Search results for " diffusion"

Diffusion Equations with Finite Speed of Propagation

2007

In this paper we summarize some of our recent results on diffusion equations with finite speed of propagation. These equations have been introduced to correct the infinite speed of propagation predicted by the classical linear diffusion theory.

Hillslope evolution by nonlinear creep and landsliding: An experimental study: Comment and Reply

2002

[Roering et al. (2001)][1] describe very careful and interesting experiments that beautifully illustrate the transition from steady downhill creep at low gradients to highly dynamic transport on steep slopes. They interpret this behavior in terms of a single nonlinear diffusion coefficient,

Global existence for a degenerate nonlinear diffusion problem with nonlinear gradient term and source

1999

Impact of Stock Price Jumps on Option Values

1999

Many empirical papers document the fact that the distribution of stock returns exhibits fatter tails than would be expected from a normal distribution. This might explain some of the pricing biases of the Black/Scholes model, which is] based on a normal return distribution. Given this result, alternative option pricing models should be based on one of the following three classes of return models: (1) a stationary process, such as a paretian stable or a student’s t-distribution, (2) a mixture of stationary distributions, such as two normal distributions with different means or variances, or a mixture of a diflusion and a pure jump process, or (3) a distribution such as a normal distribution …

HEAT FLUX IN SUPERFLUID TRANSITION AND IN TURBULENT HELIUM COUNTERFLOW

Mössbauer investigations on glass-forming organic liquids

1992

Glycerol forms a molecular glass near 180K. Fe2+ dissolved in glycerol allows the study of the dynamics of the system by Mossbauer spectroscopy. Recently it has been shown that the Mossbauer spectra can be understood in a way consistent with the results of dielectric and ultrasonic viscoelastic relaxation measurements. A jump diffusion model of Sinqwi and Sjolander with a jump rate distribution according to Davidson and Cole allowed us to fit the Mossbauer spectra of Fe in glycerol. First attempts to compare mode coupling theory with Mossbauer spectra are reported.

2H NMR Time Domain Analysis of Ultraslow Reorientations in Supercooled Liquids

1998

A method for evaluating 2H NMR stimulated echo experiments in the time domain is presented. It exhibits a high sensitivity to molecular reorientation mechanisms for small angles. Reorientations with jump angles below 25degrees can be resolved with a precision of approximately 1degrees so that, e.g., rotational diffusion and finite jump angle mechanisms become distinguishable. The method, applicable to isotropic reorientation models, is thought to extend the domain of 2D exchange spectroscopy where the best resolution is obtained in the large angle range of anisotropic reorientational mechanisms. Application to reorientation in the supercooled melt of ortho-terphenyl is presented. These data…

Ab initio simulations on charged interstitial oxygen migration in corundum

2018

We have performed this work within the framework of the EUROfusion Consortium receiving funding from the European grant agreement 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Authors thank R. Vila, A.I. Popov, A. Luchshik and R.A. Evarestov for fruitful discussions. To carry out large-scale calculations, we have used the HPC supercomputer at Stuttgart University (Germany)

Experimental Determination of Four-Time Stimulated Echoes in Liquids, Colloidal Suspensions, and Crystals

1998

Four-time stimulated echo experiments have been used to monitor the temporal evolution of the reorientation rates of deuterated molecules or colloidal suspensions. We present extended phase cycles for this seven-pulse experiment. In order to test its performance three vastly different materials are chosen. These include a crystal in which the molecules carry out well-defined 180 degrees flips and a supercooled liquid characterized by a distribution of jump angles centered around 10 degrees. As an example for rotational diffusion, data on a concentrated suspension of polystyrene spheres in a viscous medium are presented. Copyright 1998 Academic Press.

State of the art of CPMAS 13C-NMR spectroscopy applied to natural organic matter

2004

A number of different techniques are presently available for characterizing humified natural organic matter (NOM). Carbon-13 nuclear magnetic resonance spectroscopy (13C-NMR) in the solid state using cross-polarization (CP) and magic angle spinning (MAS) represents the most powerful experimental approach used to collect direct information on the structural and conformational characteristics of humic carbon backbones. Despite the problems due to the presence of paramagnetic impurities and the generally low organic matter concentration, cross-polarization magic angle spinning 13C-NMR spectroscopy (CPMAS 13C-NMR) is applied in soil chemistry and geochemistry mainly because of its relevance in …