A city scale 3D geological model to support ground source heat recovery and storage

The Cardiff Urban Geo Observatory was established to characterise, monitor and model groundwater and heat flow in a shallow urban aquifer. Mapping showed that shallow ground groundwater temperatures exceeded 150C, due to effects of the subsurface urban heat island (Farr et al, 2017). A 3D model of the superficial deposits was created to better understand the aquifer dimensions and as a framework for a hydrogeological heat flow model

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society

All-sky search for long-duration gravitational wave transients with initial LIGO

We present the results of a search for long-duration gravitational wave transients in two sets of data collected by the LIGO Hanford and LIGO Livingston detectors between November 5, 2005 and September 30, 2007, and July 7, 2009 and October 20, 2010, with a total observational time of 283.0 days and 132.9 days, respectively. The search targets gravitational wave transients of duration 10-500 s in a frequency band of 40-1000 Hz, with minimal assumptions about the signal waveform, polarization, source direction, or time of occurrence. All candidate triggers were consistent with the expected background; as a result we set 90% confidence upper limits on the rate of long-duration gravitational wave transients for different types of gravitational wave signals. For signals from black hole accretion disk instabilities, we set upper limits on the source rate density between 3.4×10-5 and 9.4×10-4 Mpc-3 yr-1 at 90% confidence. These are the first results from an all-sky search for unmodeled long-duration transient gravitational waves. © 2016 American Physical Society

GW190814: gravitational waves from the coalescence of a 23 solar mass black hole with a 2.6 solar mass compact object

We report the observation of a compact binary coalescence involving a 22.2–24.3 Me black hole and a compact object with a mass of 2.50–2.67 Me (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO’s and Virgo’s third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of - + 241 45 41 Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal mass ratio yet measured with gravitational waves, - + 0.112 0.009 0.008, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to �0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of mass ratio, component masses, and the inferred merger rate for this event challenges all current models of the formation and mass distribution of compact-object binaries

Use of the Weibull Equation to Approximate Diffusive Release from Particles in a Closed System

We consider the problem of Fickian diffusion of a solute (or heat) into or out of a suspension of particles, in a well-mixed solvent. By combining a simple numerical scheme with a Laplace transform method, we are able to efficiently solve this problem for different particle volume fractions (including accumulation of solute in the liquid phase), shapes (spheres, cubes and cylinders of different aspect ratios) and particle size distributions (assumed to be log-normal). We approximate the results by a Weibull function, and thereby provide a physical calibration for the parameters in this function when used as an approximation for our solutions. We test our calculation by measuring salt release profiles from different size distributions of agar cubes, and then use the predicted Weibull equation to deduce the diffusivity of salt in this material

Liquid phase sintering of two roughened ice crystals in sucrose solution: A comparison to theory and simulation

We construct an approximate analytic expression for the growth of the neck between two sintering roughened crystals in contact with a melt. The result combines recent work on early phase sintering [R.S. Farr, M.J. Izzard, Phys. Rev. E 77 (2008) 041608], and a numerical method presented here, based on Legendre polynomials. The expression gives an estimate which covers all times from very early to near equilibrium, and includes the effect of a grain boundary between the two crystals. The predictions are then compared to experiments on sintering of ice crystals in a sucrose solution

Diffusional Monte Carlo model of liquid-phase sintering

Liquid-phase sintering (LPS) is a consolidation process for metallic and ceramic powders. At given temperature conditions, the process occurs with constant amount of liquid phase. However, the evolution of solid-particle shape is observed, namely, the rounding of particles and the growth of big particles at the expense of the small ones, which is known as Ostwald ripening. In this work, we propose a Monte Carlo (MC) model to simulate the microstructural evolution during LPS. The model considers the change of state of the discretising elements, namely voxels, of the system. The microstructural evolution proceeds accounting for both the geometrical characteristics of the particles, such as the number of solid neighbours, and the amount of solute contained in or surrounding a randomly chosen voxel. This has been implemented in terms of two probability distribution functions (PDFs). The diffusion of solute has also been considered by means of the implementation of a three-dimensional finite-difference algorithm. The diffusional MC model that we present is able to reproduce the Ostwald ripening behaviour and, in particular, results match the case in which the process is limited by the diffusion of the solute in the liquid phase