A paleoclimate reconstruction for southwestern Texas using oxalate residue from lichen as a paleoclimate proxy.

Abstract A calcium oxalate rock coating is ubiquitous on limestone surfaces inside dry rock shelters and under rock overhangs within the canyons of the southwestern Edwards Plateau in southwestern Texas. The oxalate was likely produced by epilithic lichens that #ourished in these niches during dry climate regimes. During wet climate conditions the productivity of the lichen would be severely reduced due to physiological response to moisture regime. Thus, lichen productivity and the production of calcium oxalate may have changed through time in response to wet}dry climate #uctuations. Twenty-"ve AMS radiocarbon ages of rock crust samples collected from 14 sites demonstrate that oxalate was produced episodically during the middle and late Holocene. The occurrence of oxalate is correlated with periods of dry climate, whereas gaps in the record of oxalate deposition coincide with more mesic climate intervals. The results of this study demonstrate the potential for obtaining paleoclimate data from biogenic residues on rock surfaces

Between crime and colony: Interrogating (im)mobilities aboard the convict ship

Recent literature in carceral geography has attended to the importance of mobilities in interrogating the experience and control of spaces of imprisonment, detention and confinement. Scholars have explored the paradoxical nature of incarcerated experience as individuals oscillate between moments of fixity and motion as they are transported to/from carceral environments. This paper draws upon the convict ship – an example yet to gain attention within these emerging discussions – which is both an exemplar of this paradox and a lens through which to complicate understandings of carceral (im)mobilities. The ship is a space of macro-movement from point A to B, whilst simultaneously a site of apparent confinement for those aboard who are unable to move beyond its physical parameters. Yet, we contend that all manner of mobilities permeate the internal space of the ship. Accordingly, we challenge the binary thinking that separates moments of fixity from motion and explore the constituent parts that shape movement. In paying attention to movements in motion on the ship, we argue that studies of carceral mobility must attend to both methods of moving in the space between points A and B; as micro, embodied and intimate (im)mobilities are also played out within large-scale regimes of movement

Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 463 (2017): 159-170, doi:10.1016/j.epsl.2017.01.032.The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.TL, ZL, and DH thank NSF EAR-1349252. ZL further thanks OCE-1232620. DH, ZL, and TL acknowledge further funding from a NASA Early Career Collaboration Award. TL, AB, NP, DH, and AK thank the NASA Astrobiology Institute. TL and NP received support from the Earth-Life Transitions Program of the NSF. AB acknowledges support from NSF grant EAR-05-45484 and an NSERC Discovery and Accelerator Grants. CW acknowledges support from NSFC grant 40972021

Strong Continuum-continuum Couplings In The Direct Ionization Of Ar And He Atoms By 6-MeV/u U38+ And Th38+ Projectiles

Doubly differential cross sections have been measured as a function of the electron energy and observation angle for electron emission following collisions of 6-MeV/u U38+ and Th38+ on He and Ar. The electron-emission data show an enhancement at forward angles and a decrease at backward angles with respect to scaled-cross-section results based on the Born approximation. Comparison with classical-trajectory Monte Carlo calculations suggests that the deviation from the Born approximation can be explained by continuum-continuum couplings. By comparing with previously published data, we found that the forward enhancement as well as the backward decrease follow a q/vp (q,vp are the projectile charge and velocity) scaling. © 1989 The American Physical Society

Holomorphic Quantization on the Torus and Finite Quantum Mechanics

We construct explicitly the quantization of classical linear maps of $SL(2, R)$ on toroidal phase space, of arbitrary modulus, using the holomorphic (chiral) version of the metaplectic representation. We show that Finite Quantum Mechanics (FQM) on tori of arbitrary integer discretization, is a consistent restriction of the holomorphic quantization of $SL(2, Z)$ to the subgroup $SL(2, Z)/\Gamma_l$, $\Gamma_l$ being the principal congruent subgroup mod l, on a finite dimensional Hilbert space. The generators of the ``rotation group'' mod l, $O_{l}(2)\subset SL(2,l)$, for arbitrary values of l are determined as well as their quantum mechanical eigenvalues and eigenstates.Comment: 12 pages LaTeX (needs amssymb.sty). Version as will appear in J. Phys.

The UV-SCOPE mission: ultraviolet spectroscopic characterization of planets and their environments

UV-SCOPE is a mission concept to determine the causes of atmospheric mass loss in exoplanets, investigate the mechanisms driving aerosol formation in hot Jupiters, and study the influence of the stellar environment on atmospheric evolution and habitability. As part of these investigations, the mission will generate a broad-purpose legacy database of time-domain ultraviolet (UV) spectra for nearly 200 stars and planets. The observatory consists of a 60 cm, f/10 telescope paired to a long-slit spectrograph, yielding simultaneous, almost continuous coverage between 1203 Å and 4000 Å, with resolutions ranging from 6000 to 240. The efficient instrument provides throughputs < 4% (far-UV; FUV) and < 15% (near-UV; NUV), comparable to HST/COS and much better than HST/STIS, over the same spectral range. A key design feature is the LiF prism, which serves as a dispersive element and provides high throughput even after accounting for radiation degradation. The use of two delta-doped Electron-Multiplying CCD detectors with UV-optimized, single-layer anti-reflection coatings provides high quantum efficiency and low detector noise. From the Earth-Sun second Lagrangian point, UV-SCOPE will continuously observe planetary transits and stellar variability in the full FUV-to-NUV range, with negligible astrophysical background. All these features make UV-SCOPE the ideal instrument to study exoplanetary atmospheres and the impact of host stars on their planets. UV-SCOPE was proposed to NASA as a Medium Explorer (MidEx) mission for the 2021 Announcement of Opportunity. If approved, the observatory will be developed over a 5-year period. Its primary science mission takes 34 months to complete. The spacecraft carries enough fuel for 6 years of operations

Dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record; this is probably due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) – the largest negative δ13C excursion in Earth history. We evaluated 15 SE sections, all of which reveal the presence of sulfate minerals and/or enriched carbonate-associated sulfate concentrations, suggesting a rise in the sulfate reservoir. Notably, where data are available, the SE also reveals considerable enrichments in [Ba] relative to pre-and post-SE intervals. We propose that elevated seawater sulfate concentrations during the SE may have facilitated authigenesis of sulfate minerals. At the same time, the rise in Ba concentrations in shelf environments further facilitated barite deposition. A larger sulfate reservoir would stimulate microbial sulfate reduction and anaerobic oxidation of organic matter (including methane), contributing to the genesis of the SE. The existence of sulfate minerals throughout the SE suggests that oxidant pools were not depleted at that time, which challenges previous modelling results. Our study highlights the dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event

The Lunacy Commission.

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Measurement of Λ4H\rm ^4_{\Lambda}H and Λ4He\rm ^4_{\Lambda}He binding energy in Au+Au collisions at sNN\sqrt{s_\mathrm{NN}} = 3 GeV

Measurements of mass and $\Lambda$ binding energy of $\rm ^4_{\Lambda}H$ and $\rm ^4_{\Lambda}He$ in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=3$ GeV are presented, with an aim to address the charge symmetry breaking (CSB) problem in hypernuclei systems with atomic number A = 4. The $\Lambda$ binding energies are measured to be $\rm 2.22\pm0.06(stat.) \pm0.14(syst.)$ MeV and $\rm 2.38\pm0.13(stat.) \pm0.12(syst.)$ MeV for $\rm ^4_{\Lambda}H$ and $\rm ^4_{\Lambda}He$, respectively. The measured $\Lambda$ binding-energy difference is $\rm 0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV for ground states. Combined with the $\gamma$-ray transition energies, the binding-energy difference for excited states is $\rm -0.16\pm0.14(stat.)\pm0.10(syst.)$ MeV, which is negative and comparable to the value of the ground states within uncertainties. These new measurements on the $\Lambda$ binding-energy difference in A = 4 hypernuclei systems are consistent with the theoretical calculations that result in $\rm \Delta B_{\Lambda}^4(1_{exc}^{+})\approx -\Delta B_{\Lambda}^4(0_{g.s.}^{+})<0$ and present a new method for the study of CSB effect using relativistic heavy-ion collisions.Comment: 8 pages, 5 figure