Aerodynamic Interference on Finned Slender Body

Aerodynamic interference can occur between high-speed slender bodies when in close proximity. A complex flowfield develops where shock and expansion waves from a generator body impinge upon the adjacent receiver body and modify its aerodynamic characteristics in comparison to the isolated case. The aim of this research is to quantify and understand the multibody interference effects that arise between a finned slender body and a second disturbance generator body. A parametric wind tunnel study was performed in which the effects of the receiver incidence and axial stagger were considered. Computational fluid dynamic simulations showed good agreement with the measurements, and these were used in the interpretation of the experimental results. The overall interference loads for a given multibody configuration were found to be a complex function of the pressure footprints from the compression and expansion waves emanating from the generator body as well as the flow pitch induced by the generator shockwave. These induced interference loads change sign as the shock impingement location moves aft over the receiver and in some cases cause the receiver body to become statically unstable. Overall, the observed interference effects can modify the subsequent body trajectories and may increase the likelihood of a collision

Dual origin of viscoelasticity in polymer-carbon black hydrogels: a rheometry and electrical spectroscopy study

Nanocomposites formed by mixing nanoparticles and polymers offer a limitless creative space for the design of functional advanced materials with a broad range of applications in materials and biological sciences. Here we focus on aqueous dispersions of hydrophobic colloidal soot particles, namely carbon black (CB) dispersed with a sodium salt of carboxymethylcellulose (CMC), a food additive known as cellulose gum that bears hydrophobic groups, which are liable to bind physically to CB particles. Varying the relative content of CB nanoparticles and cellulose gum allows us to explore a rich phase diagram that includes a gel phase. We investigate this hydrogel using rheometry and electrochemical impedance spectroscopy. CB-CMC hydrogels display two radically different types of mechanical behaviors that are separated by a critical CMC-to-CB mass ratio $r_c$. For $r<r_c$, i.e., for low CMC concentration, the gel is electrically conductive and shows a glassy-like viscoelastic spectrum, pointing to a microstructure composed of a percolated network of CB nanoparticles decorated by CMC. In contrast, gels with CMC concentration larger than $r_c$ are non-conductive, indicating that the CB nanoparticles are dispersed in the cellulose gum matrix as isolated clusters, and act as physical crosslinkers of the CMC network, hence providing mechanical rigidity to the composite. Moreover, in the concentration range, $r>r_c$ CB-CMC gels display a power-law viscoelastic spectrum that depends strongly on the CMC concentration. These relaxation spectra can be rescaled onto a master curve that exhibits a power-law scaling in the high-frequency limit, with an exponent that follows Zimm theory, showing that CMC plays a key role in the gel viscoelastic properties for $r>r_c$. Our results offer a characterization of CB-CMC dispersions that will be useful for designing nanocomposites based on hydrophobic interactions.Comment: 18 pages, 10 figures, and 6 supplemental figure

L’efficacité d’un email à vocation commerciale : étude de l’influence des caractéristiques socio-démographiques des internautes sur le processus de réponse.

Le premier objectif de cet article est de proposer un cadre conceptuel présentant l’ensemble des facteurs susceptibles d’influencer la réponse de l’internaute lors de la réception d’un email à vocation commerciale. Outre les variables liées à l’email lui-même et aux spécificités de la situation, le modèle proposé distingue les facteurs individuels, propres au destinataire, des facteurs liés à l’expéditeur. Une étude relative à l’impact des caractéristiques individuelles des internautes sur la performance d’une campagne d’emailing est menée. L’analyse des résultats permet d’identifier les facteurs ayant un impact positif sur la réponse et d’élaborer un profil du répondant type à une sollicitation par email. Il s’agirait d’une femme, âgée de plus de 35 ans, inactive, et ayant des enfants. Les apports de l’étude et ses limites sont présentés en conclusion.The first objective of this article is to propose a conceptual framework, presenting the main factors that can have an impact on an internet user’s response to a commercial email. In addition to the variables related to the email itself and to the situation of its reception, the model presented here makes a clear distinction between the individual factors that are specific to the recipient and those factors that concern the sender. This study looks at the impact of the individual characteristics of an internet user on the performance of an emailing campaign. The results show significant effects for certain individual variables. Factors with a positive impact on the reaction to an email are isolated and the profile of a typical respondent to a commercial email is described. This would be a housewife, more than 35 years old, with children. Main contributions of this study, and its limits, are presented in conclusion.Direct marketing; Consumer behavior; French internet users; Email campaigns; Internautes français; Comportement du consommateur; Marketing direct; Campagnes emailing;

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

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)