266 research outputs found
Density fluctuations and phase separation in a traffic flow model
Within the Nagel-Schreckenberg traffic flow model we consider the transition
from the free flow regime to the jammed regime. We introduce a method of
analyzing the data which is based on the local density distribution. This
analyzes allows us to determine the phase diagram and to examine the separation
of the system into a coexisting free flow phase and a jammed phase above the
transition. The investigation of the steady state structure factor yields that
the decomposition in this phase coexistence regime is driven by density
fluctuations, provided they exceed a critical wavelength.Comment: in 'Traffic and Granular Flow 97', edited by D.E. Wolf and M.
Schreckenberg, Springer, Singapore (1998
Continuous Time and Consistent Histories
We discuss the use of histories labelled by a continuous time in the approach
to consistent-histories quantum theory in which propositions about the history
of the system are represented by projection operators on a Hilbert space. This
extends earlier work by two of us \cite{IL95} where we showed how a continuous
time parameter leads to a history algebra that is isomorphic to the canonical
algebra of a quantum field theory. We describe how the appropriate
representation of the history algebra may be chosen by requiring the existence
of projection operators that represent propositions about time average of the
energy. We also show that the history description of quantum mechanics contains
an operator corresponding to velocity that is quite distinct from the momentum
operator. Finally, the discussion is extended to give a preliminary account of
quantum field theory in this approach to the consistent histories formalism.Comment: Typeset in RevTe
Two Lane Traffic Simulations using Cellular Automata
We examine a simple two lane cellular automaton based upon the single lane CA
introduced by Nagel and Schreckenberg. We point out important parameters
defining the shape of the fundamental diagram. Moreover we investigate the
importance of stochastic elements with respect to real life traffic.Comment: to be published in Physica A, 19 pages, 9 out of 13 postscript
figures, 24kB in format .tar.gz., 33kB in format .tar.gz.uu, for a full
version including all figures see
http://studguppy.tsasa.lanl.gov/research_team/papers
On- and Off-ramps Generating 1/f Noise in Traffic Flow
A simple model of a motorway junction consisting of two connected periodic roads is presented; each of them is connected to the other by on- and off-ramps. This constitutes a detailed structure for the region of on- and off-ramps, which is a new aspect of this paper and a useful step towards a more realistic modelling of the vehicular dynamics near the ramps. The traffic flow through the ramps has an effect on the capacity of the main roads. This effect is identified by the formation of the so-called ”plateau” in the fundamental diagram. The value increase of one of the probabilities pin and pout decreases the value of the indicated plateau. Here pin is the probability to enter the main road through the on-ramp and pout denotes the probability to exit the main road through the off-ramp. The first important feature in the simulated system is the symmetry between the connected main roads. This symmetry does not depend on the variation of the difference between the probabilities pin and pout. The other most outstanding feature is the existence of correlations between the connected main roads, which can be traced back to the lane change of vehicles in the ramp regions. These correlations are characterized by the occurrence of 1/fα fluctuations in the global traffic flow of a chosen main road of the simulated system.A simple model of a motorway junction consisting of two connected periodic roads is presented; each of them is connected to the other by on- and off-ramps. This constitutes a detailed structure for the region of on- and off-ramps, which is a new aspect of this paper and a useful step towards a more realistic modelling of the vehicular dynamics near the ramps. The traffic flow through the ramps has an effect on the capacity of the main roads. This effect is identified by the formation of the so-called ”plateau” in the fundamental diagram. The value increase of one of the probabilities pin and pout decreases the value of the indicated plateau. Here pin is the probability to enter the main road through the on-ramp and pout denotes the probability to exit the main road through the off-ramp. The first important feature in the simulated system is the symmetry between the connected main roads. This symmetry does not depend on the variation of the difference between the probabilities pin and pout. The other most outstanding feature is the existence of correlations between the connected main roads, which can be traced back to the lane change of vehicles in the ramp regions. These correlations are characterized by the occurrence of 1/fα fluctuations in the global traffic flow of a chosen main road of the simulated system
Economics-Based Optimization of Unstable Flows
As an example for the optimization of unstable flows, we present an
economics-based method for deciding the optimal rates at which vehicles are
allowed to enter a highway. It exploits the naturally occuring fluctuations of
traffic flow and is flexible enough to adapt in real time to the transient flow
characteristics of road traffic. Simulations based on realistic parameter
values show that this strategy is feasible for naturally occurring traffic, and
that even far from optimality, injection policies can improve traffic flow.
Moreover, the same method can be applied to the optimization of flows of gases
and granular media.Comment: Revised version of ``Optimizing Traffic Flow'' (cond-mat/9809397).
For related work see http://www.parc.xerox.com/dynamics/ and
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Two-dimensional Burgers Cellular Automaton
A two-dimensional cellular automaton(CA) associated with a two-dimensional
Burgers equation is presented. The 2D Burgers equation is an integrable
generalization of the well-known Burgers equation, and is transformed into a 2D
diffusion equation by the Cole-Hopf transformation. The CA is derived from the
2D Burgers equation by using the ultradiscrete method, which can transform
dependent variables into discrete ones. Some exact solutions of the CA, such as
shock wave solutions, are studied in detail.Comment: Latex2.09, 17 pages including 7 figure
Car-oriented mean-field theory for traffic flow models
We present a new analytical description of the cellular automaton model for
single-lane traffic. In contrast to previous approaches we do not use the
occupation number of sites as dynamical variable but rather the distance
between consecutive cars. Therefore certain longer-ranged correlations are
taken into account and even a mean-field approach yields non-trivial results.
In fact for the model with the exact solution is reproduced. For
the fundamental diagram shows a good agreement with results from
simulations.Comment: LaTex, 10 pages, 2 postscript figure
Volatile Decision Dynamics: Experiments, Stochastic Description, Intermittency Control, and Traffic Optimization
The coordinated and efficient distribution of limited resources by individual
decisions is a fundamental, unsolved problem. When individuals compete for road
capacities, time, space, money, goods, etc., they normally make decisions based
on aggregate rather than complete information, such as TV news or stock market
indices. In related experiments, we have observed a volatile decision dynamics
and far-from-optimal payoff distributions. We have also identified ways of
information presentation that can considerably improve the overall performance
of the system. In order to determine optimal strategies of decision guidance by
means of user-specific recommendations, a stochastic behavioural description is
developed. These strategies manage to increase the adaptibility to changing
conditions and to reduce the deviation from the time-dependent user
equilibrium, thereby enhancing the average and individual payoffs. Hence, our
guidance strategies can increase the performance of all users by reducing
overreaction and stabilizing the decision dynamics. These results are highly
significant for predicting decision behaviour, for reaching optimal behavioural
distributions by decision support systems, and for information service
providers. One of the promising fields of application is traffic optimization.Comment: For related work see http://www.helbing.or
On the Stability of the Mean-Field Glass Broken Phase under Non-Hamiltonian Perturbations
We study the dynamics of the SK model modified by a small non-hamiltonian
perturbation. We study aging, and we find that on the time scales investigated
by our numerical simulations it survives a small perturbation (and is destroyed
by a large one). If we assume we are observing a transient behavior the scaling
of correlation times versus the asymmetry strength is not compatible with the
one expected for the spherical model. We discuss the slow power law decay of
observable quantities to equilibrium, and we show that for small perturbations
power like decay is preserved. We also discuss the asymptotically large time
region on small lattices.Comment: 34 page
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