Discussion on a paper by X. N. Duan and A. M. Chandler

The authors have presented the results of inelastic earthquake response analysis of a class of asymmetric building models and concluded that regularly asymmetric buildings excited well into the inelastic range may not be conservatively designed via modal analysis of their elastic models. The purpose of this short communication is to refer to the results in contrast to the authors' and to make some comments on their paper.     

Note on a paper by D. R. Caldwell,C. W. Van Atta And K. N. Helland

Abstract

In comparing their laboratory findings with those of other investigators, the authors incorrectly ascribed an eddy coefficient and mixing length too large by a factor of 2.2 to the results from a numerical model. An explanation is offered for the apparently small magnitude of dimensionless velocity deficit from the laboratory study.     

Hydromagnetic waves in a differentially rotating annulus. II. Resistive instabilities

Abstract

In part I of this study (Fearn, 1983b), instabilities of a conducting fluid driven by a toroidal magnetic field B were investigated. As well as confirming the results of a local stability analysis by Acheson (1983), a new resistive mode of instability was found. Here we investigate this mode in more detail and show that instability exists when B(s) has a zero at some radius s=s _c. Then (in the limit of small resistivity) the instability is concentrated in a critical layer centered on s _c . The importance of the region where B is small casts some doubt on the validity of the simplifications made to the momentum equation in I. Calculations were therefore repeated using the full momentum equation. These demonstrate that the neglect of viscous and inertial terms when the mean field is strong does not lead to spurious results even when there are regions where B is small.