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PubMed | University of Trento, Syracuse University, Rutherford Appleton Laboratory, Korea Institute of Science and Technology and 117 more.
Type: Journal Article | Journal: Physical review letters | Year: 2014

We present the results of a search for gravitational waves associated with 223 -ray bursts (GRBs) detected by the InterPlanetary Network (IPN) in 2005-2010 during LIGOs fifth and sixth science runs and Virgos first, second, and third science runs. The IPN satellites provide accurate times of the bursts and sky localizations that vary significantly from degree scale to hundreds of square degrees. We search for both a well-modeled binary coalescence signal, the favored progenitor model for short GRBs, and for generic, unmodeled gravitational wave bursts. Both searches use the event time and sky localization to improve the gravitational wave search sensitivity as compared to corresponding all-time, all-sky searches. We find no evidence of a gravitational wave signal associated with any of the IPN GRBs in the sample, nor do we find evidence for a population of weak gravitational wave signals associated with the GRBs. For all IPN-detected GRBs, for which a sufficient duration of quality gravitational wave data are available, we place lower bounds on the distance to the source in accordance with an optimistic assumption of gravitational wave emission energy of 10(-2)Mc(2) at 150 Hz, and find a median of 13 Mpc. For the 27 short-hard GRBs we place 90% confidence exclusion distances to two source models: a binary neutron star coalescence, with a median distance of 12 Mpc, or the coalescence of a neutron star and black hole, with a median distance of 22 Mpc. Finally, we combine this search with previously published results to provide a population statement for GRB searches in first-generation LIGO and Virgo gravitational wave detectors and a resulting examination of prospects for the advanced gravitational wave detectors.

PubMed | University of Trento, Syracuse University, Rutherford Appleton Laboratory, Korea Institute of Science and Technology and 112 more.
Type: Journal Article | Journal: Physical review letters | Year: 2014

Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension G below 10(-8) in some regions of the cosmic string parameter space.

Using reaction cross-beam scattering and velocity map imaging combined with simulation studies a gas-phase S 2 reaction, F- + CH Cl-, and comparing it to prior studies of F- + CH I, Martin Stei, Eduardo Carrascosa, Martin A. Kainz, Aditya H. Kelkar, Jennifer Meyer, Istvan Szabo, Gabor Czako, and Roland Wester from the Institute for Ion Physics and Applied Physics, Universitat Innsbruck in Austria, the Institute of Chemistry, Eotvos University in Hungary, and the University of Szeged in Hungary have determined that the leaving group has a strong influence on reaction dynamics by influencing the orientation of the reactants. Specifically, they found that while both the chlorine and iodine reactions form a hydrogen bonding complex at the entrance channel, key differences cause one to be a direct rebound mechanism while the other is an indirect mechanism. Their work is reported in Nature Chemistry. Reaction dynamics is the study of individual molecular collisions. While kinetic theory describes a mechanism based on aggregate behavior, reaction dynamics looks at individual particles. Reaction dynamics answers questions such as "Do the reactants need to collide in a certain way in order for a reaction to occur?" To answer questions about particular collisions, reaction dynamics studies must be conducted in the gas phase. This particular study looked at collisions using ion beams to control reactant velocity and TOF-MS to measure product velocity. In the S 2 reaction F- + CH Cl- à CH F + Cl-, fluorine serves as the nucleophile, which engages in a "nucleophilic attack" on CH Cl, and chlorine serves as the leaving group. This reaction occurs through an orchestrated process that, on the molecular level, shows that fluorine must collide directly with the electrophilic carbon, rather than the chlorine or hydrogens. Lower velocities did indicate an indirect complex-mediated mechanism, but for most velocities, this reaction undergoes a direct rebound mechanism. This is evidenced from scattering data that shows the chlorine leaving scattering in the backward direction. Lower velocities showed isotropic scattering. Even though there is evidence of a hydrogen bonding complex at the entrance channel, this reaction is not a slow, complex-dependent mechanism. The hydrogen complex, however, may affect reactant orientation. This is not the case for the analogous reaction with iodine as a leaving group: F- + CH I- à CH F + I-. Prior studies showed that while this reaction does display some backscattering, it seems to have a greater isotropic distribution and higher internal energy at most velocities, indicating an indirect complex-mediated mechanism. For this reaction, the collinear entrance channel plays a more important role in lowering the reaction energy barrier than forming a hydrogen complex. In other words, the reactants may impact each other in various ways. Simulation studies confirmed the experimental results of the chlorine reaction. Additional simulation studies showed that mass differences do not play a role in the differences between these reactions mechanisms, and impact parameter measurements indicate that reactant orientation is much more efficient in the case of the chlorine reaction compared to the iodine reaction. This is likely due to CH Cl having a larger dipole moment compared to CH I, which causes the fluorine ion to preferentially impact CH Cl in a direct rebound orientation. This study shows that given by comparing seemingly analogous gas-phase S 2 reactions, at the molecular level, their reaction dynamics are distinctly different. These differences are due to properties of the leaving group that are beyond differences in mass, and likely have to do with molecular orientation upon impact. Explore further: Theoretical chemists find new dimension to rules for reactions More information: Martin Stei et al, Influence of the leaving group on the dynamics of a gas-phase SN2 reaction, Nature Chemistry (2015). DOI: 10.1038/NCHEM.2400

Fuzi A.,IP Systems Ltd. | Madi-Nagy G.,IP Systems Ltd. | Madi-Nagy G.,Eotvos University
Periodica Polytechnica, Social and Management Sciences | Year: 2014

The paper introduces the mechanism of the Flow-based Capacity Allocation (FBA) method on the electricity market of the Central-Eastern Europe (CEE) Region, proposed by the Central Allocation Office (CAO). The method is a coordinated heterogeneous multi-unit uniform price auction where the allocation is determined by the solution of a linear programming problem. On one hand, the properties of the underlying linear programming problem are discussed: the possibilities of multiple solutions are analysed, then a non-standard sensitivity analysis method of the market spread auction is developed. On the other hand, a global optimization problem is presented that yields uniform auction prices corresponding to higher total income than at the original allocation method. Several numerical examples and results of practical test problems are presented.

de Souza R.S.,Korea Astronomy and Space Science Institute | de Souza R.S.,Eotvos University | Maio U.,National institute for astrophysics | Maio U.,Leibniz Institute for Astrophysics Potsdam | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a novel approach, based on robust principal components analysis (RPCA) and maximal information coefficient (MIC), to study the redshift dependence of halo baryonic properties. Our data are composed of a set of different physical quantities for primordial minihaloes: dark matter mass (Mdm), gas mass (Mgas), stellar mass (Mstar), molecular fraction (Xmol), metallicity (Z), star formation rate (SFR) and temperature.We find thatMdm andMgas are dominant factors for variance, particularly at high redshift. Nonetheless, with the emergence of the first stars and subsequent feedback mechanisms, Xmol, SFR and Z start to have a more dominant role. Standard PCA gives three principal components (PCs) capable to explain more than 97 per cent of the data variance at any redshift (two PCs usually accounting for no less than 92 per cent), whilst the first PC from the RPCA analysis explains no less than 84 per cent of the total variance in the entire redshift range (with two PCs explaining ≥95 per cent anytime). Our analysis also suggests that all the gaseous properties have a stronger correlation with Mgas than with Mdm, while Mgas has a deeper correlation with Xmol than with Z or SFR. This indicates the crucial role of gas molecular content to initiate star formation and consequent metal pollution from Population III and Population II/I regimes in primordial galaxies. Finally, a comparison between MIC and Spearman correlation coefficient shows that the former is a more reliable indicator when halo properties are weakly correlated. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

De Souza R.S.,Korea Astronomy and Space Science Institute | De Souza R.S.,Eotvos University | Ishida E.E.O.,Max Planck Institute for Astrophysics | Ishida E.E.O.,University of Sao Paulo | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The first supernovae (SNe) will soon be visible at the edge of the observable universe, revealing the birthplaces of Population III stars. With upcoming near-infrared missions, a broad analysis of the detectability of high-z SNe is paramount. We combine cosmological and radiationtransport simulations, instrument specifications and survey strategies to create synthetic observations of primeval core-collapse (CC), Type IIn and pair-instability (PI) SNe with the James Webb Space Telescope (JWST). We show that a dedicated observational campaign with theJWST can detect up to ~15 PI explosions, ~300 CC SNe, but less than one Type IIn explosion per year, depending on the Population III star formation history. Our synthetic survey also shows that ≈1-2 × 102 SNe detections, depending on the accuracy of the classification, are sufficient to discriminate between a Salpeter and flat mass distribution for high-redshift stars with a confidence level greater than 99.5 per cent. We discuss how the purity of the sample affects our results and how supervised learning methods may help to discriminate between CC and PI SNe. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

de Souza R.S.,Eotvos University | Ciardi B.,Max Planck Institute for Astrophysics
Astronomy and Computing | Year: 2015

We present AMADA, an interactive web application to analyze multidimensional datasets. The user uploads a simple ascii file and AMADA performs a number of exploratory analysis together with contemporary visualizations diagnostics. The package performs a hierarchical clustering in the parameter space, and the user can choose among linear, monotonic or non-linear correlation analysis. AMADA provides a number of clustering visualization diagnostics such as heatmaps, dendrograms, chord diagrams, and graphs. In addition, AMADA has the option to run a standard or robust principal components analysis, displaying the results as polar bar plots. The code is written in r and the web interface was created using the shiny framework. AMADA source-code is freely available at, and the shiny-app at © 2015 Elsevier B.V..

de Souza R.S.,Eotvos University | Dantas M.L.L.,University of Sao Paulo | Krone-Martins A.,University of Lisbon | Cameron E.,University of Oxford | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We developed a hierarchical Bayesian model (HBM) to investigate how the presence of Seyfert activity relates to their environment, herein represented by the galaxy cluster mass, M200, and the normalized cluster centric distance, r/r200. We achieved this by constructing an unbiased sample of galaxies from the Sloan Digital Sky Survey, with morphological classifications provided by the Galaxy Zoo Project. A propensity score matching approach is introduced to control the effects of confounding variables: stellar mass, galaxy colour, and star formation rate. The connection between Seyfert-activity and environmental properties in the de-biased sample is modelled within an HBM framework using the so-called logistic regression technique, suitable for the analysis of binary data (e.g. whether or not a galaxy hosts an AGN). Unlike standard ordinary least square fitting methods, our methodology naturally allows modelling the probability of Seyfert-AGN activity in galaxies on their natural scale, i.e. as a binary variable. Furthermore, we demonstrate how an HBM can incorporate information of each particular galaxy morphological type in an unified framework. In elliptical galaxies our analysis indicates a strong correlation of Seyfert-AGN activity with r/r200, and a weaker correlation with the mass of the host cluster. In spiral galaxies these trends do not appear, suggesting that the link between Seyfert activity and the properties of spiral galaxies are independent of the environment. © 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Elliott J.,Max Planck Institute for Extraterrestrial Physics | de Souza R.S.,Eotvos University | Krone-Martins A.,University of Lisbon | Cameron E.,University of Oxford | And 3 more authors.
Astronomy and Computing | Year: 2015

Machine learning techniques offer a precious tool box for use within astronomy to solve problems involving so-called big data. They provide a means to make accurate predictions about a particular system without prior knowledge of the underlying physical processes of the data. In this article, and the companion papers of this series, we present the set of Generalized Linear Models (GLMs) as a fast alternative method for tackling general astronomical problems, including the ones related to the machine learning paradigm. To demonstrate the applicability of GLMs to inherently positive and continuous physical observables, we explore their use in estimating the photometric redshifts of galaxies from their multi-wavelength photometry. Using the gamma family with a log link function we predict redshifts from the PHoto-z Accuracy Testing simulated catalogue and a subset of the Sloan Digital Sky Survey from Data Release 10. We obtain fits that result in catastrophic outlier rates as low as ~1% for simulated and ~2% for real data. Moreover, we can easily obtain such levels of precision within a matter of seconds on a normal desktop computer and with training sets that contain merely tho nds of galaxies. Our software is made publicly available as a user-friendly package developed in Python, R and via an interactive web application. This software allows users to apply a set of GLMs to their own photometric catalogues and generates publication quality plots with minimum effort. By facilitating their ease of use to the astronomical community, this paper series aims to make GLMs widely known and to encourage their implementation in future large-scale projects, such as the Large Synoptic Survey Telescope. © 2015 Elsevier B.V.

Krone-Martins A.,University of Lisbon | Ishida E.E.O.,University of Sao Paulo | Ishida E.E.O.,Max Planck Institute for Astrophysics | de Souza R.S.,Korea Astronomy and Space Science Institute | de Souza R.S.,Eotvos University
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

We report the first analytical expression purely constructed by a machine to determine photometric redshifts (Zphot) of galaxies. A simple and reliable functional form is derived using 41 214 galaxies from the Sloan Digital Sky Survey Data Release 10 (SDSS-DR10) spectroscopic sample. The method automatically dropped the u and z bands, relying only on g, r and i for the final solution. Applying this expression to other 1417 181 SDSS-DR10 galaxies, with measured spectroscopic redshifts (Zspec), we achieved a mean 〈 (Zphot - Zspec)/(1 + Zspec)〉 ≲ 0.0086 and a scatter σ(Zphot-Zspec)/(1+Zspec) ≲ 0.045 when averaged up to z ≲ 1.0. The method was also applied to the PHAT0 data set, confirming the competitiveness of our results when faced with other methods from the literature. This is the first use of symbolic regression in cosmology, representing a leap forward in astronomy-data-mining connection. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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