Control of colocated geostationary satellites

Control of the inter-satellite distances within a cluster of colocated satellites located in the same GEO window is examined with regards to the close approaches between pairs of satellites. Firstly, the orbital evolution and station keeping control of a single GEO satellite is examined and a new IBM PC based software program capable of performing both these functions autonomously from initial values of the orbital position and date is detailed and validated. Cluster design ideas are then examined in detail and the propagation software is used to generate data for a cluster of four satellites. Two test cases are examined to quantify the frequency of close approaches between individual satellite pairs, each test case using a different orbital element separation strategy but the same station keeping control scheme. The results of the study are then compared with previous research and discussions are presented on the advantages of each method. Finally, a cluster geometry correction manoeuvre, based on Hill's equations of relative motion, is presented which requires only those thrusters used by typical station keeping. This manoeuvre is integrated into the computer software and the two test cases noted previously are again propagated and the close approach results analysed to demonstrate the reduction in the number of close approaches below 5 km

Earth’s climate response to a changing Sun

For centuries, scientists have been fascinated by the role of the Sun in the Earth’s climate system. Recent discoveries, outlined in this book, have gradually unveiled a complex picture, in which our variable Sun a¬ffects the climate variability via a number of subtle pathways, the implications of which are only now becoming clear. This handbook provides the scientifically curious, from undergraduate students to policy makers with a complete and accessible panorama of our present understanding of the Sun-climate connection. 61 experts from di¬fferent communities have contributed to it, which reflects the highly multidisciplinary nature of this topic. The handbook is organised as a mosaic of short chapters, each of which addresses a specific aspect, and can be read independently. The reader will learn about the assumptions, the data, the models, and the unknowns behind each mechanism by which solar variability may impact climate variability. None of these mechanisms can adequately explain global warming observed since the 1950s. However, several of them do impact climate variability, in particular on a regional level. This handbook aims at addressing these issues in a factual way, and thereby challenge the reader to sharpen his/her critical thinking in a debate that is frequently distorted by unfounded claims

Cellular patterns during leaf development

A major problem in developmental biology is to understand how the behaviour of individual cells creates reproducible biological shapes. Moreover, the reproducibility of form also happens at the cellular level and cellular patterns are evident in the temporal as well as the spatial scales. Understanding the principles underlying these cellular patterns will contribute to linking the individual cell dynamics to the collective phenomenon of morphogenesis. The relatively flat shape, the absence of cell migration and apoptosis makes the leaf of Arabidopsis thaliana an excellent system to study morphogenesis at the cellular level. However the information about the cellular dynamics that is available has only been inferred indirectly or restricted to few cells. In this thesis, I present some methods that permitted the characterisation of cellular dynamics over long time periods at the organ level. I present the Lobe Contribution Elliptical Fourier Analysis (LOCO-EFA), that enabled the quantification of complex cell geometries and provided a shape profile to evaluate populations of cells. In turn, the shape profile of individual cells was used to develop a tracking algorithm that, integrated with a segmentation algorithm, resulted in a powerful tool to recognize cells in a succession of images and extract cell shape, cell area, cell position and cell lineages. The synergy between in vivo imaging and computational tools permitted the study of cellular patterns at unprecedented resolution. Interestingly, the dynamics of cell growth and cell shape are highly influenced by the cell age and to a limited extend, by their position. Moreover, direct measurement of cell division shows that the division zone is restricted towards the base of the leaf, but is not constant in length and that the frequency of divisions decreases over time in a rather gradual fashion. At single cell level, new events of lobe formation were identified, suggesting that the intracellular patterning underlying the multi-polar pavement cell shape is dynamic and lobes are newly formed rather than being specified at a single time point. The cellular dynamics of growth, shape and divisions using long time-lapse and imaging enabled me to revisit previous hypothesis and propose new ones about the regulation of cellular behaviour during leaf morphogenesis. (The CD-ROM referred to in the thesis contains Movies in AVI format. However these were submitted as separate files which could not be uploaded to the repository. Please contact the author for more information.

The visco-elastic properties of the arterial wall.

PhDThe visco-elastic properties of the arterial wail are of importance in determining the behaviour of the circulatory system for the pulse wave is a relatively rapid event. It has been reported that arteries show very little change in length with each heart beat. There are no reports of studies on arterial behaviour carried out under conditions that take account of these two factors. Accordingly an investigation has been made of the pressure-diameter relations of various types of dogs' arteries under static and dynamic conditions. All experiments were performed with the vessel held at the length which it occupied in vivo. Measurements were also made of the relative wall thickness and of the amount of shortening which occurred when an artery was excised. Under static conditions all arteries show an elastic modulus which increases with distension; this is less marked, in the low pressure range, for the elastic thoracic aorta. This increasing modulus results both from the presence of various wall constituents arranged in parallel and from the non-linear elastic behaviour of these elements themselves. Under dynamic conditions the artery shows increased stiffness, the magnitude of this increase is proportional to the muscularity of its wall. This increase occurs at low frequencies and is compatible with what is known of the time-dependent properties of smooth muscle. Little further increase occurs at frequencies between 2 and 20 c/a. The dilatation also lags behind the pressure changes by a small amount. These factors will influence both the velocity and the attenuation of the pulse wave. The variation with frequency of these two factors has been calculated using the data obtained in these experiments. The results of this calculation stand comparison with published values for the pulse wave velocit

Models and Analysis of Vocal Emissions for Biomedical Applications

The MAVEBA Workshop proceedings, held on a biannual basis, collect the scientific papers presented both as oral and poster contributions, during the conference. The main subjects are: development of theoretical and mechanical models as an aid to the study of main phonatory dysfunctions, as well as the biomedical engineering methods for the analysis of voice signals and images, as a support to clinical diagnosis and classification of vocal pathologies

Fundamental Concepts Associated with Hydraulic Seals for High Bandwidth Actuation

This thesis is concerned with issues relating to the development of an active sealing system for hydraulic actuators where the sealing elements can be radially extended and retracted to vary the friction and leakage characteristics. In order to determine the feasibility of the active sealing concept it is necessary to establish that varying the seal geometry may achieve useful improvements in the friction-leakage trade-off and that a practical method of achieving this seal extension can be realised. Experimental and simulation approaches for seal friction prediction have been developed and active seal prototypes produced to demonstrate the concept. Experiments were carried out to measure the constant velocity friction for single-lip and double-lip seals over a range of sliding speeds and sealed pressures with special consideration applied to the instroke-outstroke direction dependence. Additional experiments were performed with sinusoid motion to provide an indication of the transient friction characteristics. Friction was shown to increase towards the end of the outstroke cycle and decrease once the instroke motion began. Tribology simulations were produced based on the results of a FEA simulation of the rod-seal contact pressure. Empirical friction-load relationships and novel contact mechanics approaches for high loads were considered. Simulations based on the Reynolds equation including standard inverse EHL theory and the GW-average Reynolds lubrication are also presented. Experimental agreement could be improved if loading is assumed to transfer to the fluid to maintain a fluid film. A hysteresis friction model was also developed in attempt to improve the prediction of speed dependent friction. Two active seal prototypes were produced, each with an adjustable external pressure supplied to the outer circumference of the sealing element. Constant velocity friction measurements for different external pressures and the transient response following step changes in this pressure are presented.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Reincarnation in early Greek thought

Investigates by examining the works of Pythagoras, Pindar, Empedocles and Plato, the appearance of reincarnation in early Greek thought. It is a chronological survey of the movements and authors connected with the doctrine of reincarnation and an attempt to elucidate whether the doctrine can be described in terms of development and continuity.Thesis (MA) -- University of Adelaide, Dept. of Classics, 199