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Brachytherapy is radiation therapy performed by placing a radiation source near or inside a tumor. Difference between the current water-based brachytherapy dose formalism (TG-43) and new model based dose calculation algorithms (MBSCAs) can differ by more than a factor of 10 in the calculated doses. There is a need for voxel-by-voxel cross-section assignment, ideally, both the tissue composition and mass density of every voxel should be known for individual patients. A method for determining tissue composition via three material decomposition (3MD) from dual energy CT scans was developed at Linköping university. The method (named DIRA) is a model based iterative reconstruction algorithm that utilizes two photon energies for image reconstruction and 3MD for quantitative tissue classification of the reconstructed volumetric dataset. This thesis has investigated the accuracy of the 3MD method applied on prostate tissue in an anthropomorphic phantom when using two different approximations of soft tissues in DIRA. Also the distributions of CT-numbers for soft tissues in a contemporary dual energy CT scanner have been determined. An investigation whether these distributions can be used for tissue classification of soft tissues via thresholding has been conducted. It was found that the relative errors of mass energy absorption coefficient (MEAC) and linear attenuation coefficient (LAC) of the approximated mixture as functions of photon energy were less than 6 \% in the energy region from 1 keV to 1 MeV. This showed that DIRA performed well for the selected anthropomorphic phantom and that it was relatively insensitive to choice of base materials for the approximation of soft tissues. The distributions of CT-numbers of liver, muscle and kidney tissues overlapped. For example a voxel containing muscle could be misclassified as liver in 42 cases of 100. This suggests that pure thresholding is insufficient as a method for tissue classification of soft tissues and that more advanced methods should be used.

The topic of antenna pattern synthesis, in the context of beam shaping, is considered. One approach to this problem is to use the method of point matching. This method can be used to approximate antenna patterns with a set of uniformly spaced sources with suitable directivities. One specifies a desired antenna pattern and approximates it with a combination of beams. This approach results in a linear system of equations that can be solved for a set of beam coefficients. With suitable shifts between the matching points and between the source points, a good agreement between the assumed and the reproduced antenna patterns can be obtained along an observation line. This antenna modelling could be used in the program NERO to compute the field at the receiver antenna for a realistic 2D communication link. It is verified that the final result is not affected by the details of the antenna modelling.

The wireless communications have suffered, in these last years, one of the greater technological growth within the communications via radio. The application of multiple antennas, as much in transmission as in reception has taken to an impulse of the study of different models from propagation channels. Taking this into consideration, the different types from mentioned models are going to be studied. The work that the ISY department at the Institute of Technology of the Linköping University has proposed is to develop to a propagation channel model, with several antennas in reception and transmission, that one first approach allows a capacity of the channel study, in absence of measures of possible scenarios, as well as the development of a small simulator that allows to analyze its benefits.

<p>Impulse propagation in cardiac muscle is determined not only by the excitable properties of the myocyte membrane, but also by the gross and fine structure of cardiac muscle. Ionic diffusion pathways are defined by the muscle's interconnected myocytes and interweaving interstitial spaces. Resistive variations arising from spatial changes in tissue structure, including geometry, composition and electrical properties have a significant impact on the success or failure of impulse propagation. Although much as been learned about the impact of discrete resistive architecture of the intracellular space, the role of the interstitial space in the spread of electrical activity is less well understood or appreciated at the microscopic scale. </p><p>The interstitial space, or interstitium, occupies from 20-25% of the total heart volume. </p><p>The structural and material composition of the interstitial space is both complex and </p><p>heterogeneous, encompassing non-myocyte cell structures and a conglomeration of </p><p>extracellular matrix proteins. The spatial distribution of the interstitium can vary from confined spaces between abutting myocytes and tightly packed cardiac fibers to large gaps between cardiac bundles and sheets</p><p>This work presents a discrete multidomain formulation that describes the three-dimensional ionic diffusion pathways between connected myocytes within a variable interstitial physiology and morphology. Unlike classically used continuous and discontinuous models of impulse propagation, the intracellular and extracellular spaces are represented as spatially distinct volumes with dynamic and static boundary conditions that electrically couple neighboring spaces to form the electrically cooperative tissue model. The discrete multidomain model provides a flexible platform to simulate impulse propagation at the microscopic scale within a three-dimensional context. The three-dimensional description of the interstitial space that </p><p>encompasses a single cell improves the capability of the model to realistically investigate the impact of the discontinuous and electrotonic inhomogeneities of the myocardium's interstitium.</p><p>Under the discrete multidomain representation, a non-uniformly described interstitium </p><p>capturing the passive properties of the intravascular space or variable distribution and </p><p>composition of the extracellular space that encompasses a cardiac fiber creates an </p><p>electrotonic load perpendicular to the direction of the propagating wavefront. During </p><p>longitudinal propagation along a cardiac fiber, results demonstrate waveshape </p><p>alterations due to variations in loads experienced radially that would have been otherwise masked in traditional model descriptions. Findings present a mechanism for eliminating myocyte membrane participation in impulse propagation, as the result of decreased loading experienced radially from a non-uniformly resistive extracellular space. Ultimately, conduction velocity increases by decreasing the "effective" surface-to-volume ratio, as theoretically hypothesized to occur in the conducting Purkinje tissue.</p> / Dissertation

Guided wave techniques have great potential for the structural health monitoring of plate-like components. Previous research has demonstrated the effectiveness of combining laser-ultrasonic techniques with time-frequency representations to experimentally develop the dispersion relationship of a plate; the high fidelity, broad bandwidth and point-like nature of laser ultrasonics are critical for the success of these results. Unfortunately, laser ultrasonic techniques are time and cost intensive, and are impractical for many in-service applications. Therefore this research develops a complementary digital signal processing methodology that uses mounted piezoelectric elements instead of optical devices. This study first characterizes the spatial and temporal effects of oil coupled and glued piezoelectric sources, and then develops a procedure to interpret and model the distortion caused by their limited bandwidth and finite size. Furthermore, it outlines any inherent difficulties for time and frequency domain considerations. The deconvolution theory for source function extraction in the time - and frequency domain under the presence of noise is provided and applied to measured data. These considerations give the background for further studies to develop a dispersion relationship of a plate with the fidelity and bandwidth similar to results possible with laser ultrasonics, but made using mounted piezoelectric sources.

Geotechnical properties vary in space. Statistical parameters such as mean, deviation, and correlation length are characteristics for each sediment and formation history. The effects of spatial variability on the macro-scale mechanical properties of soils are investigated using Monte Carlo non-linear finite element simulations. Boundary conditions include 1) isotropic loading, 2) zero-lateral strain loading, 3) drained and undrained deviatoric loading, and 4) small-strain wave propagation. Emphasis is placed on identifying the effects of spatial variability on the stiffness and strength of soils, recognizing emergent phenomena, and creating the background for new geotechnical design methods that take into consideration spatial variability. The arithmetic mean of soil properties cannot be used to estimate the stiffness or strength of heterogeneous soils. Greater deviation and longer relative correlation length in the spatial distribution of soil properties yield a softer and weaker mechanical response. Load transfer concentrates along stiffer zones, leading to stress-focusing and lower K0 values. Drained loading promotes internal homogenization. Undrained deviatoric loading can cause percolation of internal weakness and shear strain localization. Spatial heterogeneity adds complexity to elastic wave propagation. Heterogeneous soil mixtures can be engineered to attain unique macroscale behavior

Generics has recently been adopted to many mainstream object oriented languages, such as C# and Java. As a particular design choice, generics in C# and Java use a sub-typing relation to constraint type parameters. Failing to encapsulate type parameters within generic interfaces and inability to encapsulate type constraints as part of an interface definition have been identified as deficiencies in the way this design choice has been implemented in these languages. These deficiencies can lead to verbose and redundant code. In particular, they have been reported to affect the development of highly generic libraries. To address these issues, extending object oriented interfaces and sub-typing with associated types and constraint propagation has been proposed and studied in an idealized small-scale formal setting. This thesis builds on this previous work and provides a design and implementation of the extensions in full C#. We also present a proof of soundness of the Featherweight Generic Java (FGJ) formalism extended with interfaces. This property was assumed in a proof of type safety of associated types and constraint propagation, but no proof for the property was provided.

Arterial pulse pressure is critically important to a number of diseases such as isolated systolic hypertension, coronary artery disease and heart failure. Determining the cause of increased pulse pressure has been hampered for two reasons. First, pulse pressure results from contraction of the heart and the load formed by the complex arterial tree. Pressure pulses travel from the heart to the peripheral arteries. As they reach a bifurcation or change in arterial wall properties, some of the pulses get reflected and propagate retrograde towards the heart. Second, two different modeling approaches (0-D and 1-D) describe the arterial system. The Windkessel model ascribed changes in pulse pressure to changes in total arterial compliance (Ctot) and total arterial resistance, whereas the transmission model ascribed them to changes in the magnitude, timing and sites of reflection. Our investigation has addressed both these limitations by finding that a complex arterial system degenerates into a simple 2-element Windkessel model when wavelength of the propagated pulse increases. This theoretical development has yielded three practical results. First, isolated systolic hypertension can be viewed as a manifestation of a system that has degenerated into a Windkessel, and thus increased pulse pressure is due to decreased Ctot. Second, the well-discussed Augmentation Index does not truly describe augmentation of pulse pressure by pulse reflection. Third, the simple 2-element Windkessel can be used to characterize the interaction among heart, arterial system and axial-flow left ventricular assist device analytically. The fact that arterial systems degenerate into Windkessels explains why it becomes much easier to estimate total arterial compliance in hypertension?total arterial compliance is the dominant determinant of pulsatile pressure.