Any non-complete orthonormal system in a Hilbert space can be transformed into basis by small perturbations.

We review the study of inhomogeneous perturbations about a homogeneous and isotropic background cosmology. We adopt a coordinate based approach, but give geometrical interpretations of metric perturbations in terms of the expansion, shear and curvature of constant-time hypersurfaces and the orthogonal timelike vector field. We give the gauge transformation rules for metric and matter variables ...

In This Issue In This Issue Clash of the titin he sarcomere is more than a complicated piece of structural machinery. According to new results by McElhinny et al. (page 125), a building block of striated muscle cells called MURF-1 may also indirectly regulate gene expression. MURF-1 localizes to sarcomeres thanks to its interaction with titin, a major structural component of the muscle sarcomer...