152 research outputs found
Refractive error and visual impairment in Ireland schoolchildren
Aim To report refractive error prevalence and visual impairment in Republic of Ireland (henceforth \u27Ireland\u27) schoolchildren. Methods The Ireland Eye Study examined 1626 participants (881 boys, 745 girls) in two age groups, 6â7 years (728) and 12â13 years (898), in Ireland between June 2016 and January 2018. Participating schools were selected by stratified random sampling, representing a mix of school type (primary/postprimary), location (urban/rural) and socioeconomic status (disadvantaged/advantaged). Examination included monocular logarithm of the minimum angle of resolution (logMAR) presenting visual acuity (with spectacles if worn) and cycloplegic autorefraction (1% Cyclopentolate Hydrochloride). Parents completed a questionnaire to ascertain participantsâ lifestyle. Results The prevalence of myopia (spherical equivalent refraction (SER): â€â0.50 D), hyperopia (SER: â„+2.00 D) and astigmatism (â€â1.00 DC) among participants aged 6â7 years old was 3.3%, 25% and 19.2%, respectively, and among participants aged 12â13 years old was 19.9%, 8.9% and 15.9%, respectively. Astigmatic axes were predominately with-the-rule. The prevalence of âbetter eyeâ presenting visual impairment (â„0.3 logMAR, with spectacles, if worn) was 3.7% among younger and 3.4% among older participants. Participants in minority groups (Traveller and non-white) were significantly more likely to present with presenting visual impairment in the âbetter eyeâ. Conclusions The Ireland Eye Study is the first population-based study to report on refractive error prevalence and visual impairment in Ireland. Myopia prevalence is similar to comparable studies of white European children, but the levels of presenting visual impairment are markedly higher than those reported for children living in Northern Ireland, suggesting barriers exist in accessing eye care
Refractive error and visual impairment in Ireland schoolchildren
To report refractive error prevalence and visual impairment in Republic of Ireland (henceforth \u27Ireland\u27) schoolchildren
Regional Structural Orientation of the Mount Sharp Group Revealed by In Situ Dip Measurements and Stratigraphic Correlations on the Vera Rubin Ridge
Groundâbased bedding orientation measurements are critical to determine the geologic history and processes of sedimentation in Gale crater, Mars. We constrain the dip of lacustrine strata of the Blunts Point, Pettegrove Point, and Jura members of the Murray formation using a combination of regional stratigraphic correlations and bed attitude measurements from stereo Mastcam images taken by the Mars Science Laboratory Curiosity rover. In situ bed attitude measurements using a principal component analysisâbased regression method reveal a wide range of dips and dip azimuths owing to a combination of high stereo errors, postdepositional deformation of strata (e.g., fracturing, rotation, and impact cratering), and different primary depositional dips. These constrain regional dips to be within several degrees of horizontal on average. Stratigraphic correlations between targets observed in the Glen Torridon trough and at the Pettegrove PointâJura member contact of Vera Rubin ridge (VRR) constrain dips to be between 3°SE and 2°NW, consistent with nearly flat strata deposited horizontally on an equipotential surface. The Jura member is determined to be stratigraphically equivalent to the northern portion of the Glen Torridon trough. Roverâbased dip magnitudes are generally significantly shallower than the orientation of VRR member contacts measured from High Resolution Imaging Science Experimentâbased traces, suggesting the sedimentary strata and VRR member contacts may be discordant
Late-Stage Diagenetic Concretions in the Murray Formation, Gale Crater, Mars
Concretions are prevalent features in the generally lacustrine deposits of the Murray formation in Gale crater. In this work, we document the morphologic, textural, and chemical properties of these concretions throughout 300 m of Murray formation stratigraphy from Mars Science Laboratory observations between Sols 750â1900. We interpret these observations to constrain the timing and composition of post-depositional fluid events at Gale crater. We determine that the overall diversity of concretion morphology, size, texture, and chemistry throughout the Murray formation indicates that concretions formed in multiple, likely late diagenetic, episodes with varying fluid chemistries. Four major concretion assemblages are observed at distinct stratigraphic intervals and approximately correlate with major distinct chemical enrichments in Mg-S-Ni-Cl, Mn-P, and Ca-S, among other local enrichments. Different concretion size populations and complex relationships between concretions and veins also suggest multiple precipitation events at Gale crater. Many concretions likely formed during late diagenesis after sediment compaction and lithification, based on observations of concretions preserving primary host rock laminations without differential compaction. An upsection decrease in overall concretion size corresponds to an inferred upsection decrease in porosity and permeability, thus constraining concretion formation as postdating fluid events that produced initial cementation and porosity loss. The combined observations of late diagenetic concretions and distinct chemical enrichments related to concretions allow constraints to be placed on the chemistry of late stage fluids at Gale crater. Collectively, concretion observations from this work and previous studies of other diagenetic features (veins, alteration halos) suggest at least six post-depositional events that occurred at Gale crater after the deposition of the Murray formation
Centimeter to decimeter hollow concretions and voids in Gale Crater sediments, Mars
Voids and hollow spheroids between âŒ1 and 23 cm in diameter occur at several locations along the traverse of the Curiosity rover in Gale crater, Mars. These hollow spherical features are significantly different from anything observed in previous landed missions. The voids appear in dark-toned, rough-textured outcrops, most notably at Point Lake (sols 302-305) and Twin Cairns Island (sol 343). Point Lake displays both voids and cemented spheroids in close proximity; other locations show one or the other form. The spheroids have 1-4 mm thick walls and appear relatively dark-toned in all cases, some with a reddish hue. Only one hollow spheroid (Winnipesaukee, sol 653) was analyzed for composition, appearing mafic (Fe-rich), in contrast to the relatively felsic host rock. The interior surface of the spheroid appears to have a similar composition to the exterior with the possible exceptions of being more hydrated and slightly depleted in Fe and K. Origins of the spheroids as Martian tektites or volcanic bombs appear unlikely due to their hollow and relatively fragile nature and the absence of in-place clearly igneous rocks. A more likely explanation to both the voids and the hollow spheroids is reaction of reduced iron with oxidizing groundwater followed by some re-precipitation as cemented rind concretions at a chemical reaction front. Although some terrestrial concretion analogs are produced from a precursor siderite or pyrite, diagenetic minerals could also be direct precipitates for other terrestrial concretions. The Gale sediments differ from terrestrial sandstones in their high initial iron content, perhaps facilitating a higher occurrence of such diagenetic reactions
The Economic Resource Receipt of New Mothers
U.S. federal policies do not provide a universal social safety net of economic support for women during pregnancy or the immediate postpartum period but assume that employment and/or marriage will protect families from poverty. Yet even mothers with considerable human and marital capital may experience disruptions in employment, earnings, and family socioeconomic status postbirth. We use the National Survey of Families and Households to examine the economic resources that mothers with children ages 2 and younger receive postbirth, including employment, spouses, extended family and social network support, and public assistance. Results show that many new mothers receive resources postbirth. Marriage or postbirth employment does not protect new mothers and their families from poverty, but education, race, and the receipt of economic supports from social networks do
Late-Stage Diagenetic Concretions in the Murray Formation, Gale Crater, Mars
Concretions are prevalent features in the generally lacustrine deposits of the Murray formation in Gale crater. In this work, we document the morphologic, textural, and chemical properties of these concretions throughout 300 m of Murray formation stratigraphy from Mars Science Laboratory observations between Sols 750â1900. We interpret these observations to constrain the timing and composition of post-depositional fluid events at Gale crater. We determine that the overall diversity of concretion morphology, size, texture, and chemistry throughout the Murray formation indicates that concretions formed in multiple, likely late diagenetic, episodes with varying fluid chemistries. Four major concretion assemblages are observed at distinct stratigraphic intervals and approximately correlate with major distinct chemical enrichments in Mg-S-Ni-Cl, Mn-P, and Ca-S, among other local enrichments. Different concretion size populations and complex relationships between concretions and veins also suggest multiple precipitation events at Gale crater. Many concretions likely formed during late diagenesis after sediment compaction and lithification, based on observations of concretions preserving primary host rock laminations without differential compaction. An upsection decrease in overall concretion size corresponds to an inferred upsection decrease in porosity and permeability, thus constraining concretion formation as postdating fluid events that produced initial cementation and porosity loss. The combined observations of late diagenetic concretions and distinct chemical enrichments related to concretions allow constraints to be placed on the chemistry of late stage fluids at Gale crater. Collectively, concretion observations from this work and previous studies of other diagenetic features (veins, alteration halos) suggest at least six post-depositional events that occurred at Gale crater after the deposition of the Murray formation
Low Hesperian P_(CO2) constrained from in situ mineralogical analysis at Gale Crater, Mars
Carbon dioxide is an essential atmospheric component in martian climate models that attempt to reconcile a faint young sun with planetwide evidence of liquid water in the Noachian and Early Hesperian. In this study, we use mineral and contextual sedimentary environmental data measured by the Mars Science Laboratory (MSL) Rover Curiosity to estimate the atmospheric partial pressure of CO_2 (P_(CO2)) coinciding with a long-lived lake system in Gale Crater at âŒ3.5 Ga. A reactionâtransport model that simulates mineralogy observed within the Sheepbed member at Yellowknife Bay (YKB), by coupling mineral equilibria with carbonate precipitation kinetics and rates of sedimentation, indicates atmospheric P_(CO2) levels in the 10s mbar range. At such low P_(CO2) levels, existing climate models are unable to warm Hesperian Mars anywhere near the freezing point of water, and other gases are required to raise atmospheric pressure to prevent lake waters from being lost to the atmosphere. Thus, either lacustrine features of Gale formed in a cold environment by a mechanism yet to be determined, or the climate models still lack an essential component that would serve to elevate surface temperatures, at least locally, on Hesperian Mars. Our results also impose restrictions on the potential role of atmospheric CO_2 in inferred warmer conditions and valley network formation of the late Noachian
Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars
Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fineâgrained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be subâdivided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) lowâangle crossâstratified mudstone; (iii) crossâstratified sandstone; and (iv) thickly laminated mudstoneâsandstone. The very fine grain size of the mudstone facies and abundant millimetreâscale and subâmillimetreâscale laminations exhibiting quasiâuniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Lowâangle geometric discordances in the mudstone facies are interpreted as âscour and drapeâ structures and suggest the action of currents, such as those associated with hyperpycnal riverâgenerated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvialâdeltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10^3 to 10^7 Earth years
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