Aging vs crystallisation dynamics in hyperquenched glasses and a resolution of the water Tg controversy

The possibility of observing a glass transition in water before crystallisation occurs has been debated vigorously but inconclusively over five decades [1,2]. For two decades a glass transition at 136K [2,3] was accepted but this transition has perplexing qualities [4]. Recently it has been argued[2,5],that this assignment must be wrong. The re-assignment of Tg to temperatures above the 150K crystallisation was vigorously contested [6]. Here we use detailed anneal-and-scan studies of a hyperquenched inorganic glass, which does not crystallize on heating, to interpret the perplexing aspects of the 136K water phenomenon. We show that it is indeed linked to a glass transition, though only via a cross-over phenomenon. The thermal history that gives the same behaviour ("shadow" glass transition) in the inorganic glass is linked by crossover to a "normal" glass transition 23% higher in temperature. Thus a Tg is indeed unobservable for water, while the vitreous nature of hyperquenched glassy water is strongly supported. The shadow Tg is reproducible in the inorganic glass as it is in H2O. The observed aging dynamics are very relevant to current glass theory, particularly to dynamical heterogeneity which is seen to have an energy manifestation.Comment: 23 pages, 4 figure

Topological descriptors for 3D surface analysis

We investigate topological descriptors for 3D surface analysis, i.e. the classification of surfaces according to their geometric fine structure. On a dataset of high-resolution 3D surface reconstructions we compute persistence diagrams for a 2D cubical filtration. In the next step we investigate different topological descriptors and measure their ability to discriminate structurally different 3D surface patches. We evaluate their sensitivity to different parameters and compare the performance of the resulting topological descriptors to alternative (non-topological) descriptors. We present a comprehensive evaluation that shows that topological descriptors are (i) robust, (ii) yield state-of-the-art performance for the task of 3D surface analysis and (iii) improve classification performance when combined with non-topological descriptors.Comment: 12 pages, 3 figures, CTIC 201

Digital Color Imaging

This paper surveys current technology and research in the area of digital color imaging. In order to establish the background and lay down terminology, fundamental concepts of color perception and measurement are first presented us-ing vector-space notation and terminology. Present-day color recording and reproduction systems are reviewed along with the common mathematical models used for representing these devices. Algorithms for processing color images for display and communication are surveyed, and a forecast of research trends is attempted. An extensive bibliography is provided

Spaceprint: a Mobility-based Fingerprinting Scheme for Public Spaces

In this paper, we address the problem of how automated situation-awareness can be achieved by learning real-world situations from ubiquitously generated mobility data. Without semantic input about the time and space where situations take place, this turns out to be a fundamental challenging problem. Uncertainties also introduce technical challenges when data is generated in irregular time intervals, being mixed with noise, and errors. Purely relying on temporal patterns observable in mobility data, in this paper, we propose Spaceprint, a fully automated algorithm for finding the repetitive pattern of similar situations in spaces. We evaluate this technique by showing how the latent variables describing the category, and the actual identity of a space can be discovered from the extracted situation patterns. Doing so, we use different real-world mobility datasets with data about the presence of mobile entities in a variety of spaces. We also evaluate the performance of this technique by showing its robustness against uncertainties

Weighted frames of exponentials and stable recovery of multidimensional functions from nonuniform Fourier samples

In this paper, we consider the problem of recovering a compactly supported multivariate function from a collection of pointwise samples of its Fourier transform taken nonuniformly. We do this by using the concept of weighted Fourier frames. A seminal result of Beurling shows that sample points give rise to a classical Fourier frame provided they are relatively separated and of sufficient density. However, this result does not allow for arbitrary clustering of sample points, as is often the case in practice. Whilst keeping the density condition sharp and dimension independent, our first result removes the separation condition and shows that density alone suffices. However, this result does not lead to estimates for the frame bounds. A known result of Groechenig provides explicit estimates, but only subject to a density condition that deteriorates linearly with dimension. In our second result we improve these bounds by reducing the dimension dependence. In particular, we provide explicit frame bounds which are dimensionless for functions having compact support contained in a sphere. Next, we demonstrate how our two main results give new insight into a reconstruction algorithm---based on the existing generalized sampling framework---that allows for stable and quasi-optimal reconstruction in any particular basis from a finite collection of samples. Finally, we construct sufficiently dense sampling schemes that are often used in practice---jittered, radial and spiral sampling schemes---and provide several examples illustrating the effectiveness of our approach when tested on these schemes

Multidimensional en-face OCT imaging of the retina.

Fast T-scanning (transverse scanning, en-face) was used to build B-scan or C-scan optical coherence tomography (OCT) images of the retina. Several unique signature patterns of en-face (coronal) are reviewed in conjunction with associated confocal images of the fundus and B-scan OCT images. Benefits in combining T-scan OCT with confocal imaging to generate pairs of OCT and confocal images similar to those generated by scanning laser ophthalmoscopy (SLO) are discussed in comparison with the spectral OCT systems. The multichannel potential of the OCT/SLO system is demonstrated with the addition of a third hardware channel which acquires and generates indocyanine green (ICG) fluorescence images. The OCT, confocal SLO and ICG fluorescence images are simultaneously presented in a two or a three screen format. A fourth channel which displays a live mix of frames of the ICG sequence superimposed on the corresponding coronal OCT slices for immediate multidimensional comparison, is also included. OSA ISP software is employed to illustrate the synergy between the simultaneously provided perspectives. This synergy promotes interpretation of information by enhancing diagnostic comparisons and facilitates internal correction of movement artifacts within C-scan and B-scan OCT images using information provided by the SLO channel

Probing the Unseen Depths of the Hepatic Microarchitecture via Multimodal Microscopy

Multimodal microscopy combines the advantages and strengths of different imaging modalities in order to holistically characterise the organisation of biological organisms and their comprising constituents under healthy and diseased conditions, down to the spatial resolution required to understand the morphology and function of such structures. Given the profound advantages conferred by such an approach, this work broadly aimed to develop and exploit various multimodal and multi-dimensional imaging modalities in a complimentary, combined and/or correlative manner – namely, three-dimensional scanning electron microscopy, transmission electron tomography, bright-field light microscopy, confocal laser scanning microscopy and X-ray micro-computed tomography – in order to characterise and collect new information on the normal and pathological microarchitecture of rodent and human liver tissue in 3-D under various experimental conditions. The data reported in this work includes a comparative analysis of a variety of sample preparation protocols applied to rat liver tissue to determine the suitability of such protocols for the application of serial block-face scanning electron microscopy (SBF-SEM). Next, 3-D modelling and morphometric analysis (utilising the premier SBF-SEM protocol) was performed in order to visualise and quantify key features of the hepatic microarchitecture. We further outline a large-volume correlative light and electron microscopy approach utilising selective molecular probes for confocal laser scanning microscopy (actin, lipids and nuclei), combined with the 3-D ultrastructure of the same structures of interest, as revealed by SBF-SEM (Chapter 2). Development of a straightforward combinatorial sample preparation approach, followed by a swift multimodal imaging approach – combining X-ray micro-computed tomography, bright-field light microscopy and serial section scanning electron microscopy – facilitated the cross correlation of structure-function information on the same sample across diverse length scales (Chapter 3). Next, we outline a novel “silver filler pre-embedding approach” in order to reduce artefactual charging, minimise dataset acquisition time and improve resolution and contrast in rat liver tissue prepared for SBF-SEM (Chapter 4). Next, we employ a complementary imaging approach involving serial section scanning electron microscopy and transmission electron tomography in order to comparatively analyse the structure and morphometric parameters of thousands of normal- and giant mitochondria in human patients diagnosed with non-alcoholic fatty liver disease. In so doing, we reveal functional alterations associated with mitochondrial gigantism and propose a mechanism for their formation (Chapter 5). Finally, the significance of the results obtained, and major scientific advances reported in this work are discussed in-depth against the relevant literature. This is proceeded by the future outlooks and research that remains to be done, followed by the main conclusions of this Ph.D thesis (Chapter 6). In summary, our findings firmly establish the immense importance and value of contemporary multimodal microscopy modalities in modern life science research, for holistically revealing cellular structures along the vast length scales amongst which they exist, under healthy and clinically relevant pathological conditions

Volume Holographic Hyperspectral Imaging

A volume hologram has two degenerate Bragg-phase-matching dimensions and provides the capability of volume holographic imaging. We demonstrate two volume holographic imaging architectures and investigate their imaging resolution, aberration, and sensitivity. The first architecture uses the hologram directly as an objective imaging element where strong aberration is observed and confirmed by simulation. The second architecture uses an imaging lens and a transmission geometry hologram to achieve linear two-dimensional optical sectioning and imaging of a four-dimensional (spatial plus spectral dimensions) object hyperspace. Multiplexed holograms can achieve simultaneously three-dimensional imaging of an object without a scanning mechanism