Severe Geomagnetic Disturbance of 19 Dec. 1980

76-77Features of a severe geomagnetic storm with sudden commencement on 19 Dec. 1980, recorded at Indian magnetic stations are compared and some salient statistics are presented

Performance Analysis of Fault Tolerant UAV Baseline Control Laws with L1 Adaptive Augmentation

In this paper, the performance of L1 adaptive control laws is investigated in the presence of aircraft actuator failures and atmospheric turbulence. L1 adaptive control is combined with a linear type controller and a nonlinear dynamic inversion-based outer/inner loop controller. Specific evaluation metrics are defined in terms of trajectory tracking errors and control activity during autonomous flight. Several types of trajectories with different levels of complexity are considered in this research effort. The West Virginia University unmanned aerial vehicle simulation environment is used in this analysis. The results show that the adaptive augmentation improves the tracking performance of the vehicle at nominal conditions and under a variety of abnormal flight conditions

All Invariant Moments of the Wishart Distribution

In this paper, we compute moments of a Wishart matrix variate "U" of the form E ("Q"("U")) where "Q"("u") is a polynomial with respect to the entries of the symmetric matrix "u", invariant in the sense that it depends only on the eigenvalues of the matrix "u". This gives us in particular the expected value of any power of the Wishart matrix "U" or its inverse "U"-super- -  1. For our proofs, we do not rely on traditional combinatorial methods but rather on the interplay between two bases of the space of invariant polynomials in "U". This means that all moments can be obtained through the multiplication of three matrices with known entries. Practically, the moments are obtained by computer with an extremely simple Maple program. Copyright 2004 Board of the Foundation of the Scandinavian Journal of Statistics..