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Low temperature superconducting vacuum tube maglev is one of the ultra-high-speed transportation methods that a lot of countries are competing to develop. At present, the research is in its infancy, and it is necessary to evaluate the dynamic performance of its route lines. In this paper, taking the maglev test line from Changsha to Hengyang as an example, a vehicle-route coupling model of the low-temperature superconducting electric levitation system was established, the dynamic performances of the maglev vehicle were determined. Firstly, the vertical and lateral acceleration of the carbody, levitation and guidance force were calculated. Secondly, the frequency histograms of the dynamic performance indicators were drawn, and the distributions of these indicators in different intervals was analyzed. Thirdly, the influence of the different curve radius on the dynamic performance index was obtained. The research shows that when the maglev vehicle travels across the Changsha-Hengyang line, the calculated vertical and lateral accelerations of the carbody are lower than the comfort threshold, and the dynamic performance meets the requirements. From the perspective of vehicle dynamic performance, the transition curve length of 1 400 m is reasonable. When the curve radius is 20 000 m, the vehicle speed 1 000 km/h and the cross slope of 16° match the best dynamic performances. The results in the article can provide references for the design of ultra high speed maglev lines. [ABSTRACT FROM AUTHOR]

The global biosphere is commonly assumed to have been less productive before the rise of complex eukaryotic ecosystems than it is today.sup.1. However, direct evidence for this assertion is lacking. Here we present triple oxygen isotope measurements ([increment].sup.17O) from sedimentary sulfates from the Sibley basin (Ontario, Canada) dated to about 1.4 billion years ago, which provide evidence for a less productive biosphere in the middle of the Proterozoic eon. We report what are, to our knowledge, the most-negative [increment].sup.17O values (down to -0.880/00) observed in sulfates, except for those from the terminal Cryogenian period.sup.2. This observation demonstrates that the mid-Proterozoic atmosphere was distinct from what persisted over approximately the past 0.5 billion years, directly reflecting a unique interplay among the atmospheric partial pressures of CO.sub.2 and O.sub.2 and the photosynthetic O.sub.2 flux at this time.sup.3. Oxygenic gross primary productivity is stoichiometrically related to the photosynthetic O.sub.2 flux to the atmosphere. Under current estimates of mid-Proterozoic atmospheric partial pressure of CO.sub.2 (2-30 times that of pre-anthropogenic levels), our modelling indicates that gross primary productivity was between about 6% and 41% of pre-anthropogenic levels if atmospheric O.sub.2 was between 0.1-1% or 1-10% of pre-anthropogenic levels, respectively. When compared to estimates of Archaean.sup.4-6 and Phanerozoic primary production.sup.7, these model solutions show that an increasingly more productive biosphere accompanied the broad secular pattern of increasing atmospheric O.sub.2 over geologic time.sup.8.Triple oxygen isotope measurements of 1.4-billion-year-old sedimentary sulfates reveal a unique mid-Proterozoic atmosphere and demonstrate that gross primary productivity in the mid-Proterozoic was between 6% and 41% of pre-anthropogenic levels., Author(s): Peter W. Crockford [sup.1] [sup.2] [sup.3] , Justin A. Hayles [sup.4] [sup.5] , Huiming Bao [sup.5] [sup.6] , Noah J. Planavsky [sup.7] , Andrey Bekker [sup.8] , Philip W. [...]

Two cap carbonates overlying Cryogenian panglacial deposits are found in North‐East Svalbard of which the younger (635 Ma) forms the base of the Ediacaran Period. It is represented by a transgressive succession in which laminated dolostone, typically around 20 m thick (Member D1), is succeeded transitionally by a similar thickness of impure carbonates (Member D2). In Spitsbergen, there is evidence of microbially influenced sediment stabilisation and carbonate precipitation in the lower part of D1, whilst the upper part of D1 and D2 show centimetre‐decimetre‐scale graded units with undulatory lamination interpreted as evidence of storm activity. Carbonate originated as possible freshwater whitings, as well as microbial precipitates. Exhumed and eroded hardgrounds display replacive 10–30 μm dolomite crystals with cathodoluminescence characteristics consistent with early diagenetic manganese and iron reduction. Regionally, carbon isotope values consistently decrease by around 2‰ from around −3‰ over 30 m of section which is both a temporal and a bathymetric signal, but not a global one. An exponential decline in carbonate production predicted by box models is fitted by a semi‐quantitative sedimentation model. A mass‐anomalous 17O depletion in carbonate‐associated sulphate in dolomite, inherited from precursor calcite, decreases from −0.6 to −0.3‰ in the basal 15 m of section and then approaches background values. The post‐glacial anomalous 17O depletion in carbonate‐associated sulphate and barite elsewhere has been interpreted in terms of ultra‐high pCO2 at the onset of deglaciation. Such anomalies, with larger amplitude, have been reported in Svalbard from underlying lacustrine and tufaceous limestones representing a hyperarid glacial environment. The anomalous sulphate could be produced contemporarily, or the internally drained landscape may have continued to release 17O‐anomalous sulphate as it was transgressed during cap carbonate deposition. The late Cryogenian to earliest Ediacaran record in Svalbard provides the most complete record of the basal 17O‐depletion event in the world. [ABSTRACT FROM AUTHOR]

Barite in basal Ediacaran cap carbonates in South China shows distinct, non-mass-dependent depletion in [sup.17]O, a signal most likely reflecting an extremely high pC[O.sub.2] atmosphere during Marinoan glacial meltdown. The precise geological context of the barite within the cap carbonate was not defined, however, and such information is crucial to an accurate interpretation of the anomalous [sup.17}O signal. Based on an extensive field survey of Marinoan cap carbonates in South China and detailed sedimentological, petrographic, and isotope data, we propose here a unified sequence of events that followed the deposition of the Nantuo diamictite: the cap dolostone was first deposited and later uplifted due to isostatic rebound, undergoing karstic dissolution in both shallow platform and transitional facies of the Yangtze Block; subsequent transgression initiated a consistent sequence of mineral deposition on karstic surfaces or within cavities. The [sup.17]O-depleted barite, either visible on outcrops or identifiable in thin sections, is among the first minerals precipitated when the transgression flooded the karstified cap dolostone. The calcite with extremely negative [delta][sup.13]C values occurs at the last stage of the cavity filling, well after the deposition of cap dolostone and the [sup.17]O-depleted barite, suggesting that the signal of methane hydrate was registered much later in the cap dolostone. A similar recognition of karstic dissolution and subsequent barite deposits in cap dolostones in northwest Africa and northwest Canada suggest that deposition of the [sup.17]O-depleted barites may be a global event, recording an atmospheric-biological-hydrological condition shortly (within 0-1.6 m.y.) after the initial meltdown of the Marinoan snowball Earth. doi: 10.1130/G31224.1

Volcanic eruptions release a large amount of sulphur dioxide (S[O.sub.2]) into the atmosphere (1,2). S[O.sub.2] is oxidized to sulphate and can subsequently form sulphate aerosol (3), which can affect the Earth's radiation balance, biologic productivity and high-altitude ozone concentrations, as is evident from recent volcanic eruptions (4). S[O.sub.2] oxidation can occur via several different pathways that depend on its flux and the atmospheric conditions (3). An investigation into how S[O.sub.2] is oxidized to sulphate--the oxidation product preserved in the rock record--can therefore shed light on past volcanic eruptions and atmospheric conditions. Here we use sulphur and triple oxygen isotope measurements of atmospheric sulphate extracted from tuffaceous deposits to investigate the specific oxidation pathways from which the sulphate was formed. We find that seven eruption-related sulphate aerosol deposition events have occurred during the mid-Cenozoic era (34 to 7 million years ago) in the northern High Plains, North America. Two extensively sampled ash beds display a similar sulphate mixing pattern that has two distinct atmospheric secondary sulphates. A three-dimensional atmospheric sulphur chemistry and transport model study reveals that the observed, isotopically discrete sulphates in sediments can be produced only in initially alkaline cloudwater that favours an ozone-dominated S[O.sub.2] oxidation pathway in the troposphere. Our finding suggests that, in contrast to the weakly acidic conditions today (5), cloudwater in the northern High Plains may frequently have been alkaline during the mid-Cenozoic era. We propose that atmospheric secondary sulphate preserved in continental deposits represents an unexploited geological archive for atmospheric S[O.sub.2] oxidation chemistry linked to volcanism and atmospheric conditions in the past., A close temporal correlation between large igneous provinces and major mass extinction events over the last 300 million years implies a potentially causal relationship between the two (6). There has [...]

Author(s): Huiming Bao (corresponding author) [1]; Douglas A. Campbell [1]; James G. Bockheim [2]; Mark H. Thiemens [1] The dry valleys of Antarctica are some of the oldest terrestrial surfaces [...]

Silicate melts have served as transport agents in the chemical and thermal evolution of Earth. Molecular dynamics simulations based on a deep neural network potential trained by ab initio data show that the viscosity of MgSiO3 melt decreases with increasing pressure at low pressures (up to ∼6 GPa) before it starts to increase with further compression. The melt electrical conductivity also behaves anomalously; first increasing and then decreasing with pressure. The melt accumulation implied by the viscosity turnover at ∼23 GPa along mantle liquidus offers an explanation for the low‐velocity zone at the 660‐km discontinuity. The increase in electrical conductivity up to ∼50 GPa may contribute to the steep rise of Earth's electrical conductivity profiles derived from magnetotelluric observations. Our results also suggest that small fraction of melts could give rise to detectable bulk conductivity in deeper parts of the mantle. Plain Language Summary: Dynamical behavior of silicate melts at high temperature and pressure controls melt distribution in Earth's interior. However, experimental data on the viscosity and electrical conductivity of silicate melts are limited to relatively low pressure. Moreover, the pressure dependence of viscosity is in debate, especially for depolymerized silicate melts. Using a new deep learning‐based simulation approach, we find that both the viscosity and electrical conductivity of MgSiO3 melt behave anomalously with pressure, which could have important implications for zones with seismic velocity anomalies and high electrical conductivity in Earth's interior. Key Points: The viscosity of MgSiO3 melt behaves anomalously at relatively low temperatures; first decreasing and then increasing with pressureThe electrical (ionic) conductivity shows anomalous pressure behavior at all temperaturesDeep potential molecular dynamics simulations offer us a reliable and complete data set to study transport properties of silicate melts [ABSTRACT FROM AUTHOR]