Analysis of Subchondral Bone and Microvessels Using a Novel Vascular Perfusion Contrast Agent and Optimized Dual-Energy Computed Tomography

Osteoarthritis (OA), is a chronic debilitating disease that affects millions of individuals and is characterized by the degeneration of joint subchondral bone and cartilage. These tissue degenerations manifest as joint pain, limited range of joint motion, and overall diminished quality of life. Currently, the exact mechanism(s) and cause(s) by which OA initiates and progresses remain unknown. The multi-factorial complex nature of OA (i.e. age, diabetes, obesity, and prior injuries have all been shown to play a role in OA) contributes to the current lack of a cure or effective long-term treatment for OA. One re-emerging and interesting hypothesis revolves around the delicate homeostatic microvascular environment around the cartilage – an avascular tissue. The absence of blood vessels within cartilage stresses the importance of nutrient and oxygen delivery from the neighbouring synovium and subchondral bone. Currently, the effects of changes in the subchondral bone microvessel density on cartilage health remain unknown due to the difficulties in simultaneously studying dense bone and the associated small microvessels. Computed tomography (CT) is widely used in the diagnosis of OA, as the use of x-rays provide detailed images of the bone degeneration associated with OA. However, the study of microvessels using CT has been exceptionally difficult due to their small (\u3c 10 µm) size, lack of contrast from neighbouring soft tissues, and proximity to dense bone. The purpose of this thesis was to develop a novel dual-energy micro-computed tomography (DECT) compatible vascular perfusion contrast agent and the associated instrumentation to optimize DECT on pre-clinical, cone-beam micro-CT scanners. The combination of these two techniques would facilitate the simultaneous visualization and quantification of subchondral bone and microvessels within the bone underlining the cartilage (i.e. distal femoral epiphysis and proximal tibial epiphysis) of rats that have undergone an OA-induced surgery. Results gained from this study will further provide information into the role that microvessels may play in OA

Knots and Links in Three-Dimensional Flows

The closed orbits of three-dimensional flows form knots and links. This book develops the tools - template theory and symbolic dynamics - needed for studying knotted orbits. This theory is applied to the problems of understanding local and global bifurcations, as well as the embedding data of orbits in Morse-smale, Smale, and integrable Hamiltonian flows. The necesssary background theory is sketched; however, some familiarity with low-dimensional topology and differential equations is assumed

Computation in Complex Networks

Complex networks are one of the most challenging research focuses of disciplines, including physics, mathematics, biology, medicine, engineering, and computer science, among others. The interest in complex networks is increasingly growing, due to their ability to model several daily life systems, such as technology networks, the Internet, and communication, chemical, neural, social, political and financial networks. The Special Issue “Computation in Complex Networks" of Entropy offers a multidisciplinary view on how some complex systems behave, providing a collection of original and high-quality papers within the research fields of: • Community detection • Complex network modelling • Complex network analysis • Node classification • Information spreading and control • Network robustness • Social networks • Network medicin

Using biomechanical constraints to improve video-based motion capture

In motion capture applications whose aim is to recover human body postures from various input, the high dimensionality of the problem makes it desirable to reduce the size of the search-space by eliminating a priori impossible configurations. This can be carried out by constraining the posture recovery process in various ways. Most recent work in this area has focused on applying camera viewpoint-related constraints to eliminate erroneous solutions. When camera calibration parameters are available, they provide an extremely efficient tool for disambiguating not only posture estimation, but also 3D reconstruction and data segmentation. Increased robustness is indeed to be gained from enforcing such constraints, which we prove in the context of an optical motion capture framework. Our contribution in this respect resides in having applied such constraints consistently to each main step involved in a motion capture process, namely marker reconstruction and segmentation, followed by posture recovery. These steps are made inter-dependent, where each one constrains the other. A more application-independent approach is to encode constraints directly within the human body model, such as limits on the rotational joints. This being an almost unexplored research subject, our efforts were mainly directed at determining a new method for measuring, representing and applying such joint limits. To the present day, the few existing range of motion boundary representations present severe drawbacks that call for an alternative formulation. The joint limits paradigm we propose not only overcomes these drawbacks, but also allows to capture intra- and inter-joint rotation dependencies, these being essential to realistic joint motion representation. The range of motion boundary is defined by an implicit surface, its analytical expression enabling us to readily establish whether a given joint rotation is valid or not. Furthermore, its continuous and differentiable nature provides us with a means of elegantly incorporating such a constraint within an optimisation process for posture recovery. Applying constrained optimisation to our body model and stereo data extracted from video sequence, we demonstrate the clearly resulting decrease in posture estimation errors. As a bonus, we have integrated our joint limits representation in character animation packages to show how motion can be naturally constrained in this manner

Advanced Concepts in Particle and Field Theory

Uniting the usually distinct areas of particle physics and quantum field theory, gravity and general relativity, this expansive and comprehensive textbook of fundamental and theoretical physics describes the quest to consolidate the elementary particles that are the basic building blocks of nature. Designed for advanced undergraduates and graduate students and abounding in worked examples and detailed derivations, as well as historical anecdotes and philosophical and methodological perspectives, this textbook provides students with a unified understanding of all matter at the fundamental level. Topics range from gauge principles, particle decay and scattering cross-sections, the Higgs mechanism and mass generation, to spacetime geometries and supersymmetry. By combining historically separate areas of study and presenting them in a logically consistent manner, students will appreciate the underlying similarities and conceptual connections across these fields. This title, first published in 2015, has been reissued as an Open Access publication