6,131 research outputs found
Stabilizability and percolation in the infinite volume sandpile model
We study the sandpile model in infinite volume on . In
particular, we are interested in the question whether or not initial
configurations, chosen according to a stationary measure , are
-almost surely stabilizable. We prove that stabilizability does not depend
on the particular procedure of stabilization we adopt. In and a
product measure with density (the known critical value for
stabilizability in ) with a positive density of empty sites, we prove that
is not stabilizable. Furthermore, we study, for values of such
that is stabilizable, percolation of toppled sites. We find that for
small enough, there is a subcritical regime where the distribution of
a cluster of toppled sites has an exponential tail, as is the case in the
subcritical regime for ordinary percolation.Comment: Published in at http://dx.doi.org/10.1214/08-AOP415 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Time and Energy Managed Operations (TEMO): Cessna Citation II Flight Trials
From 9-26 October 2015 the Netherlands Aerospace Centre (NLR) in
cooperation with Delft University of Technology (DUT) has executed Clean Sky flight
trials with the Cessna Citation II research aircraft. The trials consisted of several
descents and approaches at the Eelde airport near Groningen, demonstrating the
TEMO (Time and Energy Managed Operations) concept developed in the Clean Sky
Joint Technology Initiative research programme as part of the Systems for Green
Operations (SGO) Integrated Technology Demonstrator.
A TEMO descent aims to achieve an energy-managed idle-thrust
continuous descent operation (CDO) while satisfying ATC time constraints, to
maintain runway throughput. An optimal descent plan is calculated with an advanced
on-board real-time aircraft trajectory optimisation algorithm considering forecasted
weather and aircraft performance. The optimised descent plan was executed using
the speed-on-elevator mode of an experimental Fly-By-Wire (FBW) system connected
to the pitch servo motor of the Cessna Citation II aircraft. Several TEMO conceptual
variants have been flown. It has been demonstrated that the TEMO concept enables
arrival with timing errors below 10 seconds. The project was realised with the
support of CONCORDE partners Universitat Politècnica de Catalunya (UPC) and
PildoLabs from Barcelona, and the Royal Netherlands Meteorological Institute
(KNMI).Peer ReviewedPostprint (published version
Flight testing Time and Energy Managed Operations (TEMO)
The expected growth in air traffic combined with an increased public concern for the
environment, have forced legislators to rethink the current air traffic system design. The
current air traffic system operates at its capacity limits and is expected to lead to increased
delays if traffic levels grow even further. Both in the United States and Europe, research
projects have been initiated to develop the future Air Transportation System (ATS) to
address capacity, and environmental, safety and economic issues. To address the
environmental issues during descent and approach, a novel Continuous Descent Operations
(CDO) concept, named Time and Energy Managed Operations (TEMO), has been
developed co-sponsored by the Clean Sky Joint Undertaking. It uses energy principles to
reduce fuel burn, gaseous emissions and noise nuisance whilst maintaining runway capacity.
Different from other CDO concepts, TEMO optimizes the descent by using energy
management to achieve a continuous engine-idle descent, while satisfying time constraints
on both the Initial Approach Fix (IAF) and the runway threshold. As such, TEMO uses timemetering
at two control points to facilitate flow management and arrival spacing.
TEMO is in line with SESAR step 2 capabilities, since it proposes 4D trajectory
management and is aimed at providing significant environmental benefits in the arrival phase
without negatively affecting throughput, even in high density and peak-hour operations. In
particular, TEMO addresses SESAR operational improvement (OI) TS-103: Controlled Time
of Arrival (CTA) through use of datalink [1].
TEMO has been validated starting from initial performance batch studies at Technology
Readiness Level (TRL) 3, up to Human-in-the-Loop studies in realistic environments using a
moving base flight simulator at TRL 5 ([2]-[6]).
In this paper the definition, preparation, performance and analysis of a flight test
experiment is described with the objective to demonstrate the ability of the TEMO algorithm
to provide accurate and safe aircraft guidance toward the Initial Approach Fix (IAF), and
further down to the Stabilization Point (1000 ft AGL), to demonstrate the ability of the TEMO
algorithm to meet absolute time requirements at IAF and/or runway threshold and to evaluate
the performance of the system under test (e.g. fuel usage).Peer ReviewedPostprint (published version
The Io sulfur torus in 1981
A Fabry-Perot spectrometer was used to obtain images of the Io torus in emission lines of S II (wavelength 6716 and 6731) and S III (wavelength 9531) in February and March 1981, on the 2.1 meter telescope at KPNO. The S II and S III images showed a large variation in brightness and radial extent. There is an indication the S II and S III emissions in the warm torus are correlated. The S II and S III emissions in the warm torus also have similar scale heights along the magnetic field lines of approximately 0.6 to 0.72 R sub J. The east-west asymmetry in the S II images taken at similar magnetic longitudes, but 2.5 Jovian rotations apart, supports the theory of convective motions suggested by others. In addition to the images, simultaneous measurements of the S II (6731 wavelength) line profile were also made on one night using a Fabry-Perot scanning spectrometer on the 4 meter at KPNO. The S II spectral scans implied ion temperatures of 52 (+ or - 10) x 10 to the 3rd at 5.2 to 5.6 R sub J from Jupiter and a minimum temperature of at least 3 x 10 to the 5th K at 6 R sub J from Jupiter
- …