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B0707−359: a case study of change in AGN–black hole spin axis
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Structures of radio galaxies have the potential to reveal inconstancy in the axis of the beams, which reflect the stability in the spin axis of the supermassive black hole at the centre. We present radio observations of the giant radio galaxy B0707−359 whose structure offers an interesting case study of an active galactic nucleus (AGN) that may be exhibiting not only inconstancy in AGN output but also inconstancy in direction of ejection axis. Its radio morphology shows evidence for a restarting of the jets accompanied by an axis change. The observed side-to-side asymmetries of this giant radio galaxy suggest that the new jets are not in the plane of the sky. We infer that the hotspot advance velocities are unusually large and of magnitude a few tenths of the speed of light. The dual-frequency radio images are consistent with a model where the beams from the central engine ceased, creating a relic double radio source; this interruption was accompanied by triggering of a movement of the axis of the central engine at a rate of a few degrees Myr−1. The closer location of the giant radio galaxy axis to the host minor axis rather than the host major axis is supportive of the restarting and axis-change model for the formation of the double–double structure rather than the backflow model
Ferroelectric liquid crystal matrix dispersed with Cu doped ZnO nanoparticles
No full textRestricted Access.10% Cu doped ZnO nanoparticles (NPs) prepared by hydrothermal and solvothermal method have been dispersed to the pure FLC 17/100 in 1% concentration of guest entity. Electro-optical, elastic and dielectric analysis has been made for the FLC-NPs composite system with the variation of temperature. The nature of the composite system clearly shows the alteration in FLC parameters with the dispersion of NPs. The interaction between crystalline NPs and non-crystalline ferroelectric liquid crystal matrix modifies the properties of the pure FLC system. The synthesis method of NPs is also responsible for the changes taking place in physical properties of the pure FLC. The size and surface defects of the NPs amend the FLC parameters like dielectric permittivity, relaxation frequency, relaxation strength, tilt angle, spontaneous polarization and rotational viscosity etc. The coupling of spontaneous polarization and tilting of the FLC molecules are factors responsible for the resultant electro-optical (E-O) parameters of the composite system
VLA low band project: early commissioning results and vision for a primary focus-based commensal observing system
No full textRestricted Access.We present an update on the Jansky Very Large Array Low Band (VLA-LB) project, currently undergoing scientific commissioning and expected to be fully available in 2013. VLA-LB is a joint NRL and NRAO initiative to equip the VLA with broadband low frequency receivers that cover the spectrum between 66 and 470 MHz. The current system can already access the 66 to 86 MHz and 230 to 436 MHz sub-bands by working with existing 74 and 330 MHz feeds, respectively. The bandwidth at 74 MHz will increase by more than an order of magnitude while the 330 MHz bandwidth increases by approximately a factor of 6. The improved bandwidth and system temperature, coupled with the power of the WIDAR correlator, promise significantly enhanced performance compared to past VLA capabilities. Early commissioning results at “P band” (330 MHz) with a handful of antennas accessing the larger bandwidth indicate sensitivity rivaling that of the legacy 27-antenna, narrow-band old VLA capability. New feeds that can exploit a larger fraction of the available receiver bandwidth are being explored. While VLA-LB is useful as a conventional system, we are looking to enhance its power by leveraging the VLA’s capability to detect radiation at its prime and Cassegrain foci simultaneously. The ability to observe with more than one band in parallel is a powerful multiplier of a telescope’s function, and many instruments (e.g. the GMRT, WSRT and VLA) offer this. A variant is being explored for VLA-LB: observing from the prime focus during all normal Cassegrain observations. This proposed VLA-LB commensal system would piggyback normal VLA observing time to survey at low frequencies with relatively large field of views. Shared fields with other multi-beaming, dipole-based arrays that view the same sky with the VLA, e.g. the first station of the Long Wavelength Array (LWA1), would be possible. The collected data will be assembled into a database of spectra and wide-field images, suitable for studies of individual objects as well as searches for transients and high redshift spectral features (eg. HI absorption or OH mega-masers). We describe how the VLA-LB commensal system might be implemented, and explore early ideas for its scientific promise
Thermal unbinding and ordering of amphiphile bilayers in the presence of salt
No full textRestricted Access.We have studied the effect of KBr on the electrostatically stabilized fluid lamellar phase of the ionic surfactant, C12-alkenylsuccinic acid (ASA). Three distinct regimes are found in the temperature - salt phase diagram of this system at a fixed ASA concentration of 20 wt.%. A collapsed lamellar phase is formed in the low-salt regime, which exhibits an unbinding transition into uncorrelated bilayers on heating. In the intermediate salt regime the opposite trend is observed, with the uncorrelated bilayers present at low temperatures ordering into a lamellar phase at higher temperatures. As far as we are aware, this is the first report of such an ordering transition of uncorrelated bilayers. In the high salt regime, the topology of the bilayer changes, resulting in a lamellar–sponge transition. All the three transitions are reversible and the corresponding transition temperatures decrease with increasing salt concentration. The occurrence of these transitions in a single amphiphile system demonstrates the strong influence of salt on the bilayer elastic moduli as well as on the inter-bilayer interactions in the present system
Synthesis, growth, and characterization of iminodiacetic acid monohydrochloride
No full textRestricted Access.The title compound of iminodiacetic acid hydrochloride (IDAAMHCL) has been successfully synthesized by adopting conventional chemical reaction and the single crystals have been grown by solvent evaporation method at room temperature and studied its various properties and reported for the first time. The lattice dimension and the crystal structure were identified from the powder X-ray diffraction analysis. The crystalline perfection assessed by high resolution X-ray diffraction technique shows that the specimen is free from structural grain boundaries. The presence of functional groups and the protons in IDAAMHCl was confirmed by Fourier transform infra-red and NMR (1H and 13C) spectroscopic techniques. The presence of carbon, hydrogen, and nitrogen was confirmed by elemental analysis. The optical behavior of IDAAMHCl was assessed by UV-visible spectroscopy and it is found that there is no absorption in the entire visible region of the spectrum. The Z scan measurements at 532 nm with 5 ns laser pulses show that IDAAMHCL is a very good candidate for optical limiting applications.Characterization
Growth from solution
Gravity asymptotics with topological parameters
No full textOpen AccessIn four-dimensional gravity theory, the Barbero-Immirzi parameter has a topological origin, and can be identified as the coefficient multiplying the Nieh-Yan topological density in the gravity Lagrangian, as proposed by Date et al. [ Phys. Rev. D 79 044008 (2009)]. Based on this fact, a first order action formulation for spacetimes with boundaries is introduced. The bulk Lagrangian, containing the Nieh-Yan density, needs to be supplemented with suitable boundary terms so that it leads to a well-defined variational principle. Within this general framework, we analyze spacetimes with and without a cosmological constant. For locally anti–de Sitter (or de Sitter) asymptotia, the action principle has nontrivial implications. It admits an extremum for all such solutions provided the SO(3,1) Pontryagin and Euler topological densities are added to it with fixed coefficients. The resulting Lagrangian, while containing all three topological densities, has only one independent topological coupling constant, namely, the Barbero-Immirzi parameter. In the final analysis, it emerges as a coefficient of the SO(3,2) [or SO(4,1)] Pontryagin density, and is present in the action only for manifolds for which the corresponding topological index is nonzero
Apolar novel mesogenic symmetric dimers composed of ve-ring bent-core monomeric units
No full textRestricted Access.The synthesis and mesomorphic properties of parts of six different series of symmetric dimers composed of five-ring bent-core monomeric units have been investigated. By design, all the dimers are apolar as all the dipoles of the monomers cancel with each other. The mesomorphic properties have been investigated (1) as a function of the length of the terminal chain for a fixed spacer unit, and (2) as a function of the length of the spacer unit for a fixed terminal chain length. Interestingly, two orthogonal lamellar phases have been observed in many of these dimers which differ from one another only in the layer spacing. The chemical structure of the dimers has been determined using a combination of spectroscopic techniques and elemental analysis. The mesophases are characterised using complementary methods such as polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical measurements
OH Maser Sources in W49N: Probing magnetic field and differential anisotropic scattering with Zeeman pairs using the very long baseline array
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ~20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ~10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s-1. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region
Semi-counterfactual cryptography
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)In counterfactual quantum key distribution (QKD), two remote parties can securely share random polarization-encoded bits through the blocking rather than the transmission of particles. We propose a semi-counterfactual QKD, i.e., one where the secret bit is shared, and also encoded, based on the blocking or non-blocking of a particle. The scheme is thus semi-counterfactual and not based on polarization encoding. As with other counterfactual schemes and the Goldenberg-Vaidman protocol, but unlike BB84, the encoding states are orthogonal and security arises ultimately from single-particle non-locality. Unlike any of them, however, the secret bit generated is maximally indeterminate until the joint action of Alice and Bob. We prove the general security of the protocol, and study the most general photon-number–preserving incoherent attack in detail