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  • 1
    Electronic Resource
    Electronic Resource
    OASIS: a computer program for breaking phase ambiguity in one-wavelength anomalous scattering or single isomorphous substitution (replacement) data (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 980-981 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The phase problem is reduced to a sign problem once the anomalous-scatterer or the replacing-heavy-atom sites are located. OASIS adopts the CCP4 format [Collaborative Computational Project, Number 4 (1994). Acta Cryst. D50, 760–763]. It applies a direct-method procedure to break the phase ambiguity intrinsic to one-wavelength anomalous scattering (OAS) or single isomorphous replacement (SIR) data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800001424
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  • 2
    Electronic Resource
    Electronic Resource
    A computer program to derive (3+1)-dimensional symmetry operations from two-line symbols (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 73-78 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program has been written for the derivation of (3 + 1)-dimensional symmetry operations from the two-line symbols. The derivation is based on the concept of generators {[Γ(RvE), εv, sv, τv, q)|v = 1, NG}, in which {[Γ(RvE), sv)|v = 1, NG} denotes the set of generators of the basic space group represented by the upper line. The program, called SPGR4D, is written in Fortran77 and based on the program by Burzlaff & Hountas (1982). [J. Appl. Cryst. (1982), 15, 464–467] for the derivation of symmetry operations in three-dimensional space. SPGR4D has been incorporated into a new version of the direct-methods program DIMS for solving incommensurate modulated crystal structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896006711
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  • 3
    Electronic Resource
    Electronic Resource
    Combining direct methods with isomorphous replacement or anomalous scattering data. VI. Incorporation of heavy-atom information into Hauptman's distributions (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 379-383 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Heavy-atom information has been incorporated into Hauptman's distributions of three-phase structure invariants for both isomorphous replacement and anomalous scattering cases. Reliable estimates of individual phases can be obtained by introducing the phase doublet expression φH = φ′H ± |ΔφH|. A test calculation with error-free data of insulin showed results better than previous methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767388000637
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  • 4
    Electronic Resource
    Electronic Resource
    Correction for the dynamical electron diffraction effect in crystal structure analysis (1993)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 877-880 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method is proposed to correct for the dynamical electron diffraction effect in crystal structure analysis. A rough structure model is first obtained by conventional structure-analysis methods neglecting the dynamical diffraction effect. From the rough structure model, multislice calculations are used to estimate the crystal thickness through the observed dynamical diffraction wave amplitudes. With this estimated thickness, the observed diffraction wave amplitudes are calibrated to give a set of fictitious observed kinematic structure-factor magnitudes. Based on such a set of magnitudes, a traditional least-squares procedure is used to refine structural parameters. The reliability of the result is checked by the consistency between the observed dynamical diffraction wave amplitudes and those found from the multislice calculation. The process can be made iterative. Tests were performed with two known structures, Bi-2212 and Pb-doped Bi-2223 high-Tc superconductors, and satisfactory results were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767393004581
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  • 5
    Electronic Resource
    Electronic Resource
    Image deconvolution of a single high-resolution electron micrograph (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 459-463 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An X-ray crystallographic method has been introduced into the image processing of high-resolution electron microscopy. This enables the deconvolution of single electron micrographs of a crystalline sample. For this purpose the chemical composition of the sample should be known approximately, the image should be taken near the optimum defocus condition, but no preliminary knowledge of the crystal structure is needed. The method has been proved to be efficient with a high-resolution electron micrograph of chlorinated copper phthalocyanine taken on the Kyoto 500 kV electron microscope.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767390000265
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  • 6
    Electronic Resource
    Electronic Resource
    On the determination of quasicrystal structures (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 473-478 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A possible approach to direct phasing of quasicrystal diffraction data is described. The data are first converted to a set of structure-factor amplitudes of a multidimensional crystal. The Patterson function of the quasicrystal is used to derive the converting factor. A direct method is then used to solve the phase problem in multi-dimensional space. The method has been tested with a hypothetical one-dimensional quasicrystal yielding a satisfactory result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767390000289
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  • 7
    Electronic Resource
    Electronic Resource
    The application of one-wavelength anomalous scattering. I. Combining results of different methods (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 656-659 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two different techniques for employing one-wavelength anomalous scattering, one using a direct-methods approach and the other a Patterson-like function, are applied to two known protein structures. The first of these, avian pancreatic polypeptide, is in space group C2 with one molecule containing 36 amino-acid residues in the asymmetric unit. The second, ribonuclease Sa in space group P212121, has two molecules each containing 96 amino-acid residues in the asymmetric unit. Both methods give phase indications easily leading to the elucidation of the smaller structure and probably enabling the larger structure to be solved as well. For each structure the electron density maps from the phases given by the two methods are combined through a minimum function. The Fourier transform of the resultant map gives phases better than those given by the individual methods, reducing the mean phase error by 2-3°, which could be critical in some applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739000352X
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  • 8
    Electronic Resource
    Electronic Resource
    The application of one-wavelength anomalous scattering. II. An analytical approach for phase determination (1990)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 659-664 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An analytical method has been developed by which phase estimates may be uniquely determined from one-wavelength anomalous-scattering data; the method as described can be applied to structures containing one type of anomalous scatterer. The method has been tested on two structures. The first is an Hg derivative of a small protein, avian pancreatic polypeptide (App), crystallizing in space group C2 with one molecule of 36 amino-acid residues in the asymmetric unit. The second is a Pt derivative of ribonuclease Sa (RNA), crystallizing in space group P212121 with two molecules of 96 amino-acid residues in the asymmetric unit. The phases for App give an electron density map which can easily be interpreted in terms of a model. For RNA the map is less clear but has strong similarities with the true map and could probably be interpreted. If anomalous scatterers are centrosymmetrically arranged then the analysis shows that there is a simple alternative process for calculating a map, called a Bp map, which directly shows a structural image.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767390003531
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  • 9
    Electronic Resource
    Electronic Resource
    Direct methods for incommensurate intergrowth compounds. I. Determination of the modulation (1993)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 49 (1993), S. 704-708 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A direct method is proposed for the determination of the modulation in incommensurate intergrowth compounds. The method is based on a new type of Sayre equation that relates the phase of a satellite reflection to the sum of structure-factor products of pairs of main reflections. Phases of satellite reflections are thus uniquely determined by the phases of main reflections. This reflects the fact that the modulation in intergrowth structures is the result of the interaction of all of the subsystems that form the basic structure. Test calculations were done with experimental data of two known composite structures of the inorganic misfit layer compounds (LaS)1.14NbS2 and (PbS)1.18TiS2. The results showed that the method is accurate and efficient and is fully independent of any preliminary assumption of the model of modulation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767393002582
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  • 10
    Electronic Resource
    Electronic Resource
    Direct methods for incommensurate intergrowth compounds. II. Determination of the modulation using only main reflections (1994)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 511-515 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A modified Sayre equation for incommensurate intergrowth compounds is presented. With this equation, both magnitude and phase for structure factors of satellite reflections can be estimated quantitatively through the observed intensities of main reflections, provided their phases are already known. Modulation functions can then be revealed by the Fourier synthesis calculated using the observed main reflections and the estimated satellites. The method has been tested with the known structures of two inorganic misfit layer compounds, (LaS)1.14NbS2 and (PbS)1.18TiS2. Satisfactory results were obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767394000899
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