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Song J.-O.,University of Minnesota | Henry R.M.,Hutchinson Technology Inc. | Henry R.M.,Nexolve Corporation | Jacobs R.M.,University of Minnesota | Francis L.F.,University of Minnesota
Review of Scientific Instruments | Year: 2010

A magnetic microrheometer has been designed to characterize the local viscosity of liquid-applied coatings in situ during solidification. The apparatus includes NdFeB magnets mounted on computer-controlled micropositioners for the manipulation of ∼1 μm diameter superparamagnetic particles in the coating. Magnetic field gradients at 20-70 T/m are generated by changing magnet size and the gap distance between the magnets. A specimen stage located between two magnets is outfitted with a heater and channels to control process conditions (temperature and air flow), and a digital optical microscope lens above the stage is used to monitor the probe particle position. Validation studies with glycerol and polyimide precursor solution showed that microrheometry results match traditional bulk rheometry within an error of 5%. The viscosities of polyvinyl alcohol (PVA) solution and polyimide precursor solution coatings were measured at different shear rates (0.01-5 s-1) by adjusting the magnetic field gradient. The effect of proximity to the substrate on the particle motion was characterized and compared with theoretical predictions. The magnetic microrheometer was used to characterize the time-viscosity profile of PVA coatings during drying at several temperatures. The viscosity range measured by the apparatus was 0.1-20 Pa s during drying of coatings at temperatures between room temperature and 80 °C. © 2010 American Institute of Physics.


Orazem M.E.,University of Florida | Tribollet B.,University Pierre and Marie Curie | Vivier V.,University Pierre and Marie Curie | Marcelin S.,National Polytechnic Institute of Toulouse | And 6 more authors.
ECS Transactions | Year: 2013

Models invoking Constant-Phase Elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. While the physical origins of the CPE are controversial, a bigger problem remains the interpretation of impedance data in terms of physically meaningful properties such as capacitance or thickness. Four models are used to interpret the CPE parameters associated with the impedance response of human skin and two metal oxides in terms of characteristic frequencies, film thickness, and dielectric constant. These values were compared against independent measurements. The power-law model developed recently by Hirschorn et al. (1, 2) provided the most reliable interpretation. Readers are cautioned that the CPE parameter Q does not provide an accurate value for capacitance, even when the CPE exponent is greater than i0.9. © The Electrochemical Society.


Orazem M.E.,University of Florida | Frateur I.,University Pierre and Marie Curie | Tribollet B.,University Pierre and Marie Curie | Vivier V.,University Pierre and Marie Curie | And 6 more authors.
Journal of the Electrochemical Society | Year: 2013

Constant-Phase Elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. Four approaches were used to interpret CPE parameters associated with the impedance response of human skin and two metal oxides in terms of characteristic frequencies and film thickness. The values obtained with each approach were compared against independent measurements. The power-law model developed recently by Hirschorn et al.1,2 provided the most reliable interpretation for systems with a normal distribution of properties. Readers are cautioned that the CPE parameter Q does not provide an accurate value for capacitance, even when the CPE exponent a is greater than 0.9. © 2013 The Electrochemical Society.


Orazem M.E.,University of Florida | Tribollet B.,University Pierre and Marie Curie | Vivier V.,University Pierre and Marie Curie | Riemer D.P.,Hutchinson Technology Inc. | And 2 more authors.
Journal of the Brazilian Chemical Society | Year: 2014

Constant-phase elements (CPE) are often used to fit impedance data arising from a broad range of experimental systems. The power-law model has proven to be a powerful tool for interpretation of CPE parameters resulting from an axial or normal distribution of time constants. This paper addresses difficulties in applying this model associated with uncertain values for one of the model parameters. Methods are presented for bounding the value of the parameter, for calibration, and for comparative analysis in which the unknown parameter may be eliminated. The methods are illustrated by data taken from the literature for oxides on steels and for human skin. © 2014 Sociedade Brasileira de Quimica.


George M.E.,University of Minnesota | Beilman G.J.,University of Minnesota | Mulier K.E.,University of Minnesota | Myers D.E.,Hutchinson Technology Inc. | Wasiluk K.R.,University of Minnesota
Journal of Surgical Research | Year: 2010

Background: Hemorrhagic shock can lead to multiple organ failure and death. We have previously shown that noninvasive measurement of tissue oxygen saturation (StO2) has predictive value for outcomes in patients suffering hemorrhagic shock. Our study objectives were twofold: (1) to compare invasive and noninvasive measurements of local and systemic tissue hemoglobin oxygenation and (2) to compare the effects of various physiologic conditions seen in patients in hemorrhagic shock on tissue hemoglobin oxygenation. Materials and Methods: We studied pigs in controlled conditions mimicking shock induced by one of the following: hypothermia, isovolemic hemodilution, or manipulations of vascular tone. We obtained both invasive and noninvasive measurements in a hind limb of StO2, tissue hemoglobin index, femoral artery and venous flows, blood pressures, temperature, pH, pO2, pCO2, oxygen saturation, lactate, hemoglobin, and base excess. In all cases, we measured baseline values in both experimental and control hind limbs. Results: We found that tissue hemoglobin oxygenation did not vary significantly over relevant physiologic temperatures. Under all physiologic conditions tested, we found supply-dependent oxygen consumption at oxygen levels less than 7 mL O2/min/kg. Similarly, we found that local oxygen delivery in animals subjected to varying degrees of isovolemic hemodilution or altered vascular tone was correlated with supply-dependent oxygen consumption, as measured by local noninvasive StO2. Conclusions: Noninvasive StO2 measurements are valid and durable over a wide range of physiologic conditions and correlate with invasively-measured oxygen delivery. © 2010 Elsevier Inc. All rights reserved.

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