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  • 1990-1994  (9)
  • 1955-1959
  • 1915-1919
  • 1994  (9)
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5501-5507 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the pressure-induced shift and broadening of spectral holes for 14 different impurity sites in a polycrystalline solid solution of chlorin (17,18-dihydro-21H,23H-porphine) in benzophenone. In addition, we investigated the glassy phase of the same system in a frequency range which covered the entire inhomogeneously broadened band. The temperature range of the experiments was between 1.5 and 4.2 K. Pressure levels up to 10 MPa were applied. In the glassy phase, we observed a linear frequency dependence of the shift per pressure. However, in the crystalline phase, the general trend of the data clearly indicated a nonlinear frequency dependence. Yet, the individual sites, especially those with lower frequencies, showed a kind of stochastic scattering around the general trend behavior. The results were interpreted within the frame of existing models. The experiments demonstrate that matrix isolation combined with hole burning spectroscopy of large molecular impurities in polymorphic host materials under varying pressure conditions is a useful technique for determining molecular as well as bulk parameters, for examining problems of microelasticity and microplasticity, and for investigating the fundamental differences between glasses and crystals.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9262-9270 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present comparative investigations of doped benzophenone in its glass and crystal phases by using thermal cycling hole burning techniques. Chlorin and s-tetrazine were used as probe molecules. We measured the distribution of reactive barriers and the spectral diffusion behavior in both phases. The distribution in the glass is broad and is well described by a Gaussian. In the crystal, there are rather well-defined barriers, yet they are different for different sites. The respective kinetics is exponential and its temperature dependence is Arrhenius-like in contrast to the glass phase. Thermally induced spectral diffusion broadening in the glass phase is strong and shows the pattern well known from other organic glasses. In the crystal, it is much weaker, yet it is not completely absent. The experiments seem to indicate a threshold temperature ∼40 K. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 2210-2214 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Keywords: 25.30.Fj ; 21.10.Pc ; 02.60.Ed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method for the separation of structure functions in (e, e′ p) experiments is proposed, which is an extension of the traditional Rosenbluth-type techniques of [1,2]. In our approach, we use a very flexible Ansatz to describe the structure functions within an extended kinematical regionG and determine its free parameters with a x2 minimization. The procedure is tested by pseudo data (12C(e, e′p)11Bg.s.) in the quasi-free region.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-198X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-1084
    Keywords: MRI ; MRA ; Meningiomas ; Arterial displacement ; Tumor-feeding vessels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A group of 41 patients with intracranial meningiomas were examined by MR imaging (MRI) and MR angiography (MRA) to assess the. clinical value of MRA in the preoperative evaluation of these patients. The results of MRA were compared with the results of intraarterial cerebral catheter X-ray angiography (XRA; n = 19) and with the operative findings (n = 41 ): Our results showed a good correlation between MRA and XRA/surgery in demonstrating the relationship between the tumor and adjacent venous and arterial structures. Use of MRA was also helpful in demonstrating the degree of intrinsic tumor vascularity. It also supplied important information for operative planning Adjunct XRA was mandatory if detailed information about tumor-feeding vessels was requested by the neurosurgeon, especially in highly vascularized angiomatous meningiomas and in meningiomas suspected of tumor feeding by vessels of the internal carotid artery.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1434-6036
    Keywords: 61.50.−f ; 35.20.Jv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We exploited the slow relaxation of methyl group rotational tunneling states to perform optical hole burning inn-alkane crystals. The dye probe used was dimethyl-s-tetrazine and its perdeuterated derivative. We investigatedn-octane, perdeuteratedn-octane andn-hexane as host crystals. By comparing the experimentally observed hole-antihole splitting of the protonated and perdeuterated dye probe, all parameters, i.e. the tunneling splitting in the ground-and in the electronically excited state as well as the respective heights of the potential can be determined, assuming a threefold rotational symmetry axis. We found that matrix deuteration has a severe influence on the potential heights, which increase by a factor of two. With these parameters determined, many features of the complex relaxation behavior of the tunneling states can be qualitatively understood: We found Raman-type conversion processes inn-octane-h 18, Orbach-type processes inn-octane-d 18 and inn-hexane we found, in addition, a relaxation regime governed by a Direct process. The experimental activation energies as well as the cross-over temperatures are in satisfying agreement with current theories.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Genetic resources and crop evolution 41 (1994), S. 151-158 
    ISSN: 1573-5109
    Keywords: Triticum aestivum ; Aegilops tauschii (syn. Ae. squarrosa) ; Erysiphe graminis f. sp. tritici resistance genes ; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A collection of 400 Ae. tauschii (syn. Ae. squarrosa) Coss. accessions were screened for powdery mildew resistance based on the response patterns of 13 wheat cultivars/lines possessing major resistance genes to nine differential mildew isolates. 106 accessions showed complete resistance to all isolates, and 174 accessions revealed isolate-specific resistance, among which were 40 accessions exhibiting an identical response pattern as wheat cultivar ‘Ulka/*8Cc’ which is known to possess resistance gene Pm2. Expression of both complete and isolate-specific resistance from Ae. tauschii was observed in some synthetic hexaploid wheats derived from four mildew susceptible T. durum Desf. parents, each crossed with five to 38 resistant diploid Ae. tauschii accessions. Synthetic amphiploids involving different combinations of T. durum and Ae. tauschii generally showed a decrease in resistance compared with that expressed by the Ae. tauschii parental lines.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology letters 16 (1994), S. 363-366 
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Lipase biosynthesis occured in medium without lipids, but for improved production an inducer was needed. The source and concentration of an inducer had no signifficant effect. Starch as an additional carbon source stimulated lipase biosynthesis when used in small amounts. Addition of NH4NO3 as a nitrogen source, KH2PO4 as a phosphate source as well as Mg ions to the medium with inital pH 5.0 gave the best yield.
    Type of Medium: Electronic Resource
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