LES investigation into the generation of momentum deficits in the supersonic wake of a micro-ramp

Implicitly implemented large eddy simulation (LES) with a fifth-order WENO scheme was conducted in this study. Based on Navier-Stokes equations, this LES was carried out to explore the origin of momentum deficit caused by a supersonic micro-ramp at flow conditions of M a = 2.5 and Re θ = 5760. The numerical results were validated through qualitative and quantitative comparisons with existing experimental data. After describing the aerodynamic properties of the supersonic wake, such as the deficit and the streamwise vortices, the momentum deficit was later detected to originate from the lower portion of the upstream boundary layer, while the high momentum fluid originated from close to the wall at the upper portion. Position alternation trigged by the micro-ramp was finally proposed as a revised mechanism

Mutual ornamentation, age, and reproductive performance in the European starling

Ornamental traits expressed in both sexes are widespread among birds. Many studies have indicated that male ornaments develop through sexual selection. Female ornaments may be correlated effects of selection on males or have signaling functions in their own right. In the facultatively polygynous starling Sturnus vulgaris, both sexes possess iridescent throat feathers, which are actively displayed during courtship by males. This paper investigates the reproductive correlates of throat feather ornaments in both sexes. Bird-perceived hue and components of feather length covaried strongly, and a summary variable (the first principal component [PC1]) was extracted using Principal component analysis. Sex and age-related differences were found for PC1. Positive assortative mating was found with respect to age and PC1. However, the relative influences of ornamentation and age on breeding variables were hard to separate, so effects may be related to other age-related variables. This provides a cautionary note for studies of ornamentation where age is unknown. However, we argue that throat feathers in starlings may signal age and age-related quality measures in both sexes. Older females with higher PC1 scores bred earlier and laid larger clutches with higher hatching success; older males with higher PC1 scores had higher chances of becoming polygynous and attracting high reproductive quality females. PC1 showed no relationship with parental care in either sex. Direct reproductive benefits for males and indirect genetic benefits for either sex may drive mate choice based on these age-related characters. However, only experimental manipulation can determine whether ornamentation signals quality variation within age classes. Copyright 2005.avian color vision; mutual sexual selection; ornamentation; plumage coloration; reproductive performance