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Current management practices and outcomes in weaning from invasive mechanical ventilation are poorly understood. We aimed to describe the epidemiology, management, timings, risk for failure, and outcomes of weaning in patients requiring at least 2 days of invasive mechanical ventilation.

The dynamics of Earth's D″ layer at the base of the mantle plays an essential role in Earth's thermal and chemical evolution. Mantle convection in D″ is thought to result in seismic anisotropy; therefore, observations of anisotropy may be used to infer lowermost mantle flow. However, the connections between mantle flow and seismic anisotropy in D″ remain ambiguous. Here, we calculate the present‐day mantle flow field in D″ using 3D global geodynamic models. We then compute strain, a measure of deformation, outside the two large‐low velocity provinces (LLVPs) and compare the distribution of strain with previous observations of anisotropy. We find that, on a global scale, D″ materials are advected toward the LLVPs. The strains of D″ materials generally increase with time along their paths toward the LLVPs and toward deeper depths, but regions far from LLVPs may develop relative high strain as well. Materials in D″ outside the LLVPs mostly undergo lateral stretching, with the stretching direction often aligning with mantle flow direction, especially in fast flow regions. In most models, the depth‐averaged strain in D″ is >0.5 outside the LLVPs, consistent with widespread observations of seismic anisotropy. Flow directions inferred from anisotropy observations often (but not always) align with predictions from geodynamic modeling calculations. The Earth's deep mantle deforms and moves at a geological timescale. This movement is called mantle convection which controls plate tectonics. Of particular importance is the flow in the lowermost few hundred kilometers of the mantle, which is called the D″ layer. The dynamics of D″ plays an essential role in Earth's thermal and chemical evolution. Direct observation of D″ flow is not possible, but D″ flow causes deformation of minerals that can align in preferential directions, leading to variable seismic velocities along different directions. This feature is called seismic anisotropy. In this study, we use numerical simulations to investigate D″ flow and its connection to rock deformation and seismic anisotropy. We find that D″ materials are strongly deformed, consistent with observations of seismic anisotropy in this layer. The strength of rock deformation in D″ generally increases with depth and increases toward regions beneath the Central Pacific and Africa, where two continental‐sized seismic anomalies exist. Flow directions inferred from anisotropy observations often align with our numerical simulations. This study thus improves our understanding on the dynamics of the D″ layer. Geodynamic models show that D″ materials are strongly deformed, consistent with observations of seismic anisotropyStrains of materials in D″ generally increase with time as they go toward the large‐low velocity provinces and deeper depthsFlow directions inferred from anisotropy observations often align with that from geodynamic calculations Geodynamic models show that D″ materials are strongly deformed, consistent with observations of seismic anisotropy Strains of materials in D″ generally increase with time as they go toward the large‐low velocity provinces and deeper depths Flow directions inferred from anisotropy observations often align with that from geodynamic calculations

Observations of seismic waves that have passed through the Earth's lowermost mantle provide insight into deep mantle structure and dynamics, often on relatively small spatial scales. Here we use SKS, S2KS, S3KS, and PKS signals recorded across a large region including the United States, Mexico, and Central America to study the deepest mantle beneath large swaths of North America and the northeastern Pacific Ocean. These phases are enhanced via beamforming and then used to investigate polarization‐ and propagation direction‐dependent shear wave speeds (seismic anisotropy). A differential splitting approach enables us to robustly identify contributions from D″${\mathrm{D}}^{{\prime\prime}}$anisotropy. Our results show strong seismic anisotropy in approximately half of our study region, indicating that D″${\mathrm{D}}^{{\prime\prime}}$anisotropy may be more prevalent than commonly thought. In some regions, the anisotropy may be induced by flow driven by sinking cold slabs, and in other, more compact regions, by upwelling flow. Measured splitting due to lowermost mantle anisotropy is sufficiently strong to be non‐negligible in interpretations of SKS splitting due to upper mantle anisotropy in certain regions, which may prompt future re‐evaluations of upper mantle anisotropy beneath North and Central America. Earthquakes emit seismic waves that travel through Earth's deep interior. In some parts of Earth, the speed of these waves depends on their vibrational directions. In these cases, the material they travel through can be described as seismically anisotropic. Such seismic anisotropy is often caused by material deformation due to convective flow in Earth's interior. We show in this work that Earth's mantle beneath North America and the northeastern Pacific Ocean is seismically anisotropic in many places just above its boundary with the core at a depth of ∼2900km${\sim} 2900\,\text{km}$. In some of these places, the deformation may be caused by sinking subducted slabs, upwelling flow, or changes in horizontal flow at the mantle's lower boundary layer. We additionally show that potential contributions from the lowermost mantle anisotropy cannot always be neglected when measuring seismic anisotropy in other parts of the mantle. We infer D″${\mathrm{D}}^{{\prime\prime}}$seismic anisotropy beneath North America and parts of the Pacific Ocean from beamformed SKS, S2KS, S3KS, and PKS dataWe find widespread seismic anisotropy in the deepest mantle, likely induced by a variety of different convective flow regimesThe influence of the deepest mantle on SKS (usually used to infer upper mantle anisotropy) is non‐negligible in some regions We infer D″${\mathrm{D}}^{{\prime\prime}}$seismic anisotropy beneath North America and parts of the Pacific Ocean from beamformed SKS, S2KS, S3KS, and PKS data We find widespread seismic anisotropy in the deepest mantle, likely induced by a variety of different convective flow regimes The influence of the deepest mantle on SKS (usually used to infer upper mantle anisotropy) is non‐negligible in some regions

Astroglial networks closely interact with neuronal populations, but their functional contribution to neuronal representation of sensory information remains unexplored. The superior colliculus (SC) integrates multi-sensory information by generating distinct spatial patterns of neuronal functional responses to specific sensory stimulation. Here, we report that astrocytes from the mouse SC form extensive networks in the retinorecipient layer compared to visual cortex. This strong astroglial connectivity relies on high expression of gap-junction proteins. Genetic disruption of this connectivity functionally impairs SC retinotopic and orientation preference responses. These alterations are region specific, absent in primary visual cortex, and associated at the circuit level with a specific impairment of collicular neurons synaptic transmission. This has implications for SC-related visually induced innate behavior, as disrupting astroglial networks impairs light-evoked temporary arrest. Our results indicate that astroglial networks shape synaptic circuit activity underlying SC functional visual responses and play a crucial role in integrating visual cues to drive sensory-motor behavior.

Convective flow in the deep mantle controls Earth's dynamic evolution, influences plate tectonics, and has shaped Earth's current surface features. Present and past convection‐induced deformation manifests itself in seismic anisotropy, which is particularly strong in the mantle's uppermost and lowermost portions. While the general patterns of seismic anisotropy have been mapped for the upper mantle, anisotropy in the lowermost mantle (called D′′) is at an earlier stage of exploration. Here we review recent progress in methods to measure and interpret D′′ anisotropy. Our understanding of the limitations of existing methods and the development of new measurement strategies have been aided enormously by the availability of high‐performance computing resources. We give an overview of how measurements of seismic anisotropy can help constrain the mineralogy and fabric of the deep mantle. Specifically, new and creative strategies that combine multiple types of observations provide much tighter constraints on the geometry of anisotropy than have previously been possible. We also discuss how deep mantle seismic anisotropy provides insights into lowermost mantle dynamics. We summarize what we have learned so far from measurements of D′′ anisotropy, how inferences of lowermost mantle flow from measurements of seismic anisotropy relate to geodynamic models of mantle flow, and what challenges we face going forward. Finally, we discuss some of the important unsolved problems related to the dynamics of the lowermost mantle that can be elucidated in the future by combining observations of seismic anisotropy with geodynamic predictions of lowermost mantle flow. Earthquakes cause waves that travel through Earth's interior and are recorded by distant seismometers. These seismic waves behave differently depending on the material that they pass through, revealing Earth's material properties. At the very bottom of the mantle, seismic waves sometimes travel at different speeds depending on their direction. This material property is called seismic anisotropy and is caused by material deformation and flow. Global patterns of mantle flow, which is directly connected to surface processes such as the movement of tectonic plates or hotspot volcanism, can therefore be inferred from seismic anisotropy. Recent years have seen advances in anisotropy imaging in the lowermost mantle as well as in numerical calculations of flow in Earth's lowermost mantle. We review the methods that are used to infer lowermost mantle anisotropy. We further give an overview of previous results and interpretations, which include seismic anisotropy caused by upwelling plumes and ancient slab remnants. Future improvements in the fields of seismology, geodynamics, and mineral physics are needed to improve our understanding of global deep mantle flow. Measurement techniques for deep mantle anisotropy have been improved substantially in the last decadeThese improvements enable inferences of deep mantle flow with increasing confidenceKnowledge of mantle dynamics elucidates the drivers of flow, relationships among structures, and Earth's dynamic evolution Measurement techniques for deep mantle anisotropy have been improved substantially in the last decade These improvements enable inferences of deep mantle flow with increasing confidence Knowledge of mantle dynamics elucidates the drivers of flow, relationships among structures, and Earth's dynamic evolution

Ultra‐low velocity zones (ULVZs) are anomalous structures, generally associated with decreased seismic velocity and sometimes an increase in density, that have been detected in some locations atop the Earth's core‐mantle boundary (CMB). A wide range of ULVZ characteristics have been reported by previous studies, leading to many questions regarding their origins. The lowermost mantle beneath Antarctica and surrounding areas is not located near currently active regions of mantle upwelling or downwelling, making it a unique environment in which to study the sources of ULVZs; however, seismic sampling of this portion of the CMB has been sparse. Here, we examine core‐reflected PcP waveforms recorded by seismic stations across Antarctica using a double‐array stacking technique to further elucidate ULVZ structure beneath the southern hemisphere. Our results show widespread, variable ULVZs, some of which can be robustly modeled with 1‐D synthetics; however, others are more complex, which may reflect 2‐D or 3‐D ULVZ structure and/or ULVZs with internal velocity variability. Our findings are consistent with the concept that ULVZs can be largely explained by variable accumulations of subducted oceanic crust along the CMB. Partial melting of subducted crust and other, hydrous subducted materials may also contribute to ULVZ variability. Earth's core‐mantle boundary (CMB), the interface between the solid silicate mantle and the molten iron‐rich outer core, is associated with a range of anomalous structures, including ultra‐low velocity zones (ULVZs). While generally associated with reduced seismic wave velocities and sometimes increased density, prior studies have reported a wide range of ULVZ characteristics, leading to many questions regarding their origins. The lowermost mantle beneath the southern hemisphere provides a unique environment to study ULVZs because it is located away from regions of large‐scale mantle upwelling and downwelling. Our study uses core reflected P‐waves (PcP) recorded by seismic stations in Antarctica to investigate this portion of the CMB for ULVZ presence. We find widespread evidence for variable ULVZ structure. Some of the imaged ULVZs can be modeled with a single layer, but others are more complex. We suggest that the ULVZs beneath the southern hemisphere are predominantly associated with subducted oceanic crust that has variable accumulations along the CMB. In some regions, hydrated subducted materials may also experience partial melting, which may contribute to the complicated ULVZ structures imaged in some locations. Core‐reflected P‐waves are used to investigate ultra‐low velocity zones in the lowermost mantle beneath the southern hemisphereResults show widespread evidence for variable ultra‐low velocity zones, some of which may indicate layered or gradational structureVariable accumulations of subducted oceanic crust with localized partial melting can explain these anomalous structures Core‐reflected P‐waves are used to investigate ultra‐low velocity zones in the lowermost mantle beneath the southern hemisphere Results show widespread evidence for variable ultra‐low velocity zones, some of which may indicate layered or gradational structure Variable accumulations of subducted oceanic crust with localized partial melting can explain these anomalous structures

Solid sulfide electrolytes hold great promise for making all-solid state batteries a reality. Therefore, their wet chemical synthesis has become increasingly important in recent years due to various benefits such as scalability and versatility. The Li3PS4electrolyte has a relatively high ionic conductivity (≈10–4S cm–1at 25 °C) and can be synthesized in various organic solvents by reacting Li2S and P2S5. It is well-known that the choice of the solvent is critical for the synthesis. Herein, we investigated several new organic polar solvents such as sulfur-based solvents (propanethiol, thiolane, and thiophene), amines, and carbonyls (esters, carbonates, ketones) for the synthesis of Li3PS4. The relationship between the ability to perform the reaction, the ionic conductivity, and the solvents’ characteristics revealed that the electronic density of the polar function plays a key role. The results of this study can be used as a guideline to select new synthesis solvents. We also identify a particular solvent, isobutyl isobutyrate (IBIB), which allows the decomposition of the corresponding Li3PS4solvato-complex below the boiling point of the solvent with one of the highest reported ionic conductivities for the wet chemical method (2.1 × 10–4S cm–1at room temperature).

Shear‐wave splitting measurements are commonly used to resolve seismic anisotropy in both the upper and lowermost mantle. Typically, such techniques are applied to SmKS phases that have reflected (m‐1) times off the underside of the core‐mantle boundary before being recorded. Practical constraints for shear‐wave splitting studies include the limited number of suitable phases as well as the large fraction of available data discarded because of poor signal‐to‐noise ratios (SNRs) or large measurement uncertainties. Array techniques such as beamforming are commonly used in observational seismology to enhance SNRs, but have not been applied before to improve SmKS signal strength and coherency for shear wave splitting studies. Here, we investigate how a beamforming methodology, based on slowness and backazimuth vespagrams to determine the most coherent incoming wave direction, can improve shear‐wave splitting measurement confidence intervals. Through the analysis of real and synthetic seismograms, we show that (a) the splitting measurements obtained from the beamformed seismograms (beams) reflect an average of the single‐station splitting parameters that contribute to the beam; (b) the beams have (on average) more than twice as large SNRs than the single‐station seismograms that contribute to the beam; (c) the increased SNRs allow the reliable measurement of shear wave splitting parameters from beams down to average single‐station SNRs of 1.3. Beamforming may thus be helpful to more reliably measure splitting due to upper mantle anisotropy. Moreover, we show that beamforming holds potential to greatly improve detection of lowermost mantle anisotropy by demonstrating differential SKS–SKKS splitting analysis using beamformed USArray data. When earthquakes occur, seismic waves are produced that travel through the deep Earth to distant seismic stations. In some portions of the Earth, seismic waves traveling in different directions or with different vibration directions travel at different speeds. This phenomenon is known as seismic anisotropy and results from individual mineral crystals aligning with mantle flow. Therefore, by measuring seismic anisotropy, we can obtain insights into how Earth's mantle flows, a process called mantle convection. In this work, we show that seismic anisotropy can be inferred from recordings of seismic phases that are summed (or stacked) across a number of spatially separated stations (seismic arrays). The resulting stacks are also called beams. Beams have an increased signal clarity compared to single‐station seismograms, leading to several advantages for analyses of seismic anisotropy. For example, the increased signal strength in beams allows for the usage of weaker seismic phases, which are not commonly used for measuring seismic anisotropy. Moreover, measurements made on beamformed data are more robust. This new technique enables us to suggest new directions for lowermost mantle anisotropy analyses. Major limitations for shear‐wave splitting measurements are the limited number of suitable phases and low signal‐to‐noise ratios (SNRs)Beamforming enhances the SNR, enabling us to use unusual seismic phases and a larger data fraction for shear‐wave splitting measurementsThis holds potential for investigations of mantle anisotropy, particularly in the lowermost mantle Major limitations for shear‐wave splitting measurements are the limited number of suitable phases and low signal‐to‐noise ratios (SNRs) Beamforming enhances the SNR, enabling us to use unusual seismic phases and a larger data fraction for shear‐wave splitting measurements This holds potential for investigations of mantle anisotropy, particularly in the lowermost mantle

The carbon and water cycles in the Earth's interior are linked to key planetary processes, such as mantle melting, degassing, chemical differentiation, and advection. However, the role of water in the carbon exchange between the mantle and core is not well known. Here, we show experimental results of a reaction between Fe3C and H2O at pressures and temperatures of the deep mantle and core‐mantle boundary (CMB). The reaction produces diamond, FeO, and FeHx, suggesting that water can liberate carbon from the core in the form of diamond (“core carbon extraction”) while the core gains hydrogen, if subducted water reaches to the CMB. Therefore, Earth's deep water and carbon cycles can be linked. The extracted core carbon can explain a significant amount of the present‐day mantle carbon. Also, if diamond can be collected by mantle flow in the region, it can result in unusually high seismic‐velocity structures. Carbon plays a vital role in geological processes occurring in the Earth's interior. While most carbon on Earth exists in its core, whether or not the core carbon can be added to the mantle is unclear due to the lack of knowledge of possible carbon transfer mechanism at the core‐mantle boundary (CMB). We conducted experiments by reproducing the extreme pressure and temperature conditions of the CMB. Our experiments show that water can react with the metallic iron core and liberate carbon as diamond, suggesting an important relationship between Earth's water and carbon cycles. In addition, our result predicts possible existence of diamond in some regions of the deepest mantle. Water reacts with iron‐carbon alloy to form diamond at the P–Tconditions expected for Earth's core‐mantle boundarySome of Earth's mantle carbon may come from the core through water‐induced reactions at the core‐mantle boundaryDiamonds formed at the core‐mantle boundary may result in high seismic velocity structures in the region Water reacts with iron‐carbon alloy to form diamond at the P–Tconditions expected for Earth's core‐mantle boundary Some of Earth's mantle carbon may come from the core through water‐induced reactions at the core‐mantle boundary Diamonds formed at the core‐mantle boundary may result in high seismic velocity structures in the region