42,401 research outputs found
Fundamentals of Large Sensor Networks: Connectivity, Capacity, Clocks and Computation
Sensor networks potentially feature large numbers of nodes that can sense
their environment over time, communicate with each other over a wireless
network, and process information. They differ from data networks in that the
network as a whole may be designed for a specific application. We study the
theoretical foundations of such large scale sensor networks, addressing four
fundamental issues- connectivity, capacity, clocks and function computation.
To begin with, a sensor network must be connected so that information can
indeed be exchanged between nodes. The connectivity graph of an ad-hoc network
is modeled as a random graph and the critical range for asymptotic connectivity
is determined, as well as the critical number of neighbors that a node needs to
connect to. Next, given connectivity, we address the issue of how much data can
be transported over the sensor network. We present fundamental bounds on
capacity under several models, as well as architectural implications for how
wireless communication should be organized.
Temporal information is important both for the applications of sensor
networks as well as their operation.We present fundamental bounds on the
synchronizability of clocks in networks, and also present and analyze
algorithms for clock synchronization. Finally we turn to the issue of gathering
relevant information, that sensor networks are designed to do. One needs to
study optimal strategies for in-network aggregation of data, in order to
reliably compute a composite function of sensor measurements, as well as the
complexity of doing so. We address the issue of how such computation can be
performed efficiently in a sensor network and the algorithms for doing so, for
some classes of functions.Comment: 10 pages, 3 figures, Submitted to the Proceedings of the IEE
Simulation of the Elastic Properties of Reinforced Kevlar-Graphene Composites
The compressive strength of unidirectional fiber composites in the form of
Kevlar yarn with a thin outer layer of graphene was investigated and modeled.
Such fiber structure may be fabricated by using a strong chemical bond between
Kevlar yarn and graphene sheets. Chemical functionalization of graphene and
Kevlar may achieved by modification of appropriate surface-bound functional
(e.g., carboxylic acid) groups on their surfaces. In this report we studied
elastic response to unidirectional in-plane applied load with load peaks along
the diameter. The 2D linear elasticity model predicts that significant
strengthening occurs when graphene outer layer radius is about 4 % of kevlar
yarn radius. The polymer chains of Kevlar are linked into locally planar
structure by hydrogen bonds across the chains, with transversal strength
considerably weaker than longitudinal one. This suggests that introducing outer
enveloping layer of graphene, linked to polymer chains by strong chemical bonds
may significantly strengthen Kevlar fiber with respect to transversal
deformations
Mechanical characteristics of carbon fibre yacht masts
This paper provides a preliminary stress analysis of a carbon reinforced layered cylinder such as would be found in a yacht mast. The cylinder is subjected to a compressive load and both an analytical and numerical analysis of the resulting stress fields is obtained. Some conclusions are obtained regarding the failure mode for particular examples of such cylinders
Probably Approximately Correct Nash Equilibrium Learning
We consider a multi-agent noncooperative game with agents' objective
functions being affected by uncertainty. Following a data driven paradigm, we
represent uncertainty by means of scenarios and seek a robust Nash equilibrium
solution. We treat the Nash equilibrium computation problem within the realm of
probably approximately correct (PAC) learning. Building upon recent
developments in scenario-based optimization, we accompany the computed Nash
equilibrium with a priori and a posteriori probabilistic robustness
certificates, providing confidence that the computed equilibrium remains
unaffected (in probabilistic terms) when a new uncertainty realization is
encountered. For a wide class of games, we also show that the computation of
the so called compression set - a key concept in scenario-based optimization -
can be directly obtained as a byproduct of the proposed solution methodology.
Finally, we illustrate how to overcome differentiability issues, arising due to
the introduction of scenarios, and compute a Nash equilibrium solution in a
decentralized manner. We demonstrate the efficacy of the proposed approach on
an electric vehicle charging control problem.Comment: Preprint submitted to IEEE Transactions on Automatic Contro
Capacity Bounds for a Class of Interference Relay Channels
The capacity of a class of Interference Relay Channels (IRC) -the Injective
Semideterministic IRC where the relay can only observe one of the sources- is
investigated. We first derive a novel outer bound and two inner bounds which
are based on a careful use of each of the available cooperative strategies
together with the adequate interference decoding technique. The outer bound
extends Telatar and Tse's work while the inner bounds contain several known
results in the literature as special cases. Our main result is the
characterization of the capacity region of the Gaussian class of IRCs studied
within a fixed number of bits per dimension -constant gap. The proof relies on
the use of the different cooperative strategies in specific SNR regimes due to
the complexity of the schemes. As a matter of fact, this issue reveals the
complex nature of the Gaussian IRC where the combination of a single coding
scheme for the Gaussian relay and interference channel may not lead to a good
coding scheme for this problem, even when the focus is only on capacity to
within a constant gap over all possible fading statistics.Comment: 23 pages, 6 figures. Submitted to IEEE Transactions on Information
Theory (revised version
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