Diffraction of light by ultrasonic waves

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In-orbit Performance of UVIT on ASTROSAT

We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. The FUV and NUV channels have filters and gratings, whereas the VIS channel has filters. The ASTROSAT was launched on 28th September 2015. The performance verification of UVIT was carried out after the opening of the UVIT doors on 30th November 2015, till the end of March 2016 within the allotted time of 50 days for calibration. All the on-board systems were found to be working satisfactorily. During the PV phase, the UVIT observed several calibration sources to characterise the instrument and a few objects to demonstrate the capability of the UVIT. The resolution of the UVIT was found to be about 1.4 - 1.7 $arcsec$ in the FUV and NUV. The sensitivity in various filters were calibrated using standard stars (white dwarfs), to estimate the zero-point magnitudes as well as the flux conversion factor. The gratings were also calibrated to estimate their resolution as well as effective area. The sensitivity of the filters were found to be reduced up to 15\% with respect to the ground calibrations. The sensitivity variation is monitored on a monthly basis. UVIT is all set to roll out science results with its imaging capability with good resolution and large field of view, capability to sample the UV spectral region using different filters and capability to perform variability studies in the UV.Comment: 10 pages, To appear in SPIE conference proceedings, SPIE conference paper, 201

Diffraction of light by supersonic waves-Part I

The three method (Series, Bessel-function and Closed Expression) which have been used for dealing with the problem of the diffraction of light by supersonic waves have been worked out in detail and the amplitude expressions for the diffracted orders are written in extenso. In the case of the third method, the intensity expression assume a simple form

Distribution of wet bulb potential temperature in latitude and altitude

If potential temperature is denoted by θ and wet bulb potential temperature by θ', then log θ is proportional to the entropy of dry air and log θ' to the entropy of the mixture of air and water vapour. Because air is compressible, entropy is a guide to its motion, and Sir Napier Shaw was the first to prepare a diagram of the variation of log θ or θ with latitude and height, and to use it as a text on which to expound the stratification of the atmosphere. When, however, cloud in convection penetrates the air strata, log θ' takes the place of log θ as an operative factor. A world picture of θ' is required to complement that of θ

YAlO3:Cr3+ nanophosphor: Synthesis, photoluminescence, EPR, dosimetric studies

YAlO3:Cr3+ (0.1 mol%) nanophosphor has been synthesized by low temperature solution combustion method. The X-ray diffraction studies reveal an orthorhombic structure. Transmission electron microscopy reveals that the particles are spherical in shape with nano-size ∼40–65 nm. Electron paramagnetic resonance (EPR) spectrum shows a resonance signal with effective g value at g = 1.978 which can be attributed to the exchange coupled Cr3+ ion pairs in weakly distorted sites. The photoluminescence spectrum shows an intense doublet at 677 nm and 694 nm (R lines) assigned to spin-forbidden 2Eg → 4A2g transition of Cr3+ ions. EPR and PL studies reveal that the Cr3+ ions occupy Al3+ sites in YAlO3. The interesting feature reported in this work concerns the linearity with gamma dose in the wide range (0.1–6 kGy). Prominent TL glow peaks at 226 °C and 346 °C were observed for both γ and UV-rays respectively. It is observed that the peaks at 226 °C and 346 °C eventually show a linear response up to 5 kGy which makes them a candidate for high dose dosimetry of ionizing radiation. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped and Cr doped samples were determined using Chens glow peak shape method and the results are discussed in detail

AFM and photoluminescence studies of swift heavy ion induced nanostructured aluminum oxide thin films

E-beam evaporated aluminum oxide films were irradiated with 120 MeV swift Au9+ ions in order to induced nanostructure formation. Atomic force microscope (AFM) results showed the formation of nanostructures for films irradiated with a fluence of 1 à 1013 ions cm-2. The particle size estimated by section analysis of the irradiated film was in the range 25-30 nm. Glancing angle X-ray diffraction (GAXRD) revealed the amorphous nature of the films. Two strong Photoluminescence (PL) emission bands with peaks at â¼430 nm and â¼645 nm besides a shoulder at â¼540 nm were observed in all irradiated samples. The PL intensity is found to increase with increase of ion fluence. © 2008 Elsevier B.V. All rights reserved