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	Locating atoms in a quasicrystal - ESRF
		Quasicrystals are extremely well-ordered structures whose atomic arrangement is nonperiodic.
		The structure of the approximant crystals is described by a periodic packing of a large structural unit with icosahedral symmetry, whose external shell is a triacontahedron (Figure 1).
		The CdYb quasicrystalline structure is described as a quasiperiodic packing of the triacontahedral cluster, with connections along 2- and 3- fold axis as observed in the approximant: 94% of the atoms belong to such clusters.
	www.esrf.eu /news/spotlight/spotlight44/spot44 (996 words)

	Quasicrystal - Wikipedia, the free encyclopedia
		Quasicrystals are a peculiar form of solid in which the atoms are arranged in a seemingly regular, yet non-repeating structure.
		Thus a quasicrystal may be anything which is disordered in an interesting, nontrivial way: an aperiodic (quasiperiodic) sequence, a chain or a string is a one dimensional (1D) quasicrystal, a lattice or tiling is a 2D quasicrystal, a solid is three dimensional and higher dimensions are also considered.
		Quasicrystals are remarkable in that some of them display five-fold symmetry.
	en.wikipedia.org /wiki/Quasicrystal (777 words)

	QUASICRYSTAL. The Columbia Encyclopedia: Sixth Edition. 2000 (Site not responding. Last check: 2007-09-15)
		Quasicrystals seem to forge a link between conventional crystals and materials called metallic glasses, which are solids formed when molten metals are cooled so rapidly that their constituent atoms do not have adequate time to form a crystal lattice.
		Quasicrystals have been found to be common structures in alloys of aluminum with such metals as cobalt, iron, and nickel.
		Because they are extremely hard and resist deformation, quasicrystals form high-strength surface coatings, which has led to their commercial use as a surface treatment for aluminum skillets.
	www.bartleby.com /aol/65/qu/quasicrys.html (356 words)

	Introduction to Quasicrystals
		For polygonal quasicrystals this means in particular the clarification of the cluster arrangement (in case there are basic clusters that form the whole structure).
		The clusters are assumed to be columnar for polygonal quasicrystals.
		The structure of quasicrystals comprises of atoms that are arranged in a nonperiodic fashion.
	www.jcrystal.com /steffenweber/qc.html (3665 words)

	Department of Chemistry - Faculty
		Quasicrystals, first discovered in 1982 by Dan Shechtman are complex metal alloys that are most comparable to ceramic particulate fillers in polymer composites.
		The major drawback in quasicrystal applications is the brittle nature of the materials and the high temperature thermal spray coating techniques used in processing.
		By combining polymers with quasicrystals in a composite, quasicrystals are easily processed and simultaneously their unique, low abrasion and high hardness properties are introduced into the composite.
	www.chem.unc.edu /people/faculty/ashbyvs/vsaresproj.htm (1417 words)

	quasicrystal - HighBeam Encyclopedia
		QUASICRYSTAL [quasicrystal] or quasiperiodic solid, solid body that exhibits such crystalline features as symmetry and repeating patterns of unit cells (regular arrangements of atoms, molecules, or ions) but—unlike a crystal —requires more than one type of unit cell to achieve large-scale order, i.e., the structure cannot consist of the repetition of a single cell.
		The first quasicrystal was discovered in a rapidly cooled sample of an aluminum-manganese alloy by a team led by Dan S. Schechtman at the National Bureau of Standards (now the National Institute of Standards and Technology) in Gaithersburg, Md. in 1984.
		Unlike their constituent elements, quasicrystals are poor conductors of electricity.
	www.encyclopedia.com /doc/1E1-quasicrys.html (467 words)

	myelections.com Quasicrystal
		Quasicrystals are a peculiar form of solid in which the atoms of the solid are arranged in a seemingly regular, yet non-repeating structure.
		Quasicrystals helped to redefine the notion of what makes a crystal, since they do not have a repeating unit cell but do display sharp diffraction peaks.
		In a quasicrystal, flaws are locations where the 3D "subspace" is bent, or wrinkled, or broken as it passes through the higher-dimensional space.
	www.myelections.com /Quasicrystal.htm (796 words)

	Researchers Demonstrate Photonic Quasicrystal Heals Itself from Defects by Using Interactions with Light
		Quasicrystals were discovered in 1982 by another Technion Professor, Dan Shechtman, whose 1982 discovery that crystals need not be periodic created a scientific revolution.
		The phonic quasicrystal is “nonlinear:” light waves passing through it change its optical properties in real time, which in turn changes the light beam.
		But when a defect is removed from a quasicrystal, the resulting structure rearranges itself completely (while maintaining the quasi-periodic symmetry), having long-range effects far from the defect’s initial position.
	www.ats.org /news.php?id=126 (766 words)

	‘Quasicrystal’ Metal Computer Model Could Aid Ultra-Low-Friction Machine Parts
		The researchers’ computer model of the effect of adsorbed gas on the quasicrystal alloy of aluminum, nickel and cobalt will be published in an upcoming issue of the journal Physical Review Letters.
		In the simulation, Xenon atoms on the surface of a quasicrystal metal initially arrange in a quasicrystal pattern (left), but as the pressure of the gas increases the atoms arrange in a crystalline pattern (right).
		Watch the simulation, in which the image on the left is of the average position of the xenon atom, the image on the right is of the electron diffraction pattern used to determine the position of the atoms and the graph on the bottom gives the density of the xenon gas.
	www.dukenews.duke.edu /2005/09/quasicrystals.html (858 words)

	ICQ9 Abstracts
		The momentum transfer of the first-order diffraction beams from Xe coincides with that of the quasicrystal surface, indicating that the Xe inter-row spacing is related to a principal distance on the substrate.
		For a binary quasicrystal of the icosahedral glass type, the composition is mainly determined by topological close packing of the atoms in the basic 1st-shell icosahedron.
		, the ingot is a single-phase quasicrystal alloy, 3 mm in diameter and 15 mm in length.
	www.icq9.ameslab.gov /AbstractsA-Z.html (14408 words)

	Science News Online (10/12/96): Clusters and Decagons
		Instead of repeating throughout the structure at some regular interval, atoms of this so-called quasicrystal were spaced at either of two characteristic intervals, in a fixed ratio.
		When quasicrystals were discovered, some researchers immediately looked to Penrose tiling as a simple model of how quasicrystal atoms might be arranged.
		With a better understanding of why quasicrystals form, materials scientists may achieve improved control of the composition and structure of these materials, potentially leading to a variety of practical applications.
	www.sciencenews.org /sn_arch/10_12_96/bob1.htm (1169 words)

	Quasicrystal Electronic State Studies
		Eli Rotenberg, a staff scientist at the Advanced Light Source (ALS) at the Department of Energy's Lawrence Berkeley National Laboratory, Karsten Horn of the Fritz-Haber Institute, Max-Planck Society, Berlin, and their colleagues investigated the electronic structure of a quasicrystalline alloy of aluminum-nickel-cobalt (AlNiCo) by means of angle-resolved photoemission.
		The data show that electron momenta and energies are correlated with the structure of the quasicrystal.
		Peter Gille of the Ludwig-Maximilians-University, Munich, grew the quasicrystal, and the samples were prepared and characterized by Horn and by Wolfgang Theis of the Free University of Berlin.
	www.lbl.gov /Science-Articles/Archive/quasicrystal-states.html (902 words)

	Quasicrystal Caught in the Act
		Quasicrystal structures don't have a simple "unit cell" that can be repeated periodically in all directions to fill space, although they do have local patterns that repeat almost periodically.
		In decagonal quasicrystals, for example, the atomic planes are "tiled" by more than one shape, so some atoms can fluctuate between two nearby positions in a way that exchanges the positions of tiles without disrupting each tile's shape.
		According to the "random tiling" model, however, phasons cause quasicrystals to continually jostle among competing, structures with equal energies, and their true ground state would be a traditional crystal, if it could be reached.
	focus.aps.org /story/v6/st6 (605 words)

	Quasicrystals (Site not responding. Last check: 2007-09-15)
		Quasicrystals form in alloys of aluminum with transition metals such as iron or copper.
		Although lacking translational periodicity, quasicrystals display translational quasiperiodicity, leading to the dense collection of Bragg peaks in the diffraction pattern shown at the left.
		Popular structural models of quasicrystals invoke Penrose tilings like the one shown at the left (taken from the WWW site of Hillman) that covers the plane with fat and thin rhombi according to a set of "matching rules" that force a particular aperiodic structure.
	euler.phys.cmu.edu /widom/research/qc/quasi.html (481 words)

	Computational Materials Science and NanoScience Laboratory
		Quasicrystals, like normal crystals, consist of atoms that combine to form structures -- triangles, rectangles, pentagons, etc. -- that repeat in a pattern.
		The researchers' computer model of the effect of adsorbed gas on the quasicrystal alloy of aluminum, nickel and cobalt will be published in an upcoming issue of the journal Physical Review Letters.
		The challenge Curtarolo, Duke graduate student Wahyu Setyawan and their colleagues at Penn State University address in their paper is how to preserve the low-surface-friction property of a quasicrystal in the presence of a gas.
	alpha.mems.duke.edu (705 words)

	Quasicrystal Discoveries
		The quasicrystal was periodic in one direction but aperiodic in another, and its frictional properties differed by a factor of 8 along those axes.
		A quasiperiodic crystal (or quasicrystal) is an unusual form of crystal discovered in 1982.
		The quasicrystal is an ideal system to study because the aluminum–nickel–cobalt composition remained identical in both directions—the only difference was the periodicity or aperiodicity of the surfaces.
	www.chemistry.org /portal/a/c/s/1/feature_pro.html?id=c373e9063494d4d48f6a17245d830100 (461 words)

	Caspar & Fontano (1996) PNAS 93, 14271-78.
		Quasicrystal structures have been represented as projections into two- or three-dimensional space from periodic models in five- or six-dimensional space.
		A representative portion of a quasicrystal lattice can be chosen as a large unit cell of a perfectly periodic lattice that would yield the same diffraction pattern as the aperiodic lattice.
		Our surmise is that quasicrystals with icosahedral or decagonal symmetry may be modeled by periodic packing arrangements of icosahedra or pentagons in moderate-size unit cells that can be locally rearranged, conserving key bonding relations, to generate aperiodic lattices.
	www.sb.fsu.edu /~caspar/201 (6673 words)

	Aspects of quasicrystal structure
		In order to reconstruct the atomic structure of a quasicrystal using the tiling description, one must determine the symmetry, the atomic decoration of the unit cells, and the unit-cell packing.
		These criteria are applied to a continuum of 2D pentagonal quasicrystal tilings, only one of which--the Penrose tiling--was previously known to meet the criteria.
		The second study concerns the external morphology of quasicrystals grown under conditions close to thermodynamic equilibrium.
	repository.upenn.edu /dissertations/AAI9101171 (303 words)

	AN ESSENTIALLY-THREE-DIMENSIONAL QUASICRYSTAL (Site not responding. Last check: 2007-09-15)
		As the generator of an essentially-3-D quasicrystal, some detail of a 3-D Penrose transformation is given.
		An essentially 3-D quasicrystal, as ideal as possible, can be generated by the infinite-timerecursion of this transformation.
		In this respect, a quasicrystal is more closely related with an amorphous configuration than ever thought on a base of incomplete knowledge on 3-D Penrose transformation.
	members.tripod.com /vismath2/ogawa/es.htm (2313 words)

	Quasicrystal -- from Eric Weisstein's World of Physics
		Since this was long known to be crystallographically forbidden, this came as quite a shock initially, until it became apparent that materials exist which are not exact crystals but very nearly so which display symmetries forbidden by actual crystals.
		The mathematical structure behind quasicrystals had actually been discovered in 1974 by Roger Penrose when he devised Penrose tiles,
		Many known quasicrystals can be thought of as three-dimensional analogs of the Penrose tiling.
	scienceworld.wolfram.com /physics/Quasicrystal.html (153 words)

	A 3-D quasicrystal structure
		They are called quasicrystals and until recently their structure has been a mystery.
		The overlapping pattern of the decagons is closely related to the Penrose tiling, which comprises two types of rhomb, sharp and blunt (the sharp ones tend to group in pairs, as non-convex trapezia).
		The decagons formed by a Penrose tiling are larger than the decagons of the underlying quasicrystal, so one could expect a similar relationship in any 3-D analogue.
	www.steelpillow.com /polyhedra/quasicr/quasicr.htm (593 words)

	Live Observation of the Growth of Quasicrystal Grains — ESRF (Site not responding. Last check: 2007-09-15)
		Soon after their discovery in 1984, it was realised that quasicrystals (QC) constitute a new class of solids as they were found to differ both from crystals, because they lack periodicity, and from glasses, because they exhibit long-range order.
		A challenge of quasicrystal science today is to understand the local rule of the growth of these very peculiar solids [1].
		With this live observation the growth and the evolution of the quasicrystal grains can be followed and provides the first unambiguous evidence of their facetted growth with the manifestations of steps.
	www.esrf.fr /NewsAndEvents/Spotlight/spotlight8quasicrystals (357 words)

	Quasicrystal Research
		The 7th International Conference on Quasicrystals is scheduled for Sept. 20-24, 1999 at Stuttgart, Germany.
		Quasicrystals differ from crystals in the variety and frequency distributions of local environments.
		In quasicrystals a search for a pseudogap at the Fermi energy is suggested as a reason of stability and low conductivity.
	homepages.uni-tuebingen.de /peter.kramer (2044 words)

	ScienceDaily: 'Quasicrystal' Metal Computer Model Could Aid Ultra-low-friction Machine Parts (Site not responding. Last check: 2007-09-15)
		Their advance couldcontribute to wider applications of quasicrystals for extremelylow-friction machine parts, such as ball bearings and sliding parts.
		Quasicrystals, like normal crystals, consist of atoms that combine toform structures -- triangles, rectangles, pentagons, etc. -- thatrepeat in a pattern.
		Strange Quasicrystal Alloys Spring Electronic Surprise On Researchers (August 16, 2000) -- An international team of scientists has demonstrated that the electronic states of the strange metal alloys known as quasicrystals are more like those of ordinary metals than theorists believed...
	www.sciencedaily.com /releases/2005/09/050916073639.htm (1859 words)

	CA on quasicrystal (Site not responding. Last check: 2007-09-15)
		A CA rule that's different for the two types of tiles
		CLICK HERE FOR INFORMATION ABOUT SOFTWARE USED TO MAKE QUASICRYSTALS
		Software I've written -- some functional, some fun
	www.physics.emory.edu /~weeks/pics/qvote2.html (170 words)

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