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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 29 (1995), S. 191-200 
    ISSN: 1572-9680
    Keywords: windbreaks ; shelterbelt ; wind ; model ; specific protection efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effectiveness of windbreaks in windspeed reduction is often evaluated without regard to the objects to be protected. In fact, many objects may have different sensitivities to wind and often require different degrees of wind protection. Since commonly used indexes do not consider the sensitivity to wind, a concept of specific protection efficiency is developed. A critical windspeed is used to represent the sensitivity of each object. Windspeeds greater than this value are considered damaging. A dimensionless protection index is defined to evaluate windbreak efficiency. The maximum index value is 1 for the highest protection, and the index is negative when sheltered windspeed is greater than the critical windspeed. This index can be compared, summed, and averaged across different windbreaks, objects, and leeward locations. A sample of critical windspeed values was compiled from the literature. The index was evaluated using actual wind data measured under both sheltered and open conditions. The results indicated that the index can be used for evaluating windbreak effectiveness in terms of objects protected under various conditions. This model could be used as a tool for windbreak-related research and policy making.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 32 (1995), S. 297-311 
    ISSN: 1572-9680
    Keywords: relative windspeed reduction ; shelterbelt ; windbreaks ; windspeed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Windspeed reduction in shelter is generally expressed relatively and is usually assumed to be independent of open windspeed. The purpose of this study was to re-examine the relationship between open windspeed and windspeed reduction in shelter using windspeeds and wind directions measured for two windbreak systems at various distances from the windbreaks and with three windbreak porosities. Optical windbreak porosities were estimated from digitized color photographs using an intelligent (trainable) image processing program. Relative windspeed reduction in shelter was found to be related to the open windspeed. There existed a threshold windspeed at approximately 5 m s−1, below which relative windspeed reduction varied but generally decreased as the open windspeed increased. Above the threshold windspeed, open windspeed did not have an effect on relative windspeed reduction in the sheltered zone. Using the threshold windspeed reduction, the authors propose an index to evaluate the effectiveness of a windbreak for the overal windspeed protection.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 23 (1983), S. 394-398 
    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 mechanical behavior of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks (PUR/PAc IPN's) was investigated. Stress-strain and impact resistance measurements were made on IPN's with a variable PUR content. The effect of the degree of crosslinking of each network on the mechanical properties was also studied. It appears that only the ultimate elongation varies largely upon changing the crosslink degree. The results are interpreted in terms of the contribution of each network to the mechanical behavior, but also by the interpenetration of both components and by the phase continuity of the PAc network.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 17 (1977), S. 803-805 
    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: Star-shaped block copolymers were used as heat activated adhesives in glass to glass joints. The branches consisted in either AB or ABA poly(styrene-b-isoprene) block copolymers. Tensile shear strengths of simple lap joints were measured for star block copolymers differing in the length or in the number of branches. Values higher than those of the corresponding linear species were obtained. These results were related to the presence of chemical junction points created by coupling the linear copolymers.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 12 (1974), S. 133-140 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spontaneous imidization of acrylamide during polymerization has been studied in three media: benzene, diglyme, and water. The data indicate that neither medium, time, nor temperatures below 140°C cause imidization to occur. The ascription of the low nitrogen found in polyacrylamide by some investigators to imide formation appears to be in error. The low nitrogen is due rather to retained solvent and/or water, for which polyacrylamide has a strong affinity. Imidization may be brought about by strong acids. The solubility of an imidized polyacrylamide decreases with increasing imide content.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 18 (1980), S. 2217-2225 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structural evolution with temperature of an anionically synthesized ABA poly(styrene-b-isoprene) (SIS) lamellar block copolymer (total molecular weight 45,000; isoprene content 38% by weight) was studied by melt-rheological measurements, electron microscopy, and x-ray and light diffraction. Above 225°C, the dynamic viscosity was found to be independent of frequency up to a critical frequency. The variation of the elastic modulus confirmed the occurence of a transition between 215 and 225°C. For the temperature range considered, all results superimposed well on a two-branch master curve. It was concluded that above 225°C, our SIS behaves like a Newtonian material, whereas for lower temperatures and/or higher frequencies classical non-Newtonian behavior is found. The melt-rheological properties were explained by microscopy and diffraction investigations, which allowed us to follow morphological changes as the temperature was raised. It was found that the two-phase lamellar structure is progressively destroyed, and the transition temperature of 225°C corresponds to the temperature above which complete mixing occurs.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 20 (1982), S. 389-398 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The glass transition behavior of two sets of ABA poly(styrene-b-isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperatures Tg of the corresponding homopolymers. This shift increases for the rigid-phase Tg as the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only one Tg were found. The third Tg was interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 11 (1973), S. 3037-3042 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It was reported earlier that the copolymerization of acrylamide and styrene is strongly affected by the copolymerization medium. The effect was attributed to a change in the polarity of the ethylenic bond in the acrylamide monomer due to hydrogen bonding and/or dipole - dipole interaction, depending on the medium. In view of those findings, it was suggested that absolute values for the reactivity ratios for the copolymerization of these two monomers might be obtained only when the acrylamide monomer is unperturbed. Copolymerizations of these monomers at a number of ratios, therefore, were done in benzene, which does not undergo hydrogen bonding and has no dipole moment, at high dilution, when amide - amide interactions between acrylamide molecules should be essentially eliminated. The values of r1 and r2(M1 = acrylamide) were 9.14 ± 0.27 and 0.67 ± 0.08, respectively. There appears to be some indication in this system that high dilution adversely affects the reactivity of the acrylamide monomer while enhancing that of styrene. This aspect requires more study.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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