GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

We investigate giant molecular cloud (GMCs) collisions and their ability to induce gravitational instability and thus star formation. This mechanism may be a major driver of star formation activity in galactic disks. We carry out a series of three dimensional, magnetohydrodynamics (MHD), adaptive mesh refinement (AMR) simulations to study how cloud collisions trigger formation of dense filaments and clumps. Heating and cooling functions are implemented based on photo-dissociation region (PDR) models that span the atomic to molecular transition and can return detailed diagnostic information. The clouds are initialized with supersonic turbulence and a range of magnetic field strengths and orientations. Collisions at various velocities and impact parameters are investigated. Comparing and contrasting colliding and non-colliding cases, we characterize morphologies of dense gas, magnetic field structure, cloud kinematic signatures, and cloud dynamics. We present key observational diagnostics of cloud collisions, especially: relative orientations between magnetic fields and density structures, like filaments; 13CO(J=2-1), 13CO(J=3-2), and 12CO(J=8-7) integrated intensity maps and spectra; and cloud virial parameters. We compare these results to observed Galactic clouds

The Paradox of Engagement: Land Stewardship and Invasive Weeds in Amenity Landscapes

In New South Wales, Australia, rural landscapes are undergoing profound change as a result of exurbanization. Newcomers-amenity migrants-are drawn to the scenic beaches, forests, and open landscape character of this part of Australia near Sydney and they join existing communities of long-term residents, notably ranchers involved in dairy, beef, and other types of primary agricultural production. The rural to exurban transition is stimulating both intended and unintended socio-ecological changes, especially the proliferation of invasive weeds, which are considered to be a top national priority as they threaten Australia\u27s agricultural economy. Drawing on interview and survey research from three case studies in New South Wales, locations where an influx of exurbanites has led to mixed landscapes of production and consumption, we explore landowners\u27 diverse environmental ideologies, the degree to which they collaborate with one another, and their specific land-use practices. Results show that an overwhelming majority of both exurbanites and ranchers express concerns about weeds, but there is a marked lack of coordinated engagement on invasive species between the two types of groups. This chapter is an example of social disengagement over land-use and land-cover change, rather than competition or cooperation, and contributes to a political ecological understanding of the co-construction of social relations and land management regimes

Heme-binding enables allosteric modulation in an ancient TIM-barrel glycosidase

Glycosidases are phylogenetically widely distributed enzymes that are crucial for the cleavage of glycosidic bonds. Here, we present the exceptional properties of a putative ancestor of bacterial and eukaryotic family-1 glycosidases. The ancestral protein shares the TIM-barrel fold with its modern descendants but displays large regions with greatly enhanced conformational flexibility. Yet, the barrel core remains comparatively rigid and the ancestral glycosidase activity is stable, with an optimum temperature within the experimental range for thermophilic family-1 glycosidases. None of the ∼5500 reported crystallographic structures of ∼1400 modern glycosidases show a bound porphyrin. Remarkably, the ancestral glycosidase binds heme tightly and stoichiometrically at a well-defined buried site. Heme binding rigidifies this TIM-barrel and allosterically enhances catalysis. Our work demonstrates the capability of ancestral protein reconstructions to reveal valuable but unexpected biomolecular features when sampling distant sequence space. The potential of the ancestral glycosidase as a scaffold for custom catalysis and biosensor engineering is discussed.Uppsala Universit