Search results for " diffusion"

Automatic Extraction of Blood Vessels, Bifurcations and End Points in the Retinal Vascular Tree

2008

In this paper we present an effective algorithm for automated extraction of the vascular tree in retinal images, including bifurcations, crossovers and end-points detection. Correct identification of these features in the ocular fundus helps the diagnosis of important systematic diseases, such as diabetes and hypertension. The pre-processing consists in artefacts removal based on anisotropic diffusion filter. Then a matched filter is applied to enhance blood vessels. The filter uses a full adaptive kernel because each vessel has a proper orientation and thickness. The kernel of the filter needs to be rotated for all possible directions. As a consequence, a suitable kernel has been designed …

Scattering lengths and universality in superdiffusive L\'evy materials

2012

We study the effects of scattering lengths on L\'evy walks in quenched one-dimensional random and fractal quasi-lattices, with scatterers spaced according to a long-tailed distribution. By analyzing the scaling properties of the random-walk probability distribution, we show that the effect of the varying scattering length can be reabsorbed in the multiplicative coefficient of the scaling length. This leads to a superscaling behavior, where the dynamical exponents and also the scaling functions do not depend on the value of the scattering length. Within the scaling framework, we obtain an exact expression for the multiplicative coefficient as a function of the scattering length both in the a…

Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources

2014

We investigate the superconducting lifetime of long current-biased Josephson junctions, in the presence of Gaussian and non-Gaussian noise sources. In particular, we analyze the dynamics of a Josephson junction as a function of the noise signal intensity, for different values of the parameters of the system and external driving currents. We find that the mean lifetime of the superconductive state is characterized by nonmonotonic behavior as a function of noise intensity, driving frequency and junction length. We observe that these nonmonotonic behaviours are connected with the dynamics of the junction phase string during the switching towards the resistive state. An important role is played…

Incoherent quasi-elastic neutron scattering in isomeric alcohols

1992

Abstract Incoherent quasi-elastic neutron scattering (IQENS) data on liquid isomeric alcohols normal-pentanol (n-PeOH) and 2-methyl-2-butanol (2M-2BuOH) and on their mixture are presented. The diffusive motion of protons, as a function of temperature, is analyzed in the framework of the random jump diffusion model. The temperature dependence of the parameters obtained confirms the more “fragile” behaviour of the more sterically hindered 2M-2BuOH with respect to that of the linear n-PeOH.

Lower semicontinuity of weak supersolutions to the porous medium equation

2013

Weak supersolutions to the porous medium equation are defined by means of smooth test functions under an integral sign. We show that nonnegative weak supersolutions become lower semicontinuous after redefinition on a set of measure zero. This shows that weak supersolutions belong to a class of supersolutions defined by a comparison principle.

2019

The in-medium dynamics of heavy particles are governed by transport coefficients. The heavy quark momentum diffusion coefficient, $\ensuremath{\kappa}$, is an object of special interest in the literature, but one which has proven notoriously difficult to estimate, despite the fact that it has been computed by weak-coupling methods at next-to-leading order accuracy, and by lattice simulations of the pure SU(3) gauge theory. Another coefficient, $\ensuremath{\gamma}$, has been recently identified. It can be understood as the dispersive counterpart of $\ensuremath{\kappa}$. Little is known about $\ensuremath{\gamma}$. Both $\ensuremath{\kappa}$ and $\ensuremath{\gamma}$ are, however, of foremo…

Bromine speciation in volcanic plumes: new in situ derivatization LC-MS method for the determination of gaseous hydrogen bromide by gas diffusion den…

2020

The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Monitoring of BrO/SO2-ratios has recently been correlated with changes in the activity of a volcano. BrO and SO2 can both be measured autonomously and simultaneously with the same instruments from a safe distance, making their ratio potentially a strong monitoring tool. However, BrO is not a primary emitted volcanic volatile and there exist still uncertainties about the formation of BrO in volcanic plumes, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. This study describes a new method for the determination of the BrO precursor, the ga…

Selective chlorine determination by gas diffusion in a tandem flow assembly and spectrophotometric detection with o-dianisidine

2001

Abstract A fast, selective, sensitive and automated method for determination of free chlorine in industrial formulations and water samples is proposed. The automation of the flow assembly is based on the “tandem flow” approach, which uses a set of solenoid valves acting as independent switches. The operating cycle for obtaining a typical analytical transient signal can easily be programmed by means of friendly software running in the Windows environment. The manifold is provided with a gas diffusion unit which permits the removal of interfering species as well as concentrating the chlorine. The determination of chlorine is performed on the basis of the oxidation of o-dianisidine as the colo…

The Diffusion of Humans and Cultures in the Course of the Spread of Farming

2017

The spread of farming into Europe some 9000–5000 years ago involved not only the advent of new plants and animals, but also of people, tools, technologies, and knowledge. While they all can be assumed to follow Fickian diffusion gradients, the mechanisms of spread can be quite different: when people migrate, there is mass balance in the number of people, but not in the knowledge and technologies brought along. Tools, plants and animals could also travel by trade, knowledge and technology by communication; there might even be local resistance to adoption of novelty. This chapter discusses these different diffusion mechanisms in the context of numerical trait- and agent-based socio-environmen…

Optimization of impurity profile for p-n junction in heterostructures

2005

We analyze the dopant diffusion in p-n-junction in heterostructure, by solving the diffusion equation with space-varying diffusion coefficient. For a step-wise spatial distribution we find the optimum annealing time to decrease the p-n-junction thickness and to increase the homogeneity of impurity concentration in p or n regions.