12,993 research outputs found
Traffic at the Edge of Chaos
We use a very simple description of human driving behavior to simulate
traffic. The regime of maximum vehicle flow in a closed system shows
near-critical behavior, and as a result a sharp decrease of the predictability
of travel time. Since Advanced Traffic Management Systems (ATMSs) tend to drive
larger parts of the transportation system towards this regime of maximum flow,
we argue that in consequence the traffic system as a whole will be driven
closer to criticality, thus making predictions much harder. A simulation of a
simplified transportation network supports our argument.Comment: Postscript version including most of the figures available from
http://studguppy.tsasa.lanl.gov/research_team/. Paper has been published in
Brooks RA, Maes P, Artifical Life IV: ..., MIT Press, 199
A Simplified Cellular Automaton Model for City Traffic
We systematically investigate the effect of blockage sites in a cellular
automaton model for traffic flow. Different scheduling schemes for the blockage
sites are considered. None of them returns a linear relationship between the
fraction of ``green'' time and the throughput. We use this information for a
fast implementation of traffic in Dallas.Comment: 12 pages, 18 figures. submitted to Phys Rev
Experiences with a simplified microsimulation for the Dallas/Fort Worth area
We describe a simple framework for micro simulation of city traffic. A medium
sized excerpt of Dallas was used to examine different levels of simulation
fidelity of a cellular automaton method for the traffic flow simulation and a
simple intersection model. We point out problems arising with the granular
structure of the underlying rules of motion.Comment: accepted by Int.J.Mod.Phys.C, 20 pages, 14 figure
Non-LTE spectral models for the gaseous debris-disk component of Ton 345
For a fraction of single white dwarfs with debris disks, an additional
gaseous disk was discovered. Both dust and gas are thought to be created by the
disruption of planetary bodies. The composition of the extrasolar planetary
material can directly be analyzed in the gaseous disk component, and the disk
dynamics might be accessible by investigating the temporal behavior of the Ca
II infrared emission triplet, hallmark of the gas disk.
We obtained new optical spectra for the first helium-dominated white dwarf
for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra
of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur,
and calcium with chemical abundances typical for solar system asteroids. Iron
and its possible line-blanketing effects on the model structure and spectral
energy distribution was still neglected. A set of models with different radii,
effective temperatures, and surface densities as well as chondritic and
bulk-Earth abundances was computed and compared with the observed line profiles
of the Ca II infrared triplet.
Our models suggest that the Ca II emission stems from a rather narrow gas
ring with a radial extent of R=0.44-0.94 Rsol, a uniform surface density
Sigma=0.3 g/cm2, and an effective temperature of Teff=6000 K. The often assumed
chemical mixtures derived from photospheric abundances in polluted white dwarfs
- similar to a chondritic or bulk-Earth composition - produce unobserved
emission lines in the model and therefore have to be altered. We do not detect
any line-profile variability on timescales of hours, but we confirm the
long-term trend over the past decade for the red-blue asymmetry of the
double-peaked lines.Comment: 7 pages, 6 figures, 2 table
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