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  • International Union of Crystallography (IUCr)  (4)
  • 1990-1994  (4)
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Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 675-686 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Crystals of macromolecules often have two or more molecules per asymmetric unit, or contain domains of a macromolecule or a macromolecular complex that are structurally independent. In such cases the conventional molecular-replacement method attempts to determine the position of each structural unit independently. Typically, some parts of the structure can be determined more easily or more reliably than other parts. Methods are proposed whereby information from a part of a crystal structure that has been determined can be used to help determine the structure of the remainder. Two different strategies are discussed, `subtraction' and `addition'. With `subtraction' strategy the Patterson function of the known part of the structure is subtracted from the `observed' Patterson. This approach is found to be most effective in the context of the rotation function in that it eliminates peaks that are irrelevant to the desired solution. With `addition' strategy the structure factors of the known component are added to those of the search model. This procedure is most effective in the context of the translation function because it brings the structure factors calculated from the search model closer to those observed. Methods of applying the fast Fourier transform to facilitate these calculations are described. A number of examples are provided including structures of mutants of T4 lysozyme that might not have been solved without recourse to the proposed methods. A method of including information from a heavy-atom derivative in a translation function is also developed and shown to be superior in some situations to the conventional translation function.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 1878-1880 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 457-462 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: STRAT is a Fortran program to optimize the efficiency of data collection on an X-ray area detector system, starting with the crystal in any arbitrary alignment. The high speed of the algorithm makes it possible to select the `best' combination of crystal rotations from a large list of possibilities. The program is applicable to any space group and requires only a few minutes of CPU time on a VAX station 4000.60 computer. The procedure can be used for the collection of data de novo and also in cases where part of a data set has already been measured. Although specifically designed for a system with a three-circle goniostat, the procedure is adaptable to other geometries.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 2096-2098 
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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