Lopsided gas discs arising from mass inflow in barred spiral galaxies

We explore numerically the effects of mass inflow on barred spiral galaxies in the context of high-velocity clouds accreting on to galactic discs. To assess whether such events are detectable, we quantify their effect on the disc's gas distribution by calculating the lopsidedness parameter A1, and by deriving position-velocity plots of HI emission. The impact of an accretion event strongly depends on the parameters of the high-velocity cloud. For cloud mass ≥107 Mθ, infall can have a lasting impact on the gaseous disc, with A1 ≳ 0.05 for ∼1.5 Gyr. We discuss the time-variability of the lopsidedness parameter and consequences for detecting gas infall. Accretion events will be marginally noticeable in position-velocity diagrams, again depending on cloud parameters. Our models provide a possible explanation for low-amplitude lopsidedness observed in galaxies without nearby companions

Measurable versions of the LS category on laminations

We give two new versions of the LS category for the set-up of measurable laminations defined by Berm\'udez. Both of these versions must be considered as "tangential categories". The first one, simply called (LS) category, is the direct analogue for measurable laminations of the tangential category of (topological) laminations introduced by Colman Vale and Mac\'ias Virg\'os. For the measurable lamination that underlies any lamination, our measurable tangential category is a lower bound of the tangential category. The second version, called the measured category, depends on the choice of a transverse invariant measure. We show that both of these "tangential categories" satisfy appropriate versions of some well known properties of the classical category: the homotopy invariance, a dimensional upper bound, a cohomological lower bound (cup length), and an upper bound given by the critical points of a smooth function.Comment: 22 page

The Physics of Star Cluster Formation and Evolution

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe

Stability and scenario trees for multistage stochastic programs

By extending the stability analysis of [20] for multistage stochastic programs we show that their (approximate) solution sets behave stable with respect to the sum of an Lr-distance and a filtration distance. Based on such stability results we suggest a scenario tree generation method for the (multivariate) stochastic input process. It starts with an initial scenario set and consists of a recursive deletion and branching procedure which is controlled by bounding the approximation error. Some numerical experience for generating scenario trees in electricity portfolio management is reported

Cohomology of Horizontal Forms

The complex of s-horizontal forms of a smooth foliation F on a manifold M is proved to be exact for every s = 1, . . . , n = codim F, and the cohomology groups of the complex of its global sections, are introduced. They are then compared with other cohomology groups associated to a foliation, previously introduced. An explicit formula for an s-horizontal primitive of an s-horizontal closed form, is given. The problem of representing a de Rham cohomology class by means of a horizontal closed form is analysed. Applications of these cohomology groups are included and several specific examples of explicit computation of such groups-even for non-commutative structure groups-are also presented