The global carbon cycle and its changes over glacial–interglacial cycles

Carbon is an essential element for life, food and energy. It is also a key component of greenhouse gases and, thus, plays an important role in past and present climatic changes

Exploration de l'écoulement dans un échangeur de chaleur tubulaire par vélocimétrie par images de particules

8 pagesL'étude du champ de vitesse à l'intérieur d'une maquette d'échangeur de chaleur en eau à l'échelle 1 est réalisée par vélocimétrie par images de particules. La géométrie tridimensionnelle de l'installation, ses faibles dimensions et la nature fortement instationnaire de l'écoulement imposent le choix de ce moyen de mesure. Un filtrage est appliqué aux images enregistrées, avant traitement par un algorithme de flot optique utilisant une programmation dynamique. Les déformations dues à la présence de dioptres optiques sont corrigées. Les mesures mettent en évidence de fortes variations de débit à travers les différents tubes de l'échangeur et un caractère non établi de l'écoulement. L'analyse des champs turbulents confirme ce comportement

A Mechanical Model to Interpret Cell-Scale Indentation Experiments on Plant Tissues in Terms of Cell Wall Elasticity and Turgor Pressure

International audienceMorphogenesis in plants is directly linked to the mechanical elements of growing tissues, namely cell wall and inner cell pressure. Studies of these structural elements are now often performed using indentation methods such as atomic force microscopy. In these methods, a probe applies a force to the tissue surface at a subcellular scale and its displacement is monitored, yielding force-displacement curves that reflect tissue mechanics. However, the interpretation of these curves is challenging as they may depend not only on the cell probed, but also on neighboring cells, or even on the whole tissue. Here, we build a realistic three-dimensional model of the indentation of a flower bud using SOFA (Simulation Open Framework Architecture), in order to provide a framework for the analysis of force-displacement curves obtained experimentally. We find that the shape of indentation curves mostly depends on the ratio between cell pressure and wall modulus. Hysteresis in force-displacement curves can be accounted for by a viscoelastic behavior of the cell wall. We consider differences in elastic modulus between cell layers and we show that, according to the location of indentation and to the size of the probe, force-displacement curves are sensitive with different weights to the mechanical components of the two most external cell layers. Our results confirm most of the interpretations of previous experiments and provide a guide to future experimental work

Implicit FEM and Fluid Coupling on GPU for Interactive Multiphysics Simulation

International audienceWe present a method to implement on the GPU an implicit FEM solver which is fast and stable enough to handle interactions and collisions. We combine this method with GPU-based fluids and collision detection to achieve interactive multiphysics simulations entirely running on the GPU

Stable Constrained Dynamics

International audienceWe present a unification of the two main approaches to simulate deformable solids, namely elasticity and constraints. Elasticity accurately handles soft to moderately stiff objects, but becomes numerically hard as stiffness increases. Constraints efficiently handle high stiffness, but when integrated in time they can suffer from instabilities in the nullspace directions, generating spurious transverse vibrations when pulling hard on thin inextensible objects or articulated rigid bodies. We show that geometric stiffness, the tensor encoding the change of force directions (as opposed to intensities) in response to a change of positions, is the missing piece between the two approaches. This previously neglected stiffness term is easy to implement and dramatically improves the stability of inextensible objects and articulated chains, without adding artificial bending forces. This allows time step increases up to several orders of magnitude using standard linear solvers

Confidence in College Athletics

I researched the processes used by intercollegiate athletes to maintain confidence throughout their sports career, including how they prepared for games/competitions, how they dealt with pressures, and how other factors affected their performance and thought process during games. For this research, I created and administered an online survey to 70 college athletes across four sports. I found that many things gave the athletes confidence in themselves to play their sport such as family and preparation. However, some things also lowered the respondents’ confidence levels such as failing and negativity. Results imply that athletes, for the most part, seem confident and optimistic. The majority of participants had past struggles with confidence, but were able to overcome them with the support of teammates, coaches, family, and friends