Search results for "Solid"
showing 10 items of 3575 documents
The dynamics of magnetic ordering in a natural hemo-ilmenite solid solution
2007
Geophysical Journal International, 169 (3)
Ab initiothermodynamics ofBacSr(1−c)TiO3solid solutions
2005
Based on ab initio calculations for a number of the ${\mathrm{Ba}}_{\mathrm{c}}{\mathrm{Sr}}_{(1\ensuremath{-}\mathrm{c})}\mathrm{Ti}{\mathrm{O}}_{3}$ (BST) superlattices, we developed a thermodynamic approach to these solid solutions. In particular, we calculate the BST phase diagram and show that at relatively low temperatures (below $400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.5$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $c=0.1$) the spinodal decomposition of the solid solution occurs. As a result, we predict for small Ba concentrations formation of $\mathrm{Ba}\mathrm{Ti}{\mathrm{O}}_{3}$ nanoregions in a predominantly $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ matrix and …
The relaxation dynamics of a supercooled liquid confined by rough walls
2004
We present the results of molecular dynamics computer simulations of a binary Lennard-Jones liquid confined between two parallel rough walls. These walls are realized by frozen amorphous configurations of the same liquid and therefore the structural properties of the confined fluid are identical to the ones of the bulk system. Hence this setup allows us to study how the relaxation dynamics is affected by the pure effect of confinement, i.e. if structural changes are completely avoided. We find that the local relaxation dynamics is a strong function of z, the distance of the particles from the wall, and that close to the surface the typical relaxation times are orders of magnitude larger tha…
Luminescence from nearly isolated surface defects in silica nanoparticles
2015
A structured emission/excitation pattern, proper of isolated defects, arises in a vacuum from silica nanoparticles. The luminescence, centered around 3.0-3.5 eV, is characterised by a vibronic progression due to the phonon coupling with two localised modes of frequency ∼1370 cm(-1) and ∼360 cm(-1), and decays in about 300 ns at 10 K. On increasing the temperature, the intensity and the lifetime decrease due to the activation of a non-radiative rate from the excited state. Concurrently, the temperature dependence of the lineshape evidences the low coupling with non-localised modes of the matrix (Huang-Rhys factor S ~ 0.2) and the poor influence of the inhomogeneous broadening. These findin…
Measuring Multiple Residual-Stress Components using the Contour Method and Multiple Cuts
2009
The conventional contour method determines one component of residual stress over the cross section of a part. The part is cut into two, the contour (topographic shape) of the exposed surface is measured, and Bueckner’s superposition principle is analytically applied to calculate stresses. In this paper, the contour method is extended to the measurement of multiple residual-stress components by making multiple cuts with subsequent applications of superposition. The theory and limitations are described. The theory is experimentally tested on a 316L stainless steel disk with residual stresses induced by plastically indenting the central portion of the disk. The multiple-cut contour method resu…
Near-surface defect profiling with slow positrons: Argon-sputtered Al(110).
1985
We report on slow-positron measurements of atomic defect distribution near a solid surface. Defects are produced by argon-ion bombardment of an Al(110) surface in ultrahigh vacuum. Defect profiles have a typical width of 15–25 Å and contain a broader tail extending to 50–100 Å. The defect density at the outermost atomic layers saturates at high argon fluences to a few atomic percent, depending on sputtering conditions. Defect production rate at >1 keV Ar+ energies is typically 1–5 vacancy-interstitial pairs per incident ion. Molecular-dynamics simulations of the collision cascade predict similar defect distributions. Peer reviewed
Static and dynamical properties of a supercooled liquid confined in a pore
2000
We present the results of a Molecular Dynamics computer simulation of a binary Lennard-Jones liquid confined in a narrow pore. The surface of the pore has an amorphous structure similar to that of the confined liquid. We find that the static properties of the liquid are not affected by the confinement, while the dynamics changes dramatically. By investigating the time and temperature dependence of the intermediate scattering function we show that the dynamics of the particles close to the center of the tube is similar to the one in the bulk, whereas the characteristic relaxation time tau_q(T,rho) of the intermediate scattering function at wavevector q and distance rho from the axis of the p…
Boolean operations with implicit and parametric representation of primitives using R-functions
2005
We present a new and efficient algorithm to accurately polygonize an implicit surface generated by multiple Boolean operations with globally deformed primitives. Our algorithm is special in the sense that it can be applied to objects with both an implicit and a parametric representation, such as superquadrics, supershapes, and Dupin cyclides. The input is a constructive solid geometry tree (CSG tree) that contains the Boolean operations, the parameters of the primitives, and the global deformations. At each node of the CSG tree, the implicit formulations of the subtrees are used to quickly determine the parts to be transmitted to the parent node, while the primitives' parametric definition …
Standardization of Methods for Characterizing the Surface Geometry of Solids
2003
Since a comprehensive survey published in 1999 [1] much work was done in standardizing measuring methods to characterize the surface geometry of dispersed and/or porous solids and to certify reference materials. The present paper is an extension of a short communication [2]. It gives a survey on existing standards and reports on new drafts and proposals.
On dewetting dynamics of solid films of hydrogen isotopes and its influence on tritium [Beta] spectroscopy
2000
The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed T2 film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated.