Gradient-based quantitative image reconstruction in ultrasound-modulated optical tomography: first harmonic measurement type in a linearised diffusion formulation

Ultrasound-modulated optical tomography is an emerging biomedical imaging modality which uses the spatially localised acoustically-driven modulation of coherent light as a probe of the structure and optical properties of biological tissues. In this work we begin by providing an overview of forward modelling methods, before deriving a linearised diffusion-style model which calculates the first-harmonic modulated flux measured on the boundary of a given domain. We derive and examine the correlation measurement density functions of the model which describe the sensitivity of the modality to perturbations in the optical parameters of interest. Finally, we employ said functions in the development of an adjoint-assisted gradient based image reconstruction method, which ameliorates the computational burden and memory requirements of a traditional Newton-based optimisation approach. We validate our work by performing reconstructions of optical absorption and scattering in two- and three-dimensions using simulated measurements with 1% proportional Gaussian noise, and demonstrate the successful recovery of the parameters to within +/-5% of their true values when the resolution of the ultrasound raster probing the domain is sufficient to delineate perturbing inclusions.Comment: 12 pages, 6 figure

Image processing by region extraction using a clustering approach based on color

This thesis describes an image segmentation technique based on watersheds, a clustering technique which does not use spatial information, but relies on multispectral images. These are captured using a monochrome camera and narrow-band filters; we call this color segmentation, although it does not use color in a physiological sense. A major part of the work is testing the method developed using different color images. Starting with a general discussion of image processing, the different techniques used in image segmentation are reviewed, and the application of mathematical morphology to image processing is discussed. The use of watersheds as a clustering technique in two- dimensional color space is discussed, and system performance illustrated. The method can be improved for industrial applications by using normalized color to eliminate the problem of shadows. These methods are extended to segment the image into regions recursively. Different types of color images including both man made color images, and natural color images have been used to illustrate performance. There is a brief discussion and a simple illustration showing how segmentation can be used in image compression, and of the application of pyramidal data structures in clustering for coarse segmentation. The thesis concludes with an investigation of the methods which can be used to improve these segmentation results. This includes edge extraction, texture extraction, and recursive merging

Evaluation of Current Heparin Weight Based Protocol in Obese Patients

Purpose: To evaluate the difference in achieving goal activated partial thromboplastin time (aPTT) within 24 hours utilizing the institutional heparin weight based protocol between obese and non-obese patients. Methods: Retrospective, non-randomized, open label chart review in a community based hospital. Patients age 18 years or older receiving heparin therapy for greater than or equal to 24 hours identified. Patients were excluded if the protocol was utilized for acute coronary syndrome or interrupted within the initial 24 hours of therapy. Patients were also excluded if any deviations from the protocol were identified. The primary endpoint evaluated the difference in achieving goal aPTT within 24 hours between obese and non-obese patients. The secondary endpoint evaluated the difference in achieving goal aPTT within 24-48 hours and safety outcomes such as bleeds. Results: Of the 253 patients identified, 167 patients were included and 86 patients were excluded. Seventy-two (71.3%) of the nonobese and 48 (72.7%) of obese patients achieved goal aPTT within 24 hours (odd ratio [OR]: 0.98, 95 % confidence interval (CI): 0.6 to 1.58). Sixteen (15.8%) of nonobese and 13 (19.7%) of the obese patients achieved goal aPTT within 24 to 48 hours (OR: 0.77, 95 % CI: 0.3 to 1.95). Two (1.9 %) of the nonobese and 3 (4.5 %) of the obese patients had a documented major bleed (OR: 0.42 and 95 % CI: 0.69 to 2.61). Conclusion: Overall, there was no difference in achieving goal aPTT between nonobese and obese patients while utilizing our facility’s weight based heparin dosing. No major bleeding was documented that warranted discontinuation of therapy, and bleeding incidences between both groups were similar

WKB analysis of the Regge-Wheeler equation down in the frequency plane

The Regge-Wheeler equation for black-hole gravitational waves is analyzed for large negative imaginary frequencies, leading to a calculation of the cut strength for waves outgoing to infinity. In the--limited--region of overlap, the results agree well with numerical findings [Class. Quantum Grav._20_, L217 (2003)]. Requiring these waves to be outgoing into the horizon as well subsequently yields an analytic formula for the highly damped Schwarzschild quasinormal modes,_including_ the leading correction. Just as in the WKB quantization of, e.g., the harmonic oscillator, solutions in different regions of space have to be joined through a connection formula, valid near the boundary between them where WKB breaks down. For the oscillator, this boundary is given by the classical turning points; fascinatingly, the connection here involves an expansion around the black-hole singularity r=0.Comment: REVTeX4, 11pp with one EPS figure. N.B.: 'Alec' is my first, and 'Maassen van den Brink' my family name. v2: discussion and Refs. expanded; overall grooming. v3: added calculation of the highly damped QNMs, incl. the leading correction. v4: a few clarifications and minor corrections; final, to appear in JM

Spectral function and quasiparticle weight in the generalized t-J model

We extend to the spectral function an approach which allowed us to calculate the quasiparticle weight for destruction of a real electron Z_c sigma (k) (in contrast to that of creation of a spinless holon Z_h(k) in a generalized $t-J$ model, using the self-consistent Born approximation (SCBA). We compare our results with those obtained using the alternative approach of Sushkov et al., which also uses the SCBA. The results for Z_c sigma (k) are also compared with results obtained using the string picture and with exact diagonalizations of a 32-site square cluster. While on a qualitative level, all results look similar, our SCBA approach seems to compare better with the ED one. The effect of hopping beyond nearest neighbors, and that of the three-site term are discussed.Comment: 7 pages, 6 figure

Multi-Qubit Gates in Arrays Coupled by 'Always On' Interactions

Recently there has been interest in the idea of quantum computing without control of the physical interactions between component qubits. This is highly appealing since the 'switching' of such interactions is a principal difficulty in creating real devices. It has been established that one can employ 'always on' interactions in a one-dimensional Heisenberg chain, provided that one can tune the Zeeman energies of the individual (pseudo-)spins. It is important to generalize this scheme to higher dimensional networks, since a real device would probably be of that kind. Such generalisations have been proposed, but only at the severe cost that the efficiency of qubit storage must *fall*. Here we propose the use of multi-qubit gates within such higher-dimensional arrays, finding a novel three-qubit gate that can in fact increase the efficiency beyond the linear model. Thus we are able to propose higher dimensional networks that can constitute a better embodiment of the 'always on' concept - a substantial step toward bringing this novel concept to full fruition.Comment: 20 pages in preprint format, inc. 3 figures. This version has fixed typos and printer-friendly figures, and is to appear in NJ

Revisiting Salvucci’s Semi-analytical Solution for Bare Soil Evaporation with New Consideration of Vapour Diffusion and Film Flow

Bare soil evaporation is controlled by a combination of capillary flow, vapour diffusion and film flow. Relevant analytical solutions mostly assume horizontal flow conditions and ignore gravitational effects. Salvucci (1997) provided a rare example of a semi-analytical solution for vertical bare soil evaporation. However, they did not explicitly represent vapour diffusion and film flow, which are likely to account for a significant proportion of total flow during vertical evaporation from soils. Vapour diffusion and film flow can be incorporated via Salvucci’s desorptivity parameter, which represents the proportionality constant relating Stage 2 cumulative evaporation to the square root of time under horizontal flow conditions. The objective of this article is to implement vapour diffusion and film flow within Salvucci’s semi-analytical solution and test its performance by comparison with isothermal numerical simulation and relevant experimental data. The following important conclusions are drawn. Analytical solutions that assume horizontal flow conditions are inadequate for understanding vertical evaporation problems because they overestimate evaporation rates and mostly predict vapour diffusion and film flow to be of negligible influence. Salvucci’s semi-analytical solution is effective at predicting the order-of-magnitude reduction in evaporation caused by gravitational effects. However, it is unable to identify the correct importance of vapour diffusion and film flow because these processes can only be represented through its desorptivity parameter