A simple optimized amplitude pupil mask for attempting to direct imaging of Proxima b with SPHERE/ZIMPOL at VLT

Proxima b is a terrestrial exoplanet orbiting in the habitable zone of our closest star Proxima Centauri. The separation between the planet and the star is about 40 mas and this is with current instruments only reachable with direct imaging, using a visual extreme AO system like SPHERE/ZIMPOL. Unfortunately, the planet falls under the first airy ring at 2$\lambda$/D in the I band, which degrades achievable contrast. We present the design, optical simulations and testing of an amplitude pupil mask for ZIMPOL that reshapes the PSF, increasing the contrast at $r = 2\lambda$/D about an order of magnitude. The simple mask can be inserted directly into the current setup of SPHERE.Comment: 11 pages, 8 figures, Poster presented at SPIE Astronomical Telescopes and Instrumentation 201

Labor Supply Prediction when Tax Avoidance Matters

We examine how tax avoidance in the form of trade in well-functioning asset markets affects the empirical study of labor supply. We discuss the implications for tax policy analysis, and we show that a failure to account for avoidance responses may lead to huge errors when predicting how tax reform affects labor supply tax revenue, and the welfare cost of taxation. In conclusion we argue that our model may explain a number of otherwise hard to understand dimensions of tax payer response.Labor supply; tax avoidance; asset markets; tax reform simulation

Labor Supply When Tax Avoidance Matters

We examine how tax avoidance in the form of trade in well-functioning asset markets affects the empirical study of labor supply. We discuss the implications for tax policy analysis, and we show that a failure to account for avoidance responses may lead to huge errors when predicting how tax reform affects labor supply, tax revenue, and the welfare cost of taxation. In conclusion we argue that our model may explain a number of otherwise hard to understand dimensions of tax payer response.Labour supply; Tax avoidance; Asset markets; Tax reform simulation

Philosophical Reflections on Experimenting with Human Subjects

Experimenting with human subjects is going on in many fields of scientific and technological progress. It is designed to replace the overall instruction by natural, occasional, and cumulative experience with the selective information from artificial, systematic experiment which physicial science has found so effective in dealing with inanimate nature. Of the new experimentation with man, medical is surely the most legitimate; psychological, the most dubious; biological (still to come), the most dangerous. I have chosen here to deal with the first only, where the case for it is strongest and the task of adjudicating conflicting claims hardest. When I was first asked1 to comment “philosophically” on it, I had all the hesitation natural to a layman in the face of matters on which experts of the highest competence have had their say and still carry on their dialogue. As I familiarized myself with the material,2 any initial feeling of moral rectitude that might have facilitated my task quickly dissipated before the awesome complexity of the problem, and a state of great humility took its place. The awareness of the problem in all its shadings and ramifications speaks out with such authority, perception, and sophistication in the published discussions of the researchers themselves that it would be foolish of me to hope that I, an onlooker on the sidelines, could tell those battling in the arena anything they have not pondered themselves. Still, since the matter is obscure by its nature and involves very fundamental, transtechnical issues, anyone’s attempt at clarification can be of use, even without novelty. And even if the philosophical reflection should in the end achieve no more than the realization that in the dialectics of this area we must sin and fall into guilt, this insight may not be without its own gains.https://doi.org/10.1007/978-1-4684-2223-8_1

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars VI. First chromosphere model of a late-type giant

Although observational data unequivocally point out to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. 3D radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff=4010 K, log g=1.5, [M/H]=0.0), which are similar to those of the K-type giant star Aldebaran (alpha Tau). ... we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca II K, the Ca II infrared triplet line at 854.2nm, and H alpha, as well as the spectral energy distribution (SED) of the emergent radiative flux. The initial model quickly develops a dynamical chromosphere characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values on the order of up to 5000 K although the shock fronts remain quite narrow. Like for the Sun, the gas temperature distribution in the upper layers is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced with one-dimensional static models but demand for advanced 3D HD modelling. Furthermore, including a chromosphere in the models might produce significant contributions to the emergent UV flux.Comment: 14 pages, 8 figures, A&A (2017, accepted

Fast Freenet: Improving Freenet Performance by Preferential Partition Routing and File Mesh Propagation

The Freenet Peer-to-Peer network is doing a good job in providing anonymity to the users. But the performance of the network in terms of download speed and request hit ratio is not that good. We propose two modifications to Freenet in order to improve the download speed and request hit ratio for all participants. To improve download speed we propose Preferential Partition Routing, where nodes are grouped according to bandwidth and slow nodes are discriminated when routing. For improvements in request hit ratio we propose File Mesh propagation where each node sends fuzzy information about what documents it posesses to its neigbors. To verify our proposals we simulate the Freenet network and the bandwidth restrictions present between nodes as well as using observed distributions for user actions to show how it affects the network. Our results show an improvement of the request hit ratio by over 30 times and an increase of the average download speed with six times, compared to regular Freenet routing

Soft tissue preservation in amber : a comparative study on the taphonomy and limits of fossilisation of resin embedded arthropods

This doctoral thesis deals with the limits of morphological and biomolecular preservation of fossils in amber and provides new information on their taphonomy. A particular focus lies on arthropod inclusions from Cambay and Zhangpu amber deposits, which both are chemically distinct from previously studied amber occurrences. For the first time, subcellular structures could be evidenced in fossils from Eocene Cambay amber from India with electron microscopic methods. An examination of arthropods from Miocene Zhangpu amber from China shows that the frequency and extent of internal tissue preservation is not randomly distributed, but impacted by a combination of organismal characteristics and original resin chemistry. Muscle tissue, tracheal remains, and nervous tissue are the most commonly preserved, whereas abdominal tissue is infrequently detectable. This pattern is explained by an infiltration of volatile resin compounds along the tracheal system of entrapped arthropods. Chemical analyses revealed that amber fossils can be exposed to mineral precipitations of calcite and quartz, which shows that the geological environment can have a strong influence on the potential of tissue or biomolecular preservation. This is further confirmed by a lizard bone from Dominican amber in which the original bioapatite was transformed into fluorapatite. Raman spectra of the same specimen showed an intense degradation of collagen into amorphous carbon compounds, indicating a lack of intact biomolecules. In contrast to this, original single amino acids are extracted from Cambay and Zhangpu amber fossils which still enable conclusions about their phylogeny. Previous studies and the results of this thesis suggest that amino acids represent the limit of peptide preservation in amber. With respect to DNA preservation in amber, it is shown that intact DNA can be retrieved from extant resin-embedded arthropods. This provides an initial basis for step-by-step approaches towards the DNA preservation limit in amber. Numerous details regarding fossilisation in amber have not yet been investigated and hold great potential for future studies.Diese Doktorarbeit befasst sich mit den Grenzen der morphologischen und biomolekularen Erhaltung von Fossilien in Bernstein und liefert neue Informationen zu ihrer Taphonomie. Ein besonderer Schwerpunkt liegt auf Arthropodeneinschlüssen aus den Bernsteinvorkommen von Cambay und Zhangpu, welche sich chemisch von zuvor untersuchten Bernsteinablagerungen unterscheiden. Dabei konnten zum ersten Mal anhand elektronenmikroskopischer Methoden subzelluläre Strukturen in Fossilien aus dem eozänen Cambay-Bernstein aus Indien nachgewiesen werden. Eine Untersuchung von Arthropoden aus dem miozänen Zhangpu-Bernstein aus China zeigt, dass die Häufigkeit und das Ausmaß der Erhaltung der inneren Gewebe nicht zufällig verteilt sind, sondern in erster Linie durch eine Kombination von organismischen Eigenschaften und ursprünglicher Harzchemie beeinflusst werden. Muskelgewebe, Tracheenreste und Nervengewebe sind am häufigsten erhalten, wohingegen abdominales Gewebe seltener nachweisbar ist. Dieses Muster wird durch das Eindringen flüchtiger Harzverbindungen entlang des Tracheensystems eingeschlossener Arthropoden erklärt. Chemische Analysen ergaben, dass Bernsteinfossilien mineralischen Ausfällungen von Calcit und Quarz ausgesetzt sein können, was zeigt, dass die geologische Umgebung einen starken Einfluss auf das Potenzial der Erhaltung von Gewebe oder Biomolekülen haben kann. Dies wird weiter durch einen Eidechsenknochen aus Dominikanischem Bernstein bestätigt, in dem der ursprüngliche Bioapatit in Fluorapatit umgewandelt ist. Raman-Spektren derselben Probe zeigten einen intensiven Abbau von Kollagen zu amorphen Kohlenstoffverbindungen, was auf die Abwesenheit intakter Biomoleküle hinweist. Im Gegensatz dazu können ursprüngliche einzelne Aminosäuren von Fossilien aus Cambay und Zhangpu Bernstein extrahiert werden, die immer noch Rückschlüsse auf deren Phylogenie ermöglichen. Frühere Studien und die Ergebnisse dieser Arbeit legen nahe, dass Aminosäuren die Grenze der Konservierung von Peptiden in Bernstein darstellen. In Bezug auf DNA-Konservierung in Bernstein wird gezeigt, dass intakte DNA zumindest aus heutigen, in Harz eingebetteten Arthropoden gewonnen werden kann. Dies bietet eine erste Grundlage um schrittweise die Konservierungsgrenze von DNA in Bernstein zu ermitteln. Zahlreiche Details im Hinblick auf die Fossilisation in Bernstein sind noch nicht untersucht worden und beinhalten ein großes Potenzial für zukünftige Studien