Convective flows around sunspot-like objects

Results are given for calculations of convective flows around objects in the outer layers of the Sun that have similar characteristics to small sunspots. These objects are allowed to radiatively (diffusively) exchange heat with their surroundings, but convective motions and exchange are absent. This assumption is based on the simple presumption that a sunspot magnetic field maintains pressure equilibrium with the surrounding medium and prevents convective exchange with that medium.The flow structure around the object, and the question of the overall balance or redistribution of the emerging heat flux as suggested by earlier empirical models, are studied and discussed.After a period of adjustment, shortly after the sunspot-like object is placed into the domain, the layer readjusts itself so that most of the heat flux actually reappears at the surface, although some fraction of the flux is carried horizontally far from the object. There is no indication of long term storage of the heat flux that would normally appear in the place where the object resides. Finally, when the object is removed, the surrounding medium responds very quickly and soon returns to the undisturbed state before the object was in place.The present numerical treatment includes restrictions that may influence aspects of the heat redistribution, convective flows and time scales. In particular, the shape of the object and its size (somewhat smaller than a sunspot) are important, as is the number of spatial dimensions and the treatment of some boundary conditions. Since all of these issues require further investigation, some discussion is presented regarding the applicability of our results to real sunspots.     

Elemental abundances in the Milky Way stellar disk(s), bulge,and halo

We present a review of elemental abundances in the Milky Way stellar disk, bulge, and halo with a focus on data derived from high-resolution stellar spectra. These data are fundamental in disentangling the formation history and subsequent evolution of the Milky Way. Information from such data is still limited and confined to narrowly defined stellar samples. The astrometric Gaia satellite will soon be launched by the European Space Agency. Its final data set will revolutionize information on the motions of a billion stars in the Milky Way. This will be complemented by several ground-based observational campaigns, in particular spectroscopic follow-up to study elemental abundances in the stars in detail. Our review shows the very rich and intriguing picture built from rather small and local samples. The Gaia data deserve to be complemented by data of the same high quality that have been collected for the solar neighborhood.     

Models of the flexure-controlled strength,stiffness and cyclic deformation capacity of rectangular RC columns with smooth bars,including lap-splicing and FRP jackets

Cyclic tests of single concrete columns with smooth (plain) bars are not representative of building columns with lap splices at floor levels and story-long starter bars. Column specimens with fixity at top and bottom resemble building columns best, but few of those tested so far had smooth bars and even then without bar lap-splicing at floor level or FRP jackets at column ends. Empirical models based on single-column tests, especially the numerous ones with cantilever-type specimens, cannot be readily extended to columns with smooth bars in real-life buildings. Physical models of the Strut-and-Tie type are developed and are validated or calibrated through comparisons with laboratory tests. Their scope includes anchorage and splicing of bars with either 180° hooks or straight ends. Once validated, they are adapted to real-life multistory rectangular RC columns with smooth bars, in order to obtain the column properties of interest: the chord rotation at yielding and the cyclic ultimate chord rotation, with or without FRP jacketing. Different expressions apply to the top and bottom end of a column in a story, but a single one is used to estimate the column’s effective stiffness. Empirical alternatives fitted to the single-element test results have slightly less scatter than physical models, but caution is needed for their application to columns of real buildings. Simulations of the 3D seismic response of a plan wise asymmetric full size building, tested pseudo-dynamically before or after retrofitting all columns with FRPs or just two of them with RC jackets, provide certain confidence in the extension of the physical models for the estimation of the stiffness and ultimate deformation of columns with smooth bars in real-life buildings.