Concatenating Variational Principles and the Kinetic Stress-Energy-Momentum Tensor
We show how to "concatenate" variational principles over dierent 
bases into one over a single base, thereby providing a unied Lagrangian 
treatment of interacting systems. As an example we study a Klein{ 
Gordon eld interacting with a mesically charged particle. We employ 
our method to give a novel group-theoretic derivation of the kinetic 
stress-energy-momentum tensor density corresponding to the particle.
Parametrization and stress–energy–momentum tensors in metric field theories
We give an exposition of the 1972 parametrization method of Kuchař in the context of the multisymplectic approach to field theory. The purpose of the formalism developed here is to make any classical field theory, containing a metric as a sole background field, generally covariant (that is, parametrized, with the spacetime diffeomorphism group as a symmetry group) as well as fully dynamic. This is accomplished by introducing certain ‘covariance fields’ as genuine dynamic fields. As we shall see, the multimomenta conjugate to these new fields form the Piola–Kirchhoff version of the stress–energy–momentum tensor field, and their Euler–Lagrange equations are vacuously satisfied. Thus, these fields have no additional physical content; they serve only to provide an efficient means of parametrizing the theory. Our results are illustrated with two examples, namely an electromagnetic field and a Klein–Gordon vector field, both on a background spacetime.
Time behavior of gas pressure and PD activity in insulation cavities under AC voltage
In the framework of developing defect-based life models (i.e. the life model of partial discharge-induced damage growth from a micro-void in polymer matrix), ageing tests were performed on PE layered specimens with artificial cavities under constant gas pressure and constant gas volume conditions, respectively. Time behavior of the discharge repetition rate and amplitude were recorded and compared under these two conditions. Results show that pressure variation has little influence on PD activities at constant gas volume. Under constant gas pressure, the evolution of gas volume has similar characteristic to the product of discharge amplitude and repetition rate.