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Seismic detection of the martian core
Get PDFClues to a planet’s geologic history are contained in its interior structure, particularly its core. We
detected reflections of seismic waves from the core-mantle boundary of Mars using InSight seismic data
and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ±
40 kilometers. The large core implies a martian mantle mineralogically similar to the terrestrial upper
mantle and transition zone but differing from Earth by not having a bridgmanite-dominated lower
mantle. We inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a
substantial complement of light elements dissolved in the iron-nickel core. The seismic core shadow as
seen from InSight’s location covers half the surface of Mars, including the majority of potentially active
regions—e.g., Tharsis—possibly limiting the number of detectable marsquakes
Connecting AI-based Oracles to Blockchains via an Auditable Auction Protocol
Get PDFThe use of Artificial Intelligence (AI), in particular sequential decision-making (SDM) algorithms, in blockchains can greatly improve their autonomy and general features. In this context, this paper proposes the protocol CONDOR (Connecting ai-based Oracles to blockchaiN via an auDitable auctiOn pRotocol) between a smart contract and some off-chain AI-based oracles to enable the smart contract to choose among AI solution proposals while inciting those oracles to provide non-forged results. The main principle is to consider the AI outcomes as auctions that can be challenged and audited through a dispute phase. An Ethereum implementation of the aforementioned protocol was built in order to assess its scalability and time performances
Lead acid health monitoring through impedance spectroscopy achieved with recycled power supply unit
Get PDFRural electrification could be a very effective factor for economic and social development in many developing countries. Renewable energies which are generally available in these countries play a central role to limit the global footprint of the systems. Beside, brand new western systems are generally not affordable enough for many populations. Frugal innovation based on re-used materials combines several advantages: it contributes to global footprint reduction and offers very cheap solutions. In this framework, this paper studies the possibility of re-using reused components in renewable system, includingold lead acid batteries disposed from thermal engine cars. Before giving a second life to these batteries, their state of health need to be assessed, rapidly but precisely. To achieve this goal, with some recycled power electronics devices, Power Supply Unit (PSU) from discarded desktops and a cheap microcontroller with replace the expensive test devices that we generally have in our labs. The objective is using modified PSUs to apply battery evaluation methods (two pulses method and spectroscopy method) to the batteries and assessing the results
Experimental and Finite Element Analysis of the Tensile Behavior of Architectured Cu-Al Composite Wires
Get PDFThe present study investigates, experimentally and numerically, the tensile behavior of
copper-clad aluminum composite wires. Two fiber-matrix configurations, the conventional Alcore/
Cu-case and a so-called architectured wire with a continuous copper network across the crosssection,
were considered. Two different fiber arrangements with 61 or 22 aluminum fibers were
employed for the architectured samples. Experimentally, tensile tests on the two types of composites
show that the flow stress of architectured configurations is markedly higher than that of the linear
rule of mixtures’ prediction. Transverse stress components and processing-induced residual stresses
are then studied via numerical simulations to assess their potential effect on this enhanced strength.
A set of elastic-domain and elastoplastic simulations were performed to account for the influence of
Young’s modulus and volume fraction of each phase on the magnitude of transverse stresses and
how theses stresses contribute to the axial stress-strain behavior. Besides, residual stress fields of
different magnitude with literature-based distributions expected for cold-drawn wires were defined.
The findings suggest that the improved yield strength of architectured Cu-Al wires cannot
be attributed to the weak transverse stresses developed during tensile testing, while there are compelling
implications regarding the strengthening effect originating from the residual stress profile.
Finally, the results are discussed and concluded with a focus on the role of architecture and residual
stresses
L'impression 3D au service du génie des procédés : optimisation morphologique de structures complexes aux propriétés d'usages maîtrisées
Get PDFCes travaux de thèse apportent une contribution à la problématique de la conception de nouveaux objets de génie des procédés réalisés par fabrication additive. Plus particulièrement, une méthode pour la conception d’internes structurés complexes aux propriétés d’usage maîtrisées a été proposée. Des structures innovantes à géométrie complexe, ayant des propriétés géométriques et morphologiques intéressantes, pour des applications de mélange et de séparation ont été conçues, produites, caractérisées et modélisées. Ainsi, un garnissage à base de fils de section cylindrique est développé pour des applications en tant que contacteur gaz-liquide, alors qu’un ruban hélicoïdal est conçu pour des réacteurs oscillatoires continus. Dans un premier temps, différentes configurations ont été imprimées et étudiées d’un point de vue expérimental en modifiant les propriétés géométriques des structures, puis, des méthodes de caractérisation ont été appliquées sur ces internes pour mesurer leurs performances (capacité et efficacité en transfert de matière ou pourcentage du mélange). Dans un second temps, des travaux de modélisation mathématique, en se basant sur les données expérimentales et sur de l’analyse dimensionnelle, ont abouti à des corrélations adimensionnelles permettant de prédire les performances de ces internes en fonction des paramètres morphologiques. Enfin, des stratégies d’optimisation ont été mis en place sur la base de ces modèles afin d’être capable d’optimiser les paramètres géométriques en fonction des propriétés d’usage attendues
Randomized rounding algorithms for large scale unsplittable flow problems
Get PDFUnsplittable flow problems cover a wide range of telecommunication and transporta-
tion problems and their efficient resolution is key to a number of applications. In
this work, we study algorithms that can scale up to large graphs and important num-
bers of commodities. We present and analyze in detail a heuristic based on the linear
relaxation of the problem and randomized rounding. We provide empirical evidence
that this approach is competitive with state-of-the-art resolution methods either by its
scaling performance or by the quality of its solutions. We provide a variation of the
heuristic which has the same approximation factor as the state-of-the-art approxima-
tion algorithm. We also derive a tighter analysis for the approximation factor of both
the variation and the state-of-the-art algorithm. We introduce a new objective function
for the unsplittable flow problem and discuss its differences with the classical con-
gestion objective function. Finally, we discuss the gap in practical performance and
theoretical guarantees between all the aforementioned algorithms
Comparison of least-squares and instrumental variables for parameters estimation on differential drive mobile robots
Get PDFThis paper addresses the parameter estimation issue on mobile robots. A comparison between the state-of-art Least-Squares Technique and the potentially useful Instrumental Variable Method is carried out. With that objective, the whole process of kinematic and dynamic modeling, exciting trajectory design, simulation, parameter identification and cross-validation is done. The results are exhibit in simulation of a Differential Drive Mobile Robot to show that against possible noises and perturbations on mobile robotics, due to effects as slipping and not perfect rolling, Instrumental Variable is more suitable. As a use case, a mobile robot with an unbalanced mass distribution is modeled, identified and validated in simulation
Image-based effective medium approximation for fast permeability evaluation of porous media core samples
Get PDFAn image-based effective medium approximation (EMA) is developed so as to permit very fast transport properties evaluations of 3D porous media. From an image-based porous network (IBPN) built upon digital image processing of 3D binary images, we focus on throat’s local geometrical properties at the pore scale, for being the most sensible structural units which build up the local pressure. This approach is a 3D image–based extension of the critical point approach proposed in 2D fractures. We show, from analyzing various core rock samples available in the literature, that the asymptotic assumptions associated with the preeminence of critical points in throats are indeed geometrically relevant. We then describe how the image-based EMA evaluated from the conductances computed from the discrete IBPN can be reliably evaluated. The proposed method is evaluated upon the estimation of core sample permeability from binarized image obtained using X-ray tomography. Since it combines digital image treatments with statistical data post-processing without the need of computational fluid dynamics (CFD) computation, it is extremely cost efficient. The results are compared with a micro-scale Stokes flow computation in various rock samples. The sensitivity to the pore discretization also is discussed and illustrated
Optimal Pilot Sequences for Timing Estimation in Faster-than-Nyquist Systems
Get PDFTraditional synchronization techniques are usually challenged by Faster-than-Nyquist (FTN) signals which discard orthogonal pulses to the advantage of an increased spectral efficiency.
In this paper, we studied data-aided timing estimation in FTN scenarios, based on the Cramér--Rao bound minimization. We established a closed-form approximation of the bound to explain the relation between optimal pilot sequences and the waveform's parameters (i.e., signaling density and pulse shape). In particular, we showed that optimal sequences at the Nyquist-rate are non-informative in FTN scenarios if regular lowpass pulses are used
The Role of Ponds in Pesticide Dissipation at the Agricultural Catchment Scale: A Critical Review
Get PDFPonds in agricultural areas are ubiquitous water retention systems acting as reactive biogeochemical
hotspots controlling pesticide dissipation and transfer at the catchment scale. Several issues need to be addressed in order to understand, follow-up and predict the role of ponds in limiting pesticide transfer at the catchment scale. In this review, we present a critical overview of functional processes underpinning pesticide dissipation in ponds. We highlight the need to distinguish degradative and non-degradative processes and to understand the role of the sediment-water interface
in pesticide dissipation. Yet it is not well-established how pesticide dissipation in ponds governs the pesticide transfer at the catchment scale under varying hydro-climatic conditions and agricultural operation practices. To illustrate the multi-scale and dynamic aspects of this issue, we sketch a modelling framework integrating the role of ponds at the catchment scale. Such an integrated
framework can improve the spatial prediction of pesticide transfer and risk assessment across the catchment-ponds-river continuum to facilitate management rules and operations