International Journal of Agricultural Research, Innovation and Technology (IJARIT)
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Modelling coffee leaf rust dynamics to control its spread
No full textInternational audienceCoffee leaf rust (CLR) is one of the main diseases that affect coffee plantations worldwide. It is caused by the fungus Hemileia vastatrix. Damages induce severe yield losses (up to 70%). Its control mainly relies on cultural practices and fungicides, the latter having harmful ecological impact and important cost. Our goal is to understand the propagation of this fungus in order to propose a biocontrol solution, based on a mycoparasite that inhibits H. vastatrix reproduction. We develop and explore a spatio-temporal model that describes CLR propagation in a coffee plantation during the rainy and dry seasons. We show the existence of a solution and prove that there exists two threshold parameters, the dry and rainy basic reproduction numbers, that determine the stability of the equilibria for the dry and rainy season subsystems. To illustrate these theoretical results, numerical simulations are performed, using a non-standard finite method to integrate the pest model. We also numerically investigate the biocontrol impact. We determine its efficiency threshold in order to ensure CLR eradication
Parallel Hybridization for SAT: An Efficient Combination of Search Space Splitting and Portfolio
No full textInternational audienceSearch space splitting and portfolio are the two main approaches used in parallel SAT solving. Each of them has its strengths but also, its weaknesses. Decomposition in search space splitting can help improve speedup on satisfiable instances while competition in portfolio increases robustness. Many parallel hybrid approaches have been proposed in the literature but most of them still cope with load balancing issues that are the cause of a non-negligible overhead. In this paper, we describe a new parallel hybridization scheme based on both search space splitting and portfolio that does not require the use of load balancing mechanisms (such as dynamic work stealing).Les deux principales approches utilisées dans la résolution parallèle du problème de satisfiabilité propositionnelle sont DPR (Diviser Pour Régner) et portfolio. Chacune d’elles comporte des forces et des faiblesses. La décomposition dans DPR permet d’améliorer le speedup sur les instancessatisfiables tandis que la compétition dans les portfolios accroit la robustesse. Plusieurs approches hybrides pour la résolution parallèle de SAT ont été présentées dans la littérature mais la plupart d’entre elles souffrent encore des problèmes dus aux mécanismes de rééquilibrage dynamique decharges qui sont à l’origine d’un surcoût non négligeable. Nous décrivons dans ce papier un nouveau schéma d’hybridation parallèle basé sur les deux approches DPR et portfolio ne nécessitant pas la mise en œuvre des mécanismes de rééquilibrage de charges (tels que le vol de tâche)
At Least Seven Distinct Rotavirus Genotype Constellations in Bats with Evidence of Reassortment and Zoonotic Transmissions
No full textInternational audienceBats host many viruses pathogenic to humans, and increasing evidence suggests that rotavirus A (RVA) also belongs to this list. Rotaviruses cause diarrheal disease in many mammals and birds, and their segmented genomes allow them to reassort and increase their genetic diversity. Eighteen out of 2,142 bat fecal samples (0.8%) collected from Europe, Central America, and Africa were PCR-positive for RVA, and 11 of those were fully characterized using viral metagenomics. Upon contrasting their genomes with publicly available data, at least 7 distinct bat RVA genotype constellations (GCs) were identified, which included evidence of reassortments and 6 novel genotypes. Some of these constellations are spread across the world, whereas others appear to be geographically restricted. Our analyses also suggest that several unusual human and equine RVA strains might be of bat RVA origin, based on their phylogenetic clustering, despite various levels of nucleotide sequence identities between them. Although SA11 is one of the most widely used reference strains for RVA research and forms the backbone of a reverse genetics system, its origin remained enigmatic. Remarkably, the majority of the genotypes of SA11-like strains were shared with Gabonese bat RVAs, suggesting a potential common origin. Overall, our findings suggest an underexplored genetic diversity of RVAs in bats, which is likely only the tip of the iceberg. Increasing contact between humans and bat wildlife will further increase the zoonosis risk, which warrants closer attention to these viruses
Synergistic impacts of global warming and thermohaline circulation collapse on amphibians
No full textInternational audienceImpacts on ecosystems and biodiversity are a prominent area of research in climate change. However, little is known about the effects of abrupt climate change and climate catastrophes on them. The probability of occurrence of such events is largely unknown but the associated risks could be large enough to influence global climate policy. Amphibians are indicators of ecosystems' health and particularly sensitive to novel climate conditions. Using state-of-theart climate model simulations, we present a global assessment of the effects of unabated global warming and a collapse of the Atlantic meridional overturning circulation (AMOC) on the distribution of 2509 amphibian species across six biogeographical realms and extinction risk categories. Global warming impacts are severe and strongly enhanced by additional and substantial AMOC weakening, showing tipping point behavior for many amphibian species. Further declines in climatically suitable areas are projected across multiple clades, and biogeographical regions. Species loss in regional assemblages is extensive across regions, with Neotropical, Nearctic and Palearctic regions being most affected. Results underline the need to expand existing knowledge about the consequences of climate catastrophes on human and natural systems to properly assess the risks of unabated warming and the benefits of active mitigation strategies
How to improve the muscle synergy analysis methodology?
No full textInternational audienceMuscle synergy analysis is increasingly used in domains such as neurosciences, robotics, rehabilitation or sport sciences to analyze and better understand motor coordination. The analysis uses dimensionality reduction techniques to identify regularities in spatial, temporal or spatio-temporal patterns of multiple muscle activation. Recent studies have pointed out variability in outcomes associated with the different methodological options available and there was a need to clarify several aspects of the analysis methodology. While synergy analysis appears to be a robust technique, it remain a statistical tool and is, therefore, sensitive to the amount and quality of input data (EMGs). In particular, attention should be paid to EMG amplitude normalization, baseline noise removal or EMG filtering which may diminish or increase the signal-to-noise ratio of the EMG signal and could have major effects on synergy estimates. In order to robustly identify synergies, experiments should be performed so that the groups of muscles that would potentially form a synergy are activated with a sufficient level of activity, ensuring that the synergy subspace is fully explored. The concurrent use of various synergy formulations-spatial, temporal and spatio-temporal synergies- should be encouraged. The number of synergies represents either the dimension of the spatial structure or the number of independent temporal patterns, and we observed that these two aspects are often mixed in the analysis. To select a number, criteria based on noise estimates, reliability of analysis results, or functional outcomes of the synergies provide interesting substitutes to criteria solely based on variance thresholds
Performance of Unidirectional Biocomposite Developed with Piptadeniastrum Africanum Tannin Resin and Urena Lobata Fibers as Reinforcement
No full textInternational audienceThe Piptadeniastrum Africanum bark tannin extract was characterized using MALDI TOF, ATR-FT MIR. It was used in the development of a resin with Vachellia nilotica extract as a biohardener. This tannin is consisting of Catechin, Quercetin, Chalcone, Gallocatechin, Epigallocatechin gallate, Epicatechin gallate. The gel time of the resin at natural pH (pH = 5.4) is 660 s and its MOE obtained by thermomechanical analysis is 3909 MPa. The tenacity of Urena lobata fibers were tested, woven into unidirectional mats (UD), and used as reinforcement in the development of biocomposite. The fibers tenacity at 20, 30 and 50 mm lengths are respectively 65.41, 41.04 and 33.86 cN·Tex−1 . The UD biocomposite obtained had very interesting mechanical properties. Its density, tensile MOE, ultimate strength, bending MOE and MOR are respectively 926 kg·m−3 , 6 GPa, 55 MPa, 9.3 GPa and 68.3 MPa. This biocomposite can be used in a building exterior structure
Effects of companion crops and tillage on soil phosphorus in a Brazilian oxisol: a chemical and 31P NMR spectroscopy study
No full textInternational audiencePurpose Phosphorus (P) is often the main limiting factor for plant growth in highly weathered tropical soils. Phosphate use efficiency and crop yields could be increased in low-input agroecosystems through cropping systems that favor organic matter accumulation or regular additions of composts and manure. Our objective was to determine the amounts and forms of P according to companion crops (Brachiaria ruziziensis-a grass species-or Cajanus cajan-a leguminous species) and tillage systems (conventional or no-tillage). Materials and methods Soil P pools were determined (P-resin, P-Olsen, PNaOH-EDTA, and P-total) and P species were characterized by P-31 NMR spectroscopy. Results and discussion The concentrations of available and labile inorganic P (P-resin, Pi(Olsen), and Pi(NaOH-EDTA)) were greater in soil samples where companion crops (Brachiaria ruziziensis or Cajanus cajan) and maize were planted on the same row, with a more significant effect with the legume species. According to the P-31 NMR, it is mostly the proportion and amount of P-Orthophosphate that was increased, with a slight increase of the content of P-Monoester. Overall, there was a decrease of the proportion of organic P (Po-NMR/P-NMR) from 32 to 16% when the legume companion crop was associated with maize. Conclusions The tillage systems did not lead to any change in the amounts and forms of P. Companion crops are thought to increase available P through mineralization of Po from plant residues and soil organic matter, leading to an increase of fluxes between active P pools
Evaluation and optimization of ICOS atmosphere station data as part of the labeling process
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Problématique de la date de fondation de la ville de Pointe-Noire (Congo-Brazzaville)
No full textInternational audiencePointe-Noire a-t-elle été créée le 11 mai 1922 ou le 26 septembre 1921? Telle est la question majeure qui construise cette réflexion. Des débats autour de sa date de création, il n’en existe pas. En effet, la plupart des études consacrées à la ville de Pointe-Noire remonte sa date de création au décret du 11 mai 1922 portant‹‹ ouverture de travaux du chemin de fer». Cependant, on oublie qu’il existe deux textes administratifs coloniaux, faisant de Pointe-Noire en1921 un district. La documentation provient essentiellement des sources d’archives, de quelques travaux de chercheurs, et des données actuelles perçues sur le terrain ayant trait à notre étude. Ainsi, dans le cadre de nos recherches documentaires, nous nous sommes rendu compte que la création de Pointe-Noire ne remontait pas au 11 mai 1922, mais plutôt au 26 septembre 1921. C’est à partir de cette date que débute officiellement son existence, lorsque ce bourg dérisoire devint pour la première fois district. Il s’agira donc de faire un rappel historique de l’installation française à Pointe-Noire avant d’exposer les thèses qui militent en faveur de la date du 11 mai 1922. Aussi, nous essayerons de montrer les éléments attestant que la création de Pointe-Noire fut le 26 septembre 192
TENDANCE DE L'INFLATION SOUS-JACENTE EN RDC : une modélisation à partir de l'approche VAR Structurelle *
No full textIn diesem Beitrag schätzen wir ein strukturelles autoregressives Modell (SVAR), um den Trend der zugrunde liegenden Inflation in der Demokratischen Republik Kongo zu analysieren, und folgen dem Identifikationsansatz von Blanchard und Quah (1989), um langfristige Restriktionen auf der Grundlage der Wirtschaftstheorie aufzuerlegen. Tatsächlich wird die Inflation im Lichte der Lehren der Monetaristen als ein rein monetäres Phänomen wahrgenommen, und die Neuausrichtung der Geldpolitik auf das Ziel der Preisstabilität entspringt der fast einhelligen Ansicht von Ökonomen und Zentralbankern, dass die Geldpolitik die Aktivität langfristig nicht beeinflusst. Daher haben mehrere Zentralbanken Preisstabilität als oberstes Ziel ihrer Geldpolitik festgelegt. Diese wichtige Rolle können die Zentralbanken jedoch nicht in vollem Umfang wahrnehmen, ohne die Kerninflation zu kontrollieren, da nur diese auf monetäre Faktoren zurückzuführen ist. Zu diesem Zweck verwenden wir kongolesische Daten zur Wachstumsrate der Aktivität und der Inflationsrate von 2002Q1 bis 2019Q4. Unsere Ergebnisse bestätigen im Großen und Ganzen die in der Literatur gefundenen und zeigen, dass der monetäre Schock in Übereinstimmung mit der Identifikationsbeschränkung fast keine Auswirkungen auf die Wirtschaftstätigkeit hat, was dazu tendiert, die Vertikalität der Phillips-Kurve zu bestätigen und die Persistenz des negativen realen Schocks erklärt die Volatilität der Inflation in der Demokratischen Republik Kongo (DRK) erheblich.In this paper, we estimate a structural autoregressive model (SVAR) to analyze the trend of underlying inflation in the Democratic Republic of Congo and follow the identification approach of Blanchard and Quah (1989) to impose long-run restrictions based on economic theory. Indeed, in the light of the teachings of monetarists, inflation is perceived as a purely monetary phenomenon, and the refocusing of monetary policy on the objective of price stability comes from the almost unanimous view of economists and central bankers that monetary policy does not affect activity in the long term. Thus, several central banks have adopted price stability as the ultimate objective of their monetary policy. This important role cannot be fully played, however, by central banks without controlling core inflation because, only this one is due to monetary factors. To this end, we use Congolese data on the growth rate of activity and the inflation rate from 2002Q1 to 2019Q4. Our results broadly confirm those generally found in the literature and show that the monetary shock has, in accordance with the identification constraint, almost no effect on economic activity, which tends to validate the verticality of the Phillips curve and the persistence of the negative real shock considerably explains the volatility of inflation in the Democratic Republic of Congo (DRC).Dans ce papier, nous estimons un modèle autorégressif structurel (SVAR) pour analyser la tendance de l'inflation sous-jacente en République Démocratique du Congo et nous suivons la démarche d'identification de Blanchard et Quah (1989) pour imposer les restrictions de long terme en se basant sur la théorie économique. En effet, au regard des enseignements des monétaristes, l'inflation est perçue comme un phénomène purement monétaire, et le recentrage de la politique monétaire à l'objectif de stabilité des prix vient de la quasi-unanimité des économistes et banquiers centraux selon laquelle la politique monétaire n'affecte pas l'activité à long terme. De ce fait, plusieurs banques centrales ont adopté la stabilité des prix comme objectif ultime de leur politique monétaire. Cet important rôle ne peut cependant être pleinement joué que si les banques centrales peuvent maîtriser l'inflation sous-jacente, car c'est cette dernière qui est d'origine monétaire. Nous utilisons à cet effet les données congolaises sur le taux de croissance de l'activité et le taux d'inflation de 2002Q1 à 2019Q4. Nos résultats confortent globalement ceux généralement retrouvés dans la littérature et montrent que le choc monétaire n'a conformément à la contrainte d'identification, presque pas d'effet sur l'activité économique, ce qui tend à valider l'hypothèse de verticalité de la courbe de Phillips et la persistance du choc réel négatif explique considérablement la volatilité de l'inflation en République Démocratique du Congo (RDC)