Texas Christian University

About: Texas Christian University is a education organization based out in Fort Worth, Texas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 3245 authors who have published 8258 publications receiving 282216 citations. The organization is also known as: TCU & Texas Christian University, TCU.

The Performance of Control Charts for Monitoring Process Variation

Abstract: The Shewhart R–and S–charts are often used to monitor the variability of a quality characteristic of interest. In order to improve the sensitivity of these charting procedures to detecting small shifts in the process standard deviation, runs rules have been suggested. We evaluate the properties of the run length distributions of these charting procedures using a Markov chain approach. We show that the rules commonly used in practice based on the Western Electric Handbook do not have the statistical performance one might expect. Alternative runs rules are provided that provide the same in-control ARL's as the usual X-chart with runs rules. Average run length comparisons are made among various charts for monitoring variability, including cumulative sum charts and exponentially weighted moving average charts. It is shown that detection of decreases in variability is problematic with all of these methods.

Apprentice, Departure, and Demotion: An Examination of the Three Types of CEO–Board Chair Separation

Abstract: Past research has consistently shown that separation of CEO and board chair roles has no systematic effect on firm performance. In this study, we introduce the different forms of such separation: apprentice, departure, and demotion. In a study of Standard & Poor's (S&P) 1500 and Fortune 1000 firms, we find that separation of the two leadership roles positively impacts future firm performance when current performance is poor, but negatively impacts future firm performance when current performance is high. We find that this effect is most dramatic for demotion separations. Finally, we test theory about the permanency of CEO-board chair separation. Our results show that the different types of CEO-board chair separation have very distinct consequences. [ABSTRACT FROM AUTHOR]

Acute toxicities of five synthetic pyrethroid insecticides to Daphnia magna and Ceriodaphnia dubia

Abstract: The acute toxicities of four recently developed pyrethroid insecticides (bifenthrin, cyfluthrin, lambda cyhalothrin and tralomethrin) were experimentally compared to the acute toxicity of a first generation pyrethroid (permethrin), in static-flow, 48-h bioassays with Daphnia magna and Ceriodaphnia dubia. The four new generation pyrethroids exhibited greater toxicity, with LC50s ranging from 0.15 to 1.04 μg/L for D. magna and 0.07 to 0.30 μg/L for C. dubia, in comparison to permethrin with LC50s of 1.25 μg/L for D. magna and 0.55 μg/L for C. dubia. Tralomethrin and cyfluthrin were most toxic to D. magna, with LC50s of 0.15 and 0.17 μg/L, respectively. C. dubia exhibited the greatest sensitivity to the pyrethroids, with an LC50 of 0.07 μg/L for bifenthrin. C. dubia was equally or more sensitive than D. magna to all of the insecticides.