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- Kleinsatellit (4)
- Ultrakurzzeitspektroskopie (4)
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- Graduate School of Science and Technology (48) (remove)
Sonstige beteiligte Institutionen
- Technische Hochschule Nürnberg Georg Simon Ohm (2)
- Experimental Radiation Oncology, Department of Radiation Oncology, University Medical Center Mannheim (1)
- Fraunhofer Institut für Integrierte Schaltungen (IIS) (1)
- Fraunhofer Institut für Silicatforschung ISC (1)
- Hochschule Wismar (1)
- Institut für Medizintechnik Schweinfurt (IMeS) (1)
EU-Project number / Contract (GA) number
- 320377 (1)
It was the scope of this work to gain a deeper understanding of the correlation between Interface energetics of molecular semiconductors in planar organic solar cells and the corresponding optoelectronic characteristics. For this aim, different approaches were followed. At first, a direct variation of donor/acceptor (D/A) interface energetics of bilayer cells was achieved by utilizing systematically modified donor compounds. This change could be correlated to the macroscopic device performance. At second, the impact of interface energetics was illustrated, employing a more extended device architecture. By introducing a thin interlayer between a planar D/A heterojunction, an energetic staircase was established. Exciton dissociation in such devices could be linked to the cascade energy level alignment of the photo-active materials. Finally, two different fullerene molecules C60 and C70 were employed in co-evaporated acceptor phases. The expected discrepancy in their electronic structure was related to the transport properties of the corresponding organic photovoltaic cells (OPVCs). The fullerenes are created simultaneously in common synthesis procedures. Next to the photo-physical relevance, the study was carried-out to judge on the necessity of separating the components from each other by purification which constitutes the cost-determining step in the total production costs.
Die vorliegende Arbeit umfasst die Synthese, die Untersuchung von Struktur-Eigenschafts-Beziehungen und Eigenschaftsmodifikationen von Komplexen und Koordinationspolymeren basierend auf den 3d-Übergangsmetallchloriden von Mn, Fe, Co sowie Zn und N-heterozyklischen Liganden.
Durch die Kombination von mechanochemische Umsetzungen, mikrowellenassistierten Synthesen, solvensassistierten, solvothermalen und solvensfreien Reaktionen zu verschiedenen Synthesestrategien wurden 23 neue Koordinationsverbindungen synthetisiert und charakterisiert.
Ausgehend von den auf mechanochemischem Weg synthetisierten, monomeren Precursor-Komplexen [MCl2(TzH)4] (M = Mn und Fe) konnten die höhervernetzten Koordinationspolymere 1∞[FeCl(TzH)2]Cl und 1∞[MCl2(TzH)] (M = Fe und Mn) durch thermische und mikrowelleninduzierte Konversionsreaktionen als phasenreine Bulkprodukte erhalten werden. Die sukzessive Abgabe organischer Liganden und die damit verbundene Umwandlung in die höhervernetzten Spezies wurden dabei mittels temperaturabhängiger Pulverdiffraktometrie und simultanem DTA/TG-Verfahren analysiert.
Durch gezielte Variation der Lösungsmittel beim Liquid-assisted grinding, der mechanochemischen Synthese unter Zugabe einer flüssigen Phase, konnten die beiden polymorphen Koordinationspolymere α-1∞[MnCl2(BtzH)2] und β-1∞[MnCl2(BtzH)2] erhalten werden, die im monoklinen bzw. orthorhombischen Kristallsystem kristallisieren.
Solvensassistierte Umsetzungen von MnCl2 mit 1,2,4-1H-Triazol (TzH) unter Zugabe von Hilfsbasen resultierten unter anderem in der Bildung der dreidimensionalen Koordinationspolymere 3∞[MnCl(Tz)(TzH)] und 3∞{[Mn5Cl3(Tz)7(TzH)2]}2·NEt3HCl.
Die Untersuchung von Struktur-Eigenschafts-Korrelationen erfolgte systematisch an ausgewählten Verbindungen hinsichtlich ihrer dielektrischen Eigenschaften. Dabei wurden die Einflüsse intra- und intermolekularer Wechselwirkungen auf die strukturelle Rigidität und die daraus folgenden Polarisierbarkeitseigenschaften analysiert und miteinander verglichen. Die gemessenen dielektrischen Konstanten erstrecken sich von Werten im high-k-Bereich für monomere Komplexe bis hin zu den nahezu frequenzunabhängigen low-k-Werten der eindimensionalen Koordinationspolymere 1∞[MnCl2(TzH)] und 1∞[MnCl2(BtzH)2] sowie der Komplexe [ZnCl2(TzH)2] und [ZnCl2(BtzH)2]·BtzH.
Eigenschaftsmodifikationen und -optimierungen der synthetisierten Verbindungen er-folgten zum einen durch Erzeugung flexibler Kunststofffilme, in welche die eindimensionalen Koordinationspolymere 1∞[MCl2(TzH)] (M = Fe und Mn) eingebettet wurden. Zum anderen konnten in mechanochemischen Umsetzungen superparamagnetische Kompositpartikel bestehend aus einem Fe3O4/SiO2-Kern und einer kristallinen [ZnCl2(TzH)2]-Hülle erhalten werden, die in situ aus den Edukten ZnCl2 und TzH synthetisiert wurde.
This thesis will outline studies performed on the fluorescence dynamics of phenyl-benzo-
[c]-tetrazolo-cinnolium chloride (PTC) in alcoholic solutions with varying viscosity using
time-resolved fluoro-spectroscopic methods. Furthermore, the properties of femtosecond
Laguerre-Gaussian (LG) laser pulses will be investigated with respect to their temporal
and spatial features and an approach will be developed to measure and control the spatial
intensity distribution on the time scale of the pulse.
Tetrazolium salts are widely used in biological assays for their low oxidation and reduction
thresholds and spectroscopic properties. However, a neglected feature in these applications
is the advantage that detection of emitted light has over the determination of the
absorbance. To corroborate this, PTC as one of the few known fluorescent tetrazolium
salts was investigated with regard to its luminescent features. Steady-state spectroscopy
revealed how PTC can be formed by a photoreaction from 2,3,5-triphenyl-tetrazolium
chloride (TTC) and how the fluorescence quantum yield behaved in alcoholic solvents
with different viscosity. In the same array of solvents time correlated single photon counting
(TCSPC) measurements were performed and the fluorescence decay was investigated.
Global analysis of the results revealed different dynamics in the different solvents, but
although the main emission constant did change with the solvent, taking the fluorescence
quantum yield into consideration resulted in an independence of the radiative rate from
the solvent. The non-radiative rate, however, was highly solvent dependent and responsible
for the observed solvent-related changes in the fluorescence dynamics. Further studies
with the increased time resolution of femtosecond fluorescence upconversion revealed an
independence of the main emission constant from the excitation energy, however the dynamics
of the cooling processes prior to emission were prolonged for higher excitation
energy. This led to a conceivable photoreaction scheme with one emissive state with a
competing non-radiative relaxation channel, that may involve an intermediate state.
LG laser beams and their properties have seen a lot of scientific attention over the past two
decades. Also in the context of new techniques pushing the limit of technology further to
explore new phenomena, it is essential to understand the features of this beam class and
check the consistency of the findings with theoretical knowledge. The mode conversion
of a Hermite-Gaussian (HG) mode into a LG mode with the help of a spiral phase plate
(SPP) was investigated with respect to its space-time characteristics. It was found that
femtosecond LG and HG pulses of a given temporal duration share the same spectrum
and can be characterized using the same well-established methods. The mode conversion
proved to only produce the desired LG mode with its characteristic orbital angular momentum
(OAM), that is conserved after frequency doubling the pulse. Furthermore, it
was demonstrated that temporal shaping of the HG pulse does not alter the result of its
mode-conversion, as three completely different temporal pulse shapes produced the same
LG mode. Further attention was given to the sum frequency generation of fs LG beams
and dynamics of the interference of a HG and a LG pulse. It was found that if both are
chirped with inverse signs the spatial intensity distribution does rotate around the beam
axis on the time scale of the pulse. A strategy was found that would enable a measurement
of these dynamics by upconversion of the interference with a third gate pulse. The results
of which are discussed theoretically and an approach of an experimental realization had
been made. The simulated findings had only been reproduced to a limited extend due to
experimental limitations, especially the interferometric stability of the setup.
There is great interest in affordable, precise and reliable metrology underwater:
Archaeologists want to document artifacts in situ with high detail.
In marine research, biologists require the tools to monitor coral growth and geologists need recordings to model sediment transport.
Furthermore, for offshore construction projects, maintenance and inspection millimeter-accurate measurements of defects and offshore structures are essential.
While the process of digitizing individual objects and complete sites on land is well understood and standard methods, such as Structure from Motion or terrestrial laser scanning, are regularly applied, precise underwater surveying with high resolution is still a complex and difficult task.
Applying optical scanning techniques in water is challenging due to reduced visibility caused by turbidity and light absorption.
However, optical underwater scanners provide significant advantages in terms of achievable resolution and accuracy compared to acoustic systems.
This thesis proposes an underwater laser scanning system and the algorithms for creating dense and accurate 3D scans in water.
It is based on laser triangulation and the main optical components are an underwater camera and a cross-line laser projector.
The prototype is configured with a motorized yaw axis for capturing scans from a tripod.
Alternatively, it is mounted to a moving platform for mobile mapping.
The main focus lies on the refractive calibration of the underwater camera and laser projector, the image processing and 3D reconstruction.
For highest accuracy, the refraction at the individual media interfaces must be taken into account.
This is addressed by an optimization-based calibration framework using a physical-geometric camera model derived from an analytical formulation of a ray-tracing projection model.
In addition to scanning underwater structures, this work presents the 3D acquisition of semi-submerged structures and the correction of refraction effects.
As in-situ calibration in water is complex and time-consuming, the challenge of transferring an in-air scanner calibration to water without re-calibration is investigated, as well as self-calibration techniques for structured light.
The system was successfully deployed in various configurations for both static scanning and mobile mapping.
An evaluation of the calibration and 3D reconstruction using reference objects and a comparison of free-form surfaces in clear water demonstrate the high accuracy potential in the range of one millimeter to less than one centimeter, depending on the measurement distance.
Mobile underwater mapping and motion compensation based on visual-inertial odometry is demonstrated using a new optical underwater scanner based on fringe projection.
Continuous registration of individual scans allows the acquisition of 3D models from an underwater vehicle.
RGB images captured in parallel are used to create 3D point clouds of underwater scenes in full color.
3D maps are useful to the operator during the remote control of underwater vehicles and provide the building blocks to enable offshore inspection and surveying tasks.
The advancing automation of the measurement technology will allow non-experts to use it, significantly reduce acquisition time and increase accuracy, making underwater metrology more cost-effective.
The attitude and orbit control system of pico- and nano-satellites to date is one of the bottle necks for future scientific and commercial applications. A performance increase while keeping with the satellites’ restrictions will enable new space missions especially for the smallest of the CubeSat classes. This work addresses methods to measure and improve the satellite’s attitude pointing and orbit control performance based on advanced sensor data analysis and optimized on-board software concepts. These methods are applied to spaceborne satellites and future CubeSat missions to demonstrate their validity. An in-orbit calibration procedure for a typical CubeSat attitude sensor suite is developed and applied to the UWE-3 satellite in space. Subsequently, a method to estimate the attitude determination accuracy without the help of an external reference sensor is developed. Using this method, it is shown that the UWE-3 satellite achieves an in-orbit attitude determination accuracy of about 2°.
An advanced data analysis of the attitude motion of a miniature satellite is used in order to estimate the main attitude disturbance torque in orbit. It is shown, that the magnetic disturbance is by far the most significant contribution for miniature satellites and a method to estimate the residual magnetic dipole moment of a satellite is developed. Its application to three CubeSats currently in orbit reveals that magnetic disturbances are a common issue for this class of satellites. The dipole moments measured are between 23.1mAm² and 137.2mAm². In order to autonomously estimate and counteract this disturbance in future missions an on-board magnetic dipole estimation algorithm is developed.
The autonomous neutralization of such disturbance torques together with the simplification of attitude control for the satellite operator is the focus of a novel on-board attitude control software architecture. It incorporates disturbance torques acting on the satellite and automatically optimizes the control output. Its application is demonstrated in space on board of the UWE-3 satellite through various attitude control experiments of which the results are presented here.
The integration of a miniaturized electric propulsion system will enable CubeSats to perform orbit control and, thus, open up new application scenarios. The in-orbit characterization, however, poses the problem of precisely measuring very low thrust levels in the order of µN. A method to measure this thrust based on the attitude dynamics of the satellite is developed and evaluated in simulation. It is shown, that the demonstrator mission UWE-4 will be able to measure these thrust levels with a high accuracy of 1% for thrust levels higher than 1µN.
The orbit control capabilities of UWE-4 using its electric propulsion system are evaluated and a hybrid attitude control system making use of the satellite’s magnetorquers and the electric propulsion system is developed. It is based on the flexible attitude control architecture mentioned before and thrust vector pointing accuracies of better than 2° can be achieved. This results in a thrust delivery of more than 99% of the desired acceleration in the target direction.
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.
Remote sensing time series is the collection or acquisition of remote sensing data in a
fixed equally spaced time period over a particular area or for the whole world. Near
daily high spatial resolution data is very much needed for remote sensing applications
such as agriculture monitoring, phenology change detection, environmental
monitoring and so on. Remote sensing applications can produce better and accurate
results if they are provided with dense and accurate time series of data. The current
remote sensing satellite architecture is still not capable of providing near daily
or daily high spatial resolution images to fulfill the needs of the above mentioned
remote sensing applications. Limitations in sensors, high development, operational
costs of satellites and presence of clouds blocking the area of observation are some
of the reasons that makes near daily or daily high spatial resolution optical remote
sensing data highly challenging to achieve. With developments in the optical sensor
systems and well planned remote sensing satellite constellations, this condition
can be improved but it comes at a cost. Even then the issue will not be completely
resolved and thus the growing need for high temporal and high spatial resolution
data cannot be fulfilled entirely. Because the data collection process relies on satellites
which are physical system, these can fail unpredictably due to various reasons
and cause a complete loss of observation for a given period of time making a gap
in the time series. Moreover, to observe the long term trend in phenology change
due to rapidly changing environmental conditions, the remote sensing data from
the present is not just sufficient, the data from the past is also important. A better
alternative solution for this issue can be the generation of remote sensing time series
by fusing data from multiple remote sensing satellite which has different spatial and
temporal resolutions. This approach will be effective and efficient. In this method
a high temporal low spatial resolution image from a satellite such as Sentinel-2 can
be fused with a low temporal and high spatial resolution image from a satellite such
as the Sentinel-3 to generate a synthetic high temporal high spatial resolution data.
Remote sensing time series generation by data fusion methods can be applied to
the satellite images captured currently as well as the images captured by the satellites
in the past. This will provide the much needed high temporal and high spatial
resolution images for remote sensing applications. This approach with its simplistic
nature is cost effective and provides the researchers the means to generate the
data needed for their application on their own from the limited source of data available
to them. An efficient data fusion approach in combination with a well planned
satellite constellation can offer a solution which will ensure near daily time series of
remote sensing data with out any gap. The aim of this research work is to develop
an efficient data fusion approaches to achieve dense remote sensing time series.
Mini Unmanned Aerial Vehicles (MUAVs) are becoming popular research platform and
drawing considerable attention, particularly during the last decade due to their afford- ability and multi-dimensional applications in almost every walk of life. MUAVs have obvious advantages over manned platforms including their much lower manufacturing and operational costs, risk avoidance for human pilots, flying safely low and slow, and realization of operations that are beyond inherent human limitations. The advancement in Micro Electro-Mechanical System (MEMS) technology, Avionics and miniaturization of sensors also played a significant role in the evolution of MUAVs. These vehicles range from simple toys found at electronic supermarkets for entertainment purpose to highly sophisticated commercial platforms performing novel assignments like offshore wind power station inspection and 3D modelling of buildings etc. MUAVs are also more environment friendly as they cause less air pollution and noise. Unmanned is therefore unmatched. Recent research focuses on use of multiple inexpensive vehicles flying together, while maintaining required relative separations, to carry out the tasks efficiently compared to a single exorbitant vehicle. Redundancy also does away the risk of loss of a single whole-mission dependent vehicle. Some of the valuable applications in the domain of cooperative control include joint load transportation, search and rescue, mobile communication relays, pesticide spraying and weather monitoring etc. Though realization of multi-UAV coupled flight is complex, however obvious advantages justify
the laborious work involved...