Continuum viscoplastic simulation of a granular column collapse on large slopes: μ(I) rheology and lateral wall effects

We simulate here dry granular flows resulting from the collapse of granular columns on an inclined channel (up to 22°) and compare precisely the results with laboratory experiments. Incompressibility is assumed despite the dilatancy observed in the experiments (up to 10%). The 2-D model is based on the so-called μ(I) rheology that induces a Drucker-Prager yield stress and a variable viscosity. A nonlinear Coulomb friction term, representing the friction on the lateral walls of the channel, is added to the model. We demonstrate that this term is crucial to accurately reproduce granular collapses on slopes ≳10°, whereas it remains of little effect on the horizontal slope. Quantitative comparison between the experimental and numerical changes with time of the thickness profiles and front velocity makes it possible to strongly constrain the rheology. In particular, we show that the use of a variable or a constant viscosity does not change significantly the results provided that these viscosities are of the same order. However, only a fine tuning of the constant viscosity (η=1 Pa s) makes it possible to predict the slow propagation phase observed experimentally at large slopes. Finally, we observed that small-scale instabilities develop when refining the mesh (also called ill-posed behavior, characterized in the work of Barker et al. [“Well-posed and ill-posed behaviour of the μ(I)-rheology for granular flow,” J. Fluid Mech. 779, 794–818 (2015)] and in the present work) associated with the mechanical model. The velocity field becomes stratified and the bands of high velocity gradient appear. These model instabilities are not avoided by using variable viscosity models such as the μ(I) rheology. However we show that the velocity range, the static-flowing transition, and the thickness profiles are almost not affected by them

Reparametrizing Swung Surfaces over the Reals

Let K⊆R be a computable subfield of the real numbers (for instance, Q). We present an algorithm to decide whether a given parametrization of a rational swung surface, with coefficients in K(i), can be reparametrized over a real (i.e., embedded in R) finite field extension of K. Swung surfaces include, in particular, surfaces of revolution

Harmonic long shears further reduce operation time in transanal endoscopic microsurgery

Background: Previous research indicates that application of 5-mm harmonic shears rather than diathermia significantly reduces operation time in transanal endoscopic microsurgery (TEM). Frequently, however, additional instruments were required to complete resection. We investigated whether the new 5-mm harmonic long shears (H-LS) are better equipped for TEM compared with regular harmonic shears (HS). Methods: Between 2001 and 2006, 162 tumors (117 adenomas, 42 carcinomas, and 3 other tumors; mean distance 6.6 cm, mean area 40 cm2) were excised in 161 patients (82 men, 79 women; mean age 66 years). Results: Eighty-eight resections were performed with HS and 74 with H-LS. Tumor and patient characteristics were similar except for specimen area. Tumors resected by H-LS were on average smaller than those resected by HS (34.4 versus 44.1 cm2; Mann-Whitney U-test: p = 0.027). Mean operation time was 48 min and proportional to area in both groups (univariate analysis of variance p<0.001). Mean operation time was 54 min using HS and 41 min using H-LS (t-test: p<0.001). After correction for area, operation time for H-LS was reduced by 14% compared with HS (t-test: p<0.001). H-LS is singly capable of completing resection in 88% compared with 26% for HS (Mann- Whitney U-test: p<0.001). Mean blood loss was 16 cc for HS and 3 cc for H-LS (p<0.001). Morbidity (11%) and mortality (0.6%) were not different between the two groups (Fisher's exact test). Conclusion: Performing transanal endoscopic microsurgery with 5-mm harmonic long shears reduces operation time compared with regular shears, and completing resection seldom requires other instruments

Stroke Based Painterly Rendering

International audienceMany traditional art forms are produced by an artist sequentially placing a set of marks, such as brush strokes, on a canvas. Stroke based Rendering (SBR) is inspired by this process, and underpins many early and contemporary Artistic Stylization algorithms. This Chapter outlines the origins of SBR, and describes key algorithms for placement of brush strokes to create painterly renderings from source images. The chapter explores both local greedy, and global optimization based approaches to stroke placement. The issue of creative control in SBR is also briefly discussed

The Fatty Liver Index: a simple and accurate predictor of hepatic steatosis in the general population

BACKGROUND: Fatty liver (FL) is the most frequent liver disease in Western countries. We used data from the Dionysos Nutrition & Liver Study to develop a simple algorithm for the prediction of FL in the general population. METHODS: 216 subjects with and 280 without suspected liver disease were studied. FL was diagnosed by ultrasonography and alcohol intake was assessed using a 7-day diary. Bootstrapped stepwise logistic regression was used to identify potential predictors of FL among 13 variables of interest [gender, age, ethanol intake, alanine transaminase, aspartate transaminase, gamma-glutamyl-transferase (GGT), body mass index (BMI), waist circumference, sum of 4 skinfolds, glucose, insulin, triglycerides, and cholesterol]. Potential predictors were entered into stepwise logistic regression models with the aim of obtaining the most simple and accurate algorithm for the prediction of FL. RESULTS: An algorithm based on BMI, waist circumference, triglycerides and GGT had an accuracy of 0.84 (95%CI 0.81–0.87) in detecting FL. We used this algorithm to develop the "fatty liver index" (FLI), which varies between 0 and 100. A FLI < 30 (negative likelihood ratio = 0.2) rules out and a FLI ≥ 60 (positive likelihood ratio = 4.3) rules in fatty liver. CONCLUSION: FLI is simple to obtain and may help physicians select subjects for liver ultrasonography and intensified lifestyle counseling, and researchers to select patients for epidemiologic studies. Validation of FLI in external populations is needed before it can be employed for these purposes