The Ca2+Ca^{2+}-activated Cl−Cl^- current ensures robust and reliable signal amplification in vertebrate olfactory receptor neurons

Activation of most primary sensory neurons results in transduction currents that are carried by cations. One notable exception is the vertebrate olfactory receptor neuron (ORN), where the transduction current is carried largely by the anion $Cl^-$. However, it remains unclear why ORNs use an anionic current for signal amplification. We have sought to provide clarification on this topic by studying the so far neglected dynamics of $Na^+$, $Ca^{2+}$, $K^+$ and $Cl^-$ in the small space of olfactory cilia during an odorant response. Using computational modeling and simulations we compared the outcomes of signal amplification based on either $Cl^-$ or $Na^+$ currents. We found that amplification produced by $Na^+$ influx instead of a $Cl^-$ efflux is problematic due to several reasons: First, the $Na^+$ current amplitude varies greatly depending on mucosal ion concentration changes. Second, a $Na^+$ current leads to a large increase in the ciliary $Na^+$ concentration during an odorant response. This increase inhibits and even reverses $Ca^{2+}$ clearance by $Na^+/Ca^{2+}/K^+$ exchange, which is essential for response termination. Finally, a $Na^+$ current increases the ciliary osmotic pressure, which could cause swelling to damage the cilia. By contrast, a transduction pathway based on $Cl^-$ efflux circumvents these problems and renders the odorant response robust and reliable.Comment: 31 pages, 10 figures (including SI

Left-Invariant Diffusion on the Motion Group in terms of the Irreducible Representations of SO(3)

In this work we study the formulation of convection/diffusion equations on the 3D motion group SE(3) in terms of the irreducible representations of SO(3). Therefore, the left-invariant vector-fields on SE(3) are expressed as linear operators, that are differential forms in the translation coordinate and algebraic in the rotation. In the context of 3D image processing this approach avoids the explicit discretization of SO(3) or $S_2$, respectively. This is particular important for SO(3), where a direct discretization is infeasible due to the enormous memory consumption. We show two applications of the framework: one in the context of diffusion-weighted magnetic resonance imaging and one in the context of object detection

Nitrogen tetroxide vapor scrubber using a recirculating liquid

Scrubbers required to reduce N2O4 contamination of nitrogen vent gas streams to a safe level to preclude health hazard to personnel and to preclude adverse environmental effects were developed. The scrubber principle involved is to absorb and neutralize the N2O4 component in a closed circuit circulating water/chemical solution in a vertical counter-flow, packed-tower configuration. The operational and performance test requirements for the scrubbers consist of demonstrating that the exit gas contamination level from the scrubbers does not exceed 150 ppm oxidizer under any flow conditions up to 400 scfm with inlet concentrations of up to 100,000 ppm oxidizer. Several problems were encountered during the performance testing that led to a series of investigations and supplementary testing. It was finally necessary to change the scrubber liquors in oxidizer scrubber to successfully achieve performance requirements. The scrubbers, the test configuration, and the various tests performed are described

Moduli spaces of parabolic twisted generalized Higgs bundles

In this thesis we study moduli spaces of decorated parabolic principal G-bundles on a compact Riemann surface X. In [Sch08] Alexander Schmitt constructed the moduli space of affine generalized Higgs bundles consisting of a principal G-bundle P on X and a global section into an associated vector bundle as a GIT-quotient. Affine Higgs bundles are generalizations of several well-studied objects, such as G-Higgs bundles, Bradlow pairs or quiver representations. In this work we generalize this GIT-construction of the moduli space of affine Higgs bundles to the case of affine parabolic Higgs bundles. A parabolic structure on P over a fixed finite subset S of punctures of the compact Riemann Surface X is given by reductions over S to parabolic subgroups of G. Our main result shows the existence of the resulting moduli space of decorated parabolic bundles as a quasi-projective scheme. The moduli space of parabolic G-Higgs bundles (see [Sim94]) is obtained from our construction by slight modifications of the semistability concept. Other important applications include the construction of a (generalized) projective Hitchin morphism into an affine scheme as well as an extension of the results of Nikolai Beck [Be14] on moduli spaces of pointwisely decorated principal bundles.In der vorliegenden Dissertation untersuchen wir Modulräume dekorierter parabolischer G-Hauptfaserbündel über einer kompakten Riemannschen Fläche X. Alexander Schmitt konstruiert in [Sch08] erstmals den Modulraum affiner Higgsbündel bestehend aus einem G-Hauptfaserbündel P über X sowie einem globalen Schnitt in ein assoziiertes Bündel als GIT-Quotient. Affine-Higgsbündel enthalten als wichtige Spezialfälle unter anderem G-Higgsbündel, Bradlow-Paare und gewisse Köcherdarstellungen. In dieser Arbeit erweitern wir diese GIT-Konstruktion des Modulraums affinier Higgsbündel auf den Fall affiner parabolischer Higgsbündel. Eine parabolische Struktur auf P über einer vorgegebenen Menge S von Punktierungen der kompakten Riemannschen Fläche X ist gegeben durch Reduktionen in Quotienten von P nach parabolischen Untergruppen von G. Als Hauptresultat zeigen wir, dass der resultierende Modulraum dekorierter parabolischer Hauptfaserbündel als quasi-projektives Schema über C existiert. Nach kleineren Modifikationen des Semistabilitätsbegriffes ergibt sich der Modulraum parabolischer G-Higgsbündel (siehe [Sim94]) für eine gewisse Wahl der assoziierenden Darstellung, d.h. für die adjungierte Darstellung von G auf ihrer Lie Algebra, als Spezialfall unserer allgemeinen Konstruktion. Weitere wichtige Anwendungen beinhalten die Konstruktion einer (verallgemeinerten) projektiven Hitchin-Abbildung vom Modulraum in ein affines Schema sowie eine Erweiterung der Ergebnisse von Nikolai Beck [Be14] zu Modulräumen punktweise dekorierter G-Hauptfaserbündel

Non-synaptic inhibition between grouped neurons in an olfactory circuit.

Diverse sensory organs, including mammalian taste buds and insect chemosensory sensilla, show a marked compartmentalization of receptor cells; however, the functional impact of this organization remains unclear. Here we show that compartmentalized Drosophila olfactory receptor neurons (ORNs) communicate with each other directly. The sustained response of one ORN is inhibited by the transient activation of a neighbouring ORN. Mechanistically, such lateral inhibition does not depend on synapses and is probably mediated by ephaptic coupling. Moreover, lateral inhibition in the periphery can modulate olfactory behaviour. Together, the results show that integration of olfactory information can occur via lateral interactions between ORNs. Inhibition of a sustained response by a transient response may provide a means of encoding salience. Finally, a CO(2)-sensitive ORN in the malaria mosquito Anopheles can also be inhibited by excitation of an adjacent ORN, suggesting a broad occurrence of lateral inhibition in insects and possible applications in insect control