Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

The effect of the metallicity-specific star formation history on double compact object mergers

Abstract: We investigate the impact of uncertainty in the metallicity-specific star formation rate over cosmic time on predictions of the rates and masses of double compact object mergers observable through gravitational waves. We find that this uncertainty can change the predicted detectable merger rate by more than an order of magnitude, comparable to contributions from uncertain physical assumptions regarding binary evolution, such as mass transfer efficiency or supernova kicks. We statistically compare the results produced by the COMPAS population synthesis suite against a catalogue of gravitational-wave detections from the first two Advanced LIGO and Virgo observing runs. We find that the rate and chirp mass of observed binary black hole mergers can be well matched under our default evolutionary model with a star formation metallicity spread of 0.39 dex around a mean metallicity 〈Z〉 that scales with redshift z as 〈Z〉 = 0.035 × 10−0.23z, assuming a star formation rate of 0.01×(1+z)2.77/(1+((1+z)/2.9)4.7)M⊙ Mpc−3 yr−1. Intriguingly, this default model predicts that 80 per cent of the approximately one binary black hole merger per day that will be detectable at design sensitivity will have formed through isolated binary evolution with only dynamically stable mass transfer, i.e. without experiencing a common-envelope event.

Helical milling of CFRP–titanium layer compounds

Abstract: Helical milling is used to generate boreholes by means of a milling tool being operated on a helical path into the workpiece. The bore diameter can be adjusted through the diameter of the helical path. In comparison to conventional drilling operations this process often results in lower burr formation and fiber delamination. Therefore helical milling is used in the aircraft industry for cutting composites and composite-metal compounds. One of these compounds, which is regarded as difficult to machine, is a layer compound consisting of unidirectional carbon fiber reinforced plastic (CFRP) and TiAl6V4. This paper presents the impact of the axial and tangential feed during helical milling on process forces and borehole quality is shown.

Symmetry of steady periodic surface water waves with vorticity

Abstract: For large classes of vorticities we prove that a steady periodic gravity water wave with a monotonic profile between crests and troughs must be symmetric. The analysis uses sharp maximum principles for elliptic partial differential equations.