Turbulent Disks are Never Stable: Fragmentation and Turbulence-Promoted Planet Formation

A fundamental assumption in our understanding of disks is that when the Toomre Q>>1, the disk is stable against fragmentation into self-gravitating objects (and so cannot form planets via direct collapse). But if disks are turbulent, this neglects a spectrum of stochastic density fluctuations that can produce rare, high-density mass concentrations. Here, we use a recently-developed analytic framework to predict the statistics of these fluctuations, i.e. the rate of fragmentation and mass spectrum of fragments formed in a turbulent Keplerian disk. Turbulent disks are never completely stable: we calculate the (always finite) probability of forming self-gravitating structures via stochastic turbulent density fluctuations in such disks. Modest sub-sonic turbulence above Mach number ~0.1 can produce a few stochastic fragmentation or 'direct collapse' events over ~Myr timescales, even if Q>>1 and cooling is slow (t_cool>>t_orbit). In trans-sonic turbulence this extends to Q~100. We derive the true Q-criterion needed to suppress such events, which scales exponentially with Mach number. We specify to turbulence driven by MRI, convection, or spiral waves, and derive equivalent criteria in terms of Q and the cooling time. Cooling times >~50*t_dyn may be required to completely suppress fragmentation. These gravoturbulent events produce mass spectra peaked near ~M_disk*(Q*M_disk/M_star)^2 (rocky-to-giant planet masses, increasing with distance from the star). We apply this to protoplanetary disk models and show that even minimum mass solar nebulae could experience stochastic collapse events, provided a source of turbulence.Comment: 15 pages, 5 figures (+appendix), accepted to ApJ (added clarifications and discussion to match accepted version

Comparative Genome Analysis of Fungal Antagonists Marinomonas ostreistagni 398 and M. spartinae 468.

Under certain conditions, the Spartina alterniflora and Juncus roemerianus grasses in marshes undergo progressive decline in an event known as Saltwater Marsh Dieback, which may be attributed to the presence of the plant pathogenic fungi Fusarium. The microbiomes of S. alterniflora and J. roemerianus from Deer Island, MS were characterized and Fusarium suppressing bacteria were identified. Among isolates capable of antagonizing Fusarium were Marinomonas ostreistagni 398 and M. spartinae 468. Despite the progress in understanding the diversity of Marinomonas, our ability to explain ecological, metabolic, and biochemical traits of marinomonads at the genomic sequence level remains limited. Analysis revealed that Marinomonas genomes form three distinct clades supported by the relatedness of orthologous genes. Heterogeneity is reflected in the core genome representing only 50-60% of any individual strain. Genes for the synthesis of siderophores and other secondary metabolites were identified. Clade- and strain-specific genomic regions contained mobile genetic elements. These results provide insights into the genomic diversity of Marinomonas by characterizing genes for the adaptation to hypersaline environments, pathways involved in the interaction with plants, and the production of antimicrobial compounds

Family Factors in the Delinquency Puzzle

The purpose of the present study was to evaluate the impact of different family factors on juvenile delinquency. Specifically, this thesis examined parental monitoring, attachment to parents, and family structure by investigating their single and combined effects on delinquency. In addition, the current study addresses the effects family factors have on different levels of delinquent behavior. Four hypotheses were tested. The first one, suggests that children living in single-parent homes will exhibit higher levels of self reported delinquency than those in two-parent families. The second states that attachment to both mothers and fathers will have an impact on delinquency. The third proposes that high levels of parental monitoring will lead to lower levels of self-reported delinquency. The final hypothesis involves a combined model, including attachment and monitoring as a better predictor of delinquency than family status. Data was collected from a sample of 5,935 eighth-grade students attending public schools in eleven different sites across the country, during the spring of 1995. Results of regression analysis strongly supported three hypotheses and yielded limited support to the fourth. Specifically, children from single-parent homes reported higher levels of self-reported delinquency than did children from two-parent homes. Moreover, strong attachments and high parental monitoring revealed lower levels of delinquency. In addition, a model containing both parental attachments and monitoring was a better predictor of delinquency than family status alone. However, the significance of single parent families did not drop significantly with the addition of the new variables. The discussion provides possible explanations for the family differences that were found. The present study reemphasizes the need to examine the combined impact of family factors on delinquent behavior

No Going Back: Un-Fixing the Future of De-Extinction

‘Extinction is a colossal problem facing the world’ proclaims the Colossal Laboratories & Biosciences website, adding, ‘And Colossal is the company that’s going to fix it’. For Colossal, this involves combining the science of genetics with ‘the business of discovery’ in order to bring back the woolly mammoth, which will not only help ‘rewild’ lost habitats, but also contribute toward ‘making humanity more human’. De-extinction is the process through which extinct species can be brought back into existence, often with the goal of reintroducing species to the wild and restoring ecosystems. While still in its nascent state, the science of de-extinction is currently expanding and advancing through, for instance, projects like Colossal’s, raising numerous ethical, social and technological debates about what defines a species, and thus its regeneration; how such definitions shape conservation paradigms; and, ultimately, what we mean when we talk about life, death and species extinction. With their commitment to ‘reversing climate change’ while also ‘advanc[ing] the economies of biology and healing through genetics’, Colossal’s work has not only been deemed ‘game-changing’ in terms of “saving” endangered species, but also in terms of ‘future proofing’ the environment by reshaping how the world thinks about the power of genetics for solving pressing challenges in the life sciences today, including the challenge of extinction. In this de-extinction example, then, the problem of extinction is actualized in relation to solutions aimed at enacting further control over the planet, this time by ‘rewinding’ and ‘reversing’ ecological destruction, so as to fix the human-caused disaster, and in so doing, fix the future. In this essay, I trace the line between ‘the business of discovery’ and ‘making humanity more human’ in order to draw out what I see as some of the broader refrains and fixations that have come to infect future-oriented ecological discourse in these times of dying. Looking to the example of Colossal, I examine the ways in which extinction, and the corollary project of de-extinction, has become at once a territorializing force that works to re-install monohumanist fantasies of planetary control, and a potentially deterritorializing force for letting go and giving up