journal
MENU ▼
Read by QxMD icon Read
search

Acta Crystallographica. Section A, Foundations and Advances

journal
https://www.readbyqxmd.com/read/29978850/ted-janssen-1936-2017
#1
Bernd Souvignier
No abstract text is available yet for this article.
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978849/spatio-temporal-symmetry-crystallographic-point-groups-with-time-translations-and-time-inversion
#2
Vincent S Liu, Brian K VanLeeuwen, Jason M Munro, Haricharan Padmanabhan, Ismaila Dabo, Venkatraman Gopalan, Daniel B Litvin
The crystallographic symmetry of time-periodic phenomena has been extended to include time inversion. The properties of such spatio-temporal crystallographic point groups with time translations and time inversion are derived and one representative group from each of the 343 types has been tabulated. In addition, stereographic symmetry and general-position diagrams are given for each representative group. These groups are also given a notation consisting of a short Hermann-Mauguin magnetic point-group symbol with each spatial operation coupled with its associated time translation...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978848/primitive-substitution-tilings-with-rotational-symmetries
#3
April Lynne D Say-Awen, Ma Louise Antonette N De Las Peñas, Dirk Frettlöh
This work introduces the idea of symmetry order, which describes the rotational symmetry types of tilings in the hull of a given substitution. Definitions are given of the substitutions σ6 and σ7 which give rise to aperiodic primitive substitution tilings with dense tile orientations and which are invariant under six- and sevenfold rotations, respectively; the derivation of the symmetry orders of their hulls is also presented.
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978847/indexing-of-grazing-incidence-x-ray-diffraction-patterns-the-case-of-fibre-textured-thin-films
#4
Josef Simbrunner, Clemens Simbrunner, Benedikt Schrode, Christian Röthel, Natalia Bedoya-Martinez, Ingo Salzmann, Roland Resel
Crystal structure solutions from thin films are often performed by grazing-incidence X-ray diffraction (GIXD) experiments. In particular, on isotropic substrates the thin film crystallites grow in a fibre texture showing a well defined crystallographic plane oriented parallel to the substrate surface with random in-plane order of the microcrystallites forming the film. In the present work, analytical mathematical expressions are derived for indexing experimental diffraction patterns, a highly challenging task which hitherto mainly relied on trial-and-error approaches...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978846/a-markov-theoretic-description-of-stacking-disordered-aperiodic-crystals-including-ice-and-opaline-silica
#5
A G Hart, T C Hansen, W F Kuhs
This article reviews the Markov theoretic description of one-dimensional aperiodic crystals, describing the stacking-faulted crystal polytype as a special case of an aperiodic crystal. Under this description the centrosymmetric unit cell underlying a topologically centrosymmetric crystal is generalized to a reversible Markov chain underlying a reversible aperiodic crystal. It is shown that for the close-packed structure almost all stackings are irreversible when the interaction reichweite s > 4. Moreover, the article presents an analytic expression of the scattering cross section of a large class of stacking-disordered aperiodic crystals, lacking translational symmetry of their layers, including ice and opaline silica (opal CT)...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978845/x-ray-molecular-orbital-analysis-i-quantum-mechanical-and-crystallographic-framework
#6
Kiyoaki Tanaka
Molecular orbitals were obtained by X-ray molecular orbital analysis (XMO). The initial molecular orbitals (MOs) of the refinement were calculated by the ab initio self-consistent field (SCF) MO method. Well tempered basis functions were selected since they do not produce cusps at the atomic positions on the residual density maps. X-ray structure factors calculated from the MOs were fitted to observed structure factors by the least-squares method, keeping the orthonormal relationship between MOs. However, the MO coefficients correlate severely with each other, since basis functions are composed of similar Gaussian-type orbitals...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978844/plesiotwins-versus-diperiodic-twins
#7
Massimo Nespolo
Plesiotwins and diperiodic twins have in common the fact of being characterized by a low degree of lattice restoration. Plesiotwins differ from twins by the fact that the relative orientation of the individuals is obtained by a non-crystallographic rotation about the normal to the composition plane, whereas for twins this rotation is crystallographic, apart from possible small deviations coming from metric pseudosymmetries. In the case of plesiotwins, the low degree of lattice restoration comes from a large coincidence site lattice (CSL) in the composition plane...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978843/a-numerical-method-for-deriving-shape-functions-of-nanoparticles-for-pair-distribution-function-refinements
#8
Tedi Marie Usher, Daniel Olds, Jue Liu, Katharine Page
In the structural refinement of nanoparticles, discrete atomistic modeling can be used for small nanocrystals (< 15 nm), but becomes computationally unfeasible at larger sizes, where instead unit-cell-based small-box modeling is usually employed. However, the effect of the nanocrystal's shape is often ignored or accounted for with a spherical model regardless of the actual shape due to the complexities of solving and implementing accurate shape effects. Recent advancements have provided a way to determine the shape function directly from a pair distribution function calculated from a discrete atomistic model of any given shape, including both regular polyhedra (e...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978842/a-group-theoretical-approach-to-enumerating-magnetoelectric-and-multiferroic-couplings-in-perovskites
#9
Mark S Senn, Nicholas C Bristowe
A group-theoretical approach is used to enumerate the possible couplings between magnetism and ferroelectric polarization in the parent Pm{\overline 3}m perovskite structure. It is shown that third-order magnetoelectric coupling terms must always involve magnetic ordering at the A and B sites which either transforms both as R-point or both as X-point time-odd irreducible representations (irreps). For fourth-order couplings it is demonstrated that this criterion may be relaxed allowing couplings involving irreps at X-, M- and R-points which collectively conserve crystal momentum, producing a magnetoelectric effect arising from only B-site magnetic order...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978841/precise-implications-for-real-space-pair-distribution-function-modeling-of-effects-intrinsic-to-modern-time-of-flight-neutron-diffractometers
#10
Daniel Olds, Claire N Saunders, Megan Peters, Thomas Proffen, Joerg Neuefeind, Katharine Page
Total scattering and pair distribution function (PDF) methods allow for detailed study of local atomic order and disorder, including materials for which Rietveld refinements are not traditionally possible (amorphous materials, liquids, glasses and nanoparticles). With the advent of modern neutron time-of-flight (TOF) instrumentation, total scattering studies are capable of producing PDFs with ranges upwards of 100-200 Å, covering the correlation length scales of interest for many materials under study. Despite this, the refinement and subsequent analysis of data are often limited by confounding factors that are not rigorously accounted for in conventional analysis programs...
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29978840/a-symmetry-roadmap-to-new-perovskite-multiferroics
#11
Patrick M Woodward
No abstract text is available yet for this article.
July 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724971/b-t-m-terry-willis-1927-2018
#12
Gerry Lander, Colin Carlile
No abstract text is available yet for this article.
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724970/report-of-the-executive-committee-for-2016
#13
M Dacombe, A T Ashcroft
The report of the Executive Committee for 2016 is presented.
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724969/quantitative-theory-of-diffraction-by-cylindrical-scroll-nanotubes
#14
Azat Khadiev, Zufar Khalitov
A quantitative theory of Fraunhofer diffraction by right- and left-handed multiwalled cylindrical scroll nanotubes is developed on the basis of the kinematical approach. The proposed theory is mainly dedicated to structural studies of individual nanotubes by the selected-area electron diffraction technique. Strong and diffuse reflections of the scroll nanotube were studied and explicit formulas that govern relations between the direct and reciprocal lattice of the scroll nanotube are achieved.
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724968/surface-embeddings-of-the-klein-and-the-m%C3%A3-bius-kantor-graphs
#15
Martin Cramer Pedersen, Olaf Delgado-Friedrichs, Stephen T Hyde
This paper describes an invariant representation for finite graphs embedded on orientable tori of arbitrary genus, with working examples of embeddings of the Möbius-Kantor graph on the torus, the genus-2 bitorus and the genus-3 tritorus, as well as the two-dimensional, 7-valent Klein graph on the tritorus (and its dual: the 3-valent Klein graph). The genus-2 and -3 embeddings describe quotient graphs of 2- and 3-periodic reticulations of hyperbolic surfaces. This invariant is used to identify infinite nets related to the Möbius-Kantor and 7-valent Klein graphs...
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724967/the-fundamentals-of-crystal-orientation
#16
Danut Dragoi
The method described in this paper improves the old methods of crystal orientation, applies new parametric equations for crystallography, and increases the precision and accuracy of measurements. The method applies to inorganic and organic crystals. A breakthrough in crystal orientation happened about 25 years ago when two equations dependent on the Bragg angle and an arbitrary direction in the crystal were developed. Unfortunately, they were analytically insolvable and their unique solution was found numerically...
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724966/dependence-of-x-ray-plane-wave-rocking-curves-on-the-deviation-from-exact-bragg-orientation-in-and-perpendicular-to-the-diffraction-plane-for-the-asymmetrical-laue-case
#17
Minas K Balyan
For the asymmetrical Laue case the X-ray plane-wave transmission and reflection coefficients and rocking curves are analysed as a function of the deviation angles from the exact Bragg orientation in the diffraction plane and in the direction perpendicular to the diffraction plane. New peculiarities of the rocking curves are obtained. The peculiarities of both the effective absorption coefficient and rocking curves in thick crystals are also investigated.
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724965/aflow-sym-platform-for-the-complete-automatic-and-self-consistent-symmetry-analysis-of-crystals
#18
David Hicks, Corey Oses, Eric Gossett, Geena Gomez, Richard H Taylor, Cormac Toher, Michael J Mehl, Ohad Levy, Stefano Curtarolo
Determination of the symmetry profile of structures is a persistent challenge in materials science. Results often vary amongst standard packages, hindering autonomous materials development by requiring continuous user attention and educated guesses. This article presents a robust procedure for evaluating the complete suite of symmetry properties, featuring various representations for the point, factor and space groups, site symmetries and Wyckoff positions. The protocol determines a system-specific mapping tolerance that yields symmetry operations entirely commensurate with fundamental crystallographic principles...
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724964/a-method-to-estimate-statistical-errors-of-properties-derived-from-charge-density-modelling
#19
Bertrand Fournier, Benoît Guillot, Claude Lecomte, Eduardo C Escudero-Adán, Christian Jelsch
Estimating uncertainties of property values derived from a charge-density model is not straightforward. A methodology, based on calculation of sample standard deviations (SSD) of properties using randomly deviating charge-density models, is proposed with the MoPro software. The parameter shifts applied in the deviating models are generated in order to respect the variance-covariance matrix issued from the least-squares refinement. This `SSD methodology' procedure can be applied to estimate uncertainties of any property related to a charge-density model obtained by least-squares fitting...
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29724963/partially-coherent-ptychography-by-gradient-decomposition-of-the-probe
#20
Huibin Chang, Pablo Enfedaque, Yifei Lou, Stefano Marchesini
Coherent ptychographic imaging experiments often discard the majority of the flux from a light source to define the coherence of the illumination. Even when the coherent flux is sufficient, the stability required during an exposure is another important limiting factor. Partial coherence analysis can considerably reduce these limitations. A partially coherent illumination can often be written as the superposition of a single coherent illumination convolved with a separable translational kernel. This article proposes the gradient decomposition of the probe (GDP), a model that exploits translational kernel separability, coupling the variances of the kernel with the transverse coherence...
May 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
journal
journal
48285
1
2
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read
×

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"