Simultaneous Image Registration and Monocular Volumetric Reconstruction of a fluid flow

We propose to combine image registration and volumetric reconstruction from a monocular video of a draining off Hele-Shaw cell filled with water. A Hele-Shaw cell is a tank whose depth is small (e.g. 1 mm) compared to the other dimensions (e.g. 400 800 mm2). We use a technique known as molecular tagging which consists in marking by photobleaching a pattern in the fluid and then tracking its deformations. The evolution of the pattern is filmed with a camera whose principal axis coincides with the depth of the cell. The velocity of the fluid along this direction is not constant. Consequently,tracking the pattern cannot be achieved with classical methods because what is observed is the integration of the marked particles over the entire depth of the cell. The proposed approach is built on top of classical direct image registration in which we incorporate a volumetric image formation model. It allows us to accurately measure the motion and the velocity profiles for the entire volume (including the depth of the cell) which is something usually hard to achieve. The results we obtain are consistent with the theoretical hydrodynamic behaviour for this flow which is known as the laminar Poiseuille flow

Image registration algorithm for molecular tagging velocimetry applied to unsteady flow in Hele-Shaw cell

In order to develop velocimetry methods for confined geometries, we propose to combine image registration and volumetric reconstruction from a monocular video of the draining of a Hele-Shaw cell filled with water. The cell’s thickness is small compared to the other two dimensions (e.g. 1x400 x 800 mm3). We use a technique known as molecular tagging which consists in marking by photobleaching a pattern in the fluid and then tracking its deformations. The evolution of the pattern is filmed with a camera whose principal axis coincides with the cell’s gap. The velocity of the fluid along this direction is not constant. Consequently, tracking the pattern cannot be achieved with classical methods because what is observed is the integral of the marked molecules over the entire cell’s gap. The proposed approach is built on top of direct image registration that we extend to specifically model the volumetric image formation. It allows us to accurately measure the motion and the velocity profiles for the entire volume (including the cell’s gap) which is something usually hard to achieve. The results we obtained are consistent with the theoretical hydrodynamic behaviour for this flow which is known as the Poiseuille flow

Tunable hydrogen release from amine-boranes via their insertion into functional polystyrenes

International audiencePolystyrene-g-boramines random copolymers are dihydrogen reservoirs with tunable dehydrogenation temperatures, which can be adjusted by selecting the boramine content in the copolymers. They display a unique dihydrogen thermal release profile, which is a direct consequence of the insertion of the amine-boranes in a polymeric scaffold, and not from a direct modification of the electronics or sterics of the amine-borane function. Finally, the mixture of polystyrene-g-boramines with conventional NH3-BH3 (borazane) allows for a direct access to organic/inorganic hybrid dihydrogen reservoirs with a maximal H2 loading of 8 wt%

Cascadia in Comparative Perspectives: Canada-U.S. Relations and the Emergence of Cross-Border Regions

This paper draws on findings from research on the Canadian-American border led by the Policy Research Initiative (PRI) since 2004 and on the recent PRI survey of Canadian-American leaders, as well as on the author’s fieldwork on multilevel governance issues arising from the emerging cross-border regions in Europe and North America. Relying on four analytical lenses—the economy, local and central politics and policies, and local cultures—this paper examines how emerging cross-border regions, and particularly the Cascadia region, are changing Canadian-American relations. Specific attention is given to the varied forms of co-operation across policy fields in order to detail (1) the general and specialized and (2) the formal and informal relations and (3) the emerging border regions. This paper underlines the importance of understanding cross-border relations at the sub-national level in order to understand Canada-U.S. relations. The overall argument is that the appearance of cross-border regions indicates a progressive emergence of policy parallelism in a multitude of policy arenas, particularly, a specifically North American form of integration

Vélocimétrie 3D par marquage moléculaire et recalage d’image pour le passage d’une bulle isolée en cellule de Hele-Shaw

Cet article décrit l’application de techniques de vision par ordinateur à la mesure de vitesse pour deux écoulements générés en Cellule de Hele-Shaw (CH). Un Écoulement Laminaire de Poiseuille (ELP) est généré par la vidange de la CH remplie d’un liquide préalablement au repos. La figure 1 donne un aperçu de la configuration expérimentale. Nous proposons un nouvel algorithme combinant le Recalage d’Image Direct (RID) et une reconstruction volumique en vision monoculaire permettant de suivre le mouvement d’un motif marquant le liquide au niveau moléculaire. La méthode nous permet d’obtenir une mesure expérimentale de l’ELP dans des géométries à accès optique limité. Précédemment, des mesures de vitesse de cet écoulement académique ont principalement été obtenues pour des régions d’intérêt restreintes (1 mm3 par µPIV (Sinton [2004])) ou sans prise en compte directe du mouvement dans la profondeur de la CH (par PIV classique (Roudet et al. [2011])). Par comparaison, notre approche nous permet de mesurer le développement de l’ELP pour un volume conséquent en milieu confiné (ici 147×147×1 mm3). Dans un deuxième temps, nous nous intéresserons à la mesure de vitesse en amont d’une bulle en ascension dans une CH à partir d’images générées numériquement. Les phénomènes observés sont de nature déformable et nous cherchons à faire une mesure tridimensionnelle à partir d’observations 2D uniquement. Nous proposons donc une méthode reposant sur deux éléments : d’une part, une modélisation 3D du liquide et de son mouvement en CH et, d’autre part, des contraintes physiques générales et souples. Garbe et al. [2008] proposent une variante d’estimation classique par flot optique en intégrant un modèle volumique pour un écoulement gazeux en micro-canal. Cependant, dans Garbe et al. [2008], le modèle d’ELP est utilisé comme un « a priori » très fort. L’article est organisé de la manière suivante. Nous décrivons le dispositif expérimental et le marquage moléculaire par photobleaching en §2. Notre algorithme de suivi et de reconstruction est détaillé en §3. Les résultats sont présentés en §4. En §5, nous concluons et discutons des applications potentielles de notre travail

Introduction: Constructing a Cross Border Cascadia Region

For the last 20 years the scholarship on borders has shifted from a narrow geographical perspective where borders were conceptualized as boundary lines drafted on maps and containers of polities, states, and sovereignties that were mutually recognized by international treaties, to complex geographical spaces, where borders result from political and policy mechanisms where people (agents) and institutions, policies and cultures and economic flows (structures) re-invent borderland, border-regions and border-zones, and ultimately the boundary line itself. Collectively, the research covered in this special issue suggests several avenues for future collaboration: on Cascadia-based research and on cross-border regional comparisons

Modelling waving crops using large-eddy simulation: Comparison with experiments and a linear stability analysis

International audienceIn order to investigate the possibility of modelling plant motion at the landscape scale, an equation for crop plant motion, forced by an instantaneous velocity field, is introduced in a large-eddy simulation (LES) airflow model, previously validated over homogeneous and heterogeneous canopies. The canopy is simply represented as a poroelastic continuous medium, which is similar in its discrete form to an infinite row of identical oscillating stems. Only one linear mode of plant vibration is considered. Two-way coupling between plant motion and the wind flow is insured through the drag force term. The coupled model is validated on the basis of a comparison with measured movements of an alfalfa crop canopy. It is also compared with the outputs of a linear stability analysis. The model is shown to reproduce the well-known phenomenon of honami which is typical of wave-like crop motions on windy days. The wavelength of the main coherent waving patches, extracted using a bi-orthogonal decomposition (BOD) of the crop velocity fields, is in agreement with that deduced from video recordings. The main spatial and temporal characteristics of these waving patches exhibit the same variation with mean wind velocity as that observed with the measurements. However they differ from the coherent eddy structures of the wind flow at canopy top, so that coherent waving patches cannot be seen as direct signatures of coherent eddy structures. Finally, it is shown that the impact of crop motion on the wind dynamics is negligible for current wind speed values. No lock-in mechanism of coherent eddy structures on plant motion is observed, in contradiction with the linear stability analysis. This discrepancy may be attributed to the presence of a nonlinear saturation mechanism in LES. © 2010 Cambridge University Press

Electrocardiographic correlates of mechanical dyssynchrony in recipients of cardiac resynchronization therapy devices

SummaryBackgroundThe relationship between electrical and mechanical indices of cardiac dyssynchronization in systolic heart failure (HF) remains poorly understood.ObjectivesWe examined retrospectively this relationship by using the daily practice tools in cardiology in recipients of cardiac resynchronization therapy (CRT) systems.MethodsWe studied 119 consecutive patients in sinus rhythm and QRS≥120ms (mean: 160±17ms) undergoing CRT device implantation. P wave duration, PR, ePR (end of P wave to QRS onset), QT, RR–QT, JT and QRS axis and morphology were putative predictors of atrioventricular (diastolic filling time [DFT]/RR), interventricular mechanical dyssynchrony (IVMD) and left intraventricular mechanical dyssynchrony (left ventricular pre-ejection interval [PEI] and other measures) assessed by transthoracic echocardiography (TTE). Correlations between TTE and electrocardiographic measurements were examined by linear regression.ResultsStatistically significant but relatively weak correlations were found between heart rate (r=−0.5), JT (r=0.3), QT (r=0.3), RR–QT intervals (r=0.5) and DFT/RR, though not with PR and QRS intervals. Weak correlations were found between: (a) QRS (r=0.3) and QT interval (r=0.3) and (b) IVMD>40ms; and between (a) ePR (r=−0.2), QRS (r=0.4), QT interval (r=0.3) and (b) LVPEI, though not with other indices of intraventricular dyssynchrony.ConclusionsThe correlations between electrical and the evaluated mechanical indices of cardiac dyssynchrony were generally weak in heart failure candidates for CRT. These data may help to explain the discordance between electrocardiographic and echocardiographic criteria of ventricular dyssynchrony in predicting the effect of CRT