a partir de processos fora do equilíbrio. Nossos resultados mostraram que existem regiões para qualquer densidade onde a fase fluida é a mais estável, e portanto, o modelo de Uhlenbeck-Ford pode ser usado como sistema de referência para cálculos de energia livre de sistemas na fase fluidaAbstract: The Uhlenbeck-Ford model, which is an artificial system characterized by a logarithmic and repulsive interatomic potential, was originally defined for the theoretical study of imperfect gases, based on the fact that all the many-body integrals, involved in calculating virial coefficients, can be calculated analytically. Thus, this model has an exact expression for the equation of state and the Helmholtz free energy in the fluid phase. A modified potential by a scale factor of this model was proposed as a reference system in the implementation of atomistic simulation methods for free energy calculation in the fluid phase. In this paper, we construct the phase diagram of the Uhlenbeck-Ford model dependent on a scale factor, finding the coexistence lines between fluid and solid phases, with crystalline structures (BCC and FCC). The stability of the different phases was studied by analyzing the free energy curves, which were obtained using the atomistic simulation technique of Molecular Dynamics, using nonequilibrium processes. Our results show that for any density, there exist regions in which the fluid phase is the most stable and therefore the Uhlenbeck-Ford model can be used as a reference system for free energy calculations of systems in the fluid phaseMestradoFísicaMestre em Física1370441/2014CAPE

Uniaxial-deformation behavior of ice I-h as described by the TIP4P/Ice and mW water models

CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOUsing molecular dynamics simulations, we assess the uniaxial deformation response of ice I-h as described by two popular water models, namely, the all-atom TIP4P/Ice potential and the coarse-grained mW model. In particular, we investigate the response to both tensile and compressive uniaxial deformations along the [0001] and [0 (1) over bar 10] crystallographic directions for a series of different temperatures. We classify the respective failure mechanisms and assess their sensitivity to strain rate and cell size. While the TIP4P/Ice model fails by either brittle cleavage under tension at low temperatures or large-scale amorphization/melting, the mW potential behaves in a much more ductile manner, displaying numerous cases in which stress relief involves the nucleation and subsequent activity of lattice dislocations. Indeed, the fact that mW behaves in such a malleable manner even at strain rates that are substantially higher than those applied in typical experiments indicates that the mW description of ice I-h is excessively ductile. One possible contribution to this enhanced malleability is the absence of explicit protons in the mW model, disregarding the fundamental asymmetry of the hydrogen bond that plays an important role in the nucleation and motion of lattice dislocations in ice I-h.1491619CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçãosem informação2013/08293-72016/23891-

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

© 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 licenseBackground: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit