Spectacular nucleosynthesis from early massive stars

Stars formed with initial mass over 50 Msun are very rare today, but they are thought to be more common in the early universe. The fates of those early, metal-poor, massive stars are highly uncertain. Most are expected to directly collapse to black holes, while some may explode as a result of rotationally powered engines or the pair-creation instability. We present the chemical abundances of J0931+0038, a nearby low-mass star identified in early followup of SDSS-V Milky Way Mapper, which preserves the signature of unusual nucleosynthesis from a massive star in the early universe. J0931+0038 has relatively high metallicity ([Fe/H] = -1.76 +/- 0.13) but an extreme odd-even abundance pattern, with some of the lowest known abundance ratios of [N/Fe], [Na/Fe], [K/Fe], [Sc/Fe], and [Ba/Fe]. The implication is that a majority of its metals originated in a single extremely metal-poor nucleosynthetic source. An extensive search through nucleosynthesis predictions finds a clear preference for progenitors with initial mass > 50 Msun, making J0931+0038 one of the first observational constraints on nucleosynthesis in this mass range. However the full abundance pattern is not matched by any models in the literature. J0931+0038 thus presents a challenge for the next generation of nucleosynthesis models and motivates study of high-mass progenitor stars impacted by convection, rotation, jets, and/or binary companions. Though rare, more examples of unusual early nucleosynthesis in metal-poor stars should be found in upcoming large spectroscopic surveys.Comment: 11 pages + 22 page appendix, accepted to ApJ

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

Neurophysiological Oscillations as Biomarkers of Neurodevelopmental Disorders

Mechanism-based biomarkers are needed to guide clinical trials for neurodevelopmental disorders by indexing disease pathology or a treatment response. In this dissertation, I describe electroencephalogram (EEG) biomarkers in two neurodevelopmental disorders, Dup15q syndrome and Angelman syndrome. Dup15q syndrome is caused by duplications of 15q11.2-q13.1, including UBE3A—a paternally imprinted gene involved in synapse development—and several gamma-aminobutyric acid type-A (GABA-A) receptor subunit genes. In Angelman syndrome, the majority of cases are caused by deletions of 15q11.2-q13.1, though some cases are caused by UBE3A dysfunction alone. Both disorders are characterized by epilepsy, intellectual disability, and phenotypic overlap with autism spectrum disorder (ASD).In Chapter 1, I introduce biomarkers and neurodevelopmental disorders. In Chapter 2, I infer the emergence of stable oscillations from neural noise in typically developing (TD) preschool age children. In Chapter 3, I describe a beta EEG phenotype of Dup15q syndrome, which distinguishes children with this disorder from TD and nonsyndromic ASD controls. In Chapter 4, I compare this phenotype with beta oscillations induced with midazolam, a GABA-A modulator, in healthy adult participants. Furthermore, two cases of paternal Dup15q syndrome (i.e., duplications of the UBE3A-silenced allele) also show this EEG phenotype, suggesting that it is a marker of GABAergic pathology. In Chapter 5, I describe a delta EEG phenotype of Angelman syndrome (previously described by Sidorov and colleagues in 2017) that is stronger in children with a deletion genotype than those with a non-deletion genotype. Furthermore, I find lower beta power and higher theta power in the deletion genotype. Thus, beta power and theta power appear to reflect GABAergic dysfunction, whereas delta power appears to reflect UBE3A dysfunction but is modulated by GABA-A receptor gene deletion. Chapter 6 summarizes this work and provides a discussion about implications and next steps. In conclusion, neurophysiological oscillations are likely markers of gene-specific disease pathology in Dup15q syndrome and Angelman syndrome. Clinical trials targeting specific gene products (e.g., GABA-A receptors) may utilize these EEG measures as biomarkers of target engagement or surrogate endpoints