Bøger udgivet af Cuvillier

Autonomous driving is one of the key disciplines in the automotive field and currently under intensive development, especially with the objective of saving more people¿s lives on the roads due to significant reductions in the number of traffic accidents. Therefore, the software components within autonomous cars must be tested efficient and precisely. One of the most challenging aspects of autonomous cars are the safety-critical driving scenarios. Their criticality has seldom been measured in terms of further forensic analysis or software solutions in the field of artificial intelligence. Therefore, data related to safety-critical driving scenarios must be obtained another way. In this context, kinematic models can be used to represent these scenes by describing the vehicle¿s movements based on defined boundary constraints as well as providing synthesized data through the simulation of a model for the training and validation of the underlying machine learning algorithms, such as neural networks or generative algorithms. In this paper, three of the most significant safety-critical driving scenarios, namely emergency braking, turning, and overtaking, are modeled accordingly.

Hydraulic fracturing in combination with horizontal well is playing a key role in the efficient development of unconventional gas/oil reservoirs and deep geothermal resources. However, the integral operation, especially from the perspective of THM (Thermal-Hydraulic-Mechanic) interactions have not been studied systematically. In this thesis, targeted improvements were achieved through developing a series of mathematical/physical models, and their implementation into the existing numerical tools (FLAC3Dplus and TOUGH2MP-FLAC3D), including: (a) a new thermal module for FLAC3Dplus based entirely on the finite volume method (FVM), which is especially developed for the fracturing process and can also achieve the modeling of gel breaking; (b) a rock damage module of TOUGH2MP-FLAC3D, which also considers the impacts of rock damaging process on evolution of permeability; © an in-depth improved FLAC3Dplus simulator that obtains the ability to simulate a 3D fracture propagation with arbitrary orientation. After the corresponding verifications, the improved tools were applied in different case studies to reveal: a) influences of the fluid¿s viscosity on the fracturing results in tight sandstone reservoirs; b) the induced seismicity during the fracturing operation and the reactivation of the natural faults; and c) the fracture propagation with arbitrary orientation.

Optical frequency combs (OFC) have revolutionized various applications in applied and fundamental sciences that rely on the determination of absolute optical frequencies and frequency differences. The latter requires only stabilization of the spectral distance between the individual comb lines of the OFC, allowing to tailor and reduce system complexity of the OFC generator (OFCG). One such application is the quantum test of the universality of free fall within the QUANTUS experimental series. Within the test, the rate of free fall of two atomic species, Rb and K, in micro-gravity will be compared.The aim of this thesis was the development of a highly compact, robust, and space-suitable diode laser-based OFCG with a mode-locked optical spectrum in the wavelength range around 780 nm. A diode laser-based OFCG was developed, which exceeds the requirements with a spectral bandwidth > 16 nm at20 dBc, a comb line optical power > 650 nW (at 20 dBc), a pulse repetition rate of 3.4 GHz, and an RF linewidth of the free-running pulse repetition rate

This work presents progress in the root-cause analysis of power saturation mechanisms in continuous wave (CW) driven GaAs-based high-power broad area diode lasers operated at 935 nm. Target is to increase efficiency at high optical CW powers by epitaxial design.The novel extreme triple asymmetric (ETAS) design was developed and patented within this work to equip diode lasers that use an extremely thin p-waveguide with a high modal gain. An iterative variation of diode lasers employing ETAS designs was used to experimentally clarify the impact of modal gain on the temperature dependence of internal differential quantum efficiency (IDQE) and optical loss. High modal gain leads to increased free carrier absorption from the active region. However, less power saturation is observed, which must then be attributed to an improved temperature sensitivity of the IDQE.The effect of longitudinal spatial hole burning (LSHB) leads to above average non-linear carrier loss at the back facet of the device. At high CW currents the junction temperature rises. Therefore, not only the asymmetry of the carrier profile increases but also the average carrier density in order to compensate for the decreased material gain and increased threshold gain. This carrier non-pinning effect above threshold is found in this work to enhance the impact of LSHB already at low currents, leading to rapid degradation of IDQE with temperature.This finding puts LSHB into a new context for CW-driven devices as it emphasizes the importance of low carrier densities at threshold. The carrier density was effectively reduced by applying the novel ETAS design. This enabled diode lasers to be realized that show minimized degradation of IDQE with temperature and therefore improved performance in CW operation.

Due to the finite nature of petroleum resources and depletion of conventional reservoirs, the exploitation of unconventional resources has been a key to meeting world energy needs. Natural gas, a cleaner fossil fuel compared to oil and coal, has an increasing role in the energy mix. It is expected that the peak global natural gas production will remain between 3.7-6.1 trillion m3 per year between 2019 and 2060.Therefore, addressing the technical challenges posed by reservoir exploitation technologies in an environmentally responsible manner is critical for efficient energy production and energy secure of the world.

High precision, high quality, and high throughput of ultrashort pulse laser ablation of bulk material are the most demanded properties that are required to let this process technology compete with other micro-machining techniques. Previous attempts to increase volumetric ablation rates of ultrashort pulse laser processes were based on the increase of fluence or pulse repetition rates. They run into limitations mainly set by the occurrence of bumpy surfaces due to overheating of bulk material.In this work, the potential of laser beam shaping for the enhancement of ablation rates is studied systematically for the first time. The question regarding the physically shortest possible process time for ablation of 2.5D-structures by means of an ultrashort pulse laser is answered using a heat conduction model, which is extended by the ability to consider spatially shaped beams. The strategy of laser beam stamping is implemented in a novel optical setup and proven both theoretically and experimentally to have a great potential for increasing ablation rates.

A compact and portable laser light source emitting in the wavelength range between 210 nm and 230 nm would enable numerous applications outside of laboratory environments, such as sterilization and disinfection of medical equipment, water purification or gas and air analysis using absorption spectroscopy. Such a source is also highly attractive for the identification and quantification of proteins and biomolecules by means of laser-induced fluorescence or Raman spectroscopy.In this thesis, a novel concept to realize such a compact and portable laser light source with low power consumption and an emission around 222 nm is investigated. The developed concept is based on single-pass frequency doubling of a commercially available high-power GaN laser diode emitting in the blue spectral range.Due to the low frequency doubling conversion efficiencies in this wavelength range of about 10-4 W-1, a laser diode with high optical output power above 1 W is required as pump source. Moreover, it has to exhibit narrowband emission in the range of the acceptance bandwidth of the applied nonlinear BBO crystal.Since GaN-based high-power laser diodes typically show broad emission spectra of ¿¿ = 1¿2 nm, stabilizing and narrowing their wavelength by using external wavelength-selective elements is investigated and presented for the first time.With the understanding for the novel concept gained in this work, a compact ultraviolet laser light source was realized. It has a power consumption of less than 10 W and is exceptionally robust due to its immoveable components. The demonstrated output power of 160 ¿W enables numerous industrial and everyday applications for which previous laser systems have been too complex and overly cost- and energy-intensive.

Im Zeitalter der Digitalisierung müssen Unternehmen ihre Prozesse, Produkte und Geschäftsmodelle anpassen, um ihre Innovations- sowie Wettbewerbsfähigkeit aufrecht zu erhalten. Aufgrund dessen müssen Unternehmen ihre bestehenden Kompetenzen erneuern, indem sie neues Wissen aus der digitalen Sphäre wertstiftend integrieren. Dies stellt jedoch eine erhebliche Herausforderung dar, insbesondere für etablierte Unternehmen, da die konvergente und generative Natur der digitalen Innovation nicht nur den Prozess der Wissensintegration dynamischer macht, sondern auch die Vielfalt und Menge des Wissens erhöht, das über die Unternehmensgrenzen hinweg integriert werden muss. Um diese Herausforderung näher zu beleuchten und Lösungsansätze zu evaluieren, wurden vier Studien durchgeführt und in dieser kumulativen Dissertation zusammengestellt. Diese Studien geben Einblicke in die Besonderheiten der Wissensintegration im Kontext digitaler Innovationen und fördern das Verständnis dafür, wie etablierte Unternehmen die damit verbundenen Herausforderungen bewältigen können. Dabei wird insbesondere der Einsatz von Grenzressourcen, wie bspw. Programmierschnittstellen (APIs), untersucht, da sie einen wesentlichen Mechanismus zur Skalierung der Wissensintegration in digital(isierenden) Geschäftsökosystemen darstellen.

The following study reveals some comprehensive details and increases the transparency concerning the acquisition of business services. Especially for the DACH region, valuable and first of their kind insights are revealed. Altogether, ten major areas are addressed and analysed, focusing on a comparison with goods purchasing and typical procedures that are applied within professional purchasing organisations. It becomes clear, that different key aspects are relevant for business services and that a distinction to goods purchasing is necessary. This relates for example to an individual servicestrategy, the application of adequate evaluation procedures and the consideration of a social component for a purchasing success. Moreover, specific regulations for goods and services will further increase. In addition, the required knowledge of a purchaser, especially in the field of value-adding business services, will increase. Firms need to invest more in their purchasers in order to always assure high expertise. In contrary, the level of automation will increase for non-value-adding processes, leading to a touchless acquisition of goods and services. Within these conflicting priorities, firms need to develop comprehensive and competitive strategies to overcome the challenges related to the purchasing of business services. Therefore, the Performance Excellence Study provides a starting point for a further enhancement and a continuous improvement in business service purchasing.

Various thermal wood modification technologies have been developed in Europe during the past decades that differ notably in the process conditions applied. However, the changes in wood properties by thermal modification, the underlying modes of action and their link to the process conditions are still not fully understood. This thesis investigates the influence of different process conditions in open and closed reactor systems on the resulting properties of thermally modified wood. In closed reactor systems, elevated water vapor pressure accelerates the thermal degradation of wood polymers and results in high mass loss levels even at mild treatment temperatures. However, in addition to the loss in wood mass, a strong influence of drying and softening of wood at elevated temperatures as well as an increased cell wall matrix stiffness by modification of the lignin carbohydrate complex under dry heat conditions influences the wood properties, i.e. water sorption. For wood thermally modified in open reactor systems at different peak temperatures and durations, the surface performance is investigated with regard to the susceptibility to surface cracking, photodegradation and coatability. The results provide explanations why the performance of thermally modified wood in exterior applications does not always meet the expectations derived from its enhanced resistance against decay fungi.

The improvement of microbial fuel cell (MFC) performance in a real wastewater treatment plant requires the investigation of several aspects. Firstly, a suitable cell design and electrochemical test procedure has to be set up and operated. Secondly, it is necessary to identify which electrode is the limiting electrode. Thirdly, it requires developing catalysts for the performance determining electrode. Fourthly, a method needs to be developed for the attachment of solid catalysts to the surface of the electrode. Finally, all these steps need transfer to technical scale. The data suggest that the MFC fabricated with the catalyst prepared using graphite, ¿-MnO2 and MoS2 in a weight proportion of 20:1:1 exhibited the highest optimal power density of 120 mW/m2. However, after ultrasonic treatment, the power density significantly improved to 183 mW/m2. The long term performances of the MFCs fabricated using catalysts prepared with different graphite, ¿-MnO2 (ß -MnO2) and MoS2 proportions decreased in the order of 20:1:1 (ß -MnO2) > 20:1:1 (ultrasonic) > 10:1 (ß-MnO2) >20:1:1 (¿-MnO2) > 30:2:1 (¿-MnO2) >30:1:2 (¿-MnO2).

Fifteen years ago, Horizons in Molecular Biology symposium was conceived by the graduate students of International Max Plank Research School in Molecular Biology to widen their own horizons beyond the rut of classes and lab work. Ever since, Horizons has grown from a humble idea to one of the most sought-after events in Göttingen and Germany. Horizons aims to bridge the gap between young scientists and experienced researchers by promoting them to engage in a productive dialog and exchange information. This year, we have planned four exhilarating days of presentations, poster sessions, panel discussions, and workshops aimed toinform, inspire and pique the interest of the young, scientific mind. One could describe Horizons as a platform built to facilitate interactions between participants and speakers! We therefore invite you to engage with our roster of distinguished speakersfrom diverse fields of work during their presentation or even over a cup of coffee. Do not miss this opportunity to network with your favourite speakers and participants from around the world. Should you require an introduction, we are glad to help you! From academia to far and beyond! Our Career Fair is specially tailored to meet the needs and expectations of abudding researcher. In addition to our informative talks and educational workshops, we also have a ¿Speed Dating¿ event where you can gain valuable insights from the diverse speakers in a personalized and informal setting. Make sure to sign up for this unique experience!The life of a PhD student can be full of many rewarding moments driven by curiosity and hardships. However, in the journey towards a PhD, the highs are often fraught with disheartening lows too. Being all too familiar with the experience, we thought that advice from thosewho persevered and succeeded could shed some light on the ¿tricks of the trade¿. To this aim, the Panel Discussion titled ¿Troubles of a young scientist: Fantastic ideas and where to Find them¿ will take place on the final day of the conference. Learning from the experiences of accomplished scientists is of vital importance, however, here at Horizons, we believe it is equally imperative to support and network with ourpeers. The Poster Sessions and Awarded Student Talks provide just such an opportunity. We encourage everyone to actively participate in the sessions and vote for which poster appealed to you the most!We look forward to having you here with us and hope to make this not only an educational experience, but also a memorable one.

Two members of the Benyviridae family, Beet soil borne mosaic virus (BSBMV) and Beet necrotic yellow vein virus (BNYVV), possess identical genome organisation, host range and high sequence similarity. To understand functional differences in molecular biology, pathogenicity mechanisms, symptom expression as well as interaction with the host and between viral species, a reverse genetic system represents a prerequisite. Infectious cDNA full length clones of both viruses were constructed by isothermal in vitro recombination. Artificial formation of BNYVV and BSBMV RNA1+2 reassortants were viable and spread long distance in N. benthamiana. Small genomic RNAs were exchangeable and systemically infected B. macrocarpa. Moreover, fluorescence labelled full length clones were achieved by replacing a part of the RNA2 encoded coat protein read through domain. Co infection experiments with labelled BSBMV and BNYVV showed that both viruses remained spatially separated after N. benthamiana agroinoculation. In contrast, a mixture of BSBMV with an unrelated virus resulted in no co infection exclusion. In super infection experiments, BSBMV and BNYVV were unable to establish a secondary infection in plants that were previously infected with BNYVV or BSBMV. In addition, a virus induced gene silencing (VIGS) system was developed. Both viruses were equipped with fragments of the magnesium chelatase subunit H and phytoene desaturase genes. Silencing phenotypes in N. benthamiana induced by both target genes, were comparable to those described in the literature.

This thesis presents an enhanced dynamic performance evaluation method for line-concentrating solar thermal collectors. Due to its dispatchability and large storage capacity, concentrating solar power is considered of high relevance in the future renewable energy mix for both, electricity generation and industrial process heat supply. To fully exploit this potential and legitimize investments within this sector, a reliable and meaningful performance testing is essential. The proposed flexible, dynamic performance evaluation method allows for a significant reduction of testing time, effort, and consequently costs¿especially for complex test conditions as they prevail for systems of larger dimensions such as line-concentrating collectors. For this reason, the present thesis comprehensively addresses diverse aspects of dynamic in situ performance testing. It includes a wide application of the elaborated procedure to diverse test collectors, ranging from small-scale medium-temperature linear Fresnel collectors to large-scale high-temperature parabolic troughs, considering different heat transfer fluids and receiver designs. It therefore proves to be a powerful and beneficial extension of the current testing standard to more complex test situations. Flexible and simultaneously reliable certification procedures are considered crucial for the further establishment of solar thermal technologies and their global acceptance.

The present work aims at investigating the turbulence in pipe flow. Experiments have been performed in two unique pipe facilities: CoLaPipe (CottbusLarge-Pipe) and CICLoPE (Center for International Cooperation in Long Pipe Experiments). The first part of the thesis is focusing on the development of flow considering pressure fluctuations measured along the axial direction to find the location where the flow becomes fully developed turbulent. Results show that application of ring disturbance to the incoming flow initiates turbulence much earlier upstream. The second aim of the thesis is determining the streamwise lengths of large-scale structures in fully developed turbulent state with respect to their wavenumber dependency and spatial correlation using hot-wire anemometry and Particle Image Velocimetry. Meandering structures usually referred as VLSM (very large-scale motions), have been identified with claimed extension up to 20R, where R is the pipe radius. The location of the outer spectral peaks (OSP) which represent the largest energy content per wavenumber outside the viscous wall region is moving towards to the wall as the Reynolds number increases.