3,146 research outputs found
A network approach for power grid robustness against cascading failures
Cascading failures are one of the main reasons for blackouts in electrical
power grids. Stable power supply requires a robust design of the power grid
topology. Currently, the impact of the grid structure on the grid robustness is
mainly assessed by purely topological metrics, that fail to capture the
fundamental properties of the electrical power grids such as power flow
allocation according to Kirchhoff's laws. This paper deploys the effective
graph resistance as a metric to relate the topology of a grid to its robustness
against cascading failures. Specifically, the effective graph resistance is
deployed as a metric for network expansions (by means of transmission line
additions) of an existing power grid. Four strategies based on network
properties are investigated to optimize the effective graph resistance,
accordingly to improve the robustness, of a given power grid at a low
computational complexity. Experimental results suggest the existence of
Braess's paradox in power grids: bringing an additional line into the system
occasionally results in decrease of the grid robustness. This paper further
investigates the impact of the topology on the Braess's paradox, and identifies
specific sub-structures whose existence results in Braess's paradox. Careful
assessment of the design and expansion choices of grid topologies incorporating
the insights provided by this paper optimizes the robustness of a power grid,
while avoiding the Braess's paradox in the system.Comment: 7 pages, 13 figures conferenc
Robustness of Trans-European Gas Networks
Here we uncover the load and fault-tolerant backbones of the trans-European
gas pipeline network. Combining topological data with information on
inter-country flows, we estimate the global load of the network and its
tolerance to failures. To do this, we apply two complementary methods
generalized from the betweenness centrality and the maximum flow. We find that
the gas pipeline network has grown to satisfy a dual-purpose: on one hand, the
major pipelines are crossed by a large number of shortest paths thereby
increasing the efficiency of the network; on the other hand, a non-operational
pipeline causes only a minimal impact on network capacity, implying that the
network is error-tolerant. These findings suggest that the trans-European gas
pipeline network is robust, i.e., error tolerant to failures of high load
links.Comment: 11 pages, 8 figures (minor changes
Coverage Centrality Maximization in Undirected Networks
Centrality metrics are among the main tools in social network analysis. Being
central for a user of a network leads to several benefits to the user: central
users are highly influential and play key roles within the network. Therefore,
the optimization problem of increasing the centrality of a network user
recently received considerable attention. Given a network and a target user
, the centrality maximization problem consists in creating new links
incident to in such a way that the centrality of is maximized,
according to some centrality metric. Most of the algorithms proposed in the
literature are based on showing that a given centrality metric is monotone and
submodular with respect to link addition. However, this property does not hold
for several shortest-path based centrality metrics if the links are undirected.
In this paper we study the centrality maximization problem in undirected
networks for one of the most important shortest-path based centrality measures,
the coverage centrality. We provide several hardness and approximation results.
We first show that the problem cannot be approximated within a factor greater
than , unless , and, under the stronger gap-ETH hypothesis, the
problem cannot be approximated within a factor better than , where
is the number of users. We then propose two greedy approximation
algorithms, and show that, by suitably combining them, we can guarantee an
approximation factor of . We experimentally compare the
solutions provided by our approximation algorithm with optimal solutions
computed by means of an exact IP formulation. We show that our algorithm
produces solutions that are very close to the optimum.Comment: Accepted to AAAI 201
Robustness of Network Measures to Link Errors
In various applications involving complex networks, network measures are
employed to assess the relative importance of network nodes. However, the
robustness of such measures in the presence of link inaccuracies has not been
well characterized. Here we present two simple stochastic models of false and
missing links and study the effect of link errors on three commonly used node
centrality measures: degree centrality, betweenness centrality, and dynamical
importance. We perform numerical simulations to assess robustness of these
three centrality measures. We also develop an analytical theory, which we
compare with our simulations, obtaining very good agreement.Comment: 9 pages, 9 figure
The Dynamics of Vehicular Networks in Urban Environments
Vehicular Ad hoc NETworks (VANETs) have emerged as a platform to support
intelligent inter-vehicle communication and improve traffic safety and
performance. The road-constrained, high mobility of vehicles, their unbounded
power source, and the emergence of roadside wireless infrastructures make
VANETs a challenging research topic. A key to the development of protocols for
inter-vehicle communication and services lies in the knowledge of the
topological characteristics of the VANET communication graph. This paper
explores the dynamics of VANETs in urban environments and investigates the
impact of these findings in the design of VANET routing protocols. Using both
real and realistic mobility traces, we study the networking shape of VANETs
under different transmission and market penetration ranges. Given that a number
of RSUs have to be deployed for disseminating information to vehicles in an
urban area, we also study their impact on vehicular connectivity. Through
extensive simulations we investigate the performance of VANET routing protocols
by exploiting the knowledge of VANET graphs analysis.Comment: Revised our testbed with even more realistic mobility traces. Used
the location of real Wi-Fi hotspots to simulate RSUs in our study. Used a
larger, real mobility trace set, from taxis in Shanghai. Examine the
implications of our findings in the design of VANET routing protocols by
implementing in ns-3 two routing protocols (GPCR & VADD). Updated the
bibliography section with new research work
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