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  • Polymer and Materials Science  (5)
  • selection function  (2)
  • 73.60  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Hydrogen sulphide doping of GaAs and AlxGa1−xAs grown by molecular beam epitaxy (MBE) (1985)
    Springer
    Applied physics 36 (1985), S. 147-151 
    Details
    ISSN: 1432-0630
    Keywords: 68.55 ; 73.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract H2S gas has been used during molecular beam epitaxy (MBE) growth of GaAs and Al x Ga1−x As as sulphur vector forn-type doping. Doping efficiencies are less than 10−3 at usual growth temperatures, and are limited by an incorporation competitive surface process, probably 2Ga+H2S→Ga2S+H2. In AlxGa1−x As forx≧0.2 the doping efficiency is further reduced by carrier freeze-out at deep levels. Measured thermal activation energies depend on growth conditions and remain relatively low even up to the direct-indirect bandgap crossover for substrate temperatures in the 585–645
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00624935
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  • 2
    Electronic Resource
    Electronic Resource
    Using selection functions to describe changes in environmental variables (1995)
    Springer
    Environmental and ecological statistics 2 (1995), S. 225-237 
    Details
    ISSN: 1573-3009
    Keywords: environmental monitoring ; selection function ; natural selection ; EMAP ; environmental assessment ; fitness function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The selection function (which shows how the frequency of sampling units with the value X = x at one point in time must change in order to produce the distribution that occurs at a later point in time) is proposed for describing the changes over time in an environmentally important variable X. It is shown that the theory of selection functions as used in the study of natural selection and resource selection by animals requires some modifications in this new application and that a selection function is a useful tool in long-term monitoring studies because all changes in a distribution can be examined (rather than just changes in single parameters such as the mean), and because graphical presentations of the selection function are easy for non-statisticians to understand. Estimation of the selection function is discussed using a method appropriate for normal distributions and bootstrapping is suggested as a method for assessing the precision of estimates and for testing for significant differences between samples taken at different times. Methods are illustrated using data on water chemical variables from a study of the effects of acid precipitation in Norway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00456670
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  • 3
    Electronic Resource
    Electronic Resource
    Using selection functions to describe changes in environmental variables (1995)
    Springer
    Environmental and ecological statistics 2 (1995), S. 225-237 
    Details
    ISSN: 1573-3009
    Keywords: environmental monitoring ; selection function ; natural selection ; EMAP ; environmental assessment ; fitness function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The selection function (which shows how the frequency of sampling units with the value X = x at one point in time must change in order to produce the distribution that occurs at a later point in time) is proposed for describing the changes over time in an environmentally important variable X. It is shown that the theory of selection functions as used in the study of natural selection and resource selection by animals requires some modifications in this new application and that a selection function is a useful tool in long-term monitoring studies because all changes in a distribution can be examined (rather than just changes in single parameters such as the mean), and because graphical presentations of the selection function are easy for non-statisticians to understand. Estimation of the selection function is discussed using a method appropriate for normal distributions and bootstrapping is suggested as a method for assessing the precision of estimates and for testing for significant differences between samples taken at different times. Methods are illustrated using data on water chemical variables from a study of the effects of acid precipitation in Norway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00456672
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of pressure-induced structural changes on the ionic conductivity of zwitterionic polymers (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 359-363 
    Details
    ISSN: 0887-6266
    Keywords: zwitterionic polymers ; ionic conductivity ; dielectric properties ; a.c. spectroscopy ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In this investigation, ionic conductivity measurements are performed on N-oxide polymers neutralized with NaOH. The polymer samples were conformed in disk shapes using an Instron machine considering various values of the pressure required to compact the samples. The dielectric properties of these systems were obtained by the a.c. spectroscopy technique. Results indicate a substantial variation in the ionic conductivity due to the pressure-induced structural changes on the morphology of these samples, as confirmed by WAXS studies. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320218
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  • 5
    Electronic Resource
    Electronic Resource
    Crosslinking of plasticized poly(vinyl chloride) by substitution and free radical reaction (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 61 (1996), S. 1251-1257 
    Details
    ISSN: 0021-8995
    Keywords: 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: Two new methods to obtain crosslinking plasticized poly(vinyl chloride) (PVC) are shown. One is by the substitution reaction of PVC with the sodium salt of γ-mercaptopropyl trimetoxysilane and the other is by the free-radical reaction of azide-modified PVC with γ-acryloxypropyltrimetoxysilane and vinyltri(2-metoxyetoxy)silane. The content of gel and the number average molecular weight between crosslinking (Mc) were determined by Soxhlet extraction and by using the Flory-Rehner equation. The reactions of PVC with the above organosilanes under normal processing conditions of the polymer lead to high gel contents and, therefore, low Mc. The ultimate tensile strength and elongation at break at 110°C of these polymers are greatly enhanced over those of the uncrosslinked polymer. The results are improved compared to those taken from literature for similar systems. © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Crystalline modifications of cellulose. Part IV. Determination of x-ray intensity data (1960)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 42 (1960), S. 165-171 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intensities of x-ray reflections from ordered regions of Cellulose I (ramie) an Cellulose II (Fortisan) have been determined by photometering the x-ray diagrams. The results are reported as intensities of resolvable reflections, to provide a basis for comparison with postulated crystal structures to be described in Part V of this series. In many cases reflections from several crystallographic planes could not be resolved and the total intensity for the group of reflections is given. This procedure does not make full use of the experimental results; the factors which would have to be taken into account in a more complete interpretation of the data are discussed.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1960.1204213919
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  • 7
    Electronic Resource
    Electronic Resource
    Orientation in nylon spherulites: A study by X-ray diffraction (1962)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 60 (1962), S. 1-20 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A microbeam x-ray diffraction method has been used to study orientation in spherulites grown from the melt of nylon 66 and in one case of nylon 610. It is concluded that in positively birefringent spherulites the crystallographic a axis is parallel to the spherulite radius. The zigzag extinction pattern shown by such spherulites in a polarizing microscope can be understood in terms of this orientation. The results on negatively birefringent spherulites are not in agreement with earlier results of Keller and it is suggested that further work on such spherulites is desirable. Evidence is cited which shows that zero birefringent spherulites have random orientation. The spheruloids or spheruloidal aggregates which grow at the same time as negatively birefringent spherulites are found to have well defined optical properties when grown in thin films and confused optical properties when grown in thick film. This difference is reflected in differences in the x-ray diagrams. In thin films a unique orientation exists in which a direction close to the crystallographic b axis lies parallel to the radius while the (002) plane lies near the surface of the film. This orientation provides an explanation of the observed optical properties. In thick film the (002) plane again tends to lie near the surface of the film, but orientation relative to the radius varies from place to place, thus causing confused optical properties.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1962.1206016901
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  • 8
    Electronic Resource
    Electronic Resource
    Crystallinity and the structure of celluloses (1963)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A: General Papers 1 (1963), S. 671-685 
    Details
    ISSN: 0449-2951
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Observations on the x-ray scattering by ball-milled cellulose and cellulose derivatives, amorphous oligosaccharides, and Fortisan H are reported and an approximate shape is established for the scattering curve of the noncrystalline component of celluloses. Using this shape measurements have been made of the minimum crystallinity which is consistent with the observed x-ray diagram of regenerated cellulose.From a comparison of this minimum crystallinity with crystallinity determined by the infrared-deuteration method, it is concluded that at least 14% of the total material cannot be truly described as either perfectly crystalline or perfectly amorphous. This fraction of material of intermediate order is registered as crystalline by x-ray diffraction, but infrared spectroscopy suggests that it does not possess the precise molecular configuration characteristic of crystalline material. Support for this view of structure is reported from observations of differences in hydrogen-bonding in amorphous regions of regenerated and bacterial celluloses. Infrared results show that OH groups which lie in the surface of crystallites are hydrogen-bonded in a random amorphous manner and it is concluded that the material of intermediate order can be accounted for in terms of chains lying in the surface of crystallites of cross-section 29 A. × 65 A.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1963.100010208
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