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21.
I Kingstone Lesley Jabez Urmila Das Manivannan Ramalingam Saratbabu Anne 《先进技术聚合物》2021,32(1):111-122
Even though literature available on EPDM is abundant, the data on physical, mechanical, thermal, interface properties and ablative performance as specifically required for the design and acceptance of internal insulation of large Composite Rocket Motor Casing is scant in the plethora of literature available in the subject of EPDM insulation. This gave the impetus to take up this experimental work wherein most promising formulation of EPDM with Kevlar and silica as reinforcing fillers and with only silica as reinforcing filler were thoroughly characterized for the insulation requirements of large Composite Rocket Motor Casing and compared with the performance of proven Nitrile rubber based insulation. The significant findings which are unique, are discussed in this paper. 相似文献
22.
A simple spectrophotometric method has been proposed for the determination of widely used pyrethroid pesticides, cypermethrin
and fenvalerate. The method is based on the hydrolysis of these pesticides, upon which they release cyanide. The cyanide is
reacted with bromine and pyridine to form glutaconic aldehyde, which is then coupled with sulphanilic acid to give an orange
red dye in acidic medium having maximum absorbance at 480 nm. Beer’s law is obeyed in the ranges of 0.18–1.12 and 0.08–0.64
μg/mL for fenvalerate and cypermethrin, respectively. The proposed method is sensitive and found to be free from interferences
of a large number of foreign species and other pesticides. The proposed method could be applied to the determination of fenvalerate
and cypermethrin in their formulations and environmental samples. 相似文献
23.
Susmita Kundu Urmila Kar K. Chakrabarty 《The European physical journal. Special topics》2013,222(3-4):699-709
DC shunt and series drives are extensively used in the industry. The occurrence of bifurcation and chaos in dc shunt and permanent magnet drives are well known. It is observed that the behavior of the drives not only depends on the value of system parameters but also on the value of initial conditions. Multiple attractors can exist for same parameter value. Different choice of initial conditions gives different periodic behavior of the system. The drive is intended to operate in a parameter range to give period-1 behavior. We report the existence of sub- harmonic oscillations in the period-1 region of the bifurcation diagram along with co-existing attractor with fractal basin boundaries in PWM controlled dc series drives. The series drive is extensively used in electric traction and other applications. The dc drives are run with dc input voltage. This dc voltage may be derived from a dc source or an ac source with a rectifier. The dc series drive shows different bifurcation behavior when different types of input voltage and switching elements are used. The existence of period-1, period-2 and period-4 orbits are observed with different initial conditions in the desired period-1 region of the bifurcation diagram. The dependence of system’s behavior on initial condition may render the system’s behavior unpredictable. These phenomena may have serious implication in performance. 相似文献
24.
25.
Urmila H. Patel Vijay M. Barot Mitesh C. Patel 《Molecular Crystals and Liquid Crystals》2016,624(1):190-204
A novel bio-organic molecule, 3-(3-chloro-4-methoxy-phenyl)-1-(4,5-dimethoxy-2-methyl phenyl) prop-2-en-1-one (I), has been synthesized and characterized by FTIR, 1H, and 13C NMR. To understand the role of solvents, UV-vis absorption, and fluorescence study has been carried out using different solvents. The single-crystal X-ray diffraction technique has been studied to confirm the three dimensional structure of the compound and the hydrogen bond interactions involved in the stability of the structure. The ab-initio and density functional theory (DFT) are used to optimize the molecular structure. The calculated results show that the predicted geometry can well reproduce structural parameters. In addition, frontier molecular orbitals and Mullikan charge distributions are carried out by using RHF and B3LYP methods. The synthesized compound has been screened for its antimicrobial and antifungal activities against different panel of organisms. 相似文献
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27.
Urmila Tamrakar Sunitha B. Mathew V. K. Gupta Ajai K. Pillai 《Journal of Analytical Chemistry》2009,64(4):386-389
An analytical method employing a combination of solid phase extraction and spectrophotometry is proposed for the determination
of a widely used herbicide atrazine. This combination is very simple and cheaper than chromatography and mass spectrometry
based methods. The proposed method also reduced the use of toxic solvents. The method is based on the reaction of atrazine
with pyridine to form a quaternary halide, which forms a carbinol base in the presence of alkali. Carbinol undergoes cleavage
of heterocyclic ring to form glutaconic aldehyde that is subsequently coupled with sulphanilic acid to give a yellow orange
dye which is measured spectrophotometrically at 460 nm. Beer’s law is obeyed in the range 0.07–0.7 μg/mL of atrazine. Molar
absorptivity and Sandell’s sensitivity were found to be 2.2 × 105 L/mol cm and 0.0009 μg/cm2, respectively. Breakthrough volume is found to be more than 100 mL. The use of solid phase extraction increases the sensitivity
ten times. The proposed method is sensitive and found to be free from the interference of a large number of foreign species
and other pesticides. The developed method was applied to spiked environmental and biological samples, the recovery was in
the range from 95.2 to 99.2% with RSD of 0.36%.
The article is published in the original. 相似文献
28.
The optimization models and algorithms with their implementations on flow over time problems have been an emerging field of research because of largely increasing human-created and natural disasters worldwide. For an optimal use of transportation network to shift affected people and normalize the disastrous situation as quickly and Efficiently as possible, contraflow configuration is one of the highly applicable operations research (OR) models. It increases the outbound road capacities by reversing the direction of arcs towards the safe destinations that not only minimize the congestion and increase the flow but also decrease the evacuation time significantly. In this paper, we sketch the state of quickest flow solutions and solve the quickest contraflow problem with constant transit times on arcs proving that the problem can be solved in strongly polynomial time O(nm2(log n)2), where n and m are number of nodes and number of arcs, respectively in the network. This contraflow solution has the same computational time bound as that of the best min-cost flow solution. Moreover, we also introduce the contraflow approach with load dependent transit times on arcs and present an Efficient algorithm to solve the quickest contraflow problem approximately. Supporting the claim, our computational experiments on Kathmandu road network and on randomly generated instances perform very well matching the theoretical results. For sufficiently large number of evacuees, about double flow can be shifted with the same evacuation time and about half time is sufficient to push the given flow value with contraflow reconfiguration. 相似文献
29.
Urmila Pal Chaudhuri Lei Yang Laura R. Whiteaker Arunendu Mondal Matthew R. Fultz Douglas R. Powell Robert P. Houser 《Polyhedron》2007,26(18):5420-5431
Mononuclear copper(II) complexes of a family of pyridylmethylamide ligands HL, HLMe, HLPh, HLMe3 and HLPh3, [HL = N-(2-pyridylmethyl)acetamide; HLMe = N-(2-pyridylmethyl)propionamide; HLPh = 2-phenyl-N-(2-pyridylmethyl)acetamide; HLMe3 = 2,2-dimethyl-N-(2-pyridylmethyl)propionamide; HLPh3 = 2,2,2-triphenyl-N-(2-pyridylmethyl)acetamide], were synthesized and characterized. The reaction of copper(II) salts with the pyridylmethylamide ligands yields complexes [Cu(HL)2(OTf)2] (1), [Cu(HLMe)2](ClO4)2 (2), [Cu(HL)2Cl]2[CuCl4] (3), [Cu(HLMe3)2(THF)](OTf)2 (4), [Cu(HLMe3)2(H2O)](ClO4)2 (5a and 5b), [Cu(HLPh3)2(H2O)](ClO4)2 (6), [Cu(HL)(2,2′-bipy)(H2O)](ClO4)2 (7), and [Cu(HLPh)(2,2′-bipy)(H2O)](ClO4)2 (8). All complexes were fully characterized, and the X-ray structures vary from four-coordinate square-planar, to five-coordinate square-pyramidal or trigonal-bipyramidal. The neutral ligands coordinate via the pyridyl N atom and carbonyl O atom in a bidentate fashion. The spectroscopic properties are typical of mononuclear copper(II) species with similar ligand sets, and are consistent their X-ray structures. 相似文献
30.
A simple potentiometric method for the determination of organoisothiocyanates is described. The isothiocyanate is treated in acetonitrile medium with an excess of primary amine to convert it into a substituted thiourea and the surplus amine is converted into a dithiocarbamate by addition of carbon disulphide. The solution is then titrated with a copper(II) solution in acetonitrile. The three-step titration curve enables the results to be calculated on the bash of the dithiocarbamate and/or thiourea formed. The method has been successfully applied to the analysis of a commercial insecticide formulation based on isothiocyanate and important mixtures containing isothiocyanates. 相似文献