797 research outputs found
Masse grasse, masse maigre et sensibilité à l'insuline chez les femmes obèses postménopausées tolérantes et intolérantes au glucose
L'obésité est associée à une augmentation des problèmes métaboliques, cardiovasculaires et orthopédiques, ainsi qu'à un risque accru de cancer. En ce sens, l'augmentation de la masse grasse, ainsi que sa redistribution au niveau abdominal, et principalement viscéral, observées au cours du vieillissement se révèlent être des problématiques de santé de premier ordre. Chez la femme, le changement de statut hormonal causé par la cessation de la sécrétion d'oestrogènes favorise grandement ce problème. Plus spécifiquement, l'obésité viscérale étant la plus fortement liée au développement de désordres métaboliques, la majorité des études ont porté sur la relation entre ce compartiment adipeux et le métabolisme du glucose chez diverses populations. Cependant, les résultats d'études récentes ont porté notre attention sur les relations possibles entre la masse grasse sous-cutanée, la masse maigre et la sensibilité à l'insuline. Étonnamment, nous avons constaté que peu d'études se sont penchées sur les relations entre leurs changements et ceux de la sensibilité à l'insuline suite à une intervention de perte de poids par restriction calorique, cette méthode étant l'intervention la plus utilisée pour réduire le poids corporel. Aussi, des études ont rapporté une influence de l'état initial du métabolisme du glucose sur l'effet de ce type d'intervention sur les variables métaboliques. L'objectif du présent projet, était principalement d'étudier les relations entre les changements de la sensibilité à l'insuline et les changements de la asse [i.e. masse] maigre et de la masse grasse suite à un programme de perte de poids par restriction calorique chez les femmes obèses postménopausées tolérantes et intolérantes au glucose. Pour se faire, nous avons utilisé un échantillon 84 femmes postménopausées en surpoids ou obèses (indice de masse corporelle moyen de 32,7 « 4,5 kg/m 2 ). Ces femmes devaient être postménopausées, avoir un indice de masse corporelle supérieure à 27 kg/ m[indice supérieur 2] sédentaires, non fumeuses et ne devaient pas présenter de complications de santé significatives. Cet échantillon a été divisé en deux groupes selon le statut de tolérance au glucose obtenu par le biais d'une surcharge orale de glucose de 75 g réalisée avant le début de l'intervention. Les participantes ont été catégorisées en deux groupes selon leur niveau de glucose à 2 heures, un groupe de femmes tolérantes au glucose ou normoglycémiques (TG) : glucose plasmatique 7,8 mmol/L ; n= 16. Les mesures de la masse grasse et de la masse maigre ont été obtenues par absorption biphotonique à rayons x. La masse grasse viscérale et sous-cutanée ont été mesurées à l'aide de la tomographie axiale, tandis que la sensibilité à l'insuline a été mesurée lors d'un clamp euglycémique-hyperinsulinémique. Avant l'intervention, nous avons observé des associations négatives entre la sensibilité à l'insuline et les mesures de la masse maigre chez les femmes ayant une tolérance au glucose normale. Cependant, chez les femmes présentant une intolérance au glucose aucune association n'a été observée. Ces résultats suggèrent des différences au niveau de la physiologie musculaire chez les femmes intolérantes au glucose. Nous avons observé des diminutions significatives de la masse grasse totale, ainsi que de la masse grasse viscérale et sous-cutanée suite à l'intervention dans les 2 groupes. Cependant, aucune diminution significative de la masse maigre, ni amélioration de la sensibilité à l'insuline n'ont été observées suite à l'intervention. Finalement, nous n'avons pas noté de relation significative entre les changements de masse maigre et les changements de la sensibilité à l'insuline. L'étude des relations entre le niveau de masse maigre et le métabolisme du glucose requiert davantage d'investigation afin de mieux comprendre les divers facteurs impliqués dans ses altérations. Nos résultats suggèrent qu'il demeure approprié d'encourager la perte de poids par modification des habitudes de vie chez les femmes obèses dans l'optique d'amélioration du profil métabolique
Evolution of Genes Neighborhood Within Reconciled Phylogenies: An Ensemble Approach
Context
The reconstruction of evolutionary scenarios for whole genomes in terms of genome rearrangements is a fundamental problem in evolutionary and comparative genomics. The DeCo algorithm, recently introduced by Bérard et al., computes parsimonious evolutionary scenarios for gene adjacencies, from pairs of reconciled gene trees. However, as for many combinatorial optimization algorithms, there can exist many co-optimal, or slightly sub-optimal, evolutionary scenarios that deserve to be considered.
Contribution
We extend the DeCo algorithm to sample evolutionary scenarios from the whole solution space under the Boltzmann distribution, and also to compute Boltzmann probabilities for specific ancestral adjacencies.
Results
We apply our algorithms to a dataset of mammalian gene trees and adjacencies, and observe a significant reduction of the number of syntenic conflicts observed in the resulting ancestral gene adjacencies
On the Age of the Widest Very Low Mass Binary
We have recently identified the widest very low-mass binary (2M0126AB),
consisting of an M6.5V and an M8V dwarf with a separation of ~5100 AU, which is
twice as large as that of the second widest known system and an order of
magnitude larger than those of all other previously known wide very low-mass
binaries. If this binary belongs to the field population, its constituents
would have masses of ~0.09 Msun, at the lower end of the stellar regime.
However, in the discovery paper we pointed out that its proper motion and
position in the sky are both consistent with being a member of the young (30
Myr) Tucana/Horologium association, raising the possibility that the binary is
a pair of ~0.02 Msun brown dwarfs. We obtained optical spectroscopy at the
Gemini South Observatory in order to constrain the age of the pair and clarify
its nature. The absence of lithium absorption at 671 nm, modest Halpha
emission, and the strength of the gravity-sensitive Na doublet at 818 nm all
point toward an age of at least 200 Myr, ruling out the possibility that the
binary is a member of Tucana/Horologium. We further estimate that the binary is
younger than 2 Gyr based on its expected lifetime in the galactic disk.Comment: accepted for publication in The Astrophysical Journa
Novel scaling behavior of the Ising model on curved surfaces
We demonstrate the nontrivial scaling behavior of Ising models defined on (i)
a donut-shaped surface and (ii) a curved surface with a constant negative
curvature. By performing Monte Carlo simulations, we find that the former model
has two distinct critical temperatures at which both the specific heat
and magnetic susceptibility show sharp peaks.The critical exponents
associated with the two critical temperatures are evaluated by the finite-size
scaling analysis; the result reveals that the values of these exponents vary
depending on the temperature range under consideration. In the case of the
latter model, it is found that static and dynamic critical exponents deviate
from those of the Ising model on a flat plane; this is a direct consequence of
the constant negative curvature of the underlying surface.Comment: 11 pages 5 figure
Association between Abdominal Fat (DXA) and Its Subcomponents (CT Scan) before and after Weight Loss in Obese Postmenopausal Women: A MONET Study
Introduction. Subcutaneous fat (ScF) and visceral fat (VF) measurements using CT scan are expensive and may imply significant radiation doses. Cross-sectional studies using CT scan showed that ScF and VF are significantly correlated with abdominal fat measured by DXA (AF-DXA). The association has not been studied after a weight loss. Objective. To determine (1) the associations between AF-DXA and ScF and VF before and after weight loss and (2) the associations between their changes. Methods. 137 overweight/obese postmenopausal women were divided in two groups (1-caloric restriction or 2-caloric restriction + resistance training). AF was assessed using DXA and CT scan. Results. Correlations between AF-DXA and ScF (before: r = 0.87, after; r = 0.87; P < .01) and, AF-DXA and VF (before: r = 0.61, after; r = 0.69; P < .01) are not different before and after the weight loss. Correlations between delta AF-DXA and delta ScF (r = 0.72; P < .01) or delta VF (r = 0.51; P < .01) were found. Conclusion. The use of AF-DXA as a surrogate for VF after weight loss is questionable, but may be interesting for ScF
Probability of local bifurcation type from a fixed point: A random matrix perspective
Results regarding probable bifurcations from fixed points are presented in
the context of general dynamical systems (real, random matrices), time-delay
dynamical systems (companion matrices), and a set of mappings known for their
properties as universal approximators (neural networks). The eigenvalue spectra
is considered both numerically and analytically using previous work of Edelman
et. al. Based upon the numerical evidence, various conjectures are presented.
The conclusion is that in many circumstances, most bifurcations from fixed
points of large dynamical systems will be due to complex eigenvalues.
Nevertheless, surprising situations are presented for which the aforementioned
conclusion is not general, e.g. real random matrices with Gaussian elements
with a large positive mean and finite variance.Comment: 21 pages, 19 figure
Non-Hermitian Random Matrix Theory and Lattice QCD with Chemical Potential
In quantum chromodynamics (QCD) at nonzero chemical potential, the
eigenvalues of the Dirac operator are scattered in the complex plane. Can the
fluctuation properties of the Dirac spectrum be described by universal
predictions of non-Hermitian random matrix theory? We introduce an unfolding
procedure for complex eigenvalues and apply it to data from lattice QCD at
finite chemical potential to construct the nearest-neighbor spacing
distribution of adjacent eigenvalues in the complex plane. For intermediate
values of , we find agreement with predictions of the Ginibre ensemble of
random matrix theory, both in the confinement and in the deconfinement phase.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Geometric effects on critical behaviours of the Ising model
We investigate the critical behaviour of the two-dimensional Ising model
defined on a curved surface with a constant negative curvature. Finite-size
scaling analysis reveals that the critical exponents for the zero-field
magnetic susceptibility and the correlation length deviate from those for the
Ising lattice model on a flat plane. Furthermore, when reducing the effects of
boundary spins, the values of the critical exponents tend to those derived from
the mean field theory. These findings evidence that the underlying geometric
character is responsible for the critical properties the Ising model when the
lattice is embedded on negatively curved surfaces.Comment: 16 pages, 6 figures, to appear in J. Phys. A: Math. Ge
Generalized twisted modules associated to general automorphisms of a vertex operator algebra
We introduce a notion of strongly C^{\times}-graded, or equivalently,
C/Z-graded generalized g-twisted V-module associated to an automorphism g, not
necessarily of finite order, of a vertex operator algebra. We also introduce a
notion of strongly C-graded generalized g-twisted V-module if V admits an
additional C-grading compatible with g. Let V=\coprod_{n\in \Z}V_{(n)} be a
vertex operator algebra such that V_{(0)}=\C\one and V_{(n)}=0 for n<0 and let
u be an element of V of weight 1 such that L(1)u=0. Then the exponential of
2\pi \sqrt{-1} Res_{x} Y(u, x) is an automorphism g_{u} of V. In this case, a
strongly C-graded generalized g_{u}-twisted V-module is constructed from a
strongly C-graded generalized V-module with a compatible action of g_{u} by
modifying the vertex operator map for the generalized V-module using the
exponential of the negative-power part of the vertex operator Y(u, x). In
particular, we give examples of such generalized twisted modules associated to
the exponentials of some screening operators on certain vertex operator
algebras related to the triplet W-algebras. An important feature is that we
have to work with generalized (twisted) V-modules which are doubly graded by
the group C/Z or C and by generalized eigenspaces (not just eigenspaces) for
L(0), and the twisted vertex operators in general involve the logarithm of the
formal variable.Comment: Final version to appear in Comm. Math. Phys. 38 pages. References on
triplet W-algebras added, misprints corrected, and expositions revise
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