The Experts below are selected from a list of 8469 Experts worldwide ranked by ideXlab platform
Soren Knudsen Kaer - One of the best experts on this subject based on the ideXlab platform.
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estimation of membrane Hydration Status for standby proton exchange membrane fuel cell systems by complex impedance measurement constant temperature stack characterization
International Journal of Hydrogen Energy, 2013Co-Authors: Benoit Bidoggia, Soren Knudsen KaerAbstract:Abstract Fuel cell-based backup units are characterized by long standby periods but they must be ready to start at any instant in the shortest possible time. In the case of low temperature proton exchange membrane fuel cells, the estimation of the Hydration Status of the fuel cell's membrane during standby is important for determining the cell's ability to perform a fast and safe startup. In this article, non-conventional electrochemical impedance spectroscopy (EIS) is suggested as a method to estimate the membrane's Hydration Status. The proposed technique differs from standard EIS in that the current through the fuel cell cannot contain a DC component, since hydrogen is absent. A 56-cell fuel cell stack has been symmetrically fed with air, whose temperature and relative humidity were controlled, and its complex impedance was measured at different frequencies and for different values of relative humidity at constant temperature. Power regression models were applied to the data, and the relationships between complex impedance and relative humidity were found. The results showed that the proposed technique is a viable way for estimating the membrane Hydration Status of a fuel cell stack during standby. Moreover, the most suitable frequency values at which the measurements should be performed are given.
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Estimation of membrane Hydration Status for standby proton exchange membrane fuel cell systems by impedance measurement: First results on variable temperature stack characterization
2013 Eighth International Conference and Exhibition on Ecological Vehicles and Renewable Energies (EVER), 2013Co-Authors: Benoit Bidoggia, Soren Knudsen KaerAbstract:Fuel cells are getting growing interest in both backup systems and electric vehicles. Although these systems are characterized by periods of standby, they must be able to start at any instant in the shortest possible time. However, the membranes of which proton exchange membrane fuel cells are made, tend to gradually dry out when the fuel cell is not operating, increasing the time required to start up the system. A precise estimation of the Hydration Status of the membrane during standby is thus important for the design of a fuel cell system capable of a fast and safe start up. In previous works, the measurement of the complex impedance of a fuel cell stack during standby is used as an index of its membrane Hydration Status. In this article, the complex impedance of a fuel cell stack has been measured and characterized as a function of relative humidity and temperature. A non-conventional electrochemical impedance spectroscopy (EIS) technique has been used, allowing the performance of a fuel cell diagnostic when the fuel cell stack does not contain any hydrogen, which would otherwise not be possible. The results appeared to confirm that measuring the impedance of an entire fuel cell stack could be a viable way for estimating the Hydration Status and the temperature of its membrane before the system is started up. A summarizing table with the complete characterization of the fuel cell stack is included in this article.
Benoit Bidoggia - One of the best experts on this subject based on the ideXlab platform.
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estimation of membrane Hydration Status for standby proton exchange membrane fuel cell systems by complex impedance measurement constant temperature stack characterization
International Journal of Hydrogen Energy, 2013Co-Authors: Benoit Bidoggia, Soren Knudsen KaerAbstract:Abstract Fuel cell-based backup units are characterized by long standby periods but they must be ready to start at any instant in the shortest possible time. In the case of low temperature proton exchange membrane fuel cells, the estimation of the Hydration Status of the fuel cell's membrane during standby is important for determining the cell's ability to perform a fast and safe startup. In this article, non-conventional electrochemical impedance spectroscopy (EIS) is suggested as a method to estimate the membrane's Hydration Status. The proposed technique differs from standard EIS in that the current through the fuel cell cannot contain a DC component, since hydrogen is absent. A 56-cell fuel cell stack has been symmetrically fed with air, whose temperature and relative humidity were controlled, and its complex impedance was measured at different frequencies and for different values of relative humidity at constant temperature. Power regression models were applied to the data, and the relationships between complex impedance and relative humidity were found. The results showed that the proposed technique is a viable way for estimating the membrane Hydration Status of a fuel cell stack during standby. Moreover, the most suitable frequency values at which the measurements should be performed are given.
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Estimation of membrane Hydration Status for standby proton exchange membrane fuel cell systems by impedance measurement: First results on variable temperature stack characterization
2013 Eighth International Conference and Exhibition on Ecological Vehicles and Renewable Energies (EVER), 2013Co-Authors: Benoit Bidoggia, Soren Knudsen KaerAbstract:Fuel cells are getting growing interest in both backup systems and electric vehicles. Although these systems are characterized by periods of standby, they must be able to start at any instant in the shortest possible time. However, the membranes of which proton exchange membrane fuel cells are made, tend to gradually dry out when the fuel cell is not operating, increasing the time required to start up the system. A precise estimation of the Hydration Status of the membrane during standby is thus important for the design of a fuel cell system capable of a fast and safe start up. In previous works, the measurement of the complex impedance of a fuel cell stack during standby is used as an index of its membrane Hydration Status. In this article, the complex impedance of a fuel cell stack has been measured and characterized as a function of relative humidity and temperature. A non-conventional electrochemical impedance spectroscopy (EIS) technique has been used, allowing the performance of a fuel cell diagnostic when the fuel cell stack does not contain any hydrogen, which would otherwise not be possible. The results appeared to confirm that measuring the impedance of an entire fuel cell stack could be a viable way for estimating the Hydration Status and the temperature of its membrane before the system is started up. A summarizing table with the complete characterization of the fuel cell stack is included in this article.
Martin R. Prince - One of the best experts on this subject based on the ideXlab platform.
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pelvic cardiovascular magnetic resonance venography venous changes with patient position and Hydration Status
Journal of Cardiovascular Magnetic Resonance, 2019Co-Authors: Ashkan H. Behzadi, Neil M. Khilnani, Weiguo Zhang, Amanda J. Bares, Srikanth R. Boddu, Robert J. Min, Martin R. PrinceAbstract:To determine the effect of Hydration as well as prone versus supine positioning on the pelvic veins during cardiovascular magnetic resonance (CMR) venography. Under institutional review board approval, 8 healthy subjects were imaged with balanced steady state free precession, non-contrast CMR venography to measure common and external iliac vein volumes and common femoral vein cross-sectional area in the supine, prone and decubitus positions after deHydration and again following re-Hydration. CMR venography from 23 patients imaged both supine and prone were retrospectively reviewed and measurements of common femoral and iliac veins areas were compared using Wilcoxon test. Common femoral vein area on CMR venography increased with prone positioning (83 ± 35 mm2) compared to supine positioning (59 ± 21 mm2) (p = 0.02) and further increased with Hydration to 123 ± 44 mm2 (p < 0.01). With right and left side down decubitus positioning, the common femoral vein area on deHydration increased from 29 ± 17 mm2 in the ante-dependent position to 134 ± 36 mm2 in the dependent position (p < 0. 001). Similarly, common and external iliac veins increased in volume with prone, 5.4 ± 1.9 cm3 and 5.8 ± 1.9 cm3 compared to supine positioning 4.6 ± 1.8 cm3 and 4.5 ± 1.9 cm3 (p = 0.01) and further increase with Hydration to 6.7 ± 2.1 cm3 and 6.3 ± 1.9 cm3 (p = 0.01). CMR venography on patients also demonstrated an increase in mean common femoral vein luminal area from 103 ± 44 mm2 in supine position to 151 ± 52 mm2 with prone positioning (p < 0.001) as well as increases in common and external iliac vein volumes from 6.5 ± 2.6 cm3 and 8.0 ± 3.4 cm3 in the supine position to 7.5 ± 2.5 cm3 and 9.3 ± 3.6 cm3 with prone positioning (p < 0.01). Common femoral and common/external iliac vein size on CMR venography may be affected by position and Hydration Status. Routine clinical CMR venography of the pelvis could include prone positioning and avoiding deHydration to maximize pelvic vein distension.
Alan C. Utter - One of the best experts on this subject based on the ideXlab platform.
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validity of urine specific gravity when compared with plasma osmolality as a measure of Hydration Status in male and female ncaa collegiate athletes
Journal of Strength and Conditioning Research, 2016Co-Authors: Lesley Sommerfield, Jennifer Zwetsloot, Juliane O Young, Traci L Haines, Mason C. Calhoun, Steven R. Mcanulty, Melanie D. Austin, Jonathan D. Mehlhorn, Jeffrey M Mcbride, Alan C. UtterAbstract:The purpose of this study was to evaluate the response of urine specific gravity (Usg) and urine osmolality (Uosm) when compared with plasma osmolality (Posm) from euHydration to 3% deHydration and then a 2-hour reHydration period in male and female collegiate athletes. Fifty-six National Collegiate Athletic Association (NCAA) wrestlers (mean ± SEM); height 1.75 ± 0.01 m, age 19.3 ± 0.2 years, and body mass (BM) 78.1 ± 1.8 kg and 26 NCAA women's soccer athletes; height 1.64 ± 0.01 m, age 19.8 ± 0.3 years, and BM 62.2 ± 1.2 kg were evaluated. Hydration Status was obtained by measuring changes in Posm, Uosm, Usg, and BM. Male and female subjects dehydrated to achieve an average BM loss of 2.9 ± 0.09% and 1.9 ± 0.03%, respectively. Using the medical diagnostic decision model, the sensitivity of Usg was high in both the hydrated and dehydrated state for males (92%) and females (80%). However, the specificity of Usg was low in both the hydrated and dehydrated states for males (10 and 6%, respectively) and females (29 and 40%, respectively). No significant correlations were found between Usg and Posm during either the hydrated or dehydrated state for males or females. Based on these results, the use of Usg as a field measure of Hydration Status in male and female collegiate athletes should be used with caution. Considering that athletes deal with Hydration Status on a regular basis, the reported low specificity of Usg suggests that athletes could be incorrectly classified leading to the unnecessary loss of competition.
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validity of urine specific gravity when compared with plasma osmolality as a measure of Hydration Status in male and female ncaa collegiate athletes
Journal of Strength and Conditioning Research, 2016Co-Authors: Lesley Sommerfield, Jennifer Zwetsloot, Juliane O Young, Traci L Haines, Mason C. Calhoun, Steven R. Mcanulty, Melanie D. Austin, Jonathan D. Mehlhorn, Jeffrey M Mcbride, Alan C. UtterAbstract:Sommerfield, LM, McAnulty, SR, McBride, JM, Zwetsloot, JJ, Austin, MD, Mehlhorn, JD, Calhoun, MC, Young, JO, Haines, TL, and Utter, AC. Validity of urine specific gravity when compared with plasma osmolality as a measure of Hydration Status in male and female NCAA collegiate athletes. J Strength Cond Res 30(8): 2219-2225, 2016-The purpose of this study was to evaluate the response of urine specific gravity (Usg) and urine osmolality (Uosm) when compared with plasma osmolality (Posm) from euHydration to 3% deHydration and then a 2-hour reHydration period in male and female collegiate athletes. Fifty-six National Collegiate Athletic Association (NCAA) wrestlers (mean ± SEM); height 1.75 ± 0.01 m, age 19.3 ± 0.2 years, and body mass (BM) 78.1 ± 1.8 kg and 26 NCAA women's soccer athletes; height 1.64 ± 0.01 m, age 19.8 ± 0.3 years, and BM 62.2 ± 1.2 kg were evaluated. Hydration Status was obtained by measuring changes in Posm, Uosm, Usg, and BM. Male and female subjects dehydrated to achieve an average BM loss of 2.9 ± 0.09% and 1.9 ± 0.03%, respectively. Using the medical diagnostic decision model, the sensitivity of Usg was high in both the hydrated and dehydrated state for males (92%) and females (80%). However, the specificity of Usg was low in both the hydrated and dehydrated states for males (10 and 6%, respectively) and females (29 and 40%, respectively). No significant correlations were found between Usg and Posm during either the hydrated or dehydrated state for males or females. Based on these results, the use of Usg as a field measure of Hydration Status in male and female collegiate athletes should be used with caution. Considering that athletes deal with Hydration Status on a regular basis, the reported low specificity of Usg suggests that athletes could be incorrectly classified leading to the unnecessary loss of competition.
Ashkan H. Behzadi - One of the best experts on this subject based on the ideXlab platform.
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pelvic cardiovascular magnetic resonance venography venous changes with patient position and Hydration Status
Journal of Cardiovascular Magnetic Resonance, 2019Co-Authors: Ashkan H. Behzadi, Neil M. Khilnani, Weiguo Zhang, Amanda J. Bares, Srikanth R. Boddu, Robert J. Min, Martin R. PrinceAbstract:To determine the effect of Hydration as well as prone versus supine positioning on the pelvic veins during cardiovascular magnetic resonance (CMR) venography. Under institutional review board approval, 8 healthy subjects were imaged with balanced steady state free precession, non-contrast CMR venography to measure common and external iliac vein volumes and common femoral vein cross-sectional area in the supine, prone and decubitus positions after deHydration and again following re-Hydration. CMR venography from 23 patients imaged both supine and prone were retrospectively reviewed and measurements of common femoral and iliac veins areas were compared using Wilcoxon test. Common femoral vein area on CMR venography increased with prone positioning (83 ± 35 mm2) compared to supine positioning (59 ± 21 mm2) (p = 0.02) and further increased with Hydration to 123 ± 44 mm2 (p < 0.01). With right and left side down decubitus positioning, the common femoral vein area on deHydration increased from 29 ± 17 mm2 in the ante-dependent position to 134 ± 36 mm2 in the dependent position (p < 0. 001). Similarly, common and external iliac veins increased in volume with prone, 5.4 ± 1.9 cm3 and 5.8 ± 1.9 cm3 compared to supine positioning 4.6 ± 1.8 cm3 and 4.5 ± 1.9 cm3 (p = 0.01) and further increase with Hydration to 6.7 ± 2.1 cm3 and 6.3 ± 1.9 cm3 (p = 0.01). CMR venography on patients also demonstrated an increase in mean common femoral vein luminal area from 103 ± 44 mm2 in supine position to 151 ± 52 mm2 with prone positioning (p < 0.001) as well as increases in common and external iliac vein volumes from 6.5 ± 2.6 cm3 and 8.0 ± 3.4 cm3 in the supine position to 7.5 ± 2.5 cm3 and 9.3 ± 3.6 cm3 with prone positioning (p < 0.01). Common femoral and common/external iliac vein size on CMR venography may be affected by position and Hydration Status. Routine clinical CMR venography of the pelvis could include prone positioning and avoiding deHydration to maximize pelvic vein distension.
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Additional file 3: of Pelvic cardiovascular magnetic resonance venography: venous changes with patient position and Hydration Status
2019Co-Authors: Ashkan H. Behzadi, Neil M. Khilnani, Weiguo Zhang, Amanda J. Bares, Srikanth R. Boddu, Robert Min, Martin PrinceAbstract:Table S3a. Common femoral vein area normalized by weight (mm2/kg) in supine vs. prone positioning and deHydration vs. Hydration Status in 8 healthy subjects. Table S3b. Common femoral vein area normalized by weight (mm2/kg) in decubitus dependent vs. ante-decubitus positions for deHydration vs. Hydration Status in 8 healthy subjects. Table S3c. Common iliac vein volume normalized by weight (mm3/kg) in supine vs. prone positioning with deHydration vs. Hydration in 8Â healthy subjects. Table S3d. External iliac vein volume normalized by weight (mm3/kg) in supine vs. prone positioning with deHydration vs. Hydration in 8Â healthy subjects. (DOCX 21 kb
