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Start date: 1975End date: 1975Subject: search.filters.subject.530

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Now showing 1 - 6 of 6
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    Nuclear magnetic shielding tensors for 1H, 13C, and 15N in organic solids
    (1975) Spiess, Hans Wolfgang; Haeberlen, Ulrich; Kempf, Jürgen; Schweitzer, Dieter
    A survey will be given of nuclear magnetic shielding tensors obtained by multiple pulse techniques for 1H in carboxylic acids and by high field NMR for 13C in carbonyl- and carboxyl groups of aromatic compounds and for 15N in pyridine and nitrobenzene.
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    Phonon emission spectra of thin metallic films
    (1975) Frick, Wolfgang; Waldmann, Dieter; Eisenmenger, Wolfgang
    Thin metallic films evaporated on an Al 2 O 3-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.
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    Elementare Anregungen und kombinierte Streuung in einem System nicht im Gleichgewicht befindlicher Phononen
    (1975) Bulgadaev, S. A.; Levinson, I. B.; Pertschi, Ottmar (Übersetzer)
    Renormalisation of the long-wave optical phonon spectrum due to the strongly nonequilibrium quasimonochromatic distribution of acoustic phonons with a frequency equal to half that of the optical phonon is studied. It is shown that in such systems of acoustic phonons long-lived long-wave excitations are presen whose frequency is close to that of the optical phonon. These elemmentary excitations are manifest in the light combinational scattering spectrum and lead to a complex structure of the Stokes scattering line.
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    15N and 13C spin lattice relaxation in neat liquids at high magnetic fields
    (1975) Schweitzer, Dieter; Spiess, Hans Wolfgang
    General features of 15N spin lattice relaxation in nitrobenzene, pyridine and triethanolamine are discussed and compared with l3C relaxation mechanisms.
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    Transannular interactions in [2.2] phanes as studied by magnetic resonance and optical spectra
    (1975) Schweitzer, Dieter; Colpa, Johannes Pieter; Behnke, J.; Hausser, Karl H.; Haenel, Matthias; Staab, Heinz A.
    The interaction of π-electrons in [2.2] phanes was studied both experimentally and theoretically. The fluorescence and phosphorescence spectra were measured at liquid helium temperature; in addition, the zero field splitting parameters D and E were determined by ODMR in zero field and by ordinary ESR at X-band. The results for the phanes with two identical aromatic units can be summarized as follows: The rather small reduction of the D and E values of the order of 10% with respect to the monomers indicates, in agreement with the theoretical treatment given in part II, that the two unpaired electrons of the excited triplet state have a high probability to be at a given time in the same half of the molecule. While the fluorescence spectra show the typical behaviour of emission spectra of dimers or excimers, the phosphorescence spectra exhibit some remaining structure. This behaviour which indicates a somewhat weaker coupling among the triplet orbitals as compared to the singlet orbitals can also be understood on the basis of theoretical considerations. For a phane with two different aromatic units the behaviour is found to be more similar to the corresponding aromatic monomer with the lower excited states with some perturbation by the other part of the phase also in agreement with theoretical expectation.
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    Beurteilung der Bildqualität mit Hilfe der optischen Übertragungsfunktion
    (1975) Tiziani, Hans J.
    Die optische Übertragungsfunktion (OTF) erweist sich als sehr wertvolles Hilfsmittel zum Vergleich und zur Beurteilung der Qualität optischer Systeme. Das in der Firma Wild entwickelte Meßgerät wird kurz vorgestellt. Messungen und die anhand der Linsendaten gefundenen Rechenwerte werden verglichen. Dabei konnte gute Übereinstimmung der Ergebnisse der Modulations-Übertragungsfunktion (MTF) festgestellt werden. Mit Hilfe eines auf Experimenten basierenden Modells konnte eine Schwellwertkurve gefunden werden, welche den Vergleich der auf der Modulations-Übertragungsfunktion basierenden Ergebnisse mit denen von konventionellen Auflösungstests ermöglichte. Zusätzlich wird versucht, die vielen anfallenden Daten aus Rechnung und Messung zu Vergleichszwecken zu reduzieren, um so praktisch brauchbare Fokussier- und Gütemaße zu erarbeiten.