The violent youth of bright and massive cluster galaxies and their maturation over 7 billion years

In this study, we investigate the formation and evolution mechanisms of the brightest cluster galaxies (BCGs) over cosmic time. At high redshift (z ∼ 0.9), we selected BCGs and most massive cluster galaxies (MMCGs) from the Cl1604 supercluster and compared them to low-redshift (z ∼ 0.1) counterparts drawn from the MCXC meta-catalogue, supplemented by Sloan Digital Sky Survey imaging and spectroscopy. We observed striking differences in the morphological, colour, spectral, and stellar mass properties of the BCGs/MMCGs in the two samples. High-redshift BCGs/MMCGs were, in many cases, star-forming, late-type galaxies, with blue broad-band colours, properties largely absent amongst the low-redshift BCGs/MMCGs. The stellar mass of BCGs was found to increase by an average factor of 2.51 ± 0.71 from z ∼ 0.9 to z ∼ 0.1. Through this and other comparisons, we conclude that a combination of major merging (mainly wet or mixed) and in situ star formation are the main mechanisms which build stellar mass in BCGs/MMCGs. The stellar mass growth of the BCGs/MMCGs also appears to grow in lockstep with both the stellar baryonic and total mass of the cluster. Additionally, BCGs/MMCGs were found to grow in size, on average, a factor of ∼3, while their average Sérsic index increased by ∼0.45 from z ∼ 0.9 to z ∼ 0.1, also supporting a scenario involving major merging, though some adiabatic expansion is required. These observational results are compared to both models and simulations to further explore the implications on processes which shape and evolve BCGs/MMCGs over the past ∼7 Gyr

Direct Numerical Simulation of the Transition Process in a Separated Supersonic Ramp Flow

Despite intensive theoretical and experimental research, transition to turbulence in separated hypersonic ramp flows is still a challenge to predict. One of the most successful approaches to model the dominant mechanisms is direct numerical simulation, which has demonstrated the capability to generate reliable datasets. In the present study, different supersonic test cases are chosen from literature and compared with simulations using a high-order version of the DLR FLOWer code. The results using higher-order Pade-filter approaches are encouraging. With this validation as a background, a supersonic ramp case was chosen for study. Different ramp-angles and Reynolds numbers were investigated to determine a transitional test case, for which turbulence can be resolved behind re-attachment. A hypersonic ramp with 12° angle of attack was then chosen for three-dimensional DNS of the transition process. These DNS were carried out with different grid extents in the wall-normal direction and different sweep angles of the incoming flow with good success. Simulations of laminar-turbulent breakdown are presented using various perturbation spectra at the inflow

Do ridge habitats contribute to pteridophyte diversity in tropical montane forests? A case study from southeastern Ecuador

We address the question to which degree ridge habitats in tropical montane forests contribute to overall plant diversity by analysing patterns of pteridophyte (i.e. lycophytes and ferns) assemblages on ridges and slopes in three montane forest sites near Podocarpus National Park, Ecuador. The analyses, which involved 158 pteridophyte species (110 terrestrial, 96 epiphytic, 48 both) from 28 plots of 20 m x 20 m (or an equivalent of 400 m(2)), showed that more species were typical of one of the three study sites than of one of the two habitats (ridge/slope). As found in previous studies, alpha diversity on ridges was lower than on slopes, accounted for by the absence of numerous species that are found on slopes. Pteridophyte assemblages on ridges were more similar across study sites than those on slopes. Thus, unlike the structurally comparable (i.e. stunted, open) Amazonian forests, the studied montane ridge forests harbour fairly homogenous pteridophytes assemblages with very few specialised species. Our study implies that slope forests are of higher conservation priority for pteridophytes in the study region than ridge habitats. However, comparative studies are needed because other geographical regions and other groups of organisms may not share this pattern