Facteur g

Résumé

Le facteur g (diminutif de « facteur général », general factor en anglais et également connu sous le nom d'intelligence générale, capacité mentale générale ou facteur d'intelligence générale), est un concept développé dans le cadre des recherches en psychométrie sur les habiletés cognitives. C’est une variable qui caractérise les corrélations positives que la recherche empirique a trouvées de façon constante entre les tests d’aptitudes mentales, quel que soit le contenu des tests. . Les termes intelligence générale, habileté mentale générale, QI ou simplement intelligence sont souvent utilisés de façon interchangeable pour se référer au noyau commun partagé par les tests d'aptitudes cognitives. Le concept et l'interprétation du facteur g font l'objet de vives discussions dans les milieux scientifiques. Les réalités mathématique et physique du facteur g sont mises en cause par certains spécialistes en statistiques et psychométrie. Mise en évidence L’existence du facteur g

Source officielle

https://fr.wikipedia.org/wiki/Facteur_g

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (8)

Chargement

Afficher plus

Publications associées

Chargement

Personnes associées

Chargement

Unités associées

Chargement

Concepts associés (18)

Concepts associés

Chargement

Cours associés (2)

Cours associés

Chargement

Séances de cours associées (2)

Séances de cours associées

Chargement

Publications associées (8)

High frequency electron spin resonance study of peapods

Luka Ciric, László Forró, Bálint Náfrádi

We present high frequency Electron Spin Resonance (ESR) results on a peapod sample. In a previous low frequency ESR study on peapods and double-walled nanotubes the observation of a non-Lorentzian line shape was reported. This effect was tentatively attributed to the presence of two distinct Lorentzian signals, coming from the outer tube and from the inner tube or from fullerenes. Here we report ESR measurements in a broad frequency (and magnetic field) range, which help to resolve this uncertainty. Since, with increasing magnetic field, no splitting of the line is observed, just a linear increase with frequency, we attribute the non-Lorentzian shape to g-factor distribution. The extracted line width weakly increases with temperature. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2008

Chargement

Singlet-Triplet Excitations and High-Field Magnetization in CuTe2O5

Helmuth Berger, Zhe Wang

By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spin-gapped system CuTe2O5, we identified the singlet-triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of h(upsilon 0) = 4.94 meV at the Gamma point (Q similar or equal to 0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field H-c1(a) = 37.6 T for H perpendicular to bc-plane and H-c1(bc) = 40.6 T for H parallel to bc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet-triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the S-z = 0 triplet state and the S-z = +/- 1 triplet states, respectively, due to the Dzyaloshinskii-Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.

2011

Chargement

Speed has always been a critical consideration in magnetic resonance imaging (MRI), promising dramatic gains in imaging speed, a reduction in motion and susceptibility artifacts, and ultimately increased throughput for clinical studies. This thesis presents several new approaches to increase temporal resolution of a three dimensional (3D) echo planar imaging (EPI) sequence and explores the benefits of using high temporal resolution for both event-related brain activation and resting state networks fMRI studies. In the first approach, a new k-space traversal strategy for segmented 3D EPI is introduced which we termed as 3D reduced excitation EPI (3D RE-EPI). In this approach, two partitions are encoded per radio frequency (RF) excitation, effectively reducing the number of excitations used to acquire a 3D EPI dataset by a factor of two. With this strategy, whole-brain images with a nominal voxel size of 2mmisotropic could be acquired with a temporal resolution under half a second, using traditional parallel imaging acceleration upto 4x in the partition-encoding direction and using novel data acquisition speed-up of 2x. With 8x data acquisition speed-up in the partition-encoding direction, 3D RE-EPI produced acceptable image quality without introduction of noticeable additional artifacts. Due to increased temporal signal-to-noise ratio (tSNR) and better characterization of physiological fluctuations, the new strategy allowed detection of more resting state networks compared to standardmulti-slice two dimensional (2D) EPI and segmented 3D EPI. The approach above suffered from geometry factor (g-factor related) signal-to-noise ratio (SNR) losses, while using very high parallel imaging acceleration factor. To achieve substantial increase in the temporal resolution whilemaintaining low g-factors when high parallel imaging acceleration factors are used, the combination of segmented 3D EPI using 2D controlled aliasing with generalized autocalibrating partially parallel acquisitions (GRAPPA) was implemented in the next approach termed 3D-EPI-CAIPI. FunctionalMRI data with whole-brain coverage, a voxel size of 2 mm isotropic and a temporal resolution of 371 ms was acquired with acceptable image quality. 10-fold parallel imaging accelerated 3D-EPI-CAIPI data was shown to lower g-factor losses by as much as 10% with respect to segmented 3D EPI at 7 Tesla. Additional resting state networks were detected using 3D-EPI-CAIPI compared to a comparable standard 2D EPI acquisition. This was attributed to the improved statistics due to an increased number of volumes acquired in a given duration and because of the improved characterization of physiological signal fluctuations. Functional MRI with 400 ms temporal resolution allowed the detection of time-to-peak variations in temporal, occipital and frontal cortices haemodynamic responses due to multisensory facilitation of the order of ~200 ms. To conclude, this thesis introduces several novel techniques to increase temporal resolution of fMRI. Besides building theoretical foundations for these techniques, their applications for studying human brain functional connectivity, event-related brain activation and the ability to characterize physiological signal fluctuations at ultra-high field strength (7 Tesla) are evaluated.

EPFL2014

Chargement

Afficher plus

EPFL2014