A weekend of downs and ups

On Friday I awoke to the sad news that my friend Lloyd Morrison had died. Lloyd was a legendary Wellington businessman and philanthropist whom I had got to know through our shared struggle. He had acute myeloid leukemia. Lloyd had founded infrastructure investment firm, Infratil, was a prime mover behind a campaign to change the New Zealand flag, and a generous patron of the arts and the local soccer franchise, the Phoenix. He was a far-sighted visionary, unconventional, extraordinarily intelligent, and passionate about Wellington and New Zealand.

Later on Saturday my spirits were lifted by a visit from Miang's cousin Lily and her husband Anthony, who had flown over from Sydney for the weekend. Saturday was the 6th anniversay of my marriage to Miang. I joined them all later in the afternoon for a drive around the Miramar Peninsula and the South Coast, including a climb up to the Ataturk Memorial. The latter exhausted me. Walking is now quite painful for me, but I try to force myself to exercise for 30 minutes each day.

On Sunday morning Catherine texted me to say that her friend Kent Gardner had been made UK New Zealander of the year at an awards ceremony in London. Kent was behind the "Step Up for Christchurch campaign", a fundraiser involving climbing the Gherkin tower owned by his company.

And this afternoon, Sunday, the weather was so beautiful that Miang and I decided to go to Pukerua Bay, the place where we had celebrated our first anniversary in 2007. She swam in the sea while I watched happily from a seat on a bank above the shore.



Part 3: Antarctica, Porous media and soft matter
Another odd area of interest for me in the 1980s was Earth field NMR. We did the first spin echo experiments using 180° audiofrequency pulses. Later, in 1994, Craig and I were to take this apparatus to Antarctica to measure brine content in sea ice. We were joined in 1996 by an American postdoctoral fellow, Joe Seymour. Joe not only contributed to our Antarctic program, measuring brine diffusion in sea ice, but also introduced me to chemical engineering, his own undergraduate specialty. Joe and I set out to see what we could do with pulsed-gradient spin echo (PGSE) NMR to measure dispersion, the process whereby molecules starting together are separated by flow. This collaboration was very fruitful, and porous media dispersion and diffusion studies became a major part of our research interests.

My Slovenian link was also revived in a wonderfully productive sabbatical visit by Janez Stepisnik. We were able to demonstrate experimentally the validity of his idea that the spectrum of molecular velocity autocorrelation functions could be measured using modulated gradient spin echo NMR. By the 1990s we had been exploring the use of NMR microscopy to study heterogeneous flow in shear cells, combining rheology with NMR, inspired by Ed Samulski, a U.S. sabbatical visitor to my lab. Our work in rheo-NMR led to another serendipitous collaboration that in turn generated a major field of research in my laboratory. In 1996 we were introduced to worm-like micelles (WLMs) by visiting Dutch physicist Bas Smeulders. Later, we used NMR microscopy to measure shear banding effects in WLMs, and we have been pursuing the complex rheodynamics of these systems ever since.

Of all the work we have done, the most cited has been the “q-space diffraction” and “q-space imaging” research. The history of this is interesting. In a review paper on PGSE NMR, published in the Australian Journal of Physics, I pointed out the formal analogy between PGSE NMR and the incoherent fraction of inelastic neutron scattering. In neutron inelastic scattering, the symbol q is used as the reciprocal space dimension conjugate to dynamic displacement. The term “q-space” first appeared, in the NMR context, in the title of a paper on NMR velocimetry that I published with Craig Eccles and Yang Xia in Journal of Physics E, in 1988. But the impetus to see the potential of diffraction effects in diffusion studies came about as a result of a visit made in 1989 to Ken Packer’s group at BP research in the UK. Ken, of course, had been the first to see non-Gaussian echo attenuation when he carried out a PGSE NMR experiment on pipe flow. Those 1989 discussions with Ken centered on the idea that the Fourier transform of the “q-encoded” echo was the propagator for displacements, and this led to speculation as to whether diffraction effects might be seen for small-molecule diffusion in porous media. I worked though the theory of this. A simple limiting case was that of the isolated pore, where it turned out that in the long diffusion time limit, the propagator reduces to the autocorrelation function of the pore structure.

We dashed off a short paper on q-space diffraction and oscillatory echo attenuation effects to the Journal of Magnetic Resonance. Concurrently (and submitted before us to Magnetic Resonance in Medicine), Al Garroway and David Cory had come up with a similar idea, namely that the Fourier transform of the echo decay for an isolated pore was the pore autocorrelation function. Of course, the key step was to do the experiment. Working on an isolated pore was difficult (that experiment came later). It was much easier to work on an interconnected porous medium imbibed with water. The interesting theory extension to interconnected porous media was based on the idea that, in effect, the pore structure factor is convolved with the pore lattice structure and modulated by a diffusive envelope. With a reasonably ordered system, diffraction effects might be seen there. On return to New Zealand, I suggested to my PhD student Andrew Coy that he try the diffraction experiment on a close-packed monodisperse latex sphere system. The oscillatory features of diffraction were immediately evident on the echo attenuation function, and a paper in Nature, jointly with the Packer group, resulted. In a later, more detailed paper on this in the Journal of Chemical Physics, we were greatly assisted by some subtle theory insights provided by BP theorist, Dave MacGowan.

Later, Andrew and I verified the isolated pore predictions by using an array of rectangular glass microcapillaries, and this work subsequently led to a number of papers on the subject from our group. The advantage of q-space imaging is that one is not constrained by voxel signal-to-noise limitation. These days, the method is used as a contrast in medical imaging, where the distributions of displacements so obtained tell something about compartmentation of tissue, along with compartment size.

The photos are respectively of Lloyd, Miang at Pukerua Bay, and Ed and me two years ago.