5,598 research outputs found
Complexity dichotomy on partial grid recognition
Deciding whether a graph can be embedded in a grid using only unit-length
edges is NP-complete, even when restricted to binary trees. However, it is not
difficult to devise a number of graph classes for which the problem is
polynomial, even trivial. A natural step, outstanding thus far, was to provide
a broad classification of graphs that make for polynomial or NP-complete
instances. We provide such a classification based on the set of allowed vertex
degrees in the input graphs, yielding a full dichotomy on the complexity of the
problem. As byproducts, the previous NP-completeness result for binary trees
was strengthened to strictly binary trees, and the three-dimensional version of
the problem was for the first time proven to be NP-complete. Our results were
made possible by introducing the concepts of consistent orientations and robust
gadgets, and by showing how the former allows NP-completeness proofs by local
replacement even in the absence of the latter
Metric Dimension for Gabriel Unit Disk Graphs is NP-Complete
We show that finding a minimal number of landmark nodes for a unique virtual
addressing by hop-distances in wireless ad-hoc sensor networks is NP-complete
even if the networks are unit disk graphs that contain only Gabriel edges. This
problem is equivalent to Metric Dimension for Gabriel unit disk graphs. The
Gabriel edges of a unit disc graph induce a planar O(\sqrt{n}) distance and an
optimal energy spanner. This is one of the most interesting restrictions of
Metric Dimension in the context of wireless multi-hop networks.Comment: A brief announcement of this result has been published in the
proceedings of ALGOSENSORS 201
Galaxy cluster mergers as triggers for the formation of jellyfish galaxies: case study of the A901/2 system
The A901/2 system is a rare case of galaxy cluster interaction, in which two
galaxy clusters and two smaller groups are seen in route of collision with each
other simultaneously. Within each of the four substructures, several galaxies
with features indicative of jellyfish morphologies have been observed. In this
paper, we propose a hydrodynamic model for the merger as a whole, compatible
with its diffuse X-ray emission, and correlate the gas properties in this model
with the locations of the jellyfish galaxy candidates in the real system. We
find that jellyfish galaxies seem to be preferentially located near a boundary
inside each subcluster where diffuse gas moving along with the subcluster and
diffuse gas from the remainder of the system meet. The velocity change in those
boundaries is such that a factor of up to 1000 increase in the ram
pressure takes place within a few hundred kpc, which could trigger the high
rate of gas loss necessary for a jellyfish morphology to emerge. A theoretical
treatment of ram pressure stripping in the environment of galaxy cluster
mergers has not been presented in the literature so far; we propose that this
could be a common scenario for the formation of jellyfish morphologies in such
systems.Comment: Accepted for publication in MNRAS. 10 pages, 9 figure
Advanced Vehicle Tracking system using GSM/GPRS and GPS
Vehicle Tracker is a Universal Anti-Larceny System for all kinds of motorcycles. The gadget is inserted inside a vehicle whose position is to be resolved and followed continuously. The composed device works utilizing Global Positioning System (GPS) and Global system for mobile communication/General Packet Radio Service (GSM/GPRS) technology that is the most widely recognized courses for vehicle tracking system. GPS and high sensitivity antenna are used for effective and precise location tracking of motorcycle through mobile application. Accelerometer sensor will alert the user of a possible larceny by detecting the slightest transition of the motorcycle. Immobilizer relay to remotely enable/incapacitate motorcycle ignition. Ignition switch status monitoring is utilized to detect key insertion. Fuel level sensor used to detect fuel larceny and to determine the information about fuel level in automobile tank
Self-Assembly of 4-sided Fractals in the Two-handed Tile Assembly Model
We consider the self-assembly of fractals in one of the most well-studied
models of tile based self-assembling systems known as the Two-handed Tile
Assembly Model (2HAM). In particular, we focus our attention on a class of
fractals called discrete self-similar fractals (a class of fractals that
includes the discrete Sierpi\'nski carpet). We present a 2HAM system that
finitely self-assembles the discrete Sierpi\'nski carpet with scale factor 1.
Moreover, the 2HAM system that we give lends itself to being generalized and we
describe how this system can be modified to obtain a 2HAM system that finitely
self-assembles one of any fractal from an infinite set of fractals which we
call 4-sided fractals. The 2HAM systems we give in this paper are the first
examples of systems that finitely self-assemble discrete self-similar fractals
at scale factor 1 in a purely growth model of self-assembly. Finally, we show
that there exists a 3-sided fractal (which is not a tree fractal) that cannot
be finitely self-assembled by any 2HAM system
Optimal self-assembly of finite shapes at temperature 1 in 3D
Working in a three-dimensional variant of Winfree's abstract Tile Assembly
Model, we show that, for an arbitrary finite, connected shape , there is a tile set that uniquely self-assembles into a 3D
representation of a scaled-up version of at temperature 1 in 3D with
optimal program-size complexity (the "program-size complexity", also known as
"tile complexity", of a shape is the minimum number of tile types required to
uniquely self-assemble it). Moreover, our construction is "just barely" 3D in
the sense that it only places tiles in the and planes. Our
result is essentially a just-barely 3D temperature 1 simulation of a similar 2D
temperature 2 result by Soloveichik and Winfree (SICOMP 2007)
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