Environmental Risk Factors for Parkinson's Disease

Parkinson’s disease (PD) is a progressive, degenerative, neurological disease. The progressive disability associated with PD results in substantial burdens for those with the condition, their families and society in terms of increased health resource use, earnings loss of affected individuals and family caregivers, poorer quality of life, caregiver burden, disrupted family relationships, decreased social and leisure activities, and deteriorating emotional well-being. Currently, no cure is available and the efficacy of available treatments, such as medication and surgical interventions, decreases with longer duration of the disease. Whilst the cause of PD is unknown, genetic and environmental factors are believed to contribute to its aetiology. Descriptive and analytical epidemiological studies have been conducted in a number of countries in an effort to elucidate the cause, or causes, of PD. Rural residency, farming, well water consumption, pesticide exposure, metals and solvents have been implicated as potential risk factors for PD in some previous epidemiological studies. However, there is substantial disagreement between the results of existing studies. Therefore, the role of environmental exposures in the aetiology of PD remains unclear. The main component of this thesis consists of a case-control study that assessed the contribution of environmental exposures to the risk of developing PD. An existing, previously unanalysed, dataset from a local case-control study was analysed to inform the design of the new case-control study. The analysis results suggested that regular exposure to pesticides and head injury were important risk factors for PD. However, due to the substantial limitations of this existing study, further confirmation of these results was desirable with a more robustly designed epidemiological study. A new exposure measurement instrument (a structured interviewer-delivered questionnaire) was developed for the new case-control study to obtain data on demographic, lifestyle, environmental and medical factors. Prior to its use in the case-control study, the questionnaire was assessed for test-retest repeatability in a series of 32 PD cases and 29 healthy sex-, age- and residential suburb-matched electoral roll controls. High repeatability was demonstrated for lifestyle exposures, such as smoking and coffee/tea consumption (kappas 0.70-1.00). The majority of environmental exposures, including use of pesticides, solvents and exposure to metal dusts and fumes, also showed high repeatability (kappas >0.78). A consecutive series of 163 PD case participants was recruited from a neurology clinic in Brisbane. One hundred and fifty-one (151) control participants were randomly selected from the Australian Commonwealth Electoral Roll and individually matched to the PD cases on age (± 2 years), sex and current residential suburb. Participants ranged in age from 40-89 years (mean age 67 years). Exposure data were collected in face-to-face interviews. Odds ratios and 95% confidence intervals were calculated using conditional logistic regression for matched sets in SAS version 9.1. Consistent with previous studies, ever having been a regular smoker or coffee drinker was inversely associated with PD with dose-response relationships evident for packyears smoked and number of cups of coffee drunk per day. Passive smoking from ever having lived with a smoker or worked in a smoky workplace was also inversely related to PD. Ever having been a regular tea drinker was associated with decreased odds of PD. Hobby gardening was inversely associated with PD. However, use of fungicides in the home garden or occupationally was associated with increased odds of PD. Exposure to welding fumes, cleaning solvents, or thinners occupationally was associated with increased odds of PD. Ever having resided in a rural or remote area was inversely associated with PD. Ever having resided on a farm was only associated with moderately increased odds of PD. Whilst the current study’s results suggest that environmental exposures on their own are only modest contributors to overall PD risk, the possibility that interaction with genetic factors may additively or synergistically increase risk should be considered. The results of this research support the theory that PD has a multifactorial aetiology and that environmental exposures are some of a number of factors to contribute to PD risk. There was also evidence of interaction between some factors (eg smoking and welding) to moderate PD risk.

The predicate marker li in Mauritian Creole

There is a morpheme 'li' in Mauritian Creole (MC), which is homophonous with the 3sg pronoun, and which, in the early creole, occurs frequently between the subject and the predicate in affirmative, present tense clauses. I propose that that 'li' may have originated as a resumptive pronoun, co-referential with the subject, but following the grammaticalization of new determiner elements to mark the semantic contrasts of [±definite] and singular vs. plural, 'li' has now grammaticalized into a predicate marker. Its presence is sensitive to both the nature of the predicate, and to the definiteness and specificity features of the subject NP. My analysis is within the framework of Truth Conditional Semantics, where indefinite NPs are analyzed as variables that get introduced into the discourse, and must be bound by an operator to yield a closed proposition, with a truth value. Drawing on a comparison with a cognative morpheme 'i' in Seychellois Creole, I claim that its path to grammaticalization is linked to that of the specificity marking 'la'.

A case-control study of employment status and mortality in a cohort of Australian youth

Recent studies have demonstrated a link in young populations between unemployment and ill health. The purpose of this study is to correlate mortality with employment status in two cohorts of young Australian males, aged 17-25 years, from 1984 to 1988. Two youth cohorts consisting of an initially unemployed sample (n = 1424 males) and a population sample (n = 4573 males), were surveyed annually throughout the study period. Those lost to follow-up during the survey period were matched with death registries across Australia. Employment status was determined from weekly diaries and death certificates and was designated as: employed or student; unemployed; not in the work force (excluding students). Conditional logistic regression, using age- and cohort- matched cases (deaths) and controls (alive), was used to estimate the odds ratio (OR) of dying with regard to employment status, taking into account potential confounders such as ethnicity, aboriginality, educational attainment, pre-existing health problems, socio-economic status of parents, and other factors. Twenty three male survey respondents were positively matched to death registry records. Compared to those employed or students (referent group), significantly elevated ORs were found to be associated with neither being in the workforce nor a student for all cause, external cause, and external cause mortality other than suicide. Odds ratios were adjusted for age, survey cohort, ethnicity, pre-existing physical and mental health status, education level, and socio-economic status of parent(s). A statistically significant increasing linear trend in odds ratios of male mortality for most cause groups was found across the employment categories, from those employed or student (lowest ORs), through those unemployed; to those not in the workforce (highest ORs). Suicide was higher, but not statistically significantly, in those unemployed or not in the workforce. Suicide also was associated, though not significantly, with the respondent not living with their parents when they were 14 years of age. No association was found between mortality and past unemployment experience, as measured by length of time spent unemployed, or the number of spells of unemployment experienced during the survey. The results of this study underscore the elevated risk to survival in young males as a consequence of being neither employed nor a student. (C) 1999 Elsevier Science Ltd. All rights reserved.

Quantum controlled-NOT gate with 'hot' trapped ions

We present a novel method of performing quantum logic gates in trapped ion quantum computers which does not require the ions to be cooled down to the ground state of their vibrational modes, thereby avoiding one of the principal experimental difficulties encountered in realizing this technology. Our scheme employs adiabatic passages and a phase shift conditional on the phonon number state.

Quasistationarity of continuous-time Markov chains with positive drift

We shall study continuous-time Markov chains on the nonnegative integers which are both irreducible and transient, and which exhibit discernible stationarity before drift to infinity sets in. We will show how this 'quasi' stationary behaviour can be modelled using a limiting conditional distribution: specifically, the limiting state probabilities conditional on not having left 0 for the last time. By way of a dual chain, obtained by killing the original process on last exit from 0, we invoke the theory of quasistationarity for absorbing Markov chains. We prove that the conditioned state probabilities of the original chain are equal to the state probabilities of its dual conditioned on non-absorption, thus allowing us to establish the simultaneous existence and then equivalence, of their limiting conditional distributions. Although a limiting conditional distribution for the dual chain is always a quasistationary distribution in the usual sense, a similar statement is not possible for the original chain.

Sensitivity to measurement perturbation of single-atom dynamics in cavity QED

We consider continuous observation of the nonlinear dynamics of single atom trapped in an optical cavity by a standing wave with intensity modulation. The motion of the atom changes the phase of the field which is then monitored by homodyne detection of the output field. We show that the conditional Hilbert space dynamics of this system, subject to measurement-induced perturbations, depends strongly on whether the corresponding classical dynamics is regular or chaotic. If the classical dynamics is chaotic, the distribution of conditional Hilbert space vectors corresponding to different observation records tends to be orthogonal. This is a characteristic feature of hypersensitivity to perturbation for quantum chaotic systems.

Quantum control and quantum entanglement

We discuss quantum error correction for errors that occur at random times as described by, a conditional Poisson process. We shoo, how a class of such errors, detected spontaneous emission, can be corrected by continuous closed loop, feedback.