Theory and Simulations of Refractive Substructure in Resolved Scatter-Broadened Images

At radio wavelengths, scattering in the interstellar medium distorts the appearance of astronomical sources. Averaged over a scattering ensemble, the result is a blurred image of the source. However, Narayan & Goodman (1989) and Goodman & Narayan (1989) showed that for an incomplete average, scattering introduces refractive substructure in the image of a point source that is both persistent and wideband. We show that this substructure is quenched but not smoothed by an extended source. As a result, when the scatter-broadening is comparable to or exceeds the unscattered source size, the scattering can introduce spurious compact features into images. In addition, we derive efficient strategies to numerically compute realistic scattered images, and we present characteristic examples from simulations. Our results show that refractive substructure is an important consideration for ongoing missions at the highest angular resolutions, and we discuss specific implications for RadioAstron and the Event Horizon Telescope.Comment: Equation numbering in appendix now matches published version. Two minor typos correcte

Optimal Correlation Estimators for Quantized Signals

Using a maximum-likelihood criterion, we derive optimal correlation strategies for signals with and without digitization. We assume that the signals are drawn from zero-mean Gaussian distributions, as is expected in radio-astronomical applications, and we present correlation estimators both with and without a priori knowledge of the signal variances. We demonstrate that traditional estimators of correlation, which rely on averaging products, exhibit large and paradoxical noise when the correlation is strong. However, we also show that these estimators are fully optimal in the limit of vanishing correlation. We calculate the bias and noise in each of these estimators and discuss their suitability for implementation in modern digital correlators.Comment: 8 Pages, 3 Figures, Submitted to Ap

Developing And Delivering The Virtual MBA Course

The use of the Internet offers a unique opportunity to bring together individuals in an interactive setting for social and educational purposes. Colleges and universities have augmented their brick and mortar classes with virtual course offerings using the Internet for distance education. This paper will examine the origins of distance education and offer insights and recommendations for developing and delivering an on-line MBA course in Privacy and Information Security

An Inconvenient Truth About ‘Bundling’ Commitment, Engagement, & Embeddedness: Unbundling to Extend Theory on Turnover Motivations and Beyond

This paper critiques a research practice that we call “bundling,” which has produced highly popular constructs in the organizational behavior literature, including organizational commitment, employee engagement, and organizational embeddedness. We show how these bundled constructs, using broad labels from common parlance, have produced overlapping meanings, confounded theoretical mechanisms, and imposed limiting “ideal employee” conceptions in the literature, organizations, and ultimately, societal discourse about employees. We argue that “unbundling” these constructs can provide multiple benefits to theory, empirical inquiry, and practical assessment of complex employee motives. As a demonstration, we unbundle the three focal constructs to integrate and clarify their component relations within the nomological net of turnover motivation. Thereby, we enrich conceptions of proximal withdrawal states, while synthesizing the most comprehensive model of turnover motivations. Finally, we discuss further research implications suggested by unbundling our focal constructs, and unbundling more generally

An Examination of Capital Outlay Funding Mechanisms in Oklahoma

This is an exploratory study designed to assist in understanding how funding mechanisms in Oklahoma influence school districts in pursuing capital outlay projects, including an emphasis on the differences between rural and non-rural schools. This study also includes an examination of how school performance as determined by the academic performance index is affected by these same mechanisms. The funding mechanisms considered include capital outlay expenditures per pupil, net assessed valuation per pupil, bond issue passage rates, participation in free lunch program, and rurality. Descriptive statistics are presented along with t-tests, correlations, and regressions analysis.Rural and non-rural were found to be significantly different in net assessed valuation and capital outlay expenditure but not bond passage rate. Socio-economic status was significantly related to and a predictor of capital outlay expenditures. Capital outlay expenditure, net assessed valuation, nor rurality was significantly related to district API scores