Showing papers by "Somnath Ghosh published in 2014"
TL;DR: The general physical conditions required for capturing sliding drops on an inclined plane that is equipped with electrically tunable wetting defects are determined and it is shown that electrically Tunable defects can be used to guide sliding drops along actively switchable tracks—with potential applications in microfluidics.
Abstract: Controlling the motion of drops on solid surfaces is crucial in many natural phenomena and technological processes including the collection and removal of rain drops, cleaning technology and heat exchangers Topographic and chemical heterogeneities on solid surfaces give rise to pinning forces that can capture and steer drops in desired directions Here we determine general physical conditions required for capturing sliding drops on an inclined plane that is equipped with electrically tunable wetting defects By mapping the drop dynamics on the one-dimensional motion of a point mass, we demonstrate that the trapping process is controlled by two dimensionless parameters, the trapping strength measured in units of the driving force and the ratio between a viscous and an inertial time scale Complementary experiments involving superhydrophobic surfaces with wetting defects demonstrate the general applicability of the concept Moreover, we show that electrically tunable defects can be used to guide sliding drops along actively switchable tracks—with potential applications in microfluidics
96 citations
TL;DR: In this paper, the effect of silicate content (SiO2/Na2O) of an activator on physical and mechanical properties of alkali-activated blast furnace slag paste has been investigated.
Abstract: The effect of silicate content (SiO2/Na2O) of an activator on physical and mechanical properties of alkali-activated blast furnace slag paste has been investigated. The paste was produced by activating blast furnace slag with sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution. The SiO2/Na2O ratio varied from 0.2 to 1.2. The test specimens were cast and cured in water (fully immersed condition) at room temperature and the direct compressive strength at the age of 3, 7, 14, 21, 28 days were obtained. It has been observed that the compressive strength and ultrasonic pulse velocity of test specimen increases with the increase in silicate content up to a silicate ratio of 0.8. Compressive strength is found to be a maximum 44.53 MPa at 28 days. It is noticed further that the compressive strength increases with age. It is also observed that the silicate ratio has a significant influence on porosity, water absorption and water sorptivity. The mineralogical and micro-structural changes were studied using XRD and SEM/EDX, while porosity, total pore volume, pore-size distribution, etc., were studied using mercury intrusion porosimetry.
26 citations
TL;DR: A mild heterogeneous oxidizing agent, cupric bromide has been used for the oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridine derivatives in excellent yields with the isolation of products by simple work-up procedure.
25 citations
TL;DR: In this paper, a chalcogenide glass based tapered microstructured optical fiber (MOF) was used to generate high power parabolic pulses (PPs) at the mid-IR wavelength.
Abstract: This paper presents a theoretical design of chalcogenide glass based tapered microstructured optical fiber (MOF) to generate high power parabolic pulses (PPs) at the mid-IR wavelength (~2 μm). We optimize fiber cross-section by the multipole method and studied pulse evolution by well-known symmetrized split-step Fourier Method. Our numerical investigation reveals the possibility of highly efficient PP generation within a very short length (~19 cm) of this MOF for a Gaussian input pulse of 60 W peak power and full width at half maximum (FWHM) of 3.5 ps. We examined quality of the generated PP by calculating the misfit parameter including the third order dispersion and fiber loss. Further, the effects of variations in input pulse power, pulse width and pulse energy on generated PP were also studied from the point of view of tolerances in fabrication of such a device.
11 citations
17 Nov 2014
TL;DR: In this paper, the antibacterial properties of ZnO NPs were investigated against both Gram-positive and Gram-negative bacteria, and the surface oxygen vacancy and thereby reactive oxygen species (ROS) production were quantified by photoluminescence (PL) and electron paramagnetic resonance (EPR) spin trapping experiments, respectively.
Abstract: ZnO nanoparticles (NPs) are well known for their bactericidal properties. Various mechanisms are proposed for their bactericidal activity. An ambiguity still prevails to know which mechanism or property is mainly influencing the bactericidal activity of ZnO NPs. The antibacterial properties of ZnO NPs were investigated against both Gram-positive and Gram-negative bacteria. Different ZnO samples with different degrees of surface oxygen vacancies were prepared from ZnO2. The surface oxygen vacancy and thereby reactive oxygen species (ROS) production in aqueous ZnO solution are quantified by photoluminescence (PL) and electron paramagnetic resonance (EPR) spin trapping experiments, respectively. Systematic experiments have been performed to validate a precise antibacterial mechanism of ZnO particle.
8 citations
TL;DR: In this paper, the effect of incorporating blast furnace slag on mechanical properties and durability of resulting fly ash geopolymer paste sample was investigated, and the results showed that the addition of blast furnaces slag considerably improved the mechanical properties of the fly ash paste.
Abstract: In this program consequence of incorporating blast furnace slag on mechanical properties and durability of resulting fly ash geopolymer paste sample was investigated. The program consisted immersion of geopolymer samples having percentage blast furnace slag ranging from 10 to 20 of fly ash in a 10% magnesium sulfate solution up to a period of 15 weeks and evaluation of its resistance in terms visual appearance, change in weight and compressive strength at regular interval. Addition of blast furnace slag considerably improved mechanical properties and durability of geopolymers paste.
7 citations
TL;DR: In this paper, the effect of synthesis parameter, silicon/aluminum molar ratio, on the engineering properties of alkali-activated blast-furnace slag paste has been investigated.
Abstract: The effect of synthesis parameter, silicon/aluminum molar ratio, on the engineering properties of alkali-activated blast-furnace paste has been investigated. The article presents the study of the compressive strength and microstructure of alkali-activated blast-furnace slag paste specimens prepared using sodium silicate and potassium hydroxide solution as activators. The experimental results have indicated that the compressive strength, bulk density, apparent porosity, water absorption and microstructure of the specimens are significantly affected by the silicon/aluminum molar ratio of alkali-activated ground granulated blast-furnace slag (AAS) paste. The compressive strength at 28 d of 44·90–46·30 MPa was obtained for silicon/aluminum ratios of 2·03–2·26. Increasing silicon/aluminum ratio beyond 2·26 resulted in a decrease in compressive strength of AAS paste due to delayed precipitation of calcium silicate hydrate products. The microstructural changes of hardened AAS paste were studied using scanning el...
6 citations
TL;DR: A numerically designed all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6m through degenerate four-wave mixing by considering a continuous wave CO laser of 5?10?W power emitting at 5.6??m as the pump is reported in this article.
Abstract: We report a numerically designed highly nonlinear all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6??m through degenerate four-wave mixing by considering a continuous wave CO laser of 5?10?W power emitting at 5.6??m as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, a narrow (N)- and/or broad (B)- band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20?dB is achievable for the N-band source at 6.46??m with a maximum power conversion efficiency (Cm) ~ 33%, while a amplification ~22?????2?dB is achievable for a B-band source over the wavelength range of 5?6.3??m with a Cm?>?40%.
4 citations
TL;DR: In this article, the role of a prominent photonic bandgap (PBG) in the phenomenon of transverse localization of light in a semi-infinite lossless waveguide lattice consisting of evanescently coupled disordered one-dimensional optical waveguides has been investigated numerically.
Abstract: The role of a prominent photonic bandgap (PBG) in the phenomenon of transverse localization of light in a semi-infinite lossless waveguide lattice consisting of evanescently coupled disordered one-dimensional optical waveguides has been investigated numerically. The interplay between the underlying photonic bandgap due to inherent periodicity of the optical system and various levels of deliberately induced transverse disorder in its refractive index periodicity has been studied. We show that the PBG indeed plays an important role and that its simultaneous presence could catalyze realization of localized light even when the strength of disorder is not sufficiently strong to independently cause localization of light. An important outcome of this study revealed that the PBG could be gainfully exploited to tailor the spectral window for localization of light in potential applications such as lasing in a disordered optical lattice.
3 citations
TL;DR: In this article, the crystal structures of N -2-chlorophenyl ( acetamide) and phenyl (2-bromomethyl) benzoate have been determined from laboratory X-ray powder diffraction data.
Abstract: Crystal structures of N -(2-chlorophenyl) acetamide ( 1 ) and phenyl (2-bromomethyl) benzoate ( 2 ) have been determined from laboratory X-ray powder diffraction data. In addition to intermolecular N–H···O and C–H···O hydrogen bonds, the crystal packing in ( 1 ) and ( 2 ) exhibits weak C–H···Cl/Br interactions, which facilitate formation of three-dimensional architectures. Hirshfeld surface analysis of compounds ( 1 ), ( 2 ), and a few related chloro- and bromo-phenyl derivatives retrieved from the CSD indicates that 83–97% of Hirshfeld surface areas in this class of compounds are due to H···H, H···π, H···O, and H···Cl/Br contacts.
2 citations
01 Jan 2014
TL;DR: Scanning electron microscopy along with EDAX was conducted in a manner to evaluate microstructural and mineralogical aspects of geopolymer specimens to evaluate workability, strength and micro-structure.
Abstract: The research evolves the parametric study of geopolymer paste resulting from various combination of alkali activation. In this experimental study 4 series of geopolymer paste differing in the combination of alkali activation were prepared by activating low calcium fly ash. For every case activators were subjected to a controlled temperature (35C) for duration of 24 hours. The geopolymer specimens were allowed for a hot curing under 85C temperature for 48 hours. The parameters like workability, strength and micro-structure were analyzed. Scanning electron microscopy along with EDAX was conducted in a manner to evaluate microstructural and mineralogical aspects of geopolymer specimens.
TL;DR: In this article, the initial and secondary absorption and compressive strength of AAS paste have been investigated based on the Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic Cement Concretes, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, 2004, pp. 1-4.
Abstract: The initial/secondary absorption and compressive strength of alkali-activated slag (AAS) paste has been investigated. Emphasis has been given to secondary absorption of AAS paste based on the method described in ASTM C1585-04 [Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic Cement Concretes, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA, 2004, pp. 1–4]. The paste was produced by activating blast furnace slag with sodium hydroxide/potassium hydroxide and sodium silicate solution. The major parameters studied were alkali content, silicate content, and the type of activator. Experimental investigation revealed that initial rate of absorption (Si) and secondary rate of absorption (Ss) decreases with increase in alkali and silicate content up to a certain limit with an increase in compressive strength. The maximum compressive strength was found to be 50.40 MPa for the specimens having lowest sorptivity. It was also found that the sorptivity ratio (Si/Ss) plays a significant role on compressive strength in turn on the durability of AAS composites. This paper is an attempt to introduce the simple method of measuring initial and secondary sorptivity described in ASTM C1585-04 to study the strength and durability of AAS. The microstructure study was carried out using SEM/EDAX.
TL;DR: In this article, a right amount of disorder in the form of refractive index variation has been introduced to achieve transverse localization of light in 1D semi-infinite photonic lattices.
Abstract: A right amount of disorder in the form of refractive index variation has been introduced to achieve transverse localization of light in 1D semi-infinite photonic lattices. Presence of longitudinally-invariant transverse disorder opens-up a new waveguiding mechanism.
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TL;DR: In this paper, numerically designed highly nonlinear all glass chalcogenide microstructured optical fiber for efficient generation of light around 6 micron through degenerate four wave mixing by considering continuous wave CO laser of 5 to 10 Watts power emitting at 5.6 micron as the pump.
Abstract: We report numerically designed highly nonlinear all glass chalcogenide microstructured optical fiber for efficient generation of light around 6 micron through degenerate four wave mixing by considering continuous wave CO laser of 5 to 10 Watts power emitting at 5.6 micron as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, narrow and broad band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 decibel is achievable for the narrow band source at 6.46 micron with a maximum power conversion efficiency of 33 percent while amplification of 22 decibel is achievable for a B-band source over the wavelength range of 5 to 6.3 micron with a conversion efficiency of 40 percent.
01 Jan 2014
TL;DR: In this paper, the authors evaluate the curing temperature at which the fly ash based geopolymer can achieve its best mechanical properties with the presence of supplementary calcium source and find out the right curing temperature in a manner to obtain the optimized strength under compression.
Abstract: The aim of this research is to evaluate the curing temperature at which the fly ash based geopolymer can achieve its best mechanical properties with the presence of supplementary calcium source. Wide range of curing temperature from 55 o C-85 o C was imposed to sample GP (without any calcium compound) and sample GB (with 15% of slag as supplementary material) to have their comparative performance. The prime objective is to find out the right curing temperature in a manner to obtain the optimized strength under compression.