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991.
W.Wade Adams Robert M. Briber Edward S. Sherman Roger S. Porter Edwin L. Thomas 《Polymer》1985,26(1):17-26
The microstructure of a series of solid state extruded polyethylene fibres was examined by wide- and small-angle X-ray scattering. By measuring absolute intensities using a two dimensional position sensitive detector, accurate values of the small-angle invariant for anisotropic samples were obtained. This measurement coupled with wide-angle X-ray scattering and d.s.c. permitted determination of the density of the noncrystalline component. The use of a two phase model for solid state extruded polyethylene is justified if consideration is given to the effective densities of the crystalline and noncrystalline phases, which change with deformation. The effective density of the crystalline phase decreases by 1% (0.999–0.990 g cm?3) from the unextruded billet compared to a 36 draw ratio extrudate, while the noncrystalline phase density increases by 6% (0.84–0.89 g cm?3). These changes lead to an overall decrease in the mean squared electron density fluctuation of 63%. The average axial crystallite length measured by wide-angle X-ray scattering increases with extrusion draw ratio while the SAXS long period decreases and weakens considerably. These observations and the electron microscopy results from the previous paper, (Polymer, 1982, 23, 1069), are fully consistent with the key features of the Peterlin model of fibre microstructure. 相似文献
992.
993.
W. D. Halstead 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1970,20(4):129-132
The thermal decomposition and vaporisation of ammonium sulphate, (NH4)2SO4, is shown to take place via two distinct sets of reactions. In the first, ammonium pyrosulphate, (NH4)2S2O7, is the primary condensed phase product: 2(NH4)2SO4 ← (NH4)2S2O7+2NH3+H2O The second stage concerns the decomposition of the pyrosulphate. Ammonia, sulphur dioxide, nitrogen and water are the major products, the dominant reaction being 3(NH4)2S2O7 ← 2NH3+6SO2+2N2+9H2O 相似文献
994.
The hyperfiltration of chromic plating rinse water, which contains a special type of surfactant, was examined using different annealed CA membranes. At low concentrations the surfactant influences the volume flow more than the rejection. An effect of the electrolytes can be neglected at low concentration. Increasing surfactant concentration as well as rising electrolyte concentration cause a remarkable drop of both volume flow and electrolyte rejection. This was measured with tetraethylammonium perfluoroctanolsulfonate, a commonly used surfactant for chromic plating. 相似文献
995.
Branched-chain/cyclic alkanes have been obtained, by solvent extraction and molecular-sieve adsorption, from a UK low-temperature (Rexco) coal tar, a USA fluidized-bed pyrolysis (FMC COED) coal tar, and a novel supercritical-gas-extract of a Turkish (Elbistan) lignite. Mass spectrometry (with gas chromatography and field-desorption) established the presence of mono-, di (including sesquiterpanes), tri-, tetra- (steranes only), and pentacyclic (triterpanes only) alkanes, including several steranes and triterpanes not previously reported as coal-tar constituents. The potential of cyclic alkanes as geochemical markers, even for commercial coal products subjected to appreciable heat treatment, is demonstrated by the identification of C12, C13, C15 and C16 dicyclics (including isoprenoid alkanes), C17-C26 tricyclics, and C27 and C29 hopane-type pentacyclics (triterpanes) in FMC, and of C16-C38 monocyclics, C34-C36 dicyclics, C22-C36 tricyclics, C27-C30 tetracyclics (steranes), and C27, C29, C30, C31, C32, and C33 hopane-type pentacyclics (triterpanes) in Rexco tar. Tetra- and pentacyclic alkanes were also preserved in the lignite extract. 相似文献
996.
Poly (2,2-bithienyl-5,5-diylvinylene) (PBTV) films formed by anodic oxidation of 2×10–3 M solutions of trans-1,2-di(2-thienyl)-ethylene (trans-DTE) in acetonitrile were studied by voltammetry and ellipsometry. For the doped and undoped films, refraction indices and absorption coefficients in the wavelength range of 400–800 nm were determined as functions of thickness. Differences in the structure were found depending on the height of the oxidation potential. A decrease in thickness by doping was observed and is discussed in terms of a possible cis-trans isomerization. The optical spectrum of the undoped polymer showed a high degree of -electron delocalization (high degree of conjugation).This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday. 相似文献
997.
Bailey DL Jones T Spinks TJ Gilardi MC Townsend DW 《IEEE transactions on medical imaging》1991,10(3):256-260
The noise-equivalent count-rate (NEC) performance of a neuro-positron emission tomography (PET) scanner has been determined with and without interplane septa on uniform cylindrical phantoms of differing radii and in human studies to assess the optimum count rate conditions that realize the maximum gain. In the brain, the effective gain in NEC performance for three-dimensions (3-D) ranges from >5 at low count rates to approximately 3.3 at 200 kcps (equivalent to 37 kcps in 2-D). The gains of the 3-D method assessed by this analysis are significant, and are shown to be highly dependent on count rate and object dimensions. 相似文献
998.
999.
1000.
The tensile strength of glass optical fibres when coated with various polymers has been measured as a function of -ray dose. Fibres protected with acrylate, silicone + acrylate or polyimide coatings showed little degradation after receiving a total dose of 1 MGy (they retained >95% of their preirradiated strength). For a fibre with an extruded nylon overcoat the nylon became very brittle after 0.5 MGy, but as far as could be assessed, the strength of the central glass fibre was little affected. Two other types of fibre, both protected with fluorinated polymers, were severely weakened after 0.1 MGy (their tensile strength being reduced to < 40% of their pre-irradiated strength). Experimental results are given supporting the hypothesis that the degradation results from gaseous fluorine-containing species chemically attacking the surface of the glass fibre. 相似文献