Chemical NOx budget in the upper troposphere over the tropical South Pacific

The chemical NOx budget in the upper troposphere over the tropical South Pacific is analyzed using aircraft measurements made at 6-12 km altitude in September 1996 during the Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM) Tropics A campaign. Chemical loss and production rates of NOx along the aircraft flight tracks are calculated with a photochemical model constrained by observations. Calculations using a standard chemical mechanism show a large missing source for NOx; chemical loss exceeds chemical production by a factor of 2.4 on average. Similar or greater NOx budget imbalances have been reported in analyses of data from previous field studies. Ammonium aerosol concentrations in PEM-Tropics A generally exceeded sulfate on a charge equivalent basis, and relative humidities were low (median 25% relative to ice). This implies that the aerosol could be dry in which case N2O5 hydrolysis would be suppressed as a sink for NOx. Suppression of N2O5 hydrolysis and adoption of new measurements of the reaction rate constants for NO2 + OH + M and HNO3 + OH reduces the median chemical imbalance in the NOx budget for PEM-Tropics A from 2.4 to 1.9. The remaining imbalance cannot be easily explained from known chemistry or long-range transport of primary NOx and may imply a major gap in our understanding of the chemical cycling of NOx in the free troposphere. Copyright 2000 by the American Geophysical Union

Tracking mortality in near to real time provides essential information about the impact of the COVID-19 pandemic in South Africa in 2020

Background. Producing timely and accurate estimates of the impact of COVID-19 on mortality is challenging for most countries, but impossible for South Africa (SA) from cause-of-death statistics. Objectives. To quantify the excess deaths and likely magnitude of COVID-19 in SA in 2020 and draw conclusions on monitoring the epidemic in 2021. Methods. Basic details of deaths registered on the National Population Register by the Department of Home Affairs (DoHA) are provided to the South African Medical Research Council weekly. Adjustments are made to the numbers of weekly deaths to account for non-registration on the population register, as well as late registration of death with the DoHA. The weekly number of deaths is compared with the number predicted based on the Holt-Winters time-series analysis of past deaths for provinces and metropolitan areas. Excess deaths were calculated for all-causes deaths and natural deaths, using the predicted deaths as a baseline. In addition, an adjustment was made to the baseline for natural deaths to account for the drop in natural deaths due to lockdown. Results. We estimated that just over 550 000 deaths occurred among persons aged ≥1 year during 2020, 13% higher than the 485 000 predicted before the pandemic. A pronounced increase in weekly deaths from natural causes peaked in the middle of July across all ages except <20 years, and across all provinces with slightly different timing. During December, it became clear that SA was experiencing a second wave of COVID-19 that would exceed the death toll of the first wave. In 2020, there were 70 000 - 76 000 excess deaths from natural causes, depending on the base. Using the adjusted base, the excess death rate from natural causes was 122 per 100 000 population, with a male-to-female ratio of 0.78. Deaths from unnatural causes halved for both males and females during the stringent lockdown level 5. The numbers reverted towards the predicted number with some fluctuations as lockdown restrictions varied. Just under 5 000 unnatural deaths were averted. Conclusions. Tracking the weekly numbers of deaths in near to real time has provided important information about the spatiotemporal impact of the pandemic and highlights that the ~28 000 reported COVID-19 deaths during 2020 substantially understate the death toll from COVID-19. There is an urgent need to re-engineer the system of collecting and processing cause-of-death information so that it can be accessed in a timely way to inform public health actions

Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism

Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny

Influence of biomass combustion emissions on the distribution of acidic trace gases over the southern Pacific basin during austral springtime

This paper describes the large-scale distributions of HNO3, HCOOH, and CH3COOH over the central and South Pacific basins during the Pacific Exploratory Mission-Tropics (PEM-Tropics) in austral springtime. Because of the remoteness of this region from continental areas, low part per trillion by volume (pptv) mixing ratios of acidic gases were anticipated to be pervasive over the South Pacific basin. However, at altitudes of 2–12 km over the South Pacific, air parcels were encountered frequently with significantly enhanced mixing ratios (up to 1200 pptv) of acidic gases. Most of these air parcels were centered in the 3–7 km altitude range and occurred within the 15°−65°S latitudinal band. The acidic gases exhibited an overall general correlation with CH3Cl, PAN, and O3, suggestive of photochemical and biomass burning sources. There was no correlation or trend of acidic gases with common industrial tracer compounds (e.g., C2Cl4 or CH3CCl3). The combustion emissions sampled over the South Pacific basin were relatively aged exhibiting C2H2/CO ratios in the range of 0.2–2.2 pptv/ppbv. The relationships between acidic gases and this ratio were similar to what was observed in aged air parcels (i.e., \u3e3–5 days since they were over a continental area) over the western North Pacific during the Pacific Exploratory Mission-West Phases A and B (PEM-West A and B). In the South Pacific marine boundary layer a median C2H2/CO ratio of 0.6 suggested that this region was generally not influenced by direct inputs of biomass combustion emissions. Here we observed the lowest mixing ratios of acidic gases, with median values of 14 pptv for HNO3, 19 pptv for HCOOH, and 18 pptv for CH3COOH. These values were coincident with low mixing ratios of NOx(\u3c10 pptv), CO (≈50 parts per billion by volume (ppbv)), O3 (\u3c 20 ppbv), and long-lived hydrocarbons (e.g., C2H6 \u3c300 pptv). Overall, the PEM-Tropics data suggest an important influence of aged biomass combustion emissions on the distributions of acidic gases over the South Pacific basin in austral springtime

Evolution of a mafic volcanic field in the central Great Basin, south central Nevada

This is the published version. Copyright 2012 American Geophysical Union. All Rights Reserved.Evolution of a mafic volcanic field is investigated through a study of Pliocene age rocks in the Reveille Range in south central Nevada. Pliocene activity began with the eruption of relatively abundant hawaiite (episode 1, 5–6 Ma), which was followed by trachytic volcanism (4.3 Ma) and by a second episode of lower-volume hawaiite and basanite (episode 2, 3.0–4.7 Ma). Incompatible elements indicate an asthenospheric source. Isotopically, episode 2 basalts cluster around 87Sr/86Sr = 0.7035 and εNd = +4.2, but episode 1 samples vary to high 87Si/86Sr (up to 0.7060) over a narrow range of εNd (+0.8 to +4.5). Trachytic rocks (MgO ∼ 0.5%) are isotopically akin to the episode 1 basalts. Geochemical variation requires the addition of a crustal component (high 87Sr/86Sr, Sr/Nd, Pb/La, low εNd) to the episode 1 hawaiites and trachytic samples, probably by assimilation of carbonate-rich sedimentary wall rock. The volcanic field developed in at least two eruptive cycles of approximately equal duration. Basanites (deeper and lower percentage melts) appear only in the younger episode. Eruptive episodes were apparently linked to separate melting events in the mantle. Through time, basalts were produced in diminishing volumes by lower percentage melting, magma generation and storage was at greater depths, and magma ascent was at higher velocities. Spatially, the melting anomalies were large in the Pliocene but progressively diminished in size so that by Pleistocene time, volcanism was restricted to a small area near the northern end of the initial outbreak

Active Shooter Preparedness Among Dental Hygiene Students

Purpose: Active shooter incidents (ASIs) occurring in dental hygiene academic settings present unique challenges and research examining institutional preparation of dental hygiene students for such incidents is lacking. The purpose of this pilot project was to examine the perceived preparedness, confidence, and awareness of dental hygiene students regarding ASIs. Methods: A validated 24-item electronic survey was distributed to dental hygiene students (n=68) at one institution to measure their preparedness, confidence, and awareness regarding ASIs. Descriptive statistics and Pearson correlations were used for data analysis. Results: Fifty-seven dental hygiene students completed the survey for a response rate of 84%. Many participants felt slightly prepared (n=26, 45.6%) or not prepared (n=15, 26.3%) to respond to an ASI in the classroom. Most were slightly confident (n=26, 45.6%) or not confident (n=16, 26.3%) in helping to control the classroom during an ASI. Over half (n=32, 56.1%) were not certain if their institution provided active shooter trainings and were not certain if drills occurred (n=25,43.8%). Perceived preparedness was positively correlated with confidence in helping to control an ASI in the classroom (r(56)=.616, p=.000). Positive correlations were also identified with perceived preparedness to respond in a lab or clinic with the assumption that ASIs are taken seriously at their institution (r(56)=.375, p=.004). Conclusion: A general lack of preparedness and confidence for responding to ASIs may exist among dental hygiene students along with a lack of awareness regarding trainings and drills. Educational institutions should implement best practices for preparing dental hygiene students for ASIs

Ion holes in the hydrodynamic regime in ultracold neutral plasmas

We describe the creation of localized density perturbations, or ion holes, in an ultracold neutral plasma in the hydrodynamic regime, and show that the holes propagate at the local ion acoustic wave speed. We also observe the process of hole splitting, which results from the formation of a density depletion initially at rest in the plasma. One-dimensional, two-fluid hydrodynamic simulations describe the results well. Measurements of the ion velocity distribution also show the effects of the ion hole and confirm the hydrodynamic conditions in the plasma

Determination of rolling element bearing condition via acoustic emission

Acoustic emission is an emerging technique for condition monitoring of rolling element bearings and potentially offers advantages for detection of incipient damage at an early stage of failure. Before such a technique can be applied with confidence for health monitoring, it is vital to understand the variation of acoustic emission generation with operating conditions in a healthy bearing. This paper investigates the effects of increased speed and load on the generation of acoustic emission within cylindrical roller bearings, and it was found that the root mean square signal level increased significantly with increasing speed whereas increasing load had a far weaker effect. The AERMS value for each experiment was compared with the trend of the Lambda value. The bearing was operating under full film lubrication regime, so it was determined that increases in AERMS were not caused by asperity contact. By consideration of trends in frequency energy amplitude, it was determined that excitation of the bearings resonant frequencies were responsible for an increase of energy in the frequency range of 20–60 kHz. The excitation energy at 330 kHz (the acoustic emission sensor’s resonant frequency) increased with load, indicating a link between high-frequency emission and stress at the contact zone. Following characterisation of the bearing under normal operating conditions, an accelerated life test was conducted in order to induce fatigue failure. The frequency response demonstrated that throughout a period of constant wear, the energy amplitude at the bearings resonant frequency increased with time. As the bearing failure became more significant, the energy of the high-frequency components above 100 kHz was spread over a broader frequency range as multiple transient bursts of energy were released simultaneously by fatigue failure of the raceways. This paper demonstrates the potential of acoustic emission to provide an insight into the bearing’s behaviour under normal operation and provide early indication of bearing failure