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  • 1
    ISSN: 0016-7835
    Schlagwort(e): Key words Ontong Java Plateau ; Thorium-230 ; Barium ; Productivity ; Lysocline ; Sediment focusing ; Vertical mass accumulation rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract  We discuss geochemical proxies, reflecting processes of primary productivity, CaCO3 dissolution, and sediment redistribution in a piston core (RNDB 74P) from the Ontong Java Plateau. Due to the shallow water depth, biogenic carbonate is well preserved and a very good δ18O stratigraphy is available down to isotopic stage 11. 230Thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing. Due to the constant production of 230Th in the water column, the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above. The 230Thex 0/CaCO3 ratio reflects the well-known Pacific CaCO3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes. The record of the grain size fraction 〉63 μm supports these results. The downcore concentrations and accumulation rates of barium (Ba) are on a higher level during interglacials and show several peaks. Normalization of Ba with 230Thex 0 delivers a more uniform level of the Ba accumulation rates throughout the core. This pattern suggests a constantly higher biological productivity (nearly tenfold) in this area throughout the past 200 kyr compared with an open ocean environment. Barium peaks observed at the climatic transitions 2/1 and 6/5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location. A possible explanation might be the onset of the modern circulation pattern. The transition from Ba-enriched deep water to lower contents in the Atlantic might have resulted in an enhanced deposition of Ba in the Pacific.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2183-2192 
    ISSN: 0887-624X
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The hydrolytic degradation of technical poly(ethylene terephthalate) (PET) was investigated by means of different methods such as size-exclusion chromatography (SEC), viscometry, light-scattering, thin-layer chromatography, end-group titration, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The long-term degradation was simulated by exposing PET filament yarns to aqueous neutral conditions at 90°C for up to 18 weeks. By means of MALDI-MS and thin-layer chromatography, the formation of different oligomers was obtained during polymer degradation. As expected, an ester scission process was found generating acid terminated oligomers (H-[GT]m-OH) and T-[GT]m-OH and ethylene glycol terminated oligomers (H-[GT]m-G), where G is an ethylene glycol unit and T is a terephthalic acid unit. Additionally, the scission of the ester bonds during the chemical treatment led to a strong decrease in the number of cyclic oligomers ([GT]m). The occurrence of di-acid terminated species demonstrated a high degree of degradation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2183-2192, 1997
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    International journal of earth sciences 85 (1996), S. 536-545 
    ISSN: 1437-3262
    Schlagwort(e): Ontong Java Plateau ; Thorium-230 ; Barium ; Productivity ; Lysocline ; Sediment focusing ; Vertical mass accumulation rate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie
    Notizen: Abstract We discuss geochemical proxies, reflecting processes of primary productivity, CaCO3 dissolution, and sediment redistribution in a piston core (RNDB 74P) from the Ontong Java Plateau. Due to the shallow water depth, biogenic carbonate is well preserved and a very goodδ 18O stratigraphy is available down to isotopic stage 11.230Thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing. Due to the constant production of230Th in the water column, the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above. The230Thex 0/CaCO3 ratio reflects the well-known Pacific CaCO3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes. The record of the grain size fraction 〉63 µm supports these results. The downcore concentrations and accumulation rates of barium (Ba) are on a higher level during interglacials and show several peaks. Normalization of Ba with230Thex 0 delivers a more uniform level of the Ba accumulation rates throughout the core. This pattern suggests a constantly higher biological productivity (nearly tenfold) in this area throughout the past 200 kyr compared with an open ocean environment. Barium peaks observed at the climatic transitions 2/1 and 6/5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location. A possible explanation might be the onset of the modern circulation pattern. The transition from Ba-enriched deep water to lower contents in the Atlantic might have resulted in an enhanced deposition of Ba in the Pacific.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 387-392 
    ISSN: 0021-8383
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Syntheses of 1-(β-D-Arbinofuranosyl)-pyrimidinesNew synthetic methods of 1-(β-D-arabinofuranosyl)-pyrimidines are described. 1-(β-D-arabinofuranosyl)-uracil, 1-(β-D-arabinofuranosyl)-5-fluorouracil, 1-(β-D-arabinofuranosyl)-thymine, and 1-(β-D-arabinofuranosyl)-cytosine can be obtained in a high yield by the splitting of the anhydrobond in 2,2′-anhydropyrimidines in dipolar aprotic solvents, such as HMPT, DMF, and DMSO, respectively, in the presence of activated elemental copper.Unlike the formation of cyclopyrimidiens ribonucleosides are directly transformed to the corresponding arabinofuranosyl derivatives by the reaction with diphenylcarbonate and NaHCO3 in the presence of copper. The reaction proceeds probably via an intermediate formation of the cycloproduct. Further aspects on the mechanism are described.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 985-993 
    ISSN: 0021-8383
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A New Method of the Introduction of CF3- and C2F5-Groups into Pyrimidine Derivatives and their Antiherpes ActivityA new method of the perfluoroalkylation of uracil derivatives is described. The irradiation of aqueous solutions of uracil and uracilnucleosides with bis-(perfluoroalkyl) mercury (CnF2n+1)2Hg n = 1, 2 under the exclusion of oxygen in the presence of catalytic amounts of azo-bis-isobutyronitril at 254 nm for several hours gave new 5-perfluoroalkylated compounds. In this way we obtained 5-trifluoromethyluracil (5a), 5-pentafluoroethyluracil (5b), 5-trifluoromethyl-2′-deoxyuridine (6a), 5-pentafluoroethyl-2′-deoxyuridine (6b) and 1-(ß-D-arabinofuranosyl)-5-trifluoromethyluracil (7a) in different yields. The perfluoroalkylated compounds were tested against HSV-1 and HSV-2 viruses on human lungefibroblasts. The compounds are markedly less potent than other known nonfluorinated compounds.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 1787-1798 
    ISSN: 0001-1541
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A correlation is presented for the thermodynamic properties of pure fluids containing small or large molecules. The residual Helmholtz energy is given in terms of perturbed-hard-chain (PHC) theory, extended to polar fluids with a multipolar expansion. The novel feature of this correlation is a separation of the Helmholtz energy into low-density and high-density contributions. The low-density contribution follows from a virial expansion and the high-density contribution from a perturbation expansion. For intermediate densities, a continuous function is used to interpolate between the two density limits. This modification of PHC theory improves agreement with experimental second virial coefficients, vapor pressures, and saturated liquid densities. Since all molecular parameters used here have a well-defined physical significance, they can be reliably estimated for high-molecular-weight-fluids where experimental data are scarce. More important, separation into low-density and high-density contributions allows separate mixing rules for each density region; this flexibility in mixing rules significantly improves representation of mixture properties, as discussed in Part II.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 63 (1901), S. 562-568 
    ISSN: 0021-8383
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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