Search results for " diffusion"
showing 10 items of 521 documents
A Positive Definite Advection Scheme for Use in Long Range Transport Models: Extension to Monotonicity
1992
Numerical modeling of atmospheric transport processes requires the solution of the continuity equation for prognostic variables such as momentum, heat, water vapor, liquid water or chemical species of the atmosphere. Although in the literature many advection schemes are known to solve this problem (Lax and Wendroff 1964, Crowley 1968, Tremback et al. 1987, Bott 1989a,b), these algorithms show different disadvantages, which sometimes yield undesirably poor numerical results. For instance, the upstream method is known to produce large numerical diffusion. The higher order versions of the advection schemes of Tremback et al. (1987) are much less diffusive. Unfortunately, the schemes are not po…
Measurements of ultrafast spin-profiles and spin-diffusion properties in the domain wall area at a metal/ferromagnetic film interface
2017
AbstractExciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization…
Respiratory Gas Transport in Heart
1973
The purpose of this paper is to describe an attempt to obtain a better understanding of the dynamics of the oxygen supply of the myocardium under physiological and pathophysiological conditions by examining the oxygen diffusion in the heart muscle tissue during systole and diastole. In comparison to other organs the oxygen supply of the myocardium is characterized by a number of specific features. The most important one is that the gas exchange in the myocardium is a nonsteady-state diffusion process.
Experimental Investigations on Hair Fibers as Diffusion Bridges and Opiates as Solutes in Solution
1996
Diffusion experiments were performed using clipped hair fibers as diffusion bridges and aqueous solutions of morphine, codeine and dihydrocodeine. Natural as well as predamaged hair fibers were investigated. The test series were conducted at ambient temperature and at high humidity. After 312 or 372 hours the middle segments of the strands were clipped, washed and analyzed by GC/MS. Only when virgin hair samples were used the solutes passed along the fiber at full length resulting in a positive immunological finding at the end of the diffusion bridge. Most of the washing fluids were positive for opiates. All centerpieces had a high opiate content. The opiate concentration in damaged hair wa…
Sbarchi
2021
During 2020, the Mediterranean Sea was again the testing ground for migration flows from North Africa and the Middle East to Italy, Greece and Spain. 2020 was also a complex year due to the spread of the COVID-19 pandemic. Movements between countries were affected by the spread of the virus that spared no one and imposed the need to reflect on 'global health' and the consequences that this has, also in the relationship between countries and in travel.
Local and nonlocal weighted pLaplacian evolution equations with Neumann boundary conditions
2011
In this paper we study existence and uniqueness of solutions to the local diffusion equation with Neumann boundary conditions and a bounded nonhomogeneous diffusion coefficient g ≥ 0, {ut = div (g|∇u|p-2∇u) in ]0; T[×Ωg|∇u|p-2u·n = 0 on ]0; T[×∂Ω; for 1 ≤ p < ∞. We show that a nonlocal counterpart of this diffusion problem is ut(t; x)= ∫ω J(x-y)g(x+y/2)|u(t; y)-u(t; x)| p-2 (u(t; y)-u(t; x)) dy in ]0; T[× Ω,where the diffusion coefficient has been reinterpreted by means of the values of g at the point x+y/2 in the integral operator. The fact that g ≥ 0 is allowed to vanish in a set of positive measure involves subtle difficulties, specially in the case p = 1.
A nonlocal p-Laplacian evolution equation with Neumann boundary conditions
2008
In this paper we study the nonlocal p-Laplacian type diffusion equation,ut (t, x) = under(∫, Ω) J (x - y) | u (t, y) - u (t, x) |p - 2 (u (t, y) - u (t, x)) d y . If p > 1, this is the nonlocal analogous problem to the well-known local p-Laplacian evolution equation ut = div (| ∇ u |p - 2 ∇ u) with homogeneous Neumann boundary conditions. We prove existence and uniqueness of a strong solution, and if the kernel J is rescaled in an appropriate way, we show that the solutions to the corresponding nonlocal problems converge strongly in L∞ (0, T ; Lp (Ω)) to the solution of the p-Laplacian with homogeneous Neumann boundary conditions. The extreme case p = 1, that is, the nonlocal analogous t…
Dynamic nuclear polarisation of biological matter
1986
Polarised targets as used in high energy physics experiments may be of considerable interest in biological structure research using polarized neutrons. So far, this promising method has been facing difficulties in getting reasonable polarization of the target nuclei. We report on a polarized "frozen spin" target which has been prepared from an enzyme dissolved in a mixture of heavy water and deuterated propanediol doped with a completely deuterated paramagnetic radical. Clusters of 700 protons defined by the structure of lysozyme embedded in a fully deuterated matrix were polarized to 75% within an hour by 4 mm microwave irradiation in a magnetic field of 2.5 tesla at a temperature of 0.3 K…
Solubility and diffusion of nitrogen in maltodextrin/protein tablets.
2002
The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree …
Cross-diffusion driven instability for a Lotka-Volterra competitive reaction-diffusion system
2008
In this work we investigate the possibility of the pattern formation for a reaction-di®usion system with nonlinear di®usion terms. Through a linear sta- bility analysis we ¯nd the conditions which allow a homogeneous steady state (stable for the kinetics) to become unstable through a Turing mechanism. In particular, we show how cross-di®usion e®ects are responsible for the initiation of spatial patterns. Finally, we ¯nd a Fisher amplitude equation which describes the weakly nonlinear dynamics of the system near the marginal stability.