899 research outputs found
Chaquitaclla, stratégies de labour et intensification en agriculture andine
* illus. 25 ref.National audienceBeche d'origine prehispanique, la chaquitaclla n'a pas ete eliminee par les outils introduits depuis la conquete. Dans les Andes du Perou et de Bolivie, elle reste actuellement l'outil le mieux adapte aux conditions de montagne pour labourer la longue jachere paturee, caracteristique des systemes agropastoraux d'altitude. Face a la faible productivite du labour a la chaquitaclla, les paysans ont mis au point des strategies de labour qui tendent a optimiser la production par jour de travail investi, independamment des rendements par hectare obtenus. Ces strategies se traduisent par trois itineraires techniques differencies afin de tirer parti de la diversite des conditions agroecologiques. La comprehension des logiques de production revele que les paysans andins ont su developper une agriculture de pente, ignoree dans les evaluations du milieu ou les terres sont reduites aux terres mecanisables. L'intensification, en eliminant la jachere favorise l'emploi de l'araire en traction attelee mais, dans ces regions d'altitude ou les processus d'intensification restent limites, les interrelations entre agriculture et elevage persistent a travers la jachere paturee et la chaquitaclla reste un instrument de labour indispensable. Cet article souligne la necessite de la connaissance des pratiques paysannes et des dynamiques agraires dans la definition d'une recherche technologique sur les outils de travail du sol
Chakitaklla : estrategia de barbecho e intensificacion de la agricultura andina
Ce document est un apport au débat sur le travail du sol et la modernisation dans l'agriculture andine. C'est le résultat d'une synthÚse d'expériences sur le terrain et de recherches menées pendant de nombreuses années par les auteurs dans le Centre des Andes, le Sud du Pérou et le Nord-Ouest de la Bolivi
Inferring the Dynamics of Diversification: A Coalescent Approach
A novel approach to infer diversification dynamics shows that biodiversity is still expanding but at a slower rate than in the past
Philippe Geslin, L'apprentissage des mondes. Une anthropologie appliquée aux transferts de technologies. Paris, Octares/MSH, 1999 + CD-ROM.
Le livre « La mer, la terre et le palĂ©tuvier. Ethnologie et transferts de technologies. L'exemple du sel chez les Susu de GuinĂ©e » est le titre de la thĂšse dont Philippe Geslin a tirĂ© cet ouvrage. Il y prĂ©sente et analyse l'histoire, tronquĂ©e par les Ă©vĂ©nements politiques, de son implication comme anthropologue dans un transfert de technologie des marais salants de GuĂ©rande en France vers la GuinĂ©e oĂč les Susu produisent traditionnellement du sel par chauffage d'une saumure (eau de mer ..
Mécanismes de prise en charge su sélénite - Se (IV) - chez l'algue verte unicellulaire Chlamydomonas reinhardtii. Bioaccumulation et effets induits sur la croissance et l'ultrastructure
Le sĂ©lĂ©nium est un Ă©lĂ©ment essentiel, mais qui devient trĂšs toxique Ă des concentrations plus Ă©levĂ©es. Il est prĂ©sent dans lâenvironnement Ă des concentrations variant du nM au ”M et la pollution par cet Ă©lĂ©ment est un phĂ©nomĂšne mondial. Ce travail vise Ă accroĂźtre les connaissances relatives Ă lâinteraction entre le sĂ©lĂ©nite -Se(IV)- et un organisme phytoplanctonique dâeau douce : lâalgue verte unicellulaire Chlamydomonas reinhardtii. Les objectifs des expĂ©riences rĂ©alisĂ©es Ă©taient : i) dâĂ©tudier les mĂ©canismes de prise en charge du sĂ©lĂ©nite, Ă lâaide dâexpositions de courte durĂ©e ( ”M), suggĂ©rant quâun transport de haute affinitĂ© mais rapidement saturĂ© pourrait intervenir Ă faibles concentrations, doublĂ© par un transport de faible affinitĂ© qui ne saturerait quâĂ fortes concentrations (~mM). Ce dernier pourrait faire intervenir les transporteurs du sulfate et du nitrate, comme le suggĂšre lâinhibition de la prise en charge du sĂ©lĂ©nite par ces Ă©lĂ©ments. Les modifications de spĂ©ciation du Se(IV) avec le pH nâont Ă priori pas induit dâeffet significatif sur la biodisponibilitĂ©. Sur la base de la relation entre concentration en Se et densitĂ© cellulaire maximale atteinte, nous avons calculĂ© une EC50 de 80 ”M ([64; 98]). Nous nâavons pas mis en Ă©vidence de mĂ©canismes dâadaptation, avec une toxicitĂ© similaire pour des algues prĂ©-exposĂ©es ou non au sĂ©lĂ©nite. Les observations au MET ont suggĂ©rĂ© que le chloroplaste soit la premiĂšre cible de la cytotoxicitĂ© de lâĂ©lĂ©ment, avec des effets sur le stroma, les thylakoĂŻdes et le pyrĂ©noĂŻde. Aux concentrations les plus Ă©levĂ©es, nous avons observĂ© une augmentation du nombre et du volume des grains dâamidon, ainsi que la formation de granules denses aux Ă©lectrons. Les analyses en spectromĂ©trie par dispersion en Ă©nergie ont montrĂ© que ceux-ci contenaient du sĂ©lĂ©nium et Ă©taient Ă©galement riches en calcium et phosphore. Nous avons montrĂ© que lâinhibition de croissance Ă©tait fortement corrĂ©lĂ©e Ă la bioaccumulation, et que cette derniĂšre Ă©tait inhibĂ©e par des concentrations croissantes en sulfate. Enfin, le facteur de concentration, calculĂ© sur la base du poids sec, variait entre 690 et 7100.Selenium is an essential element, but becomes very toxic at higher concentrations. It occurs in the environment at concentrations ranging from nM to ”M and selenium pollution is a worldwide phenomenon. This work aims at improving the knowledge on the interactions between selenite - Se(IV) - and a freshwater phytoplanktonic organism : the unicellular green algae Chlamydomonas reinhardtii. The aim of the performed experiments were : i) to investigate selenite -Se(IV°)- uptake mechanisms in C. reinhardtii, using Se75 as a radiotracer in short-term exposures ( ”M), suggesting that a high affinity but rapidly saturated transport mechanism could be used at low concentrations, in parallel with a low affinity mechanism that would only saturate at high concentrations (~mM). The latter could involve transporters used by sulphate and nitrate, as suggested by the inhibition of selenite uptake by those elements. Se(IV) speciation changes with pH did not induce significant effect on bioavailability. On the basis of the relationship between Se concentration and maximal cell density achieved, an EC50 of 80 ”M ([64; 98]) was derived. No adaptation mechanisms were observed as the same toxicity was quantified for Se-pre-exposed algae. Observations by TEM suggested chloroplasts as the first target of selenite cytotoxicity, with effects on the stroma, thylakoids and pyrenoids. At higher concentrations, we could observe an increase in the number and volume of starch grains. For cells collected at 96 h, electron-dense granules were observed. Energy-dispersive X-ray microanalysis revealed that they contained selenium and were also rich in calcium and phosphorus. Finally, growth inhibition was highly correlated to the bioaccumulation of selenite. The latter was inhibited by increasing concentrations of sulphate, and calculated dry weight concentration factors varied between 690 and 7100
RPANDA: an R package for macroevolutionary analyses on phylogenetic trees
A number of approaches for studying macroevolution using phylogenetic trees have been developed in the last few years. Here, we present RPANDA, an R package that implements modelâfree and modelâbased phylogenetic comparative methods for macroevolutionary analyses. The modelâfree approaches implemented in RPANDA are recently developed approaches stemming from graph theory that allow summarizing the information contained in phylogenetic trees, computing distances between trees, and clustering them accordingly. They also allow identifying distinct branching patterns within single trees. RPANDA also implements likelihoodâbased models for fitting various diversification models to phylogenetic trees. It includes birthâdeath models with i) constant, ii) timeâdependent and iii) environmentalâdependent speciation and extinction rates. It also includes models with equilibrium diversity derived from the coalescent process, as well as a likelihoodâbased inference framework to fit the individualâbased model of Speciation by Genetic Differentiation, which is an extension of Hubbell's neutral theory of biodiversity. RPANDA can be used to (i) characterize trees by plotting their spectral density profiles (ii) compare trees and cluster them according to their similarities, (iii) identify and plot distinct branching patterns within trees, (iv) compare the fit of alternative diversification models to phylogenetic trees, (v) estimate rates of speciation and extinction, (vi) estimate and plot how these rates have varied with time and environmental variables and (vii) deduce and plot estimates of species richness through geological time. RPANDA provides investigators with a set of tools for exploring patterns in phylogenetic trees and fitting various models to these trees, thereby contributing to the ongoing development of phylogenetics in the life sciences
Flow Moods: Recommending Music by Moods on Deezer
The music streaming service Deezer extensively relies on its Flow algorithm,
which generates personalized radio-style playlists of songs, to help users
discover musical content. Nonetheless, despite promising results over the past
years, Flow used to ignore the moods of users when providing recommendations.
In this paper, we present Flow Moods, an improved version of Flow that
addresses this limitation. Flow Moods leverages collaborative filtering, audio
content analysis, and mood annotations from professional music curators to
generate personalized mood-specific playlists at scale. We detail the
motivations, the development, and the deployment of this system on Deezer.
Since its release in 2021, Flow Moods has been recommending music by moods to
millions of users every day.Comment: 16th ACM Conference on Recommender Systems (RecSys 2022) - Industry
pape
Track Mix Generation on Music Streaming Services using Transformers
This paper introduces Track Mix, a personalized playlist generation system
released in 2022 on the music streaming service Deezer. Track Mix automatically
generates "mix" playlists inspired by initial music tracks, allowing users to
discover music similar to their favorite content. To generate these mixes, we
consider a Transformer model trained on millions of track sequences from user
playlists. In light of the growing popularity of Transformers in recent years,
we analyze the advantages, drawbacks, and technical challenges of using such a
model for mix generation on the service, compared to a more traditional
collaborative filtering approach. Since its release, Track Mix has been
generating playlists for millions of users daily, enhancing their music
discovery experience on Deezer.Comment: RecSys 2023 - Industry track with oral presentatio
Integrating ecology into macroevolutionary research
On 9 March, over 150 biologists gathered in London for the Centre for Ecology and Evolution spring symposium, âIntegrating Ecology into Macroevolutionary Researchâ. The event brought together researchers from London-based institutions alongside others from across the UK, Europe and North America for a day of talks. The meeting highlighted methodological advances and recent analyses of exemplar datasets focusing on the exploration of the role of ecological processes in shaping macroevolutionary patterns
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