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81.
82.
Nanostructured lanthanum–strontium manganites were synthesized using two different co-precipitation approaches, one in bulk solution, and the other in reverse micelles of CTAB/1-hexanol/water microemulsion. In both cases, precursor cations were precipitated by using oxalic acid. The properties of the materials synthesized by using these two methods were compared in order to reveal potential advantages of the microemulsion-assisted approach. The influence of the annealing conditions on the properties of synthesized manganites was investigated by using X-ray diffraction, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis and magnetic measurements. 相似文献
83.
This work is aimed at the optimization of the yield and purity of non-symmetrical trialkyl sulfonium halide salts. The effects of parameters such as solvent, temperature and concentration were studied. The products were carefully analyzed and the crystal structure of [{n-CH3(CH2)15}(CH3)2S]Br determined. The overall aim of the present study is future syntheses of low-dimensional magnetic materials. 相似文献
84.
《ournal of non Newtonian Fluid Mechanics》2007,141(2-3):148-166
This work deals with the development of a numerical method for simulating viscoelastic axisymmetric free surface flow of an Oldroyd B fluid. A novel formulation is developed for the computation of the non-Newtonian extra-stress components on rigid boundaries and on the symmetry axis. The full free surface stress conditions are employed. The resulting governing equations are solved by finite differences on a Marker-and-cell (MAC) type grid. Validation is provided by simulating a pipe flow problem. The classical die-swell problem is solved and swelling ratios are provided. The height of the splash caused by a falling liquid drop for various Reynolds and Weissenberg numbers is then studied, and the height of the splash is shown to diminish with increasing viscoelasticity. 相似文献
85.
86.
《Tetrahedron: Asymmetry》2006,17(18):2596-2598
Two diversity-driven asymmetric syntheses of a potent NK1 receptor antagonist 1 were achieved. These syntheses provided two complementary approaches that were well positioned for further modifications of several different sites of medicinal chemistry interests in the NK1 structural motifs. The de novo piperidine ring construction approach delivered key intermediates that were best suited for piperidine C4 and C5 SAR investigations. The CNRS method fit well for modifications at C6 and the two exocyclic groups. 相似文献
87.
Methods to synthesize magnetic Fe3O4 nanoparticles and to modify the surface of particles are presented in the present investigation. Fe3O4 magnetic nanoparticles were prepared by the co-precipitation of Fe3+ and Fe2+, NH3·H2O was used as the precipitating agent to adjust the pH value, and the aging of Fe3O4 magnetic nanoparticles was accelerated by microwave (MW) irradiation. The obtained Fe3O4 magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of Fe3O4 crystallites was found to be around 8–9 nm. Thereafter, the surface of Fe3O4 magnetic nanoparticles was modified by stearic acid. The resultant sample was characterized by FT-IR, scanning electron microscopy (SEM), XRD, lipophilic degree (LD) and sedimentation test. The FT-IR results indicated that a covalent bond was formed by chemical reaction between the hydroxyl groups on the surface of Fe3O4 nanoparticles and carboxyl groups of stearic acid, which changed the polarity of Fe3O4 nanoparticles. The dispersion of Fe3O4 in organic solvent was greatly improved. Effects of reaction time, reaction temperature and concentration of stearic acid on particle surface modification were investigated. In addition, Fe3O4/polystyrene (PS) nanocomposite was synthesized by adding surface modified Fe3O4 magnetic nanoparticles into styrene monomer, followed by the radical polymerization. The obtained nanocomposite was tested by thermogravimetry (TG), differential scanning calorimetry (DSC) and XRD. Results revealed that the thermal stability of PS was not significantly changed after adding Fe3O4 nanoparticles. The Fe3O4 magnetic fluid was characterized using UV–vis spectrophotometer, Gouy magnetic balance and laser particle-size analyzer. The testing results showed that the magnetic fluid had excellent stability, and had susceptibility of 4.46×10−8 and saturated magnetization of 6.56 emu/g. In addition, the mean size d (0.99) of magnetic Fe3O4 nanoparticles in the fluid was 36.19 nm. 相似文献
88.
Nanosized Fe0.2Ni0.8 particles were prepared by reducing their salts with sodium borohydride (NaBH4) in cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB) and n-butanol/isooctane at 25 °C. According to the TEM and X-ray diffraction analyses, the synthesized particles were around 4–12 nm in size. Due to their nanodimensions, the particles had a primitive cubic (pc) structure rather than the body-centered cubic (BCC) structure of the bulk material. An examination of the synthesis from the reverse micelle reveals that the morphology of the iron–nickel alloy nanoparticles depends mainly on the microemulsion's composition. The magnetization of the nanoparticles was much lower than that of the bulk material, reflecting the influence of the nanodimensions on the particles’ magnetizations. 相似文献
89.
90.
《Tetrahedron: Asymmetry》2006,17(23):3219-3225
The immobilisation of alcohol dehydrogenase from Lactobacillus brevis (E.C. 1.1.1.2) on an amino-epoxy support (amino-epoxy Sepabeads®) has been investigated with regards to increasing stability under storage and process conditions. After the standard immobilisation procedure resulted in no significant stabilisation, we found a fourfold increase in stability by blocking the remaining functional groups on the enzyme-support preparations with glycine or mercaptoethanol. However, stabilising the multi-point covalent attachment could only be achieved by additionally cross-linking the adsorbed proteins with glutardialdehyde. By this means, we achieved a high stabilisation effect, resulting in a half-life time of over 1200 h when stored at 30 °C. This means a 60-fold increase in stability compared to the soluble enzyme.To determine the operational stability, the enzyme-support preparation was applied to the production of (R)-phenylethanol from acetophenone in a plug-flow reactor, which could be operated for over 10 weeks with an excellent enzyme utilisation. 相似文献