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An effectivefield theory approach to Compton scattering in plasma
No full textRestricted Access.We study Compton scattering in plasma medium via an effectivefield theory, by incorporating the contributions of longitudinal as well as transverse permittivities with their temperature dependent dispersive terms. We show that the introduction of the longitudinal mode not only increases the cross-section many-fold than in the case of vacuum, but also leads as a consequence to a well collimated and mono-energetic spectrum of scattered electrons, with the divergence ∼6 mrad, suggesting that this approach has potential application to laser plasma accelerators
ATLBS extended source sample : The evolution in radio source morphology with flux density
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Based on the Australia Telescope Low Brightness Survey (ATLBS) we present a sample of extended radio sources
and derive morphological properties of faint radio sources. One hundred nineteen radio galaxies form the ATLBS
Extended Source Sample (ATLBS-ESS) consisting of all sources exceeding 30 in extent and integrated flux
densities exceeding 1 mJy. We give structural details along with information on galaxy identifications and source
classifications. The ATLBS-ESS, unlike samples with higher flux-density limits, has almost equal fractions of FR-I
and FR-II radio galaxies, with a large fraction of the FR-I population exhibiting 3C31-type structures. Significant
asymmetry in lobe extents appears to be a common occurrence in the ATLBS-ESS FR-I sources compared with
FR-II sources. We present a sample of 22 FR-Is at z > 0.5 with good structural information. The detection of
several giant radio sources, with size exceeding 0.7 Mpc, at z > 1 suggests that giant radio sources are not less
common at high redshifts. The ESS also includes a sample of 28 restarted radio galaxies. The relative abundance
of dying and restarting sources is indicative of a model where radio sources undergo episodic activity in which an
active phase is followed by a brief dying phase that terminates with restarting of the central activity; in any massive
elliptical a few such activity cycles wherein adjacent events blend may constitute the lifetime of a radio source and
such bursts of blended activity cycles may be repeated over the age of the host. The ATLBS-ESS includes a 2 Mpc
giant radio galaxy with the lowest surface brightness lobes known to date
Electrontransfer studies of redox probes in bovine milk
No full textRestricted Access.In this work, we show that milk can act as an electrolytic medium to study electrochemical processes in the absence of any supporting electrolyte. The electrontransfer properties of three different redox systems in bovine homogenized whole milk, skimmed milk, and reconstituted milk powder have been studied by cyclic voltammetry and impedance spectroscopy using a three-electrode system with a gold disk working electrode, a platinum sheet counter electrode, and a standard calomel reference electrode. It has been shown that the milk incredibly sustains the redox reactions in the absence of any supporting electrolyte and the electrochemical responses are comparable to those obtained when the same reactions were carried out in standard solvent preparations containing supporting electrolytes. The study clearly demonstrates the potential of developing new innovative techniques based on the intricate concepts of electrochemistry to study various aspects of milk that may help in the development of analytical sensors for the diary industry
Multi-frequency studies of radio relics in the galaxy clusters A4038, A1664, and A786
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We present a multi-frequency study of radio relics associated with the galaxy clusters A4038, A1664, and A786. Radio images, integrated spectra, spectral index maps, and fits to the integrated spectra in the framework of the adiabatic compression model are presented. Images of the relic in A4038 at 150, 240, and 606 MHz with the Giant Meterwave Radio Telescope have revealed extended ultra-steep spectrum (α ~ -1.8 to -2.7) emission of extent 210 × 80 kpc2. The model of passively evolving radio lobes compressed by a shock fits the integrated spectrum best. The relic with a circular morphology at the outskirts of the cluster A1664 has an integrated spectral index of ~ - 1.10 ± 0.06 and is best fit by the model of radio lobes lurking for ~4 × 107 yr. The relic near A786 has a curved spectrum and is best fit by a model of radio lobes lurking for ~3 × 107 yr. At 4.7 GHz, a compact radio source, possibly the progenitor of the A786 relic, is detected near the center of the radio relic. The A786 radio relic is thus likely a lurking radio galaxy rather than a site of cosmological shock as has been considered in earlier studies
Roles of radiation and ram pressure in driving galactic winds
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We study gaseous outflows from disk galaxies driven by the combined effects of ram pressure on cold gas clouds and radiation pressure on dust grains. Taking into account the gravity due to disk, bulge, and dark matter halo, and assuming continuous star formation in the disk, we show that radiation or ram pressure alone is not sufficient to drive escaping winds from disk galaxies and that both processes contribute. We show that in the parameter space of star formation rate (SFR) and rotation speed of galaxies the wind speed in galaxies with rotation speeds vc <= 200 km s-1 and SFR <= 100 M sun yr-1 has a larger contribution from ram pressure, and that in high-mass galaxies with large SFR radiation from the disk has a greater role in driving galactic winds. The ratio of wind speed to circular speed can be approximated as {v_w / v_c} \sim 10^{0.7} \, [SFR/ 50 \, {M_{\odot } \,yr^{-1}}] ^{0.4} \ [{v_c/ 120\, km\,s^{-1}}]^ {-1.25}. We show that this conclusion is borne out by observations of galactic winds at low and high redshift and also of circumgalactic gas. We also estimate the mass loading factors under the combined effect of ram and radiation pressure, and show that the ratio of mass-loss rate to SFR scales roughly as v -1 c Σ g -1, where Σ g is the gas column density in the disk
Scientific objectives of Einstein telescope
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz to 10 kHz, with sensitivity a factor 10 better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas
Ehrenfest’s theorem and nonclassical states of light: 1. Ehrenfest’s theorem in quantum mechanic
No full textOpen AccessWhen it was first enunciated, Ehrenfest’s Theorem provided a necessary and important link between classical mechanics and quantum mechanics. Today, the content of the theorem is understood to be a natural and immediate consequence of the equation of motion for operators when quantum mechanics is formulated in the Heisenberg picture. Nevertheless, the theorem leads to useful approximations when systems with Hamiltonians of higher than quadratic order in the dynamical variables are considered. In this two-part article, we use it to provide a convenient illustration of the differences between so-called classical and nonclassical states of radiation
Nonlinear optical studies of lead lanthanum borate glass doped with Au nanoparticles
No full textRestricted Access.Synthesis, characterization and optical nonlinearity of lead lanthanum borate glass embedded with gold nanoparticles have been investigated. DSC thermogram shows characteristics glass transition temperature at Tg = 775 K. Glasses doped with Au were subjected to heat treatment at 823 K with different annealing time and then, slowly cooled to room temperature show striking ruby color. SAED and TEM analyses have confirmed that f.c.c. Au nanoparticles of ~ 40 nm size are present in these glasses. An absorption peak centered on 563 nm has been observed in heat treated samples, which is attributed to surface plasmon resonance of gold nanoparticles. Nonlinear optical studies with open aperture Z-Scan technique show saturable absorption for heat treated samples at low intensity and reverse saturable absorption in samples without heat treatment at high intensity