Presented in this thesis is a summary of the development of gallium arsenide position sensitive detectors. These are aimed at various applications with the original motivation being experimental particle physics. An account is given of basic semiconductor physics relevant to particle detectors. A review of electronics applicable to reading out charged signals from semiconductor detectors is included. Applications of gallium arsenide X-ray detectors are described together with results from a Monte-Carlo simulation of the spectrum obtained from an X-ray source. The design, fabrication and laboratory testing of detectors is presented for pixel and microstrip detectors and other test structures. Test beam results are also presneted for pixel and microstrip detectors. An introduction to ATLAS detector simulation is also given, with examples of detector descriptions for the GaAs Forward Semiconductor Tracker. Results from a generator level study of b-jets from the process Hbb and predictions of influences in the Forward Tracker are also given.

LHCb is one of the four Large Hadron Collider (LHC) experiments based at CERN, the European Organisation for Nuclear Research. The LHC experiments will start taking an unprecedented amount of data when they come online in 2007. Since no single institute has the compute resources to handle this data, resources must be pooled to form the Grid. Where the Internet has made it possible to share information stored on computers across the world, Grid computing aims to provide access to computing power and storage capacity on geographically distributed systems. LHCb software applications must work seamlessly on the Grid allowing users to efficiently access distributed compute resources. It is essential to the success of the LHCb experiment that physicists can access data from the detector, stored in many heterogeneous systems, to perform distributed data analysis. This thesis describes the work performed to enable distributed data analysis for the LHCb experiment on the LHC Computing Grid.

The rôle that shear plays in the dynamical response and associated stability of elastic bodies is investigated within this thesis from two perspectives. Forming the major part of the study is the investigation of infinitesimal wave propagation within elastic material which has been subjected to a static pre-strain corresponding to simple shear. Initially we consider a prototype problem wherein the theory of incremental motions provides the mechanism for analyzing Rayleigh waves propagating along the surface of an incompressible elastic half-space. This is looked at from a plane strain point of view but, significantly, the direction of propagation is not along a principal axis. Using co-ordinates measured relative to the Eulerian axes in the governing equation and boundary conditions, corresponding to the vanishing of incremental tractions, we derived the secular equation for infinitesimal waves in terms of wavespeed, shear and hydrostatic stress parameters for a particular class of materials. The dependence of the wavespeed on these parameters is illustrated and bifurcation criteria are found through setting the wavespeed to zero, this corresponding to quasi-static incremental displacements. For a general form of incompressible, isotropic strain-energy function we are also able to provide the bifurcation criteria incorporating an additional, material parameter. We also consider the compressible counterpart to this problem and follow the same approach, where possible, in establishing the secular equation for compressible materials. This approach is also adopted for the next problem in which an infinite layer of incompressible elastic material, having uniform width, is pre-strained and within which infinitesimal waves are propagated along the layer. Owing to the layer width the waves are now dispersive and for three types of incremental boundary conditions we provide dispersion equations involving wavespeed, shear, hydrostatic stress and layer thickness (wavelength) parameters for the same particular class of materials. The interdependence of these parameters is comprehensively detailed for this class along with the bifurcation analysis which is again extended so that it may be applicable to a general incompressible, isotropic material.

No description available.

Chapter 1 of this thesis contains an introduction to the nature, sources and methods proposed for the detection of gravitational waves. Emphasis is placed on the techniques and noise sources associated with laser interferometric gravitational wave detectors and the resulting implications for the choice of a laser source for this type of detector. This information is mainly derived from the literature. Chapter 2 contains details of experiments to construct an electronic feedback system to stabilise the intensity at both low and high frequencies of a miniature diode-pumped monolithic Nd:YAG ring laser. This work was performed in collaboration with Dr Anne Campbell and Prof. Jim Hough, with advice on directly driving the diode laser from Charles Harb, (Australian National University, Canberra). Also described are investigations into the factors limiting the performance of the stabilisation systems. This was carried out with the added help of Ken Skeldon. Chapter 3 describes experiments to measure the frequency noise of a Nd:YAG ring laser at relaxation oscillation frequencies. Also described are investigations into the noise of a commercial Nd:YAG ring laser. These experiments were carried out in collaboration with Dr. Anne Campbell and Prof. Jim Hough. Chapter 4 describes experiments on the intracavity frequency doubling of a high power flashlamp-pumped Nd:YAG rod laser using different cavity designs. These experiments were carried out mainly by the author with some advice from Prof. Jim Hugh, Dr. Anne Campbell, Dr. Gavin Newton and Dr. Malcolm Gray (Australian National University, Canberra) and with some invaluable experimental help from Dr. J. Hong (formerly of the University of St. Andrews).

The majority of work contained in this thesis involves characterisation of the mechanical losses in fused silica ribbon fibres to determine their potential for use in suspending the 40kg test masses for Advanced LIGO. The design of fibres is discussed here, demonstrating the advantages of rectangular cross sections over the circular cross sections already used in GEO600, with experimental work used to show the viability of this suspension scheme. The losses of a number of modes of oscillation of fibres were investigated using different suspension designs to reduce excess loss mechanisms. Measurements made of the material loss of the fused silica, using cantilever bending modes of a fibre held at one end, gave values slightly higher than those used in the design of noise curves for Advanced LIGO. The measurements also showed a reduced thermoelastic damping effect from that theoretically calculated from which an altered value for the Young’s modulus of the fibres was found compared to the value for bulk fused silica. Measurements performed using the violin modes and pendulum modes of the fibres showed that, while excess loss mechanisms were characterised and in the case of the violin mode measurement shown to be negligible, the level of dilution of loss calculated theoretically was not achieved. The source of increased loss is thought to be due to the energy being concentrated closer to lossy welded regions of the fibre. The losses measured for the linear pendulum were the lowest ever measured. Measurements of the vertical bounce mode of a small mass suspended between two fibres has shown clear evidence that there is no intrinsic stress dependence of the material loss of fused silica and has given further evidence that the majority of loss in the fibres comes from a thin highly dissipative layer on the surface. The strength of ribbon fibres has been shown to be sufficient to carry the working load of the Advanced LIGO masses, with a 20kg test suspension being created, however there was a wide variation in measured fibre breaking strengths thought to be due to bending in the fibre coupling longitudinal force into shear stress. Issues regarding thermal stress at welds are discussed with suggested solutions for construction of Advanced LIGO suspensions.

Microwave radiometry can provide a non-invasive, non-destructive and inherently safe method of temperature measurement suitable for a range of medical and industrial applications. The measured radiometric signal is formed by a convolution of the actual material temperature distribution with a coupling spatial response, or weighting function, over the viewed volume of material. The form of this weighting function depends on both the electromagnetic coupling structure (either antenna or cavity) and on the geometry and dielectric properties of the material. Through reciprocity, the weighting function can be found by computation or measurement of the power dissipation distribution (also known as the specific absorption rate (SAR)) when the coupling structure is actively excited. Knowledge of the weighting function is used to interpret the measured radiometric temperature. Chapter 1 introduces the method of microwave radiometry, its range of applications and considers the key features of weighting function determination. The suitability and validity of finite difference time domain (FDTD) SAR and weighting function modelling was investigated for the largely travelling - wave fields appropriate to surface contact antennas. An FDTD simulator, the Basic Electromagnetic Simulation Tool [3], was used to computationally model a range of antenna configurations that could then be compared directly with experimental results. Chapter 2 introduces several numerical techniques and justifies the choice of FDTD modelling. An introduction to the theory of the FDTD technique and a description of the BEST software is also given. Simulations of systems where electromagnetic field distributions are known (or can be determined experimentally) allowed the direct comparison of simulation results with theoretical predictions. Chapters 3 and 4 consider various validation examples; a monopole radiator above ground plane and TEOl waveguide in chapter 3, experimental field determination in lossy dielectrics using the non-resonant perturbation method in chapter 4. In all cases considered, simulation and experiment agree within a reasonable magnitude of error. With the successful validation of its microwave modeling capabilities, the BEST program was then used to predict the weighting functions expected for practical radiometer antennas for microwave temperature measurement. Of primary importance are the variations of the effective coupling distance into the viewed material with dielectric changes, particularly those due to water content, and with measurement frequency. Knowledge of this behaviour is essential for estimating, at one extreme, relatively small but physiologically important temperature gradients within the human body, and at the other extreme, the large and rapidly varying temperature patterns induced during industrial processes. By measuring the microwave temperature at different microwave frequencies, it is possible to retrieve information on the temperature at varying depths within the material. To aid in the interpretation of these measurements, the BEST program was used to ascertain the form of the weighting function at two frequencies, 1.35 GHz and 3.2 GHz, for a specific dual - frequency antenna in a range of phantom materials. The phantom materials were composed of a mixture of water, protein and salts, with the intention being to simulate common biological materials. To consider foodstuffs a mashed potato phantom was used. Chapter 5 includes the design of this dual frequency antenna and its application to measuring the radiometric temperature of non-isothermal mashed potato mixtures. The specific manipulation of the potato mixture (through heating and cooling) to produce known temperature profiles (quasi-linear and quasi-quadratic) is also considered in this chapter. Further validation of the BEST weighting function determination is possible by comparison with these experimental temperature measurements. Chapter 6 initially covers the modelling of the dielectric properties of the mashed potato and protein / saline mixtures. In particular, a model of the variation of the dielectric constant and loss factor of the mashed potato material, covering a wide range of temperatures at 1.35GHz and 3.2GHz, is presented and shown to agree with published literature. The effects on the computed weighting function of variation of several key factors, including measurement frequency and material temperature, are then considered for both phantom types. Further, limitations in the computational modelling in terms of finite bounds and the modelling of layers are investigated. Finally, techniques for obtaining the physical temperature distribution from multi - frequency microwave readings are considered in chapter 7 and their applicability at two frequencies is discussed. By making use of the data collected from the dual - frequency antenna and simulated microwave temperatures, the various methods of temperature profile retrieval are compared.

This thesis describes experimental and theoretical investigations into new particle handling and separation methods and techniques. It makes a major contribution to the rapidly expanding field of cell separation technology. A novel dielectrophoretic cell separation system has been developed, which is capable of processing large sample volumes (~50mL) in a flow through system. Previously reported dielectrophoretic cell separator systems typically process sample volumes in the 100mL range. The electrode configuration developed for this work allows the isolation and concentration of single particle types from large sample volumes; a method which could be further developed into a new rare-cell separation technology. In addition, a new technique of particle fractionation was developed termed ‘Dielectrophoretic Chromatography’. A cell separation chip was designed and built using standard micro-fabrication techniques. Experimental work was undertaken to demonstrate the function and limitations of the device. Numerical modelling of the particle motion in the device is presented and compared with experimental work for a number of different particle types, applied voltages and fluid flow rates. The dielectrophoretic separation system comprises a microfluidic channel, of cross-section 100mm x 10mm and length 50mm, with two sets of interdigitated microelectrode arrays. The first set of arrays, with characteristic electrode size 40mm, called a focussing device, has electrodes patterned onto the top and bottom surfaces of the flow channel. The second electrode array, which is part of the same device, has an electrode array patterned only on the bottom of the channel. Two sizes of secondary electrode array were used 20mm and 40mm. AC voltages (from 1V to 10V peak) are applied to the microelectrode, with a frequency between 10kHz to 180MHz. A dielectrophoretic force is exerted on the particles as they flow along the channel. The first electrode array uses negative dielectrophoresis to focus the stream of particles entering the device into a narrow sheet (one particle diameter thick) midway between the upper and lower channel surfaces. The second electrode array, down stream from the first is separately controllable.

The work of this thesis involves the analysis of mechanical losses associated with coated test masses manufactured from fused silica, to determine the existence and level of excess loss associated with the coatings on these substrates. In particular, a major part of this analysis requires the calculation of the ratio of the strain energy stored in the dielectric coating to the strain energy stored in the substrate for a number of the resonant modes of the test mass. This is extremely difficult to calculate analytically for all but the simplest of modes. Finite element analysis had to be used to calculate the modeshapes of a number of resonant modes of the test masses. A piece of analytical software was specifically written to use the output of the finite element analysis package to calculate these energy ratios. The majority of this thesis is concerned with the methodology and usage of this software in the context of a number of analyses of different coated test masses. In addition, a technique was developed to allow experimental determination of modeshapes. This method could then be used to confirm or identify the nature of different modes. An initial investigation suggested that the loss associated with the coating s may prove significant for future generations of detectors such as Advanced LIGO. Further investigations suggested that the principle source of coating loss was due to the materials used in the coatings themselves. These investigations also suggested that for the coatings used, which were manufactured using tantalum pentoxide and silica, the tantalum pentoxide had a higher mechanical loss than the silica. Investigations into different coating materials have been initiated. Finally, preliminary tests on a coated sapphire mirror have been completed which give an upper limit to the loss of a coating on a sapphire mass. These tests required comprehensive changes to be made to the analytical energy ratio software to allow the analysis of anisotropic materials such as sapphire and to allow the output from different finite element packages to be used.

Multilayer magnetic thin films have attracted much attention both in the scientific community and the magnetic recording industry due to their commercial value. The work presented in this thesis is mainly a study of the magnetisation reversal mechanism of the free layer of the spin-valve. A spin-valve is a metallic multilayered structure that exhibits giant magnetoresistance. It consists of two soft ferromagnetic layers separated by a thin nonmagnetic layer. The magnetisation of one of the ferromagnetic layers is fixed by an adjacent antiferromagnetic layer by exchange bias coupling. The magnetisation direction of the other ferromagnetic layer can be rotated by applying a small external field. Hence, it is called the free layer. The free layer magnetisation reversal process for a range of spin-valves is presented in Chapter 3. The spin-valves discussed in this chapter have different magnetostriction coefficients, magnetocrystalline anisotropie and coercivities. Some are top spin-valves and some are bottom spin-valves. They also have different exchange biasing structures, which are the antiferromagnet and the synthetic antiferromagnet. Marked differences in free layer reversal mode are apparent for these spin-valves. Reversal could be by simple magnetisation rotation or by rotation combined with complex processes. However, experimental results showed that a simple reversal process was often associated with films with low magnetostriction and magnetocrystalline anisotropy. The texture of the film was found to have no significant effect on the observed free layer reversal mechanism. The effect on the free layer reversal process of replacing the antiferromagnet with a synthetic antiferromagnet is discussed in Chapter 4. Three bottom spin-valves with different synthetic antiferromagnetic structures were studied. The experimental results showed no significant difference in free layer reversal process in these spin-valves. Domain structures were studied for a series of bottom spin-valves annealed in different magnetic fields. Magnetic imaging showed a significant improvement in films annealed at 20 000 Oe. No difference in magnetic domain structures for films annealed in 250 Oe and 10 000 Oe was evident.