138,068 research outputs found
Interpolative method for transport properties of quantum dots in the Kondo regime
We present an interpolative method for describing coherent transport through
an interacting quantum dot. The idea of the method is to construct an
approximate electron self-energy which becomes exact both in the limits of weak
and strong coupling to the leads. The validity of the approximation is first
checked for the case of a single (spin-degenerate) dot level. A generalization
to the multilevel case is then discussed. We present results both for the
density of states and the temperature dependent linear conductance showing the
transition from the Kondo to the Coulomb blockade regime.Comment: 8 pages, 3 figures, includes lamuphys.sty, submitted to the
Proceedings of the XVI Sitges Conference on Statistical Mechanic
Optimal Galaxy Distance Estimators
The statistical properties of galaxy distance estimators are studied and a
rigorous framework is developed for identifying and removing the effects of
Malmquist bias due to obsevational selection. The prescription of Schechter
(1980) for defining unbiased distance estimators is extended to more general --
and more realistic -- cases. The derivation of `optimal' unbiased distance
estimators of minimum dispersion, by utilising information from additional --
suitably correlated -- observables, is discussed and the results applied to a
calibrating sample from the Fornax cluster, as used in the Mathewson spiral
galaxy redshift survey. The optimal distance estimator derived from I-band
magnitude, diameter and 21cm line width has an intrinsic scatter which is 25 \%
smaller than that of the Tully-Fisher relation quoted for this calibrating
sample. (Figures are available on request).Comment: Plain Latex, 19 pages, Sussex-AST-93/9-
A Cautionary Note on Cosmological Magnetic Fields
This note is concerned with potentially misleading concepts in the treatment
of cosmological magnetic fields by magnetohydrodynamical (MHD) modelling. It is
not a criticism of MHD itself but rather a cautionary comment on the validity
of its use in cosmology. Now that cosmological data are greatly improved
compared with a few decades ago, and even better data are imminent, it makes
sense to revisit original modelling assumptions and examine critically their
shortcomings in respect of modern science. Specifically this article argues
that ideal MHD is a poor approximation around recombination, since it
inherently restricts evolutionary timescales, and is often misapplied in the
existing literature.Comment: 5 page
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