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Interaction of galactic wind with halo gas and the origin of multiphase extraplanar material
No full textOpen AccessWe study the interaction of a galactic wind with hot halo gas using hydrodynamical simulations. We find that the outcome of this interaction depends crucially on the wind injection density and velocity. Various phases of extraplanar media such as infalling clouds, outflowing clouds and O vi regions can originate in the interaction zones of wind with the halo gas, depending on the injection velocity and density. In our simulations, the size of the clouds is of the order of 100 pc. The total mass contained in the clouds is 105–107 M⊙ and they have a normal distribution of velocities in the galactic standard of rest frame. For high injection density and velocity, a significant number of clouds move outwards and resemble the case of cold neutral outflows. Furthermore, a 105–106 K phase is formed in our simulations, which has a column density ∼1018 cm−2 and resembles the observed O vi regions. The injection velocity and density are linked with the mass-loading factor of the outflow, efficiency of energy injection due to supernovae and star-formation rate. Comparison of the predicted morphology of extraplanar gas with observations can serve as a useful diagnostic for constraining the feedback efficiency of outflows
First all-sky search for continuous gravitational waves from unknown sources in binary systems
No full textOpen AccessWe present the first results of an all-sky search for continuous gravitational waves from unknown spinning neutron stars in binary systems using LIGO and Virgo data. Using a specially developed analysis program, the TwoSpect algorithm, the search was carried out on data from the sixth LIGO science run and the second and third Virgo science runs. The search covers a range of frequencies from 20 Hz to 520 Hz, a range of orbital periods from 2 to ∼2,254 h and a frequency- and period-dependent range of frequency modulation depths from 0.277 to 100 mHz. This corresponds to a range of projected semimajor axes of the orbit from ∼0.6×10−3 ls to ∼6,500 ls assuming the orbit of the binary is circular. While no plausible candidate gravitational wave events survive the pipeline, upper limits are set on the analyzed data. The most sensitive 95% confidence upper limit obtained on gravitational wave strain is 2.3×10−24 at 217 Hz, assuming the source waves are circularly polarized. Although this search has been optimized for circular binary orbits, the upper limits obtained remain valid for orbital eccentricities as large as 0.9. In addition, upper limits are placed on continuous gravitational wave emission from the low-mass x-ray binary Scorpius X-1 between 20 Hz and 57.25 Hz
Universal large deviations for the tagged particle in single-file motion
No full textOpen AccessWe consider a gas of point particles moving in a one-dimensional channel with a hard-core interparticle interaction that prevents particle crossings—this is called single-file motion. Starting from equilibrium initial conditions we observe the motion of a tagged particle. It is well known that if the individual particle dynamics is diffusive, then the tagged particle motion is subdiffusive, while for ballistic particle dynamics, the tagged particle motion is diffusive. Here we compute the exact large deviation function for the tagged particle displacement and show that this is universal, independent of the individual dynamic
One-element interferometer
No full textOpen AccessWe apply the phase-switching method of Ryle to convert single dish radio telescopes to one-element interferometers and thereby accord them the benefit of correlation measurements, viz. to measure only the flux from the celestial sources avoiding contributions from the receiver and the atmosphere. This application has many uses: (a) enables single dishes to image the sky efficiently without the need to scan, measuring all sources, point, extended, spectral and continuum, with both bolometric and coherent receivers; (b) enables adding reliable short-spacing data to existing interferometers such as Atacama Large Millimetre-wave Array,, mitigating calibration issues; (c) enables ground-based NIR/MIR imaging to accurately remove atmospheric contributions; (d) can be adapted to provide an alternate surface measurement method for telescopes
4-[2-(Trimethylsilyl)ethynyl]benzoates: Synthesis and evaluation for mesomorphic properties of some novel calamitic molecules
No full textRestricted Access.A series of novel terminal trimethylsilylacetylene benzoate derivatives with various linking groups were synthesized using Friedel-Craft's O-acylation reaction. The chemical structures of the novel 4-[2-(trimethylsilyl)ethynyl]benzoates were confirmed by standard spectroscopic techniques. The compounds were investigated for their liquid crystalline properties employing polarised optical microscopy and differential scanning calorimetry. The esters 5c – 5f, 5h and 5n possessing three phenyl rings exhibited liquid crystalline property of SmA/SmC phases with wide thermal range
Two-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The Goldenberg–Vaidman (GV) protocol for quantum key distribution uses orthogonal encoding states of a particle. Its security arises because operations accessible to Eve are insufficient to distinguish the two states encoding the secret bit. We propose a two-particle cryptographic protocol for quantum secure direct communication, wherein orthogonal states encode the secret, and security arises from restricting Eve from accessing any two-particle operations. However, there is a non-trivial difference between the two cases. While the encoding states are perfectly indistinguishable in GV, they are partially distinguishable in the bipartite case, leading to a qualitatively different kind of information-versus-disturbance trade-off and also options for Eve in the two cases
Effect of dispersed colloidal gold nanoparticles on the electrical properties of a columnar discotic liquid crystal
No full textRestricted Access.A dispersion of colloidal gold nanoparticles (GNPs) in a triphenylene-based discotic liquid crystal (DLC), namely 2,3,6,7,10,11-hexabutyloxytriphenylene (HAT4), possessing a hexatic plastic columnar phase (Colhp) phase, has been studied by differential scanning calorimetry, polarized light microscopy, UV-Vis absorption spectroscopy, X-ray diffraction and dielectric spectroscopy. GNPs have been dispersed at three different concentrations in pure HAT4 viz. 0.2, 0.6 and 1.2 wt%. It has been observed that with the increase of GNPs concentration, the Colhp–isotropic liquid transition temperature decreases substantially but the crystal–Colhp transition temperature does not changes significantly. Electrical conductivity increases by at least five orders of magnitude for the highest concentration of GNPs (1.2 wt%) as compared to the pure material i.e. HAT4. Observed results suggest that although extremely low concentrations of GNPs are not very useful, a moderate concentration is highly useful for increasing the conductivity of the Colhp phase and also to implant surface plasmon resonance. These results may be exploited to enhance the efficiency of electro-optical devices by using HAT4–GNPs composites
Acceleration of neutrals in a nanosecond laser produced nickel plasma
No full textOpen AccessTime of flight dynamics of slow neutrals, fast neutrals, and ions from a nanosecond laser produced nickel (Ni) plasma are investigated. Species arrival times confirm the hypothesis that fast neutrals are formed by the recombination of fast ions with free electrons. Both neutrals and ions are found to accelerate for a short interval immediately after ablation, which is attributed to internal Coulomb forces which create electrostatic potentials resulting in the charged particle acceleration. This process is further enhanced by laser-plasma energy coupling. Emission from neutrals could be measured for longer axial distances in the plume compared to that of ions confirming that the ions recombine to form neutrals as they move away from the target surface
Effects of temperature and ground-state coherence decay on enhancement and amplification in a delta atomic system
No full textOpen AccessWe study phase-sensitive amplification of electromagnetically induced transparency in a warm Rb85 vapor wherein a microwave driving field couples the two lower-energy states of a Λ energy-level system thereby transforming into a Δ system. Our theoretical description includes effects of ground-state coherence decay and temperature effects. In particular, we demonstrate that driving-field-enhanced electromagnetically induced transparency is robust against significant loss of coherence between ground states. We also show that for specific field intensities, a threshold rate of ground-state coherence decay exists at every temperature. This threshold separates the probe-transmittance behavior into two regimes: probe amplification vs probe attenuation. Thus, electromagnetically induced transparency plus amplification is possible at any temperature in a delta system