51,197 research outputs found
Statistical Analysis of Bus Networks in India
Through the past decade the field of network science has established itself
as a common ground for the cross-fertilization of exciting inter-disciplinary
studies which has motivated researchers to model almost every physical system
as an interacting network consisting of nodes and links. Although public
transport networks such as airline and railway networks have been extensively
studied, the status of bus networks still remains in obscurity. In developing
countries like India, where bus networks play an important role in day-to-day
commutation, it is of significant interest to analyze its topological structure
and answer some of the basic questions on its evolution, growth, robustness and
resiliency. In this paper, we model the bus networks of major Indian cities as
graphs in \textit{L}-space, and evaluate their various statistical properties
using concepts from network science. Our analysis reveals a wide spectrum of
network topology with the common underlying feature of small-world property. We
observe that the networks although, robust and resilient to random attacks are
particularly degree-sensitive. Unlike real-world networks, like Internet, WWW
and airline, which are virtual, bus networks are physically constrained. The
presence of various geographical and economic constraints allow these networks
to evolve over time. Our findings therefore, throw light on the evolution of
such geographically and socio-economically constrained networks which will help
us in designing more efficient networks in the future.Comment: Submitted to PLOS ON
The Network Analysis of Urban Streets: A Primal Approach
The network metaphor in the analysis of urban and territorial cases has a
long tradition especially in transportation/land-use planning and economic
geography. More recently, urban design has brought its contribution by means of
the "space syntax" methodology. All these approaches, though under different
terms like accessibility, proximity, integration,connectivity, cost or effort,
focus on the idea that some places (or streets) are more important than others
because they are more central. The study of centrality in complex
systems,however, originated in other scientific areas, namely in structural
sociology, well before its use in urban studies; moreover, as a structural
property of the system, centrality has never been extensively investigated
metrically in geographic networks as it has been topologically in a wide range
of other relational networks like social, biological or technological. After
two previous works on some structural properties of the dual and primal graph
representations of urban street networks (Porta et al. cond-mat/0411241;
Crucitti et al. physics/0504163), in this paper we provide an in-depth
investigation of centrality in the primal approach as compared to the dual one,
with a special focus on potentials for urban design.Comment: 19 page, 4 figures. Paper related to the paper "The Network Analysis
of Urban Streets: A Dual Approach" cond-mat/041124
Network effects and total economic impact in transport appraisal
It is claimed that transport infrastructure projects have network effects which are not taken into account in the appraisal of these projects. This paper reviews the concept of network effects, relates this to transport appraisal practice, and links to the concept of ‘total economic impact’. The limitations of transport modelling and appraisal in estimating total economic impact are reviewed. Good quality appraisals should be capable of picking up relevant network effects in the transport market, but the state of the art remains limited on the linkages between transport and the wider economy
Empirical analysis of the ship-transport network of China
Structural properties of the ship-transport network of China (STNC) are
studied in the light of recent investigations of complex networks. STNC is
composed of a set of routes and ports located along the sea or river. Network
properties including the degree distribution, degree correlations, clustering,
shortest path length, centrality and betweenness are studied in different
definition of network topology. It is found that geographical constraint plays
an important role in the network topology of STNC. We also study the traffic
flow of STNC based on the weighted network representation, and demonstrate the
weight distribution can be described by power law or exponential function
depending on the assumed definition of network topology. Other features related
to STNC are also investigated.Comment: 20 pages, 7 figures, 1 tabl
Impact of network structure on the capacity of wireless multihop ad hoc communication
As a representative of a complex technological system, so-called wireless
multihop ad hoc communication networks are discussed. They represent an
infrastructure-less generalization of todays wireless cellular phone networks.
Lacking a central control authority, the ad hoc nodes have to coordinate
themselves such that the overall network performs in an optimal way. A
performance indicator is the end-to-end throughput capacity.
Various models, generating differing ad hoc network structure via differing
transmission power assignments, are constructed and characterized. They serve
as input for a generic data traffic simulation as well as some semi-analytic
estimations. The latter reveal that due to the most-critical-node effect the
end-to-end throughput capacity sensitively depends on the underlying network
structure, resulting in differing scaling laws with respect to network size.Comment: 30 pages, to be published in Physica
Internet routing paths stability model and relation to forwarding paths
Analysis of real datasets to characterize the local stability properties of the Internet routing paths suggests that extending the route selection criteria to account for such property would not increase the routing path length. Nevertheless, even if selecting a more stable routing path could be considered as valuable from a routing perspective, it does not necessarily imply that the associated forwarding path would be more stable. Hence, if the dynamics of the Internet routing and forwarding system show different properties, then one can not straightforwardly derive the one from the other. If this assumption is verified, then the relationship between the stability of the forwarding path (followed by the traffic) and the corresponding routing path as selected by the path-vector routing algorithm requires further characterization. For this purpose, we locally relate, i.e., at the router level, the stability properties of routing path with the corresponding forwarding path. The proposed stability model and measurement results verify this assumption and show that, although the main cause of instability results from the forwarding plane, a second order effect relates forwarding and routing path instability events. This observation provides the first indication that differential stability can safely be taken into account as part of the route selection process
Critical Cooperation Range to Improve Spatial Network Robustness
A robust worldwide air-transportation network (WAN) is one that minimizes the
number of stranded passengers under a sequence of airport closures. Building on
top of this realistic example, here we address how spatial network robustness
can profit from cooperation between local actors. We swap a series of links
within a certain distance, a cooperation range, while following typical
constraints of spatially embedded networks. We find that the network robustness
is only improved above a critical cooperation range. Such improvement can be
described in the framework of a continuum transition, where the critical
exponents depend on the spatial correlation of connected nodes. For the WAN we
show that, except for Australia, all continental networks fall into the same
universality class. Practical implications of this result are also discussed
Optimal Traffic Networks
Inspired by studies on the airports' network and the physical Internet, we
propose a general model of weighted networks via an optimization principle. The
topology of the optimal network turns out to be a spanning tree that minimizes
a combination of topological and metric quantities. It is characterized by a
strongly heterogeneous traffic, non-trivial correlations between distance and
traffic and a broadly distributed centrality. A clear spatial hierarchical
organization, with local hubs distributing traffic in smaller regions, emerges
as a result of the optimization. Varying the parameters of the cost function,
different classes of trees are recovered, including in particular the minimum
spanning tree and the shortest path tree. These results suggest that a
variational approach represents an alternative and possibly very meaningful
path to the study of the structure of complex weighted networks.Comment: 4 pages, 4 figures, final revised versio
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