Etude comparative des jets elliptiques et tourbillonnaires

Cette étude présente une simulation numérique tridimensionnelle des caractéristiques aérodynamiques de jets turbulents soufflés à travers deux diffuseurs à géométries différentes. Le premier diffuseur à une forme elliptique avec différents rapports d'aspect, tandis que le second engendre des jets tourbillonnaires à travers un orifice muni d'ailettes inclinées de 60°. Une comparaison des résultats numériques du jet tourbillonnaire et ceux du jet elliptique, en gardant le même diamètre hydraulique pour l'orifice de soufflage et les mêmes conditions d'écoulement vers le milieu ambiant, est présentée et commentée. La simulation numérique est réalisée via le modèle de turbulence des contraintes de Reynolds (RSM). La méthode numérique utilisée est celle des volumes finis avec un maillage non structuré de type tétraédrique. A la lumière des résultats obtenus, on constate que le jet tourbillonnaire assure, comparativement à tous les jets elliptiques étudiés, une meilleure stabilité dynamique avec un important épanouissement radiale des vitesses et ce dans toutes les sections du jet résultant

Numerical study of the interaction of multiple swirling jets mounted with unbalanced positions

The objective of this study is to examine the influence of various parameters on the optimization of various blowing configurations of multiple swirling jets experimentally and numerically. This study show that the number of vanes and their inclination of the diffuser, the sense of rotation of peripheral jets relative to the central jet and their arrangement in temperatures and positions, affects the quality of the thermal homogenization of ambiance. Experiences concerning the interaction of several jets show that the resulting jet is clearly more homogenized under swirling influence. Among the studied different configuration, the one which consists of a swirling central jet controlling the behavior of tow swirling jets in counter-rotation, is shown to be the most effective in terms of thermal homogenization. The current study is carried out under uniform heat flux condition for each diffuser, the air being the working fluid and flow rate was adjusted at the Reynolds numbers Re0= 3.104. In this work, the three dimensional simulations have been carried out using the finite volume CFD solver Fluent, in which the standard k-e , k-e R.N.G and the Reynolds stress turbulence model (RSM) were used for turbulence computations. Overall predictions obtained with the RSM model are in better agreement with the experimental data compared to those of the standard k-e model. The analysis of the flow features clearly demonstrate that the interaction between swirling jets induces the redistribution of temperature in the mixing zone, while allowing the spreading of the resulting jet. It appears that the central jet plays an important role in the enhancement of the thermal homogenization. The findings of this study show that a balance and an imbalance in temperature and position between the central and peripheral jets, affect the quality of the thermal homogenization of the ambiance

Numerical analysis of reinforced concrete beams pre cracked reinforced by composite materials

This work constitutes a contribution to the analysis of the behavior of beams reinforced by composite materials. The analysis was made by a study on concrete elements, and in pre-cracked reinforced concrete then reinforced with carbon fiber fabric bonded in tusi using an epoxy resin. In order to study the influence of the initial state of cracking, one of the beams was reinforced without it being pre-cracked and was compared to a pre-cracked and reinforced beam then to another loaded until rupture without being pre-cracked or reinforced and neither reinforced. the beams were pre-cracked and reinforced in their stretched part and on the lateral part with bands of different dimensions in order to avoid delamination on the one hand and to study the recovery of the composite under the effect of shearing and detachment on the other hand. However, the arrival of these structures brings new scientific problems and in particular the mode of rupture. The aim of this work is to increase the bearing capacity, reduce the deflection and limit the opening of cracks by ensuring better behavior of this element. The results obtained showed that the bonding of composite materials on reinforced concrete structures gave an increase in the ultimate breaking load and a reduction in deformations in concrete and steels. The results of this method coincide perfectly with those from the literature. The reinforcement allowed a significant increase in the breaking load and a reduction in the deflection at break up to 80%. The theoretical model based on the theory of modified reinforced concrete made it possible to predict with good precision the behavior in bending until the ultimate and it would be possible to use the fabric and the epoxy resin for the reinforcement in bending in building site, beams

Physico-chemical behaviour of irradiated polyimide thin films

The effect of Cu 3+ ion-beam irradiation on the microstructure of two polyimide ( PI ) films ( PMDA-ODA, Kapton ® and BTDA-ODA ) was examined using ATR-FTIR and XPS spectroscopy. The electrical conductivity, Mechanical and Electromechanical properties were also examined. It was found that Cu 3+ ion-beam irradiation was directly responsible for the disruption of the main chain imidic groups in the polymer, which indicated the breakdown of the backbone linkages of the polymer, via cleavage of the nitrogen of the imide and elimination of hydrogen from the PI molecular structure. Electrical conductivity characteristics of the PMDA-ODA films, revealed that they behaved as typical semiconductor films. The resistance of the irradiated films was found to be inversely proportional to temperature, confirming their semiconducting behaviour with calculated thermally sensitive activation barriers in the range 0.4–2.3 eV. The disruption of the main chain imidic groups in the polymer and the formation of the carbon rich channels affected both the tensile strength and the electromechanical properties of the PI films. This is evidenced by changes in Young’s Modulus, and they became slightly brittle at the highest levels of irradiation fluence. The electromechanical properties of PMDA-ODA irradiated films possessed GF values much higher those of conventional composites and an order of magnitude higher than any previously reported. Thus, the irradiated PI films are suitable as sensitive strain gauges with applications as strain sensors, provided they are protected from intense radiation sources

Improvement of thermal homogenization using multiple swirling jets

The aim of this study is to examine different blowing configurations of multiple swirling jets for use it in terminal units of ventilation applications. The influence of several parameters such as the inclined vanes of diffuser and the sense of rotation of the single or multiple swirling jets, their number and their arrangement on the flow resulting dynamically and thermally is experimentally investigated. Flow rate was adjusted at Reynolds numbers, Re0, ranging from 104 to 30.103. The current study is carried out under uniform heat flux condition for each diffuser at Reynolds number of 30.103, the air being the working fluid. Experiences concerning the fusion of several jets show that the resulting jet is clearly more homogenized under swirling influence. The findings of this study show that the gap between the jets and their sense of rotation relative to the central jet, affects the quality of the homogenization of ambiance. Among the studied different configuration, the one which consists of a swirling central jet controlling the behavior of six swirling jets in counter-rotation is shown to be the most effective in terms of thermal destratification

Caractérisation thermique et dynamique d'un multi jet tourbillonnaire à orifices déséquilibrés en positions

Le but de cette étude est d'examiner l'influence du déséquilibre en position du jet central par rapport aux jets adjacents, dans une configuration de 6 jets hélicoïdaux entourant un jet hélicoïdal central. Afin d'identifier la configuration la plus efficace en termes d'amélioration du mélange en sortie de jet Le jet central joue le rôle de guide dans cette configuration de déséquilibre en position. Il pilote les jets adjacents. Cette configuration pourrait intéresser les industriels vue sa contribution pour l'amélioration du confort thermiqu

Simulation numérique à trois dimensions d'une flamme de diffusion en utilisant un schéma réactionnel quasi-global et détaillé

Dans le présent travail, on s'intéresse à la simulation numérique en trois dimensions (3D) des flammes de diffusion d'un écoulement turbulent et réactif dans une chambre de combustion d'une turbine à gaz. Un des objectifs est d'étudier l'influence des modèles de combustion et les mécanismes réactionnels sur la prédiction de l'écoulement du champ de température et la modélisation des émissions polluantes NOx. Les résultats numériques obtenus sont comparés aux résultats antérieur

Case report: 7p22.3 deletion and 8q24.3 duplication in a patient with epilepsy and psychomotor delay—Does both possibly act to modulate a candidate gene region for the patient’s phenotype?

Background: Psychomotor delay, epilepsy and dysmorphic features are clinical signs which are described in multiple syndromes due to chromosomal imbalances or mutations involving key genes implicated in the stages of Early Embryonic Development. In this context, we report a 10 years old Tunisian patient with these three signs. Our objective is to determine the cause of developmental, behavioral and facial abnormalities in this patient.Methods: We used banding cytogenetics (karyotype) and Array Comparative Genomic Hybridization (Array CGH) to this purpose.Results: The karyotype was in favor of a derivative of chromosome 7 in the patient and Array CGH analysis revealed a loss of genetic material in 7p22.3-p22.1 (4,56 Mb) with a gain at 8q24.23-q24 (9.20 Mb) resulting from maternal 7/8 reciprocal translocation. An in silico analysis of the unbalanced region was carried out and showed that the 7p22.3-p22.1 deletion contains eight genes. Among them, BRAT1 gene, previously described in several neurodevelopmental diseases, may be a candidate gene which absence could be correlated to the patient’s phenotype. However, the 8q24.23-q24 duplication could be involved in the phenotype of this patient.Conclusion: In this study, we report for the first time a 7p deletion/8q duplication in a patient with psychomoteur delay, epilepsy and facial dysmorphism. Our study showed that Array CGH still useful for delivering a conclusive genetic diagnosis for patients having neurodevelopmental abnormalities in the era of next-generation sequencing

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Repenser l’échec entrepreneurial des petites entreprises émergentes

International audienceCréer une entreprise demeure aujourd’hui une initiative très risquée. Même si les statistiques montrent que la disparition précoce d’une jeune petite entreprise est un destin plus probable que sa survie, la littérature scientifique sur l’entrepreneuriat se concentre sur la réussite entrepreneuriale. Les petites entreprises émergentes qui échouent demeurent un groupe peu étudié. En plus, il n’y a pas de consensus surla signification de l’échec entrepreneurial qui, d’ailleurs, par sa nature multidimensionnelle et complexe, peut revêtir plusieurs configurations. Dans le but de mieux percevoir l’échec entrepreneurial, le présent article propose une typologie articulée autour des trois théories : la théorie d’écologie des populations des organisations, l’approche fondée sur les ressources et la théorie de la « brèche aspirations-réalisations». L’écologie des populations des organisations perçoit l’échec en termes de mortalité. Basée sur la primauté des ressources, l’approche du même nom analyse l’échec en termes de défaillance économique. La troisième théorie accorde un rôle important à la motivation entrepreneuriale. Pour la théorie de la « brèche aspirations-réalisations », l’échec est associé à la déception personnelle du fondateur àla suite de la non-concrétisation de ses aspirations et attentes initiales. À travers la combinaison de ces trois approches, cet article élabore une typologie de huit catégories ou scénarios d’échec. Il tente d’aller au-delà de la dichotomie classique qui oppose l’ « échec total » et la « réussite absolue ». Il introduit les scénarios d’« échec marginal » et d’« échec partiel ». Une analyse qualitative exploratoire fondée sur l’étude de 10 cas a servi à illustrer cette typologie