仿瓷胶粘剂的研究

本文介绍一种仿瓷环氧胶粘剂,该胶耐酸耐碱,可室温固化,在室温下粘接不锈钢试样,其剪切强度可达30.7MPa;而在130℃时其剪切强度为1.7MPa。可用于修复搪瓷,粘接金属和陶瓷等。     

Thermal decomposition of ammonium sulphate

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     

Noise equivalent count measurements in a neuro-PET scanner with retractable septa

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.     

The degradation in tensile strength of polymer-coated glass optical fibres under γ-irradiation

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.     

The formation of β′-sialon from a montmorillonite-polyacrylonitrile composite by carbothermal reduction: an NMR,TGA, XRD and EM study

The products of carbothermal reduction in N₂ of a nanocomposite between dodecylammonium-exchanged montmorillonite and polyacrylonitrile (PAN) have been studied by solid-state ²⁷Al and ²⁹SiNMR spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetry. Comparison with analogous reactions involving sodium-exchanged montmorillonite and dodecylammonium-exchanged montmorillonite (without PAN) shows that in the presence of PAN, the formation of silica, cordierite or mullite is almost completely suppressed. The only crystalline phase detected between 1000 and 1300 °C was a -sialon, having a much higher SiAl ratio (7.051) than that of the precursor clay (2.441). Reduction of the octahedral AlO₆ begins near 1200 °C, forming increasing amounts of Al(N,O)₄ tetrahedra with temperature, so that by 1600 °C, complete reduction to AlN₄ (i.e. bulk AlN) has occurred. In contrast, reduction of the tetrahedral SiO₄ is appreciable at 1100 °C, and is almost complete (SiN₄ tetrahedra only) by 1200 °C. No intermediate Si(N,0)₄ environments are found. By 1600 °C, only the SiC₄ environment (i.e. bulk SiC) remains. A mechanism is suggested, involving the formation of alternating slabs of an amorphous aluminosilicate and carbon at 1000 °C, followed by diffusion of silicon from the outer regions of the aluminosilicate band towards the centre, and sequential reduction of Si(OSi)₄ and Si(OSi)₃ (OAl) groups.     

Fabrication and characterization of thin films with perpendicular magnetic anisotropy for high-density magnetic recording

Perpendicular magnetic anisotropy (PMA) was first observed in thin films of cobalt-chromium alloys in 1974, and perpendicular magnetic recording was proposed in 1977. After less than ten years, a new technology for high-density magnetic recording is firmly established. This breakthrough of the science and technology of magnetic recording has been made possible mainly through the ingenuity and concerted efforts of Iwasaki and other researchers. The preparation, characterization, and application of the Co-Cr films featuring PMA have been extensively studied. This paper reviews the large number of reports on PMA films with emphasis in three areas: (1) processing of PMA films; (2) correlation of magnetic properties and microstructures of PMA films; and (3) state-of-the-art techniques for fabricating PMA films.Nomenclature PMA Perpendicular magnetic anisotropy - PMR Perpendicular magnetic recording - B Magnetic induction - H Magnetic field - H _c Coercivity - H _c, Perpendicular coercivity - H _d Demagnetizing field - H _K Anisotropy field - H Perpendicular anisotropy constant - M _r Remanent magnetization - M _s Saturation magnetization - P _Ar Argon pressure - T _s Substrate temperature - V _b Substrate bias voltage - Incidence angle - ₅₀ Half-width dispersion angle in the rocking curve - _c Curie temperature - _o Internal stress     

Augmented Online Sequential Quaternion Extreme Learning Machine

Neural Processing Letters - Online sequential extreme learning machine (OS-ELM) is one of the most popular real-time learning strategy for feedforward neural networks with single hidden layer due...     

Finite Time Synchronization of Delayed Quaternion Valued Neural Networks with Fractional Order

Neural Processing Letters - In this article, the finite time (FT) synchronization problem of fractional order quaternion valued neural networks with time delay is investigated. Without separating...