93,223 research outputs found
L'amitié réciproque. : [estampe] / F. Boucher inven. ; L. Bonnet Sculp.
No full text[L'amitié réciproque]Référence bibliographique : IFF18 BONNET (Louis-Marin), 34Référence bibliographique : Hérold, 18
The viability of modified gravity theories
No full textPhDThis thesis studies the viability of classes of modified gravity (MG) theories based on generalisations
of the Einstein-Hilbert action. Particular emphasis is given to f(R) theories in
both the metric and Palatini formalisms, scalar-tensor theories and generalised Gauss-Bonnet
theories. An urgent task at present is to devise stringent tests in order to reduce the range of
candidate models based on these theories. In this thesis a detailed study is made of the viability
of these models using constraints from requirement of stability, background cosmological
dynamics, local gravity constraints (LGC) and matter density perturbations.
In each case the conditions required for stability and viability of the background dynamics
are presented. In the case of generalised Gauss-Bonnet theories the circumstances leading
to the existence and stability of cosmological scaling solutions are established.
In the scalar-tensor theories considered here, which includes metric-f(R) theories as a
special case, there is a strong coupling of the scalar field to matter in the Einstein frame
which violates all LGC. It is shown that using a chameleon mechanism, models that are
compatible with LGC may be constructed. It is found that such models, which are also
consistent with background dynamics, are constrained to be close to the CDMmodel during
the radiation/matter epochs and can lead to the divergence of the equation of state of dark
energy. In contrast, such constraints only impose mild restrictions on Palatini-f(R) models.
Still more stringent constraints are provided by studying matter density perturbations.
In particular, it is shown that the unconventional evolution of perturbations in the Palatini
formalism leads to f(R) models in this case to be practically identical to the CDM model.
For each case it is also shown that (for viable models) matter perturbation equations derived
under a sub-horizon approximation are reliable even for super-Hubble scales provided the
oscillating mode does not dominate over the matter-induced mode. Such approximate equations
are especially reliable in the Palatini formalism, where the oscillating mode is absent.
In summary, the analyses carried out in this thesis suggest that subjectingMG theories to observational
constraints confines the viable range of models to be very close to (and in some
cases indistinguishable from) the CDM model
« Le pastel en gravure, inventé et exécuté par Louis Bonnet. 1769 »
No full textNumérisation effectuée à partir d'un document original.Recueil formé de huit épreuves de gravure d'un portrait de femme d'après F. Boucher (1757), avec l'explication par Louis Bonnet de l'application successive des différentes couleurs
La Laveuse. : [estampe] / F. Boucher del. ; L. Bonnet Sculp.
No full text[La Laveuse]Référence bibliographique : IFF18 BONNET (Louis-Marin), 12Référence bibliographique : Hérold, 1
[Figure de femme] : [estampe] / [d'après Boucher] ; F. Boucher F ; L. Bonnet Sculp
No full text[Figure de femme, coiffée d'un voile]Référence bibliographique : IFF18 BONNET (Louis-Marin), 6Référence bibliographique : Hérold, 1
Gauss–Bonnet gravitational baryogenesis
No full textAbstractIn this letter we study some variant forms of gravitational baryogenesis by using higher order terms containing the partial derivative of the Gauss–Bonnet scalar coupled to the baryonic current. This scenario extends the well known theory that uses a similar coupling between the Ricci scalar and the baryonic current. One appealing feature of the scenario we study is that the predicted baryon asymmetry during a radiation domination era is non-zero. We calculate the baryon to entropy ratio for the Gauss–Bonnet term and by using the observational constraints we investigate which are the allowed forms of the R+F(G) gravity controlling the evolution. Also we briefly discuss some alternative higher order terms that can generate a non-zero baryon asymmetry, even in the conformal invariance limit
Higher Dimensional Static and Spherically Symmetric Solutions in Extended Gauss–Bonnet Gravity
No full textWe study a theory of gravity of the form f ( G ) where G is the Gauss–Bonnet topological invariant without considering the standard Einstein–Hilbert term as common in the literature, in arbitrary ( d + 1 ) dimensions. The approach is motivated by the fact that, in particular conditions, the Ricci curvature scalar can be easily recovered and then a pure f ( G ) gravity can be considered a further generalization of General Relativity like f ( R ) gravity. Searching for Noether symmetries, we specify the functional forms invariant under point transformations in a static and spherically symmetric spacetime and, with the help of these symmetries, we find exact solutions showing that Gauss–Bonnet gravity is significant without assuming the Ricci scalar in the action
Introduction [à: Lux philologiae : l'essor de la philologie au XVIIIe siècle, Genève, Droz, 2021]
No full textL'élevage en Afrique occidentale et centrale
No full textBonnet-Dupeyron F. L'élevage en Afrique Occidentale et Centrale. In: Bulletin de l'Association de géographes français, N°169-170, 22e année, Mars-mai 1945. pp. 40-50
West and Central Africa 1945
No full textMap of Livestock in West and Central Africa; Breeders, Transhumance, Nomadism / Compiled by Mr. F. Bonnet-DupeyronColor
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