15 research outputs found
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω0T<5.58Ă10-8, Ω0V<6.35Ă10-8, and Ω0S<1.08Ă10-7 at a reference frequency f0=25 Hz. © 2018 American Physical Society
On the progenitor of binary neutron star merger GW170817
On 2017 August 17 the merger of two compact objects with masses consistent with two neutron stars was discovered through gravitational-wave (GW170817), gamma-ray (GRB 170817A), and optical (SSS17a/AT 2017gfo) observations. The optical source was associated with the early-type galaxy NGC 4993 at a distance of just âŒ40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of âŒ2 kpc away from the galaxy's center. We use this minimal set of facts and the mass posteriors of the two neutron stars to derive the first constraints on the progenitor of GW170817 at the time of the second supernova (SN). We generate simulated progenitor populations and follow the three-dimensional kinematic evolution from binary neutron star (BNS) birth to the merger time, accounting for pre-SN galactic motion, for considerably different input distributions of the progenitor mass, pre-SN semimajor axis, and SN-kick velocity. Though not considerably tight, we find these constraints to be comparable to those for Galactic BNS progenitors. The derived constraints are very strongly influenced by the requirement of keeping the binary bound after the second SN and having the merger occur relatively close to the center of the galaxy. These constraints are insensitive to the galaxy's star formation history, provided the stellar populations are older than 1 Gyr
Alguns grupos de microrganismos em manteigas vendidas no municĂpio de SĂŁo Paulo Microorganism groups found in butter sold in the City of S. Paulo, Brazil
Foram colhidas 105 amostras de manteiga de 5 marcas diferentes vendidas em supermercados da cidade de SĂŁo Paulo (Brasil) com a finalidade de verificar as condiçÔes microbiolĂłgicas de manteigas e comparĂĄ-las com os padrĂ”es recomendados. Semanalmente foi colhida uma amostra de cada marca, durante 21 semanas. A partir da parte aquosa de cada amostra, foram realizadas as contagens de bactĂ©rias mesĂłfilas e psicrĂłfilas (em ĂĄgar padrĂŁo e ĂĄgar gelisato), coliformes, proteolĂticas e de bolores e leveduras e os resultados comparados com alguns parĂąmetros propostos por vĂĄrios pesquisadores. Os valores obtidos nas contagens dos vĂĄrios grupos de microrganismos estudados, em muitos casos podem ser considerados altos, os quais podem ser resultado do processamento e/ou conservação, realizados em condiçÔes nĂŁo satisfatĂłrias.<br>One hundred and five samples of five different brands of butter in the supermarkets of the City of S. Paulo, Brazil were brought in for testing every week for 21 weeks. From the aqueous phase, counts were made for mesophilic and psichrophilic (using the standard plate count, agar and gelysate agar), coliform, proteolytic, and lipolytic bacteria, as well as for yeasts and molds. Results were compared with parameters proposed by several researchers. In many cases, the count values can be considered high, but these high counts may be due to inadequate processing and/or inadequate storage
Interactive Nonlinear Multiobjective Optimization Methods
An overview of interactive methods for solving nonlinear multiobjective
optimization problems is given. In interactive methods, the decision
maker progressively provides preference information so that the most
satisfactory Pareto optimal solution can be found for her or his. The
basic features of several methods are introduced and some theoretical
results are provided. In addition, references to modifications and applications
as well as to other methods are indicated. As the role of
the decision maker is very important in interactive methods, methods
presented are classified according to the type of preference information
that the decision maker is assumed to provide.peerReviewe
Estimating the contribution of dynamical ejecta in the kilonova associated with GW170817
The source of the gravitational-wave (GW) signal GW170817, very likely a binary neutron star merger, was also observed electromagnetically, providing the first multi-messenger observations of this type. The two-week-long electromagnetic (EM) counterpart had a signature indicative of an r-process-induced optical transient known as a kilonova. This Letter examines how the mass of the dynamical ejecta can be estimated without a direct electromagnetic observation of the kilonova, using GW measurements and a phenomenological model calibrated to numerical simulations of mergers with dynamical ejecta. Specifically, we apply the model to the binary masses inferred from the GW measurements, and use the resulting mass of the dynamical ejecta to estimate its contribution (without the effects of wind ejecta) to the corresponding kilonova light curves from various models. The distributions of dynamical ejecta mass range between Mej = 10 -Âł - 10-ÂČ Mâ for various equations of state, assuming that the neutron stars are rotating slowly. In addition, we use our estimates of the dynamical ejecta mass and the neutron star merger rates inferred from GW170817 to constrain the contribution of events like this to the r-process element abundance in the Galaxy when ejecta mass from post-merger winds is neglected. We find that if 10% of the matter dynamically ejected from binary neutron star (BNS) mergers is converted to r-process elements, GW170817-like BNS mergers could fully account for the amount of r-process material observed in the Milky Way