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  • Polymer and Materials Science  (9)
  • MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT  (6)
  • 1995-1999  (3)
  • 1990-1994  (12)
  • 1
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 43 (1992), S. 1-7 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Uniaxial gereckte, in der ß-Modifikation vorliegende PVDF-Filme wurden bei anliegendem elektrischen Feld infrarotspektroskopisch untersucht. In bis zu 13 Feldstärkecyclen wurden dabei sowohl die Feldstärke als auch die Richtung des anliegenden Feldes variiert. Die feldinduzierten Frequenzänderungen der Banden bei 445 cm-1 (CF2-rocking) und 510 cm-1 (CF2-bending) wurden detailliert registriert. Modellrechnungen zum Einfluß des Feldes auf die Schwingungsfrequenzen demonstrieren die Möglichkeit, mit Hilfe der Infrarotspektroskopie zwischen entgegengesetzten Dipolrichtungen zu unterscheiden. Die experimentellen Ergebnisse deuten auf die Existenz eines remanenten Feldes in der Probe infolge der Einwirkung des äßeren Feldes hin.
    Notes: Infrared spectra of uniaxially drawn ß-PVDF films under the influence of an electric field were registered. The direction and the strength of the applied field were changed in up to 13 cycles. The field-induced frequency changes of the bands at 445 cm-1 (CF2-rocking) and 510 cm-1 (CF2-bending) were studied in detail. Model calculations concerning the influence of the field on band frequencies are presented revealing the possibility to discriminate by IR spectroscopy between opposite dipole directions. The experimental results suggest the formation of a remanent field in the samples during poling.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 42 (1991), S. 319-322 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In Poly(vinylidenfluorid) (PVDF) kann die Dipoldrehung im elektrischen Feld anhand der Absorptionsänderung der Infrarotbanden bei 445 cm-1 und 510 cm-1 verfolgt werden. Anknüpfend an vorhergehende Untersuchungen wurde an PVDF-Folien mit aufgedampften infrarotdurchlässigen Elektroden ein stufenweise erhöhtes Feld angelegt und das Infrarotspektrum aufgenommen. In Anlehnung an das früher entwickelte Modell wurden die normierten Absorptionen der beiden Banden gegeneinander aufgetragen, wobei sich eine Abweichung vom erwarteten linearen Zusammenhang in der Feldabhängigkeit der Absorption beider Banden zeigte. Interpretiert wird diese Abweichung mit der feldinduzierten Zunahme des Anteils langer Trans-Sequenzen.
    Notes: In poly(vinylidene fluoride) (PVDF) the rotation of the dipoles in an electric field can be followed by the change of the infrared absorption bands at 445 cm-1 and 510 cm-1. Referring to preceding measurements on PVDF foils with evaporated infrared transparent electrodes a stepwise increased field was applied. Following the formerly developed model, the normalized absorptions of both bands were plotted one against the other. A deviation from the expected linear relation in the field dependence of both absorption bands was found. This behaviour is interpreted by an increase of the amount of long trans sequences.
    Additional Material: 4 Ill.
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  • 4
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The aromatic heterocyclic polymer polyoxadiazole is of interest for special applications because of its high thermal stability. Using a laboratory equipment the spinning parameters jet draw rate and plastic drawing have been varied. The effect of spinning conditions on the material parameters elongation at break, tenacity and modulus was investigated. To achieve higher values of tenacity and modulus, a jet draw rate of 2 and plastic drawing ratio of 1.5 to 2.0 were found to be optimal. Also the increase of fibre length at stress-free heating has been studied. With varying jet draw rate and plastic drawing ratio both positive and negative changes of fibre length have been observed. The results are explained by superposition of spontaneous extension and shrinkage.
    Notes: Polyoxadiazol, ein aromatisches heterocyclisches Polymer, ist aufgrund seiner hohen thermischen Stabilität für eine Reihe von Einsatzzwecken interessant. Mit einer Laborspinnanlage wurden die Spinnbedingungen Düsenverzug und Grad der plastischen Reckung variiert und deren Einfluß auf die Materialparameter wie Bruchdehnung, Festigkeit und Modul untersucht. Zur Erreichung höherer Festigkeiten und Moduli erwiesen sich ein mittlerer Düsenverzug von 2 und ein eher niedriger plastischer Reckgrad von 1,5 bis 2 als günstig. Ebenfalls untersucht wurde die Längenzunahme der Fäden bei lastfreier Temperung. Je nach Düsenverzug und plastischem Reckgrad wurden sowohl positive als auch negative Längenänderungen gefunden, die mit der überlagerung von spontaner Dehnung und Schrumpf erklärt werden.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 46 (1995), S. 64-67 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Permittivity ∊′ and dielectric loss ∊″ of novolac have been determined in the temperature interval from  - 150 to 150°C and in the frequency interval from 102.5 to 106 Hz. Novolac exhibits a main and a secondary relaxation process. For the main relaxation a master curve of ∊″ was calculated, the shape of which was described by the Havriliak - Negami function (HN). The parameters of the HN fit were interpreted by a model that relates the values to the polymer structure. Furthermore, the temperature dependence of the dielectric relaxation times was analyzed by a WLF approach for the main relaxation and an Arrhenius approach for the secondary relaxation. The dielectric relaxation times of the main relaxation were correlated with the electrical conductivity and the melt viscosity.
    Additional Material: 4 Ill.
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  • 6
    ISSN: 1057-9257
    Keywords: gallium nitride ; nanocrystallites ; detonation ; gallium azide ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: High quality nanoscale, phase-pure hexagonal gallium nitride (GaN) crystallites have been synthesized by the thermal induced detonation of molecular precursors of the type (R3N)Ga(N3)3 (R=CH3, C2H5, etc.). The method allows the control of the particle size regime from 2 to about 1000 nm. X-ray diffraction and Rietveld simulations revealed an anisotropic platelet-like shape of the particles. The obtained GaN material was as well characterized by transmission electron microscopy and electron diffraction, photoluminescence spectroscopy, SEM, IR, RAMAN, thermal gas effusion/mass spectrometry, thermal analysis, elemental analysis. Gas absorption measurements (BET method) showed a specific surface area of about 90 m2 · g-1. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intact cells of Saccharomyces cerevisiae were examined as an aqueous paste by 13C-nmr spectroscopy with direct polarization and magic-angle spinning. The spectra obtained were highly resolved, showing numerous resonances in the 60-105 ppm range that were assigned to carbons of a liquid-like domain of the cell wall glucan. Assignments were confirmed by running the spectrum of S. cerevisiae in which the cell wall glucans were labeled with [13C] by feeding the cell [13C ] galactose. The spectra indicate that the glucan in the cell wall of intact S. cerevisiae assumes a helical conformation and suggest that strain 17A fed with galactose preferentially incorporates the resulting glucose into β(1 → 3)-linkages. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 29 (1995), S. 619-626 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The mechanisms of wear in ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator-tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet-like flakes from initial machining marks, and the other by the formation of fine ripples and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 9
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2013-08-31
    Description: A top-down image processing scheme is described. A three-dimensional model of a robotic working environment, with robot manipulators, workpieces, cameras, and on-the-scene visual enhancements is employed to control and direct the image processing, so that rapid, robust algorithms act in an efficient manner to continually update the model. Only the model parameters are communicated, so that savings in bandwidth are achieved. This image compression by modeling is especially important for control of space telerobotics. The background for this scheme lies in an hypothesis of human vision put forward by the senior author and colleagues almost 20 years ago - the Scanpath Theory. Evidence was obtained that repetitive sequences of saccadic eye movements, the scanpath, acted as the checking phase of visual pattern recognition. Further evidence was obtained that the scanpaths were apparently generated by a cognitive model and not directly by the visual image. This top-down theory of human vision was generalized in some sense to the frame in artificial intelligence. Another source of the concept arose from bioengineering instrumentation for measuring the pupil and eye movements with infrared video cameras and special-purpose hardware.
    Keywords: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
    Type: NASA, Ames Research Center, Vision Science and Technology at NASA: Results of a Workshop; p 49
    Format: application/pdf
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