A late, infrared flash from the afterglow of GRB 050319

We report the detection of a bright, near-infrared flash from the afterglow of GRB 050319, 6.15 hours after the burst. The IR flash faded rapidly from J=13.12 mag. to J > 15.5 mag. in about 4 minutes. There are no reported simultaneous observations at other wavelengths making it an unique event. We study the implications of its late timing in the context of current theoretical models for GRB afterglows.Comment: Accepted in ApJ (Letters

Performance Comparison of Symmetric and Offset Reflector Antennas Adaptively Illuminated by Novel Triple Mode Feedhorn

Parabolic symmetric and offset reflector antennas adaptively illuminated using a novel triple-mode feedhorn (TE11+TM01+TE21) with different mode combinations and impedance and radiation performances are presented. The combination of the radiating modes in a feedhorn with proper amplitude and fixed phase values helps in electronically pointing the main beam of the radiating patterns such as that obtained in a beam-steering antenna with limited beam-scan range. This type of radiation performance virtually creates a displaced phase center location for the feedhorn, which, consequently, adaptively illuminates the reflector antenna surface. Impedance-matching bandwidths are preserved for both reflector antennas similar to the case of feedhorn alone. The copolarization gain and peak cross-polarization levels are far better with the offset reflector antenna than the symmetric reflector antenna. Such reflector antennas find applications in ground moving target indicator (GMTI) and space based radars. The investigation results are solely computed using FEKO full-wave analysis tool

University small satellite program-ANUSAT

Indian Space Research Organization (ISRO) over the last 3 decades has steadily progressed towards establishment of space system for communication, Earth observation and disaster warning for national development. Also, the launchers for placing both Earth observation and communication satellites have been developed. While these efforts are being sustained on a continuous basis, ISRO initiated Small Satellite Program few years ago for demonstration of new technologies that can be adopted to operational mission as well as Small Satellite Earth Observation program to complement the existing earth observation mission. Also realizing the importance of steady flow of engineers and scientists in Space Technology, ISRO has been pursuing to promote development of micro-satellite at Indian universities that will provide hands-on experience to the university students in Space Technology and also developing new technologies for the future. Anna University at Chennai, India, has taken up the first micro-satellite program within the university environment. The micro-satellite development will be carried out at Aerospace Research Centre in Anna University with review and funding support from ISRO. The project will be implemented through involvement of students, researchers and faculty staff. The satellite is a simple spinning satellite carrying store and forward payload being the first mission and weighs less than 50 kg. The Project has commenced in January 2002. The preliminary design review of the satellite has been completed in December 2002. The micro-satellite is scheduled for launch in 2005 as an auxiliary payload in ISRO's launcher PSLV (Polar Satellite Launch Vehicle)

H I 21-cm Cosmology and the Bispectrum: Closure Diagnostics in Massively Redundant Interferometric Arrays

New massively redundant low frequency arrays allow for a novel investigation of closure relations in interferometry. We employ commissioning data from the Hydrogen Epoch of Reionization Array to investigate closure quantities in this densely packed grid array of 14m antennas operating at 100 MHz to 200 MHz. We investigate techniques that utilize closure phase spectra for redundant triads to estimate departures from redundancy for redundant baseline visibilities. We find a median absolute deviation from redundancy in closure phase across the observed frequency range of about 4.5deg. This value translates into a non-redundancy per visibility phase of about 2.6deg, using prototype electronics. The median absolute deviations from redundancy decrease with longer baselines. We show that closure phase spectra can be used to identify ill-behaved antennas in the array, independent of calibration. We investigate the temporal behavior of closure spectra. The Allan variance increases after a one minute stride time, due to passage of the sky through the primary beam of the transit telescope. However, the closure spectra repeat to well within the noise per measurement at corresponding local sidereal times (LST) from day to day. In future papers in this series we will develop the technique of using closure phase spectra in the search for the HI 21cm signal from cosmic reionization

Fock space exploration by angle resolved transmission through quantum diffraction grating of cold atoms in an optical lattice

Light transmission or diffraction from different quantum phases of cold atoms in an optical lattice has recently come up as a useful tool to probe such ultra cold atomic systems. The periodic nature of the optical lattice potential closely resembles the structure of a diffraction grating in real space, but loaded with a strongly correlated quantum many body state which interacts with the incident electromagnetic wave, a feature that controls the nature of the light transmission or dispersion through such quantum medium. In this paper we show that as one varies the relative angle between the cavity mode and the optical lattice, the peak of the transmission spectrum through such cavity also changes reflecting the statistical distribution of the atoms in the illuminated sites. Consequently the angle resolved transmission spectrum of such quantum diffraction grating can provide a plethora of information about the Fock space structure of the many body quantum state of ultra cold atoms in such an optical cavity that can be explored in current state of the art experiments.Comment: 40 double spaced, single column pages, 40 .eps figures, accepted for publication in Physical Review

Removal of turbidity from washing machine discharge using Strychnos potatorum seeds: Parameter optimization and mechanism prediction

In this research an attempt has been made to utilize the Strychnos potatorum seed powder as an environmentally friendly coagulant for the removal of turbidity from washing machine discharge. The performance of this system was also compared with synthetic water. Experimental studies were conducted for the maximum removal of turbidity from washing machine discharge and synthetic turbid water which were varied from 50 to 145 NTU. The effect of operating parameters such as initial turbidity, S. potatorum dosage and pH of the solution was optimized for the maximum removal of turbidity. It was seen that the percentage removal of turbidity lay was between 68-89% and 65-84% for synthetic turbid water and washing machine discharge sample respectively, at an ideal pH of 6-7. The experimental values were compared with the Langmuir and Freundlich isotherm models to understand the extent of influence of the sorption of the particles onto the S. potatorum seed powder. Better results with respect to concordance of experimental data were observed with Langmuir isotherm model, indicating a monolayer sorption of particles onto the S. potatorum seed powder. It was observed from the isotherm study that the sorption may also be influenced in the removal of turbidity to some extent from the washing machine discharge and synthetic water. The prepared material can be effectively utilized for the removal of turbidity from the water