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Abstract
Close-in giant exoplanets with temperatures greater than 2,000 K ('ultra-hot Jupiters') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble Space Telescope (HST) and Spitzer Space Telescope1-3. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis3-12. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS13 instrument on the JWST. The data span 0.85 to 2.85 mu m in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at >6s confidence) and evidence for optical opacity, possibly attributable to H-, TiO and VO (combined significance of 3.8s). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy-element abundance ('metallicity', M/H= 1.03- 0.51+1.11 times solar) and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the substellar point that decreases steeply and symmetrically with longitude towards the terminators.
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Abstract
Gross primary production (GPP) by boreal forests is highly sensitive to environmental changes. However, GPP simulated by land surface models (LSMs) remains highly uncertain due to the lack of direct photosynthesis observations at large scales. Carbonyl sulfide (COS) has emerged as a promising proxy to improve the representation of GPP in LSMs. Because COS is absorbed by vegetation following the same diffusion pathway as CO2 during photosynthesis and not emitted back to the atmosphere, incorporating a mechanistic representation of vegetation COS uptake in LSMs allows using COS observations to refine GPP representation. Here, we perform ecosystem COS flux and GPP data assimilations to constrain the COS- and GPP-related parameters in the ORCHIDEE LSM for boreal evergreen needleleaf forests (BorENF). Assimilating ecosystem COS fluxes at Hyytiala forest increases the simulated net ecosystem COS uptake by 14%. This increase largely results from changes in the internal conductance to COS, highlighting the need to improve the representation of COS internal diffusion and consumption. Moreover, joint assimilation of ecosystem COS flux and GPP at Hyytiala improves the simulated latent heat flux, contrary to the GPP-only data assimilation, which fails to do so. Finally, we scaled this assimilation framework up to the boreal region and find that the joint assimilation of COS at Hyytiala and GPP fluxes at 10 BorENF sites increases the modeled vegetation COS uptake up to 18%, but not GPP. Therefore, this study encourages the use of COS flux observations to inform GPP and latent heat flux representations in LSMs.
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Postdocs and scientists cheer on Rapids Bridge in Rock Creek Park during Postdoc Appreciation Day
August 21, 2023
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Crafting a Competitive Postdoctoral Application: Insider Tips from EPL Experts

Abstract
An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (<= 10(3) s(-1)), where up to 352 diffraction images can be collected from a single pulse train. The set-up employs piezo-driven dDACs capable of compressing samples in >= 340 mu s, compatible with the maximum length of the pulse train (550 mu s). Results from rapid compression experiments on a wide range of sample systems with different X-ray scattering powers are presented. A maximum compression rate of 87 TPa s(-1) was observed during the fast compression of Au, while a strain rate of similar to 1100 s(-1) was achieved during the rapid compression of N-2 at 23 TPa s(-1).
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Abstract
Feiite (Fe3TiO5) is a high-pressure Fe-Ti oxide mineral recently discovered in martian meteorite Shergotty. Feiite is isostructural with Fe4O5, a high-pressure iron oxide stable at pressures >10 GPa. The stability of feiite has yet to be studied, as it has not previously been synthesized in the laboratory. To determine the minimum pressure at which feiite can be synthesized, we have conducted multi-anvil experiments at 1200 & DEG;C and at pressures ranging from 7 to 12 GPa. Major element compositions and XRD patterns indicate that we successfully synthesized feiite with an orthorhombic unit cell (Cmcm structure) in experiments conducted at pressures 8 GPa or greater. Relative to A(2)B(2)O(5) phases with similar structure, feiite can be synthesized at lower pressures. The coexistence of feiite and liuite (FeTiO3-perovskite) in Shergotty indicates that the upper pressure limit of feiite stability is above 15 GPa. To investigate the effect of oxygen fugacity on the composition and stability of feiite, we conducted an additional series of experiments at 1200 & DEG;C and 10 GPa pressure in which we varied the Fe3+/Fe-total ratio of the experimental starting materials. In doing so, we identified a minimum Fe3+ content necessary to stabilize the feiite structure (Fe3+/Fe-total = 0.26 at 10 GPa and 1200 ?). The importance of Fe3+ for feiite stability suggests this phase would not form in lunar or HED meteorites, where iron-titanium oxides contain little to no ferric iron. Though our experimental results can only place a lower limit on the shock pressures experienced in Shergotty, the determined pressure stability indicates feiite could also be present in diamond-bearing terrestrial rocks sourced from the upper mantle or transition zone. Additionally, the presence of feiite would be an indicator of source Fe3+/ Fe-total.
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Abstract
Minerals are information-rich materials that offer researchers a glimpse into the evolution of planetary bodies. Thus, it is important to extract, analyze, and interpret this abundance of information to improve our understanding of the planetary bodies in our solar system and the role our planet's geosphere played in the origin and evolution of life. Over the past several decades, data-driven efforts in mineralogy have seen a gradual increase. The development and application of data science and analytics methods to mineralogy, while extremely promising, has also been somewhat ad hoc in nature. To systematize and synthesize the direction of these efforts, we introduce the concept of "Mineral Informatics," which is the next frontier for researchers working with mineral data. In this paper, we present our vision for Mineral Informatics and the X-Informatics underpinnings that led to its conception, as well as the needs, challenges, opportunities, and future directions of the field. The intention of this paper is not to create a new specific field or a sub-field as a separate silo, but to document the needs of researchers studying minerals in various contexts and fields of study, to demonstrate how the systemization and enhanced access to mineralogical data will increase cross- and interdisciplinary studies, and how data science and informatics methods are a key next step in integrative mineralogical studies.
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Abstract
The flux of eruptible magma into a magmatic plumbing system influences eruption size and timing. If magma transfer is possible between two hydraulically-connected magma lenses, system destabilization can tap a larger magma volume than stored in any one melt lens. This study identifies two distinct magma reservoirs beneath Ambrym, a basaltic island volcano in Vanuatu, during the time period February 2019 to January 2022. Using InSAR time series and a data assimilation approach, we estimate pressure changes within two reservoirs (located 5-7 and 4-6 km b.s.l.). Furthermore, a theoretical model demonstrates that the reservoirs may not currently be hydraulically connected, despite evidence of physical mixing of magma derived from each reservoir during the December 2018 eruption. These findings further our understanding of how magmatic plumbing systems at basaltic calderas may change after rift-zone eruptions.
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Abstract
Nitrite, an intermediate product of the oxidation of ammonia to nitrate (nitrification), accumulates in upper oceans, forming the primary nitrite maximum (PNM). Nitrite concentrations in the PNM are relatively low in the western North Pacific subtropical gyre (wNPSG), where eddies are frequent and intense. To explain these low nitrite concentrations, we investigated nitrification in cyclonic eddies in the wNPSG. We detected relatively low half-saturation constants (i.e., high substrate affinities) for ammonia and nitrite oxidation at 150 to 200 meter water depth. Eddy-induced displacement of high-affinity nitrifiers and increased substrate supply enhanced ammonia and nitrite oxidation, depleting ambient substrate concentrations in the euphotic zone. Nitrite oxidation is more strongly enhanced by the cyclonic eddies than ammonia oxidation, reducing concentrations and accelerating the turnover of nitrite in the PNM. These findings demonstrate a spatial decoupling of the two steps of nitrification in response to mesoscale processes and provide insights into physical-ecological controls on the PNM.
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Abstract
We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST R band to Spitzer 4.5 mu m. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600 R-circle dot circumstellar shell of dusty material with a mass similar to 5 x 10(-5)M(circle dot) surrounding a log(L/L-circle dot) = 4.74 +/- 0.07 and T-eff 3920(-160)(+200) K RSG. This luminosity is consistent with RSG models of initial mass 11M(circle dot), depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5 mu m imaging, exhibiting similar to 70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with kappa-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as alpha Orionis (Betelgeuse).
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