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  1. Abstract

    Biophysical cohesion, introduced predominantly by Extracellular Polymeric Substances (EPS) during mineral flocculation in subaqueous environments, plays important role in morphodynamics, biogeochemical cycles and ecosystem processes. However, the mechanism of how EPS functioning with cohesive particles and affects settling behaviors remain poorly understood. We measure initial flocculation rate, floc size and settling velocity of mineral and artificial EPS (Xanthan gum) mixtures. Combining results from these and previous studies demonstrate coherent intensification of EPS-related flocculation compare with those of pure mineral and oil-mineral mixtures. Importantly, the presence of EPS fundamentally changes floc structure and reduces variability of settling velocity. Measured data shows that ratios of microfloc and macrofloc settling velocity for pure mineral flocs is 3.9 but greatly reduced to a lowest value of 1.6 due to biological EPS addition. The low variability of settling velocity due to EPS participation explains the seemingly inconsistent results previously observed between field and laboratory studies.

  2. Koper, Keith (Ed.)
    On 10 February 2021, an MW 7.7 thrust earthquake ruptured the megathrust along the southeast Loyalty Islands within the strong bend in the plate boundary between the Australian plate and the North Fiji Basin. The mainshock involved rupture with ~50 s duration, with pure thrust slip concentrated in an east-west trending slip patch with up to 4.2 m of slip extending from 10 to 25 km depth. Slip at depths <10 km depth is negligible on the curved fault surface, which conforms to the SLAB2 interface model. Static stress drop estimates are ~5.5 MPa, and the radiated energy is 2.38 x 1015 J, with moment-scaled value of 5.7 x 10-6. The relatively shallow rupture from 10-25 km was moderately efficient in generating tsunami, with waves amplitudes up to 20 cm recorded in New Caledonia, New Zealand, Kermadec, and Fiji. Numerous M5+ normal-faulting aftershocks occur south of the trench, indicating effective stress change transfer from the megathrust to the bending flange of Australian plate that is negotiating the bend in the trench. Highly productive sequences involving paired thrust and normal faulting have occurred repeatedly westward along the northwest-trending portion of the Loyalty Islands region, also indicating unusually efficient stress communication.
  3. The explicit breaking of the axial symmetry by quantum fluctuations gives rise to the so-called axial anomaly. This phenomenon is solely responsible for the decay of the neutral pion π0into two photons (γγ), leading to its unusually short lifetime. We precisely measured the decay width Γ of theπ0 γγprocess. The differential cross sections for π0photoproduction at forward angles were measured on two targets, carbon-12 and silicon-28, yieldingΓ(π0 γγ)=7.798±0.056(stat.)±0.109(syst.) eV, where stat. denotes the statistical uncertainty and syst. the systematic uncertainty. We combined the results of this and an earlier experiment to generate a weighted average ofΓ(π0 γγ)=7.802±0.052(stat.)±0.105(syst.) eV. Our final result has a total uncertainty of 1.50% and confirms the prediction based on the chiral anomaly in quantum chromodynamics.