1,721,548 research outputs found
The arithmetic symmetry of monoatomic 2-nets
No full textA recent paper [Pitteri & Zanzotto (1998). Acta Cryst. A54, 359-373] has proposed a framework for the study of the `arithmetic symmetry' of multilattices (discrete triply periodic point sets in the affine space). The classical approach to multilattice symmetry considers the well known `space groups', that is, the groups of affine isometries leaving a multilattice invariant. The ensuing classification counts 219 affine conjugacy (or isomorphism) classes of space groups in three dimensions, and 17 classes in two dimensions (`plane groups'). The arithmetic criterion gives a finer classification of multilattice symmetry than space (or plane) groups do. This paper is concerned with the systematic investigation of the arithmetic symmetry of multilattices in the simplest nontrivial case, that is, monoatomic 2-nets (planar lattices with two identical atoms in their unit cell). We show the latter to belong to five distinct arithmetic types. We also give the complete description of a fundamental domain for the action of the global symmetry group of 2-nets on the space of 2-net metrics
The arithmetic symmetry of colored crystals: classification of 2-color 2-lattices
No full textA framework for the detailed classification of general crystal structures, based on an arithmetic criterion, has been proposed in recent years. In this paper it is shown how this method can also be applied to enumerate colored crystals. To illustrate this approach, the systematic classification in the simplest case, i.e. of `2-color 2-lattices', in two and three dimensions (two- and three-dimensional crystals with two differently colored atoms per unit translational cell) is presented. 51 distinct types of 2-color 2-lattices are found in three dimensions (ten types in two dimensions); this gives a complete catalog of the simplest crystal structures that are theoretically possible for two-element compounds. Among the 51 2-lattices, all those which already have a Strukturberichte denomination are retrieved, as well as the 22 `black-and-white lattices' considered in the theory of magnetic crystals. The symmetry hierarchies and symmetry-breaking possibilities for 2-color 2-lattices are also determined in two and three dimensions
On the arithmetic classification of crystal structures
No full textAn arithmetic criterion for the classification of crystal structures with points in their unit cell (`-lattices') was described by Pitteri & Zanzotto [Acta Cryst. (1998), A54 359-373]. In this paper, a systematic analysis of monoatomic 2-lattices is given, showing that there exist 29 distinct arithmetic types of these structures, some of which share the same space groups. As all monoatomic 2-lattices are constituted by a single crystallographic orbit, these structures are also classified by the established criterion of Fischer & Koch [Koch & Fischer (1975). Acta Cryst. A31, 88-95; Fischer & Koch (1996). International Tables for Crystallography, Vol. A. Dordrecht: Kluwer] involving the lattice complexes. The two classifications are found to coincide in this simplest case. By examination of some examples taken from the allotropes of the elements, it is also shown how the arithmetic criterion can be used to classify more complex crystals, such as monoatomic 4-lattices. This gives a group-theoretical framework for distinguishing structures when the space-group classification fails to do so, and Fischer & Koch's criterion, as presented in the literature, may not be immediately applied
Symmetry breaking in monoatomic 2-lattices
No full textIn this paper we describe all the possibilities for symmetry-breaking transformations in monoatomic 2-lattices (crystal structures with two identical points in their unit translational cell). This is done by establishing the symmetry hierarchies (partial ordering) for the arithmetic classes of symmetry groups of these crystals, shown in Fig. 1. We also study the ‘Ericksen–Pitteri neighbourhoods’ for monoatomic 2-lattices, thus making a local analysis of their configuration space. We give details about two physically relevant cases, analysing the neighbourhoods and the possible symmetry-breaking mechanisms for the hexagonal close-packed and the diamond structures (Figs. 2 and 3)
Predicting the impact of advertisements on web pages aesthetic impressions
No full textIn this paper we study the impact of advertisements on a
predictive model for web pages impressions, calculated according to a set
of features on the rendered page images. We analysed the effects on two
different predictors, the colourfulness and the visual complexity.
We compared the prediction against ground-truth values, obtained through
a user study. We conclude that the prediction model behaves correctly
for the complexity, but it is not able to predict the increase on the
colourfulness ratings
Risk factors for oral mucositis in paediatric oncology patients receiving alkylant chemotherapy
No full textCoupling PIV measurements and numerical modelling of RBCs mechanics to predict thrombogenicity of mechanical prosthetic heart valves.
No full text
First-principles study of the structural and elastic properties of zirconia
No full textZirconia (ZrO2) is a most important substance in materials science and technology due to its wide-ranging applications. Accordingly, there have been several investigations of its observed crystalline polymorphs. However, a systematic analysis of the elastic properties of the ZrO2 structures is still lacking. In this paper the structural and elastic properties of the experimentally confirmed phases of zirconia are studied with density-functional theory. Comparisons are drawn among various methods of computing the elastic parameters as well as with existing experimental data and other theoretical investigations
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