Exchange narrowing of NMR line shapes in randomly diluted magnetic systems

An analysis of 19F NMR linewidths in the randomly diluted magnetic system KMnxMg1-xF3 is presented. It is shown that good agreement with measured linewidths can be obtained if in the usual asymptotic spin-diffusion assumption for the spin autocorrelation function 〈Siα(τ)Siα(0)〉avατ-d(x)/2, d(x) is taken to be independent of x above the percolation concentration. Experimental results in the system KNixMg1-xF3 are also presented. These data exhibit striking differences with the behavior of isostructural KMnxMg1-xF3 whose origin is discussed

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Superconductivity and magnetism in the KxMoO2-delta

Coexistence between superconductivity and magnetism is reported for the KxMoO2-delta samples. Photoemission experiments show that the presence of Mo3+ ions is responsible for the weak ferromagnetic ordering observed in the KxMoO2-delta samples. Magnetic ordering temperature and superconducting critical temperature (T-C) ratio range from 7 to 18 in this compound. These are the highest ratios reported so far for a magnetic superconductor. T-C decreases with increasing potassium composition (x). For the first time, T-C near 10 K is reported in the K-Mo-O system. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757003]FAPESP [2009/14524-6, 2009/54001-2, 2010/06637-2]FAPESPCNPq [508308/2010-0, 309084/2010-5, 490182/2009-7]CNPqFACEPEFACEPE [0589/1.05-08]CAPESCAPESNSF [DMR-0907036]NS

Sistemas de Informação no Brasil: uma análise dos artigos científicos dos anos 90

Este artigo apresenta uma avaliação do estado da arte da área de conhecimento de Sistemas de Informação, no Brasil, a partir da análise de 163 artigos publicados entre janeiro de 1990 e setembro de 1997, em revistas científicas de Administração. Para tanto, analisaram-se os temas abordados nos artigos, as estratégias e as metodologias de pesquisa utilizadas nas pesquisas empíricas, e avaliou-se a qualidade destas pesquisas. Constatou-se que ainda existe forte proporção de ensaios teóricos publicados (41% no período 1990-7 e 34% no período 1996-7), que há um predomínio de temas sobre desenvolvimento e uso de Sistemas de Informação no Brasil, que as pesquisas qualitativas (os estudos de caso) e as pesquisas survey são as metodologias utilizadas em 72% das pesquisas empíricas; a qualidade científica dos artigos ainda é baixa, em razão da não explicitação de como as teorias de base são operacionalizadas, da descrição incompleta dos procedimentos metodológicos e da não validação dos instrumentos de pesquisa

Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo

Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020