Summary Some extension of Haldane's multivariate median is carried out by minimization principle of a specified distance function.
Then, making use of the median, three types of measures of multivariate skewness are introduced and their asymptotic null
distributions are obtained. 相似文献
A series of chiral benzylidene-aniline compounds, 4-alkoxybenzylidene 4′-(2-methylbutyloxycarbonyl)anilines, have been synthesized and their mesomorphic properties are examined. They showed a monotropic chiral smectic C phase in conjunction with enantiotropic smectic A phase, and their chiral smectic C—smectic A phase transition temperatures are around room temperatures. Their spontaneous polarization values are moderately higher than those of DOBAMBC “4-decyloxybenzylidene 4′-amino-(2-methylbutyl)cinnamate”. 相似文献
Cellulose - A bleached softwood kraft pulp was phosphorylated with (NH4)2HPO4 and urea at 150 ℃ for 0‒40 min, and the structures and properties of the resulting... 相似文献
Mechanical, thermal and oxygen barrier properties of regenerated cellulose films prepared from aqueous cellulose/alkali/urea
solutions can be markedly improved by controlling the drying conditions of the films. By pre-pressing followed by vacuum drying
under compression, the tensile strength, Young’s modulus, coefficient of thermal expansion and oxygen permeability of the
dried films reached 263 MPa, 7.3 GPa, 10.3 ppm K−1 and 0.0007 ml μm m−2 day−1 kPa−1, respectively. Thus, films produced in this way show the highest performance of regenerated cellulose films with no orientation
of cellulose chains reported to date. These improved properties are accompanied by a clear increase in cellulose II crystallinity
from 50 to 62% during pre-pressing/press-vacuum drying process. At the same time, the film density increased from 1.45 to
1.57 g cm−3, and the moisture content under equilibrium conditions decreased from 14.1 to 9.8%. Hence, the aqueous alkali/urea solvent
system has potential applications in producing new and environmentally friendly cellulose films with high performances through
control of the drying conditions. 相似文献
Dried cotton linters and ramie cellulose samples were oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/NaBr/NaClO and NaBr/NaClO (i.e., TEMPO-free) in water at pH 10. The carboxy contents, degrees of polymerization (DPs), X-ray diffraction patterns, and solid-state 13C NMR spectra were measured or obtained for the oxidized products with and without subsequent NaBH4 reduction. Cellulose nanofibrils were prepared from the oxidized cellulose samples by sonication in water and observed by atomic force microscopy and transmission electron microcopy. Because the cellulose molecules were depolymerized with NaBr/NaClO, the depolymerization behavior of the cellulose samples with TEMPO/NaBr/NaClO can be mainly explained by depolymerization with NaBr/NaClO (i.e., not TEMPO-related compounds or reactions). However, because C6-aldehydes formed in the disordered regions periodically present along the longitudinal direction of each cellulose microfibril, the viscosity-average DP values of the TEMPO/NaBr/NaClO-oxidized cellulose samples decreased to 200–300, while those with subsequent NaBH4 reduction exhibited much higher DP values. The nanofibrils prepared from the TEMPO/NaBr/NaClO-oxidized cellulose samples had smallest fibril heights or widths of 5–6 nm. However, significant amounts of unfibrillated bundles with heights of 10–40 mm were present in the nanofibril/water dispersions. The high carboxy contents of the TEMPO/NaBr/NaClO-oxidized cellulose samples (1.62–1.63 mmol/g) indicated that significant amounts of carboxy groups were likely present in the disordered regions, probably forming tail-like polyglucuronate chains. Solid-state 13C NMR analysis revealed that some of the glucosyl units originally with the tg C6–OH conformation were transformed to other conformations by TEMPO/NaBr/NaClO oxidation, while the crystalline C4 signal areas remained constant.
