J. Patrick Reilly died on October 28 in Silver Spring, Maryland, at the age of 87. He was a leader in the field of bioelectricity, and especially the study of electrical stimulation.
Reilly was also known for his 1998 book Applied Bioelectricity: From Electrical Stimulation to Electropathology, which covered many of the same topics as Chapters 6–8 in IPMB: The Hodgkin-Huxley model of a nerve action potential, the electrical properties of cardiac tissue, the strength-duration curve, the electrocardiogram, and magnetic stimulation. However, you can tell that Russ and I are physicists while Reilly is an engineer. Applied Bioelectricity focuses less on deriving equations from fundamental principles and providing insights using toy models, and more on predicting stimulus thresholds, analyzing stimulus wave forms, examining electrode types, and assessing electrical injuries. That’s probably why he included the word “Applied” in his title. Compared to IPMB, Applied Bioelectricity has no homework problems, fewer equations, a similar number of figures, more references, and way more tables.
Reilly’s preface begins
The use of electrical devices is pervasive in modern society. The same electrical forces that run our air conditioners, lighting, communications, computers, and myriad other devices are also capable of interacting with biological systems, including the human body. The biological effects of electrical forces can be beneficial, as with medical diagnostic devices or biomedical implants, or can be detrimental, as with chance exposures that we typically call electric shock. Whether our interest is in intended or accidental exposure, it is important to understand the range of potential biological reactions to electrical stimulation.
I don’t recall meeting Reilly, which is a bit surprising given the overlap in our research areas. I certainly have been aware of his work for a long time. He was a skilled musician as well as an engineer. I would like to get a hold of his book Snake Music: A Detroit Memoir. It sounds like he had a difficult childhood, and there were many obstacles he had to overcome to make himself into a leading expert in bioelectricity. Thank goodness he persevered. J. Patrick Reilly, we’ll miss ya.
Figure 16.25 shows the evolution of the detector and
source configurations [of CT]. The third generation configuration is
the most popular. All of the electrical connections are made
through slip rings. This allows continuous rotation of the
gantry and scanning in a spiral as the patient moves through
the machine. Interpolation in the direction of the axis of rotation
(the z axis) is used to perform the reconstruction for a
particular value of z. This is called spiral CT or helical CT.
Kalender (2011) discusses the physical performance of CT
machines, particularly the various forms of spiral machines.
Kalender obtained his PhD in 1979 from the University of Wisconsin’s famous medical physics program. He then went to the University of Tübingen in Germany. There, according to Wikipedia, “he took and successfully completed all courses in the pre-clinical medicine curriculum.” This is interesting, because just a few years earlier Russ Hobbie did the same thing in Minnesota.
Between 1971 and 1973 I audited all the courses medical students take in their first 2 years at the University of Minnesota. I was amazed at the amount of physics I found in these courses and how little of it is discussed in the general physics course.
With deep sadness, the ESR announces the passing of Prof. Willi Kalender on October 20, 2024 at the age of 75. A pioneering figure in diagnostic imaging and medical physics, Prof. Kalender significantly influenced the field through his groundbreaking research and leadership.
Redish, E. F., “Using Math in Physics: 7. Telling the Story,” Phys. Teach., 62: 5–11, 2024.
I knew Joe, and valued his friendship. Rather than writing about him myself, I’ll share some of his thoughts in his own words. He had a wonderful series of papers in The Physics Teacherabout using math in physics. The last of the series (published this year) was about using math to tell a story (Redish, E. F., “Using Math in Physics: 7. Telling the Story,” Phys. Teach., Volume 62, Pages 5–11, 2024). He wrote
Even if students can make the blend—interpret physics
correctly in mathematical symbology and graphs—they still
need to be able to apply that knowledge in productive and
coherent ways. As instructors, we can show our solutions to
complex problems in class. We can give complex problems to
students as homework. But our students are likely to still have
trouble because they are missing a key element of making
sense of how we think about physics: How to tell the story of
what’s happening.
We use math in physics differently than it’s used in math
classes. In math classes, students manipulate equations with
abstract symbols that usually have no physical meaning. In
physics, we blend conceptual physics knowledge with
mathematical symbology. This changes the way that we use
math and what we can do with it.
We use these blended mental structures to create stories about
what’s happening (mechanism) and stabilize them with
fundamental physical laws (synthesis).
One of the problems that students run into, that teachers of physics run into teaching biology students, is we use all these trivial toy models, right? Frictionless vacuum. Ignore air resistance. Treat it as a point mass. And the biology students come in and they look at this and they say, “These are not relevant. This is not the real world.” And they know in biology, that if you simplify a system, it dies. You can’t do that. In physics we do this all the time. Simple models are kind of a core epistemological resource for us. You find the simplest example you possibly can and you beat it to death. It illustrates the principle. Then you see how the mathematics goes with the physics. The whole issue of finding simple models is where a lot of the creative art is in physics.
From our extended conversations, both with each other and
with other biologists, chemists, and physicists, we conclude
that, “science is not just science.” Scientists in each discipline
employ a tool kit of different types of scientific reasoning.
A particular discipline is not characterized by the exclusive
use of a set of particular reasoning types, but each discipline
is characterized by the tendency to emphasize some types
more than others and to value different kinds of knowledge
differently. The physicist’s enthusiasm for characterizing an
object as a disembodied point mass can make a biologist uncomfortable, because biologists find in biology that function
is directly related to structure. Yet similar sorts of simplified
structures can be very powerful in some biological analyses.
The enthusiasm that some biologists feel toward our students learning physics is based not so much on the potential
for students to learn physics knowledge, but rather on the
potential for them to learn the types of reasoning more often
experienced in physics classes. They do not want their students to think like physicists. They want them to think like
biologists who have access to many of the tools and skills
physicists introduce in introductory physics classes…
We conclude that the process is significantly more complex
than many reformers working largely within their discipline
often assume. But the process of learning each other’s ropes—at least to the extent that we can understand each other’s
goals and ask each other challenging questions—can be both
enlightening and enjoyable. And much to our surprise, we
each feel that we have developed a deeper understanding of
our own discipline as a result of our discussions.
You can listen to Joe talk about physics education research on the Physics Alive podcast.
First and foremost, Bill was an exceptional scientist. He pioneered the biochemical investigation of calcium and sodium ion channels; molecular portals that allow the controlled passage of ions across cell membranes. The proper passage of ions into the cell is essential for healthy brain, heart, and muscle function. Early work from Catterall elucidated the molecular basis of ion channel gating whereas later studies with UW Pharmacology colleague Dr. Ning Zheng revealed details of how these clinically relevant macromolecular machines operate at the atomic level. With this latter information, Catterall was able to ascertain how a variety of toxins as well as local anesthetics and antiarrhythmic drugs act to “lock the gate” on these ion channels. Bill was recognized for these pivotal discoveries by election to the National Academy of Sciences USA and the Royal Society London. He also received prestigious awards including the Gairdner Award from Canada, the Robert R. Ruffolo Career Achievement Award in Pharmacology from the American Society of Pharmacology and Therapeutics, and a Lifetime Achievement Award from the International Union of Pharmacologists.
To learn more, listen to Catterall discuss his work in a three-part series of lectures for iBiology.
William Catterall (U. Washington) Part 1: Electrical Signaling: Life in the Fast Lane
I will give Kabat the final word, quoting the last paragraph of his article.
In early October 2020, Bob’s daughter Margaret called me to tell me that Bob had died. I looked for an obituary in the New York Times, and was shocked when none appeared, likely due to the increased deaths from the pandemic. I wrote to an epidemiologist colleague and friend, who knew Bob’s work on ELF-EMF [extremely low frequency electromagnetic fields] and microwave energy, and who had served on a committee to assess possible health effects of the Pave Paws radar array on Cape Cod. My friend Bob Tarone wrote back, “Very sad to hear that. Adair was not directly involved in the Pave Paws study, but we relied heavily on his superb published papers on the biological effects of radio-frequency energy in our report. He and his wife were superb scientists. Losing too many who don’t seem to have competent replacements. Too bad honesty and truth are in such short supply in science today.” He concurred that there should have been an obituary in the Times.
I just learned that my friend Craig Henriquez passed away last summer. Craig earned his PhD at Duke University in their Department of Biomedical Engineering under the guidance of the renowned bioelectricity expert Robert Plonsey. His 1988 dissertation, titled “Structure and Volume Conductor Effects on Propagation in Cardiac Tissue,” was closely related to work I was doing at that time. Craig sent me a copy of his dissertation after he graduated. I really wanted to read it, but I was swamped with my my new job at the National Institutes of Health and helping care for my newborn daughter Stephanie. There wasn’t time to read it at work, and when I got home it was my turn to watch the baby, as my wife had been with her all day. The solution was to read Craig’s dissertation out loud to Stephanie as she crawled around in her play pen. She seemed to like the attention and I got to learn about Craig’s work.
Craig and I are nearly the same age. He was born in 1959 and I in 1960. Our careers progressed along parallel lines. After he graduated he stayed at Duke and joined the faculty. I recall he told me at the time that he didn’t know if he would make a career in academia, but he certainly did. He was on the Duke faculty for 35 years. In the early 1990s three young researchers at Duke—Craig, Natalia Trayanova, and Wanda Krassowska—were all from my generation. They were my friends, collaborators, and sometimes competitors as we worked to establish the bidomain model as the state-of-the-art representation of the electrical properties of cardiac tissue.
Roth’s calculation was not the first attempt to solve the active
bidomain model using a numerical method. In 1984, Barr and Plonsey
had developed a preliminary algorithm to calculate action potential
propagation in a sheet of cardiac tissue. Simultaneous with Roth’s
work, Henriquez and Plonsey were examining propagation in a perfused
strand of cardiac tissue. For the next several years,
Henriquez continued to improve bidomain computational methods
with his collaborators and students at Duke. His 1993 article published
in Critical Reviews of Biomedical Engineering remains the definitive
summary of the bidomain model.
Craig and I were both interested in determining if Madison Spach’s electrical potential data from cardiac tissue samples should be interpreted as evidence of discontinuous propagation (Spach’s hypothesis) or a bath effect.
The original calculations of action potential propagation in a continuous
bidomain strand perfused by a bath hinted at different
interpretations of Spach’s data. As discussed earlier, the wave front is
not one-dimensional because its profile varies with depth below the
strand surface. The same effect occurs during propagation
through a perfused planar slab, more closely resembling Spach’s experiment.
The conductivity of the bath is higher than the conductivity
of the interstitial space, so the wave front propagates ahead on the surface
of the tissue and drags along the wave front deeper below the surface,
resulting in a curved front. The extra electrotonic load
experienced at the surface slows the rate of rise and the time constant
of the action potential foot. Plonsey, Henriquez, and
Trayanova analyzed this effect, and subsequently so did Henriquez
and his collaborators and Roth.
Craig became an associate editor of the IEEE Transactions on Biomedical Engineering, and he would often send me papers to review. He was a big college basketball fan. We would email each other around March, when our alma maters—my Kansas Jayhawks and his Duke Blue Devils—would face off in the NCAA tournament. His research interests turned to nerves and the brain, and he co-directed a Center of Neuroengineering at Duke. He eventually chaired Duke’s biomedical engineering department, and at the time of his death he was an Associate Vice Provost.
I found out about Craig’s death when I was submitting a paper to a journal. This publication asks authors to suggest potential reviewers, and I was about to put Craig’s name down as a person who would give an honest and constructive assessment. I googled him to get his current email address, and discovered the horrible news. What a pity. I will miss him.
Short bio published in the IEEE Transactions on Biomedical Engineering in January, 1990.
Craig Henriquez talking about cardiac tissue and the bidomain model.
My friend and collaborator Paul Maccabee died on July 24. Paul was a pioneer in the field of magnetic stimulation, a topic that Russ Hobbie and I discuss in Chapter 8 of Intermediate Physics for Medicine and Biology. Paul’s career and mine had many parallels. We both worked on magnetic stimulation in the late 1980s and early 1990s. We both collaborated with a leading neurophysiologist: Paul with Vahe Ammasian and me with Mark Hallett. We both recognized the importance of laboratory animal experiments for identifying physiological mechanisms. We both were comfortable working with biomedical engineers, I entered that field from physics and Paul from medicine.
Paul was about 15 years older than me and I viewed him as a role model. I believe I first met him at the 1989 International Motor Evoked Potential Symposium in Chicago, a key early conference dedicated to magnetic stimulation. Our paths crossed at other scientific meetings and his research had a major impact on my own. For years I taught a graduate class on bioelectricity at Oakland University and I had my students read Paul’s 1993 Journal of Physiology paper (described below) which I assigned because it’s a classic example of a well-written scientific article. According to Google Scholar that paper has been cited 374 times, and it should be cited even more.
Although this experiment [performed by Jan Nilsson and Marcela Panizza at the National Institutes of Health, see reference 49] confirmed [Peter Basser and my] prediction [that neural excitation occurs where the gradient of the induced electric field is largest, see reference 58],
there were nevertheless concerns because of the heterogeneous
nature of the bones and muscles in the human
arm. At about the same time Nilsson and Panizza were
doing their experiment at NIH, Paul Maccabee was performing
an even better experiment at the New York Downstate Medical Center in Brooklyn. Maccabee obtained his
MD from Boston University and collaborated in Brooklyn
with the internationally acclaimed neuroscientist Vahe Ammasian [1, 40–43]. This research culminated in their
1993 article in the Journal of Physiology, in which they
examined magnetic stimulation of a peripheral nerve lying
in a saline bath [44]. First, they measured the electric field
Ey (they assumed the nerve would lie above the coil along
the y-axis) and its derivative along the nerve produced
by a figure-8 coil located under the bath (Figure 9). They
found that the electric field was maximum directly under
the center of the coil, but the magnitude of the gradient
dEy/dy was maximum a couple centimeters either side of
the center.
Figure 9. Contour plots of the electric field (Ey, red) and its spatial derivative (dEy/dy, blue) induced by a figure-eight coil (purple) placed under a tank filled with saline and measured using a bipolar recording electrode. The y direction is downward in the figure, parallel to the direction of the nerve (see Figure 10). Adapted from Figure 2 of Maccabee et al. [44].
Next they placed a bullfrog sciatic nerve in the dish and
recorded the electrical response from one end (Figure 10).
They found a 0.9 ms delay between the recorded action
potentials when the polarity of a magnetic stimulus was
reversed (the yellow and red traces on the right). Given a
propagation speed of about 40 m/s, the shift in excitation
position was about 3.6 cm, consistent with what Basser and
I would predict.
Figure 10. Recordings from an electrode (black dot) at the distal
end of a bullfrog sciatic nerve (green) that was immersed in a
trough filled with saline (blue) and stimulated with a figure-8
coil (purple). The nerve emerged from the saline to rest on the
recording electrode in air. The compound nerve action potentials
were elicited by a stimulus of one polarity (orange), then the other
(red). Adapted from Figure 3 of Maccabee et al. [44].
So far, their study was similar to what we performed
at NIH in a human, but then they did an experiment that
we could not do. To determine how a heterogeneity would
impact their results, they placed two insulating cylinders
on either side of the nerve (Figure 11). These cylinders
modified the electric field, moving the negative and positive
peaks of the activating function closer together. They
observed a corresponding reduction in the latency shift.
This experiment provided insight into what happens when
a human nerve passes between two bones, or some similar
heterogeneity.
Figure 11. Magnetic stimulation of a sheep phrenic nerve immersed in a homogeneous (left) and inhomogeneous (right) volume conductor. The figure-8 coil (purple) was positioned under the nerve (green). The yellow circles indicate the position of the insulating cylinders. The electric field Ex (red) and its gradient dEx/dx (blue) were measured along the nerve trajectory. The compound nerve action potentials at the recording electrode were measured for a magnetic stimulus of one polarity (orange) and then the other (green). Adapted from Figure 5 of Maccabee et al. [44].
Finally, they changed the experiment by bending the
nerve and found that a bend caused a low threshold “hot
spot,” and that excitation at that spot occurred where
the electric field, not its gradient, was large. This result
was consistent with Nagarajan and Durand’s analysis of
excitation of truncated nerves [47].
In my opinion, Maccabee’s [44] article is the most
impressive publication in the magnetic stimulation literature.
Only Barker’s original demonstration of transcranial
magnetic stimulation can compete with it [2].
One frustrating feature of the activating function approach
is that excitation does not occur directly under the center
of a figure-8 coil, where the electric field is largest, but off to one side, where the gradient peaks (Figure 9). Medical
doctors do not want to guess how far from the coil center
excitation occurs; they would prefer a coil for which “x”
marks the spot. It occurred to me that such a coil could
be designed using two adjacent figure-8 coils. I called this
the four-leaf coil (Figure 12). John Cadwell from Cadwell Laboratories (Kennewick, Washington) built such a
coil for me. Having seen the excellent results that Maccabee
was obtaining using his nerve-in-a-dish setup, I sent the
coil to him so he could test it. The resulting paper [65]
showed that for one polarity of the stimulus the magnitude
of the gradient of the electric field was largest directly
under the coil center so the axons there were depolarized
(“x” really did mark the spot of excitation). In addition, if
the polarity of the stimulus was reversed, the magnitude
of the gradient remained large under the coil center, but
it now tended to hyperpolarize rather than depolarize the
axons. Maccabee and I hoped that such hyperpolarization
could be used to block action potential propagation, acting
like an anesthetic. The Brooklyn experiments verified all
the predictions of the activating function model for the
four-leaf coil. Unfortunately, Maccabee never observed
any action potential block. Perhaps, the hyperpolarization
required for block was greater than the coil could produce.
Figure 12. A four-leaf coil (purple) used to stimulate a peripheral nerve (blue). Adapted from Figure 1 of Roth et al. [65].
Although my name was listed first on our joint 1994 article, Paul could easily have been the lead author. The coil shape was my idea but he performed all the experiments. I never set foot in Brooklyn; I just mailed the coil to him.
Paul was a giant in the field of magnetic stimulation. The articles I list above are only a few of the many he published. For a medical doctor he had a strong grasp of electricity and magnetism. I lost track of him over the years but had the good fortune to reconnect with him a few months ago by email.
I miss Paul Maccabee. Anyone who studies, uses, or benefits from magnetic stimulation owes him a debt of gratitude. I know I do.
John Moulder, from Khurana et al. (2008) Med. Phys., 35:5203, with permission from Wiley.
John Moulder, a leading expert in radiation biology, died about a year ago (on July 17, 2022; I wasn’t aware of his death until last week). When Russ Hobbie and I discuss the possible health risks of weak electric and magnetic fields in Intermediate Physics for Medicine and Biology, we cite a website about powerlines and cancer “that unfortunately no longer exists.” (However, in a previous blog post I found that is does still exist.) We also cite several papers that Moulder wrote with his collaborator Ken Foster about potential electromagnetic field hazards, including
Radiation biologist John Moulder, of the Medical College of Wisconsin, began
maintaining a website titled “Power Lines and Cancer FAQs [frequently asked questions],”
which exhaustively summarized the evidence pro and con. Although this
website is no longer available online, an archived pdf of it is [13]. In a 1996 article
published by IEEE Engineering in Medicine and Biology, Moulder reviewed dozens
of studies, and concluded that:
Given the relative weakness of the epidemiology, combined with the extensive and unsupportive
laboratory studies, and the biophysical implausibility of interactions at relevant field
strengths, it is often difficult to see why there is still any scientific controversy over the issue
of power-frequency fields and cancer. [14]
Through his awarded research grant and cooperative agreements from the
NIH and beyond, John leaves behind a legacy of excellent, rigorous, and
robust scientific findings, research collaborators who benefited from
his expertise and dedication, and a cadre of well-trained students.
Although it is impossible to list here all the lives that were touched,
and the careers that were impacted by John’s influence, the authors can
state with certainty that the field of medical preparedness for a
radiation public health emergency would not be where it is now without
the steadying hand and role played by Dr. Moulder, both in the early days
in the program and during his final years as an active researcher.
We are grateful for his years of research and join the entire radiation
community in mourning the loss of a great investigator and person.
John Moulder, you were a voice of reason in a crazy world. We’ll miss you.
To hear Moulder in his own words, go to times 4:40 and 5:05 in this video about Power Line Fears.
Oakland University physicist Abe Liboff died recently. A notice from President Ora Hirsch Pescovitz, published on the OU website, stated:
It is with deep sadness that I inform you of the death of Professor Emeritus Abraham Liboff who passed away on January 9, 2023. Dr. Liboff joined the Oakland University community in the Department of Physics on August 15, 1972, where he served until his retirement in August 2000.
During his tenure here at OU, Dr. Liboff was Chair of the Department of Physics. He is credited with 111 research publications, more than two dozen patents and nearly 3,400 scholarly citations during his career.
I arrived at OU in 1998, so his time at OU and mine overlapped by a couple years. I remember having a delightful breakfast with him during my job interview. He was one of the founders of OU’s medical physics PhD program that I directed for 15 years. His office was just a few doors down the hall from mine and he helped me get started at Oakland. I’ll miss him.
Although I loved the man, I didn’t love Abe’s cyclotron resonance theory of how magnetic fields interact with biological tissue. It’s difficult to reconcile admiration for a scientist with rejection of his scientific contributions. Rather than trying to explain Abe’s theory, I’ll quote the abstract from his article “Geomagnetic Cyclotron Resonance in Living Cells,” published in the Journal of Biological Physics (Volume 13, Pages 99–102, 1985).
Although considerable experimental evidence now exists to indicate that low-frequency magnetic fields influence living cells, the mode of coupling remains a mystery. We propose a radical new model for electromagnetic interactions with cells, one resulting from a cyclotron resonance mechanism attached to ions moving through transmembrane channels. It is shown that the cyclotron resonance condition on such ions readily leads to a predicted ELF-coupling at geomagnetic levels. This model quantitatively explains the results reported by Blackman et al. (1984), identifying the focus of magnetic interaction in these experiments as K+ charge carriers. The cyclotron resonance concept is consistent with recent indications showing that many membrane channels have helical configurations. This model is quite testable, can probably be applied to other circulating charge components within the cell and, most important, leads to the feasibility of direct resonant electromagnetic energy transfer to selected compartments of the cell.
In my book Are Electromagnetic Fields Making Me Ill? I didn’t have the heart to attack Abe in print. When discussing cyclotron resonance effects, I cited the work of Carl Blackman instead, who proposed a similar theory. What’s the problem with this idea? If you calculate the cyclotron frequency of a calcium ion in the earth’s magnetic field, you get about 23 Hz (see Eq. 8.5 in Intermediate Physics for Medicine and Biology). However, the thermal speed of a calcium ion at body temperature is about 440 m/s (Eq. 4.12 in IPMB). At that speed, the radius of the cyclotron orbit would be 3 meters (roughly ten feet)! The mean free path of a ion in water, however, is about an angstrom, which means the ion will suffer more than a billion collisions in one orbit; these interactions should swamp any cyclotron motion. Moreover, ion channels have a size of about 100 angstroms. In order to have a orbital radius similar to the size of a ion channel, the calcium ion would need to be moving extremely fast, which means it would have a kinetic energy vastly larger than the thermal energy. The theory just doesn’t work.
Since Liboff isn’t around to defend himself, I’ll let Louis Slesin—the editor and publisher of Microwave News—tell Abe’s side of the story. Read Slesin’s Reminiscence on the Occasion of Abe Liboff’s 90th Birthday. Although I don’t agree with Slesin on much, we both concur that Abe was a “wonderful and generous man.” If you want to hear about cyclotron resonance straight from the horse’s mouth, you can hear Abe talk about his career and work in a series of videos posted on the Seqex YouTube channel. (Seqex is a company that sells products based on Abe’s theories.) Below I link to the most interesting of these videos, in which Abe tells how he conceived of his cyclotron resonance idea.
Problem 24. The differential form of Ampere’s law,
Eq. 8.24, provides a relationship between the current density
j and the magnetic field B that allows you to measure
biological current with magnetic resonance imaging (see, for
example, Scott et al. (1991)). Suppose you use MRI and find
the distribution of magnetic field to be
Bx = C(yz2 − yx2)
By = C(xz2 − xy2)
Bz = C4xyz
where C is a constant with the units of T m−3. Determine
the current density. Assume the current varies slowly enough
that the displacement current can be neglected.
To solve this homework problem, calculate the curl of the magnetic field to get, within a proportionality constant, the current density.
By the way, the problem doesn’t ask you to do this, but you might want to verify that the divergence of B is zero as it must be according to Maxwell’s equations, and that the divergence of j is zero (conservation of current).
Using MRI to measure current density was one of those ideas I wish I’d thought of, but I didn’t. When Peter Basser and I wrote a paper analyzing an alternative (and less successful) method to detect action currents using MRI, we cited four of Joy’s articles in our very first sentence! I first met Joy when we co-chaired a session at the 2009 IEEE Engineering in Medicine and Biology Society Conference in Minneapolis. I had the honor of being the external examiner for one of Joy’s graduate students, Nahla Elsaid, at her 2016 dissertation defense. Joy was a delightful guy, and a joy to work with.
I’ll miss him.
MICHAEL LAWRENCE GRAHAME JOY (July 31, 1940–July 5, 2020) was born in Toronto and died at Drynoch Farm in Caledon, on his own terms, in his own time. He was predeceased by his wife Jane (née Andras) and will be dearly missed by his wife Carol Fanning, his son Rob, his daughters Gwen and Ellen, their partners, his grandchildren (Asha, Nel, Tallulah, Freya, Kelvin, and Skyler) and generations of nieces, nephews, cousins, former students, friends and colleagues.
Mike was professor emeritus at the University of Toronto; Institute of Biomaterials & Biomedical Engineering; Department of Electrical & Computer Engineering. He was a pioneer in the development of Magnetic Resonance and Electric Current Density Imaging and earned numerous significant grants, awards and citations.
Mike, (Muncle Ike, Zeepa) was truly a unique individual. He was a man of many interests who always had time for the numerous children who would follow him like shadows as he puttered on his latest amazing project. He could turn the most mundane chore into both an adventure and a learning experience. He imparted his love of nature, enquiry and adventure on his young assistants, whether tinkering on his jet boat Feeble, constructing a zip line, building model rockets, fishing, or going on long walks where “getting lost” was all part of the fun.
Mike enjoyed being surrounded by those he loved. His birthday parties at the Bay were the highlight of the summer while the Christmas tree parties at the Farm kicked off the festive season. Whether at summer picnics, Church, dinners, gatherings, bridge games, visiting family at Nares Inlet or summer afternoons on the side porch, he was always at the center of things with his distinctive laugh and quick sense of humour.
Mike left his imprint on so many. His was a life well lived and well loved. In lieu of flowers, please consider a donation to the Georgian Bay Land Trust, one of the many conservation projects Mike supported.
I might say what got me into this. To introduce something that will
come later, I’m going to talk partly about how microorganisms
swim. That will not, however, turn out to be the only important
question about them. I got into this through the work of a former
colleague of mine at Harvard, Howard Berg. Berg got his Ph.D.
with Norman Ramsey, working on a hydrogen maser, and then he
went back into biology, which had been his early love, and into
cellular physiology. He is now at the University of Colorado at
Boulder, and has recently participated in what seems to me one of
the most astonishing discoveries about the questions we're going to
talk about. So it was partly Howard's work, tracking E. coli and
finding out this strange thing about them, that got me thinking about
this elementary physics stuff.
Section 4.10 of Intermediate Physics for Medicine and Biology analyzes chemotaxis, and cites Berg’s 1977 paper with Purcell “Physics of Chemoreception” (Biophysical Journal, Volume 20, Pages 119–136). Below is the abstract.
Statistical fluctuations limit the precision with which a microorganism can,
in a given time T, determine the concentration of a chemoattractant in the surrounding
medium. The best a cell can do is to monitor continually the state of occupation
of receptors distributed over its surface. For nearly optimum performance only a
small fraction of the surface need be specifically adsorbing. The probability that a
molecule that has collided with the cell will find a receptor is Ns/(Ns + πa), if N
receptors, each with a binding site of radius s, are evenly distributed over a cell of
radius a. There is ample room for many independent systems of specific receptors.
The adsorption rate for molecules of moderate size cannot be significantly enhanced
by motion of the cell or by stirring of the medium by the cell. The least fractional
error attainable in the determination of a concentration c is approximately
(TcaD)−1/2, where D is the diffusion constant of the attractant. The number of
specific receptors needed to attain such precision is about a/s. Data on bacteriophage
adsorption, bacterial chemotaxis, and chemotaxis in a cellular slime mold are evaluated.
The chemotactic sensitivity of Escherichia coli approaches that of the cell of
optimum design.
I will end with Berg’s introduction to his masterpiece Random Walks in Biology. If you want to learn about diffusion, start with Berg’s book.
Biology is wet and dynamic. Molecules, subcellular organelles, and cells, immersed in an aqueous environment, are in continuous riotous motion. Alive or not, everything is subject to thermal fluctuations. What is this microscopic world like? How does one describe the motile behavior of such particles? How much do they move on the average? Questions of this kind can be answered only with an intuition about statistics that very few biologists have. This book is intended to sharpen that intuition. It is meant to illuminate both the dynamics of living systems and the methods used for their study. It is not a rigorous treatment intended for the expert but rather an introduction for students who have little experience with statistical concepts.
The emphasis is on physics, not mathematics, using the kinds of calculations that one can do on the back of an envelope. Whenever practical, results are derived from first principles. No reference is made to the equations of thermodynamics. The focus is on individual particles, not moles of particles. The units are centimeters (cm), grams (g), and seconds (sec).
Topics range from the one-dimensional random walk to the motile behavior of bacteria. There are discussions of Boltzmann’s law, the importance of kT, diffusion to multiple receptors, sedimentation, electrophoresis, and chromatography. One appendix provides an introduction to the theory of probability. Another is a primer on differential equations. A third lists some constants and formulas worth committing to memory. Appendix A should be consulted while reading Chapter 1 and Appendix B while reading Chapter 2. A detailed understanding of differential equations or the methods used for their solution is not required for an appreciation of the main theme of this book.
Howard Berg. Marvels of Bacterial Behavior. Part 1.
Howard Berg. Marvels of Bacterial Behavior. Part 2.
I am an emeritus professor of physics at Oakland University, and coauthor of the textbook Intermediate Physics for Medicine and Biology. The purpose of this blog is specifically to support and promote my textbook, and in general to illustrate applications of physics to medicine and biology.
