Search for gravitational waves from Scorpius X-1 in the second Advanced LIGO observing run with an improved hidden Markov model

We present results from a semicoherent search for continuous gravitational waves from the low-mass x-ray binary Scorpius X-1, using a hidden Markov model (HMM) to track spin wandering. This search improves on previous HMM-based searches of LIGO data by using an improved frequency domain matched filter, the J-statistic, and by analyzing data from Advanced LIGO's second observing run. In the frequency range searched, from 60 to 650 Hz, we find no evidence of gravitational radiation. At 194.6 Hz, the most sensitive search frequency, we report an upper limit on gravitational wave strain (at 95% confidence) of h095%=3.47×10-25 when marginalizing over source inclination angle. This is the most sensitive search for Scorpius X-1, to date, that is specifically designed to be robust in the presence of spin wandering. © 2019 American Physical Society

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

Constraints on cosmic strings using data from the first Advanced LIGO observing run

Cosmic strings are topological defects which can be formed in grand unified theory scale phase transitions in the early universe. They are also predicted to form in the context of string theory. The main mechanism for a network of Nambu-Goto cosmic strings to lose energy is through the production of loops and the subsequent emission of gravitational waves, thus offering an experimental signature for the existence of cosmic strings. Here we report on the analysis conducted to specifically search for gravitational-wave bursts from cosmic string loops in the data of Advanced LIGO 2015-2016 observing run (O1). No evidence of such signals was found in the data, and as a result we set upper limits on the cosmic string parameters for three recent loop distribution models. In this paper, we initially derive constraints on the string tension Gμ and the intercommutation probability, using not only the burst analysis performed on the O1 data set but also results from the previously published LIGO stochastic O1 analysis, pulsar timing arrays, cosmic microwave background and big-bang nucleosynthesis experiments. We show that these data sets are complementary in that they probe gravitational waves produced by cosmic string loops during very different epochs. Finally, we show that the data sets exclude large parts of the parameter space of the three loop distribution models we consider

Seafood and health: A teacher resource for secondary students

No abstract availabl

Awesome aquaculture: Towards building a sound seafood and health knowledge base in young students

No abstract availabl

Lattice Strain in Magnetic Ultrathin Films

A clear understanding of the mechanisms of interfacial magnetic anisotropy rests on the structural characterisation of magnetic multilayers which, typically, consist of two ferromagnetically coupled (F) layers separated by a non-magnetic spacer layer. Fe/Cu/Fe trilayers are of special interest since the coupling between the F layers of Fe changes from F to antiferromagnetic depending on the thickness of the Cu spacer layer. Here, a magnetic multilayer system, grown by molecular beam epitaxy (MBE), was modified by inserting Cr in the Cu : Ag(001)/8.7 Fe/3 Cu/6 Cr/3 Cu/5 Fe/10 Au where the integers refer to monolayers. Polarized K-edge XAFS spectra (E parallel to the substrate) were obtained from fluorescence measurements in the total reflection geometry. The multiple scattering paths were analysed for the Cr edge. The initial Cu grew pseudomorphically in a BCC structure on Fe/Ag(001). The Cr proved to be tetragonally distorted from its BCC structure. The overlayers of Fe on Cu are contracted by 1.27% within the plane and conserve the c lattice parameter of Fe, though the atomic volume is contracted by 2.8%. The Cu adopts a BCT, rather than keeping its bulk FCC, structure and the corresponding decrease in its atomic volume from the FCC is only 0.3%

Effective Coordination Numbers in Ultrathin Metallic Films

Nanostructures bave become a major field in material science. With molecular beam epitaxy it is possible to engineer multilayers with unusual anisotropic properties and metastable structures. For ultrathin films, or particles of small size, the coordination numbers are less than their bulk values. In fitting E X A F S data it is useful to be able to place limits on the coordination numbers or their ratios. W e have calculated the effective coordination numbers Ni , i= 1 to 5 for thin films with different crystal structures. The thickness o f the film is specified by the number o f layers Nz in the z-direction and the area in the x y plane by the number o f rows of atoms NXY along the side of a square domain. For fixed Nz, with the x-ray beam unpolarized or its electric vector parallel or perpendicular to the substrate (xy plane), the effective H approach hyperbolically the coordination number for a layer o f infinite area. Simple analytical expressions are fitted to the numerical results fix- bcc and fee crystals from which the H can be calculated for both NXY and Nz ≥ 2. Comparison is made with the effective coordination numbers obtained from polarized E X A F S measurements on epitaxial metallic films less than 10 monolayers thick

Modelling stress evolution during cable fabrication

A brief description of a software environment in FORTRAN77 for the modelling of multi-physics phenomena is given. The numerical approach is based on finite volume methods but extended to unstructured meshes (ie. FV-UM). A range of interacting solution procedures for turbulent fluid flow, heat transfer with solidification/melting and elasto-visco-plastic solid mechanics are implemented in the first version of PHYSICA, which will be released in source code form to the academic community in late 1995