Structure of molecular packing probed by polarization-resolved nonlinear four-wave mixing and coherent anti-Stokes Raman-scattering microscopy

International audienceWe report a method that is able to provide refined structural information on molecular packing in biomolecular assemblies using polarization-resolved four-wavemixing and coherent anti-Stokes Raman-scattering microscopy. These third-order nonlinear processes allow quantifying high orders of symmetry which are exploited here to reveal a high level of detail in the angular disorder behavior at the molecular scale in lipid membranes

Ultimate use of two-photon fluorescence microscopy to map orientational behavior of fluorophores

International audienceThe orientational distribution of fluorophores is an important reporter of the structure and function of their molecular environment. Although this distribution affects the fluorescence signal under polarized-light excitation, its retrieval is limited to a small number of parameters. Because of this limitation, the need for a geometrical model (cone, Gaussian, etc.) to effect such retrieval is often invoked. In this work, using a symmetry decomposition of the distribution function of the fluorescent molecules, we show that polarized two-photon fluorescence based on tunable linear dichroism allows for the retrieval of this distribution with reasonable fidelity and without invoking either an a priori knowledge of the system to be investigated or a geometrical model. We establish the optimal level of detail to which any distribution can be retrieved using this technique. As applied to artificial lipid vesicles and cell membranes, the ability of this method to identify and quantify specific structural properties that complement the more traditional molecular-order information is demonstrated. In particular, we analyze situations that give access to the sharpness of the angular constraint, and to the evidence of an isotropic population of fluorophores within the focal volume encompassing the membrane. Moreover, this technique has the potential to address complex situations such as the distribution of a tethered membrane protein label in an ordered environment

Earthworm management in tropical agroecosystems

The effects of earthworms on soil structure and the resulting physical properties in natural or cultivated systems were studied in different sites of the Macrofauna project. Four main results were obtained from these experiments : (1) In kaolinitic soils (Lamto, Manaus, Yurimaguas), irrespective of clay content, andogeic earthworms play a major role in soil structure formation and maintenance, while in smectitic soils (Martinique), the effects of earthworms on soil structure formation and maintenance are not as clear. In the Vertisols of Martinique, the effect of roots and organic materials seem predominant in soil structure development and earthworms play a secondary role. (2) Endogeic earthworm species have different effects on soil properties. Large earthworms such as #Pontoscolex corethrurus or #Millsonia anomala egest large and compact casts. They increase the proportion of large aggregates in soil and the bulk density ; they are called "compacting species". Conversely, small earthworm species such as eudrilid worms feed at least partly on large compact casts and egest smaller and fragile aggregates. They decrease the proportion of large aggregates in soil and the bulk density ; they are called "decompacting species". The effects of "compacting species" on soil structure formation seem to be linked to the presence of organic residues at the soil surface. In agroecosystems of Yurimaguas (Peru), the intense activity of #P. corethrurus$ and the coalescence of surface casts lead to the formation of a compact surfacecrust with impedes water infiltration in the absence of organic residues, but a favourable macroaggregate structure develops in the presence of organic residues and leguminous mulch. (3) The introduction of earthworms in agroecosystems changes soil physical properties and especially water retention and infiltration... (D'après résumé d'auteur

Precise design of environmental data warehouses

People use data warehouses to help them make decisions. For example, public policy decision-makers can improve their decisions by using this technology to analyze the environmental effects of human activity. In production systems, data warehouses provide structures for extracting the knowledge required to optimize systems. Designing data warehouses is a complex task; designers need flexible and precise methods to help them create data warehouses and adapt their analysis criteria to developments in the decision-making process. In this paper, we introduce a flexible method based on UML (Unified Modeling Language). We introduce a UML profile for building multi-dimensional models and for choosing different criteria according to analysis requirements. This profile makes it possible to specify integrity constraints in OCL (Object Constraint Language). We apply our method to the construction of an environmental system for analyzing the use of certain agricultural fertilizers. We integrate various data sources into a multi-dimensional model showing several categories of analysis, and the consistency of data can be checked with OCL constraints

Thioflavine-T and Congo Red reveal the polymorphism of insulin amyloid fibrils when probed by polarization-resolved fluorescence microscopy.

International audienceAmyloid fibrils are protein misfolding structures that involve a β-sheet structure and are associated with the pathologies of various neurodegenerative diseases. Here we show that Thioflavine-T and Congo Red, two major dyes used to image fibrils by fluorescence assays, can provide deep structural information when probed by means of polarization-resolved fluorescence microscopy. Unlike fluorescence anisotropy or fluorescence detected linear dichroism imaging, this technique allows to retrieve simultaneously both mean orientation and orientation dispersion of the dye, used here as a reporter of the fibril structure. We have observed that insulin amyloid fibrils exhibit a homogeneous behavior over the fibrils' length, confirming their structural uniformity. In addition, these results reveal the existence of various structures among the observed fibrils' population, in spite of a similar aspect when imaged with conventional fluorescence microscopy. This optical nondestructive technique opens perspectives for in vivo structural analyses or high throughput screening

Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications

UTILISATION ÉNERGÉTIQUE ET AZOTÉE DES PRINCIPAUX TOURTEAUX ET DES GRAINES DE LÉGUMINEUSES PAR LE RAT EN CROISSANCE; COMPARAISON AU BLÉ TENDRE ET AU BLÉ DUR

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UTILISATION ÉNERGÉTIQUE ET AZOTÉE DE RÉGIMES COMPORTANT DES ACIDES CAPRYLIQUE, LAURIQUE ET MYRISTIQUE PAR LE RAT EN CROISSANCE INFLUENCE DU NIVEAU D'ALIMENTATION

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Determination of plasma non-esterified fatty acids in herbivores and man : a comparison of values obtained by manual or automatic chromatographic, titrimetric, colorimetric and enzymatic methods

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