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Full-Text Articles in Physical Sciences and Mathematics
Accurate Calibration Of The Four-Detector Photopolarimeter With Imperfect Polarizing Optical Elements, R. M.A. Azzam, Ali G. Lopez
Accurate Calibration Of The Four-Detector Photopolarimeter With Imperfect Polarizing Optical Elements, R. M.A. Azzam, Ali G. Lopez
Electrical Engineering Faculty Publications
The first three columns of the instrument matrix A of the four-detector photopolarimeter (FDP) are determined by Fourier analysis of the output current vector I(P) as a function of the azimuth angle P of the incident linearly polarized light. Therefore 12 of the 16 elements of A are measured free of the imperfections of the (absent) quarter-wave retarder (QWR). The effect of angular beam deviation by the polarizer is compensated for by taking the average, (1/2) [I(P) + I(P + 180°)], of the FDP output at 180°-apart, optically equivalent, angular positions of the polarizer. The remaining fourth column of A …
Analytical Determination Of The Complex Dielectric Function Of An Absorbing Medium From Two Angles Of Incidence Of Minimum Parallel Reflectance, R. M.A. Azzam
Electrical Engineering Faculty Publications
The real and imaginary parts of the complex dielectric function (or complex refractive index) of an opaque substrate or a thick film can be determined from two pseudo-Brewster angles measured in two transparent incidence media of different refractive indices. This two-angle method is simple in that it involves no photometric or polarimetric analysis and in that the solution for the optical properties in terms of the measured angles is explicit, analytical, and direct (i.e. noniterative). The two-angle method is demonstrated for an opaque TiN film on a Cleartran ZnS substrate as a specific example. The effect of angle-of-incidence errors on …
On The Size Distribution Of Newly Formed Grains In Red Supergiant Atmospheres, C Gregory Seab, Theodore P. Snow
On The Size Distribution Of Newly Formed Grains In Red Supergiant Atmospheres, C Gregory Seab, Theodore P. Snow
Physics Faculty Publications
Theoretical ultraviolet extinction curves have been calculated for comparison with observed curves for circumstellar dust in M supergiants. The theoretical curves assumed a silicate grain composition, because silicate grains are expected in the oxygen-rich environments that are observed. Calculations were performed with and without the inclusion of scattering into the beam, with largely similar results. A comparison of the computed curves with the observed ultraviolet extinction curve for circumstellar dust in Scorpii indicates that the size distribution of the circumstellar grains must cut off near 800 Å that is, there are few or no grains smaller than this. Our conclusion …
Predicting Peculiar Interstellar Extinction From Gaseous Abundances, Charles L. Joseph, Theodore P. Snow, C Gregory Seab
Predicting Peculiar Interstellar Extinction From Gaseous Abundances, Charles L. Joseph, Theodore P. Snow, C Gregory Seab
Physics Faculty Publications
Molecular and atomic abundances are examined for 19 lines of sight through dense clouds, each with a peculiar selective extinction curve. The interstellar clouds in the present study appear to fall into two distinct categories: CN-rich, with relatively small amounts of neutral iron, or CN-poor, with large amounts of neutral iron. Lines of sight, having a CN/(Fe i) abundance ratio about two (~ 0.3 dex) or greater, are found to have a shallow (2.57 ± 0.55 mag) 2175 Å feature relative to the underlying extinction, while the strength of the bump is 3.60 ± 0.36 for the other dense clouds …
A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab
A Search For Interstellar And Circumstellar C60, T P. Sno, C G. Seab
Physics Faculty Publications
It has recently been suggested that the diffuse interstellar bands may be formed by ionized polyhedral carbon molecules such as C60(+). While specific laboratory measurements of absorption bands of this molecular ion have not been made, a feature due to the neutral molecule C60 has been discovered at 3860A. Examination of spectra of several reddened stars, as well as one star known to have circumstellar carbonaceous dust, shows no sign of the feature, leading to upper limits of the order of 10 to the 14th/sq cm for the column density of C60. These limits are not yet sensitive enough to …