48,068 research outputs found
Evidence for Gamma-ray Jets in the Milky Way
Although accretion onto supermassive black holes in other galaxies is seen to
produce powerful jets in X-ray and radio, no convincing detection has ever been
made of a kpc-scale jet in the Milky Way. The recently discovered pair of 10
kpc tall gamma-ray bubbles in our Galaxy may be a sign of earlier jet activity
from the central black hole. In this paper, we identify a gamma-ray cocoon
feature in the southern bubble, a jet-like feature along the cocoon's axis of
symmetry, and another directly opposite the Galactic center in the north. Both
the cocoon and jet-like feature have a hard spectrum with spectral index ~ -2
from 1 to 100 GeV, with a cocoon luminosity of (5.5 +/- 0.45) x 10^35 erg/s and
luminosity of the jet-like feature of (1.8 +/- 0.35) x 10^35 erg/s at 1 to 100
GeV. If confirmed, these jets are the first resolved gamma-ray jets ever seen.Comment: 14 pages, 11 figures, accepted by Ap
MATCH - A Software Package for Robust Profile Matching Using S-Plus
This manual details the implementation of the profile matching techniques introduced in Robust Estimation of Air-Borne Particulate Matter (Wiens, Florence and Hiltz, Environmetrics, 2001 - included as an appendix). The program consists of a collection of functions written in S. It runs in S-Plus, including the student version. A graphical user interface is supplied for easy implementation by a user with only a passing familiarity with S-Plus. A description of the software is given, together with an extensive example of an analysis of a data set using the software. The software is available at http://www.stat.ualberta.ca/~wiens/publist.htm where it is linked to the listing for Wiens, Florence and Hiltz (2001).
Planetary science questions for the manned exploration of Mars
A major goal of a manned Mars mission is to explore the planet and to investigate scientific questions for which the intensive study of Mars is essential. The systematic exploration of planets was outlined by the National Academy of Science. The nearest analogy to the manned Mars mission is the Apollo program and manned missions to the Moon, but the analogy is limited. The case is argued here that Mars may have to be explored far more systematically than was the pre-Apollo Moon to provide the detailed information necessary if plans are made to use any of the resources available on Mars. Viking missions provided a wealth of information, yet there are great gaps in the fundamental knowledge of essential facts such as the properties of the Martian surface materials and their interaction with the atmosphere. Building on a strong data base of precursor missions, human exploration will allow great leaps in understanding the Martian environment and geologic history and its evolutionary role in the solar system
How Many Universes Do There Need To Be?
In the simplest cosmological models consistent with General Relativity, the
total volume of the Universe is either finite or infinite, depending on whether
or not the spatial curvature is positive. Current data suggest that the
curvature is very close to flat, implying that one can place a lower limit on
the total volume. In a Universe of finite age, the "particle horizon" defines
the patch of the Universe which is observable to us. Based on today's best-fit
cosmological parameters it is possible to constrain the number of observable
Universe sized patches, N_U. Specifically, using the new WMAP data, we can say
that there are at least 21 patches out there the same volume as ours, at 95%
confidence. Moreover, even if the precision of our cosmological measurements
continues to increase, density perturbations at the particle horizon size limit
us to never knowing that there are more than about 10^5 patches out there.Comment: 5 pages, 1 figure; received "honourable mention" in 2006 GRF essay
contest; v2: improved analysis with newly available WMAP Monte Carlo Markov
Chain; version published in IJMP
Model-Robust Designs for Quantile Regression
We give methods for the construction of designs for linear models, when the
purpose of the investigation is the estimation of the conditional quantile
function and the estimation method is quantile regression. The designs are
robust against misspecified response functions, and against unanticipated
heteroscedasticity. The methods are illustrated by example, and in a case study
in which they are applied to growth charts
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