- Thermal Behavior of Langmuir-Blodgett Films. 1. Electron Diffraction Studies on Monolayers of Cadmium Stearate, Arachidate, and Behenate
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Electron diffraction patterns of monolayers of several cadmium fatty acid salts were studied as a function of the sample temperature.A sharp decrease of the diffraction peak intensities at temperatures well below the main melting temperature of the headgroup lattice indicates a pretransitional disordering.It depends on the chain length and starts at ca. 35 deg C for cadmium stearate, at ca. 55 deg C for cadmium arachidate, and at ca. 75 deg C for cadmium behenate.The hexagonal geometry of the diffraction patterns does not change with temperature, and the radial and angular full width at half-maximum increase only slightly compared to the pronounced decrease of the intensity.This indicates that the overall bond orientational and traslational order of the molecules is preserved and that the intesity decrease is caused by thermally induced random tilt orientational disorder or bending of the chains.
- Riegler, Johann E.
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- Thioalkanoates as site-directing nucleating centers for the preparation of patterns of CdS nanoparticles within 3-D crystals and LB films of Cd alkanoates
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A method is described for the preparation of hybrid organic/inorganic structures where the inorganic component comprises semiconductor nanoparticles aligned in periodic layers within three-dimensional (3-D) crystalline powders and Langmuir-Blodgett (LB) films. The preparation process comprises the organization of metal ions in the form of periodic arrays within 3-D crystals or the LB films, followed by a topotactic gas/solid reaction. The method is illustrated for the organization of CdS nanoparticles within alkanoic acids. The order of the nanoparticles is achieved by introducing site directing nucleation centers of Cd thioalkanoates within Cd alkanoates, in the form of solid solutions. The formed particles are attached to the organic matrix via -C(O)S-Cd-S- bonds. The structure of those supramolecular architectures has been characterized by a variety of complementary methods, including transmission electron microscopy (TEM) and electron diffraction (ED), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other spectroscopic measurements.
- Guo, Shouwu,Konopny, Leandro,Popovitz-Biro, Ronit,Cohen, Hagai,Porteanu, Horia,Lifshitz, Efrat,Lahav, Meir
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- A solvothermal route to capped CdSe nanoparticles
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We present a convenient and safe one-pot route to capped 3 nm CdSe nanoparticles making use of common starting materials and inexpensive, low-boiling solvents under solvothermal conditions; H2Se required for the reaction is generated in situ through the aromatization of tetralin by Se.
- Gautam,Rajamathi,Meldrum,Morgan,Seshadri
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- Effect of Substrates on the Infrared External Reflection Spectra of Langmuir-Blodgett Films
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The Fourier transform infrared (FTIR) polarized external reflection (ER) spectra of 9-monolayer cadmium stearate Langmuir-Blodgett (LB) films were measured on various kinds of materials (Ge, ZnSe, and GaAs) in order to investigate whether their spectra could be used for a quantitative analysis of the molecular orientation. The FTIR ER spectra on double-side-polished substrates with LB films on both sides would not fit in, even qualitatively, with the 5-layer system (IR//air/LB/substrate/LB/air) theoretical prediction. On the other hand, the ER spectra of a single-side-deposited LB film (IR//air/substrate/LB/air) were qualitatively explained by a simple 3-layer system (IR//substrate/LB/air) in which the reflection in the substrate was treated as a single reflection. This indicated that the output rays from the substrate in the conventional 5-layer system did not interfere sufficiently with each other. A 5-layer system calculation without any interference effect qualitatively explained the ER spectra of LB films on a double-side-polished substrate. It was eventually concluded that double-side-polished materials are not suitable for a precise analysis of ER spectra, since it is almost impossible to estimate the area ratio of interferential and non-interferential rays.
- Hasegawa, Takeshi,Nishijo, Jujiro,Kobayashi, Yoshihiro,Umemura, Junzo
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- A strategy for the synthesis of nanocrystal films of metal chalcogenides and oxides by employing the liquid-liquid interface
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The interface between water and an organic liquid has been exploited to prepare nanocrystals of CdS. The technique involves introducing an appropriate precursor of cadmium in the organic layer and the sulfiding reagent in the aqueous layer. The size distribution of the nanocrystals formed at the interface can be controlled by varying parameters such as the reactant concentration, temperature, viscosity of the medium, reaction time and the choice of the reagents. The CdS nanocrystals have been characterized by TEM, electronic absorption and emission spectroscopy. Nanocrystaline γ-Fe 2O3 and ZnO can be prepared by taking cupferron complex of the metals in the organic layer and NaOH in the aqueous layer.
- Gautam, Ujjal K.,Ghosh, Moumita,Rao
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- Crystal structure control of CdSe nanocrystals in growth and nucleation: Dominating effects of surface versus interior structure
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For the most studied nanocrystal system in the literature, experimental results in this paper revealed that formation of either zinc blende or wurtzite CdSe nanocrystals was dominated by the ligand-surface interaction, instead of the interior structure difference. This conclusion was considered to be reasonable, given the very small energy difference between wurtzite and zinc blende CdSe (only 1.4 meV per CdSe unit and about 1000 times smaller than the energy of a single cadmium-ligand bond). Cadmium carboxylate ligands in the form of cadmium fatty acid salts promoted formation of the zinc blende structure. Conversely, cadmium phosphonate ligands with a long hydrocarbon chain favored the formation of the wurtzite structure. The effects of either cadmium carboxylate or cadmium phosphonate ligands were found to play a determining role during both nucleation and growth. Different from our expectation, fatty amine was found to be only a secondary factor for crystal structure determination. With an appropriate choice of capping ligands, it was possible to achieve precise control of the crystal structure of the CdSe nanocrystals in both nucleation and growth for either the zinc blende or wurtzite structure.
- Gao, Yuan,Peng, Xiaogang
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- Electron transmission through molecular layers
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This article discusses general issues associated with electron transmission through thin molecular films. On the experimental side, we emphasize recent investigations of photoemission through organized organic films adsorbed on metal surfaces. Theoretical and numerical approaches to transmission and tunneling through such films are discussed. We focus on the relation between the structure of the film and its transmission properties. In the experimental work, these are controlled by varying the organic layer, by changing its thickness and by inducing disorder via thermal heating and by depositing mixtures of two molecular types. In numerical simulations of simple model systems, we consider the dimensionality of the process, effect of molecular ordering, and relation between electronic band structure in the film and its transmission properties. It is shown that electron transmission through thin molecular layers constitutes a sensitive tool for investigating molecular film properties in addition to providing a convenient prototype system for the study of electron transport in molecular electronic devices.
- Naaman,Haran,Nitzan,Evans,Galperin
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- A low temperature phase transition in Langmuir-Blodgett films
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The influences of temperature on the SFG spectra of Langmuir-Blodgett films of cadmium steì?arate, ferric stearate, stearic acid and octadecanamide are reported. Upon cooling, all films display reversible discontinuous shifts of a??8 cm-1 in the r+, r- and r fermi modes of the terminal methyl groups at a??150 K. Reversible changes in the relative intensities of these methyl group peaks, most pronounced in the PPP spectra, are also observed and attributed to a change in the environment of the methyl group that accompanies a discontinuous transition in the ordering of their alkyl chains. The onset of new spectral features at higher frequency is attributed to the observation of ordered water molecules contained within the films. The correlation between the onset of the water features and the onset of the reversible, discontinuous, spectroscopic changes of the amphiphiles argues for a causal connection between the two. In addition to the discontinuous behavior upon cooling, monolayer films of stearic acid and octadecanamide display activity of methylene modes upon exposure to vacuum. Films displaying SFG-active methylene groups at room temperature had them gradually become completely SFG-inactive by 100 K. Heating the films to room temperature revealed that the methylene group activity was reversible. Monolayer films of cadmium ste;arate and ferric stearate do not display this methylene activity upon exposure to vacuum, suggesting that this behavior may be linked to solvation of the amphiphile's headgroup. These observations suggest that water plays a key role in the stability and structure of LB supported monolayers, and have important implications to those interested in low temperature (cryogenic) effects of biological systems. ? 2008 American Chemical Society.
- Johansson, Thomas P.,Leach, Gary W.
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- Molecular-orientation change in Langmuir films of stearic acid and cadmium stearate upon surface compression, as studied by infrared external-reflection spectroscopy
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For interpretating the various phases appearing in a two-dimensional system, we have recorded in situ polarized FT-IR external reflection spectra of Langmuir films of stearic acid and cadmium stearate on the water surface at various surface areas, and evaluated the molecular orientation angles quantitatively. In the stearic acid monolayer, the orientation angle of the hydrocarbon chain from the surface normal decreased from 20° to almost 0° upon monolayer compression. In the cadmium stearate monolayer, on the other hand, the orientation angle (near 0°) did not change upon monolayer compression, though it was widely scattered at large surface areas, because of the formation of a rigid crystalline island. These results correspond well to the π-A isotherms.
- Sakai, Hiroshi,Umemura, Junzo
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- Charge and energy transfer between CdSe quantum dots and polyaniline
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CdSe quantum dots (QDs) and polyaniline (PAni) were mixed to prepare CdSe QDs/PAni complex. PAni can quench the fluorescence of CdSe QDs. Fluorescence intensity of CdSe QDs/PAni complex is related to the size of CdSe QDs and the concentration of PAni. UV-
- Xu, Liang,Huang, Xingbin,Dai, Wenjiang,Sun, Punan,Chen, Xuanlin,An, Limin
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- Symmetry-Breaking for Formation of Rectangular CdSe Two-Dimensional Nanocrystals in Zinc-Blende Structure
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Formation of CdSe nanocrystals with two-dimensional quantum confinement (CdSe 2D nanocrystals) was studied with preformed CdSe nanocrystals in the size range between 1.7 and 2.2 nm as seeds. Specifically, the 2D CdSe nanocrystals were encased with six {100} facets of the zinc-blende (face-center-cubic) structure, that is, 1.5 nm in thickness with quite large atomically flat {100} basal planes (~8 nm width and X ≈ 45 nm length). Symmetry breaking between the thickness and lateral directions occurred in the early stage by rapid formation of single-dot intermediates with flat yet polar {100} basal planes and the desired thickness from the seeds through intraparticle ripening. Two single-dot intermediates fused together through their reactive side facets - mostly the nonpolar {110} ones - to form 2D embryos with the same thickness. Such oriented attachment continued selectively onto the reactive side facets of the 2D embryos. Simultaneously, intraparticle ripening occurred slowly on the side facets of the 2D nanocrystals, which converted unstable side facets gradually to four stable {100} ones. When ~3 stable {100} side facets were developed, oriented attachment would continue on the remaining active one, which would result in the second symmetry breaking between two lateral directions. Cadmium acetate assisted both formation of single-dot intermediates and oriented attachment. Cadmium alkanoates with a long hydrocarbon chain selectively stabilized polar {100} facets on the nanocrystals including single-dot intermediates and shuttled insoluble acetate to the reactive surface of the nanocrystals.
- Chen, Yiya,Chen, Dongdong,Li, Zheng,Peng, Xiaogang
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- Structure of organic thin films grown on surface-modified tantalum oxide
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We fabricated an ordered monolayer film of a long-chain fatty acid or a perfluorofatty acid onto an anodized tantalum oxide (Ta2O 5) amorphous surface by the Langmuir-Blodgett (LB) method, and grew a pentacene or C60 thin film on it. Remarkable improvements of morphology and crystallinity of the organic thin films were observed on the CH3-terminated monolayer film of the fatty acid. Copyright
- Onoki, Ryo,Abe, Shigeomi,Ueno, Keiji,Nakahara, Hiroo,Saiki, Koichiro
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- A solvothermal route to CdS nanocrystals
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A novel solvothermal route for the preparation of organic soluble CdS nanocrystals, involving the reaction of cadmium stearate with sulfur in the presence of tetralin has been described. Tetralin in the presence of S gives H2S, getting aromatized to naphthalene. By using trioctylphosphineoxide as the capping agent, nanocrystals of 4 nm are obtained. Use of dodecanethiol cap results in 5 nm as well as 10 nm nanocrystals which can be separated readily. The nanocrystals have the cubic zinc blende structure and exhibit blue shifts of the absorption maximum.
- Gautam, Ujjal K.,Seshadri, Ram,Rao
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- Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy
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Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113Cd and 77Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe3O, CdSe2O2, and CdSeO3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113Cd-113Cd and 77Se-77Se and heteronuclear 113Cd-77Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77Se{113Cd} scalar heteronuclear multiple quantum coherence (J-HMQC) experiments were used to selectively measure one-bond 77Se-113Cd scalar coupling constants (1J(77Se, 113Cd)). With knowledge of 1J(77Se, 113Cd), heteronuclear 77Se{113Cd} spin echo (J-resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe2O2 and SeCd4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.
- Adamson, Marquix A. S.,Blome-Fernández, Rafael,Chen, Yunhua,Dorn, Rick W.,Flintgruber, Anne H.,Hanrahan, Michael P.,Medina-Gonzalez, Alan M.,Rossini, Aaron J.,Vela, Javier,Wei, Lin
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p. 8747 - 8760
(2021/06/28)
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- Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art
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This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C1 6:0) and stearic (C18:0) and the polyunsaturated oleic acid (C1 8:1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C-C stretching region (1120-1040 cm-1), and IR distinguishes the metal cation in the COO- stretching absorption region (1650-1380cm-1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings.
- Otero, Vanessa,Sanches, Diogo,Montagner, Cristina,Vilarigues, Mrcia,Carlyle, Leslie,Lopes, Joo A.,Melo, Maria J.
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p. 1197 - 1206
(2015/02/19)
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- Relating structure with morphology: A comparative study of perfect Langmuir-Blodgett multilayers
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Atomic force microscopy and X-ray reflectivity of metal-stearate (MSt) Langmuir-Blodgett films on hydrophilic Silicon (1 0 0), show dramatic reduction in 'pinhole' defects when metal M is changed from Cd to Co, along with excellent periodicity in multilayer, with hydrocarbon tails tilted 9.6° from vertical for CoSt (untilted for CdSt). Near edge X-ray absorption fine structure (NEXAFS) and Fourier transform infra-red (FTIR) spectroscopies indicate bidentate bridging metal-carboxylate coordination in CoSt (unidentate in CdSt), underscoring role of headgroup structure in determining morphology. FTIR studies also show increased packing density in CoSt, consistent with increased coverage.
- Mukherjee, Smita,Datta, Alokmay,Giglia, Angelo,Mahne, Nichole,Nannarone, Stefano
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- PROCESS FOR PRODUCING SEMICONDUCTOR NANOCRYSTAL CORES, CORE-SHELL, CORE-BUFFER-SHELL, AND MULTIPLE LAYER SYSTEMS IN A NON-COORDINATING SOLVENT UTILIZING IN SITU SURFACTANT GENERATION
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A process for producing semiconductor nanocrystal cores, core-shell, core-buffer-shell, and multiple layer systems is disclosed. The process involves a non-coordinating solvent and in situ surfactant generation.
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Page/Page column 6
(2008/06/13)
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- Synthesis of biodiesel via homogeneous Lewis acid catalyst
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Nowadays, most biodiesel (fatty acids methyl esters, FAME) is produced by the transesterification of triglycerides (TG) of refined/edible type oils using methanol and an homogeneous alkaline catalyst. However, production costs are still rather high compared with the ones of petroleum-based diesel fuel. To lower costs and make biodiesel competitive less-expensive feedstocks such as waste fats or non-edible type oils could be used. The use of homogeneous alkaline catalysts in the transesterification of such types of fats and oils poses great difficulties due to the presence of large amounts of free fatty acids (FFA). This paper studies the use of carboxylic salts as a possible alternative, because these catalysts are active also in the presence of high FFA concentrations. The most active catalyst (Cd, Mn, Pb, Zn carboxylic salts) have been individuated and a correlation of the activities with the cation acidity has been found.
- Di Serio,Tesser,Dimiccoli,Cammarota,Nastasi,Santacesaria
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p. 111 - 115
(2008/10/09)
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- Kinetic roughening of the interfaces of Langmuir-Blodgett films
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We report x-ray scattering and atomic force microscopy measurements on the interfacial roughening of cadmium stearate Langmuir-Blodgett (LB) films of different total thickness. It is shown that the growth front becomes rougher as the film grows thicker. The initial sublayers in the films follow the fluctuations of the substrate. However, intrinsic roughening induced by pinholes shows up very soon so that the interfaces eventually exhibit logarithmic correlation. All experiments are explained quantitatively using the correlation function derived from a recently proposed growth equation for imperfect LB films. This supports the idea that the interfacial morphology in LB films is determined by the competition between the roughening arising from pinholes and the smoothening due to the surface tension of the membranes.
- Li, Xiu-Hong,Li, Ming,Mai, Zhen-Hong
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- Preparation of metal carboxylates and their stabilizing performance under intense high-pressure shear treatment
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Solid-phase synthesis of certain metal carboxylates and their effect on stabilization of polyvinyl chloride under intense high-pressure shear treatment were studied.
- Akhmetkhanov,Kolesov,Kadyrov,Karmilov,Zaikov
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p. 842 - 845
(2007/10/03)
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- Liquid Phase Oxidation of s-Butyltoluene
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Oxidation of s-butyltoluene (SBT) to its hydroperoxide (ROOH) by oxygen has been studied in the presence and absence of catalysts in aqueous suspension at 80 deg to 116 deg C and 1 to 8.5 kg/cm2 O2 pressure.The oxidation rate is higher at higher pressures and the selectivity to ROOH formation is the highest when no catalyst is used.Effects of various reaction parameters have been studied in the absence of catalyst.A reaction temperature of 100 deg, SBT-water ratio of 1:2 and oxygen pressure of more than 3 kg/cm2 are found to be the most suitable for ROOH formation.Oxidation above 11.5percent ROOH level leads mainly to byproducts including s-butylbenzoic acid.
- Kulsrestha, Girendra N.,Pathania, Bikram S.,Sharma, Krishna G.,Sharma, Jaipal S.,Negi, Janaki,Bhattacharyya, Kshitindra K.
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p. 636 - 638
(2007/10/02)
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