285 research outputs found
Classifying Cantor Sets by their Fractal Dimensions
In this article we study Cantor sets defined by monotone sequences, in the
sense of Besicovitch and Taylor. We classify these Cantor sets in terms of
their h-Hausdorff and h-Packing measures, for the family of dimension functions
h, and characterize this classification in terms of the underlying sequences.Comment: 10 pages, revised version. To appear in Proceedings of the AMS
Firefighting as a game
The Firefighter Problem was proposed in 1995 [16] as a deterministic discrete-time model for the spread (and containment) of a fire. Its applications reach from real fires to the spreading of diseases and the containment of floods. Furthermore, it can be used to model the spread of computer viruses or viral marketing in communication networks.
In this work, we study the problem from a game-theoretical perspective. Such a context seems very appropriate when applied to large networks, where entities may act and make decisions based on their own interests, without global coordination.
We model the Firefighter Problem as a strategic game where there is one player for each time step who decides where to place the firefighters. We show that the Price of Anarchy is linear in the general case, but at most 2 for trees. We prove that the quality of the equilibria improves when allowing coalitional cooperation among players. In general, we have that the Price of Anarchy is in T(n/k) where k is the coalition size. Furthermore, we show that there are topologies which have a constant Price of Anarchy even when constant sized coalitions are considered.Peer ReviewedPostprint (author’s final draft
Abundance Measurements of Titan's Stratospheric HCN, HCN, CH, and CHCN from ALMA Observations
Previous investigations have employed more than 100 close observations of
Titan by the Cassini orbiter to elucidate connections between the production
and distribution of Titan's vast, organic-rich chemical inventory and its
atmospheric dynamics. However, as Titan transitions into northern summer, the
lack of incoming data from the Cassini orbiter presents a potential barrier to
the continued study of seasonal changes in Titan's atmosphere. In our previous
work (Thelen et al., 2018), we demonstrated that the Atacama Large
Millimeter/submillimeter Array (ALMA) is well suited for measurements of
Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km)
through the use of spatially resolved (beam sizes <1'') flux calibration
observations of Titan. Here, we derive vertical abundance profiles of four of
Titan's trace atmospheric species from the same 3 independent spatial regions
across Titan's disk during the same epoch (2012 to 2015): HCN, HCN,
CH, and CHCN. We find that Titan's minor constituents exhibit large
latitudinal variations, with enhanced abundances at high latitudes compared to
equatorial measurements; this includes CHCN, which eluded previous
detection by Cassini in the stratosphere, and thus spatially resolved abundance
measurements were unattainable. Even over the short 3-year period, vertical
profiles and integrated emission maps of these molecules allow us to observe
temporal changes in Titan's atmospheric circulation during northern spring. Our
derived abundance profiles are comparable to contemporary measurements from
Cassini infrared observations, and we find additional evidence for subsidence
of enriched air onto Titan's south pole during this time period. Continued
observations of Titan with ALMA beyond the summer solstice will enable further
study of how Titan's atmospheric composition and dynamics respond to seasonal
changes.Comment: 15 pages, 16 figures, 2 tables. Accepted for publication in Icarus,
September 201
Finding secluded places of special interest in graphs.
Finding a vertex subset in a graph that satisfies a certain property is one of the most-studied topics
in algorithmic graph theory. The focus herein is often on minimizing or maximizing the size
of the solution, that is, the size of the desired vertex set. In several applications, however, we also
want to limit the “exposure” of the solution to the rest of the graph. This is the case, for example,
when the solution represents persons that ought to deal with sensitive information or a segregated
community. In this work, we thus explore the (parameterized) complexity of finding such secluded
vertex subsets for a wide variety of properties that they shall fulfill. More precisely, we study the
constraint that the (open or closed) neighborhood of the solution shall be bounded by a parameter
and the influence of this constraint on the complexity of minimizing separators, feedback vertex
sets, F-free vertex deletion sets, dominating sets, and the maximization of independent sets
Finding secluded places of special interest in graphs
Finding a vertex subset in a graph that satisfies a certain property is one of the most-studied topics in algorithmic graph theory. The focus herein is often on minimizing or maximizing the size of the solution, that is, the size of the desired vertex set. In several applications, however, we also want to limit the “exposure” of the solution to the rest of the graph. This is the case, for example, when the solution represents persons that ought to deal with sensitive information or a segregated community. In this work, we thus explore the (parameterized) complexity of finding such secluded vertex subsets for a wide variety of properties that they shall fulfill. More precisely, we study the constraint that the (open or closed) neighborhood of the solution shall be bounded by a parameter and the influence of this constraint on the complexity of minimizing separators, feedback vertex sets, F-free vertex deletion sets, dominating sets, and the maximization of independent sets
- …