User:Tohline
Joel E. Tohline
A Fellow of the AAAS, Tohline has authored approximately one hundred articles in scientific journals and proceedings, primarily on problems related to complex fluid flows in astrophysical settings. His expertise in utilizing high-performance computers to accurately simulate the processes by which stars form and to simulate catastrophic events that will give rise to bursts of gravitational radiation is recognized worldwide. Fifteen students have completed their doctoral dissertation research under his direction (an additional four under his co-direction) and, over the years, he has been a lead investigator on federal and state research or research-infrastructure grants totaling more than ten million dollars.
Tohline earned a B.S. in Physics from Centenary College of Louisiana in 1974 and a Ph.D. in Astronomy from the University of California, Santa Cruz in 1978. Before joining the LSU faculty in 1982, Tohline held a J. Willard Gibbs Instructorship in the Astronomy Department at Yale University and a postdoctoral fellowship at Los Alamos National Laboratory. He has served as a member of the Advisory Council for the Directorate of Mathematical & Physical Sciences of the U.S. National Science Foundation (NSF), as Chair of the Committee of Visitors for the NSF Astronomy Division, as co-editor of the Vizualization Corner for Computing in Science and Engineering (a magazine published jointly by the American Institute of Physics and the IEEE Computer Society), as a member of the Applications Strategy Council of Internet2, on the Program Advisory Council of LIGO, as Chairman of LSU's Department of Physics & Astronomy, and as Director of LSU's Center for Computation & Technology.
Retired at the end of the 2013 calendar year — after more than thirty-one years of service at Louisiana State University (LSU) — Tohline retains the titles of Director Emeritus of LSU's Center for Computation & Technology as well as Professor Emeritus in LSU's Department of Physics & Astronomy. In retirement, he remains active in research. Two, quite expansive, ongoing efforts are briefly outlined in the paragraphs immediately following this biosketch. In the context of these two broadly defined research efforts, he has identified a number of well-defined theoretical or computational research projects that seem especially ripe for development at the present time. Some of these projects are listed below — each project title serving as a hypertext link to more descriptive, accompanying online material.
Major Ongoing Effort #1: Online Textbook (under continual development)
The Structure, Stability and Dynamics of Self-Gravitating Fluids
- Preface: Much of our present, basic understanding of the structure, stability, and dynamical evolution of individual stars, short-period binary star systems, and the gaseous disks that are associated with numerous types of stellar systems (including galaxies) is derived from an examination of the behavior of a specific set of coupled, partial differential equations. These equations — most of which also are heavily utilized in studies of continuum flows in terrestrial environments — are thought to govern the underlying physics of all macroscopic "fluid" systems in astronomy. Although relatively simple in form, they prove to be very rich in nature... <more>
Major Ongoing Effort #2: VisTrails Utilization
A brief accounting of my earliest experiences with VisTrails can be found on the page, titled Learning How to Use VisTrails, on my LSU website. While on sabbatical leave at the SCI Institute during the 2010 Spring semester, I became much more proficient in my use of this very versatile scientific visualization tool. Here are some examples:
- A Customized Python Module for CFD Flow Analysis within VisTrails
- Visualizing a Journal that can serve the Computational Sciences Community
- January 2014: As I methodically march through various vtk (Visualization Took Kit) tools in an effort to gain a much better understanding of their capabilities, I will be documenting progress here.
- Tutorial developed by Tohline: Simple Cube
- Tutorial developed by Tohline: XY Plots
- Tutorial developed by Tohline: Generating Spheroids, Ellipsoids, and Quadrics 🎦
- Assembling an Animation (🎦) on my Mac — NOTE: You can view an animated GIF's frames in Preview on the Mac
- ZebraImaging and Southwestern Medical Center
- Riemann Meets COLLADA & Oculus Rift S
Suggested Doctoral Dissertation-Level Research Projects
Over the years — dating back to my time as a J. Willard Gibbs Instructor at Yale University (1978 - 1980) and throughout my academic career at LSU (see an accompanying list) — I have helped more than twenty physics and/or astronomy graduate students identify a suitable topic for their doctoral dissertation research. Although, in retirement, I am no longer formally advising doctoral students, I continue to recognize dissertation-level research projects that are ripe for investigation. Here are brief descriptions of a number of such projects. As time goes along, I expect to add chapters to my online H_Book that will supply each of these projects with a more substantive background foundation. I would be happy to hand each of these projects off to an appropriately qualified graduate student who expresses sufficient interest in tackling the project in depth.
Constructing Compressible Analogs of Riemann Ellipsoids
We have known, for well over 100 years, that rapidly rotating, ellipsoidal-shaped equilibrium configurations can be constructed with a variety of different internal fluid velocity profiles — giving rise to Jacobi, Dedekind, or Riemann ellipsoids — if the fluid configuration has uniform density and is incompressible. Computational fluid-dynamic (CFD) simulations have demonstrated that dynamically stable compressible analogs of Riemann ellipsoids can be constructed, under certain conditions. The objective here is to develop a numerical technique, akin to the Hachisu self-consistent field (HSCF) technique, by which a wide range of such equilibrium configurations can be constructed a priori, without relying on CFD techniques.
- Shangli Ou developed an HSCF-type technique that successfully constructs approximate equilibrium configurations that are analogs of Riemann ellipsoids
- Some thoughts regarding how a more satisfactory velocity flow-field might be incorporated into Ou's technique in order to achieve this project objective
- Apart from my astronomy colleagues at LSU, I have had especially useful discussions of this project with Eric Hirschmann (BYU), David Neilsen (BYU), Shawn W. Walker (2007) (LSU Mathematics & CCT), and Ricardo H. Nochetto (U. Maryland, Mathematics)
- Relevant to …
Globular Cluster Formation During Galaxy-Galaxy Collisions
The manuscript presented immediately below presents an hypothesis regarding globular cluster formation that came to me as a EUREKA! moment one day (in the mid-to-late 1990s) while I was attending a Physics & Astronomy departmental colloquium at LSU. The colloquium speaker was, as I recall, someone from U. C. Berkeley with experimental space sciences expertise; and the topic of the colloquium was Galactic cosmic rays … <more>
As a matter of course during his presentation, the colloquium speaker reminded the audience — and me, in particular — that, in our Galaxy, the dense, cold "protostellar" cores of molecular clouds are coupled to the interstellar magnetic field (only) because the gas is partially ionized by Galactic cosmic rays. Furthermore, the Galaxy's charged-particle cosmic-ray flux is highest near the mid-plane of the Galaxy's disk because the cosmic rays are trapped by the disk's relatively ordered, large-scale interstellar magnetic field. All of a sudden, it occurred to me that, if our Galaxy were to collide with another galaxy …
- Its disk and, along with it, the interstellar magnetic field would very likely become much less organized;
- Cosmic rays would no longer be well confined to the disk and — as a consequence of streaming out of the disk at relativistic speeds — the flux of cosmic rays would fairly rapidly drop within the Galaxy's molecular clouds;
- The dense, protostellar cores of molecular clouds would fairly rapidly decouple from the magnetic field because the cores would no longer be sufficiently ionized.
EUREKA! This would create an environment highly conducive to rapid star formation, perhaps throughout an entire giant molecular cloud (GMC) complex. This would trigger a rapid burst of star formation and, perhaps, a transformation of the GMC into a massive, bound star cluster. It is this idea and accompanying reasoning that is fleshed out in the paper that I wrote in 2000 (while on sabbatical leave at Caltech) in collaboration with Nick Scoville and Andrew Strong:
- Original manuscript (submitted to The Astrophysical Journal in June, 2000): J. E. Tohline, N. Z. Scoville, & A. W. Strong (2000)
This paper was never published because the journal referee (see accompanying material) requested a more extensive demonstration of the proposed model's viability, which I considered to be well beyond the scope and essential purpose of this paper. I remain firmly convinced that the idea has a great deal of merit. I offer this original manuscript as a foundation on which an appropriately qualified graduate student might build a more extensive demonstration of the viability of this proposed mechanism for globular cluster formation.
Other Less Challenging or Less Well-Defined Research Projects
Stability of Bipolytropic Configurations
Using primarily analytic techniques, our objective is to evaluate the free energy of spherically symmetric, bipolytropic configurations (aka composite polytropes), then, use variations in the free energy function to identify equilibrium states (scalar virial theorem) and to assess the relative dynamical stability of the states.
- Early discussions with LSU graduate student, Kundan Kadam; see also construction of <math>~(n_c, n_e) = (0, 0)</math> bipolytrope
- Outline of Work Completed, to Date, on the free energy of pressure-truncated polytropes
- Relevant to …
| Schönberg-Chandrasekhar Mass | |
| Stellar Evolution from Main Sequence to Red Giant | |
| Bonnor-Ebert Spheres | |
| Origin of Planetary Nebulae | |
Gravitational-Wave Signals from Core-Collapse Supernovae
To date, gravitational radiation has not been directly detected by any scientific instrument on Earth. The advancement of detector techniques in association with the development of new observatories worldwide — such as LIGO and VIRGO — promises to change this situation in the near future. When gravitational-wave signals are detected from core-collapse supernovae, the expectation is that these signals — primarily tracing out wave amplitude as a function of time — will exhibit a great deal of structure, reflecting several different phases of the collapse. We propose to construct a semi-analytic signal template to help the gravitational-wave community more fully understand the underlying physics that is fundamentally responsible for generating the (anticipated) signal's characteristic features.
| Gravitational Free-Fall Collapse | |
| Homologous Collapse of Stellar Cores (Goldreich & Weber 1980) | |
Musings Regarding Dark Matter and Dark Energy
[Joel E. Tohline recollection on 3/8/2015] It was during my first year (July 1978 – June 1979) as a J. Willard Gibbs Instructor in the Astronomy Department at Yale University that I started wondering whether the nearly ubiquitous display of “flat rotation curves” in disk galaxies might be explained, not via the dark matter hypothesis, but by invoking a 1/r force-law for gravity at large distances. My reasoning was simple:
- I was uncomfortable with the “dark matter” hypothesis, which smelled to me like the story of ether, all over again.
- If Isaac Newton had been handed Vera Rubin’s observations — which showed that orbital velocities were approximately constant with distance — instead of Kepler's observations — which showed that orbital velocities behaved as <math>~v \propto r^{-1/2}</math> — he likely would have hypothesized that the gravitational acceleration due to a central point mass is proportional to <math>~r^{-1}</math> instead of <math>~r^{-2}</math>.
While I put quite a lot of thought into this idea in the late '70s and early '80s — and I still give it some thought from time to time because I consider the astrophysics community's fundamental understanding of "dark matter" and now, too, "dark energy" to be weak — I produced only two publications on the topic, neither of which was in a refereed archival journal:
- Stabilizing a Cold Disk with a 1/r Force Law
- Does Gravity Exhibit a 1/r Force on the Scale of Galaxies?
From time to time, I plan to post here some of the research notes that I have generated on this topic over the years, as well as recollections of discussions of the topic that I have had with professional colleagues. I begin by posting a scanned copy of one of my most cherished possessions from my time at Yale.
- Notes from Beatrice Tinsley showing that she, too, had given some thought to the implications of a 1/r force-law for gravity in 1978.
- Attraction associated with a uniform-density sphere — my derivation in the early '80s, with the kind assistance of LSU Professor Attipat K. Rajagopal.
Challenges to Young, Applied Mathematicians
Note from J. E. Tohline to Students with Good Mathematical Skills: The astronomy community's understanding of the Structure, Stability, and Dynamics of stars and galaxies would be strengthened if we had, in hand, closed-form analytic solutions to the following well-defined mathematical problems. (Solutions can be obtained numerically with relative ease, but here the challenge is to find a closed-form analytic solution.) As is true with most meaningful scientific research projects, it is not at all clear whether each of these problems has a solution. In my judgment, however, it seems plausible that a closed-form solution can be discovered in each case and such a solution would be of sufficient interest to the astronomical community that it would likely be publishable in a professional astronomy or physics journal. At the very least, each of these projects represents an opportunity for a graduate student, an undergraduate, or even a talented high-school student (perhaps in connection with a mathematics science fair project?) to hone her/his research skills in applied mathematics. Also, I would be thrilled to include a solution to any one of these problems — along with full credit to the solution's author — as a chapter in this online H_Book. Having retired from LSU, I am not in a position to financially support or formally advise students who are in pursuit of a higher-education degree. I would nevertheless be interested in sharing my expertise — and, perhaps, developing a collaborative relationship — with individuals who are interested in pursuing answers to the questions posed by this identified set of problems.
Useful Links
- MediaWiki; Images and ImageMaps; Math; Interwiki Links
- Wiki Editing (Formatting Cheatsheet)
- To set a redirect: #REDIRECT [[User:Tohline/page]]
- To set internal link: [[User:Tohline/page | text]]
- Wiki Markup; MediaWiki CSS Style Sheet and Example
- LaTeX examples; A comprehensive LaTeX symbol list
- Character Entities; HTML Character Entities; MathSymbols
- templates
- vtk READER file formats
- NIST Digital Library of Mathematical Functions; see also the related CUP Publication
- Displaying a Formula in WikiMedia
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© 2014 - 2021 by Joel E. Tohline |