Tomography refers to the cross-sectional imaging of an object from either transmission or reflection data collected by illuminating the object from many different directions. Classical tomography fails to reconstruct the optical properties of thick scattering objects because it does not adequately account for the scattering component of the neutron beam intensity exiting the sample. We proposed a new method of computed tomography which employs an inverse problem analysis of both the transmitted and scattered images generated from a beam passing through an optically thick object. This inverse problem makes use of a computationally efficient, two-dimensional forward problem based on neutron transport theory that effectively calculates the detector readings around the edges of an object. The forward problem solution uses a Step-Characteristic (SC) code with known uncollided source per cell, zero boundary flux condition and Sn discretization for the angular dependence. The calculation of the uncollided sources is performed by using an accurate discretization scheme given properties and position of the incoming beam and beam collimator. The detector predictions are obtained considering both the collided and uncollided components of the incoming radiation. The inverse problem is referred as an optimization problem. The function to be minimized, called an objective function, is calculated as the normalized-squared error between predicted and measured data. The predicted data are calculated by assuming a uniform distribution for the optical properties of the object. The objective function depends directly on the optical properties of the object; therefore, by minimizing it, the correct property distribution can be found. The minimization of this multidimensional function is performed with the Polack Ribiere conjugate-gradient technique that makes use of the gradient of the function with respect to the cross sections of the internal cells of the domain. The forward and inverse models have been successfully tested against numerical results obtained with MCNP (Monte Carlo Neutral Particles) showing excellent agreements. The reconstructions of several objects were successful. In the case of a single intrusion, TNTs (Tomography Neutron Transport using Scattering) was always able to detect the intrusion. In the case of the double body object, TNTs was able to reconstruct partially the optical distribution. The most important defect, in terms of gradient, was correctly located and reconstructed. Difficulties were discovered in the location and reconstruction of the second defect. Nevertheless, the results are exceptional considering they were obtained by lightening the object from only one side. The use of multiple beams around the object will significantly improve the capability of TNTs since it increases the number of constraints for the minimization problem.

Zugl.: München, Techn. Univ., Diss., 2009

München, Techn. University, Diss., 2009.

No description available.

Analysis and visualization of dynamic scenes is often constrained by the amount of spatio-temporal information available from the environment. In most scenarios, we have to account for incomplete information and sparse motion data, requiring us to employ interpolation and approximation methods to fill for the missing information. Scattered data interpolation and approximation techniques have been widely used for solving the problem of completing surfaces and images with incomplete input data. We introduce approaches for such data interpolation and approximation from limited sensors, into the domain of analyzing and visualizing dynamic scenes. Data from dynamic scenes is subject to constraints due to the spatial layout of the scene and/or the configurations of video cameras in use. Such constraints include: (1) sparsely available cameras observing the scene, (2) limited field of view provided by the cameras in use, (3) incomplete motion at a specific moment, and (4) varying frame rates due to different exposures and resolutions. In this thesis, we establish these forms of incompleteness in the scene, as spatio-temporal uncertainties, and propose solutions for resolving the uncertainties by applying scattered data approximation into a spatio-temporal domain. The main contributions of this research are as follows: First, we provide an efficient framework to visualize large-scale dynamic scenes from distributed static videos. Second, we adopt Radial Basis Function (RBF) interpolation to the spatio-temporal domain to generate global motion tendency. The tendency, represented by a dense flow field, is used to optimally pan and tilt a video camera. Third, we propose a method to represent motion trajectories using stochastic vector fields. Gaussian Process Regression (GPR) is used to generate a dense vector field and the certainty of each vector in the field. The generated stochastic fields are used for recognizing motion patterns under varying frame-rate and incompleteness of the input videos. Fourth, we also show that the stochastic representation of vector field can also be used for modeling global tendency to detect the region of interests in dynamic scenes with camera motion. We evaluate and demonstrate our approaches in several applications for visualizing virtual cities, automating sports broadcasting, and recognizing traffic patterns in surveillance videos.

Scattered x-radiation levels associated with various diagnostic procedures were measured with ionization chamber instruments in the small and large animal radiology facilities at the Ontario Veterinary College of the University of Guelph. The occupational radiation exposures incurred by veterinary radiography personnel were monitored using McMaster University's Panasonic UD-702E TLD system. The stray radiation levels and the dosimetric information are compared and discussed. An optimum protocol for radiological health protection surveillance is described. / Thesis / Master of Science (MSc)

Personal är utsatt för spridd strålning när de måste närvara vid CT trauman. Ögat är känsligt för joniserande strålning och det är bevisat att katarakt och strålning har ett samband. Vid CT-multitrauma används många projektioner och långa exponeringar. Studiens syfte är att undersöka hur mycket spridd strålning som personal utsätts för. Hur många gånger/år kan samma personal stå med innan rekommendationerna från ICRP på 20 mSv/år är uppnådd? Det är en kvantitativ studie som utförts empiriskt på två sjukhus med ett fantom. En Siemens 128 slice och en Toshiba 80 slice har använts vid mätningarna. Ett traumaprotokoll användes och en testmätning gjordes och därefter de riktiga mätningarna med dosimetrar från Landauer, placerade på sju mätpunkter i ögonhöjd på olika avstånd från gantryt. Den spridda strålningen var högst närmast gantryt och avtog med avståndet förutom två punkter som hade lägre mätresultat och kan förklaras på grund av dess vinkel från gantryt. Röntgensjuksköterskans ansvar är att informera om var personal bäst kan stå med vid CT trauman och att informera om vikten att variera personal. / Staff who has to attend CT-trauma examination is exposed to scattered radiation. The eye is sensitive to ionizing radiation and there is evidence that cataract and radiation are correlated. At CT-multitrauma long exposures and many projections is taken. The purpose of this study is to examine how much scattered radiation the staff is exposed to. How many times/year can one person in the staff attend a CT-trauma-examination before the ICRP recommendation dose of 20 mSv/year is reached? It is a quantitative study that has been done empirically at two hospitals with a phantom. A Siemens 128 slice and a Toshiba 80 slice were used in the measurements. A trauma protocol was used. One test measurement was done before the real measurements with dosimeters from Landuer placed at seven measure points at eye level at different distances from the gantry. The scattered radiation was highest close to the gantry and decreased with the distance except from two points that had lower measure results and this can be explained by the angle between the gantry and the dosimeter. It’s the radiographer’s responsibility to inform staff of the best place to stand at CT-trauma-examinations and to inform of the importance of alternating staff.

This thesis concerns cleavability. A space X is said to be cleavable over a space Y along a set A subset of X if there exists a continuous function f from X to Y such that f(A) cap f(X setminus A) = emptyset. A space X is cleavable over a space Y if it is cleavable over Y along all subsets A of X. In this thesis we prove three results regarding cleavability. First we discover the conditions under which cleavability of an infinite compactum X over a first-countable scattered linearly ordered topological space (LOTS) Y implies embeddability of X into Y. In particular, we provide a class of counter-examples in which cleavability does not imply embeddability, and show that if X is an infinite compactum cleavable over ω₁, the first uncountable ordinal, then X is embeddable into ω₁. We secondly show that if X is an infinite compactum cleavable over any ordinal, then X must be homeomorphic to an ordinal. X must also therefore be a LOTS. This answers two fundamental questions in the area of cleavability. We also leave it as an open question whether cleavability of an infinite compactum X over an uncountable ordinal λ implies X is embeddable into λ. Lastly, we show that if X is an infinite compactum cleavable over a separable LOTS Y such that for some continuous function f from X to Y, the set of points on which f is not injective is scattered, then X is a LOTS. In addition to providing these three results, we introduce a new area of research developed from questions within cleavability. This area of research is called almost-injectivity. Given a compact T₂ space X and a LOTS Y, we say a continuous function f from X to Y is almost-injective if the set of points on which f is not injective has countable cardinality. In this thesis, we state some questions concerning almost-injectivity, and show that if lambda is an ordinal, X is a T₂ compactum, and f is an almost-injective function from X to lambda, then X must be a LOTS.

Scattered vegetation is an essential part of the landscape in the Czech Republic. It is typical mainly for farm land which has experienced deep changes during the last century, which were probably the deepest changes in the last millennium. The thesis focuses on valuation of the scattered vegetation from the fifties till present. As a reset of collectivism, land consolidation in-to large land units, grassland ploughing and disturbance of scenic elements started. These broke the ecological balance of the landscape. The priority was given to the objective of increasing agricultural production. However, this intense way of farming changed sharply after the year 1989 during the transition to free market economy when the intensity of agricultural production decreased and a lot of less efficient areas were left abandoned. At the same time, modern legislativ protecting important scenic elements and scattered vegetation was adopted. At the beginning of the new century the Czech Republic joined the European Union resulting in changes in the environmental and agricultural policy. My thesis is aiming to analyse all the elements of scattered vegetation on one study area and with the help of this analysis tries to get the response of the scattered vegetation to the factors mentioned above. Specifically, I...

Non-forest woody vegetation is an important landscape feature of agricultural/rural landscape. Ph.D. thesis deals with evaluation of current state of non-forest woody vegetation, historical development and changes in configuration and composition in landscape. Non-forest woody vegetation was investigated in two physical-geographical different model areas (Kutnohorsko Region and White Carpathians). The thesis is based on own data collected in the field and digitized on historical aerial photos and current ortho-photos. After that, data were analyzed in relation to natural conditions and changes of landscape structure since 50s of 20th century until present. Comparing both model areas, assumed differences in character of non-forest woody vegetation, species composition, dominated type as well as relation to habitats/locations were confirmed. However, rapid changes of landscape structure in the last 60 years were caused by the same driving forces such as re-allotment, mechanization and intensification of agriculture. After 1989, processes such extensification of agriculture and land abandonment played the main role in landscape, especially in mountain regions. The second aim of the Ph.D. thesis was to identify changes in spatial configuration of non- forest woody vegetation in two...