How much do we really lose?—Yield losses in the proximity of natural landscape elements in agricultural landscapes

Natural landscape elements (NLEs) in agricultural landscapes contribute to biodiversity and ecosystem services, but are also regarded as an obstacle for large‐scale agricultural production. However, the effects of NLEs on crop yield have rarely been measured. Here, we investigated how different bordering structures, such as agricultural roads, field‐to‐field borders, forests, hedgerows, and kettle holes, influence agricultural yields. We hypothesized that (a) yield values at field borders differ from mid‐field yields and that (b) the extent of this change in yields depends on the bordering structure. We measured winter wheat yields along transects with log‐scaled distances from the border into the agricultural field within two intensively managed agricultural landscapes in Germany (2014 near Göttingen, and 2015–2017 in the Uckermark). We observed a yield loss adjacent to every investigated bordering structure of 11%–38% in comparison with mid‐field yields. However, depending on the bordering structure, this yield loss disappeared at different distances. While the proximity of kettle holes did not affect yields more than neighboring agricultural fields, woody landscape elements had strong effects on winter wheat yields. Notably, 95% of mid‐field yields could already be reached at a distance of 11.3 m from a kettle hole and at a distance of 17.8 m from hedgerows as well as forest borders. Our findings suggest that yield losses are especially relevant directly adjacent to woody landscape elements, but not adjacent to in‐field water bodies. This highlights the potential to simultaneously counteract yield losses close to the field border and enhance biodiversity by combining different NLEs in agricultural landscapes such as creating strips of extensive grassland vegetation between woody landscape elements and agricultural fields. In conclusion, our results can be used to quantify ecocompensations to find optimal solutions for the delivery of productive and regulative ecosystem services in heterogeneous agricultural landscapes

An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E ~ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462, in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry shows a parallactic signature of the effect of the Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 +/- 1.3 M_Sun and a distance of 1.58 +/- 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic-disk stars at similar distances by an amount corresponding to a transverse space velocity of ~45 km/s, suggesting that the BH received a modest natal 'kick' from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial-velocity measurements of Galactic X-ray binaries, and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first ever for an isolated stellar-mass BH using any technique

zu Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen

In this thesis, the stability and the dynamics of wet granular materials under shear are explored. Inspired by the Green’s function approach, a theoretical model for yielding of a wet pile on an inclined plane is presented. It enables one to predict the critical inclination angle at which the pile fluidizes. The theory is based on the balance of forces acting on each particle at the vicinity of the fluidization and has two major consequences. First, the theory shows that yielding of a wet pile does depend on the gravitational acceleration, whereas a dry pile fluidizes for any arbitrary small non-zero gravitational acceleration when the inclination angle exceeds a certain value depending on the geometry. Second, the theory shows that a wet pile yields in the bottom layer where the pile touches a non-slip boundary. There is excellent agreement between the theory and extensive MD-type simulations where one calculates forces between each individual pair of particles. The dynamics of driven wet particles is studied in two different ways. First, we explore dynamics of wet particles in a channel driven by gravity. Second, we apply a spatially sinusoidal driving force. In both cases we find discontinuous hysteretic solid-fluid transitions, i.e. solid-to-fluid and fluid-to-solid transitions and encountered at different forcing of the system. We calculate phase diagrams separating solid and fluid states and thresholds for the solid-to-fluid and the fluid-to-solid transitions. Beside that, we study the spatial and temporal distributions of drift velocity, granular temperature, area fraction, stress tensor, interparticle force etc. i Kurzzusammenfassung In dieser Arbeit wird die Stabilität und Dynamik feuchter granularer Medien unter der Einwirkung von Scherkräften untersucht. In Anlehung an den Greenschen Formalismums wir