Designing heterogeneous porous tissue scaffolds for additive manufacturing processes

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer, which represents the geometric internal feature or the spine. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. To avoid the twisting of the internal channels, reorientation and relaxation techniques are introduced to establish the point matching of ruling lines. An optimization algorithm is developed to construct sub-regions from these ruling lines. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the subregions peripherally into pore cells and consecutive iso-porosity curves are generated using the isopoints from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. A continuous zig-zag pattern deposition path crossing through the medial region is used for the initial layer and a biarc fitted isoporosity curve is generated for the consecutive layer with C-1 continuity. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive manufacturing processes

Search for New Physics in Tau-pair Events in ATLAS at the LHC

With the start-up of the Large Hadron Collider (LHC), a new world-largest particle accelerator, an exciting period in particle physics research will begin. ATLAS, one of the two general purpose detectors constructed at the LHC, is intended to search for new phenomena which involve highly massive particles whose detection was beyond the reach of past, lower-energy experiments. In this thesis, the potential of ATLAS to discover a new heavy particle in the two tau lepton final state is discussed based on fully simulated data samples. The tau-pair signature is important as it is sensitive to particles which couple preferentially to the third generation fermions as well as it offers potential for measuring polarisation asymmetry. It is shown that such particle could be discovered in this channel already at early stage of ATLAS operation. After collecting more data, measurement of tau polarisation would then provide an interesting constraint on the nature of the resonance. Searches for new physics in channels involving taus require excellent understanding of tau leptons' signatures in the ATLAS detector. Development of an algorithm for efficient and robust identification of hadronically decaying taus is a team work of many people in ATLAS. Improvements to the algorithm are also discussed in the thesis