Habit and growth type of snow crystals was consolidated by Kobayashi in 1961 as far as single crystalline forms are concerned. But much has been left unknown about poly-crystalline forms of snow crystals. Kronberg-Wilson's concept of Coincidence-Site Lattice was successfully introduced to explain the structure of “twin prisms” and twelve-branched snow crystals as rotation twins which have each a twin axis parallel to the composition plane. A generalized CSL theory is now proposed to explain the structure and growth of poly-crystalline shaped crystals including a combination of bullets, a spacial assemblage of plane branches, and some of the “peculiar shaped crystals” as rotation twins which have each a twin axis perpendicular to the composition plane. Thus an important step is forwarded for the understanding of the morphology of snow crystals. Methods of microscopic observation in situ of growing ice crystals are described with the aid of illustrations and photographs.
In situ observations of thin film growths in ultra high vacuum electron microscopes (UHVEMs) are reviewed. The purposes of the in situ studies are summarized and recently obtained results with use of UHVEMs are described. Design features of a new UHVEM constructed by the present authors are compared with those of other UHVEMs with stress on some advantages of the new instrument for the routine in situ studies. The clean substrate preparation techniques are discussed and some new results obatined by the instrument concerning on growth features of various metals on other metals, analysis of coalescence process under more well defined conditions than Pashley's and mobility of stable clusters are briefly summarized. Finally LEED and AES methods as for the studies of thin film growths are discussed with special stress on mutually complementary nature of these techniques and the UHVEM in situ method.
Polyacrylonitrile was turned into two kinds of semicoductors by different processes of pyrolysis up to 500°C. Then they were irradiated with X-rays in the air, and variationsyof their impedance after cessation of irradiation were measured. The variation of impedance is closely connected with scission and recombination of the conjugated double bond chain, with enlargement and narrowing of space between two chains and also with generation and recombination of ions and electrons. And these variations of structure cause a variation of resistance at any place and that of capacitance in the neighborhood of the electrode. Two kinds of processes of impedance variation appear after cessation of irradiation; Qne of them disappears within about 30 minutes, and the other persists for more than 2 hours. And both processes occur extensively at the part where the chemical bond is imperfectly cojugated. Generally speaking, it seems that the main reaction which is caused by X-rays irradiation is the scission of the conjugated double bond.
Image focussing characteristics of the defocused optical system under different illumination modes are investigated by means of the transmission cross coefficients T(f, 0), T(f, -f) and the optical transfer function under linear approximation in a partially coherent optical system. Images of Siemens star for corresponding optical condition are simulated and assessed from the viewpoint of the system performance. It is shown that special features of imaging characteristics of the defocused optical system are encountered in coherent, near-coherent and annular illumination modes. The corresponding images for a largely defocused optical system differ remarkably from the original object. It is also clarified that contrast reversal in the image occurs more easily under the illumination closer to a coherent rather than incoherent one. Furthermore, other informations on image ap pearance in partially coherent, defocused optical system are presented. Finally, theoretical considerations which have been verified experimentally.