13,872 research outputs found
Turbulence forecasting
In order to forecast turbulence, one needs to have an understanding of the cause of turbulence. Therefore, an attempt is made to show the atmospheric structure that often results when aircraft encounter moderate or greater turbulence. The analysis is based on thousands of hours of observations of flights over the past 39 years of aviation meteorology
Airline meteorological requirements
A brief review of airline meteorological/flight planning is presented. The effects of variations in meteorological parameters upon flight and operational costs are reviewed. Flight path planning through the use of meteorological information is briefly discussed
An improved Ant Colony System for the Sequential Ordering Problem
It is not rare that the performance of one metaheuristic algorithm can be
improved by incorporating ideas taken from another. In this article we present
how Simulated Annealing (SA) can be used to improve the efficiency of the Ant
Colony System (ACS) and Enhanced ACS when solving the Sequential Ordering
Problem (SOP). Moreover, we show how the very same ideas can be applied to
improve the convergence of a dedicated local search, i.e. the SOP-3-exchange
algorithm. A statistical analysis of the proposed algorithms both in terms of
finding suitable parameter values and the quality of the generated solutions is
presented based on a series of computational experiments conducted on SOP
instances from the well-known TSPLIB and SOPLIB2006 repositories. The proposed
ACS-SA and EACS-SA algorithms often generate solutions of better quality than
the ACS and EACS, respectively. Moreover, the EACS-SA algorithm combined with
the proposed SOP-3-exchange-SA local search was able to find 10 new best
solutions for the SOP instances from the SOPLIB2006 repository, thus improving
the state-of-the-art results as known from the literature. Overall, the best
known or improved solutions were found in 41 out of 48 cases.Comment: 30 pages, 8 tables, 11 figure
Spatial-temporal rainfall simulation using generalized linear models
We consider the problem of simulating sequences of daily rainfall at a network of sites in such a way as to reproduce a variety of properties realistically over a range of spatial scales. The properties of interest will vary between applications but typically will include some measures of "extreme'' rainfall in addition to means, variances, proportions of wet days, and autocorrelation structure. Our approach is to fit a generalized linear model (GLM) to rain gauge data and, with appropriate incorporation of intersite dependence structure, to use the GLM to generate simulated sequences. We illustrate the methodology using a data set from southern England and show that the GLM is able to reproduce many properties at spatial scales ranging from a single site to 2000 km 2 ( the limit of the available data)
Discrete local altitude sensing device Patent
Device for use in descending spacecraft as altitude sensor for actuating deceleration retrorocket
Radio and X-ray observations of an exceptional radio flare in the extreme z=4.72 blazar GB B1428+4217
We report on the extreme behaviour of the high redshift blazar GB B1428+4217
at z=4.72. A continued programme of radio measurements has revealed an
exceptional flare in the lightcurve, with the 15.2 GHz flux density rising by a
factor ~3 from ~140 mJy to ~430 mJy in a rest-frame timescale of only ~4 months
-- much larger than any previous flares observed in this source. In addition to
new measurements of the 1.4-43 GHz radio spectrum we also present the analysis
and results of a target-of-opportunity X-ray observation using XMM-Newton, made
close to the peak in radio flux. Although the X-ray data do not show a flare in
the high energy lightcurve, we are able to confirm the X-ray spectral
variability hinted at in previous observations. GB B1428+4217 is one of several
high-redshift radio-loud quasars that display a low energy break in the X-ray
spectrum, probably due to the presence of excess absorption in the source.
X-ray spectral analysis of the latest XMM-Newton data is shown to be consistent
with the warm absorption scenario which we have hypothesized previously. Warm
absorption is also consistent with the observed X-ray spectral variability of
the source, in which the spectral changes can be successfully accounted-for
with a fixed column density of material in which the ionization state is
correlated with hardness of the underlying power-law emission.Comment: 8 pages, 5 figures, MNRAS accepte
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