Careers in astronomy in Germany and the UK

We discuss the outcomes of surveys addressing the career situation of astronomers in Germany and the UK, finding social and cultural differences between communities as well as gender bias in both.Comment: Astronomy and Geophysics. 13 page pdf with colour image

A Two-Year Time Delay for the Lensed Quasar SDSS J1029+2623

We present 279 epochs of optical monitoring data spanning 5.4 years from 2007 January to 2012 June for the largest image separation (22.6 arcsec) gravitationally lensed quasar, SDSS J1029+2623. We find that image A leads the images B and C by dt_AB = (744+-10) days (90% confidence); the uncertainty includes both statistical uncertainties and systematic differences due to the choice of models. With only a ~1% fractional error, the interpretation of the delay is limited primarily by cosmic variance due to fluctuations in the mean line-of-sight density. We cannot separate the fainter image C from image B, but since image C trails image B by only 2-3 days in all models, the estimate of the time delay between image A and B is little affected by combining the fluxes of images B and C. There is weak evidence for a low level of microlensing, perhaps created by the small galaxy responsible for the flux ratio anomaly in this system. Interpreting the delay depends on better constraining the shape of the gravitational potential using the lensed host galaxy, other lensed arcs and the structure of the X-ray emission.Comment: Accepted for publication in The Astrophysical Journal. Changes in response to referee's comment

Ring-shaped phosphinoamido-magnesium-hydride complexes : syntheses, structures, reactivity, and catalysis

A.S. is grateful to the Australian Research Council for project support and a fellowship.A series of magnesium(II) complexes bearing the sterically demanding phosphinoamide ligand, L−=Ph2PNDip−, Dip=2,6-diisopropylphenyl, including heteroleptic magnesium alkyl and hydride complexes are described. The ligand geometry enforces various novel ring and cluster geometries for the heteroleptic compounds. We have studied the stoichiometric reactivity of [(LMgH)4] towards unsaturated substrates, and investigated catalytic hydroborations and hydrosilylations of ketones and pyridines. We found that hydroborations of two ketones with pinacolborane using various Mg precatalysts is very rapid at room temperature with very low catalyst loadings, and ketone hydrosilylation using phenylsilane is rapid at 70 °C. Our studies point to an insertion/σ-bond metathesis catalytic cycle of an in situ formed “MgH2” active species.PostprintPostprintPeer reviewe

A deep q-learning-based optimization of the inventory control in a linear process chain

Due to growing globalized markets and the resulting globalization of production networks across different companies, inventory and order optimization is becoming increasingly important in the context of process chains. Thus, an adaptive and continuously self-optimizing inventory control on a global level is necessary to overcome the resulting challenges. Advances in sensor and communication technology allow companies to realize a global data exchange to achieve a holistic inventory control. Based on deep q-learning, a method for a self-optimizing inventory control is developed. Here, the decision process is based on an artificial neural network. Its input is modeled as a state vector that describes the current stocks and orders within the process chain. The output represents a control vector that controls orders for each individual station. Furthermore, a reward function, which is based on the resulting storage and late order costs, is implemented for simulations-based decision optimization. One of the main challenges of implementing deep q-learning is the hyperparameter optimization for the training process, which is investigated in this paper. The results show a significant sensitivity for the leaning rate α and the exploration rate ε. Based on optimized hyperparameters, the potential of the developed methodology could be shown by significantly reducing the total costs compared to the initial state and by achieving stable control behavior for a process chain containing up to 10 stations

The faintest radio source yet: EVLA observations of the gravitational lens SDSS J1004+4112

We present new radio observations of the large-separation gravitationally-lensed quasar SDSS J1004+4112, taken in a total of 6 hours of observations with the Extended Very Large Array (EVLA). The maps reach a thermal noise level of approximately 7microJy. We detect four of the five lensed images at the 30-65microJy level, representing a source of intrinsic flux density, after allowing for lensing magnification, of about 2microJy, intrinsically probably the faintest radio source yet detected. This reinforces the utility of gravitational lensing in potentially allowing us to study nanoJy-level sources before the advent of the SKA. In an optical observation taken three months after the radio observation, image C is the brightest image, whereas the radio map shows flux density ratios consistent with previous optical observations. Future observations separated by a time delay will give the intrinsic flux ratios of the images in this source.Comment: 9 pages, 2 figures. Revised version to correct an error in the flux scale (was too low by a factor of 1.85) caused by a problem in the processing of calibration tables in the first versio

Non-parametric strong lens inversion of SDSS J1004+4112

In this article we study the well-known strong lensing system SDSS J1004+4112. Not only does it host a large-separation lensed quasar with measured time-delay information, but several other lensed galaxies have been identified as well. A previously developed strong lens inversion procedure that is designed to handle a wide variety of constraints, is applied to this lensing system and compared to results reported in other works. Without the inclusion of a tentative central image of one of the galaxies as a constraint, we find that the model recovered by the other constraints indeed predicts an image at that location. An inversion which includes the central image provides tighter constraints on the shape of the central part of the mass map. The resulting model also predicts a central image of a second galaxy where indeed an object is visible in the available ACS images. We find masses of 2.5x10^13 M_O and 6.1x10^13 M_O within a radius of 60 kpc and 110 kpc respectively, confirming the results from other authors. The resulting mass map is compatible with an elliptical generalization of a projected NFW profile, with r_s = 58_{-13}^{+21} arcsec and c_vir = 3.91 +/- 0.74. The orientation of the elliptical NFW profile follows closely the orientation of the central cluster galaxy and the overall distribution of cluster members.Comment: 11 pages, accepted for publication in MNRA

Effects of dating errors on nonparametric trend analyses of speleothem time series

A fundamental problem in paleoclimatology is to take fully into account the various error sources when examining proxy records with quantitative methods of statistical time series analysis. Records from dated climate archives such as speleothems add extra uncertainty from the age determination to the other sources that consist in measurement and proxy errors. This paper examines three stalagmite time series of oxygen isotopic composition (δ<sup>18</sup>O) from two caves in western Germany, the series AH-1 from the Atta Cave and the series Bu1 and Bu4 from the Bunker Cave. These records carry regional information about past changes in winter precipitation and temperature. U/Th and radiocarbon dating reveals that they cover the later part of the Holocene, the past 8.6 thousand years (ka). We analyse centennial- to millennial-scale climate trends by means of nonparametric Gasser–Müller kernel regression. Error bands around fitted trend curves are determined by combining (1) block bootstrap resampling to preserve noise properties (shape, autocorrelation) of the δ<sup>18</sup>O residuals and (2) timescale simulations (models StalAge and iscam). The timescale error influences on centennial- to millennial-scale trend estimation are not excessively large. We find a "mid-Holocene climate double-swing", from warm to cold to warm winter conditions (6.5 ka to 6.0 ka to 5.1 ka), with warm–cold amplitudes of around 0.5‰ δ<sup>18</sup>O; this finding is documented by all three records with high confidence. We also quantify the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the current warmth. Our analyses cannot unequivocally support the conclusion that current regional winter climate is warmer than that during the MWP

Vegetation dynamics amplifies precessional forcing

The astronomical theory of climate variations predicts that the climatic precession which changes the seasonal distance between Earth and Sun does not affect the annual mean irradiation at any given latitude. However, previous modeling studies suggest that during interglacials, the interaction between atmosphere, vegetation and ocean can transform the seasonal forcing by precession into an annual mean global signal. Here, we show that this result can be generalized. A distinct precessional signal emerges in a climate system model over many precessional cycles. While neither the atmosphere-ocean nor the atmosphere-vegetation model are able to produce a large amplitude of global temperature in the precessional band, only the mutual amplification of biogeophysical feedback and sea ice- albedo feedback allows a strong amplification of the precessional signa

Carbon isotopes in stalagmites and drip water : Tracers of soil processes

Stalagmites in caves are new climate archives recording meteorological parameters and processes occurring in the soil above caves. Due to advances in mass spectroscopy (TIMS and ICPMS) stalagmites can be dated reliably by the 230Th/U-method. Carbon isotopes, recorded in stalagmites, are of interest because they depend on climate influenced soil processes above caves. In this thesis 14C and 13C in speleothem environments were used as tracers to investigate soil processes for the present day situation and during the Holocene. The present day situation is studied by using monthly collected drip water samples from two caves (Ernesto cave in Trentino, Italy, and Bunker cave in Sauerland, Germany), which were analysed for their carbon isotope content. To interpret the isotopic composition a drip water model including various modes of limestone dissolution with respect to carbon isotopes was developed for the first time. The modelled carbon isotope composition of the drip water agrees well with the measurements. The annual trend in the carbon isotopes, observed in the drip water samples, can be attributed to changes in the water supply in the soil for Ernesto cave and to changes of the soil air carbon isotopic composition for Bunker cave. The information about the soil-cave-systems obtained in the investigation of the present day situation was applied to interpret the carbon isotopes of Holocene stalagmites of both caves. An inverse modelling method was developed to determine the soil CO2 content from measured carbon isotope pairs (14C, 13C). The results indicate that the soil CO2 content increased during the late Holocene in the soil above Ernesto cave due to a rising vegetation density. The Bunker cave stalagmite reveals a constant soil pCO2 in the past