arXiv subjects

P. Hill

Publications and source records attributed to P. Hill.

8 recordsLinked to original sources

arXiv2025

Low thermal noise mirror coatings utilising titanium dioxide and germanium dioxide mixtures

Upgrades to ground-based gravitational-wave observatories will require mirror coatings with reduced thermal noise, enabling improved detector sensitivity and extended astrophysical reach. Recent studies have shown that optical coatings utilising amorphous materials that exhibit a larger fraction of corner-sharing between adjacent structural units of metal-centered polyhedra are a promising route for reducing mechanical dissipation and thus thermal noise at room temperature. We report on multilayer optical coatings that are fabricated using germanium dioxide mixed with titanium dioxide (TiO$_2$:GeO$_2$) for the high index layers, and silicon dioxide (SiO$_2$) for the low index material. Single layers of TiO$_2$:GeO$_2$ are characterised to optimise the mixture proportion and based on that highly reflective multilayer stacks were deposited. Exceptional optical absorption at 1064 nm below 1 part-per-million (ppm) is observed in the multilayer stacks after heat treatment. The annealing process also induces the formation of blisters which leads to increased optical scattering. However, there is indication that blisters can be suppressed by decreasing the water partial pressure in the deposition chamber. Direct thermal noise measurements provide experimental verification of a significant 25\% reduction of thermal noise over the mirrors currently employed, which combined with sub-ppm levels of optical absorption show the potential of TiO$_2$:GeO$_2$ to improve the sensitivity of gravitational-wave observatories.

physics.ins-det↗

arXiv2024

Atmospheric Turbulence Removal with Video Sequence Deep Visual Priors

Atmospheric turbulence poses a challenge for the interpretation and visual perception of visual imagery due to its distortion effects. Model-based approaches have been used to address this, but such methods often suffer from artefacts associated with moving content. Conversely, deep learning based methods are dependent on large and diverse datasets that may not effectively represent any specific content. In this paper, we address these problems with a self-supervised learning method that does not require ground truth. The proposed method is not dependent on any dataset outside of the single data sequence being processed but is also able to improve the quality of any input raw sequences or pre-processed sequences. Specifically, our method is based on an accelerated Deep Image Prior (DIP), but integrates temporal information using pixel shuffling and a temporal sliding window. This efficiently learns spatio-temporal priors leading to a system that effectively mitigates atmospheric turbulence distortions. The experiments show that our method improves visual quality results qualitatively and quantitatively.

cs.CV↗

arXiv2023

The Golden Meteorite Fall: Fireball Trajectory, Orbit and Meteorite Characterization

The Golden (British Columbia, Canada) meteorite fall occurred on Oct 4, 2021 at 0534 UT with the first recovered fragment (1.3 kg) landing on an occupied bed. The meteorite is an unbrecciated, low-shock (S2) ordinary chondrite of intermediate composition, typed as an L/LL5. From noble gas measurements the cosmic ray exposure age is 25 Ma while gas retention ages are all >2 Ga. Short-lived radionuclides and noble gas measurements of the pre-atmospheric size overlap with estimates from infrasound and lightcurve modelling producing a preferred pre-atmospheric mass of 70-200 kg. The orbit of Golden has a high inclination (23.5 degs) and is consistent with delivery from the inner main belt. The highest probability (60%) of an origin is from the Hungaria group. We propose that Golden may originate among the background S-type asteroids found interspersed in the Hungaria region. The current collection of 18 L and LL chondrite orbits shows a strong preference for origins in the inner main belt, suggesting multiple parent bodies may be required to explain the diversity in CRE ages and shock states.

astro-ph.EP↗

arXiv2018

Three-dimensional solid-state qubit arrays with long-lived spin coherence

Three-dimensional arrays of silicon transistors increase the density of bits. Solid-state qubits are much larger so could benefit even more from using the third dimension given that useful fault-tolerant quantum computing will require at least 100,000 physical qubits and perhaps one billion. Here we use laser writing to create 3D arrays of nitrogen-vacancy centre (NVC) qubits in diamond. This would allow 5 million qubits inside a commercially available 4.5x4.5x0.5 mm diamond based on five nuclear qubits per NVC and allowing $(10 μm)^3$ per NVC to leave room for our laser-written electrical control. The spin coherence times we measure are an order of magnitude longer than previous laser-written qubits and at least as long as non-laser-written NVC. As well as NVC quantum computing, quantum communication and nanoscale sensing could benefit from the same platform. Our approach could also be extended to other qubits in diamond and silicon carbide.

quant-ph↗

arXiv2018

Detecting Volcano Deformation in InSAR using Deep learning

Globally 800 million people live within 100 km of a volcano and currently 1500 volcanoes are considered active, but half of these have no ground-based monitoring. Alternatively, satellite radar (InSAR) can be employed to observe volcanic ground deformation, which has shown a significant statistical link to eruptions. Modern satellites provide large coverage with high resolution signals, leading to huge amounts of data. The explosion in data has brought major challenges associated with timely dissemination of information and distinguishing volcano deformation patterns from noise, which currently relies on manual inspection. Moreover, volcano observatories still lack expertise to exploit satellite datasets, particularly in developing countries. This paper presents a novel approach to detect volcanic ground deformation automatically from wrapped-phase InSAR images. Convolutional neural networks (CNN) are employed to detect unusual patterns within the radar data.

cs.CV↗

arXiv2015

The effect of magnetic islands on ITG turbulence driven transport

In this work, we address the question of the influence of magnetic islands on the perpendicular transport due to steady-state ITG turbulence on the energy transport time scale. We demonstrate that turbulence can cross the separatrix and enhance the perpendicular transport across magnetic islands. As the perpendicular transport in the interior of the island sets the critical island size needed for growth of neoclassical tearing modes, this increased transport leads to a critical island size larger than that predicted from considering collisional conductivities, but smaller than that using anomalous effective conductivities. We find that on Bohm time scales, the turbulence is able to re-establish the temperature gradient across the island for islands widths $w \lesssim λ_{turb}$, the turbulence correlation length. The reduction in the island flattening is estimated by comparison with simulations retaining only the perpendicular temperature and no turbulence. At intermediate island widths, comparable to $λ_{turb}$, turbulence is able to maintain finite temperature gradients across the island.

physics.plasm-ph↗

arXiv2014

Plasma turbulence simulations with X-points using the flux-coordinate independent approach

In this work, the Flux-Coordinate Independent (FCI) approach to plasma turbulence simulations is formulated for the case of generic, static magnetic fields, including those possessing stochastic field lines. It is then demonstrated that FCI is applicable to nonlinear turbulent problems with and without X-point geometry. In particular, by means of simulations with the FENICIA code, it is shown that the standard features of ITG modes are recovered with reduced toroidal resolution. Finally, ITG turbulence under the influence of a static island is studied on the transport timescale with ITER-like parameters, showing the wide range of applicability of the method.

physics.plasm-ph↗

arXiv2014

A Singularity-Free Coordinate System for X-point Geometries

A Flux Coordinate Independent (FCI) approach for anisotropic systems, not based on magnetic flux coordinates has been introduced in [F. Hariri and M. Ottaviani, Comput. Phys. Commun., 184,2419 (2013)]. In this paper, we show that the approach can tackle magnetic configurations including X-points. Using the code FENICIA, an equilibrium with a magnetic island has been used to show the robustness of the FCI approach to cases in which a magnetic separatrix is present in the system, either by design or as a consequence of instabilities. Numerical results are in good agreement with the analytic solutions of the sound-wave propagation problem. Conservation properties are verified. Finally, the critical gain of the FCI approach in situations including the magnetic separatrix with an X-point is demonstrated by a fast convergence of the code with the numerical resolution in the direction of symmetry. The results highlighted in this paper show that the FCI approach should be able to address turbulent transport problems in X-point geometries.

physics.plasm-ph↗