Quasicrystals
Mostrando 1-12 de 18 artigos, teses e dissertações.
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1. Solid-state Morphology Evolution of Sodium Neutralized Poly(ethylene-ran-methacrylic acid) Ionomer Under Dry and Wet Thermal Annealing
The DSC low temperature endothermic peak shown by sodium neutralized poly(ethylene-random-methacrylic acid) (E/MAA-Na+) ionomers in the range of 50-70 ºC is attributed to the endothermic reordering of polyethylene chain segments belonging to two populations of quasi-crystals set from melt, initially showing no birefringence. Dry or wet thermal annealing imp
Mat. Res.. Publicado em: 08/08/2019
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2. Clay Mineralogy of Brazilian Oxisols with Shrinkage Properties
ABSTRACT Shrinkage capacity (caráter retrátil in Portuguese) is a new diagnostic characteristic recently introduced in the Brazilian System of Soil Classification (SiBCS) to indicate shrink and swell properties observed in subtropical soils from highland plateaus in southern Brazil, specifically in Oxisols with brown colors. In soils located in road cuts e
Rev. Bras. Ciênc. Solo. Publicado em: 24/08/2017
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3. Chromatic Dispersion of an Optical Fiber Based on Photonic Quasicrystals with Twelve-Fold Symmetry and its Application as Directional Coupling
Abstract Optical fibers composed by photonic quasicrystals it is based on aperiodic structures characterized by at least two different symmetrical patterns from the base matrix. In this work, an optical fiber composed by quasi-periodic and symmetric matrix was analyzed using the finite element method in conjunction with cylindrical perfectly matched layers.
J. Microw. Optoelectron. Electromagn. Appl.. Publicado em: 2015-12
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4. Fabrication and corrosion resistance of Mg-Zn-Y-based nano-quasicrystals alloys
A wedge-shaped copper mold was used to fabricate micro quasicrystals(QCs). Stable Mg-Zn-Y-based nano-QCs were directly synthesized through this simple route instead of crystallization from metallic glasses or complicated forming processes at high temperature. The study showed that on the tips of the wedge-shaped ingots, the minimum diameter of nano-QCs appro
Materials Research. Publicado em: 31/01/2012
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5. Propriedades dinâmicas e ergódicas de shifts multidimensionais / Dynamic and ergodic properties of multidimensional shifts
Focaremos sobre aspectos dinâmicos e ergódicos de shifts multidimensionais, atentando especialmente para suas relações com estados fundamentais e quase-cristais em reticulados. Por exemplo, em mecânica estatística, dado um potencial invariante por translação, seus estados fundamentais são medidas de probabilidade invariantes por translação suporta
IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia. Publicado em: 15/08/2011
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6. Eixo quinário: um elemento de simetria presente em moléculas e quasi-cristais - um experimento didático em cristalografia
Axis of quinary symmetry occur in molecular symmetry, as in the case of fullerenes, and in crystalline symmetry, in the quasicrystals. Minerals with pentagonal faces do not have this element of symmetry, as the pyrite (FeS2) which shows a ridge that is different from the other ones, in any face of the crystal. The purpose of this paper is to demonstrate conc
Química Nova. Publicado em: 2010
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7. Obtenção e evolução da fase icosaedral quasicristalina em ligas Al-Cu-Fe e Al-Cu-Fe-B por Melt-Spinnin / OBTAINING AND EVOLUTION OF PHASE ICOSAHEDRAL QUASICRISTALINA IN ALLOYS Al-Cu-Fe AND Al-Cu-Fe-B BY MELT-SPINNING
Melt spinnng processing is one of the most common processes to obtaining quasicrystaline structures. This is because of the fast cooling rate it imposes on the system, favoring such type of structure. This work deals with the production of quasycristaline phases (Al60Cu27,5Fe12,5 e Al57Cu27,5Fe12,5B3) via melt-spinning. The alloys were initially cast via ind
Publicado em: 2009
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8. Polaritons em materiais magnéticos nanoestruturados
Neste trabalho apresentamos um estudo teórico sobre as propriedades dos polaritons magnéticos em super-redes organizadas em padrões periódico e quasiperiódico. Na super-rede periódica, objetivando descrever o comportamento destes modos, tanto no volume quanto na superfície, foi utilizada a teoria do meio efetivo, que facilita enormemente a álgebra en
Publicado em: 2007
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9. Unified structure theory of icosahedral quasicrystals: Evidence from neutron powder diffraction patterns that AlCrFeMnSi, AlCuLiMg, and TiNiFeSi icosahedral quasicrystals are twins of cubic crystals containing about 820 or 1012 atoms in a primitive unit cube
A unified structure theory of icosahedral quasicrystals, combining the twinned-cubic-crystal theory and the Penrose-tiling-six-dimensional-projection theory, is described. Values of the primitive-cubic lattice constant for several quasicrystals are evaluated from x-ray and neutron diffraction data. The fact that the low-angle diffraction maxima can be indexe
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10. New perspectives on forbidden symmetries, quasicrystals, and Penrose tilings
Quasicrystals are solids with quasiperiodic atomic structures and symmetries forbidden to ordinary periodic crystals—e.g., 5-fold symmetry axes. A powerful model for understanding their structure and properties has been the two-dimensional Penrose tiling. Recently discovered properties of Penrose tilings suggest a simple picture of the structure of qu
The National Academy of Sciences of the USA.
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11. Icosahedral quasicrystals of intermetallic compounds are icosahedral twins of cubic crystals of three kinds, consisting of large (about 5000 atoms) icosahedral complexes in either a cubic body-centered or a cubic face-centered arrangement or smaller (about 1350 atoms) icosahedral complexes in the β-tungsten arrangement
The twofold-axis electron-diffraction photographs of icosahedral quasicrystals are of three kinds, reflecting three different structures of the cubic crystals that by icosahedral twinning form the quasicrystals. The first kind, represented by Al13Cu4Fe3, contains two very large icosahedral complexes, each of about 4680 atoms, in the body-centered arrangement
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12. Icosahedral quasicrystals as twins of cubic crystals containing large icosahedral clusters of atoms: The 1012-atom primitive cubic structure of Al6CuLi3, the C-phase Al37Cu3Li21Mg3, and GaMg2Zn3
Single-grain precession x-ray diffraction photographs of Al6CuLi3 have been successfully indexed on the basis of icosahedral twinning of cubic crystals with a 1012-atom primitive cubic unit with edge 25.70 Å, giving support to the proposal that the so-called icosahedral quasicrystals are twins of crystals containing eight large icosahedral clusters in the �