CM Murchison : nebular formation of fine-grained chondrule rims followed by impact processing on the CM parent body

We examine the primitive carbonaceous chondrite, CM Murchison, to infer details concerning its formation and subsequent processing on the CM parent body. We use X-ray computed tomography (XCT) to measure the 3D morphology and spatial relationship of fine-grained rims (FGRs) of Type I chondrules and find that the relationship between FGR volume and interior core radius is well described by a power law function as proposed for FGR accretion in a turbulent nebula by Cuzzi (2004). We also find evidence that the rimmed chondrules were slightly larger than Kolmogorov-stopping-time nebular particles. Evidence against parent body FGR formation includes a positive correlation between rim thickness and chondrule size and no correlation between interior chondrule roughness (used as a proxy for degree of aqueous alteration) and FGR volume. We find that the chondrules are foliated and that the FGRs are compressed in the direction of maximum stress, resulting in rims that are consistently thicker in the plane of foliation. After accretion to the CM parent body, the material within Murchison experienced brittle deformation, porosity loss, and aqueous alteration. XCT reveals that partially altered chondrules define a prominent foliation and weak lineation. The presence of a lineation and evidence for a component of rotational, noncoaxial shear suggest that the deformation was caused by impact. Olivine optical extinction indicates that the sample is classified as shock stage S1 and electron microscopy reveals that plastic deformation was minimal and that brittle deformation was the dominant microstructural strain-accommodating mechanism. Evidence such as serpentine veins parallel to the foliation fabric and crosscutting alteration veins strongly suggest that some aqueous alteration post-dated or was contemporaneous with the deformation and that multiple episodes of fracturing and mineralization occurred. Finally, using the deformed shape of the chondrules we estimate the strain and infer that the original bulk porosity of Murchison before deformation was 32.2 – 53.4%. Our findings suggest that significant porosity loss, deformation, and compaction from impact can occur on chondrite parent bodies whose samples record only a low level of shock, and that significant chondrule deformation can result from brittle processes and does not require plastic deformation of grains.Geological Science

The Mineralogy And Chemistry Of Micrometeorites

Prior to their retrieval from low Earth orbit (LEO), the individual solar cells that make up the 'V2' solar array panel from the Huhble Space Telescope (HST) were prone to hypervelocity (>5 km/s ) impact damage from micrometeoroids and space debris. The analysis of such passive collector surfaces allows sampling of micrometeoroids that have not undergone any terrestrial atmospheric alteration and better defines the population of space debris particles below the 1mm size range. Herein a new approach has been taken to try and identify the nature and origin of impact derived residues generated in the individual solar cells from the HST. A total of 25 solar cells were selected on the basis that they contained impact craters (100-1000μm diameter) rather than larger impact holes (1-3mm diameter), as preliminary studies indicated that they were more likely to retain impact residues. These were subsequently analysed using digitised hack-scattered electron imaging, coupled with digitised x-ray elemental mapping and micro-spot analysis to locate, identify and classify the residues. 29 impact craters were located on solar cells. In the analysis of the residues; 3 were identified residues as space debris in origin, 6 unclassified and 20 as micrometeoroid. The space debris derived residues were identified as remnants of a paint fragment, a stainless steel particle and a fragment of a printed circuit board. The micrometeoroid derived residues were sub-classified in terms of mineral chemistry, with apparent mafic- and phyllo- silicates being the dominant components, with minor iron-nickel metal and iron sulfides, suggesting a broadly chondritic origin. Fe-Ni rich residue was also identified that would appear to belong to a group of non-chondritic particles previously unrecognised. Possible refractory or Ca/Al rich inclusions from a primitive micrometeoroid were also observed as near intact Ca-rich fragments, the textures of the individual grains suggested that they were not merely terrestrial contamination. Laboratory impact studies, using a light-gas-gun to accelerate small fragments (125- 250μm) of known meteorite mineralogies up to 5km/s, and then impact them into solar cells have generated a suite of residues that are analogues of those observed from LEO studies. The silicate minerals generated residues that were intimately associated with the host melt glass. Metallic sulfides and metals generated surface and sub-surface immiscible droplets. Several craters also contained near-intact fragments of minerals. Overall. despite the small sample set examined. the observed dominance of micrometeoroid to space debris residue chemistry (correlating to particle size range of 8-80μm) corresponds well to the accepted flux models

On the growth of zinc oxide nanowires towards photoelectrochemical applications

Zinc oxide is regarded as an attractive semiconductor alternative to the most commonly used silicon and GaAs owing to its abundancy, thermodynamic stability and the large variety of morphologies it can be grown into. Among these morphologies, nanowires (NWs) have gathered vast attention as an ideal research platform for new and enhanced functionalities of ZnO. One of these functionalities is the integration of ZnO into the renewable production of hydrogen from water splitting. In this thesis, the growth of ZnO NWs, its doping and surface functionalization are studied with the aim of developing highly efficient photoelectrochemical (PEC) water splitting photoanodes. Before delving in the functional application, a growth study of the ZnO NWs was necessary to understand the factors that control this growth. For this, a seed mediated chemical bath deposition (CBD) approached was explored in detail and adopted. Control over NW growth was obtained by tuning the seed layer deposition with two different techniques (atomic layer deposition and sol-gel processing) and by controlling the CBD parameters. This study demonstrated that NW diameter, length, growth orientation and crystallinity can be controlled by this approach. To modulate the optoelectronic properties, ZnO NWs were doped with two different transition metals, copper and cobalt. A detailed study of the optoelectronic properties of these doped-ZnO NWs revealed that the introduction of cobalt into the ZnO lattice considerably improved the optoelectronic properties of ZnO. This enhancement was induced by the introduction of traps states in the bandgap of ZnO prompted by the interaction between the sp orbitals of ZnO and the d orbitals of Co. In particular, a 1% nominal doping yielded the most promising results of this study. Further improvement of the ZnO properties towards PEC water splitting was achieved by functionalizing the surface of the NWs with iridium and a metal-organic framework the zeolitic imidazolate framework-8 (ZIF-8). The successful integration was demonstration by electron microscopic analysis that showed the control of this conformal surface functionalization. The integration of Co-doping and ZIF-8 functionalization resulted in a large enhancement of the PEC performance of the ZnO NWs, doubling the photogenerated current and the stability over time while also increasing the incident photon-to-current efficiency from 11% for ZnO NWs to 75% in the blue and ultraviolet region for ZnO:Co@ZIF-8 core-shell NWs

AUTOMATED FEATURE EXTRACTION AND CONTENT-BASED RETRIEVAL OFPATHOLOGY MICROSCOPIC IMAGES USING K-MEANS CLUSTERING AND CODE RUN-LENGTH PROBABILITY DISTRIBUTION

The dissertation starts with an extensive literature survey on the current issues in content-based image retrieval (CBIR) research, the state-of-the-art theories, methodologies, and implementations, covering topics such as general information retrieval theories, imaging, image feature identification and extraction, feature indexing and multimedia database search, user-system interaction, relevance feedback, and performance evaluation. A general CBIR framework has been proposed with three layers: image document space, feature space, and concept space. The framework emphasizes that while the projection from the image document space to the feature space is algorithmic and unrestricted, the connection between the feature space and the concept space is based on statistics instead of semantics. The scheme favors image features that do not rely on excessive assumptions about image contentAs an attempt to design a new CBIR methodology following the above framework, k-means clustering color quantization is applied to pathology microscopic images, followed by code run-length probability distribution feature extraction. Kulback-Liebler divergence is used as distance measure for feature comparison. For content-based retrieval, the distance between two images is defined as a function of all individual features. The process is highly automated and the system is capable of working effectively across different tissues without human interference. Possible improvements and future directions have been discussed

Structural analysis of molecular nanostructures and thin films

Phthalocyanines (Pcs) form crystals whose structure and morphology depend on the growth conditions, leading to changes in the physical properties which are still little understood. Pc thin films and nanostructures have already been exploited in optoelectronic applications and could form the basis of spintronic devices but little or contradictory structural information is available because they are challenging systems to study. Hence the precise determination of the molecular order in these systems is of considerable interest both from a fundamental and technological point of view but requires a combination of complementary techniques. Crystalline powders of α-copper phthalocyanine (CuPc), α-metal-free phthalocyanine (H2Pc) and their mixtures are studied using powder X-ray diffraction (XRD) and found to be isomorphous and adopt a triclinic structure first proposed for α-CuPc (Hoshino et al., 2003). This information is used to study highly textured crystalline α-Pc thin films. The texture reduces the available crystallographic information but allows for the manipulation of the anisotropic physical properties. The Pc molecular plane lies 82±11° to the substrate when deposited on a weakly interacting substrate but at 7 or 9±5° when templated by a layer of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). Such an interpretation is different to all those previously given. The change in the texture is confirmed by high resolution transmission electron microscopy (HRTEM) of ultramicrotomed cross-sections of the films. The optimum TEM operating conditions were first determined on sections of CuPc single crystals which demonstrated an information limit of ~5Å with HRTEM. The technique was then applied to the films and the morphology, crystallinity and texturing of the layers is largely retained by the sectioning process. With further refinements it is hoped that this technique could be used to study the properties of interfaces and individual domains in multilayers and blends of organic thin films. Lastly the crystal structure of a new CuPc phase designated as η which forms nanowires as thin as 10nm and shows enhanced absorption in the infra-red (IR) is proposed. XRD, transmission electron diffraction (TED) and lattice potential energy (LPE) minimisation were used to determine the crystal structure: monoclinic P21/a, Z = 2, a = 24.8±0.2Å, b = 3.77±0.02Å, c = 13.2±0.1Å and β = 106±1°. The LPE minimisation was validated by correctly predicting the atomic coordinates of β-CuPc to within 0.05Å

Machine vision techniques for inspection of dry-fibre composite preforms in the aerospace industry

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents the results of a three year investigation into machine vision techniques for in-process automated inspection of dry-fibre composite preforms. Efficient texture analysis based techniques have been developed, tested, and implemented in a prototype robotic assembly cell. Industrial constraints have been considered in the development of all the algorithms described. A single channel texture analysis model is described which can successfully segment images containing only a few textures. The model is based on convolution of the image with small kernels optimised for the task, and is elegant in the sense that it is computationally simple and easily realisable in low cost hardware. A new convolution kernel optimisation algorithm is described. It is demonstrated that convolution kernels can also be optimised to perform as edge operators in simple textured images. A novel boundary refinement algorithm is described which reduces the inspection errors inherent in texture based boundary estimates. The algorithm takes the form of a local search, using the texture estimate as a guiding template, and selects edge points by maximising a merit function. Optimum parameters for the merit function are obtained using multiple training images in conjunction with simple function optimisation algorithms.This study is funded by the Engineering and Physical Sciences Research Council (EPSRC) and Dowty Aerospace Propellers Ltd