Large piezoelectric single crystals of the Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZN-PT) binary system have been successfully obtained using a conventional flux method and a suitable ratio of PZN-PT: PbO flux. The largest crystal had dimensions of 43×42×40 mm and weighed 415 g. In order to improve growth behavior and reduce the number of nuclei, the temperature gradient program of the crucible was optimized; that is, the bottom of the crucible was made cooler (>50° C) than the top during cooling. A charged composition of 45 mol% PZN-PT and 55 mol% PbO showed good growth results. A large bar-mode electromechanical coupling factor, k 33', (84%) for phased array ultrasonic transducers was obtained. This confirms that large PZN-PT single crystals for phased-array ultrasonic transducers can be grown using a flux method.

We show that for any link L, there exists a Seifert surface for L that is obtained by successively plumbing flat annuli to a disk D, where the gluing regions are all in D. This furnishes a new way of coding links. We also present an algorithm to read the code directly from a braid presentation.

No abstract

We show that Rubinstein-Scharlemann graphics for 3-manifolds can be regarded as the images of the singular sets (: discriminant set) of stable maps from the 3-manifolds into the plane. As applications of our understanding of the graphic, we give a method for describing Heegaard surfaces in 3-manifolds by using arcs in the plane, and give an orbifold version of Rubinstein-Scharlemann's setting. Then by using this setting, we show that every genus one 1-bridge position of a nontrivial two bridge knot is obtained from a 2-bridge position in a standard manner.

No abstract

The effects of disturbance by trampling and vegetation removal on herbaceous communities and their microenvironments were examined at two sites with different levels of shade. The dominant species of the original vegetation were the perennial herb Artemisia princeps at the sunny site and the dwarf-bamboo Pleioblastus chino at the shady site. With no disturbance and marked dominance of these species, diversity was low. After vegetation removal there was a rapid recovery, leading to a more diverse vegetation with many more species, each with a lower dominance. Continuous trampling induced a short vegetation while the light intensity under the foliage was increased. At the sunny site, species richness was depressed by trampling because the soil water potential decreased markedly during summer and only the stress-tolerant annual Digitaria adscendens grew vigorously. Thus, the lowest species diversity was observed in the heavily trampled vegetation in late summer. At the shady site, soil water availability was not affected by trampling. This allowed the survival of many species and prevented a strong decline in diversity.The results suggest that the pattern of change in diversity in communities subjected to various disturbances, was always determined by the original environments.

No abstract

No abstract