Showing papers by "Somnath Ghosh published in 2016"
TL;DR: A non-Hermitian system consisting of 1D planar optical waveguides with suitable amount of simultaneous gain and loss is studied, which can be explained by the swapping of mode identities in the vicinity of the exceptional point, together with the failure of adiabatic evolution in non- hermitian systems.
Abstract: Non-Hermitian systems host unconventional physical effects that be used to design new optical devices. We study a non-Hermitian system consisting of 1D planar optical waveguides with suitable amount of simultaneous gain and loss. The parameter space contains an exceptional point, which can be accessed by varying the transverse gain and loss profile. When light propagates through the waveguide structure, the output mode is independent of the choice of input mode. This “asymmetric mode conversion” phenomenon can be explained by the swapping of mode identities in the vicinity of the exceptional point, together with the failure of adiabatic evolution in non-Hermitian systems.
88 citations
TL;DR: In this paper, the authors investigated the dependence of the apparent slip length (β) on the particle concentration for suspensions of colloidal hard spheres flowing through microchannels with smooth walls.
13 citations
TL;DR: MSDs for the entire cylinder confirm earlier findings that both narrowing the cylinder and populating it cause a slower dynamics, and shed new light on the diffusive dynamics of concentrated colloids in narrow capillaries.
Abstract: We studied both global and local effects of cylindrical confinement on the diffusive behavior of hard sphere (HS) colloids. Using confocal scanning laser microscopy (CSLM) and particle tracking, we measured the mean squared displacement (MSD) of 1 micron sized silica particles in water–glycerol. This combination of fluid and setup allowed us to measure MSDs in a 4-dimensional parameter space, defined by the HS volume fraction (Φ: 0.05–0.39), cylinder radius (R: 2.5–20 micron), distance to the wall (z) and lagtime (τ: 0.03–60 s). MSDs for the entire cylinder confirm earlier findings that both narrowing the cylinder and populating it cause a slower dynamics. Additionally a decrease in R was found to cause a stronger ordering of the fluid. The effect of confinement on dynamics was further examined as a function of (z) location. For the largest cylinder (with minor curvature), we found that the strong decrease in MSD near the wall, becomes much less pronounced for higher Φ. Analyzing the radial (r) and azimuthal (θ) components, we found pronounced differences in the z-dependence that were ‘hidden’ in the total MSD. Near the wall, the r-MSD shows a much steeper z-dependence while at larger z, it shows a remarkable anti-correlation with the (peaked) density n(z). Also the dependence of the r-MSD on lagtime correlates with n(z): diffusive in between layers, but subdiffusive inside layers. These observations bring earlier findings together, while also shedding new light on the diffusive dynamics of concentrated colloids in narrow capillaries.
9 citations
TL;DR: It is numerically demonstrated that with suitably chosen system openness and coupling strengths, the excess noise generation among the interacting nonorthogonal states can be suppressed close to the ideal value of one with a simultaneous order of magnitude enhancement in the quality-factor of the longer-lived state.
Abstract: We study the formation of longer-lived states via internal coupling near a special avoided resonance crossing between the interacting states in an open optical system. Away from the parity-time symmetry limit, we discuss unconventional cavity resonance states created by a spatially varying gain/loss profile. Now, via S-matrix formalism, we have numerically demonstrated that with suitably chosen system openness and coupling strengths, the excess noise generation among the interacting nonorthogonal states (calculated as Petermann factor K) can be suppressed close to the ideal value of one with a simultaneous order of magnitude enhancement in the quality-factor of the longer-lived state.
7 citations
TL;DR: In this paper, a parabolic pulse at wavelength 2.1μm from a Gaussian input pulse with 1.9-ps FWHM and 75-W peak power was reported, and three different dispersion regimes of propagation were considered to study the suitability to support most stable propagation of the pulse.
5 citations
01 Oct 2016
TL;DR: This work proposes a scheme that enables cluster merging in a distributed environment to eliminate the problem and shows the proposed protocol has up to 50 times shorter convergence time and save up to 90% more energy during the merging process compared to the existing global schedule protocols.
Abstract: In wireless sensor networks (WSNs), conserving the nodes' energy is one the main motivations in designing the medium access control (MAC) layer protocols. A common approach is to allow the nodes to turn their radio modules off periodically according to certain schedules. The nodes that operate on a common schedule and located in a common physical area form a virtual cluster. The nodes in the cluster borders have more active period to maintain the connectivity between clusters, thus, have shorter life spans. This work proposes a scheme that enables cluster merging in a distributed environment to eliminate the problem. The proposed scheme uses the schedule offset, the time difference between the starts of the active periods in two schedules, as the criteria for deciding the direction of the merging. We evaluate the performance of the proposed protocol using a mathematical estimation and simulation. The result shows the proposed scheme has up to 50 times shorter convergence time and save up to 90% more energy during the merging process compared to the existing global schedule protocols.
1 citations
Posted Content•
TL;DR: In this article, a self-similar propagation of parabolic optical pulses through a highly nonlinear and passive photonic bandgap fiber at 2.8 micron has been demonstrated, with fullwidth-at-half-maxima of 4.12 ps and energy of 39 pJ at the output.
Abstract: We numerically demonstrate self-similar propagation of parabolic optical pulses through a highly nonlinear and passive specialty photonic bandgap fiber at 2.8 micron. In this context, we have proposed a scheme endowed with a rapidly varying, but of nearly-mean-zero longitudinal dispersion and modulated nonlinear profile in order to achieve self-similarity of the formed parabolic pulse propagating over longer distances. To implement the proposed scheme, we have designed a segmented bandgap fiber with suitably tapered counterparts to realize such customized dispersion with chalchogenide glass materials. A self-similar parabolic pulse with full-width-at-half-maxima of 4.12 ps and energy of ~ 39 pJ as been achieved at the output. Along with a linear chirp spanning over the entire pulse duration, 3dB spectral broadening of about 38 nm at the output has been reported.
Journal Article•
TL;DR: In this paper, a two stage desulphurisation treatment is employed in which the blast furnace hot metal is first treated by co-injection of Mg and CaC reagents, and subsequent treatment with a 2 synthetic slag former (CaO-Al O ) added to the ladle during tapping from the Basic 2 3 Oxygen furnace.
Abstract: Rail is the most important constituent of the track structure and plays a very vital role in the reliability of railway system as a whole. Quality of rail steel with reference to its chemical composition has been a matter of prime importance for the manufacturers as well as Railways. Sulphur is a detrimental element in rails since it causes hot shortness during rolling, centerline segregation during casting, poor weldability for the rails etc. To improve quality of rails, a substantially low range of sulphur < 0.015% (Railway's specified norms <0.03%) has been targeted in Bhilai Steel Plant by adequate sulphur control measures in steelmaking process. A two stage desulphurisation treatment is now employed in which the blast furnace hot metal is first treated by co-injection of Mg and CaC reagents, and subsequent treatment with a 2 synthetic slag former (CaO-Al O ) added to the ladle during tapping from the Basic 2 3 Oxygen furnace. Improvement in the internal quality of the cast bloom has been established by introduction of Electro Magnetic Stirring. The centerline segregation is minimized vis-a-vis the properties of the cast product and rails improved by the successful implementation of step by step control measures.