User:Tohline/Appendix/Ramblings/MyDoctoralStudents

Chronology of Research Endeavors

Preface

Looking back, it seems clear to me that the technical book that has had the most influence on my research career has been [EFE], that is, Chandrasekhar's (originally, 1969) Ellipsoidal Figures of Equilibrium. Chandrasekhar evaluated the relative stability of a wide variety of astrophysically interesting (usually Newtonian self-gravitating), rotating equilibrium configurations by employing his own exceptional mathematical skills and those of his students — notably, Norman Lebovitz. When I entered graduate school at UC, Santa Cruz in 1974, [EFE] was the set of glasses through which most astronomers examined stability. Having access to only meager computing resources, Chandrasekhar's descriptions of the onset of instabilities, or evolution between nearly adjacent states, was usually limited to linear-amplitude deviations from equilibrium. From the beginning, I have been interested in using (steadily improving) computational resources to repeat, then extend the analyses found in [EFE] … (1) to configurations with non-homogeneous and compressible structures; and (2) into the nonlinear regime.

The MediaWiki-formatted text that you are reading — titled, The Structure, Stability, & Dynamics of Self-Gravitating Fluids — is my attempt to explain in detail what has been learned as a result of our (and the broader astrophysics community's) extension of the foundation work presented in [EFE]. The chapters of this ever-developing book that, on any date, I consider ready for public consumption can be found on the MediaWiki page that I refer to as the Tiled Menu. The graduate students who have come through my group over the years have made important contributions to the healthy development of this research field. The Outline of Research Activities that is presented, below, highlights and summarizes these contributions.

Doctoral Students Tohline Has Advised

Doctoral Students Whom Tohline has Advised at LSU
Year of Ph.D.	Student Name	ED†	Jointly Advised?
1988	Harold Williams	<math>~\odot</math>
1989	Dimitris M. Christodoulou	<math>~\odot</math>
1992	John Woodward	<math>~\odot</math>
1994	Horst Väth	<math>~\odot</math>	w/ Detlev Koester (Univ. of Kiel, Germany)
1996	Kimberly C. (Barker) New	<math>~\odot</math>
1998	Saied Andalib	<math>~\odot</math>
1998	Erik Young	<math>~\odot</math>	w/ Ganesh Chanmugam (LSU Physics & Astronomy)
1999	Paul Fisher	<math>~\odot</math>
1999	John E. Cazes	<math>~\odot</math>
1999	Howard S. Cohl	<math>~\odot</math>
2001	Eric I. Barnes	<math>~\odot</math>
2001	Patrick M. Motl	<math>~\odot</math>	w/ Juhan Frank (LSU Physics & Astronomy)
2004	Shangli Ou	<math>~\odot</math>
2006	Ravi Kumar Kopparapu	<math>~\odot</math>
2006	Richard P. Muffoletto	<math>~\odot</math>	w/ John Tyler (LSU Computer Science)
2010	Wes P. Even	<math>~\odot</math>
2010	Jay M. Call	<math>~\odot</math>
2011	Dominic C. Marcello	<math>~\odot</math>
2014	Zachary D. Byerly	<math>~\odot</math>
†ED = Electronic Dissertation Annotated NOTE: In order to see a larger version of the primary image — or its annotated thumbnail companion, shown here, on the right — click once on the image, then click a second time on Full Resolution.

Outline of Research Activities

Color Coding
Astrophysics (star formation)	Astrophysics (galaxy dynamics)	Astrophysics (sources of gravitational radiation)
Computational Fluid Dynamics (CFD) algorithm development	Visualization Tools	Other

Here, a brief summary is presented of contributions that we have made toward advancing the astrophysics community's understanding of the structure, stability, & dynamics of self-gravitating fluids. The role that individual LSU graduate students have made to this story has been highlighted. The colored bar on the left identifies, in broad terms, the category of research that is being described in each paragraph; the Color Coding table shown immediately above explains what broad category is associated with each color/

Years 1976 - 1978

		Tohline's dissertation research under the guidance of Peter Bodenheimer (UCSC) and David Black (NASA/Ames Research Center) was an early attempt to examine whether of not isothermal gas clouds whose mass exceeds the Jeans mass spontaneously fragment during a phase of free-fall collapse. The adopted Eulerian computational hydrodynamics scheme was first-order donor-cell based on the 2D (axisymmetric, cylindrical-coordinate) scheme described by Black & Bodenheimer (1976) but extended by Tohline to a 3D grid; a typical simulation was carried out on the CDC 7600 at NASA/Ames and involved 303 ∼ 3 × 104 grid cells.	[PhD] [4] [5] [7]
		At each integration time step of a simulation, the self-consistently determined, time-dependent Newtonian gravitational potential was determined by combining (1) an FFT technique in the azimuthal coordinate direction, with (2) a Buneman Cyclic Reduction technique in R and Z.
		Richard Durisen — a NASA/Ames postdoc at the time — said to me something along the lines of, "Hey! When you finish developing that hydrocode, let's get together and examine the dynamical stability of rapidly rotating, equilibrium configurations."

Years 1978 - 1982

		While at Yale University (1978 - 1980) and at Los Alamos National Laboratory (1980 - 1982), Tohline worked closely with Richard Durisen (Indiana University) to examine the onset and nonlinear development of nonaxisymmetric instabilities in differentially rotating, n = 3/2 polytropes whose internal angular momentum distribution was that of an n' = 0 sequence. Generally speaking, unstable eigenfrequencies matched earlier predictions (by other groups) based on linear stability analyses; unstable eigenfunctions displayed a two-armed spiral character. As the amplitude of unstable modes grew to nonlinear amplitude, the developed spiral arms were able to effectively redistribute angular momentum, preventing fragmentation/fission of the configurations. Over this time period, numerical simulations were carried out on the IBM 360/95 at the NASA/Goddard Institute for Space Studies and on an early Cray at Los Alamos, where computational efficiencies were gained by taking advantage of the Cray's vector hardware capabilities.	[16] [10] [12] [13] [14]
		Nelson Caldwell — a Yale graduate student at the time — showed Tohline some of his early work focused on the observationally determined properties of elliptical galaxies that display prominent dust lanes. Additional discussions led to a collaboration between Caldwell, Tohline, and Gregory Simonson — also a Yale graduate student at the time — in which the observed orientation of dust lanes can be explained in terms of dissipative settling of gas disks and, as a consequence, can be used to deduce the underlying geometry (e.g., oblate or prolate spheroidal) of each galaxy's mass distribution. With guidance from Tohline, Simonson completed a Yale University doctoral dissertation in which this settling model was extended to the context of polar rings in spiral galaxies. When Tohline presented a seminar in the Department of Astronomy at Indiana University on the topic of "dust lanes in elliptical galaxies," Durisen asked what would happen to a settling gas disk if the underlying galaxy mass distribution was tumbling end over end — e.g., a cigar spinning about its shortest axis. The ensuing discussions led to a fruitful collaboration between Durisen and Tohline in which it became clear that steady-state warped disks could result. (After Tohline moved to LSU, extensions of this research work resulted in collaborative publications with several LSU graduate students — D. Christodoulou, K. New, H. Väth — and in Paul Fisher's doctoral dissertation research project.)

Years 1982 - 1988

		During his first half-a-dozen years on the faculty at LSU, Tohline continued to work closely with Richard Durisen (Indiana University) to examine the onset and nonlinear development of nonaxisymmetric instabilities in differentially rotating polytropes. Harold Williams joined this effort as a graduate student in Tohline's group. He broadened the study to include configurations having a range of compressibility and different distributions of angular momentum; this became the central thrust of his doctoral dissertation. Williams also advanced the capabilities of the group's computational tools by implementing a second-order accurate finite-difference scheme to carry out integrations of the governing hydrodynamic equations. Over this time period, numerical simulations were carried out, to a large extent, on LSU's IBM main-frame computer. But, via NSF funding, the group also was allocated time on Cray hardware at the Minnesota's supercomputer center; Tohline and Williams both received training, for example, on Minnesota's newly acquired Cray-2. Izumi Hachisu (Kyoto University, Japan) joined the group in a postdoctoral research position for a couple of years. Drawing from his own research background, Hachisu provided us with a blueprint for developing a very efficient numerical algorithm for constructing rapidly rotating equilibrium configurations with spheroidal, toroidal, or binary-star geometric shapes — see our relevant chapter discussion. Over the past several decades, this Hachisu Self-Consistent-Field technique has allowed us to construct a wide range of different self-gravitation configurations as initial states for stability analyses and for examining the nonlinear growth of unstable modes using computational fluid techniques.	[19] [22] [<math>~\odot</math>] [25] [27] [33] [20] [PDF]
		A quantitative comparison was made between the results obtained from simulations carried out with two different "finite-difference" CFD codes and one "smoothed particle hydrodynamics" algorithm.
		We obtained the Fortran source code of a volume-rendering algorithm that had been developed by Gabor T. Herman who, at the time, was in the University of Pennsylvania's radiology department. With the significant aid of Monika Lee — our computer systems manager — the code was tuned to execute on the astronomy group's VAX 11/750 and its attached International Imaging System. A string of individual digital images was pieced together to generate animation sequences showing the behavior of our time-evolving fluid systems; this was accomplished by operating in tandem: a Lenco Color Encoder, a Lyon Lamb Mini-VAS animation controller, and a 3/4-inch broadcast-quality Sony U-matic video recorder. Jeffrey E. Anderson — an undergraduate student at LSU (1985-89) — played a key role in operating this set of tools to assist in our analysis of the results of our CFD simulations.

Creation of NSF Supercomputing Centers

Taken from §1.2.2 of the 1995 Report of the Task Force on the Future of the NSF Supercomputer Centers Program: "Four Centers* were established in 1985, and a fifth added in 1986, all providing “vector supercomputing services” for the research community and training for the many researchers who lacked experience with these systems. These Centers were points of convergence where researchers learned to think in the new computational paradigm and to explore new vistas in resolution, accuracy, and parametric description of their problems." "Experiments in allocating resources, developing software support services, and starting standardized graphics and database descriptions to accelerate scientific visualization were all initiated during this phase." "Additionally, each Center established relationships with universities, both geographically close and far, to form consortia of members who had a stake in the resources of the Centers and in their future development. An important feature of these relationships was the formation of peer-review allocation boards, in which experts in computational science could direct attention to the performance of user’s computer codes. Special attention was given to improvements of those codes with low performance. Direct interactions with experts at the Centers frequently facilitated significant performance improvements." *Extracted from footnote [4]: "The original four centers were (1) The National Center for Supercomputing Applications (NCSA) at the University of Illinois, Urbana-Champaign, (2) The Cornell Theory Center (CTC), (3) The John von Neuman Center (JvNC), a consortium located at Princeton University, (4) The San Diego Supercomputer Center (SDSC), located at the University of California, San Diego and operated by General Atomics. The fifth — added in 1986 — was the Pittsburgh Supercomputing Center (PSC), directed by the University of Pittsburgh and Carnegie Mellon University and operated by Westinghouse.

Years 1988 - 1994

		Using the HSCF-technique, John W. Woodward constructed geometrically thick, axisymmetric accretion disk structures having a range of disk-to-central-object mass ratios. He used CFD techniques to determine which configurations were dynamically stable and which were dynamically unstable toward the development of nonaxisymmetric disk structure. Over this time period, we requested and received NSF allocations of supercomputing time at the Cornell Theory Center. The CTC's main "vector" hardware resource consisted of a group of Floating Point Systems (FPS) array processors attached to an IBM main-frame. The CTC was our Center of choice because LSU also had decided to attach several FPS array processors to its IBM main-frame. We gained a great deal of early insight regarding the development of parallel computing algorithms through Woodward's extensive interactions with the CTC's technical staff, especially Francesca Verdier.	[38] [<math>~\odot</math>] [<math>~\odot</math>] [PDF]
		Building on the foundation ideas developed earlier in collaboration with Caldwell and Simonson, Dimitris M. Christodoulou used a so-called tilted-ring model of approximately a dozen warped spiral galaxy disks to decipher the geometric shape — whether oblate- or prolate-spheroidal — of each galaxy's underlying dark matter halo. In an effort to better understand how the warped structure of spiral disks develop over time, Christodoulou also used the group's CFD code to model the settling of disks that are initially flat, but tilted at some nonzero angle with respect to the equatorial plane of the potential well defined by an underlying, axisymmetric halo. (Due to constraints imposed by available computational resources, only disks with initially thick geometric structures were modeled dynamically; there was insufficient grid resolution to realistically model thin disks.)
		As he was completing his dissertation research, John Woodward took it upon himself to rewrite our 2nd-order-accurate CFD code so that it ran efficiently on the Department of Physics & Astronomy's new, 8K-node SIMD-architecture MasPar MP1 computer. Our 3D, cylindrical-coordinate-based simulations nicely mapped to the MasPar's architecture if we adopted a spatial grid resolution of 64 (in Z) × 128 (in R) — that is, 8K meridional-plane grid zones — by 128 azimuthal zones "stacked in memory."
		A NeXTcube was added to our equipment ranks. Having a built-in RGB-to-NTSC signal converter, the NeXT replaced our Lenco Color Encoder; it also provided a friendly programming environment through which Woodward (and others) was able to completely automate the sequence of steps required to generate a video from a stack of digital images.

© 2014 - 2021 by Joel E. Tohline |   H_Book Home   |   YouTube   | Appendices: | Equations | Variables | References | Ramblings | Images | myphys.lsu | ADS | Recommended citation:   Tohline, Joel E. (2021), The Structure, Stability, & Dynamics of Self-Gravitating Fluids, a (MediaWiki-based) Vistrails.org publication, https://www.vistrails.org/index.php/User:Tohline/citation