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

Interaction of separation and transition in laminar separation bubbles in a 3D boundary layer

The influence of different disturbance combinations and increasing sweep on a family of pressure-induced laminar separation bubbles is studied systematically by means of direct numerical simulation (DNS). Three types of disturbance waves are tested against their potential to stimulate the growth of background disturbances of fundamental or subharmonic frequency. The focus is on 2D-disturbances, which are normally the most amplified disturbances in unswept separation bubbles. For the present 3D-base flows, they are found to lose their dominance for sweep angles larger than 10° to 15°. Instead, oblique waves with a propagation direction between 0° and -6° relative to the potential streamline trigger the strongest growth of background disturbances. Spatial linear stability theory (LST) was utilised to select the mosta mplified disturbances for each sweep angle. LST turned out to be as reliable as in unswept laminar separation bubbles and its excellent agreement with DNS within the linear domain was not adversely affected by the sweep angle

The effect of sweep on laminar separation bubbles

The effect of a systematic variation of the sweep angle on the disturbance amplification and onset of transition is studied in a generic family of swept laminar separation bubbles (LSB) by means of direct numerical simulation. The detailed analysis of a transition scenario with fundamental resonance in a 30°-LSB shows, that the saturation of background disturbances is the key event, after which a rapid breakdown of transitional structures to smaller scales and thus turbulent flow occurs. The stages of transition are similar to unswept LSB, but two-dimensional disturbances lose their dominance for sweep angles larger than 15°. Instead, oblique Tollmien-Schlichting waves which travel approximately along the direction of the potential streamline experience the maximal amplification in the linear stage and stimulate the strongest growth of background disturbances after saturation

Nanoherding: Plasma-chemical synthesis and electric-charge-driven self organization of SiO2 nanodots

We report on the chemical synthesis of the arrays of silicon oxide nanodots and their self-organization on the surface via physical processes triggered by surface charges. The method based on chemically active oxygen plasma leads to the rearrangement of nanostructures and eventually to the formation of groups of nanodots. This behavior is explained in terms of the effect of electric field on the kinetics of surface processes. The direct measurements of the electric charges on the surface demonstrate that the charge correlates with the density and arrangement of nanodots within the array. Extensive numerical simulations support the proposed mechanism and prove a critical role of the electric charges in the self-organization. This simple and environment-friendly self-guided process could be used in the chemical synthesis of large arrays of nanodots on semiconducting surfaces for a variety of applications in catalysis, energy conversion and storage, photochemistry, environmental and biosensing, and several others