Difference between revisions of "User:Tohline"

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* [[User:Tohline/DarkMatter/UniformSphere|Attraction associated with a uniform-density sphere]] — my derivation in the early '80s, with the kind assistance of LSU Professor Attipat K. Rajagopal.
* [[User:Tohline/DarkMatter/UniformSphere|Attraction associated with a uniform-density sphere]] — my derivation in the early '80s, with the kind assistance of LSU Professor Attipat K. Rajagopal.
* [[User:Tohline/DarkMatter/CK2015|Remarks on Christodoulou & Kazanas (2015)]]




Revision as of 21:46, 8 October 2015

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.

| Tohline's LSU Homepage | Resume ]


 
 
 

Major Ongoing Effort #1: Online Textbook (under continual development)

HBook title Fluids.png

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:

  1. A Customized Python Module for CFD Flow Analysis within VisTrails
  2. Visualizing a Journal that can serve the Computational Sciences Community
  3. 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.
  4. Tutorial developed by Tohline: Simple Cube
  5. Tutorial developed by Tohline: XY Plots
  6. Tutorial developed by Tohline: Generating Spheroids, Ellipsoids, and Quadrics   🎦
  7. Assembling an Animation (🎦) on my Mac


 
 
 

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.

    Schönberg-Chandrasekhar Mass
    Stellar Evolution from Main Sequence to Red Giant
    Bonnor-Ebert Spheres
    Origin of Planetary Nebulae
 

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. Our desire 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 Walker (LSU Mathematics & CCT), and Ricardo H. Nochetto (U. Maryland, Mathematics)
  • Relevant to …
    The fission hypothesis for binary star formation
    Fission-related CFD simulations conducted at LSU
    Fission of liquid drops in spacelab experiments
 

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:

  1. I was uncomfortable with the “dark matter” hypothesis, which smelled to me like the story of ether, all over again.
  2. 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:

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.



 
 
 

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

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