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排序方式: 共有103条查询结果,搜索用时 15 毫秒
1.
NIKITIN S.; PR?TZEL-WOLTERS D. 《IMA Journal of Mathematical Control and Information》1991,8(4):431-439
In 1983 Morse proved, for unknown scalar one-dimensional linearsystems, the nonexistence of rational or polynomial universalstabilizers (UAS). In 1983, Nussbaum gave an example of an analyticUAS. In our paper, it is shown that there exist time-invariantpolynomial UAS's with multidimensional gain adaptation. Thedesign procedure is developed for linear, minimum-phase systemsof relative degree one. Convergence of the closed-loop systemis proved. Some numerical simulations are provided. 相似文献
2.
Xiao Chi Ma Bao Jing Zhang Sha Deng Shan Shan Huang Ke Xin Liu Jing Ming Jia 《中国化学快报》2009,20(3):317-319
A new ent-labdane diterpenoid lactone with a new natural product was isolated from Andrographis paniculata. Their structures were elucidated on the basis of spectral evidences including 2D NMR. 相似文献
3.
V. A. Belyakov V. A. Burdov R. Lockwood A. Meldrum 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1080-1082
Results from our calculations of the electron tunneling rates between silicon nanocrystals are presented. It is shown that
tunnel transitions can be more efficient than radiative interband recombination and substantially influence emission in ensembles
of silicon nanocrystals. 相似文献
4.
5.
N. Grassie J. B. Colford I. G. Meldrum 《Journal of polymer science. Part A, Polymer chemistry》1971,9(10):2817-2834
The rate of polymerization of thiophene, at concentrations of catalyst (SnCl4), and thiophene of the same order as was subsequently used in studying the reaction between thiophene and di(chloromethyl)benzene, is of the order of 10-2%/hr at 30°C. There is no significant self-condensation of DCMB under the same conditions. Since the reaction between thiophene and DCMB is complete at 30°C in minutes rather than hours, it is assumed that self-condensation of thiophene or DCMB during the reaction between them will be negligible and should not influence the course of the reaction or the structure of the resulting polymer. Reaction at 30°C is much too fast for convenient study. A temperature of 0°C is more appropriate and was used in subsequent kinetic work. The first two products of the condensation of p-di(chloromethyl)benzene (DCMB) with thiophene have been identified by a combination of mass, infrared, and nuclear magnetic resonance spectroscopy as thenylchloromethylbenzene (TCMB) and dithenylbenzene (DTB). DCMB, TCMB, and DTB have been estimated quantitatively during the course of the reaction by gas-liquid chromatography (GLC), and it has been established that the rates of each of the two reaction steps is first-order with respect to the chloro compound (DCMB and TCMB respectively), thiophene, and SnCl4. Rate constants for these two consecutive reactions were calculated to be k1 = 2.79 × 10-4l.2/mole2-sec, k2 = 6.37 × 10-3l.2/mole2-sec; the corresponding energies of activation are E1 = 7.93 kcal/mole, E2 = 7°67 kcal/mole. These rate constants are appreciably higher than values previously obtained for the corresponding DCMB–benzene reactions. 相似文献
6.
An alternative approach to synthesize pedamide,a key building block of pederin was described.Iodine-induced asymmetric heterocyclization was used as the key step to construct the skeleton,a tetrahydropyran ring with three chiral centers.Brown's asymmetric allylation and Lewis acid-mediated allylation were investigated to introduce chains and chiral alcohols.Sharpless dihydroxylation decorated the side chain.And high optically pure target was obtained by removing the epimers formed in these reactions on c... 相似文献
7.
A convenient route for the synthesis of 3,4-dihydrocoumarin derivates from salicylaldehyde derivates and 1,3-dicarbonyl compounds under solvent-free microwave irradiation conditions was described. In this way, a range of compounds was obtained in moderate to good yields in a short reaction time. 相似文献
8.
Yuguang Jin Yanqing Tian Weiwen Zhang Sei-Hum Jang Alex K.-Y. Jen Deirdre R. Meldrum 《Analytical and bioanalytical chemistry》2010,398(3):1375-1384
The relationship between bacteria and host phagocytic cells is key to the induction of immunity. To visualize and monitor
bacterial infection, we developed a novel bacterial membrane permeable pH sensor for the noninvasive monitoring of bacterial
entry into murine macrophages. The pH sensor was constructed using 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran
(TCF) as an electron-withdrawing group and aniline as an electron-donating group. A piperazine moiety was used as the pH-sensitive
group. Because of the strong electron-donating and -withdrawing units conjugated in the sensing moiety M, the fluorophore
emitted in the red spectral window, away from the autofluorescence regions of the bacteria. Following the engulfment of sensor-labeled
bacteria by macrophages and their subsequent merger with host lysosomes, the resulting low-pH environment enhances the fluorescence
intensity of the pH sensors inside the bacteria. Time-lapse analysis of the fluorescent intensity suggested significant heterogeneity
of bacterial uptake among macrophages. In addition, qRT-PCR analysis of the bacterial 16 S rRNA gene expression within single
macrophage cells suggested that the 16 S rRNA of the bacteria was still intact 120 min after they had been engulfed by macrophages.
A toxicity assay showed that the pH sensor has no cytotoxicity towards either E. coli or murine macrophages. The sensor shows good repeatability, a long lifetime, and a fast response to pH changes, and can be
used for a variety of bacteria. 相似文献
9.
Poly(trimethylene terephthalate)(PTT) is an excellent fiber material.Its thermal degradation and isothermal crystalline behaviors were in this study investigated using thermogravimetric analysis(TGA),thermogravimetric analysis-Fourier transform infrared spectroscopy(TGA-FTIR) analysis,differential scanning calorimetry(DSC) and X-ray diffraction(XRD).The thermal degradation mechanism of PTT follows Mclafferty rearrangement principle.The PTTwithintrinsicviscosity(Ⅳ) of 0.74 dL/g has a maximum crystallinity... 相似文献
10.
Hetherington NB Kulak AN Sheard K Meldrum FC 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):1955-1958
Single crystals of calcite with regular patterned surfaces comprising close-packed arrays of hemispherical cavities or domes were produced by crystallization on colloidal monolayers or PDMS replicas of these monolayers, respectively. Perfect replication of the substrate topography was achieved for all colloidal particles, irrespective of their size and surface chemistry when the substrate geometry permitted unrestricted ion flow to the growing crystal. This work demonstrates that crystallization within a mould provides a very general route to producing single crystals with curved surfaces and unusual morphologies and that such patterning can be applied from the micro- to the nanoscale. 相似文献