3,101 research outputs found
Collective effects in traffic on bi-directional ant-trails
Motivated by recent experimental work of Burd et al., we propose a model of
bi-directional ant-traffic on pre-existing ant-trails. It captures in a simple
way some of the generic collective features of movements of real ants on a
trail. Analyzing this model, we demonstrate that there are crucial qualitative
differences between vehicular- and ant-traffics. In particular, we predict some
unusual features of the flow rate that can be tested experimentally. As in the
uni-directional model a non-monotonic density-dependence of the average
velocity can be observed in certain parameter regimes. As a consequence of the
interaction between oppositely moving ants the flow rate can become
approximately constant over some density interval
Physics of Transport and Traffic Phenomena in Biology: from molecular motors and cells to organisms
Traffic-like collective movements are observed at almost all levels of
biological systems. Molecular motor proteins like, for example, kinesin and
dynein, which are the vehicles of almost all intra-cellular transport in
eukayotic cells, sometimes encounter traffic jam that manifests as a disease of
the organism. Similarly, traffic jam of collagenase MMP-1, which moves on the
collagen fibrils of the extracellular matrix of vertebrates, has also been
observed in recent experiments. Traffic-like movements of social insects like
ants and termites on trails are, perhaps, more familiar in our everyday life.
Experimental, theoretical and computational investigations in the last few
years have led to a deeper understanding of the generic or common physical
principles involved in these phenomena. In particular, some of the methods of
non-equilibrium statistical mechanics, pioneered almost a hundred years ago by
Einstein, Langevin and others, turned out to be powerful theoretical tools for
quantitaive analysis of models of these traffic-like collective phenomena as
these systems are intrinsically far from equilibrium. In this review we
critically examine the current status of our understanding, expose the
limitations of the existing methods, mention open challenging questions and
speculate on the possible future directions of research in this
interdisciplinary area where physics meets not only chemistry and biology but
also (nano-)technology.Comment: 33 page Review article, REVTEX text, 29 EPS and PS figure
A Model for Collective Dynamics in Ant Raids
Ant raiding, the process of identifying and returning food to the nest or
bivouac, is a fascinating example of collective motion in nature. During such
raids ants lay pheromones to form trails for others to find a food source. In
this work a coupled PDE/ODE model is introduced to study ant dynamics and
pheromone concentration. The key idea is the introduction of two forms of ant
dynamics: foraging and returning, each governed by different environmental and
social cues. The model accounts for all aspects of the raiding cycle including
local collisional interactions, the laying of pheromone along a trail, and the
transition from one class of ants to another. Through analysis of an order
parameter measuring the orientational order in the system, the model shows
self-organization into a collective state consisting of lanes of ants moving in
opposite directions as well as the transition back to the individual state once
the food source is depleted matching prior experimental results. This indicates
that in the absence of direct communication ants naturally form an efficient
method for transporting food to the nest/bivouac. The model exhibits a
continuous kinetic phase transition in the order parameter as a function of
certain system parameters. The associated critical exponents are found,
shedding light on the behavior of the system near the transition.Comment: Preprint Version, 30 pgs., 18 figures, complete version with
supplementary movies to appear in Journal of Mathematical Biology (Springer
Planning and Scheduling Transportation Vehicle Fleet in a Congested Traffic Environment
Transportation is a main component of supply chain competitiveness since it plays a major role in the inbound, inter-facility, and outbound logistics. In this context, assigning and scheduling vehicle routing is a crucial management problem. Despite numerous publications dealing with efficient scheduling methods for vehicle routing, very few addressed the inherent stochastic nature of travel times in this problem. In this paper, a vehicle routing problem with time windows and stochastic travel times due to potential traffic congestion is considered. The approach developed introduces mainly the traffic congestion component based on queueing theory. This is an innovative modeling scheme to capture the stochastic behavior of travel times. A case study is used both to illustrate the appropriateness of the approach as well as to show that time-independent solutions are often unrealistic within a congested traffic environment which is often the case on the european road networkstransportation; vehicle fleet; planning; scheduling; congested traffic
Balancing building and maintenance costs in growing transport networks
The costs associated to the length of links impose unavoidable constraints to
the growth of natural and artificial transport networks. When future network
developments can not be predicted, building and maintenance costs require
competing minimization mechanisms, and can not be optimized simultaneously.
Hereby, we study the interplay of building and maintenance costs and its impact
on the growth of transportation networks through a non-equilibrium model of
network growth. We show cost balance is a sufficient ingredient for the
emergence of tradeoffs between the network's total length and transport
effciency, of optimal strategies of construction, and of power-law temporal
correlations in the growth history of the network. Analysis of empirical ant
transport networks in the framework of this model suggests different ant
species may adopt similar optimization strategies.Comment: 4 pages main text, 2 pages references, 4 figure
Counterflow Extension for the F.A.S.T.-Model
The F.A.S.T. (Floor field and Agent based Simulation Tool) model is a
microscopic model of pedestrian dynamics, which is discrete in space and time.
It was developed in a number of more or less consecutive steps from a simple CA
model. This contribution is a summary of a study on an extension of the
F.A.S.T-model for counterflow situations. The extensions will be explained and
it will be shown that the extended F.A.S.T.-model is capable of handling
various counterflow situations and to reproduce the well known lane formation
effect.Comment: Contribution to Crowds and Cellular Automata Workshop 2008. Accepted
for publication in "Cellular Automata -- 8th International Conference on
Cellular Automata for Research and Industry, ACRI 2008, Yokohama, Japan,
September 23-26, Springer 2008, Proceedings
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