312 research outputs found
Dimension and cut vertices: an application of Ramsey theory
Motivated by quite recent research involving the relationship between the
dimension of a poset and graph-theoretic properties of its cover graph, we show
that for every , if is a poset and the dimension of a subposet
of is at most whenever the cover graph of is a block of the cover
graph of , then the dimension of is at most . We also construct
examples which show that this inequality is best possible. We consider the
proof of the upper bound to be fairly elegant and relatively compact. However,
we know of no simple proof for the lower bound, and our argument requires a
powerful tool known as the Product Ramsey Theorem. As a consequence, our
constructions involve posets of enormous size.Comment: Final published version with updated reference
On the dimension of posets with cover graphs of treewidth
In 1977, Trotter and Moore proved that a poset has dimension at most
whenever its cover graph is a forest, or equivalently, has treewidth at most
. On the other hand, a well-known construction of Kelly shows that there are
posets of arbitrarily large dimension whose cover graphs have treewidth . In
this paper we focus on the boundary case of treewidth . It was recently
shown that the dimension is bounded if the cover graph is outerplanar (Felsner,
Trotter, and Wiechert) or if it has pathwidth (Bir\'o, Keller, and Young).
This can be interpreted as evidence that the dimension should be bounded more
generally when the cover graph has treewidth . We show that it is indeed the
case: Every such poset has dimension at most .Comment: v4: minor changes made following helpful comments by the referee
Dimension of posets with planar cover graphs excluding two long incomparable chains
It has been known for more than 40 years that there are posets with planar
cover graphs and arbitrarily large dimension. Recently, Streib and Trotter
proved that such posets must have large height. In fact, all known
constructions of such posets have two large disjoint chains with all points in
one chain incomparable with all points in the other. Gutowski and Krawczyk
conjectured that this feature is necessary. More formally, they conjectured
that for every , there is a constant such that if is a poset
with a planar cover graph and excludes , then
. We settle their conjecture in the affirmative. We also discuss
possibilities of generalizing the result by relaxing the condition that the
cover graph is planar.Comment: New section on connections with graph minors, small correction
Tree-width and dimension
Over the last 30 years, researchers have investigated connections between
dimension for posets and planarity for graphs. Here we extend this line of
research to the structural graph theory parameter tree-width by proving that
the dimension of a finite poset is bounded in terms of its height and the
tree-width of its cover graph.Comment: Updates on solutions of problems and on bibliograph
Collaborative Honeypot Defense in UAV Networks: A Learning-Based Game Approach
The proliferation of unmanned aerial vehicles (UAVs) opens up new
opportunities for on-demand service provisioning anywhere and anytime, but also
exposes UAVs to a variety of cyber threats. Low/medium interaction honeypots
offer a promising lightweight defense for actively protecting mobile Internet
of things, particularly UAV networks. While previous research has primarily
focused on honeypot system design and attack pattern recognition, the incentive
issue for motivating UAV's participation (e.g., sharing trapped attack data in
honeypots) to collaboratively resist distributed and sophisticated attacks
remains unexplored. This paper proposes a novel game-theoretical collaborative
defense approach to address optimal, fair, and feasible incentive design, in
the presence of network dynamics and UAVs' multi-dimensional private
information (e.g., valid defense data (VDD) volume, communication delay, and
UAV cost). Specifically, we first develop a honeypot game between UAVs and the
network operator under both partial and complete information asymmetry
scenarios. The optimal VDD-reward contract design problem with partial
information asymmetry is then solved using a contract-theoretic approach that
ensures budget feasibility, truthfulness, fairness, and computational
efficiency. In addition, under complete information asymmetry, we devise a
distributed reinforcement learning algorithm to dynamically design optimal
contracts for distinct types of UAVs in the time-varying UAV network. Extensive
simulations demonstrate that the proposed scheme can motivate UAV's cooperation
in VDD sharing and improve defensive effectiveness, compared with conventional
schemes.Comment: Accepted Aug. 28, 2023 by IEEE Transactions on Information Forensics
& Security. arXiv admin note: text overlap with arXiv:2209.1381
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