It has been proposed that relapse vulnerability in previously dependent individuals results from augmentation of drug-induced reinforcement due to repeated associations between the interoceptive properties of the drug and reduction of acute withdrawal distress. To test this hypothesis, male Sprague-Dawley rats self-administered 0.05 mg/kg/inf heroin on continuous and progressive ratio (PR) schedules. During this period, they also received injections of vehicle or escalating doses of heroin. Following tests of naloxone-precipitated withdrawal (0.01 or 0.1 mg/kg, SC), as well as abstinence (4 days), and extinction training (9 sessions), they were pre-treated with vehicle or yohimbine (0.5 mg/kg, IV) and tested for resumption of heroin self-administration (0.05 mg/kg/inf) on continuous and PR schedules (Experiments 1 & 2), or tested for reinstatement in extinction conditions. Differences between vehicle- and heroin-injected rats were noted on self-administration on the continuous reinforcement schedule, but not on the PR schedule, in spite of greater signs of withdrawal precipitated by naloxone in the heroin-injected rats. More importantly, there were no group differences in resumption of heroin self-administration, and this was not altered by yohimbine. These results suggest that relapse vulnerability cannot be uniquely ascribed to the altered reinforcing action of drugs; contextual and other conditioning factors must play a role in modulating resumption of drug intake after periods abstinence.

Past research has shown that preference for a stimulus is correlated positively with reinforcer efficacy – more preferred stimuli tend to be more potent reinforcers. Researchers have recently examined the use of progressive ratio (PR) reinforcement schedules to evaluate preference. However, research on the concordance between preference and performance under a progressive ratio schedule is limited. Therefore, two experiments were conducted to extend this research. In Experiment 1 I compared the relative reinforcing efficacy of six stimuli obtained under a PR schedule to the mean preference hierarchy obtained through paired-stimulus preference assessments conducted before and after PR reinforcement sessions. In Experiment 2 I evaluated the PR schedule for quantifying the reinforcing value of three stimuli from Experiment 1 (i.e., one high, one medium, and one low preference stimulus). The results of Experiment 1 indicated that items that yielded higher breaking points and responses per minute were also more preferred. However, concordance between percent preference and breaking points and response rates for less preferred items was more variable. The results of Experiment 2 showed that high preference stimuli increased responding over baseline for all participants. However, low preference reinforcers also increased responding over baseline for some participants.

In this dissertation we present a novel computational method, as well as its software implementation, to compare two samples by a nonparametric likelihood-ratio test. The basis of the comparison is a mean-type hypothesis. The software is written in the R-language [4]. The two samples are assumed to be independent. Their distributions, which are assumed to be unknown, may be discrete or continuous. The samples may be uncensored, right-censored, left-censored, or doubly-censored. Two software programs are offered. The first program covers the case of a single mean-type hypothesis. The second program covers the case of multiple mean-type hypotheses. For the first program, an approximate p-value for the single hypothesis is calculated, based on the premise that -2log-likelihood-ratio is asymptotically distributed as ­­χ2(1). For the second program, an approximate p-value for the p hypotheses is calculated, based on the premise that -2log-likelihood-ratio is asymptotically distributed as ­χ2(p). In addition we present a proof relating to use of a hazard-type hypothesis as the basis of comparison. We show that -2log-likelihood-ratio is asymptotically distributed as ­­χ2(1) for this hypothesis. The R programs we have developed can be downloaded free-of-charge on the internet at the Comprehensive R Archive Network (CRAN) at http://cran.r-project.org, package name emplik2. The R-language itself is also available free-of-charge at the same site.

Past research has shown that preference for a stimulus is correlated positively with reinforcer efficacy – more preferred stimuli tend to be more potent reinforcers. Researchers have recently examined the use of progressive ratio (PR) reinforcement schedules to evaluate preference. However, research on the concordance between preference and performance under a progressive ratio schedule is limited. Therefore, two experiments were conducted to extend this research. In Experiment 1 I compared the relative reinforcing efficacy of six stimuli obtained under a PR schedule to the mean preference hierarchy obtained through paired-stimulus preference assessments conducted before and after PR reinforcement sessions. In Experiment 2 I evaluated the PR schedule for quantifying the reinforcing value of three stimuli from Experiment 1 (i.e., one high, one medium, and one low preference stimulus). The results of Experiment 1 indicated that items that yielded higher breaking points and responses per minute were also more preferred. However, concordance between percent preference and breaking points and response rates for less preferred items was more variable. The results of Experiment 2 showed that high preference stimuli increased responding over baseline for all participants. However, low preference reinforcers also increased responding over baseline for some participants.

No description available.

The focus of this research was to investigate the use of functionalized/non-functionalized multi walled carbon nanotubes (MWCNTs) as reinforcements for the Portland cement paste. The unique geometrical characteristics of the carbon nanotubes (CNTs), as well as its unique mechanical properties such as high strength, ductility and stiffness, were the vital motivation for this study. In this research, we combined this unique material (CNTs) with concrete which is the most used man-made material. When compared to other composite materials, a limited amount of research has been conducted on the CNTs/cement composites. In order to investigate how the aspect ratio of functionalized/non-functionalized MWCNTs affects the mechanical properties of cementitious composites, ten different mixes of the MWCNTs/cement composites were prepared and tested. The different batches had a fixed water/cement ratio of 0.4, and variations of MWCNTs length, concentration and surface treatment. The cement nanocomposites were cast in small-scale specimens (beams) for the three-point flexural testing. Four major mechanical properties were evaluated at ages of 7, 14, and 28 days from the casting day: the maximum flexural strength, ultimate strain capacity (ductility), modulus of elasticity, and modulus of toughness. The results for the different nanocomposite batches were compared with the plain cement (reference) batch. The mechanical testing results showed that at 28 days almost all of the MWCNTs composites increased the flexural strength of the cement nanocomposites. At 28 days, the long MWCNTs increased the flexural strength more than the short MWCNTs. In general, the ultimate strain (ductility) of the short MWCNTs nanocomposites was higher than the ultimate strain of the long MWCNTs nanocomposites. The flexural strength of short 0.2 percent MWNT and long 0.04 percent MWNT (OH) increased by 269 percent and 83 percent, respectively, compared to the plain cement sample at 28 days. The highest ductility at 28 days for the short 0.1 percent MWNT and the short 0.2 percent MWNT was 86 percent and 81 percent, respectively. Clear evidence was obtained from the SEM images for micro-crack bridging; many of the MWCNTs were stretching across the micro-cracks. In conclusion, CNTs as nano reinforcements, can effectively improve certain mechanical properties of the cement paste composites.

University of Technology, Sydney. Faculty of Business. / Recent regulatory changes in developed economies have sought to apply uniform standards for corporate governance following a series of high profile corporate collapses between 2000 and 2002. The various regulatory responses raised questions in the governance literature on the appropriateness of a “one size fits all” approach. However, empirical outcomes in this literature do not provide a consistent picture on how, or even whether, governance choices vary with firm characteristics. This thesis addresses the lack in empirical direction by investigating the discriminatory power of a fundamental firm variable, the price-to-book ratio (P/B), that is often applied in Australian and other studies to predict governance outcomes. It evaluates how a joint price-to-book, price-to- earnings, firm classification (P/B, P/E) captures variations in governance choices by Australian firms and compares the results with those using a conventional P/B classification. Choices for two key mechanisms – the level of independence of the board of directors and the quality of its external auditors, are examined as they feature prominently in regulatory reforms. The results show that a joint P/B, P/E classification captures significant differences in the use of both mechanisms confirming that governance frameworks vary with firm characteristics. Consistent with expectations, these differences are recorded for board independence within high and within low P/B firms. Significant variations are also identified in the choice of auditor quality within both P/B classes of firms. By enabling a more parsimonious analysis of firm characteristics through the joint P/B, P/E framework, these results enhance our understanding of the choice of independent directors and high quality auditors. They also lend support to the general proposition that a “one size fits all” governance framework could lead to unnecessary costs for firms as they seek optimal governance arrangements that suit their specific information environments.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references (leaves 36-38).

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 272-286). Also available via the Internet.