This thesis proposes models for the calculation of upper and lower limiting values to the backscatter factor (BSF) that can be used to evaluate measured and modelled BSF values. The upper limit to the BSF is obtained from a Monte Carlo simulation of an infinite parallel beam incident on a semi-infinite phantom in which the dose contribution from all orders of photon scatter is considered. The lower limit is calculated using an analytical photon transport model which considers only the primary dose and the scatter dose from photons that have undergone a single scattering interaction in the phantom. A parametrization of the limiting values in terms of photon energy and irradiation field size is presented and comparisons are made with BSF's from the literature. To further illustrate the utility of the limiting BSF's, comparisons are also made with current TLD-measured BSF's and Monte Carlo simulations of the BSF.

My aim is to demonstrate that professionals perceive they have a right to refuse to provide their services and are currently acting accordingly. This thesis explores whether a professional right to refuse services exists; if so, the limits of this right; and whether a professional 'right' to refuse services ought to exist and in what circumstances. This requires analysis of whether refusals to provide professional services might be considered unethical conduct according to existing codes of ethics and moral theories, unprofessional conduct within the norms of professional regulatory and disciplinary bodies, or illegal conduct according to Canadian law, in particular, human rights law. The issues are examined primarily with reference to physicians who treat patients and some comparisons are made with physician clinical researchers and lawyers. The shift from a duty-based system of professional service to a rights-based system of professional privileges has led to conflicting goals of professional self-regulation, and some possible resolutions to this conflict are explored.

Deaf people who know and use American Sign Language, ASL, outperform normally hearing people on certain visuospatial tests. This enhanced visuospatial performance is interpreted as being the result of knowing and using a visual and spatial grammar. An alternative explanation is that this enhanced visuospatial performance is due to sensory compensation, that is, a heavy reliance on vision throughout development due to deafness. The present study tested this alternative explanation. Eight congenitally and profoundly deaf adults (4 women, 4 men) who did not know sign language and eight normally hearing controls (4 women, 4 men) were tested on four visuospatial tasks requiring mental rotation in two and three dimensions (Card Rotation, Paper Form Board, Space Relations and Spatial Visualization). Subjects were matched for age, sex, and education. Spatial solution strategy and handedness were also assessed. Results showed that both groups were significantly faster and more accurate on the two-dimensional tasks than on the three-dimensional tasks. Additionally, hearing women and deaf men were significantly faster than the deaf women over all tasks. The two groups used similar solution strategy for all tasks except Spatial Visualization, where more deaf subjects used a mental rotation strategy. These findings suggest that sensory compensation per se does not lead to enhanced visuospatial skill.

Fibrinogen, thrombin receptor and heparin cofactor II are three major thrombin substrates recognized specifically through its exosite, a regulatory binding site. Based on the native protein sequences, four peptides were selected to study the specificity of exosite interactions on structural basis using transferred NOE methods. The binding sequences of all the peptides are identified and possible thrombin binding sites of thrombin receptor and heparin cofactor II peptides are speculated by comparing with known hirudin-thrombin complex structures. A new binding mode may exist in thrombin-fibrinogen contacts according to its exosite binding sequence and interaction patterns. In terms of the binding sequence, it suggested that the most important factor in thrombin exosite specific binding is the hydrophobic residues position rather than the analogous sequence.

Advertising of products and services has become an accepted and integral part of everyday life, and advancements in mass media technology have made it easy to convey information to a large proportion of the population. However, when addressing health related services and products, the messages contained in today's advertisements have taken on a new purpose and tone. The healthcare industry in North America, especially pharmaceutical companies, and to a lesser extent the diagnostic imaging and the medical device industry, use direct-to-consumer (DTC) advertising to convey a message to a target population. On its face, the promotion of health awareness is an acceptable and worthy practice, but ethical concerns are raised when the health industry plays an instrumental role in creating "illnesses" or "conditions" for which they are providing treatments. / At one time, to protect health consumers, legislation and regulations prohibited directly advertising of prescription healthcare products and services to consumers, since it was thought that physicians were the ones best equipped to deal with this information. However, times have changed, and DTC advertising now is openly allowed in some countries, and in others in some narrowly specific situations. / This thesis examines the ethical and practical issues raised by this development, arguing that the negative consequences of permitting Direct-to-Consumer advertising far exceeds any positive benefits. If governments do not take an active role in preventing the further commercialization of medicine, Canada (and other countries as well) may be destined to become a nation of worried well.

Quality of measurement is a fundamental issue in medical research and clinical practice, of relevance for any inference or decision-making process. Reliability, as an estimate of the variability in the domain of repeated measurements, is an important component of the quality of measurements. / Reliability indices are frequently used and presented in the medical literature and a considerable amount of methodological research has been conducted on this topic in the last decades. However, the debate is still open on some theoretical and operational aspects. Available knowledge concerning reliability, particularly for categorical data, is not easily accessible since it is often confined to specialized journals and almost disregarded by statistical textbooks. Therefore, a thorough understanding is difficult to achieve for a researcher potentially involved in reliability studies. / My main objective was to pursue a conceptual and global understanding of the role of reliability in the domain of categorical data. In order to achieve this goal I reviewed and synthesized the literature according to some specific objectives: (a) to provide an overview on the founding concepts and methods in the measurement of reliability for categorical variables, also contrasting them with what has been done in the domain of continuous variables; (b) to present and discuss the main limitations of traditional indices, particularly the kappa statistic; (c) to briefly introduce some possible alternative methods and areas for future development; (d) to emphasize the implications of reliability for epidemiological and clinical research. / Finally, in order to illustrate the application of some of the methods discussed, I used a real set of data, concerning 209 slides of lymphomas tissue samples, reviewed by a panel of four pathologists, according to a standard classification based on 10 categories.

The expression of HIV-1 in cells of monocytic origin was investigated. In order to do this, the cell line U-937 was chosen because it possesses many characteristics of immature monocytes and can be easily infected by HIV-1. We found that long-term chronically-infected cells generate a high amount of defective particles, unable by themselves to successfully infect any target cells. Two main phenotypes were detected, one showing defectiveness in reverse transcriptase activity, and the other one showing inability to express fully mature glycoproteins. / We also investigated the biological relevance of these defective particles, particularly in a situation where two cells generating defective virions are fused together by chemical methods. We show evidence that defective virions can complement each other in a hybrid cell and generate fully infectious particles resembling wild-type virus. Such a phenomenon may occur by genetic recombination, as suggested by Southern blot analysis. This finding may prove of clinical relevance since cells of phagocytic lineage can fuse in vivo naturally or by virus-mediated mechanisms. / We next tried to assess the efficacy of the antiviral drug, AZT, in controlling HIV-1 replication in such monocyte-like cells. AZT was found unable to completely abolish HIV-1 replication in vitro but was able to delay in a dose-dependent fashion the expression of the virus. In addition, we also studied the effect of AZT in clonal derivatives of U-937 cells, and found that the inhibitory effect was proportional to the degree of susceptibility of these cells to the virus. / Finally, we analyzed the susceptibility of U-937 cells by using such clonal derivatives and found that some displayed either high or low susceptibility to infection by HIV-1. The susceptibility which correlated with the amounts of intracellular viral DNA and TNF-alpha mRNA expression was found not to depend on levels of CD4 receptors, a result which suggests that other factors are involved in modulating replication in those cells.

Objective. To estimate the distributions of thermal and vibration sensory thresholds in a healthy population taking into account important covariates. / Methods. Sensory thresholds were measured using quantitative sensory testing for 148 volunteers free of neuropathic disease. Independent effects of age, gender, height, and skin temperature were estimated using multiple linear regression. Parametric and nonparametric methods were used to estimate the distributions of interest. / Results. Significant age-related increases were observed for vibration thresholds (p $<$ 0.0001) and in the foot for thermal thresholds (p $<$ 0.0002). Height was significantly associated with vibration thresholds in the foot (p $<$ 0.003). Selected percentiles are estimated for thermal trends in the hand. Age-adjusted continuous distributions for the remaining thresholds are presented with corrections for height where appropriate. / Conclusions. Our results provide reference values for thermal and vibration sensory thresholds of a healthy population. Future patient test results may be compared with estimated age-specific percentiles to assess levels of abnormality.

The work described herein represents a preliminary step in the characterisation of the human Tom20 protein and its role in the mammalian mitochondrial import machinery. A hexahistidine-tagged form of the human homologue of Tom20 has been over-expressed in Escherichia coli and purified under native conditions. This Tom20 protein has been shown, in these studies, to compete for the import of a matrix-destined mitochondrial precursor protein, pre-ornithine carbamoyltransferase (pOCT), into mitochondria isolated from a mammalian source (rat heart), as well as to directly bind the presequence-bearing pOCT in vitro. Furthermore, a protocol has been established for the isolation of import-competent outer membrane vesicles from rat liver mitochondria. These vesicles have been preliminarily characterised in terms of the import of two outer membrane-destined DHFR fusion proteins, Tom70(1-29)-DHFR and Tom20(1-28)-DHFR, and have been shown to exhibit similar characteristics/requirements for protein import as seen for intact mitochondria: temperature sensitivity, the dependence upon cytosolic ATP, and the requirement for protease-sensitive outer membrane surface components.

Thesis (Ph.D.)--University of California, San Francisco, 2009. / Source: Dissertation Abstracts International, Volume: 71-02, Section: B, page: . Adviser: Xin Chen.