830 research outputs found
Contribution à la prévision du méandrement du sillage des éoliennes à axe horizontal
La production Ă©olienne industrielle sâorganise sous la forme de centrales regroupant de quelques unitĂ©s Ă la centaine dâĂ©oliennes. Ces centrales sont dissĂ©minĂ©es sur le territoire terrestre ou maritime en des lieux soigneusement sĂ©lectionnĂ©s sur la base de nombreux critĂšres, dont le potentiel Ă©olien. Cela concerne la qualitĂ© des vents incidents, lâinfluence de la complexitĂ© gĂ©omĂ©trique du site mais aussi les interactions aĂ©rodynamiques entre Ă©oliennes qui pourraient dĂ©grader la qualitĂ© du vent incident et donc la production Ă©nergĂ©tique. En fonction de la direction des vents, la proximitĂ© des Ă©oliennes organisĂ©es en parc induit trĂšs frĂ©quemment des interactions de sillages entre deux ou plusieurs machines alignĂ©es. Le sillage gĂ©nĂ©rĂ© par une Ă©olienne se caractĂ©rise principalement par un dĂ©ficit de vitesse du vent et une augmentation de la turbulence sur plusieurs centaines de mĂštres en aval. Lâinteraction du sillage dâune Ă©olienne sur une seconde se traduit par une diminution du rendement ainsi quâune augmentation des charges aĂ©rodynamiques fatiguant prĂ©maturĂ©ment les matĂ©riaux. De plus, les grandes Ă©chelles de la turbulence atmosphĂ©rique ont tendance Ă modifier la trajectoire des sillages Ă©oliens avec un caractĂšre instationnaire, appelĂ© mĂ©andrement (« meandering »). Ce phĂ©nomĂšne mal quantifiĂ© jusquâĂ maintenant doit ĂȘtre caractĂ©risĂ© pour ĂȘtre correctement modĂ©lisĂ©s dans les calculs de prĂ©vision dâeffets de sillage. La modĂ©lisation physique en soufflerie est lâapproche utilisĂ©e par le laboratoire PRISME pour Ă©tudier cette problĂ©matique. Cela consiste Ă reproduire Ă Ă©chelle rĂ©duite (de lâordre du 1/500Ăšme) les propriĂ©tĂ©s aĂ©rodynamiques (moyennes et turbulentes) de la basse couche atmosphĂ©rique. Le rotor est modĂ©lisĂ©, sur la base du concept de disque actuateur, par un disque poreux et les propriĂ©tĂ©s stationnaires et instationnaires du sillage lointain sont Ă©tudiĂ©es par lâintermĂ©diaire de mesures de vitesse par anĂ©momĂ©trie fil chaud multi-points, PIV et LDV. Par le biais de ces expĂ©riences en soufflerie, des rĂ©ponses sont apportĂ©es sur les causes du mĂ©andrement, son amplitude et sa prĂ©vision
Mapping the energy and diffusion landscapes of membrane proteins at the cell surface using high-density single-molecule imaging and Bayesian inference: application to the multi-scale dynamics of glycine receptors in the neuronal membrane
Protein mobility is conventionally analyzed in terms of an effective
diffusion. Yet, this description often fails to properly distinguish and
evaluate the physical parameters (such as the membrane friction) and the
biochemical interactions governing the motion. Here, we present a method
combining high-density single-molecule imaging and statistical inference to
separately map the diffusion and energy landscapes of membrane proteins across
the cell surface at ~100 nm resolution (with acquisition of a few minutes).
When applying these analytical tools to glycine neurotransmitter receptors
(GlyRs) at inhibitory synapses, we find that gephyrin scaffolds act as shallow
energy traps (~3 kBT) for GlyRs, with a depth modulated by the biochemical
properties of the receptor-gephyrin interaction loop. In turn, the inferred
maps can be used to simulate the dynamics of proteins in the membrane, from the
level of individual receptors to that of the population, and thereby, to model
the stochastic fluctuations of physiological parameters (such as the number of
receptors at synapses). Overall, our approach provides a powerful and
comprehensive framework with which to analyze biochemical interactions in
living cells and to decipher the multi-scale dynamics of biomolecules in
complex cellular environments.Comment: 23 pages, 4 figure
Compression-based inference of network motif sets
Physical and functional constraints on biological networks lead to complex
topological patterns across multiple scales in their organization. A particular
type of higher-order network feature that has received considerable interest is
network motifs, defined as statistically regular subgraphs. These may implement
fundamental logical and computational circuits and are referred as ``building
blocks of complex networks''. Their well-defined structures and small sizes
also enables the testing of their functions in synthetic and natural biological
experiments. The statistical inference of network motifs is however fraught
with difficulties, from defining and sampling the right null model to
accounting for the large number of possible motifs and their potential
correlations in statistical testing. Here we develop a framework for motif
mining based on lossless network compression using subgraph contractions. The
minimum description length principle allows us to select the most significant
set of motifs as well as other prominent network features in terms of their
combined compression of the network. The approach inherently accounts for
multiple testing and correlations between subgraphs and does not rely on a
priori specification of an appropriate null model. This provides an alternative
definition of motif significance which guarantees more robust statistical
inference. Our approach overcomes the common problems in classic testing-based
motif analysis. We apply our methodology to perform comparative connectomics by
evaluating the compressibility and the circuit motifs of a range of
synaptic-resolution neural connectomes
QALC - the Question-Answering program of the Language and Cognition group at LIMSI-CNRS
International audienc
Variational inference of fractional Brownian motion with linear computational complexity
We introduce a simulation-based, amortised Bayesian inference scheme to infer
the parameters of random walks. Our approach learns the posterior distribution
of the walks' parameters with a likelihood-free method. In the first step a
graph neural network is trained on simulated data to learn optimized
low-dimensional summary statistics of the random walk. In the second step an
invertible neural network generates the posterior distribution of the
parameters from the learnt summary statistics using variational inference. We
apply our method to infer the parameters of the fractional Brownian motion
model from single trajectories. The computational complexity of the amortized
inference procedure scales linearly with trajectory length, and its precision
scales similarly to the Cram{\'e}r-Rao bound over a wide range of lengths. The
approach is robust to positional noise, and generalizes well to trajectories
longer than those seen during training. Finally, we adapt this scheme to show
that a finite decorrelation time in the environment can furthermore be inferred
from individual trajectories
Approximate information maximization for bandit games
Entropy maximization and free energy minimization are general physical
principles for modeling the dynamics of various physical systems. Notable
examples include modeling decision-making within the brain using the
free-energy principle, optimizing the accuracy-complexity trade-off when
accessing hidden variables with the information bottleneck principle (Tishby et
al., 2000), and navigation in random environments using information
maximization (Vergassola et al., 2007). Built on this principle, we propose a
new class of bandit algorithms that maximize an approximation to the
information of a key variable within the system. To this end, we develop an
approximated analytical physics-based representation of an entropy to forecast
the information gain of each action and greedily choose the one with the
largest information gain. This method yields strong performances in classical
bandit settings. Motivated by its empirical success, we prove its asymptotic
optimality for the two-armed bandit problem with Gaussian rewards. Owing to its
ability to encompass the system's properties in a global physical functional,
this approach can be efficiently adapted to more complex bandit settings,
calling for further investigation of information maximization approaches for
multi-armed bandit problems
A geomorphological investigation of lateral spreading and translational sliding within the Storegga Slide
Lateral spreading and translational sliding are two of the most prevalent types of slope
failures within the Storegga Slide. This has been concluded from a thorough analysis
of three acoustic data sets from the Storegga Slide complex â high-resolution multibeam
bathymetry, TOBI sidescan sonar imagery and 3D seismic data.We have applied
quantitative geomorphometric techniques to the bathymetry data set and analysed the
texture of sidescan sonar images using Grey-Level Occurrence Matrices (GLCMs).
Both techniques have been shown to improve the geological interpretation of submarine
environments (e.g. Micallef et al., 2006), and allowed an objective characterisation
of the slide surface to be carried out. These results were then combined with
the interpretation of the seismic data set and all the geological information currently
available for Storegga in the literature. In this way we were able to define the types
and boundaries of the different styles of mass movements, and represent them on a
geomorphological map. Further insight is provided into the origin and the mode of
failure of lateral spreading and translational sliding. Finally we attempt to describe
the characteristic morphology of lateral spreading and demonstrate that it is a very
common slope failure process in the Norwegian margin.peer-reviewe
Appropriate dynamic-stall models for performance predictions of VAWTs with NLF blades
This paper illustrates the relative merits of using Natural Laminar Flow (NLF) airfoils in the design of Vertical Axis Wind Turbines (VAWT). This is achieved by the application of the double-multiple-streamtube model of Paraschivoiu to the performance predictions of VAWTs equipped with conventional and NLF blades. Furthermore, in order to clearly illustrate the potential benefit of reducing the drag, the individual contributions of lift and drag to power are presented. The dynamic-stall phenomena are modelled using the method of Gormont as modified by several researchers. Among the various implementations of this dynamic-stall model available in the literature, the most appropriate and general for NLF
applications has been identified through detailed comparisons between predicted performances and experimental data. This selection process is presented in the paper. It has been demonstrated that the use of NLF airfoils in VAWT applications can lead to significant
improvements with respect to conventional design only in a very low wind speed range, the extent of which is negligible with respect to the VAWT operational wind speeds
- âŠ