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  • 1
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    Variability of the Intermediate Atlantic Water of the Arctic Ocean over the Last 100 Years (2004)
    American Meteorological Society
    Details
    Publication Date: 2004-12-01
    Description: Recent observations show dramatic changes of the Arctic atmosphere–ice–ocean system, including a rapid warming in the intermediate Atlantic water of the Arctic Ocean. Here it is demonstrated through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century Atlantic water variability was dominated by low-frequency oscillations (LFO) on time scales of 50–80 yr. Associated with this variability, the Atlantic water temperature record shows two warm periods in the 1930s–40s and in recent decades and two cold periods earlier in the century and in the 1960s–70s. Over recent decades, the data show a warming and salinification of the Atlantic layer accompanied by its shoaling and, probably, thinning. The estimate of the Atlantic water temperature variability shows a general warming trend; however, over the 100-yr record there are periods (including the recent decades) with short-term trends strongly amplified by multidecadal variations. Observational data provide evidence that Atlantic water temperature, Arctic surface air temperature, and ice extent and fast ice thickness in the Siberian marginal seas display coherent LFO. The hydrographic data used support a negative feedback mechanism through which changes of density act to moderate the inflow of Atlantic water to the Arctic Ocean, consistent with the decrease of positive Atlantic water temperature anomalies in the late 1990s. The sustained Atlantic water temperature and salinity anomalies in the Arctic Ocean are associated with hydrographic anomalies of the same sign in the Greenland–Norwegian Seas and of the opposite sign in the Labrador Sea. Finally, it is found that the Arctic air–sea–ice system and the North Atlantic sea surface temperature display coherent low-frequency fluctuations. Elucidating the mechanisms behind this relationship will be critical to an understanding of the complex nature of low-frequency variability found in the Arctic and in lower-latitude regions.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 2
    Electronic Resource
    Electronic Resource
    Thermal and X-ray investigations of ethylene-α-olefin copolymers obtained with highly active supported Ti-Mg and V-Mg catalysts (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 33 (1994), S. 111-114 
    Details
    ISSN: 0959-8103
    Keywords: copolymers ; ethylene ; α-olefins ; transition metal catalysts ; thermal stability ; crystallization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Copolymers of ethylene with propylene, butene-1 and hexene-1 were prepared using a titanium-magnesium (TMC) or a vanadium-magnesium catalyst (VMC). The copolymers were examined for thermal stability by TGA, melting and crystallization behaviour by DSC and crystallinity by XRD. Fractionated samples of ethylene-hexene-1 copolymers were also similarly characterized. Results indicate that VMC produces copolymers with a higher degree of crystallinity and greater compositional homogeneity than TMC.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pi.1994.210330113
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Kinetic study of ethylene polymerization with chromium oxide catalysts by a radiotracer techniquePaper presented to the Symposium on Macromolecular Chemistry, Budapest, August 1969. (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 9 (1971), S. 3129-3146 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quenching of polymerization with a chromium oxide catalyst by radioactive methanol 14CH3OH enables one to determine the concentration of propagation centers and then to calculate the rate constant of the propagation. The dependence of the concentration of propagation centers and the polymerization rate on reaction time, ethylene concentration, and temperature was investigated. The change of the concentration of propagation centers with the duration of polymerization was found to be responsible for the time dependence of the overall polymerization rate. The propagation reaction is of first order on ethylene concentration in the pressure range 2-25 kg/cm2. For catalysts of different composition, the temperature dependence of the overall polymerization rate and the propagation rate constant were determined, and the overall activation energy Eov and activation energy of the propagation state Ep were calculated. The difference between Eov and Ep is due to the change of the number of propagation centers with temperature. The variation of catalyst composition and preliminary reduction of the catalyst influence the shape of the temperature dependence of the propagation center concentration and change Eov.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.150091104
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  • 4
    Electronic Resource
    Electronic Resource
    Dependence of reactivity of propagation centers of oxide catalysts for ethylene polymerization on catalyst composition and activation conditionsPresented to the Symposium on Macromolecular Chemistry, Budapest, August 1969. (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 9 (1971), S. 771-784 
    Details
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The propagation rate constant Kp was used as a measure of reactivity of propagation centers in ethylene polymerization with oxide catalysts. This constant was determined by a radiotracer quenching technique for oxide catalysts of different compositions and activation conditions. For catalysts based on various transition metal oxides, an increase of Kp was observed in the series W 〈 Mo 〈 Cr and V 〈 Cr. In the case of chromium oxide catalyst it was shown that Kp value does not depend on the content of the transition metal in a catalyst. A change of propagation center reactivity was found when oxides of different composition (SiO2, Al2O3, ZrO2, TiO2) were used as supports. An increase of the vacuum activation temperature of a catalyst results in increasing Kp. Pretreatment of catalyst with different reducing agents (SO2, CO2, NH3, HCN) results in the change of Kp value in comparison in comparison with the catalyst activated by the vacuum treatment only. The data obtained on the variation of the reactivity of the propagation centers permit one to draw a conclusion about the composition of surface compounds as acitve centers of the oxide polymerization catalysts.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.150090315
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