Work Fluctuations and Stochastic Resonance

We study Brownian particle motion in a double-well potential driven by an ac force. This system exhibits the phenomenon of stochastic resonance. Distribution of work done on the system over a drive period in the time asymptotic regime have been calculated. We show that fluctuations in the input energy or work done dominate the mean value. The mean value of work done over a period as a function of noise strength can also be used to characterise stochastic resonance in the system. We also discuss the validity of steady state fluctuation theorems in this particular system.Comment: 5 page

VLBA polarimetric observations of the CSS quasar 3C147

Aims. We report new VLBA polarimetric observations of the compact steep-spectrum (CSS) quasar 3C147 (B0538+498) at 5 and 8.4GHz. Methods. By using multifrequency VLBA observations, we derived milliarcsecond-resolution images of the total intensity, polarisation, and rotation measure distributions, by combining our new observations with archival data. Results. The source shows a one-sided structure, with a compact region, and a component extending about 200 mas to the south-west. The compact region is resolved into two main components with polarised emission, a complex rotation measure distribution, and a magnetic field dominated by components perpendicular to the source axis. Conclusions. By considering all the available data, we examine the possible location of the core component, and discuss two possible interpretations of the observed structure of this source: core-jet and lobe-hot spot. Further observations to unambiguously determine the location of the core would help distinguish between the two possibilities discussed here.Comment: 11 pages, 12 figure

Cultivar Variation for Capsaicinoid Content in some Processed Products of Chilli

Determination of capsaicinoids content in various products from seven chilli cultivars was made. Capsaicin, the major element among capsaicinoids, is found primarily in the fruit of Capsicum to which it provides spicy flavor. Extraction of capsaicin in the present study was done using acetonitrile as the solvent, and High Performance Liquid Chromatography was used for its quantification. Whole dried-fruits of 'Bhut Red' (Capsicum chinense) showed the highest concentration of capsaicin (2.59%) and level of pungency (4,40,000 SHU), whereas, salted mash of 'Lemon Drop' (Capsicum baccatum) had the lowest capsaicin concentration (0.07%) and pungency level (12,000 SHU). As capsaicinoids are important in food and pharmaceutical industries, developing products from selected cultivars of chilli with high pungency and high capsaicinoid content will prove useful in order to ensuring health security

Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution

Aims - We report new Very Large Array polarimetric observations of Compact Steep-Spectrum (CSS) sources at 8.4, 15, and 23GHz. Methods - Using multi-frequency VLA observations we have derived sub-arcsecond resolution images of the total intensity, polarisation, and rotation measure (RM) distributions. Results heading - We present multi-frequency VLA polarisation observations of CSS sources. About half of the sources are point-like even at the resolution of about 0.1x0.1 arcseconds. The remaining sources have double or triple structure. Low values for the percentage of polarised emission in CSS sources is confirmed. On the average, quasars are more polarised than galaxies. A wide range of RM values have been measured. There are clear indications of very large RMs up to 5\,585 rad m**(-2). CSS galaxies are characterized by RM values that are larger than CSS quasars. The majority of the objects show very large values of RM. Conclusions - The available data on sub-arcsecond-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to about 36,000 rad m**(-2). RM estimates indicate an overall density of the magneto-ionic medium larger than classical radio sources.Comment: Accepted for publication by Astronomy & Astrophysic

Radio bubbles in the composite AGN-starburst galaxy NGC6764

We present multi-frequency radio continuum as well as HI observations of the composite galaxy NGC6764, which has a young, circumnuclear starburst and also harbours an active galactic nucleus (AGN). These observations have been made at a number of frequencies ranging from ~600 MHz to 15 GHz using both the GMRT and the VLA. They reveal the structure of the bipolar bubbles of non-thermal, radio emission which are along the minor axis of the galaxy and extend up to ~1.1 and 1.5 kpc on the northern and southern sides respectively. Features in the radio bubbles appear to overlap with filaments of H_alpha emission. The high-resolution observations reveal a compact source, likely to be associated with the nucleus of the galaxy, and a possible radio jet towards the south-west. We have compiled a representative sample of galaxies with bubbles of non-thermal radio emission and find that these are found in galaxies with an AGN. The HI observations with the GMRT show two peaks of emission on both ends of the stellar-bar and depletion of HI in the central region of the galaxy. We also detect HI in absorption against the central radio peak at the systemic velocity of the galaxy. The HI-absorption spectrum also suggests a possible weak absorption feature blue-shifted by ~120 km/s, which requires confirmation. A similar feature has also been reported from observations of CO in emission, suggesting that the circumnuclear starburst and nuclear activity affect the kinematics of the atomic and molecular gas components, in addition to the ionised gas seen in H_alpha and [N II]

Relativistic and slowing down: the flow in the hotspots of powerful radio galaxies and quasars

Pairs of radio emitting jets with lengths up to several hundred kiloparsecs emanate from the central region (the `core') of radio loud active galaxies. In the most powerful of them, these jets terminate in the `hotspots', compact high brightness regions, where the jet flow collides with the intergalactic medium (IGM). Although it has long been established that in their inner ($\sim$parsec) regions these jet flows are relativistic, it is still not clear if they remain so at their largest (hundreds of kiloparsec) scales. We argue that the X-ray, optical and radio data of the hotspots, despite their at-first-sight disparate properties, can be unified in a scheme involving a relativistic flow upstream of the hotspot that decelerates to the sub-relativistic speed of its inferred advance through the IGM and viewed at different angles to its direction of motion. This scheme, besides providing an account of the hotspot spectral properties with jet orientation, it also suggests that the large-scale jets remain relativistic all the way to the hotspots.Comment: to appear in ApJ