Un composite époxy/fibre de verre élaboré à partir de matériaux simplifiés a été soumis en parallèle à du vieillissement artificiel (UV et thermohydrique) et à du vieillissement naturel (climat tropical humide). Une étude des matériaux (résine seule et composite) à travers un large panel de techniques de caractérisation physico-chimiques, mécaniques et de moyens d’observation (MEB, AFM) a permis d’identifier clairement la structure, la morphologie et les principales propriétés du réseau époxy-amine de l’état initial. Une caractérisation systématique des échantillons par couches de 20 microns d’épaisseur a permis, en particulier, d’identifier un gradient de structure et de propriétés dans les 200 premiers microns à la surface des plaques de résine et de composite. Ce gradient est attribué à l’évaporation du durcisseur amine lors de l’élaboration des matériaux. Dans les plaques de composites, le DMA ainsi que l’AFM ont permis de mettre en évidence une zone d’interphase autour des fibres pour laquelle le réseau époxy-amine présente des caractéristiques différentes de celles de la résine en masse.La même méthodologie a été adoptée pour suivre l’évolution de ces matériaux lors des vieillissements artificiels et naturels.Les études séparées des vieillissements UV et thermohydrique ont permis de mettre en évidence les altérations chimiques et physico-chimiques de la matrice seule d’une part, et des interphases fibres/matrice d’autre part. Le vieillissement photochimique se montre le plus dégradant pour la surface des plaques, alors que les effets du vieillissement thermohydrique sont principalement observés au niveau des interfaces fibres/matrice dans les composites. Dans les deux cas également, nous pouvons proposer des mécanismes simplifiés de dégradation de la résine époxy-amine.Enfin, les résultats de caractérisation après le vieillissement naturel nous permettent de faire des corrélations avec les vieillissements artificiels et de pointer les effets prépondérants des deux paramètres de vieillissement, ainsi que d’avancer un facteur d’accélération. / A simplified glass fiber/epoxy composite was exposed to artificial ageing conditions (UV and Hygrothermal) and natural ageing (humid tropical climate). A wide range of physicochemical, mechanical and observation techniques (SEM, AFM) were used to clearly identify the structure, morphology and the main properties of the epoxy-amine network of the resin alone and composite in the initial state. A gradient in structure and properties was shown up in the first 200 microns of resin and composite plates surfaces thanks to the systematic characterization of sample layers of 20 microns thickness. It is attributed to an amine deficit during the sample elaboration process. In composite plates, DMA and AFM measurements have highlighted the existence of an interphase area around the fibers with a higher molecular mobility and a lower stiffness than the epoxy-amine network in the bulk resinThe same methodology was used to follow the materials evolution during artificial and natural ageing.The effects of UV and hygrothermal ageing were analyzed independently on the resin and on the composite in order to identify the chemical and physicochemical alterations of the matrix on one hand and of fiber/matrix interphases on the other hand. Photochemical ageing effects are mainly localized on materials surfaces, while the hygrothermal ageing affects mainly fiber/matrix interfaces in composite. In both cases simplified degradation mechanisms of epoxy-amine network are proposed.Finally, the characterization results after natural exposure allow us to establish correlations with artificial ageing. Predominant effects are identified and an acceleration factor is proposed.

Australia's population and workforce are ageing. The reason for an ageing population is the post World War II baby boom, followed by low birth rates in subsequent generations. Combined with healthier lifestyles, advances in medical science and the subsequent increase in longevity, this means that there are more older people than ever before and this trend will continue for several more decades. However, workforce demographics are also affected by ageing, and Australian organisations will need to employ more older workers in the near future to meet predicted shortfalls of skilled workers. Although there have been studies examining the current low employment rates of older workers, the identification of negative stereotypes associated with older workers, and related problems and challenges (such as age discrimination), no study of the working intentions of older Australian workers has been reported. Therefore, the aim of this research is to explore the meaning of working for older workers to better understand whether and why older Australian workers might want to continue working. In particular, this thesis explores what it is about working that makes some people want to continue beyond the traditional age of retirement, while others wish to cease work as soon as they are able. There are clear implications for individuals, organisations and public policy emanating from the extension to working lives. The research aims and objectives were best met within a phenomenological approach, and the data collection consisted of four studies. The setting for the research was a single organisation; an Australian university. Three of these studies were qualitatively-driven, within an interpretivist paradigm: (i) in-depth interviews with older employees (aged 50 years or older) to determine their meanings of working; (ii) interviews with managers to determine whether there were any organisational factors encouraging older workers to retire early; and (iii) interviews with retirees to determine their meanings of working and retirement. The fourth study was quantitative and examined the demographics of the organisation and the relevant HRM policy documents. The thesis uses the meaning of working as the initial theoretical conceptual perspective, and derives a new conceptual perspective for managing older workers, which is outlined in the last chapters. The research draws from two perspectives - the organisation and the individual. The organisational perspective examines the management of organisational staffing in the context of future demographic changes. The individual perspective is explored via the meaning of working to older workers. The key findings from the research in the chosen university suggest that despite the Commonwealth Government's attempts to encourage older workers to continue working, the majority of the older workers, irrespective of employment category, did not want to continue working beyond the traditional retirement age of 65 years. Reasons included wanting to spend more time with a life partner, becoming more involved with interests outside of work, and removing themselves from the negative circumstances in the organisation. However, of those who wanted to continue working, the majority was from the academic employment category (both employees and retirees), and the minority was from the administrative or general employment category. Additionally, the academic participants rated working in their lives as important or very important; higher than the ratings provided by the general staff participants. Explanations are offered as to reasons for such differences between the employment categories. The consequences of these findings include the need for a new approach to managing older workers, and particularly at the end of their working lives and into retirement. Australian organisations cannot afford to continue losing staff to early retirement, yet this trend appears to continue. Suggestions to meet this challenge are made at three levels: public policy, the organisation and the individual. Implications for future research are presented in the final chapter.

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Chronic in ammation and variations in blood flow have been implicated in the pathogenesis of cardiovascular disease. It is also possible that inflammatory and rheological processes are involved in the development of mild cognitive impairment and dementia, either through their association with vascular disease or via some other, more direct effect on the brain. Evidence is increasing for a causal relationship between Alzheimer's disease and inflammation, possibly related to inflammatory activation of microglia. Inflammatory processes may also be involved in the pathogenesis of cerebral small vessel disease, which in turn has been linked to cognitive impairment and dementia. There is also evidence showing that rheological factors affect cerebral blood flow. However, despite these findings, the associations between inflammatory and rheological markers and cognitive ability have not been extensively studied in large groups of ageing people. The primary aim of this thesis was to test for associations between late-life levels of inflammatory and rheological markers (C-reactive protein (CRP), fibrinogen, tumor necrosis factor (TNF)-α, interleukin (IL)-6, plasma viscosity, and haematocrit) and cognitive ability. A genetic analysis was then performed to model single nucleotide polymorphisms (SNPs) in the genes encoding the markers against cognition in an attempt to determine the weight of evidence for a causal inflammation-cognition association. Four studies were used to test these aims with the majority of the analysis being performed on the Aspirin for Asymptomatic Atherosclerosis (AAA) Trial (n = 3,350), and the Edinburgh Type 2 Diabetes Study (ET2DS) (n = 1,066). The Edinburgh Artery Study (n = 534), and the 1936 Lothian Birth Cohort (n = 1,091), were used as replication cohorts for the genetic analysis. All cohorts comprised community-dwelling, elderly citizens (aged around 70 years) living in central Scotland. With the exception of the ET2DS, all data used were for secondary analyses. Cognitive ability was assessed in all studies using comprehensive batteries of neuropsychological tests that included a measure of crystallised intelligence in the form of a vocabulary test. As performance on such tests varies little across a lifespan, adjusting for these scores in the late-life models enabled the determination of estimated lifetime cognitive change. In the case of the 1936 Lothian Birth Cohort an actual age-11 IQ measure was available in addition to the cognitive follow-up scores recorded at age-70. Linear regression showed small but significant associations between CRP, fibrinogen, and plasma viscosity, and cognition and estimated lifetime cognitive decline in the AAA Trial. Similar results were observed in the ET2DS for CRP, IL-6, and TNF-α. These associations tended to be of a magnitude whereby the markers explained 1% of the variance of the cognitive test scores. The cognitive domains most consistently associated with the markers were processing speed, and a data derived general intelligence factor. A novel genetic analysis was then undertaken to model SNPs against cognitive ability and decline. Most of the results generated were null findings. However, strongly significant associations were found between the rs2227412 fibrinogen beta gene SNP and the cognitive test scores in the ET2DS. Furthermore, the genotype associated with the lowest cognitive scores was also related to higher levels of plasma fibrinogen. Whilst replication of the association between the fibrinogen SNPs and cognition was not found across all cohorts, these results still indicate a potentially causal role for this haemostatic/inflammatory marker. To date, the majority of inflammation-cognition associations have focussed on the acute-phase protein CRP. The main outcomes from this thesis suggest that its close correlate, fibrinogen, is an equally, if not more important factor in the complex process of cognitive ageing.

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