@phdthesis{Borchers2020,
  author    = {Borchers, Kai},
  title     = {Decentralized and Pulse-based Clock Synchronization in SpaceWire Networks for Time-triggered Data Transfers},
  doi       = {10.25972/OPUS-21560},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-215606},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2020},
  abstract  = {Time-triggered communication is widely used throughout several industry do- mains, primarily for reliable and real-time capable data transfers. However, existing time-triggered technologies are designed for terrestrial usage and not directly applicable to space applications due to the harsh environment. In- stead, specific hardware must be developed to deal with thermal, mechanical, and especially radiation effects. SpaceWire, as an event-triggered communication technology, has been used for years in a large number of space missions. Its moderate complexity, her- itage, and transmission rates up to 400 MBits/s are one of the main ad- vantages and often without alternatives for on-board computing systems of spacecraft. At present, real-time data transfers are either achieved by prior- itization inside SpaceWire routers or by applying a simplified time-triggered approach. These solutions either imply problems if they are used inside dis- tributed on-board computing systems or in case of networks with more than a single router are required. This work provides a solution for the real-time problem by developing a novel clock synchronization approach. This approach is focused on being compatible with distributed system structures and allows time-triggered data transfers. A significant difference to existing technologies is the remote clock estimation by the use of pulses. They are transferred over the network and remove the need for latency accumulation, which allows the incorporation of standardized SpaceWire equipment. Additionally, local clocks are controlled decentralized and provide different correction capabilities in order to handle oscillator induced uncertainties. All these functionalities are provided by a developed Network Controller (NC), able to isolate the attached network and to control accesses.},
  subject      = {Daten{\"u}bertragung},
  language  = {en}
}
@phdthesis{Baier2018,
  author    = {Baier, Pablo A.},
  title     = {Simulator for Minimally Invasive Vascular Interventions: Hardware and Software},
  isbn      = {978-3-945459-22-5},
  doi       = {10.25972/OPUS-16119},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161190},
  school      = {Universit{\"a}t W{\"u}rzburg},
  pages     = {118},
  year      = {2018},
  abstract  = {A complete simulation system is proposed that can be used as an educational tool by physicians in training basic skills of Minimally Invasive Vascular Interventions. In the first part, a surface model is developed to assemble arteries having a planar segmentation. It is based on Sweep Surfaces and can be extended to T- and Y-like bifurcations. A continuous force vector field is described, representing the interaction between the catheter and the surface. The computation time of the force field is almost unaffected when the resolution of the artery is increased. The mechanical properties of arteries play an essential role in the study of the circulatory system dynamics, which has been becoming increasingly important in the treatment of cardiovascular diseases. In Virtual Reality Simulators, it is crucial to have a tissue model that responds in real time. In this work, the arteries are discretized by a two dimensional mesh and the nodes are connected by three kinds of linear springs. Three tissue layers (Intima, Media, Adventitia) are considered and, starting from the stretch-energy density, some of the elasticity tensor components are calculated. The physical model linearizes and homogenizes the material response, but it still contemplates the geometric nonlinearity. In general, if the arterial stretch varies by 1\% or less, then the agreement between the linear and nonlinear models is trustworthy. In the last part, the physical model of the wire proposed by Konings is improved. As a result, a simpler and more stable method is obtained to calculate the equilibrium configuration of the wire. In addition, a geometrical method is developed to perform relaxations. It is particularly useful when the wire is hindered in the physical method because of the boundary conditions. The physical and the geometrical methods are merged, resulting in efficient relaxations. Tests show that the shape of the virtual wire agrees with the experiment. The proposed algorithm allows real-time executions and the hardware to assemble the simulator has a low cost.},
  subject      = {Computersimulation},
  language  = {en}
}