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Open Access
Towards improved targetless registration and deformation analysis of TLS point clouds using patch-based segmentation
(2023) Yang, Yihui; Schwieger, Volker (Prof. Dr.-Ing. habil. Dr. h.c.)
The geometric changes in the real world can be captured by measuring and comparing the 3D coordinates of object surfaces. Traditional point-wise measurements with low spatial resolution may fail to detect inhomogeneous, anisotropic and unexpected deformations, and thus cannot reveal complex deformation processes. 3D point clouds generated from laser scanning or photogrammetric techniques have opened up opportunities for an area-wise acquisition of spatial information. In particular, terrestrial laser scanning (TLS) exhibits rapid development and wide application in areal geodetic monitoring owing to the high resolution and high quality of acquired point cloud data. However, several issues in the process chain of TLS-based deformation monitoring are still not solved satisfactorily. This thesis mainly focuses on the targetless registration and deformation analysis of TLS point clouds, aiming to develop novel data-driven methods to tackle the current challenges. For most deformation processes of natural scenes, in some local areas no shape deformations occur (i.e., these areas are rigid), and even the deformation directions show a certain level of consistency when these areas are small enough. Further point cloud processing, like stability and deformation analyses, could benefit from the assumptions of local rigidity and consistency of deformed point clouds. In this thesis, thereby, three typical types of locally rigid patches - small planar patches, geometric primitives, and quasi-rigid areas - can be generated from 3D point clouds by specific segmentation techniques. These patches, on the one hand, can preserve the boundaries between rigid and non-rigid areas and thus enable spatial separation with respect to surface stability. On the other hand, local geometric information and empirical stochastic models could be readily determined by the points in each patch. Based on these segmented rigid patches, targetless registration and deformation analysis of deformed TLS point clouds can be improved regarding accuracy and spatial resolution. Specifically, small planar patches like supervoxels are utilized to distinguish the stable and unstable areas in an iterative registration process, thus ensuring only relatively stable points are involved in estimating transformation parameters. The experimental results show that the proposed targetless registration method has significantly improved the registration accuracy. These small planar patches are also exploited to develop a novel variant of the multiscale model-to-model cloud comparison (M3C2) algorithm, which constructs prisms extending from planar patches instead of the cylinders in standard M3C2. This new method separates actual surface variations and measurement uncertainties, thus yielding lower-uncertainty and higher-resolution deformations. A coarse-to-fine segmentation framework is used to extract multiple geometric primitives from point clouds, and rigorous parameter estimations are performed individually to derive high-precision parametric deformations. Besides, a generalized local registration-based pipeline is proposed to derive dense displacement vectors based on segmented quasi-rigid areas that are corresponded by areal geometric feature descriptors. All proposed methods are successfully verified and evaluated by simulated and/or real point cloud data. The choice of proposed deformation analysis methods for specific scenarios or applications is also provided in this thesis.
Open Access
Investigating superconductivity by tunneling spectroscopy using oxide heterostructures
(2017) Fillis-Tsirakis, Evangelos; Mannhart, Jochen (Prof. Dr.)
Open Access
Behavior of sulfur oxides in air and oxy-fuel combustion
(2019) Spörl, Reinhold; Scheffknecht, Günter (Univ.-Prof. Dr. techn.)
This thesis evaluates the behavior of sulfur oxides in pulverized fuel (PF) fired air and oxy-fuel systems. Sulfur oxides are responsible for certain operational problems and considerable gas cleaning requirements in air as well as oxy-fuel firing. A better understanding of the related issues will allow for a technical and economical optimization of the oxy-fuel combustion technology. A range of experimental investigations studying the stability and retention of sulfur oxides in ashes and deposits, acid gas (SO2, SO3, and HCl) control in air and oxy-fuel combustion by dry sorbent injection, and SO3 formation were conducted. The experimental work is in parts supported by theoretical considerations and thermodynamic equilibrium simulation. Studies for different coals and lignites showed that in practically relevant oxy-fuel configurations the exclusion of airborne N2 from combustion leads to an increase of the SO2 concentrations in oxy-fuel, compared to air firing, by a factor of about 3.4 to 4.2, referring to dry, and of about 2.9 to 3.5, when referring to wet flue gas conditions. The increased SO2 levels in oxy-fuel combustion are responsible for an increased stability of sulfates in oxy-fuel power boiler systems so that for example the decomposition temperature CaSO4 rises by about 50 to 80 °C, depending on flue gas atmospheres. The enhanced stability of sulfates in deposits at high temperatures when operating with increased SO2 levels was experimentally demonstrated. Compared to air firing, a considerable increase of the sulfur retention in the ash by 10 to 12 percentage points has been observed for oxy-fuel recycle combustion of Lusatian lignites. This leads to lower SO2 emissions and higher SO3 levels in process ashes and deposits. The results indicate that for fuels, such as the used lignites, the temperature level at which fouling by sulfatic deposits is problematic may be shifted to higher temperatures in oxy-fuel combustion and that the sintering of deposits by sulfation may be more pronounced. In contrast, in air and oxy-fuel combustion experiments with a hard coal with a low sulfur retention potential differences in the SO3 contents and degrees of sulfation of ashes and deposits were small. Besides higher SO3 contents and sulfation degrees, no other significant changes between the deposit samples from air and oxy-fuel combustion were identified. Experiments on dry sorbent injection in air and oxy-fuel mode showed that an increase of the average flue gas residence time in the furnace by flue gas recirculation and, to a lesser extent, the higher sulfate stability enhance the desulfurization efficiency in oxy-fuel recycle combustion considerably. SO2 capture efficiencies in oxy-fuel recycle combustion of 50 % to more than 80 % at moderate molar sulfur to calcium ratios between 1.7 and 2.9 were reached, when injecting CaCO3 and Ca(OH)2 together with the fuel or directly to the furnace. Under comparable injection conditions, the oxy-fuel performance was by as much as 29 percentage points higher than in air firing. Also an efficient SO3 and HCl control by DSI could be demonstrated. Experiments on formation of SO3 show that higher SO2 levels in oxy-fuel firing are the most important parameter responsible for the observed increase of the SO3 concentrations.
Open Access
Nonlinear optical microspectroscopy with few-cycle laser pulses
(2017) Wan, Hui; Wrachtrup, Jörg (Prof. Dr.)
Nonlinear optical (NLO) microscopy is a powerful tool in physics, chemistry, and material science it probes intrinsic optical properties of the sample without the need of labeling. In order to investigate the ultrafast processes in nonlinear materials with high spatial resolution, we need to combine both ultrashort pulses and techniques focusing them to the diffraction limit. Previously, few-cycle laser pulses have often been tightly focused using conventional microscope objectives. However, the propagation of an ultrashort pulse in optical materials, particularly in the glass of a high numerical aperture (N.A.) microscope objective, results in spatial and temporal distortions of the pulse electric field, which can severely affect its quality in the focus. By purely passive group delay dispersion (GDD) and third-order dispersion (TOD) management, in this thesis, we experimentally demonstrate in-focus diffraction-limited and bandwidth-limited few-cycle pulses by using high N.A. objectives. Based on these achievements, the performance of a novel few-cycle NLO microscope for both second-harmonic generation (SHG) imaging and microspectroscopy in the frequency- and time-domains was characterized. The inverse linear dependence of SHG intensity on the in-focus pulse duration was demonstrated down to 7.1 fs for the first time. The application of shorter in-focus pulses for the enhancement of SHG image contrast was successfully demonstrated on a single collagen (type-I) fibril as a biological model system for studying protein assemblies under physiological conditions. Beyond imaging, a collagen fibril has been found to act as a purely non-resonant χ(2) soft matter under the present excitation conditions, and its ratio of forward- to epi-detected SHG intensities allowed for the estimation of the fibril thickness, which corresponds well with atomic force microscopy (AFM) measurements. The ultrafast dephasing of the localized surface plasmon resonance (LSPR) in the metallic nanoparticles, that only occurs on a time scale of a few femtoseconds, has gained a lot of attraction in the field of nanoplasmonics. This thesis is the first systematic experimental demonstration of time-resolving ultrashort plasmon dephasing in single gold nanoparticles by using interferometric SHG spectroscopy with in-focus 7.3 fs excitation pulses in combination with linear scattering spectroscopy performed on the same nanoparticle. For nanorods, nanodisks, and nanorectangles, strong plasmon resonance enhanced SHG is observed, where the SHG intensity strongly depends on the spectral overlap between the LSPR band and the excitation laser spectrum. For single nanorods and nanorectangles, the polarization dependence of the SHG intensity was found to follow second-order dipole scattering, and the effect of size and shape on the LSPR properties was directly observed in the time-domain. Good agreement between experimental and simulated values of dephasing times and resonance wavelengths is obtained, which confirms that a common driven damped harmonic oscillator model for the LSPR in the nanoparticle can qualitatively explain both the linear scattering spectra in the frequency-domain and the SHG response in the time-domain. Resonance bands in linear transmission and scattering spectra have also been observed for nanoholes with sizes smaller than the wavelength of the incident light in a metal film, which are assigned to LSPR modes of the electric field distribution around the nanohole with qualitatively similar resonance properties as a nanoparticle. The polarization-resolved nonlinear optical properties of the single nanoholes with different shapes and symmetries were also reported. The objective of this thesis has been systematic SHG studies of the size effect in the LSPR of single nanoholes in metal films and of their ultrafast dephasing dynamics. Although, enhancement of both the forward- and epi-detected SHG emissions from single rectangular nanoholes are observed,however,no ultrafast dephasing dynamics of LSPRs in rectangular nanoholes could be time-resolved with our in-focus 7.3 fs excitation laser pulses, which indicates that contributions from LSPR enhanced SHG to the detected SHG signal are negligible. More work needs to be done in order to overcome the current experimental limitations. However, in this thesis, the polarization dependence of the forward- and epi-detected SHG intensity from the single rectangular nanohole was found to follow that of a second-order dipole pattern. While the SHG dipole pattern observed for rectangular nanoparticles is oriented parallel to its long-axis, the SHG dipole pattern of its complementary rectangular nanohole is oriented perpendicular to its long-axis. This observation represents the first experimental demonstration of Babinet’s principle in second-order nonlinear scattering of a single rectangular nanohole in a gold film.
Open Access
Konkurrenz und Diffusion von Technologien auf Märkten unter Standardisierungsdruck : Modellbildung, Simulation und Prognose
(2019) Valentowitsch, Johann; Burr, Wolfgang (Prof. Dr.)
Die Häufigkeit und Intensität technologischer Standardkriege hat in Folge rasanter Entwicklungen auf den Gebieten der Informations- und Kommunikationstechnologien in den letzen Jahren spürbar zuge-nommen. Aus diesem Grund rückten in jüngster Vergangenheit Prozesse der Technologiediffusion und -adoption verstärkt in den Fokus der wirtschaftswissenschaftlichen Forschung. Trotz zahlreicher Beiträge auf diesem Gebiet ist unser heutiges Verständnis von den zugrunde liegenden Wettbewerbs- und Marktdynamiken jedoch nach wie vor stark limitiert. Wie in dieser Arbeit ausführlich gezeigt wird, sind die meisten konventionellen Difffusionsmodelle heute nicht in der Lage, die volle Bandbreite der kompetitiven Dynamiken zu erfassen, die sich im Rahmen technologischer Standardkriege regelmäßig auf Märkten unter Standardisierungsdruck entfalten. Aus heutiger Sicht bleibt die Modellbildung häufig darauf beschränkt, einfache Generationenfolgen von Technologien abzubilden. Bei dieser Form von Technologiesubstitution lassen sich jedoch nicht, die für Standardkriege typischen, erbittert geführten Dominanzkämpfe beobachten, die sich in Folge von mangelnder Interkomplementarität zwishen den konkurrierenden Technologien im Markt herausbilden. Zur Beschreibung derartiger Prozesse bedarf es daher anderer Modelle, die eine stärkere Fokussetzung auf die eigentlichen Wettbewerbsprozesse und Marktdynamiken setzen. Um den gegenwärtigen Mangel an wettbewerbsorientierten Modellen zu begegen, wird in dieser Arbeit unter Heranziehung von ökonomischen Adoptions- und Diffusionstheorien sowie unter Berücksichtigung der mittlerweile sehr umfangreichen Forschungsergebnisse auf den Gebieten der Standard- und Netzwerkforschung ein neues Modell formuliert, das sich zur Analyse von Diffusionsdynamiken auf Märkten unter Standardisierungs- und Wettbewerbsdruck heranziehen lässt. Mit Hilfe des neuen Modells kann gezeigt werden, dass die Adoption neuer Technologien durch drei wesentliche Faktoren erklärt werden kann, nämlich durch das innovative und imitative Verhalten der Innovationsnachfrager auf der einen Seite sowie das Größenverhältnis der konkurrierenden Anwendernetzwerke zueinander auf der anderen Seite. Der im Rahmen des Modells implementierte Adoptionsmechanismus leitet sich dabei vornehmlich aus der Klasse so genannter Mixed-Influence-Diffusionsmodelle ab. Allerdings erweitert das neue Modell den klassischen Mixed-Influence-Gedanken, indem es den Betrachtungshorizont auf mehrere Diffusionstechnologien ausweitet und dabei marktliche Interdependenzen zwischen den Technologien im Diffusionsprozess zulässt. Die Modellierung in dieser Arbeit verfolgt somit einen integrativen Ansatz, der unterschiedliche theoretische Sichtweisen in einem kompakten Modell vereinen soll. Um das aufgestellte Wettbewerbsmodell zu validieren, werden ökonomische Zeitreihendaten zu ausgewähtlen Standardkriegen verwendet, die in der Vergangenheit zu temporären Technologie-Lock-ins auf den jeweiligen Märkten geführt haben. Wie mit Hilfe dieser Datenreihen gezeigt werden kann, erklärt das neue wettbewerbsorientierte Modell dabei einen Großteil der beobachteten Adoptionsvarianz in den Daten und führt insgesamt betrachtet zu einem guten Daten-Fit. Zudem weisen ex ante Prognosen der Adoptionsraten, die auf Basis des Wettbewerbsmodells generiert wurden, eine höhere Genauigkeit auf als Schätzungen, die auf Grundlage des zu Referenzzwecken mitbetrachteten Standardmodells von Bass erstellt wurden. Aufgrund seiner hohen Prädiktabilität bietet das aufgestellte Wettbewerbsmodell zahlreiche Eisatzmöglichkeiten in Wissenschaft und Praxis. Diese werden im Rahmen der Arbeit ausführlich diskutiert und auf ihren Nutzen für die betriebswirtschaftliche Prognosepraxis hin untersucht.
Open Access
Ein Beitrag zur Stützung eines Software GNSS Empfängers mit MEMS-Inertialsensoren
(2016) Gäb, Michael; Kleusberg, Alfred (Prof. Dr.-Ing.)
Die genaue Bestimmung von Position und Geschwindigkeit mit einem globalen Navigationssatellitensystem (engl. Global Navigation Satellite System) (GNSS) in Echtzeit bildet eine essentielle Grundlage für viele Anwendungen in der Navigation. Bei mobilen Navigationsanwendungen finden häufig GNSS-Messungen unter ungünstigen Beobachtungsbedingungen statt, so dass Fehler in den Ergebnissen auftreten können. In diesem Fall ist der GNSS-Empfänger in Bewegung, so dass die Empfangsumgebung sich ständig ändert. So können Objekte, wie z.B. Gebäude, Bäume, Tunnel usw. zu Reflektionen, Dämpfung bzw. Abschattung der GNSS-Signale führen. Eine hohe zusätzliche Dynamik bzgl. der beobachteten Dopplerfrequenzverschiebung erfährt das empfangene GNSS-Signal durch die Bewegung des GNSS-Empfängers. Das beeinflusst die Signalnachführung (Tracking) und verursacht Fehler bei der Positions- und Geschwindigkeitsbestimmung oder eine Bestimmung ist sogar unmöglich. Eine Verbesserung der Positions- und Geschwindigkeitsbestimmung wird durch die gleichzeitige Messung mit einem GNSS-Empfänger und einem inertialen Navigationssystem (engl. Inertial Navigation System) (INS) ermöglicht. Kostengünstige INS beinhalten heute Mikro-Elektro-Mechanische Systeme (engl. Micro Electro Mechanical Systems) (MEMS), die als MEMS-Inertialsensoren bezeichnet werden. Die gemeinsame Nutzung der Messdaten von GNSS und INS wird als GNSS/INS-Integration bezeichnet. Diese Arbeit befasst sich mit der Tiefen GNSS/INS-Integration, so dass mit der Information eines INSs in die Tracking Loop des GNSS-Empfängers eingegriffen wird, um Verbesserungen beim Tracking des Signals und der daraus bestimmten GNSS-Beobachtungen zu erzielen. Dieser Eingriff wird auch als Stützung (engl. aiding) bezeichnet. Die Stützung erfolgt über die Regelgrößen (Dopplerfrequenz und Codephase) in der Tracking Loop für den jeweiligen Kanal des GNSS-Empfängers. Dazu werden die Regelgrößen zunächst prädiziert, bevor diese beim Tracking des empfangenen GNSS-Signals berücksichtigt werden können. Für die Prädiktion müssen die Position und Geschwindigkeit des Satelliten und des Empfängers vorliegen. Außerdem müssen die Uhrenfehlerrate des Satelliten und des Empfängers bekannt sein. Aus diesen Größen kann die Dopplerfrequenz und daraus die Rate der Codephase berechnet werden. Die zeitliche Integration der Codephasenrate ergibt die aktuelle Codephase. Aus den Ephemeriden des GNSS-Satelliten kann die Position, die Geschwindigkeit und die Uhrenfehlerrate für einen zeitnahen beliebigen Zeitpunkt berechnet werden. Die Uhrenfehlerrate des Empfängers wird hierbei mittels einer Extrapolation vorausbestimmt. Mit den MEMS-Inertialsensoren kann die Position und Geschwindigkeit des Empfängers fortgeführt werden. Diese Fortführung erfolgt über eine Lose GNSS/INS-Integration mittels einer Strapdown-Rechnung und einem Kalman-Filter für 15 Fehlerzustände. Als Stützwerte für den Kalman-Filter dienen hier die Position und Geschwindigkeit des SGEs. Die Stützung sollte bei einem Signalabriss oder für die Stabilisierung des Trackings eingeschaltet werden. Die Stützungsmethode wird mit einem Software GNSS-Empfänger (SGE) und einer Inertiale Messeinheit (engl. inertial measurement unit) (IMU) aus MEMS-Inertialsensoren (MEMS-IMU) in der Landfahrzeugnavigation getestet und analysiert. Der SGE ist für die Signale des globalen Positionierungssystem (engl. Global Positioning System) (GPS) mit dem C/A-Code auf der L1-Frequenz entwickelt und bestimmt die Position und Geschwindigkeit mit einer Messrate von 1 kHz. Die MEMS-IMU beeinhaltet 6 Freiheitsgrade mit jeweils einem 3-achsigen MEMS-Beschleunigungs- und MEMSDrehratensensor. Die Messrate des MEMS-Beschleunigungssensors beträgt 1 kHz und die Messrate des MEMS-Drehratensensors beträgt 800 Hz. Mit diesem Messsystem ist es möglich, die Prädiktion der Regelgrößen für jede Millisekunde durchzuführen, so dass diese bei jedem Tracking-Durchlauf mit dem C/A-Code vorliegen. Aufgrund der hohen Messraten können nur wenige Minuten Messdaten erfasst werden und die Auswertung erfolgt in der Nachbearbeitung (engl. post-processing). Die Stützungsmethode wird durch Fahrten mit einem Messfahrzeug getestet. Dazu werden Messfahrten mit verschiedenen Fahrmanöver ausgeführt, um im empfangenen GPS-Signal unterschiedliche Raten in der Dopplerfrequenz zu erzeugen. Eine Fahrt unter Bäumen ermöglicht den Einfluss des zeitlichen Verlaufs im Signal-Rauschverhältnis (engl. signal-to-noise ratio) (S/N) des empfangenen GPS-Signals auf die Stützungsmethode zu untersuchen. Bei dieser Messfahrt treten auch immer wieder kurzzeitige Signalabrisse auf. Die in der vorliegenden Arbeit dokumentierten Messfahrten und Ergebnisse zeigen, dass die Stützung für einen SGE erfolgreich in der Landfahrzeugnavigation durchgeführt werden kann. Die prädizierten Regelgrößen werden für die verschiedenen Messfahrten zuverlässig berechnet und das Tracking kann damit stabilisiert und sogar bei einem Signalabriss vorgesteuert werden. Außerdem können Ausreißer direkt in den Beobachtungen minimiert werden, so dass Verbesserungen in der Positions- und Geschwindigkeitsbestimmung des SGEs erzielt werden können.
Open Access
Wertschöpfung und Erlösgenerierung etablierter Unternehmen mit digitalen Innovationen : eine explorative Analyse anhand digitaler Services für das vernetzte Automobil
(2021) Bosler, Micha; Burr, Wolfgang (Prof. Dr.)
Digitale Innovationen implizieren für etablierte Unternehmen, deren Kerngeschäft ehemals auf rein physischen Angeboten basierte, radikale Veränderungen der Wertschöpfung und Erlösgenerierung. Neuartige Kombinationen digitaler und physischer Ressourcen bieten einerseits Innovationspotenziale, andererseits wandeln sich die wirtschaftlichen Rahmenbedingungen fundamental. Da bisherige Veröffentlichungen zu digitalen Innovationen meist auf grundlegenden, konzeptionellen Überlegungen basieren, zeigt sich sowohl hinsichtlich empirischer Untersuchungen als auch theoretischer Erklärungen ein Forschungsdefizit. Daran setzt die vorliegende Arbeit an. Als konkreter Untersuchungsgegenstand dienen digitale Services für vernetzte Fahrzeuge. Mittels einer multiplen Fallstudienanalyse von vier Automobilherstellern trägt die explorative Studie zu einem tieferen Verständnis des Innovationsumfelds, den wertschöpfenden Aktivitäten, der damit intendierten Erlösgenerierung und den auftretenden Herausforderungen bei. Als primäre Datenquelle dienen 23 Experteninterviews. Die fallübergreifend generalisierten Erkenntnisse verdeutlichen, welche vielseitigen Veränderungen und Schwierigkeiten für etablierte Unternehmen entstehen, wenn digitale Innovationen ergänzend zu bestehenden Produkten veröffentlicht werden. Gerade das Kerngeschäft der Automobilhersteller zeichnet sich eigentlich durch sehr lange Entwicklungs- und Produktlebenszyklen aus. Entscheidungen über die Umfänge künftiger Baureihen, einschließlich der technologischen Innovationen, werden traditionell mit mehrjähriger Vorlaufzeit getroffen, um Risiken zu minimieren und zum Produktionsbeginn ein perfektioniertes Fahrzeug bei höchsten Qualitätsstandards zu gewährleisten. Das erweist sich als völlig konträr zum digitalen Geschäft, wo insbesondere die Schnelligkeit zum ausschlaggebenden Kriterium für Wettbewerbsvorteile wird. Es braucht deutlich kürzere Innovationsprozesse, hohe Investitionen, mehr Risikobereitschaft und eine veränderte Denkweise, die sich von ehemals bewährten Praktiken löst. Die erfolgreiche Veröffentlichung digitaler Innovationen geht - neben der langwierigen Transformation der eigenen Ressourcenbasis - mit einer Ausdehnung in Wertschöpfungsnetzwerke sowie der intensiven Integration von Partnern einher. Ohnehin endet das Geschäftsmodell der Hersteller nicht mehr mit dem Verkauf des Fahrzeugs an den Händler. Die Unternehmen agieren erstmals direkt im Endkundengeschäft und erhoffen sich kontinuierliche Einnahmen in Form kostenpflichtiger Services. Angesichts der Möglichkeit der nachträglichen Einführung digitaler Innovationen werden die vernetzten Automobile über ihren gesamten Lebenszyklus veränderbar. Allerdings sind die Automobilhersteller nicht nur mit einem veränderten Produktverständnis, sondern auch mit neuen Anforderungen der Kunden an digitale Dienste konfrontiert, die zunächst überhaupt erkannt und daraufhin berücksichtigt werden müssen. Abschließend richtet sich der Fokus auf die Theoretisierung digitaler Innovationen. Ausgehend von den empirisch identifizierten Zusammenhängen werden Eignung und Anpassungsbedarf ausgewählter Ansätze - wie Dynamic Capabilities, der Practice-based View oder das Dominante Design - diskutiert.
Open Access
Automated composition of adaptive pervasive applications in heterogeneous environments
(2012) Schuhmann, Stephan Andreas; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c.)
Distributed applications for Pervasive Computing represent a research area of high interest. Configuration processes are needed before the application execution to find a composition of components that provides the required functionality. As dynamic pervasive environments and device failures may yield unavailability of arbitrary components and devices at any time, finding and maintaining such a composition represents a nontrivial task. Obviously, many degrees of decentralization and even completely centralized approaches are possible in the calculation of valid configurations, spanning a wide spectrum of possible solutions. As configuration processes produce latencies which are noticed by the application user as undesired waiting times, configurations have to be calculated as fast as possible. While completely distributed configuration is inevitable in infrastructure-less Ad Hoc scenarios, many realistic Pervasive Computing environments are located in heterogeneous environments, where additional computation power of resource-rich devices can be utilized by centralized approaches. However, in case of strongly heterogeneous pervasive environments including several resource-rich and resource-weak devices, both centralized and decentralized approaches may lead to suboptimal results concerning configuration latencies: While the resource-weak devices may be bottlenecks for decentralized configuration, the centralized approach faces the problem of not utilizing parallelism. Most of the conducted projects in Pervasive Computing only focus on one specific type of environment: Either they concentrate on heterogeneous environments, which rely on additional infrastructure devices, leading to inapplicability in infrastructure-less environments. Or they address homogeneous Ad Hoc environments and treat all involved devices as equal, which leads to suboptimal results in case of present resource-rich devices, as their additional computation power is not exploited. Therefore, in this work we propose an advanced comprehensive adaptive approach that particularly focuses on the efficient support of heterogeneous environments, but is also applicable in infrastructure-less homogeneous scenarios. We provide multiple configuration schemes with different degrees of decentralization for distributed applications, optimized for specific scenarios. Our solution is adaptive in a way that the actual scheme is chosen based on the current system environment and calculates application compositions in a resource-aware efficient manner. This ensures high efficiency even in dynamically changing environments. Beyond this, many typical pervasive environments contain a fixed set of applications and devices that are frequently used. In such scenarios, identical resources are part of subsequent configuration calculations. Thus, the involved devices undergo a quite similar configuration process whenever an application is launched. However, starting the configuration from scratch every time not only consumes a lot of time, but also increases communication overhead and energy consumption of the involved devices. Therefore, our solution integrates the results from previous configurations to reduce the severity of the configuration problem in dynamic scenarios. We prove in prototypical real-world evaluations as well as by simulation and emulation that our comprehensive approach provides efficient automated configuration in the complete spectrum of possible application scenarios. This extensive functionality has not been achieved by related projects yet. Thus, our work supplies a significant contribution towards seamless application configuration in Pervasive Computing.
Open Access
Construction of robust Escherichia coli strains for large-scale production
(2022) Ziegler, Martin; Takors, Ralf (Prof. Dr.-Ing.)
The biotechnical production of many fine chemicals, proteins or pharmaceuticals depends on large-scale microbial cultivations. Due to limited mixing, heterogeneities in process relevant parameters such as nutrient concentrations arise in such fermentations. Escherichia coli (E. coli) is a model organism frequently used in the biotechnological industry. If E. coli is cultivated under heterogeneous conditions, biological reactions of the microorganism result in reduced process performance. Since large-scale fermentations are not economically feasible in academic settings, scale-down reactors that mimic aforementioned heterogeneities are used to investigate heterogenous fermentations. Previous studies in scale-down reactors unraveled that, depending on the process strategy, the unstable supply of a limiting primary carbon or nitrogen source such as glucose or ammonium is one of the underlying causes of process performance loss. Low concentrations of glucose or ammonium elicit the stringent response as a biological starvation reaction which comprises extensive transcriptional reactions. In the first project that contributes to this thesis, the regulatory and transcriptional reactions of the strains E. coli MG1655 and E. coli SR to repeated exposure to ammonium starvation zones were examined in a scale-down reactor. The scale-down reactor followed a two-compartment approach and consisted of a stirred tank reactor and a plug-flow reactor simulating passage through a starvation zone. E. coli SR is a strain with modulated stringent response. It was observed that short-term starvation stimuli do not trigger this regulatory program in E. coli SR and the transcriptional reaction was noticeably reduced. Long-term adaptation of the strain to repeated cycles of limitation and starvation also clearly differed from E. coli MG1655. Despite lack of the stringent response, E. coli SR showed no deficits in the assimilation of the limiting ammonium or in biomass yield on ammonium. In the second project of this thesis, a series of deletion strains with robust phenotype against glucose starvation zones were constructed. Candidate genes were identified and successively removed from the genome of E. coli MG1655 by Recombineering. The fundamental growth parameters of the strains were determined in shaking flask fermentations and no noticeable differences compared to E. coli MG1655 were found. Chemostat cultivations in a scale-down reactor with glucose as the limiting nutrient source revealed that the final strain of the deletion series, E. coli RM214, had a significantly lower maintenance coefficient under heterogeneous conditions than E. coli MG1655. Moreover, in an exemplary heterologous protein productionscenario E. coli RM214 rhaB- pJOE4056.2_tetA proved to be more robust to heterogeneities and showed a significantly higher product yield than E. coli MG1655 rhaB- pJOE4056.2_tetA. In the third project of this thesis, the production of pyruvate in E. coli MG1655 by inhibition of pyruvate dehydrogenase through CRISPR interference was investigated. A central goal was to achieve the stable production in nitrogen-limited conditions. For this, different target sequences in the operon pdhR-aceEF-lpd were tested and the strains cultivated in shaking flask fermentations. All tested target sequences were generally suitable to trigger the accumulation of pyruvate. Combined CRISPR interference against two target sequences did not lead to an increased pyruvate yield in most cases. In addition, the strains E. coli MG1655 pdCas9 psgRNA_aceE_234 and E. coli MG1655 pdCas9 psgRNA_aceE_234_pdhR_329 were characterized in two phase fermentations in lab-scale reactors. The initial phase was an unlimited exponential growth phase and was followed by an ammonium-limited production phase. E. coli MG1655 pdCas9 psgRNA_aceE_234 only produced pyruvate during the exponential phase, and reuptake of pyruvate occurred in the second phase. In contrast, E. coli MG1655 pdCas9 psgRNA_aceE_234_pdhR_329 stably produced pyruvate during the exponential and the ammonium-limited phase and is a potential chassis strain for the growth-decoupled production of pyruvate derived bioproducts. The overarching research issues of the projects were the characterization of strains in heterogeneous conditions and the development of new strategies to improve their performance. The collected data leads me to conclude that the construction of robust microbial strains for large-scale applications is both expedient and feasible. Tailored genetic modifications are the method of choice to achieve this goal. Furthermore, suitable genetic constructs offer promising possibilities for the stable growth-decoupled production of chemicals in nitrogen-limited conditions.
Open Access
High-resolution spatio-temporal measurements of the colmation phenomenon under laboratory conditions
(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2022) Mayar, Mohammad Assem; Wieprecht, Silke (Prof. Dr.-Ing.)
The fine sediment infiltration and accumulation into the gravel bed of rivers, the so-called colmation phenomenon, is a pernicious process exacerbated by anthropogenic activities. Owing to the importance and complexity of this phenomenon, it has been widely studied over the last decades. Various devices and methods have been developed to assess this phenomenon, where most of them are destructive and sample-based, resulting in an alteration of the natural conditions. Therefore, non-intrusive techniques, which provide spatial and temporal details with a high-resolution, are required to discretize the mechanisms involved in the colmation process. To address these issues, investigations under laboratory conditions may simplify the complexity of nature and enable individual and exactly defined boundary conditions to be investigated. Therefore, this thesis aims at (i) developing a non-intrusive and undisturbed measurement method for the high-resolution spatio-temporal measurements of the sediment infiltration processes and the development of sediment accumulation in an artificial river bed under laboratory conditions, (ii) applying this method to certain experiments for the assessment of the effects of different boundary conditions on sediment infiltration, and (iii) investigating the colmation phenomenon (also known as clogging) of gravel beds. For this purpose, the gamma-ray attenuation method is used together with an artificial gravel bed arranged from the spheres with various diameters and placed in a laboratory flume. This new method works based on the gamma radiation that passes through the infiltrated sediments, water, and bed spheres, in which the gamma-ray attenuation is linked to the variations of the infiltrated sediments’ quantity. The main simplification of this approach is that gravel beds are represented by the combinations of different-sized spheres. This gives the opportunity to fully distinguish infiltrating sediments from the bed material, reduce the complexity of the natural environment, and allows for repetitive measurements of the same position with different boundary conditions. From the results of this study, first, the gamma-ray attenuation measurement method was optimized to resolve the inconsistencies in the measurements. Subsequently, the concept of the non-intrusive and undisturbed measurement is proved through box experiments. Additional reproducibility experiments in the laboratory flume, for a similar bed structure, showed only small deviations between two experiments with the same setup. Consequently, the established technique was used in a series of experiments to evaluate the effects of different supply rates, total supply masses, and sediment particle size boundary conditions on the sediment infiltration and colmation processes. Vertical profiles of the infiltrated sediment were quantified through high spatial resolution measurements. Furthermore, to evaluate the infiltrating sediment accumulation development, and the temporal variations of the infiltrated sediments, the vertical profile measurements were first repeated after a specific time-period to track interval-averaged variations in all positions of the vertical axis. Next, a specific position of the vertical axis was measured continuously during the entire experiment in a high temporal resolution. The measured vertical profiles illustrate the vertical distribution, colmation, and unimpeded percolation of the infiltrated sediments. The dynamic one-point measurement precisely identifies the three phases (the start of the pore-filling, the required time to fill the pore, and the final amount of infiltrated sediments including natural fluctuation during the ongoing experiments) of the sediment infiltration or the possible clogging. As a limitation, the gamma-ray attenuation system’s current configuration only works in artificial gravel beds because of the given density difference between infiltrated sediments and the artificial bed structure. Intense radiations that pass through the natural bed's thickness are capable of detecting a significant amount of infiltrated sediments. However, small amounts of infiltrated sediments will create only a minimal shift in attenuation, which might be confused with the statistical error. In addition, the legal restriction against using radioactive material in the natural environment is another reason for not applying it in the field. Furthermore, the gamma-ray attenuation method cannot resolve the sediment distribution in the measurement horizon and provides an integrative result for each measurement position. In addition, if a mixture of silt, clay, and sand is supplied to the experiment, the gamma-ray attenuation system will produce a bulk result of all the infiltrated materials. To conclude, despite the limitations mentioned above, the gamma-ray attenuation method offers a unique opportunity for the non-intrusive and undisturbed measurements of the sediment infiltration or the special case of colmation, with a high spatio-temporal resolution. This method has the potential to quantify the investigated processes on a millimetric spatial scale, if the measurement time is not a constraint, or vice versa, in a high temporal resolution (seconds) for a specific position, if spatial scale is not important. Moreover, the gamma-ray attenuation approach can simultaneously measure the longitudinal distribution of the sedimentological processes, if multiple instruments or a single device with several radiation-emitting-holes is in operation. Last, but not least, rather than the spheres, artificial gravel beds could be made of any substance with a composition significantly different from the infiltrating sediments, and the boundary conditions of the experiments can be improved in order to attain conditions close to nature. Finally, the gamma-ray attenuation method can be integrated with advanced flow measurement instruments such as Particle Image Velocimetry (PIV) and other high-resolution endoscopic devices to track the behavior of fine sediment infiltration and its clogging process in the porous gravel beds as it occurs in nature.

Universität Stuttgart

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