4,394 research outputs found
Assessing and improving an approach to delay-tolerant networking
Delay-tolerant networking (DTN) is a term invented to describe and encompass
all types of long-delay, disconnected, disrupted or intermittently-connected
networks, where mobility and outages or scheduled contacts may be experienced.
'DTN' is also used to refer to the Bundle Protocol, which has been proposed as
the one unifying solution for disparate DTN networking scenarios, after
originally being designed solely for use in deep space for the 'Interplanetary
Internet.' We evaluated the Bundle Protocol by testing it in space and on the
ground. We have found architectural weaknesses in the Bundle Protocol that may
prevent engineering deployment of this protocol in realistic delay-tolerant
networking scenarios, and have proposed approaches to address these weaknesses.Comment: 2 pages; First Annual CCSR Research Symposium (CRS 2011), Centre for
Communication Systems Research, 30 June 201
SaVi: satellite constellation visualization
SaVi, a program for visualizing satellite orbits, movement, and coverage, is
maintained at the University of Surrey. This tool has been used for research in
academic papers, and by industry companies designing and intending to deploy
satellite constellations. It has also proven useful for demonstrating aspects
of satellite constellations and their geometry, coverage and movement for
educational and teaching purposes. SaVi is introduced and described briefly
here.Comment: 2 pages; First Annual CCSR Research Symposium (CRS 2011), Centre for
Communication Systems Research, 30 June 201
Lattice Boltzmann Methods for Wind Energy Analysis
An estimate of the United States wind potential conducted in 2011 found that the energy available at an altitude of 80 meters is approximately triple the wind energy available 50 meters above ground. In 2012, 43% of all new electricity generation installed in the U.S. (13.1 GW) came from wind power. The majority of this power, 79%, comes from large utility scale turbines that are being manufactured at unprecedented sizes. Existing wind plants operate with a capacity factor of only approximately 30%. Measurements have shown that the turbulent wake of a turbine persists for many rotor diameters, inducing increased vibration and wear on downwind turbines. Power losses can be as high as 20-30% in operating wind plants, due solely to complex wake interactions occurring in wind plant arrays. It is my objective to accurately predict the generation and interaction of turbine wakes and their interaction with downwind turbines and topology by means of numerical simulation with high-performance parallel computer systems.
Numerical simulation is already utilized to plan wind plant layouts. However, available computational tools employ severe geometric simplifications to model wake interactions and are geared to providing rough estimates on desktop PCs. A three dimensional simulation tool designed for modern parallel computers based upon lattice Boltzmann methods for fluid-dynamics, a general six-degree-of-freedom motion solver, and foundational beam solvers has been proposed to meet this simulation need. In this text, the software development, verification, and validation are detailed. Fundamental computational fluid dynamics issues of boundary conditions and turbulence modeling are examined through classic cases (Cavity, Jeffery-Hammel, Kelvin-Helmholtz, Pressure wave, Vorticity wave, Backward facing step, Cylinder in cross-flow, Airfoils, Tandem cylinders, and Turbulent flow over a hill) to asses the accuracy and computational cost of developed alternatives. Simulations of canonical motion (falling beam), fluid-structure-interaction cases (Hinged wing and Flexible pendulum), and realistic horizontal axis wind turbine geometries (Vestas v27, NREL 5MW, and MEXICO) are validated against benchmarks and experiments. Results from simulations of the three turbine array at the Scaled Wind Farm Test facility are presented for two steady wind conditions
Ultimate Intelligence Part I: Physical Completeness and Objectivity of Induction
We propose that Solomonoff induction is complete in the physical sense via
several strong physical arguments. We also argue that Solomonoff induction is
fully applicable to quantum mechanics. We show how to choose an objective
reference machine for universal induction by defining a physical message
complexity and physical message probability, and argue that this choice
dissolves some well-known objections to universal induction. We also introduce
many more variants of physical message complexity based on energy and action,
and discuss the ramifications of our proposals.Comment: Under review at AGI-2015 conference. An early draft was submitted to
ALT-2014. This paper is now being split into two papers, one philosophical,
and one more technical. We intend that all installments of the paper series
will be on the arxi
Long Period Variables in the Magellanic Clouds: OGLE + 2MASS + DENIS
(abridged) The 68000 I-band light curves of variable stars detected by the
OGLE survey in the Large and Small Magellanic Clouds (MCs) are fitted by
Fourier series, and also correlated with the DENIS and 2MASS databases and with
lists of spectroscopically confirmed M-, S- and C-stars. Lightcurves and the
results of the lightcurve fitting (periods and amplitudes) and DENIS and 2MASS
magnitudes are presented for 2277 M-,S-,C-stars in the MCs. The following
aspects are discussed: the K-band period-luminosity relations for the
spectroscopically confirmed AGB stars, period changes over a timespan of about
17 years in a subset of about 400 LPVs, and candidate obscured AGB stars.Comment: Astronomy and Astrophysics, accepte
Period-magnitude relations for M giants in Baade's Window NGC6522
A large and complete sample of stars with K < 9.75 in the NGC6522 Baade's
Window is examined using light curves from MACHO and IJK from DENIS. All 4 of
the sequences ABCD in the K vs logP diagram of the LMC are seen in the Bulge.
The Bulge sequences however show some differences from the Magellanic Clouds.
The sequences may be useful as distance indicators. A new diagram of the
frequency of late-type variables is presented. The catalogued SR variables of
the solar nbd are found to be a subset of the total of SRs, biased towards
large amplitude.Comment: 11 pages 11 fig
Long period variables in 47 Tuc: direct evidence for lost mass
We have identified 22 new variable red giants in 47 Tuc and determined
periods for another 8 previously known variables. All red giants redder than
V-I_c=1.8 are variable at the limits of our detection threshold, which
corresponds to delta V ~ 0.1 mag. This colour limit corresponds to a luminosity
log L/L_sun=3.15 and it is considerably below the tip of the RGB at log
L/L_sun=3.35. Linear non-adiabatic models without mass loss on the giant branch
can not reproduce the observed PL laws for the low amplitude pulsators. Models
that have undergone mass loss do reproduce the observed PL relations and they
show that mass loss of the order of 0.3 M_sun occurs along the RGB and AGB. The
linear pulsation periods do not agree well with the observed periods of the
large amplitude Mira variables, which pulsate in the fundamental mode. The
solution to this problem appears to be that the nonlinear pulsation periods in
these low mass stars are considerably shorter than the linear pulsation periods
due to a rearrangement of stellar structure caused by the pulsation. Both
observations and theory show that stars evolve up the RGB and first part of the
AGB pulsating in low order overtone modes, then switch to fundamental mode at
high luminosities.Comment: 11 pages, accepted for publication in A&
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