Variational data assimilation is performed using either a T40 18 layer version of the National Meteorological Center spectral model or a limited-area shallow-water equations model, with operationally analyzed fields as well as simulated datasets. Issues of incomplete observations, control of gravitational oscillations, and inclusion of “on-off” physical processes are addressed in the framework ...

One the most cited papers in astronomy is Ken Freeman's 1970 paper on exponential disks in galaxies. In this contribution I review what has been done in this area since then and what we can infer about systematic properties of disks in galaxies from surface photometry, HI synthesis observations and measurements of stellar kinematics. Most disks have radial truncations at 3.6 ± 0.6 radial scalel...