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RecG(wed): A probable novel regulator in the resolution of branched DNA structures in mycobacteria
No full textStructure-specific helicases, such as RecG, play an important role in the resolution of recombination intermediates. A bioinformatic analysis of mycobacterial genomes led to the identification of a protein (RecG(wed)) with a C-terminal ``edge'' domain, similar to the wedge domain of RecG. RecG(wed) is predominately found in the phylum Actinobacteria and in few human pathogens. Mycobacterium smegmatis RecG(wed) was able to bind branched DNA structures in vitro but failed to interact with single- or double-stranded DNA. The expression of recG(wed) in M. smegmatis cells was up-regulated during stationary phase/UV damage and down-regulated during MMS/H2O2 treatment. These observations indicate the possible involvement of RecG(wed) in transactions during recombination events, that proceed though branched DNA intermediates. (C) 201
Will the integration of renewable energy enable sustainable transition of Indian electricity system?
No full textElectricity systems worldwide are transitioning from conventional carbon intensive firm power generating systems to intermittent and variable renewable energy dominated low carbon systems. Although the dimensions of transition vary from one electricity system to another, there is concurrence in terms of need for and the subsequent issues related to renewable energy integration. In this study, we attempt to verify whether these transitions lead to a sustainable electricity system as measured through three dimensions - economic, social and environmental. This is performed by adopting an integrated framework, which connects the indicator based multi-hierarchical and multidimensional macro model of electricity system sustainability assessment with the bottom up optimization model of generation expansion planning and generation scheduling. We explore multiple scenarios and characterize Indian electricity system on select indicators under three sustainability dimensions. We aggregate this annual characterization to compute National Electricity System Sustainability Index (NESSI). NESSI value for base year is 0.377 (2013) and within the select scenarios, it varies from 0.481 to 0.510 in 2031. These variations in extent of sustainability are influenced by underlying technology choices. Thus, Indian electricity system is transitioning towards a more sustainable state. We provide additional insights on how the important questions concerning generation technology pathways for electricity system sustainability transition can be queried and the underlying choices this process involves
Boundary layer transition experiments with embedded streamwise vortices
No full textExperiments were conducted with a counter-rotating, streamwise vortex pair embedded in flat plate boundary layers, in a low-turbulence wind tunnel, to understand the role of local separation on transition. Steady, streamwise vortices were generated downstream of gaps in spanwise-uniform, smooth hills (of height h) affixed to the plate, 175 mm from its leading edge. The flow between is directed away from the plate. At the four tunnel speeds 1.8-3.5 m/s considered, the Reynolds numbers based on displacement thickness at this location varied from 248 to 346. Small, medium and large gaps of 2, 4 and 8 mm, respectively, were set up; they were about a third to twice the boundary layer thickness (2/3<b/h<8/3). With the closest vortex pairs, transition was observed at all freestream speeds considered. With larger spacing, transition occurred at the highest speed only. The vortex pair caused the flow to separate in all but the largest-gap cases. Separation was steady and reattachment unsteady in all cases. Velocity fluctuations grew slightly upstream of re-attachment in transitional cases. No evidence was found for separation or re-attachment as a direct cause for transition; transition occurred even without separation. Instead, whenever transition was observed, its origin could be traced to instability of a streak of sufficient amplitude that had been created by the vortex pair. Streak instability appeared as fluctuations growing along its sides and spreading. Anomalous behaviour was also observed with moderate spacing, where transition did not occur in spite of flow separation and streak amplitudes in excess of known thresholds for streak instability
Multiple triple-point fermions in Heusler compounds
No full textUsing the density functional theoretical calculations, we report a new set of topological semimetals X(2)YZ (X = {Cu, Rh, Pd, Ag, Au, Hg}, Y = {Li, Na, Sc, Zn, Y, Zr, Hf, La, Pr, Pm, Sm, Tb, Dy, Ho, Tm} and Z = {Mg, Al, Zn, Ga, Y, Ag, Cd, In, Sn, Ta, Sin)), which show the existence of multiple topological triple point fermions along four independent (C) over tilde (3) axes. These fermionic quasiparticles have no analogues elementary particle in the standard model. The angle-resolved photoemission spectroscopy is simulated to obtain the exotic topological surface states and the characteristic Fermi arcs. The inclusion of spin-orbit coupling splits the triple-point to two Dirac points. The triple-point fermions are exhibited on the easily cleavable (1 1 1) surface and are well separated from the surface (Gamma) over bar point, allowing them to be resolved in the surface spectroscopic techniques. This intermediate linearly dispersive degeneracy between Weyl and Dirac points may offer prospective candidates for quantum transport applications
Understanding Surfactant Stabilization of MoS2 Nanosheets in Aqueous Dispersions from Zeta Potential Measurements and Molecular Dynamics Simulations
No full textThe sonication-assisted exfoliation of MoS2 in aqueous media in the presence of ionic surfactants to give stable dispersions is an attractive procedure for obtaining single or few-layered nanosheets, as it is easily scalable and does not involve toxic or high boiling solvents. Here, we have investigated the origin of the stability of aqueous dispersions of MoS2 nanosheets obtained by sonication in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) by zeta potential measurements at different ionic strengths and molecular dynamics (MD) simulations. Our measurements show that the dispersions are stabilized by electrostatic repulsive interactions between the delaminated MoS2 nanosheets, which acquire a positive charge because of the adsorption of the cationic surfactant. MD simulations were performed to understand the interaction between MoS2 nanosheets and the CTAB surfactant chains in the dispersion and the structure and arrangement of the adsorbed surfactant chains. Our simulations are able to reproduce the experimentally measured variation of the zeta potential with ionic strength. In addition, the relative contribution and role of different intermolecular interactions between various components of the dispersion was estimated by simulating the potential of mean force (PMF) between two surfactant-adsorbed MoS2 sheets. On the basis of experiment and simulations, we are able to establish that the stability of aqueous dispersions of MoS2 in the presence of an ionic surfactant can be understood based on classical models of charged interfaces
A step towards environmental benign Mg/Pb based binary metal mixed halide perovskite material
No full textToday's the best performing perovskite solar cells utilise Pb2+ as a major bivalent cation source, however, the presence of toxic Pb is major issue that put its commercialization in dire straits. In this report, we unveiled the chemical synthesis and characterisation of Mg/Pb binary metal mixed halide perovskite with chemical formula CH3NH3PbxMg1-xI3-yCly using MgCl2 as a compositional gradient with nominal value of x from 0.1 to 0.9. The FESEM images of compositions corresponding to higher proportion of Cl- (or MgCl2) demonstrate improved particle (or grain) size of similar to 8-12 mu m. There is a close resemblance of stoichiometric ratio of Pb:Mg obtained from EDX analysis with that of incorporated stoichiometric ratio of Pb:Mg. Further, Mg and Cl incorporation is strengthened by the characteristic spectral peak for core level electron of Mg(2p) and Cl(2p) other than Pb(4f) and I(3d) in the XPS survey spectrum of composition x = 0.5. These binary Mg/Pb Perovskite with bandgap in the range 1.57-1.59 eV behave as comparatively less toxic potential candidate for the single junction module. The IR studies at room temperature show observable shift in peak positions on comparing two extreme compositions i.e., x = 0.1 and x = 1.0. It is noticeable that both standard CH3NH3PbI3 and binary Mg/Pb Perovskite with nominal value x = 0.7 have comparable thermal stability, however, the composition x = 0.1 have lower thermal stability than x = 0.7. The carrier lifetimes measurements by Microwave Detected Photoconductivity (MDP) showed an improvement of lifetime to 142 mu s for nominal value x = 0.9 compared to 76 mu s in case of MAPbI(3) film. Correspondingly we see a 160 mV improvement in open-circuit voltage (V-OC) in the solar cells fabricated with nominal value x = 0.9 (V-OC = 1.07 V) as compared to standard MAPbI(3) cells (V-OC = 0.90 V). The champion cell with nominal value x = 0.9 shows PCE of 14.2% where as the best PCE of MAPbI(3) cell is 14.50% under a reverse scan
Challenges in extractive metallurgy and mineral dressing
No full textIt appears at present that there is little scope of doing innovative work in metal extraction and mineral beneficiation so most of the schools in west do not pay much attention to this classical area and we follow them. But there is a need to take a re-look at the classical areas because of changing scenario. Over the years, we exploited high grade ores so what is left now is inferior grade ores but we require to produce quality metal economically from these. Secondly the slag generated during extraction and refining cannot be dumped in open space any more but has to be utilized and finally new type of wastes, electronic waste and batteries, are being generated at a very rapid rate. These wastes contain valuable as well toxic metals and they must be recovered. These are the new challenges. Two case studies of innovative approach in mineral beneficiation is presented. (C) 2018 Elsevier Ltd. All rights reserved
Iterative Sparse Channel Estimation and Data Detection for Underwater Acoustic Communications Using Partial Interval Demodulation
No full textWe present an iterative scheme for sparse channel recovery and data detection in cyclic-prefix orthogonal frequency division multiplex communication over doubly spread underwater acoustic channels. We consider the sequence of observations from partial interval demodulators (PIDs), and cast them into an observation model amenable for sparse channel recovery. We propose a two-stage iterative algorithm for channel estimation and data detection. In the first stage, we recover the channel from pilot-only observations and estimate the unknown data symbols from the postcombined PID outputs. In the second stage, we use the data symbols estimated in the first stage to reconstruct the dictionary matrix corresponding to a full interval demodulator, re-estimate the channel using the entire observations including the data sub-carriers, and use it to detect the unknown data symbols from the PID outputs. Theoretically, we show that the PID outputs help in tracking the time-varying channel better by providing additional measurements to estimate the intercarrier interference due to Doppler spread compared to full interval demodulation. Also, we derive the Cramer-Rao lower bound on the mean squared error in channel estimation, and empirically show that the proposed two-stage algorithm meets the bound at high signal-to-noise ratio. Numerical studies on simulated channels and publicly available experimental channel data in WATERMARK show that the proposed algorithm considerably improves data detection performance, in terms of bit error rate, over that from a traditional full length demodulator output, in highly Doppler distorted scenarios
Transporters Through the Looking Glass: An Insight into the Mechanisms of Ion-Coupled Transport and Methods That Help Reveal Them
No full textCell membranes, despite providing a barrier to protect intracellular constituents, require selective gating for the influx of important metabolites including ions, sugars, amino acids, neurotransmitters and efflux of toxins and metabolic end-products. The machinery involved in carrying out this gating process comprises of integral membrane proteins that use ionic electrochemical gradients or ATP hydrolysis, to drive concentrative uptake or efflux. The mechanism through which ion-coupled transporters function is referred to as alternating-access. In the recent past, discrete modes of alternating-access have been described with the elucidation of new transporter structures and their snapshots in altered conformational states. Despite X-ray structures being the primary sources of mechanistic information, other biophysical methods provide information related to the structural dynamics of these transporters. Methods including EPR and smFRET, have extensively helped validate or clarify ion-coupled transport mechanisms, in a near-native environment. This review seeks to highlight the mechanistic details of ion-coupled transport and delve into the biophysical tools and methods that help in understanding these fascinating molecules
Phase transition induced micromechanical actuation in VO2 coated cantilever
No full textStructural phase transition assisted micromechanical actuation of a vanadium dioxide (VO2) coated silicon microcantilever is presented. A 300 nm polycrystalline VO2 film was deposited over the silicon surface at 520 degrees C using metal organic chemical vapor deposition. The formation of the M1 monoclinic phase of the as-deposited VO2 film was confirmed by X-ray diffraction studies and further verified by temperature variable Raman spectroscopy. The heated VO2 film exhibits semiconductor-to-metal transition at 74 degrees C, which produces a change in the electrical resistance almost of three orders in magnitude. Consequently, the VO2 film undergoes structural phase transition from the monoclinic phase (011)(M1) to a tetragonal phase (110)(R). This generates a compressive stress within the VO2 film resulting in large, reversible cantilever deflection. This deflection was measured with a non-contact 3D optical profilometer, which does not require any vacuum conditions. Upon heating, the VO2 coated silicon cantilever produced a large reversible tip deflection of 14 mu m at 50 degrees C. Several heating and cooling cycles indicate steep changes in the cantilever tip deflection with negligible hysteresis. In addition, the effect of thermal stress induced cantilever deflection was estimated to be as small as 6.4%, and hence can be ignored. These results were found to be repeatable within controlled experimental conditions. Published by AIP Publishing