SARAS 2: A Spectral Radiometer for probing Cosmic Dawn and the Epoch of Reionization through detection of the global 21 cm signal

The global 21 cm signal from Cosmic Dawn (CD) and the Epoch of Reionization (EoR), at redshifts $z \sim 6-30$, probes the nature of first sources of radiation as well as physics of the Inter-Galactic Medium (IGM). Given that the signal is predicted to be extremely weak, of wide fractional bandwidth, and lies in a frequency range that is dominated by Galactic and Extragalactic foregrounds as well as Radio Frequency Interference, detection of the signal is a daunting task. Critical to the experiment is the manner in which the sky signal is represented through the instrument. It is of utmost importance to design a system whose spectral bandpass and additive spurious can be well calibrated and any calibration residual does not mimic the signal. SARAS is an ongoing experiment that aims to detect the global 21 cm signal. Here we present the design philosophy of the SARAS 2 system and discuss its performance and limitations based on laboratory and field measurements. Laboratory tests with the antenna replaced with a variety of terminations, including a network model for the antenna impedance, show that the gain calibration and modeling of internal additives leave no residuals with Fourier amplitudes exceeding 2~mK, or residual Gaussians of 25 MHz width with amplitudes exceeding 2~mK. Thus, even accounting for reflection and radiation efficiency losses in the antenna, the SARAS~2 system is capable of detection of complex 21-cm profiles at the level predicted by currently favoured models for thermal baryon evolution.Comment: 44 pages, 17 figures; comments and suggestions are welcom

Communicating with Constituents in 140 Characters or Less:

This paper affords an opportunity to study the early adoption, implementation and performance of an emerging technology by analyzing which members of Congress have been early adopters and extensive users of Twitter, and which have attracted the most followers. Our research questions and measures draw from the diffusion of innovation literature and early studies of online politics. Three multivariate analyses reveal that two motivators of adoption, party (Republican) and campaign resources are also drivers leading to extensive usage, but the other two, an urban constituency and the member’s own age do not. Instead, a large vote share in the last election joins party and funding in explaining high usage. The latter two plus high influential power differentiate between members with large and small numbers of followers. Collectively, these findings suggest that at this early developmental stage, Twitter is not a game changer, but an additional communications medium. They also underscore the contribution of diffusion of innovation literature to understanding how these interrelationships change depending upon whether we are examining adoption, implementation or performance

Photocatalytic degradation of imidachloprid under solar light using metal ion doped TiO2 nanoparticles: influence of oxidation state and electronic configuration of dopants

Anatase TiO2 was doped with metal ions like Th4+, V5+ and Mo6+ and tested for the degrdn. of imidachloprid under solar light. X-​ray diffraction results inferred that all the dopants stabilized the anatase phase irresp. of their nature, oxidn. state and ionic size. The undoped and transition metal ion doped TiO2 were completely transformed to rutile phase at 700° while rare earth Th4+ doped sample completely transformed to rutile phase at 1000°. The rare earth dopant stabilized the anatase phase by hindering the growth of crystallite size. Among the photocatalysts used, Th4+ (0.06​%)​-​TiO2 showed highest activity and its efficiency was 2.8 times higher than that of Degussa P-​25. The Th4+ ion lowered the band gap of TiO2 to 2.6 and 2.5 eV facilitating solar light absorption. Detrapping of the trapped charge carriers depends on electronic configuration and the oxidn. state of the dopants

The Receiver System for the Ooty Wide Field Array

The legacy Ooty Radio Telescope (ORT) is being reconfigured as a 264-element synthesis telescope, called the Ooty Wide Field Array (OWFA). Its antenna elements are the contiguous 1.92 m sections of the parabolic cylinder. It will operate in a 38-MHz frequency band centred at 326.5 MHz and will be equipped with a digital receiver including a 264-element spectral correlator with a spectral resolution of 48 kHz. OWFA is designed to retain the benefits of equatorial mount, continuous 9-hour tracking ability and large collecting area of the legacy telescope and use modern digital techniques to enhance the instantaneous field of view by more than an order of magnitude. OWFA has unique advantages for contemporary investigations related to large scale structure, transient events and space weather watch. In this paper, we describe the RF subsystems, digitizers and fibre optic communication of OWFA and highlight some specific aspects of the system relevant for the observations planned during the initial operation.Comment: 10 pages, 5 figures, 1 table, (Accepted for publication in J. Astrophysics and Astronomy

Analysis of Different Routing Algorithm for 2D-Torus Topology NoC Architecture under Load Variation

The recital of Network-on-Chip (NoC) depends on the underlying routing techniques. There are a lot of requirements that has to be met. Such performance metrics are minimum latency, least power and maximum throughput. This paper deals with XY route, PROM routing, FTXY routing and DyAD routing on 5x5 2D torus topology. The simulation is performed on nirgam NoC simulator version 2.1 for constant bit rate traffic condition. The simulation results reveals the dominance of XY, PROM, FTXY and DyAD algorithms depicting the minimum values of overall average latency per channel (in clock cycles per flit) as 0.409836 overall average latency per channel (in clock cycles per packet) as 6.2535, average throughput as 16.68, and total network power as 35.6768 mw, achieved for FTXY routing algorithm

Chandra High Resolution X-ray Spectroscopy of AM Her

We present the results of high resolution spectroscopy of the prototype polar AM Herculis observed with Chandra High Energy Transmission Grating. The X-ray spectrum contains hydrogen-like and helium-like lines of Fe, S, Si, Mg, Ne and O with several Fe L-shell emission lines. The forbidden lines in the spectrum are generally weak whereas the hydrogen-like lines are stronger suggesting that emission from a multi-temperature, collisionally ionized plasma dominates. The helium-like line flux ratios yield a plasma temperature of 2 MK and a plasma density 1 - 9 x10^12 cm^-3, whereas the line flux ratio of Fe XXVI to Fe XXV gives an ionization temperature of 12.4 +1.1 -1.4 keV. We present the differential emission measure distribution of AM Her whose shape is consistent with the volume emission measure obtained by multi-temperature APEC model. The multi-temperature plasma model fit to the average X-ray spectrum indicates the mass of the white dwarf to be ~1.15 M_sun. From phase resolved spectroscopy, we find the line centers of Mg XII, S XVI, resonance line of Fe XXV, and Fe XXVI emission modulated by a few hundred to 1000 km/s from the theoretically expected values indicating bulk motion of ionized matter in the accretion column of AM Her. The observed velocities of Fe XXVI ions are close to the expected shock velocity for a 0.6 M_sun white dwarf. The observed velocity modulation is consistent with that expected from a single pole accreting binary system.Comment: 6 figures, AASTEX style, accepted for publication in Ap

A reliable micro-grid with seamless transition between grid connected and islanded mode for residential community with enhanced power quality

This paper presents a reliable micro-grid for residential community with modified control techniques to achieve enhanced operation during grid connected, islanded and resynchronization mode. The proposed micro-grid is a combination of solar photo-voltaic (PV), battery storage system and locally distributed DG systems with residential local loads. A modified power control technique is developed such that, local load reactive power demand, harmonic currents and load unbalance is compensated by respective residential local DG. However, active power demand of all local residential load is shared between the micro-grid and respective local DG. This control technique also achieves constant active power loading on the micro-grid by supporting additional active power local load demand of respective residential DG. Hence, proposed modified power control technique achieves transient free operation of the micro-grid during residential load disturbances. An additional modified control technique is also developed to achieve seamless transition of micro-grid between grid connected mode and islanded mode. The dynamic performance of this micro-grid during grid connected, islanded and re-synchronization mode under linear and non-linear load variations is verified using real time simulator (RTS)