On the Toppling of a Sand Pile

International audienceIn this paper, we provide the first study of the sand pile model SPM(0) where we assume that all the grains are numbered with a distinct integer.We obtain a lower bound on the number of terminal sand piles by establishing a bijection between a subset of these sand piles and the set of shifted Young tableaux. We then prove that this number is at least factorial

The exchanges on the coastline of the southern Gaul in the first Iron Age: from “Hellenisation” concept to “Mediterraneisation”

International audienc

On the effectiveness of the incremental approach to minimal chordal edge modification

Because edge modification problems are computationally difficult for most target graph classes, considerable attention has been devoted to inclusion-minimal edge modifications, which are usually polynomial-time computable and which can serve as an approximation of minimum cardinality edge modifications, albeit with no guarantee on the cardinality of the resulting modification set. Over the past fifteen years, the primary design approach used for inclusion-minimal edge modification algorithms is based on a specific incremental scheme. Unfortunately, nothing guarantees that the set E of edge modifications of a graph G that can be obtained in this specific way spans all the inclusion-minimal edge modifications of G. Here, we focus on edge modification problems into the class of chordal graphs and we show that for this the set E may not even contain any solution of minimum size and may not even contain a solution close to the minimum; in fact, we show that it may not contain a solution better than within an Ω(n) factor of the minimum. These results show strong limitations on the use of the current favored algorithmic approach to inclusion-minimal edge modification in heuristics for computing a minimum cardinality edge modification. They suggest that further developments might be better using other approaches.publishedVersio

Piv study of mixing characteristics in a stirred vessel with a non-Newtonian fluid

PIV is used to analyze the flow induced by a Rushton turbine in a shear-thinning fluid, at constant input power, constant impeller velocity but different concentrations. The rheology of each shear-thinning fluid is first addressed. The mean velocity fields are compared. POD methodology is applied to estimate coherent structures and turbulence levels. Finally, the heterogeneity of shear rate is estimated and the spatial distribution of dissipation rate of total kinetic energy is addressed

Monitoring temporal opacity fluctuations of large structures with muon tomography : a calibration experiment using a water tower tank

Usage of secondary cosmic muons to image the geological structures density distribution significantly developed during the past ten years. Recent applications demonstrate the method interest to monitor magma ascent and volcanic gas movements inside volcanoes. Muon radiography could be used to monitor density variations in aquifers and the critical zone in the near surface. However, the time resolution achievable by muon radiography monitoring remains poorly studied. It is biased by fluctuation sources exterior to the target, and statistically affected by the limited number of particles detected during the experiment. The present study documents these two issues within a simple and well constrained experimental context: a water tower. We use the data to discuss the influence of atmospheric variability that perturbs the signal, and propose correction formulas to extract the muon flux variations related to the water level changes. Statistical developments establish the feasibility domain of muon radiography monitoring as a function of target thickness (i.e. opacity). Objects with a thickness comprised between $\simeq$ 50 $\pm$ 30m water equivalent correspond to the best time resolution. Thinner objects have a degraded time resolution that strongly depends on the zenith angle, whereas thicker objects (like volcanoes) time resolution does not.Comment: 11 pages, 9 figures. Final version published in Scientific Reports, Nature, 14 march 201

Aleti Tunu Bibi: Contextualizing a New Rock Art Site in East Timor and the Wider Asia-Pacific Region

Recent archaeological surveys and excavations on the island of Atauro, East Timor, identified several rock shelters with evidence for prehistoric occupation. Well-preserved rock art was found at one of these sites, Aleti Tunu Bibi. Here we present a description of the site and rock art, including the motifs and design elements, and interpret the site within the context of East Timor and the wider Asia-Pacific region. Most of the art was painted in red (likely ochre) or, in a few circumstances, black pigment (likely charcoal). Ochre was found in Pleistocene and early Holocene layers during excavations of the site. The only observed drawing, the outline of a boat in dry black charcoal, may represent a “boat of the dead” similar to those depicted on Dongson drums in the region, one of which was found recently in East Timor. That a boat is depicted in the drawing suggests that it may have been executed sometime after 2000 b.p. The Aleti Tunu Bibi rock art fits within the description of other East Timor painted rock art and shares some attributes with other sites in East Timor. However, the Aleti Tunu Bibi rock art is also distinct from sites on the mainland, and its presence on Atauro Island supports previous hypotheses of substantial local or temporal variation, and possibly indicates a pre-Austronesian origin for this tradition on the island

Amélioration du taux de greffe de cellules myogéniques pour la dystrophie musculaire de Duchenne : surexpression du récepteur à l'IGF-1 sur des cellules humaines et utilisation du facteur de croissance MGF

La transplantation de myoblastes est une thérapie envisagée pour le traitement de la Dystrophie musculaire de Duchenne (DMD). La mort précoce des cellules injectées et leurs faibles migrations limitent son succès. Le MGF-Ct24E, un peptide synthétique qui représente le peptide E de l’isoforme Ec de l’IGF-1, a été utilisé. Il a augmenté la prolifération cellulaire en médiant son effet par un récepteur différent de celui à l’IGF-1. Des injections systémique et intramusculaire ont amélioré le taux de greffe, ce qu’un pré-traitement et une co-injection du peptide n’a pas permis. La surexpression du récepteur à l’IGF-1 avec un lentivirus a augmenté la prolifération des cellules et n’a eu aucun effet sur leur différentiation. La sélection de cellules surexprimant fortement le récepteur à l’IGF-1 et phosphorylant fortement Akt a amélioré le succès de transplantation. Ces résultats offrent une perspective encourageante pour l’amélioration de la transplantation cellulaire pour des patients atteints de DMD.Myogenic cells transplantation is one of the promising therapies to treat dystrophic patients. Early cells death and poor migration are important problems who limit this therapy’s success. MGF-Ct24E, a synthetic copy of the peptide E from the IGF-1 Ec isoform, was used. The peptide increases the proliferation of cells and did no effect on the differentiation. Injected systematically and intramuscularly, MGF-Ct24E increased the graft success. When the cells were pretreated with the peptide and co-injected with it, no increase in the graft success was seen. The overexpression of IGF-1 receptor on human cells with a lentivirus increased the proliferation rate and did no effect on their differentiation. When the cells were selected for a high expression of the IGF-1 receptor and for a high phosphorylation of Akt, the graft success was increased. Together, those results are offering an interesting avenue for the amelioration of cells transplantation in DMD

Muon tomography applied to active volcanoes

Muon tomography is a generic imaging method using the differential absorption of cosmic muons by matter. The measured contrast in the muons flux reflects the matter density contrast as it does in conventional medical imaging. The applications to volcanology present may advantadges induced by the features of the target itself: limited access to dangerous zones, impossible use of standard boreholes information, harsh environmental conditions etc. The Diaphane project is one of the largest and leading collaboration in the field and the present article summarizes recent results collected on the Lesser Antilles, with a special emphasis on the Soufri\`ere of Guadeloupe.Comment: 7 pages, 7 figures, International Conference on New Photo-detectors,PhotoDet2015, 6-9 July 2015, Moscow, Troitsk, Russia. Submitted to Po