West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ...ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica's coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica's Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.
Exposure of austenitic stainless steels to liquid lead–bismuth eutectic with low concentration of dissolved oxygen typically results in selective leaching of highly-soluble alloying elements and ...ferritization of the dissolution-affected zone. In this work, focused ion beam, transmission electron backscatter diffraction and scanning transmission electron microscopy were utilized to elucidate early-stage aspects of the dissolution corrosion process of cold-worked austenitic stainless steels exposed to static, oxygen-poor liquid lead–bismuth eutectic at 450°C for 1000h. It was found that deformation-induced twin boundaries in the cold-worked steel bulk provide paths of accelerated penetration of the liquid metal into the steel bulk.
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Changes to the grounding line, where grounded ice starts to float, can be used as a remotely sensed measure of ice‐sheet susceptibility to ocean‐forced dynamic thinning. Constraining this ...susceptibility is vital for predicting Antarctica's contribution to rising sea levels. We use Landsat imagery to monitor grounding line movement over four decades along the Bellingshausen margin of West Antarctica, an area little monitored despite potential for future ice losses. We show that ~65% of the grounding line retreated from 1990 to 2015, with pervasive and accelerating retreat in regions of fast ice flow and/or thinning ice shelves. Venable Ice Shelf confounds expectations in that, despite extensive thinning, its grounding line has undergone negligible retreat. We present evidence that the ice shelf is currently pinned to a sub‐ice topographic high which, if breached, could facilitate ice retreat into a significant inland basin, analogous to nearby Pine Island Glacier.
Key Points
Grounding line change mapped along Bellingshausen margin of West Antarctica with Landsat and InSAR from 1975 to 2015
Results show majority of grounding line retreated along entire margin implicating ocean‐forced dynamic thinning
Grounding line at Venable Ice Shelf currently pinned but potential for retreat as at Pine Island Glacier
We discuss the challenge of selecting materials for nuclear applications and outline the need for comprehensive databases to assist scientists and engineers in choosing materials that meet ...interdependent physical, chemical, and nuclear criteria. In conventional engineering, chemical and physical properties and the electronic structure of materials are typically the primary considerations; nuclear applications must also consider the nuclear physics characteristics of a material. Development of databases that correlate physical, chemical, and nuclear properties would accelerate and facilitate innovations in nuclear design.
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Significance A complete description of nanoscale thermal transport is a fundamental problem that has defied understanding for many decades. Here, we uncover a surprising new regime of nanoscale ...thermal transport where, counterintuitively, nanoscale heat sources cool more quickly when placed close together than when they are widely separated. This increased cooling efficiency is possible when the separation between nanoscale heat sources is comparable to the average mean free paths of the dominant heat-carrying phonons. This finding suggests new approaches for addressing the significant challenge of thermal management in nanosystems, with design implications for integrated circuits, thermoelectric devices, nanoparticle-mediated thermal therapies, and nanoenhanced photovoltaics for improving clean-energy technologies.
Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier’s law for heat conduction dramatically overpredicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. Finally, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.
Small scale mechanical testing has many beneficial features including the ability to sample the properties of a single crystal over a wide temperature range. This manuscript presents the results of ...high temperature, in-situ scanning electron microscope microcompression testing of a single crystal of UO2. Observations indicated that the UO2 microcompression specimens deformed in a ductile fashion at temperatures of 350 °C and above. The slip traces on the micro-compression specimens after deformation appeared on the {100}1/2 system at the temperatures and orientation tested. Lastly, the Peierls stress of UO2 is calculated using the microcompression data.
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Recent satellite-remote sensing studies have documented the multi-decadal
acceleration of the Antarctic Ice Sheet in response to rapid rates of
ice-sheet retreat and thinning. Unlike the Greenland ...Ice Sheet, where
historical, high-temporal-resolution satellite and in situ observations have
revealed distinct changes in land-ice flow within intra-annual timescales,
observations of similar seasonal signals are limited in Antarctica. Here, we
use high-spatial- and high-temporal-resolution Copernicus Sentinel-1A/B synthetic
aperture radar observations acquired between 2014 and 2020 to provide the
first evidence for seasonal flow variability of the land ice feeding George
VI Ice Shelf (GVIIS), Antarctic Peninsula. Our observations reveal a
distinct austral summertime (December–February) speed-up of
∼0.06±0.005 m d−1 (∼ 22±1.8 m yr−1) at, and immediately inland of, the grounding line of the
glaciers nourishing the ice shelf, which constitutes a mean acceleration of
∼15 % relative to baseline (time-series-averaged) rates of
flow. These findings are corroborated by independent, optically derived
velocity observations obtained from Landsat 8 imagery. Both surface and
oceanic forcing mechanisms are outlined as potential controls on this
seasonality. Ultimately, our findings imply that similar surface and/or
ocean forcing mechanisms may be driving seasonal accelerations at the
grounding lines of other vulnerable outlet glaciers around Antarctica.
Assessing the degree of seasonal ice-flow variability at such locations is
important for quantifying accurately Antarctica's future contribution to
global sea-level rise.
This work features the synthesis of nanoscale cavities using a He ion beam implantation method. A multitechnique (AFM, TEM, nanoindentation) post synthesis approach allows for the characterization of ...a 200 nm thin implantation region containing nanocavities. It was found that at lower doses, the cavities arrange themselves in a superlattice and are close to equilibrium pressure while at higher doses the self-organization of the nanoscale cavities is lost, forming cavities that change in nature resulting in a degradation of the mechanical properties. Close correlation between theory and experimental observation is achieved considering for the observed phenomena.
Abstract
The collapse of several ice shelves in the Antarctic Peninsula since the late 20th century has resulted in the upstream acceleration of multiple formerly buttressed outlet glaciers, raising ...questions about the stability of Antarctica's remaining ice shelves and the effects their demise may have upon inland ice. Here, we use high temporal resolution Sentinel-1A/B synthetic aperture radar-derived observations to assess the velocity response of Larsen C Ice Shelf (LCIS) to the calving of colossal iceberg A-68 in 2017. We find marked oscillations in ice-shelf flow across LCIS in the months following A-68's calving, beginning with a near-ice-shelf-wide slowdown of 11.3 m yr
−1
on average. While falling close to the limits of detectability, these ice-flow variations appear to have been presaged by similar oscillations in the years prior to A-68's breakaway, associated primarily with major rifting events, together reflecting potentially hitherto unobserved ice-shelf mechanical processes with important implications for ice-shelf weakening. Such ice-flow oscillations were, however, short-lived, with more recent observations suggesting a deceleration below longer-term rates of ice flow. Collectively, our observations reveal complex spatial-temporal patterns of ice-flow variability at LCIS. Similarly abrupt fluctuations may have important implications for the stability of other ice shelves, necessitating the continued, close observation of Antarctica's coastline in the future.
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