Abdulaziz Elfessi

Effects of methylmercury exposure on glutathione metabolism, oxidative stress, and chromosomal damage in captive-reared common loon (Gavia immer) chicks

We quantified the level of dietary mercury (Hg), delivered as methylmercury chloride (CH3HgCl), associated with negative effects on organ and plasma biochemistries related to glutathione (GSH) metabolism and oxidative stress, and chromosomal damage in captive-reared common loon (Gavia immer) chicks reared from hatch to 105 days. Mercury-associated effects related to oxidative stress and altered glutathione metabolism occurred at 1.2 microg Hg/g and 0.4 microg Hg/g, an ecologically relevant dietary mercury level, but not at 0.08 microg Hg/g. Among the variables that contributed most to dissimilarities in tissue chemistries between control and treatment groups were increased levels of oxidized glutathione (GSSG), GSH peroxidase, and the ratio of GSSG to GSH in brain tissue; increased levels of hepatic GSH; and decreased levels of hepatic glucose-6-phosphate dehydrogenase (G-6-PDH). Our results also suggest that chronic exposure to environmentally relevant dietary Hg levels did not result in statistically significant somatic chromosomal damage in common loon chicks.

Estimation of a linear function of the parameters of an exponential distribution from doubly censored samples

In this paper improved estimators of the scale and its reciprocal, [theta](0-1), and the location, [mu], of a two-parameter exponential distribution are given based on a doubly censored sample. Also the problem of estimating the linear function [mu] + z[theta] is considered, where z is a given constant. It is shown that the improved estimators are better than the best affine equivariant estimators.

Estimating biomass of submersed vegetation using a simple rake sampling technique

We evaluated the use of a simple rake sampling technique for predicting the biomass of submersed aquatic vegetation. Vegetation sampled from impounded areas of the Mississippi River using a rake sampling technique, was compared with vegetation harvested from 0.33-m2 quadrats. The resulting data were used to model the relationship between rake indices and vegetation biomass (total and for individual species). We constructed linear regression models using log-transformed biomass data for sites sampled in 1999 and 2000. Data collected in 2001 were used to validate the resulting models. The coefficient of determination (R2) for predicting total biomass was 0.82 and ranged from 0.59 (Potamogeton pectinatus) to 0.89 (Ceratophyllum demersum) for individual species. Application of the model to estimate total submersed aquatic vegetation is illustrated using data collected independent of this study. The accuracy and precision of the models tested indicate that the rake method data may be used to predict total vegetation biomass and biomass of selected species; however, the method should be tested in other regions, in other plant communities, and on other species.

Effects of subcutaneous transmitter implants on behavior, growth, energetics, and survival of Common Loon chicks

Abstract High rates of Common Loon (Gavia immer) chick mortality have been documented in Wisconsin, especially on acidic lakes, but causes and timing of chick mortality are poorly understood. We modified and evaluated a subcutaneous transmitter implant technique for Common Loon chicks using wild and captive reared chicks. Results indicated that behavior, growth, energy expenditure, and survival did not differ significantly between chicks marked with miniature transmitters (mass 0.76 g, representing <0.8% of body mass at hatching) and unmarked chicks.

A Voluntary Program to Curtail Boat Disturbance to Waterfowl During Migration

Abstract A voluntary waterfowl avoidance area (VWAA) was established on Lake Onalaska in Navigation Pool 7 of the Upper Mississippi River, Wisconsin, USA, in 1986, to reduce boating disturbance to migratory waterfowl. We monitored boater compliance with the VWAA program in 1993 and 1997. Of 1,664 “boating events” observed on Lake Onalaska, boats intruded into the VWAA on 127 occasions. Boating events have increased from 1.82 boating events/h in 1986-88 to 1.97 in 1993 and 2.58 in 1997. Despite a 60% increase in boating traffic, the lake-wide disturbance rates in 1997 were comparable to that in 1981. We attribute this to a significant reduction in the proportion of lake-wide boating events that resulted in disturbance, a direct consequence of the VWAA program. Rate of intrusion into the VWAA was 0.11 per boating event in 1997 compared to 0.18 per boating event in 1986-88. Boating disturbances to waterfowl within the VWAA occurred at about half the rate (0.24 to 0.28 disturbances·hr-1) observed prior to establishment of the program (0.48 disturbances·hr-1). We also identified access points used by boaters and boating activities that were most likely to result in intrusion into the VWAA and associated disturbance to waterfowl. Results of these analyses have provided useful information to resource managers for targeting public education efforts. The VWAA program has contributed to the value of Lake Onalaska as a waterfowl refuge and demonstrates an effective collaboration among government agencies and non-governmental organizations.

A note on the common mean of two normal populations with order restricted variances

Consider the problem of estimating the common mean of two normal populations when the order of the unknown variances is known. In this article we have constructed a simple improved estimator which is better than the usual Graybill-Deal estimator in terms of stochastic domination.

Estimation of the smaller and larger of two uniform scale parameters

Assume independent random samples are drawn from two populations which are uniformly distributed with unknown scale parameters. The problem is to estimate the minimum and the maximum of the two unknown scales. In this paper, several simple estimators are proposed which are better than the natural estimators in terms of standardized bias, risk under squared error loss and the Pitman nearness criterion.

Grading Styles and Instructor Attitudes

The authors examined how instructor attitudes relate to grading behavior using two attitude instruments (ascription of responsibility and approval motivation) and resulting data collected from general education instructors at a midwestern comprehensive university. The results of the research show that approval motivation is significantly related to grading behavior. The authors also found that male instructors are more likely to ascribe responsibility to the individual than are female instructors, and tenured faculty are more likely to ascribe responsibility to the individual than are nontenured instructors. Implications and directions for future research are discussed.

A Bayesian Look at Classical Estimation: The Exponential Distribution

Many undergraduate students are introduced to frequentist or classical methods of parameter estimation such as maximum likelihood estimation, uniformly minimum variance unbiased estimation, and minimum mean square error estimation in a reliability, probability, or mathematical statistics course. Rossman, Short, and Parks (1998) present some thought provoking insights on the relationship between Bayesian and classical estimation using the continuous uniform distribution. Our aim is to explore these relationships using the exponential distribution. We show how the classical estimators can be obtained from various choices made within a Bayesian framework.

On robust estimation of the common scale parameter of several Pareto distributions

The problem of robust estimation of the common scale parameter of several Pareto distributions with unknown and possibly unequal shape parameters is considered. In this paper, a wide class of estimators dominating the maximum likelihood estimator (MLE) is derived under a class of convex loss functions. The problem discussed in this paper arises quite frequently in socio-economics, reliability, life testing, and survival analysis.