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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/28447598/convex-polyhedra-with-minimum-and-maximum-names
#1
Yury L Voytekhovsky
The paper reports the combinatorial types of convex n-acra (i.e. n-vertex polyhedra) for which the minimum (min.) and maximum (max.) names are attained. Hence, min. and max. names can be independently found without generating the whole combinatorial variety of convex n-acra (e.g. by the routine recurrence Fedorov algorithm) and calculating names for each n-acron.
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447597/resonant-and-non-resonant-magnetic-scatterings-with-circularly-polarized-x-rays-magnetic-scattering-factor-and-electron-density-of-gadolinium-iron-garnet
#2
Yo Sasaki, Maki Okube, Satoshi Sasaki
Theoretical and experimental studies on resonant magnetic scattering have been carried out using circularly polarized X-rays. Polarization dependence of the asymmetric ratio between right- and left-handed polarized scattering amplitudes has revealed that resonant and non-resonant magnetic scatterings can be observed simultaneously. In this study, synchrotron X-ray intensity experiments were conducted on Gd iron garnet (GdIG) at the pre-edge of the Fe K absorption edge. The asymmetric ratio between circular polarizations exhibited three peaks due to the resonant magnetic responses of Fe(3+) in the Fe2 (24d) site...
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447596/on-the-penrose-and-taylor-socolar-hexagonal-tilings
#3
Jeong Yup Lee, Robert V Moody
The intimate relationship between the Penrose and the Taylor-Socolar tilings is studied, within both the context of double hexagon tiles and the algebraic context of hierarchical inverse sequences of triangular lattices. This unified approach produces both types of tilings together, clarifies their relationship and offers straightforward proofs of their basic properties.
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447595/groupoids-and-labelled-quotient-graphs-a-topological-analysis-of-the-modular-structure-in-pyroxenes
#4
Jean Guillaume Eon
The analysis of the modular structure of pyroxenes, recently discussed in Nespolo & Aroyo [Eur. J. Mineral. (2016), 28, 189-203], has been performed on the respective labelled quotient graphs (LQGs). It is shown that the structure and maximum symmetry of the module, i.e. its layer group, can be determined directly from the LQG. Partial symmetry operations between different modules have been associated with automorphisms of the quotient graph that may not be consistent with net voltages over the respective cycles...
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447594/diffuse-single-crystal-scattering-corrected-for-molecular-form-factor-effects
#5
Ella Schmidt, Reinhard B Neder
This paper shows that chemical short-range order in two-component molecular crystals can be solved directly by separating the influence of the molecular form factor from the diffraction pattern. This novel technique is demonstrated by analysing the diffuse scattering of tris-tert-butyl-1,3,5-benzene tricarboxamide.
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447593/edge-2-transitive-trinodal-polyhedra-and-2-periodic-tilings
#6
Olaf Delgado-Friedrichs, Michael O'Keeffe
All trinodal, edge-2-transitive polyhedra and 2-periodic tilings are enumerated and described. These are of special interest for the design and synthesis of materials such as metal-organic polyhedra and frameworks.
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447592/the-phantom-derivative-method-when-a-structure-model-is-available-about-its-theoretical-basis
#7
Maria Cristina Burla, Giovanni Luca Cascarano, Carmelo Giacovazzo, Giampiero Polidori
This study clarifies why, in the phantom derivative (PhD) approach, randomly created structures can help in refining phases obtained by other methods. For this purpose the joint probability distribution of target, model, ancil and phantom derivative structure factors and its conditional distributions have been studied. Since PhD may use n phantom derivatives, with n ≥ 1, a more general distribution taking into account all the ancil and derivative structure factors has been considered, from which the conditional distribution of the target phase has been derived...
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28447591/non-crystallographic-symmetry-of-liquid-metal-flat-crystallographic-faults-and-polymorph-transformation-of-the-m7c3-carbide
#8
Alexander L Talis, Valentin S Kraposhin, Sergey Yu Kondrat'ev, Vladimir I Nikolaichik, Ekaterina V Svyatysheva, Ayal A Everstov
The fine lamellar fault structure of primary M7C3 carbide particles in the heat-resistant Fe-Cr-Ni-C alloy of the HP series (0.45C-25Cr-35Ni) in the cast condition has been revealed using transmission electron microscopy. The lamellar fault structure is regarded as an inheritance of the initial melt structure. A one-to-one correspondence between the crystal structures of M7C3, M5C2, M3C and M23C6 carbides and constructions of the projective 103 Desargues configuration and its subconfigurations is shown. Mutual mapping between 103 Desargues subconfigurations determines transformations of the ten-vertex equal-edged triangulated clusters appearing as building units of these carbides...
May 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248666/report-of-the-executive-committee-for-2015
#9
M Dacombe
The report of the Executive Committee for 2015 is presented.
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248665/douglas-doug-dorset-1942-2016
#10
Lisa Baugh, Mark Disko, William Lamberti, Karl Strohmaier, William Duax, John Fryer, Sven Hovmöller, Xiaodong Zou, Laurence Marks, Stavros Nicolopoulos
No abstract text is available yet for this article.
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248664/monte-carlo-simulation-of-an-anharmonic-debye-waller-factor-to-the-t-4-order
#11
Kun Lun Wang, Xian Bin Huang, Jing Li, Qiang Xu, Jia Kun Dan, Xiao Dong Ren
In an increasing number of cases the harmonic approximation is incommensurate with the quality of Bragg diffraction data, while results of the anharmonic Debye-Waller factor are not typically available. This paper presents a Monte Carlo computation of a Taylor expansion of an anharmonic Debye-Waller factor with respect to temperature up to the fourth order, where the lattice was a face-centred cubic lattice and the atomic interaction was described by the Lennard-Jones potential. The anharmonic Debye-Waller factor was interpreted in terms of cumulants...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248663/the-phase-problem-for-one-dimensional-crystals
#12
Rick P Millane
The phase problem for diffraction amplitudes measured from a one-dimensional crystal is examined. In the absence of any a priori information, the solution to this problem is shown to be unique up to a parameterized, low-dimensional set of solutions. Minimal additional a priori information is expected to render the solution unique. The effects of additional information such as positivity, molecular envelope and helical symmetry on uniqueness are characterized. The results are pertinent to structural studies of polymeric and rod-like biomolecular assemblies that form one-dimensional, rather than three-dimensional, crystals...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248662/b7-as-a-supergroup-of-crystal-and-quasicrystal-symmetries
#13
Kazimierz Stróż
In sharp contrast to the generation of a finite group that includes all the 14 types of Bravais lattices as its subgroups [Hosoya (2000). Acta Cryst. A56, 259-263; Hosoya (2002). Acta Cryst. A58, 208], it was proved that a signed permutation group Bk may be interpreted as the supergroup of both crystal and quasicrystal symmetries. Minimal dimension k = 6 is adequate for lattices referred to their three non-coplanar shortest vectors, or for symmetry groups of most quasicrystal types. If one prefers complete, well defined semi-reduced lattice descriptions or needs a dodecagonal group, the B7 supergroup is necessary...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248661/hyperbolic-crystallography-of-two-periodic-surfaces-and-associated-structures
#14
Martin Cramer Pedersen, Stephen T Hyde
This paper describes the families of the simplest, two-periodic constant mean curvature surfaces, the genus-two HCB and SQL surfaces, and their isometries. All the discrete groups that contain the translations of the genus-two surfaces embedded in Euclidean three-space modulo the translation lattice are derived and enumerated. Using this information, the subgroup lattice graphs are constructed, which contain all of the group-subgroup relations of the aforementioned quotient groups. The resulting groups represent the two-dimensional representations of subperiodic layer groups with square and hexagonal supergroups, allowing exhaustive enumeration of tilings and associated patterns on these surfaces...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248660/a-theoretical-investigation-of-orientation-relationships-and-transformation-strains-in-steels
#15
K Koumatos, A Muehlemann
The identification of orientation relationships (ORs) plays a crucial role in the understanding of solid phase transformations. In steels, the most common models of ORs are the ones by Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS). The defining feature of these and other OR models is the matching of directions and planes in the parent face-centred cubic γ phase to ones in the product body-centred cubic/tetragonal α/α' phase. In this article a novel method that identifies transformation strains with ORs is introduced and used to develop a new strain-based approach to phase-transformation models in steels...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248659/dynamic-quantum-crystallography-lattice-dynamical-models-refined-against-diffraction-data-ii-applications-to-l-alanine-naphthalene-and-xylitol
#16
Anna A Hoser, Anders Ø Madsen
In the first paper of this series [Hoser & Madsen (2016). Acta Cryst. A72, 206-214], a new approach was introduced which enables the refinement of frequencies of normal modes obtained from ab initio periodic computations against single-crystal diffraction data. In this contribution, the performance of this approach is tested by refinement against data in the temperature range from 23 to 205 K on the molecular crystals of L-alanine, naphthalene and xylitol. The models, which are lattice-dynamical models derived at the Γ point of the Brillouin zone, are able to describe the atomic vibrations of L-alanine and naphthalene to a level where the residual densities are similar to those obtained from the independent atom model...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248658/asymmetry-in-serial-femtosecond-crystallography-data
#17
Amit Sharma, Linda Johansson, Elin Dunevall, Weixiao Y Wahlgren, Richard Neutze, Gergely Katona
Serial crystallography is an increasingly important approach to protein crystallography that exploits both X-ray free-electron laser (XFEL) and synchrotron radiation. Serial crystallography recovers complete X-ray diffraction data by processing and merging diffraction images from thousands of randomly oriented non-uniform microcrystals, of which all observations are partial Bragg reflections. Random fluctuations in the XFEL pulse energy spectrum, variations in the size and shape of microcrystals, integrating over millions of weak partial observations and instabilities in the XFEL beam position lead to new types of experimental errors...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248657/a-projection-based-reformulation-of-the-coincident-site-lattice-%C3%AE-for-arbitrary-bicrystals-at-finite-temperature
#18
B Runnels
The coincident site lattice and, specifically, the `Σ value' of a grain boundary are a ubiquitous metric for experimental classification of grain boundaries. However, the mathematical nature of Σ - a pathological function taking values of either an integer or infinity - has been relatively unexplored. This work presents a framework for interpreting Σ as the inverse of a projection defined using the standard L(2) inner product over continuous fields that represent lattices. `Pre-mollifiers' are used to introduce thermal regularization in the context of the inner product, and a closed-form analytic result is derived...
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28248656/approximating-coincidence-turning-a-new-page-for-bicrystallography
#19
Srikanth Patala
No abstract text is available yet for this article.
March 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/28042807/ordering-of-convex-polyhedra-and-the-fedorov-algorithm
#20
Yury L Voytekhovsky
A method of naming any convex polyhedron by a numerical code arising from the adjacency matrix of its edge graph has been previously suggested. A polyhedron can be built using its name. Classes of convex n-acra (i.e. n-vertex polyhedra) are strictly (without overlapping) ordered by their names. In this paper the relationship between the Fedorov algorithm to generate the whole combinatorial variety of convex polyhedra and the above ordering is described. The convex n-acra are weakly ordered by the maximum extra valencies of their vertices...
January 1, 2017: Acta Crystallographica. Section A, Foundations and Advances
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