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Showing papers by "Somnath Ghosh published in 2010"


Journal ArticleDOI
TL;DR: Highly stable silver nanoparticles in agar-agar (Ag/agar) as inorganic-organic hybrid were obtained as free-standing film by in situ reduction of silver nitrate by ethanol and the mechanical strength of the film determined by nanoindentation technique showed almost retention of the strength even after repeated cycle.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of fly ash based geopolymer mortar specimens in Magnesium Sulphate solution was evaluated in terms of visual appearance, variation of pH of solution, change in weight and change in compressive strength over the exposure period.
Abstract: An experimental investigation was conducted to study the performance of fly ash based geopolymer mortar specimens in Magnesium Sulphate solution. Specimens were manufactured from low calcium fly ash by activation with a mixture of Sodium Hydroxide and Sodium Silicate solution and cured thermally. 10% by weight Magnesium Sulphate solution was used to soak the specimen up to 24 weeks. Performance of the specimens was evaluated in terms of visual appearance, variation of pH of solution, change in weight, and change in compressive strength over the exposure period. White deposits occurred on the surface of specimen which was initially soft but later converted to hard crystals. pH of solution increased noticeably during the initial weeks which indicate migration of alkalis from mortar specimens. At the end of 24 weeks samples experienced very little weight gain and recorded a loss of compressive strength by up to 56%.

95 citations


01 Jan 2010
TL;DR: In this article, the effect of incorporating silica fume in the fly ash geopolymer on its porosity and compressive strength was investigated, and the results of an experimental study performed to investigate effect of integrating silica Fume in fly ash was presented.
Abstract: This paper presents the results of an experimental study performed to investigate effect of incorporating silica fume in the fly ash geopolymer on its porosity and compressive strength. Geopolymer specimens were prepared by activating fly ash incorporated with additional silica fume in the range of 2.5% to 5% with a mixture of sodium hydroxide and sodium silicate having Na2O content of 8%. The characterization of the geopolymer specimens was done with ESEM/EDAX and MIP tests. Addition of silica fume up to 5% enhanced compressive strength of geopolymer mortars. However, further increase of silica fume caused a decrease in compressive strength. SEM micrographs for specimens incorporated with silica fume showed better microstructure and exhibited lesser porosity. MIP results of paste specimens indicate higher pore volume in the specimen prepared with additional silica fume while for mortar specimens; the pore volume was seen lesser in specimens with additional silica fume. Silica fume may be used as an additional material to improve or modify some properties of the resulting geopolymer.

53 citations


Journal ArticleDOI
TL;DR: The interaction of 9-phenyl acridine (ACPH) with calf thymus DNA (CT-DNA) based on various biophysical and molecular modelling studies indicates that binding of ACPH is through partial intercalation in the minor groove of DNA.
Abstract: Acridines and their derivatives are well-known probes for nucleic acids as well as being relevant in the field of drug development to establish new chemotherapeutic agents. We have shown from molecular modelling studies that 9-phenyl acridine and some of its derivatives can act as inhibitors of topoisomerase I and thus have potential to act as anticancer agents. Rational design of new compounds for therapeutics requires knowledge about their structural stability and interactions with various cellular macromolecules. In this regard it is important to know how these molecules would interact with DNA. Here we report the interaction of 9-phenyl acridine (ACPH) with calf thymus DNA (CT-DNA) based on various biophysical and molecular modelling studies. Spectrophotometric studies indicated that ACPH binds to CT-DNA. DNA melting studies revealed that binding of ACPH to CT-DNA resulted in a small increase in melting temperature, which is unlikely in case of classical intercalator; rather, it indicates external binding. Viscosity measurements show that ACPH exhibits groove binding. Competitive binding of ACPH to CT-DNA pre-bound to ethidium bromide (EB) showed slow quenching. Measurement of the binding constant of ACPH by fluorescent intercalator displacement (FID) assay corroborated the notion that there was groove binding. Molecular modelling studies also supported this finding. Results indicate that binding of ACPH is through partial intercalation in the minor groove of DNA.

27 citations


Journal ArticleDOI
TL;DR: Spectrofluorimetric studies reveal that the copper complex exhibits partial DNA intercalation as well as partial DNA minor groove binding properties and agarose gel electrophoresis study with different radical scavengers concludes that the production of both hydroxyl radicals and reactive oxygen species is responsible for this nuclease activity.
Abstract: The DNA binding property of a Cu(II) complex, viz., [Cu(mal)(2)](picH)(2).2H(2)O, (mal)(2) = malonic acid, picH = protonated 2-amino-4-picoline, has been investigated in this study. The binding of this complex with plasmid and chromosomal DNA has been characterized by different biophysical techniques. From the absorption and fluorescence spectroscopic studies, it has been observed that the said copper complex binds strongly with pUC19 plasmid and CT DNA with a binding affinity of 2.368 x 10(3) and 4.0 x 10(3) M(-1), respectively, in 10 mM citrate-phosphate buffer, pH 7.4. Spectrofluorimetric studies reveal that the copper complex exhibits partial DNA intercalation as well as partial DNA minor groove binding properties. Consequently, in agarose gel electrophoresis study, it has been observed that the complex alone induces positive supercoiling in plasmid DNA while in the presence of H(2)O(2) it exhibits nuclease activity. The induction of the breakage in DNA backbone depends upon the relative concentrations of H(2)O(2) and copper complex followed by the time of incubation with DNA. Optical DNA melting study, isothermal titration calorimetry, and absorption spectroscopy have been used to characterize the nuclease activity of this complex in the presence of H(2)O(2). Further, (1)H NMR study indicates that Cu(II) in the complex is converted into the Cu(I) state by the reduction of H(2)O(2). Finally, agarose gel electrophoresis study with different radical scavengers concludes that the production of both hydroxyl radicals and reactive oxygen species is responsible for this nuclease activity.

20 citations


Journal ArticleDOI
TL;DR: In this paper, a chirped cladding is proposed as a novel tailoring tool to simultaneously attain wider transmission window and reduced temporal dispersion in an all-solid Bragg-like microstructured optical fiber as compared to its perfectly periodic cladding counterpart.
Abstract: Chirped cladding is proposed as a novel tailoring tool to simultaneously attain wider transmission window and reduced temporal dispersion in an all-solid Bragg-like microstructured optical fiber as compared to its perfectly periodic cladding counterpart. This design route for photonic bandgap microstructured fibers could be exploited as an additional degree of freedom for bandgap engineering. A suitably chirped clad fiber could be gainfully exploited to deliver femto-second pulse with ultra wide bandwidth. Further, generation of self-similar parabolic profile pulse is demonstrated by simulating propagation of an input Gaussian pulse through a 2 m long sample of such a linearly tapered Bragg like fiber.

19 citations


Journal ArticleDOI
TL;DR: In this paper, the formation and spatial modulation of strongly coupled gallium selenide quantum dot (QD) nanoassemblies suspended in a nematic liquid-crystal (NLC) matrix at room temperature are demonstrated.
Abstract: We demonstrate the formation and spatial modulation of strongly coupled gallium selenide quantum dot (QD) nanoassemblies suspended in a nematic liquid-crystal (NLC) matrix at room temperature. Using static and dynamic optical techniques we show that the coupled QDs aggregate with a well-defined directionality commensurate with the NLC director axis. This results in highly anisotropic spectral properties of the QD assembly. The spatial orientation of the aggregates is selectively controlled in situ by the application of in-plane electric fields. The strong interdot coupling further increases the excitonic recombination rate which is both direction and electric field dependent. This electrical modulation, a noninvasive process, could potentially be an important functionality for the design and creation of building blocks for novel optoelectronic devices.

18 citations


Journal ArticleDOI
TL;DR: The biphasic activation of the sensor proteins, ATM, and DNA-PK and no activation of ATR by proton irradiation is found and the mechanism of excessive cell killing in proton beam-irradiated cells was found to be upregulation of Bax and down regulation of Bcl-2.
Abstract: The aim of the current study was to determine the signaling differences between gamma- and proton beam-irradiations. A549 lung adenocarcinoma cells were irradiated with 2 Gy proton beam or gamma-radiation. Proton beam was found to be more cytotoxic than gamma-radiation. Proton beam-irradiated cells showed phosphorylation of H2AX, ATM, Chk2, and p53. The mechanism of excessive cell killing in proton beam-irradiated cells was found to be upregulation of Bax and downregulation of Bcl-2. The noteworthy finding of this study is the biphasic activation of the sensor proteins, ATM, and DNA-PK and no activation of ATR by proton irradiation.

14 citations


Journal ArticleDOI
TL;DR: In this paper, a systematic study of hydrogenated amorphous silicon nitride films deposited by varying gas flow rate ratio (R ǫ = SiH 4 /NH 3 ) using Photo-Chemical Vapour Deposition (PCVD) was conducted.

13 citations


Journal ArticleDOI
TL;DR: Theoretical total cross sections for the double charge transfer in proton-helium collisions were analyzed using the four-body boundary corrected continuum intermediate state approximation in the energy range of 30 to 500 keV as discussed by the authors.
Abstract: Theoretical total cross sections for the double charge transfer in proton-helium collisions are analysed using the four-body boundary corrected continuum intermediate state approximation in the energy range of 30 to 500 keV. We have also obtained differential double capture cross sections as a functions of projectile scattering angle. The intermediate continuum state of each of the active electron has been taken into account in this formalism. Our calculated results are compared with the previous experimental and theoretical values. The agreement is very encouraging.

9 citations


Journal ArticleDOI
TL;DR: In this article, a new procedure for benzoylation of aromatic and aliphatic amines was developed in neat phase without use of any solvent or alkali, and the procedure was shown to work well in the case of amines.
Abstract: A new procedure for benzoylation of aromatic and aliphatic amines has been developed in neat phase without use of any solvent or alkali.

Journal ArticleDOI
TL;DR: In this paper, the tensile shear strength and fatigue strength of lap shear joint of two automotive steel sheets are determined and compared and micrographs of fatigue fractured surfaces are examined to understand fracture micro-mechanisms.
Abstract: Fatigue performance of spot welded lap shear joint is primarily dependent on weld nugget size, sheet thickness and corresponding joint stiffness. Two automotive steel sheets having higher strength lower thickness and lower strength higher thickness are resistance spot welded with established optimum welding condition. The tensile-shear strength and fatigue strength of lap shear joint of the two automotive steel sheets are determined and compared. Experimental fatigue life of spot welded lap shear joint of each steel are compared with predicted fatigue lives using different stress intensity factor solutions for kinked crack and spot weld available in literature. Micrographs of fatigue fractured surfaces are examined to understand fracture micro-mechanisms.

Journal ArticleDOI
TL;DR: In this article, an all-optical method of controlling hysteretic emission of evanescently coupled GaAs microdisk pairs is presented. But the method is not suitable for large arrays.
Abstract: Optical microresonators crafted from semiconducting materials are powerful systems for both understanding and harnessing the interactions between light and matter. We report an all-optical method of controlling the hysteretic emission of evanescently coupled GaAs microdisk pairs. Under partial excitation, the coupled lasing emission demonstrates optical bistability caused by saturable absorption. We observe that the presence of hysteresis can be modulated by the polarization state of the incident excitation. This optical control is an important functionality which, if extended to a large array, could lead to the creation of optical flip-flop and gated logic devices with multinode capabilities.

Journal ArticleDOI
TL;DR: In this article, a method for the synthesis of α-diazocarbonyl/sulfonyl compounds from active methylene precursors using tosyl azide or 4-carboxybenzenesulfonyls azide and potassium carbonate is presented.
Abstract: A highly efficient methodology in solid state has been developed for the synthesis of α-diazocarbonyl/sulfonyl compounds from active methylene precursors using tosyl azide or 4-carboxybenzenesulfonyl azide and potassium carbonate, devoid of any aqueous work-up, save a column filtration over silica gel.

Proceedings ArticleDOI
TL;DR: In this paper, a numerical investigation on the transverse localization of light in a lattice of disordered coupled waveguides is presented. And the interplay of disorder with medium's nonlinearity in localization from application point of view is studied.
Abstract: We report a numerical investigation on the transverse localization of light in a lattice of disordered coupled waveguides. The interplay of disorder with medium’s nonlinearity in localization from application point of view is studied.