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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/29072203/prices-of-iucr-journals
#1
A T Ashcroft
No abstract text is available yet for this article.
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072202/prime-numbers-and-the-riemann-hypothesis-by-barry-mazur-and-william-stein-cambridge-university-press-2016-pp-xi-142-price-gbp-17-99-paperback-isbn-9781107499430
#2
Massimo Nespolo
No abstract text is available yet for this article.
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072201/the-rome-de-lisle-problem
#3
Yury L Voytekhovsky, Dmitry G Stepenshchikov
The `Rome de Lisle problem' on the vertex and edge truncations has been formulated and solved for all crystal closed simple forms (two, eight, five and 15 for orthorhombic, trigonal + hexagonal, tetragonal and cubic syngonies, respectively). The collections of simple forms obtained are enumerated and considered as special combinations of simple forms in symmetry classes.
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072200/a-note-on-x-ray-spherical-wavefields-in-the-laue-case-for-perfect-crystals
#4
Takashi Saka
Spherical wavefields in the Laue case are obtained when the real part of the crystal structure factor is zero or small compared with the imaginary part. The results are the same as in the conventional case where the real part is large. Through this work, it is shown that virtual wavefields on the vacuum side should be taken into account to explain the obtained results. It is also shown that, to obtain the virtual wavefields, a modification of the conventional spherical wave theory is necessary.
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072199/about-difference-electron-densities-and-their-properties
#5
Maria Cristina Burla, Benedetta Carrozzini, Giovanni Luca Cascarano, Carmelo Giacovazzo, Giampiero Polidori
Difference electron densities do not play a central role in modern phase refinement approaches, essentially because of the explosive success of the EDM (electron-density modification) techniques, mainly based on observed electron-density syntheses. Difference densities however have been recently rediscovered in connection with the VLD (Vive la Difference) approach, because they are a strong support for strengthening EDM approaches and for ab initio crystal structure solution. In this paper the properties of the most documented difference electron densities, here denoted as F - Fp, mF - Fp and mF - DFp syntheses, are studied...
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072198/extrinsic-faulting-in-3c-close-packed-crystal-structures-computational-mechanics-analysis
#6
Ernesto Estevez-Rams, Raimundo Lora-Serrano, Arbelio Penton-Madrigal, Massimo Nespolo
Extrinsic faulting has been discussed previously within the so-called difference method and random walk calculation. In this contribution it is revisited under the framework of computational mechanics, which allows expressions to be derived for the statistical complexity, entropy density and excess entropy as a function of faulting probability. The approach allows one to compare the disordering process of an extrinsic fault with other faulting types. The ℇ-machine description of the faulting mechanics is presented...
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072197/the-phase-problem-for-two-dimensional-crystals-i-theory
#7
Romain D Arnal, Rick P Millane
Properties of the phase problem for two-dimensional crystals are examined. This problem is relevant to protein structure determination using diffraction from two-dimensional crystals that has been proposed using new X-ray free-electron laser sources. The problem is shown to be better determined than for conventional three-dimensional crystallography, but there are still a large number of solutions in the absence of additional a priori information. Molecular envelope information reduces the size of the solution set, and for an envelope that deviates sufficiently from the unit cell a unique solution is possible...
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072196/-bb-z-module-defects-in-crystals
#8
Abdullah Sirindil, Marianne Quiquandon, Denis Gratias
An analysis is presented of the new types of defects that can appear in crystalline structures where the positions of the atoms and the unit cell belong to the same {\bb Z}-module, i.e. are irrational projections of an N > 3-dimensional (N-D) lattice Λ as in the case of quasicrystals. Beyond coherent irrationally oriented twins already discussed in a previous paper [Quiquandon et al. (2016). Acta Cryst. A72, 55-61], new two-dimensional translational defects are expected, the translation vectors of which, being projections of nodes of Λ, have irrational coordinates with respect to the unit-cell reference frame...
November 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862168/accelerated-scattering-of-convex-polyhedra
#9
Yury L Voytekhovsky
The formulas for the minimum (minn) and maximum (maxn) names in the classes of convex n-acra (i.e. n-vertex polyhedra) are found for any n. The asymptotic behaviour (as n → ∞) for maxn+1/maxn, minn+1/minn, minn+1/maxn and maxn/minn is established. They characterize in detail the accelerated scattering of [minn, maxn] ranges on a real line.
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862167/real-time-detection-and-resolution-of-atom-bumping-in-crystallographic-models
#10
Yu Liu
A basic principle in crystal structure determination is that there should be proper distances between adjacent atoms. Therefore, detection of atom bumping is of fundamental significance in structure determination, especially in the direct-space method where crystallographic models are just randomly generated. Presented in this article is an algorithm that detects atom bonding in a unit cell based on the sweep and prune algorithm of axis-aligned bounding boxes and running in the O(n log n) time bound, where n is the total number of atoms in the unit cell...
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862166/the-wavevector-substar-group-in-reciprocal-space-and-its-representation
#11
Il Hwan Kim, Jong Ok Pak, Il Hun Kim, Song Won Kim, Lin Li
A new concept of the wavevector substar group is established which, in the study of translational symmetry breaking of a crystal, only considers the particular arms of the wavevector star taking part in the phase transition; this is in contrast with the traditional Landau theory which considers all of the arms of the wavevector star. It is shown that this new concept can be used effectively to investigate the interesting physical properties of crystals associated with translational symmetry breaking. It is shown that studies on complicated phase transitions related to reducible representations, such as those in perovskite KMnF3 multiferroics and the high-temperature superconductor La2/3Mg1/2W1/2O3 (La4Mg3W3O18), are much simplified by the new concept...
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862165/mathematical-aspects-of-molecular-replacement-iv-measure-theoretic-decompositions-of-motion-spaces
#12
Gregory S Chirikjian, Sajdeh Sajjadi, Bernard Shiffman, Steven M Zucker
In molecular-replacement (MR) searches, spaces of motions are explored for determining the appropriate placement of rigid-body models of macromolecules in crystallographic asymmetric units. The properties of the space of non-redundant motions in an MR search, called a `motion space', are the subject of this series of papers. This paper, the fourth in the series, builds on the others by showing that when the space group of a macromolecular crystal can be decomposed into a product of two space subgroups that share only the lattice translation group, the decomposition of the group provides different decompositions of the corresponding motion spaces...
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862164/close-packed-structure-dynamics-with-finite-range-interaction-computational-mechanics-with-individual-layer-interaction
#13
Edwin Rodriguez-Horta, Ernesto Estevez-Rams, Raimundo Lora-Serrano, Reinhard Neder
This is the second contribution in a series of papers dealing with dynamical models in equilibrium theories of polytypism. A Hamiltonian introduced by Ahmad & Khan [Phys. Status Solidi B (2000), 218, 425-430] avoids the unphysical assignment of interaction terms to fictitious entities given by spins in the Hägg coding of the stacking arrangement. In this paper an analysis of polytype generation and disorder in close-packed structures is made for such a Hamiltonian. Results are compared with a previous analysis using the Ising model...
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862163/davide-viterbo-1939-2017
#14
Carlo Mealli, Marco Milanesio
No abstract text is available yet for this article.
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28862162/philip-coppens-1930-2017
#15
Pierre Becker
No abstract text is available yet for this article.
September 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28660868/creating-symmetry-the-artful-mathematics-of-wallpaper-patterns-by-frank-a-farris-princeton-university-press-2015-pp-248-price-gbp-27-95-usd-35-00-hardcover-isbn-9780691161730
#16
Gregory McColm
No abstract text is available yet for this article.
July 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28660867/close-packed-structures-with-finite-range-interaction-computational-mechanics-of-layer-pair-interaction
#17
Edwin Rodriguez-Horta, Ernesto Estevez-Rams, Reinhard Neder, Raimundo Lora-Serrano
The stacking problem is approached by computational mechanics, using an Ising next-nearest-neighbour model. Computational mechanics allows one to treat the stacking arrangement as an information processing system in the light of a symbol-generating process. A general method for solving the stochastic matrix of the random Gibbs field is presented and then applied to the problem at hand. The corresponding phase diagram is then discussed in terms of the underlying ℇ-machine, or optimal finite-state machine. The occurrence of higher-order polytypes at the borders of the phase diagram is also analysed...
July 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28660866/hard-sphere-displacive-model-of-deformation-twinning-in-hexagonal-close-packed-metals-revisiting-the-case-of-the-56%C3%A2-a-contraction-twins-in-magnesium
#18
Cyril Cayron
Contraction twinning in magnesium alloys leads to new grains that are misoriented from the parent grain by a rotation (56°, a). The classical shear theory of deformation twinning does not specify the atomic displacements and does not explain why contraction twinning is less frequent than extension twinning. The paper proposes a new displacive model in line with our previous work on martensitic transformations and extension twinning. A continuous angular distortion matrix that transforms the initial hexagonal close-packed (h...
July 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28660865/thermoelectric-transport-properties-in-magnetically-ordered-crystals
#19
Hans Grimmer
The forms of the tensors describing thermoelectric transport properties in magnetically ordered crystals are given for frequently used orientations of the 122 space-time point groups up to second order in an applied magnetic field. It is shown which forms are interchanged for the point groups of the hexagonal crystal family by two different conventions for the connection between the Hermann-Mauguin symbol and the orientation of the Cartesian coordinate system. The forms are given in Nye notation, which conspicuously shows how the forms for different point groups are related...
July 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28660864/reduction-of-small-angle-scattering-profiles-to-finite-sets-of-structural-invariants
#20
Jérôme Houdayer, Frédéric Poitevin
This paper shows how small-angle scattering (SAS) curves can be decomposed in a simple sum using a set of invariant parameters called Kn which are related to the shape of the object of study. These Kn, together with a radius R, give a complete theoretical description of the SAS curve. Adding an overall constant, these parameters are easily fitted against experimental data giving a concise comprehensive description of the data. The pair distance distribution function is also entirely described by this invariant set and the Dmax parameter can be measured...
July 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
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