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Atomistic simulations of a multicomponent asymmetric lipid bilayer
No full textRestricted Access.The cell membrane is inherently asymmetric and heterogeneous in its composition, a feature that is crucial for its function. Using atomistic molecular dynamics simulations, the physical properties of a 3-component asymmetric mixed lipid bilayer system comprising an unsaturated POPC (palmitoyloleoylphosphatidylcholine), a saturated PSM (palmitoylsphingomyelin), and cholesterol are investigated. Our simulations explore both the dynamics of coarsening following a quench from the mixed phase and the final phase-segregated regime obtained by equilibrating a fully segregated configuration. Following a quench, the membrane quickly enters a coarsening regime, where the initial stages of liquid ordered, lo, domain formation are observed. These growing domains are found to be highly enriched in cholesterol and PSM. Consistent with this, the final phase-segregated regime contains large lo domains at equilibrium, enriched in cholesterol and PSM. Our simulations suggest that the cholesterol molecules may partition into these PSM-dominated regions in the ratio of 3:1 when compared to POPC-dominated regions. PSM molecules exhibit a measurable tilt and long-range tilt correlations within the lo domain as a consequence of the asymmetry of the bilayer, with implications to local membrane deformation and budding. Tagged particle diffusion for PSM and cholesterol molecules, which reflects spatial variations in the physical environment encountered by the tagged particle, is computed and compared with recent experimental results obtained from high-resolution microscopy
Gravitational waves from a particle in circular orbits around a schwarzschild black hole to the 22nd post-Newtonian order
No full textRestricted Access.We extend our previous results of the 14th post-Newtonian (PN) order expansion of gravitational waves for a test particle in circular orbits around a Schwarzschild black hole to the 22PN order, i.e. v^{44} beyond the leading Newtonian approximation where v is the orbital velocity of a test particle. Comparing our 22PN formula for the energy flux with high precision numerical results, we find that the relative error of the 22PN flux at the innermost stable circular orbit is about 10^{-5}. We also estimate the phase difference between the 22PN waveforms and numerical waveforms after a two-year inspiral. We find that the dephase is about 10^{-9} for μ/M = 10^{-4} and 10^{-2} for μ/M = 10^{-5} where μ is the mass of the compact object and M the mass of the central supermassive black hole. Finally, we construct a hybrid formula of the energy flux by supplementing the 4PN formula of the energy flux for circular and equatorial orbits around a Kerr black hole with all the present 22PN terms for the case of a Schwarzschild black hole. Comparing the hybrid formula with the the full numerical results, we examine the performance of the hybrid formula for the case of Kerr black hole
Electro-catalytic activity of multiwall carbon nanotube-metal (Pt or Pd) nanohybrid materials synthesized using microwave-induced reactions and their possible use in fuel cells
No full textRestricted Access.Microwave induced reactions for immobilizing platinum and palladium nanoparticles on multiwall carbon nanotubes are presented. The resulting hybrid materials were used as catalysts for direct methanol, ethanol and formic acid oxidation in acidic as well as alkaline media. The electrodes are formed by simply mixing the hybrids with graphite paste, thus using a relatively small quantity of the precious metal. We report Tafel slopes and apparent activation energies at different potentials and temperatures. Ethanol electro-oxidation with the palladium hybrid showed an activation energy of 7.64 kJ mol−1 which is lower than those observed for other systems. This system is economically attractive because Pd is significantly less expensive than Pt and ethanol is fast evolving as a commercial biofuel
Low frequency imagingof fields at high galactic latitude with the murchison widefield array 32 element prototype
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The Murchison Widefield Array (MWA) is a new low-frequency, wide-field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory in Western Australia. We have used a 32 element MWA prototype interferometer (MWA-32T) to observe two 50° diameter fields in the southern sky, covering a total of ~2700 deg2, in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields in the 110-200 MHz band. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide-field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110-200 MHz band
Spectral and polarization study of the double relics in Abell 3376 using the Giant Metrewave Radio Telescope and the Very Large Array
No full textRestricted Access.Double radio relics in galaxy clusters are rare phenomena that trace shocks in the outskirts of merging galaxy clusters. We have carried out a spectral and polarization study of the spectacular double relics in the galaxy cluster A3376 using the Giant Metrewave Radio Telescope at 150 and 325 MHz and the Very Large Array at 1400 MHz. The polarization study at 1400 MHz reveals a high degree of polarization (∼30 per cent) and aligned magnetic field vectors (not corrected for Faraday rotation) in the eastern relic. A highly polarized (>60 per cent) filamentary radio source of size ∼300 kpc near the eastern relic and north of the bent-jet radio galaxy is detected for the first time. The western relic is less polarized and does not show aligned magnetic field vectors. The distribution of spectral indices between 325 and 1400 MHz over the radio relics shows steepening from the outer to the inner edges of the relics. The spectral indices of the eastern and the western relics imply Mach numbers in the range 2.2–3.3. Remarkable features such as the inward filament extending from the eastern relic, the highly polarized filament, the complex polarization properties of the western relic and the separation of the brightest cluster galaxy from the intracluster medium by a distance >900 kpc are noticed in the cluster. A comparison with simulated cluster mergers is required to understand the complex properties of the double relics in the context of the merger in A3376. An upper limit [log(P1.4 GHz W Hz−1) < 23.0] on the strength of a Mpc size radio halo in A3376 is estimated