We briefly summarize motivations for testing the weak equivalence principle and then review recent torsion-balance results that compare the differential accelerations of beryllium-aluminum and ...beryllium-titanium test-body pairs with precisions at the part in 1013 level. We discuss some implications of these results for the gravitational properties of antimatter and dark matter and speculate about the prospects for further improvements in experimental sensitivity.
Recent acceleration of Greenland's ocean‐terminating glaciers has substantially amplified the ice sheet's contribution to global sea level. Increased oceanic melting of these tidewater glaciers is ...widely cited as the likely trigger, and is thought to be highest within vigorous plumes driven by freshwater drainage from beneath glaciers. Yet melting of the larger part of calving fronts outside of plumes remains largely unstudied. Here we combine ocean observations collected within 100 m of a tidewater glacier with a numerical model to show that unlike previously assumed, plumes drive an energetic fjord‐wide circulation which enhances melting along the entire calving front. Compared to estimates of melting within plumes alone, this fjord‐wide circulation effectively doubles the glacier‐wide melt rate, and through shaping the calving front has a potential dynamic impact on calving. Our results suggest that melting driven by fjord‐scale circulation should be considered in process‐based projections of Greenland's sea level contribution.
Plain Language Summary
As the world warms, loss of ice from the Greenland Ice Sheet will be a significant source of sea level rise. Greenland loses ice partly through the flow of huge rivers of ice called tidewater glaciers that dump solid ice directly into the ocean. Over the past two decades, tidewater glaciers around Greenland have accelerated dramatically, increasing Greenland's contribution to global mean sea level. There is mounting evidence that these accelerations have been driven by ocean warming, and a resulting increase in the rate at which the ocean melts the front of tidewater glaciers (called submarine melting). Yet submarine melting is at present poorly understood, in part due to the danger and difficulty of collecting data close to tidewater glaciers. We present observations of the ocean in front of a tidewater glacier that are unprecedented in their proximity to the glacier. These data reveal an ocean circulation which flushes warm water along the front of the glacier, driving high rates of submarine melting. We then use a numerical model to identify what drives this circulation. Our results are an important step toward understanding a key process which will modulate future sea level contribution from the Greenland ice sheet.
Key Points
Ocean observations that are unprecedented in their spatial detail and proximity to a Greenlandic tidewater glacier are reported
Despite being highly localized, plumes drive fjord‐wide circulation and hence glacier‐wide submarine melting at tidewater glaciers
Fjord‐scale submarine melting drives significant mass loss and may promote calving, hence is a key process determining glacier stability
Electrochemistry and the Future of the Automobile Wagner, Frederick T; Lakshmanan, Balasubramanian; Mathias, Mark F
The journal of physical chemistry letters,
07/2010, Letnik:
1, Številka:
14
Journal Article
Recenzirano
Electrification of the automobile provides a means of sustaining personal mobility in the face of petroleum resource limitations and environmental imperatives. Lithium ion (Li ion) batteries and ...hydrogen fuel cells provide pure-electrification solutions for different mass and usage segments of automotive application. Battery electric vehicles based on current and targeted Li ion battery technology will be limited to small-vehicle low-mileage-per-day applications; this is due to relatively low specific energy (kWh/kg) and long recharge time constraints. We briefly discuss new generations of Li ion positive and negative electrode intercalation compounds that are needed and under development to achieve energy storage density, durability, and cost targets. Lithium−air batteries give promise of extending the range, but scientists and engineers must surmount a plethora of challenges if growing research investments in this area are to prove effective. Hydrogen fuel cell vehicles have demonstrated the required ∼300 mile range and the ability to operate in all climates, but the cost of Pt-based catalysts, a low efficiency of utilization of presently cost-effective renewable sources of primary energy (e.g., electricity from wind), and the development of hydrogen infrastructure present significant challenges. Dramatic decreases in the amount of Pt used are required and are being brought to fruition along several lines of development that are described in some detail.
Polar amplification is a widely discussed phenomenon, and a range of mechanisms have been proposed to contribute to it, many of which involve atmospheric and surface processes. However, substantial ...questions remain regarding the role of ocean heat transport. Previous studies have found that ocean heat transport into the Arctic increases under global warming, but the reasons behind this remain unresolved. Here, we investigate changes in oceanic heat fluxes and associated impacts on polar amplification using an idealized ocean‐sea ice‐climate model of the Northern Hemisphere. We show that beneath the sea ice, vertical temperature gradients across the halocline increase as the ocean warms, since the surface mixed layer temperatures in ice‐covered regions are fixed near the freezing point. These enhanced vertical temperature gradients drive enhanced horizontal heat transport into the polar region and can contribute substantially to polar amplification.
Plain Language Summary
The Arctic region is warming at a faster rate than the rest of the globe. A number of mechanisms that may contribute to this have been identified, the most well‐known being the surface albedo feedback that occurs due to the higher reflectivity of ice compared to open water. However, substantial gaps remain in our understanding of what drives the polar amplification of global warming, and projections of how much the polar regions will warm in the future vary widely. Here, we look at the contribution to Arctic warming from the vertical transfer of heat in the upper ocean. In the Arctic Ocean, a large amount of heat is stored in relatively warm waters at depth, with a cold layer of water and sea ice cover above. The results indicate that the amount of heat from this warm water that reaches the sea ice cover will increase under global warming, enhancing the rate of warming in the Arctic region.
Key Points
We identify an oceanic mechanism that increases the vertical heat flux in the upper Arctic Ocean under global warming
The enhanced heating occurs in regions with sea ice, and it causes increased ocean heat transport into the Arctic
This mechanism is a substantial contributor to polar amplification in our model simulations
Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, ...relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10⁶ ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Cobalt oxide spinel (Co3O4) with an ordered nanostructure is used as a resistive gas sensor for carbon monoxide (CO) in low ppm concentrations. The operating temperature has a strong impact on the ...concentration-dependent sensing behavior. At lower temperature (473K) the sensor response is governed mainly by surface coverage with CO and/or CO2, whereas at higher temperature (563K) oxygen diffusion in the crystal lattice of Co3O4 strongly affects the sensing behavior.
To investigate the opinions of clinician referrers on the presence and type of management advice in reports of positron-emission tomography (PET)-computed tomography (CT) examinations.
Eighteen ...clinicians were interviewed using a structured questionnaire about their opinions on further management advice in PET-CT reports.
Opinions varied amongst clinicians, but some themes predominated: (1) advice on further imaging tests and areas outside the referrer's area of expertise are more welcome than other types of advice; (2) a differential diagnosis or clinical significance is of greater value than specific management advice; (3) some referrers do not want any further advice.
Before advising on further management, reporters should consider clinicians' opinions regarding this. Seeking the opinion of clinicians in other hospitals may be necessary. A review of the Royal College of Radiologists Actionable Reports standard to ensure it is more in line with the opinions of clinicians may be useful.
The longitudinal, multisource, multimethod study presented herein examines the role of employees' work-family integration in the spillover of daily job satisfaction onto daily marital satisfaction ...and affective states experienced by employees at home. The spillover linkages are modeled at the within-individual level, and results support the main effects of daily job satisfaction on daily marital satisfaction and affect at home, as well as the moderating effect of work-family integration on the strength of the within-individual spillover effects on home affect. That is, employees with highly integrated work and family roles exhibited stronger intraindividual spillover effects on positive and negative affect at home.
We demonstrate the unprecedented proton exchange membrane fuel cell (PEMFC) performance durability of a family of dealloyed Pt-Ni nanoparticle catalysts for the oxygen reduction reaction (ORR), ...exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight into key factors controlling the stability of the cathode catalyst by studying the influence of particle size, the dealloying protocol and post-acid-treatment annealing on nanoporosity and passivation of the alloy nanoparticles. Scanning transmission electron microscopy coupled to energy dispersive spectroscopy data revealed the compositional variations of Ni in the particle surface and core, which were combined with an analysis of the particle morphology evolution during PEMFC voltage cycling; together, this enabled the elucidation of alloy structure and compositions conducive to long-term PEMFC device stability. We found that smaller size, less-oxidative acid treatment and annealing significantly reduced Ni leaching and nanoporosity formation while encouraged surface passivation, all resulting in improved stability and higher catalytic ORR activity. This study demonstrates a successful example of how a translation of basic catalysis research into a real-life device technology may be done.
This communication describes the preparation of carbon-supported truncated-octahedral Pt3Ni nanoparticle catalysts for the oxygen reduction reaction. Besides the composition, size, and shape ...controls, this work develops a new butylamine-based surface treatment approach for removing the long-alkane-chain capping agents used in the solution-phase synthesis. These Pt3Ni catalysts can have an area-specific activity as high as 850 μA/cm2 Pt at 0.9 V, which is ∼4 times better than the commercial Pt/C catalyst (∼0.2 mA/cm2 Pt at 0.9 V). The mass activity reached 0.53 A/mgPt at 0.9 V, which is close to a factor of 4 increase in mass activity, the threshold value that allows fuel-cell power trains to become cost-competitive with their internal-combustion counterparts. Our results also show that the mass activities of these carbon-supported Pt3Ni nanoparticle catalysts strongly depend on the (111) surface fraction, which validates the results of studies based on Pt3Ni extended-single-crystal surfaces, suggesting that further development of catalysts with still higher mass activities is highly plausible.
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