Oxygen and hydrogen isotopes were used in this study to detect a hydraulic connection between a sinkhole lake and a karst spring. In karst areas, surface water that flows to a lake can drain through sinkholes in the lakebed to the underlying aquifer, and then flows in karst conduits and through aquifer matrix. At the study site located in northwest Florida, USA, Lake Miccosukee immediately drains into two sinkholes. Results from a dye tracing experiment indicate that lake water discharges at Natural Bridge Spring, a first‐magnitude spring 32 km downgradient from the lake. By collecting weekly water samples from the lake, the spring, and a groundwater well 10 m away from the lake during the dry period between October 2019 and January 2020, it was found that, when rainfall effects on isotopic signature in spring water are removed, increased isotope ratios of spring water can be explained by mixing of heavy‐isotope‐enriched lake water into groundwater, indicating hydraulic connection between the lake and the spring. Such a detection of hydraulic connection at the scale of tens of kilometers and for a first‐magnitude spring has not been previously reported in the literature. Based on the isotope ratio data, it was estimated that, during the study period, about 8.5% the spring discharge was the lake water that drained into the lake sinkholes.
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Purpose 129Xe MRI and MRS signals from airspaces, membrane tissues (M), and red blood cells (RBCs) provide measurements of pulmonary gas exchange. However,129Xe MRI/MRS studies have yet to account for hemoglobin concentration (Hb), which is expected to affect the uptake of129Xe in the membrane and RBC compartments. We propose a framework to adjust the membrane and RBC signals for Hb and use this to assess sex‐specific differences in RBC/M and establish a Hb‐adjusted healthy reference range for the RBC/M ratio.
Methods We combined the 1D model of xenon gas exchange (MOXE) with the principle of TR‐flip angle equivalence to establish scaling factors that normalize the dissolved‐phase signals with respect to a standard (14 g/dL).129Xe MRI/MRS data from a healthy, young cohort (
n = 18, age = 25.0 3.4 years) were used to validate this model and assess the impact of Hb adjustment on M/gas and RBC/gas images and RBC/M.Results Adjusting for Hb caused RBC/M to change by up to 20% in healthy individuals with normal Hb and had marked impacts on M/gas and RBC/gas distributions in 3D gas‐exchange maps. RBC/M was higher in males than females both before and after Hb adjustment (
p < 0.001). After Hb adjustment, the healthy reference value for RBC/M for a consortium‐recommended acquisition of TR = 15 ms and flip = 20° was 0.589 0.083 (mean SD).Conclusion MOXE provides a useful framework for evaluating the Hb dependence of the membrane and RBC signals. This work indicates that adjusting for Hb is essential for accurately assessing129Xe gas‐exchange MRI/MRS metrics.
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Abstract Patterns of
δ 18O andδ 2H in Earth's precipitation provide essential scientific data for use in hydrological, climatological, ecological and forensic research. Insufficient global spatial data coverage promulgated the use of gridded datasets employing geostatistical techniques (isoscapes) for spatiotemporally coherent isotope predictions. Cluster‐based isoscape regionalization combines the advantages of local or regional prediction calibrations into a global framework. Here we present a revision of a Regionalized Cluster‐Based Water Isotope Prediction model (RCWIP2) incorporating new isotope data having extensive spatial coverage and a wider array of predictor variables combined with high‐resolution gridded climatic data. We introduced coupling ofδ 18O andδ 2H (e.g.,d ‐excess constrained) in the model predictions to prevent runaway isoscapes when each isotope is modelled separately and cross‐checked observed versus modelledd ‐excess values. We improved model error quantification by adopting full uncertainty propagation in all calculations. RCWIP2 improved the RMSE over previous isoscape models by ca. 0.3 ‰ forδ 18O and 2.5 ‰ forδ 2H with an uncertainty <1.0 ‰ forδ 18O and < 8 ‰ forδ 2H for most regions of the world. The determination of the relative importance of each predictor variable in each ecoclimatic zone is a new approach to identify previously unrecognized climatic drivers on mean annual precipitationδ 18O andδ 2H. The improved RCWIP2 isoscape grids and maps (season, monthly, annual, regional) are available for download athttps://isotopehydrologynetwork.iaea.org . -
Abstract The transport of Ca2+across membranes precedes the fusion and fission of various lipid bilayers. Yeast vacuoles under hyperosmotic stress become fragmented through fission events that requires the release of Ca2+stores through the TRP channel Yvc1. This requires the phosphorylation of phosphatidylinositol‐3‐phosphate (PI3P) by the PI3P‐5‐kinase Fab1 to produce transient PI(3,5)P2pools. Ca2+is also released during vacuole fusion upon
trans‐ SNARE complex assembly, however, its role remains unclear. The effect of PI(3,5)P2on Ca2+flux during fusion was independent of Yvc1. Here, we show that while low levels of PI(3,5)P2were required for Ca2+uptake into the vacuole, increased concentrations abolished Ca2+efflux. This was as shown by the addition of exogenous dioctanoyl PI(3,5)P2or increased endogenous production of by the hyperactivefab1 T2250A mutant. In contrast, the lack of PI(3,5)P2on vacuoles from the kinase deadfab1 EEE mutant showed delayed and decreased Ca2+uptake. The effects of PI(3,5)P2were linked to the Ca2+pump Pmc1, as its deletion rendered vacuoles resistant to the effects of excess PI(3,5)P2. Experiments with Verapamil inhibited Ca2+uptake when added at the start of the assay, while adding it after Ca2+had been taken up resulted in the rapid expulsion of Ca2+. Vacuoles lacking both Pmc1 and the H+/Ca2+exchanger Vcx1 lacked the ability to take up Ca2+and instead expelled it upon the addition of ATP. Together these data suggest that a balance of efflux and uptake compete during the fusion pathway and that the levels of PI(3,5)P2can modulate which path predominates. -
Abstract Described are the first two molecular designs of the triply periodic Schwarz P surface using merely the Schläfli t{3,7} pattern of sp2‐hybridized carbon atoms. Each atom is exactly part of one heptagon and two hexagon rings so that two heptagons do not share the same edge or vertex. Such pattern, called hyperbolic soccer ball obeys the isolated‐heptagon rule with the minimum possible number of hexagons between heptagons similar to the isolation of pentagons from hexagons in the C60 fullerene. Both of the designed P surfaces are unbalanced, that is, they have two unequal sides, and belong to space groups
P432 of the cubic system, andP4/ncc of the tetragonal system, respectively. Unit cells have a multiple of 24 heptagons similar to the only one previously known in literature Schwarzite with the hyperbolic soccer ball pattern—the D surface of Vanderbilt and Tersoff. The geometry of the periodic structures and unit cell parameters were fully optimized by DFT calculations using CASTEP software with PBE and PBESOL functionals under generalized gradient approximation. The effect of P and D surface dilution by hexagons on the calculated density, elastic and electronic properties is discussed.