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  • Oxford University Press  (98,441)
  • American Association for the Advancement of Science (AAAS)
  • American Association of Petroleum Geologists (AAPG)
  • Periodicals Archive Online (PAO)
  • 2015-2019  (104,509)
  • 1970-1974  (27,575)
  • 1945-1949  (7,057)
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  • 101
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    Tomography of crust and lithosphere in the western Indian Ocean from noise cross-correlations of land and ocean bottom seismometers (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉We use seismic noise cross-correlations to obtain a 3-D tomography model of 〈span〉SV〈/span〉-wave velocities beneath the western Indian Ocean, in the depth range of the oceanic crust and uppermost mantle. The study area covers 2000 × 2000 km〈sup〉2〈/sup〉 between Madagascar and the three spreading ridges of the Indian Ocean, centred on the volcanic hotspot of La Réunion. We use seismograms from 38 ocean bottom seismometers (OBSs) deployed by the RHUM-RUM project and 10 island stations on La Réunion, Madagascar, Mauritius, Rodrigues, and Tromelin. Phase cross-correlations are calculated for 1119 OBS-to-OBS, land-to-OBS, and land-to-land station pairs, and a phase-weighted stacking algorithm yields robust group velocity measurements in the period range of 3–50 s. We demonstrate that OBS correlations across large interstation distances of 〉2000 km are of sufficiently high quality for large-scale tomography of ocean basins. Many OBSs yielded similarly good group velocity measurements as land stations. Besides Rayleigh waves, the noise correlations contain a low-velocity wave type propagating at 0.8–1.5 km s〈sup〉−1〈/sup〉 over distances exceeding 1000 km, presumably Scholte waves travelling through seafloor sediments. The 100 highest-quality group velocity curves are selected for tomographic inversion at crustal and lithospheric depths. The inversion is executed jointly with a data set of longer-period, Rayleigh-wave phase and group velocity measurements from earthquakes, which had previously yielded a 3-D model of Indian Ocean lithosphere and asthenosphere. Robust resolution tests and plausible structural findings in the upper 30 km validate the use of noise-derived OBS correlations for adding crustal structure to earthquake-derived tomography of the oceanic mantle. Relative to crustal reference model CRUST1.0, our new shear-velocity model tends to enhance both slow and fast anomalies. It reveals slow anomalies at 20 km depth beneath La Réunion, Mauritius, Rodrigues Ridge, Madagascar Rise, and beneath the Central Indian spreading ridge. These structures can clearly be associated with increased crustal thickness and/or volcanic activity. Locally thickened crust beneath La Réunion and Mauritius is probably related to magmatic underplating by the hotspot. In addition, these islands are characterized by a thickened lithosphere that may reflect the depleted, dehydrated mantle regions from which the crustal melts where sourced. Our tomography model is available as electronic supplement.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 102
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    A geothermal application for GOCE satellite gravity data: modelling the crustal heat production and lithospheric temperature field in Central Europe (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Since the completion of the Gravity field and steady-state Ocean Circulation Explorer mission (GOCE), global gravity models of uniform quality and coverage are available. We investigate their potential of being useful tools for estimating the thermal structure of the continental lithosphere, through simulation and real-data test in Central-Eastern Europe across the Trans-European Suture Zone. Heat flow, measured near the Earth surface, is the result of the superposition of a complex set of contributions, one of them being the heat production occurring in the crust. The crust is enriched in radioactive elements respect to the underlying mantle and crustal thickness is an essential parameter in isolating the thermal contribution of the crust. Obtaining reliable estimates of crustal thickness through inversion of GOCE-derived gravity models has already proven feasible, especially when weak constraints from other observables are introduced. We test a way to integrate this in a geothermal framework, building a 3-D, steady state, solid Earth conductive heat transport model, from the lithosphere–asthenosphere boundary to the surface. This thermal model is coupled with a crust-mantle boundary depth resulting from inverse modelling, after correcting the gravity model for the effects of topography, far-field isostatic roots and sediments. We employ a mixed space- and spectral-domain based forward modelling strategy to ensure full spectral coherency between the limited spectral content of the gravity model and the reductions. Deviations from a direct crustal thickness to crustal heat production relationship are accommodated using a subsequent substitution scheme, constrained by surface heat flow measurements, where available. The result is a 3-D model of the lithosphere characterised in temperature, radiogenic heat and thermal conductivity. It provides added information respect to the lithospheric structure and sparse heat flow measurements alone, revealing a satisfactory coherence with the geological features in the area and their controlling effect on the conductive heat transport.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 103
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    Interferometric time-lapse velocity analysis: application to a salt-water disposal well in British Columbia, Canada (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉We investigate the possibility of passive monitoring of a salt-water disposal well in British Columbia, Canada, using continuously recorded ambient seismic noise. We find seismic velocity variations induced by a reduction of injection pressure in an effort to mitigate an elevated level of seismicity, most likely associated with the disposal of salt water. The relative velocity variations are derived from time-shifts measured between consecutive cross-correlation functions for each station pair in a surface array composed of five broad-band seismometers. The probable driving mechanisms responsible for the velocity changes are reduced pore pressures and/or lowered poroelastic stresses beyond the injection wellbore, respectively. Hydrologic data (e.g. snow and rainfall), noise energy trends and fluctuations in the incident direction of dominant noise sources do not correlate with the estimated relative velocity variations. Velocity variations are detected ahead of the zone of induced seismicity, thus indicating that seismic interferometry may aid in mitigation efforts to reduce the risk of induced seismicity by (1) providing verifiable and repeatable measurements of physical changes within the surrounding area and (2) providing hard constraints for modelling efforts to constrain how and where pore-pressure fronts change.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 104
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    A physically based model for the electrical conductivity of water-saturated porous media (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Electrical conductivity is one of the most commonly used geophysical method for reservoir and environmental studies. Its main interest lies in its sensitivity to key properties of storage and transport in porous media. Its quantitative use therefore depends on the efficiency of the petrophysical relationship to link them. In this work, we develop a new physically based model for estimating electrical conductivity of saturated porous media. The model is derived assuming that the porous media is represented by a bundle of tortuous capillary tubes with a fractal pore-size distribution. The model is expressed in terms of the porosity, electrical conductivity of the pore liquid and the microstructural parameters of porous media. It takes into account the interface properties between minerals and pore water by introducing a surface conductivity. Expressions for the formation factor and hydraulic tortuosity are also obtained from the model derivation. The model is then successfully compared with published data and performs better than previous models. The proposed approach also permits to relate the electrical conductivity to other transport properties such as the hydraulic conductivity.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 105
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    Removing mantle lithosphere under orogens: delamination versus convective thinning (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Thinning of the lithosphere under continental collisional orogens is often attributed to delamination or convective thinning. Both processes remove part or all of the mantle lithosphere that has become denser and gravitationally unstable. Previous studies mostly focused on the different thermomagmatic consequences of these two processes; the dynamic links between them, and the critical conditions for one or the other process to dominate lithosphere thinning, remain uncertain. Here, we used high-resolution thermomechanical models with various rheology (linear viscous, power-law viscous and/or the extended Drucker–Prager plasticity) to systematically investigate the dynamics of delamination and convective thinning under collisional orogens. Our results show that convective thinning is favoured in models of linear (Newtonian) viscous rheology and low viscosity $({10^{19}}\!-\! {10^{20}}\,\,{\rm{Pa}} \, {\rm{s}})$. Power-law viscous rheology promotes strain localization, which reduces the effective viscosity and may lead to localized rising of the asthenosphere to the crustal base, thus triggering delamination. Further strain localization and stronger delamination are predicted with inclusion of plastic rheology in the model. These results indicate that convective thinning and delamination are dynamically linked and can occur in the same orogeny. Their relative dominance during orogenesis may be distinguished by the resulting spatiotemporal evolutions of thermal perturbation, magmatism and elevation changes. We applied the models to show that the evolution of the Central Anatolian Plateau is consistent with the dominance of convective thinning, whereas delamination played a major role in thinning the mantle lithosphere under central-northern Tibetan Plateau.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 106
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    Anthropogenic seismicity as aftershocks for geo-resource production? Implications for Mmax estimates (reservoir impoundment cases) (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Developing a model for anthropogenic seismic hazard remains an open challenge whatever the geo-resource production. We analyse the (〈span〉M〈/span〉〈sub〉max〈/sub〉) largest reported magnitude on each site where (RTS) Reservoir Triggered Seismicity in documented (37 events, 1933–2008), for aftershocks of reservoir impoundment loading. We relate each reservoir impoundment to its magnitude-equivalent 〈span〉M〈/span〉*〈sub〉reservoir〈/sub〉 = 〈span〉M〈/span〉*(〈span〉L〈/span〉〈sub〉r〈/sub〉). We use (〈span〉L〈/span〉〈sub〉r〈/sub〉) the reservoir length as a proxy for a rupture length of the reservoir main shock-equivallent. This latter is derived from the empirical relationship that exists for tectonic earthquake among magnitude and rupture length. We resolve (i) 〈span〉M〈/span〉〈sub〉max〈/sub〉 for RTS are bounded by 〈span〉M〈/span〉*〈sub〉reservoir〈/sub〉 at a 95 per cent confidence level; (ii) in average 〈span〉M〈/span〉〈sub〉max〈/sub〉 are smaller than 〈span〉M〈/span〉*〈sub〉reservoir〈/sub〉 by 2.2 units (iii) 50 per cent of the 〈span〉M〈/span〉〈sub〉max〈/sub〉 occurrence is within 2 ± 1 yr from the reservoir impoundment. These triggering patterns support the signature of fluid driven seismicity during the slow reservoir impoundment emerges as a weaker efficiency (larger Δ〈span〉M〈/span〉 = 〈span〉M〈/span〉*〈sub〉reservoir〈/sub〉 – 〈span〉M〈/span〉〈sub〉max〈/sub〉) to trigger 〈span〉M〈/span〉〈sub〉max〈/sub〉 events than from earthquake interactions.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 107
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    Holocene slip rate of the frontal thrust in the western Qilian Shan, NE Tibetan Plateau (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉The activities of frontal thrusts in the northern Qilian Shan are critical for understanding the deformation of the Qilian Shan and the northeastern Tibetan Plateau. In this study, we estimate the slip rate of the active Fodongmiao–Hongyazi thrust along the northern margin of the Qilian Shan. High-resolution satellite imagery interpretations and detailed field investigations suggest that the fault displaced late Pleistocene terraces and formed fresh prominent north-facing fault scarps. To quantify the slip rate of the fault, we measured the displacements along the fault scarps using an unmanned aerial vehicle system and dated the displaced geomorphic surfaces using optically stimulated luminescence (OSL) and 〈sup〉14〈/sup〉C methods. The vertical slip rate of the fault is estimated at 1.0 ± 0.3 mm yr〈sup〉−1〈/sup〉 for the western segment. The slip rates for two branches in the eastern segment are 0.3 ± 0.1 and 0.6 ± 0.1 mm yr〈sup〉−1〈/sup〉. Using a fault dip of 40 ± 10°, we constrain the corresponding shortening rates to 1.4 ± 0.5 and 1.2 ± 0.4 mm yr〈sup〉−1〈/sup〉, respectively. The rates are consistent with values over different timescales, which suggests steady rock uplift and northeastward growth of the western Qilian Shan. Crustal shortening occurs mainly on the range-bounding frontal thrust.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 108
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    A computational method for earthquake cycles within anisotropic media (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉We present a numerical method for the simulation of earthquake cycles on a 1-D fault interface embedded in a 2-D homogeneous, anisotropic elastic solid. The fault is governed by an experimentally motivated friction law known as rate-and-state friction which furnishes a set of ordinary differential equations which couple the interface to the surrounding volume. Time enters the problem through the evolution of the ordinary differential equations along the fault and provides boundary conditions for the volume, which is governed by quasi-static elasticity. We develop a time-stepping method which accounts for the interface/volume coupling and requires solving an elliptic partial differential equation for the volume response at each time step. The 2-D volume is discretized with a second-order accurate finite difference method satisfying the summation-by-parts property, with boundary and fault interface conditions enforced weakly. This framework leads to a provably stable semi-discretization. To mimic slow tectonic loading, the remote side-boundaries are displaced at a slow rate, which eventually leads to earthquake nucleation at the fault. Time stepping is based on an adaptive, fourth-order Runge–Kutta method and captures the highly varying timescales present. The method is verified with convergence tests for both the orthotropic and fully anisotropic cases. An initial parameter study reveals regions of parameter space where the systems experience a bifurcation from period one to period two behaviour. Additionally, we find that anisotropy influences the recurrence interval between earthquakes, as well as the emergence of aseismic transients and the nucleation zone size and depth of earthquakes.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 109
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    Palaeomagnetism of Late Triassic volcanic rocks from the western margin of Khorat Basin, Thailand and its implication for ambiguous inclination shallowing in Mesozoic sediments of Indochina (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Palaeomagnetic constraints are essential factors in the reconstruction of the Mesozoic convergence of Eastern Asia blocks. As one of the key blocks, Indochina was constrained only by sedimentary-rocks-derived palaeomagnetic data. To evaluate whether the palaeomagnetic data used to restore the Late Triassic position of Indochina suffered inclination shallowing effects, we conducted a palaeomagnetic and geochronologic study on a coeval volcanic clastic rocks sequence in the western margin of the Khorat Basin, Thailand. The U-Pb SIMS dating on zircons indicates the age of the sampling section is between 205.1 ± 1.5 and 204.7 ± 1.4 Ma. Site mean directions are D〈sub〉g〈/sub〉/I〈sub〉g〈/sub〉 = 217.2°/−39.4° (κ〈sub〉g〈/sub〉 = 45.1, α〈sub〉95g〈/sub〉 = 10.1°) before and D〈sub〉s〈/sub〉/I〈sub〉s〈/sub〉 = 209.2°/−44.5° (κ〈sub〉s〈/sub〉 = 43.8, α〈sub〉95s〈/sub〉 = 10.2°) after tilt correction. The new data set indicates a positive reversal test result at ‘Category C’ level. The characteristic remanent magnetization recorded by the coexistent magnetite and hematite is interpreted to be primary remanence acquired during the initial cooling of the volcanic clastic rocks. The consistence of the corresponding palaeolatitudes derived from the volcanic clastic rocks and the former reported sedimentary rocks suggests that there is probably no significant inclination shallowing bias in the sedimentary-rocks-derived palaeomagnetic data. Therefore, the estimates of the Late Triassic position of Indochina are confirmed to be reliable. The Indochina Block had collided to the southern margin of Eurasia by the Late Triassic and played an important role in the Mesozoic convergence of the Eastern Asia blocks.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 110
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    A non-perturbative method for gravitational potential calculations within heterogeneous and aspherical planets (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉We present a numerically exact method for calculating the internal and external gravitational potential of aspherical and heterogeneous planets. Our approach is based on the transformation of Poisson’s equation into an equivalent equation posed on a spherical computational domain. This new problem is solved in an efficient iterative manner based on a hybrid pseudospectral/spectral element discretization. The main advantage of our method is that its computational cost reflects the planet’s geometric and structural complexity, being in many situations only marginally more expensive than boundary perturbation theory. Several numerical examples are presented to illustrate the method’s efficacy and potential range of applications.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 111
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    A generalized Rytov approximation for accurate calculation of phase variation in strong perturbation media (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉In the case of long-range propagation of forward scattering, due to the accumulation of phase changes caused by the velocity perturbations, the validity of the Born approximation will be violated. In contrast, the phase-change accumulation can be handled by the Rytov approximation, which has been widely used for long-distance propagation with only forward scattering or small-angle scattering involved. However, the weak scattering assumption (i.e. small velocity perturbation) in the Rytov approximation limits its scope of application. To address this problem, we analyse the integral kernel of the Rytov transform using the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation and we demonstrate that the integral kernel is a function of velocity perturbation and scattering angle. By applying a small scattering angle approximation, we show that the phase variation has a linear relationship with the slowness perturbation, no matter how strong the magnitude of perturbation is. Therefore, the new integral equation is then referred to as the generalized Rytov approximation (GRA) because it overcomes the weak scattering assumption of the Rytov approximation. To show the limitations of the Rytov approximation and the advantages of the proposed GRA method, first we design a two-layer model and we analytically calculate the errors introduced by the small scattering angle assumption using plane wave incidence. We show that the phase (traveltime) variations predicted by the GRA are always more accurate than the Rytov approximation. Particularly, the GRA produces accurate phase variations for the normal incident plane wave regardless of the magnitude of velocity perturbation. Numerical examples using Gaussian anomaly models demonstrate that the scattering angle has a crucial impact on the accuracy of the GRA. If the small scattering angle assumption holds, the GRA can produce an accurate phase approximation even if the velocity perturbation is very strong. On the contrary, both the first-order Rytov approximation and the GRA fail to get satisfying results when the scattering angle is large enough. The proposed GRA method has the potential to be used for traveltime modelling and inversion for large-scale strong perturbation media.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 112
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    Mapping geologic features onto subducted slabs (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Estimating the location of geologic and tectonic features on a subducting plate is important for interpreting their spatial relationships with other observables including seismicity, seismic velocity and attenuation anomalies, and the location of ore deposits and arc volcanism in the over-riding plate. Here we present two methods for estimating the location of predictable features such as seamounts, ridges and fracture zones on the slab. One uses kinematic reconstructions of plate motions, and the other uses multidimensional scaling to flatten the slab onto the surface of the Earth. We demonstrate the methods using synthetic examples and also using the test case of fracture zones entering the Lesser Antilles subduction zone. The two methods produce results that are in good agreement with each other in both the synthetic and real examples. In the Lesser Antilles, the subducted fracture zones trend northwards of the surface projections. The two methods begin to diverge in regions where the multidimensional scaling method has its greatest likely error. Wider application of these methods may help to establish spatial correlations globally.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 113
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    Microbial metabolites control the thymic development of mucosal-associated invariant T cells (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉How the microbiota modulate immune functions remains poorly understood. Mucosal-associated invariant T (MAIT) cells are implicated in mucosal homeostasis and absent in germ-free mice. Here, we show that commensal bacteria govern murine MAIT intrathymic development, as MAIT cells did not recirculate to the thymus. MAIT development required 〈i〉RibD〈/i〉 expression in bacteria, indicating that production of the MAIT antigen 5-(2-oxopropylideneamino)-6-〈scp〉d〈/scp〉-ribitylaminouracil (5-OP-RU) was necessary. 5-OP-RU rapidly traveled from mucosal surfaces to the thymus, where it was captured by the major histocompatibility complex class Ib molecule MR1. This led to increased numbers of the earliest MAIT precursors and the expansion of more mature receptor–related orphan receptor t–positive MAIT cells. Thus, a microbiota-derived metabolite controls development of mucosally targeted T cells, in a process blurring the distinction between exogenous and self-antigens.〈/p〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 114
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    Detection of weak seismic sequences based on arrival time coherence and empiric network detectability: an application at a near fault observatory (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Microseismic monitoring is a primary tool for understanding and tracking the progress of mechanical processes occurring in active rock fracture systems. In geothermal or hydrocarbon fields or along seismogenic fault systems, the detection and location of microseismicity facilitates resolution of the fracture system geometry and the investigation of the interaction between fluids and rocks, in response of stress field perturbations. Seismic monitoring aims to detect locate and characterize seismic sources. The detection of weak signals is often achieved at the cost of increasing the number of false detections, related to transient signals generated by a range of noise sources, or related to instrumental problems, ambient conditions or human activity that often affect seismic records. A variety of fast and automated methods has been recently proposed to detect and locate microseismicity based on the coherent detection of signal anomalies, such as increase in amplitude or coherent polarization, at dense seismic networks. While these methods proved to be very powerful to detect weak events and to reduce the magnitude of completeness, a major problem remains to discriminate among weak seismic signals produced by microseismicity and false detections. In this work, the microseimic data recorded along the Irpinia fault zone (Southern Apennines, Italy) are analysed to detect weak, natural earthquakes using one of such automated, migration-based, method. We propose a new method for the automatic discrimination of real vs false detections, which is based on empirical data and information about the detectability (i.e. detection capability) of the seismic network. Our approach allows obtaining high performances in detecting earthquakes without requiring a visual inspection of the seismic signals and minimizing analyst intervention. The proposed methodology is automated, self-updating and can be tuned at different success rates.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 115
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    A multitaper spectral estimator for time-series with missing data (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉A multitaper estimator is proposed that accommodates time-series containing gaps without using any form of interpolation. In contrast with prior missing-data multitaper estimators that force standard Slepian sequences to be zero at gaps, the proposed missing-data Slepian sequences are defined only where data are present. The missing-data Slepian sequences are frequency independent, as are the eigenvalues that define the energy concentration within the resolution bandwidth, when the process bandwidth is $[ { - 1/2,\,\,\,1/2} )$ for unit sampling and the sampling scheme comprises integer multiples of unity. As a consequence, one need only compute the ensuing missing-data Slepian sequences for a given sampling scheme once, and then the spectrum at an arbitrary set of frequencies can be computed using them. It is also shown that the resulting missing-data multitaper estimator can incorporate all of the optimality features (i.e. adaptive-weighting, 〈span〉F〈/span〉-test and reshaping) of the standard multitaper estimator, and can be applied to bivariate or multivariate situations in similar ways. Performance of the missing-data multitaper estimator is illustrated using length of day, seafloor pressure and Nile River low stand time-series.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 116
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    Full-waveform matching of VP and VS models from surface waves (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉The analysis of surface wave dispersion curves (DCs) is widely used for near-surface 〈span〉S〈/span〉-wave velocity (VS) reconstruction. However, a comprehensive characterization of the near-surface requires also the estimation of 〈span〉P〈/span〉-wave velocity (VP). We focus on the estimation of both VS and VP models from surface waves using a direct data transform approach. We estimate a relationship between the wavelength of the fundamental mode of surface waves and the investigation depth and we use it to directly transform the DCs into VS and VP models in laterally varying sites. We apply the workflow to a real data set acquired on a known test site. The accuracy of such reconstruction is validated by a waveform comparison between field data and synthetic data obtained by performing elastic numerical simulations on the estimated VP and VS models. The uncertainties on the estimated velocity models are also computed.〈/span〉
    Print ISSN: 2051-1965
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    Topics: Geosciences
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    Seismic signal recognition by unsupervised machine learning (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Seismic signal recognition can serve as a powerful auxiliary tool for analysing and processing ever-larger volumes of seismic data. It can facilitate many subsequent procedures such as first-break picking, statics correction, denoising, signal detection, events tracking, structural interpretation, inversion and imaging. In this study, I propose an automatic technique of seismic signal recognition taking advantage of unsupervised machine learning. In the proposed technique, seismic signal recognition is considered as a problem of clustering data points. All the seismic sampling points in time domain are clustered into two clusters, that is, signal or non-signal. The hierarchical clustering algorithm is used to group these sampling points. Four attributes, that is, two short-term-average-to-long-term-average ratios, variance and envelope are investigated in the clustering process. In addition, to quantitatively evaluate the performance of seismic signal recognition properly, I propose two new statistical indicators, namely, the rate between the total energies of original and recognized signals (RTE), and the rate between the average energies of original and recognized signals (RAE). A large number of numerical experiments show that when the signal is slightly corrupted by noise, the proposed technique performs very well, with recognizing accuracy, precision and RTE of nearly 1 (i.e. 100 per cent), recall greater than 0.8 and RAE about 1–1.3. When the signal is moderately corrupted by noise, the proposed technique can hold recognizing accuracy about 0.9, recognizing precision nearly to 1, RTE about 0.9, recall around 0.6 and RAE about 1.5. Applications of the proposed technique to real microseismic data induced from hydraulic fracturing and reflection seismic data demonstrate its feasibility and encouraging prospect.〈/span〉
    Print ISSN: 2051-1965
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    Topics: Geosciences
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    The Mount Meron infrasound array: an infrasound array without a noise reduction system (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Measurements of seismo-acoustic events by collocated seismic and infrasound arrays allow for studying the two wavefields that were produced by the same event. However, some of the scientific and technical constraints on the building of the two technologies are different and may be contradicting. For the case of a new station, an optimal design that will satisfy the constraints of the two technologies can be found. However, in the case of upgrading an existing array by adding the complementing technology, the situation is different. The site location, the array configuration and physical constraints are fixed and may not be optimal for the complementing technology, which may lead to rejection of the upgrade. The International Monitoring System (IMS) for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) includes 37 seismic arrays and 51 infrasound arrays. Although the CTBT verification regime is fixed in the treaty, an upgrade of the existing arrays by adding more technologies is possible.The Mount Meron seismic array (MMAI), which is part of the IMS, is composed of 16 sites. Microbarometers were installed at five MMAI sites to form the Mount Meron infrasound array. Due to regulation and physical constraints, it was not possible to relocate the sites nor to install analogue noise reduction filters (i.e. a pipe array). In this study, it is demonstrated that the installation of the MMAI infrasound array is beneficial despite the non-optimal conditions. It is shown that the noise levels of the individual array sites are between the high and median global noise levels. However, we claim that the more indicative measures are the noise levels of the beams of interest, as demonstrated by analysing the microbaroms originated from the Mediterranean Sea. Moreover, the ability to detect events relevant to the CTBT is demonstrated by analysing man-made events during 2011 from the Libya region.〈/span〉
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    The effect of stress changes on time-dependent earthquake probabilities for the central Wasatch fault zone, Utah, USA (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Static and quasi-static Coulomb stress changes produced by large earthquakes can modify the probability of occurrence of subsequent events on neighbouring faults. This approach is based on physical (Coulomb stress changes) and statistical (probability calculations) models, which are influenced by the quality and quantity of data available in the study region. Here, we focus on the Wasatch fault zone (WFZ), a well-studied active normal fault system having abundant geological and palaeoseismological data. Palaeoseismological trench investigations of the WFZ indicate that at least 24 large, surface-faulting earthquakes have ruptured the fault's five central, 35–59-km long segments since ∼7 ka. Our goal is to determine if the stress changes due to the youngest palaeoevents have significantly modified the present-day probability of occurrence of large earthquakes on each of the segments. For each segment, we modelled the cumulative (coseismic + post-seismic) Coulomb stress changes (∆CFS〈sub〉cum〈/sub〉) due to earthquakes younger than the most recent event on the segment in question and applied the resulting values to the time-dependent probability calculations. Results from the Coulomb stress modelling suggest that the Brigham City, Salt Lake City, and Provo segments have accumulated ∆CFS〈sub〉cum〈/sub〉 larger than 10 bar, whereas the Weber segment has experienced a stress decrease of 5 bar, in the scenario of recent rupture of the Great Salt Lake fault to the west. Probability calculations predict high probability of occurrence for the Brigham City and Salt Lake City segments, due to their long elapsed times (〉1–2 ka) when compared to the Weber, Provo and Nephi segments (〈1 ka). The range of calculated coefficients of variation has a large influence on the final probabilities, mostly in the case of the Brigham City segment. Finally, when the Coulomb stress and the probability models are combined, our results indicate that the ∆CFS〈sub〉cum〈/sub〉 resulting from earthquakes post-dating the youngest events on each of the five segments substantially affects the probability calculations for three of the segments: Brigham City, Salt Lake City and Provo. The probability of occurrence of a large earthquake in the next 50 yr on these three segments may, therefore, be underestimated if a time-independent approach, or a time-dependent approach that does not consider ∆CFS, is adopted.〈/span〉
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    Exploration of continuous seismic recordings with a machine learning approach to document 20 yr of landslide activity in Alaska (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Quantifying landslide activity in remote regions is difficult because of the numerous complications that prevent direct landslide observations. However, building exhaustive landslide catalogues is critical to document and assess the impacts of climate change on landslide activity such as increasing precipitation, glacial retreat and permafrost thawing, which are thought to be strong drivers of the destabilization of large parts of the high-latitude/altitude regions of the Earth. In this study, we take advantage of the capability offered by seismological observations to continuously and remotely record landslide occurrences at regional scales. We developed a new automated machine learning processing chain, based on the Random Forest classifier, able to automatically detect and identify landslide seismic signals in continuous seismic records. We processed two decades of continuous seismological observations acquired by the Alaskan seismic networks. This allowed detection of 5087 potential landslides over a period of 22 yr (1995–2017). We observe an increase in the number of landslides for the period and discuss the possible causes.〈/span〉
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    A scalar radiative transfer model including the coupling between surface and body waves (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉To describe the energy transport in the seismic coda, we introduce a system of radiative transfer equations for coupled surface and body waves in a scalar approximation. Our model is based on the Helmholtz equation in a half-space geometry with mixed boundary conditions. In this model, Green’s function can be represented as a sum of body waves and surface waves, which mimics the situation on Earth. In a first step, we study the single-scattering problem for point-like objects in the Born approximation. Using the assumption that the phase of body waves is randomized by surface reflection or by interaction with the scatterers, we show that it becomes possible to define, in the usual manner, the cross-sections for surface-to-body and body-to-surface scattering. Adopting the independent scattering approximation, we then define the scattering mean free paths of body and surface waves including the coupling between the two types of waves. Using a phenomenological approach, we then derive a set of coupled transport equations satisfied by the specific energy density of surface and body waves in a medium containing a homogeneous distribution of point scatterers. In our model, the scattering mean free path of body waves is depth dependent as a consequence of the body-to-surface coupling. We demonstrate that an equipartition between surface and body waves is established at long lapse-time, with a ratio which is predicted by usual mode counting arguments. We derive a diffusion approximation from the set of transport equations and show that the diffusivity is both anisotropic and depth dependent. The physical origin of the two properties is discussed. Finally, we present Monte Carlo solutions of the transport equations which illustrate the convergence towards equipartition at long lapse-time as well as the importance of the coupling between surface and body waves in the generation of coda waves.〈/span〉
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    Study on the layout of GNSS sites for strike-slip faults (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉In the profile analysis of faults, the distribution of GNSS sites directly affects the accuracy of the results of slip rate and locking depth. This paper discusses strategies for designing the layout of GNSS stations perpendicular to strike-slip faults in terms of site spacing and the Minimum Effective Distance, which is 20 times the locking depth of the fault. Three layout models are proposed considering the complexity of strike-slip faults: (1) Equal spacing layout, in which many stations are deployed in the far field, only a few are deployed in the near field. (2) Equal deformation layout, in which stations are densely arranged in the near field and sparsely arranged in the far field according to the frequency of deformation curve. (3) Equal slope spacing layout, in which stations are arranged according to the nonlinear degree of the deformation curve, with dense distribution in regions with high nonlinearity and sparse distribution in approximately linear regions. The three models were used to redistribute the sites in the Qiaojia to Dongchuan segment of the Xiaojiang fault profile, and their performances were compared with that of the current sites distribution of the segment. The results showed that model 1 is optimal for fitting the accuracy of slip rate and model 3 is optimal for the accuracy of locking depth. Overall, model 3 appears to be the best choice, considering that the accuracy of the locking depth is more difficult to control. One of the main purposes of deployment is to identify the seismogenic depth of the fault. With the locking depth of the fault gradually approaching the depth of the seismogenic layer during an interseismic period, the accuracy of observations of sites deployed at a preset value of historical seismogenic depth of the fault would improve.〈/span〉
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    How HY-2A/GM altimeter performs in marine gravity derivation: assessment in the South China Sea (2019)
    Oxford University Press
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    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉HY-2A is China's first satellite altimeter mission, launched in Aug. 2011. Its geodetic mission (GM) started from 2016 March 30 till present, collecting sea surface heights for about five 168-d cycles. To test how the HY-2A altimeter performs in marine gravity derivation, we use the least-squares collocation method to determine marine gravity anomalies on 1′ × 1′ grids around the South China Sea (covering 0°–30°N, 105°E–125°E) from the HY-2A/GM-measured geoid gradients. We assess the qualities of the HY-2A/GM-derived gravity over different depths and areas using the bias and tilt-adjusted ship-borne gravity anomalies from the U.S. National Centers for Environmental Information (NCEI) and the Second Institute of Oceanography, Ministry of Natural Resources (MNR) of P. R. China. The RMS difference between the HY-2A/GM-derived and the NCEI ship-borne gravity is 5.91 mGal, and is 5.33 mGal when replacing the HY-2A value from the Scripps Institution of Oceanography (SIO) V23.1 value. The RMS difference between the HY-2A/GM-derived and the MNR ship-borne gravity is 2.90 mGal, and is 2.76 mGal when replacing the HY-2A value from the SIO V23.1 value. The RMS difference between the HY-2A and SIO V23.1 value is 3.57 mGal in open sea areas at least 20 km far away from the coast. In general, the difference between the HY-2A/GM-derived gravity and ship-borne gravity decreases with decreasing gravity field roughness and increasing depth. HY-2A results in the lowest gravity accuracy in areas with islands or reefs. Our assessment result suggests that HY-2A can compete with other Ku-band altimeter missions in marine gravity derivation.〈/span〉
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    N6-methyladenosine RNA modification-mediated cellular metabolism rewiring inhibits viral replication (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Host cell metabolism can be modulated by viral infection, affecting viral survival or clearance. The cellular metabolism rewiring mediated by 〈i〉N〈/i〉〈sup〉6〈/sup〉-methyladenosine (m〈sup〉6〈/sup〉A) modification in virus-host interaction remains largely unknown. Here we report that in response to viral infection, host cells impair the enzymatic activity of RNA m〈sup〉6〈/sup〉A demethylase ALKBH5. This increases the m〈sup〉6〈/sup〉A methylation on α-ketoglutarate dehydrogenase (OGDH) mRNA to reduce its mRNA stability and protein expression. Reduced OGDH decreases the production of metabolite itaconate that is required for viral replication. With reduced OGDH and itaconate production in vivo, ALKBH5-deficient mice display an innate immune response-independent resistance to viral challenge. Our findings reveal that m〈sup〉6〈/sup〉A RNA modification-mediated down-regulation of OGDH-Itaconate pathway reprograms cellular metabolism to inhibit viral replication, proposing potential targets for controlling viral infection.〈/p〉
    Print ISSN: 0036-8075
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    Topics: Natural Sciences in General
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    Phase-change heterostructure enables ultralow noise and drift for memory operation (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Artificial intelligence and other data-intensive applications have escalated the demand for data storage and processing. New computing devices, e.g., phase-change random access memory (PCRAM) based neuro-inspired devices, are promising options for breaking the von Neumann barrier by unifying storage with computing in memory cells. However, current PCRAM devices have considerable noise and drift in electrical resistance that erodes the precision and consistency of these devices. We designed a phase-change heterostructure (PCH) consisting of alternately stacked phase-change and confinement nanolayers to suppress the noise and drift, allowing reliable iterative RESET and cumulative SET operations for high-performance neuro-inspired computing. Our PCH architecture is amenable to industrial production as an intrinsic materials solution, without complex manufacturing procedure nor much increased fabrication cost.〈/p〉
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    Choosing male or female (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    Innovations in an ATPase/ATP synthase (2019)
    American Association for the Advancement of Science (AAAS)
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    Certification for gene-edited forests (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    A reverse route into metastasis (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Structure and conformational plasticity of the intact Thermus thermophilus V/A-type ATPase (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉V (vacuolar)/A (archaeal)-type adenosine triphosphatases (ATPases), found in archaea and eubacteria, couple ATP hydrolysis or synthesis to proton translocation across the plasma membrane using the rotary-catalysis mechanism. They belong to the V-type ATPase family, which differs from the mitochondrial/chloroplast F-type ATP synthases in overall architecture. We solved cryo–electron microscopy structures of the intact 〈i〉Thermus thermophilus〈/i〉 V/A-ATPase, reconstituted into lipid nanodiscs, in three rotational states and two substates. These structures indicate substantial flexibility between V〈sub〉1〈/sub〉 and V〈sub〉o〈/sub〉 in a working enzyme, which results from mechanical competition between central shaft rotation and resistance from the peripheral stalks. We also describe details of adenosine diphosphate inhibition release, V〈sub〉1〈/sub〉-V〈sub〉o〈/sub〉 torque transmission, and proton translocation, which are relevant for the entire V-type ATPase family.〈/p〉
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    Familial roots of an opioid epidemic (2019)
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    Publication Date: 2019
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    Venezuela's upheaval threatens Yanomami (2019)
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    Publication Date: 2019
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    Probing an evolutionary riddle (2019)
    American Association for the Advancement of Science (AAAS)
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    Stand out as a speaker (2019)
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    Slow earthquake segmentation (2019)
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    Exploring genetic interaction manifolds constructed from rich single-cell phenotypes (2019)
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    Publication Date: 2019
    Description: 〈p〉How cellular and organismal complexity emerges from combinatorial expression of genes is a central question in biology. High-content phenotyping approaches such as Perturb-seq (single-cell RNA-sequencing pooled CRISPR screens) present an opportunity for exploring such genetic interactions (GIs) at scale. Here, we present an analytical framework for interpreting high-dimensional landscapes of cell states (manifolds) constructed from transcriptional phenotypes. We applied this approach to Perturb-seq profiling of strong GIs mined from a growth-based, gain-of-function GI map. Exploration of this manifold enabled ordering of regulatory pathways, principled classification of GIs (e.g., identifying suppressors), and mechanistic elucidation of synergistic interactions, including an unexpected synergy between 〈i〉CBL〈/i〉 and 〈i〉CNN1〈/i〉 driving erythroid differentiation. Finally, we applied recommender system machine learning to predict interactions, facilitating exploration of vastly larger GI manifolds.〈/p〉
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    Reading an anguished brain (2019)
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    Numerical operations in living cells by programmable RNA devices (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Integrated bioengineering systems can make executable decisions according to the cell state. To sense the state, multiple biomarkers are detected and processed via logic gates with synthetic biological devices. However, numerical operations have not been achieved. Here, we show a design principle for messenger RNA (mRNA) devices that recapitulates intracellular information by multivariate calculations in single living cells. On the basis of this principle and the collected profiles of multiple microRNA activities, we demonstrate that rationally programmed mRNA sets classify living human cells and track their change during differentiation. Our mRNA devices automatically perform multivariate calculation and function as a decision-maker in response to dynamic intracellular changes in living cells.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Water scaling of ecosystem carbon cycle feedback to climate warming (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉It has been well established by field experiments that warming stimulates either net ecosystem carbon uptake or release, leading to negative or positive carbon cycle–climate change feedback, respectively. This variation in carbon-climate feedback has been partially attributed to water availability. However, it remains unclear under what conditions water availability enhances or weakens carbon-climate feedback or even changes its direction. Combining a field experiment with a global synthesis, we show that warming stimulates net carbon uptake (negative feedback) under wet conditions, but depresses it (positive feedback) under very dry conditions. This switch in carbon-climate feedback direction arises mainly from scaling effects of warming-induced decreases in soil water content on net ecosystem productivity. This water scaling of warming effects offers generalizable mechanisms not only to help explain varying magnitudes and directions of observed carbon-climate feedback but also to improve model prediction of ecosystem carbon dynamics in response to climate change.〈/p〉
    Electronic ISSN: 2375-2548
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    Cranial endocast of a stem platyrrhine primate and ancestral brain conditions in anthropoids (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Understanding of ancestral conditions for anthropoids has been hampered by the paucity of well-preserved early fossils. Here, we provide an unprecedented view of the cerebral morphology of the 20-million-year-old 〈i〉Chilecebus carrascoensis〈/i〉, the best-preserved early diverging platyrrhine known, obtained via high-resolution CT scanning and 3D digital reconstruction. These analyses are crucial for reconstructing ancestral brain conditions in platyrrhines and anthropoids given the early diverging position of 〈i〉Chilecebus.〈/i〉 Although small, the brain of 〈i〉Chilecebus〈/i〉 is not lissencephalic and presents at least seven pairs of sulci on its endocast. Comparisons of 〈i〉Chilecebus〈/i〉 and other basal anthropoids indicate that the major brain subdivisions of these early anthropoids exhibit no consistent scaling pattern relative to the overall brain size. Many gross cerebral features appear to have transformed in a mosaic fashion and probably have originated in platyrrhine and catarrhine anthropoids independently, involving multiple, independent instances of size increase, as well as some secondary decreases.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Data-driven phenotype discovery of FMR1 premutation carriers in a population-based sample (2019)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2019
    Description: 〈p〉The impact of the 〈i〉FMR1〈/i〉 premutation on human health is the subject of considerable controversy. A fundamental unanswered question is whether carrying the premutation allele is directly correlated with clinical phenotypes. A challenging problem in past genotype-phenotype studies of the 〈i〉FMR1〈/i〉 premutation is ascertainment bias, which could lead to invalid research conclusions and negatively affect clinical practice. Here, we created the first population-based 〈i〉FMR1〈/i〉-informed biobank to find the pattern of health characteristics in premutation carriers. Our extensive phenotyping shows that premutation carriers experience a clinical profile that is significantly different from controls and is evident throughout adulthood. Comprehensive understanding of the clinical risk associated with this genetic variant is critical for premutation carriers, their families, and clinicians and has important implications for public health.〈/p〉
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    Weakening Atlantic Nino-Pacific connection under greenhouse warming (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Sea surface temperature variability in the equatorial eastern Atlantic, which is referred to as an Atlantic Niño (Niña) at its warm (cold) phase and peaks in boreal summer, dominates the interannual variability in the equatorial Atlantic. By strengthening of the Walker circulation, an Atlantic Niño favors a Pacific La Niña, which matures in boreal winter, providing a precursory memory for El Niño–Southern Oscillation (ENSO) predictability. How this Atlantic impact responds to greenhouse warming is unclear. Here, we show that greenhouse warming leads to a weakened influence from the Atlantic Niño/Niña on the Pacific ENSO. In response to anomalous equatorial Atlantic heating, ascending over the equatorial Atlantic is weaker due to an increased tropospheric stability in the mean climate, resulting in a weaker impact on the Pacific Ocean. Thus, as greenhouse warming continues, Pacific ENSO is projected to be less affected by the Atlantic Niño/Niña and more challenging to predict.〈/p〉
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    Quantitative prediction of erythrocyte sickling for the development of advanced sickle cell therapies (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Sickle cell disease is induced by a mutation that converts normal adult hemoglobin to sickle hemoglobin (HbS) and engenders intracellular polymerization of deoxy-HbS and erythrocyte sickling. Development of anti-sickling therapies requires quantitative understanding of HbS polymerization kinetics under organ-specific conditions, which are difficult to assess with existing experimental techniques. Thus, we developed a kinetic model based on the classical nucleation theory to examine the effectiveness of potential anti-sickling drug candidates. We validated this model by comparing its predictability against prior in vivo and in vitro experimental results. We used the model to quantify the efficacy of sickling inhibitors and obtain results consistent with recent screening assays. Global sensitivity analysis on the kinetic parameters in the model revealed that the solubility, nucleation rate prefactor, and oxygen affinity are quantities that dictate HbS polymerization. This finding provides quantitative guidelines for the discovery of intracellular processes to be targeted by sickling inhibitors.〈/p〉
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    Paramo islands through the Pleistocene (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    Off-on switching of enzyme activity by near-infrared light-induced photothermal phase transition of nanohybrids (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉The off-on manipulation of enzyme activity is a challenging task. We report a new strategy for reversible off-on control of enzyme activity by near-infrared light. Enzymes acting on macromolecular substrates are embedded with an ultrasmall platinum nanoparticle and decorated with thermoresponsive copolymers, which exhibit upper critical solution temperature (UCST) behavior. The polymer-enzyme nanohybrids form microscale aggregates in solution below the UCST to prevent macromolecular substrates from approaching the enzymes and thus inhibit the enzyme activity, and they disassemble above the UCST to reactivate the enzyme. Upon near-infrared irradiation, platinum nanoparticles inside the enzymes generate heat through a photothermal effect to cause phase transition of the copolymers. Therefore, we can reversibly switch off and on the activities of three enzymes acting on polysaccharide, protein, and plasmid. The enzyme activities are increased by up to 61-fold after laser irradiation. This study provides a facile and efficient method for off-on control of enzyme activity.〈/p〉
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    Discriminative T cell recognition of cross-reactive islet-antigens is associated with HLA-DQ8 transdimer-mediated autoimmune diabetes (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Human leukocyte antigen (HLA)–DQ8 transdimer (HLA-DQA1*0501/DQB1*0302) confers exceptionally high risk in autoimmune diabetes. However, little is known about HLA-DQ8 transdimer–restricted CD4 T cell recognition, an event crucial for triggering HLA-DQ8 transdimer–specific anti-islet immunity. Here, we report a high degree of epitope overlap and T cell promiscuity between susceptible HLA-DQ8 and HLA-DQ8 transdimer. Despite preservation of putative residues for T cell receptor (TCR) contact, stronger disease-associated responses to cross-reactive, immunodominant islet epitopes are elicited by HLA-DQ8 transdimer. Mutagenesis at the α chain of HLA-DQ8 transdimer in complex with the disease-relevant GAD65〈sub〉250–266〈/sub〉 peptide and in silico analysis reveal the DQ α52 residue located within the N-terminal edge of the peptide-binding cleft for the enhanced T cell reactivity, altering avidity and biophysical affinity between TCR and HLA-peptide complexes. Accordingly, a structurally promiscuous but nondegenerate TCR-HLA-peptide interface is pivotal for HLA-DQ8 transdimer–mediated autoimmune diabetes.〈/p〉
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    Parallel processing of polarization and intensity information in fiddler crab vision (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Many crustaceans are sensitive to the polarization of light and use this information for object-based visually guided behaviors. For these tasks, it is unknown whether polarization and intensity information are integrated into a single-contrast channel, whereby polarization directly contributes to perceived intensity, or whether they are processed separately and in parallel. Using a novel type of visual display that allowed polarization and intensity properties of visual stimuli to be adjusted independently and simultaneously, we conducted behavioral experiments with fiddler crabs to test which of these two models of visual processing occurs. We found that, for a loom detection task, fiddler crabs process polarization and intensity information independently and in parallel. The crab’s response depended on whichever contrast was the most salient. By contributing independent measures of visual contrast, polarization and intensity provide a greater range of detectable contrast information for the receiver, increasing the chance of detecting a potential threat.〈/p〉
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    A prokaryotic-eukaryotic hybrid viral vector for delivery of large cargos of genes and proteins into human cells (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Development of safe and efficient nanoscale vehicles that can deliver large molecular cargos into human cells could transform future human therapies and personalized medicine. Here, we design a hybrid viral vector composed of a prokaryotic virus (bacteriophage T4) and a eukaryotic virus [adeno-associated virus (AAV)]. The small 25-nm AAV is attached to the large 120 nm x 86 nm T4 head through avidin-biotin cross-bridges using the phage decoration proteins Soc and Hoc. AAV "piggy-backed" on T4 capsid, by virtue of its natural ability to enter human cells acted as an efficient "driver," delivering the largest payloads of foreign DNA (up to 170 kb) and protein (up to 1025 molecules) reported to date, and elicited robust immune responses in mice against flu and plague pathogens and conferred complete protection against lethal pneumonic plague challenge. The T4-AAV represents a unique platform for assembly of natural building blocks into potential therapeutics against genetic and infectious diseases.〈/p〉
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    Viruses mobilize plant immunity to deter nonvector insect herbivores (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉A parasite-infected host may promote performance of associated insect vectors; but possible parasite effects on nonvector insects have been largely unexplored. Here, we show that 〈i〉Begomovirus〈/i〉, the largest genus of plant viruses and transmitted exclusively by whitefly, reprogram plant immunity to promote the fitness of the vector and suppress performance of nonvector insects (i.e., cotton bollworm and aphid). Infected plants accumulated begomoviral βC1 proteins in the phloem where they were bound to the plant transcription factor WRKY20. This viral hijacking of WRKY20 spatiotemporally redeployed plant chemical immunity within the leaf and had the asymmetrical benefiting effects on the begomoviruses and its whitefly vectors while negatively affecting two nonvector competitors. This type of interaction between a parasite and two types of herbivores, i.e., vectors and nonvectors, occurs widely in various natural and agricultural ecosystems; thus, our results have broad implications for the ecological significance of parasite-vector-host tripartite interactions.〈/p〉
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    Aging promotes reorganization of the CD4 T cell landscape toward extreme regulatory and effector phenotypes (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Age-associated changes in CD4 T-cell functionality have been linked to chronic inflammation and decreased immunity. However, a detailed characterization of CD4 T cell phenotypes that could explain these dysregulated functional properties is lacking. We used single-cell RNA sequencing and multidimensional protein analyses to profile thousands of CD4 T cells obtained from young and old mice. We found that the landscape of CD4 T cell subsets differs markedly between young and old mice, such that three cell subsets—exhausted, cytotoxic, and activated regulatory T cells (aT〈sub〉regs〈/sub〉)—appear rarely in young mice but gradually accumulate with age. Most unexpected were the extreme pro- and anti-inflammatory phenotypes of cytotoxic CD4 T cells and aT〈sub〉regs〈/sub〉, respectively. These findings provide a comprehensive view of the dynamic reorganization of the CD4 T cell milieu with age and illuminate dominant subsets associated with chronic inflammation and immunity decline, suggesting new therapeutic avenues for age-related diseases.〈/p〉
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    Accurate high-throughput screening based on digital protein synthesis in a massively parallel femtoliter droplet array (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉We report a general strategy based on digital counting principle that enables an efficient acquisition of enzyme mutants with desired activities from just a few clones within a day. We prepared a high-density femtoliter droplet array, consisting of 1 million uniform droplets per 1 cm〈sup〉2〈/sup〉 to carry out high-throughput protein synthesis and screening. Single DNA molecules were randomly distributed into each droplet following a Poisson process to initiate the protein synthesis with coupled cell-free transcription and translation reactions and then recovered by a microcapillary. The protein yield in each droplet was proportional to the number of DNA molecules, meaning that droplets with apparent intensities higher than the Poisson distribution–predicted maximum can be readily identified as the exact hits exhibiting the desired increased activity. We improved the activity of an alkaline phosphatase up to near 20-fold by using less than 10 nl of reagents.〈/p〉
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    Life on the thermodynamic edge: Respiratory growth of an acetotrophic methanogen (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Although two-thirds of the nearly 1 billion metric tons of methane produced annually in Earth’s biosphere derives from acetate, the in situ process has escaped rigorous understanding. The unresolved question concerns the mechanism by which the exceptionally marginal amount of available energy supports acetotrophic growth of methanogenic archaea in the environment. Here, we show that 〈i〉Methanosarcina acetivorans〈/i〉 conserves energy by Fe(III)-dependent respiratory metabolism of acetate, augmenting production of the greenhouse gas methane. An extensively revised, ecologically relevant, biochemical pathway for acetotrophic growth is presented, in which the conservation of respiratory energy is maximized by electron bifurcation, a previously unknown mechanism of biological energy coupling. The results transform the ecological and biochemical understanding of methanogenesis and the role of iron in the mineralization of organic matter in anaerobic environments.〈/p〉
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    North American April tornado occurrences linked to global sea surface temperature anomalies (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Annual tornado occurrences over North America display large interannual variability and a statistical linkage to sea surface temperature (SST) anomalies. However, the underlying physical mechanisms for this connection and its modulation in a rapidly varying seasonal environment still remain elusive. Using tornado data over the United States from 1954 to 2016 in combination with SST-forced atmospheric general circulation models, we show a robust dynamical linkage between global SST conditions in April, the emergence of the Pacific-North American teleconnection pattern (PNA), and the year-to-year tornado activity in the Southern Great Plains (SGP) region of the United States. Contrasting previous studies, we find that only in April SST-driven atmospheric circulation anomalies can effectively control the northward moisture-laden flow from the Gulf of Mexico, boosting low-level moisture flux convergence over the SGP. These strong large-scale connections are absent in other months because of the strong seasonality of the PNA and background moisture conditions.〈/p〉
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    Thiol-to-amine cyclization reaction enables screening of large libraries of macrocyclic compounds and the generation of sub-kilodalton ligands (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Macrocyclic compounds are an attractive modality for drug development, but the limited availability of large, structurally diverse macrocyclic libraries hampers the discovery of leads. Here, we describe the discovery of efficient macrocyclization reactions based on thiol-to-amine ligations using bis-electrophiles, their application to synthesize and screen large libraries of macrocyclic compounds, and the identification of potent small macrocyclic ligands. The thiol-to-amine cyclization reactions showed unexpectedly high yields for a wide substrate range, which obviated product purification and enabled the generation and screening of an 8988 macrocycle library with a comparatively small effort. X-ray structure analysis of an identified thrombin inhibitor (〈i〉K〈/i〉〈sub〉i〈/sub〉 = 42 ± 5 nM) revealed a snug fit with the target, validating the strategy of screening large libraries with a high skeletal diversity. The approach provides a route for screening large sub-kilodalton macrocyclic libraries and may be applied to many challenging drug targets.〈/p〉
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    Dysregulation of ectonucleotidase-mediated extracellular adenosine during postmenopausal bone loss (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Adenosine and its receptors play a key role in bone homeostasis and regeneration. Extracellular adenosine is generated from CD39 and CD73 activity in the cell membrane, through conversion of adenosine triphosphate to adenosine monophosphate (AMP) and AMP to adenosine, respectively. Despite the relevance of CD39/CD73 to bone health, the roles of these enzymes in bona fide skeletal disorders remain unknown. We demonstrate that CD39/CD73 expression and extracellular adenosine levels in the bone marrow are substantially decreased in animals with osteoporotic bone loss. Knockdown of estrogen receptors ESR1 and ESR2 in primary osteoprogenitors and osteoclasts undergoing differentiation showed decreased coexpression of membrane-bound CD39 and CD73 and lower extracellular adenosine. Targeting the adenosine A2B receptor using an agonist attenuated bone loss in ovariectomized mice. Together, these findings suggest a pathological association of purine metabolism with estrogen deficiency and highlight the potential of A2B receptor as a target to treat osteoporosis.〈/p〉
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    Contrasting genomic shifts underlie parallel phenotypic evolution in response to fishing (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Humans cause widespread evolutionary change in nature, but we still know little about the genomic basis of rapid adaptation in the Anthropocene. We tracked genomic changes across all protein-coding genes in experimental fish populations that evolved pronounced shifts in growth rates due to size-selective harvest over only four generations. Comparisons of replicate lines show parallel allele frequency shifts that recapitulate responses to size-selection gradients in the wild across hundreds of unlinked variants concentrated in growth-related genes. However, a supercluster of genes also rose rapidly in frequency and dominated the evolutionary dynamic in one replicate line but not in others. Parallel phenotypic changes thus masked highly divergent genomic responses to selection, illustrating how contingent rapid adaptation can be in the face of strong human-induced selection.〈/p〉
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    A light-harvesting array in diatoms (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Cancer cell evolution through the ages (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Spontaneous degradation in hormone synthesis (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Targeting transmissible cancers in animals (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Brexit backer Boris Johnson stokes fears for U.K. scientists (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    A preference for alcohol (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Laboratory mice born to wild mice have natural microbiota and model human immune responses (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Laboratory mouse studies are paramount for understanding basic biological phenomena but also have limitations. These include conflicting results caused by divergent microbiota and limited translational research value. To address both shortcomings, we transferred C57BL/6 embryos into wild mice, creating "wildlings." These mice have a natural microbiota and pathogens at all body sites and the tractable genetics of C57BL/6 mice. The bacterial microbiome, mycobiome, and virome of wildlings affect the immune landscape of multiple organs. Their gut microbiota outcompete laboratory microbiota and demonstrate resilience to environmental challenges. Wildlings, but not conventional laboratory mice, phenocopied human immune responses in two preclinical studies. A combined natural microbiota- and pathogen-based model may enhance the reproducibility of biomedical studies and increase the bench-to-bedside safety and success of immunological studies.〈/p〉
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    Stabilizing halide perovskite surfaces for solar cell operation with wide-bandgap lead oxysalts (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉We show that converting the surfaces of lead halide perovskite to water-insoluble lead (II) oxysalt through reaction with sulfate or phosphate ions can effectively stabilize the perovskite surface and bulk material. These capping lead oxysalt thin layers enhance the water resistance of the perovskite films by forming strong chemical bonds. The wide-bandgap lead oxysalt layers also reduce the defect density on the perovskite surfaces by passivating undercoordinated surface lead centers, which are defect-nucleating sites. Formation of the lead oxysalt layer increases the carrier recombination lifetime and boosts the efficiency of the solar cells to 21.1%. Encapsulated devices stabilized by the lead oxysalt layers maintain 96.8% of their initial efficiency after operation at maximum power point under simulated air mass (AM) 1.5 G irradiation for 1200 hours at 65°C.〈/p〉
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    NIH fetal tissue research requirements raise worries (2019)
    American Association for the Advancement of Science (AAAS)
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    Regulate GM fungi to protect ecosystems--Response (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
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    Loss of control in aging brains (2019)
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    Fishing for answers (2019)
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    Fields of dreams (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
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    The pigment-protein network of a diatom photosystem II-light-harvesting antenna supercomplex (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Diatoms play important roles in global primary productivity and biogeochemical cycling of carbon, in part owing to the ability of their photosynthetic apparatus to adapt to rapidly changing light intensity. We report a cryo–electron microscopy structure of the photosystem II (PSII)–fucoxanthin (Fx) chlorophyll (Chl) a/c binding protein (FCPII) supercomplex from the centric diatom 〈i〉Chaetoceros gracilis〈/i〉. The supercomplex comprises two protomers, each with two tetrameric and three monomeric FCPIIs around a PSII core that contains five extrinsic oxygen-evolving proteins at the lumenal surface. The structure reveals the arrangement of a huge pigment network that contributes to efficient light energy harvesting, transfer, and dissipation processes in the diatoms.〈/p〉
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    A weedy challenge (2019)
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    Building a better RSV vaccine (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Seeing my science clearly (2019)
    American Association for the Advancement of Science (AAAS)
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    Interfering with macrophage activation (2019)
    American Association for the Advancement of Science (AAAS)
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    The CRISPR animal kingdom (2019)
    American Association for the Advancement of Science (AAAS)
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    A proof of concept for structure-based vaccine design targeting RSV in humans (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Technologies that define the atomic-level structure of neutralization-sensitive epitopes on viral surface proteins are transforming vaccinology and guiding new vaccine development approaches. Previously, iterative rounds of protein engineering were performed to preserve the prefusion conformation of the respiratory syncytial virus (RSV) fusion (F) glycoprotein, resulting in a stabilized subunit vaccine candidate (DS-Cav1), which showed promising results in mice and macaques. Here, phase I human immunogenicity data reveal a more than 10-fold boost in neutralizing activity in serum from antibodies targeting prefusion-specific surfaces of RSV F. These findings represent a clinical proof of concept for structure-based vaccine design, suggest that development of a successful RSV vaccine will be feasible, and portend an era of precision vaccinology.〈/p〉
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    Regional and correlative sweat analysis using high-throughput microfluidic sensing patches toward decoding sweat (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Recent technological advancements in wearable sensors have made it easier to detect sweat components, but our limited understanding of sweat restricts its application. A critical bottleneck for temporal and regional sweat analysis is achieving uniform, high-throughput fabrication of sweat sensor components, including microfluidic chip and sensing electrodes. To overcome this challenge, we introduce microfluidic sensing patches mass fabricated via roll-to-roll (R2R) processes. The patch allows sweat capture within a spiral microfluidic for real-time measurement of sweat parameters including [Na〈sup〉+〈/sup〉], [K〈sup〉+〈/sup〉], [glucose], and sweat rate in exercise and chemically induced sweat. The patch is demonstrated for investigating regional sweat composition, predicting whole-body fluid/electrolyte loss during exercise, uncovering relationships between sweat metrics, and tracking glucose dynamics to explore sweat-to-blood correlations in healthy and diabetic individuals. By enabling a comprehensive sweat analysis, the presented device is a crucial tool for advancing sweat testing beyond the research stage for point-of-care medical and athletic applications.〈/p〉
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Surface states in bulk single crystal of topological semimetal Co3Sn2S2 toward water oxidation (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉The band inversion in topological phase matters bring exotic physical properties such as the topologically protected surface states (TSS). They strongly influence the surface electronic structures of the materials and could serve as a good platform to gain insight into the surface reactions. Here we synthesized high-quality bulk single crystals of Co〈sub〉3〈/sub〉Sn〈sub〉2〈/sub〉S〈sub〉2〈/sub〉 that naturally hosts the band structure of a topological semimetal. This guarantees the existence of robust TSS from the Co atoms. Co〈sub〉3〈/sub〉Sn〈sub〉2〈/sub〉S〈sub〉2〈/sub〉 crystals expose their Kagome lattice that constructed by Co atoms and have high electrical conductivity. They serves as catalytic centers for oxygen evolution process (OER), making bonding and electron transfer more efficient due to the partially filled orbital. The bulk single crystal exhibits outstanding OER catalytic performance, although the surface area is much smaller than that of Co-based nanostructured catalysts. Our findings emphasize the importance of tailoring TSS for the rational design of high-activity electrocatalysts.〈/p〉
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    An sp-hybridized molecular carbon allotrope, cyclo[18]carbon (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉Carbon allotropes built from rings of two-coordinate atoms, known as cyclo[〈i〉n〈/i〉]carbons, have fascinated chemists for many years, but until now they could not be isolated or structurally characterized, due to their high reactivity. We generated cyclo[18]carbon (C〈sub〉18〈/sub〉) using atom manipulation on bilayer NaCl on Cu(111) at 5 Kelvin by eliminating carbon monoxide from a cyclocarbon oxide molecule C〈sub〉24〈/sub〉O〈sub〉6〈/sub〉. Characterization of cyclo[18]carbon by high-resolution atomic force microscopy revealed a polyynic structure with defined positions of alternating triple and single bonds. The high reactivity of cyclocarbon and cyclocarbon oxides allows covalent coupling between molecules to be induced by atom manipulation, opening an avenue for the synthesis of other carbon allotropes and carbon-rich materials from the coalescence of cyclocarbon molecules.〈/p〉
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    Sub-single-exciton lasing using charged quantum dots coupled to a distributed feedback cavity (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Colloidal semiconductor quantum dots (QDs) are attractive materials for realizing highly flexible, solution-processable optical gain media, but they are difficult to use in lasing because of complications associated with extremely short optical-gain lifetimes limited by nonradiative Auger recombination. By combining compositional grading of the QD’s interior for hindering Auger decay with postsynthetic charging for suppressing parasitic ground-state absorption, we can reduce the lasing threshold to values below the single-exciton-per-dot limit. As a favorable departure from traditional multi-exciton–based lasing schemes, our approach should facilitate the development of solution-processable lasing devices and thereby help to extend the reach of lasing technologies into areas not accessible with traditional, epitaxially grown semiconductor materials.〈/p〉
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    Putting a price on the powerhouse (2019)
    American Association for the Advancement of Science (AAAS)
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    Training to reduce cognitive biases (2019)
    American Association for the Advancement of Science (AAAS)
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    Benefits of diversity (2019)
    American Association for the Advancement of Science (AAAS)
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    Active cell migration is critical for steady-state epithelial turnover in the gut (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Steady-state turnover is a hallmark of epithelial tissues throughout adult life. Intestinal epithelial turnover is marked by continuous cell migration, which is assumed to be driven by mitotic pressure from the crypts. However, the balance of forces in renewal remains ill-defined. Combining biophysical modeling and quantitative three-dimensional tissue imaging with genetic and physical manipulations, we revealed the existence of an actin-related protein 2/3 complex–dependent active migratory force, which explains quantitatively the profiles of cell speed, density, and tissue tension along the villi. Cells migrate collectively with minimal rearrangements while displaying dual—apicobasal and front-back—polarity characterized by actin-rich basal protrusions oriented in the direction of migration. We propose that active migration is a critical component of gut epithelial turnover.〈/p〉
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    Successful Ebola treatments promise to tame outbreak (2019)
    American Association for the Advancement of Science (AAAS)
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    Gravitational redshift in the Galactic Center (2019)
    American Association for the Advancement of Science (AAAS)
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    Hippocampal sharp-wave ripples linked to visual episodic recollection in humans (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Hippocampal sharp-wave ripples (SWRs) constitute one of the most synchronized activation events in the brain and play a critical role in offline memory consolidation. Yet their cognitive content and function during awake, conscious behavior remains unclear. We directly examined this question using intracranial recordings in human patients engaged in episodic free recall of previously viewed photographs. Our results reveal a content-selective increase in hippocampal ripple rate emerging 1 to 2 seconds prior to recall events. During recollection, high-order visual areas showed pronounced SWR-coupled reemergence of activation patterns associated with recalled content. Finally, the SWR rate during encoding predicted subsequent free-recall performance. These results point to a role for hippocampal SWRs in triggering spontaneous recollections and orchestrating the reinstatement of cortical representations during free episodic memory retrieval.〈/p〉
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    Glia in the skin activate pain responses (2019)
    American Association for the Advancement of Science (AAAS)
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    Strain-stabilized perovskites (2019)
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    Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black hole (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉The general theory of relativity predicts that a star passing close to a supermassive black hole should exhibit a relativistic redshift. In this study, we used observations of the Galactic Center star S0-2 to test this prediction. We combined existing spectroscopic and astrometric measurements from 1995–2017, which cover S0-2’s 16-year orbit, with measurements from March to September 2018, which cover three events during S0-2’s closest approach to the black hole. We detected a combination of special relativistic and gravitational redshift, quantified using the redshift parameter . Our result, = 0.88 ± 0.17, is consistent with general relativity ( = 1) and excludes a Newtonian model ( = 0) with a statistical significance of 5.〈/p〉
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    NextGen voices: Submit Now Peer mentoring: Your advice needed! (2019)
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    Thermal unequilibrium of strained black CsPbI3 thin films (2019)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2019
    Description: 〈p〉The high-temperature, all-inorganic CsPbI〈sub〉3〈/sub〉 perovskite black phase is metastable relative to its yellow, nonperovskite phase at room temperature. Because only the black phase is optically active, this represents an impediment for the use of CsPbI〈sub〉3〈/sub〉 in optoelectronic devices. We report the use of substrate clamping and biaxial strain to render black-phase CsPbI〈sub〉3〈/sub〉 thin films stable at room temperature. We used synchrotron-based, grazing incidence, wide-angle x-ray scattering to track the introduction of crystal distortions and strain-driven texture formation within black CsPbI〈sub〉3〈/sub〉 thin films when they were cooled after annealing at 330°C. The thermal stability of black CsPbI〈sub〉3〈/sub〉 thin films is vastly improved by the strained interface, a response verified by ab initio thermodynamic modeling.〈/p〉
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    An E-Z resolution (2019)
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    An unusual superconductor (2019)
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    Teosinte ligule allele narrows plant architecture and enhances high-density maize yields (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Increased planting densities have boosted maize yields. Upright plant architecture facilitates dense planting. Here, we cloned 〈i〉UPA1〈/i〉 (〈i〉Upright Plant Architecture1〈/i〉) and 〈i〉UPA2〈/i〉, two quantitative trait loci conferring upright plant architecture. 〈i〉UPA2〈/i〉 is controlled by a two-base sequence polymorphism regulating the expression of a B3-domain transcription factor (〈i〉ZmRAVL1〈/i〉) located 9.5 kilobases downstream. 〈i〉UPA2〈/i〉 exhibits differential binding by DRL1 (DROOPING LEAF1), and DRL1 physically interacts with LG1 (LIGULELESS1) and represses LG1 activation of 〈i〉ZmRAVL1〈/i〉. 〈i〉ZmRAVL1〈/i〉 regulates 〈i〉brd1〈/i〉 (〈i〉brassinosteroid C-6 oxidase1〈/i〉), which underlies 〈i〉UPA1〈/i〉, altering endogenous brassinosteroid content and leaf angle. The 〈i〉UPA2〈/i〉 allele that reduces leaf angle originated from teosinte, the wild ancestor of maize, and has been lost during maize domestication. Introgressing the wild 〈i〉UPA2〈/i〉 allele into modern hybrids and editing 〈i〉ZmRAVL1〈/i〉 enhance high-density maize yields.〈/p〉
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    Witnessing a wearables transition (2019)
    American Association for the Advancement of Science (AAAS)
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    Decoding sweat to monitor health (2019)
    American Association for the Advancement of Science (AAAS)
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    News at a glance (2019)
    American Association for the Advancement of Science (AAAS)
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    Response to Comment on "Impacts of historical warming on marine fisheries production" (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉Szuwalski argues that varying age structure can affect surplus production and that recruitment is a better metric of productivity. We explain how our null model controlled for age structure and other processes as explanations for the temperature-production relationship. Surplus production includes growth, recruitment, and other processes and provides a more complete description of food production impacts than does recruitment alone.〈/p〉
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    Specialized cutaneous Schwann cells initiate pain sensation (2019)
    American Association for the Advancement of Science (AAAS)
    In: Science
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    Publication Date: 2019
    Description: 〈p〉An essential prerequisite for the survival of an organism is the ability to detect and respond to aversive stimuli. Current belief is that noxious stimuli directly activate nociceptive sensory nerve endings in the skin. We discovered a specialized cutaneous glial cell type with extensive processes forming a mesh-like network in the subepidermal border of the skin that conveys noxious thermal and mechanical sensitivity. We demonstrate a direct excitatory functional connection to sensory neurons and provide evidence of a previously unknown organ that has an essential physiological role in sensing noxious stimuli. Thus, these glial cells, which are intimately associated with unmyelinated nociceptive nerves, are inherently mechanosensitive and transmit nociceptive information to the nerve.〈/p〉
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