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Search Results: 1 - 10 of 130340 matches for " V. Mazel "
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Combination of FTIR and X-RAYS Synchrotron-Based Micro-Imaging Techniques for the Study of Ancient Paintings. A Practical Point of View
M. Cotte,E. Checroun,V. Mazel,V. A. Solé
E-Preservation Science , 2009,
Abstract: Applications of FTIR to the study of ancient paintings haveencountered two major steps: the development of FTIRmicroscopes, which enable to watch the sample and toselect the regions of interest; and the migration of thoseFTIR microscopes towards synchrotron facilities, thatoffers a significant improvement in terms of spatial resolutionand spectral quality. Even if access to synchrotrons isby nature limited, it is worth applying for such installationsas they usually provide a set of micro-imaging techniques.FTIR end-stations should then be considered as part of awider analytical platform. Combining micro FTIR with microX-ray fluorescence, micro X-ray diffraction or micro X-rayabsorption spectroscopy for the study of paintings enablesa deeper insight into paintings at the micrometer scale.Several examples of X-ray/infrared combinations are given.The focus is given to practical aspects, in particular to thecritical issue of sample preparation. Alternatives to theclassical polished cross-sections are proposed and evaluated.Data treatment is also discussed.
Pouvoir aristocratique et église aux Xe-XIe siècles. Retour sur la révolution féodale dans l’ uvre de Georges Duby
Florian Mazel
Bulletin du Centre d’études Médiévales d’Auxerre , 2008, DOI: 10.4000/cem.4173
Abstract: Aucune recherche historique, aussi concrète et détaillée soit-elle, ne peut faire totalement l’économie de concepts généraux. Elle ne commet d’erreur à cet égard qu’à les tenir pour évidents, car ces prétendues évidences dissimulent alors les vrais problèmes fondamentaux dont la réflexion historienne doit sans cesse reprendre la discussion à nouveaux frais. (…) Elle devra faire preuve d’humilité face à la recherche strictement spécialisée. Ce qui ne signifie nullement qu’elle ne doive être ...
Synonymous Genes Explore Different Evolutionary Landscapes
Guillaume Cambray,Didier Mazel
PLOS Genetics , 2008, DOI: 10.1371/journal.pgen.1000256
Abstract: The evolutionary potential of a gene is constrained not only by the amino acid sequence of its product, but by its DNA sequence as well. The topology of the genetic code is such that half of the amino acids exhibit synonymous codons that can reach different subsets of amino acids from each other through single mutation. Thus, synonymous DNA sequences should access different regions of the protein sequence space through a limited number of mutations, and this may deeply influence the evolution of natural proteins. Here, we demonstrate that this feature can be of value for manipulating protein evolvability. We designed an algorithm that, starting from an input gene, constructs a synonymous sequence that systematically includes the codons with the most different evolutionary perspectives; i.e., codons that maximize accessibility to amino acids previously unreachable from the template by point mutation. A synonymous version of a bacterial antibiotic resistance gene was computed and synthesized. When concurrently submitted to identical directed evolution protocols, both the wild type and the recoded sequence led to the isolation of specific, advantageous phenotypic variants. Simulations based on a mutation isolated only from the synthetic gene libraries were conducted to assess the impact of sub-functional selective constraints, such as codon usage, on natural adaptation. Our data demonstrate that rational design of synonymous synthetic genes stands as an affordable improvement to any directed evolution protocol. We show that using two synonymous DNA sequences improves the overall yield of the procedure by increasing the diversity of mutants generated. These results provide conclusive evidence that synonymous coding sequences do experience different areas of the corresponding protein adaptive landscape, and that a sequence's codon usage effectively constrains the evolution of the encoded protein.
Model $\infty$-categories II: Quillen adjunctions
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We prove that various structures on model $\infty$-categories descend to corresponding structures on their localizations: (i) Quillen adjunctions; (ii) two-variable Quillen adjunctions; (iii) monoidal and symmetric monoidal model structures; and (iv) enriched model structures.
All about the Grothendieck construction
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We provide, among other things: (i) a Bousfield--Kan formula for colimits in $\infty$-categories (generalizing the 1-categorical formula for a colimit as a coequalizer of maps between coproducts); (ii) $\infty$-categorical generalizations of Barwick--Kan's Theorem B$_n$ and Dwyer--Kan--Smith's Theorem C$_n$ (regarding homotopy pullbacks in the Thomason model structure, which themselves vastly generalize Quillen's Theorem B); and (iii) an articulation of the simultaneous and interwoven functoriality of colimits (or dually, of limits) for natural transformations and for pullback along maps of diagram $\infty$-categories.
A user's guide to co/cartesian fibrations
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We formulate a model-independent theory of co/cartesian morphisms and co/cartesian fibrations: that is, one which resides entirely *within the $\infty$-category of $\infty$-categories*. We prove this is suitably compatible with the corresponding quasicategorical (and in particular, model-dependent) notions studied by Joyal and Lurie.
Model $\infty$-categories III: the fundamental theorem
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We prove that a model structure on a relative $\infty$-category $(M,W)$ gives an efficient and computable way of accessing the hom-spaces $hom_{M[[W^{-1}]]}(x,y)$ in the localization. More precisely, we show that when the source $x \in M$ is *cofibrant* and the target $y \in M$ is *fibrant*, then this hom-space is a "quotient" of the hom-space $hom_M(x,y)$ by either of a *left homotopy relation* or a *right homotopy relation*.
Hammocks and fractions in relative $\infty$-categories
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We study the *homotopy theory* of $\infty$-categories enriched in the $\infty$-category $sS$ of simplicial spaces. That is, we consider $sS$-enriched $\infty$-categories as presentations of ordinary $\infty$-categories by means of a "local" geometric realization functor $Cat_{sS} \to Cat_\infty$, and we prove that their homotopy theory presents the $\infty$-category of $\infty$-categories, i.e. that this functor induces an equivalence $Cat_{sS} [[ W_{DK}^{-1} ]] \xrightarrow{\sim} Cat_\infty$ from a localization of the $\infty$-category of $sS$-enriched $\infty$-categories. Following Dwyer--Kan, we define a *hammock localization* functor from relative $\infty$-categories to $sS$-enriched $\infty$-categories, thus providing a rich source of examples of $sS$-enriched $\infty$-categories. Simultaneously unpacking and generalizing one of their key results, we prove that given a relative $\infty$-category admitting a *homotopical three-arrow calculus*, one can explicitly describe the hom-spaces in the $\infty$-category presented by its hammock localization in a much more explicit and accessible way. As an application of this framework, we give sufficient conditions for the Rezk nerve of a relative $\infty$-category to be a (complete) Segal space, generalizing joint work with Low.
The universality of the Rezk nerve
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We functorially associate to each relative $\infty$-category $(R,W)$ a simplicial space $N^R_\infty(R,W)$, called its Rezk nerve (a straightforward generalization of Rezk's "classification diagram" construction for relative categories). We prove the following local and global universal properties of this construction: (i) that the complete Segal space generated by the Rezk nerve $N^R_\infty(R,W)$ is precisely the one corresponding to the localization $R[[W^{-1}]]$; and (ii) that the Rezk nerve functor defines an equivalence $RelCat_\infty [[ W_{BK}^{-1} ]] \xrightarrow{\sim} Cat_\infty$ from a localization of the $\infty$-category of relative $\infty$-categories to the $\infty$-category of $\infty$-categories.
Quillen adjunctions induce adjunctions of quasicategories
Aaron Mazel-Gee
Mathematics , 2015,
Abstract: We prove that a Quillen adjunction of model categories (of which we do not require functorial factorizations and of which we only require finite bicompleteness) induces a canonical adjunction of underlying quasicategories.
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