Search results for " Diffusion"
showing 10 items of 521 documents
Approximation of exit times for one-dimensional linear diffusion processes
2020
International audience; In order to approximate the exit time of a one-dimensional diffusion process, we propose an algorithm based on a random walk. Such an algorithm was already introduced in both the Brownian context and the Ornstein-Uhlenbeck context, that is for particular time-homogeneous diffusion processes. Here the aim is therefore to generalize this efficient numerical approach in order to obtain an approximation of both the exit time and position for a general linear diffusion. The main challenge of such a generalization is to handle with time-inhomogeneous diffusions. The efficiency of the method is described with particular care through theoretical results and numerical example…
Pressure solution compaction of sodium chlorate and implications for pressure solution in NaCl
1999
Sodium chloride (NaCl) has been extensively used as a material to develop, test and improve pressure solution (PS) rock deformation models. However, unlike silicate and carbonate rocks, NaCl can deform plastically at very low stresses (0.5 MPa). This could mean that NaCl is less suitable for use as an analogue for rocks that do not deform plastically at conditions where PS is important. In order to test the reliability of NaCl as a rock analogue, we carried out a series of uniaxial compaction experiments on sodium chlorate (NaClO3) at room pressure and temperature (P‐T) conditions and applied effective stresses of 2.4 and 5.0 Mpa. NaClO3 is a very soluble, elastic‐brittle salt, that cannot …
Exact simulation of first exit times for one-dimensional diffusion processes
2019
International audience; The simulation of exit times for diffusion processes is a challenging task since it concerns many applications in different fields like mathematical finance, neuroscience, reliability horizontal ellipsis The usual procedure is to use discretization schemes which unfortunately introduce some error in the target distribution. Our aim is to present a new algorithm which simulates exactly the exit time for one-dimensional diffusions. This acceptance-rejection algorithm requires to simulate exactly the exit time of the Brownian motion on one side and the Brownian position at a given time, constrained not to have exit before, on the other side. Crucial tools in this study …
Green Synthesis, Molecular Characterization and Associative Behavior of Some Gemini Surfactants without a Spacer Group.
2013
A series of new gemini surfactants without a spacer group, disodium 2,3-dialkyl-1,2,3,4-butanetetracarboxylates, were synthesized in a green chemistry context minimizing the use of organic solvents and applying microwaves (MW) when activation energy was required. Once the desired architecture was confirmed by means of the nuclear magnetic resonance technique (1H-NMR, 1H-1H COSY) for all the studied surfactants, the critical micellization concentration was determined by conductance measurements. The diffusion coefficient of micelles formed by the four compounds was characterized using pulsed field gradient (PFG)-NMR. Diffusion coefficients were found to be dependent on the concentration and …
Multi-scale analysis of apparent diffusion coefficient (ADC) predicts cervical nodal status in patients with head and neck squamous cell carcinoma
2013
The study assess multi-scale diffusion parameters (median volumetric nodal region of interest values, inter-voxel histogram distributions, and intra-voxel diffusion heterogeneity as assessed by the stretched exponential model) as classifiers of nodal status in patients with head and neck squamous cell carcinoma (SCC). Low b value (0, 50, 100) derived nodal ADC (perfusion sensitive) was the key parameter facilitating discrimination of metastatic from benign nodes in patients with head and neck SCC. The stretched exponential derived α value together with histogram features of ADC provide an accurate decision tree model for classification of nodal disease.
A PHENOMENOLOGICAL OPERATOR DESCRIPTION OF INTERACTIONS BETWEEN POPULATIONS WITH APPLICATIONS TO MIGRATION
2013
We adopt an operatorial method based on the so-called creation, annihilation and number operators in the description of different systems in which two populations interact and move in a two-dimensional region. In particular, we discuss diffusion processes modeled by a quadratic hamiltonian. This general procedure will be adopted, in particular, in the description of migration phenomena. With respect to our previous analogous results, we use here fermionic operators since they automatically implement an upper bound for the population densities.
Global stability analysis of a delay cell-population model of hepatitis B infection with humoral immune response
2021
In this work, we propose and investigate a delay cell population model of hepatitis B virus (HBV) infection. We suppose spatial diffusion of free HBV particles, and use a Beddington-DeAngelis incid...
Computational general relativistic force-free electrodynamics
2021
Scientific codes are an indispensable link between theory and experiment; in (astro-)plasma physics, such numerical tools are one window into the universe's most extreme flows of energy. The discretization of Maxwell's equations - needed to make highly magnetized (astro)physical plasma amenable to its numerical modeling - introduces numerical diffusion. It acts as a source of dissipation independent of the system's physical constituents. Understanding the numerical diffusion of scientific codes is the key to classify their reliability. It gives specific limits in which the results of numerical experiments are physical. We aim at quantifying and characterizing the numerical diffusion propert…
Optimization of ZnO:Al/Ag/ZnO:Al structures for ultra-thin high-performance transparent conductive electrodes
2012
Al-doped ZnO (AZO)/Ag/AZO multilayer coatings (50-70 nm thick) were grown at room temperature on glass substrates with different silver layer thickness, from 3 to 19 nm, by using radio frequency magnetron sputtering. Thermal stability of the compositional, optical and electrical properties of the AZO/Ag/AZO structures were investigated up to 400 °C and as a function of Ag film thickness. An AZO film as thin as 20 nm is an excellent barrier to Ag diffusion. The inclusion of 9.5 nm thin silver layer within the transparent conductive oxide (TCO) material leads to a maximum enhancement of the electro-optical characteristics. The excellent measured properties of low resistance, high transmittanc…
La diffusion des NTIC au sein du réseau urbain français et le rôle des acteurs publics
2001
The study deals with the ways in which the general public and the government make use of new information and communication technologies. We analyze the physical locations of Internet sites with “fr” as their domain names. The data were provided by the French NIC center (AFNIC). Using this sample (a quarter of all French sites), we find a rather even distribution of French sites in the Paris area plus the other main French cities, and the remainder of France. In addition, we try to enumerate the initiatives of the public actors responsible for the regional planning of the new information and communication technologies. Firstly, we clarify the economic and legal framework in which public acto…