87,940 research outputs found
The average mixing matrix signature
Laplacian-based descriptors, such as the Heat Kernel Signature and the Wave Kernel Signature, allow one to embed the vertices of a graph onto a vectorial space, and have been successfully used to find the optimal matching between a pair of input graphs. While the HKS uses a heat di↵usion process to probe the local structure of a graph, the WKS attempts to do the same through wave propagation. In this paper, we propose an alternative structural descriptor that is based on continuoustime quantum walks. More specifically, we characterise the structure of a graph using its average mixing matrix. The average mixing matrix is a doubly-stochastic matrix that encodes the time-averaged behaviour of a continuous-time quantum walk on the graph. We propose to use the rows of the average mixing matrix for increasing stopping times to develop a novel signature, the Average Mixing Matrix Signature (AMMS). We perform an extensive range of experiments and we show that the proposed signature is robust under structural perturbations of the original graphs and it outperforms both the HKS and WKS when used as a node descriptor in a graph matching task
A novel entropy-based graph signature from the average mixing matrix
In this paper, we propose a novel entropic signature for graphs, where we probe the graphs by means of continuous-time quantum walks. More precisely, we characterise the structure of a graph through its average mixing matrix. The average mixing matrix is a doubly-stochastic matrix that encapsulates the time-averaged behaviour of a continuous-time quantum walk on the graph, i.e., the ij-th element of the average mixing matrix represents the time-averaged transition probability of a continuous-time quantum walk from the vertex vi to the vertex vj. With this matrix to hand, we can associate a probability distribution with each vertex of the graph. We define a novel entropic signature by concatenating the average Shannon entropy of these probability distributions with their Jensen-Shannon divergence. We show that this new entropic measure can encaspulate the rich structural information of the graphs, thus allowing to discriminate between different structures. We explore the proposed entropic measure on several graph datasets abstracted from bioinformatics databases and we compare it with alternative entropic signatures in the literature. The experimental results demonstrate the effectiveness and efficiency of our method
Violation and persistence of the K-quantum number in warm rotating nuclei
The validity of the K-quantum number in rapidly rotating warm nuclei is
investigated as a function of thermal excitation energy U and angular momentum
I, for the rare-earth nucleus 163Er. The quantal eigenstates are described with
a shell model which combines a cranked Nilsson mean-field and a residual
two-body interaction, together with a term which takes into account the angular
momentum carried by the K-quantum number in an approximate way. K-mixing is
produced by the interplay of the Coriolis interaction and the residual
interaction; it is weak in the region of the discrete rotational bands (U
\lesim 1MeV), but it gradually increases until the limit of complete violation
of the K-quantum number is approached around U \sim 2 - 2.5 MeV. The calculated
matrix elements between bands having different K-quantum numbers decrease
exponentially as a function of , in qualitative agreement with recent
data.Comment: 29 pages, 7 figure
Irregularity in gamma ray source spectra as a signature of axionlike particles
Oscillations from high energy photons into light pseudoscalar particles in an
external magnetic field are expected to occur in some extensions of the
standard model. It is usually assumed that those axionlike particles (ALPs)
could produce a drop in the energy spectra of gamma ray sources and possibly
decrease the opacity of the Universe for TeV gamma rays. We show here that
these assumptions are in fact based on an average behavior that cannot happen
in real observations of single sources. We propose a new method to search for
photon-ALP oscillations, taking advantage of the fact that a single observation
would deviate from the average expectation. Our method is based on the search
for irregularities in the energy spectra of gamma ray sources. We predict
features that are unlikely to be produced by known astrophysical processes and
a new signature of ALPs that is easily falsifiable.Comment: 6 pages, 3 figures, matches accepted version, improved discussion on
magnetic field models in v
Production of Stop, Sbottom, and Stau at LEP2
We present a comprehensive study of pair production and decay of stops,
sbottoms, and staus in annihilation at LEP2. We give numerical
predictions within the Minimal Supersymmetric Standard Model for cross sections
and decay rates, and discuss the important signatures. In the case of stau
production we also study the polarization of the tau in the decays stau_1 ->
tau + neutralino_{1,2}.Comment: 15 pages, LateX, 13 figures appended as uuencoded PS-file. LateX file
and figures are also available via anonymous ftp at
ftp://info.oeaw.ac.at/pub/hephy-pub/64
Determining the Spectral Signature of Spatial Coherent Structures
We applied to an open flow a proper orthogonal decomposition (pod) technique,
on 2D snapshots of the instantaneous velocity field, to reveal the spatial
coherent structures responsible of the self-sustained oscillations observed in
the spectral distribution of time series. We applied the technique to 2D planes
out of 3D direct numerical simulations on an open cavity flow. The process can
easily be implemented on usual personal computers, and might bring deep
insights on the relation between spatial events and temporal signature in (both
numerical or experimental) open flows.Comment: 4 page
Possible Capture of keV Sterile Neutrino Dark Matter on Radioactive beta-decaying Nuclei
There exists an observed "desert" spanning six orders of magnitude between
O(0.5) eV and O(0.5) MeV in the fermion mass spectrum. We argue that it might
accommodate one or more keV sterile neutrinos as a natural candidate for warm
dark matter. To illustrate this point of view, we simply assume that there is
one keV sterile neutrino nu_4 and its flavor eigenstate nu_s weakly mixes with
three active neutrinos. We clarify different active-sterile neutrino mixing
factors for the radiative decay of nu_4 and beta decays in a self-consistent
parametrization. A direct detection of this keV sterile neutrino dark matter in
the laboratory is in principle possible since the nu_4 component of nu_e can
leave a distinct imprint on the electron energy spectrum when it is captured on
radioactive beta-decaying nuclei. We carry out an analysis of its signatures in
the capture reactions nu_e + ^{3}H \to ^{3}He + e^- and nu_e + ^{106}Ru \to
^{106}Rh + e^- against the beta-decay backgrounds, and conclude that this
experimental approach might not be hopeless in the long run.Comment: 14 pages, 3 figures, more discussions and references added. To appear
in PL
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