Unstable topography of biphasic surfactant monolayers

We study the conformation of a heterogeneous surfactant monolayer at a fluid-fluid interface, near a boundary between two lateral regions of differing elastic properties. The monolayer attains a conformation of shallow, steep `mesas' with a height difference of up to 10 nm. If the monolayer is progressively compressed (e.g. in a Langmuir trough), the profile develops overhangs and finally becomes unstable at a surface tension of about K(delta c_0)^2, where (delta c_0) is the difference in spontaneous curvature and K a bending stiffness. We discuss the relevance of this instability to recently observed folding behavior in lung surfactant monolayers, and to the absence of domain structures in films separating oil and water in emulsions.Comment: 7 pages, 7 figures, LaTex using epl.cls, accepted for Europhys Let

Hint of 150 MHz radio emission from the Neptune-mass extrasolar transiting planet HAT-P-11b

Since the radio-frequency emission from planets is expected to be strongly influenced by their interaction with the magnetic field and corona of the host star, the physics of this process can be effectively constrained by making sensitive measurements of the planetary radio emission. Up to now, however, numerous searches for radio emission from extrasolar planets at radio wavelengths have only yielded negative results. Here we report deep radio observations of the nearby Neptune-mass extrasolar transiting planet HAT-P-11b at 150 MHz, using the Giant Meterwave Radio Telescope (GMRT). On July 16, 2009, we detected a 3-sigma emission whose light curve is consistent with an eclipse when the planet passed behind the star. This emission is at a position 14 arcsec from the transiting exoplanet's coordinates; thus, with a synthetized beam of FWHM~16 arcsec, the position uncertainty of this weak radio signal encompasses the location of HAT-P-11. We estimate a 5% false positive probability that the observed radio light curve mimics the planet's eclipse light curve. If the faint signature is indeed a radio eclipse event associated with the planet, then its flux would be 3.87 mJy +/- 1.29 mJy at 150 MHz. However, our equally sensitive repeat observations of the system on November 17, 2010 did not detect a significant signal in the radio light curve near the same position. This lack of confirmation leaves us with the possibility of either a variable planetary emission, or a chance occurrence of a false positive signal in our first observation. Deeper observations are required to confirm this hint of 150 MHz radio emission from HAT-P-11b.Comment: Accepted for publication in Astronomy & Astrophysic

Path Planning in the Presence of Dynamically Moving Obstacles with Uncertainty

In this paper, the problem of path-planning with dynamically moving elliptical obstacles is addressed. A new analytical result for computing the axes aligned bounding box for the ellipses with bounded uncertainty in the position of the centre and the orientation is presented. Genetic algorithm is utilised for finding the shortest path from the initial to goal position avoiding the moving obstacles.Defence Science Journal, 2010, 60(1), pp.55-60, DOI:http://dx.doi.org/10.14429/dsj.60.10

Further evidence for intra-night optical variability of radio-quiet quasars

Although well established for BL Lac objects and radio-loud quasars, the occurrence of intra-night optical variability (INOV) in radio-quiet quasars is still debated, primarily since only a handful of INOV events with good statistical significance, albeit small amplitude, have been reported so far. This has motivated us to continue intra-night optical monitoring of bona-fide radio-quiet quasars (RQQs). Here we present the results for a sample of 11 RQQs monitored by us on 19 nights. On 5 of these nights a given RQQ was monitored simultaneously from two well separated observatories. In all, two clear cases and two probable case of INOV were detected. From these data, we estimate an INOV duty cycle of $\sim$8% for RQQs which would increase to 19% if the `probable variable' cases are also included. Such comparatively small INOV duty cycles for RQQs, together with the small INOV amplitudes ($\sim$1%), are in accord with the previously deduced characteristics of this phenomenon.Comment: 15 Pages, 4 Tables, 24 Figures; Accepted in BAS