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61.
A new, simple and sensitive method for the spectrophotometric indirect determination of ascorbic acid in fruits, beverages, and pharmaceuticals is described. In this method, the ascorbic acid reduces Cu2+ to Cu+ and reacts with 2,9‐dimethyl‐1,10‐phenanothroline (neucoproine) to form Cu (neucoproine)+ complex, and it was extracted with N‐phenylbenzimidoylthiourea (PBITU) in chloroform. The apparent value of molar absorptivity of the complex in terms of ascorbic acid is (3.52) × 104 L mole?1 cm?1 at λmax, 460. The detection limit of ascorbic acid is 40 μg L?1 and the method obeys Beer's law over the concentration range of 0.1–4.0 μg mL?1. The proposed method was successfully applied for the determination of ascorbic acid in various samples. The validity of the present method was checked by the flow injection analysis (FIA) method. 相似文献
62.
Devendra Kumar Alka D. Gupta Mrignaini Khullar 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):707-713
A novel class of fire- and heat-resistant matrix resins has been synthesized by thermal polymerization of ethynyl-substituted aromatic cyclotriphosphazenes. Thermal polymerization of new tris[4-(4′-ethynylbenzanilido)phenoxy]tris(phenoxy) cyclotriphosphazene ( III ) and tris[4-(4′-ethynylphthalimido)phenoxy]tris(phenoxy)cyclotriphosphazene ( VII ) at 250°C for 1–1.5 h gave tough polymers. The thermal stabilities of the polymers were evaluated in nitrogen and in air by thermogravimetric analysis (TGA). The synthesised polymers were stable to 400–410°C and showed char yield of 78–65% at 800°C in nitrogen and of 78–69% at 700°C in air. The ethynyl-substituted polymer precursor ( III ) was synthesised by the reaction of tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene ( I ) with 4-ethynylbenzoyl chloride. The polymer precursor ( VII ) was synthesised by a solution condensation of I with 4-ethynylphthalic anhydride followed by in situ thermal cyclodehydration at 150°C. The structure of polymer precursors was characterized using proton nuclear magnetic resonance (1H-NMR), infrared (IR) spectroscopy, and elemental analysis. The curing of polymer precursors was monitored by differential scanning calorimetery (DSC) and IR spectroscopy. The synthesised matrix resins are potential candidates for the development of heat- and fire-resistant fiber-reinforced composites. © 1993 John Wiley & Sons, Inc. 相似文献
63.
Jagdev Singh Devendra Kumar Manish Kumar Bansal 《Mathematical Methods in the Applied Sciences》2020,43(5):2106-2116
In this paper, we find the approximate solution of a nonlinear differential equations pertaining to M-series, -function, and I-function of two variables by making use of the Hermite, Legendre, and Jacobi polynomials. The nonlinear differential equations play a key role in distinct branches of engineering and physics and many vibration problems. The results obtained in the present study are general in nature and can be used to obtain the solution of various problems of physics and engineering. 相似文献
64.
Joe G. Jesu Raj Devendra D. Pathak Pramesh N. Kapoor 《Central European Journal of Chemistry》2012,10(2):413-413
The original version of the article was published in Cent. Eur. J. Chem. 10(1) (2012), pp 165–171. Unfortunately, the original
version of this article contains mistakes in the affiliation section. Dr Devendra D. Pathak’s affiliation is Department of
Applied Chemistry, Indian School of Mines, Dhanbad 826 004, India. Dr Pramesh N. Kapoor’s affiliation is Department of Chemistry,
University of Delhi, Delhi 110 007, India. 相似文献
65.
66.
Journal of Mathematical Chemistry - Recently, the two-dimensional elliptic singularly perturbed boundary value problems have received attention. These problems have not been much explored... 相似文献
67.
Attempts have been made to synthesize a few compositions Ce0.80La0.15Al0.05O1.90, Ce0.80Sm0.10Gd0.05Al0.05O1.90, and Ce0.80Gd0.10Sm0.05Al0.05O1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and
multiple doping on the ionic conductivity of CeO2 for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples
have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied
by scanning electron microscopy. Contributions of grains σ
g and grain boundaries σ
gb to the total conductivity σ
T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature
range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide
ion conductivity of ceria in the materials investigated in the present study. 相似文献
68.
Third order nonlinear optical properties of amorphous Znx–Sy–Se100−x−y chalcogenide films have been investigated using single beam transmission z-scan technique at 1064 nm of Nd:YAG laser. Measurement of optical properties of amorphous Znx–Sy–Se100−x−y chalcogenide films prepared by thermal evaporation technique has been made. X-ray diffraction patterns of chalcogenide films confirm the amorphous nature. Optical band gap (Eg) has been estimated using Tauc's plot method from transmission spectra that is found to decrease with increase in content due to valence band broadening and band tailing the system. Nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ3) of chalcogenide films have been estimated. Self-focusing effect has been observed in closed aperture and reverse saturable absorption in open aperture scheme. Limiting threshold and dynamic range have been calculated from optical limiting studies. The increase in nonlinearity with increase in Zn content has been observed that is understood to be due to decrease in band gap on Zn doping. High nonlinearity makes these films a potential candidate for waveguides, fibers and two photon absorption in optical limiters. 相似文献
69.
Rohit Kumar Durgesh Kumar Tripathi Alamelu Devanathan Devendra Kumar Chauhan 《光谱学快报》2014,47(7):554-563
The present work is a methodological study to investigate the effect of chromium (VI) stress on wheat seedlings. Point detection capability of laser-induced breakdown spectroscopy (LIBS) was utilized for the monitoring of in-situ chromium uptake in wheat (Triticum aestivum) seedlings. Chromium accumulation and its effects on other elements in wheat seedling were investigated by comparing the intensities of spectral lines of chromium and other minerals present in the LIBS spectra. In-situ LIBS spectra of the different parts of the wheat seedlings were recorded by directly focusing the laser beam on the surface of root, stem, and leaf of the seedlings grown with and without chromium-containing solutions. The spectra obtained from the different parts (root, stem, and leaf) of the wheat plant were analyzed to determine the distribution pattern/accumulation of chromium. Effect of the chromium uptake on the distribution pattern of other elements like calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K) was also investigated. It was observed that chromium concentrations in plant organs decreased in the following order: roots > leaves > stems. 相似文献
70.
Jayesh Patel Frej Mighri Abdellah Ajji Devendra Tiwari Tapas K. Chaudhuri 《Applied Physics A: Materials Science & Processing》2014,117(4):1791-1799
In this work, we describe a simple spin-coating deposition technique for lead sulphide (PbS) and cadmium sulphide (CdS) films from a methanolic metal–thiourea complex. The characterization of the films by X-ray diffraction and X-ray photoelectron spectroscopy techniques revealed that pure cubic phase PbS and CdS layers were formed via this method. As shown by atomic force microscopy and scanning electron microscopy results, both films were homogeneous and presented a smooth surface. Optical properties showed that the energy band gap of PbS and CdS films were around 1.65 and 2.5 eV, respectively. The PbS film is p-type in nature with an electrical conductivity of around 0.8 S/cm. The hole concentration and mobility were 2.35 × 1018 cm?3 and 2.16 × 10?3 cm2/V/s, respectively, as determined from Hall measurement. Both films were used to develop a thin film solar cell device of graphite/PbS/CdS/ITO/glass. Device characterization showed the power conversion efficiency of around 0.24 %. The corresponding open circuit voltage, short circuit current and fill factor were 0.570 V, 1.32 mA/cm2 and 0.32, respectively. 相似文献