Diffusion Fundamentals (E-Journal)
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The effect of surface roughness on Nuclear Magnetic Resonance relaxation
Get PDFMost theoretical treatments of Nuclear Magnetic Resonance (NMR) measurements of porous media assume ideal pore geometries for the pores (i.e. slabs, spheres or cylinders) with welldefined surface-to-volume ratios (S/V). This same assumption is commonly adopted for naturally occurring materials, where the pore geometry can differ substantially from these ideal shapes. In this paper the effect of the roughness of the pore surface on the T2 relaxation spectrum is studied. By homogenization of the problem using an electrostatic approach it is found that the effective surface relaxivity can increase dramatically in the presence of rough surfaces. This leads to a situation where the system responds as a pore with a smooth surface, but with significantly increased surface relaxivity. As a result the standard approach of assuming an idealized geometry with known surface to-volume and inverting the T2 relaxation spectrum to a pore size distribution is no longer valid. The effective relaxivity is found to be fairly insensitive to the shape of the roughness but strongly dependent on the width and depth of the surface geometry
The occurence of cocaine in Egyptian mummies: new research provides strong evidence for a trans-Atlantic dispersal of humans
Get PDFOne of the unsolved problems of modern science is whether the pre-Columbian peoples of the New World developed completely independently of cultural influences from the Old World or if there was a trans-oceanic contact? A number of scientists agree that there are many – and often remarkable – similarities between the cultures of pre-Columbian America and those of the Mediterranean world. Nevertheless, there is no agreement, as yet, on how cultural diffusion can be differentiated from independent invention. Scientific analysis shows that scholarly positions are often strongly pre-formed from paradigms (scientific based assumptions), which tend to hinder consideration of solid scientific data offered by geo-biology and its trans-disciplinary examination of the subject under investigation here. An unambiguous answer to the question, what historical processes led to the emergence of the ancient American agriculture, hasn\\u27\u27t been given. However, the archaeological discovery of crops with clear trans-oceanic origin, in addition to advances in molecular biology, increasingly support the hypothesis that humans from the distant past influenced each other across the oceans at a much earlier stage. The vegetation and zoo-geography indicate, by numerous examples that some species could only have spread through perhaps unintentional (passive) human transmission [1]. There are two very old crops found in the „New World‟, which contradict the paradigm of a completely independent origin for American agriculture. These are the African Bottle Gourd (Lagenaria siceraria L.) and the ancestral cotton species (Gossypium herbaceum L.) of the domesticated spin able sub-genus of tetraploid cotton. The historical spread of both types has been under discussion for decades, especially in respect of trans-oceanic human contact with the American continent. There has also been a debate in the \"Old World\" ever since the discovery of nicotine and cocaine in Egyptian mummies, centering around whether \"New World\" plants (or the ingredients) might have been transmitted in the reverse direction, back to the presumed start in centers of the Ancient World\\u27\u27s oldest civilizations
Polymers in disordered environments
Get PDFUsing a combination of analytical theory and newly developed numerical algorithms, we analyze the most pertinent conformational characteristics of three paradigmatic types of polymers in disordered environments: (i) flexible polymers in quenched, self-similar disorder as represented by a self-avoiding random walk on a critical percolation cluster, (ii) semiflexible polymers in quenched, steric disorder as represented by an equilibrium hard-disk fluid and (iii) semiflexible polymers subject to the random energy landscape that emerges from a surrounding network of similar semiflexible polymers
Interference and IR-microscopy for studies of nanoporous materials: an insightful view on intracrystalline molecular transport
Get PDFInvestigating the relationship between social learning efficiency and the diffusion of innovations
Get PDFDiffusion and conformational dynamics in locally perturbed model membrane systems
Get PDFIn this article, we review our results on diffusion and phase separation in lipid membranes, as well as on interaction of membranes with colloidal particles, biomacromolecules, and supramolecular assemblies, which were obtained within the framework of the Saxon Research Unit FOR 877 “From Local Constraints to Macroscopic Transport”
