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<5.58×10-8, Ω0V<6.35×10-8, and Ω0S<1.08×10-7 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 ∼40 Mpc, consistent with the gravitational-wave measurement, and the merger was localized to be at a projected distance of ∼2 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

Intrazeolite Metal Carbonyl Kinetics: Substitution Reactions Of Mo(12co)6 In Sodium Zeolite Y

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The first quantitative and detailed kinetic study of simple thermal reactions of a molecule encapsulated in a zeolite cavity is reported. Substitution reactions of Mo(12CO)6 with PMe3 in the α-cages of a Na56Y zeolite host proceed cleanly to form cis-Mo(CO)4(PMe3)2 by what are essentially pseudo-first-order dissociative and associative processes. Reactions with 13CO proceed only by the dissociative path, which is 103 times faster than corresponding reactions in homogeneous solution. Dissociative substitution by PMe3 is retarded by applied pressures of 12CO, as expected, but it is also retarded to a significant extent by increased Mo(CO)6 and PMe3 loadings. Substitution by 13CO is similarly retarded by increasing pressures of the entering 13CO. The activation parameters, ΔHd‡ = 61 ± 5 kJ mol-1 and ΔSd‡ = -139 ± 15 J K-1 mol-1, are unusual for a dissociative process but can be interpreted on the basis of structural information concerning pertinent reactant and product guests obtained mainly from FT-mid-IR, EXAFS, and DOR-MAS-NMR analytical methods. The kinetics data reveal that the α-cages of Na56Y provide precisely defined activating environments of a unique kind. From a coordination chemistry point of view, these "nanoreactors" appear to behave as macrospheroidal multidentate multisite anionic ligands (which we call "zeolates") toward extraframework charge-balancing cations to which metal carbonyl reactant, product, and ligand guests can become attached. The best model that emerges from this study pictures a supramolecular assembly of Mo(12CO)6 and PMe3, 13CO, or 12CO, housed within the α-cage of Na56Y, anchored to extraframework Na+ cations, and subject to loading-dependent cooperative interactions. These interactions appear to control the extent of activation of Mo(12CO)6 through the degree of ordering (lock and key) of the {Mo(12CO)5⋯12CO)‡ dissociative transition state. All involve α-cage Na+ anchoring interactions, probably together with some influence of oxygens of the six-rings. Substitution by PMe3 can also occur by two associative paths, one that involves PMe3 molecules chemisorbed to NaII + ions in the nanoreactors, and another that we believe involves PMe3 molecules physisorbed in the region of the 12-ring windows of the α-cages. Strikingly, these associative reactions are somewhat slower than corresponding reactions in homogeneous solution, and they are much less subject to loading effects than the dissociative reactions.115412151230Sponsor: FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Intrazeolite Metal Carbonyl Kinetics: 12co Substitution In Mo(12co)6-na56y By Pme3 And 13co

The first kinetic study is reported for archetypical substitution reactions of PMe3 and 13CO with the well defined intrazeolite system, Mo(12CO)6-Na56Y, for which excellent isosbestic points and first order behaviour are obtained, the activation parameters indicate a highly ordered 'supramolecular' transition state consisting of activated Mo(12CO)6 and PMe3 or 13CO all anchored to the Na+ ions in the α-cage of the host lattice.314114