The rapid expansion of broad-band seismic networks over the last decade has paved the way for a new generation of global tomographic models. Significantly improved resolution of global upper-mantle ...and crustal structure can now be achieved, provided that structural information is extracted effectively from both surface and body waves and that the effects of errors in the data are controlled and minimized. Here, we present a new global, vertically polarized shear speed model that yields considerable improvements in resolution, compared to previous ones, for a variety of features in the upper mantle and crust. The model, SL2013sv, is constrained by an unprecedentedly large set of waveform fits (∼3/4 of a million broad-band seismograms), computed in seismogram-dependent frequency bands, up to a maximum period range of 11-450 s. Automated multimode inversion of surface and S-wave forms was used to extract a set of linear equations with uncorrelated uncertainties from each seismogram. The equations described perturbations in elastic structure within approximate sensitivity volumes between sources and receivers. Going beyond ray theory, we calculated the phase of every mode at every frequency and its derivative with respect to S- and P-velocity perturbations by integration over a sensitivity area in a 3-D reference model; the (normally small) perturbations of the 3-D model required to fit the waveforms were then linearized using these accurate derivatives. The equations yielded by the waveform inversion of all the seismograms were simultaneously inverted for a 3-D model of shear and compressional speeds and azimuthal anisotropy within the crust and upper mantle. Elaborate outlier analysis was used to control the propagation of errors in the data (source parameters, timing at the stations, etc.). The selection of only the most mutually consistent equations exploited the data redundancy provided by our data set and strongly reduced the effect of the errors, increasing the resolution of the imaging.
Our new shear speed model is parametrized on a triangular grid with a ∼280 km spacing. In well-sampled continental domains, lateral resolution approaches or exceeds that of regional-scale studies. The close match of known surface expressions of deep structure with the distribution of anomalies in the model provides a useful benchmark. In oceanic regions, spreading ridges are very well resolved, with narrow anomalies in the shallow mantle closely confined near the ridge axis, and those deeper, down to 100-120 km, showing variability in their width and location with respect to the ridge. Major subduction zones worldwide are well captured, extending from shallow depths down to the transition zone. The large size of our waveform fit data set also provides a strong statistical foundation to re-examine the validity field of the JWKB approximation and surface wave ray theory. Our analysis shows that the approximations are likely to be valid within certain time-frequency portions of most seismograms with high signal-to-noise ratios, and these portions can be identified using a set of consistent criteria that we apply in the course of waveform fitting.
Laboratory facilities employing high pulsed currents and voltages, and called generally "pulsed-power facilities," allow experimenters to produce a variety of hydrodynamical structures replicating, ...often in a scalable fashion, a broad range of dynamical astrophysical phenomena. Among these are astrophysical jets and outflows, astrophysical blast waves, magnetized radiatively dominated flows, and, more recently, aspects of simulated accretion disks. The magnetic field thought to play a significant role in most of the aforementioned objects is naturally present and controllable in pulsed-power environments. The size of the objects produced in pulsed-power experiments ranges from a centimeter to tens of centimeters, thereby allowing the use of a variety of diagnostic techniques. In a number of situations astrophysical morphologies can be replicated down to the finest structures. The configurations and their parameters are highly reproducible; one can vary them to isolate the most important phenomena and thereby help in developing astrophysical models. This approach has emerged as a useful tool in the quest to better understand magnetohydrodynamical effects in astronomical environments. The present review summarizes the progress made during the last decade and is designed to help readers identify and, perhaps, implement new experiments in this growing research area. Techniques used for the generation and characterization of the flows are described.
The deployment of USArray during the last decade has produced dense sampling of the central part of the North American continent with broadband seismic data. Regional tomography is now mapping the ...deep structure of the continent in great detail, in particular beneath the western US where USArray initiated. At the scale of the entire continent, however, the resolution of seismic imaging is uneven, much poorer away from the footprint of the array than beneath it. Important questions regarding the deep structure, lateral extent and evolution of the North American Craton, most of it not covered by USArray, thus remain difficult to answer. Here we present a new model of the upper mantle beneath North America constrained by waveform fits of 717 thousand vertical-component, broadband seismograms, of which over 228 thousand are from the Transportable Array component of USArray, a few tens of thousands from other USArray-affiliated stations, and the rest from global networks and arrays. Automated, multimode waveform inversion was used to extract structural information from surface and S waveforms, yielding resolving power from the crust down to the transition zone. Our unprecedentedly large waveform dataset, with highly complementary USArray and global-network subsets within it, produces improved resolution for a variety of features in North American upper mantle, compared to other available models. The internal structure of the North American Craton is resolved in detail. The lithosphere beneath the 1 Ga failed Mid-Continental Rift shows wavespeeds not as high as beneath surrounding cratons; it was probably altered. The sharp northern boundaries of the cratonic lithosphere closely follow the coastlines, with North America's and Greenland's lithospheric roots clearly separate. Sharp velocity gradients in western Canada indicate that the craton boundary at depth closely follows the Rocky Mountain Front at the surface. High velocities between the Great Bear Arc and Beaufort Sea provide convincing evidence for the recently proposed ‘MacKenzie Craton’, unexposed at the surface.
•New S-wave tomographic model of the North American upper mantle.•Global network seismic data combined with USArray and other regional networks.•The combination offers improved resolution at the scale of the entire North America.•Comparison with seven global and nine continental and regional scale models.•Higher resolution of cratonic structure and boundaries.
SUMMARY
We present a new global thermochemical model of the lithosphere and underlying upper mantle constrained by state of the art seismic waveform inversion, satellite gravity (geoid and gravity ...anomalies and gradiometric measurements from ESA's GOCE mission), surface elevation and heat flow data: WINTERC-G. The model is based upon an integrated geophysical–petrological approach where seismic velocities and density in the mantle are computed within a thermodynamically self-consistent framework, allowing for a direct parametrization in terms of the temperature and composition variables. The complementary sensitivities of the data sets allow us to constrain the geometry of the lithosphere–asthenosphere boundary, to separate thermal and compositional anomalies in the mantle, and to obtain a proxy for dynamic surface topography. At long spatial wavelengths, our model is generally consistent with previous seismic (or seismically derived) global models and earlier integrated studies incorporating surface wave data at lower lateral resolution. At finer scales, the temperature, composition and density distributions in WINTERC-G offer a new state of the art image at a high resolution globally (225 km average interknot spacing). Our model shows that the deepest lithosphere–asthenosphere boundary is associated with cratons and, also, some tectonically active areas (Andes, Persian Gulf). Among cratons we identify considerable differences in temperature and composition. The North American and Siberian Cratons are thick (>260 km) and compositionally refractory, whereas the Sino-Korean, Aldan and Tanzanian Cratons have a thinner, fertile lithosphere, similar to younger continental lithosphere elsewhere. WINTERC-G shows progressive thickening of oceanic lithosphere with age, but with significant regional differences: the lithospheric mantle beneath the Atlantic and Indian Oceans is, on average, colder, more fertile and denser than that beneath the Pacific Ocean. Our results suggest that the composition, temperature and density of the oceanic mantle lithosphere are related to the spreading rate for the rates up to 50–60 mm yr–1: the lower spreading rate, the higher the mantle fertility and density, and the lower the temperature. At greater spreading rates, the relationship disappears. The 1-D radial average of WINTERC-G displays a mantle geothermal gradient of 0.55–0.6 K km–1 and a potential temperature of 1300–1320 °C for depths >200 km. At the top of the mantle transition zone the amplitude of the maximum lateral temperature variations (cratons versus hotspots) is about 120 K. The isostatic residual topography values, a proxy for dynamic topography, are large (>1 km) mostly in active subduction settings. The residual isostatic bathymetry from WINTERC-G is remarkably similar to the pattern independently determined based on oceanic crustal data compilations. The amplitude of the continental residual topography is relatively large and positive (>600 m) in the East European Craton, Greenland, and the Andes and Himalayas. By contrast, central Asia, most of Antarctica, southern South America and, to a lesser extent, central Africa are characterized by negative residual topography values (>–400 m). Our results show that a substantial part of the topography signal previously identified as residual (or dynamic) is accounted for, isostatically, by lithospheric density variations.
Azimuthal seismic anisotropy, the dependence of seismic wave speeds on propagation azimuth, is largely due to fabrics within the Earth's crust and mantle, produced by deformation. It thus provides ...constraints on the distribution and evolution of deformation within the upper mantle. Here, we present a new global, azimuthally anisotropic model of the crust, upper mantle and transition zone. Two versions of this new model are computed: the rough SL2016svAr and the smooth SL2016svA. Both are constrained by a very large data set of waveform fits (∼750 000 vertical component seismogram fits). Automated, multimode waveform inversion was used to extract structural information from surface and S wave forms in broad period ranges (dominantly from 11 to 450 s, with the best global sampling in the 20–350 s range), yielding resolving power from the crust down to the transition zone. In our global tomographic inversion, regularization of anisotropy is implemented to more uniformly recover the amplitude and orientation of anisotropy, including near the poles. Our massive waveform data set, with complementary large global networks and high-density regional array data, produces improved resolution of global azimuthal anisotropy patterns. We show that regional scale variations, related to regional lithospheric deformation and mantle flow, can now be resolved by the global models, in particular in densely sampled regions. For oceanic regions, we compare quantitatively the directions of past and present plate motions and the fast-propagation orientations of anisotropy. By doing so, we infer the depth of the boundary between the rigid, high-viscosity lithosphere (preserving ancient, frozen fabric) and the rheologically weak asthenosphere (characterized by fabric developed recently). The average depth of thus inferred rheological lithosphere-asthenosphere boundary (LAB) beneath the world's oceans is ∼115 km. The LAB depth displays a clear dependence on the age of the oceanic lithosphere, closely matching the 1200 °C half-space cooling isotherm for all oceanic ages. In continental regions, azimuthal anisotropy is characterized by smaller-scale 3-D variations. Quantitative comparisons of the tomographic models with global SKS splitting measurements confirm the basic agreement of the two types of anisotropy analysis; they also offer a new insight into the average rheological thickness of continental lithosphere. In spite of significant recent improvements in the resolution of upper-mantle anisotropic structure, correlations between the anisotropic components of current global tomographic models remain much lower than between the isotropic ones. Our comparisons of the current models show which features are resolved consistently by different models, and therefore provide a means to estimate the robustness of anisotropic patterns and amplitudes. Significantly lower correlations are observed at depths greater than ∼300 km, compared to those shallower, which suggests that global azimuthal anisotropy models are yet to reach consensus on the nature of anisotropy in the transition zone.
In nanographite films, for the first time, when measuring the current–voltage characteristics, the Josephson current at room temperature has been detected, which confirms the earlier observations in ...nanographite films of the effects of weak superconductivity: zeroing of the temperature dependence at 650 K of the constant voltage on the sample when exposed to an alternating microwave voltage due to the inverse Josephson effect, as well as observation in a magnetic force microscope of local regions with the structure of magnetic vortices at room temperature. The obtained value of the critical current of 0.8 μA is significantly lower than the expected value for the superconducting gap, as well as for pinning at the Bean–Levingston barrier. Measures for increasing the critical current are proposed.
The review of structural, electronic and magnetic properties of nanographite films is presented. The superconducting correlations such as AC-to-DC conversion associated with the reversed Josephson ...Effect, pinning of vortices on columnar topological structure of film surface observed in atomic force and magnetic force microscope, non-zero current at zero voltage in scanning tunneling microscope in local area of nanographite film surface have been found. These results are broadly in line with other our observations on abrupt resistivity jump accompanied by light emission having potential applications as switchers and compact light emitter. Further experiments on studies of local conductivity related to ion irradiation hoping to find a zero resistance state are proposed.
SUMMARY
We present a tomographic model of the crust, upper mantle and transition zone beneath the South Atlantic, South America and Africa. Taking advantage of the recent growth in broadband data ...sampling, we compute the model using waveform fits of over 1.2 million vertical-component seismograms, obtained with the automated multimode inversion of surface, S and multiple S waves. Each waveform provides a set of linear equations constraining perturbations with respect to a 3-D reference model within an approximate sensitivity volume. We then combine all equations into a large linear system and solve it for a 3-D model of S- and P-wave speeds and azimuthal anisotropy within the crust, upper mantle and uppermost lower mantle. In South America and Africa, our new model SA2019 reveals detailed structure of the lithosphere, with structure of the cratons within the continents much more complex than seen previously. In South America, lower seismic velocities underneath the transbrasilian lineament (TBL) separate the high-velocity anomalies beneath the Amazon Craton from those beneath the São Francisco and Paraná Cratons. We image the buried portions of the Amazon Craton, the thick cratonic lithosphere of the Paraná and Parnaíba Basins and an apparently cratonic block wedged between western Guyana and the slab to the west of it, unexposed at the surface. Thick cratonic lithosphere is absent under the Archean crust of the São Luis, Luis Álves and Rio de La Plata Cratons, next to the continental margin. The Guyana Highlands are underlain by low velocities, indicating hot asthenosphere. In the transition zone, we map the subduction of the Nazca Plate and the Chile Rise under Patagonia. Cratonic lithosphere beneath Africa is more fragmented than seen previously, with separate cratonic units observed within the West African and Congo Cratons, and with cratonic lithosphere absent beneath large portions of Archean crust. We image the lateral extent of the Niassa Craton, hypothesized previously and identify a new unit, the Cubango Craton, near the southeast boundary of the grater Congo Craton, with both of these smaller cratons unexposed at the surface. In the South Atlantic, the model reveals the patterns of interaction between the Mid-Atlantic Ridge (MAR) and the nearby hotspots. Low-velocity anomalies beneath major hotspots extend substantially deeper than those beneath the MAR. The Vema Hotspot, in particular, displays a pronounced low-velocity anomaly under the thick, high-velocity lithosphere of the Cape Basin. A strong low velocity anomaly also underlies the Cameroon Volcanic Line and its offshore extension, between Africa and the MAR. Subtracting the global, age-dependent VS averages from those in the South Atlantic Basins, we observe areas where the cooling lithosphere is locally hotter than average, corresponding to the location of the Tristan da Cunha, Vema and Trindade hotspots. Beneath the anomalously deep Argentine Basin, we image unusually thick, high-velocity lithosphere, which suggests that its anomalously great depth can be explained, at least to a large extent, by isostatic, negative lithospheric buoyancy.
Abstract
Aims
Delay of progression from paroxysmal to persistent atrial fibrillation (AF) is an important measure of long-term success of AF treatment. However, published data on the impact of ...catheter ablation on AF progression are limited. This study evaluates whether radiofrequency (RF) catheter ablation delays the progression of AF compared with antiarrhythmic drug (AAD) treatment using current AF management guidelines.
Methods
This prospective, randomized, controlled, two-arm, open-label trial was conducted at 29 hospitals and medical centres across 13 countries. Patients were randomized 1 : 1 to RF ablation or AAD treatment. The primary endpoint was the rate of persistent AF/atrial tachycardia (AT) at 3 years.
Results
After early study termination following slow enrolment, 255 (79%) of the planned 322 patients were enrolled (RF ablation, n = 128, AAD, n = 127); 36% of patients in the RF ablation group and 41% in the AAD group completed 3 years of follow-up. For the primary endpoint, the Kaplan–Meier estimate of the rate of persistent AF/AT at 3 years was significantly lower with RF ablation 2.4% (95% confidence interval (CI), 0.6–9.4%) than with AAD therapy 17.5% (95% CI, 10.7–27.9%); one-sided P = 0.0009. Patients ≥65 years were ∼4 times more likely to progress to persistent AF/AT than patients <65 years, suggesting RF ablation can delay disease progression hazard ratio: 3.87 (95% CI, 0.88–17.00); P = 0.0727. Primary adverse events were reported for eight patients in the RF ablation group.
Conclusions
Radiofrequency ablation is superior to guideline-directed AAD therapy in delaying the progression from paroxysmal to persistent AF.
Financial cosmopolitanism is usually seen as an attribute of the first wave of globalization from the late 19th century until the First World War. The article is devoted to the activity of the ...business elite of Russian origin in Europe on the examples of the fate of large banker families members: Raffalovich, Lessin, Nemirovsky and others. The author shows the diverse connections between the European bourgeoisie and the artistic circles. Several phases of the development of the phenomenon of financial cosmopolitanism are distinguished in relations to Russia and to the Russian big bourgeoisie in exile up to the end of 1920s.
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