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1.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
2.
Anwar Usman Ibrahim Abdul Razak Suchada Chantrapromma Hoong‐Kun Fun Varughese Philip A. Sreekanth M. R. Prathapachandra Kurup 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o652-o654
The title compound, C16H17N5S, is in the thione form and crystallizes with two independent molecules in the asymmetric unit. In both molecules, the pentamethyleneimine five‐membered ring adopts an envelope conformation, and in one of the molecules this ring shows positional disorder. The thione S and hydrazine N atoms are in the Z configuration with respect to the C—N bond. 相似文献
3.
Varughese M. Alexander 《Tetrahedron letters》2005,46(40):6957-6959
Bismuth(III) nitrate pentahydrate is found to be an efficient catalyst for the Pechmann condensation reaction of phenols and β-ketoesters under solvent-free conditions. The reaction protocol is simple and is followed by aqueous work-up leading to the formation of the corresponding coumarin derivatives in good yield and high purity. 相似文献
4.
Sunil Varughese 《Tetrahedron letters》2005,46(14):2411-2415
A novel organic assembly, formed between 3,5-dinitro-4-methylbenzoic acid and trans-1,2-bis(4-pyridyl)ethene under hydrothermal conditions in the presence of Pr(III) and a layered structure obtained by direct co-crystallization of the reactants at ambient conditions is reported. The structures of the complexes were established, unambiguously, by single crystal X-ray diffraction methods. 相似文献
5.
Dr. Sunil Varughese Dr. Mangalampalli S. R. N. Kiran Prof. Upadrasta Ramamurty Prof. Gautam R. Desiraju 《化学:亚洲杂志》2012,7(9):2118-2125
Nanoindentation and scratch experiments on 1:1 donor–acceptor complexes, 1 and 2 , of 1,2,4,5‐tetracyanobenzene with pyrene and phenanthrene, respectively, reveal long‐range molecular layer gliding and large interaction anisotropy. Due to the layered arrangements in these crystals, these experiments that apply stress in particular directions result in the breaking of interlayer interactions, thus allowing molecular sheets to glide over one another with ease. Complex 1 has a layered crystal packing wherein the layers are 68° skew under the (002) face and the interlayer space is stabilized by van der Waals interactions. Upon indenting this surface with a Berkovich tip, pile‐up of material was observed on just one side of the indenter due to the close angular alignment of the layers with the half angle of the indenter tip (65.35°). The interfacial differences in the elastic modulus (21 %) and hardness (16 %) demonstrate the anisotropic nature of crystal packing. In 2 , the molecular stacks are arranged in a staggered manner; there is no layer arrangement, and the interlayer stabilization involves C? H???N hydrogen bonds and π???π interactions. This results in a higher modulus (20 %) for (020) as compared to (001), although the anisotropy in hardness is minimal (4 %). The anisotropy within a face was analyzed using AFM image scans and the coefficient of friction of four orthogonal nanoscratches on the cleavage planes of 1 and 2 . A higher friction coefficient was obtained for 2 as compared to 1 even in the cleavage direction due to the presence of hydrogen bonds in the interlayer region making the tip movement more hindered. 相似文献
6.
Pure water which is free of toxic chemicals is necessary for human health. So, detection and control of heavy metal ions in water is very important. Keeping this in mind, selective and sensitive optical sensor based on surface plasmon resonance for detection of various heavy metals in water using gold nanoparticles was explained in this present study. These AuNPs were prepared using Hibiscus cannabinus leaf extract as reducing agent with the average particle size of 22 nm. These gold nanoparticles are considerably selective and sensitive towards Fe3+ and it was used to detect the concentration of Fe3+ ions in water in the range 29.82–173.74 μM by tracking the absorbance changes of SPR band and the sensitivity of the system towards the Fe3+ concentration and it was found to be 0.0037 μM?1. We hope that these gold nanoparticles can be used for detecting Fe3+ ions concentration, in the water purification processes. 相似文献
7.
Achamma Kurian C V Bindhu S S Harilal Riju C Issac V P N Nampoori C P G Vallabhan 《Pramana》1994,43(5):401-406
A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution
is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration
gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations,
the variation of diffusion coefficient with concentration can be determined. 相似文献
8.
Magnetic iron oxide nanoparticles for biorecognition: evaluation of surface coverage and activity 总被引:1,自引:0,他引:1
Koh I Wang X Varughese B Isaacs L Ehrman SH English DS 《The journal of physical chemistry. B》2006,110(4):1553-1558
Modifying the surfaces of magnetic nanoparticles (MNPs) by the covalent attachment of biomolecules will enable their implementation as contrast agents for magnetic resonance imaging or as media for magnetically assisted bioseparations. In this paper we report both the surface coverage and the activity of IgG antibodies on MNPs. The antibodies were immobilized on gamma-Fe2O3 nanoparticles by conventional methods using aminopropyltriethoxy silane and subsequent activation by glutaraldehyde. Novel fluorescence methods were used to provide a quantitative evaluation of this well-known approach. Our results show that surface coverage can be stoichiometrically adjusted with saturated surface coverage occurring at approximately 36% of the theoretical limit. The saturated surface coverage corresponds to 34 antibody molecules bound to an average-sized MNP (32 nm diameter). We also show that the immobilized antibodies retain approximately 50% of their binding capacity at surface-saturated levels. 相似文献
9.
C V Bindhu S S Harilal Riju C Issac Geetha K Varier V P N Nampoori C P G Vallabhan 《Pramana》1995,44(3):231-235
Pulsed photoacoustic measurements have been carried out in toluene at 532 nm wavelength using a Q-switched frequency doubled
Nd:YAG laser. The variation of photoacoustic signal amplitude with incident laser power indicates that at lower laser powers
one photon absorption takes place at this wavelength while a clear two photon absorption occurs in this liquid at higher laser
powers. The studies made here demonstrate that pulsed photoacoustic technique is simple and effective for the investigation
of multiphoton processes in liquids. 相似文献