On the use of machine learning algorithms in the measurement of stellar magnetic fields

Regression methods based in Machine Learning Algorithms (MLA) have become an important tool for data analysis in many different disciplines. In this work, we use MLA in an astrophysical context; our goal is to measure the mean longitudinal magnetic field in stars (H_ eff) from polarized spectra of high resolution, through the inversion of the so-called multi-line profiles. Using synthetic data, we tested the performance of our technique considering different noise levels: In an ideal scenario of noise-free multi-line profiles, the inversion results are excellent; however, the accuracy of the inversions diminish considerably when noise is taken into account. In consequence, we propose a data pre-process in order to reduce the noise impact, which consists in a denoising profile process combined with an iterative inversion methodology. Applying this data pre-process, we have found a considerable improvement of the inversions results, allowing to estimate the errors associated to the measurements of stellar magnetic fields at different noise levels. We have successfully applied our data analysis technique to two different stars, attaining by first time the measurement of H_eff from multi-line profiles beyond the condition of line autosimilarity assumed by other techniques.Comment: Accepted for publication in A&

Network conduciveness with application to the graph-coloring and independent-set optimization transitions

We introduce the notion of a network's conduciveness, a probabilistically interpretable measure of how the network's structure allows it to be conducive to roaming agents, in certain conditions, from one portion of the network to another. We exemplify its use through an application to the two problems in combinatorial optimization that, given an undirected graph, ask that its so-called chromatic and independence numbers be found. Though NP-hard, when solved on sequences of expanding random graphs there appear marked transitions at which optimal solutions can be obtained substantially more easily than right before them. We demonstrate that these phenomena can be understood by resorting to the network that represents the solution space of the problems for each graph and examining its conduciveness between the non-optimal solutions and the optimal ones. At the said transitions, this network becomes strikingly more conducive in the direction of the optimal solutions than it was just before them, while at the same time becoming less conducive in the opposite direction. We believe that, besides becoming useful also in other areas in which network theory has a role to play, network conduciveness may become instrumental in helping clarify further issues related to NP-hardness that remain poorly understood

Foliations and Chern-Heinz inequalities

We extend the Chern-Heinz inequalities about mean curvature and scalar curvature of graphs of $C^{2}$-functions to leaves of transversally oriented codimension one $C^{2}$-foliations of Riemannian manifolds. That extends partially Salavessa's work on mean curvature of graphs and generalize results of Barbosa-Kenmotsu-Oshikiri \cite{barbosa-kenmotsu-Oshikiri} and Barbosa-Gomes-Silveira \cite{barbosa-gomes-silveira} about foliations of 3-dimensional Riemannian manifolds by constant mean curvature surfaces. These Chern-Heinz inequalities for foliations can be applied to prove Haymann-Makai-Osserman inequality (lower bounds of the fundamental tones of bounded open subsets $\Omega \subset \mathbb{R}^{2}$ in terms of its inradius) for embedded tubular neighborhoods of simple curves of $\mathbb{R}^{n}$.Comment: This paper is an improvment of an earlier paper titled On Chern-Heinz Inequalities. 8 Pages, Late

Confronting cold dark matter cosmologies with strong clustering of Lyman break galaxies at z∼3z\sim3

We perform a detailed analysis of the statistical significance of a concentration of Lyman break galaxies at $z \sim 3$ recently discovered by Steidel et al. (1997), using a series of N-body simulations with $N=256^3$ particles in a (100\himpc)^3 comoving box. While the observed number density of Lyman break galaxies at $z\sim3$ implies that they correspond to systems with dark matter halos of \simlt 10^{12}M_\odot, the resulting clustering of such objects on average is not strong enough to be reconciled with the concentration if it is fairly common; we predict one similar concentration approximately per ($6\sim 10$) fields in three representative cold dark matter models. Considering the current observational uncertainty of the frequency of such clustering at $z\sim3$, it would be premature to rule out the models, but the future spectroscopic surveys in a dozen fields could definitely challenge all the existing cosmological models a posteriori fitted to the $z=0$ universe.Comment: the final version which matchs that published in ApJ Letters (Feb 1998); compared with the previous versions, the predictions for the SCDM model are slightly changed; Latex, 11 pages, including 3 ps figure

The Effect of Radiative Cooling on the Sunyaev-Zel'dovich Cluster Counts and Angular Power Spectrum: Analytic Treatment

Recently, the entropy excess detected in the central cores of groups and clusters has been successfully interpreted as being due to radiative cooling of the hot intragroup/intracluster gas. In such a scenario, the entropy floors $S_{\rm floor}$ in groups/clusters at any given redshift are completely determined by the conservation of energy. In combination with the equation of hydrostatic equilibrium and the universal density profile for dark matter, this allows us to derive the remaining gas distribution of groups and clusters after the cooled material is removed. Together with the Press-Schechter mass function we are able to evaluate effectively how radiative cooling can modify the predictions of SZ cluster counts and power spectrum. It appears that our analytic results are in good agreement with those found by hydrodynamical simulations. Namely, cooling leads to a moderate decrease of the predicted SZ cluster counts and power spectrum as compared with standard scenario. However, without taking into account energy feedback from star formation which may greatly suppress cooling efficiency, it is still premature to claim that this modification is significant for the cosmological applications of cluster SZ effect.Comment: 16 pages, 3 figures, uses aastex.cls. ApJ accepte

Behavioural validation of the ADACOR2 Self-organized holonic multi-agent manufacturing system

Global economy is driving manufacturing companies into a paradigm revolution. Highly customizable products at lower prices and with higher quality are among the most imposed influence factors. To respond properly to these external and internal constraints, such as work absence and machine failures, companies must be in a constant adaptation phase. Several manufacturing control architectures have been proposed throughout the years displaying more or less success to adapt into different manufacturing situations. These architectures follow different design paradigms but recently the decentralization and distribution of the processing power into a set of cooperating and collaborative entities is becoming the trend. Despite of the effort spent, there is still the need to empower those architectures with evolutionary capabilities and self-organization mechanisms to enable the constant adaption to disturbances. This paper presents a behavioural mechanism embed in the ADACOR2 holons. A validation procedure for this mechanism is also presented and results extracted. This validation is achieved through the use of a benchmark and results are compared with classical hierarchical and heterarchical architectures as also with the ADACOR.info:eu-repo/semantics/publishedVersio

LANDSAT and radar mapping of intrusive rocks in SE-Brazil

The feasibility of intrusive rock mapping was investigated and criteria for regional geological mapping established at the scale of 1:500,00 in polycyclic and polymetamorphic areas using the logic method of photointerpretation of LANDSAT imagery and radar from the RADAMBRASIL project. The spectral behavior of intrusive rocks, was evaluated using the interactive multispectral image analysis system (Image-100). The region of Campos (city) in northern Rio de Janeiro State was selected as the study area and digital imagery processing and pattern recognition techniques were applied. Various maps at the 2:250,000 scale were obtained to evaluate the results of automatic data processing