Iodine monoxide in the Antarctic snowpack

Recent ground-based and space borne observations suggest the presence of significant amounts of iodine monoxide in the boundary layer of Antarctica, which are expected to have an impact on the ozone budget and might contribute to the formation of new airborne particles. So far, the source of these iodine radicals has been unknown. This paper presents long-term measurements of iodine monoxide at the German Antarctic research station Neumayer, which indicate that high IO concentrations in the order of 50 ppb are present in the snow interstitial air. The measurements have been performed using multi-axis differential optical absorption spectroscopy (MAX-DOAS). Using a coupled atmosphere snowpack radiative transfer model, the comparison of the signals observed from scattered skylight and from light reflected by the snowpack yields several ppb of iodine monoxide in the upper layers of the sunlit snowpack throughout the year. Snow pit samples from Neumayer Station contain up to 700 ng/l of total iodine, representing a sufficient reservoir for these extraordinarily high IO concentrations

Modelling and simulation of wave-based structural health monitoring-systems using the spectral element method

Eine Vielzahl lasttragender technischer Strukturen bedarf zur Gewährleistung der Betriebssicherheit einer regelmäßigen Überprüfung ihrer Integrität, da aus technologischen, wirtschaftlichen oder ökologischen Gründen keine dauerfeste Auslegung möglich ist. Über die gesamte Lebensdauer dieser Strukturen stellen die notwendigen Inspektionen, die in der Regel mit hohem manuellen Arbeitsaufwand einhergehen, einen großen wirtschaftlichen Faktor dar. Zudem bewirkt der menschliche Faktor ein nicht unerhebliches Risiko, Schäden zu übersehen. Daher existiert eine hohe Nachfrage nach Methoden, die eine selbständige Strukturüberwachung mit permanent installierter Sensorik ermöglichen. Derartige Verfahren werden unter dem Oberbegriff "Structural Health Monitoring (SHM)" zusammengefasst. Der Fokus dieser Arbeit liegt auf Verfahren zur Überwachung dünnwandiger Strukturen, die auf so genannten geführten Wellen basieren. Diese Wellen, die mit Hilfe piezoelektrischer Elemente angeregt und detektiert werden, interagieren stark mit Strukturdiskontinuitäten (Rissen, Delaminationen) und weisen daher eine hohe Sensitivität schon gegenüber kleinen Schädigungen auf. Eine erhebliche Herausforderung ist jedoch die Auslegung eines derartigen SHM-Systems für konkrete Strukturen: Die Anpassung und Optimierung von Parametern wie Aktuator- und Sensorpositionen, Signalformen und Auswertealgorithmen erfolgt bisher meist durch eine große Anzahl von Vorversuchen und ist damit zeitaufwändig und kostenintensiv. Zudem wird ein tiefgreifendes Verständnis der bei der Wellenausbreitung ablaufenden Vorgänge benötigt. Nach einer Zusammenfassung notwendiger Grundlagen stellt diese Arbeit ein leistungsfähiges Simulationsverfahren basierend auf Spektralelementen vor, mit dem Wellenausbreitungsvorgänge in flachen Schalenstrukturen mit einer höheren Effizienz simuliert werden können, als dies mit konventionellen Finiten Elementen möglich ist. Dadurch wird es möglich, ein derartiges SHM-System im Stadium der Vorentwicklung schon vor einer realen Installation virtuell abzubilden und z.B. die Detektierbarkeit von Schädigungen zu untersuchen. Auf der Basis von Simulationsmodellen werden in verschiedenen Studien grundlegende Eigenschaften der Wellenausbreitung untersucht. Dabei werden unter anderem unterschiedliche Modelle der piezoelektrischen Aktuatoren und Sensoren sowie verschiedene Schädigungsmodelle betrachtet. Die Sensitivität diverser Sensorkonfigurationen hinsichtlich typischer Schädigungen einer versteiften Schalenstruktur wird detailliert analysiert. Ein Vergleich mit verschiedenen experimentellen Studien erlaubt eine Validierung des vorgestellten Simulationsverfahrens

Two-dimensional, Time-dependent, Multi-group, Multi-angle Radiation Hydrodynamics Test Simulation in the Core-Collapse Supernova Context

We have developed a time-dependent, multi-energy-group, and multi-angle (S$_n$) Boltzmann transport scheme for radiation hydrodynamics simulations, in one and two spatial dimensions. The implicit transport is coupled to both 1D (spherically-symmetric) and 2D (axially-symmetric) versions of the explicit Newtonian hydrodynamics code VULCAN. The 2D variant, VULCAN/2D, can be operated in general structured or unstructured grids and though the code can address many problems in astrophysics it was constructed specifically to study the core-collapse supernova problem. Furthermore, VULCAN/2D can simulate the radiation/hydrodynamic evolution of differentially rotating bodies. We summarize the equations solved and methods incorporated into the algorithm and present results of a time-dependent 2D test calculation. A more complete description of the algorithm is postponed to another paper. We highlight a 2D test run that follows for 22 milliseconds the immediate post-bounce evolution of a collapsed core. We present the relationship between the anisotropies of the overturning matter field and the distribution of the corresponding flux vectors, as a function of energy group. This is the first 2D multi-group, multi-angle, time-dependent radiation/hydro calculation ever performed in core collapse studies. Though the transport module of the code is not gray and does not use flux limiters (however, there is a flux-limited variant of VULCAN/2D), it still does not include energy redistribution and most velocity-dependent terms.Comment: 19 pages, plus 13 figures in JPEG format. Submitted to the Astrophysical Journa

Shapley Ratings in Brain Networks

Recent applications of network theory to brain networks as well as the expanding empirical databases of brain architecture spawn an interest in novel techniques for analyzing connectivity patterns in the brain. Treating individual brain structures as nodes in a directed graph model permits the application of graph theoretical concepts to the analysis of these structures within their large-scale connectivity networks. In this paper, we explore the application of concepts from graph and game theory toward this end. Specifically, we utilize the Shapley value principle, which assigns a rank to players in a coalition based upon their individual contributions to the collective profit of that coalition, to assess the contributions of individual brain structures to the graph derived from the global connectivity network. We report Shapley values for variations of a prefrontal network, as well as for a visual cortical network, which had both been extensively investigated previously. This analysis highlights particular nodes as strong or weak contributors to global connectivity. To understand the nature of their contribution, we compare the Shapley values obtained from these networks and appropriate controls to other previously described nodal measures of structural connectivity. We find a strong correlation between Shapley values and both betweenness centrality and connection density. Moreover, a stepwise multiple linear regression analysis indicates that approximately 79% of the variance in Shapley values obtained from random networks can be explained by betweenness centrality alone. Finally, we investigate the effects of local lesions on the Shapley ratings, showing that the present networks have an immense structural resistance to degradation. We discuss our results highlighting the use of such measures for characterizing the organization and functional role of brain networks

Detection of vibrational emissions from the helium hydride ion (HeH+^+) in the planetary nebula NGC 7027

We report the detection of emission in the v=1-0 P(1) (3.51629 micron) and P(2) (3.60776 micron) rovibrational lines of the helium hydride cation (HeH+) from the planetary nebula NGC 7027. These detections were obtained with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. The confirm the discovery of HeH+ reported recently by Guesten et al. (2019), who used the GREAT instrument on the SOFIA airborne observatory to observe its pure rotational J=1-0 transition at 149.137 micron. The flux measured for the HeH+ v=1-0 P(1) line is in good agreement with our model for the formation, destruction and excitation of HeH+ in NGC 7027. The measured strength of the J=1-0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v=1-0 P(2) line, by factors of 2.9 and 2.3 respectively. Possible causes of these discrepancies are discussed. Our observations of NGC 7027, covering the 3.26 - 3.93 micron spectral region, have led to the detection of more than sixty spectral lines including nine rovibrational emissions from CH+. The latter are detected for the first time in an astronomical source.Comment: 49 pages, including 17 figures. Accepted for publication in Ap

Geodynamically consistent inferences on the uniform sampling of Earth's paleomagnetic inclinations

Paleomagnetism is a key method to reconstruct the Earth's paleogeography and thus essential for understanding tectonic evolution, but it assumes that the Earth's magnetic field structure has always averaged to a geocentric axial dipole (GAD). The GAD hypothesis may be tested using the observed inclination frequency distribution, but only if continents sampled all of the Earth's latitudes uniformly, which is not known. Here, we provide new insight into the uniform sampling problem by employing a suite of 3D spherical mantle convection models that feature the self-consistent evolution of mantle convection, plate tectonics and continental drift over timescales of 2 Gyr or more. Our results suggest that continents unlikely sampled latitudes uniformly during the Phanerozoic, consistent with previous suggestions. This finding is robust for a variety of geodynamic evolutions with different mantle and lithosphere structures, at least in the absence of true polar wander. For longer sampling durations, uniform sampling typically becomes more feasible, but may only be achieved with confidence after time scales of minimum 1.3 Gyr. This time scale depends on the structure of the mantle and lithosphere and may be shortest when upper mantle viscosity is small such that reduced resistive drag at the cratonic base allows for faster continental drift. Weak plates (low plastic yield strength) promote more dispersed continent configurations, which tends to facilitate uniform sampling. If these conditions are not met, the uniform sampling time scale can easily exceed several billion years. Even the minimum estimate of 1.3 Gyr challenges the validity of using the Phanerozoic inclination frequency distribution to infer the past average magnetic field structure; the approach could however still be applicable using the Precambrian inclination record. (C) 2018 Elsevier B.V. All rights reserved.Peer reviewe

Trust for E-Business Management

How do we develop and sustain trust? What is the process for building trust between business partners in virtual environments? Is there a significant difference between the development and sustainability of trust online or offline? In this paper, we first introduce the concept of e-business and discuss the importance of trust for ensuring effective collaboration. Secondly, we discuss the relationships between e-collaboration and trust for managing e-business. Thirdly, we suggest a framework, which may help facilitate the development and sustainability of trust in an online environment. Finally, implications for the development and sustainability of trust online, which can be used to understand the interplay among technologies, e-business and collaboration is provided. We suggest that the implications of this study are three-fold: trustworthy relationships among business partners, effective sustainable collaboration, and optimal use of ICT for supporting e-business activities