1,947 research outputs found
Derivation, Properties, and Simulation of a Gas-Kinetic-Based, Non-Local Traffic Model
We derive macroscopic traffic equations from specific gas-kinetic equations,
dropping some of the assumptions and approximations made in previous papers.
The resulting partial differential equations for the vehicle density and
average velocity contain a non-local interaction term which is very favorable
for a fast and robust numerical integration, so that several thousand freeway
kilometers can be simulated in real-time. The model parameters can be easily
calibrated by means of empirical data. They are directly related to the
quantities characterizing individual driver-vehicle behavior, and their optimal
values have the expected order of magnitude. Therefore, they allow to
investigate the influences of varying street and weather conditions or freeway
control measures. Simulation results for realistic model parameters are in good
agreement with the diverse non-linear dynamical phenomena observed in freeway
traffic.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://www.theo2.physik.uni-stuttgart.de/treiber.htm
Gas-Kinetic-Based Traffic Model Explaining Observed Hysteretic Phase Transition
Recently, hysteretic transitions to `synchronized traffic' with high values
of both density and traffic flow were observed on German freeways [B. S. Kerner
and H. Rehborn, Phys. Rev. Lett. 79, 4030 (1997)]. We propose a macroscopic
traffic model based on a gas-kinetic approach that can explain this phase
transition. The results suggest a general mechanism for the formation of
probably the most common form of congested traffic.Comment: With corrected formula (3). For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Structure and Instability of High-Density Equations for Traffic Flow
Similar to the treatment of dense gases, fluid-dynamic equations for the
dynamics of congested vehicular traffic are derived from Enskog-like kinetic
equations. These contain additional terms due to the anisotropic vehicle
interactions. The calculations are carried out up to Navier-Stokes order. A
linear instability analysis indicates an additional kind of instability
compared to previous macroscopic traffic models. The relevance for describing
granular flows is outlined.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Time-evolving measures and macroscopic modeling of pedestrian flow
This paper deals with the early results of a new model of pedestrian flow,
conceived within a measure-theoretical framework. The modeling approach
consists in a discrete-time Eulerian macroscopic representation of the system
via a family of measures which, pushed forward by some motion mappings, provide
an estimate of the space occupancy by pedestrians at successive time steps.
From the modeling point of view, this setting is particularly suitable to
treat nonlocal interactions among pedestrians, obstacles, and wall boundary
conditions. In addition, analysis and numerical approximation of the resulting
mathematical structures, which is the main target of this work, follow more
easily and straightforwardly than in case of standard hyperbolic conservation
laws, also used in the specialized literature by some Authors to address
analogous problems.Comment: 27 pages, 6 figures -- Accepted for publication in Arch. Ration.
Mech. Anal., 201
Interpreting the Wide Scattering of Synchronized Traffic Data by Time Gap Statistics
Based on the statistical evaluation of experimental single-vehicle data, we
propose a quantitative interpretation of the erratic scattering of flow-density
data in synchronized traffic flows. A correlation analysis suggests that the
dynamical flow-density data are well compatible with the so-called jam line
characterizing fully developed traffic jams, if one takes into account the
variation of their propagation speed due to the large variation of the netto
time gaps (the inhomogeneity of traffic flow). The form of the time gap
distribution depends not only on the density, but also on the measurement cross
section: The most probable netto time gap in congested traffic flow upstream of
a bottleneck is significantly increased compared to uncongested freeway
sections. Moreover, we identify different power-law scaling laws for the
relative variance of netto time gaps as a function of the sampling size. While
the exponent is -1 in free traffic corresponding to statistically independent
time gaps, the exponent is about -2/3 in congested traffic flow because of
correlations between queued vehicles.Comment: For related publications see http://www.helbing.or
Emergence of heterogeneity and political organization in information exchange networks
We present a simple model of the emergence of the division of labor and the
development of a system of resource subsidy from an agent-based model of
directed resource production with variable degrees of trust between the agents.
The model has three distinct phases, corresponding to different forms of
societal organization: disconnected (independent agents), homogeneous
cooperative (collective state), and inhomogeneous cooperative (collective state
with a leader). Our results indicate that such levels of organization arise
generically as a collective effect from interacting agent dynamics, and may
have applications in a variety of systems including social insects and
microbial communities.Comment: 10 pages, 6 figure
Freezing by Heating in a Driven Mesoscopic System
We investigate a simple model corresponding to particles driven in opposite
directions and interacting via a repulsive potential. The particles move
off-lattice on a periodic strip and are subject to random forces as well. We
show that this model - which can be considered as a continuum version of some
driven diffusive systems - exhibits a paradoxial, new kind of transition called
here ``freezing by heating''. One interesting feature of this transition is
that a crystallized state with a higher total energy is obtained from a fluid
state by increasing the amount of fluctuations.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://angel.elte.hu/~vicsek
Breakdown and recovery in traffic flow models
Most car-following models show a transition from laminar to ``congested''
flow and vice versa. Deterministic models often have a density range where a
disturbance needs a sufficiently large critical amplitude to move the flow from
the laminar into the congested phase. In stochastic models, it may be assumed
that the size of this amplitude gets translated into a waiting time, i.e.\
until fluctuations sufficiently add up to trigger the transition. A recently
introduced model of traffic flow however does not show this behavior: in the
density regime where the jam solution co-exists with the high-flow state, the
intrinsic stochasticity of the model is not sufficient to cause a transition
into the jammed regime, at least not within relevant time scales. In addition,
models can be differentiated by the stability of the outflow interface. We
demonstrate that this additional criterion is not related to the stability of
the flow. The combination of these criteria makes it possible to characterize
commonalities and differences between many existing models for traffic in a new
way
Incised-valley morphologies and sedimentary-fills within the inner shelf of the northern Bay of Biscay
This study is a first synthesis focused on incised-valleys located within the
inner shelf of the Bay of Biscay. It is based on previously published results
obtained during recent seismic surveys and coring campaigns. The morphology of
the valleys appears to be strongly controlled by tectonics and lithology. The
Pleistocene sedimentary cover of the shelf is very thin and discontinuous with
a maximum thickness ranging between 30 and 40 m in incised-valley fills. Thus
the incised bedrock morphology plays a key-role by controlling hydrodynamics
and related sediment transport and deposition that explains some variations of
those incised-valley fills with respect to the previously published general
models
Challenges in Complex Systems Science
FuturICT foundations are social science, complex systems science, and ICT.
The main concerns and challenges in the science of complex systems in the
context of FuturICT are laid out in this paper with special emphasis on the
Complex Systems route to Social Sciences. This include complex systems having:
many heterogeneous interacting parts; multiple scales; complicated transition
laws; unexpected or unpredicted emergence; sensitive dependence on initial
conditions; path-dependent dynamics; networked hierarchical connectivities;
interaction of autonomous agents; self-organisation; non-equilibrium dynamics;
combinatorial explosion; adaptivity to changing environments; co-evolving
subsystems; ill-defined boundaries; and multilevel dynamics. In this context,
science is seen as the process of abstracting the dynamics of systems from
data. This presents many challenges including: data gathering by large-scale
experiment, participatory sensing and social computation, managing huge
distributed dynamic and heterogeneous databases; moving from data to dynamical
models, going beyond correlations to cause-effect relationships, understanding
the relationship between simple and comprehensive models with appropriate
choices of variables, ensemble modeling and data assimilation, modeling systems
of systems of systems with many levels between micro and macro; and formulating
new approaches to prediction, forecasting, and risk, especially in systems that
can reflect on and change their behaviour in response to predictions, and
systems whose apparently predictable behaviour is disrupted by apparently
unpredictable rare or extreme events. These challenges are part of the FuturICT
agenda
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