47 - Nov 20 thru Nov 26 2000, Vol X
 
The
Structure, Stability, and Dynamics
of Self-Graviting Systems
Prof. Salem
Al-AbdelRahman
The purpose of Joel Tohline’s on-line textbook, “The Structure, Stability,
and Dynamics of Self-Graviting Systems,” is twofold. The textbook aims
“to document in an electronically accessible format many of the key physical
principles that underlie modern discussions of the structure, stability,
and dynamic evolution of astrophysical fluid systems.” The second purpose
is “to take advantage of the added dimensions offered by the hypertext
medium - particularly color, animation, and text linkage - to effectively
illustrate many of these physical principles”.
Tohline, professor of physics at Louisiana State University and a member
of CIP’s Advisory Committee, is a thorough believer in the superiority
of hypertext and multimedia materials over conventional printed matter
for teaching science and presenting scientific research. His textbook,
which is currently under development, maybe found at http://www.phys.lsu.edu/astro/H_Book.current/H_Book.shtml.
According to Tohline, hypermedia documents are particularly valuable
in presenting scientific results that involve visualization. It seems illogical
to reduce a computer-generated animation sequence to a still image (or
even a set of still images) for publication, when the animation itself
could be distributed electronically over the Internet. Tohline cites his
work on computational-fluid-dynamics (CFD) simulations using a heterogeneous
computing environment as an instance in which hypermedia should be used
to present a visualization that is an integral part of a simulation experiment.
The heterogeneous environment couples a massively parallel Cray T3E super
computer with an SGI workstation in order to animate the CFD results. Tohline’s
research group has developed an efficient CDF algorithm, but to make the
results understandable, they must be visualized.
Accordingly, the Cray super computer pauses at intervals and dumps
out a data set that the SGI renders as an image. This image is stored as
on animation frame. Eight hours’ worth of commutation on the Cray yields
around 30 frames of an animation that may eventually contain up to 2000
frames. The animation is produced as a natural by-product of the simulation.
An animation of this sort is best presented in the form in which it was
originally created, rather than through the artificial and information
-squandering process of reducing it to a still image. “When we are doing
a large-scale numerical simulation,” Tohline says, “it is difficult to
put the results down on the printed page. Look at any page [in a magazine
like CIP] and you’ll see, for example, a color figure that is one frame
out of an animation sequence. It took the authors more effort to make the
figure than it did to make the animation, and the printed journal cannot
show the animation!” For this reason, Tohline believes that hypermedia
will ultimately supplant print as the preferred form for printing scientific
research.
With his online text-book, Tohline hopes to participate in and suggest
the future directions of this process. “A printed journal is just a small
subset of the kind of information that most scientists would like to make
available on a regular basis.” Tohline says. “We shouldn’t abandon the
printed page, but I believe that the printed page will be like a readers’
digest, with short excerpts of what is available on-line.
Visitors to Tohline’s Web site will find animations in plenty, presented
as Java applets, MPEG movies, VRML simulation, and visualizations of data
generated by Mathematics. These animations are integrated into the presentation
of the course material but are also offered to the visitor independently,
with the invitation to “Try a Java (or movie, VRML, or mathematical, or
HSCF [hachisu Self-Consistent-Field Technique]) example!” Tables show which
sections of the textbook are accompanied by animations, which are not,
and which areas of the text are still being written.
Tohline wrote some of the animation programs himself and has involved
students in writing others. (Peter Nelson, an LSU undergraduate, has been
instrumental in helping Tohline to manage the layout of the textbook at
it has grown in size). Visitors to the site can also read brief explanations
of the principal partial-differential equations that govern self-gravitating
systems, with variables and constants in the equations hyperlinked to their
definitions in a glossary. Students can test their understanding by doing
sample problems and check their work by exploring the hyperlinked answers.
The open-endedness of hyper-media documents and the collaborative possibilities
they invite are among their most important advantages of on-line publication
for Tohline. In a recent semester he taught a course using the on-line
text-book, in which he would assign students specific projects in areas
not yet covered in the text. These projects involved designing small problems,
writing chapters in HTML that presented the solutions, and putting the
work on-line for viewing by other students. These assignments opened up
the possibility of including the students’ chapters in the text and crediting
the students for their work.
Likewise, according to Tohline, experts in particular fields could
contribute hypertext chapters in what has the potential to become far more
of a collaborative than an individual project. The ability to update hyper-media
documents continually and convenient multi-author collaboration imply the
possibility of creating a text-book that resists becoming obsolete.
Tohline hopes to be ready by the end of December to advertise his text-book’s
existence to the astrophysics community, along with an invitation to others
to participate in the book’s evolution.
“The material is sufficiently complete that it could appear in a book,
though it never will,” Tohlin says. “Virtually everyone who sees what I
am doing asks when I will publish it [in print], but there are many features
that would be lost if I did.”
In Tohline’s view, hypermedia and not print is the best form in which
his work can appear: “I strongly feel that this will be the medium of all
scholarly publication, not just that aimed at students.”
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