			Home About us Contact

Spherical Clusters (spherical + cluster)

Distribution by Scientific Domains

Chemistry	40%

Selected Abstracts

Mesoscopic Morphology of Proton-Conducting Polyelectrolyte Membranes of Nafion® Type: A Self-Consistent Mean Field Simulation

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2006
Dmitry Y. Galperin
Abstract Summary: A SCMF simulation is presented for a coarse-grained model of Nafion®. Based on a number of simplifying assumptions, this study predicts distinct morphological changes in the material upon alteration of temperature and water content. We found that the hydration level corresponding to the microphase segregation depends on the temperature of the system. Spherical clusters constituting the hydrophilic microphase of the membrane at relatively low water content (but above the transition point) grow in size, coalesce and form a network of channels responsible for the ionic transport at higher hydration levels. This hydrophilic phase is shielded from the hydrophobic matrix by the sidechains of Nafion®, their end-groups being turned towards the water clusters. The results obtained are similar to those reported from dissipative particle dynamics studies and support the "cluster-network" model for the low hydration levels and the "sponge" model at higher hydration levels. The simulation approach chosen proved to be effective for the mesoscopic structure analysis of the heterogeneous polymeric material. Schematic representation of the structure of Nafion®-water blends. [source]

X-ray fluorescence holography: a novel treatment for crystal structure determination

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2003
F. N. Chukhovskii
It is shown that it is possible to use a linear regression algorithm direct method to solve crystal structures from X-ray fluorescence holography (XFH) data. It is found that, in contrast to conventional X-ray structure determination methods, which do not always work unambiguously, the sustainable method utilizing the XFH data generally provides the unique phase-retrieval structure solution and is able, in many cases, to replace the above for determining both the absolute values (moduli) and phases of structure factors. The XFH scan with a fluorescing Cu atom from a spherical cluster of a Cu3Au single crystal, at an energy of 10,keV for the incident unpolarized plane-wave X-radiation, is numerically simulated to test the performance of the method in finding a unique solution for the structure factors involved in the restoration procedure using the linear regression algorithm. [source]

Electrochemical deposition of Pt nanoparticles on diamond substrates

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2009
Jingping Hu
Abstract Platinum nanoparticles were deposited on polished smooth, as-grown large grain and small grain diamond substrates by a potentiostatic method. The influence of deposition potential and the morphology of BDD substrates were studied. A progressive nucleation along with spherical clusters was observed on smooth BDD electrode, accompanied with a heterogeneous segregation of platinum on diamond facets of higher electrochemical activities and a weak binding to the substrate. In contrast, an instantaneous nucleation was observed on as-grown small grain and large grain BDD electrodes, with a dendritic microstructure and a much larger specific active area. The platinum decorated as-grown smaller grain BDD electrodes show a much better electrochemical stability than the other electrodes investigated. [source]

Clustering in the Presence of Scatter

BIOMETRICS, Issue 2 2009
Ranjan Maitra
Summary:, A new methodology is proposed for clustering datasets in the presence of scattered observations. Scattered observations are defined as unlike any other, so traditional approaches that force them into groups can lead to erroneous conclusions. Our suggested approach is a scheme which, under assumption of homogeneous spherical clusters, iteratively builds cores around their centers and groups points within each core while identifying points outside as scatter. In the absence of scatter, the algorithm reduces to k -means. We also provide methodology to initialize the algorithm and to estimate the number of clusters in the dataset. Results in experimental situations show excellent performance, especially when clusters are elliptically symmetric. The methodology is applied to the analysis of the United States Environmental Protection Agency's Toxic Release Inventory reports on industrial releases of mercury for the year 2000. [source]

Structural Preferences of Single-Walled Silica Nanostructures: Nanospheres and Chemically Stable Nanotubes

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2006
Mikko Linnolahti Dr.
Abstract Structural preferences of single-walled and coordinatively saturated spherical and tubular nanostructures of silica have been determined by ab initio calculations. Two families of spherical (SiO2)n clusters derived from Platonic solids and Archimedean polyhedra are depicted, with n ranging from 4,120. The analogue of a truncated icosidodecahedron, Ih -symmetric Si120O240, is favored in energy, closely followed by the Ih -symmetric Si60O120 -truncated icosahedron. The silica nanotubes derived from spherical clusters are capped by Si2O2 rings, whereas the tubular section consists of single oxygen bridges. Periodic studies performed with open-ended silica nanotubes and the ,-quartz polymorph of silica, along with a comparisons to fullerenes and carbon nanotubes, suggest that tubes with diameters of approximately 1 nm should be chemically stable. [source]