287 research outputs found

    Analysis of the surface state's influence on the thermohydraulic behavior of an incompressible fluid in convective laminar flow through a microchannel with corrugated surfaces

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    Le travail entrepris dans cet article présente une étude numérique thermo-énergétique de l'écoulement convectif laminaire dans un microcanal rectangulaire lisse ou la présence de discontinuités sur ses parois. Les ondulations présentent les discontinuités de la surface du mur. La paroi inférieure du microcanal portée à une température constante et uniforme. Le nombre de Reynolds utilisé, Re, a été choisi dans la gamme (50 à 350). La solution du système d'équations régissant le problème a été réalisée par un schéma de volumes finis associé à l'algorithme SIMPLE (Semi Implicit Method for Pressure Linked Equation) pour surmonter le problème de couplage pression-vitesse. L'étude s'est concentrée principalement sur les effets des deux paramètres pertinents : le nombre de Reynolds et la forme géométrique des microcanaux. Les deux champs de vitesse axiale et de température ont été analysés, et le nombre moyen de Nusselt, le coefficient de frottement et la quantité de chaleur évacuée. Les résultats montrent que la structure de l'écoulement est fortement perturbée par la présence de discontinuités sur les parois, et le nombre de Nusselt moyen augmente toujours la fonction du nombre de Reynolds pour les quatre cas étudiés, tandis que l'évolution du coefficient de frottement peut être croissante ou décroissant en fonction du nombre de Reynolds

    Three-dimensional analysis of flow characteristics in a heat exchanger equipped with a perforated heat sink

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    Finning or perforations are frequently used in heat exchange devices to increase the heat exchange between the contact surfaces and the surrounding fluid. Thus, the work undertaken in this paper is in the same context to search for a new design to improve the thermohydrodynamic performance of a heat exchanger.  In this context, the latter considered being equipped with a solid or perforated heat sink to identify the perforations' efficiency in optimizing the heat exchanger's performance. The thermohydrodynamic phenomenon governed by the partial differential equations system derived from the laws of conservation: continuity equation for mass, Navier-Stokes equations for momentum, and the energy equation. For the numerical solution, the finite volume method used, and the problem of pressure-velocity coupling intervening at the level of the Navier-Stokes equations solved using the SIMPLE algorithm. Calculations are made for a perforated deflector with different diameters and an unperforated deflector. For both cases, the inlet velocity was chosen in a range from 0.0018 to 0.009 m/s. The results are presented either as maps for the isothermal fields and velocity contours obtained for the meridian planes shown in the figures or as curves for the axial velocity and heat flow. Finally, a qualitative comparison of the different calculated results made, and it could deduce that a perforated deflector is much more efficient than a solid or solid deflector fixed at the same position. The increase in terms of transfers can go from 1.33% to 12.97%, and an excellent material reduction (from 2.32% to 55.85%) corresponds to a low flow resistance compared to the non-perforated case

    Rotating hyperdeformed quasi-molecular states formed in capture of light nuclei and in collision of very heavy ions

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    International audienceWithin a rotational liquid drop model including the nuclear proximity energy the l-dependent potential barriers governing the capture reactions of light nuclei and of very heavy ions have been determined. Rotating quasi-molecular hyperdeformed states appear at high angular momenta. The energy range of these very deformed high spin states is given for light systems. The same approach explains the observation of ternary cluster decay from56Ni and 60Zn through hyperdeformed shapes at angular momenta around 45 . The apparently observed superheavy nuclear systems in the U+Ni and U+Ge reactions at high excitation energy might correspond to these rotating isomeric states formed at very high angular momenta even though the shell effects vanish

    Numerical Evaluation the Impact of the Inserts Shape on Thermo-Flow Behavior in a Heat Exchanger

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    The improvement of transfers in a heat exchanger can be achieved either by increasing its coolant thermal conductivity or by modifying its geometrical configuration. In this paper, we will be interested in the latter technique by choosing a three-dimensional configuration represented by a channel of rectangular section, on which solid fins of square, circular, or diamond section (vortex generator) have been transversally mounted, which are moreover adiabatic and non-rotating. A convective and forced airflow traverses the channel, and the study focused in principle on the effects of the shape of the fins on the structure of the flow and the rate of heat transfer. The problem is governed by the Navier-Stokes system, coupled with the energy equation de-scribing the thermal process. The resolution of the equation system governing the hydrodynamic phenomenon is performed numerically in three dimensions. To do this, the governing equations of the thermo-hydrodynamic phenomenon are discretized by a finite volume scheme. As for turbulence, it is modeled using the standard model k-ɛ, and the problem of pressure-velocity coupling is solved by the SIMPLE algorithm (Semi Implicit Method for Pressure Linked Equation). The computed results are presented as curves for the Nusselt number, friction factor, thermal enhancement factor, or amount of heat dissipated, and as a map for the contour of the axial velocity norm and the temperature field distribution

    Quality study of wastewater treated by waste Water Treatment plant (WWTP) in the city of Sana'a (Yemen) used for agriculture.

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    The wastewater treated by the PWTS Sanaa (Yemen), are discharged into Wadi Bani Houat to be used for irrigation of agricultural fields (cereals and "qat"). The quality of water discharged by the station is affected by neo-contamination part of untreated water diverted through bypass and also untreated effluent intake of a river that flows into the canal about 15 Km from the station. The various measurements show that the levels of contaminants studied, decrease at the exit of the station but undergo severe degradation after canal-branch river. Similarly, we noted illegal contributions at this place made of waste thrown into the canal by the surrounding population. The salinity is classified C4S2, C3S3, C4S3 and C4S4 in RICHARDS diagram, leading to poor quality water for irrigation. The ratio COD / BOD5 reaching a value of 2 after treatment and self purification of water, up to a value of 4, at a distance of 12 km along the canal before dropping to a value below 2 at the areas of retention dams located north of the study area, showing a self-purification capacity. NO2- (nitrite ions) appear downstream canal in the dams, highlighting the impact of agricultural activity on water quality. Minors cations and traces show different concentrations varying spatially and temporally along the canal during the dry and wet seasons. Overruns by FAO and Yemen standards were observed for some components such as phenol, organic micropolluant showing levels higher than standard along the canal in all seasons. The principal component analysis showed the correlation between the measured quantities and the vulnerability of sampling sites to different pollutants.  

    8Be, 12 C, 16 O, ... nuclei and alpha clustering within a Generalized Liquid Drop Model

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    International audienceA Liquid Drop Model previously used to describe smoothly the transition between two-(or three) body and one-body shapes in entrance and exit channels of nuclear reactions has been used to determine the potential barriers governing the evolution of the light nuclei : 8Be, 12C, 16O, 20Ne, 24Mg and 32S

    A comparative review of dynamic neural networks and hidden Markov model methods for mobile on-device speech recognition

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    The adoption of high-accuracy speech recognition algorithms without an effective evaluation of their impact on the target computational resource is impractical for mobile and embedded systems. In this paper, techniques are adopted to minimise the required computational resource for an effective mobile-based speech recognition system. A Dynamic Multi-Layer Perceptron speech recognition technique, capable of running in real time on a state-of-the-art mobile device, has been introduced. Even though a conventional hidden Markov model when applied to the same dataset slightly outperformed our approach, its processing time is much higher. The Dynamic Multi-layer Perceptron presented here has an accuracy level of 96.94% and runs significantly faster than similar techniques

    Phytochemical profile, antioxidant and antiproliferative activities of olive leaf extracts from autochthonous Tunisian cultivars

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    The aim of the present study was to investigate the biological activities of Tunisian olive leaf extracts and to correlate these activities to their phytochemical composition. The phenolic profile of four Tunisian autochthonous cultivars Chemlali, Sayali, Neb jmel, and Meski was determined using LC/MS-MS. The antioxidant activity of olive leaf extracts was evaluated using DPPH test. The antiproliferative effect was also investigated using MTT assay. The phytochemical screening showed that phenolic content and phenolic class repartition were significantly affected by olive leaf cultivars. Twenty-one components were identified and oleurpein, luteolin 4-glucoside, luteolin 7-glucoside, and apigenin 7-glucoside were the major phenolic components. Among all extracts, Sayali exhibited the strongest antioxidant and antiproliferative activities (IC50 41.36 µg ml−1 / EC50 147.11 µg ml−1). The MTT result showed that olive leaf extract reduced MCF-7 cell viability in a dose-dependent manner. Western blot analysis demonstrated that olive leaf extracts exhibited antiproliferative activity through apoptosis induction

    Characterizing the target selection pipeline for the Dark Energy Spectroscopic Instrument Bright Galaxy Survey

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    We present the steps taken to produce a reliable and complete input galaxy catalogue for the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey (BGS) using the photometric Legacy Survey DR8 DECam. We analyse some of the main issues faced in the selection of targets for the DESI BGS, such as star–galaxy separation, contamination by fragmented stars and bright galaxies. Our pipeline utilizes a new way to select BGS galaxies using Gaia photometry and we implement geometrical and photometric masks that reduce the number of spurious objects. The resulting catalogue is cross-matched with the Galaxy And Mass Assembly (GAMA) survey to assess the completeness of the galaxy catalogue and the performance of the target selection. We also validate the clustering of the sources in our BGS catalogue by comparing with mock catalogues and the Sloan Digital Sky Survey (SDSS) data. Finally, the robustness of the BGS selection criteria is assessed by quantifying the dependence of the target galaxy density on imaging and other properties. The largest systematic correlation we find is a 7 per cent suppression of the target density in regions of high stellar density
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