1,721,178 research outputs found
C 1s core-level photoemission spectra of stilbene on Si(100)2x1 surface from first-principles calculations
Full text linkAdsorption of the cis and trans stilbene on the Si(100)2 x 1 surface was studied using plane waves density functional theory (DFT). Configurations across a silicon dimer, along the dimers and along the channels between dimers were probed for the two isomers. Trans and cis stilbene both bind preferentially across the dimers. In the former case only the ethylenic carbon atoms are involved and the aromatic character is preserved. In the latter case the adsorption interaction involves also the two phenyl rings with the conversion to two 1,3-cyclohexadiene, yielding a more stable local minimum. The corresponding calculated C 1s core level shifts are distributed in an energy range of about 2.5 eV. The overall shape of the spectra of the two adsorbed isomers shows differences consistent with chemical changes observed upon adsorption. There is a good agreement between the simulated and the experimentally observed spectrum of trans stilbene on the Si surface
Corticocortical systems underlying high-order motor control
Full text linkCortical networks are characterized by the origin, destination, and reciprocity of their connections, as well as by the diameter, conduction velocity, and synaptic efficacy of their axons. The network formed by parietal and frontal areas lies at the core of cognitive-motor control because the outflow of parietofrontal signaling is conveyed to the subcortical centers and spinal cord through different parallel pathways, whose orchestration determines, not only when and how movements will be generated, but also the nature of forthcoming actions. Despite intensive studies over the last 50 years, the role of corticocortical connections in motor control and the principles whereby selected cortical networks are recruited by different task demands remain elusive. Furthermore, the synaptic integration of different cortical signals, their modulation by transthalamic loops, and the effects of conduction delays remain challenging questions that must be tackled to understand the dynamical aspects of parietofrontal operations. In this article, we evaluate results from nonhuman primate and selected rodent experiments to offer a viewpoint on how corticocortical systems contribute to learning and producing skilled actions. Addressing this subject is not only of scientific interest but also essential for interpreting the devastating consequences for motor control of lesions at different nodes of this integrated circuit. In humans, the study of corticocortical motor networks is currently based on MRI-related methods, such as resting-state connectivity and diffusion tract-tracing, which both need to be contrasted with histological studies in nonhuman primates
Fragmentation pathways of acetic acid upon adsorption on Si(100)2 x 1
No full textThe reaction of acetic acid on the Si(100)2 x 1 surface has been investigated by density functional calculations on a two-dimers cluster model. We found that, once in the physisorbed state, acetic acid can proceed to react via two different pathways. in the first one, the cleavage of the hydroxylic bond is followed by a number of migrations of the dissociated hydrogen as well as structural rearrangements that eventually lead to the incorporation of an oxygen atom into the silicon surface, with a Si-O-Si structure. The second reaction pathway involves an initial C-H bond breakage, and evolves into a C-C bond cleavage and binding of the separate methyl and carboxylic fragments on top of a silicon dimer. C 2008 Elsevier B.V. All rights reserved
Water and hexane in an ionic liquid: Computational evidence of association under high pressure
No full textHigh pressures may strongly affect the mesoscopic structure of some ionic liquids. In particular, the so called sponge-like structure is gradually destroyed when an increasing pressure is applied. Here we show how a polar solute, an apolar solute or a mixture thereof behave in the ionic liquid trihexyl, tetradecylphosphonium bis (trifluoromethyl-sulfonyl) imide when the pressure is raised up to 10 kbar. Our calculations clearly show an association between molecules that would not interact in ordinary conditions
Pre-Peak in Protic Ionic Liquids: do classical and QM Simulations reproduce this Medium-Range Order Phenomenon?
No full textX-Ray Diffraction Studies of Ionic Liquids: from Spectra to Structure and Back
No full textIn this chapter we will review the capabilities of X-Ray diffraction experiments in the field of ionic liquids, carried out with the Energy Dispersive variant of the technique. Besides its widespread use in the determination of solid (crystal) structure, in fact, X-Ray diffraction can also be conveniently used to obtain information about the liquid” structure. After the description of data collection and treatment,
and a small review of the underlying theory, we will show several examples of the
structure factors and the radial distribution functions that can be obtained from dif
fraction patterns. These two quantities can be considered as a fingerprint of the
ionic liquid, and depend intimately upon the relative disposition of the ions in the liquid phase. Among the most noteworthy spectral features that can be pointed
out, we will discuss those deriving from hydrogen-bond interactions, as well as the
First Sharp Diffraction Peak (FSDP) that highlight the presence of medium range
order (MRO) in the liquid. We will describe several measurements on the protic
IL butylammonium nitrate and its water mixtures at different molar fractions,
where both features can be found, and show how EDXD patterns can account for
the modulation of these features with the composition. In the end, we will show
how the change of FSDP spectral feature that occurs during the fusion of alky-
lammonium chlorides can be tracked with a multiangular ADXD Rietveld diffrac-
tometer
Visuo-motor transformations for arm reaching
No full textVisuomanual co-ordination requires the merging of ocular and arm information in a common frame of reference. Here we consider behavioural evidence in humans for the use of a viewer-centred frame in the specification of end point positions of reaching. We then review anatomical and neurophysiological data in the non-human primate that indicate a prominent role of the parietal cortex in the process of multisensory fusion that leads to egocentric representations of space. Finally, we discuss the functional anatomy of the human parietal cortex in visuomanual co-ordination as revealed by neuroimaging
Adsorption sates and site conversions of phenylacetylene on Si (100)2 1 calculated by DFT
No full textThe adsorption on Si(100)2 1 of PhenylAcetilene (PA), a bifunctional molecule with a phenyl
ring and a triple bond, may occur through each group, selectively, or both functional groups
simultaneously. The most favorable adsorption sites upon adsorption were calculated by DFT.
Furthermore, several energy barriers were calculated: The ones connecting the physisorbed to
the chemisorbed states, as well as the interconversion barriers of di®erent chemisorbed states.
The conversion of physisorbed-to-chemisorbed states has barriers of 0.11 0.19 eV. The barriers
of sites inter-conversions are all higher (1.11 1.36 eV) and suggest a di±cult post-chemisorption
surface rearrangeme
A Review on Energy Dispersive X-ray Diffraction technique applied to disordered systems
No full textA review. The recent growing interest in amorphous and liq. materials has triggered new studies aiming at the detn. of local structures. Due to the large varieties of the non-cryst. materials the motivations of such studies were of different types, but in all cases reliable and relatively fast detn. of the local structures were required. In this review we present the application of the Wide Angle X-ray Scattering (WAXS) by energy dispersive detection as a tool to investigate a large variety of amorphous and liq. materials. We present, among them, samples of biol. and pharmaceutical interest, different types of catalysts, mol. liqs., polymers with different industrial applications as well as metal-phtalocyanines and materials devoted to the org. synthesis such as the cetylalkylammonium tribromides
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