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Review of Moran, P.: De origine scoticae linguae (O’Mulconry’s Glossary): An Early Irish Linguistic Tract, with a Related Glossary, Irsan.
Get PDFDuality and modular symmetry in the quantum Hall effect from Lifshitz holography
Get PDFThe temperature dependence of quantum Hall conductivities is studied in the context of the AdS/CMT paradigm using a model with a bulk theory consisting of (3+1)-dimensional Einstein-Maxwell action coupled to a dilaton and an axion, with a negative cosmological constant. We consider a solution which has a Lifshitz like geometry with a dyonic black-brane in the bulk. There is an Sl(2,R) action in the bulk corresponding to electromagnetic duality, which maps between classical solutions, and is broken to Sl(2,Z) by Dirac quantisation of dyons. This bulk Sl(2,Z) action translates to an action of the modular group on the 2-dimensional transverse conductivities. The temperature dependence of the infra-red conductivities is then linked to modular forms via gradient flow and the resulting flow diagrams show remarkable agreement with existing experimental data on the temperature flow of both integral and fractional quantum Hall conductivities
Seismic imaging at a mineral-deposit scale using highfrequency surface waves (0.5–24 Hz) in ambient noise wavefield
Get PDFAmbient noise, surface-wave tomography (ANSWT) is now a routine technique for imaging crustal and upper
mantle structure at a regional scale. Its cost efficiency and environmental friendliness also make ANSWT an
attractive method for mineral exploration. However, the application of the technique in mineral exploration
requires the retrieval of wide-band, high-frequency surface waves from seismic noise, so as to obtain highresolution
images of shallow structures. We present a new workflow optimized to extend the bandwidth of highfrequency
surface waves retrieved. It comprises short time-window stacking, cross-coherence and an improved
phase velocity measurement method. We tested the workflow on data from a large-N array over a Cu-PGE deposit
in Ontario, Canada, and successfully measured phase velocities for numerous inter-station pairs in a broad
frequency ranges from 0.55 Hz to 23.8 Hz. Analysis of the phase velocity maps reveals a west-dipping highvelocity
anomaly that matches the west-dipping, multi-staged gabbro intrusions associated with the deposit
The mortal and divine histories of Mongán mac Fiachnai in Cín Dromma Snechtai
No full textIt has long been claimed that Early Irish literature portrays a form of reembodiment which is the equivalent of Pythagorean metempsychosis. But his is not what we find in most examples. Where a human is said to have traversed multiple embodiments, the process of reembodiment generally comes to an end once the person in question has been restored to their proper form and bequeathed their memories of ancient history to the Church. However, some of the earliest stories about Mongán mac Fiachnai do not fit this pattern. Immacaldam Choluim Cille and Scél asa mberar co mbad hé Find mac Cumaill Mongán offer no indication that Mongán’s sequence of embodiments is drawing to an end, or
which of his bodies may properly be his. This study will interpret the open-endedness of Mongán’s rebirths, in these two instances, in light of related stories which have also been attributed to Cín Dromma Snechtai. Doing so will allow us to determine the degree to which Mongán’s rebirths show
parallels with Pythagorean metempsychosis, and the meaning these rebirths had for their medieval Christian context. Moreover, it will demonstrate further links between the tales that the current consensus places in Cín Dromma Snechtai
Evolution of the Alfvén Mach number associated with a coronal mass ejection shock
Get PDFThe Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II bandsplitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme
ultraviolet by the Solar Ultraviolet Imager on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array. We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4–2.4 at a heliocentric distance of ∼1.6 R⊙. The emission ceased when the CME nose reached ∼2.4 R⊙, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission
Regional-scale structure and dynamics of the crust, upper mantle and transition zone from waveform tomography with massive datasets
Get PDFIn the last decade, the number of seismic stations deployed globally increased dramatically, allowing to construct tomographic models with increasing resolution. Seismic data coverage however, is not homogeneous across the globe, and many regions are sampled by a distribution of ray paths that is both lower than average and uneven. In this work, we compute regional-scale tomographic models from massive, global waveform datasets, that we optimise for Africa, South America and the South- and North Atlantic Oceans, where coverage is highly heterogeneous. To maximise coverage in the study areas, we assemble a very large dataset of both regional and global teleseismic waveforms, retrieving all freely available data in the Atlantic Ocean and surrounding continents. We then invert the waveforms using the Automated Multimode Inversion (AMI) of S-, Multiple S- and Surface waves. AMI produces a set independent linear equations with uncorrelated uncertainties for each source-receiver path, describing the path-average P- and S-wave velocity structure and dispersion curves within approximate sensitivity kernels. We then combine all the equations in a linear system and solve it for the 3D distribution of P- and S-wave velocities and 2-psi azimuthal anisotropy in the crust, upper mantle and transition zone. Similarly, we combine all phase velocity dispersion curves and invert them to produce 2D phase velocity maps independently at different periods. Finally, we exploit the mutual consistency of our very large dataset to automatically identify and remove the least consistent measurements from both our 3D models and phase velocity maps. In order to obtain the best possible models, for each study area we compute a different model that is tuned to yield the best results in the region. In South America and the South Atlantic Ocean, we parametrise our 3D model SA2109 on a ~300 km triangular grid and fine tune its regularisation with the aid of spike tests to yield robust results across the area. In South America, we image a cratonic lithosphere that is more complex than previously proposed and identify the boundaries of the cratonic cores of the Paran? and Parna?ba cratons; we also retrieve clear images of the Nazca slab, the Pampean slab gap, the subduction of the Chile Rise and the southernmost end of the subduction. In the South Atlantic Ocean, we image the low velocities of the Mid-Ocean Ridge (MOR) and a number of hotspots. Using age-averaging techniques, we are able to identify the different cooling of the oceanic lithosphere in different oceanic basins, as well as the seismic signature of the Tristan da Cunha hotspot, masked by the MOR in tomographic images. In Africa, our 3D model AF2109 reveals the presence of many smaller cratonic cores within the previously proposed boundaries of the West African and Congo cratons. Comparing the model with the outlines of cratons from field geology, we find that under the crust of the Angola, Tanzania and southwestern Kaapvaal shields, the craton lacks its lithospheric roots. By using a global dataset of diamondiferous kimberlites, we assess that in these areas, thick cratonic lithosphere was once present. Comparing the location and age of the kimberlites with our tomographic images, we infer that the Angola, Tanzania and Kaapvaal cratons lost a large portion of their cratonic lithosphere in the past 200 Million years (M.y). By combining the age of the youngest diamondiferous kimberlites in the area with Large Igneous Provinces and reconstructing the location of the cratonic erosion during the past 150 M.y., we infer that the erosion of the cratonic lithosphere followed the impact of mantle plumes on the cratons. In the Northeast Atlantic, we compute the 3D tomographic model NAT2019, which we parametrise over a very dense ~120 km grid. To tackle the very uneven coverage in the area, the model is regularised with 3D-varying coefficients that change in concert with data sampling. The model reveals the presence of a large, low-velocity anomaly, rooted under eastern Greenland in the transition zone, that rises, upwards and eastwards, towards Iceland. At 50-100 km depth, the low velocity anomalies distributes along the Reykjanes and Kolbeinsey Ridges. We interpret the low-velocity body as the Iceland Plume, captured by the MOR. Our model shows thinner lithosphere in the western part of the Northeast Atlantic, under the Greenland Plate. This is consistent both with the location of the ascent of the plume we image and the distribution of seamounts, more numerous on the Greenland Plate. Finally, we use the phase velocity dispersion curves produced by AMI to compute a set of 98 Love and Rayleigh phase velocity maps on a grid with average 225 km spacing that allows to extract densely spaced, robust dispersion curves anywhere on the globe. The data coverage at most periods is global, and the phase velocities, although computed independently for each period, vary smoothly across the produced maps. Compared to previous datasets, our maps sample the presence of strong lateral heterogeneities in the scale of few hundreds of kilometres. At short and intermediate periods, where the range of the sampled depths is narrowest, we can match the results to known geological structures such as cratons, orogenic belts and mid-ocean ridges. We then extract dispersion curves at all points of the model grid, that show, when clustered together, distinct trends for the oceanic and continental lithosphere. We tested the resolution of our dispersion measurements at a regional scale in northwestern Mongolia; at short periods, our dispersion curves sample the different structure between the Hangai Dome and the neighbouring Lake Region, ~500 km apart, with lower velocities underneath the Hangai Dome, in agreement with its higher elevation
Seismic ground vibrations give advanced early-warning of subglacial floods
Get PDFGlacier runoff and melt from volcanic and geothermal activity accumulates in glacier dammed lakes in glaciated areas around the world. These lakes eventually drain, creating hazardous subglacial floods that are usually only confirmed after they exit the glacier and reach local
river systems, which can be many tens of kilometres from the flood source. Once in the river systems, they travel rapidly to populated areas. Such delayed detection represents a
potentially lethal shortcoming in early-warning. Here we demonstrate how to advance early warning potential through the analysis of four such floods in a glaciated region of Iceland. By comparing exceptional multidisciplinary hydrological, GPS and seismic ground vibration(tremor) data, we show that array analysis of seismic tremor can be used for early location and tracking of the subglacial flood front. Furthermore the timing and size of the impending
flood can be estimated, prior to it entering the river system. Advanced warnings of between 20 to 34 hours are achieved for large (peak discharge of more than 3000 m3/s, accumulation time of ~ 5.25 years) to small floods (peak discharges from 210 to 380 m3/s, accumulation times of ~ 1.3 years) respectively
