Alamouti OFDM/OQAM systems with time reversal technique

Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation (OFDM/OQAM) is a multicarrier modulation scheme that can be considered as an alternative to the conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) for transmission over multipath fading channels. In this paper, we investigate the combination of the OFDM/OQAM with Alamouti system with Time Reversal (TR) technique. TR can be viewed as a precoding scheme which can be combined with OFDM/OQAM and easily carried out in a Multiple Input Single Output (MISO) context such as Alamouti system. We present the simulation results of the performance of OFDM/OQAM system in SISO case compared with the conventional CP-OFDM system and the performance of the combination Alamouti OFDM/OQAM with TR compared to Alamouti CP-OFDM. The performance is derived by computing the Bit Error Rate (BER) as a function of the transmit signal-to-noise ratio (SNR)

Experimental and numerical study of the hydrodynamics of an isolated bubble in non-Newtonian liquid phase in a thin gap bubble column

International audienceDevelopment of photobioreactors (PBR) for microalgae cultivation is a primary concern, keeping in mind the applicative potential of these photosynthetic microorganisms. For this purpose, optimization of culture parameters and PBRs design are the two possible solutions in order to obtain high volumetric productivities. The thin-gap intensified PBR allows to obtain these performances via an increase of culture concentration for a given illuminated surface. When compared with usual PBRs, the confinement results in a high change of the hydrodynamics and mass transfer[1]. To optimize these production systems, our study focuses on the characterization of local hydrodynamics in a 2D bubble column of 4 mm thickness (FIG. 1). Furthermore, it has been shown that the increase in cell concentration is accompanied by rheological properties modifications of the microalgae suspension. To mimic such high concentration of Chlorella vulgaris cultures which have non-Newtonian shear thinning behaviour at concentrations ranging from 30-40 g/L[2], solutions of Xanthan Gum (XG) and Carboxymethyl cellulose (CMC) are used respectively at the concentrations of 1 g/L and 2 g/L. In order to put forward the effect of the rheological behaviour, demineralized water is also used as a Newtonian fluid. In this preliminary work, the main purpose is to estimate the terminal velocity (V t) of an isolated bubble in this confined column. In fact, if the terminal velocity for an isolated bubble is modified due to wall effects, there will have consequences for hydrodynamics and mass transfer of the whole bubble column: for instance, bubble residence time or gas hold up will be modified[1]. B.Figueroa Espinoza et al. [3] reported the confinement effect for a single clean bubble, pointing out that the drag coefficient widely increases for oscillating bubbles rising in a Hele-shaw cell. The experimental part consists in studying the local hydrodynamics behaviour of isolated bubbles of different diameters for three liquid media: water, CMC and XG solutions. Capillaries tubes, having diameters (d c) of 0.127, 0.264, 0.508, 0.762 or 1.016 mm are used to generate isolated bubbles at different diameter sizes with the help of a low-pressure syringe pump (NEMESYS, GERMANY). Bubble injection is performed 7 cm away from the lateral wall which can be considered sufficient to avoid wall influence on the hydrodynamics of isolated bubble. Bubble size and instantaneous bubble velocity are estimated by a shadowgraphy method using the DANTEC DYNAMICS Shadow Strobe. These measurements are performed at mid height of the column, where bubble terminal velocities have been reached. The experimental terminal velocities for different bubble diameters (d b) in water, CMC and XG liquid media are reported in Table 1 and plotted in FIG. 2(a). Water measurements are also compared to the correlation established by M.Jamialahmadi et al.[4] and the data of R.Clift et al. [5] which concern isolated bubble in pure water in infinite liquid medium (FIG. 2(b)). It is found that for an isolated bubble rising in quiescent liquid, with a diameter lower than 4 mm, the terminal velocity is divided by V t ratio between 1.2 and 1.6 for water. Besides this in non-Newtonian solutions, for lower bubble diameters the terminal velocity is less than water medium and as the bubble diameter increases it becomes constant this phenomena was also experienced by Shahram Amirnia et al.[6]. In parallel to experiments, a numerical study is performed to characterize the behaviour of one single bubble in the confined space between two walls in Newtonian and Non-Newtonian media. Simulations are performed with academic Ansys Fluent 17.2 solver using volume of fluid (VOF) method for interface tracking along with continuum surface Force (CSF) model to treat surface tension. Firstly, mesh independency verification has been performed by 2D and 3D simulations of a 3 mm diameter bubble in infinite medium. These results have been validated with the results of F.Bertola et al.[7](FIG.2(b)). Thereafter the same confined geometry as experimental setup has been adopted to simulate the bubble diameters determined experimentally. Numerical results are reported in FIG. 2(b) and seem to be in good agreement with the experiments results (FIG 2(b))

Determining the impacts of climate change on Spatio-temporal patterns of meteorological drought using SPI: A case study of Ain Defla, Algeria.

As an associated aspect of climate change, drought has become a severe challenge in different parts of the world, especially in regions where life depends on predominantly rain-fed agriculture. The Ain Defla study area is mostly agricultural land, most of its activity depends on rain. In recent years, droughts of varying impact and severity have affected crops. Therefore, this study aimed to identify and study the regions that are most vulnerable to drought in terms of time and space. Moreover, it provides a detailed picture of the drought in the region and finds appropriate solutions in the event of its return in the future. The Standardized Precipitation Index (SPI) and the deviation from the average (EM) were calculated annually for 38 years for 13 stations from 1981 to 2019 within the study area. GIS was used to compile digital maps to visualize the spatial distribution of rainfall (P) and the difference in rainfall (EM) and determine the aridity using SPI values within the region based on the statistical method of Kriging. The Ain Defla region was subjected to drought of varying intensity and impact during the years (1983, 1989 and 2000), which extends with a decreasing value from east to west. Some wet years were also observed (2013 and 2018). Most years were in the moderate category by 60%. It is possible to rely on rain-fed agriculture in the western regions, that were less prone to drought during the study period compared to the eastern part, an area where drought is stable on an ongoing basis

DIVERSITÉ FLORISTIQUE DU MASSIF DU NADOR EN ZONE STEPPIQUE (TIARET, ALGÉRIE)

This study is devoted to Nador massif located in the steppe environment of Tiaret region in the west of Algeria. This massif is characterized by a diversity of flora composed of 121 taxa belonging to 38 families and 98 genera. Biological spectrum indicates a predominance of therophytes (38%) and chamaephytes (19%), geophytes (14%). The most important families are Poaceae and Asteraceae. Mediterranean element is relatively dominant (55%) according to chorologic plane. Shannon-Weaver e diversity index is relatively high (4.55) indicating a richly diverse site. Disturbance index (63.6%) reflects highly significant degree of massif vegetation disturbance, which also reflects a more open environment. To better understand the structure of vegetation using the classification is imperativ

QUAND INNOVATION RIME AVEC TRADITION : VERS L'EXPLORATION D'UN NOUVEAU REGARD PORTE SUR LES PRODUITS ARTISANAUX

Nous assistons depuis quelques années à un changement dans les habitudes du consommateur tunisien. De nos jours, il achète et apprécie de plus en plus les produits locaux et plus spécialement artisanaux. Ce nouveau comportement s'est manifesté suite à l’apparition de nouvelles marques artisanales tunisiennes, proposant des produits revisités alliant à la fois les traditions et les tendances les plus branchées. A travers cette étude, nous cherchons à enrichir la littérature en exposant dans un premier temps l'évolution qu'a subie le produit artisanal tunisien. Ce développement théorique, nous permettra conséquemment d'explorer empiriquement le nouveau regard que porte le consommateur tunisien quant à ce produit, très longtemps banalisé.Ce travail nous apportera un éclairage quant à la problématique suivante : Quel regard portent les consommateurs tunisiens à l'égard des nouveaux produits artisanaux ?Pour répondre à cette problématique, nous nous sommes inspirés en premier lieu des travaux de Schumpeter (1930). Le but ici est de mettre en exergue les innovations subies par le produit artisanal en se référant à l'innovation organisationnelle, l’innovation de produit, l’innovation par la conquête de nouveau marché, l’innovation par la commercialisation ainsi que l’innovation par l’utilisation de nouvelles sources de matières premières. Dans un second temps, nous avons eu recours à une étude qualitative, dans laquelle nous avons réalisé 21 entretiens individuels non-directifs avec les consommateurs.Nos résultats ont montré que les produits artisanaux sont devenus très appréciés par le consommateur tunisien, considérés par la plupart d'entre eux comme des produits très à la mode. Ce constat contredit les résultats des anciennes recherches qui discutent d'un produit bénéficiant depuis longtemps d'une image figée, obsolète et archaïque.Cette recherche a également permis d'exhiber, des liens entre les tendances actuelles de consommation et le produit artisanal revisité, en montrant que ce dernier répond parfaitement aux besoins du consommateur postmoderne à savoir ; la recherche de disparition de frontière, la quête d'authenticité et de nostalgie, la soif d'accomplissement, la recherche de rassurance…Les résultats de cette recherche ont permis dès lors d'apporter des recommandations utiles aux professionnels du domaine, notamment les artisans, les créateurs, et les designers.Cependant cette étude présente un certain nombre de limite qu'il convient de mentionner. Nous citons, la méthode de collecte de données qui a été faite par convenance engendrant ainsi une forte représentativité des étudiants au détriment des autres classes socioprofessionnelles. Il serait donc pertinent de réaliser une étude auprès d'un échantillon plus variés, pouvant même inclure des professionnels du domaine et de comparer les perceptions des consommateurs et des artisans. The purchasing behaviors of the Tunisian consumers have changed during these recent years. Now, he purchases and values more local goods, especially handicrafts ones. This new mindset come out because of the emergence of new Tunisian crafts companies that sell updated products that combine both traditional and modern styles.Our objective consists first, to outline the evolution of the Tunisian artisanal product. Therefore, this theoretical advancement will enable us to empirically study the new consumer perspective on this long-trivialized commodity in Tunisia.We were initially motivated to address our issue based on the work of Schumpeter (1930). The purpose of this article is to draw attention to the innovations that the artisanal product has to deal with, by discussing organizational innovation, product innovation, innovation by breaking into new markets, innovation through commercialization, and innovation by the use of new raw material sources. The second method involved a qualitative study in which we performed 21 non-directive one-to-one interviews with consumers.Our findings demonstrate that Tunisian consumer is actually attracted by the handcrafted brand that considered it fashionable. This discovery runs counter to prior research's findings regarding a product that has long been associated with a basic and archaic appearance.This research demonstrates also the relationship between current consumer trends and the revisited artisanal product, confirming that the new version of the artisanal product satisfies perfectly the needs of the postmodern consumer, namely the quest for erasure of boundaries, the quest for authenticity and nostalgia, the thirst for achievement, and the quest for reassurance.Our results will help experts in the sector, such as craftspeople, creators and designers to understand consumer perceptions regarding the product, to reconsider their strategies.However, this study has a few limitations. We specially point out the data collection technique, which was carried out for the sake of convenience and led to a significant representation of students at the expense of other socio-professional classes. Therefore, it will be interesting to perform a study with a more diverse sample, possibly including industry professionals in order to determine whether there is a perception gap between consumers and artisans

Anaerobic co-digestion of dairy raw by-products and Ulva sp. macroalgae: effect of organic and inorganic additives

An investigation has been carried out for biogas production from dairy raw materials (DRM) and Ulva sp. macroalgae as a co-substrate in order to find a usefulness for these species. Some nutrient media have been selected to optimize methane yield. The effect of the mineral additive medium (medium I), based on bicarbonate compound, and the organic additive one (medium II), based on glucose, on the anaerobic digestibility of DRM has been assessed by using a single-stage anaerobic process. Four batch experiments (batch 1, batch 2, batch 3 and batch 4) have been performed and correspond respectively to DRM without inoculum, DRM with additive medium I, DRM with additive medium II and DRM and Ulva sp. with additive medium I. Measurements of methane produced, chemical oxygen demand (COD), proteins, lipids, carbohydrates and volatile fatty acids have been carried out. It has been found that the mineral additive medium provided a higher specific methane yield compared to the organic additive one, the methane yield was about 0.208 $\mathrm{L}_{\mathrm{CH}_4}/\mathrm{g}_{\mathrm{VS}}$. The co-digestion of DRM with Ulva sp. showed that the methane yield reached was about 0.118 $\mathrm{L}_{\mathrm{CH}_4}/\mathrm{g}_{\mathrm{VS}}$, and revealed that the use of Ulva sp. as co-substrate reduces the concentration of volatile fatty acids, and enhances the biogas quality which contains 96% of methane and only 0.5 to 2% of hydrogen sulphide. Furthermore, a first-order kinetic model has been applied to describe proteins, lipids and carbohydrates biodegradation and showed that these three compounds follow a different kinetics according to the composition of the medium and the presence or not of additive medium

OPTIMISATION DE L'HYDRODYNAMIQUE DANS DES PHOTOBIOREACTEURS A HAUTE PRODUCTIVITE VOLUMIQUE POUR EVITER LE DEVELOPPEMENT DE BIOFILM

International audienc