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81.
We report a method for the measurement of nematic liquid crystal (NLC) cell parameters i.e., switching voltage, birefringence, retardation, dielectric anisotropy, average tilt angle and change in refractive index with applied DC voltage to LC material. The proposed method is based on optical interferometry and Fourier transform fringe analysis technique, in which we obtain 2-dimensional (2D) phase map of the interferograms as a function of applied voltage. Mach-Zehnder interferometer (MZI) was used for the study of cell parameters and interferograms were recorded at different applied DC voltages to NLC cell using CCD camera. From the phase map, 2D-refractive index distribution of the LC cell with applied voltage was reconstructed. Analytical equations are derived based on optical interferometry and then solved to obtain cell parameters. The present method is fast and can give 2D-cell parameters from only two quick interferograms. 相似文献
82.
Nidhi Andhariya Bhupendra Chudasama R. V. Mehta R. V. Upadhyay 《Journal of nanoparticle research》2011,13(9):3619-3631
Core–shell nanostructures have emerged as an important class of functional materials with potential applications in diverse
fields, especially in health sciences. In this article, nanoengineering of novel magnetic colloidal dispersion containing
surface modifiable silica with a core of single domain magnetite nanoparticles loaded with photosensitizer (PS) drug “Methylene
blue” (MB) has been described. Magnetite core is produced by the well-established chemical coprecipitation technique and silica
shell is formed over it by the modified hydrolysis and condensation of TEOS (tetraethyl orthosilicate). Conditions for reaction
kinetics have been established to tailor the core–shell structures in the form of nanospheres and nanocapsules. MB is loaded
into the nanostructures by demethylation reaction. The major conclusion drawn from this study is that the synthesis route
yields stable, non-aggregated MB loaded superparamagnetic magnetite-silica nanostructures with tailored morphology, tunable
loading, and excellent magnetic properties. 相似文献
83.
Florian Meirer Jordi Cabana Yijin Liu Apurva Mehta Joy C. Andrews Piero Pianetta 《Journal of synchrotron radiation》2011,18(5):773-781
The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano‐ and micrometer‐scale factors at the origin of macroscopic behavior. While different electron‐ and X‐ray‐based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X‐ray imaging set‐up is proposed, combining full‐field transmission X‐ray microscopy (TXM) with X‐ray absorption near‐edge structure (XANES) spectroscopy to follow two‐dimensional and three‐dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields. 相似文献
84.
This paper presents a method for the evaluation of the capacitance of the dielectric coated metallic plates forming a corner using the method of moments based on the pulse basis function and the point matching. Two integral equations are formed based on the boundary conditions for the potential on the conductor surface and continuity of the normal component of the displacement flux density at the dielectric-free space interface. A set of simultaneous equations are formed from the two integral equations using the method of moments. The total free charge on the conductor surface is found from the solution of the set of simultaneous equations. Numerical data on the capacitance and the charge distribution are presented. The validity of the analysis has been justified by comparing the data on the capacitance that is available in the literature for a metallic structure with the data on the capacitance computed with the present method for a similar structure considering a very low dielectric constant as well as a very thin dielectric coating. Further validation has been carried out by comparing the capacitance data of the specific case when the angle between two metallic plates is 180° forming a dielectric coated metallic rectangular plate for which the capacitance data are available in the literature. 相似文献
85.
86.
Kishor Mehta Pier-Giorgio Fuochi Andr s Kov cs Marco Lavalle Peter Hargittai 《Radiation Physics and Chemistry》1999,55(5-6):773-779
Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio 1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA. 相似文献
87.
We report the inverse Meyer–Neldel (MN) rule in the thermally activated crystallization of a hybrid composite of phenol formaldehyde using two experimental approaches. In the first experiment, the annealing time dependence of the pre-exponential factor K 0 and the activation energy of crystallization E c were studied. In the second experiment, the annealing temperature dependence of the same parameters was investigated. We observed the inverse Meyer–Neldel rule between the pre-exponential factor K 0 and the activation energy of crystallization E c in both cases. 相似文献
88.
A conceptually new Diels-Alder approach, involving a diene moiety grafted on a preformed epoxyquinone platform and a 4-hydroxy-indenone as the dienophile, delivers the pentacyclic framework of fluostatin C in one key step. 相似文献
89.
V. K. Aswal J. V. Joshi P. S. Goyal Rajesh Patel R. V. Upadhyay R. V. Mehta 《Pramana》2004,63(2):285-290
Small-angle neutron scattering studies have been carried out to check the structural integrity of citryltrimethylammonium
bromide (CTABr) micelles in a magnetic fluid for different magnetic fluid concentrations at two different temperatures 303
and 333 K. It is found that the CTABr micelles grow with increasing magnetic fluid concentration and there is a decrease in
the micellar size with increase in temperature. 相似文献
90.