Poly(N-isopropylacrylamide) (PNIPAm) co-polymers responsive to temperature and pH were prepared with side chain chemistries in order to exhibit phase transitions under physiologically relevant conditions. Fluorescence spectroscopy, gel retardation assays, dynamic light scattering and atomic force microscopy were used to characterize the binding of plasmid DNA to these materials and to control polymers poly(ethyleneimine) (PEI) and poly(ethyleneimine)-octanamide. Complexes of plasmid DNA with thermoresponsive cationic polymers containing PNIPAm displayed variations in gel retardation behaviour above and below polymer phase transition temperatures, with a high molecular weight linear cationic PNIPAm co-polymer forming complexes with reduced affinity above LCST whereas a branched PEI-PNIPAm co-polymer bound with higher affinity above the PNIPAm phase transition. The thermoresponsive polymers also exhibited changes in particle morphology across the same temperature ranges with polymer DNA complexes prepared at N/P ratios of 2:1 generating spherical particles varying in radius between 30-70 nm at 25 degrees C and 60-100 nm at 40-45 degrees C. The transport of DNA within these complexes to cell nuclei was demonstrated to occur within 24 h in tissue culture via confocal microscopy, and low level transfection of mouse muscle cells by a reporter gene encoding green fluorescent protein was achieved with the branched thermoresponsive PEI-PNIPAm conjugate.

We developed a multimethod modeling approach to evaluate strategic alternatives for GM's OnStar communications system. We used dynamic modeling to address some decisions GM faced in 1997, such as the company's choice between incremental and aggressive marketing strategies for OnStar. We used an integrated simulation model for analyzing the new telematics industry, consisting of six sectors: customer acquisition, customer choice, alliances, customer service, financial dynamics, and dealer behavior. The modeling effort had important financial, organizational, and societal results. The OnStar business now has two million subscribers, an 80 percent market share of the emerging telematics market, and has been valued at between $4 and $10 billion. The OnStar project set the stage for a broader GM initiative in service businesses that ultimately could yield billions in incremental earnings. Most important, OnStar has saved many lives that otherwise would have been lost in vehicle accidents.

No abstract

A study of the effects of various sample preparation techniques for scanning electron microscopy has been undertaken in an attempt to resolve conflicting descriptions of the surface topography of human peripheral blood lymphocytes. By fixing cells in suspension--a technique thought most likely to avoid the production of artefacts--no clearly defined morphological classification of lymphocytes could be made, and when T- and B-lymphocyte enriched preparations were studied their surfaces appeared similar. Both T- and B-rosetted cells showed identical morphological changes as a result of their interaction with red blood cells. The smooth cells described in other reports were found only under certain conditions of preparation. It is therefore not possible to distinguish between T- and B-cell populations, using the S.E.M., on the basis of surface morphology alone.