Interstellar MHD Turbulence and Star Formation

This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: i) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; ii) the nature of the clumps produced by thermal instability, noting that, contrary to classical ideas, they in general accrete mass from their environment; iii) the density-magnetic field correlation (or lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; iv) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; v) the formation of cold, dense clouds aided by thermal instability; vi) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, and vii) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and diperses them while they collapse.Comment: 43 pages. Invited chapter for the book "Magnetic Fields in Diffuse Media", edited by Elisabete de Gouveia dal Pino and Alex Lazarian. Revised as per referee's recommendation

Physical Processes in Star Formation

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00693-8.Star formation is a complex multi-scale phenomenon that is of significant importance for astrophysics in general. Stars and star formation are key pillars in observational astronomy from local star forming regions in the Milky Way up to high-redshift galaxies. From a theoretical perspective, star formation and feedback processes (radiation, winds, and supernovae) play a pivotal role in advancing our understanding of the physical processes at work, both individually and of their interactions. In this review we will give an overview of the main processes that are important for the understanding of star formation. We start with an observationally motivated view on star formation from a global perspective and outline the general paradigm of the life-cycle of molecular clouds, in which star formation is the key process to close the cycle. After that we focus on the thermal and chemical aspects in star forming regions, discuss turbulence and magnetic fields as well as gravitational forces. Finally, we review the most important stellar feedback mechanisms.Peer reviewedFinal Accepted Versio

Structural and technical details of the Kirkwood-Buff integrals from the optimization of ionic force fields: focus on fluorides

Results on the structural details of Kirkwood-Buff integrals obtained from the optimization of ionic force fields are presented. We have proposed and make use of an optimization scheme for ionic force fields, which is based on the modification of the cation-anion mixing rules, the calculation of the thermodynamics properties of various monovalent salt solutions according to the Kirkwood-Buff theory of solutions and the comparison to relevant experimental findings. Here, we complete and extend our calculations and analysis as we focus on the technical details of this optimization procedure and the case of fluorides, which have been proven difficult to handle. Important insight is given on the dependence of the radial distribution functions, the short-ranged potentials of mean force, and the Kirkwood-Buff integrals of the salt solutions on the different scaling factors in the mixing rules. Specifically, the way the structural details and inherent characteristics of the above properties are affected by the quantitative and qualitative differences in the mixing rules for a variety of common biologically relevant monovalent salts is mainly addressed. We conclude on the efficiency of this scheme, again with a focus on the fluorides. In the end, we provide a variation of the ion-pair mixing rules scaling factors with salt concentration to identify regimes for which different mixing rules prefactors lead to well-optimized force fields. All results are obtained through Molecular Dynamics simulations using previously optimized force fields for the monovalent ions

The genetic and ecophysiological diversity of Microcystis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171576/1/emi15615.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171576/2/emi15615-sup-0002-FigureS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171576/3/emi15615_am.pd