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Aspects of Epitaxial Design and Estimation of 2DEG Mobility in InAlN/AlN/InGaN/GaN High Electron Mobility Transistors
No full textIn this paper, a epitaxial design of InAlN/AlN/InGaN/GaN high electron mobility transistors (HEMTs), considering the vital aspects related to its device exploration is proposed. Mobility of two dimensional electron gas in the proposed, practically viable structures of InxGa1-xN-channel (0.1 < x < 0.4) HEMT is estimated. It is shown that 2DEG mobility is predominantly limited by alloy scattering rather than phonon scattering, unlike in conventional GaN-channel HEMTs. Finally, room temperature mobility of 2DEG in InGaN-channel HEMT is simulated on the basis of alloy scattering and phonon scattering only. Results are in close proximity with reported experimental results. We observe that, for n(s) approximate to 2 x 10(13) cm(-2), mobility drops rapidly from approximate to 900 to approximate to 550 cm(2) V-1 . s(-1) as `x' is increased from 0.1 to 0.2 and thereafter it decreases at a relatively lesser rate. Severe degradation in mobility is predicted for x > 0.3
Linear and Nonlinear Optical Properties of Tricyanopropylidene-Based Merocyanine Dyes: Synergistic Experimental and Theoretical Investigations
No full textNew merocyanines dyes with tricyanopropylidene-based acceptor units connected to dihexylaminophenyl or dihexylaminothiophenyl donor moieties through polyenic bridges of different lengths have been designed. All derivatives exhibited a strong dipolar character and showed a typical intramolecular charge transfer (ICT) transition. NMR spectroscopy experiments combined with DFT calculations demonstrated that both the nature of the donor-acceptor pair and the length of the conjugated linker strongly impact the electronic structure of the dyes and induce alteration in the bond-length alternation (BLA) and marked shifts in the ICT absorption bands. Hyper-Rayleigh scattering experiments revealed an exponential increase in the second-harmonic generation response as the polyenic chain length was increased. Strikingly, the largest chromophores with the strongest donor-acceptor pair exhibited a very high first hyperpolarizabilty together with a cyanine-like electronic structure, which apparently contradicts the paradigm of optimal BLA predicted by the two-state model. Although it decreased as the polyenic chain length increased, all dyes also exhibited high thermal stability, which demonstrates their potential for applications in nonlinear optical devices
The kinematic genesis of vortex formation due to finite rotation of a plate in still fluid
No full textWe present a combined experimental and numerical study of an idealized model of the propulsive stroke of the turning manoeuvre in fish. Specifically, we use the framework of Lagrangian coherent structures (LCSs) to describe the kinematics of the flow that results from a thin plate performing a large angle rotation about its tip in still fluid. Temporally and spatially well-resolved velocity fields are obtained using a two-dimensional, incompressible finite-volume solver, and are validated by comparisons with experimentally measured velocity fields and alternate numerical simulations. We then implement the recently proposed variational theory of LCSs to extract the hyperbolic and elliptic LCSs in the numerically generated velocity fields. Detailed LCS analysis is performed for a plate motion profile described by <(theta)over dot>(t) = Omega(max) sin(2)(omega t) during 0 <= t <= t(o) and zero otherwise. The stopping time t(o) is given by t(o) = pi/omega = 10 s, the value of Omega(max) chosen to give a stopping angle of theta(max) = 90 degrees, resulting in a Reynolds number Re = c(2) Omega(max)/nu = 785.4, where c is the plate chord length and nu = 10(-6) m(2) s(-1) the kinematic viscosity of water. The flow comprises a starting and a stopping vortex, resulting in a pair of oppositely signed vortices of unequal strengths that move away from the plate in a direction closely aligned with the final plate orientation at t/t(o) approximate to 2. The hyperbolic LCSs are shown to encompass the fluid material that is advected away from the plate for t > t(o), henceforth referred to as the advected bulk. The starting and stopping vortices, identified using elliptic LCSs and hence more objective than Eulerian vortex detection methods, constitute only around two thirds of the advected bulk area. The advected bulk is traced back to t = 0 to identify five distinct lobes of fluid that eventually form the advected bulk, and hence map the long-term fate of various regions in the fluid at t = 0. The five different lobes of fluid are then shown to be delineated by repelling LCS boundaries at t = 0. The linear momentum of the advected bulk region is shown to account for approximately half of the total impulse experienced by the plate in the direction of its final orientation, thus establishing its dynamical significance. We provide direct experimental evidence for the kinematic relevance of hyperbolic and elliptic LCSs using novel dye visualization experiments, and also show that attracting hyperbolic LCSs provide objective characterization of the spiral structures often observed in vortical flows. We conclude by showing that qualitatively similar LCSs persist for several other plate motion profiles and stopping angles as well
Low-noise phase of a two-dimensional active nematic system
No full textWe consider a collection of self-driven apolar particles on a substrate that organize into an active nematic phase at sufficiently high density or low noise. Using the dynamical renormalization group, we systematically study the two-dimensional fluctuating ordered phase in a coarse-grained hydrodynamic description involving both the nematic director and the conserved density field. In the presence of noise, we show that the system always displays only quasi-long-ranged orientational order beyond a crossover scale. A careful analysis of the nonlinearities permitted by symmetry reveals that activity is dangerously irrelevant over the linearized description, allowing giant number fluctuations to persist although now with strong finite-size effects and a nonuniversal scaling exponent. Nonlinear effects from the active currents lead to power-law correlations in the density field, thereby preventing macroscopic phase separation in the thermodynamic limit
Green to gray: Silicon Valley of India
No full textRapid growth, population concentration and the expansion of urban areas towards peri-urban regions have led to changes in urban structure and composition, and consequently changes in urban ecology. The purpose of this study is to estimate trees in the urban environment through quantification of vegetation cover using multi resolution spatial data supplemented with tree data acquired from field using pre-calibrated GPS. Optimal resolution for extracting trees was attained through fusion of multi resolution (spectral and spatial) data. Results highlight region with spatial extent of 741 sq. km with 9.5 million human population has about 1.48 million trees. Further, urban growth increment is expected to cover 95% of the landscape with paved surfaces by 2020 decreasing vegetation cover while severely affecting the local ecology and environment in addition to human survival. (C) 2017 Elsevier Ltd. All rights reserved
Intramolecular HB Interactions Evidenced in Dibenzoyl Oxalamide Derivatives: NMR, QTAIM, and NCI Studies
No full textExtensive NMR spectroscopic studies revealed information on the occurrence of bifurcated intramolecular hydrogen bond in the dibenzoyl oxalamide derivatives. One-dimensional NMR experiments, viz., solvent dilution, temperature perturbation, and two-dimensional experimental techniques, such as N-15-H-1 HSQC and F-19-H-1 HOESY, have been exploited to derive unambiguous confirmation of the participation of organic fluorine in the hydrogen-bonding interaction. The experimental NMR findings have been ratified by density functional theory based calculations, viz., NCI (noncovalent interaction) and QTAIM (quantum theory of atoms in molecules)
A Framework for Interpretation of the Compressibility Behavior of Soils
No full textThis paper aims at the development of a regression-aided analytical framework for modeling and analyzing the compressibility behavior of over-consolidated soils. A three-parameter rectangular hyperbola function (3P-RH) was proposed for describing the void ratio-effective stress relationship. Validation of the 3P-RH was carried out by a compiled database gathered from the literature. Simple analytical solutions were then proposed for determining the compressibility curve variables including the compression (C-c) and recompression (C-r) indices and the preconsolidation pressure (P-c), which are intended to replace the current subjective graphical method by providing consistent results. Equations for the preconsolidation pressure were derived in accordance with four common graphical constructions covering various levels of geometrical complexity (slightly to highly subjective). A probabilistic comparison among the graphical constructions was then carried out. Furthermore, a sensitivity analysis with respect to the proposed preconsolidation pressure functions was considered to evaluate the influence of the 3P-RH fitting parameters (alpha and beta) on the preconsolidation pressure value. The proposed 3P-RH compressibility model accompanied by the suggested analytical solutions for solving the compressibility curve variables construct a unique framework for modeling the compressibility behavior of soils with an acceptable degree of accuracy and, more importantly, by a simple objective approach
Efficient interfacial charge transfer through plasmon sensitized Ag@Bi2O3 hierarchical photoanodes for photoelectrocatalytic degradation of chlorinated phenols
No full textThe present work demonstrates an extremely proficient and robust study of efficient interfacial charge transfer through plasmonic Ag decorated Bi2O3 hierarchical photoanodes for the photoelectrochemical treatment of chlorinated phenols. Unique 2D flake-like Bi2O3 hierarchical nanostructures were grown onto a fluorine-doped tin oxide (FTO) substrate by a simple chemical bath deposition method using triethanolamine as complexing agent. The formation of Bi2O3 on FTO was governed by the decomposition of a nucleated bismuth-hydroxyl complex (Bi2O1)(x)(OH)x) and modification to the electrode was carried out by the deposition of Ag via a chemical reduction method using hydrazine hydrate. Both the fabricated electrodes were well characterized for their photo-and electro-optical properties. Efficient charge separation was observed due to the surface plasmon resonance phenomenon of silver nanoparticles with the favorable intrinsic properties of Bi2O3 under application of a small electric bias of 1 V preventing the recombination of charge carriers and thereby increasing the rate of photoelectrocatalytic degradation of the chlorinated phenols. PEC degradation using the Ag@Bi2O3 photoelectrode followed the trend 4-CP o 2,4-DCP o 2,4,6-TCP o P-CP due to efficient attack at the chlorinated positions by reactive oxygen species with increasing chlorine substitution and also due to the absence of an expected Ag@Bi2O3 was 1.5 times higher than a Bi2O3 nanoflake electrode for 4-CP over 2 h. The fabricated Ag@Bi2O3 proved to be an efficient photoelectrode with synergistic solar-induced photoactivity. A detailed mechanistic study in the presence of scavengers suggests degradation by produced hydroxyl radical species. Thus, physical insights into the degradation of chlorinated phenols were obtained
Invariants of velocity gradient tensor in supersonic turbulent pipe, nozzle, and diffuser flows
No full textVelocity gradient tensor (VGT) analysis of high-order accurate direct numerical simulation data of supersonic pipe, nozzle, and diffuser flows at computationally moderate Reynolds numbers is performed. Joint probability density functions of second and third invariants of the VGT conditioned on positive and negative dilatation levels are presented in the near-wall viscous layer, buffer layer, log layer, and core region of these flows. For flow regions with positive dilatation, there is a preference for unstable flow topologies, while regions with negative dilatation show a preference for stable flow topologies. Published by AIP Publishing
Model-based approach for planning renewable energy transition in a resource-constrained electricity systemA case study from India
No full textGlobally, electricity systems are going through transitions. The contributions from renewable energy-based power generation, both in installed capacity and electricity generation, are moving from marginal to the mainstream. India is not an exception; it is aggressively pursuing this transition by fixing steep targets for renewable capacity additions. While the cost of renewable energy sources is expected to fast reach grid parity, the policy interventions play a critical role in ramping up the efforts to support the proposed investments in renewable capacity and renewable electricity generation. In this respect, this research attempts to analyze the effectiveness of renewable energy policies such as Renewable Purchase Obligation (RPO) and Renewable Energy Certificate mechanisms in tapping the renewable energy potential in India. We propose a mixed-integer linear programming model-based approach to evaluate the effectiveness of the above interventions in the Indian context. The model is developed and validated as a low carbon electricity planning tool to optimally meet the dynamic electricity demand and RPO targets as well as to manage the unmet total electricity demand and RPO targets. The Karnataka state electricity system (a state in south India) is chosen as a case study. The results suggest that Karnataka Electricity System is moving toward a sustainable renewable energy future even without any support from nonsolar Renewable Energy Certificate policy. However, policy interventions are critical for optimally utilizing the solar generation capacity