Crustal structure of the Azores Archipelago from Rayleigh wave ellipticity data

Determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings, and to assess seismic hazard in the islands. The Azores Archipelago is located near a triple junction system and is possibly under the influence of a mantle plume, being at the locus of a wide range of geodynamic processes. However, its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands. To address these limitations, in this study we invert teleseismic Rayleigh wave ellipticity measurements for 1-D shear wave speed (VS) crustal models of the Azores Archipelago. Moreover, we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models. We find that data from the westernmost seismic stations used in this study require a shallower Moho depth (∼10 km) than data from stations in the eastern part of the archipelago (∼13–16 km). This apparent increase in the Moho depth with increasing distance from the mid-Atlantic ridge (MAR) is expected. However, the rate at which Moho deepens away from the MAR is greater than that predicted from a half-space cooling model, suggesting that local tectonic perturbations have modified crustal structure. The 1-D VS models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations, which correlates well with the ages of the islands except Santa Maria Island. We interpret the relatively low VS profile found beneath Santa Maria Island as resulting from underplating, which agrees with previous geological studies of the island. Compared to a recent receiver function study of the region, the shallow structure (top ∼2 km) in our models shows lower shear wave speed, which may have important implications for future hazard studies of the region. More generally, the new seismic crustal models we present in this study will be useful to better understand the tectonics, seismicity, moment tensors and strong ground motions in the region

Efficient Generalized Spherical CNNs

Many problems across computer vision and the natural sciences require the analysis of spherical data, for which representations may be learned efficiently by encoding equivariance to rotational symmetries. We present a generalized spherical CNN framework that encompasses various existing approaches and allows them to be leveraged alongside each other. The only existing non-linear spherical CNN layer that is strictly equivariant has complexity OpC2L5q, where C is a measure of representational capacity and L the spherical harmonic bandlimit. Such a high computational cost often prohibits the use of strictly equivariant spherical CNNs. We develop two new strictly equivariant layers with reduced complexity OpCL4q and OpCL3 log Lq, making larger, more expressive models computationally feasible. Moreover, we adopt efficient sampling theory to achieve further computational savings. We show that these developments allow the construction of more expressive hybrid models that achieve state-of-the-art accuracy and parameter efficiency on spherical benchmark problems

Fast emulation of anisotropies induced in the cosmic microwave background by cosmic strings

Cosmic strings are linear topological defects that may have been produced during symmetry-breaking phase transitions in the very early Universe. In an expanding Universe the existence of causally separate regions prevents such symmetries from being broken uniformly, with a network of cosmic string inevitably forming as a result. To faithfully generate observables of such processes requires computationally expensive numerical simulations, which prohibits many types of analyses. We propose a technique to instead rapidly emulate observables, thus circumventing simulation. Emulation is a form of generative modelling, often built upon a machine learning backbone. End-to-end emulation often fails due to high dimensionality and insufficient training data. Consequently, it is common to instead emulate a latent representation from which observables may readily be synthesised. Wavelet phase harmonics are an excellent latent representations for cosmological fields, both as a summary statistic and for emulation, since they do not require training and are highly sensitive to non-Gaussian information. Leveraging wavelet phase harmonics as a latent representation, we develop techniques to emulate string induced CMB anisotropies over a 7.2 degree field of view, with sub-arcminute resolution, in under a minute on a single GPU. Beyond generating high fidelity emulations, we provide a technique to ensure these observables are distributed correctly, providing a more representative ensemble of samples. The statistics of our emulations are commensurate with those calculated on comprehensive Nambu-Goto simulations. Our findings indicate these fast emulation approaches may be suitable for wide use in, e.g., simulation based inference pipelines. We make our code available to the community so that researchers may rapidly emulate cosmic string induced CMB anisotropies for their own analysis

Irradiation-induced Ag nanocluster nucleation in silicate glasses: analogy with photography

The synthesis of Ag nanoclusters in sodalime silicate glasses and silica was studied by optical absorption (OA) and electron spin resonance (ESR) experiments under both low (gamma-ray) and high (MeV ion) deposited energy density irradiation conditions. Both types of irradiation create electrons and holes whose density and thermal evolution - notably via their interaction with defects - are shown to determine the clustering and growth rates of Ag nanocrystals. We thus establish the influence of redox interactions of defects and silver (poly)ions. The mechanisms are similar to the latent image formation in photography: irradiation-induced photoelectrons are trapped within the glass matrix, notably on dissolved noble metal ions and defects, which are thus neutralized (reverse oxidation reactions are also shown to exist). Annealing promotes metal atom diffusion, which in turn leads to cluster nuclei formation. The cluster density depends not only on the irradiation fluence, but also - and primarily - on the density of deposited energy and the redox properties of the glass. Ion irradiation (i.e., large deposited energy density) is far more effective in cluster formation, despite its lower neutralization efficiency (from Ag+ to Ag0) as compared to gamma photon irradiation.Comment: 48 pages, 18 figures, revised version publ. in Phys. Rev. B, pdf fil

CSF levels of glutamine synthetase and GFAP to explore astrocytic damage in seronegative NMOSD

OBJECTIVE: To explore levels of astrocytopathy in neuromyelitis optica spectrum disorder (NMOSD) by measuring levels of the astrocytic enzyme glutamine synthetase (GS) and glial fibrillary acidic protein (GFAP), an established astrocytic biomarker known to be associated with disease activity in multiple sclerosis. METHODS: Cerebrospinal fluid concentrations of GS and GFAP were measured by ELISA in patients with NMOSD (n=39, 28 aquaporin-4 (AQP4)-Ab-seropositive, 3 double-Ab-seronegative, 4 myelin oligodendrocyte glycoprotein (MOG)-Ab-seropositive and 4 AQP4-Ab-seronegative with unknown MOG-Ab-serostatus), multiple sclerosis (MS) (n=69), optic neuritis (n=5) and non-neurological controls (n=37). RESULTS: GFAP and GS concentrations differed significantly across groups (both p<0.001), showing a similar pattern of elevation in patients with AQP4-Ab-seropositive NMOSD. GS and GFAP were significantly correlated, particularly in patients with AQP4-Ab-seropositive NMOSD (rs=0.70, p<0.001). Interestingly, GFAP levels in some patients with double-Ab-seronegative NMOSD were markedly increased. CONCLUSIONS: Our data indicate astrocytic injury occurs in some patients with double-Ab-seronegative NMOSD, which hints at the possible existence of yet undiscovered astrocytic autoimmune targets. We hypothesise that elevated GS and GFAP levels could identify those double-Ab-seronegative patients suitable to undergo in-depth autoimmune screening for astrocytic antibodies

The investigation of acute optic neuritis: a review and proposed protocol

Optic neuritis is an inflammatory optic neuropathy that affects many patients with multiple sclerosis (MS) at some point during their disease course. Differentiation of acute episodes of MS-associated optic neuritis from other autoimmune and inflammatory optic neuropathies is vital for treatment choice and further patient management, but is not always straightforward. Over the past decade, a number of new imaging, laboratory and electrophysiological techniques have entered the clinical arena. To date, however, no consensus guidelines have been devised to specify how and when these techniques can be most rationally applied for the diagnostic work-up of patients with acute optic neuritis. In this article, we review the literature and attempt to formulate a consensus for the investigation of patients with acute optic neuritis, both in standard care and in research with relevance to clinical treatment trials

Update on biomarkers in neuromyelitis optica

Neuromyelitis optica (NMO) (and NMO spectrum disorder) is an autoimmune inflammatory disease of the CNS primarily affecting spinal cord and optic nerves. Reliable and sensitive biomarkers for onset, relapse, and progression in NMO are urgently needed because of the heterogeneous clinical presentation, severity of neurologic disability following relapses, and variability of therapeutic response. Detecting aquaporin-4 (AQP4) antibodies (AQP4-IgG or NMO-IgG) in serum supports the diagnosis of seropositive NMO. However, whether AQP4-IgG levels correlate with disease activity, severity, response to therapy, or long-term outcomes is unclear. Moreover, biomarkers for patients with seronegative NMO have yet to be defined and validated. Collaborative international studies hold great promise for establishing and validating biomarkers that are useful in therapeutic trials and clinical management. In this review, we discuss known and potential biomarkers for NMO