Filtern
Erscheinungsjahr
Dokumenttyp
Gehört zur Bibliographie
- ja (23)
Schlagworte
- Unterricht (5)
- Sorben (4)
- Brandenburg (3)
- Wenden (3)
- Lehrplan (2)
- Sorbian identity (2)
- sorbische Identität (2)
- Biosensors (1)
- Bisexualität (1)
- Curriculum (1)
Institut
- Institut für Informatik und Computational Science (6)
- Zentrum für Lehrerbildung und Bildungsforschung (ZeLB) (5)
- Institut für Slavistik (3)
- Referat für Presse- und Öffentlichkeitsarbeit (2)
- Department Erziehungswissenschaft (1)
- Hasso-Plattner-Institut für Digital Engineering GmbH (1)
- Institut für Biochemie und Biologie (1)
- Institut für Geowissenschaften (1)
- Institut für Mathematik (1)
- Institut für Physik und Astronomie (1)
Low thermal conductivity boulder with high porosity identified on C-type asteroid (162173) Ryugu
(2019)
C-type asteroids are among the most pristine objects in the Solar System, but little is known about their interior structure and surface properties. Telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. This includes observations of C-type asteroid (162173) Ryugu1,2,3. However, on arrival of the Hayabusa2 spacecraft at Ryugu, a regolith cover of sand- to pebble-sized particles was found to be absent4,5 (R.J. et al., manuscript in preparation). Rather, the surface is largely covered by cobbles and boulders, seemingly incompatible with the remote-sensing infrared observations. Here we report on in situ thermal infrared observations of a boulder on the C-type asteroid Ryugu. We found that the boulder’s thermal inertia was much lower than anticipated based on laboratory measurements of meteorites, and that a surface covered by such low-conductivity boulders would be consistent with remote-sensing observations. Our results furthermore indicate high boulder porosities as well as a low tensile strength in the few hundred kilopascal range. The predicted low tensile strength confirms the suspected observational bias6 in our meteorite collections, as such asteroidal material would be too frail to survive atmospheric entry7
Rigorous runtime analysis is a major approach towards understanding evolutionary computing techniques, and in this area linear pseudo-Boolean objective functions play a central role. Having an additional linear constraint is then equivalent to the NP-hard Knapsack problem, certain classes thereof have been studied in recent works. In this article, we present a dynamic model of optimizing linear functions under uniform constraints. Starting from an optimal solution with respect to a given constraint bound, we investigate the runtimes that different evolutionary algorithms need to recompute an optimal solution when the constraint bound changes by a certain amount. The classical (1+1) EA and several population-based algorithms are designed for that purpose, and are shown to recompute efficiently. Furthermore, a variant of the (1+(λ,λ))GA for the dynamic optimization problem is studied, whose performance is better when the change of the constraint bound is small.