Revisiting the role of friction coefficients in granular collapses: confrontation of 3-D non-smooth simulations with experiments

In this paper, transient granular flows are examined both numerically and experimentally. Simulations are performed using the continuous 3D granular model introduced in Daviet & Bertails-Descoubes (2016), which represents the granular medium as an inelastic and dilatable continuum subject to the Drucker-Prager yield criterion in the dense regime. One notable feature of this numerical model is to resolve such a non-smooth rheology without any regularisation. We show that this non-smooth model, which relies on a constant friction coefficient, is able to reproduce with high fidelity various experimental granular collapses over inclined erodible beds, provided the friction coefficient is set to the avalanche angle - and not to the stop angle, as generally done. In order to better characterise the range of validity of the fully plastic rheology in the context of transient frictional flows, we further revisit scaling laws relating the shape of the final collapse deposit to the initial column aspect ratio, and accurately recover established power-law dependences up to aspect ratios in the order of 10. The influence of sidewall friction is then examined through experimental and simulated collapses with varying channel widths. The effective flow thickness is estimated in relation to the channel width, thereby challenging previously held assumptions on its estimation. Finally, we discuss the potential extension of the constant coefficient model with a hysteretic model to refine predictions of early-stage collapse dynamics, illustrating the impact of such phenomenology on transient flows and paving the way to more elaborate analysis.Comment: 25 figures and 6 movie

La répression du désordre dans une ville portuaire : l'exemple de la ville de Québec, 1850-1875

La période 1850-1875 est un véritable « âge d’or » pour les activités portuaires dans la ville de Québec, mais également un sommet en termes de nombre d’arrestations pour désordre. Ce mémoire vise à examiner la répression du désordre urbain dans la ville portuaire de Québec et les effets de la saison estivale de navigation qui, par le gonflement temporaire de la population, mettait à l’épreuve l’ensemble des institutions urbaines. L’appareil judiciaire et pénal a dû s’adapter à l’intensité saisonnière du désordre, de façon à répondre aux nouvelles exigences établies par les élites urbaines, notamment en ce qui a trait à l’exercice d’une justice plus expéditive. Cette ambition d’une gestion efficace du désordre saisonnier s’est rapidement heurtée à des ressources carcérales limitées. La présence des marins ne semble pas être l’unique dénominateur permettant d’expliquer l’intensité de la répression du désordre pendant l’été. Par ailleurs, les mesures prises pour réprimer les délits des marins en matière de discipline maritime, notamment en termes de manque au devoir et de désertion, répondirent davantage aux impératifs des intérêts économiques qu'à une volonté réelle de contrôler et d’enrayer le problème. Enfin, ce mémoire permet de mieux comprendre le rôle de la ville portuaire de Québec dans le dynamisme du commerce transatlantique dans la seconde moitié du XIXe siècle.The period from 1850 to 1875 was a true "golden age" for port activity in Quebec City, but it also saw a peak in the number of arrests for public disorder. This thesis examines the repression of urban disorder in the port city of Quebec and the effects of the summer navigation season which, by temporarily inflating the city's population, put urban institutions to the test. The judicial and penal systems had to adapt to the yearly summer increase in disorder in order to respond to the changing desires of urban elites, especially in regards to more expeditious justice. The search for a more effective response to seasonal disorder rapidly came up against the limitations of the city's prison. The presence of sailors does not seem to have been the only factor contributing to the rise in the repression of public disorder during the summer months. Moreover, measures taken against sailors for offences relating to maritime discipline, in particular refusal of duty and desertion, stemmed more from the imperatives of economic interests than from a true desire to control or to address the problem of urban disorder. Finally, this thesis also contributes to a better understanding of the role of the port city of Quebec in the dynamics of transatlantic trade in the second half of the 19th century

Swelling of dry heated whey protein microparticles in different physicochemical conditions

This study was conducted in order to promote innovation and new product development in the dairy industry with 100% dairy ingredients. Whey protein microparticles (PMI) produced by dry heating are studied for texturizing properties in food matrices. The production process consists of mixing whey proteins and lactose at an alkaline pH value, drying the solution and dry-heating the powder. We investigate the functional or swelling properties of these PMI by measuring the amount of water entrapped (WE) in microparticles and viscosity (h) of their suspensions prepared in different physicochemical conditions. The results of the study allowed defining the best ranges of conditions to use theses PMI for food applications

Modelling of the radiative properties of an opaque porous ceramic layer

Solid Oxide Fuel Cells (SOFCs) operate at temperatures above 1,100 K where radiation effects can be significant. Therefore, an accurate thermal model of an SOFC requires the inclusion of the contribution of thermal radiation. This implies that the thermal radiative properties of the oxide ceramics used in the design of SOFCs must be known. However, little information can be found in the literature concerning their operating temperatures. On the other hand, several types of ceramics with different chemical compositions and microstructures for designing efficient cells are now being tested. This is a situation where the use of a numerical tool making possible the prediction of the thermal radiative properties of SOFC materials, whatever their chemical composition and microstructure are, may be a decisive help. Using this method, first attempts to predict the radiative properties of a lanthanum nickelate porous layer deposited onto an yttria stabilized zirconium substrate can be reported

Functionalization of SiC-based materials by a selective YBa2Cu3O7-δ coating via sol–gel route in order to optimize their optical properties

SiC-based materials are good candidates for the application as solar receivers except concerning their optical properties. Indeed, considering the use at high temperature, materials used as solar receivers have to efficiently absorb the visible-near infrared waves (corresponding to solar spectral range) and simultaneously reflect the mid and far-infrared rays but SiC is absorbent in all the whole visible-infrared spectral domain. In this challenging work, a suitable YBa2Cu3O7-δ oxide which can present appropriate optical properties is studied. It was synthesized following a sol–gel route and it was obtained with a high level of purity. YBa2Cu3O7-δ pellets were realized and heat treated at different temperatures revealing that the higher the heat treatment is, the better the oxygen stoichiometry (7-δ) is and the smoothest the surface is. This directly acts on the YBa2Cu3O7-δ optical properties. Considering these results, an YBa2Cu3O7-δ coating was realized on SiC pellets by dip-coating. A homogenous and covering layer of about 10 μm was obtained presenting very promising optical properties which were predominant in the FIR-MIR range whereas absorptance was increased in NIR-visible range

Prediction of thermal radiative properties (300–1000 K) of La2NiO4+δ ceramics.

A multiscale numerical model is developed to predict the thermal radiative properties (TRP) of rough La2NiO4+δ coatings. The model integrates intrinsic and extrinsic contributions related to the chemical composition and the texture, respectively. High-temperature infrared reflectivity and thermogravimetric measurements on a La2NiO4+δ single crystal make it possible to understand the role of the excess oxygen in the intrinsic TRP. We show that dense ceramics with thicknesses higher than 4 μm are optically thick, and that one can adjust the surface roughness parameters to predict their TRP

Micro-confinement of bacteria into w/o emulsion droplets for rapid detection and enumeration

International audienceToday, rapid detection and identification of bacteria in microbiological diagnosis is a major issue. Reference methods usually rely on growth of microorganisms, with the drawback of lengthy time-to-result. The method provides global information on a clonal population that is known to be inhomogeneous relative to metabolic states and activities. Therefore, there may be a significant advantage of methods that allow characterisation of individual bacteria from a large population, both for test time reduction and the clinical value of the characterisation. We report here a method for rapid detection and real-time monitoring of the metabolic activities of single bacteria. Water-in-oil emulsions were used to encapsulate single Escherichia coli cells into picolitre (pL)-sized microreactor droplets. The glucuronidase activity in each droplet was monitored using the fluorogenic reporter molecule MUG (4-methylumbelliferyl- - d-glucuronide) coupled to time-lapse fluorescence imaging of the droplets. Such bacterial confinement provides several major advantages. (1) Enzymatic activities of a large number of single bacterium-containing droplet could be monitored simultaneously, allowing the full characterisation of metabolic heterogeneity in a clonal population. We monitored glucuronidase enzymatic activity and growth over ∼200 single bacteria over a 24-h period. (2) Micro-confinement of cells in small volumes allows rapid accumulation of the fluorescent metabolite, hence decreasing the detection time. Independent of the initial concentration of bacteria in the sample, detection of the presence of bacteria could be achieved in less than 2 h. (3) Considering the random distribution of bacteria in droplets, this method allowed rapid and reliable enumeration of bacteria in the initial sample. Overall, the results of this study showed that confinement of bacterial cells increased the effective concentration of fluorescent metabolites leading to rapid (2 h) detection of the fluorescent metabolites, thus significantly reducing time to numeration

Шероховатость поверхностей при финишной алмазно-абразивной обработке

Показано, что шероховатость полированной поверхности зависит от отношения частот собственных колебаний молекулярных фрагментов на поверхностях инструмента и обрабатываемой детали. На шероховатость обработанной поверхности наибольшее влияние оказывают число молекулярных фрагментов, из которых состоят частицы шлама, их наиболее вероятный размер, частоты собственных колебаний фрагментов обрабатываемого материала и инструмента, теплопроводность обрабатываемого материала и режимы обработки

Insulin Growth Factor-1 Status in Hidradenitis Suppurativa: A French Institutional Pilot Study

Background: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease of the follicles in the apocrine glands and is associated with a deficiency in the innate immunity of the skin. It is characterized by the occurrence of nodules, ab- scesses, fistulas, scars. Objective: Although a relationship has already been demonstrated between HS and innate immunity, IGF-1 status in patients with HS is still unknown. The objec- tive of this pilot study was to determine IGF-1 status in patients with HS as well as its potential relationship with the clinical profile of the disease. Methods: This monocentric and cross-sectional study involved 39 patients hospi- talized at the Dermatology Department of CHU Nantes between November 2014 and January 2018. Clinical data and IGF1 status were collected during the follow- up consultation. Results: Forty-nine percent of the patients had very low levels of IGF-1. At the clinical level, these patients were young and with a short duration of disease. The major difference was that IGF1-deficient patients had a higher BMI than others. The others factors differing between the two patient groups did not reach statisti- cal significance. Conclusion: This exploratory pilot study indicates that HS with a low level of IGF-1 could represent a specific phenotype of patients with HS. These pre- liminary results have to be confirmed with a larger cohort, as they could have practical consequences in the therapeutic care of these patients