Robust numerical schemes for Eulerian spray DNS and LES in two-phase turbulent flows

International audienceLarge Eddy Simulation (LES) and Direct numerical Simulation (DNS) of polydisperse evaporating sprays with Eulerian models are very promising tools for high performance computing of combustion applications. They are able to describe the turbulent dispersion and evaporation and properly predict the combustion regimes. However, the spray system of conservation equations has a convective part which is either similar to gas dynamics Euler equations with a real gas type state law or to the pressureless gas dynamics (PGD), depending on the local flow regime and droplet Stokes number; so, they usually involve singularities due to model closure assumptions and require dedicated numerical schemes. Besides, it is desirable to cope with exactly zero droplet density in some zones of the flow, especially near the injection zone, where droplets are injected in only some spatial locations. Even if the issue has been successfully tackled in de Chaisemartin (2009); Fréret et al. (2010) in the framework of PGD with the use of accurate kinetic schemes, it cannot be directly extended to general gas dynamics. The purpose of the present contribution is to introduce a new generation of numerical methods based on relaxation schemes which are able to treat both PGD and general gas dynamics, as well as to cope in a robust manner with vacuum zones and natural singularities of the resulting system of conservation equations. The proposed hybrid relaxation scheme and algorithms are validated through comparisons with analytical solutions and other numerical strategies on 1D and 2D configurations. They exhibit a very robust behavior and are a very promising candidate for more complex applications since they provide solutions to key numerical issues of the actual Eulerian spray DNS and LES models

Résultats des duodéno-pancréatectomies céphaliques pour cancers péri-ampullaires (analyse d'une série rétrospective tri-centrique de 135 patients)

AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-Bib. Serv.Santé Armées (751055204) / SudocSudocFranceF

Response to "individualized care in patients undergoing laparoscopic cholecystectomy"

Comment onHow to predict difficult laparoscopic cholecystectomy? Proposal for a simple preoperative scoring system. [Am J Surg. 2016]Individualized care in patients undergoing laparoscopic cholecystectomy. [Am J Surg. 2017]International audienceno astrac

Disease-free survival following resection in non-ductal periampullary cancers: A retrospective multicenter analysis

International audienceBACKGROUND:Predictors of recurrence following pancreaticoduodenectomy are well described for ductal periampullary cancers but lack reliability for non-ductal tumors. The purpose of this study is to analyze the disease-free survival (DFS) and to define the predictors of recurrence following resection for ampullary (AC), bile duct (BDC) and duodenal cancers (DC).MATERIALS AND METHODS:Clinico-pathological data of patients operated on between 2001 and 2011 were retrospectively reviewed. The effect of lymphatic invasion was specified using the lymph node ratio (LNR) and the number of positive nodes (NPN), with thresholds calculated with the likelihood ratio. Kaplan-Meier disease-free survival (DFS) curves were compared for all covariates by a log-rank test. Multivariate logistic regression analyses were performed to identify predictors of recurrence.RESULTS:135 patients were identified. Mean follow-up was 49 ± 35 months. Median DFS was not reached for AC and was 36 and 18 months for DC and BDC, respectively. Five-year DFS was 52%, 43% and 32% for AC, DC and BDC, respectively. Predictors of recurrence were T4 tumors, neural invasion and preoperative biliary drainage for DC, ≥3 positive nodes and ≥4% loss of BMI for AC, and T3-T4 tumors for BDC.CONCLUSION:Loss of BMI ≥4% is a strong predictor of recurrence in AC, and the recurrence risk increases with the total number of lymph nodes invaded (0; 1-3; ≥4). Only T stage influences recurrence for BDC. Considering DC, the adverse effect of preoperative biliary drainage should be validated in randomized series

Predictive factors of severe complications for ampullary, bile duct and duodenal cancers following pancreaticoduodenectomy: Multivariate analysis of a 10-year multicentre retrospective series

International audienceBackground: Postoperative outcomes following pancreaticoduodenectomy are well described for pancreatic cancers. Due to a lower incidence rate, complication rates and relative predictive factors are less detailed for ampullary, bile duct and duodenal cancers.Methods: Medical charts of patients operated on between 2001 and 2011 for an ampullary, bile duct or duodenal cancer were reviewed. Data were retrospectively studied with respect to demographics, surgical management, postoperative complications and histological findings. Specific complication rates were reported, and predictive factors for severe morbidity and mortality were determined by multivariate analysis.Results: 135 patients were identified: 55 ampullary, 55 bile duct and 25 duodenal cancers. Twelve patients (8.9%) deceased postoperatively, and 36 others (26.7%) presented severe complications. Sixty-seven percent of the pancreas was soft, and pancreatic hardness was found to be the main protective factor against severe morbidity (HR = 0.36, 95% CI = 0.14-0.94, P = 0.037). Age and postpancreatectomy haemorrhage were independent predictors for death (HR = 14.63, 95% CI = 1.57-135.77, P = 0.018, and HR = 14.71, 95% CI = 2.86-75.62, P = 0.001, respectively). Only the use of an external transanastomotic duct stent significantly reduced both the morbidity (HR = 0.37, 95% CI = 0.16-0.83, P = 0.016), and the mortality (HR = 0.12, 95% CI = 0.02-0.69, P = 0.017).Conclusions: Pancreaticoduodenectomy for ampullary, bile duct and duodenal cancers is a high-risk procedure. The systematic use of transanastomotic duct stents would significantly decrease the complication rate. Older patients should beneficiate from specific preoperative evaluation using an adapted index. Omental flap techniques to prevent a postpancreatectomy haemorrhage should be efficient. Effects of preoperative octreotid to harden the pancreas should be clarified

Influence of loading speed on the mechanical properties of the colon

Trauma is a leading cause of death for young people in developed countries, becoming a public health issue. After the spleen and liver, the digestive tract is the third most frequently affected organ during blunt abdominal trauma. Gastrointestinal injuries are responsible for significant morbidity and mortality due to the difficulty in diagnosing such intestinal lesions and the resulting delay in treatment. In-depth studies are required to understand the pathophysiological mechanisms that are responsible for these intestinal lesions. Virtual trauma studies using numerical models of the intra-abdominal organs are among the most promising means that are used to study and predict the occurrence of intestinal injuries during abdominal trauma. Mechanical behaviour of the colon has only been studied under quasi-static loads. This study involves the experimental characterization of the mechanical behaviour of the colon using tensile tests to determine the mechanical response under different loads