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No description available.

No description available.

No description available.

No description available.

We investigate the application of computer vision techniques to rigid object recognition in Computed Tomography (CT) security scans of baggage items. This imagery is of poor resolution and is complex in nature: items of interest can be imaged in any orientation and copious amounts of clutter, noise and artefacts are prevalent. We begin with a novel 3D extension to the seminal SIFT keypoint descriptor that is evaluated through specific instance recognition in the volumetric data. We subsequently compare the performance of the SIFT descriptor against a selection of alternative descriptor methodologies. We demonstrate that the 3D SIFT descriptor is notably outperformed by simpler descriptors which appear to be more suited for use in noise and artefact-prone CT imagery. Rigid object class recognition in 3D volumetric baggage data has received little attention in prior work. We evaluate contrasting techniques between a traditional approach derived from interest point descriptors and a novel technique based on modelling of the primary components of the primate visual cortex. We initially demonstrate class recognition through the implementation of a codebook approach. A variety of aspects relating to codebook generation are investigated (codebook size, assignment method) using a range of feature descriptors. Recognition of a number of object classes is performed and results from this show that the choice of descriptor is a critical aspect. Finally, we present a unique extension to the established standard model of the visual cortex: a volumetric implementation. The visual cortex model comprises a hierarchical structure of alternating simple and complex operations that has demonstrated excellent class recognition results using 2D imagery. We derive 3D extensions to each layer in the hierarchy resulting in class recognition results that signficantly outperform those achieved using the earlier traditional codebook approach. Overall we present several novel solutions to object recognition within 3D CT security images that are supported by strong statistical results.

With recent advances in laser technology we have seen laser intensities reach the order of 10^22 W/cm2, with higher intensities anticipated in the near future. This thesis concerns a classical approach to the simulation of laser matter interactions for intensities above the relativistic threshold of 10^18 W/cm2. A pulsed plane wave model is used to simulate the laser fields. In particular this thesis aims to determine the effect of radiation reaction on relativistic interactions as well as proposing an effective method of vacuum laser acceleration from rest. We consider the equations of motion accounting for radiative effects and present their analytic plane wave solution. A novel numerical scheme to solve the equations of motion for arbitrary field configurations is presented. The method is manifestly covariant and exact for constant fields. Radiative reaction effects are explored using the numerical method and we find that the electron gains energy from the radiation field produced by its acceleration. Methods of vacuum laser acceleration are studied and we predict a significant acceleration using two co-propagating lasers where the frequency of the two lasers differ significantly. We also look at analytic and numerical solutions of the radiation spectrum, observing an increase in oscillations in the spectrum for larger intensities. We see more photons radiated when we include radiative terms in our calculations.

This thesis describes investigations into improvements in the field of automated people tracking using multi-modal infrared (IR) and visible image information. The research question posed is; “To what extent can infrared image information be used to improve visible light based human tracking systems?” Automated passive tracking of human subjects is an active research area which has been approached in many ways. Typical approaches include the segmentation of the foreground, the location of humans, model initialisation and subject tracking. Sensor reliability evaluation and fusion methods are also key research areas in multi-modal systems. Shifting illumination and shadows can cause issues with visible images when attempting to extract foreground regions. Images from thermal IR cameras, which use long-wavelength infrared (LWIR) sensors, demonstrate high invariance to illumination. It is shown that thermal IR images often provide superior foreground masks using pixel level statistical extraction techniques in many scenarios. Experiments are performed to determine if cues are present at the data level that may indicate the quality of the sensor as an input. Modality specific measures are proposed as possible indicators of sensor quality (determined by foreground extraction capability). A sensor and application specific method for scene evaluation is proposed, whereby sensor quality is measured at the pixel level. A neuro-fuzzy inference system is trained using the scene quality measures to assess a series of scenes and make a modality decision. Results show a high degree of accuracy in selecting the optimum modality in a number of separate environmental conditions. The use of colour to identify subjects post-occlusion is typical in tracking. Effectiveness is reduced as the subject count increases with a consequent increased likelihood of similarity between subjects. Experiments are proposed to determine whether a specific histogram parameter configuration, capable of discriminating between subjects in multiple environmental conditions, can be established. An exhaustive search approach for establishing an improved histogram configuration is undertaken using a novel evaluation metric, which assesses the separation of results from intra-subject and intersubject histogram comparisons. Multi-modal, multi-dimensional results show that a 2-D Hue and IR configuration provides greater discrimination than either visible or IR configurations. A tracking system is developed to demonstrate that the methods and configurations can be applied holistically in a real situation. The system is evaluated in a variety of scenarios using challenging subject data aimed at establishing the limits of the system’s capabilities. Through addressing the research question, contributions to the field have been made consisting of: demonstrating the use of a trained neuro-fuzzy inference system to evaluate modality attributes, and the establishment of a generalised multi-modal histogram-based similarity measure to assist in re-establishing subject identity postocclusion. The modular nature of these methods has been demonstrated by inclusion in a developed feature-rich tracking system.

Antimony doped Tin oxide (SnO2:Sb, or ATO) is of interest as an alternative to Indium Tin Oxide (ITO) for large area optoelectronic applications. There is a particular interest in the potential for solution based coatings based on nanoparticulate suspensions of SnO2:Sb. However, solution processed films typically require a high temperature (~700⁰C) annealing step to achieve the desired electrical and optical properties. This is disadvantageous for applications that would benefit from low cost, low temperature/flexible substrates. As an alternative to conventional high temperature annealing, excimer laser processing can provide highly localized energy dissipation, and is an attractive technique to functionalise coated materials. Therefore the work presented in this thesis investigates the use of excimer laser processing to optimise the electrical and optical properties of solution deposited SnO2:Sb thin films for use in electroluminescent display devices. Thin films of SnO2:Sb were deposited using dip coating, inkjet printing and the spin coating technique. By varying the numbers of spin coatings deposited, a series of samples were prepared on Eagle XG glass substrates with different thicknesses of SnO2:Sb (ranging from 0.2 μm to 1.4 μm). The initial sheet resistance, optical transmission and crystal structure of the deposited films was studied. The films were subsequently post processed using three different annealing techniques: (i) Laser Processing: samples were laser processed in air to optimise the sheet resistance and optical transmission. Excimer (KrF, 248 nm, 20 ns pulse) irradiation of between 1 and 1000 pulses was applied at fluences in the range 20-70 mJ/cm2. (ii) Thermal Annealing: samples were thermally annealed at temperatures in the range 100⁰C - 700⁰C in air. (iii) Combined Processing: samples were initially annealed in air at temperatures in the range 100⁰C - 400⁰C and then KrF laser processed with the optimum laser fluence (60 mJ/cm2) and number of laser pulses (1000). It has been found that grain boundary scattering limits the electron conduction when films were laser processed or low temperature thermal annealed and with higher temperature thermal annealing ionized impurity scattering dominates. The sheet resistance of the as-deposited films were in the MΩ range with the optical transmission was >85% (at 550 nm). Further to KrF laser processing, the sheet resistance of the SnO2:Sb films was reduced to around 20 kΩ/sq and the optical transmission remained >75%. The films that were thermally annealed at 700⁰C showed a resultant sheet resistance of around 120 Ω/sq, and the combined processed films showed a resultant sheet resistance of 700 Ω/sq, which facilitated use as transparent electrodes in electroluminescent device fabrication. TEM studies indicated grain growth associated with the post processing for all three techniques, and Hall effect measurement confirms improvement in carrier concentration (i.e. 2 x 1019 cm3 for KrF laser processed films and 2.8 x 1020 cm3 for thermally annealed films as compared to 1.8 x 1017 cm3 for as-deposited). Luminescent studies of Alternating Current Electroluminescent (ACEL) display devices fabricated with spin coated SnO2:Sb transparent electrodes showed that the combined processing of low temperature thermal annealing (400C) followed by laser treatment gives the same order of luminescence as high temperature (700C) processed devices. The results presented demonstrated that spin coating deposition followed by combined low temperature/photonic post processing offers the potential to use solution processed SnO2:Sb layers for low temperature, low cost transparent electrode applications.

This thesis investigates the measurement of spatial correlations of photon pairs generated through spontaneous parametric down-conversion with single-photon sensitive multi-pixel detectors. A custom designed and fabricated 8£1 fibre array detector for time to position multiplexing was characterised. This detector was then commissioned in an experiment measuring the spatial correlations of photon pairs in position, momentum and intermediate bases. The fibre array measured eight positions simultaneously with one Single-Photon Avalanche Diode, which led to an eight-fold increase in the data acquisition rate compared to traditional experiments, where a single SPAD was scanned across the detection plane. To capture all of the emitted light, an electron-multiplying CCD (EMCCD) camera was used. The spatial correlations were measured for the first time in momentumand position bases with a single-photon sensitive camera. Additionally, over 2500 spatial states were accessed,which, to date, is the highest number of accessed states, using the transverse positions of correlated photon pairs. The detected photon pairs were tested, if they fulfil the requirements of entanglement. The calculated variance product was 1 order of magnitude and almost three orders of magnitude below the classical limit of separability for the fibre array and the EMCCD camera respectively. Finally the image enhancement of using a correlated light source with a noise rejection algorithm was investigated experimentally and theoretically.