This paper presents a comprehensive evaluation of the near-field acoustics an aircraft auxiliary power unit (APU), based on experimental data acquired from in-situ APU. The aim is to establish whether can be implemented for online condition monitoring. APU Cranfield University’s demonstrator aircraft, Boeing 737-400, has been instrumented acquire (near-field and far-field) vibration in synchron...

The modern theory of class field towers has its origins in the study of the p-class field tower over a quadratic imaginary number field, so it is fitting that this problem be the first in the discipline to be nearing a solution. We survey the state of the subject and present a new cohomological condition for a quadratic imaginary number field to have an infinite p-class field tower (for p odd)....