Search results for "surface layer"
showing 10 items of 72 documents
Bright hot impacts by erupted fragments falling back on the Sun: UV redshifts in stellar accretion
2014
A solar eruption after a flare on 7 Jun 2011 produced EUV-bright impacts of fallbacks far from the eruption site, observed with the Solar Dynamics Observatory. These impacts can be taken as a template for the impact of stellar accretion flows. Broad red-shifted UV lines have been commonly observed in young accreting stars. Here we study the emission from the impacts in the Atmospheric Imaging Assembly's UV channels and compare the inferred velocity distribution to stellar observations. We model the impacts with 2D hydrodynamic simulations. We find that the localised UV 1600A emission and its timing with respect to the EUV emission can be explained by the impact of a cloud of fragments. The …
Stock market dynamics and turbulence: parallel analysis of fluctuation phenomena
1997
Abstract We report analogies and differences between the fluctuations in an economic index and the fluctuations in velocity of a fluid in a fully turbulent state. Specifically, we systematically compare (i) the statistical properties of the S&P 500 cash index recorded during the period January 84–December 89 with (ii) the statistical properties of the velocity of turbulent air measured in the atmospheric surface layer about 6 m above a wheat canopy in the Connecticut Agricultural Research Station. We find non-Gaussian statistics, and intermittency, for both processes (i) and (ii) but the deviation from a Gaussian probability density function are different for stock market dynamics and turbu…
Adsorption and diffusion of a molybdenum atom on theTiO2(110)surface: A first-principles study
2007
A study on the structure and energetics of a single molybdenum atom adsorbed on the $\mathrm{Ti}{\mathrm{O}}_{2}(110)$ surface is reported. All possible adsorption sites have been determined. Moreover, it is found that incorporation of the Mo atom into the first surface layer leads to considerably more stable structures than on any adsorption site. Different channels for migration of the molybdenum atom have been identified. The diffusion barriers of these channels have been determined. The results on structure and energetics are discussed by analyzing the electronic properties of the $\mathrm{Mo}∕\mathrm{Ti}{\mathrm{O}}_{2}(110)$ systems.
Critical behavior of the surface-layer magnetization at the extraordinary transition in the three-dimensional Ising model.
1990
We have used a vectorized multispin-coding Monte Carlo method to determine the behavior of the surface-layer magnetization ${\mathit{m}}_{1}$ at the bulk transition in a simple-cubic Ising film with strongly enhanced surface coupling, i.e., at the extraordinary transition. In contrast to recent renormalization-group calculations we find no evidence for a discontinuous slope in the temperature dependence of ${\mathit{m}}_{1}$; the data are consistent with a free-energy-like (T-${\mathit{T}}_{\mathit{c}}$${)}^{2\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$ behavior plus background terms.
Effect of Cu-Zn coated steel fibers on high temperature resistance of reactive powder concrete
2019
Abstract Even though many studies have reported about the impacts of shape, length and distribution of steel fiber reinforcement on global concrete properties, there is a lack of information about the influence of coating type of steel fibers on high temperature resistance of concrete. This paper describes the effect of Cu-Zn coated steel fibers on selected properties of reactive powder concrete (RPC) after exposure to elevated temperatures. The initial corrosion of zinc in Cu-Zn surface layer is found to be already activated by the alkaline environment of the fresh concrete. The RPC samples reinforced with Cu-Zn coated steel fibers are heated to 600 °C and 1000 °C, and the influence of the…
Thermally induced structural modifications and O2 trapping in highly porous silica nanoparticles
2014
Abstract In this work we investigate by Raman spectroscopy the effect of isochronal (2 h) thermal treatments in air in the temperature range 200–1000 °C of amorphous silicon dioxide porous nanoparticles with diameters ranging from 5 up to 15 nm and specific surface 590–690 m2/g. Our results indicate that the amorphous structure changes similarly to other porous systems previously investigated, in fact superficial SiOH groups are removed, Si–O–Si linkages are created and the ring statistic is modified, furthermore these data evidence that the three membered rings do not contribute significantly to the Raman signal detected at about 495 cm−1. In addition, after annealing at 900 and 1000 °C we…
Surface versus bulk composition of a phosphate glass
1994
Transmission and conversion electron Mossbauer spectroscopy as well as photoelectron spectroscopy were applied to study alterations of the surface layer of an iron containing industrial phosphate glass as compared with its bulk. In the surface layer, after polishing and exposure to ambient atmosphere, Fe 2+ is partially oxidized to Fe 3+ . This oxidation, however, does not increase the O/P ratio in this layer, because it goes along with a strong leaching of network modifiers. This leaching leads to a net decrease of the O/P ratio because it overcompensates the relative oxygen increase by Fe 2+ oxidation and by uptake of water
Electronic and magnetic properties of Mn 12 molecular magnets on sulfonate and carboxylic acid prefunctionalized gold surfaces
2012
Structural, electronic, and magnetic properties of [Mn 12O 12(bet) 16(EtOH) 4](PF 6) 14·4CH 3CN·H 2O (in short Mn 12bet, bet = betaine = +N(CH 3) 3-CH 2-COO -) single-molecule magnets (SMMs) deposited on previously functionalized gold surfaces have been investigated. Self-assembled monolayers (SAMs) either of sodium mercaptoethanesulfonate (MES) or mercaptopropionic acid (MPA) are used as functionalization to avoid the direct interaction between the Mn 12bet molecules and the Au surface with the aim of preserving the main functional properties of the molecules. Scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) analysis show deposited Mn 12bet SMMs well-isolated …
M�ssbauer study of the spatial distribution of the active species in Cs doped Fe2O3-V2O5 catalysts
1995
From a Cs doped Fe2O3-V2O5 (Fe:V=1.4) catalyst exhibiting an inhomogeneous composition after calcination, three different fractions have been separated by visual inspection. One fraction has been found to consist of mainly α-Fe2O3, another one of mainly FeVO4. The third fraction (S1 in the text) is the catalytically most active fraction containing besides both of the former components an amorphous phase of FexVyOz and also the dopant. By combining the results from transmission and conversion electron Mossbauer spectra it has been concluded that the amorphous component is enriched in the surface region of the crystallites of the catalyst. In addition, the formation of a thin surface layer of…
First-principles calculations on surface hydroxyl impurities in BaF2
2012
Abstract OH − impurities located near the (1 1 1) BaF 2 surface have been studied by using density functional theory (DFT) with hybrid exchange potentials, namely DFT-B3PW. Twenty surface OH − configurations were studied, and the hydroxyls located on the first surface layer are the energetically most favorable configurations. For the (1 1 1) BaF 2 surface atomic layers, the surface hydroxyls lead to a remarkable XY -translation and a dilating effect in the Z -direction, overcoming the surface shrinking effect in the perfect slab. Bond population analysis shows that the surface effect strengthens the covalency of surface OH − impurities. The studies on band structures and density of states (…