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  • 1
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 255-261 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The applications of isomorphous labels for neutron and anomalous X-ray diffraction on powder samples in combination with phase and intensity information from electron microscopy (EM) are currently investigated. In particular, several groups have performed neutron diffraction on bacteriorhodopsin from Halobacterium halobium selectively deuterated at certain amino acids or at the chromophore retinal in order to show structural details which were not detectable from the EM data alone. In these investigations the difference Fourier method has been used to determine label positions. The limitation of this method with respect to the strength of the label is well known in X-ray single-crystal studies. In the present paper, it is shown to what extent the applicability of the method is weakened by the transfer of EM information to the neutron diffraction data when powder samples are used. The analysis is based on computer simulation experiments. A procedure is described to test the validity of the approach. With respect to neutron diffraction the method is applicable to data of moderate resolution when the relative steps in the density maps for neutron and electron diffraction are similar. Label positions can be obtained with an accuracy of ±1 Å from data of moderate resolution. In addition, it is shown how anomalous X-ray diffraction can be used in determining label positions using EM phases and intensity information. A procedure is described to obtain the correct label position, despite the fact that in this case the non-equal intensities I(+h) and I(−h) are superimposed on the same powder ring.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Graefe's archive for clinical and experimental ophthalmology 176 (1968), S. 155-159 
    ISSN: 1435-702X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Augenlinse ist ein inhogmoenes optisches Medium. Es besteht ein Gradient der optischen Dichte, der von höheren Werten im Zentrum zu niederen Werten in der Peripherie fällt. Mit Vielstrahl-Intereferometrie konnte die sich daraus ergebenden Isoindizialkurven vonGullstrand erstmals an Linsenschnitten sichtbar gemacht werden. Es müssen noch Schwierigkeiten bei der Präparation der Schnitte überwunden werden, da diese weder deformiert noch denaturiert sein dürfen. Nach ihrer Lösung wird aber die Linse mit dieser Methode viel genauer gemessen werden können als mit dem bisher benutzten Abbe-Refraktometer.
    Notizen: Summary The lens of the eye is no optical homogenous medium. There is a gradient of optical density falling from higher values in the centre to lower values in the periphery. With multiray-interferometry the resulting isoindicial curves ofGullstrand could be demonstrated for the first time on thin sections of the lens. There are still difficulties in the preparation of the slices to overcome as they must be neither deformed nor denaturated. If they are solved, the lens may be measured much more accurately with this method than with the formerly used refractometer ofAbbe.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    European biophysics journal 14 (1987), S. 289-292 
    ISSN: 1432-1017
    Schlagwort(e): Ion distribution ; tetramethylammonium ; purple memgrane ; bacteriorhodopsin ; neutron diffraction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Physik
    Notizen: Abstract The two-dimensional distribution of deuterated tetramethylammonium (TMA+) ions on the surface of purple membranes of Halobacterium halobium was determined by neutron diffraction. The measurements were performed on stacks of these membranes with a high concentration of TMA+ molecules in the water layer between the membranes. A difference Fourier analysis of samples with deuterated and undeuterated ions showed an excess of 8.5 TMA+ ions per elementary cell in the lipid areas compared to the protein areas. A total number of 90 ions per elementary cell in the intermembrane space was estimated from the preparation procedure. The excess in the lipid domains may result from the higher affinity of TMA+ ions for the lipid head groups and/or from the fact that the protein (bacteriorhodopsin) protrudes slightly out of the lipid surface.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1434-601X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract It is shown that nuclear spin polarized ion beams can be generated by ion beam surface interaction at grazing incidence. An optical detection method for the nuclear polarization after foil excitation of such beams is described and used for a hyperfine structure quantum-beat measurement on the14N II −2p 3p 3 D-state.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 299 (1981), S. 23-31 
    ISSN: 1434-601X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The fine structure (fs) intervals of the LiI-nd 2 D-terms have been measured with a relative accuracy of 10−3 with the beam-foil-quantum beat method forn=4–7 in proportion to the well known 3d 2 D-fs-splitting. The results establish a systematic deviation from a screened hydrogenic calculation of the fs-intervals.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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