University of North Texas

About: University of North Texas is a education organization based out in Denton, Texas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 11866 authors who have published 26984 publications receiving 705376 citations. The organization is also known as: Fight, North Texas & UNT.

Effectiveness of Subpixel Analysis in Detecting and Quantifying Urban Imperviousness from Landsat Thematic Mapper Imagery

Abstract: The quantification of urban imperviousness using remotely sensed spectral data is next to impossible unless a spectral fraction of impervious components in an urban pixel can be detected. In this research, a multiple‐signature subpixel analysis technique coupled with a layered classification approach was developed to map urban imperviousness of each pixel of an urban scene into eight 10‐percent levels. The subpixel analysis was based on the idea of removing background spectra from the total radiance of a pixel and testing the residual spectrum against the signature spectrum. This study demonstrated that although the subpixel analysis was able to quantify urban imperviousness from most of the urban pixels, it experienced some difficulty in handling the spectral heterogeneity of diverse urban features. The layered classification approach was used to identify the extreme cases. An experiment of classifying Landsat TM data into eight levels of urban imperviousness revealed that 83.0% (kappa = 0.787) ...

Venturing into Foreign Markets: The Case of the Small Service Firm

Abstract: The study contrasts foreign market entry behavior of small and large service firms. The sample consisted of 141 firms of which 54 were small firms and 87 were larger firms. The study provides empir...

X-ray Insights into the Nature of PHL 1811 Analogs and Weak Emission-line Quasars: Unification with a Geometrically Thick Accretion Disk?

Abstract: We present an X-ray and multiwavelength study of 33 weak emission-line quasars (WLQs) and 18 quasars that are analogs of the extreme WLQ, PHL 1811, at z ≈ 0.5‐2.9. New Chandra 1.5‐9.5 ks exploratory observations were obtained for 32 objects while the others have archival X-ray observations. Significant fractions of these luminous type 1 quasars are distinctly X-ray weak compared to typical quasars, including 16 (48%) of the WLQs and 17 (94%) of the PHL 1811 analogs with average X-ray weakness factors of 17 and 39, respectively. We measure a relatively hard ( = 1.16 +0.37 -0.32 ) effective power-law photon index for a stack of the X-ray weak subsample, suggesting X-ray absorption, and spectral analysis of one PHL 1811 analog, J1521+5202, also indicates significant intrinsic X-ray absorption. We compare composite SDSS spectra for the X-ray weak and Xray normal populations and find several optical‐UV tracers o f X-ray weakness; e.g., Fe II rest-frame equivalent width and relative color. We describe how orientation effects under our previously proposed “shielding-gas” scenario can likely unify the X-ray weak and X-ray normal populations. We suggest that the shielding gas may naturally be understood as a geometrically thick inner accretion disk that shields the broad line region from the ionizing continuum. If WLQs and PHL 1811 analogs have very high Eddington ratios, the inner disk could be significantly puffed up (e.g., a slim disk). Shielding of t he broad emission-line region by a geometrically thick disk may have a significant role in setting the broad dis tributions of C IV rest-frame equivalent width and blueshift for quasars more generally. Subject headings: accretion, accretion disks ‐ galaxies: active ‐ galaxies: n uclei ‐ quasars: emission lines ‐ X-rays: galaxies