Abstract: A sensitive, yeast-based genetic system for identifying agents causing double-strand DNA damage is described. The system comprises a yeast strain containing either chromosomes having divergent (homeologous) DNA sequences, a single nonhomologous chromosome or a single artificial chromosome with suitable genetic markers so that double-strand damage leading to the loss of such chromosome due to the inability to undergo recombinational repair with a homolog is detected.

Abstract: A method of producing plasmids with heteroduplex DNA sequences, in which probe plasmids containing DNA inserts that correspond to probe sequences and test plasmids containing DNA inserts that correspond to a population of test sequences are first constructed. The vector portions of the plasmids used in these constructions have similar sequences. When test and probe plasmids are cleaved with appropriate restriction enzymes and then denatured to separate strands, complementary regions of the linear strands which correspond to vector sequences can anneal. The molecules that harbor test and probe inserts that are related by sequence complementarity form non-covalently closed circular molecules. These molecules can replicate after transformation into an appropriate host organism. There is a replication bias against plasmids which anneal through vector sequences, but which do not contain homologous probe and test inserts.

Abstract: A regenerative heat engine designed to produce power for the operation of equipment such as an artificial heart is disclosed. The heat engine includes a temperature control heat pipe located around the periphery of the engine cylinder and a temperature distribution heat pipe located around the periphery of the heat source. A flywheel and bellows seal is included as part of the displacer piston drive, and a flexure support is positioned on the hot end of the displacer piston to allow the piston to move longitudinally while restricting lateral motion.