RESUMEN
This paper derives theoretical results for determining bifurcation curves which provide bounds on anticipated "escape" regimes in a two-dimensional parameter space for an equation which is a natural extension of a commonly used second-order parametrically excited nonlinear pendulum equation. An application of these results is made for an equation which often arises in smectic liquid-crystal problems. The results for this application are more refined yet qualitatively similar to those obtained by different methods reported in the literature.
RESUMEN
The aim of this article is to establish some theoretical linear and nonlinear stability results for a dynamic equation that frequently appears in the smectic-C and ferroelectric smectic-C* liquid crystal literature. We consider finite planar samples confined between bounding plates as well as infinite samples. Many of the results depend on extensions of work for a nonlinear diffusion equation. Critical maximum magnitudes of applied static electric fields are determined, below which stability of a certain constant equilibrium state is ensured.
RESUMEN
The velocity renormalization group is used to determine lnalpha contributions to QED bound state energies. The leading-order anomalous dimension for the potential gives the alpha(5)lnalpha Lamb shift. The next-to-leading-order anomalous dimension determines the alpha(6)lnalpha, alpha(7)ln (2)alpha, and alpha(8)ln (3)alpha corrections to the energy. These are used to obtain the alpha(8)ln (3)alpha Lamb shift and alpha(7)ln (2)alpha hyperfine splitting for hydrogen, muonium, and positronium, as well as the alpha(2)lnalpha and alpha(3)ln (2)alpha corrections to the ortho- and parapositronium lifetimes. This shows for the first time that these logarithms can be computed from the renormalization group.