Moment properties of estimators for an exponential regression with type 1 censoring

b

Improved estimators for the shape parameter in gamma regression

A regression model is considered in which the response variables have gamma distributions with a common shape parameter. A review is given of existing estimators for the shape parameter. Bias expressions for the maximum likelihood estimates of the regression coe f f i c i ent s and the shape parameter are developed. A new estima t o r f o r t h e shape parameter based on bias correction for the maximum likelihood estimator is shown to have markedly better variance and mean square error properties in small to moderate sized samples. Approximations to the low order moments of the Pearson statistic are derived for gamma regression models with general link functions. These are used for the case of a logarithmic link to develop new estimators for the shape parameter which have better moment properties than the estimators based on the Pearson statistic which have been used previously. Finally, the small sample variance and mean square error efficiencies of the estimators relative to the maximum likelihood estimator are evaluated by simulation for the case of a single explanatory variable and a logarithmic link, for a range of sample sizes less than or equal to 100

Degradation on wood by insects and the effects on furniture production

In the tropics, biodegradation of wood progresses rapidly due to the biologically favourable temperatures and humidity conditions all year round. The population growth rate of insects is high and they reproduce throughout the year. To understand the degradation caused by insects on wood and how it can affect furniture production, the nature of the particular insect attack and the characteristic forms of damage must be understood. In this paper, the characteristic habits of major insect pests, particularly ambrosia beetles, powderpost beetles and termites are described. The diagnostic signs of infestation and how the different forms of damage affect furniture production are discussed. Precautionary as well as remedial measures are also described

Doctor of Philosophy

dissertationIt is well documented that more than 50% of all human cancers have a mutated p53 gene status, rendering it inactive. The resulting tumor-derived p53 variants, similar to wild-type (wt) p53, retain their ability to oligomerize via the tetramerization domain. Upon hetero-oligomerization, mutant p53 enforces a dominant negative effect over active wt-p53 in cancer cells. To overcome this barrier, we have designed a chimeric superactive p53 (p53-CC) with an alternative oligomerization domain (CC) from breakpoint cluster region (Bcr). This approach led to the hypothesis that swapping the oligomerization domain of p53 with an alternative oligomerization domain will prevent hetero-oligomerization and transdominant inhibition by mutant p53 in cancer cells. The tumor suppressor activity of the chimeric p53-CC was evaluated in vitro and found to be similar to that of wt-p53 regardless of cancer type or endogenous p53 status. However, co-immunoprecipitation and viral transduction of p53-CC and wt-p53 into a breast cancer cell line that harbors a tumor derived transdominant mutant p53 validated that p53-CC indeed evades sequestration and consequent transdominant inhibition by endogenous mutant p53. Following proof-of-concept studies, the superior tumor suppressor activity of p53-CC and its ability to cause tumor regression of the MDA-MB-468 aggressive p53-dominant negative breast cancer tumor model was demonstrated in vivo. In addition, the underlying differential mechanisms of activity for p53-CC and wt-p53 delivered using viral-mediated gene therapy approach in the MDA-MB-468 tumor model were investigated. Finally, since domain swapping to create p53-CC could result in p53-CC interacting with endogenous Bcr, which is ubiquitous in cells, modifications on the CC domain were necessary to minimize potential interactions with Bcr. Hence, the possible design of mutations that will improve homo-dimerization of CC mutants and disfavor hetero-oligomerization with wild-type CC (CCwt) were investigated, with the goal of minimizing potential interactions with endogenous Bcr in cells. Indeed, the resulting lead candidate p53-CCmutE34K-R55E avoided binding to endogenous Bcr and retained p53 tumor suppressor activity. Although breast cancer was the main focus of this dissertation, the application of this research extends to many other types of cancer, including the deadliest cancers (pancreatic, lung, and ovarian), which currently lack effective treatments

Jice Abood to Mr. Meredith (7 October 1962)

https://egrove.olemiss.edu/mercorr_pro/2043/thumbnail.jp