Evaluation et amélioration du comportement de Atriplex lentiformis (Torr.) S. Watson en milieux salés au Sénégal

La salinisation des sols constitue l’une des principales menaces à la  productivité agricole dans les zones estuariennes du Sénégal. La mycorhization pourrait améliorer l’efficacité de la méthode biologique de désalinisation des sols. Atriplex lentiformis associé ou non au champignon Rhizophagus irregulare a été observé en milieu réel, et en serre dans un dispositif bi-factoriel (mycorhization et salinité) en blocs complets randomisés avec 3 répétitions. Les variables mesurées sont la hauteur, le diamètre, la litière, la teneur en eau, en sodium des plants, la salinité et l’acidité du sol. Les résultats montrent un taux de mortalité supérieur à 90% en milieu réel. Les individus plantés sur ados ont développé un enracinement superficiel alors que les semis naturels ont présenté un système racinaire pivotant et profond. La mycorhization a entraîné une réduction de la mortalité de 5,56%, une importante persistance des feuilles, une teneur en eau plus élevée dans les tiges et racines que dans les feuilles et enfin un stockage de sodium plus élevé dans les feuilles. La dose de sel 186 g.l-1 a été létale pour Atriplex lentiformis, mycorhizé ou non. La symbiose endomycorhizienne améliore ainsi le comportement de Atriplex lentiformis en milieu salé.Mots clés : Atriplex lentiformis, mycorhization, salinité, stress, Sénégal

Nonlinear geometric analysis of a mistuned bladed disk

This paper deals with the dynamical analysis and uncertainty quantification of a mistuned industrial rotating integrally bladed disk, for which the operating regime under consideration takes into account the nonlinear geometric effects induced by large displacements and deformations. First, a dedicated mean nonlinear reduced-order model of the tuned structure is explicitly constructed using three-dimensional solid finite elements. The random nature of the mistuning is then modeled by using the onparametric probabilistic approach extended to the nonlinear geometric context. Such a computational strategy provides an efficient tool, which is applied to a computational model of an industrial centrifugal compressor with a large number of degrees of freedom. This allows for putting in evidence some new complex dynamical behaviors

Ins and outs of the cultural polis: informality, culture and governance in the global South

This paper provides an epistemological critique of informality by focusing on cultural governance in two cities of the global South, Rio de Janeiro, Brazil, and Dakar, Senegal. Aiming to enrich debates about urban creativity and urban cultural policy, which are still mainly focused on and articulated from the global North, we consider the broad field of ‘informality’ research as an entry point for such a discussion. Using case studies from African and Latin American contexts, we focus on the interstices of cultural policy and the borderlands of (in)formality, examining how governmental institutions are entangled in informal processes, and how grassroots cultural interventions become part of mainstream cultural circuits. The analysis sheds light on how these creative spaces of cultural production, located in Southern contexts of urban extremes, contribute to the vitality of informal urbanisms and unsettle predominant views that see them merely as sites ofinfrastructural poverty and social exclusion. The paper suggests that a creative remapping of informality, through an inquiry of the ‘ins’ and ‘outs’ of the cultural polis, could improve our translating capacity of academic discourse into institutional/policy-related operations

Ultra Large Castings to Produce Low Cost Aluminum Vehicle Structures

Through a cooperative effort with the U.S. Department of Energy (DOE) Office of Heavy Vehicle Technologies (OHVT), Alcoa is developing a casting process to produce ultra large thin wall components. The casting process is a low pressure, metal mold, multiport injection vertical casting process. The specific system for demonstration of the process is located at Alcoa's Technology Center and will be capable of producing parts extending 3 M long, 1.7 M wide and 0.4 M high. For example, single castings of car floor pan frames or side wall aperture structures are candidates for this installation. This shall provide a major opportunity to reduce the cost of lightweight transportation vehicle structures by (a) reducing the components or part count and (b) reducing the cost of assembly. To develop and demonstrate the process, an inner panel of the Chrysler minivan liftgate will be first produced on this system. Through computer analyses, the cast inner panel design was developed to satisfy both structural performance and casting process requirements. Currently, this is an 11 part assembly of steel components. At the time of this abstract, the numerous system components are in various phases of fabrication and site preparation is fully underway, with system shakedown beginning in the second quarter of 1999. Successful demonstration of caster system operation is anticipated to occur during the third quarter and production of a high quality product during the fourth quarter. Although the process is targeted toward reducing the cost of lightweight trucks, buses and autos, consideration is being given to application in the aircraft industry

High-pressure photoluminescence study of ordered Ga_0.5In_0.5P alloys grown on GaAs by organometallic vapor phase epitaxy

Photoluminescence (PL) measurements on Ga0.5In0.5P grown by organometallic vapor phase epitaxy on GaAs substrates at various growth temperatures have been made as a function of pressure up to about 4.5 GPa. In the pressure range 0-3.8 GPa the PL spectrum exhibits a shift to higher energies. It is found that the pressure coefficient of the PL peak energy depends significantly on the growth temperature and hence on the degree of ordering. These results are partly explained in terms of repulsion between the Gamma-folded energy states in the CuPt-type ordered structure

Affine term structure models : a time-changed approach with perfect fit to market curves

We address the so-called calibration problem which consists of fitting in a tractable way a given model to a specified term structure like, e.g., yield or default probability curves. Time-homogeneous jump-diffusions like Vasicek or Cox-Ingersoll-Ross (possibly coupled with compounded Poisson jumps, JCIR), are tractable processes but have limited flexibility; they fail to replicate actual market curves. The deterministic shift extension of the latter (Hull-White or JCIR++) is a simple but yet efficient solution that is widely used by both academics and practitioners. However, the shift approach is often not appropriate when positivity is required, which is a common constraint when dealing with credit spreads or default intensities. In this paper, we tackle this problem by adopting a time change approach. On the top of providing an elegant solution to the calibration problem under positivity constraint, our model features additional interesting properties in terms of implied volatilities. It is compared to the shift extension on various credit risk applications such as credit default swap, credit default swaption and credit valuation adjustment under wrong-way risk. The time change approach is able to generate much larger volatility and covariance effects under the positivity constraint. Our model offers an appealing alternative to the shift in such cases.Comment: 44 pages, figures and table

MasakhaPOS: Part-of-Speech Tagging for Typologically Diverse African languages

In this paper, we present AfricaPOS, the largest part-of-speech (POS) dataset for 20 typologically diverse African languages. We discuss the challenges in annotating POS for these languages using the universal dependencies (UD) guidelines. We conducted extensive POS baseline experiments using both conditional random field and several multilingual pre-trained language models. We applied various cross-lingual transfer models trained with data available in the UD. Evaluating on the AfricaPOS dataset, we show that choosing the best transfer language(s) in both single-source and multi-source setups greatly improves the POS tagging performance of the target languages, in particular when combined with parameter-fine-tuning methods. Crucially, transferring knowledge from a language that matches the language family and morphosyntactic properties seems to be more effective for POS tagging in unseen languages

Impacts of ocean deoxygenation on fisheries

The effects of deoxygenation on fisheries can, at times, be difficult to truly isolate and quantify, but nevertheless are important. Effects manifest themselves through the dynamics of the populations and the fishery, and often co-vary with other environmental variables. Furthermore, oxygen and fisheries dynamics are both dependent on local conditions, making most analyses complicated and dependent on extensive data and modelling to account for the site-specific conditions

MasakhaNER 2.0: Africa-centric Transfer Learning for Named Entity Recognition

African languages are spoken by over a billion people, but are underrepresented in NLP research and development. The challenges impeding progress include the limited availability of annotated datasets, as well as a lack of understanding of the settings where current methods are effective. In this paper, we make progress towards solutions for these challenges, focusing on the task of named entity recognition (NER). We create the largest human-annotated NER dataset for 20 African languages, and we study the behavior of state-of-the-art cross-lingual transfer methods in an Africa-centric setting, demonstrating that the choice of source language significantly affects performance. We show that choosing the best transfer language improves zero-shot F1 scores by an average of 14 points across 20 languages compared to using English. Our results highlight the need for benchmark datasets and models that cover typologically-diverse African languages