<span
style="font-weight: bold;">Bancelin, M.
J’étudie un système
appellé capillary pumped loop(CPL) ou boucle de refroidissement
à pompage capillaire. L’objectif du système est de
refroidir des éléments d’électronique de puissance
d’une chaine de traction ferroviaire. La CPL est constituée d’un
évaporateur (où sont posés les
éléments à refroidir) et où le fluide
s’évapore et d’un condenseur. Le mouvement du fluide n’est pas
assuré par une pompe comme dans les machines thermiques
traditionnelles mais par un saut de pression capillaire.
En effet, l’évaporateur est constitué dune mèche
poreuse(responsable du saut de pression capillaire) : le liquide arrive
par le bas de cette mèche, monte par capillarité et se
vaporise. La vapeur ainsi produite est évacuée vers une
conduite vapeur puis vers le condenseur où elle se condense. Le
liquide ainsi produit retourne à l’évaporateur et le
cycle recommence.
Cette technologie de refroidissement est utilisée dans le
spatial sur les satellites depuis de nombreuses années. ALSTOM
veut l’appliquer dans le ferroviaire mais cela pose des
problèmes. En effet, les flux de chaleur engendrés par
l’électronique de puissance sont tels qu’il arrive qu’une poche
de vapeur envahisse le poreux et l’assèche ce qui provoque
l’arrêt du pompage capillaire et le désamorçage de
la boucle toute entière.
Mon objectif est donc de mettre au point un modèle physique
permettant de rendre compte des écoulements(de liquide et de
vapeur) qui ont lieu au sein de la mèche poreuse. Il s’agit
concrètement d’étudier les échanges couplés
de masse et d’énergie en milieu poreux avec un changement de
phase. Ce modèle aurait pour but de prévoir le
désamorçage du système.
Je dispose chez ALSTOM d’une CPL instrumenté sur laquelle je ne
peux mesurer que des températures en divers points de la boucle
et quelques pressions. Je n’ai pas accès à la
mèche poreuse et ne dispose pas de l’instrumentation
nécessaire afin de voir ce qui s’y passe. je peux simplement
constater si le système désamorce ou pas (arrêt du
pompage capillaire)...
<span
style="font-weight: bold;">Batot, G.
We commonly know that the cell is the unit of living beings, but we
have often got the biased image of a non-understandable biologic object
: a big amino acids and proteins mixture. How does that organization
persist ? We don’t know enough, we just have a great catalog of
chemical reactions which take place inside the cell. However, since few
years, it is now possible to make real mechanical experiments which
results are meaningful and hopeful. In fact, recently a lot of elements
indicate that the rigidity of cell’s living environment is important in
it’s development [6,8]. The object of this report is to study the
influence of the substrat’s rigidity on the cell. Firstly we detailed
the existed knowledge of cellular contraction. Secondly we observed
precisely the rigidity-sensing phenomen through different experiments
where we caught a single cell between two lamellas. Finally we analyzed
how to simulate and find numerically the result of our previous
experiences.
Bimbard, E.
This report presents a way of preparing and characterizing
electromagnetic in an arbitrary coherent superposition of Fock states
up to the 2 photon level. We used the process of spontaneous parametric
down-conversion, in which a pump photon is non deterministically split
in two entangled lower frequency photons. One of the outputs is used as
trigger, in which we detect incoming photons to herald the presence of
photons in the other arm, called signal. We can then perform
measurements on the remotely prepared light in the signal channel, via
the technique of time domain homodyne tomography to characterize the
produced states. This experiment was used to produce single-photon Fock
states until now, via a simple detection of trigger photons. We
developed it to a more complex level, where making use of weak coherent
states mixed with the trigger beam, we can remotely prepare the
expected states in the signal channel and analyse them.
Blein, A.
The discovery of the cosmic microwave background (CMB) in 1965 provided
an observational basis for cosmology which was crucial in determining
our standard cosmological model, that of a spatially flat Universe
consisting mainly of dark matter. The Q/U Imaging ExperimenT (QUIET) is
designed to make very sensitive measurements of the polarization of the
CMB, which contains valuable cosmological information. We present a
brief overview of the theoretical framework for the study of CMB
anisotropies, as well as the basis for the operation of the QUIET
polarization modules. We then describe the data analysis which has been
done thus far to perform data cuts and enable us to produce anisotropy
maps and power spectrums. We have created a 50 Hz phase switch flag
which will be discussed, and an extensive study of the 50 Hz imbalance
has been made.
Bonart, J.
Les équations fondamentales de la magnétohydrodynamique -
à savoir l’équation de Navier-Stokes
généralisée par un terme décrivant la force
de Lorentz et par l’équation d’induction - mènent
à des instabilités linéaires intéressantes,
dès qu’elles sont placées dans un
référentiel tournant. Au début nous nous sommes
intéressés au profil de rotation du soleil : Nous
partions du modèle proposé dans [1] ("A simple model for
solar isorotation contours", S. Balbus 2009, MNRAS) qui tente de
reproduire le profil de rotation du soleil et en améliorant ce
modèle nous obtenions des résultats remarquables. Ensuite
nous avons généralisé les relations de dispersions
des ondes magnétohydrodynamique dans un
référentiel tournant en considérant un milieu
d’une résistance non négligeable. Cette recherche a
mené à une découverte d’un nouveau type
d’instabilité très intéressant que nous avons pu
expliquer avec un modèle de double-diffusion.
Boulier, T.
In 1960 Dzyaloshinskii, Lifshitz and Piatevskii showed that under some
circumstances the Casimir force between 2 macroscopic bodies could be
repulsive[4, 3]. This was measured last year by J. Munday[10], from the
Capasso Group (Harvard School of Engineering and Applied Sciences).
This internship was focused on designing an experiment attempting to
use this force to counterbalance gravity and make micrometer-sized
spherical particles levitate above a plate. This work was conducted
under the direction of F. Capasso, Professor at the Harvard School of
Engineering and Applied Science. The system used is the same as in the
previous experiment which measured the force (Gold - Liquid
Bromobenzene - Silica). The distance between the plate and the sphere
is measured indirectly, by observing with a holographic-microscopic
setup the modifications
in the Brownian motion of the sphere (a hydrodynamic effect due to the
very close presence of the plate, from which we can derive the
distance[8, 7]). After thinking and putting into place the setup some
levitation was qualitatively observed, but its origin has not yet been
proved to be a repulsive Casimir effect
Calandre, T.
The purpose of this internship was to characterize a two-dimensional
system composed of hard particles, which have a ‘snowman’ shape (two
sticked-together- disks, not necessarily of same diameter). Ideal
system (without any interactions, except for hard core interactions)
was modelized by computer simulation, while I tried different ’real’
systems, with different kind of interactions between particles. To do
that, I have used different interface’s properties, such as an air water
interface. The aim of this work was to characterize these unstressed
systems, in order, then, to study their behavior under stress.
Dechant, B.
In the framework of this “stage” High Harmonic Generation has been
studied both on a theoretical-conceptual and on an experimental level.
After putting the current developments into the historical context and
giving some motivations for the study of high harmonic generation, the
basics of this phenomenon are briefly reviewed. Some emphasis is put on
the crucial points of phase-matching as well as the spectral properties
of harmonic spectra and ways how to satisfy the phase-matching
condition and modify the spectra are presented. Also, the interesting
implications of high harmonic generation in the time domain - namely
the generation of sub-femtosecond pulses - are outlined. Next, the
important step from single-coulour high harmonic generation towards
two-colour high harmonic generation is made. The availability of
certain relative parameters between the fundamental and second harmonic
fields is pointed out and ways to use these new degrees of freedom to
control the properties (spectral, temporal, spatial) of high harmonics
are described. In the second part of this report, the experimental
results are presented and discussed both for the one-colour high
harmonic generation experiment with a 30fs pulse and some of the
two-colour experiments.
Filippone, M.
Le sujet de mon stage est l’étude du rapport entre l’intrication
quantique et les transitions de phase dans des systèmes de spin
total S à la limite thermo-
dynamique (S → ∞) et à température nulle. Ces
systèmes étant gouvernés par des hamiltoniens de
la forme :
H = −A S^m_x − B S^n_z
m et n entiers positifs et S_i opérateurs de spin. J’ai
déterminé les ordres et les points des transitions et
j’ai étudié comment certaines mesures d’emmêlement
sur le fondamental du système, comme la concurrence et
l’entropie d’intrication, nous renseignent sur la présence et la
nature de ces transitions. Cela est intéressant vu la
difficulté qu’il y a à definir des paramètres d’ordre
dans les systèmes sujets à transition de phase.
A cause des ambiguités des comportements de ces mesures, nous
avons décidé d’étudier aussi le comportement aux
transitions de la susceptibilité de la fidélité et,
maintenant, je suis en train d’étudier la présence
d’emmêlement à des températures non nulles.
Freulon, V.
In this experimental work, different parts of the setup required to
measure the current-phase relation in a ring containing a function made
of ferromagnetic barrier are studied. Hall crosses are first produced
in a clean room using Gallium Arsenide substrate and connected. The
measurement setup is tehn improved so as to be able to detect jumps
with a lower amplitude than 1 microT in the magnetic field. A method
based on amplitude modulation is also used. The corsses are also used
to test the magnetic field produced by a superconducting electromagnet.
It is finally shown that the considered junctions behave just like
Josephson junctions.
Guénot, D.
We study the effect of the motion of cold ion Coulomb crystals in a
linear Paul trap on coherent coupling with an optical field in a cavity
at the single photon level. After studying the different modes of
vibration of a Coulomb crystal and the ions dynamic, we show how to use
the coupling between the ions and the cavity field in order to
characterize these modes and extract some thermodynamical properties
and structural information of the plasma.
Hesse, J
L’intêret de mon project est d’apprendre plus sur l’optimisation
des activités dans le cerveau. Andrea Hasenstaub qui mesure la
consumation d’énérgie des "fast-spiking PV+ interneurons"
dans son labo. Elle a déjà fait un "single compartment
model" de ce neuron, mais elle m’a demandé de faire un
modèle plus réaliste. Son idée est que un
"fast-spiking" neurone doit en même temps être rapide et
avoir un bilan d’énergie optimale. Elle peut déjà
montrer que cela marche pas mal, mais son graphe pour l’énergie
pour un seul spike a la mauvaise courbure. Je fais le modèle
avec NEURON. Une autre question que je traîte est si les
junctions gap dans un reseau d’interneurone augmentent ou baissent
l’activité, spécialement dans le reseau des amacrine
cells dans le rétine. Alors mon projet consiste en
modélisation sur le niveau de neurons.
Jian, P.
The field of quantum optics investigates the properties of light at a
quantum level. It has successfully been used for tests of the quantum
mechanics, and for the development of quantum information science. In
particular, the field of multimode quantum imaging explores how the
spatial properties of optical images can be used for quantum optics
experiments. The goal is to reproduce in a single laser beam with
multiple spatial modes the same results as in multiple
non-copropagating beams. We report here two techniques we have
developed for the manipulation and the detection of a multimode beam.
We present a novel method for the manipulation of beams : we show that
any linear operation can be done on a multimode beam using a Spatial
Light Modulator and present an algorithm for the design of any mode
conversion. We also report how a scheme of multipixel homodyne
detection can be used for the detection of the properties of a
multimode beam.
Kral, Q.
Tout le travail est basé sur des observations d’un nuage
moléculaire en effondrement. Les premières phases de la
formation d’étoiles de grosses masses sont encore assez mal
comprise. On essaye de simuler l’effondrement d’un nuage de 1000 masses
solaires et de regarder dans quelles conditions la simulation se
rapproche le plus de se que l’on observe. L’energie thermique du nuage
est assez bien connue, on essaye par contre de voir l’impact de la
turbulence interstellaire (typiquement, l’explosion de supernovae ou
des vents provenants du milieu environnant) et du champ
magnétique sur l’effondrement de ce nuage. On peut ainsi
espèrer comprendre un peu plus en détails l’impact de ces
deux phénomènes qui d’habitude sont traités
indépendamment, et "trancher" suivant les deux scénarios
qui ont été proposés pour la formation
d’étoile de grosses masses. Pour les simulations
numériques, ramses3d est utilisé.
Kurkjian, H.
In order to achieve quantum computation on neutral atoms, for example
in an optical lattice, it is necessary to control each atomic q-bit
independently, this could never be performed to this day. During this
internship, we aimed to achieve single-atom addressing of Ytterbium
atoms in optical lattice using very strong magnetic field gradients to
spatially resolve their levels. To this day, we have shown successful
optical tweezer atom moving as well as cooling down to a temperature
below 1microK in a crossed dipole trap, and have successfully observed
global fluorescence and could even go down to observing only one
hundred atoms’ fluorescence. Checking our Signal to Noise ratio, we
estimated that with a few improvements, we are very close to
single-atom detection. Single-atom detection is naturally the first
step towards single-atom addressing. For fluorescence observing, we
notably invested time building up a new 399 nm frequency locked laser
system : some of the light obtained from an External Cavity Laser Diode
was locked to the resonance of a high finesse Ultra-Low Expansion
cavity after acousto-optic modulation, while another part was amplified
and send to the experiment for Magneto-Optical Trapping (MOT) and
fluorescence detection. Finally, I would like to highlight the
importance I attached, during this internship, in acquiring
experimental knowledge of atomic Physics basic technique, that which my
previous studies couldn’t bring me.
Lallemand, I.
Réalisé sous la direction d’Emmanuelle Gouillar t au sein
du laboratoire Surface du Verre et Interfaces (Saint-Gobain/CNRS), ce
stage visait à aborder les mécanismes du mélange
d’un fluide à seuil (carbopol) d’un point de vue
expérimental. L’utilisation de fluides possédant cette
propriété rhéologique au sein de nombreux
mélangeurs industriels motivait cette étude, pour
laquelle un protocole de mélange chaotique avait
été préalablement retenu mais dont de nombreux
aspects restaient à définir. La première par tie du
stage a été consacrée à la conception et
à l’assemblage du dispositif expérimental, dans lequel
une petite tache opaque de fluide à seuil est
mélangée à un fluide transparent de même
rhéologie selon une géométrie 2D au sein d’un
réser voir en rotation. La mesure de l’intensité
lumineuse transmise à l’aide d’une caméra permet ainsi
d’obtenir l’évolution temporelle du champ de concentration de la
tache, dont sont extraites des grandeurs statistiques permettant de
caractériser l’efficacité du mélange (moyenne et
écar t standard). Au cours de la deuxième par tie du
stage, les motifs de mélange obtenus pour différentes
configurations des vitesses de rotation des mélangeurs et du
réser voir ont d’abord été étudiés
sur les images fournies par la caméra. Dans cer tains cas, nous
avons pu obser ver la formation de lobes dont nous avons notamment
relié le nombre au rappor t de la période de rotation du
réser voir à celle des mélangeurs. Par la suite,
en dépit de la découver te tardive d’un défaut de
la table lumineuse, le ralentissement de la décroissance de
l’écar t standard du champ de concentration a pu être
observé sur plusieurs expériences, et relié
à la présence de lobes.
Lanéry, S.
My subject was about the theoretical study of temperature measurement
on very small systems (far beyond what is at the moment feasible
experimentally). Fur this purpose I modeled such a measurement process :
the "thermometer" is made of a small spins set (up to about a hundred)
and brought in contact with a bath at some temperature (in particular I
interested myself to temperatures extremely low compared to the energy
splitting).The measured value of the temperature is deduced from a
measurement of the total magnetization and the central point is to
study the fluctuations of this measured temperature, with analytical
and numerical aspects.
Le Brun, A.
This report carried out after a long internship done during the second
half of the first year of my Master within the cosmology group of the
Max Planck Institut for Astrophysics (MPA) in Garching, Germany is
about the growth of dark matter haloes in the Millennium-II simulation.
The purpose is to study some of the numerous aspects of this growth in
the framework of the standard cosmological model or ΛCDM model by
making use of the Millennium-II simulation which have been recently
completed at MPA. This growth is not only interesting by itself but
also because it can be related to the growth of the galaxies that
inhabit those haloes. My report will contain firstly a short
introduction to the cosmological standard model, some information about
the Millennium-II simulation and about galaxies, then a brief
description of the work conducted during this internship and lastly
some of the results obtained concerning the growth of the dark matter
haloes and of the galaxies they host. I was thus interested in trying
to explain why some types of galaxies were much denser in the past than
they are at the present time.
Lehe, R.
I investigate the heating of charged particles (electrons, protons,
ions) by magnetohydrodynamic turbulence, using numerical simulations.
The purpose of this work is to contribute to a research effort that aims
at understanding heating processes in astrophysical plasmas (e.g., in
the solar wind or solar corona, in accretion disks, etc...). The
simulations evolve the turbulent magnetohydrodynamic fields using the
Athena code, and compute the tra jectories of individual test particles
in those fields. A major part of my work consisted in developing the
particle integrator, and I describe it here in some detail. The results
of the simulation highlight different heating regimes depending on, for
instance, the particles’ charge-to-mass ratio, their energy, or the
resistivity of the fluid. An interpretation in terms of cyclotron
resonance and Landau resonance is discussed.
Louis, T.
This thesis concludes the internship I did at the LNB Lab under the
supervision of Anze Slozar and David Schlegel and deals with the
detection of the physical phenomenon called Baryon acoustic
oscillations. This work is part of a more general project that aims to
constraint the dynamics of the Universe to ultimately better understand
the dark energy. This field is right on the boundaries between theory
and observation, for previous observation projects have led to the
acquiring of a great quantity of theoretical data. This thesis focuses
on finding better ways to treat those data and to extract the most
relevant ideas.
Nicolas, T.
In this report, I present recent advances in the building of a new
cooling device for atoms or molecules, based on Helium buffer-gas
cooling. We aim at temperatures ranging from 4K to 15K, and an
interseting feature of our device is its size : about 8” wide for 16”
high, small compared to other experiments on cold atoms/molecules,
which typical size is usually around 1m. The species to be cooled are
first heated until their vapor pressure is high enough, and then guided
to a cold Copper cell using a continuous Helium flow : this is the buffer
gas. In the short term, we aimed at obtaining a continuous, cold,
optically coherent, high optical density (around 100) and clean
(compared to laser ablation sources) flow of Rubidium. The optical
coherence of the sample was to be demonstrated using EIT
(Electromagnetically Induced Transparency). When the device is ready
and when its versatility is proven, it is going to be shared with other
research groups to test various ideas that are now theoretically
studied. These ideas range from quantum information and cold chemistry
to production of lasers with interesting frequencies, like 123 nm,
corresponding to the Lyman α line in Hydrogen. After 6 months, we had
built and assembled all the various parts of the cryostat, and cooled
the first samples of Rubidium. The lowest temperature we measured was
21K, but with a very low optical density of 0.4. We could increase the
optical density to 2.9 by increasing the Helium flow, but this was to
the expense of temperature, which reached 400K. This is because the
Helium flow was too high to allow enough time to thermalize with the
walls and then cool the atomes of Rubidium. However one of our
objectives has been achieved since the source is effectively clean,
stable and continuous : one absorption signal was measured stable for
about 20 minutes. New improvements are now being done on the device to
be able to control the density of the buffer gas in the cell (very
important parameter) without changing the flow (since too high flows
don’t allow enough time for the buffer gas to thermalize).
<span
style="font-weight: bold;">Oger, G.
I present a numerical model first introduced by Vicsek et al. [3] for
the collective motion of self-propelled particles. In this model a
group of point-wise particles move at each time step by taking the
average direction of their neighboring particles, with a random
perturbation (noise). It can be seen as a non-equilibrium equivalent of
models like the Ising model for spins. First I investigate the dynamic
behavior and phase transition of the system (from random motion to
orientationnaly ordered motion) to find the results of Vicsek, with a
lot of similarities to equilibrium systems. Then I introduce a new
parameter in the system : hydrodynamic interactions to take into account
the fluid particles are moving in, and I try to characterize their
action on the order of the system.
Paillat, S.
The experiments conducted during this training course constitute a
first investigation of a phenomenon which can appear in certain
volcanic eruptions : eruptions of gas without magma. The forecast of
these types of dangerous eruptions is a challenge for volcanologists.
Experiments using materials analogous to the crust (gelatine) are set
up. The aim is to measure the material surface deformation caused by
the movement of gas through this gelatine. Air is simply injected
though the gelatine with a pressure difference between a tank
containing the gelatine and the laboratory and the acceleration of the
gelatine near its surface is measured.
Whereas a continuous air flow is injected, the flow through the
gelatine is discontinuous. Slugs of air are observed reaching
periodically the surface of the gelatine. The movement of these slugs
and their release at the gelatine surface are directly correlated with
the period measured for the surface acceleration. Other types of flow
are observed but not analysed in this report. The experimental
observations show that the period of the surface oscillation varies
systematically with the rigidity of the gelatine (characterised by the
Young’s modulus) and the volumetric flowrate of the gas through the
crack formed. In addition, the horizontal dimensions of the crack
(width and thickness) increase systematically with gas volumetric
flowrate, whereas the vertical dimension of the crack is related to the
gelatine depth and rigidity, and the initial conditions of gas
injection. Dimensional considerations are used to identify an
approximate relationship that explains the systematic experimental
observations. The ratio of the volume of gas in each gas slug and the
period of oscillation is simply proportional to the initial continuous
volumetric gas flux, as expected. A range of possible pressure scales
exist for the flow and elastic deformation, and it is found that the
ratio of elastic pressure of the gelatine and the pressure required to
open the crack by the flow control the flowrate and oscillation period.
The longer horizontal dimension of the crack emerges as the length
scale that controls the flow, and two dimensionless groups formed from
these parameters satisfactorily collapse the experimental data. Further
quantitative analysis requires more experimental observations, which
will also help to constrain the processes that open the crack and
partition the initially continuous flow into discrete gas
slugs.
Parrain, D.
Quantum optics investigates the behaviour of light at a quantum level.
Laser is an essential tool in this field because it delivers spatially
and temporaly coherent light. Optical cavities or resonators are used
in order to control modes delivered by the laser. A cavity is said
locked when it delivers continuously a given mode. This is realised by
a feedback control on the lenght of the cavity. Usually, this feedback
control is done with analog instrument. This report aims at showing a
manner of digitally locking an optical cavity. the digital program we
developped also permits to analyse the quality of the lock in order to
improve it.
Piatecki, S.
I devoted this internship to studying how the ground state of a lattice
of classical antiferromagnetically coupled spins can be affected by the
presence of electrons. The model I used let electrons hop from site to
site with a tight-binding hamiltonian ; electrons interact with the
local moments according to Hund’s coupling, which tends to align the
local spins parallel to their spins. I first concentrated on the
interplay of electrons with four spins coupled two by two, then with
spins on a checkerboard lattice. Eventually, I developed a description
of the ground-state in terms of loops.
Ramananarivo, S.
A landslide happens when the soil resistance along a failure surface
isn’t sufficient to counteract the moving forces. Previous studies
showed that the presence of roots, even dead ones, increases the soil
shearing resistance. The goal of this project is to study the
reinforcement effect of roots with regard to natural time evolution of
the growing root system. The root architecture and several mechanical
properties related to soil stability will be measured over a growing
period, in conjunction with the evolution of soil shear resistance.
Raynaud, R.
The study of transient detectability both requires the simulation of a
light curve according to a model of transients, and the definition of an
observing strategy according to LOFAR technical specifications. Then,
the efficiency of a strategy is quantified via the determination of a
probability of detection. The analyse of the level curves of the
probability as function of the flux scale and the time scale of the
source enables to find the best strategy for different transients. The
results show a correlation between the probabilities of detection and
characterisation : for fast transients, the former becomes constant
while the latter falls near zero. Moreover, if the probability of
detection just mainly depends on the sensitivity of the telescope—which
varies with the bandwidth, the frequencies of observation and the
integration time—, the probability of characterisation is in addition
sensitive both to the whole duration of observation and to the time
elapsed between each data point.
Reys, V.
The following report describes how the Schwinger-Dyson formalism may be
used to understand the dynamics of the ghosts and gluons in the
Gribov-Zwanziger action. An overview of this theory will be presented,
and then we will establish the Schwinger-Dyson equations of these
fields. These equations will be used to obtain the values of the
critical infrared exponents of the various propagators.
Solard, G.
We study conjugate operators to the energy-momentum operators in
standard free massless quantum field theory. They are conjugate in the
sense that they verify non-trivial commutation relations with the
energy-momentum operators. Thus one can say that they are coordinate
operators. We first show a way to build such operators starting from the
generators of conformal transformations which give them a natural role
in the conformal algebra. But since some difficulties arise from this
definition, we will settle for simpler and less constrained operators.
We then use these newly defined operators to device an S-matrix in
curved space. Finally, we try to construct fields using these new
coordinates operators.
Stril, A.
The Joint Dark Energy Mission (JDEM) will probe the expansion rate of
the universe through di_erent techniques (graviational weak lensing,
supernovae dimming, and baryon acoustic oscillations). The measurements
should allow to rule out or con_firm some dark energy models
(cosmological constant, quintessence, etc). We use the Fisher matrix
formalism to quantify the merit of this experiences and assess their
combined power in constraining the dark energy equation of state and
the gravitational growth of structure.
I am also working on topics related to the Sunyaev-Zel’dovich (SZ)
effect such as probing the Lemaître-Tolman-Bondi model and trying
to establish a thermal SZ signal - halo mass relation of a galaxy
cluster catalog.
Tourkine, P.
The work presented here is split into two parts. The first part
concerns Stephan adhesion for Newtonian and yield stress fluids. This
Stephan adhesion is the reason why two rigid plates confining some
fluid are hard to pull apart. This part deals with the adhesive
strength of those material from the theoretical and experimental point
of view. It also presents the instabilities associated with these
adhesive pull of tests, including cavitation and the Saffman-Taylor
instability, known as fingering. The second and main part presents the
work done with magnetorheological fluids. We discovered a new kind of
instability, that arises in the same pull of adhesive tests just like
the fingering, which we call flowering. We analyse this instability
mostly from the phenomenological point of view, in a simpler wall like
geometry.
<span
style="font-weight: bold;">Valon, L.
Up until now, the time dependent properties of the cell have been
described using a viscoelastic formulation. During my internship, I
validated a new description of cell mechanics called poroelasticity. In
contrast to the single phase viscoelastic description of the cell,
poroelasticity models the cell as a biphasic system constituted of a
solid porous meshwork bathed in a liquid phase. In my experiments, I
used an atomic force microscope to apply a localized external
mechanical stress onto the cell and measure ensuing cellular
relaxation. I showed that the poroelastic formulation fits the
experimental data significantly better than the viscoelastic model at
both short and long time-scales. In addition, the poroelastic
formulation can also accurately model major changes in the cell
physiology. I showed that the cellular fluid fraction played a major
role in the time-dependent properties of the cell and that actin
filaments were more important than microtubules in modulating cellular
poroelasticity. This poroelastic description should permit a better
understanding of the role of the cytoskeleton, the fluid phase and
macromolecular crowding in cell mechanics. All of these elements are
involved in internal diffusivity and therefore may play an important
role for the cell motility and cellular shape changes during the cell
cycle and especially metaphase.