Inverse square L\'evy walks are not optimal search strategies for d≥2d\ge 2

The L\'evy hypothesis states that inverse square L\'evy walks are optimal search strategies because they maximise the encounter rate with sparse, randomly distributed, replenishable targets. It has served as a theoretical basis to interpret a wealth of experimental data at various scales, from molecular motors to animals looking for resources, putting forward the conclusion that many living organisms perform L\'evy walks to explore space because of their optimal efficiency. Here we provide analytically the dependence on target density of the encounter rate of L\'evy walks for any space dimension $d$ ; in particular, this scaling is shown to be {\it independent} of the L\'evy exponent $\alpha$ for the biologically relevant case $d\ge 2$, which proves that the founding result of the L\'evy hypothesis is incorrect. As a consequence, we show that optimizing the encounter rate with respect to $\alpha$ is {\it irrelevant} : it does not change the scaling with density and can lead virtually to {\it any} optimal value of $\alpha$ depending on system dependent modeling choices. The conclusion that observed inverse square L\'evy patterns are the result of a common selection process based purely on the kinetics of the search behaviour is therefore unfounded.Comment: Accepted in Phys. Rev. Let

Improvement of the Parallel Compressor Model and Application to Inlet Flow Distortion

This paper introduces a semi-analytical approach which enables one to deal with distorted inflow in axial fans or compressors. It is inspired by the classical parallel compressor (PC) theory but relies on a local flow-loading coefficient formalism. It is applied to non-uniform flow conditions to study the aerodynamic behavior of a low-speed fan in response to upstream flow distortion. Experimental measurements and 3D RANS simulations are used to evaluate the prediction of fan performance obtained with the local PC method. The comparison proves that, despite its simplicity, the present approach enables to correctly capture first order phenomena, offering interesting perspectives for an early design phase if different fan geometries are to be tested and if the upstream distortion maps are available

253: The effect of statins on the risk of first non-fatal myocardial infarction: A population-based observational study using the PGRx information system

BackgroundDespite demonstrated positive effects in a number of clinical trials, the evidence is lacking as to the impact of statins on the risk of first myocardial infarction (MI) in real life settings.ObjectivesTo assess the impact of real life statin utilization on the risk of first non-fatal MIMethodsCase-control methodology using the pharmacoepidemiological information system PGRx. Data on comorbidities, risk factors and medications were obtained from medical records and patient telephone interviews. General practices (n=371) and cardiology centres (n=60) across France were employed in the study. Cases were patients with the first MI ≤ 1 month before the date of recruitment (n=2238). Controls were patients seen by a general practitioner (GP) with no restriction as to the reasons of consultation (n=2238), matched to MI cases on gender, age, frequency of visits to a doctor, date of recruitment and personal history of non-cardiovascular chronic disease. Statin exposure was defined as any utilisation in the two-year prior to date of MI in cases or recruitment date in controls. Adjusted odds ratios (OR) of the risk of first MI was estimated by multiple conditional logistic regression models. Comparative effectiveness and propensity to use of individual statin molecules were assessed.ResultsThe use of statins was associated with a lower MI risk (adjusted OR 0.67 [95% CI 0.56 - 0.79] for current use (within 2 months before the index date) and 0.73 [0.62 0.86] for any use within 24 months). Among individual statins, rosuvastatin was associated with the lowest MI risk (adjusted OR 0.49 [0.35 - 0.68] for any use in 24 months preceding the index date) followed by simvastatin (0.62 [0.46 - 0.84]).ConclusionsIn this first major population-based observational study we reproduced the results observed in recent meta-analyses accounting for real life compliance and population variability. The results could be of interest and applicable to other industrialised countries as the observed risk reduction was constant across MI risk levels

Body Force Modeling of the Aerodynamics of a Low-Speed Fan under Distorted Inflow

New propulsive concepts, such as boundary layer ingestion, involve stronger interactions between the engine and its environment, and are thus more complex flows compared to classical architectures. Usual turbomachinery design tools are inadequate, and new numerical methodologies are needed to accurately predict the engine performance with affordable CPU resources. The present paper examines the relevance of a reduced-order modeling approach—the body force modeling (BFM) method—for a low-speed cooling fan with inflow distortion. The formulation itself accounts for the blade metal blockage and compressibility effects, and it relies on a semiempirical loss model, independent of computational fluid dynamics (CFD) calibration. The BFM results obtained in the present work are assessed against full-annulus unsteady Reynolds-averaged Navier-Stokes (URANS) results and experiments. The comparison shows that the BFM approach successfully quantifies the fan stage performance. Furthermore, the distortion transfer across the stage is examined and the flow patterns observed are found to be the same as in the URANS results and in the measurements. Hence, this methodology, coming at a low CPU cost, is well-adapted to the early design phase of an innovative propulsion system

Body force modeling of the aerodynamics of a low-speed fan under distorted inflow

New propulsive concepts such as Boundary Layer Ingestion involve stronger interactions between the engine and its environment, and thus more complex flows compared to classical architectures. Usual turbomachinery design tools are inadequate, and new numerical methodologies are needed to accurately predict the engine performance with affordable CPU resources. The present paper examines the relevance of a reduced-order modeling approach, the body force modeling (BFM) method, for a low-speed cooling fan with inflow distortion. The formulation itself accounts for the blade metal blockage, compressible effects and it relies on a physics-based loss model, independent of CFD calibration. The BFM results obtained in the present work are assessed against full-annulus URANS results and experiments. The comparison shows that the BFM approach successfully quantifies the fan stage performance. Furthermore, the distortion transfer across the stage is examined and the flow patterns observed are found to be the same as in the URANS results and in the measurements. Hence, this methodology, coming at a low CPU cost, is well-adapted to the early design phase of an innovative propulsion system

La carte Vitale permet de prédire l'antibiorésistance à l'échelon individuel

International audienc

Front acceleration by dynamic selection in Fisher population waves

We introduce a minimal model of population range expansion in which the phenotypes of individ- uals present no selective advantage and differ only in their diffusion rate. We show that such neutral phenotypic variability can yield alone phenotype segregation at the front edge even in absence of genetic noise, and significantly impact the dynamical properties of the expansion wave. We present an exact asymptotic traveling wave solution and show analytically that phenotype segregation ac- celerates the front propagation. The results are compatible with field observations such as invasions of cane toads in Australia or bush crickets in Britain

Full-Annulus Simulation of the Surge Inception in a Transonic Centrifugal Compressor

International audienceno abstrac

Do Triclosan affect hearing development of Cyprinodon variegatus larvae?

The aquatic environment represents the final sink for many chemicals, including bactericidal agents. Among them Triclosan (TCS) has been shown to affect the thyroid system of teleost. Larval stages are particularly vulnerable to deleterious effects of endocrine disrupters because of potential impairment of fish development and behaviour. Thyroid hormones are critical to the development of the brain and auditory system. Thus, TCS could affect the development of the brain and hearing. The aims of this study were: to investigate hearing development in sheepshead minnows (Cyprinodon variegatus) using the ABR technique (Auditory Brainstem Response) and to investigate the effects of triclosan on hearing development. Exposure to TCS was conducted from fertilization of eggs on at concentrations likely to be found in the environment: 20, 50 and 100 µgl-1. We characterized previously the ontogenic variation of thyroid hormones in embryos and larvae of sheepshead minnows. We observed an increase of thyroid hormones level around the 12th and the 15th day post hatching (dph), that may be associated with the transition from larval to juvenile stage during the development of this species. We concluded, that this period could be defined as a critical exposure window to pollutants. We determined hearing thresholds for sheepshead minnows of different ages. Our sheepshead minnows show ontogenic variations in the hearing ability during their development. At 30 days post hatching, their hearing ability is quite bad, with a narrow bandwidth of detected frequencies. But their hearing ability considerably enhance during their development to reach the adult hearing ability at around 80 days post hatching when this species reach sexual maturity. So we observe during the developmental phase of this fish species clear ontogenic improvements of the hearing ability and they showed an ontogenetic expansion in the frequency bandwidth they were able to detect. The effects of TCS in this development have yet to be determined but will be fully discussed. This study proposes an interesting new endpoint in thyroid disruption research