Browsing by Author "R.A. Singh"

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AC impedance studies on the molecular semiconductors based on aromatic diamines-iodine charge-transfer complexes
(2004) R.K. Gupta; R.A. Singh
Molecular semiconductors based on charge-transfer complexes of benzidine, o-olidine and N, N′-diphenylbenzidine with iodine having different mole ratios have been prepared and characterized by thermal, spectral and electrical methods. The thermal decomposition behaviour of these materials indicate that they are thermally stable up to 130°C and then proceed to stoichiometric weight loss corresponding to iodine and aromatic diamines respectively. The electrical conductivity has its highest value for N, N′-diphenylbenzidine- iodine complexes and lowest for benzidine-iodine complexes which may be due to more extensive conjugation of radical cation in the former than in the later. Impedance studies show (RC(RC), R (RC) and (RC) equivalent circuit for benzidine, o-tolidine and N, N′-diphenylbenzidine-iodine complexes respectively. The electrical data have been discussed in light of dynamic bond percolation model in which the distribution, density and availability of potential hopping sites change as a result of electronic and structural changes in the material.
Biomimetic synthesis and characterization of semiconducting hybrid organic-inorganic composite materials based on polyaniline-polyethylene glycol-CdS system
(Indian Academy of Sciences, 2011) A. Singh; N.P. Singh; R.A. Singh
Triple hybrid materials based on polyaniline-polyethylene glycol and cadmium sulphide have been prepared by the duffusion-limited biomimetic route and characterized by a number of spectroscopic, XRD, SEM, thermal and electrical measurements. These hybrid materials have been prepared by controlled precipitation of cadmium sulphide by passing H2S gas and mixing the resultant colloid with the acidic solution of aniline. In situ polymerization of adsorbed anilinium ions on anionic surface of CdS resulted in hybrids. Water-soluble polyethylene glycol led to diffusion-limited growth of polyaniline and CdS resulting in a nanosized hybrid material as indicated by UV-visible spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM). AC impedance spectroscopic studies on binary and ternary nanocomposites of polyaniline with polyethylene glycol and cadmium sulphide separately and triple hybrid system have been reported. Equivalent circuits were determined and discussed in the light of contributions made from different sources such as grain, grain boundary and electrode. © Indian Academy of Sciences.
Comparative performance of different intercropping systems with pigeonpea (Cajanus cajan) under rainfed conditions of Vindhyan region
(1994) R.A. Singh; A.K. Singh
[No abstract available]
Comparative performance of upland rice (Oryza sativa)-based intercropping systems under rainfed conditions of Vindhyan region
(1996) A.K. Singh; R.A. Singh; R.P. Singh
A field experiment was conducted during 1988-1989 on sandy clay-loam soils of Vindhyan plateau under rainfed conditions, to maximize the productivity of upland rice (Oryza sativa. L.)-based intercropping systems. The normal-sown rice (Oryza sativa (L.) intercropped with sesame (Sesamum indicum L.) was more compatible and advantageous than other combinations. The highest yield recovery of rice (94.8%) and sesame (83.3%) was recorded from this system. Soybean [Glycine max (L.) Merr.] and blackgram or urdbean (Phaseolus mungo L.) were equally competitive with normal or paired-row-sown rice, but reduced the yield of rice by 7.8 and 11 % in normal sown and 10.9 and 10.5% in paired-row-sown rice respectively. All the growth parameters and yield attributes of rice were favourably more under sole cropping, followed by normal rice intercropped with sesame. This combination recorded the highest rice-equivalent yield (48.09 q/ha) and yield advantage (78%), followed by paired rice + sesame intercropping system.
Comparative study of cryptand-based (triple-head and triple-tail) amphiphiles at the air-water interface
(ACS, 2000) Gopal Das; Parimal K. Bharadwaj; U. Singh; R.A. Singh; Ray J. Butcher
Two cryptands have been derivatized by reacting with acid chlorides of different alkyl chain lengths (between C4 and C18) to get a set of cryptand-based (triple-head and triple-tail) neutral amphiphiles. The cavity of either cryptand headgroup can accommodate a first-row transition metal ion forming stable cryptates. The free as well as the Cu(II)-complexed amphiphiles are studied at the air-water interface in a Langmuir-Blodgett trough. They form stable monolayers at the air-water interface, which can be transferred onto different substrates (viz., glass, fluorite, and quartz). They form Y-type Langmuir-Blodgett films. The amphiphile L5 crystallizes in the monoclinic space group P21/c with a = 10.091(3) angstrom, b = 29.994(8) angstrom, c = 18.174(5) angstrom, Z = 4, Rf = 0.1048, Rwf = 0.02660, and GOF = 0.925. The amphiphile L6 crystallizes in the trigonal space group P31c with a = 15.118(2) angstrom, b = 15.118(2) angstrom, c = 11.734(2) angstrom, Z = 2, Rf = 0.033, Rwf = 0.062, and GOF = 0.813. The solid-state structures of both the amphiphiles show a 3-fold symmetry about a point in the center of the cryptand headgroup. The hydrophobic tails of the cryptands are packed in the lattice both in interdigitizing and in noninterdigitizing manners.
Cytology and teliospore development of entyloma thirumalachari
(1975) R.A. Singh; M.S. Pavgi
Cytology and development of Entyloma thirumalachari Pavgi and Singh, parasitic on Blumea oxydonta DC. have been described. During teliospore germination, the diploid nucleus migrates into and divides in the promycelium. The first division is reductional followed by an equational one. Some of the meiotic divisional stages were observed and the haploid chromosome complement determined to be n = 6. Several aberrations in teliospore germination and nuclear behavior were observed and their repercussions discussed. Sporidial development and their conjugation, parasitic mycelium and formation of clamp connections, and development of teliospores in the host tissue have been studied. The fungus possesses a diplobiontic rhythm of life cycle, which is well adapted for its effective dissemination and survival under the ecological conditions to which the host is subjected. © 1990 Taylor & Francis Group, LLC.
Effect of EDTA on luminescence property of Eu+3 doped YPO 4 nanoparticles
(2010) A.K. Parchur; G.S. Okram; R.A. Singh; R. Tewari; Lina Pradhan; R.K. Vatsa; R.S. Ningthoujam
Nanoparticles of Eu3+ doped YPO4 have been prepared using ethylene glycol (EG). Ethylene diamine tetra acetic acid (EDTA) is used as a complexing agent. X-ray diffraction results show that the nanoparticles are crystalline in tetragonal structure. Based on William-Hall relation, the effective crystallite size and strain developed in lattice are found to be 28 nm and 0.002, respectively. With the addition of EDTA, there is a slight shift towards the lower wavelength in emission peaks. Asymmetric ratio of electric to magnetic dipole transition intensities are found to decrease with addition of EDTA. Emission intensity decreases with EDTA because of decrease of particle size as well as decrease of number of Eu3+ activators per unit volume. These materials are dispersible in water, which may have potential biological applications. © 2010 American Institute of Physics.
Effect of row orientation and plant density on yield and quality of rainfed barley
(Martinus Nijhoff/Dr. W. Junk Publishers, 1981) R.A. Singh; H.B. Singh
Grain and straw yields of barley improved significantly due to N-S, row orientation, 30 cm row spacing and 90 kg/ha seed rate. A plant rectangularity of 13.6 was found most conducive for grain and straw yeilds of barley. None of the malt quality characters were affected wignificantly due to row orientation. A row spacing of 30 cm and a seed rate of 90 kg/ha improved the malt quality characters of barley. Increase in protein percentage at 30 cm row spacing deteriorated the malt quality. © 1981 Martinus Nijhoff/Dr. W. Junk b.v. Publishers.
Effect of soil compaction and nitrogen placement on weed population, yield and moisture use pattern of rainfed wheat
(Kluwer Academic Publishers, 1976) R.A. Singh; O.P. Singh; Mahatim Singh
Field experiments showed that soil compaction did not affect wheat yield significantly under rainfed conditions. Weed population was significantly reduced due to soil compaction. Compaction decreased total moisture use and increased water use efficiency. There was better and profitable utilization of stored soil moisture from the compaction treatments as compared to no compaction treatment. Placement of nitrogen about 10 to 15 cm deep in the soil directly below the seed resulted in significant increase in the yield of wheat crop grown under rainfed conditions. Weed population was not affected due to nitrogen placement. Total moisture use reduced due to nitrogen placement. Under rainfed conditions, deep placement of nitrogen was important for increasing the efficiency of fertilizer as well as water utilization by wheat crop. © 1976 Martinus Nijhoff Publishers.
Electrical properties of junction between aluminium and poly(aniline)-poly(vinyl chloride) composite
(2004) R.K. Gupta; R.A. Singh
Schottky barrier diode based on composite of polyaniline with polyvinyl chloride has been fabricated and characterized using aluminium as Schottky contact and platinum as an Ohmic contact. Current-voltage (I-V) plots were non-linear and capacitance-voltage (C-V) plots were almost linear in reverse bias indicating rectification behavior. The observed current-voltage characteristics can be satisfactorily fitted using the modified Schottky equation. Various junction parameters were calculated from the temperature-dependent I-V and C-V data and discussed. These results indicate that the composite materials have better mechanical strength and diode quality compared to that of pure polymer. © 2004 Elsevier B.V. All rights reserved.
Electronic transition moments in the spectra of substituted naphthalenes
(Kluwer Academic Publishers-Plenum Publishers, 1981) R.A. Singh; S.N. Thakur
[No abstract available]
Excited state normal vibrations and force field of ethynylbenzene
(1997) K.M. Singh; R.A. Singh; S.N. Thakur
Accurate vibrational frequencies of ethynylbenzene and three of its deuterated isomers in first excited state (1B2) have been used in the determination of intramolecular force constants and the assignments of vibrational frequencies have been discussed in the light of calculated potential energy distributions. The vibrational modes corresponding to normal frequencies ν30 and ν31 exhibit mode scrambling on ring deuteration. Evidence of Duschinsky mixing in going from ground to the excited state has been found in the vibrational modes ν6, ν13, ν31 and ν34 which are active in one photon absorption and also in ν30 which is active in two photon excitation spectrum.
Fabrication and characteristics of Schottky diode based on composite organic semiconductors
(2005) Ram Krishna Gupta; R.A. Singh
Schottky barrier diode based on composite of polyaniline with polystyrene has been fabricated and characterized using indium as Schottky contact and platinum as an ohmic contact. Current-voltage (I-V) plots were non-linear and capacitance-voltage (C-V) plots were almost linear in reverse bias indicating rectification behavior. Various junction parameters were calculated from the temperature dependent I-V and C-V data and discussed. These results indicate that the composite materials have better mechanical strength and diode quality compare to that of pure polymer. © 2004 Elsevier Ltd. All rights reserved.
Ground state normal vibrations and force field of ethynylbenzene
(1995) K.M. Singh; R.A. Singh; S.N. Thakur
An accurate intramolecular force field for ethynylbenzene and its three deuterated isomers is determined from experimentally observed vibrational frequencies. Vibrational assignments are discussed in the light of the calculated potential energy distribution. Mode ν15 of a2 symmetry is assigned at 655 and 657 cm-1 in C6D5CCH and C6D5CCD, respectively. The vibrational frequency of 162 cm-1 is given double assignment as ν24 and ν36. Harmonic mode scrambling is observed in ν27, ν29, ν30 and ν31 in going from the parent molecule to the one with ring deuteration. © 1995.
High resolution electronic absorption spectrum of 1, 3, 5-trifluorobenzene
(2007) R.P. Tiwari; S.N. Thakur; R.A. Singh
The near ultraviolet electronic absorption spectrum of 1,3,5 trifluorobenzene has been photographed on a 10.6 m concave grating spectrograph. The electronic forbidden transition 1A'2 ←- 1A'1 is explained as arising due to perturbation of the electronic state by non-totally symmetric vibration V6. Besides V6, the other modes of e' species V8, V9, V18, and v19 are also active and give rise to false origins. The vibrational frequencies for V9, V18, V 19, V8, V13, V1 and V16 modes in the first electronic excited state 1A'2 are reported for the first time.
High-resolution electronic absorption spectrum of 2-fluoronaphthalene
(2006) R.A. Singh; S.N. Thakur
The vapour phase absorption spectrum 2-fluoronaphthalene has been recorded under high resolution. The vibronic bands involving ground and excited normal vibrations have been assigned on the basis of their rotational contours. Many new vibrational frequencies have been reported for the first time in the excited state of 2-fluoronaphthalene.
Improved photo-luminescence behaviour of Eu3+ activated CaMoO4 nanoparticles via Zn2+ incorporation
(Royal Society of Chemistry, 2015) B.P. Singh; Maheshwary; P.V. Ramakrishna; Saurabh Singh; V.K. Sonu; Santosh Singh; P. Singh; A. Bahadur; R.A. Singh; S.B. Rai
Zn2+ (0, 2, 5, 7 and 10 at%) co-doped CaMoO4:2Eu3+ nanophosphors have been synthesized via the polyol method using ethylene glycol (EG) as both capping agent and reaction medium at 150°C. From XRD analysis, all 900°C annealed Zn co-doped CaMoO4:Eu3+ nanophosphors have a tetragonal scheelite phase. Some extra phase evolution has been observed for the as-prepared Zn doped samples. The intensity and crystallinity of XRD patterns increase as heat treatment increases to 900°C. The valence states of the involved compositions (Zn co-doped CaMoO4:Eu) were investigated by X-ray photoelectron spectroscopy (XPS) and it was found that Ca, Mo, Eu and Zn are in their +2, +6, +3 and +2 oxidation states, respectively. TG-DSC studies of the as-prepared samples corroborate their thermal stability. A TEM (Transmission electron microscopy) study reveals that the particles have spherical morphology. Photoluminescence studies have been carried out under ∼266, and 395 nm excitation wavelengths. Zn co-doping in the CaMoO4:Eu matrix produces a high distortion and modifies the crystal field around the Eu3+ ion and improves the PL intensity. CIE co-ordinates of the 900°C annealed 10 at% Zn co-doped CaMoO4:Eu sample under 266 nm excitation is x = 0.64 and y = 0.35, which are close to the standard of NTSC (x = 0.67 and y = 0.33). These investigations reveal that Zn co-doped CaMoO4:Eu3+ nano-materials can be used as potential red emitting phosphors, an area which is a bottleneck in the development of low cost LEDs. © The Royal Society of Chemistry.
In vitro effects of divalent metal ions and metabolic modulators on purified glutamine synthetase from brain of teleostean fish
(Informa Healthcare, 1992) R.A. Singh; S.N. Singh
The purified brain glutamine synthetase of a teleostean fish, Clarias batrachus has been examined under the influence of divalent metal ions activation and in vitro studies using different amino acids and metabolic modulators. All observations of the enzyme activity are based on transferase reaction at optimum temperature and pH. The enzyme exhibits an absolute requirement for Mn2+ (most potent) Mg2+ and Co2+. The activity is markedly inhibited by leucine, asparagine, isoleucine, carbamyl phosphate, uridine monophosphate and glutamate and activated by αketoglutarate. The significance of these results has been discussed in brief with emphasis on its involvement in teleostean physiology and metabolism. © 1992 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
Inhibition of copper corrosion in aqueous sodium chloride solution by N-Octadecylbenzidine/1-Docosanol mixed Langmuir-Blodgett films
(National Assoc. of Corrosion Engineers International, 2001) A. Jaiswal; R.A. Singh; R.S. Dubey
Mixed Langmuir-Blodgett (LB) films on N-octadecylbenzidine (NODB)/l-docosanol were deposited onto a copper surface to investigate the inhibition of corrosion of copper in 3.4% sodium chloride (NaCL) solution by wietht loss, corrosion potential, and potentiodynamic polarization measurements. The surface of the copper specimen before and after corrosion was also examined by scanning electron microscopy (SEM). The mixed monolayers of NODB/l-docosanol inhibited the corrosion of copper efficiently. The inhibition efficiency increased wiht the number of monolayers, and the maximum inhibition of about 94% was obtained by 10 monolayers of basis of "blocking action" of LB films of NODB/ l-docosonal on the copper surface.
Inhibition of corrosion by poly(N-hexadecylaniline)/docosanol mixed Langmuir-Blodgett films on copper in sea water
(2006) R.K. Gupta; R.A. Singh
Electrochemical and weight loss techniques have been used for investigation of inhibition of corrosion on copper metal by Langmuir-Blodgett (LB) films of poly(N-hexadecylaniline)/docosanol in sea water. LB films of poly(N-hexadecylaniline)/docosanol were deposited onto the copper specimens. The open-circuit potential and potentiodynamic polarization curves were observed to shift in noble direction, which indicated that these LB films could inhibit the corrosion of copper metal in sea water. © 2005 Elsevier B.V. All rights reserved.