A graph-spectral approach to shape-from-shading

In this paper, we explore how graph-spectral methods can be used to develop a new shape-from-shading algorithm. We characterize the field of surface normals using a weight matrix whose elements are computed from the sectional curvature between different image locations and penalize large changes in surface normal direction. Modeling the blocks of the weight matrix as distinct surface patches, we use a graph seriation method to find a surface integration path that maximizes the sum of curvature-dependent weights and that can be used for the purposes of height reconstruction. To smooth the reconstructed surface, we fit quadrics to the height data for each patch. The smoothed surface normal directions are updated ensuring compliance with Lambert's law. The processes of height recovery and surface normal adjustment are interleaved and iterated until a stable surface is obtained. We provide results on synthetic and real-world imagery

Recovery of surface orientation from diffuse polarization

When unpolarized light is reflected from a smooth dielectric surface, it becomes partially polarized. This is due to the orientation of dipoles induced in the reflecting medium and applies to both specular and diffuse reflection. This paper is concerned with exploiting polarization by surface reflection, using images of smooth dielectric objects, to recover surface normals and, hence, height. This paper presents the underlying physics of polarization by reflection, starting with the Fresnel equations. These equations are used to interpret images taken with a linear polarizer and digital camera, revealing the shape of the objects. Experimental results are presented that illustrate that the technique is accurate near object limbs, as the theory predicts, with less precise, but still useful, results elsewhere. A detailed analysis of the accuracy of the technique for a variety of materials is presented. A method for estimating refractive indices using a laser and linear polarizer is also given

Shape-from-shading using the heat equation

This paper offers two new directions to shape-from-shading, namely the use of the heat equation to smooth the field of surface normals and the recovery of surface height using a low-dimensional embedding. Turning our attention to the first of these contributions, we pose the problem of surface normal recovery as that of solving the steady state heat equation subject to the hard constraint that Lambert's law is satisfied. We perform our analysis on a plane perpendicular to the light source direction, where the z component of the surface normal is equal to the normalized image brightness. The x - y or azimuthal component of the surface normal is found by computing the gradient of a scalar field that evolves with time subject to the heat equation. We solve the heat equation for the scalar potential and, hence, recover the azimuthal component of the surface normal from the average image brightness, making use of a simple finite difference method. The second contribution is to pose the problem of recovering the surface height function as that of embedding the field of surface normals on a manifold so as to preserve the pattern of surface height differences and the lattice footprint of the surface normals. We experiment with the resulting method on a variety of real-world image data, where it produces qualitatively good reconstructed surfaces

Micro- and nano-analyses of fracture-filling after flooding on-shore chalk with different IOR fluids

Master's thesis in Petroleum Geosciences EngineeringWater injection into the Ekofisk-reservoir was introduced in 1987 to enhance oil recovery (EOR) dissolution and precipitation by exposing chalk to various brines at reservoir conditions, which further increased deformation of chalk matrix. This deformation affected mechanical properties of the tested samples and is referred to as water weakening of chalk. This thesis has focused on identifying mineral changes and mapping the distribution of precipitated mineral during flooding of samples which have an artificial fracture and will compare hollow cylinder to intact chalk cores. Methods used to achieve a mineralogic map are: • Optical Light Microscopy (OLM) • Light microscopy (LM) • X-ray diffraction (XRD) • Scanning Electron Microscopy (SEM) • Focused Ion Beam (FIB) sample for Transmission Electron Microscopy (TEM) • Mineral Liberation Analyzer (MLA) All cores tested, either intact or hollow and representing all combinations of brine injected, distributed an increased abundance of chlorite. The most sensational observation was the precipitation of magnesite inside the core of the hollow cylinder flooded by MgCl2, and the distinct boundary that this distribution created. Ilmenite was also observed at the same location, while calcite was limited to the matrix itself. Pyrite was not observed in the reference rock, but this was however identified in cores flooded by both MgCl2 and SSW. One non-fractured core injected by SSW experienced clogging after 20 days of flooding. The two samples from this core provided similar composition as the reference rock, hence the reduction of permeability was related to the composition of the brine (SSW) as the comparable core injected with MgCl2 experienced a more dramatic calcite dissolution. This core that clogged also experienced a rapid creep phase and imply that pores could have been clogged solely due to the compression and dissolution of grain to grain contacts during flooding. These results, among others, allows an interpretation that dissolution of original grains and distribution of precipitated minerals is dependent on a variety of processes. The type of brine injected, distribution of porous network and the distance from the inlet are essential parameter which affect the precipitation in the hollow core, so verified in this study. The reactivity and the content of silicate and clay minerals may also influence the process

Quantitative analysis of the links between forest structure and land surface albedo on a global scale

Forests are critical in regulating climate by altering the Earth's surface albedo. Therefore, there is an urgent need to enhance our knowledge about the effects of forest structure on albedo. Here, we present a global assessment of the links between forest structure and albedo at a 1-km spatial resolution using generalized additive models (GAMs). We used remotely sensed data to obtain variables representing forest structure, including forest density, leaf area index, and tree cover, during the peak growing season in 2005 with pure forest pixels that cover similar to 7% of the Earth's surface. Furthermore, we estimated black-sky albedo at a solar zenith angle of 38 degrees using the most recent collection of the moderate resolution imaging spectroradiometer (MODIS; version 6) at shortwave, near-infrared, and visible spectral regions. In addition, for the first time, we mapped the magnitude of the relationship between forest structure and albedo at each pixel with a 0.5-degree spatial resolution. Our results suggested that forest structure may modulate albedo in most of the sub-biomes. The response of shortwave albedo was always positive to the leaf area index and negative to the tree cover (except for deciduous broadleaf forests in mediterranean and temperate regions), while the response to forest density varied across space in 2005. The spatial map affirmed that the links between forest structure and albedo vary over geographical locations. In sum, our study emphasized the importance of forest structure in the surface albedo regulation. This paper provides the first spatially explicit evidence of the magnitude of relationships between forest structure and albedo on a global scale.Peer reviewe

Surface Enhanced Spatially Offset Raman Spectroscopy for the Detection of Breast Cancer Using Turbid Optical Phantoms

Breast cancer is a prevalent disease within today’s modern society, affecting 1 in 8 women and 1 in 870 men within a lifetime. With the introduction of mammographic breast screening in 1987 and marked improvements to targeted therapies, mortality rates declined, highlighting the need for early diagnosis and tailored treatment to halt disease progression in its foremost stages. Histology assessed biopsies, alongside initial two-view mammographic imaging, are paired as the current diagnostic “gold standard”. The need to incorporate several techniques, applying an “all-angles” approach to diagnostics, provides an effective, streamlined diagnostic pathway, reducing patient wait times between testing and results – crucial in preventing disease progression. Optical spectroscopic techniques for the characterisation of biomolecular compounds and structures present within tissue are fast becoming the biomedical analysis tools of choice, coming to the forefront of clinical applications. Raman spectroscopy is one such technique providing highly chemically specific results, in a non-ionising and non-invasive way. When used in conjunction with metal nanoparticle probes, the inherently weak Raman signals of the biomolecules surrounding the nanoparticle surface undergo extensive levels of enhancement – an eponymous technique, Surface Enhanced Raman Scattering (SERS). This thesis is split into two principal areas of study. The first explores extrinsic SERS nanoparticles at depth within optical phantoms, “imaged” in a Transmission orientation, mimicking the composition of the breast within a cranio-caudal mammographic imaging position. The second concerns the micro-Raman quantification of gold nanoparticles, functionalised to a biocompatible level for the active targeting of hydroxyapatite – a calcium apatite form which, when dominant within breast microcalcifications, act as a biomarker for malignancy. Key aspects drawn from the results include a greater understanding of Raman reporter gold nanoparticles at depth, and how the absorption profile of the sample material affects the garnered intensity profile. The synthesis of a novel nanoparticle probe was also founded, with promising future applications in terms of targeting and theranostic capabilities. Furthermore, a protocol into the implementation of an automated mapping system within an open optical set up is given, detailing the software, hardware and electrical installation requirements. The advantages of Raman spectroscopy integration within current diagnostic practices are highlighted, with limitations such as nanoparticle biocompatibility issues, the inherent optical properties of biological tissues, and system conditions touched upon.Cobalt Healt