215 research outputs found
Travel Behaviour Response to Major Transport System Disruptions: Implications for Smarter Resilience Planning
No abstract available
The Dynamical History of Chariklo and its Rings
Chariklo is the only small Solar system body confirmed to have rings. Given
the instability of its orbit, the presence of rings is surprising, and their
origin remains poorly understood. In this work, we study the dynamical history
of the Chariklo system by integrating almost 36,000 Chariklo clones backwards
in time for one Gyr under the influence of the Sun and the four giant planets.
By recording all close encounters between the clones and planets, we
investigate the likelihood that Chariklo's rings could have survived since its
capture to the Centaur population. Our results reveal that Chariklo's orbit
occupies a region of stable chaos, resulting in its orbit being marginally more
stable than those of the other Centaurs. Despite this, we find that it was most
likely captured to the Centaur population within the last 20 Myr, and that its
orbital evolution has been continually punctuated by regular close encounters
with the giant planets. The great majority (> 99%) of those encounters within
one Hill radius of the planet have only a small effect on the rings. We
conclude that close encounters with giant planets have not had a significant
effect on the ring structure. Encounters within the Roche limit of the giant
planets are rare, making ring creation through tidal disruption unlikely
Forth Road Bridge Closure Survey: Analysis of Commuter Behaviour: Final Findings Report May 2016
First paragraph: This document presents the findings of surveys conducted on both commuter & non-commuting travel behaviour during the Forth Road Bridge closure. The survey captured 923 commuters (842 full time and 81 part time workers) and 441 non-commuters giving a total sample of 1,364 respondents. We anticipate that the survey will most likely have been filled out by those experiencing significant adverse impacts and, as such, the findings should be interpreted as an upper bound of impacts amongst those affected
Travel Behaviour Response to Major Transport System Disruptions: Implications for Smarter Resilience Planning
No abstract available
The intrinsic and interstellar broad-band linear polarization of nearby FGK dwarfs
We present linear polarization measurements of nearby FGK dwarfs to parts-per-million (ppm) precision. Before making any allowance for interstellar polarization, we found that the active stars within the sample have a mean polarization of 28.5 ± 2.2 ppm, while the inactive stars have a mean of 9.6 ± 1.5 ppm. Amongst inactive stars, we initially found no difference between debris disc host stars (9.1 ± 2.5 ppm) and the other FGK dwarfs (9.9 ± 1.9 ppm). We develop a model for the magnitude and direction of interstellar polarization for nearby stars. When we correct the observations for the estimated interstellar polarization, we obtain 23.0 ± 2.2 ppm for the active stars, 7.8 ± 2.9 ppm for the inactive debris disc host stars and 2.9 ± 1.9 ppm for the other inactive stars. The data indicate that whilst some debris disc host stars are intrinsically polarized most inactive FGK dwarfs have negligible intrinsic polarization, but that active dwarfs have intrinsic polarization at levels ranging up to ∼45 ppm. We briefly consider a number of mechanisms, and suggest that differential saturation of spectral lines in the presence of magnetic fields is best able to explain the polarization seen in active dwarfs. The results have implications for current attempts to detect polarized reflected light from hot Jupiters by looking at the combined light of the star and planet
Measuring the severity of close encounters between ringed small bodies and planets
Rings have recently been discovered around the trans-Neptunian object (TNO) 136108 Haumea and the Centaur 10199 Chariklo. Rings are also suspected around the Centaur 2060 Chiron. As planetary close encounters with ringed small bodies can affect ring longevity, we previously
measured the severity of such encounters of Chariklo and Chiron using the minimum encounter distance, dmin. The value of dmin that separates noticeable encounters from non-noticeable encounters we called the ‘ring limit’, R. R was then approximated as 10 tidal disruption distances, 10Rtd. In this work, we seek to find analytical expressions for R that fully account for the effects of the planet mass, small body mass, ms, ring orbital radius, r, and velocity at
infinity, v∞, for fictitious ringed Centaurs using ranges 2 × 1020 kg ≤ms≤ 1 Pluto mass and 25 000 ≤r ≤ 100 000 km. To accomplish this, we use numerical integration to simulate close encounters between each giant planet and ringed Centaurs in the three-body planar problem. The results show that R has a lower bound of approximately 1.8Rtd. We compare analytical and experimental R values for a fictitious Haumea, Chariklo, and Chiron with r= 50 000 km.
The agreement is excellent for Haumea, but weaker for Chariklo and Chiron. The agreement is best for Jupiter and Saturn. The ring limits of the real Haumea, Chariklo, and Chiron are <4Rtd. Experimental R values for the fictitious bodies make better approximations for the R values of the real bodies than does 10Rtd. Analytical values make good first approximations
Numerical implementation of the exact dynamics of free rigid bodies
In this paper the exact analytical solution of the motion of a rigid body
with arbitrary mass distribution is derived in the absence of forces or
torques. The resulting expressions are cast into a form where the dependence of
the motion on initial conditions is explicit and the equations governing the
orientation of the body involve only real numbers. Based on these results, an
efficient method to calculate the location and orientation of the rigid body at
arbitrary times is presented. This implementation can be used to verify the
accuracy of numerical integration schemes for rigid bodies, to serve as a
building block for event-driven discontinuous molecular dynamics simulations of
general rigid bodies, and for constructing symplectic integrators for rigid
body dynamics.Comment: Shortened paper with updated references, 28 pages, 3 figure
Discontinuous Molecular Dynamics for Semi-Flexible and Rigid Bodies
A general framework for performing event-driven simulations of systems with
semi-flexible or rigid bodies interacting under impulsive torques and forces is
outlined. Two different approaches are presented. In the first, the dynamics
and interaction rules are derived from Lagrangian mechanics in the presence of
constraints. This approach is most suitable when the body is composed of
relatively few point masses or is semi-flexible. In the second method, the
equations of rigid bodies are used to derive explicit analytical expressions
for the free evolution of arbitrary rigid molecules and to construct a simple
scheme for computing interaction rules. Efficient algorithms for the search for
the times of interaction events are designed in this context, and the handling
of missed interaction events is discussed.Comment: 16 pages, double column revte
Efficient intra- and inter-night linking of asteroid detections using kd-trees
The Panoramic Survey Telescope And Rapid Response System (Pan-STARRS) under
development at the University of Hawaii's Institute for Astronomy is creating
the first fully automated end-to-end Moving Object Processing System (MOPS) in
the world. It will be capable of identifying detections of moving objects in
our solar system and linking those detections within and between nights,
attributing those detections to known objects, calculating initial and
differentially-corrected orbits for linked detections, precovering detections
when they exist, and orbit identification. Here we describe new kd-tree and
variable-tree algorithms that allow fast, efficient, scalable linking of intra
and inter-night detections. Using a pseudo-realistic simulation of the
Pan-STARRS survey strategy incorporating weather, astrometric accuracy and
false detections we have achieved nearly 100% efficiency and accuracy for
intra-night linking and nearly 100% efficiency for inter-night linking within a
lunation. At realistic sky-plane densities for both real and false detections
the intra-night linking of detections into `tracks' currently has an accuracy
of 0.3%. Successful tests of the MOPS on real source detections from the
Spacewatch asteroid survey indicate that the MOPS is capable of identifying
asteroids in real data.Comment: Accepted to Icaru
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