161 research outputs found
Effects of ion-exchange treatment on bromate formation and oxidation efficiency during ozonation
Ion-exchange treatment is a promising technique for removing hydrophilic compounds during drinking water treatment. In this study, we applied several different ion exchangers (i.e., anion exchange resins and a hydrotalcite compound) to bromide removal to minimize bromate formation during ozonation. It was found that ion-exchange treatment affected ozone and hydroxyl radical concentration profiles as well as bromate ion concentration after ozonation. Selecting an appropriate ion exchanger is important to achieve both the oxidation of target contaminants and the reduction of bromate ion during ozonation
Revisiting geochemical controls on patterns of carbonate deposition through the lens of multiple pathways to mineralization
The carbonate sedimentary record contains diverse compositions and textures that reflect the evolution of oceans and atmospheres through geological time. Efforts to reconstruct paleoenvironmental conditions from these deposits continue to be hindered by the need for process-based models that can explain observed shifts in carbonate chemistry and form. Traditional interpretations assume minerals precipitate and grow by classical ion-by-ion addition processes but are unable to reconcile a number of unusual features contained in Proterozoic carbonates. The realization that diverse organisms produce high Mg carbonate skeletal structures by non-classical pathways involving amorphous intermediates raises the question of whether similar processes are also active in sedimentary environments. This study examines the hypothesis that non-classical pathways to mineralization are the physical basis for some of the carbonate morphologies and compositions observed in natural and laboratory settings. We designed experiments with a series of different solution Mg : Ca ratios and saturation environments to investigate the effects on carbonate phase, Mg content, and morphology. Our observations of diverse carbonate mineral compositions and textures suggest geochemical conditions bias the mineralization pathway by a systematic relationship to Mg : Ca ratio and the abundance of carbonate ions. Environments with low Mg levels produce calcite crystallites with 0–12 mol% MgCO_3. In contrast, the combination of high initial Mg : Ca and rapidly increasing saturation opens a non-classical pathway that begins with extensive precipitation of an amorphous calcium carbonate (ACC). This phase slowly transforms to aggregates of very high Mg calcite nanoparticles whose structures and compositions are similar to natural disordered dolomites. The non-classical pathways are favored when the local environment contains sufficient Mg to inhibit calcite growth through increased solubility—a thermodynamic factor, and achieves saturation with respect to ACC on a timescale that is shorter than the rate of aragonite nucleation—a kinetic factor. Aragonite is produced when Mg levels are high but saturation is insufficient for ACC precipitation. The findings provide a physical basis for anecdotal claims that the interplay of kinetic and thermodynamic factors underlies patterns of carbonate precipitation and suggest the need to expand traditional interpretations of geological carbonate formation to include non-classical pathways to mineralization
Measurement of tibial nerve excursion during ankle joint dorsiflexion in a weight-bearing position with ultrasound imaging
The ability of peripheral nerves to stretch and slide is thought to be of paramount importance to maintain ideal neural function. Excursion in peripheral nerves such as the tibial can be measured by analysis of ultrasound images. The aim of this study was to assess the degree of longitudinal tibial nerve excursion as the ankle moved from plantar flexion to dorsiflexion in a standardised weight-bearing position. The reliability of ultrasound imaging to measure tibial nerve excursion was also quantified
Measurement of a small atmospheric ratio
From an exposure of 25.5~kiloton-years of the Super-Kamiokande detector, 900
muon-like and 983 electron-like single-ring atmospheric neutrino interactions
were detected with momentum MeV/, MeV/, and
with visible energy less than 1.33 GeV. Using a detailed Monte Carlo
simulation, the ratio was measured to be , consistent with previous results from the
Kamiokande, IMB and Soudan-2 experiments, and smaller than expected from
theoretical models of atmospheric neutrino production.Comment: 14 pages with 5 figure
Constraints on neutrino oscillation parameters from the measurement of day-night solar neutrino fluxes at Super-Kamiokande
A search for day-night variations in the solar neutrino flux resulting from
neutrino oscillations has been carried out using the 504 day sample of solar
neutrino data obtained at Super-Kamiokande. The absence of a significant
day-night variation has set an absolute flux independent exclusion region in
the two neutrino oscillation parameter space.Comment: 11 pages, 3 figures, submitted to PRL, single-spacin
Observation of the east-west anisotropy of the atmospheric neutrino flux
The east-west anisotropy, caused by the deflection of primary cosmic rays in
the Earth's magnetic field, is observed for the first time in the flux of
atmospheric neutrinos. Using a 45 kt-year exposure of the
Super-Kamiokande detector, 552 e-like and 633 mu-like horizontally-going
events are selected in the momentum range between 400 and 3000 MeV/c.
The azimuthal distribution of e-like and mu-like events agrees with the
expectation from atmospheric neutrino flux calculations that account for the
geomagnetic field, verifying that the geomagnetic field effects in the
production of atmospheric neutrinos in the GeV energy range are well
understood.Comment: 8 pages,3 figures revtex, submitted to PR
Calibration of Super-Kamiokande Using an Electron Linac
In order to calibrate the Super-Kamiokande experiment for solar neutrino
measurements, a linear accelerator (LINAC) for electrons was installed at the
detector. LINAC data were taken at various positions in the detector volume,
tracking the detector response in the variables relevant to solar neutrino
analysis. In particular, the absolute energy scale is now known with less than
1 percent uncertainty.Comment: 24 pages, 16 figures, Submitted to NIM
Measurement of radon concentrations at Super-Kamiokande
Radioactivity from radon is a major background for observing solar neutrinos
at Super-Kamiokande. In this paper, we describe the measurement of radon
concentrations at Super-Kamiokande, the method of radon reduction, and the
radon monitoring system. The measurement shows that the current low-energy
event rate between 5.0 MeV and 6.5 MeV implies a radon concentration in the
Super-Kamiokande water of less than 1.4 mBq/m.Comment: 11 pages, 4 figure
Evidence for oscillation of atmospheric neutrinos
We present an analysis of atmospheric neutrino data from a 33.0 kiloton-year
(535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith
angle dependent deficit of muon neutrinos which is inconsistent with
expectations based on calculations of the atmospheric neutrino flux.
Experimental biases and uncertainties in the prediction of neutrino fluxes and
cross sections are unable to explain our observation. The data are consistent,
however, with two-flavor nu_mu nu_tau oscillations with sin^2(2theta)>0.82
and 5x10^-4 < delta m^2 < 6x10^-3 eV^2 at 90% confidence level.Comment: 9 pages (two-column) with 4 figures. Small corrections to Eqn.4 and
Fig.3. Final version to appear in PR
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