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Numerical simulation of the observed near-surface East India Coastal Current on the continental slope
No full textWe simulate the East India Coastal Current (EICC) using two numerical models (resolution an oceanic general circulation model (OGCM) called Modular Ocean Model and a simpler, linear, continuously stratified (LCS) model, and compare the simulated current with observations from moorings equipped with acoustic Doppler current profilers deployed on the continental slope in the western Bay of Bengal (BoB). We also carry out numerical experiments to analyse the processes. Both models simulate well the annual cycle of the EICC, but the performance degrades for the intra-annual and intraseasonal components. In a model-resolution experiment, both models (run at a coarser resolution of ) simulate well the currents in the equatorial Indian Ocean (EIO), but the performance of the high-resolution LCS model as well as the coarse-resolution OGCM, which is good in the EICC regime, degrades in the eastern and northern BoB. An experiment on forcing mechanisms shows that the annual EICC is largely forced by the local alongshore winds in the western BoB and remote forcing due to Ekman pumping over the BoB, but forcing from the EIO has a strong impact on the intra-annual EICC. At intraseasonal periods, local (equatorial) forcing dominates in the south (north) because the Kelvin wave propagates equatorward in the western BoB. A stratification experiment with the LCS model shows that changing the background stratification from EIO to BoB leads to a stronger surface EICC owing to strong coupling of higher order vertical modes with wind forcing for the BoB profiles. These high-order modes, which lead to energy propagating down into the ocean in the form of beams, are important only for the current and do not contribute significantly to the sea level
Gravitational couplings in N=2 string compactifications and Mathieu Moonshine
No full textWe evaluate the low energy gravitational couplings, F-g in the heterotic E-8 x E-8 string theory compactified on orbifolds of K3 x T-2 by g' which acts as a Z(N) automorphism on K3 together with a 1/N shift along T-2. The orbifold corresponds to the conjugacy classes of the Mathieu group M-24. The holomorphic piece of F-g is given in terms of a poly logarithm with index 3-2g and predicts the Gopakumar-Vafa invariants in the corresponding dual type II Calabi-Yau compactifications. We show that low lying Gopakumar-Vafa invariants for each of these compactifications including the twisted sectors are integers. We observe that the conifold singularity for all these compactifications occurs only when states in the twisted sectors become massless and the strength of the singularity is determined by the genus zero Gopakumar-Vafa invariant at this point in the moduli space
Maneuverability of Magnetic Nanomotors Inside Living Cells
No full textSpatiotemporally controlled active manipulation of external micro-/nanoprobes inside living cells can lead to development of innovative biomedical technologies and inspire fundamental studies of various biophysical phenomena. Examples include gene silencing applications, real-time mechanical mapping of the intracellular environment, studying cellular response to local stress, and many more. Here, for the first time, cellular internalization and subsequent intracellular manipulation of a system of helical nanomotors driven by small rotating magnetic fields with no adverse effect on the cellular viability are demonstrated. This remote method of fuelling and guidance limits the effect of mechanical transduction to cells containing external probes, in contrast to ultrasonically or chemically powered techniques that perturb the entire experimental volume. The investigation comprises three cell types, containing both cancerous and noncancerous types, and is aimed toward analyzing and engineering the motion of helical propellers through the crowded intracellular space. The studies provide evidence for the strong anisotropy, heterogeneity, and spatiotemporal variability of the cellular interior, and confirm the suitability of helical magnetic nanoprobes as a promising tool for future cellular investigations and applications
Autoignition of hydrogen in shear flows
No full textIn this paper, we compare the autoignition characteristics of laminar, nitrogen-diluted hydrogen jets in two different oxidizer flow configurations: (a) co-flowing heated air and (b) wake of heated air, using two-dimensional numerical simulations coupled with detailed chemical kinetics. In both cases, autoignition is observed to initiate at locations with low scalar dissipation rates and high HO2 depletion rates. It is found that the induction stage prior to autoignition is primarily dominated by chemical kinetics and diffusion while the improved scalar mixing imparted by the large-scale flow structures controls the ignition progress in later stages. We further investigate the ignition transience and its connection with mixing by varying the initial wake conditions and fuel jet to oxidizer velocity ratios. These studies reveal that the autoignition delay times are independent of initial wake flow conditions. However, with increased jet velocity ratios, the later stages of ignition are accelerated, mainly due to enhanced mixing facilitated by the higher scalar dissipation rates. Furthermore, the sensitivity studies for the jet inwake configuration showa significant reduction in ignition delay even for about 0.14% (by volume) hydrogen dilution in the oxidizer. In addition, the detailed autoignition chemistry and the relative roles of certain radical species in the initiation of the autoignition process in these non-premixed jets are investigated by tracking the evolution of important chain reactions using a Lagrangian particle tracking approach. The reaction H-2 + O-2 <-> HO2 + H is recognized to be the dominant chain initiation reaction that provides H radicals essential for the progress of subsequent elementary reactions during the pre-ignition stage. Published by AIP Publishing
Role of hydrodynamic shear layer stability in driving combustion instability in a premixed propane-air backward-facing step combustor
No full textThis paper presents a global hydrodynamic stability analysis of flow fields in a backward-facing step combustor, assuming weakly nonparallel flow. The baseline experiments in a ``long'' combustor of length of 5.0 m shows the presence of two combustion instability states characterized by coherent low- and high-amplitude acoustic pressure oscillations. The analysis is performed for propane-air mixtures at three values of phi = 0.63, 0.72, and 0.85, which correspond to quiet, low-amplitude and high-amplitude instability states in the long combustor experiments. Base flow velocity and density fields for the hydrodynamic stability analysis are determined from time-averaged particle image velocimetry measurements made after the length of the duct downstream of the step has been shortened to eliminate acoustic pressure oscillations. The analysis shows that the shear layer mode is self-excited for the f = 0.72 case with an oscillation frequency close to that of the long combustor's fundamental acoustic mode. We showfrom an analysis of the weakly forced, variable density Navier-Stokes equations that self-excited hydrodynamic modes can be weakly receptive to forcing-suggesting that the low-amplitude instability in the long combustor is due to semi-open loop forcing of heat-release oscillations by the shear layer mode. At f = 0.85, the analysis shows that the flowis hydrodynamically globally stable but locally convectively unstable. Spatial amplification of velocity disturbances by the convectively unstable flow causes high-amplitude combustion instability in the long combustor case. These results show that combustion instability can be sustained by two different mechanisms by which acoustic and hydrodynamic modes being either strongly coupled result in fully closed loop forcing, or weakly coupled result in semi-open loop forcing of the flame by a self-excited hydrodynamic mode
Efficient Synthesis of Aryl Boronates via Cobalt-Catalyzed Borylation of Aryl Chlorides and Bromides
No full textAn efficient catalytic system based on a Co(II)-NHC precursor has been developed for the cross coupling of bis(pinacolato)diboron with aryl halides including aryl chlorides, affording the aryl boronates in good to excellent yields. A wide range of functional groups are tolerated under mild reaction conditions. The reaction shows excellent chemoselectivity for bromide over chloride. Preliminary mechanistic investigations show that the catalytic cycle may rely on a cobalt(I)-(III) redox couple
Influence of copper oxide grown on various conducting substrates towards improved performance for photoelectrocatalytic bacterial inactivation
No full textThis paper analyzes the role of the conducting layer substrates (Cu and fluorine-doped tin oxide (FTO)) on grown copper oxide (CuO) in order to improve the performance of catalytic bacterial inactivation. Growth of CuO onto Cu substrate was via thermal oxidation of Cu whereas hydrothermal method was employed for CuO growth onto Fro. The surface morphology of CuO varied with respect to the substrates choice and epitaxy, developing particulated thin film and thin film consisting vertically aligned nanorods on Cu and FTO, respectively. Photo- and electro-based reactions were carried out to understand the effect of light, bias, bias-catalyst and light-bias-catalyst combinations, respectively, for the fast killing of E. coli. The experimental results showed a striking improvement in photoelectrocatalytic inactivation of E. coil using plain fabricated copper oxide substrate. The choice of conducting substrate material plays a crucial role in terms of both morphology controlled CuO growth under different facile methods and also governs the electron transfer efficiency to achieve an improved catalytic efficiency. The reaction mechanism was discussed by deriving an appropriate detailed model which is able to predict the experimental data in all the cases. This study gives an insight on energy saving and less carbon footprint approach for bacterial killing in a short interval. (C) 2017 Elsevier B.V. All rights reserved
Orthorhombic vs. hexagonal epitaxial SrIrO3 thin films: Structural stability and related electrical transport properties
No full textMetastable orthorhombic SrIrO3 (SIO) is an arch-type spin-orbit coupled material. We demonstrate here a controlled growth of relatively thick (200 nm) SIO films that transform from bulk ``6H-type'' structure with monoclinic distortion to an orthorhombic lattice by controlling growth temperature. Extensive studies based on high-resolution X-ray diffraction and transmission electron microscopy infer a two distinct structural phases of SIO. Electrical transport reveals a weak temperature-dependent semi-metallic character for both phases. However, the temperature-dependent Hall-coefficient for the orthorhombic SIO exhibits a prominent sign change, suggesting a multiband character in the vicinity of E-F. Our findings thus unravel the subtle structure-property relation in SIO epitaxial thin films. Copyright (C) EPLA, 201
Higher-dimensional Sachdev-Ye-Kitaev non-Fermi liquids at Lifshitz transitions
No full textWe address the key open problem of a higher-dimensional generalization of the Sachdev-Ye-Kitaev (SYK) model. We construct a model on a lattice of SYK dots with nonrandom intersite hopping. The crucial feature of the resulting band dispersion is the presence of a Lifshitz point where two bands touch with a tunable power-law divergent density of states (DOS). For a certain regime of the power-law exponent, we obtain a class of interaction-dominated non-Fermi-liquid (NFL) states, which exhibits exciting features such as a zero-temperature scaling symmetry, an emergent (approximate) time reparameterization invariance, a power-law entropy-temperature relationship, and a fermion dimension that depends continuously on the DOS exponent. Notably, we further demonstrate that these NFL states are fast scramblers with a Lyapunov exponent lambda(L) proportional to T, although they do not saturate the upper bound of chaos, rendering them truly unique
Insulin signaling pathway protects neuronal cell lines by Sirt3 mediated IRS2 activation
No full textCellular stress like ER and oxidative stress are the principle causative agents of various proteinopathies. Multifunctional protein PARK7/DJ-1 provides protection against cellular stress. Recently, insulin/IGF also has emerged as a neuro-protective molecule. However, it is not known whether DJ-1 and insulin/IGF complement each other for cellular protection in response to stress. In this study, we show for the first time, that in human and mouse neuronal cell lines, down regulation of DJ-1 for 48 h leads to compensatory upregulation of insulin/IGF signaling (IIS) pathway genes, namely, insulin receptor, insulin receptor substrate, and Akt under normal physiological conditions as well as in cellular stress conditions. Moreover, upon exogenous supply of insulin there is a marked increase in the IIS components both at gene and protein levels leading to down regulation and inactivation of GSK3. By immunoprecipitation, it was observed that Sirt3 mediated deacetylation and activation of FoxO3a could not occur under DJ-1 downregulation. Transient DJ-1 downregulation also led to Akt mediated increased phosphorylation and nuclear exclusion of FoxO3a. When DJ-1 was downregulated increased interaction of Sirt3 with IRS2 was observed leading to its activation resulting in IIS upregulation. Thus, transient downregulation of DJ-1 leads to stimulation of IIS pathway by Sirt3 mediated IRS2 activation. Consequently, antiapoptotic program is triggered in neuronal cells via Akt-GSK3-FoxO3a axis. (c) 2018 BioFactors, 44(3):224-236, 201