A statistical mechanics framework for the large-scale structure of turbulent von K{\'a}rm{\'a}n flows

In the present paper, recent experimental results on large scale coherent steady states observed in experimental von K{\'a}rm{\'a}n flows are revisited from a statistical mechanics perspective. The latter is rooted on two levels of description. We first argue that the coherent steady states may be described as the equilibrium states of well-chosen lattice models, that can be used to define global properties of von K{\'a}rm{\'a}n flows, such as their temperatures. The equilibrium description is then enlarged, in order to reinterpret a series of results about the stability of those steady states, their susceptibility to symmetry breaking, in the light of a deep analogy with the statistical theory of Ferromagnetism. We call this analogy "Ferro-Turbulence

Green thermoelectrics: Observation and analysis of plant thermoelectric response

Plants are sensitive to thermal and electrical effects; yet the coupling of both, known as thermoelectricity, and its quantitative measurement in vegetal systems never were reported. We recorded the thermoelectric response of bean sprouts under various thermal conditions and stress. The obtained experimental data unambiguously demonstrate that a temperature difference between the roots and the leaves of a bean sprout induces a thermoelectric voltage between these two points. Basing our analysis of the data on the force-flux formalism of linear response theory, we found that the strength of the vegetal equivalent to the thermoelectric coupling is one order of magnitude larger than that in the best thermoelectric materials. Experimental data also show the importance of the thermal stress variation rate in the plant's electrophysiological response. Therefore, thermoelectric effects are sufficiently important to partake in the complex and intertwined processes of energy and matter transport within plants

Macroeconomic Dynamics in a finite world: the Thermodynamic Potential Approach

This paper presents a conceptual model describing the medium and long-term co-evolution of natural and socio-economic subsystems of Earth. An economy is viewed as an out-of-equilibrium dissipative structure that can only be maintained with a flow of energy and matter. The distinctive approach emphasized here consists in capturing the economic impact of natural ecosystems being depleted and destroyed by human activities via a pinch of thermodynamic potentials. This viewpoint allows: (i) the full-blown integration of a limited quantity of primary resources into a non-linear macrodynamics that is stock-flow consistent both in terms of matter-energy as well as economic transactions; (ii) the inclusion of natural and forced recycling; (iii) the inclusion of a friction term which reflects the impossibility of producing goods and services in high metabolising intensity without exuding energy and matter wastes; (iv) the computation of the anthropically produced entropy as a function of intensity and friction. Analysis and numerical computations confirm the role played by intensity and friction as key factors for sustainability. Our approach is flexible enough to allow for various economic models to be embedded into our thermodynamic framework.Comment: 30 pages, 10 figure

A statistical mechanics framework for the large-scale structure of turbulent von Kármán flows

In the present paper, recent experimental results on large scale coherent steady states observed in experimental von Kármán flows are revisited from a statistical mechanics perspective. The latter is rooted on two levels of description. We first argue that the coherent steady states may be described as the equilibrium states of well-chosen lattice models, that can be used to define global properties of von Kármán flows, such as their temperatures. The equilibrium description is then enlarged, in order to reinterpret a series of results about the stability of those steady states, their susceptibility to symmetry breaking, in the light of a deep analogy with the statistical theory of Ferromagnetism. We call this analogy ''Ferro-Turbulence'

Prediction and experimental evidence of the optimisation of the angular branching process in the thallus growth of Podospora anserina

Based upon apical growth and hyphal branching, the two main processes that drive the growth pattern of a fungal network, we propose here a two-dimensions simulation based on a binary-tree modelling allowing us to extract the main characteristics of a generic thallus growth. In particular, we showed that, in a homogeneous environment, the fungal growth can be optimized for exploration and exploitation of its surroundings with a specific angular distribution of apical branching. Two complementary methods of extracting angle values have been used to confront the result of the simulation with experimental data obtained from the thallus growth of the saprophytic filamentous fungus Podospora anserina. Finally, we propose here a validated model that, while being computationally low-cost, is powerful enough to test quickly multiple conditions and constraints. It will allow in future works to deepen the characterization of the growth dynamic of fungal network, in addition to laboratory experiments, that could be sometimes expensive, tedious or of limited scope.Comment: Submitted to Scientific Repor

Global Genetic Diversity of Human Metapneumovirus Fusion Gene

We analyzed 64 human metapneumovirus strains from eight countries. Phylogenetic analysis identified two groups (A and B, amino acid identity 93%–96%) and four subgroups. Although group A strains predominated, accounting for 69% of all strains, as many B as A strains were found in persons >3 years of age

Modelling and analysis of turbulent datasets using Auto Regressive Moving Average processes

International audienceWe introduce a novel way to extract information from turbulent datasets by applying an Auto Regressive Moving Average (ARMA) statistical analysis. Such analysis goes well beyond the analysis of the mean flow and of the fluctuations and links the behavior of the recorded time series to a discrete version of a stochastic differential equation which is able to describe the correlation structure in the dataset. We introduce a new index ϒ that measures the difference between the resulting analysis and the Obukhov model of turbulence, the simplest stochastic model reproducing both Richardson law and the Kolmogorov spectrum. We test the method on datasets measured in a von Kármán swirling flow experiment. We found that the ARMA analysis is well correlated with spatial structures of the flow, and can discriminate between two different flows with comparable mean velocities, obtained by changing the forcing. Moreover, we show that the ϒ is highest in regions where shear layer vortices are present, thereby establishing a link between deviations from the Kolmogorov model and coherent structures. These deviations are consistent with the ones observed by computing the Hurst exponents for the same time series. We show that some salient features of the analysis are preserved when considering global instead of local observables. Finally, we analyze flow configurations with multistability features where the ARMA technique is efficient in discriminating different stability branches of the system

‘It doesn’t reveal itself’: erosion and collapse of the image in contemporary visual practice

The article explores the extent to which ‘pictorial art’ resists legibility, transparency and coherence. The analysis of three artistic case studies, Idris Khan, Maria Chevska and Jane and Louise Wilson, serves to investigate established hierarchies in our perception of visual referents. In the discussion, the article inquires the means of erosion, veiling and dissemblance as ways to critique assumption of the homogeneity of the image. All artists cast a view of the external world by diverting it, defacing it and distancing themselves from the external environment. However, the distancing is never disconnected from the everyday and never succumbs to abstraction. The article argues that the crisis of the image offers a productive framework that allows artists to draw attention to the absence of logical structure and the instability of the visual sign

Cavitation acoustique dans l'eau pure

Any liquid can be superheated or stretched beyond its boiling curve. It will then remain in a metastable state, until a vapor bubble appears : this is the cavitation phenomenon. The study of the metastability limit gives information about the cohesion of the liquid and its equation of state. The case of water is of special interest ; indeed competiting theories predict qualitatively different temperature variations of the stability limit : either monotonic (the cavitation pressure increase with temperature), or with a minimum. We have stretched water with an ultrasonic wave, generated by a hemispherical piezoelectric ceramic, during a short time and a small volume, far from any wall, which reduces the effect of impurities. We obtain very accurate and reproducible results, allowing us to study in details the statistic of cavitation and to define a cavitation thresold. The ceramic was calibrated using two independent methods : needle hydrophones, and a method based on the variation of the static pressure. Both of them lead to the same result. We find a monotically increasing cavitation pressure, from -26 MPa at 0 Celsius C to -16 MPa at 80 Celsius C. These values are among the most negative reported, but far away from the values expected theoritically (-120 Mpa), and observed only once (Zheng etal , 1991, Science 254, 829). We discuss the possible origin of this discrepancy : it can be due either to the presence of impurities in the liquid, whose nature and concentration we discuss, or to an unexpected change in the equation of state of water at large negative pressures.Tout liquide peut être surchauffé ou détendu au delà de sa courbe d'ébullition. Il est dans un état métastable, jusqu'à ce qu'une bulle de vapeur apparaisse, c'est le phénomène de cavitation. L'étude de la limité de métastabilité renseigne sur la cohésion du liquide et sur son équation d'état. Le cas de l'eau est spécialement intéressant : des théories concurrentes prédisent des variations en température de cette limite qualitativement différentes : monotone (la pression de cavitation augmente avec la température), ou avec un minimum. Nous mettons l'eau sous tension à l'aide d'une onde ultrasonore, émise par une céramique piézo-électrique hémisphérique. L'onde est focalisée pendant une courte durée et dans un petit volume loin de toute paroi, ce qui minimise l'influence d'éventuelles impuretés. Nous obtenons des résultats très reproductibles, permettant de mesurer la statistique de cavitation et de définir précisément son seuil dans différents types d'eaux. La céramique est calibrée de deux manières : avec des hydrophones à aiguille, et avec une méthode basée sur la variation de la pression statique du liquide. Les deux méthodes sont en accord et donnent une pression de cavitation monotone de -26 MPa à 0 Celsius C à -16 MPa à 80 Celsius C. Cela fait partie des pressions les plus négatives observées dans l'eau mais reste loin de la valeur théorique attendue (environ -120 MPa) et observée dans une seule expérience (Zheng etal , 1991, Science 254, 829). Nous discutons les causes possibles de ce désaccord : il peut être du soit à la présence d'impuretés, dont nous discutons la nature et la concentration, soit à une courbure inattendue de l'équation d'état aux pressions très négatives

Les aromatases humaine et équine (Etudes d'impacts des xénobiotiques)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF