Observations of the Crab Nebula and Pulsar with the Large-Sized Telescope Prototype of the Cherenkov Telescope Array

CTA (Cherenkov Telescope Array) is the next generation ground-based observatory for gamma-ray astronomy at very-high energies. The Large-Sized Telescope prototype (\LST{}) is located at the Northern site of CTA, on the Canary Island of La Palma. LSTs are designed to provide optimal performance in the lowest part of the energy range covered by CTA, down to $\simeq 20$ GeV. \LST{} started performing astronomical observations in November 2019, during its commissioning phase, and it has been taking data since then. We present the first \LST{} observations of the Crab Nebula, the standard candle of very-high energy gamma-ray astronomy, and use them, together with simulations, to assess the basic performance parameters of the telescope. The data sample consists of around 36 hours of observations at low zenith angles collected between November 2020 and March 2022. \LST{} has reached the expected performance during its commissioning period - only a minor adjustment of the preexisting simulations was needed to match the telescope behavior. The energy threshold at trigger level is estimated to be around 20 GeV, rising to $\simeq 30$ GeV after data analysis. Performance parameters depend strongly on energy, and on the strength of the gamma-ray selection cuts in the analysis: angular resolution ranges from 0.12 to 0.40 degrees, and energy resolution from 15 to 50\%. Flux sensitivity is around 1.1\% of the Crab Nebula flux above 250 GeV for a 50-h observation (12\% for 30 minutes). The spectral energy distribution (in the 0.03 - 30 TeV range) and the light curve obtained for the Crab Nebula agree with previous measurements, considering statistical and systematic uncertainties. A clear periodic signal is also detected from the pulsar at the center of the Nebula.Comment: Submitted to Ap

Cost-optimal design and automated production of sandwich structures for wind turbine rotor blades

The publicly funded research project BladeMaker aims at industrializing the production of wind turbine rotor blades to achieve a reproducible high quality and cost reductions. Along with other processes it addresses the automated production of sandwich structures through an in-situ foaming process of the core. For the skins, two alternative processes are presented: two-sided infusion of dry non-crimp fabrics and automated tape laying of prepreg tapes. Manual lay-up of pre-manufactured PVC foam kits is replaced by an automated application of liquid, in-situ expanding polyurethane (PU) foam directly into the mold. The benefits are considerably lower material costs, easier material transportation and the reduction of scrap. This innovative process also brings new challenges in terms of material performance and structural design, since the density-specific material properties of PUs are in general lower than of the typically used PVC-foams. Material properties of PUs depend on the selection of the specific PU system as well as on foaming parameters and especially on the density. A parameter study for a representative sandwich element has been carried out to make a trade-off between structural performance, weight and costs. Assuming that global buckling of the sandwich plate and skin wrinkling of the sandwich skins are the two dimensioning failure modes, the critical loads were calculated for different core thicknesses and PU densities. The main requirement was to achieve at least the same critical load with a PU-sandwich as with the PVC-sandwich. Finally, the material costs and the structural mass were evaluated to determine the cheapest and the lightest configuration. The contribution of additional flow meshes and resin uptake of the core material was taken into account. Results for the representative sandwich element show that the mass difference is small and that PU sandwich structures allow for significant cost reductions

Kommunikation für Nonprofit-Organisationen

Nonprofit-Organisation weisen im Vergleich zu kommerziellen Unternehmen einige Besonderheiten auf. Dies hat wiederum Auswirkungen auf die Kommunikationspolitik für Nonprofit-Unternehmen. Der Beitrag setzt an diesem Punkt an und gibt zunächst einen Überblick über die Herausforderungen, Ziele und Aufgaben der Kommunikationspolitik im Nonprofit-Bereich. Anschließend liegt der Fokus auf der strategischen Kommunikationsplanung. Im Rahmen der operativen Kommunikationsplanung wird schließlich aufgezeigt, welche Kommunikationsinstrumente für Nonprofit-Organisation besonders geeignet sind