Temperature-dependent kinetic studies of the adsorption of critical pollutants onto reactive comp... more Temperature-dependent kinetic studies of the adsorption of critical pollutants onto reactive components in soils and removal technologies provide invaluable rate information and mechanistic insight. Using attenuated total internal reflection Fourier transform infrared spectroscopy, we collected in situ spectra as a function of time, concentration, and temperature in the range of 5−50°C (278−323 K) for the adsorption of arsenate (iAs) and dimethylarsinate (DMA) on hematite nanoparticles at pH 7. These experimental data were modeled with density functional theory (DFT) calculations on the energy barriers between surface complexes. The Langmuir adsorption kinetic model was used to extract values of the fast (<5 min) and slow (6−10 min) observed adsorption rate, initial rate constants of adsorption and desorption, Arrhenius parameters, effective activation energies (ΔE a), and pre-exponential factors (A). The trend in the kinetic parameters correlated with the type of surface complexes that iAs and DMA form, which are mostly bidentate binuclear compared to a mix of outer sphere and monodentate, respectively. The observed initial adsorption rates were found to be more sensitive to changes in the aqueous concentration of the arsenicals than slow rates. On average, iAs adsorbs 2.5× faster and desorbs 4× slower than dimethylarsinate (DMA). The ΔE a and A values for the adsorption of iAs bidentate complexes are statistically higher than those extracted for outersphere DMA by a factor of 3. The DFT results on adsorption energies and ΔE a barriers are consistent with the experimental data and provide a mechanistic explanation for the low ΔE a values observed. The presence of defect sites with under-coordinated Fe atoms or exchangeable surface water (i.e., Fe−OH 2 groups) lowers activation barriers of adsorption. These results suggest that increasing organic substitutions on arsenate at the expense of As−O bonds decreases the effective energy barrier for complex formation and lowers the number of collisional orientations that result in binding to the hematite surface.
NASA uses the Automatic Cloud Coverage Assessment (ACCA) algorithm to determine the ration of clo... more NASA uses the Automatic Cloud Coverage Assessment (ACCA) algorithm to determine the ration of cloud cover to non-cloud cover in an image from the Landsat 7 satellite. In an attempt to reduce the overall processing time of the algorithm, NASA has opted to convert the software version of the ACCA algorithm into a hardware implementation. Since previous attempts to convert the cloud detecting algorithm, using an advanced hardware description language (VHDL), have rendered inaccurate results, yhe purpose of this project is to detail the methods to debug and test the VHDL implementation of the ACAA algorithm and to advance the implementation of the algorithm as time permitted
Journal of The American College of Surgeons, May 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Temperature-dependent kinetic studies of the adsorption of critical pollutants onto reactive comp... more Temperature-dependent kinetic studies of the adsorption of critical pollutants onto reactive components in soils and removal technologies provide invaluable rate information and mechanistic insight. Using attenuated total internal reflection Fourier transform infrared spectroscopy, we collected in situ spectra as a function of time, concentration, and temperature in the range of 5−50°C (278−323 K) for the adsorption of arsenate (iAs) and dimethylarsinate (DMA) on hematite nanoparticles at pH 7. These experimental data were modeled with density functional theory (DFT) calculations on the energy barriers between surface complexes. The Langmuir adsorption kinetic model was used to extract values of the fast (<5 min) and slow (6−10 min) observed adsorption rate, initial rate constants of adsorption and desorption, Arrhenius parameters, effective activation energies (ΔE a), and pre-exponential factors (A). The trend in the kinetic parameters correlated with the type of surface complexes that iAs and DMA form, which are mostly bidentate binuclear compared to a mix of outer sphere and monodentate, respectively. The observed initial adsorption rates were found to be more sensitive to changes in the aqueous concentration of the arsenicals than slow rates. On average, iAs adsorbs 2.5× faster and desorbs 4× slower than dimethylarsinate (DMA). The ΔE a and A values for the adsorption of iAs bidentate complexes are statistically higher than those extracted for outersphere DMA by a factor of 3. The DFT results on adsorption energies and ΔE a barriers are consistent with the experimental data and provide a mechanistic explanation for the low ΔE a values observed. The presence of defect sites with under-coordinated Fe atoms or exchangeable surface water (i.e., Fe−OH 2 groups) lowers activation barriers of adsorption. These results suggest that increasing organic substitutions on arsenate at the expense of As−O bonds decreases the effective energy barrier for complex formation and lowers the number of collisional orientations that result in binding to the hematite surface.
NASA uses the Automatic Cloud Coverage Assessment (ACCA) algorithm to determine the ration of clo... more NASA uses the Automatic Cloud Coverage Assessment (ACCA) algorithm to determine the ration of cloud cover to non-cloud cover in an image from the Landsat 7 satellite. In an attempt to reduce the overall processing time of the algorithm, NASA has opted to convert the software version of the ACCA algorithm into a hardware implementation. Since previous attempts to convert the cloud detecting algorithm, using an advanced hardware description language (VHDL), have rendered inaccurate results, yhe purpose of this project is to detail the methods to debug and test the VHDL implementation of the ACAA algorithm and to advance the implementation of the algorithm as time permitted
Journal of The American College of Surgeons, May 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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