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High-resolution imaging of the ATLBS regions:The radio source counts
No full textRestricted Access. An open-access version is available at arXiv.org. Articles older than 2 years are open to all at the journal siteThe Australia Telescope Low-brightness Survey (ATLBS) regions have been mosaic imaged at a radio frequency of 1.4 GHz with 6'' angular resolution and 72 μJy beam-1 rms noise. The images (centered at R.A. 00h35m00s, decl. -67°00'00'' and R.A. 00h59m17s, decl. -67°00'00'', J2000 epoch) cover 8.42 deg2 sky area and have no artifacts or imaging errors above the image thermal noise. Multi-resolution radio and optical r-band images (made using the 4 m CTIO Blanco telescope) were used to recognize multi-component sources and prepare a source list; the detection threshold was 0.38 mJy in a low-resolution radio image made with beam FWHM of 50''. Radio source counts in the flux density range 0.4-8.7 mJy are estimated, with corrections applied for noise bias, effective area correction, and resolution bias. The resolution bias is mitigated using low-resolution radio images, while effects of source confusion are removed by using high-resolution images for identifying blended sources. Below 1 mJy the ATLBS counts are systematically lower than the previous estimates. Showing no evidence for an upturn down to 0.4 mJy, they do not require any changes in the radio source population down to the limit of the survey. The work suggests that automated image analysis for counts may be dependent on the ability of the imaging to reproduce connecting emission with low surface brightness and on the ability of the algorithm to recognize sources, which may require that source finding algorithms effectively work with multi-resolution and multi-wavelength data. The work underscores the importance of using source lists—as opposed to component lists—and correcting for the noise bias in order to precisely estimate counts close to the image noise and determine the upturn at sub-mJy flux density
Timing and Spectral properties of Be/X-ray pulsar EXO 2030+375 during a Type I outburst
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations) Articles older than 2 years are open to all at the journal siteWe present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy-dependent pulse profiles were clearly detected up to 100 keV. Narrow dips are seen in the profiles up to ~70 keV. The presence of prominent dips at several phases in the profiles up to such high energy ranges was not seen before. At higher energies, these dips gradually disappeared and the profile appeared to be single-peaked. The 1.0-200.0 keV broadband spectrum is found to be well described by a partial covering high-energy cutoff power-law model. Several low-energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with the above continuum model yielding similar parameter values. The partial covering with a partially ionized absorber resulted in a marginally better fit. The spectral fitting did not require any cyclotron feature in the best-fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of the additional column density was estimated to be high compared to other pulse phases. While using a partially ionized absorber, the value of the ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar
Towards an anomaly-free quantum dynamics for a weak coupling limit of Euclidean gravity
No full textopen Access.The GNewton→0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)3 gauge theory. The Poisson-bracket algebra of its Hamiltonian and diffeomorphism constraints is isomorphic to that of gravity. Motivated by recent results in parametrized field theory and by the search for an anomaly-free quantum dynamics for loop quantum gravity, the quantum Hamiltonian constraint of density weight 4/3 for this U(1)3 theory is constructed so as to produce a nontrivial loop quantum gravity type representation of its Poisson brackets through the following steps. First, the constraint at finite triangulation and the commutator between a pair of such constraints are constructed as operators on the “charge” network basis. Next, the continuum limit of the commutator is evaluated with respect to an operator topology defined by a certain space of “vertex smooth” distributions. Finally, the operator corresponding to the Poisson bracket between a pair of Hamiltonian constraints is constructed at finite triangulation in such a way as to generate a “generalized” diffeomorphism and its continuum limit is shown to agree with that of the commutator between a pair of finite-triangulation Hamiltonian constraints. Our results, in conjunction with the recent work of Henderson, Laddha and Tomlin in a (2+1)-dimensional context, constitute the necessary first steps toward a satisfactory treatment of the quantum dynamics of this model
Patterning of polar active filaments on a tense cylindrical membrane
No full textOpen Access.We study the dynamics and patterning of polar contractile filaments on the surface of a cylindrical cell using active hydrodynamic equations that incorporate couplings between curvature and filament orientation. Cables and rings spontaneously emerge as steady state configurations on the cylinder, and can be stationary or moving, helical or segments moving along helical trajectories. Contractility induces coalescence of proximal rings. We observe phase transitions in the steady state patterns upon changing cell diameter and make several testable predictions. Our results are relevant to the dynamics and patterning of a variety of active biopolymers in cylindrical cells
Three-photon absorption and vibrational spectroscopic study of 2-methylamino-5-chlorobenzophenone
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)In this paper, the vibrational spectral analysis and three-photon absorption properties of an organic material of 2-methylamino-5-chlorobenzophenone have been reported. The geometry and harmonic vibrational wavenumbers are calculated with the help of B3LYP density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology (SQM). SQM force fields have also been used to calculate potential energy distribution (PED) in order to make conspicuous vibrational assignments. The nonlinear absorption properties have been investigated in ethanol solution at 532 nm using the Z-scan technique employing laser pulses of 5 ns duration. Open aperture Z-scan data reveal the presence of effective three-photon absorption for ns pulses at 532 nm resulting in a strong optical limiting behavior, indicating possible photonic applications
Graduate from research institutes
No full textOpen AccessNobel Laureate CV Raman was one of the most celebrated physicists of India. In 1948, he established Raman Research Institute (RRI), Bangalore, to organise research and study different disciplines under science/physics