Studies on the conditions required for optimum recovery of Tetrahymena pyriformis strain S (Phenoset A) after freezing to and thawing from -196 C

The toxicity of several cryoprotective agents was tested at room temperature (23 C) against Tetrahymena pyriformis strain S (Phenoset A) at different stages of growth cycle. Polyvinylpyrrolidone (PVP-40) at 10 per cent (v/v) concentration was without effect at any stage in the growth cycle, while 1.2 M glycerol immobilized the cells which were disrupted very shortly afterwards. The toxicity of 0.25 M glucose was largely independent of the position of the cells in the growth cycle, but the toxicity of 0.25 M sucrose and 1.4 M dimethylsulfoxide (DMSO) was most marked in late log- and stATIONARY-PHASE CELLS. After log-phase cells had been equilibrated with 1.4 M DMSO for 1 hr, the number of cells surviving cooling at defined rates from 0.45 to 12 C/min decreased as the final temperature decreased from -30 to -60 C. A temperature of -53 C was found to be the optimum from which cells cooled at a given rate could be cooled rapidly to -196 C. Nevertheless, when cells were cooled at defined rates to -35, -45, or -53 C and then rapidly to -196 c the optimum rate of cooling to these temperatures was found to be 1 C/min. The optimum rate of cooling to -60 C prior to plunging into liquid nitrogen was found to be 2.7 C/min.

Problems and pitfalls in the use of rating schemes to describe visual art

Two teams of two raters each rated slides of artists' productions according to descriptive variables on which accord was high. However, raters disagreed in evaluation of merit. Difficulties encountered in making these ratings and their implications for research in aesthetics are discussed.

Some new techniques for processing remotely obtained images by self-generated spectral masks

An extension of a new technique that enables parallel, simultaneous processing of remotely obtained images is presented. The technique holds out promise for automatic on-board classification of data. The central feature involves the generation of binary masks, directly from the image, based on object reflectance data, that groups objects into equivalence classes. These masks, called equivalence class masks, can be used in various logical combinations to isolate classes of objects with a priori known reflectance or radiance signatures. Experimental verification of the technique is furnished for simple scenes. A computational scheme, based on a sequence of integrated irradiance measurements on the image, that enables the identification of objects within an equivalence class is suggested.