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  • Articles: DFG German National Licenses  (6)
  • 1995-1999  (6)
  • 1960-1964
  • 1950-1954
  • 1910-1914
  • 1999  (6)
  • 1
    ISSN: 1434-6036
    Keywords: PACS. 63.20.Dj Phonon states and bands, normal modes, and phonon dispersion - 76.80.+y Mössbauer effect; other -ray spectroscopy - 39.30.+w Spectroscopic techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Mössbauer studies were performed on single crystals of guanidinium nitroprusside with different orientations of their principal crystallographic axes (a, b, c) with respect to the incident radiation. The markedly anisotropic Lamb-Mössbauer factor f LM , i.e. f LM (a) = 0.118(8), f LM (b) = 0.174(8), f LM (c) = 0.202(8) is in contrast to that of nitroprussides with inorganic anions. The observed anisotropy is ascribed to the anisotropic vibrational mean-square displacement of the nitroprusside anions as a whole which is due to the specific packing of both, anions and cations, as well as the very weak chemical bonding between the ions, typical only for guanidinium nitroprusside. The vibrational anisotropy of iron atoms in barium nitroprusside that has been observed by X-ray structural investigations has a different origin and therefore does not result in an anisotropic Lamb-Mössbauer factor. We have also investigated metastable states in guanidinium nitroprusside that have been populated by means of incoherent irradiation from light-emitting diodes. With a specific orientation of the guanidinium nitroprusside single crystal a population of the metastable states up to 26% could be achieved. Populations of comparable size on lithium, sodium and potassium nitroprussides have only been reached using coherent laser irradiation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1436-6274
    Keywords: Schlüsselwörter Wirbelfrakturen ; Spongiosaplastik ; Korrekturverlust ; Transplantatnekrose ; Key words Spine fractures ; Bone graft ; Loss of correction ; Transplant necrosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: In the treatment of thoracolumbar fractures of the spine an osteosynthesis in the real sense is not possible. The result of the injury is not only bony destruction but also in most cases biomechanical instability of the motion segment. The goal of operative treatment is stability. Besides internal fixation bone transplantation is necessary to achieve bony fusion. A common procedure is transpedicular bone grafting. Posterior stabilization with an internal fixator is combined with cancellous bone transplantation, which is placed into the vertebral body and the intervertebral space through the pedicles. Resection of the intervertebral disc is necessary to obtain bone healing under the protection of the implant. In a clinical study after the stabilizing operation, we found a correction loss of 30–60% that was independent of the fracture type, implant or operation procedure. The lack of healing of the bone graft was the reason for the correction loss. Besides the unfavorable vascularization of the intervertebral space which cannot be influenced by operation, the morphological arrangement and spatial expansion of the cancellous bone transplant are important for obtaining contact with the endplate of the cranially situated vertebral body. The assessment of the 3D reconstructions, generated from the digitized picture data of CT scans, shows small volumes of cancellous bone grafts with no or poor contact to the neighboring vertebral body. Our results indicate that transpedicular bone grafting cannot be recommended for the operative treatment of unstable thoracolumbar spinal fractures, since in most cases no bony fusion occurs. In our opinion combined anterior-posterior stabilizations are more often indicated.
    Notes: In der operativen Behandlung instabiler Frakturen der thorakolumbalen Wirbelsäule ist eine Osteosynthese im eigentlichen Sinn nicht möglich. Bei der Verletzung tritt nicht nur ein isolierter knöcherner Schaden ein, sondern in den meisten Fällen auch eine biomechanische Instabilität des betroffenen Bewegungssegments. Das Ziel der operativen Behandlung besteht darin, Stabilität zu erzeugen. Neben der Instrumentation mit internen Fixationssystemen ist eine Knochentransplantation erforderlich, um eine knöcherne Spondylodese zu erzielen. Die häufigste Form der Knochentransplantation ist die transpedikuläre Spongiosaplastik, bei welcher im Rahmen der dorsalen Implantation des Fixateur interne über die Pedikel des Wirbels Spongiosa in den Wirbelkörper und den Intervertebralraum plaziert wird. Voraussetzung für die knöcherne Einheilung des Transplantats unter dem Schutz des stabilisierenden Implantats ist die vorherige Resektion des intervertebralen Bandscheibengewebes. In der klinischen Studie wurden Korrekturverluste in der Größenordnung von 30–60% im Bereich der operierten Bewegungssegmente unabhängig vom Frakturtyp, Implantat oder Operationsverfahren nachgewiesen. Verantwortlich war im wesentlichen die fehlende Einheilung der transplantierten Spongiosa. Neben der ungünstigen Vaskularisation im Intervertebralraum, welche operativ unbeeinflußbar ist, kommt der morphologischen Anordnung des Transplantats, seiner räumlichen Ausdehnung und damit der Möglichkeit, mit dem benachbarten Wirbel in Kontakt zu kommen, eine besondere Bedeutung zu. Die Auswertung von 3D-Rekonstruktionen, welche aus den CT-Bilddaten gewonnen wurden, zeigt unbefriedigend kleine Spongiosavolumina, die keinen oder eine nur ungenügenden Kontakt zum Nachbarwirbel herstellen. Die vorliegenden NMR-Untersuchungen belegen eine mangelnde Vitalität der transplantierten Spongiosa. Da überwiegend keine knöcherne Fusion von instabilen Bewegungssegmenten oder nur unter Entwicklung von erheblichen Korrekturverlusten eintritt, ist die transpedikuläre Spongiosaplastik nach den obigen Ergebnissen nicht für die operative Stabilisierung thorakolumbaler Frakturen geeignet. Als Konsequenz aus den Ergebnissen muß die Indikation zur kombiniert dorso-ventralen Stabilisierung häufiger gestellt werden. Möglicherweise werden in Zukunft endoskopische minimalinvasive Techniken weiter perfektioniert, um invasive, patientenbelastende Verfahren zu vermeiden und das Komplikationsrisiko zu senken.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Guanidinium nitroprusside GNP, (CN3H6)2[Fe(CN)5NO] has been investigated in single‐crystalline form by nuclear resonant forward scattering (NFS) using synchrotron radiation (Mössbauer spectroscopy in the time domain). This method provides a direct measure of effective absorber thickness and therefore also of the Lamb–Mössbauer factor f LM. GNP has the advantage that all [Fe(CN5)NO]2- anions are practically aligned within the crystal. For the two different crystal orientations, with the crystallographic a- and c-direction parallel to the synchrotron beam, respectively, we have obtained f LM (a)= 0.122(10) and f LM (c)= 0.206(10), i.e., GNP exhibits significant anisotropic vibrational behavior. The quantum beat pattern of the NFS spectra obtained for the two different crystal orientations is discussed on the basis of radiation characteristics of the polarized synchrotron beam and the multipole transitions of oriented 57Fe nuclei.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 123-124 (1999), S. 561-570 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nuclear forward scattering (NFS) of synchrotron radiation was applied to investigate the electronic and magnetic properties of (i) the diamagnetic “picket-fence” porphyrin FeO2(SC6HF4)(TPpivP), which is a model for oxygenated hemoglobin and myoglobin and (ii) the paramagnetic “picket-fence” porphyrin [Fe(CH3COOH)(TPpivP)]—, which is a model for the ferrous state of the prosthetic group, termed P460, of the multi-heme enzyme hydroxylamine oxidoreductase from the bacterium Nitrosomonas europeae.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 123-124 (1999), S. 571-593 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Relaxation phenomena show up in standard energy-domain Mössbauer spectra via line broadening. The evaluation of such spectra is in most cases done by applying the stochastic theory of lineshape mainly developed in the 60's and 70's. Due to the time structure and the polarization of the synchrotron radiation nuclear resonance forward scattering in the time domain gives valuable additional information on relaxation mechanisms. We report here mainly on Nuclear Forward Scattering (NFS) experiments, investigating the paramagnetic relaxation of high-spin Fe2+ and Fe2+ ions, superparamagnetic relaxation and briefly on recent investigations of charge fluctuations in Eu3S4.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 123-124 (1999), S. 841-846 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Temperature dependent nuclear inelastic-scattering (NIS) of synchrotron radiation was applied to investigate both spin states of the spin-crossover complex [Fe(tpa)(NCS)2] (tpa = tris(2-pyridylmethyl)amine). A remarkable increase of the iron–ligand bond stretching upon spin crossover has unambiguously been identified by comparing the measured NIS spectra with theoretical simulations based on density-functional calculations.
    Type of Medium: Electronic Resource
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