排序方式: 共有89条查询结果,搜索用时 31 毫秒
81.
Various routes to a variety of azridine‐2‐carboxylates have been described and the stereochemistry of these compounds has been determined by spectroscopic methods. Further, greater diversity of β‐lactams via ring expansion of these azridines‐2‐carboxylates were obtained by a general, efficient and direct stereospecific approach. 相似文献
82.
83.
A novel biologically active flavonol glycoside (1), C26H28O17, m.p. 216-217 degrees C, was isolated from the chloroform soluble fraction of the ethanol extract of the stems of Teramnus labialis. Its structure was characterized as 3,5,7,3',4',5'-hexahydroxyflavone-3-O-beta-D-glucopyranosyl(1-->3)-O-alpha-L-arabinopyranoside by spectral analysis. The chloroform extract of compound (1) showed antibacterial and antifungal activities. 相似文献
84.
Shivani Pandey Tripti Vimal Dharmendra Pratap Singh Swadesh Kumar Gupta Prachi Tripathi Chinmay Phadnis 《Liquid crystals》2013,40(12):1811-1820
Cd1?xZnxS/ZnS core/shell-structured quantum dot (QD)-doped ferroelectric liquid crystal (FLC) Felix 17/000 has been investigated in the present study. In the SmC* phase, the effect of QD on the dielectric and electro-optical properties of FLC has been studied as a function of dopant concentration. A substantial change in the different parameters like tilt angle, spontaneous polarisation, response time and relative permittivity has been observed for the composite system. Nearly two times faster response of the composite system with lower operating voltage is one of the promising results of the present study. The faster optical response along with the decreased value of spontaneous polarisation can be utilised in low power consumption liquid crystal displays. 相似文献
85.
The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated. An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field, with linear absorption and due to saturation effects for arbitrary large intensity. The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters. Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode. Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence. The beam is more focussed at lower intensity in both cases viz. extraordinary and ordinary mode. 相似文献
86.
Kaushlendra Agrahari Govind Pathak Rohit Katiyar Geeta Yadav Tripti Vimal Shivani Pandey 《Molecular Crystals and Liquid Crystals》2017,652(1):195-205
Dielectrics, polarizing optical microscopic and electro-optical measurements have been carried out on a core/shell quantum dot Cd1?xZnxS/ZnS dispersed ferroelectric liquid crystal (FLC). In the present study, quantum dots were dispersed into two different concentrations of 0.1 and 0.25 wt./wt.% in pure FLC. The electro-optical parameters of pure and QDs dispersed FLC were carried out as a function of applied voltage. A significant improvement in optical response time of QDs dispersed FLC system is one of the major finding of the present study which may be useful for fabrication of faster liquid crystal system. 相似文献
87.
Shivani Suri K. K. Bamzai Vishal Singh 《Journal of Thermal Analysis and Calorimetry》2011,105(1):229-238
Non-isothermal kinetic parameter of pure and cadmium-doped barium phosphate single crystal grown by room temperature solution
technique have been investigated. Single crystal X-ray diffraction establishes grown crystal to be orthorhombic in nature.
Scanning electron microscopy supplemented with energy dispersive X-ray analysis was used to study the surface features and
to find the exact stoichiometric composition of the grown crystal. Fourier transform infrared spectroscopy studies confirm
the presence of various functional groups. The effect of cadmium doping on pure barium phosphate single crystal was studied
using thermogravimetry analysis. Thermogravimetry studies shows that the pure crystal was stable up to a temperature of 330 °C
whereas doped crystal was stable up to a temperature of 240 °C, i.e., pure crystals were more stable than doped ones. Various
solid-state reaction kinetics, i.e., activation energy (E
a), frequency factor (Z), and entropy (ΔS*) was calculated out to find the mechanism of thermal decomposition at different stages for pure and cadmium doped barium
phosphate. 相似文献
88.
Laser-induced acoustic desorption (LIAD) combined with ClMn(H(2)O)(+) chemical ionization (CI) was tested for the analysis of nonpolar lipids and selected steroids in a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). The nonpolar lipids studied, cholesterol, 5α-cholestane, cholesta-3,5-diene, squalene, and β-carotene, were found to solely form the desired water replacement product (adduct-H(2)O) with the ClMn(H(2)O)(+) ions. The steroids, androsterone, dehydroepiandrosterone (DHEA), estrone, estradiol, and estriol, also form abundant adduct-H(2)O ions, but less abundant adduct-2H(2)O ions were also observed. Neither (+)APCI nor (+)ESI can ionize the saturated hydrocarbon lipid, cholestane. APCI successfully ionizes the unsaturated hydrocarbon lipids to form exclusively the intact protonated analytes. However, it causes extensive fragmentation for cholesterol and the steroids. The worst case is cholesterol that does not produce any stable protonated molecules. On the other hand, ESI cannot ionize any of the hydrocarbon analytes, saturated or unsaturated. However, ESI can be used to protonate the oxygen-containing analytes with substantially less fragmentation than for APCI in all cases except for cholesterol and estrone. In conclusion, LIAD/ClMn(H(2)O)(+) chemical ionization is superior over APCI and ESI for the mass spectrometric characterization of underivatized nonpolar lipids and steroids. 相似文献
89.
Organic/inorganic hybrid materials prepared by the sol–gel approach have rapidly become a fascinating new field of research
in materials science. The explosion of activity in this area in the past decade has made tremendous progress in both the fundamental
understanding of the sol–gel process and the development and applications of new organic/inorganic hybrid materials. Polymer-inorganic
nanocomposite present an interesting approach to improve the separation properties of polymer material because they possess
properties of both organic and inorganic such as good permeability, selectivity, mechanical strength, and thermal and chemical
stability. Composite material derived by combining the sol–gel approach and organic polymers synthesis of hybrid material
were the focus area of review It has also been demonstrated in this review that a more complete understanding of their structure–property
behavior can be gained by employing many of the standard tools that are utilized for developing similar structure–property
relationships of organic polymers. This review article is introductory in nature and gives introduction to composite materials/nanocomposite,
their applications and the methods commonly employed for their synthesis and characterization. A brief literature survey on
the polysaccharide templated and polysaccharide/protein dual templated synthesis of silica composite materials is also presented
in this review article. 相似文献