180 research outputs found
Reduction Techniques for Graph Isomorphism in the Context of Width Parameters
We study the parameterized complexity of the graph isomorphism problem when
parameterized by width parameters related to tree decompositions. We apply the
following technique to obtain fixed-parameter tractability for such parameters.
We first compute an isomorphism invariant set of potential bags for a
decomposition and then apply a restricted version of the Weisfeiler-Lehman
algorithm to solve isomorphism. With this we show fixed-parameter tractability
for several parameters and provide a unified explanation for various
isomorphism results concerned with parameters related to tree decompositions.
As a possibly first step towards intractability results for parameterized graph
isomorphism we develop an fpt Turing-reduction from strong tree width to the a
priori unrelated parameter maximum degree.Comment: 23 pages, 4 figure
Fermi-LAT Observation of Supernova Remnant S147
We present an analysis of gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region
around SNR S147 (G180.0-1.7). A spatially extended gamma-ray source detected in
an energy range of 0.2--10 GeV is found to coincide with SNR S147. We confirm
its spatial extension at >5sigma confidence level. The gamma-ray flux is (3.8
\pm 0.6) x 10^{-8} photons cm^{-2} s^{-1}, corresponding to a luminosity of 1.3
x 10^{34} (d/1.3 kpc)^2 erg s^{-1} in this energy range. The gamma-ray emission
exhibits a possible spatial correlation with prominent Halpha filaments of
S147. There is no indication that the gamma-ray emission comes from the
associated pulsar PSR J0538+2817. The gamma-ray spectrum integrated over the
remnant is likely dominated by the decay of neutral pi mesons produced through
the proton--proton collisions in the filaments. Reacceleration of pre-existing
CRs and subsequent adiabatic compression in the filaments is sufficient to
provide the required energy density of high-energy protons.Comment: 12 pages, accepted for publication in Ap
Bipolar cemented hip hemiarthroplasty in patients with femoral neck fracture who are on hemodialysis is associated with risk of stem migration
Background and purpose Femoral neck fractures are considerably more common in patients on hemodialysis than in the general population. We determined the outcome of bipolar hemiarthroplasty for hip fracture in patients with long-term hemodialysis and compared it with that of a matched-paired group of patients with intact renal function
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