Showing papers by "Somnath Ghosh published in 2018"
TL;DR: In this paper, the field emission properties of indium-decorated vertically aligned multi-walled carbon nanotube (MWCNT) films are investigated, and the superior FE properties are achieved for 4-nm-thick indiumcoated MWCNTs as compared to those coated with higher thicknesses of Indium and pristine CNTs.
Abstract: Field emission (FE) properties of indium-decorated vertically aligned multi-walled carbon nanotube (MWCNT) films are investigated. The superior FE properties are achieved for 4-nm-thick indium-coated MWCNTs as compared to those coated with higher thicknesses of indium and pristine CNTs. Optimization in the FE properties is primarily attributed to transformation of sp2- to sp3-hybridized carbons and indium thickness. Other factors important for the better FE properties are enhanced density of states near the Fermi level and slightly improved field enhancement factor at relatively low applied electric fields.
20 citations
TL;DR: The study presents a profile for structural and thermodynamic parameters, for the binding of 4NCO with DNA, which was hydrophobic in nature and the process of binding was spontaneous, endothermic and entropy-driven.
16 citations
TL;DR: In this paper, an all-lossy dual-mode planar waveguide structure is proposed for topological control of light signals, where the topological properties of an EP are achieved by patterning the longitudinal loss profile only.
Abstract: Recent technological advances have boosted research related to $e\phantom{\rule{0}{0ex}}x\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}s$ (EPs), singularities arising in non-Hermitian quantum mechanics that once seemed purely mathematical. Device-level implementation of EPs has been primarily in gain-loss-balanced toroidal optical microcavities, but too much gain can cause such a system to become unstable. This study proposes an all-lossy dual-mode planar waveguide structure, in which the topological properties of an EP are achieved by patterning the longitudinal loss profile only. This scheme needs no active pumping, is accessible to many conventional optical elements, and offers a platform for topological control of light signals.
16 citations
TL;DR: In this paper, the growth of vertically aligned carbon nanotube bundles on Si substrate by thermal chemical vapor deposition technique was reported without any carrier gas or lithography-assisted deposition.
Abstract: We report the growth of vertically aligned carbon nanotube bundles on Si substrate by thermal chemical vapor deposition technique. Vertical alignment was achieved without any carrier gas or lithography-assisted deposition. Growth has been carried out at 850 °C for different quantities of solution of xylene and ferrocene ranging from 2.25 to 3.00 ml in steps of 0.25 ml at a fixed concentration of 0.02 gm (ferrocene) per ml. To understand the growth mechanism, deposition was carried out for different concentrations of the solution by changing only the ferrocene quantity, ranging from 0.01 to 0.03 gm/ml. A tunable vertical alignment of multi-walled carbon nanotubes (CNTs) has been achieved by this process and examined by scanning and transmission electron microscopic techniques. Micro-crystalline structural analysis has been done using Raman spectroscopy. A systematic variation in field emission (FE) current density has been observed. The highest FE current density is seen for the film grown with 0.02 gm/ml concentration, which is attributed to the better alignment of CNTs, less structural disorder and less entanglement of CNTs on the surface. The alignment of CNTs has been qualitatively understood on the basis of self-assembled catalytic particles.
15 citations
TL;DR: In this paper, a 1D planar optical waveguide with transverse distribution of inhomogeneous loss profile, which exhibits an exceptional point (EP), is presented, where the interaction between them in the vicinity of the EP is controlled by proper adjustment of the inhomogeneity in attenuation profile only.
Abstract: We report a 1D planar optical waveguide with transverse distribution of inhomogeneous loss profile, which exhibits an exceptional point (EP). The waveguide hosts two leaky resonant modes; where the interaction between them in the vicinity of the EP is controlled by proper adjustment of the inhomogeneity in attenuation profile only. We study the adiabatic dynamics of propagation constants of the coupled modes by quasi-static encirclement of control parameters around the EP. Realizing such an encirclement with the inhomogeneous loss distribution along the direction of light propagation, we report the breakdown of adiabatic evolution of two coupled modes through the waveguide in presence of an EP. Here, during conversion the output mode is irrespective of the choice of input excited mode but depends on the direction of light transportation. This topologically controlled, robust scheme of asymmetric mode conversion in the platform of the proposed all-lossy waveguide structure may open up an extensive way-out for implementation of state-transfer applications in chirality driven waveguide-based devices.
14 citations
TL;DR: It is suggested that the apoptotic effect of DHP-8 in A375 and HepG2 cells was mediated by AKT and survivin pathways through SIRT1 activation, and the possible potential and therapeutic role of D HP-8 is emphasized in skin and liver cancer.
Abstract: 1,4-Dihydropyridines (1,4-DHPs) are important as a class of heterocyclic compounds that exhibit wide range of biological actions. Many of its derivatives are already characterized as medicinally important drugs and used worldwide. In this study, we have screened some novel Hantzsch 1,4-DHP compounds using both in silico (QSAR and Pharmacophore) and in vitro (cytotoxic screening). 1,4-DHP showed selective cytotoxicity against five human cancerous cell lines; A375, A549, HeLa, HepG2 and SH-SY5Y but limited effect towards normal skin keratinocyte (HaCaT), lung fibroblast (WL-38) and healthy peripheral blood mononuclear cells. In A375 and HepG2 cells, one of the 1,4-DHP derivative (DHP-8) was found to inhibit cell proliferation, and simultaneously increased the apoptotic population as well as mitochondrial membrane depolarization. Furthermore, the mitochondrial signal was triggered with the activation of cleaved Caspase9, Caspase3 and PARP. The treatment with DHP-8 also increased the expression level of SIRT1, subsequently decreasing the level of pAKTser473 and survivin. Reduced pAKTser473 expression led to decrease the phosphorylated inactive form of GSK3βser9 and as a result, proteasomal degradation of Mcl-1 occurred in both the cell lines. Here, we suggest that the apoptotic effect of DHP-8 in A375 and HepG2 cells was mediated by AKT and survivin pathways through SIRT1 activation. The involvement of DHP-8 in SIRT1 activation was further verified by co-treatment of nicotinamide with DHP-8 in both A375 and HepG2 cells. Overall, this study emphasizes the possible potential and therapeutic role of DHP-8 in skin and liver cancer.
14 citations
TL;DR: In this article, the effect of silica fume-blended fly ash-based geopolymer paste on temperature fluctuation (heating and cooling cycle at certain temperatures) showed better performance than nonblended flies ashbased specimens.
Abstract: This article represents that the mechanical and microstructural properties and durability of fly ash-based geopolymers blended with silica fume and borax are better than those of conventional fly ash-based geopolymers. Fly ash itself contains the sources of silica and alumina which are required for geopolymerisation. But a sufficient amount of high-reactive silica is able to rapidly initiate geopolymerisation with activation. Pure potassium hydroxide pellets and sodium silicate solution were used for preparation of alkaline activator solution. Fly ash geopolymer paste exhibited better mechanical properties in the presence of silica fume with slight portion of borax. The effect of silica fume-blended geopolymer paste on temperature fluctuation (heating and cooling cycle at certain temperatures) showed better performance than nonblended fly ash-based specimens. Durability property was evaluated by immersion of geopolymer specimens in 10% magnesium sulfate solution for a period of one year. The change in weight, strength, and microstructure was studied and compared. In the magnesium sulfate solution, a significant drop of strength to around 37.26% occurred after one year for nonblended fly ash-based specimens. It is evident that specimens prepared incorporating silica fume had the best performance in terms of their properties.
5 citations
01 Jan 2018
TL;DR: In this paper, the compressive strength and the underlying micro-structural change of fly ash geopolymer paste with silica fume and murram as supplements up to 10% and 2.5% of the total weight respectively were investigated.
Abstract: The present study aims to investigate the compressive strength and the underlying micro-structural change of fly ash geopolymer paste with silica fume and murram as supplements up to 10% and 2.5% of the total weight respectively. The workability property of the geopolymer paste samples was evaluated at a green state using a unique methodology based on the polar graph. Besides, various geopolymer paste samples were subjected to heat curing at different temperatures and also for different durations to find the influence of heat curing to the obtained compressive strengths. The present study also probed into the underlying micro-structural changes of the corresponding geopolymer paste samples through SEM (Scanning Electron Microscopy), MIP (Mercury Intrusion Porosimetry) and EDX (Energy Dispersive X-Ray Analysis). Through the present analysis, it can be concluded that blending of silica fume and murram with fly ash based geopolymer paste results in a sustainable high performance binder even at lower alkalinity with lower heat consumption as well as lower water content which can be considered as a better alternative of cement concrete binder to march towards environmental sustainability.
4 citations
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TL;DR: In this paper, a three level non-Hermitian Hamiltonian with three interacting eigenstates is presented, where the matrix elements are optimized in such a way that the intermediate eigenstate interacts with both the other states and the underlying system hosts at least two different second order EPs.
Abstract: The appearance of topological singularities, namely exceptional points (EPs) is an intriguing feature of parameter-dependent open quantum or wave systems. EPs are the special type of nonHermitian degeneracies where two (or more) eigenstates of the underlying system coalesce. In this paper, we present a three level non-Hermitian Hamiltonian which hosts three interacting eigenstates. The matrix elements are optimized in such a way that the intermediate eigenstate interacts with both the other states and the underlying system hosts at least two different second order EPs. The impact of quasi-static parameter variation along a cyclic contour around the embedded EPs on the dynamics of interacting eigenvalues is well investigated in the context of cascaded state conversion. Such dynamics of the eigenvalues shows a clear signature of the third order EP with a combined effect of both the second order EPs. Moreover, we examine the accumulation of phases around the identified EPs and study the hallmark of phase exchange during cascaded state conversions accompanied by the parametric encirclement of the third order EP.
3 citations
15 May 2018-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, a-SiNx:H films under irradiation with 100'MeV Ag7+ ions using elastic recoil detection analysis (ERDA) experiment is reported.
Abstract: Hydrogen loss from a-SiNx:H films under irradiation with 100 MeV Ag7+ ions using elastic recoil detection analysis (ERDA) experiment is reported. The results are explained under the basic assumptions of the molecular recombination model. The ERDA hydrogen concentration profiles are composed of two distinct hydrogen desorption processes, limited by rapid molecular diffusion in the initial stages of irradiation, and as the fluence progresses a slow process limited by diffusion of atomic hydrogen takes over. Which of the aforesaid processes dominates, is determined by the continuously evolving Hydrogen concentration within the films. The first process dominates when the H content is high, and as the H concentration falls below a certain threshold (Hcritical) the irradiation generated H radicals have to diffuse through larger distances before recombining to form H2, thereby significantly bringing down the hydrogen evolution rate. The ERDA measurements were also carried out for films treated with low temperature (300 °C) hydrogen plasma annealing (HPA). The HPA treated films show a clear increase in Hcritical value, thus indicating an improved diffusion of atomic hydrogen, resulting from healing of weak bonds and passivation of dangling bonds. Further, upon HPA films show a significantly higher H concentration relative to the as-deposited films, at advanced fluences. These results indicate the potential of HPA towards improved H retention in a-SiNx:H films. The study distinguishes clearly the presence of two diffusion processes in a-SiNx:H whose diffusion rates differ by an order of magnitude, with atomic hydrogen not being able to diffuse further beyond ∼ 1 nm from the point of its creation.
3 citations
TL;DR: It appears from the good performed cultivars less incidence of major insects and diseases during flowering to fruiting period, cultivars Arka Neelamani for table purpose can be recommended for commercial cultivation under Bankura conditions of West Bengal.
Abstract: The experiment was carried out for two consecutive years during 2010 and 2012 at the experimental grape orchard at Horticultural Research and Development Farm, Govt. of W.B, Taldangra, Bankura. The experiment was conducted in randomized block design with four replications. The vines were trained on ‘Y’-trellies system and spacing of 2×3 m2. The vine was pruned on 30th January. As per fruit maturity, the cultivars Pusa Navrang were considered to be the earliest harvesting. Among the twelve cultivars, maximum fruit yield was recorded in Arka Neelamani (7.81 kg vine-1). The number of bunches/vine were varied significantly among the cultivars with number of bunches/ vine highest in cultivar Arka Trishna. But bunch weight was highest in cultivar Arkavati (264.2 g). Size of the bunch was maximum in Arka Kanchan. However, different cultivars of grape exhibited significant variation with respect to average ten berries weight. The ten berries weight was highest in Arka Magestic. The cultivars Arka Trishna gave the highest juice %, total soluble solids, lowest acidity, highest TSS/acid ratio and sugar content. Ascorbic acid content highest was recorded from cultivar Pusa Navrang as compared to other cultivars. Incidence of major insects and diseases determine the economic feasibility of a cultivar in the area. It appears from the good performed cultivars less incidence of major insects and diseases during flowering to fruiting period. On the basis of marketable yield, fruit quality and tolerance to pest, cultivars Arka Neelamani for table purpose can be recommended for commercial cultivation under Bankura conditions of West Bengal.
TL;DR: In this paper, an asymmetric behavior of optical pulses during their propagation through a time-varying linear optical medium is reported, and the peak power and accumulated chirp of the output pulse in both propagation directions are also opposite in nature, irrespective of their initial state.
Abstract: We report an asymmetric behavior of optical pulses during their propagation through a time-varying linear optical medium. The refractive index of the medium is considered to be varying with time and complex, such that a sufficient amount of gain and loss is present to realize their effect on pulse propagation. We have exploited the universal formula for optical fields in time-varying media. Numerically simulated results reveal that pulses undergo opposite temporal shifts around their initial center position during their bi-directional propagation through the medium along with corresponding spectral shifts. Moreover, the peak power and accumulated chirp (time derivative of accumulated phase) of the output pulse in both propagation directions are also opposite in nature, irrespective of their initial state. Numerically simulated behavior of the pulses agrees well with the analytical solutions.
TL;DR: In this paper, two CW light beams of 1.55 micron operating wavelength are launched as inputs to 1D waveguide lattices with controllable weak disorder in refractive index profile and direct observation of phase singularities in the speckle pattern along the length is numerically demonstrated.
Abstract: Co-existence and interplay between mesoscopic light dynamics with singular optics in spatially random but temporally coherent disordered waveguide lattices is reported. Two CW light beams of 1.55 micron operating wavelength are launched as inputs to 1D waveguide lattices with controllable weak disorder in refractive index profile. Direct observation of phase singularities in the speckle pattern along the length is numerically demonstrated. Quantitative analysis of onset of such singular behavior and diffusive wave propagation is analyzed for the first time.
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TL;DR: In this paper, a quantum inspired open optical system is mathematically implemented with an analogous three state non-Hermitian Hamiltonian exhibiting two special avoided-resonance-crossings, where interesting characteristics alongside a third-order exceptional point is explored towards robust ultra-selective state switching.
Abstract: A quantum inspired open optical system is mathematically implemented with an analogous three state non-Hermitian Hamiltonian exhibiting two special avoided-resonance-crossings; where interesting characteristics alongside a third-order exceptional point is explored towards robust ultra-selective state switching.
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TL;DR: In this paper, a dual-mode symmetric planar optical waveguide with transverse variation of inhomogeneous loss profile is considered, where modal evolution alongside an exceptional point (EP) is reported in the context of selective optical mode conversion.
Abstract: We explore exceptional points (EP) in a dual-mode symmetric planar optical waveguide with transverse variation of inhomogeneous loss profile; where modal evolution alongside an EP is reported in the context of selective optical mode conversion.
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TL;DR: In this article, the authors exploit scattering-matrix in a gain-loss assisted optical-microcavity, interplay between asymmetric-state-conversion and cavity-control parameters around exceptional points is analyzed.
Abstract: Exploiting scattering-matrix in a gain-loss assisted optical-microcavity, interplay between asymmetric-state-conversion and cavity-control parameters around exceptional points is analyzed; where occupying a least area by coupled states during switching, maximum conversion-efficiency with minimal asymmetry is achieved.