315 research outputs found
Following red blood cells in a pulmonary capillary
The red blood cells or erythrocytes are biconcave shaped cells and consist
mostly in a membrane delimiting a cytosol with a high concentration in
hemoglobin. This membrane is highly deformable and allows the cells to go
through narrow passages like the capillaries which diameters can be much
smaller than red blood cells one. They carry oxygen thanks to hemoglobin, a
complex molecule that have very high affinity for oxygen. The capacity of
erythrocytes to load and unload oxygen is thus a determinant factor in their
efficacy. In this paper, we will focus on the pulmonary capillary where red
blood cells capture oxygen. We propose a camera method in order to numerically
study the behavior of the red blood cell along a whole capillary. Our goal is
to understand how erythrocytes geometrical changes along the capillary can
affect its capacity to capture oxygen. The first part of this document presents
the model chosen for the red blood cells along with the numerical method used
to determine and follow their shapes along the capillary. The membrane of the
red blood cell is complex and has been modelled by an hyper-elastic approach
coming from Mills et al (2004). This camera method is then validated and
confronted with a standard ALE method. Some geometrical properties of the red
blood cells observed in our simulations are then studied and discussed. The
second part of this paper deals with the modeling of oxygen and hemoglobin
chemistry in the geometries obtained in the first part. We have implemented a
full complex hemoglobin behavior with allosteric states inspired from
Czerlinski et al (1999).Comment: 17 page
Existence of global strong solutions to a beam-fluid interaction system
We study an unsteady non linear fluid-structure interaction problem which is
a simplified model to describe blood flow through viscoleastic arteries. We
consider a Newtonian incompressible two-dimensional flow described by the
Navier-Stokes equations set in an unknown domain depending on the displacement
of a structure, which itself satisfies a linear viscoelastic beam equation. The
fluid and the structure are fully coupled via interface conditions prescribing
the continuity of the velocities at the fluid-structure interface and the
action-reaction principle. We prove that strong solutions to this problem are
global-in-time. We obtain in particular that contact between the viscoleastic
wall and the bottom of the fluid cavity does not occur in finite time. To our
knowledge, this is the first occurrence of a no-contact result, but also of
existence of strong solutions globally in time, in the frame of interactions
between a viscous fluid and a deformable structure
Science results from the imaging Fourier transform spectrometer SpIOMM
SpIOMM is an imaging Fourier transform spectrometer designed to obtain the
visible range (350 to 850 nm) spectrum of every light source in a circular
field of view of 12 arcminutes in diameter. It is attached to the 1.6-m
telescope of the Observatoire du Mont Megantic in southern Quebec. We present
here some results of three successful observing runs in 2007, which highlight
SpIOMMs capabilities to map emission line objects over a very wide field of
view and a broad spectral range. In particular, we discuss data cubes from the
planetary nebula M27, the supernova remnants NGC 6992 and M1, the barred spiral
galaxy NGC7479, as well as Stephans quintet, an interacting group of galaxies.Comment: 10 pages, 7 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II", SPIE conference, Marseille, 23-28 June
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Aerosols in the lung: multi-domain transport and coupling
International audienceIn this paper, we present a framework that couples three-dimensional (3D) to one-dimensional (1D) transport models to predict particle deposition in the respiratory airways throughout respiration. During respiration, the time dependent flow rate and particle concentration can be passed between the domains (inspiration: 3D to 1D, expiration: 1D to 3D). This framework enables us to predict particle transport and deposition in the whole lung and throughout both inspiration and expiration
The motion of a fluid-rigid disc system at the zero limit of the rigid disc radius
We consider the two-dimensional motion of the coupled system of a viscous
incompressible fluid and a rigid disc moving with the fluid, in the whole
plane. The fluid motion is described by the Navier-Stokes equations and the
motion of the rigid body by conservation laws of linear and angular momentum.
We show that, assuming that the rigid disc is not allowed to rotate, as the
radius of the disc goes to zero, the solution of this system converges, in an
appropriate sense, to the solution of the Navier-Stokes equations describing
the motion of only fluid in the whole plane. We also prove that the trajectory
of the centre of the disc, at the zero limit of its radius, coincides with a
fluid particle trajectory.Comment: 29 pages, 0 figure
Airflow and Particle Deposition Simulations in Health and Emphysema: From In Vivo to In Silico Animal Experiments
International audienceImage-based in-silico modeling tools provide detailed velocity and particle deposition data. However, care must be taken when prescribing boundary conditions to model lung physiology in health or disease, such as in emphysema. In this study, the respiratory resistance and compliance were obtained by solving an inverse problem; a 0D global model based on healthy and emphysematous rat experimental data. Multi-scale CFD simulations were performed by solving the 3D Navier Stokes equations in an MRI-derived rat geometry coupled to a 0D model. Particles with 0.95 um diameter were tracked and their distribution in the lung was assessed. Seven 3D-0D simulations were performed: healthy, homogeneous, and five heterogeneous emphysema cases. Compliance (C) was significantly higher (p = 0.04) in the emphysematous rats (C = 0.37 +/- 0.14 cm^3 / cmH_2O) compared to the healthy rats (C = 0.25 +/- 0 0.04 cm^3 / cmH_2O), while the resistance remained unchanged (p = 0.83). There were increases in airflow, particle deposition in the 3D model, and particle delivery to the diseased regions for the heterogeneous cases compared to the homogeneous cases. The results highlight the importance of multi-scale numerical simulations to study airflow and particle distribution in healthy and diseased lungs. The effect of particle size and gravity were studied. Once available, these in-silico predictions may be compared to experimental deposition data
Introduction
This collected volume gives a concise account of the most relevant scientific results of the COST Action IS1104 "The EU in the new complex geography of economic systems: models, tools and policy evaluation", a four-year project supported by COST (European Cooperation in Science and Technology). It is divided into three parts reflecting the different
perspectives under which complex spatial economic systems have been studied: (i) the Macro perspective looks at the interactions among international or regional trading partners; (ii) the Meso perspective considers
the functioning of (financial, labour) markets as social network structures; and, finally, (iii) the Micro perspective focuses on the strategic choices of single firms and households. This Volume points also at
open issues to be addressed in future research
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