Incompressible limit of mechanical model of tumor growth with viscosity

Various models of tumor growth are available in the litterature. A first class describes the evolution of the cell number density when considered as a continuous visco-elastic material with growth. A second class, describes the tumor as a set and rules for the free boundary are given related to the classical Hele-Shaw model of fluid dynamics. Following the lines of previous papers where the material is described by a purely elastic material, or when active cell motion is included, we make the link between the two levels of description considering the 'stiff pressure law' limit. Even though viscosity is a regularizing effect, new mathematical difficulties arise in the visco-elastic case because estimates on the pressure field are weaker and do not imply immediately compactness. For instance, traveling wave solutions and numerical simulations show that the pressure may be discontinous in space which is not the case for the elastic case.Comment: 17 page

Variational Ansatz for an Abelian to non-Abelian Topological Phase Transition in ν=1/2+1/2\nu = 1/2 + 1/2 Bilayers

We propose a one-parameter variational ansatz to describe the tunneling-driven Abelian to non-Abelian transition in bosonic $\nu=1/2+1/2$ fractional quantum Hall bilayers. This ansatz, based on exact matrix product states, captures the low-energy physics all along the transition and allows to probe its characteristic features. The transition is continuous, characterized by the decoupling of antisymmetric degrees of freedom. We futhermore determine the tunneling strength above which non-Abelian statistics should be observed experimentally. Finally, we propose to engineer the inter-layer tunneling to create an interface trapping a neutral chiral Majorana. We microscopically characterize such an interface using a slightly modified model wavefunction.Comment: 5 pages, 4 Figures and Supplementary Materials. Comments are welcome

A simple derivation of BV bounds for inhomogeneous relaxation systems

We consider relaxation systems of transport equations with heterogeneous source terms and with boundary conditions, which limits are scalar conservation laws. Classical bounds fail in this context and in particular BV estimates. They are the most standard and simplest way to prove compactness and convergence. We provide a novel and simple method to obtain partial BV regularity and strong compactness in this framework. The standard notion of entropy is not convenient either and we also indicate another, but closely related, notion. We give two examples motivated by renal flows which consist of 2 by 2 and 3 by 3 relaxation systems with 2-velocities but the method is more general

Minimizing Energy Consumption of MPI Programs in Realistic Environment

Dynamic voltage and frequency scaling proves to be an efficient way of reducing energy consumption of servers. Energy savings are typically achieved by setting a well-chosen frequency during some program phases. However, determining suitable program phases and their associated optimal frequencies is a complex problem. Moreover, hardware is constrained by non negligible frequency transition latencies. Thus, various heuristics were proposed to determine and apply frequencies, but evaluating their efficiency remains an issue. In this paper, we translate the energy minimization problem into a mixed integer program that specifically models most current hardware limitations. The problem solution then estimates the minimal energy consumption and the associated frequency schedule. The paper provides two different formulations and a discussion on the feasibility of each of them on realistic applications

Cattle trade network in Madagascar highlands and Rift Valley fever virus circulation

In 2008-2009 a RVF outbreak occurred in the Anjozorobe area, a temperate and mountainous area of Madagascar highlands. A serological study conducted there in 2009 showed an IgG seroprevalence rate of 28%. Data analysis suggested a recurrent circulation of RVFV. The objectives of this study were to describe the cattle trade network in this area and analyze the link between network structure and RVFV circulation. Questionnaire survey among 386 breeders from 47 villages was carried out to collect trade data. Yearly village-level seroconversion rate was estimated in 2010 by testing 516 cattle negative in 2009. Association between the occurrence of seroconversion and network centrality parameters, distance to the nearest water point and 2009 seroprevalence level was tested. Due to the non-independence of the centrality parameters, a bootstrap procedure was used to assess the effects of the independent variables. Average village-level seroconversion was 7%, ranging from 0-20%. Two types of trading practice were observed: exchanges and buy/sale. The corresponding networks appeared both scale-free, and a significant but low correlation was observed between them. A negative association was observed between the occurrence of seroconversion in the village and the 2009 seroprevalence level, as well as the distance to the nearest water point. After RVFV introduction, vector-based transmission may support the within-village circulation. The node degree in the exchange network was positively linked with the occurrence of seroconversion. It was not the case for the buy/sale network. Both networks could thus have distinct roles in RVFV circulation. The exchanges network could be the support for RVFV introduction in villages, the buy/sale network being probably rather implicated in the introduction of RVFV in the area, from other parts of Madagascar. (Texte intégral

A kinematic and dynamic comparison of surface and underwater displacement in high level monofin swimming

International audienceFin-swimming performance can be divided into underwater and surface water races. World records are about 10% faster for underwater swimming vs. surface swimming, but little is known about the advantage of underwater swimming for monofin swimming. Some authors reported that the air-water interface influences the kinematics and leads to a narrow vertical amplitude of the fin. On the one hand, surface swimming is expected to affect drag parameters (cross-sectional area (S) and active drag (AD)) when compared to underwater swimming. On the other hand, the surface swimming technique may also affect efficiency (η). The aim of this study is therefore to evaluate and compare drag parameters and efficiency during underwater and surface swimming. To this end, 12 international level monofin swimmers were measured during both underwater and surface swimming. Kinematic parameters (both dimensional and non-dimensional), η (calculated according to the Elongated-Body Theory), and AD (computed with Velocity Perturbation Method) were calculated for an underwater and a surface fin-swimming trial, performed at maximal speed. As expected, results showed significantly lower velocities during surface swimming vs. underwater ( = 2.5 m.s vs. = 2.36 m.s, < .01). Velocities during underwater and surface swimming were strongly correlated ( = .97, < .01). Underwater swimming was also associated with higher vertical amplitudes of the fin compared to surface swimming ( = 0.55 m vs. = 0.46 m, < .01). Length-specific amplitudes (A/L) were in the order of 20% during underwater swimming as for undulating fish, and significantly higher than during surface swimming (A/L = 17%, < .01). Efficiency for surface swimming was about 6% lower than for underwater swimming ( = 0.79 vs. = 0.74, < .01). This decrease could be associated with an increase in swimming frequency for surface swimming ( = 2.15 Hz vs. = 2.08 Hz, < .01). Active drag during surface swimming was about 7% higher than for underwater swimming ( = 78.9 N vs. = 84.7 N, < .01). A significantly smaller cross-sectional area for surface swimming ( = 0.053 m vs. = 0.044 m, < .01) and higher drag coefficient for surface swimming ( = 0.47 vs. = 0.69, < .01) were measured. Finally, correlation between cross-sectional area and vertical amplitude of the fin was reported for both underwater and surface swimming. These results suggest that the performance improvement during underwater swimming is not only linked to a wave drag reduction effect but also to a specific swimming technique due to the free surface

De la hausse des prix au retour du productionnisme ; les enjeux du sommet sur la sécurité alimentaire de juin 2008 à Rome

8 pagesLa hausse des prix pétroliers et alimentaires sur les marchés internationaux est intervenue dans un contexte de crise des institutions dédiées à l'agriculture. Alors que les émeutes que la flambée des prix a provoquées dans le monde ne témoignent pas d'un début de pénurie alimentaire mais d'une pauvreté urbaine aggravée, le thème de la crise s'est déplacé vers la question agricole. Le sommet sur la sécurité alimentaire organisé par la FAO a été le théâtre de cette instrumentation de la crise pour justifier une relance de la production agricole. La focalisation sur les disponibilités alimentaires est porteuse de risques de nouvelles tensions foncières et de replis sur les espaces nationaux et ne règle pas pour autant la pauvreté et les inégalités à l'origine des émeutes