Polymerization of n-butyl methacrylate monomer is used as a rapid and simple means for embedding fixed biological material. The solid resin provides an optically clear matrix for cutting very thin sections, one at a time, with a slightly modified conventional rotary microtome. Advance of the embedded specimen toward the knife is obtained from the thermal expansion of a brass specimen holder. These ultrathin sections have uniform thickness, large area, and integrity of tissue structure. They are suitable for producing transmission images at the higher magnifications of the conventional light, phase-contrast, and electron microscopes. Metallic shadowing of the sections provides greater contrast as well as a threedimensional aspect to the structural details of the tissue. Micrographs and a bibliography are presented.
Dynamic-Ioad-stretch and stretch-energy data were obtained for two types of nylon and one type of cotton parachute webbing. These data were compared wit h similar data obtained from static tenRile tests of the materials. The dynamic and static breaking strengths of the web bing were also obtained. The nylon specimens showed a reduced strength, stretch, and capacity for energy absorption under dynamic loading as compared with static loading. The cotton specimens showed under dynamic loading about the same strength, reduced stretch, and increased energy absorption. The energy absorbed by the broken nylon specimens was more t han three times that of the broken cotton specimens.
Static and impact tests were made on spliced specimens of :V1e-inch-diameter three-strand nylon rope and He-inch-diameter, four-strand, sisal rope.The stretch of the ropes under impact and static loading up to failure was measured, and from these data energy-stretch behavior was determined.It was found that the energy required to cause failure under impact loading was greater than the energy required to cause failure under static loading. The stretch of the rope at failure was practically the same under impact and static loading.The results of these tests indicate that energy values computed from static tests of these ropes give a safe estimate of the performance of the rope under impact loading.
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