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Acta Crystallographica. Section A, Foundations and Advances

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https://www.readbyqxmd.com/read/27809210/prices-of-iucr-journals
#1
M H Dacombe
No abstract text is available yet for this article.
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809209/an-alternative-to-the-goodness-of-fit
#2
Julian Henn
An alternative measure to the goodness of fit (GoF) is developed and applied to experimental data. The alternative goodness of fit squared (aGoFs) demonstrates that the GoF regularly fails to provide evidence for the presence of systematic errors, because certain requirements are not met. These requirements are briefly discussed. It is shown that in many experimental data sets a correlation between the squared residuals and the variance of observed intensities exists. These correlations corrupt the GoF and lead to artificially reduced values in the GoF and in the numerical value of the wR(F(2))...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809208/quantitative-theory-of-diffraction-by-ordered-coaxial-nanotubes-reciprocal-lattice-and-diffraction-pattern-indexing
#3
Zufar Khalitov, Azat Khadiev, Diana Valeeva, Dmitry Pashin
A quantitative theory of diffraction by right- and left-handed coaxial nanotubes with an ordered structure is developed. Their reciprocal lattices, including pseudo-orthogonal nodes, are studied. The explicit formulas that govern relations between direct and reciprocal lattices of a nanotube are achieved and a simple descriptive tool for diffraction pattern indexing is proposed.
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809207/the-complete-classification-of-five-dimensional-dirichlet-voronoi-polyhedra-of-translational-lattices
#4
Mathieu Dutour Sikirić, Alexey Garber, Achill Schürmann, Clara Waldmann
This paper reports on the full classification of Dirichlet-Voronoi polyhedra and Delaunay subdivisions of five-dimensional translational lattices. A complete list is obtained of 110 244 affine types (L-types) of Delaunay subdivisions and it turns out that they are all combinatorially inequivalent, giving the same number of combinatorial types of Dirichlet-Voronoi polyhedra. Using a refinement of corresponding secondary cones, 181 394 contraction types are obtained. The paper gives details of the computer-assisted enumeration, which was verified by three independent implementations and a topological mass formula check...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809206/residue-based-scattering-factors
#5
Hongliang Xu
A glob is defined as a group of atoms in the crystal which can be chosen in various ways. Globs themselves can be used as scattering elements in the theory of structure determination, just as atoms are used at present. In this paper, amino-acid residues are chosen to form globs and empirical formulas for residue-based scattering factors have been developed.
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809205/direct-observation-of-incommensurate-structure-in-mo3si
#6
Ahmet Gulec, Xiaoxiang Yu, Matthew Taylor, John H Perepezko, Laurence Marks
Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809204/thermal-evolution-of-mg-al-and-ni-al-layered-double-hydroxides-the-structure-of-the-dehydrated-phase
#7
Svetlana Cherepanova, Natalya Leont'eva, Vladimir Drozdov, Vladimir Doronin
Simulation of X-ray diffraction patterns on the basis of the models of one-dimensional disordered crystals was used to investigate the structure of the dehydrated phase produced by dehydration of Mg-Al and Ni-Al layered double hydroxides at a temperature of ∼473-498 K. It was found that the removal of water molecules transforms the initial structure, which is a mixture of 3R1 and 2H1 polytypes, into a structure that comprises preferentially fragments of 3R2 and 1H polytypes and has some turbostratic disorder...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809203/towards-atomistic-understanding-of-polymorphism-in-the-solvothermal-synthesis-of-zro2-nanoparticles
#8
Ann Christin Dippel, Kirsten M Ø Jensen, Christoffer Tyrsted, Martin Bremholm, Espen D Bøjesen, Dipankar Saha, Steinar Birgisson, Mogens Christensen, Simon J L Billinge, Bo B Iversen
Varying atomic short-range order is correlated with the ratio of the monoclinic (m) to tetragonal (t) phase in ZrO2 nanoparticle formation by solvothermal methods. Reactions from Zr oxynitrate in supercritical methanol and Zr acetate in water (hydrothermal route) were studied in situ by X-ray total scattering. Irrespective of the Zr source and solvent, the structure of the precursor in solution consists of edge-shared tetramer chains. Upon heating, the nearest-neighbor Zr-O and Zr-Zr distances shorten initially while the medium-range connectivity is broken...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809202/a-total-scattering-debye-function-analysis-study-of-faulted-pt-nanocrystals-embedded-in-a-porous-matrix
#9
Federica Bertolotti, Daniele Moscheni, Andrea Migliori, Stefano Zacchini, Antonio Cervellino, Antonietta Guagliardi, Norberto Masciocchi
Faulted face-centred cubic platinum nanocrystals, grown within a nanoporous silica matrix, have been extensively characterized by the Debye function analysis method applied to wide-angle synchrotron X-ray total scattering data. A method for building databases of sampled interatomic distances of weakly faulted materials is proposed, maintaining statistical significance and allowing complete populations of differently sized and shaped nanocrystals to be used within the DEBUSSY approach. This study suggests that anisotropic Pt nanoclusters are formed in the presence of a shape-directing (templating) agent, and tentatively describes the effects of post-synthetic temperature treatments on fault probability, size, shape and dispersion of the nanocrystal populations...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809201/observing-structural-reorientations-at-solvent-nanoparticle-interfaces-by-x-ray-diffraction-putting-water-in-the-spotlight
#10
Mirijam Zobel
Nanoparticles are attractive in a wide range of research genres due to their size-dependent properties, which can be in contrast to those of micrometre-sized colloids or bulk materials. This may be attributed, in part, to their large surface-to-volume ratio and quantum confinement effects. There is a growing awareness that stress and strain at the particle surface contribute to their behaviour and this has been included in the structural models of nanoparticles for some time. One significant oversight in this field, however, has been the fact that the particle surface affects its surroundings in an equally important manner...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809200/100-years-of-debye-s-scattering-equation
#11
Luca Gelisio, Paolo Scardi
Debye's scattering equation (DSE) has spanned a century of scientific development, from the dawn of quantum mechanics and the investigation of the structure of atoms and molecules to the era of nanotechnology, paving the way to total scattering methods. The formulation offers the most accurate representation of the intensity scattered by randomly oriented atomic aggregates, constructed by superimposing the signal from each atomic distance in the molecule. The present paper reviews some of the milestone applications, from the interpretation of the intensity curves from gases and vapours, to aggregates of increasing size and more extended order...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809199/peter-j-w-debye-a-whole-life-devoted-to-science
#12
Giuseppe Dalba
In 1915 P. Debye, one of the most prominent scientists in the field of condensed-matter physics and physical chemistry, published an X-ray scattering equation for randomly oriented scattering sites. This formula, since then used for describing the structure of powders, liquids and gases, has become a model for material analysis at the nanoscale. This paper re-examines briefly Debye's works on the origin and evolution of the scattering equation and its first uses. The career of the great scientist and some of his other numerous and diverse contributions to science are also reviewed...
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27809198/celebrating-100-years-of-the-debye-scattering-equation
#13
Paolo Scardi, Simon J L Billinge, Reinhard Neder, Antonio Cervellino
One hundred years of the Debye scattering equation are celebrated with a series of articles arising from the DSE 2015 conference.
November 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580208/mathematical-stereochemistry-by-shinsaku-fujita-de-gruyter-2015-pp-xviii-437-price-eur-129-95-usd-182-00-gbp-97-99-isbn-978-3-11-036669-3
#14
Gregory Chirikjian
No abstract text is available yet for this article.
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580207/vojtech-jaroslav-kopsk%C3%A3-1936-2016
#15
D B Litvin, V Janovec
No abstract text is available yet for this article.
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580206/how-to-name-and-order-convex-polyhedra
#16
Yury L Voytekhovsky
In this paper a method is suggested for naming any convex polyhedron by a numerical code arising from the adjacency matrix of its edge graph. A polyhedron is uniquely fixed by its name and can be built using it. Classes of convex n-acra (i.e. n-vertex polyhedra) are strictly ordered by their names.
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580205/a-topological-coordinate-system-for-the-diamond-cubic-grid
#17
Lidija Čomić, Benedek Nagy
Topological coordinate systems are used to address all cells of abstract cell complexes. In this paper, a topological coordinate system for cells in the diamond cubic grid is presented and some of its properties are detailed. Four dependent coordinates are used to address the voxels (triakis truncated tetrahedra), their faces (hexagons and triangles), their edges and the points at their corners. Boundary and co-boundary relations, as well as adjacency relations between the cells, can easily be captured by the coordinate values...
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580204/indirect-fourier-transform-in-the-context-of-statistical-inference
#18
Michael Muthig, Sylvain Prévost, Reinhold Orglmeister, Michael Gradzielski
Inferring structural information from the intensity of a small-angle scattering (SAS) experiment is an ill-posed inverse problem. Thus, the determination of a solution is in general non-trivial. In this work, the indirect Fourier transform (IFT), which determines the pair distance distribution function from the intensity and hence yields structural information, is discussed within two different statistical inference approaches, namely a frequentist one and a Bayesian one, in order to determine a solution objectively From the frequentist approach the cross-validation method is obtained as a good practical objective function for selecting an IFT solution...
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580203/on-representing-rotations-by-rodrigues-parameters-in-non-orthonormal-reference-systems
#19
A Morawiec
A Rodrigues vector is a triplet of real numbers used for parameterizing rotations or orientations in three-dimensional space. Because of its properties (e.g. simplicity of fundamental regions for misorientations) this parameterization is frequently applied in analysis of orientation maps of polycrystalline materials. By conventional definition, the Rodrigues parameters are specified in orthonormal coordinate systems, whereas the bases of crystal lattices are generally non-orthogonal. Therefore, the definition of Rodrigues parameters is extended so they can be directly linked to non-Cartesian bases of a crystal...
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
https://www.readbyqxmd.com/read/27580202/improving-the-efficiency-of-molecular-replacement-by-utilizing-a-new-iterative-transform-phasing-algorithm
#20
Hongxing He, Hengrui Fang, Mitchell D Miller, George N Phillips, Wu Pei Su
An iterative transform method proposed previously for direct phasing of high-solvent-content protein crystals is employed for enhancing the molecular-replacement (MR) algorithm in protein crystallography. Target structures that are resistant to conventional MR due to insufficient similarity between the template and target structures might be tractable with this modified phasing method. Trial calculations involving three different structures are described to test and illustrate the methodology. The relationship of the approach to PHENIX Phaser-MR and MR-Rosetta is discussed...
September 1, 2016: Acta Crystallographica. Section A, Foundations and Advances
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