10,007 research outputs found
Zur Biologie von Dipoena torva (Araneae: Theridiidae)
Data are given concerning stratification, phenology, feeding and mating behaviour of the theridiid spider Dipoena torva (THORELL, 1875). The species was found predominantly at heights of around 10 metres on the sterns of oaks and pines in Berlin, Germany. The sex ratio was more or less 1: 1. Adult spiders were active during summer whereas juveniles were only found before and after the main activity period of adults. This species seems to be active during the. daytime. The main food consists of ants. The mating behaviour is described. The occurrence of D. torva is a result of certain biotic and abiotic factors such as the abundance of ants, the understorey and structural factors.Es werden Daten zur Phänologie, der Stratifikation sowie dem Beutefang und Fortpflanzungsverhalten der Theridiidae Dipoeoa torva (THORELL 1875) vorgestellt. Die Art wurde hauptsachlich in 10 Meter Höhe an den Stämmen alter Kiefern und Eichen in Berlin gefunden, Männchen und Weibchen etwa in gleicher Anzahl. Die Adulten sind sommeraktiv, Juvenile bzw. Subadulte werden vor und nach der Hauptaktivitätszeit der Adulten gefangen. Die Art ist tagaktiv. Nahrungsgrundlage scheinen bevorzugt Ameisen zu sein. Das Paarungsverhalten wird kurz beschrieben. Das Vorkommen der Art wird vor dem Hintergrund biotischer und abiotischer Faktoren diskutiert
Stratum change of Drapetisca socialis re-examined (Araneae, Linyphiidae)
It has been widely accepted that the biology of Drapetisca socialis includes a pronounced stratum change of this species from the forest soil into the crowns of beech trees. On old pine trees, however, D. socialis never exceeded its activity range to heights greater than 10 metres. These results lead to an re-examination of existing results, and to a review of several studies on tree-dwelling spiders. A synopsis of all data revealed that D. socialis changes stratum along stems of trees into greater heights in forests, but only very seldom, and then obviously only by chance, reaches high tree crowns. Earlier results of a stratum change into the crowns of old beech are only assumptions. The requirement for studies including samples from the bottom to the top of trees is proposed
Direct simulation of liquid-gas-solid flow with a free surface lattice Boltzmann method
Direct numerical simulation of liquid-gas-solid flows is uncommon due to the
considerable computational cost. As the grid spacing is determined by the
smallest involved length scale, large grid sizes become necessary -- in
particular if the bubble-particle aspect ratio is on the order of 10 or larger.
Hence, it arises the question of both feasibility and reasonability. In this
paper, we present a fully parallel, scalable method for direct numerical
simulation of bubble-particle interaction at a size ratio of 1-2 orders of
magnitude that makes simulations feasible on currently available
super-computing resources. With the presented approach, simulations of bubbles
in suspension columns consisting of more than fully resolved
particles become possible. Furthermore, we demonstrate the significance of
particle-resolved simulations by comparison to previous unresolved solutions.
The results indicate that fully-resolved direct numerical simulation is indeed
necessary to predict the flow structure of bubble-particle interaction problems
correctly.Comment: submitted to International Journal of Computational Fluid Dynamic
Hypervelocity stars in the Gaia era: Runaway B stars beyond the velocity limit of classical ejection mechanisms
Young massive stars in the halo are assumed to be runaway stars from the
Galactic disk. Possible ejection scenarios are binary supernova ejections (BSE)
or dynamical ejections from star clusters (DE). Hypervelocity stars (HVSs) are
extreme runaway stars that are potentially unbound from the Galaxy. Powerful
acceleration mechanisms such as the tidal disruption of a binary system by a
supermassive black hole (SMBH) are required to produce them. Therefore, HVSs
are believed to originate in the Galactic center (GC), the only place known to
host an SMBH. The second Gaia data release (DR2) offers the opportunity of
studying HVSs in an unprecedented manner. We revisit some of the most
interesting high-velocity stars, that is, 15 stars for which proper motions
with the Hubble Space Telescope were obtained in the pre-Gaia era, to unravel
their origin. By carrying out kinematic analyses based on revised
spectrophotometric distances and proper motions from Gaia DR2, kinematic
properties were obtained that help constrain the spatial origins of these
stars. Stars that were previously considered (un)bound remain (un)bound in
Galactic potentials favored by Gaia DR2 astrometry. For nine stars (five
candidate HVSs plus all four radial velocity outliers), the GC can be ruled out
as spatial origin at least at confidence level, suggesting that a
large portion of the known HVSs are disk runaway stars launched close to or
beyond Galactic escape velocities. The fastest star in the sample, HVS3, is
confirmed to originate in the Large Magellanic Cloud. Because the ejection
velocities of five of our non-GC stars are close to or above the upper limits
predicted for BSE and DE, another powerful dynamical ejection mechanism (e.g.,
involving massive perturbers such as intermediate-mass black holes) is likely
to operate in addition to the three classical scenarios mentioned above.Comment: Accepted for publication in A&A (Astronomy and Astrophysics
Optimized parallel tempering simulations of proteins
We apply a recently developed adaptive algorithm that systematically improves
the efficiency of parallel tempering or replica exchange methods in the
numerical simulation of small proteins. Feedback iterations allow us to
identify an optimal set of temperatures/replicas which are found to concentrate
at the bottlenecks of the simulations. A measure of convergence for the
equilibration of the parallel tempering algorithm is discussed. We test our
algorithm by simulating the 36-residue villin headpiece sub-domain HP-36
wherewe find a lowest-energy configuration with a root-mean-square-deviation of
less than 4 Angstroem to the experimentally determined structure.Comment: 22 pages, 7 figure
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