349 research outputs found
Tests pour la dépendance entre les sections dans un modÚle de Poisson
Les simulations et figures ont été réalisées avec le logiciel R.Pour des données de panel, les mesures répétées dans le temps peuvent remettre
en cause lâhypothĂšse dâindĂ©pendance entre les individus. Des tests ont Ă©tĂ©
dĂ©veloppĂ©s pour pouvoir vĂ©rifier sâil reste de la dĂ©pendance entre les rĂ©sidus dâun
modÚle. Les trois tests que nous présentons dans ce mémoire sont ceux de Pesaran
(2004), Friedman (1937) et Frees (1995). Ces trois tests se basent sur les résidus
(et leurs corrélations) et ont été construits pour des modÚles linéaires. Nous voulons
Ă©tudier dans ce mĂ©moire les performances de ces trois tests dans le cadre dâun
modĂšle linĂ©aire gĂ©nĂ©ralisĂ© de Poisson. Dans ce but, on compare tout dâabord leurs
performances (niveaux et puissances) pour deux modĂšles linĂ©aires, lâun ayant un
terme autorĂ©gressif et lâautre non. Par la suite, nous nous intĂ©ressons Ă leurs performances
pour un modĂšle linĂ©aire gĂ©nĂ©ralisĂ© de Poisson en sâinspirant de Hsiao,
Pesaran et Pick (2007) qui adaptent le test de Pesaran (2004) pour un modĂšle
linĂ©aire gĂ©nĂ©ralisĂ©. Toutes nos comparaisons de performances se feront Ă lâaide de
simulations dans lesquelles nous ferons varier un certain nombre de paramĂštres
(nombre dâobservations, force de la dĂ©pendance, etc.). Nous verrons que lorsque
les corrĂ©lations sont toutes du mĂȘme signe, le test de Pesaran donne en gĂ©nĂ©ral
de meilleurs résultats, à la fois dans les cas linéaires et pour le modÚle linéaire
gĂ©nĂ©ralisĂ©. Le test de Frees prĂ©sentera de bonnes propriĂ©tĂ©s dans le cas oĂč le signe
des corrélations entre les résidus alterne.For panel data, repeated measures over time can challenge the hypothesis of
dependence between subjects. Tests were developped in order to assess if some
dependence remains among residuals. The three tests we present in this master
thesis are from Pesaran (2004), Friedman (1937) and Frees (1995). These three
tests, constructed specifically for linear models, are based on the residuals generated
from models (and their correlations). We wish to study in this master thesis
the performances of these three tests in the case of generalized linear Poisson
models. For that goal, we compare them between each other (level, power, etc.)
using two linear models, one with an autoregressive term and the other without.
Next, inspired by Hsiao, Pesaran and Pick (2007) who adapt the test from Pesaran
(2004), we will study their performances in a generalized Poisson model.
All of our comparisons are done with simulations by modifying some variables
(number of observations, strength of the dependence). We will observe that when
the correlation is always of the same sign, Pesaranâs test is the best in most cases,
for the linear models and the generalized linear model. Freesâ test will show good
performances when the sign of the correlations alternates
Impacts of a power-law non-thermal electron tail on the ionization and recombination rates
We have investigated the effects of a non-thermal electron population on the
ionization and recombination rates. The considered electron distribution is
defined as a Maxwellian function below a break energy E_b and as a power-law
function of index alpha above this energy. We have calculated the collisional
(direct and excitation autoionization) ionization coefficient rates as well as
the (radiative and dielectronic) recombination rates. Practical methods are
given to calculate these rates in order to be easily included in a computer
code. The ionization rates are very sensitive to the non-thermal electron
population and can be increased by several orders of magnitude depending on the
temperature and parameters of the power-law function (E_b and alpha). The
non-thermal electrons have a much weaker effect on the (radiative and
dielectronic) recombination rates. We have determined the mean electric charge
of elements C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni for different values of
the break energy and power-law index. The ionization balance is affected
significantly, whereas the effect is smaller in ionizing plasmas.Comment: 16 pages, 19 figures, accepted for publication in A&
Ethylenedithio--Tetrathiafulvalene--Helicenes: Electroactive Helical Precursors with Switchable Chiroptical Properties
International audienceElectroactive fused ethylenedithio-tetrathiafulvalene-[4]helicene and -[6]helicenes have been synthesized through a strategy involving the preparation of 2,3-dibromo-helicene derivatives as intermediates. The dihedral angles between the terminal helicenes, as determined by single crystal X-ray analyses, amount to 22.7° and 50.7° for the [4]helicene and [6]helicene, respectively. The solid state architectures show interplay between S···S and ··· intermolecular interactions. The chiroptical properties of the enantiopure EDT-TTF-[6]helicene derivatives have been investigated and supported by TD DFT calculations. Remarkable redox switching of the circular dichroism signal between the neutral and radical cation species has been achieved
Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983
An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044,
is presented. Gas density and temperature profiles are calculated for the inner
500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness
profile are well described with a beta model with beta=0.74, but the central
regions require the introduction of a second component. The temperature profile
is flat at the exterior with a slight dip towards the centre. The total mass
profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW
profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B
ratio profile shows that, at large scale, light traces mass to a reasonable
extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with
mass observed in the optical. The M_Fe/L_B ratio is about two times less than
that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to
level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties
of the emission measure profile are consistent with the empirical relation
\mgas \propto \Tx^{1.94}, and not with the self-similar relation \mgas \propto
\Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot
cluster A1413 shows that the profiles are well scaled using the empirically
determined relation S \propto \Tx^{0.65}, suggesting that the slope of the S-T
relation is shallower than in the self-similar model. The form of the entropy
profiles is remarkably similar, and there is no sign of a larger isentropic
core in the cooler cluster. These data provide powerful agruments against
preheating models. In turn, there is now increasing observational support for a
trend of f_gas with system mass, which may go some way towards explaining the
observed scaling behaviour. (Abridged.)Comment: Final refereed version to appear in A&A; Figs 2, 7, 11 and 12 are low
re
Light chain amyloidosis
Light chain amyloidosis (AL) is the most common subtype of amyloidosis except wild type tranthyretine amyloidosis and is caused by the deposition of misfolded monoclonal light chains of immunoglobulins produced by a monoclonal B cell, mainly of plasma cell origin. Affected patients may present with amyloidosis alone or in association with other plasma cell or lymphoid dyscrasias (multiple myeloma, Waldenström macroglobulinemia or other B lymphoma). Diagnosis of amyloidosis is histological. Cardiac and renal involvement are the most frequent and present in nearly two thirds of patients as hypertrophic heart disease and/or nephrotic syndrome, respectively. AL amyloidosis is a clonal plasma cell disorder and is treated by chemotherapy dedicated to eradicate the underlying clone. Assessment of the severity of the disease with the Mayo Clinic score is used to guide the choice of treatment. First-line treatment combine bortezomib, cyclophosphamide or melphalan and dexamethasone for severe cases, plus or minus daratumumab, an anti-CD-38 monoclonal antibody, following the excellent results of the ANDROMEDA phase 3 study; mild cases can still benefit from melphalan and dexamethasone
Size-Selective Separation of Gold Nanoparticles using Isoelectric Focusing Electrophoresis (IEF)
Isoelectric focusing in a polyacrylamide pH gradient gel is used to analyze the size distribution of gold nanoparticles synthesized by a chemical route with mercaptosuccinic acid as a ligand. The isoelectric point of the nanoparticles is shown to be size dependent, allowing fractionation by electrophoresis. Each fraction has a narrow size distribution with a standard deviation lower than 0.4 nm
AMRA: Augmented Reality Assistance for Train Maintenance Tasks
International audienceThe AMRA project, carried out by a consortium including industrials and research partners, aims at implementing an Augmented Reality (AR) system for mobile use in industrial applications such as train maintenance and repairs in industrial sites. The adopted solution is a video see-through system where a tablet-PC is used as an augmented window. The overall architecture of a prototype is unfolded, and its key points are detailed. For instance, a visual registration system has been developed to accurately overlay a video stream with information. A robust, real time registration, using a single camera tied to the tablet-PC, is performed. Besides, a hierarchical description of maintenance procedure is set up and enriched by new media such as photos, video and/or 3D models. These 3D models have been specially tailored to meet maintenance tasks requirements. The obtained multimedia contents allow easy access to technical documentation through a man machine interface managing a multimedia engine. All these features have been combined in the AMRA prototype which have been evaluated by a maintenance operator
project: III. Gas mass fraction shape in high redshift clusters
We study the gas mass fraction, behavior in
project. The typical shape of high redshift galaxy
clusters follows the global shape inferred at low redshift quite well. This
result is consistent with the gravitational instability picture leading to self
similar structures for both the dark and baryonic matter. However, the mean
XMM$ clusters, the apparent gas
fraction at the virial radius is consistent with a non-evolving universal value
in a high matter density model and not with a concordance.Comment: Accepted, A&A, in pres
Salt Removal During Off-GelTM Electrophoresis of Protein Samples
The Off-Gelâą technology was recently described for protein fractionation in a solution placed on top of an immobilized pH gradient gel. In addition, this process was found to remove salts from the biological samples to analyze. This desalting effect is studied experimentally in a conductometric prototype cell. A simplified analytical model is developed to understand this process and a good agreement is found with the conductivity measurements. To illustrate the desalting of a biological sample, a 1 mg·mLâ1 solution of ÎČ-lactoglobulin A in 0.1 M NaCl is subjected to electrophoresis in a single compartment Off-Gelâą cell. The analysis of the resulting sample by ESI-MS demonstrates the effective removal of salt. A finite element diffusion-migration model is also used to illustrate how the nonuniformity of the electric field in the cell, associated with the salt migration, can slow down the desalting process
Relativistic electron beams above thunderclouds
Non-luminous relativistic electron beams above thunderclouds have been detected by the radio signals of low frequency &sim;40â400 kHz which they radiate. The electron beams occur &sim;2â9 ms after positive cloud-to-ground lightning discharges at heights between &sim;22â72 km above thunderclouds. Intense positive lightning discharges can also cause sprites which occur either above or prior to the electron beam. One electron beam was detected without any luminous sprite which suggests that electron beams may also occur independently of sprites. Numerical simulations show that beams of electrons partially discharge the lightning electric field above thunderclouds and thereby gain a mean energy of &sim;7 MeV to transport a total charge of &sim;â10 mC upwards. The impulsive current &sim;3 &times; 10<sup>&minus;3</sup> Am<sup>â2</sup> associated with relativistic electron beams above thunderclouds is directed downwards and needs to be considered as a novel element of the global atmospheric electric circuit
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