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  • 1
    Electronic Resource
    Electronic Resource
    Successional pattern above timberline in south-central Chile (1979)
    Springer
    Plant ecology 40 (1979), S. 39-47 
    Details
    ISSN: 1573-5052
    Keywords: Andes ; Chile ; Pattern analysis ; Succession ; Vulcanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the above-timberline zone of south-central Chile, stepped microtopography commonly develops on slopes of unstable volcanic ash deposits. Between the Nothofagus timberline and the high-altitude sparse fellfields, a scrubgrassland vegetation dominated by prostrate shrubs such as Empetrum rubrum and Pernettya spp. and tussock grasses such as Hierochloe utriculata and Cortaderia pilosa characteristically occurs on the stepped microtopography. Species interactions and species-microtopography interactions during the course of succession on the recent volcanic deposits were investigated by means of pattern analysis. Scales of pattern associated with individual plant morphology and interspecific interactions are present but, in general, the scales of pattern attributed to environmental variation are more evident. Cyclic changes occur in the scrub-grassland under the influence of periodic burial by the unstable ash substrate and the life cycles of the dominant prostrate shrubs. Such cyclic changes are part of a long-term linear successional trend following disturbance by catastrophic vulcanism. In contrast to the basic assumption of classic successional theory, in both the short-term and long-term the physical habitat in the above-timberline zone of south-central Chile is fundamentally unstable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00052013
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  • 2
    Electronic Resource
    Electronic Resource
    Catastrophic influences on the vegetation of the Valdivian Andes, Chile (1978)
    Springer
    Plant ecology 36 (1978), S. 149-167 
    Details
    ISSN: 1573-5052
    Keywords: Andes ; Catastrophic events ; Chile ; Colonization ; Fire ; Forest structure ; Nothofagus forest ; Succession ; Vulcanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In association with a devastating earthquake in 1960, thousands of debris avalanches, landslides, and mudflows occurred in the Andes of south-central Chile. Catastrophic mass movements associated with seismic activity have affected the Andes of south-central Chile several times in the past 400 years and have profoundly influenced the regional vegetation. The most widespread forest types in the Andean Cordillera of the Province of Valdivia (latitude 39°25′ to 40°40′ S) are dominated byNothofagus spp. andEucryphia cordifolia and characteristically have an intermediate layer of shade-tolerant trees. These forest types represent relatively early successional phases following forest destruction by catastrophic phenomena. The supporting evidence for this interpretation includes: (1) the nature of the colonization of the surfaces exposed by the 1960 mass movements, (2) the structure of the existing forest vegetation, (3) the ecological characteristics of the dominant trees, and (4) the historical frequency of similar catastrophic events in the Andes of south-central Chile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02342598
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  • 3
    Electronic Resource
    Electronic Resource
    Thermal analysis of polydimethylsiloxanes. I. Thermal degradation in controlled atmospheres (1969)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 7 (1969), S. 537-549 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermogravimetric analyses (TGA) of catalyst-free polydimethylsiloxanes (PDMS) have been carried out in controlled atmospheres and a kinetic analysis of the results has enabled the various decomposition processes to be separated and identified. The calculated activation energy for thermal depolymerization is 42 ± 3 kcal/mole, while thermo-oxidation has an apparent activation energy of 30 ± 2 kcal/mole. Quantitative analyses of the major degradation products and molecular weight distribution studies of the residues from degradation studies under isothermal conditions have shown that in vacuo, PDMS fractions depolymerize to cyclic dimethylsiloxanes and low molecular weight linear residues by a randomly initiated mechanism which, it is postulated, involves the formation of an intramolecular, cyclic, four-centered transition state followed by siloxane bond rearrangement. This mechanism is a basic property of linear PDMS fractions and is independent of molecular weight. Molecular weight distribution (MWD) changes observed from further isothermal investigations on hydroxy endblocked PDMS fractions, have shown the presence of a chain-lengthening process in vacuo below the depolymerization temperature. This process, with an apparent activation energy of 8.6 ± 1 kcal/mole, is attributed to the intermolecular condensation of terminal hydroxyl groups.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1969.160070308
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal analysis of polysiloxanes. II. Thermal vacuum degradation of polysiloxanes with different substituents on silicon and in the main siloxane chain (1970)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 1823-1830 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermogravimetric (TG) investigations of various substituted polysiloxanes of the type \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm R}_1 {\rm R}_2 {\rm SiO\rlap{--} )}_n $\end{document} have been carried out in vacuo and the activation energies for the depolymerization processes calculated from the resulting thermograms. (R1 and R2 are methyl, ethyl, n-propyl, trifluoropropyl, or phenyl.) It is postulated that the activation energy is mainly a function of the inductive effect of the substituent group and that electron-withdrawing groups attached to silicon increase the activation energy, whereas electron-donating groups decrease it. A linear relation is found between the Taft constant σ* for the substituent on silicon and the calculated activation energy for depolymerization. Product analysis results from isothermal degradations indicate that the degradation mechanism in a silmethylene siloxane polymer and a silethylene-siloxane polymer is very similar to that in polydimethylsiloxanes (PDMS). For the \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} ({\rm R}_1 {\rm R}_2 {\rm SiO\rlap{--} )}_n $\end{document} polymers, the amount of cyclotrisiloxane in the degradation products increases with the size of the substituent on silicon, and it is postulated that the rate of depolymerization is mainly influenced by short-range steric interactions between the substituents on the silicon atoms of the siloxane chain.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1970.160081016
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  • 5
    Electronic Resource
    Electronic Resource
    The monomer tert-butyl p-vinylperbenzoate (TBVP): Free-radical polymerization, crosslinking, and grafting (1974)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 12 (1974), S. 2957-2960 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1974.170121222
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  • 6
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    High-performance light-emitting diodes based on carbene-metal-amides (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-04-15
    Description: Organic light-emitting diodes (OLEDs) promise highly efficient lighting and display technologies. We introduce a new class of linear donor-bridge-acceptor light-emitting molecules, which enable solution-processed OLEDs with near-100% internal quantum efficiency at high brightness. Key to this performance is their rapid and efficient utilization of triplet states. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs within 350 nanoseconds at ambient temperature, after reverse intersystem crossing to singlets. We find that molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, so that rapid interconversion is possible. Calculations indicate that exchange energy is tuned by relative rotation of the donor and acceptor moieties about the bridge. Unlike other systems with low exchange energy, substantial oscillator strength is sustained at the singlet-triplet degeneracy point.
    Keywords: Physics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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