Infinite Point Group Quasicrystals: Symmetry Basis for Noncrystalline Diamond-like Materials

The construction of a diamond-like tetracoordinated quasicrystal (possible only in the infinite point group R) is considered in the framework of algebraic geometry. The physical and materials research applications of this approach are discussed.     

Theory of the Structure of Coherent Boundaries in ZrO<Subscript>2</Subscript> Nanoparticles

A general algorithm is proposed for constructing coherent boundaries. This algorithm is based on the interrelation between the spatial coherence of structural fragments in nanoparticles and the geometric connection in the corresponding associated bundle. A local approach is used to describe the structure of coherent boundaries in zirconia nanoparticles. The inference is made that the models of structures thus obtained should be preferred over the models constructed in terms of the theory of coincident site lattice.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Shevchenko, Samoilovich, Talis, Madison.     

Geometrical Model of Polymorphous Transformations in Titanium and Zirconium

A geometrical model of transformation of a body-centered cubic lattice of α-phase into a hexagonal close-packed lattice of α-phase is developed with the aim of explaining the special features of the crystal geometry of formation of martensite phases in titanium and zirconium and in alloys based on them. The transformation is described as mutual reconstruction of coordination polyhedra of the cubic and hexagonal lattices through an intermediate configuration of the crystal structure of ω-phase. In the language of algebraic geometry the transition is implemented as reconstruction of an 11-atom cluster that represents a union of three octahedra around a common edge into an 11-atom cluster composed of 11 tetrahedra united over faces. Experimentally observed orientation relations and habit planes at α → ω and β → α transformations are describable by elements of the structure of the mentioned clusters.     

Polytope topological approach to describing martensite transformation

Conclusions  

Crystallography of in-situ transformations of the <Emphasis Type="Italic">M</Emphasis><Subscript>7</Subscript>C<Subscript>3</Subscript> carbide in the cast Fe–Cr–Ni alloy

In the process of holding of the cast heat-resistant Fe–Cr–Ni (0.45C–25Cr–35Ni) alloy at 1150°C, the eutectic chromium carbide present in its structure undergoes a gradual transition M ₇C₃ → M ₂₃C₆. The gradual formation of domains of the M ₂₃C₆ carbide inside the particles of the M ₇C₃ carbide makes it possible to assume that the observed phase transition is the well-known carbide transformation of the in situ type. The mechanism of the in situ transformation of the crystal structure of the carbide from M ₇C₃ into M ₂₃C₆ with a change in the number of nearest metal neighbors of carbon atoms is explained within the previously developed combinatory model of polymorphic transitions in the metals.     

Mechanism of Nucleation of Precipitates of Carbides of Refractory Metals Under Hot Rolling of Automotive Sheet Steel

Metal Science and Heat Treatment - The problem of formation of properties in microalloyed sheet steels is considered. The cause and the possible mechanism of precipitation of carbides of refractory...     

Experimental investigation of in-situ transformations of the <Emphasis Type="Italic">M</Emphasis><Subscript>7</Subscript>C<Subscript>3</Subscript> carbide in the cast Fe–Cr–Ni alloy

The microstructure and the phase composition of a heat-resistant Fe–Cr–Ni alloy (0. 45C–25Cr–35Ni) has been investigated in the cast state and after annealing at 1150°C for 2–100 h. After a 2-h high-temperature annealing, the fragmentation of the crystal structure of the eutectic M ₇C₃ carbides into domains of ~500 nm in size with a partial transition into M ₂₃C₆ carbides is observed. After a 100-h holding, the complete transition of the hexagonal M ₇C₃ carbides into M ₂₃C₆ with a face-centered cubic structure occurs. The carbide transition M ₇C₃ →M ₂₃ can be considered to be an in situ transformation.     

Temporal limitations in the effective binding of attended target attributes in the mutual masking of visual objects.

The problem of feature binding has been examined under conditions of distributed attention or with spatially dispersed stimuli. We studied binding by asking whether selective attention to a feature of a masked object enables perceptual access to the other features of that object using conditions in which spatial attention was directed at a single location where all objects appeared. In an identification condition, the task required reporting the same property of each object. High rates of identification showed good perceptual availability. In a search condition, the task required reporting the property (e.g., shape) that was associated with a specific value of the searched property (e.g., surface texture) of the same object. Focusing of attention on a target’s searched property value did not result in a high rate of identifying the target’s other property, and strong object masking was found. Backward masking between spatially superimposed visual objects appears to be primarily due to a difficulty in feature binding of a target object rather than to a substitution of an integrated object by the following stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)