The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen

The cosmological background of ionizing radiation has been dominated by quasars once the Universe aged by ~2 billion years. At earlier times (redshifts z>3), the observed abundance of bright quasars declined sharply, implying that cosmic hydrogen was reionized by stars instead. Here, we explain the physical origin of the transition between the dominance of stars and quasars as a generic feature of structure formation in the concordance LCDM cosmology. At early times, the fraction of baryons in galaxies grows faster than the maximum (Eddington-limited) growth rate possible for quasars. As a result, quasars were not able to catch up with the rapid early growth of stellar mass in their host galaxies.Comment: 5 pages, 1 figure, Accepted for publication in JCA

Neuroimaging-based classification of PTSD using data-driven computational approaches: a multisite big data study from the ENIGMA-PGC PTSD consortium

Background: Recent advances in data-driven computational approaches have been helpful in devising tools to objectively diagnose psychiatric disorders. However, current machine learning studies limited to small homogeneous samples, different methodologies, and different imaging collection protocols, limit the ability to directly compare and generalize their results. Here we aimed to classify individuals with PTSD versus controls and assess the generalizability using a large heterogeneous brain datasets from the ENIGMA-PGC PTSD Working group. Methods: We analyzed brain MRI data from 3,477 structural-MRI; 2,495 resting state-fMRI; and 1,952 diffusion-MRI. First, we identified the brain features that best distinguish individuals with PTSD from controls using traditional machine learning methods. Second, we assessed the utility of the denoising variational autoencoder (DVAE) and evaluated its classification performance. Third, we assessed the generalizability and reproducibility of both models using leave-one-site-out cross-validation procedure for each modality. Results: We found lower performance in classifying PTSD vs. controls with data from over 20 sites (60 % test AUC for s-MRI, 59 % for rs-fMRI and 56 % for D-MRI), as compared to other studies run on single-site data. The performance increased when classifying PTSD from HC without trauma history in each modality (75 % AUC). The classification performance remained intact when applying the DVAE framework, which reduced the number of features. Finally, we found that the DVAE framework achieved better generalization to unseen datasets compared with the traditional machine learning frameworks, albeit performance was slightly above chance. Conclusion: These results have the potential to provide a baseline classification performance for PTSD when using large scale neuroimaging datasets. Our findings show that the control group used can heavily affect classification performance. The DVAE framework provided better generalizability for the multi-site data. This may be more significant in clinical practice since the neuroimaging-based diagnostic DVAE classification models are much less site-specific, rendering them more generalizable.Stress-related psychiatric disorders across the life spa

Assessing Reef island sensitivity based on LiDAR-derived morphometric indicators

Reef islands are some of the most highly sensitive landforms to the impacts of future environmental change. Previous assessments of island morphodynamics primarily relied on historical aerial and satellite imagery. These approaches limit analysis to two-dimensional parameters, with no ability to assess long-term changes to island volume or elevation. Here, we use high-resolution airborne LiDAR data to assess three-dimensional reef island features for 22 islands along the north-western coast of Australia. Our primary objective was to utilize two regional LiDAR datasets to identify characteristics indicative of island sensitivity and future vulnerability. Results show reef platform area to be an accurate predictor of island area and volume suggesting larger island volumes may reflect (1) increased carbonate production and supply from the reef platform and/or (2) enhanced shoreline protection by larger reef platforms. Locations of foredune scarping (an erosional signature) and island orientations were aligned to the regional wind and wave climate. Reef island characteristics (island area, volume, elevation, scarping, and platform area) were used to rank islands according to sensitivity, using a new Island Sensitivity Characteristics Index (ISCi) where low ISCi indicates stable islands (large areas and volumes, high elevations, and fewer scarped areas) and high ISCi indicates unstable islands (small areas and volumes, low elevations, and more scarped areas). Comparison of two LiDAR surveys from 2016 and 2018 validates the use of 3D morphometrics as important (direct) measurements of island landform change, and can complement the use of 2D parameters (e.g., area) moving forward. Results demonstrate that ongoing use of airborne LiDAR and other 3D technology for monitoring coral reef islands at regional scales will enable more accurate quantification of their sensitivity to future impacts of global environmental change

Reef to island sediment connections within an inshore turbid reef island system of the eastern Indian Ocean

Reef islands are low-lying sedimentary landforms formed from the accumulation of unconsolidated skeletal material generated by carbonate-producing reef organisms. The coupling between ecological (extant community assemblage) and sedimentary processes (sediment composition and supply) that maintain these reef-fronted landforms make them increasingly sensitive to the impacts of future environmental change. To understand this interconnection we examine the benthic reef community assemblage and sediment characteristics (composition and texture) at Eva Island, an inshore turbid reef island system located in the Pilbara region of Western Australia. Benthic surveys and sediment composition identified molluscs as a unique primary sand-sized sediment constituent (34% of reef and sediments, respectively), alongside coral, despite low mollusc abundance in the reef ecology (n = 94 extant individuals). This result, alongside homogeneity within reef and island biosedimentary facies, suggest a coupling between source (reef) and sink (island) environments may exist, with the sediment reservoir providing suitable sand-grade material for island nourishment. In light of these findings, assuming island building can keep up with rising sea levels, Eva may be resilient to the immediate impacts of climate change. However, dependency on a few primary sediment constituents (molluscs and coral that are sensitive to environmental perturbations) may compromise long-term resilience (over decades), particularly the direct effect on sediment producing habitats and sensitive calcifying organisms under future changing climatic conditions

Alcohol consumption in a general antenatal population and child neurodevelopment at 2 years

BACKGROUND:Prenatal alcohol exposure (PAE) is a community health problem with up to 50% of pregnant women drinking alcohol. The relationship between low or sporadic binge PAE and adverse child outcomes is not clear. This study examines the association between PAE in the general antenatal population and child neurodevelopment at 2 years, accounting for relevant contributing factors. METHODS:This prospective population-based cohort recruited 1570 pregnant women, providing sociodemographic, psychological and lifestyle information and alcohol use for five time periods. PAE categories were 'low', 'moderate/high', 'binge', in trimester 1 or throughout pregnancy. Measures of cognitive, language and motor development (Bayley Scales of Infant and Toddler Development) were available for 554 children, while measures of sensory processing (Infant/Toddler Sensory Profile) and social-emotional development (Brief Infant Toddler Social Emotional Assessment) were available for 948. RESULTS:A positive association in univariate analysis with low-level PAE throughout pregnancy and cognition (β=4.1, 95% CI -0.02 to 8.22, p=0.05) was attenuated by adjusting for environmental/social deprivation risk factors (β=3.06 (-1.19 to 7.30), p=0.16). Early binge drinking, plus continued PAE at lower levels, was associated with the child being more likely to score low in sensation avoidance (adjusted OR 1.88 (1.03 to 3.41), p=0.04). CONCLUSION:Early binge exposure, followed by lower-level PAE, demonstrated an increase in sensation-avoiding behaviour. There were, however, no significant associations between PAE and neurodevelopment following adjustment for important confounders and modifiers. Follow-up is paramount to investigate subtle or later onset problems.Jane L Halliday, Evelyne Muggli, Sharon Lewis, Elizabeth J Elliott, David J Amor, Colleen O’Leary ... et al