In wind tunnel the reproduction of vortex shedding behind circular cylinders at high Reynolds number regimes is incomplete

Wind tunnel tests of 2D rough cylinders are presented. The goal is to simulate the alternate vortex shedding in flow regimes encountered in wind engineering applications, where the full scale Reynolds number is larger than the one that can be reproduced in wind tunnel with small scaled models. Measurements are mainly the synchronized unsteady wall pressures on the cylinder which are post processed using bi-orthogonal decompositions. By comparing the small scale results with those from a previous large scale experiment, we show that the technique of rough cylinder is incomplete and can approach roughly global parameters only.Comment: Proceedings of the 12th International Conference on Flow-Induced Vibration, 5-8 July 2022, Paris Saclay pp 509-51

Conception et fabrication d'un filtre accordable avec la technologie des MEMS pour les applications micro-ondes

Depuis plusieurs décennies le domaine des communications sans fil est en pleine expansion. Ce phénomène entraîne la nécessité d'améliorer continuellement les systèmes, d'un point de vue tant algorithmique que matériel. Des filtres plus sélectifs, au coût et à l'encombrement réduit, aux pertes d'insertion minimes font partie des objectifs. L'augmentation du nombre et de la qualité des transmissions passe par le partage du spectre de fréquences, donc par la possibilité de pouvoir changer la fréquence de transmission. Les filtres accordables sont essentiels afin d'avoir des systèmes reconfigurables permettant ces sauts de fréquences. Pour réaliser un tel filtre, l'émergence de la technologie des MEMS ouvre de nouvelles perspectives. Déjà présente dans des domaines très variés, ses premiers pas en hyperfréquence remontent aux années 1990. Les recherches à ce sujet ont mis en évidence les avantages des MEMS RF: miniaturisation, faible consommation de puissance, faible pertes, linéarité de leur comportement, tout en étant compatible avec une intégration monolithique de type MMIC. Cette étude, destinée aux communications dans la bande 1,35 GHz-2,7 GHz, diffère de la majorité des articles parus sur ce sujet pour lesquels les applications au dessus de 15 GHz prédominent. Le filtre réalisé dans ce projet est un filtre demi longueur d'onde à accordage capacitif, utilisant des valeurs discrètes de capacités sélectionnées à l'aide d'un interrupteur MEMS ohmique conçu spécifiquement pour cette application. Le composant MEMS RF a été dimensionné puis caractérisé théoriquement et par le biais de simulation couplées électromécaniques afin d'obtenir un comportement prédictif le plus fiable possible. Le filtre accordable incluant les composants MEMS a été fabriqué par nos soins à l'Université McGill de Montréal. La bande de fonctionnement du filtre se situe entre 1,536 GHz et 2,174 GHz, ses pertes d'insertion varient de 5,5dB@2,174GHz à 11,7dB@1,536GHz, et sa bande passante de 20 MHz à 40 MHz

Robustness of the BYM model in absence of spatial variation in the residuals

<p>Abstract</p> <p>Background</p> <p>In the context of ecological studies, the Bayesian hierarchical Poisson model is of prime interest when studying the association between environmental exposure and rare diseases. However, adding spatially structured extra-variability in the model fitted to the data when such extra-variability does not exist conditionally on the covariates included in the model (<it>over-fitting</it>) may bias the estimation of the ecological association between covariates and relative risks toward the null. In order to investigate that possibility, a simulation study of the impact of introducing unnecessary residual spatial structure in the estimation model was conducted.</p> <p>Results</p> <p>In the case where no underlying extra-variability from the Poisson process exists, the simulation results show that models accounting for structured and unstructured residuals do not underestimate the ecological association, unless covariates have a very strong autocorrelation structure, i.e., 0.98 at 100 km on a territory of diameter 1000 km."</p

On the galloping instability of two-dimensional bodies having elliptical cross sections.

Galloping, also known as Den Hartog instability, is the large amplitude, low frequency oscillation of a structure in the direction transverse to the mean wind direction. It normally appears in the case of bodies with small stiffness and structural damping, when they are placed in a flow provided the incident velocity is high enough. Galloping depends on the slope of the lift coefficient versus angle of attack curve, which must be negative. Generally speaking this implies that the body is stalled after boundary layer separation, which, as it is known in non-wedged bodies, is a Reynolds number dependent phenomenon. Wind tunnel experiments have been conducted aiming at establishing the characteristics of the galloping motion of elliptical cross-section bodies when subjected to a uniform flow, the angles of attack ranging from 0° to 90°. The results have been summarized in stability maps, both in the angle of attack versus relative thickness and in the angle of attack versus Reynolds number planes, where galloping instability regions are identified

Reshaping Suburbia: A Comparative Study of Markham Centre and Vaughan Metropolitan Centre

The Greater Toronto Area is projected to become the fastest-growing region in the province of Ontario, surpassing a population threshold of 10 million by 2046. As a result, suburban municipalities are planning for the development of intensified, high-density, and mixed-use downtown centres to accommodate the forecasted growth. This study aims to uncover and understand the planning and development processes directing new metropolitan forms located in suburban cities. This research employs comparative case study methods to analyze the two emerging suburban downtowns of Markham Centre and Vaughan Metropolitan Centre that have been planned since the 1990s. Through the use of an in-depth review of existing literature of key themes, policy documents, and seven interviews with industry professionals, I examine the causes and purposes which form suburban downtowns. Herein, I argue that despite retaining both suburban and urban characteristics, suburban downtowns do represent an evolution from traditional suburban built form which duly redefine perceptions of suburbia

Detection of clusters of a rare disease over a large territory: performance of cluster detection methods

International audienceBackgroundFor many years, the detection of clusters has been of great public health interest. Several detection methods have been developed, the most famous of which is the circular scan method. The present study, which was conducted in the context of a rare disease distributed over a large territory (7675 cases registered over 17 years and located in 1895 units), aimed to evaluate the performance of several of the methods in realistic hot-spot cluster situations.MethodsAll the methods considered aim to identify the most likely cluster area, i.e. the zone that maximizes the likelihood ratio function, among a set of cluster candidates. The circular and elliptic scan methods were developed to detect regularly shaped clusters. Four other methods that focus on irregularly shaped clusters were also considered (the flexible scan method, the genetic algorithm method, and the double connected and maximum linkage spatial scan methods). The power of the methods was evaluated via Monte Carlo simulations under 27 alternative scenarios that corresponded to three cluster population sizes (20, 45 and 115 expected cases), three cluster shapes (linear, U-shaped and compact) and three relative risk values (1.5, 2.0 and 3.0).ResultsThree situations emerged from this power study. All the methods failed to detect the smallest clusters with a relative risk lower than 3.0. The power to detect the largest cluster with relative risk of 1.5 was markedly better for all methods, but, at most, half of the true cluster was captured. For other clusters, either large or with the highest relative risk, the standard elliptic scan method appeared to be the best method to detect linear clusters, while the flexible scan method localized the U-shaped clusters more precisely than other methods. Large compact clusters were detected well by all methods, with better results for the circular and elliptic scan methods.ConclusionsThe elliptic scan method and flexible scan method seemed the most able to detect clusters of a rare disease in a large territory. However, the probability of detecting small clusters with relative risk lower than 3.0 remained low with all the methods tested

IMECE2002-33375 STUDY OF THE ACOUSTIC OSCILLATIONS BY FLOWS OVER CAVITIES. PART 1. INTERNAL FLOWS

ABSTRACT We present a study of acoustic oscillations induced by an internal airflow over a shallow and a deep cavity. The KelvinHelmholtz instability is interacting with an acoustic mode of the duct, leading to a resonance which produces a very high sound level. The influence of upstream boundary layer thickness and neck thickness is studied. Some results obtained by modifying the upstream lip shape, by crenel addition, are also given. It is also shown that the numerical simulations using a lattice-gas method give relatively good results by comparison with the experiments. Especially the resonance with the duct acoustics was qualitatively reproduced

Residential exposure to solar ultraviolet radiation and incidence of childhood hematological malignancies in France

Few studies have investigated the relationship between solar ultraviolet radiation (UV) and childhood hematological malignancies (CHM). This study addresses the associations between residential UV exposure at diagnosis and the incidence of types and subtypes of CHM, by age and gender, in France, over a long period, on the fine scale of the 36,326 Communes that constitute mainland France. The 9,082 cases of acute leukemia and 3,563 cases of lymphoma diagnosed before the age of 15 years from 1990 to 2009 were provided by the French National Registry of Childhood Hematological Malignancies. The incidence of CHM was calculated by Commune, year, age and gender and expressed as the standardized incidence ratio (SIR). UV data from 1988 to 2007 were extracted from the EUROSUN database. The annual daily average UV exposure of the children ranged from 85.5 to 137.8 J/cm2. For each additional 25 J/cm2, there was a significant increase in precursor B-cell acute lymphoblastic leukemia (PBC-ALL) in children aged less than 5 years (SIR 1.18; 95 % CI 1.10–1.27). Further analysis of PBC-ALL in the young children suggested a better fit of models with a threshold, with the risk increasing above 100 J/cm2, for which the SIR was 1.24 (95 % CI 1.14–1.36) for a 25 J/cm2 increase. The results remained stable in analyses stratifying by deprivation index or degree of urbanization of the Communes. The study suggests that higher residential UV exposure may be positively associated with a higher incidence of PBC-ALL in early childhood

Hydrodynamic coefficients and forces on multihulls in shallow water with constant or variable depth

Numerical and hydro dynamical procedures are developed to compute bidimensional hydrodynamic coefficients and forces on multihulls associated with harmonic oscillations in shallow water with constant or variable depth. The forces are composed of two parts and include the sum of incident and diffracted forces and hydrodynamic reaction. The latter one is used to determinate the hydrodynamic coefficients (added mass and damping). The numerical method used is the Boundary Element Method. We can compute flow around multihulls sections. An application to cylindrical, right triangular and rectangular hull forms is presented. First published online: 27 Oct 201