An electromagnetic forcing device

The paper describes the drawbacks of an electromagnetic forcing device, of the type commonly used to study forced vibration of structures, and presents details of a feedback control system designed to overcome them. The work described was initiated when attempting to generate sinusoidal forcing in a nonlinear beam-vibration study. Magnetic-material nonlinearities and spatial inhomogenieties in the magnetic field led to unwanted harmonics in the force the beam experienced, and feedback was used to reduce these effects. A brief description of the principles of feedback control is presented and the problems encountered in applying the concepts to the electromagnetic forcing device are discussed. Details of the system, its problems, operating characteristics and limitations are presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43929/1/11340_2006_Article_BF02324136.pd

Spin tunnelling in mesoscopic systems

We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings articl

Experimental Investigation on the Deformation Response of Hybrid 3D Woven Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97059/1/AIAA2012-1572.pd