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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/30182949/calculation-of-absorption-and-secondary-scattering-of-x-rays-by-spherical-amorphous-materials-in-an-asymmetric-transmission-geometry-corrigendum
#1
J C Bendert, M E Blodgett, K F Kelton
A revised version of Table 2 of Bendert et al. [Acta Cryst. (2013). A69, 131-139] is provided.
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182948/intensive-x-ray-standing-wave-like-fields-localized-near-a-surface-of-a-crystalline-superlattice
#2
I R Prudnikov
A peculiar kind of intensive X-ray standing wave is analytically shown to exist. Such an X-ray interference field is localized in the vicinity of a surface of a crystalline superlattice and its amplitude decays exponentially in both directions perpendicular to the surface. The appearance of the standing wave is accompanied by a deep dip in a chosen Bragg peak of the superlattice.
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182947/vertex-collisions-in-3-periodic-nets-of-genus-4
#3
Montauban Moreira de Oliveira, Geovane Matheus Lemes Andrade, Eliel Roger da Silva, Jean Guillaume Eon
Unstable nets, by definition, display vertex collisions in any barycentric representation, among which are approximate models for the associated crystal structures. This means that different vertex lattices happen to superimpose when every vertex of a periodic net is located at the centre of gravity of its first neighbours. Non-crystallographic nets are known to be unstable, but crystallographic nets can also be unstable and general conditions for instability are not known. Moreover, examples of unstable nets are still scarce...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182946/experimental-and-theoretical-investigations-of-an-x-ray-lll-interferometer-with-a-wedge-shaped-mirror-plate
#4
Tigran H Eyramjyan, Tamara S Mnatsakanyan, Minas K Balyan
An X-ray LLL interferometer with a wedge-shaped mirror plate is experimentally and theoretically investigated. Experimentally obtained interference patterns show that the Moiré fringes are superposed on Pendellösung fringes and the period of the Pendellösung fringes is not changed after passing the analyzer plate. An eikonal theory of interference-fringe formation in an LLL interferometer with a wedge-shaped mirror plate is developed, and provides predictions that coincide with experimentally obtained results...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182945/the-real-part-of-the-dispersion-surface-in-x-ray-dynamical-diffraction-in-the-laue-case-for-perfect-crystals
#5
Takashi Saka
The real part of the dispersion surface in X-ray dynamical diffraction in the Laue case for perfect crystals is analysed using a Riemann surface. In the conventional two-beam approximation, each branch or wing of the dispersion surface is specified by one sheet of the Riemann surface. The characteristic features of the dispersion surface are analytically revealed using four parameters, which are the real and imaginary parts of two quantities that specify the degree of departure from the exact Bragg condition and the reflection strength...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182944/energy-flow-of-bloch-waves-in-x-ray-dynamical-diffraction-in-the-laue-case-for-perfect-crystals
#6
Takashi Saka
The direction of energy flow for Bloch waves during X-ray dynamical diffraction in perfect crystals is investigated. The energy flow is spread uniformly within the Borrmann fan in the conventional Laue case where the imaginary part of the crystal structure factor is much smaller than the real part. However, when the imaginary part is large, as in the case of X-rays with energies close to the absorption edge for single atoms in crystals, the energy flow direction is found to be restricted, and the results are discussed in relation to the Bragg case...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182943/x-ray-reflectivity-of-chemically-vapor-deposited-diamond-single-crystals-in-the-laue-geometry
#7
S Stoupin, J P C Ruff, T Krawczyk, K D Finkelstein
The absolute X-ray reflectivity of chemically vapor-deposited (CVD) single-crystal diamond plates was measured in the Laue geometry in the double-crystal non-dispersive setting with an asymmetric Si beam-conditioner crystal. The measurements were supplemented by rocking-curve topography. The measured reflectivity curves are examined in the framework of the Darwin-Hamilton approach using a set of two independent parameters: the characteristic thickness of mosaic blocks and their average angular misorientation...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182942/application-of-differential-resonant-high-energy-x-ray-diffraction-to-three-dimensional-structure-studies-of-nanosized-materials-a-case-study-of-pt-pd-nanoalloy-catalysts
#8
Valeri Petkov, Sarvjit Shastri, Jong Woo Kim, Shiyao Shan, Jin Luo, Jinfang Wu, Chuan Jian Zhong
Atoms in many of the increasingly complex nanosized materials of interest to science and technology do not necessarily occupy the vertices of Bravais lattices. The atomic scale structure of such materials is difficult to determine by traditional X-ray diffraction and so their functional properties remain difficult to optimize by rational design. Here, the three-dimensional structure of Ptx Pd100-x nanoalloy particles is determined, where x = 0, 14, 36, 47, 64 and 100, by a non-traditional technique involving differential resonant high-energy X-ray diffraction experiments conducted at the K edge of Pt and Pd...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182941/specular-reflection-intensity-modulated-by-grazing-incidence-diffraction-in-a-wide-angular-range
#9
K V Nikolaev, I A Makhotkin, S N Yakunin, R W E van de Kruijs, M A Chuev, F Bijkerk
Grazing-incidence X-ray diffraction (GID) is a well known technique for the characterization of crystal surfaces. A theoretical study has been performed of the sensitivity of GID to the structure of a crystal surface and distorted nanometre-thin surface layers. To simulate GID from crystals that have a complex subsurface structure, a matrix formalism of the dynamical diffraction theory has been applied. It has been found that the azimuthal rocking curves of a crystal that has a distorted subsurface, measured over a wide angular range, show asymmetric thickness oscillations with two distinguishable sets of frequencies: one corresponding to the diffraction in the single-crystal subsurface layer and the second corresponding to the diffraction in the single-crystal substrate...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182940/the-phase-problem-for-two-dimensional-crystals-ii-simulations
#10
Romain D Arnal, Yun Zhao, Alok K Mitra, John C H Spence, Rick P Millane
Phasing of diffraction data from two-dimensional crystals using only minimal molecular envelope information is investigated by simulation. Two-dimensional crystals are an attractive target for studying membrane proteins using X-ray free-electron lasers, particularly for dynamic studies at room temperature. Simulations using an iterative projection algorithm show that phasing is feasible with fairly minimal molecular envelope information, supporting recent uniqueness results for this problem [Arnal & Millane (2017)...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182939/fast-analytical-evaluation-of-intermolecular-electrostatic-interaction-energies-using-the-pseudoatom-representation-of-the-electron-density-i-the-l%C3%A3-wdin-%C3%AE-function-method
#11
Daniel Nguyen, Zbigniew Kisiel, Anatoliy Volkov
The previously reported [Volkov et al. (2004). Chem. Phys. Lett. 391, 170-175] exact potential and multipole moment (EP/MM) method for evaluation of intermolecular electrostatic interaction energies using the nuclei-centered pseudoatom representation of electron densities is significantly improved in terms of both speed and accuracy by replacing the numerical quadrature integration of the exact potential with a fully analytical technique. The resulting approach, incorporated in the XDPROP module of the software package XD, has been tested on several molecular systems ranging in size from water-water to dodecapeptide-dodecapeptide dimers using electron densities constructed via the University at Buffalo Aspherical Atom Databank...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182938/variation-of-second-order-piezoelectric-coefficients-with-respect-to-a-finite-strain-measure
#12
Grzegorz Jurczak
In this article the consequence of a change of finite strain measure is theoretically considered for nonlinear piezoelectric crystals. Analytical predictions show that second-order piezoelectric coefficients are finite strain measure dependent. Therefore, the use of any finite strain measure in constitutive modelling of piezoelectric materials requires an adequate choice of higher-order piezoelectric coefficients. This allows one to avoid unwanted corrections to the elastic and electric fields in the case of nonlinear modelling of piezoelectric materials, e...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182937/incorporating-particle-symmetry-into-orientation-determination-in-single-particle-imaging
#13
Miklós Tegze, Gábor Bortel
In coherent-diffraction-imaging experiments X-ray diffraction patterns of identical particles are recorded. The particles are injected into the X-ray free-electron laser (XFEL) beam in random orientations. If the particle has symmetry, finding the orientation of a pattern can be ambiguous. With some modifications, the correlation-maximization method can find the relative orientations of the diffraction patterns for the case of symmetric particles as well. After convergence, the correlation maps show the symmetry of the particle and can be used to determine the symmetry elements and their orientations...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182936/explicit-construction-of-the-voronoi-and-delaunay-cells-of-w-a-n-and-w-d-n-lattices-and-their-facets
#14
Mehmet Koca, Nazife Ozdes Koca, Abeer Al-Siyabi, Ramazan Koc
Voronoi and Delaunay (Delone) cells of the root and weight lattices of the Coxeter-Weyl groups W(An ) and W(Dn ) are constructed. The face-centred cubic (f.c.c.) and body-centred cubic (b.c.c.) lattices are obtained in this context. Basic definitions are introduced such as parallelotope, fundamental simplex, contact polytope, root polytope, Voronoi cell, Delone cell, n-simplex, n-octahedron (cross polytope), n-cube and n-hemicube and their volumes are calculated. The Voronoi cell of the root lattice is constructed as the dual of the root polytope which turns out to be the union of Delone cells...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182935/estimating-the-structure-factors-in-x-ray-diffraction
#15
Paul F Fewster
This article takes the concepts of the `new diffraction theory' [Fewster (2014). Acta Cryst. A70, 257-282] and examines the implications for the interpretation of experimental results and the estimation of structure factors. Further experimental evidence is included to justify the conclusions in the theory, showing that the residual intensity at twice the Bragg angle is a diffraction effect and not associated with the crystal shape. This `enhancement' effect is independent of whether kinematical or dynamical theories are applied and can lead to a clearer understanding of how the dynamical effects are suppressed in imperfect crystals...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182934/structure-evolution-of-h-c-p-c-c-p-metal-oxide-interfaces-in-solid-state-reactions
#16
C Li, G Habler, T Griffiths, A Rečnik, P Jeřábek, L C Götze, C Mangler, T J Pennycook, J Meyer, R Abart
The structure of crystalline interfaces plays an important role in solid-state reactions. The Al2 O3 /MgAl2 O4 /MgO system provides an ideal model system for investigating the mechanisms underlying the migration of interfaces during interface reaction. MgAl2 O4 layers have been grown between Al2 O3 and MgO, and the atomic structure of Al2 O3 /MgAl2 O4 interfaces at different growth stages was characterized using aberration-corrected scanning transmission electron microscopy. The oxygen sublattice transforms from hexagonal close-packed (h...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182933/response-to-fraser-wark-s-comments-on-a-new-theory-for-x-ray-diffraction
#17
Paul F Fewster
The criticisms of my theory, as given by Fraser & Wark [(2018), Acta Cryst. A74, 447-456], are built on a misunderstanding of the concept and the methodology I have used. The assumption they have made rules out my description from which they conclude that my theory is proved to be wrong. They assume that I have misunderstood the diffraction associated with the shape of a crystal and my calculation is only relevant to a parallelepiped and even that I have got wrong. It only appears wrong to Fraser & Wark because the effect I predict has nothing to do with the crystal shape...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182932/comments-on-a-new-theory-for-x-ray-diffraction
#18
Jack T Fraser, Justin S Wark
In an article entitled A new theory for X-ray diffraction [Fewster (2014). Acta Cryst. A70, 257-282], hereafter referred to as NTXRD, it is claimed that when X-rays are scattered from a small crystallite, whatever its size and shape, the diffraction pattern will contain enhanced scattering at angles of exactly 2θB , whatever the orientation of the crystal. It is claimed that in this way scattering from a powder, with randomly oriented crystals, gives rise to Bragg scattering even if the Bragg condition is never satisfied by an individual crystallite...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182931/measuring-stress-induced-martensite-microstructures-using-far-field-high-energy-diffraction-microscopy
#19
Ashley Nicole Bucsek, Darren Dale, Jun Young Peter Ko, Yuriy Chumlyakov, Aaron Paul Stebner
Modern X-ray diffraction techniques are now allowing researchers to collect long-desired experimental verification data sets that are in situ, three-dimensional, on the same length scales as critical microstructures, and using bulk samples. These techniques need to be adapted for advanced material systems that undergo combinations of phase transformation, twinning and plasticity. One particular challenge addressed in this article is direct analysis of martensite phases in far-field high-energy diffraction microscopy experiments...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/30182930/an-algebraic-approach-to-cooperative-rotations-in-networks-of-interconnected-rigid-units
#20
Branton Campbell, Christopher J Howard, Tyler B Averett, Thomas A Whittle, Siegbert Schmid, Shae Machlus, Christopher Yost, Harold T Stokes
Crystalline solids consisting of three-dimensional networks of interconnected rigid units are ubiquitous amongst functional materials. In many cases, application-critical properties are sensitive to rigid-unit rotations at low temperature, high pressure or specific stoichiometry. The shared atoms that connect rigid units impose severe constraints on any rotational degrees of freedom, which must then be cooperative throughout the entire network. Successful efforts to identify cooperative-rotational rigid-unit modes (RUMs) in crystals have employed split-atom harmonic potentials, exhaustive testing of the rotational symmetry modes allowed by group representation theory, and even simple geometric considerations...
September 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
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