Search results for " Boundary"
showing 10 items of 686 documents
A numerical model of the cloud-topped planetary boundary-layer: cloud processing of aerosol particles in marine stratus
1999
Abstract In a numerical study with the one-dimensional chemical microphysical stratus model CHEMISTRA the effect of stratiform clouds on aerosol particles is investigated. The microphysical part of CHEMISTRA consists of a detailed description of cloud microphysical processes by means of a joint two-dimensional particle distribution for aerosols and cloud droplets. In the chemical part of the model the particle spectrum is subdivided into three categories referring to inactivated aerosols, small and large cloud droplets. Aqueous phase chemical reactions are separately treated in the two droplet size classes. Numerical results are presented demonstrating that the uptake of trace gases by clou…
The Role of Zr in the High-Temperature Oxidation of Fe<sub>3</sub>Al
2008
The paper describes an examination of the effect of the addition of zirconium as a third element on the heat-resisting properties and explains the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The Fe3Al and Fe3Al-0,05Zr specimens have been isothermally oxidized in the temperature range of 1173-1473 K in synthetic air for 100 hrs. The formed oxide layer, about 1,5-2 μm thick, was Al2O3. An examination of the cross-sectioned scales by SEM-EDS showed that the alumina layer consisted of a small inner columnar layer and an outer equiaxed grain layer. Additionally, very fine (50-150 nm) oxide grains rich in Zr, further identified as ZrO2, were found across the alumina sca…
Planar systems with critical points: multiple solutions of two-point nonlinear boundary value problems
2005
Abstract Two-point boundary value problems for the second-order ordinary nonlinear differential equations are considered. First, we consider the planar systems equivalent to equation x ″ = f ( x ) , where f ( x ) has multiple zeros and the respective system has centers and saddle points in various combinations. Estimations of the number of solutions are given. Then results are extended to nonautonomous equations which have superlinear behavior at infinity.
Study of the reactive dynamics of nanometric metallic multilayers using Molecular Dynamics: the Al−Ni system
2012
A molecular dynamics study of a layered Ni-Al-Ni system is developed using an embedded atom method potential. The specific geometry is designed to model a Ni-Al nanometric metallic multilayer. The system is initially thermalized at the fixed temperature of 600 K. We first observe the interdiffusion of Ni and Al at the interfaces, which is followed by the spontaneous phase formation of B2-NiAl in the Al layer. The solid-state reaction is associated with a rapid system's heating which further enhances the diffusion processes. NiAl phase is organized in small regions separated by grain boundaries. This study confirms the hypothesis of a layer-by-layer development of the new phase. For longer t…
Facies stacking and extinctions across the Triassic–Jurassic boundary in a peritidal succession from western Sicily
2017
An uppermost Triassic–lowermost Jurassic carbonate platform succession, which is 430 m thick, in northwestern Sicily is described with the aim to provide new data on the sedimentological and biological variations across the Triassic–Jurassic boundary in peritidal environments. The studied succession belonged to the rimmed carbonate shelf that developed during the upper Triassic along the margins of the Ionian Tethys. The peritidal sediments consist of metre-scale shallowing-upward cycles formed by subtidal, intertidal and supratidal facies. Three main informal units are differentiated along the section on the basis of the variations recorded by the subtidal facies. The lower and middle unit…
Mercury contents and isotope ratios from diverse depositional environments across the Triassic–Jurassic Boundary: Towards a more robust mercury proxy…
2021
Abstract Mercury is gaining prominence as a proxy for large igneous province (LIP) volcanism in the sedimentary record. Despite temporal overlap between some mass extinctions and LIPs, the precise timing of magmatism relative to major ecological and environmental change is difficult to untangle, especially in marine settings. Changes in the relative contents of Hg in sedimentary rocks through time, or ‘Hg anomalies’, can help resolve the timing of LIP activity and marine extinctions. However, major questions remain unanswered about the fidelity of Hg as a proxy for LIP magmatism. In particular, depositional (e.g., redox) and post-depositional (e.g., oxidative weathering) processes can affec…
General framework for testing Poisson-Voronoi assumption for real microstructures
2020
Modeling microstructures is an interesting problem not just in Materials Science but also in Mathematics and Statistics. The most basic model for steel microstructure is the Poisson-Voronoi diagram. It has mathematically attractive properties and it has been used in the approximation of single phase steel microstructures. The aim of this paper is to develop methods that can be used to test whether a real steel microstructure can be approximated by such a model. Therefore, a general framework for testing the Poisson-Voronoi assumption based on images of 2D sections of real metals is set out. Following two different approaches, according to the use or not of periodic boundary conditions, thre…
A second-order sparse factorization method for Poisson's equation with mixed boundary conditions
1992
Abstract We propose an algorithm for solving Poisson's equation on general two-dimensional regions with an arbitrary distribution of Dirichlet and Neumann boundary conditions. The algebraic system, generated by the five-point star discretization of the Laplacian, is solved iteratively by repeated direct sparse inversion of an approximating system whose coefficient matrix — the preconditioner — is second-order both in the interior and on the boundary. The present algorithm for mixed boundary value problems generalizes a solver for pure Dirichlet problems (proposed earlier by one of the authors in this journal (1989)) which was found to converge very fast for problems with smooth solutions. T…
A symmetric Galerkin boundary/domain element method for finite elastic deformations
2000
Abstract The Symmetric Galerkin Boundary Element Method (SGBEM) is reformulated for problems of finite elasticity with hyperelastic material and incompressibility, using fundamental solutions related to a (fictitious) homogeneous isotropic and compressible linear elastic material. The proposed formulation contains, besides the standard boundary integrals, domain integrals which account for the problem's nonlinearities through some (fictitious) initial strain and stress fields required to satisfy appropriate “consistency” equations. The boundary/domain integral equation problem so obtained is shown to admit a stationarity principle (a consequence of the Hu-Washizu one), which covers a number…
BEM application on an external problem comparison with both theoretical and finite elements results and observations on divergence strip
1992
Abstract By means of a computer program the Boundary Element Method is applied to a central hole in an undefined plate with uniform load along the boundary. Results are compared with those obtained by Kirsch's theoretical solution and a previous analysis by the Finite Element Method. The calculus of percentage error shows the advantage of the Boundary Element Method on the external problem with regard to the Finite Element Method. The error causes near the boundary internal points are analysed with the existence of a strip, where the result is not reliable in evidence.