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Ori O.,Actinium Chemical Research | Ori O.,West University of Timisoara | Cataldo F.,Actinium Chemical Research | Putz M.V.,West University of Timisoara | And 3 more authors.
Fullerenes Nanotubes and Carbon Nanostructures | Year: 2016

Present topological study focuses on the formation mechanism of clusters of vacancies in graphenic layers. An original effect that explains both accumulation and self-healing of vacancies represents the original outcome of our investigation whose results, based on the long-range topological properties of the honeycomb lattices, are applicable to defective graphene sheets and general honeycomb lattices when other elements other than carbon are present. Some speculations about the role of long-range bondonic states in such a kind of lattices contribute to the understanding of electronic and transport properties in graphenic nanomaterials. © 2016 Taylor & Francis Group, LLC.

Kaatz F.H.,Mesalands Community College | Bultheel A.,Catholic University of Leuven | Ori O.,Actinium Chemical Research | Ori O.,West University of Timisoara
Journal of Mathematical Chemistry | Year: 2016

Abstract: The vacancy concentration dependence on temperature and diameter of noble metal (gold, silver, and copper) nanoclusters is investigated using a Kinetic Monte Carlo method. Icosahedral and decahedral nanoclusters are studied, with diameters up to 3.73 nm for icosahedral clusters and up to 6.65 nm for decahedral clusters. The cohesive energy is calculated using a coordination number approach, resulting in a linear relation with cluster size. Random Schottky defects are frozen into the clusters at low temperatures (100–600 K) and we find that the vacancy concentration increases with smaller diameters and higher temperatures. We develop a model for this behavior, which explains the temperature and size dependence. This model predicts silver icosahedra to have the highest concentration of vacancies in the clusters studied. Vacancy concentrations are related to the ratio of surface/interior sites based on nearest neighbor calculations. The modified enthalpy and entropy of constant diameter clusters are derived from a logarithmic model for the Gibbs energy. Melting entropy and enthalpy are calculated in this coordination type model and compare well with previously published molecular dynamics results. Graphical Abstract: [Figure not available: see fulltext.] © 2016 Springer International Publishing Switzerland

Parker W.G.,Petrified Forest National Park | Parker W.G.,University of Texas at Austin | Hungerbuhler A.,Mesalands Community College | Martz J.W.,Denver Museum of Nature and Science
Earth and Environmental Science Transactions of the Royal Society of Edinburgh | Year: 2013

The genus Machaeroprosopus has long been considered invalid because the type specimen of the Late Triassic phytosaur species, M. validus, has been lost. Re-examination of the primary literature regarding the establishment of the Late Triassic phytosaur genus Machaeroprosopus demonstrates that M. buceros is the correct type species, not M. validus. Thus, the genus level name Machaeroprosopus has priority over the genera Pseudopalatus and Arribasuchus and all nominal species should be reassigned. Reassignment of these species to Machaeroprosopus satisfies the requirements of the International Code of Zoological Nomenclature (ICZN) and preserves historical context. The name Pseudopalatinae is retained as the valid clade name for these phytosaurs because its usage falls outside of the ICZN. © 2013 The Royal Society of Edinburgh.

Hungerbuhler A.,Mesalands Community College | Mueller B.,Texas Tech University | Chatterjee S.,Texas Tech University | Cunningham D.P.,Texas Tech University
Earth and Environmental Science Transactions of the Royal Society of Edinburgh | Year: 2013

The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with bevelled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital-parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redondasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus. © 2013 The Royal Society of Edinburgh.

Kaatz F.H.,Mesalands Community College | Bultheel A.,Catholic University of Leuven
Computational Materials Science | Year: 2015

Nanoclusters create the possibility of designing novel properties and devices based on finite structures, with small dimensions. Clusters are of interest for catalytic, optical, biochemical, and structural characteristics. We examine clusters of icosahedral, cuboctahedral, and decahedral symmetry. Examples of these types of structures are shown from gold and platinum nanoclusters. Starting with only the atomic coordinates, we create an adjacency and distance matrix that facilitates the calculation of topological indices, including the Wiener, hyper-Wiener, reverse Wiener, Szeged, Balaban, and Kirchhoff indices. Some of these indices correlate to properties of the cluster. We find these indices exhibit polynomial and inverse behavior as a function of an increasing number of shells. Additionally, all the indices can be modeled with power law curves, as a function of N, the number of atoms. The magnitude of the exponent in the power law is associated with an index. The asymptotic limits of the topological indices are determined as a function of N. A conjecture previously published on the asymptotic behavior of the Wiener index is experimentally confirmed. © 2014 Elsevier B.V. All rights reserved.

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