@phdthesis{Hochleitner2018,
  author    = {Hochleitner, Gernot},
  title     = {Advancing melt electrospinning writing for fabrication of biomimetic structures},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162197},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2018},
  abstract  = {In order to mimic the extracellular matrix for tissue engineering, recent research approaches often involve 3D printing or electrospinning of fibres to scaffolds as cell carrier material. Within this thesis, a micron fibre printing process, called melt electrospinning writing (MEW), combining both additive manufacturing and electrospinning, has been investigated and improved. Thus, a unique device was developed for accurate process control and manufacturing of high quality constructs. Thereby, different studies could be conducted in order to understand the electrohydrodynamic printing behaviour of different medically relevant thermoplastics as well as to characterise the influence of MEW on the resulting scaffold performance. For reproducible scaffold printing, a commonly occurring processing instability was investigated and defined as pulsing, or in extreme cases as long beading. Here, processing analysis could be performed with the aim to overcome those instabilities and prevent the resulting manufacturing issues. Two different biocompatible polymers were utilised for this study: poly(ε-caprolactone) (PCL) as the only material available for MEW until then and poly(2-ethyl-2-oxazoline) for the first time. A hypothesis including the dependency of pulsing regarding involved mass flows regulated by the feeding pressure and the electrical field strength could be presented. Further, a guide via fibre diameter quantification was established to assess and accomplish high quality printing of scaffolds for subsequent research tasks. By following a combined approach including small sized spinnerets, small flow rates and high field strengths, PCL fibres with submicron-sized fibre diameters (f{\O} = 817 ± 165 nm) were deposited to defined scaffolds. The resulting material characteristics could be investigated regarding molecular orientation and morphological aspects. Thereby, an alignment and isotropic crystallinity was observed that can be attributed to the distinct acceleration of the solidifying jet in the electrical field and by the collector uptake. Resulting submicron fibres formed accurate but mechanically sensitive structures requiring further preparation for a suitable use in cell biology. To overcome this handling issue, a coating procedure, by using hydrophilic and cross-linkable star-shaped molecules for preparing fibre adhesive but cell repellent collector surfaces, was used. Printing PCL fibre patterns below the critical translation speed (CTS) revealed the opportunity to manufacture sinusoidal shaped fibres analogously to those observed using purely viscous fluids falling on a moving belt. No significant influence of the high voltage field during MEW processing could be observed on the buckling phenomenon. A study on the sinusoidal geometry revealed increasing peak-to-peak values and decreasing wavelengths as a function of decreasing collector speeds sc between CTS > sc ≥ 2/3 CTS independent of feeding pressures. Resulting scaffolds printed at 100 \%, 90 \%, 80 \% and 70 \% of CTS exhibited significantly different tensile properties, foremost regarding Young's moduli (E = 42 ± 7 MPa to 173 ± 22 MPa at 1 - 3 \% strain). As known from literature, a changed morphology and mechanical environment can impact cell performance substantially leading to a new opportunity of tailoring TE scaffolds. Further, poly(L-lactide-co-ε-caprolactone-co-acryloyl carbonate) as well as poly(ε-caprolactone-co-acryloyl carbonate) (PCLAC) copolymers could be used for MEW printing. Those exhibit the opportunity for UV-initiated radical cross-linking in a post-processing step leading to significantly increased mechanical characteristics. Here, single fibres of the polymer composed of 90 mol.\% CL and 10 mol.\% AC showed a considerable maximum tensile strength of σmax = 53 ± 16 MPa. Furthermore, sinusoidal meanders made of PCLAC yielded a specific tensile stress-strain characteristic mimicking the qualitative behaviour of tendons or ligaments. Cell viability by L929 murine fibroblasts and live/dead staining with human mesenchymal stem cells revealed a promising biomaterial behaviour pointing out MEW printed PCLAC scaffolds as promising choice for medical repair of load-bearing soft tissue. Indeed, one apparent drawback, the small throughput similar to other AM methods, may still prevent MEW's industrial application yet. However, ongoing research focusses on enlargement of manufacturing speed with the clear perspective of relevant improvement. Thereby, the utilisation of large spinneret sizes may enable printing of high volume rates, while downsizing the resulting fibre diameter via electrical field and mechanical stretching by the collector uptake. Using this approach, limitations of FDM by small nozzle sizes could be overcome. Thinking visionary, such printing devices could be placed in hospitals for patient-specific printing-on-demand therapies one day. Taking the evolved high deposition precision combined with the unique small fibre diameter sizes into account, technical processing of high performance membranes, filters or functional surface finishes also stands to reason.},
  subject      = {scaffold},
  language  = {en}
}
@phdthesis{TranGia2014,
  author    = {Tran-Gia, Johannes},
  title     = {Model-Based Reconstruction Methods for MR Relaxometry},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-109774},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {In this work, a model-based acceleration of parameter mapping (MAP) for the determination of the tissue parameter T1 using magnetic resonance imaging (MRI) is introduced. The iterative reconstruction uses prior knowledge about the relaxation behavior of the longitudinal magnetization after a suitable magnetization preparation to generate a series of fully sampled k-spaces from a strongly undersampled acquisition. A Fourier transform results in a spatially resolved time course of the longitudinal relaxation process, or equivalently, a spatially resolved map of the longitudinal relaxation time T1. In its fastest implementation, the MAP algorithm enables the reconstruction of a T1 map from a radial gradient echo dataset acquired within only a few seconds after magnetization preparation, while the acquisition time of conventional T1 mapping techniques typically lies in the range of a few minutes. After validation of the MAP algorithm for two different types of magnetization preparation (saturation recovery \& inversion recovery), the developed algorithm was applied in different areas of preclinical and clinical MRI and possible advantages and disadvantages were evaluated.},
  subject      = {Kernspintomographie},
  language  = {en}
}
@article{GageikBenzMontenegro2015,
  author    = {Gageik, Nils and Benz, Paul and Montenegro, Sergio},
  title     = {Obstacle Detection and Collision Avoidance for a UAV with Complementary Low-Cost Sensors},
  series = {IEEE Access},
  volume    = {3},
  journal   = {IEEE Access},
  doi       = {10.1109/ACCESS.2015.2432455},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-125481},
  pages     = {599 - 609},
  year      = {2015},
  abstract  = {This paper demonstrates an innovative and simple solution for obstacle detection and collision avoidance of unmanned aerial vehicles (UAVs) optimized for and evaluated with quadrotors. The sensors exploited in this paper are low-cost ultrasonic and infrared range finders, which are much cheaper though noisier than more expensive sensors such as laser scanners. This needs to be taken into consideration for the design, implementation, and parametrization of the signal processing and control algorithm for such a system, which is the topic of this paper. For improved data fusion, inertial and optical flow sensors are used as a distance derivative for reference. As a result, a UAV is capable of distance controlled collision avoidance, which is more complex and powerful than comparable simple solutions. At the same time, the solution remains simple with a low computational burden. Thus, memory and time-consuming simultaneous localization and mapping is not required for collision avoidance.},
  language  = {en}
}
@phdthesis{Gageik2015,
  author    = {Gageik, Nils},
  title     = {Autonome Quadrokopter zur Innenraumerkundung : AQopterI8, Forschung und Entwicklung},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-130240},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {Diese Forschungsarbeit beschreibt alle Aspekte der Entwicklung eines neuartigen, autonomen Quadrokopters, genannt AQopterI8, zur Innenraumerkundung. Dank seiner einzigartigen modularen Komposition von Soft- und Hardware ist der AQopterI8 in der Lage auch unter widrigen Umweltbedingungen autonom zu agieren und unterschiedliche Anforderungen zu erf{\"u}llen. Die Arbeit behandelt sowohl theoretische Fragestellungen unter dem Schwerpunkt der einfachen Realisierbarkeit als auch Aspekte der praktischen Umsetzung, womit sie Themen aus den Gebieten Signalverarbeitung, Regelungstechnik, Elektrotechnik, Modellbau, Robotik und Informatik behandelt. Kernaspekt der Arbeit sind L{\"o}sungen zur Autonomie, Hinderniserkennung und Kollisionsvermeidung. Das System verwendet IMUs (Inertial Measurement Unit, inertiale Messeinheit) zur Orientierungsbestimmung und Lageregelung und kann unterschiedliche Sensormodelle automatisch detektieren. Ultraschall-, Infrarot- und Luftdrucksensoren in Kombination mit der IMU werden zur H{\"o}henbestimmung und H{\"o}henregelung eingesetzt. Dar{\"u}ber hinaus werden bildgebende Sensoren (Videokamera, PMD), ein Laser-Scanner sowie Ultraschall- und Infrarotsensoren zur Hindernis-erkennung und Kollisionsvermeidung (Abstandsregelung) verwendet. Mit Hilfe optischer Sensoren kann der Quadrokopter basierend auf Prinzipien der Bildverarbeitung Objekte erkennen sowie seine Position im Raum bestimmen. Die genannten Subsysteme im Zusammenspiel erlauben es dem AQopterI8 ein Objekt in einem unbekannten Raum autonom, d.h. v{\"o}llig ohne jedes externe Hilfsmittel, zu suchen und dessen Position auf einer Karte anzugeben. Das System kann Kollisionen mit W{\"a}nden vermeiden und Personen autonom ausweichen. Dabei verwendet der AQopterI8 Hardware, die deutlich g{\"u}nstiger und Dank der Redundanz gleichzeitig erheblich verl{\"a}sslicher ist als vergleichbare Mono-Sensor-Systeme (z.B. Kamera- oder Laser-Scanner-basierte Systeme). Neben dem Zweck als Forschungsarbeit (Dissertation) dient die vorliegende Arbeit auch als Dokumentation des Gesamtprojektes AQopterI8, dessen Ziel die Erforschung und Entwicklung neuartiger autonomer Quadrokopter zur Innenraumerkundung ist. Dar{\"u}ber hinaus wird das System zum Zweck der Lehre und Forschung an der Universit{\"a}t W{\"u}rzburg, der Fachhochschule Brandenburg sowie der Fachhochschule W{\"u}rzburg-Schweinfurt eingesetzt. Darunter fallen Labor{\"u}bungen und 31 vom Autor dieser Arbeit betreute studentische Bachelor- und Masterarbeiten. Das Projekt wurde ausgezeichnet vom Universit{\"a}tsbund und der IHK W{\"u}rzburg-Mainfranken mit dem Universit{\"a}tsf{\"o}rderpreis der Mainfr{\"a}nkischen Wirtschaft und wird gef{\"o}rdert unter den Bezeichnungen „Lebensretter mit Propellern" und „Rettungshelfer mit Propellern". Außerdem wurde die Arbeit f{\"u}r den Gips-Sch{\"u}le-Preis nominiert. Absicht dieser Projekte ist die Entwicklung einer Rettungsdrohne. In den Medien Zeitung, Fernsehen und Radio wurde {\"u}ber den AQopterI8 schon mehrfach berichtet. Die Evaluierung zeigt, dass das System in der Lage ist, voll autonom in Innenr{\"a}umen zu fliegen, Kollisionen mit Objekten zu vermeiden (Abstandsregelung), eine Suche durchzuf{\"u}hren, Objekte zu erkennen, zu lokalisieren und zu z{\"a}hlen. Da nur wenige Forschungsarbeiten diesen Grad an Autonomie erreichen, gleichzeitig aber keine Arbeit die gestellten Anforderungen vergleichbar erf{\"u}llt, erweitert die Arbeit den Stand der Forschung.},
  subject      = {Quadrokopter},
  language  = {de}
}
@phdthesis{Strohmeier2021,
  author    = {Strohmeier, Michael},
  title     = {FARN - A Novel UAV Flight Controller for Highly Accurate and Reliable Navigation},
  doi       = {10.25972/OPUS-22313},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-223136},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {This thesis describes the functional principle of FARN, a novel flight controller for Unmanned Aerial Vehicles (UAVs) designed for mission scenarios that require highly accurate and reliable navigation. The required precision is achieved by combining low-cost inertial sensors and Ultra-Wide Band (UWB) radio ranging with raw and carrier phase observations from the Global Navigation Satellite System (GNSS). The flight controller is developed within the scope of this work regarding the mission requirements of two research projects, and successfully applied under real conditions. FARN includes a GNSS compass that allows a precise heading estimation even in environments where the conventional heading estimation based on a magnetic compass is not reliable. The GNSS compass combines the raw observations of two GNSS receivers with FARN's real-time capable attitude determination. Thus, especially the deployment of UAVs in Arctic environments within the project for ROBEX is possible despite the weak horizontal component of the Earth's magnetic field. Additionally, FARN allows centimeter-accurate relative positioning of multiple UAVs in real-time. This enables precise flight maneuvers within a swarm, but also the execution of cooperative tasks in which several UAVs have a common goal or are physically coupled. A drone defense system based on two cooperative drones that act in a coordinated manner and carry a commonly suspended net to capture a potentially dangerous drone in mid-air was developed in conjunction with the project MIDRAS. Within this thesis, both theoretical and practical aspects are covered regarding UAV development with an emphasis on the fields of signal processing, guidance and control, electrical engineering, robotics, computer science, and programming of embedded systems. Furthermore, this work aims to provide a condensed reference for further research in the field of UAVs. The work describes and models the utilized UAV platform, the propulsion system, the electronic design, and the utilized sensors. After establishing mathematical conventions for attitude representation, the actual core of the flight controller, namely the embedded ego-motion estimation and the principle control architecture are outlined. Subsequently, based on basic GNSS navigation algorithms, advanced carrier phase-based methods and their coupling to the ego-motion estimation framework are derived. Additionally, various implementation details and optimization steps of the system are described. The system is successfully deployed and tested within the two projects. After a critical examination and evaluation of the developed system, existing limitations and possible improvements are outlined.},
  subject      = {Drohne <Flugk{\"o}rper>},
  language  = {en}
}
@misc{ReitemeyerWeinmann2022,
  author    = {Reitemeyer, Malte and Weinmann, Felix},
  title     = {Detection of UAP with a Nano Satellite},
  doi       = {10.25972/OPUS-26139},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-261391},
  pages     = {36},
  year      = {2022},
  abstract  = {Continued reports over the past decades of unknown aerial phenomena (short UAP) have given high relevance to the investigation and research of these. Especially reports by US Navy pilots and official investigations by the US Office of the director of national intelligence have emphasized the value of such efforts. Due to the inherently limited scope of earth based observations, a satellite based instrument for detection of such phenomena may prove especially useful. This paper as such investigates the possible viability of such an instrument on a nano satellite mission.},
  subject      = {Satellit},
  language  = {en}
}
@techreport{BoeschStielerLydonetal.2023,
  author    = {B{\"o}sch, Carolin and Stieler, Malena and Lydon, Salomon and Hesse, Martin and Ali, Hassan and Finzel, Matthias and Faraz Ali, Syed and Salian, Yash and Alnoor, Hiba and John, Jeena and Lakkad, Harsh and Bhosale, Devraj and Jafarian, Timon and Parvathi, Uma and Ezzatpoor, Narges and Datar, Tanuja},
  title     = {Venus Research Station},
  issn      = {2747-9374},
  doi       = {10.25972/OPUS-32869},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-328695},
  pages     = {232},
  year      = {2023},
  abstract  = {Because of the extreme conditions in the atmosphere, Venus has been less explored than for example Mars. Only a few probes have been able to survive on the surface for very short periods in the past and have sent data. The atmosphere is also far from being fully explored. It could even be that building blocks of life can be found in more moderate layers of the planet's atmosphere. It can therefore be assumed that the planet Venus will increasingly become a focus of exploration. One way to collect significantly more data in situ is to build and operate an atmospheric research station over an extended period of time. This could carry out measurements at different positions and at different times and thus significantly expand our knowledge of the planet. In this work, the design of a Venus Research Station floating within the Venusian atmosphere is presented, which is complemented by the design of deployable atmospheric Scouts. The design of these components is done on a conceptual basis.},
  subject      = {Venus},
  language  = {en}
}
@phdthesis{Drobczyk2024,
  author    = {Drobczyk, Martin},
  title     = {Ultra-Wideband Wireless Network for Enhanced Intra-Spacecraft Communication},
  doi       = {10.25972/OPUS-35956},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-359564},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Wireless communication networks already comprise an integral part of both the private and industrial sectors and are successfully replacing existing wired networks. They enable the development of novel applications and offer greater flexibility and efficiency. Although some efforts are already underway in the aerospace sector to deploy wireless communication networks on board spacecraft, none of these projects have yet succeeded in replacing the hard-wired state-of-the-art architecture for intra-spacecraft communication. The advantages are evident as the reduction of the wiring harness saves time, mass, and costs, and makes the whole integration process more flexible. It also allows for easier scaling when interconnecting different systems. This dissertation deals with the design and implementation of a wireless network architecture to enhance intra-spacecraft communications by breaking with the state-of-the-art standards that have existed in the space industry for decades. The potential and benefits of this novel wireless network architecture are evaluated, an innovative design using ultra-wideband technology is presented. It is combined with a Medium Access Control (MAC) layer tailored for low-latency and deterministic networks supporting even mission-critical applications. As demonstrated by the Wireless Compose experiment on the International Space Station (ISS), this technology is not limited to communications but also enables novel positioning applications. To adress the technological challenges, extensive studies have been carried out on electromagnetic compatibility, space radiation, and data robustness. The architecture was evaluated from various perspectives and successfully demonstrated in space. Overall, this research highlights how a wireless network can improve and potentially replace existing state-of-the-art communication systems on board spacecraft in future missions. And it will help to adapt and ultimately accelerate the implementation of wireless networks in space systems.},
  subject      = {Raumfahrttechnik},
  language  = {en}
}