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161.
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A range of nematogenic materials which incorporate a 2,6-disubstituted naphthyl moiety and a terminal cyano-substituent have been synthesized by using palladium-catalysed cross-coupling procedures involving arylboronic acids and alkynylzinc reagents with aryl iodides, bromides and trifluoromethanesulphonates (triflates). The compounds have very high nematic phase stability, but their melting points are also quite high. The birefringences were measured using an extrapolation technique and the values were found to be between 0·26 and 0·42. 相似文献
164.
Norman Gray. 《Mathematics of Computation》2002,71(237):311-318
In a series of papers, B. C. Carlson produced tables of elliptic integrals, evaluating them in terms of easily computed symmetrical functions, using a group of multivariate recurrence relations. These relations are, however, cumbersome to use by hand and, in the absence of a specific reductive algorithm, difficult to use with computer algebra. This paper presents such an algorithm, guaranteed to reduce a general elliptic integral to a set of fundamental ones.
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O. Gundogdu P.M. Jenneson U. Tuzun G.M. Gray J.N. Hay 《Applied Physics A: Materials Science & Processing》2006,85(3):317-324
Polyviologen polymers are potential template agents for hydrolytic sol–gel processing of silica particles. The resultant polyviologen-silica hybrid nanopowders are amorphous aggregates of roughly spherical shape, which can be harvested from the sol–gel solution and processed to green body products under different environmental conditions. A bench-top X-ray microtomography system, with a spatial resolution of 5 μm is used to produce three-dimensional images of the dynamic processing of the nanopowders. Various processing routes are imaged using a custom built environmental chamber where the temperature, atmospheric pressure, and compaction force can be controlled. This allows processes such as vacuum sintering and microwave sintering to be studied. The three-dimensional images reveal the axial and radial distributions of the molten polyviologen polymer within a matrix of agglomerates of the silica nanoparticles. Such observations are crucial to the optimisation of the processes that are used to produce the green body products so as to preserve desirable nano-intensive properties. PACS 82.35.Np; 87.59.-e; 81.07.Pr; 87.59.Bh 相似文献
167.
A simple method for modelling the textures of liquid-crystalline phases, recently proposed by Bedford et al., is here rewritten in matrix form. A formal similarity is found between their method and the continuum theory of liquid crystals. Disclination patterns are simulated by solving a modified matrix equation. 相似文献
168.
R. P. Chiarello H. You H. K. Kim T. Roberts R. T. Kempwirth D. Miller K. E. Gray K. G. Vandervoort N. Trivedi S. R. Phillpot Q. J. Zhang S. Williams J. B. Ketterson 《Surface science》1997,380(2-3):245-257
We performed in-situ X-ray reflectivity measurements of gold films during sputter deposition on polished silicon substrates. The measurements were performed at several substrate temperatures and under two argon pressures. The gold surfaces were also examined by scanning tunneling microscopy after deposition to obtain their real-space topographic images. These images were used to complement the X-ray reflectivity measurements in determining the effect of argon pressure on the gold surface and its height-height difference functions. An approximation for height-height difference functions was employed to analyze the X-ray reflectivity data. The measured interface width during growth followed a simple power law, consistent with recent theoretical results of dynamic scaling behavior. The scaling exponents, however, do not agree well with predictions based on some models in 2 + 1 dimensions. 相似文献
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Partially degraded (hydroxypropyl)cellulose methanolysates were acetylated in an acetic anhydride/dioxane mixture with a perchloric acid catalyst, yielding (acetoxypropyl)cellulose (APC) samples with an unit ester content per anhydroglucose unit of three. Eight APC samples of molar masses from 10,000 to 1.8 × 105 g/mol were prepared. On heating, all the samples displayed biphasic behavior prior to isotropization. The isotropization temperature of the samples increased rapidly with molar mass, attaining a limiting value of 174°C. The substitution of hydroxyl groups of HPC by acetyl groups lowered the limiting value. Lyotropic mesophases of APC in dimethyl acetamide (DMAc) showed isotropization temperatures that increase nonlinearly with increasing APC concentration. For chains with contour lengths exceeding 72 nm, the critical concentration for mesophase formation, 0, does not depend on the chain length. However, for short chains the 0 value increases rapidly with decreasing chain length. The cholesteric reflection wavelength, λ0, of a thermotropic APC sample of low molar mass is greater than that of a higher molar mass sample at a given temperature and increases with increasing temperature for all samples. Partially acetylated (hydroxypropyl)cellulose displays reflection colors at lower temperatures than the fully acetylated APC. 相似文献