1,721,270 research outputs found
Poor performance of right brain-damaged patients on Raven's coloured matrices: derangement of general intelligence or of specific abilities?
No full text[Relationship between various verbal intelligence tests and monohemispheric cerebral lesions]
No full textSemantic disorders of auditory language comprehension in right brain-damaged patients
No full textA test of auditory language comprehension was given to 110 right brain-damaged patients and to 94 normal controls in order to check if patients with lesions of the right (nondominant) hemisphere make a significantly higher number of semantic errors than normals. Confirmation of the hypothesis was obtained, but the relationship between semantic errors and lesion of the right hemisphere did not seem a simple and direct one. In fact, most of the lexical-semantic errors were due to associated variables (such as unilateral spatial agnosia and general mental deterioration) and not to the lesion of the right hemisphere per se. These data do not suggest a specific semantic capacity of the nondominant hemisphere but rather stress the fragility of the lexical-semantic organization at the cortical level
Immediate visual-spatial memory in hemisphere-damaged patients: impairment of verbal coding and of perceptual processing
No full textDigital agnosia and lesions of the parietal lobe
No full text130 patients with focal brain damage have been submitted to non-verbal finger identification tasks. The results of this research can be summarized as follows: -when bilateral finger agnosia is studied with non-verbal tasks, no difference can be shown between right and left parietal lesions; -in left brain damaged patients the bilateral form of finger agnosia is generally due to large lesions involving the parietal lobe; -in right brain damaged patients the unilateral form of finger agnosia is almost always due to lesions centered on the parietal region
Redox levels in aqueous solution: Effect of van der Waals interactions and hybrid functionals
No full textWe investigate redox levels in aqueous solution using a combination of ab initio molecular dynamics (MD) simulations and thermodynamic integration methods. The molecular dynamics are performed with both the semilocal Perdew-Burke-Ernzerhof functional and a nonlocal functional (rVV10) accounting for van der Waals (vdW) interactions. The band edges are determined through three different schemes, namely, from the energy of the highest occupied and of the lowest unoccupied Kohn-Sham states, from total-energy differences, and from a linear extrapolation of the density of states. It is shown that the latter does not depend on the system size while the former two are subject to significant finite-size effects. For the redox levels, we provide a formulation in analogy to the definition of charge transition levels for defects in crystalline materials. We consider the H+/H-2 level defining the standard hydrogen electrode, the OH-/OH* level corresponding to the oxidation of the hydroxyl ion, and the H2O/OH* level for the dehydrogenation of water. In spite of the large structural modifications induced in liquid water, vdW interactions do not lead to any significant structural effect on the calculated band gap and band edges. The effect on the redox levels is also small since the solvation properties of ionic species are little affected by vdW interactions. Since the electronic properties are not significantly affected by the underlying structural properties, it is justified to perform hybrid functional calculations on the configurations of our MD simulations. The redox levels calculated as a function of the fraction alpha of Fock exchange are found to remain constant, reproducing a general behavior previously observed for charge transition levels of defects. Comparison with experimental values shows very good agreement. At variance, the band edges and the band gap evolve linearly with alpha. For alpha similar or equal to 0.40, we achieve a band gap, band-edge positions, and redox levels in overall good agreement with experiment. (C) 2015 AIP Publishing LLC
Structural, Dynamical, and Electronic Properties of Liquid Water: A Hybrid Functional Study
No full textWe study structural, dynamical, and electronic properties of liquid water through ab initio molecular dynamics (MD) simulations based on a hybrid functional which includes nonlocal van der Waals (vdW) interactions. The water dimer, the water hexamer, and two phases of ice are studied as benchmark cases. The hydrogen-bond energy depends on the balance between Fock exchange and vdW interactions. Moreover, the energetic competition between extended and compact structural motifs is found to be well described by theory provided vdW interactions are accounted for. Applied to the hydrogen-bond network of liquid water, the dispersion interactions favor more compact structural motifs, bring the density closer to the experimental value, and improve the agreement with experimental observables such as radial distribution functions. The description of the self-diffusion coefficient is also found to improve upon the combined consideration of Fock exchange and vdW interactions. The band gap and the band edges are found to agree with experiment within 0.1 eV
Electronic Levels of Excess Electrons in Liquid Water
No full textWe provide a consistent description of the electronic levels associated with localized and delocalized excess electrons in liquid water by combining hybrid-functional molecular dynamics simulations with a grand canonical formulation of solutes in aqueous solution. The excess electron localizes in a cavity with an average radius of 1.8 angstrom and a majority coordination of five water molecules. The vertical binding energy, the optical s p transitions, and the adiabatic redox level are found to agree closely with their experimental counterparts. The energy level associated with electron delocalization V-0 is inferred to lie at -0.97 eV with respect to the vacuum level
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