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  • 1
    Electronic Resource
    Electronic Resource
    Influence of krummholz mat microclimate on needle physiology and survival (1987)
    Springer
    Oecologia 73 (1987), S. 82-90 
    Details
    ISSN: 1432-1939
    Keywords: Timberline ; Krummholz ; Microclimate ; Picea engelmannii ; Abies lasiocarpa ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Microclimate and photosynthesis of krummholz mat growth forms of Picea engelmanii (Parry) and Abies lasiocarpa [Hook.] Nutt. were investigated to determine structural features which may aid survival in alpine environments. The structure of krummholz mats was described in terms of the vertical distribution of leaf area index and leaf area density, which exceeded 50 m-1 (based on total leaf surface area) near the canopy surface and approached zero below 30 cm from the surface in both species. Photosynthetic photon flux density (PPFD, 0.4–0.7 μm wavelengths) and wind decreased by an average of 6 and 50-fold, respectively, between 1 m above and 10 cm below mat surfaces in both species. Needle temperatures on a P. engelmannii krummholz mat during July averaged about 2°C above air temperature during the day, with a maximum overtemperature of greater than 20°C above T air during one sunlit period. At night, needle temperatures averaged 3–4°C below T air. Net photosynthesis in year-old P. engelmannii shoots reached a maximum at 15–20°C during July and August. Surface shoots were light saturated at near 1200 μmoles m-2s-1 PPFD, and had higher photosynthetic rates than subsurface, predominantly shaded shoots above 800 μmoles m-2s-1. Shade shoots had higher photosynthetic rates when PPFD was below 600 μmoles m-2s-1, and at 250 μmoles m-2s-1 shade shoots maintained about 50% of the net photosynthetic rate of sun shoots at light saturation. Shade shoots appeared capable of benefitting photosynthetically from elevated temperatures within krummholz mats despite relatively low light levels. Especially rapid photosynthesis may occur when canopy needles are illuminated by sunflecks and needle temperatures rise by 10° C or more. Snow cover appears crucial for the survival of needles during winter. Snow accumulated within krummholz needle canopies before the sub-canopy zone of unfoliated branches became filled. The concentrated needle growth in the krummholz canopy captured snow in early autumn without support from ground-level snowpack. Early snow cover in both species prevented cuticle abrasion and resulted in high winter needle water contents and viabilities for subsurface compared to surface needles which became abraded, severely dehydrated, and had high mortality between December and February, especially on windward sides of shoots. Extremely high concentrations of needles within krummholz mat canopies created an aerodynamic structure which elevated needle temperatures to more optimal photosynthetic levels in summer and resulted in more efficient snow accumulation in winter. These factors appear crucial for winter needle survival. Thus, krummholz mats appear to be an important adaptation in growth form which provides survival benefits in both summer and winter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376981
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of cold soil and snowcover on photosynthesis and leaf conductance in two Rocky Mountain conifers (1989)
    Springer
    Oecologia 80 (1989), S. 546-552 
    Details
    ISSN: 1432-1939
    Keywords: Soil temperature ; Photosynthesis ; Picea engelmannii ; Pinus contorta ; Roots ; Snow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influence of cold soil and snowcover on photosynthesis and conductance of Picea engelmannii and Pinus contorta was investigated early in the growing season in the Medicine Bow Mountains, Wyoming, USA. Trees of both species growing in cold soil (〈1°C) associated with snowpack had 25–40% lower leaf photosynthesis than trees in warm soils (〉10°C). In cold soils leaf conductance of both species was lower, but more so in Pinus, leading to lower intercellular CO2 concentrations and greater stomatal limitation of photosynthesis. Soil temperature had no effect on predawn and midday shoot water potentials of Pinus and Picea and lower photosynthesis and conductance did not appear to be a result of lower bulk shoot water potential. Predawn, as well as midday, water potentials of Pinus were consistently higher than Picea suggesting that Pinus may have deeper roots, although trenching experiments indicated young Picea trees have more extensive lateral root systems than similar sized Pinus trees. Young Picea trees (〈2 m in height) in snowbanks were capable of utilizing warmer soil 4 m from their base. Under similar conditions Pinus in snowbanks had lower photosynthesis and conductance than controls and Pinus did not appear capable of utilizing warmer soils nearby. Under full sunlight, PPFD reflected from the snow surface was 400–1400 μmol m-2 s-1 higher than from snow-free surfaces. This reflected light resulted in a 10%–20% increase in photosynthesis of Picea. The beneficial effect of reflected light was apparent whether or not photosynthesis was reduced by low soil temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380080
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  • 3
    Electronic Resource
    Electronic Resource
    Chromatographic investigation of the oxygen exchange reaction between carbon monoxide and carbon dioxide (1974)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 20 (1974), S. 762-770 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The theory of perturbation chromatography and isotopic tracers has been applied to the investigation of the oxygen exchange reaction between carbon monoxide and carbon dioxide in the presence of a copper-zinc oxide catalyst at 205°C and atmospheric pressure. By analyzing the retention times of carbon-14 monoxide and carbon-14 dioxide tracers in six binary carbon monoxide/carbon dioxide carrier gas streams, it has been possible to shed light on the mechanism of the exchange reaction. Two types of carbon monoxide adsorption and two types of carbon dioxide adsorption were identified. Based on a numerical simulation of the experimental data, it has been concluded that the exchange reaction proceeds via the dissociative adsorption of carbon dioxide. Furthermore, the surface oxygen species formed during the dissociative adsorption of carbon dioxide appears to be the active site for the exchange reaction.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690200418
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  • 4
    Electronic Resource
    Electronic Resource
    A static vapor pressure apparatus for mixtures (1967)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 13 (1967), S. 590-593 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A static vapor pressure apparatus is described which is especially suitable for mixtures. A vapor pressure flask with a built-in condenser allows the mixture to be degassed without change in composition. The entire apparatus is assembled from simple parts. Equilibrium is rapidly attained with either an external pressure or a liquid of known vapor pressure used as a reference.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690130334
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  • 5
    Electronic Resource
    Electronic Resource
    Photoelastic phenomena in plastics during impact (1962)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 2 (1962), S. 237-242 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: The study of strain patterns in deformed, transparent plastic placed between crossed Polaroids can shed considerable light on the responses of these plastics to stress. This article describes a study of the differing responses of three thermoplastics of varying degrees of toughness to the notched Izod impact test. The growth and waning of the strain patterns during impact are followed by means of high-speed cinematography; interpretation of the phenomena thus observed is aided by thin section microscopy of partially deformed specimens.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760020312
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