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  • International Union of Crystallography (IUCr)
  • 2010-2014  (32)
  • 1980-1984  (5,963)
  • 1955-1959  (1,463)
  • 1950-1954  (1,308)
  • 1925-1929
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  • 1
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    Structural insight into activity enhancement and inhibition of H64A carbonic anhydrase II by imidazoles (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: Human carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the hydration and dehydration of CO2 and HCO3−, respectively. The reaction follows a ping-pong mechanism, in which the rate-limiting step is the transfer of a proton from the zinc-bound solvent (OH−/H2O) in/out of the active site via His64, which is widely believed to be the proton-shuttling residue. The decreased catalytic activity (∼20-fold lower with respect to the wild type) of a variant of CA II in which His64 is replaced with Ala (H64A CA II) can be enhanced by exogenous proton donors/acceptors, usually derivatives of imidazoles and pyridines, to almost the wild-type level. X-ray crystal structures of H64A CA II in complex with four imidazole derivatives (imidazole, 1-methylimidazole, 2-methylimidazole and 4-methylimidazole) have been determined and reveal multiple binding sites. Two of these imidazole binding sites have been identified that mimic the positions of the `in' and `out' rotamers of His64 in wild-type CA II, while another directly inhibits catalysis by displacing the zinc-bound solvent. The data presented here not only corroborate the importance of the imidazole side chain of His64 in proton transfer during CA catalysis, but also provide a complete structural understanding of the mechanism by which imidazoles enhance (and inhibit when used at higher concentrations) the activity of H64A CA II.
    Keywords: human carbonic anhydraseH64Aactivity enhancementrescueactivationimidazole
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 2
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    The structure of a purple acid phosphatase involved in plant growth and pathogen defence exhibits a novel immunoglobulin-like fold (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: Phosphatases function in the production, transport and recycling of inorganic phosphorus, which is crucial for cellular metabolism and bioenergetics, as well as in bacterial killing, since they are able to generate reactive oxygen species via Fenton chemistry. Diphosphonucleotide phosphatase/phosphodiesterase (PPD1), a glycoprotein plant purple acid phosphatase (PAP) from yellow lupin seeds, contains a bimetallic Fe–Mn catalytic site which is most active at acidic pH. Unlike other plant PAPs, PPD1 cleaves the pyrophosphate bond in diphosphonucleotides and the phosphodiester bond in various phosphodiesters. The homohexameric organization of PPD1, as revealed by a 1.65 Å resolution crystal structure and confirmed by solution X-ray scattering, is unique among plant PAPs, for which only homodimers have previously been reported. A phosphate anion is bound in a bidentate fashion at the active site, bridging the Fe and Mn atoms in a binding mode similar to that previously reported for sweet potato PAP, which suggests that common features occur in their catalytic mechanisms. The N-terminal domain of PPD1 has an unexpected and unique fibronectin type III-like fold that is absent in other plant PAPs. Here, the in vitro DNA-cleavage activity of PPD1 is demonstrated and it is proposed that the fibronectin III-like domain, which `overhangs' the active site, is involved in DNA selectivity, binding and activation. The degradation of DNA by PPD1 implies a role for PPD1 in plant growth and repair and in pathogen defence.
    Keywords: purple acid phosphatasediphosphonucleotide phosphatasephosphodiesterasePPD1bimetallic Fe–Mnfibronectin type III domaincrystal structureSAXS
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 3
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    Acemetacin cocrystals and salts: structure solution from powder X-ray data and form selection of the piperazine salt (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: Acemetacin (ACM) is a non-steroidal anti-inflammatory drug (NSAID), which causes reduced gastric damage compared with indomethacin. However, acemetacin has a tendency to form a less soluble hydrate in the aqueous medium. We noted difficulties in the preparation of cocrystals and salts of acemetacin by mechanochemical methods, because this drug tends to form a hydrate during any kind of solution-based processing. With the objective to discover a solid form of acemetacin that is stable in the aqueous medium, binary adducts were prepared by the melt method to avoid hydration. The coformers/salt formers reported are pyridine carboxamides [nicotinamide (NAM), isonicotinamide (INA), and picolinamide (PAM)], caprolactam (CPR), p-aminobenzoic acid (PABA), and piperazine (PPZ). The structures of an ACM–INA cocrystal and a binary adduct ACM–PABA were solved using single-crystal X-ray diffraction. Other ACM cocrystals, ACM–PAM and ACM–CPR, and the piperazine salt ACM–PPZ were solved from high-resolution powder X-ray diffraction data. The ACM–INA cocrystal is sustained by the acid...pyridine heterosynthon and N—H...O catemer hydrogen bonds involving the amide group. The acid...amide heterosynthon is present in the ACM–PAM cocrystal, while ACM–CPR contains carboxamide dimers of caprolactam along with acid–carbonyl (ACM) hydrogen bonds. The cocrystals ACM–INA, ACM–PAM and ACM–CPR are three-dimensional isostructural. The carboxyl...carboxyl synthon in ACM–PABA posed difficulty in assigning the position of the H atom, which may indicate proton disorder. In terms of stability, the salts were found to be relatively stable in pH 7 buffer medium over 24 h, but the cocrystals dissociated to give ACM hydrate during the same time period. The ACM–PPZ salt and ACM–nicotinamide cocrystal dissolve five times faster than the stable hydrate form, whereas the ACM–PABA adduct has 2.5 times faster dissolution rate. The pharmaceutically acceptable piperazine salt of acemetacin exhibits superior stability, faster dissolution rate and is able to overcome the hydration tendency of the reference drug.
    Keywords: cocrystalhydratemelt crystallizationpiperazinepowder X-ray diffractionstructure determination from powder data (SDPD)
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 4
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    Serial crystallography on in vivo grown microcrystals using synchrotron radiation (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: Crystal structure determinations of biological macromolecules are limited by the availability of sufficiently sized crystals and by the fact that crystal quality deteriorates during data collection owing to radiation damage. Exploiting a micrometre-sized X-ray beam, high-precision diffractometry and shutterless data acquisition with a pixel-array detector, a strategy for collecting data from many micrometre-sized crystals presented to an X-ray beam in a vitrified suspension is demonstrated. By combining diffraction data from 80 Trypanosoma brucei procathepsin B crystals with an average volume of 9 µm3, a complete data set to 3.0 Å resolution has been assembled. The data allowed the refinement of a structural model that is consistent with that previously obtained using free-electron laser radiation, providing mutual validation. Further improvements of the serial synchrotron crystallography technique and its combination with serial femtosecond crystallography are discussed that may allow the determination of high-resolution structures of micrometre-sized crystals.
    Keywords: protein microcrystallographyserial crystallographyin vivo grown microcrystals
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 5
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    Femtosecond X-ray diffraction from two-dimensional protein crystals (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: X-ray diffraction patterns from two-dimensional (2-D) protein crystals obtained using femtosecond X-ray pulses from an X-ray free-electron laser (XFEL) are presented. To date, it has not been possible to acquire transmission X-ray diffraction patterns from individual 2-D protein crystals due to radiation damage. However, the intense and ultrafast pulses generated by an XFEL permit a new method of collecting diffraction data before the sample is destroyed. Utilizing a diffract-before-destroy approach at the Linac Coherent Light Source, Bragg diffraction was acquired to better than 8.5 Å resolution for two different 2-D protein crystal samples each less than 10 nm thick and maintained at room temperature. These proof-of-principle results show promise for structural analysis of both soluble and membrane proteins arranged as 2-D crystals without requiring cryogenic conditions or the formation of three-dimensional crystals.
    Keywords: two-dimensional protein crystalfemtosecond crystallographysingle layer X-ray diffractionmembrane protein
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 6
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    New perspectives in biological crystallography (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Keywords: biological crystallographyeditorialIUCrJ
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 7
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    Serial crystallography using synchrotron radiation (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Keywords: protein microcrystallographyserial crystallographyin vivo-grown microcrystals
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 8
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    Anharmonicity and isomorphic phase transition: a multi-temperature X-ray single-crystal and powder diffraction study of 1-(2′-aminophenyl)-2-methyl-4-nitroimidazole (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: The harmonic model of atomic nuclear motions is usually enough for multipole modelling of high-resolution X-ray diffraction data; however, in some molecular crystals, such as 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole [Paul, Kubicki, Jelsch et al. (2011). Acta Cryst. B67, 365–378], it may not be sufficient for a correct description of the charge-density distribution. Multipole refinement using harmonic atom vibrations does not lead to the best electron density model in this case and the so-called `shashlik-like' pattern of positive and negative residual electron density peaks is observed in the vicinity of some atoms. This slight disorder, which cannot be modelled by split atoms, was solved using third-order anharmonic nuclear motion (ANM) parameters. Multipole refinement of the experimental high-resolution X-ray diffraction data of 1-(2′-aminophenyl)-2-methyl-4-nitro-1H-imidazole at three different temperatures (10, 35 and 70 K) and a series of powder diffraction experiments (20 ≤ T ≤ 300 K) were performed to relate this anharmonicity observed for several light atoms (N atoms of amino and nitro groups, and O atoms of nitro groups) to an isomorphic phase transition reflected by a change in the b cell parameter around 65 K. The observed disorder may result from the coexistence of domains of two phases over a large temperature range, as shown by low-temperature powder diffraction.
    Keywords: anharmonicityisomorphic phase transitionexperimental charge densityX-ray closed-circuit helium cryostatHansen–Coppens modelmultiple-temperature powder diffraction
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 9
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    The enrichment ratio of atomic contacts in crystals, an indicator derived from the Hirshfeld surface analysis (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-04-08
    Description: The partitioning of space with Hirshfeld surfaces enables the analysis of fingerprint molecular interactions in crystalline environments. This study uses the decomposition of the crystal contact surface between pairs of interacting chemical species to derive an enrichment ratio. This quantity enables the analysis of the propensity of chemical species to form intermolecular interactions with themselves and other species. The enrichment ratio is obtained by comparing the actual contacts in the crystal with those computed as if all types of contacts had the same probability to form. The enrichments and contact tendencies were analyzed in several families of compounds, based on chemical composition and aromatic character. As expected, the polar contacts of the type H...N, H...O and H...S, which are generally hydrogen bonds, show enrichment values larger than unity. O...O and N...N contacts are impoverished while H...H interactions display enrichment ratios which are generally close to unity or slightly lower. In aromatic compounds, C...C contacts can display large enrichment ratios due to extensive π...π stacking in the crystal packings of heterocyclic compounds. C...C contacts are, however, less enriched in pure (C,H) hydrocarbons as π...π stacking is not so favourable from the electrostatic point of view compared with heterocycles. C...H contacts are favoured in (C,H) aromatics, but these interactions occur less in compounds containing O, N or S as some H atoms are then involved in hydrogen bonds. The study also highlights the fact that hydrogen is a prefered interaction partner for fluorine.
    Keywords: enrichment ratioHirshfeld surface analysiscrystal packingfingerprint plots
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 10
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    Chemical crystallography and crystal engineering (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Keywords: Editorialchemical crystallographycrystal engineering
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 11
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    Automated nucleic acid chain tracing in real time (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The crystallographic structure solution of nucleotides and nucleotide complexes is now commonplace. The resulting electron-density maps are often poorer than for proteins, and as a result interpretation in terms of an atomic model can require significant effort, particularly in the case of large structures. While model building can be performed automatically, as with proteins, the process is time-consuming, taking minutes to days depending on the software and the size of the structure. A method is presented for the automatic building of nucleotide chains into electron density which is fast enough to be used in interactive model-building software, with extended chain fragments built around the current view position in a fraction of a second. The speed of the method arises from the determination of the `fingerprint' of the sugar and phosphate groups in terms of conserved high-density and low-density features, coupled with a highly efficient scoring algorithm. Use cases include the rapid evaluation of an initial electron-density map, addition of nucleotide fragments to prebuilt protein structures, and in favourable cases the completion of the structure while automated model-building software is still running. The method has been incorporated into the Coot software package.
    Keywords: nucleic acid chain tracingCoot
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 12
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    Location of Cu2+ in CHA zeolite investigated by X-ray diffraction using the Rietveld/maximum entropy method (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Accurate structural models of reaction centres in zeolite catalysts are a prerequisite for mechanistic studies and further improvements to the catalytic performance. The Rietveld/maximum entropy method is applied to synchrotron powder X-ray diffraction data on fully dehydrated CHA-type zeolites with and without loading of catalytically active Cu2+ for the selective catalytic reduction of NOx with NH3. The method identifies the known Cu2+ sites in the six-membered ring and a not previously observed site in the eight-membered ring. The sum of the refined Cu occupancies for these two sites matches the chemical analysis and thus all the Cu is accounted for. It is furthermore shown that approximately 80% of the Cu2+ is located in the new 8-ring site for an industrially relevant CHA zeolite with Si/Al = 15.5 and Cu/Al = 0.45. Density functional theory calculations are used to corroborate the positions and identity of the two Cu sites, leading to the most complete structural description of dehydrated silicoaluminate CHA loaded with catalytically active Cu2+ cations.
    Keywords: CHA zeolitescatalytic activitylocation of Cu2+synchrotron powder X-ray diffractionRietveld/maximum entropy method
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 13
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    The indexing ambiguity in serial femtosecond crystallography (SFX) resolved using an expectation maximization algorithm (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Crystallographic auto-indexing algorithms provide crystal orientations and unit-cell parameters and assign Miller indices based on the geometric relations between the Bragg peaks observed in diffraction patterns. However, if the Bravais symmetry is higher than the space-group symmetry, there will be multiple indexing options that are geometrically equivalent, and hence many ways to merge diffraction intensities from protein nanocrystals. Structure factor magnitudes from full reflections are required to resolve this ambiguity but only partial reflections are available from each XFEL shot, which must be merged to obtain full reflections from these `stills'. To resolve this chicken-and-egg problem, an expectation maximization algorithm is described that iteratively constructs a model from the intensities recorded in the diffraction patterns as the indexing ambiguity is being resolved. The reconstructed model is then used to guide the resolution of the indexing ambiguity as feedback for the next iteration. Using both simulated and experimental data collected at an X-ray laser for photosystem I in the P63 space group (which supports a merohedral twinning indexing ambiguity), the method is validated.
    Keywords: indexing ambiguityserial femtosecond crystallography (SFX)XFELsprotein crystallographyexpectation maximization algorithm
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 14
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    Time dependence of X-ray polarizability of a crystal induced by an intense femtosecond X-ray pulse (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The time evolution of the electron density and the resulting time dependence of Fourier components of the X-ray polarizability of a crystal irradiated by highly intense femtosecond pulses of an X-ray free-electron laser (XFEL) is investigated theoretically on the basis of rate equations for bound electrons and the Boltzmann equation for the kinetics of the unbound electron gas. The photoionization, Auger process, electron-impact ionization, electron–electron scattering and three-body recombination have been implemented in the system of rate equations. An algorithm for the numerical solution of the rate equations was simplified by incorporating analytical expressions for the cross sections of all the electron configurations in ions within the framework of the effective charge model. Using this approach, the time dependence of the inner shell populations during the time of XFEL pulse propagation through the crystal was evaluated for photon energies between 4 and 12 keV and a pulse width of 40 fs considering a flux of 1012 photons pulse−1 (focusing on a spot size of ∼1 µm). This flux corresponds to a fluence ranging between 0.8 and 2.4 mJ µm−2. The time evolution of the X-ray polarizability caused by the change of the atomic scattering factor during the pulse propagation is numerically analyzed for the case of a silicon crystal. The time-integrated polarizability drops dramatically if the fluence of the X-ray pulse exceeds 1.6 mJ µm−2.
    Keywords: femtosecond pulseX-ray diffractionpolarizabilityelectron densityrate equations
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 15
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    Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Description: Melting of native tapioca starch granules in aqueous pastes upon heating is observed in situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) and solution viscometry. Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure. Before melting, WAXS results reveal mixed crystals of A- and B-types (∼4:1 by weight), whereas SAXS results indicate that the semicrystalline layers are composed of lamellar blocklets of ca 43 nm domain size, with polydisperse crystalline (≃7.5 nm) and amorphous (≃1.1 nm) layers alternatively assembled into a lamellar spacing of ≃8.6 nm with 20% polydispersity. Upon melting, the semicrystalline lamellae disintegrate into disperse and molten amylopectin nanoclusters with dissolved and partially untangled amylose chains in the aqueous matrix which leads to increased solution viscosity. During subsequent cooling, gelation starts at around 347 K; successively increased solution viscosity coincides with the development of nanocluster aggregation to a fractal dimension ≃2.3 at 303 K, signifying increasing intercluster association through collapsed amylose chains owing to decreased solvency of the aqueous medium with decreasing temperature.
    Keywords: tapioca starch granulesgelatinizationgelationSAXS/WAXSviscosity
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 16
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    Molecular self-assembly of nylon-12 nanorods cylindrically confined to nanoporous alumina (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Description: Molecular self-assembly of nylon-12 rods in self-organized nanoporous alumina cylinders with two different diameters (65 and 300 nm) is studied with transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) in symmetrical reflection mode. In a rod with a 300 nm diameter, the tendency of the hydrogen-bonding direction of a γ-form crystal parallel to the long axis of the rod is not clear because of weak two-dimensional confinement. In a rod with a diameter of 65 nm, the tendency of the hydrogen-bonding direction of a γ-form crystal parallel to the long axis of the rod is more distinct because of strong two-dimensional confinement. For the first time, selected-area electron diffraction (SAED) is applied in a transmission electron microscope to a polymer nanorod in order to determine the hydrogen-bond sheet and lamellar orientations. Results of TEM–SAED and WAXD showed that the crystals within the rod possess the γ-form of nylon-12 and that the b axis (stem axis) of the γ-form crystals is perpendicular to the long axis of the rod. These results revealed that only lamellae with 〈h0l〉 directions are able to grow inside the nanopores and the growth of lamellae with 〈hkl〉 (k ≠ 0) directions is stopped owing to impingements against the cylinder walls. The dominant crystal growth direction of the 65 nm rod in stronger two-dimensional confinement is in between the [−201] and [001] directions due to the development of a hydrogen-bonded sheet restricted along the long axis of the rod.
    Keywords: molecular self-assemblynanorodsselected-area electron diffractioncylindrical confinement
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 17
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    Viruses and viral proteins (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Description: For more than 30 years X-ray crystallography has been by far the most powerful approach for determining the structures of viruses and viral proteins at atomic resolution. The information provided by these structures, which covers many important aspects of the viral life cycle such as cell-receptor recognition, viral entry, nucleic acid transfer and genome replication, has extensively enriched our vision of the virus world. Many of the structures available correspond to potential targets for antiviral drugs against important human pathogens. This article provides an overview of the current knowledge of different structural aspects of the above-mentioned processes.
    Keywords: bacteriophagesgenome deliveryfusion proteinsRNA-dependent RNA polymerasesviral proteasesviral receptorsviruses
    Electronic ISSN: 2052-2525
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  • 18
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    Contributions of charge-density research to medicinal chemistry (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Description: This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug–receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug–receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography.
    Keywords: charge-density researchmedicinal chemistrydrug designinvariomHansen–Coppens multipole modelquantum theory of atoms in molecules
    Electronic ISSN: 2052-2525
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  • 19
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    Capability of X-ray diffraction for the study of microstructure of metastable thin films (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
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    Publication Date: 2014-11-12
    Description: Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species.
    Keywords: metastable thin filmsmicrostructureX-ray diffraction
    Electronic ISSN: 2052-2525
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  • 20
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    Binding site asymmetry in human transthyretin: insights from a joint neutron and X-ray crystallographic analysis using perdeuterated protein (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Human transthyretin has an intrinsic tendency to form amyloid fibrils and is heavily implicated in senile systemic amyloidosis. Here, detailed neutron structural studies of perdeuterated transthyretin are described. The analyses, which fully exploit the enhanced visibility of isotopically replaced hydrogen atoms, yield new information on the stability of the protein and the possible mechanisms of amyloid formation. Residue Ser117 may play a pivotal role in that a single water molecule is closely associated with the γ-hydrogen atoms in one of the binding pockets, and could be important in determining which of the two sites is available to the substrate. The hydrogen-bond network at the monomer–monomer interface is more extensive than that at the dimer–dimer interface. Additionally, the edge strands of the primary dimer are seen to be favourable for continuation of the β-sheet and the formation of an extended cross-β structure through sequential dimer couplings. It is argued that the precursor to fibril formation is the dimeric form of the protein.
    Keywords: transthyretinamyloid assemblyneutron crystallographydeuteration
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 21
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    The first X-ray diffraction measurements on Mars (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The Mars Science Laboratory landed in Gale crater on Mars in August 2012, and the Curiosity rover then began field studies on its drive toward Mount Sharp, a central peak made of ancient sediments. CheMin is one of ten instruments on or inside the rover, all designed to provide detailed information on the rocks, soils and atmosphere in this region. CheMin is a miniaturized X-ray diffraction/X-ray fluorescence (XRD/XRF) instrument that uses transmission geometry with an energy-discriminating CCD detector. CheMin uses onboard standards for XRD and XRF calibration, and beryl:quartz mixtures constitute the primary XRD standards. Four samples have been analysed by CheMin, namely a soil sample, two samples drilled from mudstones and a sample drilled from a sandstone. Rietveld and full-pattern analysis of the XRD data reveal a complex mineralogy, with contributions from parent igneous rocks, amorphous components and several minerals relating to aqueous alteration. In particular, the mudstone samples all contain one or more phyllosilicates consistent with alteration in liquid water. In addition to quantitative mineralogy, Rietveld refinements also provide unit-cell parameters for the major phases, which can be used to infer the chemical compositions of individual minerals and, by difference, the composition of the amorphous component.
    Keywords: X-ray diffractionMarsextraterrestrial mineralogyCuriosity rover
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 22
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    Beyond simple small-angle X-ray scattering: developments in online complementary techniques and sample environments (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Small- and wide-angle X-ray scattering (SAXS, WAXS) are standard tools in materials research. The simultaneous measurement of SAXS and WAXS data in time-resolved studies has gained popularity due to the complementary information obtained. Furthermore, the combination of these data with non X-ray based techniques, via either simultaneous or independent measurements, has advanced understanding of the driving forces that lead to the structures and morphologies of materials, which in turn give rise to their properties. The simultaneous measurement of different data regimes and types, using either X-rays or neutrons, and the desire to control parameters that initiate and control structural changes have led to greater demands on sample environments. Examples of developments in technique combinations and sample environment design are discussed, together with a brief speculation about promising future developments.
    Keywords: SAXSWAXSSANScomplementary techniquessample environment
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 23
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    Pressure effects on lipids and bio-membrane assemblies (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Membranes are amongst the most important biological structures; they maintain the fundamental integrity of cells, compartmentalize regions within them and play an active role in a wide range of cellular processes. Pressure can play a key role in probing the structure and dynamics of membrane assemblies, and is also critical to the biology and adaptation of deep-sea organisms. This article presents an overview of the effect of pressure on the mesostructure of lipid membranes, bilayer organization and lipid–protein assemblies. It also summarizes recent developments in high-pressure structural instrumentation suitable for experiments on membranes.
    Keywords: biological membraneslipidsbilayerslipid–protein assemblieshigh-pressure studies
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 24
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    Nanocrystalline materials: recent advances in crystallographic characterization techniques (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Most properties of nanocrystalline materials are shape-dependent, providing their exquisite tunability in optical, mechanical, electronic and catalytic properties. An example of the former is localized surface plasmon resonance (LSPR), the coherent oscillation of conduction electrons in metals that can be excited by the electric field of light; this resonance frequency is highly dependent on both the size and shape of a nanocrystal. An example of the latter is the marked difference in catalytic activity observed for different Pd nanoparticles. Such examples highlight the importance of particle shape in nanocrystalline materials and their practical applications. However, one may ask `how are nanoshapes created?', `how does the shape relate to the atomic packing and crystallography of the material?', `how can we control and characterize the external shape and crystal structure of such small nanocrystals?'. This feature article aims to give the reader an overview of important techniques, concepts and recent advances related to these questions. Nucleation, growth and how seed crystallography influences the final synthesis product are discussed, followed by shape prediction models based on seed crystallography and thermodynamic or kinetic parameters. The crystallographic implications of epitaxy and orientation in multilayered, core-shell nanoparticles are overviewed, and, finally, the development and implications of novel, spatially resolved analysis tools are discussed.
    Keywords: nanocrystalline materialsplasmonicsshape prediction models
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 25
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    Reconciling the regulatory role of Munc18 proteins in SNARE-complex assembly (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Membrane fusion is essential for human health, playing a vital role in processes as diverse as neurotransmission and blood glucose control. Two protein families are key: (1) the Sec1p/Munc18 (SM) and (2) the soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) proteins. Whilst the essential nature of these proteins is irrefutable, their exact regulatory roles in membrane fusion remain controversial. In particular, whether SM proteins promote and/or inhibit the SNARE-complex formation required for membrane fusion is not resolved. Crystal structures of SM proteins alone and in complex with their cognate SNARE proteins have provided some insight, however, these structures lack the transmembrane spanning regions of the SNARE proteins and may not accurately reflect the native state. Here, we review the literature surrounding the regulatory role of mammalian Munc18 SM proteins required for exocytosis in eukaryotes. Our analysis suggests that the conflicting roles reported for these SM proteins may reflect differences in experimental design. SNARE proteins appear to require C-terminal immobilization or anchoring, for example through a transmembrane domain, to form a functional fusion complex in the presence of Munc18 proteins.
    Keywords: SM proteinsSNARE proteinssyntaxinMunc18membrane trafficking
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 26
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    Investigating increasingly complex macromolecular systems with small-angle X-ray scattering (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The biological solution small-angle X-ray scattering (BioSAXS) field has undergone tremendous development over recent decades. This means that increasingly complex biological questions can be addressed by the method. An intricate synergy between advances in hardware and software development, data collection and evaluation strategies and implementations that readily allow integration with complementary techniques result in significant results and a rapidly growing user community with ever increasing ambitions. Here, a review of these developments, by including a selection of novel BioSAXS methodologies and recent results, is given.
    Keywords: biological solution small-angle X-ray scattering (BioSAXS)synchrotron radiationbeamlinesstructural complexitybiostructural research
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 27
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    Diffuse scattering and partial disorder in complex structures (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The study of single-crystal diffuse scattering (SCDS) goes back almost to the beginnings of X-ray crystallography. Because SCDS arises from two-body correlations, it contains information about local (short-range) ordering in the sample, information which is often crucial in the attempt to relate structure to function. This review discusses the state of the field, including detectors and data collection and the modelling of SCDS using Monte Carlo and ab initio techniques. High-quality, three-dimensional volumes of SCDS data can now be collected at synchrotron light sources, allowing ever more detailed and quantitative analyses to be undertaken, and opening the way to approaches such as three-dimensional pair distribution function studies (3D-PDF) and automated refinement of a disorder model, powerful techniques that require large volumes of low-noise data.
    Keywords: single-crystal diffuse scatteringdisordersynchrotron light sources
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 28
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    X-ray techniques for innovation in industry (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The smart specialization declared in the European program Horizon 2020, and the increasing cooperation between research and development found in companies and researchers at universities and research institutions have created a new paradigm where many calls for proposals require participation and funding from public and private entities. This has created a unique opportunity for large-scale facilities, such as synchrotron research laboratories, to participate in and support applied research programs. Scientific staff at synchrotron facilities have developed many advanced tools that make optimal use of the characteristics of the light generated by the storage ring. These tools have been exceptionally valuable for materials characterization including X-ray absorption spectroscopy, diffraction, tomography and scattering, and have been key in solving many research and development issues. Progress in optics and detectors, as well as a large effort put into the improvement of data analysis codes, have resulted in the development of reliable and reproducible procedures for materials characterization. Research with photons has contributed to the development of a wide variety of products such as plastics, cosmetics, chemicals, building materials, packaging materials and pharma. In this review, a few examples are highlighted of successful cooperation leading to solutions of a variety of industrial technological problems which have been exploited by industry including lessons learned from the Science Link project, supported by the European Commission, as a new approach to increase the number of commercial users at large-scale research infrastructures.
    Keywords: X-ray techniquesindustryinnovation
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 29
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    Structure and function of dioxygenases in histone demethylation and DNA/RNA demethylation (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Iron(II) and 2-oxoglutarate (2OG)-dependent dioxygenases involved in histone and DNA/RNA demethylation convert the cosubstrate 2OG and oxygen to succinate and carbon dioxide, resulting in hydroxylation of the methyl group of the substrates and subsequent demethylation. Recent evidence has shown that these 2OG dioxygenases play vital roles in a variety of biological processes, including transcriptional regulation and gene expression. In this review, the structure and function of these dioxygenases in histone and nucleic acid demethylation will be discussed. Given the important roles of these 2OG dioxygenases, detailed analysis and comparison of the 2OG dioxygenases will guide the design of target-specific small-molecule chemical probes and inhibitors.
    Keywords: dioxygenaseshistone demethylationDNA/RNA demethylationN6-methyladenosineALKBH5
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 30
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    EXAFS and XANES analysis of oxides at the nanoscale (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Worldwide research activity at the nanoscale is triggering the appearance of new, and frequently surprising, materials properties in which the increasing importance of surface and interface effects plays a fundamental role. This opens further possibilities in the development of new multifunctional materials with tuned physical properties that do not arise together at the bulk scale. Unfortunately, the standard methods currently available for solving the atomic structure of bulk crystals fail for nanomaterials due to nanoscale effects (very small crystallite sizes, large surface-to-volume ratio, near-surface relaxation, local lattice distortions etc.). As a consequence, a critical reexamination of the available local-structure characterization methods is needed. This work discusses the real possibilities and limits of X-ray absorption spectroscopy (XAS) analysis at the nanoscale. To this end, the present state of the art for the interpretation of extended X-ray absorption fine structure (EXAFS) is described, including an advanced approach based on the use of classical molecular dynamics and its application to nickel oxide nanoparticles. The limits and possibilities of X-ray absorption near-edge spectroscopy (XANES) to determine several effects associated with the nanocrystalline nature of materials are discussed in connection with the development of ZnO-based dilute magnetic semiconductors (DMSs) and iron oxide nanoparticles.
    Keywords: EXAFSXANESoxide nanomaterialsnanocrystalline materials
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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    High pressure and multiferroics materials: a happy marriage (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: The community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. The in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties and the coupling to structural instabilities.
    Keywords: high pressuremultiferroicsmaterials science
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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    Crystallography of metal–organic frameworks (2014)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2014-11-12
    Description: Metal–organic frameworks (MOFs) are one of the most intensely studied material types in recent times. Their networks, resulting from the formation of strong bonds between inorganic and organic building units, offer unparalled chemical diversity and pore environments of growing complexity. Therefore, advances in single-crystal X-ray diffraction equipment and techniques are required to characterize materials with increasingly larger surface areas, and more complex linkers. In addition, whilst structure solution from powder diffraction data is possible, the area is much less populated and we detail the current efforts going on here. We also review the growing number of reports on diffraction under non-ambient conditions, including the response of MOF structures to very high pressures. Such experiments are important due to the expected presence of stresses in proposed applications of MOFs – evidence suggesting rich and complex behaviour. Given the entwined and inseparable nature of their structure, properties and applications, it is essential that the field of structural elucidation is able to continue growing and advancing, so as not to provide a rate-limiting step on characterization of their properties and incorporation into devices and applications. This review has been prepared with this in mind.
    Keywords: MOFsnon-ambient crystallographycrystal growth
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
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  • 33
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    Electronic Resource
    Crystal data and structural relation between Pb6GeO8.Pb11Ge3O17 and PbO (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 307-310 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Transparent yellow-greenish single crystals of Pb6GeO8 were obtained by spontaneous crystallization from a melt with a molar ratio of PbO:GeO2 = 4.7:1. The compound is monoclinic, probable space group P21/a, a = 52.665 (12), b = 15.063 (4), c = 23.949 (6) Å and β = 111.03 (5)°; Dm(293 K) = 8.65 (3), Dx = 8.653 Mg m−3 for Z = 64 formula units. Pb11Ge3O17 was synthesized by sintering high-purity oxides PbO and GeO2 of molar ratio 3.69:1 at 990 K. The compound is also monoclinic, probable space groups C2/c or Cc, a = 25.117 (5), b = 15.440 (2), c = 45.529 (13) Å and β = 103.20 (4)°; Dm(293 K) = 8.55 (2), Dx = 8.560 Mg m−3 for Z = 32.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012125
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    Electronic Resource
    Crystal data for AgGaxIn1−xSe2 and CuGaxIn1−xSe2 (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 311-315 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Series of chalcopyrite-type solid solutions AgGaxIn1−xSe2 and CuGaxIn1−xSe2, 0≤x≤1, have been prepared by direct synthesis from the melt. The space group is I\bar 42d (No. 122), Z = 4. The unit-cell parameters a and c and the ratio c/a change linearly with x. Powder data at 298 K are given for AgGaSe2, AgGa0.80In0.20Se2, AgGa0.70In0.30Se2, AgGa0.40In0.60Se2, AgGa0.20In0.80Se2 and AgInSe2, and for CuGaSe2, CuGa0.60In0.40Se2, CuGa0.30In0.70Se2 and CuInSe2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012149
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    Electronic Resource
    Electronic Resource
    Commission on Crystallographic Apparatus. Microdensitometer Project report I. Inter-Experimental Agreement (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 318-337 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012174
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  • 36
    Electronic Resource
    Electronic Resource
    Longer filament lifetimes for rotating-anode X-ray machines using a beam-deflecting magnet (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 338-339 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: If the length of the focal spot is increased while the width remains constant, X-ray output can be increased without changing the specific loading on the anode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012198
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  • 37
    Electronic Resource
    Electronic Resource
    An impurity-doped crystal plate as an X-ray monochromator (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 391-394 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: To increase the integrated reflexion intensity of a monochromating crystal, the strain distributed due to impurity introduction can be utilized and, compared with conventional mechanical processing, can be a more controllable method. From this viewpoint, numerical computations on the dynamical diffraction theory for distorted crystals have been performed for the 220 reflexion of Cu Kα X-rays by Si crystals with several different strain distributions; the one changing linearly with depth from −10−3 at the surface to zero at 28 μm depth gives the maximum integrated intensity within the restriction that the full width of the intensity profile is 100′′. The integrated intensity in this case is 5.3 and 4.5 times as strong as that of a perfect crystal plate for σ and π polarizations respectively. It is more enhanced for shorter wavelengths, e.g. nine times for Mo Kα. In addition, that intensity profiles for distributed strains are cut sharply at both ends is certainly favourable for the purpose of monochromating white X-rays. A preliminary experiment with an intentionally processed sample showed a fourfold intensity increase for a σ-polarized Cu Kα line with a full width of 80′′.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012368
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    Electronic Resource
    Electronic Resource
    Notes and News (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 401-401 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880012423
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  • 39
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    Electronic Resource
    Appareil de microdéformation à chaud pour topographie aux rayons X. Application à des bicristaux de germanium (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 88-92 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The device described here has been designed to perform microcreep experiments and, simultaneously, to get X-ray topographic images of the sample. Such dynamic experiments are now possible with white synchrotron radiation (LURE-DCI Orsay). The sample material, germanium, is hard to machine; so a simple shape was chosen (rectangular platelet 20 × 5 × 0–2 mm). The grip system is quite simple and the whole assembly is compact enough to be adapted to fit a standard goniometer head. Temperatures as high as 923 K in air and forces up to few tens of Newtons can be reached. The first experiments on Ge bicrystals have shown the device to perform as expected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880011545
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  • 40
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    Electronic Resource
    Assessment of synchrotron electron-beam damage in diamond by optical, cathodoluminescence and X-ray topographic methods (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 78-87 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A polished plate of type Ia natural diamond, containing regions which had been bombarded by electrons of energy between 2.0 and 4.5 GeV to total doses of 1̃024 electrons m−2 in polarized-photon production experiments, was examined, both before and after annealing at 1133 K for 8 h, using birefringence, cathodoluminescence photography and spectroscopy, X-ray topography and a novel method for mapping differences of interplanar spacing; `dilatation topography'. The annealing effected some reduction of overall strain, but it also generated an enhancement of diffraction contrast and cathodoluminescence at certain grown-in defects that the specimen contained. By means of dilatation topographs, interplanar spacings in a region of maximum electron-beam damage were compared with those in least-damaged regions some millimetres away. In the case of (110) planes that had been grazed by the electron beam, the maximum relative expansion, Δd/d, in damaged regions so found was reduced from 1.2 × 10−3 to 0.9 × 10−3 by the annealing. Evidence was obtained that the magnitude of expansion in the region of maximum damage was dependent upon crystallographic direction. Criteria are suggested for selection of diamonds to be used in polarized-photon production experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880011533
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  • 41
    Electronic Resource
    Electronic Resource
    Crystal data for two kinds of molecular alloys between sebacic and dodecanedioic acids (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 93-95 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Cell data for monoclinic sebacic acid COOH(CH2)8COOH, C10H18O4, and dodecanedioic acid COOH(CH2)10COOH, C12 H22O4, are accurately given: (C10) a = 15.064 (6), b = 4.987 (4), c = 10.142 (6) Å, β = 133.14 (5)°; (C12) a = 17.594 (8), b = 4.933 (3), c = 10.174 (5) Å, β = 132.35 (3)°. It is shown that crystallographic data for molecular alloys [C10]x[C12]1 −x are significantly different for those prepared by fusion (m.a.f.) and those by sublimation (m.a.s.). X-ray powder data are given for the two series of solid solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880011557
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  • 42
    Electronic Resource
    Electronic Resource
    Crystal data for hexamethylenetetraselenafulvalene-perfluorotetracyanoquinodimethane (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 95-96 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The cell constants for the title compound, HMTSFT–CNQ4, (C12F4N4).(C12H12Se4), M.W. 748.21, were determined from a single crystal exposed on a Syntex P{\bar 1} automated diffractometer and then refined from precision powder data with Cr Kα1 (2.28962 Å): a = 21.906 (5), b = 12.918 (3), c = 4.0184 (10) Å and β = 91.658 (10)°; U = 1136.7 Å3, Z = 2, space group C2/m; Dc = 2.186 Mg m−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889880011569
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  • 43
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    A goniometer for the measurement of stresses in single crystals and coarse-grained specimens (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 128-131 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A &psgr;-φ goniometer with two axes of rotation, driven by stepping motors, was designed as an attachment for a horizontal &thgr;/2&thgr; goniometer. By means of this arrangement it is possible to measure strains and compute stresses in single crystals and in separate crystals of a bicrystal or a coarse-grained polycrystalline specimen. The available rotations also make it possible to investigate residual macrostresses and textures in polycrystalline specimens. Results of the test measurements on a tensile specimen of a molybdenum single-crystal are given.
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    The correlation function, intersect distribution and scattering from a cube (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 132-134 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A calculation of γ(r), the correlation function which gives the X-ray scattering of a cubic object of uniform density, is given for the full range of r. A new method, which can be applied to other systems, is used. The function γ(r) and its first derivative are everywhere continuous, but γ′′(r) is discontinuous at r = L and r = L□2 (L = cube edge length). This leads to an intersect distribution of unexpected shape. The scattering intensity as a function of angle is calculated by Fourier inversion of γ(r).
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    Experimental separation of the coherent component of X-ray scattering prior to RDF analysis of non-crystalline polymers (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 135-140 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An experimental method is described which enables the inelastically scattered X-ray component to be removed from diffractometer data prior to radial density function analysis. At each scattering angle an energy spectrum is generated from a Si(Li) detector combined with a multi-channel analyser from which the coherently scattered component is separated. The data obtained from organic polymers has an improved signal/noise ratio at high values of scattering angle, and a commensurate enhancement of resolution of the RDF at low r is demonstrated for the case of PMMA (ICI `Perspex'). The method obviates the need for the complicated correction for multiple scattering.
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    Calcul du Profil des bandes de diffraction produites par des empilements de feuillets de nature différente (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 148-153 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Until now, the calculation of intensities diffracted by layer structures has only been treated in the two extreme cases, namely (i) the layers interfere completely and (ii) the layers do not interfere (turbostratic structures). The present paper develops the mathematical treatment which allows the calculation in the intermediate case, namely when layers are only partially interfering.
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    Circular diffuse scattering from a niobium tungsten bronze, 3Nb2O5.8WO3, studied by 1 MV higher-resolution electron microscopy (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 141-147 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A niobium tungsten bronze crystal with a nominal composition 3 Nb2O5.8WO3 gives circular diffuse scattering in the electron diffraction pattern. The diffuse rings change shape and size when the crystal is reduced at high temperature. The observations are explained by improving the cluster model proposed by De Ridder, Van Tendeloo, Van Dyck & Amelinckx [Phys. Status Solidi A (1977), 41, 555–560]; the present clusters are composed of nine pentagonal-tunnel sites. The 1 MV high-resolution electron microscope images reveal that the clusters have several different atomic arrangements and compositions. The relation between the clusters and the micro-domains, formed in the initial stage of long-range ordering, is clarified.
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    An assessment of the performance of a diffracted-beam monochromator in single-crystal diffractometry (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 163-167 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analysis of Bragg X-ray intensities collected on a single-crystal diffractometer with a pyrolitic graphite monochromator in the diffracted beam has revealed small systematic errors which are a consequence of the necessarily large illuminated area of monochromator crystal.
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    Small-angle X-ray scattering from solutions of flow-oriented colloidal particles (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 154-162 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The amount of information which can be obtained from a small-angle X-ray experiment can be considerably increased by orienting the solute particles with external forces during the scattering experiment. In this paper it is shown that orientation by flow, for instance through a capillary tube, gives additional information about size, shape, flexibility and rotational diffusion of the particles. The only requirement, in order to obtain flow-oriented samples, is that the solute particles must be relatively large and asymmetric. On the other hand, if the scattering curve is dependent on the flow rate through the capillary, it can immediately be concluded that the solute particles are asymmetric (or they are deformed in the hydrodynamic field). Equations describing the relationship between flow rate, molecular shape and scattered intensity are given, and theoretical intensity patterns for some representative cases are presented. It follows that there is a fundamental difference in scattering patterns for oblate and prolate ellipsoids of revolution. This difference can be used to differentiate between these two cases. Some experimental results obtained using inorganic model colloids are presented.
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    Small-angle scattering. Information content and error analysis (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 168-175 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of the small-angle scattering problem based on Shannon sampling is presented. It is shown that this approach leads to an accurate assessment of the information contained in a given data set and rigorous estimates of the errors inherent in the parameters derived therefrom.
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    Design criteria for a laboratory EXAFS facility (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 3-7 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: There has recently been an increased amount of interest in laboratory equipment for extended X-ray absorption fine-structure (EXAFS) measurements. In an earlier paper a facility for performing such measurements easily in a few hours was described in some detail. In this paper, further development of the techniques is reported. The use of high-power rotating-anode X-ray generator, the design of an X-ray curved-crystal spectrometer, the factors governing the proper choice of monochromator crystals and the design of fast-counting detectors and electronics are discussed. In addition, it is shown how errors caused by characteristic lines in the spectrum can be eliminated by use of a flux stabilization circuit.
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    Neutron photographic measurements of protein single-crystal reflections (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 24-27 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Photographic neutron intensity measurements on a 2 mm3 single-crystal of triclinic lysozyme are compared with conventional neutron diffractometer data. The reflections were recorded with the oscillation technique. The structure factors were derived from the optical densities scanned by an automatic microdensitometer and processed by computer programs. A statistical analysis shows that the photographic data are of about the same accuracy as recently collected diffractometer data. For the same flux and crystal volume the data collection time is reduced by up to two orders of magnitude.
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    A device for accurate single-crystal X-ray diffraction investigations at non-ambient temperatures: 83–1120 K (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 43-50 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A device is described which uses liquid nitrogen to generate a cold or hot gas stream which is blown directly onto the crystal mounted on an X-ray diffractometer. With a specially constructed high-vacuum (〈 1.3 × 10–5 Pa) jacketed silica Dewar tube, it can operate between 83 and 1120 K with a stability over long time periods of ± ¼ K below and ± 1 K above ambient temperature. In the latter case the short-time stability is ± ¼ K for hours. It gives an inert atmosphere at elevated temperatures and allows extensive data collection for the accurate determination of crystal structures. The evaporator, the automatic refilling system and the silica Dewar tube are described.
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    A fitting method for X-ray diffraction profiles (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 60-61 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A fitting method is proposed for X-ray diffraction profiles which requires only a small number of parameters.
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    Crystal data for two series of solid solutions: (RbxK1−x)MgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 61-62 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Complete solid solution is observed amongst the compounds of the type M1MgCr2(VO4)3 (where M1 = K, Rb or Tl). The solid-solution series obtained show linear changes in peak positions and peak intensities in their X-ray diffraction patterns. The crystallographic behaviour with respect to the value of x for (RbxK1−xMgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 solid solutions is discussed.
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    Crystal data for ferric molybdate: Fe2(MoO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 64-65 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Indexed powder patterns of the monoclinic phase, stable at room temperature, and of the orthorhombic phase, stable for T 〉 786 K, are given. The cell dimensions are: a = 15.737 (8), b = 9.231 (5), c = 18.224 (9) Å, β = 125.46 (2)° at 295 K; a = 9.330 (3), b = 12.868 (5), c = 9.242 (3) Å at 818.6 K. Linear equations describing the thermal expansion of the two phases of ferric molybdate are reported. To verify if ferric molybdate can incorporate excess MoO3, measurements on non-stoichiometric samples were also made: no evidence of the presence of excess MoO3 was found.
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    Crystal data for high-temperature As2O5 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 68-68 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-temperature As2O5 at 768 ± 5 K is tetragonal with a = 8.577 (1), c = 4.637 (1) Å, V = 341.2 Å3, Z = 4, Dc = 4.475 Mg m−3. Indexed powder data are given.
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    Characteristics of a flat multiwire area detector for protein crystallography (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 85-93 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A flat, relatively thin (9 mm) xenon-filled multiwire proportional counter with two-dimensional, 2 μs delay line readout of a 270 × 300 mm active area has been developed for use as a position-sensitive area X-ray detector in the 8 keV energy region (Cu Kα) used in crystallographic structure work with large biological molecules. Its quantum detection efficiency for 8 keV X-ray photons is about 0.5, a value which is spatially uniform to within ± 2%. Its dead-time loss fraction at a typical data collection rate of 30000 photons s−1 is 12%. The detector has spatial resolution for X-rays of 0.6 mm FWHM in the horizontal direction and 2 mm, the anode wire spacing, in the vertical direction. The effects of parallax are found to be limited and do not seriously increase the apparent size of the diffracted beams. The position sensitivity of this detector is geometrically linear to within 0.5 mm across its active surface. Routine maintenance of the detector requires the attention of a skilled technician but is not time consuming. For four years, this detector has been used to measure millions of reflection intensities from crystals of many different proteins. The down time due to the detector has averaged less than four days per year, considerably less than the down time of other components of the data collection system. Four new protein structures have now been solved using data from this detector. Also, a considerable amount of data have been collected at higher resolution or at different temperatures with crystals of other proteins.
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    An assessment of instrumental parameters which control the accuracy of stress measurement using the X-ray diffractometer method (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 124-130 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The sources of systematic error in the X-ray diffractometer method of stress measurement are discussed. The errors in stress measurement and correction procedures for their elimination are described and quantitatively assessed.
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    The use of cell and symmetry information for single-crystal orientation on diffractometers (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 117-123 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffraction aspect and rough cell parameters of a crystal to be studied are usually known before mounting the crystal on a diffractometer. Such data are used for orientation purposes in the method described. An ordered list of indexed 2θ values is calculated from which an optimum 2θ for a peak search is derived. The peaks found are centered, their possible unique indices are derived by comparison of the observed 2θ values with the calculated values. Two intense reflections with few indexing ambiguities are selected to define the crystal orientation. Their possible pairs of indices are found by considering combinations of indices related to the unique indices by the Laue-group symmetry and for which the calculated angle between the reciprocal vectors is comparable with the observed angle. Only the non-equivalent orientations defined by these initial pairs will be accepted. An initial pair will be rejected if the indices of both reflections can be transformed into those of a previously accepted pair by a single Laue-group symmetry operator of the first kind. The correct setting is usually obvious from a very short list of possible orientations and is retained. This simple approach has been programmed and treats all symmetries without branching of the logic. Rhombohedral crystals can be referred to hR or rP cells. The possible non-equivalent settings due to metric ambiguities, to pseudo-symmetry or to symmetry are exhaustively listed, but no symmetry-related setting is indicated. This scheme has automatically oriented more than 40 crystals from the seven crystal systems in 20–50 min each. The wavelength, the cell parameters and the short symbol of a valid space group in the correct diffraction aspect are the only input.
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    Neutron powder diffraction of forsterite, Mg2SiO4: a comparison with single-crystal investigations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 137-139 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Neutron time-of-flight powder data have been collected for forsterite [Mg2SiO4; Pbnm (D162h, No. 62); Z = 4, a = 4.7534 (1), b = 10.1989 (2), c = 5.9813 (1) Å] with the ZING-P′ high-resolution diffractometer at Argonne National Laboratory. Forty-seven variables, including anisotropic temperature-factor coefficients, were refined with a profile-fitting procedure to R(profile) = 2.10% and R(Rietveld) = 3.53%. Positional and thermal parameters are in good agreement with those determined from recent X-ray and neutron single-crystal diffraction experiments. Results suggest that powder data can be used to obtain accurate positional parameters and reasonable temperature factors for moderately complex structures.
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    Adaptation of a Kratky camera to use with a one-dimensional position-sensitive detector (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 139-141 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A Kratky small-angle X-ray camera was modified so as to allow the use of a one-dimensional (one-dimensional) position-sensitive detector (PSD) with it. The modification was designed in such a way that most of the calibrations, necessary for subsequent correction of the collected intensity data, can be performed with little alteration in the collimation geometry or the electronics settings. In particular, the calibration of the uniformity of detector efficiency can be performed by repeated vertical travel of the detector at a constant speed across a beam scattered from a sample.
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    XPKFIT: peak separation with arbitrary relations among the component peaks (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 145-148 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A computer program for the separation of a composite peak into the components and the background has been written in Fortran. Each component is approximated by a function of the form y(x) = c [1 + ({{x - d}\over{e}})^{2}]^{-f}, where c, d, e and f are the parameters to be determined by a least-squares method. Arbitrary, known or assumed relations among the parameters of different components may be read in to reduce the number of independent parameters and save computation time or, in other cases, to offer a better chance of separating a complex composite peak by varying a subset of the parameters.
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    BLOKJE, a computer program to calculate the domain of an atom in a structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 151-153 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A computer program has been written with the aim of calculating the domain of an atom in a structure. The domain may be limited by planes situated half-way between the atoms, or at a distance that takes into account the relative radii of the atoms. Data concerning this domain and the corresponding coordination polyhedron are computed and printed. Punched cards, to be used in a special plotting program, can also be produced. Three types of weighted coordination number are calculated.
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    The use of continuous diffraction data as a phase constraint. I. One-dimensional theory (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 160-168 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Intensity can often be measured as a continuous function of scattering angle in diffraction from non-crystalline specimens. An analysis of the amount of information contained in one-dimensional continuous diffraction data is presented here. This analysis, based on the sampling theorem and the theory of entire functions, indicates that there is a limited but often rather large number of possible phase solutions to any given continuous intensity distribution. A refinement technique has been developed which allows phase solutions to be found that are consistent with the diffraction data and with other physical and chemical data. In favourable cases, when diffraction data is used in coordination with other kinds of data, there can be enough information in a diffraction pattern to identify a unique structural solution.
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    Fundamentals of crystal growth 1 by F. Rosenberger (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 401-402 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    The small-angle neutron scattering spectrometer at the University of Missouri research reactor (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 370-382 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A small-angle neutron scattering (SANS) spectrometer has been constructed at the University of Missouri Research Reactor Facility (MURR). The design of the MURR–SANS is unusual in that the size of the reactor containment building constrains the flight path to be vertical. This is achieved by Bragg scattering upward through 90° from a set of slightly misaligned pyrolytic graphite crystals to provide a neutron beam at 4.75 Å with a wavelength spread of approximately 4.1%. The beam incident on the sample is defined by two matched variable apertures located either 3.0 or 4.5 m apart. The evacuated scattered flight path is designed with removable extensions to match the primary flight path in length. The instrument has an automatic sample handling capability provided by its own dedicated PDP 11/03 computer. The detector is a large assembly of commercially available linear 3He detectors as an economic alternative to a crossed-wire two-dimensional multi-detector. An array of 43 position-sensitive proportional counters, 24 in (609.6 mm) long and 0.5 in (12.7 mm) in diameter, using charge division gives a spatial resolution of 5 x 12.7 mm. The area-averaged detector efficiency is about 84% at a wavelength of 4.75 Å. The range of scattering vectors that can be measured is 0.005 〈 Q〈 0.15 Å−1. The instrument is well suited to a wide variety of experiments on specimens having characteristic dimensions between 20 and 500 Å. MURR–SANS is designed as a user-oriented facility which provides both reasonable resolution and intensity on sample at a modest cost, and forms part of a neutron scattering center.
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    A study of the ordered structures of the Au–Mn system by high-voltage–high-resolution electron microscopy. II. Two-dimensional antiphase structures based on the DO22 structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 392-400 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two-dimensional antiphase domain structures existing in the composition range 20–23 at.% Mn were investigated by a high-resolution structure-imaging technique with a 1 MV electron microscope. The structures are based on the DO22 structure and consist of parallelogram-shaped domains containing 4 × 3 columns of Mn atoms and lozenge-shaped domains with 4 × 4 and 3 × 3 columns, and the domains are separated by two-dimensional antiphase boundaries parallel to the ({\bar 2}40) and (240) planes of the fundamental face-centred structure. The configuration of the domains changes delicately with a slight change of composition or annealing temperature, and the symmetry of the structure is lowered below about 670 K. The ideal structure models have compositions of about 22.7 at.% Mn. The images of about half of the specimen area of the 22.6 at.% Mn alloy annealed at 570 K do not correspond to these new structures, but bear a resemblance to the image expected from the two-dimensional antiphase structure proposed by Watanabe [J. Phys. Soc. Jpn (1960), 15, 1030–1040] for Au3Mn, which is based on the L12 structure and has boundaries parallel to the (100) and (010) planes.
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    Comparison of two numerical methods for the integration of the Takagi–Taupin equations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 432-436 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two methods for the numerical resolution of the Takagi-Taupin equations are compared. It is shown that for a small integration step Taupin's [Acta Cryst. (1967), 23, 25–35] extension to two dimensions of the one-dimensional Runge–Kutta third-order method is more accurate than the algorithm of Authier, Malgrange & Tournarie [Acta Cryst. (1968), A24, 126–136] but, for a given precision, Authier, Malgrange & Tournarie's method is faster than Taupin's so the former will usually be preferred for numerical calculation.
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    Dependence of cooling rate of SAXS spectra from a B2O3–PbO–Al2O3 glass (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 444-446 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The phase separation of an 80% B2O3–15% PbO–5% Al2O3 (weight %) glass after splat-cooling was studied by small-angle X-ray scattering. The wavenumber which receives maximal amplification and the scattering intensity corresponding to this wavenumber were determined as a function of the cooling rate of the glass. The experimental results qualitatively agree with the main features of previous calculations based on the linear theory of spinodal decomposition, but no quantitative agreement is obtained.
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    Phase assignment to diffraction patterns based on the analytic properties of scattered fields applied to the structure of nerve myelin (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 455-461 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of published X-ray diffraction data from nerve myelin is given based on the properties of analytic functions. Functions defined by a finite Fourier transform may be described by their distribution of zeros. This description allows a phase function to be determined from real data, which is unique in principle. A solution to the phase assignment is given and compared with corresponding published solutions derived by other methods. The strong measure of agreement for the phases of the first nine diffraction orders, and the stability of this agreement against the efforts of experimental error, leads to the conclusion that these phases are probably correct.
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    Crystal data for [2.1.2.1]paracyclophan C30H28 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 465-465 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The powder data for [2.1.2.1]paracyclophan is reported. This compound is monoclinic with a = 21.44 (4), b = 17.22 (6), c = 9.70 (4) Å, γ = 141.30 (3)°, Z = 4.
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    Report of Executive Committee for 1980 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 491-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    A method of determining cubic parameters suited to the conditions of high- and low-temperature powder diffractometry (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 5-14 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method of measuring accurate cubic lattice parameters is developed which is suited to the type of conditions encountered in high- and low-temperature powder diffractometry. This is based on the fact that the absolute Bragg angle of each line in an indexed cubic diffraction pattern can be determined from a knowledge of the differences in angles between lines. Accurate zero-angle alignment, therefore, is unnecessary. Furthermore, it is shown that the peak or centroid shift of the line profiles arising from the instrumental and physical aberrations can be determined directly from the measured angular data without assuming a specific angular dependence. In practice the accuracy of the method is of the order of 0.0002 Å for a lattice parameter of approximately 8 Å.
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    Diffraction line profiles and Scherrer constants for materials with cylindrical crystallites (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 20-26 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Calculations of diffraction line profiles and Scherrer constants for crystallites whose external shape has cubic symmetry are extended to crystallites of cylindrical shape. The analysis includes the limiting cases of acicular crystals and disks and, to a reasonable degree of approximation in many cases, to hexagonal prisms. These shapes have applications in size determination for materials which form prismatic crystallites, particularly those which belong to the hexagonal system or have been derived from substances with this symmetry.
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    X-ray line profile analysis of deformed Al (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 35-38 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Warren–Averbach profile analysis was modified to study the deformed state of Al. The X-ray diffraction effect of dislocations locating on cell boundaries may be treated as `size broadening', while that of dislocations inside cells is `strain broadening', which may be treated with Wilkens's theory. X-ray Debye profile measurement was performed on deformed, recovered and annealed samples of commercial pure Al. Some information concerning the dislocation glide systems and distribution as well as the differences between the deformed and recovered state were given by the Debye profile analysis. The results are in good agreement with those obtained by other authors, which prove the reliability and correctness of the method.
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    An improved EXAFS-function calculation procedure for materials with small interatomic separation (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 39-47 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The extended structure of the Pt L3 X-ray absorption edge for some platinum compounds was measured and Fourier inverted. It is shown that the way in which the contribution of the isolated atom is subtracted from the absorption spectrum may influence the shape of the first peak in the Fourier transform and possibly lead to erroneous structural interpretations concerning the first-neighbour shell of the absorbing atom. These errors are the more important the smaller the separation between the absorbing atom and its nearest neighbours. An improved method of subtraction of the isolated-atom absorption is proposed and checked.
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    An X-ray film powder profile refinement of the crystal structure of Ta5P3 (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 605-607 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The crystal structure of Ta5P3 has been refined from Guinier–Hägg X-ray powder film data [Malmros & Thomas (1977). J. Appl. Cryst. 10, 7–11] using positional parameters from its structural isomorph Nb5P3 as starting values. The space group is orthorhombic Pnma (No. 62), with refined cell parameters a = 25.3210 (4), b = 3.4013 (1), c = 11.4614 (2) Å, V = 987.12 (5) Å3 and Z = 4. Final R = 4.9% [comparable with the R(F) of single-crystal work]. The structure exhibits the triangular prismatic Ta coordination about the P atoms and the dense packing of the Ta atoms, both familiar in many metal-rich phases formed between transition metals and non-metals of type P, As, S and Se.
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    The space group of γ-In2Se3 and γ1-(GaxIn1−x)2Se3: erratum (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 13 (1980), S. 611-611 
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    Notes: In the paper Revised and new crystal data for indium selenides by Popovic, Tonejc, Grzeta-Plenkovic, Celustka & Trojko [J. Appl. Cryst. (1979), 12, 416–420] it was concluded that P6122 or P6522 was the probable space group of the second high-temperature, γ, phase of In2Se3. Also, in the paper Phases, lattice parameters and thermal expansion of (GaxIn1−x)2Se3, 1 ≥ x ≥ 0, between room temperature and melting point by Tonejc, Popovic & Grzeta-Plenkovic [J. Appl. Cryst. (1980), 13, 24– 30] the same space groups were suggested for the phase γ1, existing in the In-rich region. However, the space group in both cases should be P61 or P65. This is in agreement with the work of Likforman, Carré & Hillel [Acta Cryst. (1978), B34, 1 5] who solved the crystal structure of one of the forms of In2Se3, and with the work of Schulte-Kellinghaus & Krämer [Acta Cryst. (1979), B35, 3016 3017] who solved the crystal structure of AlInS3. Likforman, Carré & Hillel [Acta Cryst. (1978), B34, 1 5] call their phase the low-temperature form of In2Se3.
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    Characterization of Brazilian high-ash coals by small-angle X-ray diffraction methods (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 251-254 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Changes in the microporosity of several types of Brazilian high-ash coals have been analyzed by small-angle X-ray scattering as a function of thermal treatment. Pore size, determined using Guinier plots, decreased following thermal treatment of the samples. The modification of porosity induced by thermal treatment was similar for high-ash and low-ash coals, from which it may be inferred that mineral content is not a determining factor in the process of pore formation. Internal surface area for the samples was calculated with SAXS data. A correlation is established between the internal surface area values obtained and the carbon content and heat-treatment temperatures of the samples.
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    Etude des composés à chaînes aliphatiques. I. Synthèse et caractérisation cristallographique des bis(n-alcanoates) de pipérazinium, 2[CxH2x−1O2−].[C4H12N22+] (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 279-281 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Crystal data for the series of piperazinium bis(n-alkanoates) of the type 2[CxH2x − 1O2−] [C4H12N22+] for x = 1 to 16 are presented. Most of these compounds have triclinic unit cells whose dimensions, obtained from single-crystal work, have been used to index their powder diagrams. The a ({\bar a} = 5.718 Å) and b ({\bar b} = 7.481 Å) cell dimensions remain nearly constant while the c dimension and the volume of the unit cell increase linearly with x, the number of carbon atoms in the alkanoate anion. Presumably the aliphatic sequence in the alkanoate anion adopts the fully extended conformation and lies in the bc plane and nearly along the c direction.
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    A simple procedure for fitting a backgound to a certain class of measured spectra (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 226-229 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A numerical procedure using orthogonal polynomials is used for extracting the background in measured spectra. An X-ray spectrum obtained with the energy-dispersive method is considered as an example.
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    Thermal expansion of α-HgI2 (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 461-462 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Lattice-constant thermal expansions, Δa/a and Δc/c, have been measured on α-HgI2 single crystals from 293 K up to the red-to-yellow transition temperature. The curves Δa/a(T) and Δc/c(T) are linear. The thermal expansion coefficients are determined: α[100] = (1.0 ± 0.1) × 10−5 K−1 and α[001] = (4.6 ± 0.1) × 10−5 K−1. No evidence of a red-to-orange phase transition could be found.
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    Structural ordering in amorphous TbFe2 and YFe2 (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 452-460 
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    Notes: Total neutron scattering data were collected on sputtered YFe2 at 298 K and TbFe2 at 423 K with a wavelength of 0.7 Å. The TbFe2 data were collected above the magnetic ordering temperature of 383 K. In addition, the elastic neutron scattering of TbFe2 was measured with the use of a pyrolytic graphite analyzer at a wavelength of 1.5 Å, and its total X-ray scattering was measured with Mo radiation and a silicon-lithium drifted detector. Experimental radial distribution functions, with statistical error limits, were calculated. Errors due to an incorrect background, scaling of the data and termination effects were minimized. The scale and shape of the experimental background and the coordination numbers, internuclear distances and disorder parameters, for the first six coordination spheres, have been determined. The contribution of paramagnetic inelastic scattering from TbFe2 to the total neutron scattering is quite appreciable. The shape of the background scattering, which goes through a maximum, is indicative of residual coherence and suggests short-range magnetic ordering where neighboring atom spins are aligned. These effects are not observed in YFe2, nor in the elastic TbFe2 data. The metallic glasses have a structural topology which is quite different from that found in their crystalline analogues. The transition-metal substructure, consisting of corner-sharing tetrahedra, is the only aspect of the crystalline topology preserved in the amorphous phase. The structural parameters suggest a tendency of the rare-earth atoms to cluster, thereby decreasing the number of Fe nearest neighbors relative to the crystalline structure.
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    A new CeO2 form obtained as oxidation product of CeO2+SiO2-doped hot-pressed silicon nitride (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 55-59 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: By using data from the Wallace & Ward [J. Appl. Cryst. (1975), 8, 255–260] cylindrical texture camera integrated with other traditional X-ray powder film techniques for very low and very high diffraction angles, a new high-temperature modification of CeO2 was identified and indexed resulting in a trigonal or hexagonal unit cell with a = 8.36(2) and c = 10.42(2) Å, (axial ratio 1.264) and Z = 16. The new phase is an oxidation product of CeO2-doped hot-pressed silicon nitride. It can be quenched to room temperature under appropriate conditions. Its stability on reheating is strictly related to its interaction with the silicate phase.
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    A simple method for the determination of structure-factor phase relationships and crystal polarity using electron diffraction (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 60-64 
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    Notes: Multiple electron scattering between weak beams has been used as the basis for a simple method to determine the absolute polarity of some non-centrosymmetric crystals. For crystals with the sphalerite structure many orientations have been found in which small departures from centrosymmetry produce large effects on the convergent-beam diffraction patterns (microdiffraction). The effects are reasonably independent of thickness and so can be analyzed qualitatively without the use of computers.
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    A novel method for indexing multiple diffraction peaks (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 570-571 
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    Notes: A method is proposed for unambiguously indexing X-ray multiple diffraction patterns obtained with irregularly shaped crystals on a four-circle diffractometer. The method is derived from the orientation matrix together with the operation of crystal rotation. It is shown that this method facilitates the procedures in the experimental method for phase determination.
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    Crystal data for the fluoroalleghanyite series nMn2SiO4MnF2(1,n〈4) (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 574-576 
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    Notes: Unit-cell constants for synthetic fluoroalleghanyite compounds have been determined by the refinement of X-ray powder diffraction data. Manganese norbergite: Pbnm, a = 4.862(2), b = 10.797(3), c = 9.188(2) Å, U = 482.4(4) Å3, Z = 4; alleghanyite: P21/b, a = 4.871(2), b = 10.818(6), c = 8.206(5) Å, α = 108.58(5)°, U = 414.1(7) Å3, Z = 2; manganhumite: Pbnm, a = 4.888 (2), b = 10.712(2), c = 21.749(6), U = 1138.8(5) Å3, Z = 4; sonolite: P21/b, a = 4.889(1), b = 10.668(3), c = 14.239(5), α = 100.83(5)°, U = 731.9(5) Å3, Z = 2. The JCPDS Powder Diffraction File numbers are: for manganese norbergerite 33–1500; for alleghanyite 33–1499; for manganhumite 33–1498; for sonolite 33–1497.
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    A systematic method for aligning double-focusing mirrors (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 577-577 
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    Notes and News (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 577-578 
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    Mössbauer spectroscopy and its chemical applications edited by J. G. Stevens and G. K. Shenoy (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 579-579 
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    Neutron transmutation doped silicon edited by J. Guldberg (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 579-580 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Crystal data for a new family of phases, Li3Mg2XO6:X=Nb, Ta, Sb (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 116-119 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Three members of a new family of phases, Li3Mg2XO6: X = Nb, Ta, Sb, have been prepared by solid-state reaction of MgO and Li3XO4. Unit-cell parameters of Li3Mg2TaO6 determined by electron diffraction and refined by X-ray powder diffraction are a = 8.883(2), b = 5.802(2), c = 17.437(6) Å, with space group Fddd; z = 8. Powder diffraction data of Li3Mg2NbO6 and Li3Mg2SbO6 were indexed by analogy with those of Li3Mg2TaO6 and unit-cell dimensions obtained by least-squares refinement: Li3Mg2NbO6 a = 8.552(2), b = 5.897(1), c = 17.721(5) Å; Li3Mg2SbO6 a = 8.614 (1), b = 5.908(1), c = 17.759(5) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882011522
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    Etude cristallographique de la phase de transition M'' dans Al–8%Zn–1%Mg (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 590-593 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of the transition phase M′ in AlZnMg alloys has been studied by Buerger X-ray precession photographs and transmission electron microscopy. The M′ phase, also called η′ or R, has a hexagonal or pseudo-hexagonal cell with a = 4.96, c = 14.03 Å. It is confirmed that M′ precipitates are hexagonal platelets with the following epitaxy: (00.1)M′//(111)Al and |10.0|M′//1{\bar 1}0|Al. It is shown that none of the known models of the unit cell accounts for the observed scattered intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012734
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  • 95
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    Accurate separation of X-ray α1–α2 doublets by the `substitution method' (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 602-604 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An improved `substitution method' for the separation of X-ray diffraction α1−α2 doublets is based on the possibility of refining both the proportionality constant between the α1 and α2 contributions to the line intensity and the doublet separation expressed in terms of the diffraction angle or of a related variable in the reciprocal space. Optimization of these two parameters, with a proper evaluation of the error, clearly shows the statistical nature of the oscillations appearing on the high-angle side of the pure α1 component after correction; their elimination by polynomial smoothing can therefore be performed and a procedure is suggested for achieving this result. A computer program, based on these principles, has been written and tested in many practical cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012758
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  • 96
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    Time-of-flight neutron small-angle scattering from a superconducting composite wire (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 611-614 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The precipitation behavior in the Ti–27at.%Nb–6at.%Ta–6at.%Zr alloy aged at 643 K was examined by means of time-of-flight neutron small-angle scattering. When the alloy was aged, fine-scale α precipitates appeared. During the precipitation process, each precipitate grew in size, but the total number of precipitates remained nearly constant up to 1 Ms of ageing. The increase of critical superconducting current density could be connected with increasing size of α precipitates. The specimen for the measurements consisted of a composite containing 3721 filaments in a copper matrix. The use of neutrons was shown to give great advantages for the investigation of precipitation phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012771
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  • 97
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    Ultra-high-vacuum heating camera for in situ synchrotron radiation X-ray topographic studies: erratum (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 632-632 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The wrong original was used for Fig. 6(b) of Gastaldi, Jourdan, Marzo, Allasia & Jullien [J. Appl. Cryst. (1982), 15, 391–395]. The correct version of Fig. 6(b) is given. In Fig. 6(c) the growth time increases from right to left.
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  • 98
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    Crystal data for high-temperature dicalcium lead propionate, Ca2Pb(CH3CH2COO)6 (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 635-636 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The high-temperature paraelectric phase of dicalcium lead propionate, DCLP, at 363 ± 5 K is tetragonal, with a = 12.574 (6), c = 17.403 (9) Å, V = 2751.4 Å3, Z = 4 and corresponds to the space group P41212 (or P43212). The thermal expansion curve shows the transition somewhere between 328 and 343 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012837
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  • 99
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    Crystallographers (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 638-638 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012850
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  • 100
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    Prices of Acta Crystallographica and Journal of Applied Crystallography (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 638-639 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012862
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