102 research outputs found
Van der Waals effects on grazing incidence fast atom diffraction for H/LiF(001)
We theoretically address grazing incidence fast atom diffraction (GIFAD) for
H atoms impinging on a LiF(001) surface. Our model combines a description of
the H-LiF(001) interaction obtained from Density Functional Theory calculations
with a semi-quantum treatment of the dynamics. We analyze simulated diffraction
patterns in terms of the incidence channel, the impact energy associated with
the motion normal to the surface, and the relevance of Van der Waals (VdW)
interactions. We then contrast our simulations with experimental patterns for
different incidence conditions. Our most important finding is that, for normal
energies lower than 0.5 eV and incidence along the channel, the inclusion
of Van der Waals interactions in our potential energy surface yields a greatly
improved accord between simulations and experiments. This agreement strongly
suggests a non-negligible role of Van der Waals interactions in H/LiF(001)
GIFAD in the low-to-intermediate normal energy regime
Trajectory-dependent energy loss for swift He atoms axially scattered off a silver surface
Angle- and energy-loss- resolved distributions of helium atoms grazingly
scattered from a Ag(110) surface along low indexed crystallographic directions
are investigated considering impact energies in the few keV range. Final
projectile distributions are evaluated within a semi-classical formalism that
includes dissipative effects due to electron-hole excitations through a
friction force. For mono-energetic beams impinging along the ,
and directions, the model predicts the presence of
multiple peak structures in energy-loss spectra. Such structures provide
detailed information about the trajectory-dependent energy loss. However, when
the experimental dispersion of the incident beam is taken into account, these
energy-loss peaks are completely washed out, giving rise to a smooth
energy-loss distribution, in fairly good agreement with available experimental
data
Thermodynamic study of metal sulphides conversion to oxides in hydrometallurgy
This paper presents thermodynamic study of the conversion of metal sulphides to oxides of the CuAg sulphide concentrate as a final product after mechano-chemical leaching of tetrahedrite. The conversion of sulphides to oxides is carried out by oxidation leaching in NaOH solution. The thermodynamic calculation was performed for the sulphide concentrate containing the following sulphides: CuS, CuFeS2, FeS, Sb2S3, As2S3, Bi2S3 and HgS. Based on the change of Gibbs free energy (ΔG°) and the equilibrium constant (K), conversion of metal sulphides to oxides from the qualitative assessment of the chemical reaction can occur as the result of the thermodynamic reaction abilities
Competition between electron and phonon excitations in the scattering of nitrogen atoms and molecules off tungsten and silver surfaces
We investigate the role played by electron-hole pair and phonon excitations
in the interaction of reactive gas molecules and atoms with metal surfaces. We
present a theoretical framework that allows us to evaluate within a
full-dimensional dynamics the combined contribution of both excitation
mechanisms while the gas particle-surface interaction is described by an
ab-initio potential energy surface. The model is applied to study energy
dissipation in the scattering of N on W(110) and N on Ag(111). Our results
show that phonon excitation is the dominant energy loss channel whereas
electron-hole pair excitations represent a minor contribution. We substantiate
that, even when the energy dissipated is quantitatively significant, important
aspects of the scattering dynamics are well captured by the adiabatic
approximation.Comment: 4pages and 3 figure
Non-adiabatic effects during the dissociative adsorption of O2 at Ag(111)? A first-principles divide and conquer study
We study the gas-surface dynamics of O2 at Ag(111) with the particular
objective to unravel whether electronic non-adiabatic effects are contributing
to the experimentally established inertness of the surface with respect to
oxygen uptake. We employ a first-principles divide and conquer approach based
on an extensive density-functional theory mapping of the adiabatic potential
energy surface (PES) along the six O2 molecular degrees of freedom. Neural
networks are subsequently used to interpolate this grid data to a continuous
representation. The low computational cost with which forces are available from
this PES representation allows then for a sufficiently large number of
molecular dynamics trajectories to quantitatively determine the very low
initial dissociative sticking coefficient at this surface. Already these
adiabatic calculations yield dissociation probabilities close to the scattered
experimental data. Our analysis shows that this low reactivity is governed by
large energy barriers in excess of 1.1 eV very close to the surface.
Unfortunately, these adiabatic PES characteristics render the dissociative
sticking a rather insensitive quantity with respect to a potential spin or
charge non-adiabaticity in the O2-Ag(111) interaction. We correspondingly
attribute the remaining deviations between the computed and measured
dissociation probabilities primarily to unresolved experimental issues with
respect to surface imperfections.Comment: 18 pages including 6 figure
Cholesterol Crystals Activate the NLRP3 Inflammasome in Human Macrophages: A Novel Link between Cholesterol Metabolism and Inflammation
Chronic inflammation of the arterial wall is a key element in the pathogenesis of atherosclerosis, yet the factors that trigger and sustain the inflammation remain elusive. Inflammasomes are cytoplasmic caspase-1-activating protein complexes that promote maturation and secretion of the proinflammatory cytokines interleukin(IL)-1beta and IL-18. The most intensively studied inflammasome, NLRP3 inflammasome, is activated by diverse substances, including crystalline and particulate materials. As cholesterol crystals are abundant in atherosclerotic lesions, and IL-1beta has been linked to atherogenesis, we explored the possibility that cholesterol crystals promote inflammation by activating the inflammasome pathway.Here we show that human macrophages avidly phagocytose cholesterol crystals and store the ingested cholesterol as cholesteryl esters. Importantly, cholesterol crystals induced dose-dependent secretion of mature IL-1beta from human monocytes and macrophages. The cholesterol crystal-induced secretion of IL-1beta was caspase-1-dependent, suggesting the involvement of an inflammasome-mediated pathway. Silencing of the NLRP3 receptor, the crucial component in NLRP3 inflammasome, completely abolished crystal-induced IL-1beta secretion, thus identifying NLRP3 inflammasome as the cholesterol crystal-responsive element in macrophages. The crystals were shown to induce leakage of the lysosomal protease cathepsin B into the cytoplasm and inhibition of this enzyme reduced cholesterol crystal-induced IL-1beta secretion, suggesting that NLRP3 inflammasome activation occurred via lysosomal destabilization.The cholesterol crystal-induced inflammasome activation in macrophages may represent an important link between cholesterol metabolism and inflammation in atherosclerotic lesions
Functional Promoter Polymorphisms Govern Differential Expression of HMG-CoA Reductase Gene in Mouse Models of Essential Hypertension
3-Hydroxy-3-methylglutaryl-coenzyme A [HMG-CoA] reductase gene (Hmgcr) is a susceptibility gene for essential hypertension. Sequencing of the Hmgcr locus in genetically hypertensive BPH (blood pressure high), genetically hypotensive BPL (blood pressure low) and genetically normotensive BPN (blood pressure normal) mice yielded a number of single nucleotide polymorphisms (SNPs). BPH/BPL/BPN Hmgcr promoter-luciferase reporter constructs were generated and transfected into liver HepG2, ovarian CHO, kidney HEK-293 and neuronal N2A cells for functional characterization of the promoter SNPs. The BPH-Hmgcr promoter showed significantly less activity than the BPL-Hmgcr promoter under basal as well as nicotine/cholesterol-treated conditions. This finding was consistent with lower endogenous Hmgcr expression in liver and lower plasma cholesterol in BPH mice. Transfection experiments using 5′-promoter deletion constructs (strategically made to assess the functional significance of each promoter SNP) and computational analysis predicted lower binding affinities of transcription factors c-Fos, n-Myc and Max with the BPH-promoter as compared to the BPL-promoter. Corroboratively, the BPH promoter-luciferase reporter construct co-transfected with expression plasmids of these transcription factors displayed less pronounced augmentation of luciferase activity than the BPL construct, particularly at lower amounts of transcription factor plasmids. Electrophoretic mobility shift assays also showed diminished interactions of the BPH promoter with HepG2 nuclear proteins. Taken together, this study provides mechanistic basis for the differential Hmgcr expression in these mouse models of human essential hypertension and have implications for better understanding the role of this gene in regulation of blood pressure
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