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Organelle morphogenesis by active membrane remodeling
No full textRestricted Access.Intracellular organelles are subject to a steady flux of lipids and proteins through active, energy consuming transport processes. Active fission and fusion are promoted by GTPases, e.g., Arf–Coatamer and the Rab–Snare complexes, which both sense and generate local membrane curvature. Here we investigate, through Dynamical Triangulation Monte Carlo simulations, the role that these active processes play in determining the morphology and composition segregation in closed membranes. We find that the steady state shapes obtained as a result of such active processes, bear a striking resemblance to the ramified morphologies of organelles in vivo, pointing to the relevance of nonequilibrium fission–fusion in organelle morphogenesi
Experimental test of environment-assisted invariance
No full textOpen AccessEnvariance, or environment-assisted invariance, is a recently identified symmetry for maximally entangled states in quantum theory with important ramifications for quantum measurement, specifically for understanding Born's rule. We benchmark the degree to which nature respects this symmetry by using entangled photon pairs. Our results show quantum states can be (99.66±0.04)% envariant as measured using the quantum fidelity, and (99.963±0.005)% as measured using a modified Bhattacharya coefficient, as compared with a perfectly envariant system which would be 100% in either measure. The deviations can be understood by the less-than-maximal entanglement in our photon pairs
Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures
No full textRestricted Access.Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14–37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane
Union Minister Dr Harsha Vardhan Asks Scientists to Develop at Least one Technology in Strategic Sector in Each Laboratory.
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Ultra-low casting of Pt based nano-ink for electrooxidation of glycerol and ethylene glycol fuels in alkaline medium
No full textRestricted Access.For the first time we present an ultra-low casting of Pt based nano-ink on carbon paste electrodes (CPEs) for electrooxidation of glycerol and ethylene glycol fuels in alkaline medium. The platinum loaded carbon nanotube (Pt-CNT) synthesized by a microwave induced reaction has been extensively characterized by microscopic, spectroscopic and thermal gravimetric techniques. Pt-CNT has shown 6 and 33 fold improved activity for the Glycerol electrooxidation reaction (GOR) and ethylene glycol electrooxidation reaction (EGOR) vis-à-vis the commercial Johnson Matthey Pt-C. The low onset potentials and high current densities achieved using this novel nano ink is indicative of its plausible role in fuel cell applications
Enhancement in the thermodynamic, electrical and optical properties of hexabutoxytriphenylene due to copper nanoparticles
No full textRestricted Access.In the present article, we have studied the effect of copper nano-particles on the thermal, optical and dielectric parameters of a liquid crystalline material 2,3,6,7,10,11-hexabutyloxytriphenylene (in short HAT4) showing wide temperature range (~ 65 °C) hexatic columnar mesophase. A composite has been prepared by dispersing 0.6 wt.% of copper nano-particles. UV–vis spectroscopy has been used to record the absorption spectra. It has been observed that the presence of copper nano-particles introduces surface plasmon resonance and reduces the optical band gap of HAT4. Though isotropic to mesophase transition temperature is unaffected but mesophase-crystal transition temperature has decreased and hence range of the mesophase has enhanced due to the presence of copper nano-particles. While dc conductivity has increased by about two orders of magnitudes, dielectric permittivity has also moderately increased. With the enhanced properties, HAT4-copper nano-particle composite is useful for one dimensional conduction and photovoltaic applications
Nonlinear optical investigations in nine-atom silver quantum clusters and graphitic carbon Nitride Nanosheets
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Absorption saturation due to surface plasmon resonance affects the optical limiting efficiency of metal nanoparticles (NPs) by raising the limiting threshold to higher laser fluences. It has been shown that in gold, compared to the larger NPs, smaller quantum clusters (QCs) exhibit better optical limiting with lower limiting thresholds due to the absence of absorption saturation. Here we report optical limiting properties of two novel materials, namely, nine-atom silver (Ag9) QCs and graphitic carbon nitride (GCN) nanosheets. The relatively large nonlinear absorption of Ag9 QCs compared to Ag NPs is revealed from open-aperture Z-scan measurements carried out using 532 nm, 5 ns laser pulses. Optical nonlinearity in the QCs arises mostly from free carrier absorption and a relatively weak saturable absorption. The superior limiting efficiency of Ag9 QCs is complemented by excellent chemical stability, which makes silver quantum clusters ideal candidates for optical limiting applications. The two-dimensional sheet-like structure of GCN is ideal for grafting metals and semiconductors, and we show that even though the nonlinearity of pristine GCN is low it can be improved substantially by grafting lightly with Ag9 QC
Ensemble effect of intrinsic defects and Mn ions on the enhancement of third order nonlinearity of ZnO nanoparticles
No full textRestricted Access.Mn doped ZnO nanoparticles were synthesized by the chemical co-precipitation method and XRD confirms the hexagonal structure of nanoparticles with good crystallinity. From TEM analysis, the average crystallite size of the nanoparticles is evaluated as 7–13 nm. All the prepared nanoparticles exhibit reverse saturable absorption in open aperture Z-scan measurements. The experimental data best fits for two-photon absorption along with saturable absorption and the obtained β values are found to be in the range of 0.3–0.5 × 10−10 m W−1. The enhancement of β upon increasing Mn concentration is attributed to the increase of absorption due to defect states created by Mn doping. EPR and PL measurements provide evidence of the presence of zinc vacancy defects. The self-defocusing nonlinearity exhibited in Mn doped ZnO nanoparticles at 532 nm indicates the reverse saturable absorption (RSA) based optical limiting behavior
Variations of the harmonic components of the X-ray pulse profile of PSR B1509–58
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We used the Fourier decomposition technique to investigate the stability of the X-ray pulse profile of a young pulsar PSR B1509–58 by studying the relative amplitudes and phase differences of its harmonic components with respect to the fundamental using data from the Rossi X-Ray Timing Explorer. Like most young rotation powered pulsars, PSR B1509–58 has a high spin down rate. It also has less timing noise, allowing accurate measurement of higher order frequency derivatives which in turn helps in the study of the physics of pulsar spin down. Detailed investigation of pulse profiles over the years will help us establish any possible connection between the timing characteristics and the high energy emission characteristics for this pulsar. Furthermore, the study of pulse profiles of short period X-ray pulsars can also be useful when used as a means of interplanetary navigation. The X-ray pulse profile of this source has been analyzed for 15 yr (1996–2011). The long term average amplitudes of the first, second and third harmonics (and their standard deviation for individual measurements) compared to the fundamental are 36.9% (1.7%), 13.4% (1.9%) and 9.4% (1.8%) respectively. Similarly, the phases of the three harmonics (and standard deviations) with respect to the fundamental are 0.36 (0.06), 1.5 (0.2) and 2.5 (0.3) radian respectively. We do not find any significant variation of the harmonic components of the pulse profile in comparison to the fundamental