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Dimers in microtubules possess a dipole moment with components along three axes. The interaction energy among all dipole components in a microtubule was calculated for an un-deformed and an elliptically deformed microtubule in a "dry" condition. The interaction energy was found to increase with deformation. The total interaction energy among all dipoles is positive, which implies that the un-deformed cylindrical shape of a microtubule represents a condition of minimum energy. This suggests that the cylindrical shape of microtubules is a consequence of dipole-dipole interactions. There may be other causes as well but these are not discussed in this paper. From these results, the contributions of the dipole-dipole interaction energy to the microtubule longitudinal and transverse flexural rigidities were calculated. It is shown that the longitudinal contribution to the elastic modulus is approximately 50-60% of the total measured value while the calculated transverse contribution is smaller than the longitudinal contribution by a factor of approximately 3. The ratio of the measured axial to the measured transverse flexural rigidity is approximately 125, in agreement with recent observations. However, these values are uncertain for reasons discussed in the text.

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To date, zinc oxide varistors have been subjected to uniaxial compression to 5 kbars and hydrostatic pressures to 10 kbars. These results show a behavior between current and pressure empirically described by IL∼P7. This paper presents results of experiments in which zinc oxide varistors were subjected to hydrostatic compression up to 25 kbars. Results show a significant departure from previously reported results. The leakage current remains constant at first until a pressure of 6–7 kbars is attained. It then rises sharply and nonlinearly to a maximum value of about 55 μA at a pressure of 15 kbars, and subsequently the leakage current decreases by about two orders of magnitude as the pressure increases from 15 to 25 kbars. The limit of 25 kbars is determined by the pressure cell design and materials used. The results presented here also suggest that the varistor behavior with pressure depends on thermal annealing and strain-induced damage processes.

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