Turbulence and Compression Studies on the SSX Plasma Wind Tunnel
Turbulence in conventional fluids is characterized by stochastic motion, transfer of energy from large scales to small, and ultimately viscous dissipation at molecular scales. Turbulence in highly conductive plasma is complicated by the addition of electrodynamics, motion of charged particles, and the prospect of both viscous and resistive dissipation.
In this talk, I will present recent results from the SSX plasma wind tunnel at Swarthmore College. We have measured flow speeds up to 100 km/s, temperatures up to one million K, and magnetic fields up to 0.5 T in SSX. I will discuss projects aimed at understanding the dissipation mechanisms in plasma turbulence, as well as the physics of plasma compression.
The National Science Foundation and Other Federal Science Agencies: Promoting the Progress of Science
Vyacheslav (Slava) Lukin, National Science Foundation
Thu., Oct. 4, 2018, 4:30 PM in Science Center 183 (note time and room)
The National Science Foundation (NSF: http://www.nsf.gov/) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..." NSF supports fundamental research and education across all fields of science and engineering, with funds reaching all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Along with the Department of Energy (DOE), National Institutes of Health (NIH), National Aeronautics and Space Administration (NASA), and a number of other US federal agencies supporting scientific research, NSF provides the backbone of support for basic and early applied research across both mission-oriented and academic research and education institutions in the United States.
In this colloquium, I will provide a brief overview of the National Science Foundation, describe some of the frontier research areas NSF is supporting, and I will leave plenty of time for Q&A about the broader US landscape and mechanisms of support for basic scientific research. My perspective will be based on 20 years of research experience that began in Swarthmore’s Physics & Astronomy Department and has taken me through R1 research universities, DOE & DOD national laboratories, to become a Program Director in the NSF’s Division of Physics.
Computational Methods for Approaching Slow Manifolds, Tracking Extreme Events, and Understanding Multi-Scale Fluid Dynamics
Jeff Oishi, Bates College
Fri., Oct. 5, 2018, 12:30 PM in Science Center 199
Fluid dynamics and plasma physics present a dazzling array of problems with very wide scale separation in both space and time. Such problems are typified by turbulence, which can exhibit factors of 10^12 between the largest and smallest spatial scales and 10^13 between the fastest and slowest dynamical times. These problems, and many others, are modeled using partial differential equations (PDEs). I will present a series of strategies for accurately and expediently solving the PDEs describing the motions of fluids and plasmas in order to extract physical insight into a wide variety of systems. I will focus on the solution to a pair of geophysical and astrophysical problems involving turbulent convection, magnetic fields, and rotation. In particular, I will discuss the application of a new class of models called Direct Statistical Simulation, applicable for a broad class of problems with anisotropic flows, that is those with one direction significantly different than the other two.
In doing so, I will also address the not insignificant but often overlooked challenge of putting new discoveries in applied mathematics into the hands of practitioners in a wide variety of disciplines. I will highlight the use of the Dedalus Project, a flexible toolkit for solving almost arbitrary PDEs that my collaborators and I have developed.
Problems in Physics: What Are They and How Do Physicists and Students Construct Them?
Anna Phillips '09, Tufts University
Thu., Oct., 25, 2018, 4:30 PM in Science Center 181
Physicists treat well-formulated problems as knowledge objects: we discuss them, share them, and include open and solved problems in textbooks. Yet what constitutes a problem, as well as how problems come to be, is an understudied topic in philosophy of physics. In this talk, I discuss examples of historical problems in physics. I also argue that the process of formulating, articulating, and refining problems is central to the inquiry of both physicists and science students at all levels, and present examples of students formulating problems.
Sponsored by the departments of Physics & Astronomy and Educational Studies
Douglas Jerolmack, University of Pennsylvania
Fri., Nov. 2, 2018, 12:30 PM in Science Center 199
The Earth's surface is composed of a staggering diversity of particulate-fluid mixtures: dry to wet, dilute to dense, colloidal to granular, attractive to repulsive particles, laminar to turbulent flows, and steady to highly-unsteady forcing. This material variety is matched by the range of relevant stresses and strain rates, from rapid and catastrophic landslides to the slow relaxation of soil over geologic timescales. Geophysical flows sculpt landscapes, but also threaten human lives and infrastructure. From a physics point of view, virtually all Earth and planetary landscapes are composed of ``soft matter''. Geophysical materials, however, often involve compositions and flow geometries that have not yet been examined in physics. I explore how a soft-matter perspective has helped to illuminate, and even predict, the rich dynamics of Earth materials and their associated landscapes. I also highlight some novel phenomena of geophysical flows that challenge, and will hopefully inspire, more fundamental work in physics.
Nick Murphy, Harvard-Smithsonian Center for Astrophysics
Fri., Dec. 7, 2018, 12:30 PM in Science Center 199
PlasmaPy is a new community-developed open source Python package for plasma physics. This project strives to produce the core functionality that is needed to foster the creation of a fully open source Python ecosystem for heliospheric, laboratory, and astrophysical plasma physics. In this talk, I will tell the story of how PlasmaPy came to be. I will discuss our motivation for the project, the many lessons we have learned along the way, and the importance of community in an open source project. I will describe the best practices for scientific computing that we are adopting. I will end with a tour of PlasmaPy’s current capabilities and plans for ongoing work.