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

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

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

Physical, chemical and biological variability in the Dr. C. Gelsi reservoir(NW Argentine) : a temporal and spatial approach

With the purpose of understanding the phytoplankton dynamics in two vertical profiles of the Dr. C. Gelsi reservoir (Tucumán, Argentina, monthly samplings were conducted from October 1997 to March 1999 in the limnetic zone and at the intersection of the Salí and Tapia tributary. The reservoir was characterized as warm monomictic, with bicarbonate, chloride, sodium, calcium and/or magnesium waters. In both sites total nitrogen concentration was higher than 1 mg/l, whereas that of orthophosphate reached 0.2 mg/l. Out of the eleven organochlorine pesticides analyzed, the presence mainly of lindane and methoxychlor, with higher concentrations in the warm months was confirmed. Bacterial load values were compatible with water quality standards, and variations in the number of actinomycetes colonies in the sediments were correlated, among other parameters, with dissolved oxygen. In the two zones studied a total of 57 phytoplankton taxa, 49 % green algae, 37 % diatoms, 9 % Cyanobacteria and 5 % dinoflagelates, were identified. Central diatoms (Aulacoseira granulata and Cyclotella meneghiniana) prevailed in the phytoplankton and, in a lesser degree, the other groups, low values of specific diversity being obtained. A principal components analysis based on the absolute abundance of species and on some physico-chemical parameters ordinated the samples of the various levels, this abundance being more evident in the limnetic zone. There was also a tendency to the separation of stratifications from the two consecutive years and homogeneity in the samples from the mixing period was noticed. On the basis of the saprobic index, water quality was from β − α-mesosaprobic to α-mesosaprobic.Con el objeto de interpretar la dinámica del fitoplancton en dos perfiles verticales del embalse Dr. C. Gelsi (Tucumán, Argentina), se realizaron muestreos mensuales desde octubre de 1997 a marzo de 1999, en la zona limnética y en la intersección de los tributarios, ríos Salí y Tapia. El embalse fue caracterizado como monomíctico cálido, con aguas bicarbonatadas, cloruradas, sódicas, cálcicas y/o magnésicas. En ambos sitios, la concentración media de nitrógeno total fue superior a 1 mg/l, mientras que la de ortofosfato llegó a 0.2 mg/l. De los once plaguicidas organoclorados analizados se comprobó, principalmente, la presencia de lindano y metoxicloro, con concentraciones más elevadas en los meses cálidos. Los valores de carga bacteriana fueron compatibles con las normas de calidad de agua y las variaciones del número de colonias de actinomycetes en los sedimentos estuvieron correlacionadas entre otros parámetros con el oxígeno disuelto. En las dos zonas estudiadas se identificaron un total de 57 taxones: 49 % algas verdes, 37 % diatomeas, 9 % Cyanobacteria y 5 % dinoflagelados. Las diatomeas centrales (Aulacoseira granulata y Cyclotella meneghiniana) predominaron en el fitoplancton y en menor orden, los otros grupos, obteniéndose bajos valores de diversidad específica. Los análisis de componentes principales basados en la abundancia absoluta de las especies y en algunos parámetros fisicoquímicos, ordenaron las muestras de los distintos niveles, siendo ésta más evidente en la zona limnética. Asimismo, hubo una tendencia a la separación de las estratificaciones de los dos años consecutivos y se observó homogeneidad en las muestras provenientes del período de mezcla. Sobre la base del índice sapróbico, la calidad del agua fue β − α-mesosapróbicas a α-mesosapróbicas

Scattering evaluation of equivalent surface impedances of acoustic metamaterials in large FDTD volumes using RLC circuit modelling

Most simulations involving metamaterials often require complex physics to be solved through refined meshing grids. However, it can prove challenging to simulate the effect of local physical conditions created by said metamaterials into much wider computing sceneries due to the increased meshing load. We thus present in this work a framework for simulating complex structures with detailed geometries, such as metamaterials, into large Finite-Difference Time-Domain (FDTD) computing environments by reducing them to their equivalent surface impedance represented by a parallel-series RLC circuit. This reduction helps to simplify the physics involved as well as drastically reducing the meshing load of the model and the implicit calculation time. Here, an emphasis is made on scattering comparisons between an acoustic metamaterial and its equivalent surface impedance through analytical and numerical methods. Additionally, the problem of fitting RLC parameters to complex impedance data obtained from transfer matrix models is herein solved using a novel approach based on zero crossings of admittance phase derivatives. Despite the simplification process, the proposed framework achieves good overall results with respect to the original acoustic scatterer while ensuring relatively short simulation times over a vast range of frequencies