Robert J. Kauten

Magnetic resonance imaging of concentration and velocity profiles of pure fluids and solid suspensions in rotating geometries

Steady and unsteady state velocity and concentration profiles are presented for a 40% by volume suspension of polymethyl methacrylate (PMMA) spheres in polyalkylene glycol (PG). The profiles were obtained by using the noninvasive technique of nuclear magnetic resonance imaging (MRI) in three experimental geometries: coaxial rotating cylinders (i.e., for generating wide‐gap Couette flow), coaxial cylinders in which a straight flight rotates with the inner cylinder and spans the annulus between the surfaces, and a single screw extruder. Concentration profiles document the presence of particle migration from high shear to low shear regions in the concentric cylinder apparatus and in the extruder. However, concentration gradients across the gap in the straight‐flight cylinder are not exhibited, indicating the relative importance of mixing in that geometry. Velocity profiles for the pure PG fluid and for suspension flows which remain well‐mixed agree quantitatively with profiles predicted for Newtonian fluids....

Magnetic resonance imaging applications in food research

Abstract The physicochemical processes occurring in the interior of foods are difficult to measure and quantify using traditional techniques. Magnetic resonance imaging techniques improve our ability to quantify fundamental processes, such as crystalization, dehydration, gelation, diffusion and flow, occurring within food products. Magnetic resonance imaging enables the non-invasive measurement of the mobility, saturation and composition of a chemical species; fat crystallization, emulsion stability, fruit maturation, freezing, fat content and volumetric changes can be monitored.

Application of NMR imaging to the study of velocity profiles during extrusion processing

Abstract Characterization of the flow of a food material through an extruder is essential to the design and control of extrusion systems. The complexity of flow and mixing patterns during extrusion presents a perplexing yet fascinating modeling challenge for food scientists. Flow velocity profiles can be evaluated non-invasively using NMR imaging to monitor the motion of a magnetically marked band of fluid across the diameter of the extruder; distortion of the band illustrates motion. This paper demonstrates the ability of the technique to provide qualitative and quantitative descriptions of flow patterns in a single-screw extruder.

Flow profiles in a tube rheometer using magnetic resonance imaging

The velocity profiles of non-Newtonian fluids have been measured in a tube rheometer using magnetic resonance imaging (MRI). This experimental method of flow visualization is a non-invasive and non-destructive means to characterize flow behavior. The fluids examined in this paper are carboxymethylcellulose solution (CMC) and tomato juice. The velocity profiles obtained experimentally for the CMC solution by MRI were in good agreement with the analytical predictions. Velocity profiles obtained by imaging for tomato juice showed much greater dispersion of velocity than expected in the laminar flow regime

Sublethal effects of hypoxia in the abalone (Haliotis rufescens) as measured by in vivo31P NMR spectroscopy

Abstract 1. 1. Effects of hypoxia were investigated in red abalones (Haliotis rufescens) using a flow-through exposure system and in vivo31P NMR spectroscopy. 2. 2. Following seawater acclimation, abalones were exposed to air for 1 hr, then seawater for 2.5 hr to check recovery; parallel controls were performed without air exposure. 3. 3. In foot muscle, hypoxia produced a decrease in phosphoarginine concentration and intracellular pH, an increase in inorganic monophosphate concentration, and no change in that of ATP; upon resubmergence, all effects generally recovered. 4. 4. The changes induced by hypoxia during normal tidal changes are consistent with the blockage of mitochondrial oxidative phosphorylation. 5. 5. Use of in vivo NMR allows measurement of the biochemical effects of natural stress factors in live, intact aquatic organisms in the laboratory.

Interactive effects of pentachlorophenol and hypoxia in the abalone (Haliotis rufescens) as measured by in vivo 31P NMR spectroscopy

Abstract The effects of hypoxia and pentachlorophenol (PCP) were investigated in red abalones (Haliotis rufescens) using flow-through exposure and in vivo 31P nuclear magnetic resonance spectroscopy (NMR). Following acclimation to clean seawater, three abalones were separately exposed to a 6-h sublethal concentration of PCP (1.2 mg 1−1) until the spectral resonance for inorganic monophosphate (Pi) was half-height to that of phosphoarginine (PA); the endpoint assured that all individuals were metabolically equivalent at the start of air exposure. They were exposed to clean seawater for 2 h to allow the effects from PCP to stabilize, then air for 45 min, and finally clean seawater for 15 h to check recovery. The effects of PCP in foot muscle included a decrease in the concentrations of PA and adenosine triphosphate ([PA] and [ATP], respectively), an increase in Pi, and a decrease in intracellular pH (pHi). Upon air exposure, [PA] and pHi rapidly declined further, [Pi] increased, and [ATP] did not change; the magnitudes were similar to those from emergence alone. After resubmergence, both [PA] and [Pi] recovered rapidly from the effects of hypoxia, but slowly from those of PCP. While pHi initially declined further, both [ATP] and pHi recovered to near-initial levels after 15 h. In general, the metabolic effects of hypoxia did not change upon pretreatment with PCP; the biochemical interaction of the two factors was additive. Another three abalones were separately exposed to PCP at an environmentally relevant concentration of 120 μg 1−1 for 6 h, air for 1 h, then the same PCP concentration for 2.5 h to check recovery. At the lower concentration, PCP produced no discernable effects, and those of hypoxia were similar to those without PCP. Since PCP produced no additional effects with or without hypoxia, it does not significantly impact red abalones at currently measured environmental concentrations. Use of in vivo NMR allows measurement of the interactive effects of multiple stress factors in live aquatic organisms, allowing assessment of the actual environmental effects of pollutants in the laboratory.

Flow fields in straight and tapered screw extruders using magnetic resonance imaging

Abstract Improving the fundamental knowledge of fluid transport in extrusion is essential for the improved control and design of extruder systems. In particular, velocity profiles give valuable insight into residence time distributions and shear history which control final product characteristics. Due to the complicated geometry of extruders, mathematical models to predict flow behavior have been based on simplifying assumptions. Experimental verification of theory has proved to be a challenge due to the difficulty in obtaining complete flow profiles. This paper demonstrates the use of MRI to study flow in extruder geometries. Images of the velocity profile in both a straight screw and a tapered screw extruder have been generated using this non-invasive technique. Good agreement exists between experimental and theoretical velocity profiles for open and closed discharge for both straight and tapered screws.

Phase separation in optically opaque emulsions

Abstract Creaming of the dispersed oil phase in opaque oil-in-water emulsions was followed as a function of time and position using proton magnetic resonance. Measurements of T 1 along a vertical slice were used to quantify the oil-phase concentration. Emulsions were also described by laser-diffraction particle-size analysis to compare particle-size analysis with creaming behavior as determined by T 1 measurements in model triolein-in-water emulsions and more complex milk fat-in-water emulsions. Particle-size distributions failed to accurately predict the measured creaming behavior in the emulsions studied. Measurements of component nuclear relaxation were shown to be useful for characterizing oil-phase migration as a function of surfactant level, dispersed phase volume, and crystallization behavior of the lipid phase in emulsions.

1H-NMR heme resonance assignments by selective deuterations in low-spin complexes of ferric hemoglobin A

The heme methyl and vinyl alpha-proton signals have been assigned in low-spin ferric cyanide and azide ligated derivatives of the intact tetramer of hemoglobin A, as well as the isolated chains, by reconstituting the proteins with selectively deuterated hemins. For the hemoglobin cyanide tetramer, assignment to individual subunits was effected by forming hybrid hemoglobins possessing isotope-labeled hemins in only one type of subunit. The heme methyl contact shift pattern has 1-methyl and 5-methyl shifts furthest downfield in both chains and the individual subunits of the intact hemoglobin in both the cyanide- and azide-ligated species, which is consistent with a dominant rhombic perturbation due to the proximal His-F8 imidazole pi bonding in the known structure for human adult hemoglobin. The individual chain and subunit assignments confirm that the detailed electronic/magnetic properties of the heme pocket are essentially unaltered upon assembling the R-state tetramer from the isolated subunits.

Influence of salinity on the actions of pentachlorophenol in haliotis as measured by in vivo 31P NMR spectroscopy

Abstract The actions of pentachlorophenol (PCP) under various water salinities was investigated in live, intact red ( Haliotis rufescens ) and black abalone ( H. cracherodii ) by in vivo 31 P nuclear magnetic resonance (NMR) spectroscopy. Based on PCP toxicity in red abalone (6 h LC 50 1.6 mg l −1 ; 6 h NOEL=0.8 mg l −1 ), animals were exposed in flowing seawater (14°C) to a sublethal PCP concentration of 1.2 mg l −1 and a water salinity of either 25, 35 or 45 ‰. Phosphagen changes in foot muscle were monitored by surface-probe localized 31 P NMR. Upon PCP exposure, phosphoarginine (PA) levels declined and inorganic phosphate (Pi) levels concurrently increased. Dosing was terminated at a standard metabolic endpoint (MEP), defined as the time for the spectral peak height for Pi to reach one-half that of PA. This was on average 3.3±0.2 and 6.8±0.7 h at ambient salinity; 5.3±0.7 and 7.1±0.7 h for high salinity; and 4.0±0.5 and 6.5±1.0 h at low salinity, for red and black abalone, respectively. During recovery, all biochemical endpoints returned to normal; however, both onset and intensity of effects were influenced by changes in seawater salinity. Disposition of [U- 14 C]PCP in both species was also examined to determine if the effects observed with NMR had a kinetic basis. Three sets of abalone ( n =3) from each species were exposed to each salinity (25, 35 and 45 ‰), plus 1.2 mg l −1 of [U- 14 C]PCP. Red abalone were exposed for 3.5 h and black abalone for both 3.5 and 6.5 h (they represent the lowest average MEP for both species). Residues were quantified via tissue digestion and liquid scintillation counting. The 3.5 h total concentration factors (TCFs) for red abalone were not significantly different among the three salinities ( P >0.05) and ranged from 104 to 133. However, low salinity seemed to deter the uptake of [U- 14 C]PCP in black abalone, as the TCF was over three times lower for abalone exposed to 25 ‰ at both 3.5 h (TCF=19±11) and 6.5 h (TCF=38±8) than at 35 ‰ (3.5 h TCF=62±6; 6.5 h TCF=119±11) and 45 ‰ (3.5 h TCF=67±14, 6.5 h TCF=115±8). Furthermore, the 3.5 h TCF for red abalone exposed to PCP at all salinities was similar to the 6.5 h TCF for black abalone exposed at 35 and 45 ‰. Thus, black abalone appear to have greater resistance to the combined effects of PCP and salinity variations, which appears to be due to slower uptake of the biocide. While PCP is a potent uncoupler of mitochondrial oxidative phosphorylation, use of varying water salinities simulated an additional stress imposed on intertidal animals by transient or seasonal environmental changes.