Journal of Next-Generation Research 5.0
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Les déterminants des fluctuations des prix vivriers au Cameroun
No full textInternational audienceThis study analyses fluctuations in the prices of food crops in the urban markets of Cameroon. Our methodology is based on the computation of an indicator of price volatility and the application of the vector autoregresion model (VAR). The results show in Douala and Yaoundé, over the period 1994-2012, the combined effects of the storable or tradable nature of food produce, the persistence of past volatility, as well as fluctuations in the prices of substitutes.Cette étude propose d’expliciter les fluctuations des prix des produits vivriers sur les marchés urbains camerounais. La méthodologie repose sur la mesure d’un indicateur d’instabilité du prix et l’application d’un modèle vectoriel autorégressif (VAR). Les résultats montrent à Douala et Yaoundé, entre 1994 et 2012, les effets combinés du caractère stockable ou échangeable du produit vivrier, de la persistance des niveaux de volatilité passée, ainsi que de la volatilité des prix des substituts
Growth and shape of a laboratory alluvial fan
No full textInternational audienceUsing laboratory experiments, we investigate the influence of water and sediment discharges on the morphology of an alluvial fan. In our flume, a single-thread laminar river deposits corundum sand into a conical fan. We record the fan progradation with top-view images and measure its shape using the deformation of a Moiré pattern. The fan remains virtually self-affine as it grows, with a nearly constant slope. We find that, when the sediment discharge is small, the longitudinal slope of the fan remains close to that of a river at the threshold for sediment transport. Consequently the slope depends on the water discharge only. A higher sediment discharge causes the fan's slope to depart from the threshold value. Due to the downstream decrease of the sediment load, this slope gets shallower towards the fan's toe. This mechanism generates a concave fan profile. This suggests that we could infer the sediment flux that feeds a fan based on its proximal slope
Malaria and environment : Search for specific landscape indicators of its distribution in the village of Grande Comore
No full textInternational audienceMalaria has long been endemic in the Union of Comoros. Grande Comore has experienced the highest rates of malaria among the Comorian islands for 90 years. Between 2010 and 2016, more than 82% of reported malaria cases were reported to the Grande Comore. Maintaining a high incidence rate of malaria on the island of Grande Comore, unlike the remaining islands, intrigues malaria control leaders in the Union of the Comoros. This study aims at describing the spatial patterns of the epidemiology of malaria and at identifying environmental indicators through a geographical approach in Grande Comore. Monthly cases, as reported by the ?Programme National de lutte Contre le paludisme? (PNLP) in 2016, were geo-referenced in the island of Grande Comore, at two different scales: by health district and villages. Using SPOT 5 satellite images of Grande Comore, we described and classified the land use by an Object-Based Image Analysis (OBIA) method. We used this classification to calculate landscape metrics within 1km, 1.5km and 2km radius of each village (percentage of surface area covered by each land use class, the patch and edge densities). We realized statistical and spatial analyses to show the relationships between malaria and environmental information. We applied the Global Moran's I and the Anselin Local Moran's I to test spatial correlation of malaria incidence between villages. In 2016, 1,372 malaria cases were recorded in 116 villages. The average incidence of all the villages was 301 cases per 100,000 inhabitants. We observed significant and positive correlation between malaria incidence with grassland (RR=0.03,
Automatic classification of volcano seismic signatures
No full textInternational audienceThe prediction of volcanic eruptions and the evaluation of associated risks remain a timely and unresolved issue. This paper presents a method to automatically classify seismic events linked to volcanic activity. As increased seismic activity is an indicator of volcanic unrest, automatic classification of volcano seismic events is of major interest for volcano monitoring. The proposed architecture is based on supervised classification, whereby a prediction model is built from an extensive data set of labeled observations. Relevant events should then be detected. Three steps are involved in the building of the prediction model: (i) signals preprocessing, (ii) representation of the signals in the feature space, and (iii) use of an automatic classifier to train the model. Our main contribution lies in the feature space where the seismic observations are represented by 102 features gathered from both acoustic and seismic fields. Ideally, observations are separable in the feature space, depending on their class. The architecture is tested on 109,609 seismic events that were recorded between June 2006 and September 2011 at Ubinas Volcano, Peru. Six main classes of signals are considered: long-period events, volcanic tremors, volcano tectonic events, explosions, hybrid events, and tornillos. Our model reaches 93.5% ± 0.50% accuracy, thereby validating the presented architecture and the features used. Furthermore, we illustrate the limited influence of the learning algorithm used (i.e., random forest and support vector machines) by showing that the results remain accurate regardless of the algorithm selected for the training stage. The model is then used to analyze 6 years of data
Patients négligés, effets imprévus. L’expérience des cas suspects de maladie à virus Ebola
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Concede or clash? Solitary sharks competing for food assess rivals to decide
No full textInternational audienceTo adapt to their environment, organisms can either directly interact withtheir surroundings or use social information (i.e. information provided byneighbouring individuals). Social information relates to the external featuresof surrounding peers, and little is known about its use by solitary species.Here, we investigated the use of social cues in a solitary marine predatorby creating artificial aggregations of free-ranging sicklefin lemon sharks(Negaprion acutidens). Using a novel monitoring protocol, we analysedboth dominance interactions and tolerance associations between sharks com-peting for food in relation with the number, the morphology and thebehaviour of rivals. Sharks produced more agonistic displays and spentmore time around the bait as competitors were more abundant. Moreover,the morphological attributes of competitors had very limited influence onthe structure of shark social interactions. Instead, sharks appeared to estab-lish tolerance relationships with competitors according to their individualbehaviour. Furthermore, the more two sharks were observed together at agiven study site, the fewer agonistic interactions they exchanged. We discussthese findings as evidence of the use of social cues in a non-gregariouspredatory species and suggest directions for future research
Validation d'un modèle empirique LAI~VI pour le forçage d'un modèle de croissance de la végétation herbacée à la Réunion
No full textArticle publié en anglais (p. 2-8), avec un résumé étendu en français (p.9-10) et 2 planches couleur hors-texte (p.55-56)International audienceThe Leaf Area Index (LAI) is a parameter of many growth models used to predict biomass. LAI was used, for instance, in the Mosicas (Martiné, 1999) and Gamede (Vayssières et al., 2009) growth models for sugarcane and grass respectively, on Reunion Island, France. Those models have exhibited some limitations and prediction error can be significant. The aim of our study was to estimate LAI from satellite imagery in order to force a grass growth model. Around 430 samples were obtained from nine experimental plots situated around Saint-Pierre and Plaine-des-Cafres (South-West of the island) from April to August 2015. The sample LAI values were averaged by plot and associated with average vegetation indices (VIs), computed from Spot5take5 data (simulation of Sentinel-2 data). From testing of different VIs we observed a stronger correlation between NDVI (Normalized Difference Vegetation Index) and LAI compared to other VIs. The relation was so great that we found correlation values of 0.87 and 0.92 for temperate and tropical grass, respectively.En raison de son insularité et de la croissance constante de sa population, la Réunion est exposée à certains problèmes agricoles, tels que la pression foncière et les problèmes environnementaux. Parallèlement le secteur des ruminants souhaite développer la production et accroître l’autosuffisance de l’île pour la production de viande et de lait, en dépit des contraintes sévères de disponibilité des terres. Des périodes de sécheresse plus fréquentes ont été observées ces dernières années. Pour compenser le manque d’herbe, les agriculteurs importent descompléments d’alimentation, ce qui entraîne des coûts élevés pour l’économie agricole. Aujourd’hui, l’enjeu majeur est de pouvoir estimer la disponibilité des fourrages, à l’échelle du territoire, afin d’optimiser la distribution des fourrages tout au long de l’année et anticiper le besoin d’importation de fourrage. Notre étude s’est attachée à combiner deux méthodes dans une approche hybride, basée sur un modèle de croissance corrigé par des données d’images satellitaires où la prédiction du modèle est remplacée par des données satellitaires. La première étape présentée ici consistait à analyser la relation entre le LAI calculé à partir d’images SPOT5 à haute résolution spatiale (10 m) et plusieurs indices de végétation (IV), puis à comparer différents modèles de régression, capables de prédire le rendement de la biomasse à l’échelle des parcelles et des fermes. L’étude a été menée durant la phase de désorbitation de SPOT5, la phase appelée SPOT5take5. Quatre indices ont été étudiés : NDVI, NDWI, MSAVI2, RDVI. L’étude a été menée sur 9 parcelles) réparties selon un gradient d’altitude afin d'appréhender les différentes espèces de graminées (tropicales et tempérées) présentes sur l'île. Le LAI a été estimé grâce à un appareil mesurant le rayonnement photo-synthétiquement actif absorbé (Accupar Ceptometer model LP 80, Decagon Devices), et chaque mesure a été géolocalisée. On lie ensuite la moyenne de l’indice de végétation avec la moyenne de LAI à l’échelle de la parcelle. La relation est exprimée par une équation de type exponentielle, approchée avec une régression standard. L’analyse de l’erreur est faite grâce au coefficient de corrélationet la somme des erreurs au carré. Après élimination des données aberrantes, 34 valeurs issues des moyennes par parcelles sont exploitables pour établir la relation en indice de végétation et LAI. Les 4 indices étudiés montrent une corrélation importante entre IV et LAI. Toutefois, c’est le NDVI qui montre de meilleurs résultats avec un coefficient de corrélation entre 0,92 et 0,94 (p<0.0001). On observe tout de même une sous-estimation du LAI par le NDVI, dû à une saturation du NDVI au-delà de 0,7. Ces résultats permettent de conclure à une futureutilisation de cette méthode d’estimation du LAI dans le but de couplage de données satellites à des modèles de croissance de l’herbe. Cette méthode sera donc reconduite en utilisant des images Sentinel-2 pour être opérationnelle
Litsea cubeba leaf essential oil from Vietnam: chemical diversity and its impacts on antibacterial activity
No full textInternational audienceAbstractThe threat of bacterial resistance to antibiotics has created an urgent need todevelop new antimicrobials. The aim of this study was to characterize thechemical diversity of Litsea cubeba leaf essential oil (EO) and its impacts onthe antibacterial activity against pathogenic bacteria. Essential oils collectedfrom seven provinces in North Vietnam (n = 25) were characterized by theirhigh content in either 1,8-cineole or linalool. Linalool-type EOs were moreeffective against the eight bacterial strains tested than 1,8-cineole-type. Oilsamples, LC19 (50% 1,8-cineole) and BV27 (94% linalool), were selected toinvestigate their antibacterial mechanisms against Escherichia coli. A strongbactericidal effect was observed after 4 and 2 h of exposure respectively.Microscopic analysis of treated E. coli cultures clearly showed that EOs causedchanges in cell morphology, loss of integrity and permeability of the cellmembrane, as well as DNA loss. However, the effects of both EOs weredistinct. LC19 mostly affected cell membrane, led to a significant cellfilamentation rate and altered cell width, whereas BV27 damaged cellmembrane integrity leading to cell permeabilization and altered nucleoidmorphology with the appearance of spot and visibly altered compaction
Microorganisms as sources of biobased colorants. Going deep into the rainbow of colorful fungi, yeasts, microalgae and bacteria
No full textInternational audienceIngredients derived from microbial fermentation or extracted from microalgae are steadily gaining ground in the food industries (the food industry being taken here as an example of industrial application, among many others). Thickening or gelling agents (e.g. polysaccharides such as xanthan, curdlan, gellan), flavour enhancers (yeast hydrolysate, monosodium glutamate), polyunsaturated fatty acids (PUFAs), flavour compounds (gamma-decalactone, diacetyl, methyl-ketones), vitamins, essential amino acids, and acidulants (lactic acid, citric acid) are some examples illustrating this trend of the biobased economy. Efforts have been made and continue to be done in order to reduce the production costs of pigments produced by algal ponds and microbial fermentation, since synthetic pigments or those extracted from natural plant sources can often be produced more economically. The successful marketing of natural pigments such as -carotene, lutein, and astaxanthin derived from microalgae (i.e. non-conventional sources) or extracted from flowering plants (conventional sources), both as food colorants and nutritional supplements, reflects the presence and importance of niche markets in which consumers are willing to pay a premium for ‘natural healthy ingredients’. Among other non-conventional sources, filamentous fungi and bacteria are known to produce an extraordinary range of pigments that include several chemical classes such as carotenoids, melanins, azaphilones, flavins, phenazines, quinones, and more specifically, monascins, violacein, and indigo. The success of any class of pigment produced by fermentation depends on its acceptance by the consumers, regulatory approval, and the capital investment required bringing the product onto the market. Twenty years ago, influential representatives from food industry expressed doubts about the successful commercialization of microalgae-derived and fermented food grade pigments due to the high investment required for open ponds, photo-bioreactors and fermentation facilities, and the extensive and lengthy toxicity studies required by the regulatory authorities. Poor public perception of fungal-derived products for food use had also to be taken into account. Nowadays, some microbial and algal food grade pigments obtained by fermentation are existing on the market worldwide. Among them, fungal Monascus pigments, Arpink red™ (now Natural Red™) produced by Penicillium oxalicum, microalgal phycocyanin from Arthrospira (Spirulina) platensis, riboflavin from the mold fungus Ashbya gossypii, lycopene and -carotene from the tropical mold Blakeslea trispora, carotene from the microalgae Dunaliella salina, and astaxanthin from the bacterium Paracoccus carotinifaciens and microalgae Haematococcus pluvialis, respectively. As an example, the production yield of -carotene may be as high as 17g/L of the Blakeslea trispora culture medium.Based on proprietary research works conducted on carotenoids and azaphilones for 20 years in our laboratory, the talk will emphasize the crucial role that microorganisms and microalgae are currently playing and are likely to continue to play in future as microbial cell factories for the production of food grade pigments and biobased colourants in general. This is due to the versatility in their pigment colour and chemical profile, amenability for easy large-scale cultivation, and a long history of production by well-investigated production strains
