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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 29 (1973), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The significance of root pressure in the transport of xylem sap has been investigated in Cocos nucifera L. and a few other palms. Despite the fact that excised palm roots can generate considerable pressures in situ, the quantity of water transported is only a small fraction of the demand resulting from transpiration. Most water transport is induced by negative pressure gradients, as in other higher plants. The development of considerable negative pressures has been demonstrated both directly and indirectly.Acoustic detection was used for the first time to monitor cavitation in water-stressed Cocos leaves. Its detection implies the ready disruption of xylem sap under these tensions. We suggest that root pressure might serve to refill cavitated xylem conduits when water is abundantly available and transpiration practically zero. However, little or no positive pressure could be demonstrated in intact palms subjected to low water stress: experimentally.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The amounts of vitamin D usually produced in the intact human skin are unknown. Ultraviolet irradiation of the skin cures childhood rickets4"7; in this case endogenous production must be at least equivalent to the minimum curative dietary dose of 200-400 lu daily8. Extrapolation of these results to ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2072
    Keywords: Monkey ; Behavior ; Nicotine ; d-Amphetamine ; Caffeine ; Cannabinol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects in squirrel monkeys of nicotine, d-amphetamine, caffeine and dimethylheptyl tetrahydrocannabinol have been examined in three standard behavioral procedures: Fixed Interval, Fixed Ratio and Continuous Shock Avoidance, and two procedures developed to test neuromuscular performance: Physical Activity and Steadiness. Nicotine increased responding in the first half of Fixed Intervals and in Continuous Avoidance; d-amphetamine increased responding under all procedures except Physical Activity; caffeine increased responding under all procedures except Fixed Ratio and DMHP increased responding under all procedures except Continuous Avoidance, where responding was reduced. Nicotine and d-amphetamine caused disruption in the Physical Activity procedure. Thus the different procedures revealed different aspects of the behavioral effects of the drugs. Findings are consistent with interpretation that it is the temporal pattern of the responding under the different procedures that is the dominant factor in determining the behavioral effects of the drugs.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 8 (1970), S. 2141-2151 
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Low molecular weight poly(ethylene terephthalate) samples were crystallized isothermally at 120-245°C from both the amorphous state and the melt. Isothermal annealing of these polymers at 215°C provided polymers which exhibited multiple melting peaks in thermal analysis, referred to as form I and form II, as assigned by Bell and Dumbleton. In these samples the peak temperature of the form II melting endotherm and the average crystallite size are dependent on the temperature of initial crystallization. This result requires a mechanism for retaining some structural feature during the conversion from morphological form I to form II. DSC thermograms obtained at varying heating rates on samples showing only form II endotherms support the assignment of superheating as the cause of the shift to higher peak temperatures with increasing heating rate.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 1671-1682 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An understanding of the physical and chemical processes involved in the melt polymerization of polyesters in the higher inherent viscosity ranges is of fundamental importance in polyester preparation. For example, the volatile condensation product must diffuse to a polymer-vapor interface before polymerization can take place. Thus, the rate of polymerization of a polyester may be dependent not only upon the chemical kinetics of the polymerization reaction but also upon the diffusion of the condensation product through the polymer melt. The objective of the work presented in this paper was to determine to what degree diffusion or reaction kinetics, or both, limit the melt polycondensation of poly(ethylene terephthalate). Degrees of polymerization in melts between 0.0285 and 0.228 cm in depth at 270°C were measured for various reaction times and were compared with the predictions of mathematical models. The polycondensation rates under these conditions depend upon both the polycondensation rate constant k1 and the diffusivity D of ethylene glycol through the melt. Estimates of the values to these parameters are: k1 = 0.0500 (moles/mole of repeat unit)-1 sec-1; D = 1.66 × 10-4 cm2/sec.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 9 (1971), S. 931-948 
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantitative analyses of the products of thermal degradation of poly(ethyl acrylate), poly(n-propyl acrylate), poly(n-butyl acrylate) and poly(2-ethylhexyl acrylate) have been made, principally by the combined application of GLC and mass and infrared spectroscopy. Data are recorded in mass balance tables. The major gaseous products are carbon dioxide and the olefin corresponding to the ester group. The minor gaseous products include the corresponding alkane, the alkane/olefin ratio being of the order of 10-2-10-3, and traces of carbon monoxide and hydrogen. The alcohol corresponding to the alkyl group is the major liquid product but there are also traces of monomer and the corresponding methacrylate. Alcohol production exhibits autocatalytic properties. The chain fragment fractions of the products are colored yellow and have average chain lengths of 3.2, 3.3, 3.6, and 5.6 for the ethyl, n-propyl, n-butyl and 2-ethylhexyl esters, respectively. The infrared spectra are similar to those of the parent polymers but with well defined differences. Insolubility develops in the ethyl, n-propyl, and n-butyl esters, but the residual material from poly(2-ethylhexyl acrylate) remains soluble even at very advanced stages of degradation. All of these products and reaction characteristics are accounted for in terms of radical reactions with a unique initiation step.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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