Diffusion in Confined Geometries Burada, P. Sekhar; Hänggi, Peter; Marchesoni, Fabio ...
Chemphyschem,
January 12, 2009, Letnik:
10, Številka:
1
Journal Article
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Diffusive transport of particles or, more generally, small objects, is a ubiquitous feature of physical and chemical reaction systems. In configurations containing confining walls or constrictions, ...transport is controlled both by the fluctuation statistics of the jittering objects and the phase space available to their dynamics. Consequently, the study of transport at the macro‐ and nanoscales must address both Brownian motion and entropic effects. Herein we report on recent advances in the theoretical and numerical investigation of stochastic transport occurring either in microsized geometries of varying cross sections or in narrow channels wherein the diffusing particles are hindered from passing each other (single‐file diffusion). For particles undergoing biased diffusion in static suspension media enclosed by confining geometries, transport exhibits intriguing features such as 1) a decrease in nonlinear mobility with increasing temperature or also 2) a broad excess peak of the effective diffusion above the free diffusion limit. These paradoxical aspects can be understood in terms of entropic contributions resulting from the restricted dynamics in phase space. If, in addition, the suspension medium is subjected to external, time‐dependent forcing, rectification or segregation of the diffusing Brownian particles becomes possible. Likewise, the diffusion in very narrow, spatially modulated channels is modified via contact particle–particle interactions, which induce anomalous sub‐diffusion. The effective sub‐diffusion constant for a driven single file also develops a resonance‐like structure as a function of the confining coupling constant.
A tight squeeze: The mathematical formalism for modelling the diffusion of a Brownian particle immersed in a confined suspension fluid (picture) is outlined. Particle transport along a channel subject to stationary pumping is described. A review of results for the diffusion of a single file along a periodically corrugated channel (picture, bottom) is presented.
Summary
Psoriasis vulgaris is a common and often chronic inflammatory skin disease. The incidence of psoriasis in Western industrialized countries ranges from 1.5% to 2%. Patients afflicted with ...severe psoriasis vulgaris may experience a significant reduction in quality of life. Despite the large variety of treatment options available, surveys have shown that patients still do not received optimal treatments. To optimize the treatment of psoriasis in Germany, the Deutsche Dermatologi sche Gesellschaft (DDG) and the Berufsverband Deutscher Dermatologen (BVDD) have initiated a project to develop evidence‐based guidelines for the management of psoriasis. They were first published in 2006 and updated in 2011. The Guidelines focus on induction therapy in cases of mild, moderate and severe plaque‐type psoriasis in adults including systemic therapy, UV therapy and topical therapies.
The therapeutic recommendations were developed based on the results of a systematic literature search and were finalized during a consensus meeting using structured consensus methods (nominal group process).
Summary
The German guideline for the treatment of psoriasis vulgaris was updated using GRADE methodology. The guideline is based on a systematic literature review completed on December 1, 2016, and ...on a formal consensus and approval process. The second part of this short version of the guideline covers the following special patient populations and treatment situations: tuberculosis screening before and during psoriasis treatment, choice of psoriasis treatment for individuals wishing to have children, as well as during pregnancy and breast‐feeding, and patients with joint involvement and vaccinations. In addition, recommendations on the choice of treatment are presented for patients with the following comorbidities: hepatitis and other hepatic impairment, HIV, malignancies, neurological and psychiatric disorders, ischemic heart disease and congestive heart failure, diabetes mellitus, renal impairment and inflammatory bowel disease.
Entropic transport: a test bed for the Fick–Jacobs approximation P. Sekhar Burada; Gerhard Schmid; Peter Hänggi
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
08/2009, Letnik:
367, Številka:
1901
Journal Article
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Biased diffusive transport of Brownian particles through irregularly shaped, narrow confining quasi-one-dimensional structures is investigated. The complexity of the higher dimensional diffusive ...dynamics is reduced by means of the so-called Fick-Jacobs approximation, yielding an effective one-dimensional stochastic dynamics. Accordingly, the elimination of transverse, equilibrated degrees of freedom stemming from geometrical confinements and/or bottlenecks causes entropic potential barriers that the particles have to overcome when moving forward noisily. The applicability and the validity of the reduced kinetic description are tested by comparing the approximation with Brownian dynamics simulations in full configuration space. This non-equilibrium transport in such quasi-one-dimensional irregular structures implies, for moderate-to-strong bias, a characteristic violation of the Sutherland-Einstein fluctuation-dissipation relation.
This work presents a novel high-resolution photogrammetric measuring technique (PHOTOSED) to study in detail the erosion behavior of cohesive sediments, or cohesive/non-cohesive sediment mixtures. ...PHOTOSED uses a semiconductor laser to project a pseudo-random pattern of light points on a sediment surface and applies the Dense Optical Flow (DOF) algorithm to measure the erosion volume based on displacements of the projected light points during the sediment erosion process. Based on intensive calibration and verification experiments, the accuracy and applicability of the method has been validated for a wide range of erosion volumes, encompassing several orders of magnitude, which is required for investigations of natural sediment mixtures. The high spatial resolution of PHOTOSED is especially designed to detect the substantial variability of erosion rates during exemplary erosion experiments, which allows for further in-depth investigations of the erosion process of cohesive sediments and cohesive/non-cohesive sediment mixtures.
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