Uv-visible characterization of gold exchanged in beta zeolite

info:eu-repo/semantics/publishe

Influence of Hydrodynamic Interactions on the Kinetics of Colloidal Particle's Adsorption

The kinetics of irreversible adsorption of spherical particles onto a flat surface is theoretically studied. Previous models, in which hydrodynamic interactions were disregarded, predicted a power-law behavior $t^{-2/3}$ for the time dependence of the coverage of the surface near saturation. Experiments, however, are in agreement with a power-law behavior of the form $t^{-1/2}$. We outline that, when hydrodynamic interactions are considered, the assymptotic behavior is found to be compatible with the experimental results in a wide region near saturation.Comment: 4 pages, 1 figures, Phys. Rev. Lett. (in press

Cell dynamics simulations of sphere-forming diblock copolymers in thin films on chemically patterned substrates

The morphology of sphere-forming block copolymers assembled in thin films on patterned surfaces is theoretically analyzed. The patterns on the lower surface are alternating bands of a given width distinctively attracting or repelling a given block. We find that long- range order can be achieved, and it depends on the commensurability of the characteristic length of the block domains with both band periodicity and slit thickness. The comparison of the simulation results with experimental data shows a very good agreement. Furthermore, we show that the proper selection of the band periodicity and, consequently, of the film thickness permits the system to switch from hexagonal packing to body-centered orthohedra. Therefore, we show that it exists a way to control the formation of long-range ordered structures of different types in this kind of system

The architecture of amyloid-like peptide fibrils revealed by X-ray scattering, diffraction and electron microscopy

Structural analysis of protein fibrillation is inherently challenging. Given the crucial role of fibrils in amyloid diseases, method advancement is urgently needed. A hybrid modelling approach is presented enabling detailed analysis of a highly ordered and hierarchically organized fibril of the GNNQQNY peptide fragment of a yeast prion protein. Data from small-angle X-ray solution scattering, fibre diffraction and electron microscopy are combined with existing high-resolution X-ray crystallographic structures to investigate the fibrillation process and the hierarchical fibril structure of the peptide fragment. The elongation of these fibrils proceeds without the accumulation of any detectable amount of intermediate oligomeric species, as is otherwise reported for, for example, glucagon, insulin and [alpha]-synuclein. Ribbons constituted of linearly arranged protofilaments are formed. An additional hierarchical layer is generated via the pairing of ribbons during fibril maturation. Based on the complementary data, a quasi-atomic resolution model of the protofilament peptide arrangement is suggested. The peptide structure appears in a [beta]-sheet arrangement reminiscent of the [beta]-zipper structures evident from high-resolution crystal structures, with specific differences in the relative peptide orientation. The complexity of protein fibrillation and structure emphasizes the need to use multiple complementary methods

Prospecciones arqueológicas en la reserva "Eduardo Avaroa" (sud Lipez, dpto. Potosí, Bolivia)

Este trabajo informa sobre los resultados de prospecciones arqueológicas recientemente realizadas en el extremo suroccidental del Altiplano de Lípez (Potosí, Bolivia), actualmente incluido en la Reserva Nacional de Fauna Andina "Eduardo Avaroa". Se describen suscintamente alrededor de medio centenar de sitios prehispánicos correspondientes a períodos alfareros. En base al análisis de estas evidencias se formula un esquema tentativo de algunos cambios experimentados por la ocupación humana en esta zona entre el Período Alfarero Temprano y la conquista Inka.This paper reports on the results of an archaeological survey recently conducted in the southwestern portion of Altiplano de Lipez (Potosí, Bolivia), an area that currently falls within the National Reserve of Andean Fauna "Eduardo Avaroa". About 50 prehistoric sites dating to ceramic periods are briefly descríbed. On the basis of this evidence we propose a preliminary scheme of some of the changes experienced by human occupation of the area since the Early Ceramic Period through the Inka conquest.Sociedad Argentina de Antropologí