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Thesis (M. Eng. in Biomedical Engineering)--Massachusetts Institute of Technology, Dept. of Biological Engineering, 2013., Cataloged from PDF version of thesis., Includes bibliographical references (p. 37-40)., Spinal Cord injury (SCI) leads to paralysis, decrease in quality of life and high lifetime medical costs. Direct nerve Functional Electrical Stimulation (FES) induces muscles to contract by electrically stimulating nerves, which shows promise for clinical applications in restoring muscle function in SC. However, Functional Electrical Stimulation is limited by the lack of graded response in muscle contraction and by high fatigability due to the reversal of recruitment order of motor units. Previous work showed that ion-selective membranes can be used to modulate Ca 2 ions in situ, decreasing the current threshold for nerve stimulation and eliciting a more graded muscle contraction response. This work developed polyimide-based cuff ion-selective electrodes to enable the future application of this technique in vivo. The developed electrodes were flexible, elastic and conductive. In vitro tests of the electrodes by stimulation of frog sciatic nerve reproduced the decrease in stimulation current threshold, which had been observed in planar glass-based electrodes, in the flexible polyimide-based electrodes. Additionally, cuffing the stimulated nerves with ion-selective electrodes was more effective at decreasing current threshold than planar stimulation. This work also analyzed data on twitch width, contraction time and relaxation time to infer effects of ion-selective electrodes on recruitment order. Stimulation with the ion-selective electrodes had higher twitch width, contraction time and relaxation time than traditional electrical stimulation at all force levels. The difference was particularly high at low force levels, indicating an effect of Calcium ion depletion on recruitment order., by Ragheb Mohamad Fawaz El Khaja., M.Eng.in Biomedical Engineering

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012., Cataloged from PDF version of thesis., Includes bibliographical references (p. 43-44)., Carbon Dioxide emissions from power production are believed to have significant contributions to the greenhouse effect and global warming. Alternative energy resources, such as solar radiation, may help abate emissions but suffer from high costs of power production and temporal variations. On the other hand, Carbon Capture and Sequestration allows the continued use of fossil fuels without the CO2 emissions but it comes at an energetic penalty. The Advanced Zero Emissions Plant (AZEP) minimizes this energy loss by making use of Ion Transport Membrane (ITM)-based oxy-combustion to reduce the cost of carbon dioxide separation. This work seeks to assess if there are any thermodynamic gains from hybridizing solar-thermal energy with AZEP. The particular focus is hybridizing of the bottoming cycle with supplemental solar heating. A simple model of parabolic solar trough was used to hybridize a model of the AZEP cycle in ASPEN Plus*. Two cycle configurations are studied: the first uses solar parabolic troughs to indirectly vaporize high pressure steam through Therminol and the second uses parabolic troughs to directly preheat the high pressure water stream prior to vaporization. Simulations of the solar vaporizer hybrid by varying the total area of collectors (holding fuel input constant) show an increase of net electric output from 439MW for the non-hybridized AZEP to 533MW with an input solar share of 38.8%. The incremental solar efficiency is found to be around 16% for solar shares of input ranging from 5% to 38.8%. Moreover, simulations of variable solar insolation for collector area of 550,000 m2 , show that incremental solar efficiency increased with solar insolation reaching a plateau around 17%. Simulations of the direct solar preheater, show a net electric output of 501.3 MW for a solar share of 35%, (an incremental solar efficiency of 13.73%). The power generation and hence incremental efficiency is lower than in hybridization with steam vaporization with the sam, by Ragheb Mohamad Fawaz El Khaja., S.B.