Band engineering in layered metal dichalcogenides leads to a variety of physical phenomena and has obtained considerable attention recently. In this work, pressure-induced metallization and superconductivity in pristine 1T-SnSe2 is reported via electrical transport and synchrotron X-ray diffraction experiments. Electrical transport results show that the metallization emerges above 15.2 GPa followed by appearance of superconducting transition at 18.6 GPa. The superconductivity is robust with a nearly constant T-c approximate to 6.1 K between 30.1 and 50.3 GPa. High-pressure synchrotron X-ray diffraction experiments indicate that the 1T-SnSe2 phase maintains up to 46.0 GPa. Although the theoretical predicted structural transition and decomposition of SnSe2 into Sn3Se4 and Se are not detected, it is argued that the structural instability under high pressure might be crucial for the superconductivity. These findings demonstrate that 1T-SnSe2 is a very rare system from which superconductivity can be driven via multiple ways.

Noncentrosymmetric molybdenum nitride Rh2Mo3N is a conventional s-wave superconductor at ambient pressure. Here we report the evolution of structural and electronic properties of Rh2Mo3N under high pressure. X-ray diffraction measurements reveal the stability of pristine beta-Mn-type cubic structure up to 47.9 GPa, accompanied by the continuously enhanced distortion of Mo6N octahedra. Electronic transport experiments show the robustness of superconductivity under pressure, i.e., the superconducting transition temperature T-c varies only similar to 0.7 K upon compression up to 38.5 GPa. Meanwhile, detailed analyses of both structural and transport results consistently reveal a critical pressure of similar to 14.0 GPa. In agreement with the enhancement of octahedral distortion, the temperature dependence of upper critical magnetic field accords with a p-wave model at 22.0 GPa and an s-wave model at 6.0 GPa. These results suggest the emergence of novel superconductivity in the distorted Rh2Mo3N cubic phase under pressure, which could be attributed to the enhanced strength of antisymmetric spin-orbit coupling (ASOC) via pressure-modified local octahedral distortion. Our findings may shed light on the searching and understanding of unique triplet-pairing superconductivity in other inversion-broken superconductors with strong ASOC.

Surface ozone (O-3) pollution events are becoming more frequent and have recently emerged as a severe air pollution problem in China. However, the spatial-temporal distribution of surface O-3, as well as its primary synoptic and meteorological drivers, remains poorly understood. The purpose of this study was to identify the key synoptic and meteorological drivers of O-3 pollution in different regions of China. To achieve this goal, this study established meteorology overlaps of regional O-3 pollution events in space and time and applied a comprehensive statistical model selection method for optimal synoptic and meteorological models, based on a newly released O-3 dataset for 2015-2018. It was observed that extreme regional O-3 pollution events (duration >7 d) occurred more frequently and exhibited a high co-occurrence frequency (>50%) with air stagnation (AS). Moreover, the beginning and end of 69% of the regional O-3 pollution events coincided with regional daily maximum temperature changes. The intensity of AS is the dominant driver of O-3 pollution event intensity across most of the six selected megacity regions. Although other meteorological drivers, such as the intensity of hot days (HD) and meridional wind of 10 m were also important, their impacts varied according to the region. Overall, increase in extreme AS and HD led to the worsening of regional O-3 pollution events. These findings imply that mitigating regional O-3 pollution should consider changing synoptic and meteorological conditions.

Inspired by the rich physical properties of thermoelectric materials, we have investigated the electrical transport, vibrational, and structural properties of efficient thermoelectric material Cu3Sb0.98Al0.02Se4 under pressure up to 40.1 GPa. At a critical pressure of 8.5 GPa, a superconducting phase sets in and persists in the pressure range studied. A superconducting dome in the temperature-pressure phase diagram of Cu3Sb0.98Al0.02Se4 was observed. Meanwhile, pressure-induced structural transition from its initial phase to disorder body-centered cubic structure in Cu3Sb0.98Al0.02Se4 has been verified by the X-ray diffraction and Raman scattering measurements. Interestingly, the onset of superconductivity coincides with the structural transition, accompanied with the reduction of volume. The superconducting phase was observed in the ultimate formation of the Cu-Sb-Al-Se alloy and was determined to be Im-3m. Based on Hall coefficient measurements, we evaluated the carrier concentration of Cu3Sb0.98Al0.02Se4, which shows a dramatic increase in the superconducting state. These results suggest that the novel superconductor is realized through the charge transfers and the first-order structural transformation. (C) 2021 Elsevier B.V. All rights reserved.

Climate change alters weather patterns and hydrological cycle, thus potentially aggravating water quality impairment. However, the direct relationships between climate variability and water quality are complicated by a multitude of hydrological and biochemical mechanisms dominate the process. Thus, little is known regarding how water quality responds to climate variability in the context of changing meteorological conditions and human activities. Here, a longitudinal study was conducted using trend, correlation, and redundancy analyses to explore stream water quality sensitivity to temperature, precipitation, streamflow, and how the sensitivity was affected by watershed climate, land cover percentage, landscape configuration, fertilizer application, and tillage types. Specifically, daily pollutant concentration data of suspended solid (SS), total phosphorus (TP), soluble reactive phosphorus (SRP), total Kjeldahl nitrogen (TKN), nitrate and nitrite (NOx), and chloride (Cl) were used as water quality indicators in four Lake Erie watersheds from 1985 to 2017, during which the average tem-perature has increased 0.5 degrees C and the total precipitation has increased 9%. Results show that precipitation and flow were positively associated with SRP, NOx, TKN, TP, and SS, except for SRP and NOx in the urban basin. The rising temperatures led to increasing concentrations of SS, TKN, and TP in the urban basin. SRP and NOx sensitivity to precipitation was higher in the years with more precipitation and higher precipitation seasonality, and the basins with more spatially aggregated cropland. No-tillage and reduced tillage management could decrease both precipitation and temperature sensitivity for most pollutants. As one of the first studies leveraging multiple watershed environmental variables with long-term historical climate and water quality data, this study can assist target land use planning and management policy to mitigate future climate change effects on surface water quality.

The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm s(-1) measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this bold precision are summarized here. Beginning with the High Accuracy Radial Velocity Planet Searcher spectrograph, technological advances for precision radial velocity (RV) measurements have focused on building extremely stable instruments. To reach still higher precision, future spectrometers will need to improve upon the state of the art, producing even higher fidelity spectra. This should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. Key data analysis challenges for the precision RV community include distinguishing center of mass (COM) Keplerian motion from photospheric velocities (time correlated noise) and the proper treatment of telluric contamination. Success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. COM velocities produce Doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from Keplerian signals. Exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. However, higher precision RV measurements are required to serve as a discovery technique for potentially habitable worlds, to confirm and characterize detections from transit missions, and to provide mass measurements for other space-based missions. The future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with Doppler measurements.

Regular intra-tooth variations in the delta(18)O value of mammalian tooth enamel phosphate (delta(18)O(p)) have been considered a potential measure of seasonal changes in continental climate variables since they were first observed. In order to investigate this possibility in more detail, analyses were made of teeth from a number of mammalian herbivores (sheep, cattle, elk, and pigs) that lived over a wide range of geographic locations, ecological settings, and climatic conditions (Iowa, Florida, Wyoming, Iceland,. England, Croatia, and the Philippines). The lack of intra-tooth delta(18)O(p) variations in teeth of cattle that were given tap water to drink provides strong evidence that the underlying cause of observed intra-tooth variations is primarily a change in the isotopic composition of ingested water. In concert with this interpretation, the range of intra-tooth delta(18)O(p) values and their absolute values from each locality mirror observed differences in the range and absolute delta(18)O values of local precipitation (delta(18)O(pt)) and in climate variables. Thus intra-tooth delta(18)O(p) values can indeed be considered a qualitative measure of seasonal climate change in continental settings. Quantitative use of intra-tooth delta(18)O(p) values as a climate proxy is possible, but is hindered by lack of detailed information on aspects of mammalian physiology, behavior, and perhaps local hydrology that may also play a role in influencing delta(18)O(p). This problem is exemplified by the different range in delta(18)O(p) values measured for sheep and cattle from the same locality around York, UK (3.4 vs. 2.6 parts per thousand, respectively). The observed difference most likely reflects a difference in the relative amount of leaf water ingested by the two species. Future studies of well-constrained samples are required to test physiological models and to develop empirical relations that accurately relate delta(18)O(p) to delta(18)O(pt). In addition to their use as indicators of seasonality, intra-tooth variations in delta(18)O(p) values provide valuable information for longer-term climate change and paleobiological investigations. Copyright (C) 1998 Elsevier Science Ltd.

Oxygen isotope records of Cenozoic sea water temperatures indicate that a rapid warming event known as the Latest Paleocene Thermal Maximum (LPTM) occurred during the otherwise gradual increase in world temperatures during the Late Paleocene and Early Eocene. Oxygen isotope analysis of the carbonate and phosphate components of hydroxyapatite found in mammalian tooth enamel and body scales of river-dwelling fish from the Bighorn Basin in Wyoming were made to investigate corresponding changes in the terrestrial climate. A comparison of carbonate and phosphate isotope data from modern and fossil material indicates that some diagenetic alteration of the fossil material has occurred, although systematically larger intra-tooth ranges in the oxygen isotope composition of carbonate indicate that it is more likely to have been affected than phosphate. Carbonate and phosphate from the ecologically diverse mammals and fishes both record a shift to higher oxygen isotope ratios at the same time and of the same duration as the LPTM. These shifts reflect a change in the isotopic composition of regional precipitation, which in turn provides the first evidence for continental climate change during the LPTM. Assuming the present-day relation between the oxygen isotope composition of precipitation and temperature applies to conditions in the past, and that animal physiology and behavior is relatively invariant over time, the isotopic shift is equivalent to an increase of surface temperature in western North America of several degrees. This result is consistent with the magnitude of high-latitude ocean warming, and provides a basis for relating marine and terrestrial oxygen isotope records to records of terrestrial biotic change. (C) 1998 Elsevier Science B.V. All rights reserved.

Correlations between mean annual temperature (MAT) and the weighted average oxygen isotope composition of yearly precipitation (delta(18)O(pt)) are well-known, but the utility of modern relations to make reliable estimates of temperature change over geological time is uncertain. This question has been addressed by using seasonal subsets of the global data base of temperature and isotopic measurements to represent two different climate modes. A comparison of middle- to high-latitude delta(18)O(pt)/temperature relations for each climate mode reveals (1) a significant offset between them, and (2) a difference in the strength of their correlations. The offset in relations is due to differences in temperature and water vapor budget in the tropics, and can lead to serious underestimates of temperature change. Differences in the strength of correlations arise from the influence of climate mode-specific, non-temperature factors on delta(18)O(pt). The overall result is that no single relation can be used in all cases to make unambiguous temperature estimates using a temporal record of delta(18)O(pt) values. One way to overcome these problems is to reconstruct delta(18)O(pt)/temperature relations for the time periods being investigated. If an appropriate proxy for delta(18)O(pt) is available, it may also be possible to estimate temperature without relying on delta(18)O(pt)/temperature relations. A promising alternative to these options is to use records of delta(18)O(pt) to test predictions of global climate models, an approach that may allow a reliable and more complete reconstruction to be made of climate change over geologic time. (C) 1999 Elsevier Science B.V. All rights reserved.