Optical tweezers have become an invaluable tool for measuring and exerting forces in the pico-Newton regime. Force measurements have in the past concentrated on using only one trapped particle as a probe, partly due to the difficulties in tracking more than one par- ticle at high enough frame rate. Recent advances in video camera technology allow the collection of images at several kHz. However, there has been little use of high-speed cameras in optical tweezers, partly due to data management problems and affordability. This the- sis presents seven experiments carried out during my PhD involving the use of several different high-speed cameras. Chapter 3 presents the use of a CMOS high-speed camera with in- tegrated particle tracking built by Durham Smart Imaging. The camera was used in a Shack-Hartmann sensor setup to determine rapidly and non-ambiguously the sign and magnitude of the orbital angular momentum of a helically-phased beam light beam, as an alternative to interferometric techniques. Chapter 4 presents a di- rect comparison of a CCD high-speed video camera with a quadrant photodiode to track particle position. Particle tracking was possible at high enough accuracy and bandwidth to allow convenient trap calibration by thermal analysis. Chapter 5 reports an investigation of the resulting change in trap stiffness during the update of trap positions in holographic optical tweezers. Chapter 6 presents the re- sults from using a high-speed camera to successfully track multiple particles in a microfluidic channel to measure the viscosity at sev- eral points simultaneously. The last three chapters investigate the hydrodynamic interactions between trapped particles under different conditions and comparisons were made with theory.

The ^(12)C([gamma],pp) reaction has been studied in the photon energy range E_=200-450MeV at the Mainz Microtron, MAMI. The linearly polarised photon beam was produced via the coherent bremsstrahlung technique with a diamond radiator and tagged with the Glasgow Tagging Spectrometer. The beam was incident on a ^(12)C target and the reaction products were detected in the 4pi Crystal Ball detector. The experimental study examines the photon asymmetry Sigma over a wider photon energy range than previous measurements and presents the first measurement of the angular dependence of Sigma. The photon asymmetry has a negative magnitude for missing energies Em<70MeV where direct emission of nucleon pairs is expected. A strong peak at low Em is observed in Sigma for photon energies above and below Delta resonance energies. The asymmetry is studied in two missing energy regions Em<40MeV and E_m=40-70MeV where direct knockout from (1p)(1p) and (1s)(1p) shells is expected. For both missing energy regions the photon energy dependence of Sigma is rather flat, and the magnitude of Sigma([gamma],pp) generally exceeds Sigma([gamma],pn) for photon energies below 300MeV. Similar values are observed for photon energies less than 300MeV$. At low Em and photon energies below 300MeV, the results suggest that different mechanisms contribute to ^(12)C([gamma],pp) and ^(12)C([gamma],pn) reactions. The similarity in Sigma above photon energies of 300MeV suggests that both channels are dominated by contributions from isobaric currents. A strong angular dependence of Sigma is presented which follows a trend remarkably similar to deuteron photodisintegration. Theoretical calculations using an unfactorised distorted wave treatment of direct two-nucleon emission do not agree with the magnitude of the photon asymmetry. For Em above 100MeV and photon energy > 300MeV, Sigma has a substantially negative value which is attributed to two-step reactions following initial quasifree pion production.

Imagine a thin sheet that performs optical illusions on the scene behind it. For example, a window that appears to reverse depth and to image objects in front of the sheet, or alternatively swimming goggles that cancel the refraction of surrounding water. This thesis will explore how such sheets may be realized. With the refinement of optical fabrication technologies, it is now possible to mass-produce miniaturized optical components. Repeating them over the surface of a sheet, their combined effect may realize optical effects from the structure, rather than the substance, of the sheet. Specifically, such components may realize arbitrary ray-direction mappings at each point on the sheet. Here such mappings, metarefractions, are explored from a range of perspectives. This thesis will explore the inception, theoretical development and ultimately the experimental realization of metarefraction. At its core, this work is primarily mathematical in nature but draws upon both experimental and computational techniques in order to test and visualize the concepts that will be discussed. Examples of such ray-direction mappings will be explored as will their ray- and wave-optical implications. This thesis is structured as follows: Initially, the definition of metarefraction, along with some existing examples, is presented. Then, ray mappings are related to negative refraction, a subject that metarefraction has a surprising number of parallels to. New forms of metarefraction are then introduced, before being incorporated into imaging systems. Later, ray-optical transformations, such as metarefraction, are shown to be limited by implicit wave-optical restrictions. In some cases, these vastly reduce the number of light fields that may be exactly transformed. After this, the most general possible metarefraction is sought, and a simple case is realized experimentally. Further restrictions are then determined, before finishing with a discussion and summary, and by considering possible directions that future work could develop in.

Non-Relativistic QCD (henceforth NRQCD) is a non-relativistic effective theory that models the strong interaction. We use this formulation to perform lattice simulations of the bound states of b quarks, known as the Upsilon spectrum. These simulations are performed on a range of gauge ensembles provided by the MILC collaboration that include three flavours of quark content - one at the approximate mass of the strange quark, and two degenerate flavours that range from about a half to a tenth of the mass of the strange quark. We implement a random wall algorithm in the creation of our b quark propagators, and develop a technique to combine the random wall with smearing functions, which are used to assist in picking out the relevant quantum numbers in the the resulting meson correlator. This is the first time these techniques have been used in this manner. We employ a Bayesian fitting procedure to extract energies and amplitudes from our simulated correlators. By using the 2S−1S Upsilon splitting on each configuration, and matching to experimental results, we are able to extract the lattice spacings for each ensemble from which we determine the heavy quark potential scale parameter r1. In concert with results from our collaborators, we outline the procedure for combining multiple determinations of r1, and present the collaborative result. We then use this parameter in a determination of the strong coupling constant αs in the MS scheme. We investigate the dispersion relation of the NRQCD action, and note some undesirable features that we are able to resolve with the precision attainable using the random wall. We look at a number of ways to address these issues, including non-perturbative and perturbative tuning of coefficients. Using the perturbative coefficients, we then proceed to calculate heavy-heavy currents, which are perturbatively matched to the continuum, and allow us to give results for the Upsilon leptonic width.

This thesis presents the first, preliminary, measurements of the Σ and G polarisation observables from strangeness photoproduction on a frozen spin polarised target, for the reactions γp→K⁺Λ and γp→K⁺Σ⁰. The data were collected at the Thomas Jefferson National Accelerator Facility using the CLAS detector in Experimental Hall B in conjunction with the FROST longitudinally polarised frozen spin target and a linearly polarised photon beam in the energy range W = 1.66 to 2.32 GeV. The work forms part of a wider experimental program seeking to obtain experimental data on the excitation spectrum of the nucleon in order to better understand its structure via the measurement of polarisation observables, whose sensitivity to resonances makes them a desirable quantity to measure. By studying strangeness reactions, it may be possible to find "missing" baryon resonances, predicted by symmetric quark models but not observed in previous experiments, whose results are consistent with the di-quark model. It is thought these "missing" resonances remain undiscovered because they have different coupling strengths for different reaction channels, such as the strangeness reactions, whereas the current data is dominated by studies of πN reactions. Measurements of the photon asymmetry, Σ, have been made which agree with previous CLAS measurements, validating the use of the FROST polarised target for the measurement of other polarisation observables, such as the G beam-target double observable. The G observable was measured on the FROST target via two techniques; from beam asymmetry measurements for the two available states of target polarisation, and a novel double asymmetry method intended to combine all the available polarised data. Some inconsistencies between the G measurements for each state of target polarisation are observed, particularly at forward angles, and are much greater once dilution effects from the target material are accounted for. As well as these dilution effects, the double asymmetry technique is also limited by insufficient constraint of the associated parameters from the limited data available on the reactions studied. For K⁺Λ, the results are compared to the Kaon-MAID isobaric model calculations, both with and without the inclusion of the missing D₁₃ resonance. Both calculations are inconclusive when compared with the data, although at higher energies the calculation without the D₁₃ state better matches the trend of the results. For K⁺Σ, the model prediction, which does not include any missing states, shows agreement with the trend of the data for some of the energy bins. In light of this new data, refitting of the models should be undertaken, as the next step in the theoretical interpretation of these results. These measurements provide new information to the world dataset of polarisation observables, and with further analysis of the associated systematics of beam polarisation and dilution, the data will provide new insights into the process of strangeness photoproduction.

The Large Hadron Collider beauty (LHCb) experiment at the Large Hadron Collider (CERN), is the next generation B physics experiment designed to precisely constrain the Cabibbo-Kobayashi-Maskawa (CKM) matrix measurements with unprecedented accuracy, as well as search for new physics. The success of the LHCb experiment relies upon excellent particle identification. The central particle identification detectors for the LHCb experiment are the Ring Imaging Cherenkov (RICH) detectors which are reliant upon their optics being well aligned. The optical specifications for the second RICH detector (RICH2) are for the mirrors to be aligned to within 0.1 mrad so as not to degrade the inherent 0.7 mrad resolution of the detector. As the mirrors move out of alignment over time, the performance of the RICH will deteriorate, unless corrected. This thesis describes the design and characterisation of the Laser Mirror Alignment Monitoring System and its image analysis software for selected mirrors of RICH2. This thesis also describes the results of a unique method of combining data from the Laser Mirror Alignment Monitoring System and Tracking system, to recover the positions of all mirror segments in the RICH2 detector. The laser alignment monitoring system resolution has been measured to be 0.013 mrad for both θy and θx rotations, with a long term stability of 0.014 mrad in θ­­­­y and 0.006 mrad in θx. The resolution of the final mirror alignment procedure using data tracks is 0.18 mrad for θy mirror rotations and 0.12 mrad for θx mirror rotations.

Hybrid semiconductor pixel detector technology is presented in this thesis as an alternative to current imaging systems in medical imaging and synchrotron radiation applications. The technology has been developed from research performed in High Energy Physics, in particular, for the ATLAS experiment at the LHC, planned for 2005. This thesis describes work done by the author on behalf of the MEDIPIX project, a collaboration between 13 international institutions for the development of hybrid pixel detectors for non-HEP applications. Chapter 1 describes the motivation for these detectors, the origin of the technology, and the current state of the art in imaging devices. A description of the requirements of medical imaging on X-ray sensors is described, and the properties of film and CCDs are discussed. The work of the RD19 collaboration is introduced to show the evolution of these devices. Chapter 2 presents the basic semiconductor theory required to understand the operation of these detectors, and a section on image theory introduces the fundamental parameters which are necessary to define the quality of an imaging device. Chapter 3 presents measurements made by the author on a photon counting detector (PCD1) comprising a PCC1 (MEDIPIX1) readout chip bumpbonded to silicon and gallium arsenide pixel detectors. Tests on the seperate readout chip and the bump-bonded assembly are shown with comparisons between the performance of the two materials. Measurements of signal-tonoise ratio, detection efficiency and noise performance are presented, along with an MTF measurement made by the Freiburg group. The X-ray tube energy spectrum was calibrated by REGAM. The performance of the PCD in a powder diffraction experiment using a synchrotron radiation source is described in chapter 4. This chapter reports the first use of a true 2-D hybrid pixel detector in a synchrotron application, and a comparison with the existing scintillator based technology is made. The measurements made by the author have been presented at the 1st International Workshop on Radiation Imaging Detectors at Sundsvall, Sweden, June 1999. The PCD1 operates in single photon counting mode, which attempts to overcome the limitations of charge integrating devices such as CCDs. The pros and cons of the two detection methods are discussed in chapter 5, and a comparison was made of the PCD1 performance with the performance of a commercial dental X-ray sensor. The two detectors are compared in terms of contrast and signal-to-noise ratio for identical X-ray fluences. The results were presented at the 2nd International Workshop on Radiation Imaging Detectors, Freiburg, Germany, 2nd-6th July 2000. The author was involved in the conversion of the LabWindows MRS software to a LabView platform, which was presented in an MSc- thesis in the University of Glasgow by F. Doherty. All image processing, data manipulation and analysis code was written by the author.

The work presented in this thesis is a study of the magnetic properties of various magnetic force microscopy (MFM) tips using Lorentz electron microscopy and tomography. The implementation of tomography and differential phase contrast (DPC) microscopy allows the stray field distribution in the half space in front of MFM tips to be measured with a spatial resolution of <30 nm and a field resolution of <2 mT. This information will allow the development of better models for MFM imaging performance and, potentially, the quantification of MFM images.

Spatially representative sampling of both natural and anthropogenic deposits in the environment is limited by their inherent heterogenic distribution. This problem is compounded when trying to relate ground measurements which are spatially restricted to remote sensing observations which are not. This work examined these widely experienced problems in the context of the measurement of natural (K, U and Th) and anthropogenic ( 137Cs and ' 34Cs) radioactivity through the three techniques of soil sampling with laboratory based gamma ray spectrometry, in-situ gamma ray spectrometry, and airborne gamma ray spectrometry. These three methods were applied systematically to estimate the radioactivity across a tight geometry valley in Renfrewshire. Activity estimates from field based and airborne gamma spectrometry were compared with each other and with the results of high resolution gamma spectrometry of soil samples to examine the relationship between each method under variable topographic conditions. These results demonstrated that the distribution, and post depositional migration, of activity had important influences on all measurement techniques, and affected the ability to make comparisons between them. Further detailed studies were then conducted to examine these influences. The effects of variations in soil composition and characteristics on environmental gamma ray spectrometry were evaluated by calculation and experimental determination. Corrections to standard laboratory gamma spectrometric procedures were developed to improve systematic precisio:i. These investigations also reviewed soil sampling depth for direct effective comparison with in-situ gamma spectrometry. The effects of small scale sampling errors on activity estimates were demonstrated to have a quantifiable influence on the precision of activity estimation. Lateral variability of activity distribution of natural radioactivity and anthropogenic radioactivity deposited both from the atmosphere and from marine sources has been studied in detail at a number of sites. The extent of variability depends on the nature of activity, its deposition mode and local environmental characteristics. Spatial variability represents an important constraint on the interpretation of activity estimates derived from all methods examined, and on comparisons between them. Statistically representative sampling plans were developed and applied to enable spatial comparisons to be made between soil sample derived activity estimates and in-situ and remotely sensed observations. The influence of the vertical activity distribution on in-situ and airborne measurements has been recognised as an important variable affecting calibration. The use of the information from the scattered gamma ray spectrum to quantify and correct for source burial effects was examined in a series of modelling experiments. A relationship between 'Cs source burial and forward scattering was determined and subsequently applied to a salt marsh environment which showed pronounced subsurface maxima. A spectrally derived calibration correction coefficient was shown to account for variations in source burial across a single site. This provides a potential means for surmounting one of the principal limitations of in-situ gamma spectrometry. As a result of this work it has been possible to account for important environmental factors which affect gamma ray spectrometry in the laboratory, in the field and from aircraft. This has led to the development of sound methodology for comparison between sampling, field based and remote sensing techniques.

In the construction of naval vessels stealth is an important design feature. With recent advances in electromagnetic sensor technology the war time threat to shipping posed by electromagnetically triggered mines is becoming more significant and consequently the need to understand, predict and reduce the electromagnetic signature of ships is growing. There are a number of components to the electromagnetic field surrounding a ship, with each component originating from different physical processes. The work presented in this study is concerned with the magnetic signature resulting from the magnetisation of the ferromagnetic material of the ship, under the influence of the earth's magnetic field. The detection threat arising from this induced magnetic signature has been known for many years, and consequently, warships are generally fitted with degaussing coils which aim to generate a masking field to counteract this signature. In this work computational models are developed to enable the induced magnetic signature and the effects of degaussing coils to be studied. The models are intended to provide a tool set, to aid the electromagnetic signature analyst in ensuring that pre-production designs of a vessel lie within specified induced magnetic signature targets. Techniques presented where also allow the rapid calculation of currents in degaussing coils. This is necessary because the induced magnetisation of a vessel changes with orientation. Three models are presented within this work. The first model represents a ship as a simple geometric shape, a prolate spheroidal shell, of a given relative permeability. Analytical expressions are derived which characterise the magnetic perturbation to a previously uniform magnetic field, the earth's magnetic field, when the spheroid is placed within its influence. These results provide a quantitative insight into the shielding of large internal magnetic sources by the hull. This model is intended for use in preliminary design studies. A second model is described which is based on the finite element method. This is a numerical model which has the capability of accurately reproducing the relatively complex geometry of a ship and of including the effects of degaussing coils. For these reasons this model is intended for detailed quantitative studies of the induced magnetic signature. A method is described to calculate the optimal set of degaussing coil currents required to minimise the induced magnetic signature. The induced signature without and with degaussing is presented. For the successful application of the finite element method the generation of a mesh is of extreme importance. In this work a mesh generation procedure is described which permits meshes to be generated around a collection of planar surfaces. The relatively complex geometry of a ship can be easily specified as a number of planar surfaces and from this, the finite element mesh can be automatically generated. The automatic mesh generation detailed in this work eliminates an otherwise labour intensive step in the analysis procedure. These techniques are sufficiently powerful to allow meaningful calculations for real ships to be performed on desk-top computers of modest power. An example is presented which highlights the application of this model to a hypothetical ship structure. The third model detailed is specifically designed to study the induced magnetic signature of mine countermeasures vessels. Here the induced magnetic signature is no longer dominated by the gross structure of the ship, which is constructed from non-magnetic materials, but arises from the combined effect of the individual items of machinery onboard the craft.