Search

This article presents necessary and sufficient conditions for the existence and design of an unknown input Functional observer. The existence of the observer can be verified by computing a nullspace of a known matrix and testing some matrix rank conditions. The existence of the observer does not require the satisfaction of the observer matching condition (i.e. Equation (16) in Hou and Muller 1992, ‘Design of Observers for Linear Systems with Unknown Inputs’,IEEE Transactions on Automatic Control, 37, 871–875), is not limited to estimating scalar functionals and allows for arbitrary pole placement. The proposed observer always exists when a state observer exists for the unknown input system, and furthermore, the proposed observer can exist even in some instances when an unknown input state observer does not exist. [ABSTRACT FROM PUBLISHER]

A subpopulation of human lymphoid cells called natural killers is able to lyse certain normal and neoplastic targets in an in vitro cytotoxicity assay. The molecules which enable them to recognize sensitive cells, or permit turnout cells to escape remain unknown. In the studies described here we have compared some of the plasma membrane characteristics of a NK-sensitive human leukaemia cell line (K562) with those of a partially resistant subclone derived from it (K562-Clone I). Gel electrophoresis of cell-surface proteins radiolabelled by lactoperoxidase-catalysed iodination, periodate-borohydride tritiation, or biosynthetically by incubation with [3H]fucose did not reveal any reproducible differences between the sensitive and resistant lines. However, analysis of glycolipids showed that Clone I incorporated significantly more fucose than did the parental line, and that it synthesized a minor population of complex structures not found in the original K562. A subclone of Clone I(Clone I-Con ArI), made resistant to the toxic effects of concanavalin A, became sensitive once again to NK, and showed the parental glycolipid profile. These results suggest that the Clone I line, selected for resistance to NK, may have altered one or more of its intermediate oligosaccharides or pathways of fucose incorporation into glycolipid, and points to one process by which a tumour cell might modulate its surface to escape recognition by natural killers. [ABSTRACT FROM AUTHOR]