681 research outputs found
Decomposition of 3-connected cubic graphs
AbstractWe solve a conjecture of Foulds and Robinson (1979) on decomposable triangulations in the plane, in the more general context of a decomposition theory of cubic 3-connected graphs. The decomposition gives us a natural way to obtain some known results about specific homeomorphic subgraphs and the extremal diameter of 3-connected cubic graphs
The Formation of Large Galactic Disks: Revival or Survival?
Using the deepest and the most complete set of observations of distant
galaxies, we investigate how extended disks could have formed. Observations
include spatially-resolved kinematics, detailed morphologies and photometry
from UV to mid-IR. Six billion years ago, half of the present-day spiral
progenitors had anomalous kinematics and morphologies, as well as relatively
high gas fractions. We argue that gas-rich major mergers, i.e., fusions between
gas-rich disk galaxies of similar mass, can be the likeliest driver for such
strong peculiarities. This suggests a new channel of disk formation, e.g. many
disks could be reformed after gas-rich mergers. This is found to be in perfect
agreement with predictions from the state-of-the-art LCDM semi-empirical
models: due to our sensitivity in detecting mergers at all phases, from pairs
to relaxed post-mergers, we find a more accurate merger rate. The scenario can
be finally confronted to properties of nearby galaxies, including M31 and
galaxies showing ultra-faint, gigantic structures in their haloes.Comment: Proceedings of the annual meeting of the French Astronomical Society,
2011, 6 pages, 1 Figur
Computing Hilbert Class Polynomials
We present and analyze two algorithms for computing the Hilbert class
polynomial . The first is a p-adic lifting algorithm for inert primes p
in the order of discriminant D < 0. The second is an improved Chinese remainder
algorithm which uses the class group action on CM-curves over finite fields.
Our run time analysis gives tighter bounds for the complexity of all known
algorithms for computing , and we show that all methods have comparable
run times
The Milky Way and other spiral galaxies
Cosmologists have often considered the Milky Way as a typical spiral galaxy,
and its properties have considerably influenced the current scheme of galaxy
formation. Here we compare the general properties of the Milky Way disk and
halo with those of galaxies selected from the SDSS. Assuming the recent
measurements of its circular velocity results in the Milky Way being offset by
~2 sigma from the fundamental scaling relations. On the basis of their location
in the (M_K, R_d, V_flat) volume, the fraction of SDSS spirals like the
MilkyWay is only 1.2% in sharp contrast with M31, which appears to be quite
typical. Comparison of the Milky Way with M31 and with other spirals is also
discussed to investigate whether or not there is a fundamental discrepancy
between their mass assembly histories. Possibly the Milky Way is one of the
very few local galaxies that could be a direct descendant of very distant,
z=2-3 galaxies, thanks to its quiescent history since thick disk formation.Comment: 4 pages, 1 Figure, to appear in the Proceedings of the Conference
"Assembling the Puzzle of the Milky Way", held at Le Grand Bornand, April
201
Le crédit agricole dans la filière-bois
Le crédit agricole a vu peu à peu ses possibilités d'intervention accrues ; il peut maintenant intervenir à tous les stades de la filière-bois. Il est également le financier des collectivités locales pour leurs activités sylvicoles
Bounded Search Tree Algorithms for Parameterized Cograph Deletion: Efficient Branching Rules by Exploiting Structures of Special Graph Classes
Many fixed-parameter tractable algorithms using a bounded search tree have
been repeatedly improved, often by describing a larger number of branching
rules involving an increasingly complex case analysis. We introduce a novel and
general search strategy that branches on the forbidden subgraphs of a graph
class relaxation. By using the class of -sparse graphs as the relaxed
graph class, we obtain efficient bounded search tree algorithms for several
parameterized deletion problems. We give the first non-trivial bounded search
tree algorithms for the cograph edge-deletion problem and the trivially perfect
edge-deletion problems. For the cograph vertex deletion problem, a refined
analysis of the runtime of our simple bounded search algorithm gives a faster
exponential factor than those algorithms designed with the help of complicated
case distinctions and non-trivial running time analysis [21] and computer-aided
branching rules [11].Comment: 23 pages. Accepted in Discrete Mathematics, Algorithms and
Applications (DMAA
Which factors and situations for human functional failures? Developing grids for accident causation analysis
This report describes the work undertaken in Task 5.2 of the TRACE project. Human failures are
explained by factors characterizing the state of the system and of their interactions. A grid of factors
which could lead to these human functional failures is given along with a grid of pre-accident driving
situations. In addition to this, an overview is included of the background work undertaken to
establish a methodology for classification of these factors and situations. Factors related to the ‘User’,
‘Vehicle’ and ‘Environment’ are described and classifications for use at a ‘descriptive’, ‘generic’ and
‘in-depth’ level are determined, to allow analysis at different levels of detail of accident data. These
factors and situations will be used along with the Task 5.1 functional failures to help identify typical
failure generating scenarios in Task 5.3, and the subsequent analysis of real world accident data in
other work packages in TRACE. They will also be a useful basis for future improvements in the
collection of accident causation data, avoiding the common over simplification whereby road users
are seen as the main reason for the ‘failure’ in the accident scenario
Could M31 come from a major merger and eject the LMC away?
We investigated a scenario in which M31 could be the remnant of a major
merger and at the origin of the LMC. Galaxy merger simulations were run in
order to reproduce some M31 properties. We succeeded in reproducing some of the
most important M31 large-scale features like the thick disk or the polar ring,
and gave a possible explanation for the formation of the Giant Stream. We also
found that the LMC could be expelled by this high energetic phenomenon.Comment: 4 pages, 2 figures, Proceeding IAU277; more information on coordinate
system for the LMC proper motio
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