Major Scientific Achievements:
We pioneered the use of NMR velocity imaging in multiphase and granular flows. In particular, we obtained concentration and velocity profiles of concentrated (40-60% by volume of solids) suspensions in pipe flow as well as in couette geometry for the first time. We were the first group to measure the velocity profiles within a continuously flowing particulate flow, i.e., flows of solid particles without any liquid carrier. We have also examined the standard formulation of restricted diffusion measurements by NMR and have derived a criterion for its validity in terms of pulse sequence parameters, diffusion coefficient, and the size of the confining space. Further work has led to a derivation of an exact analytic expression for signal attenuation due to diffusion when the gradient pulse cannot be considered to be short. Finally, we have made contributions in NMR techniques and experimental methods; flow imaging schemes, Abel transforms for cylindrical geometries, coil design, and analog compensation for gradient-induced eddy current suppression.
1. Porous media flow. Studying pollutant transport in geological media is an obvious application. Interest in transport phenomena in porous media is interdisciplinary and provides a template for enhanced understanding of NMR measurements in complex flow systems. We have also performed experiments to test the efficacy of unobtrusive waterproofing for buildings and monuments by measuring the penetration into porous media. Studies of flows in biofilms have yielded information about the interaction between flow and growth. Collaborations with Purdue University, Sandia National Laboratories, and University of New Mexico are active in this area.
2. Floatation and sedimentation. We have studied two and three phase floatation and settling by NMR imaging. In the earlier two phase studies, the fluid phase was imaged and the solid phase presented itself by the absence of NMR signal. Therefore, the spatially resolved signal intensity was directly proportional to the liquid concentration C which is taken to be 1-S where S is the normalized concentration of the solid phase. If system starts with a distribution of initial concentration of particles, the hindered settling function as a function of the concentration can be obtained in one experimental run instead of one run per concentration. The three phase system was chosen to have two solid phases, one glass beads that give no NMR signal and the other a plastic phase that can be detected by special NMR sequences. Thus, two of the phases were detected directly and the third phase indirectly. In this way, we are able to study the effect of a second solid phase on the floatation or settling of the first solid phase.
3. Concentrated suspension in pipe flow. We pioneered this area of research. After obtaining velocity and concentration profiles in concentrated suspensions for the first time and confirming the shear-induced migration effect, we have gone on to what happens near the walls by going to a larger pipe. We are also studying suspension flows in complex geometries, e.g., sudden constrictions and expansions. This has the practical ramification, for example, of how to keep mixtures of materials homogeneous while filling a large container through a small inlet. This work is supported by a DOE grant from Basic Energy Sciences. We also have a research contract with Sandia National Laboratories for this project.
4. Dynamics and evolution of homogeneous and heterogeneous mixtures of granular materials flowing in horizontal rotating cylinders. We measure not only concentration and velocity of these particles but also collisional parameters such as the correlation times of collisions. Applications include processing and transport of grains in the food, construction and pharmaceutical industries as well as geophysical phenomena such as avalanches and debris flows. We have had PETC funding for this work and current support is through DOE Basic Energy Sciences. Collaborators include Colorado School of Mines.
5. Development of fast imaging. This is a hardware development project with many fallout benefits possible. We took an approach that is different from the main-line efforts of shielding unwanted gradients. Instead, we developed a digital eddy-current compensation scheme that is self-iterating, repeatable, and fully compensating. We derived an algorithm that calculates the desired input waveshapes from the NMR-detected gradient variations. We will use serial-input MDACs that allow a great reduction in the number of lines that control the time-constants and amplitudes of the output waveform. This work has been done in collaboration with I. J. Lowe at Carnegie-Mellon University.
6. Development of real-time image processing. In collaboration with K. Kose of University of Tsukuba, we are implementing a PC-based image processing unit that will perform 2-D Fourier transforms to produce images in a small fraction of a second. The combination of this and the previous item should allow us to do nearly real-time NMRI with a delay of around 100 ms. The Japanese Ministry of Education supported Professor Koses visit here.
7. Search for appropriate gases for use in NMR studies of porous media. We are investigating the possibility of using (non-hyperpolarized) gases to study porous media such as ceramics, rocks and lungs. One advantage of gases for such studies is that the diffusion coefficient can be changed by changing pressure, thus, making it possible to adjust the diffusion length with respect to the size of the restrictive spaces. Different gases have different affinities to the walls of the medium, giving rise to different information. We have investigated 3He, butane, halothane, and SF6, among other gases. Some of this work is being carried out with a contract from Sandia National Laboratories.
8. Development of dedicated NMR instrumentation for flow studies. We have a research grant from NASA to develop an NMR instrument that is specifically designed for measuring flow and diffusion properties of materials that, at the same time, is relatively inexpensive and simple to use. The main components of this apparatus are a permanent magnet and a DSP-based controller. This work is in collaboration with Ben Ovryn of NASA Glenn Research Center.
9. Development of "remote sensing" NMR. This is an effort to extend past efforts by some others to detect NMR signals from a region outside of a magnet that might enclose a standard NMR sample. It includes a design of a unilateral magnet which projects a uniform field region to one side of itself so that NMR signals may be detected from there. Possible applications include underground water detection, remote sensing of processes taking place behind physical barriers (such as vats of corrosive, poisonous, etc., materials), and studies of large animals that will not fit inside standard magnets.
10. Imaging lungs. We are developing a technique of imaging obstructed ventilation in lungs by taking advantage of the ease of making spin-density images of SF6, C2F6, and related gases and of the way inert gases provide an index of gas exchange. Where the ratio of ventilation to blood perfusion is low, inert gases accumulate if the inhaled mixture is mostly oxygen. Then, in spin density images, these regions of poor gas exchange appear bright compared to healthy regions of the lung. It is possible to measure low ventilation-perfusion ratios with this technique.
11. Imaging force chain structure in 3D granular materials. We are developing an adaptation of Magnetic Resonance Elastography (MRE) to image the force chain structure within 3D granular piles.
New Mexico Resonance's educational commitment
NMR is a non-profit organization whose aim is the betterment and understanding of flow phenomena through interdisciplinary research related to nuclear magnetic resonance and education related to the science of flowing matter with emphasis on international collaboration. Our educational effort is composed of several elements enumerated below.
Specifically, we have the following educational activities.
1) Adjunct Professorships at University of New Mexico: S. A. Altobelli (Mechanical Engineering), A. Caprihan (Electrical Engineering), and E. Fukushima (Physics).
2) Subcontracting of research to University of New Mexico to support graduate students.
3) Collaborations with universities to afford them research opportunities. Examples: Montana State University and University of New Mexico.
4) Supervising graduate student research projects at University of New Mexico.
5)Student research assistantship programs at high school, college, and graduate school levels.
6) An active postdoctoral fellows program.
7) We have a summer faculty program for visiting faculty at various levels to do research in our laboratory and we also host visiting professors on sabbatical leaves.