39,357 research outputs found
Book Review
Review of: MARY R. ENGLISH, SITING LOW-LEVEL RADIOACTIVE WASTE DISPOSAL FACILITIES: THE PUBLIC POLICY DILEMMA. (Quorum Books 1992) [278 pp.], Appendices, index, introduction, references. LC-91-42774; ISBN 0-89930-560-1. [$49.95 cloth. One Madison Avenue, New York NY 10010.
Perturbative renormalization of the electric field correlator
The momentum diffusion coefficient of a heavy quark in a hot QCD plasma can
be extracted as a transport coefficient related to the correlator of two
colour-electric fields dressing a Polyakov loop. We determine the perturbative
renormalization factor for a particular lattice discretization of this
correlator within Wilson's SU(3) gauge theory, finding a ~12% NLO correction
for values of the bare coupling used in the current generation of simulations.
The impact of this result on existing lattice determinations is commented upon,
and a possibility for non-perturbative renormalization through the gradient
flow is pointed out.Comment: 15 pages. v2: published versio
Performance of the square root information filter for navigation of the Mariner 10 spacecraft
The use is described of a sequential least squares filter in the orbit determination for the Mariner Venus-Mercury (Mariner 10) spacecraft. The orbit determination strategy outlining the use of both the sequential filter and a conventional batch filter is given. Highlighted are the mission events from launch to the first Mercury encounter with emphasis on the sequential filter performance. Advantages to the mission derived from the sequential filter are pointed out
On the choice of parameters in solar structure inversion
The observed solar p-mode frequencies provide a powerful diagnostic of the
internal structure of the Sun and permit us to test in considerable detail the
physics used in the theory of stellar structure. Amongst the most commonly used
techniques for inverting such helioseismic data are two implementations of the
optimally localized averages (OLA) method, namely the Subtractive Optimally
Localized Averages (SOLA) and Multiplicative Optimally Localized Averages
(MOLA). Both are controlled by a number of parameters, the proper choice of
which is very important for a reliable inference of the solar internal
structure. Here we make a detailed analysis of the influence of each parameter
on the solution and indicate how to arrive at an optimal set of parameters for
a given data set.Comment: 14 pages, 15 figures. Accepted for publication on MNRA
The Age of the Universe and the Cosmological Constant Determined from Cosmic Microwave Background Anisotropy Measurements
If Omega_tot = 1 and structure formed from adiabatic initial conditions then
the age of the Universe, as constrained by measurements of the cosmic microwave
background (CMB), is t_0=14.0 +/- 0.5 Gyr. The uncertainty is surprisingly
small given that CMB data alone constrain neither h nor Omega_Lambda
significantly. It is due to the tight (and accidental) correlation, in these
models, of the age with the angle subtended by the sound horizon on the
last--scattering surface and thus with the well-determined acoustic peak
locations. If we assume either the HST Key Project result h = 0.72 \pm .08 or
simply that h > 0.55, we find Omega_Lambda > 0.4 at 95% confidence--another
argument for dark energy, independent of supernovae observations. Our analysis
is greatly simplified by the Monte Carlo Markov chain approach to Bayesian
inference combined with a fast method for calculating angular power spectra.Comment: 5 pages, including 2 figures and one table final published versio
- …