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Over six decades of research, two methods have been used to extract the natural radionuclides 210Pb and 210Po from seawater- the precipitation of iron hydroxide (Fe(OH)3) and coagulation of cobalt ammonium pyrrolidine dithiocarbamate (Co-APDC). Although the two methods had been intercompared for 210Pb and shown to agree, they were never intercompared for 210Po until Roca-Martí et al. (2021), in which only unfiltered samples were used. Here we document that Fe(OH)3 may be less effective in extracting 210Po from a seawater sample than Co-APDC. We hypothesize that cycling of 210Po through the marine food web can produce a fraction of dissolved 210Po complexed with organic ligands and not efficiently precipitated by Fe(OH)3. We compare the Fe(OH)3 and Co-APDC methods through field sampling at the DYFAMED site in the Mediterranean Sea and complementary laboratory incubation experiments using phytoplankton. Lower dissolved 210Po activities are extracted with Fe(OH)3 relative to Co-APDC immediately after sampling at times of high primary productivity. No difference between the methods was found for 210Pb. Time-series experiments with stored filtered, acidified samples show that Fe(OH)3 can yield higher activities of 210Po after extended storage (~2 months), approaching values obtained with Co-APDC immediately after sample collection. In laboratory incubation experiments with diatoms and coccolithophores, exudates produced by diatoms showed higher 210Po activities using the Co-APDC method; no difference between the methods was apparent for coccolithophores. Direct comparison of the methods during a time of high productivity at the DYFAMED site suggests that POC export fluxes based on the Fe(OH)3 method can be overestimated by ~50% in the primary productivity zone and by much larger extents in the mesopelagic. Additional field study results from the Northeast Atlantic and Pacific Oceans support these observations. We recommend the Co-APDC method be used for marine studies involving 210Po, especially in biologically active waters and if samples are processed soon after collection. 

Abstract Distributions of the natural radionuclide²¹⁰Po and its grandparent²¹⁰Pb along the GP15 Pacific Meridional Transect provide information on scavenging rates of reactive chemical species throughout the water column and fluxes of particulate organic carbon (POC) from the primary production zone (PPZ).²¹⁰Pb is in excess of its grandparent²²⁶Ra in the upper 400–700 m due to the atmospheric flux of²¹⁰Pb. Mid‐water²¹⁰Pb/²²⁶Ra activity ratios are close to radioactive equilibrium (1.0) north of ∼20°N, indicating slow scavenging, but deficiencies at stations near and south of the equator suggest more rapid scavenging associated with a “particle veil” located at the equator and hydrothermal processes at the East Pacific Rise. Scavenging of²¹⁰Pb and²¹⁰Po is evident in the bottom 500–1,000 m at most stations due to enhanced removal in the nepheloid layer. Deficits in the PPZ of²¹⁰Po (relative to²¹⁰Pb) and²¹⁰Pb (relative to²²⁶Ra decay and the²¹⁰Pb atmospheric flux), together with POC concentrations and particulate²¹⁰Po and²¹⁰Pb activities, are used to calculate export fluxes of POC from the PPZ.²¹⁰Po‐derived POC fluxes on large (>51 μm) particles range from 15.5 ± 1.3 mmol C/m²/d to 1.5 ± 0.2 mmol C/m²/d and are highest in the Subarctic North Pacific;²¹⁰Pb‐derived fluxes range from 6.7 ± 1.8 mmol C/m²/d to 0.2 ± 0.1 mmol C/m²/d. Both²¹⁰Po‐ and²¹⁰Pb‐derived POC fluxes are greater than those calculated using the²³⁴Th proxy, possibly due to different integration times of the radionuclides, considering their different radioactive mean‐lives and scavenging mean residence times. 

Abstract Understanding the mechanism of selective extinction is important in predicting the impact of anthropogenic environmental changes on current ecosystems. The selective extinction of externally shelled cephalopods at the Cretaceous-Paleogene (K-Pg) mass extinction event (ammonoids versus nautiloids) is often studied, but its mechanism is still debated. We investigate the differences in metabolic rate between these two groups to further explore the causes of selective extinction. We use a novel metabolic proxy—the fraction of metabolic carbon in the stable carbon isotope ratio of shell material (Cmeta)—to determine metabolic rate. Using this approach, we document significant differences in Cmeta among modern cephalopod taxa (Nautilus spp., Argonauta argo, Dosidicus gigas, Sepia officinalis, and Spirula spirula). Our results are consistent with estimates based on oxygen consumption, suggesting that this proxy is a reliable indicator of metabolic rate. We then use this approach to determine the metabolic rates of ammonoids and nautiloids that lived at the end of the Cretaceous (Maastrichtian). Our results show that the nautiloid Eutrephoceras, which survived the K-Pg mass extinction event, possessed a lower metabolic rate than co-occurring ammonoids (Baculites, Eubaculites, Discoscaphites, and Hoploscaphites). We conclude that the lower metabolic rate in nautiloids was an advantage during a time of environmental deterioration (surface-water acidification and resulting decrease in plankton) following the Chicxulub asteroid impact. 

Abstract Macroscopic phase coherence in superconductors enables quantum interference and phase manipulation at realistic device length scales. Numerous superconducting electronic devices are based on the modulation of the supercurrent in superconducting loops. While the overall behavior of symmetric superconducting loops has been studied, the effects of asymmetries in such devices remain under-explored and poorly understood. Here we report on an experimental and theoretical study of the flux modulation of the persistent current in a doubly connected asymmetric aluminum nanowire loop. A model considering the length and electronic cross-section asymmetries in the loop provides a quantitative account of the observations. Comparison with experiments give essential parameters such as persistent and critical currents as well as the amount of asymmetry which can provide feedback into the design of superconducting quantum devices. 

Loss of tidal wetlands is a world-wide phenomenon. Many factors may contribute to such loss, but among them are geochemical stressors such as exposure of the marsh plants to elevated levels on hydrogen sulfide in the pore water of the marsh peat. Here we report the results of a study of the geochemistry of iron and sulfide at different seasons in unrestored (JoCo) and partially restored (Big Egg) salt marshes in Jamaica Bay, a highly urbanized estuary in New York City where the loss of salt marsh area has accelerated in recent years. The spatial and temporal 2-dimensional distribution patterns of dissolved Fe 2+ and H 2 S in salt marshes were in situ mapped with high resolution planar sensors for the first time. The vertical profiles of Fe 2+ and hydrogen sulfide, as well as related solutes and redox potentials in marsh were also evaluated by sampling the pore water at discrete depths. Sediment cores were collected at various seasons and the solid phase Fe, S, N, C, and chromium reducible sulfide in marsh peat at discrete depths were further investigated in order to study Fe and S cycles, and their relationship to the organic matter cycling at different seasons. Our results revealed that the redox sensitive elements Fe 2+ and S 2– showed significantly heterogeneous and complex three dimensional distribution patterns in salt marsh, over mm to cm scales, directly associated with the plant roots due to the oxygen leakage from roots and redox diagenetic reactions. We hypothesize that the oxic layers with low/undetected H 2 S and Fe 2+ formed around roots help marsh plants to survive in the high levels of H 2 S by reducing sulfide absorption. The overall concentrations of Fe 2+ and H 2 S and distribution patterns also seasonally varied with temperature change. H 2 S level in JoCo sampling site could change from <0.02 mM in spring to >5 mM in fall season, reflecting significantly seasonal variation in the rates of bacterial oxidation of organic matter at this marsh site. Solid phase Fe and S showed that very high fractions of the diagenetically reactive iron at JoCo and Big Egg were associated with pyrite that can persist for long periods in anoxic sediments. This implies that there is insufficient diagenetically reactive iron to buffer the pore water hydrogen sulfide through formation of iron sulfides at JoCo and Big Egg. 

Using a data sample of $427.9{\mathrm{fb}}^{-1}$ collected by the Belle II detector at or near the $\mathrm{\Upsilon }\left(4S\right)$ and $\mathrm{\Upsilon }\left(10753\right)$ resonances, the cross sections for $e^{+}{e}^{-}\to h^{+}{h}^{-}J/\psi (h=\pi /K/p)$ at center-of-mass energies ranging from 3.8 GeV or the production threshold to $5.5/6.0/7.0\mathrm{GeV}$ have been measured via initial-state radiation. The cross sections for the processes $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ and $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ are consistent with previously published results. The cross sections for these channels obtained by combining with previous Belle results are also given. The process $e^{+}{e}^{-}\to p\overline{p}J/\psi$ is investigated for the first time. The yields are small and no significant structure is observed in the cross section versus energy. Searches for vector charmoniumlike states in the $h^{+}{h}^{-}J/\psi$ systems, and for associated intermediate states in the $h^{\pm }J/\psi$ systems, are also presented. 

We report a measurement of the branching fraction for the leptonic decay $B^{+}\to {\mu }^{+}{\nu }_{\mu }$ . This work presents the first $B^{+}\to {\mu }^{+}{\nu }_{\mu }$ result using Belle II data, an updated Belle measurement that supersedes the previous result, and their combination, which yields the most precise search to date. The analysis is based on $1076{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of 10.58 GeV with the Belle and Belle II detectors at the KEKB and SuperKEKB colliders, respectively. We measure $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })=(4.4\pm 1.9\pm 1.0)\times {10}^{-7}$ , where the first uncertainty is statistical and the second systematic. The observed significance relative to the background-only hypothesis is 2.4 standard deviations. We set a 90% confidence level upper limit of $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })<6.7\times {10}^{-7}$ using a frequentist approach and a 90% credibility level upper limit of $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })<7.2\times {10}^{-7}$ using a Bayesian approach. These are the most stringent limits to date. The result is interpreted as an exclusion region in the parameter space of type II and type III two-Higgs-doublet models. We search for stable sterile neutrinos with masses $m_N\in [0,1.5]\mathrm{GeV}$ . No signal is observed, and the resulting exclusion on the squared mixing parameter $|U_{\mu N}{|}^2$ provides improvement over previous limits. We report a measurement of the partial branching fraction of semileptonic $B\to X_u\ell {\nu }_{\ell }$ decays with $p_{\mu }^B>2.2\mathrm{GeV}$ , obtaining $\mathrm{\Delta }\mathcal{B}(B\to X_u\ell {\nu }_{\ell })=(2.72\pm 0.05\pm 0.29)\times {10}^{-4}$ . We present a model-dependent study of weak annihilation decays using the muon momentum spectrum. We observe a signal of 2.4 standard deviations above the background-only hypothesis in regions where the distribution resembles that of $B\to X_u\ell {\nu }_{\ell }$ decays.