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  • 1
    Digitale Medien
    Digitale Medien
    Ultraviolet photoemission study of oligothiophenes: π-band evolution and geometries (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 4077-4092 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Ultraviolet photoelectron spectroscopy (UPS) has been applied to the investigation of the electronic structure of oligothiophenes with 4–8 thiophene rings. In a series of α-linked oligomers (αn with n being the number of rings), a systematic evolution of the π band is observed. Several peaks which correspond to the π band are observed in the region of 0.7–3 eV below the Fermi level (EF), and the bandwidth becomes broader with increasing n. The nonbonding π band is observed at 3.5 eV below EF and its energy is almost independent of the number of thiophene units. UPS spectra of α7 and α8 are fairly similar to the spectra of polythiophene, showing that these oligomers are good model compounds of the polymer. The ionization threshold energy of α7 and polythiophene was observed to be 5.3 eV. The effect of irregularity on the π-electron system was also studied by using oligomers which contain a β linkage or a vinylene group at the middle of the molecule. The UPS spectra showed that the β linkages significantly affect the electronic structure of polythiophene, while the vinylene group does not. In order to analyze the UPS spectra and to investigate the electronic structures of oligomers, the orbital energies and the geometries of these oligomers are calculated by the semiempirical MNDO-SCF-MO (modified neglect of diatomic overlap self-consistent-field molecular orbital) method. Theoretically simulated spectra of these oligothiophenes derived from the obtained orbital energies by Gaussian broadening are compared with the observed ones. The agreement between the observed and calculated spectra is very good, particularly in the π region. It is shown from the optimized geometry that (1) αn 's have planar structure and π electrons are delocalized, (2) the oligomer with β linkages has nonplanar structure leading to limited delocalization of π electrons, and (3) the oligomers with a vinylene group are almost planar and the disturbance by the vinylene group on the delocalization is small.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.458561
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  • 2
    Digitale Medien
    Digitale Medien
    Absolute Configuration of (+)-1-Phenyl-1,2,3,4-tetrahydroisoquinoline Hydrochloride (1998)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 651-653 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270197018581
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  • 3
    Digitale Medien
    Digitale Medien
    Uniform oligomers as reference materials for molecular weight determination of polymers (1997)
    Springer
    Accreditation and quality assurance 2 (1997), S. 137-139 
    Details
    ISSN: 1432-0517
    Schlagwort(e): Key words Uniform oligomer ; Reference materials ; Supercritical fluid chromatography ; Size exclusion chromatography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract  Uniform oligomers are special oligomers having no molecular weight distribution. They have been used as reference materials for polymer characterization, especially for accurate molecular weight determination in lower molecular weight ranges. These oligomers are used for different purposes. First, they are used in the calibration for chromatographic or spectroscopic data. Second, they are applied to identifying peaks appearing in chromatographies such as supercritical fluid chromatography (SFC) of oligomeric mixtures. Finally, they could give accurate instrumental or physicochemical constants used in polymer characterizations. The uniform oligomers have been prepared by using preparative chromatographies as separation methods. In some cases, step-wise syntheses have been applied together with the chromatographic methods. Recently, we prepared uniform oligostyrenes and oligo(oxyethylene)s whose molecular weights are greater than 1000 by using preparative size exclusion chromatography. More recently, using preparative SFC, some Japanese researchers have prepared high molecular weight and uniform oligomers such as oligo(methylmethacrylate)s. In this article, we briefly review recent progress mainly made by Japanese researchers in the field of preparation, analysis and applications of these pure oligomers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s007690050118
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  • 4
    Digitale Medien
    Digitale Medien
    Seasonality of Great Earthquake Occurrence at the Northwestern Margin of the Philippine Sea Plate (1999)
    Springer
    Pure and applied geophysics 155 (1999), S. 689-700 
    Details
    ISSN: 1420-9136
    Schlagwort(e): Key words: Seasonality, great earthquakes, Philippine Sea plate, atmospheric pressure, earthquake triggering.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract —A significant seasonality is found in the occurrence time of past great earthquakes (M≥ 7.9) in the northwestern margin of the Philippine Sea plate. Among the thirteen earthquakes cataloged, five took place in December, and all the earthquakes are included in the seven months from August to February. The probability that such a skewed distribution occurs by chance is as small as 2.0%. This seasonal concentration of earthquakes suggests that a small stress increase may trigger an earthquake when the future focal zone is at a critical condition to release a large rupture. As a candidate factor of the earthquake triggering, we tested a possibility of stress change caused by annual variation of the atmospheric pressure. However, the incremental stress is no larger than 30 Pa, and it hardly accounts for the seasonality of the great earthquakes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s000240050283
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  • 5
    Digitale Medien
    Digitale Medien
    Fragment mass dependence of angular anisotropy in 15 MeV proton-induced fission of 244Pu (1998)
    Springer
    The European physical journal 2 (1998), S. 153-155 
    Details
    ISSN: 1434-601X
    Schlagwort(e): PACS:25.85.-w Fission reactions – 25.85.Ge Charged-particle-induced fission
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: Angular distributions of fission fragments with mass number A=97-159 have been measured by the radiochemical recoil-catcher method in the proton-induced fission of 244Pu with the incident energy of 15 MeV. Angular anisotropies of extreme asymmetric mass division products even up to the fragment mass ratio of A H /A L ∼ 1.85 are found not any different from those of the typical asymmetric mass division products with A∼ 138, which indicates that no clear evidence is observed for the existence of an additional saddle point configuration in the extreme asymmetric mass division. The correlation between the saddle point state evaluated from the angular anisotropy and the mass division mode is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100500050104
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  • 6
    Digitale Medien
    Digitale Medien
    Determination of chlorine, bromine and iodine in rock samples by radiochemical neutron activation analysis (1997)
    Springer
    Journal of radioanalytical and nuclear chemistry 216 (1997), S. 107-112 
    Details
    ISSN: 1588-2780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik
    Notizen: Abstract Chlorine, bromine and iodine (hereafter, halogens) were detemined for rock samples by radiochemical neutron activation analysis. The powdered samples and reference standards prepared from chemical reagents were simultaneously irradiated for 10 to 30 minutes with or without a cadmium filter in a TRIGA-II reactor at the Institute for Atomic Energy, Rikkyo University. The samples were subjected to radiochemical procedures of halogens immediately after the irradiation. Iodine was firstly precipitated as PdI2, and chlorine and bromine were successively precipitated as Ag-halides at the same time. In this study, geological standard rocks, sedimentary rocks and meteorites were analyzed for trace halogens. In some Antarctic meteorites, iodine contents were observed to be anomalously high. Chlorine contents also are somewhat high. The overabundance of iodine and chlorine must be caused by terrestrial contamination on the Antarctica.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02034504
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  • 7
    Digitale Medien
    Digitale Medien
    Stability of metallofullerenes following neutron capture reaction on the metal ion (1998)
    Springer
    Journal of radioanalytical and nuclear chemistry 234 (1998), S. 95-100 
    Details
    ISSN: 1588-2780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik
    Notizen: Abstract The stability of 16 kinds of metallofullerenes (9 elements) was investigated against the recoil phenomena associated with the capture of neutrons by the metal atoms inside the carbon cages. The yields of the unaffected species were obtained by use of the HPLC separation method and radioactivity measurements. Recoil energy distributions of the metal atoms were calculated theoretically and the effective energy required for destruction of metallofullerenes from inside by recoiling atoms was estimated to be about 10 to 15 eV for the metallofullerenes containing lanthanide atoms.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02389754
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  • 8
    Digitale Medien
    Digitale Medien
    Analysis of archaeological samples by the internal monostandard method of PGAA (1998)
    Springer
    Journal of radioanalytical and nuclear chemistry 234 (1998), S. 27-32 
    Details
    ISSN: 1588-2780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik
    Notizen: Abstract Nondestructive determination of major and trace elements within voluminous materials has been demonstrated by prompt γ-ray neutron activation analysis. Some fragmented pieces of pottery bowls considered to have been produced in the late 18th century were analyzed by a new internal monostandard method, and noticeable differences of the elemental contents and significant correlations of the elemental distributions were observed among the samples. The possibility of identification of producing areas of unearthened material is demonstrated by the analytical results and the applicability of this method to the investigation of precious samples in a completely nondestructive way is verified in practice.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02389742
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  • 9
    Digitale Medien
    Digitale Medien
    Stability of radio-metallofullerenes against beta-decay (1999)
    Springer
    Journal of radioanalytical and nuclear chemistry 239 (1999), S. 179-185 
    Details
    ISSN: 1588-2780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik
    Notizen: Abstract The effect of β−-decay on the stability of metallofullerenes was investigated for three decay chains of155Sm-155Eu,161Gd-161Tb and177Yb-177Lu. For the former two cases, the metallofullerenes were found stable even after the β−-decay while in the case of177Yb, the metallofullerene became unstable after β−-decay. The present results point to the fact that metallofullerenes are stable against ordinary β−-decay unstable after β−-decay. The present results point to the fact that metallofullerenes are stable against ordinary β−-decay recoil energies, but they become unstable if the oxidation state of the metal atom is changed by nuclear transformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02349553
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  • 10
    Digitale Medien
    Digitale Medien
    Systematic behavior of mass-yield curves in low-energy fission of actinides (1990)
    Springer
    Journal of radioanalytical and nuclear chemistry 142 (1990), S. 231-251 
    Details
    ISSN: 1588-2780
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik
    Notizen: Abstract Mass yield curves of spontaneous fissions, thermal-neutron induced fissions, monochromatic-neutron and proton induced fissions of actinides are reviewed. Mean masses of light and heavy asymmetric mass yield peaks are listed. The subtle change of the shape of the asymmetric heavy peak is expressed in terms of the parameters of two Gaussians that fit the observed data well. One Gaussian is narrow in width and always peaks at A=133–136 while the other is broader and peaks at A=140−144. The FWHM of the heavy asymmetric peak becomes minimum for the fissioning mass A=240−245. An analysis of the projectile energy dependence of mass yield curves indicated, at least, two distinctively different behaviors, one for asymmetric products and the other for symmetric products. From the energy dependence of the peak-to-valley rations, the “extra-energy” required for symmetric mass division, or the difference in the fission barrier heights, in the nomeuclature of the two-mode hypothesis, is deduced for a wide range of fission nuclides.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02039465
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