"Microscopic" Cleavages in Bornite from the Jinmu Mine, SW Japan and their Implications

During microscopic and electron probe investigation of the copper ores from the Jinmu mine, Hiroshima Prefecture, SW Japan, we have found well-developed "microscopic" cleavages oriented in two or three directions in the bornite matrix. They are represented by the regularly arranged intergrowths, lattice or lamellar. According to their distribution density and size (width), the cleavages are divided into three types. (1) Type 1, densely developed and very fine (less than about 0.1 micron in width), visible only under higher magnifications (x 400 or greater); (2) Type 2, less densely developed and fine (about 1micron in width); and (3) Type 3, sparsely developed and coarse (up to about 10 microns in width). The Type 1 cleavages are less common in the Jinmu ores, while they are very rare in natural sulfides. The very fine and coarse lamellae are always chalcopyrite, while the fine ones are mainly wittichenite and/or some chalcopyrite. Under the electron beam only the image of chalcopyrite forms a dark set of lines (backscat-tered image) and appears as dented (topographic image). It is important to note that their abundances of the cleavage types differ significantly from one place to another, even within a polished section. This fact suggests that there might be a compositional heterogeneity in the original solid solution, that is, a difference in the degree of supersaturation, with the higher degree for the Type 1 and Type 2 assemblages than for the Type 3 assemblages. As experimentally confirmed by SUGAKI (1955), the crystallographic intergrowths described are concluded to have been formed by exsolution from the solid solution during cooling. In spite of the difference of the degree of supersaturation, the exsolution reactions under discussion are assumed to be of stepwise in such that the lamellae exsolved in the order of the Type 3→Type 2→Type 1 with decreasing temperatures

The influence of the distance between the backrest of a chair and the position of the pelvis on the maximum pressure on the ischium and estimated shear force.

PURPOSE: For some people with leg disorders, the alternative to becoming bedridden is sitting in a wheelchair for long periods of time. The purpose of this study was to investigate the relation between the backrest of a chair and the position of the pelvis on the maximum pressure at the ischium and the estimated shear force encountered while sitting in a chair.METHODS: Ten healthy males aged 22.4 +/- 2.3 years without pathologies in the leg and/or trunk participated in this study. The subjects were instructed to sit in a chair and the pressure and shear forces were measured under three sitting conditions: In the standard position, a 5 cm forward position and a 10 cm forward position. The effects of the positions of the pelvis on the maximum pressure at the ischium were measured by an instrument for measuring pressure distribution and the shear forces were estimated using an experimental model proposed by us.RESULTS: Comparisons were made among the three sitting positions; the range of displacement of the maximum pressure point was not significant. The estimated shear force on the seat was 15.5 +/- 12.4 N in the standard position, 34.4 +/- 8.5 N in the 5-cm forward position, and 53.2 +/- 16.7 N in the 10 cm forward position. There were significant differences among the three values (p < 0.01).CONCLUSIONS: Displacing the pelvis forward and leaning against the backrest tends to increase the shear force and raise the risk of decubitus ulcers

Influence of Active Fingertip Contact with a Stable Surface on Postural Sway and Electromyographic Activities of the Lower Extremity Muscles Immediately after Descending a Step

Recent studies have shown that active contact cues from a fingertip provide information that leads to reduced postural sway during static standing. Although the falling risk increases immediately after descending a step, little is known about the influence of active fingertip contact with a stable surface. The purpose of this study was to investigate the influence of fingertip contact on the sway and the EMG (Electromyographic) activities of lower extremity muscles immediately after descending a step. Nine healthy male volunteers participated in this study. Sway was measured by the center of pressure (COP) and compared under three conditions: (1) standing without touching, (2) standing with the right index fingertip lightly touching (<1N), and (3) standing forcefully touching (5~10N). EMG activities were measured associated with sway and compared. More areas of COP were observed while standing without touching than while standing with light or forceful touching, but there was no significant difference between the two touching conditions. No significant differences in the length of COP and the EMG activities were observed among the three conditions. The results suggested that the fingertip touch contact with a stable surface decreased sway immediately after descending a step by finely controlling the lower extremity muscles