Search results for "boundary"
showing 10 items of 1626 documents
Thermoconvective instability and local thermal non-equilibrium in a porous layer with isoflux-isothermal boundary conditions
2014
The effects of lack of local thermal equilibrium between the solid phase and the fluid phase are taken into account for the convective stability analysis of a horizontal porous layer. The layer is bounded by a pair of plane parallel walls which are impermeable and such that the lower wall is subject to a uniform flux heating, while the upper wall is isothermal. The local thermal non-equilibrium is modelled through a two-temperature formulation of the energy exchange between the phases, resulting in a pair of local energy balance equations: one for each phase. Small-amplitude disturbances of the basic rest state are envisaged to test the stability. Then, the standard normal mode procedure is…
Low-pressure-MOCVD LaMnO3±δ very thin films on YSZ (100) optimized for studies of the triple phase boundary
2000
Abstract This paper deals with the preparation of LaMnO 3± δ (LM) layers by low pressure-metal organic chemical vapor deposition (LP-MOCVD) using La(tmhd) 3 and Mn(acac) 3 as organometallic precursors. By thermogravimetric analysis, these precursors were found to be suitable for LP-MOCVD in a well-defined range of total pressure and temperature of sublimation. The activation energies of the sublimation process were found to be independent of the pressure within the appropriate range (0.06–3 kPa) and their values were 177 and 100.5 kJ mol −1 for La(tmhd) 3 and Mn(acac) 3 , respectively. LM layers of various thickness ranging between a few and a few hundred nanometers with a controlled La/Mn …
Thixotropy of Highly Viscous Sodium (Carboxymethyl)cellulose Hydrogels
1997
A general method to quantify the thixotropic behavior of systems with very low thixotropy is proposed. The areas enclosed by the rheograms τ=fγ. must be fitted to functions with well-determined boundary conditions. From these equations the corresponding thixotropic areas are obtained, together with the theoretical area enclosed by the rheogram corresponding to the maximum rheodestruction. The proposed method is applied to high viscosity sodium (carboxymethyl)cellulose gels.
Variational formulations and extra boundary conditions within stress gradient elasticity theory with extensions to beam and plate models
2016
Abstract The principle of minimum total potential energy and the primary principle of virtual power for stress gradient elasticity are presented as kinematic type constructs dual of analogous static type principles from the literature (Polizzotto, 2014; Polizzotto, 2015a). The extra gradient-induced boundary conditions are formulated as “boundary congruence conditions” on the microstructure’s deformation relative to the continuum, which ultimately require that the normal derivative of the stresses must vanish at the boundary surface. Two forms of the governing PDEs for the relevant boundary-value problem are presented and their computational aspects are discussed. The Timoshenko beam and th…
A mechanically based approach to non-local beam theories
2011
A mechanically based non-local beam theory is proposed. The key idea is that the equilibrium of each beam volume element is attained due to contact forces and long-range body forces exerted, respectively, by adjacent and non-adjacent volume elements. The contact forces result in the classical Cauchy stress tensor while the long-range forces are modeled as depending on the product of the interacting volume elements, their relative displacement and a material-dependent distance-decaying function. To derive the beam equilibrium equations and the pertinent mechanical boundary conditions, the total elastic potential energy functional is used based on the Timoshenko beam theory. In this manner, t…
Analytical solution for the magneto-electro-elastic bimorph beam forced vibrations problem
2009
Based on the Timoshenko beam theory and on the assumption that the electric and magnetic fields can be treated as steady, since elastic waves propagate very slowly with respect to electromagnetic ones, a general analytical solution for the transient analysis of a magneto-electro-elastic bimorph beam is obtained. General magneto-electric boundary conditions can be applied on the top and bottom surfaces of the beam, allowing us to study the response of the bilayer structure to electromagnetic stimuli. The model reveals that the magneto-electric loads enter the solution as an equivalent external bending moment per unit length and as time-dependent mechanical boundary conditions through the def…
Shipborne measurements of Antarctic submicron organic aerosols: an NMR perspective linking multiple sources and bioregions
2020
Special issue Marine organic matter: from biological production in the ocean toorganic aerosol particles and marine clouds (ACP/OS inter-journalSI).-- 15 pages, 8 figures, 1 table, supplement https://doi.org/10.5194/acp-20-4193-2020
Trace and density results on regular trees
2019
We give characterizations for the existence of traces for first order Sobolev spaces defined on regular trees.
Symmetric Galerkin BEM for Non Linear Analysis of Historical Masonries
2015
The preservation of the historical and monumental buildings, but also of the considerable heritage of old constructions made by traditional techniques, is one of the actual problems of the structural mechanics. The level of knowledge of their structural behavior in presence of external actions is made through calculus methods and simple procedures in order to allow a reading of the material suffering degree and as a consequence of the related safety. Unfortunately, often the masonry panels show openings located in an irregular way and cracks having small or big dimensions. In these cases the employment of strategies, as for example the identifying of the masonry piers and the transformation…
BRT in the Philippines: A Solution to Manila and Cebu Traffic Problems?
2019
Abstract Bus Rapid Transit (BRT), where buses run on dedicated roads at high frequency, almost in a metrorail manner, has been adopted as a backbone of urban mobility in the cities of many developing countries. Originally developed in South America (Curitiba, Brazil and Bogotá, Colombia), it has entered Asia with force, from Indonesia (Jakarta’s Transjakarta) to India and China. In the case of the Philippines, where intercity bus transportation is widely used due to the current lack of a railway network, city traffic, especially in Manila, is heavily congested, partly due to a high number of city buses running half-empty, the small proportion of road space relative to the vehicle population…