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Small changes in the pointing direction of NGST will be required as part of target acquisition and dithering. Some portion of these changes may be accomplished by moving the entire observatory, other portions might be accomplished by moving a mirror. The purpose of this document is to outline the expected scientific drivers for different kinds of motions, estimate their scale and frequency, and assess their importance to the overall science goals of the observatory. Such information is an important input to deciding how efficient and accurate to make the small-angle maneuvers, and in deciding how they should be accomplished.

Neutron small-angle scattering of E. coli ribosomes. A contrast variation study

Summary form only given, substantially as follows. The authors with the aid of neutron small-angle scattering with the contrast-variation method have established that for 50S and 70S ribosomal particles the RNA-protein distribution is such that the RNA component is located predominantly towards the interior and the protein towards the exterior of the particle. In contrast, the 30S subunit is much more homogeneous in its RNA-protein distribution. The shape of the 50S subunit has been determined at low resolution. The authors have extended these studies to 30S and 70S particles and found that the scattering density of the 70S ribosomes as for the 50S subunit decreases from the centre to the outer surface of the particle. Thus for 70S and 50S particles the r-RNA is located mainly in the interior and the bulk of the protein is distributed concentrically on the outer surface.Anglai