Oriented grain growth and modification of ‘frozen anisotropy’ in the lithospheric mantle

Seismic anisotropy throughout the oceanic lithosphere is often assumed to be generated by fossilized texture formed during deformation at asthenospheric temperatures close to the ridge. Here we investigate the effect of high-temperature and high-pressure static annealing on the texture of previously deformed olivine aggregates to simulate residence of deformed peridotite in the lithosphere. Our experiments indicate that the orientation and magnitude of crystallographic preferred orientation (CPO) will evolve due to the preferential growth of grains with low dislocation densities. These observations suggest that texture and stored elastic strain energy promote a style of grain growth that modifies the CPO of a deformed aggregate. We demonstrate that these microstructural changes alter the orientation distributions and magnitudes of seismic wave velocities and anisotropy. Therefore, static annealing may complicate the inference of past deformation kinematics from seismic anisotropy in the lithosphere.This research is supported by NSF EAR-1131985 (to PS), with additional support from the Institute of Materials Science and Engineering at Washington University in St. Louis. DW and LNH acknowledge support from the Natural Environment Research Council Grant NE/M000966/1

Reply to: “Impact of marine processes on flow dynamics of northern Antarctic Peninsula outlet glaciers” by Rott et al.

Replying to Rott et al. Nature Communications https://doi.org/10.1038/s41467-020-16658-y (2020)Publisher PDFPeer reviewe

Study of the reaction e^{+}e^{-} -->J/psi\pi^{+}\pi^{-} via initial-state radiation at BaBar

We study the process $e^+e^-\to J/\psi\pi^{+}\pi^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BaBar detector at center-of-mass energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454 $\mathrm{fb^{-1}}$. We investigate the $J/\psi \pi^{+}\pi^{-}$ mass distribution in the region from 3.5 to 5.5 $\mathrm{GeV/c^{2}}$. Below 3.7 $\mathrm{GeV/c^{2}}$ the $\psi(2S)$ signal dominates, and above 4 $\mathrm{GeV/c^{2}}$ there is a significant peak due to the Y(4260). A fit to the data in the range 3.74 -- 5.50 $\mathrm{GeV/c^{2}}$ yields a mass value $4244 \pm 5$ (stat) $\pm 4$ (syst)$\mathrm{MeV/c^{2}}$ and a width value $114 ^{+16}_{-15}$ (stat)$\pm 7$(syst)$\mathrm{MeV}$ for this state. We do not confirm the report from the Belle collaboration of a broad structure at 4.01 $\mathrm{GeV/c^{2}}$. In addition, we investigate the $\pi^{+}\pi^{-}$ system which results from Y(4260) decay

Highlight Talk: Recent Results from VERITAS

VERITAS is a state-of-the-art ground-based gamma-ray observatory that operates in the very high-energy (VHE) region of 100 GeV to 50 TeV. The observatory consists of an array of four 12m-diameter imaging atmospheric Cherenkov telescopes located in southern Arizona, USA. The four-telescope array has been fully operational since September 2007, and over the last two years, VERITAS has been operating with high efficiency and with excellent performance. This talk summarizes the recent results from VERITAS, including the discovery of eight new VHE gamma-ray sources

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow, Sole and Cowton’s Greenland research has been supported by a number of UK NERC research grants (NER/O/S/2003/00620; NE/F021399/1; NE/H024964/1; NE/K015249/1; NE/K014609/1) and Slater has been supported by a NERC PhD studentshipPurpose of the review:  This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet’s hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet Recent findings:   There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary:  Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland’s future mass balance remains challenging.Publisher PDFPeer reviewe

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA

Hepatitis C virus RNA quantification in right and left lobes of the liver in patients with chronic hepatitis C

Quantification of hepatitis C virus RNA in liver tissue is likely to be useful in the study of the natural history, pathogenesis, progression and treatment of hepatitis C virus-associated liver disease. Quantitative measurements of hepatitis C virus RNA in liver biopsy samples using the branched DNA (bDNA) signal amplification assay were carried out. The aims of this study were threefold: first, to assess the level of hepatitis C virus RNA in biopsy samples from the right and left lobes of the liver; second, to evaluate the correlation between hepatitis C virus RNA levels in serum and liver; and third, to investigate the relationship between serum and liver hepatitis C virus RNA levels and the severity of hepatic histology in non-cirrhotic patients with chronic hepatitis C. There was a strong correlation (r = 0.92, P < 0.01) between hepatitis C virus RNA levels in the right and left lobes of the liver as well as a strong correlation between hepatitis C virus RNA levels in liver and serum (r = 0.82, P < 0.01). However, there was no significant correlation between the severity of hepatic histology and levels of hepatitis C virus RNA in serum and liver among patients with chronic active hepatitis classified according to Knodell's hepatic activity index (KI). Our results indicate that hepatitis C virus RNA quantification from a single liver biopsy is representative of both lobes in patients with chronic hepatitis, and suggest that serum hepatitis C virus RNA levels are a meaningful reflection of hepatitis C virus RNA levels in the liver

Supraglacial lakes on the Greenland ice sheet advance inland under warming climate

Supraglacial lakes (SGLs) form annually on the Greenland ice sheet1,2 and, when they drain, their discharge enhances ice-sheet flow3 by lubricating the base4 and potentially by warming the ice5. Today, SGLs tend to form within the ablation zone, where enhanced lubrication is offset by efficient subglacial drainage6,7. However, it is not clear what impact a warming climate will have on this arrangement. Here, we use an SGL initiation and growth8 model to show that lakes form at higher altitudes as temperatures rise, consistent with satellite observations9. Our simulations show that in southwest Greenland, SGLs spread 103 and 110 km further inland by the year 2060 under moderate (RCP 4.5) and extreme (RCP 8.5) climate change scenarios, respectively, leading to an estimated 48–53% increase in the area over which they are distributed across the ice sheet as a whole. Up to half of these new lakes may be large enough to drain, potentially delivering water and heat to the ice-sheet base in regions where subglacial drainage is inefficient. In such places, ice flow responds positively to increases in surface water delivered to the bed through enhanced basal lubrication4,10,11 and warming of the ice5, and so the inland advance of SGLs should be considered in projections of ice-sheet change