[Seminar]

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Title: The physics of mixing in supersonic interstellar turbulence.

Speaker: Dr. Liubin Pan

Affiliation: Harvard-Smithsonian Center for Astrophysics 

Time:  July 29, 2013 (Monday) 15:00 p.m.

Venue: Meeting Room 401 (Main Building)

Abstract:　

Mixing of heavy elements in the interstellar medium occurs in the presence of a supersonic turbulent velocity field. I will first discuss the general physics of passive scalar mixing in isothermal supersonic turbulence. Using simulated turbulent flows in a range of Mach numbers, M, we find that, when normalized to the flow dynamical time, the mixing timescale increases with M for M <3, and becomes essentially constant for M>3. This result suggests that compressible modes are less efficient in enhancing mixing than solenoidal modes. The second topic of my talk is motivated by the pollution process of primordial gas in high-redshift galaxies, which determines the transition from Pop III to Pop II star formation. The transition occurs as metals produced by the first stars pollute the surrounding gas and increase its metallicity beyond a critical value, Z_c (10^-8 < Z_c <10^-5). Using both theoretical and numerical methods, we investigate how the mass fraction of pristine fluid elements with Z < Z_c evolves in compressible turbulent flows. Our theoretical approach is based on the probability distribution function (PDF) method for turbulent mixing.
　　 Adopting the so-called self-convolution PDF models, we derived evolution equations for the pristine gas fraction, and showed that they provide successful fits to the simulation results. Combining the analytical method and numerical results, we set up a subgrid model that can used in large-scale simulations for the pollution of primordial gas in early galaxies。

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南方基地
　　丽江天文观测站
　　中国科学院天体结构与演化重点实验室
　　云南天文台学术委员会
　　2013-7-26