Interaction with constraints in 3D modeling

Journal ArticleInteractive geometric modeling is an important part of the industrial product design process. This paper describes how constraints can be used to facilitate the interactive definition of geometric objects and assemblies. We have implemented a geometric modeling system that combines the definition of objects by interactive construction operations and specification of geometric constraints. The modeling operations automatically generate constraints to maintain the properties intended by their invocation, and constraints, in turn, determine the degrees of freedom for further interactive mouse-controlled modeling operations. A symbolic geometry constraint solver is employed for solving systems of constraints

Ultrafast modulation of the chemical potential in BaFe2_2As2_2 by coherent phonons

Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe$_2$As$_2$ around the high-symmetry points $\Gamma$ and $M$. A global oscillation of the Fermi level at the frequency of the $A_{1g}$(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the $A_{1g}$ phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling.Comment: 6 pages, 3 figure

Ultrafast modulation of the chemical potential in BaFe2As2 by coherent phonons

Time- and angle-resolved extreme ultraviolet photoemission spectroscopy is used to study the electronic structure dynamics in BaFe2As2 around the high-symmetry points Γ and M. A global oscillation of the Fermi level at the frequency of the A1g(As) phonon mode is observed. It is argued that this behavior reflects a modulation of the effective chemical potential in the photoexcited surface region that arises from the high sensitivity of the band structure near the Fermi level to the A1g(As) phonon mode combined with a low electron diffusivity perpendicular to the layers. The results establish a novel way to tune the electronic properties of iron pnictides: coherent control of the effective chemical potential. The results further suggest that the equilibration time for the effective chemical potential needs to be considered in the ultrafast electronic structure dynamics of materials with weak interlayer coupling. © 2014 American Physical Society

Surface-phase transitions in the charge-density-wave systems 1T-TaSe2 and 1T-TiSe2

Das Ziel der Arbeit ist es, die elektronische Struktur der Oberfläche der Übergangsmetalldichalkogenide 1T-TaSe2 und 1T-TiSe2 zu untersuchen. 1T-TaSe2 zeigt einen Metall-Isolator-Übergang der mit Mott-Physik in Verbindung gebracht wird und sich in der Volumenleitfähigkeit nicht nachweisen lässt. Zeit- und winkelaufgelöste Photoelektronenspektroskopie wurde genutzt, um die Dynamik der elektronischen Struktur an der Oberfläche von 1T-TaSe2 impulsaufgelöst nach Anregung mit einem Infrarot-Laserpuls zu untersuchen. Es konnten zwei zeitlich getrennte Abläufe beobachtet werden: Zum einen der quasi sofortige Verlust der elektronischen Ordnung im Bereich der Zeitauflösung von t < 40 fs und zum anderen die kohärente Unterdrückung der periodischen Gitterverzerrung auf der Zeitskala der Oszillationsfrequenz eines kohärenten Phonons. Die schnellen Reaktionszeiten zeigen, dass tatsächlich elektronische Wechselwirkung die Ursache dieses Metall-Isolator-Übergangs ist. Des Weiteren wurde die Tiefenabhängigkeit der Ladungsdichtewelle in 1T-TaSe2 bei tiefen Temperaturen anhand der Aufspaltung der Ta-4f-Rumpfniveaus von 1T-TaSe2 studiert. Die Analyse zeigt eine Vergrößerung der Aufspaltung von 40 meV an der Oberfläche und damit eine Stärkung der Ladungsdichtewelle. Die Größe der Aufspaltung korreliert mit der des thermischen Metall-Isolator-Übergangs, welcher folglich lediglich an der Oberfläche des Materials auftritt. Im zweiten Teil der Arbeit wird der gezielte Einfluss von Elektronendotierung auf die elektronische Bandstruktur an der Oberfläche des Ladungsdichtewelle-Materials 1T-TiSe2 mit winkelauflösender Photoelektronenspektroskopie analysiert. Im Detail wird der Einfluss der zusätzlichen Ladungsträger auf die Ladungsdichtewelle untersucht. Bei hohen Elektronendotierung konnte eine vollständige energetische Entkopplung der obersten Einheitszelle nachgewiesen werden.The goal of the present work is to investigate the electronic structure of the surfaces of the transition-metal dichalcogenides 1T-TaSe2 and 1T-TiSe2. In particular the modification of the electronic structure by enhanced interactions at the surface is studied. 1T-TaSe2 shows a pronounced metal-to-insulator transition, which may be related to Mott physics and is not observable in bulk sensitive transport measurements. The first part of this work investigates the origin and the spatial extend of this transition. Time- and angle-resolved extreme ultraviolet photoelectron spectroscopy is used to determine the momentum-dependent electronic structure dynamics in the layered material 1T-TaSe2. Extracted spectroscopic order parameters display a global two-time-scale dynamics indicating a quasi-instantaneous loss of the electronic orders and a subsequent coherent suppression of the lattice distortion on a time scale related to the frequency of the charge-density-wave amplitude mode. The fast reaction of the system reveals electronic interplay as the driving force to this phase transition. Moreover, the depth dependency of the charge-density wave in 1T-TaSe2 at low temperatures is studied by hard X-ray photoelectron spectroscopy. The additional charge- density-wave-induced splitting of the Ta-4f-core levels, which serves as an excellent order parameter for the strength of the charge-density wave, is investigated. The findings corroborate the idea of a surface confined metal-to-insulator transition triggered by an enhancement of the charge-density wave at the surface. The second part of the present work focuses on the modification of the electronic structure at the surface of 1T-TiSe2 enforced by electron doping. Angle-resolved photo- electron spectroscopy is used to investigate the influence on the charge-density wave in this material in detail. At high doping levels the charge-density wave vanishes and the complete electronically decoupling of the uppermost layer is observed

Imbalances in Dissolved Elemental Export Fluxes Disclose “Hidden” Critical Zone Compartments

In streams, short-term element-specific solute fluxes are often not balanced with long-term chemical weathering fluxes determined in the residual solids from fractional element loss and denudation rate. The ratio of both estimates—the “Dissolved Export Efficiency” (DEE)—is frequently <1, indicating deficits in the stream dissolved load. To explore the cause of the stream deficits, we performed a daily water sampling campaign for one year in a forested headwater watershed in Southern Germany. We sampled surface runoff, above-canopy and below-canopy precipitation, subsurface flow from the organic soil layer, upper, and deep mineral soil, and groundwater. Regolith samples were obtained from a drill core and revealed the weathering front to lie between 7 and 15 m depth. We found a DEE < 1 for K, Si, Al, Fe. These elements are characterized by shallow slopes in C-Q relationships, and the imbalances were found to originate in the deep saprolite. Their export pathway potentially includes “hidden” Critical Zone compartments or fluxes, presumably unsampled colloids that are exported preferentially during rare flushing events with stochastic temporal distribution. The DEE of nutritive elements like Ca, Mg, and P is also <1. These elements are characterized by steeper C-Q slopes, and their imbalance can be explained by deep nutrient uptake followed by nutrient retainment in re-growing forest biomass or export in plant debris. The collective evidence for these imbalances, including previous evidence from metal stable isotopes, suggests that the deep Critical Zone represents the location for chemical or biogenic retention and release of solutes

Routing in dezentral gesteuerten, modularen Fördersystemen

Durch die fortschreitende Digitalisierung der industriellen Produktionskette (Industrie 4.0) werden auch neue Anforderungen an industrielle Fördersysteme gestellt. So müssen diese autonom und flexibel auf Änderungen innerhalb der Produktion reagieren, zu denen z.B. Layoutänderungen zählen. Bereits existierende Steuerungsalgorithmen für modulare Fördersysteme können schon heute Konflikte verhindern, zu denen Kollisionen, Verklemmungen, Livelocks und das Verhungern zählen. Jedoch ist keiner der existierenden Algorithmen zeitfensterbasiert. Durch einen zeitfensterbasierten Steuerungsalgorithmus wird es möglich, unmittelbar die wichtigste Zielgröße eines Fördersystems zu optimieren: Den Durchsatz. In dieser Arbeit wird ein zeitfensterbasierter Steuerungsalgorithmus für modulare Fördersysteme vorgestellt. Die Korrektheit des Algorithmus wird bewiesen, seine Laufzeit bestimmt und das Systemverhalten in einer Simulationsumgebung untersucht

Pharmacotherapeutische Studien über das Hyoscin

http://tartu.ester.ee/record=b2172885~S1*es

Interaction with constraints in 3D modeling

Journal ArticleInteractive geometric modeling is an important part of the industrial product design process. This paper describes how constraints can be used to facilitate the interactive definition of geometric objects and assemblies. We have implemented a geometric modeling system that combines the definition of objects by interactive construction operations and specification of geometric constraints. The modeling operations automatically generate constraints to maintain the properties intended by their invocation, and constraints, in turn, determine the degrees of freedom for further interactive mouse-controlled modeling operations. A symbolic geometry constraint solver is employed for solving systems of constraints