Search results for "Computation"

Modeling anti-allergic natural compounds by molecular topology.

2013

Molecular topology has been applied to the search of QSAR models able to identify the anti-allergic activity of a wide group of heterogeneous compounds. Through the linear discriminant analysis and artificial neural networks, correct classification percentages above 85% for both the training set and the test set have been obtained. After carrying out a virtual screening with a natural product library, about thirty compounds with theoretical anti-allergic activity have been selected. Among them, hesperidin, naringin, salinomycin, sorbitol, curcumol, myricitrin, diosmin and kinetin stand out. Some of these compounds have already been referenced as having anti-allergic activity.

Interaction features for prediction of perceptual segmentation:Effects of musicianship and experimental task

2016

As music unfolds in time, structure is recognised and understood by listeners, regardless of their level of musical expertise. A number of studies have found spectral and tonal changes to quite successfully model boundaries between structural sections. However, the effects of musical expertise and experimental task on computational modelling of structure are not yet well understood. These issues need to be addressed to better understand how listeners perceive the structure of music and to improve automatic segmentation algorithms. In this study, computational prediction of segmentation by listeners was investigated for six musical stimuli via a real-time task and an annotation (non real-tim…

Neighborhood Effects in Visual Word Recognition and Reading

2015

LA NOTION DE COLLOCATION FONDAMENTALE UNE ETUDE DE CORPUS

2016

Dans cette étude les « collocations fondamentales » sont envisagées comme des unités polylexicales significatives (unies par des liens collocationnels) fréquentes (dans l'usage) ou non fréquentes (lorsqu'elles sont pertinentes pour la communication) qui représentent pour les locuteurs natifs les contextes les plus essentiels d'un mot donné. Nous avons extrait du corpus frWaC (Baroni et al. 2010) environ 20 000 associations à partir de dix mots pivots issus du Dictionnaire Fondamental de Gougenheim (1971) ; puis, au moyen de la fréquence et de mesures d'association, nous avons sélectionné un échantillon d'environ 400 associations candidates au statut de collocations fondamentales et demandé …

Maux de l'économie, mots des économistes

1990

International audience; La méthodologie économique a largement séparé les discours (hypthèses, théorie, corps de pensée) de l'action (représentée essentiellement par les applications ou les descriptions monographiques). Dans cet essai, avec la plus large prudence répondant à une démarche balbutiante, nous tentons de donner des représentations synthétiques, sur longue période, de l'évolution de la littérature économique ; ceci au moyen des méthodes usuelles de l'analyse des données. Il reste, quelque soit les résultats auxquels nous parvenons, que ce type de traintement repose sur l'hypothèse d'avoir pris en compte chaque production de littérature comme un objet statistique simple. L'applica…

Analytical model of transit time broadening for two-photon excitation in a three-level ladder and its experimental validation

2012

We revisit transit time broadening for one of the typical experiment designs in molecular spectroscopy, that of a collimated supersonic beam of particles crossing a focused Gaussian laser beam. In particular, we consider a Doppler-free arrangement of a collimated supersonic beam of Na${}_{2}$ molecules crossing two counterpropagating laser beams that excite a two-photon transition in a three-level ladder scheme. We propose an analytical two-level model with a virtual intermediate level to show that the excitation line shape is described by a Voigt profile and provide the validity range of this model with respect to significant experimental parameters. The model also shows that line broadeni…

An adaptive method for Volterra–Fredholm integral equations on the half line

2009

AbstractIn this paper we develop a direct quadrature method for solving Volterra–Fredholm integral equations on an unbounded spatial domain. These problems, when related to some important physical and biological phenomena, are characterized by kernels that present variable peaks along space. The method we propose is adaptive in the sense that the number of spatial nodes of the quadrature formula varies with the position of the peaks. The convergence of the method is studied and its performances are illustrated by means of a few significative examples. The parallel algorithm which implements the method and its performances are described.

Accurate molecular geometries of the protonated water dimer

2000

The equilibrium geometry of the protonated water dimer, H5O2+, was studied using Moller–Plesset perturbation theory and coupled-cluster theory. Constrained geometry optimizations were carried out for the C2 and Cs symmetric structures within the counterpoise framework and near the limit of a complete basis set. In the constrained optimization, the degrees of freedom of the complex are reduced to an intrafragmental distortion and an interfragmental coordinate, making the procedure tractable for large basis sets and explicitly correlated linear r12 methods. The energy of the stationary point of C2 symmetry was found to be 1.2 kJ mol−1 below the energy of the Cs structure.

Performance of polarization-consistent vs. correlation-consistent basis sets for CCSD(T) prediction of water dimer interaction energy

2019

Abstract Detailed study of Jensen’s polarization-consistent vs. Dunning’s correlation-consistent basis set families performance on the extrapolation of raw and counterpoise-corrected interaction energies of water dimer using coupled cluster with single, double, and perturbative correction for connected triple excitations (CCSD(T)) in the complete basis set (CBS) limit are reported. Both 3-parameter exponential and 2-parameter inverse-power fits vs. the cardinal number of basis set, as well as the number of basis functions were analyzed and compared with one of the most extensive CCSD(T) results reported recently. The obtained results for both Jensen- and Dunning-type basis sets underestimat…

New insights in chemical reactivity from quantum chemical topology.

2021

International audience; Based on the quantum chemical topology of the modified electron localization function ELFx, an efficient and robust mechanistic methodology designed to identify the favorable reaction pathway between two reactants is proposed. We first recall and reshape how the supermolecular interaction energy can be evaluated from only three distinct terms, namely the intermolecular coulomb energy, the intermolecular exchange‐correlation energy and the intramolecular energies of reactants. Thereafter, we show that the reactivity between the reactants is driven by the first‐order variation in the coulomb intermolecular energy defined in terms of the response to changes in the numbe…