78,492 research outputs found
Sufficient burn-in for Gibbs samplers for a hierarchical random effects model
We consider Gibbs and block Gibbs samplers for a Bayesian hierarchical
version of the one-way random effects model. Drift and minorization conditions
are established for the underlying Markov chains. The drift and minorization
are used in conjunction with results from J. S. Rosenthal [J. Amer. Statist.
Assoc. 90 (1995) 558-566] and G. O. Roberts and R. L. Tweedie [Stochastic
Process. Appl. 80 (1999) 211-229] to construct analytical upper bounds on the
distance to stationarity. These lead to upper bounds on the amount of burn-in
that is required to get the chain within a prespecified (total variation)
distance of the stationary distribution. The results are illustrated with a
numerical example
Counting lifts of Brauer characters
In this paper we examine the behavior of lifts of Brauer characters in
p-solvable groups where p is an odd prime. In the main result, we show that if
\phi \in IBrp(G) is a Brauer character of a solvable group such that \phi has
an abelian vertex subgroup Q, then the number of lifts of \phi in Irr(G) is at
most |Q|. In order to accomplish this, we develop several results about lifts
of Brauer characters in p-solvable groups that were previously only known to be
true in the case of groups of odd order.Comment: A different proof of Theorem 1 is in the paper "The number of lifts
of Brauer characters with a normal vertex" by J.P. Cossey, M.L.Lewis, and G.
Navarro. Hence, we do not expect to try to publish this note. We feel that
the proof in this paper is of independent interes
Lifts and vertex pairs in solvable groups
Suppose is a -solvable group, where is odd. We explore the
connection between lifts of Brauer characters of and certain local objects
in , called vertex pairs. We show that if is a lift, then the vertex
pairs of form a single conjugacy class. We use this to prove a
sufficient condition for a given pair to be a vertex pair of a lift and to
study the behavior of lifts with respect to normal subgroups
The interannual variability of polar cap recessions as a measure of Martian climate and weather: Using Earth-based data to augment the time line for the Mars observer mapping mission
The recessions of the polar ice caps are the most visible and most studied indication of seasonal change on Mars. Circumstantial evidence links these recessions to the seasonal cycles of CO2, water, and dust. The possible advent of a planet encircling storm during the Mars Observer (MO) mission will provide a detailed correlation with a cap recession for that one Martian year. That cap recession will then be compared with other storm and nonstorm years. MO data will also provide a stronger link between cap recessions and the water and CO2 cycles. Cap recession variability might also be used to determine the variability of these cycles. After nearly a century of valiant attempts at measuring polar cap recessions, including Mariner 9 and Viking data, MO will provide the first comprehensive dataset. In contrast to MO, the older data are much less detailed and precise and could be forgotten, except that it will still be the only information on interannual variability. By obtaining simultaneous Earth-based observations (including those from Hubble) during the MO mission, direct comparisons can be made between the datasets
The great dust storm of 1986
It is reported that on the global scale, no major dust storm activity was seen during telescopic observations of Mars during the several months or so preceeding this conference. However, the corresponding season on Mars was early fall, which is at the beginning of the dust storm season. It was too early to tell, therefore, if a great dust storm was going to occur that year. Current observations and what they show about present atmospheric conditions and the recession of the South Polar Cap is discussed
(2360) Proposal to reject the name Chenopodium caudatum (Amaranthaceae / Chenopodiaceae)
nomenclature Chenopodium caudatu
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