Professor Glynn Holt
For the unsuspecting who enter Prof. Glynn Holt’s office, the massive, meticulously-chalked equation engulfing an entire blackboard by his desk is the sort of thing that either induces glazed expressions or activates antiperspirant.
For Holt, an Associate Professor of Mechanical Engineering in the College of Engineering, it’s a conversation starter – a way for the gregarious, sharp-witted Texan to share at once his affinity for acoustics and the science of bubbles and his gift for making the mind-bogglingly complex suddenly simple. “I’m telling you right now, you’re going to understand that equation by the time you leave here,” he says. “I’m not joking.”
And sure enough, he isn’t. An hour or so of conversation later, accompanied by a few Powerpoint slides, some basic algebraic principles, and some eye-opening video shot during a previous summer visit to Florida’s Gatorama, and Holt delivers on his promise, decoding a rather unlikely head-scratcher: the frequency with which your average gator oscillates its back in the water to splash out a ritual mating call.
Now in his 17th year on faculty, it’s the sort of solid-fundamentals-meets-Mr.-Wizard approach that’s earned Holt a devoted following among undergrads and grad students alike. “I’ve always been a student of nature, and an important part of my philosophy… is teaching students how wonderful it is to observe, and in turn, I hope, making some complex concepts understandable for a layman audience,” says Holt. “If I can find something both fundamental and interesting that elucidates the principles of acoustics, then that’s a great teaching opportunity.”
Not an easy task. Certainly not when considering the heady subject matter Holt’s classes regularly explore, from the engineering principles behind sound, to the ability of bubbles – gases trapped inside liquids – to produce energy, including extreme heat, diamond-producing pressures and bright light.
Holt is fond of extolling – and demonstrating – 19th century British scientist Michael Faraday’s belief in the wonder of observation. Freshmen taking his intro-level acoustics course will often spend their first week pouring through news articles to find something acoustics-related – for instance, how the sound inside Greece’s ancient Epidaurus Amphitheater remains so pitch-perfect – and learning enough to explain to their classmates. Grad students in Holt’s math-heavy Acoustics Bubble Dynamics course, meanwhile, are typically released into his elaborate suite of high-tech “toys” to perform original research. “You have to know it from doing it,” he says. “You can read books and journals, but you can’t synthesize from that. That’s why I force them into a research lab to do some sonoluminescence, to do something really meaningful and compare their predictions from mathematical models with experiments.”
It’s a teaching style that strongly mirrors Holt’s own introduction to acoustics at the University of Mississippi more than 30 years ago. Admittedly not the ‘sciency’ type before entering college, Holt’s freshman physics class intrigued him just enough to take his first summer job in a physics professor’s lab. There, amidst the buzz and clatter of burners, bubbling liquids, and exotic gadgetry, Holt had a chance to tinker and to learn hands-on. He’d create microphones in a pure hydrogen environment, using a heat furnace – while mixing hydrogen and oxygen – to create ‘flame water.’ “Maybe I didn’t understand everything right away, but I got to do some really cool experiments in a very hands-on kind of way. It was an amazing environment to be in.” Holt was hooked. He’d go on to earn his bachelor’s in Physics, and in the years ahead, pursue his PhD in Physics, winning a coveted DAAD Scholarship to study in Germany under aquatic acoustics expert Werner Lauterborn. Upon returning stateside, he completed his Ph.D. experiment in chaos and bubbles at Ole Miss under the guidance of longtime mentor and renowned physicist Larry Crum.
It was during his post-doctoral research at Yale – this time experimenting with ‘anti-bubbles,’ or drops – that Holt’s career prospects ‘took off’ in more ways than one. A protégé of late Yale acoustics pioneer Robert Apfel, that special connection helped afford Holt the engineering opportunity of a lifetime: service as alternate Payload Specialist for two Space Shuttle Columbia missions during the early 1990s. Holt would spend nearly five years in NASA’s science operations area, experimenting, among other things, in drop physics, plant and crystal growth, levitation technology, and in the behaviors of surface active materials (like soaps) in zero gravity settings. While his status as an alternate – like a backup quarterback – effectively kept him earthbound, Holt underwent identical training alongside his primary Payload Specialist counterparts, working at NASA’s Johnson, Marshall and Jet Propulsion laboratories, and ultimately with Science Operations crew for mission STS 50 (1992) and the air-to-ground crew during STS 73 (1995).
While space flight and microgravity experimentation quite literally propelled him into another world, it wasn’t in Holt’s longterm flight path. “My interest was in smaller research projects and being in a classroom setting. I wanted to be around students, do some teaching and mentoring in a lab. In a lab, you can let your students do something. You didn’t get that at the Jet Propulsion Laboratory.”
A teacher and tinkerer at heart, Holt arrived at BU in 1996 as a research scientist. He began formally teaching classes in Spring 1997, and quickly adopted a style of enlivening lectures and the black-and-white of college textbooks with vivid, often spectacular demonstrations of concepts like sonoluminescence – or when bubbles within a liquid are excited by sound, implode and emit bursts of light. “I really want to teach the students to think through a problem, to see how the principles they’re learning translate into what they do and observe.” It has, by all accounts, made a lasting impact. Today, many of Holt’s former students are, themselves, successful engineers, from medical physicists and staff scientists at major industries to classroom teachers and college faculty members.
Holt’s research discoveries, meanwhile, have also made a considerable footprint in both the scientific and biomedical device communities. With two important patents to his name, his publications on bubble-enhanced ultrasound heating have helped further modernize high-intensity focused ultrasound surgery devices by allowing them to operate at lower, safer outputs through bubble heating. He continues to explore such exotic bubble phenomena as nanosecond freezing of water.
As such, Holt remains happiest as that kid doing really cool experiments in his professor’s physics lab more than 30 years ago. “I didn’t get into this to make a lot of money or a name for myself. I did it because I get a kick out of observing things and then transmitting that experience and fascination to others.” Like proving bubbles are anything but boring, and uncovering the mating habits of amorous alligators.