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  1. Abstract

    The abundance and distribution of44Ti tells us about the nature of the core-collapse supernovae explosions. There is a need to understand the nuclear reaction network creating and destroying44Ti in order to use it as a probe for the explosive mechanism. The44Ti(α, p)47V reaction is a very important reaction and it controls the destruction of44Ti. Difficulties with direct measurements have led to an attempt to study this reaction indirectly. Here, the first step of the indirect study which is the identification of levels of the compound nucleus48Cr is presented. A 100-MeV proton beam was incident on a50Cr target. States in48Cr were populated in the50Cr(p, t)48Cr reaction. The tritons were momentum-analysed in the K600 Q2D magnetic spectrometer at iThemba LABS.

     
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    Free, publicly-accessible full text available September 1, 2024
  2. Stony coral tissue loss disease (SCTLD) was first observed in St. Thomas, U.S. Virgin Islands (USVI) in January 2019. This disease affects at least 20 scleractinian coral species; however, it is not well understood how reef diversity affects its spread or its impacts on reef ecosystems. With a large number of susceptible species, SCTLD may not follow the diversity-disease hypothesis, which proposes that high species diversity is negatively correlated with disease prevalence. Instead, SCTLD may have a higher prevalence and a greater impact on reefs with higher coral diversity. To test this, in 2020 we resampled 54 sites around St. Thomas previously surveyed in 2017 or 2019 by the National Oceanic and Atmospheric Administration National Coral Reef Monitoring Program. These sites represented a variety of species diversity values [categorized into poor (<12 spp. rich.) and rich (12 spp. rich.)] in multiple disease zones (Endemic: disease present  9 months; Epidemic: disease present 2–6 months; Control and Emergent: disease present no disease/<2 months). We hypothesized that, contrary to the diversity-disease hypothesis, sites with high species diversity (as measured by species richness or Simpson’s index) would have higher disease prevalence within the epidemic zone, and that high species diversity sites would have a greater impact from disease within the endemic zone. Results indicated a significant positive relationship between disease prevalence and diversity in the epidemic zone, and a similar trend in the endemic zones. Additionally, a negative relationship was seen between pre-outbreak diversity and loss of diversity and coral cover within the endemic zone. This supports the hypothesis that higher diversity predicts greater disease impact and suggests that SCTLD does not follow the diversity-disease hypothesis. Within the epidemic zone, the species with the highest SCTLD prevalence were Dendrogyra cylindrus, Colpophyllia natans, and Meandrina meandrites, while in the endemic zone, Diploria labyrinthiformis, Pseudodiploria strigosa, Montastraea cavernosa, and Siderastrea siderea had the highest SCTLD prevalence. Understanding the relationship between species diversity and SCTLD will help managers predict the most vulnerable reefs, which should be prioritized within the USVI and greater Caribbean region. 
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  3. null (Ed.)