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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section A 518 (1990), S. 572-582 
    ISSN: 0375-9474
    Keywords: Nuclear reaction
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 514-516 
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: AlN bulk ceramic has been implanted with energetic Co ions. In order to accurately characterise the atomic surrounding of the implanted ions, X-ray absorption measurements were carried out at 80 K in the fluorescence mode at the Co K edge in the as-implanted and annealed states. Simulation of the EXAFS oscillations allowed us to identify a first stage where Co is inserted in the AlN matrix followed by a second stage where Co precipitates form.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6036
    Keywords: PACS. 61.72.Ww Doping and impurity implantation in other materials – 76.80.+y Mössbauer effect; other gamma-ray spectroscopy – 71.70.Jp Nuclear states and interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The time-differential-perturbed γ-γ angular-correlation technique (TDPAC) with ion-implanted 181Hf tracers has been applied to study the hyperfine interactions of 181Ta impurities in the cubic bixbyite structure of Er 2 O 3 and Gd 2 O 3 . The TDPAC experiments were performed in air in the temperature range 300-1073 K (in the case of Er 2 O 3 ) and 300-1173 K (in the case of Gd 2 O 3 ). Three electrical-quadrupole interactions were found in each oxide in the whole studied temperature range. Two of them were attributed to the electric-field gradients (EFG) acting on 181Ta probes substitutionally located on the two nonequivalent free-of-defects cation sites of the bixbyite structure. The EFG results are compared with predictions of the point-charge model and discussed together with previous results obtained with the probes 111Cd and 181Ta in other isomorphous sesquioxides. The temperature dependence of the hyperfine parameters for both oxides is also discussed in terms of dilatometric expansion data.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica-supported molybdenum (1.6 and 5.0 wt%) and molybdenum (5 wt%)-sodium (0.4 wt%) catalysts have been characterized by laser Raman spectroscopy (LRS), time differential perturbed angular correlation (TDPAC), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The presence of different molybdenum species was correlated with activity and selectivity to formaldehyde during the methane partial oxidation reaction. The main species identified on the Mo(5.0 wt%) /SiO2 surface were MoO3 and monomeric species with a single Mo=O terminal bond. The pre-impregnation of the silica support with sodium strongly diminishes the Mo=O concentration due to the formation of Na2Mo2O7 species and tetrahedral monomers with a high degree of symmetry. As a result of these modifications, both methane conversion and formaldehyde formation are strongly inhibited. The combination of LRS and TDPAC techniques resulted in a powerful tool for the identification and quantification of the molybdenum species present on the surface of a silica support.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two indium-containing silicalite zeolites (In/H–ZSM5) catalysts prepared by wet impregnation and ionic exchange were characterized by the Perturbed Angular Correlation (PAC) technique using 111In as probe to determine the nature of the indium species. Some of these species take part in the catalytic reaction of the selective reduction (SCR) of NOx with methane. PAC experiments were performed at 500ºC in air before and after reduction–reoxidation treatments on the catalysts in order to determine the origin of the different hyperfine interactions and then the degree of ionic exchange. Complementary catalytic activity characterizations were also performed. PAC experiments performed on the catalyst obtained by wet impregnation showed that all In-atoms form In2O3 crystallites while almost 70% of In-atoms form In2O3 in the catalyst obtained by ionic exchange. The PAC experiments of both catalysts performed after the reduction–reoxidation treatment revealed the presence of two hyperfine interactions, different from those corresponding to indium in In2O3. These hyperfine interactions should be associated to disperse In species responsible of the catalytic activity located in the ionic exchange-sites of the zeolites.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 60 (1990), S. 679-682 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract TDPAC measurements were carried out on111In-implanted α-Nb2O5 samples at room temperature, after isochronal annealings up to 1270 K in 200 mbar oxygen and up to 1070 K in 10−5 mbar, respectively. The observed hyperfine interactions were compared to point charge model calculations which predict 15 and 2 equivalent cation sites in α-Nb2O5 and NbO2. The data in each system could be reproduced with one antishielding factor β=Vzz exp/Vzz pc for all sites, i. e. β(Nb2O5)=19.2 and β(NbO2)=31.2, respectively.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 120-121 (1999), S. 457-462 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report here first Perturbed Angular Correlation (PAC) results of the electric field gradient (EFG) characterisation at 111Cd impurities located at both non-equivalent cation sites of the bixbyite structure of Lutetium sesquioxide, between room temperature (RT) and 1273 K. The comparison with results coming from a systematic 111Cd PAC study in bixbyites and with point-charge model (PCM) predictions shows the presence of a trapped defect at RT in the neighbourhood of the asymmetric cation site, which is completely removed at T 〉 623 K. The anomalous EFG temperature dependence in Lu2O3 can be described in the frame of a “two-state” model with fluctuating interactions, which enables the experimental determination of the acceptor energy level introduced by the Cd impurity in the band-gap of the semiconductor and the estimation of the oxygen vacancy density in the sample.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    European journal of clinical microbiology & infectious diseases 10 (1991), S. 334-341 
    ISSN: 1435-4373
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Typhoid fever remains an important public health problem throughout the world with a higher morbidity and mortality rate in the developing countries. Early establishment of the diagnosis and prompt initiation of treatment with chloramphenicol, ampicillin or trimethoprim-sulfamethoxazole is not necessarily followed by complete resolution of the infection. Between 1 % and 6 % of patients with typhoid fever become chronic biliary carriers ofSalmonella typhi. These carriers are potential factors in the continued transmission of the disease. The increasing emergence worldwide of strains showing multiple resistance to the agents traditionally used in therapy has encouraged investigators to seek alternatives such as third generation cephalosporins and recently the new 4-quinolones, which have greater activity againstSalmonella typhi including multi-resistant strains. The fluoroquinolones seem to be the treatment of choice in those regions where resistant strains ofSalmonella typhi are prevalent.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 62 (1991), S. 353-358 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In connection with a general study of the evolution of tin-oxygen thin films, we report here on the hyperfine interactions of181Ta substitutionally replacting tin in the isolated phases SnO and SnO2. For this purpose, pure SnO pressed powder and a thin SnO2 film were implanted with181Hf. In both cases, unique quadrupole frequencies were found after thermal annealing treatments. The results indicate that the following hyperfine parameters: υ Q = 740.6(2.1) MHz, η=0.07(2) and υ Q = 971.5(1.9) MHz, η=0.72(1) characterize181Ta in SnO and SnO2, respectively.
    Type of Medium: Electronic Resource
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