1,225 research outputs found
Guarding Networks Through Heterogeneous Mobile Guards
In this article, the issue of guarding multi-agent systems against a sequence
of intruder attacks through mobile heterogeneous guards (guards with different
ranges) is discussed. The article makes use of graph theoretic abstractions of
such systems in which agents are the nodes of a graph and edges represent
interconnections between agents. Guards represent specialized mobile agents on
specific nodes with capabilities to successfully detect and respond to an
attack within their guarding range. Using this abstraction, the article
addresses the problem in the context of eternal security problem in graphs.
Eternal security refers to securing all the nodes in a graph against an
infinite sequence of intruder attacks by a certain minimum number of guards.
This paper makes use of heterogeneous guards and addresses all the components
of the eternal security problem including the number of guards, their
deployment and movement strategies. In the proposed solution, a graph is
decomposed into clusters and a guard with appropriate range is then assigned to
each cluster. These guards ensure that all nodes within their corresponding
cluster are being protected at all times, thereby achieving the eternal
security in the graph.Comment: American Control Conference, Chicago, IL, 201
The Calcium Phosphate−Calcium Carbonate System: Growth of Octacalcium Phosphate on Calcium Carbonates
The kinetics of nucleation and crystal growth of octacalcium phosphate [Ca8(PO4)6H2·5H2O, OCP] from calcium phosphate supersaturated solutions inoculated with seed crystals was investigated at 37 °C, pH 7.40, at conditions of constant solution supersaturation. Stable calcium phosphate solutions, supersaturated with respect to OCP and hydroxyapatite [Ca5(PO4)3OH, HAP] were inoculated with calcium carbonate-based bone cement powder consisting of mixed aragonite and calcite crystals and with well-characterized calcite seed crystals. On all substrates tested, OCP nucleated followed by crystal growth of the nuclei formed past the lapse of induction times, inversely proportional to the solution supersaturation. From the dependence of the induction time on the solution supersaturation with respect to OCP, a value of 10 mJ m−2 was calculated for the nucleating phase. The rates of OCP crystal growth on the carbonate substrates showed linear dependence on the solution supersaturation that in combination with the independence from the fluid dynamics in the reactor suggested a surface diffusion-controlled mechanism. Moreover, the independence of the crystallization rates on the amount of the inoculating seed crystals suggested that nucleation and growth took place exclusively on the crystalline substrates. The transient calcium phosphate phase, OCP, was stabilized in our experiments, and it was the only phase growing at constant driving force, despite the fact the solutions were supersaturated with respect to HAP as well
Optimal Detection of Faulty Traffic Sensors Used in Route Planning
In a smart city, real-time traffic sensors may be deployed for various
applications, such as route planning. Unfortunately, sensors are prone to
failures, which result in erroneous traffic data. Erroneous data can adversely
affect applications such as route planning, and can cause increased travel
time. To minimize the impact of sensor failures, we must detect them promptly
and accurately. However, typical detection algorithms may lead to a large
number of false positives (i.e., false alarms) and false negatives (i.e.,
missed detections), which can result in suboptimal route planning. In this
paper, we devise an effective detector for identifying faulty traffic sensors
using a prediction model based on Gaussian Processes. Further, we present an
approach for computing the optimal parameters of the detector which minimize
losses due to false-positive and false-negative errors. We also characterize
critical sensors, whose failure can have high impact on the route planning
application. Finally, we implement our method and evaluate it numerically using
a real-world dataset and the route planning platform OpenTripPlanner.Comment: Proceedings of The 2nd Workshop on Science of Smart City Operations
and Platforms Engineering (SCOPE 2017), Pittsburgh, PA USA, April 2017, 6
page
Consensus of Multi-Agent Networks in the Presence of Adversaries Using Only Local Information
This paper addresses the problem of resilient consensus in the presence of
misbehaving nodes. Although it is typical to assume knowledge of at least some
nonlocal information when studying secure and fault-tolerant consensus
algorithms, this assumption is not suitable for large-scale dynamic networks.
To remedy this, we emphasize the use of local strategies to deal with
resilience to security breaches. We study a consensus protocol that uses only
local information and we consider worst-case security breaches, where the
compromised nodes have full knowledge of the network and the intentions of the
other nodes. We provide necessary and sufficient conditions for the normal
nodes to reach consensus despite the influence of the malicious nodes under
different threat assumptions. These conditions are stated in terms of a novel
graph-theoretic property referred to as network robustness.Comment: This report contains the proofs of the results presented at HiCoNS
201
Sensor placement for fault location identification in water networks: A minimum test cover approach
This paper focuses on the optimal sensor placement problem for the
identification of pipe failure locations in large-scale urban water systems.
The problem involves selecting the minimum number of sensors such that every
pipe failure can be uniquely localized. This problem can be viewed as a minimum
test cover (MTC) problem, which is NP-hard. We consider two approaches to
obtain approximate solutions to this problem. In the first approach, we
transform the MTC problem to a minimum set cover (MSC) problem and use the
greedy algorithm that exploits the submodularity property of the MSC problem to
compute the solution to the MTC problem. In the second approach, we develop a
new \textit{augmented greedy} algorithm for solving the MTC problem. This
approach does not require the transformation of the MTC to MSC. Our augmented
greedy algorithm provides in a significant computational improvement while
guaranteeing the same approximation ratio as the first approach. We propose
several metrics to evaluate the performance of the sensor placement designs.
Finally, we present detailed computational experiments for a number of real
water distribution networks
Ion interactions in ionic liquids
Ionic liquids are being intensively investigated as more sustainable chemicals for many applications
due to their advantageous physicochemical properties. The main reason for this interest
is the synthetic flexibility associated with them, as there is a never-ending number of different
possible combinations of anions and cations, which can lead to compounds with very distinct
properties. However, the research interest has progressed fast into developing ionic liquids for
specific applications, while we are still lacking fundamental knowledge on the interactions taking
place inside of them. As a result of this, many models fail to provide accurate predictions
about the properties or reactivity of ionic liquids. This thesis presents fundamental research
on the structure-property relationships of ionic liquids, emphasising on aspects like the effects
of specific functional groups or symmetry on their physical properties. Furthermore, Electron
Paramagnetic Resonance spectroscopy is introduced as a versatile tool for characterising the
chemical environment inside of an ionic liquid. Using nitroxide spin probes as ‘spies’, we are
trying to identify the relationship between the bulk properties (e.g. viscosity) and the interactions
the radicals feel in their immediate environment. The results indicate that depending on
the examined ionic liquid and the used spin probe there is a plethora of microscale interactions
which are in no way deduced from the physicochemical studies of bulk properties.Open Acces
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