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Triangular cells are formed during early logarithmic growth of Trigonopsis variabilis. Good triangularity is obtained with methionine, proline, hydroxyproline, or alanine as a nitrogen source. 相似文献
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K. Becker 《Radiation and environmental biophysics》1968,5(3):207-222
Summary A review is given on recent developments in the field of charged particle track registration in insulating solids by preferential etching. The basic mechanism of latent track formation in minerals and inorganic glasses seems to be a spike formation process. In the more sensitive organic polymers, radiation induced chemical changes along the track probably predominate. The sensitivity, etching kinetics, and stability of tracks in plastics and some of the factors which affect them are discussed on the basis of experimental data.Several microscopic and macroscopic methods for simplified or automatic track counting are described briefly. Among the many applications of the etching method, neutron dosimetry via (n, f), (n, ), and recoil reactions are discussed in some detail. Other applications in nuclear physics, chemistry, biology, space research, and for age determinations in geological and archeological samples are listed.Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.Based on a lecture at the University of Tennessee, February 13, 1968. 相似文献
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Becker K 《Radiation research》1968,36(1):107-118
The number and diameter of microscopically visible alpha-particle tracks which can be etched in the surface of sensitive plastic foils such as cellulose triacetate are increased by the presence of oxygen. Pre- or posttreatment of foils with water or humid air increases the etching speed but not the foils' sensitivity. Treatment of foils with diluted H202 increases the sensitivity slightly, but the etching speed considerably. Some parameters of the oxygen/humidity effect are described; its possible consequences for the interpretation of the latent track formation process and its practical applications are discussed briefly. 相似文献
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Marion Himes 《The Journal of cell biology》1967,35(1):175-181
The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with B chromosomes; (b) the proportion of DNA to histone is identical with that of nuclei containing only normal chromosomes; (c) the amount of nonhistone protein in proportion to DNA in interphase is less in nuclei with B chromosomes than in normal nuclei. In condensed B chromosomes the ratio of nonhistone protein to DNA is similar to that in other condensed chromatin, such as metaphase chromosomes and degenerating nuclei. The B chromosomes appear to have no effect on nucleolar RNA and protein. Replication of B chromosomes is precisely controlled and is comparable to that of the ordinary chromosomes not only in synthesis for mitosis but also in formation of polyploid nuclei of root cap and protoxylem cells. 相似文献
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