1,672 research outputs found
A Proposal to Detect Dark Matter Using Axionic Topological Antiferromagnets
Antiferromagnetically doped topological insulators (A-TI) are among the
candidates to host dynamical axion fields and axion-polaritons; weakly
interacting quasiparticles that are analogous to the dark axion, a long sought
after candidate dark matter particle. Here we demonstrate that using the axion
quasiparticle antiferromagnetic resonance in A-TI's in conjunction with
low-noise methods of detecting THz photons presents a viable route to detect
axion dark matter with mass 0.7 to 3.5 meV, a range currently inaccessible to
other dark matter detection experiments and proposals. The benefits of this
method at high frequency are the tunability of the resonance with applied
magnetic field, and the use of A-TI samples with volumes much larger than 1
mm.Comment: 6 pages, 4 figures. v2 accepted for publication in Physical Review
Letters. Many points clarified, some parameter estimates revise
Low and variable ecosystem calcification in a coral reef lagoon under natural acidification
© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 63 (2018): 714â730, doi:10.1002/lno.10662.Laboratoryâbased CO2 experiments and studies of naturally low pH coral reef ecosystems reveal negative impacts of ocean acidification on the calcifying communities that build coral reefs. Conversely, in Palau's low pH lagoons, coral cover is high, coral communities are diverse, and calcification rates of two reefâbuilding corals exhibit no apparent sensitivity to the strong natural gradient in pH and aragonite saturation state (Ωar). We developed two methods to quantify rates of Net Ecosystem Calcification (NEC), the ecosystemâlevel balance between calcification and dissolution, in Risong Lagoon, where average daily pH is ⌠7.9 and Ωar ⌠2.7. While coral cover in the lagoon is within the range of other Pacific reefs (⌠26%), NEC rates were among the lowest measured, averaging 25.9â±â13.7 mmol mâ2 dâ1 over two 4 d study periods. NEC rates were highly variable, ranging from a low of 13.7 mmol mâ2 dâ1 in March 2012 to a high of 40.3 mmol mâ2 dâ1 in November 2013, despite no significant changes in temperature, salinity, inorganic nutrients, Ωar, or pH. Our results indicate that the coral reef community of Risong Lagoon produces just enough calcium carbonate to maintain net positive calcification but comes dangerously close to net zero or negative NEC (net dissolution). Identifying the factors responsible for low NEC rates as well as the drivers of NEC variability in naturally low pH reef systems are key to predicting their futures under 21st century climate change.This work was supported by NSF award
1220529 to A.L.C., S.J.L., and K.E.F.S. and a Woods Hole Oceanographic
Institution Postdoctoral Scholarship to K.E.F.S
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