33 research outputs found
Le diagnostic rapide de pré-aménagement (Diarpa) : Un outil d'aide à l'aménagement des zones de bas-fonds
En Afrique sub-saharienne, les bas-fonds représentent un potentiel important pour une agriculture sécurisée et diversifiée. Cependant, les aménagements de bas-fonds sont souvent jugés peu opérationnels par les utilisateurs. Pour permettre une meilleure adaptation aux besoins des populations et aux contraintes du milieu, un outil d'aide à la décision, le diagnostic rapide de pré-aménagement, Diarpa, a été mis au point afin de définir le type et les caractéristiques des aménagements. Il s'appuie sur sept indicateurs qui sont, soit mesurés sur le site (perméabilité des sols, profondeur de l'horizon imperméable, pente longitudinale du bas-fond, profil de l'axe d'écoulement, écoulements de base, dynamique de la nappe), soit calculés (crue décennale rapportée à la largeur du bas-fond). Une clé d'utilisation de ces indicateurs permet de recommander le type d'aménagement le plus adapté. Le coût peut être évalué à partir des indicateurs ayant une incidence directe (débit de crue, largeur et pente du bas-fond) et intégré dans une analyse socio-économique tenant compte des impacts attendus et de la capacité des bénéficiaires à supporter les investissements et les charges récurrentes. Le Diarpa a été validé au sud du Mali pour les digues déversantes ; dans la zone soudanienne, c'est un outil opérationnel pour la planification des programmes de mise en valeur des bas-fonds et pour le choix de l'aménagement. (Résumé d'auteur
SPLEND1D, a reduced one-dimensional model to investigate the physics of plasma detachment
Studying the process of divertor detachment and the associated complex
interplay of plasma dynamics and atomic physics processes is of utmost
importance for future fusion reactors. Whilst simplified analytical models
exist to interpret the general features of detachment, they are limited in
their predictive power, and complex 2D or even 3D codes are generally required
to provide a self-consistent picture of the divertor. As an intermediate step,
1D models of the Scrape-Off Layer (SOL) can be particularly insightful as the
dynamics are greatly simplified, while still self-consistently including
various source and sink terms at play, as well as additional important effects
such as flows. These codes can be used to shed light on the physics at play, to
perform fast parameter scans, or to interpret experiments. In this paper, we
introduce the SPLEND1D (Simulator of PLasma ENabling Detachment in 1D) code: a
fast and versatile 1D SOL model. We present in detail the model that is
implemented in SPLEND1D. We then employ the code to explore various elements of
detachment physics for parameters typical of the Tokamak \`a Configuration
Variable (TCV), including the atomic physics and other processes behind power
and momentum losses, and explore the various hypotheses and free parameters of
the model
Iris-Wasm: robust and modular verification of WebAssembly programs
WebAssembly makes it possible to run C/C++ applications on the web with near-native performance. A WebAssembly program is expressed as a collection of higher-order ML-like modules, which are composed together through a system of explicit imports and exports using a host language, enabling a form of higher- order modular programming. We present Iris-Wasm, a mechanized higher-order separation logic building on a specification of Wasm 1.0 mechanized in Coq and the Iris framework. Using Iris-Wasm, we are able to specify and verify individual modules separately, and then compose them modularly in a simple host language featuring the core operations of the WebAssembly JavaScript Interface. Building on Iris-Wasm, we develop a logical relation that enforces robust safety: unknown, adversarial code can only affect other modules through the functions that they explicitly export. Together, the program logic and the logical relation allow us to formally verify functional correctness of WebAssembly programs, even when they invoke and are invoked by unknown code, thereby demonstrating that WebAssembly enforces strong isolation between modules
Reduction in benefits of total flux expansion on divertor detachment due to parallel flows
The Super-X divertor (SXD) is an alternative divertor configuration
leveraging total flux expansion at the outer strike point (OSP). Key features
for the attractiveness of the SXD are facilitated detachment access and
control, as predicted by the extended 2-point model (2PM). However, parallel
flows are not consistently included in the 2PM. In this work, the 2PM is
refined to overcome this limitation: the role of total flux expansion on the
pressure balance is made explicit, by including the effect of parallel flows.
In consequence, the effect of total flux expansion on detachment access and
control is weakened, compared to predictions of the 2PM. This new model
partially explains discrepancies between the 2PM and experiments performed on
TCV, in ohmic L-mode scenarios, where in core density ramps in lower
single-null (SN) configuration, the impact of the OSP major radius Rt on the
CIII emission front movement in the divertor outer leg - used as a proxy for
the plasma temperature - is substantially weaker than 2PM predictions; and in
OSP sweeps in lower and upper SN configurations, with a constant core density,
the peak parallel particle flux density at the OSP is almost independent of Rt,
while the 2PM predicts a linear dependence. Finally, analytical and numerical
modelling of parallel flows in the divertor is presented, to support the
argument. It is shown that an increase in total flux expansion can favour
supersonic flows at the OSP. Parallel flows are also shown to be relevant by
analysing SOLPS-ITER simulations of TCV
Comparison of detachment in Ohmic plasmas with positive and negative triangularity
Detachment is investigated using core density ramps for lower single null
Ohmic L-mode plasmas across a wide range of upper, lower, and total
triangularity () in the TCV tokamak. It is universally found that
detachment is more difficult to access with negative triangularity (NT)
shaping. The outer divertor leg of discharges with could
not be cooled below 5 eV using core density ramps alone. The behavior of the
upstream plasma and geometrical divertor effects (e.g. a reduced connection
length at negative lower triangularity) do not fully explain the challenges of
detaching NT plasmas. Langmuir probe measurements of the target heat flux
widths () remained constant within 30% across an upper triangularity
scan, while the spreading factor was found to be lower by up to 50% in NT,
indicating a generally lower integral SOL width. An interesting pattern has
been observed in the particle balance where the line-averaged core density was
typically higher in NT discharges for a given fuelling rate. Conversely, the
divertor neutral pressure and integrated particle content were typically lower
for the same line-averaged density. This indicates that NT plasmas may be
closer to the sheath-limited regime than their PT counterparts, which could
explain why NT is more challenging to detach
Late glacial and Holocene landscape change and rapid climate and coastal impacts in the Canal Beagle, southernmost Patagonia
Palaeoenvironmental data for the Late Glacial and Holocene periods are provided from Caleta Eugenia, in the eastern sector of Canal Beagle, southernmost Patagonia. The record commences at c. 16 200 cal a bp following glacier retreat in response to climatic warming. However, cooler conditions persisted during the Late Glacial period. The onset of more temperate conditions after c. 12 390 cal a bp is indicated by the arrival of southern beech forest and later establishment at c. 10 640 cal a bp, but the woodland growth was restricted by lower levels of effective moisture. The climate signal is then truncated by a rapid marine incursion at c. 8640 cal a bp which lasted until a more gradual emergence of the coast at c. 6600 cal a bp. During this period the pollen record appears to be dominated by the southern beech woodland. A punctuated hydroseral succession follows the isolation of the site from the sea leading to the re‐establishment of a peat bog. Between c. 5770 cal a bp and the present there were several periods of short rapid climatic change leading to drier conditions, probably as a result of late Holocene periods of climatic warming
Late glacial and Holocene landscape change and rapid climate and coastal impacts in the Canal Beagle, southernmost Patagonia
Palaeoenvironmental data for the Late Glacial and Holocene periods are provided from Caleta Eugenia, in the eastern sector of Canal Beagle, southernmost Patagonia. The record commences at c. 16 200 cal a bp following glacier retreat in response to climatic warming. However, cooler conditions persisted during the Late Glacial period. The onset of more temperate conditions after c. 12 390 cal a bp is indicated by the arrival of southern beech forest and later establishment at c. 10 640 cal a bp, but the woodland growth was restricted by lower levels of effective moisture. The climate signal is then truncated by a rapid marine incursion at c. 8640 cal a bp which lasted until a more gradual emergence of the coast at c. 6600 cal a bp. During this period the pollen record appears to be dominated by the southern beech woodland. A punctuated hydroseral succession follows the isolation of the site from the sea leading to the re‐establishment of a peat bog. Between c. 5770 cal a bp and the present there were several periods of short rapid climatic change leading to drier conditions, probably as a result of late Holocene periods of climatic warming
Hunter–gatherer mobility and technological landscapes in southernmost South America: a statistical learning approach
The present work aims to quantitatively explore and understand the relationship between mobility types (nautical versus pedestrian), specific technological traits and shared technological knowledge in pedestrian hunter–gatherer and nautical hunter–fisher–gatherer societies from the southernmost portion of South America. To that end, advanced statistical learning techniques are used: state-of-the-art classification algorithms and variable importance analyses. Results show a strong relationship between technological knowledge, traits and mobility types. Occupations can be accurately classified into nautical and pedestrian due to the existence of a non-trivial pattern between mobility and a relatively small fraction of variables from some specific technological categories. Cases where the best-fitted classification algorithm fails to generalize are found significantly interesting. These instances can unveil lack of information, not enough entries in the training set, singular features or ambiguity, the latter case being a possible indicator of the interaction between nautical and pedestrian societies.HAR-2009-06996, CSD2010-00034, HAR2017-
90883-REDC, CULM-HAR2016-77672-P (Ministerio de Ciencia e Innovacio´n de Espan˜ a); PIP-0706, PIP-0348
(Consejo Nacional de Investigaciones Cientı´ficas y Tecnolo´gicas-Argentina) and PICT 2012-2148 (Ministerio de
Ciencia, Tecnologı´a e Innovacio´n Productiva de la Repu´ blica Argentina); PROC/12-120610-A (SESAR WPE Long
Term and Innovative Research-European Commission); and Project GR-7846 (Wenner-Gren Foundation for
Anthropological Research