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  • Polymer and Materials Science  (88)
  • Earth Resources and Remote Sensing
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  • 1
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 313-321 
    ISSN: 0887-624X
    Keywords: liquid crystals ; cyanate ; cyclotrimerization ; liquid crystalline thermoset ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid crystalline aromatic monocyanate (M) and dicyanates (D1 and D2) with trans-stilbene (—Ph—CH=CH—Ph—) structure were synthesized and their cyclotrimerization reactions were studied by differential scanning calorimetry and infrared spectroscopy. Monocyanate M underwent cyclotrimerization to yield a trimerized material with discotic properties. Dicyanate D2 and its cured product failed to exhibit any mesophase. In contrast, polycyclotrimerization of dicyanate D1 obtained a liquid crystalline thermoset with its schlieren texture prolonged over a wide temperature range. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 58 (1995), S. 1585-1592 
    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: Polycyclotrimerization of a flexible aromatic dicyanate with a Schiff base structure was studied by means of differential scanning calorimetry (DSC). The study on dynamic DSC evaluated an apparent activation energy (Ea) of 75.8 kJ/mol and autocatalytic first-order kinetics with rate expression Af(α) = 1.96 X 105 (1 + 4.39 α) (1 - α) min-1. The kinetic feature can be explained by a proposed mechanism consisting of hydroxyl-catalyzed and autocatalytic paths. The lower value of Ea compared with other aromatic dicyanates is due to the electron-withdrawing linkage of the inherent imine ( - CH=N) structure. The kinetic feature is affected by the content of the residual impurities (e.g., phenols or absorbed water) in the corresponding sample. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
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  • 3
    Publication Date: 2019-07-13
    Description: Monitoring global agricultural crop conditions during the growing season and estimating potential seasonal production are critically important for market development of US. agricultural products and for global food security. The Goddard Space Flight Center Earth Sciences Data and Information Services Center Distributed Active Archive Center (GES DISC DAAC) is developing an Agricultural Information System (AIS), evolved from an existing TRMM Online Visualization and Analysis System (TOVAS), which will operationally provide satellite remote sensing data products (e.g., rainfall) and services. The data products will include crop condition and yield prediction maps, generated from a crop growth model with satellite data inputs, in collaboration with the USDA Agricultural Research Service. The AIS will enable the remote, interoperable access to distributed data, by using the GrADS-DODS Server (GDS) and by being compliant with Open GIS Consortium standards. Users will be able to download individual files, perform interactive online analysis, as well as receive operational data flows. AIS outputs will be integrated into existing operational decision support systems for global crop monitoring, such as those of the USDA Foreign Agricultural Service and the U.N. World Food Program.
    Keywords: Earth Resources and Remote Sensing
    Type: ASPRS 2005 Annual Convention; Mar 07, 2005 - Mar 11, 2005; Baltimore, MD; United States
    Format: application/pdf
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  • 4
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Modifizierung von Polyacrylnitril wurde durch Bildung von Polyacrylamidoxim und nachfolgende Kondensation mit Ti-, Zr- und Hf-Verbindungen durch Anwendung der Grenzflächentechnik erzielt.Die thermischen Eigenschaften dieser Produkte werden angegeben. Der anfänglich bei 200 bis 350 °C erfolgende Abbau verläuft wahrscheinlich über cyclische Produkte, während der Abbau oberhalb 500°C in Luft durch Oxydation des verbliebenen Produktes erfolgt.
    Notes: The modification of poly(acrylonitrile) was effected via formation of poly(acrylamideoxime) followed by condensation with Ti, Zr and Hf compounds. Modification was effected utilizing generally the interfacial technique.Thermal properties are reported. Initial degradation in the 200 to 350°C region probably occurs via the formation of cyclic products whereas at temperatures 〉500°C degradation in air occurs via oxidation of the remaining product.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 1093-1104 
    ISSN: 0887-6266
    Keywords: EPR ; spin label ; spin probe ; spin relaxation ; correlation time distributions ; electron double resonance ; amorphous polymers ; side group liquid crystalline polymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The motion of nitroxide spin probes and spin labels in amorphous polymers is studied below the glass transition temperature with a two-dimensional pulsed electron double-resonance experiment. Polystyrene and a liquid crystalline side group polymer are studied using both spin probes and spin labels covalently bound to specific sites along the polymer chain. Two methyl acrylic polymers differing only in their side group structure and polyvinylacetate are compared and large differences in the molecular dynamics deduced from both the nuclear and the electron spin relaxation rates are observed as the glass transition is approached. The results demonstrate the complexity of small amplitude motion in simple polymers below the glass transition temperature and show that it is very sensitive to the packing in the polymer. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A detailed study has been made of the rate of take-up of vapors of methylene chloride and acetone by thin films of cellulose acetate (37.9% acetyl) as a function of vapor pressure, film thickness, and temperature. It was found that the method of film preparation and conditioning greatly influenced the kinetics of the take-up. Films, which were not completely dry, exhibit a much faster rate of take-up than dry films. Dry films could he obtained by either long treatment in a vacuum oven, or by water leaching followed by vacuum drying for five days. In either case, identical kinetic results are obtained. The mercury cast films used in this work give reproducible results and show a much slower rate of take-up than a comparable glass cast film.It was found that there was no fundamental difference in the rate of take-up for the vapors of methylene chloride and acetone, although in the liquid state the former is a limited swelling agent, while the latter is a solvent. For both these yapors there is a characteristic pressure above which several anomalies appear, which make a complete quantitative explanation of the data rather difficult. The most important of these anomalies is that, if one plots the amount of vapor taken up as a function of time, an inversion of slope is observed. This inversian is very marked and is a function of film thickness. Another anomaly that appears is that the absolute amount of vapor sorbed for thinner films is greater than that for thicker films for an appreciable time interval. The effect of temperature is complex. Above the pressures where the inversion of a slope occurs, the rate is lower a t higher temperatures for a considerable range of the sorption. These effects cannot be explained on the basis of a generalized diffusion equation with the boundary conditions which have been considered so far, i.e., assuming that the outer film surface is always in equilibrium with the vapor.
    Additional Material: 11 Ill.
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  • 7
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies have been made of sorption and desorption of acetone by films of cellulose nitrate (11 and 12% N) at 30°C. by following the weight of vapor takeup or loss as a function of time. The takeup-time curves show marked inflections and plots of takeup versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt t$\end{document} are initially nonlinear for both sorption and desorption, indicating that Fick's law with the usual boundary conditions is not obeyed. The rate of vapor takeup is also considerably more rapid and different in character for films cast on glass than for films cast on mercury. A striking result is that for successive sorption-desorption cycles the rate of sorption decreases markedly, e.g., by a factor of 16 for five cycles. Studies of the optical anisotropy of the films show that the orientation of the polymer molecules normal to the plane of the film is increased by the diffusion process and it is concluded that this accounts for the decreased rate for successive sorption-desorption cycles and provides an explanation for the diffusion anomalies. A possible cause of this orientation is the observed anisotropic swelling combined with slow movement of the polymer segments.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 21 (1956), S. 554-557 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of water vapor on the rate of diffusion of organic molecules has been studied at 40°C. by the sorption method for the systems water-acetone-polyvinyl acetate, water-carbon tetrachloride-polyvinyl acetate, water-acetone-cellulose acetate (37.9% acetyl) and water-benzene-polystyrene. For the first three systems the rate of diffusion of the organic vapor is markedly faster for the mixture of water and organic vapor than for the pure organic vapor. With polyvinyl acetate, the rate of diffusion of 80 mm. of acetone is increased about 25-fold if 36 mm. of water vapor is mixed with the acetone. Diffusion of the larger carbon tetrachloride molecule is accelerated by water even more than is acetone. Water vapor at a pressure of 36 mm. causes about a 30-fold increase in the rate of diffusion of 80 mm. of acetone into cellulose acetate even though the diffusion of acetone itself into cellulose acetate is anomalous. With polystyrene the presence of water vapor causes no acceleration of the diffusion of benzene which is the expected result since, in contrast to the other two polymers, polystyrene sorbs only very small amounts of water. It is concluded that the marked effect of water vapor on the diffusion of organic vapors into polyvinyl acetate and cellulose acetate involves (a) a rapid diffusion of water into the polymer and (b) more rapid diffusion of the organic vapor into the “water plasticized” polymer than into the dry polymer.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dilute solution viscosity properties of fractions of two linear and one branched sample of polyvinyl acetate in benzene and of two linear and one branched fraction in several solvents were measured at 35°C. Values of total slope, b (from plots of ηsp/c vs. c), and intrinsic viscosities were obtained under the requirement that k′ + β = 0.500 ± 0.002. Empirical plots of log b vs. log [η] gave lines which were straight within the limits of accuracy of the data. For the linear fractions in benzene, Huggins' k′ was constant and the slope of the log b vs. log [η] line was 2; for the branched fractions in benzene, k′ increased with [η] and the slope of the log b vs. log [η] line was greater than 2. The log b vs. log [η] plots form the basis for a “one-point” method for determining [η]. Consideration of these data along with results reported in the literature indicates that k′ is measurably sensitive to branching only for fractions possessing a certain minimum combination of size and complexity. However, in some cases where the variations of k′ are inconclusive, use of the slope of the log b vs. log [η] line may provide a reliable indication of branching. It was found that a comparison between the branched and linear series could also be made at constant values of [η] or b. Two linear fractions in different solvents obeyed a type of Huggins relationship in which k′ did not vary with solvent and the slope of the log b vs. log [η] line was 2. For a higher molecular weight branched fraction, however, k′ varied from solvent to solvent and the slope of the log-log plot was about 1.7. These data do not support a reference point concept of “true” intrinsic viscosity based on a simple linear relationship between b and [η]. Preliminary results dealing with the effects of the shear rate indicated that the measured viscosity properties of branched fractions may be more seriously affected by changes in shear rate than those of linear fractions.
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