Ultrathin polymer films of poly(vinyl alkanal acetal) were made by the Langmuir-Blodgett (LB) technique, which enables one to fabricate the layered structure with a thickness of only 1nm per layer. The polymer monolayer on a water surface was successively deposited on a solid substrate as a two-dimensional form, but after the deposition, thermal relaxation of the layered structure occurred under elevated temperatures. The structural change in the nanometer dimension could be sensitively and quantitatively probed by the use of energy transfer between fluorescent chromophores incorporated into each layer. The diffusion constants observed as a function of temperature are in the order of 10-18-10-15cm2 s-1. The thermal properties of the LB films are well characterized by the glass transitions of bulk polymers.
Regions representing about 80% of the 16S rDNA sequences of nine phytoplasma isolates were amplified by polymerase chain reaction (PCR). These partial 16S rDNA sequences amplified from the various phytoplasmas were used in DNA heteroduplex mobility assays (HMA). Based on DNA distances derived from HMA analysis, the nine phytoplasma isolates may be classified into four distinct groups: group I, paulownia witches'-broom (China), potato purple top (France); group II, tomato stolbur (France); group III, eastern aster yellows (U. S.A.), faba bean phyllody (Sudan), vinca phyllody (Sudan), tomato big bud (Australia); group IV, crotalaria witches'-broom (Thailand), clover proliferation (Canada).