Potassium dihydrogen phosphate (KDP) is widely used for high-power laser frequency conversion. Its applications, however, are limited by a characteristically low laser damage threshold. This damage is associated with extrinsic impurity inclusions, whose exact nature has not been previously identified. We have now demonstrated that KDP grown in solutions containing organic impurities incorporates select organic compounds into the crystal matrix. Furthermore, we have observed a strong correlation between the concentration of these compounds and the crystal laser damage threshold and density.
In the penultimate paragraph of the article entitled "EPR in Chromatophores from Rhodospirillum rubrum and in Quantasomes from Spinach Chloroplasts," by G. M. Androes, M. F. Singleton, and M. Calvin, which appeared in these PRO-CEEDINGS, 48, 1022-1031(1962, the results of Chance and Nishimura were incorrectly quoted. This paragraph (on page 1030) should read as follows:"The photo-induced EPR observed in the chromatophores occurs reversibly at all temperatures studied, while that observed in the quantasomes occurs irreversibly at low temperature. This difference in behavior is not paralleled by certain photoinduced changes in optical density which occur in these types of photosynthetic materials, and which are assigned to the same kind of molecule in both types of system. Chance and Nishimura"9 have found changes in optical density at -550, -520, and -420 mgt in the bacterium Chromatium which occur irreversibly at 800K, while Witt et al.20 have found changes in optical density at -555, -420, and -400 m,4 which occur irreversibly in Chlorella at -150'C. The changes in both types of material are assigned to a cytochrome. Thus, it appears that the photoinduced EPR observed in these systems is not directly associated with the photoinduced oxidation of a cytochrome." M. CALVIN 1022 BIOCHEMISTRY: ANDROES, SINGLETON, AND CALVIN PROC. N. A. S.Summary.-Production of a diffusible collagenolytic factor operating at neutral pH and physiologic temperature on undenatured collagen was demonstrated in living animal tissues in culture. Cultivation of bullfrog tadpole tissues (skin, gut, and gills) on thermally reconstituted neutral calf and guinea pig skin collagen gels resulted in degradation of the substrate to dialyzable collagen peptides. This substrate was not attacked by the common proteolytic enzymes, by Cathepsin C, by tadpole tissue extracts, or by killed tadpole tissue. It is proposed that the experimental system used here may be developed into a quantitative assay for collagenolytic activity in small tissue fragments.
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