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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/29269601/an-introduction-to-clifford-algebras-and-spinors-by-jayme-vaz-jr-and-rold%C3%A3-o-da-rocha-jr-oxford-university-press-2016-pp-256-price-gbp-55-00-hardback-isbn-9780198782926
#1
Oussama Hijazi
No abstract text is available yet for this article.
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269600/group-theory-of-chemical-elements-structure-and-properties-of-elements-and-compounds-by-abram-i-fet-de-gruyter-2016-pp-viii-185-price-eur-119-95-usd-168-00-gbp-108-99-hardcover-isbn-978-3-11-047518-0
#2
https://www.readbyqxmd.com/read/29269599/multislice-imaging-of-integrated-circuits-by-precession-x-ray-ptychography
#3
Kei Shimomura, Makoto Hirose, Yukio Takahashi
A method for nondestructively visualizing multisection nanostructures of integrated circuits by X-ray ptychography with a multislice approach is proposed. In this study, tilt-series ptychographic diffraction data sets of a two-layered circuit with a ∼1.4 µm gap at nine incident angles are collected in a wide Q range and then artifact-reduced phase images of each layer are successfully reconstructed at ∼10 nm resolution. The present method has great potential for the three-dimensional observation of flat specimens with thickness on the order of 100 µm, such as three-dimensional stacked integrated circuits based on through-silicon vias, without laborious sample preparation...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269598/the-limit-of-application-of-the-scherrer-equation
#4
M A R Miranda, J M Sasaki
The Scherrer equation is a widely used tool to obtain crystallite size from polycrystalline samples. Its limit of applicability has been determined recently, using computer simulations, for a few structures and it was proposed that it is directly dependent on the linear absorption coefficient (μ0) and Bragg angle (θB). In this work, a systematic study of the Scherrer limit is presented, where it is shown that it is equal to approximately 11.9% of the extinction length. It is also shown that absorption imposes a maximum value on it and that this maximum is directly proportional to sin θB/μ0...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269597/a-one-step-mechanism-for-new-twinning-modes-in-magnesium-and-titanium-alloys-modelled-by-the-obliquity-correction-of-a-58%C3%A2-a-2b-prototype-stretch-twin
#5
Cyril Cayron
The \{ 11{\overline 2}2\} and \{ 11{\overline 2}6\} twinning modes were recently discovered by Ostapovets et al. [Philos. Mag. (2017), 97, 1088-1101] and interpreted as \{ {10{\overline 1}2} \}-\{ {10{\overline 1}2} \} double twins formed by the simultaneous action of two twinning shears. Another interpretation is proposed here in which the two conjugate twinning modes result from a one-step mechanism based on a (58°, a + 2b) prototype stretch twin and differ from each other only by their obliquity correction...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269596/improving-the-convergence-rate-of-a-hybrid-input-output-phasing-algorithm-by-varying-the-reflection-data-weight
#6
Hongxing He, Wu Pei Su
In an iterative projection algorithm proposed for ab initio phasing, the error metrics typically exhibit little improvement until a sharp decrease takes place as the iteration converges to the correct high-resolution structure. Related to that is the small convergence probability for certain structures. As a remedy, a variable weighting scheme on the diffraction data is proposed. It focuses on phasing low- and medium-resolution data first. The weighting shifts to incorporate more high-resolution reflections when the iteration proceeds...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269595/construction-of-weavings-in-the-plane
#7
Eden Delight Miro, Aliw Iw Zambrano, Agnes Garciano
This work develops, in graph-theoretic terms, a methodology for systematically constructing weavings of overlapping nets derived from 2-colorings of the plane. From a 2-coloring, two disjoint simple, connected graphs called nets are constructed. The union of these nets forms an overlapping net, and a weaving map is defined on the intersection points of the overlapping net to form a weaving. Furthermore, a procedure is given for the construction of mixed overlapping nets and for deriving weavings from them.
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269594/small-angle-x-ray-scattering-tensor-tomography-model-of-the-three-dimensional-reciprocal-space-map-reconstruction-algorithm-and-angular-sampling-requirements
#8
Marianne Liebi, Marios Georgiadis, Joachim Kohlbrecher, Mirko Holler, Jörg Raabe, Ivan Usov, Andreas Menzel, Philipp Schneider, Oliver Bunk, Manuel Guizar-Sicairos
Small-angle X-ray scattering tensor tomography, which allows reconstruction of the local three-dimensional reciprocal-space map within a three-dimensional sample as introduced by Liebi et al. [Nature (2015), 527, 349-352], is described in more detail with regard to the mathematical framework and the optimization algorithm. For the case of trabecular bone samples from vertebrae it is shown that the model of the three-dimensional reciprocal-space map using spherical harmonics can adequately describe the measured data...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29269593/quasicrystals-what-do-we-know-what-do-we-want-to-know-what-can-we-know
#9
Walter Steurer
More than 35 years and 11 000 publications after the discovery of quasicrystals by Dan Shechtman, quite a bit is known about their occurrence, formation, stability, structures and physical properties. It has also been discovered that quasiperiodic self-assembly is not restricted to intermetallics, but can take place in systems on the meso- and macroscales. However, there are some blank areas, even in the centre of the big picture. For instance, it has still not been fully clarified whether quasicrystals are just entropy-stabilized high-temperature phases or whether they can be thermodynamically stable at 0 K as well...
January 1, 2018: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/29072203/prices-of-iucr-journals
#10
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
#11
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
#12
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
#13
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
#14
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
#15
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
#16
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
#17
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
#18
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
#19
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
#20
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
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