Search results for " diffusion"

Diffusion, thermodiffusion, and thermal diffusion of polystyrene in solution

1962

Physics, Techniques and Review of Neuroradiological Applications of Diffusion Kurtosis Imaging (DKI)

2016

In recent years many papers about diagnostic applications of diffusion tensor imaging (DTI) have been published. This is because DTI allows to evaluate in vivo and in a non-invasive way the process of diffusion of water molecules in biological tissues. However, the simplified description of the diffusion process assumed in DTI does not permit to completely map the complex underlying cellular components and structures, which hinder and restrict the diffusion of water molecules. These limitations can be partially overcome by means of diffusion kurtosis imaging (DKI). The aim of this paper is the description of the theory of DKI, a new topic of growing interest in radiology. DKI is a higher or…

Magic numbers, excitation levels, and other properties of small neutral math clusters (N < 50)

2006

The ground-state energies and the radial and pair distribution functions of neutral math clusters are systematically calculated by the diffusion Monte Carlo method in steps of one math atom from 3 to 50 atoms. In addition the chemical potential and the low-lying excitation levels of each cluster are determined with high precision. These calculations reveal that the “magic numbers” observed in experimental math cluster size distributions, measured for free jet gas expansions by nondestructive matter-wave diffraction, are not caused by enhanced stabilities. Instead they are explained in terms of an enhanced growth due to sharp peaks in the equilibrium concentrations in the early part of the e…

A dynamic air–liquid interface system for in vitro mimicking of the nasal mucosa

2022

The development of an in vitro 3D model for the growth of the nasal mucosa cells can improve the therapy and the study of pathological states for subjects with chronic airway conditions. We have previously characterized a system consisting of a scaffold with an internal channel and a perfusion bioreactor with two independent flows provided by an external and an internal circuit, respectively. In this paper, this system was designed as a model of the nasal cavity, in which cells, grown on the inner surface of the scaffold channel, would be in contact at the same time with both culture medium, supplied by the external circuit, and air, provided with the internal flow. To ensure adequate nutri…

Transport of dipeptides and phosphono dipeptides through an immobilized liquid membrane. Stereoselectivity of the process

1993

Abstract Dipeptide and phosphono dipeptide hydrochlorides permeated well through a 1-decanol membrane supported in a porous polyethylene hollow fiber matrix. This transfer is easily accomplished either by passive or by carrier-facilitated (with Kryptofixes 222 or 5 present in the membrane phase) transport. The transport is stereoselective with l-l dipeptides being transported faster than their l-d isomers.

Nonlinear Diffusion in Transparent Media

2021

Abstract We consider a prototypical nonlinear parabolic equation whose flux has three distinguished features: it is nonlinear with respect to both the unknown and its gradient, it is homogeneous, and it depends only on the direction of the gradient. For such equation, we obtain existence and uniqueness of entropy solutions to the Dirichlet problem, the homogeneous Neumann problem, and the Cauchy problem. Qualitative properties of solutions, such as finite speed of propagation and the occurrence of waiting-time phenomena, with sharp bounds, are shown. We also discuss the formation of jump discontinuities both at the boundary of the solutions’ support and in the bulk.

The differences between distributed shared memory caching and proxy caching

2000

The authors discuss the similarities in caching between the extensively studied distributed shared memory systems and the emerging proxy systems. They believe that several of the techniques used in distributed shared memory systems can be adapted and applied to proxy systems.

From the Golgi-Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring a…

2007

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrai…

Swing options in commodity markets: a multidimensional Lévy diffusion model

2013

Author's version of an article in the journal: Mathematical Methods of Operations Research. Also available from the publisher at: http://dx.doi.org/10.1007/s00186-013-0452-7 We study valuation of swing options on commodity markets when the commodity prices are driven by multiple factors. The factors are modeled as diffusion processes driven by a multidimensional Lévy process. We set up a valuation model in terms of a dynamic programming problem where the option can be exercised continuously in time. Here, the number of swing rights is given by a total volume constraint. We analyze some general properties of the model and study the solution by analyzing the associated HJB-equation. Furthermo…

Solid-state diffusion phenomena in heterogeneous gas-solid reactions : Application to oxides sulfidation

2018

Phase transition phenomena involving the mobility of the reaction interface are involved in a wide variety of chemical reactions and applications. A good example is the sulfidation reaction experienced by the metal oxide-based materials used in the framework of gas purification or catalysts preparation applications. These reactions involve solid-state diffusion phenomena of the reactive species (atomic or ionic form) through the layer of product formed during the reaction (oxide, sulfide, or metal phase). In many cases, solid-state diffusion has a direct impact on the reaction mechanisms while determining the growth direction of the formed phases, as well as the overall kinetics of the reac…