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Graduate Seminar Announcement for April 14

Apr 11, 2014

*****Seminar Announcement*****
PHYS 600, Monday, April 14, 4:00 pm
Currens Hall 205
All physics faculty and students are invited.

Speaker: Aisha Farag
Graduate Student, Physics Department, WIU
Title: Variatin of Optical Band Gap with Composition in ND3+ Doped Lead Bora-Tellurite Glasses

Abstract:

Study of optical absorption near the fundamental absorption edge is a useful method for the investigation of optically-induced transitions, band structure and the optical band gap in glasses. For the present work, glasses (x-0.5) PbO - 20 TeO_2 - (80-x) B_2 O_3 - 0.5 Nd_2 O_3 where x = 20, 30, 40, 50, 60, 70 mol%, have been prepared by the melt quenching technique. Optical absorption spectra obtained for these glasses show that the fundamental absorption edge lies in the wavelength range 350-500 nm. The edge shows a shift towards longer wavelengths (lower energy) with increasing PbO content. The absorption spectra were analyzed using the Mott-Davis model to determine optical energy gaps of these glasses. The optical band gap of these glasses decreases from 2.98 to 2.69 eV with increasing PbO content from 19.5 to 69.5 mol %. The decrease in the band gap is due to the structural modifications and alterations in the covalence of the Pb-O bond.

Speaker: Eric Andersen
Graduate Student, Physics Department, WIU
Title: Doppler Correction of 6 cm Data from ATCA

Abstract:

A survey for formaldehyde emission towards a selection of massive star-forming regions in the Southern Hemisphere was conducted during a 3-day period in 2004 using the Australia Telescope Compact Array (ATCA). Reduction of the data was complicated due to the fact that ATCA does not Doppler-track. The identification and characterization of new formaldehyde masers requires a precise determination of the LSR velocity of the sources. A proven recipe for reduction of the data using the software package AIPS provides reliable information about the location and intensity of the sources, but the velocities associated with the observed spectral lines are not calculated correctly by the software. A non-standard approach was taken to perform the Doppler correction, using values provided by a web-based sky frequency calculator on the Australia Telescope National Facility (ATNF) website. The calculated LSR velocities of formaldehyde absorption towards specific sources in the molecular cloud complex Sgr-B2 were compared with published data to verify the accuracy of our velocity-correction process. Line data generated using our experimental data-reduction method were found to agree with the published data to within approximately 0.1 km/s.

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