A fluid power application of alternative robust control strategies

This thesis presents alternative methods for designing a speed controller for a hydrostatic power transmission system. Recognising that such a system, comprising a valve controlled motor supplied by the laboratory ring main and driving a hydraulic pump as a load, contains significant non-linearities, the thesis shows that robust 'modern control' approaches may be applied to produce viable controllers without recourse to the use of a detailed model of the system. In its introduction, it considers why similar approaches to the design of fluid power systems have not been applied hitherto. It then sets out the design and test, in simulation and on a physical rig, of two alternative linear controllers using H∞ based methods and a 'self organising fuzzy logic' controller (SOFLC). In the linear approaches, differences between the characteristics of the system and the simple models of it are accommodated in the controller design route as 'perturbations' or 'uncertainties'. The H∞ based optimisation methods allow these to be recognised in the design. “Mixed sensitivity” and “Loop shaping” methods are each applied to design controllers which are tested successfully on the laboratory rig. The SOFLC in operation does not rely on a model, but instead allows fuzzy control rules to evolve. In the practical tests, the system is subjected to a range of disturbances in the form of supply pressure fluctuations and load torque changes. Also presented are test results for proportional and proportional plus integral (PI) controllers, to provide a reference. It is demonstrated qualitatively that performance using the linear controllers is superior to that using proportional and PI controllers. An increased range of stable operation is achieved by the controller designed using “loop shaping” – performance is enhanced by the use of two controllers selected automatically according to the operating speed, using a “bumpless” transfer routine. The SOFLC proved difficult to tune. However, stable operation was achieved.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Childhood cancer and paternal employment in agriculture: the role of pesticides.

Previous studies have suggested that the offspring of men potentially exposed to pesticides at work may be at increased risk of kidney cancer (Wilms' tumour), brain tumours, Ewing's bone sarcoma and acute leukaemia. This paper examines the association between potential occupational exposure of fathers to pesticides and offspring's death from cancer in a large national database. Records for 167703 childhood deaths occurring during 1959-63, 1970-78 and 1979-90 in England and Wales have been analysed. Among the offspring of men with potential occupational exposure to pesticides there were 5270 deaths, of which 449 were due to cancer. Associations were assessed using proportional mortality ratios (PMRs), with adjustment for age, year of death and paternal social class. Of the childhood cancers previously linked with potential paternal occupational exposure to pesticides, the only statistically significant excess was for kidney cancer (PMR=1.59, 95% CI=1.18-2.15, based on 42 deaths). Although these results offer some support for the suggestion that paternal occupational exposure to pesticides may be related to the subsequent development of kidney cancer in offspring, other explanations cannot be excluded. In the light of the findings presented here and elsewhere, further, more detailed, research into the nature of this relationship is warranted

Development of an occupational airborne chemical exposure matrix

Background Population-based studies of the occupational contribution to chronic obstructive pulmonary disease generally rely on self-reported exposures to vapours, gases, dusts and fumes (VGDF), which are susceptible to misclassification. Aims To develop an airborne chemical job exposure matrix (ACE JEM) for use with the UK Standard Occupational Classification (SOC 2000) system. Methods We developed the ACE JEM in stages: (i) agreement of definitions, (ii) a binary assignation of exposed/not exposed to VGDF, fibres or mists (VGDFFiM), for each of the individual 353 SOC codes and (iii) assignation of levels of exposure (L; low, medium and high) and (iv) the proportion of workers (P) likely to be exposed in each code. We then expanded the estimated exposures to include biological dusts, mineral dusts, metals, diesel fumes and asthmagens. \ud Results We assigned 186 (53%) of all SOC codes as exposed to at least one category of VGDFFiM, with 23% assigned as having medium or high exposure. We assigned over 68% of all codes as not being exposed to fibres, gases or mists. The most common exposure was to dusts (22% of codes with >50% exposed); 12% of codes were assigned exposure to fibres. We assigned higher percentages of the codes as exposed to diesel fumes (14%) compared with metals (8%). Conclusions We developed an expert-derived JEM, using a strict set of a priori defined rules. The ACE JEM could also be applied to studies to assess risks of diseases where the main route of occupational exposure is via inhalation

Excavations of a second iron age enclosure on Winnall Down, Winchester, Hampshire, 2006

Aerial survey during the 1970s identified two plough-levelled enclosures, 300m apart, on Winnall Down, Winchester. One of these, Winnall Down I, was excavated by Fasham (1985) in advance of the M3 motorway extension, and revealed evidence for intensive Bronze Age and Iron Age occupation. The adjacent enclosure, Winnall Down II, was not examined by Fasham however, and its date and relationship to Winnall Down I was not known. This paper details the results of a small-scale research excavation on Winnall Down II. It established that some occupation within both enclosures was contemporaneous and this arrangement implies complex agreements over land apportionment and agricultural activities

Early to mid-Holocene human-river interactions in the Lower Danube Valley: new research at Poiana (Teleorman County)

This paper presents new research in an alluvial basin of the Lower Danube Valley between Turnu Măgurele and Zimnicea in southern Teleorman County. In terms of archaeology, the area had not been previously systematically investigated. During the twentieth century, and especially before the late 1960s to early 1970s, there were major landscape changes as result of massive desiccation and impoundment. Most prehistoric and ancient archaeological finds were previously discovered incidentally. The earliest traces of human activity were identified on the loess terraces bordering the north of the Danube floodplain. Noteworthy is the research focused on the Upper Palaeolithic at Ciuperceni, first carried out in the late 1970s, and then, more recently, between 2006 and 2008. Other prehistoric evidence has been discovered during systematic research around Poiana village (formerly Flămânda)on former Danube terraces and the northern bank of former Lake Bercelui. Importantly, the oldest evidence could date to the Mesolithic, followed by the early and developed (late) Neolithic. Starting in 2013, a collaborative research project between Cardiff and Lincoln Universities from the UK and the Teleorman County Museum aims to better understand this chronological sequence and will investigate the palaeoenvironmental and hydrological histories of the Danube and the impact of the river on human communities over time