Crystallization of alkyl-aromatic polyimides (polyalkanimides)

Polyalkane imides based on 3,3′,4,4′-diphenyloxidetetracarboxylic, pyromellitic and 1,4,5,8-naphthalenetetracaboxylic acids, and aliphatic diamines containing 4, 6, 8, 10, or 12 methylene groups have been studied. Relations governing the effect of structure on solubility, heat resistance, density, and crystallizability have been established. Conformation analysis has been carried out and models of the macromolecules have been constructed. The morphology of the crystalline polymers has been studied. For the polymers of the given class, crystallization capability is shown to be associated with the conformational flexibility of the macromolecular unit determining a given acid moiety by the number of methylene groups in the diamine unit.     

缺项样条插值(Ⅰ)

[1] proved that S_n(x) was uniquely determined, and gave the error bounds of approximation of f(x) ∈C~4 [0,1] by S_n(x). B. K. Swartz and R. S. Varga [2] also gave the degree of approximation of f(x) ∈C~6 [0, 1] by S_n(x). Z. R. Guo [3] obtained the saturation theorem for this approximation. Z. R. Guo [4-5] were also concerned in this kind of interpolation and gave the degree of approximation. In this paper we consider the general lacunary interpolation by quintic splines.     

Fluorescence fluctuation spectroscopy and its artifacts: simulations and tests

Fluorescence fluctuation spectroscopy (FFS)[1,2] is a kind of fluorescence detection techniques suitable for monitoring interaction and transportation processes in a small detection zone of biological systems. FFS detects and analyzes the fluorescence signal of the fluorescent molecules in the detection zone to retrieve the dynamical parameters of the system including concentration, diffusion coefficient and interaction constants. FFS utilizes various statistical methods to analyze the data,…     

Heating-induced micelle to vesicle transition in the cationic-anionic surfactant systems: Comprehensive study and understanding

Heating-induced micelle to vesicle transition (MVT), which has been rarely reported in surfactant systems, was systemically studied in a number of mixed cationic-anionic surfactant systems. According to the turbidity measurements, the investigated systems can be divided into two classes: Class A and B. Heating-induced MVT was observed in Class A at certain total surfactant concentrations and mixed surfactant ratios, while no such transition was found in Class B. Further investigations revealed that the heating-induced MVT is more likely to take place in the cationic-anionic surfactant systems with relatively stronger molecule interaction and larger micelle aggregation number. The effects of several physicochemical factors, such as the variation of mixed surfactant ratios and the addition of n-decanol on the heating-induced MVT, were also studied.     

Novel one-pot total syntheses of deoxyvasicinone, mackinazolinone, isaindigotone, and their derivatives promoted by microwave irradiation

[reaction: see text]. Total syntheses of deoxyvasicinone (1), mackinazolinone (2), and 8-hydroxydeoxyvasicinone (3) via novel microwave-assisted domino reactions, as well as a novel three-component one-pot total synthesis of isaindigotone (5) promoted by microwave irradiation, are reported. The efficient reaction process enabled us to rapidly access related natural product derivatives and to identify a new class of cytotoxic agents.     

Iron-catalyzed propylene epoxidation by nitrous oxide: studies on the effects of alkali metal salts

SBA-15-supported iron catalysts with and without alkali metal salt modifications were studied for propylene oxidation by nitrous oxide. The reaction route could be dramatically changed from allylic oxidation to epoxidation by modification of the FeOx/SBA-15 catalyst with alkali metal salts. The KCl-1 wt % FeOx/SBA-15 (K/Fe = 5) catalyst exhibited the best catalytic performances for propylene epoxidation, over which ca. 50% propylene oxide selectivity could be gained at a 10% propylene conversion at 648 K. Characterizations with diffuse reflectance UV-Vis, XANES, and Raman spectroscopic techniques revealed that the modification with KCl increased the dispersion of the iron species and changed the local coordination of iron into a tetrahedral configuration on the inner surface of SBA-15. This tetrahedrally coordinated iron site, which was probably stabilized by potassium ions, was proposed to account for the epoxidation of propylene by nitrous oxide. At the same time, the reactivity of lattice oxygen was inhibited, and the acidity of the FeOx/SBA-15 was eliminated. These changes should also contribute to the increase in the selectivity to propylene oxide. The counteranions in the alkali metal salts exerted a significant influence on the catalytic behaviors probably via an electronic effect.     

High-accuracy optical clock via three-level coherence in neutral bosonic 88Sr

An optical atomic clock scheme is proposed that utilizes two lasers to establish coherent coupling between the 5s2 1S0 ground state of 88Sr and the first excited state, 5s5p 3P0. The coupling is mediated by the broad 5s5p 1P1 state, exploiting the phenomenon of electromagnetically induced transparency. The effective linewidth of the clock transition can be chosen at will by adjusting the laser intensity. By trapping the 88Sr atoms in an optical lattice, long interaction times with the two lasers are ensured; Doppler and recoil effects are eliminated. Based on a careful analysis of systematic errors, a clock accuracy of better than 2 x 10(-17) is expected.     

Hybrid optoelectronic bistability in a fiber Bragg grating by use of a tunable fiber laser

We report the observation of hybrid optoelectronic bistability in a fiber Bragg grating (FBG) by use of an electro-optically tuned cw fiber laser in which another wavelength-matched FBG is employed to constitute a tunable resonant cavity. The potential application of such a device as a fiber-optic sensor is also discussed.