Semi-analytical Modeling of Planetesimal Formation. Implications for Planet Formation and the Solar Nebula

Planetesimals are the hypothetical building blocks of planets, halfway between dust aggregation and the formation of planetary embryos. The typical diameter of newborn planetesimals was found to be around 100 km. The timedependent production of these planetesimals and their radial distribution in disks around young stars is still unclear. This thesis proposes a semi-analytical model for the planetesimal formation rate that is regulated by the radial pebble flux. The model is implemented into a code that solves the evolution of gas as well as the growth and radial motion of grains. Within this model, planetesimals form as soon as micron-sized dust has grown to pebble-size (typically ~ mm–cm) and a critical pebble flux is reached. The resulting spatial planetesimal profile is steeper compared to the initial dust and gas distribution. E.g., for a temperature profile T∝r^-0.5, the planetesimal profile is expected to follow Σ_p∝r^-2.25 in the inner disk regions. The maximum local planetesimal production is reached for a planetesimal formation efficiency that allows the planetesimal formation timescale and the pebbles drift timescale to be equal. A disk parameter study is performed which enables to set limits on possible parameters for the Solar Nebula by comparing the produced planetesimal profiles with mass constraints for initial planetesimals. This thesis shows that the Solar Nebula was not too large, enclosing most of the mass within 50 au. Outside of 50 au, particle traps needed several hundreds of orbits to form or never formed there. Compared to the mass constraints, the most appealing case that is analyzed in this thesis has a disk mass of around 0.1 solar masses, a fragmentation speed of particles of 2 m/s, and moderate to weak turbulence (α = 3⋅10^-4). The model introduced in this thesis does not require fine tuning in order to meet mass constraints for the Solar Nebula which stresses the applicability of the proposed parameterization to models of planet formation. By sorting pebbles by their origins, this thesis shows that a significant amount of pebble mass passed major ice lines before forming planetesimals in the inner Solar Nebula or before they were accreted by planetary embryos at the current positions of the asteroid belt and Earth. The relative contribution to planetesimals from regions of different particle origins changes for different times of planetesimal formation. This thesis concludes with the importance of pebble transport and the planetesimal formation efficiency for shaping the spatial distribution of planetesimals. The presented planetesimal formation rate model can be used to bridge the gap between the phases of dust growth and the formation of planetary embryos

Supervised Autonomous Locomotion and Manipulation for Disaster Response with a Centaur-like Robot

Mobile manipulation tasks are one of the key challenges in the field of search and rescue (SAR) robotics requiring robots with flexible locomotion and manipulation abilities. Since the tasks are mostly unknown in advance, the robot has to adapt to a wide variety of terrains and workspaces during a mission. The centaur-like robot Centauro has a hybrid legged-wheeled base and an anthropomorphic upper body to carry out complex tasks in environments too dangerous for humans. Due to its high number of degrees of freedom, controlling the robot with direct teleoperation approaches is challenging and exhausting. Supervised autonomy approaches are promising to increase quality and speed of control while keeping the flexibility to solve unknown tasks. We developed a set of operator assistance functionalities with different levels of autonomy to control the robot for challenging locomotion and manipulation tasks. The integrated system was evaluated in disaster response scenarios and showed promising performance.Comment: In Proceedings of IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Madrid, Spain, October 201

Fast Object Learning and Dual-arm Coordination for Cluttered Stowing, Picking, and Packing

Robotic picking from cluttered bins is a demanding task, for which Amazon Robotics holds challenges. The 2017 Amazon Robotics Challenge (ARC) required stowing items into a storage system, picking specific items, and packing them into boxes. In this paper, we describe the entry of team NimbRo Picking. Our deep object perception pipeline can be quickly and efficiently adapted to new items using a custom turntable capture system and transfer learning. It produces high-quality item segments, on which grasp poses are found. A planning component coordinates manipulation actions between two robot arms, minimizing execution time. The system has been demonstrated successfully at ARC, where our team reached second places in both the picking task and the final stow-and-pick task. We also evaluate individual components.Comment: In: Proceedings of the International Conference on Robotics and Automation (ICRA) 201

Umweltberichterstattung von Unternehmen im Internet. Der aktuelle Stand für Deutschland

Von den Umweltberichten deutscher Unternehmen werden bisher erst unter 3% im Internet veröffentlicht. Die Tendenz ist steigend. Hier werden die im Internet verfügbaren Umweltberichte ausgewertet und Gründe für die Nutzung des Internet für die Umweltberichterstattung vorgetragen. Der Beitrag ist in fünf Abschnitte gegliedert: Zur thematischen Einführung werden betriebliche Umweltberichte durch eine Morphologie charakterisiert (Abschnitt 2). Es schließen sich die IKT-spezifischen Herausforderungen an umweltberichterstattende Unternehmen als Ansatzpunkte für Umweltberichte im Internet an (Abschnitt 3). Damit ist die Basis für eine Systematisierung der internetbasierten Unterstützungspotenziale zur Umweltberichterstattung gelegt (Abschnitt 4). Der Systematik folgt eine detaillierte Bestandsaufnahme der Umweltberichte deutscher Unternehmen im Internet in fünffacher Hinsicht (Abschnitt 5): Die zugrunde gelegte Untersuchungsmethodik zur Bestandsaufnahme wird erläutert (Abschnitt 5.1). Die ergänzend herangezogenen empirischen Studien zu Umweltberichten im Internet werden ausgewertet (Abschnitt 5.2). Die Ergebnisse bzgl. Inhalt und Darstellung von Umweltberichten im Internet werden ausführlicher beschrieben (Abschnitt 5.3) und durch Erklärungsansätze interpretiert (Abschnitt 5.4). Abschließend werden auf der Grundlage der konzeptionell erschließbaren Unterstützungspotenziale einerseits und der empirischen Studien andererseits zentrale Tendenzen zur zukünftigen Entwicklung von Umweltberichten im Internet vorgetragen (Abschnitt 5.5)

Regulation of natriuretic peptide (urodilatin) release in a human kidney cell line

Regulation of natriuretic peptide (urodilatin) release in a human kidney cell line.BackgroundTo identify the molecular mechanisms underlying the release of a renal natriuretic peptide (NP) we selected a human kidney cell line (HEK 293) that displays several characteristics of distal tubular cells.MethodsCells were exposed to different extracellular and intracellular stimuli, and the effect on NP release was measured with a specific urodilatin radioimmunoassay, as well as with an atrial NP (ANP) radioimmunoassay.ResultsIn the absence of stimuli, HEK 293 cells showed a basal release of urodilatin immunoreactivity and ANP immunoreactivity. Raising the osmolality of the secretion medium with sodium chloride and various other osmolytes rapidly increased cellular NP secretion. Elevation of intracellular cAMP levels by forskolin plus 3-isobutyl-1-methylxanthine and administration of phorbol-12-myristate-13-acetate together with the calcium-ionophore A23187 also resulted in respective increases in the amount of secreted peptide. HEK 293 cells exhibit the endogenous expression of both particulate and soluble guanylyl cyclases. In the presence of 8-Br-cGMP, cell cultures showed the enhanced secretion of an ANP immunoreactive peptide only, indicating that guanylyl cyclase activation provoked the secretion of ANP immunoreactivity but not of urodilatin immunoreactivity.ConclusionsThe human embryonic kidney cell line HEK 293 represents a renal cellular model system in which we have identified a rapid and regulated release of NPs in response to the osmotic effect of increased extracellular sodium chloride and various intracellular stimuli

Parametrization of the Coulomb interaction matrix with point-group symmetry

Coulomb integrals, i.e., matrix elements of bare or screened Coulomb interaction between one-electron orbitals, are fundamental objects in many approaches developed to tackle the challenging problem of calculating the electronic structure of strongly correlated materials. In this paper, Coulomb integrals are analyzed by considering both the point group symmetry of the site occupied by the atom in the crystal or molecule and the permutation symmetries of the orbitals in the integrals. In particular, the case where one-electron orbitals form the basis of a general (i.e. a real, complex or pseudo-complex) irreducible representation is considered. Explicit formulas are provided to calculate all integrals of the interaction tensor in terms of a minimum set of independent ones. The effect of a symmetry breaking is also investigated by describing Coulomb integrals of a group in terms of those of one of its subgroups. We develope the specific example of O(3) as the larger group which can therefore be used to quantify the deviation of a specific system from the spherical symmetry. Possible applications of the presented framework include the calculation of solid-state and molecular spectroscopies via multiplet techniques, dynamical mean-field theory or the GW approximation.Comment: 14 pages, 1 figur