I was born in Hutchinson, Kansas, on June 26, 1947, and lived there until I graduated from high school in 1965. I did my undergraduate work at the University of Kansas - Lawrence, graduating in 1969 with a Batchelor of Arts in Mathematics and a Batchelor of Science in Physics. During those four years, I held various undergraduate scholarships (including General Motors and Summerfield), was elected to Phi Beta Kappa in 1968, became a Woodrow Wilson Fellow in 1969, and graduated from the University of Kansas With Highest Distinction and Honors in Physics. I was also voted The Outstanding Senior in Physics that year by the KU physics faculty.
My graduate study was completed at the University of Wisconsin - Madison,
resulting in a Master of Science in Physics and a Doctor of Philosophy
in Physics in 1970 and 1975, respectively. The area of concentration for my
Ph.D. thesis was officially Solid State Theoretical Physics, but in retrospect
a better label would have been Mathematical Physics. I was actively pursuing
research in two fields during that period: (1) electrical conduction problems
in substitutionally disordered metallic alloys (CPA or the coherent potential approximation)
and (2) nonlinear wave
propagation problems (solitons). Although the work on disordered alloys
culminated in a thesis, the most important aspect of this work for my
subsequent career was the strong and very broad background it gave me in techniques for
solving problems involving heterogeneous media. The work on nonlinear p.d.e.'s
introduced me to the inverse scattering methods which had just been discovered
for solving some of the soliton problems and led directly to my continuing
fascination with both inverse problems and nonlinear wave propagation problems.
My first post-doctoral position was held at the Mathematics Research Center,
again at the University of Wisconsin - Madison. During that year, I continued
the work I had initiated during graduate school on nonlinear p.d.e.'s. I was
the first to explain an anomalous diffusion process observed in some plasma
physics experiments at Wisconsin.
The nonlinear diffusion equation I
introduced and the techniques developed (together with my subsequent
collaborators) for analyzing these equations have received a modest amount of
attention from the applied math community.
My next position was Research Physicist at Continental Oil Company
in Ponca City, Oklahoma, from 1976-1977.
Prior to holding this position I had exactly zero experience
with geology and geophysics.
My decision to go to Conoco was based almost entirely on the fact that
Jerry Ware, who interviewed and hired me, had written a paper with K. Aki on inverse problems
for the acoustic wave equation solving the Marchenko equation.
(The Marchenko equation is
closely related to the inverse scattering methods I had been
studying for soliton theory.)
I studied wave propagation problems and inverse problems for sound waves in
the earth during that year.
I wrote an internal report on velocity analysis with special
emphasis on shear waves, since Conoco was developing
shear wave vibrators and recording the first shear wave data sets during
the year I was there.
I also worked on maximum entropy spectral analysis, which provided a rather unusual introduction
to signal processing methods.
I was also working closely with Bob Stolt who is
well-known for his work on seismic inversion problems and wave equation migration. I was first
introduced to Biot's theory of poroelasticity during my stay at Conoco.
I did most of my early work on anisotropy due to fine layering
during this year at Conoco, and got a good start on
my ideas about inverse scattering theory.
I also attended my first SEP meeting during this year as a sponsor(!)
representing Conoco - along with Stolt and Pierre Goupillaud.
This year made a lasting impression on me and I think it is fair to say
that almost all of my subsequent work has been focused on problems
that I learned about during my short stay at Conoco.
My next position was Visiting Member at the Courant Institute
of Mathematical Sciences at New York University and was sponsored by a
National Science Foundation post-doctoral fellowship (1977-78).
During that year, I completed much of the work I
had been pursuing for several years: I finished my work on inverse problems
and the resulting papers (written mostly in collaboration with Rob Greene) are
quite well-known, especially for the fast inversion algorithm we introduced.
I also began a long-term and fruitful collaboration with Charlie Holland on
nonlinear diffusion problems, building on and substantially extending the
work on this subject I had begun at Wisconsin.
My next position was Member of Technical Staff in the Ocean Systems Studies
Center at Bell Telephone Laboratories - Whippany, NJ. During the three years
(1978-81) I held this position, I worked
- for all practical purposes as a mechanical engineer -
on a variety of technological problems
for the U. S. Navy.
My after hours research during this period also produced two major
results: Returning to my background in heterogeneous media, I presented a
fairly complete analysis of methods for estimating both elastic constants and
attenuation for wave propagation through
composite materials.
I also combined these ideas with some additional work on
the problem of a first principles determination of the constants in Biot's
equations for wave propagation in fluid-saturated porous media; the result was
that I was the first to show that the second bulk compressional wave seen in
experiments at Schlumberger (by Tom Plona) was completely consistent with Biot's theory.
During this period, I also spent about two years serving as Associate Editor of
the Journal of Mathematical Physics, while John Klauder was Editor.
The position I held the longest (from July, 1981 to July, 2006) was Physicist at the Lawrence Livermore
National Laboratory, Livermore, CA. From 1981-1985, I resided in the Earth
Sciences Department at LLNL and the majority of my research concerned porous
media. This work can be divided into two parts: wave propagation studies and
fluid flow studies. The studies of wave propagation in porous media have
centered around a major effort to produce a truly comprehensive theory,
capable of treating most of the complications which are met in practice when
the theory is applied to wet geological materials, rocks, soils, etc.
Various
aspects of this work were done in collaboration with Brian Bonner, Ray Chin,
Gerry Hedstrom, and Louis Thigpen, and more recently with
Patricia Berge, David Elata, Vladimir Grechka, Steve Pride, and Herb Wang.
Much of this research
has been funded through a continuing research grant from the Department of
Energy's Office of Basic Energy Sciences. The studies of fluid flow
in porous media began as an attempt to apply variational principles to the
problem of estimating fluid permeability of heterogeneous porous materials
such as rocks, and grew (in collaboration with Steve Blair, and more recently
with Pat Berge as well) into a new capability of estimating
permeability from images of cross sections of rocks.
In 1985, I moved to the
Electronics Engineering Department to lead a group of about 14 scientists and
engineers who work in the general area of Imaging and Remote Sensing Research.
Since most of the research of this group was and still is in collaboration with the personnel in
the Earth Sciences Department and since much of it involves
inverse problems and tomography,
this move was not a very big step from my point of view.
I stayed in the Engineering Department from 1985-1990.
During this period, my research uncovered the idea of feasibility
constraints for nonlinear inversion problems.
This idea is important for practical inversion methods such
as those required for real data in seismic traveltime tomography
and
also for electrical impedance tomography.
Some of the work in fully developing these ideas was completed while I was
on sabbatical at the Courant Institute, New York University, 1987-88,
funded in part by the Air Force Office of Scientific Research.
When I returned from my sabbatical in 1988, the underground imaging group
fused with another EE group, the Signal and Image Processing Research Group.
The resulting mega-group contained 25 scientists and engineers, and
as Leader of this group it occupied all my time for four months.
Since I did not want to become a full-time manager, I asked that the
group be split back into its two components. The result of this fission was
that I became the Leader of the Signal and Image Processing Research Group and Mike Buettner
became the Leader of the Imaging and Remote Sensing Research Group.
This move was also a natural one since I had been working actively
with various members of this group for several years in
developing my work on image processing.
I eventually regretted this decision however, since my personal interests lie more in
underground imaging than in the pure signal and image processing
discipline.
In July of 1990, I gave a series of lectures at MIT/ERL on my research in inverse theory. I have subsequently developed these lectures into a set of lecture notes of which over 400 copies have now been distributed worldwide. (, the notes are now available online.) I am trying to turn the lecture notes into a book, but have not found enough (after hours) time to finish this project yet.
In 1990, I returned to the Earth Sciences Department to lead the Geophysical Imaging and Analysis Group. My two main motivations for this move were to try to build up a more coherent underground imaging capability at Livermore and to allow myself the opportunity to split my own research effort more equally between porous media and inversion. As circumstances developed, I actually spent most of my time for the next seven years working on porous media and composite materials. Inverse theory was on the back burner.
During the period (1990-1998), I explored the possibilities of
computing coefficients in Biot's equations for more realistic
rock models including the possibility of multiple solid
constituents. Together with Graeme Milton, I discovered
that there exist a few exact results in this theory when there are
only two or three solid constituents present.
I must say that I
was quite surprised and excited by these results, since I never expected to
find such simple exact results for any class of inhomogeneous materials.
During this period, Pat Berge and I also discovered that it was possible to
make sense of the range of applicability of various common choices of
approximate effective medium theories.
In the general area of inverse theory,
I have been studying issues of resolution in inverse problems.
I also pursued other issues related to underground imaging
during my 1995-1996 sabbatical at Stanford.
A grant from the Air Force Office of Scientific Research permitted me
to do some collaborative work on inverse problems with Professor George Papanicolaou
and Liliana Borcea
in the Mathematics Department at Stanford that year.
We finished one paper in the area of electrical impedance tomography in May, 1996.
We continued this work and wrote another paper in the same area;
both papers subsequently were published in Inverse Problems.
Graeme Milton (Utah) and I completed a very interesting paper on
extending Hashin-Shtrikman bounds for two-phase composites
in three-dimensions to
bulk and shear moduli for viscoelastic (materials with complex
moduli) composites.
This paper came out in the Proceedings of the Royal Society of London A
in October, 1997.
A two-dimensional (anisotropic) version of this work was completed
in collaboration with Leonid Gibiansky. That paper was published in the same
journal in the summer of 2000.
Steve Pride (LBL) and I have written two papers on the application
of volume averaging techniques to derivation of poroelastic equations.
One paper
has been published by Journal of the Mechanics and Physics of
Solids, and the other has been published
in the special issue on poroelasticity of International Journal of
Solids and Structures.
Other papers have been written and published in various
geophysics, acoustics, and physics journals in the 2000-2005 time frame.
In November, 2003, I gave a series of lectures over the course of two days on the topic of Poroelasticity at the University of Petroleum, Beijing, China. This lecture series was part of the celebration surrounding the 50th anniversary of the founding of this University.
I have recently changed jobs (July, 2006), and am now a Senior Staff Scientist at the Lawrence Berkeley National Lab in Berkeley, CA. I currently serve as the Head of the Geophysics Department in the Earth Sciences Division.
My five most cited publications are these.
In summary, I continue to do research in wave propagation and fluid flow in porous media, but I am also involved in development of new field methods for remote sensing and in construction of new algorithms for solving related inverse problems. One current emphasis in the area of inverse problems is in electrical and electromagnetic inversion of field data for environmental applications. Another arising in the past few years has been time-reversal imaging and characterization of multiple targets, several of these papers being in collaboration with David Chambers (LLNL). Current interests also include anisotropy, image processing of rock cross sections, spectral analysis, and novel applications of effective medium theories. I am also in the process of publishing a series of papers on the concept of the ``random polycrystals of laminates'' model that I believe will eventually prove to be a very useful tool for studying a variety of different and difficult subjects in both heterogeneous and porous media. I believe this method will also be very useful for benchmarking computer codes, as the results provide both estimates and rigorous bounds on the effective constants.
I had the honor of receiving the third Maurice Anthony Biot Medal for work in the field of mechanics of porous materials given by the American Society of Civil Engineers during the Third Biot Poromechanics Conference in Norman, Oklahoma, May 25, 2005.
I am a member of the American Physical Society, the American Geophysical Union, The Acoustical Society of America, and the Society of Exploration Geophysicists.
And that concludes this summary of my career to date.
