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Single Data Set (single + data_set)
Selected AbstractsA differential thermal expansion approach to crystal structure determination from powder diffraction dataJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008P. Fernandes Differential thermal expansion over the range 90,210,K has been applied successfully to determine the crystal structure of chlorothiazide from synchrotron powder diffraction data using direct methods. Key to the success of the approach is the use of a multi-data-set Pawley refinement to extract a set of reflection intensities that is more `single-crystal-like' than those extracted from a single data set. The improvement in reflection intensity estimates is quantified by comparison with reference single-crystal intensities. [source] The structure of orange HgI2.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002The metastable orange crystals of HgI comprise three different crystal structures, all of which are built from corner-linked HgI supertetrahedra. Two of them are end members with the maximum degree of order (MDO) of a polytypic layer structure; the third shows a three-dimensional linkage. This paper presents the determination from X-ray diffraction data of the tetragonal polytypic structures and their stacking disorder. Diffraction patterns show sharp Bragg reflections and rods of diffuse intensity with pronounced maxima. In a first step, the diffuse intensity was neglected and all maxima were treated as Bragg reflections. The crystal was supposed to be a conglomerate of the two MDO structures diffracting independently, and their parameters and volume ratio were refined against the single data set. The geometries and anisotropic displacement parameters of the layers in the two structures are shown to be nearly identical. Layer contacts in the two stacking modes are identical. The structures are fractal complications of the stable red form of HgI. In a second step, the stacking disorder has been quantitatively analyzed with a Markov chain model. Two probabilities describing next-nearest-layer interactions were visually adjusted to observed intensity profiles extracted from image-plate detector data. Results consistently show that the crystal comprises nearly equal volumes of MDO structures with an average domain thickness of about 5 layers or 30,Å. [source] Stepped frequency ground-penetrating radar survey with a multi-element array antenna: Results from field application on archaeological sites,ARCHAEOLOGICAL PROSPECTION, Issue 3 2010Neil Linford Abstract A series of trial geophysical surveys were conducted with a 3d-Radar GeoScope ground-penetrating radar (GPR) utilizing a multi-element array antenna. This system offers the potential for rapid data acquisition at very high sample densities over a wide frequency bandwidth. Field tests, conducted over the Roman town at Silchester, Hampshire, UK, suggested that a revised antenna configuration was necessary to obtain optimum results from the system, which was then successfully deployed in the collection of over 5,ha of survey data at a sample density of 0.075,m,×,0.075,m. The wide area survey produced a wealth of archaeological detail to complement and expand upon the extensive record of excavation, aerial photography and other geophysical results. Initial trial surveys were conducted with a range of antenna arrays (B2431, B1831 and B1823) incorporating different sized elements to fully exploit the wide potential bandwidth of the system. However, the differing response of elements proved difficult to combine within a single data set and a marked increase in quality was obtained with the use of a prototype V1821 antenna array of identical sized elements. Some concerns remain regarding both the suitability of air-launched antenna arrays to certain site conditions, as one early survey visit to Silchester produced very poor results that remain unexplained, and the maximum penetration depth compared with an impulse GPR using ground-coupled antenna. © 2010 Crown copyright. [source] Away from the edge II: in-house Se-SAS phasing with chromium radiationACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2005Hao Xu Recently, the demands of high-throughput macromolecular crystallography have driven continuous improvements in phasing methods, data-collection protocols and many other technologies. Single-wavelength anomalous scattering (SAS) phasing with chromium X-ray radiation opens a new possibility for phasing a protein with data collected in-house and has led to several successful examples of de novo structure solution using only weak anomalous scatterers such as sulfur. To further reduce data-collection time and make SAS phasing more robust, it is natural to combine selenomethionine-derivatized protein (SeMet protein) with Cr,K, radiation to take advantage of the larger anomalous scattering signal from selenium ( = 2.28 e,) compared with sulfur ( = 1.14 e,). As reported herein, the crystal structure of a putative chorismate mutase from Clostridium thermocellum was determined using Se-SAS with Cr,K, radiation. Each protein molecule contains eight selenomethionine residues in 148 amino-acid residues, providing a calculated Bijvoet ratio of about 3.5% at the Cr,K, wavelength. A single data set to 2.2,Å resolution with approximately ninefold redundancy was collected using an imaging-plate detector coupled with a Cr source. Structure solution, refinement and deposition to the Protein Data Bank were performed within 9,h of the availability of the scaled diffraction data. The procedure used here is applicable to many other proteins and promises to become a routine pathway for in-house high-throughput crystallography. [source] | ||||||||||