A thorough understanding of the phase portrait, or more precisely the stability region and the stability boundary of a nonlinear dynamic system is the foundation of all methods in stability studies for testing the stability of an initial state, that is whether it is inside the stability region. This paper presents quite complete results on the phase portrait of a class of large nonlinear dynamic systems which includes the power system. Also the connection between the constant energy surface and the stability boundary of the power system is explored. This gives valuable insight into classical stability tests which are based on the constant energy surface. The approach to stability monitoring of the power system deriving from these results is outlined.

We review how the science of studying street protest has changed, identifying opportunities for innovation and collaboration.

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We present the simultaneous measurement of three-dimensional deformations by electronic speckle pattern interferometry using five object beams and three colors. Each color, corresponding to an orthogonal direction of displacement, is separated through dichroic filtering before being recorded by a separate CCD camera. Carrier fringes are introduced by tilting the beam path in one arm of each of the three interferometers. The measured deformation modulates these carrier fringes and is extracted using the Fourier-transform method to achieve high displacement sensitivity. The field of view is on the order of a millimeter, making the system suitable for study of microstructural deformations. We compare experimental results with calculated values to validate out-of-plane and in-plane deformation measurements and demonstrate sensitivity on the order of 10 nm.