Friction and the oscillatory motion of granular flows

This contribution reports on numerical simulations of 2D granular flows on erodible beds. The broad aim is to investigate whether simple flows of model granular matter exhibits spontaneous oscillatory motion in generic flow conditions, and in this case, whether the frictional properties of the contacts between grains may affect the existence or the characteristics of this oscillatory motion. The analysis of different series of simulations show that the flow develops an oscillatory motion with a well-defined frequency which increases like the inverse of the velocity's square root. We show that the oscillation is essentially a surface phenomena. The amplitude of the oscillation is higher for lower volume fractions, and can thus be related to the flow velocity and grains friction properties. The study of the influence of the periodic geometry of the simulation cell shows no significant effect. These results are discussed in relation to sonic sands.Comment: 7 pages, 8 figure

Prosecutor and lawyers in plea bargaining with complete information

In criminal law, when a conflict is solved by plea bargaining, the negotiation is mainly made between the prosecutor and the lawyer. Adopting a complete information framework about his type (selfish or altruistic), this paper compares two lawyer payment systems: flat fees and hourly-wage fees. We identify the system of fees in which the sentence is the lowest. We first show that under flat fees the prosecutor provides less effort when he faces an altruistic lawyer. Second, we show that under some conditions an altruistic lawyer may accept a higher sentence than a selfish lawyer.plea bargaining, lawyer's selfishness, system of fees

Viscoroute 2.0: a tool for the simulation of moving load effects on asphalt pavement

As shown by strains measured on full scale experimental aircraft structures, traffic of slow-moving multiple loads leads to asymmetric transverse strains that can be higher than longitudinal strains at the bottom of asphalt pavement layers. To analyze this effect, a model and a software called ViscoRoute have been developed. In these tools, the structure is represented by a multilayered half-space, the thermo-viscoelastic behaviour of asphalt layers is accounted by the Huet-Sayegh rheological law and loads are assumed to move at constant speed. First, the paper presents a comparison of results obtained with ViscoRoute to results stemming from the specialized literature. For thick asphalt pavement and several configurations of moving loads, other ViscoRoute simulations confirm that it is necessary to incorporate viscoelastic effects in the modelling to well predict the pavement behaviour and to anticipate possible damages in the structure.Comment: 27 pages

The 15N-enrichment in dark clouds and Solar System objects

The line intensities of the fundamental rotational transitions of H13CN and HC15N were observed towards two prestellar cores, L183 and L1544, and lead to molecular isotopic ratios 140 6 14N/15N 6 250 and 140 6 14N/15N 6 360, respectively. The range of values reflect genuine spatial variations within the cores. A comprehensive analysis of the available measurements of the nitrogen isotopic ratio in prestellar cores show that molecules carrying the nitrile functional group appear to be systematically 15N-enriched com- pared to those carrying the amine functional group. A chemical origin for the differential 15N-enhance- ment between nitrile- and amine-bearing interstellar molecules is proposed. This sheds new light on several observations of Solar System objects: (i) the similar N isotopic fractionation in Jupiter's NH3 and solar wind N+; (ii) the 15N-enrichments in cometary HCN and CN (that might represent a direct inter- stellar inheritance); and (iii) 15N-enrichments observed in organics in primitive cosmomaterials. The large variations in the isotopic composition of N-bearing molecules in Solar System objects might then simply reflect the different interstellar N reservoirs from which they are originating

Rates and efficiencies of reactions of ruminal biohydrogenation of linoleic acid according to pH and polyunsaturated fatty acids concentrations

Data from a previous study about the effects of pH and of linolenic acid (C18:3n-3) andlinoleic acid (C18:2n-6) concentrations on C18:2n-6 biohydrogenation in ruminal cultures were used to calculate the rates and efficiencies of the three reactions of C18:2n-6 biohydrogenation (isomerisation of C18:2n-6 to CLA; reduction of CLA to trans-octadecenoic acids; reduction of trans-octadecenoic acids to stearic acid). First, low pH was confirmed to inhibit isomerisation and was shown to inhibit the second reduction, leading to an accumulation of vaccenic acid. This later effect had only been observed in some in vivo studies using high concentrate diets, because in in vitro experiments, the very low pH frequently used depresses isomerisation which consequently generates very low amount of substrates for reductions whose variations become difficult to ascertain. Second, C18:2n-6 at high concentration was confirmed to saturate its own isomerisation and the increase of CLA production due to high initial C18:2n-6 was shown to inhibit the two subsequent reductions. Third, C18:3n-3 at high concentrations was confirmed to inhibit C18:2n-6 isomerisation. Moreover, the second reduction was shown to be saturated, probably by all trans-octadecenoic acids intermediates of C18:2n-6 and C18:3n-3 biohydrogenation, leading to an accumulation of trans-octadecenoic acids, especially vaccenic acid. This fatty acid is partly desaturated into CLA in the mammary gland, which explains the synergy between C18:2n-6 and C18:3n-3 for milk CLA noticed by others in vivo. This approach helped explain the actions of pH and of C18:2n-6 and C18:3n-3 concentrations on C18:2n-6 biohydrogenation and allows some explanations about differences noticed between studies

Les catastrophes: un horizon commun de la globalisation environnementale?

Les catastrophes font de plus en plus figure d’horizon de la globalisation environnementale. La représentation des menaces qu’elles font peser à l’échelle planétaire et leur irruption sur la scène politique sont souvent vues comme le résultat d’alertes scientifiques transnationales. Pourtant, lorsque l’on considère les désastres dans différents contextes, force est de constater la pluralité de communautés scientifiques théorisant de diverses façons le lien entre changement environnemental et catastrophes. En rendant compte de la variété de ces régimes épistémiques développés en Europe, en Amérique du Nord et dans les pays dits du Sud et de leur focalisation respective sur la crise environnementale, la préparation aux catastrophes ou la vulnérabilité due au développement, l’article met à jour la coexistence de différentes ontologies du global et leur hiérarchisation dans un espace politique transnational

L'occupation rurale gallo-romaine de la vallée de la Selle : première approche

Le plateau dominant la vallée de la Selle présente des traces d'occupations dès la période moustérienne. Les premiers enclos fossoyés apparaissent à La Tène moyenne-finale. Ces occupations seront perennisées dans leur structuration générale jusqu'au début de la période romaine (site d'Intercampus) ou disparaitront au profit d'une nouvelle forme d'habitat : les villae. Dès la période laténienne, les exploitations sont en interaction, à lépoque romaine, la nature des exploitations change. Les villae forment un ensemble qui devaient être en relation et réalisaient des échange entre elles et revendaient leur production aux agglomérations les plus proches. La particularite de la vallée de la Selle est sa proximité avec la ville d'Amiens et pose donc la question de l'interface entre la ville et la campagne

Book review: le gouvernement des catastrophes

Le gouvernement des catastrophes, Sandrine Revet, Julien Langumier (Eds), Karthala, 2013, 286 p

Protecting the most vulnerable? The management of a disaster and the making/unmaking of victims after xenophobic violence in 2008 in South Africa

In 2008, South Africa witnessed a bout of xenophobic violence, requiring the state to declare a disaster to manage a massive displacement of migrants and foreigners. How did the South African state come to care for these populations, whereas it had previously sought to avoid providing protection to foreigners, and was seen as responsible for fostering xenophobia, if not violence? Analyzing the management of the disaster at the local level (in Cape Town), and the various discourses and mobilizations involved in it, this article shows how widespread violence and displacement rendered migrant vulnerabilities visible in the urban space and forced the state to temporarily recognize and protect those who became seen as “victims.” It also questions the idea that xenophobia and failure to comply with international norms were responsible for the lack of protection of migrants and foreigners. Rather, it is the kind of protection displayed, restricted to the “most vulnerable,” that failed to address the root causes of the violence and envision broader social integration issues. The article provides further theorization on what it means to treat violence as disaster and points out to the need to envisage critically humanitarian and social assistance by including them in broader welfare patterns