Frequency stabilization of an ultraviolet semiconductor disk laser

We report a tunable, narrow-linewidth UV laser based on intracavity second-harmonic generation in a red semiconductor disk laser. Single-frequency operation is demonstrated with a total UV output power of 26 mW. By servo-locking the fundamental frequency to a reference Fabry–Pérot cavity, the linewidth of the UV beam has been reduced to 16 kHz on short timescales and 50 kHz on a 1 s timescale, relative to the reference

Angsträume und Stressempfinden im urbanen Kontext

Die vorliegende Veröffentlichung befasst sich mit der Fragestellung, wie Angsträume im urbanen Raum wahrgenommen werden können und ob diese quantifizierbar bzw. raumzeitlich lokalisierbar sind. Diese subjektiven Eindrücke sind in Bezug auf die Gestaltung von Städten sehr bedeutend, werden allerdings aufgrund fehlender Aufnahmemethodik in der Planung vielfach noch nicht berücksichtigt, da ein quantifizierbares Instrument fehlt. Bislang wurde sich diesem Thema primär mit Hilfe von Fragebogenerhebungen genähert, welche ausschließlich die individuelle subjektive Wahrnehmung der Teilnehmerin bzw. des Teilnehmers wiedergibt. Ein wesentlicher Baustein dieses Papers ist somit die Frage, ob Angsträume quantifizierbar, raumzeitlich lokalisierbar und die damit zusammenhängenden Emotionen messbar sind. Was zeichnet einen Angstraum aus? Nach Schmidt „beschleunigen [Angsträume] unseren Puls und Schritt“ (Schmidt 2015) und lösen negative Gefühle aus. Eine der wenigen existierenden Definitionen, die auch im raumplanerischen Kontext verwendet werden kann, ist von Hiller. Dieser beschreibt den Angstraum als „einen öffentlichen (oder halböffentlichen) Ort, an dem Menschen Angst haben, Opfer von Kriminalität zu werden“ (Hiller 2010: 2). Am Beispiel von Dortmund-Dorstfeld wird der Frage nachgegangen, ob raumbezogener Stress messbar und somit objektivierbar ist. Gibt es Unterschiede zwischen subjektivem Stressempfinden und durch Sensorik gemessenen Stress? Sind mithilfe dieser Methoden Angsträume zu lokalisieren? Und schlussendlich auch die Frage, ob es Wahrnehmungsunterschiede zwischen den Geschlechtern gibt. Grundlage für diesen Beitrag ist die Forschungsarbeit „Sind Emotionen messbar? – Angsträume und Stressempfinden im urbanen Raum am Beispiel der Stadt Dortmund“ (Schlosser 2017)

Application of cross-flow filtration for determining the solubility of iron species in open ocean seawater

Measurements of soluble iron species (organic and inorganic) are important for understanding the transport of iron within the ocean and its bioavailability. Recent developments in ultrafiltration equipment and analytical detection techniques for low level Fe determination has turned the spotlight on obtaining data on soluble iron species. However there have, until now, been few studies that have characterized the performance of an ultrafiltration system with respect to well described soluble iron complexes. In the present work, we describe a methodological study characterizing the behavior of soluble and colloidal iron species in seawater by combining a crossflow ultrafiltration system (Vivaflow 50TM) with a radioisotope (55Fe). During this study, we were able to maintain excellent mass balances by including all components: not only the solution phases (retentate and permeate) but wall-adsorbed and filter-adsorbed iron, which were recovered by an acid-rinsing step. Wall and filter adsorption were unavoidable when solutions were saturated with respect to Fe'. However in undersaturated solutions, such as with an excess of desferrioxamine B, wall and filter adsorption were minimized, indicating that these effects should be slight for natural samples where iron-binding ligands are in excess. Our results have important implications for the use of ultrafiltration membranes for open ocean iron biogeochemical studies

Controls on seawater Fe(III) solubility in the Mauritanian upwelling zone

Iron solubility measurements in the Mauritanian upwelling and the adjacent Open Ocean of the Tropical Atlantic show for all stations lower values in the surface mixed layer than at depth below the pycnocline. We attribute this distribution to a combination of loss terms, chiefly photo-oxidation of organic ligands in the surface, and supply terms, predominantly from the release of ligands from the decomposition of organic matter. Significant correlations with pH, oxygen and phosphate for all samples below the surface mixed layer indicate that biogenic remineralisation of organic matter results in the release of iron binding ligands into the dissolved phase. The comparison of the cFe(S)/PO(4)(3-) ratio with other published data from intermediate and deep waters in the Pacific suggests an enhanced release of iron chelators in the more productive Mauritanian upwelling zone. Citation: Schlosser, C., and P.L. Croot (2009), Controls on seawater Fe(III) solubility in the Mauritanian upwelling zon

Freshwater balance and the sources of deep and bottom waters in the Arctic Ocean inferred from the distribution of H218O

Data from sections across the Eurasian Basin of the Arctic Ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the Arctic Ocean and on sources of the deep waters of the Nansen, Amundsen and Makarov basins. Using salinity, H218O, and mass balances we estimate the river-runoff and the sea-ice melt water fractions contained in the upper waters of the Arctic Ocean and infer pathways of the river-runoff signal from the shelf seas across the central Arctic Ocean to Fram Strait. The average mean residence time of the river-runoff fraction contained in the Arctic Ocean halocline is determined to be about 11 to 14 years. Pacific water entering through Bering Strait is traced using silicate and its influence on the halocline waters of the Canadian Basin is estimated. Water column inventories of river-runoff and sea-ice melt water are calculated for a section just north of Fram Strait and implications of these inventories for sea-ice export through Fram Strait are discussed. Comparison of the ratios of shelf water, Atlantic water and the deep waters of the Arctic Ocean indicate that the sources of the deep and bottom waters of the Eurasian Basin are located in the Barents and Kara seas

The harmonic H∞H^\infty-functional calculus based on the S-spectrum

The aim of this paper is to introduce the $H^\infty$-functional calculus for harmonic functions over the quaternions. More precisely, we give meaning to Df(T) for unbounded sectorial operators T and polynomially growing functions of the form Df, where f is a slice hyperholomorphic function and $D=\partial_{q_0}+e_1\partial_{q_1}+e_2\partial_{q_2}+e_3\partial_{q_3}$ is the Cauchy-Fueter operator. The harmonic functional calculus can be viewed as a modification of the well known S-functional calculus f(T), with a different resolvent operator. The harmonic $H^\infty$-functional calculus is defined in two steps: First, for functions with a certain decay property, one can make sense of the bounded operator Df(T) directly via a Cauchy-type formula. In a second step, a regularization procedure is used to extend the functional calculus to polynomially growing functions and consequently unbounded operators Df(T). The harmonic functional calculus is an important functional calculus of the quaternionic fine structures on the S-spectrum, which arise also in the Clifford setting and they encompass a variety of function spaces and the corresponding functional calculi. These function spaces emerge through all possible factorizations of the second map of the Fueter-Sce extension theorem. This field represents an emerging and expanding research area that serves as a bridge connecting operator theory, harmonic analysis, and hypercomplex analysis

Arctic river-runoff: mean residence time on the shelves and in the halocline

The mean residence time of river-runoff on the shelves and in the halocline of the Arctic Ocean is estimated from salinity and tracer data (tritium, 3He and the 18O/16O ratio). These estimates are derived from comparison of apparent tracer ages of the halocline waters using a combination of tracers that yield different information: (1) the tritium “vintage” age, which records the time that has passed since the river-runoff entered the shelf; and (2) the tritium/3He age, which reflects the time since the shelf waters left the shelf. The difference between the ages determined by these two methods is about 3–6 years. Correction for the initial tritium/3He age of the shelf waters (about 0.5–1.5 years) yields a mean residence time of the river-runoff on the shelves of the Siberian Seas of about 3.5 ± 2 years