RESUMO
Algebraic reconstruction techniques (ART) are iterative procedures for recovering objects from their projections. It is claimed that by a careful adjustment of the order in which the collected data are accessed during the reconstruction procedure and of the so-called relaxation parameters that are to be chosen in an algebraic reconstruction technique, ART can produce high-quality reconstructions with excellent computational efficiency. This is demonstrated by an example based on a particular (but realistic) medical imaging task, showing that ART can match the performance of the standard expectation-maximization approach for maximizing likelihood (from the point of view of that particular medical task), but at an order of magnitude less computational cost.
RESUMO
Whereas Salmonella typhimurium 7136 will not grow at reduced water activity (aw), it was survival in such items as intermediate-moisture foods is of interest. Initial studies demonstrated that the addition of 0.3 M acetate (pH 4.7) to glycerol-Trypticase soy broth (BBL Microbiology Systems) solutions (aw 0.86) reduced the viability of S. typhimurium cells. The extent of death of cells exposed to reduced aw was increased by decreasing the pH or increasing the concentration of acetate. Acidification of glycerol-Trypticase soy broth reduced the D40 degrees C value exhibited by cells exposed to a range of aw solutions (0.65 to 0.92). Acetate appeared to affect survival more dramatically as aw values approached the minimum growth limit. Acidification with acetate also reduced cell survival in a variety of humectant solutions with an aw of 0.86 (glycerol, dextrose, and NaCl).
