Status of MICROSCOPE, a mission to test the Equivalence Principle in space

MICROSCOPE is a French Space Agency mission that aims to test the Weak Equivalence Principle in space down to an accuracy of $10^{-15}$. This is two orders of magnitude better than the current constraints, which will allow us to test General Relativity as well as theories beyond General Relativity which predict a possible Weak Equivalence Principle violation below $10^{-13}$. In this communication, we describe the MICROSCOPE mission, its measurement principle and instrument, and we give an update on its status. After a successful instrument's commissioning, MICROSCOPE is on track for on-schedule launch, expected in 2016.Comment: Proceedings of LISA Symposium X; accepted for publication in Journal of Physics: Conference Serie

Modélisation de l'interaction multimodale 3D

National audienceDans cet article, nous nous intéressons à la nécessité de réduire l'écart entre les considérations de conception en Informatique Graphique (IG) et en Interface Homme-Machine (IHM) afin de démocratiser l'usage et l'utilisation des environnements virtuels 3D (EV3D) pour des utilisateurs non-experts ou occasionnels. Notre approche consiste en une modélisation de l'interaction multimodale 3D (3DIM). Notre modèle 3DIM contribue à ramener l'ensemble des problématiques 3D et les exigences de l'utilisateur sur la compréhension et la caractérisation du lien entre un ensemble de tâches utilisateur et le graphe de scène de l'EV3D

Protocol for the assessment of viral retention capability of membranes

A series of experiments has been carried out to determine the Log removal value (LRV) of MS2 bacteriophages suspended in various buffers (osmosed water, tap water, aqueous solutions of NaCl and phosphate buffer solution) during filtration through hollow fiber membranes made of cellulose acetate. Viral concentrations in permeate and retentate were determined using two different methods, namely plaque forming unit (PFU) counting, which reveals only infectious particles and quantitative RT-PCR which detects the total (infectious + inactivated) number of viral genomes regardless of their infectivity.From this experimental study, we propose guidelines for preparing the challenging solutions and measuring their concentration which ensure a reliable assessment of the membrane performance

Dealing with missing data: An inpainting application to the MICROSCOPE space mission

Missing data are a common problem in experimental and observational physics. They can be caused by various sources, either an instrument's saturation, or a contamination from an external event, or a data loss. In particular, they can have a disastrous effect when one is seeking to characterize a colored-noise-dominated signal in Fourier space, since they create a spectral leakage that can artificially increase the noise. It is therefore important to either take them into account or to correct for them prior to e.g. a Least-Square fit of the signal to be characterized. In this paper, we present an application of the {\it inpainting} algorithm to mock MICROSCOPE data; {\it inpainting} is based on a sparsity assumption, and has already been used in various astrophysical contexts; MICROSCOPE is a French Space Agency mission, whose launch is expected in 2016, that aims to test the Weak Equivalence Principle down to the $10^{-15}$ level. We then explore the {\it inpainting} dependence on the number of gaps and the total fraction of missing values. We show that, in a worst-case scenario, after reconstructing missing values with {\it inpainting}, a Least-Square fit may allow us to significantly measure a $1.1\times10^{-15}$ Equivalence Principle violation signal, which is sufficiently close to the MICROSCOPE requirements to implement {\it inpainting} in the official MICROSCOPE data processing and analysis pipeline. Together with the previously published KARMA method, {\it inpainting} will then allow us to independently characterize and cross-check an Equivalence Principle violation signal detection down to the $10^{-15}$ level.Comment: Accepted for publication in Physical Review D. 12 pages, 6 figure

Subquadratic-time algorithm for the diameter and all eccentricities on median graphs

On sparse graphs, Roditty and Williams [2013] proved that no $O(n^{2-\varepsilon})$-time algorithm achieves an approximation factor smaller than $\frac{3}{2}$ for the diameter problem unless SETH fails. In this article, we solve an open question formulated in the literature: can we use the structural properties of median graphs to break this global quadratic barrier? We propose the first combinatiorial algorithm computing exactly all eccentricities of a median graph in truly subquadratic time. Median graphs constitute the family of graphs which is the most studied in metric graph theory because their structure represents many other discrete and geometric concepts, such as CAT(0) cube complexes. Our result generalizes a recent one, stating that there is a linear-time algorithm for all eccentricities in median graphs with bounded dimension $d$, i.e. the dimension of the largest induced hypercube. This prerequisite on $d$ is not necessarily anymore to determine all eccentricities in subquadratic time. The execution time of our algorithm is $O(n^{1.6408}\log^{O(1)} n)$. We provide also some satellite outcomes related to this general result. In particular, restricted to simplex graphs, this algorithm enumerates all eccentricities with a quasilinear running time. Moreover, an algorithm is proposed to compute exactly all reach centralities in time $O(2^{3d}n\log^{O(1)}n)$.Comment: 43 pages, extended abstract in STACS 202

Modélisation de l'interaction multimodale 3D (Rencontres doctorales)

Dans cet article, nous nous intéressons à la nécessité de réduire l'écart entre les considérations de conception en Informatique Graphique (IG) et en Interface Homme-Machine (IHM) afin de démocratiser l'usage et l'utilisation des environnements virtuels 3D (EV3D) pour des utilisateurs non-experts ou occasionnels. Notre approche consiste en une modélisation de l'interaction multimodale 3D (3DIM). Notre modèle 3DIM contribue à ramener l'ensemble des problématiques 3D et les exigences de l'utilisateur sur la compréhension et la caractérisation du lien entre un ensemble de tâches utilisateur et le graphe de scène de l'EV3D

Approximating Highly Inapproximable Problems on Graphs of Bounded Twin-Width

For any $\varepsilon > 0$, we give a polynomial-time $n^\varepsilon$-approximation algorithm for Max Independent Set in graphs of bounded twin-width given with an $O(1)$-sequence. This result is derived from the following time-approximation trade-off: We establish an $O(1)^{2^q-1}$-approximation algorithm running in time $\exp(O_q(n^{2^{-q}}))$, for every integer $q \geqslant 0$. Guided by the same framework, we obtain similar approximation algorithms for Min Coloring and Max Induced Matching. In general graphs, all these problems are known to be highly inapproximable: for any $\varepsilon > 0$, a polynomial-time $n^{1-\varepsilon}$-approximation for any of them would imply that P$=$NP [Hastad, FOCS '96; Zuckerman, ToC '07; Chalermsook et al., SODA '13]. We generalize the algorithms for Max Independent Set and Max Induced Matching to the independent (induced) packing of any fixed connected graph $H$. In contrast, we show that such approximation guarantees on graphs of bounded twin-width given with an $O(1)$-sequence are very unlikely for Min Independent Dominating Set, and somewhat unlikely for Longest Path and Longest Induced Path. Regarding the existence of better approximation algorithms, there is a (very) light evidence that the obtained approximation factor of $n^\varepsilon$ for Max Independent Set may be best possible. This is the first in-depth study of the approximability of problems in graphs of bounded twin-width. Prior to this paper, essentially the only such result was a~polynomial-time $O(1)$-approximation algorithm for Min Dominating Set [Bonnet et al., ICALP '21].Comment: 30 pages, 3 figures, 1 tabl

Couplage de techniques d'interaction avancées avec des environnements virtuels 3D interactifs

The work of this thesis fit on the boundary between two complementary research areas: the field of 3D Virtual Environment (3DVE) from Computer Graphics (CG) and Virtual Reality (RV) and the field of Human-Computer Interaction (HCI). They rely on three assessments. Firstly, we observe that 3DVE takes more importance in our daily life (video games, serious games, e-commerce, museums, through the web and on mobile devices). Secondly, HCI becomes more complex with the emergence of advance forms of interaction like ambient computing, tangible interaction or spatial and gestural interactions. This evolution goes along with a diversification of devices (3D mouse, the Wiimote, the Kinect or the Leap Motion). Thirdly, the design of interaction techniques with 3DVE brings up some different considerations taken into account by the communities in the field of 3DVE and HCI. Therefore, take advantage of the latest considerations of EV3D communities (metaphors, quality of 3D interaction) and HCI (advance forms of interaction) results in the need to develop the coupling between advance forms of interaction techniques and EV3D. In this context, the objective of this thesis work is to contribute to the development of interactive 3D environments in multiple situations, including large audience situations. The approach we developed aimed to create a bridge between 3D and HCI design considerations. We intend to improve the coupling of advance interaction techniques with interactive 3D virtual environment. After analyzing methods for the design of interaction techniques for 3DVE, a first contribution consists in a design framework of 3D interaction. This framework aggregates design issues stem from 3D and HCI and help the designer to identify several elements involve in the coupling of interaction with a 3DVE. This design framework is based on the analysis of the links between user tasks and elements of the 3DVE impacted by these tasks. In order to precisely characterize each link, we have introduced the 3DIM (3D Interaction Modality) notation that describes the characteristics of the different elements constituting a "3D Interaction Modality" for the accomplishment of a user's interaction task in a 3DVE. We have grouped these elements into six blocks: the user, the physical actions, the physical objects, the input devices, the 3D behaviors and the 3D interactive objects. We complete our framework with analytical properties for guiding the designer and provide descriptive, evaluative and generative power at our conceptual model of advanced interaction techniques for 3DVE. Collaborating with the Museum of "Le Pic du Midi" observatory in France, we used our framework to design and implement tangible interaction and technique based on smartphone usage. Museum visitors can use these techniques in a 3DVE of the "Telescope Bernard Lyot" to explore and understand its functioning. We have conducted three users' studies in order to explore the design space of using a smartphone to interact with 3DVE. We used the smartphone in different ways to navigate, select and manipulate a 3D object displayed on a large remote screen. We explored several design solutions with a smartphone as a touch device, as a tangible object or mid-air interaction around the device.Les travaux de cette thèse s'inscrivent à la frontière entre deux domaines de recherche complémentaires : le domaine des Environnements Virtuels 3D (EV3D) issus de l'Informatique Graphique (IG) et de la Réalité Virtuelle (RV) et le domaine de l'Interaction Homme-Machine (IHM). Ils s'appuient sur trois constats. D'une part, on observe une place grandissante des EV3D dans notre quotidien (jeux vidéo, jeux sérieux, e-commerce, dans les musées, à travers le web et sur les dispositifs mobiles). D'autre part, les IHM se complexifient notamment avec l'apparition de formes avancées d'interaction comme l'informatique ambiante, l'interaction tangible, ou encore l'interaction spatiale et gestuelle, et s'accompagne d'une diversification des dispositifs d'interaction (souris 3D, la Wiimote, la Kinect, le Leap Motion). Enfin, la conception de techniques d'interaction avancées avec des EV3D fait apparaitre des considérations différentes prises en compte par les communautés des domaines EV3D et IHM. Par conséquent, tirer profit des considérations les plus récentes des communautés EV3D (métaphores, qualité de l'interaction 3D) et IHM (formes avancées de technique d'interaction) se traduit par un besoin de développer le couplage entre formes avancées de technique d'interaction et EV3D. Dans ce contexte, l'objectif de ces travaux de thèse est de contribuer à l'essor des environnements 3D interactifs dans de multiples situations, et notamment des situations grand public, en adoptant une approche visant à faire converger les approches 3D et IHM pour mieux établir le couplage de Techniques d'Interaction Avancées avec des Environnements Virtuels 3D Interactifs. Après une analyse des méthodes de conception de techniques d'interaction pour les EV3D, une première contribution de nos travaux consiste en un cadre de conception de l'interaction 3D. En y agrégeant les problématiques issues de la 3D et de l'IHM, ce cadre de conception permet d'identifier les différents éléments de couplages impliqués lors d'une interaction avec un EV3D. Il se base sur l'analyse des liens entre les tâches utilisateurs et les éléments de l'EV3D impactés par ces tâches. Afin de caractériser finement chaque lien, nous avons introduit la notation 3DIM (3D Interaction Modality) qui décrit les caractéristiques des différents éléments constituant une " modalité d'interaction 3D " permettant la réalisation d'une tâche d'interaction de l'utilisateur dans un EV3D. Nous avons regroupé ces éléments en 6 blocs : l'utilisateur, les actions physiques, les objets physiques manipulés, les dispositifs utilisés, les comportements 3D et les éléments 3D. Nous complétons ce cadre conceptuel par des propriétés analytiques qui permettent de guider le concepteur et procurent ainsi un caractère descriptif, évaluatif et génératif à notre modèle conceptuel de techniques d'interaction avancées pour des EV3D. Dans la cadre d'une collaboration avec le musée de l'observatoire du Pic du Midi, une mise en œuvre de ce cadre nous a conduit à concevoir et développer des techniques d'interaction tangibles et basées smartphone. Ces techniques sont utilisées par les visiteurs du musée dans un EV3D représentatif du Télescope Bernard Lyot pour l'explorer et comprendre son fonctionnement. Nous avons mené trois évaluations utilisateur afin d'explorer l'usage d'un smartphone utilisé de trois manière différentes : comme dispositif tactile, comme un objet tangible ou comme support pour une interaction gestuelle autour du dispositif pour naviguer, sélectionner ou manipuler un objet 3D dans un EV3D affiché sur un grand écran distant

Visualisation de nuages de points 3D acquis par un laser : impact de la vision stéréoscopique et du suivi de la tête sur une recherche de cible

International audienceIn military context, we study the visualization of 3D point clouds sense by a drone flying around a battlefield area equipped with a 3D laser. We propose a user experiment protocol in order to study the effect of stereo and head tracking rendering on a target research task with a virtual reality headset. Our first results show a clear advantage when stereo and head tracking rendering are activated.Nous étudions dans un contexte militaire la visualisation de nuages de points 3D acquis par un laser embarqué sur un drone tournant autour d’une zone de combat. Nous proposons un protocole expérimental permettant d’évaluer l’impact de la vision stéréoscopique et du suivi de la tête sur une recherche de cible avec un casque de réalité virtuelle. Les premiers résultats montrent un avantage lorsque la vision stéréoscopique et le suivi de la tête sont activés

Approximation algorithms for Job Scheduling with reconfigurable resources

We consider here the MultiBot problem for the scheduling and the resource parametrization of jobs related to the production or the transportation of different products inside a given time horizon. Those jobs must meet known in advance demands. The time horizon is divided into several discrete identical periods representing each the time needed to proceed a job. The objective is to find a parametrization and a schedule for the jobs in such a way they require as less resources as possible. Though this problem derived from the applicative context of reconfigurable robots, we focus here on fundamental issues. We show that the resulting strongly NP-hard Multibot problem may be handled in a greedy way with an approximation ratio of $\frac{4}{3}$.Comment: 26 pages, 4 figure