53 research outputs found
Principal null directions of perturbed black holes
The properties of principal null directions of a perturbed black hole are
investigated. It shown that principal null directions are directly observable
quantities characterizing the space-time. A definition of a perturbed
space-time, generalizing that given by Stewart and Walker is proposed. This
more general framework allows one to include descriptions of a given space-time
other than by a pair where is a four-dimensional differential
manifold and a Lorentz metric. Examples of alternative characterizations
are the curvature representation of Karlhede and others, the Newman-Penrose
representation or observable quantities involving principal null directions.
The conditions are studied under which the various alternative choices of
observables provide equivalent descriptions of the space-time.Comment: To appear in Class. Quantum Gra
Dynamics of Gravitational Waves in 3D: Formulations, Methods, and Tests
The dynamics of gravitational waves is investigated in full 3+1 dimensional
numerical relativity, emphasizing the difficulties that one might encounter in
numerical evolutions, particularly those arising from non-linearities and gauge
degrees of freedom. Using gravitational waves with amplitudes low enough that
one has a good understanding of the physics involved, but large enough to
enable non-linear effects to emerge, we study the coupling between numerical
errors, coordinate effects, and the nonlinearities of the theory. We discuss
the various strategies used in identifying specific features of the evolution.
We show the importance of the flexibility of being able to use different
numerical schemes, different slicing conditions, different formulations of the
Einstein equations (standard ADM vs. first order hyperbolic), and different
sets of equations (linearized vs. full Einstein equations). A non-linear scalar
field equation is presented which captures some properties of the full Einstein
equations, and has been useful in our understanding of the coupling between
finite differencing errors and non-linearites. We present a set of monitoring
devices which have been crucial in our studying of the waves, including Riemann
invariants, pseudo-energy momentum tensor, hamiltonian constraint violation,
and fourier spectrum analysis.Comment: 34 pages, 14 figure
Diffusion and sorption of volatile organic compounds in building materials - impact on indoor air quality
The prevalence of building related synptoms and the inflammatory potency of dust in offices
Reduced heat stress in offices in the tropics using solar powered drying of the supply air â
EXAMINATION OF INFLUENCE OF MASS TRANSFER COEFFICIENT ON EMISSION RATE IN MEDIUM DENSITY FIBERBOARD BY TEST CHAMBER EXPERIMENT AND CFD ANALYSIS : Study on test chamber method for measuring emission rate of formaldehyde
Documentation Of Field And Laboratory Emission Cell âFLECâ:Identification Of Emission Processes From Carpet, Linoleum, Paint, And Sealant By Modeling
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