4,472 research outputs found
Covariant Hamiltonian boundary term: Reference and quasi-local quantities
The Hamiltonian for dynamic geometry generates the evolution of a spatial
region along a vector field. It includes a boundary term which determines both
the value of the Hamiltonian and the boundary conditions. The value gives the
quasi-local quantities: energy-momentum, angular-momentum and center-of-mass.
The boundary term depends not only on the dynamical variables but also on their
reference values; the latter determine the ground state (having vanishing
quasi-local quantities). For our preferred boundary term for Einstein's GR we
propose 4D isometric matching and extremizing the energy to determine the
reference metric and connection values.Comment: 6 pages, contribution to the Proceedings of the Second LeCosPA
Symposium "Everything about Gravity", Taipei, 14-18 Dec., 201
9,10-Dihydro-7H-benzo[de]imidazo[2,1-a]isoquinolin-7-one
In the title compound, C14H10N2O, all non-H atoms are essentially coplanar (r.m.s. deviation = 0.013 Å). The crystal structure is stabilized by π–π stacking interactions [centroid–centroid distance = 3.506 (3) Å]
Quasi-local energy for cosmological models
First we briefly review our covariant Hamiltonian approach to quasi-local
energy, noting that the Hamiltonian-boundary-term quasi-local energy
expressions depend on the chosen boundary conditions and reference
configuration. Then we present the quasi-local energy values resulting from the
formalism applied to homogeneous Bianchi cosmologies. Finally we consider the
quasi-local energies of the FRW cosmologies. Our results do not agree with
certain widely accepted quasi-local criteria.Comment: Contributed to International Symposium on Cosmology and Particle
Astrophysics (CosPA 2006), Taipei, Taiwan, 15-17 Nov 200
- …