Optical conductivity study of screening of many-body effects in graphene interfaces

Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many body interaction through the effective fine structure constant, $\alpha_{g}^{*}$. The $\alpha_{g}^{*}$ for GOQ indicates a strong correlation with an almost energy independent value of about 1.37. In contrast, $\alpha_{g}^{*}$ value of GOC is photon energy dependent, is almost two orders of magnitude lower at low energies indicating very weak correlation.Comment: Main Article (4 pages, 4 figures); Supporting Online Material (12 pages, 9 figures

Point Defects and Localized Excitons in 2D WSe2

Identifying the point defects in 2D materials is important for many applications. Recent studies have proposed that W vacancies are the predominant point defect in 2D WSe2, in contrast to theoretical studies, which predict that chalcogen vacancies are the most likely intrinsic point defects in transition metal dichalcogenide semiconductors. We show using first principles calculations, scanning tunneling microscopy (STM) and scanning transmission electron microscopy experiments, that W vacancies are not present in our CVD-grown 2D WSe2. We predict that O-passivated Se vacancies (O_Se) and O interstitials (Oins) are present in 2D WSe2, because of facile O2 dissociation at Se vacancies, or due to the presence of WO3 precursors in CVD growth. These defects give STM images in good agreement with experiment. The optical properties of point defects in 2D WSe2 are important because single photon emission (SPE) from 2D WSe2 has been observed experimentally. While strain gradients funnel the exciton in real space, point defects are necessary for the localization of the exciton at length scales that enable photons to be emitted one at a time. Using state-of-the-art GW-Bethe-Salpeter-equation calculations, we predict that only Oins defects give localized excitons within the energy range of SPE in previous experiments, making them a likely source of previously observed SPE. No other point defects (O_Se, Se vacancies, W vacancies and Se_W antisites) give localized excitons in the same energy range. Our predictions suggest ways to realize SPE in related 2D materials and point experimentalists toward other energy ranges for SPE in 2D WSe2

Severity of light pollution and its multifaceted impact: A mini review on the dark side of light

There is a surging concern regarding the adverse effects of light pollution on human well-being. This manuscript aims to emphasise the deleterious effects of uncontrolled night-light exposure on the health and mood of individuals residing in a highly populated elite metropolitan society compared to those residing in remote villagesin a scattered manner. A comprehensive study has been undertaken on the influence of unnecessary and excessive illumination of light during late-night hours on individuals' day-to-day lives. Prolonged exposure to unwanted intense artificial lighting disrupts the secretion of melatonin, interferes with the circadian rhythm, and unusual sleep patterns. Such disturbances can lead to significant health issues, including insomnia, depression, cardiovascular diseases, as well as an increased risk of breast and prostate cancer. Findings emphasize the need for a more holistic understanding of how artificial light, in intensity and periodicity, affects the physical and mental health of humans and the ecological system in entirety, specifically in urban settings

On Certain Gluing of semigroup rings and indispensable resolution of semigroup rings

In this paper, our aim is twofold: First, by using the technique of gluing semigroups, we give infinitely many families of a projective closure with the Cohen-Macaulay (Gorenstein) property. Also, we give an effective technique for constructing large families of one dimensional Gorenstein local rings associated to monomial curves, which supports Rossi question, saying that every Gorenstein local ring has a non-decreasing Hilbert function. In the second part, we study strong indispensable minimal free resolutions of semigroup rings, focusing on the operation of the join of affine semigroups, which provide class of examples supporting Charalambous and Thoma question on the class of lattice ideal which has a strong indispensable free resolution.Comment: 12 Pages, comments are welcom

Performance Analysis of Non-linear Jacketed CSTR based on Different Control Strategies

This paper aims at finding the optimum controller for a jacketed Continuous Stirred Tank Reactor (CSTR) under non-ideal conditions. Various conventional control methods show poor response for non-linear processes. This paper outlines the design procedure of the Internal Model Controller (IMC) and Model Reference Adaptive Control (MRAC). The performance of the jacketed CSTR process is analyzed based on Internal Model Control and adaptive control. Simulation results have been compared with conventional PID contro