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  • 1
    Electronic Resource
    Electronic Resource
    Molecular stress and strain in an oriented extended-chain polymer of finite molecular length (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 6161-6174 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00122a025
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructural Characterization of Crosslinkable p-Phenylene Terephthalamide-Terephthalic Acid Derivative Copolymer Fibers (1994)
    s.l. : American Chemical Society
    Macromolecules 27 (1994), S. 6507-6514 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00100a040
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  • 3
    Electronic Resource
    Electronic Resource
    The Gassiot Committee of the Royal Society and Meteorological Research (1961)
    [s.l.] : Nature Publishing Group
    Nature 190 (1961), S. 212-213 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN 1871, Mr. John Peter Gassiot conveyed to the Royal Society £10,000 of Italian Irrigation Bonds for the purpose of assisting magnetical and meteoro logical observations with self-recording instruments, primarily in the Kew Observatory. The Society set up its Gassiot Committee in the same ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/190212a0
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  • 4
    Electronic Resource
    Electronic Resource
    Maximum-entropy data restoration using both real- and Fourier-space analysis (1989)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 45 (1989), S. 686-698 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An extension of the maximum-entropy (ME) data- restoration method is presented that is sensitive to periodic correlations in data. The method takes advantage of the higher signal-to-noise ratio for periodic information in Fourier space, thus enhancing statistically significant frequencies in a manner which avoids the user bias inherent in conventional Fourier filtering. This procedure incorporates concepts underlying new approaches in quantum mechanics that consider entropies in both position and momentum spaces, although the emphasis here is on data restoration rather than quantum physics. After a fast Fourier transform of the image, the phases are saved and the array of Fourier moduli are restored using the maximum-entropy criterion. A first-order continuation method is introduced that speeds convergence of the ME computation. The restored moduli together with the original phases are then Fourier inverted to yield a new image; traditional real-space ME restoration is applied to this new image completing one stage in the restoration process. In test cases with various types of added noise and in examples of normal and high-resolution electron-microscopy images, dramatic improvement can be obtained from two to four stages of iteration, even in cases where traditional ME restoration provides little improvement. It is shown that in traditional Fourier filtering spurious features can be induced by selection or elimination of Fourier components without regard to their statistical significance. With the present approach there is no such freedom for the user to exert personal bias, so that features present in the final image and power spectrum are those which have survived the tests of statistical significance in both real and Fourier space. However, it is still possible for periodicities to 'bleed' across sharp boundaries. An 'uncertainty' relation is derived describing the inverse relationship between the resolution of these boundaries and the level of noise that can be eliminated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767389005970
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  • 5
    Electronic Resource
    Electronic Resource
    Absorption Spectrum of Cobaltous Chloride in Deuterium Oxide (1938)
    [s.l.] : Nature Publishing Group
    Nature 142 (1938), S. 756-756 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SMALL differences in the colour of solutions of copper sulphate and silver permanganate when dissolved in deuterium oxide instead of ordinary water have been reported by Bell1, and Hein and Bähr2 respectively. Displacement of the absorption lines in the spectrum of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/142756a0
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  • 6
    Electronic Resource
    Electronic Resource
    A multi-slit spectrograph and Hα Doppler system (1974)
    Springer
    Solar physics 37 (1974), S. 343-350 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A multiple entrance slit spectrograph was built for time-lapse photography of the spectra of flares and other transient solar phenomena. This spectrograph employs narrow-band filters to limit the wavelength range of the spectrograph to several angstroms centered at Hα or other spectral lines. The passband of the filter, and the dispersion of the spectrograph determine the number of parallel slits through which light may be passed to achieve multiple adjacent spectral displays. By using a 7 Å filter, a dispersion of 10.8 Å mm−1, and 35 mm film, adjacent Hα spectra are imaged from 30 parallel slits. A system of mirrors and relay lenses transfers the slitjaw image to the same film plane as the spectral image. A 2 frame camera is used to simultaneously record both images on adjacent frames. Filtering of the reference spatial image to 1.0 Å allows the observer to see the position of the slits relative to the Hα centerline structure and to match the brightness of the spatial image to the spectral display. A polarizing beamsplitter, prior to the slits, provides a prefiltered second solar image to a narrow band Hα Doppler filter for simultaneous photography in the wings of the Hα line. The multislit monochromatic spectrograph and Hα Doppler system constitute a flexible instrument in which components may be substituted to achieve different passbands width, image scales, dispersions and corresponding numbers and spacings of adjacent spectra at a selected wavelength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152493
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  • 7
    Electronic Resource
    Electronic Resource
    UNESCO and Trieste (1974)
    [s.l.] : Nature Publishing Group
    Nature 252 (1974), S. 629-629 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR,?Your leader of November 8 was critical of the line you thought the United Kingdom would be taking on the question of the International Centre for Theoretical Physics, Trieste, at the recent 18th General Conference of UNESCO, and attributed this probable attitude largely to Sir Harold Thompson ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/252629a0
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  • 8
    Electronic Resource
    Electronic Resource
    Micromechanisms of kinking in rigid-rod polymer fibres (1991)
    Springer
    Journal of materials science 26 (1991), S. 5171-5183 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The tensile strengths of fibres of the rigid-rod polymers poly(paraphenylene benzobisthiazole) (PBZT) and poly(paraphenylene benzobisoxazole) (PBZO) are excellent, and therefore are of particular interest for high-performance structural applications. However, these fibres are a factor of ten weaker in compression, with failure occurring by strain localization in welldefined kink bands. Here, we study the morphology of PBZT and PBZO kink bands in detail, in order to help elucidate the molecular mechanisms involved in this deformation process. We found that the typical dimensions of a kink in the direction of the fibre axis (∼ 30 nm) were smaller than the length of an average PBZT or PBZO molecule (100 nm). Also, the boundary between the kinked and unkinked regions was well-defined. Low-dose, high-resolution electron microscopy (HREM) of the kink interior revealed local, high-angle changes in chain orientation, indicative of covalent bond bending or breaking. The kink boundaries exhibit “sharp” or “smooth” features which seem to be related to the local tensile or compressive nature of the stress field. A model for kink nucleation and propagation in terms of partial dislocations is presented and discussed. A stress analysis using this model has been developed, and comparison with experimental data suggests that kinks tend to propagate towards regions of higher compressive stress. This observation is interpreted in terms of dislocation pinning (in areas of hydrostatic tension) and the nucleation of dislocation pairs (in areas of hydrostatic compression) due to the asymmetric nature of the intermolecular energy potential. Finally, practical methods for improving compressive strength based on these mechanistic insights are proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01143210
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  • 9
    Electronic Resource
    Electronic Resource
    Microstructure and mechanical properties ofin-situ network composite fibres of PBZT with nylon (1991)
    Springer
    Journal of materials science 26 (1991), S. 2365-2371 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A method for preparing composite fibres by infiltrating nylon into swollen poly(p-phenylene benzobisthiazole) (PBZT) fibre is described. PBZT fibre forms a microfibrillar network structure during the coagulation process.In-situ network composite (IC) fibres may be prepared by exchanging the coagulant with a solution containing the desired matrix material. These new composite fibres exhibit nearly identical mechanical properties and similar thermomechanical properties to those of so-called molecular composite (MC) fibres prepared from isotropic solutions of PBZT and nylon in methane sulphonic acid (MSA), The mechanical properties of these fibres were determined before and after heat treatment under tension. The structure of pure PBZT and its composite fibres (ICs' and MCs') were characterized using nitrogen adsorption (Brunauer-Emmett-Teller (BET) experiments), small-angle X-ray scattering, and scanning and transmission electron microscopy (SEM and TEM, respectively). The structure of both composite fibres was found to be a microfibrillar network of PBZT in a matrix of amorphous nylon. The average diameters of the PBZT microfibrils were in the range of 10 to 20 nm forin-situ network composites and approximately 4 nm for molecular composites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01130183
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  • 10
    Electronic Resource
    Electronic Resource
    The compressive deformation of cross-linkable PPXTA fibres (1997)
    Springer
    Journal of materials science 32 (1997), S. 2291-2303 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A study has been conducted on the compressive deformation behaviour of thermally cross-linkable poly(p-1,2-dihydrocyclobuta phenylene terephthalamide) (PPXTA) fibres. The morphology of the failure zones was examined by scanning electron microscopy and dark-field transmission electron microscopy. On increasing the heat-treatment temperature from 260–400°C, and therefore with increasing cross-link density, fewer kinks per unit length were displayed after compressive deformation. The kink specific energy was estimated to increase by a factor of 30, as determined by quantitative measurements of kink density at a given strain and of the critical strain to kink formation. Thus, the intermolecular cross-links still allowed deformation to proceed by kinking, but significantly raised the energy of kink formation. Finally, rupture zones were predominantly observed in axially compressed PPXTA fibres heat-treated at 440°C. Compressive failure of the fibres changed from kink-dominated failure to brittle rupture with increased heat-treatment temperature, evidently as the result of cross-linking or of chain degradation. A dislocation model of the kink boundary developed by Vladimirov et al. was analysed and critically compared with our data. The analysis of this theory with our experimental results suggested that the dramatic change in compressive behaviour with cross-linking was due to a transition from fine intermolecular shear to blocky interfibrillar shear.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018528401426
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