21,260 research outputs found
Kernel-based Inference of Functions over Graphs
The study of networks has witnessed an explosive growth over the past decades
with several ground-breaking methods introduced. A particularly interesting --
and prevalent in several fields of study -- problem is that of inferring a
function defined over the nodes of a network. This work presents a versatile
kernel-based framework for tackling this inference problem that naturally
subsumes and generalizes the reconstruction approaches put forth recently by
the signal processing on graphs community. Both the static and the dynamic
settings are considered along with effective modeling approaches for addressing
real-world problems. The herein analytical discussion is complemented by a set
of numerical examples, which showcase the effectiveness of the presented
techniques, as well as their merits related to state-of-the-art methods.Comment: To be published as a chapter in `Adaptive Learning Methods for
Nonlinear System Modeling', Elsevier Publishing, Eds. D. Comminiello and J.C.
Principe (2018). This chapter surveys recent work on kernel-based inference
of functions over graphs including arXiv:1612.03615 and arXiv:1605.07174 and
arXiv:1711.0930
A Novel Approach to Multimedia Ontology Engineering for Automated Reasoning over Audiovisual LOD Datasets
Multimedia reasoning, which is suitable for, among others, multimedia content
analysis and high-level video scene interpretation, relies on the formal and
comprehensive conceptualization of the represented knowledge domain. However,
most multimedia ontologies are not exhaustive in terms of role definitions, and
do not incorporate complex role inclusions and role interdependencies. In fact,
most multimedia ontologies do not have a role box at all, and implement only a
basic subset of the available logical constructors. Consequently, their
application in multimedia reasoning is limited. To address the above issues,
VidOnt, the very first multimedia ontology with SROIQ(D) expressivity and a
DL-safe ruleset has been introduced for next-generation multimedia reasoning.
In contrast to the common practice, the formal grounding has been set in one of
the most expressive description logics, and the ontology validated with
industry-leading reasoners, namely HermiT and FaCT++. This paper also presents
best practices for developing multimedia ontologies, based on my ontology
engineering approach
Statistical multi-moment bifurcations in random delay coupled swarms
We study the effects of discrete, randomly distributed time delays on the
dynamics of a coupled system of self-propelling particles. Bifurcation analysis
on a mean field approximation of the system reveals that the system possesses
patterns with certain universal characteristics that depend on distinguished
moments of the time delay distribution. Specifically, we show both
theoretically and numerically that although bifurcations of simple patterns,
such as translations, change stability only as a function of the first moment
of the time delay distribution, more complex patterns arising from Hopf
bifurcations depend on all of the moments
Cosmological Constant and Noncommutativity: A Newtonian point of view
We study a Newtonian cosmological model in the context of a noncommutative
space. It is shown that the trajectories of a test particle undergo
modifications such that it no longer satisfies the cosmological principle. For
the case of a positive cosmological constant, spiral trajectories are obtained
and corrections to the Hubble constant appear. It is also shown that, in the
limit of a strong noncommutative parameter, the model is closely related to a
particle in a G\"odel-type metric.Comment: 14 pages, 3 figures, Introduction was changed and references added.
Final version accepted for publication in JMPL
The polar ring galaxy AM1934-563 revisited
We report long-slit spectroscopic observations of the dust-lane polar-ring
galaxy AM1934-563 obtained with the Southern African Large Telescope (SALT)
during its performance-verification phase. The observations target the spectral
region of the Ha, [NII] and [SII] emission-lines, but show also deep NaI
stellar absorption lines that we interpret as produced by stars in the galaxy.
We derive rotation curves along the major axis of the galaxy that extend out to
about 8 kpc from the center for both the gaseous and the stellar components,
using the emission and absorption lines. We derive similar rotation curves
along the major axis of the polar ring and point out differences between these
and the ones of the main galaxy. We identify a small diffuse object visible
only in Ha emission and with a low velocity dispersion as a dwarf HII galaxy
and argue that it is probably metal-poor. Its velocity indicates that it is a
fourth member of the galaxy group in which AM1934-563 belongs. We discuss the
observations in the context of the proposal that the object is the result of a
major merger and point out some observational discrepancies from this
explanation. We argue that an alternative scenario that could better fit the
observations may be the slow accretion of cold intergalactic gas, focused by a
dense filament of galaxies in which this object is embedded (abridged).Comment: 19 pages, 13 figures, submitted to MNRAS. Some figures were bitmapped
to reduce the size. Full resolution version is available from
http://www.saao.ac.za/~akniazev/pub/AM1934_563.pd
Directed transport as a mechanism for protein folding in vivo
We propose a model for protein folding in vivo based on a Brownian-ratchet
mechanism in the multidimensional energy landscape space. The device is able to
produce directed transport taking advantage of the assumed intrinsic asymmetric
properties of the proteins and employing the consumption of energy provided by
an external source. Through such a directed transport phenomenon, the
polypeptide finds the native state starting from any initial state in the
energy landscape with great efficacy and robustness, even in the presence of
different type of obstacles. This model solves Levinthal's paradox without
requiring biased transition probabilities but at the expense of opening the
system to an external field.Comment: 16 pages, 7 figure
On the order of BEC transition in weakly interacting gases predicted by mean-field theory
Predictions from Hartree-Fock (HF), Popov (P), Yukalov-Yukalova (YY) and
-matrix approximations regarding the thermodynamics from the normal to the
BEC phase in weakly interacting Bose gases are considered. By analyzing the
dependence of the chemical potential on temperature and particle
density we show that none of them predicts a second-order phase
transition as required by symmetry-breaking general considerations. In this
work we find that the isothermal compressibility predicted by
these theories does not diverge at criticality as expected in a true
second-order phase transition. Moreover the isotherms
typically exhibit a non-singled valued behavior in the vicinity of the BEC
transition, a feature forbidden by general thermodynamic principles. This
behavior can be avoided if a first order phase transition is appealed. The
facts described above show that although these mean field approximations give
correct results near zero temperature they are endowed with thermodynamic
anomalies in the vicinity of the BEC transition. We address the implications of
these results in the interpretation of current experiments with ultracold
trapped alkali gases.Comment: 16 pages, 5 figure
The metallicity extremes of the Sagittarius dSph using SALT spectroscopy of PNe
In this work we present the first spectroscopic results obtained with the
Southern African Large Telescope (SALT) telescope during its
perfomance-verification phase. We find that the Sagittarius dwarf spheroidal
galaxy (Sgr) Sgr contains a youngest stellar population with [O/H] -0.2 and age
t>1 Gyr, and an oldest population with [O/H]=-2.0. The values are based on
spectra of two planetary nebulae (PNe), using empirical abundance
determinations. We calculated abundances for O, N, Ne, Ar, S, Cl, Fe, C and He.
We confirm the high abundances of PN StWr2-21 with 12+log(O/H) = 8.57+/-0.02
dex. The other PN studied, BoBn1, is an extraordinary object in that the neon
abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn1 yield
the original stellar metallicity, corresponding to 12+log(O/H) = 6.72+/-0.16
dex which is 1/110 of the solar value. The actual [O/H] is much higher: third
dredge-up enriched the material by a factor of ~12 in oxygen, ~240 in nitrogen
and ~70 in neon. Neon as well as nitrogen and oxygen content may have been
produced in the intershell of low-mass AGB stars. Well defined broad WR lines
are present in the spectrum of StWr2-21 and absent in the spectrum of BoBn1.
This puts the fraction of [WR]-type central PNe stars to 67% for dSph galaxies.Comment: 14 pages, 4 figures, accepted to MNRA
Ground-state dispersion and density of states from path-integral Monte Carlo. Application to the lattice polaron
A formula is derived that relates the ground-state dispersion of a many-body
system with the end-to-end distribution of paths with open boundary conditions
in imaginary time. The formula does not involve the energy estimator. It allows
direct measurement of the ground-state dispersion by quantum Monte Carlo
methods without analytical continuation or auxiliary fitting. The formula is
applied to the lattice polaron problem. The exact polaron spectrum and density
of states are calculated for several models in one, two, and three dimensions.
In the adiabatic regime of the Holstein model, the polaron density of states
deviates spectacularly from the free-particle shape.Comment: 8 pages, 9 figure
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