In-situ comparison of the NOy instruments flown in MOZAIC and SPURT

Two aircraft instruments for the measurement of total odd nitrogen (NOy) were compared side by side aboard a Learjet A35 in April 2003 during a campaign of the AFO2000 project SPURT (Spurengastransport in der Tropopausenregion). The instruments albeit employing the same measurement principle (gold converter and chemiluminescence) had different inlet configurations. The ECO-Physics instrument operated by ETH-Zürich in SPURT had the gold converter mounted outside the aircraft, whereas the instrument operated by FZ-Jülich in the European project MOZAIC III (Measurements of ozone, water vapour, carbon monoxide and nitrogen oxides aboard Airbus A340 in-service aircraft) employed a Rosemount probe with 80 cm of FEP-tubing connecting the inlet to the gold converter. The NOy concentrations during the flight ranged between 0.3 and 3 ppb. The two data sets were compared in a blind fashion and each team followed its normal operating procedures. On average, the measurements agreed within 7%, i.e. within the combined uncertainty of the two instruments. This puts an upper limit on potential losses of HNO3 in the Rosemount inlet of the MOZAIC instrument. Larger transient deviations were observed during periods after calibrations and when the aircraft entered the stratosphere. The time lag of the MOZAIC instrument observed in these instances is in accordance with the time constant of the MOZAIC inlet line determined in the laboratory for HNO3

Dreidimensionale Objektraumerfassung durch aktive optische Mikrosysteme

Diese Dissertation befasst sich mit der Fragestellung einer optimalen Nutzung verstimmbarer mikrooptischer Bauelemente für den Einsatz in abbildenden Optiksystemen. Neue Ansätze zur Miniaturisierung abbildender Systeme beruhen auf Komponenten mit variablen optischen Eigenschaften wie der Linsenbrennweite oder dem Blendendurchmesser. Diese können auf die jeweiligen Abbildungsbedingungen angepasst werden und so eine möglichst hohe Leistungsfähigkeit bei gleichzeitig kleinem Bauraum erzielen. Eingeschränkt wird der Verstimmbereich jedoch meist durch die verwendeten Materialen und Aktuierungskonzepte. Dies erfordert neue Wege in der Konzeptionierung solcher Systeme, welche neben den zahlreichen Vorzügen eines variablen Bauelementes auch die Schwachstellen dieser einbeziehen müssen. Im Folgenden werden flüssigkeitsgefüllte Linsen mit Membranen aus Aluminiumnitrid untersucht, welche über einen angelegten Druck verstimmt werden können. Es erfolgen eine Untersuchung der Einzelkomponenten sowie Design, Aufbau und Charakterisierung eines scannenden Systems und eines Zoomobjektives, welche ohne bewegliche Teile auskommen. Aufgrund der hohen mechanischen Stabilität der verwendeten Membranen ist auch eine Realisierung von Linsen mit zylindrischem Oberflächenprofil möglich. Hiermit wird ein anamorphotisches System, mit in horizontaler und vertikaler Bildrichtung individuell einstellbaren Abbildungsmaßstäben, demonstriert. Die thermomechanischen Eigenschaften des Aluminiumnitrids ermöglichen auch die Umsetzung eines Prismas zur variablen Strahlablenkung in Transmission. Es wird gezeigt, dass dessen Ausrichtung einen wesentlichen Einfluss auf die Stärke der Ablenkung und die Abbildungsqualität hat. Neue Konzepte für verstimmbare Blenden ermöglichen die Anpassung der Öffnung ohne bewegliche Teile. Beispielsweise lässt sich von elektrochromen Materialien die Transmission elektrisch gesteuert beeinflussen. Ein Nachteil dieses Materialsystems ist die nicht ideale Absorption im Randbereich der Blende. Welche Leistungsfähigkeit von diesen Blenden zu erwarten ist und welcher Einstellbereich gewählt werden sollte, zeigen Untersuchungen hinsichtlich einer maximalen Abbildungstiefe. Ausgehend von konkreten Bauelementen, erbringt diese Arbeit allgemeingültige Designstrategien für die Auslegung verstimmbarer Linsen, Prismen und Blenden.The idea to transfer the function of the evolutionary masterpiece eye to a technical device can be seen as the starting point of this thesis. The pivotal point behind this is the optimum system design with tunable micro-optical components for imaging applications. The capabilities to adjust optical elements and adapting properties as resolution, magnification, angle of field, or depth of focus with respect to a required imaging quality become more and more important. Thus enables to combine high performance and minimum system size. In many cases, multifunctional elements are based on new materials whose properties are not optimized for optical applications and actuation concepts that are limited in tuning range. Dealing with both sides will be a major challenge to achieve optimum systems. Following fluidic micro-lenses with tunable, pressure controlled membranes of aluminum nitride (AlN) are used to realize imaging systems with scanning and zooming functionality. Due to the outstanding mechanical stability of AlN, it is possible to create lenses with nearly ideal spherical and cylindrical shape. This enables to establish an anamorphic system with separately tunable magnification in horizontal and vertical image direction that works without moving elements. In addition the thermo-mechanical properties of AlN allow to realize a tunable prism. The tilt angle of these prisms is rather limited. Thus it is shown how to increase the deflection by an appropriate positioning whereby the image quality stays nearly constant. To influence intensity, image aberrations and depth of focus of micro-optical systems there are several new concepts of tunable micro-apertures that enable to stop down without moving parts. Many of them are based on opaque fluids or materials whose transmission spectrum can be changed. Due to material characteristics and system design a totally absorbing aperture is hard to achieve. By using a geometric ray-model it is analyzed what is the residual transmission's impact on the depth of focus. A design strategy is developed to perform an optimum aperture geometry. The results are verified by diffractive simulations and experimental measurements. Based on concrete samples, this thesis provides generalized strategies for design and fabrication of tunable elements as lenses, prims and apertures

Undisturbed climbing fiber pruning in the cerebellar cortex of CX3CR1-deficient mice

Pruning, the elimination of excess synapses is a phenomenon of fundamental importance for correct wiring of the central nervous system. The establishment of the cerebellar climbing fiber (CF)-to-Purkinje cell (PC) synapse provides a suitable model to study pruning and pruning-relevant processes during early postnatal development. Until now, the role of microglia in pruning remains under intense investigation. Here, we analyzed migration of microglia into the cerebellar cortex during early postnatal development and their possible contribution to the elimination of CF-to-PC synapses. Microglia enrich in the PC layer at pruning-relevant time points giving rise to the possibility that microglia are actively involved in synaptic pruning. We investigated the contribution of microglial fractalkine (CX3CR1) signaling during postnatal development using genetic ablation of the CX3CR1 receptor and an in-depth histological analysis of the cerebellar cortex. We found an aberrant migration of microglia into the granule and the molecular layer. By electrophysiological analysis, we show that defective fractalkine signaling and the associated migration deficits neither affect the pruning of excess CFs nor the development of functional parallel fiber and inhibitory synapses with PCs. These findings indicate that CX3CR1 signaling is not mandatory for correct cerebellar circuit formation. Main Points - Ablation of CX3CR1 results in a transient migration defect in cerebellar microglia. - CX3CR1 is not required for functional pruning of cerebellar climbing fibers. - Functional inhibitory and parallel fiber synapse development with Purkinje cells is undisturbed in CX3CR1-deficient mice

“Computational Imaging” zur Optimierung optischer Abbildungssysteme

Durch eine definierte Phasenmodifizierung in optisch abbildenden Systeme (Wave front Coding) und digitale Nachverarbeitung des aufgenommenen Bildes lässt sich eine Vergrößerung der Schärfentiefe bei gleichbleibender Apertur erreichen. Es werden Design- und Fertigungsprozess einer refraktiven kubischen Phasenplatte sowie Experimente zur Punktabbildung beschrieben

Developmental Easing of Short-Term Depression in “Winner” Climbing Fibers

The postnatal development of cerebellar climbing fiber (CF) to Purkinje neuron (PN) synapses is characterized by a substantial pruning during the first 3 weeks after birth, switching from multiple- to single-CF innervation. Previous studies suggested that CF maturation is governed by bidirectional changes of synaptic plasticity. The strengthening of surviving “winner” CFs, which translocate from the PN soma to the dendrite, is thought to be guided by long-term potentiation (LTP), while weakening of to-be-eliminated “loser” CFs, which remain on the soma, was proposed to be due to long-term depression (LTD). However, there are conflicting results from previous studies, whether or not strengthening of winner and weakening of loser CFs during postnatal development is accompanied by changes in short-term plasticity and, thus, whether pre- or postsynaptic forms of LTD and LTP are operational. We, therefore, analyzed the developmental profile of paired-pulse depression (PPD) in “weak” and “strong” CFs in 3–21-day old Igsf9-eGFP mice, which allow visual identification of GFP-labeled CFs. We found that in 3–8-day old mice strong CFs are marked by a stronger PPD compared to weak CFs. Surprisingly, PPD of strong CFs eases during maturation, while PPD in weak CFs remains unchanged. This easing of PPD is neither due to changes in presynaptic influx-release coupling nor to an increased saturation of postsynaptic receptors. Thus, our results imply that synaptic contacts of CFs show distinct features of PPD depending on their affiliation to winner or loser CFs and depending on their somatic or dendritic location

Wave-front Coding for increased depth of field of optical systems

Wave-front Coding is used for increasing the depth of field of optical systems. We demonstrate the functionality by using a cubic phase plate. We present design considerations, the fabrication process of the refractive phase plate as well as experimental results with a specific focus on fabrication errors

Learning-based autonomous vascular guidewire navigation without human demonstration in the venous system of a porcine liver

Purpose The navigation of endovascular guidewires is a dexterous task where physicians and patients can benefit from automation. Machine learning-based controllers are promising to help master this task. However, human-generated training data are scarce and resource-intensive to generate. We investigate if a neural network-based controller trained without human-generated data can learn human-like behaviors. Methods We trained and evaluated a neural network-based controller via deep reinforcement learning in a finite element simulation to navigate the venous system of a porcine liver without human-generated data. The behavior is compared to manual expert navigation, and real-world transferability is evaluated. Results The controller achieves a success rate of 100% in simulation. The controller applies a wiggling behavior, where the guidewire tip is continuously rotated alternately clockwise and counterclockwise like the human expert applies. In the ex vivo porcine liver, the success rate drops to 30%, because either the wrong branch is probed, or the guidewire becomes entangled. Conclusion In this work, we prove that a learning-based controller is capable of learning human-like guidewire navigation behavior without human-generated data, therefore, mitigating the requirement to produce resource-intensive human-generated training data. Limitations are the restriction to one vessel geometry, the neglected safeness of navigation, and the reduced transferability to the real world

Measurements of total odd nitrogen (NOy) aboard MOZAIC in-service aircraft: instrument design, operation and performance

A small system for the unattended measurement of total odd nitrogen (NOy, i.e., the sum of NO and its atmospheric oxidation products) aboard civil in-service aircraft in the framework of MOZAIC is described. The instrument employs the detection of NO by its chemiluminescence with O-3 in combination with catalytic conversion of the other NOy compounds to NO at 300degreesC on a gold surface in the presence of H-2. The instrument has a sensitivity of 0.4-0.7 cps/ppt and is designed for unattended operation during 1-2 service cycles of the aircraft (400-800 flight hours). The total weight is 50 kg, including calibration system, compressed gases, mounting, and safety measures. The layout and inlet configuration are governed by requirements due to the certification for passenger aircraft. Laboratory tests are described regarding the conversion efficiency for NO2 and HNO3 (both > 98%). Interference by non-NOy species is <1% for CH3CN and NH3, <5 x 10(-5) % for N2O (corresponding to <0.2 ppt fake NOy from ambient N2O) and 100% for HCN. The time response of the instrument is <1 s (90% change) for NO2. The response for HNO3 is nonlinear: 20 s for 67%, 60 s for 80%, and 150 s for 90% response, respectively